A method for preparing flame-retardant PET by recycling particles of PET release film

Abstract

The present invention discloses a method for preparing flame-retardant PET from recycled PET release film particles, comprising the following steps: S1, crushing and cleaning the recycled PET release film to obtain recycled PET release film particles; S2, preparing multi-effect flame-retardant modified functional microspheres; and S3, mixing the recycled PET release film particles, ABS, the multi-effect flame-retardant modified functional microspheres, and an additive, and then melt-extruding and granulating the mixture through a twin-screw extruder to obtain flame-retardant PET. The method for preparing flame-retardant PET from recycled PET release film particles provided by the present invention can utilize discarded PET release film to prepare a PET material having excellent flame retardancy, UV resistance, and good mechanical strength.

Description

Technical Field

[0001] The invention relates to the technical field of waste recycling, and in particular to a method for preparing flame-retardant PET by recycling particles of PET release film. Background Art

[0002] PET release film is made by coating the surface of PET film with silicone oil, and is therefore also called silicone oil film or peeling film. Applying silicone oil can reduce the adsorption force on the surface of the PET film, achieving a release effect. PET release film is used in large quantities and is disposable. If improperly handled, a large amount of waste PET will place tremendous pressure on environmental protection. Since the main raw material of PET release film is PET, if it is properly recycled, it will not only have environmental value but also bring high economic benefits. Currently, there are two main methods for recycling waste PET. The chemical method has disadvantages such as complex process and high cost, and is therefore less practical in the industry. The physical recycling process is relatively simple, mainly through the melt granulation method, and is more widely used. For example, patent CN114752107A discloses a method for recovering and preparing high-performance PET composite materials from waste PET film.

[0003] However, physically recycled PET materials usually have reduced mechanical properties and need to be improved before they can be used effectively. Conventional PET materials themselves have poor flame retardancy, with a limiting oxygen index (LOI) of around 20-22%, which greatly limits their application scenarios. Currently, the flame retardancy of PET materials is usually improved by adding flame retardants for blending and modification. Inorganic flame retardant additives are widely used. For example, patent CN111303592B discloses a method for preparing a phosphorus-aluminum halogen-free, low-smoke, intrinsically flame-retardant IFR-PET. However, inorganic flame retardant additives generally have defects such as poor compatibility with organic systems and easy surface migration.

[0004] On the other hand, UV exposure accelerates the decomposition of organic components in PET materials, deteriorating their overall performance and shortening their service life. Improving PET's resistance to UV aging can enhance its performance, extend its service life, and expand its application range. Adding UV-resistant components is an effective means of improving PET's resistance to UV aging. For example, patent CN110982051B discloses a flame-retardant, UV-resistant PET and its preparation method.

[0005] Using recycled PET release film to prepare PET materials with flame retardant properties and certain UV resistance will have great social and economic benefits. In theory, by adding flame retardant components and UV resistance components to PET materials at the same time, its flame retardant and UV resistance can be improved. However, due to the compatibility issues between flame retardant components and UV resistance components and organic systems, and the interaction between components, the actual application effects are generally difficult to meet the requirements.

[0006] Therefore, it is necessary to improve the existing technology to provide a reliable solution. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing flame-retardant PET by recycling particles of PET release film in view of the above-mentioned deficiencies in the prior art.

[0008] To solve the above technical problems, the present invention adopts a technical solution: a method for preparing flame-retardant PET by recycling particles of PET release film, comprising the following steps:

[0009] S1, crushing the recovered PET release film, and then washing it to obtain PET release film recovery particles;

[0010] S2. Preparation of multi-effect flame retardant modified functional microspheres:

[0011] S2-1, preparing aluminum-doped ceria porous microspheres using a template method;

[0012] S2-2, using raw materials including lycopene, octyl salicylate, sodium foscarnet and ethylenediamine, carbon dots were in situ grafted onto aluminum-doped ceria porous microspheres by a hydrothermal method to prepare carbon dot grafted microspheres;

[0013] S2-3, loading flame retardant on carbon dot grafted microspheres to prepare multi-functional microspheres;

[0014] S2-4, coating the multi-effect functional microspheres with a PET film to obtain multi-effect flame retardant modified functional microspheres;

[0015] S3. Mix 100 parts by weight of PET release film recycled particles, 24-47 parts by weight of ABS, 2-15 parts by weight of multi-effect flame retardant modified functional microspheres, and 3.6-16 parts by weight of additives according to the weight ratio, and then melt-extrude and granulate through a twin-screw extruder to obtain flame-retardant PET.

[0016] Preferably, the step S1 is specifically as follows:

[0017] S1-1. Crushing the recovered PET release film into pieces of 0.2-3 cm, adding it to deionized water, and steaming it at 55-95°C for 0.5-3 hours;

[0018] S1-2, filtering, adding the obtained PET particles to an ethanol-water solution, ultrasonically oscillating for 30-90 minutes, filtering, washing the obtained PET particles with deionized water, and air-drying at 80-105° C. for 2-6 hours to obtain PET release film recovery particles; wherein the ethanol-water solution is obtained by mixing ethanol and deionized water in a volume ratio of 1:8-1:3.

[0019] Preferably, the step S2-1 specifically includes:

[0020] S2-1-1. Preparation of PS microsphere template:

[0021] 0.1-0.5 g of sodium lauryl sulfate was added to deionized water, stirred until dissolved, nitrogen was introduced for 10-30 min, heated to 70-95° C., 0.08-0.3 g of potassium persulfate was added, and stirred for 3-10 min to obtain a mixture 1;

[0022] 0.1-0.4 g of styrene and 0.075-0.3 g of n-butanol were mixed and stirred to obtain a mixture 2, which was then added dropwise to the mixture 1. The mixture was allowed to react for 20-60 minutes after the addition was complete. 2-8 g of styrene was then added dropwise to the mixture 1. The mixture was reacted at 75-90° C. for 2-6 hours, cooled, centrifuged, and the solid product was washed with ethanol and deionized water in sequence, and dried to obtain PS microspheres.

[0023] S2-1-2. Preparation of aluminum-doped ceria porous microspheres by template method:

[0024] 1-4 g of PS microspheres were added to 100-400 mL of deionized water and ultrasonically dispersed for 10-30 min. 0.2-0.9 g of PVP, 0.4-1.5 g of cerium nitrate, and 0.05-0.3 g of aluminum nitrate were added to the obtained dispersion and stirred for 3-15 min to obtain a microsphere precursor solution.

[0025] The microsphere precursor solution was transferred to a polytetrafluoroethylene-lined reactor, reacted at 170-220°C for 2-8 hours, and the obtained product was centrifuged. The solid product obtained by centrifugation was washed with deionized water, vacuum-dried at 60-80°C for 2-10 hours, and finally calcined at 450-600°C for 1-8 hours to obtain aluminum-doped cerium dioxide porous microspheres.

[0026] Preferably, the step S2-2 specifically includes:

[0027] S2-2-1. Add 0.2-0.8 g of aluminum-doped cerium dioxide porous microspheres and 0.05-0.2 g of PVP to 30-100 mL of ethanol-water solution and sonicate for 10 minutes to obtain a microsphere dispersion; the volume ratio of ethanol to deionized water in the ethanol-water solution is 1:3-1:1;

[0028] S2-2-2. Add 0.5-2 g of lycopene, 0.4-1.6 g of octyl salicylate, and 0.15-0.6 g of sodium foscarnet to 50-200 mL of an aqueous ethanol solution, and stir at 50-75° C. for 5-20 min to obtain a raw material dispersion; the volume ratio of ethanol to deionized water in the aqueous ethanol solution is 1:3-2:1;

[0029] S2-2-3. Add the raw material dispersion to the microsphere dispersion, stir for 3-15 minutes, then add 0.25-1 mL of ethylenediamine, and then ultrasonically disperse for 2-8 minutes to obtain a mixed precursor solution;

[0030] S2-2-4. Transfer the mixed precursor solution to a polytetrafluoroethylene-lined reactor and continue the reaction at 180-230°C for 2-8 hours;

[0031] S2-2-5. After the reaction is completed, cool to room temperature, centrifuge the product at 3000-8000 r / min for 1-5 min, wash the solid product with deionized water and ethanol in sequence, and vacuum dry at 60-80°C for 3-10 h to obtain carbon dot grafted microspheres.

[0032] Preferably, the step S2-3 specifically includes:

[0033] S2-3-1. Add 1-4 g of carbon dot-grafted microspheres to 30-100 mL of deionized water and sonicate for 2-10 min to obtain a dispersion of carbon dot-grafted microspheres.

[0034] S2-3-2. Add 1.25-5 g of magnesium nitrate to 10-40 mL of deionized water and stir until completely dissolved to obtain a magnesium salt solution;

[0035] S2-3-3. Add the magnesium salt solution to the carbon dot grafted microsphere dispersion under stirring, continue stirring for 5-20 minutes, keep stirring, and add 20-100 mL of 0.5-2 mol / L NaOH solution to the obtained mixed solution. After the reaction is completed, filter, wash the solid product with deionized water until it is neutral, and vacuum dry at 60-95°C for 6-24 hours to obtain multi-functional microspheres.

[0036] Preferably, the step S2-4 specifically includes:

[0037] S2-4-1. Add 2.5-10 g of multifunctional microspheres to 100-500 mL of 1,4-butanediol and disperse by ultrasonic for 5-30 min.

[0038] S2-4-2. Add 5-20 g of dimethyl terephthalate and 0.05-0.2 g of cobalt acetate to the dispersion obtained in step S2-4-1, and perform an ester exchange reaction at 160-210° C. and 100-250 r / min using nitrogen as a protective gas;

[0039] S2-4-3. After the transesterification reaction is completed, add 0.04-0.15g of antimony trioxide, heat at 190-225℃ for 5-15min, then evacuate to 10-30Pa, raise the temperature to 250-330℃, and carry out polycondensation reaction for 2-8h;

[0040] S2-4-4. After the reaction is completed, filter and wash the solid product with ethanol, vacuum dry at 75-110°C for 2-10h, and grind to obtain multi-effect flame retardant modified functional microspheres.

[0041] Preferably, the step S3 is specifically as follows:

[0042] 100 parts by weight of PET release film recycled particles, 24-47 parts by weight of ABS, 2-15 parts by weight of multi-effect flame retardant modified functional microspheres, and 3.6-16 parts by weight of additives are added to a mixer and mixed for 3-10 minutes; the resulting mixture is then added to a twin-screw extruder for melt extrusion and granulation to obtain flame-retardant PET;

[0043] The screw speed is 280-450 rpm, and the temperatures of each section of the screw are: 220-235°C in the feeding section, 240-250°C in the conveying section, 255-265°C in the melting section, and 250-255°C in the die head.

[0044] Preferably, the auxiliary agent includes 3-8 parts by weight of a toughening agent, 0.4-5 parts by weight of a compatibilizer, and 0.2-3 parts by weight of a lubricant.

[0045] Preferably, the ABS comprises 15-40% by mass of butadiene, 12-33% by mass of acrylonitrile, and 38-57% by mass of styrene, and the molecular weight of the ABS is 90,000-150,000.

[0046] Preferably, the toughening agent is one or two of ethylene-ethyl acrylate copolymer and glycidyl methacrylate random terpolymer;

[0047] The compatibilizer is compatibilizer SAG-002 or styrene-acrylonitrile-glycidyl methacrylate copolymer compatibilizer;

[0048] The lubricant is pentaerythritol ester or ethylene bis stearamide.

[0049] The beneficial effects of the present invention are:

[0050] The method for preparing flame-retardant PET by recycling particles of PET release film provided by the present invention can utilize discarded PET release film to prepare PET material with excellent flame retardancy, UV resistance and good mechanical strength;

[0051] The present invention constructs a composite structural system comprising porous cerium oxide hollow microspheres as a core carrier, carbon dot functional particles uniformly grafted onto the core carrier, an inorganic flame retardant stably loaded onto the core carrier, and a polymer PET film coated on the outer layer to form a modified film layer as a multi-effect flame retardant modified functional microsphere. Firstly, the carbon dots, inorganic flame retardant, and porous cerium oxide hollow microspheres can be uniformly dispersed in an organic system, while avoiding loss of the mechanical strength of the organic system. Furthermore, the functional components, cerium oxide microspheres and carbon dots, can simultaneously improve flame retardancy and UV resistance, and the two complement each other to achieve a synergistic enhancement effect in improving both properties.

[0052] The present invention loads the magnesium hydroxide flame retardant on porous hollow cerium oxide microspheres and then coats them with a polymer PET film, thereby achieving uniform dispersion of the inorganic flame retardant in the organic matrix material and effectively inhibiting the surface migration of the inorganic magnesium hydroxide flame retardant in the organic system.

[0053] The cerium oxide microspheres in the present invention have a certain flame retardant effect. In addition to improving the lattice stability and providing assistance to the strength of the microspheres, the aluminum element doped therein is also an excellent inorganic flame retardant that precipitates at high temperatures. It achieves flame retardancy by combining with oxygen to dilute the oxygen concentration and covering the surface of the material for physical isolation. 3+ To Ce 4+ Ce produced during the conversion process 4+ It can effectively separate electrons and holes under light excitation. This variable valence makes CeO2 have excellent electron transfer properties. Since the main mechanism of ultraviolet absorption of carbon dots is electron transition, the electron transfer properties of CeO2 can enhance the ultraviolet absorption ability of carbon dots.

[0054] The carbon dots loaded on the cerium oxide microspheres in the present invention have certain flame retardant properties themselves. During the combustion process, they form a carbon layer to construct a heat insulation barrier, reduce the release of combustible volatile components, and suppress flames; further, the carbon dots are also doped with elements such as N and P, which can precipitate at high temperatures to achieve a composite flame retardant effect; and the ultraviolet absorption spectrum range of the carbon dots in the present invention can cover the ultraviolet short-wave region where CeO2 absorption has defects, thereby achieving full-band ultraviolet absorption; further, the carbon dots grafted on ceria have strong reducing ability, which can remove high-energy oxygen atoms formed by escaping from CeO2 crystals, thereby significantly reducing the oxidation catalytic activity of ceria, and can effectively overcome the defects of weak anti-ultraviolet ability in the short-wave region and high oxidation catalytic activity when ceria is used as an external shielding material. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 The synthetic flow chart of the multi-effect flame retardant modified functional microspheres of the present invention;

[0056] Figure 2 IR spectrum of carbon dot grafted microspheres (Al-CeO2@CDs) prepared in Example 2 of the present invention;

[0057] Figure 3 Ultraviolet absorption spectra of aluminum-doped ceria porous microspheres Al-CeO2 (curve a) and carbon dot-grafted microspheres Al-CeO2@CDs (curve b) prepared in Example 2 of the present invention;

[0058] Figure 4 is the cone calorimetry test result of the present invention;

[0059] Figure 5 These are the carbonyl index test results of the PET materials prepared in Example 2 and Comparative Examples 1-5 at different aging times. DETAILED DESCRIPTION

[0060] The present invention is further described in detail below with reference to the embodiments so that those skilled in the art can implement the invention with reference to the description.

[0061] It should be understood that terms such as “having”, “including” and “comprising” used herein do not preclude the existence or addition of one or more other elements or combinations thereof.

[0062] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Materials and reagents used in the following examples are commercially available unless otherwise specified. In the following examples, where specific conditions are not specified, the experiments were conducted under conventional conditions or those recommended by the manufacturer. Reagents and instruments used, where the manufacturer is not specified, are commercially available conventional products.

[0063] The present invention provides a method for preparing flame-retardant PET by recycling particles of PET release film, comprising the following steps:

[0064] S1. Preparation of PET release film and recovery of particles

[0065] S1-1. Crushing the recovered PET release film into pieces of 0.2-3 cm, adding it to deionized water, and steaming it at 55-95°C for 0.5-3 hours;

[0066] S1-2, filtering, adding the obtained PET particles to an ethanol-water solution, ultrasonically oscillating for 30-90 minutes, filtering, washing the obtained PET particles with deionized water, and air-drying at 80-105° C. for 2-6 hours to obtain PET release film recovery particles; wherein the ethanol-water solution is obtained by mixing ethanol and deionized water in a volume ratio of 1:8-1:3.

[0067] S2. Preparation of multi-effect flame retardant modified functional microspheres

[0068] S2-1. Preparation of aluminum-doped ceria porous microspheres (Al-CeO2) using a template method:

[0069] S2-1-1. Preparation of PS microsphere template:

[0070] 0.1-0.5 g of sodium lauryl sulfate was added to deionized water, stirred until dissolved, nitrogen was introduced for 10-30 min, heated to 70-95° C., 0.08-0.3 g of potassium persulfate was added, and stirred for 3-10 min to obtain a mixture 1;

[0071] 0.1-0.4 g of styrene and 0.075-0.3 g of n-butanol were mixed and stirred to obtain a mixture 2, which was then added dropwise to the mixture 1. The mixture was allowed to react for 20-60 minutes after the addition was complete. 2-8 g of styrene was then added dropwise to the mixture 1. The mixture was reacted at 75-90° C. for 2-6 hours, cooled, centrifuged, and the solid product was washed with ethanol and deionized water in sequence, and dried to obtain PS microspheres.

[0072] S2-1-2. Preparation of aluminum-doped ceria porous microspheres by template method:

[0073] 1-4 g of PS microspheres were added to 100-400 mL of deionized water and ultrasonically dispersed for 10-30 min. 0.2-0.9 g of PVP, 0.4-1.5 g of cerium nitrate, and 0.05-0.3 g of aluminum nitrate were added to the obtained dispersion and stirred for 3-15 min to obtain a microsphere precursor solution.

[0074] The microsphere precursor solution is transferred to a polytetrafluoroethylene-lined reactor, reacted at 170-220°C for 2-8 hours, the obtained product is centrifuged, the solid product obtained by centrifugation is washed with deionized water, vacuum-dried at 60-80°C for 2-10 hours, and finally calcined at 450-600°C for 1-8 hours to obtain aluminum-doped ceria porous microspheres;

[0075] S2-2, using lycopene ( Figure 1 Chinese formula Ⅱ), octyl salicylate ( Figure 1 Chinese formula Ⅰ), sodium foscarnet ( Figure 1 Carbon dots were in situ grafted onto aluminum-doped ceria porous microspheres using the following raw materials:

[0076] S2-2-1. Add 0.2-0.8 g of aluminum-doped cerium dioxide porous microspheres and 0.05-0.2 g of PVP to 30-100 mL of ethanol-water solution and sonicate for 10 minutes to obtain a microsphere dispersion; the volume ratio of ethanol to deionized water in the ethanol-water solution is 1:3-1:1;

[0077] S2-2-2. Add 0.5-2 g of lycopene, 0.4-0.8 g of octyl salicylate, and 0.15-0.6 g of sodium foscarnet to 50-200 mL of an ethanol-water solution, and stir at 50-75° C. for 5-20 min to obtain a raw material dispersion; the volume ratio of ethanol to deionized water in the ethanol-water solution is 1:3-2:1;

[0078] S2-2-3. Add the raw material dispersion to the microsphere dispersion, stir for 3-15 minutes, then add 0.05-1 mL of ethylenediamine, and then ultrasonically disperse for 2-8 minutes to obtain a mixed precursor solution;

[0079] S2-2-4. Transfer the mixed precursor solution to a polytetrafluoroethylene-lined reactor and continue the reaction at 180-230°C for 2-8 hours;

[0080] S2-2-5. After the reaction is completed, cool to room temperature, centrifuge the product at 3000-8000 r / min for 1-5 min, wash the solid product with deionized water and ethanol in sequence, and vacuum dry at 60-80°C for 3-10 h to obtain carbon dot grafted microspheres.

[0081] S2-3, loading flame retardant on carbon dot grafted microspheres to prepare multi-functional microspheres Al-CeO2@CDs@Mg(OH)2:

[0082] S2-3-1. Add 1-4 g of carbon dot-grafted microspheres to 30-100 mL of deionized water and sonicate for 2-10 min to obtain a dispersion of carbon dot-grafted microspheres.

[0083] S2-3-2. Add 1.25-5 g of magnesium nitrate to 1-400 mL of deionized water and stir until completely dissolved to obtain a magnesium salt solution;

[0084] S2-3-3. Add the magnesium salt solution to the carbon dot grafted microsphere dispersion under stirring, continue stirring for 5-20 minutes, keep stirring, and add 20-100 mL of 0.5-2 mol / L NaOH solution to the obtained mixed solution. After the reaction is completed, filter, wash the solid product with deionized water until it is neutral, and vacuum dry at 60-95°C for 6-24 hours to obtain multi-functional microspheres.

[0085] S2-4, coating the multi-effect functional microspheres with PET film to obtain multi-effect flame retardant modified functional microspheres Al-CeO2@CDs@Mg(OH)2-PET:

[0086] S2-4-1. Add 2.5-10 g of multifunctional microspheres to 100-500 mL of 1,4-butanediol and disperse by ultrasonic for 5-30 min.

[0087] S2-4-2. Add 5-20 g of dimethyl terephthalate and 0.05-0.2 g of cobalt acetate to the dispersion obtained in step S2-4-1, and perform an ester exchange reaction at 160-210° C. and 100-250 r / min using nitrogen as a protective gas;

[0088] S2-4-3. After the transesterification reaction is completed, add 0.04-0.15g of antimony trioxide, heat at 190-225℃ for 5-15min, then evacuate to 10-30Pa, raise the temperature to 250-330℃, and carry out polycondensation reaction for 2-8h;

[0089] S2-4-4. After the reaction is completed, filter and wash the solid product with ethanol, vacuum dry at 75-110°C for 2-10h, and grind to obtain multi-effect flame retardant modified functional microspheres.

[0090] S3. Preparation of flame-retardant PET

[0091] 100 parts by weight of PET release film recycled particles, 24-47 parts by weight of ABS, 2-15 parts by weight of multi-effect flame retardant modified functional microspheres, 3-8 parts by weight of toughening agent, 0.4-5 parts by weight of compatibilizer, and 0.2-3 parts by weight of lubricant are added to a mixer and mixed for 3-10 minutes; the resulting mixture is then added to a twin-screw extruder for melt extrusion and granulation to obtain flame-retardant PET;

[0092] The screw speed is 280-450 rpm, and the temperatures of each section of the screw are: 220-235°C in the feeding section, 240-250°C in the conveying section, 255-265°C in the melting section, and 250-255°C in the die head.

[0093] The ABS comprises 15-40% by mass of butadiene, 12-33% by mass of acrylonitrile and 38-57% by mass of styrene, and the molecular weight of the ABS is 90,000-150,000.

[0094] Among them, the toughening agent is one or two of ethylene-ethyl acrylate copolymer (EEA) and glycidyl methacrylate random terpolymer (GMA-ethylene-methyl acrylate); the compatibilizer is compatibilizer SAG-002 or styrene-acrylonitrile-glycidyl methacrylate copolymer compatibilizer (SAG2030); and the lubricant package is pentaerythritol ester or ethylene bisstearamide.

[0095] In the present invention, the mechanical properties of the PET material can be improved by compounding and adding ABS and various additives.

[0096] The multi-effect flame-retardant modified functional microspheres synthesized in the present invention can simultaneously improve the flame retardancy and UV resistance of the PET material without losing its mechanical strength.

[0097] 1. Synthesis Mechanism

[0098] Reference Figure 1 , which is the synthesis process of multi-effect flame retardant modified functional microspheres;

[0099] 1) The present invention first uses PS microspheres as templates and uses a template method to prepare aluminum-doped ceria porous hollow microspheres, i.e., aluminum-doped ceria porous microspheres (Al-CeO2). The diameter of the microspheres is about 450-550 nm, the thickness of the spherical shell is about 80-100 nm, and the surface of the spherical shell has numerous micropores with a pore diameter of about 10-25 nm.

[0100] 2) A large number of N- and P-doped carbon dots were then in situ grafted onto the surface, hollow inner walls, and pores of the aluminum-doped ceria porous microspheres via a hydrothermal method to prepare carbon dot-grafted microspheres (Al-CeO2@CDs). These carbon dots possess numerous carboxyl, hydroxyl, amino, and phosphorus-oxygen functional groups on their surfaces, along with numerous double bonds, resulting in strong UV absorption while retaining the robust reducing properties of lycopene.

[0101] 3) A large amount of magnesium hydroxide flame retardant was deposited in the interior and pores of aluminum-doped cerium dioxide porous microspheres by in-situ precipitation method to prepare multi-functional microspheres Al-CeO2@CDs@Mg(OH)2. In this process, carbon dots played a bridging role, and the electrostatic attraction and / or complexation of the functional groups on them could make a large amount of Mg 2+ The multifunctional microspheres were uniformly connected to the aluminum-doped ceria porous microspheres and then fixed by generating magnesium hydroxide precipitation.

[0102] 4) Finally, by polymerizing and coating the PET film on the surface of the multi-effect functional microspheres, the multi-effect flame retardant modified functional microspheres Al-CeO2@CDs@Mg(OH)2-PET were finally prepared. In this process, the double bonds on the carbon dots can participate in the polymerization reaction. At this time, the carbon dots play a bridging role again, which can enhance the connection strength between the multi-effect functional microspheres and the surface-coated PET film.

[0103] 2. Synergistic Mechanism

[0104] The multi-effect flame retardant modified functional microspheres of the present invention mainly have the following functions:

[0105] 1. Give PET materials excellent flame retardant properties; 2. Give PET materials excellent UV resistance; 3. Coating modification to improve compatibility; The following explains its principles from the above three aspects.

[0106] 1. Flame retardant properties:

[0107] In the first aspect, the present invention loads magnesium hydroxide flame retardant on porous hollow cerium dioxide microspheres and then coats them with a polymer PET film. The loading effect of the porous hollow cerium dioxide microspheres can achieve uniform dispersion of the inorganic flame retardant in the organic matrix material, and the protective effect of the coating film can effectively inhibit the surface migration of the inorganic magnesium hydroxide flame retardant in the organic system, thereby ensuring the long-term effectiveness of the flame retardant and preventing the performance of the organic matrix material from being significantly reduced due to the incorporation of the inorganic flame retardant.

[0108] Secondly, cerium oxide microspheres, as oxides, have the functions of promoting cross-linking and carbonization and capturing free radicals at high temperatures, so they can exhibit a certain flame retardant effect. In addition to improving the lattice stability and providing assistance to the strength of the microspheres, the aluminum doped in them is also an excellent inorganic flame retardant. It achieves flame retardancy by combining with oxygen to dilute the oxygen concentration and covering the surface of the material for physical isolation.

[0109] Thirdly, the carbon dots supported on the cerium oxide microspheres possess inherent flame retardancy. During combustion, they form a char layer, creating a thermal barrier that reduces the release of combustible volatile components and suppresses flames. Furthermore, the carbon dots in this invention are doped with elements such as nitrogen and phosphorus, which precipitate at high temperatures to provide a composite flame retardant effect. This flame retardancy primarily involves combining with oxygen to dilute the oxygen concentration, generating non-combustible gases that further dilute the oxygen concentration.

[0110] It can be seen that in the present invention, the core carrier cerium oxide microspheres, the functional modified ionic carbon dots and the polymer protective film layer PET film in the multi-effect flame retardant modified functional microspheres have a synergistic enhancement effect in improving flame retardancy.

[0111] 2. Anti-ultraviolet performance

[0112] A. The role and shortcomings of cerium oxide

[0113] Cerium oxide has strong UV absorption capabilities. The UV light it absorbs is mainly used for electronic energy level transitions and does not trigger photocatalysis. Conventional TiO2 and ZnO UV-resistant materials, while they can provide UV protection, have high photocatalytic activity and promote the decomposition of organic matter. Therefore, cerium oxide has certain advantages in this regard, making it a potential ideal UV shielding material. However, cerium oxide still has the following drawbacks when used as a UV-resistant material:

[0114] A1. It has high oxidation catalytic activity, among which the CeO2 crystal structure is unstable. 4+ Converted to Ce 4+ The trend of the ions to form a negative charge excess causes some oxygen anions to leave their equilibrium position and jump outside the crystal, forming highly active high-energy oxygen atoms, thereby showing oxidation catalytic activity ([1] Yu Xiaoli, Cao Hongzhang, Zhang Yuxi, et al. Research progress on the anti-ultraviolet properties of cerium dioxide [J]. Rare Earth, 2013 (4): 5.).

[0115] The method usually used to deal with this defect is to dope ions, such as Ca 2+ 、F - (L.Sronek, J.Majimel, Y.Kihn, et al., "New Highly Divided Ce-Ca-Based Oxyfluorides with UV-ShieldingProperties: Study of the Ce 1-x Ca x O 2-x and Ce 1-x Ca x O 2-x-y / 2 F ySeries”, Chem. Mater. 2007, 19, 5110-5121), but CeO2 still has certain oxidation catalytic activity after doping.

[0116] A2. The anti-ultraviolet ability of cerium dioxide is related to the particle size, and is mainly effective for medium-wave (290-320) and long-wave regions (320-400nm), and its anti-ultraviolet ability for short-wave region (200-290nm) is relatively weak.

[0117] A3. As an inorganic material, it has poor compatibility with organic systems. If it agglomerates in an organic system, it will not only fail to exert its anti-UV effect, but will also cause the performance of the organic system to deteriorate.

[0118] B. Functions and shortcomings of carbon dots

[0119] As a new type of nanoparticles, carbon dots have many unique properties. Because of their certain ultraviolet light absorption properties, they can be used as ultraviolet absorbers ([1] Yu Shujuan, Luo Zhenjing, Yuan Guangzhi, et al. Synthesis of carbon dot-based ultraviolet absorbers and their application in polyethylene / wood powder composites [J]. Polymer Materials Science and Engineering, 2021.).

[0120] However, conventional carbon dots used as UV absorbers have the following defects:

[0121] B1, easy to agglomerate and difficult to disperse;

[0122] B2. The ultraviolet absorption spectrum is narrow.

[0123] The present invention can effectively overcome the above-mentioned defects by constructing an aluminum-doped ceria porous microsphere structure system of grafted carbon dots coated with a PET polymer film. The specific mechanism is as follows:

[0124] (1) In the present invention, aluminum is doped into cerium dioxide, and aluminum is dispersed into the cerium oxide lattice, which can improve the stability of cerium oxide to a certain extent; the carbon dots grafted on cerium dioxide have strong reducing ability, which can remove high-energy oxygen atoms formed by escaping from CeO2 crystals, thereby significantly reducing the oxidation catalytic activity of cerium dioxide; further, due to the coating of the PET polymer film, it can greatly reduce the escape of high-energy oxygen atoms into the PET matrix and affect the performance of the PET matrix material; therefore, through the effects of the above aspects, the defect of high oxidation catalytic activity when cerium dioxide is used as an external shielding material can be effectively overcome, and compared with conventional Ca 2+ 、F - The plasma doping solution, in addition to the advantage of better inhibition of oxidation catalytic activity, also brings the following benefits:

[0125] The above scheme of the present invention is mainly to remove high-energy oxygen atoms through the reduction of carbon dots, rather than to inhibit Ce 3+ To Ce 4+ Transformation, so Ce 3+ To Ce 4+ The transformation still exists, and the Ce produced by this process 4+ It can produce effective separation of electrons and holes under light excitation. This variable valence makes CeO2 have good electron transfer properties. The main mechanism of ultraviolet absorption of carbon dots is electron transition. The electron transfer properties of CeO2 can enhance the ultraviolet absorption ability of carbon dots.

[0126] Because the carbon dots in the present invention absorb light across the 200nm-458nm range, they cover the short-wavelength UV region where CeO2 absorption is defective, thereby achieving full-band UV absorption. The carbon dots exhibit strong absorption at 208nm, primarily attributable to π→π* and n-π* transitions of ring structures and / or C=O. The strong absorption at 295nm is primarily attributed to n-σ* transitions of heteroatoms such as carbon, nitrogen, and oxygen.

[0127] The groups on the benzene ring in salicylate form intrinsic hydrogen bonds with adjacent groups, forming a chelate ring that strongly absorbs ultraviolet light. Phosphorus doping in the carbon dots enhances their electron-donating capacity, which also contributes to enhanced UV absorption.

[0128] It can be seen that CeO2 and carbon dots have a significant complementary enhancement effect in improving the ultraviolet absorption ability, which can well overcome the above-mentioned defects A1, A2 and B2.

[0129] (2) The porous structure of the cerium dioxide in the present invention enables uniform loading of carbon dots, overcoming the defects of easy agglomeration and difficulty in dispersion of carbon dots. Furthermore, the polymer PET film is used to coat the cerium dioxide grafted with carbon dots, which greatly improves the compatibility between cerium dioxide and the organic system, allowing cerium dioxide and carbon dots to be evenly dispersed in the matrix material and increasing the connection strength between cerium dioxide and the organic matrix material, thereby effectively overcoming the above-mentioned defects A3 and B1. At the same time, in this process, the intermediate bridging effect of the carbon dots (as described above) can strengthen the connection between cerium dioxide and the PET film. It can be seen that in promoting the dispersion of carbon dots in the matrix material, carbon dots and cerium dioxide also play a complementary and reinforcing role.

[0130] 3. Coating modification to improve compatibility

[0131] Due to the good bonding between carbon dots and the PET coating film, and the strong interaction between carbon dots and cerium oxide, the coating of the PET film layer makes the microspheres very compatible with the organic matrix material. On the contrary, the microspheres can serve as connection points and share the load, so the mechanical strength of the organic matrix material will not be lost.

[0132] In summary, it can be seen that the present invention constructs a composite structural system as a multi-effect flame retardant modified functional microsphere by using porous cerium oxide hollow microspheres as the core carrier, carbon dot functional particles uniformly grafted on the core carrier, inorganic flame retardant stably loaded on the core carrier, and polymer PET film coated on the outer layer to form a modified film layer. First, it can achieve uniform dispersion of carbon dots, inorganic flame retardants, and porous cerium oxide hollow microspheres in the organic system, and avoid the loss of mechanical strength of the organic system. At the same time, the functional components cerium oxide microspheres and carbon dots can simultaneously improve flame retardancy and UV resistance, and the two have a synergistic enhancement effect in improving the two properties through complementary reinforcement.

[0133] The above is the overall concept of the present invention. Detailed examples and comparative examples are provided below to further illustrate the present invention.

[0134] Example 1

[0135] A method for preparing flame-retardant PET by recycling particles of PET release film comprises the following steps:

[0136] S1. Preparation of PET release film and recovery of particles

[0137] S1-1. Crushing the recovered PET release film into pieces of 0.2-3 cm, adding it to deionized water, and steaming it at 65°C for 1 hour;

[0138] S1-2, filtering, adding the obtained PET particles to an ethanol-water solution, ultrasonically oscillating for 60 minutes, filtering, washing the obtained PET particles with deionized water, and air-drying at 95°C for 4 hours to obtain PET release film recovery particles; wherein the ethanol-water solution is obtained by mixing ethanol and deionized water in a volume ratio of 1:4.

[0139] S2. Preparation of multi-effect flame retardant modified functional microspheres

[0140] S2-1. Preparation of aluminum-doped ceria porous microspheres using a template method:

[0141] S2-1-1. Preparation of PS microsphere template:

[0142] 0.2 g of sodium lauryl sulfate was added to deionized water, stirred until dissolved, nitrogen was introduced for 15 min, heated to 75° C., 0.18 g of potassium persulfate was added, and stirred for 5 min to obtain a mixture 1;

[0143] 0.2 g of styrene and 0.15 g of n-butanol were mixed and stirred to obtain a mixture 2, which was then added dropwise to the mixture 1. The mixture was allowed to react for 45 minutes after the addition was completed. 5 g of styrene was then added dropwise to the mixture 1. The mixture was reacted at 85° C. for 3 hours, cooled, and centrifuged. The solid product was washed with ethanol and deionized water in sequence, and dried to obtain PS microspheres.

[0144] S2-1-2. Preparation of aluminum-doped ceria porous microspheres by template method:

[0145] 3 g of PS microspheres were added to 200 mL of deionized water and ultrasonically dispersed for 15 min. 0.45 g of PVP, 0.8 g of cerium nitrate, and 0.15 g of aluminum nitrate were added to the resulting dispersion and stirred for 5 min to obtain a microsphere precursor solution.

[0146] The microsphere precursor solution was transferred to a polytetrafluoroethylene-lined reactor and reacted at 190°C for 4 hours. The obtained product was centrifuged, and the solid product obtained by centrifugation was washed with deionized water, vacuum-dried at 70°C for 6 hours, and finally calcined at 550°C for 3 hours to obtain aluminum-doped ceria porous microspheres.

[0147] S2-2. Using raw materials including lycopene, octyl salicylate, sodium foscarnet and ethylenediamine, carbon dots were in situ grafted onto aluminum-doped ceria porous microspheres by a hydrothermal method to prepare carbon dot grafted microspheres:

[0148] S2-2-1. Take 0.4 g of aluminum-doped cerium dioxide porous microspheres and 0.1 g of PVP and add them to 50 mL of ethanol-water solution. Ultrasonicate for 10 minutes to obtain a microsphere dispersion; the volume ratio of ethanol to deionized water in the ethanol-water solution is 1:2;

[0149] S2-2-2. Add 1 g of lycopene, 0.8 g of octyl salicylate, and 0.3 g of sodium foscarnet to 100 mL of an ethanol aqueous solution, and stir at 65° C. for 10 min to obtain a raw material dispersion; the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:1;

[0150] S2-2-3. Add the raw material dispersion to the microsphere dispersion, stir for 5 minutes, then add 0.5 mL of ethylenediamine, and then ultrasonically disperse for 3 minutes to obtain a mixed precursor solution;

[0151] S2-2-4. Transfer the mixed precursor solution to a polytetrafluoroethylene-lined reactor and continue the reaction at 210°C for 4 hours;

[0152] S2-2-5. After the reaction is completed, cool to room temperature, centrifuge the product at 5000 r / min for 3 min, wash the solid product with deionized water and ethanol in sequence, and vacuum dry at 70°C for 6 h to obtain carbon dot grafted microspheres.

[0153] S2-3, loading flame retardant on carbon dot grafted microspheres to prepare multi-functional microspheres:

[0154] S2-3-1. Add 2 g of carbon dot-grafted microspheres to 50 mL of deionized water and sonicate for 5 min to obtain a dispersion of carbon dot-grafted microspheres.

[0155] S2-3-2. Add 2.5 g of magnesium nitrate to 20 mL of deionized water and stir until completely dissolved to obtain a magnesium salt solution;

[0156] S2-3-3. Add the magnesium salt solution to the carbon dot grafted microsphere dispersion under stirring, continue stirring for 10 minutes, keep stirring, and add 50 mL of 1 mol / L NaOH solution to the obtained mixed solution. After the reaction is completed, filter, wash the solid product with deionized water until it is neutral, and vacuum dry at 85°C for 12 hours to obtain multi-functional microspheres.

[0157] S2-4, coating the multi-effect functional microspheres with PET film to obtain multi-effect flame retardant modified functional microspheres:

[0158] S2-4-1. Add 5 g of multifunctional microspheres to 250 mL of 1,4-butanediol and disperse by ultrasonication for 10 min.

[0159] S2-4-2. Add 10 g of dimethyl terephthalate and 0.1 g of cobalt acetate to the dispersion obtained in step S2-4-1, and perform an ester exchange reaction at 185°C and 170 r / min using nitrogen as a protective gas;

[0160] S2-4-3. After the transesterification reaction is completed, add 0.8 g of antimony trioxide, heat at 210 ° C for 10 minutes, then evacuate to 18 Pa, raise the temperature to 275 ° C, and carry out polycondensation reaction for 4 hours;

[0161] S2-4-4. After the reaction is completed, filter and wash the solid product with ethanol, vacuum dry at 95°C for 4 hours, and grind to obtain multi-effect flame retardant modified functional microspheres.

[0162] S3. Preparation of flame-retardant PET

[0163] 100 parts by weight of PET release film recycled particles, 29 parts by weight of ABS, 8 parts by weight of multi-effect flame retardant modified functional microspheres, 2 parts by weight of toughening agent, 0.8 parts by weight of compatibilizer, and 0.6 parts by weight of lubricant were added to a mixer and mixed for 5 minutes; the resulting mixture was then added to a twin-screw extruder for melt extrusion and granulation to obtain flame-retardant PET;

[0164] The screw speed is 410 rpm, and the temperatures of each section of the screw are: 230°C in the feeding section, 245°C in the conveying section, 260°C in the melting section, and 250°C in the die head.

[0165] ABS includes 32% by mass of butadiene, 25% by mass of acrylonitrile and 43% by mass of styrene, and the molecular weight of ABS is 90,000-150,000.

[0166] Among them, the toughening agent is ethylene-ethyl acrylate copolymer (EEA), the compatibilizer is compatibilizer SAG-002, and the lubricant is ethylene bis stearamide.

[0167] Example 2

[0168] A method for preparing flame-retardant PET by recycling particles of PET release film comprises the following steps:

[0169] S1. Preparation of PET release film and recovery of particles

[0170] S1-1. Crushing the recovered PET release film into pieces of 0.2-3 cm, adding it to deionized water, and steaming it at 65°C for 1 hour;

[0171] S1-2, filtering, adding the obtained PET particles to an ethanol-water solution, ultrasonically oscillating for 60 minutes, filtering, washing the obtained PET particles with deionized water, and air-drying at 95°C for 4 hours to obtain PET release film recovery particles; wherein the ethanol-water solution is obtained by mixing ethanol and deionized water in a volume ratio of 1:4.

[0172] S2. Preparation of multi-effect flame retardant modified functional microspheres

[0173] S2-1. Preparation of aluminum-doped ceria porous microspheres using a template method:

[0174] S2-1-1. Preparation of PS microsphere template:

[0175] 0.2 g of sodium lauryl sulfate was added to deionized water, stirred until dissolved, nitrogen was introduced for 15 min, heated to 75° C., 0.18 g of potassium persulfate was added, and stirred for 5 min to obtain a mixture 1;

[0176] 0.2 g of styrene and 0.15 g of n-butanol were mixed and stirred to obtain a mixture 2, which was then added dropwise to the mixture 1. The mixture was allowed to react for 45 minutes after the addition was completed. 5 g of styrene was then added dropwise to the mixture 1. The mixture was reacted at 85° C. for 3 hours, cooled, and centrifuged. The solid product was washed with ethanol and deionized water in sequence, and dried to obtain PS microspheres.

[0177] S2-1-2. Preparation of aluminum-doped ceria porous microspheres by template method:

[0178] 3 g of PS microspheres were added to 200 mL of deionized water and ultrasonically dispersed for 15 min. 0.45 g of PVP, 0.8 g of cerium nitrate, and 0.15 g of aluminum nitrate were added to the resulting dispersion and stirred for 5 min to obtain a microsphere precursor solution.

[0179] The microsphere precursor solution was transferred to a polytetrafluoroethylene-lined reactor and reacted at 190°C for 4 hours. The obtained product was centrifuged, and the solid product obtained by centrifugation was washed with deionized water, vacuum-dried at 70°C for 6 hours, and finally calcined at 550°C for 3 hours to obtain aluminum-doped ceria porous microspheres.

[0180] S2-2. Using raw materials including lycopene, octyl salicylate, sodium foscarnet and ethylenediamine, carbon dots were in situ grafted onto aluminum-doped ceria porous microspheres by a hydrothermal method to prepare carbon dot grafted microspheres:

[0181] S2-2-1. Take 0.4 g of aluminum-doped cerium dioxide porous microspheres and 0.1 g of PVP and add them to 50 mL of ethanol-water solution. Ultrasonicate for 10 minutes to obtain a microsphere dispersion; the volume ratio of ethanol to deionized water in the ethanol-water solution is 1:2;

[0182] S2-2-2. Add 1 g of lycopene, 0.8 g of octyl salicylate, and 0.3 g of sodium foscarnet to 100 mL of an ethanol aqueous solution, and stir at 65° C. for 10 min to obtain a raw material dispersion; the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:1;

[0183] S2-2-3. Add the raw material dispersion to the microsphere dispersion, stir for 5 minutes, then add 0.5 mL of ethylenediamine, and then ultrasonically disperse for 3 minutes to obtain a mixed precursor solution;

[0184] S2-2-4. Transfer the mixed precursor solution to a polytetrafluoroethylene-lined reactor and continue the reaction at 210°C for 4 hours;

[0185] S2-2-5. After the reaction is completed, cool to room temperature, centrifuge the product at 5000 r / min for 3 min, wash the solid product with deionized water and ethanol in sequence, and vacuum dry at 70°C for 6 h to obtain carbon dot grafted microspheres.

[0186] S2-3, loading flame retardant on carbon dot grafted microspheres to prepare multi-functional microspheres:

[0187] S2-3-1. Add 2 g of carbon dot-grafted microspheres to 50 mL of deionized water and sonicate for 5 min to obtain a dispersion of carbon dot-grafted microspheres.

[0188] S2-3-2. Add 2.5 g of magnesium nitrate to 20 mL of deionized water and stir until completely dissolved to obtain a magnesium salt solution;

[0189] S2-3-3. Add the magnesium salt solution to the carbon dot grafted microsphere dispersion under stirring, continue stirring for 10 minutes, keep stirring, and add 50 mL of 1 mol / L NaOH solution to the obtained mixed solution. After the reaction is completed, filter, wash the solid product with deionized water until it is neutral, and vacuum dry at 85°C for 12 hours to obtain multi-functional microspheres.

[0190] S2-4, coating the multi-effect functional microspheres with PET film to obtain multi-effect flame retardant modified functional microspheres:

[0191] S2-4-1. Add 5 g of multifunctional microspheres to 250 mL of 1,4-butanediol and disperse by ultrasonication for 10 min.

[0192] S2-4-2. Add 10 g of dimethyl terephthalate and 0.1 g of cobalt acetate to the dispersion obtained in step S2-4-1, and perform an ester exchange reaction at 185°C and 170 r / min using nitrogen as a protective gas;

[0193] S2-4-3. After the transesterification reaction is completed, add 0.8 g of antimony trioxide, heat at 210 ° C for 10 minutes, then evacuate to 18 Pa, raise the temperature to 275 ° C, and carry out polycondensation reaction for 4 hours;

[0194] S2-4-4. After the reaction is completed, filter and wash the solid product with ethanol, vacuum dry at 95°C for 4 hours, and grind to obtain multi-effect flame retardant modified functional microspheres.

[0195] S3. Preparation of flame-retardant PET

[0196] 100 parts by weight of PET release film recycled particles, 33 parts by weight of ABS, 10 parts by weight of multi-effect flame retardant modified functional microspheres, 2.5 parts by weight of toughening agent, 1 part by weight of compatibilizer, and 0.6 parts by weight of lubricant were added to a mixer and mixed for 5 minutes; the resulting mixture was then added to a twin-screw extruder for melt extrusion and granulation to obtain flame-retardant PET;

[0197] The screw speed is 410 rpm, and the temperatures of each section of the screw are: 230°C in the feeding section, 245°C in the conveying section, 260°C in the melting section, and 250°C in the die head.

[0198] ABS includes 32% by mass of butadiene, 25% by mass of acrylonitrile and 43% by mass of styrene, and the molecular weight of ABS is 90,000-150,000.

[0199] Among them, the toughening agent is ethylene-ethyl acrylate copolymer (EEA), the compatibilizer is compatibilizer SAG-002, and the lubricant is ethylene bis stearamide.

[0200] Example 3

[0201] A method for preparing flame-retardant PET by recycling particles of PET release film comprises the following steps:

[0202] S1. Preparation of PET release film and recovery of particles

[0203] S1-1. Crushing the recovered PET release film into pieces of 0.2-3 cm, adding it to deionized water, and steaming it at 65°C for 1 hour;

[0204] S1-2, filtering, adding the obtained PET particles to an ethanol-water solution, ultrasonically oscillating for 60 minutes, filtering, washing the obtained PET particles with deionized water, and air-drying at 95°C for 4 hours to obtain PET release film recovery particles; wherein the ethanol-water solution is obtained by mixing ethanol and deionized water in a volume ratio of 1:4.

[0205] S2. Preparation of multi-effect flame retardant modified functional microspheres

[0206] S2-1. Preparation of aluminum-doped ceria porous microspheres using a template method:

[0207] S2-1-1. Preparation of PS microsphere template:

[0208] 0.2 g of sodium lauryl sulfate was added to deionized water, stirred until dissolved, nitrogen was introduced for 15 min, heated to 75° C., 0.18 g of potassium persulfate was added, and stirred for 5 min to obtain a mixture 1;

[0209] 0.2 g of styrene and 0.15 g of n-butanol were mixed and stirred to obtain a mixture 2, which was then added dropwise to the mixture 1. The mixture was allowed to react for 45 minutes after the addition was completed. 5 g of styrene was then added dropwise to the mixture 1. The mixture was reacted at 85° C. for 3 hours, cooled, and centrifuged. The solid product was washed with ethanol and deionized water in sequence, and dried to obtain PS microspheres.

[0210] S2-1-2. Preparation of aluminum-doped ceria porous microspheres by template method:

[0211] 3 g of PS microspheres were added to 200 mL of deionized water and ultrasonically dispersed for 15 min. 0.45 g of PVP, 0.8 g of cerium nitrate, and 0.15 g of aluminum nitrate were added to the resulting dispersion and stirred for 5 min to obtain a microsphere precursor solution.

[0212] The microsphere precursor solution was transferred to a polytetrafluoroethylene-lined reactor and reacted at 190°C for 4 hours. The obtained product was centrifuged, and the solid product obtained by centrifugation was washed with deionized water, vacuum-dried at 70°C for 6 hours, and finally calcined at 550°C for 3 hours to obtain aluminum-doped ceria porous microspheres.

[0213] S2-2. Using raw materials including lycopene, octyl salicylate, sodium foscarnet and ethylenediamine, carbon dots were in situ grafted onto aluminum-doped ceria porous microspheres by a hydrothermal method to prepare carbon dot grafted microspheres:

[0214] S2-2-1. Take 0.4 g of aluminum-doped cerium dioxide porous microspheres and 0.1 g of PVP and add them to 50 mL of ethanol-water solution. Ultrasonicate for 10 minutes to obtain a microsphere dispersion; the volume ratio of ethanol to deionized water in the ethanol-water solution is 1:2;

[0215] S2-2-2. Add 1 g of lycopene, 0.8 g of octyl salicylate, and 0.3 g of sodium foscarnet to 100 mL of an ethanol aqueous solution, and stir at 65° C. for 10 min to obtain a raw material dispersion; the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:1;

[0216] S2-2-3. Add the raw material dispersion to the microsphere dispersion, stir for 5 minutes, then add 0.5 mL of ethylenediamine, and then ultrasonically disperse for 3 minutes to obtain a mixed precursor solution;

[0217] S2-2-4. Transfer the mixed precursor solution to a polytetrafluoroethylene-lined reactor and continue the reaction at 210°C for 4 hours;

[0218] S2-2-5. After the reaction is completed, cool to room temperature, centrifuge the product at 5000 r / min for 3 min, wash the solid product with deionized water and ethanol in sequence, and vacuum dry at 70°C for 6 h to obtain carbon dot grafted microspheres.

[0219] S2-3, loading flame retardant on carbon dot grafted microspheres to prepare multi-functional microspheres:

[0220] S2-3-1. Add 2 g of carbon dot-grafted microspheres to 50 mL of deionized water and sonicate for 5 min to obtain a dispersion of carbon dot-grafted microspheres.

[0221] S2-3-2. Add 2.5 g of magnesium nitrate to 20 mL of deionized water and stir until completely dissolved to obtain a magnesium salt solution;

[0222] S2-3-3. Add the magnesium salt solution to the carbon dot grafted microsphere dispersion under stirring, continue stirring for 10 minutes, keep stirring, and add 50 mL of 1 mol / L NaOH solution to the obtained mixed solution. After the reaction is completed, filter, wash the solid product with deionized water until it is neutral, and vacuum dry at 85°C for 12 hours to obtain multi-functional microspheres.

[0223] S2-4, coating the multi-effect functional microspheres with PET film to obtain multi-effect flame retardant modified functional microspheres:

[0224] S2-4-1. Add 5 g of multifunctional microspheres to 250 mL of 1,4-butanediol and disperse by ultrasonication for 10 min.

[0225] S2-4-2. Add 10 g of dimethyl terephthalate and 0.1 g of cobalt acetate to the dispersion obtained in step S2-4-1, and perform an ester exchange reaction at 185°C and 170 r / min using nitrogen as a protective gas;

[0226] S2-4-3. After the transesterification reaction is completed, add 0.8 g of antimony trioxide, heat at 210 ° C for 10 minutes, then evacuate to 18 Pa, raise the temperature to 275 ° C, and carry out polycondensation reaction for 4 hours;

[0227] S2-4-4. After the reaction is completed, filter and wash the solid product with ethanol, vacuum dry at 95°C for 4 hours, and grind to obtain multi-effect flame retardant modified functional microspheres.

[0228] S3. Preparation of flame-retardant PET

[0229] 100 parts by weight of PET release film recycled particles, 32 parts by weight of ABS, 12 parts by weight of multi-effect flame retardant modified functional microspheres, 2.5 parts by weight of toughening agent, 1.2 parts by weight of compatibilizer, and 0.8 parts by weight of lubricant were added to a mixer and mixed for 5 minutes; the resulting mixture was then added to a twin-screw extruder for melt extrusion and granulation to obtain flame-retardant PET;

[0230] The screw speed is 410 rpm, and the temperatures of each section of the screw are: 230°C in the feeding section, 245°C in the conveying section, 260°C in the melting section, and 250°C in the die head.

[0231] ABS includes 32% by mass of butadiene, 25% by mass of acrylonitrile and 43% by mass of styrene, and the molecular weight of ABS is 90,000-150,000.

[0232] Among them, the toughening agent is ethylene-ethyl acrylate copolymer (EEA), the compatibilizer is compatibilizer SAG-002, and the lubricant is ethylene bis stearamide.

[0233] Example 4

[0234] A method for preparing flame-retardant PET by recycling particles of PET release film comprises the following steps:

[0235] S1. Preparation of PET release film and recovery of particles

[0236] S1-1. Crushing the recovered PET release film into pieces of 0.2-3 cm, adding it to deionized water, and steaming it at 65°C for 1 hour;

[0237] S1-2, filtering, adding the obtained PET particles to an ethanol-water solution, ultrasonically oscillating for 60 minutes, filtering, washing the obtained PET particles with deionized water, and air-drying at 95°C for 4 hours to obtain PET release film recovery particles; wherein the ethanol-water solution is obtained by mixing ethanol and deionized water in a volume ratio of 1:4.

[0238] S2. Preparation of multi-effect flame retardant modified functional microspheres

[0239] S2-1. Preparation of aluminum-doped ceria porous microspheres using a template method:

[0240] S2-1-1. Preparation of PS microsphere template:

[0241] 0.2 g of sodium lauryl sulfate was added to deionized water, stirred until dissolved, nitrogen was introduced for 15 min, heated to 75° C., 0.18 g of potassium persulfate was added, and stirred for 5 min to obtain a mixture 1;

[0242] 0.2 g of styrene and 0.15 g of n-butanol were mixed and stirred to obtain a mixture 2, which was then added dropwise to the mixture 1. The mixture was allowed to react for 45 minutes after the addition was completed. 5 g of styrene was then added dropwise to the mixture 1. The mixture was reacted at 85° C. for 3 hours, cooled, and centrifuged. The solid product was washed with ethanol and deionized water in sequence, and dried to obtain PS microspheres.

[0243] S2-1-2. Preparation of aluminum-doped ceria porous microspheres by template method:

[0244] 3 g of PS microspheres were added to 200 mL of deionized water and ultrasonically dispersed for 15 min. 0.45 g of PVP, 1.2 g of cerium nitrate, and 0.17 g of aluminum nitrate were added to the resulting dispersion and stirred for 5 min to obtain a microsphere precursor solution.

[0245] The microsphere precursor solution was transferred to a polytetrafluoroethylene-lined reactor and reacted at 190°C for 4 hours. The obtained product was centrifuged, and the solid product obtained by centrifugation was washed with deionized water, vacuum-dried at 70°C for 6 hours, and finally calcined at 550°C for 3 hours to obtain aluminum-doped ceria porous microspheres.

[0246] S2-2. Using raw materials including lycopene, octyl salicylate, sodium foscarnet and ethylenediamine, carbon dots were in situ grafted onto aluminum-doped ceria porous microspheres by a hydrothermal method to prepare carbon dot grafted microspheres:

[0247] S2-2-1. Take 0.5 g of aluminum-doped cerium dioxide porous microspheres and 0.1 g of PVP and add them to 50 mL of ethanol-water solution. Ultrasonicate for 10 minutes to obtain a microsphere dispersion. The volume ratio of ethanol to deionized water in the ethanol-water solution is 1:2.

[0248] S2-2-2. Add 1 g of lycopene, 0.8 g of octyl salicylate, and 0.3 g of sodium foscarnet to 100 mL of an ethanol aqueous solution, and stir at 65° C. for 10 min to obtain a raw material dispersion; the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:1;

[0249] S2-2-3. Add the raw material dispersion to the microsphere dispersion, stir for 5 minutes, then add 0.5 mL of ethylenediamine, and then ultrasonically disperse for 3 minutes to obtain a mixed precursor solution;

[0250] S2-2-4. Transfer the mixed precursor solution to a polytetrafluoroethylene-lined reactor and continue the reaction at 210°C for 4 hours;

[0251] S2-2-5. After the reaction is completed, cool to room temperature, centrifuge the product at 5000 r / min for 3 min, wash the solid product with deionized water and ethanol in sequence, and vacuum dry at 70°C for 6 h to obtain carbon dot grafted microspheres.

[0252] S2-3, loading flame retardant on carbon dot grafted microspheres to prepare multi-functional microspheres:

[0253] S2-3-1. Add 2 g of carbon dot-grafted microspheres to 50 mL of deionized water and sonicate for 5 min to obtain a dispersion of carbon dot-grafted microspheres.

[0254] S2-3-2. Add 2.2 g of magnesium nitrate to 20 mL of deionized water and stir until completely dissolved to obtain a magnesium salt solution;

[0255] S2-3-3. Add the magnesium salt solution to the carbon dot grafted microsphere dispersion under stirring, continue stirring for 10 minutes, keep stirring, and add 50 mL of 1 mol / L NaOH solution to the obtained mixed solution. After the reaction is completed, filter, wash the solid product with deionized water until it is neutral, and vacuum dry at 85°C for 12 hours to obtain multi-functional microspheres.

[0256] S2-4, coating the multi-effect functional microspheres with PET film to obtain multi-effect flame retardant modified functional microspheres:

[0257] S2-4-1. Add 5 g of multifunctional microspheres to 250 mL of 1,4-butanediol and disperse by ultrasonication for 10 min.

[0258] S2-4-2. Add 10 g of dimethyl terephthalate and 0.1 g of cobalt acetate to the dispersion obtained in step S2-4-1, and perform an ester exchange reaction at 185°C and 170 r / min using nitrogen as a protective gas;

[0259] S2-4-3. After the transesterification reaction is completed, add 0.8 g of antimony trioxide, heat at 210 ° C for 10 minutes, then evacuate to 18 Pa, raise the temperature to 275 ° C, and carry out polycondensation reaction for 4 hours;

[0260] S2-4-4. After the reaction is completed, filter and wash the solid product with ethanol, vacuum dry at 95°C for 4 hours, and grind to obtain multi-effect flame retardant modified functional microspheres.

[0261] S3. Preparation of flame-retardant PET

[0262] 100 parts by weight of PET release film recycled particles, 29 parts by weight of ABS, 8 parts by weight of multi-effect flame retardant modified functional microspheres, 2 parts by weight of toughening agent, 0.8 parts by weight of compatibilizer, and 0.6 parts by weight of lubricant were added to a mixer and mixed for 5 minutes; the resulting mixture was then added to a twin-screw extruder for melt extrusion and granulation to obtain flame-retardant PET;

[0263] The screw speed is 410 rpm, and the temperatures of each section of the screw are: 230°C in the feeding section, 245°C in the conveying section, 260°C in the melting section, and 250°C in the die head.

[0264] ABS includes 32% by mass of butadiene, 25% by mass of acrylonitrile and 43% by mass of styrene, and the molecular weight of ABS is 90,000-150,000.

[0265] Among them, the toughening agent is ethylene-ethyl acrylate copolymer (EEA), the compatibilizer is compatibilizer SAG-002, and the lubricant is ethylene bis stearamide.

[0266] The following comparative examples are provided

[0267] Comparative Example 1

[0268] This example is basically the same as Example 2, except that the multi-effect flame retardant modified functional microspheres are not added in this example.

[0269] Comparative Example 2

[0270] This example is basically the same as Example 2, except that the multi-effect flame retardant modified functional microspheres in this example are prepared by the following method:

[0271] S2-1. Preparation of aluminum-doped cerium dioxide porous microspheres using a template method (the specific steps are the same as those in Example 2)

[0272] S2-2, loading flame retardant on aluminum-doped cerium dioxide porous microspheres to prepare multi-functional microspheres:

[0273] S2-2-1. Add 2 g of aluminum-doped cerium dioxide porous microparticles into 50 mL of deionized water and sonicate for 5 min to obtain an aluminum-doped cerium dioxide porous microparticle dispersion.

[0274] S2-2-2. Add 2.5 g of magnesium nitrate to 20 mL of deionized water and stir until completely dissolved to obtain a magnesium salt solution;

[0275] S2-2-3. Add the magnesium salt solution to the aluminum-doped cerium dioxide porous microsphere dispersion under stirring, and continue stirring for 10 minutes. Keep stirring and add 50 mL of 1 mol / L NaOH solution to the obtained mixed solution. After the reaction is completed, filter and wash the solid product with deionized water until it is neutral. Vacuum dry it at 85°C for 12 hours to obtain multi-functional microspheres.

[0276] S2-3, coating the multi-effect functional microspheres with PET film to obtain multi-effect flame retardant modified functional microspheres. (The specific steps are the same as those in Example 2)

[0277] Comparative Example 3

[0278] This example is basically the same as Example 2, except that carbon dots and magnesium hydroxide powder are used instead of the multi-effect flame retardant modified functional microspheres in Example 2, and the amount of carbon dots added is 4 parts by weight, and the amount of magnesium hydroxide powder added is 6 parts by weight.

[0279] The carbon dots were prepared by the following method:

[0280] 1. Add 1 g of lycopene, 0.8 g of octyl salicylate, and 0.3 g of sodium foscarnet to 100 mL of ethanol-water solution, and stir at 65°C for 10 minutes to obtain a precursor solution; the volume ratio of ethanol to deionized water in the ethanol-water solution is 1:1;

[0281] 2. Transfer the precursor solution to a polytetrafluoroethylene-lined reactor and continue the reaction at 210°C for 4 hours;

[0282] 3. After the reaction is completed, the mixture is cooled to room temperature, and the product is centrifuged at 5000 r / min for 3 min. The supernatant is dialyzed using a dialysis bag with a molecular weight cutoff of 900 Da for 10 h. The dialyzate is freeze-dried to obtain carbon dots.

[0283] Comparative Example 4

[0284] This example is basically the same as Example 2, except that: in this example, aluminum-doped cerium dioxide porous microspheres, carbon dots, and magnesium hydroxide powder are used instead of the multi-effect flame retardant modified functional microspheres in Example 2, and the amount of aluminum-doped cerium dioxide porous microspheres added is 4 parts by weight, the amount of carbon dots added is 3 parts by weight, and the amount of magnesium hydroxide powder added is 3 parts by weight;

[0285] The preparation method of aluminum-doped cerium dioxide porous microspheres is the same as that in Example 2.

[0286] The carbon dots are prepared by the following method:

[0287] 1. Add 1 g of lycopene, 0.8 g of octyl salicylate, and 0.3 g of sodium foscarnet to 100 mL of ethanol-water solution, and stir at 65°C for 10 minutes to obtain a precursor solution; the volume ratio of ethanol to deionized water in the ethanol-water solution is 1:1;

[0288] 2. Transfer the precursor solution to a polytetrafluoroethylene-lined reactor and continue the reaction at 210°C for 4 hours;

[0289] 3. After the reaction is completed, the mixture is cooled to room temperature, and the product is centrifuged at 5000 r / min for 3 min. The supernatant is dialyzed using a dialysis bag with a molecular weight cutoff of 900 Da for 10 h. The dialyzate is freeze-dried to obtain carbon dots.

[0290] Comparative Example 5

[0291] This example is basically the same as Example 2, except that: in this example, multi-effect functional microspheres are used instead of the multi-effect flame retardant modified functional microspheres in Example 2, and the preparation method of the multi-effect functional microspheres is the same as that in Example 2.

[0292] Performance testing and characterization

[0293] Reference Figure 2 , is the infrared spectrum of the carbon dot grafted microspheres (Al-CeO2@CDs) prepared in step S2-2 of Example 2, wherein 3245 cm -1 The absorption peak at 3584 cm is attributed to the stretching vibration of the -OH bond. -1 The absorption peak at 2930 cm is attributed to the stretching vibration of the -NH bond. -1 The absorption peak at 1992 cm is attributed to the stretching vibration of the C-H bond. -1 and 2124cm -1 is the stretching vibration peak of Al-O bond, 1650cm -1 The absorption peak at 1587 cm is attributed to the C=C bond. -1 The absorption peak at 1143 cm is attributed to the C=O bond of the carboxyl group. -1 The absorption peak at 1075 cm is attributed to the P=O bond of the carboxyl group. -1 The absorption peak at 304 cm is attributed to the -OP bond of the carboxyl group. -1 The absorption peak at is attributed to the Ce-O-Ce bond. The above infrared spectrum analysis shows that the carbon dots have rich functional groups on their surface and are successfully grafted onto the aluminum-doped ceria porous microspheres.

[0294] Reference Figure 3 , are the ultraviolet absorption spectra of the aluminum-doped cerium dioxide porous microspheres Al-CeO2 (curve a) prepared in step S2-1 of Example 2 and the carbon dot-grafted microspheres Al-CeO2@CDs (curve b) prepared in step S2-2. It can be seen from curve a that the ultraviolet resistance of Al-CeO2 in the shortwave region (200-290nm) is relatively weak. After grafting carbon dots (curve b), the ultraviolet resistance of Al-CeO2@CDs in the shortwave region (200-290nm) is significantly improved, and it has strong ultraviolet absorption ability in the entire ultraviolet region.

[0295] The following performance tests were performed on the products obtained in Examples 1-3 and Comparative Examples 1-6. The test items included:

[0296] (1) Mechanical strength test: PET material was prepared into samples and tested according to the standard: GB / T1040.2-2006;

[0297] Refer to Table 1 below for the mechanical strength test results:

[0298] Table 1

[0299] Tensile strength / MPa Elongation at break / % Bending strength / MPa Example 1 48.2 23.6 68.7 Example 2 49.5 24.3 69.9 Example 3 48.6 23.9 69.1 Example 4 47.8 22.7 67.4 Comparative Example 1 48.8 24.0 69.5 Comparative Example 2 46.5 21.4 66.3 Comparative Example 3 37.2 16.3 51.5 Comparative Example 4 34.7 15.1 46.7 Comparative Example 5 39.5 17.6 53.0

[0300] From the test results in Table 1, it can be seen that Examples 1-4 have good mechanical strength and do not lose the mechanical properties of the material due to the doping of the multi-effect flame retardant modified functional microspheres, while Comparative Examples 2-5 all show varying degrees of decline.

[0301] (2) Flame retardant performance testing, including:

[0302] (2-1)Limiting oxygen index;

[0303] Prepare a test specimen with a size of 100 mm × 10 mm × 5 mm, and measure the LOI value of the sample with reference to GB / T2406.2-2009 "Plastics combustion performance test method oxygen index method".

[0304] (2-2) UL-94 grade

[0305] Prepare test specimens with a size of 100 mm × 10 mm × 5 mm. Refer to GB / T2408-2008 "Determination of burning behavior of plastics - Horizontal and vertical methods" to test the vertical burning performance of flame retardant copolymers. The specimen size is 100 mm × 10 mm × 5 mm.

[0306] The test specimens were irradiated with UV light for 72 hours with an irradiance of 0.89 W / m and a wavelength of 340 nm. The UL-94 grade after aging was then tested according to GB / T 2408-2008.

[0307] The limiting oxygen index and UL-94 grade test results are shown in Table 2 below:

[0308] Table 2

[0309]

[0310]

[0311] From the test results in Table 3, it can be seen that Examples 1-4 have excellent flame retardancy and good anti-ultraviolet aging performance, while the flame retardancy and anti-ultraviolet aging performance of Comparative Examples 1-5 are relatively degraded.

[0312] (2-3) Test specimens with dimensions of 100 mm × 10 mm × 5 mm were prepared. The cone calorimetry test was performed according to ISO 5660-1:2002. The cone calorimeter was used for testing. The radiation power was set to 60 kW / m 2 The sample size is 100mm×10mm×5mm. The cone calorimetry test results are shown in Table 3 and Figure 4 shown.

[0313] Table 3

[0314] TTI(s) <![CDATA[HRR(kW / m 2 )]]> <![CDATA[THR(MJ / m 2 )]]> Example 1 65 299.44 22.0 Example 2 68 287.53 21.4 Example 3 66 291.26 21.7 Example 4 64 302.15 22.5 Comparative Example 1 48 445.33 58.9 Comparative Example 2 59 358.25 37.4 Comparative Example 3 52 391.72 42.0 Comparative Example 4 55 373.08 39.6 Comparative Example 5 57 361.21 38.5

[0315] Among them, TTI represents ignition time, HRR represents heat release rate, and THR represents total heat release.

[0316] Reference Figure 4 , is the total heat release curve of Example 2 and Comparative Examples 1-5. From Table 3 and Figure 4 It can be seen from the results that Examples 1-4 have better flame retardant properties, while Comparative Examples 1-5 have shorter ignition times, increased heat release rates, and higher total heat releases, but their flame retardant properties are relatively reduced.

[0317] (3) Anti-ultraviolet aging performance test:

[0318] The PET materials prepared in each example were prepared into film samples with a thickness of 0.2 mm. The average light transmittance of the film samples in different ultraviolet regions was tested: UVA (400-315 nm), UVB (315-280 nm) and UVC (280-190 nm). The test results are shown in Table 4 below.

[0319] Table 4

[0320] Transmittance TUVA (%) Transmittance TUVB (%) Transmittance TUVC (%) Example 1 0.14 0.1 0.16 Example 2 0.11 0.08 0.13 Example 3 0.13 0.08 0.14 Example 4 0.15 0.12 0.17 Comparative Example 1 31.6 29.5 33.0 Comparative Example 2 9.4 7.2 18.9 Comparative Example 3 18.5 19.7 17.8 Comparative Example 4 17.1 18.4 16.0 Comparative Example 5 9.8 8.1 14.3

[0321] From the results in Table 4, it can be seen that the PET materials of Examples 1-4 have excellent UV resistance across the entire wavelength range, while the UV resistance of Comparative Examples 1-5 is significantly reduced.

[0322] The carbonyl index of the PET materials prepared in Example 2 and Comparative Examples 1-5 was tested at different aging times to further study their UV aging resistance. The test results are as follows: Figure 5 As shown, it can be seen that the carbonyl index of Example 2 increases slowly, while that of Comparative Examples 1-5 increases rapidly, indicating that the UV aging resistance of Comparative Examples 1-5 is worse than that of Example 2.

[0323] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for preparing flame-retardant PET by recycling particles of PET release film, characterized in that: The following steps are involved: S1, crushing the recovered PET release film, and then washing it to obtain PET release film recovery particles; S2. Preparation of multi-effect flame retardant modified functional microspheres: S2-1, preparing aluminum-doped ceria porous microspheres using a template method; S2-2, using raw materials including lycopene, octyl salicylate, sodium foscarnet and ethylenediamine, carbon dots were in situ grafted onto aluminum-doped ceria porous microspheres by a hydrothermal method to prepare carbon dot grafted microspheres; S2-3, loading flame retardant on carbon dot grafted microspheres to prepare multi-functional microspheres; The step S2-3 specifically includes: S2-3-1. Add 1-4 g of carbon dot-grafted microspheres to 30-100 mL of deionized water and sonicate for 2-10 min to obtain a dispersion of carbon dot-grafted microspheres. S2-3-2. Add 1.25-5 g of magnesium nitrate to 10-40 mL of deionized water and stir until completely dissolved to obtain a magnesium salt solution; S2-3-3. Add the magnesium salt solution to the carbon dot grafted microsphere dispersion under stirring, continue stirring for 5-20 minutes, and add 20-100 mL of 0.5-2 mol / L NaOH solution dropwise to the resulting mixed solution. After the reaction is completed, filter and wash the solid product with deionized water until neutral, and vacuum dry at 60-95°C for 6-24 hours to obtain multi-functional microspheres. S2-4, coating the multi-effect functional microspheres with a PBT film to obtain multi-effect flame retardant modified functional microspheres; The step S2-4 specifically includes: S2-4-1. Add 2.5-10 g of multifunctional microspheres to 100-500 mL of 1,4-butanediol and disperse by ultrasonication for 5-30 min. S2-4-2. Add 5-20 g of dimethyl terephthalate and 0.05-0.2 g of cobalt acetate to the dispersion obtained in step S2-4-1, and perform an ester exchange reaction at 160-210° C. and 100-250 r / min using nitrogen as a protective gas; S2-4-3. After the transesterification reaction is completed, add 0.04-0.15g of antimony trioxide, heat at 190-225℃ for 5-15min, then evacuate to 10-30Pa, raise the temperature to 250-330℃, and carry out polycondensation reaction for 2-8h; S2-4-4. After the reaction is completed, filter and wash the solid product with ethanol, vacuum dry at 75-110°C for 2-10 hours, and grind to obtain multi-effect flame retardant modified functional microspheres; S3. Mix 100 parts by weight of PET release film recycled particles, 24-47 parts by weight of ABS, 2-15 parts by weight of multi-effect flame retardant modified functional microspheres, and 3.6-16 parts by weight of additives according to the weight ratio, and then melt-extrude and granulate through a twin-screw extruder to obtain flame-retardant PET.

2. The method for preparing flame-retardant PET by recycling particles from PET release film according to claim 1, characterized in that: The step S1 is specifically as follows: S1-1. Crushing the recovered PET release film into pieces of 0.2-3 cm, adding it to deionized water, and steaming it at 55-95°C for 0.5-3 hours; S1-2, filtering, adding the obtained PET particles to an ethanol-water solution, ultrasonically oscillating for 30-90 minutes, filtering, washing the obtained PET particles with deionized water, and air-drying at 80-105° C. for 2-6 hours to obtain PET release film recovery particles; wherein the ethanol-water solution is obtained by mixing ethanol and deionized water in a volume ratio of 1:8-1:

3.

3. The method for preparing flame-retardant PET by recycling particles from PET release film according to claim 1, characterized in that: The step S2-1 specifically includes: S2-1-1. Preparation of PS microsphere template: 0.1-0.5 g of sodium lauryl sulfate was added to deionized water, stirred until dissolved, nitrogen was introduced for 10-30 min, heated to 70-95° C., 0.08-0.3 g of potassium persulfate was added, and stirred for 3-10 min to obtain a mixture 1; 0.1-0.4 g of styrene and 0.075-0.3 g of n-butanol were mixed and stirred to obtain a mixture 2, which was then added dropwise to the mixture 1. The mixture was allowed to react for 20-60 minutes after the addition was complete. 2-8 g of styrene was then added dropwise to the mixture 1. The mixture was reacted at 75-90° C. for 2-6 hours, cooled, centrifuged, and the solid product was washed with ethanol and deionized water in sequence, and dried to obtain PS microspheres. S2-1-2. Preparation of aluminum-doped ceria porous microspheres by template method: 1-4 g of PS microspheres were added to 100-400 mL of deionized water and ultrasonically dispersed for 10-30 min. 0.2-0.9 g of PVP, 0.4-1.5 g of cerium nitrate, and 0.05-0.3 g of aluminum nitrate were added to the obtained dispersion and stirred for 3-15 min to obtain a microsphere precursor solution. The microsphere precursor solution was transferred to a polytetrafluoroethylene-lined reactor, reacted at 170-220°C for 2-8 hours, and the obtained product was centrifuged. The solid product obtained by centrifugation was washed with deionized water, vacuum-dried at 60-80°C for 2-10 hours, and finally calcined at 450-600°C for 1-8 hours to obtain aluminum-doped cerium dioxide porous microspheres.

4. The method for preparing flame-retardant PET by recycling particles from PET release film according to claim 3, characterized in that: The step S2-2 specifically includes: S2-2-1. Add 0.2-0.8 g of aluminum-doped cerium dioxide porous microspheres and 0.05-0.2 g of PVP to 30-100 mL of ethanol-water solution and sonicate for 10 minutes to obtain a microsphere dispersion; the volume ratio of ethanol to deionized water in the ethanol-water solution is 1:3-1:1; S2-2-2. Add 0.5-2 g of lycopene, 0.4-1.6 g of octyl salicylate, and 0.15-0.6 g of sodium foscarnet to 50-200 mL of an aqueous ethanol solution, and stir at 50-75° C. for 5-20 min to obtain a raw material dispersion; the volume ratio of ethanol to deionized water in the aqueous ethanol solution is 1:3-2:1; S2-2-3. Add the raw material dispersion to the microsphere dispersion, stir for 3-15 minutes, then add 0.25-1 mL of ethylenediamine, and then ultrasonically disperse for 2-8 minutes to obtain a mixed precursor solution; S2-2-4. Transfer the mixed precursor solution to a polytetrafluoroethylene-lined reactor and continue the reaction at 180-230°C for 2-8 hours; S2-2-5. After the reaction is completed, cool to room temperature, centrifuge the product at 3000-8000 r / min for 1-5 min, wash the solid product with deionized water and ethanol in sequence, and vacuum dry at 60-80°C for 3-10 h to obtain carbon dot grafted microspheres.

5. The method for preparing flame-retardant PET by recycling particles from PET release film according to claim 1, characterized in that: The step S3 is specifically as follows: 100 parts by weight of PET release film recycled particles, 24-47 parts by weight of ABS, 2-15 parts by weight of multi-effect flame retardant modified functional microspheres, and 3.6-16 parts by weight of additives are added to a mixer and mixed for 3-10 minutes; the resulting mixture is then added to a twin-screw extruder for melt extrusion and granulation to obtain flame-retardant PET; The screw speed is 280-450 rpm, and the temperatures of each section of the screw are: 220-235°C in the feeding section, 240-250°C in the conveying section, 255-265°C in the melting section, and 250-255°C in the die head.

6. The method for preparing flame-retardant PET by recycling particles from PET release film according to claim 5, characterized in that: in, The auxiliary agent comprises 3-8 parts by weight of a toughening agent, 0.4-5 parts by weight of a compatibilizer and 0.2-3 parts by weight of a lubricant.

7. The method for preparing flame-retardant PET by recycling particles from PET release film according to claim 6, characterized in that: in, The ABS comprises 15-40% by mass of butadiene, 12-33% by mass of acrylonitrile and 38-57% by mass of styrene, and the molecular weight of the ABS is 90,000-150,000.

8. The method for preparing flame-retardant PET by recycling particles from PET release film according to claim 7, characterized in that: The toughening agent is one or two of ethylene-ethyl acrylate copolymer and glycidyl methacrylate random terpolymer; The compatibilizer is compatibilizer SAG-002 or styrene-acrylonitrile-glycidyl methacrylate copolymer compatibilizer; The lubricant is pentaerythritol ester or ethylene bis stearamide.

Images