Controllable crosslinking system of soy protein-based adhesives via soybean polysaccharide for wood composites

The development of soy protein-based adhesives is an environment-friendly strategy to fabricate formaldehyde-free wood composite with desired properties. However, it remains challenge to effectively control crosslinking process and therefore tailor the property of soy protein-based adhesives. Herein, inspired by the components of defatted soy flour, a controllable crosslinking system of soy protein and epichlorohydrin-modified polyamidoamine was developed by adjusting the soybean polysaccharide contents. The results confirmed that soluble polysaccharide involved into the crosslinking system via Maillard reaction. Even though the weight ratios of polysaccharide in the adhesives increased from 0% to 60%, the water-insoluble contents of the cured adhesives were slightly driven down from 89.15% to 84.98%, meanwhile thermal stability of the cured adhesives can be improved 1.4 times. Moreover, polysaccharide can be used as a small molecular additive to reduce initial viscosity of the adhesive and achieve improved spread property and mechanical interlock with plywood. Notably, the soaked wet bond strength of the resultant plywood reached 1.58 MPa and the cycled wet bond strength reached 1.17 MPa, which meet the requirement of outdoor use, when the contents of polysaccharide in the adhesives were 40%. Therefore, this study may provide a facile and cost-effective approach to prepare a high-performance soy protein-based adhesive.

Automated summary

This study developed a controllable crosslinking system of soy protein-based adhesives by adjusting the soybean polysaccharide contents. The results showed that increasing the polysaccharide content can reduce the water-insoluble contents and improve the thermal stability of the adhesives. Additionally, polysaccharide can be used as an additive to reduce viscosity and improve spread property and mechanical interlock with plywood. The resultant plywood met the requirement of outdoor use with soaked wet bond strength of 1.58 MPa and cycled wet bond strength of 1.17 MPa at 40% polysaccharide content.