DYE RECYCLING METHODS

This invention relates to methods for recycling dyes from a dyed textile, comprising methods for stripping dyes from dyed textiles for re-use in dyeing methods and methods for dyeing using recycled dyes obtained from methods disclosed herein.

BACKGROUND

The global textile industry is massive and supplies textiles to many industries, for example the clothing and furniture industries. In addition to forming textiles from fibers, filaments, yarn and thread, the process of dyeing the formed textiles represents a large part of the textile industry. Textile manufacturers acquire large amounts of virgin synthetic dyes for use in colouring their fabrics.

With a growing awareness of the large amount of waste produced by the textile industry, there is demand for sustainable materials and sustainable solutions for producing new materials and recycling waste products. Millions of tonnes of waste textiles and clothing produced each year remain unsold because supply outstrips demand or the products are no longer considered fashionable. Little attention has been given to dye recycling technologies to reduce virgin synthetic dye demand within the textile industry but providing an effective way of recycling dyes would be an attractive proposition from both sustainability and economical standpoints.

A dye recycling technology would provide those in the textile industry with an opportunity to reclaim and utilise dyes trapped within textile waste (fabric scraps) and deadstock lying unused and unwanted within textile facilities. It would also provide a unique economic advantage since textile manufacturers would i) buy less virgin synthetic dyes, and ii) be able to re-use the less dyed or dye-free (decoloured) fabric (stripped fabric) or sell it for upcycling purposes, as dye-free fabric is highly desired by textile recyclers for upcycling applications.

The present disclosure provides a method that enables the use of dyed waste textiles as a feedstock in a dyeing process. The disclosed method enable the use of dyes extracted from textiles to dye textiles, alleviating the need for using virgin dyes in dyeing methods. The disclosed method is a sustainable dyeing solution.

SUMMARY OF INVENTION

In a first aspect of the invention, there is provided a method for recycling dye from a dyed textile, the method comprising the following steps: providing a textile coloured with a dye; and adding the textile to a bath comprising a solution of ionic liquid, thereby causing the dye to strip from the textile and to disperse within said solution.

Optionally, the dye is a disperse dye, an acid dye, a basic dye, a reactive dye, a vat dye. Preferably, the dye is a disperse dye.

Optionally, the solution of ionic liquid is an aqueous solution of protic ionic liquid. Preferably, the solution of ionic liquid is an aqueous solution of protic ionic liquid and the dyed textile is coloured with a disperse dye.

Optionally, the solution of ionic liquid is an aqueous ionic liquid solution (i.e. an ionic liquid mixed with water as a co-solvent), or the solution of ionic liquid comprises ionic liquid and one or more organic co-solvents. Optionally, the organic co-solvents used are selected from ethanol, acetone, or dimethyl sulfoxide, preferably the co-solvents used are selected from ethanol and acetone. That is, the solution of ionic liquid is formed using the aforementioned co-solvents (water, ethanol, acetone, or dimethyl sulfoxide) in combination with an ionic liquid, thereby forming a solution when mixed together.

Optionally, the solution of ionic liquid is a protic ionic liquid, and said protic ionic liquid is an ammonium-based, imidazolium based, amino acid based, or an acetate based protic ionic liquid. Preferably the cation is an alkylammonium or a mixture thereof, preferably protic alkylammoniums, although aprotic alkylammoniums may also be used if the ionic liquid is not a protic ionic liquid.

Optionally, the solution of ionic liquid is a protic ionic liquid, and said protic ionic liquid is the reaction product of ammonium or imidazolium with hydrogen sulfate (HSO₄) or chloride anions, such as dimethylbuytlammonium hydrogen sulfate, 1-methylimidazolium hydrogen sulfate, triethylammonium hydrogen sulfate or 1-methylimidazolium chloride.

Optionally, the ionic liquid is aprotic ionic liquid comprising 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylammonium metanehylsulfonate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-ethyl-3-methyl-imazodlium chloride, 1-ethyl-3-methyl-imidazolium bromide, N.N-dimethylbutylammonium acetate, or dimethylethanolammonium formate. Preferably, cations include protic alkylammonium, protic methylimidazolium, protic pyridinium, aprotic tetraalkylammonium or aprotic dialkylimidazolium ions

Optionally, the ionic liquid is based on anions selected from: hydrogen sulfate, a carboxylate such as acetate, formate, or propionate, including branched and/or halogenated carboxylates such as trifluoroacetate, alkyl sulfates such as ethyl sulfate or methyl sulfate, alkylsulfonates such as metanesulfonate or ethanesulfonate, a halide such as chloride, bromide, or fluoride, dicyanamide, trifluoromethylsulfonate, thiocyanate, bi(trifluoromethylsulfonyl)imide, trifluoromethylsulfonate, tetrafluoroborate, hexafluorophosphate, or amino acid-based anions such as lysinate, serinate, or arginate; or cations selected from: protic or aprotic alkylammoniums for example alkylammoniums such as N,N-dimethylbutylammonium, triethylammonium, tetraethylammonium, butylammonium, dimethylethanolammonium, alkylimidazolium such as 1-methylimidazolium, 1-ethyl, 3-methylimidazolium, alkylpyridinium, or alkylpyrrolidinium, choline.

Optionally, the ionic liquid comprises N,N-dimethylbutylammonium hydrogen sulfate, 1-methylimidazolium chloride, 1-methylimidazolium bromide, Triethylammonium hydrogen sulfate, 1-ethyl,3-methylimidazolium ethyl sulfate, 1-ethyl,3-methylimidazolium methyl sulfate, N,N-dimethylbutylammonium methanesulfonate, 1-butyl,3-methylimidazolium bi(trifluoromethylsulfonyl)imide, Choline hydrogen sulfate, Choline chloride, 1-methylimidazolium ethyl sulfate, Butylammonium methanesulfonate, Butylammonium trifluoroacetate, N,N-dimethylbutylammonium trifluoroacetate, Choline hydrogen sulfate, 1-ethyl,3-methylimidazolium chloride, 1-ethyl,3-methylimidazolium bromide, 1-butyl,3-methylimidazolium chloride, 1-methylimidazolium hydrogen sulfate, 1-methylimidazolium methanesulfonate, 1-methylimidazolium methyl sulfate, or Dimethylethanolammonium formate.

Preferably, the ionic liquid is triethylammonium hydrogen sulfate ([TEA] [HSO₄]), N,N dimethyl-N-butylammonium hydrogen sulfate ([DMBA] [HSO₄]), 1-methylimidazolium hydrogen sulfate ([HMIM] [HSO₄]), I butylimidazolium hydrogen sulfate ([HBIM] [HSO₄]), or 1-ethyl,3-methylimidazolium ethyl sulfate ([Emim][EthSO₄]).

Optionally, after the stripping step the stripped textile is removed from the bath.

Optionally, the textile is added to the bath for 0.5-3 hours, preferably for 0.75-1.5 hours, before it is removed. Most preferably, the textile is added to the bath for 0.75-1 hours before it is removed.

Optionally, the concentration of ionic liquid in the solution (which may be referred to as the ionic liquid solution or the solution of ionic liquid) in the stripping step is 95 wt %-65 wt %, preferably 80 wt %-70 wt %.

Optionally, the method further comprises heating the protic ionic solution (the solution of ionic liquid) to a temperature of 70° C. to 200° C., preferably 100° C. to 200° C., more preferably to a temperature of 140° C.-160° C. Most preferably, the method further comprises heating the ionic solution to a temperature of around 150° C.

Optionally, the loading of dyed textile per kilogram of the solution of ionic liquid is 10 g-500 g, preferably 50 g-300 g, more preferably 100 g-250 g.

Optionally, the dyed textile is one or more dyed textile strips around 3 mm-500 mm wide, preferably around 5 mm-70 mm wide, more preferably 10 mm-40 mm (such as 20 mm) wide. Advantageously, it has been found that using textile of these sizes improves dye stripping efficiency.

Optionally, the dyed textile is a synthetic textile comprising a polyester such as polyethylene terephthalate (PET), a polycotton, acrylic, nylon, or polyester blends, or is a natural textile comprising cellulose such as cotton, linen, viscose or lyocell.

Optionally, the method further comprises cooling the solution of ionic liquid with dye dispersed therein after the stripping step to a temperature of around 10° C.-80° C. and preferably to a temperature of around room temperature.

Optionally, the method further comprises a dyeing step where the solution of ionic liquid with dye dispersed therein obtained from the stripping step is used to dye a textile, the dyeing step comprising: adding a textile to be dyed to the bath comprising the solution of ionic liquid and dye dispersed therein, thereby exposing the textile to the dye and dyeing the textile.

Optionally, the loading of textile to be dyed per kilogram of the solution is 10 g-500 g, preferably 50 g-300 g, more preferably 100 g-250 g.

Optionally, once the textile to be dyed has been added to the bath, the dyeing step further comprises heating step comprising heating the textile to be dyed and solution of protic ionic liquid with dye dispersed therein to 40° C.-200° C. for 0.25 hours-4 hours, preferably 40° C.-200° C. for 0.25 hours-2 hours. Preferably, the heating step comprises heating the textile to be dyed and solution of protic ionic liquid with dye dispersed therein to 60° C.-150° C. for 0.5 hours-1 hours. Most preferably, the dyeing heating step is a two-stage pre-heating step comprising heating the solution of protic ionic liquid with dye dispersed therein to 50° C.-80° C. (preferably 70° C.) for 0.5 hours followed by 100° C.-180° C. (preferably 150° C.) for 0.5 hours.

Optionally, when the solution of ionic liquid is an aqueous ionic liquid solution the dyeing step further comprises a hydrating step of adding water to the bath to reduce the concentration of protic ionic liquid in the aqueous solution to 70 wt %-10 wt %, preferably 65 wt %-20 wt %, more preferably to 60 wt %-40 wt %.

Optionally, when the solution of ionic liquid is an aqueous ionic liquid solution, the method further comprises a dehydration step after the dyeing step wherein heat is applied to the bath to increase the concentration of protic ionic liquid in the aqueous solution through evaporation to 95 wt %-65 wt %, preferably 80 wt %-70 wt %.

Optionally, the method further comprises a clean-up step after the dyeing step, the clean-up step comprising removing any remaining dye from the solution. The clean-up step reduced the amount of dye within the solution of ionic liquid, thereby forming a ‘cleaned solution of ionic liquid’ which may contain substantially no dye i.e. is fully cleaned of dye. Preferably, the clean-up step comprises removing remaining dye through an adsorption process such as by using an activated carbon column or by using adsorbents.

Optionally, the clean-up step comprises removing any remaining dye from the solution of ionic liquid and recovering said removed dye as a solid using an adsorbent.

Optionally, the dye is recovered by heating the solution of ionic liquid with dye dispersed therein to a temperature of 20° C.-80° C., preferably to 40° C.-60° C., until a desired amount of the dye dispersed in the solution of ionic liquid has adsorbed into the adsorbent, thereby forming a dye-rich adsorbent comprising dye. Optionally, the heating in the clean-up step is for a time period of around 12-48 hours, preferably 24 hours.

Optionally, the clean-up step further comprises washing the dye-rich adsorbent with a solvent, thereby removing dye from the dye-rich adsorbent. Preferably, the solvent used to wash the dye-rich absorbent is acetone.

Optionally, the adsorbent is selected from organic adsorbents such as an activated carbon adsorbent or a polymeric adsorbent such as commercial activated carbon and Amberlite XAD-4.

Optionally, the clean-up step is simultaneous to the stripping step. That is, adsorbents are added to the bath and are present during the stripping step.

Optionally, the method further comprises removing the textile from the bath after dye has been partially stripped therefrom in the stripping step and before the clean-up step (i.e. removing the dye stripped textile from the bath before the clean-up step is carried out), and then re-introducing said textile to the cleaned solution of ionic liquid after the clean-up step and recycling dye from said textile using a method as disclosed herein using said cleaned solution of ionic liquid as the solution of ionic liquid.

Optionally, the recovered solid dye is used to dye a textile to be dyed in a water-based dyeing or ionic liquid-base dyeing process.

Optionally, the textile to be dyed is a synthetic textile comprising a polyester such as polyethylene terephthalate (PET), an acrylic, nylon or polyester blends such as polycotton, or is a natural textile comprising cellulose such as cotton, viscose or lyocell.

According to a second aspect of the invention, there is provided a method of dyeing a textile, the method comprising the steps: providing a textile; adding the textile to a bath, the bath comprising a solution of ionic liquid and a dye dispersed therein obtained from a dye recycling method as disclosed herein, thereby exposing the textile to the dye and dyeing the textile.

According to a third aspect of the invention, there is provided a method for recycling dye from a dyed textile, the method comprising the following steps: providing a textile coloured with disperse dye; adding the textile to a bath comprising an aqueous solution of protic ionic liquid, thereby causing the dye to strip from the textile and to disperse within the aqueous solution; removing the stripped textile from the bath; and adding a textile to be dyed to the bath comprising the aqueous solution comprising protic ionic liquid and dispersed dye, thereby exposing the textile to the dye and dyeing the textile.

The optional and preferred features described in relation to the first aspect may be applied as optional and preferred features of the second and third aspects to equal effect. The optional features may be applied to the first, second and third aspects independently, and in any combination.

According to a fourth aspect of the invention, there is provided a method for recycling dye from a dyed textile, the method comprising the following steps: providing a natural textile material comprising cellulose coloured with a dye; adding the textile to a bath comprising a solution of ionic liquid; heating the bath, thereby causing the cellulosic material to break down.

Optionally, the heating is carried out to maintain the aqueous solution of ionic liquid in the bath at a temperature of at least 90° C., preferably at least 150° C., more preferably 90° C.-300° C., most preferably 150° C.-200° C.

Optionally, the broken down cellulosic material has a solid loading of 10 g-500 g per kg of the textile, preferably 50 g-250 g per kg of the textile.

Optionally, the method further comprises removing the broken down cellulosic material from the bath and milling said broken down cellulosic material to form a dye powder for use in dyeing a textile in a subsequent dyeing process. Preferably, the recovered powder is suitable (and may be used as part of this method) for dying textiles to be dyed, such as textiles which are synthetic rich like textiles comprising polyester or nylon.

Optionally, the dye powder is mixed, during or after milling, with one or more other dye powders of different pigment, thereby creating a dye powder of a desired pigment colour.

The optional and preferred features described in relation to the first aspect may be applied as optional and preferred features of the fourth aspect to equal effect. The optional features from the first aspect may be applied to the fourth aspect independently, and in any combination.

According to a fifth aspect, there is provided a method for recycling dye from a dyed textile, the method comprising the following steps: providing a textile coloured with a dye, said dye being a disperse dye; adding the textile to a bath comprising a solution of ionic liquid, thereby causing the dye to strip from the textile and to disperse within said solution, wherein said solution of ionic liquid is an aqueous solution of protic liquid.

The optional and preferred features described in relation to the first aspect may be applied as optional and preferred features of the fifth aspect to equal effect (where those optional and preferred features of the first aspect aren't already present as limitations of the fifth aspect in its broadest sense). The optional features from the first aspect may be applied to the fifth aspect independently, and in any combination.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects of the invention will now be described, by way of example only, with reference to the accompanying drawing, in which:

FIG. 1a shows a UV-vis spectrum of polyester textiles stripped of dye using methods disclosed herein using different bathing times;

FIG. 1b shows images of dye stripped polyester textiles from FIG. 1a;

FIG. 2 shows UV-vis spectrum of aqueous solutions of protic ionic liquid after being used for stripping polyester textiles using methods disclosed herein with varied bathing times;

FIG. 3 shows UV-vis spectrum of aqueous solutions of protic ionic liquid after being used for stripping polyester textiles using methods disclosed herein with varied concentrations of protic ionic liquid (IL) in said aqueous solutions;

FIG. 4a shows UV-vis spectrum of aqueous solutions of protic ionic liquid after being used for stripping polyester textiles using methods disclosed herein with varied bathing temperatures;

FIG. 4b shows UV-vis spectrum of polyester textiles stripped of dye using methods disclosed herein with varied bathing temperatures;

FIG. 5 shows UV-vis spectrum of polyester textiles stripped of dye using methods disclosed herein with varied textile solids loading used in the bath, and comparing these spectrum to a UV-vis spectrum of the original dyed polyester textile;

FIG. 6 shows UV-vis spectrum of polyester textiles stripped of dye using methods disclosed herein with varied textile piece sizing, and comparing these spectrum to a UV-vis spectrum of the original dyed polyester textile;

FIG. 7a shows UV-vis spectrum of acrylic textile stripped of dye using methods disclosed herein, and comparing the spectrum to a UV-vis spectrum of the original brown dyed acrylic

FIG. 7b shows images of a dye stripped textile from the UV-vis spectrum shown in FIG. 7a, compared to the original brown dyed acrylic.

FIG. 8a shows UV-vis spectrum of polyester textiles dyed using pink recycled disperse dyes obtained from methods disclosed herein and using dyeing methods disclosed herein with varied concentrations of protic ionic liquid in the extracted dye solutions, and comparing these spectrum to a UV-vis spectrum of the original pink dyed polyester textile;

FIG. 8b shows K/S values based on results shown in FIG. 8a;

FIG. 9a shows UV-vis spectrum of polyester textiles dyed using red recycled disperse dyes obtained from methods disclosed herein and using dyeing methods disclosed herein with varied concentrations of protic ionic liquid in the extracted dye solutions, and comparing these spectrum to a UV-vis spectrum of the original dyed polyester textile;

FIG. 9b shows K/S values based on results shown in FIG. 9a;

FIG. 10 shows the K/S values of different coloured textiles before and after dye stripping using a method as disclosed herein;

FIG. 11a show a dilution-adjusted UV-vis spectrum for original and cleaned dye extraction solutions of a first clean-up experiment (ionic liquid solution comprising dispersed dye subjected to a clean-up step as disclosed herein);

FIG. 11b shows a dilution-adjusted UV-vis spectrum for original and cleaned dye extraction solutions of a second clean-up experiment (ionic liquid solution comprising dispersed dye subjected to a clean-up step as disclosed herein);

FIG. 12a shows effect of K/S value reduction resulting from an example multiple stage clean-up in accordance with the methods described herein;

FIG. 12b shows reduction in K/S values at the strongest colour intensity (620 nm) over all cycles of the example multiple stage clean-up in accordance with the methods described herein;

FIG. 13a shows absorbent recovered solid dye recovered using methods disclosed herein;

FIG. 13b shows K/S values of a dyed textile material, and of a textile material dyed with a solid dye recovered using methods as disclosed herein;

FIG. 14a shows absorbance of solutions of ionic liquid comprising dye (at the peak wavelength in the visible spectrum) during simultaneous stripping and dye recovery/clean-up steps using methods of the type disclosed herein;

FIG. 14b shows absorbance of solutions of ionic liquid comprising dye (at the peak wavelength in the visible spectrum) during simultaneous stripping and dye recovery/clean-up steps using methods of the type disclosed herein;

FIG. 15a shows the reduction in K/S values of a blue pre-consumer PET textile using dye recycling methods as disclosed herein with ionic liquids with different co-solvents (co-solvent indicated, all 20 wt %);

FIG. 15b shows the reduction in K/S values of a blue pre-consumer PET textile using dye recycling methods as disclosed herein with aqueous ionic liquid solutions of varied concentrations;

FIG. 16a shows K/S values for of a blue pre-consumer PET textile before and after being subjected to dye recycling methods of the type disclosed herein where the solution of ionic liquid is formed using water and ethanol as co-solvents;

FIG. 16b shows K/S values for of a blue pre-consumer PET textile before and after being subjected to dye recycling methods of the type disclosed herein where the solution of ionic liquid is formed using water and acetone as co-solvents;

FIG. 17a shows the K/S values for undyed nylon fabric and nylon dyed fabric using cellulosic coloured powder obtained from methods disclosed herein using a) water as a dye bath and, b) ionic liquid solution as a dye bath; and

FIG. 17b shows K/S values for undyed polyester and a newly dyed polyester using cellulosic coloured powder obtained from methods disclosed herein using a) water as a dye bath and, b) ionic liquid solution as a dye bath.

DETAILED DESCRIPTION

Described herein are methods which may be used to recycle dye from a dyed textile. That is, to strip a dye to a part or substantially full extent from a textile so that the dye may be used as an alternative to a virgin dye in a dyeing process. The methods described herein may be used with textile dyed with disperse dyes, acid dyes, basic dyes, reactive dyes, vat dyes. Described herein are also methods which may be used to dye a textile using a dye stripped from a textile in accordance with a method disclosed herein, as part of the recycle method. The methods described herein are in relation to stripping dyed textile (comprising dyed yarns made from fibres) but could equally be applied to single dyed yarns or fibres. Described herein are also methods which may be used to disintegrate cellulosic-rich textile fibres into coloured powder which can be used as dyestuff to dye new textile fabric or starting material for pigments.

The methods are based on using low-cost and easily obtainable ionic liquids (e.g. protic ionic liquids) to strip dye from a waste dyed textile to produce a decolourised textile suitable for re-use, as well as separating the dye so that it may be used in downstream dyeing processes.

The following is an example of a method in accordance with this disclosure, comprising recycling dye from a textile dyed with disperse dye and using a protic ionic liquid.

Accordingly, described herein is a method for recycling dye from a dyed textile comprising the steps: providing a textile coloured with a disperse dye; adding the textile to a bath comprising an aqueous solution of protic ionic liquid, thereby causing a stripping step where the dye in the dyed textile is stripped from the textile and disperses (i.e. dissolves) within the aqueous solution (forming an aqueous solution of protic ionic liquid dye dispersion); and optionally removing the stripped textile from the bath after the stripping step.

Recycling the dye in the method relates to stripping (extracting) dye from a dyed textile, so that dye from the textile may be re-used in another disperse dye process. Advantageously, protic ionic liquids used in accordance with this method have been found effective in stripping dye from textiles without substantially degrading the dye. When the textile to be dyed is added to the bath the action of the aqueous solution of protic ionic liquid penetrates fibres of the textile causing them to swell, and for the disperse dye to be stripped therefrom. Once stripped from the textile, the dye forms a dispersion within the aqueous solution in the bath. The bath comprising the aqueous solution and dye dispersion is then suitable for use in dyeing a textile in another dye process. The stripped textile may advantageously be dyed another colour using a different dyeing process or used in other applications such as upcycling.

Particularly useful protic ionic liquids are ammonium-based, imidazolium based, amino acid based, or an acetate based protic ionic liquids. The protic ionic liquid may, for example, be the reaction product of ammonium or imidazolium with hydrogen sulfate (HSO₄) or chloride anions, such as dimethylbuytlammonium hydrogen sulfate, 1-methylimidazolium hydrogen sulfate, triethylammonium hydrogen sulfate or 1-methylimidazolium chloride.

The method may be carried out with textiles dyed with other dyes such as, but not limited specifically to, acid dyes, basic dyes, reactive dyes, or vat dyes. Accordingly, the following could be read in the context of other dyes and not just disperse dyes.

The method may be carried out using alternative ionic liquids to the aqueous solution of protic ionic liquid. Ionic liquids comprising the following could be used alternatively: ionic liquids comprising anions selected from: hydrogen sulfate, a carboxylate such as acetate, formate, or propionate, including branched and/or halogenated carboxylates such as trifluoroacetate, alkyl sulfates such as ethyl sulfate or methyl sulfate, alkylsulfonates such as metanesulfonate or ethanesulfonate, a halide such as chloride, bromide, or fluoride, dicyanamide, trifluoromethylsulfonate, thiocyanate, bi(trifluoromethylsulfonyl)imide, trifluoromethylsulfonate, tetrafluoroborate, hexafluorophosphate, or amino acid-based anions such as lysinate, serinate, or arginate; or cations selected from: protic alkylammoniums or aprotic alkylammoniums for example alkylammoniums such as N,N-dimethylbutylammonium, triethylammonium, tetraethylammonium, butylammonium, dimethylethanolammonium, alkylimidazolium such as 1-methylimidazolium, 1-ethyl, 3-methylimidazolium, alkylpyridinium, alkylpyrrolidinium, or choline.

Preferably, the ionic liquid may be selected from N,N-dimethylbutylammonium hydrogen sulfate, 1-methylimidazolium chloride, 1-methylimidazolium bromide, Triethylammonium hydrogen sulfate, 1-ethyl,3-methylimidazolium ethyl sulfate, 1-ethyl,3-methylimidazolium methyl sulfate, N,N-dimethylbutylammonium methanesulfonate, 1-butyl,3-methylimidazolium bi(trifluoromethylsulfonyl)imide, Choline hydrogen sulfate, Choline chloride, 1-methylimidazolium ethyl sulfate, Butylammonium methanesulfonate, Butylammonium trifluoroacetate, N,N-dimethylbutylammonium trifluoroacetate, Choline hydrogen sulfate, 1-ethyl,3-methylimidazolium chloride, 1-ethyl,3-methylimidazolium bromide, 1-butyl,3-methylimidazolium chloride, 1-methylimidazolium hydrogen sulfate, 1-methylimidazolium methanesulfonate, 1-methylimidazolium methyl sulfate, or Dimethylethanolammonium formate.

Preferably, the ionic liquid is triethylammonium hydrogen sulfate ([TEA] [HSO₄]), N,N dimethyl-N-butylammonium hydrogen sulfate ([DMBA] [HSO₄]), 1- methylimidazolium hydrogen sulfate ([HMIM] [HSO₄]), I butylimidazolium hydrogen sulfate ([HBIM] [HSO₄]), or 1-ethyl,3-methylimidazolium ethyl sulfate ([Emim][EthSO₄]).

Ionic liquids can be prepared by methods known to the person skilled in the art or obtained commercially. For example, the ionic liquids can be made from a simple alkylamine, such as triethylamine, and sulfuric acid in a one-step synthesis, for example as described in George et al., (2015) “Design of low-cost ionic liquids for lignocellulosic biomass treatment” Green Chemistry 17:1728-173.

The textile may be added to the bath for 0.5-3 hours, preferably for 0.75-1.5 hours, before it is removed. For example, the textile may be added for 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3 hours before it is removed. That is, the textile which is to be stripped of dye in the stripping step has these residence times in the bath (time in contact with the aqueous solution of protic ionic liquid) before it is removed from the bath. Preferably, the textile is added to the bath for 0.75-1 hours before it is removed. Advantageously, adding the textile to the bath for these amounts of time balances dye stripping efficiency (the amount of dye stripped from the textile) and degradation of the stripped dye.

The concentration of protic ionic liquid in the aqueous solution in the stripping step may be 95 wt %-50 wt %, preferably 85 wt %-65 wt %, more preferably 80 wt %-70 wt %. For example, the concentration of protic ionic liquid in the aqueous solution in the stripping step may be 65 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt % or 95 wt %. Advantageously, providing the protic ionic liquid with these concentrations has been found to provide improved dye stripping efficiency.

The method may further comprise heating the protic ionic solution to a temperature of 100° C. to 200° C., preferably to a temperature of 140° C.-160° C. Most preferably, the method further comprises heating the protic ionic solution to a temperature of around 150° C. Advantageously, heating in accordance with these temperatures has been found to provide improved dye stripping efficiency while substantially avoiding dye degradation.

The loading of dyed textile per kilogram of the aqueous solution added in the stripping step may be 10 g-500 g (10 g of textile per kilogram of the aqueous solution—500 g of textile per kilogram of the aqueous solution), preferably 50 g-300 g, and more preferably 100 g-250 g, for example 50 g, 60 g, 70 g, 80 g, 90 g, 100 g, 120 g, 130 g, 140 g, 150 g, 160 g, 170 g, 180 g, 190 g, 200 g, 210 g, 220 g, 230 g, 240 g or 250 g.

The dyed textile may be one or more dyed textile strips (originating from, for example, rolls of textile or garments) of around 3 mm-500 mm wide, preferably around 5 mm-70 mm wide, more preferably 10 mm-40 mm (such as 20 mm) wide. The strips may be of varying length and thicknesses. Advantageously, it has been found that using textile of these sizes improves dye stripping efficiency.

The dyed textile may be a synthetic textile comprising a polyester such as polyethylene terephthalate (PET), a polycotton or an acrylic, nylon, polyester blends, or is a natural textile comprising cellulose such as cotton, viscose or lyocell.

The method may comprise a cooling step to cool the aqueous solution with dispersed dye after the stripping step to a temperature of around 10° C.-80° C. and preferably to a temperature of around room temperature (around 21° C.). Cooling after the stripping step advantageously reduces any degradation of the dye in the aqueous solution.

The method may further comprise a dyeing step where the aqueous solution with dispersed dye obtained from the stripping step is used to dye a textile, the dyeing step comprising: adding a textile to be dyed to the bath comprising the aqueous solution of protic ionic liquid and dispersed dye, thereby exposing the textile to the dye and dyeing the textile. Optionally, extra dye may be added to the ionic liquid solution comprising dye in order to achieve a certain colour shade.

Advantageously, the stripping step followed by the dyeing step provide a closed-loop method of recycling a disperse dye where a disperse dye is stripped (extracted) from a textile such as a waste textile product and subsequently used to dye a new textile product. When added to the bath for the dyeing step, the aqueous solution penetrates the fibres of the textile to be dyed and allows the dye dispersion to diffuse into the fibres where they remain due to hydrogen bonding and Van der Waals forces. It has surprisingly been found that the protic ionic liquid acts both as an effective stripping agent during the stripping step and an effective dispersing agent during the dyeing step.

The loading of textile to be dyed per kilogram of the solution may be 50 g-500 g, preferably 50 g-300 g, more preferably 100 g-250 g, for example 50 g, 60 g, 70 g, 80 g, 90 g, 100 g, 120 g, 130 g, 140 g, 150 g, 160 g, 170 g, 180 g, 190 g, 200 g, 210 g, 220 g, 230 g, 240 g or 250 g. Preferably, the loading of the textile for the dyeing step enables substantially all the dye available for dyeing dispersed in the solution to be used up in the dyeing step.

With the textile to be dyed in the bath, the dyeing step may further comprise a dyeing heating step where the aqueous solution of protic ionic liquid and dispersed dye is heated to 40° C.-200° C., preferably to 60° C.-150° C., for 0.25-2 hours and preferably 0.5 to 1 hours. Preferably, the dyeing heating step is a two-stage pre-heating step comprising heating the aqueous solution of protic ionic liquid and dispersed dye to 50° C.-80° C. (preferably 70° C.) for 0.5 hours followed by 100° C.-180° C. (preferably 150° C.) for 0.5 hours. The heating step has been found to provide improved dyeing efficiency while substantially avoiding dye degradation.

The dyeing step may further comprise a hydrating step of adding water to the bath to reduce the concentration of protic ionic liquid in the aqueous solution to 65 wt %-10 wt %, preferably to 60 wt %-40 wt %.%. For example, the concentration of protic ionic liquid in the aqueous solution in the stripping step may be diluted to 65 wt %, 60 wt %, 55 wt %, 50 wt %, 45 wt %, 40 wt %, 35 wt %, 30 wt %, 25 wt %, 20 wt %. This concentration of protic ionic liquid in the aqueous solution excludes any amount of dispersed dye. The dye is diluted during the hydration step. Increasing the water concentration in the aqueous solution within this amount has been found to advantageously improve dyeing efficiency (given the hydrophobic nature of disperse dye) without diluting the disperse dye to an ineffectual amount for the purposes of the dyeing step.

The method may comprise a clean-up step after the dyeing step, comprising removing any remaining dispersed dye from the solution. Preferably, the clean-up step involves removing any remaining dispersed dye from the solution using an activated carbon column process. Some dye may remain in solution after the dyeing step due to high solubility of the dye in the aqueous solution of protic ionic liquid. The optional clean-up step advantageously removes substantially all dye from the solution so that the solution may be used in a later stripping step as disclosed herein. If it is known that the colour of the dye to be stripped from a textile in a later stripping step is the same as the colour of remaining dye in solution then such a clean-up step is not necessary.

The method may further comprise a dehydration step after the dyeing step wherein heat is applied to the bath to increase the concentration of protic ionic liquid in the aqueous solution through evaporation to 95 wt %-65 wt %, preferably 80 wt %-70 wt %. %. For example, the concentration of protic ionic liquid in the aqueous solution in the stripping step may be 65 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt % or 95 wt %. The dehydration step advantageously enables recycling of the protic ionic liquid in the aqueous solution for use in a further extraction/stripping method. These hydration and dehydration steps have been found to provide a balance between improved dyeing efficiency and energy consumption.

The textile to be dyed may be a synthetic textile comprising a polyester such as polyethylene terephthalate (PET), a polycotton an acrylic, nylon, or polyester blends. Preferably the synthetic textile comprises hydrophobic fibres. The textile to be dyed may be or comprise a natural textile comprising cellulose such as cotton, viscose or lyocell.

Also described herein is a method of dyeing a textile, the method comprising the steps: providing a textile; adding the textile to a bath, the bath comprising an aqueous solution of protic ionic liquid and a dispersed dye obtained from a stripping method as disclosed herein, thereby exposing the textile to the dye and dyeing the textile.

The optional and preferred features described in relation to the optional dyeing step for the method of recycling dye from a dyed textile described herein may be applied as optional and preferred features for the method of dyeing a textile described herein.

The recycling methods involving stripping a dye from a dyed textile and dyeing a textile described herein may be combined to provide a method for recycling dye from a dyed textile, the method comprising the following steps: providing a textile coloured with disperse dye; adding the textile to a bath comprising an aqueous solution of protic ionic liquid, thereby causing the dye to strip from the textile and to disperse within the aqueous solution; removing the stripped textile from the bath; and adding a textile to be dyed to the bath comprising the aqueous solution comprising protic ionic liquid and dispersed dye, thereby exposing the textile to the dye and dyeing the textile. Optionally, these steps are in sequence.

Also described herein is a method for recycling dye from a dyed textile, the method comprising providing a natural textile material comprising cellulose which has been coloured with a dye, adding the textile to a bath comprising a solution of ionic liquid, and heating the bath with the textile therein, thereby causing the cellulosic material to break down. The term ‘break down’ means that the threads the textile is made from at least partially break up into smaller pieces. Can we define a specific extent of how the textile is broken down (e.g. particle size etc.)?

The heating of the content of the bath is carried out to maintain the solution of ionic liquid at a temperature of at least 90° C., preferably at least 150° C., more preferably 90° C.-300° C., most preferably 150° C.-200° C.

The method optionally comprises, once the cellulose based textile has at least partially broken down, removing the broken down cellulosic material from the bath and milling it to form a dye powder for use in dyeing a textile in a subsequent dyeing process. Optionally, the broken down cellulosic material removed from the bath is dried before the milling is carried out.

Once dye powder has been obtained, said powder may be mixed with one or more other dye powders of different pigment either before or after the milling process, thereby creating a dye powder of a desired pigment colour.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, mean “including but not limited to”, and are not intended to (and do not) exclude other components.

It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention. Each feature disclosed in this specification, unless stated otherwise, may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of the invention are applicable to all aspects of the invention and may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).

It will be appreciated that many of the features described above, particularly of the preferred embodiments, are inventive in their own right and not just as part of an embodiment of the present invention. Independent protection may be sought for these features in addition to or alternative to any invention presently claimed.

Reference is now made to the following examples, which illustrate the invention in a non-limiting manner.

EXAMPLES
Preparation of Aqueous Solution of Protic Ionic Liquid

N,N,N-dimethylbutylamine (101.19 g, 1 mol) was added in 500 mL round-bottom flask and cooled in an ice bath. 200 mL of 5 M H₂SO₄(1 mol) was added dropwise using a funnel while stirring. The reaction proceeded for at least 5 hours with continuous stirring. Excess water was removed using the rotary evaporator. The ionic liquid was recovered as a clear, viscous liquid. The water content of the ionic liquid was adjusted to 20 wt % using Volumetric Karl Fisher Titrator (V20 Mettler-Toledo).

Characterisation Methods

Reflectance spectroscopy (ultraviolet-visible spectroscopy (or UV-vis)) was used to determine reflectance % of the textiles. From the UV-vis spectrums, K/S values were calculated to measure % of colour reduction relative to the original fabric and therefore determine extent of stripping and dyeing (allowing stripping efficiency to be studied). The K/S value represents the colour depth/intensity in a material (also referred to as colour strength), the higher the value, the higher the intensity and vice versa. The K/S value is calculated based on the following equation:

$\frac{K}{S} = \frac{{(1 - R_{\min})}^{2}}{2 R_{\min}}$

Where, K is the absorbance, S is the scattering and R_minis the lowest reflectance value (highest absorbance) at characteristic wavelength λ of every colour, e.g. in the case of red dyed polyester λ=517 nm.

Absorption spectroscopy (UV-vis spectroscopy) was used to measure concentration of dye dispersed within the aqueous solution of protic ionic liquid. To characterise the aqueous protic ionic liquid+dye solutions, the dilutions of the protic ionic liquid+dye solutions were done using ethanol as a solvent due to the insolubility of disperse dyes in water. Dye concentration within the aqueous solution is directly proportional to measured absorbance. From the UV-vis absorbance spectrums, a higher absorbance indicates more dye dispersed within the aqueous solution, and vice versa for a lower absorbance.

The colour strength of the fabric samples and absorbance of the aqueous solution of protic ionic liquid were analysed by using a Shimadzu UV-1800 UV spectrophotometer. A background spectrum was first acquired from the empty sample holder. The spectra were acquired from 200 to 900 nm with a data interval of 1 nm.

The water content of the protic ionic liquid solutions before and after the hydration step (the dilution step) were determined using Karl Fisher volumetric Titrator (Mettler-Toledo) in triplicates and the average concentration was calculated accordingly.

Results and Discussion
Dye Extraction of Disperse Dye from Textiles Using an Aqueous Protic Ionic Solution as the Ionic Liquid

Extraction time (i.e. the residence time of the dyed textile in the bath) was studied to investigate its effect on the dye stripping. A bath of an aqueous solution comprising 80 wt % protic ionic liquid (N,N,N-dimethylbutylammonium hydrogen sulfate) was used, prepared in accordance with the method disclosed herein. The temperature of the bath for the stripping step was fixed at 150° C. The original dyed textile added to the bath was a real post-consumer red 100% polyester obtained from a charity shop. FIG. 1a shows the UV-vis reflectance spectrum of decoloured (stripped) textile at different times, with a solid loading (g of textile per kg of aqueous solution) of 100 g per kg of solution. From the UV-vis spectrums shown in FIG. 1a, K/S values were calculated to measure % of colour reduction relative to the original fabric as presented in Table 1 below.

As shown in Table 1, colour reduction of 51% was achieved in 30 minutes with further reduction to 66% in 45 minutes and 79% in 60 minutes. At 90 minutes of stripping time, the colour reduction reached to 96% and further increasing treatment time to 120 minutes resulted in 98% reduction and the fabric looked substantially decolourised as seen in FIG. 1b.

TABLE 1

Time (minutes)
K/S
% Colour reduction

30
12.90
50.9%

45
8.80
66.4%

60
5.44
79.3%

90
1.08
95.9%

120
0.46
98.3%

150
0.32
98.8%

Original red polyester
26.29

As the process is a dye recycling process, one aim is to obtain satisfactory dye removal while maintaining the dye from decomposition in the aqueous solution of protic ionic liquid so that it may be re-used. The state and concentration of the dye in the aqueous solution was monitored at the same time as the data shown in FIG. 1a and Table 1 to see the impact stripping time has on the dye concentration (and dye degradation), to check a balance is maintained between the dye extraction efficiency and the stability and state of the dye dispersed in the dyeing bath once stripped. FIG. 2 shows the UV-vis absorbance spectrum of the bath containing the aqueous solution of protic ionic liquid and dye.

FIG. 2 shows the dye absorbance (which correlates directly to the dye concentration) was the highest at 30 minutes, and it started to decrease at longer times indicating that the dye started to decompose. At 90 minutes time, the dye in the aqueous solution reduced in concentration (and therefore started showing a fainter colour of red in the solution).

In separate tests from those described above, the effect of varying concentration of protic ionic liquid in the aqueous solution was studied in terms of its impact on the dye extraction efficiency (shown in FIG. 3). FIG. 3 shows the UV-vis absorbance spectrum of the bath containing the aqueous solution of protic ionic liquid and dye after the stripping step was carried out in accordance with the method disclosed herein under the conditions: the bath heated to a temperature of 150° C., a dyed PET textile held in the bath for 30 minutes, and a solid loading of 50 g textile per kg of an aqueous solution of N,N,N-dimethylbutylammonium hydrogen sulfate (prepared using the methods disclosed herein).

FIG. 3 shows how changing the concentration of protic ionic liquid in the aqueous solution influences extraction efficiency. Absorbance levels (proportional to dye concentration in the aqueous solution, and in turn dye stripped from the textile) drop by around 50% when decreasing the protic ionic liquid concentration in the aqueous solution from 80 wt % to 70 wt %. The absorbance levels, and therefore the dye concertation, drop when reducing the concentration to 50 wt %. The concentration of protic ionic liquid is understood to impact the extent to which the fibres in the textile are caused to swell and in turn the stripping efficiency of the dye from a textile.

The impact of bath temperature on the dye stripping efficiency in the present method was studied. The data shown in FIGS. 4a and 4b was obtained by carrying out a method as described herein using an aqueous solution of protic ionic liquid with an 80 wt % protic ionic liquid concentration. The bath was heated to various temperatures (170° C., 150° C., and 120° C.) and the textile was held in the bath for 30 minutes, and the solids loading of the textile was 50 g textile per kg of the aqueous solution of protic ionic liquid. The textile used was 100% post-consumer polyester.

As shown in FIG. 4a, there was a surprising absorbance optimum found at 150° C. Operating the process at lower temperature of 120° C. didn't extract as much dye as at 150° C. and operating the process at 170° C. provided a low absorbance spectrum indicating decomposition of the dye.

FIG. 4b shows the reflectance of the stripped textiles after 40 minutes in the bath vs. the reflectance of the original fabric. Both fabrics extracted at 150° C. and 170° C. showed similar levels of colour reduction of the textile.

The impact of textile solid loading on dye stripping efficiency in the present method was studied. The data shown in FIG. 5 was obtained by performing UV-vis reflectance spectroscopy on a textile subjected to a method as described herein, using an aqueous solution of protic ionic liquid with an 80 wt % protic ionic liquid concentration, where the bath was heated to 150° C., and the textile was held in the bath for 45 minutes. The textiles tested were red 100% polyester textile. FIG. 5 shows the impact of the solid loading on the dye extraction efficiency as a function of the solid loading. From the UV-vis spectrums shown in FIG. 5, K/S values were calculated to measure % of colour reduction relative to the original fabric as presented in Table 2 below. Increasing the solid loading from 7% (70 g of textile per kg of aqueous protic ionic liquid) to 21% (210 g of textile per kg of aqueous protic ionic liquid) was found to decrease the extraction efficiency of the dye very slightly where the colour reduction decreased from 79% to 71%, respectively (see Table 2).

Operating the methods disclosed herein at higher solid loading is important from an economic perspective, as it allows more dye to be recycled.

The impact of textile sizing on dye stripping efficiency in the present method was also studied. The data shown in FIG. 6 was obtained by performing UV-vis reflectance spectroscopy on textiles of varying sizes subjected to a method as described herein, using an aqueous N,N,N-dimethylbutylammonium hydrogen sulfate solution (80 wt % N,N,N-dimethylbutylammonium hydrogen sulfate), where the bath was heated to 150° C., the solids loading of the textile was 21%m and the textile was held in the bath for 30 minutes. The textiles tested were red 100% polyester textile, and the physical size of the dyed polyester textile was varied between a whole piece (size of 4×4 cm²) and the same dyed polyester textile cut into threads (strips) of approximately 0.5 cm wide. From the UV-vis spectrums shown in FIG. 6, K/S values were calculated to measure % of colour reduction relative to the original fabric as presented in Table 2 below.

FIG. 6 and Table 2 show that the colour reduction improves significantly when using the polyester thread/strips vs. the whole woven piece of fabric from 77% to 98%. This shows the advantageous extraction ability of the protic ionic liquid used, that high extraction can be achieved by increasing the surface area of exposure, while at the same time maintaining the stability of the dye dispersion in the bath for later use as a dye bath.

TABLE 2

K/S
% Colour reduction

7% loading - whole piece
7.82
79.3%

21% loading - whole piece
6.15
72.8%

21% loading - polyester
0.534
98.0%

threads

Original red polyester
26.30
—

The dye recycle method disclosed herein was carried out with dyed acrylic textile dyed with disperse dye. FIG. 7a shows the UV-vis reflectance spectrums for the before and after dye stripping of brown coloured post-consumer acrylic textile using a method as disclosed herein, and FIG. 7b shows images of the same acrylic textile before (right) and after (left) dye stripping. An aqueous solution of protic ionic liquid with a concentration of 80 wt % protic ionic liquid was used as the bath, the bath was set at a temperature of 150° C. and the acrylic textile held therein for 30 minutes. The solid loading of acrylic used was 100 g textile per kg of the aqueous solution of protic ionic liquid. From the UV-vis spectrums shown in FIG. 7a, K/S values were calculated to measure % of colour reduction relative to the original fabric as presented in Table 3 below. The amount of dye stripping achieved was very high with colour reduction of 92%.

TABLE 3

Acrylic textile
dye extracted

brown
acrylic textile

K/S
12.32
0.95

Colour reduction %
—
92.27%

Dyeing with Recycled Dye

Recycled dye solutions obtained from methods disclosed herein (i.e. aqueous solutions of protic ionic liquids with dye dispersed therein, which also may be described as ‘extracted dye solutions’ or ‘stripped dye solutions’) were used in dyeing baths to colour new PET-based textiles using methods disclosed herein.

The dyeing method comprised adding the textile to an extracted dye solution in a bath and heating to 70° C. for 30 minutes, followed by heating the dye bath to 150° C. for additional 30 minutes. The dyed textile was then removed from the bath. UV-vis reflectance spectroscopy was then carried out on the dyed textile. This method was used to dye new 100% PET white polyester textile pieces using the extracted red dye solution from the 100% polyester described in relation to FIGS. 1a and 1b and an extracted dye solution from a 100% pink polyester textile, the solution comprising an aqueous solution of N,N,N-dimethylbutylammonium hydrogen sulfate (80 wt % N,N,N-dimethylbutylammonium hydrogen sulfate). The dyeing method was carried out using both extracted dye solutions, and also where both solutions were diluted with water to vary the concentration of the protic ionic liquid in the aqueous solution to study the impact on dyeing efficiency.

The white polyester came from a T-shirt purchased from Highstreet retailer H&M, cut into smaller rectangular pieces of approximately 6×7 cm². The solid loading used in the dyeing experiments was 100 g per kg of the aqueous solution of protic ionic liquid.

Four concentrations for the aqueous solutions comprising protic ionic liquid were studied: 80 wt % (which in both cases did not require dilution of the extracted dye solution), 60 wt %, 40 wt % and 20 wt % (these latter three concentrations requiring the extracted dye solution to be diluted with water). The diluted solutions were prepared by diluting the extracted dye solutions (both originally comprising aqueous solutions of protic ionic liquids at 80 wt % concentration) with water. This process essentially reduces the dye concentration in the dye bath medium by factor of 1.03, 2 and 4 for 60, 40 and 20 wt % protic ionic liquid solutions, respectively (see dilution factors are shown in Table 4 below).

TABLE 4

IL concentration in
Dye dilution factor in

the dye bath
the dye bath

80%
—

60%
1.03

40%
2

20%
4

FIG. 8a shows the UV-vis reflectance spectrums for the dyed fabrics using the extracted pink dye solution as well as the spectrum of the original pink polyester fabric from which the dye was extracted, and FIG. 8b shows the corresponding calculated K/S ratio. Dyeing using the extracted dye solution as it is after the extraction process (i.e. 80 wt % with protic ionic liquid) resulted in the lowest K/S of 1.6. Reducing the protic ionic liquid content in the solution dye bath from 80 wt % to 60 wt % increased the K/S ratio to 3.7 (dye concentration dilution factor of 1.03), which is 55% higher compared to the dyeing at 20 wt % water. Increasing the water concentration further by using 40 wt % protic ionic liquid slightly decreased the K/S ratio compared to the fabric dyed at 60 wt %. However, the K/S was still higher compared the dyed fabric using 80 wt % IL with no dilution. Further increasing the water concentration resulted in decreasing the K/S value, becoming relatively close to the K/S value of the fabric dyed with 80 wt % protic ionic liquid in the solution. It is important to note that even though the K/S values of the dyed fabric decreases after 60 wt % protic ionic liquid, the dyeing efficiency is still very high considering the fact the dye concentration in the bath is diluted by a factor of 2 and 4 in the 40 wt % and 20 wt % protic ionic liquid dye baths, respectively. FIG. 9a shows UV-vis reflectance spectrums for the dyed fabrics using the extracted red dye solution as well as the spectrum of the original red polyester fabric from which the dye was extracted, and FIG. 9b shows the corresponding calculated K/S ratio. The results shown in FIGS. 9a and 9b follow the same trends as the results in FIGS. 8a and 8b.

Recycling of Dyes from Textiles Using Other Ionic Liquid Solutions

FIG. 10 shows the K/S ratio of different coloured textiles, namely nylon, acrylic, polyester, polycotton, polyester/spandex using a method of this disclosure, before and after dye extraction and using an ionic liquid solution of 80 wt % N,N dimethylbutylammonium hydrogen sulfate at 150° C. for 30 to 45 minutes. The colour reduction in these materials ranged between 92% to 44%.

Clean-Up of the Aqueous Solution of Ionic Liquid Comprising Stripped Dye

Aqueous solutions comprising stripped dye obtained from methods disclosed herein (i.e. aqueous solutions of ionic liquids with dye dispersed therein, which also may be described as ‘extracted dye solutions’ or ‘stripped dye solutions’) may be ‘cleaned’ using adsorbents, to remove dissolved dyes and thus remove colour from the solution. In this way, residual colour can advantageously be removed from the ionic liquid solution, and then the same ionic liquid solution can be cleaned and re-used between textile waste batches of different colour.

An example clean-up method comprises adding an adsorbent material to a stripped dye solution in a glass screw-top jar, and heating to 45° C. for up to 24 hours while stirring magnetically. The mixture is then filtered through filter paper under vacuum in order to separate the adsorbent (which is rich in dye, and will hereafter be referred to as a ‘dye rich absorbent’) and recover the “cleaned” dye solution. Commercial adsorbent material AmberLite™ was used to clean-up the ionic liquid used dye bath. The ratio of AmberLite™ to dye solution was 1:10 (weight basis).

The solid loading used in the extraction experiments for both was 100 g per kg of solution of ionic liquid.

- 1. A first clean-up experiment used an extracted dye solution obtained by extracting pre-consumer light blue virgin PET cut into rectangular pieces of approximately 6×7 cm². The ionic liquid solution used contained 80 wt % N,N,dimethylbutylammonium hydrogen sulfate and 20 wt % water.
- 2. A second clean-up experiment used an extracted dye solution obtained by extracting pre-consumer dark blue recycled PET cut into rectangular pieces of approximately 1×1 cm². The ionic liquid solution used contained 80 wt % 1-ethyl,3-methylimidazolium ethyl sulfate and 20 wt % dimethyl sulfoxide.

FIGS. 11a and 11b show the dilution-adjusted UV-vis absorbance spectra for the original and cleaned dye extraction solutions, for the first and second clean-up experiments respectively. Similar levels of dye removal from the extracted dye solutions were observed in both experiments, ranging from 71% to 74%, demonstrate that clean-up of the dye-rich ionic liquid is achieved, allowing the solution to be cleaned and re-used between textile waste batches of different colour.

Recycling of the Ionic Liquid Solution to Extract Dyes in Multiple Stages, with Clean-Up Stages Between Stages

The decoloured solid textile waste material obtained from a dye recycling method of the type disclosed herein may be separated from the ionic liquid solution by filtration, and the resulting dye-rich dye solution (the stripped dye solution or solution of ionic liquid comprising dispersed dye/dye dispersed therein) may be ‘cleaned’ using adsorbent material, using a clean-up method described herein. Following clean-up, the cleaned ionic liquid solution may be recovered and used to re-extract the once-extracted decoloured material. The cleaning and re-use of the dye solution may be repeated further times (e.g. two, three, four times etc.), such that the textile waste material is extracted several times using the same ionic liquid solution. Using this method is has been found that a high colour removal can be achieved by cleaning and re-using the ionic liquid solution to extract the same batch of textile waste multiple times. An example showing this approach of cleaning and re-using the ionic liquid solution is described below with results shown in FIGS. 12a and 12b.

FIG. 12a shows the K/S ratio (determined from the UV-vis reflectance spectra) for the starting fabric, and for the fabric extracted after 1-4 cycles. FIG. 12b shows the corresponding reduction in K/S ratio at the strongest colour intensity (620 nm) over all four cycles. Increasing number of cycles leads to increasing decolourisation of the starting material, with 93% colour removal achieved after 4 cycles. In absolute terms, colour removal decreases with each cycle, starting at 40% in cycle 1 and finishing at 5% in cycle 4. Accordingly, it has been found that the ionic liquid solution can be effectively re-used to re-extract textile waste material following clean-up, and that multiple extraction cycles can be used using recycled ionic liquid solution to increase the degree of decolourisation.

Recovery of Dye from a Stripped Dye Solution Using Adsorbents

Following clean-up of a stripped dye solution using the clean-up method disclosed herein (i.e. use of adsorbent material to clean stripped dye solutions), the dye-rich adsorbent may be recovered by vacuum filtration through standard laboratory set-up of filter paper, and the adsorbed dye may be desorbed using organic solvent (e.g. acetone), which may then be removed by evaporation, allowing the extracted dye to be recovered as a solid. This recovered solid dye may then be re-dissolved into fresh ionic liquid, and be used to dye virgin material. In other words, following removal of the dye from the stripped dye solution using a clean-up method of the type disclosed herein, the dye may advantageously be recovered from the adsorbent and then be re-used for dyeing. An example of this approach to using an extracted/recovered solid dye is described below.

The textile waste material used was pre-consumer PET, cut into rectangular sections of approximately 1×1 cm². All extractions were carried out at 150° C. for 30 minutes at a solids loading of 1:10 wt/wt. The ionic liquid solution used contained 80 wt % 1-ethyl,3-methylimidazolium ethyl sulfate and 20 wt % dimethyl sulfoxide. The clean-up method comprised adding a commercial adsorbent material AmberLite XAD-4 (a non-ionic polymeric adsorbent) at a solids loading of 1:10 wt/wt to the extracted dye solution (the stripped dye solution) in a glass screw-top jar, and heating to 45° C. for 24 hours while stirring magnetically. Before use, Amberlite XAD-4 was washed with water and acetone, and then air-dried before use. The mixture was filtered through filter paper and Büchner funnel under vacuum in order to separate the dye-rich adsorbent and recover a “cleaned” dye solution. The adsorbent material was washed 4 times using de-ionized water to remove any residual ionic liquid. The dye in the dye-rich absorbent was then desorbed from the adsorbent by adding 50 mL of acetone and shaking for one hour, with the dye-rich acetone recovered by filtering through filter paper. A total of 4 desorption cycles were carried out using fresh acetone each time, with the resulting dye-rich acetone from each cycle then added together. Rotary evaporation was used to remove the acetone from the dye-rich solution (collected from 4 desorption cycles), leading to recovery of the dye as a solid material.

The recovered solid dye was added to fresh ionic liquid solution, containing 60 wt % 1-ethyl,3-methylimidazolium ethyl sulfate and 40 wt % water. The resulting dye-rich solutions were used to dye virgin uncoloured PET fabric, at 150° C. for 30 minutes at a solids loading of 1:10 wt/wt, using the dyeing method disclosed herein (i.e. aqueous solutions of ionic liquids with dye dispersed therein).

FIG. 13a shows the recovered dye as a solid material at the bottom of a round-bottomed flask. FIG. 13b shows the K/S ratio (determined from the UV-vis reflectance spectra) of the starting material from which the dye was extracted, and of the materials dyed using both ionic liquid solutions. Accordingly, using methods disclosed herein it is possible for extracted dye to be recovered as a solid material, and then used to successfully dye new material. Using the recovered dye, virgin textile material may advantageously be dyed to a very similar colour intensity to the starting material, displaying similar K/S ratios across the entire visible spectrum.

Simultaneous Ionic Liquid Clean-Up and Dye Recovery

A dye recycling method of the type disclosed herein may be used to strip dye from a textile in the presence of an adsorbent (added to the ionic liquid solution). The extracted dye adsorbs onto the adsorbing material during the extraction of dye from the textile, and has been found to advantageously increase the degree of decolourisation by maintaining a high concentration gradient in the extracting medium (the ionic liquid solution). An example of a simultaneous ionic liquid clean-up and dye recovery approach is given, wherein dye two pre-consumer PET materials was extracted/recycled using methods disclosed herein, said materials being cut into rectangular sections of approximately 6×7 cm². Two different commercial adsorbent materials were used—activated carbon and AmberLite XAD-4—at solids loadings of 1:5 wt/wt and 2:5 wt/wt respectively with respect to the ionic liquid solution. Extractions were carried out using N,N-dimethylbutylammonium hydrogen sulfate, with a solids loading of textile material of 1:10 wt/wt, for varying durations and at varying temperatures.

FIGS. 14a and FIG. 14b show the absorbance of the resulting dye-rich ionic liquid solution, at the peak wavelength in the visible spectrum. Addition of adsorbent material into the extracting medium can be seen to improve colour removal, reaching near-quantitative levels after 60 minutes at 150° C. for 60 minutes. The successful adsorption of the dye onto the adsorbent material during the extraction can be seen through the large reductions in absorbance of the dye-rich IL solution at characteristic wavelengths.

Ionic Liquid Performance

The dye extraction/stripping performance of several different ionic liquid solutions in the dye recycling methods disclosed herewith have been compared with a dyed pre-consumer PET textile. The ionic liquids compared are: N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO₄]), 1-ethyl,3-methylimidazolium chloride ([emim]Cl), 1-ethyl,3-methylimidazolium bromide ([emim]Br), 1-methylimidazolium chloride ([Hmim]Cl), 1-ethyl,3-methylimidazolium ethyl sulfate ([emim][EtSO4]), 1-ethyl,3-methylimidazolium methyl sulfonate ([emim][MeSO3]), and dimethylethanolammonium formate ([DMEta][HCOO]). Although as disclosed herein, the method disclosed herein is not limited to only being used with these ionic liquid solutions and other ionic liquid solutions may be used.

FIG. 15a shows the reduction in K/S ratio of blue pre-consumer PET using several ionic liquids with differing co-solvents (co-solvent indicated, all 20 wt %). All extractions were carried out at 150° C. for 30 and 60 minutes, at a solids loading of 1:10 wt/wt. The largest difference in performance between ionic liquids was in terms of extraction kinetics, with large differences in extraction at 30 minutes (50-93%) but relatively small differences after 60 minutes (78-92%).

FIG. 15b shows the reduction in K/S ratio of blue pre-consumer PET using several ionic liquids with differing water contents. All extractions were carried out at 120° C. for 120 minutes, at a solids loading of 1:10 wt/wt.

Using Organic Solvents as Co-Solvents

The ionic liquid solution used with the methods disclosed herein, for example, N,N-dimethylbutylammonium hydrogen sulfate, may be used with organic co-solvents.

The following example uses N,N-dimethylbutylammonium hydrogen sulfate as an ionic liquid solution to extract dye from a pre-consumer PET textile. The co-solvents used were ethanol and acetone, with results compared to water as a co-solvent.

FIG. 16a shows the reduction in K/S ratio of a blue pre-consumer PET using water and ethanol as co-solvents, with extractions carried out at 150° C. for 30 and 60 minutes, at solids loadings of 1:10 wt/wt. Replacing water with ethanol as a co-solvent has been found to improve extraction/stripping performance, seen through faster kinetics of extraction due to increased solubility of the dye in the non-aqueous environment. Extraction was found to be complete after 30 minutes using ethanol as a co-solvent, whereas there is a large increase in extraction from 30-60 minutes using water as a co-solvent.

FIG. 16b shows the reduction in K/S ratio of a blue pre-consumer PET using water and acetone as co-solvents, with extractions carried out at 140° C. for 30 and 60 minutes, at solids loadings of 1:10 wt/wt. The use of acetone as a co-solvent can potentially improve the dye extraction performance, with higher decolourisation than water and ethanol co-solvents.

Accordingly, extraction performance can be improved, in terms of decolourisation kinetics and dye stability, through the use of organic solvents as co-solvents over water. However, the use of organic solvents increase safety concerns in the process and reduces the process' environmental credentials.

Disintegration of Cellulosic-Based Textiles

Another route of recycling dyes from textile waste fibres considers the disintegration of the textile fibre into the ionic liquid solution, particularly cellulosic-based textiles such as linen, hemp, viscose, lyocell, cotton. It has been found that upon heating cellulosic-rich textile as the dyed textile in the methods disclosed herein to temperatures above >90° C., or more favourably >120° C., the fibres start disintegrating into smaller pieces and eventually into a coloured powder form while dye from the textile is dispersed in the ionic liquid solution. The coloured powder may then separated from the ionic liquid, washed thoroughly with water and dried. The coloured powder may then grinded mechanically into finer particles and used as dyestuff to dye new piece of textile fibre, specifically synthetic fibre where dyeing takes place via trapping the dyestuff into the swollen fibre under heating. The dye bath can be either a conventional aqueous-based dye bath or ionic-liquid based dye bath.

In the following example the dye recycle method disclosed herein was carried out with a dyed post-consumer 100% linen cellulosic-based fabric. The coloured post-consumer linen fabric was cut and immersed in ionic liquid solution of 80 wt % N,N dimethylbutylammonium hydrogen sulfate at 150° C. for 45 minutes. The conditions caused the fabric to disintegrate into coloured powder while some of the dye was stripped into the ionic liquid solution. The coloured powder was then separated from the ionic liquid, washed with water and dried. The coloured powder was then grinded into finer particles using a pestle. The coloured powder was then used as a dye to dye 100% nylon fabric at 120° C. for 60 minutes and the dye concentration was 10% owf (on weight fabric; 10 g dyestuff powder/100 g fabric). The dyeing in this step can be conducted conventionally using water bath or using ionic liquid as dyeing medium. The dyed nylon fabric was then washed thoroughly with water and commercial detergents (Ariel™3-1 washing pods). FIG. 17a presents the K/S values for the undyed nylon fabric and the nylon dyed fabric using cellulosic coloured powder using a) water as a dye bath and, b) ionic liquid solution as a dye bath. Both dye baths were used without the addition of auxiliary chemicals and the undyed nylon fabric was used without applying a pre-treatment step.

Another example is shown in FIG. 17b and used 100% cotton denim immersed in an ionic liquid solution of 80 wt % N,N dimethylbutylammonium hydrogen sulfate for 150° C. for 60 minutes. The cotton powder was then used as a dye (5% owf) to dye polyester fabric at 150° C. for 45 minutes. FIG. 17b presents the K/S ratio of the undyed polyester and the newly dyed polyester using a) water as a dye bath and, b) ionic liquid solution as a dye bath. Dye baths were used without the addition of auxiliary chemicals and the undyed nylon fabric was used without applying a pre-treatment step.

DYE RECYCLING METHODS

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