MECHANICAL AND SWELLING PROPERTIES OF POLYSTYRENE-POLYOLEFIN BLENDS

Differential scanning calorimetry and swelling characterization have been extended to low density polyethylene-polystyrene blends. The thermal data reveal high incompatibility between the two components in the blend. Swelling measurements in the state of quasi-equilibrium show a marked anisotropy of the cylindrical extruded specimens. Mechanical measurements in the tensile mode were carried out at room temperature on blends of the same atactic polystyrene with each of four polyolefins with increasing side-chains featured in a previous work. As the composition is varied from the pure polystyrene to the pure polyolefin the stress-strain curve changes gradually from one exhibiting brittle fracture to one showing increasingly ductile yield. At a critical concentration that ranges generally from 30 up to 50% polystyrene there is clearly an inversion of phases. Below such value the blend consists of a polyolefin matrix with polystyrene fibrils oriented in the direction of extrusion, as inferred by the swelling data. Beyond this critical composition the blends consist of a glassy polystyrene matrix with polyolefin inclusions. In the latter case the anisotropy is due to the cylindrical shape of the entire specimen. © 1979 Chapman and Hall Ltd.