Dutch researchers have made new aircraft parts from discarded carbon fibre composite. Parts that will probably be the first in the world to actually be used. It is a good example of how much potential composite has, now and in the future.
For techies and engineers, carbon fibre composite is a rewarding material: it is as strong as steel but very light. It is widely used in laptops, racing bikes, drones, satellites and car parts, among others. Even several new aircraft models already consist of 80% carbon fibre composite. With this, it seems to have the potential to eventually take the place of aluminium.
Whether that will actually happen, however, remains to be seen. This is because carbon fibre composite also has a major drawback, namely that it is difficult to recycle (unlike aluminium). This is especially true for the type of carbon fibre composite that is currently widely used, thermosets. Recycling these requires a pyrolysis process; it has to go into the furnace to burn off the plastic from the fibres. This in turn is detrimental to the fibres, whereas carbon fibre composite derives its strength from the length of the fibres.
The carbon fibre market is currently about 80% thermosets and 20% thermoplastics. Over 15 companies worldwide have started recycling carbon fibre composites in the last decade. However, the total recycling capacity is still limited. Recycled carbon fibres are up to a third cheaper than new carbon fibres and production takes a tenth of the energy. Applications: including the roof of the BMW i3 and i8.
Solution
Dutch researchers have found something on this. First of all, they focus on thermoplastics. 'Leftover thermoplastics can be heated and deformed into a new product. This makes it possible to recycle both the fibres and the plastic at the same time,' Thomas de Bruijn, researcher in Lightweight Construction at Saxion University of Applied Sciences in Enschede, told Scientias.nl De Bruijn is working with various partners in the TPC-Cycle project on a way to recycle leftover thermoplastic carbon fibre composite. The holy grail is to turn precious carbon fibre composite from which aircraft are made into parts for an aircraft after recycling.
Hundreds of millions of euros
Nijverdal is home to the main European production facility of TenCate Advanced Composites. This Dutch company produces thermoplastic carbon fibre composites, something which experts say will be increasingly in demand in the future (growth of 200 to 300%). This, in turn, will create more thermoplastic waste. 'It is estimated that around 1,000 tonnes of this type of waste will be generated in the Netherlands alone by 2024,' says De Bruijn. 'The value of this is around 100 million euros,' making the Netherlands an important country when it comes to high-quality thermoplastic composite waste.
Up to 60% loss
Now, most carbon fibre composite waste is created when making products with this material. Parts are cut from a sheet of composite and the framework that remains is thrown away. 'On average, the amount of cutting waste is 30% of a sheet,' says De Bruijn. 'But that can be as high as 60%, according to research already done by Dr Soraia Pimenta and Professor Silvestre Taveira Pinho of Imperial College London and other scientists.'To recycle this cutting waste, it is necessary to first reduce it to pieces you can process properly. The smaller it is, the easier it is to process. But the bigger it is, the better its mechanical properties are and the more value it has. 'We make sure the shredded composite consists of pieces that are between 10-15 millimetres in size, which keeps the strength and stiffness of the material high,' says De Bruijn. After shredding, the material is mixed, heated and pressed into a mould to the right shape.
Nothing goes to waste
This way, both the fibre and the plastic are preserved in a new product, instead of the plastic being chipped off the fibres in an oven and lost. This offers gains for the environment, as fewer steps are needed to recycle the composite. This method also consumes less energy than thermoset recycling. Recycled thermoplastics may therefore carry a higher price tag than the carbon fibres remaining after recycling thermoset. But both types of recyclate are less expensive than new carbon fibre composite. De Bruijn further explains: 'We also know better what properties our recycled material has, because it has remained intact.' The only drawback is that the cutting waste still needs to be shredded. 'But short fibres can be used to make much more complex products than long fibres, because these fibres have to go somewhere,' continues De Bruijn. 'No sharp bends or thickness variations can be made with them. With short fibres, you can. You can also make ribs with short fibres, which is a big advantage. Normally, the stiffness of the product depends on the long fibres. But with ribs, you can also create stiffness. That gives more possibilities to optimise a product.'
De Bruijn is now working with GKN Aerospace's Fokker business to develop a semi-structural access hatch for the exterior of a helicopter. This uses cutting waste - derived from TenCate's laminate - left over from the production of thermoplastic composite parts for the same helicopter. Numerous tests are still needed, but the first helicopter is expected to fly with this in spring 2018. That would be an international first.
'It has been shown that after some five times of recycling - where the material is reduced in size - almost no properties are lost,' says De Bruijn. 'Provided you control the process of heating well. Otherwise, the thermoplastic can degrade. I do wonder if composites are really going to be recycled more than five times, given the long service life of products. An aircraft fuselage or a passenger compartment of a car is in use for more than 10 years. Then you can make semi-structural parts with it, such as an access door, cabin parts or seats. You can recycle it like this ten times before it can only be made into a crate. By then, many decades have passed.'
The TPC-Cycle project runs from 1 September 2015 to 30 August 2019. Budget: 1.2 million euros, including from the RAAK programme of Regieorgaan SIA, part of the NWO.
Project partners: Saxion, ThermoPlastic composites Research Centre, GKN Aerospace's Fokker business, TenCate Advanced Composites, Dutch Thermoplastic Components, Cato Composite Innovations and Nido Recycling Techniek.
Research
IDTechEX recently pubked a report highlighting the potential of composites. 'The composites industry seems an established market but under the surface there are many important innovations going on at every stage of the supply chain. Innovations that offer many opportunities to a wide variety of companies.' The market for all synthetic fibres used in composite parts is forecast to grow to $9 billion by 2027. There will be growth in new type of fibres as well as established materials.
By: Kelly Bakker
Source: Scientias.co.uk
