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 °C. 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 (σ b ) and Young's modulus decreased and breaking elongation (ε 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 thermoplastic 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 (σ b = 4.23 MPa and ε 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.