Resin distribution and mechanical properties of furfurylated Chinese fir wood in relation to furfuryl alcohol concentration

Furfurylation is a promising wood modification approach, but the reduced wood toughness largely limits its application in structural areas. In this study, the mechanical properties of Chinese fir wood treated with furfuryl alcohol (FA) solutions at varying concentrations (5% to 45%) was investigated, focusing on how the distribution of FA resin across multiple scales influences these properties. The findings highlighted that the mechanical performance of furfurylated wood is strongly dependent on the distribution of FA resin. The inhomogeneous distribution of FA resin in the core and surface layers enhanced the bending strength and stiffness of furfurylated wood. At low FA concentrations (below 25%), FA resin mainly deposited in the wood cell walls, while at higher concentrations, FA resin accumulated in cell lumens with the cell walls nearly saturated, causing a 60% reduction in bending toughness. Remarkably, further resin deposition in cell lumens above 25% FA did not compromise toughness. This reduction in toughness was largely attributed to the FA resin infiltrating the cell walls. For the structural application of furfurylated wood, either restricting resin infiltration into the cell walls or modifying FA resin to mitigate brittleness are proposed, thus achieving an optimal balance between dimensional stability and toughness.