Influence of manufacturing on electrical performances of graphite nanoplatelet filled polystyrene
Paper in proceedings, 2011
Manufacturing strategy is important for the appropriate incorporation of filler into a polymeric matrix, and this in particular refers to nanofilers. Direct-graphite nanoplatelets (GNP) were used as filler in polystyrene (PS). The as-received GNP material contained microscopic size agglomerates formed by nanoscopic size graphite nanoplatelets. Refining of the microagglomerates (break-up) and production of graphene layers (exfoliation) desirably needs to take place during manufacturing. Herein, several melt processing methods used to prepare GNP/PS are in focus. The manufacturing methods used include both, melt and solvent routes, and include elongational flow mixing (EFM), high shear energy micro compounding, roll-milling/calendering, and Brabender mixing chamber, as well as sonication and surfactant assisted solvent processing using N-methyl-pyrrolidone (NMP). We analyze particle break-up and exfoliation, and the effects on electrical conductivity and surface smoothness of the composite, both of importance in high-voltage applications. The composite is characterized by melt rheology, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) with MeX surface topography software, optical microscopy with image analysis, X-ray Diffraction (XRD), and electrical resistivity measurements.
We find that manufacturing processes influence the material´s morphology and properties in different ways. As could be expected, sonication and surfactant assisted solvent processing yielded both good deagglomeration and production of thin graphene stacks/layers. Elongational flow dispersive mixing, studied here using a recently developed mixer (RMX, Scamex, France), efficiently refines the GNP microagglomerates, and the particle break-up is closely comparable to that in solvent processing. Both the processes yield composites having smoother surfaces compared to the ones from other processing methods. Solvent processing and micro-compounding are more efficient than the other processes in the production of exfoliated thin graphene stacks/ layers. Thin graphene stacks/layers, particularly, provide electrical conductivity, at lower amount of filler content.
Acknowledgments: The Swedish Foundation for Strategic Research (SSF) financial support is acknowledged (HP, MR, RWR).