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Born again: Obsolete composites find a second life with RESET

Yesterday’s composite aircraft parts that are beyond serviceable standard have the chance to be reincarnated into new components for the airliners of the future, thanks to Clean Sky’s RESET project.

For decades, aircraft reaching the end of their operational life have been stripped down for parts, and some components refurbished and recertified – aluminium can often be recycled into lower grade products, such as drinks cans. But with the increasing use of composite material in today’s airliners – for example, the Airbus A350XWB airframe structure is 53% composite by weight compared to 25% in the A380-800 (and compared to just 5% in the A310-300 of 1985) – it’s environmentally essential to find a solution for the recycling of aircraft thermoplastics. Specifically, PEEK (Polyether ether ketone) and PPS (Polyphenylene sulphide), usually reinforced with Carbon Fibre, are the most common high per formance materials considered as leftovers when their lifecycle has come to an end. These materials were the subject matter of Clean Sky’s RESET, a project which ran from January 2016 until December 2017, coordinated by the Leitat Technological Institute based in Barcelona, which took on the challenge – with some surprising results.

”RESET was part of the Eco-Design activities under AIRFRAME ITD and the id ea here was to recycle some parts of the aircraft which were made from composite” explains Clean Sky’s Project Officer Elena Pedone. ”The RESET team at Leitat have managed to recycle previously used aircraft composite material and from it they’ve manufactured some parts and then they compared the commercial ones versus the recycled ones. Following some analysis they observed that, actually, the recycled parts have similar mechanical characteristics; therefore the technology developed in this project could be realistically commercialised in the aeronautic sector in the next few years and possibly spilled over to other economic sectors”.

Work carried out in the course of the project included studying the waste material to ensure a correct material selection. Specific characteristics were defined along this task based on different sorting criteria. These included looking at the thermoplastic matrix (PEEK and PPS); their chemical nature of reinforcement (using carbon fibres); the reinforcement shape – whether it was short or long fibres, woven or nonwoven; and examining the fibre content (polymer to fibre ratio). Taking these properties as a starting point, a table of criteria was developed and the scrap material from part manufacturers was selected as a main source for the waste stream.

In a second work package the main objective was the conditioning and characterization of the recycled material and the development of a new family of different composites with recycled CFRP (Carbon Fibre Reinforced Polymer) based on Polyphenylene Sulphide (PPS) by means of an extrusion process.

”Two par ts were created by injection moulding and two by thermoforming which were then tested – a thermoplastic bracket and a thermoplastic cleat” explains Leitat’s scientific coordinator of the project Claudia Aguilar. ”The mechanical properties of the material were found to be comparable with the commercial counterpart and composites prepared with recycled carbon fibre. The RESET project improves the recycling process in the aeronautic sector. Concretely, it developed a recycling process to be applied to thermoplastics. The recycled material, coming from the aeronautic sector, is used as raw material to produce new parts for aircraft. Up to 70% of recycled material was used to produce a new family of composite materials”.

Regarding the social and environmental benefits of the project, Aguilar says that ”the reduction of ozone depletion, freshwater toxicity and mineral depletion have been the main benefits achieved in the RESET project. Comparing injection and thermoforming processes, the first one generates less impact than the second case: on average 40% of impacts are reduced when injection moulding is developed instead of thermoforming”.

And as for the project’s implications for Europe’s aircraft industry, Aguilar adds that ”the recycling process of RESET allows European aviation to limit the environmental footprint and to reduce production costs of new aircraft parts. Hence, the project makes the aviation industry more competitive and greener”.

Clean Sky’s Pedone adds that ”the environmental impact of RESET is self-evident and also aligns with the European Union’s initiatives and ambitions towards a circular economy, and then the potential social impact of this project is also very high”.