Recent Advances in Recycling Polyester–Cotton Blended Textiles: Review

Abstract

Polyester–cotton (PES/CO) blends represent one of the most widely used textile classifications globally, yet their fibre-to-fibre recycling remains technically challenging due to the chemical dissimilarity of the two fibres. Existing reviews typically address textile recycling in broad terms, leaving a gap in critically evaluating the specific separation chemistries, recovered-fraction quality, and industrial maturity of PES/CO recycling routes. This review addresses that gap by providing a focused and comparative assessment of technologies designed for PES/CO fractionation. The paper analyses both polyester-removal and cellulose-removal routes, covering depolymerisation (hydrolysis, glycolysis, methanolysis, aminolysis), dissolving systems (NMMO, ionic liquids, DES, cold alkaline), and enzymatic or acid-based degradation. Each route is evaluated using technical criteria including fraction purity, cellulose degree of polymerisation, polyester monomer recovery, fibre quality, chemical consumption and energy requirement, solvent recovery, reaction conditions, and scalability. The review finds that chemical depolymerisation of PES and selective dissolution of cellulose currently show the strongest potential for high-quality fibre-to-fibre recycling, particularly when solvent recovery systems are integrated. However, significant barriers remain, including incomplete fraction purity, degradation of cellulose DP, limited recovery of high-quality polyester intermediates, high chemical consumption, and insufficient industrial-scale demonstrations. Overall, this review provides a differentiated and critical synthesis of PES/CO recycling technologies, clarifying their readiness levels and outlining the key scientific and industrial challenges that must be addressed to enable circularity in blended textile waste streams.

1. Introduction

Population growth, improved living standards, and the reduction in the life cycle of textile products have led to a significant increase in global fibre consumption [1,2]. In Europe, annual textile waste per person exceeds 15 kg, with 85% of it coming from discarded garments and household textiles [3]. The textile industry is a significant contributor to environmental pollution and is considered one of the least circular sectors globally [4,5,6]. Earlier estimates suggested that the textile and fashion industry contributed around 10% of global CO₂ emissions [7]; however, more recent assessments indicate substantially lower values. For instance, the Apparel Impact Institute (2025) reports that the sector accounted for approximately 944 million tonnes of greenhouse gas emissions in 2023 equivalent to nearly 2% of total global emissions highlighting both the uncertainties in earlier figures and the need for updated, data-driven evaluations [8]. The European Environment Agency (EEA) data shows that textile acquisitions in the EU in 2020 resulted in 270 kg of carbon dioxide emissions per individual, while consumption of textile products generated 121 million tons of greenhouse gas emissions [9].

Textile waste is generated during various stages of the textile manufacturing process, including spinning, weaving, dyeing, finishing, garment manufacturing, and consumer level [10,11,12]. It can be classified into post-industrial waste, pre-consumer, and post-consumer waste (see Figure 1). Post-industrial waste is materials that come from waste from industrial textile production. It is pristine and chemically clean and is a preferred resource for fibre mechanical recycling. Pre-consumer waste is a textile product before it reaches the customer, whereas unused textiles are typically clean. Post-consumer waste is generated by the end-user of the products. It has fulfilled its intended purposes or can no longer be used. In addition, it can be contaminated and contain damaged fibrous materials, which makes it difficult to process for the fibre mechanical recycling.

Textile waste typically consists of various types of fibres, such as cotton, polyester, nylon, wool, acrylic, and viscose. These fibres are used alone or combined as a blend, for instance, polyester/cotton (i.e., PES/CO), which is the predominant blend composition used by the industry due to its optimal properties such as comfort, water absorption, dimensional stability, and durability [13], surpassing the individual properties of cotton or polyester fibres when used alone. The use of PES/CO blends has grown, and the market is projected to reach $15.90 Billion by 2023, with a steady compound annual growth rate (CAGR) of 2.8% from 2023 to 2033 [14].

PES/CO blends are considered to have the most challenging textile waste streams to recycle, due to the chemical dissimilarity of the two fibre components. Traditional melting processes for PES/CO cause thermal degradation of the cotton, making it unusable [15]. Chemical recycling methods using acids or alkalis offer partial separation, yet alkalis that effectively dissolve cotton also hydrolyse PES, whereas acid treatments degrade cotton fibres [16]. These reactions weaken fibre integrity, limiting recovery efficiency and increasing processing costs. Despite the environmental and economic benefits of textile recycling, such as lowering CO₂ emissions and generating employment, current systems remain inadequate. Approximately 75% of textile waste is still discarded, with only 1% recycled into new garments [17]. Much of the unmanaged waste breaks down into microplastics or micro-sized fibres that enter ecosystems [18] and may have potential impacts on human health and the environment, although these effects are still under investigation.

The literature for this review was identified through a structured search conducted in the Scopus database, using the keywords “polyester cotton blend recycling,” “cotton recycling from textile waste,” “chemical recycling of polyester cotton blends”, “chemical recycling of PET/CO textiles,” and “polyester recycling from textile waste.” These terms were applied individually and in combination to capture studies addressing chemical and mechanical recycling routes for PES/CO blends. The search returned peer-reviewed articles, conference papers, and relevant reviews covering polyester removal, cellulose removal, pretreatment, solvent systems, and fibre-to-fibre regeneration. This review provides a comprehensive analysis of the significance of and need for recycling PES/CO blends. Although several reviews discuss textile recycling in general, there remains a clear gap in critically evaluating PES/CO-specific separation technologies, their mechanistic foundations, recovered-fraction quality, efficiency of the process, yield, and industrial maturity. This review addresses that gap by focusing exclusively on PES/CO blends and analysing the technologies designed for their separation and fibre-to-fibre recovery. The manuscript examines mechanical and thermomechanical recycling routes, but the greater emphasis is placed on chemical recycling routes, which have gained significant attention for their ability to overcome the limitations of mechanical and thermomechanical recycling, including the poor fibre quality, ineffective colour removal, contamination percentage, and limited suitability for high-value fibre-to-fibre applications. The review provides a detailed comparison of polyester-removal and cellulose-removal processes, including depolymerisation, selective dissolution, enzymatic degradation, and other emerging chemistries.

2. Recent Advances in the Recycling of Polyester and Cotton Blends

Recycling PES/CO blends has both challenges and gains. The technique is arduous because it involves the segregation of the polyester and cotton parts [19]. Recycled fibres often undergo quality deterioration, resulting in reduced strength. Nevertheless, the recycling of PES/CO blends might result in substantial ecological advantages [20]. Recycling reduces the need for new materials, thereby preserving resources such as oil and water. Recycling further mitigates the environmental repercussions of textile waste, which is a significant global issue. Redirecting PES/CO blends away from landfills aids in reducing the total amount of textile waste [21]. Recycling of PES/CO blends opens new business models, while avoiding incineration contributes to a significant reduction in CO₂ emissions. Emerging technologies, including chemical recycling, are being developed to enhance the recycling of these mixtures, which may ultimately yield significant advances in sustainable fashion [21]. In addition, recycling plays a role in establishing a circular economy, which in turn decreases the environmental impact of the textile sector and encourages sustainable patterns of production and consumption. To summarise, the recycling of PES/CO mixes presents both challenges and opportunities for expansion. As these technologies progress and become more economically feasible, the equilibrium between suffering and benefit is expected to tilt in favour of the benefit.

Table 1. Summary of different recycling technologies for PES/CO textile waste.

Recycling Technology	Feedstock	Output	Pros	Cons	Status	Challenges and Technology Maturity/Limitations	Commercial Players or Upscaling Recycling
Fibre mechanical recycling	Textile waste contains a high share of cotton or polyester [22].	Fibres for yarn spinning and fibres for the production nonwoven textiles.	Simple process and requires relatively low investment. Mechanically opened carding has been well established for several decades.	Different tenacity of PES and CO causes breakage during the recycling, creating short fibres, uneven lengths, spinning issues, leads unpredictable quality. Recycling done without colour removal which causes less interest among consumers. Contaminants will be retained in the output materials.	Technology has currently reached the TRL of 9	Material losses (due to harsh treatment), Shorter fibre length.	Soft mechanical recycling by Purfi [23] Rester Oy [24] Utexbel [25]
Chemical Recycling (cellulose recycling via dissolution method)	Waste textiles are mostly composed of cellulose fibres. The presence of other fibres as impurities depends on the technology.	Regenerated cellulose fibres for textile manufacturing.	High possibility of cellulose recovery	Dyes and other contaminants influence the process to some extent; purification as a pretreatment is required.	TRL for blends is 5–7 and for 100% CO is 9.	Controlling the process is challenging at large scale	Purification of cotton-based waste textiles & preparation of Lyocell fibres (EVRNU; NuCyclTM) [26] Recycling by dissolution in NMMO (Lenzing; REFIBRATM) [27]
					TRL 4–6	Difficult to achieve a feasible level of chemical recovery, chemicals are usually expensive	Recycling by dissolution by ionic liquid (Ioncell) [28,29]
					TRL7	Acceptance of noncellulosic fibres ~12%	Recycling by the formation of cellulose carbamate and the dissolution of cellulose. Polyester removal by alkaline hydrolysis (Infinited Fiber Company: InfinnaTM) [30,31]
					TRL 5	High loss of cellulose solution with PES/CO blends	Biocelsol: cellulose dissolution in cold alkali and separation of PES via filtering [32]
						Dissolution in DMSO: not feasible for safe in large-scale operations [33]	-
Chemical recycling of PES from PES/CO blends. Depolymerisation continued with repolymerisation	PES and its blends (i.e., cellulose, or other types)	Monomers, Oligomers	Recycled PES can be used for textiles as well as other applications (i.e., packaging, composites)	Contaminants and achieving homogeneity of output materials are challenging.	TRL for blends is 4–7	Glycolysis: causes cellulose hornification, widely patented, high initial investment Alkaline hydrolysis: Slow compared to other degrading methods, may cause cellulose hornification Methanolysis: Causes cellulose hornification, high initial investment. Aminolysis: Toxic and expensive chemicals Ammonolysis: Harmful for cellulose solubility, not suitable for blended textiles	CuRe [34], (Glycolysis, PES) Rewin textiles (Glycolysis, PES) [35], Circ (Alkaline hydrolysis, PES/CO blends) [36,37]
Acid hydrolysis-based separation of PES and CO	Mostly PES/CO blends.	PES fibres/pellets, Cellulose fines or sugars			TRL 4		PolyTexx® and CellTexx® by BlockTexx [38] HKRITA: GreenMachine [39] NBG [40]
Enzymatic hydrolysis	Fibre blends	Fibres, monomers, oligomers, and polymers	Target-specific polymer enzyme selectivity. Less polymer damage in milder reactions.	High water footprint. High consumption of chemicals Higher process cost due to enzyme expenses.	TRL of 5–6	Efficiency is low and depends on many parameters, including material purity. The process is generally lengthy and complex. The literature provides very limited investigation of PES/CO blends.	Carbios [41] Evoralis [42] Samsara Eco [43]

presents a comprehensive overview of several recycling processes for general and PES/CO textile waste, and specifically highlights the feedstock, output, advantages, disadvantages, and commercial players associated with each technology. Figure 2 describes a categorisation of PES/CO blend separation techniques based on technologies that either eliminate cellulose or eliminate polyester. Separation may also include decolourisation or removal of other functionalisation chemicals from the fibres, such as water repellent, flame retardant, and antimicrobial textiles.

2.1. Sorting Textile Waste

Generally, the textile waste with multiple components, such as a combination of fibres like PES/CO blends, buttons, zippers, sewing threads, and labels, can be challenging to sort. In the past decade, sorting has mainly been done manually, resulting in a limited fraction of materials suitable for recycling. Current research focuses on automating the process to generate superior quality fractions. Automatic sorting methods (i.e., using spectroscopy) have superior speed and accuracy in evaluating fibre composition, achieving a 30 times higher production rate than human sorting per hour [44]. Near-infrared (NIR) technology is being used in textile recycling to improve the quality of recycled fractions [45]. NIR spectroscopy is used to identify textile waste material, which depends on various parameters such as humidity, temperature, and contaminants. Influential factors include single or multi-layer materials, type of contaminants, moisture, surface properties, colours, garment accessories, and functional finishes [45]. Additionally, the ageing process of textile materials can hinder material recognition, leading to false results and reducing their efficiency [45].

2.2. Fibre Mechanical Recycling

Fibre mechanical recycling is a process where PES/CO waste is transformed into a fibrous form (opened), which is then re-spun into new yarns. However, this process can lead to the loss of value, materials, and properties. For materials like cotton, shredding and fibre opening (i.e., mechanical actions) can reduce fibre length, affecting yarn and fabric quality [46]. To improve durability, virgin polyester is added to recycled cotton [47]. Despite advancements, achieving 50% mechanically recycled content remains challenging. Additionally, the uneven fibre length hinders twist insertion in ring or open-end spinning, causing loose fibres, detachment, and microfibre release during the consumer use (i.e., washing and wearing) phase.

2.3. Chemical Recycling of PES/CO Blends

Chemical recycling is a tertiary recycling method that involves the separation and chemical treatment of textile waste. It is considered a viable option, especially for blended fabrics such as PES/CO, as it allows both fractions of blended material to be recovered using a single method [21].

2.3.1. Pre-Treatment of Textiles

Pretreatment is an important, decisive preliminary step in the chemical recycling of PES/CO textile blends, because nearly all separation and dissolution chemistries impose strict requirements on incoming feedstock purity, fibre condition, size of the feedstock, intrinsic viscosity, and chemical load. Thus, pretreatment is essential rather than optional. Chemical recycling routes, whether they dissolve cellulose, depolymerise PES, or regenerate fibres, depend heavily on the removal of various contaminations and additives to the feedstock, including the finishing agents, dyes, metal ions, and surface contaminants. Most of these contaminants interfere with solvent penetration, catalytic activity, or polymer stability, and overall reaction reduces fraction separations. In cotton dissolution recycling routes for fibre-regeneration, pretreatments become even more critical. To dissolve pulp quality, stringent industrial specifications must be met, including eliminating harmful metal ions that deactivate solvents, removing finishing chemicals that hinder dissolution, removal of dyes that cause colour carryover, activating cellulose to improve reactivity, and adjusting intrinsic viscosity to ensure stable dissolution and spinnability [48]. These pretreatment requirements apply regardless of whether cellulose dissolution occurs before or after polyester removal, and they influence the efficiency, selectivity, and yield of every downstream step. In practice, pretreatment can be integrated directly into the recycling process or performed externally by specialised companies, creating a multi-actor value chain where pretreatment providers play a central role in enabling high-quality chemical recycling. Industrial actors such as Södra’s OnceMore [49], Circ for cotton–polyester blends [37], and Circulose [50] and SaXcell [51] for cotton-only streams have developed dedicated pretreatment technologies that stabilise feedstock quality, remove interfering substances, and deliver purified fibre fractions tailored for chemical recycling processes. Their contributions are essential because chemical recycling systems cannot operate effectively without consistent, contaminant-free input materials, and the variability of post-consumer textiles makes pretreatment indispensable for achieving reliable separation, dissolution, and regeneration outcomes. As a result, pretreatment is not a side topic but a decisive enabler of separation success, determining solvent efficiency, polymer recovery, product purity, and overall process viability across the PES/CO chemical recycling landscape.

2.3.2. Polyester Dissolving and Degrading Methods to Separate Cotton

In polyester chemolysis, the polyester fraction is either dissolved or depolymerised usually at high temperatures. In the dissolution process, polyester is dissolved into its solvents such as DMSO, m-cresol, or phenol [52]. In depolymerisation, polyester is either completely depolymerised into its monomers or partially depolymerised into oligomers, depending on the reaction duration. The depolymerisation processes include conventional methods such as alkaline hydrolysis (Figure 2), methanolysis, glycolysis, aminolysis, ammonolysis, and more recently discovered hydrothermal and enzymatic processes.

Enzymatic hydrolysis of PES

Enzymatic treatment has emerged as a promising, selective, and environmentally benign strategy for separating cotton from PES/CO blend textile waste. Polyester exhibits high chemical resistance, making its dissolution or depolymerisation challenging under mild conditions. Ideonella sakaiensis 201-F6, first identified by Japanese researchers in 2016 [53], produces two enzymes, PETase and MHETase, that can break down polyester. PETase hydrolyses polyester into mono(2-hydroxyethyl) terephthalic acid (MHET), while MHETase converts MHET into the monomers terephthalic acid (TPA) and ethylene glycol (EG), which can be recovered for repolymerisation or chemical upcycling. However, these enzymes still need to be tested on blended textiles to determine their effectiveness in hydrolysing polyester components. Meanwhile, engineered cutinase has also been used to break down polyester; however, further research is needed to determine its effectiveness in separating cotton for studying the recycling of textile blend waste [54].

Alkaline hydrolysis of PES

The separation of cotton and polyester from PES/CO blend textiles via alkaline hydrolysis is based on the degradation of PES to terephthalic salt and ethylene glycol (EG) (Figure 3). The salt can be precipitated as terephthalic acid (TPA) under acidic conditions. The TPA could be manufactured back into PES. In the process, the cotton fraction that remains in fibre form is separated by filtration. Around three decades ago, polyester in PES/CO blends was selectively degraded through alkaline hydrolysis in NaOH, enabling efficient separation of cotton fibres for subsequent lyocell dissolution and regeneration [55]. In another study, a laboratory-scale NaOH hydrolysis process (NaOH 10%, 80–90 °C, 100 min) efficiently separates polycotton by complete degradation of PES, yielding high-purity cotton without severe degradation. It was found out that the use of benzyltributylammonium chloride (0.05–1.0 mol) accelerated PES breakdown, minimising process time [56]. Bengtsson et al. [57] found that alkaline hydrolysis selectively depolymerises polyester into monomers (TPA and EG), while viscose is recovered as a polymeric form. However, the intrinsic viscosity of the viscose fibres dropped by 35% from about 200 mL/g to 130–150 mL/g, making it unsuitable for fibre-to-fibre recycling but viable for sugar platforms [58]. Villar et al. [59] studied the influence of the phase transfer catalysts (ammonium-based salt) on the degradation of PES, resulting in an exponential increase in degradation, especially with lower alkali concentrations. Cho et al. [60] conducted a study on the pretreatment of blended PES/CO textile waste using a NaOH-ethanol system. The mixture had low digestibility, but the use of NaOH-ethanol pretreatment effectively removed PES from the waste. Across alkaline-hydrolysis studies, conditions have varied. However, moderate NaOH concentrations, controlled temperatures, and selective catalysis determine cellulose preservation. Palme’s method offers the cleanest PES/CO separation compared with Villar’s [59] and Cho’s [60] systems. Alkaline hydrolysis methods to produce high-purity cotton for industrial use appear to be under development at pilot and demonstration scales by several companies [31,36,37].

Methanolysis

Methanolysis is another technique employed to recycle polyester from the textile waste containing polyester (PES). The process involves mechanically shredding the polyester textile waste into small pieces and then heating it (i.e., 170 °C; 20 bars for 4 h) with methanol and a catalyst, such as zinc acetate or antimony trioxide. The polyester is broken down into its monomers, mainly dimethyl terephthalate (DMA) and ethylene glycol [61]. The products are isolated from the methanol and catalyst, purified using distillation or crystallisation, and then utilised in the synthesis of new polyester materials via polycondensation. The harsh condition of the reaction with the temperature over 100 °C causes cellulose hornification, leading to less reactive cotton fibres and thus difficulties in dissolution if the cotton fraction is to be used to spin regenerated cellulose fibres [62]. Meanwhile, organo-catalytic processes on the PES/CO fabrics efficiently depolymerises PES into DMT and EG without monomer purification. With solvent/catalyst recirculation (at a ratio of 3:1), the method applies to multiple polyesters and polycotton, yielding cotton suitable for viscose spinning [63].

Glycolysis

Glycolysis is a chemical process in which waste PES reacts with ethylene glycol, potentially leading to the creation of the monomer bis(2-hydroxyethyl terephthalate) (BHET). BHET has been widely employed in the manufacturing of diverse polymeric materials, such as unsaturated polyester resins, and novel biocompatible systems. Currently, there are numerous environmentally friendly catalysts available, such as pellets made of Mg-Al double oxides, to accelerate conversion reactions [64]. Andini et al. [65] studied a blend of 50/50 PES/CO to investigate the effects of cotton on polyester under glycolysis treatment. Overall, the experiment demonstrated that polyester is reactive and elevated temperatures (from 150–210 °C) expedite the breakdown of polyester molecules to oligomers and further to monomers. Cotton from the PES/CO blended textile waste does not undergo the chemical process of glycolysis. It remains in fibre form, but the harsh reaction conditions of glycolysis, especially the high temperatures above 100 °C, cause cellulose hornification, leading to less reactive cotton fibres and thus difficulties in dissolution [62] and creates issues within subsequent processes. From the textile recycling routes, glycolysis is the most patented [66,67]. Furthermore, it is evident that the glycolysis process is a straightforward method for recycling 100% PES textile waste. However, further study is required on the impact of low temperature glycolysis on cellulose hornification to determine the suitability of cellulose regeneration fibre-to-fibre recycling [62,64]. Rewin textiles [35] and CuRe technology [34] are upscaling their technologies toward commercial textile-to-textile recycling.

Aminolysis

Aminolysis is an underutilised technique for PES chemolysis, using various amines with a treatment temperature range of 20–100 °C. The conversion of PES into products utilising methylamine, ethylamine, dimethylamine, trimethylamine, NH₃, and NaOH has comparable reaction rates; NH₃ perhaps shows a lower rate of reaction [68,69,70]. This method utilises a range of amines as degradative agents and catalysts, such as lead acetate, glacial acetic acid, sodium acetate, and potassium sulfate, to degrade PES [69,70]. Apart from that, aminolysis can be used to degrade the elastane, which is mostly blended with cotton and polyester [71]. Currently, there are no known commercial-scale examples of PES aminolysis. However, partial aminolysis is exploited for enhancing PES properties (e.g., fibre colouration) in the manufacture of fibres with defined processing properties [72,73]. Despite the diverse chemistry and broad range of applications of aminolysis-derived products, the field remains underexplored. Additionally, to the best of our knowledge, there are no known examples of the aminolysis of PES/CO blends. Thus, there is clear scope for further exploration of this treatment.

Ammonolysis

Ammonolysis is a chemical reaction that uses concentrated ammonia solution at temperatures from 70 to 180 °C and a pressure of 2 MPa. This process can be carried out with or without a catalyst, usually zinc acetate. The primary byproducts are terephthalamide and EG, which serve as intermediates in the production of terephthalonitrile [72]. There is a limited literature on ammonolysis, most likely due to limited research on different materials and a lack of economic interest.

Dissolving methods

DMSO, phenol, and m-cresol are solvents used in certain advanced PES recycling methods; however, each presents serious limitations, as DMSO has notable toxicity and safety concerns and shows relatively low efficiency in dissolving PES, while phenol and m-cresol pose significant handling hazards due to their corrosive and toxic nature. In addition to these safety issues, all three solvents provide lower dissolution efficacy compared with more optimised alternatives, ultimately leading to higher operational costs and limited practical feasibility. Furthermore, the recycling process might require specialised safety infrastructure, and it is not feasible for large-scale operations. Dissolution of PES in DMSO also requires 150 °C or above, leading to cotton fraction hornification [74]. Dissolution of the polyester fraction from the PES/CO blend in organic solvents, such as 1,3-dimethylimidazolidinone, butyl benzoate, benzyl acetate, benzaldehyde, dipropylene glycol methyl ether acetate, tetramethylene sulfone, and a mixture of dichloromethane and trifluoroacetic acid, has been the focus of various studies [75,76,77]. However, the efficiency of separation and the purity of achieved fractions have not been clearly addressed. Details of the studies are presented in Table 2.

Hydrothermal liquefaction

Hydrothermal liquefaction (HTL) is an innovative technique that allows for the recycling of blended textiles (i.e., PES/CO) [78]. Mei et al. [21] developed the most effective treatment parameters for PES/CO blended fabrics using a high-pressure reactor. The fabric sample was heat-treated at 230 °C for 10 min, resulting in nearly complete removal of PES. However, the cotton component of the fabric remained in its original cloth form. This allows cotton to maintain its fabric form and be reused in different applications. The extracted PES confirmed that it did not undergo decomposition into monomers. HTL can retain cellulose in fibre form, but requires high temperatures, which may provide opportunities for the thermal degradation of the PES part [21]. Similar to PES chemolysis, HTL likely induces cellulose hornification, making it unsuitable for fibre-to-fibre recycling [62]. Current HTL studies rarely address cotton fibre integrity, leaving its recyclability effects insufficiently understood.

Table 2. Summary of the polyester-removing process for PES/CO textile waste.

Method	Conditions for the Cellulose Removal	Notes	Ref
PES dissolution in organic solvent	Inputs: PES/CO (60/40). PES/CO waste was dissolved in a solvent (e.g., 1,3-dimethylimidazolidinone, butyl benzoate, benzyl acetate, benzaldehyde, dipropylene glycol methyl ether acetate) that was heated to a temperature range of 70–110 °C for a duration of 1–2 h. Subsequently, the solvent was chilled to separate the dissolved polyester, using a liquid-to-solid ratio of 8–10.	The process of separating polycotton is straightforward, with minimal toxicity and energy usage. However, it requires a significant amount of chemicals for cleaning and recovery. Output: PES powder, yield 15–57%; solid cotton material, yield not given	[75]
PES dissolution in organic solvent	Inputs: PES/CO (50/50). PES/CO was subjected to a solvent (tetramethylene sulfone) treatment at a temperature of 150 °C for 90 min. Subsequently, the temperature was increased to 190 °C for 35 min, resulting in precipitation of the dissolved polyester in the coagulation bath.	It is important to ensure that the input material is completely dry to prevent PES degradation. Output: PES powder, yield not given; cotton as fabric, yield not given	[76]
PES dissolution in organic solvent	Inputs: PES/CO (50/50; 75/25; 25/75). The dissolution of the PES fraction of PES/CO was achieved by using a mixture of dichloromethane and trifluoroacetic acid at a liquid-to-solid ratio of 0.2.	This treatment was done at room temperature; perhaps it works and is most suitable for PES-rich blends. Output: PES and Cotton	[77]
PES dissolution in dimethylcyclohexylamine	Inputs: PES/CO (20/80; blue). PES fraction of a PES/CO mixture was dissolved using dimethylcyclohexylamine at a liquid-to-solid ratio of 40–120. The dissolution process was carried out at 50 °C for 8 h.	This process achieved the recycling process as maximum (i.e., 96%), included successful decolouration pretreatment Output: PES powder, yield 77%; cotton fibres, yield 100%	[79]
PES dissolution in triethylamine	Inputs: PES/CO. Use triethylamine at 50 °C for 20 min to deteriorate polyester and release cotton fibres from PES/CO combination.	Possible for the reduction of mechanical properties of extracted cotton fibres. Output: Cotton fibres and PES	[80]
Alkaline hydrolysis of PES	Inputs: PES/CO (52/48). Treat PES/CO with 10% NaOH at 90 °C in presence of benzyltributylammonium chloride for 15–240 min.	Neutralising alkali waste using strong acid may waste a lot of chemicals and water. Output: Cotton fibres and PES powder (TPA)	[56]
Alkaline hydrolysis of PES	Inputs: PES/Viscose (30/70). Treat PES/CO with 5% NaOH at 90 °C for 1–24 h.	The treatment reduces the molecular weight for the cellulose (Viscose) fraction. Also, oxygen free environment reduces the cellulose degradation. Output: TPA, EG, and Viscose	[58]
Enzymatic hydrolysis of PES	Inputs: PES/CO (65/35; 80/20). To hydrolyse PES part of a PES/CO mixture, use a commercial cutinase at 55 °C for 24 h.	Treatment does not react or affect the colourants and finishes in the PES/CO waste. Output: TPA and Glucose	[81]
Glycolysis of PES	Inputs: PES/CO Ethylene glycol at a liquid-to-solid ratio of 6 was heated to 196 °C in the presence of zinc acetate (0.1%) as the catalyst.	The recovered cellulose exhibits minimal degradation and maintains mechanical properties, making it suitable for spinning. Output: BHET and Cellulose	[82]
Glycolysis of PES	Inputs: PES/CO (50/50) Ethylene glycol at a liquid-to-solid ratio of 3.75 with the presence of BHET and sodium carbonate as catalyst with 200 °C for 5 h.	Processing recovered cellulose-to-cellulose acetate involves pulping and acetylation. Output: BHET, TPA, and Cellulose	[83]
Hydrothermal treatment of PES	Inputs: PES/CO (20/80) At specific temperature, pressure, and time, subcritical water reaction dissolves PES and weakens cellulose using a phase-transfer catalyst or co-solvent.	The method uses non-toxic, ecologically friendly, affordable, and green subcritical water instead of harsh chemicals. Hydrolysis may occur in the cellulose fraction. Output: TPA, EG, and Cellulose	[84]

Table 2. Summary of the polyester-removing process for PES/CO textile waste.

Method	Conditions for the Cellulose Removal	Notes	Ref
PES dissolution in organic solvent	Inputs: PES/CO (60/40). PES/CO waste was dissolved in a solvent (e.g., 1,3-dimethylimidazolidinone, butyl benzoate, benzyl acetate, benzaldehyde, dipropylene glycol methyl ether acetate) that was heated to a temperature range of 70–110 °C for a duration of 1–2 h. Subsequently, the solvent was chilled to separate the dissolved polyester, using a liquid-to-solid ratio of 8–10.	The process of separating polycotton is straightforward, with minimal toxicity and energy usage. However, it requires a significant amount of chemicals for cleaning and recovery. Output: PES powder, yield 15–57%; solid cotton material, yield not given	[75]
PES dissolution in organic solvent	Inputs: PES/CO (50/50). PES/CO was subjected to a solvent (tetramethylene sulfone) treatment at a temperature of 150 °C for 90 min. Subsequently, the temperature was increased to 190 °C for 35 min, resulting in precipitation of the dissolved polyester in the coagulation bath.	It is important to ensure that the input material is completely dry to prevent PES degradation. Output: PES powder, yield not given; cotton as fabric, yield not given	[76]
PES dissolution in organic solvent	Inputs: PES/CO (50/50; 75/25; 25/75). The dissolution of the PES fraction of PES/CO was achieved by using a mixture of dichloromethane and trifluoroacetic acid at a liquid-to-solid ratio of 0.2.	This treatment was done at room temperature; perhaps it works and is most suitable for PES-rich blends. Output: PES and Cotton	[77]
PES dissolution in dimethylcyclohexylamine	Inputs: PES/CO (20/80; blue). PES fraction of a PES/CO mixture was dissolved using dimethylcyclohexylamine at a liquid-to-solid ratio of 40–120. The dissolution process was carried out at 50 °C for 8 h.	This process achieved the recycling process as maximum (i.e., 96%), included successful decolouration pretreatment Output: PES powder, yield 77%; cotton fibres, yield 100%	[79]
PES dissolution in triethylamine	Inputs: PES/CO. Use triethylamine at 50 °C for 20 min to deteriorate polyester and release cotton fibres from PES/CO combination.	Possible for the reduction of mechanical properties of extracted cotton fibres. Output: Cotton fibres and PES	[80]
Alkaline hydrolysis of PES	Inputs: PES/CO (52/48). Treat PES/CO with 10% NaOH at 90 °C in presence of benzyltributylammonium chloride for 15–240 min.	Neutralising alkali waste using strong acid may waste a lot of chemicals and water. Output: Cotton fibres and PES powder (TPA)	[56]
Alkaline hydrolysis of PES	Inputs: PES/Viscose (30/70). Treat PES/CO with 5% NaOH at 90 °C for 1–24 h.	The treatment reduces the molecular weight for the cellulose (Viscose) fraction. Also, oxygen free environment reduces the cellulose degradation. Output: TPA, EG, and Viscose	[58]
Enzymatic hydrolysis of PES	Inputs: PES/CO (65/35; 80/20). To hydrolyse PES part of a PES/CO mixture, use a commercial cutinase at 55 °C for 24 h.	Treatment does not react or affect the colourants and finishes in the PES/CO waste. Output: TPA and Glucose	[81]
Glycolysis of PES	Inputs: PES/CO Ethylene glycol at a liquid-to-solid ratio of 6 was heated to 196 °C in the presence of zinc acetate (0.1%) as the catalyst.	The recovered cellulose exhibits minimal degradation and maintains mechanical properties, making it suitable for spinning. Output: BHET and Cellulose	[82]
Glycolysis of PES	Inputs: PES/CO (50/50) Ethylene glycol at a liquid-to-solid ratio of 3.75 with the presence of BHET and sodium carbonate as catalyst with 200 °C for 5 h.	Processing recovered cellulose-to-cellulose acetate involves pulping and acetylation. Output: BHET, TPA, and Cellulose	[83]
Hydrothermal treatment of PES	Inputs: PES/CO (20/80) At specific temperature, pressure, and time, subcritical water reaction dissolves PES and weakens cellulose using a phase-transfer catalyst or co-solvent.	The method uses non-toxic, ecologically friendly, affordable, and green subcritical water instead of harsh chemicals. Hydrolysis may occur in the cellulose fraction. Output: TPA, EG, and Cellulose	[84]

In the polyester-removal recycling from PES/CO textile waste, the chemistries, hornification, DP loss, and mechanical deterioration vary with solvent strength and reaction conditions. For instance, organic-solvent routes (dimethylimidazolidinone, butyl benzoate, benzyl acetate, benzaldehyde, or dipropylene glycol methyl ether acetate) at 70–110 °C generally preserve cotton quality but may cause mild hornification; tetra-methylene sulfone at 150–190 °C risks PES degradation if feedstock is not fully dry, but cotton remains largely intact. Room-temperature dichloromethane–trifluoroacetic acid avoids DP loss and is most suitable for PES-rich blends. Dimethylcyclohexylamine at 50 °C maintains cellulose quality, and very efficient colour removal, while triethylamine may weaken fibres. Alkaline hydrolysis can reduce cellulose DP, whereas cutinase-based enzymatic hydrolysis avoids hornification entirely. Glycolysis at 196–200 °C preserves cellulose mechanical properties. Hydrothermal treatment using subcritical water may weaken cellulose and induce partial hydrolysis, though it remains a green alternative yielding TPA, EG, and cellulose. Overall, enzymatic hydrolysis, dimethylcyclohexylamine dissolution, and glycolysis minimise deterioration.

As discussed in the various polyester-removal technologies for recycling of PES/CO textile waste, several routes show stronger commercial viability based on solvent recovery, reaction severity, fibre/fraction quality, and industrial compatibility with the existing infrastructure. For example, the use of solvent dissolution methods that operate at 70–110 °C for 1–2 h, including dimethylimidazolidinone, butyl benzoate, benzyl acetate, benzaldehyde, or dipropylene glycol methyl ether acetate, and offer simple and straightforward separation with low toxicity and energy consumption, though they require substantial solvent for cleaning and recovery and yield only 15–57% PES powder. Tetra-methylene sulfone dissolution at 150–190 °C enables polyester precipitation but demands completely dry feedstock to avoid PES degradation. Dimethylcyclohexylamine dissolution at 50 °C for 8 h achieves high recycling efficiency (96%), effective decolouration, and strong yields (77% PES, 100% cotton), making it one of the most promising solvents-based routes. Triethylamine at 50 °C for 20 min rapidly deteriorates PES to release cotton, though cotton mechanical properties are expected to degrade. Alkaline hydrolysis using 10% NaOH at 90 °C with benzyltributylammonium chloride produces TPA and cotton fibres but requires extensive neutralisation, increasing chemical and water consumption, and overall cost for the process, thus hindering commercial feasibility. Hydrolysis of PES/viscose blends with 5% NaOH at 90 °C reduces cellulose molecular weight, though oxygen-free conditions mitigate degradation. Enzymatic hydrolysis using cutinase at 55 °C for 24 h selectively degrades PES without affecting dyes or finishes, yielding TPA and glucose under mild conditions, but this technology in early stage. Glycolysis at 196–200 °C with zinc acetate or sodium carbonate produces BHET, TPA, and cellulose with minimal cellulose degradation, supporting fibre-to-fibre potential; however, it requires higher energy. Hydrothermal treatment using subcritical water offers a green alternative, generating TPA, EG, and cellulose, but may induce cellulose hydrolysis. Overall, dimethylcyclohexylamine dissolution, enzymatic hydrolysis, and glycolysis currently exhibit the strongest commercial potential.

2.3.3. Cotton Dissolving/Degrading Methods to Separate Polyester

In the PES/CO blends, separation technologies involve removing cellulose from PES using various strategies, including dissolution by various solvents like NMMO, ionic liquids, cold alkali, and depolymerisation by using acidic hydrolysis, acid-catalysed hydrothermal treatment, oxidation, and enzymatic hydrolysis (Figure 2).

Cellulose dissolution using NMMO

N-methylmorpholine-N-oxide (NMMO) is a well-established solvent for cellulose breakdown to convert into regenerated cellulose (i.e., Lyocell process) or even reconstituted into nanocellulose [85]. The Lyocell process, a viable alternative to viscose manufacture (i.e., use of CS₂), utilises a reduced number of chemicals and effectively recovers N-methylmorpholine N-oxide monohydrate (NMMO) and water. The lyocell process relies on high temperatures (80–120 °C) and stabilisers such as propyl gallate [86,87]. This environmentally friendly and easily decomposable technology is far more sustainable compared to the viscose process [86,87]. Haule et al. [88] successfully dissolved pulps made from various common post-consumer cotton waste fabrics in an NMMO solution and spun them into fibres. The molecular and mechanical characteristics of the fibres were assessed and compared to the conventional lyocell fibres. Silva et al. [89] investigated the relationship between the degree of polymerisation (DP) and the mechanical properties of cotton textile waste as a feedstock for developing new fibres. The tensile strength of chemically recycled fibres derived from waste cotton lint exhibited a direct correlation with the DP. The NMMO process is commercialised for cellulosic textile recycling, but controlling the process presents various challenges [90]. For example, the limits for metal residuals are very low. Jeihanipour et al. [91] used NMMO dissolution at 120 °C for the separation of PES from 50/50 PES/CO and 60/40 Viscose/PES blend textiles. Cellulosic fractions were dissolved, and solid PES was separated from the solution using a 1 mm sieve, washed first with a fresh NMMO solution to remove the remaining cellulosic material, and then with water. The cellulosic materials were precipitated with hot water and used to produce bioethanol and biogas. Lyocell technology-based regenerated cellulose fibres containing recycled cotton are developed with NuCycl^® [26], REFIBRA^TM [27] and SaXcell^® trademarks [51].

Cellulose dissolution using Ionic liquid

Fibre spinning technology using ionic liquids such as solvents offers an alternative to the lyocell method (i.e., NMMO). Ionic liquids are effective green solvents for cellulose and lignocellulose because of their notable temperature stability and strong ability to dissolve these materials [92]. By using aprotic solvents such as DMSO, the process of dissolving cellulose in ionic liquid can be expedited through pre-swelling, which facilitates the penetration of ionic liquid into the cellulose fibre [93,94,95]. Wu et al. [96], used 1-allyl-3-methylimidazole chloride ([Amim]Cl)/Dimethyl sulfoxide (DMSO) and 1-ethyl-3-methylimidazolium diethyl phosphate ([Emim]DEP)/DMSO systems as solvents to effectively dissolve cotton from waste PES/CO garments. Cotton dissolution efficiency in the [Emim]DEP/DMSO system depends strongly on fabric size, capacity of the fabrics, temperature, and time. Small 1 × 1 cm polycotton pieces dissolve completely: higher fabric loading lowers efficiency. Optimal conditions (0.4 g fabric; 80 °C; 60 min) yield 99.9% cotton dissolution, but higher temperatures or longer durations reduced cellulose DP with this process. The solid PES fraction was separated by filtration and used for melt-spinning. Cotton solution was used to prepare regenerated cellulose fibres. In another work [97], 1-allyl-3-methylimidazolium chloride (AMIMCI) and 1-butyl-3-methylimidazolium acetate (BMIMAc) ionic liquids were used to dissolve the cellulose component from PES/CO blended fabrics. A separation procedure for cotton and polyester using Ioncell technology with [DBNH][OAc] as the solvent, allowing selective dissolution of the cellulose component, was presented by Haslinger et al. [29]. Cellulose fibres regenerated by dry-yet-wet spinning had properties like those of Lyocell fibres. Unfortunately, some degradation (a decrease in MMD and tensile properties) of the recovered PES materials was observed. Ma et al. [98] discovered that the utilisation of a binary solvent, specifically dimethyl sulfoxide (DMSO), in combination with an ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim]OAc), mitigates issues associated with using ionic liquid alone, such as elevated viscosity of the cellulose solution during the spinning process. This approach also reduces solvent costs by 77% and enables solvent recovery and reuse via distillation. Additionally, it could enable the removal of the colour of cotton textile depending on the type of pretreatment.

Cellulose dissolution using DESs

Deep eutectic solvents (DESs) represent an additional class of chemicals examined for their possible use in dissolving cellulose [99,100,101]. These compounds often display similar characteristics to ionic liquids but are regarded as more economical and ecologically sustainable [99]. DESs are synthesised by the amalgamation of a quaternary ammonium salt with either a hydrogen bond donor or a metal salt. Certain DESs have been used for the dissolution, modification, and plasticisation of cellulose derived from cotton textiles and other cellulosic materials [100]. DESs have been used to segregate PES/CO blends, presenting a viable method for the effective recovery and recycling of these textile components. Yang et al. [102] employed a low-eutectic solvent/DESs, consisting of zinc chloride, water, and phosphoric acid to separate the PES/CO blended fabric. This solvent environment effectively dissolved the cellulose component of the mixed fabrics while leaving the PES unaffected. Moreover, DESs possess distinctive characteristics that enable it to eliminate the colour of post-consumer textile waste [74]. The resulting polyester fibre was used in the melt-spinning process, resulting in recycled polyester fibre. The process of producing regenerated cellulose fibres involved extracting cellulose from the DESs solution system through coagulation, followed by dissolving it in a NaOH/urea/H₂O solvent for wet spinning. In another work, a DESs–NaOH hybrid system enabled efficient PES/CO separation by selectively loosening the PES portion, accelerating alkaline degradation at 98 °C for 60 min with 5% NaOH. This yielded high-purity TPA and preserves the cellulose portion (<3% loss), offering a green, selective, and scalable solution for PET/cotton recycling [103]. Another combination such as menthol–benzoic acid DESs enables rapid PES/CO separation, dissolving both polymers within 5 min at high temperature (i.e., 216 °C) without affecting their properties. The process achieves complete cotton recovery (100%) and high PES yield (97%), offering an efficient alternative to organic solvents for the PES/CO separation [104].

Cellulose dissolution using a cold alkaline solution

Biocelsol

Biocelsol technology represents a promising approach for producing regenerated cellulosic fibres using enzyme-assisted processing. Unlike the viscose route, it replaces hazardous chemicals such as carbon disulphide with enzymatic activation, which enhances cellulose solubility in aqueous NaOH systems, typically cold sodium zincate (ZnO/NaOH). The resulting solution is filtered and converted into fibres via wet spinning in acidic coagulation baths, allowing compatibility with existing viscose infrastructure. The obtained fibres are white by nature and have exceptionally good adsorption capacity. The concept, introduced in the late 1980s, demonstrated that enzymatic modification increases cellulose accessibility and dissolution efficiency [105]. Initial investigations focused extensively on the use of purified, tailored enzyme systems to modify cellulose [106,107], followed by its successful dissolution and regeneration into diverse cellulosic forms [108]. Advances in process engineering have enabled continuous enzymatic treatment using twin-screw extrusion for 30 min, with integrated dissolution steps [32]. Biocelsol yields inherently white fibres with high adsorption capacity, suitable for functional applications. Recently, VTT successfully separated the cellulosic part from the PES/CO blended pre-consumer textiles using Biocelsol technology, and spun fibres from the dissolved cellulose [109]. Although current operating costs are slightly higher than viscose (i.e., ~10%; which including the recovery of chemicals) [110], the process offers substantially reduced environmental impact and strong potential for further optimisation and industrial scalability.

Cellulose carbamate

Cellulose carbamate (CCA) is a carbamic acid ester derivative of cellulose that exhibits solubility in alkaline media, making it a promising alternative to the conventional viscose process for textile fibre regeneration from wood pulp. It is synthesised via the reaction of cellulose with isocyanic acid, which is generated in situ through the thermal decomposition of urea above its melting point (133 °C) [111]. The carbamation reaction is typically conducted at 135–180 °C; temperatures above 175 °C led to undesirable side reactions, including cyanuric acid formation and ammonia release [112]. Early industrial approaches, such as the DuPont process, involved steeping, pressing, drying, baking, and washing. The Cellca process improved urea distribution by introducing liquid ammonia as a swelling agent [113]. Later developments employed NaOH-activated cellulose processed in mechanical kneaders, where structural disruption enhances urea penetration. This method generally includes: (a) first, a mixture of activated cellulose or pulp and urea is produced in a mixing unit with shearing treatment, (b) the mixture is dried, then (c) reacted at a temperature between 120 and 180 °C to the reaction product, the cellulose carbamate [114]. Recent production of cellulose carbamate involves reacting urea with optionally activated pulp at temperatures above 132 °C, where urea decomposes into isocyanic acid and ammonia [115,116,117,118], in either dry conditions or inert media [119,120]. Urea-based deep eutectic solvents also enable efficient carbamate formation, particularly when wet pulp is treated at 120 °C [121]. Industrial implementation, notably by Infinited Fiber Company, applies this chemistry to cotton recycling with effective removal of synthetic fibres and dyes [30,31]. Following carbamate formation, the material is dissolved in cold sodium zincate (ZnO/NaOH) solution to produce a spinning dope. After filtration, fibres are regenerated via wet spinning in either acidic or alkaline coagulation baths [122,123]. Notably, the CCA process is compatible with existing viscose infrastructure, particularly in terms of dope handling and fibre regeneration, thereby offering potential for industrial integration.

Enzymatic hydrolysis of cellulose

Enzymatic hydrolysis is a biochemical process in which cellulolytic enzymes cleave the glycosidic bonds of cellulose, converting it into glucose. In PES/CO blended textiles, enzyme hydrolysis plays a crucial role by selectively degrading the cellulosic fraction while leaving the PES portion untouched. As PES lacks hydrolysable glycosidic bonds, it remains as a solid residue, enabling physical separation after the cellulosic fraction has been enzymatically converted into soluble sugars or fines. In the studied PES/CO (50/50) textile waste, enzymatic treatment was performed using a cellulase-based enzyme blend. Results showed that cotton conversion strongly depended on enzyme concentration, and kinetic analysis demonstrated that degradation increased steadily over time, reaching a maximum cellulose-to-glucose conversion of 65% after 72 h [59]. Boondaeng et al. [124] explored several pretreatment techniques to modify textile waste to enhance enzymatic hydrolysis. The combination of NaOH pretreatment and a mild hydrothermal treatment in an autoclave at 121 °C for 15 min was chosen for its ability to produce a high enzymatic hydrolysis yield, with a cellulose content of 94.2 ± 0.57%. The NaOH treatment hydrolysed PES and swelled cotton fibres by penetrating the amorphous region and disrupting neighbouring crystalline regions of cellulose. Alkali pretreatments are said to significantly improve enzymatic hydrolysis, increasing it by up to 90% by reducing the crystallinity.

Acid hydrolysis of cellulose

Acid hydrolysis offers an effective pathway for selectively depolymerizing cellulose in PES/CO blends, enabling component separation for closed-loop chemical recycling. Under strong mineral acids (H₂SO₄), the glycosidic bonds in cotton cellulose are cleaved, allowing dissolution of the carbohydrate fraction while leaving the polyester matrix intact [125,126,127]. This selectivity arises from the higher hydrolytic stability of PES, which resists degradation under conditions sufficient to convert cellulose into soluble sugars or oligomers. In optimised hydrolysis conditions, including acid concentration, temperature, and reaction duration enhances cellulose depolymerisation efficiency while preventing PES damage, thereby maintaining polyester’s physical properties for reuse. Additionally, it improved the operational design to minimise secondary degradation products and enhance filtration of hydrolysed cellulose liquor. This approach supports sustainable recycling by enabling high-purity component separation through controlled acid-driven fractionation [128]. Processes such as HKRITA’s Green Machine demonstrate large-scale hydrothermal separation, in which cotton is decomposed into cellulosic powders, enabling fibre-to-fibre polyester recovery with over 97% yield while using only heat, water, and small amounts of green chemicals [39]. Meanwhile, BlockTexx’s S.O.F.T.™ process uses chemical separation to recover PET pellets (PolyTexx^®) and high-grade microcrystalline cellulose (CellTexx^®) [38]. Also, Nordic Bioproducts is developing an acid hydrolysis-based process to separate cotton and polyester into their own fractions [40]. Together, these technologies demonstrate the feasibility of scalable chemical recycling systems that integrate acid hydrolysis and complementary chemistries to recover both polyester and cellulose from blended textiles.

Oxidation of cellulose

TEMPO mediated oxidation for the separation of PES/CO blends

TEMPO-mediated oxidation has emerged as a promising method for chemically recycling PES/CO blends by selectively oxidising cellulose while preserving PES portion. In TEMPO/NaClO/NaBr systems, the primary hydroxyl groups in cotton cellulose are converted to carboxylates, weakening the fibre structure and enabling separation from the polyester matrix. Studies on PES/CO blends show that optimising the reaction parameters such as pH, temperature, oxidant loading, and reaction time directly influences the degree of oxidation and the ease of fibre disintegration [129]. High pH (i.e., 10 to 11; optimum to maintain 10.5) and elevated temperatures (≤60 °C) are sufficient to promote selective cellulose oxidation and cotton fractionation while remaining below the threshold for significant polyester alkaline hydrolysis. However, yields remain lower than pure-cotton oxidation due to blend heterogeneity. Importantly, TEMPO oxidation does not significantly degrade polyester molecular weight, making it suitable for high-quality polyester recovery. This method represents a valuable chemical fractionation route for sustainable textile recycling and circular material flows [129]. In general, the higher oxidation levels accelerate cellulose degradation, reducing polymer length and strength. K-periodate causes limited damage, while TEMPO both with NaBr/NaClO and bromide-free systems produce more carboxyls and stronger chain scission (i.e., selectively oxidises the C₆ primary hydroxyl to carboxyl group). Although extensive oxidation weakens fibres, it enhances reactivity, making highly oxidised oxy-cellulose more suitable for chemical recycling of cotton textiles into new value-added materials [130].

Table 3. Summary of cellulose-removing technologies for PES/CO textile waste.

Method	Conditions for the PES Removal	Notes	Refs
Dissolve CO in NMMO	Inputs: PES/CO (50/50, orange; 40/60 blue). NMMO + PES/CO waste treated for 2 h to dissolve cellulose, separate non-cellulosic fibres, and precipitate cellulose and use for ethanol and biogas production.	The cellulose recoveries from the blends ranged from 40% to 95%. Rotary evaporators are used for recycling NMMO with the same efficiency as fresh ones. Output: PES fibres, EtOH, and biogas.	[91]
Dissolve CO in Ionic liquid (AmimCl)	Inputs: PES/CO (30/70). AmimCl was combined 24:1 (L/S; g/g) with waste textile, heated at 80 °C for 3 h, then centrifuged to remove cellulose solution.	The technique yielded 55–65% cellulose and 92–96% PES. After disintegration and regeneration, cellulose I became cellulose II. Output: High purity of PES fibres (above 92%) was recovered, cellulose portion (above 55%) was dissolved completely, and regenerated cellulose films were made.	[131]
Dissolve CO in Ionic liquid (DBNH-OAc)	Inputs: PES/CO (50/50) fabrics; colour: White. DBNH-OAc is mixed with PES/CO waste to 5.7–6.7 (L/S; g/g) at 80 °C for 1 h.	DBNH-OAc dissolves without stabilisers and at lower temperatures than NMMO. Possible degradation of PES. Commercial Viscose and Tencel fibres are weaker than Ioncell fibres. Output: Regenerated cellulose fibres and PES	[28,29]
Dissolve CO in Ionic liquid (BmimCl and MmimDMP)	Inputs: PES/CO (50/50); colour: red and black. PES/CO waste treated with BmimCl/MmimDMP at a 20:1 L/S ratio with 130 °C for 3–10 h.	Process recovers cellulose from cellulose I to cellulose II. Output: nanocellulose recovered from separated cotton fibre. Polyester fibres also separated. No information on the efficiency and purity on both PES and CO.	[132]
Cellulose extraction by acetylation	Inputs: PES/CO (65/35). Stirring pulverised PES/CO waste with (CH3CO)2O and [Hmim]HSO4 at 100 °C for 12 h acetylated the cellulose. The solid comprising cellulose acetate and PES underwent extraction using of acetone or DMF.	Recovered PES was 96.2%, and cellulose was 84.5% from the PES/CO waste. Chances of PES degradations. Output: Cellulose acetate and PES	[133]
Cellulose extraction by acid hydrolysis (HNO3 and HCl)	Inputs: PES/CO (50/50); colour: white and colour. For the white PES/CO waste, 1 M HCl, and for the coloured ones, HNO3, with the refluxed conditions for 7 h at 90 °C.	Generally difficult to separate cellulose from fibre blends because part of the fibre remained bound to polyester, which reduced yield and diminished quality. But chemical processes can transform it into cellulose derivatives like CMC an CA. Output: Powder form of CMC and CA, PES.	[134]
Cellulose extraction by acid hydrolysis (H2SO4)	Inputs: PES/CO (60/40 and 55/45); colour: red and undyed. The waste textile was hydrolysed with 64 wt% H2SO4 at 50 °C for 90 min. The reaction was quenched with water, and the mixture was filtered to separate synthetic fibres from CNCs.	Properties of CNCs derived from PES/CO waste were comparable to those obtained from pure cotton. Certain 85% cellulose recovery. Output: CNC and PES cloth.	[135,136]
Cellulose extraction by acid hydrolysis (H3PW12O40)	Inputs: PES/CO (65/35); colour: red and black. PES/CO waste was hydrolysed for 6 h at 140 °C with an acid concentration of 3.47 M and a bath ratio of 1:20.	Diethyl ether makes easy to remove and recycle acids 98% without degradation of PES and MCC yields, and it keeps working even after several reuses. Output: Polyester, TPA, and MCC.	[137]
Cellulose extraction by hydrothermal treatment	Inputs: PES/CO (35/65); Colour: blue. Filtration of solid residues followed hydrothermal treatment of the waste textile at 150 °C in a 1.5 wt% HCl solution for 3 h at 60% consistency.	It yielded 49.3% cellulose powder, converting 84.5% of PES/CO waste into cellulose, 48.21% into MCC, and 15.57% glucose, while over 96% of PES was recovered. Output: Cellulose, MCC, Glucose, and PES.	[138]
Cellulose extraction by enzyme hydrolysis treatment	Inputs: PES/CO/wool. Waste textile underwent enzymatic treatment using a cellulase mixture in a sodium citrate buffer at temperatures 50 °C (i.e., 400 rpm) for a duration of 5 days. Subsequently, the treated textile was filtered to recover PES.	With most of the cellulose removed, the yeast fermentation process yielded ethanol from the recovered glucose, and the recovered PES exhibited purities over 90%. Output: Glucose, EtOH, and PES.	[139]
Cellulose extraction by enzyme hydrolysis (mechanical agitation)	Inputs: PES/CO. The waste textile was hydrolysed in 0.1 M acetate buffer with an enzyme dosage of 200 mg/g, pH 5.0, and 50 °C for 9 h.	Possibility for the cellulose degradations up to 45%. Output: MFC and PES fabric.	[140]
DES	Inputs: PES/CO; waste was treated with choline chloride–organic acid or choline chloride–urea) at moderate temperatures (≈60–120 °C).	DES selectively dissolves or depolymerises cellulose, while PES remains largely insoluble and can be separated mechanically. Considered a greener alternative to ionic liquids due to low volatility, lower toxicity, and ease of preparation. Effective for cellulose dissolution or controlled degradation under mild conditions. Output: Solubilised or partially depolymerised cellulose (recoverable as pulp, oligomers, or sugars after precipitation); solid PES fibres recovered.	[101,125]
Cellulose carbamate (CCA) technology	Inputs: PES/CO; PES/CO textiles treated with urea-based systems at elevated temperatures (typically 130–150 °C). Cellulose carbamate is soluble in alkaline aqueous media, enabling separation from PES fibres.	Outputs: Industrially relevant and aligned with viscose-type processing routes. PES fibres remain largely unaffected and can be mechanically recovered. Carbamate cellulose can be regenerated into fibres or films.	[141]
Oxidation	Inputs: PES/CO blended textiles treated under aqueous conditions using oxidative systems (e.g., peroxide-based or TEMPO-mediated oxidation).	Operates under relatively mild temperatures and avoids extreme alkaline or acidic environments. Outputs: Cellulose is converted into oxidised or depolymerised fractions suitable for further valorisation, while PES fibres remain largely intact with limited molecular-weight loss.	[129]

Note: carboxymethyl cellulose (CMC), cellulose acetate (CA), cellulose nano crystal (CNC), micro crystalline cellulose (MCC), Microfibrillar cellulose (MFC).

provides detailed conditions and descriptions of research conducted for the methods, including strengths and limitations of each technology.

Recycling PES/CO blends presents significant industrial and economic challenges because the two different technologies include PES removal and cellulose removal, which operate under fundamentally different reaction conditions and solvent systems, and obtain different outcomes.

Among the cellulose-removal technologies for recycling of PES/CO textile waste, several routes demonstrate higher commercial viability due to their solvent-recovery efficiency, industrial familiarity, scalability, and quality of recovered fractions. For instance, NMMO dissolution is currently the closest to industrial implementation because it leverages the already commercialised Lyocell process, achieves cellulose recoveries between 40–95%, and allows efficient NMMO recycling as well as preserves PES quality during the CO separation. Ionic liquids such as DBNH-OAc also show strong potential, dissolving cellulose at lower temperatures than NMMO and producing regenerated fibres comparable to Ioncell. So far, the cost of the solvent and their recovery remain barriers for industrial deployment. Cellulose carbamate (CCA) technology aligns well with viscose-type industrial infrastructure, enabling cellulose carbamate regeneration into fibres while separating the PES, which is largely unaffected. Acid hydrolysis using H₂SO₄ yields CNCs comparable to pure cotton with ~85% cellulose recovery and high PES recovery, making it industrially relevant due to familiarity with sulphuric-acid processing. Hydrothermal treatment yields 49.3% cellulose powder, 48.21% MCC, 15.57% glucose, and >96% PES recovery but requires high energy consumption. Acid hydrolysis and hydrothermal extraction are effective but generate corrosive waste streams and require specialised high-pressure equipment. Meanwhile, enzymatic hydrolysis offers mild conditions and high PES purity (>90%), yet long reaction days and cellulose loss limit their scalability. Other ionic liquids (BmimCl, Mmim-DMP) require high temperatures (130 °C) and long durations but more study is required to understand quality of the fractions, while acetylation and strong-acid routes (HNO₃, HCl) risk PES degradation or poor cellulose quality. DES systems provide greener alternatives with selective cellulose dissolution under mild conditions but remain early-stage. Overall, NMMO, DBNH-OAc, CCA, and H₂SO₄ routes are currently the most commercially viable pathways for PES/CO fibre-to-fibre recycling. Unlike polyester-removal routes, cellulose-removal pathways preserve polyester fibres at >90–96% purity, enabling mechanical reintegration into textile manufacturing. However, cellulose is transformed into regenerated forms such as cellulose acetate, Ioncell, CNC, MCC, or MFC, requiring downstream valorisation rather than direct reuse.

Across cellulose-removal chemistries for PES/CO waste, fibre deterioration varies with solvent strength and reaction condition. For example, NMMO dissolution preserves PES but cellulose recovery ranges widely (40–95%). AmimCl and DBNH-OAc maintain high PES purity (92–96%) but regenerated cellulose shifts from cellulose I to II, indicating structural modification. BmimCl/Mmim-DMP at 130 °C risks cellulose weakening. Acetylation yields high recoveries (96.2% PES, 84.5% cellulose) but may degrade PES. Strong-acid routes (HCl, HNO₃) reduce cellulose quality, whereas H₂SO₄ produces CNCs comparable to pure cotton. Hydrothermal treatment partially hydrolyses cellulose. Enzymatic routes minimise hornification but may cause up to 45% cellulose loss. DES and CCA systems preserve PES and offer milder cellulose modification.

For instance, the PES-removal routes, including glycolysis, alkaline hydrolysis, and organic-solvent dissolution, typically require high temperatures (70–200 °C and for 1–8 h) and substantial chemical consumption for processing, as these conditions increase energy requirements, need special equipment, and elevate operational costs. Although these methods preserve cellulose property, enabling high-quality dissolving pulp suitable for fibre-to-fibre regeneration, the recovered PES is degraded into monomers (i.e., TPA, EG, BHET) or oligomers. This necessitates repolymerisation before fibre spinning, adding further economic and environmental burdens. Solvent recovery is another major bottleneck: organic solvents used in PES-removal routes are costly (i.e., at industry levels) to recycle and often require multi-step purification, reducing industrial feasibility as well as the current economic comparison with the virgin PES.

Table 4. Summary of polyester and cellulose-removing technologies for PES/CO textile waste.

	Polyester-Removing	Cellulose-Removing
Operating conditions & energy	Often high temperature processing. Organic solvent dissolution typically requires 70 °C to 190 °C for 1–8 h. Glycolysis and chemical hydrolysis operate at high temperatures (90 °C to 200 °C). Enzymatic and some solvent mixes under room temperature [77,80] offer mild exceptions.	Highly diverse; mild to severe temperature. Ionic liquids and DES operate under mild temperature (50 °C to 130 °C), and acid and hydrothermal extractions run at 50 °C to 150 °C for up to 12 h. On the other hand, enzymatic methods require low temperatures (50 °C) but suffer from extremely long processing times (~5 days).
Chemical recovery & sustainability	High chemical consumption, organic solvent dissolution ([75]), and alkaline hydrolysis demand significant chemical volumes for washing, neutralisation, and solvent recovery. Hydrothermal offers a green, non-toxic alternative but demands specialised high-pressure equipment.	High potential for circularity. Ionic liquids, DES, and NMMO are highly recyclable, making them ecologically attractive. Strong acid hydrolysis (e.g., H2SO4, HCl) poses waste disposal challenges, though inorganic acids like H3PW12O40 allow up to 98% recovery.
Effect on recovered cellulose	Preserves cellulose structure. Because polyester is targeted for dissolution or degradation, the solid cellulose fraction is generally recovered with minimal degradation and without degradation of the structure ([82]), making it highly suitable for spinning (i.e., solution spinning) back into textiles.	Transforms or degrades cellulose. Cellulose is deliberately dissolved and regenerated into new forms (e.g., cellulose acetate, Ioncell, CMC, CNC, or microfibrillated cellulose). Enzymatic routes purposefully hydrolyse cellulose completely into glucose for biofuel (ethanol/biogas) production.
Effect on recovered PES	Degrades or powderises PES. Methods like glycolysis, alkaline hydrolysis, and enzymatic treatment break PES down into its chemical building blocks (TPA, EG, BHET) or powder form, requiring chemical repolymerisation to spin new fibres.	Preserves PES fibres. Because the cellulose is dissolved or hydrolysed away, high-purity, structural PES fibres (often >90–96% purity) are recovered mechanically, largely retaining their original textile properties.
TRL	Medium–high (glycolysis, hydrolysis)	Low–medium (IL/DES); medium (acid routes)
Major bottlenecks	Solvent cost, PES repolymerisation, corrosion	Cost of the solvent (i.e., Ionic liquids), long enzymatic process (i.e., 5 days), cellulose regeneration steps
Product quality	High grade cellulose; degraded PES monomers	High-purity PES fibres; regenerated cellulose

summarises both techniques with more commercial point of view.

Industrial feasibility depends on balancing reaction severity, solvent recyclability, quality of the outcome product requirements, and economic facts. PES removal routes are technologically mature but chemically intensive, while cellulose-removal routes offer higher circularity potential but face scale-up challenges. In fact, TRL for both removal technologies varies widely: glycolysis and alkaline hydrolysis are commercially established, whereas IL/DES systems remain at pilot scale. Ultimately, achieving industrial-scale PES/CO circularity requires integrating solvent-loop closure, feedstock pretreatment, fibre-quality preservation, and cost-effective downstream valorisation.

3. Challenges and Economic Environmental Potentials

Textile collection and sorting across Europe face significant operational and economic challenges. Although countries such as Spain, Poland, and the Netherlands have annual sorting capacities of 40,000–234,000 metric tons, domestic feedstock is not fully utilised. More than half of the textiles collected in the Netherlands are sorted abroad, while local facilities rely heavily on imports from countries like Germany [142]. This imbalance is driven by cost differences in collection fees across regions, making foreign textiles cheaper than domestic ones. Profitability remains highly dependent on high-quality rewearable textiles, which generate up to 90% of income for sorters, yet these only represent a portion of the collected material. As a result, economic vulnerability increases when the quality of incoming textiles declines. The global second-hand market is becoming saturated, reducing demand and prices for rewearables and pushing lower-value items into recycling streams. However, non-rewearable textiles currently make up about 26% of sorted output and often lack profitable end-markets. Chemical fibre-to-fibre recycling technologies remain insufficiently mature to process the growing volume of low-value post-consumer textiles. Downcycling options such as insulation or wipers offer extremely low margins (€0.02–€0.77/kg), raising concerns about long-term financial sustainability [142]. With rising collection rates and shrinking resale value, Europe faces increasing pressure to develop economically viable recycling pathways.

Life Cycle Assessment (LCA) on chemical recycling provides profound environmental savings compared to linear manufacturing. Previous studies indicate that replacing virgin cotton with recycled cotton fibres offers many advantages, including saving resources and avoiding impact on biodiversity due to cotton agriculture (such as excessive water usage and fertiliser/pesticide usage, followed by ecotoxicity) [19,143]. Simultaneously, recycling PES reduces fossil resource depletion by up to 24% and produces a lower net carbon footprint compared to waste incineration [144,145]. Comparative LCA studies show that environmental viability hinges on two variables: chemical recycling must maintain a solvent recovery rate above 99% to avoid heavy toxicity penalties, and the localised facility must be powered by a low-carbon, renewable energy grid. If powered by a coal-heavy grid, the processing emissions can negate the environmental credits achieved by displacing virgin materials.

Chemical recycling of PES/CO blends presents significant business opportunities as the textile industry shifts toward circular economic models. By recovering both polyester and cellulose from blended waste, companies can reduce dependence on costly virgin materials and stabilise supply chains. Advanced chemical separation technologies enable the production of high-quality recycled polymers and cellulose streams, creating valuable feedstocks for apparel, packaging, and technical textiles. This capability gives firms a competitive edge as demand for sustainable materials increases. Business models centred on recycled PES/CO products can enhance brand reputation, attract environmentally conscious consumers, and open premium market segments. Moreover, integrating chemical recycling into operations can stimulate new revenue streams through partnerships with waste collectors, fashion brands, and manufacturing industries seeking closed-loop solutions. The scalability of chemical recycling further strengthens profitability by processing large waste volumes efficiently. Ultimately, PES/CO chemical recycling supports environmental goals while unlocking substantial economic growth potential for forward-thinking companies.

4. Conclusions and Future Scope

This review focuses on PES/CO separation technologies, addressing a gap in the existing literature that discusses textile recycling. By concentrating exclusively on PES/CO blends, the review highlights how the dissimilarity of chemical and physical properties of polyester and cellulose creates unique barriers for fibre-to-fibre recycling. Fibre mechanical recycling remains limited by fibre purity, colour removal, and degradation of material quality, presence of short fibres need for more advanced chemical routes. The comparative analysis of polyester depolymerisation and cellulose-removal pathways shows that each technology presents distinct advantages and constraints. Alkaline hydrolysis preserves cellulose properties, while methanolysis and glycolysis offer efficient polyester recovery but face challenges related to cost, reaction severity, and suitability for blended feedstocks and their percentage of the blend proportion. Emerging routes such as aminolysis and ammonolysis demonstrate interesting mechanistic potential but require further validation beyond laboratory conditions, particularly regarding cellulose hornification and regenerated-fibre quality. Dissolution-based processes including NMMO, ionic liquids, DES, and cold alkaline systems provide routes for cellulose recovery, yet they face economic, solvent-recovery, and scalability limitations when applied to PES/CO blends. Enzymatic and acid-based degradation offer milder conditions and improved cellulose quality, but their industrial maturity remains low.

Overall, the review underscores that no single technology currently achieves high-quality recovery of both fractions at industrial scale. Advancing PES/CO fibre-to-fibre recycling will require coordinated progress in fraction purity, cellulose DP preservation, polyester monomer recovery, solvent management, and process integration. Strengthening circularity for blended textiles will depend on continued research, transparent evaluation of technology readiness, and supportive policy frameworks that encourage scalable, low-impact recycling solutions.