Innovative approaches in textile recycling: expanding the horizons of sustainable practices

Climate change is increasingly noticeable and is one of the greatest challenges facing current and future generations.1 The textile industry is one of the largest emitters of greenhouse gases.2 Global sales in the clothing industry amounted to €1.5 trillion in 2022 and are forecast to rise to €1.93 trillion by 2028.3 However, 10% of global carbon dioxide (CO₂) emissions and 35% of the microplastics found in the world’s oceans are generated by the manufacturing of textile products.2,4 

The water consumption of this sector is enormous; almost 3000 l of fresh water are used in the production of a cotton top. In Bangladesh, for example, this leads to an annual lowering of the groundwater level by 2–3 m.5 Dye residues and other toxic chemicals are often discharged untreated into water bodies in the main producing countries, making the textile industry the third largest source of water pollution.6,7 

The average European needs around 400 kg of natural resources, such as cotton or energy sources, per year.8 In order to curb climate change, only 2000 kg of CO₂ may be emitted per capita per year – so only clothing accounts for 1/8 of the permitted volume.9 

The prevailing ‘fast fashion’ trend continues to exacerbate these problems. Rapidly changing product collections, manufactured in countries with lower labor costs and lower quality standards, are sold at low prices in European markets. While fashion brands offered two to three collections per year in the last century, today there are over 50.3,10,11 

In addition to clothing, technical textiles made from materials such as glass and carbon fibers are also a burden on the environment.12 Although the quantities are significantly lower compared with clothing and home textiles, the manufacturing processes are much more energy, resource, and emission intensive.12,13 

Sustainability and recycling of textile products have become imperative. Current developments are addressed and summarized in many publications. In recent publications addressing the issue, a distinction is usually made between mechanical, chemical, and bio-based recycling.14–20 The processes presented and their developments are divided into open-loop and closed-loop. Open-loop processes are defined as processes in which new, different products are developed from the products being recycled. In contrast, closed-loop processes involve recycling a product into a similar product.21,22 

Current descriptions of recycling processes are always limited to recycling back to the fiber, polymer or monomer state.12,23,24 These processes are referred to as product-to-fiber and product-to-resource processes in the context of this work, as new fibers are usually spun even if the processes return the textiles to a polymer or monomer state. From then on, the materials pass through the entire textile process chain again. The underrepresented other processes are a knowledge gap that will be investigated in this thesis. This work is intended to be a holistic presentation of textile recycling processes for clothing, home, and technical textile materials.

This publication is based on the structure illustrated in Figure 1. Previous research has primarily focused on mechanical, chemical, and bio-based processes, collectively summarized under the terms ‘product-to-fiber’ and ‘product-to-resource’. However, other significant approaches have received comparatively less attention: processes that revert to the yarn level (‘product-to-yarn’) and those that remain at the textile fabric level (‘product-to-fabric’). These approaches have not yet been sufficiently researched. Likewise, processes that have no possibility of producing fibers again are referred to as ‘product-to-fiber’. The category ‘product-to-resource’ is introduced to provide a holistic picture. The ‘product-to-product’ category, which includes extended use and second-hand processes but does not include recycling processes, is not covered in this study. The aim of this work is to provide a holistic picture of the technologies available for recycling textiles. This is important to gain a more comprehensive understanding of recycling processes in the textile industry and to develop more sustainable solutions.

Pyrolysis is the process of degradation of organic compounds by the application of heat in the absence of oxygen. The result of such a reaction can be solid (carbonized), liquid (bio-oil), or gaseous.25 The solid components are used in various approaches for new applications, such as adsorbents for removing pollutants, electrodes for sodium-ion batteries, supercapacitors, or as cement fillers.26,27 

The process is particularly suitable for repurposing textiles that cannot be separated or otherwise recycled.28,29 Being highly robust, the process allows for the processing of not only fiber blends but also soiled and finished textiles without the need for chemical pre-treatment. The textile products must be dried before the process, as remaining water would lower the temperature and worsen the result of the depolymerisation.30–32 

The addition of CO₂ and CO₃O₄ to the pyrolytic reaction increases the proportion of polyester monomers in the solid components of the reaction products. This enables them to the spinning of new fibers. The proportion and purity of these components are the subject of current research.33 

In the field of technical textiles, the process of pyrolysis is used to dissolve fiber-matrix composites. High-performance fibers such as carbon or glass fibers are produced at high temperatures. Depending on the subsequent application, carbon fibers, for example, are graphitized at 3000°C.34–37 

Some matrix materials already decompose at temperatures between 500°C and 700°C, which are far below those that affect the fibers.35 After the reaction, the matrix materials are also available in solid, liquid, and gaseous form and can be fed into new value-added processes. The dissolution of the fiber-matrix composite leads to a partial dissolution of the textile surface, i.e. yarns are partially untwisted and surfaces are isolated. As a result, the mechanical properties of the recovered yarns, for example, are impaired.35 

The process of gasification enables the conversion of carbonaceous materials into a combustible gas mixture. Carbon is converted into a gas consisting mainly of carbon monoxide, hydrogen, and methane at high temperatures and usually with the addition of a reaction partner such as oxygen, water vapor, or air. The difference to pyrolysis is the higher process temperatures (800°C–1400°C) and the presence of oxygen during the reaction to enable oxidation reactions. However, pyrolytic reactions in the form of polymer degradation also take place during gasification, as shown in Figure 2.38–40 

Textile waste is mechanically shredded and then fed into the gasification reactor. For polyester and cotton, it was found that the higher the temperature, the higher the gas yield. The resulting gases can be used to generate energy or as fuel.41,42 

This approach is a purely open-loop process, as no new fibers are spun from the composted materials. Currently, composting is mainly used for organic household and agricultural waste, less so for textile products.43 Fibrous material of purely organic origin becomes a very effective fertilizer through targeted modelling of the bacterial and fungal environment.44,45 

Animal wool contains important nutrients such as sulfur, sodium, and calcium. Wool also has excellent water retention behaviour and is slow to release nitrogen. These properties make wool an excellent fertiliser.46 The use of composted wool waste as a fertilizer has been shown to increase plant yields and thus offers utilization possibilities.46–48 

Chemicals used for dyeing and functionalizing textiles are a major problem in the composting of textiles. If the textiles are composted into fertilizer for plants or similar, these can have harmful effects on the environment. The use of various rhizophoric bacteria can significantly reduce these effects.49 

Fermentation is a biochemical process in which organic compounds are converted into acids, gases, or alcohol by microorganisms such as bacteria and fungi, as shown in Figure 3.

Stella et al. categorize the various fermentation processes in the context of textile recycling according to whether or not hydrolysis takes place at the same time as fermentation and whether or not the process is supported.50 

The glucose monomer is recovered from polysaccharide compounds, such as cotton, as already described in Equation 8. This is used to synthesize new products such as bioethanol, organic acids, or enzymes.51–53 

The fermentation process consists of several stages. Initially, used textile products are mechanically shredded, with optimal results achieved through pre-treatment. For the fermentation of cotton, an acid-based process is commonly employed. Arshi et al.54 have highlighted the potential of ionic liquids as a promising alternative. Subsequently, glucose is enzymatically broken down and, in the final step, fermented in a bioreactor at 37°C.54,55 

The mechanical recycling of textiles focuses on the dissolution of the textile surface through to the separation of the fibers. The bonds are loosened by applying mechanical force. Mechanical recycling can be divided into two categories, the most important process steps of which are shown in Figure 5. The first is pure mechanical recycling, also known as shredding, in which the fibers are separated and oriented by carding. Alternatively, there is thermochemical recycling, where the textile surfaces are dissolved, melted, and then new fibers are spun. This process is limited to thermoplastic fiber materials.

The most widespread of the established processes is purely mechanical recycling. The great advantage is the simplicity and the corresponding flexibility of the process. This process is applicable for both natural and synthetic fibers and for pre- and post-consumer textile waste.23,28,56 

The textile waste is sorted upstream of the actual recycling process. Ideally, the materials and colors are the same. This achieves optimum visual and mechanical properties. The problem of sorting is one of the biggest challenges in the field of textile recycling, as fiber blends such as cotton and polyester are standard, but are difficult to recycle together.28,57 In addition to the textile materials, there are all kinds of other elements such as buttons, zippers, and other applications on the product that need to be removed.58 

The process of mechanical recycling is outlined in Figure 4. The old clothes are cut into pieces of approximately the same size (1). The rollers with coarse teeth are used to tear the textiles apart (2). The pre-torn surfaces are rubbed onto the rollers one after the other and are transported to the main drum, where they are continuously torn further (3). The main drum, which is rotated at high speed, picks up the textiles. The textiles are gripped by the needles or teeth of the drum and are torn and separated into individual fibers. As the drum rotates, the fibers come into contact with the worker and doffer rollers. The fibers are further opened and mixed by these rollers (4). The fibers are grabbed by the worker rollers, which rotate more slowly, and are pulled apart. The opened fibers are picked up by the doffer rollers and are returned to the main drum. This cycle is repeated several times to ensure that the fibers are evenly distributed and aligned in parallel. Once the fibers have been sufficiently opened and aligned, they are removed from the drum by the scraper-rolls (5). The stripper is often connected to a counter-rotating roller that detaches the fibers from the teeth of the drum. The stripped fibers are then formed into a thin fiber pile called a card sliver (6). This fiber pile is loose and uniform, ready for further processing. Fibers that are too short and foreign bodies are detached from the roller and fall off (7).59–62 

The spinning of a new yarn presents a number of challenges. Due to the breaking up into individual fibers and the resulting tearing of these, the fiber length is shorter than that of virgin fibers. This corresponds to reduced strength, worsened pilling behavior, increased numbers of thick and thin spots, and more neps. In most cases, raw materials are added to the recycled fibers in the spinning process, as otherwise the yarn properties are not suitable for further processing.24,56,63,64 

The reduction of these weak points is the subject of current research. For example, the friction between the fibers can be reduced by prior treatment with polyethylene glycol. This reduction in friction leads to increased fiber length after carding and spinnability with 100% recycled fibers.65 

The card sliver produced can also be used as a starting material for nonwoven production. In the production line, the card sliver is further opened and evenly distributed before the fibers are stacked in several layers. These layers are then bonded using processes such as needle punching or chemical or thermal bonding to produce stable nonwovens. Finally, the nonwovens can be finished with additional treatments to achieve specific properties. For example, fiber composites66 or sound-absorbing panels67 for room acoustics can be produced.68 

In this form, mechanical recycling is primarily used for home and clothing textiles. Carbon fiber is the most prominent example of high-performance fibers; it is mainly used in fiber composites.69 Production is resource and energy-intensive, but the material properties are excellent.69,70 The challenge for recycling is the dissolution of the fiber-matrix composite. In purely mechanical approaches, the fiber composite is ground up, and the resulting product is very short fibers or dust.71 These can be used as filler materials in short fiber composites such as sheet molding compounds or fiber-reinforced concrete.71,72 

Thermomechanical recycling enables the spinning of new continuous fibers. The textiles to be recycled are sorted, cut, and shredded, as shown in Figure 5. The resulting flakes are then melted and turned into fibers in melt spinning systems. The prerequisite for this is a thermoplastic material.19,73,74 

Mondragon et al. were able to show in their work using the example of thermomechanical recycling of fishing nets made of PA6 that, in contrast to purely mechanical recycling, the physical textile properties deteriorate significantly less.74 

Repeated melting and re-spinning reduces the molecular mass of the fiber material.2 A reduced molecular mass corresponds to a reduced tensile strength of the fibers due to shorter polymer chains that are less strongly cross-linked with each other. At the same time, the shorter chains lead to improved dyeing and finishing behavior, allowing more free end groups to interact with the dye molecules.75–78 

Chemical recycling processes are concerned with the dissolution of particular materials. For each material, whether cotton, polyester, or polyamide, there are specific chemical processes that facilitate the recycling of that material. The majority of the work is concentrated on the processing of material mixtures, as the specific reactions in question do not affect other materials in any way. The Figure 6 depicts the most significant process stages for the most salient procedures.

Glycolysis is a chemical process in which polymers are broken down into monomers and oligomers by reacting with glycol. It is a depolymerization process. In the context of textile recycling, glycolysis is mostly used to break down polyethylene terephthalate (PET).79–81 Polyester is the most widely used fiber raw material for clothing textiles; in 2022, polyester accounted for 55% of global fiber production.82 For this reason, the recycling of polyester is of particular interest, and the process of glycolysis was patented for this purpose as early as 1961.83 

The main advantages of the process are its comparatively low energy consumption and the ability to separate mixed textiles. This is particularly interesting for PET fibers, as these are usually mixed with cotton, elastane, and other fibers.28,84 

The process of glycolysis of polyester takes place at a temperature of around 200°C with the addition of ethylene glycol and a catalyst. The catalyst is intrinsic to the reaction. Four types of catalysts can be used: metal salts, organocatalysts, ionic liquids, zeolites, metal oxides, and nanoparticles. The reaction is exemplarily shown in Equation 1, whereby it is assumed that oligomers are formed since the PET is not realistically completely converted into bis(hydroxyethyl)terephthalate (BHET) molecules.84–88 

Andini et al. described how typical clothing waste could be completely separated into its components using zinc oxide as a catalyst. A mixture of polyester, cotton, spandex, and nylon was analyzed. After the glycolysis process, the polyester is completely present as BHET, and the spandex as diphenylmethane-containing molecules in solution. Nylon and cotton were not involved in the reaction. The BHET is crystallized, with crystals of over 90% purity. The spandex reaction products remain in solution. Cotton and nylon were separated by dissolving the nylon with amido acid. The cotton can be reused directly, and the other materials could be re-spun.84 

The result of glycolysis is influenced by dyes and chemical functionalization. Dyes, antimicrobial, and antistatic functionalization are also present in solution after the reaction and could also be recycled. Ultra violet radiation and fire protection functionalization negatively influence the result of the reaction.84,89 

Water is used as a reagent to break down polymer chains in the process described. Many organic materials used in the production of textiles are not soluble in water. Increasing the temperature and pressure can significantly increase the reactivity of the system. Hydrolytic processes can be carried out under supercritical water conditions.32,90,91 

This process (Equation 2) is used to separate different materials. The most common mixture, polyester and cotton ((C₆H₁₀O₅)_n), can be recycled, for example, by adding phosphotungstic acid (H₃[PW₁₂O₄₀]))$$ as a catalyst. Cotton is obtained as microcrystalline cellulose ((C₆H₁₀O₅)_m) and polyester as terephthalic acid (C₈H₆).92 

The selected catalyst determines the result of the reaction. It is ensured by diluted hydrochloric acid that cotton is present as a microcrystalline cellulose powder, while the polyester remains in the fiber state without significant changes to the physical textile properties.93,94 

Catalysts can be recovered from the solution, but it would be far more environmentally friendly to dispense with additional chemicals and aim for pure hydrolysis. At process temperatures of 180°C–250°C, the polyester is separated from the cotton. After treatment, the cotton fibers are still present as a textile surface, and the polyester is a separate solid in the form of small pieces. However, the cotton is slightly affected by incipient chemical degradation due to the high process temperatures. The general feasibility of pure hydrolysis for separating fiber blends has been proven.91,95 

In the field of fiber composites, the process is used to dissolve the fiber-matrix bond. The hydrolysis of the matrix leads to its degradation and separates it from the fiber. Suitable matrix materials are required for this; unsaturated polyester resins are used in rotor blades, for example, and can be degraded by hydrolysis. Such hydrolysis processes are sometimes two-stage, as the matrix material is gel-like after the first hydrolysis reaction.96,97 

The application of this process is limited to the depolymerization of polyamides such as nylon $((-NH-(CH2)5-C=O-)n)$ or polyamide 6. The product of the reaction with ammonia (⁠$NH3)$ is caprolactam (⁠$C6H11NO)$⁠, which is used for the renewed polymerisation of polyamides, as shown in Equation 3.98 

The reaction takes place at comparatively low temperatures of 200°C–320°C. Depolymerization levels of up to 68% are achieved.98,99 

Methanolysis is a process in which polyester (PET) is broken down into its monomers terephthalic acid (⁠$C8H6O4$⁠) and ethylene glycol (⁠$HOCH2CH2OH$⁠) by a depolymerisation reaction with methanol.100 

This approach enables the effective depolymerization of polyester under mild conditions (50°C) and in a short reaction time (2 h) using inexpensive alkali-methoxide catalysts.101,102 

Ionic liquids are salts that exist in a liquid state at temperatures below 100°C. They are composed of positively charged cations and negatively charged anions, which form a liquid devoid of a significant vapor phase. Modulation of the chemical–physical properties of the liquid is achieved by altering the ratio between the aforementioned components. These solvents are employed in the context of textile recycling. Due to their diverse and malleable properties, they are employed for a plethora of materials and material combinations. Following the completion of the reaction, ionic liquids can typically be recovered.103–106 

The textiles must be pre-treated before using the ionic liquids, as shown in Figure 6. Using the example of clothing textiles made from hemp fibers, these were treated using sulfuric acid H₂SO₄ and the mixture is dissolved using sodium hydroxide NaOH neutralized. The product of this reaction is rinsed with deionized water and then dried. The reaction then takes place with the ionic liquid, in this example 1.5-diazabicyclo[4.3.0]non-5-enium acetate. This results in a cellulose-1,5-diazabicyclo[4.3.0]non-5-en (DBN) acetate solution. The reaction equations are represented step by step by the Equations 5–7. After the remaining solids have been filtered out, new fibers are spun from the solution using a wet spinning process. It is possible to preserve the color of the textiles used, as this is also retained in the solution.107 The new fibers have significantly better textile-physical properties than the end-of-life products from which they were obtained. Fiber blends such as polyester and cotton can be separated using this process.108–110 

Step 1: Dissolving the hemp fibers with sulfuric acid

Step 2: Neutralization with sodium hydroxide

Step 3: Preparation of the cellulose DBN acetate solution

Despite their versatility and chemical stability, ionic liquids also have considerable disadvantages, particularly with regard to their environmental compatibility. Their high stability is accompanied by limited biodegradability, which can lead to potential accumulation in the environment.111,112 The toxic properties of ionic liquids depend largely on the type of cation and the length of the side chain, resulting in different ecological risks depending on the structure, whereby degradation products of different ionic liquids can also be toxic.111 In addition, many ionic liquids have antibacterial and antifungal properties and are capable of destroying cell walls. In combination with their poor biodegradability, this results in a considerable ecological hazard potential. Studies show that ionic liquids can damage plant cell structures, which is associated with a reduction in chlorophyll content and reduced plant growth.112–114 

Bio-based recycling processes are limited to organic fibers, such as natural fibers like cotton or synthetic fibers based on carbon polymers.115 The most important procedures are broken down in this chapter and the previous one in product-to-resource recycling. Figure 3 shows these with their key process steps.

One of the main advantages of these processes is that they require far less energy than other recycling options. Nevertheless, this approach is not automatically the most environmentally friendly; the use of chemicals for preparation and enzymes for the actual process must not be neglected. Another advantage is that since only natural fibers can be used, these processes are able to separate polycotton (cotton polyester blend), as only the cotton part is attacked, leaving the pure polyester behind.18,115–117 

The polymer fibers are reduced to their monomeric basic building blocks through the biological recycling of textiles based on enzymes, which can then be used to produce new materials. The re-spinning of fibers from monomers achieves textile-physical properties of the new material.18,50 

Enzymes degrade a specific material, which is why this process is used to separate fiber mixtures, which is difficult to achieve with other processes.118 The most common blend in the clothing industry is cotton with polyester.119 The separation of these fibers is often difficult as they are already mixed at the yarn level. As shown in Equation 8, the use of cellulases enables the polysaccharide cotton to be broken down into glucose. This can be further used in multiple ways, the other fiber material remains undissolved and can be used elsewhere in pure form.118,120–123 

In addition to natural fibers, this process can also be applied to synthetic organic fibers such as nylon. The enzymatic depolymerization of nylon involves the enzymatic cleavage of the amide bonds in the polymer chain, which leads to the formation of shorter oligomers. These oligomers can then be further broken down into monomers, which are recycled or used to respun into nylon.124,125 

So far, this method is still on a laboratory scale and is not technologically mature enough for industrial use.126 A life cycle analysis (LCA) relating to the treatment of cotton polyester blended fabrics has shown that the chemicals used in the pre-treatment process and the process temperatures required for this have the greatest impact on the environmental balance.116 The current process conditions, including a 6-h treatment at −20°C, followed by drying at 40°C for 48 h,120 result in considerable energy consumption and make the process economically unviable under current conditions.126 

The binding element of knitted surfaces is the stitch.34 These are built up stitch by stitch in a row and joined to the previous stitch. The continuity of the fiber material offers the possibility of recovering the yarn as a whole compared with other textile surfaces, shown in Figure 7.127 

In the craft sector, it is common practice to unravel knitted products in the event of faults or to recycle products.128,129 Thus, clothing can be unraveled at the end of the product life cycle. The yarn is deformed by the stitches; in the case of new products, such as unsold collections, the yarn has a knittability of 99%. End-of-life textiles, on the other hand, are damaged by washing cycles, which reduces the knittability to 95%. Ironing reduces the knittability enormously with each cycle.127 

The separation process has already been automated, but is only poorly represented in current research.130,131 

The recycling of textiles into new products without disintegrating the original surface offers a number of advantages that encompass both ecological and economic dimensions. A key advantage of this process is that the entire textile technology value chain does not have to be run through again. This saves emissions and resources.132 Instead, textiles can be recycled by specifically utilizing their existing properties and functions. For example, the waterproofness of an old tent can be retained in a new jacket, thereby preserving the original functional characteristics of the material. Furthermore, the use of potentially harmful chemicals, which are often required when processing textiles for new production, is avoided by this method.

Despite its great advantages, this recycling pathway has received little attention in a scientific context to date. The existing problems in the processing of textiles, such as the removal of button plackets, zips, and similar components, are not only challenges for established recycling processes, but also pose a particular difficulty for this approach. Seams have to be undone, damage and soiling recognized, and specific treatment measures taken. In addition, such a recycling strategy must already be taken into account during the design process. For established recycling processes, design for recycling mainly involves the use of mono-materials. For this strategy, additional decisions have to be made, such as seam type, pattern design, material, and so on. Particularly small pattern pieces are difficult to reuse later on.133–135 

In the economic context, however, this form of recycling is already established and meets with great approval.136 Numerous companies have adopted this method and offer products made from recycled textiles. A selection of successful companies with their corresponding business models is shown in Table 1. An issue that is often observed in this context is the use of old products or materials to manufacture mostly the same new products, such as backpacks or purses. Even if the manufacturing processes, insofar as they are transparent, are often manual, there is still no generally recognized, automated process that works reliably for a wide range of end-of-life products. This automation gap represents a significant hurdle and currently limits the scalability and efficiency of recycling processes.

The entire product can never be recycled by this process. Parts such as seam edges and stained or damaged areas must be recycled in another way. One possible route is shown in Figure 8 outlined above.

Although the recycling of textiles without breaking up the surface offers several advantages, particularly in terms of preserving functions and avoiding harmful chemicals, there are still challenges in both scientific and economic terms. The further development of automated processes for the treatment of used textiles has the potential to be a key to the optimization and widespread use of these recycling processes.

Mechanical recycling is currently the most widely used method in textile recycling and is characterized by its simple implementation.156–159 In many cases, no sorting or pre-treatment of the old clothing is necessary, as it can be processed directly into nonwovens for insulation materials or painter‘s underlays. The process becomes more complex when new yarn is to be produced from recycled material, as the fiber length plays a decisive role here. Sorting is also necessary to consider the different dyeing behaviour of the source materials.

Chemical recycling processes are becoming increasingly important as they enable the recovery of high-quality fibers and therefore offer greater potential added value.156,158,159 However, a major disadvantage of these processes lies in their material specificity; often only certain source materials, such as polyester-cotton blends, can be treated in a targeted manner. Companies such as Worn Again160 and Ioncell161 use chemical processes to separate cotton and polyester, for example, with Ioncell using ionic liquids for this purpose. Aquafil,162,163 on the other hand, produces the regenerated nylon ‘Econyl’ from old fishing nets. However, chemical processes require complex sorting and pre-treatment to avoid undesirable reactions. Processes such as hydrolysis or glycolysis are currently only implemented on a laboratory scale.159 

Bio-based recycling methods, such as enzymatic depolymerization, are already being used in demonstration plants, but are not yet established on an industrial scale to the same extent as mechanical or chemical processes.164 

Another field of research is the mechanical separation of knitted clothing, which has not yet been technically implemented.

As shown in Table 1, there are already numerous companies that manufacture new products from used textiles. However, these processes are mainly carried out in manufacturing operations with a high level of manual effort, for example, in sorting, cutting, and making up, and have hardly been automated to date.

This study demonstrates that no universal solution exists that can address all the challenges of the textile industry. The heterogeneous distribution of materials in textiles and the diverse usage scenarios pose considerable obstacles to a standardized recycling process. Mechanical recycling processes are characterized by their robustness against different materials and impurities, but lead to a shortening of the fiber lengths, which impairs the physical textile properties of the recyclates. In contrast, chemical recycling processes often require the use of environmentally harmful chemicals and must be precisely matched to the material to be recycled in order to achieve a quality that corresponds to that of new materials.

In addition, it has been demonstrated that processes, which have received little attention to date and are not focused on recycling at the fiber or spinning solution level, could also make a significant contribution to resource conservation. These approaches offer potential, especially when it comes to remanufacturing materials that are still usable and recycling those that are heavily soiled or worn as profitably as possible, depending on their material composition. If none of these options are viable, the last option is thermal utilization.

Future work will therefore focus on multidirectional solutions that enable a holistic view of the various utilization potentials and recycling methods. In choosing methods, the one with the least environmental impact should be selected to mitigate the impact of the textile industry. For a well-founded selection and an appropriate comparison of different recycling processes regarding their environmental impact, further research is required in the future that includes standardized LCA. It is crucial that these analyses are based on uniformly defined system boundaries, comparable input flows, and standardized assessment criteria to enable reliable and meaningful results. This is the only way to objectively assess the ecological advantages and disadvantages of different technologies and make well-founded decisions for sustainable further development and scaling.

Not applicable.