Properties and structure of soy protein isolate-ethylene glycol sheets obtained by compression molding

Thermoplastic sheets prepared from soy protein isolate (SPI) with ethylene glycol (EG) as the plasticizer were obtained by compression molding under a pressure of 15 MPa at 150 degreesC. The effects of the glycol content on the structure and properties of thermoplastic SPI were investigated by using infrared, X-ray diffraction, differential scanning calorimetry scanning electron microscopy, and tensile test. The results showed that, with increasing EG content., the tensile strength (sigma (b)) and Young's modulus decreased and breaking elongation (epsilon (b)) increased. The water resistance of the thermoplastic sheet of SPI increased with an increase of the EG content and was much higher than that of themoplastic starch sheets or a cellulose film. Further investigation were carried on the SPI sheet containing 50% EG, which displayed a maximum water resistance in boiling water, good mechanical properties (sigma (b) = 4.23 MPa and epsilon (b) = 220%) caused by interaction of SPI with EG, and light transmittance of 82% at 800 nm owing to interchain hydrogen bonds and novel crystal. Therefore, the thermoplastic materials from SPI provided a potential application as film and materials in food package and medical fields.