High-flame-retardant low-smoke halogen-free flame-retardant polyolefin sheath and preparation method thereof

Abstract

The invention belongs to the field of polyolefin sheath materials, and discloses a high-flame-retardant low-smoke halogen-free flame-retardant polyolefin sheath and a preparation method thereof. The composite material is prepared from the following raw materials in parts by weight: 45-65 parts of a polyolefin composite base material, 35-55 parts of a multi-component composite flame retardant, 4-9 parts of a special compatilizer, 0.8-2.5 parts of an antioxidant, 0.5-2 parts of a lubricant, 1.5-5 parts of a high-efficiency flame-retardant synergist and 1-3 parts of vermiculite-sepiolite composite powder, aiming at the technical defects that an existing low-smoke halogen-free flame-retardant polyolefin sheath is low in flame-retardant efficiency, poor in compatibility and high in smoke density, the mechanical property and the flame-retardant property are difficult to consider, and the invention provides the high-flame-retardant low-smoke halogen-free flame-retardant polyolefin sheath and the preparation method thereof, so that the flame-retardant property, the low smoke property and the mechanical property are synergistically improved.

Description

Technical Field

[0001] This invention relates to the field of polyolefin sheathing materials technology, specifically to a high flame retardant, low-smoke, halogen-free flame retardant polyolefin sheath and its preparation method. Background Technology

[0002] Low-smoke halogen-free flame-retardant polyolefin sheaths are widely used in construction, rail transportation, shipbuilding and other fields due to their advantages such as no halogen release during combustion and low smoke density.

[0003] However, existing low-smoke halogen-free flame-retardant polyolefin sheaths generally suffer from the following problems: To achieve the desired flame retardant effect, a large amount of flame retardant is added, which leads to a decrease in the mechanical properties of the material, including a reduction in tensile strength and elongation at break. Poor compatibility between different components can easily lead to agglomeration, affecting the uniformity and stability of the material in use. The flame retardant efficiency is limited, and some products are difficult to meet the UL94 V0 flame retardant standard. In addition, the smoke density is high and the visibility is low during a fire, which is not conducive to personnel evacuation and rescue. To address the aforementioned issues, this invention proposes a high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath and its preparation method, thereby obtaining a polyolefin sheath material with high flame retardancy, low smoke, and excellent mechanical properties, filling a gap in existing technologies. Summary of the Invention

[0004] To address the shortcomings of existing low-smoke halogen-free flame-retardant polyolefin sheaths, such as low flame-retardant efficiency, difficulty in achieving both mechanical and flame-retardant properties, poor compatibility, and high smoke density, this invention provides a high-flame-retardant, low-smoke halogen-free flame-retardant polyolefin sheath with a reasonable formulation and stable preparation process, as well as its preparation method, achieving a synergistic improvement in flame retardancy, low smoke, and mechanical properties.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The technical solution provided by this invention is: The high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath of the present invention is composed of the following raw materials in parts by weight: 45-65 parts of polyolefin composite substrate, 35-55 parts of multi-component composite flame retardant, 4-9 parts of special compatibilizer, 0.8-2.5 parts of antioxidant, 0.5-2 parts of lubricant, 1.5-5 parts of high-efficiency flame retardant synergist, and 1-3 parts of vermiculite-sepiolite composite powder.

[0006] The polyolefin composite substrate is a blend of high-density polyethylene, ethylene-vinyl acetate copolymer and polyolefin elastomer, with a weight ratio of 4:1:0.5-6:2:1. The multi-component composite flame retardant is a compound of magnesium hydroxide, aluminum hydroxide, nano-hydroxyapatite and microencapsulated ammonium polyphosphate, with a weight ratio of 2:2:0.8:1-3:3:1.2:1.8. The specific compatibilizer is glycidyl methacrylate-grafted ethylene-octene copolymer; The high-efficiency flame retardant synergist is a compound of aluminum diethylphosphinate and zirconium oxide, with a weight ratio of 3:1-5:2. The weight ratio of vermiculite to sepiolite in the vermiculite-sepiolite composite powder is 1:0.5-1:1.5; the particle size of nano-hydroxyapatite is 50-200 nm; and the particle size of the vermiculite-sepiolite composite powder is 1-5 μm. The antioxidant is a compound of antioxidant 1076 and antioxidant 626, with a weight ratio of 1:1 to 2:1. The lubricant is ethylene bis-stearamide.

[0007] The preparation method of this high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath includes the following: S1 raw material preparation Preparation of S1-1 polyolefin composite substrate: High-density polyethylene, ethylene-vinyl acetate copolymer and polyolefin elastomer are added to a high-speed mixer at a weight ratio of 4:1:0.5-6:2:1 and mixed at 60-80℃ and 600-800rpm for 8-15min to obtain polyolefin composite substrate. Preparation of S1-2 multi-component composite flame retardant: Magnesium hydroxide, aluminum hydroxide, nano-hydroxyapatite and microencapsulated ammonium polyphosphate were added to a conical mixer in a weight ratio of 2:2:0.8:1-3:3:1.2:1.8 and mixed for 30-45 minutes at room temperature and a speed of 200-300 rpm to obtain the multi-component composite flame retardant. Preparation of S1-3 special compatibilizer: Ethylene-octene copolymer, glycidyl methacrylate and dicumyl peroxide are added to a twin-screw extruder at a weight ratio of 100:3-5:0.2-0.5 and melt-grafted at 160-180℃ and screw speed of 80-120rpm. After extrusion, the mixture is pelletized to obtain glycidyl methacrylate-grafted ethylene-octene copolymer. Preparation of S1-4 high-efficiency flame retardant synergist: aluminum diethylphosphinate and zirconium oxide were added to a three-dimensional mixer at a weight ratio of 3:1-5:2 and mixed for 20-30 minutes at room temperature and a speed of 400-600 rpm to obtain the high-efficiency flame retardant synergist. Preparation of S1-5 vermiculite-sepiolite composite powder: Vermiculite and sepiolite were mixed at a weight ratio of 1:0.5-1:1.5 and added to a ball mill. Ethanol was used as the dispersion medium, the ball-to-material ratio was 5:1-8:1, the speed was 300-400 rpm, and the mixture was ball-milled for 2-3 hours. After filtration, the mixture was dried at 80-100℃ for 3-4 hours to obtain vermiculite-sepiolite composite powder. S2 raw material pretreatment: Add γ-aminopropyltriethoxysilane to the multi-component composite flame retardant obtained from S1-2. The amount of γ-aminopropyltriethoxysilane added is 0.8-1.5 wt% of the total weight of the multi-component composite flame retardant. Dry in an oven at 110-125℃ for 3-5 hours and cool to room temperature to obtain the modified composite flame retardant. S3 Mixing and Plasticizing: The polyolefin composite substrate obtained by S1-1 and the special compatibilizer obtained by S1-3 are added to a high-speed mixer and mixed for 6-12 minutes at 85-100℃ and 900-1300rpm. Then, the modified composite flame retardant, antioxidant, lubricant, high-efficiency flame retardant synergist obtained by S1-4 and vermiculite-sepiolite composite powder obtained by S1-5 are added and mixed for 10-18 minutes at 95-110℃ and 1200-1600rpm to obtain a premix. S4 Melt Blending Extrusion: The premixed material is added to a twin-screw extruder, and the temperatures of each section are set as follows: Zone 1: 145-165℃, Zone 2: 165-180℃, Zone 3: 180-195℃, Zone 4: 190-205℃, and Die Head: 185-200℃. The screw speed is 35-65 rpm, and the vacuum degree is -0.06 to -0.09 MPa. Melt blending extrusion is then performed. S5 molding process: After the extruded material is extruded through the die, it is cooled by circulating cooling water at 25-32℃, and then pulled by a traction machine at a speed of 8-18m / min. The material is then granulated by a pelletizer to obtain sheath particles. The sheath is made by extruding the sheath particles at a molding temperature of 170-190℃.

[0008] Furthermore, in S4, the length-to-diameter ratio of the twin-screw extruder is 38:1-42:1, and the screw compression ratio is 2.8:1-3.8:1; in S5, the die orifice diameter is 25-55mm, the die core diameter is 12-32mm, and the die temperature is 180-195℃.

[0009] The beneficial effects of this technical solution are: (1) This technical solution constructs a highly efficient flame retardant system through the scientific compounding of multiple composite flame retardants. Magnesium hydroxide and aluminum hydroxide provide sufficient water for crystallization. When heated and decomposed, they absorb a large amount of heat and release water vapor, diluting the concentration of combustible gases in the combustion zone. Nano-hydroxyapatite, due to its nanoscale effect, can be uniformly dispersed in the substrate and form a synergistic carbonization effect with microencapsulated ammonium polyphosphate, promoting the formation of a dense carbon layer during combustion, blocking the transfer of heat and oxygen, and significantly optimizing the flame retardant performance. Combined with a highly efficient flame retardant synergist composed of aluminum diethylphosphinate and zirconium oxide, the synergistic effect of each flame retardant component is further enhanced. While improving the flame retardant efficiency, the overall amount of flame retardant added is reduced, avoiding the performance imbalance caused by the large-scale use of a single flame retardant.

[0010] (2) The polyolefin composite substrate adopts a blend system of high-density polyethylene, ethylene-vinyl acetate copolymer and polyolefin elastomer. The three complement each other. High-density polyethylene ensures the rigidity and structural stability of the material, ethylene-vinyl acetate copolymer improves the interfacial bonding force between components, and polyolefin elastomer enhances the flexibility and impact resistance of the material, providing a balanced mechanical performance basis for the sheath material. The special compatibilizer glycidyl methacrylate grafted ethylene-octene copolymer specifically improves the compatibility between inorganic flame retardants and organic substrates, effectively inhibits the agglomeration of flame retardant particles, ensures that each component is uniformly dispersed in the material, improves the uniformity of the material structure and the stability of use, and avoids the decline in mechanical properties caused by poor compatibility.

[0011] (3) The innovative introduction of vermiculite-sepiolite composite powder creates a unique multifunctional synergistic effect. Its layered and porous composite structure can form a physical barrier during combustion, delaying the spread of flames, and can also adsorb smoke particles generated during combustion, reducing smoke density. At the same time, the composite powder has good interfacial bonding with polyolefin substrates and other functional components. Without affecting the material's processing performance, it further enhances the tensile strength and elongation at break of the material, achieving a synergistic improvement in flame retardancy, low smoke performance, and mechanical properties. This solves the technical problem that traditional low-smoke halogen-free flame-retardant polyolefin materials cannot simultaneously achieve multiple performance aspects. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the preparation process of a high flame retardant, low smoke, halogen-free flame retardant polyolefin sheath and its preparation method proposed in this invention. Detailed Implementation

[0013] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0014] The specific implementation process is as follows: Example 1: Please see Figure 1 The present invention provides a technical solution: a high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath and its preparation method, comprising the following raw material formula in parts by weight: The product contains 55 parts of a polyolefin composite substrate, comprising 40 parts of high-density polyethylene, 10 parts of ethylene-vinyl acetate copolymer, and 5 parts of polyolefin elastomer, in a weight ratio of 4:1:0.5; 45 parts of a multi-component composite flame retardant, comprising 15 parts of magnesium hydroxide, 15 parts of aluminum hydroxide, 6 parts of nano-hydroxyapatite, and 9 parts of microencapsulated ammonium polyphosphate, in a weight ratio of 2.5:2.5:1:1.5; 6 parts of a special compatibilizer; 1.5 parts of an antioxidant, comprising 0.5 parts of antioxidant 1076 and 1.0 parts of antioxidant 626, in a weight ratio of 1:2; 1.0 part of a lubricant; 3 parts of a high-efficiency flame retardant synergist, comprising 2 parts of aluminum diethylphosphinate and 1 part of zirconium oxide, in a weight ratio of 2:1; and 2 parts of vermiculite-sepiolite composite powder, comprising 0.8 parts of vermiculite and 1.2 parts of sepiolite, in a weight ratio of 1:1.5.

[0015] Preparation method S1 raw material preparation Preparation of S1-1 polyolefin composite substrate: 40 parts of high-density polyethylene, 10 parts of ethylene-vinyl acetate copolymer and 5 parts of polyolefin elastomer were added to a high-speed mixer and mixed for 12 minutes at 70°C and 700 rpm to obtain polyolefin composite substrate. Preparation of S1-2 multi-component composite flame retardant: 15 parts magnesium hydroxide, 15 parts aluminum hydroxide, 6 parts nano hydroxyapatite and 9 parts microencapsulated ammonium polyphosphate were added to a conical mixer and mixed for 35 minutes at room temperature and 250 rpm to obtain the multi-component composite flame retardant. Preparation of S1-3 special compatibilizer: 100 parts of ethylene-octene copolymer, 4 parts of glycidyl methacrylate and 0.3 parts of dicumyl peroxide were added to a twin-screw extruder and melt-grafted at 170°C and 100 rpm. After extrusion, the mixture was pelletized to obtain glycidyl methacrylate-grafted ethylene-octene copolymer. Preparation of S1-4 high-efficiency flame retardant synergist: 2 parts of aluminum diethylphosphinate and 1 part of zirconium oxide were added to a three-dimensional mixer and mixed for 25 minutes at room temperature and 500 rpm to obtain the high-efficiency flame retardant synergist. Preparation of S1-5 vermiculite-sepiolite composite powder: 0.8 parts vermiculite and 1.2 parts sepiolite were mixed and added to a ball mill. Ethanol was used as the dispersion medium, the ball-to-material ratio was 6:1, the rotation speed was 350 rpm, and the milling time was 2.5 h. After filtration, the powder was dried at 90℃ for 3.5 h to obtain vermiculite-sepiolite composite powder. S2 raw material pretreatment: Add γ-aminopropyltriethoxysilane to the multi-component composite flame retardant obtained from S1-2, the amount of which is 1.0 wt% of the total weight of the multi-component composite flame retardant. Dry in an oven at 115℃ for 4 hours and cool to room temperature to obtain the modified composite flame retardant. S3 Mixing and Plasticizing: The polyolefin composite substrate prepared by S1-1 and 6 parts of the special compatibilizer prepared by S1-3 are added to a high-speed mixer and mixed for 9 minutes at 90°C and 1100 rpm. Then, the modified composite flame retardant, 1.5 parts of antioxidant, 1.0 part of lubricant, 3 parts of the high-efficiency flame retardant synergist prepared by S1-4 and 2 parts of vermiculite-sepiolite composite powder prepared by S1-5 are added and mixed for 14 minutes at 100°C and 1400 rpm to obtain the premix. S4 Melt Blending Extrusion: The premixed material is added to a twin-screw extruder with a length-to-diameter ratio of 40:1 and a screw compression ratio of 3.2:1. The temperatures of each section are set as follows: 155℃ Zone 1, 170℃ Zone 2, 185℃ Zone 3, 195℃ Zone 4, and 190℃ die head. The screw speed is 50 rpm and the vacuum degree is -0.07 MPa. Melt blending extrusion is then performed. S5 molding process: The extruded material is extruded through a die with a die opening diameter of 40mm, a die core diameter of 20mm, and a die temperature of 185℃. It is cooled by 28℃ circulating cooling water and pulled by a traction machine at a traction speed of 12m / min. The material is then granulated by a pelletizer to obtain sheath particles. The sheath is made by extruding the sheath particles at 180℃.

[0016] Test Project Test Results Flame retardant rating V0 Oxygen Index 33.5% Minimum transmittance 68% Tensile strength 13.2MPa Elongation at break 350% 5% thermogravimetric temperature 378℃ This embodiment shows that the high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath prepared in Example 1 achieves a V0 flame-retardant rating, exhibits excellent oxygen index performance, and demonstrates highly efficient flame-retardant properties; the high minimum light transmittance value indicates low smoke density during combustion and significant low-smoke effect; the tensile strength and elongation at break are at a balanced level, indicating that the material has both good rigidity and flexibility, and strong structural stability; the high 5% thermal weight loss temperature reflects that the material has excellent thermal stability and can maintain structural integrity at high temperatures.

[0017] Example 2: Please see Figure 1 The present invention provides a technical solution: a high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath and its preparation method, comprising the following raw material formula in parts by weight: The product contains 65 parts of a polyolefin composite substrate, comprising 45 parts of high-density polyethylene, 15 parts of ethylene-vinyl acetate copolymer, and 5 parts of polyolefin elastomer, in a weight ratio of 6:2:0.67; 55 parts of a multi-component composite flame retardant, comprising 20 parts of magnesium hydroxide, 20 parts of aluminum hydroxide, 8 parts of nano-hydroxyapatite, and 7 parts of microencapsulated ammonium polyphosphate, in a weight ratio of 3:3:1.2:1.05; 9 parts of a special compatibilizer; 2.5 parts of an antioxidant, comprising 1.0 part of antioxidant 1076 and 1.5 parts of antioxidant 626, in a weight ratio of 2:3; 2.0 parts of a lubricant; 5 parts of a high-efficiency flame retardant synergist, comprising 3.6 parts of aluminum diethylphosphinate and 1.4 parts of zirconium oxide, in a weight ratio of 5:2; and 3 parts of a vermiculite-sepiolite composite powder, comprising 2 parts of vermiculite and 1 part of sepiolite, in a weight ratio of 2:1.

[0018] Preparation method S1 raw material preparation Preparation of S1-1 polyolefin composite substrate: 45 parts of high-density polyethylene, 15 parts of ethylene-vinyl acetate copolymer and 5 parts of polyolefin elastomer were added to a high-speed mixer and mixed for 15 minutes at 80°C and 800 rpm to obtain polyolefin composite substrate. Preparation of S1-2 multi-component composite flame retardant: 20 parts magnesium hydroxide, 20 parts aluminum hydroxide, 8 parts nano hydroxyapatite and 7 parts microencapsulated ammonium polyphosphate were added to a conical mixer and mixed for 45 minutes at room temperature and 300 rpm to obtain the multi-component composite flame retardant. Preparation of S1-3 special compatibilizer: 100 parts of ethylene-octene copolymer, 5 parts of glycidyl methacrylate and 0.5 parts of dicumyl peroxide were added to a twin-screw extruder and melt-grafted at 180°C and 120 rpm. After extrusion, the mixture was pelletized to obtain glycidyl methacrylate-grafted ethylene-octene copolymer. Preparation of S1-4 high-efficiency flame retardant synergist: 3.6 parts of aluminum diethylphosphinate and 1.4 parts of zirconium oxide were added to a three-dimensional mixer and mixed for 30 min at room temperature and 600 rpm to obtain the high-efficiency flame retardant synergist; Preparation of S1-5 vermiculite-sepiolite composite powder: 2 parts vermiculite and 1 part sepiolite were mixed and added to a ball mill. Ethanol was used as the dispersion medium, the ball-to-material ratio was 8:1, the speed was 400 rpm, and the mixture was ball-milled for 3 hours. After filtration, the mixture was dried at 100℃ for 4 hours to obtain vermiculite-sepiolite composite powder. S2 raw material pretreatment: Add γ-aminopropyltriethoxysilane to the multi-component composite flame retardant obtained from S1-2, the amount of which is 1.5wt% of the total weight of the multi-component composite flame retardant. Dry in an oven at 125℃ for 5h and cool to room temperature to obtain the modified composite flame retardant. S3 Mixing and Plasticizing: The polyolefin composite substrate prepared by S1-1 and 9 parts of the special compatibilizer prepared by S1-3 are added to a high-speed mixer and mixed for 12 minutes at 100°C and 1300 rpm. Then, the modified composite flame retardant, 2.5 parts of antioxidant, 2.0 parts of lubricant, 5 parts of the high-efficiency flame retardant synergist prepared by S1-4 and 3 parts of vermiculite-sepiolite composite powder prepared by S1-5 are added and mixed for 18 minutes at 110°C and 1600 rpm to obtain the premix. S4 Melt Blending Extrusion: The premixed material is added to a twin-screw extruder with a length-to-diameter ratio of 42:1 and a screw compression ratio of 3.8:1. The temperatures of each section are set as follows: Zone 1: 165℃, Zone 2: 180℃, Zone 3: 195℃, Zone 4: 205℃, and Die Head: 200℃. The screw speed is 65 rpm, and the vacuum degree is -0.09 MPa. Melt blending extrusion is then performed. S5 molding process: The extruded material is extruded through a die with a die opening diameter of 55mm, a die core diameter of 32mm, and a die temperature of 195℃. It is cooled by 32℃ circulating cooling water and pulled by a traction machine at a traction speed of 18m / min. The material is then granulated by a pelletizer to obtain sheath particles. The sheath is made by extruding the sheath particles at 190℃.

[0019] Test Project Test Results Flame retardant rating V0 Oxygen Index 35.2% Minimum transmittance 72% Tensile strength 14.5MPa Elongation at break 330% 5% thermogravimetric temperature 385℃ The examples show that the sheath material of Example 2 has a flame retardant rating of V0, and its oxygen index is at a relatively high level among all examples, indicating outstanding flame retardant performance. It has a high minimum light transmittance value, excellent low smoke effect, which is beneficial for personnel evacuation in fire scenarios. It exhibits the best tensile strength, demonstrating the material's strong rigidity and structural support capacity. Its elongation at break remains at a good level, while also taking into account flexibility. It has the highest 5% thermal weight loss temperature, indicating that the material has excellent thermal stability and can be used stably in harsh temperature environments.

[0020] Example 3: Please see Figure 1 The present invention provides a technical solution: a high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath and its preparation method, comprising the following raw material formula in parts by weight: The product contains 45 parts of a polyolefin composite substrate, comprising 30 parts of high-density polyethylene, 7.5 parts of ethylene-vinyl acetate copolymer, and 7.5 parts of polyolefin elastomer, in a weight ratio of 4:1:1; 35 parts of a multi-component composite flame retardant, comprising 10 parts of magnesium hydroxide, 10 parts of aluminum hydroxide, 4 parts of nano-hydroxyapatite, and 11 parts of microencapsulated ammonium polyphosphate, in a weight ratio of 2:2:0.8:2.2; 4 parts of a special compatibilizer; 0.8 parts of an antioxidant, comprising 0.4 parts of antioxidant 1076 and 0.4 parts of antioxidant 626, in a weight ratio of 1:1; 0.5 parts of a lubricant; 1.5 parts of a high-efficiency flame retardant synergist, comprising 1.1 parts of aluminum diethylphosphinate and 0.4 parts of zirconium oxide, in a weight ratio of 3:1; and 1 part of a vermiculite-sepiolite composite powder, comprising 0.4 parts of vermiculite and 0.6 parts of sepiolite, in a weight ratio of 1:1.5.

[0021] Preparation method S1 raw material preparation Preparation of S1-1 polyolefin composite substrate: 30 parts of high-density polyethylene, 7.5 parts of ethylene-vinyl acetate copolymer and 7.5 parts of polyolefin elastomer were added to a high-speed mixer and mixed for 8 minutes at 60°C and 600 rpm to obtain polyolefin composite substrate. Preparation of S1-2 multi-component composite flame retardant: 10 parts magnesium hydroxide, 10 parts aluminum hydroxide, 4 parts nano hydroxyapatite and 11 parts microencapsulated ammonium polyphosphate were added to a conical mixer and mixed for 30 min at room temperature and 200 rpm to obtain the multi-component composite flame retardant. Preparation of S1-3 special compatibilizer: 100 parts of ethylene-octene copolymer, 3 parts of glycidyl methacrylate and 0.2 parts of dicumyl peroxide were added to a twin-screw extruder and melt-grafted at 160℃ and screw speed of 80 rpm. After extrusion, the mixture was pelletized to obtain glycidyl methacrylate grafted ethylene-octene copolymer. Preparation of S1-4 high-efficiency flame retardant synergist: 1.1 parts of aluminum diethylphosphinate and 0.4 parts of zirconium oxide were added to a three-dimensional mixer and mixed for 20 min at room temperature and 400 rpm to obtain the high-efficiency flame retardant synergist. Preparation of S1-5 vermiculite-sepiolite composite powder: 0.4 parts vermiculite and 0.6 parts sepiolite were mixed and added to a ball mill. Ethanol was used as the dispersion medium, the ball-to-material ratio was 5:1, the speed was 300 rpm, and the mixture was ball-milled for 2 hours. After filtration, the mixture was dried at 80℃ for 3 hours to obtain vermiculite-sepiolite composite powder. S2 raw material pretreatment: Add γ-aminopropyltriethoxysilane to the multi-component composite flame retardant obtained from S1-2. The amount added is 0.8 wt% of the total weight of the multi-component composite flame retardant. Dry in an oven at 110℃ for 3 hours and cool to room temperature to obtain the modified composite flame retardant. S3 Mixed Plasticization: The polyolefin composite substrate prepared by S1-1 and 4 parts of the special compatibilizer prepared by S1-3 are added to a high-speed mixer and mixed for 6 minutes at 85°C and 900 rpm. Then, modified composite flame retardant, 0.8 parts of antioxidant, 0.5 parts of lubricant, 1.5 parts of high-efficiency flame retardant synergist prepared by S1-4 and 1 part of vermiculite-sepiolite composite powder prepared by S1-5 are added and mixed for 10 minutes at 95°C and 1200 rpm to obtain a premix. S4 Melt Blending Extrusion: The premixed material is added to a twin-screw extruder with a length-to-diameter ratio of 38:1 and a screw compression ratio of 2.8:1. The temperatures of each section are set as follows: 145℃ Zone 1, 165℃ Zone 2, 180℃ Zone 3, 190℃ Zone 4, and 185℃ die head. The screw speed is 35 rpm and the vacuum degree is -0.06 MPa. Melt blending extrusion is then performed. S5 molding process: The extruded material is extruded through a die with a die opening diameter of 25mm, a die core diameter of 12mm, and a die temperature of 180℃. It is cooled by 25℃ circulating cooling water and pulled by a traction machine at a traction speed of 8m / min. The material is then granulated by a pelletizer to obtain sheath particles. The sheath is made by extruding the sheath particles at 170℃.

[0022] Test Project Test Results Flame retardant rating V0 Oxygen Index 32.1% Minimum transmittance 65% Tensile strength 12.8MPa Elongation at break 360% 5% thermogravimetric temperature 372℃ Test results show that although the sheath material in Example 3 uses the lower limit formulation, it still reaches the V0 flame retardant rating, and the oxygen index meets the high flame retardant requirements. The elongation at break is the highest among all examples, demonstrating excellent flexibility and tensile strength, making it suitable for scenarios with high requirements for material elasticity. The minimum light transmittance and tensile strength remain at stable levels, and the 5% thermal weight loss temperature meets the usage standards, indicating that this technical solution can still achieve performance balance with low raw material usage, and has good practicality and cost advantages.

[0023] Example 4: Please see Figure 1 The present invention provides a technical solution: a high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath and its preparation method, comprising the following raw material formula in parts by weight: The product comprises: 50 parts of a polyolefin composite substrate, including 30 parts of high-density polyethylene, 10 parts of ethylene-vinyl acetate copolymer, and 10 parts of polyolefin elastomer, in a weight ratio of 3:1:1; 40 parts of a multi-component composite flame retardant, including 12 parts of magnesium hydroxide, 12 parts of aluminum hydroxide, 5 parts of nano-hydroxyapatite, and 11 parts of microencapsulated ammonium polyphosphate, in a weight ratio of 2.4:2.4:1:2.2; 7 parts of a special compatibilizer; 1.2 parts of an antioxidant, including 0.5 parts of antioxidant 1076 and 0.7 parts of antioxidant 626, in a weight ratio of 5:7; 1.2 parts of a lubricant; 2.5 parts of a high-efficiency flame retardant synergist, including 1.8 parts of aluminum diethylphosphinate and 0.7 parts of zirconium oxide, in a weight ratio of 18:7; and 1.5 parts of a vermiculite-sepiolite composite powder, including 0.75 parts of vermiculite and 0.75 parts of sepiolite, in a weight ratio of 1:1.

[0024] Preparation method Preparation of S1 raw materials: Preparation of S1-1 polyolefin composite substrate: 30 parts of high-density polyethylene, 10 parts of ethylene-vinyl acetate copolymer and 10 parts of polyolefin elastomer are added to a high-speed mixer and mixed for 10 min at 75℃ and 750 rpm to obtain polyolefin composite substrate. Preparation of S1-2 multi-component composite flame retardant: 12 parts magnesium hydroxide, 12 parts aluminum hydroxide, 5 parts nano hydroxyapatite and 11 parts microencapsulated ammonium polyphosphate were added to a conical mixer and mixed for 40 min at room temperature and 280 rpm to obtain the multi-component composite flame retardant. Preparation of S1-3 special compatibilizer: 100 parts of ethylene-octene copolymer, 4.5 parts of glycidyl methacrylate and 0.4 parts of dicumyl peroxide were added to a twin-screw extruder and subjected to melt grafting reaction at 175℃ and screw speed of 110 rpm. After extrusion, the mixture was pelletized to obtain glycidyl methacrylate grafted ethylene-octene copolymer. Preparation of S1-4 high-efficiency flame retardant synergist: 1.8 parts of aluminum diethylphosphinate and 0.7 parts of zirconium oxide were added to a three-dimensional mixer and mixed for 28 minutes at room temperature and 550 rpm to obtain the high-efficiency flame retardant synergist. Preparation of S1-5 vermiculite-sepiolite composite powder: 0.75 parts vermiculite and 0.75 parts sepiolite were mixed and added to a ball mill. Ethanol was used as the dispersion medium, the ball-to-material ratio was 7:1, the rotation speed was 380 rpm, and the milling time was 2.8 h. After filtration, the powder was dried at 95 ℃ for 3.8 h to obtain vermiculite-sepiolite composite powder. S2 raw material pretreatment: Add γ-aminopropyltriethoxysilane to the multi-component composite flame retardant obtained from S1-2, the amount of which is 1.2wt% of the total weight of the multi-component composite flame retardant. Dry in an oven at 120℃ for 4.5h and cool to room temperature to obtain the modified composite flame retardant. S3 Mixing and Plasticizing: The polyolefin composite substrate obtained by S1-1 and 7 parts of the special compatibilizer obtained by S1-3 are added to a high-speed mixer and mixed for 8 minutes at 95°C and 1200 rpm. Then, the modified composite flame retardant, 1.2 parts of antioxidant, 1.2 parts of lubricant, 2.5 parts of the high-efficiency flame retardant synergist obtained by S1-4 and 1.5 parts of vermiculite-sepiolite composite powder obtained by S1-5 are added and mixed for 16 minutes at 105°C and 1500 rpm to obtain the premix. S4 Melt Blending Extrusion: The premixed material is added to a twin-screw extruder with a length-to-diameter ratio of 41:1 and a screw compression ratio of 3.5:1. The temperatures of each section are set as follows: 160℃ Zone 1, 175℃ Zone 2, 190℃ Zone 3, 200℃ Zone 4, and 195℃ die head. The screw speed is 55 rpm and the vacuum degree is -0.08 MPa. Melt blending extrusion is then performed. S5 molding process: The extruded material is extruded through a die with a die opening diameter of 45mm, a die core diameter of 25mm, and a die temperature of 190℃. It is cooled by 30℃ circulating cooling water and pulled by a traction machine at a traction speed of 15m / min. The material is then granulated by a pelletizer to obtain sheath particles. The sheath is made by extruding the sheath particles at 185℃.

[0025] Test Project Test Results Flame retardant rating V0 Oxygen Index 34.8% Minimum transmittance 70% Tensile strength 13.8MPa Elongation at break 345% 5% thermogravimetric temperature 382℃ The examples show that the sheath material of Example 4 exhibits balanced performance across all aspects, achieving a flame retardancy rating of V0, a ​​high oxygen index, and significant flame retardant effect; it also demonstrates excellent minimum light transmittance and outstanding low smoke performance; its tensile strength and elongation at break are both at high levels, reflecting that the material possesses both good rigidity and flexibility, and strong structural stability; its 5% thermal weight loss temperature is high, indicating good thermal stability. This formulation, through the equal-proportion compounding of vermiculite and sepiolite, achieves synergistic optimization of various properties and is suitable for a variety of application scenarios.

[0026] Example 5: Please see Figure 1 The present invention provides a technical solution: a high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath and its preparation method, comprising the following raw material formula in parts by weight: The product contains 60 parts of a polyolefin composite substrate, comprising 36 parts of high-density polyethylene, 12 parts of ethylene-vinyl acetate copolymer, and 12 parts of polyolefin elastomer, in a weight ratio of 3:1:1; 50 parts of a multi-component composite flame retardant, comprising 18 parts of magnesium hydroxide, 18 parts of aluminum hydroxide, 7 parts of nano-hydroxyapatite, and 7 parts of microencapsulated ammonium polyphosphate, in a weight ratio of 2.57:2.57:1:1; 8 parts of a special compatibilizer; 2.0 parts of an antioxidant, comprising 0.8 parts of antioxidant 1076 and 1.2 parts of antioxidant 626, in a weight ratio of 2:3; 1.8 parts of a lubricant; 4 parts of a high-efficiency flame retardant synergist, comprising 2.5 parts of aluminum diethylphosphinate and 1.5 parts of zirconium oxide, in a weight ratio of 5:3; and 2.5 parts of a vermiculite-sepiolite composite powder, comprising 1 part of vermiculite and 1.5 parts of sepiolite, in a weight ratio of 1:1.5.

[0027] Preparation method Preparation of S1 raw materials: Preparation of S1-1 polyolefin composite substrate: 36 parts of high-density polyethylene, 12 parts of ethylene-vinyl acetate copolymer and 12 parts of polyolefin elastomer were added to a high-speed mixer and mixed for 14 minutes at 78°C and 780 rpm to obtain polyolefin composite substrate. Preparation of S1-2 multi-component composite flame retardant: 18 parts magnesium hydroxide, 18 parts aluminum hydroxide, 7 parts nano hydroxyapatite and 7 parts microencapsulated ammonium polyphosphate were added to a conical mixer and mixed for 42 minutes at room temperature and 290 rpm to obtain the multi-component composite flame retardant. Preparation of S1-3 special compatibilizer: 100 parts of ethylene-octene copolymer, 4.8 parts of glycidyl methacrylate and 0.45 parts of dicumyl peroxide were added to a twin-screw extruder and melt-grafted at 178°C and 115 rpm. After extrusion, the mixture was pelletized to obtain glycidyl methacrylate-grafted ethylene-octene copolymer. Preparation of S1-4 high-efficiency flame retardant synergist: 2.5 parts of aluminum diethylphosphinate and 1.5 parts of zirconium oxide were added to a three-dimensional mixer and mixed for 29 min at room temperature and 580 rpm to obtain the high-efficiency flame retardant synergist. Preparation of S1-5 vermiculite-sepiolite composite powder: 1 part vermiculite and 1.5 parts sepiolite were mixed and added to a ball mill. Ethanol was used as the dispersion medium, the ball-to-material ratio was 7.5:1, the rotation speed was 390 rpm, and the milling time was 2.9 h. After filtration, the powder was dried at 98 ℃ for 3.9 h to obtain vermiculite-sepiolite composite powder. S2 raw material pretreatment: Add γ-aminopropyltriethoxysilane to the multi-component composite flame retardant obtained from S1-2, the amount of which is 1.4wt% of the total weight of the multi-component composite flame retardant. Dry in an oven at 122℃ for 4.8h and cool to room temperature to obtain the modified composite flame retardant. S3 Mixing and Plasticizing: The polyolefin composite substrate obtained by S1-1 and 8 parts of the special compatibilizer obtained by S1-3 are added to a high-speed mixer and mixed for 11 minutes at 98°C and 1250 rpm. Then, modified composite flame retardant, 2.0 parts of antioxidant, 1.8 parts of lubricant, 4 parts of high-efficiency flame retardant synergist obtained by S1-4 and 2.5 parts of vermiculite-sepiolite composite powder obtained by S1-5 are added and mixed for 17 minutes at 108°C and 1550 rpm to obtain a premix. S4 Melt Blending Extrusion: The premixed material is added to a twin-screw extruder with a length-to-diameter ratio of 41.5:1 and a screw compression ratio of 3.6:1. The temperatures of each section are set as follows: Zone 1: 162℃, Zone 2: 178℃, Zone 3: 192℃, Zone 4: 202℃, and Die Head: 198℃. The screw speed is 62 rpm, and the vacuum degree is -0.085 MPa. Melt blending extrusion is then performed. S5 molding process: The extruded material is extruded through a die with a die opening diameter of 50mm, a die core diameter of 28mm, and a die temperature of 192℃. It is cooled by 31℃ circulating cooling water and pulled by a traction machine at a traction speed of 17m / min. The material is then pelletized by a pelletizer to obtain sheath particles. The sheath is made by extruding the sheath particles at 188℃.

[0028] Example Table Test Project Test Results Flame retardant rating V0 Oxygen Index 36.1% Minimum transmittance 75% Tensile strength 15.2MPa Elongation at break 320% 5% thermogravimetric temperature 390℃ This embodiment demonstrates that the sheath material of Example 5 has the best overall performance, with a flame retardant rating of V0, the highest oxygen index, and outstanding flame retardant efficiency; it has the highest minimum light transmittance value, excellent low smoke effect, and can minimize smoke interference during a fire; it exhibits excellent tensile strength, high material rigidity, and outstanding structural support capacity; it has the highest 5% thermal weight loss temperature, excellent thermal stability, and can be used stably for a long time in high-temperature environments, making it suitable for high-end application scenarios with stringent performance requirements.

[0029] Example 6: Please see Figure 1 The present invention provides a technical solution: a high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath and its preparation method, comprising the following raw material formula in parts by weight: The product contains 52 parts of a polyolefin composite substrate, comprising 32 parts of high-density polyethylene, 8 parts of ethylene-vinyl acetate copolymer, and 12 parts of polyolefin elastomer, in a weight ratio of 4:1:1.5; 42 parts of a multi-component composite flame retardant, comprising 14 parts of magnesium hydroxide, 14 parts of aluminum hydroxide, 6 parts of nano-hydroxyapatite, and 8 parts of microencapsulated ammonium polyphosphate, in a weight ratio of 2.33:2.33:1:1.33; 5 parts of a special compatibilizer; 1.0 part of an antioxidant, comprising 0.4 parts of antioxidant 1076 and 0.6 parts of antioxidant 626, in a weight ratio of 2:3; 0.9 parts of a lubricant; 2 parts of a high-efficiency flame retardant synergist, comprising 1.3 parts of aluminum diethylphosphinate and 0.7 parts of zirconium oxide, in a weight ratio of 13:7; and 1.2 parts of a vermiculite-sepiolite composite powder, comprising 0.5 parts of vermiculite and 0.7 parts of sepiolite, in a weight ratio of 5:7.

[0030] Preparation method S1 raw material preparation Preparation of S1-1 polyolefin composite substrate: 32 parts of high-density polyethylene, 8 parts of ethylene-vinyl acetate copolymer and 12 parts of polyolefin elastomer were added to a high-speed mixer and mixed for 11 min at 68℃ and 680 rpm to obtain polyolefin composite substrate. Preparation of S1-2 multi-component composite flame retardant: 14 parts magnesium hydroxide, 14 parts aluminum hydroxide, 6 parts nano hydroxyapatite and 8 parts microencapsulated ammonium polyphosphate were added to a conical mixer and mixed for 36 minutes at room temperature and 240 rpm to obtain the multi-component composite flame retardant. Preparation of S1-3 special compatibilizer: 100 parts of ethylene-octene copolymer, 3.5 parts of glycidyl methacrylate and 0.25 parts of dicumyl peroxide were added to a twin-screw extruder and subjected to melt grafting reaction at 165℃ and screw speed of 90 rpm. After extrusion, the mixture was pelletized to obtain glycidyl methacrylate grafted ethylene-octene copolymer. Preparation of S1-4 High-efficiency flame retardant synergist: 1.3 parts of aluminum diethylphosphinate and 0.7 parts of zirconium oxide were added to a three-dimensional mixer and mixed for 24 min at room temperature and 480 rpm to obtain the high-efficiency flame retardant synergist; Preparation of S1-5 Vermiculite-Sepiolite composite powder: 0.5 parts of vermiculite and 0.7 parts of sepiolite were mixed and added to a ball mill. Ethanol was used as the dispersion medium, the ball-to-material ratio was 6.5:1, the speed was 340 rpm, and the mixture was ball-milled for 2.3 h. After filtration, the mixture was dried at 88℃ for 3.2 h to obtain the vermiculite-sepiolite composite powder; S2 raw material pretreatment: Add γ-aminopropyltriethoxysilane to the multi-component composite flame retardant obtained from S1-2, the amount of which is 1.1 wt% of the total weight of the multi-component composite flame retardant. Dry in an oven at 118℃ for 3.8 h and cool to room temperature to obtain the modified composite flame retardant. S3 Mixing and Plasticizing: The polyolefin composite substrate obtained by S1-1 and 5 parts of the special compatibilizer obtained by S1-3 are added to a high-speed mixer and mixed for 7 minutes at 88°C and 1000 rpm. Then, the modified composite flame retardant, 1.0 part of antioxidant, 0.9 parts of lubricant, 2 parts of the high-efficiency flame retardant synergist obtained by S1-4 and 1.2 parts of vermiculite-sepiolite composite powder obtained by S1-5 are added and mixed for 12 minutes at 98°C and 1300 rpm to obtain the premix. S4 Melt Blending Extrusion: The premixed material is added to a twin-screw extruder with a length-to-diameter ratio of 39:1 and a screw compression ratio of 3.0:1. The temperatures of each section are set as follows: 150℃ Zone 1, 168℃ Zone 2, 183℃ Zone 3, 193℃ Zone 4, and 188℃ die head. The screw speed is 45 rpm and the vacuum degree is -0.075 MPa. Melt blending extrusion is then performed. S5 molding process: The extruded material is extruded through a die with a die opening diameter of 35mm, a die core diameter of 18mm, and a die temperature of 183℃. It is cooled by 27℃ circulating cooling water and pulled by a traction machine at a traction speed of 10m / min. The material is then granulated by a pelletizer to obtain sheath particles. The sheath is made by extruding the sheath particles at 175℃.

[0031] Test Project Test Results Flame retardant rating V0 Oxygen Index 33.2% Minimum transmittance 67% Tensile strength 13.5MPa Elongation at break 355% 5% thermogravimetric temperature 376℃ Test results show that the sheath material of Example 6 reaches the V0 flame retardant rating, and the oxygen index meets the high flame retardant requirements; the elongation at break is at a high level, and the flexibility is excellent, which can adapt to complex installation and use environments; the minimum light transmittance, tensile strength and 5% thermal weight loss temperature all maintain stable performance, demonstrating the good adaptability of this technical solution under different raw material ratio combinations, the formula design is flexible and can be adjusted according to actual needs, and it is highly practical.

[0032] Comparative Example 1: Please see Figure 1 The present invention provides a comparative solution: vermiculite-sepiolite composite powder, the rest being the same as in Example 1.

[0033] Test Project Test Results Flame retardant rating V1 Oxygen Index 29.8% Minimum transmittance 52% Tensile strength 11.5MPa Elongation at break 280% 5% thermogravimetric temperature 365℃ The examples show that without vermiculite-sepiolite composite powder, the flame retardancy rating of Comparative Example 1 dropped to V1, the oxygen index decreased significantly, and the flame retardancy performance declined markedly; the minimum light transmittance decreased significantly, the smoke density increased, and the low smoke effect was poor; the tensile strength and elongation at break both decreased, and the mechanical properties weakened; the 5% thermal weight loss temperature decreased, and the thermal stability decreased, fully demonstrating that vermiculite-sepiolite composite powder plays a key role in improving the flame retardancy, low smoke effect, mechanical properties, and thermal stability of the material.

[0034] Comparative Example 2: Please see Figure 1The present invention provides a comparative scheme: no special compatibilizer is used, and the rest is the same as in Example 1.

[0035] Test Project Test Results Flame retardant rating V1 Oxygen Index 30.2% Minimum transmittance 55% Tensile strength 9.8MPa Elongation at break 220% 5% thermogravimetric temperature 358℃ Without a dedicated compatibilizer, Comparative Example 2 had a flame retardant rating of V1, an oxygen index lower than Example 1, and decreased flame retardant performance; it also had a lower minimum light transmittance and a higher smoke density; its tensile strength and elongation at break decreased significantly, and its mechanical properties deteriorated markedly. This was due to the poor compatibility between the inorganic flame retardant and the organic substrate, resulting in agglomeration and a non-uniform material structure; the 5% thermal weight loss temperature decreased, and its thermal stability weakened, indicating that a dedicated compatibilizer is crucial for improving component compatibility and enhancing the overall performance of the material. Comparative Example 3: Please see Figure 1 The present invention provides a comparative solution: using a single flame retardant, with the rest being the same as in Example 1. Test Project Test Results Flame retardant rating V2 Oxygen Index 27.5% Minimum transmittance 48% Tensile strength 10.2MPa Elongation at break 250% 5% thermogravimetric temperature 352℃ After replacing the multi-component composite flame retardant with a single flame retardant, the flame retardant rating of Comparative Example 3 dropped to V2, the oxygen index decreased significantly, and the flame retardant effect declined sharply, failing to meet the high flame retardant requirements. It also had the lowest minimum light transmittance, the highest smoke density, and extremely poor low-smoke performance. The tensile strength and elongation at break were both low, indicating poor mechanical properties. Furthermore, it had the lowest 5% thermal weight loss temperature and the worst thermal stability. This suggests that the synergistic effect of the components in the multi-component composite flame retardant is far superior to that of the single flame retardant, and is the key to achieving high flame retardant performance.

[0036] Comparative Example 4: Please see Figure 1 The present invention provides a comparative scheme: except for the absence of a high-efficiency flame retardant synergist, it is the same as Example 1.

[0037] Test Project Test Results Flame retardant rating V1 Oxygen Index 30.5% Minimum transmittance 58% Tensile strength 12.5MPa Elongation at break 310% 5% thermogravimetric temperature 368℃ Without the efficient flame retardant synergist, Comparative Example 4 had a flame retardant rating of V1, an oxygen index lower than Example 1, and a decline in flame retardant performance. It also had a lower minimum light transmittance, a higher smoke density, and poor low smoke effect. Although its tensile strength and elongation at break were better than Comparative Examples 1, 2, and 3, they were still lower than Example 1. Its 5% thermal weight loss temperature was also lower than Example 1. This indicates that the efficient flame retardant synergist can effectively enhance the flame retardant effect of the multi-component composite flame retardant, while also having a positive effect on improving low smoke performance, mechanical properties, and thermal stability.

[0038] Comparative Example 5: Please see Figure 1 The present invention provides a comparative scheme: using the traditional compatibilizer maleic anhydride to graft polyethylene, and the rest is the same as in Example 1.

[0039] Test Project Test Results Flame retardant rating V0 Oxygen Index 31.8% Minimum transmittance 62% Tensile strength 11.8MPa Elongation at break 290% 5% thermogravimetric temperature 370℃ Although Comparative Example 5 achieved a V0 flame retardant rating after using a traditional compatibilizer, its oxygen index was lower than that of Example 1, indicating slightly inferior flame retardant performance. The minimum light transmittance, tensile strength, elongation at break, and 5% thermal weight loss temperature were all lower than those of Example 1, indicating that the compatibility improvement effect of the traditional compatibilizer was not as good as that of the special compatibilizer of the present invention. The special compatibilizer of the present invention can more effectively promote the uniform dispersion of each component, further improve the comprehensive performance of the material, and demonstrate the innovation and superiority of the special compatibilizer.

[0040] Comparative Example 6: Please see Figure 1 The present invention provides a comparative scheme comprising the following raw material formula in parts by weight: Polyethylene 55 parts, magnesium hydroxide 40 parts, aluminum hydroxide 10 parts, maleic anhydride grafted polyethylene 5 parts, antioxidant 1.2 parts, stearic acid 1.0 part; Preparation method 1. Add polyethylene to a high-speed mixer and mix for 10 minutes at 70°C and 700 rpm. 2. Mix magnesium hydroxide and aluminum hydroxide, add γ-aminopropyltriethoxysilane at a weight of 1.0 wt% of the total weight of the flame retardant, and dry in an oven at 115°C for 4 hours to obtain the modified flame retardant; 3. Add the modified flame retardant maleic anhydride grafted polyethylene antioxidant stearic acid to a high-speed mixer and mix with polyethylene at 90°C and 1100 rpm for 15 minutes to obtain a premix. 4. Add the premixed material to a twin-screw extruder with a length-to-diameter ratio of 40:1 and a screw compression ratio of 3.2:1. Set the temperatures of each section to 155℃, 170℃ for zone 1, 185℃ for zone 2, 195℃ for zone 3, and 190℃ for zone 4. Set the die head temperature, screw speed to 50 rpm, and vacuum degree to -0.07 MPa. Perform melt blending extrusion. 5. The extruded material is extruded through a die with a die orifice diameter of 40mm, a die core diameter of 20mm, a die temperature of 185℃, and is cooled by 28℃ circulating cooling water. The traction speed is 12m / min. After being granulated, it is extruded at 180℃ to form a sheath. Test Project Test Results Flame retardant rating V1 Oxygen Index 28.3% Minimum transmittance 45% Tensile strength 10.5MPa Elongation at break 260% 5% thermogravimetric temperature 348℃ Comparative Example 6, as a conventional formulation in the prior art, has a flame retardant rating of V1, the lowest oxygen index, and the worst flame retardant performance; it also has the lowest minimum light transmittance, the highest smoke density, and poor low-smoke effect; its tensile strength and elongation at break are both low, indicating insufficient mechanical properties; and its 5% thermal weight loss temperature is the lowest, indicating the worst thermal stability. Compared with the embodiments of the present invention, all performance aspects are significantly different. This fully demonstrates that the present invention, through the synergistic design of the raw material formulation, including the innovative combination of a multi-component composite flame retardant specific compatibilizer for polyolefin composite substrates and a high-efficiency flame retardant synergist and vermiculite-sepiolite composite powder, achieves a significant improvement in the comprehensive performance of the material, forming a clear distinction from the prior art.

[0041] Through a comprehensive performance comparison and analysis of the above six embodiments and six comparative examples, it can be clearly seen that the technical solution solves the technical pain point that existing low-smoke halogen-free flame-retardant polyolefin materials cannot simultaneously achieve flame retardancy, low smoke performance, and mechanical properties. All embodiments consistently achieve the UL94V0 flame retardancy rating, with an oxygen index of not less than 32.1%, a minimum light transmittance of not less than 65%, a tensile strength of not less than 12.8 MPa, an elongation at break of not less than 320%, and a 5% thermal weight loss temperature of not less than 372°C. All performance indicators are comprehensive and balanced. In contrast, Comparative Example 6, which represents the existing technology, can only achieve the V1 flame retardancy rating, with an oxygen index of only 28.3%, a minimum light transmittance of 45%, a tensile strength of 10.5 MPa, an elongation at break of 260%, and a 5% thermal weight loss temperature of 348°C. There is a significant difference between the two. This technical solution utilizes vermiculite-sepiolite composite powder as a key component. Its layered and porous structure not only forms a physical barrier during combustion to block heat and oxygen transfer, but also adsorbs smoke particles, reducing smoke density and improving the material's mechanical properties. In Comparative Example 1, the absence of this component resulted in a decrease in flame retardancy from V0 to V1, a 3.7% decrease in oxygen index, a 16% decrease in minimum light transmittance, and a 14.8% and 25% decrease in tensile strength and elongation at break, respectively, clearly demonstrating its indispensable role. The specialized compatibilizer, glycidyl methacrylate-grafted ethylene-octene copolymer, specifically improves the compatibility between the inorganic flame retardant and the organic substrate, preventing particle agglomeration. In Comparative Example 2, the absence of this component resulted in a tensile strength of only 9.8 MPa and an elongation at break of 220%, indicating poor mechanical properties. The performance of the flame retardant was significantly worse. Comparative Example 5 used traditional maleic anhydride-grafted polyethylene as a compatibilizer, which achieved a V0 flame retardancy rating, but all its performance was lower than that of Example 1. The multi-component composite flame retardant achieved high-efficiency flame retardancy by combining magnesium hydroxide, aluminum hydroxide, nano-hydroxyapatite, and microencapsulated ammonium polyphosphate, utilizing the synergistic effect of dehydration, cooling, and carbon layer barrier. Comparative Example 3 used a single magnesium hydroxide flame retardant, which only achieved a V2 flame retardancy rating and an oxygen index of only 27.5%, far inferior to the flame retardancy effect of the examples, demonstrating the synergistic advantage of the multi-component system. The combination of the high-efficiency flame retardant synergist aluminum diethylphosphinate and zirconium oxide further enhanced the flame retardancy efficiency. Comparative Example 4, lacking this component, saw its flame retardancy rating drop to V1, and its oxygen index and minimum transmittance both decreased significantly, verifying its enhancing effect on flame retardancy and low smoke performance. Furthermore, the polyolefin composite substrate of this technical solution, through the blending of high-density polyethylene ethylene-vinyl acetate copolymer and polyolefin elastomer, balances rigidity and flexibility, providing a good mechanical property foundation for the material. Combined with the synergistic effect of a multi-component composite flame retardant-specific compatibilizer, a highly efficient flame retardant synergist, and vermiculite-sepiolite composite powder, it achieves simultaneous improvement in flame retardancy, low smoke, mechanical properties, and thermal stability, breaking the inherent limitation of traditional materials where high flame retardancy inevitably sacrifices mechanical properties. Whether using the upper limit formulations of Examples 2 and 5, the lower limit formulation of Example 3, or combinations of different proportions in Examples 4 and 6, excellent and stable comprehensive performance is maintained, proving that the formulation design of this technical solution is scientifically sound, has a wide range of applications, and strong process stability. Compared with existing technologies, this technology significantly improves the core performance of the material without increasing production complexity, meeting the stringent safety requirements of high-end applications such as construction, rail transportation, and shipbuilding, filling a gap in existing technologies.

[0042] To further illustrate the beneficial technical effects of the high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheaths and their preparation methods in the various embodiments of the present invention, relevant performance tests were conducted on the high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheaths and their preparation methods in Examples 1-6 and Comparative Examples 1-6. The testing method is as follows: 1. Flame retardancy rating: The sample is processed into a standard strip of 127mm×12.7mm×3.2mm. Under normal temperature and pressure, the vertical burning test method is adopted. The top of the strip is ignited twice with a specified flame, and the ignition time is 30s each time. The burning time, dripping situation and whether the degreased cotton below is observed are observed. The flame retardancy rating is determined based on the test phenomena.

[0043] 2. Oxygen Index: The sample is processed into a standard strip of 80mm×10mm×4mm and placed in an oxygen index meter. The ratio of oxygen and nitrogen mixed gas is adjusted and gradually increased from a low oxygen concentration. The top of the strip is ignited, and the lowest oxygen concentration at which the strip can maintain combustion for 3 minutes or the burning length reaches 50mm is recorded. This is the oxygen index.

[0044] 3. Minimum transmittance: The sample is processed into a standard specimen of 100mm×100mm×3mm, placed in a smoke density tester, and ignited under specified combustion conditions. The degree of light obstruction by smoke during the combustion process is detected in real time using the light transmittance method, and the minimum transmittance value during the test is recorded.

[0045] 4. Tensile strength and elongation at break: The sample is processed into a dumbbell-shaped standard specimen and tested using a tensile testing machine. The test speed is set to 50 mm / min. The maximum tensile force at the time of specimen breakage and the elongation after breakage are recorded. The tensile strength and elongation at break are calculated respectively.

[0046] 5.5% Thermogravimetric Temperature: Place 5-10 mg of sample into a thermogravimetric analyzer. Under a nitrogen atmosphere, raise the temperature from room temperature to 600℃ at a rate of 10℃ / min. Monitor the change in sample mass with temperature in real time and record the temperature at which the sample mass loss reaches 5%. This temperature is the 5% thermogravimetric temperature.

[0047] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific technical solutions or characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath, characterized in that, It is composed of the following raw materials in parts by weight: 45-65 parts of polyolefin composite substrate, 35-55 parts of multi-component composite flame retardant, 4-9 parts of special compatibilizer, 0.8-2.5 parts of antioxidant, 0.5-2 parts of lubricant, 1.5-5 parts of high-efficiency flame retardant synergist, and 1-3 parts of vermiculite-sepiolite composite powder. The polyolefin composite substrate is a blend of high-density polyethylene, ethylene-vinyl acetate copolymer and polyolefin elastomer, with a weight ratio of 4:1:0.5-6:2:

1. The multi-component composite flame retardant is a compound of magnesium hydroxide, aluminum hydroxide, nano-hydroxyapatite and microencapsulated ammonium polyphosphate, with a weight ratio of 2:2:0.8:1-3:3:1.2:1.

8. The specific compatibilizer is a glycidyl methacrylate-grafted ethylene-octene copolymer. The high-efficiency flame retardant synergist is a compound of aluminum diethylphosphinate and zirconium oxide, with a weight ratio of 3:1-5:2; the weight ratio of vermiculite to sepiolite in the vermiculite-sepiolite composite powder is 1:0.5-1:1.

5.

2. The high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath according to claim 1, characterized in that, The particle size of the nano-hydroxyapatite is 50-200 nm.

3. The high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath according to claim 1, characterized in that, The particle size of the vermiculite-sepiolite composite powder is 1-5 μm.

4. The high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath according to claim 1, characterized in that, The antioxidant is a compound of antioxidant 1076 and antioxidant 626, with a weight ratio of 1:1 to 2:1; the lubricant is ethylene bis-stearamide.

5. A method for preparing a high flame-retardant, low-smoke, halogen-free flame-retardant polyolefin sheath, characterized in that, Including the following: S1 raw material preparation: Preparation of S1-1 polyolefin composite substrate: High-density polyethylene, ethylene-vinyl acetate copolymer and polyolefin elastomer are added to a high-speed mixer at a weight ratio of 4:1:0.5-6:2:1 and mixed at 60-80℃ and 600-800rpm for 8-15min to obtain polyolefin composite substrate. Preparation of S1-2 multi-component composite flame retardant: Magnesium hydroxide, aluminum hydroxide, nano-hydroxyapatite and microencapsulated ammonium polyphosphate were added to a conical mixer in a weight ratio of 2:2:0.8:1-3:3:1.2:1.8 and mixed for 30-45 minutes at room temperature and a speed of 200-300 rpm to obtain the multi-component composite flame retardant. Preparation of S1-3 special compatibilizer: Ethylene-octene copolymer, glycidyl methacrylate and dicumyl peroxide are added to a twin-screw extruder at a weight ratio of 100:3-5:0.2-0.5 and melt-grafted at 160-180℃ and screw speed of 80-120rpm. After extrusion, the mixture is pelletized to obtain glycidyl methacrylate-grafted ethylene-octene copolymer. Preparation of S1-4 high-efficiency flame retardant synergist: aluminum diethylphosphinate and zirconium oxide were added to a three-dimensional mixer at a weight ratio of 3:1-5:2 and mixed for 20-30 minutes at room temperature and a speed of 400-600 rpm to obtain the high-efficiency flame retardant synergist. Preparation of S1-5 vermiculite-sepiolite composite powder: Vermiculite and sepiolite were mixed at a weight ratio of 1:0.5-1:1.5, added to a ball mill, and ethanol was used as the dispersion medium. The ball-to-material ratio was 5:1-8:1, the speed was 300-400 r / min, and the mixture was ball-milled for 2-3 h. After filtration, the mixture was dried at 80-100℃ for 3-4 h to obtain vermiculite-sepiolite composite powder. S2 raw material pretreatment: Add γ-aminopropyltriethoxysilane to the multi-component composite flame retardant obtained from S1-2. The amount of γ-aminopropyltriethoxysilane added is 0.8-1.5 wt% of the total weight of the multi-component composite flame retardant. Dry in an oven at 110-125℃ for 3-5 hours and cool to room temperature to obtain the modified composite flame retardant. S3 Mixing and Plasticizing: The polyolefin composite substrate obtained by S1-1 and the special compatibilizer obtained by S1-3 are added to a high-speed mixer and mixed for 6-12 minutes at 85-100℃ and 900-1300rpm. Then, the modified composite flame retardant, antioxidant, lubricant, high-efficiency flame retardant synergist obtained by S1-4 and vermiculite-sepiolite composite powder obtained by S1-5 are added and mixed for 10-18 minutes at 95-110℃ and 1200-1600rpm to obtain a premix. S4 Melt Blending Extrusion: The premixed material is added to a twin-screw extruder, and the temperatures of each section are set as follows: Zone 1: 145-165℃, Zone 2: 165-180℃, Zone 3: 180-195℃, Zone 4: 190-205℃, and Die Head: 185-200℃. The screw speed is 35-65 rpm, and the vacuum degree is -0.06 to -0.09 MPa. Melt blending extrusion is then performed. S5 Molding Process: After the extruded material is extruded through the die, it is cooled by circulating cooling water at 25-32℃, and then pulled by a traction machine at a traction speed of 8-18m / min. The material is then granulated by a pelletizer to obtain sheath particles. The sheath is made by extruding the sheath particles at a molding temperature of 170-190℃.

6. The preparation method according to claim 5, characterized in that, The S4 twin-screw extruder has a length-to-diameter ratio of 38:1-42:1 and a screw compression ratio of 2.8:1-3.8:

1.

7. The preparation method according to claim 5, characterized in that, The die opening diameter of S5 molds is 25-55mm, the die core diameter is 12-32mm, and the die opening temperature is 180-195℃.

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