Processing Starch-Based Plastics

As a naturally occurring polymer, starch is environmentally friendly and abundant in the United States. However, high viscosity makes it difficult to process, and products made from starch are brittle and water sensitive. To mitigate this problem, starch often is blended with synthetic polymers. Researchers followed the "reactive" blending approach, mixing starch with various maleated polyolefins. The presence of a functional group improved the properties of blends over simple mixtures of starch and polyolefins. Up to 90 percent starch could be loaded, although products containing more than 70 percent starch by weight were sensitive to moisture. Blends could be injection molded using commercial plastic molds and have comparable cycle times. The weldline (knitline) strengths of these materials is comparable to that of synthetic polymers. The properties of these materials were stable over six months. This article addresses the effect of processing on the physical and morphological properties of starch-based blends.