Why does acetylation protect wood from microbiological attack?

Three main mechanisms have been postulated for explaining why acetylation provides protection from wood against fungal decay, which can be divided into biochemical (substrate recognition) and physical (cell-wall nanopore blocking or cell-wall moisture content reduction) hypotheses. One way of examining the possible mechanism is to modify wood with anhydrides of different molecular weight so that for a specific weight percentage gain (WPG) different numbers of hydroxyl groups are substituted. The decay behaviour of wood modified in this way can be examined and the relationship between decay mass loss and WPG or OH substitution used to determine the relative influence of cell-wall bulking and substrate recognition. This has been done for a range of wood species and the results are reported.