The main aim of this thesis is to gain an improved understanding of the use and limitations of flax fibres as a reinforcement for thermoplastic composites manufactured by the vacuum forming process. The effect of process variables on void content and on mechanical properties of flax fibre/polypropylene composites has been investigated. An isothermal vacuum forming process has been studied and the following process parameters varied : consolidation time; fibre volume fraction; moisture content; reinforcement stacking sequence. The thermal degradation of untreated and alkaline treated flax fibres and its effect on the composite properties has been investigated using fourier transform infrared spectrometry (FTIR) and thermogravimetry (TG) techniques. Characterisation of the micro structure of failure surfaces following tensile testing of the composites has also been observed using scanning electron microscopy (SEM). The results of the investigation show that an increase in consolidation time at temperature and/or a reduction in fibre volume fraction reduces void content, as expected . By contrast and in spite of the reduction in voidage levels, mechanical tests show that an increase in consolidation time reduces ultimate tensile strength (UTS), strain to failure and impact strength of the composite. This reduction in properties is attributed to increased thermal degradation of the flax fibres and consequently the composite. Degradation manifests itself as hemicellulose and pectin decomposition in the fibres, particularly at low heating rates. Alkaline treatment was investigated as a potential method of improving the thermal stability of the fibres by reducing the low thermal stability hemicellulose and pectin components. Furthermore, such treatment improves the surface roughness of the fib res and results in an improved consolidation due to the reduction in void content. However, these positive effects did not significantly improve composite strength because of an apparent reduction in reinforcement volume fraction resulting from reduced fibre volume.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:594739 |
| Date | January 2013 |
| Creators | Chaishome, Jedsada |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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