Starch-filled ternary polymer composites. II: Room temperature tensile properties

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 (phi(f)), 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(cr). Below phi(cr), deformation involves the growth of debonded regions; above phi(cr), deformation is confined to narrow damaged 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 If can be adequately described using a simplified form of the Kerner equation. (C) 2004 Society of Plastics Engineers.