Computational Spinning Model To Study Different Expressions Proposed In The Literature For The Elongational Viscosity Evaluation From Spinning Experimental Data.

Abstract

The relation between isothermal elongational flow and other flow kinematics, like shear flow,
was of interest since the early stages of rheometry. The main seeking purpose was precisely to achieve the
evaluation of the elongational viscosity as a function of elongational rate through other simpler kinematics
attained easily in experimental programs and commercial rheometers. At present, it is known that this
target is not possible. It is also clear that experimental data of the steady elongational viscosity of
viscoelastic melts at different temperatures are quite difficult to obtain. In this sense, various techniques
for determining the elongational properties of these materials were developed; the apparatuses involved
are considered expensive, difficult to operate and unsuitable for most types of materials, especially for
those having a low viscosity. A technique widely used at present dealing with a variety of polymer melts
is the isothermal fiber spinning process in its well-known version designated Rheotens. This apparatus
presents a challenging problem, which consists in translating measurements of the spinning flow
kinematics and filament forces into those variables pertaining to pure elongation flow within the
rheometric framework. According to what has been reported in the literature, different research groups
have studied this difficult problem and proposed approximate solutions for this purpose. In the present
work we use a computational model of isothermal melt spinning to study the different accuracies obtained
with expressions suggested in previous works to evaluate the elongational viscosity from spinning
experimental data. Some physical aspects concerning the requirements to attain appropriate experimental
conditions are provided, mainly those concerning the description of different zones present in the spinning
kinematics.