High Shear Rheological Behavior of Graphene Nanoplatelet (GNP) Filled Poly(ether- b -amide)s

Abstract

Thermoplastic elastomers (TPEs) are a class of polymers which have elastomeric properties yet can be processed in the melt state. TPEs based on poly(ether-block-amide) find diverse applications in medical devices and sports equipment to industrial uses. The addition of graphene nanoplatelets (GNP) to such TPEs has been shown to induce microphase separation and so understanding processing–structure–property relationships for composites of TPEs and GNP prepared at high shear rates, such as in extrusion and molding, is essential. To this end, composites of poly(ether-block-amide)s based on a poly(tetramethylene oxide) (PTMO) soft segment and a polyamide12 (PA12) hard segment, of different segment ratios, and two types of GNPs were studied using high shear rheology as a function of temperature, GNP size, and loading. Contrary to the typical increase in polymer melt viscosity reported with increasing filler content, a decrease in melt viscosity is observed for the TPE with lower PA12 content, showing complex dynamics between polymer structure, segment molecular weight and length, hydrogen bonding capacity, surface energy, GNP-PA12 compatibility, as well as GNP size, and all influence rheological behavior. Small-angle X-ray scattering (SAXS) showed in both sets of composites that on-cooling the PA12 crystal thickness increases with GNP addition, confirming that the GNP preferentially locates in the PA12 segment. The activation energy for flow, Ea, was also calculated and a decrease in Ea was obtained for the composites with higher PA12 content, while the TPE with lower PA12 content exhibited an increase in Ea, behavior which can be ascribed to interfacial slippage. This study confirms that the high shear rheological behavior and melt processing of GNP filled poly(ether-block-amide) is a function of GNP lateral dimensions and surface chemistry as well as block type and length.