Obtaining the shear stress-shear rate function and the wall shear stress-slip velocity function of PVC melts from slit-die viscometry data

Abstract

Shear stress versus shear rate and wall shear stress versus slip velocity relations are the key material property functions of any polymer melts. They are normally measured using capillary or slit viscometers. The presence of wall slip greatly complicates the treatment of the resulting viscometry data. This paper describes the conversion of the viscometry data of a number of PVC melts through slit dies with different gaps into these two material property functions. The conversion procedure, based on Tikhonov regularization, has the advantage that it is independent of rheological constitutive equation and does not require extrapolation of the experimental data. It also has the ability to cope with the unavoidable noise in the experimental data. Consequently, the resulting property functions are likely to be closer to the true material properties than some of the existing methods. For each PVC melt investigated the two material property functions will be compared against published results and their differences discussed.