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Title: Polyethersulphone/graphite conductive composites for coatings
Authors: Leesirisan, Siriwan
Issue Date: 2007
Publisher: © Siriwan Leesirisan
Abstract: In this research, the electrical conductivity and thermal properties of polyethersulphone (PES) insulating polymer were improved, at its optimum micromechanical properties, by filling with electrically and thermally conductive graphite, for use in coatings for electrostatic dissipation applications. The graphite employed was a micro-/nano-graphite with aspect ratios in the range 100-600. Two types of the graphite, untreated and treated, were used for PES composites and LiCI-doped PES composite fabrication via a solution method. The treated graphite was surface functionalised by concentrated nitric acid treatment. FT-IR indicated the effectiveness of concentrated nitric acid treatment in introducing additional -COOH groups on the surfaces of the graphite. XRD, SEM and TEM revealed the dispersion of the graphite throughout the PES matrix in both an immiscIble and disordered manner, and the existence of aggregates of graphite. Nanoindentation testing showed insignificant decreases in the nanohardness and elastic modulus of the PES/treated graphite composites when the treated graphite content was not more than 5 wt%; whereas, increasing the content of the treated graphite increased the nanoscratch resistance of the composites. Due to the high aspect ratio of the graphite, the electrical conductivities of the PES/untreated and PES/treated graphite composites were enhanced at low loadings. An initial conducting pathway was formed at lower than 3 wt% of the filler. The enhancement by 2 orders of magnitude of the electrical conductivity of a PES/treated graphite composite could be accomplished by doping with 0.06 wt% of LiC!. MDSC showed improvements in the thermal conductivity of the PES matrix by 165 and 91% with the addition of 5 wt% of the untreated and treated graphite, respectively. DSC curves illustrated higher glass transition temperatures of the PES/graphite composites and doped PES/graphite composites, compared to the pure PES. Decreases in relaxation enthalpy WIth time, due to physical ageing of PES, were smaller when the PES was filled with the graphite or LiCI-doped graphite. The decrease in relaxation enthalpy of the materials was accompanied by increases in glass transition temperature and characteristIc length. Physical ageing also led to a decrease in the electrical conductivities of the PES/graphite composites and doped PES/graphite composites.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.
URI: https://dspace.lboro.ac.uk/2134/13597
Appears in Collections:PhD Theses (Materials)

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