A new network composite material based on soy dreg modified with polyurethane prepolymer

A series of biodegradable, soy-protein-based, composite materials was prepared by introducing castor-oil-based polyurethane prepolymer (PUP) into soy dreg (SD) without the addition of plasticizers, via extrusion and a compression-molding process. The effects of the NCO/OH molar ratio and the PUP content on the structure and properties of the resulting materials were studied by Fourier-transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, tensile testing, swelling experiments, and biodegradability testing. The results revealed that the -NCO group in the PUP played a vital role in improving the compatibility and elasticity, as a result of the formation of a cross-linking network structure with the -NH2, -NH, and -OH groups in SD containing protein and cellulose. Increasing the NCO/OH molar ratio to 2.0 resulted in an enhancement of the degree of cross-linking, leading to a higher tensile strength (24 MPa), glass-transition temperature (52 degrees C) and water-resistivity of the composite materials. The unreacted SD s also served as a filler in the cross-linked networks and enhanced the tensile strength of the composites. The biodegradation testing showed that the composites exhibited biodegradability under the condition of fungus culture.