Researchers develop recyclable composites

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A research team at Washington State University (WSU) in Pullman, Wash., has created a recyclable carbon fibre-reinforced composite that could eventually replace the non-recyclable version used in everything from modern airplane wings and wind turbines to sporting goods.

Led by Jinwen Zhang, professor in the School of Mechanical and Materials Engineering, the team developed a recyclable material that’s as strong as commonly used carbon fibre composites and can also be broken down in very hot water within a pressure vessel. The new material could be easily substituted into current manufacturing processes. The research team, including scientists from the Department of Energy’s Pacific Northwest National Laboratory, reported on their work in a recent edition of the journal Macromolecular Rapid Communications.

Carbon fibre-reinforced composites are increasingly popular in many industries, as they’re both light and strong, and serve as an energy-saving, lighter alternative to metals, especially in the aviation and automotive industries. The problem, however, is that they’re difficult to break down or recycle, and disposing of them has become of increasing concern. Early versions of modern wind turbines made of composites from the 1990s, for example, are now reaching the end of their lifetimes and are creating a significant challenge for disposal.

Zhang’s team developed a composite material that uses an epoxy vitrimer – a class of plastics which are derived from, and similar to, thermosets – as an alternative to the traditional epoxy resin. The material is hard and durable like an epoxy thermoset, but can also show self-healing and malleable properties at high temperatures like a thermoplastic.

When they used their epoxy vitrimer in the composite material, they were able to degrade their material in pressurized, distilled water beginning at 160°C, dissolving it into valuable carbon fibre and other compounds, which can then be reused. The recycled carbon fibre was comparable in strength to new carbon fibre. When they raised the temperature to 180°C, the material completely dissolved. The end goal is to substitute the epoxy vitrimer they’ve developed into the manufacturing process.

“There is no need to change the chemistry of the process – it’s just a slight modification of using the epoxy vitrimer instead of traditional epoxy,” Zhang said. “The technology is simply and readily applicable.”

The research was supported through grants from the Department of Energy’s Office of Energy Efficiency & Renewable Energy and the Joint Center for Aerospace Technology Innovation.