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A Closed-Loop Recycling Process for Discontinuous Carbon Fibre Composites

Bristol student theses: Doctoral ThesisDoctor of Philosophy (PhD)

Authors

  • Rhys Tapper

Research units

Abstract

The carbon fibre reinforced polymer industry is growing rapidly and is becoming a realistic consideration for mass-manufacturing markets. The superior specific properties of composites make them ideal lightweighting materials, but their high cost, high environmental impact and limited recyclability are substantial deterrents. The aim of this work was to develop a closed-loop recyclable material and an associated closed-loop recycling process for carbon fibre reinforced composites that could present solutions to these obstacles.

The current technological outlook was evaluated to determine the progress made in composites recycling and, more importantly, the areas of development required to meet industrial demands. It was discovered that the industry requires high-value, recyclable, carbon fibre reinforced composites in order to produce an economically sustainable production cycle. The only way to provide this was to develop a closed-loop recycling process, that can reclaim fibres and matrix without mechanical property reductions. To achieve this, it was clear that a shift from thermosetting to thermoplastic matrices was required.

A closed-loop recycling methodology was produced, which enabled the closed-loop recycling of discontinuous carbon fibre thermoplastic composites. Proof-of-concept evaluation showed that it was possible to maintain mechanical properties over two recycling loops. The closed-loop material produced was improved by including a higher-performance thermoplastic matrix. Experimental analysis showed that the mechanical performance was predominantly affected by the fibre quality and not by degradation of intrinsic constituent properties. Closed-loop recycled materials exhibited a 20 % and 39 % decrease in tensile stiffness and strength after the first loop and did not substantially degrade after the second loop. However, the final mechanical properties were suitable for use in semi-structural automotive applications and were therefore of a high-value.

The closed-loop recycling process was evaluated by a life cycle assessment and resulted in the lowest environmental impact out of a range of contemporary lightweighting alternatives and conventional materials.

This body of work proves that it is possible to produce a high-performance, high-value, recyclable composite material with a low environmental impact at a potentially low cost.

Details

Original languageEnglish
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Supervisors/Advisors
Award date7 May 2019

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