The influence of processing aids on the melt rheological properties of HDPE for film blowing

Abstract

Additives serve a variety of purposes in polymer production from increasing stability during processing to improving the appearance of the final product. It is often necessary to include more than one additive to meet the processing and performance requirements of an application. The interactions of additives can be observed by measuring the properties of a material containing different combinations of additives. The objective of this research is to investigate the effects of certain lubricating additives, namely calcium stearate (CaSt₂), zinc stearate (ZnSt₂), and Viton, a fluoropolymer processing aid, on the melt rheological properties of high density polyethylene (HDPE) film resins. The rheological tests include dynamic mechanical analysis, capillary rheology, and creep recovery. Most of the experiments were run at 210°C to approximate processing conditions in the film-blowing die. The experiments were carried out on a series of samples made from the same base resin which contain calcium stearate, zinc stearate, and Viton in various combinations and concentrations. The dynamic oscillatory, creep recovery, and compounding data indicate that there are significant differences in the bulk rheological properties of samples that contain zinc stearate and samples that do not contain zinc stearate. Samples that contain zinc stearate have a lower zero shear viscosity, shorter relaxation time and narrower transition region than sample that do not contain zinc stearate. The reason for these differences has not yet been determined. Viton has a distinct effect on the shear behavior of the resin. Samples containing Viton had higher slip velocities than samples that did not contain Viton. The results suggest that the effectiveness of Viton was hindered only slightly by the presence of either stearate.