Low-filled phosphorus-nitrogen-nano-hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material and preparation method thereof

Abstract

The application belongs to the technical field of high polymer flame-retardant cable materials, and particularly relates to a low-filled phosphorus-nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material and a preparation method thereof. The cable material is prepared by melt blending granulation with ternary compounded polyolefin as a base resin, compounded metal hydroxide as an inorganic flame retardant, and addition of a phosphorus-nitrogen synergistic flame retardant compounded by microencapsulated ammonium polyphosphate and melamine cyanurate, functionalized nano hydrotalcite surface modified by a silane coupling agent, and an interface modifier. The application has excellent flame-retardant performance under a relatively low total filling amount of flame retardant, and has good mechanical performance and processing fluidity, low smoke density during combustion, no release of toxic corrosive gas, effective inhibition of flame retardant migration and precipitation, and significantly improved long-term use stability. The preparation process is simple, and the application can be widely used in low-smoke halogen-free cable insulation and sheath layer materials in the fields of electric power, communication, rail transportation and new energy.

Description

Technical Field

[0001] This invention belongs to the technical field of polymer flame-retardant cable materials, specifically relating to a low-filling phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material and its preparation method. Background Technology

[0002] Low-smoke halogen-free flame-retardant cable materials, due to their low smoke release during combustion and the absence of corrosive and toxic gases such as hydrogen halides, meet the requirements of modern society for public safety and environmental protection. They are widely used in rail transit, new energy vehicles, data centers, high-rise buildings, nuclear power, and other fields, leading to continuous market demand growth. As related industries continue to raise their requirements for cable safety performance, higher comprehensive requirements are being placed on the flame retardancy rating, mechanical properties, processing performance, and long-term stability of cable materials.

[0003] Currently, most mainstream low-smoke halogen-free flame-retardant polyolefin cable materials in the industry use high-filler metal hydroxides as flame retardants. The flame-retardant effect is achieved through the endothermic decomposition and dilution of combustible gases by inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide. To achieve the required flame-retardant rating, the amount of these inorganic flame retardants added is usually high. High-filler inorganic flame retardants can disrupt the continuous phase structure of the polyolefin matrix, leading to a decrease in the interfacial bonding force between the filler and the resin matrix, and deteriorating the mechanical properties of the material.

[0004] Meanwhile, the addition of a large amount of inorganic filler significantly increases the melt viscosity of the blend system, leading to poor material processing fluidity. This can easily cause problems such as die buildup, melt fracture, and rough product surface during wire and cable extrusion, affecting production efficiency and product appearance quality. Furthermore, due to the significant polarity difference between inorganic flame retardants and the polyolefin matrix, their interfacial compatibility is poor. During long-term use, flame retardants are prone to migrate and precipitate to the surface, causing a gradual decline in flame retardant performance and affecting the cable's service life and safety reliability.

[0005] In the existing technology, although there have been attempts to partially replace inorganic flame retardants and reduce the filling amount by adding phosphorus-based, nitrogen-based flame retardants or nanofillers, it is difficult to balance flame retardant efficiency, mechanical properties and processing performance. In particular, it is difficult to meet the requirements of high flame retardant rating, excellent mechanical properties and good processing fluidity at a low flame retardant filling amount. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a low-filling phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material and its preparation method.

[0007] The purpose of this invention is to solve the problems of mechanical property degradation, poor processing fluidity, and easy migration and precipitation of flame retardant caused by excessive flame retardant filling in existing low-smoke halogen-free flame-retardant polyolefin cable materials, and to achieve a balanced optimization of flame retardant performance, mechanical performance and processing performance under low filling conditions.

[0008] The first aspect of this invention provides a low-filled phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material, which is made of the following components in parts by weight: 100 parts of matrix resin; 100-140 parts of compound inorganic flame retardant; 5-15 parts of phosphorus-nitrogen synergistic flame retardant; Functionalized nano-hydrotalcite, 1-5 parts; Interface modifier 2-6 parts; Antioxidant 0.3–1.5 parts; Lubricant 0.5 to 2 parts.

[0009] As a further optimization, the matrix resin is a ternary compound system of ethylene-vinyl acetate copolymer, polyolefin elastomer, and metallocene linear low-density polyethylene.

[0010] As a further optimization scheme, the mass ratio of ethylene-vinyl acetate copolymer, polyolefin elastomer, and metallocene linear low-density polyethylene in the matrix resin is ::; the compounded inorganic flame retardant is composed of aluminum hydroxide and magnesium hydroxide in a mass ratio of 1:0.6 to 1:1.2; the phosphorus-nitrogen synergistic flame retardant is composed of microencapsulated ammonium polyphosphate and melamine cyanurate in a mass ratio of 1:0.5 to 1:1; and the total flame retardant filling amount of the system does not exceed 150 parts.

[0011] As a further optimization, functionalized nano-hydrotalcite is a magnesium-aluminum type hydrotalcite with a surface modified by a silane coupling agent, with an original particle size of 30-80 nm and a grafting rate of 1.5%-3.5%.

[0012] As a further optimization, the silane coupling agent is selected from at least one of γ-aminopropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and vinyltrimethoxysilane.

[0013] As a further optimization scheme, the interface modifier is a compound of maleic anhydride-grafted polyolefin elastomer and aminosilane coupling agent in a mass ratio of 2:1 to 4:1.

[0014] As a further optimization, the wall material of microencapsulated ammonium polyphosphate is melamine-formaldehyde resin or melamine resin, with a coating rate of 15% to 25% and a particle size of 10 to 30 μm.

[0015] A second aspect of this invention provides a method for preparing a low-filled phosphorus-nitrogen-nanohydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material, comprising the following steps: Surface functionalization of nano-hydrotalcite was performed using a silane coupling agent to obtain functionalized nano-hydrotalcite. The base resin, compounded inorganic flame retardant, phosphorus-nitrogen synergistic flame retardant, functionalized nano-hydrotalcite, interface modifier, antioxidant and lubricant are mixed evenly according to the formula to obtain the premix. The premixed material is mixed in an internal mixer and then fed into a twin-screw extruder for melt blending and extrusion to obtain cable material particles.

[0016] As a further optimization, the preparation method includes the following steps: Functionalization of nano-hydrotalcite: Nano-hydrotalcite is dispersed in anhydrous ethanol, a silane coupling agent is added, and the mixture is refluxed and stirred at 60-80℃ for 2-4 hours. After filtration and washing, it is vacuum dried at 80-100℃ for 6-10 hours to obtain functionalized nano-hydrotalcite. Premix: The matrix resin, compounded inorganic flame retardant, phosphorus-nitrogen synergistic flame retardant, functionalized nano-hydrotalcite, interface modifier, antioxidant and lubricant are added to a high-speed mixer and stirred at 40-60℃ for 10-20 minutes to obtain the premix. Melt blending and granulation: The premixed material is added to a mixer + twin-screw extruder for melt blending. The mixture is blended in the mixer for 12-15 minutes. When the material temperature reaches 150-160℃, it is discharged to a twin-screw extruder for extrusion. After extrusion, water cooling, pelletizing and drying, cable material particles are obtained.

[0017] As a further optimization scheme, the temperatures of the twin-screw extruder from zone one to zone eight are 135℃, 135℃, 125℃, 120℃, 115℃, 110℃, 110℃, and 100~130℃ respectively, and the screw speed is 180~260r / min.

[0018] Beneficial effects Compared with existing technologies, the low-filling phosphorus-nitrogen-nano-hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material provided by this invention achieves a dual synergistic effect of gas-phase flame retardancy and condensed-phase barrier under relatively low total flame retardant filling conditions. This is achieved through the multi-component synergistic combination of a ternary compound resin matrix, compounded inorganic flame retardants, microencapsulated phosphorus-nitrogen synergistic system, and functionalized nano-hydrotalcite, combined with a chemically bonded interface network constructed by interface modification technology. While ensuring a high flame retardant rating, it effectively improves the dispersibility and interfacial bonding of fillers in the matrix, significantly improves the mechanical properties and processing fluidity of the material, and inhibits the migration and precipitation of flame retardants, thereby improving the long-term stability of the material. The material has low smoke density and no release of toxic or corrosive gases during combustion. It is suitable for low-smoke halogen-free cable insulation and sheathing layers in fields such as power, communications, rail transportation, and new energy. The preparation process is simple and stable, and it is suitable for industrial-scale production. Detailed Implementation

[0019] The present invention is further illustrated below with specific embodiments. These embodiments are exemplary and intended to illustrate the problem and explain the present invention, and are not intended to be limiting.

[0020] The raw materials used in the embodiments and comparative examples of this invention are described as follows: The matrix resin includes ethylene-vinyl acetate copolymer (VA content of 28%), polyolefin elastomer (octene content of 20%), and metallocene linear low-density polyethylene. The inorganic flame retardants are aluminum hydroxide and magnesium hydroxide, both commercially available industrial-grade products. The phosphorus-nitrogen synergistic flame retardant is composed of microencapsulated ammonium polyphosphate and melamine cyanurate, wherein the wall material of the microencapsulated ammonium polyphosphate is melamine resin, with a coverage rate of 20%, a particle size d50 of 4–8 μm, and a degree of polymerization of not less than 1000. The functionalized nano-hydrotalcite is magnesium-aluminum type with an initial particle size of 50 nm. The interface modifier is composed of maleic anhydride-grafted polyolefin elastomer (grafting rate of approximately 1.2%) and γ-aminopropyltriethoxysilane in a mass ratio of 3:1. The antioxidant used is antioxidant 1010, and the lubricant is silicone masterbatch (organic silicon content 40-50%), both of which are conventional commercially available industrial-grade products.

[0021] Example 1 The low-filled phosphorus-nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material of this embodiment is made from the following components in parts by weight according to the formula in Table 1: 60 parts of ethylene-vinyl acetate copolymer, 15 parts of polyolefin elastomer, 25 parts of metallocene linear low-density polyethylene, 120 parts of compound inorganic flame retardant composed of aluminum hydroxide and magnesium hydroxide in a mass ratio of 1:0.8, 5 parts of functionalized nano hydrotalcite, 14 parts of phosphorus-nitrogen synergistic flame retardant composed of microencapsulated ammonium polyphosphate and melamine cyanurate in a mass ratio of 1:0.7, 4 parts of interface modifier, 0.8 parts of antioxidant, and 1 part of lubricant.

[0022] The preparation method is as follows: (1) Functionalization of nano-hydrotalcite: 50 nm magnesium-aluminum nano-hydrotalcite was dispersed in anhydrous ethanol, γ-aminopropyltriethoxysilane was added, and the mixture was stirred under normal pressure at 70 °C for 3 h. After filtration and washing, it was dried under vacuum at 90 °C for 8 h to obtain functionalized nano-hydrotalcite with a grafting rate of 2.1%.

[0023] (2) Premixing: The matrix resin, compound inorganic flame retardant, phosphorus and nitrogen synergistic flame retardant, functionalized nano hydrotalcite, interface modifier, antioxidant and lubricant are added to a high-speed mixer and stirred at 50°C for 15 minutes to obtain the premix.

[0024] (3) Melt blending and granulation: The premixed material is added to the internal mixer + twin-screw extruder for melt blending. The mixture is blended in the internal mixer for 13 minutes. When the material temperature reaches 155℃, it is discharged from the internal mixer to the twin-screw extruder. The temperatures of the first to eighth zones of the twin-screw extruder are 135℃, 135℃, 125℃, 120℃, 115℃, 110℃, 110℃, and 115℃ respectively. The screw speed is 220r / min. After extrusion, water cooling, pelletizing and drying, cable material particles are obtained.

[0025] Example 2 The low-filled phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material of this embodiment is prepared according to Table 1, and the preparation method is the same as that of Example 1.

[0026] Example 3 The low-filled phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material of this embodiment is prepared according to Table 1, and the preparation method is the same as that of Example 1.

[0027] Comparative Example 1 The cable material of this comparative example was prepared according to the raw material composition in Table 1, and the preparation method was the same as that in Example 1, except that no functionalized nano-hydrotalcite was added.

[0028] Comparative Example 2 The cable material of this comparative example was prepared according to the raw material composition in Table 1, and the preparation method was the same as that in Example 1. The difference was that nano-hydrotalcite without silane coupling agent surface modification was used, and no interface modifier was added.

[0029] Comparative Example 3 The cable material of this comparative example was prepared according to the raw material composition in Table 1, and the preparation method was the same as that in Example 1, except that no phosphorus-nitrogen synergistic flame retardant was added.

[0030] Comparative Example 4 The cable material of this comparative example was prepared according to the raw material composition in Table 1, and the preparation method was the same as that in Example 1. The difference was that the mass ratio of microencapsulated ammonium polyphosphate to melamine cyanurate in the phosphorus-nitrogen synergistic flame retardant was 1:1.5.

[0031] Comparative Example 5 The cable material of this comparative example was prepared according to the raw material composition in Table 1, and the preparation method was the same as in Example 1, except that aluminum diethylphosphonate was used instead of microencapsulated ammonium polyphosphate.

[0032] Table 1 Formula (parts by weight) Performance testing The cable material particles prepared in Examples 1-3 and Comparative Examples 1-5 were pressed into sheets at 175°C and subjected to performance tests after 16 hours. The tensile strength and elongation at break were tested according to GB / T 1040 standard; the melt flow rate was tested according to GB / T 3682 standard at 190°C and 2.16 kg; the oxygen index was tested according to GB / T 2406 standard; the smoke density was tested according to GB / T 8323 standard under flameless conditions; the vertical burning performance test was conducted by producing 1.5 mm² wires with a wall thickness of 0.7 mm using the above materials, and performing a VW-1 vertical burning test according to UL 1581 standard. The performance test results of each example and comparative example are shown in Table 2.

[0033] Table 2 Performance Test Data The test results show that the cable materials prepared in Examples 1 to 3 of this invention can all pass the VW-1 level vertical burning test, with tensile strength reaching 14.2 to 15.1 MPa, elongation at break reaching 270% to 292%, melt flow index reaching 8.8 to 10.2 g / 10 min, oxygen index reaching 36.5% to 39.5%, and flameless smoke density reaching 187 to 235. They can take into account excellent flame retardant properties, mechanical properties, and processing properties.

[0034] Compared to Example 1, Comparative Example 1, without the addition of nano-hydrotalcite, showed a smaller decrease in mechanical and processing properties, but its oxygen index was only 33%, and its smoke density was as high as 376. Furthermore, it failed the VW-1 vertical combustion test, indicating that the nano-hydrotalcite plays a crucial role in achieving efficient flame retardancy and smoke suppression through its thermal barrier and catalytic char formation in the condensed phase. Comparative Example 2, using unmodified nano-hydrotalcite without any interface modifier, experienced particle agglomeration due to the strong polarity of the hydroxyl groups on the nano-hydrotalcite surface, resulting in a decrease in tensile strength to 11.8 MPa, elongation at break to 210%, and a melt flow index of only 4.5 g / 10 min. Its processing performance was significantly deteriorated, demonstrating that surface functionalization and interface modifiers are essential for the dispersion and interfacial bonding of nano-hydrotalcite. Comparative Example 3, without the addition of a phosphorus-nitrogen synergistic flame retardant, had a relatively high elongation at break, but its oxygen index was only 32%, and it failed the VW-1 vertical combustion test. This indicates that the gas-phase flame retardancy and char formation of the phosphorus-nitrogen system are necessary components for achieving efficient flame retardancy with low filler content. Comparative Example 4 altered the ratio of phosphorus and nitrogen synergistic flame retardants. Although the oxygen index was higher, the smoke density increased to 320, and it failed the VW-1 vertical burning test, indicating that the ratio of microencapsulated ammonium polyphosphate to melamine cyanurate has a significant impact on char quality and flame retardant effect. Comparative Example 5 used aluminum diethylphosphonate instead of microencapsulated ammonium polyphosphate. Although the oxygen index was higher and it passed the VW-1 test, the smoke density was as high as 360, and the tensile strength was only 10.9 MPa, failing to meet the mechanical performance requirements. This indicates that the microencapsulated ammonium polyphosphate and melamine cyanurate compound system has unique advantages when synergistically combined with nano-hydrotalcite.

[0035] This invention achieves synergistic optimization of flame retardancy, mechanical properties, and processing performance under low filling conditions with a total flame retardant content not exceeding 150 parts (approximately 58 wt%). It utilizes the synergistic toughening effect of the EVA / POE / mLLDPE ternary resin matrix, the basic flame retardant effect of the ATH / MDH compound inorganic flame retardant, the gaseous mechanism of the microencapsulated APP / MCA phosphorus-nitrogen system, and the multiple effects of functionalized nano-LDHs in the condensed phase (thermal barrier-catalytic char formation-smoke suppression). Combined with the chemically bonded interface network constructed by the interface modifier, this invention effectively solves the performance degradation problem caused by high filling in traditional low-smoke halogen-free cable materials by synergistic toughening of the EVA / POE / mLLDPE ternary resin matrix, the basic flame retardant effect of the ATH / MDH compound inorganic flame retardant, the gas mechanism of the microencapsulated APP / MCA phosphorus-nitrogen system, and the multiple effects of functionalized nano-LDHs in the condensed phase (thermal barrier-catalytic char formation-smoke suppression). The layered structure of functionalized nano-LDHs synergistically interacts with the expanded carbon layer formed by the phosphorus-nitrogen system during combustion to form a dense ceramic-carbon composite barrier layer. This layer not only effectively blocks heat and mass transfer but also significantly inhibits flue gas release and droplet generation. Simultaneously, the interfacial bridging effect formed by the silane coupling agent and maleic anhydride grafts enables uniform dispersion of the nanofiller and effective anchoring of the flame retardant, reducing the risk of flame retardant migration and improving the long-term stability of the material.

[0036] The above embodiments are exemplary and are intended to illustrate the technical concept and features of the present invention, so that those skilled in the art can understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A low-filling phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material, characterized in that, It is made from the following components in parts by weight: 100 parts of matrix resin; 100-140 parts of compound inorganic flame retardant; 5-15 parts of phosphorus-nitrogen synergistic flame retardant; Functionalized nano-hydrotalcite, 1-5 parts; Interface modifier 2-6 parts; Antioxidant 0.3–1.5 parts; Lubricant 0.5 to 2 parts.

2. The low-filling phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material according to claim 1, characterized in that, The matrix resin is a ternary compound system of ethylene-vinyl acetate copolymer, polyolefin elastomer, and metallocene linear low-density polyethylene.

3. The low-filling phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material according to claim 2, characterized in that, In the matrix resin, the mass ratio of ethylene-vinyl acetate copolymer, polyolefin elastomer, and metallocene linear low-density polyethylene is (50-65):(10-20):(15-25); the compounded inorganic flame retardant is composed of aluminum hydroxide and magnesium hydroxide in a mass ratio of 1:0.6-1:1.2; the phosphorus-nitrogen synergistic flame retardant is composed of microencapsulated ammonium polyphosphate and melamine cyanurate in a mass ratio of 1:0.5-1:1; the total flame retardant filling amount of the system does not exceed 150 parts.

4. The low-filling phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material according to claim 3, characterized in that, The functionalized nano-hydrotalcite is a magnesium-aluminum type hydrotalcite with a surface modified by a silane coupling agent. Its original particle size is 30-80 nm and the grafting rate is 1.5%-3.5%.

5. The low-filling phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material according to claim 4, characterized in that, The silane coupling agent is selected from at least one of γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane.

6. The low-filling phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material according to claim 1, characterized in that, The interface modifier is a compound of maleic anhydride-grafted polyolefin elastomer and aminosilane coupling agent in a mass ratio of 2:1 to 4:

1.

7. The low-filling phosphorus and nitrogen-nano hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material according to claim 1, characterized in that, The wall material of the microencapsulated ammonium polyphosphate is melamine-formaldehyde resin or melamine resin, with a coating rate of 15% to 25% and a particle size of 10 to 30 μm.

8. A method for preparing a low-filled phosphorus-nitrogen-nanohydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Surface functionalization of nano-hydrotalcite was performed using a silane coupling agent to obtain functionalized nano-hydrotalcite; (2) Mix the matrix resin, compound inorganic flame retardant, phosphorus-nitrogen synergistic flame retardant, functionalized nano-hydrotalcite, interface modifier, antioxidant and lubricant evenly according to the formula to obtain a premix; (3) The premixed material is mixed in a mixer and then fed into a twin-screw extruder for melt blending and extrusion to obtain cable material particles.

9. The preparation method of the low-filled phosphorus and nitrogen-nano-hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material according to claim 8, characterized in that, Includes the following steps: (1) Functionalization of nano-hydrotalcite: Disperse nano-hydrotalcite in anhydrous ethanol, add silane coupling agent, reflux and stir at 60-80℃ for 2-4h, filter, wash and then vacuum dry at 80-100℃ for 6-10h to obtain functionalized nano-hydrotalcite. (2) Premixing: The matrix resin, compound inorganic flame retardant, phosphorus-nitrogen synergistic flame retardant, functionalized nano-hydrotalcite, interface modifier, antioxidant and lubricant are added to a high-speed mixer and stirred at 40-60℃ for 10-20 min to obtain the premix. (3) Melt blending and granulation: The premixed material is added to the internal mixer + twin-screw extruder for melt blending. The mixture is blended in the internal mixer for 12-15 minutes. When the material temperature reaches 150-160℃, it is discharged to the twin-screw extruder for extrusion. After extrusion, water cooling, pelletizing and drying, cable material particles are obtained.

10. The preparation method of the low-filled phosphorus and nitrogen-nano-hydrotalcite synergistic low-smoke halogen-free flame-retardant polyolefin cable material according to claim 9, characterized in that, The temperatures of the twin-screw extruder in zones one through eight are 135℃, 135℃, 125℃, 120℃, 115℃, 110℃, 110℃, and 100-130℃ respectively, and the screw speed is 180-260 r / min.

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