Compatibility and mechanical properties of blends of polystyrene with biodegradable polyesters

Biodegradable polyesters allow the development of acceptable bio-composites and bio-blends from agricultural-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. q 2003 Elsevier Ltd. All rights reserved.