The Characteristics of Glued Tensile Shear Strength Constituted of Wood Cut by CO2 Laser

The performance of engineered wood products is highly associated with proper bonding and an efficient cutting method. This paper investigates the influence of CO2 laser cutting on the wetting properties, the modified chemical component of the laser-cut surface, and the strength and adhesive penetration near the bondline. Beechwood is cut by the laser with varying processing parameters, cutting speeds, gas pressures, and focal point positions. The laser-cut samples were divided into two groups, sanded and non-sanded samples. Polyvinyl acetate adhesive (PVAc) was used to bond the groups of laser-cut samples. After assembly with cold pressing, the tensile shear test was carried out. Numerical modelling was carried out to determine the partial elongation and shear strain of the glue line. Based on this, the shear modulus and linear elasticity of the glue line were estimated. Scanning electron microscopy was used to assess the adhesive penetration into the porosity structure of the laser-cut samples, and the depth of the heat-affected zone. The laser-cut surface was analysed by Fourier transform infrared spectroscopy. The wetting properties of the laser-cut surface were investigated by using a contact angle goniometer. The numerical model of the strain-stress curve confirmed the experimental model. The highest modulus of the linear elasticity of the glue in the numerical calculation belongs to the joint containing laser-cut samples at a gas pressure of 21 (bar). The penetration depth of PVAc adhesive into the porosity structure of the laser-cut samples was similar to that of sawn samples. The deepest heat-affected zone in the laser-cut samples was 150 µm. A PVAc drop disappeared immediately on the laser-cut surface without sanding, but gradually on the sanded surface. In contrast, the drop on the sawn surface remained with an angle of 32°–48°. The degradation of hemicellulose and lignin was proven by the lower intensity of the C=O and C-O Bonds, compared to the sawn surface.