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Technology for improving the recycling of plastics and composites

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Plastics and composites aren’t recycled as often as we might wish, as a result of a lack of facilities, the right technologies not yet existing or not being profitable, or hazardous waste deposits. IMT Nord Europe have been working in partnership with manufacturers to develop and improve the available technologies.

Plastics and composites get a lot of bad press, but it is hard to do without them for many objects we use every day, including our cars. In order to minimise their polluting effect, they must be recycled, but this is complicated from both a technological and an economic perspective. Two researchers from IMT Nord Europe are seeking to improve processes with a view towards industrialisation.

In order to recycle plastic, outlets have to be found for these recycled materials. One of the main stumbling blocks is the presence of pollutants, including volatile organic compounds (VOCs), which can produce unpleasant and even toxic odours. There are also very strict standards governing the emission of VOCs and odours in vehicle passenger compartments. Marie-France Lacrampe, a researcher at IMT Nord Europe, is working on a solution which is striking in its simplicity: water-assisted extrusion.

Eliminating odours

Extrusion is a process traditionally used to manufacture objects made from plastic, involving pushing a doughy material through a die of the desired cross-section. Water is injected into the extruder and the steam washes the plastic, extracting the majority of any VOCs. “A few changes need to be made to the extruder”, explains Marie-France Lacrampe. Professor Lacrampe is working alongside three industrial partners and another laboratory, with the industrial pilot expected to be operational within two years.

In order to further improve this process, the researcher intends to combine water with supercritical CO2 – pressurised CO2 which becomes a highly effective solvent. The advantage is that it removes different molecules from those removed using water.

Process organisation and eco-design

Efficient recycling normally starts with designing materials which are easy to recycle. This is particularly true when it comes to food packaging, which is often made using several different materials (cartons, thermoformed tubs or re-heatable pouches, for example). “The ideal solution is to mix compatible polymers which can then be integrated into existing recycling processes”, explains Marie-France Lacrampe.

When it comes to recycling, it’s not just a question of the technology used, but how the whole process is organised. Waste must be used as locally as possible in order to cut transport and logistics costs, requiring intelligent analysis and handling of flows.

“If we want to boost recycling rates then we have to tackle what we don’t know how to do. This is particularly true for small quantities (hazardous waste deposits) and materials which we are unable to recycle or aren’t very good at recycling such as opaque PET (the plastic used to make milk bottles, for example). We are working on recycling small quantities through additive manufacturing, the industrial version of 3D printing, extruding them again with additives so that they be reused.” 

Composites – rarely recycled

If recycling plastics isn’t always easy, just imagine what it must be like for composites, materials which are generally comprised of glass or carbon fibre and a polymer matrix. A modern aircraft such as the Airbus A350 is half-made of composites, which are used in whole sectors of industry, from transport (not just aircraft, but also cars, boats and bikes) to electronics, leisure and wind power.

Once they have reached the end of their life, composites are primarily burned in order to produce energy, which isn’t ideal from either an environmental or an economic point of view. “Solutions are being developed in the aeronautics sector to recover carbon fibres”, points out Mylène Lagardère, who is also a researcher at IMT Nord Europe. “It is mostly carbon-based composites which are used in aeronautics, which are more “noble”, making them easier to recycle.” Technology for recycling fibreglass composite does exist, but it is not yet profitable.

Developing more affordable methods

There are two possible processes for recovering fibres: a chemical process in which the matrix is dissolved in a solvent (allowing the matrix to be reused) and a thermal process in which the matrix is damaged. Matrices themselves are either thermoplastic, meaning they can be melted, or thermosetting, meaning they are damaged when heated. As a result, as Mylène Lagardère explains, “each fibre-matrix combination is processed differently,  with a different process for each product.” This is what makes recycling composites so complicated. The purer the material, the easier it is to recycle.

As we can see, improving recycling is essential, and research into this subject is rightly being prioritised. “Our aim is to develop methods which are both simple and affordable”, explains Mylène Lagardère. “Our basis is the industrial problem: if we have a deposit of materials with certain properties, then we can recover a recycled material with such properties.” The issue is that, during recycling, the properties of the material always deteriorate, as the fibres are shortened.

The recycling of composites is still very much in its infancy, but a few processes are starting to emerge,  whether in water sports, where the association APER – funded by an eco-tax on new crafts – dismantles abandoned boats, or in the wind power industry. The automobile industry is also having to adapt, with legislation requiring recycled materials to be used in the production of new vehicles.

Cécile Michaut

Large quantities of composites for recycling on the horizon?

10 million tonnes of composites are produced each year worldwide, and the market is continuing to grow at a rate of 5% year on year. But recycling is set to really accelerate: composites whihe arrived on the market 20 to 30 years ago are now reaching the end of their lives. 50,000 tonnes of wind turbine rotors will need to be recycled between 2021 and 2022. In 2023, 25,000 boats, three-quarters made from composites, are to be dismantled. 4,000 railway carriages are also awaiting dismantling. Although resources remain limited (15,000 tonnes of production waste and 7,000 tonnes of materials at end of life in 2017), significant growth is anticipated. Processes mut develop and organise in order to become sustainable.

Also read on I’MTech

“We must work now to recycle composites”
Recycling carbon fibre composites: a difficult task
brominated plastics

Innovative approaches to recycling brominated plastics

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Recovering untreated plastic materials and putting them back into the recycling loop through a decontamination line is the challenge of thesis research by Layla Gripon, a PhD student at IMT Lille Douai. These extraction methods contribute to a comprehensive approach to recovering plastic materials, in particular brominated plastics.

High consumption of electronic devices implies a significant amount of waste to be processed. While waste electrical and electronic equipment (WEEE) is often seen as a gold mine of silver and rare earths, plastic materials represent 18% of these deposits. This was equivalent to 143,000 tons in France in 2018 according to a report by Ademe (Ecological Transition Agency) published in 2019. But not all this plastic material is created equal. Some of it contains atoms of bromine – a chemical compound that is widely used in industrial flame retardants. These substances meet requirements for reducing flammability hazards in devices that may get hot while in use, such as computers or televisions. There’s just one problem: many of these substances are persistent organic pollutants (called POP). This means that they are molecules that can travel great distances without being transformed, and which are toxic to the environment and our health. The amount of these molecules contained in devices is therefore regulated in the design stage, as well as in the end-of-life processing stage. In 2019, the European Union set the threshold at which waste containing bromine can no longer be recycled at 2 grams per kilo. Beyond this limit, it is destroyed through incineration or used as fuel. But couldn’t it still be recycled, with the right processing? For her thesis co-supervised by researchers at IMT Lille Douai and The Alençon Institute of Plastics and Composites (ISPA), Layla Gripon has set out to identify a method for separating brominated flame retardants from plastics. “We seek to maximize recycling by limiting the loss of unrecoverable material, while complying with regulations,” says the PhD student.

Finding the right balance between extraction efficiency and respect for the environment

Approximately 13% of WEEE plastics are above the legal threshold for brominated flame retardants, which is equivalent to 17,500 tons in France. Samples tested in the laboratory reached a concentration of bromine up to 4 times higher than the legal threshold. In order to process them, Layla Gripon tested a number of methods that do not degrade the original plastic material. The first was highly efficient, removing 80% of the bromine. It was an extraction method used diethyl ether, an organic solvent. But since it uses a lot of solvent, it is not an environmentally-friendly solution. Another technique based on solvents is dissolution-precipitation. Through this technique, plastic is dissolved in the solvent, which retains the flame retardants. “In order to limit the environmental impact of this process, we subcontracted the German Fraunhofer Institute to carry out a test. Their patented process (CreaSolv) allows them to reuse the solvents. In the end, the bromine was no longer detected after processing and the environmental impact was reduced,” she explains.

In addition, a method that is more environmentally-friendly – but less efficient, for now – uses supercritical CO2, a green, non-toxic and non-flammable solvent. This process is already used in the agri-food industry, for example, to remove caffeine from coffee. In the supercritical state, carbon dioxide exists in an intermediate state between liquid and gas. To achieve this, the gas is heated and pressurized. In practice, the closed-loop system used by Layla Gripon is simple. Shredded plastic is placed inside an autoclave in which the supercritical fluid circulates continuously. When it leaves the autoclave, the recovered gas brings various additives with it, including a portion of the flame retardants.

To improve the yield of the second method, Layla Gripon planned to use a small amount of solvent. “The tests with ethanol improved the yield, with a rate of 44% of bromine removed, but this wasn’t enough,” says the PhD student. Other solvents could be considered in the future. “The supercritical CO2 method, on the other hand, works very well on the brominated flame retardant that is currently the most widely-used in industry (tetrabromobisphenol A – TBBPA),” she adds. But the most difficult brominated plastics to process are the ones that have been prohibited for a number of years. Although they are no longer available on the market, they are still accumulating as waste.

A large-scale approach to recovering recycled plastic  

These promising processing techniques must still evolve to respond fully to the needs of the recycling industry. “If these two processes are selected for applications beyond the laboratory, their environmental impact will have to be minimized,” says the PhD student. Such methods could therefore be incorporated in the pre-processing stage before the mechanical recycling of WEEE plastics.

At the same time, manufacturers are interested in the benefits of this research initiated through the Ecocirnov1 Chair. “They’ve joined this project because the laws are changing quickly and their products must take into account the need to recover materials,” explains Éric Lafranche, a researcher who specializes in plastic materials at IMT Lille Douai and is Layla Gripon’s thesis supervisor. The objective of maximizing recycling is combined with an ambition to create new products tailored to the properties of the recycled materials.  

Read more on I’MTech: A sorting algorithm to improve plastic recycling

“Recycling today is different than it was 10 years ago. Before, we sought to recover the material, reuse it with similar properties for an application identical to its original use. But the recycled product loses some of its properties. We have to find new applications to optimize its use,” says Éric Lafranche. For example, French industrial group Legrand, which specializes in electrical installations and information networks, seeks to use recycled plastic materials in its electrical protection products. In collaboration with researchers from IMT Lille Douai, the company has implemented a multilayer injection system based on recovered materials and higher-grade raw materials on the surface. This offers new opportunities for applications for recycled plastics – as long as their end-of-life processing is optimized.

By Anaïs Culot.

1 Circular economy and recycling chair created in 2015, bringing together IMT Lille Douai, and the Alençon Institute of Plastics and Composites and Armines.