Improvement of Toughness and Mechanical Properties of Furfurylated Wood by Biosourced Epoxidized Soybean Oil

Furfuryl alcohol (FA) is an environmentally friendly chemical modifier that effectively improves the dimensional stability and mechanical properties of wood. The drawbacks of high brittleness and low toughness of furfurylated wood restrict its applications. Epoxidized soybean oil (ESO) is a biomass-derived resource and was added to FA solution as a novel plasticizer in this study. The FA–ESO solution was used to modify radiate pine wood obtained from fast-growing trees sourced from plantations. The microscopic morphology, chemical structure, and mechanical performance of the FA–ESO-modified wood were tested to evaluate the plasticizing effect of ESO on the performance of the modified wood and to assess the toughening mechanisms. It was found that ESO was an effective plasticizer that increased the toughness indictors of the furfurylated wood. When the plasticizer concentration was 20 wt %, the ultimate tensile stress and impact bending strength of the FA–ESO-modified wood were increased by 70% and 10%, respectively, compared to those of the furfurylated wood. In addition, the modified wood had a high density (approximately 910 kg/m3), good dimensional stability (antiswelling efficiency of approximately 82%), and superior mechanical properties (modulus of rupture, modulus of elasticity, and static hardness increased by 16%, 25%, and 18%, respectively). However, these exceptional performances were associated with the high molecular weight, good hydrophobicity, and proper chemical structure of ESO and the appropriate intermolecular interactions between ESO and FA resin chains. The hydrophobic FA resin and FA–ESO thermosets filled the wood cell walls and cell lumens, which improved the wood dimensional stability. Furthermore, the ring-opening polymerization reaction between FA and ESO and the long, flexible aliphatic chains of ESO increased the flexible properties of the FA resins and improved the toughness of the modified wood. The FA–ESO-modified wood had an excellent appearance and physical and mechanical properties comparable to those of tropical hardwood, which could expand the application of radiata pine to musical instruments.