Acetylated wood decay resistance

Takahashi, M., Imamura, Y. and Tanahashi, M. (1989). Effect of acetylation on decay resistance of wood against brown rot, white rot and soft rot fungi. International Research Group on Wood Preservation, Doc. No. IRGAVP 3540. 

Table 3.1 Table summarizing experiments on decay resistance of acetylated wood exposed to brown rot fungi... 

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. 

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. 

It may seem that even after 6 hours of reaction, WPG is insufficiently low to impart decay resistance to wood. The rate of vapor phase reactions is determined by the rate of permeation of reagent vapors into the wood. It has been observed that even longitudinal permeability of wood decreased by 2-10 times during acetylation (38). This probably is the reason for slow increase in WPG. In chir also a WPG of 7 percent and 10.9 percent was observed in four and eight hours acetylation respectively. In an earlier study using only 0.25 cm thick samples a WPG of 16.67% was obtained in four hours (35). Similar limitations were observed by Tarkow et al (37), who concluded that 3 mm thickness was the most optimum to obtain uniform acetylation. The effect of cross-section on acetylation is quite clear in Table II. 

Figure 1 Effect of acetylation on the decay resistance of wood against Tyromyces palustris (A). Serpula lacrymans (B), Coriolus versicolor (C), and soil burial (D). (O) Japanese cedar (Cryptomeria japonica), ( ) Japanese red pine Pinus densiflora) (A) albizzia (Albizia falcata), (A) Japanese beech (Fagus crenata). Relative weight loss = Wj/Wi X 100, W, weight loss of control wood W2. weight loss of acetylated wood.

USDA, Forest Service, Forest Products Laboratory, FPL GTR-55 Rowell RM, Imamura Y, Kowai S and Norimoto M (1989) Dimensional stability, decay resistance and mechanical properties of veneer faced low-density particlehoards made from acetylated wood. Wood and Fiber Science, 27(1)67-79 Rowell RM, Kawai S and Inone M (1995) Dimensionally stabilized, very low density fibreboard. Wood and Fiber Science, 27(4) 428-36 Rozsa AN (1994) Dielectric vacuum drying of hardwood. Proceedings 4th lUFRO International Drying Conference, Rotorua, New Zealand, 271-8 Ruddick JNR (1987) Proceeding of the incising workshop, Richmond, British Colombia, 1986. Special Publication 28. Forinteck Canada Corp., Vancouver, BC... 

Four different methods (vapour-phase acetylation using acetic anhydride, acetylation using ketene gas, liquid phase acetylation using acetic anhydride/xylene, or neat acetic anhydride) were used to acetylate pine wood chips to a variety of WPGs for the production of MUF-bonded particleboards (Nilsson etal., 1988). Composite boards were exposed to unsterile soil in fungal cellar tests. Boards made from ketene acetylated chips were not found to be resistant to decay at the maximum WPG level achieved (17 %) with a liquid acetic anhydride modification, no decay was recorded at a WPG level of c. 18 % after 12 months exposure, whereas with a vapour-phase treatment at the same WPG, evidence for decay was found. 

Imamura, Y. Nishimoto, K., Yoshida, Y., Kawai, S., Sato, T. and Nakaji, M. (1986). Production technology for acetylated low-density particleboard II. Decay and termite resistance. Wood... 

Wood acetylated with thioacetic acid showed resistance to decay and termites at low WPG around 12. The available information on pattern of substitution of hydroxyls during acetylation with acetic anhydride suggests substitution of lignin hydroxyls at low acetylation levels. Resistance to micro-organisms, particularly those consuming cellulose, even at low acetylation... 

Property enhancement by acetylation has been frequently reported over the years in other reconstituted wood products such as flakeboards, particleboards, and fiberboards [8,9,11,12,59-64]. Table 16 shows the laboratory decay test of low-density acetylated particleboards made from perishable albizzia wood. They were resistant to attack by Tyromyces palustris (brown rot), Coriolus versicolor (white rot), and Chaetomium globosum (soft rot) above 12% WPG. These acetylated boards with 20% WPG also exhibited an improved resistance to attack by the destructive Formosan termite, Coptotermes formosanus, in the laboratory. However, their performance was unsatisfactory in the wet tropics with a higher hazard of termite attack. High resistance to fungal and bacterial attack in acetylated southern pine and aspen flakeboards was evidenced in laboratory and fungus cellar tests [12]. 

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