Environment-friendly flame-retardant composite material for cable and preparation method thereof

Abstract

The invention provides an environment-friendly flame-retardant composite material for a cable and a preparation method of the environment-friendly flame-retardant composite material. The composite material is prepared from the following raw materials in parts by weight: 30 to 40 parts of an ethylene-1-octene copolymer, 25 to 35 parts of linear low-density polyethylene, 18 to 25 parts of phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres, 3 to 6 parts of metal coordination type halloysite hybrid carbon nanotubes, 5 to 8 parts of a reactive compatibilizer, 0.8 to 1.2 parts of a cross-linking agent, 0.5 to 1.0 part of an assistant cross-linking agent, 0.4 to 0.8 part of an antioxidant and 0.5 to 1.0 part of a lubricant. The flame retardance, char forming, heat conduction and smoke suppression performance of the composite material can be improved, the interfacial compatibility, the processing fluidity and the heat resistance are optimized, the thermal oxidation stability and the molten drop resistance are enhanced, and the comprehensive performance is excellent.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials for cables, specifically to an environmentally friendly flame-retardant composite material for cables and its preparation method. Background Technology

[0002] Polyvinyl chloride (PVC) has long been a common insulation and sheathing material for wires and cables due to its ease of processing and moderate cost. However, it easily releases toxic and corrosive gases such as hydrogen halides when burned, resulting in significant limitations in environmental protection and safety. Cross-linked polyethylene (XLPE) insulated power cables, with their excellent electrical insulation, heat resistance, and mechanical properties, have gradually become the mainstream choice for medium and high voltage power transmission. However, conventional XLPE materials lack sufficient flame retardancy, charring properties, and smoke suppression capabilities, making it difficult to meet the safety requirements of stringent flame-retardant applications.

[0003] Currently, the application of halogen-free flame-retardant polyolefin composite materials in the cable field still has obvious shortcomings. Most systems cannot simultaneously achieve both flexibility and structural strength, have low flame-retardant char formation efficiency, release a large amount of smoke during combustion, and have poor interfacial bonding between inorganic flame-retardant fillers and organic matrix, which easily leads to a decrease in the material's heat resistance deformation, thermo-oxidative stability and processing performance, making it impossible to fully meet the needs of high-performance environmentally friendly flame-retardant cable preparation and use. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides an environmentally friendly flame-retardant composite material for cables and its preparation method.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention discloses an environmentally friendly flame-retardant composite material for cables. By weight, the raw materials for its preparation include: 30-40 parts of ethylene-1-octene copolymer, 25-35 parts of linear low-density polyethylene, 18-25 parts of phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres, 3-6 parts of metal-coordinated halloysite hybrid carbon nanotubes, 5-8 parts of reactive compatibilizer, 0.8-1.2 parts of crosslinking agent, 0.5-1.0 parts of co-crosslinking agent, 0.4-0.8 parts of antioxidant, and 0.5-1.0 parts of lubricant.

[0006] Preferably, the reactive compatibilizer is an ethylene-alkyl acrylate-glycidyl methacrylate terpolymer; the crosslinking agent is dicumyl peroxide; and the co-crosslinking agent is triallyl cyanurate.

[0007] Preferably, the antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.5; the lubricant is modified ethylene bis-stearamide.

[0008] Preferably, the preparation method of the phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres includes the following steps: 1) Mix tetraethyl orthosilicate and aluminum isopropoxide at a molar ratio of 1:(0.25-0.35), add an equimolar amount of acetylacetone to the aluminum isopropoxide for chelation, and then add anhydrous ethanol to prepare a solution with a mass concentration of 18%-22%. Adjust the pH to 3.0-4.0 by adding 0.1mol / L dilute hydrochloric acid dropwise at 1-3mL / min at 30-40℃, and hydrolyze and activate for 1-2h to obtain a silica-alumina composite sol. 2) Under nitrogen protection, hexachlorocyclotriphosphazene was dissolved in anhydrous tetrahydrofuran, cooled to 0-5°C in an ice bath, and stirred at 150-200 r / min. A tetrahydrofuran solution containing p-phenylenediamine was added dropwise at 0.5-2 mL / min, with a molar ratio of hexachlorocyclotriphosphazene to p-phenylenediamine of 1:(2.5-3.5). After the addition was complete, the temperature was raised to 50-60°C, and the reaction was continued for 5-7 h to obtain an amino-terminated cyclotriphosphazene prepolymer solution. 3) Add the amino-terminated cyclotriphosphazene prepolymer solution to the silica-alumina composite sol, add melamine, and the molar ratio of melamine to hexachlorocyclotriphosphazene is (0.5-1.5):1. Transfer to a hydrothermal reactor at 80-90℃ and react for 10-14 hours. 4) The reactants were centrifuged at 6000–8000 r / min. The precipitate was washed three times each with anhydrous ethanol and deionized water. It was then vacuum dried to constant weight at 70–90℃ and a vacuum degree of -0.08–-0.1 MPa. Subsequently, it was heat-treated at 280–320℃ under a nitrogen atmosphere for 1.5–2.5 h, and then pulverized by an air jet mill, controlling the output particle size D. 50 The size was 3-5 μm, and phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres were obtained.

[0009] Preferably, the preparation method of the metal-coordinated halloysite hybrid carbon nanotubes includes the following steps: (1) Add halloysite nanotubes to anhydrous ethanol and disperse them for 20 to 40 min under ultrasonic power of 200 to 300 W and frequency of 20 to 40 kHz. Add γ-aminopropyltriethoxysilane at 14% to 16% of the mass of halloysite nanotubes and reflux at 55 to 65 °C for 7 to 9 h. After the reaction is completed, centrifuge at 6000 to 8000 r / min. Wash the precipitate three times with deionized water and then vacuum dry it at 70 to 90 °C and vacuum degree of -0.08 to -0.1 MPa to obtain aminated halloysite nanotubes. (2) Add multi-walled carbon nanotubes to a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, reflux at 65-75°C for 4-6 hours, cool and dilute with deionized water, filter and wash until neutral, and vacuum dry at 70-90°C to obtain carboxylated multi-walled carbon nanotubes. (3) Carboxylated multi-walled carbon nanotubes were added to deionized water and dispersed for 20 to 40 minutes under ultrasonic power of 200 to 300 W and frequency of 20 to 40 kHz. 8% to 12% of zinc nitrate hexahydrate by mass was added. After ultrasonic coordination, an amino-coated halloysite nanotube aqueous dispersion was added and ultrasonication was continued for 20 to 40 minutes. The mixture was then freeze-dried for 44 to 52 hours under conditions of -55 to -45 °C and vacuum degree <10 Pa to obtain metal-coordinated halloysite hybrid carbon nanotubes.

[0010] This invention also discloses a method for preparing an environmentally friendly flame-retardant composite material for cables, comprising the following steps: S1. Ethylene-1-octene copolymer and linear low-density polyethylene are dried in a forced-air drying oven at 55-65°C for 3-5 hours to obtain pretreated matrix resin. S2. Add the pretreated matrix resin and reactive compatibilizer to a mixer and mix for 2-4 minutes at 110-120°C and rotor speed of 35-55 r / min. Then add phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres and metal-coordinated halloysite hybrid carbon nanotubes and continue mixing at 110-120°C for 4-8 minutes to obtain the compound. S3. The compounded rubber material is transferred into a twin-screw extruder with a length-to-diameter ratio of L / D=40:1. Crosslinking agent and co-crosslinking agent are added by side feeding, along with composite antioxidant and lubricant. After extrusion, cooling and pelletizing, environmentally friendly flame-retardant composite material pellets for cables are obtained.

[0011] Preferably, in step S3, the temperatures of each section of the twin-screw extruder are: zone 1 105-110℃, zone 2 110-115℃, zone 3 110-115℃, zone 4 108-113℃, and die head 110-115℃, with a screw speed of 70-130 r / min; the crosslinking agent and co-crosslinking agent are added after the melting section and before the homogenization section of the extruder.

[0012] Preferably, the ethylene-1-octene copolymer has an octene unit content of 18–25 wt%, a melt index of 0.5–3.0 g / 10 min at 190 °C / 2.16 kg, and a weight-average molecular weight of 8 × 10⁻⁶. 4 ~12×10 4 g / mol; the linear low-density polyethylene has a melt index of 1.0~2.5g / 10min at 190℃ / 2.16kg and a weight-average molecular weight of 7×10. 4 ~10×10 4 g / mol.

[0013] The beneficial effects of this invention are as follows: Ethylene-1-octene copolymer blended with linear low-density polyethylene as the matrix resin enables the composite material to achieve both good flexibility and mechanical strength; phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres can improve the flame retardancy and char formation properties of the composite material; metal-coordinated halloysite hybrid carbon nanotubes can improve the thermal conductivity of the composite material, enhance the structural strength of the material, and significantly reduce smoke release during combustion; reactive compatibilizers can improve the interfacial compatibility between inorganic fillers and organic matrix; crosslinking agents and co-crosslinking agents can improve the heat deformation resistance, thermo-oxidative stability, and anti-dripping properties of the composite material; antioxidants can improve the long-term thermo-oxidative aging performance of the composite material; lubricants can improve the processing fluidity and filler dispersibility of the composite material, and improve the surface finish and processing stability of the product.

[0014] The preparation method of phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres allows tetraethyl orthosilicate and aluminum isopropoxide to form a uniform silicon-aluminum composite sol, providing an inorganic framework for the hybrid microspheres. The amino-terminated cyclotriphosphazene prepolymer generated by the reaction of hexachlorocyclotriphosphazene and p-phenylenediamine can react with the silicon-aluminum composite sol and melamine to form an organic-inorganic hybrid network structure. After centrifugation, washing, drying, heat treatment and pulverization, phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres with uniform particle size can be obtained. These microspheres can integrate the effects of phosphorus, nitrogen, silicon and aluminum, improving their flame retardant and char-forming properties in environmentally friendly flame-retardant composite materials for cables.

[0015] The preparation method of metal-coordinated halloysite hybrid carbon nanotubes involves modifying halloysite nanotubes with γ-aminopropyltriethoxysilane to obtain aminated halloysite nanotubes, and oxidizing multi-walled carbon nanotubes with mixed acids to obtain carboxylated multi-walled carbon nanotubes. After the carboxylated multi-walled carbon nanotubes undergo a coordination reaction with zinc nitrate hexahydrate, they can combine with the aminated halloysite nanotubes through interaction. After drying, metal-coordinated halloysite hybrid carbon nanotubes are obtained. This hybrid carbon nanotube allows the multi-walled carbon nanotubes, halloysite nanotubes, and zinc ions to work synergistically, improving their dispersibility in environmentally friendly flame-retardant composite materials for cables, while also providing thermal conductivity, smoke suppression, and reinforcing effects. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The specific information on the raw materials used in the embodiments of the present invention is shown in Table 1.

[0018] Table 1 Components Specification source Ethylene-1-octene copolymer <![CDATA[The content of octene chain units is 18-25 wt%, the melt index (190 °C / 2.16 kg) is 0.5-3.0 g / 10 min, and the weight-average molecular weight is 8×10 4 ~12×10 4 g / mol]]> Dongguan Gangsutong Plastics Co., Ltd. Linear low-density polyethylene <![CDATA[The density is 0.912 to 0.918 g / cm 3 , and the melt index is 1.0 to 2.0 g / 10 min]]> Dongguan Jinshixiang Plastic Raw Materials Co., Ltd. Tetraethyl orthosilicate Purity 99.5%, CAS: 78-10-4 Shandong Yukang Chemical Co., Ltd. Aluminum isopropoxide Purity 99.5%, CAS: 555-31-7 Fuchen (Tianjin) Chemical Reagent Co., Ltd. Acetylacetone 99% purity, CAS: 123-54-6 Hubei Chengfeng Chemical Co., Ltd. Hexachlorocyclotriphosphazene 99% purity, CAS: 940-71-6 (Alpha) Zhengzhou Alpha Chemical Co., Ltd. Anhydrous tetrahydrofuran Purity 99.9%, CAS: 109-99-9 Shandong Xinheng Chemical Co., Ltd. p-phenylenediamine 99% purity, CAS: 106-50-3 Bailingwei Technology melamine Purity 99.5%, CAS: 108-78-1 Shandong Xinheng Chemical Co., Ltd. Halloysite nanotubes Purity 99%, inner diameter 10-30nm, outer diameter 40-70nm Guangdong Jina New Materials Technology Co., Ltd. γ-aminopropyltriethoxysilane Purity 98%, CAS: 919-30-2 Wuhan Xinyang Ruihe Chemical Technology Co., Ltd. Zinc nitrate hexahydrate 99.9% purity Shanghai Baishun Biotechnology Co., Ltd. Ethylene-alkyl acrylate-glycidyl methacrylate terpolymer / Arkema's PC / terpolymer blends, such as LotaderTMAX8900 dicumyl peroxide 99% purity Hubei Chengfeng Chemical Co., Ltd. Triallyl cyanurate Purity 98%, CAS: 101-37-1 Wuhan Kemike Biomedical Technology Co., Ltd. Antioxidant 1010 99% purity BASF (China) Co., Ltd. Antioxidant 168 99% purity BASF (China) Co., Ltd. Modified ethylene bis-stearamide 99% purity, CAS: 106663-84-7 Guangzhou Ouying Chemical Co., Ltd.

[0019] Example 1: This embodiment discloses an environmentally friendly flame-retardant composite material for cables. By weight, its preparation raw materials include: 30 parts of ethylene-1-octene copolymer, 25 parts of linear low-density polyethylene, 18 parts of phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres, 3 parts of metal-coordinated halloysite hybrid carbon nanotubes, 5 parts of reactive compatibilizer, 0.8 parts of crosslinking agent, 0.5 parts of co-crosslinking agent, 0.4 parts of antioxidant, and 0.5 parts of lubricant. The octene unit content of the ethylene-1-octene copolymer is 18 wt%, the melt index at 190℃ / 2.16 kg is 0.5 g / 10 min, and the weight-average molecular weight is 8 × 10⁻⁶. 4 g / mol; the melt index of linear low-density polyethylene at 190℃ / 2.16kg is 1.0g / 10min, and the weight-average molecular weight is 7×10⁻⁶ g / mol. 4 g / mol.

[0020] The reactive compatibilizer is a terpolymer of ethylene-alkyl acrylate-glycidyl methacrylate; the crosslinking agent is dicumyl peroxide; and the co-crosslinking agent is triallyl cyanurate. The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.5; and the lubricant is modified ethylene bis-stearamide.

[0021] The preparation method of phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres includes the following steps: 1) Tetraethyl orthosilicate and aluminum isopropoxide were mixed at a molar ratio of 1:0.25. An equimolar amount of acetylacetone was added to the aluminum isopropoxide for chelation. Then, anhydrous ethanol was added to prepare a solution with a mass concentration of 18%. The pH was adjusted to 3.0 by adding 0.1 mol / L dilute hydrochloric acid dropwise at 1 mL / min at 30 °C. After hydrolysis and activation for 1 h, a silica-alumina composite sol was obtained. 2) Under nitrogen protection, hexachlorocyclotriphosphazene was dissolved in anhydrous tetrahydrofuran, cooled to 0°C in an ice bath, and stirred at 150 r / min. A tetrahydrofuran solution containing p-phenylenediamine was added dropwise at 0.5 mL / min, with a molar ratio of hexachlorocyclotriphosphazene to p-phenylenediamine of 1:2.5. After the addition was complete, the temperature was raised to 50°C and the reaction was continued for 5 h to obtain an amino-terminated cyclotriphosphazene prepolymer solution. 3) Add the amino-terminated cyclotriphosphazene prepolymer solution to the silica-alumina composite sol, add melamine, the molar ratio of melamine to hexachlorocyclotriphosphazene is 0.5:1, and transfer to a hydrothermal reactor at 80℃ to react for 10h; 4) The reactants were centrifuged at 6000 r / min. The precipitate was washed three times each with anhydrous ethanol and deionized water. It was then vacuum dried to constant weight at 70℃ and -0.08 MPa. Subsequently, it was heat-treated at 280℃ under a nitrogen atmosphere for 1.5 h, and then pulverized by an air jet mill to control the output particle size D. 50With a particle size of 3 μm, phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres were obtained.

[0022] The preparation method of metal-coordinated halloysite hybrid carbon nanotubes includes the following steps: (1) Add halloysite nanotubes to anhydrous ethanol and disperse for 20 min under ultrasonic power of 200 W and frequency of 20 kHz. Add γ-aminopropyltriethoxysilane at 14% of the mass of halloysite nanotubes and reflux at 55 °C for 7 h. After the reaction is completed, centrifuge at 6000 r / min. Wash the precipitate three times with deionized water and then vacuum dry at 70 °C and vacuum degree of -0.08 MPa to obtain aminated halloysite nanotubes. (2) Add multi-walled carbon nanotubes to a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, reflux at 65°C for 4 hours, cool and dilute with deionized water, filter and wash until neutral, and vacuum dry at 70°C to obtain carboxylated multi-walled carbon nanotubes. (3) Carboxylated multi-walled carbon nanotubes were added to deionized water and dispersed for 20 min under ultrasonic power of 200 W and frequency of 20 kHz. 8% of zinc nitrate hexahydrate by mass was added, and after ultrasonic coordination, aminated halloysite nanotube aqueous dispersion was added. Ultrasonication was continued for 20 min, and then freeze-dried for 44 h under -55℃ and vacuum degree <10 Pa to obtain metal-coordinated halloysite hybrid carbon nanotubes.

[0023] This embodiment also discloses a method for preparing an environmentally friendly flame-retardant composite material for cables, comprising the following steps: S1. Ethylene-1-octene copolymer and linear low-density polyethylene are dried in a forced-air drying oven at 55°C for 3 hours to obtain pretreated matrix resin. S2. Add the pretreated matrix resin and reactive compatibilizer to a mixer and mix for 2 minutes at 110°C and 35 r / min rotor speed. Then add phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres and metal-coordinated halloysite hybrid carbon nanotubes and continue mixing at 110°C for 4 minutes to obtain the compound. S3. Transfer the compounded rubber compound into a twin-screw extruder with a length-to-diameter ratio (L / D) of 40:1. In step S3, the temperatures of each section of the twin-screw extruder are: Zone 1 105℃, Zone 2 110℃, Zone 3 110℃, Zone 4 108℃, and the die head 110℃. The screw speed is 70 r / min. Add crosslinking agent and co-crosslinking agent (added after the melting section and before the homogenization section) through side feeding. At the same time, add composite antioxidant and lubricant. After extrusion, cooling, and pelletizing, obtain environmentally friendly flame-retardant composite material pellets for cables.

[0024] Example 2: This embodiment discloses an environmentally friendly flame-retardant composite material for cables. By weight, its preparation raw materials include: 40 parts of ethylene-1-octene copolymer, 35 parts of linear low-density polyethylene, 25 parts of phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres, 6 parts of metal-coordinated halloysite hybrid carbon nanotubes, 8 parts of reactive compatibilizer, 1.2 parts of crosslinking agent, 1 part of co-crosslinking agent, 0.8 parts of antioxidant, and 1 part of lubricant. The octene unit content of the ethylene-1-octene copolymer is 25 wt%, the melt index at 190℃ / 2.16 kg is 3.0 g / 10 min, and the weight-average molecular weight is 12 × 10⁻⁶. 4 g / mol; the melt index of linear low-density polyethylene at 190℃ / 2.16kg is 2.5g / 10min, and the weight-average molecular weight is 10×10⁻⁶ g / mol. 4 g / mol.

[0025] The reactive compatibilizer is a terpolymer of ethylene-alkyl acrylate-glycidyl methacrylate; the crosslinking agent is dicumyl peroxide; and the co-crosslinking agent is triallyl cyanurate. The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.5; and the lubricant is modified ethylene bis-stearamide.

[0026] The preparation method of phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres includes the following steps: 1) Tetraethyl orthosilicate and aluminum isopropoxide were mixed at a molar ratio of 1:0.35. An equimolar amount of acetylacetone was added to the aluminum isopropoxide for chelation. Then, anhydrous ethanol was added to prepare a solution with a mass concentration of 22%. The pH was adjusted to 4.0 by adding 0.1 mol / L dilute hydrochloric acid dropwise at 3 mL / min at 40 °C. After hydrolysis and activation for 2 h, a silica-alumina composite sol was obtained. 2) Under nitrogen protection, hexachlorocyclotriphosphazene was dissolved in anhydrous tetrahydrofuran, cooled to 5°C in an ice bath, and stirred at 200 r / min. A tetrahydrofuran solution containing p-phenylenediamine was added dropwise at 2 mL / min, with a molar ratio of hexachlorocyclotriphosphazene to p-phenylenediamine of 1:3.5. After the addition was complete, the temperature was raised to 60°C and the reaction was continued for 7 h to obtain an amino-terminated cyclotriphosphazene prepolymer solution. 3) Add the amino-terminated cyclotriphosphazene prepolymer solution to the silica-alumina composite sol, add melamine, the molar ratio of melamine to hexachlorocyclotriphosphazene is 1.5:1, and transfer to a hydrothermal reactor at 90℃ to react for 14h; 4) The reactants were centrifuged at 8000 r / min. The precipitate was washed three times each with anhydrous ethanol and deionized water. It was then vacuum dried to constant weight at 90℃ and -0.1 MPa. Subsequently, it was heat-treated at 320℃ under a nitrogen atmosphere for 2.5 h, and then pulverized by an air jet mill to control the output particle size D. 50 With a particle size of 5 μm, phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres were obtained.

[0027] The preparation method of metal-coordinated halloysite hybrid carbon nanotubes includes the following steps: (1) Add halloysite nanotubes to anhydrous ethanol and disperse for 40 min under ultrasonic power of 300 W and frequency of 40 kHz. Add γ-aminopropyltriethoxysilane at 16% of the mass of halloysite nanotubes and reflux at 65 °C for 9 h. After the reaction is completed, centrifuge at 8000 r / min. Wash the precipitate three times with deionized water and then vacuum dry at 90 °C and vacuum degree of -0.1 MPa to obtain aminated halloysite nanotubes. (2) Add multi-walled carbon nanotubes to a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, reflux at 75°C for 6 hours, cool and dilute with deionized water, filter and wash until neutral, and dry under vacuum at 90°C to obtain carboxylated multi-walled carbon nanotubes. (3) Carboxylated multi-walled carbon nanotubes were added to deionized water and dispersed for 40 min under ultrasonic power of 300 W and frequency of 40 kHz. 12% of zinc nitrate hexahydrate by mass was added. After ultrasonic coordination, an amino halloysite nanotube aqueous dispersion was added and ultrasonication was continued for 40 min. The mixture was then freeze-dried for 52 h under conditions of -45 ℃ and vacuum degree <10 Pa to obtain metal-coordinated halloysite hybrid carbon nanotubes.

[0028] This embodiment also discloses a method for preparing an environmentally friendly flame-retardant composite material for cables, comprising the following steps: S1. Ethylene-1-octene copolymer and linear low-density polyethylene are dried in a forced-air drying oven at 65°C for 5 hours to obtain pretreated matrix resin. S2. Add the pretreated matrix resin and reactive compatibilizer to a mixer and mix for 4 minutes at 120°C and 55 r / min rotor speed. Then add phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres and metal-coordinated halloysite hybrid carbon nanotubes and continue mixing at 120°C for 8 minutes to obtain the compound. S3. Transfer the compounded rubber compound into a twin-screw extruder with a length-to-diameter ratio (L / D) of 40:1. In step S3, the temperatures of each section of the twin-screw extruder are: Zone 1 110℃, Zone 2 115℃, Zone 3 115℃, Zone 4 113℃, and Die Head 115℃. The screw speed is 130 r / min. Add crosslinking agent and co-crosslinking agent (added after the melting section and before the homogenization section) through side feeding. At the same time, add composite antioxidant and lubricant. After extrusion, cooling, and pelletizing, obtain environmentally friendly flame-retardant composite material pellets for cables.

[0029] Example 3: This embodiment discloses an environmentally friendly flame-retardant composite material for cables. By weight, its preparation raw materials include: 35 parts of ethylene-1-octene copolymer, 30 parts of linear low-density polyethylene, 21 parts of phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres, 5 parts of metal-coordinated halloysite hybrid carbon nanotubes, 7 parts of reactive compatibilizer, 1 part of crosslinking agent, 0.7 parts of co-crosslinking agent, 0.6 parts of antioxidant, and 0.7 parts of lubricant. The octene unit content of the ethylene-1-octene copolymer is 21 wt%, the melt index at 190℃ / 2.16 kg is 1.8 g / 10 min, and the weight-average molecular weight is 10 × 10⁻⁶. 4 g / mol; the melt index of linear low-density polyethylene at 190℃ / 2.16kg is 1.8g / 10min, and the weight-average molecular weight is 9×10⁻⁶ g / mol. 4 g / mol.

[0030] The reactive compatibilizer is a terpolymer of ethylene-alkyl acrylate-glycidyl methacrylate; the crosslinking agent is dicumyl peroxide; and the co-crosslinking agent is triallyl cyanurate. The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.5; and the lubricant is modified ethylene bis-stearamide.

[0031] The preparation method of phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres includes the following steps: 1) Tetraethyl orthosilicate and aluminum isopropoxide were mixed at a molar ratio of 1:0.3. An equimolar amount of acetylacetone was added to the aluminum isopropoxide for chelation. Then, anhydrous ethanol was added to prepare a solution with a mass concentration of 20%. The pH was adjusted to 3.5 by adding 0.1 mol / L dilute hydrochloric acid dropwise at 2 mL / min at 35 °C. After hydrolysis and activation for 1.5 h, a silica-alumina composite sol was obtained. 2) Under nitrogen protection, hexachlorocyclotriphosphazene was dissolved in anhydrous tetrahydrofuran, cooled to 2°C in an ice bath, and stirred at 175 r / min. A tetrahydrofuran solution containing p-phenylenediamine was added dropwise at 1.2 mL / min, with a molar ratio of hexachlorocyclotriphosphazene to p-phenylenediamine of 1:3. After the addition was complete, the temperature was raised to 55°C and the reaction was continued for 6 h to obtain an amino-terminated cyclotriphosphazene prepolymer solution. 3) Add the amino-terminated cyclotriphosphazene prepolymer solution to the silica-alumina composite sol, add melamine, with a molar ratio of melamine to hexachlorocyclotriphosphazene of 1:1, and transfer to a hydrothermal reactor at 85°C to react for 12 hours. 4) The reactants were centrifuged at 7000 r / min. The precipitate was washed three times each with anhydrous ethanol and deionized water. It was then vacuum dried to constant weight at 80℃ and -0.09 MPa. Subsequently, it was heat-treated at 300℃ under a nitrogen atmosphere for 2 h, and then pulverized by an air jet mill to control the output particle size D. 50 With a diameter of 4 μm, phosphorus, nitrogen, silicon, and aluminum quaternary synergistic hybrid microspheres were obtained.

[0032] The preparation method of metal-coordinated halloysite hybrid carbon nanotubes includes the following steps: (1) Add halloysite nanotubes to anhydrous ethanol and disperse for 30 min under ultrasonic power of 250 W and frequency of 30 kHz. Add γ-aminopropyltriethoxysilane at 15% of the mass of halloysite nanotubes and reflux at 60 °C for 8 h. After the reaction is completed, centrifuge at 7000 r / min. Wash the precipitate three times with deionized water and then vacuum dry at 80 °C and vacuum degree of -0.09 MPa to obtain aminated halloysite nanotubes. (2) Add multi-walled carbon nanotubes to a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, reflux at 70°C for 5 hours, cool and dilute with deionized water, filter and wash until neutral, and vacuum dry at 80°C to obtain carboxylated multi-walled carbon nanotubes. (3) Carboxylated multi-walled carbon nanotubes were added to deionized water and dispersed for 30 min under ultrasonic power of 250 W and frequency of 30 kHz. 10% of zinc nitrate hexahydrate by mass was added. After ultrasonic coordination, an amino-coated halloysite nanotube aqueous dispersion was added and ultrasonication was continued for 30 min. The mixture was then freeze-dried for 48 h under conditions of -50 °C and vacuum degree <10 Pa to obtain metal-coordinated halloysite hybrid carbon nanotubes.

[0033] This embodiment also discloses a method for preparing an environmentally friendly flame-retardant composite material for cables, comprising the following steps: S1. Ethylene-1-octene copolymer and linear low-density polyethylene were dried in a forced-air drying oven at 60°C for 4 hours to obtain pretreated matrix resin. S2. Add the pretreated matrix resin and reactive compatibilizer to a mixer and mix for 3 minutes at 115°C and a rotor speed of 42 r / min. Then add phosphorus, nitrogen, silicon and aluminum quaternary synergistic hybrid microspheres and metal-coordinated halloysite hybrid carbon nanotubes and continue mixing at 115°C for 6 minutes to obtain the compound. S3. Transfer the compounded rubber compound into a twin-screw extruder with a length-to-diameter ratio (L / D) of 40:1. In step S3, the temperatures of each section of the twin-screw extruder are: Zone 1 108℃, Zone 2 112℃, Zone 3 112℃, Zone 4 110℃, and Die Head 112℃. The screw speed is 100 r / min. Add crosslinking agent and co-crosslinking agent (added after the melting section and before the homogenization section) through side feeding. At the same time, add composite antioxidant and lubricant. After extrusion, cooling, and pelletizing, obtain environmentally friendly flame-retardant composite material pellets for cables.

[0034] Comparative Example 1: An environmentally friendly flame-retardant composite material for cables and its preparation method are disclosed. The only difference between this material and Example 3 is that the phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres are not added, and an equal amount of ammonium polyphosphate, melamine, silica, and aluminum hydroxide physical mixture is used instead.

[0035] Comparative Example 2: An environmentally friendly flame-retardant composite material for cables and its preparation method are disclosed. The only difference between this material and Example 3 is that metal-coordinated halloysite hybrid carbon nanotubes are not added, but a physical mixture of equal amounts of multi-walled carbon nanotubes and halloysite nanotubes is used instead.

[0036] Comparative Example 3: An environmentally friendly flame-retardant composite material for cables and its preparation method are disclosed. The only difference between this material and Example 3 is that the ethylene-alkyl acrylate-glycidyl methacrylate terpolymer is not added, and an equal amount of maleic anhydride-grafted polyethylene is used instead.

[0037] Comparative Example 4: An environmentally friendly flame-retardant composite material for cables and its preparation method are disclosed. The only difference between this material and Example 3 is that aluminum isopropoxide is not added in the preparation of the phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres, and only phosphorus-nitrogen-silicon ternary hybrid microspheres are formed.

[0038] Comparative Example 5: An environmentally friendly flame-retardant composite material for cables and its preparation method are disclosed. The only difference between this material and Example 3 is that zinc ions are not added for coordination in the preparation of metal-coordinated halloysite hybrid carbon nanotubes, and only the electrostatic assembly of carbon nanotubes and halloysite nanotubes is performed.

[0039] Comparative Example 6: An environmentally friendly flame-retardant composite material for cables and its preparation method are disclosed. The only difference between this material and Example 3 is that dicumyl peroxide and triallyl cyanurate are not added, and no cross-linking occurs.

[0040] Comparative Example 7: An environmentally friendly flame-retardant composite material for cables and its preparation method are disclosed. The only difference between this material and Example 3 is that the mixing is done in one step, with all raw materials added and mixed at once.

[0041] Comparative Example 8: An environmentally friendly flame-retardant composite material for cables and its preparation method are disclosed. The only difference between this material and Example 3 is that no antioxidant is added.

[0042] The tensile properties, limiting oxygen index, vertical burning performance, smoke density rating, heat distortion temperature, thermal conductivity, thermal aging performance, and volume resistivity of the composite materials obtained in Examples 1-3 and Comparative Examples 1-8 were tested. The testing methods and standards for each property are as follows: 1. Tensile properties The test was conducted in accordance with GB / T 1040.3-2006, "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", using dumbbell-shaped specimens, a tensile speed of 200 mm / min, and a test temperature of 23℃.

[0043] 2. Limiting Oxygen Index Perform the test according to GB / T 2406.2-2009 "Determination of Oxygen Index of Plastics - Part 2: Room Temperature Test", with a sample size of 80mm×10mm×4mm.

[0044] 3. Vertical combustion performance The test shall be conducted in accordance with GB / T 2408-2008 "Vertical Method for Testing the Burning Performance of Plastics", with a sample thickness of 1.6 mm.

[0045] 4. Smoke density grade The test shall be conducted in accordance with GB / T 8627-2007, "Test Method for Smoke Density of Building Materials in Combustion or Decomposition", using the flaming combustion mode.

[0046] 5. Heat distortion temperature The test was conducted in accordance with GB / T 1634.2-2004, "Non-impact heat distortion temperature of plastics", with a test load of 0.45 MPa for all groups to ensure consistent test conditions.

[0047] 6. Thermal conductivity Perform the test according to ASTM C518, "Determination of Steady-State Thermal Resistance and Related Properties of Insulation Materials by Heat Flow Meter Method", with a sample thickness of 5 mm.

[0048] 7. Thermal aging performance The test shall be conducted in accordance with GB / T 2951.12-2008, "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers", with a thermal aging condition of 135℃×168h, and the retention rate of tensile strength and elongation at break shall be determined.

[0049] Retention rate calculation formula: Performance retention rate (%) = Performance value after aging / Performance value before aging × 100% 8. Volume resistivity Perform the test according to GB / T 1410-2006 "Test Methods for Volume Resistivity and Surface Resistivity of Solid Insulating Materials", with a test voltage of 500V.

[0050] The results are shown in Tables 2 and 3.

[0051] Table 2 Mechanical, thermal and processing properties Group Tensile strength / MPa Elongation at break / % Heat distortion temperature / ℃ Thermal conductivity / (W / m·K) Heat aging strength retention rate / % Elongation retention rate during heat aging / % Example 1 19.2 392 102 0.58 92.5 88.3 Example 2 20.5 405 108 0.64 93.1 89.6 Example 3 21.8 418 115 0.69 94.8 91.2 Comparative Example 1 16.5 302 93 0.52 80.2 68.5 Comparative Example 2 15.8 275 88 0.40 78.5 62.3 Comparative Example 3 14.2 235 86 0.55 75.1 58.6 Comparative Example 4 19.5 382 106 0.64 86.5 78.2 Comparative Example 5 18.6 352 98 0.56 88.3 80.5 Comparative Example 6 13.5 455 68 0.62 72.5 73.8 Comparative Example 7 17.8 315 92 0.58 81.5 70.5 Comparative Example 8 20.2 395 108 0.68 58.2 42.5

[0052] Table 3 Flame retardancy, smoke suppression and electrical properties Group Limiting oxygen index / % UL94 (1.6mm) Smoke Density Rating (SDR) <![CDATA[Volume resistivity / × 10 14 Ω·cm]]> Example 1 34.2 V-0 125 3.2 Example 2 35.5 V-0 112 3.8 Example 3 36.8 V-0 98 4.5 Comparative Example 1 30.5 V-1 195 2.5 Comparative Example 2 32.1 V-1 185 2.8 Comparative Example 3 31.8 V-1 178 2.2 Comparative Example 4 34.5 V-0 145 3.5 Comparative Example 5 34.8 V-0 155 3.6 Comparative Example 6 28.5 V-2 210 2.1 Comparative Example 7 32.5 V-0 168 3.0 Comparative Example 8 35.2 V-0 115 3.9 Using Example 3 as the control group, the performance differences and causes of Comparative Examples 1-8 are analyzed as follows: Comparative Example 1: Using a mixture of ordinary flame retardants, the interfacial bonding was poor and the synergistic effect was weak. The tensile strength decreased from 21.8 MPa to 16.5 MPa, the elongation at break decreased from 418% to 302%, the oxygen index decreased, and the smoke density increased significantly. This proves that the phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres are crucial for efficient flame retardancy.

[0053] Comparative Example 2: Using simple physical mixed nanofillers, a stable thermal conductivity and reinforcing network could not be formed. The thermal conductivity decreased from 0.69 to 0.40 W / m·K, the elongation at break decreased significantly, and the smoke density increased. This indicates that the structural design of metal-coordinated halloysite hybrid carbon nanotubes plays a key role in thermal conductivity, toughness, and smoke suppression.

[0054] Comparative Example 3: Using a common compatibilizer, the interface is only physically bonded, the filler dispersion deteriorates, the elongation at break drops from 418% to 235%, and the thermal aging performance decreases significantly, proving the necessity of reactive compatibilizers to achieve interface strengthening through chemical bonding.

[0055] Comparative Example 4: In the absence of aluminum, the high-temperature ceramicization effect was weakened, the smoke density grade increased from 98 to 145, and the heat aging retention rate decreased, indicating that aluminum is indispensable for improving the stability of the char layer and the smoke suppression effect.

[0056] Comparative Example 5: The lack of zinc ion coordination leads to decreased hybrid structure stability, weakened smoke suppression effect, increased smoke density, and decreased thermal conductivity, demonstrating the core role of zinc ions in structural stability, promoting char formation, and suppressing smoke.

[0057] Comparative Example 6: Without crosslinking, the heat distortion temperature dropped from 115℃ to 68℃, the flammability rating dropped to V-2, and the tensile strength decreased significantly to 13.5MPa. Although Comparative Example 6 was not crosslinked, the trace amounts of free radicals remaining during processing still led to slight branching of the matrix, and the inorganic filler was evenly dispersed. The slippage of the matrix molecular chains was not restricted by crosslinking. However, the tensile strength, heat distortion temperature, flame retardancy, and anti-dripping properties of the crosslinked material were significantly improved. The overall performance was more in line with the actual use requirements of cable materials, fully demonstrating the necessity of the crosslinking system.

[0058] Comparative Example 7: One-step mixing leads to a mismatch between crosslinking and interfacial reaction, with the elongation at break decreasing from 418% to 315% and thermal aging performance declining, proving that step-by-step mixing is crucial for the formation of chemical anchoring and uniform crosslinking.

[0059] Comparative Example 8: Without antioxidants, the strength retention rate after heat aging decreased from 94.8% to 58.2%, and the elongation retention rate decreased significantly to 42.5%, indicating that the composite antioxidant system is essential for long-life applications.

[0060] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An environmentally friendly flame-retardant composite material for cables, characterized in that, The raw materials for its preparation, by weight, include: 30-40 parts of ethylene-1-octene copolymer, 25-35 parts of linear low-density polyethylene, 18-25 parts of phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres, 3-6 parts of metal-coordinated halloysite hybrid carbon nanotubes, 5-8 parts of reactive compatibilizer, 0.8-1.2 parts of crosslinking agent, 0.5-1.0 parts of co-crosslinking agent, 0.4-0.8 parts of antioxidant, and 0.5-1.0 parts of lubricant.

2. The environmentally friendly flame-retardant composite material for cables according to claim 1, characterized in that, The reactive compatibilizer is an ethylene-alkyl acrylate-glycidyl methacrylate terpolymer; the crosslinking agent is dicumyl peroxide; and the co-crosslinking agent is triallyl cyanurate.

3. The environmentally friendly flame-retardant composite material for cables according to claim 1, characterized in that, The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.5; the lubricant is modified ethylene bis-stearamide.

4. The environmentally friendly flame-retardant composite material for cables according to claim 1, characterized in that, The preparation method of the phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres includes the following steps: 1) Mix tetraethyl orthosilicate and aluminum isopropoxide at a molar ratio of 1:(0.25-0.35), add an equimolar amount of acetylacetone to the aluminum isopropoxide for chelation, and then add anhydrous ethanol to prepare a solution with a mass concentration of 18%-22%. Adjust the pH to 3.0-4.0 by adding 0.1mol / L dilute hydrochloric acid dropwise at 1-3mL / min at 30-40℃, and hydrolyze and activate for 1-2h to obtain a silica-alumina composite sol. 2) Under nitrogen protection, hexachlorocyclotriphosphazene was dissolved in anhydrous tetrahydrofuran, cooled to 0-5°C in an ice bath, and stirred at 150-200 r / min. A tetrahydrofuran solution containing p-phenylenediamine was added dropwise at 0.5-2 mL / min, with a molar ratio of hexachlorocyclotriphosphazene to p-phenylenediamine of 1:(2.5-3.5). After the addition was complete, the temperature was raised to 50-60°C, and the reaction was continued for 5-7 h to obtain an amino-terminated cyclotriphosphazene prepolymer solution. 3) Add the amino-terminated cyclotriphosphazene prepolymer solution to the silica-alumina composite sol, add melamine, and the molar ratio of melamine to hexachlorocyclotriphosphazene is (0.5-1.5):

1. Transfer to a hydrothermal reactor at 80-90℃ and react for 10-14 hours. 4) The reactants were centrifuged at 6000–8000 r / min. The precipitate was washed three times each with anhydrous ethanol and deionized water. It was then vacuum dried to constant weight at 70–90℃ and a vacuum degree of -0.08–-0.1 MPa. Subsequently, it was heat-treated at 280–320℃ under a nitrogen atmosphere for 1.5–2.5 h, and then pulverized by an air jet mill, controlling the output particle size D. 50 The size was 3-5 μm, and phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres were obtained.

5. The environmentally friendly flame-retardant composite material for cables according to claim 1, characterized in that, The preparation method of the metal-coordinated halloysite hybrid carbon nanotubes includes the following steps: (1) Add halloysite nanotubes to anhydrous ethanol and disperse them for 20 to 40 min under ultrasonic power of 200 to 300 W and frequency of 20 to 40 kHz. Add γ-aminopropyltriethoxysilane at 14% to 16% of the mass of halloysite nanotubes and reflux at 55 to 65 °C for 7 to 9 h. After the reaction is completed, centrifuge at 6000 to 8000 r / min. Wash the precipitate three times with deionized water and then vacuum dry it at 70 to 90 °C and vacuum degree of -0.08 to -0.1 MPa to obtain aminated halloysite nanotubes. (2) Add multi-walled carbon nanotubes to a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, reflux at 65-75°C for 4-6 hours, cool and dilute with deionized water, filter and wash until neutral, and vacuum dry at 70-90°C to obtain carboxylated multi-walled carbon nanotubes. (3) Carboxylated multi-walled carbon nanotubes were added to deionized water and dispersed for 20 to 40 minutes under ultrasonic power of 200 to 300 W and frequency of 20 to 40 kHz. 8% to 12% of zinc nitrate hexahydrate by mass was added. After ultrasonic coordination, an amino-coated halloysite nanotube aqueous dispersion was added and ultrasonication was continued for 20 to 40 minutes. The mixture was then freeze-dried for 44 to 52 hours under conditions of -55 to -45 °C and vacuum degree <10 Pa to obtain metal-coordinated halloysite hybrid carbon nanotubes.

6. A method for preparing an environmentally friendly flame-retardant composite material for cables according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Ethylene-1-octene copolymer and linear low-density polyethylene are dried in a forced-air drying oven at 55-65°C for 3-5 hours to obtain pretreated matrix resin. S2. Add the pretreated matrix resin and reactive compatibilizer to a mixer and mix for 2-4 minutes at 110-120°C and rotor speed of 35-55 r / min. Then add phosphorus-nitrogen-silicon-aluminum quaternary synergistic hybrid microspheres and metal-coordinated halloysite hybrid carbon nanotubes and continue mixing at 110-120°C for 4-8 minutes to obtain the compound. S3. The compounded rubber material is transferred into a twin-screw extruder with a length-to-diameter ratio of L / D=40:

1. Crosslinking agent and co-crosslinking agent are added by side feeding, along with composite antioxidant and lubricant. After extrusion, cooling and pelletizing, environmentally friendly flame-retardant composite material pellets for cables are obtained.

7. The method for preparing the environmentally friendly flame-retardant composite material for cables according to claim 6, characterized in that, In step S3, the temperatures of each section of the twin-screw extruder are: Zone 1 105-110℃, Zone 2 110-115℃, Zone 3 110-115℃, Zone 4 108-113℃, and the die head 110-115℃, with a screw speed of 70-130 r / min; the crosslinking agent and co-crosslinking agent are added after the melting section and before the homogenization section of the extruder.

8. The method for preparing the environmentally friendly flame-retardant composite material for cables according to claim 6, characterized in that, The ethylene-1-octene copolymer has an octene unit content of 18–25 wt%, a melt index of 0.5–3.0 g / 10 min at 190 °C / 2.16 kg, and a weight-average molecular weight of 8 × 10⁻⁶. 4 ~12×10 4 g / mol; the linear low-density polyethylene has a melt index of 1.0~2.5g / 10min at 190℃ / 2.16kg and a weight-average molecular weight of 7×10. 4 ~10×10 4 g / mol.