Low-smoke halogen-free flame-retardant power cable material and preparation method thereof

Abstract

The invention relates to the technical field of cable materials, in particular to a low-smoke halogen-free flame-retardant power cable material and a preparation method thereof, and the low-smoke halogen-free flame-retardant power cable material comprises the following raw materials: ethylene-vinyl acetate, low-phosphorus grafted polyvinylidene fluoride, metal hydroxide, microencapsulated ammonium polyphosphate, zinc stearate, tetra [beta-(3, 3, 5-trimethyl-1, 3, 5-trimethyl-1, 3, 5-trimethyl-1, 3, 5-trimethyl-1, 3, 5-trimethyl-1, 3 2, 5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester and polyolefin elastomer grafted maleic anhydride are used as raw materials. According to the low-phosphorus grafted polyvinylidene fluoride, a phosphate group is introduced to a polymer main chain, so that the polarity and interfacial activity of a matrix are enhanced, stable interface bonding with other components can be formed in the processing and combustion process, the dispersity and synergism of flame-retardant components are improved, and migration and precipitation phenomena are reduced; the microencapsulated ammonium polyphosphate effectively inhibits moisture absorption and water sensitivity of the ammonium polyphosphate, and the processing thermal stability is improved; and during combustion, the microcapsule shell layer can enhance the heat insulation and oxygen isolation capability, inhibit generation of toxic smoke and improve the flame retardant efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cable materials, in particular to a low-smoke halogen-free flame-retardant power cable material and a preparation method thereof. BACKGROUND

[0002] With the continuous improvement of electrical safety requirements in the fields of urban power grid reconstruction, rail transit and data center, power cable materials are developing towards high flame retardation, low smoke, halogen-free and long-term thermal stability. Although traditional halogen-based flame retardants (such as chlorine-containing and bromine-containing compounds) have excellent flame retardation efficiency, they release a large amount of corrosive hydrogen halide gas and toxic smoke during combustion, which poses a threat to equipment and personnel safety. In order to achieve green and environmentally friendly flame retardation, polyolefin, modified polyvinyl chloride or fluoropolymer is gradually used as a base material, and inorganic flame-retardant synergistic systems such as phosphorus, nitrogen and silicon are used to develop low-smoke halogen-free flame-retardant cable materials.

[0003] However, the existing low-smoke halogen-free flame-retardant cable material still has deficiencies in the balance between flame retardation performance and material comprehensive performance. Conventional polyvinylidene fluoride has low polarity and limited interfacial bonding capacity, and when compounded with phosphorus-based flame retardants, it is prone to delamination or interfacial debonding, and has poor thermal stability and interfacial compatibility, which leads to easy precipitation or migration of the flame retardant during combustion, and insufficient flame-retardant durability. In view of this, we propose a low-smoke halogen-free flame-retardant power cable material and a preparation method thereof. SUMMARY

[0004] The present application aims to provide a low-smoke halogen-free flame-retardant power cable material and a preparation method thereof, to solve the problem of insufficient flame-retardant durability caused by the low polarity and limited interfacial bonding capacity of conventional polyvinylidene fluoride when compounded with phosphorus-based flame retardants, which leads to delamination or interfacial debonding, poor thermal stability and interfacial compatibility, and easy precipitation or migration of the flame retardant during combustion.

[0005] The present application provides a low-smoke halogen-free flame-retardant power cable material, comprising the following raw materials: ethylene-vinyl acetate, low-phosphorus grafted polyvinylidene fluoride, metal hydroxide, microencapsulated ammonium polyphosphate, zinc stearate, tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester and polyolefin elastomer grafted maleic anhydride. The low-phosphorus grafted polyvinylidene fluoride is prepared by free radical graft polymerization reaction of polyvinylidene fluoride activated by alkali and vinyl phosphonic acid diethyl ester under the action of an initiator. The microencapsulated ammonium polyphosphate is prepared by in-situ coating of silane coupling agent to form microcapsules through sol-gel method.

[0006] As preferred, the ethylene-vinyl acetate 25-30 parts by weight, low phosphorus grafting type polyvinylidene fluoride 5-8 parts by weight, metal hydroxide 42-45 parts by weight, microencapsulated ammonium polyphosphate 5-7 parts by weight, zinc stearate 0.8-1.2 parts by weight, tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester 0.3-0.5 parts by weight, and polyolefin elastomer grafted maleic anhydride 5-8 parts by weight.

[0007] As preferred, the preparation method of the low phosphorus grafting type polyvinylidene fluoride is as follows: The polyvinylidene fluoride is dissolved in N-methyl pyrrolidone at a mass ratio of 1:5-10, stirred at 80-90℃ and a speed of 300-500rpm for 2-3h; cooled to 40-50℃, and 0.05-0.10mol / L potassium hydroxide / ethanol solution is added dropwise, stirred at a speed of 100-200rpm for 0.5-1.0h; then vinyl phosphonic acid diethyl ester and azobisisobutyronitrile are added, and nitrogen is passed at a flow rate of 0.3L / min for 30min; then stirred at a speed of 500-600rpm for 10-12h under nitrogen protection at 70-75℃; after the reaction is completed, the reaction liquid is cooled to room temperature, poured into 5-10 times the volume of deionized water for precipitation, and after standing for 2h, suction filtration is performed, then washed with deionized water and ethanol each for 2 times, and vacuum dried at 50-60℃ to constant weight to obtain the low phosphorus grafting type polyvinylidene fluoride.

[0008] Azobisisobutyronitrile should be stored in low temperature and dark conditions and added in batches; N-methyl pyrrolidone should be operated in a closed reaction kettle and equipped with a tail gas condensation recovery system; and each waste liquid can be discharged after neutralization treatment to meet the discharge requirements.

[0009] As preferred, the addition amount of the vinyl phosphonic acid diethyl ester accounts for 8-12mol% of the polyvinylidene fluoride repeating unit.

[0010] As preferred, the addition amount of the azobisisobutyronitrile accounts for 2-5% of the number of moles of the vinyl phosphonic acid diethyl ester.

[0011] As preferred, the preparation method of the microencapsulated ammonium polyphosphate is as follows: The ammonium polyphosphate is dispersed in deionized water, and 1.5-2.0% of polyvinyl alcohol based on the mass of the ammonium polyphosphate is added, stirred at a speed of 400-500rpm for 10-30min at 25-30℃ to obtain an ammonium polyphosphate suspension with a solid content of 15-20%; The tetraethoxysilane and 3-methacryloyloxypropyltrimethoxysilane are mixed, the pH is adjusted to 4.0-5.0 with 0.1mol / L hydrochloric acid, and the pre-hydrolysis liquid is obtained by stirring at a speed of 200-300rpm for 2-3h at 30-35℃. The ammonium polyphosphate suspension is placed in a 40-50℃ water bath, the pre-hydrolysis solution is added dropwise, the dropwise adding time is 25-30min, and stirring is carried out at a speed of 300-400rpm for 1-2h; the temperature is raised to 65-70℃, and stirring is continued for 5-6h; after stopping stirring, the mixture is allowed to stand for 30min, centrifuged at a speed of 3000-5000rpm for 10-20min to collect the microcapsules, and then washed with deionized water and anhydrous ethanol for 3 times each, and then placed in a vacuum dryer at 50-60℃ until the weight is constant, to obtain the microencapsulated ammonium polyphosphate.

[0012] Preferably, the mixing molar ratio of the tetraethoxysilane and 3-methacryloyloxypropyltrimethoxysilane is 7-10:1.

[0013] Preferably, the mass ratio of the pre-hydrolysis solution to the ammonium polyphosphate suspension is 0.4-0.6:1.

[0014] In another aspect, the application provides a preparation method of low-smoke halogen-free flame-retardant power cable material, for preparing the low-smoke halogen-free flame-retardant power cable material as described above, comprising the following steps: S1.1, the raw materials are weighed according to parts by weight; S1.2, the ethylene-vinyl acetate, polyolefin elastomer grafted maleic anhydride and microencapsulated ammonium polyphosphate are vacuum dried at 80-90℃ for 4-6h; the zinc stearate is sieved through a 100 mesh sieve for use; S1.3, the ethylene-vinyl acetate and polyolefin elastomer grafted maleic anhydride are added into a high-speed mixer, and initial mixing is carried out at a speed of 500rpm for 2min; then the low-phosphorus grafted polyvinylidene fluoride and tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester are added, the speed is increased to 800rpm, and mixing is carried out for 3min; then the metal hydroxide is added, high-speed mixing is carried out at 1000rpm for 5min, finally the microencapsulated ammonium polyphosphate is added, the speed is reduced to 600rpm, and mixing is carried out for 3min, to obtain a premix; S1.4, the premix is transferred into a twin-screw extruder, the temperature gradient is set to 155-185℃, the screw speed is 300-400rpm, and the melt is obtained by melt blending under the condition of a vacuum degree of-0.08MPa for 8-10min; the melt is cut into granules by air-cooled die face heat cutting, and then vacuum dried at 60-70℃ for 4-6h, to obtain the low-smoke halogen-free flame-retardant power cable material.

[0015] Preferably, in S1.3, the metal hydroxide is obtained by mixing aluminum hydroxide and magnesium hydroxide according to a mass ratio of 3:1.

[0016] Compared with the prior art, the application has the following beneficial effects: The low-smoke halogen-free flame-retardant power cable material and the preparation method thereof, wherein the low-phosphorus grafted polyvinylidene fluoride introduces phosphate groups on the polymer main chain, enhances the polarity and interfacial activity of the matrix, can form a stable interfacial combination with metal hydroxide and phosphorus-based flame retardants in the process of processing and combustion, improves the dispersibility and synergistic effect of the flame-retardant components, and reduces the migration and separation phenomenon; at the same time, the fluorine skeleton endows the system with excellent heat resistance and electrical insulation stability; the microencapsulated ammonium polyphosphate is coated with a siliceous layer on the surface by a sol-gel method, which effectively improves the dispersion and combination of the flame retardant and the polymer matrix, inhibits the hygroscopicity and water sensitivity of the ammonium polyphosphate, and improves the processing thermal stability; the microcapsule shell layer can synergistically enhance the heat and oxygen insulation capacity during combustion, further inhibit the generation of toxic smoke, and improve the flame-retardant efficiency. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0018] The present application provides a low-smoke halogen-free flame-retardant power cable material, comprising the following raw materials: ethylene-vinyl acetate, low-phosphorus grafted polyvinylidene fluoride, metal hydroxide, microencapsulated ammonium polyphosphate, zinc stearate, tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester and polyolefin elastomer grafted maleic anhydride. The low-phosphorus grafted polyvinylidene fluoride is prepared by free radical graft polymerization of ethylene vinyl phosphate diethyl ester under the action of an initiator after alkali activation of polyvinylidene fluoride. The microencapsulated ammonium polyphosphate is prepared by in-situ coating of silane coupling agent on the surface of ammonium polyphosphate by a sol-gel method to form microcapsules.

[0019] The ethylene-vinyl acetate is purchased from Hubei Kovod Chemical Co., Ltd.

[0020] The polyvinylidene fluoride (CAS number: 24937-79-9, purity 98.5%) is purchased from Hubei Chushengwei Chemical Co., Ltd.

[0021] The ethylene-vinyl acetate is purchased from Hubei Kovod Chemical Co., Ltd.

[0022] The azobis isobutyronitrile (CAS number: 78-67-1, purity 99%) is purchased from Shandong Yukang Chemical Co., Ltd.

[0023] Aluminum hydroxide (CAS No. 21645-51-2, purity AR), magnesium hydroxide (CAS No. 1309-42-8, purity CP, 98%), ammonium polyphosphate (CAS No. 68333-79-9), 3-methacryloxypropyltrimethoxysilane (CAS No. 2530-85-0, purity: BR, 98%), zinc stearate (CAS No. 557-05-1, purity CP), pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (CAS No. 6683-19-8, purity 98%) were purchased from Shanghai Yuan Ye Biological Technology Co., Ltd.

[0024] Tetraethoxysilane (CAS No. 78-10-4, purity 99%) was purchased from Condus Chemical Industry (Hubei) Co., Ltd.

[0025] Polyolefin elastomer grafted maleic anhydride was purchased from Dongguan Bailing New Material Co., Ltd.

[0026] The metal hydroxide was mixed by aluminum hydroxide and magnesium hydroxide in a mass ratio of 3:1.

[0027] Example 1: Preparation method of low-smoke halogen-free flame-retardant power cable material, comprising the following steps: S1.1, the following raw materials were weighed by weight parts: ethylene-vinyl acetate 25 parts by weight, low-phosphorus grafted polyvinylidene fluoride 5 parts by weight, metal hydroxide 42 parts by weight, microencapsulated ammonium polyphosphate 5 parts by weight, zinc stearate 0.8 parts by weight, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] 0.3 parts by weight and polyolefin elastomer grafted maleic anhydride 5 parts by weight; S1.2, ethylene-vinyl acetate, polyolefin elastomer grafted maleic anhydride, and microencapsulated ammonium polyphosphate were vacuum dried at 80°C for 4h; zinc stearate was sieved through a 100 mesh sieve for use; S1.3, ethylene-vinyl acetate and polyolefin elastomer grafted maleic anhydride were added to a high-speed mixer and mixed at a speed of 500 rpm for 2 min; then low-phosphorus grafted polyvinylidene fluoride and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] were added and mixed at a speed of 800 rpm for 3 min; then the metal hydroxide was added and mixed at a high speed of 1000 rpm for 5 min; finally, the microencapsulated ammonium polyphosphate was added and mixed at a speed of 600 rpm for 3 min to obtain a premix; S1.4, the premix was transferred into a twin-screw extruder, the temperature gradient was set to 155°C, the screw speed was 300 rpm, and the melt was obtained by melt blending under the condition of vacuum degree-0.08 MPa for 8 min; the melt was cut into pellets by air-cooled die face hot cutting, and then vacuum dried at 60°C for 4h to obtain a low-smoke halogen-free flame-retardant power cable material.

[0028] The preparation method of the low-phosphorus grafted polyvinylidene fluoride is as follows: The polyvinylidene fluoride is dissolved in N-methyl pyrrolidone at a mass ratio of 1:5, stirred at 80°C at a speed of 300 rpm for 2 h; the temperature is lowered to 40°C, and 0.05 mol / L potassium hydroxide / ethanol solution is added dropwise, stirred at a speed of 100 rpm for 0.5 h; then vinyl phosphonic acid diethyl ester (10 mol% of the polyvinylidene fluoride repeating unit) and azobisisobutyronitrile (3% of the molar number of the vinyl phosphonic acid diethyl ester) are added, and nitrogen gas is passed at a flow rate of 0.3 L / min for 30 min; then the reaction is carried out at 70°C under nitrogen protection, stirred at a speed of 500 rpm for 10 h; after the reaction is completed, the reaction liquid is cooled to room temperature, poured into 5 times the volume of deionized water for precipitation, and after standing for 2 h, it is filtered, then washed with deionized water and ethanol each for 2 times, and dried under vacuum at 50°C to constant weight to obtain the low-phosphorus grafted polyvinylidene fluoride.

[0029] The preparation method of the microencapsulated ammonium polyphosphate is as follows: The ammonium polyphosphate is dispersed in deionized water, and 1.5% of the mass of the ammonium polyphosphate is added as polyvinyl alcohol, stirred at a speed of 400 rpm at 25°C for 10 min to obtain an ammonium polyphosphate suspension with a solid content of 15%; The tetraethoxysilane and 3-methacryloyloxypropyl trimethoxysilane are mixed at a molar ratio of 7:1, the pH is adjusted to 4.0 with 0.1 mol / L hydrochloric acid, and stirred at a speed of 200 rpm at 30°C for 2-3 h to obtain a pre-hydrolysis solution; The ammonium polyphosphate suspension is placed in a 40°C water bath, and the pre-hydrolysis solution (mass ratio of 0.4:1 with the ammonium polyphosphate suspension) is added dropwise, the dropwise addition time is 25 min, and stirred at a speed of 300 rpm for 1 h; the temperature is raised to 65°C, and the stirring is continued for 5 h; after the stirring is stopped, it is allowed to stand for 30 min, centrifuged at a speed of 3000 rpm for 10 min to collect the microcapsules, washed with deionized water and anhydrous ethanol each for 3 times, and then placed in a vacuum dryer at 50°C to constant weight to obtain the microencapsulated ammonium polyphosphate.

[0030] Example 2: Compared with Example 1, the difference is that the addition amount of vinyl phosphonic acid diethyl ester is 8 mol% of the polyvinylidene fluoride repeating unit.

[0031] Example 3: Compared with Example 1, the difference is that the addition amount of vinyl phosphonic acid diethyl ester is 12 mol% of the polyvinylidene fluoride repeating unit.

[0032] Example 4: Compared with Example 1, the difference is that the addition amount of azobisisobutyronitrile is 2% of the molar number of the vinyl phosphonic acid diethyl ester.

[0033] Example 5: The difference between this example and Example 1 is that the amount of azobisisobutyronitrile added is 5% of the moles of diethyl vinylphosphonate.

[0034] Determination of phosphorus grafting rate: The purified low-phosphorus grafted PVDF sample is thoroughly dried and ground into powder; a small amount of sample (about 2-5 mg) is accurately weighed into a tin cup using an elemental analyzer for testing; the instrument directly measures the mass percentage of phosphorus (P) element in the sample; by comparing with the phosphorus content of the original PVDF without grafting (theoretically 0) and combining the molecular formula of diethyl vinylphosphonate monomer, the phosphorus grafting rate (i.e. the number of phosphorus groups grafted per 100 PVDF repeat units or the mole percentage) can be calculated.

[0035] Determination of thermal stability: 5-10 mg of dried sample powder is taken and heated in a thermogravimetric analyzer from room temperature to 800°C at a constant heating rate (e.g. 10°C / min) under nitrogen (simulating inert heat processing environment) and air (simulating combustion conditions); the initial decomposition temperature is usually taken as the temperature at which 5% mass loss occurs (Td5%); the char yield is the mass percentage of residual substance at 700°C; the higher the char yield, the better the carbonization, which is beneficial to the condensed phase flame retardant.

[0036] Determination of interfacial compatibility / polarity: The polymer sample is hot-pressed into a thin film with a smooth and clean surface; using a contact angle measuring instrument, a drop of fixed volume (e.g. 2 μL) of ultrapure water and diiodomethane is dropped on the surface of the film at room temperature, and the droplet image is captured by the camera; the software automatically fits the droplet profile and calculates the contact angle (θ) with the solid surface; a decrease in water contact angle indicates an increase in material surface polarity and hydrophilicity, which is strong evidence that the PVDF has been successfully grafted with polar phosphorus-containing groups.

[0037] Table 1 Performance data of low-phosphorus grafted PVDF Phosphorus grafting ratio Thermal stability (Td5%) 700°C char yield Interfacial compatibility (water contact angle) Example 1 7.8% 415℃ 24.5% 78° Example 2 6.2% 408℃ 22.0% 82° Example 3 9.1% 418℃ 26.8% 74° Example 4 7.1% 412℃ 23.5% 80° Example 5 8.0% 414℃ 24.8% 77° As shown in Table 1, when the amount of diethyl vinylphosphonate added increases from Example 2 (8 mol%) to Example 3 (12 mol%), the grafting rate increases significantly from 6.2% to 9.1%; this indicates that increasing the monomer feed can effectively improve the grafting level.

[0038] The amount of azobisisobutyronitrile in Example 4 is insufficient (2%), resulting in insufficient free radical concentration and insufficient grafting reaction, with a grafting rate (7.1%) lower than that of Example 1 (7.8%); while the azobisisobutyronitrile in Example 5 is excessive (5%), producing more free radicals, which to some extent improves the grafting efficiency, making the grafting rate (8.0%) slightly higher than that of Example 1.

[0039] Example 3 has the highest grafting rate, so its initial decomposition temperature (Td5% is 418℃) and char yield (26.8%) are the highest, showing the best thermal stability and char forming ability.

[0040] On the contrary, Example 2 with the lowest grafting rate has the lowest thermal stability and char yield; this shows that the phosphorus grafting rate is positively correlated with the thermal stability and flame-retardant char forming ability of the material.

[0041] The original polyvinylidene fluoride has weak polarity and a large water contact angle (usually > 90°); after grafting the polar phosphorus-containing groups, the surface polarity of the material is enhanced, showing a decrease in the water contact angle.

[0042] Example 3 has the highest grafting rate, so its initial decomposition temperature (Td5% is 418℃) and char yield (26.8%) are the highest, showing the best thermal stability and char forming ability.

[0043] Example 2 has a low grafting rate, limited improvement in polarity, a large contact angle (82°), and relatively weak improvement in compatibility.

[0044] Example 6: A method for preparing a low-smoke halogen-free flame-retardant power cable material, comprising the following steps: S1.1. Weigh the following raw materials by weight parts: ethylene-vinyl acetate 30 parts by weight, low-phosphorus grafted polyvinylidene fluoride 8 parts by weight, metal hydroxide 45 parts by weight, microencapsulated ammonium polyphosphate 7 parts by weight, zinc stearate 1.2 parts by weight, tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester 0.5 parts by weight, and polyolefin elastomer grafted maleic anhydride 8 parts by weight; S1.2. Dry ethylene-vinyl acetate, polyolefin elastomer grafted maleic anhydride, and microencapsulated ammonium polyphosphate at 90℃ for 6h under vacuum; sieve the zinc stearate through a 100 mesh sieve for use; S1.3. Add ethylene-vinyl acetate and polyolefin elastomer grafted maleic anhydride to a high-speed mixer, and initially mix for 2min at a speed of 500rpm; then add low-phosphorus grafted polyvinylidene fluoride and tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, and mix at a speed of 800rpm for 3min; then add the metal hydroxide, and mix at a high speed of 1000rpm for 5min; finally add the microencapsulated ammonium polyphosphate, and mix at a speed of 600rpm for 3min to obtain a premix; S1.4. Transfer the premix into a twin-screw extruder, set the temperature gradient to 185℃, and melt blend for 10min at a screw speed of 400rpm under a vacuum degree of -0.08MPa to obtain a melt; cut the melt into pellets through a wind-cooled die face, and then dry at 70℃ for 6h under vacuum to obtain a low-smoke halogen-free flame-retardant power cable material.

[0045] The preparation method of the low-phosphorus grafted polyvinylidene fluoride is as follows: The polyvinylidene fluoride is dissolved in N-methyl pyrrolidone at a mass ratio of 1:10, stirred at 90°C at a speed of 500 rpm for 3 h; cooled to 50°C, and 0.10 mol / L potassium hydroxide / ethanol solution is added dropwise, stirred at a speed of 200 rpm for 1.0 h; then vinyl phosphonic acid diethyl ester (12 mol% of the polyvinylidene fluoride repeating unit) and azobisisobutyronitrile (3% of the molar number of the vinyl phosphonic acid diethyl ester) are added, nitrogen gas is passed in at a flow rate of 0.3 L / min for 30 min; then stirred at a speed of 600 rpm under nitrogen protection at 75°C for 12 h; after the reaction is completed, the reaction liquid is cooled to room temperature, poured into 10 times the volume of deionized water for precipitation, and after standing for 2 h, suction filtration is performed, then washed with deionized water and ethanol each for 2 times, and vacuum dried at 60°C to constant weight to obtain the low-phosphorus grafted polyvinylidene fluoride.

[0046] The preparation method of the microencapsulated ammonium polyphosphate is as follows: The ammonium polyphosphate is dispersed in deionized water, and 2.0% of the mass of the ammonium polyphosphate is added as polyvinyl alcohol, stirred at a speed of 500 rpm at 30°C for 30 min to obtain an ammonium polyphosphate suspension with a solid content of 20%; The tetraethoxysilane and 3-methacryloyloxypropyl trimethoxysilane are mixed at a molar ratio of 8:1, 0.1 mol / L hydrochloric acid is used to adjust the pH to 5.0, and stirring is performed at a speed of 300 rpm at 35°C for 3 h to obtain a pre-hydrolysis solution; The ammonium polyphosphate suspension is placed in a 50°C water bath, the pre-hydrolysis solution (mass ratio of 0.5:1 with the ammonium polyphosphate suspension) is added dropwise, the dropwise addition time is 30 min, and stirring is performed at a speed of 400 rpm for 2 h; the temperature is increased to 70°C, and stirring is continued for 6 h; after the stirring is stopped, the system is allowed to stand for 30 min, centrifugation is performed at a speed of 5000 rpm for 20 min to collect the microcapsules, the microcapsules are washed with deionized water and anhydrous ethanol each for 3 times, and then vacuum dried at 60°C to constant weight to obtain the microencapsulated ammonium polyphosphate.

[0047] Example 7: Compared with Example 6, the difference is that the mixed molar ratio of tetraethoxysilane and 3-methacryloyloxypropyl trimethoxysilane is 7:1.

[0048] Example 8: Compared with Example 6, the difference is that the mixed molar ratio of tetraethoxysilane and 3-methacryloyloxypropyl trimethoxysilane is 10:1.

[0049] Example 9: Compared with Example 6, the difference is that the mass ratio of the pre-hydrolysis solution to the ammonium polyphosphate suspension is 0.4:1.

[0050] Example 10: The difference between this example and Example 6 is that the mass ratio of pre-hydrolysis solution to ammonium polyphosphate suspension is 0.6:1.

[0051] Moisture resistance (moisture absorption rate) test: about 2g (denoted as m0) of microencapsulated ammonium polyphosphate powder is spread on a weighing dish; the sample is placed in a constant temperature and humidity chamber, and the conditions are usually set to temperature 25±2℃, relative humidity 90±5%; it is taken out every 24 hours and quickly weighed (denoted as m t ) on an analytical balance, until the weight change tends to be stable (usually for 5-7 days); moisture absorption rate (%) = [(m t -m0) / m0]x100%; the better the coating effect, the lower the moisture absorption rate.

[0052] Table 2 Performance data of microencapsulated ammonium polyphosphate Moisture resistance (moisture absorption rate) Thermal stability (Td5%) 700°C char yield Example 6 2.5% 305℃ 32.0% Example 7 2.8% 302℃ 30.5% Example 8 2.9% 308℃ 33.0% Example 9 3.5% 298℃ 29.0% Example 10 2.0% 310℃ 34.5% Comparing Comparative Example 7, Example 6 and Example 8, as the proportion of tetraethoxysilane increases, the thermal stability (Td5% and char yield) of the shell layer gradually improves; this is because the inorganic siloxane network structure can provide a more excellent thermal barrier effect.

[0053] In terms of moisture resistance and interfacial compatibility, Example 6 (8:1) achieves a balance; too high a proportion of inorganic (such as Example 8) will increase the brittleness of the shell layer, affecting the coating integrity and dispersion effect in the polymer.

[0054] Comparing Comparative Example 9, Example 6 and Example 10, as the proportion of pre-hydrolysis solution increases, it means that the coating layer is thicker.

[0055] Moisture resistance and thermal stability are significantly improved; in particular, Example 10, the thickest coating layer provides the best physical barrier, so the moisture absorption rate is the lowest and the resistance to thermal decomposition is the strongest.

[0056] It should be noted that a too thick coating layer (such as Example 10) will dilute the effective flame-retardant components of ammonium polyphosphate to some extent; and the undercoating of Example 9 will result in incomplete shell layer, causing all performances to decline.

[0057] Example 11: A method for preparing a low-smoke halogen-free flame-retardant power cable material, comprising the following steps: S1.1, weigh the following raw materials by weight parts: ethylene-vinyl acetate 28 parts by weight, low-phosphorus grafted polyvinylidene fluoride 6 parts by weight, metal hydroxide 43 parts by weight, microencapsulated ammonium polyphosphate 6 parts by weight, zinc stearate 1.0 parts by weight, tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester 0.4 parts by weight, and polyolefin elastomer grafted maleic anhydride 6 parts by weight; S1.2, ethylene-vinyl acetate, polyolefin elastomer grafted maleic anhydride, and microencapsulated ammonium polyphosphate were vacuum dried at 85℃ for 5h; zinc stearate was sieved through a 100 mesh screen for use; S1.3, ethylene-vinyl acetate and polyolefin elastomer grafted maleic anhydride were added to a high-speed mixer and initially mixed at 500 rpm for 2 min; then low-phosphorus grafted polyvinylidene fluoride and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] were added, and the speed was increased to 800 rpm for mixing for 3 min; metal hydroxide was then added, and high-speed mixing was carried out at 1000 rpm for 5 min; finally, microencapsulated ammonium polyphosphate was added, and mixing was carried out at 600 rpm for 3 min to obtain a premix; S1.4, the premix was transferred to a twin-screw extruder, and the temperature gradient was set to 180℃, the screw speed was 350 rpm, and the melt blend was carried out under a vacuum degree of -0.08 MPa for 10 min to obtain a melt; the melt was cut into pellets by air-cooled die face heat cutting, and then vacuum dried at 65℃ for 5h to obtain a low-smoke halogen-free flame-retardant power cable material.

[0058] The preparation method of the low-phosphorus grafted polyvinylidene fluoride is as follows: Polyvinylidene fluoride was dissolved in N-methylpyrrolidone at a mass ratio of 1:7, stirred at 85℃ and 400 rpm for 3h; the temperature was lowered to 45℃, and 0.08 mol / L potassium hydroxide / ethanol solution was added dropwise, stirred at 150 rpm for 0.8h; then vinyl phosphonic acid diethyl ester (12 mol% of polyvinylidene fluoride repeating units) and azobisisobutyronitrile (3% of the molar number of vinyl phosphonic acid diethyl ester) were added, and nitrogen was passed at a flow rate of 0.3 L / min for 30 min; then, under nitrogen protection and at 72℃, stirring was carried out at 550 rpm for 11h; after the reaction was completed, the reaction solution was cooled to room temperature, poured into 8 times the volume of deionized water for precipitation, and after standing for 2h, it was filtered, then washed with deionized water and ethanol for 2 times each, and vacuum dried at 55℃ to constant weight to obtain the low-phosphorus grafted polyvinylidene fluoride.

[0059] The preparation method of the microencapsulated ammonium polyphosphate is as follows: Ammonium polyphosphate was dispersed in deionized water, and 1.6% of the mass of ammonium polyphosphate was added as polyvinyl alcohol, and stirred at 28℃ and 450 rpm for 20 min to obtain a suspension of ammonium polyphosphate with a solid content of 16%; Tetraethoxysilane and 3-methacryloyloxypropyltrimethoxysilane were mixed at a molar ratio of 8:1, the pH was adjusted to 4.5 with 0.1 mol / L hydrochloric acid, and stirring was carried out at 33℃ and 250 rpm for 3h to obtain a pre-hydrolysis solution; The ammonium polyphosphate suspension was placed in a 45°C water bath, and the pre-hydrolysis solution (mass ratio of 0.5:1 to the ammonium polyphosphate suspension) was added dropwise, with stirring at 350 rpm for 2 h. The temperature was raised to 70°C, and stirring was continued for 6 h. After stopping the stirring, the mixture was allowed to settle for 30 min, and then centrifuged at 4000 rpm for 15 min to collect the microcapsules. The microcapsules were washed three times with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 55°C to constant weight, to obtain the microencapsulated ammonium polyphosphate.

[0060] Example 12: This example differs from Example 11 in that the low-phosphorus grafted polyvinylidene fluoride is 5 parts by weight.

[0061] Example 13: This example differs from Example 11 in that the low-phosphorus grafted polyvinylidene fluoride is 8 parts by weight.

[0062] Example 14: This example differs from Example 11 in that the microencapsulated ammonium polyphosphate is 5 parts by weight.

[0063] Example 15: This example differs from Example 11 in that the microencapsulated ammonium polyphosphate is 7 parts by weight.

[0064] Flame retardant performance (oxygen index method): The sample was fixed vertically in the combustion cylinder of the oxygen index tester, and the flow rates of oxygen and nitrogen were adjusted to form a specific oxygen concentration airflow. The top end of the sample was ignited with an igniter. The critical oxygen concentration of the sample was determined by observing the burning time or length of the sample using the small sample up-and-down method.

[0065] Determination of smoke density: The sample was placed in the sample holder in the smoke density test box and burned under a specified radiation intensity (sometimes assisted by an ignition flame). The light beam passed through the smoke generated by the burning, and the sensor measured the attenuation of the light flux. The system recorded and calculated the smoke density (SDR).

[0066] Determination of mechanical properties (tensile strength and elongation at break): The dumbbell-shaped sample was prepared according to the standard, and the sample was clamped in the clamps of the testing machine and stretched at a constant speed. The stress-strain curve was automatically recorded by the equipment, and the tensile strength (maximum tension divided by cross-sectional area) and elongation at break (percentage of elongation at break to original gauge length) were calculated.

[0067] Table 3 Performance data of low-smoke halogen-free flame-retardant power cable material Oxygen index Smoke density Tensile strength Elongation at break Example 11 33.5% 65 14.2 MPa 220% Example 12 32.0% 72 13.5 MPa 240% Example 13 34.2% 58 14.8 MPa 195% Example 14 32.2% 75 14.8 MPa 235% Example 15 34.8% 55 13.6 MPa 200% As can be seen from Comparative Examples 11, 12, and 13, when the amount of low-phosphorus grafted polyvinylidene fluoride is increased from 5 parts to 8 parts, its efficient charring effect is enhanced, the oxygen index (LOI) is increased from 32.0% to 34.2%, and the smoke density (SDR) is significantly reduced from 72 to 58.

[0068] Low phosphorus grafted PVDF as a polar modified polymer, its dosage increases in the promotion of compatibility and rigidity, but also to a certain extent, the polymer chain slip, resulting in elongation at break decreased (from 240% to 195%), and the tensile strength due to the interface improved slightly.

[0069] As can be seen from Comparative Examples 11, 14 and 15, when the amount of microencapsulated APP increases from 5 parts to 7 parts, the oxygen index (LOI) increases from 32.2% to 34.8%; at the same time, the barrier formed by the siliceous coating layer in the condensed phase also effectively inhibits the smoke generation, and the smoke density (SDR) decreases from 75 to 55.

[0070] As an inorganic filler, the increase in the amount of microencapsulated APP will have a negative impact on mechanical properties; the more the amount, the more stress concentration points generated in the matrix, resulting in a decrease in tensile strength and elongation at break (Example 15).

[0071] After the above determination, Example 13 is taken as the optimal example; Comparative Example 1: Compared with Example 13, the difference is that low phosphorus grafted PVDF is not added, and PVDF is used directly.

[0072] Comparative Example 2: Compared with Example 13, the difference is that microencapsulated APP is not added, and APP is used directly.

[0073] Comparative Example 3: Compared with Example 13, the difference is that low phosphorus grafted PVDF and microencapsulated APP are not added.

[0074] Table 4 Performance data of low smoke halogen-free flame-retardant power cable material Oxygen index Smoke density Tensile strength Elongation at break Example 13 34.2% 58 14.8 MPa 195% Comparative Example 1 31.5% 75 12.0 MPa 160% Comparative Example 2 30.8% 85 13.0 MPa 170% Comparative Example 3 28.5% 105 10.5 MPa 135% When using unmodified PVDF directly instead of low phosphorus grafted PVDF (Comparative Example 1), the oxygen index decreases from 34.2% to 31.5%, which proves the key role of low phosphorus grafting modification in improving the flame-retardant efficiency: unmodified PVDF has poor interfacial compatibility with the matrix and the flame retardant, and cannot effectively form a stable carbon layer, resulting in migration of the flame retardant and a decrease in flame-retardant effect; at the same time, the poor compatibility also causes a significant damage to the mechanical properties (tensile strength and elongation at break), and the smoke density also increases due to incomplete combustion.

[0075] The data of Comparative Example 2 shows the consequence of using ordinary ammonium polyphosphate, because of poor thermal stability and easy moisture absorption in processing, the flame retardant efficiency is greatly discounted, the oxygen index is only 30.8%, and due to the decomposition of ammonium polyphosphate in advance, the system produces melt drops, and the decomposition is not sufficient during combustion, resulting in a large amount of smoke, so the smoke density is as high as 85; in addition, the combination ability of ordinary ammonium polyphosphate with the matrix is weaker than that of the microencapsulated product, so it also has a negative impact on the mechanical properties.

[0076] Comparative Example 3 does not add low-phosphorus grafted polyvinylidene fluoride and microencapsulated ammonium polyphosphate, and the performance data drops sharply, the oxygen index is only 28.5%, and the smoke generation is huge; this fully proves that the unmodified polyvinylidene fluoride and ordinary ammonium polyphosphate lack synergistic effect, and even have performance conflicts, resulting in serious interface debonding, flame retardant system failure, and mechanical properties at the lowest point.

[0077] In summary, low-phosphorus grafted polyvinylidene fluoride is the key to improving the interface compatibility, flame retardant efficiency and mechanical strength; and microencapsulated ammonium polyphosphate is the core to ensure the processing stability, realize high-efficiency flame retardation and low-smoke characteristics.

[0078] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only preferred examples of the present application and are not intended to limit the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. Low smoke, halogen-free flame retardant power cable compound characterized in that, The raw materials include ethylene-vinyl acetate, low-phosphorus grafted polyvinylidene fluoride, metal hydroxide, microencapsulated ammonium polyphosphate, zinc stearate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and polyolefin elastomer grafted maleic anhydride; The low-phosphorus grafted polyvinylidene fluoride is prepared by radical graft polymerization of polyvinylidene fluoride activated by alkali and vinyl phosphonic acid diethyl ester under the action of an initiator. The microencapsulated ammonium polyphosphate is prepared by in-situ coating of silane coupling agent to form microcapsules.

2. A low smoke, halogen-free flame retardant power cable compound according to claim 1, characterized in that, The ethylene-vinyl acetate is 25-30 parts by weight, the low-phosphorus grafted polyvinylidene fluoride is 5-8 parts by weight, the metal hydroxide is 42-45 parts by weight, the microencapsulated ammonium polyphosphate is 5-7 parts by weight, the zinc stearate is 0.8-1.2 parts by weight, the pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is 0.3-0.5 parts by weight, and the polyolefin elastomer grafted maleic anhydride is 5-8 parts by weight.

3. Low smoke, halogen-free flame retardant power cable compound according to claim 2, characterized in that, The preparation method of the low-phosphorus grafted polyvinylidene fluoride is as follows: The polyvinylidene fluoride is dissolved in N-methylpyrrolidone at a mass ratio of 1:5-10, stirred at 80-90℃ and a speed of 300-500rpm for 2-3h; the temperature is lowered to 40-50℃, 0.05-0.10mol / L potassium hydroxide / ethanol solution is added dropwise, and stirred at a speed of 100-200rpm for 0.5-1.0h; then vinyl phosphonic acid diethyl ester and azobisisobutyronitrile are added, nitrogen is passed at a flow rate of 0.3L / min for 30min; then the reaction is carried out under the protection of nitrogen at 70-75℃ and a speed of 500-600rpm for 10-12h; after the reaction is completed, the reaction solution is cooled to room temperature, poured into 5-10 times the volume of deionized water for precipitation, and after standing for 2h, suction filtration is performed, then deionized water and ethanol are used for washing twice respectively, and vacuum drying is performed at 50-60℃ until the weight is constant, to obtain the low-phosphorus grafted polyvinylidene fluoride.

4. Low smoke halogen-free flame retardant power cable compound according to claim 3, characterized in that, The addition amount of the vinyl phosphonic acid diethyl ester accounts for 8-12mol% of the polyvinylidene fluoride repeating unit.

5. A low smoke, halogen-free flame retardant power cable compound according to claim 3, wherein, The addition amount of the azobisisobutyronitrile accounts for 2-5% of the number of moles of the vinyl phosphonic acid diethyl ester.

6. A low smoke, halogen-free, flame retardant power cable compound according to claim 2, wherein, The preparation method of the microencapsulated ammonium polyphosphate is as follows: The ammonium polyphosphate is dispersed in deionized water, 1.5-2.0% of the mass of the ammonium polyphosphate of polyvinyl alcohol is added, and stirring is performed at 25-30℃ and a speed of 400-500rpm for 10-30min, to obtain an ammonium polyphosphate suspension with a solid content of 15-20%; The tetraethoxysilane and 3-methacryloyloxypropyltrimethoxysilane are mixed, 0.1mol / L hydrochloric acid is used to adjust the pH to 4.0-5.0, and stirring is performed at 30-35℃ and a speed of 200-300rpm for 2-3h, to obtain a pre-hydrolysis solution; The ammonium polyphosphate suspension is placed in a 40-50℃ water bath, the pre-hydrolysis solution is added dropwise, the dropwise adding time is 25-30min, and stirring is carried out at a speed of 300-400rpm for 1-2h; the temperature is raised to 65-70℃, and stirring is continued for 5-6h; after stopping stirring, the mixture is allowed to stand for 30min, centrifuged at a speed of 3000-5000rpm for 10-20min to collect the microcapsules, and then washed with deionized water and anhydrous ethanol for 3 times each, and then placed in a 50-60℃ vacuum dryer until the weight is constant, to obtain the microencapsulated ammonium polyphosphate.

7. Low smoke halogen-free flame retardant power cable compound according to claim 6, characterized in that, The mixing molar ratio of the tetraethoxysilane and 3-methacryloyloxypropyltrimethoxysilane is 7-10:

1.

8. A low smoke, halogen-free flame retardant power cable compound according to claim 6, wherein, The mass ratio of the pre-hydrolysis solution to the ammonium polyphosphate suspension is 0.4-0.6:

1.

9. Process for the preparation of a low smoke halogen-free flame retardant power cable material for the preparation of a low smoke halogen-free flame retardant power cable material as claimed in any one of claims 1 to 8, characterized in that, The method is as follows: S1.1, the raw materials are weighed according to the weight parts; S1.2, the ethylene-vinyl acetate, polyolefin elastomer grafted maleic anhydride and microencapsulated ammonium polyphosphate are vacuum dried at 80-90℃ for 4-6h; the zinc stearate is sieved through a 100 mesh sieve for use; S1.3, the ethylene-vinyl acetate and polyolefin elastomer grafted maleic anhydride are added to a high-speed mixer, and initial mixing is carried out at a speed of 500rpm for 2min; then the low-phosphorus grafted polyvinylidene fluoride and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] are added, the speed is increased to 800rpm, and mixing is carried out for 3min; then the metal hydroxide is added, high-speed mixing is carried out at 1000rpm for 5min, finally the microencapsulated ammonium polyphosphate is added, the speed is reduced to 600rpm, and mixing is carried out for 3min, to obtain a premix; S1.4, the premix is transferred into a twin-screw extruder, the temperature gradient is set to 155-185℃, the screw speed is 300-400rpm, and the melt is obtained by melt blending under the condition of a vacuum degree of-0.08MPa for 8-10min; the melt is cut into pellets by air-cooled die face heating, and then vacuum dried at 60-70℃ for 4-6h, to obtain a low-smoke halogen-free flame-retardant power cable material.

10. A process for the preparation of low smoke and zero halogen flame retardant power cable compound as claimed in claim 9, wherein, In the S1.3, the metal hydroxide is obtained by mixing aluminum hydroxide and magnesium hydroxide according to a mass ratio of 3:

1. ​