Borate chemistry inspired by cell walls converts soy protein into high-strength, antibacterial, flame-retardant adhesive

Abstract

Urea formaldehyde, phenolic, and melamine formaldehyde resins are currently the most common wood adhesives. However, these modern wood adhesives have toxicity problems and most of the raw materials come from non-renewable resources. Ideally, future alternative adhesives will be prepared from non-toxic, inexpensive, and renewable natural materials. We found that borate chemistry can crosslink soy protein (SP) and soy polysaccharides (SPSs) to produce a strong adhesive, which is the core of the stable structure in higher plants. Hyperbranched polyester (HBPE) was added to the adhesive as a toughening agent. The resulting crosslinked protein adhesive bound wood with high strength and in some cases its force exceeded the force that the wood itself could withstand. In addition, the borate crosslinked protein adhesive displayed antimicrobial and flame-retardant properties. Simple borate chemistry can provide a way to produce low-cost, renewable, and high-performance materials.