Composite materials such as Carbon Fiber Reinforced Plastic (CFRP) offer significant advantages where high strength and low weight are required. These materials are, unfortunately, also very difficult to recycle. Composites consist of fiber reinforcement embedded within a polymer matrix. The polymer may be a thermoset, such as epoxy, or a thermoplastic, such as polyester. Separating the fibers from the matrix is a huge challenge for recycling, especially where thermoset materials are used. Production costs for composite components are also very high. Now ProDrive, a UK motorsport specialist, has developed a process that looks set to reduce production costs while enabling low-cost recycling, therefore also reducing material costs. This may open up new applications for composites in mass-market products such as cars.
Current recycling falls into one of two methods. One approach is to chip components and reusethem in low-strength applications, known as ‘downcycling.’ Applications for chips include construction aggregate while chopped fibers may be used in laptop cases and car dashboards. The matrix can be removed from the fibers using high temperature ‘cracking’ (hydrous pyrolysis). This also allows carbon to be captured and monomers to be recycled into new polymer materials.
The choice has, until recently, been between downcycling the material,and highly expensive re-processing. Typically there has actually been some combination of expensive pyrolysis and chopping of the fibers. Companies that offer composite recycling services include ELG Carbon Fibre(UK), CFK Valley Stade Recycling(Germany) and Carbon Conversions(South Carolina USA). They all use some form of pyrolysis to remove the resin so that the carbon fibers can be extracted. These methods are improving—Carbon Conversions will accept scrap material free of charge and claims that its recycled materials are of a lower cost than virgin materials. However, they do not appear to offer high-strength materials; the result is either a chopped fiber or a non-woven mat.
There is a lot of interest in bringing CRFP to mass-market automotive manufacturing. Achieving this will depend on lowering the cost of the materials, but it can only happen if the materials are also easy to recycle. Automobiles are the most recycled consumer product in the world, accounting for over 25 million tons of recycled material each year. Improving energy efficiency through lighter materials will not be beneficial if it also produces huge volumes of unrecyclable waste. Composites have already been widely adopted in the aerospace industry, but an aircraft typically remains in service for decades. Mass-market automobiles require a much lower cost route to recycling.
“End-of-life recycling is one of the biggest debates in the composites world today. The issue affects automotive manufacturers and wider industries too, such as marine, where old fibreglass boats are often broken up and sent to landfill.”- John McQuilliam, Chief Engineer at Prodrive Composites.
Best known for their involvement in motorsport, Prodrive also designs and manufactures advanced lightweight composites for many other applications. The company has now developed a process, Primary to Tertiary (P2T), which is claimed to dramatically reduce the cost of using composites while also increasing recyclability. The key to this process is a new resin which can be readily separated from the fiber reinforcement. A thermoplastic resin is used which can be cured in situ, much as a thermoset would normally be. When newly-manufactured fibers are used, this is said to result in performance on par with the best thermoset resins currently available.
Prodrive is not the first to develop resins designed for recycling. Arkema produces Elium resin which they claim is the first liquid thermoplastic resin designed for manufacturing composite parts with mechanical properties similar to thermosetting. Elium can be thermoformed, recycled and welded, just like a normal thermoplastic, providing major advantages for manufacturers. Another approach, currently still in the research phase, is to use bio-based polymers for composites. Taking things even further, BAMCO (Bamboo long fiber reinforced bio-based matrix composite) aims to use bio-based materials for both the fibers and the matrix. Such materials may be biodegradable rather than recyclable, but for now at least, they can’t match the performance of CFRP.
The resin used in the P2T process does not require curing in an autoclave. Eliminating this significant source of cost and capital investment is one of the ways that process has been made affordable. Components are, instead, vacuum-bagged. This approach can actually result in reduced tooling costs and lead time compared to traditional presses and steel body panels.
“We have been working with the AMRC and a series of large trial panels have been produced using an innovative process which can readily be automated. These trials have demonstrated that recyclable composite panels can be produced at a rate and cost to suit many industries.” - John McQuilliam, Chief Engineer at Prodrive Composites
When P2T composites are recycled, the fibers are not chopped. This means that, although there is still some loss of performance, much of the strength is retained. Recycled components are therefore of a higher quality than the chopped fiber materials which current recycling normally yields. They remain suitable for applications such as body panels. In this state they may undergo several cycles of manufacture into different products. Eventually the fibers will be chopped for low-grade applications.
“The results from our initial press trials look promising and we’re very much looking forward to supporting Prodrive in automating the process going forward,” says Hannah Tew, Partnership Lead at the AMRC Composite Centre.
Prodrive’s Primary to Tertiary process may provide the cost and waste reduction needed for mass manufacturing in composite materials. This would bring significant improvements in performance and energy efficiency. If successful, the process is likely to find applications in many other industries. Prodive is expected to enter serial production by the end of the year.