Plastic performance of soybean protein components

Soybean proteins recently have been considered as petroleum polymer alterna tives in the manufacture of adhesives, plastics, and various binders. The o bjective of this work was to characterize the plastic performance of soybea n protein components during molding processes. Two major soybean protein fr actions, 7S-rich globulin (7S-RG) and 11S-rich globulin (11S-RG) were separ ated from defatted soybean flour, and their purity was examined by sodium d odecyl sulfate-polyacrylamide gel eletrophoresis and high-performance liqui d chromatography. The thermal transition properties of the two fractions at 10% moisture content were 137.6 degrees C for 7S and 163 degrees C for 11S , as analyzed using differential scanning calorimetry (DSC). Plastics were prepared using a hot press at various molding temperatures that were select ed based on the proteins' thermal transition temperatures obtained by DSC. The plastics were evaluated for mechanical properties, water absorption, an d microstructure. The plastics prepared with temperatures at or close to th e thermal transition temperature showed a smooth, uniform, and complex stru cture. Results showed that the plastics made from 11S-RG at its thermal tra nsition temperature were stronger (35 MPa) and had lower water absorption t han those made from 7S-RG at 145 degrees C (26 MPa). The plastics made from the 7S- and 11S-RG mixture had the highest tensile strength (39 MPa) and m edium water absorption compared to those made from 7S- and 11S-RG alone. Th ese mechanical properties and water absorption behaviors were significantly affected by molding temperatures. The results obtained from this research indicated that interaction between 7S- and 11S-RG could occur during moldin g and that thermal transition temperature played an important role in therm al processing of soybean proteins.