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The recycling options
Another growth area in the drive for lower cost carbon fiber is the recycling option and one company pushing developments in the greater use of recycled material is UK-based ELG Carbon Fiber. ‘‘All of the recent market forecasts point to continued medium to high level growth in the carbon fiber market,’’ says managing director Frazer Barnes. ‘‘One of the main drivers for this growth is new applications in the automotive industry. This is a very cost sensitive market and we expect that the lower cost of recycled carbon fiber, combined with the supply chain security and environmental benefits, will make this an attractive option for some of these applications.
‘‘We generally see that using recycled carbon fiber has the potential to reduce the cost of the fiber by around 40 percent. In industries that use primarily carbon fiber tow, such as the compounding industry, this cost reduction is realized directly. Where there are further conversion steps required, such as producing a nonwoven fabric, the actual cost reduction can range from 20–40 percent. What we hear from the market is that these cost reductions, coupled with security of supply for high volumes of material with stable pricing, significantly increases the attractiveness of carbon fiber for the automotive and other transportation markets.’’
Regarding the main trends and influences driving further development of recycled carbon fiber, Frazer Barnes believes that continued product testing is key to demonstrate performance and the development of design and manufacturing guidelines, particularly for the composites industry. ‘‘In general, the composites industry is not yet aware enough of the potential for the use of recycled carbon fiber,’’ he says. ‘‘However, this is mainly because it is still a young part of the composites industry, and until recently there were not suitable product forms or design and manufacturing data available for the industry to be able to make good use of these materials.
‘‘There are significant challenges in handling recycled carbon fiber materials in downstream conversion processes, and this has been one of the main barriers to the development of suitable product forms. We have actually had a very robust process for recovering high quality fiber, with little degradation compared to virgin carbon fiber, for many years, but the challenge has been developing ways of getting this back to the market.’’
Carbon fiber reclamation firstly requires metal removal and the cutting of large composite structures to sizes suitable for downstream processing. In addition, shredding of laminates and prepreg enables efficient and consistent processing. Fiber recovery is via a modified pyrolysis process. Carbon fiber conversion is then through milling, nonwoven mat production and production of pellets.
Successful recycling of carbon fiber requires a number of hurdles to be overcome. ‘‘The major challenge is dealing with the complex nature of the waste streams,’’ Barnes explains. ‘‘Even relatively clean waste streams from composites manufacturing still contain resins of varying chemical composition and unwanted materials such as paper or plastic backing films, and the recycling process has to be optimized to ensure the complete removal of these unwanted materials without damaging the fibers. The second challenge is classification of the fibers. The composites industry has grown up with a wide variety of carbon fiber grades available from different manufacturers. Although the recycling process has only a small effect on the properties of the fiber, it is not desirable to retain the original fiber designation after fiber recovery. ELG has addressed this by introducing a generic classification system based on the Young’s modulus and tensile strength range of the recovered fibers.
‘‘The final challenge regarding carbon fiber recycling is to do with the development of the business. The major barrier that must be overcome is one faced by all new materials – lack of knowledge about mechanical properties and processing characteristics, and lack of large-scale demonstrators that prove the economic, technical and environmental justification for using these materials. Whilst there are a number of projects that are addressing these issues, the push from the manufacturing side of the supply chain to find a solution to its carbon fiber waste problem generally is not matched by a pull from the design side of the supply chain to find ways of using recycled carbon fiber products.’’
Frazer Barnes adds that the company now has a good under- standing of the performance of recycled carbon fiber materials in compounds and composites. He says that the next steps are to enhance performance further through product optimization, and to get an understanding of the long-term performance of recycled carbon fiber materials. ELG is undertaking this through internal R&D programmers, as well as working with UK universities including Warwick, Nottingham, Bristol and Oxford Brookes.
ELG Carbon Fiber has currently developed five products from reclaimed fibers. Carbiso TM MF is a milled random short length carbon fiber used to make thermoplastic and thermoset com- pounds and for additive manufacturing processes. The main benefits conferred by milled fibers are increased stiffness, higher electrical and thermal conductivity and reduced coefficient of thermal expansion. CarbisoTM CT chopped tow is a precision chopped virgin carbon fiber product with 6 mm and 12 mm fiber lengths that are claimed to be a good reinforcement for thermo- plastic injection molding compounds, cements, elastomers and coatings. Chopped tow offers higher structural and electrically
conductive properties than ELG’s milled fibers. The lightly sized fibers are compatible with most thermoset and thermoplastic matrices.
In 2017, the company is launching CT+. In comparison to the standard chopped tow CT product, this new plus version is characterized by improved flowability for ‘easy dosing’ in gravimetric feeding systems for plastic compounding. CarbisoTM MB carbon fiber masterbatch products will be fully commercialized in 2017. These pelletized products are made from chopped fibers that ELG Carbon Fiber converts for use in the compounding industry. These smaller sized pellets make them easy to dose, contain less dust when handled and are more consistent to work with.
CarbisoTM M nonwoven mats are produced from 100% recycled carbon fiber and can be processed by conventional composite techniques to manufacture structural and semi-structural parts. CarbisoTM TM hybrid nonwoven mats combine carbon fibers with thermoplastic fibers such as PP and PA. The company says that CarbisoTM M and CarbisoTM TM isotropic mats are easy to handle, drape able and compatible with most thermoset and thermoplastic polymers and deliver good mechanical properties. They are avail- able in standard 100–600 gsm weights and widths up to 2.7 m. To offer customers total flexibility and an entirely tailored solution, the mats can also be manufactured to bespoke pecifications.
‘‘ELG Carbon Fiber views high volume transportation applications as the key emerging market that could best benefit from the company’s products and services,’’ concludes Frazer Barnes. ‘‘If the vehicles of the future are manufactured from increased quantities of recycled carbon fibers, these lightweight structures will be more cost effective and in turn reduce CO2 emissions, increase compliance with fuel economy regulations and also support the European Union (EU) end-of-life-vehicle (ELV) directive.’’