Process for preparing regenerated polyester from waste polyester material

Abstract

The invention relates to a process for preparing regenerated polyester from a waste polyester material, and belongs to the technical field of waste polyester reutilization. According to the method, impurity residues in the waste polyester material are effectively reduced through two-stage chemical cleaning, and the purity of polyester fragments is improved. The polyester fragments and ethylene glycol are rapidly depolymerized through microwave heating under the action of a tetrabutyl titanate catalyst, so that the reaction efficiency and the product controllability are remarkably improved. And in the polycondensation stage, the epoxy chain extender and the modified nano silicon dioxide are added, so that the molecular structure of the regenerated polyester is further enhanced, and the mechanical property and the thermal stability of the regenerated polyester are improved. In addition, the addition of the antistatic agent prepared by taking the polyurethane coated carbon nanotube as a core and grafting a polyester compatible monomer on the outer layer effectively improves the electrical performance of the regenerated polyester, and enhances the application stability of the fiber.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycling of waste polyester, and relates to a process for preparing recycled polyester from waste polyester materials. Background Art

[0002] Waste polyester materials, especially waste polyester bottles (PET bottles), exist in large quantities due to their wide application in beverage packaging. Polyester materials possess excellent physical and chemical properties, including high strength, heat resistance, chemical corrosion resistance, and good transparency, making them an important engineering plastic. At the same time, polyester fiber, as a synthetic fiber, is widely used in the textile industry. Polyester fiber has excellent abrasion resistance, wrinkle resistance, and heat resistance, and has a soft handfeel and bright color, occupying an important position in the fields of clothing, home textiles, etc. However, with the continuous growth of the demand for polyester fiber, the problem of recycling and reusing waste polyester materials has become increasingly prominent. How to convert waste polyester materials into high-quality recycled polyester has become one of the current research hotspots.

[0003] Preparing recycled polyester from waste polyester materials has significant environmental and economic benefits. First of all, the recycling of waste polyester can reduce environmental pollution. Polyester materials are difficult to degrade under natural conditions, and a large number of waste polyester bottles will have a serious impact on the ecological environment. By recycling waste polyester bottle chips, the accumulation of plastic waste can be effectively reduced, and the environmental burden can be lowered. Secondly, using waste polyester materials to prepare recycled polyester helps to save resources and energy. Producing brand-new polyester fiber requires consuming a large amount of petroleum resources, while the production process of recycled polyester significantly reduces the dependence on petroleum resources, lowering production costs and energy consumption. In addition, recycled polyester can maintain properties similar to those of brand-new polyester fiber, meeting the requirements of the textile industry, and is a sustainable raw material choice.

[0004] However, the existing waste polyester material recycling technologies still have some deficiencies. First of all, traditional physical recycling methods, such as mechanical crushing and melt spinning, cannot completely remove impurities in waste polyester, resulting in low quality and unstable performance of recycled polyester. Secondly, although chemical recycling methods can depolymerize polyester into monomers, the conventional chemical depolymerization process has a long reaction time, high energy consumption, and requires the use of a large amount of chemical reagents, posing certain environmental risks. Moreover, the antistatic performance of polyester fiber is poor, which limits its promotion in some high-end applications. Therefore, it is necessary to develop an efficient, environmentally friendly, and economical process for preparing recycled polyester from waste polyester materials, improve the quality and performance of recycled polyester, and promote its wide application in the textile industry. Summary of the Invention

[0005] The present invention relates to a process for preparing recycled polyester from waste polyester materials, belonging to the technical field of waste polyester recycling. Through two-stage chemical cleaning, the present invention effectively reduces the impurity residue in waste polyester materials and improves the purity of polyester chips. Under the action of tetrabutyl titanate catalyst, polyester chips and ethylene glycol are depolymerized rapidly by microwave heating, significantly improving the reaction efficiency and product controllability. In the polycondensation stage, epoxy chain extender and modified nano-silica are added to further enhance the molecular structure of recycled polyester and improve its mechanical properties and thermal stability. In addition, the addition of an antistatic agent prepared by grafting a polyester-compatible monomer on the outer layer with polyurethane-coated carbon nanotubes as the core effectively improves the electrical properties of recycled polyester and enhances the application stability of the fiber.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] A process for preparing recycled polyester from waste polyester materials, comprising the following steps:

[0008] (1) Crushing waste polyester bottle chips and then performing two-stage chemical cleaning to obtain polyester chips;

[0009] (2) Mixing polyester chips with ethylene glycol, adding tetrabutyl titanate catalyst, and performing microwave-assisted depolymerization for 30 - 40 min;

[0010] (3) Adding epoxy chain extender, modified nano-silica and antistatic agent, and heating to 260 - 270 °C under a vacuum of 20 - 50 Pa for polycondensation to obtain recycled polyester materials;

[0011] (4) Spinning the recycled polyester materials by a twin-screw extruder, the spinneret has a microporous structure, the draw ratio is 3.5 - 4.5, and the heat setting temperature is 180 - 200 °C.

[0012] As a preferred technical solution of the present invention, the two-stage chemical cleaning in step (1) is that waste polyester bottle chips are ultrasonically cleaned with an alkaline cleaning solution at 50 - 70 °C for 20 - 30 min and then soaked in an ethanol-acetone mixed solution with a volume ratio of 1:1 for 30 min; the alkaline cleaning solution is: 3 - 7 wt% NaOH, 0.3 - 0.7 wt% surfactant sodium dodecylbenzenesulfonate, and the balance is deionized water.

[0013] As a preferred technical solution of the present invention, the mass ratio of the polyester chips, ethylene glycol, and tetrabutyl titanate in step (2) is 1:1.2 - 1.8:0.003 - 0.008.

[0014] As a preferred technical solution of the present invention, the epoxy chain extender in step (3) is ADR-4370, and the addition amount is 0.3 - 0.8 wt%.

[0015] As a preferred technical solution of the present invention, the addition amount of the modified nano-silica in step (3) is 1-3 wt%;

[0016] The preparation of the modified nano-silica includes the following steps:

[0017] A1. Disperse nano-silica in 3 mol / L hydrochloric acid solution and ultrasonically treat for 1-3 h, then wash and dry to obtain pretreated nano-silica;

[0018] A2. Disperse the pretreated nano-silica in a 5 wt% ethanol solution with a mass ratio of 3-5 times, stir evenly, add 3-7% of KH-550 silane coupling agent based on the mass of the pretreated nano-silica, and reflux at 80 °C for 5-7 h, then wash and vacuum dry to obtain amino-functionalized nano-silica;

[0019] A3. Mix polyethylene terephthalate and amino-functionalized nano-silica in a mass ratio of 1:0.5-1.5, under nitrogen protection, melt and stir at 230-250 °C for 40-80 min, and then obtain modified silica after cooling and grinding.

[0020] As a preferred technical solution of the present invention, the antistatic agent in step (3) is polyurethane-coated carbon nanotubes and surface-grafted ethylene glycol phthalate oligomers; the addition amount of the antistatic agent is 1-3 wt%.

[0021] As a preferred technical solution of the present invention, the preparation of the antistatic agent includes the following steps:

[0022] B1. Place multi-walled carbon nanotubes in a mixed acid solution of 65% concentrated nitric acid and 98% concentrated sulfuric acid with a volume ratio of 1:3, reflux at 70-90 °C for 3-5 h, and then wash and dry;

[0023] B2. Disperse the acidified multi-walled carbon nanotubes in 1 mol / L hydrochloric acid solution, and add aniline and ultrasonically treat for 20-40 min;

[0024] B3. Dropwise add ammonium persulfate and stir at 0-4 °C for 10-14 h to obtain polyaniline-coated carbon nanotubes;

[0025] B4. Mix polyaniline-coated carbon nanotubes and polyethylene terephthalate in a mass ratio of 1:0.5-1.5, add 0.05-0.2 wt% tetrabutyl titanate, and react at 230-250 °C for 1-3 h under nitrogen protection to obtain the antistatic agent.

[0026] As a preferred technical solution of the present invention, the mass ratio of the multi-walled carbon nanotubes, the mixed acid solution, the hydrochloric acid solution, aniline, and ammonium persulfate is 1:2-4:2-4:0.3-0.7:0.3-0.7.

[0027] Advantages of the present invention:

[0028] (1) Through two-stage chemical cleaning, the present invention uses an alkaline cleaning solution and an ethanol-acetone mixture to thoroughly remove impurities in waste polyester bottle chips, ensuring high purity of the raw materials. Under the action of tetrabutyl titanate catalyst, the microwave-assisted depolymerization technology quickly and efficiently depolymerizes polyester fragments into monomers. This process not only significantly shortens the reaction time but also reduces energy consumption. By adding an epoxy chain extender and modified nano-silica in the polycondensation stage, the molecular structure of the recycled polyester is further enhanced, improving its mechanical properties and thermal stability.

[0029] (2) The present invention uses multi-walled carbon nanotubes. Through a series of chemical treatments and reactions, carbon nanotubes coated with polyurethane are prepared, and the outer layer is grafted with ethylene glycol terephthalate oligomers. Such an antistatic agent not only has excellent antistatic performance but also has good compatibility with the recycled polyester material, can significantly reduce the surface resistance of the fiber, reduce static electricity accumulation, and improve the safety and comfort of fiber use. Specific embodiments

[0030] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following examples are used to detail the specific embodiments, structures, features, and effects of the present invention.

[0031] In the following examples and comparative examples, the ethylene glycol terephthalate was purchased from Shenzhen Hansen Plastic Technology Co., Ltd.; the multi-walled carbon nanotubes were purchased from Beijing Carbon Yang Technology Co., Ltd.; and the nano-silica was purchased from Hubei Huifu Nano Materials Co., Ltd.

[0032] Example 1

[0033] A process for preparing recycled polyester from waste polyester materials, comprising the following steps:

[0034] (1) Crushing waste polyester bottle chips and then performing two-stage chemical cleaning to obtain polyester fragments;

[0035] (2) Mixing the polyester fragments with ethylene glycol, adding tetrabutyl titanate catalyst, and performing microwave-assisted depolymerization for 35 min;

[0036] (3) Adding an epoxy chain extender, modified nano-silica, and an antistatic agent, and heating to 265 °C under a vacuum of 35 Pa for polycondensation to obtain recycled polyester materials;

[0037] (4) Spinning the recycled polyester materials through a twin-screw extruder, the spinneret has a microporous structure, the draw ratio is 4, and the heat setting temperature is 190 °C.

[0038] The two-stage chemical cleaning in step (1) is that the waste polyester bottle chips are cleaned with an alkaline cleaning solution by ultrasonic for 25 min at 60 °C and then soaked in a mixed solution of ethanol-acetone with a volume ratio of 1:1 for 30 min; the alkaline cleaning solution is: 5 wt% NaOH, 0.5 wt% surfactant sodium dodecylbenzenesulfonate, and the balance is deionized water.

[0039] In step (2), the mass ratio of the polyester fragments, ethylene glycol, and tetrabutyl titanate is 1:1.5:0.005.

[0040] The epoxy chain extender in step (3) is ADR-4370, and the addition amount is 0.5 wt%.

[0041] In step (3), the addition amount of the modified nano-silica is 2 wt%;

[0042] The preparation of the modified nano-silica includes the following steps:

[0043] A1. Disperse the nano-silica in a 3 mol / L hydrochloric acid solution, ultrasonic for 2 h, then wash and dry to obtain pretreated nano-silica;

[0044] A2. Disperse the pretreated nano-silica in a 5 wt% ethanol solution with a mass ratio of 4 times, stir evenly, add 5% of KH-550 silane coupling agent based on the mass of the pretreated nano-silica, reflux and react at 80 °C for 6 h, wash and vacuum dry to obtain amino-functionalized nano-silica;

[0045] A3. Mix polyethylene terephthalate and amino-functionalized nano-silica at a mass ratio of 1:1, under nitrogen protection, melt and stir at 240 °C for 60 min, and obtain modified silica after cooling and grinding.

[0046] The antistatic agent in step (3) is polyurethane-coated carbon nanotubes, and phthalic acid ethylene glycol ester oligomers are grafted on the surface; the addition amount of the antistatic agent is 2 wt%.

[0047] The preparation of the antistatic agent includes the following steps:

[0048] B1. Place multi-walled carbon nanotubes in a mixed acid solution of 65% concentrated nitric acid and 98% concentrated sulfuric acid with a volume ratio of 1:3, reflux at 80 °C for 4 h, then wash and dry;

[0049] B2. Disperse the acidified multi-walled carbon nanotubes in a 1 mol / L hydrochloric acid solution, add aniline and ultrasonic for 30 min;

[0050] B3. Dropwise add ammonium persulfate, stir at 2 °C for 12 h to obtain polyaniline-coated carbon nanotubes;

[0051] B4. Mix polyaniline-coated carbon nanotubes and polyethylene terephthalate in a mass ratio of 1:0.5 - 1.5, add 0.1 wt% tetrabutyl titanate, and react at 240 °C for 2 h under nitrogen protection to obtain an antistatic agent.

[0052] The mass ratio of the multi-walled carbon nanotubes, mixed acid solution, hydrochloric acid solution, aniline, and ammonium persulfate is 1:3:3:0.5:0.5.

[0053] Example 2

[0054] A process for preparing recycled polyester from waste polyester materials, comprising the following steps:

[0055] (1) Crush waste polyester bottle chips and perform two-stage chemical cleaning to obtain polyester fragments;

[0056] (2) Mix the polyester fragments with ethylene glycol, add tetrabutyl titanate catalyst, and perform microwave-assisted depolymerization for 30 - 40 min;

[0057] (3) Add an epoxy chain extender, modified nano-silica, and an antistatic agent, and heat to 260 °C under a vacuum of 20 Pa for polycondensation to obtain recycled polyester material;

[0058] (4) Spin the recycled polyester material with a twin-screw extruder, the spinneret has a microporous structure, the draw ratio is 3.5, and the heat setting temperature is 180 °C.

[0059] The two-stage chemical cleaning in step (1) is that the waste polyester bottle chips are ultrasonically cleaned with an alkaline cleaning solution at 50 °C for 20 min and then soaked in an ethanol-acetone mixed solution with a volume ratio of 1:1 for 30 min; the alkaline cleaning solution is: 3 wt% NaOH, 0.3 wt% surfactant sodium dodecylbenzenesulfonate, and the balance is deionized water.

[0060] The mass ratio of the polyester fragments, ethylene glycol, and tetrabutyl titanate in step (2) is 1:1.2:0.003.

[0061] The epoxy chain extender in step (3) is ADR-4370, and the addition amount is 0.3 wt%.

[0062] The addition amount of the modified nano-silica in step (3) is 1 wt%;

[0063] The preparation of the modified nano-silica includes the following steps:

[0064] A1. Disperse nano-silica in a 3 mol / L hydrochloric acid solution, ultrasonically treat for 1 h, then wash and dry to obtain pretreated nano-silica;

[0065] A2. Disperse the pretreated nano-silica in a 5wt% ethanol solution with a mass ratio of 3 times, stir evenly, add KH-550 silane coupling agent accounting for 3% of the mass of the pretreated nano-silica, and reflux at 80°C for 5 h. After washing and vacuum drying, amino-functionalized nano-silica is obtained.

[0066] A3. Mix polyethylene terephthalate and amino-functionalized nano-silica at a mass ratio of 1:0.5. Under nitrogen protection, melt and stir at 230°C for 40 min, and then obtain modified silica through cooling and grinding.

[0067] The antistatic agent described in step (3) is carbon nanotubes coated with polyurethane and grafted with ethylene glycol terephthalate oligomers on the surface; the addition amount of the antistatic agent is 1wt%.

[0068] The preparation of the antistatic agent includes the following steps:

[0069] B1. Place multi-walled carbon nanotubes in a mixed acid solution of 65% concentrated nitric acid and 98% concentrated sulfuric acid with a volume ratio of 1:3, reflux at 70°C for 3 h, and then wash and dry.

[0070] B2. Disperse the acidified multi-walled carbon nanotubes in a 1mol / L hydrochloric acid solution, add aniline, and ultrasonically treat for 20 min.

[0071] B3. Dropwise add ammonium persulfate and stir at 0°C for 10 h to obtain polyaniline-coated carbon nanotubes.

[0072] B4. Mix polyaniline-coated carbon nanotubes and polyethylene terephthalate glycol at a mass ratio of 1:0.5, add 0.05wt% tetrabutyl titanate, and react at 230°C for 1 h under nitrogen protection to obtain the antistatic agent.

[0073] The mass ratio of the multi-walled carbon nanotubes, mixed acid solution, hydrochloric acid solution, aniline, and ammonium persulfate is 1:2:2:0.3:0.3.

[0074] Example 3

[0075] A process for preparing recycled polyester from waste polyester materials includes the following steps:

[0076] (1) Crush waste polyester bottle chips and then perform two-stage chemical cleaning to obtain polyester fragments.

[0077] (2) Mix the polyester fragments with ethylene glycol, add tetrabutyl titanate catalyst, and carry out microwave-assisted depolymerization for 40 min.

[0078] (3) Add an epoxy chain extender, modified nano-silica, and an antistatic agent, heat to 270°C under a vacuum of 50 Pa for polycondensation to obtain recycled polyester materials.

[0079] (4) The recycled polyester material is spun by a twin-screw extruder. The spinneret has a microporous structure, the draw ratio is 4.5, and the heat setting temperature is 200 °C.

[0080] The two-stage chemical cleaning described in step (1) is that the waste polyester bottle chips are ultrasonically cleaned with an alkaline cleaning solution at 70 °C for 30 min and then soaked in an ethanol-acetone mixed solution with a volume ratio of 1:1 for 30 min. The alkaline cleaning solution is: 7 wt% NaOH, 0.7 wt% surfactant sodium dodecylbenzenesulfonate, and the balance is deionized water.

[0081] The mass ratio of the polyester chips, ethylene glycol, and tetrabutyl titanate described in step (2) is 1:1.8:0.008.

[0082] The epoxy chain extender described in step (3) is ADR-4370, and the addition amount is 0.8 wt%.

[0083] The addition amount of the modified nano-silica described in step (3) is 3 wt%;

[0084] The preparation of the modified nano-silica includes the following steps:

[0085] A1. The nano-silica is dispersed in a 3 mol / L hydrochloric acid solution and ultrasonically treated for 3 h, then washed and dried to obtain pretreated nano-silica;

[0086] A2. The pretreated nano-silica is dispersed in a 5 wt% ethanol solution with a mass ratio of 5 times, stirred evenly, and 7% of KH-550 silane coupling agent based on the mass of the pretreated nano-silica is added. The reaction is refluxed at 80 °C for 7 h, washed, and vacuum dried to obtain amino-functionalized nano-silica;

[0087] A3. Polyethylene terephthalate and amino-functionalized nano-silica are mixed at a mass ratio of 1:1.5. Under nitrogen protection, they are melt-stirred at 250 °C for 80 min, and then cooled and ground to obtain modified silica.

[0088] The antistatic agent described in step (3) is polyurethane-coated carbon nanotubes, and phthalic acid ethylene glycol oligomers are grafted on the surface; the addition amount of the antistatic agent is 3 wt%.

[0089] The preparation of the antistatic agent includes the following steps:

[0090] B1. The multi-walled carbon nanotubes are placed in a mixed acid solution of 65% concentrated nitric acid and 98% concentrated sulfuric acid with a volume ratio of 1:3, refluxed at 90 °C for 5 h, and then washed and dried;

[0091] B2. The acidified multi-walled carbon nanotubes are dispersed in a 1 mol / L hydrochloric acid solution, and aniline is added and ultrasonically treated for 40 min;

[0092] B3. Add ammonium persulfate dropwise and stir at 4 °C for 14 h to obtain carbon nanotubes coated with polyaniline;

[0093] B4. Mix the carbon nanotubes coated with polyaniline and polyethylene terephthalate in a mass ratio of 1:1.5, add 0.2 wt% tetrabutyl titanate, and react at 250 °C for 3 h under nitrogen protection to obtain an antistatic agent.

[0094] As a preferred technical solution of the present invention, the mass ratio of the multi-walled carbon nanotubes, the mixed acid solution, the hydrochloric acid solution, aniline, and ammonium persulfate is 1:4:4:0.7:0.7.

[0095] Example 4

[0096] A process for preparing recycled polyester from waste polyester materials, comprising the following steps:

[0097] (1) Crush the waste polyester bottle chips and perform two-stage chemical cleaning to obtain polyester fragments;

[0098] (2) Mix the polyester fragments with ethylene glycol, add tetrabutyl titanate catalyst, and perform microwave-assisted depolymerization for 32 min;

[0099] (3) Add an epoxy chain extender, modified nano-silica, and an antistatic agent, and heat to 262 °C under a vacuum of 35 Pa for polycondensation to obtain a recycled polyester material;

[0100] (4) The recycled polyester material is spun by a twin-screw extruder, the spinneret has a microporous structure, the draw ratio is 3.8, and the heat setting temperature is 185 °C.

[0101] The two-stage chemical cleaning in step (1) is that the waste polyester bottle chips are cleaned with an alkaline cleaning solution by ultrasonic wave at 55 °C for 22 min, and then soaked in an ethanol-acetone mixed solution with a volume ratio of 1:1 for 30 min; the alkaline cleaning solution is: 4 wt% NaOH, 0.6 wt% surfactant sodium dodecylbenzenesulfonate, and the balance is deionized water.

[0102] The mass ratio of the polyester fragments, ethylene glycol, and tetrabutyl titanate in step (2) is 1:1.4:0.006.

[0103] The epoxy chain extender in step (3) is ADR-4370, and the addition amount is 0.4 wt%.

[0104] The addition amount of the modified nano-silica in step (3) is 3 wt%;

[0105] The preparation of the modified nano-silica includes the following steps:

[0106] A1. Disperse nano-silica in a 3 mol / L hydrochloric acid solution, ultrasonic for 2 h, then wash and dry to obtain pretreated nano-silica;

[0107] A2. Disperse the pretreated nano-silica in a 5wt% ethanol solution with a mass ratio of 5 times, stir evenly, add KH-550 silane coupling agent accounting for 7% of the mass of the pretreated nano-silica, reflux at 80 °C for 5 h, wash and dry under vacuum to obtain amino-functionalized nano-silica;

[0108] A3. Mix polyethylene terephthalate and amino-functionalized nano-silica at a mass ratio of 1:0.8, under nitrogen protection, melt and stir at 235 °C for 48 min, and obtain modified silica through cooling and grinding.

[0109] The antistatic agent described in step (3) is polyurethane-coated carbon nanotubes, and terephthalic acid ethylene glycol oligomers are grafted on the surface; the addition amount of the antistatic agent is 1wt%.

[0110] The preparation of the antistatic agent includes the following steps:

[0111] B1. Place multi-walled carbon nanotubes in a mixed acid solution of 65% concentrated nitric acid and 98% concentrated sulfuric acid with a volume ratio of 1:3, reflux at 78 °C for 3 - 5 h, and then wash and dry;

[0112] B2. Disperse the acidified multi-walled carbon nanotubes in a 1mol / L hydrochloric acid solution, add aniline and perform ultrasonic treatment for 25 min;

[0113] B3. Dropwise add ammonium persulfate and stir at 1 °C for 11 h to obtain polyaniline-coated carbon nanotubes;

[0114] B4. Mix polyaniline-coated carbon nanotubes and polyethylene terephthalate at a mass ratio of 1:0.7, add 0.08wt% tetrabutyl titanate, and react at 235 °C for 3 h under nitrogen protection to obtain the antistatic agent.

[0115] The mass ratio of the multi-walled carbon nanotubes, the mixed acid solution, the hydrochloric acid solution, aniline, and ammonium persulfate is 1:2:2:0.7:0.7.

[0116] Comparative Example 1

[0117] Based on Example 1, do not perform two-stage chemical cleaning, and the rest is the same as Example 1.

[0118] Comparative Example 2

[0119] Based on Example 1, do not modify the nano-silica, and the rest is the same as Example 1.

[0120] Comparative Example 3

[0121] Based on Example 1, directly add carbon nanotubes as the antistatic agent, and the rest is the same as Example 1.

[0122] Performance test:

[0123] The elongation at break and breaking strength of Examples 1-4 and Comparative Examples 1-3 were tested according to GB / T 14344-2008; the surface specific resistance of Examples 1-4 and Comparative Examples 1-3 was tested according to the experimental method of specific resistance of synthetic staple fibers in GB / T 14342-1993.

[0124]

[0125] It can be seen from the test results that the two-stage chemical cleaning of the present invention effectively reduces the impurity residues in waste polyester materials. The addition of an epoxy chain extender and modified nano-silica enhances the molecular structure of recycled polyester and improves its mechanical properties. The addition of an antistatic agent prepared by using polyurethane-coated carbon nanotubes as the core and grafting polyester-compatible monomers on the outer layer effectively improves the electrical properties of recycled polyester.

[0126] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications within the scope of the technical solution of the present invention to obtain equivalent embodiments with equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any indirect modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A process for preparing recycled polyester using waste polyester materials, characterized in that: The following steps are involved: (1) crushing waste polyester bottle flakes and performing two-stage chemical cleaning to obtain polyester fragments; (2) mixing the polyester fragments with ethylene glycol, adding tetrabutyl titanate catalyst, and performing microwave-assisted depolymerization for 30-40 min; (3) adding epoxy chain extender, modified nano-silica and antistatic agent, heating to 260-270° C. under vacuum degree of 20-50 Pa for polycondensation to obtain recycled polyester material; (4) The recycled polyester material is spun by a twin-screw extruder, the traction multiple is 3.5-4.5, and the heat setting temperature is 180-200°C.

2. The process for preparing recycled polyester from waste polyester materials according to claim 1, characterized in that: The two-stage chemical cleaning in step (1) is to clean the waste polyester bottle pieces with an alkaline cleaning solution at 50-70° C. for 20-30 minutes by ultrasonication, and then soak them in an ethanol-acetone mixture with a volume ratio of 1:1 for 30 minutes; the alkaline cleaning solution is: 3-7wt% NaOH, 0.3-0.7wt% surfactant sodium dodecylbenzene sulfonate, and the remainder is deionized water.

3. The process for preparing recycled polyester from waste polyester materials according to claim 1, characterized in that: In step (2), the mass ratio of the polyester fragments, ethylene glycol and tetrabutyl titanate is 1:1.2-1.8:0.003-0.

008.

4. The process for preparing recycled polyester from waste polyester materials according to claim 1, characterized in that: The epoxy chain extender in step (3) is ADR-4370, and the addition amount is 0.3-0.8wt%.

5. The process for preparing recycled polyester from waste polyester materials according to claim 1, characterized in that: The modified nano-silicon dioxide added in step (3) is 1-3 wt %; The modified nano-silicon dioxide preparation comprises the following steps: A1, dispersing nano-silica in a 3 mol / L hydrochloric acid solution, ultrasonicating for 1-3 hours, and then washing and drying to obtain pretreated nano-silica; A2, dispersing the pretreated nano-silica in a 5wt% ethanol solution of 3-5 times the mass ratio, stirring evenly, adding 3-7% of the mass of the pretreated nano-silica KH-550 silane coupling agent, reflux at 80°C for 5-7h, washing and vacuum drying to obtain amino nano-silica; A3. Polyethylene terephthalate and amino-modified nano-silica are mixed in a mass ratio of 1:0.5-1.5, melt-stirred at 230-250° C. for 40-80 min under nitrogen protection, and then cooled and ground to obtain modified silica.

6. The process for preparing recycled polyester from waste polyester materials according to claim 1, characterized in that: The antistatic agent in step (3) is polyurethane-coated carbon nanotubes with surface grafted ethylene glycol terephthalate oligomers; the amount of the antistatic agent added is 1-3wt%.

7. The process for preparing recycled polyester from waste polyester materials according to claim 6, characterized in that: The preparation of the antistatic agent comprises the following steps: B1. Place the multi-arm carbon nanotubes in a mixed acid solution of 65% concentrated nitric acid and 98% concentrated sulfuric acid in a volume ratio of 1:3, reflux at 70-90° C. for 3-5 hours, and then wash and dry; B2, dispersing the acidified multi-arm carbon nanotubes in a 1 mol / L hydrochloric acid solution, adding aniline and ultrasonically treating for 20-40 min; B3, adding ammonium persulfate dropwise, stirring at 0-4°C for 10-14h to obtain polyaniline-coated carbon nanotubes; B4. Mix polyaniline-coated carbon nanotubes and polyethylene terephthalate in a mass ratio of 1:0.5-1.5, add 0.05-0.2wt% tetrabutyl titanate, and react at 230-250°C for 1-3h under nitrogen protection to obtain an antistatic agent.

8. The process for preparing recycled polyester from waste polyester materials according to claim 7, characterized in that: The mass ratio of the multi-arm carbon nanotubes, the mixed acid solution, the hydrochloric acid solution, the aniline and the ammonium persulfate is 1:2-4:2-4:0.3-0.7:0.3-0.7.

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