A method for the separation of cotton and pet blended textiles from textile waste material by a combination of water-based chemical and mechanical treatments, and products and uses related thereto

Abstract

The disclosure relates to a method for the separation of cotton and polyethylene terephthalate (PET) blended textiles from textile waste material by a combination of water- based chemical and mechanical treatments, comprising the following steps: (a) providing the textile waste material comprising (i) at least one thermoplastic polymer material, comprising PET in composition of 10-90%, preferably about 50%, and (ii) cotton consisting of almost 100% cellulose in composition of 10-90%, preferably about 50%; (b) exposing the textile waste material for TEMPO mediated oxidation, in order to assist the fibrillation of cotton into nanocellulose while keeping PET essentially intact, thereby obtaining a TEMPO oxidized polycotton mixture; (c) mechanically treating the TEMPO oxidized polycotton mixture, such as by stirring and / or grinding, in order to separate fibres and / or to reduce the size of cellulose fibres in the mixture; (d) separating nanocellulose from the mixture of step (c), such as by filtration, thereby obtaining at least a PET rich fraction and a nanocellulose rich fraction. The disclosure further relates to a nanocellulose dispersion produced by the method, a nanocellulose material obtained by the method, a nanocomposite, a recycled textile product produced by the method, a production facility for performing the method and a product.

Description

[0001] A method for the separation of cotton and PET blended textiles from textile waste material by a combination of water-based chemical and mechanical treatments, and products and uses related thereto

[0002] Technical field

[0003] The present disclosure relates to a method for the separation of cotton and polyethylene terephthalate blended textiles from textile waste material by a combination of water-based chemical and mechanical treatments, a nanocellulose dispersion produced by the method, a nanocellulose material obtained by the method, a nanocomposite, a recycled textile product produced by the method, a production facility for performing the method and a product. More specifically, the disclosure relates to a method for the separation of cotton and polyethylene terephthalate blended textiles from textile waste material by a combination of water-based chemical and mechanical treatments, and related products and uses, as defined in the introductory parts of the independent claims.

[0004] Background art

[0005] The global demand for textile production, along with textile consumption, are steadily increasing, due to the rapid population and economic growth and the development of the industrial sector. Most of the textile starting fibres are produced from fossil resources, leading to harmful emissions during the various production stages. In addition to this, the textile industry is responsible for air and water pollution, a vast energy consumption and overall carbon emissions. During the production process of textiles, there are also treatments such as dyeing or printing, that contribute to harmful emissions and waste. Furthermore, chemicals can be released into the environment during laundering. A smaller but substantial amount of textile fibres originate from cotton, a plant that requires large quantities of water and land, as well as the use of pesticides which can impact the environment.[1]

[0006] The environmental sustainability of the textile industry is complex because of its globalized nature and the lack of detailed studies on the subject. For western countries, it has been found, that the overall impact per garment use, must be reduced, even up to 100% in the next twenty years, to be considered sustainable, in accordance with the planetary boundaries.[2]-[3]

[0007] The textile industry is one of the largest contributors to carbon emissions, accounting for as much as 10% of the total global carbon emissions. This is mostly attributed to the disposal process of post-consumer fabrics, that are either incinerated or landfilled, the latter in a percentage of 75%.[2]Fast fashion has led to a dramatic increase in textile waste, making their reuse and recycling crucial. However, appropriate legislation and its implementation have been challenging, because of the many and complicated steps of textile production.[3]-[4] The present disclosure aims to separate cotton and polyester, from post-consumer textiles, using environmentally benign methods, as an effort to recycle them back into the production chain.

[0008] Summary

[0009] It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art and solve at least the abovementioned problem.

[0010] According to a first aspect there is provided a method for the separation of cotton and polyethylene terephthalate (PET) blended textiles from textile waste material by a combination of water-based chemical and mechanical treatments, comprising the following steps:

[0011] (a) providing the textile waste material comprising at least one thermoplastic polymer material, comprising PET in composition of 10-90%, preferably about 50%, and cotton consisting of almost 100% cellulose in composition of 10-90%, preferably about 50%;

[0012] (b) exposing the textile waste material for TEMPO mediated oxidation, in order to assist the fibrillation of cotton into nanocellulose while keeping PET essentially intact, thereby obtaining a TEMPO oxidized polycotton mixture;

[0013] (c) mechanically treating the TEMPO oxidized polycotton mixture, such as by stirring and / or grinding, in order to separate fibres and / or to reduce the size of cellulose fibres in the mixture;

[0014] (d) separating nanocellulose from the mixture of step, such as by filtration using a size exclusion limit of about 1 cm, thereby obtaining at least a PET rich fraction and a nanocellulose rich fraction.

[0015] Thus, nanocellulose is obtained as a result of chemical and mechanical fibrillation of cotton. A size exclusion limit is applied to separate nanocellulose from the mixture of step (c), which can be in the form of a mesh, filter, such as of paper or nylon, membrane, opening or similar. Typically, cotton used in the method of the invention would consist essentially of cellulose, such as almost 100 %. Steps (b) and (c) may be performed as integrated steps or as discrete steps, i.e. wherein step (c) is performed after step (b).

[0016] Typically, the textile waste material comprising cotton and PET blended textiles is chosen from textile clothes or shoes to be recycled, polyester blends, cotton blends containing polyester, elastane, cellulose, polyurethane and / or nylon, shredded polycotton, and shredded acrylic cotton. Thus, listed suitable sources of material are used as starting material. Other sources of textile material may also be used, as long as the other requirements presented in this disclosure are met. The PET blended textiles are typically thermoplastic polymer materials comprising synthetic fibres, such as acrylic, PET, nylon, polyurethane and elastan. Typically, PET is the major ingredient, such as about 90-98% of the synthetic fibres or more, but for some blends other components may also form an essential part. For the purposes of this invention, separation of synthetic fibres will not change the relative amounts of synthetic fibres: i.e. in an input (starting) material comprising (for example) 97% PET, 1% acrylic, 1% nylon and 1% elastan, the output (final) material will typically have the same relative amounts of different synthetic fibres. Thus, the "PET rich fraction" typically comprises PET as the main synthetic fibre component, and other synthetic fibres, such as nylon, acrylic, polyurethane, elastan etc., in smaller amounts.

[0017] According to some embodiments, the method comprises a step of additional mechanical fibrillation of the PET rich fraction of step in order to obtain separated or partially separated fibres of nanocellulose and PET fibres, respectively.

[0018] Thus, additional mechanical fibrillation of the PET rich fraction, remaining after having separated most of the nanocellulose formed after step (c), results in further separation, or at least partial separation, of fibres.

[0019] According to some embodiments, the PET rich fraction is used for nanocomposite production, such as a pellets or filament, and for fibre spinning for textile production.

[0020] According to some embodiments, the material obtained is used for producing a recycled product, such as a 3D printed recycled product.

[0021] According to some embodiments, the textile waste material comprises 10-90 % PET and 10-90 % cotton material, preferably about 50% PET and about 50% cotton.

[0022] Thus, a variation in the relative contents of the starting material can be used.

[0023] According to some embodiments, the nanocellulose rich fraction comprises at least 99 % nanocellulose, preferably at least 99,9% nanocellulose, most preferably at least 99,95% nanocellulose, and less than 1 % PET, preferably less than 0,1 % PET, most preferably less than 0,05% PET.

[0024] According to some embodiments, the PET rich fraction comprises at least 50 % PET, preferably about 67 % PET, more preferably about 90% PET, even more preferably about 95% PET and most preferably about 98% PET or more and less than 50 % cotton, preferably about 33 % cotton, more preferably about 10% cotton, even more preferably about 5% cotton and most preferably about 1% cotton or less.

[0025] According to some embodiments, the TEMPO mediated oxidation is performed at a duration of 1-4 hours, preferably at a duration of about 2- 4 hours, and most preferably at about 4 hours, at pH of about 10, and results in a final concentration of cellulose / nanocellulose of at about 1-3 wt%, preferably at about 2 wt%.

[0026] According to some embodiments, the mechanical treatment of the TEMPO oxidized mixture comprises mixing or stirring and grinding.

[0027] The terms "mixing" and "stirring" would typically have the same meaning and can be used interchangeably in this disclosure.

[0028] According to some embodiments, the separation of nanocellulose from the mixture of step comprises filtration using a size exclusion limit of about 1 cm, or smaller than about 1 mm, or smaller than about 40 pm, or smaller than about 5 pm.

[0029] According to some embodiments, the size exclusion limit is obtained by using a mesh or a filter.

[0030] In addition to a mesh or a filter, a membrane, opening in the reaction container or the like can be used.

[0031] According to some embodiments, the TEMPO oxidized mixture of step (b) is exposed to a cleaning step, in order to remove any remaining solvents, whereby the mixture is filtrated until a conductivity of below about 5-10 pS is reached.

[0032] According to some embodiments, the method is performed in an up-scaled format, wherein the volume of the TEMPO mediated oxidation is more than about 10 litres, or more than about 100 litres, the method comprises about 2-6 wt% solids, or about 4 wt% solids, at a duration of 2-4 hours.

[0033] Other volumes (larger and smaller) can also be used in an up-scaled format, such as about 10 litres, about 50 litres, about 100 litres, about 200 litres or about 1000 litres. The method of the disclosure is thus applicable both for lab scale use and up-scaled (industrial) use.

[0034] Typically, the method is performed in an up-scaled format for about 2-4 hours. However, other durations (shorter and longer) may be possible depending on the development of the method.

[0035] In some embodiments, the method is performed using a vertical screw or propeller stirring rod.

[0036] Hereby, an efficient stirring is obtained during the TEMPO mediated oxidation or as part of a separate stirring step after the TEMPO mediated oxidation.

[0037] According to some embodiments, the mixing of the mechanical treatment of step comprises intense stirring. Intense stirring can be obtained by using at least one suitable stirrer, such as of propeller shape, or a screw-shaped stirred that e.g. is used for vertical stirring in the reactor to obtain efficient stirring. The intensity can be achieved by speed, power and / or type of stirrer. According to some embodiments, the TEMPO mediated oxidation comprises placing the textile waste material to be exposed to the oxidation in a reactor vessel with water, in which reactor vessel the TEMPO mediated oxidation is performed. A suitable reactor vessel could be a beaker (small scale) or a suitable reactor having the necessary dimensions for large scale application(s). The reactor vessel could also be used for the subsequent steps of the method and / or the subsequent steps could be performed by moving the TEMPO oxidized polycotton mixture to another reactor vessel.

[0038] According to some embodiments, the at least one thermoplastic polymer material is chosen from PET, acrylic, nylon and elastane.

[0039] According to a second aspect there is provided a nanocellulose dispersion produced by the method of the first aspect, comprising about 90-98 wt% water, or about 95 wt% water and about 2-10 wt% nanocellulose, or about 5 wt% nanocellulose.

[0040] According to a third aspect there is provided a nanocellulose material obtained by the method of the first aspect, or by drying the nanocellulose dispersion of the second aspect, wherein the nanocellulose exhibits a purity of at least 99 wt%, or at least 99,9 wt%, or at least 99,97 wt%.

[0041] Typically, for textile applications a purity of about 99% is sufficient, whereas for sensitive applications, such as food / cosmetics, a higher purity is typically required, such as about 99,9%. However, the method of the invention has been able to provide nanocellulose at a purity of about 99,97%.

[0042] According to a fourth aspect there is provided a nanocomposite comprising PET and nanocellulose produced by the method of the first aspect, such as in the form of a pellets or filament.

[0043] According to a fifth aspect there is provided a synthetic fibre material obtained by the method of the first aspect, wherein the synthetic fibre material comprises a PET rich fraction comprising at least 50% PET, preferably about 67% PET, more preferably about 90% PET, even more preferably about 95% PET and most preferably about 98% PET or more and less than 50% cotton, preferably about 33% cotton, more preferably about 10% cotton, even more preferably about 5% cotton and most preferably about 1% cotton or less.

[0044] According to a sixth aspect there is provided a recycled textile product produced by the method of the first aspect. According to a seventh aspect there is provided a production facility for performing the method of the first aspect, comprising the necessary parts for performing the steps of the method, comprising:

[0045] (i) means for performing TEMPO mediated oxidation;

[0046] (ii) means for mechanically treating the TEMPO oxidized mixture, such as a mixer, e.g. a stirrer or an intense stirrer, and / or a grinder;

[0047] (iii) means for size exclusion of fibres by filtration; and

[0048] (iv) means for controlling the operation of the various parts of the production facility.

[0049] Hereby a production facility for performing the method of the disclosure is provided. The means for performing TMEPO mediated oxidation and the means for mechanically treating the TEMPO oxidized mixture may be integrated, essentially forming part of the same component, or being separate components.

[0050] According to an eighth aspect there is provided a product, a method or use as described in accordance with the present disclosure.

[0051] Thus, in this disclosure it is shown that by a combination of TEMPO mediated oxidation and mechanical fibrillation the inventors have separated one nanocellulose rich and one PET rich fraction. During TEMPO mediated oxidation cotton fibrillates into nanocellulose while PET and other synthetic fibres remain intact. The fibrillation of cotton results in nanocellulose which is much smaller than PET and it becomes possible to separate them using a mesh due to size difference. The nanocellulose rich fraction has traces of PET but PET has been separated from this fraction. The PET rich fraction contains primarily PET and other synthetic fibres, and certain amount of cotton which can be further separated by intensive mechanical treatment especially in an upscaled industrial reactor. Depending on the desired final product, one can decide to separate one fraction of nanocellulose and use the rest of nanocellulose and PET blend for nanocomposites production or one can separate further nanocellulose and PET fibrers by further mechanical treatment to produce separated fibrers for other applications. The degree of separation of nanocellulose and PET in the PET rich fraction depends on the type and intensity of mechanical fibrillation and it is expected to be more efficient in an upscaled reactor with intensive stirring which will enhance mechanical fibrillation.

[0052] Effects and features of the second through eighth aspects are to a large extent analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the second through eighth aspects.

[0053] The present disclosure will become apparent from the detailed description given below. The detailed description and specific examples disclose preferred embodiments of the disclosure by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the disclosure.

[0054] Hence, it is to be understood that the herein disclosed disclosure is not limited to the particular component parts of the device described or steps of the methods described since such device and method may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

[0055] Brief descriptions of the drawings

[0056] The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and nonlimiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings.

[0057] Figure 1: Cellulose chemical structure.

[0058] Figure 2: Overview of cellulose sources and its structure, taken in part from Li et al.[8]

[0059] Figure 3: Production of cellulose nanoparticles, modified from Michelin et al.[9]

[0060] Figure 4: Polyethylene terephthalate chemical structure.

[0061] Figure 5: Mechanism of TEMPO mediated oxidation of cellulose, under basic conditions, in water, taken from Isogai et al.

[0015]

[0062] Figure 6: Optical microscopy data for PET and cotton samples, (a): 5 min ground cotton sample, (b): 30 min ground cotton sample, (c): 5 min ground PET sample, (d): 30 min ground PET sample.

[0063] Figure 7: Scanning Electron Microscopy data of PET and cotton samples, (a): 5 min ground cotton sample, (b): 15 min ground PET sample, (c), (d): 5 min ground PET sample.

[0064] Figures 8 and 9: Comparative FTIR spectra of initial and after TEMPO-mediated oxidation pure cotton and polycotton fabrics, respectively.

[0065] Figures 10 and 11: Comparative FTIR spectra of the cotton rich and PET rich fractions after first and last filtration step, respectively. Figures 12 and 13: FTIR spectra of the pure cotton after filtration with the 5 pm membrane and the residue on the 5 pm membrane, respectively.

[0066] Figure 14: Titration curve of 100% ground cotton.

[0067] Figure 15: Titration curve of ground polycotton.

[0068] Figure 17: Scanning Electron Microscopy data of (a): pure cotton after 5 pm membrane and (b): polycotton cotton rich fraction after 5 pm membrane.

[0069] Figure 18: Scanning Electron Microscopy data for the residue on the 5 pm membrane of the polycotton, with a different sample preparation base, (a) with a silicon wafer, b) with glass.

[0070] Figures 19 and 20: EDS maps for pure cotton and polycotton after 5 pm membrane, respectively.

[0071] Figure 21: Atomic Force Microscopy for (a) pure cotton and b) polycotton after filtration with the 5 pm membrane.

[0072] Detailed description

[0073] The present disclosure will now be described with reference to the accompanying drawings, in which preferred example embodiments of the disclosure are shown. The disclosure may, however, be embodied in other forms and should not be construed as limited to the herein disclosed embodiments. The disclosed embodiments are provided to fully convey the scope of the disclosure to the skilled person.

[0074] The present disclosure relates to separation of cotton and PET blended textiles by a combination of water-based chemical and mechanical treatments. Especially, the present disclosure relates to TEMPO-mediated oxidation and mechanical treatment of cotton and polycotton textiles, and characterization, to determine the properties of the fractions and potential applications.

[0075] I. Cellulose

[0076] The environmental impacts that arise from the use of fossil-based materials has led to a shift towards more sustainable sources.[5]One of the most abundant polymers on earth is cellulose, a biopolymer which comprises a vast part of the annual biomass production. This is due to its desirable mechanical properties, easy functionalization and numerous applications. Cellulose is found in the cell walls of plants and can be extracted from a variety of sources, such as wood, cotton and even algae or be produced by bacteria.[5]-[6]

[0077] Cellulose is a hydrophilic and linear polymer, that consists of repeating D-anhydroglucose units that are linked with -1,4-glycosidic bonds. It has both crystalline and amorphous regions and the degree of crystallinity is directly dependent on the source and extraction method. For instance, the crystallinity can reach more than 40% in wood or even 90% or more in cotton.[6]- [7]

[0078] Due to its ability to form hydrogen bonds, cellulose is soluble in polar solvents. The intramolecular hydrogen bonds contribute to a linear chain arrangement, while the inter-chain hydrogen bonds and van der Waals forces, contribute to a parallel organization (stacking). Both these interactions contribute to the stability of the overall polymer structure.[5]

[0079] Besides its sustainability, cellulose offers the ability for functionalization, owing to its structure. Cellulose fibres, following different chemical and mechanical routes, can be disintegrated into cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs).[8]

[0080] 1. Cellulose nanofibrils (CNFs)

[0081] CNFs are produced by various mechanical treatments, using for instance a grinder or a microfluidizer, that allow the liberation of the elementary fibrils. The resulting fibrils have both crystalline and amorphous regions. Also, they have high aspect ratios, with 2-60 nm in width and several pm in length, and excellent characteristics, such as flexibility, high surface area, low density and great mechanical properties. The fibrillation process, however, is very energy intensive, so chemical pre-treatments are employed to lower its energy requirements and cost while producing the desirable properties.[5]-[7]At the same time, the different pre-treatments aim to functionalize the fibrils which might be useful for several applications.

[0082] 2. Cellulose nanocrystals (CNCs)

[0083] CNCs are usually produced from acid hydrolysis, during which the acid selectively dissolves the amorphous regions, leaving a crystalline network. The crystals are rod-like, with lower aspect ratios than fibrils, namely 10-50 nm in width and 100-500 nm in length. The degree of crystallinity of the product can range from 50 to 90% and the surface chemistry is dependent on the reaction conditions.

[0084] II. Polyester

[0085] Polyester fibres are the most abundantly produced synthetic fibres worldwide. Particularly, polyethylene terephthalate (PET) production, has a higher production rate growth than any other synthetic or natural fibre

[0010] PET fibres have a lot of desired properties, such as thermal stability, low production cost, controllability of their morphology and the ability to blend with other fibres, such as cotton.

[0010]

[0086] PET is a semicrystalline polymer, that is produced by the condensation of terephthalic acid and ethylene glycol, without the presence of moisture and after several processing steps, the product of the required molecular weight is recovered.

[0010] PET has numerous applications, including textile production, that can prove to be fairly harmful to the environment. More specifically, textiles are one of the biggest sources of microplastic pollution, either during their production process or during the several washing cycles.

[0011] This makes the recycling of polyester even more crucial.

[0087] III. Other synthetic fibres

[0088] In addition to polyester fibres or PET fibres, textile material may comprise other synthetic fibres. For example, such synthetic fibres are acrylic, nylon, elastane or combinations thereof. Other synthetic fibres are also conceivable. Synthetic fibres like acrylic, nylon or elastane behave in a similar way as PET fibres in the separation process of the present disclosure.

[0089] IV. Experimental methods

[0090] This project aims to separate PET and cotton, with a combination of chemical and mechanical treatments. The chemical pre-treatment used is TEMPO mediated oxidation, followed by a combination of mechanical treatments, namely a pre-grinding mixing, a grinding step and several filtrations. The next step is the characterization of the recovered fractions, to determine their properties.

[0091] 1. TEMPO mediated oxidation

[0092] In order to introduce desired groups and subsequently properties on cellulose, 2, 2', 6,6'- tetramethylpiperidine-l-oxyl (TEMPO) mediated oxidation has been widely used. t12L I13L

[0014] The TEMPO radical is water soluble, stable and is considered safe, being negative for the Ames test. Overall, TEMPO mediated oxidation, is considered a "green" method, as it is selective and highly effective in under mild conditions (room temperature, atmospheric pressure). This method is C6 selective and converts the primary alcohols to carboxylic groups. In our study, we added NaBr and NaCIO, the first acting as a co-catalyst, together with the TEMPO and the second as the oxidant. The pH of the reaction is monitored to be at around 10, in order to maintain the TEMPO reactivity and the oxidizing activity of the CIO-.

[0012] After the process, thorough cleaning to remove the remaining solvents is required, until reaching a conductivity below 5-10 pS. TEMPO mediated oxidation, also gives the advantage of enhancing and controlling the degree of fibrillation, as well as the size of the fibres.

[0093] 2. Mechanical treatment

[0094] One of the most used mechanical methods to produce CNFs is grinding. The grinders that are used for this process consist of two disks, a stationary and a rotational one. These disks produce a lot of shear force while operating and through controlling their distance, speed and flow of material into the system, individualized fibres of various sizes are produced. During mechanical disintegration, there is the risk of fibre shedding. In order to avoid that, the process is being carried out in an aqueous medium[6]-

[0016] Especially for textiles, mechanical fractionation is preferred, as it is simple, effective and with a lower energy consumption than other approaches. Both synthetic and natural fibres can undergo this method. However, blends are harder to be fractionated and efficiently separated.

[0017]

[0095] In addition, or as an alternative to grinding, stirring, and especially intense stirring, can be used to mechanically treat and separate the fibres of the TEMPO oxidized mixture. Intense stirring can be obtained by using at least one suitable stirrer, such as of propeller shape, or a screw-shaped stirred that e.g. is used for vertical stirring in the reactor to obtain efficient stirring. The intensity can be achieved by speed, power and / or type of stirrer.

[0096] Moving towards an industrial plant, a subsequent step of grinding (as part of the mixing of the mechanical treatment) becomes less necessary as the stirring during the main chemical treatment facilitates the separation of cotton and PET / synthetic fibre. In pilot scale (up-scaled format), the mixing is stronger and more effective and small-scale problems like fibre clumps around the mixer, which makes the process less effective, are avoided. In small-scale, grinding is typically more important for obtaining a proper separation.

[0097] Applications and products

[0098] The method and the materials obtained by the present disclosure can for example be used in the following applications and products:

[0099] The PET-rich fraction obtained by the method can be used for nanocomposite production (compounding).

[0100] The PET-rich fraction obtained by the method can be used for fibre spinning, which fibres can be used for production of textiles. The fibre spinning is typically important for producing high-quality yarn with the desired strength, uniformity and characteristics needed for various textile applications.

[0101] The material obtained by the method of the disclosure can be used for producing a recycled product, such as a 3D printed recycled product.

[0102] A nanocellulose dispersion produced by the method of the disclosure, comprising about 90-98 wt% water, or about 95 wt% water and about 2-10 wt% nanocellulose, or about 5 wt% nanocellulose.

[0103] A nanocellulose material obtained by the method of the disclosure, or by drying the nanocellulose dispersion of the disclosure, wherein the nanocellulose exhibits a purity of at least 99 wt%, or at least 99.9 wt%, or at least 99.97 wt%.

[0104] A nanocomposite comprising PET and / or other synthetic fibre and nanocellulose produced by the method of the disclosure, such as in the form of a pellets or filaments. A recycled textile product produced by the method of the disclosure.

[0105] A production facility for performing the method of the disclosure, comprising the necessary equipment and means for performing the steps of the method, comprising (i) means for performing TEMPO mediated oxidation, (ii) means for mechanically treating the TEMPO oxidized mixture, such as a mixer, e.g. a stirrer or an intense stirrer, and / or a grinder, and (iii) means for size exclusion of fibres by filtration.

[0106] Further, the production facility may comprise means for controlling the operation of the various components / means of the production facility.

[0107] A production facility for the separation of cotton and PET blended textiles from textile waste material typically includes several key components to ensure efficient and effective processing. Here are examples of the typical main components:

[0108] 1. Pre-treatment Area:

[0109] • Sorting and Inspection: Manual or automated systems to sort textile waste and inspect for contaminants.

[0110] • Cleaning: Equipment to remove dirt, dust, and other impurities from the textile waste.

[0111] 2. Separation System:

[0112] • Mechanical Separation: Machines like shredders or cutters to break down the textile waste into smaller pieces. In the context of this disclosure, one or more grinders and / or stirrers are typically included, as well as filters for size exclusion of fibres.

[0113] • Chemical Separation: Reactors and tanks for chemical treatments, such as alkaline hydrolysis, to separate PET from cotton. In the context of this disclosure, reactors and tanks for performing TEMPO mediated oxidation is typically included.

[0114] 3. Detection and Sorting:

[0115] • Sensors and Detectors: Optical or infrared sensors to identify and differentiate between cotton and PET fibres.

[0116] • Automated Sorting: Systems using air jets or mechanical sorting to separate the identified fibres.

[0117] 4. Control Unit:

[0118] • Central Processing System: Microprocessors or PLCs to manage and coordinate the operation of the facility.

[0119] Software: Specialized software for monitoring and controlling the separation processes. 5. Post-treatment Area:

[0120] • Drying: Equipment to dry the separated fibres.

[0121] • Purification: Systems to further purify the separated cotton and PET fibres.

[0122] 6. Storage and Handling:

[0123] • Storage Bins: Containers for storing the separated fibres.

[0124] • Conveyors: Systems to transport materials within the facility.

[0125] 7. Safety and Environmental Controls:

[0126] • Safety Features: Emergency stop buttons, protective enclosures, and alarms.

[0127] • Environmental Controls: Systems to manage waste and emissions, ensuring compliance with environmental regulations.

[0128] 8. Quality Control:

[0129] • Inspection and Testing: Equipment to test the quality of the separated fibres.

[0130] • Feedback Mechanism: Continuous monitoring and adjustment to maintain optimal performance.

[0131] These components work together to ensure the efficient and accurate separation of cotton and PET fibres from textile waste, contributing to sustainable recycling practices.

[0132] With regard to said means for controlling the operation, this refers to a system or apparatus designed to manage and regulate the various processes involved in the separation of cotton and polyethylene terephthalate (PET) fibres from textile waste. The system typically includes:

[0133] 1. Sensors and Detectors: These components are used to identify and differentiate between cotton and PET fibres within the textile waste. They may employ optical, infrared, or other types of sensing technologies to accurately detect the materials.

[0134] 2. Sorting Mechanism: Once the materials are identified, the sorting mechanism separates the cotton fibres from the PET fibres. This could involve mechanical sorting, air jets, or other separation techniques.

[0135] 3. Control Unit: The control unit is the central processing system that coordinates the operation of the sensors, detectors, and sorting mechanism. It ensures that the separation process is carried out efficiently and accurately. The control unit may include a microprocessor or programmable logic controller (PLC) that runs specialized software for managing the separation process. 4. User Interface: This allows operators to monitor and adjust the system's performance. The user interface may include a display screen, control buttons, and software for setting parameters and viewing real-time data.

[0136] 5. Feedback System: To ensure optimal performance, the system includes a feedback mechanism that continuously monitors the separation process and makes adjustments as needed. This could involve real-time data analysis and automatic calibration of the sorting mechanism.

[0137] 6. Power Supply: The system is powered by an electrical supply that ensures all components operate smoothly. This may include backup power options to prevent interruptions during the separation process.

[0138] 7. Safety Features: To protect operators and maintain safe operation, the system includes safety features such as emergency stop buttons, protective enclosures, and alarms for detecting malfunctions or hazardous conditions.

[0139] This comprehensive system ensures the efficient and accurate separation of cotton and PET fibres from textile waste, contributing to the recycling and reuse of materials in an environmentally friendly manner.

[0140] Literature review

[0141] In this section, state of the art methods are listed, which could be used in relation to the method of the present disclosure. The listed methods are hereby incorporated as references.

[0142] Lately, due to the increasing amount of textile waste, from manufacturing to consumer use and end of life, researchers are shifting their focus towards reusing and recycling them.

[0143] Reusing is considered to be the best alternative, because it prolongs the life of the textiles and is simpler than recycling.

[0018] The focus of related research includes mostly the extraction and utilization of the waste cotton and polyester and less the separation of the starting materials, in this case cotton and polyester.

[0018]

[0144] Starting with cotton recycling, the main method is chemical recycling but it can be challenging, because cotton is usually blended with synthetic fibres, dyes etc.

[0145] Asaadi et al. (2016) developed a new method for the production on virgin textile fibres. In their study, finishing cotton textiles from hospital bed sheets were dissolved in an ionic liquid, namely l,5-diazabicyclo[4.3.0]non-5-enium acetate and the spun. The resulting cotton fibres had excellent mechanical properties, such as high elastic moduli and tensile strength.

[0019]

[0146] Furthermore, Ruiz-Caldas et al. (2022) extracted cellulose nanocrystals from blended postconsumer fabrics by sulfuric acid hydrolysis. The resulting CNCs could compete with crystals extracted from virgin sources.

[0020] Ruiz-Caldas et al. (2023) produces cellulose nanocrystals from post-consumer cotton fabrics. The textiles were treated with citric acid and then mechanically fi bri Hated, using a microfluidizer. The results showed a high-yield extraction.

[0021]

[0147] Chemical recycling of PET has been widely investigated.

[0148] Guo et al. (2020) investigated the recycling of PET from textile waste through glycolysis with ethylene glycol and using Mg-AI pellets as a catalyst. The recovered PET fibres' properties could compete with virgin PET fibres.

[0022]

[0149] Dyed PET fabrics have proved to be a challenge in the recycling process.

[0150] Fei et al. (2020) used sodium formaldehyde sulfoxylate to decolorize PET from textile waste, in a simple, one step process. It was found that the decolorization process did not affect the mechanical properties of PET.

[0023]

[0151] Palme et al. (2017), used hydrolysis under basic conditions on polycotton textiles. More specifically, PET was hydrolyzed with NaOH, with the addition of a phase transfer catalyst (benzyltributylammonium chloride). As a result, PET was broken down to its monomers, terephthalic acid and ethylene glycol. Cotton was isolated as pure steam, with a yield of almost 97%. The separation of each material can be achieved without the risk of any degradation to the other.

[0024]

[0152] In an effort to recycle the cellulose as well as the polyester from end-of-life textiles, Haslinger et al. (2019), used an ionic liquid, more specifically [DBNH] [OAc], that selectively dissolves cellulose and eventually made cellulose microfibres, through spinning. However, the recovered PET was of lower quality because it degraded. Although the recovered PET cannot be recycled back into textiles, it can be used to make composites or plastic materials for packaging.

[0025]

[0153] Wang et al. (2022) used a deep eutectic solvent made from choline chloride and p- toluenesulfonic acid to isolate PET and microcrystalline cellulose. PET was recovered with a yield of more than 99%, while cellulose extraction wasn't as efficient. However, the resulting cellulose was of high crystallinity and the recovered PET had maintained its original properties.

[0026]

[0154] The invention will now be further described by the following non-limiting examples.

[0155] EXAMPLES

[0156] Example 1: Pre-study A pre-study was conducted, in order to prepare TEMPO oxidized textiles and to try out and access the effectiveness of a combination of mechanical treatments. Firstly, we have performed TEMPO mediated oxidation on 100% cotton fabrics but also on 50 % cotton and 50% polyester blended textiles. After the reaction, the textiles were filtered and dried to obtain a textile cake, in which we determined the solids concentration in order to estimate the yield. One important difference between the cotton and the cotton-PET textiles was that after the reaction, the oxidized cotton was bleached, having a pale yellow to white colour while the oxidized polycotton seemed visually not bleached.

[0157] As the goal is to separate the cotton and PET, we dispersed the TEMPO oxidized mixture in 4 L of DI water, having a concentration of about 2 wt% with a turrax mixer, to mainly reduce the size of the fibres and potentially break apart the polyester fibres. After that, the sample was fed into a MASUKO grinder and the entire disintegration process lasted 30 minutes.

[0158] Samples were taken at 5, 10, 15, 20, 25 and 30 minutes, to evaluate the effect of the grinding on the fibres. After that, we centrifuged a part of the final material but this method didn't have the desired effect because of inadequate separation.

[0159] The samples taken at 5, 10, 15, 20, 25 and 30 minutes of grinding were filtered using a Nylon membrane with a pore size of 40 pm and we obtained two fractions from each sample, one retained from the membrane and the one that passed through the membrane. The fraction that was retained by the membrane was consisting of mostly non-bleached fibres while the fraction that passed through the membrane was consisting mostly of cotton sample in nanoscale and was free of polyester, while the 10 and 15 min samples showed a small characteristic peak of the carbonyl group of the polyester. All the non-bleached samples that were retained from the membrane, were rich in PET, regardless of the grinding times.

[0160] We assume, that, when more ground, the polyester becomes smaller, passes through the filter and contaminates the cellulose fraction. As a result, it was decided that the sample from the TEMPO mediated oxidation would be ground for only 5 minutes.

[0161] The samples from the grinding step were seen under the optical microscope. The polyester fibres (Figures 7c and 7d) were clearly seen, while we couldn't see any cellulose fibres (figures 7a and 7b) from the cotton sample indicating that the cellulose is in nanoscale. However, the cotton samples were mostly free of PET contaminations. The diameters of the PET fibres were not changed with grinding time.

[0162] After the optical microscope, we used the table-top Scanning Electron Microscope (SEM) where we are able to observe PET (Figure 8b, 8c, 8d) and again, no cellulose fibres were clearly visible (Figure 8a). For the next characterization steps, we plan to use high resolution SEM and AFM. Below, some of the SEM images are shown:

[0163] Proposed process • A number of fabrics, calculated during the process each time, are cut in small, square pieces of similar dimensions, using a paper guillotine. The fabrics are of different compositions of polyester and cotton (polycotton), namely 50%-50% and 100% cotton, as a blank.

[0164] • A portion of those fabrics is used to calculate the exact polyester and cotton content by sulfuric acid hydrolysis.

[0165] • The TEMPO mediated oxidation is then carried out. The fabrics are placed in a beaker with water and the TEMPO, as well as the NaBr, while the NaCIO is added dropwise. The final concentration of cellulose is around 2 wt%, the reaction duration is 4 hours and the pH is monitored to be at around 10.

[0166] • After the end of the reactions, the solution is filtrated, until its conductivity is below 5- 10 pS.

[0167] • The TEMPO oxidized fabrics (in aqueous media) undergo a pre-grinding mixing step, using an Ultra Turrax for 20 minutes, in order to separate the clumps of the fabrics, reduce the size of the fibres and homogenize the mixture as much as possible.

[0168] • After that step, the solution is ground for 5 minutes. The goal of this process is to separate the fibres as well as possible and to obtain the desired dimensions for both fibres, in order to efficiently separate them.

[0169] • The resulting solution is filtrated, using different meshes and filter papers ranging from 40 to 5 pm, to separate the rich in cotton and rich in PET fractions.

[0170] • After filtration, the sulfuric acid hydrolysis is repeated, in order to determine the exact content of the recovered fractions. After that, the properties of the fractions are determined.

[0171] • Depending on the properties of the recovered cellulose, it can be further modified or used as is, for different applications.

[0172] • Depending on the molecular weight of the polyester, it can also be processed for more applications. Because polyester is a thermoplastic material, it can be used as a filament for 3D printing or if it is of a specific molecular weight, it can be reused for textile production.

[0173] In some embodiments, as part of the TEMPO mediated oxidation, the mixture is stirred during the reaction.

[0174] In another proposed process, instead of grinding the homogenized TEMPO oxidized fabrics, the solution can be exhibited to intense stirring for about 5 minutes in order to separate the fibres as well as possible. The stirring is done with an overhead stirrer having a propeller or a screw stirring rod.

[0175] Alternatively, stirring and grinding can be combined by performing a first step of stirring and a second step of grinding, with the purpose of separating the cellulose fibres and the synthetic fibres, respectively, as well as possible. Example 2: Experimental process results

[0176] I. Sulfuric acid hydrolysis

[0177] During this process, first we weigh the initial mass of the fabrics. The amounts of fabrics cut each time, correspond to 80 g of cellulose, so 80 g of pure cotton fabrics and 160 g of polycotton fabrics were used. Then a triplet of each fabric composition is added in a 70% sulfuric acid solution for 75 minutes. The sulfuric acid, under these conditions, breaks down the cellulose into glucose and by the end of the reaction, only the PET is left in the solution. The PET is then dried and weighed. We can calculate the exact polyester content and subsequently the cotton content of the fabrics with equations (1) and (2):

[0178] Cotton (%) = 100% — Polyester (%) (2)

[0179] The exact composition of fabrics was calculated as follows:

[0180] The pure cotton fabrics consisted of 99.96% cotton and 0.04% polyester and the blended fabrics, of 53.40% cotton and 46.60% polyester.

[0181] II. Resulting yields

[0182] 1. 100% cotton fabrics

[0183] Starting textiles: 80 g of material

[0184] TEMPO-mediated oxidation: 76.28 g of material

[0185] Grinding step: 99.1% yield

[0186] 2. Blended fabrics

[0187] Starting textiles: 160 g of material

[0188] TEMPO-mediated oxidation: 161.29 g of material (within the standard deviation)

[0189] Grinding step: 80.3% yield

[0190] Final filtration step (5pm membrane):

[0191] * Cotton rich fraction: i. 99.97% cotton ii. 0.031% PET

[0192] * PET rich fraction 32.27% cotton

[0193] 67.73% PET

[0194] Example 3: Characterization I. Fourier Transform Infrared Spectroscopy (FTIR)

[0195] The FTIR spectra confirm the presence of carboxylic groups after the TEMPO-mediated oxidation. That proves, that our chemical pre-treatment was successful. Furthermore, there is a very small polyester peak in the cotton rich fraction of the polycotton, which indicates that our cotton fraction is quite pure. Since FTIR is not an extremely sensitive method, this is only a first indication of the purity of our sample. Lastly, from the comparative spectra of the first and final filtration steps (40 and 5 pm membranes), we can conclude that the purity of our samples has improved with the 5 pm membrane.

[0196] On the FTIR spectrum of the residue on the 5 pm membrane, we can see that there is still cellulose present in our sample, so we conclude that not all the material is separated with this membrane.

[0197] II. Conductometric titrations

[0198] Table 1: Carboxylic content of different samples. The values of the carboxylic contents are in agreement with previous measurements of related research. ("Trash to treasure" project, for the preparation of thermoplastic filaments from polycotton).

[0199] III. High Resolution Scanning Electron Microscopy (SEM) From the SEM images, no discernible, individual cellulose fibres can be seen. This makes the estimation of their sizes very difficult. However, from the SEM images shown below, the polyester impurities seem to be visible. Lastly, different sample preparation methods should be investigated for these types of samples. Below, a silicon wafer and a microscope flat glass, were used as a sample base. a

[0200] IV. Energy dispersive X-ray Spectroscopy (EDS)

[0201] From the EDS maps we can confirm the presence of sodium from the TEMPO-mediated oxidation. The trace elements found in the polycotton, however, are of the most interest. Some of them may come from the dyes used. Lastly, there are elements found, such as Al, Si or O that can make up zeolites, that are often used during textile production.

[0202] V. Atomic Force Microscopy

[0203] From the AFM images, we can further confirm that there are no individual fibres in our samples. The image shows that the cellulose in the textiles is converted into nanoscaled cellulose (< 20nm) below in both the cotton and polycotton fabrics after the chemical and mechanical process followed by filtration

[0204] VI. Zeta-potential

[0205] Table 2: Zeta-potential values of different samples.

[0206] The negative charge measured, confirms that our samples are colloidally stable. Furthermore, from the values between the two different calculation steps, we assume that there are no significant losses of the charged material (cellulose) during the filtration steps. Finally, the slightly bigger error values, can be attributed to the fact that we have big fibres in our solutions.

[0207] VII. Conclusions

[0208] 1. Firstly, we can conclude that the TEMPO-mediated oxidation was effective, since we confirmed the presence of the carboxylic groups on the cellulose surface.

[0209] 2. Regarding the mechanical treatment, the number of passes from the grinder is more important and precise than the grinding time, since the polycotton is a harsher, more durable material and as a result, passes from the grinder much slower than the pure cotton.

[0210] 3. The filtration using 5um membranes resulted in separation of nanoscaled cellulose from cotton and polycotton with chemo-mechanical treatment. During separation, we noticed that the pure cotton had overall less losses than the polycotton.

[0211] 4. From the conductometric titrations, we can conclude that the polycotton has more charge than the pure cotton. We assume, that there was possibly charge on the initial textiles (e.g. from the dyes).

[0212] 5. Finally, the proposed process seems to be an overall promising method, a fact that can be supported from the purity of the cotton fraction.

[0213] 6. It is possible to further improve and fine tune the chemical and mechanical treatments as well as filtration step to tune the separation of the two fractions.

[0214] The person skilled in the art realizes that the present disclosure is not limited to the preferred embodiments described above. The person skilled in the art further realizes that modifications and variations are possible within the scope of the appended claims. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims. References

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Claims

CLAIMS1. A method for the separation of cotton and polyethylene terephthalate (PET) blended textiles from textile waste material by a combination of water-based chemical and mechanical treatments, comprising the following steps:(a) providing the textile waste material comprising (i) at least one thermoplastic polymer material, comprising PET in composition of 10-90%, preferably about 50%, and (ii) cotton consisting of almost 100% cellulose in composition of 10-90%, preferably about 50%;(b) exposing the textile waste material for TEMPO mediated oxidation, in order to assist the fibrillation of cotton into nanocellulose while keeping PET essentially intact, thereby obtaining a TEMPO oxidized polycotton mixture;(c) mechanically treating the TEMPO oxidized polycotton mixture, such as by stirring and / or grinding, in order to separate fibres and / or to reduce the size of cellulose fibres in the mixture; and(d) separating nanocellulose from the mixture of step (c), such as by filtration using a size exclusion limit of about 1 cm, thereby obtaining at least a PET rich fraction and a nanocellulose rich fraction.

2. The method of claim 1, further comprising a step of additional mechanical fibrillation of the PET rich fraction of step (d) in order to obtain separated or partially separated fibres of nanocellulose and PET fibres, respectively.

3. The method of claim 1 or 2, wherein the PET rich fraction is used for nanocomposite production, such as a pellets or filament, and for fibre spinning for textile production.

4. The method of any one of the preceding claims, wherein the material obtained is used for producing a recycled product, such as a 3D printed recycled product.

5. The method of any one of the preceding claims, wherein the textile waste material comprises 10-90 % PET and 10-90 % cotton material, preferably about 50 % PET and about 50% cotton.

6. The method of any one of the preceding claims, wherein the nanocellulose rich fraction comprises at least 99 % nanocellulose, preferably at least 99,9% nanocellulose, most preferably at least 99,95% nanocellulose, and less than 1 % PET, preferably less than 0,1 % PET, most preferably less than 0,05% PET.

7. The method of any one of the preceding claims, wherein the PET rich fraction comprises at least 50 % PET, preferably about 67 % PET, more preferably about 90% PET, even more preferably about 95% PET and most preferably about 98% PET or more and less than 5025% cotton, preferably about 33 % cotton, more preferably about 10% cotton, even more preferably about 5% cotton and most preferably about 1% cotton or less.

8. The method according to any one of the preceding claims, wherein the TEMPO mediated oxidation is performed at a duration of 1-4 hours, preferably at a duration of about 2- 4 hours, and most preferably at about 4 hours, at pH of about 10, and results in a final concentration cellulose of at about 1-3 wt%, preferably at about 2 wt%.

9. The method according to any one of the preceding claims, wherein the mechanical treatment of the TEMPO oxidized mixture comprises (i) mixing or stirring and (ii) grinding10. The method according to any one of the preceding claims, wherein the separation of nanocellulose from the mixture of step (c) comprises filtration using a size exclusion limit of about 1 cm, or smaller than 1 mm, or smaller than 40 pm.

11. The method according to any one of the preceding claims, wherein the size exclusion limit is obtained by using a mesh or a filter.

12. The method according to any one of the preceding claims, wherein the TEMPO oxidized mixture of step (b) is exposed to a cleaning step, in order to remove any remaining solvents, whereby the mixture is filtrated until a conductivity of below about 5-10 pS is reached.

13. The method of any one of the preceding claims, wherein the method is performed in an up-scaled format, wherein the volume of the TEMPO mediated oxidation is more than about 10 litres, or more than about 100 litres, comprising about 2-6 wt% solids, comprising cotton and PET, or about 4 wt% solids, comprising cotton and PET, at a duration of about 2-4 hours.

14. The method of claim 13, wherein the method is performed using a vertical screw or propeller stirring rod.

15. The method of any one of the preceding claims, wherein the mixing of the mechanical treatment of step (c) comprises intense stirring.

16. The method of any one of the preceding claims, wherein the TEMPO mediated oxidation comprises placing the textile waste material to be exposed to the oxidation in a reactor vessel with water, in which reactor vessel the TEMPO mediated oxidation is performed.

17. The method of any one of the preceding claims, wherein the at least one thermoplastic polymer material is chosen from PET, acrylic, nylon and elastane.

18. A nanocellulose dispersion produced by the method of any one of claims 1-17, comprising about 90-98 wt% water, or about 95 wt% water and about 2-10 wt% nanocellulose, or about 5 wt% nanocellulose.

19. A nanocellulose material obtained by the method of any one of claims 1-17, or by drying the nanocellulose dispersion of claim 18, wherein the nanocellulose exhibits a purity of at least 99 wt%, or at least 99,9 wt%, or at least 99,97 wt%.

20. A nanocomposite comprising PET and / or other synthetic fibre and nanocellulose produced by the method of any one of claims 1-17, such as in the form of a pellets or filament.

21. A synthetic fibre material obtained by the method of claim 1-17, wherein the synthetic fibre material comprises a PET rich fraction comprising at least 50% PET, preferably about 67% PET, more preferably about 90% PET, even more preferably about 95% PET and most preferably about 98% PET or more and less than 50 % cotton, preferably about 33 % cotton, more preferably about 10% cotton, even more preferably about 5% cotton and most preferably about 1% cotton or less.

22. A recycled textile product produced by the method of any one of claims 1-17.

23. A production facility for performing the method of any one of claims 1-17, comprising the necessary parts for performing the steps of the method, comprising:(i) means for performing TEMPO mediated oxidation;(ii) means for mechanically treating the TEMPO oxidized mixture, such as a mixer, e.g. a stirrer or an intense stirrer, and / or a grinder;(iii) means for size exclusion of fibres by filtration; and(iv) means for controlling the operation of the various parts of the production facility.

24. A product, a method or use as described in accordance with the present disclosure.

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