September 2016 by Lydia Heida
The high price of carbon fibre, coupled with a steep increase in its use in the aerospace and automotive industries, is driving the rapid growth in carbon fibre recycling which has attracted the involvement of some major players such as Boeing, Dell, BMW, Toyota and Hitachi. But some issues – such as shredding prior to treatment – remain to be taken care of.
‘Carbon fibre is still an exotic fibre, but its use will grow spectacularly in the next 20 years,’ predicts Bruno Douchy, sales director of Procotex, a Belgium-based company that recycles carbon fibre through its French subsidiary Apply Carbon. The drive for fuel efficiency is accelerating the use of carbon fibre in the aerospace and automotive industries because it is much lighter and stronger than aluminium or steel.
Some aircraft consist already of more than 50% carbon-fibre-reinforced polymer (CFRP), such as the new Airbus A350 XWB. It is used in 104 models of car, like the BMW i3 and i8 and also Ford’s Shelby GT350R Mustang, as well as in a range of other products varying from wind turbines and satellites to drones and sports goods.
Demand to double
Global demand for these fibres is expected to double to 120 000 tonnes between 2016 and 2030, and many carbon fibre producers are currently expanding their capacities; for example, Hexcel is spending US$ 250 million on a new production plant at Roussillon in France. However, up to 30% of carbon fibre is wasted during production or cutting and trimming operations to manufacture products.
Also, products that contain carbon fibre are already reaching their end-of-life stage, such as the Boeing 777s and Airbus A320s which comprise up to 20% carbon fibre by weight.
Worldwide, carbon fibre is being recycled by well over a dozen companies that have been founded in the past 20 years. Most of these businesses are located in the USA, Europe and Japan, including America’s Carbon Conversions, Hadeg of Germany, ELG Carbon Fibre of the UK and Japan’s Takayasu.
In 2014, the annual recycling capacity of these companies was estimated at between 3500 and 5000 tonnes but the figures could already be much higher given the rapid development of this industry.
The most important drivers for recycling carbon fibre are ‘its value and the ever-increasing amount of waste’, according to Ingrid Ahlborn, managing director of Hadeg. A kilogram of recycled carbon fibre is valued at around US$ 15 while the price of virgin carbon fibre is US$ 24-30.
Producing recycled carbon fibre requires one tenth of the energy needed for virgin material. Hence, there is great interest among carbon fibre manufacturers and end users in recycling it. UK-based Sigmatex, a manufacturer of carbon fibre textiles for the aerospace and automotive industries, is recycling its own dry carbon fibre production scrap into non-crimp fabric.
Meanwhile, Airbus has set a target of recycling 95% of its carbon fibre waste by 2020-25, with 5% recycled back into the aerospace sector. This year, its Composite Technology Center subsidiary located at Stade in Germany will begin preparations for serial production of an aircraft interior sidewall panel made out of recycled carbon fibre.
The most advanced collaboration is between BMW and SGL. These companies set up a joint venture in 2008 known as SGL Automotive Carbon Fibers, which has a plant at Wackersdorf in Germany and supplies carbon fibre materials to BMW. The plant recycles carbon fibre scrap from the production of BMW’s i series vehicles at other facilities.
‘We have reuse processes in place for all carbon fibre waste arising from production,’ points out Steffen Aumann, head of the BMW Group Competence Centre for Recycling. Recycled carbon fibre is used in vehicle components, such as the roof of i3 electric drive and i8 plug-in hybrid cars. In total, 10% of the CFRPs used in BMW i series vehicles is recycled material.
‘Recycling this material should become economic following the introduction of BMW’s i3 and i8 cars,’ according to Aumann. ‘When today’s cars made from carbon fibre come back for recycling from 2025 onwards, we will have industrialised carbon fibre reuse.’
EU law states that, by 2015, new vehicles had to be 85% reusable or recyclable (by mass) and 95% recoverable, which makes recycling of carbon fibre imperative. In Germany, the landfilling of carbon fibre is already prohibited.
In the USA, meanwhile, a Carbon Fiber Recycling Act is under discussion in the Senate to prevent landfilling, with US$ 10 million earmarked for a study on use of recycled carbon fibre and for a demonstration project.
Applications still limited
Currently, almost every company that recycles carbon fibre uses pyrolysis. After shredding the fibres, the resins are burned off in an oven that uses a limited amount of oxygen. ‘This is a delicate process,’ says Douchy of Procotex. ‘If the temperature in the oven is too high, or the fibres stay there too long, the fibres could be damaged.’
On the other hand, if the temperature in the oven is too low, char forms on the fibres which prevents a good bond with a new resin. A pyrolysis temperature in the range of 500-550°C appears to be the best route to recovering the highest quality of carbon fibre.
Recycled carbon fibre can achieve a tensile strength of up to 4 Ga and a tensile modulus of 400 GPa. This is well within targets for virgin products in many applications, although it doesn’t meet the requirements for primary aircraft structures.
Procotex’s milled carbon is, for example, used in composites for deep-sea applications where water pressures can be extreme. However, industrial applications using recycled carbon fibre are still extremely limited. ‘We have lots of projects running, but not on an industrial scale,’ explains Douchy. ‘We have to convince the composite industry to use recycled carbon fibre, but they still measure everything to first grade. They don’t like to switch quickly.’
‘Standards are emerging’
Some users of carbon fibre for industrial applications still consider recycled material to be of an inferior quality to virgin fibre. ‘The largest problem is the lack of standards around recycled carbon fibre from end-of-life applications,’ comments Professor Gary Leeke, head of bioenergy and resource management at Cranfield University in the UK and leader of the EXHUME project to recycle carbon fibre.
Companies can be reluctant to use this material because its actual properties are not known or they are unsure how it will perform. ‘But standards are emerging,’ says Leeke. ‘Carbon fibre recycling companies are producing very good quality material, as is proven by ELG Carbon Fibre.’
In January, this UK recycler was certified by Bureau Veritas for its recycling process, recycled carbon fibre materials and products, which are now officially meeting the stringent demands of the aviation and aerospace industry. Pilot plant imminent Worldwide, many companies and researchers are trying to develop methods to improve carbon fibre recycling.
Pyrolysis is energy-intensive and byproducts of this process – oil fractions, gases and char – are often not recovered. But the most pressing problem is that fibres need to be shredded before treatment.
The world’s largest carbon fibre producer, Toray Industries, is linking up with Toyota Tsusho Corporation, the trading arm of the Toyota Group, to build a pilot plant that uses gases from the pyrolysis process as an energy source for the recycling of carbon fibre, which should lead to a large reduction in the overall energy consumption of the pyrolysis process. ‘Testing of the plant will start in the second half of 2016,’ according to Toyota Tsusho Corporation spokesperson Norihiro Shigemichi.
Pros and cons of solvolysis
Many researchers view solvolysis as the best method to recycle carbon fibre. ‘We have performed a life-cycle analysis as part of our EXHUME project, and solvolysis came out on top,’ Leeke notes, going on to claim that this process ‘delivers the best-quality recycled carbon fibre and uses the least energy’.
Armed with this conviction, Leeke and his colleagues have developed a solvolysis process to recycle CFRP. ‘We use a mixture of water and an organic solvent that degrades the resin around 300°C and 150 bar pressure,’ he explains. Recycled fibres lose less than 5% of their strength.
‘We also clean up the solvent to reuse it for the process, and recover phenol and amine components out of the resin,’ adds Leeke. However, solvolysis has its own downsides. ‘Pyrolysis is a simple process in terms of control, whereas solvolysis involves pressure, temperature and flow control,’ Leeke points out. ‘It is much more difficult to operate and needs to be developed further to make it easier to control.’
Leeke has just applied for funding for a follow-up project on the economics of carbon fibre recycling, the quality of recycled carbon fibre and what products can be made from it. ‘If the results are good, we hope to construct a pilot plant in the next phase,’ he confirms.
Profits still hard to make
Hitachi Chemical is already running a pilot project with a capacity to recycle 12 tons of carbon fibre per year. This solvolysis process uses tricalcium phospate as a catalyst and benzyl alcohol as a solvent at ordinary pressure and 200°C. No pre-shredding of the carbon fibre is necessary and so the recycled material is of near-virgin quality.
Eliminating pre-treatment saves costs, as does treatment under ordinary pressure, while the recovered resins can be reused as high-value materials. ‘But it is still difficult to cover the costs of recycling and make a profit,’ says Hitachi Chemical’s sales manager Christoph Schick.
Meanwhile, French company Alpha Recyclage Composites runs a 2000-litre pilot batch reactor for steam thermolysis – a hybrid solvolysis-thermolysis process in which water vapour is superheated at atmospheric pressure and used to degrade the resin, with more than 99% eliminated from the fibres.
‘This process also preserves the fibre length,’ claims the company’s technical director Philippe Brosson. The recycled fibres can be converted into thermoplastics with mechanical properties that are comparable to composites made using virgin carbon fibres, according to tests performed by the MATEIS materials laboratory at the University of Lyon. An industrial demonstrator is scheduled to be operational by the beginning of 2017.
The need to develop products for recycled carbon fibre runs as a red thread through most interviews with people involved in this industry. Recently, some initiatives have been established to focus on this issue. The DiloGroup, a manufacturer of machinery for non-woven applications, installed an innovative compact line for carbon fibre recycling last year at the Institut für Textiltechnik at Augsburg in Germany which incorporates bale opening, feeding, carding, cross-lapping, needling and winding.
The aim is to make processing of recycled carbon fibres more efficient and to develop new products. Also in 2015, the Composite Recycling Technology Center was founded in the US state of Washington with a US$ 2 million grant from the US department of commerce.
This will develop products made out of scrap uncured prepreg, a term for pre-impregnated carbon fibres where a matrix material is already present. By 2021, the aim is to recycle around 5500 tonnes of scrap carbon fibre per year, which can be used for vehicle components, building materials and renewable energy systems.
Mallinda: starting low but aiming high
There has been a recent trend towards designing new types of resin to facilitate the recycling of carbon fibre composites. Since 2014, US-based Mallinda has been developing polymers which are hard like thermosets but which can be moulded, reshaped, welded, repaired and recycled at relatively mild temperatures.
The company has received more than US$ 1.2 million in funding from, among others, the US department of energy. The company’s recycling process is closed-loop and uses almost no energy. ‘We soak the composite in a solution of monomers at room temperature to depolymerise it,’ explains Mallinda’s ceo Chris Kaffer.
The resin can be reused for new composites of the same strength. But even better, the full length of woven carbon fibres can be recovered while maintaining their mechanical integrity. Mallinda’s next step will be to complete a life-cycle analysis to test how many times the fibres can be reused and the effect on fibre strength.
‘We are currently transitioning from lab scale to pilot production,’ says Kaffer. The company’s initial target is to produce around 1000 shin guards in the next nine months. ‘These shin guards can be put in a dish of boiling water and moulded around your shin,’ the ceo points out. ‘Sporting goods are a really good market to move into because the barriers of entry are low.’
The next phase of the plan is to enter high-value markets such as automotive and aerospace. ‘Certification is a high bar and requires years of testing, so commercial adoption in such stringently regulated industries can take more than a decade,’ explains Kaffer.
‘The best opportunity in aerospace for us might be for things that are not used for the construction of a plane, but more like tray tables.’
This article has been published in magazine Recycling International issue September 2016