Dimensional stability acetylation

Research on resin-bonded boards has used wood chips, or fibres, that are acetylated prior to composite manufacture. In almost all cases, acetylation has been achieved by using uncatalysed acetic anhydride. Significant improvements in dimensional stability proportional to the WPG of the wood particles have been reported when acetylated wood is used, and there is also a reduction in irreversible swelling (e.g. Bekere etal., 1978 Arora etal., 1981 Rowell etal., 1986a-e, 1989, 1990, 1991,1995 Yoshida etal., 1986 Youngquist etal., 1986a,b, 1988 Larsson and Tillman, 1989 Subiyanto etal., 1989 Vick etal., 1991 Clemons etal., 1992 Kajita and Imamura, 1993 Sasaki and Kawai,... 

Fuwape, J.A. and Oyagade, A.O. (1999). Strength and dimensional stability of acetylated Gmelina and Sitka spruce particle board. Journal of the Timber Development Association of India, 45(1/2), 5-10. 

Houts, J.H. van, Winistorfer, P.M. and Wang, S.Q. (2003). Improving dimensional stability by acetylation of discrete layers within flakeboard. Forest Products Journal, 53(1), 82-88. 

Imamura, Y., Subiyanto, B., Rowell, R.M. and Nilsson, T. (1989). Dimensional stability and biological resistance of particleboard from acetylated albizzia wood particles. Wood Research Kyoto, 76, 49-58. 

Korai, H. (2001). Effects of low bondability of acetylated fibers on mechanical properties and dimensional stability of fiberboard. Journal of Wood Science, 47(6), 430-436. 

Li, J.Z., Euruno, T. and Katoh, S. (2000a). Dimensional stability and flame resistance of silicate-acetylated and propionylated wood composites. Journal of Wood Chemistry and Technology, 20(4), 441 53. 

Okino, E.Y.A., Santata, M.A.E., Souza, M.R. de and Sousa, M.E. de (2001). Dimensional stability and mechanical properties of acetylated Hevea brasiliensis flakeboards. Journal of Tropical Forest Products, 7(1), 96-102. 

Papadopoulos, A.N. and Traboulay, E. (2002). Dimensional stability of OSB made from acetylated fir strands. Holz als Roh- und Werkstoff, 60(2), 92-95. 

Ramsden, M.J., Blake, F.S.R. and Fey, N.J. (1997). The effect of acetylation on the mechanical properties, hydrophobicity and dimensional stability of Pinus sylvestris. Wood Science and Technology, 31(2), 97-104. 

Rowell, R.M. and Plackett, D.V. (1988). Dimensional stability of flakeboards made from acetylated Pinus rculiata heartwood or sapwood flakes. New Zealand Journal of Forestry Science, 18(1), 124-131. 

Rowell, R.M., Simonson, R. and Tilhnan, A.-M. (1986a). A simplified procedure for the acetylation of chips for dimensionally stabilized particleboard products. Paperi ia Puu, 68(10), 740-744. 

Rowell, R.M., Imamura, Y., Kawai, S. and Norimoto, M. (1989). Dimensional stability, decay resistance, and mechanical properties of veneer-faced low-density particleboards made from acetylated wood. Wood and Fiber Science, 21(1), 67-79. 

Rowell, R.M., Youngquist, J.A., Rowell, J.S. and Hyatt, J.A. (1991). Dimensional stability of aspen fiberboard made from acetylated fiber. Wood and Fiber Science, 23(4), 558-566. 

Subiyanto, B., Yusuf, S., Kawai, S. and Imamura, Y. (1989). Particleboard from acetylated albizzia particles. 1. The effect of acetyl weight gain on mechanical properties and dimensional stability. Mokuzai Gakkaishi, 35(5), 412-418. 

Youngquist, J.A., Rowell, R.M. and Krzysik, A. (1986b). Mechanical properties and dimensional stability of acetylated aspen flakeboard. Holz als Roh- und Werkstoff, 44(12), 453 57. 

We are in the process of producing fiberboards from various types of acetylated lignocellulosic fibers. Most of our research has been on pine or aspen particleboards or flakeboards, so the data presented here on dimensional stability and biological resistance come mainly from these types of boards. 

The results of both liquid water and water vapor tests show that acetylation of lignocellulosic materials greatly improves dimensional stability of composites made from these materials. 

Figure 1 shows that the decay resistance of acetylated wood is directly proportional to the WPG (26). The degree of dimensional stability is also proportional to the WPG so the exclusion of cell wall or biological water may be a very important factor in the decay resistance mechanism. 

Acetylation of cellulose to the triacetate has been carried out without breaking down of the structure with acetic anhydride containing pyridine to help open up the cell wall structure and to act as a catalyst (71). This led Stamm and Tarkow (72) to test the liquid phase reaction on wood. High dimensional stabilization without break down of the structure was obtained, but excessive amounts of chemical were used. They hence devised a vapor phase method at atmospheric pressure that proved suitable for treating veneer up to thicknesses of 1/8 inch. Acetic anhydride pyridine vapors generated by heating an 80-20% mixture of the liquids were circulated around sheets of veneer suspended in a box lined with sheet stainless steel. Hardwood veneer,... 

It is well known that acetylation results in an increase of density as well as an improvement of dimensional stability and decay resistance [1,2,50]. Also, termite resistance [48,50], electric insulation [50,52], and acoustic properties [50,53] are improved. ASE effectiveness caused by acetylation is due mainly to chemical blocking of the hydroxyl groups [2]. 

It is of interest that veneer-faced low-density particleboards made from acetylated veneers and acetylated core particles showed excellent dimensional stability in both liquid water and humidity tests and were resistant to attack by fungi in an 8-week soil block test [57]. Furthermore, during the 150-day bending-creep test, the totally acetylated boards showed no strength or weight loss during exposure to T. palustris. 

Research in dimensional stabilization over the last 50 years has achieved limited but specific goals it has yet to fulfil its broader objectives. Niche markets, sueh as the use of polyethylene glycol (PEG) in the treatment of marine and waterlogged artefacts are well established. New technologies for commercial scale treatment of timber by acetylation, and for various heat treatments, have reached the market in the last decade, and may increase in importance in future. 

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