Submitted to: Polymer Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2005
Publication Date: 3/8/2005
Citation: Willett, J.L., Felker, F.C. 2005. Tensile yield properties of starch-filled poly(ester amide) materials. Polymer. p.46. Interpretive Summary: Starch is an attractive raw material for the development of biobased materials. One approach to starch utilization is to blend starch with biodegradable plastics to produce new materials. This approach is often limited, however, since the addition of starch to plastics typically gives materials with lower strength. We have combined starch with a biodegradable plastic known as poly(ester amide) or PEA, and measured their strengths for starch contents up to 40%. Under certain test conditions, corn starch-PEA materials were significantly stronger than PEA alone. On the other hand, potato starch-PEA blends generally had reduced strength. The reinforcement demonstrated by corn starch is quite unusual, and offers the potential for development of starch-based materials with enhanced properties. These results will be useful to companies and researchers who are developing starch-based materials, and offer new market opportunities for agricultural products. In addition, the results provide new fundamental insights into the properties of starch-based materials.
Technical Abstract: Composite materials were prepared with granular corn starch (CS) or potato starch (PS) and poly(ester amide) resin(PEA), with starch volume fractions (phi) up to 0.40. Tensile yield properties were evaluated at strain rates of 0.0017s-1 to 0.05s-1. Yield stress of the CS-PEA materials increased with strain rate and starch content. The strain rate effect became more pronounced as the starch content increased. A crossover effect was observed with PS-PEA materials: at low strain rates, the yield stress decreased with increasing (phi), and increase with (phi) at higher strain rates. This crossover suggests that the scale of debonding in the PS-PEA materials is comparable to the time scale of the tension test. The addition of either CS or PS to PEA induce a distinct maximum in the stress-strain curve at yield compared to the neat PEA. Debonding of starch granules from the PEA matrix occurred at lowe stresses in the PS-PEA materials than the CS-PEA. In PS-PEA, debonding occurred in bands similar in appearance to shear bands throughout the tensile specimen. After yielding, the cross-section area decreased as the debonded zones coalesced. In the CS-PEA materials, debonding zones were more diffused, and a distinct neck formed at yield. Yield stress data for the CS-PEA materials could be shifted with respect to strain rate to construct a master curve, indicating that yield properties at these strain rates were determined by the matrix response rather than debonding as observed in other starch-filled materials.