Effect of alkaline treatment on bond strength and solid content of bio-based adhesives for plywood

In this work the effect of alkaline hydrolysis on different plant proteins was studied to evaluate their wood bonding performance on beech plywood. The aim of comparing different plant proteins was to find alternatives sufficient available in Europe with comparable bonding performance to soy. Conditions of alkaline hydrolysis differed in temperature and NaOH molarity. During this study main investigated parameters were related to raw material itself, it's water dispersion and its interaction with beech veneer. The relation between protein viscosity, solids content, solubility and bonding performance of alkaline protein dispersions was investigated. Tensile shear strength measurements were performed on beech wood substrates bonded with protein dispersions to investigate bonding performance. It was found that potato protein has competitive adhesive properties compared to soy, and was additionally able to form a dispersion with a high solid content at comparably low viscosity. Potato protein alkaline dispersions with different solid content (20 and 50%) were tested for dry and wet bonding performance. It was found that the potato protein suspension treated under 1M NaOH, then hot pressed at 140 degrees C performs tensile shear strength up to 7.5 MPa in dry condition, representing wood failure, and up to 0.7 MPa after water soaking for 24 hours.