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Please use this identifier to cite or link to this item: https://dspace.lboro.ac.uk/2134/19853

Title: Stabilisation of non-equilibrium melt in a linear polyethylene in the presence of reduced graphene oxide nanoplatelets
Authors: Liu, Kangsheng
Issue Date: 2015
Publisher: © Kangsheng Liu
Abstract: In this thesis, investigation on stabilisation of non-equilibrium melt in the presence of high aspect ratio reduced graphene oxide nanosheets (rGON) was carried out. The non-equilibrium melt was prepared by melting disentangled ultrahigh molecular weight polyethylene (UHMWPE) which was synthesised using homogeneous single-site catalytic system. Rheological analyses of the disentangled UHMWPE/rGON nanocomposites prepared by physical mixing conclusively demonstrate the transformation of the melt from non-equilibrium state to equilibrium state was suppressed when the filler was added. The suppression effect on the transformation reached maximum at a certain filler content and the non-equilibrium melt state was retained within the experimental time, indicating the existence of strong filler-chain interaction that hindered the chain thermodynamics. In order to have better understanding of the suppression on the transformation, thermal analysis was performed on the non-equilibrium melts to follow the influence of non-equilibrium polymer melt on crystallisation kinetics of disentangled UHMWPE with and without rGON. The analysis was carried out by means of differential scanning calorimetry (DSC), and the changes in enthalpic relaxation process were found in good agreement with the rheological response of the melts. Thermal analysis showed the presence of two endothermic peaks in a sample of non-equilibrium melt that was left to crystallise under isothermal condition after melting. The high temperature endothermic peak (141.5 °C) was related to melting of crystals obtained on crystallisation from the disentangled domains of the heterogeneous (non-equilibrium) polymer melt, whereas the low melting temperature endothermic peak was related to melting of crystals formed from entangled domains of the melt. It was further found that with increasing the annealing time in melt (160 °C), the enthalpy of the lower melting temperature peak increased at the expense of the higher melting temperature peak, confirming transformation of the non-equilibrium polymer melt to equilibrium melt state. The enthalpic relaxation process as a function of rGON showed that at the specific content of the filler, where the suppression of the transformation reached maximum, the high endothermic peak remained independent of the annealing time of the polymer melt at 160 °C. This observation strengthened the concept that in the presence of the filler, chain dynamics was arrested to an extent that the everlasting non-equilibrium melt state having lower entanglement density was retained facilitating crystal formation having high melting endothermic temperature. This unique property of the nanocomposites provokes potential in facilitating their processability and making high demanding products in more complex dimensions.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.
Sponsor: Loughborough University
URI: https://dspace.lboro.ac.uk/2134/19853
Appears in Collections:PhD Theses (Materials)

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