ARS | Publication request: Starch Filled Ternary Polymer Composites I: Dynamic Mechanical Properties

Submitted to: Polymer Engineering & Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 14, 2003
Publication Date: January 13, 2004
Citation: ST LAWRENCE, S., WALIA, P., WILLETT, J.L. STARCH FILLED TERNARY POLYMER COMPOSITES I: DYNAMIC MECHANICAL PROPERTIES. JOURNAL OF POLYMER ENGINEERING AND SCIENCE. 2004.

Interpretive Summary: The use of starch in plastic materials is often limited by poor mechanical properties which preclude development of commercially acceptable materials. In this study, starch was added to a blend of two plastics, one of which adheres to the starch. Small amounts of this component were used in the blends. The effect of temperature on the structure and mechanical properties of these three component blends was characterized. The properties depended on the composition, the interactions between the individual materials and the distribution of the minor component which adheres to starch. It was determined that this component was preferentially located on the surface of the starch granules. This surface coating changes the temperature dependent mechanical properties. The results of this study provide a more fundamental understanding of how the addition of a second resin can impact the mechanical properties of starch-filled plastics. Scientists, engineers, and producers of starch-based plastics will be able to utilize these results to design better materials using more starch.

Technical Abstract: It has been shown that the dynamic mechanical properties of starch filled blends of polyethylene (PE) and poly (hydroxy ester ether) (PHEE) are strongly dependent on the properties and distribution of the minor component of the blend (PHEE). The effect of this minor component on the viscoelastic properties of the composite was investigated by modeling the storage modulus using a step-wise homogenization process. A comparison of theoretical and experimental data indicates that the morphology changes as the volume fraction of filler, volume fraction increases. At low volume fraction, the PHEE encapsulates isolated starch granules. Above volume fraction less than 0:2, the PHEE surface coating contributes to the formation of particle clusters. Evidence of particle encapsulation was provided by a morphological examination of fractured tensile bars. At all filler contents, the decrease in the composite's modulus at the glass transition temperature of PHEE is larger than can be accounted for if this material is simply dispersed in the matrix. When the starch granules are clustered, the decrease is also too large to be accounted for by only considering particle encapsulation. The effect of particle clustering must be included in order for the model to correctly describe the temperature dependence of the storage modulus.