The Influence of Extrusion Conditions on Mechanical and Thermal Properties of Virgin and Recycled PP, HIPS, ABS and Their Ternary Blends

Abstract

A recyclable plastics waste stream of electrical and electronic equipment has previously been found to contain acrylonitrile-butadiene-styrene copolymer (ABS, ∼40 wt%), high impact polystyrene (HIPS, ∼40 wt%), polypropylene (PP, ∼10 wt%) and a rest fraction consisting mainly of other styrene-based thermoplastics. In this work, one virgin and one recycled ternary blend consisting of these three components were melt-blended in an extruder to study the influence of processing conditions on the mechanical and thermal properties. The aim of the work has been to understand the inherent compatibility between ABS, HIPS and PP without added compatibilisers, in order to investigate the recycling potential of a real recyclable WEEE plastics fraction. Favourable processing conditions with respect to tensile properties of the virgin blend were found at intermediate screw rotations (40 to 80 min ⁻¹) and relatively low barrel temperatures (170 to 220°C), which can be understood from the low onset of thermo-oxidative degradation at 200°C. The recycled blend and recycled ABS, HIPS and PP showed higher stiffness and yield stress, but lower elongation at break than the corresponding virgin materials. The stiffness and yield stress of the blends were found mainly to follow the rule of mixtures of their components while the elongation at break exhibited adverse characteristics indicating incompatibility between ABS, HIPS and PP. The significant variations in the elongation at break of the blends appeared to be due to the ABS component. Differential scanning calorimetry showed an additional melt peak for the recycled blend compared to the virgin blend, otherwise the transitions were similar. The additional peak could be assigned to polyethylene in the PP component. The onset of the thermo-oxidative degradation was found to be at almost 190°C in the case of the recycled blend, which was high considering that it was close to that of the virgin blend and higher than expected from the rule of mixtures of the recycled components.