Highly effective impregnation and modification of spruce wood with epoxy-functional siloxane using supercritical carbon dioxide solvent

Chemical modification of wood is an established approach to improve its biological durability, water repellence, dimensional stability, and UV resistance. Norway spruce wood (Picea abies) in dry state, however, has an extraordinarily high recalcitrance towards impregnation with liquid modification reagents as drying triggers the irreversible closure of pits, i.e. the cell-to-cell valves in softwood. In the present study, it is shown that supercritical carbon dioxide is a highly suitable impregnation medium to overcome the recalcitrance of dry spruce wood. This has been exemplarily demonstrated for deca(dimethylsiloxane)-α,ω-diglycidylether (D₈M ₂ ^OG ), a linear oligosiloxane with terminal epoxy-functionalities, which could be loaded into respective wood samples affording a weight gain of up to 63%. The thermally assisted reaction of the epoxy-functional siloxane with the wood polymers was catalysed with ring-opening Tin (II) octoate. The effort resulted in a remarkably reduced wettability with water, as evident from contact angle measurements (~ 140°), and in a significant decrease (≤ 20%) of the sample’s sensitivity towards moisture-induced dimensional changes.