Lew C. Y., Claes M.,Luizi F.
Nanocyl S.A., , 4 Rue de l'Essor, Sambreville 5060, Belgium
The recent commoditisation of multiwall carbon nanotubes (CNT) in particular, as substitute for conductive carbon black (CB) based composites has attracted immense interests from different sector of industries. Typically, CNT can achieve similar or greater electrical property at a fraction of CB loading level, therefore retaining the ease of processing. It appeals especially in applications requiring stringent cleanliness property where contamination is detrimental to materials performance e.g. high-end electronics. The key challenges to successful fabrication of CNT thermoplastic nanocomposites that combined outstanding electrical and mechanical properties rest in understanding of its processing behaviour to obtain high degree of percolating morphology (i.e. inter-connective network structure of CNT in polymer matrix). In this paper, we investigated the influence of melt mixing and injection moulding parameters on the electrical conductivity of polypropylene (PP) CNT nanocomposites. The influence of polymer viscosity was also examined. Our results showed that depending on molecular weight and processing conditions, polypropylene can achieve some remarkably low percolation threshold of 1.4 and 1.8 wt% CNT, giving a volume and surface resistivities of 7.4x102 Ω•cm and 1.1x105 Ω/sq respectively. We found in this study the optimum conductivity for PP was achieved using a combination of processing conditions defined by high screw speed (above 200 rpm), high mixing temperature, moderately short mixing residence time (3-6 mins) and high mould temperature. Results also indicated that the exfoliation behaviour, given by conductivity measurements, is greatly influenced by types of intercalation pathway of polymer into CNT agglomerates.
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