Rheological properties of thermoplastic polyvinyl alcohol and polypropylene blend melts in capillary extrusions

A single screw extruder with a static mixer was used to prepare molten blends of thermoplastic polyvinyl alcohol (TPVA) and polypropylene (PP). The effects of shear rate, blending ratio and temperature on rheological properties for the blends in capillary extrusions were investigated, and ends correction was also carried out. Rheological parameters such as non-Newtonian index and activation energy were also calculated and evaluated. It was found that the viscosities of the blends were lower than those of TPVA and PP; moreover, the non-Newtonian indices and the activation energies of the blend melts were higher than those of the homopolymers. In particular, the blend with 60 wt% TPVA had the highest non-Newtonian indices and activation energies among blend melts. These results indicate that TPVA and PP blends are negative deviation blends. Furthermore, at a blending ratio of 60 wt% of TPVA, the shear-sensitivity of the viscosity was the lowest and the temperature dependence of the viscosity was the highest. In addition, an increase in temperature led to an increase in non-Newtonian index, therefore the shear-rate dependence of the blend viscosities decreased with a rise in temperature. As the shear rate was increased, the variation of the viscosity over blending ratios decreased while the activation energy of the blends decreased. Thus the effects of temperature and blending proportion on flow behavior were diminished by increasing shear rate.