Probing the development of protein-protein interactions and their role in wood bonding

There is great interest in replacing the approximately 9 million tons of urea-formaldehyde (UF) adhesive used annually in producing interior wood panels. The main drivers are to increase bio-based content and remove formaldehyde. Soy protein adhesives have successfully replaced UF in North American hardwood plywood, but cohesive failure of the protein matrix when the finished product is wet limits their use in other markets. What protein-protein interactions contribute to film wet cohesive strength and how can these interactions be promoted? In this talk we will discuss the influence of soy protein properties (surface hydrophobicity-ANS, surface amine-fluorescamne, molecular weight-gels) and bonding conditions (soy moisture content, bonding temperature) on wet bond strength (ASTM D7998), with an eye toward understanding mechanisms contributing to wet strength.

Surface hydrophobicity positively correlated with wet strength, while surface amine content did not, even when amine-reactive crosslinking agents are used. Clearly the common phrase in protein adhesive literature “denature to expose reactive groups” needs to be clarified as organic chemists typically assume “reactive groups” means amino, carboxylic, or other covalently reactive groups, not the food science definition of functionality. Additionally, there is an essential role of water (or other lubricant/denaturant) in bond formation – bonding without water results in very poor bond quality. What might water be contributing to bond formation, and how could this hypothesis be tested?