Eco-friendly soy protein isolate-based films strengthened by water-soluble glycerin epoxy resin

Soy protein isolate (SPI) have very scanty applications due to its weak resistance towards water and minimal strength. Chemical cross-linking modification is the most potent way to enhance performance of soy protein, meanwhile, glycerin is generally needed to be added as toughening agent in the preparation of soy protein adhesive. Glycerin epoxy resin (GER) is a water-soluble epoxy resin can be used to reduce volume of glycerin (GLY) addition throughout production of SPI-based films. It also ameliorates tensile strength and water resisting property of films. Mechanical performance of films was examined with universal testing machine. Compared with the untreated SPI-based film, the addition amounts of GER and GLY were 45% and 5% of SPI, respectively, the tensile modulus and tensile strength of SPI-based films were increased by 245.6% and 180.0%, respectively, as well as tensile strength reached 11.2 MPa. The elongation at break was lowered 50.6%, but the strain still close to 150.0%. The 24-h water absorption of SPI-based films was reduced by 51.5%, from 194.2% to 94.1% with GER addition for 35% of SPI. In addition, GER and SPI have stunning compatibility, GER may have promising application prospects in the industrial preparation of soy protein adhesives.