2101715-001243 -1- PROCESSES FOR CHEMICAL RECYCLING OF MIXED TEXTILE WASTE CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to U.S. Provisional Patent Application No. 63/595,513 filed on November 02, 2023, the contents of which is incorporated herein by reference in its entirety for all purposes. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH This invention was made with government support under Grant No. DE- SC0001004 awarded by the US Department of Energy. The government has certain rights in the invention. FIELD The present disclosure relates to processes for the chemical recycling of mixed textile wastes. BACKGROUND The demand for fiber production has increased due to the rise in global population and wealth. In 2021, 113 million tons of global fiber was produced to satisfy the needs of the growing global population, and 149 million tons are projected to be produced by 2030 if the global population and wealth continue to grow. The rising demand for textiles and shorter life span materials compared to a generation ago due to fast fashion result in a substantial accumulation of waste, estimated to be 92 million tons globally yearly. Less than 1% of textile waste is recycled, with approximately 73% dumped in landfills or incinerated, 14% lost during production and collection, and 12% downcycled into lower-value applications. This results in a notable loss of valuable resources and substantial environmental issues. Though mechanical recycling is a commonly used method due to recycle textile waste given its simplicity and low cost, it cannot handle multifiber textiles, additives, or colorants. Mechanical recycling also shortens fiber length and decreases fiber quality to lower-value products, such as insulation material, mattress stuffing, and wiping cloths. The most widely used textile fibers consist of poly(ethylene terephthalate) (PET) polyester, the same material as in PET bottles, whose market share was 54% of the global fiber production in 2021. While PET
2101715-001243 -2- chemical recycling techniques (such as hydrolysis, methanolysis, glycolysis, and enzymatic depolymerization) have extensively been studied, these recycling techniques are met with challenges when used on mixed textile wastes since the polyesters in the waste products are often interlaced tightly with other fibers (e.g., synthetic or natural polymers) consisting of cotton, nylon, spandex, dyes, and finishes. Mixed textile wastes require costly sorting and separation before reprocessing to avoid an undesirable mixture of products. A three-step procedure to recycle polyester from mixed textile waste to purified and decolorized bis(2- hydroxyethyl) terephthalate (BHET) has been reported using a homogeneous catalyst, high temperatures, and long reaction times for decolorization and glycolysis without addressing the remaining unreacted solids (see Z. Chen, H. Sun, W. Kong, L. Chen, W. Zuo, Closed-loop utilization of polyester in the textile industry. Green Chem.25, 4429–4437 (2023)). The compositional complexity of mixed textile waste requires direct recycling or upcycling to convert the mixed textile waste efficiently. Currently, there are no reports on chemical recycling of complex textile wastes that account for the fate of all components existing in the waste. Thus, to address the foregoing issues, we disclose herein processes for recycling mixed textile wastes that account for the fate of all components existing in the waste. SUMMARY Disclosed herein is a method for recycling a mixed textile waste, the method including (i.e., comprising) performing a microwave-assisted glycolysis on the mixed textile waste to produce a depolymerization solution, wherein the microwave- assisted glycolysis occurs at a temperature above 100°C, and wherein the mixed textile waste includes at least two materials selected from, but not limited to, polyesters, spandex, cotton or nylon. Disclosed herein are also recycled fibers and/or products produced from any one of the recycling methods disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS
2101715-001243 -3- Other features and advantages of the methods disclosed herein will be apparent to those skilled in the art reading the following detailed description in conjugation with the exemplary embodiments illustrated in the drawings, wherein: FIG.1 depicts an overview of an exemplary recycling method that converts materials in a mixed textile waste product into recyclable materials via a microwave-assisted glycolysis reaction and solvent dissolution. FIG.2 depicts glycolysis results for an exemplary interlaced polyester and cotton blend (50/50 PolyCotton). (A) Schematic of deconstruction process. Conversion of the polyester in the 50/50 PolyCotton blend (points connected by dashed lines) and yield of BHET (points connected by solid lines) as a function of time at (B) 150°C, (C) 180°C, and (D) 210°C are depicted. Reaction conditions are as follows: 0.5 g of textile (50/50 PolyCotton T-shirt), 5 mg of ZnO, and 5 ml of EG. FIG.3 depicts the solid residues that form upon the glycolysis of the 50/50 PolyCotton blend at various temperatures and times. FIG.4 depicts characterization data of the residual solid product formed from the glycolysis of the 50/50 PolyCotton blend. (A) TGA, (B) XRD, (C) FTIR. Solid residue product of the glycolysis of the 50/50 PolyCotton (solid black lines), initial 100% polyester (dashed lines), 100% cotton (dashed lines), and 50/50 PolyCotton (dashed lines). FIG.5 depicts SEM photographs of the solid residue product of the glycolysis of the 50/50 PolyCotton, a 100% polyester material, a 100% cotton material, and the 50/50 PolyCotton blend before glycolysis. FIG.6 depicts BHET yields from 100% polyester textiles containing dyes and finishes. The 100% polyester textiles were subjected to a microwave-assisted glycolysis reaction under the following conditions: 0.5 g of 100% polyester textile, 5 mg of ZnO, 5 ml of EG, 210°C, and 15 min. FIG.7 depicts solid residues of 100% polyester textiles that contained dyes and finishes. The solid residues are products of a microwave-assisted glycolysis reaction performed on the 100% polyester textiles. The conditions of the microwave-assisted glycolysis reaction are: 0.5 g of 100% polyester textile, 5 mg of ZnO, 5 ml of EG, 210°C, and 15 min.
2101715-001243 -4- FIG.8 depicts the residual solid amounts of various textile blends after being subjected to a microwave-assisted glycolysis reaction. N = 100% Nylon; (NS) = 90% nylon and 10% spandex; PCN = 100% polyester:100% cotton:100% nylon (1:1:1); PCNS = 100% polyester:100% cotton:90%nylon and 10% spandex (1:1:1). FIG.9 depicts an exemplary recycling process for mixed textile wastes. (A) Isolated components obtained from mixed textile waste with unknown compositions. (B) Proposed pathways for textile-to-textile and open-loop recycling. 3D = three-dimensional. MDI = methylene diphenyl diisocyanate. FIG.10 depicts a techno-economic analysis of an exemplary recycling process for mixed textile wastes. (A) The techno-economic analysis (TEA) process developed in ASPEN. (B) Cost breakdown for TEA analysis including capital, operating, raw material costs, and product sales. The inner and outer circles correspond to TEA results with lower and higher margins of product stream sales. DETAILED DESCRIPTION All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control. Unless stated otherwise, all percentages, parts, ratios, etc., are by weight. When an amount, concentration, or other value or parameter is given as either a range, preferred range or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range. Various aspects and embodiments of the recycling method will be described as follows. These various aspects and embodiments, however, may be embodied
2101715-001243 -5- in many different forms. Thus, the present disclosure should not be construed as being limited to these embodiments; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the technology described herein to those skilled in the art. As used herein, the term “about” refers to a value that is ± 5% of the stated value. In addition, it is understood that reference to a range of a first value to a second value includes the range of the stated values, e.g., a range of about 1 to about 5 also includes the more precise range of 1 to 5. It is also understood that the ranges disclosed herein include any selected subrange within the stated range, e.g., a subrange of about 50 to about 60 is contemplated in a disclosed range of about 1 to about 100. The present disclosure relates to a method for recycling a mixed textile waste, the method including one or more of the following: performing a microwave- assisted glycolysis on the mixed textile waste to produce a depolymerization solution, wherein the microwave-assisted glycolysis occurs at a temperature above 100°C and in a presence of a catalyst, wherein the mixed textile waste includes at least two materials selected from, but not limited to, polyesters, spandex, cotton or nylon. A representative illustration of this method is depicted in FIG.1. As used herein, a “mixed textile waste” is a composition of textile waste materials that have been isolated from various textile waste and production sites (e.g., landfills, recycling bins, post-industrial waste sites, textile production companies, clothing brands, and textile sorting companies) and optionally have been mechanically processed (e.g., carded or shredded). In exemplary embodiments, the mixed textile waste includes at least three materials selected from polyesters, spandex (or elastane), cotton and nylon. In exemplary embodiments, the mixed textile waste includes polyesters, spandex (or elastane), cotton and nylon. In exemplary embodiments, the mixed textile waste contains polyesters in a weight percentage, based on the total weight of the mixed textile waste, of about 0.1wt% to about 99wt%, about 5wt% to about 90wt%, about 10wt% to about 80wt%, about 20wt% to about 70wt%, about 30wt% to about 50wt%, or any weight percentage range or specific weight percent value falling within the range of about
2101715-001243 -6- 0.1wt% to about 99wt%. Polyesters that the mixed textile waste can include are, but not limited to, polyethylene terephthalate (PET), poly-1,4-cyclohexylene- dimethylene terephthalate (PCDT), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), plant-based polyesters and combinations thereof. In exemplary embodiments, the mixed textile waste contains cotton in a weight percentage, based on the total weight of the mixed textile waste, of about 0.1wt% to about 99wt%, about 5wt% to about 90wt%, about 10wt% to about 80wt%, about 20wt% to about 70wt%, about 30wt% to about 50wt%, or any weight percentage range or specific weight percent value falling within the range of about 0.1wt% to about 99wt%. Cottons that the mixed textile waste can include are, but not limited to, poplin, lawn, muslin, flannel, corduroy, canvas, jersey, Egyptian, brushed and combinations thereof. In exemplary embodiments, the mixed textile waste contains nylons in a weight percentage, based on the total weight of the mixed textile waste, of about 0.1wt% to about 99wt%, about 5wt% to about 90wt%, about 10wt% to about 80wt%, about 20wt% to about 70wt%, about 30wt% to about 50wt%, or any weight percentage range or specific weight percent value falling within the range of about 0.1wt% to about 99wt%. Nylons that the mixed textile waste can include are, but not limited to, nylon 6, nylon 66, nylon 6.10, nylon 4.6, nylon 12, ballistic nylon and combinations thereof. In exemplary embodiments, the mixed textile waste contains spandex (or elastane) in a weight percentage, based on the total weight of the mixed textile waste, of about 0.1wt% to about 99wt%, about 5wt% to about 90wt%, about 10wt% to about 80wt%, about 20wt% to about 70wt%, about 30wt% to about 50wt%, or any weight percentage range or specific weight percent value falling within the range of about 0.1wt% to about 99wt%. In exemplary embodiments, the mixed textile waste includes at least one textile material (e.g., a nylon, a polyester, a spandex or a cotton) containing one or more dyes and one or more finishes. Examples of dyes include, but are not limited to, fiber reactive dyes, natural dyes, VAT dyes, direct dyes, acid dyes, disperse dyes (such as, but not limited to, Red 1, Red 13, Red 15, Red 54, Red 60, Red 86,
2101715-001243 -7- Red 179, Yellow 3, Yellow 64, Yellow 23, Yellow 219, Yellow 123, Blue 1, Blue 3, Blue 19, Blue 56, Blue 79, Blue 35, Blue 106, Green 6, Green 5, Green 2, and Green 9), all-purpose dyes, azoic dyes, basic/cationic dyes, mordant dyes and sulfur dyes. Examples of finishes include, but are not limited to, antimicrobial finishes/coatings, antistatic finishes/coatings, ultraviolent resistant finishes/coatings, fire resistant finishes/coatings and water stain resistant finishes/coatings. Those of ordinary skill in the art will understand the scope of possible dyes and finishes that can be present in the mixed textile waste from the groups mentioned above and are readily capable of determining if a dye or finish falls within the above possible groups. In exemplary embodiments, the microwave-assisted glycolysis is performed at a temperature ranging from 100°C to about 250 °C, from about 120°C to about 230°C, from about 150°C to about 210°C, from about 180°C to about 210°C, or above 250°C. Those of ordinary skill in the art will understand that the temperature that the microwave-assisted glycolysis can be performed at depends on the composition of the mixed textile waste, the nature of the catalyst used in the glycolysis reaction, and the parameters of the microwave (e.g., the power of the microwave and the microwave’s ability to handle the vapor pressure produced from the reaction). The microwave can perform the glycolysis reaction at any power or power range such as, but not limited to, those falling with a range of 0.1 W to 850 W. As long as the temperature of the glycolysis reaction allows the microwave to keep the vapor pressure produced from the reaction below 30 bar, then those temperatures can be used during the glycolysis reaction. As long as the power used during the glycolysis reaction allows the microwave to keep the vapor pressure produced from the reaction below 30 bar, then those powers can be used during the glycolysis reaction. In exemplary embodiments, the microwave-assisted glycolysis is performed in the presence of a catalyst selected from, but not limited to, a metal oxide, a metal salt or a metal acetate. Examples of metal oxides include, but are not limited to, zinc oxide, cobalt oxide, chrome oxide, copper oxide, manganese dioxide, nickel oxide, sodium oxide, magnesium oxide, calcium oxide, lithium oxide, silver oxide, iron (II) oxide, iron (III) oxide, chromium (VI) oxide, and titanium (IV) oxide.
2101715-001243 -8- Examples of metal salts include, but are not limited to, sodium carbonate, sodium bicarbonate, potassium sulfate and sodium sulfate. Examples of metal acetates include, but are not limited to, zinc acetate, manganese acetate, cobalt acetate, copper acetate and lead acetate. In exemplary embodiments, the microwave-assisted glycolysis is performed in a diol such as, but not limited to, ethylene glycol, propylene glycol, 1,4- butanediol, propylene-1,3-diol, ethylene glycol/butanediol adipate (EBA), neopentyl glycol/butanediol adipate (NBA) and hexanediol adipate (HA). In exemplary embodiments, the microwave-assisted glycolysis is performed for at least 1 minute, at least 2 minutes, at least 5 minutes, at least 10 minutes, at least 15 minutes, at least 20 minutes, at least 30 minutes, at least 45 minutes, at least one hour, or any range of time of specific timepoint falling within the range of about 1 minute to about one hour. In exemplary embodiments, the microwave- assisted glycolysis is performed for more than 45 minutes. Those of ordinary skill in the art will appreciate that the duration of the microwave-assisted glycolysis reaction is dependent upon the composition of the mixed textile waste (e.g., if dyes and finishes are present), the nature of the catalyst used in the glycolysis reaction, and the parameters of the microwave (e.g., the power of the microwave). High powered microwaves could complete the glycolysis reaction in a matter of seconds depending on the complexity of the mixed textile waste composition, catalyst, solvent and type of microwave reactor vessel material used. For complex mixed textile wastes (i.e., those containing different varieties of textile materials, dyes and finishes) longer reaction times (e.g., those greater than 45 minutes) may be preferred. In exemplary embodiments, the mixed textile waste is mechanically processed before the microwave-assisted glycolysis is performed. Examples of mechanical processing include, but are not limited to, shredding and carding. In exemplary embodiments, the microwave-assisted glycolysis reaction concurrently (i.e., simultaneously) depolymerizes at least a portion of the spandex material and polyester material present in the mixed textile waste. In exemplary embodiments, the depolymerization solution includes at least one material selected from, but not limited to, bis(2-hydroxyethyl) terephthalate
2101715-001243 -9- (BHET), nylon, cotton, diphenyl-containing molecules (e.g., a diphenylmethane- containing molecule), spandex monomers, polyols (e.g., polytetrahydrofuran diols) and combinations thereof. In exemplary embodiments, the method includes diluting the depolymerization solution with an aqueous solution to separate soluble materials (e.g., BHET, diphenyl-containing molecules, spandex monomers and/or polyols) in the depolymerization solution from insoluble materials (e.g., cotton and/or nylon). In exemplary embodiments, the method includes distilling the depolymerization solution and subsequently cooling the distilled depolymerization solution. In exemplary embodiments, the subsequent cooling occurs at a temperature of about 4°C for about 24 hours and forms BHET crystals in the distilled depolymerization solution. In exemplary embodiments, the method includes removing the BHET crystals from the cooled depolymerization solution via a filtration method. In exemplary embodiments, the depolymerization solution contains cotton, nylon, polyols, or combinations thereof, and the method includes removing the cotton, nylon, polyols or combinations thereof from the depolymerization solution by filtering the depolymerization solution through a filter. In exemplary embodiments, the depolymerization solution also contains polyester depolymerization products (e.g., BHET) and diphenylmethane-containing molecules and the method includes removing the cotton, nylon, polyols or combinations thereof from the depolymerization solution before the polyester depolymerization products and diphenylmethane-containing molecules are recovered. In exemplary embodiments, the method includes washing the filtered cotton, nylon, polyols, or combinations thereof with an aqueous solution; and/or drying the washed cotton, nylon, polyols, or combinations thereof at a temperature of at least 100°C for about 24 hours. In exemplary embodiments, the washed cotton, nylon, polyols, or combinations thereof are dried on a filter paper at a temperature of at least 100°C. In these embodiments, the polyols melt into the filter paper, thus allowing for a rapid, simple separation and removal of the polyols from the washed cotton and nylons. In exemplary embodiments, the washed cotton, nylon, polyols, or combinations thereof are dried on a filter paper at room temperature (e.g., about
2101715-001243 -10- 20°C to 25°C) under vacuum. In these embodiments, the polyols do not melt into the filter paper, thus allowing for their recovery from the filter paper. In exemplary embodiments, the method includes subjecting the dried cottons and dried nylons to a 90% v/v or more formic acid solution to dissolve the dried nylons. In exemplary embodiments, the method includes separating the dissolved nylons from the cotton by filtering the 90% v/v or more formic acid solution. A formic acid solution containing less than 90% v/v formic acid can also be used as long as the solution selectively dissolves the dried nylons and not the dried cottons. In exemplary embodiments, the method converts at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95% or at least 99% of the polyesters present in the mixed textile waste into recyclable depolymerization products (e.g., BHET). In exemplary embodiments, the method includes recovering BHET from the depolymerization solution; and/or polymerizing the recovered BHET into a recycled polyester product. In exemplary embodiments, the method includes creating a yarn, filament and/or resin from the recycled polyester product. In exemplary embodiments, the method includes at least one of the following: creating a garment or house furnishing from a yarn made from the recycled polyester product; creating a rope, cord or net from a filament made from the recycled polyester product; and/or creating a boat, pipe, tank, helmet, coating, adhesive, or sealant from a resin made from the recycled polyester product. In exemplary embodiments, the method includes recovering a spandex monomer, for example ^^^ƍ-methylenedianiline (MDA), from the depolymerization solution; transforming the recovered spandex monomer, for example MDA, into a polymerizable product, for example, methylene diphenyl diisocyanate (MDI); and/or polymerizing the polymerizable product, for example MDI, into a recycled spandex product. In exemplary embodiments, the method includes recovering a polyol from the depolymerization solution and/or polymerizing the recovered polyol with either recovered MDI or virgin MDI to produce a recycled spandex product. In exemplary embodiments, the method includes recovering methylene diphenyl diisocyanate (MDI) and/or ethylene glycol derivatives of MDA from the depolymerization solution.
2101715-001243 -11- In exemplary embodiments, the method includes creating a polyurethane foam, a resin, an adhesive, a plastic, or a high-performance polymer from at least a portion of the recovered spandex monomer, polymerizable product and/or recovered polyol. In exemplary embodiments, the method includes recovering cotton from the depolymerization solution; and/or creating a yarn, a composite, a regenerated fiber, or a bioenergy material from the recovered cotton. In exemplary embodiments, the method includes recovering nylon comprising the depolymerization solution; and/or creating a yarn, an automobile part, a food packing material, a strainer, a rope, a cord, a net, or a composite material from the recovered nylon. The methods disclosed herein demonstrate efficacy in managing complex mixed textile waste, thus simulating real-world conditions of unsorted textile waste disposed in landfills. Because the sorting of unsorted textile waste disposed in landfills is recognized as a time-consuming and costly endeavor, some beneficial advantages of the methods disclosed herein are a reduction in processing costs and a rapid approach to recycling mixed textile waste. The methods disclosed herein allow for the rapid breakdown of polyester and spandex, and complete isolation of cotton and nylon from post-consumer mixed textile waste. This is significant as less than 0.5% of post-consumer textile waste generated globally is recycled due to their complex nature, while the rest is incinerated, accumulated in landfills, or leaks into the environment. Among the recycling methods, mechanical recycling of textiles has been the predominant, but due to its lower quality, the recycled fiber is used in low end applications such as insulation material, mattress stuffing, and wiping cloths. The technology disclosed herein provides a solution that addresses the unmet problem of recycling post- consumer mixed textile waste containing all major textiles used in fashion (polyester, cotton, nylon, and spandex) while retaining their quality. The methods disclosed herein are also capable of rapidly breaking down mixed textile wastes that contain dyes and finishes. The removal or separation of dyes and finishes from mixed textile wastes has been on ongoing challenge. Surprisingly, though the presence of finishes, for example fire-retardant finishes,
2101715-001243 -12- can slow the rate of glycolysis reactions. The glycolysis reactions disclosed herein can be readily modified to allow for the rapid depolymerization of these finished mixed textile materials, and the high separation and removal of dyes and finishes. Examples The present disclosure will be described in more detail with reference to the following Examples, which shows exemplary embodiments in accordance with the present disclosure. The present disclosure is not limited to these exemplary embodiments. Example 1: Chemical Recycling of Finished and Mixed Textile Wastes Materials and Methods: Chemicals and materials Control fabrics used in this Example were purchased from JoAnn, including 100% polyester (white and colored with or without finishes) and 100% cotton (bleached and scoured). The postconsumer textile waste was obtained from Goodwill provided by the University of Delaware Department of Fashion and Apparel Studies. EG (ethylene glycol) (anhydrous, 99.8%), BHET (>98.4%), zinc oxide (<50 nm), and deuterated dimethyl sulfoxide (DMSO-d
6) (99.9%) were obtained from Sigma-Aldrich. Ultrapure (type 1) water was used (Direct-Q3 UV-R). All textiles and chemicals were used as received. Reaction Procedures All experiments in this Example were performed on a Monowave 450 MW reactor (Anton Paar GmbH). This batch MW reactor controls the temperature, time, and maximum set power. An in-built infrared sensor and an external Ruby thermometer allow for temperature control.500 mg of textiles, 5 ml of EG, and 5 mg of the catalyst were placed in a MW reaction vial. The vial was inserted into the MW reactor and the reactor was programmed to maintain a constant temperature. On completion of a reaction, the reaction vial was allowed to cool down rapidly to room temperature.100 mL of distilled water was added to separate BHET and oligomers. The unreacted polymers and larger oligomers were removed using a Whatman filter paper. The filtrate containing the products dissolved in water was analyzed using HPLC. The residual water from the product solution was then evaporated under vacuum (72 mbar) at 60°C using a rotary evaporator and the
2101715-001243 -13- resulting BHET was crystallized by cooling the residual solution overnight to 4°C in a refrigerator after the addition of a small amount of distilled water to the residue. The resultant crystals were filtered using a glass filter and dried at 80°C. HPLC was used to quantify BHET concentrations with an Agilent 1260 Infinity coupled with a UV detector and a Zorbax Eclipse Plus C8 column. The mobile phase contained equal volumes of methanol and ultrapure water at a flow of ^^^^P/^PLQ^ZLWK^DQ^LQMHFWLRQ^YROXPH^RI^^^^^/^^$^%+(7^FDOLEUDWLRQ^FXUYH^ZDV^ constructed using a commercial standard. Conversions of textiles and yields of BHET were calculated using the following equations:
, wherein m,
i corresponds to the initial mass of textile samples, m
,f corresponds to the mass of the unreacted textile (obtained via filtration), mol
BHET corresponds to the BHET moles produced, and molPET corresponds to the initial moles of PET. MW
PET-RU is the molecular weight of the PET repeating unit [MW
PET-RU = 192 unified atomic mass units (u)]. Analysis of textile samples and products Textile samples and BHET crystals were characterized using a Bruker D8 ;5'^ZLWK^&X^.Į^UDGLDWLRQ^^^^ ^^^^^^^^^c^^DW^^^^N9^DQG^^^^P$^^(OHPHQWDO^ composition was measured using wavelength dispersive x-ray fluorescence (XRF) on a Rigaku Supermini 200 machine with a Pd anode.
1H NMR and
13C NMR spectra were recorded with Bruker AVIII400 and AVIII600 spectrometers in a DMSO-d6 solution. The NMR spectra were analyzed using the MestReNova software. Unknown peaks were identified with an Agilent gas chromatography– mass spectrometer with a DB5 column, LC-MS using Thermo Fisher Scientific Q- extractive Orbitrap, and electrospray ionization mass spectrometry. The attenuated
2101715-001243 -14- total reflectance-Fourier transform infrared (ATR-FTIR) data were collected using a Nicolet Nexus 640 spectrometer with a Smart Orbit Diamond ATR Accessory by scanning the sample from 400 to 4000 nm. DSC was conducted using a TA instruments Discovery 250 at a heating rate of 10°C/min and cooling rate of 5°C/min using 5 to 10 mg of sample. TGA was carried out using a TA instruments Discovery 5500 at a heating rate of 10°C/min under a N
2 atmosphere. SEM images of the textile samples were recorded on an Auriga 60 microscope (Carl Zeiss NTS GmbH) equipped with a Schottky field emission gun. Before imaging, the samples were deposited on an adhesive carbon tape and sputtered by a DESK IV sputter unit (Denton Vacuum Inc.) equipped with Au/Pd target. GPC was performed using an Agilent Technologies 1260 equipped with a PL–hexafluoroisopropanol (HFIP) gel column and refractive index detector. The mobile phase was HFIP + 10 to 20 mM trifluoroacetic acid, the flow rate was 0.3 mL/min, and the column was held at 40°C. Column calibration was performed with narrow dispersity poly(methyl methacrylate) standards. Technoeconomic assessment The process was developed for a textile feed throughput of 500 kg/hour. For evaluating the overall economics, the following assumptions were considered: (1) a grass roots or clear field project type was considered; (2) the total operating hours were 8000 hours/year; (3) a working capital percentage of 5% was assumed; (4) a total of 40% tax rate and 20% interest rate were considered for a 10-year economic life of the project; (5) a linear straight line depreciation method was considered; (6) operating costs incorporated raw material costs, operating supplies, operating labor charges, maintenance, utilities, overhead costs, and general and administrative expenses; (7) capital costs incorporated equipment purchase, equipment setting, piping, civil, instrumentation, electrical, insulation, subcontracts, overhead, escalation, and contingency costs; (8) the MW reactor efficiency was taken to be 85%, including absorbed energy yield and conversion of electricity to MW energy, and utility cost for MW reactor was calculated accordingly (see Y. Luo, E. Selvam, D. G. Vlachos, M. Ierapetritou, Economic and environmental benefits of modular microwave-assisted polyethylene terephthalate depolymerization. ACS Sustain. Chem. Eng.11, 4209–4218 (2023)); (9) Catalyst cost was taken to be $112/kg; (10)
2101715-001243 -15- for economic evaluation, dyes and polyols are not considered in the process; (11) water and EG were recycled back in the process. Experiment 1: Microwave-Assisted Glycolysis of Polyester:Cotton Blends Feedstock Characterization The feedstocks used in this Experiment are well-defined feedstocks of white 100% polyester textile, white 100% cotton textile, and a white 50/50 blend of polyester and cotton T-shirt, referred to hereafter as 50/50 PolyCotton. These feedstocks were chosen due to the polyester and cotton dominance in the fiber market, holding 54 and 22% share, respectively. The known compositions set benchmark standards for complex mixtures whose composition vary. Polyester depolymerization in the presence of cotton Before examining the effect that a microwave-assisted glycolysis reaction had on the white 50/50 blend of polyester and cotton T-shirt, the microwave- assisted glycolysis reaction was performed on the white 100% polyester feedstock and the 100% cotton textiles under the following conditions: 0.5 g of feedstock, 5 mg of ZnO, 5 ml of ethylene glycol (EG), 210°C, and 45 min. The glycolysis reaction demonstrated excellent activity on the polyester feedstock despite morphology differences from PET pellets, with 99% conversion and 90% yield of BHET. The cotton feedstock experienced a 7.8% mass loss upon glycolysis. A FTIR spectra of the cotton feedstock’s glycolysis solid-residue product resembled that of 100% cotton, indicating that cotton does not participate in glycolysis. Blank experiments of 100% cotton with and without a catalyst confirmed that minimal moisture loss (~5%) and light cotton degradation occurred due to prolonged heating rather than catalyst activity. Using the 50/50 PolyCotton T-shirt feedstock, time-dependent microwave- assisted glycolysis experiments were performed at various temperatures to understand the effect of cotton on polyester glycolysis when the two are interlaced tightly. Only the polyester reacted while the cotton remained intact. Higher temperatures accelerated the complete depolymerization of the polyester (FIG.2) . The cotton did not participate in the glycolysis chemistry. The color of the solution upon glycolysis changed from a light yellow hue at 150°C after 15 min to a
2101715-001243 -16- dark orange hue at 210°C after 45 min (FIG.2). This coloration occurred due to the gradual decomposition of cotton upon prolonged heating at elevated temperatures. At 150°C, the conversion increased at short times and then evolved slowly due to the slow depolymerization of the polyester and the cotton swelling by the solvent, which hindered mixing. At 180°C, the conversion kept increasing up to 30 min, whereas at 210°C, complete polyester conversion was achieved in less than 15 min. The BHET yield data traced, in general, the conversion data. The more notable difference between these two parameters at lower temperatures was attributed to the forming of intermediate polyester oligomers, thus indicating that the depolymerization of the 50/50 blend involved internal CƊO bond scission several units apart rather than the unzipping from the fiber backbone to the fiber monomers. At longer times the intermediate polyester oligomers converted to monomers, which was demonstrated by the occurrence of a powder forming on the dried remaining solids, indicative of oligomers (FIG.3). Such powders were absent in the dried remaining solids at 210°C after 15 min. To confirm the complete conversion of the polyester in the 50/50 blend at 210°C after 15 min, the solid residue was characterized by TGA, XRD and FTIR. The TGA data (FIG.4) showed that upon glycolysis, the characteristic polyester peak disappeared, and the curve resembled that of cotton. Similarly, the XRD and FTIR spectra upon glycolysis (FIG.4) resembled that of cotton alone (highlighted in light gray). A slight decrease in the crystallinity of the recovered cotton on the XRD spectra suggested that the glycolysis chemistry affected the crystal morphology of cotton. The small peak on the solid residue at ~1550 cm
í1 in the FTIR spectra corresponded to the leftover EG solvent. The findings were corroborated by SEM, where only convoluted cotton fibers were observed (FIG.5). Experiment 2: The Effect of Dyes and Finishes on Polyester Depolymerization Zinc oxide, an earth-abundant metal oxide, was used as a catalyst in the depolymerization (i.e., glycolysis) reaction due to its robustness, low cost, high activity, and ease of separation and recycling. A catalytic glycolysis process was performed on commercial 100% polyester textile materials containing dyes, additives, and impurities. These textiles, featuring
2101715-001243 -17- various dyes (red, blue, and yellow) and standard finishes [antimicrobial, antistatic, ultraviolet (UV) resistant, fire resistant, and water stain resistant], underwent glycolysis without pretreatment, as shown in FIG.6. Emphasis was placed on red, blue, and yellow textiles because these colors represent the three primary colors. Finish classification relied on information provided by retail store labels. Glycolysis reaction conditions were as follows: 0.5 g of 100% polyester textile, 5 mg of ZnO, 5 ml of EG, 210°C, and 15 min. The BHET yields for dyed textiles was lower than for undyed (white) polyester textiles. Disperse dyes, exclusively suitable for polyesters, bound to fibers through van der Waals forces and hydrogen bonding and appeared to interact with and hinder the catalyst’s activity. The blue textile dyes had a less profound on the catalyst’s activity due to their bulkier nature that causes steric hindrance or pore inaccessibility, resulting in a higher BHET yields. Longer reaction times could thus improve scalability and economic feasibility for the recycling of colored textiles. The resulting glycolysis product solutions were rich in dyes, further indicating the potential for the glycolysis reaction’s use in recycling methods (see FIG.7). Textiles with antimicrobial, antistatic, and water-and stain-resistant finishes exhibited similar trends. UV-and fire-resistant finishes on 100% polyester textile materials negatively affected glycolysis. The former increased textile hydrophobicity, causing mixing challenges with the hydrophilic EG solvent. The low yield for the 100% polyester textile material having a fire-resistant finish is attributed to the presence of phosphorus, which leads to char formation. Phosphorus compounds can also physically and chemically deactivate catalysts and substrates. Experiment 3: Glycolysis of a Mixture consisting of Polyester, Cotton, Nylon, and Spandex While polyester and cotton fibers are by far the dominant fibers in textile products, they are often blended with other fibers, such as spandex (or elastane) and nylon (or polyamide 6). The increasing popularity of activewear and athleisure, along with the growing demand for stretchable fabrics in the apparel and textile sectors, has fueled the demand for spandex and nylon fibers. Research on recycling combined polyester, cotton, nylon, and spandex textiles is limited, as most previous studies have focused on dual-material textiles, such as polyester-
2101715-001243 -18- cotton, cotton-nylon, cotton-elastane, and nylon-elastane blends. When multifiber textile waste has been considered, the emphasis has primarily been on recovering the polyester monomers with no information on the fate of cotton, nylon, and spandex. In view of this, a glycolysis reaction was conducted on white 100% nylon (N), 90% nylon/10% spandex (NS), 100% polyester:100% cotton:100% nylon (1:1:1) (PCN) and 100% polyester:100% cotton:90% nylon: 10% spandex (PCNS) to explore the potential codepolymerization of mixed textile materials during glycolysis. A textile composed entirely of 100% spandex does not exist, resembling more of a rubber band. As shown in FIG.8, both N and NS textiles experienced a mass decrease (15% for N and 13% for NS). These mass decreases were caused by the transformation of these textiles into powders and sticky solids. FTIR spectra of N’s solid residue resembled that of the starting textile, indicating no reactivity in glycolysis. Blank experiments with and without a catalyst confirmed that the mass loss resulted from thermal degradation at 210°C, surpassing the melting temperature of spandex (about 170°C) and approximately matching the melting temperature of nylon (about 220°C). This degradation was attributed to the degradation of spandex into sticky solids containing polytetrahydrofuran diols (spandex chain extender), which melted into the filter paper upon air-drying overnight at 70°C, and diphenylmethane-containing molecules. TGA and DSC results of the recovered nylon showed shifts to the left after glycolysis. This suggested that a reduction in nylon’s molecular weight occurred. The decomposition products were expected to be high molecular weight oligomers and/or caprolactam monomers due to peaks and changes in the number average molecular weight seen on high-performance liquid chromatography (HPLC), liquid chromatography–mass spectrometry (LC-MS), and gel permeation chromatography (GPC). To confirm whether nylon and spandex affected polyester depolymerization, glycolysis was performed on a blend of white polyester and cotton textiles mixed with N and NS textiles (PCN and PCNS in FIG.8). The observed mass loss was attributed to the complete depolymerization of polyester and the full and partial degradation of spandex and nylon, as observed earlier. The results also indicated
2101715-001243 -19- that other components in polyester-based textile wastes do not hinder the polyester depolymerization. Experiment 4: Recycling of Real Textile Waste with Unknown Compositions The properties of textiles are often tailored for specific applications by incorporating various additives during manufacturing, adding complexity to the deconstruction of discarded textiles with blended compositions. A chemical recycling process capable of deconstructing these blended compositions and real mixed textile waste is shown in FIG.9. In this process glycolysis is performed on a shredded random blend (0.5 g in total) with unknown polyester, cotton, nylon, and spandex compositions. At a reaction temperature of 210°C, polyesters in the random blend were completely converted to BHET and spandex was transformed into diphenylmethane-containing molecules and sticky polyols (spandex chain extender). Cotton and nylon remained intact. To recover BHET crystals, the product solution of the glycolysis reaction, now primarily containing BHET, EG, and water, underwent vacuum distillation to remove the water. This process leaves behind the EG fraction, which still contains BHET. The residual EG fraction was cooled overnight to 4°C in a refrigerator, forming BHET crystals. These crystals were simply filtered and dried at 80°C. The BHET, isolated through crystallization, underwent characterization by nuclear magnetic resonance (NMR), TGA, and DSC. Additional peaks, likely from decomposed dyes or organic impurities, are indicated in the recovery of nonwhite BHET crystals with 93% purity. Complete BHET decolorization can be achieved through subsequent recrystallization. The remaining EG contains the diphenylmethane-containing molecules from spandex (confirmed by LC-MS) and a mixture of unknown dyes implicated by the brown EG solution. Among all the diphenylmethane-containing molecules REWDLQHG^^^^^ƍ-methylenedianiline (MDA) was found to be the most valuable. MDA can be isolated using techniques such as solvent extraction, precipitation, or column chromatography. Unreacted cotton, nylon, and polyols (spandex chain extender) are insoluble in EG and were easily filtered off before vacuum distillation of the product solution. Washing the remaining solids with deionized water and air-drying them overnight at 100°C resulted in the degraded polyols melting into the filter paper and separating
2101715-001243 -20- from the cotton and nylon. Nylon and cotton were separated through simple solvent dissolution using 90% formic acid at room temperature. Nylon is hard to solubilize because of the strong hydrogen bond interaction between the amide groups. According to American Society for Testing and Materials (ASTM) D629, 90% formic acid is the only known solvent that solubilizes nylon at room temperature while keeping cotton intact. The dissolution of nylon occurred instantly upon contact with formic acid due to protonation of the carbonyl bonds by formic acid. Formic acid was strong enough to disrupt the hydrogen bonding between the amide groups within nylon chains but weak enough to avoid cotton degradation. The dissolved nylon was simply filtered off from cotton. The cotton was further washed with water and air-dried overnight at 70°C. Nylon was recovered by distilling out the formic acid. The isolated cotton and nylon were characterized by TGA, FTIR, DSC, and XRD. Some formic acid and dyes remained in the isolated cotton. Complete removal of formic acid can be achieved through subsequent washing with methanol and water. The remaining dyes, likely covalently bonded to cotton fibers, proved more challenging to remove. Solvent dissolution and distillation for nylon recovery substantially reduced its crystallinity. The decrease in recovered nylon’s number average molecular weight compared to 100% nylon textile without treatment was likely due to the reaction treatment at elevated temperatures. The mixed textile waste offers the potential for making multiple products (see Table 1). Table 1: Possible Products Created from Recycled Textile Waste Materials Recycled Textile Value Products Applications Waste Product ($/kg) Polyesters Yarn Garments, sportswear, jackets, 2.7 formed from coats, rainwear, suits, dresses, recycled BHET curtains, drapes, tablecloths, bedspreads, and other home furnishing products
2101715-001243 -21- F
ilament Ropes, cords, and fishing nets 1.1 Resin Boats, pipes, tanks, helmets, surfboards, coatings, 1.6 adhesives, and sealants Nylon Yarn Stretchy apparel such as leggings, socks, shirts, underwear, dresses, and 4.2 trousers and home décor such as blankets, pillows A
utomotive Tires, airbags, and seat belts 4.1 F
ood Food packaging and strainers 2.5 Industrial 3D printing, ropes, cords, and 2.6-50 fishing nets Composite FRP products such as boats, 4.0 pipes, tanks, and helmets Cotton Yarn Garments, sportswear, jackets, coats, rainwear, suits, dresses, curtains, drapes, tablecloths, 5.0 bedspreads, and other home furnishing products Composites Automotive, construction, and 2.2 packaging Regenerated Textiles, nonwovens, and 4.3 fibers hygiene products Bioenergy Heating, electricity, and $0.1 kWh transportation
2101715-001243 -22- MDA Polyurethane Insulation, cushioning, and 2.7 foams packaging Epoxy resins Glues, paints, inks, dental and bonding agents, and 2.5 adhesives microelectronic encapsulations Fiberglass Boats, pipes, tanks, and reinforced 4.0 helmets plastic High- Aerospace, electronics, and performance 12-100 engineering polymers The recovered BHET can be directly repolymerized into polyesters, with a market value ranging from $1.1 to $2.7/kg, depending on the application. The polyester obtained from the recycling process presents a clear entry point for the yarn making of textiles through melt spinning. MDA, a high-value monomer used in various industries, has a market value ranging from $2.5 to $100/kg. MDA can be reintroduced into textile production by chemically transforming it into methylene diphenyl diisocyanate (MDI), followed by polymerization with polyols to create recycled spandex. Successful fiber-to-fiber cotton recycling relies on preserving a high DP in cellulose (9000 to 15,000). However, multiple home laundering cycles lead to the aging of cotton fibers. Cutting and shredding the textile waste before chemical degradation results in fiber damage and breakage. All these result in a lower DP value of postconsumer cotton textile waste than virgin cotton. If used as is to make yarns, then the durability and strength of the yarns will be low. Alternatively, the short cotton fibers produced can be blended with virgin cotton to improve the quality of recycled yarn and reduce the cost of virgin yarn raw materials. They can also be used in composites to make regenerated fibers (e.g., viscose and lyocell) and cellulose nanocrystals or as fermentation feedstock for energy applications. The market values range from $2.2 to $5.0/kg and $0.1/kWh for bioenergy.
2101715-001243 -23- The recovered nylon can be melted and turned back into yarns or used in automotive, food, industrial, and composite applications. Its market value ranges from $2.5 to $50/kg. However, the reduced molecular weight could limit its applications for uses that require high tensile strength, stiffness, and melting point. The actual prices of all these applications vary based on region and material quality. The process in FIG.9 directly illustrates the potential for transforming mixed textile waste, regardless of its composition, back into textiles or for open-loop recycling. In the recycling process, dyes and changes in properties might hinder the use of recovered BHET, MDA, cotton, and nylon in various applications. To address this, additional steps may be needed. For example, recycled BHET that is colorized can be decolorized using activated carbon after redissolving in fresh EG at 100°C for 3 hours through subsequent recrystallization in EG, yielding white BHET at ^^99% purity. Adjusting processing conditions during manufacturing can also enhance nylon’s crystallinity by influencing its mechanical properties. Colorized nylon, like BHET, can be decolorized using activated carbon after dissolution in formic acid at 100°C for typically longer times due to the potentially higher concentration of dyes. The high solubility and low purity of MDA in EG can complicate its recovery, thus highlighting the possibility of needing to perform additional methods, such as distillation and extraction. Removing EG through vacuum distillation and using solvent-solvent extraction to separate MDA and other diphenyl-containing molecules from dyes is an efficient strategy for improving purity of isolated MDA. Because textile wastes tend to have an unknown material composition, determining the precise conversion and yield of the waste can be challenging. Nevertheless, in the broader context of global fiber production (52% polyester, 24% cotton, 6% man-made cellulosic fiber, 5% nylon, and 1% spandex), the process exemplified in this example and those disclosed herein can achieve a textile circularity rate of 88%. Example 2: Techno-economic Assessment of an Exemplary Chemical Recycling Process for Mixed Textile Wastes
2101715-001243 -24- To assess the economic feasibility of the processes disclosed and exemplified herein, a techno-economic analysis (TEA) was conducted on the exemplary process outlined in FIG.9. This approach investigated how varying product sales affect economic viability. A process flowsheet created with Advanced System for Process Engineering (ASPEN) Plus, followed by TEA evaluation, is shown in FIG.10. Focus was placed on a textile feed throughput of 500 kg/hour. The flowrates for the process streams used in the ASPEN model are provided in Table 2. Table 2: ASPEN Model Flowrates for Process Streams EG B
HET COTTON EG FORMIC MDA NYLON FEED MAKEUP Mass Flows 317.05 93.32 5496.76 12000.00 57.06 32.57 500.00 550.00 (kg/hr) COTTON 0.00 93.32 0.00 0.00 0.00 0.00 93.32 0.00 EG 0.00 0.00 5496.76 0.00 0.00 0.00 0.00 550.00 BHET 317.05 0.00 0.00 0.00 0.00 0.00 317.05 0.00 WATER 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 NYLON 0.00 0.00 0.00 0.00 0.00 32.57 32.57 0.00 FORMIC 0.00 0.00 0.00 12000.00 0.00 0.00 0.00 0.00 ACID MDA 0.00 0.00 0.00 0.00 57.06 0.00 57.06 0.00 A case with low product sales and another with high product sales were considered. The overall cost distribution of these cases are depicted in FIG.8 and provided in Table 3. Table 3: Overall Cost Distribution for Low Product Sales Case and High Product Sales Case Total Costs (USD/year) Low Product Sales High Product Sales Capital Cost $6,489,103.22 $6,489,103.22 Operating Cost $92,002,865.47 $92,335,443.10 Raw Material Cost $83,597,167.67 $83,905,109.92 Product Sales $85,339,601.32 $148,663,134.84
2101715-001243 -25- The techno-economic analysis used the profitability index (PI) as a key metric. For cases 1 and 2, PIs of 0.95 and 1.29 were obtained, respectively, with a value of 1 indicating breakeven. The costs outlined in the table of FIG.10 include capital ($6.5 million), operating ($92 million), and raw material ($84 million) with product sales, amounting to $85.4 million for case 1 and $148.7 million for case 2. These findings highlight the intricate relationship between product sales and project viability. In addition, the analysis suggests that as processing capacities increase, leveraging economies of scale, profit margins, and the project’s overall economic feasibility improve. This insight underscores the significance of scalability and strategic planning in maximizing the proposed approach’s economic potential. MW-assisted single stream of polyester recycling for BHET production provided 6.9 times reduction of global warming potential over the traditional petroleum driven pathway (see Y. Luo, E. Selvam, D. G. Vlachos, M. Ierapetritou, Economic and environmental benefits of modular microwave-assisted polyethylene terephthalate depolymerization. ACS Sustain.Chem. Eng.11, 4209–4218 (2023)). Given this reduction, the processes disclosed and exemplified herein are also expected to provide a significant reduction in global warming potential over the traditional petroleum driven pathway. It will be appreciated by those skilled in the art that the present disclosure can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the disclosure is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.