New ester-type chemical bonding wood adhesion with a dicarboxylic acid compound

Wood adhesion is one of the fundamental joint technologies for wood-based materials. We focused on an unprecedented chemical bonding wood adhesion. With the final goal of water-resistant wood adhesion using dicarboxylic acid compounds with straight alkyl chains, this study clarified the difference of adhesiveness between glutaric acid (GA) and citric acid (CA) to explore the direct effects of chemical bonding type adhesion on physical properties. In the prepared wood-based moldings, the structural analysis with 2D-NMR of the interphase between GA or CA and wood surfaces revealed that GA adhesion is cleaner and more reactive than CA adhesion, without any side reactions. GA reacted with the wood powder surface. In addition, the water resistance treatments of the GA-type wood-based molding showed a thickness reversibility that is not observed with CA-adhesion. The results indicate that GA-adhesion is very likely a chemical bonding type of wood adhesion, considering the molding process under high temperature and pressure conditions. The physical properties of the molding were evaluated to determine the adhesion properties. GA-type wood-based molding was tougher and more water-resistant than CA-type wood-based molding. The physical properties were attributed to the side-chain structure of GA. The results indicate that dicarboxylic acid compounds could be superior wood adhesives, and other dicarboxylic acids could be used for wood adhesion and the expression of material properties owing to their various side chain structures. Furthermore, the material properties could be controlled by considering the chemical structure of adhesive compounds in the future.