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Material Characterisation and Interface Optimisation of Recycled Carbon Fibre Composites

Howarth, Jack (2012) Material Characterisation and Interface Optimisation of Recycled Carbon Fibre Composites. PhD thesis, University of Sheffield.

Available under License Creative Commons Attribution-Noncommercial-No Derivative Works 2.0 UK: England & Wales.

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Composites manufactured from a novel non-woven veil of recycled carbon fibre were tested in longitudinal tension, 3-point bend and short beam shear to assess their mechanical properties with respect to other commonly available materials. It was found that their mechanical properties were intermediate between ‘high-end’ unidirectional pre-preg and ‘low-end’ chopped strand mat, and similar to that of other short-fibre reinforced plastics. A range of oxygen plasma treatments were carried out on the fibres to improve interfacial performance of the composites. It was found that treatment at an intermediate plasma power of 20 W resulted in the greatest improvement in tensile strength of a 10⁰ off-axis composite. Samples were manufactured from either 2 individual veils (IV) or from 2, 10-layer ‘pre-forms’ (PF). Both exhibited similar improvements in 10⁰ off-axis strength. Thus shadowing of the fibre within the plasma did not appear to be significant. Overtreatment at higher plasma powers (35 and 50 W for IV and 50 W for PF) resulted in a significant reduction in tensile strength and failure strain. X-ray Photoelectron Spectroscopy (XPS) showed that plasma treatment at 20 W resulted in the highest level of oxygen functionality on the fibre surface, correlating with the best interfacial performance. Plasma treatment at 10 and 35 W resulted in slightly elevated surface oxygen content, however the off-axis tensile properties of 10 W treated samples were not significantly improved compared to the untreated control. The poor mechanical performance of the over-treated samples can be attributed to either an overly strong interface resulting from increased adhesion or damage to the fibres as a result of the treatment process. There were large variations in fibre wettability across treatments, such that no discernible pattern was present between wettability and interfacial performance. XPS and ToF-SIMS analysis showed that there was almost complete coverage of the veil by the binder in the veil-making process, and that silicon contamination on the fibre itself is likely silica based, and that silicon present in the binder is PDMS.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Materials Science and Engineering (Sheffield)
Identification Number/EthosID: uk.bl.ethos.574066
Depositing User: Mr Jack Howarth
Date Deposited: 14 Jun 2013 13:12
Last Modified: 12 Oct 2018 09:18
URI: http://etheses.whiterose.ac.uk/id/eprint/4042

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