Comparison of soy-flour hydrolysates for wood adhesive systems

Soy-protein-based adhesives have not been used extensively in wood products since the 1960's because of poor performance, stability, and water-resistance issues compared to petroleum-based adhesives. The early soy-protein adhesives were made from defatted flours and were dispersed in alkaline solutions to denature proteins and make more polar amino acid groups available for adhesion bonding. Recent research has focused on soy flour adhesives due to increased phenol prices and environmental concerns related to the use and exposure to formaldehyde. Soy protein isolates can be modified in highly caustic alkaline solutions to reduce viscosity and improve adhesive properties, but the price of isolates is cost prohibitive for most industry applications. Soy flour hydrolysates produced with enzymes were evaluated in adhesive formulations. Soy hydrolysate and phenol-formaldehyde (PF) resin blends made from four types of enzymatic hydolysates were tested for the time required for polymerization, water-resistance, and their performance in medium-density fiberboard applications. Results show that for all of the aforementioned analyses that as the level of soy hydrolysate increased, properties of hydrolysate-PF blends decreased. Testing also showed distinguishable differences between alkaline and enzymatic hydrolysates, as well as differences among enzymatic treatments when used in resin blends.