Modified magnesium hydroxide, and preparation method and application thereof

Abstract

The application relates to the technical field of inorganic flame-retardant fillers and modification, in particular to modified magnesium hydroxide as well as a preparation method and application thereof, wherein the modified magnesium hydroxide comprises, from inside to outside, a core, an inner layer and an outer layer; the core comprises hexagonal flaky magnesium hydroxide which is subjected to round angle passivation treatment; the inner layer is a tetraethoxysilane modification layer, and the tetraethoxysilane is bonded to the surface of the core through Si-O-Mg covalent bonds; and the outer layer is a stearic acid coating layer. Through the screening and round angle treatment of magnesium hydroxide raw powder crystal shape, the dense bonding of the tetraethoxysilane inner layer and the hydrophobic coating of the trace stearic acid outer layer, the technical problems of poor dispersibility, weak water resistance and interference with the silane self-crosslinking system of the magnesium hydroxide are synchronously solved; the product has high activation degree, excellent water boiling resistance, uniform dispersion after high-filling of polyolefins, stable mechanical and flame-retardant properties, is especially suitable for a silane self-crosslinking cable material system, and can significantly improve the cable extrusion speed and product qualification rate.

Description

Technical Field

[0001] This invention relates to a modified magnesium hydroxide, its preparation method and application, belonging to the field of inorganic flame retardant fillers and modification technology. Background Technology

[0002] Magnesium hydroxide (Mg(OH)2, MH) is an environmentally friendly inorganic flame-retardant filler with advantages such as halogen-free, low-smoke, non-toxic, and good thermal stability. Therefore, magnesium hydroxide is widely used in polyolefin-based composite materials in fields such as wires and cables, automotive interiors, and building plastics. Among them, hexagonal plate-shaped magnesium hydroxide, due to its two-dimensional layered structure, can form a "labyrinth effect" in the matrix, resulting in better flame-retardant and oxygen-barrier effects, as well as better processing fluidity.

[0003] However, the direct use of magnesium hydroxide in polyolefin systems (such as polyethylene PE, ethylene-vinyl acetate copolymer EVA, and polypropylene PP) also presents many technical challenges. For example, magnesium hydroxide has a surface rich in polar hydroxyl groups, resulting in poor interfacial compatibility with non-polar polyolefins. To achieve satisfactory flame retardant effects (oxygen index ≥30%), the filler content of magnesium hydroxide typically needs to be as high as 120-200 parts (relative to 100 parts of resin). At such high filler contents, unmodified or insufficiently modified magnesium hydroxide is prone to agglomeration, leading to a significant decrease in the mechanical properties of the composite material (tensile strength, elongation at break), poor processing flowability, and a rough surface on the extruded product.

[0004] Silane self-crosslinking low-smoke halogen-free flame-retardant cable materials are also an important development direction in the high-end cable industry. The technical characteristics of this type of material are: first, silane is grafted onto polyolefins, extruded, and then hydrolyzed and condensed in a warm water or humid environment, transforming the linear polymer chains into a three-dimensional network structure. This crosslinking process typically requires boiling in water at around 95°C for 12 hours to complete. Boiling crosslinking significantly improves the cable's heat resistance, environmental stress cracking resistance, and mechanical strength. However, this boiling crosslinking process places extremely high demands on the water resistance of the flame-retardant filler. If the magnesium hydroxide surface modification layer is only physically adsorbed (such as single stearic acid modification), the modifier will gradually detach during the boiling process. Magnesium hydroxide is re-exposed and absorbs moisture, reducing the flame-retardant efficiency. Simultaneously, the moisture in the filler will severely deteriorate the cable's electrical insulation performance, causing the volume resistivity to drop by several orders of magnitude, and even leading to cable breakdown. More critically, the detached stearic acid or other organic modifiers may migrate to the polyolefin matrix, adsorbing and poisoning the organotin catalyst required for silane self-crosslinking, resulting in incomplete crosslinking. The gel ratio (a key indicator of the degree of crosslinking) is thus significantly reduced, preventing the cable from achieving the expected heat resistance and mechanical properties. Therefore, magnesium hydroxide used in silane self-crosslinking cable materials must possess both excellent water-boiling stability and high compatibility with the self-crosslinking system.

[0005] Existing magnesium hydroxide composite modification technologies mostly employ a one-step mixing and addition of silane coupling agents and stearic acid. Silane and stearic acid compete for adsorption on the particle surface, failing to form an ordered layer structure, making it difficult to simultaneously achieve good water resistance and dispersibility. Previous research has attempted to improve water resistance by chemically modifying magnesium hydroxide with silane coupling agents (such as KH550, A172, and KH570) or by physically coating it with stearic acid to improve dispersibility. For example, patent application CN113429631A discloses a method for preparing a magnesium hydroxide flame retardant by first modifying it with a silane coupling agent and then coating it a second time with stearic acid, and applied it to low-smoke halogen-free cable materials. However, in this technical solution: the silane coupling agent used cannot construct a continuous and dense cross-linked water-resistant layer on the magnesium hydroxide surface; the amount of stearic acid used is extremely high, far exceeding the amount required to form a similar monolayer structure, and the residual free stearic acid easily interferes with the silane self-crosslinking catalytic system; its water resistance and compatibility with the self-crosslinking system still need improvement.

[0006] Currently, there are relatively few reports on the application of modified magnesium hydroxide specifically to silane self-crosslinking low-smoke halogen-free flame-retardant cable materials while simultaneously achieving high water resistance, high dispersibility, and no interference with the crosslinking reaction. Therefore, developing a magnesium hydroxide product with controllable original powder crystal form and simultaneously solving problems related to dispersibility, water resistance, and self-crosslinking compatibility through ordered double-layer modification is of significant value in addressing the processing and performance bottlenecks of high-end silane self-crosslinking cable materials. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a modified magnesium hydroxide, its preparation method, and its applications. Through screening and rounding the crystal form of magnesium hydroxide powder, dense bonding within a tetraethoxysilane inner layer, and hydrophobic coating with trace amounts of stearic acid on the outer layer, the technical problems of poor dispersibility, weak water resistance, and interference with the silane self-crosslinking system of magnesium hydroxide are simultaneously solved. The product exhibits high activation, excellent water resistance, uniform dispersion after high-filling polyolefin production, and stable mechanical and flame-retardant properties. It is particularly suitable for silane self-crosslinking cable material systems, significantly improving cable extrusion speed and product qualification rate.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a modified magnesium hydroxide, wherein the modified magnesium hydroxide comprises, from the inside out: a core, an inner layer and an outer layer; The core contains hexagonal sheet-like magnesium hydroxide (MH) with rounded and passivated corners. The inner layer is a tetraethoxysilane modified layer, and the tetraethoxysilane (TES) is bonded to the core surface through Si-O-Mg covalent bonds; The outer layer is a stearic acid (SA) coating.

[0009] Furthermore, the hexagonal flake magnesium hydroxide has an aspect ratio of 8-15; a particle size D50 of 1-4 μm; and a hexagonal angular radius of 70°-85°.

[0010] Furthermore, the thickness of the inner layer is 5-15 nm, and the thickness of the outer layer is 1-3 nm.

[0011] This invention also discloses a method for preparing modified magnesium hydroxide, wherein the preparation method is as follows: S1. Drying and passivation of raw powder: Hexagonal sheet-shaped magnesium hydroxide is heated and stirred to obtain dried and passivated magnesium hydroxide. S2, inner tetraethoxysilane chemical bonding modification: Under warm conditions, a tetraethoxysilane dispersion is uniformly sprayed onto the dried and passivated magnesium hydroxide surface, and then heated to carry out a condensation reaction to form Si-O-Mg covalent bonds and construct a three-dimensional network inner layer. S3, Outer Covering: The modified magnesium hydroxide in step S2 is uniformly mixed with stearic acid and heated and kept warm. After the stearic acid melts, it is uniformly adhered to the outer surface to form an outer layer. S4. Post-processing: The modified magnesium hydroxide is obtained by cooling and sieving.

[0012] Furthermore, by weight, the amount of hexagonal flake magnesium hydroxide is 100 parts, the amount of tetraethoxysilane is 1.8-2.8 parts, and the amount of stearic acid is 0.3-0.7 parts.

[0013] Further, the specific operation of drying and passivating the raw powder in step S1 is as follows: put the hexagonal flake magnesium hydroxide raw powder into a high-speed mixer, and keep it at a temperature of 115-120℃ and a rotation speed of 70-80r / min for 30-35min to obtain dried and passivated magnesium hydroxide.

[0014] Further, the preparation method of the tetraethoxysilane dispersion in step S2 is as follows: according to the weight parts, under the conditions of room temperature and protection from light, 1.8-2.8 parts of tetraethoxysilane and 7-10 parts of anhydrous ethanol are mixed evenly; then 0.4-0.6 parts of deionized water are slowly added dropwise and stirred for 5-10 minutes to obtain the tetraethoxysilane dispersion, which is directly used in the modification process in step S2.

[0015] Further, the specific operation of step S2 is as follows: After drying and passivating, magnesium hydroxide is stirred at a speed of 70-80 r / min at a temperature of 88-92℃, and tetraethoxysilane dispersion is sprayed evenly to make the tetraethoxysilane and magnesium hydroxide come into uniform contact. After spraying, the temperature is raised to 118-122℃ and kept at the temperature for 40-45 min to carry out the condensation reaction.

[0016] Further, the specific operation of step S3 is as follows: under the conditions of a temperature of 108-112℃ and a stirring speed of 60-70r / min, powdered stearic acid is added, and the mixture is kept warm and stirred for 20-25min. After the stearic acid melts, it is uniformly attached to the outer surface to form an outer layer.

[0017] The present invention also discloses an application of modified magnesium hydroxide, wherein the modified magnesium hydroxide is applied to a polyolefin and silane self-crosslinking cable material system.

[0018] The beneficial effects of this invention are: This invention employs a three-layer structure design for magnesium hydroxide particles: a core with rounded corners and passivated hexagonal plates, an inner layer of tetraethoxysilane chemical bonding, and an outer layer of stearic acid coating. This design creates multiple synergistic relationships between the various structural layers and the preparation process, simultaneously solving the long-standing technical problems of poor dispersibility, weak water resistance, and interference with the crosslinking reaction in inorganic flame-retardant fillers in polyolefins, especially silane self-crosslinking cable materials.

[0019] First, there is a synergistic relationship between the specific crystal form of the core and the inner layer of tetraethoxysilane. The hexagonal flake magnesium hydroxide (8-15 aspect ratio) with rounded corner passivation not only balances flame retardancy and oxygen barrier efficiency with processing fluidity, but more importantly, its suitable aspect ratio results in a moderate hydroxyl distribution density on the particle surface and a low tendency for layer stacking, providing an excellent bonding substrate for the uniform spreading and full cross-linking of tetraethoxysilane. The unique tetrafunctional structure of tetraethoxysilane allows it to be firmly anchored to the core surface via Si-O-Mg covalent bonds after hydrolysis, and also to form a continuous, dense three-dimensional network through intermolecular condensation. This synergistic effect of chemical bonding and intermolecular cross-linking ensures the long-term water resistance of the modified layer from the source, allowing the product to maintain a water absorption rate of less than 0.40% and an activation retention rate of no less than 96% after boiling in water at 95℃ for 12 hours. This completely solves the technical problem of easy detachment of the single stearic acid physical adsorption layer under boiling conditions.

[0020] Secondly, since the inner layer of tetraethoxysilane already provides a sufficiently dense water-resistant barrier and a basic hydrophobic surface, the outer layer only requires 0.3-0.7 parts of stearic acid (far lower than the conventional 1.0-2.0 parts) to form a structure similar to a monomolecular coating, achieving the target hydrophobic effect and polyolefin compatibility. This fundamentally avoids the poisoning effect of free stearic acid on the organotin catalyst in the silane self-crosslinking system, maintaining the cable material's gelation rate above 92% and volume resistivity ≥1×10⁻⁶. 14 Ω・cm. The inner and outer layers form a synergistic relationship, ensuring high activation, high water resistance, and high gelation rate.

[0021] Furthermore, the stepwise modification process and the formation of the ordered bilayer structure are inextricably linked. The stepwise process, which first completes the condensation bonding of the tetraethoxysilane inner layer at a high temperature of 118-122℃, followed by stearic acid coating at 108-112℃, ensures that each modified layer forms sequentially at its optimal temperature. This avoids competitive adsorption between silane and stearic acid, which would prevent the formation of a continuous, dense inner layer of silane and result in disordered stearic acid accumulation. The stepwise process and the three-layer ordered structure are beneficial for obtaining modified magnesium hydroxide with excellent overall performance. Moreover, in the inner layer tetraethoxysilane chemical bonding modification process, the tetraethoxysilane dispersion is first sprayed under warm conditions, followed by heating for the condensation reaction. This allows the reactants to be uniformly dispersed and pre-anchored under mild conditions before being concentrated and solidified at high temperatures. This effectively avoids problems such as boiling of the dispersion, uneven reaction, and particle adhesion caused by direct high-temperature treatment, ensuring a complete and dense inner layer coating. This provides a key structural basis for the high compatibility of subsequent outer stearic acid-like monomolecular coating and silane self-crosslinking system.

[0022] The modified magnesium hydroxide described in this invention can be applied to polyolefin cable material systems or silane self-crosslinking cable material systems. The specific three-layer structure of the modified magnesium hydroxide product ensures that the polyolefin composite material maintains a tensile strength ≥13.0 MPa, elongation at break ≥190%, and oxygen index ≥35% even under high-filling conditions. The extruded surface is smooth without particle protrusions, and the extrusion speed is high. In summary, this invention achieves a balance of multiple performance characteristics—high activation, excellent water resistance, superior dispersibility under high filling conditions, and good compatibility with silane self-crosslinking systems—through the synergistic combination of multiple technical features such as core crystal form, silane type selection, precise stearic acid dosage, and stepwise modification process. This solves the technical problem in existing technologies where dispersibility, water resistance, and crosslinking compatibility cannot be simultaneously achieved. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the modified magnesium hydroxide described in this invention; Figure 2 This is an electron microscope image of magnesium hydroxide after drying and passivation in Example 1; Figure 3 This is a schematic diagram illustrating the principle of stearic acid coating. Figure 4 This is a processing diagram of the modified magnesium hydroxide described in this invention applied to silane self-crosslinking polyolefin cable material; Figure 5 This is an appearance diagram of the modified magnesium hydroxide described in this invention applied to silane self-crosslinking polyolefin cable material. Detailed Implementation

[0024] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0026] A modified magnesium hydroxide, wherein the modified magnesium hydroxide comprises, from the inside out: a core, an inner layer, and an outer layer; as shown in the figure. Figure 1 As shown.

[0027] The core contains hexagonal sheet-like magnesium hydroxide (MH) with rounded and passivated corners. The inner layer is a tetraethoxysilane modified layer. Tetraethoxysilane (TES) is bonded to the core surface through Si-O-Mg covalent bonds. Tetraethoxysilane can achieve four-point cross-linking to construct a three-dimensional dense layer, making the inner layer structure more compact and providing long-lasting water resistance. Moreover, the combination of tetraethoxysilane and magnesium hydroxide allows magnesium hydroxide to form a network structure under the action of tetraethoxysilane, thereby giving the modified magnesium hydroxide a certain degree of micro-elasticity. When used in cable materials, it has better flowability and processing performance. The outer layer is a monomolecular coating layer formed from stearic acid (SA), covering only the surface of the inner layer without any free stearic acid residue. This improves hydrophobicity and compatibility with polyolefins, and avoids interference with the silane self-crosslinking catalytic system. Figure 3 As shown.

[0028] Specifically, the hexagonal flake magnesium hydroxide has an aspect ratio of 8-15; a particle size D50 of 1-4 μm; a purity ≥99.0%, a whiteness ≥96, a moisture content ≤0.15%, and a hexagonal angular radius of 70°-85°. Radial elliptical passivation treatment can reduce particle stacking.

[0029] Using hexagonal flakes of MH with an aspect ratio of 8-15 as the base material, the edges and corners are passivated to form a near-spherical shape, reducing friction and stacking between particles. This solves the problem of poor dispersion of powders with small aspect ratios and avoids the defect of poor flowability of powders with large aspect ratios. It takes into account flame retardancy, processing flowability and modification uniformity. After passivation treatment, the particles are formed into rounded hexagonal flakes. Combined with subsequent inner and outer layer modification, it is more conducive to obtaining modified magnesium hydroxide with excellent flowability, lubrication and waterproof properties.

[0030] Specifically, the thickness of the inner layer is 5-15 nm, and the thickness of the outer layer is 1-3 nm.

[0031] A method for preparing modified magnesium hydroxide, wherein the preparation method comprises: S1. Drying and passivation of raw powder: Hexagonal sheet-shaped magnesium hydroxide is heated and stirred to obtain dried and passivated magnesium hydroxide. S2, inner tetraethoxysilane chemical bonding modification: Under warm conditions, a tetraethoxysilane dispersion is uniformly sprayed onto the dried and passivated magnesium hydroxide surface, and then heated to carry out a condensation reaction to form Si-O-Mg covalent bonds and construct a three-dimensional network inner layer. S3, Outer Covering: The modified magnesium hydroxide in step S2 is uniformly mixed with stearic acid and heated and kept warm. After the stearic acid melts, it is uniformly adhered to the outer surface to form an outer layer. S4. Post-processing: The modified magnesium hydroxide is obtained by cooling and sieving.

[0032] Specifically, by weight, the amount of hexagonal flake magnesium hydroxide is 100 parts, the amount of tetraethoxysilane is 1.8-2.8 parts, and the amount of stearic acid is 0.3-0.7 parts.

[0033] Specifically, the drying and passivation of the raw powder in step S1 is as follows: Hexagonal flake-shaped magnesium hydroxide raw powder is placed in a high-speed mixer and kept at 115-120℃ and 70-80 r / min for 30-35 minutes to deeply remove adsorbed water (moisture content ≤0.15%). Simultaneously, the hexagonal edges are passivated at high temperature, forming a 70°-85° arc, resulting in dried and passivated magnesium hydroxide. This treatment method can reduce particle friction and stacking tendency, exposing surface hydroxyl groups (-OH), preparing for inner layer bonding.

[0034] Specifically, the preparation method of the tetraethoxysilane dispersion in step S2 is as follows: by weight, under light-protected conditions at room temperature (25±5℃), mix 1.8-2.8 parts of tetraethoxysilane with 7-10 parts of anhydrous ethanol, and stir at 180 r / min for 10-12 min; slowly add 0.4-0.6 parts of deionized water, and stir for 5-10 min to obtain a transparent, uniform, and slightly hydrolyzed tetraethoxysilane dispersion (Si-OH mass content controlled at 15%-20%). This preparation condition can avoid premature gelation and condensation as much as possible. The tetraethoxysilane dispersion is directly used in the modification process in step S2.

[0035] Specifically, step S2 involves the following steps: After drying and passivating, the magnesium hydroxide is stirred at a speed of 70-80 r / min at a temperature of 88-92℃. The tetraethoxysilane dispersion is uniformly sprayed into the MH powder using an atomization spray method (spray pressure of 0.2 MPa and spray time of 12-15 min) to ensure uniform contact between the surface of each magnesium hydroxide particle and the tetraethoxysilane. After spraying, the temperature is raised to 118-122℃ and held for 40-45 min to promote the condensation reaction between the TES hydrolysis product (Si-OH) and the hydroxyl group (Mg-OH) on the MH surface, forming stable Si-O-Mg covalent bonds and constructing a dense three-dimensional network inner layer to prevent moisture intrusion.

[0036] Specifically, step S3 is as follows: after the inner layer modification is completed, the system is cooled to 108-112℃ and stirred at a speed of 60-70 r / min. Powdered stearic acid is added and stirred for 20-25 min. After the stearic acid melts, it is uniformly adsorbed onto the surface of the TES inner layer through van der Waals forces to form a hydrophobic layer similar to a single molecule. There are no multilayer stacking and free residues, which takes into account both hydrophobicity and compatibility with the crosslinking system.

[0037] Specifically, step S4 is as follows: after the double-layer modification is completed, stop heating, stir at 50 r / min to cool down to 65°C; discharge the material through a 1500 mesh vibrating screen to remove trace agglomerated particles and obtain a highly dispersed, water-resistant double-layer modified magnesium hydroxide product.

[0038] An application of modified magnesium hydroxide, wherein the modified magnesium hydroxide is applied to a polyolefin cable material system or a silane self-crosslinking cable material system.

[0039] I. Preparation Example: Preparation of Modified Magnesium Hydroxide.

[0040] Example 1: Preparation of modified magnesium hydroxide.

[0041] The raw materials used, by weight, are: 100 parts hexagonal flake magnesium hydroxide, 2.8 parts tetraethoxysilane, 0.7 parts stearic acid, 10 parts anhydrous ethanol, and 0.6 parts deionized water.

[0042] The measured center values ​​of the hexagonal sheet magnesium hydroxide used in this embodiment are: aspect ratio 12; D50 = 2.5 μm.

[0043] The specific preparation method of modified magnesium hydroxide is as follows: (1) Drying and passivation of raw powder: Hexagonal flake magnesium hydroxide raw powder is put into a high-speed mixer and kept at 118℃ and 75r / min for 32min to remove adsorbed water (moisture content ≤0.15%), so as to obtain dried and passivated magnesium hydroxide, as shown in the figure. Figure 2 As shown.

[0044] (2) Preparation of tetraethoxysilane dispersion: Under normal temperature and light protection conditions, 2.8 parts of tetraethoxysilane and 10 parts of anhydrous ethanol were mixed and stirred for 12 min at 180 r / min; 0.6 parts of deionized water were slowly added dropwise and stirred for 8 min to obtain a transparent, uniform, slightly hydrolyzed tetraethoxysilane dispersion.

[0045] (3) Chemical bonding modification of inner layer tetraethoxysilane: After drying and passivating, magnesium hydroxide is cooled to 90°C and stirred at a speed of 70 r / min. The tetraethoxysilane dispersion is sprayed evenly into MH powder by atomization spraying (spraying for 13 min) to ensure that the surface of each magnesium hydroxide particle is uniformly in contact with tetraethoxysilane. After spraying, the temperature is raised to 120°C and kept at that temperature for 42 min to promote the condensation reaction between TES hydrolysis products (Si-OH) and MH surface hydroxyl groups (Mg-OH) to form stable Si-O-Mg covalent bonds and construct a dense three-dimensional network inner layer.

[0046] (4) Outer layer coating: After the inner layer modification is completed, the system is cooled to 110°C and the stirring speed is 70 r / min. Powdered stearic acid is added and kept warm and stirred for 22 min. After the stearic acid melts, it is uniformly adsorbed onto the inner surface of TES through van der Waals forces to form the outer layer.

[0047] (5) Post-processing and refining: After the double-layer modification is completed, stop heating and stir at 50 r / min to cool down to 65°C; discharge through a 1500 mesh vibrating screen to remove trace agglomerated particles and obtain a highly dispersed water-resistant double-layer modified magnesium hydroxide product.

[0048] Example 2: Preparation of modified magnesium hydroxide.

[0049] The raw materials used, by weight, are: 100 parts hexagonal flake magnesium hydroxide, 2.8 parts tetraethoxysilane, 0.7 parts stearic acid, 10 parts anhydrous ethanol, and 0.6 parts deionized water.

[0050] The measured center values ​​of the hexagonal sheet magnesium hydroxide used in this embodiment are: aspect ratio 15; D50 = 4 μm.

[0051] The specific preparation method of modified magnesium hydroxide is as follows: (1) Drying and passivation of raw powder: Hexagonal flake magnesium hydroxide raw powder is put into a high-speed mixer and kept at 120℃ and 70r / min for 35min to remove adsorbed water (moisture content ≤0.15%), and magnesium hydroxide is obtained after drying and passivation.

[0052] (2) Preparation of tetraethoxysilane dispersion: Under normal temperature and light protection conditions, 2.8 parts of tetraethoxysilane and 10 parts of anhydrous ethanol were mixed and stirred for 10 min at 180 r / min; 0.6 parts of deionized water were slowly added dropwise and stirred for 10 min to obtain a transparent, uniform, slightly hydrolyzed tetraethoxysilane dispersion.

[0053] (3) Chemical bonding modification of inner layer tetraethoxysilane: After drying and passivating, magnesium hydroxide is cooled to 92°C and stirred at a speed of 80 r / min. The tetraethoxysilane dispersion is sprayed evenly into MH powder by atomization spraying (spraying for 15 min) to ensure that the surface of each magnesium hydroxide particle is uniformly in contact with tetraethoxysilane. After spraying, the temperature is raised to 122°C and kept at that temperature for 45 min to promote the condensation reaction between TES hydrolysis products (Si-OH) and MH surface hydroxyl groups (Mg-OH) to form stable Si-O-Mg covalent bonds and construct a dense three-dimensional network inner layer.

[0054] (4) Outer layer coating: After the inner layer modification is completed, the system is cooled to 112℃ and the stirring speed is 60r / min. Powdered stearic acid is added and kept warm and stirred for 25min. After the stearic acid melts, it is uniformly adsorbed onto the inner surface of TES through van der Waals forces to form the outer layer.

[0055] (5) Post-processing and refining: After the double-layer modification is completed, stop heating and stir at 50 r / min to cool down to 65°C; discharge through a 1500 mesh vibrating screen to remove trace agglomerated particles and obtain a highly dispersed water-resistant double-layer modified magnesium hydroxide product.

[0056] Example 3: Preparation of modified magnesium hydroxide.

[0057] The raw materials used, by weight, are: 100 parts hexagonal flake magnesium hydroxide, 1.8 parts tetraethoxysilane, 0.3 parts stearic acid, 7 parts anhydrous ethanol, and 0.4 parts deionized water.

[0058] The measured center values ​​of the hexagonal sheet magnesium hydroxide used in this embodiment are: aspect ratio 8; D50 = 1 μm.

[0059] The specific preparation method of modified magnesium hydroxide is as follows: (1) Drying and passivation of raw powder: Hexagonal flake magnesium hydroxide raw powder is put into a high-speed mixer and kept at 115℃ and 80r / min for 30min to remove adsorbed water (moisture content ≤0.15%), and magnesium hydroxide is dried and passivated.

[0060] (2) Preparation of tetraethoxysilane dispersion: Under normal temperature and light protection conditions, 1.8 parts of tetraethoxysilane and 7 parts of anhydrous ethanol were mixed and stirred for 12 min at 180 r / min; 0.3 parts of deionized water were slowly added dropwise and stirred for 5 min to obtain a transparent, uniform, slightly hydrolyzed tetraethoxysilane dispersion.

[0061] (3) Chemical bonding modification of inner layer tetraethoxysilane: After drying and passivating, magnesium hydroxide is cooled to 88°C and stirred at a speed of 70 r / min. The tetraethoxysilane dispersion is sprayed evenly into MH powder by atomization spraying (spraying for 12 min) to ensure that the surface of each magnesium hydroxide particle is uniformly in contact with tetraethoxysilane. After spraying, the temperature is raised to 118°C and kept at that temperature for 40 min to promote the condensation reaction between TES hydrolysis products (Si-OH) and MH surface hydroxyl groups (Mg-OH) to form stable Si-O-Mg covalent bonds and construct a dense three-dimensional network inner layer.

[0062] (4) Outer layer coating: After the inner layer modification is completed, the system is cooled to 108℃ and the stirring speed is 60r / min. Powdered stearic acid is added and kept warm and stirred for 20min. After the stearic acid melts, it is uniformly adsorbed onto the inner surface of TES through van der Waals forces to form the outer layer.

[0063] (5) Post-processing and refining: After the double-layer modification is completed, stop heating and stir at 50 r / min to cool down to 65°C; discharge through a 1500 mesh vibrating screen to remove trace agglomerated particles and obtain a highly dispersed water-resistant double-layer modified magnesium hydroxide product.

[0064] Comparative Example 1: Preparation of modified magnesium hydroxide.

[0065] Modified magnesium hydroxide was prepared using the same raw materials and methods as in Example 1. The difference was that the outer coating operation in step (4) was not performed in Comparative Example 1, that is, only tetraethoxysilane modification was performed, and stearic acid coating modification was not performed. Other process conditions were the same as in Example 1.

[0066] Comparative Example 2: Preparation of modified magnesium hydroxide.

[0067] Modified magnesium hydroxide was prepared using the same raw materials and methods as in Example 1. The difference was that the outer coating operation in step (3) was not performed in Comparative Example 2, that is, only stearic acid coating modification was performed, and tetraethoxysilane modification was not performed. Other process conditions were the same as in Example 1.

[0068] Comparative Example 3: Preparation of modified magnesium hydroxide.

[0069] Modified magnesium hydroxide was prepared using the same method as in Example 1. The difference was that the aspect ratio of the measured center value of the hexagonal flake magnesium hydroxide used in Comparative Example 3 was 6 (lower than the aspect ratio specified in this invention). Other process conditions were the same as in Example 1.

[0070] Comparative Example 4: Preparation of modified magnesium hydroxide.

[0071] Modified magnesium hydroxide was prepared using the same raw materials and methods as in Example 1. The difference lies in that in Comparative Example 4, the tetraethoxysilane modification and stearic acid coating modification were performed simultaneously, without separate steps. The specific preparation process is as follows: (1) Drying and passivation of raw powder: Same as in Example 1.

[0072] (2) Preparation of tetraethoxysilane dispersion: Same as in Example 1.

[0073] (3) One-step modification treatment: After drying and passivating, magnesium hydroxide is cooled to 90°C and stirred at a speed of 70 r / min. Tetraethoxysilane dispersion is mixed with stearic acid and added to magnesium hydroxide. The temperature is raised to 120°C and kept at 42 min to carry out the modification treatment of magnesium hydroxide.

[0074] (4) Post-processing and refining: After the modification is completed, stop heating, stir at 50 r / min to cool down to 65°C; discharge through a 1500 mesh vibrating screen to obtain the modified magnesium hydroxide product.

[0075] Comparative Example 5: Preparation of modified magnesium hydroxide.

[0076] Modified magnesium hydroxide was prepared using the same raw materials and methods as in Example 1. The difference was that no passivation treatment was performed on the magnesium hydroxide in Comparative Example 5; instead, the hexagonal flake magnesium hydroxide powder was dried at 118°C for 32 minutes. That is, the hexagonal flake magnesium hydroxide was not subjected to hexagonal edge rounding treatment. Other process conditions were the same as in Example 1.

[0077] Comparative Example 6: Preparation of modified magnesium hydroxide.

[0078] Modified magnesium hydroxide was prepared using the same raw materials and methods as in Example 1. The difference was that in step (1) of Comparative Example 6, the stirring speed was 120 r / min (i.e., the stirring speed was higher than the stirring speed specified in this invention), and other process conditions were the same as in Example 1.

[0079] Comparative Example 7: Preparation of modified magnesium hydroxide.

[0080] Modified magnesium hydroxide was prepared using the same raw materials and methods as in Example 1. The difference was that the tetraethoxysilane in Comparative Example 7 was replaced with triethoxysilane, while the other process conditions were the same as in Example 1.

[0081] Comparative Example 8: Preparation of modified magnesium hydroxide.

[0082] Modified magnesium hydroxide was prepared using the same raw materials and methods as in Example 1. The difference was that the tetraethoxysilane in Comparative Example 8 was replaced with KH550, while the other process conditions were the same as in Example 1.

[0083] Comparative Example 9: Preparation of modified magnesium hydroxide.

[0084] Modified magnesium hydroxide was prepared using the same raw materials and methods as in Example 1. The difference was that the amount of stearic acid added in Comparative Example 9 was 1.5 parts by weight (i.e., the amount of stearic acid added was increased), while other process conditions were the same as in Example 1.

[0085] Comparative Example 10: Preparation of modified magnesium hydroxide.

[0086] Modified magnesium hydroxide was prepared using the same raw materials and methods as in Example 1. The difference was that in step (3) of Comparative Example 10, the dried and passivated magnesium hydroxide was cooled to room temperature (below the temperature specified in this invention), stirred at a speed of 70 r / min, and the tetraethoxysilane dispersion was uniformly sprayed into the MH powder using an atomizing spray method. After spraying, the temperature was raised to 120°C and held for 42 min. Other process conditions were the same as in Example 1.

[0087] Comparative Example 11: Preparation of modified magnesium hydroxide.

[0088] Modified magnesium hydroxide was prepared using the same raw materials and methods as in Example 1. The difference was that in step (3) of Comparative Example 11, the dried and passivated magnesium hydroxide was kept at a temperature of 118°C (higher than the temperature specified in this invention), stirred at a speed of 70 r / min, and the tetraethoxysilane dispersion was uniformly sprayed into the MH powder using an atomizing spray method. After spraying, the temperature was raised to 120°C and held for 42 min. Other process conditions were the same as in Example 1.

[0089] II. Performance Testing: Performance testing of modified magnesium hydroxide and application performance testing of cable materials.

[0090] The modified magnesium hydroxide prepared in the above examples and comparative examples was subjected to performance tests, and the test methods involved are as follows.

[0091] 1. Performance testing of modified magnesium hydroxide powder: (1) The activation degree of hydrophobic modified powder was tested according to GB / T 19281-2014 Calcium carbonate activation degree test method: Accurately weigh 5.0000g of dried sample (modified magnesium hydroxide) and place it in a separatory funnel containing 200mL of deionized water. Shake for 3min and let stand for 30min. Separate the settled solid, dry and weigh. Calculate the activation degree by the ratio of the mass of floating powder to the total mass of the feed (after the powder is added to the water, the modified powder will float on the water surface, and the unmodified powder will absorb water and settle. The powder floating on the water surface is the floating powder).

[0092] (2) Water absorption rate test after boiling: The water absorption rate of modified magnesium hydroxide powder was determined according to GB / T35166-2017 and ASTM D570 standards. The modified magnesium hydroxide powder was dried at 105℃ to constant weight to obtain its oven-dry weight. M Weighing 0 and 200 mesh dry filter paper M 滤 The powder was immersed in deionized water at 95±1℃ for 12 hours in a sealed container. After immersion, the free water between the powder particles was removed by vacuum filtration using 200-mesh filter paper. The filter cake and filter paper were weighed immediately. M 1; .

[0093] (3) Activation retention rate test after boiling in water (water resistance index matching method): Take the modified magnesium hydroxide product, boil it in water at 95℃ for 12 hours, filter it, and dry it thoroughly at 105℃; then retest the activation degree according to the above national standard GB / T 19281-2014; activation retention rate = (activation degree after boiling / initial activation degree) × 100%.

[0094] 2. Performance testing of modified magnesium hydroxide applied to cable materials: Application system of modified magnesium hydroxide: silane self-crosslinking low smoke halogen-free flame retardant cable material.

[0095] The formulation of the application system, by weight, is as follows: 100 parts of PE / EVA matrix (PE is ExxonMobil's 3518CB, EVA is Yangzi Petrochemical's V6110M, PE:EVA=2:5), 150 parts of modified magnesium hydroxide, 0.3 parts of antioxidant 1010, 0.1 parts of antioxidant 168, 2 parts of vinylsilane, 0.05 parts of organotin catalyst, 0.8 parts of PE wax, and 0.8 parts of silicone masterbatch.

[0096] The specific preparation process of cable material is as follows: Premixing: The PE / EVA matrix, vinyl silane, organotin catalyst, antioxidant 1010, and antioxidant 168 from the above materials are fed into a mixer and mixed at 170°C for 20 minutes. After mixing, the materials are poured into a twin-screw extruder and the extruder temperature is set to 180°C to achieve silane grafting and granulation to obtain grafted granules.

[0097] Further blending, filling, and extrusion: Modified magnesium hydroxide and lubricant are added to the above grafted granules, and the mixture is uniformly blended and granulated according to the premixing process parameters to obtain cable material granules.

[0098] Crosslinking: The cable material and copper core were compositely extruded and formed, with a cable sheath thickness of 1 mm. The extrusion length and corresponding extrusion time were recorded. After forming, the mixture was boiled in 95°C water for 12 hours to complete crosslinking. The appearance of the modified magnesium hydroxide described in this invention applied to silane self-crosslinking polyolefin cable material is shown in the figure below. Figure 4 , Figure 5 As shown.

[0099] The cable material was subjected to performance testing. (1) Formula for calculating the outgoing speed: Outgoing length / Outgoing time.

[0100] (2) Peel off the cross-linked cable sheath, cut standard strips according to GB / T 1040.3-2006, and conduct tensile performance tests according to the test conditions specified in GB / T32129-2015.

[0101] Specifically, GB / T32129-2015 specifies low-smoke halogen-free flame-retardant cable materials for wires and cables.

[0102] GB / T 1040.3-2006 Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets.

[0103] (3) The cable material granules that have been blended, filled and extruded are placed on a flat vulcanizing machine (temperature 180℃, pressure 16MPa) and hot-pressed into 3mm samples. According to GB / T2406.2-2009, they are cut into standard strips by a pneumatic punching machine and tested for oxygen index according to GB / T2406.2-2009 (determination of combustion behavior of plastics by oxygen index method).

[0104] (4) The gel rate was tested according to Appendix A of JB / T 10437-2024 and the xylene extraction method of GB / T18474-2001. After the material was mixed and compressed into tablets, it was boiled in water at 95℃ for 12h to complete the silane self-crosslinking. The sample was chopped and refluxed in boiling xylene Soxhlet for 6h. The insoluble matter was dried, weighed, and the gel rate was calculated.

[0105] (5) Volume resistivity was tested according to the three-electrode method of GB / T1410-2006; the silane cross-linked sample was boiled in water at 95℃ for 12h, conditioned in an environment of 23℃ and RH50% for 24h, and the volume resistivity was obtained by using a 500V DC voltage and stabilizing the voltage for 60s.

[0106] The specific test results are shown in Tables 1 and 2 below.

[0107] Table 1. Performance test results of modified magnesium hydroxide powder

[0108] Table 2 Performance test results of modified magnesium hydroxide applied to cable materials

[0109] The data above show that the double-layer modified magnesium hydroxide prepared by the method described in this invention has high dispersibility and water resistance. Relying on an 8-15 aspect ratio hexagonal flake magnesium hydroxide substrate combined with a tetraethoxysilane inner layer chemically bonded and a trace amount of stearic acid outer layer similar to monomolecular coating, the product has an activation degree ≥99.0%. After boiling in water at 95℃ for 12 hours, the powder water absorption rate is controlled within 0.40%, and the activation retention rate is ≥96%. Under high-filling conditions in the polyolefin system for cable materials, there is no significant agglomeration. It maintains excellent flame retardancy, mechanical properties, and electrical insulation properties. The samples in each embodiment significantly improve processing fluidity, effectively reduce water absorption after boiling, and do not interfere with the silane self-crosslinking reaction. The modified magnesium hydroxide described in this invention, when applied to polyolefin and silane self-crosslinking cable materials, can achieve high filling rates, with cable tensile strength ≥13.0 MPa, elongation at break ≥190%, oxygen index ≥35%, and a smooth extruded surface without particle protrusions. Furthermore, the silane self-crosslinking cable material exhibits a gel rate ≥92% and a volume resistivity ≥1×10⁻⁶ after water boiling crosslinking. 14 Ω・cm. Furthermore, the experimental results from Examples 1-3 show that, within the range of raw material ratios and process parameters defined in this invention, as the addition amounts of tetraethoxysilane and stearic acid increase slightly within the preferred range, the integrity of the magnesium hydroxide coating gradually improves, and the water resistance and dispersion stability in polyolefins are simultaneously optimized. The changes in various product performance indicators are gradual and controllable, the process window is wide, and it facilitates stable industrial-scale production.

[0110] The comparison of the experimental results of Comparative Example 1 and Example 1 shows that when only tetraethoxysilane monolayer modification is used and no trace amount of stearic acid is added to the outer layer, the activation degree of magnesium hydroxide powder decreases significantly, the compatibility with the polyolefin interface deteriorates, the extruded surface of the composite material is rough, and the mechanical properties are low. This proves that the outer layer of a small amount of stearic acid coating is an essential key structure for improving powder dispersibility and enhancing resin compatibility.

[0111] The comparison of the experimental results of Comparative Example 2 and Example 1 shows that: only stearic acid modification is used, which lacks the inner tetraethoxysilane dense shielding layer. The modification relies on physical adsorption and bonding. After boiling in water at high temperature, a large amount of the coating layer falls off, the water resistance deteriorates sharply, and the gelation rate of the silane self-crosslinking system is also greatly reduced.

[0112] A comparison of the experimental results from Comparative Example 3 and Example 1 shows that magnesium hydroxide raw powder with an aspect ratio deviating from the 8-15 range, even with the double-layer modification process of this invention, still exhibits significantly reduced flame retardant efficiency and processing fluidity. A reduced aspect ratio leads to incomplete silane modification and coating. A smaller aspect ratio in hexagonal flake magnesium hydroxide means the particles tend to be thicker, with increased surface curvature and more sharp edges. This reduces the uniformity of the tetraethoxysilane hydrolysate spread on the particle surface. Concave areas are difficult to effectively cover due to steric hindrance and limited wetting, and particles are more prone to forming close face-to-face stacking. The surface active sites in the stacking gaps cannot be fully exposed to the modifier, resulting in insufficient chemical bonding. The final modified layer is discontinuous, with localized exposure or uneven coating thickness, failing to construct a complete water-resistant barrier. Furthermore, the incompletely modified silane particles retain a large number of unreacted hydrophilic hydroxyl groups on their surface. In polyolefin high-filling systems, this exacerbates agglomeration due to hydrogen bonding between hydroxyl groups, further weakening dispersibility and processing fluidity. Therefore, controlling the aspect ratio of magnesium hydroxide within the range of 8-15 is more conducive to forming a synergistic relationship with subsequent tetraethoxysilane modification, resulting in modified magnesium hydroxide with excellent comprehensive performance.

[0113] The comparison of the experimental results of Comparative Example 4 and Example 1 shows that the modification method of simultaneous addition of tetraethoxysilane and stearic acid in one step cannot form an ordered bilayer coating structure. The two modifiers compete with each other to adsorb the active sites on the magnesium hydroxide surface. Silane is difficult to form a continuous and dense cross-linked inner layer, and stearic acid is randomly piled up. In the end, the water absorption rate of the product increases, the activation degree decreases, and the dispersion and water resistance properties deteriorate simultaneously. This verifies that step-by-step modification is a necessary process condition for constructing an ordered bilayer structure and achieving synergistic performance improvement.

[0114] A comparison of the experimental results from Comparative Example 5 and Example 1 shows that without passivation treatment of magnesium hydroxide, the sharp edges of the hexagonal flake magnesium hydroxide were not rounded, significantly increasing the friction coefficient and stacking tendency between particles. These sharp edges not only exacerbate the mechanical interlocking between particles, leading to increased powder bulk density and decreased flowability, but also cause uneven spreading of the modifier in the corner areas and difficulty in achieving complete coating coverage during subsequent tetraethoxysilane spraying. Passivation treatment creates a 70°-85° rounded arc surface on the hexagonal flake particles, reducing inter-particle frictional resistance and providing a smooth surface with moderate curvature for the uniform spreading of tetraethoxysilane hydrolysate. The unpassivated particle surface has numerous sharp edges, resulting in disordered surface hydroxyl orientation and uneven reactivity in these areas. This prevents tetraethoxysilane from forming a uniform, continuous inner layer on the surface of a single particle, and the outer stearic acid layer also struggles to achieve a monolayer-like ordered arrangement on the rough inner layer surface, ultimately reducing the effectiveness of modified magnesium hydroxide in cables.

[0115] A comparison of the experimental results of Comparative Example 6 and Example 1 shows that if the stirring speed is too fast in step (1), the regular hexagonal lamellar structure of the hexagonal magnesium hydroxide is destroyed, and the particles tend to become irregular round or broken. The particle diameter-to-thickness ratio distribution becomes wider, the surface hydroxyl density becomes uneven, the originally flat bonded substrate becomes rough and irregular, the spreading uniformity of silane hydrolysate decreases, the chemical bonding density decreases, and the inner layer density is damaged. At the same time, the large number of newly formed edges and fine powders generated by the broken particles make the powder packing more compact and the processing flowability worsens. Therefore, even if the subsequent TES modification and stearic acid coating processes are exactly the same, excessively high stirring speed will still cause the product's activation, water resistance and dispersibility in polyolefins to decrease across the board. A comparison of the experimental results of Comparative Example 7 and Example 1 shows that if tetraethoxysilane is replaced with triethoxysilane, although triethoxysilane can still chemically bond with the hydroxyl groups on the surface of magnesium hydroxide through Si-O-Mg bonds, it only has three hydrolyzable groups. The number of silanol groups formed after hydrolysis is less than that of tetraethoxysilane, and the degree of intermolecular condensation crosslinking is significantly reduced. It is impossible to construct a continuous and dense three-dimensional SiO2 network structure on the particle surface. Only a sparsely grafted dot-like coating layer can be formed. Therefore, the dual role of tetraethoxysilane, which is both "anchored to Mg-OH and crosslinked intermolecularly", does not exist. The tetrafunctional structure of tetraethoxysilane allows a single silane molecule to form chemical bonds with multiple Mg-OH groups simultaneously, and also to condense with adjacent silane molecules to form Si-O-Si crosslinks. This integrated "bonding-crosslinking" mechanism is the chemical basis for constructing a dense, water-resistant inner layer. Triethoxysilane, on the other hand, lacks one hydrolyzable group, resulting in a significantly weakened intermolecular crosslinking ability. The sparse grafted layer formed has a large number of micropores, allowing water to easily penetrate through the gaps between silane molecules. This leads to a significant increase in water absorption and a substantial decrease in activation retention rate after boiling.

[0116] A comparison of the experimental results of Comparative Example 8 and Example 1 shows that if tetraethoxysilane is replaced with KH550, the amino organic side chains in the KH550 molecule not only exhibit a significant steric hindrance effect, hindering the approach and condensation reaction between silane molecules, thus preventing the formation of a continuous and dense cross-linked layer, but more importantly, the amino groups in KH550 are alkaline, which may cause complexation or acid-base reactions with the organotin catalyst in the silane self-crosslinking system, leading to a decrease in catalyst activity and consequently a significant decrease in the gelation rate of the cable material. The organic side chains of KH550 are structurally fundamentally different from the inorganic SiO2 network formed after the hydrolysis of tetraethoxysilane, and both their hydrophobicity and compatibility with polyolefins decrease.

[0117] A comparison of the experimental results of Comparative Example 9 and Example 1 shows that while increasing the amount of stearic acid can improve the apparent activation and initial hydrophobicity of the powder to some extent, it also results in a disordered accumulation of multiple or multi-molecular layers on the magnesium hydroxide surface, failing to form an ordered structure similar to a monolayer. In this invention, the tetraethoxysilane inner layer provides a sufficiently dense water-resistant barrier and a basic hydrophobic surface through chemical bonding. Only 0.3-0.7 parts of stearic acid are needed to form a uniform monolayer-like coating layer on the TES inner layer surface. When the amount of stearic acid is significantly increased, the excess stearic acid molecules not only destroy the ordered thin structure similar to a monolayer but also form physically adsorbed free stearic acid. These free molecules easily migrate to the matrix resin during subsequent blending with polyolefins and water boiling crosslinking, adsorbing and poisoning the organotin catalyst required for silane self-crosslinking, leading to incomplete crosslinking reaction and a significant decrease in gel rate. Meanwhile, excessive stearic acid forms a thick and uneven organic layer on the particle surface, which hinders the uniform dispersion of particles in the matrix, causing the mechanical properties of the composite material to decrease and pits or bubbles to appear on the extruded surface.

[0118] A comparison of the experimental results from Comparative Example 10 and Example 1 shows that if the initial temperature (room temperature) is low during the tetraethoxysilane modification process, ethanol evaporates very slowly at room temperature. A large amount of ethanol in the dispersion forms capillary "liquid bridges" between particles, causing adjacent magnesium hydroxide particles to hard agglomerate due to liquid bridge forces during subsequent heating, thus disrupting the single-particle dispersion. Simultaneously, the reactivity of TES hydrolysate with the hydroxyl groups on the magnesium hydroxide surface is low at room temperature, making it difficult for Si-OH to effectively anchor at Mg-OH sites. A large amount of TES hydrolysate is lost or agglomerates before it can fully contact the particle surface, resulting in a significant reduction in chemical bond density. This prevents the synergistic advantage of tetraethoxysilane's dual "anchoring-crosslinking" function and its smooth, sheet-like surface from being fully utilized. When the temperature is subsequently raised to 120°C, although the condensation reaction can proceed, the failure to achieve uniform spreading and pre-anchoring on the single-particle surface in the early stages results in an incomplete inner layer coating with uneven thickness, significantly deteriorating water resistance and also disrupting the structural basis for the uniform adhesion of the outer stearic acid layer. In the preparation method of this invention, the operation mode of first applying warm spray and then high-temperature condensation is conducive to the rapid volatilization of ethanol and the uniform spreading of TES hydrolysate, and is also conducive to the subsequent high-temperature condensation and the construction of an ordered bilayer structure.

[0119] A comparison of the experimental results from Comparative Example 11 and Example 1 shows that if the initial temperature is high during the tetraethoxysilane modification process, the ethanol immediately boils violently upon contact with the high-temperature magnesium hydroxide powder, carrying TES hydrolysates that splash violently. This results in extremely uneven distribution of the dispersion within the powder, disrupting the uniform contact between TES and the hexagonal, flat surface. Simultaneously, the localized high temperature causes intense intermolecular self-condensation of the TES hydrolysates before they are evenly spread across the particle surface, generating free SiO2 particles instead of an anchored coating layer. This wastes the modifier and results in over-coating of some particle surfaces while completely exposing others, thoroughly destroying the continuous density of the inner layer. This uneven inner layer further prevents the outer stearic acid layer from achieving a monolayer-like orderly adhesion, ultimately leading to an incomplete bilayer modified structure with decreased activation, water resistance, and dispersibility in polyolefins. In the technical solution of this invention, during the chemical bonding modification process of tetraethoxysilane, a tetraethoxysilane dispersion is first sprayed under warm conditions, and then heated to carry out a condensation reaction. That is, it is first uniformly dispersed and anchored, and then concentrated cross-linked and cured. This method is conducive to the uniform spreading of tetraethoxysilane hydrolysate on the surface of magnesium hydroxide, and also conducive to the construction of a complete and orderly double-layer modified structure, resulting in modified magnesium hydroxide with excellent application performance.

[0120] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0121] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing modified magnesium hydroxide, characterized in that, The preparation method is as follows: S1. Drying and passivation of raw powder: Hexagonal flake magnesium hydroxide is heated and stirred to obtain dried and passivated magnesium hydroxide; the aspect ratio of the hexagonal flake magnesium hydroxide is 8-15; the radius of curvature of the hexagonal edges of the passivated magnesium hydroxide is 70°-85°; S2, inner tetraethoxysilane chemical bonding modification: After drying and passivation, magnesium hydroxide is stirred at 70-80 r / min at a temperature of 88-92℃. Tetraethoxysilane dispersion is then sprayed in evenly to ensure uniform contact between the tetraethoxysilane and magnesium hydroxide. After spraying, the temperature is raised to 118-122℃ and held for 40-45 min to carry out a condensation reaction, forming Si-O-Mg covalent bonds and constructing a three-dimensional network inner layer. S3, Outer Covering: The modified magnesium hydroxide in step S2 is uniformly mixed with stearic acid and heated and kept warm. After the stearic acid melts, it is uniformly adhered to the outer surface to form an outer layer. S4. Post-processing: The modified magnesium hydroxide is obtained by cooling and sieving the material. The amount of hexagonal flake magnesium hydroxide is 100 parts by weight, the amount of tetraethoxysilane is 1.8-2.8 parts, and the amount of stearic acid is 0.3-0.7 parts.

2. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The particle size D50 of the hexagonal flake magnesium hydroxide is 1-4 μm.

3. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The thickness of the inner layer is 5-15 nm, and the thickness of the outer layer is 1-3 nm.

4. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The specific operation of drying and passivating the raw powder in step S1 is as follows: put the hexagonal flake magnesium hydroxide raw powder into a high-speed mixer, and keep it at a temperature of 115-120℃ and a rotation speed of 70-80r / min for 30-35min to obtain dried and passivated magnesium hydroxide.

5. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The preparation method of the tetraethoxysilane dispersion in step S2 is as follows: according to the weight parts, under the conditions of room temperature and protection from light, mix 1.8-2.8 parts of tetraethoxysilane with 7-10 parts of anhydrous ethanol evenly; slowly add 0.4-0.6 parts of deionized water, stir for 5-10 minutes to obtain the tetraethoxysilane dispersion, which can be directly used in the modification process in step S2.

6. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The specific operation of step S3 is as follows: under the conditions of temperature of 108-112℃ and stirring speed of 60-70r / min, add powdered stearic acid, keep warm and stir for 20-25min, and after the stearic acid melts, it is uniformly attached to the outer surface to form an outer layer.

7. An application of the modified magnesium hydroxide prepared by the method according to any one of claims 1-6, characterized in that, The modified magnesium hydroxide is applied to polyolefin and silane self-crosslinking cable material systems.

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