Emulsifier-free aqueous dispersions of functionalized graphene (FG) represent key intermediates for the production of rubber composites, enabling uniform dispersion of predominantly single FG sheets. In this comparative study on styrene-butadiene rubber (SBR) composites with conventional and novel carbon-based fillers the influence of filler type, content, and dispersion process is examined. For SBR/FG nanocomposites two aqueous dispersion blend strategies based on thermally and chemically reduced graphite oxide are explored. Electron microscopy and X-ray tomography confirm the highly effective FG dispersion in SBR leading to simultaneous improvement of mechanical properties, electrical conductivity, and gas barrier resistance.
The incorporation of nanoparticles to polymer foams not only reinforces the cell walls and struts but can also lead to a decrease of cell size and enhanced cell morphology which in turn, yield foams with superior mechanical properties. For this purpose, several studies have focused on identifying close-to-ideal nucleating agents as well as understanding the influence of processing parameters on foam cell morphology.
This research provides a systemic approach to low-density polystyrene foams produced with graphene (thermally reduced graphite oxide), talc and carbon nanotubes (MWCNTs) via foam extrusion. Remarkably, the cell morphologies of polystyrene/thermally reduced graphite oxide foams show enhanced cell homogeneity with a tremendous increase of the cell densities by more than one order of magnitude compared to neat polystyrene and its counterparts.
The influence of distinct carbon based nanofillers: expanded graphite (EG), conducting carbon black (CB), thermally reduced graphene oxide (TRGO) and multi-walled carbon nanotubes (CNT) on the thermal, dielectric, electrical and rheological properties of polybutylene terephthalate (PBT) was examined. The glass transition temperature (T g ) of PBT nanocomposites is independent of the filler type and content. The carbon particles act as nucleation agents and significantly affect the melting temperature (T m ), the crystallization temperature (T c ) and the degree of crystallinity of PBT composites. PBT composites with EG show insulating behaviour over the tested concentration range of 0.5 to 2 wt.-% and hardly changed rheological behaviour. CB, CNT and TRGO induce electrical conductivity to their particular PBT composites by forming a conducting particle network within the polymer matrix. CNT reached the percolation threshold at the lowest concentration (<0.5 wt.-%), followed by TRGO (<1 wt.-%) and CB (<2 wt.-%). With the formation of a particle network, the flow behaviour of composites with CB, CNT and TRGO is affected, i.e., a flow limit occurs and the melt viscosity increases. The degree of influence of the carbon nanofillers on the rheological properties of PBT composites follows the same order as for electrical conductivity. Electrical and rheological results suggest an influence attributed to the particle dispersion, which is proposed to follow the order of EG<< CB< TRGO
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