Reprocessability of high impact polystyrene/clay nanocomposites in extrusion

Abstract

Plastics' recycling contributes to society with economic, social and environmental benefits. Therefore, recyclability of a material is an important environmental factor to be considered in the development of new materials, such as nanocomposites. In this study, high impact polystyrene (HIPS) and its nanocomposites with 3 and 5 wt% of Cloisite 20A were processed within four extrusion cycles in a single screw extruder having Maddock mixing section. Changes in nanostructure, in thermal, flow and mechanical properties, and in morphology of neat HIPS and its nanocomposites with reprocessing cycles were investigated. X-Ray diffractograms showed that the basal interplanar distance of clay layers increased at the first extrusion cycle, indicating the formation of nanocomposites with intercalated structure, but remained almost constant along extrusion cycles. The MEV micrographs presented improved distribution and dispersion of clay agglomerates with extrusion cycles. The melt flow index and mechanical properties showed a tendency to increase and reduce or vice-versa along extrusion cycles due to competition between crosslinking and chain scission reactions. Since the degradation mechanisms of neat HIPS and its nanocomposites were similar, the observed differences between them were related to reinforcing and barrier effect of clay, content of agglomerates, and their distribution and dispersion along extrusion cycles. A distinct mechanical behavior was observed only for 5wt% clay nanocomposite due to the high proportion of agglomerates present in this composition.