Composite materials look set to be a major contributor to the current drive towards net zero. The ability to produce materials that are stronger, lighter and more efficient will likely result in transformative performance and sustainability improvements across industries such as hydrogen, wind energy and transport.
Scott Bader
However, question marks remain regarding their end-of-life, as the durability of composites, the complex mixture of materials used in their construction and the lack of recycling supply chains make them inherently difficult to recycle.
In the last ten years, B&M Longworth, specialists in the removal of polymeric contaminants from components across a range of industries, have sought to address the ever-growing composites waste problem. Their proprietary DEECOM process, which utilises a mixture of steam and rapid pressure cycles to physically remove polymer contaminants via pressolysis, proved suitable to recycle composite materials.
In 2022, together with the National Composites Centre and Cygnet Texkimp, they fully reclaimed continuous carbon fibres from a hydrogen pressure tank, using the rewound fibres to manufacture a new vessel More recently, they have shown as part of the EMPHASIZING consortium that glass fibre from an end-of-life wind turbine blade could be reclaimed using DEECOM, resized and moulded into structural parts for the automotive industry.
While recovery of the fibre reinforcement is a major achievement in the move towards circular composites, little attention has been paid to the resin to date. This accounts for as much as 50% of the total composite weight, making the full recovery of the resin and fibre the goal to achieve sustainable composites.
B&M Longworth and Scott Bader have been exploring how a pressolysis feedstock can be reutilised into composite materials.
The use of terephthalic acid isolated from the DEECOM of contaminated polyethylene terephthalate filters enabled the production of an unsaturated polyester resin containing as much as 22% pressolysis feedstock. The resulting variant of Scott Bader’s high-performance Crystic 272 resin was found to have comparable physical properties and equivalent thermomechanical performance as both a cured plastic and a glass-fibre reinforced composite.
They also proved that it was possible to use bio-based glycols to drive the renewable content to as high as 34% with no loss of performance. Despite mild discolouration of the final sample arising from feedstock contamination, the resulting materials can be utilised as structural parts with no performance loss compared to their petrochemically-derived equivalent. Furthermore, the discolouration was overcome by applying a standard gel coat.
This work demonstrates the utilisation of a chemical feedstock isolated from a pressolysis for the first time, representing a rare attempt to improve the circularity of composite resins. Hopefully, this is a step towards sustainable composites, as continued work tries to develop DEECOM into a process that can fully close the loop on composites recycling.