Treatment method for selectively degrading fiber having β - glycosidic linkage in mixed fiber

Abstract

To provide a technique capable of effectively recycling each recovered material as a single material by selectively decomposing, separating and recovering a fiber having a β - glycoside bond from a mixed fiber comprising the fiber having the β - glycoside bond such as cotton and other fibers such as polyester by a simple treatment in a short time under a non-pressurized condition.SOLUTION: A treatment method comprising selectively decomposing a fiber having a β - glycosidic bond from a mixed fiber containing the fiber having a β - glycosidic bond and a fiber composed of another material by a treatment using a deep eutectic solvent (DES) formed by mixing a hydrogen bond donor with a hydrogen bond acceptor at a molar ratio of 0.50 or more and 6.00 or less, and recovering the fiber composed of another material in a fibrous form.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a treatment method for selectively decomposing fibers having β-glycosidic bonds in a mixed fiber. [Background technology]

[0002] Modern economic society has been sustained by a social system of mass production, mass consumption, and mass waste, but various adverse effects on the environment have been confirmed, such as the depletion of natural resources, destruction of nature due to resource extraction, global warming caused by greenhouse gas emissions, and rising sea levels. Therefore, in order to continue sustainable growth through efficient use of limited resources, it has become essential to build a recycling-oriented social system that minimizes waste generation and reuses and recycles generated waste in a way that does not burden the environment.

[0003] To realize a recycling-oriented society, it is necessary to establish recycling systems such as thermal recycling, material recycling, and chemical recycling. In particular, attention is being paid to chemical recycling technology, which breaks down and refines waste plastics down to their raw material monomer units, and then uses the resulting monomers to regenerate plastic materials of the same quality as before disposal.

[0004] Polyester fibers, which are inexpensive and have suitable physical properties for clothing, are also expected to be regenerated through chemical recycling. To date, the application of technologies to regenerate polyester fibers down to the raw material monomer unit through hydrolysis and glycolysis has been investigated. However, polyester fibers are often composited with cotton through blending or interweaving to achieve both absorbency and quick-drying properties, and cotton may also be present in discarded polyester fiber clothing. When attempting to obtain raw material monomers from cotton-contaminated polyester fibers through hydrolysis or glycolysis, the resulting contamination with thermally decomposed cotton impurities significantly reduces the quality of the raw material monomers. Therefore, a method for separating cotton from polyester fibers as a pretreatment step was needed to chemically recycle cotton-contaminated polyester fibers into polyester resin of the same quality as before disposal.

[0005] Patent documents 1 and 2 propose a method for selectively decomposing only the cotton by heat treating a cotton and polyester blend in the presence of an organic acid or cellulase enzyme, recovering the cotton decomposition product in the form of granules or a solution, while separating the polyester in the form of fibers, and then reusing each of them as a single material.

[0006] Furthermore, Patent Document 3 proposes a method in which cellulose is dissolved in an ionic liquid and then precipitated from the ionic liquid to regenerate it, and Patent Document 4 proposes a method in which cellulose is decomposed in an ionic liquid to obtain monosaccharides. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2019-035022 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-089239 [Patent Document 3] International Publication No. WO2007 / 049485 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-201394 Summary of the Invention [Problem to be solved by the invention]

[0008] The method described in Patent Document 1 above involves selectively decomposing cotton-contaminated polyester fibers by heat treatment using an organic acid aqueous solution, and removing the cotton as powder from the polyester fibers. However, depending on the conditions, separation of cotton and polyester is insufficient, which poses a problem of reducing the quality of the raw material monomer for polyester obtained when the polyester fibers recovered after treatment are chemically recycled. Furthermore, sufficient separation of cotton and polyester requires treatment under pressurized conditions at 120°C to 150°C, above the boiling point of water, which is disadvantageous in that it increases costs and energy consumption due to the larger size of the process equipment.

[0009] Patent Document 2 discloses a method for treating polyester fibers containing cotton by heat treatment using an aqueous cellulase enzyme solution to decompose the cotton into glucose and sugars and remove them from the polyester fibers. This method uses an enzyme reaction, which allows treatment at a low temperature of 50°C, but because it is an enzyme reaction, the treatment time is very long (the reaction time specifically disclosed in the examples is 24 hours), which is disadvantageous in terms of production efficiency.

[0010] Furthermore, Patent Documents 3 and 4 describe methods for dissolving cellulose, such as cotton, in an ionic liquid and then obtaining regenerated cellulose or monosaccharides. This method may be applicable to selectively separating and recovering cotton from fibers containing cotton. However, if the water content of the ionic liquid is greater than 8% by mass, cellulose does not dissolve in the ionic liquid and separation becomes impossible, requiring a pre-treatment step to dehydrate the ionic liquid. Furthermore, when dissolving cellulose in an ionic liquid and recovering it as monosaccharides, an additional post-purification step using ion exchange treatment is required. Furthermore, because ionic liquids are expensive, they are preferably reused after treatment, necessitating a step to recover and purify the ionic liquid from the ion exchange resin used in the ion exchange treatment. Thus, using ionic liquids for separation and recovery requires additional steps specific to handling the ionic liquid before and after treatment, which is disadvantageous in terms of increasing overall process costs and energy consumption.

[0011] The object of the present invention is to solve the problems of the above-mentioned conventional technology and to provide a technology that selectively decomposes and separates and recovers the fibers having β-glycosidic bonds in a mixed fiber consisting of fibers having β-glycosidic bonds, such as cotton, and other fibers, such as polyester, through a short and simple process under non-pressurized conditions, thereby enabling each recovered material to be effectively recycled and reused as a single material. [Means for solving the problem]

[0012] The above problems are solved by the following [1] to [7]. [1] A processing method for selectively decomposing fibers having β-glycosidic bonds from a mixed fiber containing fibers having β-glycosidic bonds and fibers made of other materials by treating with a deep eutectic solvent (DES) formed by mixing a hydrogen bond donor with a hydrogen bond acceptor in a molar ratio of 0.50 to 6.00, and recovering the fibers made of the other materials in fibrous form. [2] The treatment method according to [1], wherein the hydrogen bond acceptor is at least one selected from quaternary ammonium salts represented by the following formula 1, or a mixture thereof: [N(C n H 2n+1 )3·R] + [Cl] - ...Formula 1 where R=-C m H 2m+1 , -CH2CH2OH, -CH2-C6H6 n=1~5 m=1~5 [3] The treatment method according to [1] or [2], wherein the hydrogen bond acceptor is at least one selected from the group consisting of choline chloride, benzyltrimethylammonium chloride, benzyltriethylammonium chloride, and benzyltributylammonium chloride, or a mixture thereof. [4] The treatment method according to any one of [1] to [3], wherein the hydrogen bond donor is a carboxylic acid, a sulfonic acid, or a mixture thereof. [5] The treatment method according to any one of [1] to [4], wherein the hydrogen bond donor is at least one selected from oxalic acid, malonic acid, succinic acid, levulinic acid, 3-phenylpropionic acid, and benzoic acid, or a mixture thereof. [6] The processing method according to any one of [1] to [5], wherein the processing is carried out under non-pressurized conditions. [7] The treatment method according to any one of [1] to [6], wherein the treatment temperature is 40°C or higher and 150°C or lower. [Effects of the Invention]

[0013] According to the present invention, a mixed fiber consisting of fibers having β-glycosidic bonds, such as cotton, and other fibers, such as polyester, can be selectively decomposed and separated and recovered by a short, simple process under non-pressurized conditions, making it possible to effectively recycle and reuse each recovered material as a single material. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below. The present invention relates to a method for selectively decomposing fibers having β-glycosidic bonds from a fiber mixture containing fibers having β-glycosidic bonds and fibers made of other materials by treating the fiber mixture with a deep eutectic solvent (DES) formed by mixing a hydrogen bond donor with a hydrogen bond acceptor in a molar ratio of 0.50 to 6.00, and recovering the fibers made of other materials in fibrous form.

[0015] The mixed fiber in the present invention refers to a fiber material obtained by combining one or more different fiber materials in addition to a fiber having a β-glycoside bond as a constituent material, and the combining method may be a known method such as blending, interweaving, or conjugate spinning in which two or more components are discharged from one spinneret hole in melt spinning. The form of the mixed fiber is not limited to thread, and may be a woven or knitted fabric, etc.

[0016] The fibers having β-glycosidic bonds are not particularly limited as long as they are fibers formed by condensation polymerization of β-glucose via glycosidic bonds or chemically modified fibers thereof, and examples thereof include cotton, linen, rayon, lyocell, cupra, polynosic, acetate, triacetate, etc. In view of ease of recycling after treatment with the DES of the present invention, unmodified cotton, linen, rayon, lyocell, cupra, and polynosic are preferred, and cotton and rayon are more preferred in view of ease of recovery in the recycling market as discarded clothing.

[0017] The other fibers are not particularly limited as long as they are fibers different from the fibers having the β-glycosidic bond, and examples thereof include polyester fibers, polypropylene fibers, polyethylene fibers, acrylic fibers, polyvinylidene chloride fibers, polyvinyl chloride fibers, polyvinyl alcohol fibers, fluorine-based fibers, polyether ester fibers, polylactic acid fibers, polyurethane fibers, and polyamide fibers. One or more of these may be used as components of the mixed fiber. Of these, polyester fibers, acrylic fibers, and polyamide fibers are preferred because they are easily recovered in the recycling market as discarded clothing. Furthermore, polyester fibers and acrylic fibers are more preferred because they are resistant to acidic conditions and therefore do not easily undergo decomposition reactions in the treatment using the DES of the present invention.

[0018] In the present invention, a blend of fibers containing β-glycosidic bonds and fibers made of other materials is treated with a deep eutectic solvent (DES) formed by mixing a hydrogen bond acceptor and a hydrogen bond donor. Deep eutectic solvents are prepared by mixing a hydrogen bond acceptor, such as a quaternary ammonium salt, with a hydrogen bond donor, such as an organic acid, and heating as needed. Although the solvent is solid before mixing, its melting point drops after mixing, allowing it to be treated as a liquid. Furthermore, many DESs are nonvolatile, which offers the advantage of allowing treatment at high temperatures under normal pressure.

[0019] In the present invention, the DES is preferably prepared by mixing the hydrogen bond donor to the hydrogen bond acceptor at a molar ratio of 0.50 to 6.00. If the molar fraction of either the hydrogen bond acceptor or the hydrogen bond donor in the DES is biased, the viscosity of the DES increases, reducing the handleability of the DES. Furthermore, if the hydrogen bond donor is mixed with the hydrogen bond acceptor at a molar ratio of less than 0.50 or more than 6.00, a eutectic is not formed, resulting in no melting point depression and making the DES difficult to use as a solvent. From the viewpoint of the handleability of the DES and the ability to decompose fibers having β-glycosidic bonds, the DES in the present invention is more preferably prepared by mixing the hydrogen bond donor to the hydrogen bond acceptor at a molar ratio of 0.75 to 3.00, even more preferably at a molar ratio of 0.90 to 1.33, and particularly preferably at a molar ratio of 1.00 to 1.33.

[0020] The compound used as the hydrogen bond acceptor is not particularly limited and can be selected arbitrarily as long as it does not interfere with the degradation process of fibers having β-glycosidic bonds. One compound may be used alone, or two or more compounds may be used in combination. However, in terms of their excellent ability to degrade fibers having β-glycosidic bonds, quaternary ammonium salts represented by the following formula 1 are preferred, with choline chloride, benzyltrimethylammonium chloride, benzyltriethylammonium chloride, and benzyltributylammonium chloride being more preferred, and choline chloride and benzyltrimethylammonium chloride being particularly preferred. This is thought to be because the smaller the value of n in formula 1, the less steric hindrance there is around the nitrogen atom of the compound used as the hydrogen bond acceptor, resulting in increased hydrogen bond formation and reactivity with fibers having β-glycosidic bonds. The value of n in formula 1 is preferably 1 to 5, more preferably 1 to 4, even more preferably 1 to 2, and particularly preferably 1. [N(C n H 2n+1 )3·R] + [Cl] - ...Formula 1 where R=-C m H 2m+1 , -CH2CH2OH, -CH2-C6H6 n=1-5, m=1~5

[0021] The compound used as the hydrogen bond donor is not particularly limited and can be selected arbitrarily as long as it does not interfere with the degradation of fibers having β-glycosidic bonds. One compound may be used alone, or two or more compounds may be used in combination. However, in terms of their excellent ability to degrade fibers having β-glycosidic bonds, carboxylic acids and sulfonic acids are preferred, with oxalic acid, malonic acid, succinic acid, levulinic acid, 3-phenylpropionic acid (PhPA), benzoic acid, and p-toluenesulfonic acid (p-TSA) being more preferred, oxalic acid, malonic acid, succinic acid, levulinic acid, 3-phenylpropionic acid, and benzoic acid being even more preferred, oxalic acid, malonic acid, and succinic acid being particularly preferred, oxalic acid and malonic acid being extremely preferred, and oxalic acid being most preferred. In the present invention, the carboxylic acid and sulfonic acid compounds may be anhydrides or hydrates. Furthermore, because the acidic hydrogen atoms of the compound used as the hydrogen bond donor are thought to affect the formation of hydrogen bonds and the reactivity with fibers containing β-glycosidic bonds, the acid dissociation constant (pKa) of the compound used as the hydrogen bond donor is preferably greater than -2.8 and less than 4.7. If the pKa is less than -2.8, the acidity of the DES becomes too high, resulting in denaturation and discoloration of fibers containing β-glycosidic bonds and the degradation of other fibers. If the pKa is greater than 4.7, the acidity is too low, preventing the degradation of fibers containing β-glycosidic bonds from proceeding sufficiently. To selectively decompose only fibers containing β-glycosidic bonds without affecting other fibers, the acid dissociation constant (pKa) of the compound used as the hydrogen bond donor is preferably greater than -2.8 and less than 4.2, more preferably greater than -2.8 and less than 2.8, and most preferably greater than -2.8 and less than 1.2.

[0022] In the present invention, the treatment of mixed fibers using DES may be carried out under any pressure conditions, but carrying out the treatment under pressurized conditions is disadvantageous in terms of increased costs due to the larger size of the process equipment and energy consumption. Since the application of treatment methods with low energy consumption is necessary to realize a recycling-oriented society, it is preferable to carry out the treatment under non-pressurized conditions. As described above, when DES is prepared by mixing hydrogen bond donors to hydrogen bond acceptors in a molar ratio of 0.50 to 6.00, the DES can be used as a liquid for treatment without adding water. Therefore, even if the treatment temperature is above the boiling point of water, the degradation treatment of fibers having β-glycosidic bonds can be carried out under normal pressure.

[0023] As mentioned above, when treating mixed fibers with DES, the treatment temperature can be appropriately selected within a range that does not interfere with the decomposition of fibers having β-glycosidic bonds. However, if the temperature is too high, the fibers having β-glycosidic bonds will be thermally denatured, and the thermally denatured fibers will remain among the other fibers recovered after treatment, which may affect the recycling of the other fibers. On the other hand, if the temperature is too low, the decomposition reaction of the fibers having β-glycosidic bonds will not proceed, and the fibers having β-glycosidic bonds will remain among the other fibers. Therefore, in order to ensure sufficient decomposition without thermal denaturation of the fibers having β-glycosidic bonds, the treatment temperature is preferably 40°C or higher and 150°C or lower, more preferably 60°C or higher and 130°C or lower, and particularly preferably 90°C or higher and 110°C or lower.

[0024] Furthermore, when treating mixed fibers with DES, if the treatment time is too short, the degradation of fibers with β-glycosidic bonds will not proceed sufficiently, while if the treatment time is too long, the degradation of other fibers will also proceed, so the treatment time is preferably from 0.5 to 6.0 hours. A treatment time of from 1.0 to 3.0 hours is more preferable, as it will enable the degradation of only fibers with β-glycosidic bonds without causing the degradation of other fibers to proceed.

[0025] Furthermore, when treating mixed fibers with DES, if the weight ratio of DES to the weight of the mixed fibers is too low, the mixed fibers and DES will not come into uniform contact, preventing the degradation reaction of fibers with β-glycosidic bonds from proceeding, and fibers with β-glycosidic bonds will remain among the other fibers. Therefore, the lower limit of the weight ratio of DES to the weight of the mixed fibers is preferably 1 or more, more preferably 5 or more, even more preferably 10 or more, and most preferably 20 or more. On the other hand, if the weight ratio of DES to the mixed fibers is too high, this will undesirably lead to increased costs and energy consumption due to the larger size of the process equipment. Therefore, the upper limit of the weight ratio of DES to the weight of the mixed fibers is preferably 100 or less.

[0026] In the present invention, a pretreatment step, a posttreatment step, or both may be included before or after the treatment of the mixed fiber with DES. Examples of the pretreatment step include a pre-washing step using water or other organic solvents to pre-remove dirt and foreign matter adhering to the mixed fiber. Examples of the post-treatment step include a DES removal step using water or other organic solvents to remove DES from the treated mixed fiber, a depilling step to physically separate and recover the decomposed fibers having β-glycosidic bonds, and a post-washing step using water or other organic solvents. Furthermore, the recovered decomposed fibers having β-glycosidic bonds, other fibers, or both may be reused or recycled as is, or may be further purified through a purification step or drying step.

[0027] In the present invention, the degradation products of fibers having β-glycosidic bonds obtained after treating the mixed fibers with DES are recovered as low-molecular-weight cellulose or β-glucose. The degradation products of fibers having β-glycosidic bonds may be recovered in either the low-molecular-weight cellulose or β-glucose form, but are preferably recovered as low-molecular-weight cellulose because this makes it easier to remove fibers having β-glycosidic bonds from other fibers. The retention rate of the weight-average molecular weight of fibers having β-glycosidic bonds, as represented by the following formula 2, is preferably 0% or more and less than 17%, more preferably 0% or more and less than 14%, even more preferably 0% or more and less than 11%, particularly preferably 0% or more and less than 8%, and most preferably 0% or more and less than 5%. (Weight-average molecular weight retention rate of recovered fibers) = (Weight-average molecular weight of recovered fibers after DES treatment) / (Weight-average molecular weight of fibers before DES treatment) × 100 Equation 2

[0028] The weight-average molecular weight of fibers having β-glycosidic bonds can be measured by any method. For example, the weight-average molecular weight can be measured by immersing a measurement sample of fibers having β-glycosidic bonds in an 8% LiCl (lithium chloride) / DMAc (dimethylacetamide) solution to a concentration of 0.6%, dissolving the cellulose over 1 to 2 weeks, and then filtering the filtrate. The weight-average molecular weight can be measured using a measuring device such as a Shimadzu Nexcera GPC system (detector: refractive index detector RI (RID-20A)), one PLgel 20μm MIXED-A column, 8% LiCl / DMAc solvent, flow rate: 0.5 mL / min, temperature: 23°C, and standard: monodisperse pullulan.

[0029] The fibers having β-glycosidic bonds recovered as low-molecular-weight cellulose may be recycled as regenerated fibers such as rayon, lyocell, cupra, or polynosic by known methods, or may be further decomposed into β-glucose by known methods such as enzymatic decomposition to further reduce the molecular weight. The recovered β-glucose can be effectively utilized by known methods, such as by converting it into ethanol by enzymatic reaction.

[0030] In the present invention, the other fibers obtained after the treatment of the mixed fibers with DES are not decomposed but are recovered in a fibrous form. If the recovery rate of the other fibers recovered in a fibrous form is too low, the amount of waste increases and the environmental load becomes high, so it is preferably at least 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The upper limit of the recovery rate is 100% when the other fibers are completely separated and recovered from the mixed fibers.

[0031] The other fibers recovered in fibrous form may be used for material recycling. For example, they may be spun again and reused as fibers, or melt-molded and reused. Furthermore, the other fibers recovered in fibrous form may be chemically recycled by decomposing them into raw material monomers through a depolymerization reaction and regenerating them through repolymerization. For example, if the other fibers recovered in fibrous form are polyester fibers, they can be depolymerized by known methods using alcohol solvents such as ethylene glycol or methanol, or water or subcritical water. If a mixed fiber containing fibers having β-glycosidic bonds and polyester fibers is directly introduced into a polyester fiber depolymerization process, thermally denatured foreign substances derived from cellulose will be mixed into the raw material monomers of the polyester fiber obtained after the reaction. However, by applying the present invention, the fibers having β-glycosidic bonds and the polyester fibers can be separated to a high degree before the depolymerization reaction, thereby suppressing the mixing of foreign substances into the raw material monomers of the polyester fiber and improving the quality. The residual rate of fibers having β-glycosidic bonds (including their lower molecular weight products; the same applies below) remaining in the other fibers obtained after the treatment of the mixed fibers with DES is preferably 0% or more and less than 26%, more preferably 0% or more and less than 21%, even more preferably 0% or more and less than 16%, particularly preferably 0% or more and less than 11%, and most preferably 0% or more and less than 6%, so as not to affect the reuse and recycling of the recovered other fibers. The amount of fibers having β-glycosidic bonds remaining in the other fibers obtained after the treatment of the mixed fibers with DES can be reduced by adjusting the type and mixing ratio of the hydrogen bond acceptor and hydrogen bond donor that constitute the DES, the reaction temperature, and the reaction time. Alternatively, fibers having β-glycosidic bonds may be removed as a multi-stage treatment process including a pretreatment process, a posttreatment process, or both, as described above. [Example]

[0032] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0033] (1) Measurement of the acid dissociation constant (pKa) of hydrogen bond donors The acid dissociation constants of the hydrogen bond donors used in the examples of the present invention were measured using an automatic potentiometric titrator (AT-610) manufactured by Kyoto Electronics Manufacturing Co., Ltd. (2) Calculation of the weight-average molecular weight retention rate of the recovered fibers with β-glycosidic bonds The molecular weights of fibers containing β-glycosidic bonds collected before and after DES treatment were measured using gel permeation chromatography (Shimadzu Corporation, Nexcera GPC System, detector: RI (RID-20A) refractive index detector, column: PLgel 20 μm MIXED-A, solvent: 8% LiCl / DMAc, flow rate: 0.5 mL / min, temperature: 23 °C, standard: monodisperse pullulan) to calculate the weight-average molecular weight. The measurement samples were prepared by immersing fibers containing β-glycosidic bonds collected before or after DES treatment in an 8% LiCl (lithium chloride) / DMAc (dimethylacetamide) solution to a concentration of 0.6%. The cellulose was completely dissolved over 1–2 weeks, and the filtrate obtained by filtration was used. The weight-average molecular weight retention of the fibers containing β-glycosidic bonds was calculated from the weight-average molecular weights before and after DES treatment using Equation 2, and the grades S–D were determined as follows. (Weight-average molecular weight retention rate of recovered fibers) = (Weight-average molecular weight of recovered fibers after DES treatment) / (Weight-average molecular weight of fibers before DES treatment) × 100 Equation 2

[0034] judgement S: 0% to less than 8% A: 8% or more but less than 11% B: 11% or more but less than 14% C: 14% or more but less than 17% D: 17% or more and 100% or less

[0035] (3) Calculation of the recovery rate of other recovered fibers The recovery rate of other fibers recovered after treatment with DES was calculated using Equation 3, and the grades S to B were determined as follows. Recovery rate of other fibers (%) = Weight of other fibers recovered after treatment (g) / Weight of other fibers in the mixed fiber before treatment (g) × 100 Equation 3

[0036] judgement S: 85% or more and 100% or less A: 80% or more but less than 85% B: 0% or more but less than 80% (4) Calculation of the remaining rate of fibers with β-glycosidic bonds remaining in the other collected fibers To calculate the residual rate of fibers with β-glycosidic bonds remaining in the other fibers collected, the infrared absorption spectrum of the mixed fibers before treatment and the other fibers collected was measured by the ATR method using a Fourier transform infrared spectrometer (FT-IR, "NicoletiS10" manufactured by Thermo Fisher Scientific). In the infrared absorption spectrum, a characteristic peak at 3333 cm originating from the hydroxyl groups of fibers with β-glycosidic bonds was observed. -1 The peak intensity of this peak was used in the calculation. Measurements were performed at 10 points, and the remaining percentage of fibers with β-glycosidic bonds remaining in the other collected fibers was calculated from the average peak intensity using Equation 4, and the grades S to D were determined as follows:

[0037] Residual rate of fibers with β-glycosidic bonds remaining in the other collected fibers = 3333 cm of the other collected fibers -1 Average peak intensity of 3333 cm for mixed fibers -1 Average peak intensity of Equation 4

[0038] judgement S: 0% to less than 11% A: 11% or more but less than 16% B: 16% or more but less than 21% C: 21% or more but less than 26% D: 26% or more and 100% or less

[0039] [Example 1] As shown in Table 1, choline chloride was selected as the hydrogen bond acceptor and oxalic acid dihydrate was selected as the hydrogen bond donor, and the hydrogen bond donor was mixed with the hydrogen bond acceptor at a molar ratio of 1.00 to prepare a DES.

[0040] Next, as shown in Table 1, a plain-woven fabric was prepared using a blended warp yarn with a cotton / polyethylene terephthalate (PET) weight ratio of 40:60 (45 cotton count) and a weft yarn with a PET weight ratio of 20:80 (45 cotton count). 20 g of the above DES was added to 1 g of the fabric and stirred at 110 °C for 1 hour under a nitrogen atmosphere without pressure. After the treatment, the fabric was washed with ion-exchanged water until the electrical conductivity of the wash water reached 1 mS / m or less. The washed sample was then dried at 90 °C in a hot air dryer. The dried sample was then de-piled using a pinholder. The 50 mL of ion-exchanged water and the sample were then placed in a screw-cap bottle and vigorously shaken by hand for 30 seconds to dissolve the β-glycosidic fibers, which were then released into the wash water as powder. Washing was repeated until no more powder was found in the washing water, and all of the washing water was recovered. The washed sample was dried at 90°C using a hot air dryer, and the dried sample was used as the recovered other fibers. The recovery rate of the other fibers and the evaluation results, as well as the remaining rate of fibers with β-glycosidic bonds remaining in the recovered other fibers and the evaluation results are shown in Table 1.

[0041] The wash water containing the decomposition product (powder) of fibers with β-glycosidic bonds that had been decomposed and dropped by treatment with DES was decanted, and the supernatant was then removed. The water was then dried at 90°C using a hot air dryer, and the dried sample was used as the recovered decomposition product of fibers with β-glycosidic bonds. The results of the evaluation of the coloration and weight-average molecular weight retention of the recovered decomposition product of fibers with β-glycosidic bonds are shown in Table 1.

[0042] [Examples 2 to 7] The same procedure as in Example 1 was carried out, except that choline chloride was selected as the hydrogen bond acceptor and oxalic acid dihydrate was selected as the hydrogen bond donor, and DES was prepared by mixing the hydrogen bond donor to hydrogen bond acceptor in a molar ratio as shown in Table 1. In Examples 2 and 7, DES was formed at 110°C, but was not liquefied, so treatment was carried out at 130°C.

[0043] [Examples 8 to 12] The same procedure as in Example 1 was carried out except that the treatment temperatures were as shown in Tables 1 and 2.

[0044] [Table 1]

[0045] [Examples 13 to 15] The same procedure as in Example 1 was carried out, except that the treatment time was as shown in Table 2.

[0046] [Examples 16 to 19] The same procedure as in Example 1 was carried out, except that the weight of the treatment liquid added to the fibers was as shown in Table 2.

[0047] [Example 20] As shown in Table 2, the same procedure as in Example 1 was carried out except that a plain woven fabric was used, which was a blended fiber containing fibers having β-glycosidic bonds and other fibers, with a 45 cotton count blended yarn having a weight fraction of rayon:PET=40:60 for the warp yarn and a 45 cotton count spun yarn made of PET for the weft yarn, so that the weight fraction of the entire fabric was rayon:PET=20:80.

[0048] [Table 2]

[0049] [Example 21] As shown in Table 3, the same procedure as in Example 1 was carried out except that a plain woven fabric was used, which was made using a blended yarn of 45 cotton count with a weight fraction of cotton:polyacrylonitrile (PAN) = 40:60 for the warp yarn and a spun yarn of 45 cotton count made of PAN for the weft yarn, as a blended fiber containing fibers having β-glycosidic bonds and other fibers, so that the weight fraction of the entire fabric was cotton:PAN = 20:80.

[0050] [Example 22] As shown in Table 3, the same procedure as in Example 1 was carried out except that a plain woven fabric was used, which was a blended fiber containing fibers having β-glycosidic bonds and other fibers, with a 45 cotton count blended yarn having a weight fraction of cotton:nylon 6 (N6) = 40:60 for the warp yarn and a 45 cotton count spun yarn made of N6 for the weft yarn, so that the weight fraction of the entire fabric was cotton:N6 = 20:80.

[0051] [Examples 23 to 29] Choline chloride was selected as the hydrogen bond acceptor, and the compounds listed in Table 3 were selected as the hydrogen bond donor. The hydrogen bond donor was mixed with the hydrogen bond acceptor at a molar ratio of 1.00 to prepare a DES.

[0052] Next, a plain woven fabric was prepared using a blended yarn of 45 cotton count with a weight fraction of cotton:polyethylene terephthalate (PET) of 40:60 as the warp yarn and a 45 cotton count spun yarn of PET as the weft yarn, with a weight fraction of cotton:PET of 20:80 as the entire fabric, as a blended fiber containing fibers having β-glycosidic bonds and other fibers. The DES was mixed with 1 g of the fabric in the amount shown in Table 3 and treated at 110°C for 1 hour in a nitrogen atmosphere without pressure. Other than the above, the same procedure as in Example 1 was carried out.

[0053] [Examples 30 to 32] The compounds listed in Table 3 were selected as hydrogen bond acceptors, and oxalic acid dihydrate was selected as a hydrogen bond donor. The hydrogen bond donor was mixed with the hydrogen bond acceptor at a molar ratio of 1.00 to prepare a DES.

[0054] Next, a plain woven fabric was prepared using a blended yarn of 45 cotton count with a weight fraction of cotton:polyethylene terephthalate (PET) of 40:60 as the warp yarn and a 45 cotton count spun yarn of PET as the weft yarn, with a weight fraction of cotton:PET of 20:80 as the entire fabric, as a blended fiber containing fibers having β-glycosidic bonds and other fibers. The DES was mixed with 1 g of the fabric in the amount shown in Table 3 and treated at 110°C for 1 hour in a nitrogen atmosphere without pressure. Other than the above, the same procedure as in Example 1 was carried out.

[0055] [Example 33] Choline chloride was selected as the hydrogen bond acceptor and oxalic acid dihydrate as the hydrogen bond donor. The hydrogen bond donor was mixed with the hydrogen bond acceptor at a molar ratio of 1.00 to prepare a DES, which was then used to prepare a 5 wt% DES aqueous solution, as shown in Table 3.

[0056] Next, as shown in Table 3, a plain woven fabric was prepared using a blended yarn with a weight fraction of cotton:polyethylene terephthalate (PET) of 40:60 as the warp yarn and a cotton count of 45 as the weight fraction of PET as the weight fraction of the entire fabric, and a spun yarn with a cotton count of 45 as the weight fraction of PET as the weight fraction of the entire fabric was prepared. 20 g of the above-mentioned DES aqueous solution was mixed with 1 g of the fabric and treated at 150°C under pressure in a nitrogen atmosphere for 1 hour. Other than the above, the same procedure was carried out as in Example 1.

[0057] [Table 3]

[0058] [Comparative Examples 1 and 2] Choline chloride was selected as the hydrogen bond acceptor and oxalic acid dihydrate as the hydrogen bond donor, and they were mixed so that the molar ratio of hydrogen bond donor to hydrogen bond acceptor was as shown in Table 4. However, even when heated to 150°C, the mixture did not liquefy and did not form a DES, so processing of the mixed fibers could not be carried out.

[0059] [Comparative Examples 3 to 5] As described in Patent Document 1, a blended fiber was treated with a 5 wt % aqueous solution of oxalic acid. A plain woven fabric was produced using a blended yarn with a weight fraction of cotton:polyethylene terephthalate (PET) of 40:60 as the warp yarn and a 45 cotton count yarn with a weight fraction of PET of 40:60 as the weft yarn, as a blended fiber containing fibers having β-glycosidic bonds and other fibers, with the fabric having a weight fraction of cotton:PET of 20:80 as the entire fabric. 8 g of a 5 wt % aqueous solution of oxalic acid was mixed with 1 g of the fabric, and the fabric was treated for 1 hour in a nitrogen atmosphere under the temperature and pressure conditions shown in Table 4. Except for the above, the fabric was treated in the same manner as in Example 1.

[0060] Comparative Example 3 was inferior to Example 33 in the recovery rate of other fibers, the residual rate of fibers having β-glycosidic bonds remaining in the recovered other fibers, and the weight-average molecular weight retention rate of the recovered fibers having β-glycosidic bonds.Comparative Examples 4 and 5 were equivalent to or better than Example 33 in the recovery rate of other fibers, but were significantly inferior in the residual rate of fibers having β-glycosidic bonds remaining in the recovered other fibers and the weight-average molecular weight retention rate of the recovered fibers having β-glycosidic bonds.

[0061] [Table 4] [Industrial Applicability]

[0062] According to the present invention, a mixed fiber consisting of fibers having β-glycosidic bonds, such as cotton, and other fibers, such as polyester, can be selectively decomposed and separated and recovered by a short, simple process under non-pressurized conditions, thereby making it possible to effectively recycle each recovered material as a single material.

Claims

1. A processing method for selectively decomposing fibers having β-glycosidic bonds from a fiber mixture containing fibers having β-glycosidic bonds and fibers made of other materials by treatment with a deep eutectic solvent (DES) formed by mixing a hydrogen bond donor with a hydrogen bond acceptor at a molar ratio of 0.50 to 6.00, and recovering the fibers made of other materials in fibrous form.

2. 2. The method according to claim 1, wherein the hydrogen bond acceptor is at least one selected from the group consisting of quaternary ammonium salts represented by the following formula 1, or a mixture thereof. [N(C ｎ H ２ｎ＋１ )< ３ ·R]< ＋ [Cl]< － ··· Formula 1 Here, R = -C ｍ H ２ｍ＋１ , -CH ２ CH ２ OH, -CH ２ -C ６ H ６ n = 1 to 5 m = 1 to 5

3. 2. The method of claim 1, wherein the hydrogen bond acceptor is at least one selected from the group consisting of choline chloride, benzyltrimethylammonium chloride, benzyltriethylammonium chloride, and benzyltributylammonium chloride, or a mixture thereof.

4. 10. The method of claim 1, wherein the hydrogen bond donor is a carboxylic acid, a sulfonic acid, or a mixture thereof.

5. 2. The method according to claim 1, wherein the hydrogen bond donor is at least one selected from the group consisting of oxalic acid, malonic acid, succinic acid, levulinic acid, 3-phenylpropionic acid, and benzoic acid, or a mixture thereof.

6. The method according to claim 1 , wherein the treatment is carried out under non-pressurized conditions.

7. The method according to claim 1, wherein the treatment temperature is 40°C or higher and 150°C or lower.

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