A method for decoloring waste colored polyester textile, product and application

Abstract

The application discloses a decoloring method, product and application of waste colored polyester textile, and belongs to the field of recycled polyester fiber recycling, wherein the decoloring method adopts a synergistic decoloring solvent system composed of ethylene carbonate, dimethyl isosorbide and dimethyl tetrahydrofuran in a specific proportion, and adds sodium borohydride reducing agent, and combines whiteness feedback control to decolor the waste colored polyester textile at 80-110 DEG C. According to the method, the introduction of dimethyl isosorbide and dimethyl tetrahydrofuran effectively reduces the decoloring temperature, improves the decoloring efficiency, and the fabric is white after decoloring; the product fiber after decoloring maintains good performance through strict control of the component proportion of the decoloring agent, can be directly used for secondary dyeing, realizes high-value regeneration benefit, and has good application prospect and social and economic value.

Description

Technical Field

[0001] This invention relates to the field of recycling polyester fibers, specifically to a method, product, and application for decolorizing waste colored polyester textiles. Background Technology

[0002] Waste polyester (polyethylene terephthalate, PET) textiles are widely available and abundant, making their efficient recycling and reuse a crucial component of the textile circular economy. However, waste polyester typically contains difficult-to-remove disperse dyes, vat dyes, and other colored substances, severely limiting its potential for physical regeneration into high-value fibers. Therefore, developing efficient, mild, and environmentally friendly decolorization methods to achieve colorless treatment of colored polyester textiles is one of the core technological challenges urgently needing to be addressed in the field of waste polyester resource utilization.

[0003] Currently, decolorization methods for colored polyester mainly include chemical reduction cleaning, supercritical fluid methods, and organic solvent treatment. Among these, organic solvent treatment utilizes the swelling or dissolving effect of organic solvents on polyester fibers, causing dyes to migrate from the fiber interior and dissolve in the solvent, thus achieving decolorization. This method boasts high decolorization efficiency and relatively minimal damage to fiber strength, attracting widespread attention in the industry. The core of organic solvent decolorization is to dissolve the dye from the amorphous regions of the fiber without degrading the polyester molecular chain. Its essence lies in using the swelling effect of the solvent to open the amorphous region structure, allowing the dye to migrate out and dissolve again in the solvent. Traditional organic solvents include toluene, acetic acid, and diethylene glycol. While these solvents have good decolorization effects, they suffer from high volatility and toxicity, as well as high solvent recovery costs, and are gradually being replaced by environmentally friendly solvents.

[0004] Ethylene carbonate (EC), also known as ethylene glycol carbonate, is an environmentally friendly solvent. Industrially, EC is mainly used as a component of lithium-ion battery electrolytes, a solvent for polyacrylonitrile and polyvinyl chloride, and as a textile spinning solution and fiber finishing agent. Studies have reported that EC has a certain decolorizing ability for disperse dye-dyed polyester fabrics (Yang Yunlong et al., "Ethylene Carbonate Extraction Decolorization of Waste Colored Polyester Fabrics," Dyeing and Printing, 2025, No. 8). However, existing research mostly uses a single EC component to decolorize colored polyester fabrics at decolorizing temperatures of 130℃–140℃ or even higher. While high temperatures can effectively improve the decolorization rate, the molecular chains of the fibers are prone to breakage at high temperatures, resulting in a significant decrease in crystallinity and affecting the strength and integrity of the fibers. Furthermore, the aforementioned study only conducted decolorization experiments on two types of colored polyester fabrics: azo-type disperse blue 366 dyed fabric and anthraquinone-type disperse red 60 dyed fabric. Even after two decolorization cycles, blue residue remained on the fabric (K / S=0.79), exhibiting a visible light blue hue. This is because the single EC component has limited solubility for the dye, thus restricting the decolorization rate. Current technologies often employ repeated washing with large amounts of solvent to achieve higher decolorization rates. This not only results in high solvent consumption and low efficiency but also causes severe cumulative fiber damage and a precipitous decline in recycled quality. In particular, for polyester products containing heterocyclic disperse dyes (such as benzothiazole and thiophene structures), the large molecular weight and unique polarity of these dyes lead to a stronger bond with the fiber, meaning their solubility in EC is more limited, making them more difficult to effectively extract and disperse by EC.

[0005] Therefore, how to reduce the decolorization temperature, improve the decolorization efficiency, avoid repeated washing, and better preserve the original shape and mechanical properties of polyester while achieving broad-spectrum, green, and efficient decolorization remains an urgent problem to be solved. Summary of the Invention

[0006] To address the aforementioned problems and achieve the above objectives, this invention provides a method, product, and application for decolorizing waste colored polyester textiles. This method uses ethylene carbonate (EC), dimethyl isosorbide (DMI), and dimethyltetrahydrofuran (DMTHF) as synergistic decolorizing solvents, combined with sodium borohydride as a reducing agent, to achieve broad-spectrum, green, and efficient decolorization of waste colored polyester textiles. The specific technical solution is as follows:

[0007] First, the present invention aims to provide a method for decolorizing waste colored polyester textiles. The decolorizing solvent of the method is a synergistic decolorizing solvent system composed of ethylene carbonate as the main solvent and dimethyl isosorbide and dimethyltetrahydrofuran as auxiliary solvents. In this system, the mass ratio of ethylene carbonate, dimethyl isosorbide and dimethyltetrahydrofuran is 1:(0.2-0.64):(0.03-0.23), and the mass ratio of dimethyl isosorbide to dimethyltetrahydrofuran is 1:(0.1-0.5).

[0008] The aforementioned method for decolorizing waste colored polyester textiles uses dyes that are one or more of azo disperse dyes, anthraquinone disperse dyes, and heterocyclic disperse dyes.

[0009] The aforementioned method for decolorizing waste colored polyester textiles includes the following steps:

[0010] A. Preparation of synergistic decolorizing solvent system: Prepare the synergistic decolorizing solvent system according to the preset mass ratio, and set aside;

[0011] B. One-time decolorization: Adjust the pH value of the synergistic decolorization solvent system prepared in step A to 5-6, and add it to a reactor equipped with a condenser reflux device and an exhaust port. Immerse the waste colored polyester textiles, add a reducing agent under stirring conditions, adjust the pH value of the system to 5-6, and carry out a single-pot decolorization reaction under preset temperature and auxiliary conditions. After the reaction is completed, perform solid-liquid separation, collect the decolorization solvent and the fabric separately, and obtain one-time decolorized polyester textiles.

[0012] C. Secondary decolorization: Test the whiteness of the polyester textiles that have been decolorized once. If the whiteness value meets the standard, dry them. Otherwise, repeat step B and immerse the polyester textiles that have been decolorized once in the co-decolorizing solvent system for secondary decolorization until the whiteness value of the textiles meets the standard.

[0013] D. Drying treatment: Dry the polyester textiles after the last decolorization treatment to obtain recycled white polyester textiles.

[0014] As a preferred technical solution, in step A, the preparation method of the synergistic decolorizing solvent system is as follows: weigh a certain mass ratio of dimethyl isosorbide and dimethyl tetrahydrofuran, place them in the same container and stir to mix evenly; then slowly pour the above mixture into a container containing ethylene carbonate, turn on the stirring device, and stir until the decolorizing system forms a uniform and stable mixture.

[0015] As a preferred technical solution, in step B, the bath ratio of the waste colored polyester textiles to the synergistic decolorizing solvent system is 1:5-15; the reducing agent is sodium borohydride, and its addition amount is 0.5%-3% of the total mass of the synergistic decolorizing solvent system; the reducing agent is slowly added dropwise to the synergistic decolorizing solvent system in the form of an alkaline stock solution, and the adding time is controlled at 5-15 min; the decolorization reaction temperature is 80-110℃, and the decolorization time is 10-40 min; the auxiliary conditions are low-frequency ultrasonic assistance, with an ultrasonic frequency of 20-40 kHz and a power density of 0.5 W / cm³. 2 The ultrasonic treatment time is 5 to 20 minutes.

[0016] As a preferred technical solution, in step C, the whiteness value meets the standard by: using a spectrophotometer with a D65 light source and a 10° observation angle to measure the CIE L*, a*, and b* color values ​​of the decolorized textile. If the L* value is ≥85, and |a*|≤2, and |b*|≤2, then the whiteness is determined to meet the standard. If any of the above conditions are not met, then step B is repeated.

[0017] As a preferred technical solution, in step D, the drying is performed by centrifugal drying at room temperature for 8 to 15 minutes until the quality no longer changes.

[0018] The aforementioned method for decolorizing waste colored polyester textiles further includes step E, in which the decolorizing solvents collected in steps B and C are regenerated and recycled using the main solvent and co-solvent through vacuum distillation.

[0019] Secondly, the present invention provides a recycled polyester textile, which is obtained by decolorizing waste colored polyester textile through the above-mentioned decolorization method. Its CIE whiteness value is ≥85, its strength retention rate is ≥95%, and its crystallinity decreases by <2%.

[0020] In addition, the present invention provides an application of the aforementioned recycled polyester textile, specifically, the recycled polyester textile is directly dyed without bleaching to prepare new colored fabric products.

[0021] The beneficial effects of this invention are:

[0022] 1) The decolorization method of this invention uses ethylene carbonate (EC), dimethyl isosorbide (DMI), and dimethyltetrahydrofuran (DMTHF) as synergistic decolorization solvents. DMI, due to its penetrability, rapidly wets the surface of the polyester fiber with the mixed solvent, while DMTHF, with its low surface tension, penetrates deep into the amorphous region of the fiber to achieve pre-swelling. This allows ethylene carbonate to deeply swell the fiber for decolorization at a relatively low temperature. The migrated dye is extracted by DMTHF and selectively dissolved by ethylene carbonate, and stably dispersed with the assistance of DMI, preventing re-contamination of the fiber. The synergistic effect of these three solvents overcomes the high-temperature limitation, achieving highly efficient decolorization at lower temperatures.

[0023] 2) The decolorization method of this invention combines physical extraction and chemical reduction in the same closed system. Sodium borohydride reduction is introduced on the basis of solvent extraction, which irreversibly destroys the color development system of azo, anthraquinone and heterocyclic dyes, and breaks through the limitation of two-phase distribution equilibrium. Experiments show that after 1 to 2 decolorizations, the whiteness value of the fabric is CIE L≥85, |a|≤2, and |b*|≤2, and it appears pure white to the naked eye, which is significantly better than the decolorization effect of EC alone.

[0024] 3) The decolorization method of this invention reduces the processing temperature and avoids repeated washing, significantly reducing fiber damage. After decolorization, the fiber strength retention rate is ≥95% and the crystallinity decreases by <2%, which is far superior to the cumulative damage caused by multiple decolorizations of a single EC. The recycled polyester can be directly used for high-quality spinning or secondary dyeing, realizing high-value recycling benefits.

[0025] 4) The decolorization method of the present invention not only has a good decolorization effect on azo and anthraquinone dyes, but also has an excellent decolorization effect on heterocyclic disperse dyes. It has good universality, solves the problem of decolorization of heterocyclic dyes, and fills the gap in the existing technology for treating heterocyclic dyed polyester.

[0026] 5) The decolorization method of this invention accurately determines the endpoint through a whiteness feedback control mechanism, avoiding over-processing and further improving the economic efficiency of the process. At the same time, the colored mixed solvent used after decolorization can be recovered and recycled through vacuum distillation. The introduction of low-boiling-point DMTHF reduces the energy consumption of recycling, meets the requirements of circular economy, and achieves the goal of closed-loop recycling and green sustainability.

[0027] In summary, this invention employs a synergistic decolorizing solvent system composed of ethylene carbonate, dimethyl isosorbide, and dimethyltetrahydrofuran in a specific ratio, with the addition of sodium borohydride as a reducing agent. Decolorization is carried out at 80–110°C, combined with whiteness feedback control, to decolorize waste colored polyester textiles. This method, through the introduction of dimethyl isosorbide and dimethyltetrahydrofuran, effectively lowers the decolorizing temperature and improves the decolorizing efficiency. The decolorized fabric is pure white, and through strict ratio control, the fibers of the decolorized product maintain good properties, allowing for direct use in secondary dyeing and realizing high-value recycling benefits. It has promising application prospects and significant social and economic value. Attached Figure Description

[0028] Figure 1 These are actual photos of the polyester fabric before and after decolorization in Example 1 of the present invention;

[0029] Figure 2 Comparative Example 1: Photos of polyester fabric before and after decolorization;

[0030] Figure 3 These are actual photos of the polyester fabric before and after decolorization in Example 4 of the present invention;

[0031] Figure 4 Examples 1-2 show actual photos of polyester fabrics before and after decolorization;

[0032] Figure 5 These are actual photos of the polyester fabric before and after decolorization in Example 5 of the present invention;

[0033] Figure 6 Examples 1-3 show actual photos of polyester fabrics before and after decolorization;

[0034] Figure 7 This is a microstructure diagram of the polyester fabric before and after decolorization in Embodiment 1 of the invention;

[0035] Figure 8 Microscopic structure diagram of polyester fabric before and after decolorization for comparative example 1 of the invention. Detailed Implementation

[0036] To lower the decolorization temperature of waste colored polyester textiles, improve decolorization efficiency, avoid repeated washing, and better preserve the original form and mechanical properties of polyester, this invention provides a decolorization method for waste colored polyester textiles. This method uses ethylene carbonate (EC), dimethyl isosorbide (DMI), and dimethyltetrahydrofuran (DMTHF) as synergistic decolorization solvents, combined with the reducing agent sodium borohydride (NaBH4), to achieve efficient decolorization of waste colored polyester textiles at a lower temperature. In the solvent system of this invention, ethylene carbonate is the main solvent, and dimethyl isosorbide and dimethyltetrahydrofuran are auxiliary solvents. Furthermore, to ensure the decolorization effect, the mass ratio of ethylene carbonate, dimethyl isosorbide, and dimethyltetrahydrofuran is 1:(0.2–0.64):(0.03–0.23), and the mass ratio of dimethyl isosorbide to dimethyltetrahydrofuran is 1:(0.1–0.5).

[0037] The decolorization method of the present invention includes the following steps: A. Preparation of synergistic decolorizing solvent system: Prepare synergistic decolorizing solvent system according to the preset mass ratio; specifically: weigh a certain mass ratio of dimethyl isosorbide and dimethyl tetrahydrofuran, place them in the same container and stir to mix evenly; then slowly pour the above mixture into the container (beaker) containing ethylene carbonate, turn on the stirring device, and stir until the decolorizing system forms a homogeneous and stable mixture, for later use.

[0038] B. Single-stage decolorization: Adjust the pH of the synergistic decolorizing solvent system prepared in step A to 5-6. Immerse the waste colored polyester textiles in the synergistic decolorizing solvent system, add a reducing agent, and conduct a single-stage decolorization reaction under preset temperature and auxiliary conditions. After the reaction is completed, perform solid-liquid separation and collect the decolorizing solvent and fabric separately to obtain single-stage decolorized polyester textiles. The bath ratio of the waste colored polyester textiles to the synergistic decolorizing solvent system is 1:5-15; the reducing agent is sodium borohydride, and its addition amount is 0.5%-3% of the total mass of the synergistic decolorizing solvent system. The decolorization reaction temperature is controlled at 80-110℃, and the decolorization time is 10-40 min; the auxiliary conditions are low-frequency ultrasonic assistance, with an ultrasonic frequency of 20-40 kHz and a power density of 0.5 W / cm³. 2 The ultrasonic treatment time is 5 to 20 minutes.

[0039] To prevent the decomposition of sodium borohydride under acidic conditions, the decolorization method of this invention involves dissolving sodium borohydride in a 0.5%–2% sodium hydroxide solution to prepare a stable alkaline stock solution (sodium borohydride concentration of 1%–5%). During the decolorization reaction, this stock solution is slowly added dropwise to the decolorization system at pH 5–6, with the addition time controlled between 5 and 15 minutes. Because NaBH4 reacts rapidly with acidic dye groups, and continuous stirring (stirring speed 120–400 r / min) is employed during the addition process, the added NaBH4 disperses quickly and comes into full contact with the dye groups, further improving the reaction efficiency. Sodium borohydride is consumed in the reduction reaction before it can decompose, preventing the accumulation of free sodium borohydride in the acidic environment and thus avoiding decomposition and failure. Meanwhile, the acidic intermediates produced by dye reduction during the reaction can neutralize some of the alkalinity, which can maintain the pH of the solvent system in the range of 5 to 6, preventing the pH of the system from being too high and corroding the polyester fibers. This ensures that the entire long-term high-temperature decolorization process is stably maintained in the weakly acidic range where the fibers are most resistant to corrosion, thus ensuring the mechanical properties of the decolorized polyester textiles.

[0040] Because 2-methyltetrahydrofuran is volatile at high temperatures, this invention employs a reactor equipped with a condenser reflux device and an exhaust port for the decolorization reaction. On the one hand, the small amount of hydrogen gas generated from the decomposition of unreacted sodium borohydride and the small amount of gaseous byproducts generated during the reaction process can be discharged through the exhaust port, ensuring operational safety. On the other hand, the volatilized 2-methyltetrahydrofuran vapor is condensed and refluxed back into the reaction system through a low-temperature cooling circulation device (cooling medium temperature ≤ 5℃), which can minimize solvent loss and ensure that the solvent ratio remains essentially constant during the reaction process.

[0041] C. Secondary Decolorization: The whiteness of the polyester textiles after the first decolorization is tested. If the whiteness value meets the standard, drying is performed; otherwise, step B is repeated, and the polyester textiles after the first decolorization are immersed again in the synergistic decolorizing solvent system for secondary decolorization until the whiteness value of the textiles meets the standard. The whiteness value meeting the standard is determined by measuring the CIE L*, a*, and b* color values ​​of the decolorized textiles using a spectrophotometer under D65 light source and 10° observation angle. If the L* value is ≥85, and |a*|≤2, and |b*|≤2, then the whiteness is considered to meet the standard. If any of the above conditions are not met, step B is repeated.

[0042] D. Drying treatment: The polyester textiles from the final decolorization treatment are dried to obtain recycled white polyester textiles. The drying process involves centrifugal drying at room temperature for 8–15 minutes until the quality no longer changes.

[0043] The decolorization method of the present invention further includes step E, which involves regenerating and recycling the main solvent and co-solvent collected in steps B and C through vacuum distillation.

[0044] The recycled polyester textiles decolorized by the method of the present invention have a CIE whiteness value ≥85, a strength retention rate ≥95%, and a crystallinity decrease of <2%. They can be directly dyed without bleaching and used to prepare new colored fabric products.

[0045] The decolorization method of this invention has a good decolorization effect on a variety of coloring dyes, including azo disperse dyes, anthraquinone disperse dyes, and heterocyclic disperse dyes, and has good broad-spectrum properties. At the same time, the three decolorization solvents of this invention are all low-toxicity, biodegradable, and friendly to human health and the environment, which meets the requirements of green development and has good application and economic value.

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. All pharmaceuticals involved in the embodiments are commercially available, and those without a purity rating are industrial or reagent grade.

[0047] Example 1

[0048] Weigh 5g of azo-disperse blue 366-dyed fabric with a tensile strength of 778.35N and a crystallinity of 40.79%. Immerse it in a synergistic decolorization system (pH adjusted to 5 with glacial acetic acid). This system is prepared with ethylene carbonate, dimethyl isosorbide, and 2-methyltetrahydrofuran in a mass ratio of 1:0.4:0.1, and the bath ratio of the fabric to the decolorizing solvent is 1:10. Add 2% sodium borohydride (by mass of the total solvent), and then sonicate at 30kHz with a power density of 0.5W / cm². 2 Under the conditions, the material was decolorized at a constant temperature of 100℃ for 30 minutes. After the decolorization was completed, the solid and liquid were separated and the decolorized liquid and polyester fabric were collected separately. The decolorized liquid was recovered by vacuum distillation. The polyester fabric was washed with hot water and centrifuged and dried at room temperature for 8-10 minutes. The fabric was weighed with a high-precision balance until the mass no longer changed, and the decolorized sample 1 was obtained.

[0049] Example 2

[0050] Weigh 5g of the same sample as in Example 1 and immerse it in a synergistic decolorizing solvent system (adjusted to pH=5 with glacial acetic acid). The system is prepared with ethylene carbonate, dimethyl isosorbide, and 2-methyltetrahydrofuran in a mass ratio of 1:0.2:0.03, and the bath ratio of the fabric in the decolorizing solvent is 1:10. Add 2% sodium borohydride by weight of the total solvent, and then perform low-frequency ultrasound at 30kHz with a power density of 0.5W / cm². 2Under the conditions, the material was decolorized at a constant temperature of 85℃ for 30 minutes. After the decolorization was completed, the solid and liquid were separated, and the decolorized liquid and polyester fabric were collected separately. The decolorized liquid was recovered by vacuum distillation, and the polyester fabric was washed with hot water and centrifuged and dried at room temperature for 8-10 minutes. The fabric was weighed with a high-precision balance until the mass no longer changed, and decolorized sample 2 was obtained.

[0051] Example 3

[0052] Weigh 5g of the same sample as in Example 1 and immerse it in a synergistic decolorizing solvent system (adjusted to pH=5 with glacial acetic acid). The system is prepared with ethylene carbonate, dimethyl isosorbide, and 2-methyltetrahydrofuran in a mass ratio of 1:0.68:0.23, and the bath ratio of the fabric in the decolorizing solvent is 1:10. Add 2% sodium borohydride by weight of the total solvent, and then perform low-frequency ultrasound at 30kHz with a power density of 0.5W / cm². 2 Under the conditions, the color was decolorized at a constant temperature of 110℃ for 30 minutes. After the decolorization was completed, the solid and liquid were separated and the decolorized liquid and polyester fabric were collected separately. The decolorized liquid was recovered by vacuum distillation. The polyester fabric was washed with hot water and centrifuged and dried at room temperature for 8-10 minutes. The fabric was weighed with a high-precision balance until the mass no longer changed, and the decolorized sample 3 was obtained.

[0053] Example 4

[0054] 5g of anthraquinone-type disperse red 60-dyed polyester fabric was weighed out. The tensile strength was 782.38N and the crystallinity was 39.86%. The sample was immersed in a synergistic decolorization system for decolorization. The decolorization process was the same as in Example 1, and decolorized sample 4 was obtained.

[0055] Example 5

[0056] 5g of polyester fabric dyed with heterocyclic disperse red 153 was weighed out. Its tensile strength was 781.32N, and its crystallinity was 39.75%. The sample was immersed in a synergistic decolorization system for decolorization, following the same process as in Example 1. After one decolorization, the whiteness value did not meet the requirements; therefore, the sample underwent a second decolorization. Due to inconvenient decolorization conditions, decolorized sample 5 was obtained.

[0057] Comparative Example 1

[0058] Weigh 5g of the same sample as in Examples 1, 4, and 5, and decolorize them using pure ethylene carbonate as the sole solvent at a liquor ratio of 1:10 for 30 minutes at 100°C. The remaining process is the same as in Example 1. Comparative samples 1-1, 1-2, and 1-3 were obtained.

[0059] Comparative Example 2

[0060] Weigh 5g of the same sample as in Examples 1, 4, and 5, and immerse each sample in a solvent system prepared with ethylene carbonate and dimethyl isosorbide in a mass ratio of 1:0.5. The remaining procedures are the same as in Example 1. Comparative samples 2-1, 2-2, and 2-3 were obtained.

[0061] Comparative Example 3

[0062] Weigh 5g of the same sample as in Examples 1, 4, and 5, and immerse each sample in a solution system prepared with ethylene carbonate and 2-methyltetrahydrofuran at a mass ratio of 1:0.5. The remaining procedures are the same as in Example 1. Comparative samples 3-1, 3-2, and 3-3 were obtained.

[0063] Comparative Example 4

[0064] Weigh 5g of the same sample as in Examples 1, 4, and 5, and immerse them in a synergistic decolorization system prepared with ethylene carbonate, dimethyl isosorbide, and 2-methyltetrahydrofuran in a mass ratio of 1:0.1:0.02. The remaining process is the same as in Example 1. Comparative samples 4-1, 4-2, and 4-3 were obtained.

[0065] Comparative Example 5

[0066] Weigh 5g of the same sample as in Examples 1, 4, and 5, and immerse them in a synergistic decolorization system prepared with ethylene carbonate, dimethyl isosorbide, and 2-methyltetrahydrofuran in a mass ratio of 1:0.65:0.25. The remaining process is the same as in Example 5, i.e., decolorization twice. Comparative samples 5-1, 5-2, and 5-3 were obtained.

[0067] Example of effect

[0068] The whiteness of the textile samples after decolorization in Examples 1-5 and Comparative Examples 1-5 was tested, and their properties were examined, including the decolorization rate, tensile strength retention rate, crystallinity, and microstructure characterization.

[0069] 1) The whiteness detection method is as follows: The color difference of the initial fabric and the fabric after extraction and decolorization under different reaction conditions is measured by a spectrophotometer, and its brightness component (L*), the component from red to green (a*), and the component from yellow to blue (b*) are recorded.

[0070] 2) The decolorization rate test method is as follows: Using a benchtop spectrophotometer, under D65 light source and an incident angle of 10°, the K / S values ​​of colored polyester fabrics before and after decolorization under different decolorization conditions are measured, and the decolorization rate D is calculated according to the formula:

[0071] D = [(K / S)1-(K / S)2] / (K / S)1×100%;

[0072] In the formula: (K / S)1 and (K / S)2 are the K / S values ​​at the maximum absorption wavelength of the fabric before and after decolorization, respectively.

[0073] 3) Tension strength retention rate: Cut the fabric before and after decolorization into strips of 6cm×3cm, and conduct tensile performance tests using an electronic fabric strength tester. Calculate the tensile strength retention rate of the fabric after decolorization according to the formula.

[0074] Fracture strength retention rate = F2 / F1 × 100%;

[0075] In the formula: F1 and F2 are the breaking strength of the fabric before and after decolorization, respectively.

[0076] 4) The crystallinity test method is as follows: Qualitative analysis of fabric samples before and after decolorization is performed using an X-ray diffractometer. The X-ray diffraction curve of the fabric is measured, and the crystallinity of the sample is calculated. Test conditions: The accelerating voltage of the copper target is 30kV, the current is 10mA, the scanning speed is 0.1° / s, and the 2θ range is 5°~60°.

[0077] 5) The microstructure characterization test method is as follows: The fiber morphology structure of the polyester fabric sample before and after decolorization is observed using a scanning electron microscope. The polyester fabric is attached to the sample stage using conductive adhesive, the gold sputtering time is 60s, the scanning voltage is 10kV, and the current is 10mA.

[0078] The results are shown in Table 1, Table 2 and... Figures 1 to 8 As shown.

[0079] Table 1. Whiteness test results of polyester textiles after decolorization in each example and comparative example.

[0080]

[0081] From Table 1 and Figures 1 to 6 The results show that the whiteness values ​​of the decolorized samples in Examples 1-5 are all ≥85, and |a*|≤2 and |b*|≤2. However, the whiteness values ​​of the decolorized samples were significantly reduced when EC was used as a single decolorizing agent (comparative samples 1-1 to 1-3) or when EC was used as a single auxiliary solvent. Although Comparative Examples 4 and 5 also contained two auxiliary solvents (DMI+DMTHF), the amount of auxiliary solvent in Comparative Example 4 was insufficient, and the whiteness of the decolorized sample was significantly lower than that of the decolorized samples in Examples 1-5.

[0082] Table 2. Performance test results of polyester textiles after decolorization in each example and comparative example.

[0083]

[0084] From Table 2 and Figure 7 and Figure 8The results show that under the reaction conditions of this invention, the decolorization effect on the fabrics is significant. The decolorization rate of fabrics dyed with Disperse Blue 366 can reach over 99%, the decolorization rate of fabrics dyed with Disperse Red 60 can reach 98.81%, and the decolorization rate of fabrics dyed with Disperse Red 153 can reach 98.23%. The strength retention rate of the samples before and after decolorization is over 95%, and there is no significant change in fiber morphology. The crystallinity decreases by less than 2%, which is better than EC alone (Comparative Example 1) plus an auxiliary solvent (Comparative Example 2 and Comparative Example 3). Although the whiteness value of the sample after decolorization in Comparative Example 5 is better and the decolorization rate is higher, its fiber strength retention rate and crystallinity are reduced significantly. Therefore, it is more appropriate to control the mass ratio of EC, DMI, and DMTHF at 1:(0.2~0.64):(0.03~0.23).

[0085] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and not restrictive in all respects. Furthermore, it should be understood that although this specification describes embodiments, it does not encompass only one technical solution. This descriptive method is merely for clarity, and those skilled in the art should consider the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for decolorizing waste colored polyester textiles, characterized in that: The decolorizing solvent in this decolorization method is a synergistic decolorizing solvent system composed of ethylene carbonate as the main solvent and dimethyl isosorbide and dimethyltetrahydrofuran as auxiliary solvents; in this system, the mass ratio of ethylene carbonate, dimethyl isosorbide and dimethyltetrahydrofuran is 1:(0.2~0.64):(0.03~0.23), and the mass ratio of dimethyl isosorbide to dimethyltetrahydrofuran is 1:(0.1~0.5); The decolorization method includes the following steps: A. Preparation of synergistic decolorizing solvent system: Prepare the synergistic decolorizing solvent system according to the preset mass ratio, and set aside; B. Single-stage decolorization: Immerse waste colored polyester textiles in the synergistic decolorizing solvent system prepared in step A, add a reducing agent, adjust the pH of the system to 5-6, and carry out a single-stage decolorization reaction under preset temperature and auxiliary conditions. After the reaction is completed, perform solid-liquid separation, collect the decolorizing solvent and the fabric separately, and obtain single-stage decolorized polyester textiles; the reducing agent is sodium borohydride, and its addition amount is 0.5%-3% of the total mass of the synergistic decolorizing solvent system; the decolorization reaction temperature is 80-110℃, and the decolorization time is 10-40 min; the auxiliary condition is low-frequency ultrasonic assistance; C. Secondary Decolorization: Test the whiteness of the polyester textiles after the first decolorization. If the whiteness value meets the standard, dry them. Otherwise, repeat step B and immerse the polyester textiles in the co-decolorizing solvent system again for secondary decolorization until the whiteness value of the textiles meets the standard.

2. The decolorization method for waste colored polyester textiles according to claim 1, characterized in that: The dyes used to color the waste colored polyester textiles are one or more of azo disperse dyes, anthraquinone disperse dyes, and heterocyclic disperse dyes.

3. The decolorization method for waste colored polyester textiles according to claim 1 or 2, characterized in that: The method also includes a drying step: the polyester textiles that have undergone the last decolorization treatment are washed with hot water and dried by centrifugation to obtain recycled white polyester textiles.

4. The decolorization method for waste colored polyester textiles according to claim 3, characterized in that: In step A, the preparation method of the synergistic decolorizing solvent system is as follows: weigh a certain mass ratio of dimethyl isosorbide and dimethyltetrahydrofuran, place them in the same container and stir to mix evenly; then slowly pour the above mixture into a beaker containing ethylene carbonate, turn on the stirring device, and stir until the decolorizing system forms a uniform and stable mixture.

5. The decolorization method for waste colored polyester textiles according to claim 4, characterized in that: In step B, The bath ratio of the waste colored polyester textiles to the synergistic decolorizing solvent system is 1:5 to 15; The low-frequency ultrasonic assistance has an ultrasonic frequency of 20–40 kHz and a power density of 0.5 W / cm². 2 The ultrasonic treatment time is 5 to 20 minutes.

6. The decolorization method for waste colored polyester textiles according to claim 5, characterized in that: In step C, the whiteness value meets the standard by using a spectrophotometer with a D65 light source and a 10° observation angle to measure the CIE L*, a*, and b* color values ​​of the decolorized textile. If the L* value is ≥85, and |a*|≤2, and |b*|≤2, then the whiteness is considered to meet the standard. If any of the above conditions are not met, then step B is repeated.

7. The decolorization method for waste colored polyester textiles according to claim 6, characterized in that: In step D, the drying process involves centrifugation at room temperature for 8–15 minutes until the mass no longer changes.

8. The decolorization method for waste colored polyester textiles according to claim 1, characterized in that: The method also includes step E, in which the decolorizing solvent collected in steps B and C is regenerated and recycled using the main solvent and co-solvent through vacuum distillation.

9. A recycled polyester textile, characterized in that: The textile is obtained by decolorizing waste colored polyester textiles using the decolorization method described in any one of claims 1-8, and the recycled polyester textile has a CIE whiteness value ≥85, a strength retention rate ≥95%, and a crystallinity decrease of <2%.

10. The application of recycled polyester textiles according to claim 9, characterized in that: The recycled polyester textiles are not bleached but directly dyed a second time to prepare new colored fabric products.

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