Method for recovering polyester and method for producing recycled polyester

Abstract

The present invention obtains a polyester having less coloring by treating a fiber product containing polyester fibers and urethane fibers, with an aromatic alcohol in a temperature range not lower than the glass transition temperature of the polyester but not higher than the glass transition temperature+100°C of the polyester.

Description

Technical Field

[0001] The present invention relates to a method for recovering polyester from a fiber product containing polyester fiber and urethane fiber, and a method for producing polyester by depolymerizing and then repolymerizing the polyester.

Background Art

[0002] Polyester is widely used as a fiber product or the like due to its excellent properties, but the effective utilization of used polyester fiber products has become a major issue including environmental problems.

[0003] As the main treatment methods, material recycling, thermal recycling, chemical recycling, etc. have been studied. Among them, from the viewpoint of less reduction in quality during recycling, chemical recycling such as depolymerizing a polyester polymer to a raw material composed of a dicarboxylic acid and a diol and then repolymerizing is excellent as a closed-loop recycling. Among them, a method using an intermediate capable of producing a recycled polyester by directly performing a polycondensation reaction is also an excellent method from the viewpoint of energy consumption.

[0004] However, the recycled polyester polymer obtained in this way had a problem of being difficult to whiten.

[0005] In particular, when the polyester fiber product contains a different polymer such as polyurethane or is a dyed product, it has been difficult to efficiently recover it while suppressing coloring.

[0006] For example, in Patent Document 1, as a coloring factor substance removal step, after making an intermediate after depolymerization, an adsorption treatment of bringing the coloring factor substance into contact with an adsorbent, a decomposition treatment of decomposing the coloring factor substance with a decomposing agent, a reduction treatment of reducing the coloring factor substance with a reducing agent, etc. have been attempted. However, although the coloring factor substances such as dyes clearly mixed in the polymer are removed to some extent, a production method for obtaining a polyester polymer with coloring suppressed to the same level as that of a polyester polymer by a normal production method without using recycled raw materials has not yet been obtained.

[0007] Further, according to the studies of the present inventors, in a fiber product composed mainly of fibers made of polyester and containing polyurethane, separation in the steps before and after depolymerization is particularly difficult, and the hue of the chemical recycled polyester after repolymerization was often brownish. And when used for recycling into fiber products etc., it was inferior in quality.

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a method for recovering a polyester with less coloring from a fiber product containing polyester fibers and polyurethane fibers.

Means for Solving the Problems

[0009] The method for recovering a polyester of the present invention is characterized in that a fiber product containing fibers composed mainly of polyester and made of a polymer having a urethane group as a constituent component is treated with a solution of an aromatic alcohol or a derivative thereof in a temperature range of not less than the glass transition temperature of the polyester and not more than the glass transition temperature of the polyester + 100°C.

[0010] The present invention preferably includes that the textile product is dyed with a disperse dye, the polyester is polyethylene terephthalate, the polymer containing a urethane group as a constituent is a polyether-based polyurethane, and the aromatic alcohol is benzyl alcohol.

[0011] Another invention of the present invention is a method for producing recycled polyester, which depolymerizes the polyester obtained by the above recovery method with aromatic dicarboxylic acid bis(hydroxyalkyl), and then repolymerizes the aromatic dicarboxylic acid bis(hydroxyalkyl) to obtain recycled polyester.

Advantages of the Invention

[0012] According to the present invention, a method for recovering polyester with less coloring from a textile product containing polyester fibers and polyurethane fibers can be provided.

Best Mode for Carrying Out the Invention

[0013] 〔Textile Product〕 The method for recovering polyester of the present invention is a method for recovering polyester from a textile product mainly composed of fibers made of polyester and containing fibers made of a polymer containing a urethane group as a constituent. Here, "mainly composed of fibers made of polyester" means that the fibers made of polyester are the most abundant fibers among the fibers constituting the textile product. The fibers made of polyester preferably account for 50 wt% or more, more preferably 80 wt% or more of the textile product.

[0014] Here, polyester is a polycondensate synthesized by dehydrating and condensing a polyvalent carboxylic acid and a polyalcohol to form an ester bond. And polyester is a polymer having an ester bond and is generally classified into aliphatic polyester, semi-aromatic polyester and wholly aromatic polyester.

[0015] The polycarboxylic acid constituting this polyester is preferably a dicarboxylic acid or its ester-forming derivative. As the dicarboxylic acid, aromatic dicarboxylic acids such as terephthalic acid and 2,6-naphthalenedicarboxylic acid are preferably used.

[0016] The polyalcohol, which is the other component constituting the polyester, is preferably a diol or its ester-forming derivative. As the diol, aliphatic glycols having 2 to 20 carbon atoms are preferably used. Examples of this 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 specifically, 1,4-cyclohexanedimethanol can be exemplified.

[0017] In the present invention, the polyester obtained by combining the above polycarboxylic acid and polyalcohol is used as a starting material. As this polyester, polyalkylene terephthalate is preferable, and among them, polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate are preferable.

[0018] The fiber product used in the present invention contains, in addition to the fibers mainly composed of the above polyester, fibers composed of a polymer having a urethane group as a constituent component.

[0019] Examples of the fibers composed of a polymer having a urethane group as a constituent component include polyurethane fibers and polyurethane-urea fibers. These often have the properties of elastic fibers.

[0020] Preferred fibers made of a polymer containing a urethane group are polyurethane fibers having a urethane bond (-NHCOO-) in the molecular chain. Polyurethane fibers are composed of a soft segment with low melting point and flexibility and a hard segment with high melting point, and have excellent elasticity. This polyurethane fiber is classified into polyether-based polyurethane fiber and polyester-based polyurethane fiber according to its soft segment.

[0021] In the present invention, polyether-based polyurethane fibers are preferred as the polyurethane fibers. Among them, polyether-based polyurethane fibers obtained by using a polyether diol such as polytetramethylene glycol as the diol component, an aromatic diisocyanate such as 4,4'-diphenylmethane diisocyanate as the diisocyanate component, and ethylenediamine as the diamine component are particularly preferred.

[0022] Examples of this polyether-based polyurethane fiber include "Leica" (registered trademark) manufactured by Asahi Kasei Fibers Corporation.

[0023] The polyurethane fiber is preferably a fiber having a high elongation elastic modulus.

[0024] The polyurethane fiber may be used as a single-component yarn, or may take forms such as blended fiber, mixed fiber yarn, covering yarn (urethane fiber core), composite yarn, etc. with polyester fiber or the like.

[0025] The content of the polyurethane fiber in the fiber product is preferably 50 wt% or less, more preferably less than 50 wt%, still more preferably 30 wt% or less, and particularly preferably 5 to 20 wt%.

[0026] The fiber product may be in the form of, for example, sportswear, uniforms, socks, etc.

[0027] In the present invention, it is a preferred embodiment that the textile product is a dyed textile product. It is also a preferred embodiment that the dyeing is carried out with a disperse dye. Furthermore, it is also a preferred embodiment that the disperse dye is a dye containing a nitrogen atom.

[0028] The recovery method of the present invention is a method for recovering polyester by treating the above-mentioned textile product with a solution of an aromatic alcohol or its derivative in a temperature range of not lower than the glass transition temperature of polyester and not higher than the glass transition temperature of polyester + 100°C.

[0029] 〔Aromatic alcohol〕 Examples of the aromatic alcohol or its derivative include benzyl alcohol, benzaldehyde, and benzoic acid. Preferably, benzyl alcohol (hereinafter sometimes referred to as "BA") is used.

[0030] 〔Treatment〕 The aromatic alcohol or its derivative is used in a heated solution state. The aromatic alcohol or its derivative may be used by mixing with other solvents. In any case, the boiling point is preferably 100°C or higher, more preferably 150 - 250°C.

[0031] The recovery method of the present invention treats the textile product under the conditions of a temperature range of not lower than the glass transition temperature of polyester and not higher than the glass transition temperature of polyester + 100°C with a solution of such an aromatic alcohol or its derivative to recover polyester.

[0032] The treatment temperature of the textile product is preferably in the range of +10°C or higher and +80°C or lower, more preferably in the range of +15°C or higher and +60°C or lower, based on the glass transition temperature of polyester.

[0033] The amount of the solution during treatment is preferably 3 - 1000 times, more preferably 5 - 500 times, and particularly preferably 8 - 50 times, based on the weight of the textile product to be treated.

[0034] The treatment is carried out by immersing the textile product in a solution. This treatment may be carried out by allowing the textile product immersed in the solution to stand, but preferably it is carried out by stirring the solution in which the textile product is immersed by means of liquid flow circulation, rotating blades, or the like.

[0035] After immersion, the textile product is de-liquored. As the de-liquoring treatment after immersion, methods such as squeezing treatment, de-liquoring treatment by centrifugation, and Soxhlet extraction can be applied.

[0036] It is preferable to repeat immersion and de-liquoring a plurality of times, preferably 5 times or more, particularly preferably 6 to 10 times of immersion and de-liquoring are repeated.

[0037] The de-liquoring treatment is carried out under the condition that the weight of the textile product containing the solution after de-liquoring is preferably 300 wt% or less, more preferably 150 to 250 wt%, particularly preferably 180 to 220 wt% based on the dry weight of the textile product.

[0038] 〔Method for producing recycled polyester〕 Another method for producing recycled polyester according to the present invention is a method for producing recycled polyester in which the polyester obtained by the above polyester recovery method is depolymerized with aromatic dicarboxylic acid bis(hydroxyalkyl), and then the aromatic dicarboxylic acid bis(hydroxyalkyl) is repolymerized.

[0039] By this method, a polyester having a small yellowness and a high whiteness can be obtained.

[0040] 〔Depolymerization〕 When depolymerizing, it is preferable to use a catalyst. As the catalyst, preferably a first transition metal-based catalyst is used. Specifically, examples include oxides, fatty acid salts, carbonates, sulfates, phosphates, oxides, hydroxides, halides, and alcoholates of the first transition metal-based.

[0041] As the first transition metal, manganese and zinc are preferably used. As the catalyst, manganese oxide, manganese acetate, zinc oxide, zinc acetate are preferably used, and manganese acetate is particularly preferably used. The catalyst may be used alone or in combination of two or more.

[0042] The catalyst is preferably used as a solution previously dissolved in an alkylene glycol. As the alkylene glycol (hereinafter sometimes abbreviated as AG), it is preferable to use the same diol as the diol component forming the skeletal structure of the polyester used in the textile product.

[0043] As the alkylene glycol, the diol constituting the polyester finally obtained by repolymerizing the intermediate aromatic dicarboxylic acid bis(hydroxyalkyl) may be used.

[0044] The same diol as the diol component forming the skeletal structure of the polyester is ethylene glycol (EG) when the polyester is polyethylene terephthalate (PET), 1,3-propanediol (trimethylene glycol, C3G) when it is polytrimethylene terephthalate, and 1,4-butanediol (C4G) when it is polybutylene terephthalate. The diol may be a mixture.

[0045] Generally, the depolymerized product of polyester often gradually has a higher degree of discoloration due to long-term storage etc., but those obtained by the recovery method and production method of the present invention are clearly less discolored. In particular, when a manganese-based catalyst is used during depolymerization, the discoloration is less.

[0046] 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% based on the polyester. Here, "mol%" indicates the ratio of the number of catalyst molecules to the structural units of the polyester. "mmol%" is 1 / 1000 times that. If the amount of catalyst used is less than the above range, the catalytic activity is not sufficient, and if it is more, the effect of suppressing discoloration decreases, which is not preferable. When using a manganese-based catalyst as the catalyst, depolymerization can be carried out with a small amount of catalyst.

[0047] During depolymerization, alkylene glycol is preferably used in an amount of 2 to 20 times, more preferably 3 to 10 times, the weight of the polyester after recovery treatment. By using a large amount of alkylene glycol during depolymerization in this way and then performing crystallization and solid-liquid separation, the amount of contamination of the depolymerization catalyst and other foreign substances can be reduced. In particular, when using manganese acetate as the catalyst, the solubility with alkylene glycol is high, and the amount of the catalyst remaining in the subsequent process can be reduced more effectively.

[0048] 〔Crystallization〕 After depolymerization using a catalyst, it is preferable to cool and crystallize in alkylene glycol. As the temperature reduction conditions during crystallization, it is preferably to reduce the temperature from a temperature of 60 °C or higher to 25 °C or lower, and more preferably to cool to 15 °C or lower.

[0049] Furthermore, it is preferable to perform solid-liquid separation after crystallization. The alkylene glycol content in the cake after solid-liquid separation is preferably 100 wt% or less, more preferably 55 wt% or less, further preferably 1 to 30 wt%, and particularly preferably 5 to 25 wt%.

[0050] After depolymerization, the cake is preferably washed with water or alkylene glycol after crystallization. The washing is preferably carried out by treating with a Nutsche filter while spraying the washing liquid. By performing these treatments, the depolymerization catalyst dissolved in the alkylene glycol and other coloring causative substances can be washed away, and a more highly purified aromatic dicarboxylic acid bis(hydroxyalkyl) can be obtained.

[0051] As the solution used for washing, a solution having a low viscosity is preferably used, and from this viewpoint, water is preferably used. The amount of the 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 preferably 0 to 40°C. If the liquid temperature is higher than this, the cake itself is likely to dissolve, resulting in a decrease in yield, which is not preferable.

[0052] After washing, aromatic dicarboxylic acid bis(hydroxyalkyl) can be obtained by drying with a vacuum dryer or the like.

[0053] For the obtained aromatic dicarboxylic acid bis(hydroxyalkyl), an adsorbent such as activated carbon may be used for adsorption treatment of foreign substances and the like.

[0054] 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 can be repolymerized without drying. This is a preferred embodiment.

[0055] 〔Aromatic dicarboxylic acid bis(hydroxyalkyl)〕 The aromatic dicarboxylic acid bis(hydroxyalkyl) thus obtained is used for the production of recycled polyester.

[0056] The aromatic dicarboxylic acid bis(hydroxyalkyl) varies depending on the polyester of the fiber product used and the alkylene glycol used for depolymerization.

[0057] When the polyester of the textile product is mainly made of polyester (polyalkylene terephthalate) using terephthalic acid as the polycarboxylic acid as a raw material, benzene dicarboxylic acid bis(hydroxyalkyl) (hereinafter, BHAT; sometimes referred to as bis-hydroxyalkyl terephthalate) can be obtained.

[0058] In this case, when C3G (1,3-propanediol (trimethylene glycol)) is used as the alkylene glycol for depolymerization, BHPT (bis-hydroxypropyl terephthalate) can be obtained. Also, when C4G (1,4-butanediol) is used as the alkylene glycol for depolymerization, BHBT (bis-hydroxybutyl terephthalate) can be obtained. Further, when ethylene glycol is used as the alkylene glycol for depolymerization, BHET (bis-hydroxyethyl terephthalate) can be obtained.

[0059] [Repolymerization] Aromatic dicarboxylic acid bis(hydroxyalkyl) becomes polyester by repolymerization by a conventionally known method. This polyester is a recycled polyester that is difficult to color and has excellent hue.

[0060] As a catalyst for repolymerization to obtain polyester, for example, known catalysts such as antimony-based, germanium-based or titanium-based catalysts can be used, and preferably antimony trioxide is used.

[0061] It is preferable to carry out the polycondensation reaction while flowing the alkylene glycol generated by the reaction outside the reactor during repolymerization. The amount of the catalyst used is preferably in the range of 10 to 1000 ppm with respect to the weight of the aromatic dicarboxylic acid bis(hydroxyalkyl).

[0062] After polycondensation using a catalyst, 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 with respect to the weight of the aromatic dicarboxylic acid bis(hydroxyalkyl).

[0063] The recycled polyester thus obtained has little discoloration such as yellowing. This effect is particularly remarkable when depolymerization is carried out using a manganese-based catalyst at a low concentration. It is considered that this is because coloring by-products are less likely to be generated, and the catalyst is easily dissociated from the aromatic dicarboxylic acid bis(hydroxyalkyl) even in subsequent processes such as crystallization, and is less likely to remain as an impurity.

[0064] 〔Properties of Recycled Polyester〕 In the recycled polyester obtained by the method for recovering the polyester of the present invention, the polyurethane component is removed. Further, when the fiber product is dyed, the dye is also removed.

[0065] The obtained recycled polyester preferably exhibits the following properties.

[0066] The obtained recycled polyester has an L value according to the International Commission on Illumination (CIE), * a * b * As the hue in a colorimeter in the a, b color space, the b value is 8 or less, preferably from 1 to -20, more preferably from 0.5 to -15. * The obtained recycled polyester has a yellowness index (YI) of preferably 15 or less, more preferably from 5 to -50, and even more preferably from 0 to -20.

[0067] The obtained recycled polyester has a whiteness (W) of 75 or more, more preferably from 80 to 100.

[0068] The obtained polyester has a whiteness (W) of 75 or more, more preferably from 80 to 100.

[0069] The nitrogen content derived from polyurethane or dye contained in the obtained recycled polyester is preferably 15 ppm or less, more preferably 10 ppm or less.

[0070] The recycled polyester after re - polymerization has an IV of the polymer preferably in the range of 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.

Examples

[0071] Hereinafter, the present invention will be described more specifically with reference to examples. Each value in the examples was determined by the following methods. “%owf” is an abbreviation of “% on the weight of fiber”.

[0072] 1) Hue (L * a * b * )(Col(Lab)) The re - polymerized polymer (5 g) was pressed between two metal plates to form a plate shape, and then heated at 140 °C for 2 hours to crystallize the sample. The sample for measurement was used with a measuring device (“ZE - 6000” manufactured by Nippon Denshoku Industries Co., Ltd.), and the values of hue L * , a * , b * were measured according to JIS Z8781 - 4:2013.

[0073] The yellowness index (YI) was determined by the following formula (1), and the whiteness (W) was determined by the following formula (2).

[0074] Yellowness index (YI): 0.34 - 71.7×a / L + 178.78×b / L (1) Whiteness (W): 100 - √{(100 - L) 2 +a 2 +b 2} (2) A higher value of the yellowness index (YI) indicates a stronger yellowish color, and a higher value of the whiteness (W) indicates a higher whiteness.

[0075] 2) Nitrogen (N) content The nitrogen content contained in fiber products such as fabrics and fibers was measured with a trace total nitrogen analyzer (TN - 110 manufactured by Mitsubishi Kasei Corporation).

[0076] 〔Example 1〕 (Polyester Recovery Process) As a textile product, a fabric composed of 360 g of dyed polyethylene terephthalate (hereinafter referred to as "PET") fibers and 40 g of polyurethane (hereinafter sometimes referred to as "PU") was prepared.

[0077] The PET fibers were yarns with IV 0.60 dl / g, Tg = 70 °C, Tm = 255 °C, 24 dtex, strength 3.9 cN / dtex, and elongation 41%. As disperse dyes, 0.87% owf of a nitrogen-containing orange dye, 0.4% owf of a nitrogen-containing red dye, and 4.7% owf of a nitrogen-containing black dye were used for dyeing, and the fiber contained 0.38 wt% of nitrogen (N). The PU fibers were polyether-based polyurethane fibers having high stretchability ("Lycra" manufactured by Asahi Kasei Fibers Corporation, 22 dtex / yarn, strength 1.6 cN / dtex, elongation 345%, 300%, elongation elastic modulus 82%, and containing 1.06 wt% of nitrogen (N)) were used.

[0078] 400 g of this textile product was put into a 5-l separable flask, and 4000 g of benzyl alcohol (BA) heated to an internal temperature of 105 °C in a separate beaker was additionally added. The mixture was stirred for 30 minutes while adjusting the internal temperature to 105 °C.

[0079] The fabric-like textile product was taken out from the separable flask and squeezed to remove the excess treatment liquid. The treatment liquid was colored, and the weight of the slightly decolorized textile product after squeezing was 970 g.

[0080] The textile product after squeezing was put back into the above separable flask again, and the steps of solution immersion and squeezing as described above were carried out a total of 6 times. Visually, the textile product was whitened by the third treatment, but even after the fourth treatment, the squeezed treatment liquid had some coloring, and finally, the treatment liquid became transparent at the sixth treatment.

[0081] The textile product after the above treatment was dried in a vacuum dryer at 80 °C for 8 hours to recover a white polyester with a high whiteness.

[0082] (Recycling Process of Polyester) To 300 parts by weight of the polyester recovered by the above method, 1500 parts by weight of ethylene glycol (EG) and 0.38 parts by weight of manganese acetate (100 mmol% based on the polyester) as a depolymerization catalyst were charged into a 2 L separable flask and sealed with nitrogen. At this time, manganese acetate was dissolved in EG in advance and then charged.

[0083] After that, the separable flask containing the sample was heated with a mantle heater to a set internal temperature of 220°C and stirred, and a depolymerization treatment was carried out at normal pressure for 4 hours. The BHET (bis(hydroxyethyl) benzene dicarboxylate) solution after this depolymerization was colorless and transparent, and no coloring was observed. Further, this solution after depolymerization was filtered through a 200 μm mesh to remove the solid content remaining inside. After gradually cooling to 70°C and then stirring and cooling, the temperature was decreased from 70°C to 40°C over a period of 0 minutes to 10 minutes, from 40°C to 30°C over a period of 10 minutes to 60 minutes, and from 30°C to 15°C over a period of 60 minutes to 180 minutes. Then, stirring was carried out for 60 minutes while maintaining the internal temperature at 15°C to lower the internal temperature and precipitate BHET crystals (for a total of 4 hours) to obtain a BHET / EG slurry.

[0084] The BHET / EG slurry was subjected to a pressing treatment with a filter press manufactured by Nippon Filter Co., Ltd. to perform solid-liquid separation of BHET and EG. At this time, the separated BHET contained 35 wt% of EG based on the cake weight recovered after the filter press. While spraying 2 weight times of pure water at 25°C on the cake after this EG separation, a water washing treatment was carried out with a Nutsche filter. Subsequently, the BHET with the solid-liquid separation completed was dried in a vacuum dryer at 50°C for 8 hours to obtain dried BHET. The obtained BHET was white and no foreign matter was observed.

[0085] Subsequently, 254 parts by weight of the obtained dried BHET was charged into a reaction vessel under normal pressure in a nitrogen atmosphere together with 0.007 parts by weight of a phosphorus-based stabilizer and 0.07 parts by weight of antimony trioxide as a repolymerization catalyst. Next, the temperature in the reactor was set to 285°C, and the pressure was gradually reduced step by step under the conditions of normal pressure for 10 minutes, 4 kPa for 10 minutes, and further 0.4 kPa for 40 minutes. While distilling off ethylene glycol and the like generated by the reaction outside the reactor, a polycondensation reaction was carried out to obtain a recycled polyester.

[0086] The Lab values of the dried product before and after the recovery treatment, the recycled polyester after repolymerization, and the physical properties such as the nitrogen content are shown in Table 1.

[0087] [Example 2] Recovery treatment and recycling treatment were carried out in the same manner as in Example 1, except that the treatment temperature of benzyl alcohol (BA) was raised from 105°C to 130°C. The color of the residual liquid after pressing in the recovery process was darker compared to Example 1, and precipitates considered to be PET dissolution products were confirmed in the residual liquid. The fiber product itself was a polyester fabric with a high whiteness. However, the weight of the treated and dried fiber product was 302 g, and the yield was slightly inferior.

[0088] The physical properties of the dried product before and after the recovery treatment and the recycled polyester after repolymerization are shown in Table 1.

[0089] [Example 3] Recovery treatment was carried out in the same manner as in Example 1, except that the treatment temperature of benzyl alcohol (BA) was raised from 105°C to 160°C. The color of the residual liquid after pressing in the recovery process was darker compared to Examples 1 and 2, and more precipitates considered to be PET dissolution products were confirmed in the residual liquid than in Example 2. The fiber product itself was a polyester fabric with a high whiteness. However, the weight of the treated and dried fiber product was 178 g, and since the yield was inferior, the recycling process was not carried out.

[0090] The physical properties of the dried product before and after the recovery treatment are also shown in Table 1.

[0091] [Example 4] Recovery and recycling processes were carried out in the same manner as in Example 1, except that an undyed white fabric was used.

[0092] The physical properties of the dried product before and after the recovery process and the recycled polyester after repolymerization are shown together in Table 1.

[0093]

Table 1

[0094] 〔Comparative Example 1〕 A recovery process was carried out in the same manner as in Example 1, except that the treatment temperature of benzyl alcohol (BA) was lowered from 105°C to 25°C. No coloring was observed in the textile product and the residual liquid after pressing in the recovery process. Also, no dissolution of PU occurred, and the textile product remained stretchable, and the weight of the treated and dried textile product did not change and was 400 g.

[0095] The physical properties of the dried product before and after the recovery process are shown in Table 2.

[0096] 〔Comparative Example 2〕 A recovery process was carried out in the same manner as in Example 1, except that the treatment temperature of benzyl alcohol (BA) was raised from 105°C to 205°C. During the treatment step at 205°C, the entire amount of the textile product containing PET was dissolved in BA, and the product after pressing could not be recovered.

[0097] The physical properties before the recovery process are shown together in Table 2.

[0098] 〔Comparative Example 3〕 A recovery process was carried out using a textile product containing the same PU fibers as in Example 1, except that undyed white fabric was used as in Example 4, benzyl alcohol (BA) in Example 1 was changed to ethylene glycol (EG), and the treatment temperature was raised from 105°C to 160°C.

[0099] It was confirmed that the PU changed color to brown during the recovery process, and that even at the stage when the sixth treatment was completed, most of the PU solid content remained. Table 2 shows the physical properties of the dried product before and after the recovery treatment and the recycled polyester after repolymerization.

[0100] 〔Comparative Example 4〕 A fiber product using the same dyed PET fibers as in Example 1 except that it did not contain PU fibers was used, and the benzyl alcohol (BA) in Example 1 was changed to ethylene glycol (EG). However, since there was no change in the fiber product and the squeezed liquid, the treatment temperature was raised from 105 °C to 160 °C to perform the recovery treatment.

[0101] Although the fiber product was slightly reduced in weight and the fabric was decolorized, coloring remained even at the stage when the sixth treatment was completed. Table 2 shows the physical properties of the dried product before and after the recovery treatment and the recycled polyester after repolymerization.

[0102]

Table 2

[0103] 〔Reference Example 1〕 A fiber product using the same dyed PET fibers as in Example 1 except that it did not contain PU fibers was used, and the recovery treatment and recycling treatment were performed in the same manner as in Example 1. The physical properties of the obtained recycled polyester were the same as those in Example 1.

[0104] Table 3 shows the physical properties of the dried product before and after the recovery treatment and the recycled polyester after repolymerization.

[0105] 〔Reference Example 2〕 A fiber product containing the same PU fibers as in Example 1 was used except that an undyed white fabric was used in the same manner as in Example 4, and the same recycling treatment as in Example 4 was performed except that the recovery process was omitted.

[0106] Table 3 shows the physical properties of the recycled polyester before and after the treatment and after repolymerization.

[0107] [Reference Example 3] A recycling process similar to Example 1 was carried out, except that a fiber product containing no PU fiber and only non-dyed PET fibers was used and the recovery process was omitted. The physical properties of the obtained recycled polyester were the same as those of Example 1.

[0108] The physical properties of the recycled polyester before treatment and after repolymerization are shown together in Table 3.

[0109] [Reference Example 4] A recycling process similar to Example 1 was carried out, except that a fiber product using the same dyed PET fibers as in Example 1 except for not containing PU fibers was used and the recovery process was omitted. The remaining nitrogen content was high and the color was yellowed.

[0110] The physical properties of the recycled polyester before treatment and after repolymerization are shown together in Table 3.

[0111]

Table 3

[0112] [Example 5] Recovery treatment and recycling treatment were carried out in the same manner as in Example 1, except that 1.5 g of manganese acetate was added to 4000 g of benzyl alcohol (BA). The weight of the fiber product after recovery treatment and further drying was 319 g. The yield was slightly inferior.

[0113] The physical properties of the recycled polyester before recovery treatment, the dried product after treatment, and after repolymerization are shown in Table 4.

[0114] [Example 6] BHET was obtained in the same manner as in Example 1. Then, the BHET was dissolved in 20 times its weight of hot water (90 °C), and 0.25 times the weight of activated carbon with respect to the BHET was added thereto. This was stirred for 1 hour. Then, Nutsche filtration was carried out to remove the activated carbon, and the temperature of the aqueous solution was lowered to precipitate BHET. Again, Nutsche filtration was carried out to recover BHET.

[0115] The recovered BHET was dried in a vacuum dryer under the conditions of 50 °C for 8 hours. The obtained dried BHET was whiter than that obtained in Example 1 and no foreign matter was found to be mixed in.

[0116] 254 parts by weight of the dried BHET was charged into a reaction vessel under normal pressure in a nitrogen atmosphere together with 0.007 parts by weight of a phosphorus-based stabilizer and 0.07 parts by weight of antimony trioxide as a repolymerization catalyst.

[0117] Next, the temperature in the reactor was set to 285 °C, and the pressure was gradually reduced step by step under the conditions of normal pressure for 10 minutes, 4 kPa for 10 minutes, and further 0.4 kPa for 40 minutes, while distilling off ethylene glycol and the like generated by the reaction outside the reactor to carry out a polycondensation reaction to obtain a recycled polyester.

[0118] Table 4 shows the Lab values and physical properties such as nitrogen content of the recycled polyester before the recovery treatment, the final dried product after the treatment, and after the repolymerization.

[0119] [Example 7] An undyed white fabric was used as the fiber product, and in the polyester recovery process, 1.5 g of manganese acetate was added to 4000 g of benzyl alcohol, and the treatment was carried out in the same process as in Example 1 except that the steps of solution immersion and pressing were only carried out once.

[0120] The physical properties of the recycled polyester before the recovery treatment, the dried product after the treatment, and after the repolymerization are also shown in Table 4.

[0121] [Table 4]

Industrial Applicability

[0122] The polyester recovered and the recycled polyester produced in the present invention can be suitably used for applications such as fibers, films, and resins.

Claims

1. Composed mainly of fibers made of polyester, An elastic fiber made of a polymer having a urethane group as a constituent and composed of a soft segment and a hard segment, contained in the form of any one of a single-component yarn, a blended fiber, a mixed fiber yarn, a covering yarn, or a composite yarn, A method for recovering polyester, characterized in that it is treated with a solution of an aromatic alcohol or its derivative in a temperature range of not lower than the glass transition temperature of the polyester and not higher than the glass transition temperature of the polyester + 100°C.

2. The method for recovering polyester according to Claim 1, wherein the fiber product is dyed with a disperse dye.

3. The method for recovering polyester according to Claim 1, wherein the polyester is polyethylene terephthalate.

4. The method for recovering polyester according to Claim 1, wherein the polymer having a urethane group as a constituent is a polyether-based polyurethane.

5. The method for recovering polyester according to Claim 1, wherein the aromatic alcohol is benzyl alcohol.

6. A method for producing recycled polyester, wherein the polyester obtained by the recovery method according to any one of Claims 1 to 5 is depolymerized with an aromatic dicarboxylic acid bis(hydroxyalkyl), and then the aromatic dicarboxylic acid bis(hydroxyalkyl) is repolymerized.

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