Recycle, remake and reuse

The concept of recycling is second nature for most of us, especially as we are faced with sorting our rubbish every week before it gets carted off in a refuse truck. However, in the world of composite fibre-reinforced plastic (CFRP) it is a relatively new phenomenon. Despite its many impressive weight and strength characteristics recyclability can prove difficult. ELG Carbon Fibre, however, has been developing processes and products from recycled material in recent years and now has the world’s largest carbon fibre recycling plant in Coseley, West Midlands. Last year it reclaimed more than 1,000 tonnes of carbon fibre from manufacturing waste and converted this into products that were returned to the market. The company, part of the global ELG Haniel Group, which also recycles high performance metals, places a strong emphasis on R&D and has worked with leading universities and research organisations to improve understanding of recycled carbon fibres and how they can be used. Reducing landfill So why is the need to find ways of recycling carbon fibre becoming increasingly important? Frazer Barnes, managing director of ELG Carbon Fibre, explains: “Waste is generated at every stage of the carbon composite supply chain starting with fibre manufacturing, conversion to intermediate products (weaving and prepregging) and the manufacture of finished parts. As a result, more than 20,000 tonnes of carbon fibre is sent to landfill each year. Manufacturers are realising this fibre can be reclaimed, reused and deliver significant cost advantages. “The use of recycled carbon fibre also offers supply chain security via use of waste products from ongoing production processes, mitigating the massive fluctuations in price and availability that have been seen in the carbon fibre industry in the past. “Reclaimed carbon fibres have similar mechanical properties to the original fibres provided that the reclaiming process is optimised for the type of feedstock being treated. Finally, there is of course significantly less environmental impact using recycled material.” The majority of ELG’s waste material comes from the aerospace and automotive sectors in Europe with additional contributions from the US and Asia. The company accepts dry, prepreg and laminate waste from these sources and ensures full traceability is maintained throughout the recycling process. The company’s longer term strategy is to build more recycling plants closer to the locations where waste is generated to additionally reduce its impact on the environment. For the most part, ELG’s raw materials come from waste carbon fibre left over from producing end user parts. However, the company is working on methods of recycling carbon fibre material that has come to the end of its product lifecycle. “The carbon fibre industry is still comparatively young,” Barnes continues. “Fifteen years ago, global use of the material was only 15,000 tonnes per annum. With the main uses of carbon fibre historically being aerospace structures, with long service lives, or sporting goods, with the challenges presented by post-consumer recycling. This means the quantities of end-of-life carbon fibre available to recycle today are limited. However, this situation is changing, and we are working on a number of projects in which we are developing end-of-life recycling solutions.” Shredding and heat ELG uses a patented furnace process called ‘continuous pyrolysis’ to convert the reclaimed fibres. Before this however extensive sorting and shredding stages are required. “Incoming feedstock comes in various forms,” Barnes notes. “These materials are sorted into approximately 40 classifications depending on fibre mechanical properties as well as the form of the waste. We also carry out tests to ensure the correct classification. Each batch of material is then allocated unique code which provides traceability through the subsequent processes. “Depending on the nature of the feedstock, material may be processed directly in the pyrolysis process or go through one or two stages of size reduction in a shredder. A significant amount of effort was used to develop a shredder that resulted in a consistent output, in terms of the size and thickness (in the case of laminates) of the particles. Very large parts or assembled structures are first cut into pieces and any metal components are removed before shredding. “Shredded feedstock may be segregated at this stage where traceability from a particular feedstock to an end product is desired, or may be stored as one of three general purpose feedstock grades in a storage bunker.” Continuous pyrolysis involves the thermal removal of resins in a controlled environment at temperatures in the range of 400-650°C. During this process the pure reclaimed fibre has all residues removed ready for the next stage of processing. The reclaimed fibre is then converted into products that can be used in the compounding and composites industries including: milled, chopped and pelletized fibres for compounding; nonwoven carbon fibre mats for composites manufacturing and nonwoven carbon fibre/thermoplastic hybrid mats for composites manufacturing. ELG has focused on finding new markets in which its recycled materials can be used. The company says that for most applications the material can provide the same strength and stiffness characteristics as ‘virgin’ carbon fibre. “The main applications of these materials are in the electronics and automotive industry. For the composite products, recycled carbon fibre materials are effective whenever the design is based on quasi-isotropic laminates, and particularly where flexural stiffness is an important requirement. For these materials, our focus is developing solutions for all sectors in the transportation industry—road, rail and aerospace.” The recycled material can also be combined with virgin carbon fibre to create materials to create added strength for particular uses. “Currently, all recycled carbon fibre materials on the market are made from short (80µm to 150mm) discontinuous fibres with only limited alignment. This places limitations on the strength and stiffness that can be achieved. These limitations can be overcome with selective use of virgin carbon fibre products, particularly applied as unidirectional tapes or fibres, to provide additional stiffness where required.” Another big advantage of using recycled carbon fibre is in terms of environmental impact. Based on ELG’s 2014 operating performance, the global warming potential of its recycled carbon fibres was around 10% that of industrial grade carbon fibres. In 2015, ELG further reduced the energy consumption (MJ/kg) of the process by 35%. ELG believes more manufacturers will see recycled carbon fibre’s potential, especially if demand increases in high volume sectors such as automotive. Barnes says: “With any new material, end users want to understand the properties of the material—not just simple static testing, but fatigue performance, environmental effects and the effects of impact, etc. With many recycled carbon fibre products being relatively new, this data is not yet available and this is a major focus of current ELG development programmes.” So what further developments are needed if recycled carbon fibre is going to be used more widely? “We mentioned the limitations of fibre orientation and the effect this has on fibre volume fractions that can be achieved and the mechanical properties of the laminates. We are addressing this with two projects underway looking at highly aligned materials based on short carbon fibres. The other area is optimising the performance of the existing products, either in mechanical performance, or to suit particular manufacturing processes. Over the last two years, we have built a strong technical team to support these developments.” www.elgcf.com Caption/images: From the shredder: ELG Carbiso CT Carbon fibre Making mats: ELG nonwoven products On a roll Pellet production Frazer Barnes, managing director of ELG Carbon Fibre