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Shredded carpet waste, which is then cleaned and mixed with ionic liquid, © ISOPREP.

Roughly 1.6 million tonnes of carpet is wasted every year in just the EU alone. Most of it goes to landfill or is incinerated as carpet is a compound material that is largely incompatible with purely mechanical recycling processes. Because of this and the fact that polypropylene, an oil-based plastic, makes up about a quarter of carpet waste, there are many resources that are lost. A team of researchers, which includes the Fraunhofer Institute for Building Physics IBP, has developed a novel recycling method in an EU project called ISOPREP. The method is the first to allow the recovery of polypropylene from carpet waste – with no perceptible reduction of quality. This means that the polypropylene recovered is not only useful for lower-value products, it is also suitable for higher-quality products.

The basis of the method is an ionic liquid that acts as a special solvent. If it consists of the right components, it selectively dissolves the polypropylene from the carpet fibres. Before that, though, the carpet waste is cleaned – separating out as much of its backing as possible – and reduced to small pieces. The pretreated waste is then put in a reactor where the solvent is applied. The polypropylene is selectively dissolved in the solvent, causing dyes and other additives to be separated effectively. The method already works on a larger laboratory scale, and the consortium is now working on transferring the process to a pilot system which can recycle one tonne of carpet waste per day. The system is slated to commence operation when the project ends in March 2022. The experts also expect that the method can be applied for other forms of waste that contain polypropylene and are unsuitable for mechanical recycling.

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