Improvement of mechanical properties and water stability of vegetable protein based plastics
Bio-renewable bio-degradable plastics are a potential solution to the growing problems of pollution caused by petroleum plastics and dependency on foreign nations for petroleum resources. One possible feed stock for these materials are vegetable proteins, especially from soy bean and corn. These proteins have relatively high molecular weights and have the potential of being processed with standard polymer processing technologies. But some issues that need to be addressed are their water instability (soy protein) and inferior mechanical properties as compared to petroleum derived plastics. In this study, soy protein isolates (SPI) and zein protein was processed with various additives and different process variables to improve their mechanical and water absorption properties.;SPI a food grade protein isolate extracted (90% protein) from soybeans was mixed with solvents such as water and glycerol and preservative salts to form the base resin. The resin was extruded in its control composition as well as with additives such as zinc stearate, zinc sulfite and blended with poly-epsilon caprolactone (PCL) to obtain pellets of five different compositions. The extrudate was pelletized and injection molded into ASTM dog-bone samples, which were used for characterization. The results indicated that the blends with PCL were relatively water stable. Thermocycling of control composition at 100°C improved the tensile strength significantly.;Zein an alcohol soluble protein from corn endosperm was casted into films after dissolution in solvents (ethanol) and addition of additives and/or plasticizers. The control formulation based on screening experiments was varied with the addition of different percentages of nanoclay. The effect of nanoclay exfoliation by ultrasonics on zein cast sheets was investigated. The results indicated that the control formulation had better mechanical properties but addition of nanoclays improved the water absorption properties in the films.