Composite flame-retardant material and preparation method thereof

Abstract

The invention relates to the technical field of flame retardance, and particularly discloses a composite flame-retardant material and a preparation method thereof. The composite flame-retardant material is prepared from the following raw materials in parts by mass: 15-20 parts of an ethylene-vinyl acetate copolymer, 5-10 parts of high-density polyethylene, 8-10 parts of a thermoplastic polyurethane elastomer, 5-10 parts of palygorskite fibers, 5-10 parts of diatomite, 1-3 parts of carbon nanotubes, 10-15 parts of modified pentaerythritol, 20-30 parts of an acid source-nitrogen source compound and 1-2 parts of cerium oxide. 3-5 parts by mass of polyethylene grafted glycidyl methacrylate and 1-2 parts by mass of silicone master batch. The composite flame-retardant material prepared by the invention has better mechanical property and flame-retardant property.

Description

Technical Field

[0001] The present application relates to the technical field of flame retardant materials, and more specifically, to a composite flame retardant material and a preparation method thereof. Background Art

[0002] With the rapid development of electronic appliances, photovoltaics, automobiles and other fields, EVA / PE-based composite materials have been widely used due to their excellent processing performance and flexibility, but their flammability needs to be flame-retardant modified to meet safety standards. The flame retardant of EVA / PE-based composite materials is still mainly halogen flame retardants and inorganic metal hydroxides. Halogen flame retardants will generate a lot of smoke and toxic corrosive gases during combustion, which is not conducive to personnel escape and firefighting, and can cause corrosion to circuit system switches and other metal equipment that cannot be caused by fire alone. Based on the concern for environmental protection and human health and safety, composite flame retardant materials have tended to be halogen-free, low-smoke and non-toxic. The addition amount of inorganic metal hydroxide usually needs to reach more than 50% to make the polymer have a good flame retardant effect. Especially for non-polar PE resins, the compatibility is poor, and it is difficult to form a good bond between the filling system interfaces, which requires the modification of inorganic flame retardants to improve the processing fluidity and physical and mechanical properties of composite materials.

[0003] The patent application document with publication number CN103724792A discloses a low-smoke, halogen-free, environmentally friendly EVA / LLDPE flame-retardant composite material. The raw material components and weight proportions are: A is the base resin: EVA and LLDPE, 100 parts; B is the compatibilizer: maleic anhydride grafted polyethylene PE-g-MAH, 20~30 parts; C is the inorganic flame retardant: modified magnesium hydroxide 80~90 parts, modified aluminum hydroxide 90~100 parts; D is an antioxidant: 0.5~1 part; E is a lubricant: 2.5~4 parts.

[0004] In this technology, highly filled inorganic flame retardants magnesium hydroxide and aluminum hydroxide are used, and a large amount of compatibilizers are compounded to construct the system. Although magnesium hydroxide and aluminum hydroxide are modified by silane coupling agents, the limited number of chemical bonds formed results in poor interfacial bonding. Under high filling amounts, when the inorganic flame retardant and the resin matrix are subjected to external forces, debonding is prone to occur due to weak interfacial bonding, resulting in a significant decrease in mechanical properties such as the tensile strength of the material. In addition, although a large amount of PE-g-MAH compatibilizer is added to compensate for interface defects, the interfacial bonding between the inorganic flame retardant and the base resin can be partially improved, but excessive amounts of compatibilizers will form too many low-modulus interface layers in the system, destroying the original tight and orderly structure of the material, and further reducing the tensile strength of the material. Summary of the invention

[0005] In order to improve the elongation at break and tensile strength of the composite flame retardant material, the present application provides a composite flame retardant material and a preparation method thereof.

[0006] In the first aspect, the present application provides a composite flame retardant material, adopting the following technical solution: A composite flame retardant material, which is made of the following raw materials: 15-20 parts by mass of ethylene-vinyl acetate copolymer, 5-10 parts by mass of high-density polyethylene, 8-10 parts by mass of thermoplastic polyurethane elastomer, 5-10 parts by mass of palygorskite fiber, 5-10 parts by mass of diatomite, 1-3 parts by mass of carbon nanotubes, 10-15 parts by mass of modified pentaerythritol, 20-30 parts by mass of acid source-nitrogen source complex, 1-2 parts by mass of cerium oxide, 3-5 parts by mass of polyethylene grafted glycidyl methacrylate, 1-2 parts by mass of silicone masterbatch; Before use, the palygorskite fiber is pretreated with maleic anhydride; The modified pentaerythritol is prepared from pentaerythritol, boric acid, a catalyst, allyl alcohol and a water-carrying agent as raw materials; The acid source-nitrogen source complex is prepared from ammonium polyphosphate, melamine phosphate, ammonium molybdate and silica sol as raw materials.

[0007] Preferably, the diameter of the palygorskite fiber is 50-100 nm, and the aspect ratio is 50-100.

[0008] Preferably, the diameter of the carbon nanotubes is 10-20 nm, and the aspect ratio ≥2000.

[0009] In this technology, the composite flame retardant material is based on the ternary blend of ethylene-vinyl acetate copolymer (EVA), high-density polyethylene (HDPE) and thermoplastic polyurethane elastomer (TPU). A toughening phase is formed by the thermoplastic polyurethane elastomer to effectively compensate for the brittleness risk introduced by the inorganic filler, ensuring the balance of strength and toughness of the matrix. At the same time, a multi-level composite structure is constructed through the rigid reinforcement of palygorskite fiber, the nano-toughening of diatomite and carbon nanotubes. The high aspect ratio fibers form a skeleton support, the lamellar structure produces a maze effect, and the carbon nanotubes bridge to construct a heat conduction network, realizing multiple functions such as stress dispersion, pyrolysis delay and suppressing combustion caused by heat accumulation through heat conduction dispersion. The expanded carbon layer catalyzed by modified pentaerythritol, acid source-nitrogen source complex and cerium oxide, combined with the nano-confinement effect of the mesoporous structure of diatomite, constructs a gas-solid dual flame retardant mechanism. While maintaining excellent mechanical properties, this material significantly improves the flame retardant grade and thermal conductivity.

[0010] Preferably, the specific steps of the pretreatment of the palygorskite fiber with maleic anhydride before use are: Add palygorskite fiber and maleic anhydride into a kneader, heat up to 140 - 160 °C, react for 20 - 30 min, and then cool to obtain pretreated palygorskite fiber.

[0011] Preferably, the mass ratio of the palygorskite fiber to maleic anhydride is (5 - 10):(0.2 - 0.5).

[0012] Preferably, the preparation method of the modified pentaerythritol includes the following steps: Mix pentaerythritol, boric acid, a catalyst, and a water-carrying agent evenly, heat up to 120 - 140 °C, react for 4 - 6 h, then add allyl alcohol, adjust the temperature to 140 - 160 °C, continue to react for 90 - 150 min, cool, neutralize, perform solid-liquid separation, wash, and dry to obtain it; The molar ratio of the pentaerythritol, boric acid, and allyl alcohol is 1:(1 - 1.2):(0.08 - 0.12).

[0013] Preferably, the catalyst is zirconium sulfate, and the dosage of the zirconium sulfate is 0.8% - 1.2% of the mass of pentaerythritol.

[0014] Preferably, the water-carrying agent includes cyclohexane and water, and the volume ratio of cyclohexane to water in the water-carrying agent is 1:(0.8 - 1.2).

[0015] In this technology, boric acid and allyl alcohol are introduced through step-by-step modification. Boric acid reacts with pentaerythritol to form a borate structure with good thermal stability. Boric acid can promote the formation of a dense carbon layer. At the same time, boric acid esterification reduces the number of hydroxyl groups of pentaerythritol and enhances the hydrophobicity. The introduction of allyl groups can form partial cross-linked structures when the subsequent material is carbonized by heat to generate free radicals, forming a denser carbon layer structure and improving the anti-cracking ability, thereby enhancing the mechanical strength. During the combustion process, B2O3 decomposed from boric acid partially forms a glassy state in the carbon layer, further strengthening the heat insulation effect. The carbon layer cross-linked by allyl groups and boric acid act synergistically to form a "physical-chemical double barrier" effect. This carbon layer can act as a barrier to block the transfer of oxygen and heat, slow down the combustion rate of the material, and significantly improve the flame retardancy of the material.

[0016] Preferably, the preparation method of the acid source-nitrogen source composite includes the following steps: Grind and mix ammonium polyphosphate and melamine phosphate evenly, disperse them in ethanol, add ammonium molybdate and mix evenly, then add silica sol, mix ultrasonically, and then spray dry to obtain it; The mass ratio of the ammonium polyphosphate to melamine phosphate is (2 - 3):1; the mass ratio of the total mass of the ammonium polyphosphate and melamine phosphate to the mass of silica sol is 1:(4 - 6); The inlet temperature of the spray drying is 140 - 160 °C, and the outlet temperature is 60 - 80 °C.

[0017] Preferably, the dosage of ammonium molybdate is 1% - 3% of the total mass of ammonium polyphosphate and melamine phosphate.

[0018] Preferably, the mass fraction of silicon dioxide in the silica sol is 20% - 30%.

[0019] In the present technology, after ammonium polyphosphate and melamine phosphate are co - ground, silica sol is used for nano - coating to form composite particles with a "core - shell" structure, and ammonium molybdate is introduced to construct a multi - dimensional flame - retardant mechanism. The "core - shell" structure improves the dispersibility and thermal stability of the flame retardant in the polymer substrate, realizing the slow release and synergistic release of active substances; the poly - acid source synergizes with molybdenum oxide to accelerate the dehydration of the carbon source to form carbon, forming a dense carbon layer to isolate heat and oxygen; the nitrogen - containing gas released by melamine phosphate dilutes the concentration of the combustible, and after molybdenum oxide sublimes, it captures free radicals to interrupt the combustion chain reaction.

[0020] Preferably, before use, both ammonium polyphosphate and melamine phosphate are ground to a particle size of ≤5 μm.

[0021] Preferably, before use, the silica sol undergoes the following pretreatment steps: The silica sol is mixed evenly with a silane coupling agent, and the pH is adjusted to 5 - 6 to obtain the pretreated silica sol; In the pretreated silica sol, the dosage of the silane coupling agent is 0.5% - 1.5% of the mass of the silica sol.

[0022] Preferably, before use, the diatomite undergoes the following pretreatment steps: The diatomite is pickled, washed, then mixed and ground with nano - hydroxyapatite, added to a polydimethylsiloxane dispersion, mixed evenly, subjected to solid - liquid separation, washed, and dried to obtain the product; The mass ratio of the diatomite to the nano - hydroxyapatite is 10:(0.8 - 1.2); the mass fraction of the polydimethylsiloxane dispersion is 2% - 4%.

[0023] Preferably, the polydimethylsiloxane dispersion further includes ethanol, and the mass fraction of the ethanol is 2% - 4%.

[0024] Preferably, the pore size distribution between the lamellae of the diatomite is 0.1 - 10 μm.

[0025] Preferably, the particle size distribution of the nano - hydroxyapatite is 1 - 50 nm.

[0026] In this pretreatment technology, the pickling process deeply purifies the surface, eliminates impurity interference, and exposes abundant active sites; the introduction of nano-hydroxyapatite constructs a strong coupling interface, forms a stable chemical anchoring effect, ensures the uniform dispersion of pretreated diatomite in the matrix, and enhances the interfacial bonding; the hydrophobic modification of polydimethylsiloxane constructs a functional gradient layer on the surface, which not only improves the compatibility with the polymer matrix but also forms a moisture-conducting channel to optimize the migration path of pyrolysis products. It can not only significantly improve the flame retardancy of the composite material but also enhance the mechanical strength and thermal stability simultaneously.

[0027] Preferably, during pickling, it is washed with an acid solution for 30 - 60 min; the acid solution includes hydrochloric acid, cetyltrimethylammonium bromide, and water, the mass fraction of hydrochloric acid is 1% - 3%, and the mass fraction of cetyltrimethylammonium bromide is 0.5% - 1%.

[0028] Preferably, the mass-volume ratio of diatomite to polydimethylsiloxane solution is 1 g : (8 - 12) mL.

[0029] Preferably, the composite flame retardant material further includes 6 - 8 parts of triphenyl borate.

[0030] In this technology, by adding triphenyl borate, its rigid benzene ring structure and boron-oxygen bonds synergistically promote condensed-phase carbonization to form a dense and high-temperature-resistant boron-containing carbon layer, effectively improving the flame retardancy grade. At the same time, triphenyl borate can also form a "boron-phosphorus-silicon" multi-component flame retardant network with components such as pretreated diatomite and modified pentaerythritol, effectively inhibiting heat transfer and free radical generation during combustion, and further improving the flame retardancy.

[0031] In the second aspect, the present application provides a preparation method of a composite flame retardant material, including the following steps: Add ethylene-vinyl acetate copolymer, high-density polyethylene, and thermoplastic polyurethane elastomer to a high-speed mixer, heat up to 160 - 170 °C, mix for 15 - 20 min, then add palygorskite fiber, diatomite, and carbon nanotubes, heat up to 165 - 175 °C, mix for 15 - 20 min, cool down to 140 - 160 °C, add modified pentaerythritol, acid source-nitrogen source complex, and cerium oxide, mix for 15 - 20 min, then add the remaining polyethylene grafted glycidyl methacrylate and silicone masterbatch, mix for 10 - 15 min, perform vacuum degassing, homogenization treatment, and hot pressing, and then cool and shape to obtain the product.

[0032] In this technology, palygorskite is pretreated with maleic anhydride, effectively improving the dispersibility and interfacial bonding strength of palygorskite fibers in subsequent matrix polymerization. In the mixing and extrusion stage, the blending of matrix polymers forms a toughening phase, effectively compensating for the brittleness of inorganic components, making the material possess both strength and toughness. Subsequently, a composite flame retardant system composed of modified pentaerythritol, acid source-nitrogen source complex, and cerium oxide is added while cooling. When heated, it generates flame retardant substances, catalyzes thermal decomposition, and catalyzes the formation of a dense carbon layer through dehydration carbonization and decomposition, isolating heat and oxygen, etc., significantly improving the flame retardant performance of the material.

[0033] Preferably, the temperature of the hot pressing is 165 - 175 °C, the pressure is 15 - 20 MPa, and the time is 6 - 10 min.

[0034] Preferably, in the vacuum degassing, the vacuum degree is -0.09 - -0.1 MPa, and the degassing treatment is 12 - 15 min.

[0035] Preferably, the homogenization treatment is carried out by melt mixing and homogenization using a twin-screw extruder.

[0036] Preferably, the parameter settings of the twin-screw extruder are as follows: the temperature of the first zone is 150 - 160 °C, the temperature of the second zone is 160 - 170 °C, the temperature of the third zone is 170 - 180 °C, the temperature of the fourth zone is 170 - 180 °C; the screw speed is stably controlled at 180 - 220 r / min.

[0037] Preferably, when adding cerium oxide, it also includes the step of adding triphenyl borate.

[0038] In summary, the present application has the following beneficial effects: 1. The composite flame retardant material of the present application uses EVA / HDPE / TPU ternary blend as the matrix, compensates for the brittleness of inorganic fillers through the TPU toughening phase, and realizes the balance between matrix strength and toughness; constructs a multi-level composite system of palygorskite fiber rigid skeleton, diatomite flake maze structure, and carbon nanotube heat conduction network, synchronously realizing stress dispersion, pyrolysis delay, and suppressing combustion caused by heat accumulation through heat conduction dispersion; utilizes the expanded carbon layer catalyzed by modified pentaerythritol (carbon source), acid source-nitrogen source complex, and cerium oxide, combined with the mesoporous nano-confinement effect of diatomite, to form a gas-solid synergistic flame retardant mechanism, ultimately significantly improving the flame retardant grade and heat conduction performance while maintaining excellent mechanical properties.

[0039] 2. In the present application, triphenyl borate is preferably used. Its rigid benzene ring structure and boron-oxygen bond synergistically promote char formation in the condensed phase, forming a dense and high-temperature resistant boron-containing carbon layer, and forming a "boron-phosphorus-silicon" multi-element flame retardant network with components such as pretreated diatomite and modified pentaerythritol, effectively inhibiting heat transfer and free radical generation during combustion, and further improving the flame retardant performance. Specific Embodiments

[0040] The following further elaborates on this application in conjunction with embodiments.

[0041] Unless otherwise specified, the raw materials in the embodiments and comparative examples of this application are all commercially available.

[0042] Polyethylene grafted glycidyl methacrylate is abbreviated as PE-g-GMA; ethylene-vinyl acetate copolymer is abbreviated as EVA; high-density polyethylene is abbreviated as HDPE; thermoplastic polyurethane elastomer is thermoplastic polyurethane elastomer microspheres with a particle size distribution of 50-80 μm, abbreviated as TPU; The diameter of palygorskite fiber is 50-100 nm, and the aspect ratio is 50-100; The diameter of carbon nanotubes is 10-20 nm, and the aspect ratio ≥2000; The pore size distribution between the lamellae of diatomite is 0.1-10 μm; The particle size distribution of nano-hydroxyapatite is 1-50 nm.

[0043] Preparation Examples 1-3 Modified Pentaerythritol Preparation Example 1 The preparation method of the modified pentaerythritol in this preparation example includes the following steps: Add 2 mol of pentaerythritol, 2.2 mol of boric acid, zirconium sulfate and a water-carrying agent into a reaction kettle equipped with a stirrer, thermometer, reflux condenser and water separator, mix evenly, slowly heat up to 130 °C, after reacting for 5 h, add 0.2 mol of allyl alcohol, heat up to 150 °C, continue to react for 120 min, then cool to room temperature, neutralize with a 5% sodium carbonate solution by mass, adjust the pH value to be close to neutral, filter, wash with deionized water 3 times, put it into a drying oven, and dry at 80 °C until constant weight to obtain modified pentaerythritol.

[0044] Among them, the water-carrying agent includes cyclohexane and water, the volume ratio of cyclohexane to water is 1:1, and the dosage of the water-carrying agent is 120 mL; The dosage of zirconium sulfate is 2.7 g.

[0045] Preparation Example 2 The preparation method of the modified pentaerythritol in this preparation example includes the following steps: Add 2 mol of pentaerythritol, 2 mol of boric acid, zirconium sulfate and a water-carrying agent into a reaction kettle equipped with a stirrer, thermometer, reflux condenser and water separator, mix evenly, slowly heat up to 120 °C, after reacting for 6 h, add 0.16 mol of allyl alcohol, heat up to 140 °C, continue to react for 150 min, then cool to room temperature, neutralize with a 5% sodium carbonate solution by mass, adjust the pH value to be close to neutral, filter, wash with deionized water 3 times, put it into a drying oven, and dry at 80 °C until constant weight to obtain modified pentaerythritol.

[0046] Among them, the water-carrying agent includes cyclohexane and water, the volume ratio of cyclohexane to water is 1:1.2, and the dosage of the water-carrying agent is 120 mL; The dosage of zirconium sulfate is 3.3 g.

[0047] Preparation Example 3 The preparation method of the modified pentaerythritol in this preparation example includes the following steps: Add 2 mol of pentaerythritol, 2.4 mol of boric acid, zirconium sulfate and the water-carrying agent into a reaction kettle equipped with a stirrer, a thermometer, a reflux condenser and a water separator, mix evenly, slowly heat up to 140 °C, after reacting for 4 h, add 0.24 mol of allyl alcohol, heat up to 160 °C, continue to react for 90 min, then cool to room temperature, neutralize with a 5% sodium carbonate solution by mass fraction, adjust the pH value to be close to neutral, filter, wash 3 times with deionized water, put it into a drying oven, and dry at 80 °C until constant weight to obtain the modified pentaerythritol.

[0048] Among them, the water-carrying agent includes cyclohexane and water, the volume ratio of cyclohexane to water is 1:0.8, and the dosage of the water-carrying agent is 120 mL; The dosage of zirconium sulfate is 2.2 g.

[0049] Preparation Examples 4-6 Acid Source-Nitrogen Source Complex Preparation Example 4 The preparation method of the acid source-nitrogen source complex in this preparation example includes the following steps: Grind 400 g of ammonium polyphosphate and 200 g of melamine phosphate to a particle size of ≤5 μm respectively, then mix evenly, add them into 1 L of ethanol, stir and mix at 800 r / min for 30 min, then add 6 g of ammonium molybdate, continue to stir and mix for 10 min, then add 2400 g of silica sol, transfer it to an ultrasonic device, and perform ultrasonic treatment at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz for 30 min to obtain a mixed solution; transfer the mixed solution to an atomization device equipped with a pressure-type nozzle (nozzle aperture is 1.2 mm) for spray drying, set the feeding rate to 8 mL / min, the atomization pressure to 0.25 MPa, the drying nitrogen flow rate to 1.2 m 3 / min, and set the inlet temperature of spray drying to 140 °C and the outlet temperature to 60 °C to obtain.

[0050] Among them, the mass fraction of silicon dioxide in the silica sol is 20%; The silica sol is pretreated through the following steps before use: Mix the silica sol and the silane coupling agent KH550 evenly, and adjust the pH to about 6 with 5% dilute hydrochloric acid by mass fraction to obtain the pretreated silica sol; In the pretreated silica sol, the dosage of silane coupling agent KH550 is 12 g.

[0051] Preparation Example 5 The preparation method of the acid source-nitrogen source composite in this preparation example includes the following steps: Grind 500 g of ammonium polyphosphate and 200 g of melamine phosphate to a particle size of ≤5 μm respectively, then mix them evenly, and then add them to 1.2 L of ethanol. Stir and mix at 800 r / min for 40 min, then add 14 g of ammonium molybdate, continue to stir and mix for 12 min, then add 3500 g of silica sol, transfer it to an ultrasonic device, and perform ultrasonic treatment at an ultrasonic power of 250 W and an ultrasonic frequency of 50 kHz for 30 min to obtain a mixed solution; transfer the mixed solution to an atomization device with a pressure nozzle (nozzle aperture is 1.2 mm) for spray drying. Set the feeding rate to 9 mL / min, the atomization pressure to 0.28 MPa, and the drying nitrogen flow rate to 1.3 m 3 / min. Set the inlet temperature of the spray drying to 150 °C and the outlet temperature to 70 °C to obtain the product.

[0052] Among them, the mass fraction of silicon dioxide in the silica sol is 25%; Before use, the silica sol undergoes the following pretreatment steps: Mix the silica sol and silane coupling agent KH550 evenly, and adjust the pH to about 5.5 with 5% dilute hydrochloric acid by mass fraction to obtain the pretreated silica sol; In the pretreated silica sol, the dosage of silane coupling agent KH550 is 35 g.

[0053] Preparation Example 6 The preparation method of the acid source-nitrogen source composite in this preparation example includes the following steps: Grind 600 g of ammonium polyphosphate and 200 g of melamine phosphate to a particle size of ≤5 μm respectively, then mix them evenly, and then add them to 1.5 L of ethanol. Stir and mix at 800 r / min for 50 min, then add 24 g of ammonium molybdate, continue to stir and mix for 15 min, then add 4800 g of silica sol, transfer it to an ultrasonic device, and perform ultrasonic treatment at an ultrasonic power of 300 W and an ultrasonic frequency of 60 kHz for 40 min to obtain a mixed solution; transfer the mixed solution to an atomization device with a pressure nozzle (nozzle aperture is 1.2 mm) for spray drying. Set the feeding rate to 10 mL / min, the atomization pressure to 0.30 MPa, and the drying nitrogen flow rate to 1.4 m 3 / min. Set the inlet temperature of the spray drying to 160 °C and the outlet temperature to 80 °C to obtain the product.

[0054] Among them, the mass fraction of silicon dioxide in the silica sol is 30%; Before use, the silica sol undergoes the following pretreatment steps: Mix the silica sol and the silane coupling agent KH550 evenly, and adjust the pH to about 5.0 with 5% (mass fraction) dilute hydrochloric acid to obtain the pretreated silica sol; In the pretreated silica sol, the dosage of the silane coupling agent KH550 is 72 g.

[0055] Example 1 This example provides a preparation method of a composite flame retardant material, which includes the following steps: Add 150 g of EVA, 50 g of HDPE, and 80 g of TPU to a high-speed mixer, heat up to 160 °C, after mixing for 15 min, add 50 g of palygorskite fiber, 50 g of diatomite, and 10 g of carbon nanotubes, heat up to 165 °C, mix for 15 min, cool down to 140 °C, add 100 g of modified pentaerythritol, 200 g of acid source-nitrogen source complex, and 10 g of cerium oxide, mix for 15 min, then add 30 g of PE-g-GMA and 10 g of silicone masterbatch, continue to mix for 10 min, transfer the mixed material to a vacuum degassing device, adjust the vacuum degree to -0.09 MPa, after degassing for 12 min, add the material after vacuum degassing to the hopper of a twin-screw extruder, start the twin-screw extruder, stably control the screw speed at 180 r / min, after the material is melt-mixed and homogenized in the extruder, extrude, put the extruded material into a preheated mold, and put the mold into a hot press, set the hot pressing temperature to 165 °C, the pressure to 15 MPa, and the hot pressing time to 10 min, after hot pressing is completed, take out the mold from the hot press, and immediately cool it by water cooling, control the cooling rate at 10 °C / min to obtain the composite flame retardant material.

[0056] Among them, the parameter settings of the twin-screw extruder are: the temperature of the first zone is 150 °C, the temperature of the second zone is 160 °C, the temperature of the third zone is 170 °C, and the temperature of the fourth zone is 170 °C.

[0057] The modified pentaerythritol comes from Preparation Example 1; the acid source-nitrogen source complex comes from Preparation Example 4.

[0058] Before use, the palygorskite fiber undergoes the following pretreatment steps: Add 50 g of palygorskite fiber and 2 g of maleic anhydride to a kneader, heat up to 140 °C, stir and react at a speed of 60 r / min for 30 min, and cool to room temperature at 5 °C / min to obtain the pretreated palygorskite fiber.

[0059] Example 2 This example provides a preparation method of a composite flame retardant material, which includes the following steps: Add 200 g of EVA, 100 g of HDPE, and 100 g of TPU to a high-speed mixer. Heat up to 170 °C and mix for 20 min. Then add 100 g of palygorskite fiber, 100 g of diatomite, and 30 g of carbon nanotubes. Heat up to 175 °C and mix for 20 min. Cool down to 160 °C, add 150 g of modified pentaerythritol, 300 g of acid source-nitrogen source complex, and 20 g of cerium oxide, and mix for 20 min. Then add 50 g of PE-g-GMA and 20 g of silicone masterbatch, and continue to mix for 15 min. Transfer the mixed material to a vacuum degassing device, adjust the vacuum degree to -0.1 MPa, and after degassing for 15 min, add the material after vacuum degassing to the hopper of a twin-screw extruder. Start the twin-screw extruder, stably control the screw speed at 220 r / min, make the material melt and mix and homogenize in the extruder, and then extrude. Put the extruded material into a preheated mold, and put the mold into a hot press. Set the hot pressing temperature at 175 °C, the pressure at 20 MPa, and the hot pressing time at 6 min. After hot pressing is completed, take out the mold from the hot press and immediately cool it by water cooling, and control the cooling rate at 8 °C / min to obtain the composite flame retardant material.

[0060] Among them, the parameter settings of the twin-screw extruder are as follows: the temperature of the first zone is 160 °C, the temperature of the second zone is 170 °C, the temperature of the third zone is 180 °C, and the temperature of the fourth zone is 180 °C.

[0061] The modified pentaerythritol comes from Preparation Example 2; the acid source-nitrogen source complex comes from Preparation Example 5; Before using the palygorskite fiber, it undergoes the following pretreatment steps: Add 100 g of palygorskite fiber and 5 g of maleic anhydride to a kneader, heat up to 160 °C, stir and react at a speed of 50 r / min for 20 min, and cool down to room temperature at 5 °C / min to obtain pretreated palygorskite fiber.

[0062] Example 3 This example provides a preparation method of a composite flame retardant material, including the following steps: Add 180 g of EVA, 75 g of HDPE, and 90 g of TPU to a high-speed mixer. Heat up to 165 °C and mix for 18 min. Then add 80 g of palygorskite fiber, 80 g of diatomite, and 20 g of carbon nanotubes. Heat up to 170 °C and mix for 18 min. Cool down to 150 °C, add 125 g of modified pentaerythritol, 240 g of acid source-nitrogen source complex, and 15 g of cerium oxide, and mix for 18 min. Then add 40 g of PE-g-GMA and 15 g of silicone masterbatch, and continue to mix for 13 min. Transfer the mixed material to a vacuum degassing device, adjust the vacuum degree to -0.1 MPa, and after degassing for 14 min, add the vacuum-degassed material to the hopper of a twin-screw extruder. Start the twin-screw extruder, stably control the screw speed at 260 r / min, and after the material is melted, mixed, and homogenized in the extruder, extrude it. Put the extruded material into a preheated mold, and place the mold in a hot press. Set the hot pressing temperature at 170 °C, the pressure at 18 MPa, and the hot pressing time at 8 min. After hot pressing is completed, take out the mold from the hot press and immediately cool it by water cooling, with the cooling rate controlled at 10 °C / min, thus obtaining the composite flame retardant material.

[0063] Among them, the parameter settings of the twin-screw extruder are as follows: the temperature of the first zone is 155 °C, the temperature of the second zone is 165 °C, the temperature of the third zone is 175 °C, and the temperature of the fourth zone is 175 °C.

[0064] The modified pentaerythritol comes from Preparation Example 3; the acid source-nitrogen source complex comes from Preparation Example 6; Before use, the palygorskite fiber undergoes the following pretreatment steps: Add 80 g of palygorskite fiber and 3.5 g of maleic anhydride to a kneader. Heat up to 150 °C and stir and react at a speed of 60 r / min for 25 min. Cool down to room temperature at a rate of 5 °C / min to obtain pretreated palygorskite fiber.

[0065] Before use, the diatomite undergoes the following pretreatment steps: Immerse 200 g of diatomite in an acid solution, stir and wash at a speed of 200 r / min for 60 min, then wash with deionized water until neutral. Then put the washed diatomite and 16 g of nano-hydroxyapatite into a ball mill, grind at a speed of 200 r / min for 60 min, add it to 1.6 L of polydimethylsiloxane dispersion liquid, stir and impregnate at a speed of 200 r / min for 60 min, centrifuge, wash 3 times with deionized water, and put it into a drying oven to dry to constant weight at 80 °C, thus obtaining pretreated diatomite.

[0066] Among them, the polydimethylsiloxane dispersion liquid includes polydimethylsiloxane, ethanol, and water, and the mass fraction of polydimethylsiloxane is 2%, and the mass fraction of ethanol is 2%; The acid solution comprises hydrochloric acid, cetyltrimethylammonium bromide and water, wherein the mass fraction of hydrochloric acid is 1% and the mass fraction of cetyltrimethylammonium bromide is 0.5%.

[0067] Example 4 The difference between this example and Example 3 lies in that: When adding cerium oxide, the step of adding 60 g of triphenyl borate is further included.

[0068] Before use, the diatomite undergoes the following pretreatment steps: Immerse 200 g of diatomite in the acid solution, stir and wash at a speed of 200 r / min for 30 min, then wash with deionized water until neutral. Then put the washed diatomite and 24 g of nano-hydroxyapatite into a ball mill, grind at a speed of 200 r / min for 90 min, add them into 2.4 L of polydimethylsiloxane dispersion, stir and immerse at a speed of 200 r / min for 90 min, centrifuge, wash 3 times with deionized water, put them into a drying oven, and dry at 80 °C until constant weight to obtain the pretreated diatomite.

[0069] Among them, the polydimethylsiloxane dispersion comprises polydimethylsiloxane, ethanol and water, the mass fraction of polydimethylsiloxane is 4%, and the mass fraction of ethanol is 4%; The acid solution comprises hydrochloric acid, cetyltrimethylammonium bromide and water, the mass fraction of hydrochloric acid is 3%, and the mass fraction of cetyltrimethylammonium bromide is 1.0%.

[0070] Other conditions are the same as those in Example 3.

[0071] Example 5 The difference between this example and Example 4 lies in that: The dosage of triphenyl borate is 80 g; The modified pentaerythritol comes from Preparation Example 1; the acid source-nitrogen source complex comes from Preparation Example 5; Before use, the diatomite undergoes the following pretreatment steps: Immerse 200 g of diatomite in the acid solution, stir and wash at a speed of 200 r / min for 45 min, then wash with deionized water until neutral. Then put the washed diatomite and 20 g of nano-hydroxyapatite into a ball mill, grind at a speed of 200 r / min for 75 min, add them into 2.0 L of polydimethylsiloxane dispersion, stir and immerse at a speed of 200 r / min for 75 min, centrifuge, wash 3 times with deionized water, put them into a drying oven, and dry at 80 °C until constant weight to obtain the pretreated diatomite.

[0072] Among them, the polydimethylsiloxane dispersion liquid includes polydimethylsiloxane, ethanol and water. The mass fraction of polydimethylsiloxane is 3%, and the mass fraction of ethanol is 3%. The acid solution includes hydrochloric acid, cetyltrimethylammonium bromide and water. The mass fraction of hydrochloric acid is 2%, and the mass fraction of cetyltrimethylammonium bromide is 0.7%.

[0073] Others are the same as in Example 4.

[0074] Comparative Example 1 The difference between this comparative example and Example 1 is that: In step S2, an equal mass of pentaerythritol is used to replace the modified pentaerythritol.

[0075] Others are the same as in Example 1.

[0076] Comparative Example 2 The difference between this comparative example and Example 1 is that: The preparation method of the modified pentaerythritol in this example includes the following steps: Add 2 mol of pentaerythritol, 2.2 mol of boric acid, zirconium sulfate and a water-carrying agent into a reaction kettle equipped with a stirrer, a thermometer, a reflux condenser and a water separator, mix evenly, slowly heat up to 130 °C, after reacting for 5 h, heat up to 150 °C, continue to react for 120 min, then cool to room temperature, neutralize with a 5% sodium carbonate solution, adjust the pH value to be close to neutral, filter, wash with deionized water 3 times, put it into a drying oven, and dry to constant weight at 80 °C to obtain the modified pentaerythritol.

[0077] Among them, the water-carrying agent includes cyclohexane and water, the volume ratio of cyclohexane to water is 1:1, and the dosage of the water-carrying agent is 120 mL; The dosage of zirconium sulfate is 2.7 g.

[0078] Others are the same as in Example 1.

[0079] Comparative Example 3 The difference between this comparative example and Example 1 is that: In step S2, the acid source-nitrogen source complex is a mixture of ammonium polyphosphate and melamine phosphate with a mass ratio of 2:1.

[0080] Before use, grind ammonium polyphosphate and melamine phosphate to a particle size ≤ 5 μm respectively.

[0081] Others are the same as in Example 1.

[0082] Comparative Example 4 The difference between this comparative example and Example 1 is that: In step S2, no TPU is added.

[0083] Others are the same as in Example 1.

[0084] Comparative Example 5 This comparative example provides a preparation method of a composite flame retardant material, including the following steps: Add 150 g of EVA, 50 g of HDPE, and 80 g of TPU to a high-speed mixer, heat up to 160 °C, mix for 15 min, then add 50 g of palygorskite fiber and 50 g of diatomite, heat up to 165 °C, mix for 15 min, cool down to 140 °C, add 100 g of modified pentaerythritol, 200 g of acid source-nitrogen source complex, and 10 g of cerium oxide, mix for 15 min, then add 30 g of PE-g-GMA and 10 g of silicone masterbatch, continue to mix for 10 min. Transfer the mixed material to a vacuum degassing device, adjust the vacuum degree to -0.09 MPa, after degassing for 12 min, add the material after vacuum degassing to the hopper of a twin-screw extruder, start the twin-screw extruder, stably control the screw speed at 180 r / min, make the material melt and mix homogeneously in the extruder, then extrude. Put the extruded material into a preheated mold, and put the mold into a hot press. Set the hot press temperature at 165 °C, the pressure at 15 MPa, and the hot press time at 10 min. After hot pressing, take out the mold from the hot press and immediately cool it by water cooling, control the cooling rate at 10 °C / min, and thus obtain the composite flame retardant material.

[0085] Among them, the parameters of the twin-screw extruder are set as follows: the temperature of the first zone is 150 °C, the temperature of the second zone is 160 °C, the temperature of the third zone is 170 °C, and the temperature of the fourth zone is 170 °C.

[0086] The modified pentaerythritol comes from Preparation Example 1; the acid source-nitrogen source complex comes from Preparation Example 4.

[0087] Before use, the palygorskite fiber undergoes the following pretreatment steps: Add 50 g of palygorskite fiber and 2 g of maleic anhydride to a kneader, heat up to 140 °C, stir and react at a speed of 60 r / min for 30 min, and cool to room temperature at a rate of 5 °C / min to obtain pretreated palygorskite fiber.

[0088] Comparative Example 6 This comparative example provides a preparation method of a composite flame retardant material, including the following steps: Add 150 g of EVA, 50 g of HDPE, and 80 g of TPU to a high-speed mixer. Heat up to 160 °C and mix for 15 min. Then add 50 g of palygorskite fiber, 50 g of diatomite, and 10 g of carbon nanotubes. Heat up to 165 °C and mix for 15 min. Cool down to 140 °C, add 100 g of modified pentaerythritol, 200 g of acid source-nitrogen source complex, and 10 g of cerium oxide, and mix for 15 min. Then add 30 g of PE-g-GMA and 10 g of silicone masterbatch, and continue to mix for 10 min. Transfer the mixed material to a vacuum degassing device, adjust the vacuum degree to -0.09 MPa, and after degassing for 12 min, add the material after vacuum degassing to the hopper of a twin-screw extruder. Start the twin-screw extruder, stably control the screw speed at 180 r / min, make the material undergo melt mixing and homogenization in the extruder, and then extrude. Put the extruded material into a preheated mold, and put the mold into a hot press. Set the hot pressing temperature at 165 °C, the pressure at 15 MPa, and the hot pressing time at 10 min. After hot pressing is completed, take the mold out of the hot press and immediately cool it by water cooling, and control the cooling rate at 10 °C / min to obtain the composite flame retardant material.

[0089] Among them, the parameter settings of the twin-screw extruder are as follows: the temperature of the first zone is 150 °C, the temperature of the second zone is 160 °C, the temperature of the third zone is 170 °C, and the temperature of the fourth zone is 170 °C.

[0090] The modified pentaerythritol comes from Preparation Example 1; the acid source-nitrogen source complex comes from Preparation Example 4.

[0091] Performance detection test Conduct performance detections on the composite flame retardant materials prepared in Examples 1 to 5 and Comparative Examples 1 to 6 respectively, and the detection results are shown in Table 1.

[0092] Among them, the tensile strength and elongation at break refer to ASTM D638-2014; the limiting oxygen index (LOI) refers to ASTM D2863-2006; the flame retardant grade test refers to the vertical burning method in UL 94.

[0093] Table 1 Performance detections of the composite flame retardant materials prepared in Examples 1 to 5 and Comparative Examples 1 to 6

[0094] Comprehensively analyze the performance detection data in Table 1: By comprehensively analyzing the performance differences between Example 1 and Comparative Examples 1 to 6, it can be seen that the modified pentaerythritol and the acid source-nitrogen source complex prepared from ammonium polyphosphate, melamine phosphate, ammonium molybdate, and silica sol not only effectively improve the flame retardant performance of the composite flame retardant material, but also improve the problem of poor compatibility with the matrix.

[0095] By adding TPU, carbon nanotubes and pretreating palygorskite with maleic anhydride, not only the balance optimization of tensile strength and elongation at break is achieved, but also the compactness of the condensed-phase carbon layer and the gas-phase free radical capture efficiency are further improved by constructing a cross-scale reinforcement-flame retardant network, and finally the flame retardant properties (LOI and flame retardant grade) are significantly improved.

[0096] Comprehensively analyzing Examples 1 to 3, it can be seen that by pretreating diatomite, its compatibility and dispersibility with the matrix are significantly improved, thereby synergistically improving the tensile strength, elongation at break and flame retardant properties of the composite material.

[0097] Comprehensively analyzing Examples 3 to 5, it can be seen that by adding triphenyl borate, although the elongation at break of the flame retardant material is reduced to a certain extent, the flame retardant properties of the material are significantly improved.

[0098] This specific embodiment is only an interpretation of the present application, and it does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A composite flame retardant material, characterized in that: The composite flame retardant material is made of the following raw materials: 15-20 parts by weight of ethylene-vinyl acetate copolymer, 5-10 parts by weight of high-density polyethylene, 8-10 parts by weight of thermoplastic polyurethane elastomer, 5-10 parts by weight of palygorskite fiber, 5-10 parts by weight of diatomaceous earth, 1-3 parts by weight of carbon nanotubes, 10-15 parts by weight of modified pentaerythritol, 20-30 parts by weight of acid source-nitrogen source complex, 1-2 parts by weight of cerium oxide, 3-5 parts by weight of polyethylene grafted glycidyl methacrylate, and 1-2 parts by weight of silicone masterbatch; The palygorskite fiber is pretreated with maleic anhydride before use; The modified pentaerythritol is prepared using pentaerythritol, boric acid, a catalyst, allyl alcohol and a water-carrying agent as raw materials; The acid source-nitrogen source composite is prepared by taking ammonium polyphosphate, melamine phosphate, ammonium molybdate and silica sol as raw materials.

2. The composite flame retardant material according to claim 1, characterized in that: Before the palygorskite fiber is used, the specific steps of pre-treating it with maleic anhydride are as follows: The palygorskite fiber and maleic anhydride were added into an internal mixer, heated to 140-160° C., reacted for 20-30 min, and cooled to obtain pretreated palygorskite fiber.

3. The composite flame retardant material according to claim 1, characterized in that: The preparation method of modified pentaerythritol comprises the following steps: Mix pentaerythritol, boric acid, catalyst and water-carrying agent evenly, heat to 120-140°C, react for 4-6 hours, add allyl alcohol, adjust the temperature to 140-160°C, continue to react for 90-150 minutes, cool, neutralize, separate solid from liquid, wash and dry to obtain; The molar ratio of pentaerythritol, boric acid and allyl alcohol is 1:(1-1.2):(0.08-0.12).

4. The composite flame retardant material according to claim 1, characterized in that: The method for preparing the acid source-nitrogen source complex comprises the following steps: After ammonium polyphosphate and melamine phosphate are ground and mixed evenly, they are dispersed in ethanol, ammonium molybdate is added and mixed evenly, and then silica sol is added, ultrasonically mixed, and spray-dried to obtain; The mass ratio of the ammonium polyphosphate and melamine phosphate is (2-3):1; the mass ratio of the total mass of the ammonium polyphosphate and melamine phosphate to the mass of the silica sol is 1:(4-6); The inlet temperature of the spray drying is 140-160°C, and the outlet temperature is 60-80°C.

5. The composite flame retardant material according to claim 4, characterized in that: The amount of ammonium molybdate used is 1% to 3% of the total mass of ammonium polyphosphate and melamine phosphate.

6. The composite flame retardant material according to claim 4, characterized in that: The silica sol undergoes the following pretreatment steps before use: The silica sol and the silane coupling agent are mixed evenly, and the pH is adjusted to 5-6 to obtain the pretreated silica sol; In the pretreated silica sol, the amount of silane coupling agent used is 0.5% to 1.5% of the mass of the silica sol.

7. The composite flame retardant material according to claim 1, characterized in that: The diatomaceous earth is subjected to the following pretreatment steps before use: The diatomite is acid-washed and washed, mixed and ground with nano-hydroxyapatite, added into a polydimethylsiloxane dispersion, mixed evenly, separated into solid and liquid, washed, and dried to obtain; The mass ratio of the diatomaceous earth to the nano-hydroxyapatite is 10:(0.8-1.2); the mass fraction of the polydimethylsiloxane dispersion is 2%-4%.

8. The composite flame retardant material according to claim 1, characterized in that: The composite flame retardant material also includes 6 to 8 parts of triphenyl borate.

9. A method for preparing the composite flame retardant material according to any one of claims 1 to 8, characterized in that: The steps include: Add ethylene-vinyl acetate copolymer, high-density polyethylene and thermoplastic polyurethane elastomer into a high-speed mixer, heat up to 160-170°C, mix for 15-20 minutes, add gypsum fiber, diatomaceous earth and carbon nanotubes, heat up to 165-175°C, mix for 15-20 minutes, cool down to 140-160°C, add modified pentaerythritol, acid source-nitrogen source complex and cerium oxide, mix for 15-20 minutes, then add the remaining polyethylene grafted glycidyl methacrylate and silicone masterbatch, mix for 10-15 minutes, vacuum degassing, homogenization treatment, hot pressing, cooling and shaping to obtain the product.

10. The method for preparing the composite flame retardant material according to claim 9, characterized in that: When adding cerium oxide, the process further comprises the step of adding triphenylborate.

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