Positive impact of carbohydrate on the crosslinking, performance, and potential applications of defatted soybean flour-based adhesive

Defatted soybean flour (DSF)-based adhesive has been successfully commercialized owing to its acceptable performance, formaldehyde-free formulation, and derivation from a biological resource. However, obscurity of the effects of DSF components on adhesive performance limits its wider commercial applications. In this study, a soybean protein isolate (SPI) and a soybean polysaccharides (SPSs) were constructed to simulate DSF and allow investigations into these components' contributions to the crosslinking characteristics and performances of DSF-based adhesive. Results from the sol-gel test, Fourier-transform infrared spectroscopy (FTIR), and 13C nuclear magnetic resonance (NMR) confirmed that the SPI and SPS mixtures reasonably simulated DSF function proportional to their contribution to DSF content and revealed that carbohydrates in DSF can be crosslinked by the crosslinker epichlorohydrin-modified polyamide (EMPA). FTIR results, rheological analyses, and bond property evaluations confirmed that reduction of SPI reactivity by carbohydrates effectively reduced apparent viscosity and crosslinking rates at room temperature and was therefore beneficial for technological applicability but may negatively impact the bonding properties of DSF-based adhesives. These results suggest that 10%–30% carbohydrate-rich wheat flour can be introduced into DSF-based adhesives to improve their technological applicability, reduce the cost, and provide instructive information for tailoring the formulation of DSF-based adhesives according to desired applications.