Thermal and mechanical properties of plastics molded from urea-modified soy protein isolates

Soy protein has been considered as a potential alternative of some petroleu m polymers in the manufacture of plastics. The purpose of this investigatio n was to characterize the thermal and mechanical properties of plastics mad e from urea-modified soy protein. Soy protein isolate was separated from th e defatted soy flour, modified with various urea concentrations, and compre ss ion-molded into plastics. Differentia scanning calorimetry showed that t he temperatures of denaturation and the enthalpies of denaturation of the m odified soy protein decreased as urea concentrations increased above 1 M. A t the same urea concentration, molded plastics made from the modified soy p roteins showed a similar temperature of denaturation as the modified soy pr otein, but a lower enthalpy of denaturation. Tensile strength and Young's m odulus of the molded plastics from the modified soy proteins increased as u rea concentration increased and reached their maximum values at 8 M urea mo dification. Both storage modulus and glass transition temperature of the pl astics from the modified soy proteins increased as urea concentration incre ased. The plastics made from the 2 M urea-modified soy proteins showed impr ovements in elongation, tough fracture behavior, and water resistance. The urea may function as a denaturant, a plasticizer, and a filler.