A method for preparing flame-retardant and wear-resistant plastic sheets by recycling waste plastics

Abstract

The invention discloses a method for preparing a flame-retardant and wear-resistant plastic sheet by recycling waste plastics, belongs to the technical field of waste plastic recycling, and is used to solve the technical problem in the prior art that the flame-retardant and wear-resistant properties of recycled plastic sheets need to be further improved. The invention comprises the following steps: adding modified polyester, flame-retardant end-capping agent, microwave accelerator and auxiliary materials into a twin-screw extruder, melting and extruding into a mold, and solidifying to obtain the plastic sheet; preparing a microwave accelerator as a microwave absorption center, while promoting depolymerization and esterification, the active functional groups directly on its surface pre-extend the modified oligomeric polyester, and the wear-resistant property of the material is significantly enhanced after chain extension by a modified cross-linking agent; after being end-capped by the flame-retardant end-capping agent, the porous alumina structure of the microwave accelerator, the silicon group in the modified cross-linking agent and the flame-retardant component in the flame-retardant end-capping agent significantly enhance the flame-retardant ability of the material through synergistic cooperation.

Description

Technical Field

[0001] The invention relates to the technical field of waste plastic recycling, and in particular to a method for preparing a flame-retardant and wear-resistant plastic plate by recycling waste plastic. Background Art

[0002] With the emergence of new composite materials, recycled plastics have gradually improved in terms of wear resistance and flame retardancy. Reinforcement materials such as glass fiber and carbon fiber are added to recycled plastics to effectively improve friction resistance and extend service life.

[0003] Moreover, flame retardancy is a basic requirement for recycled plastic sheets in many industries. With the addition of flame retardants and the improvement of modification technology, modern recycled plastic sheets can meet high standards of fire protection. Through these technological advances, recycled plastic sheets can meet high-performance wear resistance and flame retardancy requirements while ensuring environmental protection and sustainability. They are widely used in various demanding scenarios, promoting the development of the green materials industry.

[0004] Prior art CN107746491B discloses a method for recycling waste plastics into composite flame retardant materials, comprising the following steps: 1) treating waste plastics; 2) mixing materials: mixing dried waste plastic particles, fly ash, rutile titanium dioxide, lubricant, binder, phosphorus flame retardant, light stabilizer, and dilauryl thiodipropionate in a high-speed mixer according to a weight ratio of (60-80): (120-160): (20-40): (3-8): (1-6): (0.02-0.08): (0.3-0.9): (0.2-0.6) to obtain a mixture; 3) granulation; 4) extrusion molding; This invention recycles waste thermosetting plastics and overcomes the defects of plastic recycled materials such as brittleness, poor bending strength, tensile strength, elongation at break, and poor flame retardancy.

[0005] However, the above patent content is to clean the surface of waste plastics and then blend them with auxiliary materials to obtain a recycled composite flame retardant material. However, the waste plastics have too many impurities inside without impurity removal and purification treatment, and their composition is complex and their compatibility with auxiliary materials is poor. They may also undergo side reactions at high temperatures, which ultimately leads to weak interfacial bonding of the materials, resulting in the wear resistance of the materials to be further improved, and uneven dispersion of the flame retardant. The flame retardant performance improved by simple blending also needs to be further improved.

[0006] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing flame retardant and wear-resistant plastic sheets by recycling waste plastics, so as to solve the technical problem in the prior art that the flame retardant and wear-resistant properties of recycled plastic sheets need to be further improved.

[0008] The purpose of the present invention can be achieved by the following technical solution: A method for preparing flame-retardant and wear-resistant plastic sheets by recycling waste plastics, comprising the following steps:

[0009] S1, adding molten PET, microwave accelerator, neopentyl glycol and zinc acetate into a microwave generator, performing microwave depolymerization for 10-15 minutes, and post-treating to obtain modified oligomeric polyester;

[0010] The reaction equation for preparing modified oligomeric polyester is:

[0011]

[0012] Where: .

[0013] The reaction principle for preparing modified oligomeric polyesters is as follows: the heating effect of microwaves accelerates the interaction between polyester materials and alcohol reactants, thereby increasing the rate of the alcoholysis process. When microwave radiation acts on polyester, polar molecules absorb microwave energy, and the vibration and rotation within the molecules cause the temperature to rise rapidly. Unlike traditional heating methods, microwave heating directly acts on molecules through electromagnetic fields, so that heat is evenly distributed inside the material, thereby more efficiently increasing the temperature of the reaction. In addition, microwave promoters serve as microwave absorption centers, which help improve temperature distribution during microwave heating, making the temperature in the reaction system more uniform. By increasing the local temperature, metal oxides accelerate the breaking of ester bonds in polyesters, thereby increasing the rate of the alcoholysis reaction and accelerating the alcoholysis reaction.

[0014] S2, adding the modified oligomeric polyester and the modified chain extender into a microwave generator, and subjecting the resultant to microwave esterification for 30-40 minutes to obtain a cross-linked polyester;

[0015] S3, adding cross-linked polyester, flame retardant end-capping agent, triethylamine and N,N-dimethylformamide into a reactor, raising the temperature of the reactor to 50-60°C, keeping the temperature for reaction for 1-2 hours, then continuing to add modifier into the reactor, keeping the temperature for reaction for 0.5-1 hour, and post-treating to obtain modified polyester;

[0016] The overall reaction equation for preparing cross-linked polyester and modified polyester is:

[0017]

[0018] Where: ; .

[0019] The overall reaction principle for preparing cross-linked polyester and modified polyester is as follows: in the process of preparing modified oligomeric polyester and cross-linked polyester, during microwave heating, the epoxy group in the microwave accelerator is tempered and reacts with the hydroxyl group at the end of the modified oligomeric polyester, and microwave heating is used to promote the progress of the esterification reaction to obtain cross-linked polyester; in the process of preparing modified polyester, the epoxy group on the flame retardant end group is ring-opened under alkaline conditions and the catalysis of heating, and reacts with the hydroxyl group at the end of the cross-linked polyester, and finally the modified polyester is prepared.

[0020] S4, adding the modified polyester, flame retardant end-capping agent, microwave accelerator and auxiliary materials into a twin-screw extruder, melting and extruding into a mold, and solidifying to obtain a recycled plastic sheet.

[0021] Furthermore, in step S1, the pretreatment step includes: placing the waste PET fragments into a pulverizer and crushing them through a 100-mesh sieve, placing them in a reactor and introducing nitrogen protection, raising the temperature of the reactor to 250-260°C to obtain a melt, and after the melt passes through a 100-mesh sieve, obtaining molten PET; the amount ratio of molten PET, microwave accelerator, neopentyl glycol and zinc acetate is 8-10g:2-3g:50-60mL:0.3-0.5g, the power of the microwave generator is 500-540W, and the frequency is 2.1-2.3GHz; the post-treatment includes: after the depolymerization is completed, placing the reaction solution in a rotary evaporator at a temperature of 80-100°C, and distilling under reduced pressure until no liquid is produced to obtain a modified oligomeric polyester.

[0022] Furthermore, in step S1, the method for preparing the microwave accelerator comprises the following steps:

[0023] A1. Aluminum isopropoxide, isopropanol and deionized water are added to a reactor, the temperature of the reactor is raised to 50-60°C, and a 10-20wt% hydrochloric acid solution is used to adjust the pH value of the system to 3-5. After the reaction is kept warm for 1-2 hours, triethanolamine is continuously added to the reactor, and the reaction is kept warm for 20-30 minutes. After post-treatment, an aluminum gel is obtained;

[0024] The reaction principle for preparing aluminum gel is as follows: under the catalysis of acidic conditions, aluminum isopropoxide undergoes hydrolysis reaction and gradually aggregates to form a colloidal substance, and the aluminum hydroxide of the hydrolysis product gradually aggregates to form a stable gel structure. The added triethanolamine reacts with the aluminum hydroxide to further adjust the structure of the gel to obtain aluminum gel.

[0025] A2. The aluminum gel is placed in a tubular furnace and calcined to obtain porous alumina;

[0026] The reaction principle for preparing porous alumina is as follows: under high-temperature calcination, a large amount of organic structures inside the aluminum gel undergo thermal decomposition, eventually forming a uniform pore structure to obtain porous alumina.

[0027] A3. Porous alumina, ethanol, triethylamine and deionized water are added into a reactor and nitrogen is introduced for protection. After the temperature of the reactor is reduced to 10-20°C, 3-(2,3-epoxypropoxy)propyltrimethoxysilane is added into the reactor, and the reaction is kept warm for 20-30 minutes. The microwave accelerator is obtained by post-treatment.

[0028] The reaction principle for preparing the microwave accelerator is as follows: under the protection of nitrogen and low temperature, the epoxy group on 3-(2,3-epoxypropoxy)propyltrimethoxysilane is protected, and the siloxy group thereon is hydrolyzed to produce a silanol structure, which reacts with the hydroxyl group on the porous alumina to form a stable cross-linked structure to obtain the microwave accelerator.

[0029] Further, in step A1, the amount ratio of aluminum isopropoxide, isopropanol, deionized water and triethanolamine is 8-10g:20-30mL:10-20mL:2-3g, and the post-treatment includes: after the reaction is completed, after the reaction kettle is cooled to room temperature, the reaction solution is placed in a rotary evaporator at a temperature of 80-100°C, and the reduced pressure distillation is performed until no liquid is produced to obtain an aluminum gel; in step A2, the calcination operation includes: introducing nitrogen protection, heating the tubular furnace to 750-85 at a heating rate of 3-5°C / min 0℃, keep warm and calcine for 4-6h to obtain porous alumina; in step A3, the amount ratio of porous alumina, ethanol, triethylamine, deionized water and 3-(2,3-epoxypropoxy)propyltrimethoxysilane is 8-10g:20-30mL:0.3-0.5g:10-20mL:3-4g, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is raised to room temperature, the reaction liquid is filtered to collect the filter cake, and the filter cake is transferred to a drying oven at a temperature of 60℃ and vacuum dried until the filter cake has a constant weight to obtain a microwave accelerator.

[0030] Furthermore, in step S2, the amount ratio of the modified oligomeric polyester and the modified chain extender is 8-10g:2-4g, the power of the microwave generator is 600-800W, and the frequency is 2.4-2.5GHz. The preparation method of the modified chain extender is: acrylic acid, dichloroplatinene and n-heptane are added to a reactor and stirred, and nitrogen is introduced for protection. After the temperature of the reactor is increased to 40-50°C, phenyltri(dimethylsiloxy)silane is added to the reactor, and the mixture is stirred for 1-3h at a temperature of 40-50°C, and the modified chain extender is obtained by post-treatment.

[0031] The reaction equation for preparing the modified chain extender is:

[0032]

[0033] The reaction principle for preparing the modified chain extender is: under the protection of nitrogen, phenyltri(dimethylsiloxy)silane is added into the reactor, and then a hydrosilylation reaction occurs with acrylic acid under the catalysis of high temperature and catalyst, and finally the modified chain extender is prepared.

[0034] Furthermore, in step S2, the stirring rate of the reactor is 40-60rpm, the amount ratio of acrylic acid, n-heptane, dichloroplatinene and phenyltri(dimethylsiloxy)silane is 2-3g:30-40mL:0.3-0.5g:8-10g, and the post-treatment includes: after the reaction is completed, after the reactor is cooled to room temperature, the reaction liquid is placed in a rotary evaporator at a temperature of 80-100°C, and reduced pressure distillation is performed until no liquid is extracted to obtain a modified chain extender.

[0035] Furthermore, in step S3, the amount ratio of the cross-linked polyester, the flame retardant capping agent, triethylamine, N,N-dimethylformamide and the modifier is 8-10g:2-3g:0.3-0.8g:30-40mL:0.6-0.8g, the modifier is 3-(2,3-epoxypropoxy)propyltrimethoxysilane, and the post-treatment includes: after the reaction is completed, the reaction kettle is lowered to room temperature, the reaction liquid is added to a rotary evaporator with a water bath temperature of 80-100°C, and the reduced pressure distillation is carried out until no liquid is produced to obtain a modified polyester.

[0036] Furthermore, in step S3, the method for preparing the flame retardant end-capping agent comprises the following steps:

[0037] B1. Add 2-[(4,6-diamino-1,3,5-triazine-2-yl)oxy]ethanol, 3,5-dimethylbenzaldehyde, triethylamine and N,N-dimethylformamide into a reaction kettle, raise the temperature of the reaction kettle to 60-80° C., keep the temperature for 2-4 hours, and perform post-treatment to obtain modified triazine;

[0038] The reaction equation for preparing modified triazine is:

[0039]

[0040] Where: .

[0041] The reaction principle for preparing modified triazine is as follows: the amino group of 2-[(4,6-diamino-1,3,5-triazine-2-yl)oxy]ethanol contains a lone pair of electrons, and as a nucleophile, it initiates a nucleophilic attack on the carbon atom in the aldehyde group on 3,5-dimethylbenzaldehyde. In the aldehyde group, the carbon atom has a partial positive charge due to the large electronegativity of the oxygen atom, so the carbon atom becomes the target of the nucleophile attack and generates a temporary intermediate containing a nitrogen atom and a hydroxyl group. This intermediate is unstable and loses a water molecule to form a stable imine structure. Finally, the modified triazine as a reaction intermediate is prepared. The mass spectrometry analysis data of the modified triazine are: m / z: 403.20 (100.0%), 404.20 (26.7%), 405.21 (3.5%).

[0042] B2, adding modified triazine, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, aluminum chloride and dimethyl sulfoxide into a reaction kettle, raising the temperature of the reaction kettle to 30-50° C., keeping the temperature for 1-3 hours, and post-treating to obtain phosphated triazine;

[0043] The reaction equation for preparing phosphotriazine is:

[0044]

[0045] Where: .

[0046] The reaction principle for preparing phosphotriazine is as follows: under the catalysis of Lewis acid and high temperature, modified triazine and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide undergo a phosphine-hydrogen addition reaction, and finally phosphotriazine is prepared. The mass spectrometry analysis data of phosphotriazine are: m / z: 835.27 (100.0%), 836.27 (52.9%), 837.28 (13.0%), 838.28(2.8%), 837.27 (2.2%).

[0047] B3. Add phosphated triazine, epichlorohydrin, sodium carbonate, triethyl borate and N,N-dimethylformamide into the reactor, lower the temperature of the reactor to 0-5°C, keep the reaction temperature for 1-2h, and post-treat to obtain a flame retardant capping agent.

[0048] The reaction equation for preparing the flame retardant capping agent is:

[0049]

[0050] The reaction principle for preparing the flame retardant end-capping agent is as follows: under the catalysis of weak alkalinity and low temperature, the epoxy group is protected, a large number of hydroxyl groups on the phosphated triazine react with the chlorine groups on the epichlorohydrin, a large number of epoxy groups are introduced on the phosphated triazine, and finally a flame retardant chain extender is prepared. The mass spectrometry analysis data of the flame retardant end-capping agent are m / z: 877.28 (100.0%), 878.28(55.1%), 879.29 (14.2%), 880.29 (3.2%), 879.28 (2.4%).

[0051] Further, in step B1, the amount ratio of 2-[(4,6-diamino-1,3,5-triazine-2-yl)oxy]ethanol, 3,5-dimethylbenzaldehyde, triethylamine and N,N-dimethylformamide is 8-10g:3-5g:0.5-0.8g:40-50mL, and the post-treatment includes: after the reaction is completed, after the reaction kettle is lowered to room temperature, the reaction solution is placed in a rotary evaporator at a temperature of 80-100°C, and the reduced pressure distillation is performed until no liquid is produced to obtain a modified triazine; in step B2, the amount ratio of modified triazine, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, aluminum chloride and dimethyl sulfoxide is 8-10g:4-6g :0.5-0.8g:40-50mL, and the post-treatment includes: after the reaction is completed, after the reaction kettle is lowered to room temperature, the reaction liquid is placed in a rotary evaporator at a temperature of 80-100°C, and distilled under reduced pressure until no liquid is produced to obtain phosphated triazine; in step B3, the amount ratio of phosphated triazine, epichlorohydrin, sodium carbonate, triethyl borate and N,N-dimethylformamide is 8-10g:4-5g:1-2g:0.3-0.5g:40-60mL, and the post-treatment includes: after the reaction is completed, after the reaction kettle is raised to room temperature, the reaction liquid is added to a rotary evaporator with a water bath temperature of 80-100°C, and distilled under reduced pressure until no liquid is produced to obtain a flame retardant capping agent.

[0052] Further, in step S4, the modified polyester, flame retardant end-capping agent, microwave accelerator and auxiliary materials are used in a ratio of 80-100g:15-20g:15-20g:15-28g, and the auxiliary materials include: a heat stabilizer, a lubricant and an antioxidant, and the amount ratio is 3-8g:6-10g:6-10g, and the heat stabilizer is one or more of dibutyltin dilaurate, triphenyl phosphate and epoxy soybean oil; the lubricant is calcium stearate, stearic acid One or more of zinc and polyethylene wax; the antioxidant is one or more of antioxidant 1010, triphenyl phosphite and dilauryl sulfide; the temperatures of the seven temperature zones of the twin-screw extruder from the feed port to the discharge port are 280°C, 280°C, 285°C, 295°C, 295°C, 300°C, and 300°C respectively; the main engine speed of the twin-screw extruder is 80-120rpm, and the pressure is 100-150bar.

[0053] The present invention has the following beneficial effects:

[0054] 1. The present invention prepares a microwave accelerator as a microwave absorption center, which can effectively improve the absorption of microwave energy by the reaction system, ensure that the microwave energy is more effectively transmitted to the reactants, and make the reaction reach the required reaction temperature in a shorter time. In the process of promoting depolymerization and esterification, the active functional groups directly on its surface pre-extend the modified oligomeric polyester, and further significantly enhance the wear resistance of the material after chain extension by a modified cross-linking agent. At the same time, the silicon groups on the chain segments enhance the flame retardant properties of the material. After being capped by a flame retardant capping agent, a large number of benzene ring structures on the flame retardant capping agent provide support for the organic chain segments, thereby enhancing the wear resistance and flame retardant properties of the material. The porous alumina structure of the microwave accelerator, the silicon groups in the modified cross-linking agent and the flame retardant components in the flame retardant capping agent significantly enhance the flame retardant ability of the material through synergistic cooperation.

[0055] 2. The present invention uses microwave chemical reaction in the process of depolymerization and chain extension. The reaction process and conditions are simple and can produce rapid molecular polarization in the substance, and generate heat through friction between molecules. Unlike traditional heating methods, microwave heating can directly act on the reactant molecules instead of just heating the reaction container, thereby uniformly and quickly heating the reaction system and improving the reaction rate and selectivity. However, microwave heating usually has the problem of uneven heat. The present invention is to prepare a microwave promoter. The microwave promoter serves as a microwave absorption center, which can evenly distribute microwave energy and avoid local overheating, ensuring a more uniform heat distribution during the reaction, improving the stability and consistency of the reaction, and the organic groups in the microwave promoter simultaneously produce a pre-chain extension effect during the depolymerization and chain extension process, significantly improving the chain extension efficiency and enhancing the wear resistance of the material. The main porous alumina and the flame retardant component cooperate synergistically to significantly enhance the flame retardant properties of the material.

[0056] 3. The porous alumina structure of the microwave accelerator prepared by the present invention has good thermal isolation performance. Its porous structure inhibits the propagation of heat inside the material. When alumina is exposed to a high-temperature fire source, the heat is first conducted to the surface of the material, but due to the existence of its pore structure, the heat cannot quickly diffuse into the interior. This barrier effect effectively delays the temperature rise of the material and improves the flame retardant performance of the material. The silicon group in the modified cross-linking agent can react with oxygen in the air under high temperature conditions to form a dense and heat-resistant silicon oxide film with good thermal insulation and flame retardancy, which can effectively prevent the contact between the flame and the substrate and reduce the propagation speed of the flame. The flame retardant component in the flame retardant capping agent continuously decomposes during the combustion process to produce acidic substances to promote the carbonization of the triazine structure, forming a molten carbon layer, and releasing flame-retardant gas to promote the foaming of the carbon layer to form a flame retardant structure. The flame retardant ability of the material is significantly enhanced through the synergistic cooperation of the three. DETAILED DESCRIPTION

[0057] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] Example 1

[0059] This embodiment provides a method for recycling waste plastics to prepare flame-retardant and wear-resistant plastic plates, comprising the following steps:

[0060] Step 1: Preparation of modified oligomeric polyester

[0061] Weigh: 18.0g aluminum isopropoxide, 50.0mL isopropanol and 30.0mL deionized water are added to a reactor, the temperature of the reactor is raised to 50°C, and a 10wt% hydrochloric acid solution is used to adjust the system pH to 3-5. After the reaction is kept warm for 1h, 5.4g triethanolamine is added to the reactor and the reaction is kept warm for 20min. After the reaction is completed, the reactor is cooled to room temperature, and the reaction liquid is placed in a rotary evaporator at 80°C, and distilled under reduced pressure until no liquid is produced to obtain an aluminum gel;

[0062] The aluminum gel was placed in a tubular furnace for calcination, nitrogen was introduced for protection, the temperature of the tubular furnace was increased to 750°C at a heating rate of 3°C / min, and the temperature was kept for calcination for 4 hours to obtain porous alumina;

[0063] Weigh: 16.0 g of porous alumina, 40.0 mL of ethanol, 0.8 g of triethylamine and 30.0 mL of deionized water, add them into a reactor and introduce nitrogen protection, after the temperature of the reactor is reduced to 10°C, add 7.2 g of 3-(2,3-epoxypropoxy)propyltrimethoxysilane into the reactor, keep the temperature for 20 minutes, after the reaction is completed, wait for the temperature of the reactor to rise to room temperature, filter the reaction liquid to collect the filter cake, transfer the filter cake to a drying oven at a temperature of 60°C and vacuum dry it until the filter cake has a constant weight, to obtain a microwave accelerator;

[0064] The waste PET fragments were put into a pulverizer and crushed through a 100-mesh screen, and then placed in a reactor and nitrogen was introduced for protection. The temperature of the reactor was raised to 250°C to obtain a melt. After the melt passed through a 100-mesh screen, molten PET was obtained.

[0065] Weigh: 18.0 g of molten PET, 5.4 g of microwave accelerator, 100.0 mL of neopentyl glycol and 0.8 g of zinc acetate and add them into a microwave generator. The power of the microwave generator is 500 W, the frequency is 2.1 GHz, and the microwave depolymerization is performed for 10 minutes. After the depolymerization is completed, the reaction liquid is placed in a rotary evaporator at a temperature of 80° C. and distilled under reduced pressure until no liquid is produced to obtain a modified oligomeric polyester.

[0066] Step 2: Preparation of modified chain extender and flame retardant end capping agent

[0067] Weigh: 5.4g acrylic acid, 0.8g dichloroplatinene and 64.0mL n-heptane are added to a reactor and stirred at a stirring rate of 40rpm. Nitrogen protection is introduced. After the temperature of the reactor is raised to 40°C, 18.0g phenyltri(dimethylsiloxy)silane is added to the reactor and stirred for 1h. After the reaction is completed, the reactor is cooled to room temperature, and the reaction solution is placed in a rotary evaporator at a temperature of 80°C, and distilled under reduced pressure until no liquid is produced to obtain a modified chain extender;

[0068] Weigh: 18.0g 2-[(4,6-diamino-1,3,5-triazine-2-yl)oxy]ethanol, 8.4g 3,5-dimethylbenzaldehyde, 1.2g triethylamine and 88.0mL N,N-dimethylformamide and add them into a reactor, raise the temperature of the reactor to 60°C, and keep the temperature for 2h. After the reaction is completed, wait for the reactor to cool to room temperature, place the reaction liquid in a rotary evaporator at 80°C, and distill under reduced pressure until no liquid is produced to obtain a modified triazine;

[0069] Weigh: 18.0 g of modified triazine, 10.8 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 1.2 g of aluminum chloride and 80.0 mL of dimethyl sulfoxide are added to a reactor, the temperature of the reactor is raised to 30° C., and the reaction is kept warm for 1 hour. After the reaction is completed, the reactor is cooled to room temperature, and the reaction liquid is placed in a rotary evaporator at a temperature of 80° C., and distilled under reduced pressure until no liquid is produced to obtain phosphated triazine;

[0070] Weigh: 16.0 g of phosphotriazine, 8.4 g of epichlorohydrin, 2.4 g of sodium carbonate, 0.8 g of triethyl borate and 100.0 mL of N,N-dimethylformamide and add them into a reactor. The temperature of the reactor is lowered to 5°C. After the reaction is completed, the reactor is raised to room temperature. The reaction liquid is added to a rotary evaporator with a water bath temperature of 80°C, and distilled under reduced pressure until no liquid is extracted to obtain a flame retardant capping agent.

[0071] Step 3: Preparation of recycled plastic sheets

[0072] Weigh: 18.0g of modified oligomeric polyester and 5.4g of modified chain extender are added into a microwave generator with a power of 600W and a frequency of 2.4GHz. After microwave esterification for 30min, a cross-linked polyester is obtained;

[0073] Weigh: 18.0g of cross-linked polyester, 5.4g of flame retardant end-capping agent, 1.2g of triethylamine and 60.0mL of N,N-dimethylformamide are added to a reactor, the temperature of the reactor is raised to 50°C, and the reaction is kept warm for 1h. Then, 1.2g of 3-(2,3-epoxypropoxy)propyltrimethoxysilane is added to the reactor, and the reaction is kept warm for 0.5h. After the reaction is completed, the reactor is lowered to room temperature, and the reaction liquid is added to a rotary evaporator with a water bath temperature of 80°C, and the reaction is distilled under reduced pressure until no liquid is produced to obtain a modified polyester;

[0074] Weigh: 96.0g modified polyester, 18.0g flame retardant end capping agent, 18.0g microwave accelerator, 5.4g triphenyl phosphate, 8.4g polyethylene wax and 8.4g dilauryl sulfide and add into a twin-screw extruder. The temperatures of the seven temperature zones of the twin-screw extruder from the feed port toward the discharge port are 280°C, 280°C, 285°C, 295°C, 295°C, 300°C, and 300°C, respectively. The main engine speed of the twin-screw extruder is 80rpm, and the pressure is 100bar. Extruded into a mold, cured to obtain a recycled plastic sheet.

[0075] Example 2

[0076] This embodiment provides a method for recycling waste plastics to prepare flame-retardant and wear-resistant plastic plates, comprising the following steps:

[0077] Step 1: Preparation of modified oligomeric polyester

[0078] Weigh: 18.0g aluminum isopropoxide, 48.0mL isopropanol and 36.0mL deionized water are added to a reactor, the temperature of the reactor is raised to 60°C, and a 20wt% hydrochloric acid solution is used to adjust the pH of the system to 5. After the reaction is kept warm for 2h, 5.4g triethanolamine is added to the reactor and the reaction is kept warm for 30min. After the reaction is completed, the reactor is cooled to room temperature, and the reaction liquid is placed in a rotary evaporator at a temperature of 100°C, and distilled under reduced pressure until no liquid is extracted to obtain an aluminum gel;

[0079] The aluminum gel was placed in a tubular furnace for calcination, nitrogen was introduced for protection, the temperature of the tubular furnace was increased to 850°C at a heating rate of 3°C / min, and the temperature was kept for calcination for 6 hours to obtain porous alumina;

[0080] Weigh: 18.0 g of porous alumina, 54.0 mL of ethanol, 0.8 g of triethylamine and 32.0 mL of deionized water, add them into a reactor and introduce nitrogen protection. After the temperature of the reactor is reduced to 20° C., add 7.2 g of 3-(2,3-epoxypropoxy)propyltrimethoxysilane into the reactor and keep the temperature for 20 minutes. After the reaction is completed, wait for the temperature of the reactor to rise to room temperature, filter the reaction liquid to collect the filter cake, transfer the filter cake to a drying oven at a temperature of 60° C. and vacuum dry it until the filter cake has a constant weight, thereby obtaining a microwave accelerator;

[0081] The waste PET fragments were put into a pulverizer and crushed through a 100-mesh screen, and then placed in a reactor and nitrogen was introduced for protection. The temperature of the reactor was raised to 260°C to obtain a melt. After the melt passed through a 100-mesh screen, molten PET was obtained.

[0082] Weigh: 20.0g molten PET, 6.0g microwave accelerator, 120.0mL neopentyl glycol and 0.8g zinc acetate and add them into a microwave generator. The power of the microwave generator is 540W, the frequency is 2.3GHz, and the microwave depolymerization is 15min. After the depolymerization is completed, the reaction liquid is placed in a rotary evaporator at a temperature of 100°C and distilled under reduced pressure until no liquid is produced to obtain a modified oligomeric polyester.

[0083] Step 2: Preparation of modified chain extender and flame retardant end capping agent

[0084] Weigh: 5.4g acrylic acid, 0.8g dichloroplatinene and 72.0mL n-heptane are added to a reactor and stirred at a stirring rate of 60rpm. Nitrogen protection is introduced. After the temperature of the reactor is raised to 45°C, 16.0g phenyltri(dimethylsiloxy)silane is added to the reactor and stirred for 3h. After the reaction is completed, the reactor is cooled to room temperature, and the reaction liquid is placed in a rotary evaporator at a temperature of 100°C, and distilled under reduced pressure until no liquid is produced to obtain a modified chain extender;

[0085] Weigh: 20.0g 2-[(4,6-diamino-1,3,5-triazine-2-yl)oxy]ethanol, 8.4g 3,5-dimethylbenzaldehyde, 1.2g triethylamine and 80.0mL N,N-dimethylformamide are added to a reactor, the temperature of the reactor is raised to 80°C, and the reaction is kept warm for 4 hours. After the reaction is completed, the reactor is lowered to room temperature, and the reaction liquid is placed in a rotary evaporator at a temperature of 100°C, and distilled under reduced pressure until no liquid is produced to obtain a modified triazine;

[0086] Weigh: 20.0 g of modified triazine, 10.8 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 1.2 g of aluminum chloride and 90.0 mL of dimethyl sulfoxide are added to a reactor, the temperature of the reactor is raised to 40° C., and the reaction is kept warm for 3 hours. After the reaction is completed, the reactor is cooled to room temperature, and the reaction liquid is placed in a rotary evaporator at a temperature of 100° C., and distilled under reduced pressure until no liquid is produced to obtain phosphated triazine;

[0087] Weigh: 18.0 g of phosphotriazine, 9.6 g of epichlorohydrin, 2.4 g of sodium carbonate, 0.8 g of triethyl borate and 100.0 mL of N,N-dimethylformamide and add them into a reactor. The temperature of the reactor is lowered to 5°C. After the reaction is completed, the reactor is raised to room temperature. The reaction liquid is added to a rotary evaporator with a water bath temperature of 100°C, and distilled under reduced pressure until no liquid is produced to obtain a flame retardant capping agent.

[0088] Step 3: Preparation of recycled plastic sheets

[0089] Weigh: 16.0g of modified oligomeric polyester and 7.2g of modified chain extender are added into a microwave generator with a power of 800W and a frequency of 2.5GHz. After microwave esterification for 40min, a cross-linked polyester is obtained;

[0090] Weigh: 18.0g of cross-linked polyester, 5.4g of flame retardant end-capping agent, 1.6g of triethylamine and 80.0mL of N,N-dimethylformamide are added to a reactor, the temperature of the reactor is raised to 60°C, and the reaction is kept warm for 2h, and then 1.6g of 3-(2,3-epoxypropoxy)propyltrimethoxysilane is added to the reactor, and the reaction is kept warm for 1h. After the reaction is completed, the reactor is lowered to room temperature, and the reaction liquid is added to a rotary evaporator with a water bath temperature of 100°C, and the reaction is distilled under reduced pressure until no liquid is produced to obtain a modified polyester;

[0091] Weigh: 88.0g modified polyester, 18.0g flame retardant end capping agent, 16.0g microwave accelerator, 12.0g triphenyl phosphate, 16.0g polyethylene wax and 18.0g dilauryl sulfide and add into a twin-screw extruder. The temperatures of the seven temperature zones of the twin-screw extruder from the feed port toward the discharge port are 280°C, 280°C, 285°C, 295°C, 295°C, 300°C, and 300°C, respectively. The main engine speed of the twin-screw extruder is 120rpm, and the pressure is 150bar. Extrude into a mold and solidify to obtain a recycled plastic sheet.

[0092] Example 3

[0093] This embodiment provides a method for recycling waste plastics to prepare flame-retardant and wear-resistant plastic plates, comprising the following steps:

[0094] Step 1: Preparation of modified oligomeric polyester

[0095] Weigh: 16.0g aluminum isopropoxide, 54.0mL isopropanol and 36.0mL deionized water are added to a reactor, the temperature of the reactor is raised to 60°C, and a 15wt% hydrochloric acid solution is used to adjust the system pH to 4. After the reaction is kept warm for 2h, 5.4g triethanolamine is added to the reactor and the reaction is kept warm for 25min. After the reaction is completed, the reactor is cooled to room temperature, and the reaction liquid is placed in a rotary evaporator at a temperature of 90°C, and distilled under reduced pressure until no liquid is produced to obtain an aluminum gel;

[0096] The aluminum gel was placed in a tubular furnace for calcination, nitrogen was introduced for protection, the temperature of the tubular furnace was increased to 800°C at a heating rate of 5°C / min, and the temperature was kept for calcination for 5 hours to obtain porous alumina;

[0097] Weigh: 18.0 g of porous alumina, 54.0 mL of ethanol, 0.8 g of triethylamine and 36.0 mL of deionized water, add them into a reactor and introduce nitrogen protection. After the temperature of the reactor is reduced to 15° C., add 7.0 g of 3-(2,3-epoxypropoxy)propyltrimethoxysilane into the reactor and keep the temperature for 30 minutes. After the reaction is completed, wait for the temperature of the reactor to rise to room temperature, filter the reaction liquid to collect the filter cake, transfer the filter cake to a drying oven at a temperature of 60° C. and vacuum dry it until the filter cake has a constant weight, thereby obtaining a microwave accelerator;

[0098] The waste PET fragments were put into a pulverizer and crushed through a 100-mesh screen, and then placed in a reactor and nitrogen was introduced for protection. The temperature of the reactor was raised to 255°C to obtain a melt. After the melt passed through a 100-mesh screen, molten PET was obtained.

[0099] Weigh: 18.0 g of molten PET, 5.4 g of microwave accelerator, 100.0 mL of neopentyl glycol and 0.8 g of zinc acetate and add them into a microwave generator. The power of the microwave generator is 540 W, the frequency is 2.3 GHz, and the microwave depolymerization is performed for 12 minutes. After the depolymerization is completed, the reaction liquid is placed in a rotary evaporator at a temperature of 90° C. and distilled under reduced pressure until no liquid is produced to obtain a modified oligomeric polyester.

[0100] Step 2: Preparation of modified chain extender and flame retardant end capping agent

[0101] Weigh: 5.4g acrylic acid, 0.8g dichloroplatinene and 72.0mL n-heptane are added to a reactor and stirred at a stirring rate of 60rpm. Nitrogen protection is introduced. After the temperature of the reactor is raised to 50°C, 18.0g phenyltri(dimethylsiloxy)silane is added to the reactor and stirred for 2h. After the reaction is completed, the reactor is cooled to room temperature, and the reaction solution is placed in a rotary evaporator at a temperature of 90°C, and distilled under reduced pressure until no liquid is produced to obtain a modified chain extender;

[0102] Weigh: 16.0g 2-[(4,6-diamino-1,3,5-triazine-2-yl)oxy]ethanol, 8.0g 3,5-dimethylbenzaldehyde, 1.6g triethylamine and 96.0mL N,N-dimethylformamide and add them into a reactor, raise the temperature of the reactor to 70°C, and keep the temperature for 3h. After the reaction is completed, wait for the reactor to cool to room temperature, place the reaction liquid in a rotary evaporator at 90°C, and distill under reduced pressure until no liquid is produced to obtain a modified triazine;

[0103] Weigh: 18.0 g of modified triazine, 8.0 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 1.6 g of aluminum chloride and 90.0 mL of dimethyl sulfoxide are added to a reactor, the temperature of the reactor is raised to 40° C., and the reaction is kept warm for 2 hours. After the reaction is completed, the reactor is cooled to room temperature, and the reaction liquid is placed in a rotary evaporator at a temperature of 90° C., and distilled under reduced pressure until no liquid is produced to obtain phosphated triazine;

[0104] Weigh: 20.0g of phosphotriazine, 9.6g of epichlorohydrin, 3.2g of sodium carbonate, 0.8g of triethyl borate and 100.0mL of N,N-dimethylformamide and add them into a reactor. The temperature of the reactor is lowered to 0°C. After the reaction is completed, the reactor is raised to room temperature. The reaction liquid is added to a rotary evaporator with a water bath temperature of 90°C, and distilled under reduced pressure until no liquid is produced to obtain a flame retardant capping agent.

[0105] Step 3: Preparation of recycled plastic sheets

[0106] Weigh: 18.0g of modified oligomeric polyester and 7.2g of modified chain extender are added into a microwave generator with a power of 700W and a frequency of 2.4GHz. After microwave esterification for 40min, a cross-linked polyester is obtained;

[0107] Weigh: 20.0g of cross-linked polyester, 5.4g of flame retardant end-capping agent, 1.5g of triethylamine and 72.0mL of N,N-dimethylformamide are added to a reactor, the temperature of the reactor is raised to 55°C, and the reaction is kept warm for 1h. Then, 1.4g of 3-(2,3-epoxypropoxy)propyltrimethoxysilane is added to the reactor, and the reaction is kept warm for 1h. After the reaction is completed, the reactor is lowered to room temperature, and the reaction liquid is added to a rotary evaporator with a water bath temperature of 90°C, and the reaction is distilled under reduced pressure until no liquid is produced to obtain a modified polyester;

[0108] Weigh: 96.0g modified polyester, 18.0g flame retardant end capping agent, 16.0g microwave accelerator, 7.2g triphenyl phosphate, 12.0g polyethylene wax and 12.0g dilauryl sulfide and add into a twin-screw extruder. The temperatures of the seven temperature zones of the twin-screw extruder from the feed port toward the discharge port are 280°C, 280°C, 285°C, 295°C, 295°C, 300°C, and 300°C, respectively. The main engine speed of the twin-screw extruder is 100rpm, and the pressure is 125bar. Extruded into a mold, cured to obtain a recycled plastic sheet.

[0109] Comparative Example 1

[0110] The difference between this comparative example and Example 3 is that the step of modifying the porous alumina to prepare the microwave accelerator in step one is eliminated, and in steps one and three, an equal amount of porous alumina is used to replace the microwave accelerator.

[0111] Comparative Example 2

[0112] The difference between this comparative example and Example 3 is that the step of preparing the modified chain extender in step 2 is eliminated, and in step 3, an equal amount of diethylenetriaminepentaacetic acid is used to replace the modified chain extender.

[0113] Comparative Example 3

[0114] The difference between this comparative example and Example 3 is that the step of preparing the flame retardant capping agent in step 2 is eliminated, and in step 3, an equal amount of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is used to replace the flame retardant capping agent.

[0115] Performance Test:

[0116] The combustion performance was tested on the limiting oxygen index of the recycled plastic sheets prepared in Examples 1-3 and Comparative Examples 1-3 in accordance with the standard GB / T 2406.2-2009 "Determination of Combustion Behavior of Plastics by Oxygen Index Method Part 2: Room Temperature Test";

[0117] The flame retardant properties refer to the standard GB / T 2408-2021 "Horizontal and vertical methods for the determination of combustion performance of plastics" for the vertical combustion grades of the recycled plastic sheets prepared in Examples 1-3 and Comparative Examples 1-3;

[0118] The volume wear of the HPVC power pipes prepared in Examples 1-3 and Comparative Examples 1-3 was tested with reference to the standard GB / T 9867-2008 "Determination of wear resistance of vulcanized rubber or thermoplastic rubber (rotating roller abrasion machine method)";

[0119] The tensile strength of the composite polypropylene prepared in Examples 1-3 and Comparative Examples 1-3 was tested with reference to the standard GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber";

[0120] The Izod impact strength of the recycled composite polyesters prepared in Examples 1-3 and Comparative Examples 1-3 was tested with reference to the standard GB / T 1843-2008 “Determination of Izod impact strength of plastics”. The specific data are shown in Table 1.

[0121] Table 1-Performance test data of each sample

[0122]

[0123] Data Analysis:

[0124] Comparing and analyzing the data in Table 1 above, the limiting oxygen index of the recycled plastic sheet prepared by the present invention through plastic recycling is 40.5%, the vertical combustion grade is V-0, and the volume wear is 25mm. 3 , tensile strength is 36.1MPa and cantilever beam impact strength is 51.2kJ·m -2 , all data are better than the comparative example;

[0125] Data description:

[0126] The present invention prepares a microwave accelerator as a microwave absorption center, and while promoting depolymerization and esterification, the active functional groups directly on its surface pre-extend the chain of the modified oligomeric polyester, and significantly enhance the wear resistance of the material after chain extension by a modified cross-linking agent. After being capped by a flame retardant capping agent, the porous alumina structure of the microwave accelerator, the silicon group in the modified cross-linking agent and the flame retardant component in the flame retardant capping agent cooperate synergistically to significantly enhance the flame retardancy of the material.

[0127] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing flame-retardant and wear-resistant plastic sheets by recycling waste plastics, characterized in that: The following steps are involved: S1, adding molten PET, microwave accelerator, neopentyl glycol and zinc acetate into a microwave generator, performing microwave depolymerization for 10-15 minutes, and post-treating to obtain modified oligomeric polyester; S2, adding the modified oligomeric polyester and the modified chain extender into a microwave generator, and subjecting the resultant to microwave esterification for 30-40 minutes to obtain a cross-linked polyester; S3, adding cross-linked polyester, flame retardant end-capping agent, triethylamine and N,N-dimethylformamide into a reactor, raising the temperature of the reactor to 50-60°C, keeping the temperature for reaction for 1-2 hours, then continuing to add modifier into the reactor, keeping the temperature for reaction for 0.5-1 hour, and post-treating to obtain modified polyester; S4, adding the modified polyester, flame retardant end-capping agent, microwave accelerator and auxiliary materials into a twin-screw extruder, melting and extruding into a mold, and curing to obtain a recycled plastic sheet; The preparation method of the microwave accelerator comprises the following steps: A1. Aluminum isopropoxide, isopropanol and deionized water are added to a reactor, the temperature of the reactor is raised to 50-60°C, and a 10-20wt% hydrochloric acid solution is used to adjust the pH value of the system to 3-5. After the reaction is kept warm for 1-2 hours, triethanolamine is continuously added to the reactor, and the reaction is kept warm for 20-30 minutes. After post-treatment, an aluminum gel is obtained; A2, placing the aluminum gel in a tube furnace and calcining it to obtain porous alumina; A3, adding porous alumina, ethanol, triethylamine and deionized water into a reactor and introducing nitrogen protection, after the temperature of the reactor is reduced to 10-20°C, adding 3-(2,3-epoxypropoxy)propyltrimethoxysilane into the reactor, keeping the temperature for reaction for 20-30 minutes, and post-treating to obtain a microwave accelerator; The structural formula of the modified chain extender is: The structural formula of the flame retardant end-capping agent is: in:

2. The method for preparing flame-retardant and wear-resistant plastic sheet by recycling waste plastic according to claim 1, characterized in that: In step S1, the usage ratio of molten PET, microwave accelerator, neopentyl glycol and zinc acetate is 8-10g:2-3g:50-60mL:0.3-0.5g, the power of the microwave generator is 500-540W, and the frequency is 2.1-2.3GHz.

3. The method for preparing flame-retardant and wear-resistant plastic sheet by recycling waste plastic according to claim 1, characterized in that: In step A1, the amount ratio of aluminum isopropoxide, isopropanol, deionized water and triethanolamine is 8-10g:20-30mL:10-20mL:2-3g; in step A2, the calcination operation includes: introducing nitrogen protection, heating the tubular furnace to 750-850°C at a heating rate of 3-5°C / min, and calcining for 4-6h to obtain porous alumina; in step A3, the amount ratio of porous alumina, ethanol, triethylamine, deionized water and 3-(2,3-epoxypropoxy)propyltrimethoxysilane is 8-10g:20-30mL:0.3-0.5g:10-20mL:3-4g.

4. The method for preparing flame-retardant and wear-resistant plastic sheet by recycling waste plastics according to claim 1, characterized in that: In step S2, the dosage ratio of the modified oligomeric polyester and the modified chain extender is 8-10g:2-4g, wherein the preparation method of the modified chain extender is: acrylic acid, dichloroplatinene and n-heptane are added to a reactor and stirred, nitrogen is introduced for protection, the temperature of the reactor is increased to 40-50°C, phenyltri(dimethylsiloxy)silane is added to the reactor, the mixture is kept warm and stirred for 1-3h, and the modified chain extender is obtained by post-processing.

5. The method for preparing flame-retardant and wear-resistant plastic sheet by recycling waste plastics according to claim 4, characterized in that: The stirring rate of the reaction kettle is 40-60 rpm, and the usage ratio of acrylic acid, n-heptane, dichloroplatinene and phenyltri(dimethylsiloxy)silane is 2-3 g:30-40 mL:0.3-0.5 g:8-10 g.

6. The method for preparing flame-retardant and wear-resistant plastic sheet by recycling waste plastics according to claim 1, characterized in that: In step S3, the amount ratio of cross-linked polyester, flame retardant capping agent, triethylamine, N,N-dimethylformamide and modifier is 8-10g:2-3g:0.3-0.8g:30-40mL:0.6-0.8g, and the modifier is 3-(2,3-epoxypropoxy)propyltrimethoxysilane.

7. The method for preparing flame-retardant and wear-resistant plastic sheet by recycling waste plastics according to claim 1, characterized in that: In step S3, the method for preparing the flame retardant end-capping agent comprises the following steps: B1. Add 2-[(4,6-diamino-1,3,5-triazine-2-yl)oxy]ethanol, 3,5-dimethylbenzaldehyde, triethylamine and N,N-dimethylformamide into a reaction kettle, raise the temperature of the reaction kettle to 60-80° C., keep the temperature for 2-4 hours, and perform post-treatment to obtain modified triazine; B2, adding modified triazine, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, aluminum chloride and dimethyl sulfoxide into a reaction kettle, raising the temperature of the reaction kettle to 30-50° C., keeping the temperature for 1-3 hours, and post-treating to obtain phosphated triazine; B3. Add phosphated triazine, epichlorohydrin, sodium carbonate, triethyl borate and N,N-dimethylformamide into the reactor, lower the temperature of the reactor to 0-5°C, keep the reaction temperature for 1-2h, and post-treat to obtain a flame retardant capping agent.

8. The method for preparing flame-retardant and wear-resistant plastic sheet by recycling waste plastics according to claim 7, characterized in that: In step B1, the amount ratio of 2-[(4,6-diamino-1,3,5-triazine-2-yl)oxy]ethanol, 3,5-dimethylbenzaldehyde, triethylamine and N,N-dimethylformamide is 8-10g:3-5g:0.5-0.8g:40-50mL; in step B2, the amount ratio of modified triazine, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, aluminum chloride and dimethyl sulfoxide is 8-10g:4-6g:0.5-0.8g:40-50mL; in step B3, the amount ratio of phosphated triazine, epichlorohydrin, sodium carbonate, triethyl borate and N,N-dimethylformamide is 8-10g:4-5g:1-2g:0.3-0.5g:40-60mL.

9. The method for preparing flame-retardant and wear-resistant plastic sheet by recycling waste plastics according to claim 1, characterized in that: In step S4, the usage ratio of modified polyester, flame retardant end-capping agent, microwave accelerator and auxiliary materials is 80-100g:15-20g:15-20g:15-30g, and the auxiliary materials include: heat stabilizer, lubricant and antioxidant.

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