An Explanation of Structure-Property Relationships for Polymer/Clay-Nanocomposites Through Melt Flow Birefringence and Rheological Damping Function

Abstract

Rheological investigations are reported for pure polyolefin and its clay-nanocomposites to establish structure-properties relationship with respect to filler concentration. Flow birefringence is performed through an engineering geometry slit-die to obtain centerline principal stress difference during elongational flow. The centerline stress profile of clay-nanocomposite revealed additional viscoelastic nature even at low silicate concentrations whereas at the slit entrance no exceptional strain hardening was reported. Effects of higher filler concentrations are further examined during the simple shearing flow where non-terminal low frequency strain hardening only at maximum concentration of clay exhibited pseudo solid like response with improved dynamic moduli. The increase in damping coefficient with increasing clay concentration shows polymernanocomposites are more strain sensitive. The Wagner exponential damping function could adequately describe the timestrain separability at all clay concentrations studied. The results of this investigation reveal that the polymers are time-strain separable at all clay concentrations during elongational and simple shearing flows. But different molecular orientations are possible according to layers alignment along the flow direction.

Keywords

• polyolefin-clay nanocomposite
• flow birefringence
• stress optical rule
• non-linear rheology
• damping function