From the Sector

Textiles for technical applications often derive their special function via the application of coatings. This way, textiles become, for example wind and water proof or more resistant to abrasion. Usually, petroleum-based substances such as polyacrylates or polyurethanes are used. However, these consume exhaustible resources and the materials can end up in the environment if handled improperly. Therefore, the German Institutes of Textile and Fiber Research Denkendorf (DITF) are researching materials from renewable sources that are recyclable and do not pollute the environment after use. Polymers that can be produced from bacteria are here of particular interest.

These biopolymers have the advantage that they can be produced in anything from small laboratory reactors to large production plants. The most promising biopolymers include polysaccharides, polyamides from amino acids and polyesters such as polylactic acid or polyhydroxyalkanoates (PHAs), all of which are derived from renewable raw materials. PHAs is an umbrella term for a group of biotechnologically produced polyesters. The main difference between these polyesters is the number of carbon atoms in the repeat unit. To date, they have mainly been investigated for medical applications. As PHAs products are increasingly available on the market, coatings made from PHAs may also be increasingly used in technical applications in the future.

The bacteria from which the PHAs are obtained grow with the help of carbohydrates, fats and an increased CO₂ concentration and light with suitable wavelength.

The properties of PHA can be adapted by varying the structure of the repeat unit. This makes polyhydroxyalkanoates a particularly interesting class of compounds for technical textile coatings, which has hardly been investigated to date. Due to their water-repellent properties, which stem from their molecular structure, and their stable structure, polyhydroxyalkanoates have great potential for the production of water-repellent, mechanically resilient textiles, such as those in demand in the automotive sector and for outdoor clothing.

The DITF have already carried out successful research work in this area. Coatings on cotton yarns and fabrics made of cotton, polyamide and polyester showed smooth and quite good adhesion. The PHA types for the coating were both procured on the open market and produced by the research partner Fraunhofer IGB. It was shown that the molten polymer can be applied to cotton yarns by extrusion through a coating nozzle. The molten polymer was successfully coated onto fabric using a doctor blade. The length of the molecular side chain of the PHA plays an important role in the properties of the coated textile. Although PHAs with medium-length side chains are better suited to achieving low stiffness and a good textile handle, their wash resistance is low. PHAs with short side chains are suitable for achieving high wash and abrasion resistance, but the textile handle is somewhat stiffer.

The team is currently investigating how the properties of PHAs can be changed in order to achieve the desired resistance and textile properties in equal measure. There are also plans to formulate aqueous formulations for yarn and textile finishing. This will allow much thinner coatings to be applied to textiles than is possible with molten PHAs.

Other DITF research teams are investigating whether PHAs are also suitable for the production of fibers and nonwovens.

Um zu verhindern, dass Mikroplastik aus Waschmaschinen in die Umwelt gelangt, haben Forschende des Fraunhofer UMSICHT den Zentrifugalfilter fibrEX entwickelt. Der flexibel integrierbare und wartungsfreie Filter trennt aus Waschwasser mikroskopisch kleine Kunstfasern ab. Aktuell werden potenzielle Partner für die letzten Schritte bis zur Markteinführung gesucht.

Textilien aus Kunstfasern wie Polyester und Elasthan halten Regen ab, sind strapazierfähig und dabei trotzdem elastisch. Ihr Anteil in hiesigen Kleiderschränken liegt bei über 60 Prozent liegt. Auch diese Kleidung muss gewaschen werden –im Fall von Sportbekleidung sogar sehr oft. Während des Waschvorgangs werden Fragmente der Kunstfasern abgerieben, die höchstens ein Fünftel so dick sind wie ein menschliches Haar. Aufgrund von Größe und Material zählen sie zu Mikroplastik, jenen mikroskopisch kleinen Kunststoffpartikeln, die – einmal in die Umwelt gelangt – nur schwer abbaubar sind.

„Zwischen 20 und 35 Prozent des weltweit verbreiteten Mikroplastiks sind synthetische Mikrofasern aus Textilien. Synthetische Textilien sind demnach eine der größten Mikroplastik-Quellen und stehen im Fokus von Politik und Gesellschaft“, so Dr.-Ing. Ilka Gehrke, Leiterin der Abteilung Umwelt und Ressourcennutzung am Fraunhofer UMSICHT. Auf europäischer Ebene laufen bereits Prozesse zur Vorbereitung von Richtlinien gegen die Freisetzung von synthetischen Mikrofasern. „In Frankreich etwa dürfen ab 2025 keine Waschmaschinen ohne Mikrofaserfilter mehr in Verkehr gebracht werden.“

Bisher sind kaum Waschmaschinen mit entsprechenden Filtern auf dem kommerziellen Markt erhältlich. Und solche, die es zu kaufen gibt, halten zwar die Mikrofasern zurück, verlieren aber schnell an Leistung. Die Kleinstfasern werden am Filtermaterial zurückgehalten, bilden eine Deckschicht und führen so zur Verblockung des Filters. Im schlimmsten Fall kann kein Waschwasser mehr abfließen, sodass der Waschprozess zum Stillstand kommt.

Als Lösung dieses Problems haben Forschende des Fraunhofer UMSICHT den kürzlich patentierten Zentrifugalfilter fibrEX entwickelt. Anders als ein Siebsystem, nutzt er die Dichteunterschiede von Kunstfasern und Wasser und trennt beim Schleudern die beiden Komponenten voneinander. Der Zentrifugalfilter kann sowohl in die Waschmaschine eingebaut als auch als externes Gerät betrieben werden; zum Betrieb wird keine weitere nennenswerte Energie benötigt.

Nach einer einjährigen Testphase im Waschlabor und technischen Optimierungen hält fibrEX nun dauerhaft und wartungsfrei mindestens 80 Prozent der synthetischen Mikrofasern aus dem Waschwasser zurück. Es werden Waschmaschinenhersteller gesucht, fibrEX gemeinsam zur Marktreife zu bringen.

The European Pultrusion Technology Association (EPTA) has published a report from its latest conference, which focuses on advances in sustainability and recycling.

More than 130 professionals from the global pultrusion community gathered at the 16th World Pultrusion Conference in Paris on 5-6 May 2022. Organised by EPTA in collaboration with the American Composites Manufacturers Association (ACMA), the event featured 25 international speakers sharing insight on market trends, developments in materials, processing and simulation technologies, and innovative pultruded applications in key markets such as building and infrastructure, transportation and wind energy.

‘Bio-pultrusion’:  
Composites based on natural fibres offer a number of benefits, including low density and high specific strength, vibration damping, and heat insulation. The German Institutes for Textile and Fiber Research Denkendorf (DITF) are developing pultrusion processes using bio-based resins and natural fibres. Projects include the BioMat Pavilion at the University of Stuttgart, a lightweight structure which combines ‘bamboo-like’ natural fibre-based pultruded profiles with a tensile membrane.

Applications for recycled carbon fibre (rCF):
The use of rCF in composite components has the potential to reduce their cost and carbon footprint. However, it is currently used to a limited extent since manufacturers are uncertain about the technical performance of available rCF products, how to process them, and the actual benefits achievable. Fraunhofer IGCV is partnering with the Institute for Textile Technology (ITA) in the MAI ÖkoCaP project to investigate the technical, ecological and economic benefits of using rCF in different industrial applications. The results will be made available in a web-based app.

Circularity and recycling:
The European Composites Industry Association (EuCIA) is drafting a circularity roadmap for the composites industry. It has collaborated with the European Cement Association (CEMBUREAU) on a position paper for the EU Commission’s Joint Research Centre (JRC) which outlines the benefits of co-processing end-of-life composites in cement manufacturing, a recycling solution that is compliant with the EU’s Waste Framework Directive and in commercial operation in Germany. Initial studies have indicated that co-processing with composites has the potential to reduce the global warming impact of cement manufacture by up to 16%. Technologies to allow recovery of fibre and/or resin from composites are in development but a better understanding of the life cycle assessment (LCA) impact of these processes is essential. EuCIA’s ‘circularity waterfall,’ a proposed priority system for composites circularity, highlights the continued need for co-processing.

Sustainability along the value chain:
Sustainability is essential for the long-term viability of businesses. Resin manufacturer AOC’s actions to improve sustainability include programmes to reduce energy, waste and greenhouse gas emissions from operations, the development of ‘greener’ and low VOC emission resins, ensuring compliance with chemicals legislation such as REACH, and involvement in EuCIA’s waste management initiatives. Its sustainable resins portfolio includes styrene-free and low-styrene formulations and products manufactured using bio-based raw materials and recycled PET.