COMPATIBILITY AND MECHANICAL PROPERTIES OF BLENDS OF POLYSYTRENE WITH BIODEGRADABLE POLYESTERS

Authors: Biresaw, Girma; Carriere, Craig

Submitted to: Composites Part A Applied Science and Manufacturing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2003
Publication Date: 2/1/2004
Citation: Biresaw, G., Carriere, C.J. 2004. Compatibility and mechanical properties of blends of polysytrene with biodegradable polyesters. Composites Part A Applied Science and Manufacturing. 35:313-320.

Interpretive Summary: Increasing the demand for agricultural products and, hence, improving the income of farmers requires the development of new products based on agricultural raw materials; and/or increased application of agricultural raw materials in existing products. Development of competitive products based on agricultural raw materials requires that they be blended with other materials that will enhance their material properties. Biodegradable polyesters are high molecular weight polymers that were found to be capable of improving the water-resistance and other properties of ag-based raw materials, without impairing their biodegradability and biocompatibility. In this work, a study into the relationship between the mechanical and interfacial properties of blends with biodegradable polyesters are described. Such an understanding will help in the development of methods for predicting the properties of bio-based blends, thereby speeding up the development cycle of new products based on agricultural raw materials.

Technical Abstract: Biodegradable polyesters allow the development of acceptable bio-composites and bio-blends from ag-based raw materials without impairing their biodegradability and other useful properties. The tensile properties of binary blends of polystyrene (PS) with the biodegradable polyesters polycaprolactone (PCL), d,l-polylactic acid (PLA), and Eastar Bio Ultra (EBU) were investigated. Blend composition ranging from pure PS to pure biodegradable polyester, in 25% increments, were compounded, injection molded, and used in tensile tests, from which the following tensile properties were calculated: yield stress, yield strain and modulus. In general, the tensile properties of the PS/biodegradable polyester blends were found to be between the values of the corresponding pure components. Comparison of the yield stress and modulus of the blends with 25% PS showed these properties decreasing in the order: PLA/PS > PCL/PS > EBU/PS, which is the exact opposite of the reported trend in the interfacial tensions of these blends. This implies a correlation between tensile and interfacial properties that is consistent with expectations. However, the data also showed the yield strain and modulus of the pure biodegradable polyesters decreasing in the order: PLA > PCL > EBU, which is identical to the observation on the blends with 25% PS. Thus, the observed trend in the tensile properties could also be due to a contribution from the bulk properties of the biodegradable polyesters.