The bonding strength, water resistance and flame retardancy of soy protein-based adhesive by incorporating tailor-made core–shell nanohybrid compounds

A weak bonding strength and poor water resistance of soy protein-based adhesives have limited their application as a bio-based non-formaldehyde adhesive in the wood manufacturing industry. In this work, a soy protein-based adhesive was developed by incorporating tailor-made core–shell hybrids, which were synthesized by co-deposition of biomass Tannic acid (TA) as “hard cores” and silanized phenylphosphodichloride (BPOD(Si)) as “flexible shells”. For the soy protein-based adhesive system, the incorporated hybrids were designed as reinforcing elements and crosslinker to construct multiple crosslinked networks, which are beneficial to improve the bonding strength, water resistance and flame retardancy of the final adhesive. For example, the particleboards could be made by mixing with soy protein-based adhesives which show a rupture modulus of 15 MPa, an elasticity modulus of close to 2000 MPa and an internal bonding strength of 0.44 MPa, an increase of 110%, 110% and 145% respectively were registered when comparing with those of pristine soy protein-based adhesive. In addition, the soy protein-based adhesive was also designed to be potentially applied in furniture particleboard manufacturing area, and the flame retardancy could be achieved by a synergistic effect of denaturant borax and flame retardant in hybrids. Consequently, the soy protein-based adhesive showed a Limited oxygen index (LOI) value of 28.7% and the V-1 rating in UL-94 test. Therefore, this work provides a feasible method to produce non-formaldehyde and multifunctional soy protein-based adhesives.