Led by Jinwen Zhang, a professor in the School of Mechanical and Materials Engineering, researchers developed a recyclable material that is 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, report on their work in the journal, Macromolecular Rapid Communications.

Carbon fibre 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 fibre 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 pressurised, distilled water beginning at 160 degrees Celsius, dissolving it into valuable carbon fibre and other compounds, which can then be re-used. The recycled carbon fibre was comparable in strength to brand new carbon fibre. 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. 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 the recycling of 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 up-cycling 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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Researchers from Washington State University have come up with a way of using these materials by creating a new plastic composite material made partly from waste coffee grounds.

It’s hoped that the work could lead to new applications for 3D printing as well as make better use of waste materials. Reporting in the journal, ACS Sustainable Chemistry and Engineering, the researchers found that their material, made from up to 20% coffee waste, had a more than 400% increase in toughness over pure poly‑lactic acid (PLA), the type of plastic that is most commonly used in 3D printing.

PLA is a plastic material used for many medical and consumer products, such as in drug delivery, tissue engineering, food packaging, as well as for 3D printing. Made from corn starch, it is biodegradable. But, when used for 3D printing applications, products made from PLA lack strength and break easily. Products that are 3D printed, in fact, are almost entirely limited to being toys, trinkets, or display models.

Researchers have been looking to add low‑cost additives, such as wood fibre, silica, or clay, to enhance the material’s performance as well as to reduce manufacturing costs. Such additives from renewable sources could also keep waste materials from ending up in a landfill and creating additional pollution.

For their study, the WSU researchers decided to add coffee ground waste to the PLA. People around the world drink more than two billion cups of coffee every day, so waste coffee grounds are abundantly available.

We have a virtually limitless supply of coffee grounds. Our goal is to extend the life cycle for these waste products. We looked at what is overproduced and tried to make something useful out of it. Yu‑Chung Chang – Washington State University Graduate Student

The researchers didn’t use actual coffee grounds. Rather, they used a dry and odourless material that is left over after the coffee oil had been removed and used for biodiesel production. After mixing their coffee material with the PLA, they printed out and tested their specimens.

The research showed that the oil‑extracted spent coffee grounds can not only increase the impact toughness, but they also reduce the cost of overall 3D printing materials. They are hoping to continue the work and conduct further study on how the material will degrade in the environment.

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