Scots pine (Pinus sylvestris L.) sapwood modification by vinyl acetate-epoxidized plant oil copolymer

A new bio-based formulation consisting of plant oil and vinyl acetate was developed for wood modification aiming at improving some of the material’s properties. In–situ epoxidation of linseed oil (LO) and soybean oil (SO) was carried out at different times with purpose of preparing epoxidized oils with various epoxy content. For comparison, commercially available epoxidized linseed oil (ELO®) and epoxidized soybean oil (ESO®) were also included in the study. The epoxidized oils were subsequently reacted with vinyl acetate (VAc) to investigate the effect of epoxidation degree on the copolymerization reaction between epoxidized oils and VAc. Results showed that a copolymer can be formed between VAc and epoxidized LO with high epoxy content, while no reaction occurred between VAc and SO or its epoxidized derivatives. As the most reactive monomer among studied oils, the epoxidized LO with highest epoxy content (i.e. ELO®) was selected for further investigation to determine the optimal conditions for its copolymerization reaction with VAc. The effect of feed ratio, reaction temperature, reaction time and catalyst amount on the efficiency of the copolymerization reaction was evaluated by measuring the yields of formed copolymer under different conditions. DSC and NMR were used to confirm the formation of copolymer and reveal the chemical structure of the obtained copolymer.The optimized formulation was further impregnated into wood and subsequently cured, and the progress of curing process monitored using ATR–FTIR spectroscopy. It was found that an increase of curing temperature or duration resulted in improved wood dimensional stability, while weight percentage gain (WPG) was not significantly affected. In addition, insignificant correlation between WPG and anti–swelling efficiency (ASE) was found for the VAc–ELO® treated wood. From energy saving and economical point of view, 168 h of curing duration at 90°C is sufficient to achieve a satisfying dimensional stability. Moreover, the VAc–ELO® treated wood showed great leaching resistance to water. By using light– and scanning electron microscopy, it was found that the copolymer formed inside wood was mainly located in rays, resin canals and occasionally in the cell lumina. Like most wood treatments, the mechanical properties of VAc–ELO® treated wood samples were slightly decreased compared to untreated wood, especially MOR, compression parallel to the grain (∥) and hardness perpendicular to the grain (⊥). The difference between control and treated samples gradually increase as a result of increasing WPG. Durability tests showed that 8% WPG was enough to ensure decay resistance against the tested fungi (improved up to durability class 2), and thus can be used to protect wood used in above ground applications.