Influence of reprocessing on the crystallization of polypropylene in PP/PA6 blends

摘要

The non-isothermal crystallization processes of polypropylene (PP) in PP/PA6 blends were investigated by the differential scanning calorimetry method (DSC). The blends containing 20 wt. % of PA6 were prepared in a single-screw extruder. The blends were reprocessed ten times under the same conditions. DSC measurements were used to analyse of thermal properties and overall crystallization parameters of PP in the presence of PA6. In this work, the extent of crystallization, the half-time of crystallization as well as melting and the crystallization peak temperatures were determined. It was found that the crystallization temperature of PP remained practically unaltered after 2—8 extrusion processes, whereas further reprocessing (tenth time) induced significant changes in the T_(cp) value. However, a strong effect of the enhancement of polypropylene crystallization rate was observed in relation to the nucleating action of repeated extrusions. The extent of crystallization increased and the half-time of crystallization decreased according to successive reprocessing cycles. The interpretation of this difference in crystallization parameters after reprocessing of the blends is analyzed according to thermooxidation or thermo-mechanical degradation processes.