Thermoplastic composite recycling finds new outlets

Today, minimising the impact on the environment is a very important challenge for the composite industry. One of the biggest problems with respect to composite waste is linked to the complexity of the material involved and the ever- expanding quantity of waste. Production waste increases as the industry develops and many products reach their end-of-life. That’s why sustainable solutions for composite waste represent a key issue to resolve in the transition to green. In this context, thermoplastic matrix composites, used more and more, present the distinct advantage of being able to be processed several times, whereas thermoset matrix composites do not.

Within this framework, two organisations have come together to take up the challenge: Somocap, a company specialised in rubber, plastic, and composite moulding, and Compositadour, a technological platform specialised in composite material processes.

Different types of waste
In southwestern France, the two companies have identified a large quantity of thermoplastic composite waste. At this time, there are no solutions to recycle  or reuse this waste, so it ends up in a landfill. This thermoplastic composite waste can be classified into two different categories. It can either come in the form of scrap of new material from serial production, for example automated cutting or draping (Figure 1), or from already- converted material like test parts, parts that did not meet specifications, and ones that have reached end-of-life (Figure 2).

Through the R&D they conduct, Somocap and Compositadour also aim to recover composite waste from these various streams and use it to create technical parts made of staple long fibres.

The method involves reconditioning this scrap before it can be integrated into an innovative reuse process. Reconditioning is necessary because the waste identified from production cannot be reused as-is in usual processes due to its format (size and shape). This step dismantles the waste and subsequently leads to production of a new raw material. No matter the type of waste to recover, the goal is to reprocess the reconditioned material while preserving the advantages of its exceptional mechanical properties. By nature, the types of materials identified are very different in terms of thickness,  stiffness, solidity, shape, etc. Different methods must therefore be used to recondition them.

Reconditioning waste
One of the primary method involves breaking up already-consolidated composite waste and discarded finished products in a wide array of shapes  and volumes. A raw material, in the form of relatively homogeneous “fragments,” is produced through this method. As fibre lay-up gives parts great strength, in turn it requires substantial effort to break. The layers must therefore be delaminated to facilitate processing. Studies done by Somocap, Compositadour, and their partners have led to development of a grinding machine that can process this waste. It produces a new staple long fibres material (>15 mm) (Figure 3). On the other hand, for new material scrap made of a thin layer of very fine, fairly flexible unidirectional fibres, that same grinding solution would damage the fibres and impact performance. Recycling this scrap therefore involves cutting (rather than grinding) which aims to produce identical fragments of a calibrated length commonly called “chips” (Figure 4). Various cutting methods were tested: laser, rotary blade, die, ultrasound, etc. The difficulty here lies in the ability to treat every type of scrap shape with a single cutting solution. The selected technology is still being optimised and will make it possible to calibrate the composite “chips.”

Implementing processes
At the industrial scale, 2 recovery processes have been developed to implement each of the new raw materials (ground staple long fibres fragments and thin composite chips). The first process is thermocompression, or thermoforming. It involves a press and is widely- used in the moulding industry for all materials. It has the distinct advantage of being inexpensive and simple to implement. Thermoforming is well-suited to controlling new materials and obtaining the requisite performances expected, according to the type of fibres used. The developments in this area have already resulted in the creation of recycled composite parts (Figure 5).

The second process that has been deployed is new and innovative. It was developed to create very complex shapes and can produce very detailed geometries, which cannot be achieved with the typical thermoforming process (Figure 6). In addition, it requires virtually no finishing operations like contour cut-outs or trimming. As feasibility has been demonstrated, developments are continuing to industrialise this process and make it suitable for serial production.

Innovating for sustainability instrumental for future success
Up to 99% of composite waste are not currently recycled. In this context, the solutions developed  by Somocap and Compositadour will make it possible to produce technical products with simple and complex shapes from waste that has not been recycled to date. A thermocompression process can be used to produce simple shapes. A more complex process, based on Somocap’s moulding expertise, can produce complex shapes from long staple fibres. The merit of the processes developed lies in their ease of implementation and the preservation of the original fibres as long staple fibres. The two companies are optimistic about achieving a feasible way of recycling thermoplastic composites waste at the local level. Collaborative innovation on this topic has led to very promising results.

The ambition of developing simple and complex shapes is part of a roadmap to decarbonisation, which is now imperative in all sectors of industry. The team has already been awarded an eco-innovation prize, and now seeks partners to launch demonstration phases, which will eventually lead to mass production. The first applications envisaged are small- to medium-scale production of various technical components for aircraft, drones and defence equipment.

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