Plant-based epoxy allows carbon fiber recycling

Biobased

United States – Carbon fiber is ten times stronger than steel, weighs nearly half as much as aluminum, and is far stiffer than fiberglass. According to Nicholas Rorrer of the National Renewable Energy Laboratory (NREL), it still needs to be perfected before it can be used in mass-market vehicles.

Carbon fiber recycling on a large scale may already be possible, thanks to recent advances in bio-based material design. Rorrer and other NREL researchers have demonstrated that using bio-based epoxies and an anhydride hardener to make carbon fiber composites makes the material fully recyclable by introducing more easily degraded linkages, as part of a project funded by the US Department of Energy’s Vehicle Technologies Office’s Composites Core Program. In fact, the recycling process, known as methanolysis, can be triggered selectively at room temperature without affecting the fibers’ quality or orientation. That could be a big step toward creating a circular material, which could make carbon fiber cheaper and greener over time.

Carbon fiber’s advantages

Carbon fiber’s advantages come from its layered design, which makes it both strong and light. It’s a composite material made up of long carbon filaments and a glue-like epoxy coating called “thermoset.” When the liquid resin cures, the molecules bind together and around the woven carbon filaments, forming a strong and rigid lattice. The material can be molded into a variety of shapes for a variety of applications, including car bumpers, wind turbine blades, and more.

The superior products, however, are difficult to break apart due to the thermoset nature of the cured epoxy, especially without severely damaging the carbon filaments. Despite their high cost, carbon fiber products frequently end up in landfills, along with any efficiency benefits they may have accrued.

Although carbon fiber could reduce the weight of a typical passenger car by half, increasing its fuel efficiency by up to 35%, any efficiency gains are effectively offset by the GHG-intensive energy used to manufacture it. The production of carbon fiber necessitates temperatures of over 1,000°C.

Recyclable epoxy

Rorrer and his colleagues began experimenting with biomass chemistry to see if it could be used to create a new recyclable epoxy. Biomass contains higher levels of oxygen and nitrogen than petroleum hydrocarbons, providing a different set of chemical possibilities. The NREL team was able to break down the bio-based resin at room temperature using a special catalyst, a process known as “depolymerization.” They were able to recover the carbon filaments while preserving their quality and alignment as a result of this.

The breakthrough in epoxy, when combined with NREL’s research into low-cost, bio-based acrylonitrile as a carbon fiber precurso, could help make carbon fiber composites more cost-effective and environmentally friendly. Carbon fiber could become more cost-effective for mass-market electric vehicles if it can be extracted and recycled, freeing up weight and space for batteries. It would also reduce the material’s greenhouse gas (GHG) footprint by 20%–40%. Even better, it could do so without raising manufacturing costs, according to Rorrer, who estimates that NREL’s epoxy would cost about the same as today’s petroleum-based epoxy-amine resins.

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