Selected physical characteristics of polystyrene/high density polyethylene composites prepared from virgin and recycled materials

ABSTRACT: Mixtures of polystyrene and high density polyethylene were injection molded from recycled and virgin polymers to generate cocontinuous structures. The mechanical properties of these blends were evaluated to assess their conformance to rule of mixtures behavior in general and to identify areas of synergy or incompatibility in specific. Flexural and tensile data for recycled blends showed that generally the properties are not additive, except in a cocontinuous region of composition near 35/65 PS/ HDPE that has been identified previously for recycled ma-terials. Analysis of crystallinity in the HDPE phase of these blends by differential scanning calorimetry indicates a marked reduction in the level of HDPE crystallinity at the 35/65 PS/HDPE composition. Similar blends of virgin PS/ HDPE polymer do not show the differing regions of incom-patibility and synergy illustrated by the recycled materials, but rather show approximate conformance to the rule of mixtures. Furthermore, the virgin blends show virtually no crystallinity suppression and a more pronounced Tg shift in the polystyrene compared to recycled materials. Detailed characterization of the recycled materials in terms of poly-mer and particulate impurities should improve understand-ing of these differences and perhaps provide direction for obtaining enhanced synergistic behavior in virgin polyme