A significant part of carpet waste consists of petroleum-based polypropylene. As a non-recyclable product, disposing of it has previously meant incineration or landfill. However, a new solvent is now making it possible to recover virgin-standard polypropylene from carpet waste—with no perceptible reduction in quality. Developed by the Fraunhofer Institute for Building Physics IBP and its partners, the process also involves costs that are quite competitive. The development has taken place as part of the ISOPREP EU project.
The EU alone produces around 1.6 million tons of carpet waste every year. The majority of this ends up being sent to landfill or incinerated, as carpet is a composite material that is not suitable for purely mechanical recycling methods. With carpet waste analyzed in the project consisting of around a quarter polypropylene, a petroleum-based plastic, the result is a great deal of resources going to waste.
A team of researchers, including from Fraunhofer IBP, has now developed a new recycling process as part of an EU project named ISOPREP (see logo). “For the first time, this is making it possible to recover polypropylene from carpet waste—and the outcome is virgin-quality,” says Maike Illner, a researcher at Fraunhofer IBP. Not only does this allow the recovered polypropylene to be used in lower-quality products (in a process known as downcycling), but it also means that the quality is similar to that of newly manufactured polypropylene, making the material suitable for high-quality products too.
The process is based on a special solvent in the form of an ionic liquid. With the right components, it is able to selectively extract polypropylene from carpet fibers. Before the team of experts applies the solvent, the carpet waste is cleaned—something which involves removing as much of the backing as possible—and broken down. Once the pretreatment is complete, the waste is fed into a reactor in which it undergoes treatment using the solvent. The polypropylene is selectively dissolved in the solvent, a method that provides an effective way of removing dyes and other additives. The process is already being used on an extensive laboratory scale involving several liters of the solvent—and now, the research consortium has set its sights on scaling the process up to a pilot plant with the ability to recycle a ton of carpet waste per day. The pilot plant is set to commence operation by the end of the project in March 2022.