Suitable methods for recycling mixed polymer waste materials

Abstract

The present invention relates to a method suitable for recycling mixed polymer waste material, wherein the waste material comprises polyurethane (PUR) elements and dye-containing polyester elements mechanically bonded to these polyurethane elements, and the method comprises a series of steps including: dispersing the mixed polymer waste material in 2-(2-ethoxyethoxy)ethanol (DGME); leaving the polymer waste material dispersed in the DGME until at least a portion of the dye is extracted from the polyester into the DGME and at least 90% (w / w) of the PUR elements are dissolved in the DGME; separating the polyester elements from the DGME containing at least a portion of the dye and dissolved PUR elements; and reusing the polyester to manufacture a new product.

Description

Technical Field

[0001] The present invention relates to the field of recycling mixed polymer waste materials, where the waste materials include at least polyurethane (PUR) elements and dyed polyester elements mechanically connected to these polyurethane elements, particularly semi-crystalline polyesters such as polyethylene terephthalate (PET).

Background Art

[0002] Polyesters such as PET, which are commonly used for soda bottles and yarn materials for manufacturing textiles, are generally recycled because they are the most used consumer plastics. The post-consumer polyester recycling industry began as a result of environmental pressure to improve waste management. Another aspect that acts as a driving force for the polyester recycling industry is the slow natural degradation rate of polyester products. Many polyesters are non-degradable plastics under normal conditions because there are no known organisms that can consume relatively large molecules. For polyesters to degrade biologically, complex and expensive procedures need to be manipulated.

[0003] The first global efforts to recycle polyester waste materials (i.e., post-consumer polyester objects or materials) were in the 1970s, but the development of appropriate recycling methods has progressed rapidly. For example, in 2000, total PET consumption in Australia was 88,258 tons, with 28,113 tons recovered, representing a recovery rate of approximately 32%. Many researchers have reported that for PET recycling to be successful, PET flakes must meet certain minimum requirements. The main factors affecting the suitability of post-consumer PET flakes for recycling are the level and nature of contaminants present in the flakes. Minimizing the amount of these contaminants leads to improved quality of rPET (i.e., recycled PET). PET is contaminated by acid-producing contaminants, water, coloring contaminants, acetaldehyde, and other contaminants such as detergents, fuels, and pesticides through the use of PET bottles to store these substances.

[0004] Various different methods have been applied to recycle polyester waste materials, each with its own advantages and disadvantages.

[0005] Many recycling methods, such as pyrolysis and carbonization, are applied to generate energy. Pyrolysis of polyester waste was first described in the early 1980s. It is an alternative to PET disposal in landfills. Generally, polyester waste is pyrolyzed without further refining of the plastic waste. Most pyrolysis is carried out to produce aliphatic and aromatic hydrocarbons as an alternative to fossil fuels or as a source of chemicals. Carbonization is a second method of pyrolyzing polyester waste material. The polyester waste material is then simply separated, and subsequently the separated material is used as an additive in crushed stone mastic asphalt, cementitious materials, mortar, or concrete composite materials.

[0006] In recent years, chemical recycling of polyester has been developed and put into practical use. In chemical recycling (chemical decomposition) methods, the recycling of polyester waste materials is made possible by depolymerization into monomers and / or oligomers. This class can be divided into numerous subclasses depending on the type of reactants used in the decomposition. Examples include the application of ionic liquids for depolymerization or the use of castor oil for depolymerization. Polyester polymers can also be decomposed enzymatically, as first described in the 1970s. Like the use of ionic liquids and castor oil, this biochemical method has been developed to provide environmentally friendly polymer recycling procedures, in contrast to conventional chemical recycling methods. However, with respect to the complete depolymerization of polyester, the efficiency is quite low, and therefore quantitative recovery of a uniform reaction product for reuse is impossible.

[0007] Alcohol decomposition for PET depolymerization was first described in the early 1990s. This method was developed to avoid the drawbacks of acidic and alkaline hydrolysis (pollution problems) in order to provide a renewable and more environmentally friendly polymer decomposition agent. Generally, polyester is depolymerized with excess alcohol to obtain the corresponding esters of the corresponding acid and ethylene glycol. Among the alcohol decomposition methods, the reaction with methanol has been particularly important due to the low cost and availability of methanol. Ethylene glycol (a diol that falls under the class of alcohol decomposition, but whose use is sometimes classified separately as "glycol decomposition") is also primarily used in reaction extrusion to produce low molecular weight oligomers.

[0008] Because the reactivity of amine groups is higher than that of hydroxyl groups or alcohols used in the alcohol decomposition of polyesters, aminolysis and ammonialysis were developed for polyester recycling. However, the need for metal catalysts remains for alcohol decomposition.

[0009] Finally, an alternative chemical recycling of polyester is provided by controlled depolymerization of polyester using block chain severance with a specified amount of depolymerizer. This method produces polyester oligomers of a wider range of distinct molecular weights than existing chemical methods such as alcohol decomposition. However, this method requires fractionated polyester material that must be free of contaminants.

[0010] No matter how appropriate, all chemical recycling methods require the removal of at least non-polyester polymers and dyes, which are contaminants, in order to ensure high-end reuse options for recycled materials. In the art, many methods have been described that attempt to achieve the removal of dyes and PUR elements from polyester polymer materials, particularly polyester yarns in textile materials.

[0011] A specific problem is the removal of PUR elements such as PUR adhesives, foams (especially in mattresses), and yarns. PUR yarns, such as elastane, are widely used in textiles to improve the comfort and appearance of textiles that basically contain polyester yarns. PUR elements typically constitute about 1-25% w / w of any polyester material, extending to packaging, textiles, mattresses, etc. If the PUR elements are not mechanically bonded to the polyester elements (e.g., the core of a PUR mattress wrapped with (unbonded) polyester ticking), separation is easy. However, in many products, the PUR elements are mechanically bonded to the polyester elements, which makes separation difficult.

[0012] In the art, methods are known for separating mechanically connected but chemically distinct polymer elements. One such example is EP3816345 (assigned to New Wave Innovations BV). This patent discloses an apparatus for unraveling mixed polymer waste materials, comprising a chamber having an upright wall and at least two upright shafts, the upright wall having a sieve opening, and the upright shafts having at least one arm extending into the chamber across their respective axes. To prevent problems due to material accumulation on the wall, the wall is arranged as a plurality of wall sections, one wall section comprising a frame section and a sieve section. If the frame section is located at the downstream edge of the sieve section, the frame section extends less than 2 mm into the lumen beyond the first sieve section side facing the lumen of the chamber. Also, at the downstream edge of the sieve sheet, the second sieve section side facing away from the lumen extends deeper into the lumen than the upstream portion of the downstream adjacent wall section. This is a complex device, and its effectiveness depends on the type of object being processed.

[0013] Furthermore, various chemical methods for separating PUR elements from polyester elements are known in the art. WO2023044699 (assigned to Hong Kong Research Institute of Textiles & Apparel Ltd.) describes a method for separating Spandex(R), a polyurethane yarn, from a textile blend using a biosolvent such as ethyl lactate. However, this method is highly inefficient. Other solvent-based methods attempting to separate PUR elements from other polymers are described, among others, in WO2021249749 (assigned to BASF SE) and DE4109263 (assigned to Bayer AG). These are complex methods with mixed effectiveness.

[0014] US2023 / 0131718 (assigned to NanYa Plastic Corp) discloses a method for disposing of waste fabrics containing polyester, elastane, and dyes, comprising the following steps: step (a): providing waste fabrics containing polyester, elastane, and dyes; step (b): performing a first-stage treatment on the waste fabrics, including elution, to obtain a first liquid material and a first solid material. The first-stage treatment involves elution with a cosolvent such as dimethylformamide or dimethylacetamide mixed with an oxidizing agent. The oxidizing agent is a strong oxidizing agent that decomposes dyes, such as hydrogen peroxide, chlorates, hypochlorites, or ozone. The first solid material comprises recycled polyester, and the first liquid material comprises recycled elastane or degraded elastane, the latter of which makes elastane difficult to recycle.

[0015] Another approach involves combining the action of chemicals with mechanical treatments, such as the method described in DE10255840 (transferred to Daimler Chrysler AG). In this method, the removal of the polyurethane lacquer coating from the polymer substrate is achieved by treatment with an anhydrous organic alkaline solution and frictional interaction.

[0016] In either case, it is difficult and often ineffective to substantially separate the PUR elements from the polyester elements to which they are mechanically connected. Separately, these methods also hinder the removal of dyes often present in the polyester elements.

[0017] Regarding the removal of dyes, US2015 / 0059103 (assigned to Far Eastern New Century Corp (Taiwan)) discloses a method for decolorizing dyed polyester yarn, comprising separately providing dyed polyester yarn and a solvent capable of completely dissolving the dye. In this method, the solvent is heated to produce fresh vapor of the solvent, at a relatively high temperature, in the range between the glass transition temperature and the melting point of polyester. The fresh vapor is then condensed to form a condensed fluid of the solvent, and the dyed polyester yarn is then brought into contact with the condensed fluid of the solvent to dissolve the dye, and the dye is extracted from the yarn, forming a dye-containing solution and decolorized polyester yarn, which can be easily separated. It is difficult to find a solvent that can completely decolorize yarn without chemical decomposition of polyester.

[0018] US2022 / 0169786 (transferred to Syntec Co., Ltd. and JEPLAN Co., Ltd., both in Japan) discloses a method for producing decolorized polyester using a decolorizing agent containing a glycol ether type compound having a boiling point of 160°C or higher at atmospheric pressure, comprising the step of removing the dye by contacting the decolorizing agent with a colored polyester at least once while heating the decolorizing agent to a temperature below the melting point of the polyester, thereby obtaining a decolorized polyester. Depending on the type of decolorizing agent, this method may be effective, but it comes with very high energy consumption costs and serious risks due to the chemical decomposition of the polyester.

[0019] US2020 / 0270790 (assigned to NanYa Plastics Corp (Taiwan)) discloses a method for decolorizing dyed polyester yarn. This method includes the steps of providing an ether-alcohol solvent and heating the ether-alcohol solvent to its boiling point to continuously generate fresh gas having a temperature of 90°C to 200°C. In this way, the dye can be extracted from the polyester yarn to form an extract condensate containing the dye, which can be refluxed into the ether-alcohol solvent. This must be repeated many times to extract all the dye from the polyester yarn. This is a time- and energy-consuming process.

[0020] Nan Ya Corporation has another recently assigned patent application, namely US2023 / 0093536, in which, in addition to dyes, water-repellent compounds are also extracted from polyester yarn. In this method, a composite solvent containing a mixture of water and acetic acid is used in the extraction operation, which includes impregnating the polyester yarn (which may be in the form of a complete fabric) with the composite solvent to extract the dyes and water-repellent agents, and carrying out a polycondensation reaction in liquid state on the polyester fabric to increase the intrinsic viscosity of the polyester fabric and further remove residual impurities from the polyester fabric.

[0021] WO2022 / 003084 (transferred to Cure Technology BV) describes a method for removing dyes from low-viscosity oligomers by breaking down a polymer into low-viscosity oligomers before any dyes are removed, and using activated carbon or another dye-adsorbing particulate material that can be easily mixed into the material and filtered from there. However, apart from the fact that the process of separating carbon from the oligomer molten material is time-consuming and energy-consuming, the recycling of large amounts of activated carbon required for complete dye removal is a significant drawback of this method. [Prior art documents] [Patent Documents]

[0022]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

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Patent Document 9

Patent Document 10

Patent Document 11

Summary of the Invention

Problems to be Solved by the Invention

[0023] An improved method for separating mixed polymer waste materials, wherein the waste materials include polyurethane (PUR) elements and dyed polyester elements mechanically connected to these polyurethane elements, and there is a need for a method to remove PUR polymers from polyester polymers and simultaneously remove dyes from polyester. The latter polymers are often bulk polymers, which enables complete recycling of this bulk polymer, and thus it is most important to remove PUR elements and dyes therefrom. [Means for solving the problem]

[0024] To satisfy the objectives of the present invention, a method suitable for recycling mixed polymer PUR / dyed polyester waste material has been devised, the method comprising the steps of first dispersing the mixed polymer waste material in 2-(2-ethoxyethoxy)ethanol (DGME); second, leaving the polymer waste material dispersed in DGME until at least a portion of the dye is extracted from the polyester into DGME and at least 90% (w / w) of the PUR elements are dissolved in DGME; subsequently, separating the polyester elements from the DGME containing at least a portion of the dye and the dissolved PUR elements; and reusing the polyester of the polyester elements to produce a new product.

[0025] This invention is based particularly on the finding that the solvent DGME is suitable for extracting (typical) dyes from polyester elements up to 100% and simultaneously dissolving PUR elements up to 100%. The amount of dissolved dye and PUR depends on the conditions during dispersion, such as temperature and mixing (as is common in any extraction and solution process), as well as the time required to allow the dissolution of PUR and dye. Some recycling methods allow for the incomplete removal of dye and PUR.

[0026] This method yields a mixture of purified polyester elements dispersed in DGME, with the dye and PUR dissolved in the DGME. By separating the polyester elements from the DGME containing the dye and dissolved PUR elements, the polyester can be reused to manufacture new products. [Brief explanation of the drawing]

[0027] [Figure 1] The outline of the method according to the present invention is shown in general terms. [Modes for carrying out the invention]

[0028] definition Polyesters are polymers in which monomer units are linked together by ester groups. They are typically formed by polymerizing polyhydric alcohols with polybasic acids and are primarily used in the manufacture of resins, plastics, and textile fibers. It is well known that polyesters can be prepared by a condensation polymerization process in which monomers providing the "acid component" (including their ester-forming derivatives) react with monomers providing the "hydroxyl component." If desired, polyesters can also be composed of other linking groups, such as a certain proportion of carbonylamino linking groups -C(=O)-NH- (i.e., amide linking groups) or -C(=O)-NR 2- (tertiary amide linking group) may also be included. Polyesters commonly used can be aliphatic, semi-aromatic, or aromatic. Typical examples include polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), and Vectran(R), polycondensation products of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid. Of these, PET, also abbreviated as PETE, former PETP, or PET-P, is the most common thermoplastic polymer resin in the polyester family, and virgin material is considered one of the most important engineering polymers of the past few decades. It is considered a material with excellent versatility for many applications, used in clothing fibers, liquid and food containers, thermoforming for manufacturing, and in combination with glass fibers for engineering resins. It is also known by trade names such as Terylene, Arnite, Eastapac, Mylar, Lavsan, and Dacron. Polyester elements (such as polyester yarns) can contain up to 50% (w / w) non-polyester polymer chains (e.g., 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50%), but are still called polyester elements.

[0029] Dyes are coloring substances that chemically bond to the substrate to which they are applied. Typically, dyes impart color to the substrate when applied in a solution of either an aqueous solvent or an organic solvent.

[0030] Pigments are coloring substances that are completely or nearly insoluble. In contrast, dyes are typically soluble at least at some stage of their use.

[0031] Post-consumer textile waste is post-consumer fabric material that has reached or is completed at the end of its consumer life, i.e., the time during which the consumer uses it for practical or aesthetic purposes.

[0032] Depolymerization means reducing the molecular weight by breaking down the original polyester molecule into shorter molecules, such as oligomers.

[0033] Polyurethane refers to a class of polymers composed of organic units linked by carbamate (urethane) bonds. Polyurethane elements (such as polyurethane fibers or droplets of polyurethane adhesive) may contain up to 50% (w / w) non-polyurethane polymer chains (e.g., 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50%) but are still called polyurethane elements.

[0034] DGME is 2-(2-ethoxyethoxy)ethanol, a colorless liquid. It is produced by the ethoxylation of ethanol.

[0035] The aqueous solvent is a solvent containing at least 50% w / w water, preferably at least 55, 60, 65, 70, 75, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, and up to 100% w / w water.

[0036] Elastane is a polymer also known as polyurethane or polyether-polyurea copolymer. Elastane fabric is a general term used to describe trademarked textiles such as Lycra(R). This type of fabric is also called Spandex(R), and its main attribute is its remarkable elasticity. While Lycra(R), Spandex(R), and elastane are all made of the same material, the regional variation of the term "elastane" is most commonly used to refer to this type of fabric.

[0037] A portion of an element's quantity means less than the entire or complete amount of the element.

[0038] An oligomer is a chain of chemically bonded monomers containing up to 50 subunits. The term oligomer often refers to a mixture of molecules having different lengths (or different amounts of subunits), typically expressed by their average number of subunits.

[0039] Particulate matter refers to a substance that contains solid particles, i.e., small, localized objects that can be described by several physical or chemical properties such as volume, density, or mass. Typically, particles are macroscopic particles, such as powders and other granular materials.

[0040] Adsorption to particulate matter means binding to the surface of the substance, and does not exclude the possibility that the surface is, for example, the inner surface of a pore.

[0041] Mixing two materials means combining or blending these two materials to form a single macroscopic mass. The mass is preferably macroscopically homogeneous (i.e., on a 5mm scale, preferably on a 4, 3, 2, or 1mm scale, or even less than 1mm scale).

[0042] Shredding means dividing something into smaller pieces, for example, by cutting it.

[0043] Further embodiments of the present invention In a first further embodiment of the method according to the present invention, the polymer waste material is left dispersed in DGME until 95% (w / w) or more, and up to 100% (w / w), of the PUR elements are dissolved in DGME.

[0044] In another embodiment, after separating the DGME containing at least a portion of the dye and the soluble PUR element from the polyester element, the DGME is mixed with an aqueous solvent in which polyurethane solubility is less than 1%, thereby creating a liquid DGME fraction and a solid PUR fraction. In this way, PUR can then be easily separated from the dye, and the reuse of PUR and dye is possible simultaneously in a very simple and convenient manner. Advantageously, the aqueous solvent contains more than 90% w / w water. Water is safe and environmentally friendly, and PUR does not dissolve in it, so water is ideally suited for separating PUR from DGME. After mixing the DGME with the aqueous solvent, the solid PUR fraction is separated from the liquid DGME fraction, and then the dye is removed from the liquid DGME fraction to obtain purified dye and purified DGME.

[0045] In yet another embodiment, the step of reusing polyester to produce a new product includes first depolymerizing the polyester to an oligomeric ester, and then providing the polyester to a method of repolymerizing the oligomeric ester to a new polyester suitable for producing a new product. Preferably, the polyester is depolymerized to an oligomeric ester consisting of an average of 3 to 30 monomer units, preferably 5 to 20 monomer units. Although such methods are known in the art, it has been found that they can be advantageously combined with the PUR / dye dissolution method according to the present invention. The latter can yield a pure polyester that can be completely further chemically processed to yield a new (virgin-like) polyester.

[0046] Advantageously, if some of the dye remains in the polyester after the polymer waste material is dispersed in DGME, this portion can be easily removed from the oligomer ester by adsorption to particulate matter in the mixture with the oligomer ester, followed by a step of separating the oligomer ester from the particulate matter containing the adsorbed dye. In this way, a completely decolorized oligomer ester suitable for repolymerization is provided. Such decolorized oligomers have been found to be ideally suited for repolymerization into high-end quality polyesters.

[0047] It should be noted that particulate matter can be actively mixed with oligomeric esters (or mixed with polyesters to precede their depolymerization and provide the necessary mixture for depolymerization), or passively mixed, for example, by pumping the oligomeric esters (which are liquid due to their low polymerization level) through a bed of particulate material, or by any other means that enable the formation of a mixture of particulate matter and oligomeric esters.

[0048] It should also be noted that the separation step in which the oligomeric ester is separated from the particulate matter is not limited to a step in which the oligomeric ester is actively separated from the particulate matter. For example, in a method in which the oligomeric ester is pumped through a solid bed of particulate material, separation between the two components essentially occurs at the edge of the bed.

[0049] This embodiment is based on the recognition that combining two dye removal steps—namely, partially removing the dye with a solvent and then removing the remainder with a particulate adsorbent after the polyester has been broken down into oligomeric esters—provides much greater flexibility in the process of completely removing the dye from polyester. Even when 100% dye removal from polyester is required, it is not necessary to completely remove the dye in the DGME extraction step. Advantageously, removing the dye residue from the oligomeric esters using a particulate adsorbent is also relatively easy, as the amount removed is far less than the total amount of dye present in the original polyester yarn. Therefore, for example, a less efficient adsorbent may suffice.

[0050] Because the viscosity is too high to facilitate mixing with particulate matter and / or separation of particulate matter from the oligomer, the oligomer ester preferably consists of an average of up to 30 monomer units. However, a number of monomer units less than 3 is also undesirable due to the need for repolymerization to polyester. When the number of units in the oligomer is less than 3, it takes too long. This time is not only costly but also carries the risk of undesirable degradation of the polyester.

[0051] For dye adsorption, highly porous adsorbents with good selectivity are typically used. Activated carbon exhibits excellent ability to remove organic compounds such as dyes. Adsorption of dyes onto adsorbents can be by physical or chemical methods. In physical adsorption mechanisms, dye molecules adhere to the adsorbent surface under the influence of van der Waals forces and hydrogen bonding. During chemiadsorption, dye molecules or ions adhere to specific surface functional groups or sites by chemical bonding. Many different dye functional groups can be involved in multiple adsorbent adhesions across a wide range of available adsorbents.

[0052] In further embodiments, the particulate material is selected from activated carbon, zeolite, silica gel, activated alumina, inorganic minerals, chitosan, resin particles, carbon nanotubes, and aluminophosphate molecular sieves, with activated carbon (also indicated as AC) being a preferred particulate material.

[0053] In yet another embodiment of the method according to the present invention, the method includes the step of filtering the oligomer ester using a filter having a mesh size of less than 20 μm, preferably 5 to 10 μm. Due to its low viscosity, the oligomer ester can be filtered with low energy cost to remove pigments and any other small particulate matter, if present.

[0054] In a preferred embodiment of the method according to the present invention, the polyester is depolymerized to an oligomeric ester by alcohol decomposition. Such a method is known, in particular from WO2022 / 003084 (delegated to Cure Technology BV) and has been found to be particularly suitable for use in the present invention. In particular, it has been found to be advantageous to depolymerize the polyester to an oligomeric ester by a two-step procedure comprising two separate, sequential steps, in which alcohol is added in both steps to depolymerize the polyester. More particularly, it has been found to be advantageous that in the first of the two sequential steps, polyester waste is fed into an extruder operating at a temperature higher than the melting temperature of the polyester, along with a first amount of alcohol co-feeding to the extruder, to produce a fluid mixture containing at least partially depolymerized molten polyester, and in the second of the two sequential steps, the fluid mixture is fed into a continuous stirred tank reactor (CSTR) operating at a temperature higher than the melting temperature of the polyester, along with a second amount of alcohol co-feeding to the CSTR, thereby yielding an oligomeric ester.

[0055] In yet another embodiment of the method according to the present invention, the polyester is polyethylene terephthalate (PET), and the oligomer ester contains oligomers of 4 to 16 bis(2-hydroxyethyl) terephthalate (BHET) units, preferably 6 to 14 (BHET) units, most preferably 8 to 10 BHET units, in an amount exceeding 50% w / w, preferably exceeding 60, 65, 70, 75, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89% w / w, or even exceeding 90, 91, 92, 93, 94, 95, 96, 97, 98, 99% w / w, or even exceeding 100% w / w.

[0056] Preferably, at least 50% (w / w) of the dye, preferably at least 60, 70, 80, 85 or even 90%, and up to 91, 92, 93, 94, 95, 96, 97, 98 or even 99%, is extracted from the polyester into DGME.

[0057] In one embodiment, the mixed polymer waste material is a textile material that typically includes polyurethane yarn and dyed polyester yarn. Dyed polyester textile materials are widely used and are often "contaminated" with PUR elements such as elastane yarn. In fact, the majority of textile waste is waste that can be recycled using current methods.

[0058] In further embodiments of the method according to the present invention, in which the textile material includes cotton yarn in addition to PUR and polyester yarn, the cotton yarn is removed by either mechanical and / or chemical means (such methods are commonly known in the art) before the step of separating the polyester elements from the DGME containing at least some of the dye and dissolved PUR elements. This is to prevent the cotton elements or products derived therefrom from interfering with other process steps and potentially remaining in the oligomeric esters. Typically, the cotton is decolorized before being removed from the textile waste. The step of removing the cotton elements may be performed before or after the DGME extraction step.

[0059] Finally, the present invention is embodied in a method preceding one or more steps selected from the group consisting of 1) removing any decorations such as buttons, zippers, and labels from textile waste; 2) washing the textile waste (for example, to remove any coatings such as DWR (durable water repellent), spinner oil, dirt, or sint); and 3) shredding the textile waste into smaller pieces. The order in which these steps are performed is not essential to this embodiment.

[0060] The present invention will be further explained using the following specific examples. [Examples]

[0061] Figure 1 schematically shows an overview of the method according to the present invention.

[0062] Example 1 provides various experiments including a two-step depolymerization process for polyester.

[0063] Example 2 shows the initial decolorization step of a blue fabric using ethyl lactate.

[0064] Example 3 shows the initial decolorization step of the same blue fabric using DGME.

[0065] Example 4 is an example of first decolorizing a green fabric with ethyl lactate, the fabric is coated with DWR, and the fabric contains a small amount of elastane (PUR) yarn, which is mechanically bonded to polyester yarn.

[0066] Example 5 shows the results of decolorizing the same green fabric using ethyl lactate at a lower temperature.

[0067] Example 6 is another example of decolorizing the same green fabric using DGME.

[0068] Example 7 was conducted to evaluate the use of this method using textile waste containing a relatively large amount of elastane.

[0069] Example 8 shows the dissolution of compressed elastane fibers.

[0070] Example 9 provides a further example of the dissolution of compressed elastane fibers.

[0071] Example 10 demonstrates the dissolution of polyurethane foam as an element in textile waste.

[0072] Example 11 demonstrates the decolorization of a blue fabric using xylene.

[0073] Example 12 briefly describes some further comparative examples.

[0074] Figure 1 Figure 1 schematically illustrates the method according to the present invention. In the illustrated method, washed and pre-dried mixed polymer waste material, in this case textile waste containing elastane and dyed PET yarn, is treated with DGME in the first step to extract a substantial portion of the dye from the polyester yarn and dissolve all the elastane yarn. Subsequently, the PET is separated from the liquid DGME fraction and depolymerized and repolymerized in a series of steps 2-8, while simultaneously removing any remaining dye (and pigment) from the PET. Step 9 is an additional repolymerization step, including solid-state polymerization, to achieve an intrinsic viscosity (IV) greater than 0.6.

[0075] The depolymerization process is based on the generally known equilibrium reaction of PET in alcohol decomposition based on monoethylene glycol (MEG). BHET ←→ [PET] x + 1 / 2 x MEG

[0076] By adding MEG to a polyester molten material, the equilibrium shifts to the left, resulting in shorter polymer chains, ultimately oligomers (fewer than 100 repeating BHET units, particularly 50, 40, 30, 20, or even fewer than 10 units), and a decrease in viscosity. By removing the MEG, for example using vacuum or nitrogen, the short chains react with each other to form polyester again. The viscosity of the material is controlled by controlling the depolymerization rate, and therefore the oligomer length.

[0077] In step 1, the textile waste material is treated with DGME by dispersing the material in DGME and applying continuous mixing. In this way, a substantial portion of the dye is extracted from the polyester yarn and at the same time the elastane yarn is completely dissolved. The inventors refer to further examples below that show that DGME is ideally suited in this step compared to other solvents. Next, in step 2, the partially decolorized polyester fraction is fed into a conical co-rotating twin-screw extruder. The extruder is operated at 280°C to completely melt the polyester. An injection point for adding MEG (indicated as arrow 50) is provided adjacent to the end of the conical twin-screw extruder (10% of its length) to obtain the first step in depolymerization to reduce viscosity. For this purpose, about 1% MEG (w / w) is added. The reduction in IV also helps to minimize the pressure difference across the first filtration step 3 to allow filtration with an 80 micrometer mesh size. The filter also functions as a static mixer, homogenizing the mixture and distributing the added glycol with the molten polymer to allow it to react completely with the shorter polymer chains, resulting in an equilibrium molecular weight distribution (dispersion grade approximately 2). The process parameters are selected so that the MEG reacts (almost) completely and no free MEG remains (almost) present.

[0078] The partially depolymerized and filtered material is fed into a single-screw extruder in step 4. Typically, about 3–4% of MEG is fed into this extruder (indicated by arrow 50'). At the end of the extruder, the viscosity of the molten material is measured. The viscosity level is controlled by an automatic control loop (not shown in Figure 1) that controls the level of MEG fed into the single-screw extruder. This automatic control loop results in a consistent viscosity, typically an IV of 0.1–0.2, independent of the IV of the starting material. Due to the intrinsic transesterification reactions occurring in the extruder, polydispersity may remain low, preferably about 2–3, depending mainly on the residence time in the extruder (which can be adjusted during the process by controlling the initial feed rate and extruder speed).

[0079] The depolymerized material undergoes a second filtration in step 5. Since IV is approximately 0.15, the filtration size can be reduced compared to the first filter without the pressure difference across the filter becoming too high, and is preferably 40 micrometers.

[0080] In step 6, a material with an IV of approximately 0.15 (0.1-0.2) is continuously added to a continuous stirring tank reactor (CSTR). In this CSTR, MEG is also added (indicated by the 50'' arrow) to further depolymerize the material to the required viscosity / oligomer length.

[0081] In CSTR, further decolorization occurs by adding activated carbon, as indicated by arrow 60. The activated carbon may be pre-selected for its best performance in absorbing any remaining colorants (i.e., dyes) present in the polyester waste. After CSTR, the low-viscosity oligomer / activated carbon mixture is pumped through a three-stage microfiltration (20 / 10 / 5 micrometers) step 7 to remove colorant-loaded carbon particles from the oligomer. A parallel set of three filters is installed, and if the pressure difference across the filters is too high, the molten material can be pumped through the parallel set, while the first filter set can be washed.

[0082] After filtering the molten material while it is still at a high temperature of approximately 250°C, the molten material is pumped into a polycondensation reactor (step 8) operating at a temperature of approximately 260°C under a vacuum of 1 mbar to remove MEG, resulting in a shift of the BHET / PET equilibrium to the right and the formation of a PET polymer. Depending on the processing conditions, polyester with an IV of 0.4-0.6 can be obtained. The polymer is removed from the reactor and pumped through a perforated die plate, thus generating polymer strands. These strands are cooled and cut into amorphous granules to produce new polyester products.

[0083] [Example 1] Example 1 describes a two-step depolymerization process and integrated decolorization of the oligomer ester obtained according to the present invention. In particular, this example uses MEG as a reactant for depolymerizing PET in a single-screw extruder, combined with CSTR, configured as a continuous process, to provide results achieved by alcohol decomposition, particularly glycol decomposition. This process is described in detail in international patent application WO2022 / 003084 (Example 2). Although this patent application is used for recycling carpet and bottle waste, it is similarly applicable to textile waste including polyester yarn.

[0084] Reaction extrusion tests were conducted using up to 3% w / w of MEG with dry PET yarn. The glycol decomposition process occurred very rapidly. PET depolymerized to oligomers within 30 seconds. The added MEG reacted almost completely within this timeframe. Over 98% of the added MEG was used in the glycol decomposition process.

[0085] HPLC analysis confirms that a significant amount of BHET tetramerizes when more than 12% MEG is applied (see Table 1). However, this level of depolymerization is not necessary to allow the molten material to be filtered. A viscosity of (IV=±)0.1 is sufficient for the filtration process. This corresponds to 8-10 (octa-deca) oligomers, which requires 5-8% w / w MEG.

[0086] [Table 1]

[0087] At such relatively low viscosities (approximately 0.1 IV), it is very easy to remove any remaining colorant and adsorb any remaining dye using activated carbon or any other particulate material. The activated carbon itself, along with any pigment (if present), can be removed by using the filter described above with respect to Figure 1.

[0088] [Example 2] Example 2 describes the initial decolorization step of a pure blue polyester fabric using ethyl lactate as a solvent. First, a total of 75 g of blue-colored fabric, typically used as a sofa cover and made from PET fibers, was cut into small pieces and then placed in a 500 mL glass reactor equipped with a condenser, thermometer, and nitrogen inlet. Next, 450 g of ethyl lactate was added, and the contents of the glass reactor were gently heated under reflux (150-155°C) with continuous magnetic stirring using a heating mantle. After reaching reflux conditions, the contents of the glass reactor were held under these conditions for 60 minutes. During this period, the visible removal of the colorant was facilitated with the help of the ethyl lactate solvent, and the solvent turned from dark green to blue and appeared clear. Then, less colored fabric pieces were separated from the dark green to blue solvent containing the removed colorant by standard solid-liquid filtration.

[0089] Next, the fabric pieces from the first colorant removal step were placed in the same glass reactor used in the color removal step, followed by the addition of 450 g of fresh ethyl lactate. The contents of the glass reactor were gently heated under reflux (150-155°C) with continuous magnetic stirring using a heating mantle. After reaching reflux conditions, the contents of the glass reactor were held under these conditions for 60 minutes. During this period, the visible removal of the colorant was facilitated by the ethyl lactate solvent, thereby causing the fabric pieces to turn slightly green and the solvent to change from dark green to blue. The slightly green fabric pieces were then separated from the dark green to blue solvent containing the removed colorant by standard solid-liquid filtration.

[0090] It is estimated that approximately 60-80% of the dye (w / w) was removed from the fabric during the extraction process.

[0091] [Example 3] Example 3 shows the initial decolorization step of the same blue polyester fabric used in Example 2, but here diethylene glycol monoethyl ether (DGME) is used as the solvent. First, a total of 20 g of fabric was cut into small pieces and then placed in a 500 mL glass reactor equipped with a condenser, thermometer, and nitrogen inlet. Next, 125 g of diethylene glycol monoethyl ether (DGME) was added, and the contents of the glass reactor were gently heated under reflux (200-205°C) with continuous magnetic stirring. Even during heating, the fabric pieces showed almost complete color removal, and the solvent turned orange to red and appeared clear. After reaching reflux conditions, the contents of the glass reactor were held under these conditions for 15 minutes. Then, by standard solid-liquid filtration, the decolorized fabric pieces (slightly yellow) were separated from the orange to red solvent containing the removed colorant.

[0092] It is estimated that approximately 90-95% w / w of the dye was removed from the fabric during the extraction process. This partially decolorized material can then be used as input for a depolymerization process in which the remaining dye is removed with activated carbon.

[0093] [Example 4] Example 4 is an example of the initial decolorization of a green fabric with ethyl lactate, the fabric having a so-called durable water-repellent (DWR) coating on its surface. This is to evaluate whether the dye can be extracted from polyester even in the presence of such a common coating. First, a total of 1 g of green fabric, used for outdoor applications and made mainly of PET fibers and 2% elastane fibers, with a durable water-repellent (DWR) coating on its surface, was cut into small pieces. 60 g of ethyl lactate was placed in a 150 mL glass beaker equipped with a thermometer, and the contents of the glass beaker were gently heated to 150 °C (just below the boiling point) using a heating plate while continuously magnetically stirring. When the preset temperature was reached, the fabric pieces were placed in the glass beaker, and the temperature of the resulting mixture was maintained at 150 °C for 15 minutes. During this period, the visible removal of the colorant was facilitated with the help of the ethyl lactate solvent, thereby turning the fabric pieces slightly green and the solvent dark green. Next, a slightly green fabric piece was separated from the green solvent containing the removed colorant by standard solid-liquid filtration. After drying, one drop of water was applied to the surface of one of the predominantly decolorized fabric pieces. The droplet remained intact and did not spread on the surface (no wetting), indicating the presence of a water-repellent coating on the fabric surface.

[0094] Despite the presence of the DWR coating, it is estimated that the extraction process removed over 80% w / w of the dye from the fabric. This indicates that dye extraction from polyester elements using a solvent is possible even in the presence of a DWR surface coating.

[0095] [Example 5] This example demonstrates the decolorization of green fabric using ethyl lactate at a lower temperature. First, a total of 1 g of green fabric, used for outdoor applications and made primarily of PET fibers and 2% elastane fibers, with the same DWR coating as used in Example 4, was cut into small pieces. 45 g of ethyl lactate was placed in a 150 mL glass beaker equipped with a thermometer, and the contents of the glass beaker were gently heated to 185°C using a heating plate while continuously magnetically stirring. When the preset temperature was reached, the fabric pieces were placed in the glass beaker, and the temperature of the resulting mixture was maintained at 85°C for 15 minutes. During this period, the removal of the colorant was only partially facilitated with the help of the ethyl lactate solvent, and the solvent turned dark green, but the fabric pieces remained heavily colored. The fabric pieces were then separated from the green solvent containing the removed colorant by standard solid-liquid filtration. After drying, one drop of water was applied to one surface of the mainly decolorized fabric piece. The droplets remained intact, did not spread across the surface (no wetting), and indicated the presence of a water-repellent coating on the fabric surface.

[0096] It is estimated that less than 50% w / w of dye was extracted by the solvent.

[0097] [Example 6] Example 6 is another example of decolorizing a green fabric with diethylene glycol monoethyl ether, the fabric containing a small amount of elastane (PUR) yarn mechanically bonded to polyester yarn. First, a total of 2 g of the same DWR-coated green fabric used in Example 4, made primarily of PET fibers and 2% w / w elastane fibers for outdoor use, was cut into small pieces. 80 g of diethylene glycol monoethyl ether (DGME) was placed in a 150 mL glass beaker equipped with a thermometer, and the contents of the glass beaker were gently heated to 180°C using a heating plate while continuously magnetically stirring. When the preset temperature was reached, the fabric pieces were placed in the glass beaker, and the temperature of the resulting mixture was maintained at 180°C for 15 minutes. The fabric showed almost complete decolorization, the solvent was stained red, and after 5 minutes it appeared clear.

[0098] Next, by standard solid-liquid filtration, the nearly completely decolorized fabric pieces (slightly green) were separated from the red coloring solvent containing the removed colorant. Upon filtration, a white solid material began to form and precipitated in the coloring solvent. This material was hypothesized to contain, or be the polyurethane polymer from which the elastane yarn was made. After drying the fabric pieces, one drop of water was applied to the surface of one of the mainly decolorized fabric pieces. The droplet remained intact and did not spread on the surface (no wetting), indicating the presence of a water-repellent coating on the fabric surface.

[0099] [Example 7] In this example, the use of this method was evaluated using textile waste containing a relatively large amount of elastane. First, a total of 10 g of black fabric, used for outdoor applications, made from PET fibers, and mechanically joined by weaving together approximately 27% (w / w) elastane fibers, was cut into small pieces. 50 g of diethylene glycol monoethyl ether (DGME) was placed in a 150 mL glass beaker equipped with a thermometer, and the contents of the glass beaker were gently heated to 180°C using a heating plate while continuously magnetically stirring. When the preset temperature was reached, the fabric pieces were placed in the glass beaker, and the temperature of the resulting mixture was maintained at 180°C for 60 minutes. During this period, the visible removal of the colorant was facilitated with the help of the DGME solvent, thereby causing the fabric pieces to turn gray and the solvent to change from dark gray to black. Furthermore, it was observed that the fabric structure of the pieces changed, resulting in a slightly wrinkled appearance of the pieces and adhesion between the pieces. Next, gray fabric pieces were separated from the gray to black solvent containing the removed colorant by standard solid-liquid filtration. The gray to black colored filtrate was then poured into a 300 mL glass beaker containing 150 mL of demineralized water. Immediately after pouring, a dark gray suspension formed, and after several hours, some solid material appeared to be suspended. The solid material was then separated from the dark gray suspension by standard solid-liquid filtration to obtain a dark gray colored residue, which was subsequently dried in vacuum. Standard analysis of the dried residue, obtained in yield of 2.45 g, showed good agreement with the elastane standard, indicating almost complete removal and recovery of polyurethane elastane present in the textile waste.

[0100] [Example 8] Example 8 demonstrates the dissolution of compressed elastane fibers. First, elastane fibers were partially cut and hydraulically compressed on a heating plate for 30 minutes (10 kN), after which the elastane plate was cut into small pieces. Next, 0.5 g of elastane pellets and 50 g of diethylene glycol monoethyl ether (DGME) were placed in a 100 mL glass beaker equipped with a thermometer, and the contents of the glass beaker were gently heated to 180 °C using a heating plate while continuously magnetically stirring. At the preset temperature, the elastane pellets were dissolved after a first stage of visible swelling at low temperature. After 10 minutes, an additional 12 g of elastane pellets was added. The elastane pellets dissolved completely after 10 minutes, thereby making the solution yellow and clear. The solution then changed to a slightly darker yellow after 60 minutes, and was then cooled to room temperature, thereby becoming slightly opaque.

[0101] [Example 9] Example 9 provides a further example of the dissolution of compressed elastane fibers. First, elastane fibers were processed into pellets in the same manner as in Example 8. 50 g of diethylene glycol monoethyl ether (DGME) was placed in a 150 mL glass beaker equipped with a thermometer, and the contents of the glass beaker were gently heated to 180°C using a heating plate while continuously magnetically stirring. Next, 0.5 g of elastane pellets and 50 g of diethylene glycol monoethyl ether (DGME) were placed in a 100 mL glass beaker equipped with a thermometer, and the contents of the glass beaker were gently heated to 180°C using a heating plate while continuously magnetically stirring. At a preset temperature, 2.5 g of elastane pellets were placed in the glass beaker, and the temperature of the resulting mixture was maintained at 180°C. The elastane pellets swelled first and then dissolved easily, and the resulting solution appeared slightly yellow and transparent. Next, an additional 2.5 g of elastane pellets was placed in the DGME solvent containing the first dissolved portion of the elastane pellets. Similar to the first portion of the elastane pellet, the second portion of the elastane pellet dissolved readily after initial swelling, and the resulting solution was slightly darker yellow. After dissolving the second portion of the elastane pellet, 2.5 g of the third portion of the elastane pellet was placed in the glass beaker containing the dissolved first and second portions of the elastane pellet. Similar to the first and second portions of the elastane pellet, the third portion of the elastane pellet dissolved readily after initial swelling, and the resulting solution was slightly darker yellow compared to the previously dissolved portions.

[0102] In total, 25 g of elastane pellets, equivalent to 40% of the DGME solvent, were added to the DGME solvent and dissolved over 2 to 2.5 hours, yielding a dark yellow to brown solution. This solution became slightly opaque after adding 15 g of elastane pellets, or 30% of the DGME solvent.

[0103] Next, a dark yellow to brown opaque solution containing 20 g of elastane pellets, i.e., 40% dissolved in DGME solvent, was poured into a 500 mL glass beaker containing 350 mL of demineralized water. Immediately after pouring, yellow strands formed and aggregated into yellow ball-shaped material, which settled to the bottom of the glass beaker within a few minutes. The yellow solid material was then separated from the slightly opaque demineralized water by standard solid-liquid filtration and dried under vacuum. Approximately 20 g of elastane was recovered, indicating almost complete removal of the elastane.

[0104] [Example 10] This example demonstrates the dissolution of polyurethane foam as an element in textile waste. First, a large piece of yellow flexible foam made of polyurethane, used as the interior of a mattress, was cut into smaller pieces. Next, 0.25 g of the cut foam piece and 50 g of diethylene glycol monoethyl ether (DGME) were placed in a 100 mL glass beaker equipped with a thermometer, and the contents of the glass beaker were gently heated to 180°C using a heating plate with continuous magnetic stirring. At the preset temperature, the cut foam piece was slowly dissolved after a first stage of visible swelling at a low temperature. After 10 minutes, the foam piece was completely dissolved, yielding a brown, slightly opaque solution. The brown, slightly opaque solution was held at the preset temperature for 30 minutes and then cooled to room temperature. After 72 hours, the solution still appeared brown and opaque, showing no sedimentation and indicating the dissolved state of the foam.

[0105] [Example 11] This example demonstrates the decolorization of blue fabric using xylene. First, a total of 75 g of blue-colored fabric, made of PET fiber and used as a sofa cover, was cut into small pieces and then placed in a 500 mL glass reactor equipped with a condenser, thermometer, and nitrogen inlet. Next, 450 g of xylene was added, and the contents of the glass reactor were gently heated under reflux (140-145°C) with continuous magnetic stirring. After reaching reflux conditions, the contents of the reactor were held at this temperature for 60 minutes. During this period, the visible removal of the colorant was facilitated with the help of the xylene solvent, and the solvent turned dark blue and appeared clear. Then, less colored fabric pieces were separated from the solvent containing the removed colorant by standard solid-liquid filtration.

[0106] Next, the fabric pieces from the first colorant removal step were placed in a 500 mL reactor, followed by the addition of 450 g of fresh xylene. The contents of the glass reactor were gently heated under reflux (140-145°C) with continuous magnetic stirring. After reaching reflux conditions, the contents of the reactor were maintained at this temperature for 60 minutes. During this period, the visible removal of the colorant was facilitated by the xylene solvent, thereby causing the fabric pieces to turn blue and the solvent to turn dark blue. The blued fabric pieces were separated from the solvent containing the removed colorant by standard solid-liquid filtration.

[0107] Next, the fabric pieces from the second colorant removal step were placed back into a 500 mL reactor, followed by the addition of 450 g of fresh xylene. The contents of the glass reactor were gently heated under reflux (140-145°C) with continuous magnetic stirring. After reaching reflux conditions, the contents of the reactor were maintained at this temperature for 60 minutes. During this period, the visible removal of the colorant was facilitated by the xylene solvent, thereby causing the fabric pieces to turn slightly blue and the solvent to turn blue. The slightly blued fabric pieces were then separated from the solvent containing the removed colorant by standard solid-liquid filtration.

[0108] Next, the fabric sample from the third colorant removal step was placed back into a 500 mL reactor, followed by the addition of 450 g of fresh xylene. The contents of the glass reactor were gently heated under reflux (140-145°C) with continuous magnetic stirring. After reaching reflux conditions, the contents of the reactor were maintained at this temperature for 60 minutes. During this period, the fabric sample became almost white, while the solvent still appeared bluish. By separating the solvent by standard solid-liquid filtration, an almost white fabric sample was obtained.

[0109] [Example 12] Example 12 briefly describes some further comparative examples in which DGME was used to attempt to dissolve polymers of a different type than PUR or PET. The experiments were conducted using waste materials in which the polyester in contact with the dye contained either high-density polyethylene (HDPE) or polybutylene terephthalate (PBT). HDPE did not appear to dissolve in DGME, at least not to a significant degree. PBT also did not dissolve.

Claims

1. A suitable method for recycling mixed polymer waste material, wherein the waste material comprises polyurethane (PUR) elements and dye-containing polyester elements mechanically bonded to these polyurethane elements, and the method comprises the following sequential steps, namely: The step of dispersing the mixed polymer waste material in 2-(2-ethoxyethoxy)ethanol (DGME), The step of keeping the polymer waste material dispersed in the DGME until at least a portion of the dye is extracted from the polyester into the DGME and at least 90% (w / w) of the PUR element is dissolved in the DGME, A step of separating the polyester element from the DGME containing at least a portion of the dye and the dissolved PUR element, and The step of reusing the polyester element to manufacture a new product. Methods that include...

2. The method according to claim 1, characterized in that the polymer waste material is dispersed in the DGME until at least 95% (w / w) and up to 100% (w / w) of the PUR elements dissolve in the DGME.

3. The method according to claim 1 or 2, characterized in that, after separating the DGME containing at least a portion of the dye and the soluble PUR element from the polyester element, the DGME is mixed with an aqueous solvent having a polyurethane solubility of less than 1%, thereby creating a liquid DGME fraction and a solid PUR fraction.

4. The method according to claim 3, characterized in that the aqueous solvent contains more than 90% w / w of water.

5. The method according to claim 4, characterized in that the DGME is mixed with the aqueous solvent, the solid PUR fraction is separated from the liquid DGME fraction, and then the dye is removed from the liquid DGME fraction to obtain a purified dye and purified DGME.

6. The method according to any one of claims 1 to 5, characterized in that the step of reusing the polyester to manufacture a new product includes providing the polyester to a method of first depolymerizing the polyester to an oligomeric ester, and then repolymerizing the oligomeric ester to a new polyester suitable for manufacturing the new product.

7. The method according to claim 6, characterized in that the polyester is depolymerized to an oligomer ester consisting of an average of 3 to 30 monomer units, preferably 5 to 20 monomer units.

8. The method according to claim 7, characterized in that, after the polymer waste material is left dispersed in the DGME, a portion of the dye remaining in the polyester is removed from the oligomer ester by adsorption to particulate matter in the mixture with the oligomer ester, and subsequently, the oligomer ester is separated from the particulate matter containing the adsorbed dye.

9. The method according to claim 8, characterized in that the particulate material is selected from activated carbon, zeolite, silica gel, activated alumina, inorganic minerals, chitosan, resin particles, carbon nanotubes, and aluminophosphate molecular sieves.

10. The method according to any one of claims 6 to 9, characterized by comprising the step of filtering the oligomer ester using a filter having a mesh size of less than 20 μm, preferably 5 to 10 μm.

11. The method according to any one of claims 6 to 10, characterized in that the polyester is depolymerized to an oligomeric ester by alcohol decomposition.

12. The method according to claim 11, characterized in that the polyester is depolymerized to an oligomeric ester by a two-step procedure comprising two separate, sequential steps of adding an alcohol in both steps to depolymerize the polyester.

13. The method according to claim 12, characterized in that, in the first of the two consecutive steps, the polyester is supplied to an extruder operating at a temperature higher than the melting temperature of the polyester, and a first amount of alcohol is co-supplied to the polyester waste extruder, in order to produce a fluid mixture containing at least partially depolymerized molten polyester; and in the second of the two consecutive steps, the fluid mixture is supplied to a continuous stirred tank reactor (CSTR) operating at a temperature higher than the melting temperature of the polyester, and a second amount of alcohol is co-supplied to the CSTR, thereby producing the oligomeric ester.

14. The method according to any one of claims 6 to 13, wherein the polyester is polyethylene terephthalate (PET), and the oligomer ester contains more than 50% w / w, preferably more than 60, 70, 80 or even more than 90% w / w, comprising an oligomer of 4 to 16 bis(2-hydroxyethyl) terephthalate (BHET) units, preferably 6 to 14 (BHET) units, most preferably 8 to 10 BHET units.

15. The method according to any one of claims 1 to 14, characterized in that at least 50%, preferably at least 60, 70, 80, or even 90% of the dye is extracted from the polyester into the DGME.

16. The method according to any one of claims 1 to 15, characterized in that the mixed polymer waste material is a textile material.

17. The method according to claim 16, characterized in that the textile material includes polyurethane yarn as a polyurethane element and polyester yarn as a polyester element.

18. The method according to claim 17, wherein the textile material includes cotton yarn in addition to the PUR yarn and the polyester yarn, and the cotton yarn is removed by either a mechanical and / or chemical method before the step of separating the polyester element from the DGME containing at least a portion of the dye and the dissolved PUR element.

19. The method according to any one of claims 1 to 18, characterized in that, prior to the method described above, one or more steps selected from the group consisting of 1) removing any decorations such as buttons, zippers and labels from the mixed polymer waste material, 2) washing the mixed polymer waste material, and 3) shredding the mixed polymer waste material into smaller pieces.

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