EFFECTS OF POLYHYDRIC ALCOHOLS ON THE MECHANICAL-PROPERTIES OF SOY PROTEIN PLASTICS

Polyhydric alcohols, i.e., ethylene glycol, glycerol, propylene glycol , 1,3-propanediol (trimethylene glycol), and polyethylene glycol (200 and 400), were investigated for their plasticizing effects on soy prot ein plastics. Tensile strength and percentage elongation at break of c ompression-molded soy protein specimens containing each of the polyhyd ric alcohols were measured, and Young's modulus was calculated. Ethyle ne glycol and glycerol demonstrated the greatest effects on the tensil e properties. Differential scanning calorimetric (DSC) thermograms of soy protein with glycerol showed a major exothermic transition. Dynami c mechanical spectra showed that dry plastic specimens had a shear-sto rage modulus (G' = 1.76 GPa) about 50% larger than those of the high p erformance synthetic polymers tested. The shear-storage modulus was li ttle dependent on temperature change up to ca. 130 degrees C. After th e specimens were moisturized at 50% relative humidity, the G' was redu ced to 0.22 GPa. The shear-storage modulus of specimens containing 30% glycerol decreased when the temperature increased above -60 degrees C . Rheological properties of soy protein with and without glycerol were evaluated by using a torque rheometer.