On the pressure dependency of the viscosity of molten polymers

Abstract

A slit viscometer to measure the viscosity of polymer melts under processing conditions is described. Along the slit a pressure drop is generated by applying a pressure at both the entrance and the exit. In this way the pressure in the center can be controlled independently of the shear rate. The pressure gradient in the slit is measured by means of three pressure transducers which are mounted in the region of fully developed flow. Results of pressure‐dependent viscosity measurements on polystyrene, polyacrylonitrile‐butadiene‐styrene, and polypropylene are presented in a shear rate range of five decades. The flow curves obtained at different pressures and temperatures can be shifted onto a master curve. The shear thinning behavior of the three materials is adequately described with the generalized Cross‐Carreau equation, while the zero shear viscosity is modeled with a generalized Arrhenius‐W.L.F. relationship, incorporating a pressure dependency. Alternatively, it is possible to describe the zero shear viscosity in terms of the free volume fraction and the temperature.

Control of polymer properties by melt vibration technology: A review

“…Shear viscosity can be measured under pressure at various temperatures and strain rates (38)(39)(40). The measurements indicate that the non Newtonian character of' viscous behavior due to shear thinning is described by the same formula, under high pressure, than under atmospheric conditions, provided the value of 'rg is taken to reflect its pressure dependence, Tg(P), which can be determined from P-V-T experiment:; (41).…”

Application of a multi-phase multi-morphology crystallization model to isotactic polypropylenes with different molecular weight distributions

“…When solving the molecular stretch at different pressure, the pressure shift factor was used according to [49,50]: …”

Viscous dissipation influencing viscosity of polymer melt in micro channels

“…The diameters of capillary dies used are 1000µm, 500µm and 350µm, respectively, with the same aspect ratio, 16.…”

“…In the past, many researchers [15,16] concentrated on the changes in temperature and pressure of melt within dies which have an important effect on the parameters of melt, such as, in particular, viscosity and density. As we know, temperature rise depends on the melt viscosity and inversely the temperature rise affects the viscosity of melt.…”