Development of easy-handled, formaldehyde-free, high-bonding performance bio-sourced wood adhesives by co-reaction of furfuryl alcohol and wheat gluten protein

Bio-sourced wood adhesives are an alternative of actuality for petroleum-derived binders used to-day in the timber industry. Inspired by the classical furfuryl alcohol (FA) acid-catalyzed polymerization strategy, a convenient preparation method is proposed for developing wood adhesives derived from sustainable hydrolyzed wheat gluten protein (HWG) and furfuryl alcohol (FA). The obtained HWG-FA wood adhesives show a correct non-volatiles content and initial viscosity. The interaction mechanism of HWG and FA is suggested based on the analyses of FT-IR, 13C NMR, and MALDI-TOF spectra. A competitive reaction relationship was observed between FA-catalyzed self-condensation and the crosslinking of the HWG amino group by the FA hydroxymethyl groups, central to help lengthen the storage life of the adhesives. The adhesive network built-up by FA self-polymerization presents an excellent bonding performance and retardation of water intrusion. The products obtained from the reactions between HWG and FA improve the adhesive network level of crosslinking, which enhances the performance of the adhesives. Moreover, the HWG-FA wood adhesive shows outstanding wet shear strength that exceeds the China National Standard (GB/T 9846-2015, ≥ 0.7 MPa) requirement for exterior-grade plywood type I. This result has seldom been obtained in previous research concerning high biomass content wood adhesives. This research provides a method for preparation of sustainable, eco-friendly, formaldehyde-free, wood adhesive with high-performance.