The effect of molecular structure on the rheological behaviour of tetrafluoroethylene/hexafluoropropylene copolymers

The rheological properties of tetrafluoroethylene-hexafluoropropylene copolymers (TFE/HFP resins) of different molecular weight and composition were studied using both a capillary and a sliding plate rheometers. First, experiments in the sliding plate rheometer for a series of TFE/HFP resins having relatively low melting points (higher content of HFP), have shown that the dependence of the zero-shear viscosity on the molecular weight agrees very well with theoretical predictions for entangled melts. Secondly, the processability of these resins and some others having higher melting temperatures (lower content of HFP) was assessed by means of capillary rheometry. Several regions in their now curve were identified.