The Thermomechanical Processing Conditions and the Mechanical Properties of Injection Molded PP/PC Blends

摘要

This investigation aims at establishing the relationships between the thermomechanical conditions and the mechanical properties of a direct injection moulded polypropylene/polycarbonate blend (70/30wt composition). Rectangular plates (2 mm thick) were injection moulded by systematic variations of the processing conditions. The moulding programme was based on a design of experiments (DOE) approach, being considered variations in two levels of the melt (240 and 280°C)and the mould (5 and 80°C) temperatures and the injection flow rate (3.8 and 38 cmVs). For comparison purposes, neat polypropylene was also moulded under the same set of processing conditions. In both cases the thermomechanical environment was characterised by computer simulations of the mould filling phase using commercially available codes (Moldflow). Tensile specimens were cut from the injected plates. The microstructure of the mouldings was characterized by polarized light microscopy, PLM. The mechanical characterization encompass the assessment of the tensile (at 5 mm/min at 23 °C) and impact toughness (unnotched Charpy test). The results are analysed by ANOVA. The presence of PC particles affects the crystallization of PP, this being revealed on the mouldings microstructures observed by PLM that are distinct for the neat and PP/PC blends. The mechanical properties are determined differently by the processing variables.