(14d) The Effect of Mono- and Poly-Organic Acids On Thermoformed Starch-Protein Composites

Bioplastic materials derived from proteins and starch are often difficult to process in high throughput plastic polymer molders due to their high moisture content and low melt properties. Starch and protein materials degrade above 140°C, exhibiting discoloration and low mechanical strength. In this study, we investigated the effects of the presence of mono- and poly- basic organic acids for improved crosslinking on the mechanical properties of thermoformed starch and protein biomaterial. A mixture of 40% whey protein isolate (WPI) and 30% corn starch in an aqueous solution of either Acetic Acid (AA) or Citric Acid (CA) in amounts ranging from 0 to 20 % (w/w) was used to form the biobased composites. The composites were mixed with roller blades in a torque rheometer for 45 min at the preset initial temperature of 70°C. At the completion of reactive mixing, the thermoformed composite pastes were molded into ASTM D4065 strips in a Carver press for 30 min at 121°C. The dynamic mechanical properties were affected by high compounding moisture contents of 23.4% (50/50 AA/CA), 28.7% (CA), 30.3% (AA) and 34.0% (control). Flexibility increased with decreased moisture after molding with AA and CA. Result trends indicate an increasing storage modulus of the molded materials with increasing concentration of organic acids. Further reduction in moisture increased elasticity.