Ultrasonic twin screw compounding of polypropylene with carbon nanotubes, graphene nanoplates and carbon black

The effect of ultrasonic treatment on dispersion of carbon nanotubes (CNT), graphene nanoplates (GNP) and carbon black (CB) in polypropylene (PP) using twin screw extrusion (TSE) was investigated. The ultrasonic power consumption as a function of filler concentration was found to increase for PP/GNP, decrease for PP/CNT and slightly increase for PP/CB. The difference in behavior of the ultrasonic power consumption was related to the void (bubble) concentration in the polymer composites. The efficiency of the ultrasonic treatment was verified through measurements of rheological, electrical and mechanical properties as well as by morphological studies. Ranking of ultrasonic dispersion in composites from best to worse was PP/CB, PP/CNT and PP/GNP. Ranking of the rheological and electrical percolation threshold of composites from low to high was PP/CNT, PP/CB and PP/GNP. The storage modulus and complex viscosity of PP/CNT and PP/CB composites in the low frequency region increased with the ultrasonic treatment while little changes occurred in the PP/GNP composites. In the percolation region, the electrical resistivity of ultrasonically treated composites dropped by 8, 4 and 2 orders of magnitude for PP/CNT, PP/CB and PP/GNP, respectively, compared with the untreated ones. The Young's modulus, yield stress and elongation at break of the PP/CNT and PP/GNP composites were not affected by ultrasonic treatment, but the elongation at break of the treated PP/CB composite at a concentration of 10 wt% increased from 230% to 310%. Morphological studies showed that agglomerates size and agglomerates area ratio of PP/CNT and PP/CB composites reduced with ultrasonic treatment, but not for PP/GNP composites. The incorporation of various fillers increased the crystallization temperature, melt temperature and lamella thickness and decreased the spherulites size. The fillers acted as gamma form crystal nucleation agents with the ranking of nucleation ability of CNT > GNP > CB. (C) 2016 Elsevier Ltd. All rights reserved.