Corn starch was blended with styrene maleic anhydride copolymer (SMA). ethylene-propylene-g-maleic anhydride copolymer (EPMA), and corresponding nonfunctional polystyrene and ethylene propylene copolymers, The concentration of starch in the blend was varied between 50 and 80% by weight. The torque generated during blending is reported as a function of starch content, mixer speed, and mixing time. Torque increased with increasing starch content for starch/SMA blends: the reverse was true tor starch/EPMA blends. The torque was higher for the blends of the anhydride functional polymers compared to the blends of corresponding nonfunctional polymers. Water absorption of the blends increased with an increase in the starch content. Starch/SMA blends made at higher mixer speed or time were more water sensitive. Blends containing EPMA absorbed less water than SMA blends containing the same weight fraction of starch. Tensile strengths of blends containing functional groups were superior compared to the blends made from nonfunctional polymers. When the starch contents increased from 60 to 70%, the tensile strength remained unchanged for SMA blend but increased for EPMA blend. All samples supported the growth of microorganisms, which increased with increasing starch content. (C) 1994 John Wiley & Sons, Inc.
