A soy protein-based film by mixed covalent cross-linking and flexibilizing networks

In order to develop a strong, tough, water-resistant, and mildew-resistant soy protein film replacing petroleum-based films, in this study, a covalent and hydrogen bond double network structure was constructed in soy protein film using self-synthesized crosslinker triglycidylamine (TGA), soy protein (SPI), and poly(vinyl alcohol) (PVA). The covalent bond network from the crosslinking reaction between TGA and SPI as the skeleton structure improved the tensile strength and water resistance of the film. The hydrogen bond network from interaction between PVA and SPI as a sacrificial bond network to improve the toughness of the film. Compared with the SPI film, the tensile strength and the insoluble matter content of the resultant film increased by 261.2% and 22.1%, respectively. The elongation at break of film increased by 106 times and the fracture toughness improved 183 times. Notably, the resultant film has anti-fungal property, which extends the anti-mold time of film to more than two weeks. This double network construction strategy effectively enhanced the soy protein film and can be applied to reinforce other composite materials and bio adhesives.