Influence of pressure on polyamide 66 shear viscosity: a case study towards polar polymers behavior

In the present work, we consider the dependence of the viscosity of polyamide 66 (PA66) as a function of both temperature and pressure. Measurements were carried out using a standard capillary rheometer to evaluate the effect of temperature and the corresponding shift factor of viscosity data. The pressure influence was accounted for by employing an at-line rheometer equipped with a counter-pressure cell, the so-called enhanced exit pressure method. Time-temperature-pressure superposition was applied to obtain the viscosity master curve. Interestingly, PA66 displays an unusual increase of the pressure coefficient as a function of temperature. On the contrary, previous studies on nonpolar liquids or polymers for which polar interactions are relatively weak indicated that the sensitivity to pressure, measured by the so-called Barus parameter, is a decreasing function of the temperature. Thus, we attribute the peculiar behavior of PA66 to the strong polar interactions which are present and which may dominate the viscosity at relatively low temperatures and would be less dominant at higher temperatures.