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Making recycled carbon fibres viable : enhancement of thermoplastic composite quality & manufacturing procedures
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Froemder, Christina (2019) Making recycled carbon fibres viable : enhancement of thermoplastic composite quality & manufacturing procedures. EngD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3520305~S15
Abstract
Carbon fibre reinforced polymers are widely applied as a lightweight material with high specific strength in, e.g. wind, automotive and aerospace industry. Production exceeded 150 000 tonnes in 2019 and is expected to grow by 10 % annually. As these materials are used in greater volume, waste increases. Up to 40 % of the waste arises in manufacturing alone. The production and use of recycled carbon fibres (rCF) saves the material from going to landfill and provides a new feedstock source with the same weight reduction and similar fibre qualities, providing further advantages to virgin carbon fibres, such as a lower carbon footprint and significant cost savings. However, the remanufacturing of rCF and closing the loop of carbon composite production faces substantial obstacles: unknown effects of recyclate quality, a lack of interfacial properties and excessive processing time for long rCF applications.
This thesis focuses on commercial composite manufacturing processes and investigates how rCF-reinforced thermoplastics, in the form of commingled nonwoven textiles, can deliver optimised properties. A systematic experimental approach was applied to process the material, which included an extensive number of analytical methods that focused on optical, physical and chemical material characteristics, utilising rCF arising from manufacturing and End-of-life waste in a range of thermoforming processes. The starting point was an isothermal static process with a 110 minute cycle time. Numerous experiments using rapid-isothermal and stamping processes were used to optimise the cycle time and composite properties, targeting industrial applications. The initial focus was on a polypropylene (PP) matrix and this evolved to an investigation of maleic anhydride-grafted PP (MAPP) and modified rCF to enhance interfacial properties.
The results demonstrated that the isothermal process could be improved and produced an optimum process time of 27 minutes. The comprehensive process study enabled cycle times as low as 13 minutes with the rapid isothermal process and down to 1 minute with non-isothermal stamping. Both processes achieved excellent composite properties (maximum tensile strength 225 MPa, tensile modulus 21.3 GPa, 40 wt% rCF in PP), which can outperform glass fibre applications and aluminium. MAPP demonstrated enhanced interfacial characteristics and subsequent mechanical properties (+ 44% in strength) with only a minor increase in production cost (+ 9 %). The results of the rCF treatment highlighted the need for future research into water-based functionalisation.
The research established a comprehensive data set, revealed viable processing methods and proved suitability for mid-volume production, identified significant processing factors, and moved the processing scale of MAPP based nonwovens from lab to pilot scale. This work has improved the understanding of commingled nonwoven material at the industrial sponsor, ELG Carbon Fibre Ltd, in terms of handling and processing. It has also given manufacturers and designers new insight into the material characteristics and demonstrated how it can be used in an economically competitive manner. By making rCF viable, the work contributed to a more sustainable composite industry.
Item Type: | Thesis (EngD) | ||||
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Subjects: | T Technology > TA Engineering (General). Civil engineering (General) | ||||
Library of Congress Subject Headings (LCSH): | Carbon fibers -- Recycling, Carbon fiber-reinforced plastics -- Recycling, Carbon fibers -- Industrial applications | ||||
Official Date: | October 2019 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Warwick Manufacturing Group | ||||
Thesis Type: | EngD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Kirwan, Kerry ; Coles, Stuart R. | ||||
Sponsors: | Engineering and Physical Sciences Research Council ; ELG Carbon Fibre Ltd | ||||
Format of File: | |||||
Extent: | xiii, 171 leaves : illustrations (some colour) | ||||
Language: | eng |
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