Material PropertiesMelt viscosity of PP and FEP/PP blends at low shear rates

A polyfluorinated ethylene propylene (FEP) was compounded with a polypropylene (PP) in the molten state in the temperature range from 180 to 280 °C by using a twin-screw extruder. Melt shear viscosity is one of the important characteristics for flow properties of polymeric materials and when measured at low shear rates can provide useful information on macromolecular chain structure of polymeric materials. The melt shear viscosity of PP, FEP and FEP/PP blends was measured by using a Bohlin higher rheometer under experimental conditions of temperature range from 190 to 290 °C and shear rate varying from 10−2 to 102 s−1. The results showed that the dependence of the melt shear viscosity of PP and FEP/PP blends on temperature was consistent with the Arrhenius equation. The sensitivity of melt shear viscosity for PP to shear rate variation was not obvious, whilst the melt shear viscosity for FEP presented obvious shear thinning within a quite low shear rate limit. When the weight fraction (ϕPP) of PP was less than 10%, the melt shear viscosity of FEP/PP blends decreased quickly, and then decreased slightly and linearly with increase of ϕPP. Furthermore, the temperature sensitivity of the melt zero-shear viscosity for the FEP/PP blends was enhanced with an increase of ϕPP.