Can composites be remanufactured?

Posted on 17th May, 2018 Under Blog

As we strive towards a circular economy and look for opportunities for remanufacturing and material reuse, Dr David Paterson discusses the potential for composite materials, asking the question; Can composites be remanufactured?

Where are composites used?

Composites offer significant strength to weight ratio when compared to some alloys and metals and therefore are ideally suited to the aerospace market.  Commercial aircraft, military craft, helicopters, business jets, general aviation aircraft and space craft all make substantial use of composites, both inside and outside.  Additionally, composites can also be found in the wind turbine, automotive, sport, construction, and marine industries.

What are composites?

Composites in their basic form are materials in which two or more separate materials come together to create a bonded structure. One of the most commonly used composites is Carbon Fibre Reinforced Plastic (CFRP).

Why re-use?

The predicted global tonnage of CFRP by 2021 is 175,000 tones, an increase of 210% from 2014 usage Kraus and Kühnel, “Composites Market Report 2015.”  This huge anticipated increase means the production of CFRP using virgin materials is not sustainable, nor is the disposal of used CFRP at end of life with the following drivers for re-use identified:

Environment – National legislation and wider regulations such as the Waste frame work directive, the waste electrical and electronic equipment directive, the landfill directive, the End-of-life vehicle directive etc. are all designed to tackle increasing levels of waste and thus effectively force CFRP to be diverted away from landfill.

Economics – CFRP can be a very expensive material to manufacture, and so re-using end-of-life composite in different applications and extending the life span of composite materials is desirable economically for both businesses and stakeholders.

Are these components recycled or remanufactured?

Despite what is reported in some literature, CFRP is not at present being remanufactured.  CFRP is strong, robust, durable and purposely designed not to be taken apart.  Therefore the CFRP disassembly process leads to degradation of the core to a degree that makes restoration and reassembly currently unachievable.

CFRP recycling on the other hand is widespread and represents a growing area of research.

How is CFRP recycled?

There are in general two distinct ways to recycle CFRP; mechanical recycling and fibre reclamation.

Mechanical recycling takes CFRP and performs chopping, milling and grinding processes to return a fibrous mixture of fibres and epoxy. This mixture may be used again as a reinforcement in other materials and even in other composites such as concrete.

Fibre reclamation seeks to retain the significant energy and expense of manufacturing virgin carbon fibre by recycling the CFRP composite in such a way that the pre-impregnated fibres are reclaimed, and critically are able to be re-impregnated with new resin to create a new CFRP.   The process of fibre reclamation is performed via heat treatment (oxidation of the CFRP through exposure to temperatures up to and in excess of 600 degrees) or via chemical treatments (the physical breakdown of the epoxy and therefore de-bonding of fibre and epoxy). Fibre reclamation tends to degrade the fibres and in some cases produces a random mix of fibres in various directions and so the sweet spot of perfect, non-degraded, perfectly aligned fibres able to be fully re-impregnated with new resin has yet to be found.

What are the challenges for a successful composite aftermarket?

Fine tuning the process – Establishing a successful and like for like aftermarket where CFRP with reclaimed fibres could be used in exchange of virgin CFRP is rooted in fine tuning the CFRP reclamation process – noting that ground breaking research producing reclaimed fibres of very high quality (approaching virgin standards) is currently on-going.

Identifying supply streams for lesser quality fibres – Current CFRP reclamation can produce fibres which, although not suitable for like for like use, are suitable for alternative usage and so drive down the additional raw materials consumption.

One example of this comes from aerospace giants Boeing who have investigated using reclaimed fibres for non-structural applications such as chairs, or trays.

Reclamation of fibres is a key milestone in reducing the amount of virgin material used for CFRP. Moving forward the ideal scenario is to develop technologies able to extract the fibres in such a way that they are unharmed and able to be reused as like for like replacements for virgin CFRP.

Dr David Paterson is currently a Research Assistant at the Centre for Ultrasonic Engineering in the department of Electronic and Electrical Engineering at Strathclyde University. He completed a Engineering Doctorate which examined the effectiveness of ultrasound through transmission as means to determine the elastic constants of CFRP in addition to proposing new terminology, and a means to determine accurate EOL terminology, for the EOL CFRP products currently manufactured by industry and academia. email: david.a.paterson@strath.ac.uk