The measurement of the apparent elongation viscosity ( ) of several polyolefin melts was conducted in this study by using the isothermal fiber-spinning method. The White-Metzner (W-M) model was used to analyze the spinning flow of the polymer melts and, thus, the elongation viscosity was predicted at elongation strain rates ranging from 0 to approximately 5 s-1. The values of the model parameters required in the W-M model were obtained by curve-fitting the experimental data obtained from the shear measurements. The elongation viscosity predicted using the W-M model was in good agreement with the experimental results of fiber spinning. In addition, could also be estimated directly from the measured shear viscosity ( ) with a formulation using the W-M model; the subsequently obtained elongation viscosity and Trouton ratio ( ) were reasonable within a wide range of strain rates. Based on the experimental and theoretical results, the polyolefin with a high molecular weight was observed to have high elongation viscosity, and the polymer with a broad molecular weight distribution also possessed high . The TR value of the commercial polypropylene (PP-1040) began to increase from 3 at a deformation rate of 0.1 s-1 and grew up asymptotically to 10, whereas the TR of high-density polyethylene (HDPE-606) remained at 3 within the entire range of strain rates.
Polymers for Advanced Technologies 25(12), pp.1565–1571