Double-network strategy for a cost-effective soybean meal-based adhesive with required and stable water resistance for structural use

Abstract

Although soybean meal (SM)-based adhesives, modified by polyamidoamine-epichlorohydrin (PAE) resin exhibit satisfactory characteristics to replace formaldehyde-based adhesives, their broad commercialization is still limited due to poor water resistance and high cost. This study employed a novel double-network strategy to effectively crosslink SM and fabricated an SM-based adhesive with required and stable water resistance using a co-crosslinker (PM) composed of PAE and melamine-urea-glyoxal (MUG) resins. Analyses including 1 H NMR, 13 C NMR, FTIR, TGA, and XPS revealed that the robust double-network structures were constructed from MUG-SM and PAE-SM networks, which were further reinforced by the co-crosslinking between PAE and MUG resins. Thus, up to 40% of the expensive PAE could be substituted by low-cost MUG resin, resulting in a novel SM/PM adhesive with the required water resistance for structural use at a 16% reduced cost. Furthermore, PM exhibited much better storage stability than PAE and MUG resins. The presented double-network strategy sufficiently promotes the cost-effective application of SM-based adhesives in wood composites and extends it from indoor to outdoor products. • PAE resin blended with MUG resin to produce a PM resin via co-crosslinking. • Double-network structure constructed from PM-soybean meal crosslinking. • Enhanced adhesion properties produced by a double-network structure revealed. • Storage stability of PM resin in 60 days traced and characterized. • SM/PM adhesive reduced cost by 16% with comparable water resistance.