Submitted to: Polymer Engineering & Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2004
Publication Date: October 1, 2004
Citation: St Lawrence, S., Walia, P., Felker, F.C., Willett, J.L. 2004. Starch filled ternary polymer composites ii: room temperature tensile properties [abstract]. Journal of Polymer Engineering and Science. 44(10):1839-1847. Interpretive Summary: The use of starch in biodegradable plastics is often limited by its negative effect on properties, such as reductions in strength and toughness compared to the plastic with no starch. Approaches are therefore needed to increase the amount of starch which can be blended with conventional plastics while maintaining useful properties. We have found that the addition of a third component to blends of starch with polyethylene, a commercially available plastic, improves the properties of the blends. In some cases, the properties of the three-component blend are improved over the proeprties of the polyethylene itself. These results demonstrate a method to increase the starch content in plastic materials, and provide fundamental knowledge of starch-containing plastics to other scientists in industry and academia developing new biobased materials.
Technical Abstract: The room temperature tensile properties of granular starch filled low density polyethylene (PE) and starch filled blends of PE and poly(hydroxy ester ether) (PHEE) are presented. At low filler contents of phi the filled PE:PHEE blend has a higher yield stress and tensile strength than either the starch/PE composites or the unfilled matrix. The increase in the yield stress indicates that matrix yielding occurs before debonding. At high filler contents the tensile strength of the filled blend is again greater than the strength of the starch/PE composites. This increase in strength is the result of higher debonding stresses in the ternary composite. In both materials there is a change in the deformation process at a critical filler content, phi. Below phi, deformation involves the growth of debonded regions but above phi, deformation is confined to narrow damage zones. There is a reduction in the strain at failure when this change in the deformation process occurs. Although the PHEE surface coating affects the debonding stress and the tensile strength it does not affect the strain at failure or the tensile modulus. For both composite materials the increase in modulus with phi can be adequately described using a simplified form of the Kerner equation.