Esterification of wood with citric acid and sorbitol: effect of the copolymer on the properties of the modified wood. Part 3: decay resistance against basidiomycetes and its relation to moisture behaviour

Modification with citric acid and sorbitol (SorCA) or with pure citric acid (CA) both improve wood durability, yet the contribution of sorbitol remains unclear. Scots pine sapwood was treated with SorCA or CA at equal chemical loadings and exposed to Trametes versicolor , Coniophora puteana , and Rhodonia placenta in an EN 113-2 (2021) decay test. Mass loss caused by T. versicolor was low for all treatments. For C. puteana and R. placenta , mass loss decreased strongly with increasing treatment level. However, CA treated samples showed lower mass losses than SorCA treated samples at comparable weight percent gain (WPG) and comparable calculated CA-content, suggesting differences in reaction pathways within the wood matrix. Moisture contents determined after exposure differed markedly from values obtained in standardised water uptake tests. Across fungi and treatments, absolute water content increased with treatment level and was negatively associated with mass loss. It remains unclear whether this relationship indicates a causal link between moisture and decay, or is confounded by other mechanisms that increase decay resistance.