Acetylation of wood

Although most of the studies of acetylation of wood have used liquid phase reactions, there have been some reports of vapour phase reactions. Arora etal. (1979, 1980) and... 

Youngquist etal. (1988) found improvements in both resin distribution and IB values when suitable emulsifiers were used in conjunction with waterborne resins, but considered it unlikely that the improvement in performance could be justified on cost grounds. It was postulated that acetylated wood interfered with the polymerization of the resin, so that it was not fully cured. It has also been suggested that acetic acid, which may be released during board pressing, could accelerate resin curing of resol type resins. In a study to determine whether this was so, acetylation of wood was found to slightly reduce... 

Figure 4.4 Acetylation of wood with ketene gas (a) and acetoacetylation of wood with diketene (b).

Mahlberg etal. (2001) studied the effect of acetylation of wood fibres (20 % WPG) upon the mechanical properties of wood fibre PP fibre composites, with and without the addition of a novalak PF. Acetylation resulted in significant improvements in MOR, MOE and IBS in a composite containing 20 % by weight of PP fibre. With a combination of PF and PP (both 10 % by weight) and acetylated wood fibre, MOR was unchanged, MOE decreased and only IBS showed a significant improvement. Acetylation also contributed to a better dispersion of the wood fibres in the PP matrix. 

BP Chemicals developed a pilot-scale plant for the acetylation of wood fibres in collaboration with A-Cell acetyl cellulosics AB, Depac Engineering and the BioComposites... 

Ami, P.C., Gray, J.D. and Scougall, R.K. (1961b). Chemical modification of wood 11. Use of trifluoroacetic acid as a catalyst for the acetylation of wood. Journal of Applied Chemistry, 11, 163-170. 

Clermont, L.P. and Bender, F. (1957). The effect of swelling agents and catalysts on acetylation of wood. Forest Products Journal, 7(5), 167-170. 

Hill, C.A.S., Jones, D., Strickland, G. and etin, N.S. (1998). Kinetic and mechanistic aspects of the acetylation of wood with acetic anhydride. Holzforschung, 52(6), 623-629. 

Larsson Brelid, P., Simonson, R. and Risman, P.O. (1999). Acetylation of wood using microwave heating. Part 1. studies of dielectric properties. Holz als Roh- und Werkstoff, 57(4), 259-263. 

Figure 3. Effect of different moisture levels on vapor-phase acetylation of wood with thioacetic acid. Reaction time is 3 h.

The reaction is acid- or base-catalyzed, and various catalysts have been studied [1,2]. Acetylation has been the most studied of all the chemical modifications of wood. The early studies done by Tarkow et al. [48] and Goldstein et al. [49] are notable. Vast amounts of data are available on acetylation of wood. Rowell [ 1,2] reviewed past research work in this field. Norimoto [50] reviewed recent trends in this field. 

Acetylation of wood (A) was done in neat acetic anhydride at 120°C for 10 h, followed by leaching 10 h in boiling water and oven-drying overnight. Acetylation leads to the structure of pattern (A-4) + (B-6), hydrophilic hydroxyl groups being substituted with hydrophobic and bulky acetyl groups. 

Another method for the acetylation of wood involves reaction with ketene gas dissolved in acetone or toluene (57-61) ... 

In spite of the vast amount of research in the acetylation of wood, the process has not been applied commercially. Two attempts, one in the United States (38) and one in Russia (63, 64), came close to commercialization but were discontinued, presumably because they were not cost effective. 

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