Temperature Dependency of Bond Strength of Polyvinyl Acetate Emulsion Adhesives for Wood

Bond strengths of PVAc emulsion adhesives were evaluated in the range from -130 to 140 C in both tensile shear and tensile cross-lap joints of wood. Both shear and tension bond strengths strongly depended on rheological properties and tensile strengths of adhesives over the entire temperature range, and the maximum peaks of each bond strength and the film strength were observed around the Tg of PVAc. Higher shear bond strengths were observed in the lower temperature range, while the other bond strengths declined markedly. This phenomenon was explained by the possible occurrence of mechanical interlocking at wood surface and difference of its effectiveness with the direction of stress on the joint. Furthermore, a high amount of grafting effectively fortified both the bond and film strengths of adhesives throughout the temperature range investigated