Method for preparing high-transmittance heat-resistant copolyester based on waste textile regenerated DMT

Abstract

The invention discloses a method for preparing high-transmittance heat-resistant copolyester based on waste textile regenerated DMT, and belongs to the technical field. The method comprises the following steps: (a) feeding regenerated DMT, EG and a copolymerization modified monomer into a polymerization reaction kettle, and carrying out transesterification under the catalysis of a transesterification catalyst to obtain a modified regenerated BHET prepolymer; and (b) adding a stabilizer and a color correcting agent into the modified regenerated BHET prepolymer system subjected to ester exchange, firstly adding a pre-polycondensation catalyst, carrying out pre-polycondensation at 50-200Pa and 240-260 DEG C, then adding a final polycondensation catalyst, and carrying out final polycondensation at 270-295 DEG C and less than 50Pa to obtain the regenerated copolyester material with high light transmittance and high heat resistance. Closed-loop recovery from waste textiles to high-performance polyester materials is achieved, and the product has excellent heat resistance and transparency, is suitable for the fields of high-end packaging, engineering plastics, fibers and the like and has remarkable economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of chemical recycling of waste textiles into polyester technology, and more specifically, to a method for preparing high-permeability and heat-resistant copolyester based on recycled DMT from waste textiles. Background Technology

[0002] Polyethylene terephthalate (PET) is widely used in fibers, films, and engineering plastics due to its excellent mechanical properties and chemical stability. Among these, PET fiber, commonly known as polyester, holds a leading position in the synthetic fiber industry. Polyester's industrial advantages lie not only in its high cost-effectiveness and excellent durability but also in its deep compatibility with the existing textile industry system. However, with the rapid development of the polyester textile industry, the amount of waste polyester textiles generated is increasing year by year, highlighting the growing challenge of its disposal. Therefore, efficient polyester recycling is crucial.

[0003] The recycling methods for waste polyester textiles can be mainly divided into two categories: physical recycling and chemical recycling. Physical recycling uses mechanical and other physical means to process waste textiles into reusable raw materials or products. While this method has the advantages of low industrial cost and relatively simple process, its application usually requires high standards for the composition and purity of the recycled fabrics. In contrast, chemical recycling is based on a series of chemical reactions that depolymerize polyester polymers into original monomers. After separation and purification, these monomers can be repolymerized to obtain new PET materials, thus achieving a closed-loop resource cycle. The most mature chemical recycling process currently is as follows: using waste polyester clothing as raw material, ethylene glycol (EG) is used for alcoholysis to obtain polyethylene terephthalate (BHET). Then, through methanol transesterification and centrifugal recrystallization, dimethyl terephthalate (DMT) is collected. DMT is then used as raw material for transesterification and polycondensation to repolymerize and prepare recycled PET polyester.

[0004] Currently, the glass transition temperature (Tg) of recycled PET polyester chips is mostly between 70 and 80°C, exhibiting poor heat resistance and limiting their applications. Furthermore, PET is prone to crystallization during the cooling stage after melt processing, a process that often leads to decreased transparency in the finished product, affecting its appearance and usability. Therefore, developing novel copolyester materials that combine high heat resistance and high transparency has become an important research direction. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing high-transmittance and heat-resistant copolyester based on recycled DMT from waste textiles. This invention provides a method for preparing DMT through chemical recycling of waste polyester textiles, and using this recycled DMT as raw material to prepare a recycled copolyester with high light transmittance and heat resistance. This method can prepare recycled copolyesters with stable intrinsic viscosity (IV value between 0.60-0.80 dL / g), good color (b value < 10), high light transmittance (L value > 75), and excellent heat resistance (Tg ≥ 85°C). This method realizes a complete technical closed loop from "waste textiles" to "high-quality copolyester materials," opening up a new path with significant economic and environmental benefits for the resource utilization of textile waste.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing high-transparency and heat-resistant copolyester based on recycled DMT from waste textiles includes the following steps:

[0008] (a) Copolymerization modification and transesterification: Regenerated DMT, EG and copolymerization modification monomers are added to a polymerization reactor and transesterification reaction is carried out at 180~220℃ under the catalysis of transesterification catalyst to obtain modified regenerated BHET prepolymer; the copolymerization modification monomer is a compound of at least one of rigid dicarboxylic acid, low molecular weight ester monomer and rigid diol.

[0009] (b) Polycondensation: A stabilizer and a color corrector are added to the modified recycled BHET prepolymer system that has completed transesterification. A pre-polymerization catalyst is added first and pre-polymerization is carried out at a medium vacuum of 50~200Pa and 240~260℃. Then, a final polymerization catalyst is added and final polymerization is carried out at a high vacuum of <50Pa and 270~295℃. After the reaction is completed, the polyester melt is extruded, water-cooled and pelletized to obtain a recycled copolyester material with high light transmittance and high heat resistance.

[0010] The present invention is further configured such that the preparation steps of recycled DMT are as follows: waste polyester textiles are used as raw materials and are subjected to alcoholysis reaction with EG under the catalysis of alcoholysis catalyst to obtain alcoholysis product mainly composed of BHET; then the alcoholysis product is subjected to transesterification reaction with methanol to obtain crude DMT; after cooling crystallization, centrifugation and recrystallization purification, high-purity recycled DMT product is obtained.

[0011] The present invention is further configured such that, in the preparation of recycled DMT, the mass ratio of waste polyester textiles to EG is 1:2 to 3, the amount of alcoholysis catalyst added is 1 to 3% of the mass of waste polyester textiles, and the alcoholysis catalyst used is one or more of potassium carbonate, sodium carbonate, potassium hydroxide, calcium hydroxide, sodium hydroxide, manganese acetate, and zinc acetate.

[0012] The present invention is further configured such that, in the preparation of regenerated DMT, the molar ratio of alcoholysis product to methanol is 1:2-3, and the amount of transesterification catalyst added is 0.1-1% of the mass of BHET. The transesterification catalyst is one or more of zinc acetate, manganese acetate, sodium acetate, calcium acetate, tetrabutyl titanate, stannous octoate, stannous isooctanoate, stannous oxalate, and stannous chloride.

[0013] The present invention is further configured such that, in step (a), the amount of copolymerized modified monomer added is 5-15% of the mass of recycled DMT, and the mass ratio of ethylene glycol to recycled DMT is 75:35-50.

[0014] The present invention is further configured such that, in step (a), the rigid diol is one or more of polyethylene glycol, 1,2-propanediol, 1,3-propanediol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 1,4-cyclohexanediol, and isosorbide; the rigid dicarboxylic acid is one or more of furanyl dicarboxylic acid, terephthalic acid, and isophthalic acid; and the low molecular weight ester monomer is one or more of dimethyl furanyl dicarboxylate, dimethyl isophthalate, and dimethyl carbonate (DMC).

[0015] The present invention is further configured such that, in step (a), the amount of transesterification catalyst added is 0.05-0.3% of the total mass of the rigid diol and ethylene glycol, and the transesterification catalyst is an acetate catalyst.

[0016] The present invention is further configured such that, in step (b), the amount of stabilizer added is 0.1-0.5% of the mass of ethylene glycol added in the transesterification reaction; and the amount of color corrector added is 0.2-0.4% of the mass of ethylene glycol added in the transesterification reaction.

[0017] The stabilizer is one or more of triphenyl phosphate, phosphorous acid, trimethyl phosphate, and dimethyl hydroxyethyl phosphate; the colorant is one or more of organic blue or cobalt salts.

[0018] The present invention is further configured such that, in step (b), the amount of pre-polymerization catalyst added is 0.03-0.3% of the total mass of the rigid diol and ethylene glycol added in the transesterification reaction; and the amount of final polymerization catalyst added is 0.1-0.5% of the total mass of the rigid diol and ethylene glycol added in the transesterification reaction.

[0019] The pre-condensation catalyst and the final condensation catalyst are both one or more of stannous oxide, antimony glycolate, antimony trioxide, antimony acetate, tetrabutyl titanate, tetrapropyl titanate, titanium oxalate, titanium acetate and titanium tetrachloride, and the added pre-condensation catalyst is different from the final condensation catalyst.

[0020] The present invention further specifies that the obtained high-permeability heat-resistant copolyester has an intrinsic viscosity of 0.60~0.80 dL / g, a melting point of 240~250℃, an L value > 75, a b value < 10, and a Tg ≥ 85℃.

[0021] In summary, the present invention has the following beneficial effects:

[0022] (1) Using waste polyester textiles as raw materials, the construction and operation of a closed-loop recycling system of “recycling-depolymerization-regeneration-reuse” can significantly alleviate the environmental pollution problems caused by traditional polyester waste incineration and landfill disposal.

[0023] (2) The present invention adopts a purification path of methanol transesterification combined with recrystallization, which can efficiently remove impurities such as dyes and auxiliaries from waste textile raw materials, and can obtain recycled DMT with a purity of >99%. The alcoholysis, transesterification and melt polycondensation processes used in the present invention are highly compatible with existing polyester industrial production equipment, and no special or expensive equipment is required.

[0024] (3) Using recycled DMT as the core raw material, by adding several of ISB, CHDM, CBDO, FDCA and FDME as comonomers, it is possible not only to significantly improve the Tg of the copolyester and enhance the thermomechanical stability of the material, but also to control the melting point and color value of the copolyester, thereby broadening the application scenarios of recycled copolyester in high-end packaging, engineering plastics, textile fibers and other fields, and improving its high-value utilization level. Attached Figure Description

[0025] Figure 1 The images show a comparison of the appearance of polyester chips prepared in Example 2 and Comparative Example 4; in the images: (a) is the polyester chip of Comparative Example 4, and (b) is the polyester chip of Example 2. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention relates to a method for preparing high-transparency and heat-resistant copolyester based on recycled DMT from waste textiles, comprising the following steps:

[0028] (1) Waste polyester textiles are pretreated by sorting, washing, removing impurities, crushing, and cutting before being sent to the silo. The pretreated waste polyester textiles and EG are then subjected to alcoholysis reaction under the catalysis of an alcoholysis catalyst (the mass ratio of pretreated waste polyester textiles to EG is 1:2-3, the amount of alcoholysis catalyst added is 1-3% of the mass of pretreated waste polyester textiles, and the alcoholysis catalyst is one or more of potassium carbonate, sodium carbonate, potassium hydroxide, calcium hydroxide, sodium hydroxide, manganese acetate, and zinc acetate, and the alcoholysis reaction time is 3- After 6 hours, an alcoholysis product mainly composed of BHET was obtained. Subsequently, the alcoholysis product was subjected to transesterification with methanol to obtain crude DMT (the molar ratio of alcoholysis product to methanol was 1:2-3, the amount of transesterification catalyst added was 0.1-1% of the mass of BHET, and the transesterification catalyst was one or more of zinc acetate, manganese acetate, sodium acetate, calcium acetate, tetrabutyl titanate, stannous octoate, stannous isooctanoate, stannous oxalate, and stannous chloride). After cooling crystallization, centrifugation and recrystallization purification, high-purity regenerated DMT product was obtained.

[0029] (2) Copolymerization modification and transesterification: Regenerated DMT, EG and copolymerization modification monomers are put into a polymerization reactor. Under the catalysis of transesterification catalyst, transesterification reaction is carried out at 180~220℃. During this process, methanol by-product is continuously distilled out and metered until the amount of methanol distilled out reaches 90-95% of the theoretical value and no longer increases, thus obtaining modified regenerated BHET prepolymer.

[0030] In this step, the amount of copolymerized modified monomer added is 5-15% of the mass of recycled DMT, and the mass ratio of ethylene glycol to recycled DMT is 75:35-50.

[0031] The copolymerizing monomer is a complex of at least one of rigid diacids and low-molecular-weight ester monomers with a rigid diol; the rigid diol is one or more of polyethylene glycol, 1,2-propanediol, 1,3-propanediol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 1,4-cyclohexanediol, and isosorbide; the rigid diacid is one or more of furanyl dicarboxylic acid, terephthalic acid, and isophthalic acid; and the low-molecular-weight ester monomer is one or more of dimethyl furanyl dicarboxylate, dimethyl isophthalate, and dimethyl carbonate (DMC).

[0032] The amount of transesterification catalyst added is 0.05-0.3% of the total mass of rigid diol and ethylene glycol. The transesterification catalyst is an acetate catalyst, preferably zinc acetate and manganese acetate.

[0033] (3) Polycondensation: Add stabilizers and colorants to the modified recycled BHET prepolymer system that has completed transesterification. First, add a pre-polymerization catalyst and carry out pre-polymerization for 40-60 min at a medium vacuum of 50-200 Pa and 240-260 °C. Then, add a final polymerization catalyst and carry out final polymerization for 1-1.5 h at a high vacuum of <50 Pa and 270-295 °C. After the reaction is completed, the polyester melt is extruded, water-cooled, and pelletized to obtain a recycled copolyester material with high light transmittance and high heat resistance.

[0034] In this step, the amount of stabilizer added is 0.1~0.5% of the mass of ethylene glycol added in the transesterification reaction; the amount of color corrector added is 0.2~0.4% of the mass of ethylene glycol added in the transesterification reaction; the stabilizer is one or more of triphenyl phosphate, phosphorous acid, trimethyl phosphate, and dimethyl hydroxyethyl phosphate; the color corrector is one or more of organic blue or cobalt salts.

[0035] The amount of prepolymerization catalyst added is 0.03~0.3% of the total mass of the rigid diol and ethylene glycol added in the transesterification reaction; the amount of final polymerization catalyst added is 0.1~0.5% of the total mass of the rigid diol and ethylene glycol added in the transesterification reaction; both the prepolymerization catalyst and the final polymerization catalyst are one or more of stannous oxide, antimony glycolide, antimony trioxide, antimony acetate, tetrabutyl titanate, tetrapropyl titanate, titanium oxalate, titanium acetate and titanium tetrachloride, and the added prepolymerization catalyst is different from the final polymerization catalyst.

[0036] Example 1

[0037] (1) First, waste polyester textiles are pretreated by sorting, washing, removing impurities, crushing and cutting and then sent to the silo. The pretreated waste polyester and ethylene glycol are added to the alcoholysis reactor at a mass ratio of 1:2. Potassium carbonate, an alcoholysis catalyst, is added at 1.5% of the mass of the pretreated waste polyester. The reaction is carried out at 190°C and under stirring for 4 hours to obtain alcoholysis products mainly composed of BHET. Then, methanol is added at a molar ratio of methanol to BHET of 2.5:1. Zinc acetate, an ester exchange catalyst, is added at 0.5% of the mass of BHET. The ester exchange reaction is carried out at 65°C for 2 hours to obtain crude DMT. After cooling crystallization, centrifugation and recrystallization purification, a recycled DMT product with a purity higher than 99% is obtained.

[0038] (2) Weigh 750g of the refined and regenerated DMT product from step (1) and place it in a polymerization reactor; then add 37.5g of furan dicarboxylic acid (FDCA), 30g of 1,4-cyclohexanediethanol (CHDM), 22.5g of 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO) as copolymerization modifiers (total monomer addition is 12% of the mass of DMT) and 430g of EG (ethylene glycol), and add zinc acetate as transesterification catalyst at a total alcohol content (total mass of rigid diol and ethylene glycol) of 0.1wt%. Heat the reaction system to 190℃ for transesterification reaction. During this process, continuously distill off and measure the by-product methanol until the methanol distillation reaches 95% of the theoretical value and no longer increases, to obtain the modified and regenerated BHET prepolymer;

[0039] (3) To the modified regenerated BHET prepolymer system that has completed transesterification, 0.6 g of dimethyl hydroxyethyl phosphate as a stabilizer, 1 g of cobalt acetate as a colorant, and 0.22 g of tetrabutyl titanate as a prepolymerization catalyst were added sequentially. The prepolymerization reaction was carried out at 100 Pa and 250 °C for 40 min. 0.52 g of antimony glycol was added as a final polymerization catalyst, and the final polymerization reaction was carried out at 30 Pa and 285 °C for 1 h. When the system entered the high vacuum polymerization stage, the small molecule ethylene glycol obtained from the reaction was continuously extracted, and the reaction progress was judged by real-time monitoring of the change in the current of the stirring motor of the reactor. Subsequently, under nitrogen pressure (0.1 MPa), the polymer melt was extruded through the casting head, cooled in a water bath, and pelletized to obtain high-permeability heat-resistant copolyester chips.

[0040] Example 2

[0041] High-transparency and heat-resistant copolyester chips were prepared according to Example 1, except that in step (2), dimethyl furanate (FDME) of equal mass was used instead of furanate (FDCA).

[0042] Example 3

[0043] High-permeability and heat-resistant copolyester chips were prepared according to Example 1, except that the amount of copolymer modified monomers added in step (2) was changed: FDCA 37.5g, CBDO 15g, CHDM 37.5g.

[0044] Example 4

[0045] High-permeability and heat-resistant copolyester chips were prepared according to Example 1, except that in step (2), dimethyl carbonate (DMC) was used instead of furanyl dicarboxylic acid (FDCA).

[0046] Comparative Example 1

[0047] Polyester chips were prepared according to Example 1, but in step (2) the comonomers furan dicarboxylic acid (FDCA), 1,4-cyclohexanediethanol (CHDM), and 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO) were not added.

[0048] Comparative Example 2

[0049] Polyester chips were prepared according to Example 1, except that in step (2), only 37.5g of FDCA was added as a comonomer, and CBDO and CHDM were not added.

[0050] Comparative Example 3

[0051] Polyester chips were prepared according to Example 1, but only tetrabutyl titanate was used as a catalyst throughout the polycondensation process (i.e., steps (3) and (4)).

[0052] Comparative Example 4

[0053] Polyester chips were prepared according to Example 1, but only antimony glycolate was used as a catalyst throughout the polycondensation process (i.e., steps (3) and (4)). Figure 1 The images show a comparison of the appearance of polyester chips prepared in Comparative Example 4 and Example 2. (a) is a polyester chip from Comparative Example 4, and (b) is a polyester chip from Example 2.

[0054] The properties of the polyester chips prepared in Examples 1-4 and Comparative Examples 1-4 were tested respectively (intrinsic viscosity and color were tested according to GB / T14190-2017; glass transition temperature and melting point were determined according to ASTM D3418-21 standard), and the results are shown in Table 1.

[0055] Table 1

[0056]

[0057] Analysis of Table 1 shows that: by comparing the polyester properties of the examples with those of Comparative Example 1, it is shown that the specific rigid monomer combination introduced in this invention is the fundamental reason for the leap in heat resistance (Tg); by comparing with Comparative Example 2, it is shown that the modification effect of a single rigid monomer is limited, while the combination of composite monomers can significantly improve the heat resistance and transparency of the product; by comparing with Comparative Examples 3 and 4, it is shown that the segmented catalytic polycondensation process is crucial for obtaining excellent color.

[0058] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-permeability and heat-resistant copolyester based on recycled DMT from waste textiles, characterized in that, Includes the following steps: (a) Copolymerization modification and transesterification: Regenerated DMT, EG and copolymerization modification monomers are added to a polymerization reactor and transesterification reaction is carried out at 180~220℃ under the catalysis of transesterification catalyst to obtain modified regenerated BHET prepolymer; the copolymerization modification monomer is a compound of at least one of rigid dicarboxylic acid, low molecular weight ester monomer and rigid diol. (b) Polycondensation: A stabilizer and a color corrector are added to the modified recycled BHET prepolymer system that has completed transesterification. A pre-polymerization catalyst is added first and pre-polymerization is carried out at a medium vacuum of 50~200Pa and 240~260℃. Then, a final polymerization catalyst is added and final polymerization is carried out at a high vacuum of <50Pa and 270~295℃. After the reaction is completed, the polyester melt is extruded, water-cooled and pelletized to obtain a recycled copolyester material with high light transmittance and high heat resistance.

2. The method for preparing high-transparency and heat-resistant copolyester based on recycled DMT from waste textiles according to claim 1, characterized in that, The preparation steps of recycled DMT are as follows: waste polyester textiles are used as raw materials and are reacted with EG under the catalysis of an alcoholysis catalyst to obtain alcoholysis products mainly composed of BHET; then the alcoholysis products are reacted with methanol to obtain crude DMT. After cooling crystallization, centrifugation and recrystallization purification, high-purity recycled DMT products are obtained.

3. The method for preparing high-permeability and heat-resistant copolyester based on recycled DMT from waste textiles according to claim 2, characterized in that, In the preparation of recycled DMT, the mass ratio of waste polyester textiles to EG is 1:2 to 3, and the amount of alcoholysis catalyst added is 1 to 3% of the mass of waste polyester textiles. The alcoholysis catalyst used is one or more of potassium carbonate, sodium carbonate, potassium hydroxide, calcium hydroxide, sodium hydroxide, manganese acetate, and zinc acetate.

4. The method for preparing high-permeability and heat-resistant copolyester based on recycled DMT from waste textiles according to claim 2, characterized in that, In the preparation of regenerated DMT, the molar ratio of alcoholysis product to methanol is 1:2-3, and the amount of transesterification catalyst added is 0.1-1% of the mass of BHET. The transesterification catalyst is one or more of zinc acetate, manganese acetate, sodium acetate, calcium acetate, tetrabutyl titanate, stannous octoate, stannous isooctanoate, stannous oxalate, and stannous chloride.

5. The method for preparing high-transparency and heat-resistant copolyester based on recycled DMT from waste textiles according to claim 1, characterized in that, In step (a), the amount of copolymerized modified monomer added is 5-15% of the mass of recycled DMT, and the mass ratio of ethylene glycol to recycled DMT is 75:35-50.

6. The method for preparing high-permeability and heat-resistant copolyester based on recycled DMT from waste textiles according to claim 1, characterized in that, In step (a), the rigid diol is one or more of polyethylene glycol, 1,2-propanediol, 1,3-propanediol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 1,4-cyclohexanediol, and isosorbide; the rigid dicarboxylic acid is one or more of furanyl dicarboxylic acid, terephthalic acid, and isophthalic acid; and the low molecular weight ester monomer is one or more of dimethyl furanyl dicarboxylate, dimethyl isophthalate, and dimethyl carbonate (DMC).

7. The method for preparing high-transparency and heat-resistant copolyester based on recycled DMT from waste textiles according to claim 1, characterized in that, In step (a), the amount of transesterification catalyst added is 0.05-0.3% of the total mass of the rigid diol and ethylene glycol, and the transesterification catalyst is an acetate catalyst.

8. The method for preparing high-transparency and heat-resistant copolyester based on recycled DMT from waste textiles according to claim 1, characterized in that, In step (b), the amount of stabilizer added is 0.1-0.5% of the mass of ethylene glycol added in the transesterification reaction; the amount of color corrector added is 0.2-0.4% of the mass of ethylene glycol added in the transesterification reaction. The stabilizer is one or more of triphenyl phosphate, phosphorous acid, trimethyl phosphate, and dimethyl hydroxyethyl phosphate; the colorant is one or more of organic blue or cobalt salts.

9. The method for preparing high-permeability and heat-resistant copolyester based on recycled DMT from waste textiles according to claim 1, characterized in that, In step (b), the amount of pre-polymerization catalyst added is 0.03-0.3% of the total mass of the rigid diol and ethylene glycol added in the transesterification reaction; the amount of final polymerization catalyst added is 0.1-0.5% of the total mass of the rigid diol and ethylene glycol added in the transesterification reaction. The pre-condensation catalyst and the final condensation catalyst are both one or more of stannous oxide, antimony glycolate, antimony trioxide, antimony acetate, tetrabutyl titanate, tetrapropyl titanate, titanium oxalate, titanium acetate and titanium tetrachloride, and the added pre-condensation catalyst is different from the final condensation catalyst.

10. The method for preparing high-transparency and heat-resistant copolyester based on recycled DMT from waste textiles according to claim 1, characterized in that, The resulting high-permeability and heat-resistant copolyester has an intrinsic viscosity of 0.60~0.80 dL / g, a melting point of 240~250℃, an L value >75, a b value <10, and a Tg ≥85℃.

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