Effect of pressurized hot water extraction and esterification on the moisture properties and decay resistance of Scots pine (Pinus sylvestris L.) sapwood

Pressurized hot water extraction (HWE) treatment has the benefit of simultaneous extraction of hemicellulose-based carbohydrates and modification of the solid phase, but it does not drastically improve wood durability. However, removing hemicelluloses from the wood by HWE treatment creates water-filled spaces in the cell walls which could be filled with modification agent in order to improve the properties of the wood. Without drying, modification agent can be added into the saturated wood via diffusion. The esterification of wood with citric acid (CA) improves resistance to biological deterioration but increases brittleness. However, combining CA esterification with additional chemicals that form links with CA can mitigate brittleness. This study investigated esterification as a method for modifying HWE treated wood. HWE treatment with CA solution (4% w/v) was applied at 120 °C for 3 h to Scots pine (Pinus sylvestris L.) sapwood specimens. The specimens were further modified by diffusion with CA and starch derivatives followed by curing. The applied method changed the moisture properties and chemical composition of the wood. The results showed successful wood bulking. The investigated method slightly improved decay resistance to Coniophora puteana and Trametes versicolor but did not change resistance to Rhodonia placenta.