Effect of Hybrid Carbon Fillers on the Electrical and Morphological Properties of Polystyrene Nanocomposites in Microinjection Molding

Shengtai Zhou,Musa Kamal,Andrew Hrymak

doi:10.3390/nano8100779

Abstract

The effect of hybrid carbon fillers of multi-walled carbon nanotubes (CNT) and carbon black (CB) on the electrical and morphological properties of polystyrene (PS) nanocomposites were systematically investigated in microinjection molding (μIM). The polymer nanocomposites with three different filler concentrations (i.e., 3, 5 and 10 wt %) at various weight ratios of CNT/CB (100/0, 30/70, 50/50, 70/30, 0/100) were prepared by melt blending, then followed by μIM under a defined set of processing conditions. A rectangular mold insert which has three consecutive zones with decreasing thickness along the flow direction was adopted to study abrupt changes in mold geometry on the properties of resultant microparts. The distribution of carbon fillers within microparts was observed by scanning electron microscopy, which was correlated with electrical conductivity measurements. Results indicated that there is a flow-induced orientation of incorporated carbon fillers and this orientation increased with increasing shearing effect along the flow direction. High structure CB is found to be more effective than CNT in terms of enhancing the electrical conductivity, which was attributed to the good dispersion of CB in PS and their ability to form conductive networks via self-assembly. Morphology observations indicated that there is a shear-induced depletion of CB particles in the shear layer, which is due to the marked difference of shear rates between the shear and core layers of the molded microparts. Moreover, an annealing treatment is beneficial to enhance the electrical conductivity of CNT-containing microparts.

Highlights

Conductive polymer composites (CPCs) demonstrate potential applications in the areas of antistatic, electromagnetic interference shielding, thermal management, fuel cells, sensing and so forth [1,2,3,4,5,6]
Multi-walled carbon nanotubes (CNT), which are characteristic of high aspect ratio [9], intrinsically high thermal and electrical conductivity [10] have been extensively adopted as one of the most important functional fillers to fabricate conductive polymer composites (CPCs)
Commercial CNT is supplied in the form of heavily entangled bundles, which makes it difficult to disperse in a polymer matrix [10]

Summary

Introduction

Conductive polymer composites (CPCs) demonstrate potential applications in the areas of antistatic, electromagnetic interference shielding, thermal management, fuel cells, sensing and so forth [1,2,3,4,5,6]. To achieve higher electrical conductivity, the concept of hybrid fillers, i.e., the utilization of fillers with different morphologies or aspect ratios has been adopted by researchers to prepare CPCs. Zhang et al [1] revealed that the pc of polypropylene (PP) composites loaded with hybrid fillers of CNT and carbon black (CB) is much lower than that of only CNT or CB-containing counterparts. A “grape-like” structure was typically observed in PP/CB microparts, and a conductive network could be formed in CNT-containing counterparts thanks to its higher aspect ratio Such morphology was hardly detected in either the compression molded PP/GNP composites or their microparts. The effect of abrupt changes in mold cavity thickness on the electrical and morphological properties of corresponding microparts was detailed

Materials

Morphology