Development of soybeans starch based tough, water resistant and mildew-proof adhesives through multiple cross linking cooperation strategy

The exploitation of the environment-friendly and renewable biomass adhesive is a promising alternative compared to petroleum-based ones in the wood industry. In this study, soybean flour (SF) was chosen as a renewable starting material for the preparation of the biomass adhesive. The soy protein structure was unfolded by the calcium hydroxide and multiple reactive groups (-COOH, –NH2, –OH, –SH) of the protein chain were exposed. Inspired by the marine mussel protein, tannic acid (TA) with many poly-catechol/pyrogallol groups was capable of interacting with protein molecules under the alkaline conditions and the strong metal coordination between Ca2+ and TA enable to reinforce the network structure of adhesive. Furthermore, the incorporation of 1,6-Hexanediol diglycidyl ether (HDE) into the pristine protein adhesive had reacted with protein molecules via chemical covalent bonds to form the stable and toughness cross-linking network. The as-obtained adhesive showed improved bonding strength and comparable water resistance. Notably, the enhanced adhesive showed an outstanding wet shear strength of 1.12 MPa, meeting China's interior furnishing requirements (≥0.7 MPa). Additionally, in contrast to unmodified adhesive, the mildew resistance of the cooperation modified adhesive was improved and the storage life extended. This research provides a novel and green way to develop a formaldehyde-free adhesive for the wood industry.