Flame-retardant pearl wool and preparation method thereof

Abstract

The invention discloses flame-retardant pearl wool and a preparation method thereof, belongs to the technical field of polyethylene processing, and is used for solving the technical problem that the mechanical property and flame-retardant property of pearl wool in the prior art need to be further improved. The method comprises the following steps: carrying out secondary foaming on a flame-retardant pearl wool blank to obtain the flame-retardant pearl wool, namely preparing a modified inorganic flame retardant with a large number of double bonds, carrying out gas-phase polymerization to obtain light polyethylene, and in the radiation crosslinking process, taking the modified inorganic flame retardant as a radiation absorption center, so as to obtain the light polyethylene. The light polyethylene and the flame-retardant cross-linking agent with a large number of double bonds are promoted to generate a large number of free radicals to promote the cross-linking reaction, the free radicals serve as a microwave absorption center in the pre-foaming process so that pre-foaming can be more efficient and uniform, and the porous structure serves as a gas slow release center in the butane foaming process so that foaming can be more complete. And the flame retardant property of the material is improved through synergistic cooperation with the flame-retardant cross-linking agent.

Description

Technical Field

[0001] The present invention relates to the technical field of EPE preparation, and particularly relates to a flame-retardant EPE and a preparation method thereof. Background Art

[0002] The research and development process of flame-retardant EPE mainly focuses on improving mechanical properties and flame-retardant effects. In the early stage, halogen-based flame retardants were mainly added to EPE to improve flame retardancy. Although it could effectively prevent flame spread, toxic gases would be released during combustion, so the environmental friendliness was poor.

[0003] With the progress of technology, in the middle stage, phosphorus-based, nitrogen-based and inorganic flame retardants were used instead, significantly reducing the emission of harmful gases and improving the flame-retardant effect of the material. In terms of mechanical properties, by optimizing the foaming process, the internal structure of EPE became more uniform, enhancing the compressive strength and resilience.

[0004] The recent development focuses on composite materials and high-efficiency flame-retardant systems, using different types of flame retardants in combination to achieve a higher flame-retardant grade and maintain excellent mechanical properties. The future development direction is to further improve the strength and environmental characteristics of the material, making it have a wider application prospect in the fields of packaging, construction and automobiles.

[0005] The prior art CN116252453A discloses a processing method of flame-retardant EPE, including putting low-density polyethylene and talcum powder into a mixer. During mixing, the temperature of the mixer is 75 - 85°C, then adding carboxymethyl cellulose, chitosan phosphate and flame retardant a, controlling the material temperature at 100 - 120°C and stirring. Then adding antistatic agent and anti-shrinkage agent into the mixer and continuing to stir at a temperature of 100 - 120°C. Subsequently, monoglyceride is injected into it by a high-pressure injection method and mixed evenly. Then, butane is injected into the mixer along with nitrogen at a pressure of 1.3 - 1.4 Mpa, and the foaming agent and nitrogen are injected into the mixer by a high-pressure jet method and mixed evenly. Extrusion molding is carried out through the die head and die, and then it becomes EPE after cooling, traction, flattening and winding. By mixing flame retardant a inside the EPE, the EPE body has a certain flame-retardant effect, and flame retardant b is used to further increase the flame-retardant effect between the surface of the EPE and the outside world, making it form a high flame-retardant EPE material.

[0006] However, in the above patent, low-density polyethylene and auxiliary materials are melt-blended and then directly introduced with high-pressure butane gas to obtain foamed flame-retardant EPE. By adding flame retardants to the auxiliary materials and spraying flame retardants on the product, the purpose of improving the flame retardant performance of the material is achieved. However, when directly introducing high-pressure butane for foaming after blending low-density polyethylene and auxiliary materials, due to the large polarity differences among low-density polyethylene, organic auxiliary materials, and talcum powder, the mixing uniformity among materials is poor, resulting in differences in the foaming difficulty at different positions of the material, easily causing uneven foaming of the EPE, and leading to differences in the mechanical properties of the material at different positions. The mechanical properties of the material need to be further improved.

[0007] In view of the technical defects in this regard, a solution is proposed now. Summary of the Invention

[0008] The purpose of the present invention is to provide a flame-retardant EPE and its preparation method, which are used to solve the technical problems that the mechanical properties and flame retardant properties of EPE in the prior art need to be further improved.

[0009] The purpose of the present invention can be achieved through the following technical solutions: A preparation method of a flame-retardant EPE includes the following steps:

[0010] S1. Add inorganic porous flame retardant, 3-(methacryloyloxy)propyltrimethoxysilane, sodium hydroxide, and deionized water into a reaction kettle. Raise the temperature of the reaction kettle to 30 - 50 °C, keep it warm for 3 - 5 h, and then perform post-treatment to obtain a modified inorganic flame retardant.

[0011] The reaction principle for preparing the modified inorganic flame retardant is: Under the catalysis of an alkaline condition, a large number of hydroxyl groups on the surface of the inorganic porous flame retardant combine with the silanol structure generated by the hydrolysis of siloxane on 3-(methacryloyloxy)propyltrimethoxysilane, and water is removed to obtain the modified inorganic flame retardant.

[0012] S2. Under the conditions of high temperature and high pressure, ethylene gas is polymerized on the surface of the modified inorganic flame retardant under the initiation of azobisisobutyronitrile to prepare light polyethylene.

[0013] S3. Add light polyethylene, flame retardant cross-linking agent, and auxiliary materials into a twin-screw extruder, and melt-extrude to obtain composite polyethylene.

[0014] S4. Place the composite polyethylene blank in an electron beam irradiation device, and obtain a flame-retardant EPE blank after electron radiation and post-treatment.

[0015] The reaction principle for preparing the flame-retardant EPE blank is: After electron radiation, a large number of free radicals are generated from the light polyethylene in the composite polyethylene and the large number of double bond structures in the flame retardant cross-linking agent, and a polymerization reaction occurs, and finally the flame-retardant EPE embryo is prepared.

[0016] S5. Conduct secondary foaming on the flame-retardant EPE blank to obtain flame-retardant EPE.

[0017] Further, in step S1, the dosage ratio of the inorganic porous flame retardant, 3-(methacryloyloxy)propyltrimethoxysilane, sodium hydroxide, and deionized water is 6-8 g: 2-3 g: 0.3-0.5 g: 30-40 mL. The post-treatment includes: after the reaction is completed, when the temperature of the reaction kettle drops to room temperature, filter the reaction solution to collect the filter cake, and place the filter cake in a drying oven at 60°C for vacuum drying until the filter cake reaches a constant weight to obtain the modified inorganic flame retardant; in step S3, the dosage ratio of the light polyethylene, flame-retardant crosslinking agent, and auxiliary materials is 80-100 g: 15-20 g: 15-30 g. The auxiliary materials include: heat stabilizer, lubricant, and antioxidant; in step S4, the post-treatment includes: after electron radiation is completed, place the material in a crusher for crushing, and pass through a 40-80 mesh sieve to obtain the flame-retardant EPE blank.

[0018] Further, in step S3, the dosage ratio of the heat stabilizer, lubricant, and antioxidant is 3-5 g: 6-10 g: 6-10 g. The heat stabilizer is one or more of dibutyltin dilaurate, triphenyl phosphate, and epoxidized soybean oil; the lubricant is one or more of calcium stearate, zinc stearate, and polyethylene wax; the antioxidant is one or more of antioxidant 1010, triphenyl phosphite, and dilauryl sulfide; the temperatures of the eight temperature zones of the twin-screw extruder from the feed port to the discharge port direction are 160°C, 160, 165°C, 165°C, 175°C, 180°C, 180°C in sequence. The main machine speed of the twin-screw extruder is 80-120 rpm, and the pressure is 100-150 bar.

[0019] Further, in step S1, the preparation method of the inorganic porous flame retardant includes the following steps:

[0020] A1. Add ferric nitrate, aluminum nitrate, and deionized water into the reaction kettle and stir for 10-15 min. Use ammonia water with a concentration of 1-2 mol / L to adjust the system pH = 8-10, add a template agent and continue to stir for 5-10 min, and let it stand for 16-24 h. Perform post-treatment to obtain an anhydrous gel;

[0021] A2. Add the anhydrous gel into a tubular furnace for high-temperature calcination to obtain a mixed metal oxide;

[0022] A3. Add the mixed metal oxide into a crusher for crushing, and pass through a 100-200 mesh sieve to obtain the inorganic porous flame retardant.

[0023] The reaction principle for preparing the inorganic porous flame retardant is as follows: Under alkaline conditions, iron nitrate and aluminum nitrate undergo hydrolysis based on the template agent to form a cross-linked gel structure. During the high-temperature calcination process, the template agent undergoes pyrolysis, causing pore structures to form in the cross-linked structure, and finally the inorganic porous flame retardant is prepared.

[0024] Furthermore, in step A1, the stirring rate of the reaction kettle is 80 - 120 rpm, and the dosage ratio of iron nitrate, aluminum nitrate, deionized water, and the template agent is 5 - 6 g : 8 - 10 g : 40 - 50 mL : 8 - 10 g. The template agent is prepared by mixing polyethylene glycol and ethanol according to the dosage ratio of 1 - 2 mL : 10 - 15 mL. The post-treatment includes: After standing, the material is placed in a vacuum drying oven at 80°C and vacuum dried until the material reaches a constant weight to obtain an anhydrous gel; in step A2, the calcination operation includes: After introducing nitrogen protection, the tubular furnace is heated to 500 - 600°C at a heating rate of 3 - 5°C / min, held for 1 - 2 h, and then naturally cooled to room temperature to obtain a mixed metal oxide.

[0025] Furthermore, in step S2, the operation of high-pressure polymerization includes the following steps:

[0026] B1. Place the modified inorganic flame retardant and azobisisobutyronitrile in the reaction kettle and stir for 10 - 15 min at room temperature to obtain a prepolymer mixture;

[0027] B2. Place the prepolymer mixture in a high-pressure reaction kettle, raise the temperature of the high-pressure reaction kettle to 200 - 250°C, raise the pressure to 2000 - 3000 psi, introduce ethylene, and carry out constant-temperature and constant-pressure polymerization for 40 - 60 min to obtain light polyethylene.

[0028] The reaction principle for preparing light polyethylene is as follows: Promoted by high temperature and high pressure, ethylene gas contacts the free radical initiator azobisisobutyronitrile inside the prepolymer mixture and undergoes a free radical polymerization reaction with a large number of double bonds on the surface of the modified inorganic flame retardant, and finally light polyethylene is prepared.

[0029] Furthermore, in step B1, the dosage ratio of the modified inorganic flame retardant to di-tert-butyl peroxide is 8 - 10 g : 1 - 2 g, and the stirring rate of the reaction kettle is 80 - 120 rpm; in step B2, the dosage ratio of the prepolymer mixture to ethylene is 1 g : 4 - 5 g.

[0030] Furthermore, in step S3, the preparation method of the flame retardant cross-linking agent includes the following steps:

[0031] C1. Add 2,4-diamino-6-phenyl-1,3,5-triazine, isophthalaldehyde, triethylamine, and N,N-dimethylformamide to the reaction kettle, raise the temperature of the reaction kettle to 60 - 80°C, hold for 2 - 4 h for the reaction, and obtain an enamine polymer through post-treatment;

[0032] The reaction equation for preparing enamine polymer is as follows:

[0033]

[0034] The reaction principle for preparing enamine polymer is: under the catalysis of alkaline conditions and high temperature, the amino group on 2,4-diamino-6-phenyl-1,3,5-triazine reacts with the aldehyde group of isophthalaldehyde, and finally enamine polymer is prepared.

[0035] C2. Add enamine polymer, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, aluminum chloride and dimethyl sulfoxide into the reaction kettle, raise the temperature of the reaction kettle to 30 - 50 °C, keep the temperature for reaction for 1 - 3 h, and obtain phosphinated enamine polymer through post-treatment;

[0036] The reaction equation for preparing phosphinated enamine polymer is as follows:

[0037]

[0038] In the formula:

[0039] The reaction principle for preparing phosphinated enamine polymer is: under the catalysis of Lewis acid, the P-H bond on 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide undergoes a P-H addition reaction with the enamine bond on enamine polymer, and finally phosphinated enamine polymer is prepared.

[0040] C3. Add phosphinated enamine polymer, 4,4-diphenyl-2-cyclohexen-1-one, acetic acid and tetrahydrofuran into the reaction kettle, raise the temperature of the reaction kettle to 40 - 50 °C, keep the temperature for reaction for 2 - 4 h, and obtain flame retardant crosslinking agent through post-treatment.

[0041] The reaction equation for preparing flame retardant crosslinking agent is as follows:

[0042]

[0043] In the formula:

[0044] The reaction principle for preparing flame retardant crosslinking agent polymer is: under the catalysis of acetic acid, the imino group on phosphinated enamine polymer reacts with the ketone group on 4,4-diphenyl-2-cyclohexen-1-one to form a carbon-carbon double bond, and finally flame retardant crosslinking agent is prepared.

[0045] Further, in step C1, the dosage ratio of 2,4-diamino-6-phenyl-1,3,5-triazine, isophthalaldehyde, triethylamine and N,N-dimethylformamide is 8-10 g: 3-5 g: 0.5-0.8 g: 40-50 mL. The post-treatment includes: after the reaction is completed, when the temperature of the reaction kettle drops to room temperature, the reaction solution is placed in a rotary evaporator with a water bath temperature of 80-100 °C, and vacuum distilled until no liquid is produced, to obtain an enamine polymer; in step C2, the dosage ratio of the phosphated enamine polymer, 4,4-diphenyl-2-cyclohexene-1-one, acetic acid and tetrahydrofuran is 8-10 g: 4-6 g: 0.5-0.8 g: 40-50 mL. The post-treatment includes: after the reaction is completed, when the temperature of the reaction kettle drops to room temperature, the reaction solution is placed in a rotary evaporator with a water bath temperature of 80-100 °C, and vacuum distilled until no liquid is produced, to obtain a phosphated enamine polymer; in step C3, the dosage ratio of the phosphated enamine polymer, 4,4-diphenyl-2-cyclohexene-1-one, acetic acid and tetrahydrofuran is 8-10 g: 2-4 g: 0.3-0.5 g: 50-60 mL. The post-treatment includes: after the reaction is completed, when the temperature of the reaction kettle drops to room temperature, the reaction solution is placed in a rotary evaporator with a water bath temperature of 80-100 °C, and vacuum distilled until no liquid is produced, to obtain a flame retardant crosslinking agent.

[0046] Further, in step S4, the operation of electron radiation is as follows: nitrogen is introduced into the electron radiation device for protection at a flow rate of 15-20 L / min, the electron beam energy is set to 3-4 MeV, the power is 20-25 kW, the radiation dose is 200-250 kGy, and the conveyor belt speed is set to 1-3 m / min.

[0047] Further, in step S5, the operation of secondary foaming includes the following steps:

[0048] D1. Add the flame retardant EPE blank and toluene into a microwave generator. The power of the microwave generator is 5-8 kW, the power density is 2-4 W / cm 3 , the microwave frequency is 2.4-2.5 GHz, and heat to 100-120 °C until no solvent is produced, to obtain pre-foamed flame retardant EPE;

[0049] D2. Add the pre-foamed flame retardant EPE into a high-pressure reaction kettle, introduce nitrogen to exhaust air, raise the temperature of the reaction kettle to 100-120 °C, introduce butane into the reaction kettle, control the pressure to 4-5 MPa, keep warm for 40-60 min, and release the pressure at a pressure reduction rate of 0.05-0.1 MPa / s to obtain flame retardant EPE.

[0050] The present invention also provides a flame retardant EPE, which is processed by using a preparation method of a flame retardant EPE.

[0051] The present invention has the following beneficial effects:

[0052] 1. In the process of preparing flame-retardant EPE, by preparing a modified inorganic flame retardant with a large number of double bonds on its surface, its porous structure serves as the base point for gas-phase polymerization of ethylene. Through gas-phase polymerization, lightweight polyethylene is polymerized on its surface. And by preparing a flame-retardant crosslinking agent, it is melt-blended and extruded with lightweight polyethylene and auxiliary materials to obtain composite polyethylene. During the radiation crosslinking of the composite polyethylene, the modified inorganic flame retardant serves as a radiation absorption center, promoting the generation of a large number of free radicals by lightweight polyethylene and the flame-retardant crosslinking agent with a large number of double bonds to promote the crosslinking reaction. The material has more excellent mechanical properties. During the pre-foaming process, it serves as a microwave absorption center to make the pre-foaming more efficient and uniform. And during the supercritical fluid butane foaming process, the porous structure serves as a gas slow-release center to make the foaming more complete, and it cooperates with the flame-retardant crosslinking agent to improve the flame retardancy of the material, finally obtaining a flame-retardant EPE with more sufficient and uniform foaming and stronger mechanical properties.

[0053] 2. The modified inorganic flame retardant prepared by the present invention has a significant promoting effect on the process of preparing flame-retardant EPE. During the radiation crosslinking process, the modified inorganic flame retardant absorbs rays and transfers their energy to the polyethylene matrix, enhancing the local energy density. The radiation absorption material releases electrons or free radicals after absorbing rays, and these free radicals can promote the breaking of molecular chains in polyethylene to generate more active free radicals, thereby increasing the rate and degree of the crosslinking reaction, enabling the uniform crosslinking of polyethylene and the flame-retardant crosslinking agent throughout the material to form a uniform crosslinked network, endowing the material with higher mechanical properties and thermal stability;

[0054] During the pre-foaming process, the modified inorganic flame retardant serves as a microwave absorption center to improve the microwave absorption efficiency, make the temperature distribution in the material uniform, make the evaporation of the solvent toluene more uniform, and form a more uniform pore structure. During the supercritical fluid butane secondary foaming process, the modified inorganic flame retardant serves as a gas release center. Through the slow-release effect, the formed porous structure is more uniform and stable. Through the improvement of the material's apparent structure by the modified inorganic flame retardant and the microscopic crosslinking of the flame-retardant crosslinking agent, the mechanical properties of the material are finally significantly improved.

[0055] 3. In the process of preparing flame-retardant EPE, a porous and lightweight modified inorganic flame retardant is prepared. After its surface is modified by a silane coupling agent, a large number of silicon-oxygen bonds and carbon-carbon double bonds exist. During the gas-phase high-temperature and high-pressure polymerization of polyethylene, the abundant pore structure of the modified inorganic flame retardant enables polyethylene to be adsorbed within its pore structure, and polymerization occurs within its pore structure and on its surface to obtain lightweight polyethylene. A flame-retardant crosslinking agent with a polymer structure is prepared. During the combustion process, the inorganic crosslinking agent continuously decomposes to generate acidic substances, promoting the carbonization of the material. During the carbonization of the triazine ring, flame-retardant gases are continuously released, promoting the foaming of the molten carbon layer. Moreover, the abundant porous structure of the modified inorganic flame retardant enables the slow release of the flame-retardant gases, enabling the flame-retardant gases to carry away more heat, and significantly improving the flame retardancy of the flame-retardant EPE through synergistic cooperation. Description of the Drawings

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0057] Figure 1 SEM image of the prepared modified inorganic flame retardant for Example 3. Detailed Embodiments

[0058] The following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0059] Example 1

[0060] This example provides a method for preparing flame-retardant EPE, including the following steps:

[0061] S1. Prepare lightweight polyethylene

[0062] Weigh: 1.2 mL of polyethylene glycol and 12.0 mL of ethanol to prepare a template agent;

[0063] Weigh: 10.0 g of iron nitrate, 16.0 g of aluminum nitrate and 80.0 mL of deionized water are added to a reaction kettle, stirred for 10 min at a stirring rate of 80 rpm, the pH of the system is adjusted to 8 using ammonia water with a concentration of 1.0 mol / L, 16.0 g of a template agent is added and stirring is continued for 5 min, left standing for 16 h. After standing is completed, the material is placed in a vacuum drying oven at 80 °C and vacuum dried until the material reaches a constant weight to obtain an anhydrous gel;

[0064] The anhydrous gel is added to a tube furnace. After introducing nitrogen for protection, the tube furnace is heated to 500 °C at a heating rate of 3 °C / min, heat-treated for 1 h, and naturally cooled to room temperature to obtain a mixed metal oxide;

[0065] The mixed metal oxide is added to a crusher, crushed, and passed through a 100-mesh sieve to obtain an inorganic porous flame retardant;

[0066] Weigh: 14.0 g of inorganic porous flame retardant, 5.4 g of 3-(methacryloyloxy)propyltrimethoxysilane, 0.6 g of sodium hydroxide and 72.0 mL of deionized water are added to a reaction kettle. The temperature of the reaction kettle is raised to 30 °C and heat-treated for 3 h. After the reaction is completed, when the temperature of the reaction kettle is lowered to room temperature, the reaction solution is filtered by suction to collect the filter cake. The filter cake is placed in a drying oven at 60 °C and vacuum dried until the filter cake reaches a constant weight to obtain a modified inorganic flame retardant;

[0067] Weigh: 18.0 g of modified inorganic flame retardant and 3.2 g of azobisisobutyronitrile are placed in a reaction kettle and stirred at a stirring rate of 80 rpm for 10 min at room temperature to obtain a prepolymer mixture;

[0068] Weigh: 20.0 g of the prepolymer mixture is placed in a high-pressure reaction kettle. The temperature of the high-pressure reaction kettle is raised to 200 °C and the pressure is raised to 2000 psi. 80.0 g of ethylene is introduced, and polymerization is carried out at a constant temperature and pressure for 40 min to obtain light polyethylene.

[0069] S2. Preparation of composite polyethylene

[0070] Weigh: 16.0 g of 2,4-diamino-6-phenyl-1,3,5-triazine, 8.0 g of isophthalaldehyde, 1.2 g of triethylamine and 80.0 mL of N,N-dimethylformamide are added to a reaction kettle. The temperature of the reaction kettle is raised to 60 °C and heat-reacted for 2 h. After the reaction is completed, when the temperature of the reaction kettle is lowered to room temperature, the reaction solution is placed in a rotary evaporator with a water bath temperature of 80 °C and distilled under reduced pressure until no liquid is collected to obtain an enamine polymer;

[0071] Weigh: 18.0 g of enamine polymer, 10.0 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 reaction kettle. The temperature of the reaction kettle is raised to 30 °C and kept warm for 1 h. After the reaction is completed, when the temperature of the reaction kettle drops to room temperature, the reaction solution is placed in a rotary evaporator with a water bath temperature of 80 °C and distilled under reduced pressure until no liquid is collected, obtaining enamine polymer;

[0072] Weigh: 18.0 g of phosphinated enamine polymer, 7.2 g of 4-diphenyl-2-cyclohexene-1-one, 0.8 g of acetic acid and 100.0 mL of tetrahydrofuran are added to a reaction kettle. The temperature of the reaction kettle is raised to 40 °C and kept warm for 2 h. After the reaction is completed, when the temperature of the reaction kettle drops to room temperature, the reaction solution is placed in a rotary evaporator with a water bath temperature of 80 °C and distilled under reduced pressure until no liquid is collected, obtaining a flame retardant crosslinking agent;

[0073] Weigh: 96.0 g of light polyethylene, 18.0 g of flame retardant crosslinking agent, 4.2 g of dibutyltin dilaurate, 8.4 g of polyethylene wax and 8.4 g of triphenyl phosphite are added to a twin-screw extruder. The temperatures of the eight temperature zones of the twin-screw extruder from the feed inlet to the discharge outlet are 160 °C, 160, 165 °C, 165 °C, 175 °C, 180 °C, 180 °C in sequence. The main machine speed of the twin-screw extruder is 80 rpm, the pressure is 100 bar, and melting and extrusion are carried out to obtain composite polyethylene.

[0074] S3. Prepare flame retardant EPE

[0075] Place the composite polyethylene blank in an electron beam irradiation device, introduce nitrogen for protection into the electron radiation device at a flow rate of 15 L / min, set the electron beam energy to 3.0 MeV, the power to 20 kW, the radiation dose to 200 kGy, and the conveyor belt speed to 1 m / min. After the electron radiation is completed, place the material in a crusher, crush it, and pass through a 40-mesh sieve to obtain a flame retardant EPE blank;

[0076] Place the flame retardant EPE blank and toluene into a microwave generator. The power of the microwave generator is 5 kW, the power density is 2 W / cm 3 , the microwave frequency is 2.4 GHz, and heat it at 100 °C until no solvent is collected, obtaining pre-expanded flame retardant EPE;

[0077] Add the pre-expanded flame retardant EPE to a high-pressure reaction kettle, introduce nitrogen to exhaust air, raise the temperature of the reaction kettle to 100 °C, introduce butane into the reaction kettle, control the pressure to 4 Mpa, keep warm for 40 min, and release the pressure at a pressure reduction rate of 0.05 MPa / s to obtain flame retardant EPE.

[0078] Example 2

[0079] This embodiment provides a preparation method of a flame-retardant EPE, comprising the following steps:

[0080] S1. Prepare light polyethylene

[0081] Weigh: 2.0 mL of polyethylene glycol and 15.0 mL of ethanol to prepare a template agent.

[0082] Weigh: 12.0 g of ferric nitrate, 18.0 g of aluminum nitrate and 100.0 mL of deionized water, add them to a reaction kettle and stir for 15 min at a stirring rate of 120 rpm. Use ammonia water with a concentration of 2.0 mol / L to adjust the pH of the system to 10, add 16.0 g of the template agent and continue stirring for 10 min, then let it stand for 24 h. After standing, place the material in a vacuum drying oven at 80 °C and vacuum dry it until the material reaches a constant weight to obtain an anhydrous gel.

[0083] Add the anhydrous gel into a tube furnace. After introducing nitrogen for protection, the tube furnace is heated to 600 °C at a heating rate of 5 °C / min, and heat-insulated for 2 h. After natural cooling to room temperature, a mixed metal oxide is obtained.

[0084] Add the mixed metal oxide into a crusher, crush it, and pass it through a 200-mesh sieve to obtain an inorganic porous flame retardant.

[0085] Weigh: 16.0 g of the inorganic porous flame retardant, 5.4 g of 3-(methacryloyloxy)propyltrimethoxysilane, 0.8 g of sodium hydroxide and 80.0 mL of deionized water, add them to a reaction kettle, raise the temperature of the reaction kettle to 50 °C, and heat-insulate for 5 h. After the reaction is completed, wait for the temperature of the reaction kettle to drop to room temperature, then filter the reaction solution to collect the filter cake, and place the filter cake in a drying oven at 60 °C and vacuum dry it until the filter cake reaches a constant weight to obtain a modified inorganic flame retardant.

[0086] Weigh: 18.0 g of the modified inorganic flame retardant and 3.2 g of azobisisobutyronitrile, place them in a reaction kettle and stir at a stirring rate of 120 rpm for 15 min at room temperature to obtain a prepolymer mixture.

[0087] Weigh: 20.0 g of the prepolymer mixture and place it in a high-pressure reaction kettle. Raise the temperature of the high-pressure reaction kettle to 250 °C, raise the pressure to 3000 psi, introduce 100.0 g of ethylene, and carry out constant-temperature and constant-pressure polymerization for 60 min to obtain light polyethylene.

[0088] S2. Prepare composite polyethylene

[0089] Weigh: 20.0 g of 2,4-diamino-6-phenyl-1,3,5-triazine, 8.0 g of isophthalaldehyde, 1.2 g of triethylamine and 96.0 mL of N,N-dimethylformamide are added to a reaction kettle. The temperature of the reaction kettle is raised to 80 °C and kept for 4 h. After the reaction is completed, when the temperature of the reaction kettle is lowered to room temperature, the reaction solution is placed in a rotary evaporator with a water bath temperature of 100 °C, and distilled under reduced pressure until no liquid is collected to obtain an enamine polymer;

[0090] Weigh: 18.0 g of enamine polymer, 10.0 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 1.2 g of aluminum chloride and 100.0 mL of dimethyl sulfoxide are added to a reaction kettle. The temperature of the reaction kettle is raised to 30 - 50 °C and kept for 3 h. After the reaction is completed, when the temperature of the reaction kettle is lowered to room temperature, the reaction solution is placed in a rotary evaporator with a water bath temperature of 100 °C, and distilled under reduced pressure until no liquid is collected to obtain an enamine polymer;

[0091] Weigh: 18.0 g of phosphinated enamine polymer, 7.2 g of 4,4-diphenyl-2-cyclohexen-1-one, 0.8 g of acetic acid and 120.0 mL of tetrahydrofuran are added to a reaction kettle. The temperature of the reaction kettle is raised to 50 °C and kept for 4 h. After the reaction is completed, when the temperature of the reaction kettle is lowered to room temperature, the reaction solution is placed in a rotary evaporator with a water bath temperature of 100 °C, and distilled under reduced pressure until no liquid is collected to obtain a flame retardant crosslinking agent;

[0092] Weigh: 88.0 g of light polyethylene, 16.0 g of flame retardant crosslinking agent, 8.0 g of dibutyltin dilaurate, 8.0 g of polyethylene wax and 8.0 g of triphenyl phosphite are added to a twin-screw extruder. The temperatures of the eight temperature zones of the twin-screw extruder from the feed inlet to the discharge outlet are 160 °C, 160, 165 °C, 165 °C, 175 °C, 180 °C, 180 °C in sequence. The main machine speed of the twin-screw extruder is 120 rpm, the pressure is 150 bar, and melt extrusion is carried out to obtain composite polyethylene.

[0093] S3. Prepare flame retardant EPE

[0094] Place the composite polyethylene blank in an electron beam irradiation device, introduce nitrogen for protection into the electron radiation device at a flow rate of 20 L / min, set the electron beam energy to 4 MeV, the power to 25 kW, the radiation dose to 250 kGy, the conveyor belt speed to 3 m / min. After electron radiation is completed, place the material in a crusher, crush it, and pass through an 80-mesh sieve to obtain a flame retardant EPE blank;

[0095] Place the flame retardant EPE blank and toluene into a microwave generator. The power of the microwave generator is 8 kW, and the power density is 4 W / cm 3, microwave frequency 2.5 GHz, heat to 120 °C until no solvent is extracted to obtain pre-expanded flame-retardant EPE;

[0096] Add the pre-expanded flame-retardant EPE into a high-pressure reactor, purge the air with nitrogen, raise the temperature of the reactor to 120 °C, introduce butane into the reactor, control the pressure at 5 MPa, keep warm for 60 min, and then release the pressure at a rate of 0.1 MPa / s to obtain flame-retardant EPE.

[0097] Example 3

[0098] This example provides a preparation method of flame-retardant EPE, including the following steps:

[0099] S1. Prepare light polyethylene

[0100] Weigh: 1.8 mL of polyethylene glycol and 12.0 mL of ethanol to prepare a template agent;

[0101] Weigh: 12.0 g of ferric nitrate, 16.0 g of aluminum nitrate and 100.0 mL of deionized water and add them into the reactor, stir for 15 min at a stirring rate of 100 rpm, adjust the pH of the system to 9 with 1.8 mol / L ammonia water, add 16.0 g of the template agent and continue to stir for 8 min, let it stand for 20 h. After standing, place the material in a vacuum drying oven at 80 °C and vacuum dry until the material reaches a constant weight to obtain an anhydrous gel;

[0102] Add the anhydrous gel into a tube furnace, after purging with nitrogen, raise the temperature of the tube furnace to 600 °C at a heating rate of 4 °C / min, keep warm for 2 h, and then naturally cool to room temperature to obtain a mixed metal oxide;

[0103] Add the mixed metal oxide into a pulverizer, pulverize it, and pass it through a 150-mesh sieve to obtain an inorganic porous flame retardant;

[0104] Weigh: 16.0 g of inorganic porous flame retardant, 5.4 g of 3-(methacryloyloxy)propyltrimethoxysilane, 0.8 g of sodium hydroxide and 72.0 mL of deionized water and add them into the reactor, raise the temperature of the reactor to 50 °C, keep warm for 2 h. After the reaction is completed, wait for the temperature of the reactor to drop to room temperature, filter the reaction solution to collect the filter cake, and place the filter cake in a drying oven at 60 °C and vacuum dry until the filter cake reaches a constant weight to obtain a modified inorganic flame retardant;

[0105] Weigh: 18.0 g of modified inorganic flame retardant and 3.6 g of azobisisobutyronitrile and place them in the reactor and stir at a stirring rate of 100 rpm for 12 min at room temperature to obtain a prepolymer mixture;

[0106] Weigh: 20.0 g of prepolymer mixture and place it in a high-pressure reactor. Raise the temperature of the high-pressure reactor to 225 °C and the pressure to 2500 psi. Introduce 90.0 g of ethylene and polymerize at constant temperature and pressure for 50 min to obtain light polyethylene.

[0107] S2. Prepare composite polyethylene

[0108] Weigh: 18.0 g of 2,4-diamino-6-phenyl-1,3,5-triazine, 8.4 g of isophthalaldehyde, 1.2 g of triethylamine and 90.0 mL of N,N-dimethylformamide and add them to the reactor. Raise the temperature of the reactor to 70 °C and keep the temperature for 3 h. After the reaction is completed, wait for the temperature of the reactor to drop to room temperature. Place the reaction solution in a rotary evaporator with a water bath temperature of 90 °C and distill under reduced pressure until no liquid is collected to obtain an enamine polymer.

[0109] Weigh: 18.0 g of enamine polymer, 10.8 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 1.2 g of aluminum chloride and 100.0 mL of dimethyl sulfoxide and add them to the reactor. Raise the temperature of the reactor to 30 - 50 °C and keep the temperature for 2 h. After the reaction is completed, wait for the temperature of the reactor to drop to room temperature. Place the reaction solution in a rotary evaporator with a water bath temperature of 90 °C and distill under reduced pressure until no liquid is collected to obtain an enamine polymer.

[0110] Weigh: 18.0 g of phosphinated enamine polymer, 7.2 g of 4,4'-diphenyl-2-cyclohexen-1-one, 0.8 g of acetic acid and 100.0 mL of tetrahydrofuran and add them to the reactor. Raise the temperature of the reactor to 50 °C and keep the temperature for 3 h. After the reaction is completed, wait for the temperature of the reactor to drop to room temperature. Place the reaction solution in a rotary evaporator with a water bath temperature of 90 °C and distill under reduced pressure until no liquid is collected to obtain a flame retardant crosslinking agent.

[0111] Weigh: 96.0 g of light polyethylene, 18.0 g of flame retardant crosslinking agent, 4.2 g of dibutyltin dilaurate, 8.4 g of polyethylene wax and 8.4 g of triphenyl phosphite and add them to a twin-screw extruder. The temperatures of the eight temperature zones of the twin-screw extruder from the feed inlet to the discharge outlet are 160 °C, 160, 165 °C, 165 °C, 175 °C, 180 °C, 180 °C in sequence. The main machine speed of the twin-screw extruder is 100 rpm and the pressure is 125 bar. Melt and extrude to obtain composite polyethylene.

[0112] S3. Prepare flame retardant EPE

[0113] Place the composite polyethylene blank in an electron beam irradiation device, introduce nitrogen for protection into the electron radiation device at a flow rate of 18 L / min, set the electron beam energy to 4 MeV, the power to 24 kW, the radiation dose to 225 kGy, and the conveyor belt speed to 3 m / min. After the electron radiation is completed, place the material in a crusher, crush it, and pass it through an 80-mesh sieve to obtain a flame-retardant EPE blank;

[0114] Add the flame-retardant EPE blank and toluene to a microwave generator. The power of the microwave generator is 7 kW, and the power density is 3 W / cm 3 , microwave frequency 2.5 GHz, heat to 100 °C until no solvent is extracted to obtain pre-expanded flame-retardant EPE;

[0115] Add the pre-expanded flame-retardant EPE to a high-pressure reactor, introduce nitrogen to exhaust air, raise the temperature of the reactor to 100 °C, introduce butane into the reactor, control the pressure to 5 MPa, keep warm for 50 min, and release the pressure at a pressure reduction rate of 0.08 MPa / s to obtain flame-retardant EPE.

[0116] Comparative Example 1

[0117] The difference between this comparative example and Example 3 is that the step of preparing the modified inorganic flame retardant in step S1 is cancelled, and porous alumina is used to replace the modified inorganic flame retardant equally in the process of preparing light polyethylene.

[0118] Comparative Example 2

[0119] The difference between this comparative example and Example 3 is that the step of preparing the flame-retardant crosslinking agent in step S2 is cancelled, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is used to replace the flame-retardant crosslinking agent equally in the process of preparing composite polyethylene.

[0120] Comparative Example 3

[0121] The difference between this comparative example and Example 3 is that the pre-expansion of the flame-retardant EPE blank in step S3 to obtain pre-expanded flame-retardant EPE is cancelled, and the flame-retardant EPE blank is used to replace the pre-expanded flame-retardant EPE equally in the process of flame-retardant EPE.

[0122] Performance test:

[0123] Refer to the vertical burning grade of the flame-retardant EPE prepared in Examples 1-3 and Comparative Examples 1-3 according to the standard GB / T 2408-2021 "Determination of the burning performance of plastics - Horizontal and vertical methods";

[0124] Referring to the standard BB / T 0066-2017 "Polyethylene Extruded Foamed Packaging Materials", the apparent density, tensile strength, tear strength, compression strength and compression set rate of the flame-retardant EPE prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the specific data are shown in Table 1.

[0125] Table 1 - Performance Test Data Sheet of Each Specimen

[0126]

[0127]

[0128] Data Analysis:

[0129] By comparing and analyzing the data in Table 1 above, the vertical burning grade of the flame-retardant EPE prepared in the present invention is V-0, the apparent density is 16.3 kg·m -3 ⁻³, the tensile strength is 251 kPa, the tear strength is 2.1 N·mm -1 ⁻¹, the compression strength (40%) is 63 kPa and the compression set rate (50%) is only 16%. All the data are better than those of the comparative examples;

[0130] Data Explanation:

[0131] In the process of preparing the flame-retardant EPE in the present invention, a modified inorganic flame retardant with a large number of double bonds on the surface is prepared. Its porous structure serves as the polymerization site for ethylene gas-phase polymerization. Lightweight polyethylene is polymerized on its surface through gas-phase polymerization. And by preparing a flame-retardant crosslinking agent, it is melt-blended and extruded with lightweight polyethylene and auxiliary materials to obtain composite polyethylene. During the radiation crosslinking of the composite polyethylene, the modified inorganic flame retardant serves as the radiation absorption center, promoting the generation of a large number of free radicals between lightweight polyethylene and the flame-retardant crosslinking agent with a large number of double bonds to promote the crosslinking reaction. The material has more excellent mechanical properties, serves as a microwave absorption center during the pre-foaming process to make the pre-foaming more efficient and uniform, and during the supercritical fluid butane foaming process, the porous structure serves as a gas slow-release center to make the foaming more complete, and cooperates with the flame-retardant crosslinking agent to improve the flame-retardant performance of the material, and finally obtains a flame-retardant EPE with more sufficient and uniform foaming and stronger mechanical properties.

[0132] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor limit the present invention to the specific implementation manners described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A preparation method of a flame-retardant EPE, characterized in that, It includes the following steps: S1. Add an inorganic porous flame retardant, 3-(methacryloyloxy)propyltrimethoxysilane, sodium hydroxide, and deionized water into a reaction kettle. Raise the temperature of the reaction kettle to 30 - 50 °C, keep it warm for 3 - 5 h, and perform post-treatment to obtain a modified inorganic flame retardant; S2. Under the conditions of high temperature and high pressure, ethylene gas is polymerized on the surface of the modified inorganic flame retardant under the initiation of azobisisobutyronitrile to prepare light polyethylene; S3. Add the light polyethylene, a flame retardant crosslinking agent, and auxiliary materials into a twin-screw extruder, and melt and extrude to obtain composite polyethylene; S4. Place the composite polyethylene blank in an electron beam irradiation device, perform electron radiation and post-treatment to obtain a flame retardant EPE blank; S5. Perform secondary foaming on the flame retardant EPE blank to obtain flame retardant EPE.

2. The preparation method of a flame-retardant EPE according to claim 1, characterized in that, In step S1, the dosage ratio of the inorganic porous flame retardant, 3-(methacryloyloxy)propyltrimethoxysilane, sodium hydroxide, and deionized water is 6 - 8 g: 2 - 3 g: 0.3 - 0.5 g: 30 - 40 mL; in step S3, the dosage ratio of the light polyethylene, the flame retardant crosslinking agent, and the auxiliary materials is 80 - 100 g: 15 - 20 g: 15 - 30 g, and the auxiliary materials include: a heat stabilizer, a lubricant, and an antioxidant.

3. The preparation method of a flame-retardant pearl cotton according to claim 1, characterized in that, In step S1, the preparation method of the inorganic porous flame retardant includes the following steps: A1. Add ferric nitrate, aluminum nitrate, and deionized water into a reaction kettle and stir for 10 - 15 min. Use ammonia water with a concentration of 1 - 2 mol / L to adjust the pH of the system to 8 - 10, add a template agent and continue to stir for 5 - 10 min, let it stand for 16 - 24 h, and perform post-treatment to obtain an anhydrous gel; A2. Add the anhydrous gel into a tubular furnace for high-temperature calcination to obtain a mixed metal oxide; A3. Add the mixed metal oxide into a pulverizer for pulverization, and pass through a 100 - 200 mesh sieve to obtain the inorganic porous flame retardant.

4. The preparation method of a flame-retardant EPE according to claim 3, characterized in that, In step A1, the stirring rate of the reaction kettle is 80 - 120 rpm, and the dosage ratio of ferric nitrate, aluminum nitrate, deionized water, and the template agent is 5 - 6 g: 8 - 10 g: 40 - 50 mL: 8 - 10 g. The template agent is prepared by mixing polyethylene glycol and ethanol in a dosage ratio of 1 - 2 mL: 10 - 15 mL; In step A2, the high-temperature calcination operation includes: after introducing nitrogen protection, the tubular furnace is heated to 500 - 600 °C at a heating rate of 3 - 5 °C / min, kept warm for 1 - 2 h, and naturally cooled to room temperature to obtain the mixed metal oxide.

5. The preparation method of a flame-retardant EPE according to claim 1, characterized in that, In step S2, the high-pressure polymerization operation includes the following steps: B1. Place the modified inorganic flame retardant and azobisisobutyronitrile in a reaction kettle and stir. Stir at room temperature for 10 - 15 min to obtain a prepolymer mixture; B2. Place the prepolymer mixture in a high-pressure reaction kettle. Raise the temperature of the high-pressure reaction kettle to 200 - 250 °C, raise the pressure to 2000 - 3000 psi, introduce ethylene, and perform constant-temperature and constant-pressure polymerization for 40 - 60 min to obtain light polyethylene.

6. The preparation method of a flame-retardant EPE according to claim 1, wherein, In step S3, the preparation method of the flame retardant crosslinking agent includes the following steps: C1. Add 2,4-diamino-6-phenyl-1,3,5-triazine, isophthalaldehyde, triethylamine and N,N-dimethylformamide into a reaction kettle. Raise the temperature of the reaction kettle to 60 - 80 °C, keep the temperature for reaction for 2 - 4 h, and perform post-treatment to obtain an enamine polymer; C2. Add the enamine polymer, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, aluminum chloride and dimethyl sulfoxide into a reaction kettle. Raise the temperature of the reaction kettle to 30 - 50 °C, keep the temperature for reaction for 1 - 3 h, and perform post-treatment to obtain a phosphinated enamine polymer; C3. Add the phosphinated enamine polymer, 4,4-diphenyl-2-cyclohexen-1-one, acetic acid and tetrahydrofuran into a reaction kettle. Raise the temperature of the reaction kettle to 40 - 50 °C, keep the temperature for reaction for 2 - 4 h, and perform post-treatment to obtain a flame retardant crosslinking agent.

7. The preparation method of a flame-retardant EPE according to claim 6, characterized in that, In step C1, the dosage ratio of 2,4-diamino-6-phenyl-1,3,5-triazine, isophthalaldehyde, triethylamine and N,N-dimethylformamide is 8 - 10 g: 3 - 5 g: 0.5 - 0.8 g: 40 - 50 mL; in step C2, the dosage ratio of the phosphinated enamine polymer, 4,4-diphenyl-2-cyclohexen-1-one, acetic acid and tetrahydrofuran is 8 - 10 g: 4 - 6 g: 0.5 - 0.8 g: 40 - 50 mL; in step C3, the dosage ratio of the phosphinated enamine polymer, 4,4-diphenyl-2-cyclohexen-1-one, acetic acid and tetrahydrofuran is 8 - 10 g: 2 - 4 g: 0.3 - 0.5 g: 50 - 60 mL.

8. The preparation method of a flame-retardant EPE according to claim 1, wherein, In step S4, the operation of electron radiation is as follows: Pass nitrogen into the electron radiation device for protection at a flow rate of 15 - 20 L / min, set the electron beam energy to 3 - 4 MeV, the power to 20 - 25 kW, the radiation dose to 200 - 250 kGy, and set the conveyor belt speed to 1 - 3 m / min.

9. The preparation method of a flame-retardant EPE according to claim 1, characterized in that, In step S5, the operation of secondary foaming includes the following steps: D1. Add the flame-retardant EPE blank and toluene into a microwave generator. The power of the microwave generator is 5 - 8 kW, and the power density is 2 - 4 W / cm 3 , with a microwave frequency of 2.4 - 2.5 GHz and a temperature of 100 - 120 °C. Heat until no solvent is extracted to obtain the pre-expanded flame-retardant EPE; D2. Add the pre-foamed flame retardant EPE into a high-pressure reaction kettle, pass nitrogen to exhaust air, raise the temperature of the reaction kettle to 100 - 120 °C, pass butane into the reaction kettle, control the pressure to 4 - 5 MPa, keep the temperature for 40 - 60 min, and release the pressure at a pressure reduction rate of 0.05 - 0.1 MPa / s to obtain the flame retardant EPE.

10. A flame-retardant pearl cotton, characterized in that, The flame retardant EPE adopts the preparation method of a flame retardant EPE described in any one of claims 1 - 9.

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