Method of recovering polyester, and method of manufacturing recycled polyester

Abstract

To provide a method of recovering a polyester component from a fiber product containing polyester fibers and protein fibers, and a method of manufacturing a recycled polyester with reduced discoloration using the recycled polyester.SOLUTION: Provided is a recovery method of treating a fiber product containing polyester fibers and protein fibers in an aqueous solution containing a reducing agent at a temperature of 50 to 100°C, and thereafter recovering a polyester component. It is further preferable that the polyester fiber is made of a polyester having an alkylene benzene dicarboxylate as a main repeating unit, the polyester fiber has been dyed, and the protein fiber is an animal fiber. In addition, a method of manufacturing the recycled polyester that re-polymerize the polyester component obtained by the recovery method is included.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recovering a polyester component from a textile product mainly containing polyester fibers and protein fibers, and a method for producing recycled polyester using the recovered polyester component. [Background technology]

[0002] Polyester is widely used in textile products due to its excellent properties, but the effective utilization of polyester textile products after use is a major issue, including environmental concerns. In particular, textile products using yarns in which polyester fibers are blended with wool, a protein fiber, are widely used due to their ease of handling, but have the problem of difficulty in separating the polyester fibers from the protein fibers.

[0003] Therefore, for example, Patent Document 1 proposes a method for separating chemical fibers such as polyester fibers by treating them with hot water at a specified temperature and pressure. However, the separation was not sufficient using hot water treatment alone.

[0004] Furthermore, when chemical recycling, in which the polyester polymer is first depolymerized and then repolymerized, is adopted as a method for treating polyester fiber products after separation, there is a problem that foreign matter is easily mixed into fiber products that are blended with protein fibers such as wool, and discoloration of the resulting recycled polyester polymer cannot be suppressed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-164827 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for recovering polyester components from textile products containing polyester fibers and protein fibers, and a method for producing recycled polyester with little coloration using the recovered polyester. [Means for solving the problem]

[0007] The method for recovering a polyester component of the present invention includes the following inventions. (1) A method for recovering a polyester component, comprising treating a textile product containing polyester fibers and protein fibers in an aqueous solution containing a reducing agent at a temperature of 50 to 100°C, and then recovering the polyester component. (2) The method for recovering a polyester component according to (1) above, wherein the polyester fiber is made of a polyester having alkylenebenzene dicarboxylate as the main repeating unit. (3) The method for recovering a polyester component according to (1) or (2) above, wherein the polyester fiber is dyed. (4) The method for recovering a polyester component according to any one of (1) to (3) above, wherein the protein fiber is an animal hair fiber. (5) The method for recovering a polyester component according to any one of (1) to (4) above, wherein the aqueous solution containing a reducing agent contains urea and a surfactant. (6) A method for recovering a polyester component according to any one of (1) to (5) above, wherein the treatment in the aqueous solution is followed by treatment with an aromatic alcohol. (7) The method for recovering a polyester component according to any one of (1) to (6) above, wherein the polyester component to be recovered is a bis(hydroxyalkyl) aromatic dicarboxylate. (8) A method for producing recycled polyester, which comprises repolymerizing the polyester component obtained by the recovery method according to any one of (1) to (7) above. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for recovering polyester components from a textile product containing polyester fibers and protein fibers, and a method for producing recycled polyester with little coloration using the recovered polyester. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described in detail below. The method for recovering a polyester component of the present invention essentially involves treating a textile product containing polyester fibers and protein fibers in an aqueous solution containing a reducing agent at a temperature of 50 to 100°C, and then recovering the polyester component.

[0010] [Textile products] The textile product used in the present invention contains polyester fibers and protein fibers. Furthermore, it is preferable that the textile product be primarily composed of polyester fibers. Here, "primarily composed of polyester fibers" means that polyester fibers are the most abundant fibers among the fibers that make up the textile product. The polyester fibers preferably account for 50% by weight or more, more preferably 70% by weight or more, and particularly 90% by weight or more of the weight of the textile product. Furthermore, the protein fiber content is preferably 50% by weight or less, more preferably 30% by weight, and particularly preferably in the range of 1 to 10% by weight.

[0011] Examples of textile products containing such polyester fibers and protein fibers include clothing such as suits made using yarns in which polyester fibers are blended with wool, which is a protein fiber. The present invention makes it possible to separate the two fibers from fabrics made using such blended yarns of polyester fibers and wool in an economically and rational manner.

[0012] [Polyester fiber] Here, polyester fiber refers to a fiber made of a polycondensate synthesized by dehydration condensation of a polycarboxylic acid and a polyalcohol to form an ester bond. The polyester forming the fiber is a polymer having an ester bond and is generally classified into aliphatic polyester, semi-aromatic polyester, and wholly aromatic polyester.

[0013] The polycarboxylic acid constituting the polyester is preferably a dicarboxylic acid or an ester-forming derivative thereof, and more preferably an aromatic dicarboxylic acid such as terephthalic acid or 2,6-naphthalenedicarboxylic acid.

[0014] The polyalcohol, the other component constituting the polyester, is preferably a diol or an ester-forming derivative thereof. The diol is preferably an aliphatic glycol having 2 to 20 carbon atoms. Examples of the aliphatic glycol include ethylene glycol (hereinafter sometimes abbreviated as EG), 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. The aliphatic glycol may be an alicyclic glycol having 3 to 30 carbon atoms, and a specific example is 1,4-cyclohexanedimethanol.

[0015] In the present invention, a polyester obtained by combining such a polycarboxylic acid and a polyalcohol is used as one of the starting materials for forming a textile product. Among these, it is preferable that the polyester is an aromatic polyester, more specifically, a polyester having alkylenebenzene dicarboxylate as the main repeating unit, and furthermore, it is preferable that the polyester is a polyester having polyalkylene terephthalate, particularly polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, or the like as the main component.

[0016] Furthermore, when the aromatic polyester is polyalkylene terephthalate (terephthalic acid: para position), it is also preferable that the polymer contains this as the main polymer component and other minor polymer components. Here, the main polyester component means 60 mass % or more of the weight of the polymer. The minor polymer component is preferably, for example, polyalkylene isophthalate (isophthalic acid: meta position).

[0017] In particular, when the polyester is a polyalkylene terephthalate, which is an aromatic polyester, a polyester obtained by copolymerizing terephthalic acid as the dicarboxylic acid component with isophthalic acid or 5-sodium sulfoisophthalic acid as the copolymerization component is one of the preferred embodiments in terms of its high dyeability and the resulting physical properties. The recovery method of the present invention is particularly effective when such polyester fibers are dyed with a disperse dye or the like.

[0018] [Protein fiber] The textile product used in the present invention contains protein fibers in addition to the polyester fibers described above. Protein fibers are generally fibers having cystine bonds (SS). Furthermore, so-called animal hair fibers made from mammalian body hair are preferred, and more specifically, animal hair fibers such as wool, cashmere, mohair, alpaca, camel, and angora are preferred. The present invention is particularly effective for fabrics using polyester / wool blend fibers, which are consumed in large quantities.

[0019] [Polyester component recovery method (1): Reduction treatment] In the present invention, a textile product containing the above-described polyester fiber and protein fiber is used as a starting material to recover the polyester component. That is, the textile product is treated in an aqueous solution containing a reducing agent at a temperature of 50 to 100°C, and then the polyester component is recovered.

[0020] Protein fibers such as wool are polymers cross-linked by cystine bonds (SS). In the present invention, the cystine bonds are cleaved by treating the fiber with a high-temperature aqueous solution containing a reducing agent, eliminating the hardly soluble portions and recovering the polyester component from the fiber product.

[0021] The reducing agent is not particularly limited, but preferred examples include known reducing agents having a thiol group, such as thioglycolic acid, thioglycolic acid salts (ammonium thioglycolate, monoethanolamine thioglycolate, etc.), cysteamine, cysteamine salts (cysteamine hydrochloride, etc.), cysteine ​​(L-cysteine, DL-cysteine, etc.), cysteine ​​salts (L-cysteine ​​hydrochloride, DL-cysteine ​​hydrochloride, etc.), acetylcysteine ​​(N-acetyl-L-cysteine, etc.), glyceryl thioglycolate, thiolactic acid, thiolactate salts, and butyrolactone thiol. Other known reducing agents, such as sulfites (sodium sulfite, etc.), can also be used. Sodium disulfite, sodium sulfite, sodium thioglycolate, and cysteine ​​are particularly preferred.

[0022] In this step, the reaction is preferably carried out in an aqueous solution at a temperature of 70 to 100°C, more preferably 90 to 100°C. The treatment time is preferably in the range of 0.5 to 10 hours, more preferably 1 to 3 hours. Furthermore, the treatment is preferably carried out while stirring.

[0023] In order to ensure that the reducing agent is thoroughly impregnated into the textile product, it is preferable that the aqueous treatment solution contains a surfactant such as urea or sodium dodecyl sulfate. Thereafter, the water is evaporated in a dryer to produce a textile product mainly composed of polyester fibers, and the polyester component can be recovered as polyester itself by carrying out a washing process or the like.

[0024] Furthermore, in the polyester component recovery method (1) of the present invention, by carrying out the treatment under such mild conditions, it has become possible to significantly suppress reaction inhibition in subsequent treatments, particularly in the depolymerization of polyester into its reaction intermediate, bis(hydroxyalkyl) benzenedicarboxylate, etc.

[0025] In the polyester component recovery method (1) of the present invention, it is preferable to treat the polyester component with an aromatic alcohol or a derivative thereof following the reducing agent treatment. Examples of aromatic alcohols or derivatives thereof include benzyl alcohol, benzaldehyde, and benzoic acid, with benzyl alcohol (hereinafter sometimes referred to as "BA") being particularly preferred.

[0026] The aromatic alcohol or its derivative is used in the form of a heated solution. The aromatic alcohol or its derivative may be used by mixing it with another solvent. The boiling point of each solvent is preferably 100°C or higher, more preferably 150 to 250°C.

[0027] In the present invention, following the treatment with the aqueous reducing agent solution, it is preferable to treat the textile product with a solution of such an aromatic alcohol or its derivative at a temperature in the range of from the glass transition temperature of the polyester to the glass transition temperature of the polyester +100°C, and recover the polyester. A more preferred treatment temperature is in the range of from the glass transition temperature of the polyester +10°C to the glass transition temperature of the polyester +80°C, and even more preferably in the range of from the glass transition temperature of the polyester +15°C to the glass transition temperature of the polyester +60°C.

[0028] The amount of the solution used during treatment is preferably 3 to 1000 times, more preferably 5 to 500 times, and particularly preferably 8 to 50 times the weight of the textile product to be treated. The treatment is carried out by immersing the textile in a solution. This treatment may be carried out by leaving the textile in the solution, but is preferably carried out by agitating the solution in which the textile is immersed using a liquid circulation system or a rotating blade.

[0029] After immersion, the textile product is dehydrated. As a dehydration treatment after immersion, methods such as squeezing, dehydration by centrifugation, and Soxhlet extraction can be applied. It is preferable to repeat the immersion and drainage several times, preferably 5 or more times, and particularly preferably 6 to 10 times.

[0030] The dewatering treatment is carried out under conditions such that the weight of the textile product containing the solution after dewatering is preferably 300% by weight or less, more preferably 150 to 250% by weight, and particularly preferably 180 to 220% by weight, based on the dry weight of the textile product. In particular, this treatment not only allows protein fibers to be removed more thoroughly, but is also effective in removing the dyed polyester fibers when the polyester fibers are dyed with a disperse dye or the like.

[0031] [Polyester component recovery method (2): Depolymerization treatment] Furthermore, it is preferable to further depolymerize the polyester obtained by the polyester component recovery method (1). Normally, if the reducing agent treatment is not performed in the step of the polyester component recovery method (1), the cystine bonds inhibit depolymerization, and only a colored polyester component of low purity is obtained. However, by passing through the step of the polyester component recovery method (1) of the present invention, it is possible to obtain a white polyester component of high purity.

[0032] That is, it is preferable to subsequently carry out a recovery method (2) in which the polyester component obtained by the above-mentioned polyester component recovery method (1) is further depolymerized into a bis(hydroxyalkyl) aromatic dicarboxylate in an alkylene glycol containing a depolymerization catalyst. The treatment conditions for depolymerization are preferably normal pressure, at a temperature in the range of 180°C to 250°C, for 2 to 8 hours, or more preferably at a temperature in the range of 200°C to 240°C, for 3 to 6 hours while stirring.

[0033] [catalyst] The catalyst used in the depolymerization reaction of the depolymerization step is preferably a first transition metal catalyst. Specific examples include first transition metal fatty acid salts, carbonates, sulfates, phosphates, oxides, hydroxides, halides, and alcoholates. Manganese and zinc are preferably used as the first transition metal.

[0034] As the catalyst, manganese oxide, manganese acetate, zinc oxide, or zinc acetate is preferably used, with manganese acetate being particularly preferred. One or more types of catalyst may be used in combination. In particular, when manganese acetate is used as the catalyst, it has high solubility in alkylene glycol, making it possible to reduce the amount of catalyst remaining in the subsequent process. The catalyst is preferably dissolved or suspended in alkylene glycol before use.

[0035] Generally, depolymerized polyester products often gradually become discolored due to long-term storage, etc. However, the products obtained by the recovery method and production method of the present invention clearly show little discoloration. In particular, when a manganese-based catalyst is used during depolymerization, a polyester polymer with little discoloration can be obtained.

[0036] The amount of catalyst used during depolymerization is preferably 20 to 500 mmol%, more preferably 30 to 300 mmol%, and particularly preferably 50 to 150 mmol% relative to the polyester. Here, "mol%" refers to the ratio of the number of catalyst molecules to the constituent units of the polyester. "mmol%" is 1 / 1000 of that. If the amount of catalyst used is less than the above range, the catalytic activity will be insufficient, and if it is more, the effect of inhibiting discoloration will decrease, which is not preferable. If a manganese-based catalyst is used as the catalyst, depolymerization can be carried out with a small amount used.

[0037] [Alkylene glycol] The alkylene glycol (hereinafter sometimes abbreviated as AG) used in the depolymerization reaction in the depolymerization step is the same as the polyalcohol forming the skeletal structure of the polyester used in the textile product, or the same as the polyalcohol constituting the polyester obtained by repolymerizing the intermediate bis(hydroxyalkyl) aromatic dicarboxylate.

[0038] Examples of alkylene glycols that are the same as the polyalcohols that form the backbone structure of the polyester include ethylene glycol (EG) when the polyester is polyethylene terephthalate (PET), 1,3-propanediol (trimethylene glycol, C3G) when the polyester is polytrimethylene terephthalate, and 1,4-butanediol (C4G) when the polyester is polybutylene terephthalate. The alkylene glycol may be a mixture of the alkylene glycols.

[0039] The amount of alkylene glycol is preferably 2 to 20 times, and more preferably 3 to 10 times, the weight of the recovered polyester. By using a large amount of alkylene glycol during depolymerization in this manner and subsequently carrying out crystallization and solid-liquid separation, the amount of contaminating depolymerization catalyst and other foreign matter can be reduced.

[0040] [Refining process] In the method for recovering a polyester component of the present invention, it is preferable to further carry out a purification step after the polyester component recovery step. In particular, when the depolymerization step of recovery method (2) is carried out, it is preferable to include a purification step of purifying the depolymerization reaction product. The purification step includes crystallization and adsorption treatment, and it is more preferable to carry out both of them.

[0041] [Crystallization] The purification step is carried out by crystallizing the polyester components such as the depolymerization reaction product in alkylene glycol by lowering the temperature. The temperature lowering conditions for crystallization are preferably from a temperature of 60°C or higher to 25°C or lower, and more preferably to 15°C or lower. After the crystallization, solid-liquid separation is preferably carried out. The alkylene glycol content in the cake after the solid-liquid separation is preferably 100% by weight or less, more preferably 55% by weight or less, still more preferably 1 to 30% by weight, and particularly preferably 5 to 25% by weight.

[0042] When solid-liquid separation is performed after crystallization, it is preferable to wash the crystallized product with water or alkylene glycol. The washing is preferably performed by treating the product in a Nutsche filter while spraying a washing liquid. By performing these treatments, the depolymerization catalyst dissolved in the alkylene glycol and other color-causing substances can be washed away, and a more highly purified aromatic dicarboxylate bis(hydroxyalkyl) can be obtained.

[0043] The solution used for washing is preferably one with low viscosity, and from this viewpoint, water is preferably used. The amount of washing liquid is preferably 1 to 100 times, more preferably 1.5 to 10 times the weight of the cake. The liquid temperature during washing is 0 to 40°C. If the liquid temperature is higher than this, the cake itself will be more likely to dissolve, resulting in a lower yield, which is not preferred. After washing, the product is dried in a vacuum dryer or the like to obtain the aromatic dicarboxylic acid bis(hydroxyalkyl).

[0044] When the alkylene glycol used in the production method of the present invention is the same as the diol component of the polyester after repolymerization, it is also preferable to use it for repolymerization as it is without drying.

[0045] [Adsorption treatment] It is also preferable to further subject the obtained polyester component such as aromatic dicarboxylate bis(hydroxyalkyl) to adsorption treatment for foreign matter using an adsorbent such as activated carbon. Other adsorbents include those made of styrene or acrylic cross-linked copolymers, and more preferably, synthetic adsorbents made of styrene or acrylic cross-linked copolymers having a macroporous structure without functional groups.

[0046] This adsorption treatment is a process in which an aromatic dicarboxylate bis(hydroxyalkyl) composition or the like is brought into contact with an adsorbent, and organic matter derived from additives such as decomposition products of fibers and resins other than polyester contained in the composition, as well as dyes, is adsorbed onto the adsorbent, thereby obtaining a more purified polyester component such as an aromatic dicarboxylate bis(hydroxyalkyl).

[0047] This adsorption step can be carried out by dissolving the polyester component composition in water or an organic solvent to prepare an aqueous solution or solution, and then adding the adsorbent thereto, thereby bringing the two into contact in water or an organic solvent.

[0048] [Polyester component: bis(hydroxyalkyl) benzenedicarboxylate] When the polyester component contained in the textile product is recovered as a bis(hydroxyalkyl) aromatic dicarboxylate as a polyester intermediate by the above-mentioned recovery step (depolymerization), it can be particularly preferably used as an intermediate for producing recycled polyester polymer.

[0049] The aromatic bis(hydroxyalkyl) dicarboxylate produced varies depending on the polyester and alkylene glycol used in the depolymerization. When the polyester is a polyester (polyalkylene terephthalate) that mainly uses terephthalic acid as the polycarboxylic acid, bis(hydroxyalkyl) benzenedicarboxylate (hereinafter sometimes referred to as BHAT; bishydroxyalkyl terephthalate) is obtained.

[0050] Specifically, when C3G (1,3-propanediol (trimethylene glycol)) is used as the alkylene glycol for depolymerization, BHPT (bishydroxypropyl terephthalate) is obtained. When C4G (1,4-butanediol) is used as the alkylene glycol for depolymerization, BHBT (bishydroxybutyl terephthalate) is obtained. When ethylene glycol is used as the alkylene glycol for depolymerization, BHET (bishydroxyethyl terephthalate) is obtained.

[0051] [Production of recycled polymers (repolymerization)] The polyester component obtained by the recovery method of the present invention can be further repolymerized to produce recycled polyester. In particular, when the obtained polyester component is a bis(hydroxyalkyl) aromatic dicarboxylate, a recycled polyester polymer can be more efficiently produced by polycondensation reaction. The recycled polyester polymer obtained by the present invention has a low content of foreign matter, is less colored, and has excellent hue.

[0052] As the catalyst for repolymerization to obtain the recycled polyester polymer, known catalysts such as antimony, germanium or titanium catalysts can be used, for example, diantimony trioxide.

[0053] It is preferable to carry out the polycondensation reaction while discharging alkylene glycol and the like generated in the repolymerization reaction outside the reactor. The amount of catalyst used is in the range of 10 to 1000 ppm based on the weight of the aromatic dicarboxylic acid bis(hydroxyalkyl). After polycondensation, it is preferable to add a conventionally known phosphorus-based stabilizer such as orthophosphoric acid or phosphorous acid. The amount of the phosphorus-based stabilizer used is preferably in the range of 1 to 100 ppm based on the weight of the aromatic bis(hydroxyalkyl) dicarboxylate.

[0054] [Physical properties of recycled polymers] The recycled polyester polymer obtained in this manner is a polymer with little yellowness, which is considered to be inferior in quality. The polyester recovery method of the present invention is less likely to produce colored by-products. Furthermore, by adding a subsequent step such as crystallization, the catalyst is more likely to dissociate from the intermediate, such as the aromatic dicarboxylate bis(hydroxyalkyl), and is less likely to remain as an impurity. This effect is particularly pronounced when depolymerization is performed using a low concentration of a manganese-based catalyst or a high concentration of a zinc-based catalyst.

[0055] In the recycled polyester polymer obtained by the present invention, protein fibers have been removed, and if the polyester fibers in the textile product are dyed, the dyes have also been removed.

[0056] The resulting recycled polyester polymer more preferably exhibits the following properties: The resulting recycled polyester polymer meets the L certification of the International Commission on Illumination (CIE). * , a * , b * As the hue in the color space colorimeter, b * The value is preferably 8 or less. The resulting recycled polyester polymer preferably has a yellowness index (YI) of 15 or less. The resulting recycled polyester polymer preferably has a whiteness (W) of 75 or more, more preferably 80 to 100. The resulting recycled polyester polymer has an intrinsic viscosity (IV) of the polymer of preferably 0.30 to 1.50 dL / g, more preferably 0.40 to 1.30 dL / g, and particularly preferably 0.50 to 1.20 dL / g. [Example]

[0057] The present invention will be described in more detail below with reference to examples. The values ​​in the examples were determined by the following methods. "% owf" is an abbreviation for "% on the weight of fiber."

[0058] 1) Hue (L * a * b * , YI, W) A sample (5 g) was pressed between two metal plates to form a plate, which was then heated at 140°C for 2 hours to crystallize the sample to prepare a measurement sample. The measurement sample was measured for hue L according to JIS Z8781-4:2013 using a measurement device (NW-12 manufactured by Nippon Denshoku Industries Co., Ltd.). * , a * , b * The values ​​were measured. The yellowness index (YI) was calculated by the following formula (1), and the whiteness index (W) was calculated by the following formula (2). Yellowness (YI): 0.34-71.7×a * / L * +178.78×b * / L * (1) Whiteness (W):100-√{(100-L * ) 2 +a *2 +b *2} (2) The higher the yellowness index (YI) number, the more yellowish the color, and the higher the whiteness index (W) number, the more white the color.

[0059] 2) Nitrogen (N) content Measurements were made using a total nitrogen and protein analyzer (Nitto Seiko Analytech DTN-300V).

[0060] 3) Intrinsic viscosity (IV) The fiber (polymer) sample was dissolved in 10 mL of a tetrachloroethane / phenol mixed solvent (volume ratio 1 / 1), and the intrinsic viscosity (dL / g) at 35°C was measured.

[0061] [Example 1] (Textile products) The test textile was a mixture of 380 g of polyethylene terephthalate (PET) fabric and 20 g of wool fiber. The PET fiber was a yarn with an IV of 0.60 dL / g, a Tg of 70°C, a Tm of 255°C, 24 dtex, a strength of 3.9 cN / dtex, and an elongation of 41%. It was dyed with 0.87% owf nitrogen-containing orange dye, 0.4% owf nitrogen-containing red dye, and 4.7% owf nitrogen-containing black dye, resulting in a black fiber containing 0.38 wt% nitrogen (N). The wool fiber was black-dyed animal hair fiber manufactured by Sunwell.

[0062] (Polyester component recovery method (1): reduction treatment) 400 g of this textile product was placed in a 5-liter separable flask, and 3260 g of a mixed aqueous solution (2000 mL of water, 200 g of sodium disulfite, 960 g of urea, and 100 g of sodium dodecyl sulfate) that had been heated in a separate beaker until the internal temperature reached 90°C was added to the separable flask containing the textile product. With the textile product immersed in the mixed aqueous solution, the internal temperature was adjusted to 90°C and the mixture was stirred for 60 minutes (immersion treatment).

[0063] The textile was then removed from the separable flask and squeezed to remove excess treatment solution (a liquid in which wool fibers were dissolved in the mixed aqueous solution). Coloration was observed in the treatment solution, and the weight of the lightly bleached textile after squeezing was 970 g. The textile product was then dried in a dryer set at 100°C under normal pressure for 8 hours to evaporate the water content.

[0064] The dried textile product was placed back into the separable flask, and 4,000 g of benzyl alcohol (BA) was added. The internal temperature was adjusted to 105°C and stirred for 30 minutes. The fabric-like textile product was removed from the separable flask and squeezed to remove excess treatment liquid. Coloration was observed in the treatment liquid. At this stage, the color of the dyed fabric had almost completely disappeared, leaving a white fabric. The wool fiber aggregates had also disappeared, and only a fabric made of white PET fibers was observed.

[0065] After squeezing, the textile product was again placed in the separable flask, and the same steps of immersion in the solution and squeezing as above were repeated a total of six times. Visual inspection showed that the textile products had turned white after the third treatment, but even after the fourth treatment, the squeezed treatment liquid still had some coloring, and it was only after the sixth treatment that the treatment liquid finally became transparent. The treated textile was dried in a vacuum dryer at 80°C for 8 hours, and a textile made of white polyester with high whiteness was recovered as a polyester component. The weight of the treated textile was 360g, and all of the wool had been removed.

[0066] (Polyester component recovery method (2): Depolymerization treatment) The polyester in the textile product recovered by the above method was further depolymerized. First, 300 parts by weight of the polyester, 1500 parts by weight of ethylene glycol (EG), and 0.38 parts by weight (100 mmol% based on the polyester) of manganese acetate (Mn acetate) as a depolymerization catalyst were placed in a 2 L separable flask and nitrogen was sealed in. At this time, Mn acetate was dissolved in EG before being added. Thereafter, the separable flask containing the polyester was heated using a mantle heater with the internal temperature set to 220°C, and depolymerization treatment was carried out for 4 hours at normal pressure while stirring, to obtain a BHET (bis(hydroxyethyl) benzenedicarboxylate) solution.

[0067] The BHET solution after depolymerization was brown. Therefore, the depolymerized solution was further filtered through a 200 μm mesh to remove the remaining solids. After gradual cooling to 70°C, the solution was stirred and cooled, with temperature reduction treatment (1) from 70°C to 40°C for 10 minutes from 0 to 10 minutes, temperature reduction treatment (2) from 40°C to 30°C for 50 minutes from 10 to 60 minutes, and temperature reduction treatment (3) from 30°C to 15°C for 120 minutes from 60 to 180 minutes. Subsequently, the internal temperature was maintained at 15°C and stirring was continued for 60 minutes. The internal temperature was reduced over a total of 4 hours, allowing BHET crystals to precipitate, yielding a BHET / EG slurry.

[0068] The BHET / EG slurry was then compressed using a filter press manufactured by Nippon Filter Equipment Co., Ltd. to separate the BHET and EG into solid and liquid. The BHET at this stage contained 35% by weight of EG based on the dry weight of the BHET. After the solid-liquid separation was completed, the BHET was dried in a vacuum dryer at 50°C for 8 hours, and the dried BHET was recovered as a polyester component. The BHET obtained was white and free of any foreign matter.

[0069] (repolymerization of polyester) Thereafter, 254 parts by weight of the obtained dry BHET was charged into a reaction vessel under normal pressure in a nitrogen atmosphere together with 0.007 part by weight of a phosphorus-based stabilizer and 0.07 part by weight of diantimony trioxide as a repolymerization catalyst.

[0070] The temperature inside the reactor was then raised to 285°C, and the pressure was gradually reduced under the following conditions: atmospheric pressure for 10 minutes, a pressure of 4 kPa for 10 minutes, and a pressure of 0.4 kPa for 40 minutes. While products such as ethylene glycol generated in the reaction were distilled out of the reactor, a polycondensation reaction was carried out to produce recycled polyester. The color and physical properties of the recycled polyester before treatment (textile product), the recovered polyester component, and the recycled polyester after repolymerization are shown in Table 1.

[0071] [Example 2] The polyester component (BHET) was recovered in the same manner as in Example 1, except that the mixed aqueous solution used to remove proteins from the textile product was changed from sodium disulfite to cysteine, and the immersion treatment was performed in a mixed aqueous solution (2000 ml of water, 200 g of cysteine, 960 g of urea, and 100 g of sodium dodecyl sulfate). Polyester component recovery method (1): The color of the treatment liquid after squeezing in the reduction treatment was darker than in Example 1, and the textile product itself was a polyester fabric with a high degree of whiteness. Furthermore, the polyester component (BHET) obtained after depolymerization of the polyester was also white.

[0072] This depolymerized polyester component (BHET) was subjected to a polycondensation reaction to obtain a recycled polyester in the same manner as in Example 1. The colors and physical properties of the recycled polyester before treatment (textile product), the recovered polyester component, and after repolymerization are shown in Table 1.

[0073] [Example 3] The polyester component (BHET) was recovered in the same manner as in Example 1, except that the mixed aqueous solution used to remove proteins from the textile product was changed from sodium disulfite to cysteamine and the immersion treatment was changed to a mixed aqueous solution (2000 ml of water, 200 g of cysteamine, 960 g of urea, and 100 g of sodium dodecyl sulfate). Recovery of polyester component (1): The color of the treatment liquid after squeezing in the reduction treatment was darker than in Example 1, and the textile product itself was a polyester fabric with a high degree of whiteness. Furthermore, the polyester component (BHET) obtained after depolymerization of the polyester was also white.

[0074] This depolymerized polyester component (BHET) was subjected to a polycondensation reaction to obtain a recycled polyester in the same manner as in Example 1. The color and physical properties of the recovered polyester component before treatment (textile product) and the recycled polyester after repolymerization are also shown in Table 1.

[0075] [Example 4] The polyester component (BHET) was recovered in the same manner as in Example 1, except that the mixed aqueous solution used to remove proteins from the textile product was changed from sodium disulfite to sodium thioglycolate, and the immersion treatment was performed in a mixed aqueous solution (2000 ml of water, 200 g of sodium thioglycolate, 960 g of urea, and 100 g of sodium dodecyl sulfate). Polyester component recovery method (1): The color of the treatment liquid after squeezing in the reduction treatment was darker than in Example 1, and the textile product itself was a polyester fabric with a high degree of whiteness. Furthermore, the polyester component (BHET) obtained after depolymerization of the polyester was also white.

[0076] This depolymerized polyester component (BHET) was subjected to a polycondensation reaction to obtain a recycled polyester in the same manner as in Example 1. The colors and physical properties of the recycled polyester before treatment (textile product), the recovered polyester component, and after repolymerization are shown in Table 1.

[0077] [Example 5] The polyester component (BHET) was recovered in the same manner as in Example 1, except that the mixed aqueous solution used to remove proteins from the textile product was changed from sodium disulfite to sodium sulfite, and the immersion treatment was performed in a mixed aqueous solution (2000 ml of water, 200 g of sodium sulfite, 960 g of urea, and 100 g of sodium dodecyl sulfate). Recovery of polyester component (1): The color of the treatment liquid after squeezing in the reduction treatment was darker than in Example 1, and the textile product itself was a polyester fabric with a high degree of whiteness. The polyester component (BHET) obtained after depolymerization of the polyester was also white.

[0078] This depolymerized polyester component (BHET) was subjected to a polycondensation reaction to obtain a recycled polyester in the same manner as in Example 1. The colors and physical properties of the recycled polyester before treatment (textile product), the recovered polyester component, and after repolymerization are shown in Table 1.

[0079] [Table 1]

[0080] [Comparative Example 1] The mixed aqueous solution used to remove proteins from textile products (2000 ml of water, 200 g of sodium disulfite, 960 g of urea, and 100 g of sodium dodecyl sulfate) was changed to a benzyl alcohol (BA) treatment, and the internal temperature was adjusted to 90°C while stirring for 60 minutes (immersion treatment). Thereafter, the BA treatment at 105°C for 30 minutes was carried out six more times in the same manner as in Example 1, followed by depolymerization to recover the polyester component (BHET).

[0081] It was confirmed that the wool turned brown during the BA treatment process, and that most of the wool solids remained even after the sixth BA treatment. Thereafter, repolymerization was carried out in the same manner as in Example 1. Table 2 shows the color and physical properties of the recycled polyester before treatment (textile product), the recovered polyester components, and after repolymerization.

[0082] [Table 2]

[0083] Comparative Example 2 The polyester component (BHET) was recovered in the same manner as in Example 1, except that the temperature of the mixed aqueous solution (2000 ml of water, 200 g of sodium disulfite, 960 g of urea, and 100 g of sodium dodecyl sulfate) used to remove proteins from the textile product was changed from 90°C in Example 1 to 25°C. Polyester component recovery method (1): After squeezing in the reduction treatment, the color of the treatment liquid remained transparent, and the textile product itself was clearly still colored. The subsequent polyester component recovery process (2) and subsequent steps were discontinued. [Industrial Applicability]

[0084] The method of recovering polyester components from textile products containing polyester fibers and protein fibers of the present invention can be effectively used as a raw material for recycled polyester polymers. Furthermore, the recycled polyester polymers can be used as raw materials for textile products because they have the same color and physical properties as virgin polyester polymers obtained by polymerization of petroleum-derived raw materials. As a result, this method promotes the reuse of discarded textile products that would not otherwise be recycled into fibers, thereby contributing to reducing environmental impact.

Claims

1. A method for recovering a polyester component, comprising treating a textile product containing polyester fibers and protein fibers in an aqueous solution containing a reducing agent at a temperature of 50 to 100°C, and then recovering the polyester component.

2. 2. The method for recovering a polyester component according to claim 1, wherein the polyester fiber comprises a polyester having alkylenebenzene dicarboxylate as a main repeating unit.

3. 2. The method for recovering polyester components according to claim 1, wherein the polyester fibers are dyed.

4. 2. The method for recovering a polyester component according to claim 1, wherein the protein fiber is an animal hair fiber.

5. 2. The method for recovering a polyester component according to claim 1, wherein the aqueous solution containing a reducing agent contains urea and a surfactant.

6. 2. The method for recovering a polyester component according to claim 1, wherein the treatment in the aqueous solution is followed by treatment with an aromatic alcohol.

7. 2. The method for recovering a polyester component according to claim 1, wherein the polyester component to be recovered is a bis(hydroxyalkyl) aromatic dicarboxylate.

8. A method for producing a recycled polyester component, which comprises repolymerizing the polyester obtained by the recovery method according to any one of claims 1 to 7.

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