Anti-cracking flame-retardant material for cable and preparation process thereof

Abstract

This invention belongs to the field of polymer composite material preparation technology, and particularly relates to a crack-resistant and flame-retardant material for cables and its preparation process, including the following steps: dissolving PVP and ammonium citrate in an ethanol solution, adding Mg / Al-LDH and hydrophilic modified expanded graphite for dispersion, heating and adding aluminum isopropoxide solution for reaction, washing and dispersing in phytic acid solution, heating and reaction, washing and drying to obtain flame-retardant microparticles; mixing EVA, EVA-g-MAH, flame-retardant microparticles, antioxidants and lubricants and extruding them in an extruder, cooling and pelletizing the extrudate to obtain the crack-resistant and flame-retardant material for cables. This invention obtains the material by blending flame-retardant microparticles with EVA and other materials and then granulating them. The flame-retardant microparticles can meet the flame-retardant requirements of the sheath made of the material with a relatively small amount added, improving the continuity of the EVA matrix and preventing cracking of the sheath under frequent bending conditions.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite material preparation technology, and particularly relates to a crack-resistant and flame-retardant material for cables and its preparation process. Background Technology

[0002] Traditional cable sheathing materials often use EVA as the polymer matrix. EVA contains a large number of flammable hydrocarbon segments, which release a lot of heat and flammable gases when burning, which can easily cause a fire to spread.

[0003] To improve the flame retardancy of the sheath, aluminum hydroxide and magnesium hydroxide are usually added to the sheath material. For example, Chinese patent document CN103965540B discloses a thermoplastic, cold-resistant, crack-resistant, halogen-free, low-smoke flame-retardant polyolefin sheath material, which includes the following components by weight: LLDPE 20-60 parts, EVA 20-40 parts, SEEPS 10-20 parts, AEM The components are: 10-20 parts magnesium hydroxide, 50-100 parts aluminum hydroxide, 20-50 parts clinoptilolite, 10-20 parts magnesium borate whiskers, 10-5 parts antioxidant, and 2-6 parts lubricant. In the preparation of the sheath material, magnesium borate whiskers, clinoptilolite, and silane coupling agent are first added to a high-speed mixer and mixed. Then, the remaining components are added to the high-speed mixer and mixed again. The mixture is then fed into a two-stage granulator for extrusion granulation to obtain the sheath material. The sheath material is then fed into an extruder and extruded concentrically with the cable core to form a sheath outside the cable core. In a fire environment, aluminum hydroxide and magnesium hydroxide in the sheath decompose endothermically and release a large amount of water vapor after reaching their decomposition temperature. This effectively reduces the temperature rise rate of the sheath and dilutes flammable gases. Although this improves the flame retardant properties of the sheath, it can easily leave micropores or voids in the sheath, reducing its density and making it easier for oxygen and heat to penetrate. To solve this problem, the aforementioned patent adds a large amount of magnesium hydroxide and aluminum hydroxide to compensate for the loss of flame retardant properties caused by micropores or voids. This reduces the continuity of the polymer matrix, hinders the movement of polymer chain segments, and reduces the sheath's resistance to bending fatigue. Under frequent bending conditions, it is prone to cracking, shortening the service life of the sheath. Summary of the Invention

[0004] This invention provides a crack-resistant flame-retardant material for cables and its preparation process. It is prepared by blending flame-retardant microparticles with EVA and other materials and then granulating them. The flame-retardant microparticles can meet the flame-retardant requirements of the sheath made of the material with a small amount of addition, improve the continuity of the EVA matrix, and prevent the sheath from cracking when used under frequent bending conditions.

[0005] To solve the above problems, the present invention adopts the following technical solution:

[0006] A process for preparing a crack-resistant and flame-retardant material for cables includes the following steps:

[0007] S1. PVP and ammonium citrate are dissolved in an ethanol solution, Mg / Al-LDH and hydrophilic modified expanded graphite are added for dispersion, and aluminum isopropoxide solution is added for reaction after heating. After washing, the mixture is dispersed in phytic acid solution, heated for reaction, washed, and dried to obtain flame-retardant microparticles.

[0008] S2. EVA, EVA-g-MAH, flame retardant microparticles, antioxidants and lubricants are mixed and fed into an extruder for extrusion. The extrudate is cooled and pelletized to obtain crack-resistant flame retardant material for cables.

[0009] This invention provides a crack-resistant flame-retardant material for cables and its preparation process. It is prepared by granulation after blending flame-retardant microparticles and EVA matrix. The sheath made of this material can meet the flame-retardant requirements of cable sheaths with a small amount of addition, avoiding the addition of a large amount of flame-retardant microparticles that would damage the continuity of the EVA matrix, improving the sheath's resistance to bending fatigue, and inhibiting cracking during frequent bending use.

[0010] In the preparation of flame-retardant microparticles, aluminum isopropoxide hydrolyzes in an ethanol solution under the action of water molecules to generate hydrolysis products containing aluminum hydroxyl groups. These hydrolysis products can adhere to the surface of Mg / Al-LDH and hydrophilic modified expanded graphite through coordination. As the amount of hydrolysis products increases, condensation reactions occur between the hydrolysis products to form an aluminum oxide network connecting Mg / Al-LDH and hydrophilic modified expanded graphite. Phytic acid molecules can be fixed on the aluminum oxide network through coordination to obtain flame-retardant microparticles. These microparticles are then mixed with EVA and other materials to form crack-resistant flame-retardant materials for cables.

[0011] In flame-retardant microparticles, Mg / Al-LDH and hydrophilic modified expanded graphite are chemically bridged through an aluminum oxide network, and phytic acid molecules are fixedly attached to it to form an integrated structure. When a fire occurs, Mg / Al-LDH undergoes endothermic decomposition. Under the bridging effect of the aluminum-oxygen network, its decomposition products (alumina and magnesium oxide) are spatially tightly coupled with hydrophilic modified expanded graphite, forming a continuous composite skeleton. Phytic acid molecules can catalyze the dehydration and carbonization of the nearby EVA matrix at high temperatures, inhibiting the continued cracking of EVA to generate combustible gases and forming a dense carbon layer coating the composite skeleton. This results in a continuous, mechanically stable composite barrier layer, effectively inhibiting the formation of penetrating pores or cracks, blocking the transfer of heat and oxygen into the sheath, slowing the spread of flames, and improving the flame retardant performance of the sheath. The hydrophilic modified expanded graphite in the composite barrier layer has a worm-like three-dimensional network structure, which can extend the diffusion path of combustible gases, increase diffusion resistance, reduce the escape velocity, further delay the spread of flames, and improve the flame retardant performance of the sheath. Under the premise of achieving the same flame retardant level, the total amount of flame retardant particles can be significantly reduced, effectively maintaining the continuity and flexibility of the EVA matrix, significantly improving the sheath's resistance to bending fatigue, and making it less prone to cracking under frequent bending conditions.

[0012] Further, in step S1, PVP and ammonium citrate are dissolved in a 97-98 wt% ethanol solution, Mg / Al-LDH is added for dispersion, hydrophilic modified expanded graphite suspension is added and mixed, the temperature is raised to 55-65℃, aluminum isopropoxide solution is slowly added under continuous stirring, the reaction is carried out for 2-3 hours, after washing with anhydrous ethanol, it is dispersed in phytic acid solution, the temperature is raised to 45-50℃ and the reaction is carried out for 1-2 hours, after washing with deionized water and anhydrous ethanol, it is dried to obtain flame-retardant microparticles.

[0013] Aluminum isopropoxide can be hydrolyzed into hydrolysis products containing aluminum hydroxyl groups under the action of water. The surface of Mg / Al-LDH contains magnesium hydroxyl and aluminum hydroxyl groups, and the edges also have exposed magnesium and aluminum ions, which allows the hydrolysis products to be adsorbed on the surface of Mg / Al-LDH through hydrogen bonding and coordination, providing a molecular basis for subsequent connection of hydrophilic modified expanded graphite and Mg / Al-LDH through aluminum oxide network.

[0014] Furthermore, in step S1, after dissolving PVP and ammonium citrate in an ethanol solution, zinc borate and Mg / Al-LDH are added for dispersion.

[0015] The hydroxyl groups on the surface of zinc borate can form multi-point hydrogen bonds with the hydroxyl groups on the surface of Mg / Al-LDH, allowing zinc borate to be embedded and fixed in the flame-retardant microparticles along with the formation of the aluminum-oxygen network. Zinc borate dehydrates and decomposes at 290-400℃, releasing B2O3 (boron trioxide). B2O3 can melt at around 450℃ to form a glassy liquid. Phytic acid attached to the aluminum-oxygen network begins to decompose at 180-220℃, and the released phosphoric acid and other phosphorus-containing compounds can catalyze the dehydration, cross-linking and aromatization of EVA molecular chains at 250-350℃, forming a dense carbon layer coating the composite framework. After the B2O3 melts, it can fill the pores or cracks in the carbon layer through capillary action, further reducing the density of connecting pores and macroscopic cracks in the composite barrier layer and slowing down the spread of flames.

[0016] Furthermore, the hydrophilic modified expanded graphite suspension is prepared by the following method: expanded graphite is dispersed in an 8-10 wt% hydrogen peroxide solution, heated to 55-60℃ and reacted for 1-2 h, filtered, washed with deionized water and anhydrous ethanol, dispersed in anhydrous ethanol, KH-550 and deionized water are added, acetic acid solution is added dropwise to adjust the pH value to 4-5, and the reaction is carried out for 3-4 h to obtain the hydrophilic modified expanded graphite suspension.

[0017] Hydrophilic modified expanded graphite was obtained by modifying expanded graphite with KH-550. Its surface is rich in amino groups, which can act as coordination sites to coordinate with the hydrolysis products of aluminum isopropoxide. This allows the hydrolysis products to be adsorbed on the surface of hydrophilic modified expanded graphite, providing a molecular basis for the subsequent connection of hydrophilic modified expanded graphite and Mg / Al-LDH through an aluminum oxide network.

[0018] Furthermore, the drying temperature is 50-60℃, the pressure is 8-12kPa, and the time is 6-8h.

[0019] Furthermore, the phytic acid solution is prepared by mixing phytic acid with a 70-75 wt% ethanol solution, and then adding acetic acid solution to adjust the pH value to 4-4.3 to obtain the phytic acid solution.

[0020] Under pH conditions of 4-4.3, the phosphate groups of phytic acid can coordinate with the Lewis acidic aluminum sites of the aluminum oxide network, enabling phytic acid to stably adhere to the aluminum oxide network. Under the high temperature conditions of a fire, the carbon layer formed by the dehydration and carbonization of the nearby EVA matrix catalyzed by phytic acid can be rapidly attached to the composite framework, improving the mechanical stability and density of the composite barrier layer.

[0021] Furthermore, the aluminum isopropoxide solution is prepared by dissolving aluminum isopropoxide in anhydrous ethanol.

[0022] Furthermore, in step S2, the screw speed of the extruder is 200-220 rpm, and the die temperature is 170-180℃.

[0023] A crack-resistant and flame-retardant material for cables comprises the following raw materials in parts by weight: 100-110 parts EVA, 5-8 parts EVA-g-MAH, 23-28 parts flame-retardant microparticles, 0.5-0.8 parts antioxidant 1010, and 2-3 parts lubricant EBS; wherein the flame-retardant microparticles comprise the following raw materials in parts by weight: 200-210 parts 97-98wt% ethanol solution, 2-2.5 parts PVP, 0.2-0.3 parts ammonium citrate, 30-34 parts Mg / Al-LDH, 0-4 parts zinc borate, 10-15 parts hydrophilic modified expanded graphite suspension, 12-16 parts aluminum isopropoxide solution, and 200-210 parts phytic acid solution.

[0024] Furthermore, the hydrophilic modified expanded graphite suspension comprises the following raw materials in parts by weight: 30-35 parts expanded graphite, 1-1.2 parts KH-550, and 0.9-1.1 parts deionized water; the aluminum isopropoxide solution comprises 14-16 parts aluminum isopropoxide and 80-90 parts anhydrous ethanol; and the phytic acid solution comprises 4-6 parts phytic acid and 500-520 parts 70-75 wt% ethanol solution.

[0025] The present invention has the following beneficial effects:

[0026] The crack-resistant and flame-retardant material for cables produced by this invention is obtained by granulation after blending flame-retardant microparticles with EVA and other materials. The flame-retardant microparticles include Mg / Al-LDH and hydrophilic modified expanded graphite fixedly connected by an aluminum oxide network. Phytic acid molecules are attached to the aluminum oxide network. Under high-temperature fire conditions, the decomposition products of Mg / Al-LDH and hydrophilic modified expanded graphite are spatially tightly coupled to form a continuous composite skeleton. Phytic acid molecules catalyze the dehydration and carbonization of the nearby EVA matrix, coating the composite skeleton with a dense carbon layer to form a continuous composite barrier layer. This layer blocks the transfer of heat and oxygen into the sheath, inhibiting the spread of fire. The hydrophilic modified expanded graphite can inhibit the emission of combustible gases, improve the flame-retardant performance of the cable sheath, meet the flame-retardant requirements of the sheath while significantly reducing the amount of flame-retardant microparticles added, maintain the continuity of the EVA matrix, and improve the sheath's resistance to bending fatigue, making it less prone to cracking under frequent bending conditions. Detailed Implementation

[0027] Example 1

[0028] 30g of expanded graphite with a D50 of 300μm was added to 200g of 10wt% hydrogen peroxide solution and ultrasonically dispersed at 300W for 20min. The mixture was then heated to 60℃ and stirred at 300rpm for 1h. After filtration, the graphite was washed three times with deionized water and twice with anhydrous ethanol. The graphite was then added to 230g of anhydrous ethanol and ultrasonically dispersed at 300W for 10min. 1g of KH-550 (γ-aminopropyltriethoxysilane) and 0.9g of deionized water were added, and the pH was adjusted to 5 by adding 10wt% acetic acid solution. The mixture was stirred at 500rpm for 3h to obtain a hydrophilic modified expanded graphite suspension. 15g of aluminum isopropoxide was added to 80g of anhydrous ethanol and stirred at 500rpm for 20min to obtain an aluminum isopropoxide solution. 4g of phytic acid was added to 500g of 70wt% ethanol solution and stirred at 800rpm for 20min. The pH was adjusted to 4 by adding 10wt% acetic acid solution to obtain a phytic acid solution.

[0029] Add 2g PVP (polyvinylpyrrolidone, model K30) and 0.22g ammonium citrate to 200g 98wt% ethanol solution, stir at 300rpm for 20min, add 3.5g zinc borate and 30g Mg / Al-LDH (magnesium aluminum layered bimetallic hydroxide), sonicate at 500W for 30min, add 10g hydrophilic modified expanded graphite suspension, stir at 300rpm for 10min, heat to 60℃, slowly add 12g aluminum isopropoxide solution dropwise under stirring at 500rpm, after the addition is complete, stir at 500rpm for 2h, filter, wash 3 times with anhydrous ethanol, add to 200g phytic acid solution, stir at 900rpm for 20min, heat to 45℃, stir at 400rpm for 2h, filter, wash twice with deionized water, wash twice with anhydrous ethanol, dry in an environment of 50℃ and 10kPa for 6h to obtain flame-retardant microparticles.

[0030] 100g of EVA (ethylene-vinyl acetate copolymer, VA content 22%, melt index 10g / 10min), 5g of EVA-g-MAH (maleic anhydride grafted ethylene-vinyl acetate copolymer), 25g of flame retardant microparticles, 0.5g of antioxidant 1010, and 2g of EBS (ethylene bis-stearamide) were added to a mixer and stirred at 1300rpm for 10min. The mixture was then fed into an extruder and extruded at a screw speed of 200rpm and a die temperature of 170℃. The extrudate was then air-cooled and pelletized to obtain a crack-resistant flame retardant material for cables.

[0031] Example 2

[0032] 32g of expanded graphite with a D50 of 300μm was added to 200g of 10wt% hydrogen peroxide solution and ultrasonically dispersed at 300W for 20min. The mixture was then heated to 60℃ and stirred at 300rpm for 1h. After filtration, the graphite was washed three times with deionized water and twice with anhydrous ethanol. The graphite was then added to 230g of anhydrous ethanol and ultrasonically dispersed at 300W for 10min. 1.1g of KH-550 and 1g of deionized water were added, and the pH was adjusted to 5 by adding 10wt% acetic acid solution. The mixture was stirred at 500rpm for 3h to obtain a hydrophilic modified expanded graphite suspension. 15g of aluminum isopropoxide was added to 80g of anhydrous ethanol and stirred at 500rpm for 20min to obtain an aluminum isopropoxide solution. 5g of phytic acid was added to 510g of 70wt% ethanol solution and stirred at 800rpm for 20min. The pH was adjusted to 4 by adding 10wt% acetic acid solution to obtain a phytic acid solution.

[0033] Add 2.2g PVP (model K30) and 0.25g ammonium citrate to 205g 98wt% ethanol solution, stir at 300rpm for 20min, add 3.2g zinc borate and 31g Mg / Al-LDH, sonicate at 500W for 30min, add 12g hydrophilic modified expanded graphite suspension, stir at 300rpm for 10min, heat to 60℃, slowly add 16g aluminum isopropoxide solution dropwise under stirring at 500rpm, after the addition is complete, stir at 500rpm for 2h, filter, wash 3 times with anhydrous ethanol, add to 206g phytic acid solution, stir at 900rpm for 20min, heat to 45℃, stir at 400rpm for 2h, filter, wash twice with deionized water, wash twice with anhydrous ethanol, dry in an environment of 50℃ and 10kPa for 6h to obtain flame-retardant microparticles.

[0034] 102g of EVA (VA content 22%, melt index 10g / 10min), 6g of EVA-g-MAH, 27g of flame retardant microparticles, 0.6g of antioxidant 1010, and 2.5g of EBS were added to a mixer and stirred at 1300rpm for 10min. The mixture was then fed into an extruder and extruded at a screw speed of 200rpm and a die temperature of 170℃. The extrudate was air-cooled and pelletized to obtain a crack-resistant flame retardant material for cables.

[0035] Example 3

[0036] 34g of expanded graphite with a D50 of 300μm was added to 200g of 9wt% hydrogen peroxide solution and ultrasonically dispersed at 300W for 20min. The mixture was then heated to 55℃ and stirred at 300rpm for 2h. After filtration, the graphite was washed three times with deionized water and twice with anhydrous ethanol. The graphite was then added to 230g of anhydrous ethanol and ultrasonically dispersed at 300W for 10min. 1.2g of KH-550 and 0.9g of deionized water were added, and the pH was adjusted to 4 by adding 10wt% acetic acid solution. The mixture was stirred at 500rpm for 3.5h to obtain a hydrophilic modified expanded graphite suspension. 14g of aluminum isopropoxide was added to 85g of anhydrous ethanol and stirred at 500rpm for 20min to obtain an aluminum isopropoxide solution. 6g of phytic acid was added to 520g of 72wt% ethanol solution and stirred at 800rpm for 20min. The pH was adjusted to 4.3 by adding 10wt% acetic acid solution to obtain a phytic acid solution.

[0037] Add 2.3g PVP (model K30) and 0.2g ammonium citrate to 210g of 97.5wt% ethanol solution, stir at 300rpm for 20min, add 3.3g zinc borate and 32g Mg / Al-LDH, sonicate at 500W for 30min, add 14g of hydrophilic modified expanded graphite suspension, stir at 300rpm for 10min, heat to 55℃, slowly add 15g aluminum isopropoxide solution dropwise under stirring at 500rpm, after the addition is complete, stir at 500rpm for 2.5h, filter, wash 3 times with anhydrous ethanol, add to 208g phytic acid solution, stir at 900rpm for 20min, heat to 50℃, stir at 400rpm for 1h, filter, wash twice with deionized water, wash twice with anhydrous ethanol, dry in an environment of 60℃ and 12kPa for 8h to obtain flame-retardant microparticles.

[0038] 108g of EVA (VA content 22%, melt index 10g / 10min), 7g of EVA-g-MAH, 28g of flame retardant microparticles, 0.7g of antioxidant 1010, and 2.4g of EBS were added to a mixer and stirred at 1300rpm for 10min. The mixture was then fed into an extruder and extruded at a screw speed of 220rpm and a die temperature of 175℃. The extrudate was air-cooled and pelletized to obtain a crack-resistant flame retardant material for cables.

[0039] Example 4

[0040] 35g of expanded graphite with a D50 of 300μm was added to 200g of 9wt% hydrogen peroxide solution and ultrasonically dispersed at 300W for 20min. The mixture was then heated to 55℃ and stirred at 300rpm for 2h. After filtration, the graphite was washed three times with deionized water and twice with anhydrous ethanol. The graphite was then added to 230g of anhydrous ethanol and ultrasonically dispersed at 300W for 10min. 1.1g of KH-550 and 1.1g of deionized water were added, and the pH was adjusted to 4 by adding 10wt% acetic acid solution. The mixture was stirred at 500rpm for 3.5h to obtain a hydrophilic modified expanded graphite suspension. 14g of aluminum isopropoxide was added to 85g of anhydrous ethanol and stirred at 500rpm for 20min to obtain an aluminum isopropoxide solution. 4g of phytic acid was added to 505g of 72wt% ethanol solution and stirred at 800rpm for 20min. 10wt% acetic acid solution was added dropwise to adjust the pH to 4.3 to obtain a phytic acid solution.

[0041] Add 2.5g PVP (model K30) and 0.3g ammonium citrate to 208g of 97.5wt% ethanol solution, stir at 300rpm for 20min, add 3.5g zinc borate and 34g Mg / Al-LDH, sonicate at 500W for 30min, add 15g hydrophilic modified expanded graphite suspension, stir at 300rpm for 10min, heat to 55℃, slowly add 13g aluminum isopropoxide solution dropwise under stirring at 500rpm, after the addition is complete, stir at 500rpm for 2.5h, filter, wash 3 times with anhydrous ethanol, add to 210g phytic acid solution, stir at 900rpm for 20min, heat to 50℃, stir at 400rpm for 1h, filter, wash twice with deionized water, wash twice with anhydrous ethanol, dry in an environment of 60℃ and 12kPa for 8h to obtain flame-retardant microparticles.

[0042] 110g of EVA (VA content of 22%, melt index of 10g / 10min), 8g of EVA-g-MAH, 24g of flame retardant microparticles, 0.8g of antioxidant 1010, and 3g of EBS were added to a mixer and stirred at 1300rpm for 10min. The mixture was then fed into an extruder and extruded at a screw speed of 220rpm and a die temperature of 175℃. The extrudate was air-cooled and pelletized to obtain a crack-resistant flame retardant material for cables.

[0043] Example 5

[0044] 30g of expanded graphite with a D50 of 300μm was added to 200g of 8wt% hydrogen peroxide solution and ultrasonically dispersed at 300W for 20min. The mixture was then heated to 58℃ and stirred at 300rpm for 1.5h. After filtration, the graphite was washed three times with deionized water and twice with anhydrous ethanol. The graphite was then added to 230g of anhydrous ethanol and ultrasonically dispersed at 300W for 10min. 1.2g of KH-550 and 1g of deionized water were added, and the pH was adjusted to 4.5 by adding 10wt% acetic acid solution. The mixture was stirred at 500rpm for 4h to obtain a hydrophilic modified expanded graphite suspension. 16g of aluminum isopropoxide was added to 90g of anhydrous ethanol and stirred at 500rpm for 20min to obtain an aluminum isopropoxide solution. 5g of phytic acid was added to 515g of 75wt% ethanol solution and stirred at 800rpm for 20min. The pH was adjusted to 4.2 by adding 10wt% acetic acid solution to obtain a phytic acid solution.

[0045] Add 2.4g PVP (model K30) and 0.28g ammonium citrate to 206g of 97wt% ethanol solution, stir at 300rpm for 20min, add 3.8g zinc borate and 33g Mg / Al-LDH, sonicate at 500W for 30min, add 13g hydrophilic modified expanded graphite suspension, stir at 300rpm for 10min, heat to 58℃, slowly add 14g aluminum isopropoxide solution dropwise under stirring at 500rpm, after the addition is complete, stir at 500rpm for 3h, filter, wash 3 times with anhydrous ethanol, add to 204g phytic acid solution, stir at 900rpm for 20min, heat to 48℃, stir at 400rpm for 1.5h, filter, wash twice with deionized water, wash twice with anhydrous ethanol, dry in an environment of 50℃ and 8kPa for 7h to obtain flame-retardant microparticles.

[0046] 105g of EVA (VA content 22%, melt index 10g / 10min), 6g of EVA-g-MAH, 23g of flame retardant microparticles, 0.6g of antioxidant 1010, and 2.5g of EBS were added to a mixer and stirred at 1300rpm for 10min. The mixture was then fed into an extruder and extruded at a screw speed of 210rpm and a die temperature of 180℃. The extrudate was air-cooled and pelletized to obtain a crack-resistant flame retardant material for cables.

[0047] Example 6

[0048] 30g of expanded graphite with a D50 of 300μm was added to 200g of 8wt% hydrogen peroxide solution and ultrasonically dispersed at 300W for 20min. The mixture was then heated to 58℃ and stirred at 300rpm for 1.5h. After filtration, the graphite was washed three times with deionized water and twice with anhydrous ethanol. The graphite was then added to 230g of anhydrous ethanol and ultrasonically dispersed at 300W for 10min. 1.2g of KH-550 and 1g of deionized water were added, and the pH was adjusted to 4.5 by adding 10wt% acetic acid solution. The mixture was stirred at 500rpm for 4h to obtain a hydrophilic modified expanded graphite suspension. 16g of aluminum isopropoxide was added to 90g of anhydrous ethanol and stirred at 500rpm for 20min to obtain an aluminum isopropoxide solution. 5g of phytic acid was added to 515g of 75wt% ethanol solution and stirred at 800rpm for 20min. The pH was adjusted to 4.2 by adding 10wt% acetic acid solution to obtain a phytic acid solution.

[0049] Add 2.4g PVP (model K30) and 0.28g ammonium citrate to 206g of 97wt% ethanol solution, stir at 300rpm for 20min, add 33g Mg / Al-LDH, sonicate at 500W for 30min, add 13g hydrophilic modified expanded graphite suspension, stir at 300rpm for 10min, heat to 58℃, slowly add 14g aluminum isopropoxide solution dropwise while stirring at 500rpm, after the addition is complete, stir at 500rpm for 3h, filter, wash 3 times with anhydrous ethanol, add to 204g phytic acid solution, stir at 900rpm for 20min, heat to 48℃, stir at 400rpm for 1.5h, filter, wash twice with deionized water, wash twice with anhydrous ethanol, dry in an environment of 50℃ and 8kPa for 7h to obtain flame-retardant microparticles.

[0050] 105g of EVA (VA content 22%, melt index 10g / 10min), 6g of EVA-g-MAH, 23g of flame retardant microparticles, 0.6g of antioxidant 1010, and 2.5g of EBS were added to a mixer and stirred at 1300rpm for 10min. The mixture was then fed into an extruder and extruded at a screw speed of 210rpm and a die temperature of 180℃. The extrudate was air-cooled and pelletized to obtain a crack-resistant flame retardant material for cables.

[0051] The present invention also includes comparative examples and related experiments.

[0052] Comparative Example 1

[0053] The difference between this comparative example and Example 5 is that the flame-retardant microparticles are replaced with aluminum hydroxide, while the remaining operation steps and reaction conditions are the same as in Example 5, resulting in a crack-resistant flame-retardant material for cables.

[0054] Comparative Example 2

[0055] 105g of EVA (VA content 22%, melt index 10g / 10min), 6g of EVA-g-MAH, 50g of aluminum hydroxide, 0.6g of antioxidant 1010, and 2.5g of EBS were added to a mixer and stirred at 1300rpm for 10min. The mixture was then fed into an extruder and extruded at a screw speed of 210rpm and a die temperature of 180℃. The extrudate was air-cooled and pelletized to obtain a crack-resistant and flame-retardant material for cables.

[0056] Comparative Example 3

[0057] The difference between this comparative example and Example 5 is that aluminum isopropoxide was not added during the preparation of the flame-retardant microparticles. The remaining operation steps and reaction conditions are the same as in Example 5, resulting in a crack-resistant flame-retardant material for cables.

[0058] Comparative Example 4

[0059] The difference between this comparative example and Example 5 is that phytic acid was not added during the preparation of the flame-retardant microparticles. The remaining operation steps and reaction conditions were the same as in Example 5, resulting in a crack-resistant flame-retardant material for cables.

[0060] Performance testing

[0061] The anti-cracking and flame-retardant materials for cables prepared in each embodiment and comparative example were mixed in the corresponding proportions and then fed into a flat vulcanizing machine. They were hot-pressed at 175°C and 10MPa pressure for 10 minutes, cooled to room temperature, and then demolded to obtain a plate sample with a thickness of 1mm. This sample was used to simulate the material properties of the sheath prepared by extrusion process using the same formula.

[0062] Bending fatigue performance test

[0063] Each plate sample was cut into strips 1 cm wide and 15 cm long and fixed on a bending fatigue testing machine. The bending radius was set to 5 mm, the bending angle to ±90°, and the frequency to 30 times / min. The machine was stopped every 100 times, and the bending area was inspected with a magnifying glass. The number of cycles when the strip sample first showed a through crack or completely broke was recorded as the bending fatigue life. The results are shown in Table 1.

[0064] Table 1

[0065]

[0066] Flame retardant performance test

[0067] Each board sample was made into a standard specimen, and a vertical burning test was conducted in accordance with the UL-94 standard to classify the burning level. The results are shown in Table 2.

[0068] Table 2

[0069]

[0070] According to Tables 1 and 2, the bending fatigue life of the plates prepared in Examples 1 to 5 is not much different from that in Example 6, and the flame retardant performance is better than that in Example 6. This indicates that the addition of zinc borate can improve the density of the composite barrier layer and improve its flame retardant performance without affecting the bending fatigue resistance of the sheath. The flame retardant performance of the plate prepared in Example 5 is better than that in Comparative Example 1, and the bending fatigue life and flame retardant performance are better than those in Comparative Example 2. This indicates that the flame retardant material prepared by the present invention can meet the flame retardant performance of the sheath and improve the bending fatigue resistance of the sheath with a smaller amount of flame retardant particles added. The flame retardant properties of the sheet material prepared in Example 5 are better than those in Comparative Example 3, indicating that the addition of aluminum isopropoxide can integrate Mg / Al-LDH, hydrophilic modified expanded graphite, and phytic acid into a whole, forming a continuous composite barrier layer in a high-temperature environment, blocking the inward transfer of heat and oxygen, inhibiting the spread of fire, and improving the flame retardant properties of the sheath. The flame retardant properties of the sheet material prepared in Example 5 are better than those in Comparative Example 4, indicating that the addition of phytic acid can coat a dense carbon layer on the composite skeleton, forming a composite barrier layer that can effectively block the inward transfer of heat and oxygen, and improving the flame retardant properties of the sheath.

Claims

1. A preparation process for a crack-resistant and flame-retardant material for cables, characterized in that, Includes the following steps: S1. PVP and ammonium citrate are dissolved in an ethanol solution, Mg / Al-LDH and hydrophilic modified expanded graphite are added for dispersion, and aluminum isopropoxide solution is added for reaction after heating. After washing, the mixture is dispersed in phytic acid solution, heated for reaction, washed, and dried to obtain flame-retardant microparticles. S2. EVA, EVA-g-MAH, flame retardant microparticles, antioxidants and lubricants are mixed and fed into an extruder for extrusion. The extrudate is cooled and pelletized to obtain crack-resistant flame retardant material for cables.

2. The preparation process of a crack-resistant and flame-retardant material for cables according to claim 1, characterized in that, In step S1, PVP and ammonium citrate are dissolved in a 97-98 wt% ethanol solution, Mg / Al-LDH is added for dispersion, hydrophilic modified expanded graphite suspension is added and mixed, the temperature is raised to 55-65℃, aluminum isopropoxide solution is slowly added under continuous stirring, the reaction is carried out for 2-3 hours, after washing with anhydrous ethanol, it is dispersed in phytic acid solution, the temperature is raised to 45-50℃ and the reaction is carried out for 1-2 hours, after washing with deionized water and anhydrous ethanol, it is dried to obtain flame-retardant microparticles.

3. The preparation process of a crack-resistant and flame-retardant material for cables according to claim 1, characterized in that, In step S1, after dissolving PVP and ammonium citrate in an ethanol solution, zinc borate, Mg / Al-LDH, and hydrophilic modified expanded graphite are added for dispersion.

4. The preparation process of a crack-resistant and flame-retardant material for cables according to claim 2, characterized in that, The hydrophilic modified expanded graphite suspension is prepared by dispersing expanded graphite in an 8-10 wt% hydrogen peroxide solution, heating to 55-60℃ and reacting for 1-2 hours, filtering, washing with deionized water and anhydrous ethanol, dispersing in anhydrous ethanol, adding KH-550 and deionized water, adding acetic acid solution to adjust the pH to 4-5, and reacting for 3-4 hours to obtain the hydrophilic modified expanded graphite suspension.

5. The preparation process of a crack-resistant and flame-retardant material for cables according to claim 2, characterized in that, The drying process takes place at a temperature of 50-60℃, a pressure of 8-12 kPa, and a time of 6-8 hours.

6. The preparation process of a crack-resistant and flame-retardant material for cables according to claim 1, characterized in that, The phytic acid solution is prepared by mixing phytic acid with a 70-75 wt% ethanol solution, and then adding acetic acid solution to adjust the pH to 4-4.3 to obtain the phytic acid solution.

7. The preparation process of a crack-resistant and flame-retardant material for cables according to claim 1, characterized in that, The aluminum isopropoxide solution is prepared by dissolving aluminum isopropoxide in anhydrous ethanol.

8. The preparation process of a crack-resistant and flame-retardant material for cables according to claim 1, characterized in that, In step S2, the screw speed of the extruder is 200-220 rpm, and the die temperature is 170-180℃.

9. A crack-resistant and flame-retardant material for cables, characterized in that, The material is prepared using the preparation process of the anti-cracking and flame-retardant material for cables according to any one of claims 1-8, and comprises the following raw materials in parts by weight: 100-110 parts of EVA, 5-8 parts of EVA-g-MAH, 23-28 parts of flame-retardant microparticles, 0.5-0.8 parts of antioxidant 1010, and 2-3 parts of lubricant EBS; the flame-retardant microparticles comprise the following raw materials in parts by weight: 200-210 parts of 97-98wt% ethanol solution, 2-2.5 parts of PVP, 0.2-0.3 parts of ammonium citrate, 30-34 parts of Mg / Al-LDH, 0-4 parts of zinc borate, 10-15 parts of hydrophilic modified expanded graphite suspension, 12-16 parts of aluminum isopropoxide solution, and 200-210 parts of phytic acid solution.

10. A crack-resistant and flame-retardant material for cables according to claim 9, characterized in that, The preparation process of the hydrophilic modified expanded graphite suspension includes the following raw materials in parts by weight: 30-35 parts expanded graphite, 1-1.2 parts KH-550, and 0.9-1.1 parts deionized water; the aluminum isopropoxide solution includes 14-16 parts aluminum isopropoxide and 80-90 parts anhydrous ethanol; the phytic acid solution includes 4-6 parts phytic acid and 500-520 parts 70-75 wt% ethanol solution.

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