Low-temperature-resistant and anti-cracking flame-retardant polyethylene composite material and preparation method thereof

Abstract

The application belongs to the technical field of composite materials, and particularly relates to a low-temperature-resistant and anti-cracking flame-retardant polyethylene composite material and a preparation method thereof. The polyethylene composite material provided by the application comprises polyethylene resin, organic flame retardant, core-shell structure modified inorganic flame retardant, toughening agent, crosslinking agent, antioxidant and lubricant. The application adopts melamine, phenyl phosphoric dichloride and p-hydroxyphenyl boronic acid as monomers to synthesize macromolecular flame retardant through polycondensation reaction, so as to effectively improve the flame-retardant property of the composite material; a layer of flexible polymer shell is in-situ wrapped on the surface of nano aluminum hydroxide particles to form a core-shell structure, so as to effectively improve the low-temperature toughness and anti-cracking property of the composite material.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a low-temperature resistant, crack-resistant, flame-retardant polyethylene composite material and its preparation method. Background Technology

[0002] Polyethylene, as a core variety of general-purpose polymer materials, has advantages such as light weight, chemical corrosion resistance, excellent electrical insulation and low processing cost. It is mainly used in cable sheathing, pipes, building waterproofing, outdoor protection and other fields.

[0003] Polyethylene is a semi-crystalline polymer. At low temperatures, the mobility of its molecular chains decreases significantly, leading to stress concentration at the interface between crystalline and amorphous regions. This causes rapid microcrack propagation, resulting in typical brittle fracture. Furthermore, traditional polyethylene materials exhibit poor resistance to environmental stress cracking. Under mechanical stress, chemical media, or aging, slow crack growth easily occurs, ultimately causing premature material failure. To improve low-temperature toughness, traditional methods typically involve the large-scale introduction of elastomers (crack-resistant agents / cold-resistant agents). However, elastomers are inherently flammable hydrocarbons. Their addition not only dilutes the effective concentration of flame retardants but also increases the overall calorific value of the material, resulting in a situation where "toughening reduces flame retardancy." This makes it difficult to achieve both optimal low-temperature toughness and V-0 flame retardancy standards.

[0004] Furthermore, to achieve excellent flame retardant properties in polyethylene, the addition of inorganic flame retardants often needs to reach 50wt%-60wt% or more. However, a large number of rigid inorganic particles will severely disrupt the continuous phase structure of the polyethylene matrix, leading to significant embrittlement of the material. At low temperatures, the movement of polymer chain segments is frozen (glass transition effect), and this "high-filling embrittlement" phenomenon is amplified, making it extremely prone to low-temperature stress cracking. Inorganic flame retardants have a highly polar surface, while polyethylene is non-polar. Even after conventional silane coupling agent modification, at extremely high filler levels, the powder is highly susceptible to secondary agglomeration. Under the alternating stress of low-temperature thermal expansion and contraction, the microscopic interface between the inorganic agglomerates and the organic matrix will debond, forming extremely small voids and crack sources, ultimately leading to macroscopic brittle fracture.

[0005] Chinese patent application CN109135004A discloses a cold-resistant, crack-resistant, halogen-free, flame-retardant sheath material, comprising 20-50 parts of polyethylene, 10-45 parts of ethylene-vinyl acetate copolymer, 10-30 parts of halogen-free polyolefin grafted with organic acid anhydride containing double bonds, 20-50 parts of hydrated metal oxide, 5-20 parts of modified 9-hexadecene-1-ol-butadiene copolymer, 0.2-2 parts of antioxidant, 1-5 parts of lubricant, and 1-5 parts of pigment. However, the application mainly relies on ethylene-vinyl acetate copolymer and modified 9-hexadecene-1-ol-butadiene copolymer for toughening and cold resistance. In ultra-low temperature environments, the material undergoes a significant brittle-tough transition, and the low-temperature impact strength decreases significantly. Long-term low-temperature service can easily lead to brittle cracking, which cannot meet the requirements for long-term use in extremely cold regions. At the same time, the scheme uses hydrated metal oxides as the main flame retardant system. The flame retardant efficiency of a single inorganic flame retardant is low, and a high filling amount is required to achieve the basic flame retardant level. This results in a limited improvement in the limiting oxygen index of the material, making it difficult to meet the high flame retardant requirements. Summary of the Invention

[0006] In order to solve the technical problems of large amounts of inorganic flame retardant added, which affect the low-temperature toughness and poor crack resistance of the material in the above-mentioned prior art, the purpose of this invention is to provide a low-temperature resistant, crack-resistant, flame-retardant polyethylene composite material and its preparation method.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material, comprising the following components in parts by weight: 60-80 parts of polyethylene resin, 25-35 parts of organic flame retardant, 10-20 parts of core-shell structure modified inorganic flame retardant, 8-13 parts of toughening agent, 1-3 parts of crosslinking agent, 1-3 parts of antioxidant, and 1.5-2 parts of lubricant; The preparation method of the organic flame retardant is as follows: melamine and triethylamine are added to anhydrous tetrahydrofuran. Under the protection of an ice-water bath and an inert gas, a tetrahydrofuran solution of phenylphosphodichloro is added. The mixture is heated to 60-70℃ and refluxed for 6-8 hours. After cooling to room temperature, p-hydroxyphenylboronic acid and 4-dimethylaminopyridine are added. The mixture is heated to 70-80℃ and stirred for 10-12 hours. The mixture is filtered, and the filtrate is concentrated by rotary evaporation under reduced pressure. The filtrate is added to an aqueous ethanol solution to precipitate the solid precipitate. The solid precipitate is collected and dried under vacuum to obtain the organic flame retardant.

[0008] In the above scheme, organic flame retardants are used instead of inorganic flame retardants, effectively avoiding the embrittlement of composite materials caused by excessive inorganic flame retardant addition. Simultaneously, the inorganic flame retardant undergoes core-shell structure modification to improve the toughness of the composite material at low temperatures. Specifically, the organic flame retardant uses melamine, phenylphosphoryl dichloro, and p-hydroxyphenylboronic acid as monomers, synthesized through a condensation reaction into a macromolecular flame retardant containing boron, nitrogen, and phosphorus. Phosphorus promotes rapid dehydration of the polymer matrix to form a dense, continuous char layer; melamine decomposes upon heating, releasing large amounts of inert gases such as nitrogen and ammonia, diluting combustible gases and isolating oxygen; boron participates in the formation of a glassy inorganic barrier layer, further strengthening the char layer and inhibiting the spread of molten droplets and flames, effectively improving the flame retardant performance of the composite material. Furthermore, the organic flame retardant has good compatibility with polyethylene resin, and its molecules contain aromatic rings and polar groups, which can moderately toughen the composite material and delay crack propagation, significantly improving its low-temperature resistance and crack resistance.

[0009] Furthermore, in the preparation method of the organic flame retardant, the molar ratio of melamine, triethylamine and phenylphosphine dichloride is 1:(0.3-0.5):(2.5-3); the concentration of the tetrahydrofuran solution of phenylphosphine dichloride is 0.5-1.0 mol / L; and the molar ratio of phenylphosphine dichloride, p-hydroxyphenylboronic acid and 4-dimethylaminopyridine is (2.5-3):(1.2-1.5):(0.1-0.3).

[0010] Furthermore, the preparation method of the core-shell structure modified inorganic flame retardant is as follows: nano-aluminum hydroxide is immersed in acid solution, stirred and reacted at 80-90℃ for 1-3h, filtered, the filter cake is washed with deionized water until neutral, dried, ground and added to a high-speed mixer, a reactive silane coupling agent containing nitrogen and phosphorus functional groups is sprayed in, high-speed mixing is carried out for 20-30min, maleic anhydride grafted polyolefin elastomer is added, the temperature is raised to 120-130℃, kneaded for 1-2h, cooled, and the core-shell structure modified inorganic flame retardant is obtained.

[0011] In the above scheme, acid is first used to increase the number of hydroxyl groups on the surface of nano-aluminum hydroxide. Then, a reactive silane coupling agent containing nitrogen and phosphorus functional groups is used to perform preliminary surface modification of the inorganic powder. Finally, maleic anhydride-grafted polyolefin elastomer is added, causing a mild ring-opening esterification reaction between the maleic anhydride groups and the active functional groups on the surface of the silane coupling agent. This results in an in-situ coating of a flexible polymer shell on the surface of the nano-aluminum hydroxide particles, forming a core-shell structure. This flexible shell acts as a stress buffer layer on a macroscopic level. When the material is subjected to impact at extremely low temperatures, this flexible layer can generate local shear yield and absorb a large amount of impact energy, effectively blocking the stress concentration effect and preventing the initiation of microcracks at the rigid particle interface. Furthermore, the phosphorus-nitrogen-containing silane coupling agent selected in this invention not only serves to connect the inorganic and organic phases, but is also a highly efficient intumescent flame retardant catalyst. By encapsulating maleic anhydride-grafted polyolefin elastomer on the surface of inorganic particles containing phosphorus and nitrogen elements, a highly concentrated "micro flame retardant reactor" is constructed. During combustion, the phosphorus and nitrogen elements at the interface cause the attached elastomer shell to rapidly dehydrate and char, forming a dense, continuous char layer that encapsulates nano-aluminum hydroxide, thereby significantly reducing the heat released by the elastomer during combustion. This design allows a very small amount of elastomer to achieve excellent toughening effects without increasing the overall combustion heat load.

[0012] Furthermore, in the preparation method of the core-shell structure modified inorganic flame retardant, the solid-liquid ratio of nano-aluminum hydroxide to acid is 1:(20-30), the acid is composed of nitric acid and hydrochloric acid in a molar ratio of 3:1, and the concentration of the acid is 0.2-0.5 mol / L.

[0013] Furthermore, the preparation method of the reactive silane coupling agent containing nitrogen and phosphorus functional groups in the preparation method of the core-shell structure modified inorganic flame retardant is as follows: under nitrogen protection, 100-120 parts of N-aminoethyl-3-aminopropyltriethoxysilane and 80-90 parts of anhydrous ethanol are mixed, 60-70 parts of diethyl phosphite are added, the temperature is raised to 60-70℃, the mixture is stirred and reacted for 4-6 hours, and then distilled under reduced pressure to obtain the reactive silane coupling agent containing nitrogen and phosphorus functional groups.

[0014] In the above scheme, N-aminoethyl-3-aminopropyltriethoxysilane serves as a silane precursor. Its molecule simultaneously contains a triethoxysilane group that can react with the hydroxyl groups of inorganic fillers, a primary amino group that can bond with diethyl phosphite to introduce phosphorus and nitrogen flame retardant units, and an active amino site that can form a covalent bond with maleic anhydride-grafted polyolefin elastomer. Under mild conditions, it reacts with diethyl phosphite to generate a reactive silane coupling agent containing nitrogen and phosphorus functional groups. This not only forms a stable core-shell structure on the surface of the inorganic flame retardant but also achieves chemical bridging between the filler and the matrix.

[0015] Furthermore, in the preparation method of the core-shell structure modified inorganic flame retardant, the amount of the reactive silane coupling agent containing nitrogen and phosphorus functional groups is 5%-8% of the mass of nano-aluminum hydroxide; and the amount of the maleic anhydride grafted polyolefin elastomer is 3%-7% of the mass of nano-aluminum hydroxide.

[0016] Furthermore, the toughening agent is composed of ethylene-vinyl acetate copolymer and maleic anhydride-grafted POE in a mass ratio of (3-5):(1-2).

[0017] In the above scheme, the toughening agent composed of ethylene-vinyl acetate copolymer and maleic anhydride grafted POE can significantly reduce the embrittlement temperature of the composite material and improve its low-temperature resistance. At the same time, the toughening agent forms an elastic dispersed phase in the polyethylene matrix, which disperses stress concentration, prevents microcrack propagation, and improves the material's crack resistance.

[0018] Furthermore, the crosslinking agent is one of dicumyl peroxide, triallyl cyanurate, and triallyl isocyanurate.

[0019] In the above scheme, the crosslinking agent can bond the polyethylene molecular chains together, inhibiting crack growth. The crosslinked structure is not prone to molecular slippage at low temperatures, ensuring high strength and toughness at low temperatures and avoiding low-temperature brittle fracture. At the same time, the crosslinked network structure can maintain the material shape, reduce melt dripping, and assist the flame retardant in improving flame retardant performance.

[0020] Furthermore, the antioxidant is one of antioxidant 1010, antioxidant 1076, antioxidant 168 and antioxidant 1330; the lubricant is polyethylene wax.

[0021] This invention also provides a method for preparing the aforementioned low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material, comprising the following steps: S1: Add polyethylene resin, organic flame retardant, core-shell modified inorganic flame retardant, toughening agent, crosslinking agent, antioxidant and lubricant into a high-speed mixer and mix at 60-80℃ for 5-10 minutes to obtain a mixture; S2: Add the mixture obtained in step S1 into a twin-screw extruder for melt extrusion. The processing temperature of the twin screw is as follows: conveying section 120-130℃, melting section 140-150℃, mixing section 150-155℃, venting section 160-170℃, homogenizing section 170-175℃, die head 165-170℃, and main machine speed 200-300rpm, to obtain strip material. S3: The strip material obtained in step S2 is water-cooled, stretched, and granulated to obtain a low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material.

[0022] The above-mentioned scheme employs a process of mixing followed by extrusion granulation, which eliminates the need for specialized equipment and complex high-temperature, high-pressure devices. This process is short, energy-efficient, and conducive to industrial production. In the dry mixing step, the organic flame retardant and core-shell inorganic flame retardant are uniformly dispersed under shear force, reducing agglomeration and stress concentration points, significantly improving the composite material's resistance to environmental stress cracking. In the melt extrusion stage, the crosslinking agent slowly initiates mild crosslinking, achieving a uniform three-dimensional network structure, thus enhancing the composite material's creep resistance and crack resistance.

[0023] Compared with existing technologies, the low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material and its preparation method provided by this invention have the following technical advantages: (1) This invention solves the technical problem of poor low-temperature toughness and crack resistance of polymer materials through the optimized design of components, and has better processing performance and excellent flame retardancy. (2) The present invention uses melamine, phenylphosphodichloro and p-hydroxyphenylboronic acid as monomers to synthesize macromolecular flame retardants through polycondensation reaction, which effectively improves the flame retardant performance of composite materials; (3) The present invention encapsulates a flexible polymer shell on the surface of nano-aluminum hydroxide particles in situ to form a core-shell structure, which effectively improves the low-temperature toughness and crack resistance of the composite material. Detailed Implementation

[0024] The following will provide further details with reference to specific embodiments. Those skilled in the art can make various modifications based on the basic principles of this invention, but as long as they do not depart from the basic principles of this invention, they are all within the scope of this invention. The raw materials used in this specific embodiment are all commercially available products.

[0025] Preparation Example 1 The preparation method of the organic flame retardant is as follows: In a three-necked flask equipped with a condenser and a mechanical stirrer, 500 mL of anhydrous tetrahydrofuran is added as a solvent, along with 1 mol of melamine and 0.3 mol of triethylamine. Under the protection of nitrogen in an ice-water bath at 0°C, a tetrahydrofuran solution of phenylphosphine dichloride with a concentration of 0.5 mol / L (the amount of phenylphosphine dichloride used is 2.5 mol) is added. The mixture is slowly heated to 60°C and refluxed for 6 hours, resulting in a dehydrochlorination polycondensation reaction to generate a hyperbranched polyphosphoramide intermediate with abundant terminal chlorine groups. The reaction system is then cooled to room temperature, and 1.2 mol of p-hydroxyphenylboronic acid and 0.1 mol of... 4-Dimethylaminopyridine was heated to 70°C and stirred for 10 hours to carry out an esterification and end-capping reaction. During this process, the phenolic hydroxyl group on p-hydroxyphenylboronic acid reacted with the P-Cl bond of the polyphosphoramide intermediate, and boron was covalently grafted onto the periphery of the hyperbranched macromolecule. After the reaction, the generated triethylamine hydrochloride byproduct precipitate was removed by filtration. The filtrate was concentrated by rotary evaporation under reduced pressure and added to a large amount of 75% (w / w) aqueous ethanol solution to precipitate. The solid precipitate was collected and dried under vacuum at 80°C for 24 hours to obtain the organic flame retardant.

[0026] Preparation Example 2 The preparation method of the organic flame retardant is as follows: In a three-necked flask equipped with a condenser and a mechanical stirrer, 500 mL of anhydrous tetrahydrofuran is added as a solvent, along with 1 mol of melamine and 0.5 mol of triethylamine. Under the protection of nitrogen and an ice-water bath at 5°C, a tetrahydrofuran solution of 1.0 mol / L phenylphosphine dichloride (3 mol of phenylphosphine dichloride) is added. The mixture is slowly heated to 70°C and refluxed for 8 hours, resulting in a dehydrochlorination polycondensation reaction to generate a hyperbranched polyphosphamide intermediate with abundant terminal chlorine groups. The reaction system is then cooled to room temperature, and 1.5 mol of p-hydroxyphenylboronic acid and 0.3 mol of triethylamine are added. 4-Dimethylaminopyridine was heated to 80℃ and stirred for 12 h to carry out an esterification and end-capping reaction. During this process, the phenolic hydroxyl group on p-hydroxyphenylboronic acid reacted with the P-Cl bond of the polyphosphoramide intermediate, and boron was covalently grafted onto the periphery of the hyperbranched macromolecule. After the reaction, the generated triethylamine hydrochloride byproduct precipitate was removed by filtration. The filtrate was concentrated by rotary evaporation under reduced pressure and added to a large amount of 75% (w / w) aqueous ethanol solution to precipitate. The solid precipitate was collected and vacuum dried at 80℃ for 24 h to obtain the organic flame retardant.

[0027] Preparation Example 3 The preparation method of the organic flame retardant is as follows: In a three-necked flask equipped with a condenser and a mechanical stirrer, 500 mL of anhydrous tetrahydrofuran was added as a solvent, along with 1 mol of melamine and 0.42 mol of triethylamine. Under the protection of nitrogen and an ice-water bath at 3°C, a tetrahydrofuran solution of phenylphosphine dichloride with a concentration of 0.8 mol / L (the amount of phenylphosphine dichloride used was 2.7 mol) was added. The mixture was slowly heated to 68°C and refluxed for 7.5 h, resulting in a dehydrochlorination polycondensation reaction to generate a hyperbranched polyphosphoramide intermediate with abundant terminal chlorine groups. The reaction system was then cooled to room temperature, and 1.4 mol of p-hydroxyphenylboronic acid and 0.2 mol of... 4-Dimethylaminopyridine was heated to 78°C and stirred for 11 hours to carry out an esterification and end-capping reaction. During this process, the phenolic hydroxyl group on p-hydroxyphenylboronic acid reacted with the P-Cl bond of the polyphosphoramide intermediate, and boron was covalently grafted onto the periphery of the hyperbranched macromolecule. After the reaction, the precipitate of triethylamine hydrochloride byproduct was removed by filtration. The filtrate was concentrated by rotary evaporation under reduced pressure and added to a large amount of 75% (w / w) aqueous ethanol solution to precipitate. The solid precipitate was collected and dried under vacuum at 80°C for 24 hours to obtain an organic flame retardant.

[0028] Preparation Example 4 The preparation method of the organic flame retardant is as follows: In a three-necked flask equipped with a condenser and a mechanical stirrer, 500 mL of anhydrous tetrahydrofuran is added as a solvent, along with 1 mol of melamine and 0.4 mol of triethylamine. Under the protection of nitrogen and an ice-water bath at 4 °C, a tetrahydrofuran solution of phenylphosphine dichloride with a concentration of 0.7 mol / L (the amount of phenylphosphine dichloride used is 2.8 mol) is added. The mixture is slowly heated to 65 °C and refluxed for 7 h, resulting in a dehydrochlorination polycondensation reaction to generate a hyperbranched polyphosphamide intermediate with abundant terminal chlorine groups. The reaction system is then cooled to room temperature, and 1.4 mol of p-hydroxyphenylboronic acid and 0.2 mol of triethylamine are added. 4-Dimethylaminopyridine was heated to 75°C and stirred for 11 hours to carry out an esterification and end-capping reaction. During this process, the phenolic hydroxyl group on p-hydroxyphenylboronic acid reacted with the P-Cl bond of the polyphosphoramide intermediate, and boron was covalently grafted onto the periphery of the hyperbranched macromolecule. After the reaction, the precipitate of triethylamine hydrochloride byproduct was removed by filtration. The filtrate was concentrated by rotary evaporation under reduced pressure and added to a large amount of 75% (w / w) aqueous ethanol solution to precipitate. The solid precipitate was collected and dried under vacuum at 80°C for 24 hours to obtain an organic flame retardant.

[0029] Preparation Example 5 The preparation method of the reactive silane coupling agent containing nitrogen and phosphorus functional groups is as follows: under nitrogen protection, 100g of N-aminoethyl-3-aminopropyltriethoxysilane and 80g of anhydrous ethanol are mixed, 60g of diethyl phosphite is added, the temperature is raised to 60℃, the reaction is stirred for 4h, and the reaction is carried out by vacuum distillation to obtain the reactive silane coupling agent containing nitrogen and phosphorus functional groups.

[0030] The preparation method of core-shell structure modified inorganic flame retardant is as follows: 100g of nano aluminum hydroxide is immersed in an acid solution with a concentration of 0.2mol / L (nitric acid and hydrochloric acid are composed in a molar ratio of 3:1) at a solid-liquid ratio of 1:20. The mixture is stirred at 80℃ for 1h, filtered, and the filter cake is washed with deionized water until neutral. It is then dried at 80℃, ground, and added to a high-speed mixer. 5g of reactive silane coupling agent containing nitrogen and phosphorus functional groups is sprayed in while stirring at 1200rpm. The mixture is mixed at high speed for 20min. 3g of maleic anhydride-grafted polyolefin elastomer is added, and the temperature is raised to 120℃ and mixed for 1h. During this process, the maleic anhydride groups in the toughening agent undergo a mild ring-opening esterification reaction with the active functional groups on the surface of the silane coupling agent, forming a flexible polymer shell in situ on the surface of the nano aluminum hydroxide. After cooling, the core-shell structure modified inorganic flame retardant is obtained.

[0031] Preparation Example 6 The preparation method of the reactive silane coupling agent containing nitrogen and phosphorus functional groups is as follows: under nitrogen protection, 120g of N-aminoethyl-3-aminopropyltriethoxysilane and 90g of anhydrous ethanol are mixed, 70g of diethyl phosphite is added, the temperature is raised to 70℃, the reaction is stirred for 6h, and the reactive silane coupling agent containing nitrogen and phosphorus functional groups is obtained by vacuum distillation.

[0032] The preparation method of the core-shell structure modified inorganic flame retardant is as follows: 100g of nano aluminum hydroxide is immersed in an acid solution with a concentration of 0.5mol / L (nitric acid and hydrochloric acid are composed in a molar ratio of 3:1) at a solid-liquid ratio of 1:30. The mixture is stirred at 90℃ for 3h, filtered, and the filter cake is washed with deionized water until neutral. It is then dried at 90℃, ground, and added to a high-speed mixer. 8g of a reactive silane coupling agent containing nitrogen and phosphorus functional groups is sprayed in while stirring at 1200rpm. The mixture is mixed at high speed for 30min. 7g of maleic anhydride-grafted polyolefin elastomer is added, and the temperature is raised to 130℃ and mixed for 2h. During this process, the maleic anhydride groups in the toughening agent undergo a mild ring-opening esterification reaction with the active functional groups on the surface of the silane coupling agent, forming a flexible polymer shell in situ on the surface of the nano aluminum hydroxide. After cooling, the core-shell structure modified inorganic flame retardant is obtained.

[0033] Preparation Example 7 The preparation method of the reactive silane coupling agent containing nitrogen and phosphorus functional groups is as follows: under nitrogen protection, 116g of N-aminoethyl-3-aminopropyltriethoxysilane and 87g of anhydrous ethanol are mixed, 66g of diethyl phosphite is added, the temperature is raised to 65℃, the reaction is stirred for 5.2h, and the reaction is carried out by vacuum distillation to obtain the reactive silane coupling agent containing nitrogen and phosphorus functional groups.

[0034] The preparation method of the core-shell structure modified inorganic flame retardant is as follows: 100g of nano-aluminum hydroxide is immersed in an acid solution with a concentration of 0.4mol / L (nitric acid and hydrochloric acid are composed in a molar ratio of 3:1) at a solid-liquid ratio of 1:24. The mixture is stirred at 88℃ for 2.2h, filtered, and the filter cake is washed with deionized water until neutral. It is then dried at 85℃, ground, and added to a high-speed mixer. 7.5g of a reactive silane coupling agent containing nitrogen and phosphorus functional groups is sprayed in while stirring at 1200rpm. The mixture is mixed at high speed for 25min. 6g of maleic anhydride-grafted polyolefin elastomer is added, and the temperature is raised to 126℃. The mixture is then kneaded for 1.6h. During this process, the maleic anhydride groups in the toughening agent undergo a mild ring-opening esterification reaction with the active functional groups on the surface of the silane coupling agent, forming a flexible polymer shell in situ on the surface of the nano-aluminum hydroxide. After cooling, the core-shell structure modified inorganic flame retardant is obtained.

[0035] Preparation Example 8 The preparation method of the reactive silane coupling agent containing nitrogen and phosphorus functional groups is as follows: under nitrogen protection, 110g of N-aminoethyl-3-aminopropyltriethoxysilane and 85g of anhydrous ethanol are mixed, 65g of diethyl phosphite is added, the temperature is raised to 65℃, the reaction is stirred for 5h, and the reaction is carried out under reduced pressure to obtain the reactive silane coupling agent containing nitrogen and phosphorus functional groups.

[0036] The preparation method of the core-shell structure modified inorganic flame retardant is as follows: 100g of nano-aluminum hydroxide is immersed in an acid solution with a concentration of 0.4mol / L (nitric acid and hydrochloric acid are composed in a molar ratio of 3:1) at a solid-liquid ratio of 1:25. The mixture is stirred at 85℃ for 2h, filtered, and the filter cake is washed with deionized water until neutral. It is then dried at 85℃, ground, and added to a high-speed mixer. 7g of a reactive silane coupling agent containing nitrogen and phosphorus functional groups is sprayed in while stirring at 1200rpm. The mixture is mixed at high speed for 25min. 6g of maleic anhydride-grafted polyolefin elastomer is added, and the temperature is raised to 125℃ and mixed for 1.5h. During this process, the maleic anhydride groups in the toughening agent undergo a mild ring-opening esterification reaction with the active functional groups on the surface of the silane coupling agent, forming a flexible polymer shell in situ on the surface of the nano-aluminum hydroxide. After cooling, the core-shell structure modified inorganic flame retardant is obtained.

[0037] Example 1 A method for preparing a low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material includes the following steps: S1: 60g of polyethylene resin, 25g of organic flame retardant, 20g of core-shell modified inorganic flame retardant, 8g of toughening agent, 1g of dicumyl peroxide, 1g of antioxidant 1010 and 1.5g of polyethylene wax were added to a high-speed mixer and mixed at 60°C for 5 minutes to obtain a mixture; the organic flame retardant was prepared by Preparation Example 1, and the core-shell modified inorganic flame retardant was prepared by Preparation Example 5; the toughening agent was composed of ethylene-vinyl acetate copolymer and maleic anhydride grafted POE in a mass ratio of 3:1; S2: Add the mixture obtained in step S1 into a twin-screw extruder for melt extrusion. The processing temperature of the twin screw is: conveying section 120℃, melting section 140℃, mixing section 150℃, venting section 160℃, homogenizing section 170℃, die head 165℃, and main machine speed 200rpm to obtain strip material. S3: The strip material obtained in step S2 is water-cooled, stretched, and granulated to obtain a low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material.

[0038] Example 2 A method for preparing a low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material includes the following steps: S1: 80g of polyethylene resin, 35g of organic flame retardant, 10g of core-shell modified inorganic flame retardant, 13g of toughening agent, 3g of triallyl cyanurate, 3g of antioxidant 1076 and 2g of polyethylene wax were added to a high-speed mixer and mixed at 80°C for 10 minutes to obtain a mixture; the organic flame retardant was prepared by Preparation Example 2, and the core-shell modified inorganic flame retardant was prepared by Preparation Example 6; the toughening agent was composed of ethylene-vinyl acetate copolymer and maleic anhydride grafted POE in a mass ratio of 5:2; S2: Add the mixture obtained in step S1 into a twin-screw extruder for melt extrusion. The processing temperature of the twin screw is as follows: conveying section 130℃, melting section 150℃, mixing section 155℃, venting section 170℃, homogenizing section 175℃, die head 170℃, and main machine speed 300rpm to obtain strip material. S3: The strip material obtained in step S2 is water-cooled, stretched, and granulated to obtain a low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material.

[0039] Example 3 A method for preparing a low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material includes the following steps: S1: 72g of polyethylene resin, 29g of organic flame retardant, 16g of core-shell modified inorganic flame retardant, 9g of toughening agent, 2g of triallyl isocyanurate, 2g of antioxidant 168 and 1.8g of polyethylene wax were added to a high-speed mixer and mixed at 70°C for 8 minutes to obtain a mixture; the organic flame retardant was prepared by Preparation Example 3, and the core-shell modified inorganic flame retardant was prepared by Preparation Example 7; the toughening agent was composed of ethylene-vinyl acetate copolymer and maleic anhydride grafted polyolefin elastomer in a mass ratio of 4:1; S2: Add the mixture obtained in step S1 into a twin-screw extruder for melt extrusion. The processing temperature of the twin screw is as follows: conveying section 125℃, melting section 145℃, mixing section 153℃, venting section 165℃, homogenizing section 172℃, die head 168℃, and main machine speed 250rpm to obtain strip material. S3: The strip material obtained in step S2 is water-cooled, stretched, and granulated to obtain a low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material.

[0040] Example 4 A method for preparing a low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material includes the following steps: S1: 70g of polyethylene resin, 30g of organic flame retardant, 15g of core-shell modified inorganic flame retardant, 10g of toughening agent, 2g of triallyl isocyanurate, 2g of antioxidant 1330 and 1.8g of polyethylene wax were added to a high-speed mixer and mixed at 70°C for 8 minutes to obtain a mixture; the organic flame retardant was prepared by Preparation Example 4, and the core-shell modified inorganic flame retardant was prepared by Preparation Example 8; the toughening agent was composed of ethylene-vinyl acetate copolymer and maleic anhydride grafted POE in a mass ratio of 5:1; S2: Add the mixture obtained in step S1 into a twin-screw extruder for melt extrusion. The processing temperature of the twin screw is as follows: conveying section 125℃, melting section 145℃, mixing section 153℃, venting section 165℃, homogenizing section 172℃, die head 168℃, and main machine speed 250rpm to obtain strip material. S3: The strip material obtained in step S2 is water-cooled, stretched, and granulated to obtain a low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material.

[0041] Comparative Example 1 The preparation method of the polyethylene composite material described in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that a core-shell structure modified inorganic flame retardant is used instead of an organic flame retardant in this comparative example.

[0042] Comparative Example 2 The preparation method of the polyethylene composite material described in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that an organic flame retardant is used instead of a core-shell structure modified inorganic flame retardant in this comparative example.

[0043] Comparative Example 3 The preparation method of the polyethylene composite material described in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that pentaerythritol phosphate is used instead of organic flame retardant in this comparative example.

[0044] Comparative Example 4 The preparation method of the polyethylene composite material described in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that p-hydroxyphenylboronic acid was not added in the preparation method of the organic flame retardant in this comparative example.

[0045] Comparative Example 5 The preparation method of the polyethylene composite material described in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that nano-aluminum hydroxide is used in this comparative example instead of the core-shell structure modified inorganic flame retardant.

[0046] Test case Limiting oxygen index test: The polyethylene composite materials prepared in Examples 1-4 and Comparative Examples 1-5 were tested according to GB / T 2406.3-2022, and the average value of the oxygen index of 15 samples in each group was recorded. Mechanical property tests: The tensile strength and elongation at break of the polyethylene composites prepared in Examples 1-4 and Comparative Examples 1-5 were tested according to GB / T 1040.1-2025 at 25℃ and -10℃. Vertical burning test: The polyethylene composite materials prepared in Examples 1-4 and Comparative Examples 1-5 were tested according to GB / T 2408-2021; The experimental results are shown in Table 1.

[0047] Table 1 Performance Test Results

[0048] As shown in Table 1, the limiting oxygen index of the polyethylene composites prepared in Examples 1-4 is 49.6%-52.5%, the tensile strength at room temperature is 48.9-50.8 MPa, and the elongation at break is 131.4%-134.6%. The tensile strength at -10℃ is 46.3-49.5 MPa, and the elongation at break is 128.3%-130.5%. The vertical flammability rating reaches V-0, indicating that the polyethylene composites provided by this invention have good low-temperature toughness and flame retardancy. Among them, the polyethylene composite prepared in Example 3 has the best performance and is the preferred embodiment of this invention.

[0049] Compared to Example 3, Comparative Example 1 used a core-shell modified inorganic flame retardant instead of an organic flame retardant, and Comparative Example 2 used an organic flame retardant instead of a core-shell modified inorganic flame retardant. However, the limiting oxygen index decreased, and the vertical burning rating increased, indicating that the organic flame retardant and the core-shell modified inorganic flame retardant in this invention have a synergistic flame retardant effect. Comparative Example 3 used pentaerythritol phosphate instead of an organic flame retardant, but the limiting oxygen index decreased, the vertical burning rating increased, and the low-temperature performance deteriorated. This indicates that the organic flame retardant used in this invention can not only improve the flame retardant performance of polyethylene composite materials. Furthermore, it can simultaneously improve the low-temperature performance of polyethylene composites; in Comparative Example 4, the organic flame retardant preparation method did not include p-hydroxyphenylboronic acid, but the limiting oxygen index decreased, indicating that boron in the organic flame retardant can participate in the formation of a glassy inorganic barrier layer, further improving the flame retardant performance of the composite material; in Comparative Example 5, nano-aluminum hydroxide was used to replace the core-shell structure modified inorganic flame retardant, but the performance at room temperature and low temperature deteriorated, indicating that coating the surface of nano-aluminum hydroxide with a flexible polymer layer can act as a stress buffer layer in the material, effectively improving the mechanical properties of polyethylene composites at low temperatures.

[0050] The above embodiments are merely examples of the present invention and are not intended to limit the invention. All equivalent modifications or alterations made by those skilled in the art without departing from the spirit and concept of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A low-temperature resistant, crack-resistant, flame-retardant polyethylene composite material, characterized in that, The components include the following parts by weight: 60-80 parts of polyethylene resin, 25-35 parts of organic flame retardant, 10-20 parts of core-shell structure modified inorganic flame retardant, 8-13 parts of toughening agent, 1-3 parts of crosslinking agent, 1-3 parts of antioxidant, and 1.5-2 parts of lubricant; The preparation method of the organic flame retardant is as follows: melamine and triethylamine are added to anhydrous tetrahydrofuran. Under the protection of an ice-water bath and an inert gas, a tetrahydrofuran solution of phenylphosphodichloro is added. The mixture is heated to 60-70℃ and refluxed for 6-8 hours. After cooling to room temperature, p-hydroxyphenylboronic acid and 4-dimethylaminopyridine are added. The mixture is heated to 70-80℃ and stirred for 10-12 hours. The mixture is filtered, and the filtrate is concentrated by rotary evaporation under reduced pressure. The filtrate is added to an aqueous ethanol solution to precipitate the solid precipitate. The solid precipitate is collected and dried under vacuum to obtain the organic flame retardant.

2. The low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material according to claim 1, characterized in that, In the preparation method of the organic flame retardant, the molar ratio of melamine, triethylamine and phenylphosphine dichloride is 1:(0.3-0.5):(2.5-3); the concentration of the tetrahydrofuran solution of phenylphosphine dichloride is 0.5-1.0 mol / L; and the molar ratio of phenylphosphine dichloride, p-hydroxyphenylboronic acid and 4-dimethylaminopyridine is (2.5-3):(1.2-1.5):(0.1-0.3).

3. The low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material according to claim 1, characterized in that, The preparation method of the core-shell structure modified inorganic flame retardant is as follows: nano-aluminum hydroxide is immersed in acid solution, stirred and reacted at 80-90℃ for 1-3h, filtered, the filter cake is washed with deionized water until neutral, dried, ground and added to a high-speed mixer, a reactive silane coupling agent containing nitrogen and phosphorus functional groups is sprayed in, high-speed mixing is carried out for 20-30min, maleic anhydride grafted polyolefin elastomer is added, the temperature is raised to 120-130℃, kneaded for 1-2h, cooled, and the core-shell structure modified inorganic flame retardant is obtained.

4. The low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material according to claim 3, characterized in that, The solid-liquid ratio of the nano-aluminum hydroxide to the acid solution is 1:(20-30), the acid solution is composed of nitric acid and hydrochloric acid in a molar ratio of 3:1, and the concentration of the acid solution is 0.2-0.5 mol / L.

5. The low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material according to claim 3, characterized in that, The preparation method of the nitrogen- and phosphorus-functionalized reactive silane coupling agent is as follows: under nitrogen protection, 100-120 parts of N-aminoethyl-3-aminopropyltriethoxysilane and 80-90 parts of anhydrous ethanol are mixed, 60-70 parts of diethyl phosphite are added, the temperature is raised to 60-70℃, the mixture is stirred and reacted for 4-6 hours, and then distilled under reduced pressure to obtain the nitrogen- and phosphorus-functionalized reactive silane coupling agent.

6. The low-temperature resistant, crack-resistant, flame-retardant polyethylene composite material according to claim 3, characterized in that, The amount of the reactive silane coupling agent containing nitrogen and phosphorus functional groups is 5%-8% of the mass of nano-aluminum hydroxide; the amount of the maleic anhydride-grafted polyolefin elastomer is 3%-7% of the mass of nano-aluminum hydroxide.

7. The low-temperature resistant, crack-resistant, flame-retardant polyethylene composite material according to claim 1, characterized in that, The toughening agent is composed of ethylene-vinyl acetate copolymer and maleic anhydride-grafted POE in a mass ratio of (3-5):(1-2).

8. The low-temperature resistant, crack-resistant, flame-retardant polyethylene composite material according to claim 1, characterized in that, The crosslinking agent is one of dicumyl peroxide, triallyl cyanurate, and triallyl isocyanurate.

9. The low-temperature resistant, crack-resistant, flame-retardant polyethylene composite material according to claim 1, characterized in that, The antioxidant is one of antioxidant 1010, antioxidant 1076, antioxidant 168 and antioxidant 1330; the lubricant is polyethylene wax.

10. A method for preparing a low-temperature resistant, crack-resistant, flame-retardant polyethylene composite material according to any one of claims 1-9, characterized in that, Includes the following steps: S1: Add polyethylene resin, organic flame retardant, core-shell modified inorganic flame retardant, toughening agent, crosslinking agent, antioxidant and lubricant into a high-speed mixer and mix at 60-80℃ for 5-10 minutes to obtain a mixture; S2: Add the mixture obtained in step S1 into a twin-screw extruder for melt extrusion. The processing temperature of the twin screw is as follows: conveying section 120-130℃, melting section 140-150℃, mixing section 150-155℃, venting section 160-170℃, homogenizing section 170-175℃, die head 165-170℃, and main machine speed 200-300rpm, to obtain strip material. S3: The strip material obtained in step S2 is water-cooled, stretched, and granulated to obtain a low-temperature resistant, crack-resistant, and flame-retardant polyethylene composite material.

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