Submitted to: International Workshop on Biodegradable Plastics and Polymers
Publication Type: Abstract Only
Publication Acceptance Date: 4/17/2002
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Materials were prepared by extrusion compounding granular starch with biodegradable poly(ester-amide)s with starch volume fractions up to 0.40. Two resins were used: BAK 404 (Tg=42 C, Tm= 138 C), and BAK 402 (TG=36 C, Tm=173 C), both supplied by Bayer. Tensile properties were evaluated on molded specimens over a range of strain rates. The addition of corn starch (CS) to BAK 404 increased yield strength compared to the unfilled resin. The increase was more pronounced at higher strain rates. The addition of potato starch (PS) to the same resin reduced yield strength at low strain rates, while at high strain rates the opposite was observed. Starch-BAK 404 materials displayed considerable post-yield ductility (necking) until the starch volume fraction was approximately 0.30, at which a transition to "brittle" (no necking) fracture was observed. The addition of CS to BAK 402 reduced yield strength at low strain rates, and increased it at higher strain rates. Post-yield ductility of the CS-BAK 402 materials was lower than that observed for CS-BAK 404 materials. Stress whitening during tensile loading was observed in all materials, and intensified with increasing stress. When necking occurred, it was accompanied by intense stress whitening due to formation of elongated voids after debonding. The effects of strain rate on yield strength are suggested to be due to time-dependent and particle size-dependent debonding at the polymer-starch interface. In materials with BAK 402 as the matrix, yield strength shows an inverse square root dependence on particle diameter, and yield strengths for different particle sizes can be shifted with respect to strain rates to form a master curve for a reference particle size.