From Waste to Value: Advances in Recycling Textile-Based PET Fabrics

Abstract

The environmental burden of textile waste has become a critical challenge for sustainable development. This review explores recent developments in the recycling of textiles, especially polyethylene tereph-2 thalate (PET)-based fabrics, with a focus on fiber-to-fiber regeneration as a pathway toward circular textile production. Recent developments in PET recycling, such as mechanical and chemical recycling methods, are critically examined, highlighting the potential of chemical depolymerization for recovering high-purity monomers suitable for textile-grade PET synthesis. Special attention is given to electrospinning as an emerging technology for converting recycled PET into high-value nanofibers, offering functional properties suitable for advanced applications in filtration, medical textiles, and smart fabrics. The integration of these innovations, alongside improved sorting technologies and circular design strategies, is essential for overcoming current limitations and enabling scalable, high-quality recycling systems. This review aims to support the development of a more resource efficient textile industry by outlining key challenges, technologies, and future directions in PET recycling.

1. Introduction

The rapid expansion of textile production has significantly increased textile waste worldwide, emphasizing the urgent need for sustainable waste management strategies. In particular, the scale of the problem is evident in the European Union (EU), where the textile industry generates approximately 16 million tonnes of waste annually [1,2]. The textile industry is a major consumer of natural resources and a significant contributor to environmental pollution, ranking second in land use, fourth in water consumption, and fifth in greenhouse gas emissions [3]. Despite increasing awareness of these environmental impacts, most textile waste still ends up in landfills, resulting in substantial resource loss and ecological harm. Landfilling remains the predominant method of textile waste management, although it is widely recognized as unsustainable [4]. Moreover, the textile and clothing industry is recognized as one of the largest contributors to global pollution, further underscoring the urgent need for sustainable waste management strategies [5]. Textile production was 24 million tons in 1976 and has continued to grow at an annual rate of 3.4%. It reached 113 million tons in 2021 and had further increased to 124 million tons by 2023. In Europe, the major textile subsectors include clothing and accessories (37%), industrial and technical textiles (17%), fabrics (15%), and home textiles (14%) [6,7]. However, this economic growth comes with significant environmental costs. By 2030, global textile waste is expected to reach 148 million tons, and by 2050, more than 150 million tons of clothing are projected to be incinerated or landfilled [8]. Between 2000 and 2023, a total of 2066 research articles related to textile waste management were published, with nearly 40% appearing after 2020, reflecting a sharp rise in academic and industrial interest. Approximately 60% of these studies fall within environmental science, materials science, and engineering, highlighting the interdisciplinary relevance of textile waste management and recycling [9]. By 2050, textile production is projected to consume 300 million tons of mineral oil and contribute to 26% of global carbon emissions [10]. The growing waste crisis, driven by fast fashion, increasing global consumption, and population growth, not only strains landfill capacities but also significantly contributes to greenhouse gas emissions, particularly CO₂ [11,12,13]. Under anaerobic conditions, biodegradable materials like cotton decompose, releasing methane and carbon dioxide, while incineration further exacerbates CO₂ emissions and global warming. Additionally, toxic dyes and chemical additives from textile processing often enter the environment untreated, contaminating soil and water. These pollutants, along with microplastics, pose serious health risks to humans and ecosystems, both locally and globally [14]. A cost-effective and sustainable solution to this issue is recycling textiles, which reduces reliance on petrochemical raw materials and lowers carbon emissions [15]. Polyethylene terephthalate (PET) is one of the most widely used synthetic polymers, as illustrated in Figure 1, with global production projected to reach 34 billion metric tons by 2050 [16]. Primarily utilized in beverage bottles and textile fibers, PET has attracted growing attention due to environmental concerns, prompting researchers to explore its recycling for various applications. PET is synthesized through a condensation reaction between terephthalic acid (TPA) and ethylene glycol (EG), both of which are derived from petroleum feedstock [17,18]. It is a non-toxic, non-renewable, and cost-effective thermoplastic polyester known for its excellent transparency, high strength, dimensional stability, barrier properties against moisture and oxygen, and chemical resistance [19]. Its high durability, moldability, and inertness have further established PET as a key material in the fashion and textile industry [20,21]. The production of PET typically involves three main stages: (1) pre-polymerization of bis(hydroxyethyl) terephthalate (BHET), (2) polymerization, and (3) polycondensation. In the initial stage, BHET polymerization occurs through two distinct reactions. The first is an esterification reaction, where ethylene glycol (EG) reacts with terephthalic acid (TPA), while the second is a transesterification reaction, in which EG interacts with dimethyl terephthalate (DMT) [22]. PET is commercially produced in four grades: fiber (including textile, technical, and tire cord), film (such as biaxially oriented PET film and sheet grade for thermoforming), bottle (used for water bottles and carbonated soft drinks), and monofilament [23,24]. Due to the challenges associated with collection, separation, and sorting, recycling of synthetic fibers remains limited. As a result, post-consumer textile collection rates vary widely between countries, for instance, only 11% in Italy compared to 75% in Germany, while some countries have no textile recycling systems in place at all [25]. Synthetic fibers account for 75% of all fibers produced globally, and nearly 80% in Europe, including Turkey. In 2021, the global production of these fibers reached approximately 113 million tons. Among synthetic fibers, PET is the most widely used for clothing applications, accounting for 54% of total fiber production [9]. Furthermore, 16,000 research articles, including reviews, and 1000 patents have been published for polyethylene terephthalate textile recycling in the last 10 years (2015–2025). Unlike many conventional polymers, polyester can be efficiently collected and recycled into new products. Recycling PET is crucial in addressing this crisis, as it significantly reduces plastic waste in landfills and oceans. The process involves collecting used PET products, converting them into new materials, and re-purposing them for manufacturing new products [26]. To mitigate PET waste accumulation, various recycling technologies have been explored, including mechanical, chemical, and biological recycling methods. Mechanical recycling is widely used but often results in downgraded material quality, limiting the reuse of recycled fibers [4]. In contrast, chemical recycling presents a promising alternative by breaking down PET into its monomer components, allowing for the production of high-quality recycled materials, and typically involves the use of catalysts to optimize reaction conditions, minimizing energy consumption and environmental impacts [27]. Plastics resist degradation, but physical and chemical environmental factors and microbial activity can accelerate their breakdown. Prolonged exposure to sunlight and physical abrasion fragments plastics into microplastics, which microorganisms can further degrade. Consequently, biological degradation and microbial metabolism are essential for removing plastics from contaminated environments [28]. A key mechanism in enzymatic PET degradation is the surface hydrophilization of PET fibers. On the surface of PET, whether in fiber or film form, polymer chain ends may protrude, or segments of the chain may form loops. These structures undergo hydrolysis, breaking down into carboxylic acid and hydroxyl residues, thereby increasing the surface hydrophilicity [29].

Despite advancements in recycling technologies, several challenges remain in effectively processing PET textile waste. One of the primary issues is the prevalence of blended textiles, particularly polycotton (a combination of polyester and cotton) [31]. These mixed fabrics are difficult to recycle due to the complexity of separating the constituent fibers. To further improve PET textile recycling efficiency, researchers are focusing on sustainable catalysts, optimized reaction conditions, and hybrid recycling approaches. Emerging technologies such as automated sorting systems, enzymatic hydrolysis, and fiber regeneration techniques hold promise for overcoming current limitations in recycling. Additionally, integrating mechanical and chemical recycling could extend the life cycle of PET fibers, enhancing their reuse potential, while minimizing environmental impacts [4,20]. PET nanofiber mats have recently been utilized in various applications, including filtration, protective clothing, biomedical fields such as tissue engineering scaffolds, electroconductive cardiac patches, and other emerging technologies [32]. One of the top methods for processing recycled textile PET waste is the electrospinning of these materials into textile fibers, which can also generate new valuable products. Electrospinning is a versatile and efficient technique for producing continuous fibers from various polymers, with diameters ranging from tens of nanometers to several micrometers [33,34]. Numerous studies have reported the application of various polymer compounds through electrospinning, including polyethylene terephthalate [35,36]. During electrospinning, a high voltage is applied to a liquid solution or melt, creating an electric field between two oppositely charged conductors, as shown in Figure 2. This charge induces polymer stretching, leading to fiber formation [37].

There have been various studies on the electrospinning of PET, but only a few researchers have studied the electrospinning of recycled PET. Melt electrospinning has been used to produce fibers ranging from nanometers to a few micrometers, primarily for applications in smoke and air filtration, oil–water separation, and, to a lesser extent, anti-infective therapy [38]. It is important to note that research on recycled materials has been gaining increasing interest. Polymer melt spinning is an effective technique; however, this method requires significant energy due to high heat demands and often results in inferior mechanical properties due to repeated heating cycles, and an alternative approach is electrospinning recycled PET from solvents, which offers greater control over fiber morphology and could overcome these limitations [39,40]. Hossaein et al. [41] reported the fabrication and characterization of a nanofibrous membrane derived from recycled PET bottles in a mixture of DCM/TFA solvents for air filtration applications to address the ongoing global air pollution crisis. Mehdi et al. [42] explored the application of recycled PET waste bottles by electrospinning them in a mixture of TFA/Chloroform solvent with doped dyes to produce colorful, cost-effective, and energy-efficient nanofiber mats. Gawrońska used 1,1,1,3,3,3-hexafluoro-2-propanol (HFP) as a solvent to prepare an electrospinning solution from recycled PET bottles [43].

This review explores sustainable methods for recycling and modifying textile PET waste by evaluating processing technologies and assessing their global availability. It explains the typical process for recycling PET waste as textile or bottle waste. A comprehensive overview of innovative approaches to repurpose PET waste into sustainable products is provided. Furthermore, this paper reviews municipal textile waste management systems and evaluates the strengths and limitations of each recycling model. These efforts are taking place in the context of dynamic and evolving conditions shaped by new regulations, breakthrough technologies, and a growing push toward circular economy (CE) practices throughout the textile industry. Recognizing these changes is key to understanding the challenges, as well as the opportunities ahead in PET textile recycling. In ISO 5157:2023 (textile value chain related to environmental and circular economy aspects including design, production, retail, use and reuse, recycling processes, repair and disposal), the term reuse is used broadly to cover three related end-of-life processes: reuse, repair, and re-manufacturing (3R). While all these involve some level of treatment to the product, the key point is that the product itself is kept intact throughout, rather than being broken down into raw materials for making new items [6]. The circular economy is currently one of the most widely promoted strategies for transforming the fashion industry. As outlined in the EU’s Circular Economy Action Plan 2020, a dedicated EU Strategy for Textiles is underway. Even before this, some major fashion brands had already begun adopting CE principles by collecting, reselling, or reprocessing used clothing. In both industrial practice and the academic literature, two key approaches stand out: (1) recycling textiles and their components, and (2) extending product life through reuse [44]. Systemic changes such as degrowth, reduced consumption, extended product lifespans (through reuse, repair, or re-manufacturing), and minimizing waste to preserve the resources—materials, energy, water, and chemicals—involved in textile production are addressing textile supply chain waste. However, these changes take time and do not address the massive volume of textile waste already being discarded. This highlights the urgent need for effective recycling solutions. Achieving a true circular economy in textiles depends on scalable, sustainable production systems paired with advanced recycling technologies [45]. Another key aspect of tackling textile waste is analyzing and improving textile fabrication technologies to reduce the waste generated during production. One way to lessen environmental impacts is by avoiding unnecessary textile manufacturing altogether, rather than transporting large amounts of waste over long distances for recycling. However, if the original production method is already relatively low in pollution, the environmental benefits of replacing it may be minimal [46]. The future scenario analysis considered potential improvements in recycling technology and changes in energy supply, while assuming constant consumption of chemicals, water, and energy for operations. It included updated energy mixes reflecting future projections, enhanced mechanical recycling methods with much higher material recovery efficiencies, and advancements in dissolving polycotton to enable simultaneous processing of both cotton and polyester components. The scenarios also assumed the elimination of yields from filling materials across all textile waste streams. Lastly, it anticipated increased electricity recovery efficiency from incineration due to improved future incinerator technologies [47]. Furthermore, the EU Strategy for Sustainable Textiles aims to significantly reduce the use of recycled PET (rPET) derived from bottles in textile production and instead encourages textile-to-textile recycling. At the same time, the textile industry’s goal of increasing the share of rPET in the upcoming years is driving the search for alternative sources of recycled materials [7].

2. The Global Textile Market

The textile sector is the second-largest employer worldwide, playing a crucial role in national economies and providing extensive job opportunities [48]. Textiles are fundamental materials in our society due to their wide range of applications. However, textile and clothing manufacturing contribute significantly to global climate change, water scarcity, and environmental pollution. Over the past few decades, production has increased substantially and become highly globalized [30]. The development of the global textile industry can be broadly classified into two main categories: controllable and uncontrollable factors. Controllable factors include different parameters under the industry’s influence, such as adjustments in product structure, investments in modern machinery, technological innovations, material and energy efficiency, human resource management, operational methods, and leadership strategies. In contrast, uncontrollable factors encompass broader external influences such as availability and management of natural resources (including labor, land, and water), government policies, and infrastructural frameworks [49]. In recent years, the textile industry has expanded rapidly, driven by rising global living standards and the growth of fast fashion. Fast fashion is a manufacturing and retail strategy designed to swiftly adapt to evolving fashion trends, providing consumers with affordable clothing. Global fiber production has been steadily increasing, reaching approximately 123 million tons in 2023, and if this trend continues, it is projected to exceed 160 million tons by 2030 [50]. The textile and apparel market is also expanding significantly. In 2014, the European Union (EU) and the United States accounted for 50% of global textile and apparel imports, making them the largest importers. The global apparel market size is projected to grow from USD 1.6 trillion to USD 2.6 trillion by 2025, driven largely by developing economies such as India and China, which are key contributors to the industry’s expansion [51]. The textile industry has the potential to recycle between 55% and 93% of its waste into valuable products, without generating significant hazardous waste or harmful byproducts. Despite this promising capability, actual recycling rates remain relatively low. In Europe, for instance, only about 25% of textile waste is currently recycled, while the textile recycling rate stands at just 16.2% in the US [52].

3. Recycling Process

Today, nearly all PET waste is recycled. Since raw materials account for three-quarters of the total production costs of PET fibers, utilizing recycled PET is one of the most effective ways to reduce production expenses [24]. Recycling technologies are generally classified into four main classes: primary (re-extrusion), secondary (mechanical), tertiary (chemical), and quaternary recycling (energy recovery) [53]. Mechanical recycling is typically categorized as either primary or secondary recycling, depending on the type of input material being processed. Primary recycling, also known as closed-loop recycling, is one of the most commonly used methods, due to its simplicity and low cost for PET bottles or products collected by manufacturing industries as pre-consumer industrial scrap materials in their original form and salvaged directly back into the production process. It typically involves melting down plastic waste and reprocessing it into new products that are similar in form and function to the original material. Primary recycling also involves reprocessing waste materials into products of the same type and quality, allowing them to be reused without significant degradation. This approach is commonly applied to materials like metals and some thermoplastics [54]. This process generally includes steps such as collection, sorting, cleaning, and remelting. However, a key limitation of this method is the gradual deterioration of material properties over successive cycles, which reduces their usability over time [55]. Secondary recycling, or open-loop recycling, involves recovering post-consumer plastics. This occurs when the recycled material changes physical, mechanical, or chemical properties, often leading to lower-quality products, with different applications than the original. This type of recycling is prevalent in textiles and plastics, where fibers degrade over multiple recycling cycles [56,57,58]. These processes are economically attractive due to their lower complexity and reduced overall costs. A key drawback is that thermoplastics can only undergo a limited number of recycling cycles before their quality degrades, reducing their usability over time. The process involves several steps—separation, sorting, decontamination, followed by washing, drying, and grinding—before the PET waste can be reused on its own or blended, typically after melt filtration and reprocessing. While the core polymer structure remains unchanged, a key drawback of this recycling method is the gradual degradation of material properties with each cycle. This is mainly due to hydrolysis and transesterification reactions that occur during melt reprocessing, which compromise the integrity of the polymer chains [59]. Tertiary recycling involves chemical processes such as pyrolysis, gasification, and hydrolysis, breaking waste materials down into their fundamental chemical components or fuels. Quaternary recycling refers to the energy recovery process, where heat generated from the incineration of solid waste is captured and utilized, often in industrial or municipal energy systems [60,61]. The recycling potential of consumer clothing presents a crucial opportunity to mitigate the environmental impact of the textile industry. As awareness of textile waste and the demand for sustainable solutions continue to grow, the recycling of post-consumer and pre-consumer textiles has gained increased importance. Generally, there are three primary methods for recycling such materials: mechanical, chemical, and biological recycling. The choice of recycling technique largely depends on the fiber type, as different fibers possess distinct structural and chemical properties [62]. Upcycling is a creative and forward-thinking strategy that transforms PET waste into products that are not only more valuable but also more durable and functional. Unlike conventional recycling methods, which often degrade material quality, upcycling enhances it. For example, PET bottles can be converted into stylish clothing, nanofiber membranes, furniture, or decorative pieces—demonstrating one of the key advantages of this approach. By giving PET waste a second life in such meaningful and higher-value forms, upcycling not only reduces environmental impacts but also adds significant value, particularly for lower-quality or mixed textile waste that is difficult to recycle [26]. In addition, PET waste can be upcycled chemically by depolymerizing it into its monomers, with terephthalic acid (TPA) being the primary product. Various degradation methods—including alcoholysis, acidolysis, hydrolysis, and glycolysis—have been used to convert PET into TPA, allowing for the recovery of valuable fine chemicals [63]. Polymer upcycling systems also offer the potential for more energy-efficient processing and a reduced environmental footprint. It is encouraging to see that both recycling and upcycling approaches are gaining momentum in industry, and the development of innovative, catalyst-driven technologies will be crucial for advancing more sustainable plastic waste solutions [64]. Various techniques for recycling consumer garments are illustrated in Figure 3.

PET waste can be recycled through various methods, primarily chemical and mechanical recycling, each offering distinct advantages for material recovery and reuse.

3.1. Mechanical Recycling

Mechanical recycling is a widely used method for textile waste management, involving shredding, sorting, and fiber recovery. These processes enable the transformation of textile waste into reusable materials, helping to mitigate the environmental impact of the textile industry [66]. During this process, consumer products can be mechanically processed and shredded. This fractionation method is applicable to various fibers, particularly thermoplastic polymers like polyester, which can be re-melted and re-extruded [67]. The mechanical recycling process of PET begins with collection and sorting, where plastic waste is gathered from various sources and classified based on color, shape, and quality. This is followed by washing, where the waste is immersed in a detergent solution and agitated to remove dirt, debris, and other impurities. Next, the material undergoes shredding and grinding, where it is initially broken down into smaller pieces using a shredder equipped with rotating blades. The shredded plastic is then processed in a grinding machine, reducing it into fine flakes suitable for further recycling. The final size of these flakes depends on the specifications of the grinding equipment. The cleaned PET is then dried to eliminate moisture, before being melted into a molten resin, preserving its quality for reuse in industrial applications [26,62,68,69]. After washing, PET raw material undergoes a drying process to reduce moisture content, which is crucial from a molecular perspective to prevent defects during reprocessing, such as through extrusion, and to maintain the quality of recycled PET (rPET). However, some industrial operations directly process highly wet PET, relying on subsequent chain repair to achieve sufficient polymer quality [70].

In mechanical recycling, the focus is on reshaping polymers, while minimizing chemical degradation. In contrast, chemical recycling aims to break down polymer molecules into their original building blocks for reuse in synthesis [71]. Textiles can be mechanically recycled through defibration, where they are broken down into fibers and spun into yarns for textile production, with or without the addition of virgin fibers. However, mechanical recycling often results in fiber shortening, leading to lower-quality fibers and downcycling. To compensate for fiber degradation during processing, mechanically recycled fibers are frequently blended with longer virgin fibers, such as polyethylene terephthalate or cotton, to enhance their mechanical properties for woven applications. Despite these challenges, mechanical recycling remains a key strategy in textile waste valorization. Fibers recovered through mechanical recycling are used in nonwoven applications, including the automotive industry, household appliances, drainage systems, and geotextiles [67,72].

Advantages and Disadvantages

Mechanical recycling is energy efficient and can handle blended textile waste, often producing lower-grade products like insulation or fleece. High-quality fiber-to-fiber recycling requires sorted, known-fiber textiles, sometimes with upstream undyeing. Fiber recovery rates vary (60–95%) depending on input quality, and owing to textiles with zippers or buttons [7].

3.2. Chemical Recycling

Chemical recycling can be classified into three main categories, based on how much the plastic is broken down: (i) solvent-based cleaning, where materials are dissolved and recovered at the polymer level; (ii) chemical depolymerization, which breaks plastics back into their original monomers through chemical reactions; and (iii) thermal depolymerization, such as pyrolysis and gasification, which, in some cases, also qualifies as chemical recycling since it breaks polymers down into monomers and then into hydrocarbons. Thermal methods can also be used to produce fuels [9]. Chemical recycling is widely used for processing PET fiber production waste in large-scale facilities, as well as for recycling PET bottle waste. These processes are typically carried out using solvents, such as in hydrolysis, alcoholysis, glycolysis, and aminolysis, which act as chain-cleaving agents. Depending on the type of starting polymer and the cleaving agent employed, various products can be obtained, including alcohols, acids, amines, and esters [73]. Among the most common methods are glycolysis and methanolysis, while hydrolysis and steam cracking remain less commonly adopted. Although chemical recycling processes are complex and costly, they provide high economic value by yielding high-quality recycled PET, making them a promising solution for sustainable PET waste management [74].

This recycling approach enables PET recovery through depolymerization into monomers, without compromising material quality. While PET can be degraded through various chemical recycling methods, such as glycolysis and methanolysis, only hydrolysis can completely break down PET into its original monomers, TPA and EG, enabling their reuse in the production of new PET polymers. This process is essential for closing the loop in PET recycling and promoting a circular economy in the plastics and textile industries [75]. The primary degradation methods include hydrolysis [76], alcoholysis [77], and glycolysis [78], each utilizing specific catalysts to enhance reaction efficiency and minimize energy consumption. Hydrolysis can be catalyzed by acids (e.g., sulfuric acid), bases (e.g., sodium hydroxide), or enzymes, with enzymatic hydrolysis gaining attention as a more environmentally friendly alternative [79]. Additionally, the use of alcoholic co-solvents such as methanol, ethanol, and isopropanol has been found to enhance alkaline hydrolysis, facilitating polyester chain breakdown under mild conditions and yielding monomers like terephthalic acid and ethylene glycol [80].

One common chemical recycling method for PET waste is glycolytic depolymerization, typically performed by heating the plastic in excess ethylene glycol under atmospheric pressure with a metal acetate catalyst. This process produces bis(2-hydroxyethyl) terephthalate (BHET) through a reversible transesterification reaction. However, it has notable drawbacks, including the requirement for high reaction temperatures (≥190 °C) and difficulties in purifying the resulting BHET [73,81]. Another challenge of the glycolysis technique in recycling waste PET textiles is the discoloration of the waste materials. Residual dyes stain the recovered monomer, thereby reducing its quality and limiting the applications of recycled PET fabrics. Therefore, it is crucial to develop an effective pre-discoloration strategy for waste polyester textiles [82]. This method employs ethylene glycol as a solvent, with sodium sulfate as a catalyst, to break down PET into reusable intermediates, which can even serve as disperse dyes for synthetic textiles [81]. The methanolysis process can be classified into liquid, vapor, and supercritical methanolysis, depending on the physical state of methanol. Liquid-phase methanolysis typically operates at temperatures between 180 and 280 °C and pressures of 20 and 40 atm, yielding dimethyl terephthalate (DMT) and ethylene glycol (EG) with an efficiency of approximately 80–85% [83]. The hydrothermal process requires no pre-treatment and operates at water temperatures below 300 °C. It can be classified into five different methods: (i) hot water extraction, (ii) pressurized hot water extraction, (iii) liquid hot water treatment, (iv) hydrothermal carbonization, and (v) hydrothermal liquefaction. This recycling method is well suited for a variety of fibers, including synthetic fibers such as polyester and nylon, blended fibers combining natural and synthetic materials, biodegradable polymers such as polylactic acid, natural fibers like cotton and rayon, as well as technical textiles used in specialized applications like filtration, automotive, and medical fields [84]. Pyrolysis is a promising method for recovering plastics, as it can convert polymers into liquid fuels or valuable products. The pyrolysis of polyolefins produces a complex mixture of alkanes, alkenes, and aromatic compounds. This process involves cracking molecules without oxygen at temperatures ranging from 300 to 900 °C, resulting in liquid, gas, and solid fractions [85]. In the gasification process, the waste stream is mixed with an oxidizing agent, such as air, steam, or oxygen, and exposed to high temperatures ranging from 550 to 1000 °C. Under these conditions, polyesters are broken down into gaseous products such as hydrogen, carbon monoxide (CO), carbon dioxide, and methane [7]. These methods are frequently used for polymeric materials like PET and other synthetic textiles, where monomers can be recovered for polymer regeneration.

Aminolysis of PET typically involves primary amine solutions, such as ethanolamine, ethylamine, or anhydrous n-butylamine, at temperatures ranging from 20 to 200 °C. Like glycolysis, aminolysis can be carried out through various methods, including catalyst-free reactions, catalyzed processes, and microwave-assisted techniques [55]. Aminolytic degradation typically proceeds through three main stages: (1) an initial rapid attack on the amorphous regions, resulting in minimal changes in weight and crystallinity; (2) chain scission, which causes a significant weight loss and an increase in crystallinity; and (3) a gradual slowdown in the degradation rate as both amorphous and crystalline regions are attacked more slowly [25]. This process has not yet been scaled up to an industrial level, making it less economically viable. Additionally, the use of different types of amines in the aminolysis process can result in the formation of various products, such as hydrogel adsorbents or high-temperature cross-linking agents for unsaturated polyesters [6].

Advantages and Disadvantages

Chemical recycling offers a solution to the limitations of mechanical recycling by converting PET waste into high-quality raw materials, such as purified terephthalic acid (PTA) and monoethylene glycol (MEG). Additionally, chemical recycling can reduce greenhouse gas emissions and energy consumption by up to 50% compared to the production of virgin PET [26]. Despite its advantages, PET chemical recycling presents several challenges. To date, most chemolytic depolymerization processes depend on organic solvents and require harsh reaction conditions, including high-pressure and high-temperature conditions, as well as toxic degrading agents for depolymerization.Traditional chemical recycling methods can also generate waste by-products that need careful handling. For instance, processes like alcoholysis or hydrolysis, which aim to break PET down into monomers, often require large volumes of solvents. These solvents then need to be treated or neutralized before safe disposal, adding complexity to the process. Recovering these solvents is not always practical, as it can demand extra energy and drive up costs. As a result, the final recycled PET product may end up being significantly more expensive than virgin PET, which can discourage its use and ultimately contribute to lower recycling rates [86]. Furthermore, chemical recycling is hindered by the presence of polymer blends, additives, and chemicals such as dyes and anti-wrinkle agents, which interfere with the recycling process, causing extensive purification and separation steps for product recovery, leading to increased energy consumption and environmental risks. Typically, chemical recycling methods are specifically designed to target the types of polymers present in the textiles intended for recycling [66,73,82]. To mitigate these drawbacks, researchers are actively exploring greener alternatives, such as enzymatic depolymerization, bio-based solvents, and advanced catalysts, to enhance process sustainability and efficiency. Recent advancements in chemical recycling have further improved the efficiency and sustainability of PET waste processing. Studies have demonstrated the feasibility of converting polyester textile waste into valuable textile auxiliaries, using environmentally friendly depolymerization techniques [20]. The reuse of PET monomers can not only reduce the demand for virgin materials but also support the development of a circular economy in the textile sector. A common methodological approach for evaluating the environmental benefits of textile recycling is the expansion method, which accounts for the avoided impact of virgin material production, incineration, and landfill disposal [87].

3.3. Enzymatic Recycling

Enzymes speed up the breakdown of plastics by decomposing them into smaller molecules that microorganisms can digest. While biological (enzymatic) and chemical recycling share the same end goal, biological recycling remains less widely adopted. Out of the 32 reviewed papers, only seven mentioned biological recycling, compared to 20 that focused on chemical methods. This disparity likely reflects the challenges involved in working with living organisms, which can make biological processes more complex and less predictable [88]. Enzymatic hydrolysis typically takes place in bioreactors or fermentation tanks, where conditions such as temperature, pH, agitation, and the overall environment are carefully controlled. The optimal temperature range for the enzymes is between 45 and 55 °C, with a preferred pH of 4.5 to 5.5. Precise heating and cooling systems are essential to consistently maintain these conditions, ensuring the enzymes function effectively. The duration of this recycling process can vary widely, ranging from a few hours (1–4 h) to as long as one to two days (24–48 h) [84]. The recycling of modern textiles presents a significant challenge for the industry, as most garments today are composed of fiber blends. These blends, which combine multiple materials, enhance specific properties such as the water absorbency and durability of cotton/PET textiles [89]. Enzymatic hydrolysis has emerged as a promising method for the treatment of textile blends, offering a sustainable approach to fiber separation. Enzymes, which are protein-based natural catalysts, facilitate biochemical reactions and are widely used in industrial applications due to their efficiency, safety, and ease of handling. This process holds great potential in advancing a circular textile economy by enabling the selective breakdown of cellulosic components, while preserving synthetic fibers for further use [1,90]. Although plastics are man-made polymers, several enzymes are capable of degrading synthetic polyesters, even if they are not their natural substrates [91]. Enzymatic PET degradation is influenced by several interrelated factors. The reaction temperature plays a crucial role, with optimal degradation occurring above the glass transition temperature (T_g). Water absorbency is another key factor, as it is highly dependent on temperature, and the crystallinity and orientation of polymer chains. The degree of crystallinity and the arrangement of polymer chains, whether ordered or amorphous, further impact the degradation process. Additionally, surface topology, which is shaped by both crystallinity and polymer orientation, affects the accessibility of enzymes to the material, ultimately determining the efficiency of enzymatic breakdown [29]. However, in the case of wool, enzymes can break down protein fibers under mild processing conditions, converting them into their monomeric units, amino acids, a process similar to natural degradation. Meanwhile, synthetic fibers, such as PET, remain intact, allowing their efficient recovery from blended textiles [92].

Advantages and Disadvantages

Enzymatic recycling presents a promising alternative to mechanical recycling for PET, offering advantages such as selective degradation of PET, effective removal of impurities, recycling of mixed and contaminated plastics, and the production of high-quality recycled materials. Furthermore, enzymatic hydrolysis is a mild reaction condition, especially with the relatively low temperatures required. This typically results in reduced energy consumption, making the process more energy efficient. However, challenges remain, including the high cost of enzymes, the need for efficient enzyme recovery and reuse, and addressing health and safety concerns related to enzyme handling [7,26].

4. Solid Waste from Textile Industry

The majority of solid waste in the textile industry originates from fiber materials that are processed into fabrics and other textile products. Textile waste can be categorized into two main types based on physical characteristics: wastewater and solid waste [5]. A World Bank study projected a 70% increase in global municipal solid waste by 2025, with waste volume expected to rise from 1.3 billion tonnes in 2019 to 2.2 billion tonnes per year. With the continuous increase in solid waste generation, solid waste management has become a critical global environmental concern [93]. Effective management of textile waste begins with identifying its primary sources, which is shown in Figure 4 and will be explained in the text. Textile solid waste is generated during both pre-consumer and post-consumer stages. In the pre-consumer stage, waste comes from textile feedstock production and manufacturing, including swatches, sampling yardage, end-of-roll fabrics, textile samples, unsold stock, and scraps from garment production. Post-consumer waste mainly consists of textiles discarded after use by consumers. In parallel, post-consumer textile waste is relatively uniform, primarily generated after consumers have used and discarded the textiles [94]. For textile solid wastes derived from natural, biodegradable fibers, composting presents a sustainable waste management solution. However, this method is ineffective for synthetic-based textiles, which do not break down easily in natural environments and may require alternative recycling or disposal methods [95].

4.1. Production Waste

Manufacturing waste is also known as post-industrial waste. Post-industrial textile waste refers to by-products generated during the production process, such as textile dead stock or cutting room waste, yarn waste, garment cutting waste, trimming waste, print trials, dye lot errors, production surplus, and end-of-roll materials. This type of waste typically has a predictable volume, high uniformity, and a well-defined composition [96,97].

4.2. Pre-Consumer Waste

Pre-consumer textile waste, which includes by-products from the textile production process such as cotton residues, wool residues, yarn residues, and fiber residues, has significant recycling potential, with materials that have been fully or partially produced and subsequently discarded by businesses. Pre-consumer waste is easier to recycle, as it consists of known materials in various forms, such as fiber, yarn, or fabric scraps. It can be repurposed as a raw material for the production of new products or undergo reprocessing for reuse. While its content is well defined, its availability in large, uniform volumes may vary. However, repeated reprocessing may lead to a decline in yarn properties, affecting the quality and durability of the final product [5,14,97].

4.3. Post-Consumer Waste

Post-consumer waste recycling and reuse remain insufficient worldwide, and when combined with increasing consumption and poor biodegradability, polymeric waste has become a significant environmental concern. The textile, clothing, and footwear industries are experiencing substantial growth, with the global footwear market projected to reach USD 530.3 billion by 2030 [98]. Post-consumer waste, which constitutes the largest portion of textile waste, refers to fibrous products discarded after reaching the end of their service life. Since nearly all fibers are eventually processed into textile products, most of which are replaced due to wear or obsolescence, the volume of post-consumer waste is substantial and closely correlates with the rate of fiber consumption [95,99].

5. Textile-to-Textile Recycling for PET

Textile fibers are broadly classified into natural and man-made (synthetic) categories, as shown in Figure 5. Natural fibers originate from plant, animal, or mineral sources—for example, cellulosic fibers like cotton, rayon, man-made viscose, and Lyocell, and protein fibers such as wool and silk, which are rich in structural proteins like keratin [66,100,101]. In contrast, synthetic fibers such as polyester and polyamide (nylon) are chemically synthesized from oil-derived esters [102,103]. While natural fibers like cellulosic and protein types are biodegradable, petroleum-based synthetic fibers are not and may take hundreds of years to decompose. As a result, recycling synthetic fibers is crucial for reducing waste accumulation and enhancing the sustainability of the textile industry.

Textile waste comprises various natural and synthetic fibers, making direct recycling into new textiles a complex challenge. Among these fibers, polyester fabrics are the most widely used chemical fibers, accounting for the majority of global production. As PET is derived from non-renewable petroleum resources and does not readily degrade in the natural environment, the accumulation of waste polyester fabrics represents a loss of valuable materials and poses serious environmental concerns [104,105]. Due to the widespread use of PET, the accumulation of waste PET has become increasingly common. Recycling waste PET not only reduces the demand for new raw materials but also helps mitigate environmental pollution [106]. The environmental impact of industrial processes and waste disposal is evident in climate change, ozone depletion, fossil carbon depletion, resource scarcity (metal and water), formation of photochemical oxidants and particulate matter, eco-toxicity in freshwater and marine environments, eutrophication, human toxicity, acidification, and land degradation through creating microplastics [107]. Unlike other materials, fiber products are more prone to generating micro- and nano-sized particles, due to their large specific surface area. Reports indicate that synthetic polymers circulate in the atmosphere and oceans after breaking down into nanoparticles or microparticles [10]. The size fraction of plastic debris known as microplastics is arbitrarily defined as particles smaller than 5 mm. Plastic particles smaller than 0.1 µm or 1 µm are commonly referred to as nanoplastics, though some recent studies have suggested a lower limit for microplastics at 1 nm [108]. Microplastics have been identified across various environments, including air, soil, freshwater, drinking water, and oceans. They have also been detected in aquatic and terrestrial organisms, food products, as well as in human placenta and feces, as shown in Figure 6 [109,110].

Recent studies suggest that these particles pose significant health risks, including cancer, chronic diseases, and reproductive system damage [10]. Microplastics have recently been detected in human blood for the first time, with polyethylene terephthalate found in approximately 50% of tested donors, followed by polystyrene (PS, 36%) and polyethylene (PE, 23%) [111]. Figure 7 shows a classification of the recycling of textiles as upcycling and downcycling, closed-loop, and open-loop recycling. In closed-loop recycling, materials are recycled and reused in the production of nearly identical products, minimizing waste and reducing environmental impact. In contrast, open-loop recycling repurposes materials into different products, altering their properties in the process. If the recycled product is of higher quality or value than the original, it is considered upcycling, whereas downcycling results in lower-quality products [3,4].

Fiber Regeneration from Textile Waste

Textile recycling encompasses several approaches, including textile-to-non-textile, fabric-to-fabric, yarn-to-yarn, fiber-to-fiber, and polymer-to-polymer recycling. Textile-to-non-textile recycling converts waste textiles into non-textile products such as rags or insulation materials. Fabric-to-fabric recycling transforms discarded garments into new fabrics, while yarn-to-yarn recycling involves color sorting or decolorizing waste garments to produce new yarns. Fiber-to-fiber recycling regenerates waste textiles into new fibers through spinning, and polymer-to-polymer recycling depolymerizes textile polymers and repolymerizes the purified material for reuse [112].

There are two types of PET fibers: partially oriented yarn (POY) and staple fibers. These fibers are used in various end-use applications, each with distinct material properties. Recycled PET staple fibers and POY are particularly important, as they serve as key intermediate products in the nonwoven and textile industries [113]. Understanding the pros and cons of each aspect, as shown in Figure 8, of the circular economy can highlight the growing economic appeal of recycling post-consumer PET waste into textile fibers. This approach not only addresses the environmental hazards discussed above but also contributes to reducing hunger and inequality by leveraging knowledge, technology, and creativity [114].

Textile Exchange, a nonprofit organization, urged approximately 50 retailers and apparel companies to incorporate at least 25% recycled polyester into their product lines by 2020. However, by 2019, the use of recycled polyester had already increased to 36%. According to Textile Exchange’s forecast, by 2030, 20% of the total polyester produced is expected to be recycled [116]. Textile recycling involves two primary approaches: mechanical recycling and chemical recycling. Mechanical recycling is the simplest and most efficient method, involving the collection, sorting, cutting, and shredding of fabric waste into fibers. However, this process shortens fiber length and reduces quality, often requiring blending with virgin fibers to improve strength. As a result, mechanically recycled fibers are predominantly used in nonwoven applications, such as insulation and fillers, rather than being respun into yarns [117]. Thermo-mechanical recycling, a variation of mechanical processing, follows a re-extrusion process, which includes washing, cutting, compacting, drying, and feeding the material into an extruder. Compared to chemical recycling, thermo-mechanical methods are simpler and generally yield products with a higher economic value than conventional mechanical techniques [74,117]. In contrast, chemical recycling dissolves textile waste in chemical solvents, allowing it to be respun into new fibers, while preserving its inherent properties. This makes chemical recycling a promising approach for closed-loop recycling, particularly for high-quality textile applications. It is also a viable alternative for recycling materials that degrade during mechanical processing, such as cotton and fiber blends, which are difficult to melt efficiently [117]. The recycling of PET fabrics requires separating other fiber materials, including cotton and PET blends, such as Chief Value Cotton (CVC) (where cotton comprises more than 50%) and Tetoron Cotton (TC) (where PET exceeds 50%). Pure PET fabrics (100% PET, known as TK fabric) can be recycled through mechanical, chemical, or thermo-mechanical methods. Mechanical recycling of PET fabrics involves fiber shredding, primarily for use in nonwoven textiles and insulation applications [117]. Disperse dyes are the most commonly used dyes for PET fabrics. Before recycling, dyes must be removed to prevent a reduction in the degree of polymerization (DP) during the melting process. If left unseparated, these dyes may sublime during fiber regeneration, contaminating the working environment [10]. To obtain colorless PET, researchers have focused on dye-destruction technologies and polymer-to-polymer recycling. In dye-destruction methods, PET textile colors are removed through oxidation, photodegradation, or reduction, producing decolored PET [118]. PET recycling via dye destruction poses challenges, as it can cause damage to both PET fibers and dyes, raising environmental concerns [119]. Even under moderate dye-destruction conditions, fabrics often retain gray or yellowish shades [120]. Although solvent extraction is another method for removing dyes from textiles, it is constrained by the thermodynamic equilibrium, as dye concentrations inside and outside the fibers eventually stabilize, limiting complete removal [119]. A PET knitted fabric can be processed by compression and heating at its melting temperature, then ground into particles and preheated in a hot air oven before melt spinning into filaments. This preheating step helps minimize degradation during the spinning process. The structure of PET fiber is primarily determined by the drawing process. However, the properties of the spun fiber are also influenced by the spinning conditions, which affect the maximum draw ratio, as well as the fiber’s modulus, strength, diameter, and fineness [121]. Recently, ionic liquid solvents have emerged as a more sustainable approach, enabling the reintegration of dyed post-consumer textile waste into the recycling chain, while reducing environmental impacts. For textile fiber applications, profitability is achieved only when waste textile polymers are directly dissolved or melted to regenerate fibers [122]. Electrospinning provides a promising approach for recycling and utilizing plastic waste, due to its adaptability to various polymer sources. This technique is particularly effective for fabricating non-woven nanofiber mats, enabling the reuse of recycled PET as a sustainable alternative to conventional materials, thereby reducing environmental waste [36]. Traditional electrospinning is categorized into solution electrospinning and melt electrospinning, depending on the polymer state. In solution electrospinning, polymers that are compatible with suitable solvents can be electrospun into micro/nano fibers. In contrast, melt electrospinning serves as an alternative for polymers lacking appropriate solvents, expanding the range of materials that can be processed through electrospinning [123]. While most studies have primarily focused on electrospinning using PET bottles as the main raw material, Ko et al. examined the structural and physical properties of electrospun nanofibers (NF) derived from post-consumer PET textiles and compared the produced nanofibers with nanofiber-based PET bottles [124]. Another study by Ko et al. [125] explored the transformation of textile waste into functional materials for environmental remediation. The researchers fabricated electrospun nanofiber membranes (NFMs) from three types of discarded polyester sources—a Spandex/polyester t-shirt (SP t-shirt), a pure polyester t-shirt (PET t-shirt), and a PET bottle—as oil filtration. The SP t-shirt NFM exhibited oil sorption capacities 1.5 to 2 times greater than the other NFMs when tested with various oils, including vegetable oil, pump oil, silicone oil, and hexane.

6. Conclusions

The growing environmental impact of textile waste, particularly polyester-based fabrics, has intensified the need for efficient and scalable recycling methods. This review highlights the current advancements in mechanical and chemical recycling techniques, while also addressing the inherent challenges related to fiber degradation, dye contamination, and economic feasibility. Mechanical recycling, though more established, often compromises material quality and limits end-use applications. Chemical recycling methods, particularly those enabling high-purity monomer recovery, play a key role in supporting high-quality fiber regeneration. Chemical methods are typically carried out under heat, pressure, or catalysis, but they also encounter significant limitations. While chemical depolymerization can be effective for PET bottles, it is much less efficient for PET textiles, which often contain dyes, additives, and complex polymer blends that interfere with the process [63,126]. Moreover, the products obtained through chemical recycling usually involve high temperatures, pressures, chemical solvents, low economic value, and limited practical use, making it difficult to justify the high processing costs [86]. Additionally, energy recovery through incineration contributes to greenhouse gas emissions and poses serious environmental concerns, further highlighting the need for more sustainable and scalable solutions [63,126]. PET recycling faces several challenges across both mechanical and chemical approaches. Mechanical recycling tends to degrade the quality of PET, rendering the recycled fibers unsuitable for high-performance applications. While PET is relatively easy to recycle using traditional mechanical or chemical methods, these processes are typically more effective and commercially viable when using pure or bottle-grade PET. In contrast, contaminated PET, such as that found in textiles, is often downcycled into lower-grade materials like polyester fibers. However, once these fibers reach the end of their life, they become even more difficult to recycle. This is largely due to the presence of dyes, colorants, and various additives introduced during textile manufacturing, which significantly reduce the commercial viability of further processing [86]. Although mechanical recycling may produce lower-quality materials and yields, it typically involves lower economic and environmental costs compared to chemical recycling. Therefore, this may be the preferred option when it offers a better balance between technological feasibility and environmental impact [127]. Due to the limited supply of recycled PET (rPET) from plastic bottles, the textile industry now finds itself in competition with the packaging industry for this valuable resource. In response, the European Commission’s 2022 Strategy for Sustainable and Circular Textiles called for a significant reduction in the use of bottle-derived rPET in textiles. Instead, it encouraged a shift toward textile-to-textile recycling, aiming to build a more circular and sustainable system for managing textile waste. To provide a more critical perspective, it is essential to compare existing PET recycling methods in terms of efficiency, scalability, economic feasibility, and environmental impact. Mechanical recycling is the most industrially mature and cost-effective method, making it suitable for large-scale implementation. However, it suffers from quality degradation with each cycle, limiting the recyclate’s application in lower-performance products [127]. In contrast, chemical recycling, including glycolysis, hydrolysis, and electrocatalysis, enables the recovery of high-purity monomers suitable for producing virgin-grade PET [63,126]. However, these methods are energy-intensive, often require harsh solvents, and remain largely confined to laboratory or pilot scales, due to high costs and complex processes [86]. Enzymatic and hybrid approaches have recently shown promise in addressing both selectivity and environmental concerns, but they are still in early development and lack proven industrial scalability. Therefore, while each technology offers distinct advantages, the trade-offs between performance, cost, and sustainability must be carefully balanced when selecting or developing appropriate recycling strategies. Recent innovations, including enzymatic depolymerization and hybrid recycling processes, show potential to overcome existing limitations and drive sustainable transformation in textile waste management. Biorecycling can address the limitations of both mechanical and chemical recycling by producing high-quality raw materials that are identical to virgin PET. This approach not only reduces greenhouse gas emissions and energy consumption but also enhances the overall recycling efficiency of PET products [26]. Among the emerging strategies, fiber-to-fiber recycling offers a circular solution by enabling the regeneration of textile-grade fibers from consumer PET fabrics. However, achieving closed-loop systems remains technically demanding due to contamination, degradation, and fiber blends. In parallel, electrospinning has emerged as a promising technique for producing value-added PET nanofibers from recycled materials, with potential applications in filtration, biomedical, and high-performance textiles. These technologies represent critical steps toward a circular textile economy. Their success will depend on integrating material innovation with design for recycling, scalable processing, and supportive policy frameworks. Future research should focus on scalable separation and purification technologies, novel low-energy chemical pathways, and eco-friendly solvents and catalysts. Furthermore, collaborations between academia, industry, and policy-makers will be essential to bridge the gap between lab-scale innovation and industrial adoption.