ACTA FACULTATIS XYLOLOGIAE ZVOLEN 65 2/2023

ACTA FACULTATIS XYLOLOGIAE ZVOLEN

VEDECKÝ ČASOPIS SCIENTIFIC JOURNAL

65 2/2023

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 lignocelu-lózových 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.

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 lignocellulosic 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 DREVÁRSKEJ FAKULTY, TECHNICKEJ UNIVERZITY VO ZVOLENE 65 2/2023 SCIENTIFIC JOURNAL OF THE FACULTY OF WOOD SCIENCES AND TECHNOLOGY, TECHNICAL UNIVERSITY IN ZVOLEN 65 2/2023 Redakcia (Publisher and Editor’s Office): Technická univerzity vo Zvolene (Technical university in Zvolen); TUZVO Drevárska fakulta (Faculty of Wood Sciences and Technology) T. G. Masaryka 2117/24, SK-960 01 Zvolen, Slovakia Redakčná rada (Editorial Board): Predseda (Chairman): prof. Ing. Ján Sedliačik, PhD., TUZVO (SK) Vedecký redaktor (Editor-in-Chief): prof. Ing. Ladislav Dzurenda, PhD., TUZVO (SK) Členovia (Members): prof. RNDr. František Kačík, DrSc., TUZVO (SK) prof. RNDr. Danica Kačíková, MSc. PhD., TUZVO (SK) prof. Ing. Jozef Kúdela, CSc., TUZVO (SK) prof. Ing. Ladislav Reinprecht, CSc., TUZVO (SK) prof. Ing. Mariana Sedliačiková, PhD., TUZVO (SK) prof. Ing. Jozef Štefko. CSc., TUZVO (SK) doc. Ing. Hubert Paluš, PhD., TUZVO (SK) Jazykový editor (Proofreader): Mgr. Žaneta Balážová, PhD. Technický redaktor (Production Editor): Ing. Michal Dudiak, PhD. Medzinárodný poradný zbor (International Advisory Editorial Board): Bekhta Pavlo (Ukrainian Natl Forestry Univ, Ukraine), Deliiski Nencho (University of Forestry, Bulgaria.), Jelačić Denis (Univ Zagreb, Croatia), Kasal Bohumil (Tech Univ Carolo Wilhelmina Braunschweig, Germany), Marchal Remy (Arts & Metiers ParisTech, France), Muhammad Adly Rahandi Lubis (Kyungpook National University, Indonesia), Németh Róbert (Univ Sopron, Hungary), Niemz Peter (Bern Univ Appl Sci, Architecture Wood & Civil Engn, Switzerland), Orlowski Kazimierz A.(Gdansk Univ Technol, Poland), Pohleven Franc (Univ Ljubljana, Slovenia), Rogoziński Tomasz (UPP Poznań), Teischinger Alfréd (Univ Nat Resources & Life Sci, BOKU, Austria), Smardzewski Jerzy (Poznan Univ Life Sci, Poland), Vlosky Richard P. (Louisiana State Univ, USA), Wimmer Rupert (Univ Nat Resources & Life Sci, Austria).

Vydala (Published by): Technická univerzita vo Zvolene, T. G. Masaryka 2117/24, 960 01 Zvolen, IČO 00397440, 2023 Náklad (Circulation) 80 výtlačkov, Rozsah (Pages) 165 strán Tlač (Printed by): Vydavateľstvo Technickej univerzity vo Zvolene Vydanie I. – december 2023 Periodikum s periodicitou dvakrát ročne Evidenčné číslo: 3860/09 Acta Facultatis Xylologiae Zvolen je registrovaný v databázach (Indexed in): Web of Science, SCOPUS, ProQuest, AGRICOLA, Scientific Electronic Library (Russian Federation), China National Knowledge Infrastructure (CNKI) Za vedeckú úroveň tejto publikácie zodpovedajú autori a recenzenti. Rukopis neprešiel jazykovou úpravou.

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 (print) 1336–3824, ISSN (online): 2730-1176

CONTENTS 01. MICHAL DUDIAK: DENSITY OF BEECH (Fagus sylvatica L.) WOOD THROUGH A CROSS-SECTION OF THE TRUNK ...................................

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02. EVA VÝBOHOVÁ – ANNA OBERLE: CHEMICAL CHARACTERISATION OF EUROPEAN BEECH (Fagus sylvatica L.) MATURE WOOD AND FALSE HEARTWOOD.........................................

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03. ALENA PÁRNIČANOVÁ – MARTIN ZACHAR – DANICA KAČÍKOVÁ – LUCIA ZACHAROVÁ: DETERMINATION OF CHARRING RATE OF OAK WOOD ...........................................................

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04. OLENA PINCHEVSKA – KOSTYANTYN LOPATKO – LARYSA LOPATKO – ROSTISLAV OLIYNYK – JÁN SEDLIAČIK: THE EFFECT OF METAL NANOPARTICLES ON FORMALDEHYDE EMISSION FROM WOOD BASED MATERIALS ......................................

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05. ADI SANTOSO – JAMALUDIN MALIK – JAMAL BALFAS – MUHAMMAD ADLY RAHANDI LUBIS – DEAZY RACHMI TRISATYA – ERLINA NURUL AINI – ACHMAD SUPRIADI – ROHMAH PARI – MAHDI MUBAROK – JÁN SEDLIAČIK – PAVLO BEKHTA – ĽUBOŠ KRIŠŤÁK: ENHANCING THE QUALITY OF PALM VENEER WITH OIL PALM BARK EXTRACTRESORCINOL-FORMALDEHYDE RESIN IMPREGNATION .................

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06. ANASTASIA EVDOKIMOVA – MIKHAIL CHERNYKH – MAXIM GILFANOV – VLADIMIR STOLLMANN: AUTOMATION OF TEMPLATE CORRECTION ALGORITHM FOR QUALITY IMPROVEMENT OF PSEUDO-3D ENGRAVED IMAGES .......................

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07. KRASIMIRA ATANASOVA – DIMITAR ANGELSKI: ROUGHNESS PARAMETERS OF BIO-BASED COATING APPLIED TO WOOD SURFACES ....................................................................................................

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08. VALENTIN ATANASOV – GEORGI KOVATCHEV – TIHOMIR TODOROV: STUDY OF THE INFLUENCE OF BASIC PROCESS PARAMETERS ON THE ROUGHNESS OF SURFACES DURING MILLING OF SCOTS PINE WOOD .............................................................

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09. ALEKSANDAR DOICHINOV: OPTIMIZATION OF THE CNC MILLING PROCESS VIA MODIFYING SOME PARAMETERS OF THE CUTTING MODE WHEN PROCESSING MDF WORKPIECES ....................

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10. ANDRIY PAVLUK – SVYATOSLAV GOMON – YURIY ZIATIUK – PETRO GOMON – SVIATOSLAV HOMON – LEONID KULAKOVSKYI – VOLODYMYR IASNII – OLEH YASNIY – NATALIIA IMBIROVYCH: STIFFNESS OF SOLID WOOD BEAMS UNDER DIRECT AND OBLIQUE BENDING CONDITIONS ...................

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11. PAVOL GEJDOŠ – JARMILA SCHMIDTOVÁ – KRZYSZTOF KNOP: COMPARISON OF THE ATTRIBUTES OF THE WOOD PROCESSING INDUSTRY AND AUTOMOTIVE AND ENGINEERING INDUSTRIES IN THE CONTEXT OF QUALITY MANAGEMENT SYSTEMS ........................

123

12. MILOŠ HITKA – LENKA LIŽBETINOVÁ – PAVLA LEJSKOVÁ – EVA NEDELIAKOVÁ – MACIEJ SYDOR: DIFFERENCES IN EMPLOYEE MOTIVATION IN WOOD-PROCESSING ENTERPRISES IN SELECTED COUNTRIES OF CENTRAL EUROPE ..............................

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13. NATÁLIA POLÁKOVÁ – MARIANA SEDLIAČIKOVÁ – JARMILA SCHMIDTOVÁ: THE USE OF CONTROLLING IN WOODWORKING AND FURNITURE FAMILY BUSINESSES: EVIDENCE FROM SLOVAKIA ....................................................................................................

149

14. MIKULÁŠ ŠUPÍN: LAUDATIO FOR Dr. h. c. prof. Ing. MIKULÁŠ ŠUPÍN, CSc. ...................................................................................................

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 5−11, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.01

DENSITY OF BEECH (Fagus sylvatica L.) WOOD THROUGH A CROSS-SECTION OF THE TRUNK Michal Dudiak ABSTRACT Differences in the density of beech wood in an absolutely dry state in individual zones: sapwood, mature wood, and false heartwood through a cross-section of the trunk are presented in the paper. The wood density of individual zones was determined with a digital density meter. Experimental measurements and subsequent statistical processing of the measured values showed that the density of beech samples with a false heartwood has a decreasing tendency through the cross-section of the trunk from the center of the trunk to the edge. The highest density ρ0 = 703.8 ± 36.1 kg.m-3 was observed in the dry state of beech samples with false heartwood. The density of mature wood in the absolutely dry state was 5.5% less compared to false heartwood, and the density of sapwood was 13.6 % less compared to false heartwood. The proven differences in the density of absolutely dry beech wood in the individual zones do not exceed the natural range of the density values of the beech wood (Fagus sylvatica L.) mentioned in the professional literature. For the above reason, it is not necessary to take into account the changes in the density of the wood through the cross-section of the trunk in common technical applications. The presented data contribute to the objectification of information about the properties of beech wood and enrich current knowledge.

Keywords: density wood; beech wood; sapwood; mature wood; false heartwood.

INTRODUCTION European beech is a native tree of European forests. There are two species of beech on the European continent: Fagus sylvatica L. (from England and Sweden through WestCentral-South-South-East Europe to the Balkans) and Fagus Orientalis (from the eastern part of the Balkan Peninsula through the Caucasus to Asia Minor) with very similar properties.

The wood of Fagus sylvatica L. belongs to the scattered-porous coreless woods with the possibility of forming a false heartwood. Sapwood and mature beech wood are mediumheavy, flexible, and easily split. It has good mechanical properties, it is plasticized, bent and machined very well. Its high permeability makes it well impregnated, stained and dyed.

Beech wood is used to manufacture furniture, floors, sports equipment, toys and small household items. Sapwood and mature beech wood have a light white-gray color with a yellow tinge (Klement et al., 2010, Dzurenda and Dudiak 2020.

A false heartwood beech is a growth defect that results from air-wood reactions in the mature wood zone. The color of the false heartwood beech is brown with a more or less 5

saturated shade. The primary cause of a false heartwood is injury to the trunk or branches of the tree, which allows air to enter the tree trunk. The oxygen contained in the air causes the oxidation of soluble carbohydrates and starch (contained in living or partially dead parenchymal cells), resulting in the formation of brown-colored polyphenolic compounds that penetrate into the neighboring tissues and color them (Bauch and Koch 2001, Račko and Čunderlík 2010).

According to the appearance of the false heartwood in the tree trunk and its shape on the cross-section of the trunk, the false heartwood is divided into: Round, Mosaic Stars, Flames (eccentric, centric) (Mahler and Höwecke 1991).

Compared to sapwood in a growing tree, mature wood and wood with false heartwood have a lower moisture content (Sachsse 1967, Torelli 1984, Kúdela and Čunderlík 2012) and according to the work of (Babiak et al., 1990) lower permeability for liquids.

Wood density is one of the fundamental physical properties of wood, which is considered a basic indicator of wood quality (Wagenführ 2000, Bectaş et al., 2002, Mišíková 2006). The density of wood is influenced by factors such as the conditions of tree growth, the elemental composition of wood, or the position in the tree trunk (Janota and Kurjatko 1978, Govorčin et al., 2003, Gryc et al., 2008).

The aim of the work was to determine the density of dry beech wood in the zone of sapwood, mature wood and false heartwood, to compare the differences between the densities of wood through the cross-section of the trunk and to analyze their causes.

MATERIAL AND METHODS Material 34 trees with healthy false heartwood were selected for research from stands in the locations Štiavnické vrchy and Poľana, Slovakia. By transversal manipulation, a 1.2 m long cutout was made from the territorial part of each tree. By spreading out the central lumber with a thickness of h = 50 mm, blanks with a thickness of h = 32 mm were made (Fig. 1b).

Determination of density and color of samples The density of sapwood beech was determined on wood samples made from blanks located on the edge of the center log. The density of beech mature wood was determined on wood samples made from blanks lying in front of the boundary line of the false heartwood in the central timber, and the density of beech wood of false heartwood was determined on wood samples made from blanks lying in the zone of false heartwood. Subsequently, the blanks were dried using the low-temperature drying mode of Dzurenda (2022) in a conventional hot air dryer to a moisture content of w = 12 ± 0.5%, with an emphasis on preserving the original color. The bedding surfaces of the dried blanks were machined on a FS 200 horizontal plane milling machine.

To verify the correctness of the classification of the blanks into the groups of wood from the zone of sapwood, mature wood and false heartwood, the color of dry wood on the planed surface was measured with a colorimeter Color reader CR-10 (Konica Minolta, Japan). The measured values were verified with the values of the color of beech sapwood, mature wood and false heartwood on the coordinates of the CIE L*a*b* color space obtained

by Dzurenda et al. (2023) and given in Table 1.

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Tab. 1 The color of the beech wood zones in the CIE L*a*b* color space (Dzurenda et al., 2023).

Color space coordinates CIE L*a*b* L* a* b* 82.4 ± 1.9 8.1 ± 1.5 19.1 ± 1.6 78.9 ± 2.4 7.6 ± 1.7 18.9 ± 1.9 64.9 ± 4.9 12.9 ± 2.1 19.6 ± 1.7

Zones of beech wood Sapwood Mature wood False heartwood

Chrome C* 20.7 ± 1.7 20.4 ± 1.9 23.5 ± 1.8

Samples for density determination were made from the wood of blanks from the sapwood zone, mature wood and false heartwood with dimensions: thickness h = 40 mm, width w = 40 mm and length l = 100 mm. b

a

Fig. 1 a) view of the frontal section of the beech section, b) view of the milled beech wood with a proposal for sawing.

Determination of the density of dry beech wood Before measuring the density, the manufactured test bodies of the individual groups were dried at a temperature of t = 103 ± 2 °C to a constant weight in a laboratory oven (MEMMERT UM110m, Niedersachsen, Germany). After drying, the samples were placed in a desiccator, and then, after cooling, the wood density was measured.

Determination of the density of beech samples of sapwood, mature wood and false heartwood in the dry state was carried out using a digital density meter: Set for determining the density of solid substances KIT 128 from the company Radwag (Poland) (Fig. 2) working on the principle of Archimedes' law.

Fig. 2 Measurement of the density of beech wood samples.

The density of sapwood, mature wood, and false heartwood samples was calculated using the equation: m

m

0

0 ρH o .g 2

m

ρ0 = 𝑉 0 = m0 – 0m ∗ = (m − 0m ∗ ) . (ρH2o . g) [kg. m−3 ] 0

0

Where: m0 – weight of dry sample [kg], 7

(1)

V0 – dry sample volume [m3], m0∗ – weight of a dry sample immersed in distilled water [kg], ρH2 o – density of distilled water at atmospheric pressure and temperature t = 14.5°C, g – 9.81 m.s-2 the gravitational acceleration of the Earth.

The density meter has built-in software that automatically determines the wood density from the data measured and confirmed by the operator, it is compatible with the computer software Excel 2019, which transfers and records in a table all the entered and measured density data of the given wood sample (Dudiak (2021).

Statistical processing of measured data From the measured density data across the width of the trunk in individual zones, i.e., zone of sapwood, mature wood and false heartwood of beech, graphic dependences of the density distribution of beech wood through the width of the trunk were determined using the program Statistica 12 (V12.0 SP2, USA). With the help of statistical methods of evaluation using t-test and analysis of variance (ANOVA), it was evaluated whether there is a relationship between individual groups of samples and the determination of the size of the level of significance through the p-value. Program processing of the measured results partially eliminated the influence of measurement errors caused by the heterogeneity of wood and the method of measuring wood density.

RESULTS AND DISCUSSION The density values of beech wood in individual zones (sapwood, mature wood and false heartwood) evaluated using statistical methods are shown in Table 2.

Tab. 2 Statistical evaluation of measured density data of absolutely dry beech wood.

Number of measurements n

Average value ρ0 [kg.m-3]

Standard deviation sx [kg.m-3]

ρ0 +95.00 %

ρ0 -95.00 %

Significance level (p-)

30

608.2

23.8

632.0

584.4

0.000a

30

665.2

30.5

695.7

634.7

0.000a

30

703.8

36.1

739.9

667.7

0.000a

60

608.2 & 665.2

23.8 & 30.5

632.0 & 695.7

584.4 & 634.7

0.000 a

60

608.2 & 703.8

23.8 & 36.1

632.0 & 739.9

584.4 & 667.7

0.004 a

MW & FHW 60 665.2 & 703.8 Note: a statistically significant effect (p < 0.05).

30.5 & 36.1

695.7 & 739.9

634.7 & 667.7

0.362

Zones of beech wood Sapwood (SW) Mature wood (MW) False heartwood (FHW) SW & MW SW & FHW

The results of the statistical processing of the measured values of the densities of dry beech wood showed the differences in the density of the wood in the absolutely dry state through the cross-section of the trunk. The density of wood decreased from the center to the edge through the cross-section of the trunk. The difference between the density in the absolutely dry state of false heartwood and mature wood was about ∆ρ0 = 38.6 kg.m-3 (∆ρ0 = 5.5%) and between false heartwood and sapwood was about ∆ρ0 = 95.6 kg.m-3 (∆ρ0 = 13.6 %).

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The average values of the density of beech wood in individual zones are shown graphically in Fig. 3.

Fig. 3 Measured values of the density of individual zones of beech wood.

The reasons for the different density of beech wood in individual zones are: a) The density of sapwood beech in an absolutely dry state is formed by cell walls of libriforous fibers, blood vessels, parenchymatic cells and air in the lumens of these structural elements of wood matter (Čunderlík 2009); b) The higher density of mature beech wood than the density of sapwood is caused by the following factors: - lignification of cell walls, as stated by the authors Nečesaný (1958), Požgaj et al. (1997), and Čunderlík (2009); - filling of vessel lumens with tyle (Brown et al., 1952, Chovanec and Korytárová 1989, Babiak et al., 1990, Čunderlík 2009); c) An increase in the density of beech wood with a false heartwood compared to mature wood is also caused by the presence of nuclear substances formed by biochemical processes during the formation of the false heartwood (Jacenko-Chmelevskij 1954, Nečesaný 1958, Bauch and Koch 2001, Čunderlík 2009, Račko and Čunderlík 2010).

The difference between the wood densities of false heartwood and mature wood was not significant, which is documented by the approximate agreement of the minimum value of the density of false heartwood and the average values of the density of mature wood, or maximum values of mature wood density and average values density of false heartwood.

The values of the densities of beech samples in individual zones through the crosssection of the trunk are within the interval of the range of natural variability of the density of beech wood 490-880 kg.m-3 reported in (Regináč et al., 1990, Požgaj et al., 1997, Molnár et al., 2001, Makovíny 2010, Gryc et al., 2008, Kuriatko et al., 2010, Klement et al., 2010, Dzurenda and Dudiak 2020). From the above, it follows that the presented values of the densities of the analyzed samples of beech wood do not need to be taken into account in technical applications in the construction industry, in the production of furniture, or in construction and carpentry products.

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The presented values of the densities of dry beech sapwood, mature wood and false heartwood supplement the current hints about the properties of beech wood and contribute to the objectification of information about beech wood.

CONCLUSION The article presents the values of the density of beech wood in an absolutely dry state in individual zones: sapwood, mature wood, and false heartwood through a cross-section of the trunk. The average values of the density of beech wood decrease through the crosssection from the center of the trunk to its circumference. Sapwood beech has the lowest average value in the dry state ρ0 = 608.2 kg.m-3. The average value of dry mature beech wood is ρ0 = 665.2 kg.m-3, which is ∆ρ0 = 57.0 kg.m-3 higher than that of sapwood, and the density of wood with a false heartwood ρ0 = 703.8 kg.m-3 is ∆ρ0 = 95.6 kg.m-3 higher than sapwood.

The reasons for the increase in the density of mature beech wood and false heartwood are the lignification of the cell walls, the siltation of the lumens, and, in the case of false heartwood, the formation of nuclear substances in the false heartwood during the growth of the tree.

The proven differences in the density of absolutely dry beech wood in individual zones do not exceed the natural range of beech wood density values reported in the professional literature, and therefore it is not necessary to take into account the change in wood density through the cross-section of the trunk separately in common technical applications. The presented data contribute to the objectification of knowledge about the properties of beech wood, and the current ones enrich and expand them.

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ACKNOWLEDGMENT This experimental research was prepared within the grant project: VEGA 1/0256/23 Research on the sapwood and the false heartwood of Beech wood for the purpose of eliminating the differences in the color of the wood by steaming with saturated water steam and also the support of the APVV grant agency within the framework of the APVV 21-0051 project.

AUTHOR ADDRESS Michal Dudiak Technical University in Zvolen T. G. Masaryka 24 960 01 Zvolen, Slovakia xdudiak@tuzvo.sk 11

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 13−23, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.02

CHEMICAL CHARACTERISATION OF EUROPEAN BEECH (Fagus sylvatica L.) MATURE WOOD AND FALSE HEARTWOOD Eva Výbohová – Anna Oberle ABSTRACT False heartwood in European beech (Fagus sylvatica L.) is a significant defect reducing the usability of the wood for aesthetic reasons. The aim of this work was to compare the chemical composition of mature wood and false heartwood of beech regarding their different coloring. The content of the main wood components, extractives, polyphenolic compounds, and soluble carbohydrates was determined. In addition, FTIR (Fourier transform infrared spectroscopy) analysis of mature wood, border zones and false heartwood was also performed. Chemical analyses showed a slightly higher content of holocellulose in false heartwood compared to mature wood. The differences in cellulose and lignin content are minimal. The content of both lipophilic and hydrophilic extractives is higher in mature wood.

Hydrophilic extract from mature wood contains more phenolics and soluble carbohydrates compared to false heart. According to ATR-FTIR (Attenuated total reflectance Fourier transform infrared spectroscopy) analysis it can be assumed that there is an increase in the content of polyphenolic extractives in the border zone, especially in the darkest colored zone next to the false heart.

Keywords: false heartwood; European beech; chemical composition; polyphenolic extractives; FTIR.

INTRODUCTION European beech (Fagus sylvatica L.) is widely available across Europe, and it is the dominant hardwood species in the Slovak Republic. Beech wood serves primarily to produce furniture, lumber, veneer, flooring, plywood, and turned objects. Slovak consumers most often buy seating furniture, dining furniture and cabinets made of beech wood (Sedliačiková and Moresová, 2022). However, the use of beech wood is restricted by various wood defects.

One of them is the presence of false heartwood, which reduces the usability of the wood for aesthetic reasons (Klement and Vilkovská, 2019).

False heartwood formation in beech is facultative, in contrast to the obligatory colored heartwood forming species. Its occurrence frequency, extent, and type are not predictable (Hofmann et al., 2022). The existence of false heartwood in still-standing beeches is not visible on the surface, however, it can be predicted based on tree age, average growth rate, and the number of bark injuries (dead branches, knots, large scars) through which oxygen can enter the stem (Knoke, 2003).

For many years, research has focused on finding the causes of false heartwood. Some authors (Kúdela and Čunderlík, 2012, Klement and Vilkovská, 2019) state that false 13

heartwood formation is associated with the breaking down of the water transport system and decreasing vitality of the parenchyma tissues. According to Račko and Čunderlík (2010) the occurrence of ripewood zone and the oxygen penetration into structure of wood are two main causes of false heartwood formation. Oxygen penetrated into ripewood zone in the central part of trunk via wounding the trunk and breaking the branches. Since heartwood formation begins only if the oxygen concentration in the ripewood zone is large, false heartwood formation depends on largeness of branch and trunk wounds. The wounds are caused by silvicultural treatments in the forest, by wildlife or by naturally occurring events, such as wind, storms, or snow. As regards ripewood zone, its width depends on the growth condition in the forest stands and increases as the trees age (Račko and Čunderlík, 2007). In accordance with the above Suchomel and Gejdoš (2010) recommend reducing the occurrence of the false heartwood the selection for nutrients richer soils for cultivation of beech forest, shorter felling periods, less intensive cultivation, and treatment of damaged locations on the trunk surface.

A false heart is characterized by a darker color of the wood (Slabejová, 2013) whereas “healthy” false heartwood and the decay-induced discoloration are not easily distinguishable (Hörnfeldt et al., 2010). False heart can occur in different forms such as round, marble, spattering or rot heartwood (Trenčiansky et al., 2017). Dzurenda (2023) numerically documented the visual color differences between the color of beech mature wood and the color of sapwood as well as between the color of false heartwood and sapwood through the values of total color differences. The color difference between mature wood and sapwood belongs to the category of visible changes with ∆E* = 3.5. The difference between the color of the false heartwood and the color of the sapwood reached the value ∆E* = 18.1 and belongs to the category of significant color changes.

The natural durability and mechanical properties of false heartwood do not differ much from those of mature beech wood (Koch et al., 2003). However, in the case of false heartwood, the presence of mechanical barriers (tyloses) that arise as a result of oxygen penetration affects not only the length of the drying process (Koch et al., 2003) but contributes also to issues with impregnation (Hörnfeldt et al., 2010).

As the differences in several properties of wood are dependent on different chemical composition, the aim of this article is to compare the chemical composition of mature wood and false heartwood of European beech. The focus is put on the content of the main wood components, extractives, polyphenolic compounds, and soluble carbohydrates. To find out the differences in chemical composition not only between mature wood and false heart, but also at their boundary, the individual zones of beech wood were subjected to ATR-FTIR (Attenuated total reflectance Fourier transform infrared spectroscopy) analysis.

MATERIALS AND METHODS Materials European beech (Fagus sylvatica L.) wood harvested from the Štiavnické vrchy locality (Slovakia), was studied. For research, 25 lumber-logs with healthy round false heartwood were selected. Blanks with dimensions of 32 × 50 × 800 mm were produced by spreading the central lumber with a thickness of h = 50 mm and transverse handling. Three pieces of blanks were randomly selected from each central lumber.

Thin sections with distinct mature wood, border and false heartwood zones were prepared for ATR-FTIR (Attenuated total reflectance Fourier transform infrared spectroscopy) analysis (Fig. 1). Mature wood and false heartwood were separated for 14

chemical analyses. The samples were disintegrated into sawdust, and the 0.5-1 mm fraction was used for analysis.

D

A C

B

Fig. 1 Zones of beech wood analysed by ATR-FTIR spectroscopy (A – mature wood, B – border zone next to the mature wood, C – border zone next to the false heart, D –false heart)

Chemical analyses In both samples, mature wood and false heartwood, the contents of extractives and main wood components were determined. All measurements were performed on three replicates per sample. The results were expressed in percentage of dry mass. Moreover, extraction with a methanol-water mixture was also performed to determine the total phenolic content and total soluble carbohydrates. Chemical analyses were performed according to the following procedures: Ethanol-toluene solubility of wood according to ASTM D 1107-96 (2013) 2 g of sawdust were extracted with ethanol-toluene (2:1, v/v) for 7 h in a Soxhlet apparatus. The resulting extract was distilled off in a vacuum evaporator and dried in an oven at t = 103 (± 2) °C to constant weight.

Hot-water solubility of wood according to ASTM D 1110-84 (1995) 2 g of sawdust were heated in a conical flask with 100 ml of distilled water on a boiling water bath for 3 h. After filtering and washing (200 ml of boiling distilled water), the sample was dried in an oven at t = 103 (± 2) °C to constant weight.

Polysaccharide fraction (holocellulose) according to Wise method (Kačík and Solár, 2000) Extracted sawdust (5 g) was treated with NaClO2 (1.5 g) in the presence of acetic acid (10 drops) for 1 h at t = 80–90 °C. This procedure was repeated 3-fold. After washing (water, acetone), cooling and filtering, the sample was dried in an oven at t = 103 (± 2) °C to constant weight.

Cellulose according to Kürschner-Hoffer method (Kačík and Solár, 2000) Extracted sawdust (1 g) was boiled with a mixture of concentrated HNO3 and 95% ethylalcohol (1:4) in a flask under reflux for 1 h. This procedure was repeated 3-fold. After filtering and washing (ethanol + HNO3, hot water), the sample was dried in an oven at t = 103 (± 2) °C to constant weight.

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Acid-insoluble lignin according to ASTM D 1106-96 Extracted sawdust (1 g) was treated with 15 ml of 72 % H2SO4, intense stirred for 1 min at t = 12–15 °C, and then allowed to stand for 2 h at a room temperature (20 °C).

Consequently, it was quantitatively transferred to a boiling flask, diluted to 3 % concentration with 560 ml of distilled water and boiled under reflux for 4 h. The brown lignin precipitate settled, filtered through a weighed glass filter, and thoroughly washed with hot water (500 ml) followed by drying in an oven at t = 103 (± 2) °C to constant weight.

Extraction with methanol-water 2 g of sawdust were extracted with methanol-water (1:1) using an automated solvent extractor Dionex ASE 350 (Thermo Fisher Scientific, USA). The extraction conditions were as follows: 50 °C extraction temperature; 3 extraction cycles; 5 minutes static time per cycle; 50% of the cell volume as flush volume; 90 s of purging with nitrogen. Both samples (mature wood and false heart) were extracted in three replicates. The gained extract volume was adjusted with the same solvent to get 25 ml of extract. An aliquot of 2 ml served for further analysis, while the remaining 23 ml were left for extractive content determination. Finally, the mixture containing solids (after partial solvent evaporation) was dried in an oven t = 103 (± 2) °C to constant weight. The extractive content was determined gravimetrically and expressed in percentage of dry mass.

Total phenolic content (TPC) An aqueous solution of gallic acid served as a standard for calibration of the total phenolic content. Calibration solutions of 5 ml volume covered the concentration range of gallic acid between 2 – 30 µg/ml. The solution was vortexed, 0.2 ml of Folin-Ciocalteu reagent was added to each tube containing diluted standard solution, vortexed again, and 3 min later 1 ml of 20 wt.% solution of sodium carbonate was pipetted to each tube (Čermák et al., 2019). The mixture was vortexed and incubated for 30 min. The absorbance of solutions was then measured at the wavelength of 700 nm against demineralized water using UV-VIS spectrophotometer (Shanghai Metash Instruments, China).

The phenolic compounds present in the methanol-water extract were exposed to FolinCiocalteu reagent and proceeded as done in the case of gallic acid for calibration. Briefly, extract aliquot of 0.1 ml was diluted with demineralized water to get final volume of 5 ml.

Each methanol-water extract was analysed in two parallel measurements. Six values for mature wood and six values for false heartwood were obtained. The amount of phenolic compounds present in extracts was expressed in milligrams of gallic acid equivalents per gram dried weight (mg GAE/g dw).

Total soluble carbohydrates (TSC) The total carbohydrate content was expressed using phenol-sulfuric acid assay (Dubois et al., 1956) with an adaption for wood according to the protocol of Čermák et al. (2019).

The calibration was performed with an aqueous solution of D-(+)-Glucose within the concentration range 12.5 – 125 µg/ml and the response was plotted as a linear curve (R2=0.9988). Each tube contained 2 ml of diluted standard solution. 1 ml of fresh 5 wt.% phenol solution was added to each tube, followed by addition of 5 ml of concentrated sulfuric acid. After cautious mixing, the tubes were left for: 10 min cooling down (at room temperature); 20 min in water bath (at 30 °C); and finally, 30 min for color stabilization (at room temperature). Afterwards, absorbance of the samples was recorded at 490 nm against demineralized water. The aliquot volume of 0.2 ml sample of methanol-water extract was diluted with demineralized water to final volume of 2 ml and further steps were done under the same conditions as with calibration solutions of D-(+)-Glucose. Each methanol-water 16

extract was analysed in two parallel measurements. Six values for mature wood and six values for false heartwood were obtained. The final concentration of soluble carbohydrates present in the extract was expressed in milligrams of glucose equivalents per gram dried weight (mg GluE/g dw).

UV-VIS spectrum scan The spectra of extracts from mature wood and false heartwood were scanned using UV-VIS spectrophotometer Agilent Cary 60 (USA). The measured spectrum was in the range 200–500 nm and the scan rate was set at 150 nm/min. Prior to the measurement of extracts, response within the range was baseline corrected by measurement of extraction solution (i.e. methanol-water 1:1).

ATR-FTIR spectroscopy ATR-FTIR analysis was carried out using a Nicolet iS10 FTIR spectrometer equipped with Smart iTR attenuated total reflectance (ATR) sampling accessory with diamond crystal (Thermo Fisher Scientific, Madison WI, USA). The spectra were measured in the wavenumber range from 4000 cm-1 to 650 cm-1, whereas the resolution was set at 4 cm−1.

The number of scans were 32 scans for each analysis. Eight analyses were performed per each zone of wood. The spectra were normalised to the band maximum at around 1370 cm−1.

OMNIC 8.0 software (Thermo Fisher Scientific, Madison WI, USA) was used for evaluation.

RESULTS AND DISCUSSION The relative content of chemical components of both, mature wood, and false heartwood of beech, are shown in Tab.1.

Tab. 1 Chemical characteristics of mature wood and false heartwood of beech (TEE – toluene-ethanol extractives, HWE – hot water extractives).

TEE (%)

HWE (%)

Hollocellulose (%)

Cellulose (%)

Lignin (%)

2.50 (0.10)

1.80 (0.04)

75.31 (0.04)

40.57 (0.09)

20.39 (0.08)

False heartwood 1.28 (0.13) * standard deviation in parentheses

1.46 (0.04)

76.27 (0.17)

40.00 (0.18)

20.98 (0.14)

Mature wood

The content of polysaccharides, the major component of wood, is almost 1 % higher in false heartwood, than in mature wood (76.27 %. resp. 75.31 %). It is a sign of a higher proportion of hemicelluloses, because cellulose shows a comparable proportion in both samples. The difference in lignin content is also minimal. Nečesaný (1958) reports a similar distribution of the main wood components in sapwood and false heartwood of beech, but with somewhat different values for the individual components between the two zones of the tree trunk. Both groups of extractives, TEE and HWE, have a higher proportion in mature wood than in false heartwood. Lipophilic substances, fatty acids, sterols, sterol esters and triglycerides are released into the toluene-ethanol mixture. Hot water removes phenolic compounds, sugars, starches and coloring matters (Vek et al., 2016). The total content of extractives is 4.30 % in mature wood, and 2.74 % in false heartwood. In spite of their lower proportion, they play important functions and affect many properties of wood, such as color, resistance to biotic damage or heating value. Vek et al. (2014) qualitatively and 17

quantitatively evaluated the composition of low-molecular weight extractives in the sapwood and false heartwood of European beech. They found a comparable content of lipophilic extractives in sapwood and false heartwood, while the total content of hydrophilic extractives was higher in sapwood. False heartwood contained significantly larger amounts of saturated fatty acids, fatty alcohols, and triterpenoids than sapwood, however, these compounds do not contribute to wood color. Sapwood contained larger concentrations of mono- and oligosaccharides, sugar acids, carboxylic acids, simple phenols, and flavonoids than false heartwood. The content of β-sitosterol, the characteristic compounds of the nonpolar extracts, was higher in false heart. Catechin, the characteristic compounds of the polar extracts, prevailed in the sapwood.

Extraction with a methanol-water mixture was also performed to determine the total phenolic content and total soluble carbohydrates. Hydrophilic extractives are released into this extraction solution, similarly to hot water. In this case, the content of extractives was also higher in mature wood than in the false heartwood, namely 1.7 times (Tab. 2). Similar extractive content in beech sapwood (2.41%) was also detected by Sablík et al. (2016), who used the same solvent.

Tab. 2 Content of the methanol/water extractives (MWE) in mature wood and false heartwood of beech, and the total phenolic content (TPC) and total soluble carbohydrates (TSC) in these extracts MWE (%) Mature wood

TPC TSC (mg GAE/g dw) (mg GluE/g dw)

2.19 (0.02)

False heartwood 1.32 (0.03) * standard deviation in parentheses

1.63 (0.03)

5.64 (0.12)

0.62 (0.02)

1.16 (0.03)

As for phenolics, in our experiment, their content was 2.6 times higher in mature wood extract than in false heart (Tab. 2). Lower values of total phenolic content in false heartwood than in sapwood were found also by other researchers (Vek et al., 2013, Vek et al., 2015, Albert et al., 2002). The content of the total soluble carbohydrates in wood is closely related to the content of phenolic substances. In mature wood, 4.9 times higher concentration of total soluble carbohydrates than in red-coloured heartwood was observed. This result is in accordance with observation by Visi-Rajczi et al. (2003). They found glucose, fructose, and sucrose such main components of soluble carbohydrates in beech. In beech with false heartwood their amount rises before the colour boundary and decreases behind it sharply, while it is negligible in the false heartwood. In beech without false heartwood, a continuous and monotonic decrease towards the pith was observed, but high concentrations of carbohydrates were still found near the pith. According to Albert et al. (2002) the beech tree accumulates some amounts of sucrose in the tissues in front of the border and presumably synthetizes them to in situ phenols.

The above-mentioned trend (higher contents of phenolics and soluble carbohydrates in mature wood) was confirmed by the UV-VIS spectrum of methanol/water extracts (Fig. 2). Absorption maxima in both extracts were at around 230 and 280 nm, while the second maximum left a shoulder at around 300–350 nm. The mature wood extract had broader absorption peaks at these wavelengths and obviously higher absorbance at around 280 nm indicating a wider variety of present substances absorbing in this region. No absorption peaks in the visible region of light were detected. A wide variety of flavonoids and phenolic acid derivatives present in mature wood (Hofmann et al., 2022) might explain the higher absorbances of mature wood extract. Such absorption peaks between 230 and 290 nm are typical chromophores in flavonoids (Wei et al., 2022). The absence of further peaks (around 18

350 nm or 510 nm) suggests occurrence of flavan-3-ols (e.g. catechins) (Andersen, Markham, 2006) in both extracts as the most likely flavonoid type.

5

beech mature wood beech sapwood

Absorbance

4

beech falseheartwood heartwood beech false

3

2

1

0 200

300

Wavelength (nm)

400

500

Fig. 2 UV-VIS absorption spectrum of extract from beech mature wood (blue line) and beech false heartwood (red line) in the wavelength range 200–500 nm after baseline correction

However, the exact composition or predominantly present flavonoid group responsible for this spectrum would need to be deeper investigated, since UV region is not very compound specific as many compounds absorb in this wavelength region. Moreover, extractability into the solvent also plays an important role and can have an impact on the quantitative and qualitative analyses. Polyphenols of higher molecular weight or single polyphenols chemically bonded to cell wall polymers can not easily be extracted and are socalled non-extractable polyphenols (NEPP) (Pérez-Jiménez et al., 2014).

According to literature (Albert et al., 2002) in the formation of false heartwood in beech trees intensive metabolical processes occur at the colour boundary. Knowledge of the radial distribution of the chemical components of wood can contribute to clarifying the formation of false heart in beech wood. In Fig. 3 relative intensities of characteristic absorption bands of beech wood components are shown. The interpretation of FTIR spectra was performed based on the literature (Bhagia et al., 2022, Hon, Shiraishi, 2000, Németh, et al. 2016, Stark et al. 2015).

Stretching vibrations of hydroxyl -OH and of intra- and intermolecular hydrogen bonds are located at the wavenumber 3341 cm-1. Hydroxyl groups are found in all components of wood – polysaccharides, lignin and in some groups of extractives, especially in phenolic substances. The related intensity of this peak is the highest in zone C, which is the border zone next to the false heart, and the lowest in mature wood. The overlapping bands with maximum of intensity about 2916 cm-1 is associated with C-H symmetric and asymmetric stretching vibrations in methyl and methylene groups. The maximum of absorption band, characteristic of the C=O group in ketones, aldehydes, carboxyl acids, and esters, lies at 1735 cm-1. The relative peak intensity decreases in order of zones B > A > D > C. Generally, higher intensity of this band in FTIR spectra may be associated with a higher proportion of hemicelluloses which are rich in acetyl groups in xylan.

However, chemical analyses determined a lower proportion of hemicelluloses and higher proportion of extractives in the mature wood compared to false heart. For this reason, it can be assumed that some groups of extractives contribute to the higher intensity of this peak in 19

zone A compared to zone D. In addition, carbonyl groups are also formed during oxidation reactions of wood components (Pandey, 2005, Liu et al., 2016, Feist, Hon,1984).

B

1322

1422

C

D

Hx/H1370

A

897

1031

1235

1459

1504

1593

1735

2916

3341

A 0.9373 12.506 3.4888 0.8824 0.9289 1.1259 1.0867 1.8867 2.5785 1.1851 3.3827 B 0.9188 13.223 3.7571 0.9205 1.0819 1.4423 1.4913 2.3732 2.8890 1.7169 3.6295 C 1.4208 16.525 3.5071 1.1587 1.2703 1.3708 1.4097 2.5863 2.2296 1.4529 4.5063 D 1.1044 13.379 3.5709 0.9725 1.0495 1.2331 1.3511 2.1255 2.4476 1.2745 3.6692

Fig. 3 Relative intensities Hx/H1370 of absorption bands in ATR-FTIR spectra of beech wood zones (A – mature wood, B – border zone next to the mature wood, C – border zone next to the false heart, D – false heart)

Characteristic bands for aromatic skeletal vibrations lie at wavenumbers 1593, and 1504 cm-1. The higher proportion of lignin certainly contributes to the higher proportion of the aromatic skeleton in the false heart compared to the mature wood. However, the intensities of both peaks are the highest in border zones, which indicates the highest lignin content in these locations. It is remarkable, that the same distribution can also be observed in the case of hydroxyl groups at 3341 cm-1. Based on these findings, it can be assumed that the content of polyphenolic extractives increases in the border zone, especially in the darkest colored zone C. This assumption is also confirmed by other authors (Hofmann et al. 2022, Albert et al., 2002). Hofmann et al. 2022 found 125 various polyphenolic compounds in European beech wood extracts. The most abundant types of compounds were the flavan-3ols, including (+)-catechin, (-)-epicatechin and their derivatives. The second-largest group was flavonol and flavonon compounds and their conjugates. In addition, gallic acid derivatives, simple phenols, phenolic acids, and aromatic aldehydes have been identified. It was found that the concentration of many compounds increased at the color boundary and decreased sharply behind it. In the false heartwood, only free aglycones could be evidenced in low amounts, however, the presence of oxidized high-molecular-weight polymeric polyphenols was not confirmed. It is questionable whether the coloring of the false heart is caused by low molecular weight compounds identified in the zone of false heartwood or high molecular weight compounds chemically bound to the structural polymers of the cell wall as non-extractable polyphenols. The problem with insufficient isolation of phenolics from wood samples is eliminated using ATR-FTIR analysis, which enables the monitoring of functional groups and fragments of chemical compounds in the original sample. However, 20

it is not possible to identify individual groups of extractives from the FTIR spectra of a complex material such as wood.

The band at 1422 cm-1 is assigned to aromatic skeletal vibration combined with CH in-plane deformation in lignin and -CH2 bending vibration in cellulose. Its relative intensity is decreased in the order of zones C > B > D > A. The peak with a maximum at 1322 cm-1 is a result of two overlapped bands. The first have a maximum at 1316 cm-1 and is associated with CH2 wagging vibrations in cellulose. The second band is located at 1333 cm-1, and is associated with CH in-plane bending vibrations in cellulose and syringyl ring breathing with C-O stretching vibrations in lignin. Its relative intensity decreases in the order of zones C > D > B > A. The highest peak in all spectra lies at wavenumber 1031 cm-1 and is assigned to C−O and C−C stretching and C−OH bending in carbohydrates. Its relative intensity is the highest in the border zone next to the false heartwood.

CONCLUSION Based on the chemical analysis of mature wood and false heartwood in European beech (Fagus sylvatica L.) and the ATR-FTIR analysis of individual zones of radial section of wood, the following conclusions can be stated: • False heartwood contains slightly more holocellulose than mature wood.

• The differences in cellulose and lignin content are minimal.

• The content of both lipophilic and hydrophilic extractives is higher in mature wood.

• The contents of phenolics and soluble carbohydrates are higher in hydrophilic extractives from mature wood than from false heartwood.

• The intensities of absorption bands of both aromatic structures and hydroxyl groups increase in the border zone, especially in the darkest colored zone next to the false heart.

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Sablík, P., Giagli, K., Pařil, P., Baar, J., Rademacher, P., 2016. Impact of extractive chemical compounds from durable wood species on fungal decay after impregnation of nondurable wood species. European Journal of Wood and Wood Products 74, 231–236. https://doi.org/10.1007/s00107-015-0984-z

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Sedliačiková, M., Moresová, M., 2022. Are Consumers Interested in Colored Beech Wood and Furniture Products? Forests, 13, 1470. https://doi.org/10.3390/f13091470 Slabejová, G., 2013, Photostability of transparent surface coatings of beech wood. Acta Facultatis Xylologiae Zvolen, 55, 5−12.

Stark, N. M., Yelle, D. J., Agarwal, U. P., 2015. Techniques for Characterizing Lignin. Lignin in polymer composites. https://doi.org/10.1016/B978-0-323-35565-0.00004-7 Suchomel, J., Gejdoš, M., 2010. The influence of selected factors on the occurrence of false heartwood in beech (Fagus sylvatica). Acta Facultatis Xylologiae Zvolen, 52, 5−13.

Trenčiansky, M., Lieskovský, M., Merganič, J., Šulek, R., 2017. Analysis and evaluation of the impact of stand age on the occurrence and metamorphosis of red heartwood. iForest, 10, 605610. https://doi.org/10.3832/ifor2116-010 Vek, V., Oven, P., Poljanšek, I., 2013. Content of Total Phenols in Red Heart and Wound-Associated Wood in Beech (Fagus sylvatica L.).

Drvna industrija 64, 25–32. https://doi.org/10.5552/drind.2013.1224 Vek, V., Oven, P., Poljanšek, I., Ters, T., 2015. Contribution to Understanding the Occurrence of Extractives in Red Heart of Beech.

BioResources 10, 970–985. https://doi.org/10.15376/biores.10.1.970-985 Vek, V., Oven, P., Poljanšek, I., 2016. Review on Lipophilic and Hydrophilic Extractives in Tissues of Common Beech. Drvna industrija 67, 85-96. https://doi.org/10.5552/drind.2016.1511 Visi-Rajczi, E., Levente, A., Hofmann, T., Sárdi, É., Koloszár, J., Varga, Sz., Cepregi, I., 2003.

Storage and accumulation of nonstructural carbohydrates in trunks of Fagus sylvatica L. in relation to discoloured wood. Wood Science and Technology, 330-334 Wei, L., Ma, R., Fu, Y., 2022. Differences in Chemical Constituents between Dalbergia oliveri Heartwood and Sapwood and Their Effect on Wood Color. Molecules 27, 7978. https://doi.org/10.3390/molecules27227978 ACKNOWLEDGMENT This experimental research was prepared within the grant project APVV-21-0051 “Research of false heartwood and sapwood of Fagus sylvatica L. wood in order to eliminate color differences by the process of thermal treatment with saturated water steam”, and it is the result of the authors’ work with the considerable assistance of the APVV agency.

AUTHORS’ ADDRESSES Ing. Eva Výbohová, PhD. Technical University in Zvolen Faculty of Wood Sciences and Technology Department of Chemistry and Chemical Technologies T. G. Masaryka 24 960 01 Zvolen, Slovak Republic vybohova@tuzvo.sk Dipl.-Ing. Anna Oberle Mendel University in Brno Faculty of Forestry and Wood Technology Department of Wood Science and Technology Zemědělská 3 613 00 Brno, Czech Republic anna.oberle@mendelu.cz 23

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 25−33, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.03

DETERMINATION OF CHARRING RATE OF OAK WOOD Alena Párničanová – Martin Zachar – Danica Kačíková – Lucia Zacharová ABSTRACT This paper deals with the determination of selected fire properties of oak wood, i.e., charring rate, which is used in practice to model and investigate the fire causes. Thermal loading was carried out using a measuring apparatus described in Utility Model No. 9373 registered by the Industrial Property Office of the Slovak Republic. Oak wood samples with dimensions of 40 × 50 × 50 mm (l × w × t) were thermally loaded by a heat flux of 15, 20, 25 and 30 kW·m-2, using a ceramic infrared heater. Two methods of determination of the charring rate, based on reaching the temperature of 300 ⁰C in individual depths in a specific time and according to the thickness of the charred layer formed in a time interval of 1800 s measured using a caliper were compared. Both methods confirmed that the charring rate is increasing with increasing thermal loading. The charring rate determined based on the temperature of 300 ⁰C ranged from 0.65 to 0.88 mm·min-1. According to the second method, the charring rate reached values from 0.41 to 0.86 mm·min-1. More accurate results were achieved by applying the method of determination of the charring rate based on the charred layer measured by a caliper. However, the method of determination of the charring rate using thermocouples can be considered less subjective because the temperature is measured automatically, using thermocouples compared to manual measurement using a caliper. The obtained results can be used as input data for computersupported modeling of indoor fires.

Keywords: thermal loading; oak wood; charring rate; charred layer.

INTRODUCTION Currently, wood is used as a construction material because it is affordable (Hrovatin, 2005). Wood is a material that loses its mechanical properties due to thermal loading.

Therefore, it is important to ensure the strength and longevity of buildings, as well as to pay attention to their fire resistance (Zanatta et al., 2018).

As a result of the thermal loading, charring occurs in the process of pyrolysis, which takes place at high temperatures and constant pressures in an oxygen-free environment for the thermal decomposition of wood as an organic material (Kravetz et al., 2020, Qin et al., 2021, Richter et al.,2019).

The charring temperature is approximately 300 ⁰C at which a charred layer of wood is formed (Booth, 1987, White, Nordheim 1992, Chen et al., 2016, Findorák et al., 2016).

The charring rate of wood is influenced by several parameters such as wood density and moisture, external heat flux and oxygen concentration in the ambient air, as well as the type of wood and the burning direction (Salmen et al., 2011, Cachim et al., 2008, Njankouo 25

et al., 2004, Mikkola, 2007). According to STN EN 1995-1-2 (Eurocode 5), it is important to know the value of the charring rate, which enters into the calculation of the fire resistance of wooden constructions. The charring rate is determined based on the charring depth and the time of exposure to thermal loading (Martinka et al., 2018). In addition, it is also an essential parameter in investigating the causes of fire, which is in line with NFPA 921: 2021 (NFPA 921: 2021).

In accordance with NFPA 921:2017, the charring rate of wood under laboratory conditions and exposure to a heat source from one side is determined from 0.17 mm·min−1 to 4.23 mm·min−1 (NFPA 921: 2021). In line with EN 1995-1-2 2, the proposed charring rate of solid and glued laminated softwood and beech is constant, approximately 0.6 mm·min−1, and decreases with increasing density (Friquin, 2011). The value of the charring rate of grown/solid and glued laminated hardwood and beech with a bulk density greater than 450 kg·m-3 is 0.50 mm·min−1 (Špilák, 2018).

The charring rate is not constant. At the beginning of burning, the charring rate is usually faster than the rate after the formation of the charred layer, because the charred layer acts as an increasing thermal insulation between the exposed surface and the pyrolyzed wood, which results in degression of the charring rate during the first phase of combustion.

Once the first few millimeters of charring are formed, the rate is constant (Friquin, 2011).

The aim of the paper is to determine the charring rate of oak wood based on data measured by progressive laboratory methods. Two methods of measurement were compared. The first one based on the temperature of 300 ⁰C reached at a certain depth, in a certain time and the second one based on the thickness of the charred layer formed in a time interval of 1800 s.

MATERIALS AND METHODS The measurement was carried out using a measuring apparatus described in Utility Model No. 9373 registered by the Industrial Property Office of the Slovak Republic. The apparatus consists of a ceramic infrared heater with a power of 1000 W, control device METREL HSN0203 (Metrel d.d. Horjul) and digital scale Radwag PS 3500.R2.M connected to a PC. Oak wood samples were prepared from the trunk of the sessile oak (Quercus patraea) harvested during summer in the Slovak Republic. At the time of harvesting, the trunk was 110 years old, and the trunk diameter was 410 mm. The samples were sawn in tangential directions to dimensions of 50 × 40 × 50 mm (l × w × t). Samples without anatomical defects were dried in a drying oven and subsequently adjusted to a moisture content of 10 +/- 0.15 %. The density of test samples was 681 ± 0.33 kg·m-3. The surface of the samples was prepared by mechanical processing – sawing.

First, the place where the initiation burner was fixed during the measurement of each sample was marked. Subsequently, 4 holes were drilled with a 2 mm drill bit in the center of each sample at a distance of 10 mm from each point. Before the measurement thermocouples were inserted into each hole in the sample. The thickness of the samples prepared in this way was measured using a caliper at 9 different places (Fig. 1) to determine the average thickness of samples. This measurement served in the next steps to determine the thickness of the charred layer.

Subsequently, each sample was weighed and the heat flux was noted at which each sample was tested. The heat flux values were 15, 20, 25 and 30 kW·m-2, where 10 samples for each heat flux value were used, a totally 40 samples.

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Fig. 1 Illustration of 9 different points on a sample (authors).

Before starting the measurement and placing the sample under the ceramic infrared heater, the moisture content of the sample was calculated as the ratio of the weight of wet wood to the weight of absolutely dry wood. The samples used in the measurement were dried at a temperature of 103+/-2 ⁰C to a constant weight.

The sample prepared this way was placed on a stand, 30 mm under the infrared heater.

The stand was placed on the scales, which recorded the mass loss. The propane burner was turned on, the flame of which was placed 10 mm above the sample, the place that was marked in advance. The stopwatch was turned on and we waited for initiation on the sample surface.

When the sample started to burn, the propane burner was pulled away. The temperature course was measured using the ALMEMO 710 measuring device and four K-type thermocouples with a thickness of 0.5 mm, placed in the sample at a depth of 10 mm (T1), 20 mm (T2), 30 mm (T3) and 40 mm (T4) from the thermally loaded surface. Measurement of each sample took 30 minutes. Based on the measured temperature on the thermocouples (T1, T2, T3 and T4), the charring rate was determined according to equation (1). 𝛽0 =

𝑑𝑐ℎ𝑎𝑟 𝑡

(1)

Where: β0 - charring rate (mm·min-1), dchar - charred layer (mm), t - time of thermal loading (min).

After thermal loading of the samples, the charred layer was removed manually.

Subsequently, the samples were measured again with a caliper at the same nine points as it was done before the thermal degradation of the sample. The thickness of the charred layer was calculated as the difference of the average thickness of the samples before testing and the average thickness of the samples after the experiment and removing the charred layer.

RESULTS AND DISCUSSION The charring rate of the oak samples based on the time and the depth at which we reached the temperature of 300 ⁰C was calculated. Based on the measured values, the average values of the charring rate in the time interval from 0 s to 960 s (Table 1) was determined. Table 1 shows the calculated charring rate of the oak samples in the time interval 0 s to 960 s, because during the thermal loading (0 s to 1800 s) a temperature of 300 °C only on T1 in time of 960 s was reached.

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Tab. 1 Charring rate of samples in time intervals at a depth of 10 mm.

Heat flux

Time to reach the temperature of 300 ⁰C (s) 930 920 740 690

(kW·m-2) 15 20 25 30

Charring rate in time interval from 0 to 960 s (mm·min-1) 0.65 0.65 0.81 0.87

Charring rate (mm·min-1)

At a heat flux of 15 kW·m-2, the charring rate in the time interval from 0 to 960 s reached the lowest values i.e. 0.65mm·min-1. At a heat flux of 20 kW·m-2, the charring rate was slightly higher, i.e., 0.6522 mm·min-1. At a heat flux of 25 kW·m-2, the average charring rate was 0.81 mm·min-1. The highest value of the charring rate 0.87 mm·min-1 was reached at a heat flux of 30 kW·m-2. The relationship between the average charring rate of oak wood in the time interval from 0 to 960 s and the heat flux density is shown in Fig. 2.

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

y = 0.1574* heat flux0.7582 R² = 0.8877

0.87

0.81 0.65 0.65

10

15

20

25

30

35

Heat flux (kW·m-2) Fig. 2 Average charring rate in the time interval from 0 to 960 s.

One of the most important fire properties of wood is the charring rate (Martinka et al., 2018). It is influenced by a heat flux, but also by moisture content and oxygen concentration in the air (Xu et al., 2020). Our experiment confirmed that the charring rate increases with increasing heat flux acting on samples, which is also in accordance with the results of authors (Kačíková and Makovická-Osvaldová, 2009, Martinka et al., 2018).

The charring rate of the oak samples was determined based on the thickness of the charred layer, which was measured using a digital caliper. We determined the average values of the charring rate in the time interval from 0 s to 1800 s (Table 2).

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Tab. 2 Charring rate of test samples in the time interval 0 to 1800 seconds.

Heat flux

The orginal Thickness of thickness of the the sample sample after charring (kW·m-2) (mm) (mm) 15 49.53 37.27 20 49.66 33.10 25 49.65 26.12 30 49.67 23.89

Thickness of the charred layer

Charring rate

(mm) 12.26 16.56 23.53 25.78

(mm∙min-1) 0.41 0.55 0.78 0.86

Charring rate (mm·min-1)

We calculated the thickness of the charred layer of the test samples based on equation (3), i.e., depending on the thermal loading. At a heat flux of 15 kW·m-2, the smallest charred layer was formed, i.e., 12.26 mm. At a heat flux of 20 kW·m-2, the charred layer was larger, i.e., 16.56 mm. At a heat flux of 25 kW·m-2, the charred layer was 23.53 mm. The most extensive charred layer, i.e., 25.78 mm was achieved at a heat flux of 30 kW·m-2.

Measurement of the charred layer using a caliper confirmed the assumption that the charring rate increases with increasing heat flux. The relationship between the average charring rate of oak wood in the time interval from 0 to 1800 s and the heat flux density is shown in Fig. 3.

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

y = 0.0759* heat flux0.9667 R² = 0.9701

0.86 0.78 0.55

0.41

10

15

20

25

30

35

Heat flux (kW·m-2) Fig. 3 Average charring rate in the time interval from 0 to 1800 s.

The charring rate was determined based on the charred layer and the time of exposure of the samples to thermal loading. It was confirmed that the charring rate increases with increasing heat flux, as in the case of determination of the charring rate based on achieved temperature of 300 ⁰C (thermocouple T1). At a heat flux of 15 kW·m-2, the charring rate reached the lowest value, i.e., up to 0.41 mm·min-1. At a heat flux of 20 kW·m-2, the charring rate was slightly higher, i.e., 0.55 mm·min-1. At a heat flux of 25 kW·m-2, the average charring rate was 0.78 mm·min-1. The highest value of the charring rate 0.86 mm·min-1 was achieved at a heat flux of 30 kW·m-2.

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1

Charring rate (mm·min-1)

0.9

0.81

0.78

0.87

0.86

0.8 0.55

0.6 0.5

0.65

0.65

0.7

0.41

0.4

0.3 0.2 0.1 0 15

20

25

30

Heat flux (kW·m-2) Charring rate based on charred layer measured using caliper Charring rate based on achievements a temperature of 300 ⁰C Fig. 4 Comparison of charring rates measured by different methods.

A comparison of two different methods of measurement showed similar values of the charring rates (Fig. 4). Different charring rates were achieved only at a heat flux of 15 kW·m-2. The value of the charring rate of 0.65 mm·min-1 was reached by applying the measurement methods based on the charring temperature. Using the second measurement method (based on charred layer), the charring rate reached 0.41 mm·min-1. This difference could be caused by the low heat flux (15 kW·m -2) and the longer time of initiation of the tested samples. Considering the different values of the charring rate at a heat flux of 15 kW·m-2, and the subsequent comparable results reached at a heat flux of 20, 25 and 30 kW·m-2, we can state that more accurate results were achieved by applying the method of determination of the charring rate based on charred layer measured by caliper.

In comparison with the results of a similar experiment testing the spruce samples, using the same method, the charring rate had an increasing trend with increasing heat flux.

In the time interval from 0 s to 1920 s, the average charring rate varied from 1.00 mm·min1 (at a heat flux of 15 kW·m-2) to 1.84 mm·min-1 (at a heat flux of 30 kW·m-2) (Zachar et al. 2021). The charring rate of spruce wood compared to oak wood may differ due to different densities. Spruce wood burns faster due to lower density when compared to oak wood.

According to Martinka et al. (2018) who tested spruce and pine wood exposed to a heat flux from 20 to 50 kW·m-2 for 0-30 minutes, the average charring rate of spruce timber was in the range from 0.73 mm·min -1 (heat flux of 20 kW m -2) to 1.2 mm·min-1 (heat flux of 50 kW·m-2). The average charring rate of pine timber in the same time interval from 0 to 30 min was from 0.67 mm·min -1 (heat flux of 20 kW·m -2) to 0.87 mm·min-1 (heat flux of 50 kW·m-2). The charring rate increased faster between 10 and 20 minutes. This may be due to the fact that if the wood is heated for a long period, heat accumulation occurs in the wood, meaning that the wood absorbs and stores heat. The accumulated heat can then promote faster burning of the wood.

The charring rate of six Chinese wood samples with densities from 0.35 to 0.69 g·cm-3 and moisture content of about 12 % tested by a cone calorimeter ranged from 0.604 to 0.971 mm·min-1 at a heat flux of 50 kW·m-2 and a time interval of about 10 s 30

(Wen et al., 2015). The authors reported different charring rates, which is caused by different wood density (the density of oak wood ranges from 0.6 to 0.9 g·cm-3) and also moisture content (oak wood samples were dried to absolute humidity). The value of the thermal conductivity of oak wood in the tangential direction was 0.21 W·(m·K) −1 (Požgaj et al., 1997). The charred layer serves as an insulation layer, the thermal conductivity of which is approximately one-sixth of the thermal conductivity of non-degraded wood. It also slows the further thermal degradation of remaining wood (Blass, 1995).

CONCLUSION Two methods of determination of the charring rate, based on reaching the temperature of 300 ⁰C in individual depths, in a specific time and according to the thickness of the charred layer formed in a time interval of 1800 s measured using a caliper were compared.

Both methods confirmed that the charring rate has an increasing tendency with increasing thermal loading. The charring rate determined based on the temperature of 300 ⁰C, achieved a value of 0.65 mm·min-1 at a heat flux of 15 kW·m -2. According to the second method (based on charred layer measured using a caliper) the charring rate was slightly lower, i.e. 0.41 mm·min-1. Gradually, as we increased the heat flux, the charring rate also increased, up to 0.87 mm·min-1 at a heat flux of 30 kW·m-2 (first method). The charring rate determined based on the charred layer, the charring rate achieved similar value, i.e., 0.86 mm·min-1. It can be stated that more accurate results were achieved by applying the method of determination of the charring rate based on charred layer measured by caliper.

However, we consider the method of determination of the charring rate using thermocouples (reaching the temperature of 300 °C) less subjective because the temperature is measured automatically, using thermocouples compared to manual measurement using a caliper. The results can be used in further research of the fire properties of wood and as input data for computer-supported modeling of indoor fires.

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Cachim, P. B., Franssen, J. F., 2008. Comparison between the charring rate model and the conductive model of Eurocode 5. In Wiley International Science, (33): 129–143. https://doi.org/10.1002/fam.985 Chen, T., Wu, W., Wu, J., Cai, J., Wu, J., 2016. Determination of the pseudocomponents and kinetic analysis of selected combustible solid wastes pyrolysis based on Weibull model. J. Therm. Anal.

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Hasburgh, R. H., Dietenberg, M. A., 2001. Wood Products. In Thermal Degradation and Fire. https://doi.org/10.1016/B978-0-12-803581-8.03338-5 Hrovatin, J., 2005. Contemporary systems of prefabricated wooden house construction. Wood in the Construction Industry: Durability and Quality of Wooden Construction Products. Proceedings Paper, 21-26. ISBN 953-6307-80-4.

Kačíková D, Makovická-Osvaldová L., 2009. Wood burning rate of various tree parts from selected softwoods. Acta Fac. Xylologiae. 2009;51: 27–32. ISSN 1336−3824.

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Kravetz, C., Leca, C., Brito, J. O., Saloni, D., and Tilotta, DC., 2020. Characterization of selected pyrolysis products of diseased orange wood. BioResources, 15(3): 7118-7126. https://doi.org/10.15376/biores.15.3.7118-7126 Liu, C, Deng, Y, Wu, S, Lei, M, Liang, J., 2016. Experimental and theoretical analysis of the pyrolysis mechanism of a dimeric lignin model compound with α-O-4 linkage. BioResouces, 11(2): 3626-3636. https://doi.org/10.15376/biores.11.2.3626-3636 Martinka, J., Rantuch, P., Liner, M., 2018. Calculation of charring rate and char depth of spruce and pine wood from mass loss. Journal Thermal Analysis Calorimetry (132): 1105–1113. https://doi.org/10.1007/s10973-018-7039-8 Mikkola, E., 2007. Charring of Wood Based Materials. Fire safety science. 2007. s. 10. eISBN 9780203973493 NFPA 921; Guide for Fire and Explosion Investigations; National Fire Protection Association: Quincy, MA, USA, 2021.

Njankouo, J. M., Dotreppe, J. C., Franssen, J. M., 2004. Experimental study of the charring rate of tropical hardwoods. Fire and materials, 28(15): https://doi.org/10.1002/fam.831 Qin, R.; Zhou, A.; Chow, C.L.; Lau, D., 2021. Structural performance and charring of loaded wood under fire. Eng. Struct, (228): 111491. https://doi.org/10.1016/j.engstruct.2020.111491 Požgaj, A., Chovanec, D., Kurjatko, S., Babiak, M., 1997. Structure and properties of wood.

Bratislava: Príroda, a.s., ISBN 80-07-00960-4.

Richter, F.; Atreya, A.; Kotsovinos, P.; Rein, G., 2019. The effect of chemical composition on the charring of wood across scales. Proc.

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Inst, (37): 4053–4061. https://doi.org/10.1016/j.proci.2018.06.080 Salmen, L., Olsson, A. M., Stevanic, JS., Simonovic, J. Radotic, K., 2011. Structural organisation of tha wood polymers in the wood fibre structure. Proceedings Paper. 2011. s. 7-12. WOS: 000394407800002 Špilák, D., Tereňová, Ľ., Dúbravská, K., Majlingová, A., 2018. Analysis of the charred layer of wooden beams with different geometric cross-section shapes. Delta, 12(2): 65-81. https://doi.org/10.17423/delta.2018.12.2.53 Wen, L., Han, L., Zhou, H., 2015. Factors Influencing the Charring Rate of Chinese Wood by using the Cone Calorimeter.

BioResources 10, 7263-7272. https://doi.org/10.15376/biores.10.4.7263-7272 White, R.H.; Nordheim, E.V., 1992. Charring rate of wood for ASTM E 119 exposure. Fire Technol, (28): 5–30. https://doi.org/10.1007/BF01858049 Xu, M., Tu, L., Cui, Z., Chen, Z., 2020. Charring properties and temperature profiles of laminated bamboo under single side of ISO 834 fire exposure. BioResources, (15): 1445-1462. https://doi.org/10.15376 /biores.15.1.1445-1462 Zachar, M., Čabalová, I., Kačíková, D., Zacharová, L., 2021. The Effect of Heat Flux to the FireTechnical and Chemical Properties of Spruce Wood (Picea abies L.). Materials (Basel) 14, 4989. https://doi.org/10.3390/ma14174989 Zanatta, P., Peres, M. L., Gallio, E., Ribes, D. D., Lazarotto, M., Gatto, D. A., Moreira, M. L., 2018. Reduction of flammability of Pinus elliottii wood modified with TiO2 particles, Matéria (Rio de Janeiro), (23): https://doi.org/10.1590/S1517-707620180001.0481

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ACKNOWLEDGMENT This work was supported by the Scientific Grant Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic and the Slovak Academy of Sciences under the Contract VEGA no. 1/0115/22 A comprehensive approach to the study of changes in fire parameters using progressive analytical and testing methods.

This work was supported by the Slovak Research and Development Agency under the Contract no.

APVV-22-0030.

AUTHORS’ ADDRESSES Alena Párničanová (Ing.) Martin Zachar (doc., Ing., PhD.) Danica Kačíková (prof., Bc., RNDr., MSc., PhD.) Technical University in Zvolen Faculty of Wood Sciences and Technology Department of Fire Protection T. G. Masaryka 24 960 01 Zvolen Slovakia xparnicanova@is.tuzvo.sk zachar@tuzvo.sk, kacikova@tuzvo.sk Lucia Zacharová (Ing., PhD.) National Forest Centre Forest Research Institute T. G. Masaryka 2175/22 960 01 Zvolen Slovakia lucia.ambrusova@gmail.com

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 35−43, 2023 Zvolen, Technical University in Zvolen DOI: 10.17423/afx.2023.65.2.04

THE EFFECT OF METAL NANOPARTICLES ON FORMALDEHYDE EMISSION FROM WOOD BASED MATERIALS Olena Pinchevska – Kostyantyn Lopatko – Larysa Lopatko – Rostislav Oliynyk – Ján Sedliačik ABSTRACT Considering the significant production volume of wood composite materials, the search for ecological solutions to reduce formaldehyde emissions during their pressing and further operation is urgent. The effect of nanoparticles of zinc, aluminium, and iron metals on formaldehyde emission from particleboard samples during their manufacture and subsequent exposure for three weeks is examined in the paper. Nanoparticles of metals were produced by the electro-spark method. In order to determine the priority metal, the method of analysis of hierarchies and search experiments was used. Samples of particleboard were made with the addition of a modified glue based on UF resin. Nanoparticles of the metals Zn, Al, and Fe were used in concentrations of 2% and 8%, respectively, to modify the adhesive resin.

Measurements of the level of free formaldehyde were carried out on the third and seventeenth days after the pressing of particleboard samples. The results of experimental studies confirmed the theoretical calculation of priority based on the selected assessment criteria. The best results were observed when zinc was used as a filler at a concentration of 8%.

Keywords: particleboard; formaldehyde; metal nanoparticles; urea-formaldehyde resin; adhesive modification.

INTRODUCTION One of the most important factors in the production of wood composite materials is their environmental friendliness, both during manufacture and in further operation.

According to the Food and Agriculture Organisation (2020), the industrial production of wooden boards in the world reached 250 million m3, of which the production of fibreboard, particleboard, and oriented strand board (OSB) amounted to 250 million m3. Phenolformaldehyde (PF) and urea-formaldehyde (UF) resins are mainly used for their production.

According to the Fraunhofer Institute (2012), 80-85% of particleboard is manufactured using adhesives containing formaldehyde. Despite this, particleboard furniture is the most popular.

Since wood particles are poor conductors of heat, during hot pressing of particleboard, it is distributed unevenly (Bolton et al., 1989). The core of the composite reaches the curing temperature later than the outer part. Unreacted methyl (hydroxymethyl) groups and methylene ether groups remain in the hardened resins. Over time, they diffuse to the surface and slowly degrade, releasing formaldehyde into the environment. Changes in temperature and air humidity affect the acceleration of the degradation process. The release of 35

formaldehyde and volatile organic compounds from new furniture was revealed after several months (Sherzad and Jung 2022, Ghani et al., 2018).

The danger of formaldehyde is related to its effect on the human body as a whole, its primary emissions, at a concentration of 0.1-5 ppm, can contribute to respiratory tract irritation, headache, dizziness, and lacrimation. According to research by the National Academies of Sciences, Washington (1980), the negative impact of formaldehyde on the lymphatic system of the human body was revealed, which leads to myeloid leukemia, cancer of the nasal cavity, damage to bone marrow function (Lv et al., 2020, Wei et al., 2016, Wei et al., 2017, Kang et al., 2021), etc.

The issue of modifying polycondensation resins with various fillers, both organic and inorganic, is relevant. Among the inorganic fillers, the use of nanoparticles of various metals deserves attention (Lopatko et al., 2013), because they have little effect on the viscosity of the glue, but they close the vessels of the wood well, preventing the adhesive from penetrating its thin layers. Adsorption of glue and the occurrence of the “starved gluing” defect are prevented (Bekhta and Bits 2008).

It was found (Gul et al., 2017) that the influence of Fe2O3 nanoparticles as a filler improved the resistance to swelling across the thickness of medium-density fibreboard (MDF). At the same time, the pressing time of the panels was shorter due to the increase in thermal conductivity. Iron nanoparticles are able to bind free formaldehyde and react with it, releasing CO2, water, and ferrous ions. In the presence of iron with a low degree of oxidation and in a small concentration, when interacting with lignin (Wan and Frazier 2017), a Fenton reaction occurs, during which new formaldehyde molecules are formed. It is believed that the mechanism of formaldehyde reduction is the ability of metal nanoparticles to accelerate the oxidation of formaldehyde and the formation of less harmful products.

Additionally, iron oxide nanoparticles can absorb formaldehyde by adsorption and then slowly release it over time. The use of zinc in the manufacture of MDF boards (Gul et al., 2017) showed that mechanical properties and moisture resistance of the panels were improved. According to Tian et al. (2017) and Salem et al. (2013), ZnO is quite sensitive to formaldehyde molecules, it is used as part of analysers to determine free formaldehyde in the air. Moreover, when the humidity of the material increases, the adsorption of formaldehyde molecules shortens the bond distance between water molecules and zinc oxide, thereby increasing the average bond energy of the entire system. At the same time, formaldehyde is adsorbed by the ZnO surface (Jin et al., 2017, Giroto et al., 2021, Gul et al., 2021, Schmidt-Mende and Macmnus-Driscol 2007).

The ability of aluminium (Alabduljabbar et al., 2020, Kumar et al., 2013a, Shukla and Parameswrn 2007) to improve the physical and mechanical properties of UF resin and to adsorb free formaldehyde contributed to the use of aluminium oxide (Al2O3) in various thermosetting polymers. Al3+ ions have the property of reducing the duration of gluing due to the filling of micropores in wood without changing the structural structure of glue based on urea formaldehyde resins (Cademartori et al., 2018, Kumar et al., 2013a). At the same time, during the hydrolysis of aluminium salts, a certain amount of H+ ions are released, which neutralize the excess alkalinity of the resin. Therefore, the use of complexing agents with aluminium to modify urea-formaldehyde resins deepens the hardening process and increases the water resistance of the glue. In addition, aluminium, like zinc, is a catalyst for the polycondensation process (Du et al., 2019).

Despite a significant amount of research, the impact of the metal form of the nanoparticles remains open, as it is more active and potentially has the ability to bind formaldehyde better. Oxide, sulphide, or other forms of metals are usually used because they are easier to obtain (Gul et al., 2020, Tian et al., 2017, Cademartori et al., 2019, Kumar et al., 2013b, Chotikhun et al., 2018). As a result, the study of the influence of the metal form 36

of nanoparticles on the ability to bind formaldehyde was not conducted, however, there is a method that allows obtaining nanoparticles with a reduced content of oxide forms in an affordable way (Olishevskyi et al., 2018). In addition, nanoparticles can have a fairly wide range of sizes from 1 to 100 nm, and it is appropriate to determine their rational size for reducing formaldehyde emissions.

The aim of the research is to identify a priority nano-sized metal that would ensure the binding of formaldehyde in the process of manufacturing wood composite materials.

MATERIAL AND METODS For conducting exploratory experimental studies, pine wood (Pinus sylvestris) crushed into particles of the size generally used for the middle layer of particleboard with a moisture content of 4% was used. Urea-formaldehyde resin Unicol RESIN 474 (solid content 65%, gel time 50 s) was used for the bonding of particleboard samples. Nanoparticles Fe0, Al0 and Zn0 (metal forms of nanoparticles) were used as fillers. In parallel, samples were made from disintegrated wood without adding the above fillers. The number of pressed samples with a thickness of 9 mm was 12 pieces.

Metal nanoparticles (Figure 1a) were produced by the electro-spark method in the form of colloids according to a patented method (Olishevskyi et al., 2018). Colloids were evaporated to powders in a laboratory drying oven, then homogenized in a mortar and dispersed in distillate to concentrations of 2% and 8%. Dispersed solutions were introduced into the adhesive mass in a ratio of 1:2, respectively, and thoroughly mixed for 20 minutes until complete homogeneity.

The mass of the adhesive was 10% of the mass of the wood chips. Resinated chips were placed in a mould and pressed in one cycle in a laboratory press for 180 seconds under the following regime: temperature t = 130 °C, pressure p = 2.9 MPa. After that, the samples were left under the press to cool down to a temperature of t = 40 °C. The finished samples were kept for 48 hours in the room at an air temperature of t = 20 °C and relative humidity of φ = 60 ± 5%. The dimensions of the samples were d = 41 mm, h = 9 mm (Figures 1b, c).

The density of the pressed samples was 800 kg/m3 ± 10%.

a

b

c

Fig. 1 Visualisation of components and equipment for making samples: a) nanoparticles of the studied metals Al0, Zn0, and Fe0 dried to powders; b) moulds for making samples with internal d = 41 mm; c) ready-made samples using 8% of Al nanoparticles to modify UF adhesive in three repetitions and control.

To select a prioritised nanosized metal, one of the methods of fuzzy logic was used, the analytic hierarchy process (AHP), which consists of decomposing the problem into simpler component parts and gradually establishing the priorities of the evaluated components using pairwise comparisons (Burak 2013). For this reason, the selection of a priority nanosized metal, alternative options for its achievement, and criteria for evaluating the quality of alternatives are set as a goal. Nanoparticles of the following metals were 37

selected as alternatives: A1 – Fe, A2 – Al, A3 – Zn; as criteria: Cr1 – price, Cr2 – production time, l/min, Cr3 – magnetism, Cr4 – particle size, nm; Cr5 – adsorption capacity, mg/g.

After determining the priorities of all elements of the hierarchy, the method of paired comparisons is used using Saaty's scale (Burak 2013). The matrix of pairwise comparisons (MPC) of the criteria is built with respect to the goal, and the MPC of the alternatives is built with respect to each criterion.

For each matrix, the geometric mean, Gi, and the local priority, LPrn, of each row of the matrix are calculated: 1

𝐺𝑖 (𝑎𝑖1 , 𝑎𝑖2 , . . . 𝑎𝑖𝑠 ) = (𝑎𝑖1 ∗ 𝑎𝑖2 ∗. . .∗ 𝑎𝑖𝑠 ) 𝑠

(1)

Where: i – the row number of the matrix, s – the number of elements in the i-th row of the matrix. 𝑎𝑖1 = 𝑤1 /𝑤1; 𝑎𝑖2 = 𝑤1 /𝑤2; . . . 𝑎𝑖𝑠 = 𝑤1 /𝑤𝑠

(2)

w – the accepted numerical value on Saaty's scale. 𝐿𝑃𝑟𝑛 =

[(𝑤𝑛 /𝑤1 )(𝑤𝑛 /𝑤2 )...(𝑤𝑛 /𝑤𝑛 )] (𝐺1 +𝐺2 +...+𝐺𝑛 )

(3)

Where: n – the MPC line number.

To control the consistency of expert assessments, two related characteristics are used - the consistency index (CI) and the consistency ratio (CR): 𝜆

𝑚𝑎𝑥 𝐶𝐼 = 𝑚−1

(4)

𝐶𝑅 = 𝑃

(5)

𝐶𝐼

𝑚

Where: m – the size of the matrix, Рm – the consistency index for the positive inverse symmetric matrix of random estimates of size m x m, λmax – the maximum eigenvalue of MPC: 𝜆 ∑ 𝑎1𝑖 1 ∑ 𝑎2𝑖 2 ∑ 𝑎𝑛𝑖 𝑛

𝑚𝑎𝑥

(6)

Where: ∑ 𝑎1𝑖 – the sum of the values of the first column of the MPC, LPr1 – the value of the local priority of the first line of the MPC, When CR < 0.1 ... 0.2, the calculations are considered satisfactory.

The solution to the multi-criteria ranking problem is presented in the form of a global priority vector (GlPr) of alternatives in relation to the goal.

The Temtop M2000 device was used to determine the formaldehyde emission. This is a non-standard method, but it is suitable for comparing the efficiency of used formaldehyde scavengers. The resulting values of formaldehyde emission as a result of the measurement (mg/m3) were converted into ppm according to the formula (Saltzman 2013): С𝑝𝑝𝑚 =

𝐶𝑚𝑔/𝑚3 ×24.45 𝑀.𝑊.

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(7)

Where: Cppm – the concentration of free formaldehyde expressed in ppm (million), Cmg/m3 – concentration of free formaldehyde in mg/m3, M.W. – molecular weight of formaldehyde (g/mol), 24.45 – the molar volume of any gas or vapour under normal conditions.

RESULTS AND DISCUSSION According to the calculation according to equations (1 – 6) with the use of AHP, a matrix of alternatives was built for each of the criteria, and the priorities of the criteria in relation to the aim are presented in Table 1. It can be seen that the results of the calculations are consistent, as they are within the required limits of CR < 0.1 ... 0.2.

The results of determining the global priority metal from the accepted alternatives are given in Table 2.

Tab. 1 Criterion priority matrix with respect to the objective and alternatives to each criterion.

Criteria

Criterion priority

Cr1 Cr2 Cr3 Cr4 Cr5

0.042 0.068 0.137 0.152 0.600

𝐶𝑅

0.152

Alternatives А1 А2 А3 0.04 0.31 0.49 0.07 0.23 0.70 0.08 0.23 0.69 0.10 0.41 0.49 0.11 0.00 0.51 Consistency of calculations to Cr1 –0.03; to Cr2 –0.128; to Cr3 –0.164; to Cr4 –0.150; to Cr5 – 0.09;

Tab. 2 Global priorities of accepted alternatives. А1 0.101

Alternatives GlPr

А2 0.123

А3 0.542

Therefore, the highest priority was given to the alternative 3 – nanoparticles of zinc.

To determine the formaldehyde emission, the samples together with the Temtop M2000 device were placed under a hermetic transparent glass cover with a volume of 12 litres, and the indicators were taken after 15 minutes (Figure 2). After each sample, the room and glass cover were ventilated, and the device was calibrated.

a

b

c

d

Fig. 2 Indicators of the level of free formaldehyde in the control sample (a) and samples of the modified glue based on UF with the addition of 8% Al0 nanoparticles in three replicates (b, c, d) after 15 min of measurement using the Temtop M2000 device.

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The background value of formaldehyde when measuring the state of native chips was 0.034 ppm. The obtained particleboard samples with the addition of unmodified glue had an average of 0.188 ppm, which was 5.5 times higher than the background value.

The results of measurements after 48 hours of exposure are presented in Table 3.

Samples modified with 8% Zn0 showed the best result. On the third day after pressing, the formaldehyde level was 48% lower than the control and was 0.098 ppm. The addition of 2% Zn0 reduces free formaldehyde emissions by 27% to 0.140 ppm.

A reduction in formaldehyde emission was also observed when Al0 nanoparticles were used. The best result was obtained with the addition of 2% Al0 – the emission decreased by 29% compared to the control sample. At the same time, the addition of the metallic form of Al0 at a concentration of 8% reduced the level of free formaldehyde emission by only 18%.

Tab. 3 Average indicators of the level of free formaldehyde in the study samples on the third day after pressing, ppm.

Metal

Concentration, %

Var. 1

Var. 2

Var. 3

Mean ppm

Control

0

0.193

0.188

0.184

0.188

2

0.134

0.137

0.129

0.133

8

0.170

0.147

0.146

0.154

2

0.145

0.141

0.133

0.140

8

0.096

0.101

0.098

0.098

2

0.446

0.429

0.432

0.436

8

0.186

0.216

0.227

0.210

Al0 Zn0 Fe0

The results of measuring the formaldehyde level of the samples modified with Zn0 nanoparticles on the seventeenth day showed that they were almost no different from the measurements on the third day.

In the samples using the adhesive modified with aluminium nanoparticles on the seventeenth day, a slight increase in the level of formaldehyde emission was observed compared to the previous measurement on the third day. Samples modified with 2% Al0 showed a 15% increase in free formaldehyde, and samples modified with 8% Al0 showed a 5% decrease in formaldehyde.

Tab. 4 Average indicators of the level of free formaldehyde in the study samples on the seventeenth day after pressing, ppm.

Metal

Concentration, %

Var. 1

Var. 2

Var. 3

Mean ppm

Control

0

0.182

0.186

0.189

0.186

2

0.162

0.157

0.155

0.158

8

0.178

0.177

0.177

0.177

2

0.124

0.125

0.124

0.124

8

0.113

0.112

0.112

0.112

2

0.356

0.344

0.351

0.350

8

0.120

0.121

0.118

0.120

Al0 Zn0 Fe0

The results of measuring the level of formaldehyde in samples modified with iron nanoparticles showed a significant decrease compared to the measurements obtained on the third day after pressing, by an average of 30%.

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The conducted experimental studies confirmed the priority calculations for the use of nanoparticles of various metals, proving the superiority of Zn0. In addition, zinc in any form can act as a catalyst for the urea polycondensation reaction with the formation of H-bonds between C=O and N–H groups, accelerating crystallisation while at the same time forming linear oligomers of different lengths (Du et al., 2019), which may affect further formaldehyde degradation. Considering the negative effect of zinc on the physical and mechanical properties of wood composite materials, namely the promotion of brittleness of the final product (Gul et al., 2021), further research is necessary, for example, on its use in mixtures with other metals. Thus, the use of nanoparticles of Al0, despite the slight reduction in formaldehyde emissions (Kumar et al., 2013a), improves the physical and mechanical properties of wood composites.

The use of iron nanoparticles during the repeated measurement showed a positive result, which may indicate the safe use of such wood composites indoors. However, the increased toxicity of production can negatively affect the health of workers involved in their production and can also indicate the danger of their production process for the environment.

CONCLUSION Nanoparticles in metallic form were proposed to reduce formaldehyde emissions in particleboard manufacturing using an adhesive based on UF resin. The results obtained from the research experiment confirmed the effectiveness of using Zn0 and Al0 nanoparticles as modifiers of UF resin to reduce formaldehyde emissions. The application of 8% zinc showed the best result – a reduction in formaldehyde emission by an average of 44%. In order to ensure the necessary physical and mechanical properties of particleboards, further studies of the influence of the mixture of the metallic form of Zn0/Al0 nanoparticles in different concentrations on the release of formaldehyde from wood composite materials will continue.

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ACKNOWLEDGEMENTS The work was carried out with the support of the Ministry of Education and Science of Ukraine within the framework of the scientific project state registration number: 0121U110191: “Scientific research, scientific and technical developments, work under state targeted programmes of public order, training of scientific personnel, financial support of scientific infrastructure, scientific press, scientific volumes" objects that are national property, support of the State Fund for Fundamental Research”. The authors are grateful to the Ministry of Education and Science of Ukraine for the financial support of this research.

This work was supported by the Slovak Research and Development Agency under contracts No. APVV-18-0378, APVV-22-0238 and by the project VEGA 1/0264/22.

AUTHOR’S ADDRESSES Prof. Ing. Olena Pinchevska, DrSc. Ing. Larysa Lopatko, PhD. Prof. Ing. Kostyantyn Lopatko, DrSc. National University of Life and Environmental Sciences of Ukraine Department of Technology and Design of Wood Products Geroiv Oborony str. 15 03041 Kyiv Ukraine olenapinchevska@nubip.udu.ua Assoc. Prof. Rostislav Oliynyk, PhD. Kyiv National Taras Shevchenko University Geography Faculty Meteorology and Climatology Department Akademika Glushkova 2a 02000 Kyiv Ukraine rv_oliynyk@ukr.net 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

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 45−62, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.05

ENHANCING THE QUALITY OF PALM VENEER WITH OIL PALM BARK EXTRACT-RESORCINOL-FORMALDEHYDE RESIN IMPREGNATION Adi Santoso – Jamaludin Malik – Jamal Balfas – Muhammad Adly Rahandi Lubis – Deazy Rachmi Trisatya – Erlina Nurul Aini – Achmad Supriadi – Rohmah Pari – Mahdi Mubarok – Ján Sedliačik – Pavlo Bekhta – Ľuboš Krišťák ABSTRACT The oil palm plantations in Indonesia have prompted the need for technology to utilize nonproductive oil palm trees (Elaeis guineensis Jacq.). This study was aimed to collect information on the quality of oil palm trunk veneer modified using SRF impregnation from oil palm bark extract. The impregnant was synthesized by copolymerizing resorcinol (R) and formaldehyde (F) on palm bark extract (S). Fourier Transform Infrared (FTIR), PyrolysisGas Chromatography-Mass Spectroscopy (Py-GCMS), X-Ray Diffraction (XRD), and Differential Scanning Calorimetry (DSC) were used to characterize the oil palm resorcinol formaldehyde (SRF) resin. The SRF-impregnant material was used to improve the oil palm veneer's density, thickness, swelling, stiffness, and strength. The results of the DSC analysis showed that the SRF resin was thermoset. The SRF-impregnated palm veneer could increase the veneer density by 20%, lower thickness swelling below 25%, and increase the modulus of rupture (MOR) by over 10% and modulus of elasticity (MOE) by 50%.

Keywords: formaldehyde; impregnant; palm bark extract; resorcinol; veneer.

INTRODUCTION Several research groups, including Nuryawan et al. (2022), Malik and Santoso (2021), Dungani et al. (2013), Rosli et al. (2016), and Mokhtar et al. (2012) have conducted studies and initiatives to improve the characteristics and possible utilization of palm tree trunks, specifically concerning composite materials. Nevertheless, the dimensional stability of the oil palm wood is categorized as significantly low, exhibiting shrinkage variations ranging from 9.2% to 74%. Additionally, the oil palm wood strength falls within the class IV with a specific gravity of 0.3-0.4, modulus of elasticity (MOE) of 35-50 MPa, and modulus of rupture (MOR) of 50-73 MPa. Furthermore, it is worth noting that the oil palm trunk is hygroscopic, as stated by Bakar et al. (1998). Consequently, conducting a study aimed at enhancing the quality of oil palm trunks remains an intriguing endeavour. This is the primary challenge that arises when considering the utilization of palm wood a fundamental material for furniture. To attain the intended goal, it is crucial to enact specific modifications, one of which entails employing the impregnation methods using an impregnant (Dungani et al., 2013).

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Impregnant refers to a substance used in the process of impregnation treatment, which can be derived from either synthetic or natural sources, or a combination of both. Because of growing concerns over environmental and health matters, it has become imperative for impregnating materials, including solvents, to exhibit compatibility with both of these aspects (Malik, 2019). According to Kislik (2012), water is regarded as the best choice for solvents. One of the readily accessible impregnants that satisfies these conditions is oil-palm bark. This material can be extracted using a water-based solvent and subsequently polymerized to form bioresin.

The results of the impregnation method by Dungani et al. (2013) showed that impregnating either vacuum or non-vacuum palm stalk waste improved its physicalmechanical properties as a furniture material, especially when using resins that have chemical and biological resistance and low molecular weight such as phenol-formaldehyde.

Other results also show that the application of impregnant materials from biomass extraction using the impregnation technique can improve the physical and mechanical properties of wood, including increasing resistance to weather changes (Malik and Ozarska, 2019, Dungani, et al., 2020a, Dungani, et al., 2020b). Treatment with this resin also increases the decay and termite resistance of particle board (Kajita and Imamura, 1991) and solid wood (Malik et al., 2022a, Malik et al., 2022b).

The increment in characteristics does not only occur in conventional wood but also occurs in impregnated coconut and oil palm wood (Dungani et al., 2020a, Malik and Santoso, 2021). The ability to improve the characteristics and quality of wood by impregnant formulated from biomass extracts due to changes in the properties of the phenolic resin copolymer from hydrophilic or highly soluble in water during the polymerization process to become hydrophobic at the end of the polymerization process has been carried out in previous studies (Malik et al. 2020). This will only occur in the proportion of constituent materials or in modified phenolic resins where the main constituent components are resorcinol (R) and formaldehyde (F) compounds (Dunky and Pizzi, 2002). The ratio of R to F determines the characteristics of the resin formed. Engineering or modification both at the time of manufacture and when the low-energy application is highly desirable. According to Durairaj (2003) and Detlefsen (2002) to make polymerized mixtures at room temperature (without heat treatment) made from phenol (P) and formaldehyde (F), the P/F mole ratio must be <1 or F/P ≥ 1. This resin is classified as a resole (Detlefsen, 2002, Durairaj, 2003, Akay, 2012, Gardziella et al., 2000). Characterization of bio-impregnant resin is needed to estimate the effectiveness of its use.

The synthesis, characterization and application of impregnant from palm bark extract with the aim given at improving the physical and mechanical characteristics of palm veneer so that it can be used for products in the humid environment are presented in the paper.

MATERIAL AND METHODS Materials Bark from a 32-year-old oil palm (Elaeis guineensis) stem from Malingping (Banten Province), tapioca flour, 37% (w/v) formaldehyde, 40% (w/v) sodium hydroxide (NaOH), technical resorcinol crystals from Cadixo Chemicals LLP, Surat, India and distilled water were used in the experiment. The log of the oil palm (Elaeis guineensis) was stripped of its bark (debarking process). The oil palm logs were then peeled using a rotary veneer machine with a veneer thickness of 5 mm. The veneers obtained were cut into 400 mm (length) × 80 mm (width) × 5 mm (thickness). Veneers for oil palm trunks were made using a 5-feet spindle-less rotary machine as performed by Balfas and Malik (2020).

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The tools used included glassware and pycnometer (Pyrex, Glandale, US), analytical balance (Radwag AS 220.R1 Plus, Radon, Poland), VT-04E viscometer (Rion, Tokyo, Japan), oven (Memmert, Haberbosch, Germany), Universal Testing Machine (HST, Jinan, China), hot press & cold press (Becker and Van Hullen, Germany), UV-Vis spectrophotometer (Shimadzu UV-1700, Shimadzu Corporation, Japan), water bath, Digital Caliper (Mitutoyo Asia Pacific. Jakarta, Indonesia), Fourier Transform InfraRed (FTIR) Spectrometer (Alpha Platinum-ATR, Bruker), Differential Scanning Calorimetry (DSC) (Shimadzu DT-30, Japan), Py-GCMS (Shimadzu series 45 QP2010 GC/MS, Shimadzu Corporation, Japan) and X-ray Diffraction (XRD) (XRD-7000 Shimadzu).

Methods 1. Liquid extraction of oil palm bark As much as 10 kg of pieces of palm bark measuring 5 cm long, 1–5 cm wide and 0.5– 1 cm thick were air-dried and then mixed with water with a ratio of pieces of palm bark and water 1:4 (w/w), then boiled at 80 °C for 3 hours with stirring. The mixture that has reached room temperature is then filtered. The extraction process was repeated 2 times. The filtrate from the two replicates was combined into one and filtered and then 20 liters of the filtrate were taken to make impregnant materials with a condensation copolymerization reaction.

2. Synthesis of SRF resin from Liquid Extract of Oil Palm Bark The SRF resin was made by reacting liquid palm bark extract (S) with resorcinol (R) and formaldehyde (F) with a weight ratio of S:R:F = 100 : 2.5 : 10 (Malik et al., 2022a). As much as 1.0% of tapioca flour based on the total weight of the SRF was added to the mixture, and stirred until homogeneous. The reaction conditions were carried out at room temperature and alkaline pH (10 – 11) with an addition of 40% NaOH. Characterization of palm bark extract as an impregnant material and its condensation polymerization reaction products were analyzed by infrared spectroscopy (FTIR), Py-GCMS, XRD, and DSC. The measurement was undertaken once for each instrument used.

3. Characterizations of Liquid Extract and the SRF resin a. FTIR analysis Powder samples of liquid extract and SRF resin were prepared by drying at 130 °C for 3 h in an oven and then were ground to powder for analysis. As much as 15 mg of SRF impregnant of 0.125 mm size from selected samples was directly used in FTIR spectroscopy measurements. Powder samples were planted in potassium bromide (KBr) pellets in a 1:1 weight ratio and analyzed using the Bruker Alpha Platinum-ATR spectrometer. The material was scanned in absorption mode in the range from 4000 to 500 cm-1 with a resolution of 2 cm-1. b. Py-GCMS analysis In this study, pyrolysis was performed with a control pyrolyzer Py-2020iS coupled to a Shimazu QP2010 GC/MS using an Rtx-5ms capillary-type column phase (60 mm × 0.25 mm × 0.25 mm). The inlet temperature is set at 280 °C and pyrolysis at 600 °C. The samples were identified by comparing the mass spectrum with a standard spectrum (NIST 98). c. DSC analysis The SRF samples, control palm veneer, and palm veneer impregnated with SRF resin, were prepared in the powder form as much as 10-15 mg. The samples were sealed in a standard DSC pan. The samples were heated from 30 °C to 550 °C, at a heating rate of 20

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°C/minute, under a nitrogen flow of 20 mL/min. The DSC-60 detector (Shimadzu, Japan) is used. The heat difference between the sample and the reference is recorded as a thermogram. d. XRD analysis The XRD analysis was used to determine the level of crystallinity of the sample from the bio-impregnant. The tool used was the X-Ray Diffraction (XRD) Maxima-X Shimadzu® XRD-7000. The X-rays were energized from a 40 kV, 30 mA source and scans were made in the range 0 - 40 degrees at a scanning speed of two degrees per minute. The degree of crystallinity was calculated using Gaussian function curves with OriginPro 8.5.1 software (OriginLab Corporation, Northampton, MA, USA), using the following equation: 𝐴𝑟𝑒𝑎 𝑐𝑟𝑦𝑠𝑡𝑎𝑙𝑙𝑖𝑛𝑒

𝐶𝑟𝑦𝑠𝑟𝑎𝑙𝑙𝑖𝑛𝑖𝑡𝑦 (%) = 𝑇𝑜𝑡𝑎𝑙 𝑎𝑟𝑒𝑎 (𝑐𝑟𝑦𝑠𝑡𝑎𝑙𝑙𝑖𝑛𝑒+𝑎𝑚𝑜𝑟𝑝ℎ𝑜𝑢𝑠) 𝑥100

(1)

4. Impregnation of palm veneer Veneers derived from palm stems were made measuring 30 cm × 8 cm × 0.5 cm (length × width × thickness). The palm veneers were dried in an oven at 100 °C for ± 3 hours to obtain a maximum moisture content of 12% prior to the impregnation thus, it is easier for the impregnant to enter during impregnation and fill the wood pores. The impregnation technique was carried out without vacuum pressure, the palm veneer was impregnated for 15 minutes and then conditioned at room temperature (± 28 °C) for 24 hours. The impregnated veneer was air-dried for three weeks to obtain a final moisture content of 20%.

5. Testing of impregnated veneers The physical parameters of palm veneer were tested both before and after impregnation. These properties encompassed moisture content, density, and thickness swelling referring SNI-ISO 16983:2010 (BSN 2010). The mechanical properties tested are modulus of rupture (MOR) and modulus of elasticity (MOE) referring to SNI 8853:2019/ASTM D143 – 14, IDT (BSN, 2019).

The samples were oven-dried at 103 ± 2 °C until the weight was constant, then weighed in the oven-dry condition to determine the moisture content. Observation of samples for thickness swelling was carried out by cold immersion (interior test) in distilled water for 24 hours, and hot immersion (exterior test) in boiled water for 3 hours as done by Malik et al.

(2022). The thickness dimension is measured at a predetermined point and the thickness dimension is measured again after immersion at the same point. Meanwhile, the mechanical properties of the modified oil palm veneer were observed by testing the MOR and MOE with concentrated loads using a universal testing machine (Alb. Von Tarnogrocki Essen UPH 2, German). Tests with instruments were also carried out on impregnated palm veneer, which included functional group analysis by FTIR, thermal properties by DSC, chemical components contained by Py-GCMS, and degree of crystallinity by XRD.

RESULTS AND DISCUSSION A. Characteristics of Liquid Extract from Palm Bark The characteristics of the liquid extract from the palm bark are presented in Table 1.

The colour of the extract was dark brown with an acidity (pH) of 6.53 measured by a Digital pH meter (OrionStar A111, ThermoScientific, USA). The yield of liquid extract based on 1 kg of palm bark was 83.80%, with an average solids content of 0.54%. This indicated that 1 kg of palm bark contained around 838 grams of liquid extract. The solid extract of the 838 48

grams of liquid extract was around 4.5 grams and the 833.5 was water. The viscosity of the liquid extract was around 0.0125 Poise, the specific gravity was 0.997 and the index of high reactivity to formaldehyde was indicated by the Stiasny's number of 84.99% (Lee and Lan, 2006).

Tab. 1 Characteristics of liquid extract of palm bark*).

Parameters

Palm tannins

*

Appearance Yield (%)* Solids content (%)* pH (25 oC)* Viscosity (Poise)* Specific gravity * Stiasny's number (%)

Dark brown 83.80 ± 0.20 0.54 ± 0.03 6.53 ± 0.03 0.0125 ± 0.0009 0.997 ± 0.0003 84.99

Remark: *) average of 4x repetition

The results of the functional group analysis using FTIR spectroscopy on the powdered extract of the oil palm stem bark presented in Figure 1 show the absorption of OH stretching vibrations (3280 cm‒1) indicating the presence of phenolic OH groups; vibration C=C (alkene) aromatic ring (1557 cm‒1); the C-O-H bending vibration of phenol (1408 cm‒1, 1226 cm‒1); cyclic ether C-O vibrations (1100 –1300 cm‒1), C-C vibrations (656 cm‒1), and outof-plane C-H vibrations (614 cm‒1, 442 cm‒1, and 442 cm‒1).

The spectrum produced from the extract of the bark of the oil palm showed that the tannin extract from the bark of the oil palm was indicated to contain condensate tannin compounds with specific functional groups, namely phenolic and ether, in line with the research of Tondi and Petutschnigg (2015) which stated that tannin condensate has a specific wave number in the area of 1400 – 1100 cm‒1 and there is no C=O group in the area of 1720 – 1700 cm‒1.

Fig. 1 Infra-red spectra of the extract from oil palm-bark.

The results obtained were similar to the functional groups of phenolic compounds identified in previous studies (Santoso and Abdurachman, 2016) in extracts of mahogany (Swietenia sp.), Okti et al. (2018) on mangium bark extract (Acacia mangium), and palm bark extract (Malik et al., 2022), where these extracts predominantly contain OH groups, C=C aromatic rings, and ether groups.

The results of further analysis with Py-GCMS (Figure 2) showed that the oil palm bark extract contained 30 chemical components, which were dominated by carboxylic compounds (23.3%), thiols (14.94%), aldehydes (9.69%), ketones (9.18%), alcohol (4.62%), 49

etc. Compounds containing hydroxyl groups (OH), such as alcohols and carboxylates, are important components as activators in bio-impregnant wood quality improvement treatments. Several studies have stated that compounds commonly used in wood modification to improve wood properties include those containing hydroxy functional groups, namely phenols contained in PF resins, capable of increasing dimensional stability (Ryu et al., 1991, 1993; Sakai et al., 1999; Ohmae et al., 2002).

Fig. 2 Py-GCMS chromatogram of oil palm-bark extract.

Furthermore, based on the results of the analysis with X-ray diffraction, it is known that the degree of crystallinity of the compounds contained in the extract of the oil palm stem bark is 85.95% (Figure 3). This indicates that crystalline (orderly) forms dominate the structure of the compound chain. The degree of crystallinity greatly influences the properties of polymers (Cowd, 1991) so polymers with a high degree of crystallinity have higher strength and stiffness than polymers with a low degree of crystallinity. A high degree of crystallinity indicates that chains with high orderliness dominate the structure of the compound contained in the sample, and the forces between the chains are strong enough so that the chains or parts of the chains can approach each other in parallel, forming crystalline areas.

Fig. 3 The diffractogram of oil palm-bark extract.

DSC analysis is used to determine the temperature of a material transformation by quantizing its heat. This DSC analysis uses a temperature rise rate of 30 °C/minute up to 550 °C to determine the glass transition temperature, melting point, and crystallization point of palm bark extract. The results of testing the thermal properties of the palm bark extract are presented in Figure 4.

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Fig. 4 The Thermogram of oil palm-bark extract.

Based on the thermogram in Figure 4, it can be seen that the oil palm bark extract changed thermal capacity at 82.2 °C, while the temperature due to decomposition/dissociation occurred gradually, namely at 120.4 °C, 165.7 °C and 188.4 °C and as the thermal rate increased it caused the extract from the palm bark to crystallize at 191.0 °C. B. Impregnant Characteristics of Palm Bark Extract The copolymerization product of palm bark extract with resorcinol and formaldehyde in alkaline conditions produces a resin that is visually a reddish-brown liquid, thicker than the liquid extract before copolymerization, has an acidity (pH) of 7.48 with an average solid level of 11.16%, a liquid extract viscosity of 4.0 Poise, a specific gravity of 1.054 and a gelation time of more than 180 minutes (Table 2). Furthermore, based on the results of analysis with the FTIR spectrophotometer, the resin from the palm bark extract caused the absorption band of the FTIR spectrum to change compared to the initial extract conditions (Figure 5).

Tab. 2 Specifications for bio-impregnant from Palm Bark extract.

Parameters Organoleptic – Visual test* : • Form • Colour • Smell Solids content (%)* pH (25oC) *

Impregnant Liquid Reddish brown Typical phenolic 11.16 ± 0.11 7.48 ± 0.44

Viscosity (Poise)* Specific gravity * Gelatinated time (minutes) Resin immersion test in cold water (24 hours), then conditioned for 1 month Resin immersion test in boiling water (4 hours), then conditioned for 1 month Distribution of molecular weights (g/mol) Total molecular weights (g/mol) Number of chemical components/compounds Decomposition temperature (°C) Degree of Crystallinity (%) Remark: *) average of 4x repetition

51

4.0 ± 0.26 1.054 ± 0.01 more than 180 remains liquid Not dissolved Not dissolved 44 – 380 33.724 50 204.6 13.57

The shift in the OH stretching vibration occurred from previously oil palm stem bark extract to bio-impregnant in the absorption area of 3280.98 cm-1 to 3340.28 cm-1 with a decrease in intensity from 77.56% to 58.35%. Another shift occurred in the C=C aromatic group resulting in an absorption band at wave number 2923.78 cm-1 with an intensity of 92.46% to 2195.52 cm-1 with an absorption intensity of 97.57%, besides there was a new absorption band of C-H stretching vibrations of the aldehyde group which originally appeared at 1557.44 cm-1 with an intensity of 74.78% to 1580.46 cm-1 with absorption intensity of 48.74%. This absorption phenomenon occurs due to the addition of resorcinol and formaldehyde in the copolymerization process, which causes the formation of new bonds from free OH groups to ether bridges and methylene bridges in the copolymer formed (Malik et al., 2022).

Fig. 5 Infra-red spectra of the impregnant made from oil palm-bark extract.

The absorption band at wave number 1349.01 cm-1 indicates the presence of a methylene bridge (CH2) resulting from the copolymerization reaction between the phenolic extract from the bark of the oil palm stem and formaldehyde. In addition, absorption bands of C-OH bending vibrations (1210.19 cm-1) formed from the phenolic group, shifted C-O stretching vibrations of the ether bridge from the condensation polymerization of phenolic compounds (1013.90 cm-1), and reduced out-of-plane C-H vibrations (775.26 cm-1) which are typical fingerprint regions for formaldehyde and phenol.

The results of further analysis with Py-GCMS (Figure 6) show that the impregnant of this copolymerization product consists of 50 chemical components. The results of the analysis with Py-GCMS (Figure 6) show that the impregnant of the palm bark extract was dominated by alkanes (18.6%), phenols (18.07%), ketones (12.6%), aldehydes (1.8%), and so on. This phenomenon occurred due to the addition of resorcinol and formaldehyde in the copolymerization process which causes the formation of new bonds from free OH groups to ether bridges and methylene bridges in the copolymer formed.

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Fig. 6 Chromatogram of the SRF resin made from oil palm-bark extract.

The results of the analysis with Py-GCMS show that the impregnant of the palm bark extract was dominated by alkanes (18.6%), phenols (18.07%), ketones (12.6%), aldehydes (1.8%), and so on. This phenomenon occurs due to the addition of resorcinol and formaldehyde in the copolymerization process, which causes the formation of new bonds from free OH groups to ether bridges and methylene bridges in the copolymer formed.

Furthermore, using the X-ray diffraction method, the results of which are presented in Figure 7, it can be seen that there is a change in the degree of crystallinity which indicates the formation of an impregnant copolymer with a degree of crystallinity of 13.57% which is much more amorphous than the oil palm stem bark extract (85.95%).

Fig. 7 Diffractogram of the impregnant made from oil palm-bark extract.

As stated above, the degree of crystallinity greatly affects the properties of polymers (Cowd, 1991), polymers with a high degree of crystallization have higher strength and stiffness than polymers with low crystallinity. A decrease in the degree of crystallization is an indication of an increase in the polymer chain structure with high disorder. Cowd (1991) suggested that very few polymers crystallize perfectly because the length and disorder of the molecules of each polymer are different. Irregularities in the chain structure, such as branching, will prevent the chains from approaching each other so that crystallization becomes limited (Cowd, 1991).

However, this does not mean that polymers with a lower degree of crystallinity are unprofitable, in the case of copolymers from palm bark extract which are included in the category of amorphous polymers which are thought to be relatively slower in "maturation" compared to copolymers with a higher degree of crystallinity, so that in application they will have a longer pot life (Cowd, 1991), in its use as a wood impregnant, what is more needed is its springiness (stretch) not just its strength/stiffness, in this case, a chain of branches is needed to inhibit or limit the movement of the chain, so it is hoped that after "ripening" it will not become firm/brittle.

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Furthermore, the results of testing the thermal properties of the impregnant from the palm bark extract showed the glass transition, melting point, and crystallization point of the SRF copolymer (Figure 8).

Based on the thermogram obtained, the impregnant melting phase transition temperature can be determined – 97.9 °C (Figure 8). It is different from the initial condition (82.2 °C) (Figure 4), while the temperature due to decomposition/ dissociation along with an increase in thermal rate causes the impregnant from the palm bark to crystallize at a temperature of 204.6°C (Figure 8), which is also different from the initial conditions (Figure 4). A change in the heat capacity of the material accompanies the transition phase.

Fig. 8 Thermogram of the impregnant made from oil palm-bark extract.

These results indicate that changing the phase of the palm bark extract requires a fairly low enthalpy. According to Liu et al. (2015), when a low enthalpy occurs in polymers, this means that polymers are more easily formed at low temperatures. This polymerization process occurs in bio-impregnant.

Cowd (1991) suggested that polymer properties can be affected by the melting transition temperature. This temperature is closely related to the amorphous region of the polymer and causes the polymer to change from a hard and crumbly substance like glass to soft and rubbery like rubber with increasing temperature. In amorphous polymers, at temperatures below the melt transition phase, the amorphous chains “freeze” at a certain point, and the polymer is vitreous or brittle. As the temperature rises to near the melting phase transition, the chain parts can move. The polymer becomes more elastic above this temperature.

C. Chemical Characteristics of Impregnated Palm Veneer Impregnation treatment of veneer with bio-impregnant synthesized from palm bark extract showed some increase or improvement in the characteristics of the veneer. The spectrum produced from untreated palm veneer (Figure 9) shows OH stretching vibration absorption (3280.15 cm-1), indicating the presence of OH groups which bind to –H with high intensity; vibration C=C (alkene) aromatic ring (2924.46 cm-1); the C-O-H bending vibration of phenol (1418.91 cm-1, 1242.06 cm-1); C-O stretching vibrations (1018.92 cm-1), C-C vibrations (770.56 cm-1) and out-of-plane C-H vibrations (574.76 cm-1, 527.44 cm-1, and 442.94 cm-1).

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Fig. 9 Infra-red spectra of oil palm veneer without impregnant.

The spectrum of the impregnated palm veneer (Figure 10) shows the absorption of OH stretching vibrations (3313.74 cm-1) with an intensity of 94.63%, indicating the presence of phenolic compounds in the presence of OH groups that bind to –H with high intensity; vibration C=C (alkene) aromatic ring (2926.32 cm-1, intensity 97.03%).

Fig. 10 Infra-red spectra of impregnated oil palm veneer.

The C-O-H bending vibrations of phenol (1367.26 cm-1 and 1239.86 cm-1 with intensities of 97.28 % and 97.41 %, respectively); C-O stretching vibrations (1151.53 cm-1, 1019.13 cm-1) with an intensity of 96.21% and 88.96%, respectively, C-C vibrations (765.26 cm-1, with an intensity of 98.70%) and out-of-plane C-H vibrations (571.86 cm-1, 435.86 cm-1 and 415.11 cm-1 with 96.49%, 98.13% and 98.53% intensity respectively) and carbonyl functional groups (1594.10 cm-1 with 97.67% intensity). This change in wave number and absorption intensity is an indication of the occurrence of chemical bonds between the chemical components of the impregnant and the chemical components of palm veneer.

The results of further analysis with Py-GCMS (Figure 11) show that in this palm veneer, there are 50 chemical components with a molecular distribution of 32 – 278 g/mol and a total molecular weight of 30.595 g/mol, which are dominated by phenol compounds (21.67%), carboxylates (15.41%), aldehydes (7.65%), ketones (5.40%), alcohol (4.89%), and so on, which confirms the results of the analysis by FTIR (Figure 9).

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Fig. 11 Chromatogram of oil palm veneer without impregnant.

The results of the analysis with Py-GCMS (Figure 11) showed that the palm veneer was dominated by ketones (26.08%), carboxylates (22.94%), phenols (20.13%), alcohol (8.60%), aldehydes (2.76%), etc., which confirmed the results of the analysis with FTIR (Figure 9).

Furthermore, the chromatogram of the impregnated palm veneer (Figure 12) shows that although the impregnated veneer both consists of 50 chemical components, it is different from the control and impregnant chromatograms. The 50 chemical components of impregnated veneer with a molecular distribution of 32 – 278 g/mol and a total molecular weight of 30,702 g/mol, were dominated by ketones (24.09%), carboxylates (20.60%), phenols (19.64%), aldehydes (9.34%), alcohols (8.07%), and so on, which confirmed the results of the FTIR analysis (Figure 9).

Fig. 12 Chromatogram of impregnated oil palm veneer.

Furthermore, using the X-ray diffraction method (Figure 13), it can be seen that the degree of crystallinity of palm veneer was 24.09 which after impregnated for 15 minutes experienced an increase in the degree of crystallinity reaching 24.18% (Figure 14). This indicates the formation of chemical bonds between the impregnant copolymer (15.20% degree of crystallinity; Figure 7) and the molecules in the palm veneer.

Fig. 13 Diffractogram of oil palm veneer without impregnant.

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Fig. 14 Diffractogram of impregnated oil palm veneer.

Further analysis showed that the thermal properties of the glass transition impregnated palm veneer and the crystallization point (Figure 16) were 185.5 °C and 205.2 °C, respectively. On the other hand, the control palm veneer produced a glass transition (Tg) at 80.1 °C and decomposed at 204.4 °C (Figure 15).

An increase in the glass transition temperature in impregnated palm stems compared to the control indicates the formation of a more rigid and branched polymer due to crosslinking that occurs between components in the impregnant or impregnant with cellulose from palm veneer so that the structure of the palm stems becomes harder.

Fig. 15 Thermogram of oil palm veneer without impregnant.

The crystal point of the control thermogram at a lower temperature than the impregnated palm veneer thermogram showed that the impregnation treatment on the palm veneer increased the hardness of the palm veneer. An increase in thermal properties compared to veneer without impregnation emphasizes the indication of the formation of chemical bonds between the impregnant copolymer and the molecules in the palm veneer.

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Fig. 16 Thermogram of impregnated oil palm veneer.

D. Physical-Mechanical Characteristics of Impregnated Palm Veneer The results of physical-mechanical characterization tests of impregnated palm veneer including density, thickness swelling after soaking in cold water for 24 hours and thickness swelling after soaking in boiling water for 3 hours, and MOE and MOR are presented in Table 3.

Table 3. Veneer quality enhancement after impregnation treatment.

Parameters

Test sample Control 0.50 ± 0.02 6.18 ± 1.98 9.17 ± 0.73 18.74 ± 0.25 637.08 ± 70.66

Density, g/cm3 Thickness swelling in normal water for 24 hours, % Thickness swelling in boiling water for 3 hours, Modulus of rupture, MPa Modulus of elasticity, MPa

Treated 0.60 ± 0.02 3.68 ± 0.83 5.31 ± 0.58 20.84 ± 4.88 973.28 ± 30.21

In Table 3 it can be seen that over all there was an increase in the quality of all test parameters after treatment on the palm veneer: 1. Density Density is used to describe the mass of a material per unit volume. Impregnation treatment increased the density of palm veneer by up to 20% compared to untreated (control) palm veneer. This shows the filling of empty cavities in the veneer and the replacement of water with impregnant that can penetrate the cell walls. An increase in density also indicates that the impregnant forms polymers with palm veneer cellulose molecules so that it become compressed and solid (Malik et al., 2022).

2. Thickness swelling One of the applications for improving the quality of palm veneer is in composite products that will interact directly with a high-humidity environment so that composite products from palm veneer will experience thickness swelling due to a cold environment or shrinkage due to a hot environment. Therefore, a thickness swelling test was carried out as a benchmark for the quality of palm veneer, which was carried out by soaking in cold water 58

for 24 hours and in boiling water for 3 hours. The lower the thickness swelling value, the better, because the palm veneer is more stable after soaking, and vice versa if the thick swelling value shows that the palm veneer has increased in thickness quite a lot when placed in a very humid environment.

The results of the thickness swelling test of impregnated and non-impregnated veneers met the standard requirements of SNI-06-4567-1998 (1998) because the thickness swelling was <25% of the original thickness. The sample of impregnated veneer after soaking in cold water for 24 hours decreased by 40% compared to the control palm veneer, while the swelling of veneer thickness in boiling water for 3 hours decreased by 42.09%. This phenomenon is in line with the results of Malik et al. (2022), where palm stems impregnated with Palm Resorcinol Formaldehyde resin experienced a decrease in thickness swelling after being tested in the same way. This indicates that the impregnation effect causes significant impregnant penetration and the formation of a strong specific bond between the impregnant and the palm veneer so that it becomes more stable. This increase in dimensional stability appears to be due both to the filling of the cell wall and the bonds that link the hydroxy resin components within the cell wall (Hill, 2006). Regarding the thickness swelling in boiling water, the value is greater than in cold water due to the swelling of the bonds in the veneer cellulose or the stretching of the bond of the palm veneer-cellulose adhesive thus allowing more water to enter (Malik et al., 2022).

3. Modulus of Rupture and Modulus of Elasticity The mean modulus of rupture (MOR) of this impregnated product was 20.84 MPa (Table 3), an increase of >10% compared to the control (18.74 MPa). On the other hand, the average modulus of elasticity (MOE) of impregnated veneer was 973.28 MPa , an increase of 52.77% compared to that without impregnation (637.08 MPa). This indicates that the impregnant can penetrate and form a strong specific bond between the impregnant and the palm veneer so that the MOR and MOE increase.

CONCLUSION The extract derived from the bark of palm stems contains a chemical component that exhibits a high concentration of hydroxy groups (OH). This compound demonstrates a pronounced affinity towards resorcinol and formaldehyde when combined with an alkaline catalyst (40% NaOH). Consequently, the resulting copolymers formed through this reaction can be effectively utilized as impregnant. The specifications of the bio-impregnant as a whole are different from the characteristics of the palm bark extract as a raw material.

The utilization of copolymers derived from palm bark extract as a bio-impregnant has the potential to enhance the quality of palm veneer with a thickness of 5 mm following the 15-minute impregnation process. The observed changes in density, with a 20% rise, and the lowering thickness swelling when subjected to cold and boiling water immersion, were found to meet the specified requirements of being less than 25%. Furthermore, the MOR exhibited an increase of more than 10%, while the MOE showed an increase of over 50%.

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AUTHOR ADDRESS Adi Santoso, adis012@brin.go.id Jamaludin Malik, jama008@brin.go.id Jamal Balfas, jama009@brin.go.id Muhammad Adly Rahandi Lubis, muha142@brin.go.id Deazy Rachmi Trisatya, deaz001@brin.go.id Erlina Nurul Aini, erli010@brin.go.id Achmad Supriadi, achm049@brin.go.id Rohmah Pari, rohm017@brin.go.id Research Center for Biomass and Bioproducts, National Research and Innovation Agency, Cibinong, 16911, Indonesia Mahdi Mubarok, mahdi.mubarok@yahoo.fr Department of Forest Products, Faculty of Forestry and Environment, IPB University, Bogor 16680, Indonesia Ján Sedliačik, sedliacik@tuzvo.sk Pavlo Bekhta, ybekhta@is.tuzvo.sk Ľuboš Krišťák, kristak@tuzvo.sk Technical University in Zvolen, Faculty of Wood Sciences and Technology, T. G. Masaryka 24 960 01 Zvolen, Slovakia

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 63−76, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.06

AUTOMATION OF TEMPLATE CORRECTION ALGORITHM FOR QUALITY IMPROVEMENT OF PSEUDO-3D ENGRAVED IMAGES Anastasia Evdokimova – Mikhail Chernykh – Maxim Gilfanov – Vladimir Stollmann ABSTRACT The method of correcting templates of pseudo-3D images engraved on wood and wooden materials is proposed. The key elements of the method comprise initial engraving of the test model with an optic density gradient, measurement followed by further analysis of the engraving optical density, finding the threshold values of the workpiece material tone, and correction of the image output values. The algorithm is composed, and the variant for automating the template design is proposed. A more complete reproduction of light-anddark gradations of the image engraved is achieved in the material, and the template design is accelerated and simplified. The experiments confirming the efficiency of the proposed approach were carried out.

Keywords: laser engraving; wood; half-tone wedge; template correction; tone range.

INTRODUCTION Laser radiation is successfully applied in processing wood and wooden materials – surface ablation (Makarov et al., 2011), biological protection (Parfenov et al., 2011, Vidholdova et al., 2017), cutting (Hernandez-Castaneda et al., 2011, Eltavani et al., 2013, Martinez-Conde et al., 2017), marking and engraving (Gorny et al., 2009, Kubovsky et al., 2016, Geffert et al., 2017). Laser engraving allows researchers to create complex images on wood and wooden materials (Chernykh et al., 2018, Gochev et al., 2018) of high aesthetic value, decorate products with ornament (Chernykh et al., 2012, Lungu et al., 2022, Kumpan et al., 2015), improve functional and decorative properties of products’ surface (Petuchnig et al., 2013), control processing quality.

It is most difficult to achieve high quality products when engraving pseudo-3D images, since the aesthetic value and faximility of products depend not only on processing quality but also on the reflection degree of light-and-dark gradations of the original in the product (photograph, drawing). In the work (Zykova et al., 2022) the following technologically controlled components of the aesthetic value and faximility of the engraved images were pointed out: contrast, detailing and perception integrity of the image.

The contrast is defined by the processed wood tone ratio to its natural tone. The most contrast achieved on the wood of a certain species is bound by the tone limit of this species, and when it is reached, the further laser radiation power increase does not result in a darker tone and improved contrast due to the wood carbonization (Yakimovich et al., 2016).

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Tone limits of different wood species have different values (Chernykh and Yapparova, 2012). In some works (Chernykhand Yapparova, 2012, Yakimovich et al., 2016), it is proposed to evaluate the wood tone limit as the black color percentage in CMYK based on the sample scans as a half-tone wedge using Photoshop tools.

CMYK model is subtractive: every color in it is formed by the subtractionof any color from the white one (Color models…https://clcr.ru/34wiGf). The model’s name corresponds to the first three letters in its main colors – Cyan, Magenta, Yellow – and the last letter in the black color – blacK. Black color in the model allows comparing the tone contrast and intensity (frequently of a black-and-white photograph), computer original, template and image engraved on wood.

However, scanning produces an error in an image tone. To improve the quality of engraved images and preserve faximility, it is necessary to use the material tone range to full extent, due to the direct tone measurement on the material being engraved.

Another aesthetic value index – detailing – is defined by the size of minimally distinct image engraving elements and can be estimated visually by applying expert assessment method following the technique discussed in the paper (Chernykh et al., 2013).

The third index – image perception integrity is also estimated visually. This index is defined by the reproduction degree of the original light-and-dark gradations in the engraved image. Light-and-dark gradations allow the perception of an image on a flat surface as volumetric and integral.

In practice, the original light-and-dark gradations (photograph, drawing, etc.) are reproduced experimentally due to the selection of power and engraving speed. Such a method requires a large amount of experiments and samples. Other methods providing a 3D perception of engraved images are not sufficiently discussed in the literature.

MATERIALS AND METHODS The investigated tree species – birch wood.

Samples: - 1-mm-thick veneer sheet glued onto MDF base, - 5-mm-thick plywood, - 15-mm-thick wood board, Samples moisture content: 12%.

Equipment: Laser CO2 marker with CNC GCC Synrad (USA), 30 W (Fig. 1).

The engraving power was 4.5 W, the speed – 1000 mm/sec, focal distance – 300 mm, the focal plane position coincided with the surface engraved.

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Fig. 1 Laser engraving equipment.

Engraving of uncorrected template To complete the formulated tasks, we engraved the test image, for which the half-tone wedge (Fig. 2), (GOST 24930-81) with black color intensity gradient within 0-100% was used. The use of high contrast standards, e.g., 167А2 – 1996 – IEEE Standard Facsimile Test Chart: High Contrast (GrayScale) or GOST 28267-89 half-tone raster wedge as test models does not result in contrast enhancement of the engraved model, improved accuracy in finding threshold values of the workpiece material tone. This relates to the blurred laser beam trace on the wood surface due to its properties, wood natural tone and tone limit. It is possible to obtain only the contrast average value during the laser engraving on wood.

Fig. 2 Half-tone wedge (GOST 24930-81).

The image was engraved along and across the fibers on several test samples (Fig. 3) of birch wood, including: plywood, board and veneer sheet. Engraving parameters: resolution 600 dpi, power P = 30 W, frequency 20 kHz.

a

b

c

d 65

e

f Fig. 3 Engraved half-tone wedge image on birch wood: a – plywood along the fibers, b – plywood across the fibers, c, d – boards along the fibers with different tone values, e – veneer sheet along the fibers, f – veneer sheet across the fibers. Sizes of the samples 17×125 mm.

The values of optic density D of the half-tone wedge engraved image steps on all tested samples were measured using the the densitometer by “KLIMSCH” (Germany) demonstrated in Fig. 4.

Fig. 4 Densitometer and its components: 1) measuring device, 2) light source, 3) receiver.

The receiver was not used in the work since the measurements were made on reflection, not transmission. The result was immediately displayed on the screen without additional mathematical operations. The light source was placed above the measuring region and the result was displayed on the measuring device screen afterwards.

RESULTS AND DISCUSSION Engraving on uncorrected wedge template The measurement results are given in the value graphs (Fig. 5) and Tab. 1. The common regularity within one workpiece, the stability of optical density values of the first steps and decrease after the maximum is observed.

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Fig. 5 Results of measuring optical density D of the engraving on different samples with resolution R=600 dpi.

Tab. 1 Results of measuring optical density D of the engraving on different samples.

Half-tone wedge step number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Sample number I 0.33 0.33 0.33 0.37 0.37 0.40 0.48 0.60 0.68 0.77 0.81 0.89 0.91 0.94 0.90 0.82

II 0.34 0.34 0.34 0.34 0.38 0.45 0.50 0.57 0.64 0.64 0.71 0.75 0.75 0.73 0.70 0.66

III 0.41 0.42 0.42 0.45 0.48 0.53 0.66 0.78 0.94 0.98 0.99 1.01 1.01 1.08 1.11 1.04

IV 0.36 0.36 0.36 0.36 0.38 0.43 0.49 0.62 0.70 0.74 0.88 0.88 0.92 0.96 0.94 0.85

V 0.32 0.32 0.32 0.32 0.32 0.34 0.40 0.48 0.63 0.73 0.82 0.85 0.90 0.95 0.93 0.73

VI 0.32 0.32 0.34 0.34 0.41 0.47 0.63 0.67 0.78 0.74 0.81 0.87 0.81 0.84 0.82 0.82

Note: I – plywood along the fibers; II – plywood across the fibers; III – board along the fibers; IV – board lighter in tone along the fibers; V – veneer sheet along the fibers; VI – veneer sheet across the fibers.

From the presented measurements, it is seen that the preservation of the initial tone range (template black color intensity within 0-100%) when engraving the image results in the merge of the light spots similar in tone (steps 1-5 of the wedge) making them alike. A similar problem occurs in the region of dark spots (steps 14-16 of the wedge). As a result, light-and-dark gradations of pseudo-3D original are not reproduced in the light and dark 67

regions of the engraved product that deteriorates the image quality, namely, faximility and aesthetic value.

Wedge template correction It is possible to avoid the incorrect image transfer by changing the output values of the initial template, narrowing its tone range. To reach this goal, the algorithm developed based on the research results conducted on the samples of birch veneer sheet with the engraving across the fibers was proposed. The selection was conditioned by the fact that the heat flow spreads slower across the fibers and tone gradations are reproduced in a smoother form in comparison with the engraving across the fibers (Chernykh, 2014).

1. The half-tone wedge image was made on the test sample with the help of laser engraving (see Fig. 3).

2. The optic density of each step of the engraved template was measured by the densitometer.

3. The graph of the engraved template optic density values was plotted for visualization and data overview (Fig. 6).

Wedge step number Fig. 6 Results of measuring optical density of the engraving across the fibers on birch veneer sheet with resolution R=600 dpi.

4. In the graph, the first optic density value different from the workpiece optic density (step 6) corresponds to the maximum brightness value, which can be obtained by laser engraving on the selected workpiece.

5. The maximum numerical value of the optic density, followed by its decrease, corresponds to the minimum brightness value obtained by laser engraving (see Fig. 7).

6. The steps corresponding to the optic density maximum and minimum values are marked in Adobe Photoshop on the test strip original (see Fig. 2).

7. The bit value, i.e., the brightness value of the limits found, is marked as the rangeupper and lower tone thresholds (upper and lower tone thresholds of the range) (Fig. 8).

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Fig. 7 Bit value of the brightness limits.

8. In the graphic editor, e.g., Adobe Photoshop, the tab “Image – Correction – Levels” is opened through the main menu where the maximum and minimum values obtained on the half-tone wedge are entered in the window of output values of the engraved and pseudo-3D images. All light-and-dark gradations of the original can be reproduced on the workpiece only in this case, eliminating possible losses in the regions of light and dark tones.

The control check performed during the half-tone wedge laser engraving (Fig. 8) demonstrated that the engraved sample optic density increased proportionally to the wedge template optic density increase (Fig. 9). Slight deviations from the proportional dependence were connected with the texture influence.

a

b Fig. 8 The half-tone wedge: а – corrected template of the test strip, b – engraving of the test strip made on the birch veneer sheet based on the corrected template (17×125 mm).

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Point number and distance between themмеждуними Fig. 9 Graph of the engraving optic density values plotted based on the corrected half-tone wedge template.

Thus, the output threshold values of the tone range boundaries identified by the engraver were obtained. They can help in correcting any image before applying it to wood by laser engraving.

Engraving of pseudo-3D images The tone images were engraved with and without the template correction for comparison. Resolution R was 1000 dpi (Fig. 10).

a

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b

c Fig. 10 Original (a) and engravings on the birch veneer sheet: without the template correction (b), with the template correction (с), (78×130 mm).

During the visual examination, it is seen that some elements, similar in tone, and the fog blend in tone with the workpiece on the uncorrected engraving “b”, and on the engraving “с” we can see the distant tower hidden by the fog and descending vertical wire ropes are also distinctive, but on the engraving “b” these elements and the fog blend in tone with the workpiece.

12 dots, in which the optic density was measured, were singled out on each of the engravings “b” and “c” for more precise evaluation (Fig. 11). The optic density of the image of the same format as the engraving printed on a white paper was measured for comparison.

The horizontal and vertical dimensions of the image in millimeters are shown along the coordinate axes.

Fig. 11 Optic density measurement region.

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The results of optic density measurement and comparison of tone gradations are demonstrated in Fig. 12.

Fig. 12 Optic density measurement results: 1 – original; 2 – engraving without the template correction; 3 – engraving with the template correction. The distance between points is 5 mm.

It should be pointed out that the ups and downs of the graphical dependencies obtained related to light-and-dark gradations of the images – the tone is darker on the graph vertexes and lighter in the hollows.

Comparing the graphs, we should specify that line 3 is almost parallel to line 1, which indicates that the amount and location of light-and-dark gradations of the engraving based on the corrected template (line 3) correspond to the original (line 1). The original faximility and image 3-dimensionality are reproduced on this engraving. And on the engraving produced based on the uncorrected template (line 2) a part of tone gradations is lost that is especially visible in the region of light tones corresponding to dots 1-7 in Figure 11. The light-and-dark gradations are poorly expressed in the region between dots 1 and 7 and can be invisible. The instrumental analysis results confirm the conclusions of the visual evaluation presented above. Thus, the template correction allows for improving the image engraving quality.

Based on the conducted research we composed the image correction algorithm (Fig. 13) and proposed the variant of the template correction process automation.

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Fig. 13 Template correction algorithm.

Fig. 14 Automated process model.

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The image correction automated algorithm represents a scheme consisting of two blocks (Fig. 14). The first block describes the process of sending the user’s request to the engraver to specify the tone range perceived by the wood. The engraver, with the help of the densitometer and control program installed, engraves the test image and finds the tone maximum and minimum values, which can be reproduced on the given species, and then the obtained data are returned to the user.

In the second block the user sends the image to be engraved, the engraver automatically corrects it in compliance with the data obtained from block 1 and sends the engraving of the corrected image back to the user.

Thus, the necessity to manually correct the template before engraving to preserve the image faximility and aesthetic value is eliminated.

CONCLUSION The method of correcting pseudo-3D images consisting of measuring the optic density of the test model with the optic density gradient made on the material of the product to be engraved and correcting threshold values of the image template tone brightness following the optic density measurement results is proposed.

The method allows for improving the quality of the products engraved due to more complete and accurate reproduction of light-and-dark gradations and 3-dimensionality of the original image in the product.

Measurement of the optic density of images engraved on the birch wood veneer sheet demonstrated that the amount and location of light-and-dark gradations on the image made based on the corrected template correspond to the original, whereas a part of light-and-dark gradations is lost on the reference image produced based on the uncorrected template.

The developed template correction algorithm minimizes user involvement, creating prerequisites for automatizing correction and accelerating the engraving technological process.

The correction algorithm is applicable to any equipment for laser engraving; however, it is necessary to conduct an individual test for each engraver and workpiece to find threshold values of the workpiece material optical density. Using the half-tone wedge by GOST 24930-81 as a test model is practicable.

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Yakimovich, B., Chernzkh, M., Stepanova, A., Siklienka, M., 2016. Influence are selected laser parameters on quality of images engraved on the wood. Acta Facultatis Xylologiae Zvolen, 58(2): 45-50.

Zykova, M., Chernykh, M., Stollmann, V., Gilfanov, М., 2022. The influence of the laser engraving mode of wood on the aesthetic perception of images. Acta Facultatis Xylologiae Zvolen, 64(2): 87−96.

Laser CO2 marker with CNC GCC Synrad 30 W. Report, 2023 [WWW Document], URL https://www.gccworld.com/en/product/co2-laser-engraver-cutter-marking-machine.

167А2 – 1996 – IEEE Standard Facsimile Test Chart: High Contrast (Gray Scale).

ACKNOWLEDGMENT This publication was created with the financial support of the project: Comprehensive research of mitigation and adaptation measures to diminish the negative impacts of climate changes on forest ecosystems in Sovakia (FORRES), ITMS: 313011T678 (100%) supported by the Operational Programme Integrated Infrastructure (OPII) funded by the ERDF.

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AUTHORS’ ADDRESSES Anastasia Evdokimova, student, Mikhail Chernykh, Prof., DSc, Kalashnikov Izhevsk State Technical University, Department of Industrial and Artistic Processing of Materials, Izhevsk, 426069, Studenchaskaya, 7, anastasiaevdokimova893@gmail.com rid@istu.ru Maxim Gilfanov, Director of LLC “Synergy”, Izhevsk, 426063, Karlutskaya embankment, 9, gravirovkarf@ya.ru Vladimir Stollmann, Assoc. Prof., Technical University in Zvolen, Faculty of Forestry, Department of Forest Harvesting, Logistics and Amelioration, T.G. Masaryka 24, 96001 Zvolen, Slovakia stollmannv@tuzvo.sk

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 77−87, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.07

ROUGHNESS PARAMETERS OF BIO-BASED COATING APPLIED TO WOOD SURFACES Krasimira Atanasova – Dimitar Angelski ABSTRACT This research is part of a study to determine the properties of a multilayer waterborne biobased coating. The liquid system was applied to spruce (Picea abies Karst.), beech (Fagus sylvatica L.), and beech plywood by brush. The influences of the wood substrate structure and the surface characteristics before coating, the surface treatment before coating, the amount of varnish recommended by the manufacturer, and the number of applied layers on the appearance and roughness of the resulting surfaces were analyzed. The roughness was evaluated by the profile amplitude parameters and the material ratio curve parameters for each of the film formation process phases. It was necessary to apply a two-layer coating on all test surfaces to obtain a good appearance. It was also found that the amount of varnish recommended by the manufacturer is inappropriate when applied to beech and beech plywood. The wood substrate structure and its surface characteristics before coating had a determining influence on the roughness parameters in the last phase of the film formation and on the appearance of the varnished surfaces. The treatment before coating had little effect on the final coating parameters. Roughness parameters suitable for evaluating changes in surface profiles for each of the processing phases were proposed.

Keywords: roughness; waterborne coating; bio-based coating; beech; spruce.

INTRODUCTION Fossil resources are the main raw materials for manufacturing chemical products for coating formulation (https://www.covestro.com). With the global energy crisis deepening, it is necessary to replace them with alternative raw materials. At the same time, due to the ongoing pollution of the environment, it is essential to use products that do not disturb the ecological balance. A solution to both problems is to replace products made from raw fossil materials with bio-based products manufactured in an eco-friendly manner. This enables the health, safety and environmental risks of each product to be minimized over its entire lifespan, from research and production to disposal. In addition, plant-derived components impart additional anticorrosion, antifouling, antimicrobial, self-healing or ultraviolet (UV) shielding properties to the systems in which they are incorporated (Hamidi et al., 2022).

In furniture industry of Bulgaria, the use of bio-based products in the formation of protective and decorative coatings on wooden surfaces is insignificant. The reasons for this are their higher price and the lack of knowledge of film formation modes and the properties of the resulting coatings. In this regard, in the Furniture Production department of the University of Forestry, Sofia, a complex study of the properties of a multi-layer coating 77

formed by a one-component waterborne bio-based varnish system was conducted. Some properties of the coating, such as water permeability, adhesion strength, and UV resistance, as well as the influence of the process conditions on the coating's performance, were investigated. The object of the present research was to study the performance of a coating applied by brush.

Roughness is a complex indicator that changes in the processing phases and can serve for their technological and quality assessment (Sandak et al., 2005). It depends on the wood's anatomical structure and the previous processing (Kavalov and Angelski, 2015; Cota et al., 2017; Kúdela et al., 2018). When forming coatings, the surface roughness also depends on the liquid system formulation (Landry et al., 2013), the coating formation technology (Salcă et al., 2016), and the coating thickness (Slabejova et al., 2017). Roughness is described by a group of roughness parameters that are selected depending on the objectives of the respective study (Sandak et al., 2005; Magoss et al., 2019).

In this regard, the present study aims to establish the influences of the wood substrate structure and the characteristics of its surface before coating, the surface treatment before coating, the amount of varnish recommended by the manufacturer, and the number of applied layers on the appearance and roughness of the resulting surfaces, as well as to propose roughness parameters suitable for evaluating the variation of the profiles of the treated surfaces in the film formation phases and for the entire coating process.

MATERIALS AND METHODS The product being researched is called „Bio-based wood stain“. It is used for outdoor applications and is produced by Industrias Químicas Masquelack, S. A., Spain. According to the specifications of the manufacturer (https://www.masquelack.com) the varnish system is one-component and waterborne, with a deficient volatile organic compounds (VOC) content. It can be applied by brush, roller, dipping, or spraying. It is fast-drying and creates a water-resistant, breathable, flexible, open-pore film. The finished coating feels like an unvarnished natural wood surface to the touch. It has high outdoor durability and provides reliable protection from the damaging effects of sunlight on timber. It also protects against mold and algae. The coating is safe for children. The recommended amount for a one-layer coating is 70–87 g/m2.

The Bio-based wood stain is produced using renewable energy and contains DSM Decovery plant-based resins. Decovery® (Covestro Coating Resins B.V.) is a plant-based alternative to acrylic technology. Decovery® SP-7450 XP is a 39% solids bio-based copolymer emulsion (WB acrylics) designed for fast drying and fast blocking resistant coatings for industrial exterior wood applications (https://www.covestro.com).

The flow time of Bio-based wood stain is 21 s using a 4-mm flow cup. According to the calculations the solid content of the coating system is 17.34%. (Angelski and Atanasova, 2023). The dry coating is extremely thin using the selected application stain amounts (according to the manufacturer's recommendations).

For the purposes of this study, specimens of spruce (Picea abies Karst.), beech (Fagus sylvatica L.) and beech plywood are selected. The beech and spruce surfaces are planemilled. The plywood surface is sanded with a P80-120 grain size sandpaper by the manufacturer (S.C. Cildro Plywood, Romania).

The specimens, with dimensions of 340 x 70 x 20 mm and tangential wood grain orientation, were conditioned for a month at 20 ± 2°C and 65 ±5 % R.H. They were sanded with P150-grain sandpaper, and the first layer of the coating was applied by brush. After 78

drying, the surfaces were treated manually with abrasive steel wool (Scotch-brite®) and a second layer was applied.

The coating was applied and left to dry at 20 ± 2°C and 60 ±5 % R.H. The stain amounts for the two layers were Q1 = 80 g/m2 and Q2 = 30 g/m2, respectively.

To determine the surface roughness changes, the measurements were made at the same evaluation lengths after each treatment, which made it possible to analyze both the values of the studied parameters and their change after each phase ΔR. This methodology provides, to a large extent, that the influence of the initial surface be ignored. It also allows for the variance of the parameter values to be analyzed.

The roughness parameters were measured with a Mitutoyo SJ-210 surface roughness tester with a tip radius of the diamond stylus R = 5 µm, according to ISO 3274, at the following settings: - profile – R, profile filter – Gauss; - number of sampling lengths n = 6; - evaluation length ln =15 mm; - cut-off length (sampling length) λc = 2.5 mm, - λs = 8 µm; - measuring speed 0.25 mm/s.

The measurements were made perpendicular to the wood grains. The following parameters were selected for analysis and evaluation: - arithmetic mean deviation of the assessed profile (Ra), maximum height of the profile (Rz), total height of the profile (Rt), and mean width of the profile elements (RSm) according to ISO 4287; - core roughness depth (Rk), reduced peak height (Rpk), reduced valley depths (Rvk), and the material portions Mr1 and Mr2 according to ISO 13565-2.

Due to the specifics of the material ratio curve parameters for wooden surfaces, the change in composite parameters Rpk+Rk+Rvk, Rpk+Rk, and Rk+Rvk were also of interest.

In the statistical processing of the data, the variance, the coefficient of variation V (in percent), and the accuracy index p (in percent) were calculated. For all measurements presented, p < 5%. The measured values of the roughness parameters were statistically and graphically evaluated using the Excel program.

The comparison graphs (Fig. 2) illustrate the change in surface profiles as a result of film formation. They were constructed according to the principles set forth by Atanasova in previous publications (Atanasova 2022).

RESULTS AND DISCUSSION After the solidification of the first coating layer on spruce wood, the treated surfaces had a visible, clearly defined texture and the uniform, rich tobacco coloring of the early wood, without gloss. Wood grain raising was weak. When applied with a brush, the varnish system was distributed evenly, which indicates that the selected varnish amount was appropriate.

After applying and solidifying a second coating layer, the surface acquired a darker color and a faint pearl-like shine (Figure 1). The coating was open-pored. The surface felt like unvarnished natural wood to the touch. The texture was visible.

79

Spruce (Picea abies Karst.)

Beech (Fagus sylvatica L.)

Beech plywood

Fig. 1 Wood surfaces with two-layer coatings.

The change of the surface profiles as a result of a two-layer coating formation on spruce (Picea abies Karst.), beech (Fagus sylvatica L.) and beech plywood is presentеd in Fig. 2.

Fig. 2 Substrate surface profiles change as a result of two-layer coating formation.

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The average values of the roughness parameters and their change after each film formation phase, as well as the initial surface parameters for the three types of wood surfaces, are presented in Tables 1–3. The presented data shows that in each phase of the processing, the parameters change to a different extent, which means that the parameters whose values change most significantly in the specific phase are its characteristics. Similarly, the parameters that have changed most significantly at the end of the film formation process are process characteristics. It can also be seen that different parameter values are obtained for different wood substrates, despite the same treatment before coating. This means that the wood substrate structure affects the parameters of the treated surfaces to a greater extent than the treatment before coating.

From the data presented in Table 1, it can be seen that after the film formation on a spruce surface, the values of the parameters RSm, Mr1, Rpk, and Rk+Rpk changed to the greatest extent. The first processing phase is surface preparation for coating by sanding.

Sanding affects the wood substrate’s top layer, creating a new surface (Gochev, 2018). Rpk, RSm, Ra, and Rk, as well as the three composite parameters, were most suitable for evaluation. As a result of sanding, the parameter values decreased. The sanded surface is the starting surface for the film formation process.

Tab. 1 Average values of the roughness parameters of the initial surface and of the sanded surface, as well as of the single-layer and two-layer coatings on spruce wood. Change in roughness parameter values after each processing phase and for the entire film formation process.

Single layer coating ΔR, %

Two-layer coating ΔR, %

Change for the entire film forming process ΔR, %

-53.83

36.25

-19.33

9.91

36.41

-41.21

30.00

-22.44

0.83

512.45 199.67 201.31 282.72

-61.04

0.82

40.44

41.59

̅​̅​̅, µm 𝑅𝑡

88.07

47.89

59.18

47,14

-45.63

23.58

-20.34

-1.56

̅​̅​̅​̅ 𝑅𝑘, µm

28.93

14.04

9.08

15.55

-51.48

35.90

-18.47

10.80

̅​̅​̅​̅​̅ 𝑅𝑝𝑘, µm

18.21

5.64

9.57

7.13

-69.03

69.72

-25.56

26.35

̅​̅​̅​̅​̅, µm 𝑅𝑣𝑘

15.88

8.09

9.23

7.76

-49.02

14.10

-15.95

-4.10

̅​̅​̅​̅​̅​̅ 𝑀𝑟1, %

10.55

7.59

10.95

10.23

-28.05

44.34

-6.63

34.76

̅​̅​̅​̅​̅​̅, % 𝑀𝑟2

88.07

87.26

89.69

89.72

-0.91

2.78

0.03

2.81

̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅ 𝑅𝑘 + 𝑅𝑣𝑘, µm

44.06

22.13

28.31

23.31

-49.78

27.93

-17.65

5.35

61.09

27.77

37.88

30.44

-54.54

36.42

-19.65

9.61

47.29

19.68

28.65

22.68

-58.39

45.60

-20.84

15.25

Average values Roughness parameter

Change after each phase of processing

Initial surface

Sanded surface

Single layer coating

Twolayer coating

̅​̅​̅​̅, µm 𝑅𝑎

9.78

4.52

6.15

4.96

̅​̅​̅​̅, µm 𝑅𝑧

61.42

36.11

46.94

̅​̅​̅​̅​̅​̅ 𝑅𝑆𝑚, µm

̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅ 𝑅𝑝𝑘 + 𝑅𝑘 + 𝑅𝑣𝑘 , µm ̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅ 𝑅𝑝𝑘 + 𝑅𝑘, µm

Sanding ΔR, %

As a result of the application of the coating’s first layer, the values of the parameters increased due to the grain raising. Grain raising is a common undesirable phenomenon when wood substrates are treated with waterborne coating systems (Landry et al., 2013; Ramananantoandro et al., 2018; Magoss et al., 2019). The degree of wood grain raising depends on many factors, including the substrate condition (Evans, 2009; Ramananantoandro et al., 2018; Magoss et al., 2019), the coating system formulation (Landry et al., 2013), and the applied varnish amount (Atanasova, 2022). The parameters that changed most significantly were Rpk, Rpk+Rk, Mr1, Rpk+Rk+Rvk, and Ra. As a result 81

of the application of the coating’s first layer, the values of the parameters increased. When the second layer was applied, RSm increased to the greatest extent, while Rpk, Rz, and Rpk+Rk decreased the most.

The single-layer coating on beech wood was translucent, without gloss, and had a washed-out, uneven color. The latter is due to uneven coating system spreading. The selected varnish amount was too large to be applied by brush. The surface of the coating was unpleasant to the touch due to the raised wood grain. The raised wood grain was felt to a greater extent in comparison to the treated spruce wood surface due to the greater hardness of the beech wood.

After applying and solidifying a second coating layer, the surface acquired a pronounced tobacco color and a faint pearl-like shine (Fig. 1). The coating was open-pored.

The surface felt like unvarnished natural wood to the touch. The texture was visible.

It can be seen (Table 2) that in film formation on a beech surface, the values of Rpk, RSm, Mr1, and Rk+Rpk have changed to the greatest extent. For sanding evaluation, the most suitable were Rpk, Rpk+Rk, Rpk+Rk+Rvk, Ra, and Rk. As a result of sanding, the parameter values decreased.

The parameters that changed (increased) most significantly after the first layer of the coating was applied were Rpk, Mr1, Rpk+Rk, Rpk+Rk+Rvk, and Ra. When the second layer was applied, RSm increased to the greatest extent, while Rpk, Rvk, and Rz decreased the most. Of the compositional parameters, the most representative of the change was Rpk+Rk+Rvk. Tab. 2 Average values of the roughness parameters of the initial surface and of the sanded surface, as well as of the single-layer and two-layer coatings on beech wood. Change in roughness parameter values after each processing phase and for the entire film formation process.

Single layer coating ΔR, %

Two-layer coating ΔR, %

Change for the entire film forming process ΔR, %

-52.92

53.12

-9.14

39.13

36.30

-49.01

51.23

-16.88

25.70

̅​̅​̅​̅​̅​̅ 𝑅𝑆𝑚, µm

398.26 267.34 344.01 488.25

-32.87

28.68

41.93

82.63

̅​̅​̅, µm 𝑅𝑡

77.95

39.70

61.36

53.88

-49.07

54.54

-12.18

35.72

̅​̅​̅​̅, µm 𝑅𝑘

19.54

9.60

14.08

13.56

-50.88

46.72

-3.71

41.28

̅​̅​̅​̅​̅ 𝑅𝑝𝑘, µm

12.18

3.04

11.13

9.30

-75.07

266.48

-16.43

206.28

̅​̅​̅​̅​̅, µm 𝑅𝑣𝑘

15.15

8.10

8.72

7.36

-46.56

7.70

-15.55

-9.05

̅​̅​̅​̅​̅​̅, % 𝑀𝑟1

9.69

6.49

13.18

11.86

-33.02

103.07

-10.07

82.63

̅​̅​̅​̅​̅​̅ 𝑀𝑟2, %

85.65

85.21

89.26

89.70

-0.52

4.75

0.49

5.27

̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅ 𝑅𝑘 + 𝑅𝑣𝑘, µm

34.69

17.69

22.80

20.92

-48.99

28.86

-8.24

18.25

46.87

20.73

33.93

30.23

-55.77

63.67

-10.92

45.79

31.60

12.63

25.21

22.86

-60.02

99.55

-9.32

80.94

Average values Roughness parameter

Change after each phase of processing

Initial surface

Sanded surface

Single layer coating

Twolayer coating

̅​̅​̅​̅ 𝑅𝑎, µm

7.05

3.32

5.08

4.62

̅​̅​̅​̅, µm 𝑅𝑧

56.64

28.88

43.68

̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅ 𝑅𝑝𝑘 + 𝑅𝑘 + 𝑅𝑣𝑘 , µm ̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅ 𝑅𝑝𝑘 + 𝑅𝑘, µm

Sanding ΔR, %

The changes in the beech wood surface parameter values were larger than in spruce wood.

From the comparison of the orders of importance of the essential parameters characterizing the film formation on beech and spruce wood surfaces, it can be concluded 82

that the significance rating of the parameters is determined by the wood structure. The lowviscosity varnish system penetrated into the pores of the early spruce wood, thereby having less influence on the surface parameters. The same amount of varnish applied to beech remains on the surface, influencing the surface parameters until the film solidifies. The longer contact time of the liquid system with the base caused a greater change in the surface profile and in the investigated parameter values.

The single-layer coated beech plywood was the most unacceptable in appearance. Its visible texture was like that of a beech surface, but the wood grain raising was greater. The coating has no shine. Despite the relatively uniform spread of the varnish system, after its solidification, the coloring agent was distributed unevenly. This indicates that the selected varnish amount was inappropriate.

After applying and solidifying a second coating layer, the surface acquired a pronounced tobacco color and a faint pearl-like shine (Fig. 1). The coating was open-pored.

The surface felt like unvarnished natural wood to the touch. The texture was visible.

From the data presented in Table 3, it can be seen that in the case of film formation on beech wood and beech plywood surfaces, the parameters for the process effectiveness evaluation were almost equal, namely: - Rpk, Rpk+Rk, Rvk, Rk, and Mr1 for the entire process; - Rpk, Rk, Ra, as well as the three composite parameters, on sanding (their values decreased); - Rpk, Rpk+Rk, Mr1, Rk, Ra, and Rpk+Rk+Rvk, when applying the coating’s first layer (their values increased); - Rvk, Rpk, Rz, as well as the three composite parameters, when applying a coating’s second layer (their values decreased).

Tab. 3 Average values of the roughness parameters of the initial surface and of the sanded surface, as well as of the single-layer and two-layer coatings on beech plywood. Change in roughness parameter values after each processing phase and for the entire film formation process.

Single layer coating ΔR, %

Two-layer coating ΔR, %

Change for the entire film forming process ΔR, %

-76.62

107.83

-28.51

42.24

33.98

-66.46

68.33

-35.61

-2.83

̅​̅​̅​̅​̅​̅, µm 𝑅𝑆𝑚

439.13 310.65 322.65 266.48

-29.26

3.86

-12.01

-14.22

̅​̅​̅, µm 𝑅𝑡

134.08

60.18

95.13

55.61

-55.11

58.06

-25.85

-7.61

̅​̅​̅​̅ 𝑅𝑘, µm

48.74

10.24

22.06

16.63

-78.99

115.41

-22.40

62.45

̅​̅​̅​̅​̅, µm 𝑅𝑝𝑘

16.74

3.44

16.65

7.70

-79.48

384.54

-44.43

124.01

̅​̅​̅​̅​̅, µm 𝑅𝑣𝑘

26.70

10.42

8.68

2.91

-60.95

-16.74

-60.03

-72.08

̅​̅​̅​̅​̅​̅ 𝑀𝑟1, %

7.69

6.53

14.22

9.98

-15.08

117.68

-28.99

52.78

̅​̅​̅​̅​̅​̅, % 𝑀𝑟2

86.17

85.94

91.49

92.05

-0.27

6.45

-0.09

7.10

̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅ 𝑅𝑘 + 𝑅𝑣𝑘, µm

75.44

19.26

29.93

20.31

-74.47

55.37

-32.48

5.45

93.05

22.44

44.88

25.92

-75.89

100.00

-32.48

15.53

66.35

13.95

37.33

25.97

-78.98

167.61

-26.62

86.15

Average values Roughness parameter

Change after each phase of processing

Initial surface

Sanded surface

Single layer coating

Twolayer coating

̅​̅​̅​̅, µm 𝑅𝑎

15.90

3.72

7.72

5.29

̅𝑅𝑧 ̅​̅​̅, µm

104.24

34.97

58.86

̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅ 𝑅𝑝𝑘 + 𝑅𝑘 + 𝑅𝑣𝑘 , µm ̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅​̅ 𝑅𝑝𝑘 + 𝑅𝑘, µm

83

Sanding ΔR, %

The essential differences were the absence of the RSm parameter, the presence of the Rk parameter, and the more pronounced Rvk influence. This was due to the wood compression in plywood production. The plywood surface was sanded, and its texture was mainly determined by the sanding conditions. The beech wood structure does not have a significant influence (Atanasova, 2022). In terms of penetration, the plywood surface has beech surface characteristics. The grain raising was more pronounced due to the greater cell wall damage as a result of the two-step sanding (Evans, 2009).

For the three investigated surfaces and for the entire film formation process, Ra reflected the surface changes better than the Rz parameter.

The parameters Rpk and Mr1 are related (ISO 13565-2). Their calculated dispersion values were close. Therefore, there is no reason to calculate and analyze them simultaneously. Due to the more complete information that can be obtained from the composite parameters, it is recommended to measure Rpk. The graphs in Figs. 3 and 4 are based on the data presented in Tables 1–3. They compare the change in the main parameter values for the different wood bases during twolayer coating formation.

Figure 3B shows the change in the most dynamic roughness parameter -Rp. It affected considerably the values of the composite parameters in which it was included and determined the nature of their change. It cannot be claimed to be a film formation parameter, as the environment affects the outermost coating layer (Müller and Poth, 2011). This is the reason for the large variance in its values, which makes it difficult to work with. When the environmental conditions vary widely, it is recommended to replace it with Rpk+Rk (Fig. 3C) or Rk (Fig. 3D).

A

B

C

D

Fig. 3 Changes in Ra, Rpk, Rk, and Rpk+Rk for the different wood surfaces after each phase of the twolayer coating formation.

84

Fig. 4 shows that the deformations induced in the treated wood when creating wood materials were the cause of the qualitatively different behavior of the substrate surface during film formation.

A

B

Fig. 4 Changes in Rvk and RSm for the different wood surfaces after each phase of the two-layer coating formation.

The change of parameter Rpk+Rk+Rvk, as well as the change of its component parameters (in percent) during film formation, is presented in Fig. 5.

Fig. 5 Composite parameter Rpk+Rk+Rvk change and the change of the base parameters for the different wood surfaces after each phase of the two-layer coating formation.

It is impressive that the small variation of the Rk parameter for solid wood surfaces is less than 5%. In the statistical processing of the data, Rk is distinguished by its low accuracy index (p < 2.25%) and correlation coefficient (V < 19%). These results extend Gurau's conclusion (Gurau, 2022) that Rk is the most stable parameter of the parameters calculated from the Abbott curve for the film formation process as well.

CONCLUSION The presented research investigated the effect of wood substrate structure and surface characteristics prior to coating, the surface treatment before coating, the manufacturer's 85

recommended amount of varnish, and the number of applied layers on the appearance and roughness of surfaces obtained by film-forming a multilayer waterborne bio-based coating.

The liquid system was applied by brush to spruce, beech, and beech plywood. The roughness was evaluated by 12 roughness parameters after each phase of the film formation process.

The results obtained showed that: - It is necessary to apply a two-layer coating on all test surfaces.

- The amount of varnish recommended by the manufacturer is inappropriate when applied with a brush on beech and beech plywood.

- The wood substrate structure and the characteristics of its surface before coating have a determining influence on the roughness parameters in the last phase of the film-building process, as well as on the appearance of the varnished surfaces. The treatment before coating had little effect on the final coating parameters.

- Reduced peak height Rpk, core roughness depth Rk, reduced valley depths Rvk, arithmetic mean deviation of the assessed profile Ra, mean width of the profile elements RSm and the composite parameter Rpk+Rk+Rvk can be proposed as universal parameters for technological control. Reduced peak height can be replaced with sufficient accuracy by the composite parameter Rpk+Rk when environmental conditions vary widely.

The information provided by this study may be useful to optimize the film-forming process conditions for the investigated coating system, which will lead to an increase in its consumption.

REFERENCES Angelski, D., Atanasova, K., 2023. Water permeability and adhesion strength of bio-based coating applied on wood. Drvna industrija (accepted for publishing on August 29, 2023).

Atanasova, K., 2022. Influence of some factors in the formation of varnish coatings on wooden surfaces. Abstract of the PhD thesis. Publishing House at University of Forestry, Sofia, pp. 40, (in Bulgarian).

Cota, H., Ajdinaj, D., Habipi, B., 2017. The influence of machining process on wood surface roughness. Agricultural Sciences 16 (Special issue):7.

Evans, P., 2009. Reducing grain raising during the finishing of wood with water-based coatings.

Report. University of British Columbia. Vancouver, Canada, pp. 54.

Gochev, Z., 2018. Wood cutting and cutting tools. Avangard Prima, Sofia, pp. 523, ISBN 978-619239-047-1 (in Bulgarian).

Gurau, L., 2022. Testing the processing-induced roughness of sanded wood surfaces separated from wood anatomical structure. Forests, 13, 331. https://www.mdpi.com/1999-4907/13/2/331 Hamidi, N. A. S. M., Kamaruzzaman, W. M. I. W. M., Nasir, N. A. M., Shaifudin, M. S., Ghazali, M. S. M., 2022. Potential Application of Plant-Based Derivatives as Green Components in Functional Coatings: A Review.

Cleaner Materials 4. https://www.sciencedirect.com/science/article/pii/S2772397622000570 https://www.covestro.com/ https://www.masquelack.com/BIO-BASED_WOOD_STAIN.html ISO 3274:1996. Geometrical product specifications (GPS) - Surface texture: Profile method Nominal characteristics of contact (stylus) instruments.

ISO 4287:1997. Geometrical product specifications (GPS) - Surface texture: Profile method - Terms, definitions and surface texture parameters.

ISO 13565-2:1996. Geometrical Product Specifications (GPS) — Surface texture: Profile method; Surfaces having stratified functional properties — Part 2: Height characterization using the linear material ratio curve.

Kavalov, A., Angelski, D., 2015. Alternative methods for friction smoothing of wood surfaces. ISBN 978-954-332-137-7 (in Bulgarian).

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Kúdela, J., Mrenica, L., Javorek, L., 2018. The influence of milling and sanding on wood surface morphology.

Acta Facultatis Xylologiae Zvolen, 60(1): 71−83. http://10.17423/afx.2018.60.1.08 Landry, V., Blanchet, P., Cormier, L. M., 2013. Water-based and solvent-based stains: Impact on the grain raising in Yellow Birch.

BioResources 8(2), 1997-2009. https://bioresources.cnr.ncsu.edu//BioRes_08/BioRes_08_2_1997_Landry_BC_Water_Solven t_Stains_Grains_Rising_Birch_2991.pdf Magoss, E., Molnár, Z., Suri, V., 2019. Еvaluating of wetting-induced effects on the surface stability of sanded wood. Wood research 64 (3), 401-410.

Müller, B., Poth, U., 2011. Coatings Formulation. Vincentz Network, pp. 287, ISBN 978-3-86630891-6.

Ramananantoandro, T., Eyma, F., Belloncle, C., Rincé, S., Irle, M., 2018. Effects of machining parameters on raised grain occurring after the application of water-based finishes. European Journal of Wood and Wood Products 76, 1323-1333. https://www.researchgate.net/publication/320693233_Effects_of_machining_parameters_on_r aised_grain_occurring_after_the_application_of_water-based_finishes Sandak J., Martino, N., 2005. Wood surface roughness – what is it? Proceedings of the 17th International Wood Machining Seminar (IWMS 17). Rosenheim, Germany, 26-28 pp.

Salcă, E. A., Krystofiak, T., Lis, B., Mazela, B., Proszyk, S., 2016. Some coating properties of black alder wood as a function of varnish type and application method. BioResourses 11(3), 75807594. https://bioresources.cnr.ncsu.edu/resources/some-coating-properties-of-black-alderwood-as-a-function-of-varnish-type-and-application-method/ Slabejova, G., Šmidriaková, M., Moring. M., 2017. Surface roughness of water-based finishes on aspen poplar wood. Ann. WULS-SGGW, For and Wood Technol. 98: 126-131.

ACKNOWLEDGMENT This paper was supported by the National Program "Young Scientists and Postdoctoral Students-2" - Bulgaria, University of Forestry, Faculty of Forest Industry.

AUTHORS’ ADDRESSES Assist. Prof. Krasimira Atanasova, PhD Prof. Dimitar Angelski, PhD University of Forestry, Sofia Faculty of Forest Industry 10 Kliment Ohridski Blvd.

1797 Sofia Bulgaria k_atanasova@ltu.bg d.angelski@ltu.bg

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 89−98, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.08

STUDY OF THE INFLUENCE OF BASIC PROCESS PARAMETERS ON THE ROUGHNESS OF SURFACES DURING MILLING OF SCOTS PINE WOOD Valentin Atanasov – Georgi Kovatchev – Tihomir Todorov ABSTRACT Experimental results in the processing of Scots pine (Pinus sylvestris L.). are presented in the paper. They were conducted under the manufacturing conditions. Three machines are used – two jointers with different knife spindle designs and with flat knives and replaceable rigid alloy plates – a helical cutter head, as well as a planer with flat knives.

The measured parameter is Rz, and an electronic profilometer was used to measure its reading. The studies were conducted using the method of planned two-factor regression analysis. The selected factors are fundamental to the milling process – feed speed vf and radial depth of cut ae. Their levels of variation are determined on the basis of preliminary experiments, as well as the practical possibility of their realization. The results obtained with all three machines do not exceed 45 μm, and the ones for the planer make the strongest impression.

Keywords: roughness; jointer; planer; knife spindle; solid wood; Scots pine.

INTRODUCTION Longitudinal milling machines are widely used in companies to manufacture the furniture, doors, windows and other wood products. After cutting the rounded wood materials by frame saw, band saw, or circular saw machines and the subsequent hydrothermal treatment, their surfaces are rough, uneven, and unsuitable for furniture production without additional treatment. The first mechanical treatment, which is carried out after the primary cutting of the wood materials, is called “base forming” and is carried out on jointers. After the processing of this machine is done – most often on the side and edge, it is moved to setting the exact thickness of the wood materials. The device for this operation is called a planer. The working spindles of these machines rotate at high revolutions – from 3000 to 8000 min-1- which implies that the surfaces they process will be smooth and of good quality.

When processing with milling machines, two working movements are performed – cutting and feeding. The main working movement (cutting movement) is rotational and uniform. It is performed by the cutting spindle. In the milling machines included in the present work, the feeding movement is performed by the processed material. A number of theoretical dependencies are found in the literature, which, according to the authors, allow the calculation of the roughness depending on the feed speed (Filipov 1979, Glebov 2007).

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These formulas refer entirely to the depth of kinematic waves and, for simplification purposes, ignore several other factors affecting roughness.

Surface roughness is one of the main indicators that characterize the wood milling process. Apart from that, it summarizes a number of factors related to the processed material, the machine and the cutting tools, workplace conditions, the machine operator's qualification, and the kinematics of the milling process. The first factors are of such a nature that if certain norms are observed, their influence on the roughness can be minimized. The last of the mentioned factors cannot be eliminated, as it is related to the milling process and has a significant influence on the quality of the obtained surfaces. The most commonly measured parameter used to determine the roughness of milled wood surfaces is Rz, which is the arithmetic mean of the five highest protrusions and the five deepest recesses of the profile within the base length limits (Gochev, 2018; BDS EN ISO 4287:2006; BDS 4622:86). In the current study, the unevenness that occurs due to the kinematics of the milling process are of interest.

As is well known with an increase in the speed of the working movements of the longitudinal milling machines, it is clear that their productivity will also increase.

However, they can increase up to a certain value. In addition, the feed speed is limited by two technological factors – the available power of the electric motor for cutting and the desired grade of roughness. A large number of experimental studies have been conducted by various researchers. Some of them study the influence of different types of treatment of the processed material, such as: chemically impregnated and thermally treated, on the roughness of the obtained surfaces with different types of woodworking machines (Chuchała, et al., 2023; Korčok et al., 2018; Rajko et al., 2021; Adamčík et al., 2022; Kvietková et al., 2015). Others study the influence of wear and cutting tool construction (Dobrzyński et al., 2019; Vitchev, 2019). The closest to the current research are the experimental studies related to the influence of the feed speed, the cutting speed and radial depth of cut, carried out when milling wood species widely used in furniture production.

The main difference is that they were conducted under different conditions (Vitchev et al., 2018; Vitchev and Gochev, 2018). However, in the literature, the author of the current study did not find comparative experimental studies regarding the influence of different designs of cutting spindles and machines on the roughness of the milled surfaces. This determines the direction of the present study. It is part of a larger one, some of whose results were already published. For example, in Atanasov et al. (2022) and Atanasov et al., (2023), the influence of milling feed speed and radial depth of cut, the type of cutting spindle and the type of machine, on the roughness of the obtained surfaces when milling a hardwood species such as beech (Fagus sylvatica) and the tropical wood of meranti (Shorea leprosula) was studied. The research was conducted under the same conditions.

The purpose of the present study is to determine the influence of basic process parameters such as feed speed and radial depth of cut on the roughness of the obtained surfaces when processing Scots pine with different longitudinal milling machines. This also requires comparing the results between the different variants of cutting spindles and determining the range of variation of the studied factors.

MATERIAL AND METHODS For the purposes of the experiment, two jointer machines with a different construction of the knife spindle were used – with flat knives and with helical cutterhead, as well as a planer with a knife spindle with flat knives. The more important technical parameters of the machines used and their cutting tools can be seen in Table 1.

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Tab. 1 Basic parameters of machines and spindles. № 1.

2.

3.

4.

5.

6.

7.

Model Power of the motor driving the cutting mechanism, kW Maximum milling width, mm Diameter of the spindle, mm Cutting diameter, mm Cutting speed, m.s-1 Number of flat blades/ *spatial screw lines Sharpening angle of the cutting edges, °

S630 (Italy)

PF415N (Italy) www.paolonimacchine.it

DMA 41L (Bulgaria) www.stomana.net

www.steton.it

3

4

5.5

420 110 113 32.2

410 125 128 31.5

500 110 113 30.5

4

*3

4

40

40

40

The place for conducting the experiments is the manufacturing conditions of the companies Vik Stroy Ltd – town of Montana and Pentop Ltd – town of Varshets, whose main activities are the production of children's toys and seating furniture. Scots pine materials with a cross section of 50x50 mm and a length of 1000 mm were used as experimental samples. As is well known, although it does not have the mechanical properties of hardwood species (Sydor et al., 2022), its wood is widely used in furniture production. The samples were selected with a minimum number of defects. Moreover, radial lumber was used for the experiment. The density of the samples was determined by measuring the volume – with a caliper/tape measure and the mass – using an electronic scale. In addition, their moisture content was measured using a Lignomat Tester moisture meter (Germany, www.lignomat.de) and a contact thermometer TROTEC (Germany).

The studied factors influencing the roughness are essential to the milling process – feed speed and radial depth of cut. For the purposes of the experiment, a two-factor regression analysis was performed, and the results obtained in combinations between the factors were measured. Their levels of variation are determined on the basis of conducted preliminary experiments, as well as on the basis of the technical capabilities of the machines and the feed mechanisms used. Accordingly, vf ≈ 5, 10 and 15 m.min-1 and ae = 1, 3, 5 mm were chosen. To implement the feeding movement in the jointer machines, a universal roller feeding mechanism is used (HOLZ-HER, Type ETZ, Germany) which can feed the materials at a theoretical speed of 2, 4, 5, 6, 10, 12, 15 and 30 m.min-1.

During the experiment, the temperature and humidity of the working premises were also measured using the device MASTECH MS 6300 (China), because, although to a lesser extent, they influence the studied parameter. In addition, immediately before the start of the experiments, the flat knives of the machines were sharpened, and the cutting edges of the helical cutterhead were replaced.

The roughness of the milled surfaces is determined according to the standards BDS 4622: 86 and BDS EN ISO 4287:2006, through the parameter Rz. Its values were measured by profilometer SJ-210, Mitutoyo, Japan, whose general view can be seen in Figure 1. Its settings are: profile – R, profile filter – Gauss, number of sampling lengths n=6; evaluation length ln=15 mm, cut-off length λc=2.5 mm, λs=8 µm, measuring speed 0.25 mm.s-1.

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Fig. 1 General view of profilometer SJ-210, Mitutoyo (Japan), www.mitutoyo.eu.

The software products QstatLab5 and Microsoft Excel were used for the processing of the results. The experimental matrix is presented in Table 2. It shows the combinations between the factors in explicit and coded form. It is also noted that in order to make the results more reliable, the experiments with the average values of the variation levels of the factors vf ≈ 10 m.min-1 and ae = 3 mm were conducted five times.

Tab. 2 Experimental Matrix. № 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

vf, m.min-1 15 15 5 5 10 10 15 10 5 10 10 10 10 10

x1 +1 +1 –1 –1 0 0 +1 0 –1 0 0 0 0 0

ae, mm 5 1 5 1 3 5 3 1 3 3 3 3 3 3

x2 +1 –1 +1 –1 0 +1 0 –1 0 0 0 0 0 0

RESULTS AND DISCUSSION The average results of measurements for moisture content and density of test samples are φ=12% and ρ=450 kg.m-3. The average values of relative humidity and temperature in the workshops are φw≈55 % and t≈19÷20 ˚C. It means that the conditions for performing the experiment will not adversely affect the results of the study. The resulting regression equations after processing with the software product mentioned above are as follows: PF415N: Rz=25.166+7.293vf+2.862ae+4.818vf 2-0.311ae2+2.807vfae; DMA41L: Rz=23.301+4.963vf+3.716ae+3.144vf2-2.470ae2+2.713vfae; S630: Rz=25.045+3.419vf+0.354ae+1.027vf2-3.489ae2-1.343vfae.

(1) (2) (3)

When comparing the calculated value of Fc – Fisher's criterion with the critical one (Fcr – 9.01), used for verification, it becomes clear that the models are adequate, and the resulting equations can be used to describe the relevant processes. All equations show that the regression coefficient in front x1 is more significant than that in front x2. This means that the feed speed factor has a more significant influence on the studied quantity Rz – the roughness of the obtained surfaces. In addition, the symbol in front of the two studied 92

parameters is "+", which means that as the levels of variation of x1 and x2 increase, the roughness will also increase. Although radial depths of cut are not directly involved in wave formations due to the kinematics of the process but from the derived regression equations, it is observed that, although to a lesser extent, they have an effect on the roughness.

Figure 2 shows the effect of feed speed when machining with the jointer PF415N at the three radial depths of cut. The blue curve refers to ae = 3 mm. It can be seen that at the lower values of the feed speed vf (from 5 to 8 m.min-1) the roughness Rz is approximately 22.7 μm. After exceeding 10 m.min-1 the roughness starts to increase more intensively and at a feed speed of 15 m.min-1 it reaches its maximum of 37.3 μm. Thus, the difference in roughness between the initial and final feed rates is approximately 15 μm. This shows that at lower values of the feed speed, it has a minimal effect on the quality of the machined surfaces, after which it starts to change more intensively. This trend is also observed for the other studied radial depths of cut. As the radial depth of cut, the roughness also increases is probably the different chip separation when the cutting edges penetrate deeper into the wood, as well as the increase in cutting forces. Overall, the figure shows that at the lowest feed speeds, the radial depths of the cut have practically no effect on the roughness.

At all three levels of x2 variation, the roughness barely changes up to a feed speed of about 7.5 m.min-1. Subsequently, it increases, and this tendency is most sharply observed at a radial depth of cut of 5 mm. The maximum roughness value obtained is 42.6 μm at a value of x1 – 15 m.min-1 and x2 – 5 mm, respectively.

Figure 3 shows the influence of the radial depth of cut on the surface roughness when processing Scots pine with the jointer PF415N at an average feed speed (vf = 10 m.mim-1).

It is also observed that the radial depth of the cut factor has significantly less influence on the surface roughness, especially at the lower values. This is confirmed by the regression equations as well – the coefficient in front of the second factor is smaller than that in front of the first. At the low values of radial depth of cut, the roughness is approximately 22 μm, and the maximum value obtained at the highest radial depth of cut is 27.7 μm. In contrast to the previously discussed factor, in the case of radial depth of cut, a more intense increase in roughness with its increase is not noticed.

Fig. 2 Effects of feed speed on surface roughness at different radial depths of cut when machining Scots pine with jointer PF415N.

Fig. 3 Effects of radial depth of cut on surface roughness in longitudinal milling of Scots pine with jointer PF415N.

Figure 4 graphically presents the effect of feed speed on roughness (at ae=3mm), when milling Scots pine with the jointer DMA 41L with helical cutterhead. As it is known from practice, the surfaces obtained after processing with the machines with knife spindles with such a construction are of better quality. In addition, the load on the cutting spindle in 93

these machines is less. The main reason is that with helical knife spindle, the cutting of the wood grains, depending on the movement and the cutting edge, is 90°-90°, 0°-90°, 90°-0°, while with those with flat knives, it is 90°-90°, 90°-0°. The statement is also confirmed by the figure, in which the curve does not exceed that of the flat knives machine along its entire length.

In contrast to the studied jointer machines, with the planer, the feed speed does not have a significant influence on the roughness of the obtained surfaces when processing Scots pine. This is also clearly seen in Figure 5. The difference in the roughness between speed 5 and 15 m.min-1 is less than 7 μm. The main reason for this is the way in which the feed force is conducted, which is frictional – i.e., it is carried out by pressing with a particular force. In addition, there is a methodology in the literature for determining the pressing force, which is more significant for the feed roller after the knife spindle (Vlasev, 2007). For example, if we assume that the cutting forces (Fc – tangential and Fr – radial) Fc = 50 N and Fr = 30 N, as well as the values indicated in the literature for the forces with which the wood is affected by the pressing beams, friction coefficients, we will get that the pressing from the rear roller is with a force of more than 700 N. This means that when passing through the rear feed roller, some of the micro-uniformities are smoothed out, and some of the resulting deformations are plastic, while others are elastic. It is precisely due to the elastic deformations that the roughness increases as the feed speed increases. However, although with minimal differences, its values do not exceed those of the jointer with the spindle with flat knives. During the conduct of the experimental studies, a variant with feeding the part by pushing was also tested. In this way, relatively equal results were obtained with those of the jointer with flat knives. But in practice, with all planers, the feeding movement is based on a frictional principle. For this reason, the entire series of tests was carried out, although the final roughness will differ from that obtained immediately after the knife shaft. In addition, the tested machine does not have a rear pressure beam – i.e., only the rear feed roller has an influence after the knife spindle.

Fig. 4 Effects of feed speed on surface roughness in longitudinal milling of Scots pine with jointer DMA41L.

Fig. 5 Effects of feed speed on surface roughness in longitudinal milling of Scots pine with planer S630.

The next two Figures show results for the influence of the studied factors on the roughness of the surfaces for all three machines examined. Figure 6 shows the effect of feed speed when milling Scots pine with different milling machines at maximum radial depth of cut, and Figure 7 shows the effect of radial depth of cut on roughness when machining Scots pine at the highest feed speed. From the first graph, it is clear that the green curve, which refers to the planer, has the lowest roughness of the milled surfaces.

As mentioned, after the knife spindle, the rear feed roller presses the machined surface, 94

which further smoothes it. When comparing the results of the two jointers, it can be seen that the roughness of the one with the helical cutterhead has lower values. Furthermore, it is known from theory that with larger cutting radii, the depth of the kinematic waves should have lower values. In the studied machines, the cutting radius parameter is bigger in the machine DMA41L. In relation to the less important factor (ae) when operating with the planer, it seems that there is practically no connection between the radial depth of cut and the roughness during processing. However, the regression coefficient before x2 in equation 3 has a positive sign. It means that, in general, as the milling thickness ae increases, there is also a certain increase in the roughness.

Fig. 6 Effects of feed speed on surface roughness in longitudinal milling of Scots pine with different milling machines.

Fig. 7 Effects of radial depth of cut on surface roughness in longitudinal milling of Scots pine with different milling machines.

The results presented above are obtained on the basis of a large number of experimental studies carried out in manufacturing conditions. When we compare those for the jointer with flat knives and calculate the magnitude of the kinematic waves, it is noticed that the difference between the obtained roughness and calculated values for the kinematic waves varies approximately ten to twenty times. This means that the formula proposed by the authors mentioned in the introduction is not very suitable for practical roughness prediction (determined by the parameter Rz), as results show that factors unrelated to the kinematics of the cutting process also have a significant impact on the final roughness.

Comparing the results with the studies of other authors is not very correct, since the conditions of the experiments, the materials used, the machines and their cutting mechanisms are different. As all this would lead to inconsistency. For example, in Vichev and Gochev (2018), the influence of cutting and feeding speeds, as well as uncut chip thickness, are studied, but two of the factors had different levels of variation, and the machine studied is a wood shaper. Other similar experimental studies can be found in the literature. In Vitchev et al. (2021) the influence of feed speed and radial depth of cut when processing linden (Tilia Sp.) with a helical cutterhead jointer is studied. The results confirm that feed speed has a more significant influence on the roughness than the radial depth of the cut. In addition, the obtained values for processing quality for linden are slightly higher than those for the considered wood species. The reason for this is the different conditions for the experiment. Mainly in the different physico-mechanical parameters of the respective wood, the cutting speed and the diameter of the knife spindle.

Comparing the roughness of different wood species is not very correct, as their physico-mechanical properties are different. Even the same type of wood, grown under other conditions, may have different densities, compressive strength, bending strength, 95

shear strength, etc. The elastic and plastic deformations are different, as well as the strength limit of wood fibers (Gochev 2018). When comparing the results with those carried out at the same levels of variation of the studied factors, but in the processing of beech (Atanasov et al., 2022), it is noticed that the tendency is a deterioration of the quality with an increase in the density of the wood. This is slightly contrary to the expected results, since when cutting hardwood, due to its higher resistance, cracks are expected to be less.

The main reason for the worse results can be found in the faster wear of the cutting edges of the tools.

CONCLUSIONS Based on the experimental studies, the following conclusions and recommendations can be made when processing Scots pine with longitudinal milling machines: 1. For planers, it has been proven that pressing the workpiece after the knife spindle has a beneficial effect on the roughness. When calculating with actual values of forces, according to the presented methodology for force calculation of planers, it became clear that the required pressing force from the rear feed roller exceeds 700 N. This means that some of the micro-uniformities that occur during processing are plastically deformed and smoothed out. However, to a lesser extent, a tendency is observed that as the feed speed and radial depth of cut increase, the roughness class deteriorates – i.e., there are also elastic deformations of the surface of the wood materials. This allows planer machines, from a performance standpoint, to be designed with feed mechanisms that can realize a higher feed speed.

2. The roughness results show that at the highest levels of variation of the factors studied, the roughness when milling Scots pine rarely exceeds 40 µm. This means that, from the point of view of the roughness class, a feed speed of over 15 m.min-1 is possible.

During preliminary tests, however, it was found that when the feed speed exceeded 20 m.min-1, the operation of the machine became a difficult task. This gives reason to recommend that the maximum feed speed for longitudinal milling machines should not exceed 20 m.min-1. The lower limit of the feed speed is good to start from 5 m.min-1, because below it the differences in the results are minimal and besides, productivity is low.

Of course, these values are recommended and can be exceeded, but this will certainly lead to difficulties with the servicing of the machine in time.

3. Theoretical dependencies that are found in the literature refer to the depth of the waves as a consequence of the kinematic nature of the milling process. In addition, they are valid subject to a number of conditions. However, the roughness of the resulting surfaces also depends on a number of other factors. This makes them practically difficult to apply. It should not be forgotten that woodworking machines are designed to work in manufacturing, not laboratory conditions. This means that it is recommended to use equations derived from many experimental studies, such as those presented in this paper, to roughly precalculate the roughness.

4. Helical cutter heads are also recommended for constructing the cutting mechanisms of modern longitudinal milling machines. The roughness results for them are better. It means that the feed speed and, hence, the productivity can be higher.

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Product Catalogue Steton – https://www.steton.it.

Product Catalogue ZMM Stomana JSC – https://stomana.net.

Rajko, Ľ., Koleda, P., Barcík, Št., Koleda P., 2021. Technical and technological factors’ effects on quality of the machined surface and energetic efficiency when planar milling heat-treated meranti wood. “Milling of heat-treated wood”. BioResources, 16(4), 7884-7900. https://doi.org/10.15376/biores.16.4.7884-7900.

Sydor, M., Pinkowski, G., Kucerka, M., Kminiak, R., Antov, P., Rogozinski, T., 2022. Indentation Hardness and Elastic Recovery of Some Hardwood Species. Applied Sciences, (12) 5049. https://doi.org/10.3390/app12105049 Vitchev, P., 2019. Evaluation of the surface quality of the processed wood material depending on the construction of the wood milling tool. Acta facultatis xylologiae Zvolen 61(2): 81-90.

Vitchev, P., Gochev, Z., 2018. Influence of the cutting mode on the surface quality during longitudinal plane milling of articles from Scots pine. Proceedings of 9th International conference Innovations in forest industry and engineering design. ISSN1314-6149. 367−373.

Vitchev, P., Gochev, Z., Anglelski, D., 2021. Evaluation of the Surface Quality during Longitudinal Flat Milling of Spacimens from Liden Wood (Tillia Sp.). 14th International Scientific Conference WoodEMA 2021 Response of the Forest-Based Sector to Changes in the Global Economy. 373-37.

Vitchev, P., Gochev, Z., Atanasov, V., 2018. Influence of the cutting mode on the surface quality during longitudinal plane milling of articles from beech wood. Chip and chipless woodworking processes. ISSN: 2453-904X, 11(1): 183−190.

Vlasev, V., 2007. Exercise manual on woodworking machines. Sofia. 2007. 78 p. (in Bulgarian).

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AUTHORS’ ADDRESSES Chief Assist. Prof. Valentin Atanasov, PhD, Chief Assist. Prof. Georgi Kovatchev, PhD, Eng. Tihomir Todorov University of Forestry Faculty of Forest Industry Kliment Ohridski Blvd. 10 1797 Sofia Bulgaria vatanasov_2000@ltu.bg, g_kovachev@ltu.bg, loratihi@abv.bg

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 99−107, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.09

OPTIMIZATION OF THE CNC MILLING PROCESS VIA MODIFYING SOME PARAMETERS OF THE CUTTING MODE WHEN PROCESSING MDF WORKPIECES Aleksandar Doichinov ABSTRACT The modification in the surface quality of Medium Density Fiberboard (MDF) workpieces machined in a CNC milling machine is investigated in the paper. The quality of the milling process is affected by the surface roughness. The present work is focused on the influence of the following cutting parameters: rotation speed (n), feed rate (Vf) and radial depth of cut (h) in optimising the milling process and improving the quality of the milling surface. The roughness of the processed surfaces was measured with a roughness tester, type “Surftest SJ-210” (Mitutoyo, Japan). The surface quality is evaluated using the defined average ̅​̅​̅𝑧 . The results of the current study showed the arithmetical values of roughness parameters 𝑅 following optimal values of the variable factors that ensured the highest quality of the processed surface: rotation n = 18000 min-1, feed rate Vf = 3.5 m.min-1 and radial depth of cut h = 3 mm. Based on the experiments performed, graphical dependencies, presenting the influence of the individual factors on the quality of the processed surface were derived.

Keywords: surface quality; CNC-machining center; cutting mode; CNC shank cutter; MDF; rotation speed; feed rate.

INTRODUCTION The processing of wood and wood-based materials by milling is one of the most frequently used technological operations aimed at giving a certain shape and roughness to the processed surfaces.

CNC-machining centers are increasingly used in modern furniture production. They are characterized by several advantages, among others, ensuring a higher quality of the treated surface.

The influence of various factors on the quality of the milled surface has been studied by a few authors related to the characteristics of the cutting tool, the cutting modes in which the materials are processed and its characteristics. In recent years, a number of studies investigated the influence of different factors, e.g., cutting and feeding speeds, cutting forces, degree of wear of the tool, vibrations on the quality of the processed surface (Ohuchi and Murase 2001, Ohuchi and Murase 2006, Ohuchi et al., 2008, Davim et al., 2009, Sedlecký et al., 2018).

In their research, Davim et al. (2009) and Sedlecký et al. (2018) showed that the roughness values of the processed surfaces of MDF workpieces decrease with an increase in the rotation speed and a decrease in the feed rate. These results were confirmed by the results 99

of other authors (Kminiak et al., 2017; Deus et al., 2015; Vitchev and Gochev 2018). In one of their publications, Aguilera et al. (2000) investigated the roughness of milled MDF workpieces with different densities. They concluded that a deterioration in the quality of the milled surface was observed at a higher density of MDF. The surface roughness is also influenced by the characteristics and design of the cutting tools (Curti et al., 2017; Sedlecký 2017; Vitchev 2019).

Most of the factors affecting the milling process can be controlled and managed.

Therefore, their influence on the surface roughness should be studied, in order to apply optimal milling modes.

The objective of this study was to investigate the influence of the following factors: rotation speed (n), feed rate (Vf) and radial depth of cut (h) on the surface quality of MDF workpieces processed with CNC-machining center.

MATERIALS AND METHODS The experimental research was performed with a CNC-machining center, model Rover A 3.30 (Biesse, Italy) (Figure 1). The machine has three interpolated control axes (X, Y and Z), with operational steps of X = 3060 mm; Y = 1260; mm; Z = 150 mm, correspondingly.

The machine software provides the opportunity for stepless regulation of feed rate (Vf) and change of cutting speed via changing the rotation speed (n).

Fig. 1 General appearance of CNC-machining center, model А 3.30 (Biesse, Italy).

For the cutting process a new CNC finishing spiral router cutter, with a negative spiral with sharpening radius ρ0 = 6 µm, made from solid tungsten carbide (CMT, Italy, figure 2) was used. The technical characteristics of the cutting instrument are presented in table 1, where: D is the cutting circle diameter, I – the cutting length, L – the total length, s – the diameter of the shank, z – the number of spirals (number of teeth), n – maximum RPM.

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Fig. 2 CNC shank spiral finishing cutter – CMT (Italy).

Tab. 1 Technical characteristics of the utilized instrument.

D mm

I mm

L mm

d mm

Z count

n min-1

Material of the teeth

Geometry

12

35

83

12

3

18000

Solid tungsten carbide

Negative spiral

For the purpose of the experiment, unfinished MDF workpieces, were used. The processed details were with the following dimensions: length (L) x width (B) x thickness (T) = 1000 x 200 x 18 mm. The details were processed longitudinally along their edge. The fibreboards were maintained at a temperature of 20 °C ± 3 °C and the methodology for density determination is in accordance with BDS EN 323 and was performed in the laboratory of Kastamonou, Bulgaria. The measured average density amounts to 740 kg.m-3.

To evaluate the influence of the factors: rotation speed of shank cutter (n), feed rate (Vf) and radial depth of cut (h), the methodology of multifactorial planning (Vuchkov 1986) was implemented. The levels of variation in the variable factors are presented clearly and in coded mode in Table 2.

Tab. 2 Levels of variable factor’s change n, Vf and h.

Variable factors Rotation speed n = X1 [min-1] Feed rate Vf = X2 [m.min-1] Radial depth of cut h = X3 [mm]

Minimum value expl.

12000 2 1

coded -1 -1 -1

Average value expl. coded 15000 0 3.5 0 2 0

Maximum value expl.

18000 5 3

coded 1 1 1

The quality of the processed surface, depending on the variable factors, was evaluated by the roughness parameter Rz. It was defined for each base length of the studied surface area. The methodology to determine the surface roughness is in accordance with the BDS EN ISO 4287 and was also described by Gochev (2005). The roughness measurements were carried out along the MDF cross section at both ends and at the center of the sample.

The values of the roughness parameters were measured with a portable roughness tester, model Surftest SJ-210 (Mitutoyo, Japan) (Figure 3), with a reverse travel sensor and a diamond, V-shaped probe tip with radius R = 5 μm, according to BDS EN ISO 3274:2002, in the following settings: 101

- profile – R, profile filter – Gauss; - number of base lengths n1 = 5; - evaluation length ln =12.5 mm; - upper limit of filter λc = 2.5 mm; - lower filter limit λs = 8 μm; - measuring speed 0.25 mm.s-1.

Fig. 3 General appearance of the a portable measuring instrument for surface roughness, model Surftest SJ-210.

The data were statistically analysed by a specialized software Q-StatLab.

RESULTS AND DISCUSSION Based on the performed experiments and the mathematical analysis of the results, the following regression equation was derived (1): 𝑦 = 93,190 + 0,239𝑋1 + 8,174𝑋2 − 9,171𝑋3 − 2,364𝑋12 + 5,351𝑋22 − 3,324𝑋32 − 0,076𝑋1 𝑋2 + 2,634𝑋2 𝑋3 − 2,809𝑋1 𝑋3

(1)

Where: y – predicted value of the output value, defined by the roughness parameter Rz coded.

X1 – rotation speed (n) coded.

X2 – feed rate (Vf) coded.

X3 – radial depth of cut (h) coded.

Using the derived regression equation (1), numerically, the variation of the roughness parameter Rz can be predicted, depending on the values of the variable factors: rotation speed (n = X1); feed rate (Vf = X2); radial depth of cut (h = X3).

Table 3 presents the experimental matrix, on the basis of which the combinations of the studied parameters and their levels of variation were established, and the experimental study was carried out. The calculated arithmetic average values of the roughness parameter ̅​̅​̅𝑧 (μm) are also presented in Table 3. After performing the statistical and mathematical 𝑅 analysis, the regression coefficients were derived and presented in Table 4.

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Tab. 3 Planning matrix for three-factorial experiments and average values оf the roughness parameter ̅𝑹̅​̅​̅𝒛 (μm).

X1 = n min-1

№ 1 2 3 4 5 6 7 8

-1 -1 -1 -1 1 1 1 1

12000 12000 12000 12000 18000 18000 18000 18000

X2 = Vf m.min-1 -1 -1 1 1 -1 -1 1 1

2 2 5 5 2 2 5 5

-1 1 -1 1 -1 1 -1 1

X3 = h mm

̅​̅​̅ 𝑅𝑧 μm

1 3 1 3 1 3 1 3

94.20 75.28 100.47 9.79 100.12 74.67 110.79 91.17

Х1 = n min-1

№ 9 10 11 12 13 14 15

-1 1 0 0 0 0 0

12000 18000 15000 15000 15000 15000 15000

X2 = Vf m.min-1

X3 = h mm

̅​̅​̅ 𝑅𝑧 μm

0 0 -1 1 0 0 0

0 0 0 0 -1 1 0

94.31 86.69 84.82 111.61 101.56 77.52 89.08

3.5 3.5 2 5 3.5 3.5 3.5

2 2 2 2 1 3 2

Tab. 4 Regression coefficients.

Coefficient

Coded value

Coefficient

Coded value

Coefficient

Coded value

b1 b2 b3

0.239 8.174 -9.171

b11 b22 b33

-2.364 5.351 -3.324

b12 b23 b13

-0.076 2.634 -2.809

From the values of the regression coefficients, it is visible that the most significant influence on the roughness parameter had the feed rate (Vf), with regression coefficient b2 = 8.174, followed by the rotation speed of the shank cutter (n), with regression coefficient b1 = 0.239.

The changes in the roughness parameter Rz depending on the rotation speed (n) and the feed rate (Vf), are presented in Figure 4. The obtained results showed that at the two lower feed rates Vf = 2 m.min-1 and Vf = 3,5 m.min-1, the roughness changed from 81 µm to 93 µm.

Higher values of the roughness parameter Rz could be observed with the rotation speed of the shank cutter as follows: at n = 15000 min-1 and Vf = 2 m.min-1, Rz = 90 µm; at n = 15000 min-1 and Vf = 3,5 m.min-1, Rz = 93 µm. Based on the roughness graphs for the three feed rates it is visible that the highest roughness of the processed surfaces is measured at feed rate of Vf = 5 m.min-1, whereas the parameter value Rz changes within 104 µm to 106,7 µm. An increase in the rotation speed of the shank cutter results in insignificant deterioration of surface quality at every parabola in between the initial, peak and end value of Rz (Figure 4).

Fig. 4 Modification of the roughness parameter Rz depending on the rotation speed of the shank cutter (n) and the feed rate (Vf).

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The correlation between the rotation speed of the shank cutter (n) and the radial depth of the cut (h) is presented in Figure 5. The results showed that the best quality of the processed surfaces is achieved with the rotation speed of the shank cutter n = 18000 min-1 and radial depth of cut h = 3 mm. Similar results were reported by Deus et al. (2015) and İşleyen (2019). Their research showed that the roughness of MDF workpieces decreased by increasing the rotation speed of the cutting tool and the depth of cut.

A decrease in the radial depth of cut below 3 mm (h = 2 mm; h = 1 mm) resulted in an increase in the roughness of the processed surfaces. This could be due to the increased vibration in the contact area between the processed detail and the cut-off layer. This relationship is most pronounced in the thinnest radial depth of cut (h = 1 mm), where the roughness also increases with the increase of the rotation speed of the shank cutter (n) within the studied range (Figure 5). These results support the assumption that increased roughness is a result of the increased vibrations generated by the increased rotation speed of the shank cutter and at the same time could not be compensated by the smaller radial depth of cut.

Fig. 5 Modification of the roughness parameter Rz depending on the rotation speed of the shank cutter (n) and radial depth of cut (h)

The correlation between the feed rate (Vf) and radial depth of cut (h) is presented in Figure 6. The curves depict the impact of the feed rate (Vf), on the quality of processed surfaces (Rz). The results clearly show that with an increase in the feed rate, the roughness of the processed surfaces increases as well. Also here, it is visible that an increase is most pronounced in the thinnest radial depth of cut h = 1 mm (Figure 6). The strong influence of the feed rate (Vf) on the roughness of the process surface is also reported by other authors (Kminiak et al., 2020, Sedlecký 2017, Sedlecký et al., 2018, Ohuchi et al., 2008, Ohuchi and Murase 2006, Ohuchi and Murase 2001).

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Fig. 6 Modification of the roughness parameter Rz depending on the feed rate (Vf) and radial depth of cut (h).

CONCLUSION Based on the results of our study, the following conclusions can be drawn: • The roughness of the processed surface is greatly influenced by the feed rate (Vf), the rotation speed of the shank cutter (n) and radial depth of cut (h); • Depending on the specific parameters of the variable factors (Vf and h), the values of the parameter Rz vary from 75 µm to 110 µm. Under the conditions of this study, the most significant impact had the feed rate (Vf). Its increase resulted in an increase in the roughness parameter Rz. • The best quality of the processed surfaces is observed in the following optimal values of variable factors: the rotation speed of the shank cutter n = 18000 min-1, feed rate Vf = 3.5 m.min-1 and radial depth of cut h = 3 mm.

Based on the results, it could be concluded that the MDF workpieces, processed by CNC machines, should be milled at higher rotation speeds of the shank cutter (n > 16000 min-1), at lower feed rates (Vf < 5 m.min-1) and radial depth of cut h > 2 mm.

REFERENCES Aguilera, A., Meausoone, P. J., Martin, P., 2000. Wood material influence in routing operations: The MDF case, European Journal of Wood and Wood Products. Holz als Roh – und Werkstoff 58(4): 278-283, https://doi.org/10.1007/s001070050425 BDS EN 323: 2001- wood-based panels - Determination of density.

Company product catalogue „Biesse”.

Company product catalogue „CMT”.

Curti, R., Marcon, B., Collet, R., Lorong, P., Denaud, L. E., Pot, G., 2017. Cutting forces and chip formation analysis during green wood machining. 23rd IWMS Proceedings, Warsaw, Poland, pp. 152-161.

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Davim, J. P., Clemente, V. C., Silva, S., 2009. Surface roughness aspects in milling MDF (medium density fibreboard), The International Journal of Advanced, Manufacturing Technology 40(1):49-55. https://doi.org/10.1007/s00170-007-1318-z Deus, P. R. D., Alves, M. C. S., Vieira, F. H. A., 2015. The quality of MDF workpieces machined in CNC milling machine in cutting speeds, feed rate, and depth of cut, Meccanica 50(12): 28992906. https://doi.org/10.1007/s11012-015-0187-z Gochev, Z., 2005. Manual of cutting wood and wood cutting tools, Publishing House of University of Forestry, ISBN 954-332-007-1, Sofia, pp. 24-39 (in Bulgarian). İşleyen, U., Karamanoğlu. M., 2019. The influence of machining parameters on surface roughness of MDF in milling operation. Roughness of MDF, BioResources 14(2): 3266-3277, https://doi.org/10.15376/biores.14.2.3266-3277 Kminiak, R., Banski, A., Chakhov, D. K., 2017. Influence of the thickness of removed layer on the quality of created surface during milling the MDF on CNC machining centers, Acta Facultatis Xylologiae Zvolen 59(2): 137-146. https://doi.org/10.17423/afx.2017.59.2.13 Kminiak, R., Siklienka, M., Igaz, R., Krišťák, L., Gerge, T., Němec, M., Réh, R., Očkajová, A., Kučerka., M., 2020. Effect of Cutting Conditions on Quality of Milled Surface of Mediumdensity Fibreboards. BioResources 15(1): 746-766. https://doi.org/10.15376/biores.15.1.746766 Ohuchi, T., Lin, H.C., Fujiomoto, N., Murase, Y., 2008. Development of automatic system for monitoring and removing of burr in side milling process of wood and wood-based materials.

Journal-Faculty-of-Agriculture-Kyushu-University 53(1): 101-105. https://doi.org/10.5109/10078 Ohuchi, T., Murase, Y., 2001. Milling of wood and wood-based materials with a computerized numerically controlled router. Proceedings of the 15th IWMS, L.A., pp 447–455.

Ohuchi, T., Murase, Y., 2006. Milling of wood and wood-based materials with a computerized numerically controlled router V: Development of adaptive control grooving system corresponding to progression of tool wear. Journal-of-Wood-Science-52(5): 395-400, https://doi.org/10.1007/s10086-005-0779-7 Sedlecký, M., 2017. Surface roughness of medium-density fiberboard (MDF) and edge-glued panel (EGP) after edge milling.

BioResources 12(4): 8119-8133. https://doi.org/10.15376/biores.12.4.8119-8133 Sedlecký, M., Kvietková, S. M., Kminiak, R., 2018. Medium-density fiberboard (MDF) and edgeglued panels (EGP) after edge milling-surface roughness after machining with different parameters. BioResources 13(1): 2005-2021. https://doi.org/10.15376/biores.13.1.2005-2021 Thoma, H., Kola, E., Peri, L., Lato, E., Ymeri, M., 2013. Improving Time Efficiency using CNC Equipments in Wood Processing Industry. International Journal of Current Engineering and Technology, Vol.3(2): 666-671. ISSN 2277-4106, Print: 2347-5161.

Vitchev, P., 2019. Evaluation of the surface quality of the processed wood material depending on the construction of the wood milling tool. Acta facultatis xylologiae zvolen, 61(2): 81−90. https://doi.org/10.17423/afx.2019.61.2.08 81 Vitchev, P., Gochev, Z., 2018. Study on quality of milling surfaces depending on the parameters of technological process. Proceedings of 29th International Conference on Wood Science and Technology. Implementation of wood science in woodworking sector, 6-7 December, Zagreb, pp. 195-201, ISBN 978-953-292-059-8.

Vuchkov, I., Stoianov, S., 1986. Mathematical modelling and optimizing of technological objects.

Tehnika, 341 p. (in Bulgarian).

ACKNOWLEDGEMENTS This research is supported by Bulgarian Ministry of Education and Science under the National Program "Young Scientists and Postdoctoral Students - 2".

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AUTHORS’ ADDRESSES Dipl. Eng. Aleksandar Doichinov University of Forestry Faculty of Forest Industry, Department of Woodworking Machines 10 Kliment Ohridski Blvd.

1797 Sofia, Bulgaria e-mail: doichinov78@gmail.com

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 109−121, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.10

STIFFNESS OF SOLID WOOD BEAMS UNDER DIRECT AND OBLIQUE BENDING CONDITIONS Andriy Pavluk – Svyatoslav Gomon – Yuriy Ziatiuk – Petro Gomon – Sviatoslav Homon – Leonid Kulakovskyi – Volodymyr Iasnii – Oleh Yasniy – Nataliia Imbirovych ABSTRACT The article is devoted to studying the features of the work of solid pine wood beams under direct and oblique bending. The study of oblique bending is represented by different angles of inclination. The destructive load of the beams under such conditions and the deformation parameters of bending elements were determined. Experimental results were compared with theoretical ones obtained as a result of calculations in the "LIRA" software complex. Study and analysis of calculations for different types of stiffnesses (with orthotropy, without orthotropy, and with the complete wood deformation diagram) using the software package was carried out. The optimal type of stiffnesses used in the "LIRA" software complex was determined based on the graphs for beam deformation. The results of experimental and theoretical studies can be used to design roof structure elements.

Keywords: solid wood; bearing capacity; oblique bending; bending stiffness.

INTRODUCTION Wood is a renewable natural material, the use of which in various industries is growing significantly (Rudavska et al., 2018, Yasniy et al., 2022, Pinchevska et al., 2019, Homon et al., 2022, Homon et al., 2023, Wdowiak-Postulak 2020). Wood is significantly lighter compared to other materials such as concrete (Dvorkin et al., 2021), metal, various composites (Iasnii et al., 2023, Imbirovych et al., 2023). On the other hand, it is not inferior to them in terms of physical and mechanical properties. However, it prevails in many cases (De La Rosa Garsia et al., 2013; Sobczak-Piastka et al., 2020; Gomon et al., 2020). Bearing elements and structures made of wood are used in the construction of civil and industrial buildings (Vahedian et al., 2019, Soriano et al., 2016, Kudela 2017; Donadon et al., 2020), engineering structures (Bosak et al., 2022). Usually, coniferous species are used (pine, spruce, larch and others) (Homon et al., 2023, Janiak et al., 2023). Wooden elements and structures can work under various types of stress-deformed states (Sobczak-Piastka et al., 2023).

The bending of wooden elements and structures is one of the most common type of stress-deformed state in building practice (Betts et al., 2010, Gomon et al., 2022, Kúdela 2017). Such elements as floor beams, rafters, purlins, trusses work for direct (plane) and oblique bending. The study of such stress-deformed states is important today due to the increased use of wood in buildings. The direct bending of wooden beams has been studied 109

in (Gomon et al., 2019, Vahedian et al., 2019, Sobczak-Piastka et al., 2020). The work of bending elements during oblique bending needs to be studied more (experimental studies were not conducted). There are no complex studies of beams under oblique bending in the “Lira” software. This type of stress-strain state is complex and requires special attention of scientists (Kulman et al., 2017, Gomon et al., 2022, Pencik 2015, Gomon et al., 2023). And, therefore, additional experimental and theoretical studies.

The aim of the paper is to investigate the stiffness of solid wood beams made under the conditions of oblique and direct bending by experimental study and compare obtained results with results of mathematical calculations in the "LIRA SAPR" software complex.

This program allows you to simulate the stress-strain state of various structures and elements.

MATERIALS AND METHODS The experimental part of the research consisted in testing the solid wood beams for direct and oblique bending. An experimental installation for experimental studies was developed by Gomon et al., (2019).

Beams are made of C30 class pine with a length of 1650 mm (DBN B.2.6-161: 2017; NDS: 2018, EUROCODE 5:2004). The cross-section of the beams during oblique and direct bending tests was 50 x 80 mm. The marking of the experimental samples and the characteristics of their work are shown in Table 1.

Tab. 1. Test samples of beams and the characteristics of their testing.

Characteristics of work Direct bend

Oblique bend

Beam name

Cross-sectional dimensions bхh (mm)

B-1 B-2 B-3 B-4 B-5 B-6

50х80

Angle of inclination 10о 10о 25о 25о

The calculation scheme of the test in direct and oblique bending includes a freely lying beam on two supports (hinged movable and hinged fixed). Calculated beam span was 1500 mm. The load was applied in the middle third of the span by two concentrated forces. It allowed ensuring the operation excluding orthotropy of the beam under conditions of pure bending. The calculation scheme of the beam test is shown in Fig. 1.

Fig.1 The calculation scheme of beams B-1…B-6.

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The scheme of the experimental installation during direct bending tests is shown in Fig. 2.

Fig. 2 Scheme of the experimental installation for testing beams B-1, B-2 under direct bending.

Hydraulic jack DOSM-5 was used to apply the load to the beams. The value of load to beams was monitored by used a dynamometer. The distribution of the load was carried out through a metal traverse. All equipment have passed state verification before used in experimental studies. The load was applied by steps of 8-10% of the estimated destructive load, taking into account regulatory documents (DBN B.2.6-161: 2017, NDS: 2018, EUROCODE 5:2004). All deflection gauges were measured after applying each degree of load. Deflection gauges were arranged in the middle of the span during direct bending tests.

ICH-10M, 6PAO watch-type indicators were used to record the beam movement. Exposure was carried out for at least 5 minutes at each level of load.

Beams B-3...B-6 were tested under oblique bending for different angles of inclination. The angle of inclination was ensured by metal clips. Wooden supports were arranged between the metal brackets and the beam to prevent local crumpling of the wood.

The deflection gauges were arranged in the middle of the span in the places of loads applied and on the supports that allowed us to record deformations of the beam. The installation of deflection gauges was carried out in the plane and out of the plane of the beam to record movement in these planes. Ties were installed on the experimental beams at the places of applying the load in order to prevent the influence of the torque (Gomon et al., 2019). The scheme of the experimental installation for oblique bending tests is shown in Fig. 3.

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Fig. 3 Scheme of the experimental installation for testing beams B-3 ... B-6 for oblique bending.

The scheme shown in Fig. 3 allows fully withstand destructive loads for oblique bending at angles of inclination 10о and 25о.

RESULTS AND DISCUSSION The results of deformation measurements were processed after the experimental tests.

An analysis of the destructive loads of the beams was also carried out. The result of such analysis is shown in Table 2. In each series of beam experiments, 5 experiments were conducted (DBN B.2.6-161: 2017). Averaged values were used in subsequent calculations.

Tab. 2 Destructive loads of wooden beams.

Sample series

Destructive loads, F, kN

Character of work

B-1 B-2 B-3 B-4 B-5 B-6

12.2 12.3 22.0 21.9 15.0 15.1

Direct bend Direct bend Oblique bend Oblique bend Oblique bend Oblique bend

112

The analysis of experimental studies showed that during direct bending the deflections increased in proportion to increase the load. The graph of the beam bending dependence on the load for direct bending is shown in Fig. 4.

Fig. 4 Experimental full bending of beams B-1 and B-2.

Bending was measured in the horizontal (Y-Y axis) and vertical (Z-Z axis) directions during oblique bending tests: 𝑤 = √𝑤𝑦2 + 𝑤𝑧2 (1) Where: wy – bending in the axis direction Y-Y, mm, wz – bending in the axis direction Z-Z, mm.

The results of test experiments showed that the bending increased with increasing the load. An increase in inclination angle led to a faster growth of deflections.

The graph of the dependence of total deflections during oblique bending on bending moments is shown in Fig. 5.

Fig. 5 Experimental full deflections of beams B-3...B-6.

Standard deviation of experimental values of the moment at the ultimate deflection of beams series B-3...B-6 according to results was less than 10% and coefficient of variations approximately 2.6%.

After carrying out experiments and processing data the calculation of the beam characteristics was performed using the Lira SAPR software package. The beam model was constructed using 10x10x10 mm volumetric finite elements. Such samples allowed to obtain more accurate results. Type of finite elements 36. In order to determine the optimal type of 113

stiffness, it was decided to perform a calculation in the "Lira SAPR" software complex with several of their values: 1) taking into account orthotropy (Stiffness type 1); 2) excluding orthotropy (Stiffness type 2); 3) taking nonlinearity into account (Stiffness type 3).

The following wood characteristics were used for the first type of stiffness according to (DBN B.2.6-161: 2017, EN 408:2010): 𝐸𝑦 = 12000 𝑀𝑃𝑎; 𝐸𝑧 = 400 𝑀𝑃𝑎; 𝜈𝑦𝑧 = 0.018; 𝜈𝑧𝑦 = 0.45; 𝜌 = 460 𝑘𝑔/𝑚3 It is necessary to ensure that the condition is fulfilled for setting the given characteristics: 𝐸у 𝐸𝑧 =𝜈 (2) 𝜈 𝑦𝑧

𝑧𝑦

The following wood characteristics were used for calculations using the second type of stiffness according to (DBN B.2.6-161: 2017, EN 408:2010): 𝐸𝑦 = 12000 МПа; 𝜈𝑧𝑦 = 0.45; 𝜌 = 460 𝑘𝑔/𝑚3 .

Nonlinearity was considered by constructing a nonlinear deformation diagram of the material (pine wood) (Gomon et al., 2022, Yasniy et al., 2022), which is shown in Fig. 6. At the same time, the following characteristics of the material were used: 𝜈𝑧𝑦 = 0.45; 𝜌 = 510 𝑘𝑔/𝑚3 .

Fig. 6 Deformation diagram of pine wood.

The comparison of the experimental values with the theoretical values was performed at the point of occurrence the maximum allowable full deflection of the test beams.

According to current regulatory documents (DBN B.2.6-161: 2017, DSTU B V.1.2-3:2006), the maximum allowable beam deflection is l/150: 𝑙

Where: l – beam span.

1500

𝑤𝑓𝑖𝑛 = 150 = 150 = 10 𝑚𝑚,

114

(3)

The deflections ranged from 44 mm under a load of 1 kN to 578 mm under a destructive load for direct bending using the first type of stiffness. All such deflections significantly exceed the experimental values. Therefore, this type was not taken into account in the further analysis.

The values of deflections by use two other types of stiffness are shown in Fig. 7. Also, this graph shows the averaged experimental deflection-bending moment diagram for beams B-1 and B-2.

Fig. 7 Deflections of beams during direct bending.

According to the graph, the closest to the experimental deflection values are values calculated in the "Lira SAPR" software complex using stiffness of type 2 (excluding orthotropy).

The displacement isofields of beam B-1 according to stiffness type 2 and 3 at a bending moment of 2.5 kNm are shown in Fig. 8 and 9, respectively.

-28.4

-23.6

-18.9

-23.6

-18.9

-14.2

-9.45

-4.72

-0.0407

0.0407

4.08

2,5 кНм Изополя перемещений по Z(G) Единицы измерения - мм

-28.4

-14.2

-9.45

-4.72

-0.0407

0.0407

2,5 кНм Изополя перемещений по Z(G) Единицы измерения - мм

measurement units, mm

Fig. 8 Isofield of beam B-1 movements along Z axis at a moment of 2.5 kNm using the 2nd type of stiffness.

Z

Y X

Z

Y X

115

4.08

-14.6

-12.1

-9.72

-7.29

-4.86

-2.43

-0.021

0.021

2.1

2,5 кНм Изополя перемещений по Z(G) Единицы измерения - мм

-14.6

-12.1

-9.72

-7.29

-4.86

-2.43

-0.021

0.021

2.1

2,5 кНм measurement units, mm Изополя перемещений по Z(G) Единицы измерения - мм

Fig. 9 Isofield of beam B-1 movements along Z axis at a moment of 2.5 kNm using the 3rd type of stiffness.

Full beam deflections of oblique bending (angle of inclination 10о) using stiffness type 1 were 32 mm under a load of 1 kN and 426 mm under a load of 13 kN. These values significantly exceeded the experimental values. Therefore, this type of stiffness was not further analyzed, as well as with direct bending. The displacement of the beam with the other two types of stiffness are shown in the graphs (Fig. 10, Fig. 11) below at different angles of inclination.

Z

Y

X

Z

Y X

Fig. 10 Full deflections of the beams during an oblique bending at the angle of inclination of 10о.

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Fig. 11 Full deflections of the beams during an oblique bending at the angle of inclination of 25 о.

-16.2

-13.5

-10.8

-8.11

-5.41

-2.7

-0.0142

0.0142

1.42

3.25 кНм Изополя

пер емещений по Z(G) Единицы измер ения - мм

The displacement isofields of beam B-3 for the second type of stiffness at a moment of 3.25 kNm are shown in Fig. 12, Fig. 13.

-16.2

-13.5

-10.8

-8.11

-5.41

-2.7

-0.0142

0.0142

1.42

3.25 кНм measurement mm Изополя перемещений поunits, Z(G) Единицы измерения - мм

-1.82

-1.51

-1.21

-0.908

-0.605

-0.303

-0.00417

0.00417

0.303

0.418

3.25 кНм Изополя пер емещений по Y(G) Единицы измер ения - мм

Fig. 12 Isofield of beam B-3 movements long Z-Z axis at a moment of 3.25 kNm using the 2nd type of stiffness.

-1.82

-1.51

-1.21

-0.908

-0.605

-0.303

-0.00417

0.00417

0.303

0.418

3.25 кНм Изополя перемещений по Y(G) Z Y ЕдиницыXизмерения - мм

measurement units, mm

Fig. 13 Isofield of beam B-3 movements long Y-Y axis at a moment of 3.25 kNm using the 2nd type of stiffness.

A comparison of the averaged experimental diagram of the dependence of the deflections on bending moments with similar ones calculated in the "Lira" software complex is shown in Table 3. The data are given when the maximum allowable beam deflections occur.

The value of the estimated destructive load of beams for the 25-degree angle of inclination was 3.76 kNm, for the 10-degree angle – 5.51 kNm. Z

Y

X

Z

Y

X

117

Tab. 3 Comparison of experimental deflections with deflections calculated in the Lira SAPR software complex.

The value of the moment at the ultimate deflection, kNm Characteristics of work Experimental, M1 Direct bend Oblique bend (10°) Oblique bend (25°)

1 2.5 1.6

software complex "Lira" (type of stiffness) 2, М2 0.9 2.2 1.9

3, М3 1.7 4.1 3.53

Deviation

(|М1 −М2 |)

(|М1 −М3 |)

М1

М1

10 6.8 15.8

,%

,%

41.2 50 54.7

The deflection values calculated in the "Lira" software complex using stiffness type 2 are close to corresponding experimental values according to the Table 3. Deviation errors in such cases were less than 16%. Whereas the values of the deflections using the third type of stiffness differ significantly from the experimental values (error up to 54.7%).

EUROCODE 5:2004 and DBN B.2.6-161:2017 proposed a method of calculating wooden beams for oblique bending. This technique does not consider the elastic-plastic properties of wood according to full deformation diagram (Fig. 6). In Eurocode 5:2004 and DBN B.2.6-161:2017 it is presented that wood works only in the elastic stage of work. Our methodology takes into account the elastic-plastic properties of wood.

Kulman et al. (2019) presented simulation of the work of glued wooden beams with and without prestressing by the finite element method. The advantage of this work is that the bearing capacity and deflections of bending elements were determined. The main drawback is the lack of experimental studies. Modeling of beam operation was carried out only under direct bending. In this article, the work of wood was simulated only in the elastic stage. And this does not correspond to its actual work, since wood works as an elastic-plastic material.

Vahedian et al. (2019) conducted experimental studies of reinforced wooden beams and proposed a methodology for their calculation. As advantage of this paper is that the bearing capacity and deflections of flexural elements were experimentally and theoretically determined. The convergence of the results was satisfactory. The study of wooden beams work takes place only under direct bending. It was not held for the oblique.

CONCLUSION New data regarding the load-bearing capacity and deformability of wood in oblique and direct bending conditions were obtained as a result of experimental and theoretical studies. Based on the obtained results, the following conclusions were made: - the ultimate beam deflections at an inclination angle of 10° occur at an average moment value of 2.05 kNm, at an inclination angle of 25° - 1.6 kNm; - deflection values calculated by using the second type of stiffness (excluding orthotropy) in the software complex "Lira SAPR" are the closest to the experimental; - the result of the calculation of the work of beams for direct bending without orthotropy in the "Lira SAPR" software complex showed that the deviation error of deflections of experimental results is 10%, while for the works on oblique bending such error was 6.8% and 15.8% at angles of inclination of 10° and 25°, respectively; - taking orthotropy into account for the calculation beams for oblique and direct bending in the "Lira SAPR" software complex increases doubles the value of deflections on average; - nonlinearity significantly increases the value of deflections.

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The results of the research can be used in the design of beams made by solid wood of rectangular cross-section under oblique bending. According to results it was established that LIRA software complex can be used to simulate bending deformations of building materials before their use in building construction where can be possible not only direct bending forces but also oblique ones. The best accuracy of modeling and estimation of ultimate beam deflections under the destruction load, which are closest to the real value, is achieved at smaller angles of inclination of oblique bending by using the second type of stiffness (excluding orthotropy). For such bending, the deviation of the experimental data M1 with the calculation results is no more than 16%.

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Homon, S., Gomon, P., Gomon, S., Vereshko, O., Boyarska, I., Uzhegova, O., 2023. Study of change strength and deformation properties of wood under the action of active acid environment.

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AUTHORS’ ADDRESSES Senior lectures Andriy Pavluk, PhD Prof. Svyatoslav Gomon, DrSc Assoc. Prof. Yuriy Ziatiuk, PhD Assoc. Prof. Petro Gomon, PhD Prof. Sviatoslav Homon, DrSc National University of Water and Environmental Engineering Soborna Street 11 33028 Rivne, Ukraine homonsviatoslav@ukr.net 120

Assoc. Prof. Leonid Kulakovskyi, PhD National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute" Prosp. Peremohy 37, 03056 Kyiv, Ukraine kulakovskiyl@ukr.net Prof. Volodymyr Iasnii, DrSc Prof. Oleh Yasniy, DrSc Ternopil Ivan Puluj National Technical University Ruska Street 56 46001, Ternopil, Ukraine v.iasnii@gmail.com Assoc. Prof. Nataliia Imbirovych, PhD Lutsk National Technical University Lvivska Street 75 43018 Lutsk, Ukraine n.imbirovych@lntu.edu.ua

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 123−134, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.11

COMPARISON OF THE ATTRIBUTES OF THE WOOD PROCESSING INDUSTRY AND AUTOMOTIVE AND ENGINEERING INDUSTRIES IN THE CONTEXT OF QUALITY MANAGEMENT SYSTEMS Pavol Gejdoš – Jarmila Schmidtová – Krzysztof Knop ABSTRACT The aim of the paper is to compare the effect of implementing a more extensive scope of methods and quality management approaches of the enterprises in wood processing, automotive and engineering industries in Slovakia. The automotive and engineering industries have been selected for comparison because there is a significant difference in the approach of the state support and incentives of these industries as well as they are important manufacturing industries with a significant GDP share and export rate in Slovakia. At the same time, there is a presumption of several common determinants of implementing quality management systems and the circular economy potential in comparison with the woodprocessing industry. The results of performed analyses revealed the existence of significant relations among capital structure and the complexity of using the quality management methods, tools and approaches.

Keywords: quality; quality management methods tools and approaches; wood processing industry; automotive and engineering industry.

INTRODUCTION Quality management is a dynamic category and takes on new significance in the context of the current development of society in changing conditions. Modern management of top organizations currently prefers a strategic approach to the quality of all outputs and corporate activities. The main goal is to achieve maximum customer satisfaction at optimal costs. The strategy of increasing customer satisfaction leads to the improvement in productivity, efficiency and quality, which brings an increase in competitiveness, i.e., the overall success of the organization. Several studies (Ondra, 2021, Mizanbekova et al., 2017) present that the application of quality management principles leads to an increase in the competitiveness of companies, customer satisfaction and improvement of the quality parameters of products, which ultimately contributes to increasing the performance and efficiency of the company. In the paper, we want to get answers to the following research questions (RQ). RQ1: Does the capital structure of the enterprise influence the use of quality management methods, tools and techniques? RQ2: Are there differences in the application of quality management methods, tools and techniques among industries of the national economy?

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The paper deals with comparing selected industries of the national economy in the context of implementing quality management systems. The following sectors have been chosen for comparison: the wood-processing industry as an industry based on the processing of available domestic renewable raw material, where there is a high potential for its development, and the automotive and engineering sectors, which are traditional in our economy, have good support by the state and significantly contribute to the export of the Slovak Republic. In this paper, ISO 9000 standards and TQM philosophy are considered quality management approaches, while quality management procedures are represented by Six Sigma methodology. These approaches and techniques have been selected for their intensity of utilization, suitability and complexity. The contribution of the research is the comparison of selected industries of the national economy concerning the implementation of quality management approaches as well as verification of the most common reasons for the use and implementation of quality management approaches in these enterprises.

According to (Elwardi et al., 2021) and (Ribeiro et al., 2019), the ISO 9001 standard specifies the requirements for a quality management system in organizations that want and need to demonstrate their ability to consistently provide products in accordance with relevant regulations and customer requirements, and that strive to increase customer satisfaction.

(Nenadal et al., 2018) states that the positive aspect of ISO 9001 standards is the pressure to establish order in organizations by determining responsibilities and competences, process descriptions, etc. According to (Sarb et al., 2019) and (Knop, 2021), the implementation of the quality management system according to ISO 9001 is a strategic decision for an organization that can help improve its overall performance and provide a sound basic for sustainable development. This International Standard promotes the adoption of a process approach when developing, implementing and improving the effectiveness of a quality management system. This approach enables the organization to control the interrelationships and interdependencies among the process of the system, so that the overall performance of the organization can be enhanced (Su et al., 2020).

According to (Al Robaaiy and Al-Husseini, 2022) the Six Sigma is one of the tools of the modern quality management system, which is concerned with diagnosing and treating deviations to improve the performance of the processes, an attempt to manage cost through the use of accounting and statistical concepts. Six Sigma is one of the management philosophies required to achieve improved quality and process performance in systems (UDominic et al., 2021). (Al-Otaibi, 2021) claims that Six Sigma is a process improvement method that aims to discover and eliminate the causes of defects, mistakes, and errors.

According to several authors (Uluskan, 2020; Lande et al., 2016; Antony et al., 2017), Six Sigma emphasizes the financial advantages (reduced production costs and higher profitability) of reducing waste and increasing quality. According to some authors (Pande et al., 2002), the Six Sigma is the quality management system in enterprises. Other authors (Yadav et al., 2019) designate Six Sigma as a tool or methodology enabling one to reach business excellence.

TQM is a system approach towards management that aims to continuously increase customer values by designing and continually improving organizational processes and systems. Total Quality Management (TQM) is a universally applied management strategy to improve organizational performance and thereby to achieve competitiveness (Babu and Thomas, 2021). TQM can be summarized as a management system for a customer-focused organization that involves all employees in continual improvement. (Alawag et al., 2020) states that a core definition of TQM describes a management approach to long-term success through customer satisfaction. In a TQM effort, all members of an organization participate 124

in improving processes, products, services, and the culture in which they work. According to (Alhamd and Yahya, 2021), Total quality management is a structured approach to overall organizational management. (Kisel'akova et al., 2020) states that the focus of the process is to improve the quality of an organization's outputs, including goods and services, through the continual improvement of internal practices.

The aim of the paper is to compare the effect of implementing a broader scope of methods and quality management approaches (a broader scope means the use of two or more methods) of the enterprises in wood processing, automotive and engineering sectors in Slovakia.

MATERIALS AND METHODS The procedure for preparing an article can be summarized in the following steps. In the first step, we reviewed scientific papers authored by various experts dealing with the issue at hand. In the second step, we created a questionnaire comprising several questions about the company, including its size, economic performance, capital, and inquiries related to the introduction of quality management systems. Our particular focus was on obtaining answers regarding the use of quality management methods, tools, and approaches, as well as the reasons for implementing these systems and the benefits associated with them. Moving on to the third step, we distributed the questionnaire to various branches of industrial enterprises in Slovakia via email. Subsequently, in the next phase, we formulated working hypotheses and evaluated the questionnaire responses using selected statistical methods.

Following this, we compared our results with the research of other authors investigating the same issue. This comparison provided valuable insights and helped contextualize our findings. In the final step, we formulated conclusions and outlined the future direction of our research.

The research was conducted using a survey method involving the distribution of a questionnaire. The questionnaire was addressed to Slovak manufacturing enterprises of different industries divided according to NACE classification (European Industry-standard classification system, section C Manufacturing). The survey was conducted in the last two years 2020 and 2021, through the platform docs.google.form.

The current questionnaire link is as follows: https://docs.google.com/forms/d/e/1FAIpQLSfp0H8V5dEf1UTZlF2YjK_wDjLTH9lZ8U0 qgd-dPZd4H6HClQ/viewform.

To determine the necessary sample size, a formula for a population of finite size according to Yamane Taro (Lind, 2020) was as follows. 𝑁

𝑛 = 1+𝑁∙𝐸2

(1)

To determine the minimum sample size, a formula for the finite population according to Yamane Taro was applied. With a target population size of 2,504 units and the selected error e=0.05 the minimum sample size was derived as: Because the target population was divided into subgroups according to different industries, stratified sampling was applied to ensure that the sample was representative. The questionnaire was distributed to Slovak manufacturing enterprises by e-mail contacts, repeatedly in several rounds. In the end, 364 correctly filled and usable questionnaires were obtained for the research. The minimum sample size condition was met. In terms of 125

representativeness, Fig. 1 shows how the distribution of the research sample by individual industry replicates the population. The Chi-square goodness-of-fit test was applied for testing (Tab.1).

Tab. 1 Results of the test of representativeness. χ2 goodness-of-fit test criterion

Degree of freedom

p-level

5.89

15

0.981

Several methods of inductive statistics, suitable for working with categorical data and frequencies, were used to test the research hypotheses. The Pearson chi-square test was applied to test the significance of the relationship between two categorical variables. The measure is based on the observed and expected frequencies – frequencies that we would expect if there was no relationship between the variables (Box et al., 2005): χ2= ∑

(O - E) 2 E

(2)

The test statistic allows researchers to measure the degree of disagreement between the frequencies observed (O) and theoretically expected (E) – when the two variables are independent. The chi-square test becomes increasingly significant as the numbers deviate further from this expected pattern. The only assumption underlying the Chi-square statistics is that the expected frequencies are not very small (below five). The coefficient of contingency measures the relation between two categorical variables with a scale from 0 to 1, where 0 means complete independence.

95% confidence intervals were calculated for the estimation of population proportions according to the formula (Lind, 2020), where p represents a point estimate of a given proportion, n is the sample size, and z is the critical value of standardized normal distribution: p ( 1 - p) p - z α∙ √ n < π < p + z α ∙ √p (1n- p) (3) 2 2 A test criterion based on the z statistics was used to test the difference between two population proportions (Box et al. 2005): |z| =√

n1 n2 |p1 - p2 | ∙ n1 + n2 √p (1 - p)

(4)

Parameter p=(p1.n1+p2.n2)/(n1+n2), p1 and p2 are the sample proportions, and n1, n2 are the sample sizes.

All statistical analyses were carried out using the software STATISTICA 12. In hypothesis testing an alpha level of 0.05 was traditionally used as the decision rule. The output tables were edited in the Microsoft Excel spreadsheet editor.

Many studies assert that quality and its associated approaches serve as essential tools for companies to align with their strategies and enhance their performance (Sahoo, 2021; Gambi et al., 2021; Liu et al., 2021). Supporting evidence for Hypothesis H1 can also be found in publicly available data from comparisons of industrial sector performance in the national economy, sourced from the Statistical Office of the Slovak Republic and the Finstat database. Over several years, these sources have consistently indicated that the automotive and engineering industries outperform the wood-processing industry. The connection between improved performance and the utilization of quality approaches is further 126

substantiated in the study conducted by Kafetzopoulos et al. (2021). Consequently, Hypothesis H1 was formulated as follows: H1: It is assumed that enterprises of automotive and engineering industries use a wider range of quality management methods, tools and approaches (QMMTA) than the wood-processing industry.

Regarding the interplay between capital structure, performance, and the quality of business management, a potential relationship was explored in the study by Zandi et al.

(2020). It is widely acknowledged that industrial enterprises in Slovakia with foreign capital structures exhibit greater competitiveness and flexibility in responding to various changes compared to enterprises with domestic capital structures. The question that arises is whether this argument extends to the complexity of Quality Management Methods and Tools Application (QMMTA). Therefore, Hypothesis H2 was established as follows: H2: It is assumed that there is a dependence of the capital structure of selected manufacturing industries and the complexity of QMMTA use.

Some authors (Abdi and Singh, 2022; Neves et al., 2021; Nenadál et al., 2018) enumerate a wide range of reasons for implementing quality management, but they do not delineate the order of priority among these reasons. Consequently, Hypothesis H3 was formulated as follows: H3: It is assumed that in the practice of automotive, engineering and wood-processing industries, the theoretical assumptions of the reasons for the implementation of quality management systems will be confirmed, namely the product quality improvements and customer satisfaction increase.

RESULTS AND DISCUSSION To determine the minimum sample size, a formula for the finite population was applied. With a target population size of 2,504 units and the selected error e=0.05 the minimum sample size was derived as: 2 504 n= (5) 2 = 345 1 + 2 504 ∙ 0.05

Fig. 1 Proportions of different industries in the target population according to NACE codes; * NACE 32 includes NACE 5, 7, 8, 9, 18, 19 (European Industry-standard classification system, section C Manufacturing).

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NACE 24+25 were represented with the highest percentage in the research population but afterwards in research, about the using of QMMTA's (Fig. 2), those two NACE 24+25 were not considered because the aim of the paper was to compare selected industries according to the reasons that were written in the introduction.

In the context of the first hypothesis the proportions of enterprises which use a wider scale of quality management techniques and approaches are illustrated in Fig 2. The highest share 89.47% of enterprises is observed in the automotive industry. Within the enterprises of the engineering industry, it was 51.85%. As for the enterprises of the wood processing industry, the share of those that use a wider scale of QMMTA was 43.18%.

Using of Quality Management Mewthods, Techniques and Approaches 51.85% NACE 28 89.47% NACE 29 43.18% NACE 16, 17, 31 0%

20%

40%

wider scale of QMMTA

60%

80%

100%

smaller scale of QMMTA

Fig. 2 Use of QMMTA in surveyed enterprises of automotive, engineering and wood processing industry. *NACE 16 Manufacture of wood and of products of wood and cork, NACE 17 Manufacture of paper products, NACE 31 Manufacture of furniture, NACE 28 Manufacture of machinery and equipment, NACE 29 Manufacture of motor vehicles, trailers, and semi-trailers

Subsequently, the observed differences were tested using a two-sample z-test for proportions. The results of the testing are presented in Tab. 2. A significant difference (p=0.000) was confirmed in the case of the automotive and wood processing industry. No significant difference in the use of wider scale of QMMTA was confirmed between the engineering and wood processing industries (p=0.177).

Tab. 2 Results of two-sample z-test for the difference in the proportion of enterprises using a wider scale of QMMTA. Industry type 1

n1

p1

Industry type 2

n2

p2

z-test

p-level

Wood processing

44

43.18%

Automotive Engineering

19 81

89.47% 51.85%

3.41 0.93

0.000 0.177

As part of the second hypothesis, the distribution of investigated companies based on two variables – capital structure versus the using of QMMTA is shown in Fig. 3. Wider scale of QMMTA was applied in 92.31 % of the manufacturing enterprises with foreign capital structure. In the group of enterprises with mixed capital structure, it was 61.90%. As for enterprises with domestic capital, 34.52% of them stated that the wider scale of QMMTA was applied.

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Capital structure vs. QMMTA 100% 80% 60%

92.31%

40%

61.90% 34.52%

20% 0%

domestic

mixed

foreign

Capital structure wider scale of QMMTA

smaller scale of QMMTA

Fig. 3 Two-dimensional distribution of the investigated manufacturing enterprises according to capital structure and using QMMTA.

The chi-square test was used to test the dependence between the capital structure of enterprises and the use of QMMTA. A significant dependence was determined based on the corresponding p-value of the Chi-square test statistic (p=0.000). The contingency coefficient value of 0.45 indicates a moderately strong dependence.

Tab. 3 Results of Pearson chi-square test of contingency – capital structure of manufacturing enterprises versus use of QMMTA. Capital structure vs.

QMMTA

Chi-square test

Degree of freedom

p-level

Contingency coefficient

36.41

2

0.000

0.45

A more detailed look at the nature of the dependence is given based on the residual frequencies shown in Tab. 4. The confirmed support is manifested mainly by manufacturing enterprises with a domestic capital structure using QMMTA tools on a smaller scale. In comparison, enterprises with a foreign design apply a broader scale of QMMTA. Tab. 4 Contingency table of residual frequencies – structure of manufacturing enterprises versus the use of QMMTA. smaller scale of QMMTA

domestic

wider scale of QMMTA -16.5

mixed

1.6

-1,6

foreign

14.9

-14.9

Capital structure

16.5

In the third hypothesis focused on the reasons for the implementation of QMMTA, point estimates of proportions (Tab. 5) formed the starting point for the next calculations.

Within wood processing enterprises, the most frequent reasons for implementing QMMTA competitiveness, product quality, and customer satisfaction are almost in the same share: 40.91%, 36.36%, and 36.36%. The given reasons were the most frequent also in the sample of automobile enterprises, but in shares 73.68% competitiveness, 84.21% product quality, and 73.68% customer satisfaction. The investigated enterprises of the engineering industry,

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in addition to the mentioned three reasons (39.51%, 44.44%,40.47), indicated to a considerable extent, namely 44.44%, also customer requirement as a guarantee of quality.

Tab. 5 The reasons for the implementation of QMMTA and the shares of surveyed manufacturing enterprises that spoke in their favour.

Reason for implementation of QMMTA Improving market position Competitiveness Product quality Customer satisfaction Customer requirement as a guarantee of quality Participation in tenders Positive references Getting better orders

Manufacturing enterprises Wood processing Automotive 31.82% 42.11% 40.91% 73.68% 36.36% 84.21% 36.36% 73.68%

Engineering 27.16% 39.51% 44.44% 40.47%

22.73%

52.63%

44.44%

9.09% 6.82% 27.27%

10.53% 10.53% 15.79%

8.64% 6.17% 14.81%

With a reliability of 95%, confidence intervals for the most frequent reasons for implementation of QMMTA in Slovak wood processing enterprises were calculated (Tab. 6).

Tab. 6 Interval estimate of the proportion of wood processing enterprises that implement QMMTA for the following reasons.

Reasons for implementation of QMMTA competitiveness product quality customer satisfaction

95-% Confidence Intervals (26%; 55%) (22%; 51%) (22%; 51%)

The most common reasons for the implementation of OMMTA in enterprises of the wood processing industry in Slovakia are competitiveness, product quality, and customer satisfaction. For all three mentioned reasons, a 50% share was reached as the upper limit of the interval estimate.

Some of the findings in this paper are in line with other research studies. The authors agree that methods, tools and approaches to quality are important factors influencing the performance and competitiveness of enterprises. These claims are also confirmed by research studies published by Marcysiak (2021), Liu et al. (2021), Shafiq et al. (2019), Jimoh et al. (2019), Ghicajanu (2019). Therefore, the application of QMMTA in manufacturing enterprises has been addressed by several authors, including Gambi et al. (2021), Bera & Mukherjee (2018), Agarwal et. al. (2013). The research results presented in this study follow up on previous studies and complement them with a comprehensive view of the utilization of QMMTA in the manufacturing sector. Through a scale of approaches, methods and tools related to quality management, it evaluates their synergistic effect on the consequence factor which is business performance. The synergistic effect was also confirmed using a wider scale of QMMTA (Wu, 2020, Sader et al. 2019). The potential impact of the synergistic effect is given by the assumption of simultaneously applying several quality management approaches. Other authors also confirmed these research results (Abdi and Singh, 2022; Neves et al., 2021; Bravi and Murmura, 2021; Nenadál et al., 2018).

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CONCLUSION Quality management is an important part of the management, which aims to optimize work or production processes with the respect of the resulting product quality. Modern quality management currently prefers a strategic approach to quality. The main goal is to achieve maximum customer satisfaction at an optimal cost level. The aim of the paper was to analyze the use of quality management approaches and techniques in the wood processing industry and its comparison with the automotive industry and engineering industry. Using statistical tools, the established hypothesis H2 was confirmed that there is a dependence on the capital structure of selected manufacturing industries and the complexity of QMMTA use. H1 was confirmed. Although there is a significant difference between the woodprocessing industry and the automotive industry in the use of QMMTA, no significant difference was confirmed in the use of a broader scale of QMMTA between the engineering and wood-processing industries.

In the second part of the paper, the reasons why wood processing enterprises, automotive enterprises and engineering enterprises decided to implement quality management approaches and procedures were examined. The establishment of the hypothesis was based on theoretical assumptions. The hypothesis assumed that the main reasons for the implementation of selected approaches are the improvement of product quality and the increased customer satisfaction. The results indicated that the established hypothesis was again confirmed.

In terms of answers to the research questions, the following can be stated: RQ1 addressed, whether there is an influence of the capital structure of the enterprises on the use of quality management methods, tools and techniques. Based on the results of the research, it can be concluded that there is such an influence. Enterprises with predominantly domestic capital use QMMTA much less than those with foreign capital. RQ2 addressed whether there are differences in the application of quality management methods, tools and techniques among industries of the national economy. Based on the results, it can be concluded that there are such differences. The difference was mainly in the automotive industry, where the use of QMMTA was more extensive than in the engineering industry. QMMTA in the woodprocessing industry is applied to the least of the examined industries. The research contributed to the identification of differences in the use of QMMTAs within the individual examined industries, where there is still a group of enterprises within different sectors that reject the implementation of quality management systems. Therefore, there is still a relatively wide space and potential for more intensive use and implementation of quality management systems. A certain limiting factor of the present research is that the results are obtained by the questionnaire survey in the manufacturing enterprises in one country only.

However, the intention was to initiate research of current issues in a more comprehensive sense. The presented results could become an information base for comparison with related research studies in the European business environment. Identification of the causes of the relatively low level of use of QMMTA, especially in wood processing enterprises, but also determining the real benefits of their implementation are becoming the future orientation of research. Future research should include a more extensive comparative survey of selected central European countries. At the same time, certain research barriers have been identified, which include data collection and especially the reluctance of many manufacturing enterprises to provide information and data necessary for research assessment.

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In conclusion, it can be stated that the industries with a significant support from the state use a wider range of QMMTA, which leads to higher performance, competitiveness, flexibility and so on. The wood-processing industry is an industry of the national economy that deserves more significant attention and support from the state, especially because it processes domestic renewable raw material with significant potential to apply the principles of the circular economy, which, in addition to a stable economy, shall increase the quality of the environment and human life by increasing the efficiency of production.

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International Journal of Financial Research, 11 (2), 293–300. https://doi.org/10.5430/ijfr.v11n2p293 ACKNOWLEDGMENT This contribution is a part of the work on the project VEGA no. 1/0093/23 “Research of the potential of the circular economy in the Slovak business environment in the production of innovative products based on recycled materials wood - rubber – plastic“.

AUTHORS’ ADDRESSES Ing. Pavol Gejdoš, PhD. Technical University in Zvolen Faculty of Wood Sciences and Technology, Department of Business Economics T. G. Masaryka 24, 960 01 Zvolen, Slovakia gejdosp@tuzvo.sk Mgr. Jarmila Schmidtová, PhD. Technical University in Zvolen Faculty of Wood Science and Technology, Department of Mathematics and Descriptive Geometry T.G. Masaryka 24, 960 01 Zvolen, Slovakia jarmila.schmidtova@tuzvo.sk dr. Inž. Krzysztof Knop Częstochowa University of Technology Faculty of Management, Department of Production Engineering and Safety, Al. Armii Krajowej 19B, 42-200 Częstochowa, Poland krzysztof.knop@wz.pcz.pl

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 135−147, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.12

DIFFERENCES IN EMPLOYEE MOTIVATION IN WOODPROCESSING ENTERPRISES IN SELECTED COUNTRIES OF CENTRAL EUROPE Miloš Hitka – Lenka Ližbetinová – Pavla Lejsková – Eva Nedeliaková – Maciej Sydor ABSTRACT The human factor is still an irreplaceable element bearing a competitive advantage in the changed conditions of the wood-processing industry created by Industrial Revolution 4.0.

Their sophisticated use and motivation result in the company's higher performance potential, and satisfaction is reflected in higher employee loyalty. The study aims to evaluate the level of motivation of employees working in the wood-processing industry in selected Central European countries (Slovakia, the Czech Republic, and Ukraine) from the point of view of groups of motivation factors and then to compare them between countries in terms of gender and age. Differences in the mean values of the compared groups were tested, taking into account the confidence interval. The research was conducted at the beginning of 2021 when Ukraine has not been in a military conflict yet. The result of our findings is the knowledge that the most important motivation factors for Slovak employees in the wood-processing industry are those related to finance and employer-employee relationships. Czech employees also prefer the same motivation factors but place less emphasis on them. Employees of the wood-processing industry in Ukraine prefer motivation factors related to finance and career aspiration. From the point of view of motivation, the input qualitative parameters of rawwood material and its assessment in forest stands are also important. In globalization, the findings of our study can serve as insights for managers within the wood-processing industry. These insights can be particularly beneficial in enhancing the quality of human resource management, with a particular emphasis on bolstering employee motivation.

Keywords: motivation factors; differences in employee motivation; salary; career aspiration; work conditions; workplace well-being factors; social needs; wood-processing industry; Slovak Republic; Czech Republic; Ukraine.

INTRODUCTION Any organization's success, performance, and competitiveness mainly depend on the content and quality of human resource management (Gottwald et al., 2017). With the rapid development of the economy, the performance appraisal of human resource management in all types of enterprises has gained more attention (Zhang 2023). It is immediately known that the competitive advantage of companies lies precisely in their human capital and employees (Vrabcová and Urbancová 2022). They constitute the most essential aspect of any company, represent the most valuable asset, and play a vital role in its performance and 135

achieving its goals (Bogdanovic et al., 2016). Most employees must be recognized and motivated in the workplace (Baksa and Branyiczki 2023; Oladimeji et al., 2023). It positively affects their job satisfaction and optimal performance (Mendoza-Ocasal et al., 2022; Azmy and Wiadi 2023). Human resource management represents one of the most critical functions of the enterprise, which is responsible for the development of not only the enterprise but also the workforce (Smerek and Vetráková 2020; Alsafadi and Altahat 2021).

However, human resource management must follow the company's internal principles, personnel strategy, and policy (Nguyen et al., 2020).

Many enterprises currently invest large amounts of funds in human capital (Kohnová et al., 2023; Stacho et al., 2017). These investments will ultimately prove to increase the performance of businesses (Graa and Abdelhak 2016; Lazarevic et al., 2020; Jaros, Melichar and Svadlenka, 2014). However, to improve and maintain employees' productivity, it is necessary to ensure their education, training, motivation, and further development at the right time and in the right way (Vetráková and Smerek 2019; Dibiku 2023). The company's performance depends on the employees' efficiency (Jankelová et al., 2020). Benefits and improved performance are primarily due to the development of employees, individuals, and work groups (FitriMansor et al., 2014). One possibility is the implementation of motivational programs because it improves individual and organizational performance (Jankelová et al., 2021).

The quality of human potential is a crucial factor influencing the operation of the enterprise and its prosperity (Szierbowski-Seibel, 2018). Human capital is unique in terms of potential for growth and development (Balková et al., 2022; Hyrslova et al., 2017). It has the potential to create material and spiritual assets capable of meeting ever-new requirements (Erazo-Muñoz et al., 2022; Froněk et al., 2021).

Employee motivation represents an incentive to make certain decisions, engage in specific performance and effort, or persist in a particular course (Dörnyei and Ushioda 2021).

Employee motivation has always been and always will be a central issue managers and executives address (Ganta, 2014). Unmotivated or improperly motivated workers are highly likely not to perform as well as motivated workers (Maj, 2023; Riyanto et al., 2021; Skýpalová et al., 2022). In the current turbulent economic environment, the basics of what motivates employees are gaining more and more importance (Tokarcikova et al., 2020) Concerning the Central European region and cooperation, the country selection is focused on countries where the wood-processing industry forms an essential part of the GDP. Since the analyzed countries have comparable structures of the wood-processing industry, this enables their relevant comparison. The study aims to evaluate the level of motivation of employees working in the wood-processing industry in selected Central European countries (Slovakia, the Czech Republic, and Ukraine) from the point of view of groups of motivation factors (related to relationship, finance, social needs, work conditions, and career aspiration).

Subsequently, the groups of motivation factors between countries regarding gender and age were compared. The research was carried out at the beginning of 2021 when Ukraine was not yet in a military conflict, which can fundamentally affect the results. In the time of globalization, the results of our research can be used in the future by wood-processing industry enterprises to improve the quality of human resource management, especially in employee motivation.

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MATERIALS AND METHODS The wood-processing industry is a branch of the manufacturing industry dealing with processing wood and wood materials. Its industries are primarily wood processing, furniture, pulp, and paper (Sario, 2022). The total production of wood-processing enterprises in Slovakia represents an average turnover of €640 million (Statistical Office of the SR, 2019).

The wood-processing industry in the Czech Republic is focused primarily on exclusively domestic raw wood and, therefore, mainly on the processing of coniferous tree species. The structure of the industries is very similar to that of the Slovak Republic (Czech Statistics Office, 2019).

The wood-processing industry in Ukraine is one of the prosperous and well-secured sectors of the country, and last but not least, the woodworking industry of Ukraine is one of the major sources of wood in Europe. The structure of the industries is also very similar to that of the Slovak Republic (The State Committee of Statistics of Ukraine, 2019).

The object of the investigation was employees working in enterprises of the forestbased sector in the Slovak Republic, the Czech Republic, and Ukraine. The data collection took place at the end of 2021. The sample consisted of respondents from the entire territory of the monitored countries to achieve the representativeness of the sample set. The respondents were of different genders, ages, education, and job categories. The sample set was determined by quota selection according to the control characteristics of gender, age, and occupational classification.

The questionnaire was used to gain the data. It consisted of two parts (Hitka et al., 2009). The first part identified the respondents' socio-demographic profile related to age, gender, number of years of service in the company, completed education, and job position.

The second part of the questionnaire included thirty closed questions addressing employee motivation preferences. Motivation factors were categorized into five main aspects: the total financial compensation for work (including basic salary, fringe benefits, and a fair appraisal system), satisfying career aspiration (encompassing skill utilization, job performance, competence, prestige, independent decision-making, self-actualization, recognition, education, and personal growth), perception of work conditions (comprising elements such as physical effort, job security, workload, type of work, performance information, working hours, work environment, work processes, mental effort, and stress), meeting social needs (including social benefits, company vision, organization name, regional development, and environmental commitment), and assessment of relationships at the place of employment (involving workplace atmosphere, teamwork, supervisor's approach, and workplace communication).

To ensure objectivity, the motivation factors were presented to respondents in alphabetical order, thereby minimizing potential response bias. Respondents evaluated the importance of individual motivation factors with values. Rating 1 expressed the unimportance of the motivation factor for the respondent; on the other hand, value 5 said the most significant importance of the motivation factor.

The internal reliability of all measured by questionnaire-based motivational factors was evaluated. This assessment involved Cronbach's alpha coefficient, which ranges from 0 to 1 and quantifies the extent to which items in a questionnaire are interrelated or measure the same underlying construct. In other words, it helps determine if the items in a survey or test consistently measure the same concept (Mareš et al., 2015). The calculated coefficient of Cronbach's Alpha is α = 0.929, similar to McDonald's Omega coefficient which is ω = 0.933 in the case of wood-processing enterprises (Silva et al., 2003) indicating excellent 137

reliability. The power of the test for group F tests (Anova) is 0.999, with the set parameters effect size f = 0.4, α = 0.01.

The next step was to compare the analysed countries using an analysis of variance in the five areas of motivation tested. The following part used the variance analysis to compare the required employee motivation between countries based on gender and age using Statistica 14 software (TIBCO Software Inc.: Palo Alto, CA, USA). We aimed to point out statistically significant differences or similarities between the requirements within gender and age between the three countries under study. Based on the analysis of findings from the theoretical part, the following research hypotheses (RH): RH1 – it is assumed that there are differences in groups of motivation factors between individual countries.

RH2 – it is assumed that there are differences in terms of age and gender between individual countries.

RESULTS AND DISCUSSION As part of the questionnaire, the socio-demographic profile of the respondent was investigated. 4,120 respondents working in wood-processing enterprises in the Slovak Republic, the Czech Republic, and Ukraine participated in the survey. Detailed information on respondents by gender, age, completed education, and job category for each country is shown in Table 1.

Tab. 1 Structure of sampling unit.

Gender

Age group

Education completed

Job position

SK 1654 1130 524 339 510 505 300 54 376 910 314 219 1018 417

man woman Up to 30 31-40 41-50 51 plus primary lower secondary upper secondary higher manager blue collar worker white collar worker

CZ 1068 434 634 489 257 233 89 21 138 623 386 198 455 415

UA 1398 397 1001 794 452 106 46 23 21 305 1048 287 730 380

Source: own survey

The position of five groups of motivation factors (motivation factors relating to mutual relationship, career aspiration, finance, work condition, and social needs) depending on the importance of individual groups in terms of affiliation to the country was determined. The motivation factors were grouped into five fields based on an expert assessment. The results are shown in Figure 1.

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Fig. 1 Box and whisker plot: 95% confidence intervals for the mean values of the importance of individual groups of motivation factors in terms of affiliation to the country.

For employees in the Slovak Republic, the most essential motivation factors are those relating to finance and employer-employee mutual relationships. Czech employees also prefer motivation factors relating to relationships and finance, but they put less emphasis on them than employees from other countries. Employees of the wood-processing industry in Ukraine consider finance and career aspirations the most essential factors.

Similarities in the motivational needs of individual countries can be seen in the fields of finance (the Slovak Republic and Ukraine) and relationships (the Czech Republic and Ukraine). In other fields, the countries show significant differences. Following the findings, it can be concluded that the motivational needs of the monitored countries are different.

In the next part, differences in terms of age and gender for different groups of motivation factors were examined.

From the point of view of motivation factors relating to finance (basic salary, fringe benefits, fair appraisal system), it is possible to evaluate a significant difference between the monitored countries in terms of gender (Figure 2). In the Slovak Republic and the Czech Republic, an insignificant gender difference was observed. In Ukraine, the requirements between the genders are significantly different. In terms of age, the differences within countries are similar. There is a significant difference in age between countries.

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4.8 4.6 4.4

Average value

4.2 4.0 3.8 3.6 3.4 3.2

Country SK 3.0 Gender 1

2

Age >30

Gender 1

2

Gender 1

Age 31-40

2

2

Country CZ

Age <50

Country UA

Gender 1

Age 41-50

Fig. 2 Motivation factors related to finance.

In the field of motivation factors related to employer-employee relationships (atmosphere in the workplace, good work team, supervisor's approach, communication in the workplace), it can be stated that there is a similarity in the perception of the need for motivation between the Czech Republic and Ukraine. The Slovak Republic is significantly different (Figure 3). The differences between the genders were not observed. In terms of age, there is no significant difference between the countries.

4.8

4.6

Average value

4.4

4.2

4.0

3.8

3.6

Country SK 3.4 Gendre 1

Age >30

2

Gendre 1

2

Gendre 1

Age 31-40

2

Age 41-50

2

Country CZ

Age <50

Country UA

Gendre 1

Fig. 3 Motivation factors related to relationship.

From the point of view of motivation factors related to work conditions (Workplace Wellbeing Factors such as physical effort at work, job security, workload and type of work performed, information about performance results, working hours, work environment, work processes, mental effort, and stress), it is possible to see a significant difference between the observed countries in terms of gender (Figure 4), especially in Ukraine. Slovakia and the Czech Republic have similar perceptions of motivational needs within genders. There is a high similarity in this field even within age.

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4 .8 4 .6 4 .4

Average value

4 .2 4 3 .8 3 .6 3 .4 3 .2

Country SK 3 Gender 1

2

Gender 1

Age >30

2

Gender 1

Age 31-40

2

2

Country CZ

Age <50

Country UA

Gender 1

Age 41-50

Fig. 4 Motivation factors related to work conditions.

In the group of motivation factors related to social needs (social benefits, company vision, name of the organization, development of the region, relation of the organization to the environment, free time), there is no difference between the monitored countries in terms of gender (Figure 5). All three countries have similar perceptions of motivational needs within gender. There is a high similarity in this field even within age.

4 .8 4 .6 4 .4

Average value

4 .2 4 3 .8 3 .6 3 .4 3 .2

Country SK 3 Gender

1

Age >30

2

Gender

1

2

Gender

Age 31-40

1

2

Age 41-50

Gender

2

Country CZ

Age <50

Country UA

1

Fig. 5 Motivation factors related to social needs.

In the group of motivation factors related to career aspiration (possibility of applying one's own skills, job performance, competence, prestige, independent decision-making, selfactualization, recognition, education, and personal growth), there is a significant difference between the monitored countries in terms of gender (Figure 6) between Ukraine and the other two countries. Within age, there is a high similarity in this field.

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Fig. 6 Motivation factors related to career aspiration.

In our paper, the motivation factors divided into groups were investigated. The result of our findings is the knowledge that the most important motivation factors for Slovak employees in the wood-processing industry are those related to finance and relationships.

Czech employees also prefer the mentioned factors but place less emphasis on them. In the wood-processing industry in Ukraine, employees prefer motivation factors related to finance and career aspiration.

The results confirm previous research (Hitka et al., 2018), which examined the required motivation in Slovak, Czech Republic, and Lithuania. The position of the essential motivation factors in all three countries is mentioned and explained, including factors such as basic salary, the workplace atmosphere (Sommerauerová and Chocholáč 2020), the supervisor's approach, and fringe benefits. Also, the authors Sánchez-Sellero et al. (2018) confirmed the need for finance and relationships in Spanish wood-processing enterprises.

Another research carried out in the Czech Republic and the Russian Federation in 2018 shows that the most preferred motivation among Czech employees is the supervisor's approach, the atmosphere in the workplace, a good work team, a fair evaluation system, and safety at work. Czech employees highlight the motivation factors related to relationship and finance, which coincides with our research, while Russian employees prefer motivation factors related to work conditions (Ližbetinová et al., 2018). Russian employees prefer the motivation of eliminating stress in the workplace, working hours, working environment, good work team, and workload and type of work performed. Research by the author Iguisi (2009) focused on the investigation of employee motivation between the countries of France, Italy, Scotland, the Netherlands, and Nigeria noted similar measured values of preferred motivation among the given European countries and the differences between these countries compared to the preferred motivation in Nigeria. The French, Italians, Scots, and Dutch cited challenging tasks, living in a desired area, self-actualization and independent decisionmaking, contributing to the organization's success, and good working relations with a supervisor as the most important motivation factors. Nigerian respondents cited contributing to the success of their organization, challenging tasks, job security, the opportunity to work at a higher level, and working with others as the most important motivation. There are no significant differences in the required motivation among respondents from European countries (Iguisi, 2009). When investigating the motivation of Swedish and Chinese employees (Flisak and Bjerkhage 2015), the authors concluded that there are differences in the required motivation between them. Chinese employees value motivation factors related 142

to finance and social needs the most. Swedish employees prefer to be motivated by factors related to work conditions, inspiring work, and recognition at work. The study also points to changes in the motivation of Chinese employees, where the achievements of the whole company are valued more than personal benefits for an individual.

Employees in Bangladesh prefer to have authoritative leaders and decisions to follow without needing further explanations when doing their work. They also like a close relationship with a single manager, collectivism, and risk aversion. Therefore, they prefer motivation factors related to work conditions the most (Islam, 2017). A study by Artina et al. (2020) points to the compelling motivation of Indonesian employees using income, recognition, career growth, and job challenges. They avoid uncertainty, which presupposes a preference for a challenging profession and motivation to achieve a higher career. Their requirements are mainly for motivation factors related to career aspiration and finance. The (Acha-Anyi and Masaraure 2021) study in Grundfos Sub-Saharan Africa points to the fact that only monetary incentives are insufficient to motivate employees. The perception of justice, employee equality, communication, respect among employees, and dignity have gained high importance in compelling motivation. The most increased preferences are for motivation factors related to relationships. The results of the Bao and Nizam (2015) research on Finnish employees also indicate the importance of motivation factors such as working conditions, salary, and interpersonal relationships, which Finnish employees rated as the most important, the underestimation of which can cause high employee dissatisfaction. For the employees of Bosnia and Herzegovina, creating a pleasant working atmosphere, a good work team, and good relations with the supervisor are equally important in terms of motivation (Mustajbašić and Husaković 2016).

Following the research, it can be generally stated that there is a similarity in preferred motivation between European countries.

CONCLUSION In the paper, the motivational needs of employees in the wood-processing industry in the Czech Republic, Ukraine, and the Slovak Republic were defined. The investigated subjective motivation factors are divided into five groups: evaluation of the total financial compensation for work, satisfying career aspirations, perception of work conditions, meeting social requirements, and assessment of professional relationships in the workplace. The research confirmed significant differences between the Czech Republic and the remaining countries. In terms of gender and age, significant differences between countries were also noted.

Employee motivation also includes the possibility of producing quality products. For the woodworking industry, there are particularly limited possibilities in this area in terms of the quality parameters of the input raw material. The process of qualitative assessment already in the forest stands as the primary task of forestry and should be reflected in the motivational factors for the workers of the forestry-wood processing complex. These facts can subsequently be significantly reflected in the prices of wood and wood products (Suchomel and Gejdoš, 2007).

What effectively motivates employees in one country may motivate employees in another country at a different level. In today's globalization and population migration, enterprises need to employ and retain a workforce to identify the needs of individuals from other countries as well. Subsequently, it is necessary to connect them with implemented motivational programs and implement them to the changing needs of employees. The most 143

common mistake in motivation is focusing on something other than finance. Although monetary stimulus and its motivation factors are essential in most countries evaluated as essentially required motivation, one should remember to supplement this motivation with other motivation factors from other motivational groups. However, in general, across countries, if attention is paid to improving workplace relations, the overall workplace atmosphere, and building a good team, this effort will translate into an overall improvement in business performance and increase employee motivation and satisfaction.

Our research is part of other research carried out in European countries and the world.

The goal was to define the similarity of motivation factors that managers of enterprises in the wood-processing industry can use. Based on our results, it is possible to implement the strategy of creating incentive programs by company managers to increase the quality of human resource management.

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ACKNOWLEDGMENT This research was supported by VEGA 1/0161/21 Dependence of the type of corporate culture on the industries of Slovak enterprises and selected socio-demographic factors, KEGA 012UCM-4/2022 Human Resources Management in a Digital World ‒ A Bilingual (Slovak-English) Course Book with E-learning Modules based on Multimedia Content, APVV-20-0004 The effect of an increase in the anthropometric measurements of the Slovak population on the functional properties of furniture and the business processes, APVV-22-0001 Optimization of main health and safety risks in the use

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of forest biomass for energy purposes and KEGA 004TU Z-4/2023 Innovative methods for assessing the quality potential of forest stands.

AUTHORS’ ADDRESSES prof. Ing. Miloš Hitka, PhD. Technical University in Zvolen T. G. Masaryka 24 960 53 Zvolen Slovak Republic hitka@tuzvo.sk doc. Ing. Lenka Ližbetinová, PhD. Faculty of Technology The Institute of Technology and Business in České Budějovice Okružní 10 370 01 České Budějovice Czech Republic lizbetinova@mail.vstecb.cz Ing. Pavla Lejsková, PhD. The Department of Transport Management, Marketing and Logistics Faculty of Transport Engineering Univerzita Pardubice Studentská 95 53210 Pardubice Czech Republic pavla.lejskova@upce.cz doc. Ing. Eva Nedeliaková, PhD. Department of Railway Transport Faculty of Operation and Economics ofTransport and Communications University of Žilina Univerzitná 8215/1 010 26 Žilina Slovak Republic doc. Ing. Maciej Sydor, PhD. Department of Woodworking and Fundamentals of Machine Design Faculty of Forestry and Wood Technology Poznań University of Life Sciences Wojska Polskiego 28 Poznań 60-637 Poland maciej.sydor@up.poznan.pl

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 149−162, 2023 Zvolen, Technická univerzita vo Zvolene DOI: 10.17423/afx.2023.65.2.13

THE USE OF CONTROLLING IN WOODWORKING AND FURNITURE FAMILY BUSINESSES: EVIDENCE FROM SLOVAKIA Natália Poláková – Mariana Sedliačiková – Jarmila Schmidtová ABSTRACT The aim of the paper is to assess the use of controlling in family businesses within the woodworking and furniture industry in Slovakia compared to non-family businesses and to identify the underlying reasons for its implementation or lack thereof. The questionnairebased survey was evaluated using relevant statistical methods. Based on the findings, it can be concluded that most of the woodworking and furniture enterprises belong to family businesses, and they tend to use controlling to a lesser extent compared to non-family businesses. The results indicated a positive correlation between the size of the enterprise and the implementation of controlling. Additionally, a distinctive specific of the surveyed businesses which may hinder the application of controlling is considered the concordance of ownership and management roles. The study identified the state of the use of controlling in the surveyed businesses and sheds light on the factors influencing their decisions.

Keywords: controlling; family businesses; non-family businesses; woodworking and furniture industry.

INTRODUCTION Family businesses (FBs) represent a significant part of all business entities in the EU as well as in Slovakia. They are an essential part of the national economy and play an important role in the development of the social economy (Yuan, 2019). The share of FBs in Slovakia is estimated at 60 to 80% in all sectors. They produce 30 to 40% of GDP and provide 40% of employment (SBA, 2018). Despite their considerable importance, they face insufficient legislative support (SBA, 2020). A legislatively anchored definition of the term family business enabling targeted support for these businesses, has been established in Slovakia just recently by an amendment to Act No. 112/2018 Coll. on the Social Economy and Social Enterprises, becoming effective from July 2023 (MPSVR, 2022). According to the definition, a family business is characterized as a legal entity, a cooperative, and a sole trader under the condition that several members of the joint family have ties to the enterprise established by the law. Members of the joint family are considered to be spouses, relatives in the direct line, siblings, persons related to each other up to the 4th degree and their spouses.

The relationship of the family members to the company must meet the following conditions: • In the case of a legal entity: o at least two family members directly or indirectly hold the majority of voting rights, and at least one family member serves as a statutory body or is a member of the statutory body, 149

o at least two family members collectively receive more than 50% of the profit after tax from the business or o one family member is the sole partner or shareholder while also serving as a statutory body or a member of the statutory body, and at least one other family member holds a position as a statutory body member, procurator, member of the supervisory board, or has an employment relationship with the company.

• In the case of a cooperative, either the first or second condition valid for legal entities must be met.

• For a sole trader, there is a condition, that at least one family member must be employed by the sole trader.

• In the event that an external investor enters a legal entity or a cooperative and their increased participation in the business at the expense of family members is justified by the protection of their investment, the investor's influence must be limited to a certain period (NRSR, 2022).

A family business can be defined as a complex system, which is characterized by its connection between family and business, where family, ownership and business overlap simultaneously (Ramadani and Hoy, 2015; Davis, 2019). From this relationship, the specifics of FBs emerge, which significantly distinguish them from non-family ones. The peculiarities of the business-family relationship mean that FBs are managed in a specific way and differently from non-family businesses (NFBs) (Herrera and De Las Heras-Rosas, 2020).

The history of FBs is primarily associated with traditional industries, including the wood-processing industry (WPI), uniformed by the woodworking and furniture industry and the paper and pulp industry. WPI in Slovakia represents a crucial area of industry and has the potential to become a pillar of the Slovak national economy (Sedliačiková et al., 2016; Melichová et al., 2022). It relates to a rich domestic raw material base of a sustainable nature, and its suitable geographical distribution (Hajdúchová et al., 2016; Malá et al., 2018). In addition, there is a potential from the point of view of ecological direction (Loučanová et al., 2014; Olšiaková et al., 2016). However, the reality is that WPI enterprises in Slovakia face specific problems and this negative status is reinforced by the long-term failure to solve them (Drábek and Merková, 2017). The shortcomings of the Slovak WPI are considered to be outdated and worn equipment that does not meet the requirements of modern technology and related lack of innovation, lack of support and development strategy and insufficient product finalization (Krišťáková et al., 2021). Hajdúchová et al. (2016) state that one of the areas that WPI businesses should focus on, is the implementation of innovations and modern management methods, which include controlling too. Today, innovation is the main driving force for creating value and maintaining competitive advantage (Vitezić and Vitezić, 2015).

Innovative management systems, including controlling, are increasingly coming to the foreground (Tamulevičienė and Subačiené, 2019).

In today's world of globalization and turbulently changing business environment, business management processes are becoming more and more complex, and the number of alternative decision-making options is increasing, as is the level of their complexity. To remain competitive, businesses must create and implement new management systems and apply innovative business management methods. One such system that helps to detect problems and solve them in an integrated way is controlling as an innovative management system (Tamulevičienė and Subačiené, 2019). Controlling can be defined as an effective management tool, the task of which is the coordination of planning, control, as well as providing an information base to achieve set business goals (Horvath, 2009). As Ahlrichs (2012) states, strategic as well as operational management of any kind needs a specific set 150

of management tools to achieve set business goals. The management cycle with clear goals, planning and measurement of achieved results and active management with countermeasures is a basic tool of corporate controlling (Vitezić and Vitezić, 2015). The application of controlling helps to improve the functionality of the company and the decision-making process, and at the same time increases its value. The implementation of such a system could be a decisive factor that will ensure the success of the company (Tamulevičienė, 2019; Sedliačiková et al., 2021b).

A survey exploring the use of controlling in family businesses operating in the woodworking and furniture industry in Slovakia, which represents a unique combination of these three areas, has not been carried out yet. The aim of the paper is to assess the use of controlling in FBs within the woodworking and furniture industry in Slovakia compared to NFBs and to identify the underlying reasons for its implementation or lack thereof.

MATERIALS AND METHODS The methodological procedure of the paper was divided into several logical phases.

The first phase was focused on a literature review carried out by analysis of available secondary sources using the scientific methods of summarization, synthesis, comparison, analogy and deduction. Based on the published outputs on the issue of FBs, controlling, use of controlling in FBs and WPI with a focus on the woodworking and furniture industry (WWAFI), the following hypotheses were formulated: H1: It is assumed that the majority of the Slovak woodworking and furniture enterprises belong to family businesses.

FBs represent the dominant and oldest form of businesses (Comi and Eppler, 2014; Ramadani and Hoy, 2015). Petlina and Koráb (2015) and Szymanska (2015) state that the share of FBs in the EU reaches approximately 85%. Hudáková et al. (2015) consider 70 to 90% of all businesses in Slovakia FBs. This is the first step important from the point of view of identifying Slovak FBs operating in the WWAFI. H2: It is assumed that FBs operating in the WWAFI use controlling to a lesser extent compared to non-family businesses.

FBs seem to have less need to use controlling and its tools than NFBs (Hiebl, 2021).

The phenomenon of the use of controlling in FBs was dealt with by several authors such as Helsen et al. (2017), Prencipe et al. (2014), Quinn et al. (2018), Senftlechner and Hiebl (2015). They point out that the use utilization of controlling in FBs significantly differs from that in NFBs and depends on factors that cannot be observed in NFBs. H3: It is assumed that the rising trend of the use of controlling in FBs of WWAFI depends on the size of the enterprise.

Some studies suggest that the smaller need for the introduction of controlling in FBs appertains primarily micro and small FBs (Hiebl et al., 2013; Speckbacher and Wentges, 2012).

H4: It is assumed that the main specific of FBs operating in the WWAFI hindering the use of controlling, is considered the concordance of ownership and management roles.

FBs are characterized by a frequent concordance of ownership and management roles in one or several individuals. It can be assumed that conflicts of interest and information asymmetry occur less frequently or are less severe in these businesses compared to NFBs (Hiebl, 2013a; Madison et al., 2016; Quinn et al., 2020; Hiebl et al., 2019). Consequently, it can be inferred that control systems are less critical for these businesses since members of

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FBs already act in the best interest of the company without specific encouragement or guidance (Mitter, 2014; Quinn et al., 2018).

In the next phases, primary data were obtained through a questionnaire and subsequently analyzed. The second phase focused on developing a questionnaire based on the acquired theoretical knowledge. Subsequently, a pretest of the questionnaire was conducted with a sample of 30 respondents (Bačíková and Janovská 2018). The final form of the questionnaire consisted of 27 questions divided into two main sections. The first section was addressed to businesses operating in the WWAFI (both family and non-family) and the second section was determined for FBs only. The FBs were identified according to the definition set by law in Slovakia, as mentioned above. When a respondent, representing a company, confirmed the presence of any of the above-mentioned features of a family business, it was classified as a family business. Otherwise, it was considered a non-family business. The survey was carried out from December 2022 to June 2023 as the third phase.

The electronic questionnaire placed on the Google forms domain was distributed to email contacts of the woodworking and furniture manufacturing enterprises. According to Finstat (2022), a total of 3573 enterprises operating in the WWAFI were active in the surveyed period. The research sample consisted of 2500 randomly selected woodworking and furniture manufacturing enterprises according to the SK NACE classification of economic activities (code C16 and C31). The achieved return rate of the questionnaire was 14.52% (Pacáková, 2009). The fourth phase focused on the processing of data obtained from the survey. To obtain summary outputs, data matrix was compiled in the Microsoft Excel program. The data were subsequently mathematically and statistically tested in the Statistica 12 program. The assumed hypotheses were tested using relevant statistical methods. The verification of the assumed hypotheses above was preceded by a check of the minimum sample size (n), which is a prerequisite for generalizing the obtained results to the entire population according to the following test characteristic (Faeron, 2017): 𝑝(1−𝑝)

𝑛 = 𝑒2 𝑝(1−𝑝) + 𝑧2

(1)

𝑁

The representativeness of the research sample was verified through Pearson's Chisquare test of goodness of fit according to two characteristics of the basic set. These were affiliation in the category according to the SK NACE classification of economic activities and size of the enterprise. The test characteristic is as follows (Pacáková, 2009):

𝜒 2 = ∑𝑘𝑖=1

(𝑋𝑖 −𝑁𝑝𝑖 ) 𝑁𝑝𝑖

(2)

The verification of validity of the assumed hypotheses was carried out based on mathematic-statistical methods such as Test a hypothesis about a population proportion (onetailed), Test a hypothesis about two population proportions (one tailed), Pearson's chi-square test and Interval estimate (two-tailed), all of them at the level of significance (α) of 5%, i.e., the above is claimed with the confidence of 95% (Pacáková, 2009).

The Test a hypothesis about a population proportion (one-tailed) is used to test a statistical hypothesis that the proportion of a certain value of a variable in the basic set is equal to a given constant according to the following relation (Ali and Bhaskar, 2016; Pacáková, 2009):

152

𝑢=

𝑓−𝜑0

(3)

𝑓(1−𝑓) √ 𝑛

The Test a hypothesis about two population proportions (one-tailed) is used to test a statistical theory claiming that the two distributions' parameters are the same in both basic sets. The test characteristic is as follows (Pacáková, 2009; Labudová et al., 2021):

𝑧=

𝑃1 −𝑃2

(4)

𝑃 (1−𝑃 ) 𝑃 (1−𝑃 ) √ 1 𝑛 1 + 2 𝑛 2 1 2

Pearson's Chi-square test of independence is used to assess whether two categorical variables are independent of each other according to following relation (Pacáková, 2009):

𝜒 2 = ∑𝑘𝑖=1

(𝑋𝑖 −𝑁𝑝𝑖 )

(5)

𝑁𝑝𝑖

The Interval estimate (two-tailed) provides a numerical range within which the estimated parameter is likely to fall with a certain level of probability in the given basic set.

The test criterion is as follows (Pacáková, 2009; Ali and Bhaskar, 2016): 𝑓(1−𝑓)

𝑓 − 𝑢α √ 2

𝑛

𝑓(1−𝑓)

< 𝜑 < 𝑓 + 𝑢α √ 2

𝑛

(6)

The detailed results of the survey using descriptive statistics are described in the next part of the paper. They were compared and discussed with the previous findings and authors as the last phase.

RESULTS AND DISCUSSION A total of 363 Slovak businesses operating in the WWAFI according to the SK NACE classification of economic activities (code C16 and C31) participated in the survey, 73.83% woodworking and 26.17% furniture manufacturing enterprises. Most businesses belong to micro enterprises (75.76%), followed by small enterprises (20.66%). 48.21% of the businesses perform at the national level and 41.60% at the international level. They mostly operate on the market for 6 – 15 years (33.06%) and for 16 – 25 years (28.93%). The minimum sample size under the conditions of an acceptable margin of error of 5% (e=0.05), confidence level of 95 % (z=1.96), with the known size of the basic set (N=3573) was set at 347 Slovak woodworking and furniture enterprises. As 363 of these businesses participated in the survey, the minimum sample size condition was met, and the results of the survey can be generalized to the entire population of enterprises operating in the WWAFI. The research sample met the condition of its representativeness according to the two observed characteristics (the affiliation in the category according to the SK NACE classification of economic activities p=0.685; the size of the enterprise p=0.728). The distribution of the enterprises in the research sample corresponds to the distribution of the population of woodworking and furniture enterprises in Slovakia and to the distribution of their size.

A total of 252 FBs operating within WWAFI participated in the survey. The findings show that their representation reaches up to 69.42% (Tab. 1). To statistically confirm the hypothesis H1 assuming that the majority of Slovak woodworking and furniture enterprises 153

belong to FBs, Test a hypothesis about a population proportion was conducted, yielding a result of p=0.000 (Tab. 2). Based on the results, it can be concluded that the majority of Slovak woodworking and furniture manufacturing enterprises fall under the category of FBs. This step was crucial in identifying FBs operating within WWAFI. Tab. 1 Frequency table of the research sample.

Type of enterprise in the sample Family business Non-family business

Absolute frequency 252 111

Cumulative Relative frequency Cumulative relative absolute frequency (%) frequency (%) 252 69.42 69.42 363 30.58 100.00

Total

363

100

Tab. 2 Test a hypothesis about a population proportion to hypothesis H1.

Hypothesis

Research area

Alternative hypothesis

f

n

u-test

p-value

H1

Share of FBs in woodworking and furniture industry

π>50%

69.42%

363

8.03

0.000

The survey focused on the use of controlling in FBs operating in the WWAFI. The priority was to determine whether there was a difference in the use of controlling between FBs and NFBs within WWAFI. To address this issue, the hypothesis H2 was formulated, suggesting that FBs of the WWAFI use controlling to a lesser extent than NFBs. The results revealed that controlling is employed by 17.06% of FBs and 27.03% of NFBs. The hypothesis H2 was tested using the Test a hypothesis about two population proportions. The analysis, presented in Tab. 3, yielded a p-value of 0.015, which is lower than the level of significance (0.05). As a result, the hypothesis H2 was accepted, indicating that FBs within WWAFI indeed use controlling to a lesser extent compared to NFBs. Tab. 3 Test a hypothesis about two population proportions to hypothesis H2.

Hypothesis

Research area

Alternative hypothesis

fFBs

NFBs

fNFB

NNFBs

z-test

p-value

H2

Use of controlling, FBs vs. NFBs

π1>π2

17.06%

252

27.03%

111

2.18

0.015

Given the above results, a question arises, why FBs of the WWAFI use controlling to a lesser extent than NFBs. The next two hypotheses relate to reasons preventing the use of controlling in FBs of the WWAFI. The hypothesis H3 assumes the rising trend of the use of controlling depending on the size of the enterprise. The hypothesis was confirmed by Pearson's Chi-square test of independence with the result of p = 0.001 (Tab. 4). While micro enterprises do not have the tendency to use controlling, small and medium-sized enterprises do have the tendency. Based on the given results, it can be concluded that the rising trend of the use of controlling in FBs of the WWAFI depends on the size of the enterprise.

Tab. 4 Pearson's Chi-square test of independence to hypothesis H3.

Hypothesis

Research area

Chí-square

sv

p-value

Contingency coefficient

H3

Rising trend of the use of controlling depending on the size of the enterprise

14.09

2

0.001

0.23

154

The phenomenon of the use of controlling in FBs was already investigated by Amat et al. (1994) and Goffee and Scase (1985) at the end of the last century and followed by many others, for example Prencipe et al. (2014), Senftlechner and Hiebl (2015), Helsen et al. (2017), Quinn et al. (2018). The authors point out that the use of controlling in FBs depends on factors that cannot be observed in non-family-type businesses. These are specifics of FBs that significantly differentiate them from NFBs. In this regard the last hypothesis H4 assumes that the main specific feature of FBs operating in the WWAFI hindering the use of controlling, is considered the concordance of ownership and management roles. The values of specifics selected by respondents of FBs are shown in Fig. 1. Most of the respondents agreed in the opinion that the reason leading them to believe that controlling was not necessary for their company was the concordance of ownership and management roles. This specific considerably exceeds the others. As the results of Interval estimate show, this specific affects from 29% to 41% of woodworking and furniture FBs (Tab. 5). Based on the results, it can be concluded that the concordance of ownership and management roles is the specific, that predominantly hinders the implementation and utilization of controlling in FBs operating in the WWAFI, and thus accepting the hypothesis H4.

Informality

9.13%

Trust

22.62%

Concerns about reducing pro-organizational behavior

2.78%

Centralized management

9.92%

Unwillingness to share the management of the business

5.56%

Low risk of information asymmetry

10.32%

Concordance of ownership and management roles

35.32% 0%

5%

10% 15% 20% 25% 30% 35% 40%

Fig. 1 Specifics of FBs hindering the use of controlling defined by FBs of WWAFI. (Source: authors).

Tab. 5 Interval estimate to hypothesis H4.

Research area

fi

ni

Concordance of ownership and management roles Low risk of information asymmetry Unwillingness to share the management of the business

35.32% 10.32% 5.56%

89 26 14

Centralized management Concerns about reducing pro-organizational behavior Trust Informality

9.92% 2.78% 22.62% 9.13%

25 7 57 23

95%-Interval estimate lower level upper level 29% 41% 7% 14% 3% 8% 6% 1% 17% 6%

14% 5% 28% 13%

A total of 252 Slovak FBs (69.42%) was identified in the research sample of 363 woodworking and furniture manufacturing enterprises. The results clearly show that the majority of Slovak woodworking and furniture manufacturing enterprises fall under the 155

category of FBs, thus confirming the hypothesis H1. The finding aligns with the results of the SBA study (2018), which estimated the percentage of family businesses (FBs) in Slovakia to be between 60% to 80% across all sectors. It is also consistent with the survey conducted by authors Kocianová et al. (2022), who reported that the share of Slovak FBs operating within the WWAFI ranges from 66% to 74%. FBs are the most widespread type of business worldwide (Hiebl et al., 2019). They significantly contribute to the GDP and to job creation (Urbaníková et al., 2020). There can be no doubt about the considerable relevance of FBs. However, the reality is that despite their importance, most of them do not survive the first generation (Labaki et al., 2019). The business success or failure of an enterprise is often the result of decisions made by top managers. Although there are many aspects of FBs that distinguish them from NFBs, decision-making seems one of the most notable (Chrisman et al., 2005; Penney, 2019). In connection with activities of FBs in the WWAFI in Slovakia, the situation of these businesses may be even more complicated. They face specific problems, while this negative status is reinforced by their long-term nonresolution (Drábek and Merková, 2017). The academic community is increasingly focusing its attention on research of FBs and, above all, their specifics, which significantly differentiate them from the non-family ones. It also found its way in the use of controlling.

It can be expected that the utilization of controlling in FBs differs considerably from that in non-family type of enterprises (Hiebl, 2021). Many studies report that controlling tools are applied less frequently and the use of controlling is in general lower in FBs than in NFBs (García Pérez de Lema and Duréndez, 2007; Feldbauer-Durstmüller et al., 2012a; Hiebl et al., 2012; Prencipe et al., 2014; Hiebl et al., 2015; Andric and Kammerlander, 2017; Ulrich, 2018; Ruiz-Palomo et al., 2019; Bürgel et al., 2020). In this area, the results of the survey confirmed the expressed assumption of the hypothesis H2, that Slovak FBs operating in the WWAFI use controlling to a lesser extent compared to non-family ones. The application of controlling has been generally underestimated for a long time, especially in micro and small enterprises (Feldbauer-Durstmüller and Hiebl, 2015; Jánská et al., 2017; Klementová et al., 2017; Sedliačiková et al., 2021a). Some studies suggest that less need for the introduction of controlling in FBs primarily appertains micro and small FBs (Hiebl et al., 2013; Speckbacher and Wentges, 2012). The above corresponds to the results of the survey, which confirmed the assumption expressed in hypothesis H3. The hypothesis postulated a positive correlation between the size of the enterprise and the use of controlling in FBs of the WWAFI. As stated by Hiebl (2021), it can be assumed that from a certain size of the company, even FBs tend to rely more on controlling. FBs are characterized by a frequent concordance of ownership and management roles in one or several persons. It can be assumed that conflicts of interests (e.g. between an external manager who pursues short-term profit and an owner who pursues long-term goals of growth and sustainability) and thus information asymmetry (between owner and manager) occur less frequently or are less severe in these businesses than in non-family-type businesses (Hiebl, 2013a; Madison et al., 2016; Quinn et al., 2020; Hiebl et al., 2019). There is a presumption that control systems are less relevant for these businesses, as members of FBs act in the best interest of the enterprise anyway and are not encouraged or guided to do so (Mitter, 2014; Quinn et al., 2018). This explains the effort of members of FBs to ensure the long-term existence of the enterprise (Siebels and zu Knyphausen-Aufsess, 2012). Based on the results, the hypothesis H4 assuming that the main specific of FBs operating in the WWAFI hindering the use of controlling is considered the concordance of ownership and management roles, was accepted. The phenomenon of controlling is a very current and discussed topic. The complexity of today's business is increasing, and thus the requirements for decision-making support (Laval, 2018). Decision-making process is given increasing importance, especially 156

in conditions of market imbalances and economic downturn, which are increasingly common both on the domestic and global market (Grzegorzewska and Wieckowska, 2017).

The economic crisis caused by the COVID-19 pandemic, as well as the current global economic and energy crisis caused by the war in Ukraine indicate that companies must make decisions about the future direction as efficiently as possible (Sedliačiková et al., 2021a). As stated by Laval (2018), the traditional supplier of top management decision-making support is controlling. Many studies confirm that the implementation of controlling directly contributes to increasing the efficiency of management, as well as the efficiency of the enterprise as a whole (Bienkowska and Zgrzywa-Ziemak, 2014; Todorović-Dudić et al., 2017; Písař and Bílková, 2019; Csikósová et al., 2022). Enterprises using controlling have higher economic activity and stability (Písař and Bílková, 2019). In addition, many researchers also confirm the importance of the application of controlling tools in family-type businesses (Hiebl, 2021; Duréndez et al., 2016; Ruiz-Palomo et al., 2019; El Masri et al. al., 2017; Mitter, 2014; Hiebl, 2013b).

CONCLUSION The presented paper aimed to assess the use of controlling in FBs within the WWAFI in Slovakia compared to NFBs and to identify the underlying reasons for its implementation or lack thereof. A total of 363 Slovak woodworking and furniture manufacturing enterprises participated in the survey, out of which 252 were identified as FBs. The results of the survey clearly show that the majority of woodworking and furniture enterprises (69.42%) belong to FBs. FBs are characterized by their specifics, which significantly distinguish them from nonfamily ones. These influence the way FBs are managed and, thus, the decision-making process. It also found its way in the use of controlling. FBs are expected to use controlling to a lesser extent compared to non-family ones due to their specifics. The results of the survey showed, that controlling is used by 17.06% of FBs and 27.03% of NFBs of the WWAFI, thus confirming the assumption that Slovak FBs of the given sectors use controlling to a lesser extent than NFBs. Two reasons for its non-use were identified. The first one is the size of the enterprise. The correlation between the size of the enterprise and the implementation of controlling was verified. While micro enterprises do not have the tendency to use controlling, small and medium-sized enterprises do have the tendency. With regards to the specifics of FBs operating in the WWAFI concerning the use of controlling, most respondents agreed that the reason leading them to believe that controlling was not necessary for their company was the concordance of ownership and management roles. The share is estimated from 29% to 41%. The aim of the paper was met, thus, providing an insight into the situation of the use of controlling in FBs of the WWAFI in Slovakia and the reasons for its non-use. Based on the results, it can be concluded that FBs of WWAFI use controlling in an insufficient way and to a lesser extent than NFBs. For the success of FBs operating in the WWAFI, it is advised to implement modern management methods as controlling is. An effective use of controlling is a valuable resource for these businesses to achieve competitive advantages, financial health, performance and consequently sustainability. The presented findings are an incentive for further examination of differences in the use of controlling between family and non-family businesses of the WWAFI. The main limitation of the survey is that the achieved results are presented in a summary of woodworking and furniture manufacturing enterprises operating only in Slovakia. Further research should include more transition economies when comparing the use of controlling between family and non-family

157

businesses operating in the woodworking and furniture industry, e.g., the territory of the Visegrad Four.

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AUTHORS’ ADDRESSES Ing. Natália Poláková (ORCID: 0000-0002-0107-623X) prof. Ing. Mariana Sedliačiková, PhD. (ORCID: 0000-0002-4460-2818) Technical University in Zvolen Faculty of Wood Sciences and Technology, Department of Business Economics T. G. Masaryka 24, 960 01 Zvolen, Slovakia xpolakovan@is.tuzvo.sk sedliacikova@tuzvo.sk Mgr. Jarmila Schmidtová, PhD. (ORCID: 0000-0003-3985-9616) Technical University in Zvolen Faculty of Wood Science and Technology, Department of Matematics and Descriptive Geometry T.G. Masaryka 24, 960 01 Zvolen, Slovakia jarmila.schmidtova@tuzvo.sk

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ACTA FACULTATIS XYLOLOGIAE ZVOLEN, 65(2): 163−165, 2023 Zvolen, Technická univerzita vo Zvolene

LAUDATIO FOR Dr. h. c. prof. Ing. MIKULÁŠ ŠUPÍN, CSc. This year, Professor Mikuláš Šupín, former rector of the university, dean of the Faculty of Wood Sciences and Technology, and founder of the Department of Marketing, Trade, and World Forestry, celebrated a significant life anniversary.

Dr. h. c. prof. Ing. Mikuláš Šupín, CSc., was born on March 16, 1953, in Ružina, Lučenec district. In 1976, he completed his Master's studies at the Faculty of Wood Sciences and Technology at the University of Forestry and Wood Sciences and Technology in Zvolen in the field of Mechanical Wood Technology. He started working as a researcher at the Research and Development Institute of the Wood and Furniture Industry Bratislava – the workplace in Fiľakovo. In 1977, he was hired as an assistant professor at the Department of World Forestry and Wood Science at the Faculty of Wood Sciences and Technology at the University of Forestry and Wood Sciences and Technology in Zvolen. As a university teacher, he focused on world forestry, world wood resources, international trade, timber trade, sales science, marketing, digital marketing, timber marketing, global marketing, international management, international economic relations, forest economics and management, and cross-sectoral economies in all three degrees of study in the fields – 3.3.16 Economics and Enterprise Management, 3.3.20 Sectoral Economies and Management, 5.2.42 Woodworking, 5.2.43 Wood-processing Technology, 5.2.45 Constructions and Manufacturing Processes of Wood Products. He introduced and guaranteed courses, gave lectures, and developed several university textbooks in the fields of world forestry, marketing, international management, trade, and international economic relations.

In the years 1981 – 1990, the Section of World Forestry and Wood Science was part of the Department of Economics and Forestry Management (KERLH) of the Faculty of Forestry of the University of Forestry and Wood Sciences and Technology in Zvolen, where, in addition to being an assistant professor, Professor Šupín served as secretary and later as a deputy head of the Department. After returning to the Faculty of Wood Sciences and Technology in 1991, he was appointed the head of the Department of World Forestry and Wood Science. He became its head after establishing the Department of Marketing, Trade, and World Forestry of the Faculty of Wood Sciences and Technology in 1997.

The changes after November 1989 also affected the Faculty of Wood Sciences and Technology of the TU in Zvolen, mainly because since its establishment in 1952 it was conceived as the only one in Czechoslovakia. In 1992, Professor Šupín served as a vice-dean of the Faculty of Wood Sciences and Technology for Foreign Relations, and in the same year, he became the dean of the Faculty of Wood Sciences and Technology. He held the position for two terms (1992 – 1998). Among other proposals, in his speech before the academic community, he suggested measures to increase the number of people interested in studying at the Faculty of Wood Sciences and Technology TU in Zvolen after losing the opportunity to be a federal faculty.

During his tenure as a dean of the Faculty of Wood Sciences and Technology, a credit system was introduced in the study field of Wood Engineering and, among other fields, a 163

completely new study field of Enterprise Management was created, which in its concept represented university studies with a more profound practical orientation of students (two so-called combined semesters with teaching were introduced in practice) and enabled the education of highly qualified experts – managers in accordance with the requirements of the labour market. At the same time, it also became the supporting programme of the newly introduced distance education. The guarantor of the study programme was Professor Šupín.

For the preparation of this form of education, the Ministry of Education of the Slovak Republic provided funds in accordance with the Distance Education Act, including the possibility of obtaining payments from part-time students. The funds could be used to motivate teachers to prepare textbooks and teach. The distance form was designed for the Faculty of Wood Sciences and Technology and the newly founded University of the Third Age. The Faculty of Wood Sciences and Technology obtained the right to conduct PhD studies in four fields in full-time and part-time form through accreditation. The guarantor of the Department of Sectoral and Cross-Sectional Economics, specialization Economics of Trade and Industry, was Professor Šupín, who was also a member of the Trade Union Commission for the Slovak Republic.

These and other changes led to new Faculty of Wood Sciences and Technology departments. In 1995, the Department of Furniture and Wood Product Design was established. In 1997, the Department of Marketing, Trade and World Forestry was established. In 1998, the Department of Fire Protection was appointed as a new separate department of the Faculty of Wood Sciences and Technology.

Reforms of the educational process at the Faculty of Wood Sciences and Technology in the years 1992 – 98, when the dean of the Faculty of Wood Sciences and Technology was Dr. h. c. prof. Ing. M Šupín, CSc., stabilized the position of the Faculty of Wood Sciences and Technology even after the dissolution of the Czech and Slovak Federative Republic.

Among other things, he was also responsible for increasing the interest of potential applicants in studying at the Faculty. While less than 150 students were accepted in 1992 (compared to the planned 250), in 1998, more than 1550 applicants applied, of which more than 900 applied to Enterprise Management. Since 1997, the new direction of the Faculty of Wood Sciences and Technology scientific research activity has become the direction entitled Wood Valuation by its Transformation into New Generation Products Forming a Complex Interior. In December 1998, Professor Šupín was elected as chairman of the Academic Senate of the TU in Zvolen (1998 – 2001).

In 2001, Professor Šupín became the rector of the Technical University in Zvolen. The Slovak Rectors' Conference elected the rector of the TU in Zvolen as vice president of the Slovak Rectors' Conference and a representative of the Slovak Rectors' Conference in the European Association of Universities. As a rector, he faced significant changes regarding Slovakia's higher education. Above all, it was Law No. 131 on Higher Education and on Changes and Supplements to Some Laws. The TU in Zvolen ceased to exist as a state budget organization; 2002 it became a public university. It was connected to numerous organizational changes and, inevitably, new strategic goals, including implementing a threedegree study model and the university's integration into the European Research and Education Area.

During his time at the TU Zvolen, Professor Šupín was the principal investigator and co-investigator in more than fifty scientific research projects here and abroad, including research on the composition of tropical forests in Africa and Asia, Food and Agricultural Organization projects, the 6th Framework Programme of the European Union, COST, 164

VEGA, and KEGA. It has 232 registered outputs of publishing activity. It has a total of 596 recorded citations. He supervised more than 150 bachelor and master theses and trained 25 PhD. students – five of them were international students.

Dr. h. c. prof. Mikuláš Šupín, CSc. in the post of Chief State Counsellor – Superior, Director General, Division of Science and Technology – Ministry of Education, Science, Research and Sport of the Slovak Republic and Secretary of the Government Council of the Slovak Republic for Science and Technology confirmed to the development of science and technology in Slovakia in the years 2006 – 2011. Equally important is his representation of the Slovak Republic in international organizations (ČSAV, IUFRO, EUA, CERN, JRC EU, OECD EU), functions and membership in Slovak authorities (Government Council, APVV) and membership in professional organizations (WoodEMA), commissions and scientific councils of domestic and foreign universities.

We wish Dr. h. c. prof. Ing. Mikuláš Šupín, CSc., for his life jubilee, good health, and the successful fulfilment of other goals.

The members of the Department of Marketing, Trade and World Forestry.

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