Acetylation increases relative humidity threshold for ion transport in wood cell walls – A means to understanding decay resistance

The improved fungal decay resistance exhibited by modified wood has been attributed to inhibited diffusion of decay precursors and subsequent degradation products through the wood cell wall. However, data relating the effect of modification to diffusion through wood cell walls is lacking. Synchrotron X-ray fluorescence microscopy paired with an in situ humidity chamber was used to observe the transport of an implanted model metabolite, potassium (K+) ions, in wood cell walls as a function of relative humidity (RH) and extent of the wood modification acetylation. The RH threshold for K+ transport in wood cell walls increased with increasing levels of acetylation between 0 and 20 wt percentage gain (WPG), which clearly indicates that acetylation inhibits ion transport in the modified wood cell walls. The reduced equilibrium moisture content (EMCR or moisture based on wood polymer mass) thresholds were also calculated, but the trend of EMCR thresholds with WPG was inconclusive. Although the results provided support to the proposed mechanism that diffusion inhibition in acetylated wood caused decay resistance, the results could not confirm that diffusion inhibition was the most important mechanism. The observed inhibition of K+ transport in acetylated wood should motivate additional work to understand how chemical modifications affect cell wall diffusion and the implications for producing decay-resistant wood.