More than 30% of the carbon fiber produced eventually ends up as waste, including 22% in the form of manufacturing waste from processing of thermoset carbon fiber-reinforced composites. Carbon fiber demand forecast to grow to at least 117,000 tonnes by 2022 according to AVK, and at least 26,000 tonnes of this carbon fiber would be expected to end up as manufacturing waste according to carbon fiber recycler ELG Carbon Fibre Ltd.
|An oil pan made using recycled carbon fiber-reinforced polyamide (PA) 6 with PA 66 overmolding.|
|An automotive component made using resin infusion. (Photo courtesy of Prodrive)|
“Reusing these fibers reduces the cost and environmental impact of carbon fiber structures without compromising the technical benefits of these materials and provides additional capacity that could alleviate supply shortages,” says ELG Managing Director Frazer Barnes. While recycled carbon fiber’s modulus is essentially the same as that of virgin carbon fiber, it offers 20–30% cost savings and even with its 10–20% reduction in tensile strength, it remains one of the strongest of all commercially-available reinforcing fibers available today.
The latest cost analysis at ELG indicates a material cost 49% higher than steel for a recycled 34% carbon fiber epoxy composite that is 3.5 times lighter than steel. However Barnes notes that composite processing costs drive the finished part cost; selection of the most appropriate technology relative to part size, complexity and production rate is critical for cost effectiveness. Processing options include resin infusion, prepreg compression molding, and liquid compression molding for thermosets, and compression molding, sandwich panel press molding, and overmolding for thermoplastics.
When it comes to thermoplastics, polypropylene (PP) and carbon fiber do not make a good match according to Marco Gehr, Chief Operating Officer of ELG, even with recycled carbon fiber. “Carbon fiber is a niche product for niche, high-end application so makes more sense to use polyamide or polycarbonate,” he notes. “We do offer a MAH-grafted carbon fiber PP mat but we feel polyamide and polycarbonate are better options even for recycled carbon fiber, which itself is 30–40% cheaper than virgin carbon fiber.”
Hybrid solutions may make more sense according to Gehr. “A mix of glass fiber and carbon fiber would result in a product with better impact strength, which is normally a shortcoming of carbon fiber compounds alone.” Replacing 30% glass fiber reinforcement with a 10% carbon fiber reinforcement delivers a superior lightweight product but at a cost.
Catackh is a one-year-old Korean startup that is employing technology developed by KIST (Korea Institute of Science and Technology) to recycle this waste carbon fiber into reusable chopped, milled and stable fiber forms. The company also supplies various compounds based on polyolefin, polystyrene and engineering plastic resins that are 30–40% lower cost than virgin compounds according to Catackh researcher Sanghyun Lee, but still retaining 90% of the mechanical attributes. The company plans to commence shipping recycled carbon fiber and compounds in May 2019. It has capacity to recycle 300 tonnes/year of carbon fiber.