Bioinspired root-nacre synergy enables low-cost high-strength soy protein wood adhesives

Plant protein adhesives are becoming a viable substitute for traditional synthetic adhesives due to their sustainability and formaldehyde-free nature. However, their high production costs and limited market competitiveness remain significant barriers to widespread adoption. Inspired by the root-soil fixing structure of plant roots and the brick-and-mortar structure of nacre, we developed a cost-effective, high-performance and environmentally friendly adhesive utilizing soybean meal (SM), Medicago sativa meal (MSM), and kaolin. The fibrous MSM component emulates the crack-arresting function observed in plant roots, while kaolin facilitates the formation of an organic-inorganic hybrid structure analogous to nacre, synergistically enhancing both toughness and cohesive strength. Our optimized adhesive, PS-M20-K20, achieved a wet shear strength of 1.23 MPa at a production cost of $349.9/ton, representing a 23 % improvement in bonding strength and a 21.4 % reduction in cost compared to commercial soy protein adhesives. Notably, the cost of PS-M20-K20 is slightly lower than that of E₀-grade urea-formaldehyde resin with flour ($361.7/ton), while its bonding strength is 53.75 % higher. This study successfully demonstrates a biomimetic approach to develop cost-friendly, high-performance, and eco-friendly plant protein adhesives, paving the way for large-scale industrial application in the wood industry.