Circular Economy Designing Sustainable Roofing Membranes from Recycled Materials

Is it possible to recover recycled plastics from previously unused waste streams to produce high-quality fibers and films? Researchers at Fraunhofer CCPE are addressing this question. As part of the Zirk-Tex project, they are also developing innovative recycling methods to produce sustainable roofing membranes and geosynthetics. 

The market for recycled plastics, particularly polypropylene (PP) and polyethylene terephthalate (PET), still has a lot of potential. Demand for sustainable solutions is growing, but the quality of the available recycled materials must improve. Many recycling processes fail due to contaminants that complicate processing. As a result, recycled materials have often been unable to compete with virgin materials. 

The six institutes of the Fraunhofer CCPE Cluster, together with the Fraunhofer Institutes for Molecular Biology and Applied Ecology (IME) and for Optronics, Systems Engineering, and Image Analysis (IOSB), aim to refute this and bring about change. In the Zirk-Tex project, they are addressing, among other things, the question of whether it is possible to produce recycled plastics from previously unused plastic waste for high-quality films, nonwovens, and fibers that can be further processed into roofing membranes. 

Cost-Effective Production of PP and PET Roofing Membranes 

“It is less of a challenge to produce injection-molded parts, for example, from recycled plastics. But manufacturing textile products such as nonwovens for roofing membranes from them is much more difficult, since yarn-forming processes place very high demands on the recycled materials,” explains Dr. Evgueni Tarkhanov, a researcher at Fraunhofer IAP.

The reason: The raw material must be homogeneous and completely free of impurities in order to be extruded uniformly through the finest capillaries and to withstand, in some cases, very high tensile forces after extrusion. “Processing stability is the be-all and end-all of production,” Tarkhanov continued. 

Even the smallest particles of dirt or trace amounts of foreign polymers in extruded filaments constitute defects in the spinning material and increase the likelihood of filament breaks during the manufacturing process. Re-positioning the filament bundles on the yarn guides takes time and can sometimes result in the production machines having to be shut down, which entails immense costs.

Rethinking the Entire Value Chain

“To manufacture roofing membranes from post-consumer waste, we are able to replicate the entire process chain for PP and PET on a pilot scale,” says Dr. Christian Schütz, project manager and researcher at Fraunhofer LBF. This means everything from the sorting process to innovative recycling methods and on to the final application. Recycling suitable post-consumer plastics produces a granulate or compound, which is blended with additives and then further processed through spinning into nonwovens, films, or membranes.

In doing so, the research team explored the potential of two recycling processes: The PET fraction was subjected to glycolysis, a chemical recycling process followed by repolymerization, while both the PP and PET fractions were recovered using a solvent-based recycling process that involves purification. 

The residues from both recycling processes were further processed via pyrolysis (Fraunhofer UMSICHT). The practical work was accompanied by a life cycle assessment (Fraunhofer UMSICHT) and a material flow analysis of available material streams (Fraunhofer IML).

Innovative recycling processes for single-material recyclates

Using the Fraunhofer IVV’s solvent-based recycling process, the research team was able to separate PP from unwanted polymers and additives, resulting in a material that was nearly 100 percent pure. The waste stream contained 33 percent PP and 67 percent foreign plastics. After the process, polyethylene (PE), accounting for less than 2 percent, was the only significant unwanted polymer. 

The team also ensured the stability of the PP recyclate (rPP) even at high temperatures during processing. The resulting recyclate was then spun into a multifilament yarn at the Fraunhofer IAP. “By using the right additive strategy, we were also able to significantly improve the processing stability of both PP and PET recyclates,” said Schütz.

For the glycolysis of PET, the researchers used PET cups containing 13 percent unwanted impurities. Glycolysis is a form of solvolysis in which ethylene glycol is used to depolymerize PET into bis(2-hydroxyethyl) terephthalate (BHET). The resulting BHET was repolymerized into rPET at the Fraunhofer IAP and processed into a multifilament yarn with 48 filaments on a pilot melt-spinning line. 

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Date: 08.12.2025

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A real option

In addition, the researchers were able to demonstrate that the same PET fraction can be recycled using a solvent-based recycling process. “We were able to produce fibers from both PP and PET for the manufacture of nonwoven fabrics, and PP can also be used for membrane production,” Tarkhanov summarizes.

Pyrolysis of residues from the solvent-based recycling process of PP fractions yielded a high proportion of pyrolysis gas and a low proportion of coke. Pyrolysis oil fractions with high oil content and low coke content were recovered from the residues of the solvolysis of PET fractions. The products from both feedstock streams show great promise for further utilization.

In addition, the accompanying studies showed that suitable and sufficient quantities of PP and PET are available, but the logistics and sorting systems needed to access them still need to be established. “We were able to successfully demonstrate that even previously unused material streams represent a viable option for the production of high-quality recycled-based materials,” Schütz summarizes.

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The way we handle plastics must change fundamentally. There is no alternative to moving toward a circular plastics economy, in which fewer fossil resources are extracted and products are used for longer. This is where the Fraunhofer CCPE cluster comes in. Six Fraunhofer Institutes are conducting research on how products can be designed for a circular economy and how plastic waste can be transformed into valuable resources. The cluster includes the Fraunhofer Institutes for Environmental, Safety, and Energy Technology (UMSICHT), for Applied Polymer Research (IAP), for Chemical Technology (ICT), for Structural Durability and System Reliability (LBF), for Material Flow and Logistics (IML), and for Process Engineering and Packaging (IVV).

Roles of the Project Partners

• Fraunhofer Institute for Environmental, Safety, and Energy Technology UMSICHT: Investigation of the degradation processes of biopolymers; pyrolysis of the residual fractions from the recycling processes used

• Fraunhofer Institute for Applied Polymer Research IAP: Polymerization of rPET from BHET; implementation of spinning processes

• Fraunhofer Institute for Chemical Technology ICT: Chemical Recycling—Depolymerization of PET to BHET from Recycled Material Streams

• Fraunhofer Institute for Structural Durability and System Reliability LBF: Project management, development of additive packages for recycled materials and biopolymers, compounding

• Fraunhofer Institute for Material Flow and Logistics IML: Selection of Suitable Raw Material Sources

• Fraunhofer Institute for Process Engineering and Packaging IVV: Development and Implementation of Solvent-Based Recycling

• Fraunhofer Institute for Molecular Biology and Applied Ecology IME: Ecotoxicological Assessment

• Fraunhofer Institute for Optronics, System Technology, and Image Analysis IOSB: Machine-Learning-Based Sorting of PET from Textiles