A method for recycling waste polyester-cotton blended fabric

Abstract

The present application belongs to the technical field of regenerated polyester, and particularly relates to a recycling method of waste polyester-cotton blended fabric, which comprises the following steps: firstly, decolorizing the colored waste polyester-cotton blended fabric by using a decolorizing agent; then, mixing a depolymerization agent, isosorbide dimethyl ether, a first catalyst and the decolorized polyester-cotton blended fabric to perform a depolymerization reaction, wherein the decolorizing agent and the depolymerization agent are one or more than one of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, and the temperature of the depolymerization reaction is 130-150 DEG C; washing and screening the separated cotton fibers to remove the surface residual polyester powder; firstly, converting terephthalate into DMT; then, performing a re-polymerization reaction of the DMT, ethylene glycol, a second catalyst and a functional additive to obtain regenerated polyethylene terephthalate. The present application ingeniously combines the depolymerization and polyester-cotton separation processes, thereby simplifying the operation steps, reducing the energy consumption, and improving the purity of the depolymerization product.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of regenerated polyester, and particularly relates to a recycling method of waste polyester-cotton blended fabric. BACKGROUND

[0002] With the rapid development of global textile industry, the total amount of waste textiles is growing exponentially, among which polyester (PET) and cotton blended fabric (polyester-cotton blended fabric) accounts for more than 60%. This kind of fabric is widely used in clothing, home textiles and industrial fields due to its good wear resistance, strong wrinkle resistance and low cost. However, it is difficult to efficiently separate and recycle after being discarded, which seriously threatens the ecological environment and human health.

[0003] Polyester is a petroleum-based synthetic fiber, and its production relies on non-renewable resources. Cotton fiber is a natural cellulose material, and its planting process consumes a large amount of water resources and pesticides. The abandonment of both means a huge waste of resources. In addition, each piece of polyester-cotton blended fabric contains 0.5-4.0wt.% of dyes and auxiliaries, which will affect the physical and chemical properties of the regenerated product, and seriously hinder the high-value utilization of waste textiles.

[0004] Currently, the methods for recycling cotton from polyester-cotton blended fabric mainly include selective dissolution and selective depolymerization. Selective dissolution can achieve polymer-to-polymer recovery by selectively dissolving one component in the blended fabric. For example, dimethyl sulfoxide (DMSO) and N,N-dimethylcyclohexylamine (DMCHA) can be used to dissolve polyethylene terephthalate (PET) and leach dyes, and cotton can be recovered by filtration. However, this method has a slow dissolution process and high energy consumption, and is only suitable for polyester-cotton blended fabric with low polyester content. In addition, cellulose solvents such as N-methylmorpholine-N-oxide (NMMO), ionic liquids and alkaline / urea solvents can be used to selectively dissolve the cotton component in polyester-cotton blended fabric. Some ionic liquids can dissolve cotton at 80-130℃, and then regenerated cotton fibers can be obtained by wet spinning. However, this treatment process may cause degradation of cellulose and change of crystal structure, which reduces the quality of regenerated cotton. In addition, the synthesis and recovery cost of ionic liquids is high, which limits its application in industrial scenarios.

[0005] Selective depolymerization is to selectively decompose polyester in polyester-cotton blended fabric into monomers. This method has fast separation speed and can produce monomers that can be used to produce regenerated polyester from waste textiles. However, traditional PET depolymerization requires high temperature and high pressure, which easily leads to carbonization of cotton fibers or reduction of monomer purity.

[0006] To address the above problems, a number of patent technologies have emerged. Chinese invention patent CN 119192672 A discloses a low-energy consumption rapid chemical separation method for polyester-cotton fiber products. The method prepares a betaine-based eutectic solvent by mixing a hydrogen bond donor and a hydrogen bond acceptor, and combines it with an alkali solution to form a eutectic solvent / alkali composite system. The polyester-cotton fiber product is dissolved in the composite system, and after the reaction is completed, the undissolved components are separated by filtration, and then washed with water and dried. This invention can dissolve the polyester fiber component under mild conditions in a short time, and has no damage to the cotton fiber component, with the advantages of low cost, green environmental protection, etc., realizing the rapid quantitative analysis of polyester and cotton fiber components. However, long-term contact of cotton fibers with alkaline environment may cause slow oxidation or reduction of crystallinity of cellulose molecular chain, affecting its retextile performance, and the cost of betaine is relatively high, which limits its further industrial application.

[0007] Chinese invention patent CN 117626468 A discloses a method for preparing regenerated fibers by separating and recycling waste polyester-cotton. In the preparation of regenerated fibers, the waste polyester-cotton fabric is placed in a eutectic solvent, and the cellulose is separated by ultrasonic treatment. Methyl acrylate is used for pretreatment and graft modification of cellulose, and under the action of photoinitiator benzophenone, the modified cellulose is combined with diethyl allyl phosphonate. In the blending process of polylactic acid and modified cellulose, the mechanical properties of the regenerated fibers after modification and blending treatment are significantly improved, and the regenerated fibers contain phosphorus-oxygen double bonds, which effectively enhance the flame retardant performance of the regenerated fibers. However, this method involves multiple ultrasonic treatment, centrifugation, vacuum filtration, drying, etc., resulting in a long overall process time and high energy consumption. In addition, this method uses N,N-dimethylformamide (DMF) as a spinning solvent, which is toxic and may pollute the environment.

[0008] Therefore, it is an important problem to be solved to ensure complete separation of all polyester-cotton mixed textiles without affecting the quality of cotton. SUMMARY

[0009] The purpose of the present application is to solve the problems existing in the prior art and provide a recycling method for waste polyester-cotton blended fabric.

[0010] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0011] The application discloses a recycling method of waste polyester-cotton blended fabric, which comprises the following steps: firstly, decolorizing the colored waste polyester-cotton blended fabric by using a decolorizing agent, and the decolorizing object is polyester and cotton fibers in the waste polyester-cotton blended fabric; and secondly, mixing a depolymerization agent, isosorbide dimethyl ether, a first catalyst and the decolorized polyester-cotton blended fabric to perform a depolymerization reaction, and the depolymerization object is polyester in the decolorized polyester-cotton blended fabric; wherein the decolorizing agent and the depolymerization agent are one or more of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; the mass of the isosorbide dimethyl ether accounts for 10-40 wt.% of the total mass of the depolymerization agent and the isosorbide dimethyl ether; and the temperature of the depolymerization reaction is 130-150 DEG C.

[0012] If the isosorbide dimethyl ether is not added, the temperature of the depolymerization reaction needs to be relatively high to ensure that the polyester is fully depolymerized, and at this temperature, the cotton fibers are easily carbonized or the high temperature easily causes thermal degradation reaction to introduce impurities; the application solves the problem by adding the isosorbide dimethyl ether, the isosorbide dimethyl ether and the depolymerization agent form a cosolvent, which can reduce the temperature of the depolymerization reaction under the premise of ensuring that the polyester is fully depolymerized; because the isosorbide dimethyl ether and the depolymerization agent form a cosolvent system, the solvent synergistic effect significantly improves the swelling ability of the solvent to the polyester (PET); the molecular structure of the isosorbide dimethyl ether contains an ether bond and a rigid cyclic structure, the polarity thereof is moderate, the solubility parameter of the isosorbide dimethyl ether is close to that of the PET, and the permeability of the solvent to the PET is enhanced, which promotes the swelling of the amorphous region and the crystalline region of the PET; the ether oxygen atom of the isosorbide dimethyl ether can form a weak hydrogen bond with the ester group of the PET, which reduces the interchain force of the PET, so that the crystalline structure of the PET can be destroyed at a relatively low temperature, and the ester bond is broken at a relatively low temperature; in addition, the introduction of the isosorbide dimethyl ether also reduces the viscosity of the reaction system, improves the flowability of the solvent, promotes the full contact of the PET and the depolymerization agent, avoids the situation that the local temperature is too high or the reaction is uneven, and thus the overall process temperature requirement is reduced; the decomposition initial temperature of the cotton fibers (cellulose) is about 220 DEG C, and the depolymerization of the PET usually needs to be above 160 DEG C when only the depolymerization agent is used; by adding the isosorbide dimethyl ether, the depolymerization temperature can be reduced to 130-160 DEG C, which is far lower than the natural cellulose thermal degradation threshold of the cotton fibers, and the carbonization or the generation of by-products such as furfural of the cotton fibers can be avoided.

[0013] As a preferred technical scheme,

[0014] The specific process of the method is as follows: firstly, under the protection of nitrogen or inert gas, the waste polyester-cotton blended fabric is put into the decolorizing agent to perform preliminary decolorization, and then solid-liquid separation is performed to obtain a decolorized polyester-cotton blended fabric semi-product and a decolorizing solution; then, under the protection of nitrogen or inert gas, the decolorized polyester-cotton blended fabric semi-product is put into the decolorizing agent to perform deep decolorization, and then solid-liquid separation is performed to obtain a decolorized polyester-cotton blended fabric and a decolorizing solution; finally, all the decolorizing solutions are recycled to obtain recycled decolorizing agent and dyes.

[0015] In the colored waste polyester-cotton blended fabric, the short-range interaction between the dye and polyester mainly depends on the van der Waals force and hydrogen bond; under the high temperature condition of 130-140 DEG C (the dyeing temperature of polyester), the dye will enter the amorphous region of polyester, which means that, if the decolorization of this kind of dyeing system is realized by physical method, the interaction between the decolorizing agent and the dye and polyester should be considered; in the physical decolorization process, when the polyester swells in the decolorizing agent, the internal pores of the polyester will be expanded, however, to realize the decolorization, the effective interaction between the dye molecules and the decolorizing agent should be generated, if the decolorizing agent cannot dissolve the dye and at the same time destroy the binding force between the dye and polyester, even if the polyester has swelled, the dye will still remain on the polyester; therefore, in the physical decolorization process, the swelling is a necessary prerequisite for decolorization, but not a sufficient condition; for example, toluene can make the polyester swell slightly, however, due to the low solubility of toluene to the dye and the destruction of the binding force between the dye and polyester, toluene is difficult to decolorize the colored waste polyester fabric.

[0016] The present inventors have carried out a large number of experiments and theoretical calculations, and after numerous attempts and analysis, the decolorizing agent used in the present application is determined, the solubility parameter of the decolorizing agent is very close to that of polyester, this characteristic enables the decolorizing agent to smoothly penetrate into the interior of the polyester fiber without dissolving the polyester, and to cause the polyester fiber to swell; the decolorizing agent can also dissolve the dye and at the same time destroy the binding force between the dye and polyester, so that the dye can be separated from the surface of the polyester fiber.

[0017] The above-mentioned method for recycling waste polyester-cotton blended fabric, in the preliminary decolorization, the bath ratio (the mass ratio of waste polyester-cotton blended fabric and decolorizing agent) is 1:10-70, the decolorization temperature is 110-140 DEG C, and the decolorization time is 10-40 min;

[0018] After the preliminary decolorization, the decolorization rate of the waste polyester-cotton blended fabric calculated according to the K / S value is more than 96%, the strength retention rate measured according to GB / T3923.1-2013 is more than 95%, and the whiteness measured according to GB / T17644-2008 is 60-80;

[0019] In the deep decolorization, the bath ratio (the mass ratio of the decolorized polyester-cotton blended fabric semi-finished product and the decolorizing agent) is 1:10-70, the decolorization temperature is 110-140 DEG C, and the decolorization time is 10-40 min;

[0020] After the deep decolorization, the decolorization rate of the waste polyester-cotton blended fabric calculated according to the K / S value is more than 98%, the strength retention rate measured according to GB / T3923.1-2013 is more than 90%, and the whiteness measured according to GB / T17644-2008 is 70-80;

[0021] The solid-liquid separation method includes one or more of normal pressure filtration, reduced pressure filtration (suction filtration), and centrifugal filtration.

[0022] The recovery treatment method includes one or more of distillation, reduced pressure distillation, rotary evaporation, and rectification, and the purity of the recovered decolorizing agent is 98-99.9%.

[0023] The recovery method of the waste polyester-cotton blended fabric as described above, the depolymerization reaction is carried out under the protection of nitrogen or inert gas, after the depolymerization reaction, the cotton fibers are separated out first, and then the depolymerization solution is separated and purified to obtain terephthalate.

[0024] The recovery method of the waste polyester-cotton blended fabric as described above, the depolymerization agent is the same as the decolorizing agent.

[0025] The recovery method of the waste polyester-cotton blended fabric as described above, the molar ratio of the depolymerization agent to the polyester component in the decolorized polyester-cotton blended fabric is 3-30:1, and the mass addition amount of the first catalyst is 0.1-5wt.% of the mass of the decolorized polyester-cotton blended fabric.

[0026] Since the depolymerization agent is the same as the decolorizing agent, the recovered decolorizing agent can be utilized as a component of the depolymerization agent, the proportion of the recovered decolorizing agent in the depolymerization agent is 50-90wt.%, the first catalyst is a mixture of zinc acetate and an alkaline catalyst, the content of zinc acetate in the first catalyst is 50-100wt.%, and the alkaline catalyst is one or more of potassium carbonate, sodium carbonate, sodium hydroxide, and potassium hydroxide, so that the first catalyst is designed to avoid decomposition of the depolymerization agent.

[0027] The time of the depolymerization reaction is 30-200min.

[0028] The steps of separating and purifying the depolymerization solution to obtain terephthalate are as follows:

[0029] (a) The depolymerization solution is subjected to reduced pressure devolatilization at 140-190°C, and the removed volatile components are collected, and the non-volatile components that are not removed contain isosorbide dimethyl ether, which can be separated from other substances by utilizing the property that isosorbide dimethyl ether is easily soluble in water.

[0030] (b) Centrifugal separation is carried out at 70-100°C to obtain a solid product.

[0031] (c) The solid product is treated to obtain terephthalate.

[0032] The depolymerization rate of the polyester in the decolorized polyester-cotton blended fabric (= the mass reduction value of the polyester in the decolorized polyester-cotton blended fabric after depolymerization / the mass of the polyester in the decolorized polyester-cotton blended fabric before depolymerization × 100%) is 90-100%.

[0033] In the depolymerization reaction, the depolymerization agent attacks the ester group in the polyester molecular chain through nucleophilic reaction, causing the polyester molecular chain to break, and at the same time, the depolymerization agent and the ethylene glycol generated by the breaking of the polyester molecular chain spontaneously form a cyclic ethylene carbonate, thereby promoting the depolymerization reaction balance to move forward, and finally obtaining terephthalate by efficient depolymerization; since the depolymerization agent is inert to the natural cellulose structure of cotton fibers, the crystalline morphology and mechanical properties of cotton fibers are completely preserved, and the original fabric form is basically maintained, which realizes the rapid depolymerization of polyester and the effective separation of polyester-cotton fibers.

[0034] The method for recycling waste polyester-cotton blended fabric as described above further comprises washing and screening the separated cotton fibers to remove the surface residual polyester powder; the conversion rate of the cotton fibers is 98-100%.

[0035] The method for recycling waste polyester-cotton blended fabric as described above further comprises the step of converting terephthalate into DMT (if terephthalate itself is DMT, no conversion is needed), and then performing a re-polymerization reaction on the DMT, ethylene glycol, a second catalyst (tetrabutyl titanate, ethylene glycol antimony, antimony acetate, antimony trioxide, acetate or alcoholate of manganese, sodium, cobalt, zinc, magnesium, and potassium), and a functional additive (trimethyl phosphate, triphenyl phosphate, trimethyl phosphite, antioxidant 1010, titanium dioxide) to obtain regenerated polyethylene terephthalate (regenerated PET), and the conversion method is as follows: terephthalate, methanol, and sodium hydroxide (catalyst) are mixed, heated to 60 DEG C under nitrogen protection, and reacted for 3h, then heating is stopped, and after cooling to room temperature, methanol is used for washing, and the mass ratio of terephthalate, methanol, and sodium hydroxide is 1:5:0.01.

[0036] The method for recycling waste polyester-cotton blended fabric as described above, the cotton content in the waste polyester-cotton blended fabric is not more than 30wt.%.

[0037] Beneficial effects:

[0038] The decolorizing agent used in the application has excellent solubility, and its solubility parameter is similar to that of polyester, which can efficiently remove dyes and additives in waste polyester-cotton blended fabric under mild conditions, while avoiding damage to the fiber structure.

[0039] The decolorizing agent used in the application has a low boiling point, all below 130 DEG C, especially the boiling point of dimethyl carbonate is only 90 DEG C, compared with traditional high-boiling-point decolorizing agents, such as dimethyl sulfoxide with a boiling point of 189 DEG C, the distillation recovery temperature of the decolorizing agent of the application is reduced by more than 40%, and the energy consumption is reduced by about 35%. At the same time, the decolorizing agent of the application also has low toxicity and high volatility, which greatly reduces the residue in the regenerated material, not only reduces the environmental and health risks, but also improves the quality and application performance of the regenerated material, which meets the development direction of green chemistry.

[0040] The decoloring agent and the depolymerization agent used in the whole process are the same, and the decoloring agent can efficiently remove the dyes in the waste polyester-cotton blended fabric in the decoloring stage; then the decoloring agent is recycled and reused as a depolymerization agent in the depolymerization stage to participate in the ester exchange reaction to generate high-purity depolymerization monomers. The process realizes efficient cooperation of decoloring and depolymerization, simplifies the overall process flow, improves the production efficiency, and the efficient recovery of the decoloring agent significantly reduces its loss and environmental pollution, providing a more economical and efficient solution for the industrialized closed-loop recycling of waste polyester-cotton blended fabric.

[0041] The present application utilizes the synergistic effect of depolymerization agent and isosorbide dimethyl ether to achieve efficient depolymerization of polyester in waste polyester-cotton blended fabric at a relatively low depolymerization temperature, while ensuring the integrity of cotton fibers. This method cleverly combines depolymerization and polyester-cotton separation processes, not only simplifying the operation steps and reducing energy consumption, but also improving the purity of the depolymerization product. The regenerated polyester monomers obtained by depolymerization can be directly applied to polyester synthesis, and the cotton fibers do not need to be treated again and can be directly reused for spinning. The present application has effectively opened up the whole chain closed-loop path of "decoloring-separation-repolymerization" for waste polyester-cotton blended fabric, providing a new innovative idea for the green transformation of the textile industry. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The process flow chart for the recycling method of waste polyester-cotton blended fabric of the present application;

[0043] Figure 2 The scanning electron microscope images of waste polyester-cotton blended fabric before and after depolymerization in Example 1, wherein (a) is the scanning electron microscope image before depolymerization, and (b) is the scanning electron microscope image after depolymerization;

[0044] Figure 3 The infrared spectrum of waste polyester-cotton blended fabric before and after depolymerization in Example 1;

[0045] Figure 4 The nuclear magnetic resonance hydrogen spectrum of terephthalate obtained after depolymerization of waste polyester-cotton blended fabric in Example 1;

[0046] Figure 5 The infrared spectrum of terephthalate obtained after depolymerization of waste polyester-cotton blended fabric in Example 1;

[0047] Figure 6 The decoloring agent and the dye recovered in Example 1, wherein (a) is the decoloring agent, and (b) is the dye. DETAILED DESCRIPTION

[0048] The application will be further described below with reference to the specific embodiments. It should be understood that these embodiments are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the application after reading the content of the application, and these equivalent forms also fall within the scope defined by the appended claims.

[0049] The detection method of the relevant performance indicators in the following examples is as follows:

[0050] Decolorization rate: The calculation of the decolorization rate is based on the K / S value, and the K / S value is obtained by the following steps: first, a calibrated desktop spectrophotometer (model S81 of Tianjin Trust Science and Technology Co., Ltd.) is used for measurement; the test conditions are set as D65 light source, 10° viewing angle, reflection mode UV400 cutoff and φ18; in order to ensure that the fabric sample is not transparent during color measurement, the fabric sample to be measured needs to be folded twice; the fabric sample to be measured is measured five times and the average value is taken; the fabric decolorization rate is calculated according to the following formula:

[0051] ;

[0052] In the formula, is the K / S value of the fabric before decolorization, is the K / S value of the fabric after decolorization.

[0053] Strength retention rate: YG 026B electronic fabric strength tester is used to test according to the standard of GB / T 3923.1-2013 “Textiles - Determination of tensile properties of fabrics - Part 1: determination of breaking force and elongation at break (strip method)”, and the strength retention rate of the fabric is calculated according to the following formula:

[0054] 00%;

[0055] In the formula, is the breaking strength of the textile before decolorization, is the breaking strength of the textile after decolorization.

[0056] Whiteness: the L * , a * , b * values (L * , a * , b * belong to the L * a * b * index system, L * is the lightness index, a * and b * are the chroma indexes) of the fabric sample are obtained by using the S81 desktop spectrophotometer of Tianjin Trust Science and Technology Co., Ltd., and the whiteness of the fabric is calculated according to the following formula:

[0057] .

[0058] W = whiteness;

[0059] Each fabric sample was measured 5 times and the average was taken.

[0060] Conversion rate of terephthalate:

[0061] Conversion rate of terephthalate (%) = 100 x (m x M) / W ;

[0062] wherein, m = mass of collected dimethyl terephthalate (g), M = molar mass of collected terephthalate (g / mol), W = mass of polyester in the used polyester-cotton blended fabric (g), M = molar mass of the repeating unit of polyethylene terephthalate (g / mol) = 192 g / mol).

[0063] Purity of terephthalate: The purity of the collected dimethyl terephthalate was quantitatively analyzed using a GC-2010 Pro gas chromatograph produced by Shimadzu Corporation, equipped with a hydrogen flame ionization detector (FID) and a chromatographic data processing workstation, and the purity was fitted using the internal standard method. The dimethyl terephthalate content was determined using the internal standard curve method, using dipropyl phthalate as the internal standard substance, chloroform as the solvent, and the peak area for quantification. The test conditions were as follows: high-purity nitrogen (≥99.95%) as the carrier gas, a split ratio of 15:1, a chromatographic injection port temperature of 280°C, a column temperature of 60°C, a total flow rate of 3.7 mL / min, and a chromatographic column flow rate of 0.7 mL / min.

[0064] Oligomer content of terephthalate: The purity and oligomer content of the collected terephthalate were qualitatively and quantitatively analyzed using an LC-16 high-performance liquid chromatograph (HPLC) equipped with a WondaSil C18-WR (200 mm, packed particle size 5 μm) chromatographic column and a UV detector from Shimadzu Corporation, with a detection wavelength of 254 nm and a detection temperature of 40°C. A binary gradient test method was used, with methanol and water (3:1, V / V) as the mobile phases, a flow rate of 0.8 mL / min, and the purity was fitted using the external standard method.

[0065] Conversion rate of cotton fiber:

[0066] Conversion rate of cotton fiber (%) = 100 x (m x M) / W ;

[0067] wherein, The mass (g) of the collected cotton fibers. The mass (g) of the collected cotton fibers.

[0068] The colored waste polyester-cotton blended fabric used in the present application has a washing color fastness of at least 4-5 levels, which is prepared by two methods: first blending and then dyeing, and first dyeing and then blending.

[0069] First blending and then dyeing is to blend polyester staple fiber and cotton fiber into yarn or fabric according to the proportion, and then dye (using two-bath method or one-bath two-step method).

[0070] First dyeing and then blending is to dye polyester fiber and cotton fiber respectively, and then blend the two colored fibers according to the proportion to spin yarn and weave into cloth.

[0071] The polyester component is dyed by high-temperature and high-pressure dyeing method, carrier dyeing method, hot melt dyeing method or normal pressure high-temperature dyeing method using disperse dyes (azo disperse dyes, anthraquinone disperse dyes, heterocyclic disperse dyes, etc.), or dyed by immersion, fixation and other processes using cationic dyes, or dyed by acid dyeing, fixation and other processes using acid dyes, or dyed by reduction, oxidation, soaping and other processes using vat dyes; the cotton component is dyed by immersion, adsorption, fixation, soaping, washing, drying and other processes using direct dyes, reactive dyes, cationic dyes, vat dyes, etc.

[0072] Since disperse dyes are common dyes for dyeing polyester, and reactive dyes are common dyes for dyeing cotton, the following examples of the present application are described only by taking colored waste polyester-cotton blended fabric dyed by disperse dyes and reactive dyes as examples.

[0073] Example 1

[0074] A recycling method of waste polyester-cotton blended fabric, the process flow is as shown in Figure 1 The specific steps are as follows:

[0075] (1) Material preparation:

[0076] Colored waste polyester-cotton blended fabric: the dyes used are disperse green 9 (azo disperse dyes) and reactive green 19 (reactive dyes), and the cotton content is 5wt.%;

[0077] Decolorizing agent: dimethyl carbonate;

[0078] Depolymerization agent: dimethyl carbonate;

[0079] Isosorbide dimethyl ether;

[0080] First catalyst: zinc acetate;

[0081] Methanol;

[0082] Ethylene glycol;

[0083] Second catalyst: zinc acetate, tetrabutyl titanate;

[0084] Functional additives: Trimethyl phosphate, antioxidant 1010;

[0085] (2) Decolorization:

[0086] (2.1) Under the protection of nitrogen or inert gas, waste polyester-cotton blended fabric is placed in a decolorizing agent for preliminary decolorization and then solid-liquid separation is performed to obtain decolorized polyester-cotton blended fabric semi-finished product and decolorization solution.

[0087] During the initial decolorization, the liquor ratio was 1:70, the decolorization temperature was 140℃, and the decolorization time was 40 minutes.

[0088] After initial decolorization, the decolorization rate of waste polyester-cotton blended fabrics was 98%, the strength retention rate was 99%, and the whiteness was 80.

[0089] (2.2) Under the protection of nitrogen or inert gas, the decolorized polyester-cotton blended fabric semi-finished product is placed in a decolorizing agent for deep decolorization and then solid-liquid separation is performed to obtain the decolorized polyester-cotton blended fabric and the decolorization solution.

[0090] For deep decolorization, the liquor ratio is 1:10, the decolorization temperature is 110℃, and the decolorization time is 40min.

[0091] After deep decolorization, the decolorization rate of waste polyester-cotton blended fabrics is 99%, the strength retention rate is 96%, and the whiteness is 80.

[0092] Finally, all the decolorizing solutions from steps (2.1) and (2.2) need to be recovered by distillation to obtain the recovered decolorizing agent and dye (see physical image). Figure 6 As shown), the specific operating conditions are as follows: under normal pressure, the temperature is controlled at 90-95℃ to ensure that the decolorizing agent is fully evaporated until the volume of the distillate reaches more than 95% of the theoretical recovery amount;

[0093] (3) Depolymerization:

[0094] The depolymerizing agent, isosorbide dimethyl ether, first catalyst, and decolorized polyester-cotton blended fabric were mixed and subjected to a depolymerization reaction at 150°C for 180 min (under nitrogen or inert gas protection). After the depolymerization reaction, the cotton fibers were separated first, and then the depolymerization solution was subjected to vacuum devolatilization at 140°C, followed by centrifugation at 70°C to obtain a solid product. The solid product was mixed with methanol at a mass ratio of 1:10 and stirred at 60°C for 30 min. Impurities were selectively removed by dissolution-recrystallization, and finally terephthalic acid ester (DMT) was obtained by solid-liquid separation.

[0095] The recovered decolorizing agent can be used as a component of the depolymerization agent due to the depolymerization agent and the decolorizing agent, the proportion of the recovered decolorizing agent in the depolymerization agent is 50 wt.%, the mass of isosorbide dimethyl ether is 40 wt.% of the total mass of the depolymerization agent and isosorbide dimethyl ether, the molar ratio of the depolymerization agent to the polyester component in the decolorized polyester-cotton blended fabric is 30:1, and the mass of the first catalyst is 5 wt.% of the mass of the decolorized polyester-cotton blended fabric;

[0096] The depolymerization rate of the polyester in the decolorized polyester-cotton blended fabric is 100%, the conversion rate of terephthalate is 100%, the purity of terephthalate is 99.9%, and the oligomer content of terephthalate is 0.01 wt.%;

[0097] The nuclear magnetic resonance hydrogen spectrum and the infrared spectrum of the terephthalate obtained by separation and purification in this step are shown in Figure 4 , and Figure 5 It can be seen from Figure 4 that the chemical shifts and integral areas of the peaks are consistent with the theoretical values of terephthalate; wherein the chemical shift 8.11 ppm corresponds to the hydrogen proton peak on the benzene ring, and the chemical shift 4.02 ppm corresponds to the methyl hydrogen proton peak directly connected to the ester group; by calculation, the area ratio of the two peaks (benzene ring hydrogen and methyl hydrogen) is 0.67 (4.00 / 6.00≈0.67), which indicates that the depolymerization reaction product is terephthalate, and the purity is high;

[0098] (4) Other treatments:

[0099] The separated cotton fibers are washed with water and screened to remove the surface residual polyester powder; the conversion rate of the cotton fibers is 100%;

[0100] DMT, ethylene glycol, a second catalyst, and a functional additive are subjected to a re-polymerization reaction to obtain regenerated polyethylene terephthalate, and the specific steps are as follows:

[0101] DMT, ethylene glycol, zinc acetate, and functional additives (trimethyl phosphate and antioxidant 1010) are uniformly mixed to form a reaction system A, the temperature of the reaction system A is slowly increased to 220°C at a heating rate of 30°C / h for ester exchange reaction, and methanol is collected; when the methanol out rate reaches 98% (the methanol out rate = actual methanol molar number / theoretical methanol molar number × 100%, the actual methanol molar number is the collected methanol molar number, and the theoretical methanol molar number is 2 times the molar number of DMT), the ester exchange reaction is completed, and bis-hydroxyethyl terephthalate is prepared; then, the prepared bis-hydroxyethyl terephthalate and tetrabutyl titanate are uniformly mixed to form a reaction system B, the temperature of the reaction system B is slowly increased to 270°C at a heating rate of 30°C / h, the pressure of the reaction system B is gradually increased to 15 Pa by vacuumizing, and the polycondensation reaction is performed for 180 min to obtain regenerated polyethylene terephthalate;

[0102] The mass ratio of DMT, ethylene glycol, zinc acetate, tetrabutyl titanate, trimethyl phosphate, and antioxidant 1010 is 1:0.6:0.05:0.05:0.05:0.05;

[0103] The microstructure of the waste polyester-cotton blended fabric before and after depolymerization in this embodiment is as follows: Figure 2 As shown, the infrared spectra before and after depolymerization are as follows: Figure 3 As shown; by Figure 3 It can be seen that after disaggregation, it is approximately 1710cm. -1 The strong absorption peak at 3300-3600 cm⁻¹ disappears, while the peak at approximately 3300-3600 cm⁻¹... -1 The broad peak at that location is approximately 1100cm. -1 The strong absorption peak at approximately 2900 cm⁻¹ -1 The absorption peak at that location still exists, and there are no other impurity peaks interfering, indicating that the polyester has been completely depolymerized, leaving only cotton fibers after depolymerization, and the chemical structure of the cotton fibers has not been destroyed; at the same time, from Figure 2 It can be seen that after depolymerization, the microstructure of cotton fibers is basically the same as that of the original fabric, and the fabric shape is still maintained. This comparison of microstructure further confirms that the waste polyester-cotton blended fabric recycling method proposed in this invention can efficiently depolymerize polyester while perfectly preserving the fabric shape of cotton fibers, laying a structural foundation for the subsequent separation and reuse of cotton fibers.

[0104] Comparative Example 1

[0105] A method for recycling waste polyester-cotton blended fabrics is basically the same as in Example 1, except that isosorbide dimethyl ether is not used.

[0106] In the decolorized polyester-cotton blended fabric, the depolymerization rate of polyester was 70%, which was much lower than 100% in Example 1. The conversion rate of terephthalate was 65%, the purity of terephthalate was 89%, and the oligomer content of terephthalate was 10 wt.

[0107] The comparison shows that without the addition of isosorbide dimethyl ether, even when the same depolymerization temperature and time are maintained, the depolymerization rate of polyester will be significantly reduced. Some polyester will not be completely decomposed into monomers, resulting in unreacted oligomer impurities and byproducts mixed in the product. These factors work together to make subsequent polyester-cotton separation difficult.

[0108] Example 2

[0109] A method for recycling waste polyester-cotton blended fabrics, the specific steps of which are as follows:

[0110] (1) Material preparation:

[0111] Colored waste polyester-cotton blended fabric: the dyes used are disperse yellow 3 (azo disperse dye) and reactive yellow M-3RE (reactive dye), and the cotton content is 8 wt.%;

[0112] Decolorizing agent: a mixture of dimethyl carbonate and diethyl carbonate in a molar ratio of 2:1;

[0113] Depolymerizing agent: a mixture of dimethyl carbonate and diethyl carbonate in a molar ratio of 2:1;

[0114] Isosorbide dimethyl ether;

[0115] First catalyst: a mixture of zinc acetate and a basic catalyst, wherein the content of zinc acetate is 90 wt.%, and the basic catalyst is sodium carbonate;

[0116] Methanol;

[0117] Sodium hydroxide;

[0118] Ethylene glycol;

[0119] Second catalyst: manganese acetate and antimony ethylene glycol;

[0120] Functional auxiliary agent: triphenyl phosphate and antioxidant 1010;

[0121] (2) Decolorization:

[0122] (2.1) Under the protection of nitrogen or inert gas, the waste polyester-cotton blended fabric is placed in the decolorizing agent for preliminary decolorization, and then solid-liquid separation is performed to obtain a decolorized polyester-cotton blended fabric semi-product and a decolorizing solution;

[0123] Wherein, during the preliminary decolorization, the bath ratio is 1:60, the decolorization temperature is 130℃, and the decolorization time is 30 min;

[0124] After preliminary decolorization, the decolorization rate of the waste polyester-cotton blended fabric is 98%, the strength retention rate is 98%, and the whiteness is 80;

[0125] (2.2) Under the protection of nitrogen or inert gas, the decolorized polyester-cotton blended fabric semi-product is placed in the decolorizing agent for deep decolorization, and then solid-liquid separation is performed to obtain a decolorized polyester-cotton blended fabric and a decolorizing solution;

[0126] Wherein, during the deep decolorization, the bath ratio is 1:20, the decolorization temperature is 110℃, and the decolorization time is 30 min;

[0127] After deep decolorization, the decolorization rate of the waste polyester-cotton blended fabric is 99%, the strength retention rate is 95%, and the whiteness is 80;

[0128] Finally, all the decolorizing solutions in steps (2.1) and (2.2) need to be recovered by distillation to obtain the recovered decolorizing agent and dyes. The specific operation conditions are as follows: under normal pressure, the temperature is controlled at 130-135°C to ensure that the decolorizing agent is fully evaporated until the volume of the distillate reaches more than 95% of the theoretical recovery amount;

[0129] (3) Depolymerization:

[0130] After mixing the depolymerization agent, isosorbide dimethyl ether, the first catalyst, and the decolorized polyester-cotton blended fabric, the depolymerization reaction is carried out at 145°C for 200 min under nitrogen or inert gas protection. After the depolymerization reaction, the cotton fibers are first separated, and then the depolymerization solution is subjected to vacuum devolatilization at 160°C, followed by centrifugal separation at 90°C to obtain a solid product. The solid product, methanol, and sodium hydroxide are mixed in a mass ratio of 1:5:0.01, and then reacted at 65°C for 3 h under nitrogen protection to prepare an ester exchange solution. The ester exchange solution is cooled to 25°C to precipitate solids. After filtration and methanol washing, terephthalate ester is obtained.

[0131] Among them, since the depolymerization agent is the same as the decolorizing agent, the recovered decolorizing agent can be used as a component of the depolymerization agent. The proportion of the recovered decolorizing agent in the depolymerization agent is 50wt.%. The mass of isosorbide dimethyl ether is 30wt.% of the total mass of the depolymerization agent and isosorbide dimethyl ether. The molar ratio of the depolymerization agent to the polyester component in the decolorized polyester-cotton blended fabric is 25:1. The mass of the first catalyst added is 3.5wt.% of the mass of the decolorized polyester-cotton blended fabric.

[0132] The depolymerization rate of polyester in the decolorized polyester-cotton blended fabric is 100%.

[0133] (4) Other treatments:

[0134] The separated cotton fibers are washed with water and screened to remove the surface residual polyester powder. The conversion rate of the cotton fibers is 100%.

[0135] First, the terephthalate ester is converted into DMT. Then, DMT, ethylene glycol, a second catalyst, and a functional additive are subjected to a repolymerization reaction to obtain regenerated polyethylene terephthalate. The specific steps are as follows:

[0136] The DMT, ethylene glycol, manganese acetate, functional additives (triphenyl phosphate, antioxidant 1010) are mixed uniformly to form a reaction system A, the temperature of the reaction system A is slowly increased to 220℃ at a heating rate of 30℃ / h for ester exchange reaction, methanol is collected, when the methanol out rate reaches 98% (methanol out rate = actual out alcohol amount / theoretical out alcohol amount x 100%, the actual out alcohol amount is the molar number of the collected methanol, and the theoretical out alcohol amount is the molar number of DMT x 2), the ester exchange is completed, and bis-hydroxyethyl terephthalate is prepared; then the prepared bis-hydroxyethyl terephthalate and antimony glycol are mixed uniformly to form a reaction system B, the temperature of the reaction system B is slowly increased to 270℃ at a heating rate of 30℃ / h, the pressure of the reaction system B is gradually increased to 15Pa by vacuumizing, and the polycondensation reaction is carried out for 180min to obtain regenerated polyethylene terephthalate;

[0137] The mass ratio of DMT, ethylene glycol, manganese acetate, antimony glycol, triphenyl phosphate, antioxidant 1010 is 1:0.6:0.05:0.05:0.05:0.05.

[0138] Example 3

[0139] A recycling method of waste polyester-cotton blended fabric, the process flow is as shown in Figure 1 The specific steps are as follows:

[0140] (1) Material preparation:

[0141] Colored waste polyester-cotton blended fabric: the used dyes are disperse blue 183 (azo disperse dye) and reactive blue 19 (reactive dye), and the cotton content is 10wt.%;

[0142] Decolorizing agent: a mixture of dimethyl carbonate and methyl ethyl carbonate with a molar ratio of 1:1;

[0143] Depolymerization agent: a mixture of dimethyl carbonate and methyl ethyl carbonate with a molar ratio of 1:1;

[0144] Isosorbide dimethyl ether;

[0145] First catalyst: a mixture of zinc acetate and alkaline catalyst, wherein the content of zinc acetate is 80wt.%, and the alkaline catalyst is sodium hydroxide;

[0146] Methanol;

[0147] Sodium hydroxide;

[0148] Ethylene glycol;

[0149] Second catalyst: zinc acetate and antimony trioxide;

[0150] Functional additives: trimethyl phosphate and antioxidant 1010;

[0151] (2) decolorization:

[0152] (2.1) under the protection of nitrogen or inert gas, the waste polyester-cotton blended fabric is put into the decolorizing agent for preliminary decolorization, and then solid-liquid separation is performed to obtain a decolorized polyester-cotton blended fabric semi-product and a decolorizing solution;

[0153] wherein, during the preliminary decolorization, the bath ratio is 1:50, the decolorization temperature is 130°C, and the decolorization time is 25 min;

[0154] After the preliminary decolorization, the decolorization rate of the waste polyester-cotton blended fabric is 98%, the strength retention rate is 98%, and the whiteness is 80;

[0155] (2.2) under the protection of nitrogen or inert gas, the decolorized polyester-cotton blended fabric semi-product is put into the decolorizing agent for deep decolorization, and then solid-liquid separation is performed to obtain a decolorized polyester-cotton blended fabric and a decolorizing solution;

[0156] wherein, during the deep decolorization, the bath ratio is 1:30, the decolorization temperature is 120°C, and the decolorization time is 30 min;

[0157] After the deep decolorization, the decolorization rate of the waste polyester-cotton blended fabric is 99%, the strength retention rate is 95%, and the whiteness is 80;

[0158] Finally, all the decolorizing solutions in steps (2.1) and (2.2) are subjected to recovery treatment by the method of reduced pressure distillation to obtain recovered decolorizing agent and dyes, and the specific operation conditions are as follows: under the condition of reduced pressure, the temperature is controlled at 70-80°C to ensure that the decolorizing agent is fully evaporated until the volume of the distillate reaches more than 95% of the theoretical recovery amount;

[0159] (3) depolymerization:

[0160] After the decolorizing agent, isosorbide dimethyl ether, the first catalyst and the decolorized polyester-cotton blended fabric are mixed, the depolymerization reaction is carried out at 140°C for 120 min (under the protection of nitrogen or inert gas), after the depolymerization reaction, the cotton fibers are first separated out, then the depolymerization solution is subjected to reduced pressure devolatilization at 180°C, and then centrifugal separation is carried out at 100°C to obtain a solid product, the solid product, methanol and sodium hydroxide are mixed in a mass ratio of 1:5:0.01, and then ester exchange liquid is prepared by reacting at 65°C for 3 h (under the protection of nitrogen), the ester exchange liquid is cooled to 25°C to precipitate a solid, and then the solid is obtained by filtration and methanol washing to obtain terephthalate ester;

[0161] The recovered decoloring agent can be used as a component of the depolymerization agent due to the depolymerization agent and the decoloring agent, the proportion of the recovered decoloring agent in the depolymerization agent is 60 wt.%, the mass of isosorbide dimethyl ether is 25 wt.% of the total mass of the depolymerization agent and isosorbide dimethyl ether, the molar ratio of the depolymerization agent to the polyester component in the decoloring polyester-cotton blended fabric is 20:1, and the mass of the first catalyst is 2 wt.% of the mass of the decoloring polyester-cotton blended fabric.

[0162] The depolymerization rate of the polyester in the decoloring polyester-cotton blended fabric is 99%.

[0163] (4) Other treatments:

[0164] The separated cotton fibers are washed and screened to remove the surface residual polyester powder, and the conversion rate of the cotton fibers is 99%.

[0165] First, the terephthalate is converted into DMT, and then the DMT, ethylene glycol, a second catalyst and a functional additive are subjected to a re-polymerization reaction to obtain regenerated polyethylene terephthalate, and the specific steps are as follows:

[0166] DMT, ethylene glycol, zinc acetate, and functional additives (trimethyl phosphate and antioxidant 1010) are uniformly mixed to form a reaction system A, the temperature of the reaction system A is slowly raised to 220℃ at a heating rate of 30℃ / h for ester exchange reaction, and methanol is collected, and when the methanol out rate reaches 98% (methanol out rate = actual out alcohol amount / theoretical out alcohol amount x 100%, actual out alcohol amount is the number of moles of collected methanol, and theoretical out alcohol amount is the number of moles of DMT x 2), the ester exchange is completed, and bis-hydroxyethyl terephthalate is prepared; then the prepared bis-hydroxyethyl terephthalate and antimony trioxide are uniformly mixed to form a reaction system B, the temperature of the reaction system B is slowly raised to 270℃ at a heating rate of 30℃ / h, the pressure of the reaction system B is gradually raised to 15 Pa by vacuumizing, and the condensation reaction is carried out for 180 min to obtain regenerated polyethylene terephthalate;

[0167] The mass ratio of DMT, ethylene glycol, zinc acetate, antimony trioxide, trimethyl phosphate and antioxidant 1010 is 1:0.6:0.05:0.05:0.05:0.05.

[0168] Example 4

[0169] A method for recycling waste polyester-cotton blended fabric, and the specific steps are as follows:

[0170] (1) Material preparation:

[0171] Colored waste polyester-cotton blended fabric: the dyes used are disperse red 60 (anthraquinone disperse dye) and reactive red 195 (reactive dye), and the cotton content is 15 wt.%.

[0172] Decoloring agent: methyl ethyl carbonate;

[0173] Depolymerization agent: methyl ethyl carbonate;

[0174] Isosorbide dimethyl ether;

[0175] First catalyst: a mixture of zinc acetate and basic catalyst, wherein the content of zinc acetate is 70wt.%, and the basic catalyst is potassium hydroxide;

[0176] Methanol;

[0177] Sodium hydroxide;

[0178] Ethylene glycol;

[0179] Second catalyst: manganese acetate, tetrabutyl titanate;

[0180] Functional auxiliary agent: triphenyl phosphate, antioxidant 1010;

[0181] (2) Decolorization:

[0182] (2.1) Under the protection of nitrogen or inert gas, the waste polyester-cotton blended fabric is put into the decoloring agent for preliminary decolorization, and then solid-liquid separation is carried out to obtain a decolorized polyester-cotton blended fabric semi-product and a decoloring solution;

[0183] Wherein, during the preliminary decolorization, the bath ratio is 1:40, the decolorization temperature is 120℃, and the decolorization time is 20min;

[0184] After preliminary decolorization, the decolorization rate of the waste polyester-cotton blended fabric is 97%, the strength retention rate is 97%, and the whiteness is 75;

[0185] (2.2) Under the protection of nitrogen or inert gas, the decolorized polyester-cotton blended fabric semi-product is put into the decoloring agent for deep decolorization, and then solid-liquid separation is carried out to obtain a decolorized polyester-cotton blended fabric and a decoloring solution;

[0186] Wherein, during the deep decolorization, the bath ratio is 1:50, the decolorization temperature is 130℃, and the decolorization time is 20min;

[0187] After deep decolorization, the decolorization rate of the waste polyester-cotton blended fabric is 98%, the strength retention rate is 93%, and the whiteness is 78;

[0188] Finally, all the decoloring solutions in steps (2.1) and (2.2) need to be recovered and treated by reduced pressure distillation method to obtain recovered decoloring agent and dyes, and the specific operation conditions are: under reduced pressure, the temperature is controlled at 70-80℃ to ensure that the decoloring agent is fully evaporated until the volume of the distillate reaches more than 95% of the theoretical recovery amount;

[0189] (3) Depolymerization:

[0190] After the depolymerization agent, isosorbide dimethyl ether, the first catalyst and the decolorized polyester-cotton blended fabric are mixed, a depolymerization reaction is carried out at 140°C for 90 min (under nitrogen or inert gas protection), after the depolymerization reaction, the cotton fibers are first separated out, then the depolymerization solution is subjected to a vacuum devolatilization at 190°C, and then a solid product is obtained by centrifugal separation at 80°C, the solid product, methanol and sodium hydroxide are mixed in a mass ratio of 1:5:0.01, and then a transesterification solution is prepared by reacting at 65°C for 3 h (under nitrogen protection), the transesterification solution is cooled to 25°C to precipitate solids, and then the terephthalate is obtained by filtration and methanol washing;

[0191] In the present application, since the depolymerization agent is the same as the decoloring agent, the recovered decoloring agent can be used as a component of the depolymerization agent, and the proportion of the recovered decoloring agent in the depolymerization agent is 70 wt.%. The mass of isosorbide dimethyl ether is 20 wt.% of the total mass of the depolymerization agent and isosorbide dimethyl ether. The molar ratio of the depolymerization agent to the polyester component in the decolorized polyester-cotton blended fabric is 15:1. The mass of the first catalyst added is 1 wt.% of the mass of the decolorized polyester-cotton blended fabric.

[0192] The depolymerization rate of the polyester in the decolorized polyester-cotton blended fabric is 98%.

[0193] (4) Other treatments:

[0194] The separated cotton fibers are washed with water and screened to remove the surface residual polyester powder. The conversion rate of the cotton fibers is 99%.

[0195] First, the terephthalate is converted into DMT, and then the DMT, ethylene glycol, a second catalyst and a functional additive are subjected to a re-polymerization reaction to obtain regenerated polyethylene terephthalate. The specific steps are as follows:

[0196] DMT, ethylene glycol, manganese acetate and a functional additive (triphenyl phosphate and antioxidant 1010) are uniformly mixed to form a reaction system A. The temperature of the reaction system A is slowly increased to 220°C at a heating rate of 30°C / h to carry out an ester exchange reaction. Methanol is collected. When the methanol outflow rate reaches 98% (the methanol outflow rate = actual methanol molar number / theoretical methanol molar number x 100%, the actual methanol molar number is the collected methanol molar number, and the theoretical methanol molar number is 2 times the DMT molar number), the ester exchange reaction is completed, and bis-hydroxyethyl terephthalate is prepared. The prepared bis-hydroxyethyl terephthalate and tetrabutyl titanate are uniformly mixed to form a reaction system B. The temperature of the reaction system B is slowly increased to 270°C at a heating rate of 30°C / h. Vacuum is applied to gradually increase the pressure of the reaction system B to 15 Pa. A polycondensation reaction is carried out for 180 min to obtain regenerated polyethylene terephthalate.

[0197] The mass ratio of DMT, ethylene glycol, manganese acetate, tetrabutyl titanate, triphenyl phosphate, and antioxidant 1010 is 1:0.6:0.05:0.05:0.05:0.05.

[0198] Example 5

[0199] A recycling method of waste polyester-cotton blended fabric, the specific steps are as follows:

[0200] (1) Material preparation:

[0201] Colored waste polyester-cotton blended fabric: the used dyes are disperse yellow 64 (heterocyclic disperse dye) and reactive yellow 4 (reactive dye), and the cotton content is 20 wt.%;

[0202] Decolorizing agent: a mixture of methyl ethyl carbonate and diethyl carbonate with a molar ratio of 2:1;

[0203] Depolymerization agent: a mixture of methyl ethyl carbonate and diethyl carbonate with a molar ratio of 2:1;

[0204] Isosorbide dimethyl ether;

[0205] First catalyst: a mixture of zinc acetate and basic catalyst, wherein the content of zinc acetate is 60 wt.%, and the basic catalyst is a mixture of potassium carbonate and potassium hydroxide with a molar ratio of 1:1;

[0206] Methanol;

[0207] Sodium hydroxide;

[0208] Ethylene glycol;

[0209] Second catalyst: magnesium acetate and ethylene glycol antimony;

[0210] Functional additive: trimethyl phosphate and antioxidant 1010;

[0211] (2) Decolorization:

[0212] (2.1) Under the protection of nitrogen or inert gas, the waste polyester-cotton blended fabric is placed in the decolorizing agent for preliminary decolorization, and then solid-liquid separation is performed to obtain a decolorized polyester-cotton blended fabric semi-product and a decolorizing solution;

[0213] Wherein, during the preliminary decolorization, the bath ratio is 1:20, the decolorization temperature is 120℃, and the decolorization time is 15 min;

[0214] After preliminary decolorization, the decolorization rate of the waste polyester-cotton blended fabric is 97%, the strength retention rate is 96%, and the whiteness is 70;

[0215] (2.2) After the decolorized polyester-cotton blended fabric semi-product is put into the decolorizing agent for deep decolorization under the protection of nitrogen or inert gas, solid-liquid separation is carried out, and a decolorized polyester-cotton blended fabric and a decolorizing solution are obtained;

[0216] In the deep decolorization, the bath ratio is 1:60, the decolorization temperature is 130°C, and the decolorization time is 20 min;

[0217] After the deep decolorization, the decolorization rate of the waste polyester-cotton blended fabric is 98%, the strength retention rate is 92%, and the whiteness is 75;

[0218] Finally, all the decolorizing solutions in steps (2.1) and (2.2) are treated by rotary evaporation to obtain recovered decolorizing agents and dyes. The specific operation conditions are as follows: under reduced pressure, the temperature is controlled at 90-100°C to ensure that the decolorizing agent is fully evaporated until the volume of the distillate reaches more than 95% of the theoretical recovery amount;

[0219] (3) Depolymerization:

[0220] After the depolymerization agent, isosorbide dimethyl ether, the first catalyst and the decolorized polyester-cotton blended fabric are mixed, the depolymerization reaction is carried out at 135°C for 60 min (under the protection of nitrogen or inert gas). After the depolymerization reaction, the cotton fibers are first separated out, and then the depolymerization solution is subjected to reduced pressure devolatilization at 150°C, followed by centrifugal separation at 80°C to obtain a solid product. The solid product, methanol and sodium hydroxide are mixed in a mass ratio of 1:5:0.01, and then reacted at 65°C for 3 h (under the protection of nitrogen) to prepare an ester exchange solution. The ester exchange solution is cooled to 25°C to precipitate a solid. After filtration and methanol washing, terephthalate ester is obtained;

[0221] Among them, since the depolymerization agent is the same as the decolorizing agent, the recovered decolorizing agent can be used as a component of the depolymerization agent. The proportion of the recovered decolorizing agent in the depolymerization agent is 80wt.%. The mass of isosorbide dimethyl ether is 15wt.% of the total mass of the depolymerization agent and isosorbide dimethyl ether. The molar ratio of the depolymerization agent to the polyester component in the decolorized polyester-cotton blended fabric is 10:1. The mass of the first catalyst added is 0.5wt.% of the mass of the decolorized polyester-cotton blended fabric;

[0222] The depolymerization rate of the polyester in the decolorized polyester-cotton blended fabric is 95%;

[0223] (4) Other treatments:

[0224] The separated cotton fibers are washed with water and screened to remove the surface residual polyester powder. The conversion rate of the cotton fibers is 98%;

[0225] First, the terephthalate ester is converted into DMT. Then, the DMT, ethylene glycol, the second catalyst and the functional additive are subjected to a re-polymerization reaction to obtain regenerated polyethylene terephthalate. The specific steps are as follows:

[0226] DMT, ethylene glycol, magnesium acetate, functional aids (trimethyl phosphate, antioxidant 1010) are mixed uniformly to form a reaction system A, the temperature of the reaction system A is slowly raised to 220℃ at a heating rate of 30℃ / h for ester exchange reaction, methanol is collected, and when the methanol out rate reaches 98% (methanol out rate = actual out alcohol amount / theoretical out alcohol amount x 100%, actual out alcohol amount is the number of moles of collected methanol, and theoretical out alcohol amount is the number of moles of DMT x 2), the ester exchange is completed, and bis-hydroxyethyl terephthalate is prepared; then the prepared bis-hydroxyethyl terephthalate and antimony glycol are mixed uniformly to form a reaction system B, the temperature of the reaction system B is slowly raised to 270℃ at a heating rate of 30℃ / h, vacuum is extracted to gradually reach a pressure of 15Pa in the reaction system B, and polyethylene terephthalate is obtained by polycondensation reaction for 180min;

[0227] The mass ratio of DMT, ethylene glycol, magnesium acetate, antimony glycol, trimethyl phosphate, antioxidant 1010 is 1:0.6:0.05:0.05:0.05:0.05.

[0228] Example 6

[0229] A recycling method of waste polyester-cotton blended fabric, the specific steps are as follows:

[0230] (1) Material preparation:

[0231] Colored waste polyester-cotton blended fabric: the used dyes are disperse blue 73 (anthraquinone disperse dye) and reactive blue 19 (reactive dye), and the cotton content is 30wt.%;

[0232] Decolorizing agent: diethyl carbonate;

[0233] Depolymerization agent: diethyl carbonate;

[0234] Isosorbide dimethyl ether;

[0235] First catalyst: a mixture of zinc acetate and basic catalyst, wherein the content of zinc acetate is 50wt.%, and the basic catalyst is a mixture of sodium carbonate and sodium hydroxide with a molar ratio of 1:1;

[0236] Methanol;

[0237] Sodium hydroxide;

[0238] Ethylene glycol;

[0239] Second catalyst: sodium acetate and antimony trioxide;

[0240] Functional aids: triphenyl phosphate and antioxidant 1010;

[0241] (2) Decolorization:

[0242] (2.1) Put the waste polyester-cotton blended fabric into the decolorizing agent under the protection of nitrogen or inert gas for preliminary decolorization, and then perform solid-liquid separation to obtain a decolorized polyester-cotton blended fabric semi-product and a decolorizing solution;

[0243] In the preliminary decolorization, the bath ratio is 1:10, the decolorization temperature is 110°C, and the decolorization time is 10 min;

[0244] After the preliminary decolorization, the decolorization rate of the waste polyester-cotton blended fabric is 96%, the strength retention rate is 95%, and the whiteness is 60;

[0245] (2.2) Put the decolorized polyester-cotton blended fabric semi-product into the decolorizing agent under the protection of nitrogen or inert gas for deep decolorization, and then perform solid-liquid separation to obtain a decolorized polyester-cotton blended fabric and a decolorizing solution;

[0246] In the deep decolorization, the bath ratio is 1:70, the decolorization temperature is 140°C, and the decolorization time is 10 min;

[0247] After the deep decolorization, the decolorization rate of the waste polyester-cotton blended fabric is 98%, the strength retention rate is 90%, and the whiteness is 70;

[0248] Finally, all the decolorizing solutions in steps (2.1) and (2.2) are treated by rectification to obtain recovered decolorizing agents and dyes. The specific operation conditions are as follows: the reflux ratio (volume ratio of reflux liquid to distillate) is set to 3:1, the overhead temperature is controlled at 75-85°C, the bottom temperature is maintained at 90-100°C, and the overhead condenser temperature is set to 5-10°C to ensure sufficient vapor condensation;

[0249] (3) Depolymerization:

[0250] After mixing the depolymerization agent, isosorbide dimethyl ether, the first catalyst, and the decolorized polyester-cotton blended fabric, the mixture is subjected to a depolymerization reaction at 130°C for 30 min under the protection of nitrogen or inert gas. After the depolymerization reaction, the cotton fibers are first separated out, and then the depolymerization solution is subjected to a vacuum devolatilization at 170°C, followed by centrifugal separation at 70°C to obtain a solid product. The solid product, methanol, and sodium hydroxide are mixed in a mass ratio of 1:5:0.01, and then subjected to a reaction at 65°C for 3 h under the protection of nitrogen to prepare an ester exchange solution. The ester exchange solution is cooled to 25°C to precipitate a solid, which is filtered and washed with methanol to obtain terephthalate ester;

[0251] The recovered decoloring agent can be used as a component of the depolymerization agent, the proportion of the recovered decoloring agent in the depolymerization agent is 90 wt.%, the mass of the isosorbide dimethyl ether is 10 wt.% of the total mass of the depolymerization agent and the isosorbide dimethyl ether, the molar ratio of the depolymerization agent to the polyester component in the decoloring polyester-cotton blended fabric is 3:1, and the mass of the first catalyst is 0.1 wt.% of the mass of the decoloring polyester-cotton blended fabric.

[0252] The depolymerization rate of the polyester in the decoloring polyester-cotton blended fabric is 90%.

[0253] (4) Other treatments:

[0254] The separated cotton fibers are washed and screened to remove the residual polyester powder on the surface, and the conversion rate of the cotton fibers is 98%.

[0255] The terephthalate is first converted into DMT, and then the DMT, ethylene glycol, a second catalyst and a functional additive are subjected to a re-polymerization reaction to obtain regenerated polyethylene terephthalate, and the specific steps are as follows:

[0256] The DMT, ethylene glycol, sodium acetate and functional additives (triphenyl phosphate and antioxidant 1010) are uniformly mixed to form a reaction system A, the temperature of the reaction system A is slowly increased to 220°C at a heating rate of 30°C / h for ester exchange reaction, and methanol is collected, and when the methanol out rate reaches 98% (the methanol out rate = actual out alcohol amount / theoretical out alcohol amount × 100%, the actual out alcohol amount is the number of moles of collected methanol, and the theoretical out alcohol amount is the number of moles of DMT × 2), the ester exchange is completed, and bis-hydroxyethyl terephthalate is prepared; the prepared bis-hydroxyethyl terephthalate and antimony trioxide are uniformly mixed to form a reaction system B, the temperature of the reaction system B is slowly increased to 270°C at a heating rate of 30°C / h, the pressure of the reaction system B is gradually increased to 15 Pa by vacuumizing, and the condensation reaction is performed for 180 min to obtain regenerated polyethylene terephthalate;

[0257] The mass ratio of the DMT, ethylene glycol, sodium acetate, antimony trioxide, triphenyl phosphate and antioxidant 1010 is 1:0.6:0.05:0.05:0.05:0.05.

Claims

1. A recycling method of waste polyester-cotton blended fabric, characterized in that, The colored waste polyester-cotton blended fabric is first subjected to decolorization by a decolorizing agent, and the polyester and cotton fibers in the waste polyester-cotton blended fabric are the decolorization objects; then the depolymerization agent, isosorbide dimethyl ether, the first catalyst and the decolorized polyester-cotton blended fabric are mixed to perform a depolymerization reaction, and the polyester in the decolorized polyester-cotton blended fabric is the depolymerization object; the decolorizing agent and the depolymerization agent are one or more of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; the mass of the isosorbide dimethyl ether is 10-40wt.% of the total mass of the depolymerization agent and the isosorbide dimethyl ether; and the temperature of the depolymerization reaction is 130-150℃. The time of the depolymerization reaction is 30-200min. The molar ratio of the depolymerization agent to the polyester component in the decolorized polyester-cotton blended fabric is 3-30:

1.

2. The recycling method of the waste polyester-cotton blended fabric according to claim 1, characterized in that, The specific process of decolorizing the colored waste polyester-cotton blended fabric by the decolorizing agent is as follows: first, under the protection of nitrogen or inert gas, the waste polyester-cotton blended fabric is put into the decolorizing agent to perform preliminary decolorization, and then solid-liquid separation is performed to obtain a decolorized polyester-cotton blended fabric semi-product and a decolorizing solution; then, under the protection of nitrogen or inert gas, the decolorized polyester-cotton blended fabric semi-product is put into the decolorizing agent to perform deep decolorization, and then solid-liquid separation is performed to obtain a decolorized polyester-cotton blended fabric and a decolorizing solution; finally, all the decolorizing solutions are recovered to obtain recovered decolorizing agent and dyes.

3. The method for recycling waste polyester-cotton blended fabrics according to claim 2, characterized in that, In the preliminary decolorization, the bath ratio is 1:10-70, the decolorization temperature is 110-140℃, and the decolorization time is 10-40min. After the preliminary decolorization, the decolorization rate of the waste polyester-cotton blended fabric calculated according to the K / S value is 96% or more, the strength retention rate measured according to GB / T3923.1-2013 is 95% or more, and the whiteness measured according to GB / T17644-2008 is 60-80. In the deep decolorization, the bath ratio is 1:10-70, the decolorization temperature is 110-140℃, and the decolorization time is 10-40min. After the deep decolorization, the decolorization rate of the waste polyester-cotton blended fabric calculated according to the K / S value is 98% or more, the strength retention rate measured according to GB / T3923.1-2013 is 90% or more, and the whiteness measured according to GB / T17644-2008 is 70-80.

4. The method according to claim 1, wherein, The depolymerization reaction is performed under the protection of nitrogen or inert gas, and after the depolymerization reaction, the cotton fibers are first separated out, and then the depolymerization solution is separated and purified to obtain terephthalate.

5. The method according to claim 4, wherein the polyester-cotton blended fabric is a polyester-cotton blended fabric having a weight ratio of 50:50 to 70:

30. The depolymerization agent is the same as the decolorizing agent.

6. The method according to claim 5, wherein the polyester-cotton blended fabric is a polyester-cotton blended fabric. The mass addition amount of the first catalyst is 0.1-5wt.% of the mass of the decolorized polyester-cotton blended fabric. The proportion of the recovered decolorizing agent in the depolymerization agent is 50-90wt.%, the first catalyst is a mixture of zinc acetate and an alkaline catalyst, the content of zinc acetate in the first catalyst is 50-100wt.%, and the alkaline catalyst is one or more of potassium carbonate, sodium carbonate, sodium hydroxide and potassium hydroxide; The depolymerization rate of the polyester in the decolorized polyester-cotton blended fabric is 90-100%.

7. The method according to claim 4, wherein the polyester-cotton blended fabric is a polyester-cotton blended fabric. The separated cotton fibers are also washed with water and screened to remove the surface residual polyester powder, and the conversion rate of the cotton fibers is 98-100%.

8. The method according to claim 4, wherein, The method also comprises the step of converting terephthalate into DMT, and then performing a re-polymerization reaction of DMT, ethylene glycol, a second catalyst and a functional additive to obtain regenerated polyethylene terephthalate.

9. A method for recycling waste polyester-cotton blended fabrics according to claim 1, characterized in that, The waste polyester-cotton blended fabric has a cotton content of not more than 30 wt.%.

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