Thermal and Mechanial Properties of Plastics Molded from Urea-Modified Soy Protein Isolatese

摘要

Soy protein has been considered as a poential alternative of some petroleum polymers in the manufacture of plastics. The purpose of this investigation was to characterize the thermal and mechanical properties of plastics made from urea-modified soy protein. Soy protein isolae was separated from the defatted soy flour, modified with various urea concentrations, and compression-molded into plastics. Differential scanning calorimetry showed that the temperatures of denaturation and the enthalpies of denaturation of the modified soy protein decreased as urea concentrations increaed above 1M. At the same urea concentration, molded plastics made from the modified soy proteins showed a similar temperature of denaturation as the modified soy protein, but a lower enthalpy of denaturation. Tensile strength and Young's modulus of the molded plastics from the modified soy proteins increased as urea concentration increased and reached their maximum values at 8 M urea modifiation. Both storage modulus and glass transition temperature of the plasatics from the modified soy proteins increased as urea concentration increased. The plastics made from the 2 M urea-modified soy proteins showed improvements in elongation, tough fracture behavior, and water resistance. The urea may furction as a denaturant, a plasticizer, and a filler.