Journal
COMPOSITES PART B-ENGINEERING
Volume 135, Issue -, Pages 25-34Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.compositesb.2017.10.002
Keywords
Rheological percolation; Temperature effect; Viscoelastic properties; Electrical conductivity; Graphene; Poly lactide; Nanocomposite
Funding
- Australian Government through a Research Training Program (RTP) scholarship
- School of Engineering, RMIT University
- Australian Research Council (ARC) Research Hub for Future Fibres - Australian Government [IH140100018]
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Polylactide (PLA) nanocomposites with graphene nanoplatelet (GNP) contents of 0-15 wt% were prepared and characterised in terms of rheology and electrical conductivity. As expected for rigid nanofillers, GNP incorporation significantly enhanced the viscoelastic properties of the nanocomposites. Furthermore, above a certain GNP concentration the liquid-like melt flow behaviour changed into a solid-like behaviour. However, this rheological percolation threshold was found to decrease from near 9 wt% at 180 degrees C to below 6 wt% at 220 degrees C, detected and measured by Van Gurp-Palmen plots and Winter-Chambon method, respectively. It was also found that the viscoelastic properties of some of the nanocomposites increased with increasing temperature, which is in contrast to the rheology of ideal polymeric melts. The Electrical percolation threshold of the PLA/GNP system, which is determined by a sudden increase in DC conductivity and is indicative of establishment of interconnected conductive structures of GNPs within the matrix, was observed to be between 6 and 9 wt% GNPs. Morphological studies also showed physical contact between the platelets at 9 wt% while at 6 wt% they were still separated by the PLA matrix. These observations challenge the attribution of rheological percolation threshold to the formation of a percolating network of only filler particles within the matrix. A percolating network consisting of both polymer chains and filler particles might be the reason for the temperature dependency of rheological percolation threshold in the PLA/GNP system.
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