Sodium hypochlorite–based binderless technology for solid wood adhesion: application of a commercial bleaching agent for adhesion and observation of surface characteristics

In this study, several methods for a novel binderless technology were explored, the effects of treatment conditions on the adhesive performance were examined and the surface was characterized during adhesion. The method entailed a three-step process for bonding solid wood, which involved immersion in sodium hypochlorite–containing treatment solutions, surface scratching, and drying with pressing. Various treatment conditions were investigated, including solution types, immersion durations, scratch treatment materials, and pressing methods. The resulting shear strength was 9.7 MPa, which is well above the Japanese Agricultural Standards value for laminated wood (6 MPa). In this method, the specimens were immersed in a bleach solution containing a surfactant for 16 h, followed by pressurization at 1 MPa for 24 h at 60 ℃ using a pressure-controlled press. Around the bonding area in the specimens, the cells in the immersed area were significantly compressed, and the aldehyde groups of the coniferyl aldehyde in the lignin were denatured or lost. Based on these findings, a new binderless technology was developed for solid wood without a high-temperature, high-pressure pressing step.