Bond quality of soy-based phenolic adhesives in southern pine plywood

Increased demand for wood adhesives, environmental concerns, and the uncertainty of continuing availability of petrochemicals have led to recent attention on protein-based adhesives. This study was conducted to investigate the glue bond qualities of soy-based phenolic adhesive resins for southern pine plywood. Two types of soy-based resins were formulated and tested. The first was made by cross-linking soy flour with phenol-formaldehyde (pf) resins at neutral pH. The second type was obtained by cross-linking soy flour hydrolyzates with pf resin under alkaline conditions. Plywood bonded with the neutral phenolic soy resins containing 70% soy flour and 30% 1.6 g/cm² pf without the use of extenders and fillers compared favorably with the traditional southern pine pf glue mixes. Plywood bonded with alkaline phenolic soy resins, containing 40 or 50% 0.5 g/cm² PF with the addition of extender (19% corn-cob powder), provided better adhesive glue bond properties than traditional southern pine pf glue mixes. These results suggest that soy-based phenolic adhesive resins have potential for the production of exterior southern pine plywood.