Physico mechanical properties of paper from malaysian hardwood kraft pulp

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Physico-mechanical properties of paper from Malaysian Hardwood Kraft Pulp Nasrullah RCL Departement of Chemical Engineering, Syiah Kuala University, Banda Aceh Indonesia. Jl Tgk. Syech Abdurrauf No. 7 Darusalam Banda Aceh, INDONESIA,

Abstract - The recycling behaviour of Malaysian hardwood kraft pulp has been evaluated in terms of pulp and paper properties. Tensile strength, bursting strength, and density of the pulps decreased with recycling. However, the tear strength increased with recycling. Fiber strength on the other hand does not show much effect Scattering coefficient increases whilst water retention values (WRV) decreases with recycling. Keywords - recycling; Malaysian hardwood pulp; tensile; tear; burst; water retention value; scattering coefficient; density; fiber strength I. INTRODUCTION Despite economic challenges, coupled with a continuous weakening demand for graphic papers, the global consumption of papermaking fibre is on the increase reaching 407 million tonnes in 2011 with recovered paper (recycled paper) playing an important role consuming about 223 million tonnes in the same period [1]. Figure 1 shows the statistics for recovered paper from 1995 until 2011. Basically, there are three important driving forces for this high demand in recycled paper. The first being the environmental issues; secondly the economical factor, especially in countries and regions where, without abundant forest resources, recycled fibre is very often a lower cost furnish than virgin pulp. And finally, legislation has been passed in numerous countries which set minimum requirements for the recycled fibre content in certain products and mandatory collection schemes [2]. Malaysia has only one integrated pulp mill and it is expected that a sizeable amount of the paper produced is being recycled and used by other mills which relies on recycled fiber as materials for papermaking. Although the effects of recycling on paper properties has been well documented, most of the past works on paper recycling were conducted on temperate softwood and hardwoods with relatively few studies been carried out on tropical hardwoods. In an effort to provide good database on the effects of recycling on tropical hardwood fibres, this study was investigated to assess the changes in papermaking properties which take place in this type of pulp during laboratory recycling. II.

EXPERIMENTAL

2.1. Materials. Commercial dried bleached tropical mixed hardwood kraft pulp was used as raw material for this study. The pulp with a Kappa number of <1 was acquired from Sabah Forest Industries, Sabah Malaysia. 2.2. Preparation of paper handsheets. Before preparation of handsheets, the obtained pulp was lightly beaten in a Lampen mill; the resultant handsheets are designated as Cycle 0. After standard pressing and drying in a conditioned atmosphere (23oC, 50%RH), a certain number of handsheets were retained for testing, whilst the remaining handsheets were soaked for at least 6 hours prior to disintegration for 3000 revolutions in a standard pulp disintegrator. The redisintegrated pulp were used to prepare subsequent handsheets without

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International Journal of Recent Trends in Engineering & Research (IJRTER) Volume 03, Issue 1; January - 2017 [ISSN: 2455-1457]

Figure 1: Global consumption of recovered paper and papermaking wood pulp 1995-2011 [1]

further mechanical treatment further beating; this is designated as Cycle 1 handsheets. The process was repeated several times to obtain Cycle 2, Cycle 3, Cycle 4 and Cycle 5 handsheets. The grammage of the handsheets was 60 g/m². Handsheets were conditioned at 23 °C and 50 % RH for at least 24 hours before testing and were characterized in accordance with the appropriate TAPPI standard methods [3]. 2.3. Water retention value (WRV) The effect of recycling on pulp properties was evaluated in terms of water retention value (WRV) which is an empirical measure of the capacity of a test pad of fibres to hold water. It was determined by centrifugation of 2 g of wet pulps for 30 minutes at 5000 rpm, followed by drying in an oven at 105oC for 24 hours [4] and calculated according to Equation 1:

��� =

đ?‘Šđ?‘¤đ?‘’đ?‘Ą −đ?‘Šđ?‘‘đ?‘&#x;đ?‘Ś đ?‘Šđ?‘¤đ?‘’đ?‘Ą

(1)

where, Wwet is the weight of the sample after centrifuging and Wdry is the weight of sample after drying in the oven for 24 h at 105oC.

III. RESULTS AND DISCUSSION 3.1. Effect on Pulp Properties An important pulp property is the water retention value (WRV). It is a measurement of the total amount of water retained by the wet pulp and is correlated with the degree of swelling of fibers. The effect of WRV on recycling (Figure 2) is one of reduction which can be explained in terms of fiber swelling capability. This restricted swelling of recycled fibres has been ascribed to hornification (5), a process whereby there is an irreversible shrinkage of the cell fiber wall leading to less swelling.

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International Journal of Recent Trends in Engineering & Research (IJRTER) Volume 03, Issue 1; January - 2017 [ISSN: 2455-1457]

WRV (g/g)

0.9

WRV (g/g)

0.8

WRV (g/g)

0.7 0.6 0.5 0

1

2 3 4 Recycle Number

5

Figure 2: Effect of recycling on Water retention value (WRV)

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Percent Change (%)

0 0

1

2

3

4

5

-20 Tear Index Burst Index Tensile Index Zero Span Scattering Coefficient

-40 -60 -80

Recycle Number Figure 3: Effect of recycling on paper properties

3.2. Effect on Paper Properties The effect of recycling on paper properties is depicted in Figure 3 illustrating various responses as paper is recycled. Tensile strength decreased dramatically with a reduction of more than 60% of the original strength after just two recycle, after which it levelled off to a more constant rate of decline. @IJRTER-2016, All Rights Reserved

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International Journal of Recent Trends in Engineering & Research (IJRTER) Volume 03, Issue 1; January - 2017 [ISSN: 2455-1457]

Burst strength has the same effect but to a lesser degree with only a reduction of 20% after the second recycle followed by a slight reduction. This phenomenon is believed to be due to loss in interfiber bonding which could be explained by the reduction in re-swelling capability or the reduction in flexibility of rewetted pulp fibers due to fiber hornification [6] which has been discussed above. This loss in interfiber bonding is further confirmed by the scattering coefficient values which is indirectly related to surface area and fiber bonding [7]. It can be observed from Figure 3 that the there is an increase after the first recycle of about 14%, with almost no change thereafter. This is further supported by data on sheet density (Figure 4) which shows a gradual decrease with increase in recycling. Fiber density is sensitive to fibre flexibility [8] whereby flexible fibers conform well on the plane of paper, and by doing so they form a denser paper. The reduced conformability of the fibres brought by repeated recycling resulting in the fibres being stiffed or hornified, hence rendering the sheets bulkier (lower density). The reduction in sheet density is about 8% after four cycles, after which the change is insignificant. Tear, conversely showed an increase in strength, albeit not as dramatic as the changes observed in tensile and burst. The same trend has been observed by others using softwood pulp [9, 8]. The repeated drying and rewetting has “hardened� the fiber, making it less flexible, and consequently, of poor bonding potential. This creates a situation where the fiber rupture is less likely to occur and fiber pullout will predominate. Since the work needed to rupture a fiber lying along across the path of the tear is considerably less than that needed to pull it out from the sides of the tear, the tearing strength increases with recycling. The intrinsic strength of fibres as measured by the zero-span breaking length of dry sheet samples (Figure 2) shows that there is an initial increase in zero span, followed by some reduction after the third cycle. These slight positive effects, which have also been reported by Ellis and Sedlchek [10] could be due to the formation of internal bonds upon drying. This observation implies that fiber strength does not degrade with recycling, however, with further repeated wetting and drying, it is possible that the zero span will decrease because of the reduction in average fiber length since zero span strength is sensitive to fibre length [11].

1.

2. 3. 4. 5. 6.

IV. CONCLUSIONS Upon recycling, there is a reduction in the mechanical properties, notably the tensile and burst index which is most noticeable after the second cycle. Tear index on the other hand increases with recycling. Fiber strength on the other hand does not show much effect. The strength loss is similar to that observed with other types of pulp as reported in literature, with changes larger than softwood pulps. Scattering coefficient increases with recycling indicating loss of interfiber bonding. Sheet density decreases with recycling, hence bulkier sheets are produced. There is also a loss in the swelling capacity (as measured by the Water Retention Value) of the pulp with recycling. The recovery of the bonding potential which has been lost during recycling can be regain by using many techniques at our disposal thus making this pulp a valuable papermaking raw material.

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International Journal of Recent Trends in Engineering & Research (IJRTER) Volume 03, Issue 1; January - 2017 [ISSN: 2455-1457]

Density (g/cm3)

0.7 Density (g/cm^3)

0.6

0.5 0

1

2 3 4 Recycle Number

5

Figure 4: Effect of recycling on Density

REFERENCES Anonymous, http://www.paperindustryworld.com/fibre-market-in-transition/ (accessed on 30th December 2016). R. Miranda and A. Blanco, Environmental awareness and paper recycling, Cellulose Chem. Technol, 44, 431-449, 2010. 3. TAPPI Test Methods 1996-1997. Tappi Press, Atlanta USA. 4. Scandinavian Pulp, Paper and Board Testing Methods 2000. SCAN-C 62:00. 5. G.V. Laivins and A.M. Scallan, The mechanism of hornification of wood pulps. In: Proceedings of the 10th Fundamental Research Symposium. Oxford, UK, pp. 1235–1260, 1993. 6. M. Garg and S.P. Singh, Reasons of Strength Loss in Recycled Pulp, Appita Journal; 59, 274-279, 2006. 7. E. Retulainen, K. Niskanen and N. Nilsen, Fiber and bonds, Chapter 2 in Paper Physics (ed.KaarloNiskanen), Book 16 in Papermaking Science and Technology, Fapet Oy, Jyväskylä, Finland, pp 54-87, 1998. 8. E. R. Sutjipto, K. Li, S. Pongpattanasuegsa, and M.M. Nazhad, Effect of recycling on paper properties, Tappsa J., 1:19–23, 2008. 9. R.C. Howard and W.J. Bichard, The basic effect of recycling on pulp properties, Journal of Pulp and Paper Science, 18, 151–159, 1992 10. R.L. Ellis and K. Sedlchek, Recycled vs. virgin fibre characteristics: a comparison. Tappi Journal 76, 143–146, 1993. 11. R. Wathén, J. Rosti, M. Alava, L. Salminen and O. Joutsimo, Fiber strength and zero-span strength statistics –some considerations, Nordic Pulp and Paper Research Journal, 21, 193-201, 2006. 1. 2.

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