Technology radar for the textile industry
The ban on the so-called "C8 chemical", which came into force in mid-2020, and the ban on the so-called "C6 chemical", which will follow in the foreseeable future, have affected the existence of some Bavarian textile companies and their customers. Today, Bavarian textile companies make approx. 60% of their turnover with technical textiles such as protective textiles, automotive textiles or filter materials for engines and industrial technology and are currently still dependent on the use of the PFC-based C6/C8 chemistry. Identifying and researching new, PFC-free and, if possible, ecologically sustainable approaches for water, grease and dirt-repellent finishing of textiles is therefore crucial for the future of the Bavarian textile industry.
Project "Technology Radar - Alternatives for C6/C8 chemistry in the textile and apparel sector"
In the project "Technology Radar - Alternatives for C6/C8 chemistry in the textile and apparel sector" carried out by Bayern Innovativ, alternatives for C6/C8 chemistry were identified in collaboration with stakeholders from industry and science and these were evaluated in terms of innovation potential, technology readiness level and necessary research needs. The aim was thus not merely to present possible solutions, but above all to pool expert knowledge in order to obtain an assessment of the identified approaches and a statement on their future viability.
In carrying out the project, it was possible to draw on existing knowledge that had been developed as part of the study "Textile & Sustainability" in 2018. Here, potential alternative solutions to C6/C8 chemistry were identified and discussed through intensive research work and extensive expert interviews. The results presented in the study formed the basis for an expert workshop held in Nuremberg on March 6, 2019. Here, a selection of possible alternative solution approaches to C6/C8 chemistry was intensively discussed and evaluated with a small group of experts (6 experts from the textile industry and science).
In a second step, an anonymized survey was conducted as part of the Kongress Textil Innovativ on 12.03.2019 in Lindau . Twenty-six congress participants took part in the survey - experts in the various stages of the textile chain (fiber, finishing, finishing, chemistry, surface formation, mechanical engineering) and users of textile materials (sports, outdoor, fashion, technical textiles).
The knowledge gained along the way about forward-looking technology approaches was processed and presented in the form of a technology radar .
Results of the project and the "Textile & Sustainability" study
The expert opinions gathered as part of the "Textile & Sustainability" study and this project do not indicate that a clear, universal alternative solution for the C6/C8 chemistry used to date in the textile industry is emerging that enables both water-repellent and dirt- and oil-repellent properties. There are a number of possible solutions, all with different advantages and disadvantages. These are:
1. Surface modification by plasma treatment
Plasma technology has been in the sights of the textile industry and research activities for many years. It can be used to modify surfaces of fibers, yarns and textile surfaces in a targeted manner. Possible applications include not only the cleaning and chemical activation of surfaces, but also the endowment with functional groups and coating. This can also be used to achieve properties that cannot be realized with conventional wet-chemical processes.
So far, the technology for functionalizing textile materials has not been able to gain full market acceptance. One reason is the high investment costs. By contrast, plasma technology for pretreatment in coatings is state of the art: this improves wettability and thus achieves better properties and longer durability of the functions. Other plus points include lower chemical usage and a fundamentally dry process. In the wake of upcoming REACH restrictions, the technology could become more attractive for functionalizing textile materials - especially in terms of water- and oil-repellent properties.
2. Development and use of novel material composites
Research projects that investigate the effect of previously unused material composites are very promising. For example, a project at DITF from 2014 to 2016 investigated the influence of incorporating cellulose on water-repellent coatings made of polyurethane (PUR). After the addition of cellulose particles, a graduated but in some cases significant increase in water vapor permeability (and thus breathability) was achieved without significant loss of waterproofing or mechanical properties. A savings potential of up to 40% PUR is thus possible.
3. Surface structuring by means of (UV) laser
Future potential is offered by the transfer of non-industry-specific processes for the microstructuring of surfaces such as laser technology. Laser technology can be used to realize functional structures in the millimeter, micrometer as well as nanometer range - through targeted material removal or targeted elevations. Laser technology can also be used in the pretreatment of coatings. There is no single laser technology that can be used to process all materials. A wide variety of wavelengths, pulse durations and powers are available, as well as processing optics and motion mechanics. Currently, laser technology for textile applications is still too slow and not available on an industrial scale. Intensive research is being conducted in several places on future application in material processing and surface structuring for textiles.
4. Surface functionalization using printing technology
A major growth market in textile finishing is digital printing . When it comes to "fashionable" applications, digital printing already occupies an important position today. The high process speed and precision of ink application, but also the sustainability of the technology, make digital printing increasingly interesting for surface functionalization of textile materials as well. As a minimal application technology in the field of functional and technical textiles, it thus has great application potential. This is because it can be used not only to apply functions locally/partially/selectively, which reduces the use of chemicals and conserves resources, but also to represent various functions that could not be combined previously (different printing on the front and reverse sides).
5. Further development and use of paraffins/dendrimers
Over the past few years, companies, especially from the outdoor industry , increasingly taking steps to realize DWR (Durable Water Repellent) finish without PFCs (Perfluorinated Chemicals). At the moment, this type of finish is mainly produced using petrochemically manufactured kerosenes, dendrimers, polyurethanes or silicones. A number of studies have shown that a PWR finish based on hydrocarbons or silicones has a water repellency comparable to C6/C8. Against low-polarity liquids such as oils, non-fluorinated DWRs show only reduced to no repellency. End products treated with them soil more quickly and are therefore not suitable for protective workwear.
6. Further development and use of waxes/oils/greases
In addition to petrochemically produced substances, bio-based oils, greases or waxes are also conceivable as a basis for a PFC-free DWR finish. In part, corresponding systems are already available on the market, at least for the production of ourdoor textiles.
7. Combination of fiber cross-section and surface formation
The possibilities for realizing different fiber cross-sections in the spinning-out process are used in man-made fiber production to achieve fibers with special functions. In addition to round and triangular fiber cross sections, there are also star-shaped and toothed ones, for example. There are also so-called hollow fibers. Round fibers, for example, exhibit very good conductivity, while hollow fibers provide very good thermal insulation. Surface formation also offers targeted opportunities for influencing the properties of a textile, among other things through the material used, strength and impermeability. Thus, this also offers possible starting points for the generation of water-, dirt- and oil-repellent properties.
8. Further development and use of hydrophobins
Among others, the Fraunhofer Institute for Interfacial Engineering and Biotechnology has been conducting research since 2016 in collaboration with the William Küster Institute, Bönnigheim, on a textile finish based on water-repellent proteins, so-called hydrophobins. These proteins occur naturally in the cell walls of fungi, where they have a protective function. They can be produced biotechnologically and chemically anchored on cellulose fibers. This leads to a change in surface energy and thus to strong hydrophobicity for cotton and cellulosic materials. However, the technology is still in the research stage. A similar project was launched in September 2017 at RWTH Aachen University in collaboration with the Fraunhofer Institute for Applied Polymer Research. The aim of the "PPfit" research project is to develop a PFC-free protein-based technology for soil-repellent finishing for fabrics made of polyester, flame-retardant polyester and polyamide for the application area of upholstery fabrics.
9. Functionalization with chitosan
Chitin from the shells of insects or the shells of crustaceans is considered to be an almost inexhaustible renewable raw material with great future potential. It is the second most abundant biogenic polysaccharide after cellulose. At present, technically usable sources are mainly waste from food production. Chitin can now also be produced biotechnologically with the aid of certain fungi. Chitin is further processed into chitosan by alkaline or enzymatic hydrolysis. Both chitin and chitosan form crystalline microfibrils and can be processed into fibers, films, membranes or colloids. Due to the wide range of properties (biocompatible, biodegradable, low toxicity, non-allergenic, antibacterial, antiviral, fungistatic, odor-binding, fat-binding, hemostatic, coagulant, etc.), there are numerous possible applications in the fields of medicine, pharmaceuticals, cosmetics, paper, agriculture, food, wastewater treatment and textiles. Hundreds of patents exist worldwide.
At the Fraunhofer Institute for Interfacial Engineering and Biotechnology, a new biotechnological process has been developed together with six international partners since 2015 as part of the joint project "ChitoTex" to make insect chitin usable as a functional coating for yarns and fabrics in the textile industry. With partners from the textile industry, research is to be carried out into how chitosan can best be functionalized and applied to textiles. Two different approaches are being pursued. On the one hand, chitosan can be used as a sizing agent due to its ability to form films. A second possible application is the water-repellent finishing of textiles. Hydrophobic properties can be generated via chemical derivatization of the molecule. A chitosan-based finish could thus be considered as a bio-based substitute for fluorocarbons.
10. Functionalization with Cellulose
Among others, the German Textile Research Center North-West is working on the coating and finishing of textiles with various cellulose modifications. The resulting hydrophilization of synthetic fibers influences wettability, antistatic properties and interaction with process chemicals. Furthermore, water vapor permeability is optimized, ideally resulting in increased wearer comfort. The good availability of ultrafine microcelluloses makes these products promising starting chemicals for the textile industry. Although nanocelluloses currently still have disadvantages in terms of price and availability, they are also extremely interesting economically due to their special properties and the resulting range of applications. In particular, nanofibrillar cellulose (NFC) shows great potential, as it is produced on a ton scale from waste products of the wood industry and is available at prices below 10 €/kg.
Application of the Technology Radar
The evaluation of the selected technological approaches was mainly based on the following three criteria:
- How important do you consider this topic/approach for solving the C6/C8 problem? (Choice between "completely unimportant", "unimportant", "neutral", "important", "very important")
- How do you estimate the time horizon of this complex of topics/approach until market maturity? (Choice between "0-3 years", "4-7 years", "8-15 years")
- What functionality do you think could be achieved with this thematic complex/approach? (Choice between "water repellency", "dirt repellency" and "oil repellency"; multiple selection possible)
On average, all approaches were rated as important or very important. There is still a need for R & D in all approaches. Further R & amp;E projects are needed to develop the approaches and explore the potential. The experts see the least research effort in waxes/oils/greases and in the area of fiber cross-section/area formation. The greatest F&E need is seen in hydrophobins and cellulose.
The Technology Radar provides an overview of the estimated importance and F&E needs of possible technological alternatives to C6/C8 chemistry in the textile industry. If one considers the evaluation of the solution approaches differentiated according to the function to be achieved (dirt, oil or water repellency), a somewhat more concrete picture emerges. 
Evaluation of the alternative solution approaches differentiated by the function to be achieved. Plasma technology, laser technology and material composites are attributed the greatest opportunities to come to an oil repellency. In the approaches digital printing, kerosenes / dendrimers, waxes / oils / greases and fiber cross-section / surface formation are seen only low chances for achieving an oil repellency. Bio-based solutions (hydrophobins, chitosan, cellulose) are not seen to have any chance in terms of oil repellency.
All approaches are seen to have potential for soil-repellent surfaces. According to the participating experts, plasma technology and digital printing have the greatest potential for soil repellency.
Paraffins/dendrimers and waxes/oils/fats are attributed the greatest potential for water repellency by the participating experts.
