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Title: Developments of a fluidised bed process for the recycling of carbon fibre composites
Author: Jiamjiroch, Krit
ISNI:       0000 0004 2746 9562
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2012
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Carbon Fibre Reinforced Plastics (CFRPs) have very impressive properties. particularly in terms of specific strength and stiffness. and they are widely used in many industries such as in the production of high-tech sports goods and the aviation industry In addition. the quantity of (,FRPs in use has increased significantly. especially during the past few decades. After Hoeing announced the shift in their aeroplanes from alloy based to composite aircraft. there has been a very large impact on the carbon fibre market. and it is estimated that by 2014. the carbon fibre market will reach £ l. 7 billion. However. the growth of carbon fibre utilisation has resulted in an increased quantity of CFRP waste which still has the potential to be al high value material and which can be recycled and reused in non-structural applications. The aim of this study is to recycle carbon fibre using a fluidised bed and to investigate the most suitable operating conditions in order to obtain the highest quality of recycled fibre in term of fibre length. tensile properties and surface energy. All aerospace grade composite was recycled using a fluidised bed process operating between 525°C and 550°C with a fluidising velocity of 0.8 m/s and 1m/s and a bed depth of 5cm and Scm. As the recycling temperature can affect the residence time in the fluidised bed. there were two forms of recycled fibre resulted from this process: single fibre filaments elutriated from the bed and bundles of recycled fibre remained in the bed. The elutriated single filaments. recycled fibre possessed approximately 46% normalised tensile strength with 67% average normalised tensile modulus while the bundles offered higher tensile properties (the recycled fibre bundles had roughly 67% normalised tensile strength and 73% average normalised tensile modulus). Both recycled fibre type had a clean surface with no visible damage. The efforts to improve the tensile properties of recycled fibre were carried out by controlling the oxygen content. However. it was found that low oxygen content, between 6 and 18 per cent. does not improve tensile strength of a recycled carbon fibre. The main parameter associated with the single filament recycled fibre quality is temperature. An increasing temperature tends to decrease the fibre length degradation and tensile strength for recycled single filaments. both of which are due to faster char oxidation and hence. a lower residence Time before elutriation. For the recycled carbon fibre bundles. it was found that the recycled fibre quality is related to fluidising velocity and bed depth. Regarding surface energy. it has been observed that the surface energy of recycled carbon fibre depends on the quantity of acid based functional groups and these changes are slightly dependent on the recycling conditions. Finally. degradation modelling of the composite has been developed and Shown to be a useful tool in determining the behaviour of the composite in the fluidised bed. The outcomes of this research are not only useful for understanding and optimising the fluidised bed process for recycling carbon fibre. but they are also helpful in developing a better understanding of carbon fibre recycling operations based on thermal processing.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available