A magnesium hydroxide flame retardant applicable to high-speed extruded cables and its preparation method

Abstract

The present invention relates to the technical field of flame retardants, and particularly relates to a magnesium hydroxide flame retardant applicable to high-speed extrusion cables and a preparation method thereof. Through the synergistic effect of poly(propylene carbonate) and tetrabutylammonium bromide, the present invention induces magnesium hydroxide to form a flaky crystal structure with a high aspect ratio, and combines the surface modification of sodium stearate to achieve multi-scale regulation of particle morphology and interfacial properties. This flame retardant exhibits excellent dispersion stability and interfacial compatibility in high-speed extrusion processing, solving the problems of poor processing adaptability and insufficient flame retardancy efficiency caused by uneven dispersion and accumulation of frictional heat of traditional magnesium hydroxide flame retardants.

Description

Technical Field

[0001] The present invention relates to the technical field of flame retardants, and particularly relates to a magnesium hydroxide flame retardant applicable to high-speed extrusion cables and a preparation method thereof. Background Art

[0002] As an environmentally friendly inorganic flame retardant, magnesium hydroxide has become an important alternative to traditional halogen-based flame retardants due to its release of crystal water (heat absorption capacity of about 1.44 kJ / g), formation of a magnesium oxide layer with a barrier effect, and non-toxic and harmless decomposition products during the thermal decomposition process at 300 - 340°C. Its flame retardant mechanism includes triple effects: endothermic cooling, gas-phase dilution, and solid-phase barrier. This synergistic effect enables it to exhibit unique advantages in polymer materials in fields such as wires and cables, electronics, and appliances.

[0003] However, the strong polarity and high surface energy (about 200 - 300 mJ / m²) of magnesium hydroxide result in poor interfacial compatibility in non-polar polymer matrices such as polyethylene and polypropylene, and it is easy to form micron-sized aggregates (usually with a particle size > 5 μm). This phase separation phenomenon not only causes a decrease in the volume filling effect of the flame retardant (the critical addition amount needs to reach 60 - 65 wt%), but also triggers stress concentration points, reducing the tensile strength of the material by 40% - 50% and the impact strength by more than 60%. During the high-speed extrusion processing (screw speed > 500 rpm), the shear friction between the aggregated particles and the twin-screw generates local overheating (temperature fluctuation up to ±15°C), resulting in a 30% - 50% decrease in the melt flow index (MFI), seriously restricting production efficiency.

[0004] Although surface modification can improve the dispersibility by coating with stearic acid or silane coupling agents, conventional dry modification has problems such as low coating rate and poor thermal stability. Although wet modification can improve the coating uniformity, it faces industrialization bottlenecks such as complex processes (requiring solvent recovery) and increased costs. Although the recently studied nano-magnesium hydroxide can improve the dispersibility, the sharp increase in specific surface area instead exacerbates the van der Waals force between particles, making it more likely to form secondary aggregates in a high-speed shear field.

[0005] Therefore, developing a magnesium hydroxide flame retardant with good dispersibility, processing fluidity, and interfacial bonding strength has become the key to breaking through the technical upgrade bottleneck in the cable industry. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a magnesium hydroxide flame retardant applicable to high-speed extrusion cables and a preparation method thereof to solve the problem of poor adaptability of traditional magnesium hydroxide flame retardants in the processing of high-speed extrusion cables.

[0007] Based on the above purpose, the present invention provides a preparation method for a magnesium hydroxide flame retardant applicable to high-speed extrusion cables, which is prepared by the following steps:

[0008] (1) Add magnesium sulfate heptahydrate, poly(propylene carbonate), and tetrabutylammonium bromide into deionized water, heat up to 55 - 65 °C, stir at a speed of 500 - 700 rpm for 25 - 35 min, then heat up to 80 - 90 °C, add sodium hydroxide aqueous solution dropwise for the first time, stir and react for 2 - 4 h, add sodium stearate, add sodium hydroxide aqueous solution dropwise for the second time, and continue to stir for 2 - 4 h to obtain a magnesium hydroxide precursor suspension;

[0009] (2) Transfer the magnesium hydroxide precursor suspension to a Buchner funnel, perform vacuum filtration using a polytetrafluoroethylene filter membrane, and wash to obtain a filter cake;

[0010] (3) Dry the filter cake under vacuum, then add it to a ball mill, perform dry ball milling at a speed of 300 - 500 rpm for 40 - 50 min, and pass through a vibrating sieve with 300 - 350 mesh to obtain primary powder;

[0011] (4) Crush the primary powder with a jet mill to obtain a magnesium hydroxide flame retardant with a D50 particle size of 1.0 - 1.3 μm suitable for high - speed extrusion cables.

[0012] Preferably, in step (1), the dosage ratio of magnesium sulfate heptahydrate, poly(propylene carbonate), tetrabutylammonium bromide, deionized water, sodium hydroxide aqueous solution, and sodium stearate is 20 - 30 g: 3 - 4 g: 0.01 - 0.03 g: 80 - 120 mL: 63 - 77 mL: 0.5 - 1 g.

[0013] Preferably, in step (1), the concentration of the sodium hydroxide aqueous solution is 2.8 - 3.2 mol / L.

[0014] Preferably, in step (1), the volume ratio of the first addition of sodium hydroxide aqueous solution to the second addition of sodium hydroxide aqueous solution is 45 - 55: 18 - 22.

[0015] Preferably, in step (1), the weight - average molecular weight of poly(propylene carbonate) is 6000 - 10000.

[0016] Preferably, in step (2), the pore size of the polytetrafluoroethylene filter membrane is 0.4 - 0.5 μm.

[0017] Preferably, in step (3), the temperature of vacuum drying is 80 - 90 °C, and the vacuum degree is - 0.08 ± 0.01 MPa.

[0018] Preferably, in step (3), the ball milling uses zirconia balls as the ball - milling medium, and the ball - to - material ratio is 5: 1.

[0019] Preferably, in step (3), the mesh number of the vibrating sieve is 300 - 350 mesh.

[0020] Furthermore, the present invention also provides a magnesium hydroxide flame retardant applicable to high-speed extrusion of cables, which is obtained by the preparation method of the magnesium hydroxide flame retardant applicable to high-speed extrusion of cables described above.

[0021] Advantages of the present invention:

[0022] The present invention provides a preparation method of a magnesium hydroxide flame retardant. By introducing functional additives such as poly(propylene carbonate), tetrabutylammonium bromide, and sodium stearate during the preparation process, the dispersibility, processing performance, and flame retardancy efficiency of the flame retardant are significantly improved.

[0023] The poly(propylene carbonate) introduced in the present invention undergoes controlled hydrolysis in an alkaline environment, and the generated active groups form chemical bonds with the crystal planes of magnesium hydroxide, inhibiting excessive particle growth and optimizing the surface chemical properties of the particles, thereby improving the dispersion uniformity of the flame retardant in the polypropylene matrix.

[0024] The tetrabutylammonium bromide introduced in the present invention induces magnesium hydroxide to form platelet particles with a high aspect ratio through dynamic coordination and surface adsorption mechanisms, improves the particle morphology, reduces the processing shear resistance, and simultaneously enhances the interfacial bonding strength between the flame retardant and the polypropylene matrix.

[0025] The sodium stearate introduced in the present invention reduces the surface energy of the particles through surface modification and provides a lubricating effect during high-speed extrusion, effectively reducing die wear and melt temperature fluctuations, and improving the processing stability and the surface quality of the cable.

[0026] The present invention realizes the efficient preparation of the flame retardant through multi-scale regulation, is applicable to the high-speed extrusion process, and has important industrial application value. Specific embodiments

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following further elaborates on the present invention in detail with reference to specific embodiments.

[0028] Example 1

[0029] (1) Add 20 g of magnesium sulfate heptahydrate, 3 g of poly(propylene carbonate) (Mw = 6000), and 0.01 g of tetrabutylammonium bromide to 80 mL of deionized water, heat up to 55 °C, stir at a speed of 500 rpm for 25 min, then heat up to 80 °C, dropwise add 45 mL of a sodium hydroxide aqueous solution with a concentration of 2.8 mol / L, stir and react for 2 h, add 0.5 g of sodium stearate, then dropwise add 18 mL of a sodium hydroxide aqueous solution with a concentration of 2.8 mol / L, and continue to stir for 2 h to obtain a magnesium hydroxide precursor suspension;

[0030] (2) Transfer the magnesium hydroxide precursor suspension to a Buchner funnel, and vacuum filter it using a 0.4 μm polytetrafluoroethylene filter membrane. Wash it alternately with deionized water and absolute ethanol three times in sequence to obtain a filter cake.

[0031] (3) Place the filter cake in a vacuum drying oven and dry it at 80 °C and -0.07 MPa for 16 h. Add the dried product to a planetary ball mill, use zirconia balls as the ball milling medium (ball-to-material ratio 5:1), and dry ball mill at 300 rpm for 40 min. Pass it through a 300-mesh vibrating sieve to obtain primary powder.

[0032] (4) Crush the primary powder through a jet mill to obtain a magnesium hydroxide flame retardant with a D50 particle size of 1.0 μm suitable for high-speed extrusion cables.

[0033] Example 2

[0034] (1) Add 24.5 g of magnesium sulfate heptahydrate, 3.5 g of poly(propylene carbonate) (Mw = 8000), and 0.02 g of tetrabutylammonium bromide to 100 mL of deionized water. Heat it to 60 °C and stir at 600 rpm for 30 min. Then heat it to 85 °C, add dropwise 50 mL of a 3.0 mol / L sodium hydroxide aqueous solution, stir and react for 3 h. Add 0.7 g of sodium stearate, then add dropwise 20 mL of a 3.0 mol / L sodium hydroxide aqueous solution, and continue to stir for 3 h to obtain a magnesium hydroxide precursor suspension.

[0035] (2) Transfer the magnesium hydroxide precursor suspension to a Buchner funnel, and vacuum filter it using a 0.45 μm polytetrafluoroethylene filter membrane. Wash it alternately with deionized water and absolute ethanol three times in sequence to obtain a filter cake.

[0036] (3) Place the filter cake in a vacuum drying oven and dry it at 85 °C and -0.08 MPa for 18 h. Add the dried product to a planetary ball mill, use zirconia balls as the ball milling medium (ball-to-material ratio 5:1), and dry ball mill at 400 rpm for 45 min. Pass it through a 325-mesh vibrating sieve to obtain primary powder.

[0037] (4) Crush the primary powder through a jet mill to obtain a magnesium hydroxide flame retardant with a D50 particle size of 1.2 μm suitable for high-speed extrusion cables.

[0038] Example 3

[0039] (1) Add 30 g of magnesium sulfate heptahydrate, 4 g of poly(propylene carbonate) (Mw = 10000), and 0.03 g of tetrabutylammonium bromide to 120 mL of deionized water. Heat the mixture to 65 °C and stir at 700 rpm for 35 min. Then heat it to 90 °C and add dropwise 55 mL of an aqueous sodium hydroxide solution with a concentration of 3.2 mol / L. Stir and react for 4 h. Add 1 g of sodium stearate, and then add dropwise 22 mL of an aqueous sodium hydroxide solution with a concentration of 3.2 mol / L. Continue stirring for 4 h to obtain a magnesium hydroxide precursor suspension;

[0040] (2) Transfer the magnesium hydroxide precursor suspension to a Buchner funnel and perform vacuum filtration using a 0.5-μm polytetrafluoroethylene filter membrane. Wash it alternately three times with deionized water and anhydrous ethanol to obtain a filter cake;

[0041] (3) Place the filter cake in a vacuum drying oven and dry it at 90 °C and -0.09 MPa for 20 h. Add the dried product to a planetary ball mill and use zirconia balls as the ball-milling medium (ball-to-material ratio 5:1). Perform dry ball milling at 500 rpm for 50 min and pass through a 350-mesh vibrating sieve to obtain a primary powder;

[0042] (4) Crush the primary powder with a jet mill to obtain a magnesium hydroxide flame retardant with a D50 particle size of 1.3 μm suitable for high-speed extrusion cables.

[0043] Comparative Example 1:

[0044] The difference between Comparative Example 1 and Example 2 is that poly(propylene carbonate) was not added in step (1);

[0045] The specific steps are as follows:

[0046] (1) Add 24.5 g of magnesium sulfate heptahydrate and 0.02 g of tetrabutylammonium bromide to 100 mL of deionized water. Heat the mixture to 60 °C and stir at 600 rpm for 30 min. Then heat it to 85 °C and add dropwise 50 mL of an aqueous sodium hydroxide solution with a concentration of 3.0 mol / L. Stir and react for 3 h. Add 0.7 g of sodium stearate, and then add dropwise 20 mL of an aqueous sodium hydroxide solution with a concentration of 3.0 mol / L. Continue stirring for 3 h to obtain a magnesium hydroxide precursor suspension;

[0047] (2) Transfer the magnesium hydroxide precursor suspension to a Buchner funnel and perform vacuum filtration using a 0.45-μm polytetrafluoroethylene filter membrane. Wash it alternately three times with deionized water and anhydrous ethanol to obtain a filter cake;

[0048] (3) Place the filter cake in a vacuum drying oven and dry it at 85 °C under -0.08 MPa for 18 h. Add the dried product to a planetary ball mill, use zirconia balls as the ball milling medium (ball-to-material ratio 5:1), perform dry ball milling at 400 rpm for 45 min, and pass through a 325-mesh vibrating sieve to obtain the primary powder;

[0049] (4) Crush the primary powder with a jet mill to obtain a magnesium hydroxide flame retardant with a D50 particle size of 1.2 μm suitable for high-speed extrusion cables.

[0050] Comparative Example 2:

[0051] The difference between Comparative Example 2 and Example 2 is that tetrabutylammonium bromide was not added in step (1);

[0052] The specific steps are as follows:

[0053] (1) Add 24.5 g of magnesium sulfate heptahydrate and 3.5 g of poly(propylene carbonate) (Mw = 8000) to 100 mL of deionized water, heat up to 60 °C, stir at 600 rpm for 30 min, then heat up to 85 °C, add dropwise 50 mL of a 3.0 mol / L sodium hydroxide aqueous solution, stir and react for 3 h, add 0.7 g of sodium stearate, then add dropwise 20 mL of a 3.0 mol / L sodium hydroxide aqueous solution, and continue to stir for 3 h to obtain a magnesium hydroxide precursor suspension;

[0054] (2) Transfer the magnesium hydroxide precursor suspension to a Buchner funnel, perform vacuum filtration using a 0.45-μm polytetrafluoroethylene filter membrane, and wash it alternately three times with deionized water and absolute ethanol to obtain a filter cake;

[0055] (3) Place the filter cake in a vacuum drying oven and dry it at 85 °C under -0.08 MPa for 18 h. Add the dried product to a planetary ball mill, use zirconia balls as the ball milling medium (ball-to-material ratio 5:1), perform dry ball milling at 400 rpm for 45 min, and pass through a 325-mesh vibrating sieve to obtain the primary powder;

[0056] (4) Crush the primary powder with a jet mill to obtain a magnesium hydroxide flame retardant with a D50 particle size of 1.2 μm suitable for high-speed extrusion cables.

[0057] Comparative Example 3:

[0058] The difference between Comparative Example 3 and Example 2 is that sodium stearate was not added in step (1):

[0059] The specific steps are as follows:

[0060] (1) Add 24.5 g of magnesium sulfate heptahydrate, 3.5 g of poly(propylene carbonate) (Mw = 8000), and 0.02 g of tetrabutylammonium bromide to 100 mL of deionized water. Heat the mixture to 60 °C and stir it at 600 rpm for 30 min. Then heat it to 85 °C and add dropwise 50 mL of a 3.0 mol / L aqueous sodium hydroxide solution. Stir the reaction for 3 h, then add dropwise another 20 mL of a 3.0 mol / L aqueous sodium hydroxide solution and continue stirring for 3 h to obtain a magnesium hydroxide precursor suspension.

[0061] (2) Transfer the magnesium hydroxide precursor suspension to a Buchner funnel and vacuum filter it using a 0.45 μm polytetrafluoroethylene membrane. Wash it alternately three times with deionized water and anhydrous ethanol to obtain a filter cake.

[0062] (3) Place the filter cake in a vacuum drying oven and dry it at 85 °C and -0.08 MPa for 18 h. Add the dried product to a planetary ball mill and use zirconia balls as the ball-milling medium (ball-to-material ratio of 5:1). Ball-mill it dry at 400 rpm for 45 min and pass it through a 325-mesh vibrating sieve to obtain a primary powder.

[0063] (4) Crush the primary powder with a jet mill to obtain a magnesium hydroxide flame retardant with a D50 particle size of 1.2 μm suitable for high-speed extrusion cables.

[0064] Comparative Example 4:

[0065] The difference between Comparative Example 4 and Example 2 is that in step (1), first add dropwise 50 mL of a 3.0 mol / L aqueous sodium hydroxide solution, stir the reaction for 3 h, then add dropwise another 20 mL of a 3.0 mol / L aqueous sodium hydroxide solution, stir the reaction for 3 h, and then add sodium stearate and stir for 20 min to obtain a magnesium hydroxide precursor suspension.

[0066] The specific steps are as follows:

[0067] (1) Add 24.5 g of magnesium sulfate heptahydrate, 3.5 g of poly(propylene carbonate) (Mw = 8000), and 0.02 g of tetrabutylammonium bromide to 100 mL of deionized water. Heat the mixture to 60 °C and stir it at 600 rpm for 30 min. Then heat it to 85 °C, first add dropwise 50 mL of a 3.0 mol / L aqueous sodium hydroxide solution, stir the reaction for 3 h, then add dropwise another 20 mL of a 3.0 mol / L aqueous sodium hydroxide solution, stir the reaction for 3 h, and then add sodium stearate and stir for 20 min to obtain a magnesium hydroxide precursor suspension.

[0068] (2) Transfer the magnesium hydroxide precursor suspension to a Buchner funnel and vacuum filter it using a 0.45 μm polytetrafluoroethylene membrane. Wash it alternately three times with deionized water and anhydrous ethanol to obtain a filter cake.

[0069] (3) Place the filter cake in a vacuum drying oven and dry it at 85 °C and -0.08 MPa for 18 h. Add the dried product to a planetary ball mill, use zirconia balls as the ball milling medium (ball-to-material ratio is 5:1), and perform dry ball milling at a rotational speed of 400 rpm for 45 min. Pass through a 325-mesh vibrating screen to obtain the primary powder.

[0070] (4) Crush the primary powder through a jet mill to obtain a magnesium hydroxide flame retardant with a D50 particle size of 1.2 μm suitable for high-speed extrusion cables.

[0071] Performance testing:

[0072] Melt flow rate: Blend the flame retardant with polypropylene (melt index of 20 g / 10 min at 190 °C and 2.16 kg) at a mass ratio of 30:100 and granulate at 190 °C. Use a melt flow rate instrument to measure the melt flow index at 230 °C and a load of 2.16 kg. The results are shown in Table 1.

[0073] Oxygen index determination: Test according to GB / T 2406.2-2023. Blend the flame retardant with polypropylene (melt index of 20 g / 10 min at 190 °C and 2.16 kg) at a mass ratio of 15:100 and granulate at 190 °C. Extrude and coat a copper conductor at a linear speed of 500 m / min to prepare a cable with a coating thickness of 0.7 mm. Vertically install it in the combustion chamber of an oxygen index instrument, set the initial oxygen concentration to 28%, use the top ignition method, and record the lowest oxygen concentration required for continuous combustion of 30 mm in length. The results are shown in Table 1.

[0074] Vertical burning test: Test according to GB / T 2408-2021. Blend the flame retardant with polypropylene (melt index of 20 g / 10 min at 190 °C and 2.16 kg) at a mass ratio of 15:100 and granulate at 190 °C. Extrude and coat a copper conductor at a linear speed of 500 m / min to prepare a cable with a coating thickness of 0.7 mm. Vertically fix it in the combustion chamber, apply a 20-mm blue flame for 10 seconds; record the afterflame time after the first removal of the flame and whether the dripping ignites the absorbent cotton. Repeat ignition until a V-0, V-1, or V-2 classification determination is obtained. The results are shown in Table 1.

[0075] Surface quality inspection of extruded cables: Test according to GB / T 2951.11-2008. Blend the flame retardant with polypropylene (melt index of 20 g / 10 min at 190 °C and 2.16 kg) at a mass ratio of 15:100 and granulate at 190 °C. Extrude and coat a copper conductor at a linear speed of 500 m / min to prepare a cable with a coating thickness of 0.7 mm. Use a three-dimensional surface profiler to measure the surface roughness Ra value within a 10-cm length. The results are shown in Table 1.

[0076] Table 1 Performance Test Results

[0077] Melt flow rate / g / 10min Oxygen index / % Vertical burning rating Surface roughness Ra / μm Example 1 18.1 32.8 V-0 1.4 Example 2 18.5 33.5 V-0 1.2 Example 3 18.3 33.9 V-0 1.3 Comparative example 1 16.5 27.4 V-1 2.8 Comparative example 2 17.4 29.5 V-1 2.2 Comparative example 3 16.3 31.8 V-0 3.0 Comparative example 4 17.8 31.2 V-0 2.1

[0078] Data Analysis:

[0079] From the data of Examples 1 - 3 in Table 1, it can be seen that the magnesium hydroxide flame retardant prepared by the present invention for high - speed extrusion cables has excellent processing performance and flame retardant performance. The performance of the melt flow rate indicates that the flame retardant can be fully compatible with the polypropylene matrix and maintain good fluidity and processing stability during high - speed extrusion. The lower surface roughness reflects that the magnesium hydroxide flame retardant has a lubricating effect during high - speed extrusion, reducing mechanical wear with the die. This may be because the modification of sodium stearate and polypropylene carbonate reduces the roughness of the particles and improves the compatibility with the matrix, thereby optimizing the processing surface quality of the cable.

[0080] From the data of Example 2 and Comparative Example 1 in Table 1, it can be seen that the introduction of polypropylene carbonate significantly optimizes the performance of the flame retardant. This polymer may undergo controlled hydrolysis in an alkaline reaction environment, and the active groups generated therefrom form chemical bonds with the magnesium hydroxide crystal plane, thereby forming a steric hindrance layer on the particle surface. This coating effect not only inhibits the excessive growth of particles but also improves the dispersion uniformity of the flame retardant in the polypropylene melt. In addition, the decomposition products of polypropylene carbonate may participate in the char - forming reaction during combustion and cooperate with the water vapor released by magnesium hydroxide to form a multi - layer barrier structure, effectively delaying the diffusion of pyrolysis products. Surface chemical modification also reduces the interfacial tension between the particles and polymer segments, enabling the flame retardant to maintain stable flow characteristics under high - shear extrusion conditions, which is crucial for maintaining the dimensional accuracy of the cable coating layer.

[0081] As can be seen from the data of Example 2 and Comparative Example 2 in Table 1, tetrabutylammonium bromide significantly optimizes the flame retardant performance through a synergistic catalytic mechanism: as a phase transfer catalyst, its quaternary ammonium cation forms dynamic coordination with the carbonate groups of poly(propylene carbonate), reducing the activation energy of alkaline hydrolysis and promoting the directional cleavage of the polymer to generate terminal carbonate groups. These active groups bind to the hydroxyl groups on the crystal surface of magnesium hydroxide through hydrogen bonds and ionic bonds to construct a stable organic-inorganic hybrid interface layer, effectively inhibiting particle agglomeration. During the crystal growth stage, tetrabutylammonium bromide selectively adsorbs on specific crystal planes of magnesium hydroxide, inducing the formation of flaky primary particles with a high aspect ratio by regulating the surface energy distribution. This morphological feature makes it easier to obtain micron-sized particles with smooth edges during subsequent ball milling, reducing the processing shear resistance. The oligomer fragments generated by hydrolysis migrate to the polypropylene-flame retardant interface during melt blending, with their polar ends anchored on the surface of the flame retardant and the non-polar segments entangled with the polypropylene matrix, forming a gradient transition interface structure and alleviating the stress concentration caused by the difference in the moduli of the two phases. This multi-scale regulation realizes the synergistic improvement of the dispersibility, processing rheology and flame retardancy efficiency of the flame retardant.

[0082] As can be seen from the data of Example 2 and Comparative Example 3 in Table 1, the surface modification of sodium stearate significantly improves the processing compatibility of the flame retardant. Its long-chain alkyl group forms an oriented hydrophobic layer on the surface of magnesium hydroxide particles through chemical adsorption. This organic-inorganic hybrid structure not only reduces the surface energy of the particles but also inhibits the van der Waals force between the particles through steric hindrance effects. During high-speed extrusion, this surface lubricating layer reduces the accumulation of frictional heat between the flame retardant and the metal surfaces of the screw and die cavity, thus maintaining the stability of the melt temperature. In addition, the decomposition temperature of sodium stearate matches the processing window of polypropylene. It migrates partially to the matrix-flame retardant interface during melt mixing, acting as a compatibilizer and further strengthening the bonding strength of the two-phase interface.

[0083] As can be seen from the data of Example 2 and Comparative Example 4 in Table 1, the introduction of sodium stearate during the crystal growth stage can effectively improve the processing compatibility of the flame retardant. This is because the introduction of sodium stearate in the later stage of crystal growth may regulate the surface energy distribution of the particles by selective adsorption on specific crystal planes, resulting in a significant increase in the sphericity of the particles after airflow comminution. The optimization of the process sequence realizes the synergistic control of crystal morphology-surface characteristics-comminution efficiency, which is the core technical feature for obtaining high-performance flame retardants.

[0084] Those of ordinary skill in the art should understand that: the discussion of any above embodiment is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A preparation method of magnesium hydroxide flame retardant applicable to high-speed extrusion cables, characterized in that, It is prepared by the following steps: (1) Add magnesium sulfate heptahydrate, poly(propylene carbonate), and tetrabutylammonium bromide into deionized water, heat up to 55 - 65 °C, stir at a speed of 500 - 700 rpm for 25 - 35 min, then heat up to 80 - 90 °C, first add sodium hydroxide aqueous solution dropwise, stir and react for 2 - 4 h, add sodium stearate, second add sodium hydroxide aqueous solution dropwise, and continue to stir for 2 - 4 h to obtain a magnesium hydroxide precursor suspension; (2) Transfer the magnesium hydroxide precursor suspension to a Buchner funnel, vacuum filter using a polytetrafluoroethylene filter membrane, and wash to obtain a filter cake; (3) Vacuum dry the filter cake, then add it to a ball mill, dry ball mill at a speed of 300 - 500 rpm for 40 - 50 min, and pass through a vibrating sieve with 300 - 350 mesh to obtain primary powder; (4) Crush the primary powder with a jet mill to obtain a magnesium hydroxide flame retardant with a D50 particle size of 1.0 - 1.3 μm suitable for high - speed extrusion cables; In the step (1), the dosage ratio of magnesium sulfate heptahydrate, poly(propylene carbonate), tetrabutylammonium bromide, deionized water, sodium hydroxide aqueous solution, and sodium stearate is 20 - 30 g: 3 - 4 g: 0.01 - 0.03 g: 80 - 120 mL: 63 - 77 mL: 0.5 - 1 g; In the step (1), the concentration of the sodium hydroxide aqueous solution is 2.8 - 3.2 mol / L; In the step (1), the volume ratio of the first addition of sodium hydroxide aqueous solution to the second addition of sodium hydroxide aqueous solution is 45 - 55: 18 - 22.

2. The preparation method of the magnesium hydroxide flame retardant applicable to high-speed extrusion cables according to claim 1, characterized in that, In the step (1), the weight - average molecular weight of poly(propylene carbonate) is 6000 - 10000.

3. The preparation method of the magnesium hydroxide flame retardant applicable to high-speed extrusion cables according to claim 1, characterized in that, In the step (2), the pore size of the polytetrafluoroethylene filter membrane is 0.4 - 0.5 μm.

4. The preparation method of the magnesium hydroxide flame retardant applicable to high-speed extrusion cables according to claim 1, characterized in that, In the step (3), the temperature of vacuum drying is 80 - 90 °C, and the vacuum degree is - 0.08 ± 0.01 MPa.

5. The preparation method of the magnesium hydroxide flame retardant applicable to high-speed extrusion cables according to claim 1, characterized in that, In the step (3), zirconia balls are used as the ball - milling medium for ball milling, and the ball - to - material ratio is 5:

1.

6. The preparation method of the magnesium hydroxide flame retardant applicable to high-speed extrusion cables according to claim 1, characterized in that, In the step (3), the mesh number of the vibrating sieve is 300 - 350 mesh.

7. A magnesium hydroxide flame retardant applicable to high-speed extruded cables, characterized in that, It is obtained by the preparation method of the magnesium hydroxide flame retardant suitable for high - speed extrusion cables according to any one of claims 1 - 6.