A process for providing a solid fraction comprising textile fibers

Abstract

The present invention relates to a process for decoloring textiles, and for preparing a textile product for recycling. In particular, it relates to a process providing a solid fraction of textile fibers such as natural fibres and / or synthetic fibres, which process comprises the steps of: (i) providing a textile product e.g. from discarded, finely shredded or refined textiles comprising natural fibres and / or synthetic fibres, (ii) performing a pretreatment step by dispersing the textile product to an aqueous solution comprising a pretreatment agent, and thereby providing a pretreated textile product, (iii) performing a decolorization step and / or elastane removal step by dispersing the textile product to a solution comprising a decolorizing or elastane removal agent, and thereby providing a decolorized or elastane reduced textile product, (iv) optionally, performing a polyester removal and / or polyamide removal step, wherein the textile product in either step (ii) and / or step (iii) and / or step (iv) is subjected to ultrasound at a frequence of at least 20 kHz for a period t of at least 10 seconds.

Description

[0001] A PROCESS FOR PROVIDING A SOLID FRACTION COMPRISING TEXTILE FIBERS

[0002] The present invention relates to a process for decoloring textiles, and for preparing a textile product for recycling.

[0003] Background of the invention

[0004] Around 85% of all textiles thrown away amounts in 2017 to roughly 13 million tons in US alone. The textile waste is traditionally either dumped into landfill or burned.

[0005] Globally, it is estimated that 92 million tons of textile waste are created each year and is equivalent to one garbage truck filled with clothes ending up on landfill sites every second. By 2030, it is expected that more than 134 million tons of textiles are discarded every year.

[0006] Disposal of such large volumes of textile waste is an increasing problem for the apparel industry. The rising costs, reduction in available space, and concern for the environment makes the burning and landfilling of textile waste dwindling options.

[0007] Reuse or recycling of the fibres from textiles has been investigated for decades and several methods exist. However, a large percentage of the textile waste comprises blends of fibres such as polyester / cellulosic fabrics, e.g., polyester / cotton and polyester / viscose blends, and also other fibres may be included, such as elastane. The reuse or recycling of the individual blended materials is complicated by the fact that there are inherent differences in the physical properties and composition of the components. Additionally, the fabrics are treated with resinous materials and other finishing compounds, such as dyes. This makes it nearly impossible to find potential commercial end uses for this material other than rags or cloth scraps, which are of little monetary value.

[0008] Therefore, there is an interest in the industry for providing potential methods of recycling textile waste comprising blends of fibres, such as polyester / cotton fabric blends, which may be reused e.g., in textiles.

[0009] Another challenge of reusing textile waste comprising blends of fibres is the presence of dye in the textile. The decolorization of textile waste (pre- and postconsumer) is a huge issue in textile fibre-to-fibre recycling methods, due to a vast number of different dyes and the need to remove them before the textile waste materials can be dissolved and spun into recycled fibres.

[0010] WO 2022 / 229129 discloses a process providing a solid polyester fraction from a textile product comprising natural fibres, and polyester fibres, the process comprising the steps of: a) providing the textile product comprising natural fibres, and polyester fibres; b) adding a liquid decolorizing agent to the textile product, thereby providing a decolorized first solid fraction and a first liquid fraction; c) separating the first solid fraction from the first liquid fraction; d) adding a solvent to the first solid fraction and heating the mixture at a temperature between 170-190°C, thereby providing a second solid fraction comprising the natural fibres, and a second liquid fraction comprising polyester; e) separating the second liquid fraction from the second solid fraction; and e) separating the polyester fraction from the second liquid fraction, thereby providing a solid polyester fraction. WO 2023 / 143943 discloses a process for providing a solid fraction from a textile product comprising a natural fibre and / or a synthetic fibre. The process involves the treatment of the textile product with a water-soluble salt of dithionous acid followed by a treatment of an aprotic solvent, such as dimethyl sulfoxide.

[0011] Hence, it is desirable to provide a further improved process for recovering the individual solid fractions from textile products. In particular a process for recovering solid fractions, which is easy, reliable, efficient, environmentally friendly, cheap, and fast would be advantageous. It is particularly advantageous that using ultrasound makes it possible to significantly reduce the retention time which also makes it possible to increase production without increasing the number and / or size of the applied apparatuses.

[0012] Summary of the invention

[0013] Thus, an object of the present invention is to provide an improved process for treating textiles fibres for recycling. According to the invention textile blends as well as pure textiles are treated without degrading the fibres, thereby enabling used textiles to be transformed into new garments.

[0014] In particular, it is an object of the present invention to provide a process that solves the above-mentioned problems of the prior art by providing a process with significantly reduced retention time which makes the process efficient and makes it possible to reduce costs when designing the apparatuses for the process and in operation of this equipment.

[0015] According to a first aspect, the present invention relates to a process for providing a solid fraction comprising textile fibers such as natural fibres and / or synthetic fibres, the process comprises the steps of:

[0016] (i) providing a textile product e.g. from discarded, finely shredded or refined textiles comprising natural fibres and / or synthetic fibres,

[0017] (ii) performing a pretreatment step by dispersing the textile product to an aqueous solution comprising a pretreatment agent, and thereby providing a pretreated textile product,

[0018] (iii) performing a decolorization step and / or elastane removal step by dispersing the textile product to a solution comprising a decolorizing or elastane removal agent, and thereby providing a decolorized or elastane reduced textile product,

[0019] (iv) optionally, performing a polyester removal and / or polyamide removal step, wherein the textile product in either step (ii) and / or step (iii) and / or step (iv) is subjected to ultrasound at a frequence of at least 20 kHz for a period t of at least 10 seconds.

[0020] According to any embodiment of the first aspect, the frequency of the ultrasound which the textile product or textile fibers are subjected to in either step (ii) and / or step (iii) and / or step (iv) may be 20 to 400 kHz, or 20 to 100 kHz, or 20 to 50 kHz, or 20 to 40 kHz. According to any embodiment of the first aspect, the temperature at the beginning of a pretreatment step (ii), when the textile product is subjected to ultrasound, may be ambient temperature, or may be between 10-85 °C, or may be between 20-50 °C, or may be between 10-40 °C, or may be between 10-30 °C, or may be below 50 °C.

[0021] According to any embodiment of the first aspect, the temperature at the beginning of the treatment step (iii), when the textile product is subjected to ultrasound, may be ambient temperature, or may be between 10-85 °C, or may be between 20-50 °C, or may be between 10-40 °C, or may be between 10-30 °C, or may be below 50 °C, or may be below 150 °C .

[0022] According to any embodiment of the first aspect, the temperature at the beginning of the treatment step (iv), when the textile product is subjected to ultrasound, may be below 150 °C, or between 100-150 °C.

[0023] According to any embodiment of the first aspect, the period t for a step according to (ii) or (iii) may be at least 20 seconds, or at least 30 seconds, or from 30 seconds to 60 minutes, preferably from 30 seconds to 30 minutes, preferably from 30 seconds to 20 minutes, preferably from 30 seconds to 10 minutes, preferably from 30 seconds to 5 minutes, preferably from 1 minute to 30 minutes, or from 1 seconds to 20 minutes, preferably from 1 minutes to 10 minutes, preferably from 1 minutes to 5 minutes.

[0024] According to any embodiment of the first aspect, the decolorizing agent used in the decolorization, or elastane removal step (iii) may be an organic solvent e.g. selected from dihydrolevoglucosenone (Cyrene), dimethyl sulfoxide (DMSO), methyl-sulfonyl-methane (DMSO2), sulfolane (tetramethylene sulfone), or a combination thereof.

[0025] According to any embodiment of the first aspect, the process may comprise:

[0026] - (iia) at least a first pretreatment step in form of an alkaline treatment wherein the aqueous solution comprises an alkaline component such as NaOH, a detergent component, and optionally an antifoaming component, and

[0027] - (iib) at least one second pretreatment

[0028] - in form of a reductive treatment wherein the aqueous solution comprises an alkaline component such as NaOH, and a reductive component such as dithionite, or in form of an acidic treatment wherein the aqueous solution comprises an acidic component such as sulfuric acid (H2SO4) or citric acid (HOC(CO2H)(CH2CO2H)2) or hydroxy acetic acid (CH2OHCOOH) (glycolic acid), or the process comprises both processes of (iib) i.e. a reductive treatment followed by an acidic treatment, wherein at least one, or at least two, or at least three of the treatments of (iia) and (iib) is / are subjected to ultrasound at a frequence of at least 20 kHz for a period t of at least 10 seconds.

[0029] According to any embodiment of the first aspect, the decolorizing agent of the solutions of step (iii) may be an organic solvent such as Cyrene™, DMSO, Propylene Carbonate or Dimethyl Isosorbide or a combination of one or more organic solvent.

[0030] According to any embodiment of the first aspect, the decolorization or elastane removal step (iii), if not subjected to ultrasound, may be performed at a temperature within the range of 30-160 °C, preferably within the range of 50-150 °C, more preferably within the range of 70-100 °C, e.g., at a temperature of around 85 °C.

[0031] According to any embodiment of the first aspect, the textile product of step (i) may comprise natural of synthetic fibers selected from:

[0032] 0-20% elastane (PU), 0-100% polyester, 0-100% natural Cellulose Fiber such as Cotton or hemp or jute or flax etc., 0-25% Man Made Cellulose Fiber such as Viscose, Lyocell, and / or the textile product does not comprise PVC (Polyvinyl chloride), and / or less than 2wt% of PFAS, and / or Nylon, wool / down, other proteins, and / or acrylic is either not present or is present in low amounts i.e. amounts below 2wt%.

[0033] According to any embodiment of the first aspect, the textile product of step (i) may be shredded to units having a maximum dimension of 0.010 m, or 0.006 m, or 0.002 m, or 0,001 m, and optionally the textile product has been refined.

[0034] According to a second aspect of the invention, the invention relates to a solid fraction of recycled textile produced by a process according to the first aspect, which solid fraction has a content of Al < 30 mg Al / kg textile, and a content of Fe < 20 mg / kg textile and a content of Ca < 100 mg Ca / kg textile and a content of Mg < 220 mg Mg / kg textile.

[0035] According to any embodiment of the second aspect, the solid fraction may comprise or may be constituted of recycled textile fibers adapted to form a raw material for a textile production.

[0036] Definitions:

[0037] "Solid fraction" includes both a powder fraction and / or a fibrous fraction.

[0038] "Color-fractions" refer to either an aqueous solution with soluble dyes and dye residues, or to an aprotic solvent solution comprising soluble dyes and dye residues.

[0039] "Synthetic fibre" includes both synthetic fibres and semi-synthetic fibres.

[0040] "Dispersing" - when textile fibers are dispersed in a liquid or solvent it is understood that the fibers are wetted by liquid or solvent to ensure a suitable degree of wetting of the fibers. Normally, dispersing will take place while stirring or agitating, e.g. by increasing flows, the dispersed textile fibers to ensure adequate wetting.

[0041] "In general" - when this expression is used to describe an embodiment, it means that the feature may be used with all embodiments of the invention even though the feature is mentioned in the detailed part of the description

[0042] The present invention will now be described in more detail in the following.

[0043] Detailed description of the invention

[0044] In general, a process according to the invention may consist of a series of stepsl:

[0045] One or more pretreatments, Decolorization and elastane removal and optionally PET (Polyethylene terephthalate, a polyester) dissolution / removal. The textile-input for the process, also referred to as textile product, may define the number and character of the different pretreatments, pretreatments can be used in combination or separately.

[0046] The textile product can be any combination of polycotton, polyester, cotton and Man-Made Cellulose Fibres (MMCF). Elastane can be removed from the textile product, but normally not for recycling purposes. The solid fraction obtained from the textile recycling process according to the invention may be in form of a pulp and / or a powder e.g. cellulose-pulp and / or polyester powder.

[0047] Before pretreating the textile product, the textile product may be shredded to smaller pieces or homogenized. The smaller pieces of textile product may be below approximately 10x10 cm, such as below 5x5 cm, e.g., below 1x1 cm.

[0048] In general, the textile product may be subjected to a pre-treatment (ii), before subjecting the pretreated textile product to a decolorization and / or an elastane removal step by dispersing the textile product in a liquid decolorizing and / or elastane removal agent(iii).

[0049] The textile product is subjected to one or more pretreatments for a period tii,i, t,i,2, ..., tii,nwhile energy is supplied to the mixture / dispersion. The supplied energy may be in form of either heat or ultrasound or a combination of heat and ultrasound, and the type of supplied energy may be chosen individually for each pretreatment. The length of each period t,i,i, tii,2, ..., tii,n may depend on which type of energy is supplied and energy consumption for each pretreatment may be optimized accordingly.

[0050] The pretreatment may comprise one, two, three or four steps selected from:

[0051] (a) an acidic treatment;

[0052] (b) an alkaline treatment;

[0053] (c) a hydrogen peroxide treatment;

[0054] (d) a reductive treatment;

[0055] (e) or a combination of (a), (b), (c) and (d).

[0056] The acidic pre-treatment (pre-treatment (a)) may be performed using a strong acid. The strong acid may be selected from the group consisting of HCI (hydrochloric acid); H2SO4 (sulfuric acid); HNO3 (nitric acid); HBr (hydrobromic acid); HCIO4 (perchloric acid); or HI (hydroiodic acid). Preferably, the strong acid is H2SO4 (sulfuric acid).

[0057] In an embodiment of the present invention the concentration of the acid used in the acidic pre-treatment may have a concentration in the range of 0.1-3M (moles per litre), such as in the range of 0.3-2.5M, e.g., in the range of 0.5-2.0M, such as in the range of 0.6-1.5M, e.g., in the range of 0.75-1.0M.

[0058] Alternatively, organic acids may be employed for the acidic pretreatment for targeted removal of certain minerals, including calcium and other metal ions, from the textile product. This may be particularly useful in cases where mineral deposits contribute to coloration or other undesirable properties in the textile material. Organic acids such as citric acid and hydroxy acetic acid (glycolic acid) offer effective chelating properties, enabling them to bind with metal ions and facilitate their removal from the textile substrate. Other organic acids with similar chelating capabilities may also be employed in this pre-treatment step.

[0059] Citric acid (C6H8O7) may be applied in concentrations ranging from 1-10 wt%, such as within the range of 2-8 wt%; for instance, within the range of 3-6 wt%, or about 2 wt%.

[0060] Hydroxy acetic acid (CH2OHCOOH), also known as glycolic acid, may be used in concentrations ranging from 0.1-5 wt%, such as within the range of 0.3-3 wt%; for instance, within the range of 0.5-1 wt%, or about 0.75 wt%.

[0061] Normally, the acidic pretreatment is conducted for 20-30 minutes at atmospheric pressure and a temperature within the range of 20-95 °C, such as within the range of 30-90°C, e.g., within the range of 40-85°C, such as within the range of 60-75°C, e.g., about 60°C.

[0062] The alkaline pre-treatment (pre-treatment (b)) may be performed using a strong base. Strong bases are bases which completely dissociate in water into the cation and OH- (hydroxide ion). In an embodiment of the present invention hydroxides of the Group I (alkali metals) and Group II (alkaline earth) metals are considered strong bases. In a further embodiment of the present invention the strong base may be selected from a hydroxide compound. Preferably, the strong base may be selected from the group consisting of NaOH (sodium hydroxide); LiOH (lithium hydroxide); KOH (potassium hydroxide); RbOH (rubidium hydroxide); CsOH (cesium hydroxide); Ca(OH)2 (calcium hydroxide); Sr(OH)2 (strontium hydroxide); and / or Ba(OH)2 (barium hydroxide).

[0063] In an embodiment of the present invention the concentration of the base used in the alkaline pre-treatment may have a concentration within the range of 5-25 wt% (weight percent), such as within the range of 8-20 wt%; e.g., within the range of 9-15 wt%, such as about 10 wt%.

[0064] Normally, the alkaline pretreatment is conducted for 20-30 minutes at atmospheric pressure and a temperature within the range of 20-95 °C, such as within the range of 30-90°C, e.g., within the range of 40-85°C, such as within the range of 60-75°C, e.g., about 60°C.

[0065] The hydrogen peroxide pre-treatment (pre-treatment (c)) may be performed using a concentration of hydrogen peroxide within the range of 5-25 wt%, such as within the range of 8-20 wt%; e.g., within the range of 9-15 wt%, such as about 10 wt%.

[0066] The hydrogen peroxide pre-treatment (pre-treatment (c)) may include a base, preferably a strong base, e.g., a strong base as mentioned herein. Preferably, the hydrogen peroxide solution may have a concentration of strong base in the range of 5-25 wt%, such as in the range of 8-20 wt%; e.g., in the range of 9-15 wt%, such as about 10 wt%.

[0067] The hydrogen peroxide pre-treatment (pre-treatment (c)) may include a step of adjusting the pH-value of the hydrogen peroxide solution. Preferably, the pH-value of the hydrogen peroxide solution may be adjusted to a pH-value in the range of pH 9-14, such as in the range of pH 10-13; e.g., pH 12. Normally, the hydrogen peroxide pretreatment is conducted for 20-30 minutes at atmospheric pressure and a temperature within the range of 20-95 °C, such as within the range of 30-90°C, e.g., within the range of 40-85°C, such as within the range of 60-75°C, e.g., about 70°C.

[0068] Normally, the hydrogen peroxide pretreatment is conducted for 20-30 minutes at atmospheric pressure.

[0069] The reductive pre-treatment (pre-treatment (d)) may be performed using a reducing agent. In an embodiment, the reducing agent may be selected from the group consisting of Sodium dithionous acid, also known as sodium hydrosulfite (Na2S2O4), Sodium bisulfite (NaHSO3), Sodium sulfite (Na2SO3), Sodium thiosulfate (Na2S2O3), Sodium borohydride (NaBH4), Hydroxylamine, Hydrazine or SnCI2 (Stannous chloride). Preferably, the reducing agent is sodium hydrosulfite (Na2S2O4).

[0070] In an embodiment of the present invention the concentration of the reductive agent used in the reductive pre-treatment may have a concentration within the range of 1-20 wt% (weight percent), such as within the range of 2-15 wt%; e.g., within the range of 3-6 wt%, such as about 4 wt%.

[0071] Normally, the reductive pretreatment is conducted for 20-30 minutes under atmospheric pressure and a temperature within the range of 20-100 °C, such as within the range of 30- 95°C, e.g., within the range of 40-90°C, such as within the range of 60-85°C, e.g., about 80°C. During this process, the pH should be maintained in an alkaline range. Specifically, when using sodium hydrosulfite (Na2S2O4), the pH may be kept between 11-13, preferably around 12.

[0072] After pretreatment, the pretreated textile product is subjected to a decolorization and / or an elastane removal step. Normally, this step comprises mixing a liquid decolorizing agent to the textile product, hereby providing a decolorized first solid fraction and a first liquid fraction. The decolorization and / or elastane removal step comprises at least one step (tiii,i)where the textile fibres are mixed with a solvent but may comprise two or more steps (t,ii,2, tjii,n) where the textile fibres are mixed with same or different solvents.

[0073] The pretreated textile product is subjected to the decolorization treatment and / or the elastane removal step for a period t while energy is supplied to the mixture. The supplied energy may be in form of either heat or ultrasound or a combination of heat and ultrasound, and the type of supplied energy may be chosen individually for each pretreatment. The length of each period t ,i, tni.2, ..., t ,n may depend on which type of energy is supplied and energy consumption for each decolorization treatment and / or the elastane removal step may be optimized accordingly.

[0074] Depending on the solvent, the treatment temperature for the decolorization treatment and / or the elastane removal step may be between 110-150 °C and treatment time may be 20-60 minutes at 2 - 4 bar. Normally, the solvent has a boiling point above 180 °C, such as within the range of 185-300 °C. The decolorizing solvent may be selected from a group consisting of dihydrolevoglucosenone (Cyrene), dimethyl sulfoxide (DMSO), methyl-sulfonyl-methane (DMSO2), Dimethyl Isosorbide, Propylene Carbonate, gamma-valerolactone, 6-hexanolactone (carprolactone), methyl 5-(dimethylamino)-2- methyl-5-oxopentanoate (pentanoic acid), 2-Hydroxy- dimethylpropanamide (Dimethyllactamide), isosorbide dimethyl ether, l,3-Dioxolane-4- methanol, l,3-dioxane-5-ol, succinic acid dimethyl ester, dimethyl glutarate, glycerol diacetate, N,N-dimethyloctanamide, diethylglutarate, ethyl benzoate, 1,2-propanediol carbonate, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate (Polarclean), Succinic acid diethyl ester, diethyl succinate, diethylene glycol monobutyl ether, diethyl adipate, benzyl alcohol, butyl benzoate, butyl 3- hydroxybutyrate, dipropylene glycol mono-butyl ether, dipropylene glycol, propylene glycol phenyl ether, 2-phenoxy ethanol, hexylene glycol, cyclademol, CH302C(CH2)nC02CH3 (n = 2,3,4), or a combination thereof.

[0075] After the decolourization and / or elastane removal, the textile fibres may be subjected to a further solvent treatment for removal of polyester and / or polyamide. This further treatment is however only relevant if polyester and / or polyamide are / is present in the textile fibres.

[0076] In patent WO2022229129 the inventors surprisingly identified a group of solvents that, despite different chemical structures, was able to dissolve polyester at relatively narrow temperature range of 170-190 °C. Normally, the mixture of the first solid fraction and the solvent is heated at a temperature between 170- 190 °C, preferably within the range of 175- 185 °C, even more preferably at about 180 °C, thereby providing a second solid fraction comprising the natural fibres, and a second liquid fraction comprising polyester. The second liquid fraction is then separated from the second solid fraction, and finally the polyester fraction is separated from the second liquid fraction, thereby providing a solid polyester fraction. By supplying energy as ultrasound or as a combination of heat and ultrasound the temperature of the polyester dissolving process may be lowered to between 100-150 °C and the retention time may be reduced to between 5-15 minutes. If only heat is used as supplied energy, the retention time is between 20-60 minutes.

[0077] The solvent used at a polyester dissolving step (iv) may be selected from a group consisting of dihydrolevoglucosenone (Cyrene), methyl-sulfonyl-methane (DMSO2), Dimethyl Isosorbide, Propylene Carbonate, gamma-valerolactone, 6-hexanolactone (carprolactone), methyl 5-(dimethylamino)-2- methyl-5-oxopentanoate (pentanoic acid), 2-Hydroxy- / V, / V- dimethylpropanamide (Dimethyllactamide), isosorbide dimethyl ether, l,3-Dioxolane-4- methanol, l,3-dioxane-5-ol, succinic acid dimethyl ester, dimethyl glutarate, glycerol diacetate, N,N- dimethyloctanamide, diethylglutarate, ethyl benzoate, 1,2-propanediol carbonate, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate (Polarclean), diethyl succinate, diethylene glycol monobutyl ether, diethyl adipate, benzyl alcohol, butyl benzoate, butyl 3-hydroxybutyrate, dipropylene glycol mono-butyl ether, dipropylene glycol, propylene glycol phenyl ether, 2-phenoxy ethanol, hexylene glycol, cyclademol, CH302C(CH2)nC02CH3 (n = 2,3,4), or a combination thereof.

[0078] If heat is supplied as the only energy source during pretreatments, decolorization treatments and / or elastane treatments, the retention periods are relatively long, and the temperatures are relatively high. The inventors of the present invention, surprisingly found, that addition of ultrasonic wave treatment in the abovementioned treatments, reduced the need for external heating and the previous temperature dependency in each step, along with significant reductions in retention time, to achieve comparable results in the treatment. In an industrial facility, it is advantageous to minimize the energy expenditure on heating and reduce the retention time of materials within the production plant. Shortening the retention time can lead to significant reductions in the size and capacity requirements of equipment such as pumps, tanks, and columns. This, in turn, decreases the energy consumption of pumps and other related machinery, lowers the demand for construction materials like steel, and reduces the volume of chemical solutions required for each treatment. Added benefits are reduced safety concerns in operating high-temperature organic solvents, requiring ATEX safety measures to be installed. Hence, application of ultrasound allows for a more cost- effective and environmentally friendly industrial process and enhance overall operational efficiency and safety.

[0079] The purpose of subjecting recycled textile to one or more pretreatments is 'general cleaning' of surface chemicals and waste residual 'dirt', to enhance decolorization and reduce the contents of selected metals and minerals, to bring these below the limit values listed in Table 1.

[0080] Table 1

[0081] The result of the decolourization of the textile product may be indicated by %Whiteness measurements, e.g., performed according to DIN53 145 (2012). Alternatively, %Whiteness measurements may be made using a PCE-WSB 1 device, purchased from PCE- instruments.com, which complies with ISO 2471 : 1977 (Paper and board — Determination of opacity (paper backing) — Diffuse reflectance method).

[0082] To establish if and how the application of ultrasound during a pre-treatment or decolorizing treatment may contribute to or replace the traditional heat treatment and reduce retention time of treatments, the following experiments are conducted:

[0083] Examples:

[0084] Ultrasound tests are either performed in the apparatus BANDELIN SONOREX RK 100 at a frequence of 35 kHz (ULB), or in the apparatus SONICS Vibracell VCX 750 at 20 kHz (ULH).

[0085] All of the following tests are performed on a textile product, comprising a black, weaved cotton fabric, donated by the Municipality of Copenhagen, that has previously been worn as uniforms by Copenhagen Municipality's canteen staff. The textile is not treated in any way before being subjected to treatment conditions described in the tests. "Untreated textile" refers to textile from the same batch of textile product, being analysed for metal content and whiteness measurements, having received no treatments.

[0086] No additional heat was added to any of the ultrasound treatments, so all temperatures above ambient (21 °C) were due to excess heat being generated from the ultrasonic equipment. It is worth noting, that in some instances, there will be compounding effects in the ultrasound treatments, due to excess heat. Here it should be noted, that even though the heat is raised, there is still significantly shorter retention times

[0087] 1 ) Acidic treatment combined with ultrasound treatment

[0088] Metal content in textile after one acidic wash

[0089] According to all test treatments 3 g of textile is added to 60 ml of an acidic aqueous solution (7.5% Sulfuric acid). Immediately after supplying the textile to the bath of acidic aqueous solution, the bath is subjected to ultrasound for a time period.

[0090] One treatment 'Heating 30 min, 60°C' illustrate metal removal from textiles at a known process where the acidic aqueous solution is heated to 60°C for 30 minutes whereafter the content of metal is measured.

[0091] After having been subjected to the acidic treatment, the aqueous solution is removed from the textile by filtering, the textile is then rinsed with water, dried and ashed. The content of metals (mg / kg) in form of magnesium (Mg), calcium (Ca) and iron (Fe) in the ashed textile are measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

[0092] The effect of metal removal of each treatment can be seen in the table below which is also depicted in Figure 4. In the table 'Limit values' are included, indicating the upper limit of metal allowed in the final recycled raw material for textile fiber production. This is included, although the goal of this experiment was merely to investigate whether a similar or improved effect of metal removal could be found when using ultrasound, compared to the known treatment of heating the sample in acidic solution.

[0093] It is important to note the extreme reduction in treatment times of all ultrasound treated samples. It could be assumed logically, that the Limit values could be reached by either prolonging the retention times, or by adding a second acidic treatment step, if the saturation point of a specific metal has been reached in the volume of aqueous solution, which has been proven in previous trials using the known heat treatment.

[0094] Metal content in textile sample after one acidic wash

[0095] Iron

[0096] The limit value for Fe-content is 10 mg / kg. All treatments results in a Fe-content below the limit value, i.e. treatments with ultrasound for as short as 30 seconds result in satisfying values for Fe-content.

[0097] The lowest values for Fe-content are obtained by the treatment ULH 0.5 min (20 kHz) (6 mg / kg textile) and the treatment Heating to 60°C in 30 minutes (6 mg / kg textile).

[0098] Magnesium

[0099] The limit value of 220 mg / kg for Mg is significantly above all the measured values.

[0100] The lowest value for Mg-content (10 mg / kg textile) is obtained for the treatment ULB 30 min (35 kHz), and the values for treatments according to the invention are comparable or even better than the value obtained from the traditional method (14 mg / kg textile).

[0101] Calcium

[0102] None of the acidic treatments result in a Ca-content below the limit value, likely due to the saturation point being reached in the solution and / or the fact that sulfuric acid (H2SO4) reacts with calcium (Ca) to produce calcium sulphate (CaSCU), which is water-insoluble and therefore difficult to wash out after the treatment. This theory is supported by the observation of a white residue on glassware after trials, likely indicating the presence of calcium sulphate.

[0103] The lowest value (44 mg / kg textile) for Ca-content, i.e. the most efficient reduction of Ca- content in the textile, is obtained for the treatment ULB 30 min (35 kHz).

[0104] The only other treatment which is carried out for 30 minutes is the traditional treatment where the textile is heated to 60°C and not treated with ultrasound. With this treatment a content of 55 mg / kg textile is obtained.

[0105] 2) Alkaline treatment combined with ultrasound treatment

[0106] Metal content in textile after one alkaline wash

[0107] According to all test treatments 1 g of textile is added to 60 ml of an alkaline aqueous solution. Immediately after supplying the textile to the bath of alkaline aqueous solution, the bath is subjected to ultrasound for a time period. One treatment 'Heating 30 min 70°C' illustrates metal removal from textiles at a known process where the alkaline aqueous solution is heated to 70°C for 30 minutes whereafter the content of metal is measured.

[0108] The alkaline treatment is tested by treating the textile in a bath of sodium hydroxide (10% NaOH), the time period is varied as well as frequency of the ultrasound.

[0109] After having been subjected to the alkaline treatment, the aqueous solution is removed from the textile by filtering, the textile is then rinsed with water, dried and ashed. The content of metals (mg / kg) in form of iron (Fe) and aluminum (Al) in the ashed textile are measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

[0110] Similar to the previous trial with acidic pretreatments, the 'Limit values', are included, indicating the upper limit of metal allowed in the final recycled raw material for textile fiber production (see Table below which is also depicted in Figure 5). This is included, although the goal of this experiment was merely to investigate whether a similar or improved effect of metal removal could be found when using ultrasound, compared to the known treatment of heating the sample in alkaline solution. It is important to note the extreme reduction in treatment times of all ultrasound treated samples. It could be assumed logically, that the Limit values could be reached by either prolonging the retention times, or by adding a second alkaline treatment step, if the saturation point of a specific metal has been reached in the volume of aquas solution, which has been proven in previous trials using the known heat treatment.

[0111] Metal content in textile sample after one alkaline wash (triple measurement of samples) Iron

[0112] The limit value for Fe-content is 10 mg / kg, although 15 mg / kg can be acceptable for some applications. None of the treatments results in a Fe-content below the limit value, though a reduction is seen in all treatments, compared to the untreated sample.

[0113] The lowest values of 16 mg / kg for Fe-content is obtained by the known treatment of heating the sample for 30 minutes to 70°C and the treatment ULB 10 min, 21°C (35 kHz) (17 mg / kg textile).

[0114] Aluminium

[0115] The limit value for Al-content is 30 mg / kg. The only treatment resulting in an Al-content below the limit value, was the known treatment of heating the sample for 30 minutes to 70°C (18 mg / kg), while some samples was nearing the limit value, especially the treatment ULB 10 min, 21°C (33 mg / kg). Most of the samples achieved a reduction in the proximity of 50% compared to the untreated sample, which shows a clear effect of all treatments.

[0116] 3) Reductive treatment combined with ultrasound treatment

[0117] Metal content in textile after one alkaline wash

[0118] According to all test treatments 1 g of textile is added to 60 ml of a solution containing 3% Sodium hydrosulfite and 4% Sodium hydroxide. Immediately after supplying the textile to the bath of aqueous solution, the bath is subjected to ultrasound for a time period.

[0119] To expedite the process, the bath is either heated to 85 °C, or subjected to ultrasound. The ultrasound treatments are either performed in the apparatus BANDELIN SONOREX RK 100 at a frequence of 35 kHz (ULB), or in the apparatus SONICS Vibracell VCX 750 at 20 kHz (ULH). Each ultrasound treatment is started at ambient temperature which is around 20 °C and the final temperature is noted.

[0120] One treatment 'Heating 30 min 85°C' illustrates metal removal from textiles at a known process where the aqueous solution is heated to 85°C for 30 minutes whereafter the content of metal is measured.

[0121] The reductive treatment is tested by treating the textile in a bath of reductive solution. The time period varies as well as frequency of the ultrasound.

[0122] After having been subjected to the reductive treatment, the aqueous solution is removed from the textile by filtering, the textile is then rinsed with water, dried and ashed. The content of metals (mg / kg) in form of iron (Fe) and aluminum (Al) in the ashed textile are measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

[0123] Similar to the previous trial with acidic and alkaline pretreatments, the 'Limit values', are included, indicating the upper limit of metal allowed in the final recycled raw material for textile fiber production (see Table below which is also depicted in Figure 6). This is included, although the goal of this experiment was merely to investigate whether a similar or improved effect of metal removal could be found when using ultrasound, compared to the known treatment of heating the sample in reductive solution. Metal content in textile sample after one alkaline wash (triple measurement of samples)

[0124] Iron

[0125] The limit value for Fe-content is 10 mg / kg, although 15 mg / kg can be acceptable for some applications. None of the treatments results in a Fe-content below the limit value, though a reduction is seen in all treatments, compared to the untreated sample.

[0126] The lowest value of 20 mg / kg for Fe-content is obtained the treatment ULH 2 min, Tmax 49°C (20 kHz).

[0127] Aluminium

[0128] The limit value for Al-content is 30 mg / kg. The only treatment resulting in a Fe-content below the limit value, was the known treatment of heating the sample for 30 minutes to 70°C (26 mg / kg).

[0129] Most of the samples achieved a reduction in the proximity of 40-50% compared to the untreated sample, which shows a clear effect of all treatments. % Whiteness

[0130] In this instance, metal content is measured as additional information on the effect of ultrasound, even though the main goal of this treatment is not to remove metal content, but to prepare the textiles for subsequent decolorization as described in treatment 2). The effect of this pretreatment cannot be measured before the subsequent decolorization is performed. Therefore, all samples were decolorized, using the exact same procedure of immersing and stirring the samples in dimethyl sulfoxide (DMSO) at 150 °C for 60 minutes, in order to ensure that the full effect could be measured. %Whiteness measurements were made using a PCE-WSB 1 device, purchased from PCE-instruments.com, which complies with ISO 2471 : 1977 (Paper and board — Determination of opacity (paper backing) — Diffuse reflectance method) (see Table below which is also depicted in Figure 7).

[0131] %Whiteness of textile sample after reductive pretreatment and subsequent decolorization (triple measurement of samples)

[0132] A clear increase in %Whiteness is achieved in all samples, and all samples is in a somewhat similar range of %Whiteness (17.8 - 22.2), an increase of 640% - 838%, compared to the %Whiteness (2.4) of the sample that has no reductive pretreatment prior to the decolorization treatment.

[0133] The highest %Whiteness of 22.5 is seen in the sample having received the known pretreatment of Heating 30 min at 85 °C, though a similar result of 22.1 is seen in the sample ULH 1 min, Tmax 38°C (20 kHz). 4) Decolorization treatment combined with ultrasound treatment

[0134] The decolorizing agent in the decolorization treatment is dimethyl sulfoxide (DMSO), and according to this test 1 g of textile is immersed in 54 ml of an aqueous solution of DMSO (1,67 w / w% DMSO). After decolorizing, the solvent is filtered out of the textile sample and the sample is rinsed in a fixed volume of washing water. By keeping the volume of washing water constant in all samples, the colour of the washing water, can be used as an indicator of the treatment effect. The treatment effect is indicated by the colour of the washing water, which is determined by amount of dyestuff, having been removed from the sample, and thereby becoming dissolvable in the washing water.

[0135] The results of the decolorization test can be seen in figures 1-3. Fig. 1 shows washing water from washing of a sample, having been treated in a known treatment using DMSO as a decolorizing agent at 150°C for 60 minutes.

[0136] Fig. 2 shows washing water in which textile was treated with DMSO at surrounding temperature and subjected to ultrasound treatment (ULH) 20 kHz for respectively 0,5, 1 and 2 minutes.

[0137] Fig. 3 shows washing water in which textile was treated with DMSO at surrounding temperature and subjected to ultrasound treatment (ULB) 35 kHz for respectively 1, 5, 10, 20 and 30minutes.

[0138] It appears that the traditional process (result of fig. 1) is the darkest i.e. the process where the most color has been transferred from the textile to the washing water.

[0139] However, color has been transferred to the washing water without heating the textile for 30 min., but only subjected to ultrasound. Ultrasound may therefore be used as an alternative to a heating process when removing color from a textile product.

[0140] Conclusion:

[0141] Ultrasound treatments contribute to the reduction of metals and dyestuff in textiles and may replace a traditional treatment or a combination of traditional treatments where textiles are heating in an aqueous solution or organic solvents for 20 minutes or more.

[0142] Very short treatments with ultrasound i.e. treatments lasting less than 10 minutes or even less than a minute are able to significantly improve release of metals and dyes from the textile. A clear increase in %Whiteness is achieved in all samples, and all samples is in a somewhat similar range of %Whiteness (17.8 - 22.2), an increase of 640% - 838%, compared to the %Whiteness (2.4) of the sample that has no reductive pretreatment prior to the decolorization treatment.

[0143] The highest %Whiteness of 22.5 is seen in the sample having received the known pretreatment of Heating 30 min at 85 °C, though a similar result of 22.1 is seen in the sample ULH 1 min, Tmax 38°C (20 kHz).

[0144] 4) Decolorization treatment combined with ultrasound treatment

[0145] The decolorizing agent in the decolorization treatment is dimethyl sulfoxide (DMSO), and according to this test 1 g of textile is immersed in 54 ml of an aqueous solution of DMSO (1,67 w / w% DMSO). After decolorizing, the solvent is filtered out of the textile sample and the sample is rinsed in a fixed volume of washing water. By keeping the volume of washing water constant in all samples, the colour of the washing water, can be used as an indicator of the treatment effect. The treatment effect is indicated by the colour of the washing water, which is determined by amount of dyestuff, having been removed from the sample, and thereby becoming dissolvable in the washing water.

[0146] The results of the decolorization test can be seen in figures 1-3. Fig. 1 shows washing water from washing of a sample, having been treated in a known treatment using DMSO as a decolorizing agent at 150°C for 60 minutes.

[0147] Fig. 2 shows washing water in which textile was treated with DMSO at surrounding temperature and subjected to ultrasound treatment (ULH) 20 kHz for respectively 0,5, 1 and 2 minutes.

[0148] Fig. 3 shows washing water in which textile was treated with DMSO at surrounding temperature and subjected to ultrasound treatment (ULB) 35 kHz for respectively 1, 5, 10, 20 and 30minutes.

[0149] It appears that the traditional process (result of fig. 1) is the darkest i.e. the process where the most color has been transferred from the textile to the washing water.

[0150] However, color has been transferred to the washing water without heating the textile for 30 min., but only subjected to ultrasound. Ultrasound may therefore be used as an alternative to a heating process when removing color from a textile product.

[0151] Conclusion:

[0152] Ultrasound treatments contribute to the reduction of metals and dyestuff in textiles and may replace a traditional treatment or a combination of traditional treatments where textiles are heating in an aqueous solution or organic solvents for 20 minutes or more.

[0153] Very short treatments with ultrasound i.e. treatments lasting less than 10 minutes or even less than a minute are able to significantly improve release of metals and dyes from the textile.

Claims

Claims1. A process for providing a solid fraction comprising textile fibers such as natural fibres and / or synthetic fibres, the process comprises the steps of:(i) providing a textile product e.g. from discarded, finely shredded or refined textiles comprising natural fibres and / or synthetic fibres,(ii) performing a pretreatment step by dispersing the textile product to an aqueous solution comprising a pretreatment agent, and thereby providing a pretreated textile product,(iii) performing a decolorization step and / or elastane removal step by dispersing the textile product to a solution comprising a decolorizing or elastane removal agent, and thereby providing a decolorized or elastane reduced textile product,(iv) optionally, performing a polyester removal and / or polyamide removal step, characterized in that the textile product in either step (ii) and / or step (iii) and / or step (iv) is subjected to ultrasound at a frequence of at least 20 kHz for a period t of at least 10 seconds.

2. A process according to claim 1, wherein the frequency of the ultrasound is 20 to 400 kHz, or 20 to 100 kHz, or 20 to 50 kHz, or 20 to 40 kHz.

3. A process according to any previous claim, wherein the temperature at the beginning of the step (ii) if the textile product is subjected to ultrasound is ambient temperature, or is between 10-85 °C, or is between 20-50 °C, or is between 10-40 °C, or is between 10-30 °C, or is below 50 °C.

4. A process according to any previous claim, wherein the temperature at the beginning of the step (iii) or step (iv), if the textile product is subjected to ultrasound, is ambient temperature, or is between 10-85 °C, or is between 20-50 °C, or is between 10-40 °C, or is between 10-30 °C, or is below 50 °C, or below 150 °C .

5. A process according to any previous claim, wherein the period t is at least 20 seconds, or at least 30 seconds, or from 30 seconds to 60 minutes, preferably from 30 seconds to 30 minutes, preferably from 30 seconds to 20 minutes, preferably from 30 seconds to 10 minutes, preferably from 30 seconds to 5 minutes, preferably from 1 minute to 30 minutes, or from 1 seconds to 20 minutes, preferably from 1 minutes to 10 minutes, preferably from 1 minutes to 5 minutes.

6. A process according to any previous claim, wherein the decolorizing agent used in the decolorization step (iii) is an organic solvent e.g. selected from dihydrolevoglucosenone (Cyrene), dimethyl sulfoxide (DMSO), methyl-sulfonyl-methane (DMSO2), sulfolane, or a combination thereof.

7. A process according to any previous claim, wherein the process comprises(iia) at least a first pretreatment step in form of an alkaline treatment wherein the aqueous solution comprises an alkaline component such as NaOH, a detergent component, and optionally an antifoaming component, and(iib) at least one second pretreatment- in form of a reductive treatment wherein the aqueous solution comprises an alkaline component such as NaOH, and a reductive component such as dithionite,- or in form of an acidic treatment wherein the aqueous solution comprises an acidic component such as sulfuric acid (H2SO4) or citric acid (HOC(CO2H)(CH2CO2H)2) or hydroxy acetic acid (CH2OHCOOH) (glycolic acid), or the process comprises both processes of (iib) i.e. a reductive treatment followed by an acidic treatment, wherein at least one, or at least two, or at least three of the treatments of (iia) and (iib) is / are subjected to ultrasound at a frequence of at least 20 kHz for a period t of at least 10 seconds.8.. A process according to any previous claim, wherein the decolorization step (iii) if not subjected to ultrasound is performed at a temperature within the range of 30-160 °C, preferably within the range of 50-150 °C, more preferably within the range of 70-100 °C, e.g., at a temperature of around 85 °C.

9. A process according to any previous claim, wherein the textile product of step (i) wherein the textile product has been shredded to units having a maximum dimension of 0.010 m, or 0.006 m, or 0.002 m, or 0,001 m, and optionally the textile product has been refined.

10. A solid fraction of recycled textile produced by the process according to any one of the claims 1-9 which solid fraction has a content of Al < 30 mg Al / kg textile, and a content of Fe < 20 mg / kg textile and a content of Ca < 100 mg Ca / kg textile and a content of Mg < 220 mg Mg / kg textile, and which solid fraction may form a raw material for a textile production.

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