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Researchers develop recyclable composites

Closeup of Jinwen Zhang in laboratory.
Led by Jinwen Zhang, professor in the School of Mechanical and Materials Engineering, researchers developed a recyclable material that is as strong as commonly used carbon-fiber composites and can also be broken down in very hot water within a pressure vessel.

A WSU research team has created a recyclable carbon-fiber 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, researchers developed a recyclable material that is as strong as commonly used carbon-fiber 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, report on their work in the journal, Macromolecular Rapid Communications.

Carbon fiber reinforced composites are increasingly popular in many industries because they are light and strong. They serve as an energy-saving, lighter alternative to metals, especially in the aviation and automotive industries. They are, however, 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 instance, are now reaching the end of their lifetimes, creating a significant challenge for disposal.

While thermoplastics, the type of plastic used in milk bottles, can be melted and easily re-used, the carbon-fiber composites are made from thermosets. These types of plastics are cured and can’t easily be undone and returned to their original materials.

Zhang’s team developed a composite material that uses an epoxy vitrimer 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 degrees Celsius, dissolving it into valuable carbon fiber and other compounds, which can then be re-used. The recycled carbon fiber was comparable in strength to brand new carbon fiber. When they raised the temperature to 180 degrees, the material completely dissolved. The epoxy vitrimer that they developed could easily be substituted into the manufacturing process.

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

While the new recyclable material could be easily adopted by manufacturers, Zhang is also continuing work to improve recycling of the composites that are currently in the market. In recent years, he developed an environmentally friendly method to break down the material in a liquid or ethanol medium. Earlier this year, he received a $1.2 million Department of Energy grant for the upcycling of the composites waste.

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.

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