DIMENSIONAL STABILITY AND FUNGAL DURABILITY OF ACETYLATED WOOD

The reaction of wood to acetic anhydride greatly reduces moisture sorption and improves the dimensional stability of the wood due to the esterification of the accessible hydroxyl groups in the cell wall, reducing hydrogen bonding with water and bulking the cell wall back to its green volume. The sorption of both primary and secondary water are reduced. Dimensional stability is not 100% since the water molecule is smaller than the acetyl group, therefore water can access hydroxyl sites even when the wood is fully acetylated. The equilibrium moisture content is reduced in a linear relationship to the level of acetyl content. This means that the reduction in moisture content is not dependent on where the acetylation reaction takes place in the cell wall. Resistance to fungal attack increases as the level of acetylation increases. Resistance to attack by white-rot fungus occurs at a much lower level of acetylation (7-10%) than that to brown-rot fungal attack (17-19%). The cell wall moisture content may be too low at high levels of acetylation to support fungal attack, therefore initial colonization does not take place.