Abstract
The world’s largest sail manufacturer, North Sails, makes around 10,000 individual high- performance carbon fibre reinforced polymer (CFRP) sails every year. However, there is currently no waste-management plan in place for when these sails reach the end of their life (EOL). To aid the sailing industry in managing this waste in future, and thereby prevent the loss of valuable materials and the build-up of CFRP waste in our environment, this work aimed to develop a recycling methodology whereby EOL 3Di sails could be used as a feedstock for circular manufacturing.The first step in the recycling process was the reclamation of the carbon fibres (CFs) from an EOL 3Di sail via two pre-existing thermo-oxidative processes, namely the ELG (legacy) process, conducted in a controlled air atmosphere, and the DEECOM® process, conducted in a controlled super-heated (SH) steam atmosphere. At 450°C, clean CFs could be recovered using either process with no visible fibre degradation and over 95% retained stiffness compared to virgin CFs (vCFs). While high retained tensile strengths of over 90% were only achieved using the DEECOM® process, as the milder oxidising atmosphere of SH steam could be safely used for long, un-optimised processing times without degrading the CFs.
The second step involved realigning the short rCFs into aligned discontinuous fibre reinforced (ADFR) prepreg-type tape, using the University of Bristol’s hydrodynamic High- Performance Discontinuous Fibre (HiPerDiF) technology. The tensile and flexural properties of the ADFR composite (ADFRC3G) coupons manufactured using the rCFs recovered with the DEECOM® process were promising despite the low fibre volume fraction (Vf) of ~20%. The tensile modulus of these coupons was only ~8% lower than similar commercially available UD continuous CFRPs (normalised to a Vf of 20%), however, the tensile strength was ~48% lower, due to a combination of the reduced fibre strength and fibre length, the degree of fibre misalignment, and possibly poor interfacial adhesion between rCFs and the matrix.
The feasibility of recycling an EOL sail into a semi-structural component for a sailing yacht was finally demonstrated by successfully designing and manufacturing a downscaled ADFRC3G – rCF batten (a stiffener in a sail). The ADFR3G – rCF batten behaved similarly in flexure to a continuous CFRP batten, although the low Vf of the ADFR3G – rCF tape meant that two plies were required for every single thin CFRP ply used in the control CFRP batten.
A life cycle assessment showed that the environmental impact of manufacturing an ADFRC – rCF batten via the recycling scenarios laid out in this work is currently greater than landfilling the 3Di sail and manufacturing a virgin continuous CFRP batten, largely due to the inefficient operation of the recycling processes and the lower technology readiness level compared to industrial-scale landfilling and CFRP manufacturing methods.
Thus, while it became clear that the Vf and the efficiency of the recycling processes must still be increased, this work established - for the first time - a complete recycling loop for EOL 3Di sails - from sail to structure.
| Date of Award | 23 Jan 2024 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Ocean Family Foundation |
| Supervisor | Ian Hamerton (Supervisor), Marco L Longana (Supervisor) & Ole Thomsen (Supervisor) |