ACTA FACULTATIS XYLOLOGIAE ZVOLEN 61 2/2019

TECHNICKÁ UNIVERZITA VO ZVOLENE DREVÁRSKA FAKULTA

ACTA FACULTATIS XYLOLOGIAE ZVOLEN

VEDECKÝ ČASOPIS SCIENTIFIC JOURNAL

61 2/2019

Scientific journal Acta Facultatis Xylologiae Zvolen publishes peer-reviewed scientific papers covering the fields of wood: structure and properties, wood processing, machining and drying, wood modification and preservation, thermal stability, burning and fire protection of lignocelluloses materials, furniture design and construction, wooden constructions, economics and management in wood processing industry. The journal is a platform for presenting reports and reviews of books of domestic and foreign authors.

Vedecký časopis Acta Facultatis Xylologiae Zvolen uverejňuje pôvodné recenzované vedecké práce z oblastí: štruktúra a vlastnosti dreva, procesy spracovania, obrábania, sušenia, modifikácie a ochrany dreva, termickej stability, horenia a protipožiarnej ochrany lignocelulózových materiálov, konštrukcie a dizajnu nábytku, drevených stavebných konštrukcií, ekonomiky a manažmentu drevospracujúceho priemyslu. Poskytuje priestor aj na prezentáciu názorov formou správ a recenzií kníh domácich a zahraničných autorov.

VEDECKÝ ČASOPIS DREVÁRSKEJ FAKULTY, TECHNICKEJ UNIVERZITY VO ZVOLENE 61 2/2019 SCIENTIFIC JOURNAL OF THE FACULTY OF WOOD SCIENCES AND TECHNOLOGY, TECHNICAL UNIVERSITY IN ZVOLEN 61 2/2019 Redakcia (Publisher and Editor’s Office): Drevárska fakulta (Faculty of Wood Sciences and Technology) T. G. Masaryka 24, SK-960 01 Zvolen, Slovakia Redakčná rada (Editorial Board): Predseda (Chairman): Vedecký redaktor (Editor-in-Chief): Členovia (Editors):

Jazykový editor (Proofreader): Technický redaktor (Copy Editor):

prof. Ing. Ján Sedliačik, PhD. prof. Ing. Ladislav Dzurenda, PhD. prof. RNDr. František Kačík, PhD. prof. RNDr. Danica Kačíková, PhD. prof. Ing. Jozef Kúdela, CSc. prof. Ing. Ladislav Reinprecht, CSc. prof. Ing. Jozef Štefko. CSc. doc. Ing. Pavol Joščák, CSc. doc. Ing. Hubert Paluš, PhD. Mgr. Žaneta Balážová, PhD. Antónia Malenká

Medzinárodný poradný zbor (International Advisory Editorial Board): Pavlo Bekhta (UA), Nencho Deliiski (BG), Vlado Goglia (HR), Denis Jelačić (HR), Bohumil Kasal (USA), Wojciech Lis (PL), Remy Marchal (FR), Miloslav Milichovský (CZ), Róbert Németh (HU), Peter Niemz (CH), Kazimierz A. Orlowski (PL), Franc Pohleven (SI), František Potůček (CZ), Włodzimierz Prądzyński (PL), Alfréd Teischinger (AT), Jerzy Smardzewski (PL), Mikuláš Šupín (SK), Richard P. Vlosky (USA), Rupert Wimmer (AT) Vydala (Published by): Technická univerzita vo Zvolene, T. G. Masaryka 2117/24, 960 01 Zvolen, IČO 00397440, 2019 Náklad (Edition) 150 výtlačkov, Rozsah (Pages) 173 strán, 14,73 AH, 14,89 VH Tlač (Printed by): Vydavateľstvo Technickej univerzity vo Zvolene Vydanie I. – október 2019 Periodikum s periodicitou dvakrát ročne Evidenčné číslo: 3860/09 Časopis Acta Facultatis Xylologiae Zvolen je registrovaný v databáze (Indexed in): Web of Science, SCOPUS, ProQuest, AGRICOLA, Russian Science Citation Index Všetky práva vyhradené. Nijaká časť textu ani ilustrácie nemôžu byť použité na ďalšie šírenie akoukoľvek formou bez predchádzajúceho súhlasu autorov alebo vydavateľa.

© Copyright by Technical University in Zvolen, Slovak Republic.

ISSN 1336–3824

CONTENTS

01. JARMILA GEFFERTOVÁ – ANTON GEFFERT – TATIANA VILKOVSKÁ – IVAN KLEMENT – ONDREJ VACEK: SELECTED ASPECTS OF THE REACTION BEECH WOOD ................................................ 5 02. RICHARD HRČKA – BARBORA SLOVÁČKOVÁ: THE METHOD OF WOOD EMISSIVITY MEASUREMENT ......................................................... 17 03 OLENA PINCHEVSKA – JÁN SEDLIAČIK – OLEKSANDRA HORBACHOVA – ANDRIY SPIROCHKIN  IVAN ROHOVSKYI: PROPERTIES OF HORNBEAM (Carpinus betulus) WOOD THERMALLY TREATED UNDER DIFFERENT CONDITIONS ............................................ 25 04. GABRIELA SLABEJOVÁ  ZUZANA VIDHOLDOVÁ  MÁRIA ŠMIDRIAKOVÁ: SURFACE FINISHES FOR THERMALLY MODIFIED BEECH WOOD .................................................................................................. 41 05. FRANTIŠEK POTŮČEK – MOSTAFIZUR RAHMAN: DISPLACEMENT WASHING OF KRAFT PULP AT VARIOUS WASH WATER TEMPERATURE ............................................................................................. 51 06. LADISLAV REINPRECHT – DANA-MIHAELA POP – ZUZANA VIDHOLDOVÁ – MARIA CRISTINA TIMAR: ANTI-DECAY POTENTIAL OF FIVE ESSENTIAL OILS AGAINST THE WOODDECAYING FUNGI SERPULA LACRYMANS AND TRAMETES VERSICOLOR ..................................................................................................... 63 07. PAVLIN VITCHEV – DIMITAR ANGELSKI – VLADIMIR MIHAILOV: INFLUENCE OF THE PROCESSED MATERIAL ON THE SOUND PRESSURE LEVEL GENERATED BY SLIDING TABLE CIRCULAR SAW .............................................................................................. 73 08. PAVLIN VITCHEV: EVALUATION OF THE SURFACE QUALITY OF THE PROCESSED WOOD MATERIAL DEPENDING ON THE CONSTRUCTION OF THE WOOD MILLING TOOL .................................... 81 09. LINDA MAKOVICKA OSVALDOVA  JAVIER-RAMÓN SOTOMAYOR CASTELLANOS: BURNING RATE OF SELECTED HARDWOOD TREE SPECIES .......................................................................... 91 10. VADIM VIKTOROVICH TANYUKEVICH  ANASTASIA VLADIMIROVNA KULIK  OLGA IVANOVNA DOMANINA  SERGEY VLADIMIROVICH TYURIN  ALEXANDER ALEXANDROVICH KVASHA: FIRES IN ARID AGROFORESTAL LANDSCAPES AND THEIR DAMAGE ASSESSMENT ................................ 99

11. KATARÍNA DÚBRAVSKÁ  DOMINIK ŠPILÁK  ĽUDMILA TEREŇOVÁ – JAROSLAVA ŠTEFKOVÁ: CHARRING LAYER ON A CROSS-LAMINATED TIMBER PANEL CONSTRUCTION ......................... 109 12. MÁRIA MORESOVÁ – MARIANA SEDLIAČIKOVÁ – JOZEF ŠTEFKO – DANA BENČIKOVÁ: PERCEPTION OF WOODEN HOUSES IN THE SLOVAK REPUBLIC .......................................................................... 121 13. MAREK POTKÁNY – MAREK DEBNÁR – MONIKA ŠKULTÉTYOVÁ: LIFE CYCLE COST ANALYSIS FOR REFERENCE PROTOTYPE BUILDING IN ALTERNATIVES OF SILICATE AND WOOD-BASED STRUCTURE ...................................................................................................... 137 14. ANDREJ TOMIČ - MIKULÁŠ ŠUPÍN: WEBSITE SEARCH ENGINE OPTIMIZATION OF THE COMPANY IN THE WOODWORKING INDUSTRY ......................................................................................................... 153 15. MARIANA SEDLIAČIKOVÁ – ZUZANA STROKOVÁ – JOSEF

DRÁBEK – DENISA MALÁ: CONTROLLING IMPLEMENTATION: WHAT ARE THE BENEFITS AND BARRIES FOR EMPLOYEES OF WOOD PROCESSING ENTERPRISES? ................................................ 163

ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 5−15, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.01

SELECTED ASPECTS OF THE REACTION BEECH WOOD Jarmila Geffertová – Anton Geffert – Tatiana Vilkovská – Ivan Klement – Ondrej Vacek ABSTRACT The specifics of reaction beech wood in terms of basic chemical properties, colouration and dimensional properties of the wood fibres are presented in the paper. The samples of reaction and opposite beech wood were evaluated using standard chemical analyses by means of measuring the colour coordinates L*, a* and b* and determining the dimensional properties of the wood fibres using Fiber Tester. A well-known fact that reaction wood has a higher proportion of cellulose and a lower proportion of lignin than opposite wood is confirmed by the chemical analyses. The content of extractives in both samples was very similar (from 2.97 to 3.53%). The lightness (L*) of reaction wood is higher than the lightness of opposite wood, both in wet and dried wood. After the drying process, the lightness of wood increased slightly. The biggest colour differences were noticed between the wet reaction and opposite wood (E*=18.6). Except one sample, all observed values of the total colour difference were E*3. Knowledge about well-recognized colour changes in wet reaction wood could also be applied in the early identification of reaction wood in the industrial practice. Based on the fibre length distribution, the fact that reaction wood contains fewer parenchyma cells alongside with the higher representation of fibre cells and the lower representation of vessels can be concluded.

Key words: beech, reaction wood, colouration, dimensional properties of fibres.

INTRODUCTION The issue of beech wood quality, especially the early detection of reaction wood, is becoming more important in relation to future forecasts of long-term forestry planning where an increase in the representation of beech to 35.9% (KÚDELA and ČUNDERLÍK 2012) compared to 33.5% in 2016 is forecasted (Green Report 2017).

Beech wood quality is a very variable parameter, which has caused and still causes many processing problems. The method of using beech wood depends on its quality, which is determined by the structure and properties of wood, as well as the frequency of defects in this material. Their detailed knowledge, as well as knowledge of a number of factors influencing these properties (humidity, temperature, etc.), can help to minimize processing problems (KAČÍK and KUBOVSKÝ 2011, KÚDELA and ČUNDERLÍK 2012).

Beech wood has a high frequency of defects (red false heartwood, reaction wood, necrosis, rot, etc.), which markedly affect its quality. Some defects are difficult to identify during the processing of beech logs and can be detected only after the cutting or due to

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negative effects during the further processing (KÚDELA and ČUNDERLÍK 2012, MARČOK et al. 1996, Vilkovska et al. 2018).

One of the frequent defects in the beech wood structure is also reaction wood (tension wood) that forms in the part of the log and branches during the growth as a response to different external factors. Its presence in the cuttings is undesirable because reaction wood behaves very differently in humidified thermal stress than normal wood (ČUNDERLÍK et al.

1992, 1995, KÚDELA 1993, 2002). Reaction wood represents 14 to 21% of the total wood volume of beech raw material (ČUNDERLÍK and KÚDELA 1992).

Regarding the chemical composition of reaction beech wood, several literary sources indicate a higher amount of cellulose and a lower amount of lignin, in comparison to normal wood. Cellulose is a polysaccharide that is most strongly involved in these changes. Reaction wood has a higher proportion of crystalline cellulose and contains more hexoses and fewer pentosans (PANSHIN and DE ZEEUW 1980, BLAHO et al. 1993, VOZÁR et al. 1994, KAČÍKOVÁ 1997, VILKOVSKÁ et al. 2018).

The chemical wood composition is correlated with the colour of the wood surface. The wood surface colour is important for the identification of wood and also serves as a benchmark for wood quality assessment (BABIAK et al. 2004, HRČKA 2008).

Reaction wood (tension wood) in hardwood spieces has the function of transmitting greater tensile stresses, which is reflected in an increased proportion of mechanical tissues (a higher proportion of fibre cells at the expense of a lower vessel proportion) and also its higher density. The fibre cells are modified to form thick-walled wood fibres with a thin S2layer and with a thick G-layer containing non-lignified high-crystalline cellulose (ČUNDERLÍK 2009).

The aim of the paper was to complete already acquired knowledge on tension wood of beech in term of its colouration and dimensional properties of wood fibres. Tension beech wood turned out to be without any significant differences in wood density and moisture content, only having small differences in some chemical properties.

MATERIAL AND METHODS Samples of beech wood (Fagus sylvatica L.) containing the reaction zone came from Kronotimber Ltd. (Lehota pod Vtáčnikom, Slovakia). The visual detection of tension wood was based on the determination of the shiny appereance in logs. Using this method, it is neccesary to select and brush the surface of discs (thickness 10 cm) from logs and dry them under laboratory conditions (103°C per 4 hours). Then tension wood is more visible on the surface of these discs . Based on this visual detection of the reaction zone, the samples containing reaction wood (R1, R2) and the samples containing opposite wood (O1, O2) were cut out off the place of occurrence. Opposite wood was located on the opposite side of the log from the reaction zone.

The quality of reaction wood was not detected in material.

Sample dimensions after cutting: length 400 mm width 100 mm thickness 30 mm Fig. 1 Sawing method of the samples.

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Experimental measurements were only performed on two samples from each group used for monitoring the selected physical and chemical properties in work of VILKOVSKÁ et al.

(2018) due to lack of experimental material.

Selected chemical properties were measured in the disintegrated samples of reaction and opposite beech wood (0.5-1.0 mm fraction): Ethanol-toluene solubility ASTM D 1107-96 Cellulose Kürschner-Hoffer method (KAČÍK and SOLÁR 2000) Lignin ASTM D 1106-96 The measurement of the colour coordinates L*, a*, b* was made using the Color Reader CR-10 colorimeter. All measurements were made in the conditions of standard illuminant D65 and Specular Component Included (SCI) and a Xenon lamp light source including a lit area of 8mm. Only for the purpose of colouration measuring reaction wood was divided into a reaction and a pre-reaction part (the part of transition from normal to reaction wood). The colour coordinates were measured at 10 uniformly distributed points. Determined values of these coordinates were assessed and compared for wet samples and oven-dried samples and they expressed the influence of moisture on the colour of reaction and non-reaction wood.

The moisture content of the samples was determined by the gravimetric method. The monitored samples were dried to a constant weight in the oven at 104±1°C (KAČÍK and SOLÁR 2000).

The total colour difference E* between the individual parts and samples was calculated with:



E *  ( L*2  L*1 ) 2  (a2*  a1* ) 2  b2*  b1*



2

(1)

(L2*- L1*) change in the value of the black-white coordinates (specific lightness) (a2*- a1*) change in the value of the green-red coordinate (b2*- b1*) change in the value of the blue-yellow coordinate.

The suspension of wood fibres of concentration 0.05 g in 100 cm3 was prepared in order to determine the dimensional properties of the fibres from studied wood. The wood of a match shape boiled under the reverse cooler for 3 hours in the concentrate solution of CH3COOH and 30% H2O2 in ratio of 1:1 (BEREŠOVÁ and ČUNDERLÍK 1999).

After aspirating, washing and diluting, the suspension was used to measure the dimensional properties of the wood fibres on the Fiber Tester, which measures the length and width for at least 20,000 wood fibres in one measurement (KARLSSON 2006).

RESULTS AND DISCUSION Table 1 shows the average values of the absolute moisture content (wa) and selected chemical properties of reaction and opposite beech wood samples (content of extractives, cellulose and lignin).

Tab. 1 Chemical composition of beech wood samples.

Beech wood Moisture content -wa (%) Content of extractives (%) Cellulose content (%) Lignin content (%)

Sample No.1 Reaction Opposite R1 O1 60.3 67.8 3.53 3.17 42.56 41.79 19.71 21.44

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Sample No.2 Reaction Opposite R2 O2 58.6 65.7 2.97 3.07 45.91 40.57 18.31 21.40

Measured values of the moisture content (wa) showed that moisture of reaction wood was higher in both samples (sample No.1 by 7.5% and sample No.2 by 7.1%) and moisture of sample No.1 was higher than moisture of sample No.2 (reaction wood by 2.1% and opposite wood by 1.7%).

The content of extractives in both samples was very similar, while in sample No.1 more extractives were found in reaction wood (by 0.36%) and in the sample No.2 more extractives were found in opposite wood (by 0.10%).

Reaction wood of both samples contained more cellulose (sample No.1 by 0.77% and sample No.2 by 5.34%) and less lignin (sample No.1 by 1.73% and sample No.2 by 3.09%) than wood opposite, which is consistent with the literary sources mentioned above.

The visual observation of both beech wood samples showed a lighter colour of reaction wood (Figure 2). As also shown by KLEMENT et al. (2018) the lightness of reaction wood plays a key role in its visual detection.

Fig. 2 Light and curved part of reaction beech wood after drying.

Table 2 shows the colour coordinates L*, a*, b* of samples No.1 and 2 of beech wood determined in its reaction and opposite parts.

Tab. 2 Average values of the colour coordinates.

Beech wood Sample No.1 Sample No.2

L* a* b* L* a* b*

wet 71.5 7.5 25.5 78.3 3.5 14.9

Reaction part (R) oven-dried 1.2 72.1 0.7 6.9 1.2 20.8 2.3 78.0 1.0 3.7 1.3 15.8

STDEV

STDEV

1.0 0.4 0.3 0.4 0.1 0.3

wet 69.4 9.2 32.7 71.1 8.6 31.3

Opposite part (O) oven-dried 0.9 69.7 0.8 7.5 1.1 22.6 0.4 72.4 0.3 7.1 1.0 22.1

STDEV

STDEV

0.6 0.2 0.5 0.4 0.3 0.7

Based on the above results it can be stated that lightness (L*) of wet and dried reaction wood is higher than that of opposite wood in both wood samples. While the difference in the lightness between wet reaction and opposite wood for sample No.1 is L*=2.1, the difference for sample No.2 up to 7.2. Having dried this wood, this difference slightly increased to 2.4 for sample No.1 and dropped to 5.6 for sample No.2 and the lightness value slightly increased in both samples (except R2).

The change of the green-red coordinate a* between reaction and opposite wood was again greater for sample No.2 than for sample No.1. There was a shift to the green area a*=5.1 in the wet sample (R2–O2) and (R2–O2) a*=3.4 in the case of dried wood.

There was a more significant change of sample No.2 in comparison to sample No.1 in the blue-yellow coordinate b* between reaction and opposite wood. This difference was up to b*=16.4 in wet wood and b*=6.3 in dried wood.

The values of the total colour difference (E*) summarize all the colour coordinates and are listed in Table 3. These values show the colour changes of both samples in the combinations of reaction and opposite wood and wet and dried wood (o. d.).

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Tab. 3 Average values of the total colour difference (E*).

Beech wood wet - oven-dried reaction - opposite

Sample No.1 4.8 10.2 7.7 3.1

reaction opposite wet oven-dried

E*

Sample No.2 1.0 9.4 18.6 9.1

The most significant colour changes on beech wood were recorded on sample No.2 between wet reaction and opposite wood (E*=18.6). According to ALLEGRETTI et al.

(2009), colour changes 6E*12 can be evaluated as large colour differences and colour changes E*12 already as different colours. In addition to E* for reaction wet and dried wood of sample No.2, all observed values of the total colour difference were E*3.

The samples of beech wood No.1 and 2 were divided into these following parts: reaction wood, pre-reaction wood and opposite wood of wet (w) and dried (o. d.) for better monitoring of the changes of the colour coordinates (L*, a* and b*). Figures 3 to 6 show the changes of values of the given coordinates.

Comparing Figures 3 and 4 for sample No. 1 between individual zones, there is clearly notice a more abrupt change in the values of the colour coordinates in wet wood than in dried wood. Wet reaction wood shows that there is a more pronounced shift of the lightness to the white area, coordinate a* to the green area and coordinates b* to the blue area, which subsequently resulted in the lighter part of reaction wood compared to the opposite and prereaction part.

Fig. 3 Changes of the colour space coordinates for wet sample No. 1.

The changes in colour coordinate values were measured for sample 2, as shown in Figures 5 and 6.

More pronounced changes of sample No.2 of L*, a*, b* were observed again in the wet sample compared to dried sample. Even in wet pre-reaction wood, a slight shift in the colour coordinates was recorded in the white, blue and green areas. The shift in the pre-reaction portion decreased in the dried wood sample.

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Fig. 4 Changes of the colour space coordinates for oven-dried sample No.1.

Fig. 5 Changes of the colour space coordinates for wet sample No.2.

Fig. 6 Changes of the colour space coordinates for oven-dried sample No.2.

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The results obtained from the measurement of the colour parameters are in compliance with findings of KLEMENT et al. (2018).

Since tension wood is richer in cellulose and a fibre content, the dimensional properties of beech reaction and opposite wood were followed in the next part of the work.

The distribution of the length and width of the wood fibres and the content of fines were determined by the instrument called Fiber Tester. The number of all measured fibres was higher than 20,000 in one measurement.

The distribution of the length clearly showed two sets (Fig. 7).

Fig. 7 Ditribution of fibre length – sample No.1.

The first set of lengths of up to 0.5 mm consists mainly of a fine fraction up to 0.2 mm but also of the vascular cells whose length in beech reaches only 0.4 to 0.5 mm (Požgaj et al. 1993). Therefore in order to compare the dimensional properties of the fibres of reaction and opposite wood beech, only a set of lengths over 0.5 mm was considered (Table 4).

Tab. 4 Corrected average values of dimensional properties of fibres Sample No.1 No.2

reaction wood opposite wood reaction wood opposite wood

Mean length (mm) 0.926 0.910 1.008 0.927

Number of fibres (filtered) 7458 7019 7458 7019

Mean width (m) 22.02 21.97 21.64 21.32

A greater proportion of the longer fibres was determined in both samples of reaction wood. Average fibre length of the reaction wood (0.926 and 1.008 mm) is higher than opposite wood (0.910 and 0.927 mm).

In parallel to the length of the fibres, their width was also determined. In both samples, reaction wood had a slightly higher fibre width than opposite wood.

The modified portions of the average length and width fibres of reaction and opposite wood were tested by MatLab program and are shown in Figures 8 and 9: 11

Reaction vs. opposite wood Sample No. 1 Sample No. 2

F 14.38 0.81 397.43 35.07

Length Width Length Width

a

Probability 0.000 0.368 0.000 0.000

b

Fig. 8 Corrected proportion of fibres by length (a - sample No.1, b - sample No. 2).

a

b

Fig. 9 Corrected proportion of fibres by width (a - sample No.1, b - sample No. 2).

The means of groups in reaction and opposite wood are significantly different for length of samples No.1 and 2 (Figure 8a,b).

The means of groups in reaction and opposite wood are also significantly different for width of samples No.2 (Figure 9b). Means are not significantly different from reaction and opposite wood of sample No.1 (Figure 9a).

Tab. 4 Content of fines (fraction up to 0.2 mm).

Beech wood 0.0–0.1 mm 0.1–0.2 mm

reaction 3.2 11.0

Sample No.1

Content of fines (%) opposite 3.1 13.2

12

reaction 0 8.5

Sample No.2

opposite 3.2 11.5

A higher proportion of fine fraction to 0.2 mm in opposite wood was determined in both samples (No.1 and 2), with several times higher values representative of the fine fibres in the length range of 0.1 to 0.2 mm. It can be concluded that in addition to the higher representation of the fibre cells and the lower representation of the vessels in reaction wood, reaction wood contains fewer parenchyma cells (in the pulp and paper practice they tend to say "zero fibres").

CONCLUSION The achieved results confirmed the well-known fact that reaction wood contains more cellulose and less lignin than opposite wood. The content of extractives determined in both samples was very similar. A higher moisture content in reaction wood than opposite wood was proved in both samples.

On the basis of the results of colouration, it can be stated that the lightness (L*) of reaction wood is higher than of opposite wood for both wood samples, both in wet and dried wood. Having dried this wood, the lightness slightly increased.

The largest colour changes of beech wood were recorded on sample No.2 between wet reaction and opposite wood (E*=18.6). Except for E* for reaction wet and dried wood, all observed values of the total colour difference were E*3.

The colour changes are better recognizable in wet reaction wood than in dried wood and instrumentally they can be quickly quantified. This knowledge could also find its application in the early identification of reaction wood in the industrial practice.

The average length of the wood fibres in both samples was higher in reaction than in opposite wood. Regarding the width of the fibres, there were very small differences between reaction and opposite wood. A higher portion of the fine fraction of 0.2 mm was determined in opposite wood, with several times higher values representative of the fine fibres in the length range of 0.1 to 0.2 mm.

On the basis of the fibre length distribution it can be concluded that beside the higher representation of the fibre cells and the lower representation of the vessels in reaction wood, reaction wood contains fewer parenchyma cells. Therein lies the advantage of the processing of reaction wood for pulp.

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KAČÍKOVÁ, D. 1997. Charakteristika bukového reakčného dreva z hľadiska sulfátového spôsobu výroby buničín. Zvolen : Technická univerzita vo Zvolene, 1997. 55 p. ISBN 80-228-0609-9.

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KLEMENT, I., VILKOVSKA, T., BARANSKI, J., KONOPKA, A. 2018. The impact of drying and steaming processes on surface color changes of tension and normal beech wood, In Drying Technology, 2018, DOI: 10.1080/07373937.2018.1509219.

KÚDELA, J. 1993. Determination of deformation of beech prisms, containing reaction wood. In Drevársky výskum, 1993, 38(2): 19–28.

KÚDELA, J. 2002. Analýza príčin defektov v bukovom dreve počas jeho hydrotermickej plastifikácie.

In Vybrané procesy pri spracovaní dreva. Bystrá : TU vo Zvolene, 2002, 1–5.

KÚDELA, J., ČUNDERLÍK, I. 2012. Bukové drevo: štruktúra, vlastnosti, použitie. 1.vyd. Zvolen : TU vo Zvolene, 2012.152 p. ISBN 978-80-228-2318-0.

MARČOK, M., KÚDELA, J., ČUNDERLÍK, I. 1996. Possibilities of using X-ray computed tomography for identification of reaction wood. In Zborník vedeckých prác Drevárskej fakulty TU vo Zvolene, Zvolen : TU vo Zvolene, 1996, 49–58.

PANSHIN, A.J., DE ZEEUW, C. 1980. Textbook of wood technology. New York : McGraw Hill, 1980, 722 p.

POŽGAJ, A., CHOVANEC, D., KURJATKO, S., BABIAK, M., 1993. Štruktúra a vlastnosti dreva. 1.vyd.

Bratislava : Príroda, 1993. 486 s. ISBN 80-07-00600-1.

VILKOVSKA, T., KLEMENT, I., VÝBOHOVA, E. 2018. The effect of tension wood on the selected physical properties and chemical composition of beech wood (Fagus Sylvatica L.). In Acta Facultatis Xylologiae Zvolen, 2018, 60(1): 31–40, ISSN 1336-3824.

VOZÁR, M., ČUNDERLÍK, I., KAČÍK, F. 1994. Some chemical properties of tension and oppsite beech wood. In Drevársky výskum, 1994, 39(4): 23–33.

ZELENÁ SPRÁVA 2017: Správa o lesnom hospodárstve v Slovenskej republike za rok 2016. 1. vyd.

Bratislava: Ministerstvo pôdohospodárstva a rozvoja vidieka SR, Národné lesnícke centrum, 2017.

68p. ISBN 978-80-8093-235-0.

ACKNOWLEDGEMENT

The research was supported by the Ministry of Education, Science, Research and Sport of the Slovak Republic by the Scientific Grant Agency (Grant No. 1/0395/16) and by the Cultural and Educational Grant Agency (Grant No. 021 TU Z-4/2017).

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AUTHORS ADDRESS doc. Ing. Jarmila Geffertová, PhD. prof. Ing. Anton Geffert, CSc. Ing. Tatiana Vilkovská, PhD. doc. Ing. Ivan Klement, CSc. RNDr. Ondrej Vacek, PhD. Technical University in Zvolen Faculty of Wood Sciences and Technology T. G. Masaryka 24 960 01 Zvolen Slovakia geffertova@tuzvo.sk geffert@tuzvo.sk tatiana.vilkovska@tuzvo.sk klement@tuzvo.sk ondrej.vacek@tuzvo.sk

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 17−24, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.02

THE METHOD OF WOOD EMISSIVITY MEASUREMENT Richard Hrčka – Barbora Slováčková ABSTRACT The paper deals with newly proposed method of wood emissivity measurement. The emissivity is determined on the basis of Stefan-Boltzmann law and second law of thermodynamics for black body emission. The newly proposed method is inverse method based on the solution of heat conduction equation and measurement of radiated heat flux using infrared thermometer. The newly proposed method enhances the previously used method based on additional specimen of known emissivity touching the wood specimen. The method does not destruct the measured surface and does not use additional components fixed to the surface.

Key words: emissivity, thermal properties, physics of wood.

INTRODUCTION Boundary conditions prescribe the wood surface phenomena during heat transfer and significantly affect the description of temperature field in wood. The boundary condition of the third kind is used to describe the surface heat flux on the basis of surface temperature (CARSLAW and JAEGGER 1964, LYKOV 1968). The linear function between surface temperature and surface flux was used in method of wood properties measurement as wood specimens were in contact with fluid (HRČKA 2010). Wood can be also in contact with solid.

Such phenomenon is described in hot plate method (SULEIMAN et al. 1999). However, in the case of the hot plate method, the contact thermal resistance is serious problem of wood thin specimens (BUČAR and STRAŽE 2008). Therefore, thicker specimens must be used for measurement wood thermal properties, which suppose the transfer of heat through the lateral surfaces. The thermal thickness of a fuel particle may be determined from the thermal Biot number (STRÖM and THUNMAN 2013). If the Biot number is large and thermal diffusivity is small, there will be temperature gradients inside the particle as it is being heated. Woody biofuels (in the form of briquettes and chips, for example) are typically thermally thick and fall into this category (STRÖM and THUNMAN 2013). The heat transfer coefficient and Biot number are not infinity large as is describe in (BABIAK and HRČKA 2010). In general, the transfer of heat through the lateral surfaces must be involved in heat conduction equation to correctly describe the temperature field in wood specimen during wood thermal properties measurement (HRČKA and BABIAK 2017).

Boundary condition of the third kind may also be used for radiant heating or cooling (LYKOV 1968). KREMPASKÝ (1969) noted that the temperatures above 700800°C are crucial for radiation to be dominant heat transport. KREMPASKÝ (1969) noted that the convection determines heat transport from the object if its temperature is lower than 17

700800°C. The conclusions of LYKOV (1968) and KREMPASKÝ (1969) follow from their analysis of Stefan-Boltzmann law. LYKOV (1968) equaled the heat flux at the inner part of surface to the flux which is defined by Fourier law. And finally, LYKOV (1968) as well as KREMPASKÝ (1969) wrote the decomposition of Stefan-Boltzmann law to the difference of surface and surrounding temperatures. The aforementioned notes revealed the possibility to measure the wood emissivity comparing the surface flux and temperature determined from heat conduction equation at the wood surface together with data measured with infrared thermometer. The aim of the article is to describe the new method of wood emissivity measurement. The method will solve the inverse problem of wood thermal properties measurement.

THEORETICAL PART OF THE METHOD Heat transfer coefficient h (W·m2·K1) is quantity joining the heat flux across the surface qx=L (W·m2) and difference between surface temperature Tx=L and temperature of surroundings T0 (CARSLAW and JAEGGER 1964, LYKOV 1968): (1)

𝑞𝑥=𝐿 = ℎ(𝑇𝑥=𝐿 − 𝑇0 )

and according to energy-conservation law, heat quantity transferred from the body surface equals that transferred to the body surface from the inside per unit time per unit surface by heat. The radiated power P (W), as a rate of emission of electromagnetic energy, from an area S of surface (m2) at temperature T is given by formula: (2)

𝑃 = 𝑒𝜎𝑆𝑇 4

where =5.67·10-8W·m-2·K-4 is the Stefan-Boltzmann constant. The emissivity e characterizes the emitting properties of the surface and is material property. It is dimensionless number between values 0 and 1 (KELLER et al. 1993). Emissivity value of 1 characterizes blackbody. The radiation that would be emitted by black body can be approximated as closely as desired by the radiation emerging from a small opening in a cavity and the radiated power is independent of material that forms the inside walls of the cavity (ILKOVIČ 1957, KELLER et al. 1993).

Good emitter is good absorber as can be shown using second law of thermodynamics.

If closed system boundary is adiabatic wall of temperature T0 and the system consists of object of the temperature T which is different from T0, the nonzero net heat flux occurred between object and boundary: (3)

𝑃 = 𝑒𝜎𝑆(𝑇 4 − 𝑇04 )

LYKOV (1968) equaled the heat flux (1) to the flux which is defined by Fourier law.

And finally, LYKOV (1968) as well as KREMPASKÝ (1969) wrote the decomposition of right hand side of equation (3) to the difference of temperatures: 𝑃 = 𝑒𝜎𝑆(𝑇 2 + 𝑇02 )(𝑇 + 𝑇0 )(𝑇 − 𝑇0 )

(4)

and LYKOV (1968) summed the radiated flux and flux related to convection at the surface to surface flux linearly depending on surface temperature.

The deviation between decomposition (linear function, k, q are parameters): (5)

𝑃 = 𝑘𝑇 + 𝑞 = 𝑘(𝑇0 + ∆𝑇) + 𝑞 18

and original (forth power function, T0 is parameter, ΔT is difference of real temperature): (6)

𝑃 = 𝑇 4 − 𝑇04 = (𝑇0 + ∆𝑇)4 − 𝑇04

is determined according to method of least squares for different values of T0 (273,15K; 293,15K; 413,15K) and is showed in fig. 1.

Deviation between diffrenece of real and approximated tempearatures

273,15 K

293,15 K

413,15 K

0,1 0,08 0,06 0,04 0,02 0 -6

-4

-2

-0,02

0

2

4

6

-0,04 -0,06 Difference of real temperatures [°C]

Fig. 1 The precision of linear function approximation to forth power function.

The figure 1 shows the best fit of approximation is in the range of 〈0; 5〉 °C. So, the temperature at the rear face of the specimen must not exceed 5°C which was measured by infrared thermometer with 0.1°C resolution of readings.

The heat flux and temperature at the surface follows the determination of temperature field T(x, y, z, t ) according to the solution of heat conduction equation: αR

 2T  2T  2 T T  α  α  T L x 2 y 2 z 2 t

(7)

where L (m2.s-1) is thermal diffusivity in longitudinal direction, R in radial direction and T in tangential direction. The particular solution was found in the form (HRČKA and BABIAK 2017): μp μr μ z) (sinμ p )(cos y) μ m (cos m x) dT dR dL 8q T(x, y, z, t)  T0   cd L r 1 p1 m1 (μ r  (sinμ r )(cosμ r )) (μ p  (sinμ p )(cosμ p )) (μ m  (sinμ m )(cosμ m )) 

 α α α (μ 2m 2L  μ 2p 2R μ 2r T2 )t  dL dR dT  1 e   2 αL 2 αR 2 αT  μm 2  μp 2  μr 2 dT dR dL 





(sinμ r )(cos

     

(8) where q (W.m-2) is the heat flux at the center of specimens, dL, dR, dT are half of dimensions in longitudinal, radial and tangential directions, c (J.kg-1.K-1) is specific heat capacity and ρ (kg.m-3) is density at given moisture content. The extension for convection at boundaries is accompanied with heat transfer coefficients h and Biot numbers Bi (-) at boundaries.

Characteristic equations define the roots  (-) (indexes m, n, p belong to the anatomical directions L, R, T):

19

μ m tgμ m 

h Ld L  Bi L λL

μ p tgμ p 

hRdR  Bi R λR

μ r tgμ r 

h TdT  Bi T λT

with constant initial temperature through the specimen T0. The solution (7) fulfils the following boundary conditions:  λL



T  h L T x d  T0 L x x d L T x

 x 0

 λL



 λR



T  h R T yd  T0 R x yd R



 λT



T  h T T zd  T0 T x zdT

T 0 y y  0

T 0 z z  0

(9)

 (10)

where L (W.m-1.K-1) is thermal conductivity in longitudinal direction, R in radial direction and T in tangential direction, BiL, BiR, BiT are Biot numbers at principal anatomical sections.

STEPS OF MEASUREMENT 1. Wood thermal properties must be measured using the temperature field (equation 8, Hrčka 2010) together with measurement of the surface temperature at the rear face of the sample. The surface temperature is measured with infrared thermometer on which the emissivity is set to constant (known) value. The result of measurement is temperature field and radiated flux at the surface.

2. The temperature at the surface, computed from temperature field, is set to StefanBoltzmann law. The computed radiated flux is affected only by specimen emissivity.

3. The comparison of measured radiated flux (point 1) and computed radiated flux from temperature field (point 2) enables the determination of unknown emissivity using the method of least squares.

APPARATUS The sketch of apparatus arrangement is shown on figure 2.

Fig. 2 The arrangement of the apparatus.

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The apparatus consists of heating foil Ni-Cr (Vacronium), the laboratory source of direct current QPX 1200SP (Cambridgeshire, UK), thermocouples type K 5TC-TT-K-36-36 (Norwalk, USA), datalogger Almemo 2890-9 (Holzkirchen, Germany) and PC Toshiba (New York, USA). The direct current produces heat passing through the heating foil of known resistance to the adjacent samples. The temperatures at defined positions inside of samples are measured by thermocouples and data are recorded by datalogger at regular time intervals. Datalogger is connected to PC. The measurement is started and finished by PC. As far as temperature field is computed on the surface of the sample, the surface temperature is precisely determined. The radiant flux at the center of the largest area is measured with infrared (IR) thermometer Optris LaserSight (Berlin, Germany) parallel to the normal of the surface. Optris LaserSight infrared thermometer operates in spectral range 8-14µm with optical resolution in close focus mode: 1mm spot in 62mm distance from specimen capturing 90% of energy. Temperature resolution is 0.1°C and accuracy ±0.75°C is valid at temperature 22.0°C. The repeatability of reading is declared to value of 0.5°C. The emissivity is adjustable.

The emissivity of constant (known) value is set on the pyrometer and temperature is also recorded at regular time intervals. Distance to spot ratio (D:S ratio) is set to 62:1. The diameter of the measured area is 1mm and its position is indicated with two point laser before measurement. The specimens are located at the center of climatic chamber KBF 720 (Tuttlingen, Germany) with adjustable humidity, temperature of air and speed of fans inside it. The inside walls of chamber (dimensions of 115 × 100 × 60cm) are made of stainless steel.

SOFTWARE The least square method implemented in nonlinear procedure Solver (MS Excel) is used to determine unknown parameters of solution (8). The adjusting of the measured radiated flux to computed radiated flux according to temperature field is again performed in procedure Solver. The value of emissivity is the final result of adjusting the measured radiated flux to computed one.

MATERIAL OF SPECIMENS The specimens of rectangular shape of dimensions (100 × 100 × 10mm in the anatomical directions), of negligible curvature of wooden rings are used for the measurement. The surface of the specimens should be flat as much as possible; it can be prepared by sanding (P60) without visible defects. The surfaces are cleaned with compressed air before testing. It is recommended to achieve the equilibrium moisture content in the humid air with relative humidity of 65% and temperature of 20.0 °C at the beginning of experiment.

THE SOLUTION OF THE DIRECT PROBLEM The modeling of the direct problem may be as follows: 1. The initial temperature of specimens 20.0 °C is changed due to plane heat source of 145 W·m2 in the center of the specimens. The thickness of the specimens is 0.0232m and density at 12% moisture content is 707.4 kg·m-3 (HRČKA and BABIAK 2017).

21

2. The selected values of heat transport properties of wood, Biot numbers and heat transfer coefficients are shown in Table 1.

Tab. 1 Selected heat transport properties, Biot numbers and heat transfer coefficients.

L (m2·s1)

R (m2·s1)

T (m2·s1)

c (J·kg1·K1) BiL

BiR

BiT

4.0·10

1.8·10

1.4·10

1700

2.0

2.9

-7

-7

-7

L (W·m1·K1)

R (W·m1·K1) T (W·m1·K1)

hL (W·m2·K1) 14

hR (W·m2.K1) hT (W·m2·K1) 19 23

0.48

0.22

0.66

0.18

eL (-) 0.80

eR (-) 0.96

eT (-) 0.98

3. Then radiated flux was computed using values of emissivity shown in Table 1.

L theor.

R theor.

T theor.

4,00E+01

Radiated flux[W.m-2]

3,50E+01 3,00E+01 2,50E+01 2,00E+01 1,50E+01 1,00E+01 5,00E+00 0,00E+00 0

500

1000

1500

2000

2500

3000

3500

4000

Time [s] Fig. 3 Radiated flux as was modeled and computed using temperature field at specimen surface.

4. The result of direct problem is radiated flux using computed temperature from temperature field and inserted to Stefan-Boltzmann law.

COMPARISON TO ANOTHER METHODS The theoretical part of used method of wood thermal properties measurement must describe the temperature field as precise and accurate as possible (HRČKA and BABIAK 2012).

The procedure for determining the emissivity, e, using the contact method can be described in several steps (Optris ® LaserSight): 1. Place the IR thermometer at the desired location and distance from the target to be measured.

2. Measure and compensate for the target’s reflected apparent temperature.

22

3. Aim and focus the IR thermometer on the target and, if possible, freeze the image.

4. Use an appropriate IR thermometer measurement function (such as spot temperature, cross hairs or isotherms) to define a measurement point.

5. Use a contact thermometer to measure the temperature of the point or area just defined by the IR thermometer measurement function. Note this temperature.

6. Without moving the IR thermometer, adjust the emissivity control until the indicated temperature is the same as the contact temperature just taken. The indicated emissivity value is the emissivity of this temperature target measured with this IR thermometer.

7. For greater accuracy, repeat procedures from the 2nd to the 6th steps a minimum of three times and average the emissivity values.

The method uses the contact probe (thermocouple) at the surface producing additional error or a band or color with a known emissivity (reference emissivity material method). The newly proposed method uses the thermocouple at certain non-zero distance from specimen surface.

The third method drills hole to the body to simulate the condition of a black body with an emissivity near 1 and therefore is destructive. The newly proposed method is not destructive.

The forth method uses the recommended values of emissivity which was determined by producer and is shown inside manual table. There is necessity to measure and use the emissivity values for wood appropriately to measurement conditions.

The previous methods show easy measurement of emissivity. On the other hand, the methods bring into measurement discussed additional errors.

CONCLUSIONS 1. The new proposed method of thermal properties measurement is based on the heat conduction equation solution and measurement of radiated flux with infrared thermometer.

2. The results of the method are extended to wood emissivity values.

3. The method enhances the conventional method which is suggested for measurement of emissivity by producer of thermometer.

REFERENCES BABIAK, M., HRČKA, R. 2010. Measurement of wood thermal properties. In 11th International IUFRO wood drying conference: Recent advances in the field of wood drying. Skelleftea: Lulea University of Technology, 5054.

BUČAR, B., STRAŽE, A. 2008. Determination of the thermal conductivity of wood by the hot plate method: The influence of morphological properties of fir wood (Abies alba Mill.) to the contact thermal resistance. In Holzforschung, 62: 362–367.

CARSLAW, H. S., JAEGER, J. C. 1959. Conduction of heat in solids. Clarendon Press, Oxford.

HRČKA, R. 2010. Variation of thermal properties of beech wood in the radial direction with moisture content and density. In.: Wood structure and properties ´10. Zvolen : Arbora Publishers, 111115.

HRČKA, R., BABIAK, M. 2012. Some non-traditional factors influencing thermal properties of wood. In Wood Research, 57(3), 367373.

HRČKA, R., BABIAK, M. 2017. Wood thermal properties. In Wood in civil engineering. Zagreb : InTech,. dx.doi.org/10.5772/63178.

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ILKOVIČ, D. 1957. Fyzika. Bratislava : SVTL. KELLER, F.J., GETTYS, W.E., SKOVE, M.J. 1993. Physics. McGraw-Hill, 2nd Edition KREMPASKÝ, J. 1969. Meranie termofyzikálnych veličín. Bratislava : Veda.

LYKOV, A. V. 1968. Analytical heat diffusion theory. New York and London : Academic Press.

Optris ® LaserSight, Operators manual (brochure) STRÖM, H., THUNMAN, H. 2013. CFD simulations of biofuel bed conversion: A submodel for the drying and devolatilization of thermally thick wood particles. In Combustion and Flame, 160: 417– 431. dx.doi.org/10.1016/j.combustflame.2012.10.005 SULEIMAN B. M., LARFELDT J., LECKNER B., GUSTAVSSON M. 1999. Thermal conductivity and diffusivity of wood. In Wood Science and Technology, vol. 33, no. 6, pp. 465–473, 1999.

ACKNOWLEDGMENTS This work was funded by the following: the Scientific Grand Agency of the Ministry of Education SR and the Slovak Academy of Sciences (Grant No. 1/0822/17 “Surface modification of wood and coating materials in order to improve stability of the wood – coating material system.”). This paper has been included into the project APVV-16-0177 “Progressive modifications of the wood surface, film-forming materials and their interactions at the phase interface.”

ADDRESSES OF AUTHORS Doc. Ing. Richard Hrčka, PhD. Ing. Barbora Slováčková Technical University in Zvolen Faculty of Wood Sciences and Technology Department of Wood Science T. G. Masaryka 24 960 01 Zvolen Slovak Republic richard.hrcka@tuzvo.sk

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 25−39, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.03

PROPERTIES OF HORNBEAM (Carpinus betulus) WOOD THERMALLY TREATED UNDER DIFFERENT CONDITIONS Olena Pinchevska – Ján Sedliačik – Oleksandra Horbachova – Andriy Spirochkin  Ivan Rohovskyi ABSTRACT Hornbeam (Carpinus betulus) wood is not widely used in woodworking industry at present. Mechanical, physical and aesthetical properties of hornbeam wood as a material for furniture or joinery products can be improved by thermal modification. Heat-treatment technology was carried out under different conditions: temperatures of 160, 190 and 220 °С and time of 1, 10 and 20 hours. The influence of heat treating on physical (density, colour, moisture absorption and volume shrinkage), mechanical (compression strength along, across fibres and bending strength) and technological (impact resistance and wear resistance) properties of hornbeam wood were investigated. Analysis of physical and mechanical properties of hornbeam wood heat-treated for different time allowed researchers to determine optimal parameters of thermal modification: temperature of 190 °С and duration for 812 hours. It was found that the effect of high temperature on the technological properties of hornbeam wood is insignificant.

Key words: hornbeam wood, heat-treatment technology, colour, mechanical and physical properties.

INTRODUCTION Hornbeam (Carpinus betulus) is not widely used species because the wood is heavy, prone to warping and moisture change. In addition, it has an inexpressive grey colour and a vague texture. Similar to many other wood species, hornbeam, despite its high mechanical strength and low thermal expansion, is hygroscopic and vulnerable to biological attack (ATES et al. 2009, SRINIVAS and PANDEY 2012). One of the ways to improve the properties of wood, except the use of chemical harmful substances (HILL 2006) such as acetylation or the introduction of furfural, is the process of thermal modification.

Significant studies in the field of wood thermal modification were conducted in many countries since the beginning of previous century (TIEMANN 1915, STAMM et al. 1946, THERMOWOOD HANDBOOK 2003). There are several basic technologies of wood heat treatment, that include heating of dry or wet wood at high temperatures in different environments, e.g. «ThermoWood» (Finland) in a steam environment; «Retification» (France) in the nitrogen environment; «Le Bois Perdure» (France) in a mixture of water vapour and gases emitted from wood; «Oil-Heat-Treatment» (Germany) in the environment of hot vegetable oils. The difference between these processes is the application of different temperatures (160250 °С) and the environments (ALÉN et al. 2002, CALONEGO et al. 2010).

25

Under the influence of high temperatures, ecological material with modified properties is obtained. So, the dimensional stability and biological stability increase as a result of heat treatment but mechanical parameters of wood decrease (ESTEVES and PEREIRA 2009, AKYILDIZ et al. 2009). At the same time, modified wood acquires a rich colour change throughout the thickness of the material (DZURENDA 2018a). Such changes occur as a result of chemical transformation of wood structural elements. Cellulose and lignin break down more slowly than hemicellulose. Extractives partially and faster evaporate from wood during the heat treatment. Due to the decomposition of hemicellulose, the resistance of thermally treated wood increases against the impact of biological attack. The degree of chemical transformation of wood, that lead to achievement the desired colour, depends on the schedule of heat modification (VIDHOLDOVÁ et al. 2019). As wood is a natural polymer material, the process of thermal transformation is a series of chemical reactions of all structural components: cellulose, hemicellulose and lignin (GEFFERT et al. 2019). Heat modification schedule parameters have been proposed for different wood species, in particular, pine, eucalyptus (ESTEVES and PEREIRA 2009), birch and aspen (KOCAEFE et al. 2008), fir (KOL 2010), maple (KORKUT et al. 2008), poplar, ash, oak (HILL 2006) and their influence on the change of properties have been investigated so far..

The aim of this research is to determine the impact of different heat treatment schedules on the change of physical and mechanical properties of hornbeam wood, which can expand the ways of its use.

MATERIAL AND METHODS Material Hornbeam (Carpinus betulus) lumber from Zhytomyr region of Ukraine was used with the cross section of 30 × 100 mm and the length of 1000 mm. Before the heat treatment, lumber was dried in a drying kiln to the moisture content W = 8 %. Test pieces of standard sizes with no defects were cut from dried timber in quantities according to standard testing methods (quantity is specified for one processing schedule): 20 × 20 × 30 mm, 16, 121, 26 samples – to determine the basic density, shrinkage, compression strength parallel and perpendicular to the fibres, 20 × 20 × 10 mm, 16 samples – moisture absorption, 20 × 20 × 300 mm, 35 samples – modulus of rupture, 20 × 20 × 150 mm, 23 samples – wood impact resistance, 50 × 50 × 20 mm, 40 samples – wear resistance, 90 × 5 × 300 mm, 3 samples – colour.

To determine the influence of the schedule parameters of thermal modification on the change in the wood characteristics, the effect of which determines the scope of its use, the physical-mechanical and technological properties of the obtained material are determined according to standard methods: basic density (ρbas, kg/m3) (GOST 16483.1-84 1985), indicators of shrinkage (βrad, βtang, %) (GOST 16483.37-88 1990), the amount of moisture absorption (Uabs, %) (GOST 16483.19-72* 1974), bending strength (MOR, MPa) (GOST 16483.3-84 1985), compression strength along and across fibres (σ||, σ┴, МPа) (GOST 16483.10-73 1974, GOST 16483.11-72 1973), impact resistance (Н, J/cm2) (GOST 16483.16-81 1983), wear resistance (t, %) (GOST 16483.39-81 1983).

Methods Hornbeam samples were modified at temperatures of 160, 190 and 220 °С with different duration of 1, 10 and 20 hours and used for determination the effect of high temperatures on the change of wood properties. The process of wood heat modification includes the processes 26

of drying and the subsequent removal of bounded moisture leading to physical and mechanical transformations. These transformations affect the decomposition of wood structural components, what is the reason for the change of colour. In order to evaluate wood colour characteristics, there is used a colour determination system of L, a, b components (DOMASEV and HNATIUK 2009). By scanning the samples and identifying using Photoshop, the overall colour difference ∆Е is determined:



E  L2  a 2  b 2



1

2

(1)

where: ΔL2 – square of the difference in the colour lightness of heat-treated wood samples relative to the sample without processing, Δa2 and Δb2 – the square of the difference in chromatic parameters describing the ratio of green to red and blue to yellow components of colour.

The Arrhenius equation is traditionally used to determine the temperature dependence of the chemical reaction speed coefficient. The area of its application has considerably expanded, including the process of wood drying (SHI 2006, ZAREA-HOSSEINABADI et al.

2012, SOKOLOVSKYY and SINKEVYCH 2016). The use of the so-called “Arrhenius kinetics” d is proposed to calculate the rate of wood decomposition, at known heating rate, the d initial moisture content of the wood, in the case of the assumption that the degree of matter decomposition, ω, is the result of the wood mass loss (STILLER 1989): M

  r d   Aп  e Tr d where: Ап – coefficient considering the density of wood, Тr – temperature, τr – time of treatment, Мω – wood mass loss: m  mcur M   in min  m fin

where: min, mcur, mfin – the initial, current and final wood mass.

Partial solution of the equation (2) with initial conditions ωin = 0, τcur = 1 is: M  Aп  Tr   Tr  r   e  1  M r  

(2)

(3)

(4)

RESULTS AND DISCUSSION Calculations based on the results of previous experiments of mass loss determination by the equation (3) and the degree of decomposition (4) for the influence of temperature 160 °C for 20 hours showed that an increase in the decomposition of anatomical elements (Fig. 1) is associated with a mass change.

27

Decomposition degree,

6

-3

95

8

90 85 0

5

10

15

20

ω, 10

Mass loss, Мω, %

100

4 2 0 0

5

Duration, τ, h.

a

10 15 Duration, τ, h.

20

b

Fig. 1 Decomposition of hornbeam wood under the high temperature influence in time: а – mass loss; b – decomposition degree.

Thus, by fixing the mass of samples during heat modification, a change in colour influenced by the degree of anatomical elements decomposition can be observed. Moreover, the loss of wood mass is one of the most important characteristics of heat treatment and it is usually called quality index (ESTEVES and PEREIRA 2009).

It is known that the change in the properties of wood during its thermal modification is influenced by the temperature and treatment duration. Changes in the structure of wood begin under the influence of temperature of 120 ºС (HILL 2006) and result from decomposition of hemicellulose. Lignin is more resistant to temperature influence, decompose begins at the temperature of 230 °C. These processes cause changes in wood properties. In general, in all existing wood heat treatment schedules, the temperature parameter is in the range of 160280 °C (RAPP 2001).

The processing time for most schedules is within 1052 hours (RAPP 2001). During the previous experiment, the fact that the effect of temperature duration of more than 20 hours on the properties of heat-treated hornbeam wood is practically not noticeable was found. Therefore, the range of temperature influence duration on wood is chosen within 120 hours. Influence of selected schedule parameters on hornbeam wood mass loss is illustrated in Fig. 2.

30

25,00-30,00 20,00-25,00 15,00-20,00 10,00-15,00 5,00-10,00 0,00-5,00

Mass loss, M ω, %

25 20 15 10

20

Duration, τ, h.

5 0

160

190

220

1

Temperature, T, °С Fig. 2 Dependence of hornbeam wood samples mass loss after heat treatment.

28

Basic density, ρbas , kg/m

3

Mass loss of samples after heat treatment is associated with a decrease in density of thermo-modified hornbeam wood (Fig. 3).

820 800 780 760 740 720 700 680 660

control 160 °С 190 °С 220 °С 1

10

20

Duration modification, τ, h.

Fig. 3 Change of hornbeam wood basic density in relation to parameters of heat treatment.

A significant mass loss of 26% was found for samples processed at the temperature of 220 °C for 20 hours (hard schedule). In this case, the basic density of these samples decreased by 12%, samples treated at the temperature of 160 °C by 8%, and at 190 °C by 11%. A similar trend is observed in the results of other researchers (GÜNDÜZ et al. 2008; BAL 2014, SOPUSHYNSKYY et al. 2017) in the analysis of a decrease in density of alder by 5.6%, fir by 4.5% compared to untreated wood (KOL 2010). This is due to the degradation of wood polymers, mainly hemicellulose, which is the most thermally sensitive wood component (PONCSAK et al. 2006; YILDIZ et al. 2006).

Samples of untreated and thermo-modified hornbeam wood were used to determine the change of wood colour under the influence of high temperatures. The final colour of the wood was measured after stabilization of samples in room conditions for 24 hours. Test samples were scanned at the same illuminating conditions in order to avoid the occurrence of an error associated with the peculiarities of falling light. The resulting photos were processed using the Photoshop program and received components of the colour model L, a and b. Every colour in the model is determined by the brightness value L (Lightness) and two chromatic coordinates а and b. Results of measurements and calculations are given in Tab. 1.

It can be seen that during heat modification, the test pieces changed their colour across the depth according to the chosen schedule parameters and acquired colour typical for exotic wood species. It has been established that darkening of the colour (decrease of parameter L and increase ΔE) becomes more noticeable with increasing temperature and processing duration (KÚDELA AND ANDOR 2018). Reduction of the parameter L indicates that components absorbing visible light formed in the heat treatment process (AKSOY et al. 2011, DUBEY et al. 2012, ESTEVES and PEREIRA 2009, MITSUI et al. 2001, DZURENDA 2018b). At high temperature modifications, the samples are virtually black. The darkening of the colour may be due to the decomposition of hemicellulose with a simultaneous increase in the lignin fraction (KAMDEM et al. 2002). An exception is a sample No. 3 (ΔE = 13.9), the reason for this can be the oxidation of the wood surface in the air before the heat modification beginning.

29

Schedule No.

Tab. 1. Results of colour components determination for heat-treated hornbeam wood.

Modification schedule parameters

Colour parameter

L*

a*

b*

Calculated value ΔE

natural

58.4

12

16.4

–

1

oak kraft

53.2

15

18.6

6.8

10

alder mountain

46

17.6

18.8

13.9

4

20

light beech

48.4

14.4

17.4

10.5

5

1

oak stone

49.4

16.8

20.2

11.2

10

oak rustic

34.6

16.2

16.8

24.3

7

20

beech chocolate

25.2

11

10.8

33.8

8

1

walnut tiepolo

30.2

12.8

11.8

28.6

10

wenge

14.4

4.8

2.8

46.6

20

wenge louisiana

13.8

4.4

2.2

47.5

Treatment temperature (°С)

1

Visualization of hornbeam wood colour changing after heat treatment

Treatment duration (h)

Sample colour after treatment

Control

2 3

160

6

190

9

220

10

Results of measurements

Note. The table shows the mean values for five points on each sample

The effect of high temperature modification on the change of moisture absorption of hornbeam wood is shown in Fig. 4.

Moisture absorption, Uabs , %

25

Schedule № 1 Schedule № 2 Schedule № 3 Schedule № 4 Schedule № 5 Schedule № 6 Schedule № 7 Schedule № 8 Schedule № 9 Schedule № 10

20 15 10 5 0 0

1

2

3

4

5

6

7

8

9

10

Duration, τ, days Fig. 4 Change of the moisture absorption of hornbeam wood after heat treatment.

The measured moisture content of samples at room conditions is 21.4% for untreated hornbeam wood and 9.3% for wood treated under maximum hard conditions. It was 30

Shrinkage, β v, %...

established that an increase in the treatment duration helps to reduce the ability of wood to absorb humidity from the air. Thus, when processed at a temperature of 220 °С, with an increase in the duration of treatment from 1 to 20 hours, moisture absorption is reduced by 1.4 times, when processed at a temperature of 190 °C by 1.5 times, and at 160 °C by 1.2 times. A similar tendency in reduction of moisture absorption is observed in the case of heat modification of eucalyptus wood (CADEMARTORI et al. 2014), acacia (VAN CHU 2013), juniper (KASEMSIRI et al. 2012) and black pine (DÜNDAR et al. 2012). The reason for the decrease of hygroscopicity can be explained by a decrease of quantity of hydroxyl groups in heat-treated wood (PETRISSANS et al. 2003). Also, reduction the water-sorption capacity of heat-treated hornbeam wood can be associated with a decrease in the number of primary sorption centres (–ОН groups) within the framework of a wood cell wall, mainly as a result of decomposition and removal hemicellulose components from the wood (pentosanes).

The amount of volume shrinkage was determined as a change in the samples linear dimensions of heat modified wood after drying in a drying chamber at the temperature of 103 + 2 °C. Shrinkage reduction (Fig. 5) leads to improved dimensional stability of heat treated wood, expressed as an Anti-Shrink Efficiency (ASE).

18 16 14 12 10 8 6 4 2 0 1

2

3

4

5

6

7

8

9

10

Modification's schedule Fig. 5 Shrinkage in both transverse directions of samples of heat-treated and untreated hornbeam wood.

The heat treatment of hornbeam wood has led to an improvement in the stability of the sizes by reducing the volume shrinkage in 1.31.9 times. It is noted that with increasing temperature and processing duration the amount of shrinkage decreases, although the value of this indicator is influenced by the technology of heat modification (YILDIZ 2002, KAYGIN et al. 2009, AKYILDIZ et al. 2009, ESTEVES et al. 2007).

The effect of the change of mechanical properties of heat modified wood was investigated during compression tests along the fibres, across the fibres and the bending strength.

Compression testing of samples along the fibres showed that there was a grinding of the ends of samples of untreated wood (Fig. 6a). In samples heat-treated at a temperature of 160 °C, a sloping fold appears, placed at an angle of 45° (Fig. 6b). In the ruined hornbeam wood samples heat-treated by hard schedules No. 6 and No. 9 (Fig. 6 c, d), two opposing straights of the fold, forming a wedge-shaped area with a longitudinal split, are clearly noticeable. Samples of untreated hornbeam wood withstood a load of 34 kN, heat-treated with soft schedules 3642 kN and hard schedules 3447 kN.

31

а

b

c

d

Fig. 6. The result of compressive strength along fibres of untreated and thermo-modified hornbeam wood samples for 10 hours: a – untreated wood, b – temperature 160 °C, c – temperature 190 °С, d – temperature 220 °С.

Heat treatment increases the fragility of the material (Fig. 6 c, d). This is confirmed in the work of researchers (BOONSTRA et al. 2007, ZAWADZKI et al. 2013, ANDOR and LAGAŇA 2018).

The results of the compression test across the fibres of hornbeam unprocessed wood samples and heat modified by soft schedules (No. 2, 3, 5) showed that they withstand a load of 5 kN without visible destruction. The samples which are heat modified at a temperature of 190 °C withstands the maximum load of 1.5 kN, and at 220 °C for 10 hours 1.1 kN, for 20 hours 0.9 kN with signs of destruction. During the test of bending at one-point load, the maximum load without signs of destruction was for hornbeam rough wood – 3.2 kN, heat modified for different times at a temperature t = 160 °С – 3.53.6 kN; at a temperature of 190 °С – 2.34.7 kN; 220 °C – 1.72.9 kN. The influence of the heat modification of hornbeam wood on mechanical properties showed mixed results. Calculated values of the strength of samples treated by schedules No. 2 – 10 for different types of tests are shown in Fig. 7.

Strength, σ, MPа///

250 Compression strength along the fibers σ ||

200 150

Compression strength across the fibers σ┴×10-1

100

Bending strength σb.s.

50 0 1

2

3

4

5

6

7

8

9

10

Modification's schedule Fig. 7 Results of mechanical tests of untreated and heat modified hornbeam wood by different schedules.

It was found that the compressive strength along the fibres of hornbeam wood samples modified at 190 °С increased 1.3 times; samples treated at temperature of 160 °C show a significant decrease in the compressive strength limit across fibres 3.3 times at the temperature of 190 °C and 5.2 times at 220 °C. A similar loss of compressive strength across the fibres was recorded by MOLINSKI et al. (2018) for ash wood – 1.5 times. However, for the pine (BOONSTRA et al. 2007), this indicator increased by 1.07 times. Such differences are 32

Impact resistance, H, J/сm

2

related to the anatomical structure of wood, in particular, with the peculiarities of the structure of perforations in the vessels of hornbeam wood and the absence of them in ash wood.

Bending strength slightly increased by 10-20 MPa after treatment at a temperature of 160 and 190 °C and preferably in the samples processed within 1 and 10 hours. A noticeable decrease in strength 1.6 times was observed at 220 °C at the modification within 20 hours.

Several studies have found that heat treatment reduces the bending strength from 1% to 72% (JOHANSSON and MOREN 2006, ESTEVES and PEREIRA 2009, SHI et al. 2007, KORKUT 2008).

The reasons for such change of mechanical properties have been widely discussed and it has been found that reasons for reducing the strength under bending and the destruction of the samples are decomposition of hemicelluloses and crystallization of amorphous cellulose.

Impact resistance of the wood is characterized by the size of the imprint (Fig. 8), which remains on the wood sample surface from a steel ball of 65 g, which freely falls from a height of 500 ± 1 mm counting from the bottom point of the ball surface. Carried out experimental studies showed that the modification of wood practically did not affect the index of impact resistance, there is a slight increase from 10 to 13% on the radial and tangential surfaces during modification at temperatures of 160 and 190 °C. During the modification at 220 °C, the impact resistance decreased by 9% only for the radial surface. It is worth noting that, as in untreated wood samples, the thermo-modified tangential surface is more resistant to impact than the radial.

3 2

Impact resistance Htang Impact resistance Hrad

1 0 1

2

3

4

5

6

7

8

9

10

Modification's schedule Fig. 8 Change of impact resistance values of hornbeam wood after heat modification.

Similar ambiguous results were observed when determining the impact resistance of heat modified wood of exotic species by Yank scale (ARAÚJO et al. 2016), pine and birch by Brinell (KYUNG-ROK WON et al. 2012), pine and oak by Shor (KARAMANOGLU and AKYILDIZ 2013). While the Thermowood Association of Finland noted increasing impact resistance with increasing temperature (THERMOWOOD HANDBOOK 2003).

The wear resistance of the material characterizing the ability of the surface layers to withstand fracture friction is one of the indicators for durability of hornbeam wood floor coverings. The results of wear resistance from experimental studies (Fig. 9) were evaluated by the weight loss value after grinding carried out in accordance with the requirements of GOST 16483.39-81 at the relative humidity in the room φ = 65 ± 5% and the temperature of 20 ± 2 °С.

33

Wear resistance, t, %

5 Wear resistance tangental parallel to the fibers ttang || Wear resistance tangental perpendicular to the fibers ttang ┴ Wear resistance radial parallel to the fibers trad ||

4 3 2 1

Wear resistance radial perpendicular to the fibers trad ┴

0 1

2

3

4

5

6

7

8

9

10

Modification's schedule

Fig. 9 The value of wear resistance in different directions for untreated and heat modified hornbeam wood by proposed schedules.

The analysis of obtained results did not reveal the effect of used schedules on the change of the wear resistance of hornbeam wood. It can be seen, that the wear resistance along and across fibres is better 2-3 times on the tangential surface of test pieces in comparison with the wear resistance on the radial surface. Similar results were obtained during the study of wild cherry wood wear resistance (AYTIN et al. 2015).

The influence of the heat treatment schedule parameters on physical and mechanical properties of hornbeam wood was studied by complete two-factorial experiment. The obtained regression models (Table 2) were checked for the adequacy of the Cochran (Gcr) and Fisher (Fcr) criteria.

Tab. 2. Checking the adequacy of regression models for output parameters. № 1 2 3 4 5 6

G-criterion Gcalc Gtable

F-criterion Fcalc Ftable

0.48

0.60

2.13

4.11

0.41 0.39 0.32

0.60 0.60 0.60

4.10 4.00 0.22

4.11 4.11 4.11

σ|| = 88.48+0.32Х1+ 5.12Х2-1.83Х1Х2

0.32

0.60

0.25

4.11

σb.s. = 146.71-28.53Х18.03Х2-18.08Х1Х2

0.38

0.71

4.46

4.49

σ┴ = 54.70-21.6Х111.75Х2-0.67Х1Х2

0.56

0.60

2.72

4.11

0.33 0.46

0.67 0.60

2.15 3.20

4.38 3.26

0.36

0.60

0.58

3.26

0.31

0.60

0.35

2.87

0.30

0.60

0.23

2.87

0.49

0.60

1.07

2.87

Output Parameter

Regression equation

Basic density (kg/m3) Shrinkage (%) Moisture absorption (%) Compression strength along the fibres (MPa) Bending strength (MPa) Compression strength across the fibers (MPa)

ρbas = 747.02-14.63Х123.06Х2+3.27Х1Х2 βtang = 5.35-1.64Х1-1.06Х2-0.2Х1Х2 βrad = 6.43-0.73Х1-0.90Х2-0.17Х1Х2 Uabs = 15-3.86Х1-1.75Х2-0.05Х1Х2

Htang = 2.45-0.11Х1-0.03Х2-0.09Х1Х2 Hrad = 2.11-0.07Х1-0.09Х2-0.10Х1Х2 ttang || = 1.54+0.14Х10.07Х2-0.03Х1Х2 ttang ┴ = 0.93+0.03Х1+ 0.02Х2-0.001Х1Х2 8 Wear resistance trad || = 4.08+0.07Х1+ 0.10Х2+0.09Х1Х2 trad ┴ = 3.22+0.05Х1+ 0.13Х2-0.10Х1Х2 Note. X1 – temperature, X2 – duration in normalized values 7

Impact resistance

34

Normalized values of response functions, %//

Since the conditions for inequality are fulfilled, the models are accepted as adequate and can be used to describe the output parameters. The verification of the regression equations adequacy for impact resistance and abrasion has shown that the models are adequate, but the regression coefficients X1, X2 and X12 are not significant, correlation connection is also not established. That is, the heat modification of hornbeam wood does not affect these properties.

The obtained equations can be used to determine rational schedule parameters. There are many methods to find the best solutions with certain features: the alternate variation of each input variable – the long-term path to finding the optimum (the Gauss-Seidel method); the large number of variables (random search method); the difficulty in selecting the value of the step of the factor change (gradient optimum search method); the gradual transition from the consideration of the influence of the most powerful factors to insignificant (relaxation method). The method of steep climb combines the listed methods and the method of a full-factor experiment. It can be applied to nonlinear mathematical models. The essence of this method is the systematic movement towards the fastest growth or decline of the output variables, with the direction corrected when the partial extremum of the target function is achieved (SKYBA et al. 2010).

In our case, the target function was implicitly expressed, although it outlined the schedule parameters in which the properties studied acquire a partial extremum. The application of the steep climb method allowed determining the rational regime parameters of the heat modification of hornbeam wood (Fig. 10).

120 basic density ρbas

100 80

shrinkage βtang

60

shrinkage βrad

40

moisture absorption Uabs

20

compression strength σ ||

0 -20

1

2

3

4

5

6

7

8

9

bending strength σ b.s.

Modification's schedule

Fig. 10 The area of rational schedule parameters for heat modification of hornbeam wood.

It can be seen that the best results of the investigated physical and mechanical properties of heat modified hornbeam wood can be achieved with the following schedule parameters – temperature t = 190 ° С and duration in the range τ = 8-12 hours.

CONCLUSIONS The research established that the process of heat treatment of hornbeam wood occurred with the mass loss depending on the degree of decomposition of anatomical elements. A simplified Arrhenius equation was proposed to describe and calculate the degree of phased 35

decomposition taking into account the mass loss of structural components of wood at each stage of the process. The fact that with increasing temperature and treatment duration, the mass loss of hornbeam wood increases from 4.5% to 26% in the case of heat treatment by different schedules was determined. The influence of schedule parameters of the heat modified process on the change in the value of some physical properties (density, colour, moisture absorption and shrinkage) of hornbeam wood was determined. The fact that in comparison to untreated wood, heat modified hornbeam wood: the density decreases by 812% when applying different schedules accordingly; the moisture absorption decreases by an average of 23.5 times when using hard schedules; the volume shrinkage decreases by 1.31.9 times. Also, it was established that thermo-modification has the ambiguous effect on mechanical properties of hornbeam wood: the compressive strength across the fibers decreases by an average of 880%; the compression strength along the fibres is improved by 1050%; the bending strength increases by 2050% in samples thermo-modified at temperatures of 160 and 190 °C, and then decreases.

Based on the analysis of theoretical and experimental data, rational schedules of heat modification of hornbeam wood were established with the help of step climb method. The best results of physical and mechanical properties of investigated hornbeam wood were achieved with the following heat treatment schedule parameters: temperature t = 190 °С and duration within the range τ = 812 hours. Wood treated under such conditions contributes to a decrease in the shrinkage rates along and across fibres and moisture absorption values.

The basic density decreases after heat modification, hornbeam wood becomes lighter at the same hardness. These parameters indicate the dimensional stability and such wood can be used in an environment with significant temperature and humidity variations. An increase in the static bending strength and compression along the fibres, as well as maintaining the resistance of the wood to abrasion, allow producers to use the heat-treated hornbeam wood for interior and exterior applications. After heat modification, the hornbeam wood acquires a colour that simulate some tropical species. Moreover, modified wood is much cheaper and does not require additional surface finishing and impregnation with protective substances and can be used for floor coverings, garden furniture and decor, the arrangement of terraces, playgrounds, etc.

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ACKNOWLEDGEMENTS This work was supported by the Ukrainian Ministry of Education and Science under Program No 2201040. “The research, scientific and technological development, works for the state target programs for public order, training of scientific personnel, financial support scientific infrastructure, scientific press, scientific objects, which are national treasures, support of the State Fund for Fundamental Research”. The authors are grateful to Ministry of Education and Science of Ukrainian for financial support of this study.

This work was supported by the Slovak Research and Development Agency under the contracts No. APVV-17-0456 and APVV-18-0378.

AUTHOR’S ADDRESS Prof. Ing. Olena Pinchevska, DrSc. Assoc. prof. Ing. Oleksandra Horbachova, PhD. Assoc. prof. Ing. Andriy Spirochkin, PhD. National University of Life and Environmental Sciences of Ukraine Department of Technology and Design of Wood Products Heroiv Oborony str. 15 03041 Kyiv Ukraine OPinchewska@gmail.com gorbachova.sasha@ukr.net a.spirochkin@gmail.com Prof. Ing. Ján Sedliačik, PhD. Technical University in Zvolen Department of Furniture and Wood Products T.G. Masaryka 24 960 01 Zvolen Slovakia sedliacik@tuzvo.sk

Ing. Ivan Rogovskii, PhD., Senior Researcher Director of Research Institute of Engineering and Technology National University of Life and Environmental Sciences of Ukraine Heroiv Oborony str. 15 03041 Kyiv Ukraine rogovskii@nubip.edu.ua 39

ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 41−50, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.04

SURFACE FINISHES FOR THERMALLY MODIFIED BEECH WOOD Gabriela Slabejová  Zuzana Vidholdová  Mária Šmidriaková ABSTRACT Natural oils and waxes are commonly used for wooden furniture and parquet surfaces.

In the present study, linseed oil, hard wax oil and hard wax were applied as the surface finish on thermally modified beech wood. Adhesion of surface finishes to wood was evaluated by both Cross-cut test and Pull-off test. The impact resistance of the surface finishes was determined according to the standard. The film hardness was determined by the pencil test according to the standard. According to the Cross-cut test, the adhesion of oil surface finishes to native wood and to thermally modified wood was the same. Adhesion of wax surface finish to the thermally modified wood was lower than to native wood. According to the Pulloff test, the adhesion of oil surface finishes to thermally modified wood was lower than to native wood. Adhesion of wax surface finish to the thermally modified wood was the same as the adhesion to native wood. Thermally modified wood showed the increased surface hardness of the selected oil and wax surface finishes under static load (Pencil hardness test); however, under dynamic load (Impact resistance test), it showed increased brittleness.

Key words: adhesion, beech, hardness, impact resistance, oil, thermally modified wood, wax.

INTRODUCTION Thermally modified timber is wood which composition of the cell wall material, physical properties, mechanical, aesthetical, and biological properties are modified by exposure to the temperature higher than 160 °C and conditions of decreased oxygen availability. There are various procedures to carry out this process; most of which differ in the way they exclude air/oxygen from the system. The main heat treatment processes in Europe are covered by patents; and wood processes and wood products are signed by names such as FWD = Feuchte – Wärme – Druck Behandlung / Moisture – Heat – Pressure treatment in steam atmosphere in Deutschland, PlatoWood® in Saturated steam/heated air in Netherland, ThermoWood® in steam atmosphere in Finland, Le Bois Perdure = Perdure ® in steam atmosphere in France, Retiwood® in nitrogen or other gas atmosphere in France, Oil – Heat - Treated Wood = OHT® in vegetable Oil in Germany and TermoVuoto = VacWood® in vacuum atmosphere in Italy (REINPRECHT and VIDHOLDOVÁ 2011, SANDBERG et al. 2017). Different processes result in different chemical heat-induced changes in wood. A heat treatment always results in darkening of wood what is often explained by formation of coloured degradation products from hemicelluloses and extractive compounds (PONCSAK et al. 2011, KAČÍKOVÁ and KAČÍK 2011, VIDHOLDOVÁ et al. 2019).

The formation of oxidation products, such as quinones, can be a reason for darker wood 41

colour (TJEERDSMA et al. 1998, DZURENDA 2018a,b). The darkening is often seen positively, especially in temperate hardwoods, imitating and looking like tropical wood species (JIROUŠ-RAJKOVIĆ and MIKLEČIĆ 2019).

Besides improved stability, reduced hygroscopicity and smaller dimensional changes (AYTIN et al. 2015, BEKHTA et al. 2017, AHMED et al. 2017, ANDOR and LAGAŇA 2018), heat-treated wood also has some shortcomings, such as loss of toughness, reduced tensile and bending strengths, unstable colour when exterior exposure, and appearance of surface cracking (ŽIVKOVIĆ et al. 2008). The results HERRERA et al. (2018) indicate acceptable photostability of thermally modified wood, when wood is coated with decorative waterborne polyurethane and industrial UV-hardened coatings. For the same coatings, HERRERA et al.

(2015) reported improved adhesion to thermally modified wood when compared with unmodified wood. Dimensional stability of the heat-treated wood reduces peeling of coatings. As a result of migration of fats, resins and other non-polar or less polar substances contained in wood, as well as due to degradation of hydroxyl groups in wood polysaccharides, the wood surface becomes more hydrophobic (HAKKOU et al. 2005, KÚDELA et al. 2018). When coniferous wood is treated by high temperature, the resin is poured (impregnated) from the resin canals into the surrounding parts of wood and does not protrude to the surface. It has been found that the resistance of heat-treated wood to weathering (UV light and moisture changes) is not changed significantly when compared to untreated wood, making a surface treatment with coatings necessary. Low temperature radiofrequency (RF) discharge plasma was used to improve the surface and adhesive properties of wood. The enhancement of wettability of wood is necessary to promote adhesion of adhesives and coatings (NOVÁK et al. 2015).

Coatings based on oil wet the surface of thermally modified wood well. The coatings based on waterborne substances, due to lower absorption of water by the surface have longer time of hardening and penetration.

Above mentioned facts significantly influence the interaction between the surface of thermally modified wood and coating material; and subsequently the mechanical and resistance properties of the surface finish. The penetration of coating systems into thermally modified wood was not found to differ from unmodified wood, although excessive penetration of solventborne oil was found occasionally for thermally modified wood. The adhesion strength of waterborne coatings depended on the system used (ALTGEN and MILITZ 2017). The mechanical properties of surface finish were researched on veneers modified by silicone resins (SLABEJOVÁ et al. 2018) and on pigmented surface finishes for interior use (SLABEJOVÁ and ŠMIDRIAKOVÁ 2018). CHANG et al. (2019) indicated that the hardness, mass retention, tensile strength, abrasion resistance, and lightfastness of oil-modified refined lacquer films decreased as more drying oils were blended with lacquer. MIKLEČIČ et al.

(2017) measured adhesion of surface finishes to thermally modified wood after weathering aging. SAHA et al. (2010) monitored wetting of modified waterborne coating materials applied on thermally modified wood.

Coatings based on natural and synthetic oils and waxes, or in combination with aqueous dispersions, belong to the group of "green” and penetrating coating materials which enhance the natural wood grain and appearance. However, oil-based surface finishes have limited quality characteristics (low hardness, problematic light stability, and low resistance to liquids – detergents, food, and chemicals). They are poorly resistant to abrasion when used for stressed wood products (furniture surfaces – worktops) and wood flooring. Oils do not protect surfaces from weathering discolouration. They are only recommended for finishing of thermally modified wood products that are kept away from direct sunlight and rain (JIROUŠ-RAJKOVIĆ and MIKLEČIĆ 2019). Semi-transparent oil-based stains with small amount of colouring agent showed the weathering resistance from two to five years, although 42

the results differed by regions (KIM 2018). Epoxidized camelina oil and acrylated epoxidized camelina oil are promising candidates for UV-curable coating applications. These oil coatings showed good pencil hardness and strong adhesion to wood substrates (LI et al.

2018).

The presented work deals with evaluation of selected properties of oil and wax surface finishes on thermally treated beech wood: the adhesion, impact resistance, and the surface hardness.

MATERIALS AND METHODS Materials In the experiments, thermally treated and thermally untreated beech boards (native) were used. The boards were radially cut. The test specimens were made from beech wood: 1 without treatment – native wood, 2 thermally modified at 175 °C for 4 hours (TM 175 °C).

Wood was provided by the company TECHNI – PAL Polkanová (Slovakia). The dimensions of the test specimens were 1000 × 100 × 20 mm. The specimens for testing of resistance to abrasion were with dimensions of 100 × 100 × 20 mm. The test specimen surface was grinded with sandpapers with grid number of P60 and then with the number of P80. For surface finishing, the following coating materials were used:  Linseed oil (Nochema) – is used to make a base coat on wood or other absorbent surfaces under the coatings of oil or synthetic coating materials.  Hard wax oil (Renojava s.r.o.) – is a mixture of hard wax oil, siccative and aliphatic solvent. It is used to treat all types of parquets and interior furniture with both normal and high loads.  Hard wax (Hartwachs, Adler) – is a hard wax without solvents, based on natural oils and wax. It contains linseed oil, beeswax, carnauba wax, and cobalt-zircone siccative.

The following surface finishes were made: 1 linseed oil – 1 coat – the average film thickness of 40 ± 10 µm (linseed oil), 2 linseed oil + hard wax oil – 1 coat + 2 coats – the average film thickness of 80 ± 10 µm (linseed oil + oil), 3 hard wax – 1 coat – the average film thickness of 50 ± 10 µm (wax).

The surface finishes were made for all test specimens according to the recommendations listed in technical sheets.

Adhesion tests Adhesion strength of the coating films on thermally modified wood and unmodified wood was determined by the Pull-off test according to the standard STN EN ISO 4624 (2016) and by the Cross-cut test according to the standard STN EN ISO 2409 (2013).

The Cross-cut test was done as follows: a crosshatch pattern was cut through the coating film to the substrate. The adhesion of the coating film was classified according to the standard STN EN ISO 2409 (2013) (Tab. 1). The figures are examples for a cross-cut within each step of the classification. The percentages stated are based on the visual impression given by the pictures and the same percentages will not necessarily be reproduced with digital imaging.

The testing machine PosiTest AT-M (Qualitest, Canada) was used for Pull-off test.

Small 20 mm diameter dollies were glued to the coating using two-component epoxy resin (Pattex Repair Epoxy). After 24 h of curing at 20 °C and a relative air humidity of 60%, 43

perimeters of glued dollies were carefully incised to prevent propagation of failures outside the tested area. Pulling was carried at a rate of 1 mm/min up to separation of the dolly from the surface. After each test, the fracture (Fig. 1) was evaluated visually using a stereomicroscope LEICA MZ 9.5 with magnification of 4 ×.

Tab. 1 Evaluation of the cross-cut area.

Classification Surface of crosscut area from which flaking has occurred.

(Example for six parallel cuts)

0

1

2

3

4

5

none

< 5%

5% – 15%

15% – 35%

35% – 65%

> 65%

Fig. 1 Classification of failure location for the Pull-off strength test.

The impact resistance test and film hardness The impact resistance of the surface finishes was determined according to the standard STN EN ISO 6272-2 (2011). The intrusion (diameter of the intrusion) was measured at drop height of 400 mm and the surface finish was evaluated subjectively according to Tab. 2.

Tab. 2 Impact resistance: degree and evaluation.

Degree 1 2 3 4 5

Visual evaluation No visible changes No cracks on the surface and the intrusion was only slightly visible Visible light cracks on the surface, typically one to two circular cracks around the intrusion Visible large cracks at the intrusion Visible cracks were also off-site of intrusion, peeling of the coating

The film hardness was determined by the pencil test according to the standard STN EN ISO 15184 (2012). The results of the test were evaluated according to the pencil that scratched the surface (Tab. 3). The test started with the softest pencil (pencil number 1).

Tab. 3 Degrees of film hardness.

Pencil Number Pencil Hardness

1 3B

2 2B

3 B

4 HB

5 F

44

6 H

7 3H

8 4H

9 5H

10 6H

11 7H

12 8H

13 9H

RESULTS AND DISCUSSION The results of selected physical-mechanical properties of the tested surface finishes on native beech wood and thermally modified beech wood are summarised in Tab. 4.

Tab. 4 Physical-mechanical properties of tested surface treatments.

Surface finish Treated surface Adhesion – degree [0-5] (Cross-cut test)

Linseed oil Native TM 175 °C 2

2

2

Adhesion [MPa] (Pull-off test)

5.41 (0.30)

5.08 (0.18)

2 5.6

3 5.5

Impact resistance – degree [1-5] – diameter of the intrusion [mm]

Pencil hardness 6 7 – degree [1-13] NOTE: In presence is value of standard deviation

Linseed oil + oil Native TM 175 °C

Native

Wax TM 175 °C

2

3

4

5.19 (0.25)

4.72 (0.43)

4.43 (0.23)

4.43 (0.30)

3 5.3

3 5.4

2 5.2

3 5.2

5

6

8

8

Adhesion The oil surface finishes (linseed oil, linseed oil + oil) showed good adhesion at the Crosscut test. The surface finish has flaked along the edges and/or at the intersections of the cuts.

A cross-cut area up to 15% was affected on both tested wood substrates. The adhesion of wax surface finish to native wood was lower; the cross-cut area up to 35% was affected on native wood (classified as 3) and up to 65% (classified as 4) on thermally modified wood.

This situation is documented in Fig. 2.

NATIVE

WAX

TM 175 °C

1 mm

1 mm

Fig. 2 Grid damage on surface finish after Cross-cut adhesion testing.

NEJAD et al. (2013) reported the adhesion polyurethane and acrylic-based coatings on oil-treated wood and native wood. A cross-cut area up to 5% was affected on native wood, but on oil-treated wood, a cross-cut area greater than 65% was affected.

The linseed oil reached the highest adhesion measured by Pull-off strength test and the wax the lowest one. The analysis of the average adhesion of these surface coatings to native wood and to thermally modified wood by 2-factor ANOVA showed that not only the type of coating has a significant influence on the adhesion, but also the thermal modification has the influence on the adhesion (p-value < 0.0001, respectively p-value = 0.001; Tab. 5). Interaction between coating and thermal modification was found 45

to be statistically less significant (p-value = 0.044; Tab. 5). The analysis of adhesion to native wood and to thermally modified wood by Duncan test showed that statistically less significantly differences was found for both linseed oil surface finish and linseed oil + oil surface finish (p-value = 0.009, respectively 0.008; Tab. 5). The adhesion of wax surface finish to the surface of native wood and thermally modified wood was at same level (p-value = 0.974; statistically insignificant; Tab. 5).

Tab. 5 Basic analysis of variance for adhesion.

Sum of Squares

Factors Treated surface (native wood – thermally modified wood) Surface finish (linseed oil – linseed oil + oil – wax) Interaction treated surface * surface finish Absolute member Error

Degrees of Freedom

Variance

F-test

Level of significance p-value

1.072

1.000

1.072

12.476

0.001

6.844

2.000

3.422

39.827

0.000

0.570

2.000

0.285

3.320

0.044

1427.303 4.640

1 54.000

1427.303 16611.35 0.086

0

The important are not only the measured values of adhesion, but also the analysis of the damaged area after pull-off testing. Fig. 3 shows that pulling-off the dolly from the surface of native wood with linseed oil surface finish caused pulling-off the wood surface layer up to 1 mm deep. The adhesion was higher than cohesion of wood surface layer, as expected. The same damage was noticed also after pull-off test on thermally modified wood with linseed oil surface finish (Fig. 3). It can be assumed that the adhesion of the coating film was higher than the cohesion of wood surface layer. From Tab. 4 follows the cohesion of thermally modified wood surface layer adhesion with the linseed oil was lower than the cohesion to native wood.

NATIVE

Wood surface

LINSEED OIL

Dolly's surface

Wood surface

TM 175 °C

Dolly's surface

Fig. 3 Surfaces of wood and a dolly after pulling-off the surface finish of linseed oil.

After pull-off test on native wood with linseed oil + oil surface finish (Fig. 4), the damage was on the interface of linseed oil + oil, as supposed. Pulling off the wood fibres occurred on the area smaller than 5%. It can be stated the measured value represents the size of the coating film cohesion. Similar results were also reported by SLABEJOVÁ and VIDHOLDOVÁ (2019a) who evaluated the adhesion of the oil coating film and alkyd coating film to aged wood and to wood attacked by fungi. In Pull-off test, the cohesive break occurred mostly in the oil coating film.

In the case of thermally modified wood, the damage occurred in the surface layers of wood (Fig. 4). We assume that the measured value represented the size of cohesion of the surface layers of wood; and the adhesion and also the cohesion of the coating film were 46

higher. SLABEJOVÁ and VIDHOLDOVÁ (2019b) described the similar damage occurred on an oil surface finish on wood attacked by fungi. The wood surface layers were weakened and the break occurred in the oil-impregnated layer of wood.

NATIVE

Wood surface

LINSEED OIL + OIL

Dolly's surface

TM 175 °C

Wood surface

Dolly's surface

Fig. 4 Surfaces of wood and a dolly after pull-off test of surface finish of linseed oil + oil.

Fig. 5 shows that after pulling-off the dolly from the native wood surface with wax surface finish, the damage was on the interface of coating film-wood. It can be stated the measured value was the size of adhesion.

In the case of thermally modified wood, after pulling-off the dolly, the damage occurred on the interface of wood – coating film and partly in the surface layers of wood (to 30%). At breaking in the interface, the cut wood fibres were plucked from the surface. We assume the measured value was the size of adhesion. From Tab. 4, we can conclude that the adhesion of wax coating film to thermally modified wood was similar to the adhesion to native wood. The results KÚDELA et al. (2018) showed the substantially worsened wetting of the thermally modified beech wood. They also reported poorer drop spreading over the wood surface. This fact can affect the surface treatment quality with coating materials applied on thermally treated wood negatively. According to HERRERA et al. (2015) the improved hydrophobicity was not a critical factor for the application of coating systems and previous sanding process could improve coatability of modified wood.

NATIVE

Wood surface

TM 175 °C

WAX

Dolly's surface

Wood surface

Dolly's surface

Fig. 5 Surfaces of wood and a dolly after pull-off test of wax surface finish.

Impact resistance On thermally modified wood with the linseed oil surface finish, the damage at a drop height of 400 mm was graded as 3 (visible light cracks on the surface, typically one to two circular cracks around the intrusion), the degree of damage on native wood was of grade 2 (Tab. 4).

On thermally modified wood with the linseed oil + oil surface finish, the damage at a drop height of 400 mm was graded as 3; and the same on native wood. On thermally modified wood with the wax surface finish, the degree of damage at a drop height of 400 mm was of grade 3; and the damage on native wood was graded as 2 (Tab. 4). The intrusions at a drop height of 400 mm are comparable with the intrusions on pigmented polyester-polyurethane surface finish on MDF veneered with beech veneer reported by SLABEJOVÁ and 47

ŠMIDRIAKOVÁ (2018). On beech veneer with silicone coating, under the same conditions, diameter of the intrusions was by a half smaller (2.5–3 mm) (SLABEJOVÁ et al. 2018). Impact resistance of a surface finish is influenced by quality of the coating and also by hardness of the substrate. Diameter of the intrusion depends on hardness of the substrate; and damage of the coating film depends on the film's brittleness and elasticity. TESAŘOVÁ et al. (2017) reported a hypothesis about the relationship between the physical-mechanical properties of lacquers films and the ultimate tensile stress of free coating films. On the tested oil surface finishes, the biggest damage was graded as 3; while SLABEJOVÁ and ŠMIDRIAKOVÁ (2018) and SLABEJOVÁ et al. (2018) reported the degree of damage of grades 4 or 5 on polyesterpolyurethane and silicone surface finishes. However, oil-based surface finishes have low hardness and it show low brittleness.

Film hardness The wax surface finish showed the highest film hardness (degree 8; Tab. 4); and the surface hardness was not affected by the wood surface quality (thermally modified wood).

Surprisingly, surface finishes of linseed oil and linseed oil + oil had better scratch resistance on thermally modified wood than on native wood. NEJAD et al. (2013) reported similar results of higher pencil hardness for polyurethane and acrylic-based coatings on oil-treated wood if compared with the hardness on native wood. The surface hardness (Pencil hardness test) is a property of a coating film; but it was demonstrated that the measured hardness is influenced by the hardness of substrate.

CONCLUSION Based on the results we can conclude:  According to the Cross-cut test, the adhesion of oil surface finishes (linseed oil, linseed oil + oil) to native wood and to thermally modified wood was the same.

Adhesion of wax surface finish to the thermally modified wood was lower than to native wood.  According to the Pull-off test, the adhesion of oil surface finishes (linseed oil, linseed oil + oil) to thermally modified wood was lower than to native wood. Adhesion of wax surface finish to the thermally modified wood was the same as the adhesion to native wood.  The best adhesion to wood surface was found for linseed oil surface finish, the worst adhesion for wax surface finish.  Thermally modified wood showed the increased surface hardness of the selected oil and wax surface finishes under static load (Pencil hardness test); however, under dynamic load (Impact resistance test), it showed increased brittleness.

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ACKNOWLEDGMENTS This work was supported by the Slovak Research and Development Agency under the contract No. APVV-17-0583 and No. APVV-16-0177, and by the Scientific Grant Agency of the Ministry of Education SR Grant No. VEGA 1/0729/18, and No. VEGA 1/0822/17. We thanks also to P. Buček fom the company TECHNI – PAL Polkanová (Slovakia) for his technical assistance.

AUTHORS’ ADDRESSES Ing. Gabriela Slabejová, PhD. Ing. Zuzana Vidholdová, PhD. Ing. Mária Šmidriaková, PhD. Technical University in Zvolen Faculty of Wood Sciences and Technology Department of Furniture and Wood Products/ Department of Wood Technology T.G. Masaryka 24 960 01 Zvolen Slovakia slabejova@tuzvo.sk zuzana.vidholdova@tuzvo.sk smidriakova@tuzvo.sk 50

ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 51−61, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.05

DISPLACEMENT WASHING OF KRAFT PULP AT VARIOUS WASH WATER TEMPERATURE František Potůček – Mostafizur Rahman ABSTRACT The aim of the paper was to investigate the influence of the wash liquid temperature on the displacement washing efficiency of unbeaten unbleached kraft coniferous pulp. The simple axially dispersed plug flow model comprising one dimensionless criterion, the Péclet number, was used for displacement washing of black liquor from packed fibre bed using pure wash water with temperature of 10 to 60 °C. The pulp fibre beds were characterised by their hydraulic resistance, average specific resistance, porosity, and equivalent pore diameter, influencing the flow of wash liquid through pulp bed. From breakthrough curves, the wash yield and the Péclet number were evaluated. The results obtained showed that the wash yield is mainly influenced by the Péclet number characterising the time dependence of alkali lignin removal from the pulp bed, however, the effect of the wash water temperature upon the wash yield was not proved in the given temperature range.

Key words: displacement washing, fibre bed resistance, kappa number, kraft pulp, wash yield.

INTRODUCTION The displacement of a solute from within the pulp fibre pad is affected by several process variables. Besides pad consistency, pad thickness, wash liquid velocity, initial pad liquor concentration, and others, the influence of the wash liquid temperature on the washing efficiency is mentioned by several authors (LEE 1979; HAKAMÄKI, KOVASIN 1985; POIRIER et al. 1987; SMITH, DUFFY 1999; TRINH et al. 1989).

LEE (1979) reported that displacement efficiency characterised by the sodium-ion yield had an increasing trend with increasing the fibre pad temperature ranging from 20 to 55 °C. For a blend of softwood and hardwood kraft pulps, an efficiency increase depended on the fibre bed consistency. Lower increase in sodium-ion yield of 0.85 to 0.88 was at the pad consistency of 3.5%, while, for the consistency of 17%, an increase of 0.65 to 0.82 was achieved. The greater effect of temperature on washing efficiency at high pad consistency is ascribed to the relative greater portion of stagnant liquor in fibre pads comparing with low consistency when the free liquor occupying the interstitial spaces between fibres prevails.

HAKAMÄKI and KOVASIN (1985) investigated the effect of temperature within the limits of 30 to 90 °C for brownstock washing. Using a drum washer, an increase in washer capacity was observed with increasing the pulp temperature, but the effect of temperature on the washing efficiency was not evaluated.

51

SMITH and DUFFY (1999) performed the displacement washing of bleached kraft pulp at the black liquor temperature of 1 to 70 °C. The highest sodium-ion yield of 0.692 to 0.713 was recorded for the high black liquor temperature of 70 °C, while a temperature decreasing to 1 °C led to a decrease in the wash yield by 4.5 to 7%.

On the contrary, POIRIER et al. (1987) and TRINH et al. (1989) who investigated the displacement washing of kraft softwood pulp reported that the temperature changes over the range of 60 to 90 °C had no effect on the displacement washing efficiency determined for both sodium-ion and alkali lignin yields.

Different pulps and experimental techniques belong among several reasons for some contradictions in the results of various authors. Furthermore, it is possible that the effect of temperature on washing efficiency was obscured by interactions with other process variables (TRINH et al. 1989). In pulp-liquor pad, the spent pulping liquor is located both in the interstitial spaces between fibres and in the fibre walls. While the free liquor between fibres can be easily removed by displacement (SANTOS, HART 2014), the transport of the liquor from the fibre walls to the liquor flowing through pad pores is influenced by the diffusion of solutes, depending on the driving concentration force and temperature. The leaching of solutes from within fibre walls is relatively slow in comparison with displacement mechanism. Moreover, the diffusion coefficient of lignin in liquids is very low and is influenced markedly with increasing temperature above 70 °C (FAVIS et al. 1983).

Therefore, it seems that the displacement washing efficiency can be mainly affected by a longitudinal dispersion in the pulp fibre pad. Viscosity and density differences of displacing and displaced liquids can lead to the formation of fingering or channelling (NUNGE, GILL 1969; LEE 1984; POTŮČEK 2003). It can be supposed that channelling between dissimilar miscible liquids during displacement in a pad of wood pulp fibres occurs primarily as a result of preferential penetration of the wash liquid in regions of the porous structure having a higher permeability.

The objective of this paper was to investigate the effect of wash liquid temperature ranging of 10 to 60 °C on the displacement wash yield of alkali lignin. The influences of wash water temperature upon some characteristics affecting hydraulic resistance of the static pulp bed and mobility of wash water were evaluated as well.

EXPERIMENTAL PART Displacement washing runs simulated under the laboratory conditions were performed in a cylindrical glass cell with inside diameter of 35 mm under constant pulp bed height of 30 mm. The fibre pulp bed occupied the space between the permeable septum and a piston, covered with 45 mesh screens (sieve opening of 0.354 mm, nominal wire diameter of 0.224 mm) to prevent fibre losses from the bed.

Pulp beds were formed from a dilute suspension of unbeaten unbleached kraft pulp in black liquor. Properties of black liquor were as follows: solids content of 21.4 % (of which ash presented 64 % and organic substances 36 %), density of 1097 kg m–3 at 22 °C, pH value of 12.0, and alkali lignin concentration 56 g dm–3. Kraft softwood pulp was cooked industrially from a blend of spruce and pine. In accordance with ČSN ISO 302 the degree of delignification of kraft pulp was characterised by the kappa number of 24.9. Using the Kajaani instrument, the length of pulp fibres in the wet state was expressed in terms of the weighted and numerical averages, equal to 2.19 mm and 1.22 mm, respectively. The fibre coarseness had a value of 0.167 mg m–1.

A sample of the wet kraft pulp with a consistency of about 42 % was disintegrated manually and then gently mixed with 100 cm3 of the black liquor for approximately 20 min.

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The 4% pulp suspension was poured into the washing cell and pulp pad was allowed to form by gravity drainage. The pad was compressed to a thickness of 30 mm and a consistency of 128 to 134 kg m–3, with an average of 130 kg m–3. The pulp beds were not mechanically conditioned and were used as formed.

Distilled water was used as wash liquid for all runs. The temperature of wash liquid prior to entering the washing cell was maintained at six different levels within the limits of 10 to 60 °C. To investigate the displacement washing process, the stimulus-response method was chosen. Distilled water was distributed uniformly through the piston to the top of bed at the start of the washing experiment, approximating a step change in alkali lignin concentration. At the same time the displaced liquor was collected at atmospheric pressure from the bottom of the bed through the septum. The washing effluent was sampled at different time intervals until the effluent was colourless. Using an ultraviolet spectrophotometer operating at a wavelength of 295 nm, samples of the washing effluent leaving the pulp bed were analysed for alkali lignin. At all wash liquid temperatures, washing runs were once replicated. Displacement washing experiments with pulp fibres including washing equipment were described in detail in the preceding paper (POTŮČEK 1997).

After completing the washing run, the volumetric flow rate of wash liquid was measured gravimetrically at the pressure drop of 7 kPa to determine a permeability and average effective porosity of the pulp bed. Analogous measurements at various consistencies of the bed were focused on the determination of the effective specific surface of pulp fibres based on fibre mass, am, and on fibre volume, aV, according to INGMANSON (1953). The evaluation of the specific fibre surfaces was described in detail earlier (POTŮČEK 1997; POTŮČEK, MARHANOVÁ 1998).

Treatment of experimental data Pulp fibre bed characteristics Generally, the superficial velocity of wash liquid, u, flowing through a porous medium, such as the pulp fibre bed, directly proportional to the driving force, pressure difference ΔP, and indirectly proportional of the hydraulic resistance, R, is given by Darcy´s law in the form

uB

P h

(1)

which holds in the streamline flow regime (BIRD et al. 1968). Then, the hydraulic resistance of pulp bed to the flow of the liquid is expressed as R

h B

(2)

where μ is the liquid viscosity, h is the bed thickness, and B is the average permeability which expresses a measure of the liquid conductivity through the porous bed.

By assuming that the pore network consists of many distinct, continuous, and regular channels, the permeability can be expressed using the well-known classical macroscopic Kozeny-Carman equation in the form

B

3 (1   ) 2 aV2 K

(3)

where ε is the average effective bed porosity defined as a ratio of the volume of the pore space open to flow to the volume of the porous pulp bed (LINDSAY 1994), and aV is the specific surface of fibres. The Kozeny constant, K, depending only upon the shape of pores and the ratio of the tortuous length that liquid traverses in passing through the bed to the 53

actual bed thickness has an average value of 5.55 for randomly packed fibre beds (INGMANSON 1953; LINDSAY 1994).

If the mass of fibres in the bed mF = h A ρF where A is the cross-sectional area and ρF is the consistency of pulp, then the average specific bed resistance, α = (B ρF)–1 (HERWIJN et al. 1995), may be written as



(1   ) 2 aV2 K

 3 F

(4)

The average specific bed resistance, α, is a measure of the resistance offered by the fibre bed to the flow of wash liquid.

If the Kozeny-Carman equation is applicable for the flow through porous bed (MCCABE et al. 2001), the equivalent pore diameter

deq  8.2

uh  P

(5)

can be calculated in the streamline flow regime, knowing the superficial wash liquid velocity, u, and the pressure drop across the pulp bed, ΔP. Washing breakthrough curves The shape of the washing curve can be characterised in terms of the dimensionless Péclet number derived from the mass balance of the tracer (POTŮČEK 2001), in our case alkali lignin, for a given system in unsteady state in the following form Pe 

hu D

(6)

where h is the thickness of the pulp bed, u is the wash liquid superficial velocity, D is the longitudinal dispersion coefficient, and ε is the average effective porosity of packed bed.

Evaluation of the Péclet number from the breakthrough curves was described in detail in the previous papers (POTŮČEK 1997, 2001). In short, after converting the washing curve obtained as a response to the step input signal to a normalised dependence of dimensionless exit solute concentration upon the dimensionless time, one may reduce it by differentiation to the corresponding response to the pulse input signal which can be characterised by its variance (LEVENSPIEL 1962). For closed system of finite length, the relationship between the variance and the Péclet number was derived by LAAN (1957).

The displacement washing curve area is directly proportional to the amount of alkali lignin removed from the pulp bed. The traditional wash yield, WYRW=1, can be expressed as RW 1

WYRW 1

e d ( RW ) 0 RW  0  RW  e d ( RW )  0 RW  0



(7)

where RW is the wash liquor ratio, defined as the mass of wash liquid passed through the bed to the given time divided by the mass of mother liquor originally present in the bed, ρe is the exit lignin concentration and ρ0 is the initial lignin concentration in the bed at RW = 0.

Thus, the wash yield is defined as the amount of solute washed out at RW = 1 divided by the total amount of solute removed from the pulp bed during the washing run.

54

RESULTS AND DISCUSSION Pulp fibre bed characteristics The change in the wash water temperature influenced the wash water mobility, defined as the permeability to water viscosity ratio, B/μ (Fig. 1). The wash water mobility had an increasing trend with increasing the temperature which had a substantial impact on the wash water viscosity. As would be expected, the hydraulic bed resistance defined by Eq. (2) decreased with increasing the wash water temperature (cf. Fig. 2). The decreasing trend of the hydraulic bed resistance was due to a decrease in the wash water viscosity with increasing the temperature. It must be stressed also that all displacement washing runs were carried out under the streamline flow regime when the Reynolds number of the wash water (defined in Symbols) varied in the range of 8.5  10–3 to 3.4  10–2. These results also confirmed that, for given pressure difference of 7 kPa, the volumetric flow rate of wash liquid through pulp fibre bed increases with increasing the temperature.

Fig. 1 Influence of wash water temperature on the mobility of wash water.

Fig. 2 Influence of wash water temperature on the hydraulic pulp bed resistance.

In contrast to the hydraulic bed resistance influenced by the wash liquid viscosity and the bed permeability (Fig. 2), the specific bed resistance seems to be almost independent upon the wash water temperature (cf. Fig. 3). Most of the values of the average specific resistance lies within the limits of 1.3  109 to 1.6  109 m kg–1. A relatively great difference in the average specific bed resistance obtained for 50 and 60 °C can be ascribed to the formation of pulp beds from fibre suspension. Pulp beds formed from 4% suspension comprising relatively long fibres of spruce and pine having the tendency to form bundles of multiple fibres together appeared to be quite flocculated. With respect to this fact, the permeability ranging of 4.2  10–12 to 5.6  10–12 m2 was achieved at the wash water temperature of 50 and 60 °C. Owing to the differences in local porosity and pore size distribution, the pulp bed can be characterised as non-homogeneous and stochastic system.

In spite of this fact, our results agree well with those reported by INGMANSON (1953) who found that the temperature in the range of 10 to 40 °C had no effect on the specific bed resistance. For unbeaten coniferous bleached sulphite pulp at water temperature of 30 °C, INGMANSON (1953) reported the average specific bed resistance of 0.81  109 m kg–1 at the pressure drop of 7 kPa. For given pulp consistency, the average specific bed resistance is influenced by the average effective bed porosity and the specific surface of fibres. The dependence of the average effective bed porosity, calculated from Eq. (3) on the basis of permeability measurements after displacement washing, upon the wash water temperature is shown in 55

Fig. 4. The influence of the wash water temperature upon the specific surface of pulp fibres is illustrated in Fig. 5. For comparison, for unbeaten coniferous bleached sulphite pulp at a water temperature of 30 °C, INGMANSON (1953) reported the specific fibre surface of 886 m2 kg–1.

Fig. 3 Influence of wash water temperature on the average specific pulp fibre resistance.

Fig. 5 Influence of wash water temperature on the specific surface of pulp fibres.

Fig. 4 Influence of wash water temperature on the average effective porosity.

Fig. 6 Influence of wash water temperature on the equivalent pore diameter.

An increase in the average effective porosity with increasing the wash water temperature could be associated with a drop of the thickness of liquid layer immobilised on the fibre surface (POTŮČEK, PULCER 2006). Then, with decreasing thickness of stagnant liquid layer the effective surface of pulp fibres should be increased (cf. Fig. 4 and 5) since the effective specific volume of fibres involves the volume of fibres in the water-swollen state, including the volume of the liquid immobilised on their surface. However, in case that the specific fibre surface increases with decreasing the thickness of the stagnant liquid layer, the pore diameter should be increased. Of course in our case, when an increase in the specific fibre surface and in the effective bed porosity is accompanied by a decrease in the equivalent pore diameter (cf. Fig. 6), the possible explanation of these facts based on accessibility of small pores to the wash water flow seems to be plausible. A decrease of the equivalent pore diameter with increasing the wash liquid temperature may be attributed to an increase of the number of pores opened to flow when the small pores become accessible to the wash liquid flow.

56

It is interesting that the equivalent pore diameter is of the same order of magnitude as the coniferous fibre width (BLAŽEJ, KRKOŠKA 1989). However, it should be emphasized that, in this work, as well as in the preceding paper (POTŮČEK, PULCER 2006), the specific fibre surface were determined for water suspensions where the degree of swelling can be lower, comparing with alkaline solutions such as black liquor. Also, much of the pore space in pulp fibre bed, e. g., many lumens, micropores in the cell wall, and dead-end pores opened only at one end, may be inaccessible to wash water flow in the presence of given pressure gradient.

Wash yield A response to a step change in concentration, called washing or breakthrough curve, was measured as the time dependence of the lignin concentration in the stream leaving the pulp fibre bed. In order to normalise the response record, the washing curves were plotted as the dependence of the dimensionless concentration of alkali lignin in the outlet stream, expressed as a ratio of the exit concentration to the initial lignin concentration, ρe/ρ0, against the wash liquor ratio, RW. Breakthrough curves measured for the wash water temperature of 20 and 60 °C are shown in Fig. 7. It should be also noted that the displacement washing runs were finished at the wash liquor ratio between 6 and 7 when the lignin concentration in output stream was less than one thousandth of the initial lignin concentration in the pulp bed. However, for a better optical comparison, the experimental points connected by means of the cubic spline method are illustrated only for RW < 3 in Fig. 7. From the dimensionless concentration profile of alkali lignin in the exit stream, it is obvious that the displacement of lignin was non-ideal. The pulp bed consisted of compressible porous fibres where geometrical similarity does not exist. Moreover, the formation of a pulp bed in a washing cell influences the shape of the breakthrough curves. Even if the experimental conditions were strictly identical, the fibre bed was always different with respect pore size distribution. Due to inhomogeneities of the fibre bed, the different local porosities influenced significantly the flow of wash liquid through the bed. Hence, for example, at the wash water temperature of 20 and 60 °C, the washing process illustrated in Fig. 7 was characterised by the Péclet numbers of 5.5 and 11.1, respectively.

Influence of the Péclet number on the wash yield for various wash water temperatures is shown in Fig. 8. For comparison, the dependence of WYRW=1 vs. Pe calculated by BRENNER (1962) for unmovable bed of non-porous particles is illustrated as well. From the results it is obvious that the change in the wash water temperature had no unambiguous effect on the wash yield. However, in the majority of runs, the wash yield was found to be greater than 0.8.

In spite of the scatter in the data, it is evident that the wash yield increases with increasing the Péclet number. However, the experimental points are located below the curve derived for the packed bed of non-porous particles by BRENNER (1962). The reason is that, for packed bed of non-porous particles, the washing process is reduced to the displacement mechanism accompanied by interfacial mixing between displaced and displacing fluids.

However, in the case of a packed bed of compressible porous particles in the swollen state, such as pulp fibres, the leaching may play a significant role mainly in the spaces of the pulp bed in which the inter-particle pores were filled up with the wash liquid and the concentration driving force enables the transfer of alkali lignin macromolecules from the fibre walls towards the wash liquid.

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Fig. 7 Comparison of breakthrough curves measured at wash water temperature of 20 °C (1) and 60 °C (2) with theoretical responses for ideal mixing vessel (3) and plug flow (4).

Fig. 8 Wash yield as a function of the Péclet number for various wash water temperatures.

It showed that the displacement washing efficiency expressed by the wash yield depends mainly upon the dispersion of the wash liquid inside pulp bed whereas the effect of the wash liquid temperature was negligible (cf. Fig. 8). Thus, based on our own data measured for the kraft pulp bed, the following equation was derived for the quantitative evaluation of the effect of the Péclet number on the wash yield

WYRW 1  0.629 Pe0.116

(8)

with a mean relative deviation of 0.75 %, 95% confidence limits of the coefficient (0.619; 0.640) and of the power of the Péclet number (0.108; 0.124). The Akaike information criterion was found to be –140. In accordance with our preceding papers (POTŮČEK, MIKLÍK 2011; POTŮČEK, RAHMAN 2018), our results confirmed unambiguously that the wash yield increases with the increase of the Péclet number.

For comparison with the correlation given by Eq. (8), the theoretical wash yield of the displacement in a packed bed of non-porous particles calculated according to BRENNER (1962) was expressed as a function of the Péclet number in the form

WYRW 1  0.688 Pe0,0823 for the Péclet number within the range from 3.2 to 24.

Fig. 9 Influence of wash water temperature on the kappa number of washed pulp.

58

(9)

Since the alkali lignin is transported from inside the fibre walls into free wash liquid by diffusion mechanism under assumption that the driving force exists, it may be expected that the greater wash liquor temperature will have a positive impact on alkali lignin leaching from the pulp fibres. Our displacement washing results showed that the kappa number of washed pulp was lower than kappa number of unwashed pulp, which was 24.9, and decreased with increasing the wash water temperature (cf. Fig. 9). Of course, a decrease in the kappa number can be caused not only by the change of residual lignin amount but also of other components, such as extractives, hexeneuronic acids, and some chemical structures with double bonds and/or carbonyl groups (ALA-KAILA et al. 2003). Nevertheless, higher efficiency of leaching of black liquor components did not have a significant influence upon the wash yield.

CONCLUSION Displacement washing of pulp fibres is influenced by a number of phenomena occurring in porous medium, such as pore size distribution, different local porosity of the bed, geometrical properties of fibres including their swelling, and others. The pulp fibre bed ranks therefore among non-homogeneous and stochastic systems. The shape of washing curve is strongly influenced by a highly complex network of pores and its tail also by leaching of a solute from within fibre walls into the wash liquid. In spite of these facts, several conclusions valid within the framework of our study can be drawn.

The results obtained for the wash water temperature range of 10 to 60 °C showed that (i) with increasing wash water temperature the hydraulic bed resistance, as well as the equivalent pore diameter decrease, on the contrary, the average effective bed porosity, as well as the specific surface of fibres and wash water mobility show an increasing trend even if, at given wash liquid temperature, a relatively great scattering for pulp bed parameters must be taken into account with respect to the quality of bed formation inducing anomalous dispersion in this porous medium; (ii) the average specific bed resistance seems to be independent on the wash water temperature mainly in the range of 20 to 50 °C. On the other hand, an increase in pulp bed temperature resulting in a drop of liquid viscosity will increase the wash water flowrate and thus the washer capacity; (iii) the efficiency of displacement washing is dependent primarily on the inhomogeneity of the pulp fibre bed, having an impact on the shape of the breakthrough curves recording concentration of solute removed from the pulp bed. The data obtained for pulp fibre beds at various wash liquid temperature were well fitted by the correlation between the wash yield and the Péclet number (Eq. (8)) and error did not exceed 0.75 %; (iv) the influence of molecular transport processes, depending on the temperature, upon the washing efficiency was not markedly evident in the range of the wash water temperatures investigated in this work. However, the kappa number of washed pulp decreased with increasing the wash water temperature, indicating that the higher temperature had a favourable impact on lignin leaching rate from the fibre walls.

SYMBOLS am aV B

specific surface of fibres based on fibre mass, m2 kg–1 specific surface of fibres based on volume, defined as a ratio of specific surface (in m2 kg–1) and specific volume (in m3 kg–1), m–1 permeability, m2 59

D longitudinal dispersion coefficient, m2 s–1 deq equivalent diameter of pores defined by Eq. (5), m h bed thickness, m K Kozeny constant ΔP pressure difference, Pa Pe Péclet number defined by Eq. (6) R hydraulic bed resistance defined by Eq. (2), Pa s m–1 Re Reynolds number (= 4uρWL/(aV(1 – ε)μ)) RW wash liquor ratio t wash liquid temperature, °C u superficial wash liquid velocity, m s–1 WYRW = 1 wash yield defined by Eq. (7) Greek letters α average specific bed resistance defined by Eq. (4), m kg–1 ε average bed porosity μ liquid viscosity, Pa s ρe exit lignin concentration, kg m–3 ρF consistency of pulp, kg m–3 ρWL density of wash liquid, kg m–3 ρ0 initial lignin concentration, kg m–3 REFERENCES ALA-KAILA, K., LI, J., SEVASTYANOVA, O., GELLERSTEDT, G. 2003. Apparent and actual delignification response in industrial oxygen-alkali delignification of birch kraft pulp. In Tappi Journal, 2003, vol. 2, no. 10, p. 23–27.

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Bratislava: Alfa 1989, 584 p. ISBN 80-05-00119-3. (in Slovak) BRENNER, H. 1962. The diffusion model of longitudinal mixing in beds of finite length. Numerical values. In Chemical Engineering Science, 1962, vol. 17, p. 229–243.

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J28–J35.

ACKNOWLEDGEMENTS This work was supported by the Internal Grant Agency of University of Pardubice under the research project SGS_2019_005.

AUTHORS´ ADDRESS: Prof. Ing. František Potůček, CSc. Md. Mostafizur Rahman, MSc. University of Pardubice, Faculty of Chemical Technology Institute of Chemistry and Technology of Macromolecular Materials Studentská 95 532 10 Pardubice Czech Republic frantisek.potucek@upce.cz mmrbcsir@yahoo.com

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 63−72, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.06

ANTI-DECAY POTENTIAL OF FIVE ESSENTIAL OILS AGAINST THE WOOD-DECAYING FUNGI SERPULA LACRYMANS AND TRAMETES VERSICOLOR Ladislav Reinprecht – Dana-Mihaela Pop – Zuzana Vidholdová – Maria Cristina Timar ABSTRACT The antifungal efficiency of five selected essential oils – cinnamon, oregano, thyme, basil, and clove against the brown-rot fungus Serpula lacrymans and the white-rot fungus Trametes versicolor are discussed in the paper. The antifungal screenings were performed in Petri dishes filled with solidified malt agar medium by the poisoned ring-paper method.

Two parameters measured on the 4th, 7th, 10th, and 13th days: (1) ISoil – the growth inhibition index of fungal mycelia on the malt agar medium-soil to 12 mm rings of antibiotics test paper impregnated with 0 wt.%, 0.25 wt.%, 1 wt.%, 10 wt.% or 100 wt.% concentration of essential oils; and (2) IPaper – the slowed or totally stopped growth of fungal mycelia on 12 mm rings of antibiotics test paper poisoned with essential oils were evaluated. Antifungal efficiency of basil oil containing mainly linalool is the highest. On the contrary, antifungal efficiency of clove oil containing mainly eugenol is the lowest.

Key words: essential oils, decaying fungi, screening test, fungicidal effect.

INTRODUCTION Preservation of wood from decay and other biodegradation processes plays an important role during its storage, transportation, and service. Environmental issues from conventional toxic chemical preservatives containing heavy metals, condensed or chlorinated aromatic hydrocarbons, and several other pollutants having a higher toxicity for humans, in connection as well as with their disposal problems, have urged the search for more ecological friendly preservative substances—including natural ones (REINPRECHT 2010, MEDEIROS et al. 2016, CAI et al. 2019).

This work studies the methods of wood protection related to the use of essential oils from plants. These methods have many advantages: a) plants can be produced in large amounts as agricultural products; b) some essential oils combine antifungal with insecticidal and anti-bacterial effects; c) essential oils are usually health-friendly and many of them are used in medicine, aromatherapy, or cosmetics; and d) essential oils cause only small problems in terms of liquidation of treated products after their service-life. On the contrary, some disadvantages of using essential oils for wood preservation can also occur, e.g., a) high volatility; b) non-stabile concentration of effective compounds (BATISH et al. 2008, CAI et 63

al. 2019); and c) a relatively lower biocidal efficacy in comparison to traditional fungicides (REINPRECHT et al. 2013).

Essential oils are natural products of various origin characterized by a strong smell.

They have high variability in their chemical composition, both in qualitative and quantitative terms. Their main components belong to various chemical classes such as terpenes, phenols, aliphatic alcohols, ethers, aldehydes, ketones, esters, amines, amides, (DHIFI et al. 2016).

A certain fungicidal efficacy of essential oils against decaying fungi, staining fungi, and moulds (microscopic fungi) was demonstrated by XIE et al. (2017) as well as by more other researchers. For example, CHENG et al. (2008) demonstrated the anti-decay activity of cinnamaldehyde and eugenol congeners; CHITTENDEN and SINGH (2011) found the fungicidal effect of geranium oil and of eugenol and cinnamaldehyde extracts against several decaying and staining fungi; MOHAREB et al. (2013) proved that from 18 essential oils, the following six oils isolated from plants had a more significant inhibition effect against the decaying fungi Hexagonia apiaria and Ganoderma lucidum: Artemisia monosperma, Cupressus sempervirens, Citrus limon, Thuja occidentalis, Schinus molle, and Pelargonia graveolens; SU et al. (2013) demonstrated the antifungal activity of essential oils containing α-cadinol and elemol isolated from leaves and fruits of Juniperus formosana; REINPRECHT et al. (2013) in screening tests with poisoned rings of Whatman paper and PÁNEK et al. (2014) in standard tests with preserved wood samples demonstrated that thyme and oregano oils were the most effective against moulds Aspergillus niger and Penicillium brevicompactum and against the brown-rot fungus Coniophora puteana, while clove, savory and birch oils had a lower biocidal efficacy; POP et al. (2018), by the CT screening test method in Petri dishes (i.e. using two half disks of poisoned Whatman paper with a diameter of 80 mm), demonstrated fungicidal potential of cinnamon and clove oils against the decaying fungi Postia placenta and Trametes versicolor; BAHMANI and SCHMIDT (2018) tested the bioactivity of 16 essential oils against common moulds (Aspergillus niger, Penicillium commune) and important decaying fungi (Coniophora puteana, Trametes versicolor, Chaetomium globosum) found the highest efficiency for lavender, lemon grass and thyme oils.

The aim of our experiments is to determine the antifungal potential of selected essential oils against the growth activity of two important wood-decaying fungi Serpula lacrymans and Trametes versicolor.

MATERIALS AND METHODS Essential oils Five essential oils under the label Steaua Divina, Romania—cinnamon, oregano, thyme, basil, and clove (tab. 1)—were used in the experiment as 0.25 wt.%, 1 wt.%, or 10 wt.% ethanol solutions and as the original 100% concentrate.

Antifungal screenings The antifungal activities of individual essential oils (Table 1) against the brown-rot fungus Serpula lacrymans (Schumacher ex Fries) S.F.Gray /S. lacrymans (Wulfen) J. Schrӧt. – by IndexFungorum/, strain BAM 87 (Bundesanstalt für Materialforshung und -prüfung, Berlin), and the white-rot fungus Trametes versicolor (Linnaeus ex Fries) Pilat /T. versicolor (L.) Lloyd – by IndexFungorum/, strain BAM 116 (Bundesanstalt für Materialforshung und prüfung, Berlin) were determined by the poisoned ring-paper method (REINPRECHT et al.

2003) using paper rings immersed in individual wood-protecting substances.

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Tab. 1 Essential oils used in the experiment.

Common name

Scientific name

Cinnamon

Cynnamomum verum

Oregano

Origanum vulgare

Thyme

Thymus vulgaris

Basil

Ocimum basilicum

Clove

Eugenia caryophyllata

Major effective components Cinnamaldehyde (33%), Linalool (17%), Eugenol (17%), Cinnamyl acetate (12%), Linalyl acetate (2.3%) Carvacrol (64%), p-Cymene (12.6%), Terpineol (4.8%), Linalool (3.7%) Thymol (47.6%), -Terpinene (30.9%), p-Cymene (8.4%), Carene (3.8%) Linalool (47%), -Elemene (7.8%), Farmesene (6.9%), Guainene (5.3%) Eugenol (88.6%), Eugenyl acetate (5.6%), -Caryophyllene (1.4%), 2-Heptanone (0.95%)

The antifungal screenings were performed in glass Petri dishes with a diameter of 100 mm, filled in an autoclave sterilized and in Petri dish solidified 3–4 mm thick layer of 4.5 wt.% malt agar medium (HiMedia, Ltd., India). First, in the central points of Petri dishes the agar malt media were inoculated with ca 5  5 mm mycelia of decaying fungi S. lacrymans or T. versicolor. Then, 4 rings of Antibiotic Test Paper (Fischer Scientific, Czech Republic) with a diameter of 12 mm were placed in each Petri dish, with a distance of 20 mm from the border of the fungal inoculate; into each Petri dish were placed 3 rings of poisoned paper impregnated at atmospheric pressure during 30 seconds with an individual type and concentration of essential oil, and 1 ring of control paper impregnated with 96% ethanol. All paper rings, before placing into Petri dishes, were conditioned 1 hour at a temperature of 22  1 °C. In totally for each series, i.e. for each type of essential oil and its concentration, as well as for each fungus species, six poisoned papers were tested. The antifungal screenings were implemented in sterilized thermostats at a temperature of 22  1 °C for 13 days.

In literature, several other screening methods are recommended for determining the fungicidal performance of potential wood-protecting substances, e.g. POP and VARODI (2017) compared five different screening methods at testing fungicidal efficacy of copper sulphate and biocide Romalit N. Evaluation of screenings Evaluation of the antifungal efficiency of individual essential oils was performed based on two fungal growth parameters: ISoil is the growth inhibition index of fungal mycelium on the solidified malt agar medium, valued from a distance change between the border of growing fungal mycelium and the border of poisoned paper; this index was established to the time when the inhibiting zone of fungal mycelium to the border of control paper (IZc) was already minimal ca 0 mm in a Petri dish; this index could be for lower concentrations of essential oils ascertained only during the first days of screenings; this index also depended on the oil type because bioactive vapours of some essential oils (e.g. basil and cinnamon) in the space of Petri dishes could, in accordance with ZYANI et al. (2011), to suppress a growth of fungal mycelium to the control papers, as documented in Figures 1 and 2 by stars in some graphs having 100% growth inhibition indexes and in Figures 4 and 5 by photos for 10 wt.% and 100 wt.% oil concentrations.

ISoil = (IZOil – IZC)/(20 – IZC) × 100 [%]

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(1)

where: IZOil is the inhibiting zone to the poisoned paper impregnated with essential oil [mm], IZC is the inhibiting zone to the control paper [mm], 20 is the initial distance between the border of fungal mycelium-inoculate and the border of paper [mm].

IPaper is the growth inhibition index of fungal mycelium on the poisoned paper ring impregnated with essential oil; this index is smaller than 100% from the moment when the fungal mycelium starts to contact the oil-poisoned paper or just starts to grow on its surface.

IPaper = (Lc – LOil)/( Lc) × 100 [%]

(2)

where: LC is the mycelium length acquisition on the control paper between two time intervals (e.g. 3 days between 4th and 7th day) [mm], LOil is the mycelium length acquisition on the poisoned paper impregnated with essential oil between two time intervals of an identical duration, as was determined for the control paper (e.g. 3 days between the 10th and 13th days) [mm].

RESULTS AND DISCUSSION The results from the antifungal screenings of five essential oils are summarized in Figures 1, 2 and 3 and documented by photographs in Figures 4 and 5. The efficiency of tested essential oils in a concentration of 0.25 wt.% was none or only minimal. All essential oils started to be more effective against the growth of fungal mycelia at using their 10 wt.% concentration, at which their 100 wt. % concentrates totally stopped fungal mycelia growth on the rings of oil-poisoned papers (except for clove oil) and concentrates of basil and cinnamon oils even on the malt agar medium.

Basil oil, containing 47% of linalool, had the best antifungal potential. For example, at its application in 10 wt.% concentration, the growth inhibition indexes of fungal mycelia on the malt agar medium soil were the highest (ISoil = 100% for S. lacrymans after 4th day; ISoil = 25% for S. lacrymans after 7th day; ISoil = 100% for T. versicolor after 4th and 7th day), as shown in Figures 1 and 2, and the growth of mycelia on the oil-poisoned papers occurred only after 10 days (S. lacrymans) or 13 days (T. versicolor), as shown in Figure 3. However, the efficiency of 10 wt.% concentration of basil oil against fungi stopped after 13 days when mycelia intensively grew on oil-poisoned paper surfaces, as shown in Figures 4 and 5.

Generally, achieved results (Figures 1 – 3) indirectly shoved that basil oil will have a more evident antifungal efficiency only at higher amounts in preserved materials.

Clove oil, containing 88.6% of eugenol, proved to be the least effective against decaying fungi. Clove oil had the lowest growth inhibition indexes of fungal mycelia on the malt agar medium, as shown in Figures 1 and 2, at which growth of fungal mycelia on the oil-poisoned papers occurred relatively faster than for other oils, as shown in Figures 3, 4 and 5. For example, at the application of clove oil in 10 wt.% concentration, the results obtained the lowest or no growth inhibition indexes of fungal mycelia on the malt agar medium (ISoil from 31.5% to 0% after 4 and 7 days), as shown in Figures 1 and 2.

Other essential oils had a medium antifungal efficiency in this order “Cinnamon  Thyme  Oregano”, and this order is documented by the growth inhibition indexes of mycelia on the malt agar medium (ISoil), as shown in Figures 1 and 2, and on the oil-poisoned papers (IPaper), as shown in Figure 3.

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Serpula lacrymans

Trametes versicolor

Fig. 1 ISoil – the growth inhibition index of fungal mycelium on the malt agar medium on its growth to oil-poisoned papers. Evaluated after 4 days (n = 6).

Note: Stars in some graphs having 100% growth inhibition indexes indicate that growth of fungal mycelium was suppressed also on the malt agar medium to the control papers.

Serpula lacrymans

Trametes versicolor

Fig. 2 ISoil – the growth inhibition index of fungal mycelium on the malt agar medium on its growth to oil-poisoned papers. Evaluated after 7 days (n = 6).

Note: Stars in some graphs having 100% growth inhibition indexes indicate that growth of fungal mycelium was suppressed also on the malt agar medium to the control papers.

Serpula lacrymans

Trametes versicolor

Fig. 3 IPaper – the growth inhibition index of fungal mycelium on the oil-poisoned paper. Evaluated between 3 days: 7 day  3 days between 4th–7th day /quick growth/; 10 day  3 days between 7th–10th day; 13 day  3 days between 10th–13th day /late or none growth/ (n = 6).

Note: Stars in some graphs having 100% growth inhibition indexes indicate that growth of fungal mycelium was suppressed also on the control papers due to evaporation of VOC from essential oils.

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Cinnamon

Oregano Thyme 100 wt.% essential oils

Basil

Clove

4th day

7th day

10th day

13th day

10 wt.% essential oils 4th day

7th day

10th day

13th day

Fig. 4 Photos from the screening of essential oils (100 wt.% and 10 wt.%) against the brown-rot fungus Serpula lacrymans by the poisoned ring-paper method (3 poisoned and 1 C-control paper in the dish).

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Cinnamon

Oregano Thyme 100 wt.% essential oils

Basil

Clove

4th day

7th day

10th day

13th day

10 wt.% essential oils 4th day

7th day

10th day

13th day

Fig. 5 Photos from the screening of essential oils (100 wt.% and 10 wt.%) against the white-rot fungus Trametes versicolor by the poisoned ring-paper method (3 poisoned and 1 C-control paper in the dish).

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POP et al. (2018), using another screening method for testing two essential oils, for cinnamon oil also established a higher efficiency against decaying fungi P. placenta and T. versicolor than for clove oil. REINPRECHT et al. (2013) in screenings performed similarly with method of this work found that thyme and oregano oils are relatively more effective against C. puteana and T. versicolor than birch oil, clove oil and savory oil.

Essential oils used in this work had not a higher inhibitory potential against the brownrot fungus Serpula lacrymans than against the white-rot fungus Trametes versicolor (Figures 1–3 and Figures 4 and 5). On the contrary, VODA et al. (2003) and PÁNEK et al. (2014) in experiments with impregnated wood samples found that the efficiency of essential oils is higher against the brown-rot fungus C. puteana in comparison to the white-rot fungus T. versicolor. This phenomenon related to white-rot fungi was explained by BAYRAMOGLU and ARICA (2009), who have found an apparently higher production of extracellular ligninolytic enzyme laccase by the white-rot fungus T. versicolor. Laccase not only disrupts lignin but also inactivates effective phenolic compounds in essential oils, e.g. thymol, carvacrol or eugenol.

Individual types of essential oils obtained from plants contain many different tens to hundreds of constituents (BAHMANI and SCHMIDT 2018). Several constituents of essential oils, e.g. various monoterpenes and phenols, can inhibit growth and enzymatic function of decaying fungi. The individual components of some oil may act synergistically while several compounds may have even a stimulating action on fungi. Various possible action mechanisms by which the activity of wood-damaging fungi may be reduced or inhibited have been proposed by REINPRECHT (2010), i.e. the potential fungicides should have one or more of these effects: inhibition of fungi respiration; inhibition of protein, carbohydrate, nucleic acid and microtubules biosynthesis; disruption of fungi cell membranes due to the inhibition of sterol biosynthesis; inactivation of celluloses, phenoloxidases, and other enzymes produced by fungi.

The fungicidal activities and action mechanisms of an individual essential oil type can be variable, and these are usually more component (Table 1) and usually have an unequal composition in dependence on the place of plant cultivation and the method of oil production (DHIFI et al. 2016). In these views, as well as on the basis of several experiments performed in world, including experiments from our laboratories, the general tasks and questions for the future research of essential oils for wood protection are as follows: determine the minimum effective concentration of a defined individual oil type for wood protection; select the most effective oils and their compounds as a function of their efficacy and cost; achieve stability of oils against evaporation, leaching, and UV-radiation in exteriors; produce effective selected oil compounds in factories and test the potential synergistic effect of chemical compounds in oils from naturally produced plants; analyse potential synergistic effects between various oils and additives introduced into different wood species against wood-destroying fungi, moulds, and bacteria.

CONCLUSION o From the individual essential oils—cinnamon, oregano, thyme, basil, and clove—the relatively highest antifungal efficiency against the brown-rot fungus Serpula lacrymans and the white-rot fungus Trametes versicolor had basil oil. On the contrary, the antifungal efficiency of clove oil is the lowest. o Tested essential oils had a comparable efficacy against both wood decaying fungi S. lacrymans and T. versicolor.

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o

Essential oils with high antifungal efficiency can potentially be used as healthfriendly wood biocides, preferentially in interiors, however unfortunately only in higher concentrations – which may be an issue due to odor and possible skin and other allergies.

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VODA, K., BOH, B., VRTAČNIK, M., POHLEVEN, F. 2003. Effect of the antifungal activity of oxygenated aromatic essential oils compounds on the white-rot Trametes versicolor and the brownrot Coniophora puteana. In International Biodegradation  Biodeterioration 51(1): 51–59.

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ZYANI, M., MORTABIT, D., EL ABED, S., REMMAL, A., KORAICHI, S.I. 2011. Antifungal activity of five plant essential oils against wood decay fungi isolated from an old house at the Medina of Fez. In International Research Journal of Microbiology 2: 104-108.

ACKNOWLEDGMENTS This work was supported by the Scientific Grant Agency of the Ministry of Education of Slovak Republic Grant No. VEGA 1/0729/18, and by the PhD research project undertaken at Transilvania University in Brasov, Romania.

ADRESSES OF AUTHORS prof. Ing. Ladislav Reinprecht , CSc. Faculty of Wood Sciences and Technology Department of Wood Technology T. G. Masaryka 24 960 01 Zvolen Slovak Republic reinprecht@tuzvo.sk Ing. Dana-Mihaela Pop Transilvania University in Brasov Str.Univeristatii 1 500036 Brasov Romania pop.dana.mihaela@unibv.ro Ing. Zuzana Vidholdová, PhD. Technical University in Zvolen Faculty of Wood Sciences and Technology Department of Wood Technology T. G. Masaryka 24 960 01 Zvolen Slovak Republic zuzana.vidholdova@tuzvo.sk prof. Maria Cristina Timar, PhD. Transilvania University in Brasov Str.Univeristatii 1 500036 Brasov Romania cristinatimar@unibv.ro

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 73−80, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.07

INFLUENCE OF THE PROCESSED MATERIAL ON THE SOUND PRESSURE LEVEL GENERATED BY SLIDING TABLE CIRCULAR SAW Pavlin Vitchev – Dimitar Angelski – Vladimir Mihailov ABSTRACT The aim of the current study is to investigate the changes in the sound pressure level generated at the operator’s position of sliding table circular saw depending on the type of the processed material, the cutting height (h) and the tool overhang effect (T) (T1 = 7; T2 = 14; T3 = 21 mm). The experiments were performed with specimens from chipboard oriented strand board (OSB) and plywood with cutting height of 15, 30, 45 mm.

The generated sound pressure level was measured using the method of “sound free field” taking into account the influence of the background noise and the characteristics of the sound field. The measurement of the A-weighted sound pressure level was performed using precise digital sound level meter CEL-620B1 (CASELLA, United Kingdom). The obtained results showed that the sound pressure level is influenced by the type of the processed material and it is changed at the cutting height of 15 mm as follows: plywood – 89.5 dB(A); OSB – 88 dB(A) and chipboard – 86.5 dB(A). An increase in the tool overhang effect from 7 mm to 14 mm resulted in an increase in the sound pressure level by 3÷4 dB(A) on average for all three types of processed material.

Key words: sound pressure level (SPL), noise, circular saw machine, chipboard, oriented strand boards (OSB), plywood.

INTRODUCTION The woodworking and furniture industry is notorious for the high noise emissions generated by the used machinery and equipment. The high level of noise emission is one of the main risk factors with a negative impact on the human health, including noise-induced hearing loss and other disorders (BREZIN 1992, BADIDA et al. 2010, BREZIN et al. 2015, ANTOV et al. 2017). According to the European Directive 2003/10/ЕО, the upper limit for a workplace noise exposure based on the eight-hour working day is determined to be LEX, 8h = 85 dB(А).

The circular saw machines used in the woodworking and furniture industry are considered the noisiest after the hammermills and the thicknessers (HSE 2007).

The main factors influencing the noise level generated by the circular saws are generally derived from the characteristics: (i) the processed materials – type, length, thickness, moisture, etc.; (ii) the cutting tool – shape and number of teeth, thickness, cutting angles, presence of different sound absorbing and vibrating cuts on the tool body, etc.; (iii) the cutting mode – feed rate, cutting speed, and others (HSE, 2007; HSE, 2009).

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One of the main conditions followed by the woodworking machine producers on the market, is the lower noise level generated by their machines. A number of scientific studies investigate the noise emission levels, generated by woodworking circular saws in relation to the parameters of the tool, the characteristics of the processed material and the cutting mode (CHENG et al 1998, GOGLIA 1999, HATTORI 2001, SVOREN et al. 2007, VITCHEV et al. 2018).

According to BIES (1992) the sound power of an idling sawing machine is highly influenced by the characteristics of the circular saw. In its study, the author concludes that the fluctuating lift forces acting on the teeth account for the increased level of the aerodynamic noise.

Other important factors affecting the noise level of a saw blade are the tooth pitch and the number of the saw blade teeth. KOPECKY et al. (2012) measured significantly higher (by 4.1 dB) noise levels generated by the circular saw with irregular tooth pitch when compared to the circular saw with regular tooth pitch. KVIETKOVA et al. (2015) investigated the influence of the varying number of saw blade teeth on the generated noise during transverse cutting of beech wood. They showed that the noise values were greater in the case of saw blades with fewer teeth.

Various structural characteristics of the circular saw can also affect the level of the generated noise. A number of studies investigate the influence of the compensating slots in the body of a circular saw blade on the noise level during idling ход (BELJO-LUCIC et al.

2001, SVOREN et al. 2007, SVOREN et al. 2009, KVIIETKOVA et al. 2015). In various studies the presence of compensating slots result in a significant decrease of the noise levels by 2 to 6.5 dB. The construction material of the saw blade teeth is also proven to affect the noise generation. More importantly, properly selected construction material with high internal damping potential, may reduce the noise generation up to 11dB (HATTORI et al. 1999, HATTORI et al. 2001).

The objectives of the current study were to investigate the changes in the sound pressure level generated at the operator’s position of sliding table circular saw, depending on the type of the processed material, the cutting height (h) and the tool over-hang effect (T).

METHODOLOGY The experiments were carried out using woodworking sliding table circular saw machine WA 6 (Altendorf, Germany) (Fig. 1). The machine was located on a concrete floor in a room with dimensions, length, width and height – L × B × H = 18 × 6 × 3.5 m, respectively.

Fig. 1 Circular saw machine with sliding table, WA6 (Altendorf, Germany).

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The main saw blade of the machine is driven through a belt drive, by an electric motor with N = 4 kW power ensuring rotational speed n = 4500 min1 of the circular saw. The scoring saw was not used in the current experiments. In order to limit the background noise level and to measure only the noise generated by the circular saw machine, the aspiration system as well as the other technological equipment did not work.

For the aim of the study, a circular saw blade (Freud, Italy) was used. The technical parameters are presented in Table 1, where: D is the outer diameter; d – bore; B – width of cut; γ – hook angle; β – sharpening angle; z – number of teeth; n1 – maximum rotation speed, tooth shape W (alternating left and right tilts). The technical characteristics of the machine and the saw blade ensure cutting speed of Vc = 71.65 m.s-1.

Tab. 1 Technical characteristics of the used circular saw.

Teeth shape W

D mm

d mm

B mm

 

β 

z No

n1 min-1

Material of the teeth

300

30

3.2

10

65

72

6300

Metalceramic hard alloy

The experiments were performed with three different wood based materials at three different cutting heights, as follow:  Particle boards (without deterioration layer): cutting height 15, 30 (2 × 15) and 45 (3 × 15) mm and density ρ = 660 kg/m3;  Oriented strand boards (OSB): cutting height 15, 30 (2 × 15) and 45 (3 × 15) mm and density ρ = 640 kg/m3;  Plywood boards (birch wood): cutting height 15, 30 (2 × 15) and 45 (3 × 15) mm and density ρ = 720 kg/m3.

The length of the processed planes was L = 1500 mm and the width of the processed specimens was 50 mm. In this way the likelihood of the additional noise generated as a result of vibrations in the cut-out material is reduced.

The influence of three different levels of the circular saw over-hang: T1 = 7 mm; T2 = 14 mm; T3 = 21 mm (Fig. 2) was also investigated.

Fig. 2 Schematic representation of the circular saw over-hang effect.

Further, the A-weighted sound pressure level (SPL) depending on the type and the thickness of processed material and the tool over-hang effect was assessed using the method of “sound free field”. The measurements were performed in one point, as described in the 75

BDS ISO 7960 (Annex A), namely: height from the floor – 1500 mm; 400 mm – forward of the axis of rotation of the saw; 200 mm on the left side of the saw in the direction of feeding (Fig. 3).

Fig. 3 Schematic representation of the microphone position.

The sound pressure level is measured during idling with mounted circular saw. The height position of the cutting tool over the machine's working plot is equal to the cutting height plus the foreseen overhang (T) of the circular saw over the workpiece.

In the analyses of the results for the sound pressure level, the effects of background noise and sound field characteristics with corresponding correction coefficients K1 and K2 were taken into account and the actual sound pressure level was determined using the following equation: Lp = Lp’ – K1 – K2

(1)

where: Lp – the actual sound pressure level, dB; Lp’ – the measured sound pressure level, dB; K1 – correction coefficient for the background noise, in the current study K1 = 0, since the difference between the background and the generated noise is more than 15 dB, i.e. ΔL > 15 dB; K2 – correction coefficient for the test environment, in the current study K2 = 2.1, i.e.

K2 < 4 – the room is suitable for using the method “Measurement in sound-free field”.

The measurements were performed using precise digital sound level meter CEL620B1 (CASELLA, United Kingdom).

Before the initiation of the experiments, the entire measurement track had been calibrated, using a standard sound source from the same company. The measurements were performed in accordance with BDS EN ISO 3744 and BDS ISO 7960.

RESULTS AND DISCUSSION It is well-known that the noise levels generated during idling differ from those generated during cutting. Therefore, we assessed and analyzed the results obtained from the 76

two different working modes independently. During the cutting mode of the machine, four series of specimens were processed and the mean sound pressure level is taken into account when analyzing the results.

The influence of the tool overhang effect on the sound pressure level in dB(A), generated during idling and cutting mode, is presented in Fig. 4. The results show that during idling with a mounted cutting tool, the sanitary standard of 85 dB(A) is not exceeded only at T = 7 mm. For the other two overhang values of the saw, the levels of the noise emission are significantly increased.

Sound pressure level, Lp, dB(A)

Idling noise

Chipboard

OSB

Plywood

98.5

98 94.5

95 92.5

92.3 92

93.3

90 88.5

89 86.5 86

92.5

88 86

84.5

83 80 7

14

21

Circular saw over-hang T, mm Fig. 4 Changes in the sound pressure level depending on the type of the processed material (height 15 mm) and the tool over-hang effect, measured at rotational speed n = 4500 min1.

The highest sound pressure levels were measured during processing the specimens from plywood. As shown in Fig. 4, the maximum value of 98.5 dB(A) was achieved at tool overhang T = 21 mm, which is by 5 dB(A) higher when compared to 93.5 dB(A), measured at T = 7 mm. Regarding the influence of the processed material, the lowest noise levels were measured during processing of specimens from chipboard, followed by OSB and plywood.

The measured values at T = 7 nm are as follows: for chipboard – 86.5 dB(A), for OSB – 88.5 dB(A) and for plywood – 93.5 dB(A). With the increase of the overhang effect of the circular saw, the air compression and the turbulence generated by the tool rotation increase as well.

As a result, the aerodynamic noise increases significantly, which explains the observed higher levels of generated noise. Our results are in good correlation with the observations of other authors (BIES 1992, BELJO-LUCIC et al. 2001, SVOREN et al. 2007, KOPECKY et al.

2012).

The influence of the cutting height on the changes of the sound pressure level is shown in Fig. 5. The results show that the noise levels are not significantly influenced by the cutting height from 15 to 30 mm for the respective processed materials.

An increase in the cutting height from 30 to 45 mm resulted in an increase in the sound pressure level in a similar manner for all three processed materials. The increased sound pressure level, measured at cutting height of 45 mm is by 2 dB(A) higher compared to the cutting height 30 mm for the all three processed materials.

77

Sound pressure level, Lp, dB(A)

93 Idling noise

Chipboard

OSB

Plywood

90.8

91 89.7

89.5 89

88

87.8 87.2

87 87 85

89.7 88.5 87.5

86 84.5

83 15

30

45

Cutting height h, mm Fig. 5 Changes in the sound pressure level depending on the cutting height, measured at rotational speed of the circular saw n = 4500 min1.

The obtained results correlate and in some cases surpass the values for sound pressure level provided by different companies and presented in the technical characteristics of the circular saws (LEUCO, FREUD, LEITZ etc.). The difference in the noise levels, generated by processing of the different specimens could also be explained by the different structures of the wood. Significantly higher noise levels measured during processing of the plywood specimens, which also have the highest density (ρ = 720 kg/m3) compared to the other materials is probably due to, on one hand, the presence of adhesive layers between the individual veneer sheets, and on the other hand – the mutual perpendicular arrangement of the veneer sheets resulting in both longitudinal and transverse cuts of the wood fibers.

During processing of OSB, higher noise levels are measured, when compared to the values measured during chipboard processing. These results can be explained by the relatively chaotic layout of the large-scale particles, as a result of which cavities are formed in the slab which contribute to the production of greater noise during cutting.

The chipboards have relatively homogenous structure in the longitudinal and transverse direction of the three materials used. Those structural characteristics of the material may explain the lowest level of noise generated during cutting.

CONCLUSIONS The experimental results of this study aimed at investigating the changes in the sound pressure level, generated by woodworking sliding table circular saw and depending on the type of the processed material and the tool overhang effect.

Based on the obtained results the following conclusions can be drawn:  During idling with a mounted tool and at tool over-hang T = 7 mm, the generated sound pressure level is under the sanitary standard of 85 dB(A) (see Fig. 4). In practice, these conditions are not realistic because during idling the tool overhang is equal to the thickness of the processed material plus the tool overhang during cutting.

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 During cutting mode of the machine, the sanitary standard of 85 dB(A) is increased during processing of the all three wood based materials.  The overhang of the circular saw above the cutting height influenced significantly the generated sound pressure level. This is due to the increased levels of the aerodynamic noise generated by the rotation of the cutting tool. Therefore, in order to ensure lower noise levels, the tool overhang should be minimal.  Regarding the processed wood based materials, the highest sound pressure level was generated during cutting of specimens from plywood (89.5 dB(A) followed by OSB (88 dB(A) and chipboard (86.5 dB(A).  The results from the current study can be used to determine the safe exposure duration for operators of the woodworking sliding table circular saw.

REFERENCES ANTOV, P., NEYKOV, N. 2017. Costs of occupational accidents in the Bulgarian woodworking and furniture industry. In Proceedings of the 3rd International Scientific Conference Wood technology & Product design, 11-14 September 2017, Ohrid, Republic of Macedonia, Vol. III, p. 213221, ISBN 978-608-4723-02-8.

BADIDA, M., ANNOVA, J. LUMNITZER, E. KISS, I. 2010. Evaluation of hearing loss of human in working condition using audiometrical measurements. In International Journal of Engineering 8 (2): 141144.

BDS EN ISO 3744:2010, Acoustics – Determination of sound power levels and sound energy levels of noise sources using sound pressure – Engineering methods for an essentially free field over a reflecting plane.

BDS ISO 7960:2005, Airborne noise emitted by machine tools – Operating conditions for woodworking machines.

BELJO-LUCIC, R., GOGLIA, V. 2001. Some possibilities for reducing circular saw idling noise. In Journal of wood science 47 (5): 389393.

BIES, D. A. 1992. Circular saw aerodynamic noise. In Journal of Sound and Vibration 154 (3): 495513.

BREZIN, V. 1992. Ohrana na truda v durvoobrabotvaneto. Zemizdat 1992. p. 215, ISBN 954-05-075-3.

BREZIN, V., ANTOV, P. 2015. Injenerna Ekologia. Publishing House of University of Forestry 2015. p. 259, ISBN 978-954-332-135-3.

CHENG, WH., YOKOCHI, H., KIMURA, S. 1998. Aerodynamic sound and self-excited vibration of circular saw with step thickness - I: Comparison of dynamic characteristics between the common circular saw and the circular saw with step thickness. In Journal of wood science, 44(3): 177–185, ISSN: 1435-0211, E-ISSN: 1611-4663.

Directive 2003/10/EC of the European Parliament and of the Council of 6 February 2003 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (noise) (Seventeenth individual Directive within the meaning of Article 16 (1) of Directive 89/391/EEC).

Available at: http://eur-lex.europa.eu/legalcontent/EN/TXT/ ?uri=CELEX:32003L0010.

GOGLIA, V. 1999. Some possibilities of reducing circular saw idling noise. In Proceedings of 14th Inter-national Wood Machining Seminar, Volume 2, 1219 September, Paris, France, pp. 345353.

HATTORI, N., IIDA, T. 1999. Idling noise from circular saws made of metals with different damping capacities. In Journal of wood science 45(5): 392–395, ISSN: 1435-0211, E-ISSN: 1611-4663.

HATTORI, N. 2001. Suppression of the whistling noise in circular saws using commercially – available damping metal. In Holz als Roh-und Werkstoff, 59, pp. 394398.

HEALTH AND SAFETY EXECUTIVE (HSE) 2007. Noise at woodworking machines. Leaflet WIS13, HSE books.

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HEALTH AND SAFETY EXECUTIVE (HSE) 2009. Noise at woodworking machines, Woodworking Information Sheet No 13.

KOPECKY, Z., ROUSEK, M., VESELY, P., SVOREN, J., KAROLCZAK, P. 2012. Effect of irregular tooth pitch on the noise level of circular saw-blade. In Proceedings of the 8th International Science Conference Chip and Chipless Woodworking Processes, 1113 September, Zvolen, Slovakia, pp.

155159.

KOPECKY, Z., ROUSEK, M. 2012a. Impact of dominant vibrations on noise level of dimension circular sawblades. In Wood research 57(1): 151–160, ISSN 1336-4561.

KRILEK, J., KOVAC, J., BARCIK, S., SVOREN, J., STEFANEK, M., KUVIK, T. 2016. The influence of chosen factors of a circular saw blade on the noise level in the process of cross cutting wood. In Wood research, 61(3): 475–486, ISSN 1336-4561.

KVIETKOVA, M., GAFF, M., GASPARIK, M., KMINIAK, R., KRIS, A. 2015. Effect of Number of Saw Blade Teeth on Noise Level and Wear of Blade Edges during Cutting of Wood. In Bioresources, 10 (1): 16571666.

SVOREN, J., NASCAK, L. 2007. Effect of compression slots, copper corks in the body of a circular saw blade and unbalanced pitch of several teeth on noise level of circular saws in cutting process. In Proceedings of the 2nd International Science Conference Woodworking Technique, 11-15 September, Zalesina, Croatia, pp. 311317, ISBN 953-6307-94.

SVOREŇ, J., MURÍN, L. 2009. The effect of the shape of the compensating slots in the body of a circular saw blade on noise level of a circular saws in the cutting process. In Proceedings of the ACOUSTICS High Tatras 2009 “34th International Acoustical Conference - EAA Symposium”, ISBN 978-80-228-2031-8.

VITCHEV, P., ANGELSKI, D., ATANASOV, V., MIHAILOV, V. 2018. Study on the influence of certain factors on the sound pressure level generated during cutting with the circular saw. In Pro Ligno 14(4): 6572, ISSN-L 1841-4737, ISSN (online) 2069-7430.

ACKNOWLEDGEMENTS This paper was supported by the grant No BG05M2OP001-2.009-0034-C01, financed by the Science and Education for Smart Growth Operational Program (2014-2020) and co-financed by the EU through the ESIF.

AUTHORS’ ADDRESSES Chief Assist. Prof. Pavlin Vitchev, PhD Assoc. Prof. Dimitar Angelski, PhD Assist. Prof. Vladimir Mihailov University of Forestry Faculty of Forest Industry 10 Kliment Ohridski Blvd.

1797 Sofia Bulgaria p_vitchev@ltu.bg d.angelski@ltu.bg v.mihailov@ltu.bg

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 81−90, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.08

EVALUATION OF THE SURFACE QUALITY OF THE PROCESSED WOOD MATERIAL DEPENDING ON THE CONSTRUCTION OF THE WOOD MILLING TOOL Pavlin Vitchev ABSTRACT The aim of the current study is to investigate the changes in the surface quality of specimens from Scots pine (Pinus Sylvestris L.) wood during longitudinal milling. Further, the influence of the cutter head construction of three different cutting tools (CH-1, CH-2, CH-3) on the surface quality was evaluated at different rotational frequencies n (from 4000 min1 to 8000 min1) and feed speed vf (from 3.5 m·min1 to 10.5 m·min1). The surface roughness was measured with a digital profilometer, model „Surf test SJ-210“ (Mitutoyo, Japan). Based on the experimental results, three regression equations are derived and the changes in the roughness parameter Rz in relation to the evaluated factors are graphically presented. Our results show that the values of the roughness parameter range from 25.7 μm to 39.6 μm. The highest surface quality is achieved when the surface is processed with the cutting tool CH-3, which cutting teeth edges are located at a certain angle (30) to the axis of cutting rotation. The optimal values of the evaluated variables, at which the height quality of the processed surfaces is achieved, are as follows: rotational frequency n = 6500 min1, at which the reached cutting speed is vc = 42 m·s1, and feed speed is vf = 7 m·min1.

Key words: wood milling, surface roughness, cuter head construction, cutting mode.

INTRODUCTION Milling is one of the main technological processes involved in the processing of solid wood and wood-based materials. It is well-known that this technological procedure aims to give a certain shape of the processed material as well as to ensure the highest possible class of surface roughness, i.e. a better surface quality. The quality of the milling surface is influenced by a number of factors, among others: the characteristics of the material to be processed (SANDAC et al. 2004), the characteristics of the cutting tool and the cutting mode (KETURAKIS et al. 2007, MOLITOR et al. 2011, GOCHEV 2014b, SIKLIENKA et al. 2016, GOCHEV 2018, KORCOK et al. 2018, VANCO et al. 2017, VITCHEV et al. 2018c). Due to the anisotropic structure of the wood, the roughness of the surface depends on the direction of the wood fibers (SANDAC et al. 2004). Therefore, this is another important factor in evaluating the surface roughness. Some of the above mentioned factors can be monitored during the milling process. Therefore, they are a subject of wider investigation in order to be managed in a more precise and adequate way.

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A number of scientific studies investigate the changes in the processed surface quality during longitudinal, transversal and vertical (profile) milling. Their main objectives are to provide a higher surface quality by investigating and evaluating the optimal parameters, processing conditions and characteristics of the cutting tool (COSTES et al. 2002, PRAKASVUDHISARN et al. 2009, ROUSEK et al. 2010, GONZALEZ-ADRADOS et al. 2012, GOCHEV 2014a, KAVALOV et al. 2015, РANAYOTOV et al. 2015, KMINIAK et al. 2016, KMINIAK et al. 2017, KUBS et al. 2017, ANGELSKI et al. 2018, SEDLECKY et al. 2018, VITCHEV et al. 2018a, VITCHEV et al. 2018b, DOBRZVNSKI et al. 2019).

The aim of the current study is to investigate the changes in the surface quality during longitudinal milling of specimens from Scots pine (Pinus Sylvestris L.) wood depending on the cutter head construction of the three cutting tools, measured at different rotational frequency (n) and feed speed (vf).

MATERIALS AND METHODS The experiments were carried out using woodworking spindle moulder machine, type T1002S (ZMM “Stomana” GmbH, Bulgaria) (Fig. 1). The machine was equipped with a two-speed three-phase electric motor with power 3.2/4.0 kW, which through a belt drive provides the following rotating frequency of the working shaft: 3000, 4000, 5000, 6000, 8000 and 10000 min1.

Fig. 1 Woodworking spindle moulder machine, type T1002S – general view.

Three cutting tools with different cutter head construction (Metal World, Italy), named CH-1, CH-2 and CH-3, are used in the current study. The technical characteristics are given in Table 1, where D is the diameter of the cutter head; d – diameter of the threaded hole; L – longitude of the main cutting edge; γ – hook angle; z – number of teeth; fz – feed per tooth.

The three cutting tools differ in their construction. In particular, the CH-1 has a monolith construction; the CH-2 has an assembled construction with cutting elements parallel to the axis of cutting rotation and the CH-3 has an assembled construction with cutting teeth edges allocated at 30 to the axis of cutting rotation.

In the current study, specimens from Scots pine (Pinus Sylvestris L.) wood with the following characteristics: density ρ = 490 kg·m3 and moisture content W = 12.7 % were used. The wood characteristics are determined according to BDS ISO 3131 and BDS ISO 3130. The processed samples had the following dimensions: longitude (l) 1000 mm and milling width (b) 40 mm. The details were fed automatically by a roller feeder.

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Tab. 1 Technical characteristics of the used cutting tools.

General look of the milling cutters

D mm

d mm

L mm

 

 

z No

fz mm

Cutting tool material

125

30

50

43

18

4

2.5

Metal-ceramic hard alloy

125

30

50

47

16

4

1.8

Metal-ceramic hard alloy

125

30

50

46

16

4

1.9

Metal-ceramic hard alloy

CH-1

CH-2

CH-3

In order to evaluate the complex influence of the three assessed variables: rotation frequency (n) of the milling tool, feed rate (vf) and thickness of the cut-out layer (h) (milling height) on the quality of the processed surfaces, the methodology of multifactorial planning and subsequent regression analysis were used (VUCHKOV et al. 1986). The measurements were performed in accordance with a preliminary designed matrix for three factorial experiment plan of G. Box (BOX et al. 1951, BOX et al. 1999). In Table 2 the levels of the input variables in explicit and coded form are presented. The values are in line with the most frequently used in practice.

Tab. 2 Values of the variables n, vf and h.

Variables Rotation frequency n = X1, min-1 Feed rate vf = Х2, m·min1 Thickness of the cut-out layer h = Х3, mm

Minimum value expl. coded 4000 -1 3.5 -1 1 -1

Average value expl. coded 6000 0 7 0 2 0

Maximum value expl. coded 8000 1 10.5 1 3 1

The roughness parameter Rz, μm was used to assess the quality of the treated surfaces, depending on the variables. It was determined separately for five base lengths in the longitudinal direction of the wood fibers of each part. For each base length the parameter Rz was determined by the mathematical equation: 𝑅𝑧 =

∑5𝑖=1|𝑦𝑝 |+∑5𝑖=1|𝑦𝑉 | 𝑖 𝑖 5

(1)

, 𝜇𝑚

ypi – the height of the biggest roughness of the profile, μm; yvi – the depth of the greatest slot of the profile, μm.

The surface roughness of each workspace was determined using the mean average value from the five measurement. The applied methodology is in accordance with the Bulgarian standard BDS EN ISO 4287 and is described in details (GOCHEV 2005). The measurements were performed with the digital profilomer, model “Surftest SJ-210“ 83

(Mitutoyo, Japan) (Fig. 2). For the mathematical and statistical analysis of the results, a specialized software Q Stat Lab 5 was used.

Fig. 2 Profilometer, model Surftest SJ-210 – general view.

RESULTS AND DISCUSSION Based on the performed experiments and after statistical analysis of the data, the following regression equation (2), (3) and (4) were used for the cutting tools CH-1, CH-2 and CH-3, respectively: 𝑦𝐶𝐻−1 = 32,138 − 2,895𝑋1 − 1,4𝑋2 + 1,323𝑋3 + 4,604𝑋12 − 2,351𝑋22 − 2,206𝑋32 − 1,353𝑋1 𝑋2 − 1,288𝑋2 𝑋3 + 0,005𝑋1 𝑋3 (2) 𝑦𝐶𝐻−2 = 28,568 + 2,574𝑋1 + 1,243𝑋2 + 1,177𝑋3 + 4,093𝑋12 − 2.092𝑋22 − 1,962𝑋32 − 1,202𝑋1 𝑋2 − 1,145𝑋2 𝑋3 + 0,005𝑋1 𝑋2 (3) 𝑦𝐶𝐻−3 = 26,090 − 2,351𝑋1 − 1,134𝑋2 + 1,076𝑋3 + 3,735𝑋12 − 1,91𝑋22 − 1,79𝑋32 − 1,099𝑋1 𝑋2 − 1,046𝑋2 𝑋3 + 0,006𝑋1 𝑋3 (4) where: y – the expected surface quality of the processed detail, defined by the roughness parameter Rz in coded form; X1 – rotation frequency of the cutting tool (n) in coded form; X2 – feed speed (vf) in coded form; X3 – thickness of the cut-out layer (h) in coded form.

The level of statistical significance (α = 0.05) of the results, derived from the regression equations is presented in Table 3.

Tab. 3. Characteristics of the derived regression equations Regression equation (2) with tool CH-1 (3) with tool CH-2 (4) with tool CH-3

Intergroup dispersion

Intragroup dispersion

Fisher dispersion F

Tabulated coefficient (Fisher’s criteria) FT

Coefficient of determination R2

23.55513

9.23233

2.55137

3.02038

0.69662

18.61965

7.29236

2.55331

3.02038

0.69678

15.52592

6.09147

2.54880

3.02038

0.69641

84

From the values of the F-distribution and the tabulated coefficient FT it is visible that for the three regression equations the Fisher criteria for the adequacy of the model, namely F≤FT are fulfilled, Therefore, the results could be further analyzed.

The regression equations were used to predict the surface quality of the specimens from Scots pine wood, processed with different cutting tools during longitudinal milling and depending on the changes in the rotation frequency (n), feed speed (vf) and the thickness of the cut-out layer (h).

The planning matrix for the three-factorial experiment and the mean average value of the roughness parameter Rz, for cutting tools: CH-1, CH-2 and CH-3 and determined for different combinations of variables, are presented in Table 4.

The changes in the surface roughness depending on the construction and the rotation frequency of the cutting tool (n), measured at the average changes of the variables vf = 7 m·min1; h = 2 mm are presented in Fig. 3. It is visible that the highest value of the roughness parameter Rz is determined for the cutting tool CH-1, followed by CH-2 and CH-3. This can be explained by the higher feed per tooth (fz) value, as a result of the monolith construction of CH-1. Another reason could be the cutting edges, located parallel to the axis of rotation, which made a simultaneous contact along the entire length of the work surface.

The roughness parameter values for the cutting tool CH-1 range from 39.64 μm to 31.7 μm.

Tab. 4 Planning matrix for three-factorial experiments and mean average values of the roughness parameter ̅𝑹̅​̅​̅𝒛 (μm) No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

X1 = n, min-1 -1 -1 -1 -1 1 1 1 1 -1 1 0 0 0 0 0

4000 4000 4000 4000 8000 8000 8000 8000 4000 8000 6000 6000 6000 6000 6000

X2 = vf, m·min1 -1 -1 1 1 -1 -1 1 1 0 0 -1 1 0 0 0

3.5 10 10 3.5 3.5 10 10 3.5 0 0 -1 1 0 0 0

X3 = h, mm -1 1 -1 1 -1 1 -1 1 0 0 0 0 -1 1 0

1 3 1 3 1 3 1 3 2 2 2 2 1 3 2

̅𝑹̅​̅​̅𝒛 μm CH-1 29.77 41.12 36.11 32.25 31.64 32.88 22.43 28.82 41.03 35.21 29.96 31.96 32.02 30.27 31.78

CH-2 26.47 36.55 32.10 28.66 28.12 29.28 20.00 25.52 36.18 31.30 26.70 28.41 28.46 26.91 28.25

CH-3 24.17 33.38 29.31 26.18 25.67 26.74 18.29 23.32 33.04 28.58 24.39 25.94 26.07 24.57 25.79

The assembled construction of the cutting tools CH-2 and CH-3 is responsible for the lower feed per tooth (fz) value (Table 1), which assures better quality of the processed surface in comparison with CH-1. The values of the roughness parameter Rz for the cutting tool CH2 range from 35.24 μm to 28.18 μm.

The values of the roughness parameter Rz for the cutting tool CH-3 range from 32.08 μm to 25.74 μm. The cutting edges of the cutting tool CH-3 located at an angle to the axis of rotation provide for a gradual contact between the tool and the processed material. This additionally improves the quality of the processed surface.

85

40 Cuting tool CH-1

Surface roughness, Rz, μm

38

Cuting tool CH-2

36

Cuting tool CH-3

34 32 30 28 26 24 4000

4500

5000

5500

6000

6500

7000

7500

8000

Rotation frequency of the cuting tool n, min-1

Fig. 3 Changes in the surface quality depending on the construction and the rotation frequency of the cutting tool, determined at feed speed vf = 7 m·min1 and thickness of the out-cut layer h = 2 mm.

The results from the current study clearly show that the rotational speed of the cutting tool (n) significantly influenced the quality of the processed surface (Fig. 3). The peak values of the roughness parameter Rz were detected at the highest rotational speed of the tool n = 4000 min-1. An increase in the rotational frequency improved the surface quality of the processed material. The best quality for all three cutting tools was reached at rotational speed n = 6500 min-1. Our results were in good correlation with the results obtained from other authors (GOCHEV 2014B, KUBS et al. 2017) which conclude that higher rotational speed results in better quality of the machined surface. In the current study, however, we also observed a deterioration of the surface quality at rotational frequency higher that n = 6500 min-1. In particular, with an increase in rotational frequency of the cutting tool from 6500 min-1 to 8000 min-1, the values of the roughness parameter Rz increased by 2 μm for the three cutting tools. The deterioration of the surface quality was probably due to the changes in the dynamic behavior of the machine and to the increased vibrations of the cutting tool resulting from the higher rotational speed.

Figure 4 presents the relationship between the changes in the roughness of the processed material (Rz) and the feed speed (vf) for the three cutting tools, measured at rotational speed of the cutting tool n = 6000 min-1 and the thickness of the out-cut layer h = 2 mm. The roughness curves depicted in Fig. 4 were in good correlation with the results presented in Fig. 3, namely the highest surface quality was achieved with cutting tool CH-3, followed by CH-2. The highest value of the roughness parameter Rz was measured for the cutting tool CH-1.

It is well-known that the feed speed influences the surface quality. In the scientific literature, there is a large source of information, showing that independently of the wood type of the processed material, the surface roughness increases with the increase of the feed speed (BARCIK et al., 2009, GOCHEV 2014b, SIKILIENKA et al. 2016, KUBS et al. 2017).

Although not very pronounced, this trend is visible also from the results of the current study.

The graphs in Fig. 4 show that the best surface quality is reached at the lowest feed speed vf = 3.5 m·min1. An increase in the feed speed up to 7 m·min1 results in the deterioration of the surface quality. Interestingly enough, an increase in the feed speed from 7 m·min1 to 10.5 m·min1 led to a slight decrease, by 05-0.8 μm, in the roughness parameter Rz. This 86

decrease, however, is insignificant and it could be concluded that under the conditions of this study, an increase in the feed speed from 7 m·min1 to 10.5 m·min1 did not change the surface roughness of the processed material.

34

Surface roughness, Rz, μm

33 32 31 30 29 28 27 26 25

Cuting tool CH-1

24

Cuting tool CH-2

23

Cuting tool CH-3

22 3.50

4.35

5.21

6.06

7.00

Feed rate vf,

7.85

8.71

9.56

10.50

m·min-1

Fig. 4 Changes in the surface quality depending on the construction and feed speed, measured at rotational speed of the cutting tool n = 6000 min-1 and the thickness of the out-cut layer h = 2 mm.

Based on the obtained results, the roughness of surface processed with the three cutting tools – CH-1, CH-2 и CH-3, corresponds to a roughness class IX (GOCHEV, 2018).

According to KAVALOV et al. (2014), surfaces of specimens from monolith wood with roughness Rz = 30 μm are qualified as “good quality surface”. This surface quality is considered suitable for further processing, such as gluing and coating.

CONCLUSION The experimental results of this study aimed at investigating the changes in the surface quality of the specimens from Scots pine (Pinus Silvestryis L.) wood, measured at different rotational speed (n) and feed speed (vf) during longitudinal milling and in relation to the characteristics of the head cutter.

Based on the obtained results, the following conclusions were drawn:  The surface quality is influenced by the construction of the cutting tool, which indirectly influences the cutting mode. Under the conditions of this study, the highest surface quality is achieved by using an assembled milling tool with cutting edges located at a certain angle to the axis of rotation (see Fig. 3).  The influence of the rotational speed of the cutting tool, or the cutting speed, on the quality of the processed surface, assessed by the roughness parameter Rz is confirmed by the obtained results. An increase in the rotational frequency from 4000 min1 to 6500 min-1 resulted in better surface quality, improved by 35% when compared to higher rotational frequency (from 6500 min1 to 8000 min1). The observed

87

deterioration of the surface quality at higher rotational frequency values can be explained with the increased vibrations of the cutting tool (see Fig. 3).  For a milling tool with cutting diameter D = 125 mm used for processing of Scots pine wood specimens, the optimal rotational speed range is from 6000 min-1 to 6500 min1. This range ensures a cutting speed (vc) from 39 m·s1 to 42 m·s1.

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ACKNOWLEDGEMENTS This paper was supported by National Program of Republic of Bulgaria “Young Scientists and Postdoctoral Students”, Institution – University of Forestry, Faculty of Forest Industry.

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AUTHORS’ ADDRESSES Chief Assist. Prof. Pavlin Vitchev, PhD University of Forestry Faculty of Forest Industry Department Woodworking machines 10 Kliment Ohridski Blvd.

1797 Sofia Bulgaria p_vitchev@ltu.bg

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 91−97, 20189 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.09

BURNING RATE OF SELECTED HARDWOOD TREE SPECIES Linda Makovicka Osvaldova  Javier-Ramón Sotomayor Castellanos ABSTRACT The paper is aimed at determining the fire-technical properties of the selected central European hardwood tree species: black locust, European white birch, European beech, sessile oak and Norway maple. The measurements will be mentioned in a database of tree species. The reactions of the tree species were monitored using the following evaluation criteria: (mass) burning rate, time when the peak value was achieved and the ratio of the two values. The evaluation criteria reflected the behavior of the material when exposed to radiation or flame source and the two combined, or simultaneous exposure to both flame and radiant heat source according to the selected mode of the thermal load. The results presented in the paper showed the effect of the source itself, as well as the effect of the given tree species on the evaluation criteria. The experiment results proved that, when exposed to a radiant heat source, the shape of the curves was different for all the given tree species. Oak and locust tree showed high resistance to ignition and burning. In the case of flame and combined heat source, where the size of the peak in the first few seconds of the experiment is of the greatest importance, the shape of the curves differed. In this case, locust and oak tree reached positive values.

Key words: hardwood, burning rate, flame source, radiant heat source.

INTRODUCTION For an objective evaluation of the materials for fire protection purpose, a large number of evaluation criteria has been created. In most cases, the criteria evaluate the changes in physical properties which occur in the process of heating or the actual burning of such material. One of the oldest criterion is the change in weight – i.e. weight loss. This criterion is a part of many modern contemporary methods. A logical fact is that material shrinks when burning and the criterion of weight loss is a clear indicator of this happening. In most cases, this criterion is measured over a certain period of time specified in the conditions for the given test method.

Weight loss was the first evaluation criterion used to assess the ignition and burning of materials. It had been applied for the Schlytter method in 1898 (OSVALD 1997) and it was used for numerous series of test methods in the decades to follow. The materials containing water started to be evaluated in the 80´s (wood, plasterboard materials, etc.), however, this evaluation criterion provided misleading information.

Water evaporating from the material caused the change in weight which was figured in the total weight loss as the result of burning. A certain disproportion, quality evaluation and application of the test results occurred. Various test methods therefore began to make 91

use of other evaluation criteria. Modern test methods start to use this evaluation criterion anew. It is no longer measured discontinuously (initial and final weight) but it is a continuous measurement in short time intervals allowing to assess this change as weight loss and mass burning rate. Various studies deal with the topic using various types of wood and woodbased materials (MITTEROVA et al. 2014; OSVALDOVA 2005; ZACHAR, MARKOVA 2009; SOTOMAYOR, MAKOVICKA 2017).

Wood is a material capable of flame as well as flameless burning (smouldering). It is important to observe weight loss not only during the time interval which is prescribed for the test but also after the completion of the test. A situation - when weight loss increases due to flameless burning or, on the contrary, weight loss reaches negative values (especially when using samples of larger dimensions) when the samples absorb moisture from the surrounding environment - might happen.

The aim of the experiments was to record the change in weight loss in its dynamic form for the selected tree species, to monitor burning rate as well as its significant indicators, the peak value and the time necessary to achieve the value and their mutual ratio.

METHODOLOGY OF THE EXPERIMENT Test specimens The following wood species were used for the experiment: black locust ACA (Robinia pseudoacacia L.), European white birch BIR (Betula verucosa Ehrh.), common beech BEE (Fagus silvatica L.), sessile oak OAK (Quercus petraea Liebl.), and Norway maple MAP (Acer platanoides L.).

The dimensions of each test specimen was 40 × 20 × 20 mm. The input values, the weight and the size of the test specimens were stated and the density at the given moisture level was calculated (the difference was not greater than ± 15 kg/m3 for the given tree type) prior to the experiment. The moisture content of the test specimens was 8 ± 1 %. 15 samples were made and tested for each tree species. Average values of these 15 measurements are stated in the paper. The test specimens were sorted in alphabetical order but, given the length of paper, they were not specified from the wood processing point of view.

Tab. 1 Average values of the weighted standard deviation.

Wood ACA BEE BIR MAP OAK

Density kg/m3 784.21 694.67 644.38 619.55 751.14

Weighted standard deviation  378.38 317.23 300.01 285.69 365.38

Selected weighted standard deviation 384.84 322.65 305.14 290.57 371.63

Test procedure Radiant heat source (R) Test specimens were placed under the thermal radiator and, at the same time, Sarto Connect program was launched. This program recorded the weight of test specimens every 10 seconds. This means that the computer recorded the weight of test specimens in 10 second intervals. After 15 minutes, Sarto Collect stopped operating. If the test specimen burned down within the 15 minutes, the experiment was over. The heat output of the radiator was 1000 W. The distance between the sample and the radiator was 30 mm.

Flame source (F) 92

The test procedure was identical to the one described in the previous paragraph. Unlike the previous experiment, a flame source, a small burner and propane butane were used for this experiment as prescribed by STN EN ISO 11925-2 directive (STN EN ISO 11925-2:2003).

Combined Thermal Load (C) Combined thermal load means the exposure of the test specimens to a radiant heat source and a flame source using the same device (as for the radiant heat source experiment) and the same measuring procedure of the input parameters of test specimens. The surface of test specimens was exposed to a flame source. If no ignition occurred, it was repeated in 10 second intervals. After 15 minutes, Sarto Collect stoped operating. If the test specimen burned down within 15 minutes, the experiment was over.

Evaluation criteria Relative burning rate was determined according to the relations (1) and (2). 𝜕𝛿 𝑣𝑟 = | 𝜕𝜏𝑚 | (%/s) or numerically |𝛿 (𝜏)−𝛿 (τ+Δτ)| 𝑣𝑟 = 𝑚 Δτ𝑚 (%/s) where: vr - relative burning rate (%/s), m - relative weight loss in time () (%), m( - relative weight loss in time () (%),  - the time interval when the weights are subtracted (s).

(1) (2)

Ratio P represented the maximum burning rate divided by the time when it was reached. The ratio was determined according to the relation (3). 𝑃=

𝑣𝑟𝑚𝑎𝑥 𝜏

(%/s2)

(3)

where: P- the ratio of maximum burning rate divided by the time when it was reached (%/s2), vr max- maximum burning rate (%/s), - the time when the maximum burning rate was achieved (s).

Results and discussion The aim of the experiment was to compare the reaction of the selected tree species on thermal heat source, radiation heat source, flame heat source or a combination of the three types. The aim was not to evaluate the effect of the source. Burning rate course for each type of heat source is shown in Figures 1 to 3 and the average peak values are given in Table 1.

Fig. 1 Burning rate course of the selected tree species exposed to radiant heat source.

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Fig. 2 Burning rate course of the selected tree species exposed to flame source.

Fig. 3 Burning rate course of the selected tree species exposed to a combined heat source.

Tab. 2 Average values of the selected evaluation criteria.

Evaluation criteria Burning rate (%/s) Time maximum burning rate (s) Ratio P (%/s2)

Heat source R F C R F C R F C

ACA 0.00035 0.00065 0.00201 320 50 130 1.08 12.92 15.47

Wood species BEE BIR MAP 0.00154 0.00100 0.00091 0.00068 0.00098 0.00095 0.00248 0.00369 0.00284 290 320 310 40 30 40 130 100 110 5.32 3.12 2.94 16.99 35.59 23.67 19.07 36.92 25.86

OAK 0.00047 0.00073 0.00219 340 60 140 1.38 12.23 15.63

The best indexes for each evaluation criteria were reached for the tree species with the highest density - locust and oak, whereas the worst ones were achieved for birch. In this case we assume that - besides density - chemical composition of the tree species (percentage of hemicellulose as well as other polysaccharide components of the wood of the given tree species) had an effect on the experiment results.

94

The experiment demonstrating various methods of wood ignition of the selected trees species (flame heat source, radiant heat source or both) was carried out by simulating real fires conditions. Radiant heat source is a common cause of fires. Since several test methods use flame heat source to determine fire technical properties of wood (OSVALD 1997), flame heat source was observed in more detail. The worst-case scenario is the combination of the two heat sources - radiant heat source "prepares the ground” for the material to burn. In such cases, even a weak flame is enough for the fire to develop in a short time span and its intensity may be relatively high. Thermal radiation in the interior is a crucial factor contributing to heat transfer caused by flames and hot surfaces. Radiation, i.e. heat flow, of 150 kW/m2 and the temperature of gases reaching 1 000 °C can be observed in a fully developed fire. The thermal radiation values in the first stage of fire are usually ranging between 2050 kW/m2 (LIZHONG et al. 20002001).

Heat release rate is an important parameter used to predict the fire hazard of materials.

It is defined as the amount of energy produced by a material in the process of burning per a unit of time (kW/m2). According to (KARLSSON, QUINTIERE 2000), the curve of heat release rate is not constant in the entire course of burning. We came to the same conclusion during our experiments, although, instead of heat release rate course, mass burning rate course was used as the main criterion. The course of these curves differs, since it depends on the tree type as well as on the type of the source and the ignition method. Heat release rate, together with mass burning rate, are used to characterize the behavior of the material in the first stage of a fire (until flashover) (TRAN 1992, STROUP et al. 2004, SOTOMAYOR CASTELLANOS et al.

2017).

Burning rate is the main factor used even in modeling the fire resistance of wooden structures. TRAN and WHITE (1992) set the values for both - burning rate and weight loss if the heat flows range between 1555 kW/m2. In this range, there is a linear increase in burning rate as the heat flow grows. It significantly depends on the tree species, its density and its main structural elements. Higher values were reached for the samples made from deciduous wood. The results suggest that charring rate is directly proportional to burning rate and inversely proportional to the density of non-degraded wood samples.

Trees with high density wood - locust and oak - proved themselves to be the best indicators for each evaluation criteria. Birch achieved the worst results. Although the goal of the experiment was not to compare loading conditions (for individual heat sources), we want to draw attention to different course of the curves for the each thermal load (see Fig. 13). In addition to significant impact of wood density and its moisture content, the percentage of basic structural elements of wood, when assessing materials from the firefighting perspective, appears to be significant as well. As stated by MAKOVICKÁ et al. (2016) and OSVALD (2016), wood density has a direct impact on its ignition and combustion. The two authors studied the impact of density not only by comparing different tree species, but also by monitoring different densities within one tree type. The impact of density manifested itself for one tree type even when treated with a fire retardant MAKOVICKÁ et al. (2016).

In this case, we can note that chemical composition of the tree species (mainly the percentage of hemicellulose and other polysaccharide components) had an impact on the results as stated in the works of BUBENÍKOVÁ et al. (2004), KAČÍKOVÁ et al. (2013), and MARTINKA et al. (2014). Several authors (ROWELL et al. 1984, TRAN, WHITE 1992, JANSSENS 2004, FANGRAT et al. 1998) confirmed that there is a statistically significant correlation between the number of the basic structural components of wood, e.g. lignin and the burning rate. The higher the lignin content is, the lower the burning rate is.

In the follow-up stages of the experiment, we recommend to evaluate the results from the point of view of the tree density and the percentage of basic structural components of wood. We recorded some minor variations in the behavior of the tree species i.e. beech which 95

burning rate was higher when exposed to radiant heat source and the peak value was reached sooner than in the case of birch.

These results are essential for testing other non-European tree species. Although they were obtained using a non-standardized test, the measurements have a great information value dividing different types of tree species whilst paying attention to details. The results are applicable in practice, mainly when assessing facade elements and other types of wood cladding and their susceptibility to ignite due to radiant heat from adjacent building fire, directly from a heat source or the combination of the two.

CONCLUSION Based on the given values we consider justified - when monitoring the fire-technical properties of a material - to apply both heat sources i.e. flame or radiant heat source or the combination of the two. Their intensity does not need to be high in order to determine the reaction of materials to the process that will bring about burning.

Standardized methods generally use samples of larger dimensions to determine their reaction to fire, which is logical and natural, but we recommend multiple small samples and a more thorough statistical evaluation as a follow-up method. The test confirmed that our experiment had some information value and determined the properties of wood in relation to its ignition, burning and a subsequent fire. Such methods are recommended even when testing other tree species i.e. tropical tree species or some modern tree modifications such as thermowood, aesthetic and also flame retardant treatment.

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FANGRAT, J., HASEMI, Y., YOSHIDA, M., KIKUCHI, S. 1998. Relationship between Heat of Combustion, Lignin Content and burning Weight Loss. 1998. In Fire and Materials, Vol. 22, 1998, 1, s. 16. www3.interscience.willey.com (2005-06-17) JANSSENS, M. L. 2004. Modeling of the thermal degradation of structural wood members exposed to fire. In In Fire and Materials, Vol. 28, 1998, s. 199207. ww3.interscience.willey.com (2005-06-17).

KAČÍKOVÁ, D., KAČÍK, F., ČABALOVÁ, I., ĎURKOVIČ, J. 2013. Effects of thermal treatment on chemical, mechanical and colour traits in Norway spruce wood. In Bioresource Technology 2013, 144:669.

KARLSSON, B., QUINTIERE, J. G. 2000. Enclosure Fire Dynamics. London; New York, Washington : CRR Press LLC. 400 s. ISBN 0-8493-1300-7.

LIZHONG, Y., XIAOJUN, CH., ZHIHUA, D. 20002001. Experimental Study on Fire Performance of Wood at Early Stage of Fire. In Journal of Applied Fire Science, Vol. 10, 20002001, No. 3, p.

251264.

MAKOVICKA OSVALDOVA, L., GASPERCOVA, S., MITRENGA, P., OSVALD, A. 2016. The influence of density of test specimens on the quality assesment of retarding effects of fire retardants. In Wood Research. Vol. 61, no. 1, 2016, s. 35–42. ISSN 1336-4561.

MARTINKA, J., HRONCOVA, E., CHREBET, T., BALOG, K. 2014. The influence of spruce wood heat treatment on its thermal stability and burning process. In European Journal of wood and wood products, 2014, (Holz als corner- und Werkstoff) ISSN 0018-3768.

MITTEROVA, I., ZACHAR, M., RUZINSKA, E., MAJLINGOVA, A. 2014. Ignitability of Unprotected and Retardant Protected Samples of Spruce Wood. Environmental and Safety Aspects of Renewable

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Materials and Energy Sources, Advances Materials Research, Trans Tech Publications Ltd, 2014, ISSN: 1022-6680 ISSN cd: 1022-6680 ISSN web: 1662-8985, ISSN/ISO: Adv. Mater.Res. 330335.

OSVALD, A. 1997. Fire resistance properties of wood and wood-based materials. Zvolen, Technical University, 1997. 52 pp. ISBN 80-228-0656-0.

OSVALD, A. 2016. Hustota – fyzikálna veličina ovplyvňujúca výsledky testov požiarneho skúšobníctva. In Advances in fire & safety engineering, V. International Scientific Conference. Žilina : Žilinská univerzita v Žiline v EDIS – vydavateľskom centre ŽU, 2016, (nestránkované) ISBN: 978-80-554-1269-6 OSVALDOVA, L. 2005. Comparison char layer thickness and weight loss in spruce and larch, In Symphosium of young reserachers, Zvolen, Technical University, 2005, pp. 124129. ISBN: 80– 228–1514–4.

ROWELL, R. M., SUSOTT, A. R., DEGROOT, F. W., SHAFIZADEH, F. 1984. Bonding fire retardants to wood : Part I. Thermal behavior of chemical bonding agents. In Wood and Fiber Science, 16(2): 214223.

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SOTOMAYOR CASTELLANOS, J.R., MAKOVICKA OSVALDOVA, L. 2017. Resistencia al fuego de madera laminada. In Investigación e Ingeniería de la Madera. Vol. 13, nu. 3, 2017, s. 421. ISSN 23959320.

STROUP, D. W., BRYNER, N. P., LEE, J., MCELROY, J., ROADARNEL, G., TWILLEY, W. H. 2004.

Structural Collapse Fire Tests: Single Story Wood Frame Structures. http://fire.nist.gov/bfrlpubs (2005-04-11) TRAN, H. C. 1992. Experimental Data on Wood Materials. In Babrauskas, V., Grayson, S.J., eds.

Heat Release in Fires. New York : Elsevier Applied Science, 1992. s. 357372. www3.interscience.willey.com (2005-06-19).

TRAN, H.C., WHITE, R.H. 1992. Burning Rate of Solid Wood Measured in Heat Release Rate Calorimeter. In Fire and Materials, Vol. 16, 1992, p. 197206. www3.interscience.willey.com (200506-19).

ZACHAR, M., MARKOVA, I. 2009. Monitoring of difference in thermal degradation of poplar samples.

2009, In Acta Facultatis Xylologiae Zvolen, 51(1): 3346.

ACKNOWLEDGEENTS This work was supported by the Scientific Grant Agency VEGA. (Project 1/022/16|6| Fire safe insulation systems based on natural materials).

AUTHOR ADDRESS doc. Ing. Linda Makovicka Osvaldova, PhD. University of Zilina Faculty of Security Engineering Department of fire engineering Slovakia linda.makovicka@fbi.uniza.sk Javier-Ramón Sotomayor Castellanos Faculty of Engineering in Wood Technology, Universidad Michoacana de San Nicolás de HidalgoMorelia, Michoacán Mexico madera999@yahoo.com

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 99−107, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.10

FIRES IN ARID AGROFORESTAL LANDSCAPES AND THEIR DAMAGE ASSESSMENT Vadim Viktorovich Tanyukevich  Anastasia Vladimirovna Kulik  Olga Ivanovna Domanina  Sergey Vladimirovich Tyurin  Alexander Alexandrovich Kvasha ABSTRACT Impact of shelter forest belts of Robinia pseudoacacia L. on spread of fires and the damage caused by them was investigated in arid agroforestal landscapes of Russia. A mathematical model for arid regions of the world was obtained. According to the model, the area of fires in agrarian lands in habitats with forest shelter belts of the 1st class life-state varies by an average of 1.22 ha/hour comparing to plantations of the 2nd and 3rd classes – up to 1.56 ha/hour. The forest belts could suffer low (a forest stand is not substantially damaged), medium (more than 10% of live trees) and severe (less than 10% of live trees) degree of damages by fire. The damage caused in this case amounts to US$ 220, 853 and 2,210 / ha. The world community has been recommended a method for fighting fires in arid agroforestal landscapes “Don Fire Protection” developed at the Don State Agrarian University. A new scientific direction “agroforestry pyrology” is substantiated; agroforestal landscapes exposed to wildfires is its research object and the main task is to study the patterns of occurrence, behaviour and consequences of fires on forest-meliorated lands in order to develop fire-safe technology of protective afforestation under global climate warming.

Key words: agroforestal landscape; fire; shelterbelt planting; damage assessment; agroforestry pyrology.

INTRODUCTION One of the global climate aridization consequences is the deterioration of fire conditions at the most valuable categories of lands used by man for agricultural production and food security, namely, agricultural land (FAO/UHO 2007). As a rule, they are combined with forest plantations that protect agricultural land from affecting by arid climate conditions. Such landscapes in the Russian scientific literature received the name of agroforestal.

In 2017, one of the largest landscape fires named Thomas occurred in the Ventura District (California, USA) which is characterized by climate aridization in recent decades.

The fire area was 270 thousand acres. Damage was estimated at US$ 34 million. According to the official data of the Global Fire Monitoring Center (GFMC) and the UN Office for Disaster Risk Reduction (UNISDR), the landscape fire problem in climate aridization conditions is relevant for agrarian regions of France, Portugal and Croatia, arid subregions of Asia, Africa and South America (DUBENOK et al. 2017; Headquarters of Russian Emergency Situations Ministry in the Rostov region, 2018). In Australia, the largest 99

wildfires occurred in 2003, 2005, 2007, especially large with an area of 430 thousand hectares in February 2009 against the background of air temperature +43 °C and wind speeds of up to 30 m/s. In Botswana, the most dangerous was the 2008 Janzie fire over an area of over 3.5 million hectares and a total loss for the economy of US$ 250,000. The worst drought of 2007 provoked a powerful seven day landscape fire in Greece with an area of more than 270 thousand hectares, 84 people have died. Regular wildfires occur in Israel, Indonesia, Mongolia, Canada, the frequency of which correlates with dry years (ERISOV et al. 2016).

A similar problem is characteristic for arid agricultural regions of Russia with its extensive agroforestal landscapes. The largest fires were recorded in 1998 and 2010. The number of fires exceeded 32 thousand, the total area covered by fire was more than 2 million hectares; the damage to the economy was estimated at 100 billion rubles (ERISOV et al.

2016). Rostov region, the most important food region of Russia, suffers from fire most. The area of arable land here exceeds 8.8 million hectares. To combat desertification processes and to improve the productivity of agricultural land, shelterbelt plantings have been created there with total area of over 125 ha, preferably of Robinia pseudoacacia L., providing protective afforestation of arable land in the range of 1.92%  3.28% (DUBENOK et al. 2017).

According to official data of the EMERCOM of Russia in the Rostov region, in 2016 the area of landscape fires in the region was 1320 hectares, in 2015 - 1048 hectares, in 2014 - 1895 hectares. A significant part of the fires in the region is recorded in the areas where the steppe rivers flow, especially in their bends (Headquarters of Russian Emergency Situations Ministry in the Rostov region, 2018). This is due to the active agricultural use of such lands.

Along with the well-known economic (damage to dwellings, destruction of cultivated vegetation) and environmental consequences, a fire leads to a decrease in land-reclamation and environmental protection efficiency of shelter forest belts (DUBENOK et al. 2017).

The general features of landscape fires in arid conditions are considered in detail in literature (ERISOV et al. 2016; SIDARENKO 2014; KIRILLOV, EGOROVA 2012; KOBEC 2017; TEDIM et al. 2015; PATON et al. 2015; MCGEE et al. 2015; SOTO et al. 2015; BUERGELT, SMITH 2015; SAGALA et al. 2015; CHEN, CHEN 2015; SCHMERBECK, KRAUS 2015; PONOMAREV et al. 2015; GROOT et al. 2015); however, the features of fire spreading over agricultural lands crossed by shelter forest belts, as well as the assessment of damage to such plantations require additional research.

The working hypothesis was that, being a biophysical boundary, the narrow shelterbelt plantings are capable either to restrain the spread of wildfires, or to speed up this process depending on their life-state.

The purpose of the studies conducted in the Rostov region of Russia in 20122018 was to develop a mathematical model characterizing the dynamics of fires in agroforestal landscapes of arid regions that could be applied in other regions of the world with similar climatic conditions, and also to clarify the principles for assessing damage caused by fire, and to recommend to the world community a low-cost and effective technology to combat this natural disaster.

RESEARCH METHODS An original method was developed to achieve the research goals. The climatic conditions of the region were analysed according to the long-term data of the meteorological station of Rostov-on-Don city.

Fire danger classes (FDCs) were established in July-August depending on weather conditions in accordance with the scale approved by the order of the Federal Forestry Agency

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dated July 5, 2011, No. 287. The speed of fire spreading in agroforestal landscapes was determined during their extinguishing.

Pyrogenic damage to shelterbelt plantings was assessed according to the adapted classification of burned-out forests (DUBENOK et al. 2017): a) Fire-damaged forest belts with the number of viable trees no more than 10% severely damaged stands; b) Forest belts where more than 10% of the vital trees are preserved - mediumdamaged stands; c) Plantings where the stand has been fully preserved or a single dying of the trees has occurred - low damaged stands.

In accordance with the generally accepted methodology, there were laid out 5 sample plots in each severe-, medium- and low- damaged fire stands, respectively, in typical robinian fire-damaged forest belts of the region. The enumeration survey on sample plots was carried out according to the generally accepted method, with the determination of the stock of trees damaged by fire.

Taxation indicators for the treated forest belts before the fires were established according to the inventory data of reclamative afforestations maintained by LLC Research and Production Center “Kadastr”. State classes of the forest belts were assessed according to the scale by P.V. KUDRYASHOV et al. (1985).

To take into account the aboveground phytomass in forest belts damaged to different extents during a month after the fire, model trees were selected along the conditional cross section line in each row, the mass of which was divided into 3 fractions (barky trunks, branches, and green mass); the dry matter content was established using the thermoscales method in the laboratory. The obtained values were compared with previously published data on the phytomass of forest belts that were not exposed to fires in the region, determining the amount of burnt plant mass (DUBENOK et al. 2017).

In assessing damage by tree plantations, the order by the Rosleskhoz dated April 3, 1998, No. 53 and the Order of the Rostov Region Government dated April 26, 2012 No. 316 were followed. The damage caused by the decrease in the environment-forming functions of forest belts was calculated as the product of damage from wood loss by the coefficient of ecological significance of plantations (2.0). Assessing the damage to the environment due to pollution caused by forest belt burning products, the Decree of the Government of the Russian Federation dated September 13, 2016 No. 913 was applied, as well as the coefficient determined by the ecological situation and the significance of the atmospheric air condition for the Rostov region — 1.6 (approved by the Ministry of Natural Resources of the Russian Federation on November 27, 1992). Calculations were carried out in US $ in 2019 prices.

RESULTS AND DISCUSSION The geographical area under the study was located within the Rostov region and covered the Don-Donetsk plain, the eastern part of the North Priazovskaya plain (up to the north coast of the Taganrog Bay), the eastern and southern branches of the Donetsk Ridge, the north-western part of the Kuban-Priazovskaya lowland, the Lower Don terraced accumulative lowland, as well as the space between the Don-Salsky watershed and the valley of the river Manych. This region is characterized by hot European climate-type summer (average air temperature is +23 ° C), with prevailing clear weather (sunshine duration 907 hours, total solar radiation 2017 MJ/m2), with a precipitation amount of about 152 mm/year and dry hot east winds with speeds of 56 m/s. This causes a high risk of occurrence of medium and strong intensity grass fires in agroforestal landscapes. A similar problem is 101

noted in other arid regions of the world (KOBEC 2017; TEDIM et al. 2015; PATON et al. 2015; MCGEE et al. 2015; SOTO et al. 2015; BUERGELT, SMITH 2015; SAGALA et al. 2015; CHEN, CHEN 2015; SCHMERBECK, KRAUS 2015; PONOMAREV et al. 2015; GROOT et al. 2015).

The main part of afforestation belts (72%) in agroforestal landscapes of the region under study is formed by Robinia pseudoacacia L. These are mainly wind-managing plantings of dense structure, III quality class, I - III classes of state on a scale (KUDRYASHOV et al. 1985), created according to the technology generally accepted for the steppe zone of Russia.

Wildfires occurred on inarable lands and agricultural fields in July and August. The main combustible materials on farmlands are dead stands of rhizomatous vegetation (Elytrigia repens L.), and crop residues. The fires occurred in the period from 12.00 to 18.00 Moscow time, with FDC = III and the prevailing east wind speed of 56 m/s. The cause of ignition is arid climate, careless handling of fire, agricultural machinery and vehicles operation. The average fire area was 2.7 ha. The fire front spread at a speed of 13 m/min in a westerly direction, entering the shelterbelt plantings.

The analysis of forest inventory materials, as well as our own research (DUBENOK et al. 2017) allowed us to establish the average taxation indicators of black locust windmanaging forest belts in the area under study before their damage by landscape wildfires: the forest belt routes are located in the north-south direction; their composition is 10 Rb; planting height 10.5 ± 0.2 m; stem diameter 11.0 ± 0.2 cm; timber stock 64.0 ± 0.8 m3/ha; the 4-th age class, stocking 1.0; the structure is dense; number of rows is 4; width 12 m; average area is 2.17 ha; state classes are IIII. It has been established that in forest belts of the 1st state class (inventory numbers 25, 26, 28, 30, 36), with more than 75% share of healthy trees in the stand, the fire propagation speed decreased 2 times (less than 1 m/min) compared to open areas of agricultural land.

In afforestation belts of II state class (inventory number 8, 24, 50, 51, 54; share of dry trees in plantations is 2549%), landscape wildfires spread out at about the same speed as in open agricultural lands (23 m/min).

In the shelterbelt locust plantations of the third state class (inventory numbers 1, 3, 18, 20, 23; share of healthy trees in forest belts before the fire is less than 50%)) the wildfire propagation speed increased almost 2 times (up to 67 m/min) compared to agricultural lands.

Regression analysis of data by process parameters of wildfire propagation in arid agroforestal landscapes allowed us to obtain a multiple regression equation that describes the relationship between the fire affected area and fire duration, as well as the state class of the afforestation belts:

S wfa  2616 ,54  67 ,85  T  1670 ,14  K

at R  0.933

(1)

Where - wildfire area in agroforestal landscapes, m2; T - the landscape wildfire duration, minutes; K - the state class of belts afforestation; R is the multiple correlation coefficient. The use of multiple relationship (1) is limited by the following conditions typical for arid regions of the world: protective forest cover of arable land is 1.92 - 3.28%; FDC = III, wind speed is 56 m/s.

It results from Equation (1) that if all other things being equal, in agroforestal landscapes with I class state shelterbelt planting, the area of steppe fires increases, on average, by 1.22 ha / hour; and if forest belts of IIIII classes are available - from 1.40 to 1.56 hectares / hour, respectively.

This fire behavior pattern can be commented on as follows. Wildfires are localized within the shelterbelt plantings of I life state class. This is due to the fact that there is 102

practically no wood fuel in the form of deadwood and dead trees in such forest belts. The stand canopy of closed healthy plantations transmits little light to the soil, what prevents the penetration of additional combustible material into the forest belts: the steppe grassy vegetation which is dry by mid-summer. Earlier, we noted that such plantings effectively restrain the wind flow (DUBENOK et al. 2017), what also prevents the spreading of fire in the forest belts themselves. After a landscape wildfire, the forest stand is vital, without signs of significant pyrogenic damage that makes it possible to assess the forest belts as poorly damaged.

Forest belts of II state class do not significantly affect the speed of the wind flow, what we mentioned earlier in our publication (DUBENOK et al. 2017), and the amount of combustible material compared to plantations of I state class is higher here: there are dry tree vegetation and low-productive live ground cover from steppe grasses, and also litter fall.

It marked the transit of wildfire through robin forest belts here. There are more than 10% of living trees after pyrogenic damage here; living ground cover is burnt almost completely.

This allows evaluating these stands as moderately damaged.

Slagging in forest belts of III state class with dry and weak trees and a burning temperature of about 708 °С, active overgrowth of the undergrowth by rhizomatous and root-weeping weeds, severe wind permeability of such plantations which we described earlier (DUBENOK et al. 2017) contribute to an increase in the spread rate of wildfires in agroforestal landscapes. A surface fire quickly passes through such plantings to agricultural lands adjacent to them from the leeward side: fields with crop residues and inarable lands with steppe grass vegetation. There are less than 10% of living trees in these plantations after fires; live ground cover burns out. Such forest belts were rated by us as severely damaged.

The dependence presented above is consistent with the general features of fires in agroforestal landscapes of the Volgograd Region and some other regions of Russia described

by KIRILLOV and EGOROVA (2012). This indicates the correctness of the mathematical model proposed by us that describes the fire behavior in arid agroforestal landscapes in multifactorial fashion. The above equation (1) theoretically justifies the feasibility of reconstructing pure compositions in shelterbelt planting of the class II and higher in order to reduce fire danger in agroforestal landscapes with arid climate. In addition, the model can be used to predict the development of this type of fire, which will help in a timely manner to evacuate the population and make rational use of the forces and means to extinguish and localize wildfires.

Earlier, in pyrology such regression dependence by the area calculation was not used, but only a set of equations by Amosov were used (SIDARENKO 2014) describing the fire propagation speed (m / min) along the front (Vfr), the wings (V w) and rear (V rear) in a forest conditions: V fr  a 0  (a 1  a 2 y ) x  a 3 y (2)

V V

 0.35 V fr  0,17 rear  0.10 V fr  0.20

(3) (4)

w

Where a0, a1, a2, and a3 are constant coefficients established for certain types of forests; y is the moisture content of combustible material, %; x - wind speed, m/s.

The main disadvantage of these equations is the impossibility of their application in agroforestal landscapes characterized by intersection of open territory (agricultural fields) with biophysical boundaries, namely the narrow shelterbelt planting which, as shown earlier, significantly affects wind speed in inter-belt fields. At the same time, the moisture content of the combustible material (mainly aboveground phytomass of trees) applied in formula (2), is related to the life state of plants and is taken into account in formula (1) (DUBENOK et al. 2017).

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The following indicators necessary for an objective assessment of the damage caused by wildfires to arid agroforestal landscapes can be proposed: the extent of damage to forest belts that we have previously proposed (low, medium, severe); wood stock of dead trees; burnt aboveground phytomass; the amount of pollutant emissions into the atmosphere. The total application of these parameters in economic calculations will allow us to take into account both direct economic losses from wood loss and indirect environmental losses associated with the burning of phytomass and release of toxic substances into the atmosphere, as indicated by the work of other authors (ERISOV et al. 2016; SIDARENKO 2014; PONOMAREV et al. 2015; GROOT et al. 2015). An example of the corresponding calculation is presented in table 1.

Tab. 1 An example of the calculation of damage caused by wildfires in arid agroforestal landscapes.

The degree of damage to forest belts by landscape fires Low Medium Severe

Timber stock of dead trees, m3/ha Small-size Fuel wood workable wood 4.05 1.71 15.75 6.65 40.95 17.29

Burnt ground phytomass, t/ha

The amount of emissions of pollutants into the atmosphere, t/ha

1.4 5.3 11.0

0.225 0.853 1,771

As a rule, small-size workable wood accounts for 70% of the stock, and fuel wood takes 30%. Taking into account the charge rates, US$ 9.47 / m3 and US$ 5.11 / m3, respectively, the data in Table 1, it was possible to calculate that, under arid conditions, the damage from landscape wildfires for one hectare of poorly damaged shelterbelt planting will amount to US$ 72.06. With average and severe damage to forest belts by fire, the damage from wood loss is estimated at US$ 280.23 / ha and US$ 728.59 / ha, respectively.

The most significant is the damage from the reduction of the environment-forming functions of shelterbelt plantings. So, in the case of severe damage by a landscape fire to one afforestation belt hectare, the amount of this damage can reach US$ 1,457.18. Accordingly, with a moderate degree of damage, this figure will reach US$ 560.46 / ha, and no more than US$ 144.12 / ha for a low one.

Taking into account the amount of pollutants released into the atmosphere when 1 ton of aboveground phytomass is burnt (Table 1), the rates for emission charges (carbon dioxide - 0.02 US$/ton; hydrocarbons - 0.16 US$/ton; nitrogen oxides, suspended particles – 1.42 US$/t), and the coefficient which takes into account the environmental situation ratio for Russian North Caucasus (1.6), we were able to establish that the damage caused by emissions from the forest belts to the atmospheric air is estimated from US$ 3.34 / ha (low damage by fires) up to US$ 24.98 / ha (forest belts heavily damaged by fire). One hectare of shelterbelt planting moderately damaged by fire causes environmental damage in the amount of no more than US$ 12.22.

With a high degree of damage to the forest shelter belts, the total damage from fires may exceed US$ 2,210 / ha. This amount correlates with the cost of a complete reconstruction of such fire-damaged forest plantations in the Rostov region. With a low degree of damage to forest belts by fire, the total damage is less significant and is no more than US$ 220 / ha, what correlates with the cost of environmental harvesting.

The features of wildfires in agroforestal landscapes, as well as the results of fire damage assessment described in this paper, allow us to recommend the Don Fire Protection System (DONOZ) originally developed in Don State Agrarian University for fire monitoring, prediction, preparedness, prevention and control purposes on agricultural lands in the arid climate conditions (SHILER, SIDARENKO 2001).

The fire prevention system "DonOZ" includes: 104

-

Early detection of fires during the fire hazardous period by using ground patrols, aviation and space monitoring measures; - Use the irrigation network, and irrigation and drainage equipment located on agricultural lands when fire extinguishing; - Organization of temporary spills of small rivers or streams on fire hazardous areas with the help of taphoons.

The advantage of the DonOZ system recommended is the possibility of using sprinklers, irrigation pipelines, and mobile pumping stations for fire-fighting purposes of domestic and foreign manufacture. According to the developers, the use of this set of measures capable of providing the systematic moistening of land with a norm of 30–50 m3/ha during fire-hazardous periods, makes it possible to create powerful fire barriers around important economic facilities and settlements.

Thus, we can say that fire development processes on agroforestal landscapes are unique. In addition to climatic conditions, they depend on a number of parameters inherent only in these areas: the technology of creation and width of forest belts, their species composition, life state, taxation indicators, phytoproductiveness of stand and ground living cover, structure and protective forest cover of agricultural lands, as well as agricultural background of adjacent farmlands.

This allows us to justify the new scientific direction at the junction of agroforestry and pyrology: agroforestry pyrology. The object of research in this case will be agroforestal landscapes exposed to wildfires. The main objectives of the research are the study of the patterns of fire occurrence and behavior, and their economic impacts on the forest-meliorated lands of arid regions of the world. The practical result of research within the framework of our proposed research area may be the development of fire-safe technologies for protective afforestation in regions of the world with an arid climate.

CONCLUSION The paper substantiates a new scientific direction: agroforestry pyrology, which studies the nature of fires in conditions of agroforestal landscapes, assesses damage caused by fire, and also develops technologies for fire-safe protective afforestation in regions of the world with arid climate.

The mathematical dependence of the wildfire area in agroforestal landscapes on its duration and the state class of the afforestation belts is obtained. It can be used to predict the fire development on agricultural lands in arid regions of the world with the aim of rational use of fire-fighting forces and means, making decisions about evacuation of the population.

It was established that the damage from the timber loss by forest belts accounted for 33%, and the losses from environmental damage and reduction in environmental protection functions accounted for 67% of the total losses caused by wildfire to agroforestal landscapes.

The world community has been recommended to use the Russian “Don Fire Protection” system for the prevention and suppression of wildfires in agroforestal landscapes under conditions of climate aridization. It is low-cost and at the same time effective in use, as it is built on application of irrigation and drainage equipment available on farmlands for fire-fighting purposes.

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AUTHORS ADDRESS Vadim Viktorovich Tanyukevich Doctor of Science in Agriculture, Professor https://orcid.org/0000-0003-4427-8357 Anastasia Vladimirovna Kulik Candidate of Science in Agriculture Federal State Budgetary Scientific Institution Federal Research Center for Agroecology of RAS 400062, 97, Universitetsky av.

Volgograd Russia

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Olga Ivanovna Domanina Graduate student Sergey Vladimirovich Tyurin Graduate student Alexander Alexandrovich Kvasha Graduate student Federal State Budgetary Educational Institution of Higher Education Don State Agrarian University 346493, settl. Persianovsky October district Rostov region Russia

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 109−119, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.11

CHARRING LAYER ON A CROSS-LAMINATED TIMBER PANEL CONSTRUCTION Katarína DúbravskáDominik Špilák - Ľudmila Tereňová – Jaroslava Štefková ABSTRACT When the wood is thermally loaded, the microscopic changes of wood structure and macroscopic changes appear and are examined. The macroscopic changes include formation of char layer on the surface of the wood-based material. The main aim of the medium-scale test is to assess the char layer formation on the surface of the sample under thermal loading.

The test sample was made of CLT (cross-laminated timber) panel with no surface treatment with the dimensions of 1000 × 1500 × 80 mm. It was a 3-layer panel made of spruce lamellas.

The test sample underwent a medium-scale test during which it was exposed to a radiation panel for 40 minutes. Intensity of the radiation panel was 43.1 kW·m2. During the test, the temperature on the exposed side of the test sample was recorded by a thermocouple. The test sample immediately began to degrade and char. After complete charring of the CLT panel layer on the exposed side, its rupture and consequent falling off appeared. The middle layer of the CLT panel was minimal, only in the area where the outer layer fell off. The results of the medium-scale test were compared to the results of the simulation which were achieved from the Ansys 18.1 program. When the medium-scale test and simulation results were compared, some differences were found. The main difference was found when the char layer fell off from the CLT panel and further charring into the depth of the sample followed in the medium-scale test.

Keywords: cross-laminated timber panel, char layer, medium-scale test, Ansys 18.1 program simulation.

INTRODUCTION Cross-laminated timber panel (CLT panel) is considered a large-area material. As stated by ÖSTMAN et al. (2018), this material is classified into D-s2,d0 or Dfl-sl reaction to fire class depending on thickness and density. It is then a combustible material which burns on the surface, releases heat and as so it develops fire and forms smoke according to FRANGI et al. (2009). They also state that CLT panel performance under a thermal load is characterized by fire performance of the individual layers. The significant changes can be observed on its surface by KUČEROVÁ et al. (2009). By OSVALD (2015), a significant macroscopic change, which can be observed, is formation of a char layer which is formed on the surface during a thermal load of the wood by OSVALD (2011), LEŠKO and LOPUŠNIAK (2015), KUKLÍK (2005). This process (KAČÍKOVÁ et al. 2006) starts temperatures higher than 250°C. The char layer form cracked black layer, which has worse thermal conductivity and 109

slows down the transfer of heat into deeper layers (PAULĎURO and KAČÍKOVÁ 2014). The fact that the char layer functions as an insulation layer and slows down degradation of the remaining cross-section material is also stated by FONSECA and BARREIRA (2009).

As stated by ÖSTMAN et al. (2018), charring of the CLT panel can be different from the charring of the homogenous wood panel due to the method of gluing the individual layers together and due to bonding between the wood layers (local increased charring). The charring of the CLT panel is not influenced by orientation of the layers, in particular parallelly or perpendicularly to the whole panel orientation (FRAGIACOMO et al. 2013).

When a CLT panel is thermally loaded, two situations can appear (FRANGI et al.

2008): - Char layer does not disaffiliate. If the exposed layer of the CLT panel is charred in the whole depth and remains at the place, it works as heat insulation of the remaining layers of the CLT panel.

- Char layer disaffiliates. If the char layer of the exposed side of the CLT panel disaffiliates, it does not protect the remaining layers against the effects of the fire and charring of the internal layers takes place. The process of charring progresses faster as a result of a higher temperature of the flame. This process is similar to increased charring which can be observed at the protected wood surfaces after disaffiliation of fire cladding.

The effect of the kind of adhesive bonding the individual layers of a CLT panel was dealt by MENIS (2012), FRIQUIN et al. (2010), KLIPPEL et al. (2014). If the individual layers of CLT panel are bonded by PUR adhesive, the falling off of the char layer occurs rather often. This was also observed by KLIPPEL et al. (2014) and MENIS (2012).

Disaffiliation of the char layer (FRANGI et al. 2009) is influenced by the position of the panel (vertical or horizontal), thickness of individual layers, and adhesive performance at elevated temperatures.

The aim of the paper is evaluation of the CLT panel under thermal load and evaluation of the char layer formed at the construction made of CLT panel. At the same time, the results achieved by the medium-scale test shall be compared to the results of the Ansys 18.1 program simulation.

EXPERIMENTAL Methodology of a medium-scale test The test sample was made of cross-laminated timber with no surface finish. It was a threelayer panel whose individual layers were made of spruce wood with the moisture content up to 12% (± 2%). The panel´s dimensions were 1000 × 1500 × 80 mm. The thickness of outer layers was 20 mm and the middle layer was 40 mm thick. The weight was defined as 5,0 kN·m3 according to DIN 1055-1:2002 for static calculations. The density of the sample was approximately 470 kg·m3. The manufacturer states the material is classified as D-s2,d0 class of Reaction to fire by the Decision of the European Commission 2003/43/ES. The sample was loaded by a radiation panel for 40 minutes. The sample was placed in distance of 200 mm from the radiation panel. This distance equals the radiation intensity of 43,11 kW·m2 for the radiation panel in the size of 480 × 280 mm. The energy supply for the ceramic radiation panel was propane -butane gas of a constant flow.

The macroscopic change, particularly, formation of the char layer on the surface, was observed during the medium-scale test.

Methodology of the simulation To observe the CLT panel behaviour under thermal load, the finite element computational 110

method of Ansys 18.1 was used. The simulation was set for the change of material properties according to STN EN 1995-1-5 (2008), while different properties of wood along the fibre and across the fibre were taken into the consideration. The mechanical loading consisted of only the own eight of the panel. Thermal loading consisted of two sources – the radiation heat whose source was the radiation panel and a flame which appeared after the ignition temperature was reached of the spruce wood. The output of the radiation panel was set for 43.1 kW·m2. Due to the fact the room was closed, only the natural air flow caused by the different temperature of heated gases and the surroundings appeared. The heat transfer between the wooden beam and the air changed depending on the temperature. The aim of the computer simulation was to simulate the conditions of medium-scale test and compare the results gained from test with the results of the computational simulation.

Geometry and discretization The simulation consisted of the dynamic thermal analysis using Ansys 18:1 program. During the simulation, the following element types available in the program – SOLID90, SURF152, TARGET170, CONTA174 were used. SOLID90 and SURF152 are thermal elements serving for simulation of heat transfer, where SOLID90 is a 10-node thermal element simulating heat transfer into the depth of the material, while SURF152 is a four-node thermal element simulating conduction, convection and radiation on the surface (ANSYS Inc 2013).

The nodes of SURF152 must share the nodes of the underlying solid element i.e SOLID90.

TARGET170 and CONTA174 are elements simulating heat transfer between individual layers of CLT panel (between wood and PUR adhesive) (ANSYS Inc 2013).

The beam model was projected by Ansys 18.1 program via the tetrahedron pattern network enabling higher number of elements maintaining the same number of nodes. To save computational efforts and bigger refinement of the final network of finite elements, the function of symmetry split in the program and the symmetrical shape of the panel was used to divide the CLT panel vertically in half as well as the radiation panel force in half. The total number of nodes was 555,839 and the total number of elements was 618,482 (Fig. 1).

The given number of nodes and elements provides a very fine network and higher accuracy of the simulation results.

Fig. 1 The network of finite elements.

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RESULTS AND DISCUSSION CLT panel behavior in medium-scale tests The test sample surface started to thermally degrade right from the start of the test. By ZACHAR et al. (2017), the combustion process and typical behavior of materials during thermal degradation is determined by initiation energy which is necessary for the material to ignite. The thermal degradation was accompanied by the color change of the surface and by production of the smoke. The surface area gradually grew (Fig. 2) and its color changed from brown to black. The flames on the surface appeared approximately in the 7th minute (Fig. 3).

As stated by VAVRUŠKOVÁ and LOKAJ (2009), the wooden objects exposed to fire and temperature of about 300°C flame up on the surface and burn quite intensely at the beginning. The vigorous flame combustion lasted for about three minutes, then its intensity decreased gradually. In the 12th minute, it showed as a non-flaming combustion. As stated

by OSVALD and GAFF (2017), combustion is typical in two phases for most combustible materials - the first stage typical by flaming combustion of gaseous products and the second stage represented by non-flaming combustion of the residues of the materials rich in carbon.

Fig. 2 The test sample at the beginning of the medium-scale test.

Fig. 3 The test sample in the seventh minute.

When observing the macroscopics changes at progressing stages of thermal degradation of wood under elevated temperatures in longer time it is possible to observe only the formation of the char layer (OSVALD 2015).

As mentioned earlier (FRANGI et al. 2008), behavior of CLT panel in conditions of fire is characterized by the behavior of individual layers of the CLT panel. The process of 112

charring of the first layer of the CLT panel and the rate of charring is similar to the behavior of massive timber sample, taking in account the local increased charring at bonding of the layers. This fact is also confirmed by FRANGI et al. (2008), the depth of charring of the CLT panel is identical as for the homogenous timber until the first layer is completely charred. As MARTINKA et al. (2016) state, charred layer on the test sample surface slows down heating of non-degraded surface which results in decreasing the thermal degradation rate, gaseous products release rate, and heat release rate. The char layer works as an insulation layer. VAVRUŠKOVÁ and LOKAJ (2009), BLASS (1995) mention that thermal conductivity is approximately one sixth of the thermal conductivity of non-degraded wood.

It also slows down the further thermal degradation of remaining wood.

As mentioned earlier, in case of charring of a complete layer on the loaded side, two situations can occur: the char layer protects the residual cross-section against heat or the char layer can fall off. During thermal loading of the sample, the second situation appeared. The charred layer fell off in 37th minute. In this time the outer layer of the CLT sample was completely charred in the whole thickness at some places. We suppose the fall-off of this layer was caused by two effects – the pressure between the layers of the CLT panel and structure of the char layer. Approximately after 23rd minute, the temperature between the inner layer of the CLT panel and the outer layer on the exposed side ranged over 100°C. In the temperature span between 20°C and 150°C dehydration of wood starts, according to KAČÍKOVEJ et al. (2011), when wood loses water starting with free water and ending with bound water. A part of this water is cumulated between the individual layers of a CLT panel, therefore the pressure is formed at the mentioned contact. At the same time, heating of the PUR adhesive film releases and cumulates volatile products.

Charring of the inner layer started after fall-off of the outer layer of the panel. Fig. 5 shows charring of the inner layer especially at the places where outer layer has fallen off.

The authors KLIPPEL et al. (2014) state that charring rate of the next layer of a CLT panel is twice as fast.

ZOUFAL et al. (2009) define the depth of charring as the distance between the outer surface of the intact timber and the position of the charring line. At the place where the falloff of the first layer appeared, the depth of charring was 28 mm (maximal value). At the places where the char insulation did not protect the remaining wood, the thermal degradation of the inner layer occurred.

Simulation results Simulation result is illustration of charring ratio of CLT panel in 40 minute time span. Figure 6 shows a detail of the left half of the simulated panel without the char layer which has been removed. The color fields divide the CLT panel into the following layers: green color shows the char layer and border of charring, dark blue and dark green color depict the pyrolysis layer and light blue shows intact wood.

Maximal depth of the char layer in direction of the xaxis in the area of radiation panel achieved 15 mm, on the upper edge of CLT panel it achieved 19 mm. The program determined the average depth only on the bases of the thermally loaded area of the CLT panel after 40 minutes of thermal loading. The value of the average depth of charring was 9 mm. Based on the data on charring depth, the conclusion that charring of wood appeared only on the exposed layer of the CLT panel was reached, i.e. the first layer of the CLT panel exposed to thermal loading charred. The maximal depth of the pyrolysis in the direction of the x axis achieved 35 mm, on the upper edge it achieved 41mm (Fig.7).

According to the computer simulation, the flames appeared in 9th minute (Fig.8), having achieved the ignition temperature of spruce wood. The flame spread by linearvelocity across the surface until it reached the upper edge of the panel. Maximal measured

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temperature on the surface on the exposed panel was 648°C. On the non-exposed side of the panel, the temperature did not increase.

Fig. 2 Char layer fall-off during the medium-scale test.

Fig. 3 Cross-section of the sample after the medium-scale test.

Fig. 4 Charring after 40 minutes.

Fig. 5Pyrolysis layer.

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800 700

Temperature

600 500 400 300 200 100 0 80 160 240 320 400 480 560 640 720 800 880 960 1 040 1 120 1 200 1 280 1 360 1 440 1 520 1 600 1 680 1 760 1 840 1 920 2 000 2 080 2 160 2 240 2 320 2 400

0

Time Maximum top slab temperature (medium-scale test) Maximum connection middle - top slab temperature (simulation) Maximum connection bottom - middle slab temperature (simulation) Maximum bottom slab temperature (simulation) Maximum top slab temperature (simulation)

Fig. 6 Thermal load.

The area of non-degraded wood in the cross-section has a significant impact on the value of its fire resistance since the wood under thermal degradation loses its mechanical and thermal insulation properties.

Evaluation of the char layer and the charring rate was also dealt by MENIS (2012). This author points out the fact that if the individual layers of the CLT panel are glued by PUR adhesive when exposed to fire effects the fall-off the char layer does occur. This phenomenon was observed on the samples when there was used five different PUR adhesives. MENIS (2012) also explains that fall-off the char layer did not appear when the bond between two layers was provided by MUF adhesive.

CLT panel performance in fire was also investigated by FRANGI et al. (2009). A small horizontal furnace was used to perform a fire test. The test was conducted the samples where different adhesives were used. The charring rate for the sample with MUF adhesive was constant. After charring of the first layer of the CLT panel, it did not fall off and protected the remaining wood against elevated temperatures.

During the test samples with PUR adhesive, the charring rate was not constant. Once the first layer has charred, it fell off. This fact led towards an increase in charring rate compared with charring of a homogenous wooden panel. Three other test samples in thicknesses of 60 mm which had a 20 mm thick layer on the exposed side were evaluated.

The 28 mm thick charring occurred at 41st minute, 42nd minute and 44th minute.

FRIQUIN et al. (2010) dealt with the charring rate and charring depth of a CLT panel.

They investigated the dependence on the fire scenario which affected the samples. The CLT panel was exposed to thermal loading equaling to Standard curve, Parametric curve and a Swedish curve of fire. At the same time, the changes in charring depending on the fire stage were observed. The char depth and charring rate were interpreted graphically. The results regarding charring are as follows FRIQUIN et al. (2010):

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- When the test samples were exposed to thermal loading corresponding to the parametric fire curve, 20 mm char depth in case of 120thick test sample (the first layer thickness 19.5 mm) appeared in the 22nd minute. 20 mm charring depth in case of 240 mm thick test sample appeared in 29thminute.

- When the test samples were exposed to thermal loading corresponding to the standard fire curve, 20 mm char depth in case of 180 mm thick test sample (32 mm thickness of the first layer) appeared in approximately in 43rd minute. 20 mm charring depth in case of 240 mm thick test sample (31.5 mm thickness of the first layer) appeared in 45th minute.

- When the test samples were exposed to thermal loading corresponding to Swedish curve, 10 mm char depth in case of 240 mm thick test sample (29.5 mm thickness of the first layer) appeared in approximately in 20th minute.

The test samples exposed to thermal loading by a standard fire curve were tested for 150 minutes and longer. In that case, the charring depth of 28 mm appeared approximately in 48th minute on the 240 mm thick sample. In case of a parametric fire, charring was recorded approximately before 30th minute FRIQUIN et al. (2010): In case of Swedish fire curve, the recorded char depth appeared approximately before 20th minute FRIQUIN et al.

(2010).

The fire performance of CLT panel was also dealt by KLIPPEL and FRANGI (2016).

They summarised the other authors´results which focused on the influence of the adhesive on falling off the charred layer. There, CLT panel behavior in a fire was compared subjected to the use of PUR, MUF and PRF adhesive to glue individual layers. Based on the conducted research they came to the conclusion that in case of PUR adhesive use falling off the charred layer occurs in most tests. While, when MUF or PRF adhesive is used, the charred layer does not fall off.

CONSLUSIONS On a CLT panel surface, a char layer is formed when it is thermally loaded in the same manner as on all wood-based materials. The process of charring depends on the fire behavior of individual layers of the CLT panel.

The results of the medium-scale test and the simulation by Ansys 18.1 program can be resumed into the following points:  Maximal temperature on the exposed side of the panel in the medium-scale test was 711°C, maximal temperature on the exposed side of the panel in the simulation was 648°C.  The flame on the surface of the sample appeared in 7th minute in the mediumscale test, the flame on the surface of the panel appeared in the 9th minute,  In simulation, the formation of a char layer on the edge of the test sample was predicted. Due to the thermal degradation at this place, rounding appeared. In case of medium-sale test, there was no charring on the edge, so there was no rounding on the edge.  In simulation, the charring of the first layer of the CLT panel was incomplete, therefore, it did not fall off. Even if the complete charring did appear, it is uncertain if the program would consider its falling off. The reason is that the kind of adhesive does not have such a significant impact in the simulation.  In the medium-scale test, a complete charring of the first layer appeared. In the place where the charred mass fell off, the charring of the inner layer appeared.

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As can be noticed, the simulation results and the medium-scale results are partially different. In case of the medium-scale test, the char layer was formed especially in the place radiation panel exposure. In simulation, the char layer was formed in the center (the place of radiation panel exposure) up to the edge of the test sample.

Ansys 18.1 program does not allow us to imitate the wood structure in detail including its defects. This fact might be the reason of different temperature development recorded on the exposed side. Meanwhile, in this type of simulation, it is not possible to imitate the falloff of the char layer, which appeared in the medium-scale test. This phenomenon bears a significant impact. If the char layer does not fall off, it protects by insulation the remaining wood mass and thermal degradation progresses more slowly. If the char layer falls off, the charring of the inner layer occurs. The charring rate proceeds twice as fast at the beginning.

The increased charring rate was also mentioned by FRANGI et al. 2008 as the consequence of pre-heating of the timber in the layer.

The differences in the results are caused by the temperature of charring. It is necessary to put in the temperature of charring in Ansys 18.1 program. The temperature of charring was determined as 300°C according to STN 1995-1-2 (2008). However, KAČÍKOVÁ et al.

(2001) state that charring of wood can appear at as low as 250°C.In the medium-scale test, the temperature of charring lower than 300°C imposed the differences in the depth of charring. The simulation program generates the simulation according to the input temperature of charring. The standard states the temperature of charring as 300°C for wood, in general; however, the individual species might have different temperatures of charring, which was not considered by the program. The charring temperature by the wood species has been specified only if in particular studies and as so it is not included in the standard.

The amendment of the standard for the temperature of charring by wood species would need to be considered as it would produce the more accurate results in further investigation.

The main contribution of the research is the finding that the results of medium-scale tests of wooden construction members and the results achieved by the computational simulation are different, yet only to a certain extent. Medium-scale testing is, therefore, more suitable to state real fire behavior parameters for construction members and computational simulation is suitable for designing and dimensioning construction members and for predicting the behavior under thermal loading.

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ZOUFAL, R., BAUMA, M., KARPAŠ, J., 2009. Hodnoty požárni odolnosti stavebních konštrukcí podle Eurokódů. Praha : PAVUS, a.s., 2009. 126 s. ISBN 978-80-904481-0-0.

ACKNOWLEDGEMENT This work was supported by the Slovak Research and Development Agency under the contract No. APVV-17-0005(70 %) and by the Cultural and Educational Grant Agenca of the Ministry of Education, Science, Research and Sport of the Slovak Republic on the basis of the project No. KEGA 009TUZV-4/2017 (30 %).

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AUTHORS´ ADDRESSES Ing. Katarína Dúbravská, PhD. Ing. Dominik Špilák Ing. Ľudmila Tereňová, PhD. Technical University in Zvolen Faculty of Wood Sciences and Technology Department of Fire Protection T. G. Masaryka 24 960 01 Zvolen Slovakia katarina.dubravska@tuzvo.sk xspilakd@is.tuzvo.sk ludmila.terenova@tuzvo.sk Mgr. Jaroslava Štefková, PhD. Technical University in Zvolen Institute of Foreign Languages 960 01 Zvolen Slovakia jaroslava.stefkova@tuzvo.sk

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 121−135, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.12

PERCEPTION OF WOODEN HOUSES IN THE SLOVAK REPUBLIC Mária Moresová – Mariana Sedliačiková – Jozef Štefko – Dana Benčiková ABSTRACT Trends in construction industry lead to using natural renewable materials; that is why the interest in wood as a material in the construction field has greatly increased (globally) in the past decades. The main objective of the paper is to define the perception of wooden houses in the changing customer behavior over the time. Moreover, the key factors and economic and social aspects, in the context of tradition, competitiveness, and green economy affecting the way of establishing the houses and entrenching the market are identified. Future perspectives of the wooden house development in a selected region in the Slovak Republic are influenced this way as well. Empirical research was conducted in a form of a questionnaire, and surveyed the given issue in the Žilina region. The results enabled identification of the main economic and social aspects affecting the perceptions of wooden houses in the contemporary society. The age, income, historical events in the given region and the promotion of wooden houses in the market are the main reasons which influence the perception of wooden houses in the Žilina region. In conclusion, specific measures were proposed. Their implementation into business practice will help eliminate the bias with regard to wooden houses as perceived by non-professional and professional public, and thus, help wooden houses to establish faster and more effectively in the Žilina region. The results proved that so-called myths about wooden houses should be removed, and thus, the awareness of the issue among both non-professional and professional public must increase.

The best way to achieve this aim is to implement effective marketing to attract consumers.

Key words: wooden houses, silicate houses, economic and social aspects, green economy.

INTRODUCTION In the history of mankind, people have always attempted to build a shelter to live in, which would comply with the basic needs with regard to their survival. WILE (1920) highlights the fact that living cannot only be considered a form of retreat or shelter from the outside weather influence, but the house itself should be evaluated as a space for family life.

At present, there are tendencies that make us overlook this aspect of living. Authors WOOLLEY et al. (2006), ALMUSAED et al. (2015) and KLEMENTOVA et al. (2016) agree that conditions of living are mostly affected by family income, both in towns and in the countryside. The climate change has made the building contractors and construction workers search such solutions which serve people and their comfort, and at the same time reduce the influence on the environment (ALMUSAED et al. 2015). One of the materials which appears suitable in this regard is wood. Last years have brought in extensive discussions (ADAMUČŠIN 2012; FÁBRI 2016) about the role of wood in construction in Slovakia. Wood 121

as a construction material holds an irreplaceable position in the industry, due to a complex of mechanical, thermal, esthetic, utility and technological qualities, as well as due to its effect on the environment. In European countries, wood is considered to be a strategic, while at the same time renewable, raw material, which is highly profitable for national economies.

Authors COOPER (2006), JANSEN (2014), and BROTO (2015) point out the worldwide development of numerous construction materials, systems, and technologies that relate to the sustainability problem. At the same time, innovative researches (KOLB 2011; RIVERS 2015; POTKÁNY et al. 2018) have been conducted while taking account of ecological characteristics of these materials, systems, and technologies. On the other hand, social and economic questions related to sustainability have been discussed insufficiently. It is essential to realize that requirements to be sustainable bring higher requirements for construction, includes not only the environmental, but also economic and social aspects, which greatly influence the society’s welfare. With regard to the above stated, the main objective of the paper is to define the position of wooden houses in the contemporary society; as well as to identify the key factors, and economic and social aspects in the context of traditions, competitiveness, and green economy, which have an impact on the way these houses establish and entrench in the market, and also influence the future perspectives of their development.

THEORETICAL BACKGROUND As noted by KOČNER et al. (2015) and BIKAR et al. (2018), sustainability is now an important issue for every country in the world. In order to maintain the ecological and economic balance of utilizing the natural resources, bio-economics (green economics) is beginning to grow in importance. As agreed by BROTO (2015), ALMUSAED et al. (2015) and MALA et al. (2018), the definition of sustainability is of a multi-dimensional character, within which such economic, environmental and social solutions should be elaborated that would ensure better understanding of this context. Majority of researches conducted with regard to sustainability have only focused on two dimensions: the economic, and the environmental one. WOOLLEY et al. (2006) have investigated buildings made from natural materials, and techniques of their construction; JONASSON et al. (2014) focused on comparing houses in passive standard, and on how they affect the environment; and ALMUSAED et al. (2015) looked into the ecological and energetic demands of construction materials. The social issues are permanently underestimated with regards to the discussed problem. In a specific example of construction technology, as claimed by DE LOTTO (2008), and AFSOON et al. (2016), it is not just the technology developed in response to the society’s demand, but it has a potential to define the future society. In each and every environment, culture and work relate to production, and reflect not only the strategy of local development, but also the characteristics, esthetic preferences, as well as climate, financial, cultural, historical, and other specifics of the given field.

An effort to improve human life and raise its quality has become an immanent part of human history. The idea of a rightful and happy life, which represents an essential part of the world history, religious and philosophical teachings, utopian and visionary doctrines, as well as the political requests for change of systems, is implicitly incorporated within them.

This can be seen in the development of wooden constructions (WOOLLEY et al. 2006, KOLB 2011, HONTUS 2015). The current wooden houses (THURZO 2004, KOLB 2011) which have gone through a long-term development, fulfill all the requirements for living, and at the same time minimize the effects on the environment. However, fulfillment of the living need, as one of the basic human needs, is generally greatly determined by the level of social and 122

economic development of the society. Within the conditions of market economy, the responsibility for acquiring one’s own living is mainly shifted towards the citizens themselves (WILE 1920, ADAMUŠČIN 2012, STURGILL et al. 2016), while the availability of living is thus directly proportional to the financial possibilities of individuals and households. Therefore, the construction is affected by numerous factors, e.g. social, economic, cultural, ethical, religious, etc. These factors significantly influence people’s preferences, which, naturally, reflects in the choice of construction material. With regard to the above stated, we may claim that the immediate satisfaction of the living need is rather differentiated in individual countries, and also in different regions within a country.

The basic requirement for contemporary family houses is mainly for them to possess an optimal layout. At the same time, the interest in high quality technical and esthetic solutions of the interior is rising, and so is the technical equipment of the house. What is brought forward is the question of thermal regulation, reducing the living (operational) costs, and saving the energies and water. More and more frequently, there are requirements regarding healthy environment, i.e. such environment that tends to prefer use of safe and harmless construction products and materials (RHEE 2018). Wood as a construction material (KOLB 2011) can fulfill all these requirements. Preference of construction materials depends on many factors. Besides environmental orientation of individuals, an important role is played by social, economic, climate or religious preferences. At the same time, as noted by KOLB (2011) and ZIMMER et al. (2017), the lack of trust towards wooden constructions at present is still rather high, and is affected by – sometimes untrue – myths, among which rank: higher probability of fire, low lifespan of the construction, more complex and complicated mortgage deal, worse heating conditions, woodworm, mold, and fungi susceptibility, etc.

According to KOLB (2011), silicate houses have a dominant position in Slovakia.

According to RIVERS (2015), among the advantages of silicate houses belong: no need for additional protection by conservation of materials, resistance against insects and mold, and, furthermore, the ability to protect against electric smog. Thanks to their long lifespan and economy, the investments into silicate houses guarantee their permanent value. However, on the other hand, ecological thinking is what currently becomes a very important issue for people (ALMUSAED et al. 2015, VILUMA 2017), while having an impact on the choice of material. Moreover, the requirements placed on construction in a form of norms, regulations, and standards, are constantly growing. In line with this, the state provides support to construction of wooden houses, which can significantly contribute to preferring them among others.

The choice of construction material, as pointed out by ADAMUŠČIN (2012) and AFSOON et al. (2016), does not only affect the current economic and social factors, but has an impact on everything we have lived through, and what we have learned from our ancestors.

According to DVOŘÁKOVÁ (2008), the main reason for restrictions, and later for almost complete replacement of wooden houses by other types, was the early regulations of Maria Theresa and Joseph II, known as “Fire Decrees”. Later, in 1950s, reinforced concrete (ferroconcrete) was used on a large scale. The changes in preferences of construction materials stopped concerning solely cities and towns, and started penetrating into the lives of Slovak villages. Gradually, radical social and economic changes in the process of rural conversion were occurring. As noted by THURZO (2004), in 1960s, an extensive fire engulfed wooden houses built mainly in the northern part of the Žilina region. This fact had a significant effect on the follow-up construction. Slowly, a radical social and economic change arrived, and the process of rural conversion was accelerated. Time-wise, this process connected with a more and more significant penetration of global technological development, which impacted all aspects of social life. The result was a complete 123

reconstruction of villages into their current look. Silicate houses became a symbol of higher living standard, and a higher quality of life.

Construction of a family house is a complex and demanding process (CRUZ NOIA 2015, ZIMMER et al. 2017). For many people, this is one of the most serious and most important decisions, which accompany them for the rest of their life. Construction of a family house must be planned and prepared. Before the actual construction, the future owner should be clear on the choice of the building procedure and methods, as well as the choice of materials and technologies used in construction. However, the construction may be performed in multiple ways, while the most economical one appears to be building the house on one’s own. This is suitable for those who do not have sufficient financial resources to build a house through a construction enterprise. This method is cheaper, however, it is more timedemanding. A silicate house, as claimed by RIVERS (2015), is the best solution for future owners if they build it themselves, and it is quite common in Slovakia. On the other hand, with wooden houses, this method is not recommended since the construction process is more complex and requires not only practice, but also certain professional knowledge (KOLB 2011, ZHAO et al. 2012). At the same time, the process of building a silicate construction by individuals themselves can be interrupted, or even stopped, at any time, due to lack of finance.

METHODOLOGY The methodology of the paper consisted of three phases. In the first phase, it was necessary to perform the analysis of Slovak, but mainly foreign, literature, while elaborating a summary of various authors’ views. In this phase, the following methods of scientific research were used: summary, synthesis of knowledge, and the methods of analogy and deduction. The second phase focused on the analysis of primary sources obtained via the empirical research, by the questioning method. The questionnaire aimed at finding out how well people living in the Žilina region are informed about wooden houses, as well as to identify the main determinants which represent barriers to wooden houses being established in the market. The questionnaire was hierarchized into four independent parts, as described below:  Part A – Demographics, and economic and social characteristics of inhabitants of ZSK.  Part B – Preferences with regard to building a family house.  Part C – Awareness of wooden houses among ZSK inhabitants.  Part D – Wooden houses vs silicate houses.

In the first part of the questionnaire research, it was necessary to identify the economic and social profile of respondents. Questions focused on finding out the gender of the respondents, their permanent residence, their current living situation and the location (town or village). We were interested in the respondents’ family status, age, education, number of children, current job, and their monthly income. Part B aimed to find out the respondents’ preferences as to building a family house. The questions asked about the type of house the respondents prefer, the construction material, the sources they used to finance (or will use to finance) the construction, and how much they are willing to invest in their own living. The third part of the questionnaire contained questions which aimed at finding out the awareness of ZSK inhabitants with regard to wooden houses. Questions were phrased to ask the following: if respondents consider wood to be a suitable construction material to build a family house, what type of wooden object they would choose to build, what they understand as a wooden house, if they currently own a wooden house (wooden construction), if they use this building for business purposes, and which sources they obtained the information related 124

to wooden houses from. In the last part of the questionnaire (D), the questions asked the respondents to compare the qualities of wooden and silicate houses. All questions used in the research were constructed as closed questions. Respondents were always offered a selection of answers, in order to achieve a higher validity of the collected information.

The questionnaire research was conducted between May 14 and October 4, 2018. The online questionnaire was distributed among 3,428 inhabitants of ZSK via the Internet. The reason why this particular number of ZSK inhabitants was addressed was to ensure the representativeness of the selected sample. In total, 728 filled in questionnaire returned, therefore the return rate was 21.24%.

In order to determine the representativeness of the selected sample, we used a statistical method most likely to be applied in economic and marketing surveys, while being referred to as one of the most exact methods. In order to obtain the correct calculation of sample representativeness, which is quoted below (RIMARČÍK 2007), it was necessary to substitute the right variables into the formula. The result of the relation is the “n” variable, which refers to the minimum necessary number of respondents. The variable “z” is the coefficient of reliability of a statement. If z = 1, then the minimum of 63% reliability of the research is proved. At the value of z = 2, the reliability is proved at 95.4%, and at z=3, the reliability of the research is 99.7%. The variables “p” and “q” are numbers of questioned respondents, expressed as a percentage, who are/are not familiar with the given problem; or who incline to one or the other alternative. Regarding the fact that the choice of respondents is purely random, and the extent of knowledge of respondents with regard to the problem is unknown, the whole sample is divided in half, in order for the product of values p and q to be the maximum, i.e. p and q = 50%. The value “Δ” is the maximum acceptable error. The goal of the research was to obtain a holistic view of the researched problem, therefore, the coefficient of reliability was determined to be at value 2, with the 95.4% reliability of a statement. The value of maximum acceptable error was determined at 5%. Based on the methodology of determining the size of the representative sample, according to formula (1), we may determine the minimum size of the sample of respondents: 𝑛≥

(𝑧 2 × 𝑝 × 𝑞)

(1)

∆2

After substituting the relevant values into the formula, we were able to calculate the size of the representative sample (minimum number for the sample): 𝑛≥

(𝑧 2 × 𝑝 × 𝑞) ∆2

→

𝑛≥

(22 × 05 × 0.5) 0.052

→

𝑛 ≥ 400

It is clear from the calculation that the sample must be formed by at least 400 respondents, inhabitants with permanent residence in ZSK. Since there were 728 research participants, the results of the research may be generalized to the whole basic sample; thus the research is representative.

Based on the available literary sources, four basic hypotheses were formulated as follows: H1: We assume that more than 60% of people living in the Žilina region prefer a silicate house to a wooden house.

Preference of construction material depends on many factors. Besides the ecological way of thinking of individuals, an important role should be seen in social, economic, as well as climatic, religious, or personal preferences. At the same time, as noted by KOLB (2011) and Zimmer et al. (2017), the distrust for wooden houses is currently still rather high, and it is highly influenced by – often untrue – myths. That is why, according to KOLB (2011), silicate houses have a dominant position in Slovakia.

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H2: We assume that the majority of people who have made a decision to build a wooden house in the Žilina region, and have built it, use it for business purposes in the field of accommodation and catering services.

As stated by Michalová (2010), the service sector has long been considered to be the fastest growing sector since 1990s. As wooden houses are a part of folklore architecture in the Žilina region, entrepreneurs in tourism attempt to attract customers by the region’s unique atmosphere, which is created by shepherd’s huts and chalets, or wooden houses built from solid wood.

H3: We assume that the main reason for preferring silicate houses to wooden houses in the Žilina region is building the house by individuals themselves.

The construction of a family house is a complex and demanding process. For many people, it is one of the most serious and most important decisions, which accompany them throughout their further lives. The construction of a family house must be well-planned and prepared. The most economical way to build a house is by people themselves. This is suitable for those builders who do not possess a sufficient amount of finances to build the house though a contractor (CRUZ NOIA 2015; ZIMMER et al. 2017).

When verifying the hypotheses, we used the statistical software Statistics10. In order to evaluate the stated hypotheses, the selected mathematic-statistical methods were used: binomial test, Friedman test, Wilcoxon test. In the third phase, such measures were proposed, the implementation of which into practice will help eliminate the bias with regard to wooden houses as perceived by non-professional and professional public, and thus help wooden houses to establish faster and more effectively in the Žilina region.

RESULTS AND DISCUSSION The results of a questionnaire survey, as well as verification of hypotheses focused on finding out the preferences of construction material to build a family house in the Žilina region, the awareness of the inhabitants of ZSK with regard to wooden houses and the identification of the main determinants representing barriers to the establishment of wooden houses in the market are presented in the following section.

The respondents who participated in our questionnaire survey consisted of 384 women (52.7%) and 344 men (47.3%), all from the Žilina region. The addressed respondents live primarily in rural areas/villages (396 or 54.4%), while 332 (45.6%) respondents live in a town/city. As to permanent residence of the respondents from the Žilina region, 25.5% live in Orava, 23.1% respondents in Liptov, 16.3% in Turiec, 18.4% in Kysuce, and 16.6% are from Horné Považie. The most populated representation as to age was by respondents between 3645 years of age (28.4%), followed by the group between 2635 (26.5%).

Respondents at 18 years of age and below did not participate in the research. The results are shown in Figure 1.

The largest group of respondents (according to their relationship status) is represented by married couples (49%), followed by single respondents (25.5%). Living (unmarried) spouses represent 12.6% of the addressed respondents, and 12.8% of respondents are divorced. Most respondents have two children (35.6%), or one child (26%). 15.5% of our respondents have three, and 11.4% have four or more children. 11.5% or respondents do not have any children. 45.6% live in a silicate house, while the second largest group is people living in an owned apartment (18.4%). Living in a wooden family house was claimed by 14.8% inhabitants of the Žilina region. 10.3% live in a rented apartment, and 7% in a small studio. The category “other” was chosen by 3.8% respondents.

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40% 20.70%

20% 10% 0%

28.40%

26.50%

30%

11.20%

9.50%

3.70% 19-25

26-35

36-45

46-55

56-65

over 66

Source: authors; based on the results of the questionnaire survey.

Fig. 1 Age of respondents.

With regard to the highest achieved level of education, the largest group is represented by those respondents who have obtained the bachelor’s (33.9%) and the master’s degree (25.7%). High school without the final certificate was achieved by 13.5% of the addressed, high school with the final certificate by 22.3%, and only 4.7% respondents have achieved the doctoral degree. Respondents with highest achieved elementary level of education did not participate in our survey.

As to the employee status, 39% of respondents are employed in private sector, 33.7% are sole traders. Public sphere employees are represented by 3.6% of ZSK inhabitants, and 4.9% are students. Entrepreneurs who have actively participated in our research are represented by 3.8%, retired people by 6.6%, and 8.4% of respondents are unemployed. We have further inquired about the monthly income, while 12% of the addressed respondents earn up to €400. The most populated group of respondents earn between €601800 (33.5%), and the income between €8011,000 is claimed by 20.2%) of respondents. The results are shown in Figure 2.

40%

33.50%

30% 20% 10% 0%

20.20%

19.90% 12%

8.70%

under 400 eur €401 – 600

€601 – 800

€801 – 1,000

€1,001 – 1,200

5.70% €1,201 and over

Source: authors; based on the results of the questionnaire survey.

Fig. 2 Monthly income of respondents.

In the next section of the questionnaire, attention was given to preferences of construction material when building a family house. This question relates to hypothesis H1: We assume that more than 60% of people living in the Žilina region prefer a silicate house to a wooden house. Respondents could choose from the following materials: silicate house, wooden construction, steel construction, and other. According to the questionnaire results, when building a family house, 70.6% of respondents would prefer to use silicates, i.e. would build a silicate house. On the other hand, only 22.8% would prefer to build a wooden house.

Validity of hypothesis H1 was tested through binomial test. The results have proved that

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hypothesis H1 can be confirmed, i.e. it stands that more that 60% of people living in the Žilina region prefer a silicate house to a wooden house (p-value = 0).

Due to highly developed tourism in the Žilina region, it was futher important to investigate if the respondents who own wooden constructions use them as a family house, or for business purposes in the accommodation and catering field. Of 728 respondents, 33.5% own a wooden construction, while it serves them in the above mentioned field. On the other hand, 14.8% claim to own a wooden construction while using it as a family house.

4.4% of respondents use their wooden construction for business purposes, however, in a different field than mentioned above (not catering or accommodation). Cottages and traditional cottages used for business purposes are owned by 63.4% of respondents, a wooden shepherd’s hut (known as ‘koliba’) by 18.5%, ranch by 8.7%, and an eco-house by 5.10% of respondents. The option “other” was indicated by 4.30% of our respondents. The presented results confirm the validity of hypothesis H2, i.e. it stands that the majority of people who have made a decision to build a wooden house in the Žilina region, and have built it, use it for business purposes in the field of accommodation and catering services (validated by binomial test, with p-value = 0.000).

In the third phase of our research, we tried to find out what respondents consider to be the main benefit of silicate houses when compared to wooden ones. The main benefit silicate houses provide to respondents is the possibility to build the house themselves (33.1%), and to conserve the construction (17.4%). While building a house on one’s own enables the builder (future owner) to save finances, conserving the construction (interrupting it temporarily) is mainly used in situations when the builders use their own finances and do not want to borrow money. Among other reasons that respondents view as benefiting them with regard to silicate houses are the fast construction process (17%), and lifespan (durability) of the house (12%). This question relates to hypothesis H3, which was tested by the Friedman test, followed by the Wilcoxon test. The result of the Friedman test has confirmed that the individual benefits of a silicate house are not of the same significance (pvalue = 0.00). By Wilcoxon test, we identified the rank of significance of the individual benefits. It can be stated that the main reason for preferring silicate houses to wooden houses in the Žilina region is building the house by individuals themselves (p-value = 0.000). Hypothesis H3 was confirmed.

In the following section, the paper presents the perception of respondents of selected qualities of wooden houses when compared to silicate houses.

The length of the construction process of a wooden house is viewed negatively by 51.3% respondents, in comparison with a silicate house. On the other hand, 39.9% view this quality positively with regard to wooden houses. The fact that a wooden house may be built on one’s own is viewed positively by 26% of respondents, while 62.2% view this quality negatively. These results were also confirmed by findings obtained in the previous question, where we inquired about the benefits of silicate houses. Resistance of the house against pests is viewed negatively by 66% of respondents, and positively by only 25.6%. Similar situation was observed with regard to resistance of wooden houses against weather conditions and natural disasters, where the negative view was presented by almost 50%, and positive one by only 27.6% of respondents (22.4% of respondents could not state their clear preferences).

Lifespan of the wooden house (its durability respectively), was viewed positively by 22.7% of respondents. Interestingly, when asked about fire safety, wooden houses are not trusted by as many as 61% of the addressed respondents. This belief may be affected by historical events, as 23.5% of respondents have stated that the majority of wooden houses that were built in the past were destroyed by the fire. When evaluating the safety of wooden houses with regard to breaking in, 52.7% of respondents could not clearly decide if this was a positive or a negative quality of the wooden house. The ability to secure a wooden house 128

against breaking in and against burglary is trusted by only 8.5% of the addressed people.

Changes in volume and shape of a wooden house due to temperature and humidity is perceived negatively by 53% of respondents. Among professional public, it is known that wooden houses have excellent acoustic qualities. When examining the opinions of respondents as to this feature, 39.6% of respondents provided a negative view, and only 20% view acoustics of wooden houses positively. From the obtained answers, it can be observed that non-professional public does not possess sufficient and/or relevant information about qualities of wooden houses. The obtained results correspond with the research of FÁBRI (2016). Similar to this, thermal-insulation qualities of wooden houses are viewed negatively by 40.2% of our respondents.

Among other examined factors belong financial demands to build a wooden house, trust for Slovak producers of wooden houses, operation costs, and the possibility to start the construction at any time of the year. With all the above factors, negative responses prevailed, which means that respondents perceive them in a more negative way with wooden houses than with silicate houses. The opposite trend was shown in factors such as natural and ecological material, simplicity of remodeling the house, house liquidation, size of utility space in relation to the built-up area, and the feeling of peace and well-being in the house.

These factors were perceived more positively with regard to wooden houses when compared to silicate houses. The most positively viewed factors regarding wooden houses were: natural and ecological material (70.6%), feeling of peace and well-being in the house (68.3%), house liquidation (63.8%), and the size of utility space in relation to the built-up area (44.2%).

Besides the preference of construction material itself, it was necessary to find out what knowledge (awareness, information) prevails among non-professional public in relation to wooden constructions. The awareness of wooden constructions among non-professionals is one of the key areas that should be given an increased attention. Wood as a construction material for a family house is considered to be suitable by 40.4% of respondents. 46.8% have stated that they do not consider wood to be suitable as a construction material for a family house. 12.8% of respondents could not state their clear preferences. As noted in Figure 3, the term wooden construction (wooden house) is most frequently understood by respondents as a traditional wooden cottage (32.9%), and as a timber house (31.3%). 20.7% of respondents perceive a wooden house as a construction the skeleton of which is built from wood (which happens to be the current definition of a wooden construction).

40%

32.90%

31.30%

30%

20.70%

20%

10.20%

10% 0%

traditional cottage

cottage

4.30% timber house

fake timber house

0.60% house with a wooden skeleton

other

Source: authors; based on the results of the questionnaire survey.

Fig. 3 What respondents understand under the term wooden construction.

From the results, it can be concluded that as many as 79.3% of respondents do not perceive the term wooden construction correctly (the correct answer is ‘house with a wooden skeleton’). It is this fact that should be viewed as one of the main barriers to the successful establishment of wooden houses in the Slovak market.

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The information that the respondents have about wooden houses was obtained mainly due to them owning a wooden construction (33.5%). Internet represented the source of information for 16.5% of respondents. 11.9% work in the wooden construction field, and 11.6% obtained the information from friends. The results prove that the awareness of wooden constructions among non-professional public is rather low.

40%

33.50%

30% 20% 10% 0%

11.60% 5.10% family

friends

16.50% 6.20% internet magazines and books

4.90%

6.90%

TV

school

11.90% 3.40% trade fair

I work with WH

I own a WH

Source: authors; based on the results of the questionnaire survey.

Fig. 4 Source of information of non-professional public about wooden houses (WH).

By summarizing the results of the questionnaire survey, following conclusions were formulated. The obtained results correspond with the research of KOLB (2011), who found out that wooden constructions in Slovakia have a minority representation among houses.

Similar to that, REGEC (2017) states that in Slovakia, it is approximately 1,000 wooden constructions that are built in the course of one year. Even 29.7% of ZSK inhabitants are considering to build a family house within the next three years. On the other hand, 25.1% of respondents prefer to live in a parental home. The sum that respondents are willing to invest into own living is mostly €50,001100,000 (36.30%), or €100,001150,000 (32%), followed by a group of respondents who are willing to spend maximum of €50,000. Own resources or financial help of relatives (parents, grandparents, etc.) are planned to be used for financing one’s living by 36.1% of respondents. Own resources and a mortgage would be used by 30.9% of respondents, and own resources solely would be used by 20.2%. The most preferred type of house is a bungalow (40.9%), one storey house with the attic usable for living (29.7%), and a two storey house (25.5%). With regard to construction material, when building a family house, 70.6% of respondents would prefer silicate construction, i.e. would build a silicate house. Wood as a construction material would be used by only 22.8% of the addressed respondents. At present, only 40.4% of respondents consider wood to be a suitable construction material for a family house. Wood is mostly used by inhabitants of the Žilina region to build an arbor (28.4%) or a porch (21.3%). This situation was pointed out by authors THURZO (2004) and DVOŘÁKOVÁ (2008) explaining the reasons for significant limitation of existence of wooden constructions in Slovakia by historical events, such as the development of town wooden constructions as a result of the inability to solve the problems of fire safety, and the follow-up Fire Decrees (issued by Maria Theresa and Joseph II), which restricted, or directly prohibited wooden constructions in towns. Since 1816, the ban on building adjacent farm buildings and fences was introduced. Next reason for the above described situation may be the state program named “Savings and replacement of wood in construction” introduced in the end of 1950s and beginning of 1960s, which enabled forcing out wooden houses not only from construction but also from education and research, this being within the concept of developing prefabricated concrete systems. Wooden houses gradually began to be replaced by silicate houses, while this trend has – in majority – lasted 130

until the present day. The above stated knowledge is also supported by the results of our survey. We further focused our attention on finding out the amount of information and awareness of respondents about wooden constructions. Wooden construction (wooden house) is most frequently understood by inhabitants of ZSK as a traditional wooden cottage (32.9%) or as a timber house (31.3%), while 20.7% of respondents perceive it as a house the skeleton of which has been built from wood (which is also the current definition of a wooden construction). As a whole, the obtained results from the research have shown that as many as 79.3% of respondents do not understand the term “wooden construction/ wooden house” correctly. This fact may be considered a key barrier to proper establishment and development of wooden constructions in ZSK. The information which the respondents possess about wooden houses was obtained mainly because they own a wooden construction (31.4%).

Similar findings were concluded by FÁBRI (2016) who claims that at present, wooden houses mainly address the young generation of people, i.e. those who are searching for healthy and good quality, while at the same time cost-effective, living. As to sizes and dimensions of family houses, people prefer to opt for an adequate proportion between simplicity, efficiency, and comfort. The type of houses in question mainly dominates in rural areas (villages), where traditional constructions are given new, modern look by the architects.

Recently, the most popular and sought type of family house is an uncomplicated house with an inclined roof, built in a low-energetic (passive) standard, with a simple archetypal form.

The last question of the survey focused on finding out how the respondents perceive the selected qualities of wooden houses in comparison with silicate houses. The main benefit of silicate houses is seen in the ability of future owners to build the house themselves (27.6%), and the possibility to conserve the construction (20.20%). While the former option helps the builder save finances, the latter is used by those who use their own financial resources to build the house and do not wish to borrow money. Overall, it can be concluded that the respondents perceive the majority of the characteristic determinants related to wooden houses in a more negative way than those of silicate houses. More than a half of respondents evaluated the following qualities of wooden houses as negative: length of the construction process, possibility to build the house on one’s own, resistance of wood (as a construction material) against pests, resistance of wood to weather conditions and natural disasters, lifespan of the construction, fire safety, volume and shape changes caused by temperature and size, and the financial demands of the construction. On the contrary, among the positives of wooden construction belong, according to respondents: natural and ecological character of wood as a construction material, easier liquidation of the house, the proportion of utility space to the built-up area, and the feeling of peace and well-being in the house. From the outcomes, it can be concluded that among non-professional, as well as professional, public, the so called myths related to wooden constructions still prevail. These cause a distorted picture of people as to the real qualities of wooden constructions. Author KOLB (2011) and RIVERS (2015) clearly state that wood has always been used as a construction material for building houses, and fulfills all the requirements for being considered the healthiest construction material. REGEC (2017) identifies with the obtained results, claiming that the reason why wooden constructions are not popular in Slovakia (when compared to e.g. Germany, Austria, etc.) is the insufficient professional preparedness of construction enterprises, and a very insignificant influence of the “good” examples of constructed wooden houses in Germany or Scandinavia. As the same time, the author notes that in Slovakia, promotion of benefits and limitations of wooden constructions in comparison with silicate houses is rather insufficient. Wooden constructions in Slovakia do not have a large impact on the image of people who have built it/had it built, nor they raise the owners’ social status, as it is in other EU countries. This is despite the fact that at present, great emphasis is given to ecology, the condition that wooden houses undoubtedly fulfill.

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Similar to the previous opinion, FÁBRI (2016) mentions several reasons for lower popularity of wooden constructions in our country, including: lack of financial resources of young families (which relate to low income and the inability to repay a long-term loan); the price of the construction site and utility systems and networks; the price of the wooden construction itself (mainly due to high prices of good quality construction material); insufficient support from the government; insufficient awareness of the public about the benefits and limitations of wooden constructions, etc. HAVLÍK (2013) points out that the current situation, i.e. low interest of Slovaks in wooden constructions is caused by almost no publicity, as well as by the existence of biases originating in the past. A wooden house is still perceived among people as living for the poor (FÁBRI, 2016). In the past, it was the low quality wooden constructions that contributed to the spreading and the long-term existence of biases in the society. The author also highlights wrong education in this regard, where the weakness of wooden houses is suggested in a fairy tale about three pigs, which people encounter from the very childhood. Apart from this, KOLB (2011) and JOCHIM (2012) suggest that the reason why the boom of wooden constructions in Slovakia is held back is mainly the old fire norms, which are out-to-date and do not allow construction of multiple-story buildings made of wood. Practice from western countries has shown that it is possible to build multiple-story buildings from wood, examples being from London or Milano, where nine-story wooden constructions were built; or Canada and Sweden, where thirty-story wooden buildings can be found.

The key measure that may help wooden houses to be established in ZSK faster and more effectively is a change in marketing strategy of the existing enterprises which deal with wooden houses and their construction. It is essential to start to communicate actively with customers, and to present them with the most updated information about modern wooden constructions. As agreed by HINGSTON (2002), Ali (2003), and JUŠČIUS et al. (2016), there is no universal “magical” marketing strategy. Among the main questions that an entrepreneur should be able to answer are: What are the demographics of my customers? Where do they live? Where do they meet (in person or online)? How do they search for products of my enterprise? The answers to these questions determine which marketing strategies will be successful (which are viable), and, on the other hand, which may be a waste of time. In business practice, it stands that to find a universal strategy, which would be revolutionary, is impossible. It is essential to know one’s enterprise and its customers, and only then one can choose the right marketing strategy. The further text presents several selected methods of implementing marketing which are currently preferred and at the same time are successful, and which can thus help in the establishment of wooden houses in the market. It is up to each enterprise to select the right strategy, and to choose the right way how to present itself in the market. The first option is utilization of the advertising platform on Facebook.

This is a cheap and effective way how to introduce virtually anything into the market. Its main advantage is targeting a specific group of customers according to their interests, age, gender, behavior in the online world, and many other factors. We may state that these days, doing business is practically impossible without making presence on social media. Another option is Google My Business – GMB. To use this tool to support one’s enterprise (JUŠČIUS et al. 2016) is suitable mainly in the case of local enterprises, as well as those which focus on the domestic market. It is GMB that represents the biggest strength that may be used. The GMB service combines multiple Google platforms into one package which contains Google+, profile of Google Maps services, Google reviews, access to data through the service Google Analytics, Google Statistics, etc. The third option is to use content marketing, which may be very useful with regard to wooden houses. Content marketing focuses (unlike paid advertising) on long-term results. Among the main recommendations as to content marketing belong: preparing a good quality content, dealing with relevant topics, optimizing 132

the content for readers, and creating and promoting the content. Content is not limited by a number of contributions. It includes videos, podcasts, online courses, and further possibilities of other media which people obtain the information from. This way, it will be possible to publish educational articles and videos which will teach potential customers about the real qualities of wooden houses, as well as about their advantages and disadvantages. Another method which can be applied is a so-called webinar. It is in fact a seminar which is conducted online. The webinar may take a form of a presentation, demonstration, or a discussion. Professional discussions on the Internet or on television, focusing on refuting the myths related to wooden houses, informing about their advantages and disadvantages, and on comparing them to silicate houses belong to the ways of promoting wooden houses in the market of the Žilina region. The help from employees of wood-processing enterprises may be desirable for building awareness of wooden houses, since personal recommendations are considered to be of the best ways to find new, suitable, customers these days. The last options we wish to mention are: a marketing campaign in printed media (e.g. regional newsletter), organizing events in the community – volunteering (exercising corporate social responsibility), mail campaign, active performances at public events, or co-financing these events.

The results of the conducted empirical research proved that it is essential to pay more attention to support and promotion of wooden constructions, which can help to eliminate biases held about them by non-professional and professional public, and thus enable faster and more effective establishment of wooden houses in the Žilina region.

CONCLUSION Wood has an irreplaceable position among construction materials due to a whole complex of mechanical, thermal, esthetic, utility, and technological qualities, as well as for its impact on the environment. The current wooden houses, which have gone through a long development process, fulfill all conditions for living, and at the same time minimize the impact on the environment. Satisfying the living need (need for a shelter), as one of the basic human needs, is generally highly determined by the level of social and economic development of a given society. In the conditions of the market economy, the responsibility for procuring one’s own house is transferred to the citizen; while the accessibility to a place to live is thus directly proportional to the economic possibilities of individuals and/or households. Therefore, the construction of a house is affected by multiple factors, e.g. social, economic, cultural, ethical, religious, and others. These factors greatly influence people’s preferences affecting the choice of construction material. Distrust towards wooden houses is currently still high, and is influenced by – often untrue – myths. These myths can cause an inaccurate (distorted or biased) opinion of the public with regard to wooden houses, mainly among those people who do not own this type of house.

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ACKNOWLEDGEMENT The paper has been written as a partial result of the projects VEGA No. 1/0010/17 and projects APVV-17-0206, APVV-17-0456, APVV-17-0583 and APVV-18-0520.

AUTHORS’ ADDRESSES Ing. Mária Moresová doc. Ing. Mariana Sedliačiková, PhD. Technical University in Zvolen Faculty of Wood Sciences and Technology Department of Business Economics T. G Masaryka 24 960 01 Zvolen Slovakia maria.moressova@tuzvo.sk sedliacikova@tuzvo.sk prof. Ing. Jozef Štefko, CSc. Technical University in Zvolen Faculty of Wood Sciences and Technology Department of Wooden Constructions T. G Masaryka 24 960 01 Zvolen Slovakia stefko@tuzvo.sk PhDr. Dana Benčiková, PhD. Matej Bel University in Banská Bystrica Faculty of Economics Department of Language Communication in Business Tajovského 10 Banská Bystrica Slovakia dana.bencikova@umb.sk

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 137−152, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.13

LIFE CYCLE COST ANALYSIS FOR REFERENCE PROTOTYPE BUILDING IN ALTERNATIVES OF SILICATE AND WOOD-BASED STRUCTURE Marek Potkány – Marek Debnár – Monika Škultétyová ABSTRACT The paper is aimed at the use of the LCC method and quantification of costs for alternative silicate and wood-based composition of exterior walls in reference building.

YTONG and Porotherm were selected as the materials for the silicate detached house, while for the wood-based structure, the most often used outside wall compositions made by Slovak producers were studied. The methodology was applied in accordance with the standard EN 15459, 15978 within the monitored life cycle stage cradle to use, while considering the realistic average interest rate of 3% p.a., inflation rate of 2.5% and 30-year lifespan.

Although the investment costs are higher, the findings confirm that a well-made wood-based structure can, during its operation, save costs of 1015 €/month. After considering the other potential benefits of wood-based structures and mainly after taking account their environmental aspect, the wood-based structures provide a solution for moving the building industry towards the sustainability goals.

Keywords: life cycle costing, wooden house, silicate house, operation costs.

INTRODUCTION The issue of securing one of the basic live needs – housing, is the topic for every one of us. This topic is associated with the desire for building one’s independence and is even stronger when deciding to raise a family. There are several options for fulfilling this need.

According to our current survey, approx. 30% of people in Slovakia decide to build a house.

The rest decide to buy or rent a flat or share the flat or house with parents or friends. The current trend in housing is building a wood-based detached house. It is an ecological, fast and economically interesting method of building structures. GOSSELIN et al. (2016) state that main motivation for using wood in buildings is linked with sustainability, technical aspects, cost reduction, building erection speed and aesthetics. ŠTEFKO et al. (2014) and also MAŤOVÁ and KAPUTA (2018) confirm these facts. There are, however, many prejudices against the wood-based alternatives which eventually promote traditional silicate buildings.

Results of the study by ÖSTMAN et al. (2018), HU et al. (2016), DRAGHICI and MAICAN (2018) and also GOSSELIN et al. (2016) pointed out to the questionable technical aspects of wood (acoustic performance, stability and wood shrinkage, humidity, protection against insects, wind, rot, water, earthquakes) and other main barriers (national building codes, cost, material durability, fire resistance). Under the conditions of Slovak producers, the use of domestic renewable raw material for evaluation and availability is also a problem. This is stated in the 137

studies GEJDOŠ and DANIHELOVÁ (2015) and also GEJDOŠ et al. (2018). In Slovakia, it can be estimated that wood-based structures comprise less than 10% of new constructions.

Although a slight increase has been recorded in the recent years, the potential in this field in Slovakia has not still been used to its fullest. ŠUŠTIAKOVÁ (2016) compares the situation in Slovakia with Austria, where the national programmes encourage the increase of the ratio of wood-based structures to 8090%. Similar ratio can be observed in Scandinavia or North America. When deciding about the construction of a house regardless the form (silicate or wood-based structure), an important role is played by the limited sources of financing. It is important to consider not only the investment required at the time of construction, but also the operating costs or costs associated with the house disposal, which will be required in the future. Apparently, when making the decision, one must consider also the costs associated with the whole life cycle of a structure. The method Life Cycle Costing (LCC) is suitable for such type of decision making.

So that the investors are able to decide which type of house they will select only after familiarising with the basic technical and technological characteristics of the alternatives.

Further aspects that are taken into account include the principles of healthy, comfortable and modern housing. Considering the basic requirements for constructing a house, the attention is paid mainly to the issue associated with the energy demands. According to the standard EN 15 459, from 1 January 2021 all new constructions will need to approach the zero energy consumption after deducting the energy obtained from the renewable resources. For a new structure to meet the conditions of the energy certificate (Directive no. 2010/31/EU on the energy performance of buildings), the investor has to consider the increased investment costs. Along with the energy certification of buildings, this directive introduces cost effective measures for energy performance of buildings connected to decreasing the energy demands for operating the buildings affecting the primary energy and CO2 emissions. These measures should secure meeting the cost optimal levels of minimum requirements for energy performance of buildings. Wood-based structures in their finished state absorb CO2 during their whole life cycle. In addition, when they are compared with other construction materials, they are produced in a low-energy production process with minimum emission. This fact was confirmed also in the studies of GUSTAVSSON, JOELSSON and SATHRE (2010), BIN and PARKER (2012) and GUSTAVSSON et al. (2017).

Following the previous claims it can be stated that currently the main challenge of the building industry, along with fulfilling the essential preferences of building users, is mainly the effort to reduce the energy demands of buildings. Fulfilling this objective gradually results not only in decreasing the demands for financing the building operation, but also decreasing the amount of emissions and thus improving the environment. Correct decisions regarding the thermal performance of buildings during their build up decrease the future operating costs.

The climate conditions of our region cause that the highest energy consumption is associated with covering the thermal losses and decreasing the thermal gains, i.e. heating, cooling and ventilating. The amount of such energy demand is according to the EN 154591:2017 Energy performance of buildings affected mainly by: urban design and orientation of the structure, architectural design, structural concepts and physical and thermal performance of the building and technical parameters of the equipment providing the building microclimate optimisation. The future building owner has to make the decision on the amount of current costs for planned investment and thus influence the amount of future annual operating costs. They have to decide either to invest more into building the structure, which will eventually lead to decreased operating costs or they select a cheaper building process associated with higher annual operating costs. With the return on investment it is inevitable to consider also the inflation change of energy costs increase. In order to make a 138

qualified decision it is necessary to follow 5 steps according to the EN 15 459: financial analysis (impact of economic parameters), financial prediction of individual build up variants (calculations), determining the discount rate, quantification of the current life cycle cost value for each alternative, recalculation of annual costs of LCC via annuity current value for each alternative.

According to the law on energy performance of buildings No. 555/2005 the cost effective level means the level of energy performance of buildings leading to the lowest costs during the estimated economic cycle of the building. Since the law orders to determine the cost optimum for the whole building life cycle, the use of LCC analysis is an inevitable part of the economic assessment of the cost optimum. According to PELZETER (2007) the LCC analysis can provide actual information on the preferences regarding the individual building technologies for building houses exclusively from the economic aspect during their whole life cycle. Already the name of the analysis implies that it is the calculation focused on longer time period, i.e. more than 5 years. The Life Cycle Costing method is, according to AGUACIL et al. (2017) and BECCHIO et al. (2015), a summarising view of all costs and expenses associated with the building expressed in form of standard economic calculations relative to the actual value as per the day of decision making. It means that while deciding today about the investment, one is trying to take into consideration also the end of the building lifecycle.

Such view allows us to consider the acquisition price as well as the future expenses and costs. Quite complex issue, that needs to be focused on according to the studies of MORTENSEN et al. (2014), NEROUTSOU and CROXFORD (2016) and NIEMILÄ et al. (2017), is determining the length of the life cycle. The standard mentions the basic procedures.

Nevertheless, in the case of such a complex product as building of a house is, comprised of elements with various lifespan lengths, affected also by the external depreciation, determining the lifespan length is much more difficult. In case of determining the lifespan of buildings it is important to consider this issue responsibly in order to get real results.

Therefore, the main aim of this paper is to use the LCC method and subsequently quantify the investment and operating costs for Reference Prototype Building for alternative compositions of exterior walls comparing the silicate structure and wood-based structure.

MATERIALS AND METHODS The present study deals with constructing a house in two basic forms, one being the traditional silicate structure and the other one wood-based structure. From the results of an on-line questionnaire survey (https://www.survio.com/survey/d/H9O7W5K1K8K6N3H5R) presented in the study by DEBNÁR and POTKÁNY (2016), it is possible to characterise the Reference Prototype Building (RPB), which considers the current preferences of the potential customer. A more detailed description of the layout and character of the RPD are illustrated in Figure 1. The present study deals with constructing a house in two basic forms, one being the traditional silicate structure and the other one wood-based structure. The method of constructing is affected by the selected form as well as by the used materials and construction processes. After careful consideration of all aspects, two alternatives were selected – silicate structure with load bearing materials YTONG and Porotherm (alternative A1 and A2, Figure 2) and 3 various compositions of exterior walls (alternatives A3A5) for a wood-based structure. These alternatives used the outside wall compositions certified and preferred by prominent producers of wood-based structures houses in Slovakia (Figure 3).

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EAST VIEW OF HOUSE

SOUTH VIEW OF HOUSE

GROUND FLOOR

FIRST FLOOR

Fig. 1 Layout and character description of the Reference Prototype Building.

Fig. 2 Components of exterior walls for alternatives A1-A2.

1. white paint 2. textured wallpaper 3. gypsum fibreboard, 15 mm 4. installation gap, 60mm 5. Fermacell board, 12.5 mm 6. spruce wood frame construction with insulation, 140 mm 7. wood fibreboard insulation, 60 mm 8. mesh with putty 9. plaster, 3 mm

1. white paint 2. textured wallpaper 3.gypsum fibreboard, 15 mm 4. installation gap, 60mm 5. Fermacell board, 12.5 mm 6. spruce wood frame construction with insulation, 140 mm 7. wood fibreboard insulation, 100 mm 8. mesh with putty 9. plaster, 3mm

1. white paint 2. textured wallpaper 3. gypsum fibreboard, 15 mm 4. installation gap, 60mm 5. Fermacell board, 12.5 mm 6. spruce wood frame construction with insulation, 140 mm 7. wood grill with mineral wool, 80 mm 8. wood fibreboard insulation, 120 mm 9. mesh with putty 10. plaster, 3 mm

Fig. 3 Components of exterior walls for alternatives A3-A5.

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Tab. 1 General information on the Reference Prototype Building.

Specification

Alternatives A1

A2

A3

A4

A5

Usable floor area (m ) 146 146 156 156 156 2 Base plate area (m ) 92 (11.5x8) 92 (11.5x8) 92 (11.5x8) 92 (11.5x8) 92 (11.5x8) Household size (no. of people) 4-5 4-5 4-5 4-5 4-5 Number of rooms 5 5 5 5 5 Number of floors 2 2 2 2 2 Type of roof Saddle roof Saddle roof Saddle roof Saddle roof Saddle roof Construction type Porotherm YTONG S Timber frame Timber frame Timber frame Indoor temperature (°C) 20 20 20 20 20 −1 Air exchange rate (h ) 1 1 1 1 1 Heat transfer coefficient 0.161 0.179 0.161 0.141 0.109 External wall U [W/m2K] Roof U [W/m2K] 0.13 0.13 0.13 0.13 0.13 2 Ground floor U [W/m K] 0.10 0.10 0.10 0.10 0.10 First floor ceiling U [W/m2K] 0.13 0.13 0.13 0.13 0.13 2 Triple glass Ug [W/m K] 0.60 0.60 0.60 0.60 0.60 2 Windows UW [ W/m K ] 0.62 0.62 0.62 0.62 0.62 Energy consumption 5445 6095 5445 5033 4391 [kW/h/year] Basic information on Loan/ own source (80%: 20%); average interest rate of loan is 3.0% p.a. in financing realistic prediction and time of loan is 30 years.

2

Figure 4 illustrates the structure of roof construction elements and floor in the RPD, while Table 1 provides the input information for carrying out the analysis of life cycle for individual alternatives.

A. concrete roofing felt B. laths C. diffusion foil D. wood roof truss construction with insulation, 200 mm E. wood Grill with mineral wool, 60 mm F. Fermacell board, 12.5 mm G. wood grill with mineral wool, 60 mm H. plasterboard, 12.5 mm I. paint

A. wood decking, 22 mm B. wood Grill with mineral wool, 80 mm C. wood ceiling construction with mineral wool, 220 mm D. Fermacell board, 12.5 mm E. wood grill with mineral wool, 60 mm F. plasterboard, 12.5 mm G. paint

A. laminate floor, 12 mm B. concrete layer with heating system, 50 mm C. PE protective film D. mineral wool, 40 mm E. wood decking, 22 mm F. wood ceiling beams with insulation, 220 mm G. wood grill, 18 mm H. plasterboard, 12.5 mm I. paint

Fig. 4 Components of roof and ceiling for the Reference Prototype Building.

The main heating source selected was represented by the currently most preferred type of a gas condensing boiler. In order to determine the energy consumption per year equation 1 was used. This equation is defined by the standard STN 73 0540-2/Z1: 2016: (1) Qh = 82.1 x (HT + HV) – 0.95 x (Qs + Qi) 141

Where: Qh is the heat required for heating [kWh/ year], HT is the thermal loss caused by heating, HV is the heat loss caused by ventilation, Qs represents the passive solar gains and Qi are free heat gains from people associated with the structure orientation and window size.

Thermal loss of the heating system (Heating system efficiency) can be quantified using the equation 2: Ql = Qh x (1 – A x B x C) (2) Where A is the efficiency of the floor heating system, B is the distribution system performance = 0.97 and C is the operation of the heat production system (gas condensing boiler) = 0.98.

The overall energy requirement for heating (Q) can be determined according to the equation 3: Q = Qh + Ql

(3)

Where Qh is the energy consumption [Kw/h], and Ql is the heat loss of the heating system [Kw/h].

LCC calculation, according to the STN EN 15 459, tries to consider all costs which were generated during the course of the whole product life cycle. In the present case, the product is the building of a house. The scheme of the life cycle is presented in Figure 5. The individual phases take into account also the time of generating individual expenses and the type of expenses. For the sake of the present study, the phases cradle to use of the building (Product, Construction and Use Stage) are evaluated. In a simplified form, individual cost groups can be defined as investment costs and operating costs. When quantifying the costs associated with the stages maintenance, repair, replacement and refurbishment, these costs can be considered irrelevant, since in the case of all alternatives they represent the same value (e.g. window maintenance, heating element replacement, bathroom fixtures).

Fig. 5 Life cycle scheme, source: EN 15 978.

Within the LCC calculation method the equation 4 was used in order to determine the life cycle costs. The inflation factor – If (equation 4), used for recalculating the costs for Net Present Values, is the deciding element regarding the implementation of the time factor.

LCC = IC + OC x If + I

(4)

Where IC – Investments costs, OC – operating costs (cost for space heating only), If – inflation factor and I – Interest for loans (30 years). n

(1+r)x[(1+r)n-1]

1

r

If = ∑ (1+r)n = 142

(5)

Where n – years of lifecycle, n = 30 years is the period of the loan and r – change in energy price (prediction). Investment costs (IC) are the sum of the costs of building a new structure and the investor should bear in mind that the amount of investment costs affects the future amount of operating costs (OC), while the highest operating costs are usually caused by energy consumption. Median of the calculated costs from 5 potential construction companies was used for all evaluated alternatives for determining the investment costs. The addressed producers (construction companies) have the major share in the given market segment. This was also a reason why the investment cost calculation was considered representative.

An important element of the entire calculation should be, according to ALFARIS et al.

(2017) and BADEA et al. (2014), the risk analysis encompassing the difficult predictability of the future costs (e.g. resulting from an increase in the energy costs etc.). This vague character can be considered in the final LCC calculation via carrying out the analysis of change sensitivity of the input calculation parameters using various scenarios of energy prices development or interest rate development. Table 2 presents the basic parameters of LCC sensitivity analyses for alternatives A1-A5. Information from the Eurostat database regarding the average value for last 10 years and correction in optimistic and pessimistic predictions were used for the recalculation.

Tab. 2 Parameters of LCC sensitivity analyses for A1-A5 alternatives.

Prediction/ Factors Optimistic prediction Realistic prediction* Pessimistic prediction

Average inflation rate 1.25 % 2.50 % 3.75 %

Interest rate of loan 1.75 % 3.00 % 4.25 %

Source: * Eurostat average value for last 10 years and correction in Optimistic/ Pessimistic prediction.

RESULTS AND DISCUSSION Within the defined conditions for the RPB, Table 3 presents the results of the space heating energy consumption according to the standard STN 73 0540-2/Z1: 2016 Thermal performance of buildings and components, thermal protection of buildings.

Tab. 3 Determining the space heating energy consumption according to the STN 73 0540-2/Z1: 2016.

Information Built volume Vb [m3] Useful area Ab [m2] Impact of thermal bridges ∆U Transmission heat loss HT [W/K] Average heat-transfer coefficient [W/m2K] Ventilation heat loss HV Total heat loss H (HT + HV ) Passive solar gains QS [kW/h] Free heat gains from people Qi [kW/h] Total QS + Qi [kW/h] Space heating energy consumption Qh [kWh/ year] Space heating energy consump. [kWh/m2 /year] (Qh/Ab)

A1 381.8 146 0.05 52.5 0.155 45 97.5 1143 2147 3290 4879 34

A2 381.8 146 0.05 59.6 0.169 45 104.6 1143 2147 3290 5462 37

Alternative A3 A4 412.4 412.4 156 156 0.05 0.05 52.5 48 0.155 0.129 45 45 97.5 93 1143 1143 2147 2147 3290 3290 4879 4510 31 29

A5 412.4 156 0.05 41 0.109 45 87 1143 2147 3290 3935 25

The heat loss of the heating system, i.e. its efficiency, can be quantified according to the equation 2. The results are presented in Table 4. The energy consumption Q for alternatives A1-A5, which is a sum of the heat loss of the heating system and of the energy 143

consumption Qh with the selected heating source – gas condensing boiler, is essential information in order to determine the operating costs for alternatives A1-A5 (Table 5). The current price list provided by the dominant gas distributor – SPP a.s. was used for determining the energy consumption.

Tab. 4 Energy consumption for alternatives A1-A5 with gas condensing boiler.

Alternatives A1 A2 A3 A4 A5

Heat loss of the heating system Ql [kW/h year] 566 633 566 523 456

Heating energy consumption Qh [kW/h year] 4879 5462 4879 4510 3935

Energy consumption Q [kW/h year] 5445 6095 5445 5033 4391

Tab. 5 Quantification of operating cost for alterantives A1-A5.

Alternatives A1 A2 A3 A4 A5

Water Heat 4 persons €/year* 72.74 72.74 72.74 72.74 67.68

D2 Fee €/year

Price €/[kW/h]

82.92 82.92 82.92 82.92 62.92

0.045 0.045 0.045 0.045 0.047

Energy consumption [kW/h] 5445 6095 5445 5033 4391

Operating costs €/year 400 430 400 381 337

Source: Price list by SPP 2019, Available: (https://www.spp.sk/sk/domacnosti/plyn/pre-domacnosti/dokumenty-nastiahnutie/#ceny_dom), * 40 % (gas condensing boiler), 60 % (solar panels)

In order to quantify the investment costs for all alternatives, the median of calculated costs from 5 potential constructing companies was used. The building was divided into the following main construction units: foundation, ground floor, 1st floor, 1st floor ceiling, external walls, internal walls, roof, windows, doors and also item of final work. Table 6 and 7 provides information on the used components for the elements for alternatives A1-A2, A3A5.

Tab. 6 Quantification of investment cost and materials used for alternatives A1-A2.

Element

Area (m2)

Price (€/m2)

Components

External wall 157

72

69

Porotherm 38 T, YTONG YQ Cement mortar

Internal wall

Thickness (mm) 395, 465

15 773

15 280

380, 450

10 219

9 824

-

-

-

157

22

Acrylate plaster outside

10

3 333

3 274

150

9

Gypsum plaster skimming inside

5

2 222

2 182

125

29

105

3 704

3 714

100

1 202

1 207

1 381

1 384

Porotherm, YTONG Cement mortar and painting Gypsum plaster skimming Foundation

Alternative A1 A2

92

140

Concrete

5

1 121

1 123

500

12 812

12 814

3 837

3 838

Insulation Final work

37 264

38 208

-

-

Electro installation

-

3 822

3 822

-

-

Water and waste installation

-

1 077

1 077

144

Ground floor Kitchen, Living room

Bathroom, toilet

56

Laminated floor (living room)

12

2 547

2 626

82

Concrete + floor heating system

50

4 708

4 731

82

Expanded polystyrene + PE

120

1500

1500

26

Ceramic floor tiles

2 229

2 298

9

Ceramic wall tiles

1 155

1 185

Ceramic floor tiles

1 433

1 477

Bathroom accessories

2 884

2 983

Laminated floor

1 955

1 955

Carpet (bedrooms)

1 092

1 092

1st floor bedrooms

56

Bathroom

8

Concrete + floor heating system

3 027

3 027

Bathroom accessories

50

2 729

2 798

Ceramic wall tiles

1 911

1 970

Ceramic floor tiles

3 558

3 596

Plasterboard

2 047

2 126

Roof

605

19 889

20 309

Concrete roof (cladding)

100

4 945

4 945

Construction, insulation

200+220

5 300

5 300

12.5

2 967

3 093

60

2 700

2 700

12.5

3 978

4 062

9 464

9 575

Fermacell board Wood Grill + mineral wool Plasterboard ceiling, painting 92

First floor ceiling

Wood Grill from laths

80

1 010

1 010

Wood beams with mineral wool

220

3 632

3 687

Fermacell board

12.5

Wood Grill + mineral wool Plasterboard ceiling, painting

990

990

60

1 700

1 700

12.5

2 132

2 187

Windows

U-PVC frame, 3 glass

6 305

6 335

Interior doors

Laminated door

2 920

2 925

Exterior doors

Plastic door

2 433

2 489

12 261

12 392

122,611

123,924

Contribution margin (10%) Total costs (€)

Tab. 7 Quantification of Investment cost and Materials used for alternatives A3-A5.

Element External wall

Area (m2) 157

Price (€/m2)

Components Timber frame construction

Thickness (mm) 296

336

436

60

100

120

Exterior plaster system Wood Fibreboard insulation

Internal wall

A3 17 122

Alternative A4 A5 18 165 19 510

3 424

3 633

3 902

5 112

5 486

6 346

Fermacell board

12.5

856

908

975

TFC with Mineral wool

140

4 000

4 000

4 000

Installation gap

60

589

998

1 146

Gypsum Fibreboard, paint

15

3 140

3 140

3 140

125

130

3 294

3 628

3 627

Gypsum Fibreboard, paint

15

888

988

988

timber frame construction with mineral wool Gypsum Fibreboard, paint

100

1 547

1 714

1 713

15

859

926

925

145

Foundation

92

140

Concrete

500

insulation Final work

Ground floor Kitchen, Living room

Bathroom, toilet

floor bedrooms

Bathroom

1 837

1 838

1 837

37 820

38 970

3 422

3 422

3 422

Water and waste installation

-

1 077

1 077

1 077

12

2 547

2 547

2 626

50

4 708

4 731

4 731

82

Laminated floor (living room) Concrete+ floor heating system Expanded polystyrene + PE

1500

1500

1500

26

Ceramic floor tiles

2 229

2 298

2 298

9

Ceramic wall tiles

1 155

1 185

1 185

Ceramic floor tiles

1 433

1 477

1 477

Bathroom accessories

2 884

2 883

2 884

Laminated floor

1 955

1 955

1 955

Carpet (bedrooms)

1 092

1 091

1 092

3 027

3 084

3 084

Electro installation

-

-

56 82

8

Concrete + floor heating syst.

Bathroom accessories

50

2 729

2 798

2 798

1 911

1 970

1 970

Ceramic floor tiles

3 458

3 456

3 596

Plasterboard

2 547

2 576

2 647

605

19 951

20 181

20 225

Construction, insulation Fermacell board Wood Grill + mineral wool

92

120

Ceramic wall tiles

Concrete roof

floor

12 943

37 674 -

Roof

First ceiling

12 926

-

-

56

1st

12 747

Plasterboard painting

ceiling,

100

5 985

6 054

6 067

200+220

4 976

5 090

5 112

12.5

2 000

2 000

2 000

60

3 000

3 000

3000

12.5

3 990

4 036

4 045

9 464

9 575

9 575

Wood Grill from laths

80

1 010

1 010

1 010

Wood beams with mineral wool Fermacell board

220

3 632

3 687

3 687

12.5

990

990

990

Wood Grill + mineral wool

60

1 700

1 700

1 700

12.5

2 132

2 187

2 187

Windows

Plasterboard ceiling, painting U-PVC frame, 3 glass

6 294

6 448

6 350

Interior doors

Laminated door

2 919

2 933

2 944

Exterior doors

Plastic door

2 477

2 531

2 511

12 438 124,380

12 693 126,925

12 835 128,353

Contribution (10%) Total costs (€)

margin

Regarding the results of quantifying the investments, it is important to highlight that the costs of individual components are different for each and every studied alternative. It is due to the fact that in the case of every studied alternative, a unified level for contribution margin of overhead cost and profit of 10% from the quantified items of costs was selected.

The reason for selecting this approach was the individual approach of every potential constructor and keeping the confidential character of information about the contribution margin. This fact was mirrored in e.g. windows, where the ratio of costs of these components is at the level of 6,305 € (alternative A1, 5.1% of the overall investment) and 6,350 € 146

(alternative A5, 4.9% of the overall investment). The situation is similar also in the case of the doors, as well as other components. Although the components may be the same, provided by the same subcontractors, their pricing within the budget is usually different in case of every addressed construction company. It is caused by the various levels of contribution margin in cases of individual component prices. There are also differences in the item final works – Electro installation. Costs for alternatives A1-A2 are logically higher in terms of the required work.

If we wanted to express the ratio of individual elements for the studied alternatives, the highest costs were connected to the item final works. This item accounts for 30.4% (alternative A1) or 29.6% (alternative A5). The second most costly element regarding the studied alternatives were the components for the roof construction amounting to 16.2% (alternative A1) or 15.7% (alternative A5). These items are followed by the elements of the external walls (with 12.3% for alternative A2, up to 15.2% for alternative A5), as well as the foundation with a 10% ratio for the studied alternatives. It has to be mentioned that in case of all components (doors, windows, floors, bathroom fixtures), the standard (low cost) versions, which are usually included in the budgets of the construction companies for the complete house, were taken into consideration. If the customer required other components, it would certainly change the investment amount.

Figures 6 present the results of LCC analysis and its realistic, optimistic and pessimistic variant, which consider the difficult predictability of the future costs due to the increase in energy prices and changes in the interest rates (Table 5).

In the case of the realistic variant of energy price development, the inflation increase of 2.5% and average loan interest rate of 3% p.a. are predicted. Figure 6 presents the items investment costs (IC), interest of loan (I) and operating costs (OC). The lowest overall costs for a 30-year life cycle were quantified for the alternative of a silicate structure A1 at the level of 187,336 €. For the wood-based structure alternative with the type structure of the outside walls A5, the life cycle cost was quantified to 196,848 € representing a difference of 5%, with the overall difference of investment costs over 5,000 € in favour of the silicate structure. This difference could be eliminated by a targeted state support in the form of subsidies for wood-based structures and also for already built wood-based structures.

Nevertheless, in spite of a marketing campaign and prepared legislative support, such subsidies have not been approved by the state so far. Nonetheless, it must be pointed out that with the operating costs at the level of specific heat requirement, the difference of 23% (4,200 €) was in favour of the wood-based structure. (€)

Fig. 6 Results of LCC for A1-A5 alternatives for all economic parameters in €.

147

For comparison, results of the optimistic prediction with the average inflation rate of 1.25% and interest rate of loan of 1.75% are provided (Figure 6). The differences in life cycle cost are smaller. For instance, with the alternatives A2 and A3, the difference is at the level of just 3.5% in favour of a silicate structure. However, the operating cost were quantified in favour of the wood-based structure (6.5% for alternative A3 and 23.2% for alternative A5). With the pessimistic prediction and average inflation rate of 3.75% and interest rate of loan of 4.25% are the differences more noticeable than in the case of the realistic or optimistic prediction. It is apparent that the amount of cost is affected by the selection of the structural materials, to a certain extent also by the construction company, as well as by the method of financing.

Since the investment cost are paid at the time of building, i.e. theoretically in the first year of the assessed period of the life cycle, the information about the difference in the repeated monthly cost covering the loan instalment and operating cost is relevant for the economic comparison. If we consider the life cycle cost per month (Figure 7) it is interesting to find out that the realistic prediction shows differences at the level of max. 23 €/month with the alternative A1 and A5, in the case of the pessimistic and optimistic prediction it is 30 €/month and 19 €/month, respectively. This difference could be eliminated in favour of wood-based structures by the financing conditions regarding the structure of own and borrowed capital in the ration of e.g. 50%:50%, i.e. using other ration than used in the study.

However, also in such a context, the information about the amount of operating cost, being significantly lower in case of wood-based structure, would be important for the decision making process. The difference in the monthly cost would be 11.8 €/month for the realistic prediction, when comparing alternatives A5 (38.8 €/month) and A1 (50.6 €/month. With the pessimistic prediction, i.e. with a negative prediction of energy price development, the difference in the operating cost would be even higher (14.6 €/month), while with the optimistic prediction, the difference would be at the level of 9.6 €/month in favour of the wood-based structure.

However, the comparison of Life cycle cost could be unfavourable for the sector of wood-based structure also if the level of contribution margin and profit margin of the woodbased structure producers were higher than of the traditional construction companies. This can be a natural fact to a certain extent, mainly in the case when the overhead costs need to be allocated to a lower number of completed houses.

LCC / month in € (30 years period)

(€) 700 600 500 400 300 200 100 0

385

393

400

400

404

452

463

470

472

475

530

543

558

558

560

LCC LCC LCC LCC LCC A1 A2 A3 A4 A5

LCC LCC LCC LCC LCC A1 A2 A3 A4 A5

LCC LCC LCC LCC LCC A1 A2 A3 A4 A5

Optimistic economic parameters

Realistic economic parameters Per month

Pesimistic economic parameters

Fig. 7

Results of A1-A5 for all economic parameters per month in €

148

Results of LCC Analysis presented in this study for the Prototype Building – Family house in in the alternatives of silicate and wood-based structure cannot be compared with similar studies either in Slovakia or abroad. The reason is the high variability of the input components, as well as various parameters of the studied objects (e.g. the size of the building, purpose, location, materials used, economic parameters, etc.). There are many applications for the LCC in various fields, such as transport (DEBNÁR et al. 2016), energy sector (ISLAM et al. 2014, HU 2017), industrial production and civil engineering (BAEK, LEE 2013, BRADY, ABDELLATIF 2017). The LCC issue in the sector of civil engineering has been partially discussed in the studies of MORTENSEN et al. (2014), assessing the single family house in Denmark. Results of LCC analysis showed that the building refurbishment had a positive economic impact. In addition, NEROUTSOU and CROXFORD (2016) dealt with the issue of Life cycle costing of low energy housing refurbishment, with the conclusion that the investment into improving the thermal performance of the building had a positive impact on the assessment of LCC. NIEMILÄ et al. (2017) dealt with the cost-effectiveness of energy performance renovation measures in Finnish brick apartment buildings. Authors BADEA et al. (2014) presented the application of the mentioned method also in assessing the passive house, while the materials used for building the house have a positive impact on the overall operating cost in the long term regarding the assessed life cycle. Only few authors deal with combining the economic and ecological aspects of the life cycle of buildings. CHASTAS et al. (2017) is one of the authors, who proposed a conceptual combination of LCC and LCA into one assessing model. This model has not been applied practically so far, is has only been defined. The available studies mention more often the separate use of LCA. Life Cycle Assessment is a method comparing the environmental impact of products or services regarding their life cycle. According to LI and FROESE (2017) and LIN et al. (2017) the method takes into account the emissions into all components of the environment during the production, use and product disposal. The assessment considers also the processes of obtaining the raw materials, material and energy production, auxiliary processes or subprocesses. According to WU et al. (2017), VILCHES et al. (2017), WEILER et al. (2017) and SU et al. (2017) the LCA quantifies the potential impact of the product of service on the environment and is defined in the standards ISO 14040: 2006 and ISO 14044: 2006. The application of LCA in civil engineering is ever increasing and it has been repeatedly used for assessing new buildings. Examples can be found in the studies of MAOUDUS et al. (2016) and IQBAL et al. (2017). For effective elaboration of LCA studies, commercially available databases of processes, material and energy flows are used. It is one of the most important information tools of environmentally oriented product policy. MITTERPACH et al. (2018) present in their study the use of Life Cycle Impact Assessment of the designed wood based RPD while identifying the environmental impacts of individual house elements. Positive environmental impact of wood-based structures was presented also in the studies of ESTOKOVA et al. (2017), POTKÁNY et al. (2018) and BALASBANEH and MARSONO (2013).

CONCLUSION The presented findings confirm that a well-constructed wood-based structure can save costs in the operation phase although the investment cost is 4-5% higher when compared to the silicate building. The saving can reach 10 15 €/month depending on the energy price development being the result of the material selection with a different value of heat transfer coefficient. Larger use floor area of 10 m2 (7.5%) is one of the appreciable advantages of the wood-based structures associated with the RPB and higher investment is associated with this particular added value (Table 1). When considering other potential benefits of wood-based 149

structures, eliminating possible risks and highlighting their ecological and environmental aspect regarding their environmental impact, the wood-based structures are a solution to move the building industry towards sustainability goals. This way the building industry will rank among the industries completely fulfilling the requirements of green business products.

The application of the Life Cycle Cost Analysis for the Reference Prototype Building – Family house using the alternatives of a silicate building and a wood-based structure with specifying the level of investment and operating cost for heating in the conditions of the Slovak Republic can be considered a contribution of the present study. The difference in the investment and operating cost could be eliminated by a targeted support from the state in the form of subsidies for wood-based structures, as well as by supporting the use of renewable energy sources. Nevertheless, it is also important that the producers of wood-based structures do not increase the contribution margin for overhead cost and profit margin artificially. Such approach will certainly create a potential for competitiveness and for increasing the market share of the wood-based structures on the Slovak market.

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ACKNOWLEDGMENTS We wish to thank project VEGA -- Scientific Grant Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic; (Project No.1/0320/17 Economic and Social Context of European 20/20/20 Targets from the Viewpoint of Economy Low-energy Houses) and project APVV-18-0520 Innovative methods for analyzing the performance of wood and forestry complex using the principles of green growth.

ADDRESSES OF THE AUTHORS doc. Ing. Marek Potkány, PhD. Marek Debnár Ing. Monika Škultétyová Technical University in Zvolen Faculty of Wood Sciences and Technology Department of Economics, Management and Business T. G. Masaryka 24 960 01 Zvolen Slovakia potkany@tuzvo.sk

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 153−161, 2019 Zvolen, Technická univerzita vo Zvolene DOI:

INCREASING WEBSITE TRAFFIC OF WOODWORKING COMPANY USING DIGITAL MARKETING METHODS Andrej Tomič  Mikuláš Šupín ABSTRACT In the digital environment with the development of ICT, there are changes in traditional models of marketing management. Marketing practices, companies, institutions or processes are rapidly changed using digital technologies. Applying new ICT in marketing means building a new area of marketing called digital marketing. New conflicts that need to be addressed in the forest-wood complex arise. The paper deals with the application of digital marketing and the possibilities of its application in web page models in the woodworking company Drevenyprofil, in order to make online marketing, advertising, search engine optimization website in woodworking company Drevenyprofil more effective to increase website traffic and thus to boost turnover in woodworking company Drevenyprofil. In particular, the methods of online marketing analysis and marketing strategy were used.

Key words: digital marketing, search engine optimization – SEO, online marketing, advertising.

INTRODUCTION Digital marketing is the marketing of products or services using digital technologies, mainly on the internet but also including mobile phones, display advertising, and any other digital medium to reach consumers using digital marketing channels. Digital marketing channels are systems based on the internet that can create, accelerate, and transmit product value from producer to the terminal consumer by digital networks. The key objective is to promote brands through various forms of digital media. (LEBOFF 2011, ANDERSON 2019).

Digital marketing becomes a worldwide trend and a competitive advantage for interested businesses that have a website. Search engine optimization as the important part of digital marketing has a positive effect on the ranking of a website by a search engine algorithm, and focusing on the right keywords can mean an increase in the company's overall turnover (CHODELKA 2015). For websites whose main source of income is the sale of products and services over the internet, the keywords appearing on relevant phrases at the forefront are important. The website is the best source of advertising that presents the business on the Internet and conditional on customer conversion (ANDERSON 2019). If we want to reach a high number of visitors, we use a method of optimizing the pages for search engines called SEO (search engine optimization) (KUBIČEK − LINHART 2010).

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Search Engine Optimization ensures that search engines reliably locate keywords on a website and, if they are found, assign the site the highest ranking in organic search results (SCOTT 2010).

Search Engine Marketing (SEM) is a form of the Internet marketing that involves the promotion of websites by increasing their visibility in search engine results pages (SERPs) primarily through paid advertising. SEM (Search Engine Marketing) may incorporate search engine optimization (SEO), which adjusts or rewrites website content and site architecture to achieve a higher ranking in search engine results pages to enhance pay per click (PPC) listings. Search Engine Results Pages (SERP) are the pages displayed by search engines in response to a query by a searcher. The main component of the SERP is the listing of results that are returned by the search engine in response to a keyword query, although the pages may also contain other results such as advertisements. (ANDERSON 2019).

Search Engine Optimization (SEO) is increasing the amount of website visitors by getting the site to appear high on results returned by a search engine. SEM is considered internet marketing that increases a site's visibility through organic search engines results and advertising. SEM includes SEO as well as other search marketing tactics. (ĎURIŠ, 2019c) Search engine optimization (SEO) is the process of increasing the quality and quantity of website traffic by increasing the visibility of a website or a web page to users of a web search engine. SEO refers to the improvement of unpaid results (known as "natural" or "organic" results), and excludes direct traffic/visitors and the purchase of paid placement.

Primarily SEO pertains to search engine. (BODNÁROVÁ, 2019, ĎURIŠ, 2019b).

The idea of optimizing the market position has a long history, but people had no other means than physical placement of goods on the markets. For this reason, they used the markets to sell their goods, cities built on busy trade routes and opened their stores on the busiest parts of the streets. The tools to find the services and products they needed were just the basic sense of sight and hearing. With the increase in population, new needs for simpler searches have emerged. Catalogs were created, the first alphabetical order appeared, for easier orientation in the list of filled information. Instead of looking for a prospective location in the center, people began to think more logically and change their names because of the serial number (position) in the catalog. Companies called AAA were before the classical ones, which were ranked 15 less relevant by alphabetical order. The classic history of website search engine optimization used in modern marketing was created by launching the first internet search engines, such as Alta Vista. At that time, search engines used robots (bots) that searched for keywords directly under the META tag (an invisible keyword tag).

Today, optimization focuses on the modern principle of content relevance (ONLINE MARKETING 2014). SEO (Search Engine Optimization) optimization consists of offsite and onsite parts. In onsite parts of SEO specialists are solving technical issues of the website.

Technical Website Optimization begins with SEO technical audit, which includes specific recommendations for websites. Technical optimizations consist in optimizing a website into a search engine-friendly form, which affects the positions of specific keywords in a search (ĎURIŠ 2019b).

In the paper, we explored the medium-sized woodworking company Drevenyprofil.

The company is engaged in the sale of wooden profiles, especially wooden tiles and has not yet invested in online marketing. The company is based in Bratislava and has great competition in search.

MATERIALS AND METHODS Digital marketing methods such as search engine optimization (SEO), search engine marketing (SEM), content marketing, influencer marketing, content automation, campaign 154

marketing, data-driven marketing, e-commerce marketing, social media marketing, social media optimization, e-mail direct marketing, display advertising, e-books, optical disks and games are becoming more common in advancing technology. In fact, digital marketing now extends to non-Internet channels that provide digital media, such as mobile phones (SMS and MMS), callback, and on-hold mobile ring tones. In essence, this extension to nonInternet channels helps to differentiate digital marketing from online marketing, another catch-all term for the marketing methods mentioned above, which strictly occur online. (FOX 2011, ANDERSON 2019, ĎURIŠ 2019a).

Based on the recommendations (DOMES 2009), we incorporated the recommended changes and then the website was ready for offsite optimization. SEO technical audit was based on a created checklist of possible errors (KUBÍČEK − LINHART 2010).

The aim was to increase organic website traffic and by this to increase turnover of the woodworking company Drevenyprofil through the selection of relevant keywords, active linkbuilding and technical optimization of the website. Organic search is a method for entering one or several search terms as a single string of text into a search engine. Organic search results, appear as paginated lists, are based on relevance to the search terms, and exclude advertisements. Non-organic search results do not filter out pay per click advertising. (ANDERSON 2019).

Turnover can be influenced by optimizing keywords that are searched, relevant, and conversion. The percentage of keyword conversions will export from Google Analytics' application (BRANDT 2010) if the word has a high conversion rate, it will be searched. But if the site's search position will be low, focusing on that keyword influences company total turnover also (FOX 2011).

We used applications like Google Search Console (GOOGLE SEARCH CONSOLE 2019), Collabim.com's Holy Grail collection apps, Mangools.com's Keywordfinder (MANGOOLS 2019) and Google Ads (GOOGLE ADS 2019, DOMES 2012), (GOOGLE SUPPORT, 2019), (GOOGLE ANALYTICS, 2019), (WORDPRESS SLOVAKIA 2019), (YOAST SEO 2019), (WROBLEWSKI 2008), (KULHÁNKOVÁ − ČAMEK 2010) for keyword analysis.

We optimized the website for technical and content purposes to achieve company Drevenyprofil's aim of increasing organic website traffic and overall turnover (JUROŠKO 2018). In the technical section, we created a keyword analysis that we then incorporated into Drevenyprofil's website. We created an individual technical audit of recommendations errors, that affects the clickthrough rate (CTR) (DOMES 2011) of a website and the search engine's website position. We used Screaming Frog (SCREAMING FROG 2019), Google Analytics, Google Search Console, Collabim, and Ahrefs to create a technical audit.

The following recommendations were the key to increase the organic Drevenyprofil site traffic from major search engines and make it more visible on the Internet in the short and medium term (SIROVICH, DARIE 2008), as the factors on the page significantly affected search keyword positions of the websites.

The technical audit included several parts of the optimization that were evaluated as important for the woodworking company Drevenyprofil's website by browsing the website: ● Creating a robots.txt file to increase crawl budget, ● Generating a sitemap.xml that helps faster indexing, ● Creating and generating original META descriptions to increase click through rate, (WORDPRESS SLOVAKIA 2019, YOAST SEO 2019), ● Creating and generating original META titles that affects keywords positions in search (WORDPRESS SLOVAKIA 2019, YOAST SEO 2019), ● Optimizing the web page title structure (H1, H2) that affects keywords positions in search (WROBLEWSKI 2008), 155

● ● ● ● ● ●

Redirecting broken pages with 404 status code, Implementing SSL certificate and page transition to secure HTTPS version, Optimizing web page load time, Active linkbuilding which strengthens the strength of the website's domain, Optimizing content delivery in social networks (KULHÁNKOVÁ − ČAMEK 2010), Optimizing images in search, which can generate additional organic traffic (ĎURIŠ 2019a)

To achieve the results, we implemented the findings from the keyword analysis and technical SEO in the Drevenyprofil woodworking company website, which also include active linkbuilding. The main goal of the analysis was to prepare the woodworking company website Drevenyprofil into a search engine-friendly form.

In the field of search engine optimization (SEO), linkbuilding describes actions aimed at increasing the number and quality of inbound links to a webpage with the goal of increasing the search engine rankings of that page or website. Linkbuilding is the process of establishing relevant hyperlinks (usually called links) to a website from external sites. Link building can increase the number of high-quality links pointing to a website, in turn increasing the likelihood of the website ranking highly in search engine results. Linkbuilding is also a proven marketing tactic for increasing brand awareness.

Backlinks from authoritative sites were obtained as follows (UI42 2019): ● Creating high-quality content on the Drevenyprofil website (BODNÁROVÁ 2019), ● Creating and publishing statistics 'that are available to the client and owner of the website Drevenyprofil, ● Creating quality native articles posted on quality websites containing a backlink in the tracked anchor text keyword on Drevenyprofil (ŘEZNÍČEK – PROCHÁZKA 2014), ● By Buying from Visited Websites with Strong Domains, ● Competition for Builders who own Websites with Guides. The competition is based on the best workplace experience posted on the builder's website with the Drevenyprofil website (LEBOFF 2011). The reward is a 10m² free wood paneling option. For this activity, it is necessary to actively reach out to builders and construction companies (KUNA 2018).

Through the selection of relevant keywords, technical optimization of the search engine website and active linkbuilding will increase organic website traffic and increasing the turnover (QIPOINT 2019).

Subsequently, after implementing the recommendations on the Drevenyprofil website, the results were evaluated year-on-year. The results were evaluated by Google Analytics application. The implementation of the measurement code on the Drevenyprofil website was provided by the website owner. We were evaluated the results year-on-year so the impact of possible seasonality will be reduced.

RESULTS AND DISCUSSION € We created a keyword analysis individually for the woodworking company Drevenyprofil website. 13 most wanted keywords of the analysis are shown in the table 1. below:

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Tab. 1 Keywords from keywords analysis.

Keyword Tilling Tiles wall Cladding Wood tile Log linig Wall and floor tiling Tatra tile Exterior cladding Facade cladding Wood cladding House cladding Wooden cladding on the wall Tatra wood cladding

Number search in Google.sk month 6600 4400 4400 4400 4400 4400 2900 2900 2400 2400 1900 1900 1900

Keyword analysis provided us with a number of keywords, that may not be directly relevant to the business of the Drevenyprofil website.

The client specializes in the sale of wooden profiles and tiles, but not all types, and so words like log lining we deleted because the company Drevenyprofil does not offer log lining. We focused on relevant keywords such as: ● ● ● ● ● ● ● ● ● ● ● ●

Tiling Tiles wall Cladding Wooden tile Wall and floor tiling Tatra tile Exterior cladding Facade cladding Wood cladding House cladding Wooden cladding on the wall Tatra wood cladding

We chose the keywords together with the owner of the woodworking company Drevenyprofil, so the all keywords were relevant.

Tab. 2 Keyword Conversion Rate.

Keyword Tatra tile Wooden tile Tiles wall Cladding Wall and floor tiling Tiling Wooden cladding on the wall Exterior cladding Facade cladding House cladding Tatra wood cladding Wood cladding

Conversion rate in % 14.57 12.32 4.98 3.25 3.24 2.89 2.81 2.76 2.16 2.1 1.98 1.91

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The table 2. showed that the keywords "Tatra Tile" and "Wooden Tile" were the most convertible for the Drevenyprofil website and therefore it was necessary worth focusing on this key words.

Technical SEO Audit Technical SEO audit is a process during which the technical aspects of website's SEO was checked. Search engine bots crawled the web to find pages and websites. The bots then checked pages for the different ranking factors before ranking website in the search results.

Basically, the health of a website was checked and fixes needed to be improved were identified.

Afterwards, recommendations from the technical SEO audit were developed and implemented, the search engine's website authority and the relevant keywords resulting from keyword analysis were placed on the Drevenyprofil woodworking company website were created and improved.

Linkbuilding There were 229 backlinks to the website, but only 17 unique domains. To create backlinks, it was necessary to develop tactical steps to get backlinks.

Drevenyprofil backlinks were suggested to be obtained from strong "dofollow" authoritative sites and from various forums, blogs, "dofollow" and "nofollow" discussion forums to preserve the naturalness of the Drevenyprofil website profile. For Drevenyprofil website we suggested getting 5 backlinks a month.

After we implemented all activities, we compared the monitored metrics year-on-year.

While tracking the results of the SEO technical audit and Linkbuilding, we were interested in the organic traffic metrics in the last 3 months (January to March 2019) compared to last year (January to March 2018) and Drevenyprofil's company total turnover.

Tab. 3 Increase in organic traffic for the reporting period (January - March).

Month January February March

Organic website traffic (2018) 2707 2544 2728

Organic website traffic (2019) 2982 3156 3888

Increase in organic website traffic (%) 10.16 24.06 42.52

January 1, 2019 − March 31, 2019, we saw an increase in organic traffic by 25.65%.

The development of organic traffic was mainly visible at the end of the reporting period (March) when all external backlinks from the Linkbuilding strategy were indexed. The aim of increasing organic traffic were accomplished. Implemented technical SEO audit and active Linkbuilding had a positive impact on increasing organic traffic, and therefore we advised the client to continue actively in receiving backlinks.

Tab. 4 The total turnover of the woodworking company website Drevenyprofil.

Month January February March

Total turnover (2018) in €

Total turnover (2019) in €

11987.90 12180.32 11983.34

12891.93 14579.32 15930.46

Increase in total turnover in € 904.03 2399 3947.12

The total turnover for the first quarter we compared year-on-year. In March, sales increased by 3947.12 €, which was attributed to increased organic traffic and a focus on conversion and relevant keywords. The owner of the Drevenyprofil website was advised to take further steps to optimize the website, as we saw the potential in linkbuilding and other 158

SEO activities. We can evaluate search engine optimization as effective. Choosing relevant keywords had a positive impact on the overall turnover of Drevenyprofil woodworking company. The boosting organic traffic and overall website turnover were evaluated with Google Analytics application. The total turnover for the first quarter grew by 7250.15 € yearon-year, which is very beneficial for a medium-sized enterprise.

CONCLUSION€ € €€ In recent years, online advertising has become an integral part of large and small business marketing. Weak investment or absence in online marketing often results in a fall in turnover over competitors. Search engine optimization and focus on relevant and conversion keywords had a positive impact on the development of visits and the overall turnover of the woodworking company Drevenyprofil.

The assumption that an increase in the visits to the website of the woodworking company Drevenyprofil ensures the growth in turnover was confirmed.

The aim of an increase in organic traffic and in a turnover can be met through the selection of relevant keywords, technical optimization of the search engine website and active linkbuilding. We can identify search engine optimization as effective and meaningful for the future. Active linkbuilding strengthens the website domain. Thereby, the positions of not only selected keywords but of all the keywords on which the woodworking company Drevenyprofile's site is placed are improved.

Since the strategy was chosen correctly, we recommend the client for focusing on the next comparator sales channel. Comparators such as Heureka have competitor products that have a higher selling price than the selling price of Drevenyprofile's products. In this channel, we see the opportunity not only to increase the overall turnover of the Drevenyprofil website but also to make the brand more visible.

Optimization had a positive impact on the metrics under review, which proved to be effective and thus fulfilled the stated main aim.

Digital marketing methods can be effective in the case that enough attention is paid to it. Even with small changes to the website that are acceptable to search engines, it is possible to outperform your competitors to increase your sales or services offered.

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AUTHOR ̓ S ADDRESS Ing. Andrej Tomič Dr.h,c, prof. Ing. Mikuláš Šupín, CSc. Technical University in Zvolen Faculty of Wood Sciences and Technology Department of Marketing, Trade and World Forestry T. G. Masaryka 24 960 01 Zvolen Slovakia xtomic@is.tuzvo.sk supin@tuzvo.sk

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 61(2): 163−173, 2019 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2019.61.2.15

CONTROLLING IMPLEMENTATION: WHAT ARE THE BENEFITS AND BARRIES FOR EMPLOYEES OF WOOD PROCESSING ENTERPRISES? Mariana Sedliačiková – Zuzana Stroková – Josef Drábek – Denisa Malá ABSTRACT Controlling is an effective tool used to manage the future of an enterprise actively. Its implementation and enforcement is a long-term, difficult and complex process that is specific and inimitable for each enterprise. All internal stakekolders (owners, managers, employees) need to be prepared for the implementation and use of controlling in an enterprise, respecting the barriers and benefits of this management tool. The aim of the paper was to identify the most important financial and non-financial benefits and barriers affecting the employees of wood-processing enterprises in controlling implementation into business practice. The empirical research into the given issue was conducted in a form of questionnaire in Slovak wood-processing enterprises. In order to evaluate the research results, the descriptive, graphical and mathematic-statistical methods were used. Based on the research results, recommendations were formulated to highlight key financial and nonfinancial benefits, or barriers affecting employees in implementing controlling into business practice. On one hand, employees do not perceive controlling as a tool with financial benefits, but on the other hand, it represents a tool with improvement of activities with effect on cost reduction. They consider excessive control to be the most important barrier of this tool. The achieved results led to formulating and describing of three key phases of controlling implementation, which could be beneficial to owners and managers to eliminate key barriers of controlling implementation and enforcement, ensuring that controlling is fully operational and accepted by all stakeholders.

Key words: controlling, financial and non-financial benefits, barriers, wood-processing enterprises, employees.

INTRODUCTION Wood-processing industry in the Slovak Republic is relatively independent of importing the natural resources inputs, being built on a domestic resource base of sustainable character, and therefore it is able to permanently show active balance of foreign trade. In relation to the positive situation related to natural resources, their suitable geographic location, and their acceptable energetic demands for processing wood, wood-processing industry represents an important field of industry for the Slovak national economy, while thus enabling further development of small and medium enterprises (HAJDÚCHOVÁ et al.

2016). Wood-processing industry is composed of the wood, furniture, and cellulose-paper industries. These are based on processing wood, i.e. domestic ecological resource.

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According to VUKO and OJVAN (2013), JELAČIĆ et al. (2015) and TODOROVIĆ-DUDIĆ et al. (2017) managing business successfully in dynamic environment requires effective controlling system. Controlling is the process of defining objectives, planning and management control so that every decision maker can act in accordance with agreed objectives. Controlling function as a separate department contributes business efficiency trough ensuring transparency of business result and business processes. Controlling takes place when manager and controller cooperate. The role of controlling, not only financial, is to actively manage the future of the enterprise on the basis of information about its future development, including knowledge of past enterprise development (SEDLIAČIKOVÁ 2011).

Controlling as a tool of enterprise control subserve specified responsibilities and function like advisory, control and coordination (ŠATANOVÁ – POTKÁNY 2004).

According to SEDLIAČIKOVÁ (2018), psychological aspects of controlling define relations, feelings, opinions, or an imagination of people about controlling, while thus creating the base and foundations for establishing the real form of this tool. Realizing these factors enables more effective activity of the controller, and understanding the behaviors and feelings of the people involved. Between the controller, managers, and employees who are the recipients of the controller’s information and recommendations, there exist six psychological rules (aspects), which must be accepted and applied in the enterprise with regard to the effectiveness of its implementation and enforcement within the enterprise.

Among this belong: motivation, feedback, communication, building trust, enforcing, and change (WANICZEK 2002, ESCHENBACH 2004, ŠATANOVÁ et al. 2015).

According to KLEMENTOVÁ (2017) for the implementation and use of controlling in an enterprise, it is necessary to prepare all internal stakeholders, respecting the perception of barriers and benefits of this management tool. The perception of psychological factors is important specifically for employees, managers and enterprise owners. Successful implementation of controlling is also conditional on the positive direction of employees, which leads to more efficient performance, growth of economic result and fulfillment of financial plans.

According to SEDLIAČIKOVÁ et al. (2015) and JÁNSKÁ et al. (2017), the financial benefits of controlling implementation include mainly the growth of profit, enterprises ROI growth, and increased enterprise value. HAVLÍČEK (2015) and RATANOVÁ et al. (2011) highlight the non-financial benefits of controlling implementation such as improvement of processes performance with the effect on cost reduction.

The aim of the paper is to determine the key financial and non-financial benefits and barriers that affect employees of wood-processing enterprises related to controlling implementation into practice.

METHODOLOGY The research was focused on analyzing the financial and non-financial benefits and barriers that affect employees in implementing controlling into an enterprise. Data collection was carried out through a survey of wood-processing (WPI) enterprises in Slovakia. The contents of the first part of the questionnaire were sorting questions focused on the size of the business, the duration of the activity and the legal form of an enterprise. The second part of the questionnaire focused on general information of controlling, the most important financial and non-financial benefits and barriers to implementing controlling into an enterprise from the employees point of view.

The respondents were contacted electronically and by phone. The size of the research sample was determined using a mathematical relationship to calculate the minimum number 164

of respondents involved in the survey:

𝑛≥

(𝑧 2 ×𝑝×𝑞) ∆2

(1)

The minimum number of respondents in the formula is n; the coefficient of reliability is z; the variables p and q show the percentages of the respondents surveyed, who know or do not know the issue, or they prefer one or the other variation. The selection of respondents was purely random and their knowledge of controlling was not known, so it was necessary to divide the respondents set in half so that the product of p and q was maximal (50% to 50%). The value ∆ represents the maximum permissible significant error (KOZEL et al.

2006).

The value z = 2 was determined for higher research reliability (95.4%). The maximum error value for a representative sample was set at 5%. By substituting individual values into the formula, the minimum number of respondents for the reliability of research was determined by substituting individual values into the formula (KOZEL et al. 2006):

𝑛=

22 ×0,5×0,5 0,052

(2)

The survey was to consist of at least 400 respondents to research reliability. The questionnaire survey included 471 respondents out of total of 1,620 respondents (29.1%).

The research results were processed by the SPSS software. Via Friedman and Wilcoxon test hypotheses were tested: H1 = It was assumed that the controlling implementation into an enterprise has no financial benefit for employees.

The first hypothesis was formulated based on positive and negative employees´ attitudes towards controlling implementation as organizational change. Resistance come from employees who are generally skeptical of initiative change (REBEKA – INDRADEVI 2015). Resistance and fear prevents them to perceive financial benefits of implementing controlling, e.g. the growth of profit, enterprises ROI growth, and increased enterprise value (JÁNSKÁ et al. 2017). Successful organizational change requires top management a clear explanation of how the contemplated changes can help employees to do their job’s more efficiently and improve their carrier.

H2 = It was assumed that the improvement of activities with effect on cost reduction is the most significant non-financial benefit of implementing controlling into an enterprise.

The second hypothesis was formulated based on the claim that the most frequent nonfinancial benefit of controlling implementation is improvement of activities with effect on cost reduction (SHATALOVA et al. 2013).

H3 = It was assumed that excessive control is the most significant barrier of implementing controlling into an enterprise.

The third hypothesis was formulated based on research results, which showed that more than 50% of employees expressed concerns with implementing controlling due to excessive control from the top management, fear of not fulfilling the norms and worsening relationships in the workplace (SEDLIAČIKOVÁ et al. 2017).

RESULTS AND DISCUSSION The first part of the questionnaire focused on the characteristics of an enterprise. As to the size of enterprise, 61% micro and 34% small enterprises participated in the research.

Medium enterprises represented 3%, and large enterprises 1% of the sample. As to the 165

market duration, 36% of respondents operated on the market for over 15 years, 25% enteprises operated less than fifteen years and 25% enterprise less than five years.

Enterprises operating in the market for less than one year represented 18%. Limited liability enterprises, joint-stock enterprises and self-employed were most represented to the legal form of enterprise.

The second part of the questionnaire survey focused on general questions related to controlling, financial and non-financial benefits and barriers of implementing controlling into an enterprise. Approximately 49% of the respondents said they were active in enterprises where controlling is not implemented. A positive signal is that 31% of employees said they were operating in enterprises which planning to implement this complex management system and 14% of employees work in enterprises with controlling. In the future, we can expect a positive increase in the number of enterprises that are beginning to realize the importance of controlling.

In the case of the financial benefits of implementing controlling, respondents had a choice of five activities, where they expressed their opinion on each of them through a 3grade rating scale. Figure 1 shows that for 72% of employees, the implementating controlling into an enteprise has no financial benefit. The graphic evaluation is connected with the evaluation of H1 statistical hypthesis.

72%

72%

68%

55% 48%

43%

51%

30% 23%

22% 6%

2% Yes

No

I do Yes not know

Enterprise value growth

No

I do Yes not know

Enterprise result increase

No

I do Yes not know

Direct wage increase

5%

3%

1% No

I do Yes not know

No

I do not know

Profitability growthNo-financial benefit

Fig. 1 Financial benefits of controlling.

According to the results presented in Table 1, it can be stated that these options are not equally significant (p-level = 0.000). Using the Wilcoxon test, the order of significance of each option was determined. Since the p-level (0.000) is lower than the chosen level of significance α, it can be stated that according to employees the implementing controlling into an enterprise has no financial benefit. Based on these results, the H1 hypothesis was confirmed.

In the case of determining the most significant non-financial benefits, respondents had a choice of seven options, where they could express their opinion on each of them using a 3grade rating scale. Figure 2 shows that 78% employees consider the impovement of activities with effect on cost reduction as the most significant non-financial benefit of implementing controlling into an enterprise. Other non-financial benefits, such as detecting deviations, checking the achievement of set goals, or increasing labour productivity, are roughly at the 166

same level. The graphical evaluation of the significance of non-financial benefits is closely related to the evaluation of H2 statistical hypothesis.

Tab. 1 Friedman and Wilcoxon test of H1 hypothesis.

Friedman test N

165

Chi-Square

112.569

Df

4

Asymp. Sig.

.000

Wilcoxon test Financial FB1–FB2 FB3–FB1 FB4–FB3 FB5–FB4 benefits1 Z -1.444b -2.538b -1.373b -4.555b Asymp. Sig. .149 .011 .170 .000 (2-tailed) a. Wilcoxon Signed Ranks Test b. Based on negative ranks. c. Based on 10000 sampled tables with starting seed 743671174.

78% 61%

76%

69%

68%

66%

38% 28%

20%

Yes

No

I do Yes not know

Clarity of information needed for controlling

No

33%

28%

31% 18%

4%

2%

1%

66%

I do Yes not know

No

3%

I do Yes not know

No

I do Yes not know

Improvement of Checking the Detecting activities with achievement of deviations using effect on cost the set objectives measurable reduction at all enterprise indicators levels

No

I do Yes not know

Labour productivity growth

6%

3%

2% No

I do Yes not know

Higher process quality

No

I do not know

No benefit

Fig. 2 Non-financial benefits of controlling.

The results of Friedman test (Table 2) point out that these options are not equally important (p-level = 0.000). Subsequent use of the Wilcoxon test determined the order of significance of each option. Since the p-level (0.032) is lower than the chosen level of significance α, it can be stated that according to employees the impovement of activities with effect on cost reduction is the most significant non-financial benefit of implementing controlling into an enteprise. Based on these results, the H2 hypothesis was confirmed.

The addressed employees consider excessive control as the most important barrier of implementing controlling into an enteprise. They fear that by implementing a complex management system, they will lose their position, change working relationships, and need further education. Employees consider the inability to carry out new activities as the least significant barrier. Despite fears of further education, they are not afraid of their eventual failure. The graphical evaluation (Figure 3) of the most significant barriers of implementing controlling into an enterprise is related to the evaluation of the H3 statistical hypothesis.

FB1-enterprise value growth, FB2-enterprise result increase, FB3-direct wage increase, FB4-profitability growth, FB5-no financial benefit.

1

167

Tab. 2 Friedman and Wilcoxon test of H2 hypothesis.

Friedman test N

169

Chi-Square

174.255

Df

6

Asymp. Sig.

.000

Wilcoxon test Non-financial NF1– NF3– NF4– NF5– benefits2 NF2 NF1 NF3 NF4 Z -2.142b -.218b -1.043b .000d Asymp. Sig. .032 .827 .297 1.000 (2-tailed) a. Wilcoxon Signed Ranks Test b. Based on negative ranks. c. Based on 10000 sampled tables with starting seed 92208573. d. The sum of negative ranks equals the sum of positive ranks.

NF6– NF5 -1.444b .149

87% 69% 57% 28%

57%

40%

41%

31%

10% 3%

3%

Excessive control

Loss of current job position

3% Lower earnings

64%

63%

6%

2%

34%

2%

Inability to The need for Worsening carry out new further working acitivities education relationships

Yes

No

51% 44%

57% 40%

5%

4%

Change in corporate culture

Possible competition (new employees)

52% 47%

2% I have no concerns

I do not know

Fig. 3 The most significant barrier of controlling.

The use of Friedman test revealed that all options are not equally important (p-level = 0.000). Wilcoxon test showed that p-level (0.000) is lower than the chosen level of significance α, which means that employees consider excessive control to be the most significant barrier of implementing controlling into an enterprise. The H3 statistical hypothesis was confirmed.

After summarizing and then evaluating the questionnaire survey, it can be stated that 49% employees work in wood-processing enterprises in which controlling is not implemented. The trend of inmplementing controlling into an enterprise is not so popular in the Slovak Republic as in the countries of Western Europe. The positive signal is that more and more enterprises are planning to implement this complex management system to gain greater control over their activity. Increasing interest of implementing controlling or controlling instruments confirmed the further research. According to MIŠÚN (2017) changes are implemented and move from the largest enterprises to medium and later to smaller ones.

The aim of the research was to found out if new controlling tools, methods and procedures were introduced in the respondent enterprise. From sample 120 respondents (36.25%) answered positively and 210 negatively (63.44%).

NF1-clarity of information needed for controlling, NF2-impovement of activities with effect on cost reduction, NF3-checking the achievement of the set objectives at all enterprise level, NF4-detecting deviations using measurable indicators, NF5-labour productivity growth, NF6-higher process quality.

2

168

Tab. 3 Wilcoxon and Friedman test of H3 hypothesis.

Friedman test N Chi-Square Df Asymp. Sig.

148 101.447 8 .000

Barriers3 Z Asymp. Sig. (2tailed)

Wilcoxon test B1–B2 B3–B1 -4.648b -.906b .000

.365

B4–B3 -.216d

B5–B4 -1.444b

.829

.149

B6–B5 B7–B6 B8–B7 Z -4.648b -.906b -.216d Asymp. Sig. (2.000 .365 .829 tailed) a. Wilcoxon Signed Ranks Test b. Based on negative ranks. c. Based on 10000 sampled tables with starting seed 562334227. d. Based on positive ranks.

B9–B8 -1.444b .149

With the implementing controlling, many changes are coming to an enteprise, which can also cause some concern about this system. For this reason, the aim of the questionnaire survey was to find out what financial and non-financial benefits and barriers are seen by employees in controlling. The results of the questionnaire survey showed that employees do not see any financial benefit in controlling implementation; on the contrary, controlling for them constitutes the improvement of activities with effect on cost reduction. The findings are consistent with the results of the survey according to SEDLIAČIKOVÁ et al. (2018). It should be noted that while 72% of employees do not see any financial benefit in implementing controlling (confirmed by the H1 hypothesis), the same percentage perceives an increase in enterprise result as a significant financial benefit, which will ultimately be reflected in the compensation system. According to WRUCK (2001) behavioral changes on the parts of individuals are required for organizational change, and compensation systems affect behavior. Thus, it is critical to consider the role that compensation systems play in the process of organizational change and why establishing a strong, positive relation between rewards and performance is critical to bringing about value-creating organizational change.

Employees consider excessive control to be the most significant barrier of controlling implementation. According to ČAMBALÍKOVÁ and MIŠÚN (2017) command-and-control techniques are no longer enough in competitive in competitive environments where creativity and employee initiative are critical to business success. Their research has shown that the respondents with negative attitude while they are being controlled mentioned the lack of trust, lack of information, poor cooperation and great time consumption. Respondents who have a neutral attitude while they are being controlled understand the need of control and they take it as a natural part of processes. A proper control can have a positive effect and improve the state of things and they can also get some feedback to learn by their own mistakes. Respondents with a positive attitude to the control declared that it can help them to achieve the goals and plans, to increase the sense of responsibility and motivation and it can be beneficial to their professional growth. VERBURG et al. (2018) add controls may enhance employee performance both directly and through enhanced trust. This suggests that the link between control systems and trust is sensitive and related to the way in which behavior is controlled.

The fear of excessive control is to some extent justified and predictable. Employees B1-excessive control, B2-loss of current job position, B3-lower earnings, B4-inability to carry out new activities, B5-need for further education, B6-worsening working relationships, B7-change in corporate culture, B8-possible competition (new employees), B9-no concerns.

3

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can feel less freedom, which can result in workplace conflicts. Employees are also worried about losing their current job positions due to a lack of skills or knowledge. This concerns can be avoided by properly informing employees about the changes to be made to the enterprises. The results are consistent with findings of authors BENABOU et al. (2012) and DEGEEST et al. (2017). According the authors, if there is insufficient employee awareness at all levels at the workplace and communication is abstaining, this can lead to worsening the working relationships at workplaces.

The research focusing on the psychological factors affecting employees in the implementation and enforcement phase in an enterprise shows that controlling is not a common managemen tool. Controlling will be fully functional in the enterprises when the psychological aspect of its implementation is systematically addressed, based on the partnership position of internal stakeholders in an enterprise, on mutual communication and discussion. Very important is the timely awareness of the planned changes by managers and owners, so that workers do not create their own conclusions and attitudes based on partial information that has penetrated the lower hierarchical levels of an enterprise, thus creating a distorted picture of upcoming changes (KLEMENTOVÁ - SEDLIAČIKOVÁ 2017, KLEMENTOVÁ et al. 2017).

MINÁROVÁ et al. (2015) add that emotional intelligence may help owners and managers solve problems by using logic and emotions, be more flexible in changing conditions, help colleagues at the workplace express their needs, think and respond to problematic employees with consideration, maintain positive and optimistic attitude, and constantly learn how to improve themselves, as well as their relations at the workplace, which is fundamental for success of the enterprise.

With implementing controlling system into the business practice of wood-processing enterprises, it is important to ensure that it consists of at least three phases ledding to stakeholders´ preparation for change management. In the pre-implementation phase, it is necessary to set the main objective of controlling with focus on long-term viability of the enterprise. Following the main objective, management needs to conduct an in-depth analysis of the current situation in order to detect management weaknesses. The main task of the top management is also to choose the most suitable way of implementing the controlling, while implementation within individual departments seems to be the most reliable way in view of the employees' concerns. It is also necessary to have a controller who will manage the entire implementation process, ensure its smooth functioning and inform the top management in a timely manner of any deviations. The next step is to select the adequate control software that is the choice between professional control software and Microsoft Excel-based software support. The implementation of controlling also entails a change in the employee motivation system and the need to inform them of upcoming changes in order to avoid conflicts and misunderstandings. The role of the controller should also be to familiarize employees with the benefits of controlling, which could contribute to a succesfull process of implementing controlling and creating a positive working atmosphere. During the control implementation phase, the controller is responsible for ensuring rational distribution of activities between individual departments or to entrust this task to the heads of individual departments. Within this phase, the competencies of the individual employees are reviewed, the position of which may be different in the innovated organizational structure compared to the original one. After determining and allocation tasks, competences and responsibilities between employees, they are trained with regard to new conditions. The situation may arise where some working positions will require a higher degree of education or change management lead to the creation of new positions with the need for additional training of current employees. As the next step, controll software is modified by the supplier to include updated information from the performed analyses, including information provided by the top management and 170

controller, respectively all internal data from originally used programs is imported into the software. For the smooth implementation of controlling, it is necessary to reassess and innovate the way of communication between individual departments and the top management.The final step of the implementation phase of the controlling is the application of the trial version of the controlling into a particular enterprise area. The top management and the controller observe empoloyees´ responses and feelings connected with implementing controlling and detect any deviations that could not be predicted in advance. In this step, cooperation of all stakeholders is essential. The final phase is associated with the elimination of errors and deviations in the trial version of the controlling implementation. The role of the controller is to carry out an in-depth control to detect errors and to set out variant solutions to prevent their reoccurrence. The controller is responsible for informing management of the results of in-depth analysis and their impact on the enterprise. Its role is to make suggestions to the management with an emphasis on areas that need to be improved for the smooth running of controlling. The enterprise´s management should, after consultation with the controller, inform employees of the results and prepare them for the gradual extension of control activities to multiple areas. The final version of controlling implementation is its introduction into the whole enterprise, in which it has its unique position and creates a complex management system. The whole process of implmenting controlling is completed by its active use in an enterprise. The use of controlling in an enterprise should be succesfull, positive perceived and respected by employees by following all the previous steps.

SEDLIAČIKOVÁ (2018) is also in favor of dividing the process of controlling implementation into several successive phases. She emphasizes the need to communicate ideas and changes with employees during all phases, as employees will ultimately be the ones who will use this management tool.

CONCLUSION Controlling as such does not have a very large representation in the territory of the Slovak Republic. Many enterprises perceive this system only as a control system. However, controlling can be understood as a process of management and coordination aimed at supporting the management not only of the enterprise but also of management in the planning and implementation of business activities. Controlling has come to us from Western Europe, where its use is commonplace.

The issue of controlling and the psychological aspects affecting the enterprise employees during its implementation is a very current and quite extensive topic. It is necessary to look at controlling not only in economic terms in the context of its financial and non-financial benefits, but also psychological. By combining these two sciences, it is possible to create conditions in an enterprise that will have a positive impact on all stakeholders.

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ACKNOWLEDGEMENT The paper has been written as a partial result of the project VEGA No. 1/0010/17 and projects APVV18-0520, APVV-18-0378, APVV-17-0456 and APVV-17-0583.

ADDRESSES OF THE AUTHORS doc. Ing. Mariana Sedliačiková, PhD. doc. Ing. Josef Drábek, CSc. Ing. Zuzana Stroková, PhD. Technical University in Zvolen Department of Economics, Management and Business T. G. Masaryka 24 960 01 Zvolen Slovakia sedliacikova@tuzvo.sk drabek@tuzvo.sk strokova@tuzvo.sk doc. Ing. Denisa Malá, PhD. Matej Bel University in Banská Bystrica Department of Corporate Economics and Management Tajovského 10 975 90 Banská Bystrica Slovakia denisa.mala@umb.sk

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