Composites Today

Magazine For Composites Professionals

Reclaiming continuous carbon fibers from composite pressure tanks.

The successful trial marks the significant first step in an ambitious hydrogen innovation programme to deliver sustainable composite pressure vessels.

Engineers at the National Composites Centre, the UK’s centre of excellence for advanced composite applications, along with British SME partners B&M Longworth Ltd and Cygnet Texkimp, have successfully reclaimed continuous carbon fibres from a whole pressure vessel and re-used them to manufacture a new pressure vessel.  This is the first time this process has been achieved in the UK and represents a significant milestone in the development of Britain’s hydrogen capability.

As the gas has low energy density it needs to be compressed and stored at very high pressures, between 350 to 700 bar (5,076 – 10,152 psi).  This makes high-strength, lower-weight carbon fibre the material of choice, especially for hydrogen pressure vessels in vehicles such as cars or aircraft, where power-to-weight is critical. Demand for carbon fibre is expected to grow five-fold between 2025 and 2030, exceeding global manufacturing capacity.  Creating viable, low-cost recovery processes, that retain the inherent strength of continuous carbon fibres for recycling, is therefore key to the development of the hydrogen economy.

Until recently, recycling processes for composite components such as aircraft wings and wind turbine blades have resulted in short fibres with lower mechanical properties than virgin fibre. Whilst there are applications for this material, it is not suitable for re-use in high-performing products.

The Longworth team successfully reclaimed continuous carbon fibre, from end-of-life composite pressure tanks, using the company’s revolutionary DEECOM® process. Originally designed to remove waste polymers from filters and production equipment, the process uses superheated steam, under compression, to penetrate microscopic fissures in the composite’s polymer, where it then condenses. On decompression, it boils and expands, cracking the polymer and carrying away broken particles. This pressure swing cycle is then repeated until all the matrix (the material suspended in the polymer) has been separated from the fibre, allowing the monomers to also be reclaimed for possible reprocessing.

Crucially, the DEECOM® process leaves the primary component material intact and undamaged, allowing for any length to be retained. As a result, Cygnet Texkimp Ltd, a Cheshire-based, global leader in fibre handling and conversion technology, could use the reclaimed continuous carbon fibre to make a new pressure vessel using filament winding.

The partnership is now looking to work with manufacturers to scale and industrialise this process, sharing the knowledge of recent recycling trials. The next step is to undertake a fibre characterisation analysis of the reclaimed material and recycled vessel, as the team works towards their ultimate goal: developing disruptive technologies that enable sustainable hydrogen storage solutions.

This initial fibre recovery and recycling project, forms part of the National Composites Centre’s Hydrogen programme, developing and sharing the technical knowledge, cross-sector composite expertise and state-of-the-art technology that businesses need to achieve their hydrogen ambitions. As part of this programme, National Composite Centre engineers have worked to refine composite pressure vessel designs, producing detailed designs and analyses to minimise waste and trial the tools and manufacturing processes the industry will use to reclaim and recycle continuous carbon fibres. They have also delivered composite design specifications for cryogenic pressure vessels and are working on a certification pathway for composite pressure pipes, including those to be used offshore.

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