PAPERmaking! g FROM THE PUBLISHERS OF PAPER TECHNOLOGY Volume 2, Number 1, 2016
better homogenisation and a good mixture between kraft lignin and the chips. This is applicable for low pressing temperatures only. It is essential to find the optimum parameters and factors of pressing temperature, pressing pressure, pressing time, and particle geometry and size to produce binderless boards that meet all standard requirements, while consecutively contributing to the internal bond and strength properties of boards. Adding particular materials such as 1% wax or technical lignin can help improve the board properties if the optimum amount is used. PROPERTIES OF BINDERLESS BOARDS Table 3 shows the density, strength, and dimensional stability of binderless boards made from various natural fibres and manufacturing processes (Velasquez et al. 2003b; Okuda and Sato 2004; Van Dam et al. 2004a; Quintana et al. 2009; Hashim et al. 2010; Luo and Yang 2011, 2012; Xie et al. 2012; Saadaoui et al. 2013). The binderless boards were produced within a density range of 0.8 to 1.3g/cm 3 using nine types of materials adapted for various processes. The common tests were conducted according to available standards (JIS - A 5908 2003) to see if the boards met the recommended requirements, which are a minimum modulus of rupture (MOR) of 18MPa, minimum internal bond (IB) strength of 0.3MPa, and maximum thickness swelling (TS) of 12%. From Table 3, it can be concluded that high-density boards turned out to have the highest strength. Most of the binderless boards met the minimum requirement of MOR and IB, except for date palm (Saadaoui et al. 2013), and a few others (Quintana et al. 2009; Luo and Yang 2011, 2012), which did not meet the minimum requirement for IB. However, only wood (Xie et al. 2012) and coconut husk (Van Dam et al. 2004a) met the requirement of maximum TS of 12%. It can be seen that the modulus of rupture (MOR) value of Miscanthus sinensis board is the highest. It is assumed that the Miscanthus sinensis board has gone through a steam process that changed the chemical compounds and improved the internal bond, as well as strength of the board. The second highest MOR value is the board made of wood, followed by the board made from coconut husk and kenaf. These three boards - wood, coconut husk, and kenaf - were manufactured via a hot-press process. It is clearly shown in the table that these three boards have high values compared with other boards made from the steam process, except for Miscanthus sinensis board. The internal bonds (IB) have a great influence on the dimensional stability of boards. From the dimensional stability in the Table 3, boards made of date palm have high values of thickness swelling (TS) and water absorption (WA) because they have the lowest IB value. Conversely, the IB of kenaf is the highest. Also, the dimensional stability of kenaf board is almost 3 to 5 times higher than that of wood board and coconut husk board. The board produced from oil palm has the lowest value in density, which also affects its MOR value. It also has a low dimensional stability compared with other boards. This is in agreement with the theory stating that the hot-press process only causes small chemical changes in boards, which does not help to improve the TS and WA values. In conclusion, there are a large number of factors that affect board properties, such as material type, manufacturing process, parameters used, and parts and sizes of materials, which must be considered and given particular attention when developing binderless boards.
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Article 4 – Wood Panels
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