Highly Stable Wood Material with Low Resin Consumption via Vapor Phase Furfurylation in Cell Walls

Wood and wood-based products have the problem of dimensional instability caused by changes in moisture content. Furfurylation modification is an environmentally friendly approach for wood stabilization. However, it normally adopts a traditional liquid phase vacuum and pressure impregnation (VPI) process, which has the inherent shortcomings of huge modifier consumption, wood drying defects after impregnation, and troublesome disposal of waste liquor. In this study, a novel process, vapor phase furfurylation (VPF), was for the first time applied to wood, leading to superstable wood material (ASE > 80%) with low furfuryl alcohol (FA) resin loading (weight percentage gain <15%). This process totally avoids invalid deposition of FA resin in the cell cavities of modified wood and meanwhile ensures the furfurylation of wood cell walls, as demonstrated by scanning electron microscopy (SEM) and nanoindentation. Furthermore, the distribution of FA resin in wood with the VPF process was evaluated with dynamic vapor sorption (DVS) and imaging FT-IR. Our study demonstrated a VPF process that has the potential to produce functionally gradient furfurylated wood with high dimensional stability at a low production cost. Furthermore, VPF at 115 °C for a duration of 40 h with a maleic anhydride (MA) concentration of 4.5% was proposed as an optimized process based on orthogonal experimental design and range analysis.