Laccase-catalyzed grafting of vanillin on wood and its effect on wood decay resistance

The improvement of wood decay resistance is more inclined to eco-friendly methods such as the application of natural products, but the low durability of some natural products as wood preservatives limits their applications. In this study, vanillin catalyzed by laccase was grafted into poplar wood to increase wood decay resistance and can remain in wood for longer period. The reaction system of vanillin, ABTS, laccase and phosphate buffer solution was impregnated into poplar wood using vacuum-pressure method, and reacted at 40 °C for 6 h. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR) were used to confirm the grafting reaction actually occurring during the process. The decay resistance, leaching resistance and mechanical strength of grafted wood were evaluated. Energy-dispersive X-ray (EDX) mapping was used to characterize the vanillin distribution. The results indicated that vanillin grafted poplar wood had good decay resistance, leaching resistance and higher strength. The mass loss of grafted poplar wood exposed to white-rot fungi [ (L. ex Fr.) Quél.] and brown-rot fungi [ (Pers.: Fr.) Murr.] decreased from original 46 and 13% to 9 and 4%, respectively, even after leaching. The modulus of rupture (MOR) and modulus of elasticity (MOE) of the grafted poplar were 11 and 26% stronger than original poplar wood. Vanillin was found in wood cell wall. It was actually esterified onto wood catalyzed by the laccase.