3rd November 2024, FILK
New materials on the rise
The increasing social relevance of sustainability is putting pressure on both politicians and industry, forcing them to act towards a climate-neutral economy. The consumer goods industry in particular is undergoing a fun-damental transformation that is focussing on the design of sustainable products. It is endeavouring to replace previously established materials based on fossil polymer systems with biogenic and fully biodegradable materi-als. A wide range of alternative materials, so-called "next-generation materials", are regularly presented. These materials quickly attract positive attention due to their "vegan", "sustainable" or "green" labelling. Objective information on physical, chemical and ecological material properties as well as information on specific material behaviour, taking into account the multiple stresses and effects of wear and tear that occur during processing and use, is often not available for these material classes, or only to a limited extent. However, this knowledge of the material, application properties and manufacturing processes is of great importance for informed material selection and design decisions in the textile, fashion, leather and footwear industries.
Resources are finite
A circular economy aims at reusing consumed materials and ideally, product cycles become closed according to the cradle-to-cradle principle [1,2]. “Bio-based” means the use of biogenic raw materials to manufacture a variety of products instead of fossil gas, coal, or petroleum as part of the bioeconomy. Lastly, “biodegradable” means that a material can be degraded in the environment by microorganisms and physicochemical impact. Recently, the societies of the countries of the Global North have experienced a strong change in their mindset due to the discussion about climate change, finiteness of resources, the overutilization of ecosystems, and the pollution of the environment by non-degradable or harmful substances. This affects especially the consumer goods industry and the designers of new materials aim to replace fossil-based polymers with biogenic and fully biode-gradable materials while being animal-free and without the use of any harmful substances. Ideally, the new materials are made from domestic waste, sawdust, or organic garbage [3–5]. These materials often are aimed to replace leather.
Where we come from: Leather
Leather is a bio-based and biodegradable material with a tradition nearly as long as mankind. For centuries, it was used as a strong and long-lasting material with a broad spectrum of materials properties. Leather was used as protective and decorative clothing for sports goods and as technical material, e.g., for transmission belts, bu-ckets, or as wineskin. Until the middle of the 19th century, leather occupied the materials property gap of a flexible material besides stone, metal, and wood as hard materials and various textiles, which were not water-proof. Processing allowed adjusting the leather properties from a hard board-like appearance, e.g., as sole leather to very soft touch textile-like glove leathers. The basic structure is an animal skin, which can be described as a non-woven with different density gradients in grain, papillary and reticular layer. Leather shows a number of unique properties, which are highly valued for purposes such as strength and elasticity, water vapor permeability, abrasion resistance, durability, and longevity.
Alternatives from the last century
During industrialization, alternative materials were invented, first and foremost the oil clothes made from textiles (linen, cotton), which were soaked or coated with boiled linseed oil and added with fillers, siccative, and pigments [6]. The next level of coating textiles was achieved by the use of natural rubber but only the discovery of vulcanization led to non-sticky films [7]. More and more new materials emerged with the invention of additional synthetic polymers, which allowed the replacement of leather in many applications. Synthetic polymers enabled customized and high-performance solutions that outperformed leather by far for technical applications in gears, conveyor belts, or vessels. In the past, synthetic materials competing with leather triumphed due to lower prices, they are often easier to be processed and can be manufactured as a continuous material according to industrial needs in roll-to-roll production lines.
Synthetic alternatives usually consist of textile support covered by two or more synthetic polymer layers. Nowadays, often polyester textiles coated by PVC or polyurethane films are used, making them a completely fossil-based material. The surface optic can be designed leather-like by embossing a grain structure. Many diffe-rent terms are used to describe these materials in the market, e.g., artificial leather, synthetic leather, leathe-rette, imitation leather, faux leather, man-made leather, bonded leather, pleather, textile leather, or polyure-thane (PU)-leather. However, leather is still popular due to its beneficial properties, natural appearance, and a touch of noble material.
New strategies
In recent concerns over sustainability in any field of industrial production have led to a pressing rationale to enhance the use of natural materials and replace nonrenewable fossil-based raw materials. Although leather is bio-based and renewable, these considerations did not lead to a renaissance of leather. Instead, leather got even more under pressure due to ongoing discussions over the greenhouse gas emission of cattle breeding, the sustainability of leather production, and animal welfare. At the same time, an increasing number of people want to eat consciously meat-free or to do without any products of animal origin entirely. All these needs pose new challenges in culture and material development [3]. Alternatives were developed as well in design-driven applications such as upholstery, shoes, and clothing.
One strategy pursues the development of alternative nature-based, animal-free fibrous materials. One choice is to make use of fungi and mycelium. The extraordinary soft feel of the dry mycelium makes it a precious material for cups and handcraft accessories and already the Ice-man used it as a material in combination with leather [8,9]. Due to the complicated and restricted harvest of fungi grown in the forest (e.g. trama), new ways are paved by using biotechnological processes to produce mycelium fibre based materials [14,15]. Furthermore, fungi and symbiosis of bacteria and yeast are used to produce fibrous networks aiming to imitate the fibrous structure similar to an animal skin as single materials or as support for a coating layer. Micro-cellulosic fibre networks are produced by bacteria (e.g., Acetobacter xylinum), the mycelium fibre networks of fungi hyphae consist of chitin, cellulose, and proteoglycans [5,10,11]. These mycelia grow on organic waste [11,12]. In a se-cond strategy, it is tried to reduce the non-renewable content of artificial leather by replacing parts of the sy-nthetic component polyvinylchloride (PVC) or polyurethane (PUR) of synthetic coatings with agricultural waste-derived products as filling material, such as grain, apple pomace , or milled cactus leaves . A third way to replace all fossil-based raw materials in a coated textile has been explored by using fibres of pineapple leaves that are processed into non-woven support coated with polylactic acid (PLA) produced from corn starch [13].
Decisive: Application properties
Regardless of the type of material, it can be leather, artificial leather, or another material alternative, a couple of physical and mechanical limits are usually defined and have to be achieved in order to fulfil consumer needs for a product with high utility value, comfortable wearing properties and durability. These limits must be evalua-ted in regard to the stresses associated with the production, processing, and use of the materials. In general, examinations to qualify materials and to quantify their properties need to be performed according to standardi-zed testing procedures. An intensive examination of these materials is therefore urgently required in order to choose the best material for an intended purpose, keeping in mind that the durability of a material will add to sustainability. These interdependencies need to be addressed as well in research, production, design as in edu-cation and training (see [16,17] for properties and degradability of selected materials).
Scientifically determined material information is not only indispensable in teaching and training, but must also be made accessible to society. Raising society's awareness of a more sustainable lifestyle and consumer behaviour by translating objective key data into a "language" that everyone can understand, informed purchasing decisions can be made by the end customer and enable a transfer from science to practice. In addition, social issues such as resource conservation, the circular economy, environmental and health protection as well as the key issues of non-toxicity, ecological footprint and social responsibility shall be addressed. This stimulates a resourceefficient, circular and competitive economy in the long term, which can make a positive contribution to climate and environmental protection. Cooperation with material manufacturers and developers is not only important for informing the public, but also promotes the production of sustainable materials and the manufacture of products from these materials.
.................
1. Braungart, M.; McDonough,W.; Bollinger, A. Cradle-to-cradle design: Creating healthy emissions—a strategy for eco-effective product and system design. J. Clean. Prod. 2007, 15, 1337–1348.
2. McDonough, W.; Braungart, M.; Anastas, P.T.; Zimmerman, J.B. Applying the principles of green engineering to cradle-to-cradle design. Environ. Sci. Technol. 2003, 37, 434A–441A.
3. Peters, S. Sustainable Multipurpose Materials for Design. In Materials Experience: Fundamentals of Materials and Design; Karana, E., Pedgley, O., Rognoli, V., Eds.; Elsevier: Amsterdam, The Netherlands, 2014; pp. 169–179. ISBN 978-0-08-099359-1.
4. Peters, S. Materialrevolution II: Neue Nachhaltige Und Multifunktionale Materialien Für Design Und Architektur;Walter de Gruyter: Berlin, Germany, 2014; ISBN 3-03821-000-5.
5. Goh, W.; Rosma, A.; Kaur, B.; Fazilah, A.; Karim, A.; Bhat, R. Microstructure and physical properties of microbial cellulose produced during fermentation of black tea broth (Kombucha). II. Int. Food Res. J. 2012, 19, 153–158.
6. Tuttle, F.J. The story of coated fabrics: I-development of oilcloth. Text. Res. 1944, 14, 228–232.
7. Tuttle, F.J. The story of coated fabrics: II-rubber and pyroxylin coatings. Text. Res. 1944, 14, 260–269.
8. Peintner, U.; Pöder, R.; Pümpel, T. The iceman’s fungi. Mycol. Res. 1998, 102, 1153–1162.
9. Papp, N.; Rudolf, K.; Bencsik, T.; Czégényi, D. Ethnomycological use of Fomes Fomentarius (L.) Fr. and Piptoporus Betulinus (Bull.) P. Karst. in Transylvania, Romania. Genet. Resour. Crop Evol. 2017, 64, 101–111.
10. Domskiene, J.; Sederaviciute, F.; Simonaityte, J. Kombucha bacterial cellulose for sustainable fashion. IJCST 2019, 31, 644–652.
11. Haneef, M.; Ceseracciu, L.; Canale, C.; Bayer, I.S.; Heredia-Guerrero, J.A.; Athanassiou, A. Advanced materials from fungal mycelium: Fabrication and tuning of physical properties. Sci. Rep. 2017, 7, 41292.
12. Cerimi, K.; Akkaya, K.C.; Pohl, C.; Schmidt, B.; Neubauer, P. Fungi as source for new bio-based materials: A patent review. Fungal Biol. Biotechnol. 2019, 6, 17.
13. Available online: https://www.ananas-anam.com (accessed on 30 December 2020).
14. M. Jones, A. Gandia, S. John, und A. Bismarck, „Leather-like material biofabrication using fungi“, Nat Sustain, 2021, 4, 1, 9–16, , doi: 10.1038/s41893-020-00606-1.
15. Thomasset,A.; Schröpfer, M.; Begue, D.; Mondschein, A.; Investigations on alternative materials: Processing trials for crosslinking and finishing of mycelium materials. 11th Freiber Leather Days, 2023.
17. Meyer, M.; Dietrich, S.; Schulz, H.; Mondschein, A.: „Comparison of the Technical Performance of Leather, Artificial Leather, and Trendy Alternatives“, Coatings, 2021, 11, 2, doi: 10.3390/coatings11020226.
15. Sardroudi, N.P.; Sorolla, S.; Casas, C.; Bacardit, A.: „A Study of the Composting Capacity of Different Kinds of Leathers, Leatherette and Alternative Materials“, Sustainability, 2024,16, 6, p. 2324 doi: 10.3390/su16062324.
3rd November 2024, FILK