Investigations of Non-Linear Viscoelastic Properties for Polypropylene/Clay-Nanocomposites through Melt Flow Birefringence and Damping Function

摘要

Rheological investigations are reported for pure polypropylene and its clay-nanocomposites to establish viscoelastic properties and filler concentration relationship. Flow birefringence is performed through a slit-die to obtain centerline principal stress difference during extensional flow. The centerline stress profile of clay-nanocomposite revealed additional viscoelastic nature even at low silicate concentrations whereas no exceptional strain hardening was reported. Effects of higher filler concentrations were further examined during the simple shearing flow to consider non-linear viscoelasticity in terms of damping function. The increase in damping coefficient with increasing clay concentration showed that polymer-nanocomposites were more strain sensitive. The Wagner's exponential damping function adequately described the time-strain separability at all clay concentrations studied. The results of both investigations revealed that the polymers were time-strain separable at all clay concentrations studied during elongational and simple shearing flows, whereas the filler orientations were found to be different for different melt flow behavior.