Chemical surface densification of sugar maple through Michael addition reaction

Abstract

Wood densification is a technique to enhance wood density and hardness, presenting a promising solution to expand wood use across various applications. However, current densification methods have cost and environmental impact limitations. This project introduces a potential environmentally friendly approach involving surface chemical densification through in-situ polymerization, using carbon Michael addition reaction between biobased acrylate and malonate monomers. This reaction, conducted in mild conditions with low energy and solvent consumption, aims to enhance wood densification while minimizing environmental impact. Various malonate-acrylate systems were formulated, and were optimized based on their viscosity, conversion rate, glass transition temperature, crosslinking density, and hardness. Then, sugar maple wood samples were densified with the best formulations. Monomers with lower viscosity demonstrated higher chemical retention. Density profile and penetration depth were also higher for the samples impregnated with lower viscosity formulations, which was confirmed by scanning electron microscopy. Confocal Raman spectroscopy confirmed that formulations successfully filled lumens and vessels without reacting with the cell wall components. Brinell hardness was used to determine the hardness of natural and densified woods. One-way ANOVA data analysis showed a significant increase in hardness of densified samples compared to untreated wood; however, based on TUKEY Anova analysis, no noticeable difference was reported between impregnated samples with different formulations. Overall, results showed the potential of the Michael addition reaction in wood impregnation.