阅读说明：本技术 一种氢氧化镁的生产工艺 (Production process of magnesium hydroxide ) 是由 蔚永福 汤明松 张鹏 于 2021-02-26 设计创作，主要内容包括：本发明公开了一种氢氧化镁的生产工艺,包括：将纯化后的氯化镁溶液加入反应器中,然后加入晶型控制剂,超声；得到混合物料；将乙醇雾化物通过载气通入反应器的混合物料中；在搅拌条件下,向反应器的混合物料中持续通入氨气,直至沉淀稳定,停止通入氨气,过滤,洗涤,得到氢氧化镁；将氢氧化镁加入到球磨罐中,同时加入硬脂酸和不锈钢磨球,向球磨罐中通入液氮,将氢氧化镁、硬脂酸和不锈钢磨球全部浸没在液氮中,球磨,将球磨后的物料加热保温；将加热保温后的物料再次加入到球磨罐中,向球磨罐中通入液氮,将物料全部浸没在液氮中,球磨,得到改性氢氧化镁。本发明制备了高纯度的氢氧化镁,本发明的生产工艺简单、操作方便。(The invention discloses a production process of magnesium hydroxide, which comprises the following steps: adding the purified magnesium chloride solution into a reactor, then adding a crystal form control agent, and carrying out ultrasonic treatment; obtaining a mixed material; introducing the ethanol atomized substance into the mixed material in the reactor through carrier gas; under the condition of stirring, continuously introducing ammonia gas into the mixed material in the reactor until the precipitate is stable, stopping introducing the ammonia gas, filtering and washing to obtain magnesium hydroxide; adding magnesium hydroxide into a ball milling tank, simultaneously adding stearic acid and stainless steel grinding balls, introducing liquid nitrogen into the ball milling tank, completely immersing the magnesium hydroxide, the stearic acid and the stainless steel grinding balls in the liquid nitrogen, performing ball milling, and heating and insulating the ball-milled materials; and adding the heated and heat-preserved material into the ball milling tank again, introducing liquid nitrogen into the ball milling tank, completely immersing the material in the liquid nitrogen, and performing ball milling to obtain the modified magnesium hydroxide. The invention prepares high-purity magnesium hydroxide, and the production process is simple and convenient to operate.)

1. The production process of the magnesium hydroxide is characterized by comprising the following steps:

adding magnesium chloride into water, preparing a magnesium chloride solution, purifying the magnesium chloride solution, adding the purified magnesium chloride solution into a reactor, adding a crystal form control agent, and performing ultrasonic treatment; obtaining a mixed material;

step two, placing the ethanol aqueous solution in an ultrasonic atomizer for ultrasonic atomization to obtain ethanol atomized matter, and introducing the ethanol atomized matter into the mixed material in the reactor through carrier gas;

continuously introducing ammonia gas into the mixed material in the reactor under the stirring condition until the precipitate is stable, stopping introducing the ammonia gas, filtering and washing to obtain magnesium hydroxide;

adding magnesium hydroxide into a ball milling tank, simultaneously adding stearic acid and stainless steel grinding balls, introducing liquid nitrogen into the ball milling tank, completely immersing the magnesium hydroxide, the stearic acid and the stainless steel grinding balls in the liquid nitrogen, carrying out ball milling for 1-2 hours, heating the ball-milled materials to 80-85 ℃, and carrying out heat preservation for 90-120 min; and adding the heated and heat-preserved material into the ball milling tank again, introducing liquid nitrogen into the ball milling tank, completely immersing the material into the liquid nitrogen, and performing ball milling for 2-3 hours to obtain the modified magnesium hydroxide.

2. The process for producing magnesium hydroxide according to claim 1, wherein in the first step, the mass ratio of magnesium chloride to water is 1: 5-6; the method for purifying the magnesium chloride solution comprises the following steps: adjusting the pH value of the magnesium chloride solution to 3.5-4.5 by adopting hydrochloric acid with the concentration of 0.5-1.5 mol/L; then adding barium chloride and polyvinylpyrrolidone into the magnesium chloride solution, and carrying out pressure ultrasound for 30-60 min; filtering to obtain filtrate, namely the purified magnesium chloride solution; the molar concentration of the barium chloride is 0.8 percent greater than the molar concentration of sulfate ions in the magnesium chloride solution; the pressure of the pressurized ultrasonic wave is 2.5-3.5 MPa, and the frequency is 50-65 KHz; the mass ratio of the barium chloride to the polyvinylpyrrolidone is 1: 0.01 to 0.05.

3. The process for producing magnesium hydroxide according to claim 1, wherein the amount of the crystal form control agent added is: adding 0.3-3 g of crystal form control agent into each liter of magnesium chloride solution; the preparation method of the crystal form control agent comprises the following steps: mixing 5-8 parts of inulin, 3-4 parts of ethylene glycol, 1-2 parts of phytic acid, 0.5-0.8 part of 1-ethyl-3-methylimidazolium lactic acid and 40-60 parts of water according to parts by weight, heating to 55-65 ℃, and stirring for 60-90 min at 500-800 r/min to obtain the crystal form control agent.

4. The process for producing magnesium hydroxide according to claim 1, wherein in the second step, the volume ratio of ethanol to water in the ethanol aqueous solution is 2: 1; the power of the ultrasonic atomization is 1-10 kW, the frequency is 1.5-3.5 MHz, and the atomization rate is 50-150 mL/min; the carrier gas is inert gas, and the flow rate of the carrier gas is 1-20L/min; the mass ratio of the magnesium chloride to the ethanol water solution is 1: 6-8.

5. The process for producing magnesium hydroxide according to claim 1, wherein in the third step, the stirring speed is 150 to 300 r/min; the flow rate of the introduced ammonia gas is 300-500 mL/min.

6. The production process of magnesium hydroxide according to claim 1, wherein in the fourth step, stainless steel grinding balls are added into a ball-milling tank according to the ball material mass ratio of 10-30: 1; the stainless steel grinding ball comprises large balls and small balls in a number ratio of 2: 1; the diameter of the big ball is 15-20 mm, and the diameter of the small ball is 3-5 mm; the ball milling adopts an upright ball mill with the rotating speed of 350 r/min.

7. The process for producing magnesium hydroxide according to claim 1, wherein in the first step, the frequency of the ultrasonic wave is 35 to 45 KHz.

8. The process for producing magnesium hydroxide according to claim 1, wherein in the fourth step, the mass ratio of the magnesium hydroxide to the stearic acid is 85-125: 1.

Technical Field

The invention relates to a production process of magnesium hydroxide.

Background

The magnesium hydroxide is used as an important functional fine inorganic chemical product, is an inorganic, smoke-inhibiting and non-toxic flame-retardant material, and is widely applied to the flame-retardant field of high molecular polymers. Magnesium hydroxide is considered to be an environmentally friendly inorganic flame retardant having the most promising development prospect because of its high thermal stability, high heat absorption capacity, excellent smoke suppression capability, and low hardness as compared with widely used aluminum hydroxide flame retardant materials, and has been a hot spot of recent research.

The existing magnesium hydroxide production process has various processes, and can be divided into a lime method, an ammonia method, a sodium hydroxide method and the like according to the types of precipitating agents. The magnesium hydroxide product obtained by the lime method has low purity, the sodium hydroxide method has high cost, the filtering and washing are difficult, the mother liquor is not easy to recover, and the ammonia method can increase the solubility of the magnesium hydroxide due to weak alkalinity of ammonia, so the reaction process is easy to control, high-purity fine magnesium hydroxide can be prepared, and large-grain products which are easy to wash can also be prepared, therefore, the method is a commonly adopted method for producing the magnesium hydroxide. The ammonia method is mostly researched by an ammonia water method, and the ammonia method is rarely researched. The magnesium hydroxide has strong surface polarity and small particle size, is easy to agglomerate to form secondary particles, so that the magnesium hydroxide has poor compatibility with polymer materials, has poor dispersibility in the polymer materials and seriously influences the mechanical properties of the polymer materials, and therefore, the magnesium hydroxide cannot be directly used for the polymer materials to improve the flame retardant property of the polymer materials.

Disclosure of Invention

An object of the present invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.

To achieve these objects and other advantages in accordance with the present invention, there is provided a process for producing magnesium hydroxide, comprising the steps of:

adding magnesium chloride into water, preparing a magnesium chloride solution, purifying the magnesium chloride solution, adding the purified magnesium chloride solution into a reactor, adding a crystal form control agent, and performing ultrasonic treatment; obtaining a mixed material;

step two, placing the ethanol aqueous solution in an ultrasonic atomizer for ultrasonic atomization to obtain ethanol atomized matter, and introducing the ethanol atomized matter into the mixed material in the reactor through carrier gas;

continuously introducing ammonia gas into the mixed material in the reactor under the stirring condition until the precipitate is stable, stopping introducing the ammonia gas, filtering and washing to obtain magnesium hydroxide;

adding magnesium hydroxide into a ball milling tank, simultaneously adding stearic acid and stainless steel grinding balls, introducing liquid nitrogen into the ball milling tank, completely immersing the magnesium hydroxide, the stearic acid and the stainless steel grinding balls in the liquid nitrogen, carrying out ball milling for 1-2 hours, heating the ball-milled materials to 80-85 ℃, and carrying out heat preservation for 90-120 min; and adding the heated and heat-preserved material into the ball milling tank again, introducing liquid nitrogen into the ball milling tank, completely immersing the material into the liquid nitrogen, and performing ball milling for 2-3 hours to obtain the modified magnesium hydroxide.

Preferably, in the first step, the mass ratio of magnesium chloride to water is 1: 5-6; the method for purifying the magnesium chloride solution comprises the following steps: adjusting the pH value of the magnesium chloride solution to 3.5-4.5 by adopting hydrochloric acid with the concentration of 0.5-1.5 mol/L; then adding barium chloride and polyvinylpyrrolidone into the magnesium chloride solution, and carrying out pressure ultrasound for 30-60 min; filtering to obtain filtrate, namely the purified magnesium chloride solution; the molar concentration of the barium chloride is 0.8 percent greater than the molar concentration of sulfate ions in the magnesium chloride solution; the pressure of the pressurized ultrasonic wave is 2.5-3.5 MPa, and the frequency is 50-65 KHz; the mass ratio of the barium chloride to the polyvinylpyrrolidone is 1: 0.01 to 0.05.

Preferably, the addition amount of the crystal form control agent is as follows: adding 0.3-3 g of crystal form control agent into each liter of magnesium chloride solution; the preparation method of the crystal form control agent comprises the following steps: mixing 5-8 parts of inulin, 3-4 parts of ethylene glycol, 1-2 parts of phytic acid, 0.5-0.8 part of 1-ethyl-3-methylimidazolium lactic acid and 40-60 parts of water according to parts by weight, heating to 55-65 ℃, and stirring for 60-90 min at 500-800 r/min to obtain the crystal form control agent.

Preferably, in the second step, the volume ratio of ethanol to water in the ethanol aqueous solution is 2: 1; the power of the ultrasonic atomization is 1-10 kW, the frequency is 1.5-3.5 MHz, and the atomization rate is 50-150 mL/min; the carrier gas is inert gas, and the flow rate of the carrier gas is 1-20L/min; the mass ratio of the magnesium chloride to the ethanol aqueous solution is 1: 6-8;

preferably, in the third step, the stirring speed is 150-300 r/min; the flow rate of the introduced ammonia gas is 300-500 mL/min.

Preferably, in the fourth step, the stainless steel grinding balls are added into a ball grinding tank according to the ball material mass ratio of 10-30: 1; the stainless steel grinding ball comprises large balls and small balls in a number ratio of 2: 1; the diameter of the big ball is 15-20 mm, and the diameter of the small ball is 3-5 mm; the ball milling adopts an upright ball mill with the rotating speed of 350 r/min.

Preferably, in the first step, the frequency of the ultrasound is 35 to 45 KHz.

Preferably, in the fourth step, the mass ratio of the magnesium hydroxide to the stearic acid is 85-125: 1.

The invention at least comprises the following beneficial effects: the magnesium hydroxide with high purity and uniform particle size distribution can be prepared by the production process of the magnesium hydroxide, the compatibility of the magnesium hydroxide and a polymer is improved by the modification of stearic acid, and the production process of the magnesium hydroxide is simple and convenient to operate.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

The specific implementation mode is as follows:

the present invention is further described in detail below with reference to examples so that those skilled in the art can practice the invention with reference to the description.

It will be understood that terms such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.

Example 1:

a production process of magnesium hydroxide comprises the following steps:

adding magnesium chloride into water, preparing a magnesium chloride solution, purifying the magnesium chloride solution, adding the purified magnesium chloride solution into a reactor, adding a crystal form control agent, and performing ultrasonic treatment; obtaining a mixed material; the mass ratio of the magnesium chloride to the water is 1: 5; the frequency of the ultrasonic wave is 35 KHz;

the method for purifying the magnesium chloride solution comprises the following steps: adjusting the pH value of the magnesium chloride solution to 4 by adopting hydrochloric acid with the concentration of 0.5 mol/L; then adding barium chloride and polyvinylpyrrolidone into the magnesium chloride solution, and carrying out pressure ultrasound for 60 min; filtering to obtain filtrate, namely the purified magnesium chloride solution; the molar concentration of the barium chloride is 0.8 percent greater than the molar concentration of sulfate ions in the magnesium chloride solution; the pressure of the pressurized ultrasound is 3MPa, and the frequency is 55 KHz; the mass ratio of the barium chloride to the polyvinylpyrrolidone is 1: 0.02;

the addition amount of the crystal form control agent is as follows: adding 0.5g of crystal form control agent into each liter of magnesium chloride solution; the preparation method of the crystal form control agent comprises the following steps: mixing inulin 5kg, ethylene glycol 3kg, phytic acid 1kg, 1-ethyl-3-methylimidazolium lactic acid 0.5kg and water 40kg, heating to 55 ℃, and stirring at 800r/min for 90min to obtain a crystal form control agent;

step two, placing the ethanol aqueous solution in an ultrasonic atomizer for ultrasonic atomization to obtain ethanol atomized matter, and introducing the ethanol atomized matter into the mixed material in the reactor through carrier gas; the volume ratio of ethanol to water in the ethanol water solution is 2: 1; the power of the ultrasonic atomization is 5kW, the frequency is 2.5MHz, and the atomization rate is 100 mL/min; the carrier gas is inert gas, and the flow rate of the carrier gas is 5L/min; the mass ratio of the magnesium chloride to the ethanol aqueous solution is 1: 8;

thirdly, under the stirring condition of 300r/min, introducing ammonia gas into the mixed material in the reactor at the speed of 350mL/min until the precipitate is stable, stopping introducing the ammonia gas, filtering and washing to obtain magnesium hydroxide; the purity of the magnesium hydroxide is 99.85 percent by detection, and D₅₀＝2.55um；

Adding magnesium hydroxide into a ball milling tank, simultaneously adding stearic acid and stainless steel grinding balls, introducing liquid nitrogen into the ball milling tank, completely immersing the magnesium hydroxide, the stearic acid and the stainless steel grinding balls in the liquid nitrogen, carrying out ball milling for 2 hours, heating the ball-milled materials to 80 ℃, and carrying out heat preservation for 90-120 min; adding the heated and heat-preserved material into the ball milling tank again, introducing liquid nitrogen into the ball milling tank, completely immersing the material in the liquid nitrogen, and performing ball milling for 3 hours to obtain modified magnesium hydroxide; adding stainless steel grinding balls into a ball-milling tank according to the ball material mass ratio of 20: 1; the stainless steel grinding ball comprises large balls and small balls in a number ratio of 2: 1; the diameter of the big ball is 15mm, and the diameter of the small ball is 3 mm; the ball milling adopts an upright ball mill with the rotating speed of 350 r/min; the mass ratio of the magnesium hydroxide to the stearic acid is 100: 1; through detection, D of the modified magnesium hydroxide₅₀1.58 um; the oxygen index of the composite material prepared by compounding the modified magnesium hydroxide and nylon 66 is 29％；

Example 2:

a production process of magnesium hydroxide comprises the following steps:

adding magnesium chloride into water, preparing a magnesium chloride solution, purifying the magnesium chloride solution, adding the purified magnesium chloride solution into a reactor, adding a crystal form control agent, and performing ultrasonic treatment; obtaining a mixed material; the mass ratio of the magnesium chloride to the water is 1: 6; the frequency of the ultrasonic wave is 35 KHz;

the method for purifying the magnesium chloride solution comprises the following steps: adjusting the pH value of the magnesium chloride solution to 4 by adopting hydrochloric acid with the concentration of 1 mol/L; then adding barium chloride and polyvinylpyrrolidone into the magnesium chloride solution, and carrying out pressure ultrasound for 60 min; filtering to obtain filtrate, namely the purified magnesium chloride solution; the molar concentration of the barium chloride is 0.8 percent greater than the molar concentration of sulfate ions in the magnesium chloride solution; the pressure of the pressurized ultrasound is 3MPa, and the frequency is 55 KHz; the mass ratio of the barium chloride to the polyvinylpyrrolidone is 1: 0.03;

the addition amount of the crystal form control agent is as follows: adding 1g of crystal form control agent into each liter of magnesium chloride solution; the preparation method of the crystal form control agent comprises the following steps: mixing 8kg of inulin, 3kg of ethylene glycol, 1.5kg of phytic acid, 0.6kg of 1-ethyl-3-methylimidazol lactic acid and 50kg of water, heating to 55 ℃, and stirring for 90min at 600r/min to obtain a crystal form control agent;

step two, placing the ethanol aqueous solution in an ultrasonic atomizer for ultrasonic atomization to obtain ethanol atomized matter, and introducing the ethanol atomized matter into the mixed material in the reactor through carrier gas; the volume ratio of ethanol to water in the ethanol water solution is 2: 1; the power of the ultrasonic atomization is 5kW, the frequency is 2.5MHz, and the atomization rate is 100 mL/min; the carrier gas is inert gas, and the flow rate of the carrier gas is 10L/min; the mass ratio of the magnesium chloride to the ethanol aqueous solution is 1: 6;

thirdly, under the stirring condition of 300r/min, introducing ammonia gas into the mixed material in the reactor at the speed of 400mL/min until the precipitate is stable, stopping introducing the ammonia gas, filtering and washing to obtain magnesium hydroxide; the purity of the magnesium hydroxide is detected to be 99.87 percent, D₅₀＝2.55um；

Adding magnesium hydroxide into a ball milling tank, simultaneously adding stearic acid and stainless steel grinding balls, introducing liquid nitrogen into the ball milling tank, completely immersing the magnesium hydroxide, the stearic acid and the stainless steel grinding balls in the liquid nitrogen, carrying out ball milling for 1 hour, heating the ball-milled materials to 85 ℃, and carrying out heat preservation for 120 min; adding the heated and heat-preserved material into the ball milling tank again, introducing liquid nitrogen into the ball milling tank, completely immersing the material in the liquid nitrogen, and carrying out ball milling for 2 hours to obtain modified magnesium hydroxide; adding stainless steel grinding balls into a ball-milling tank according to the ball material mass ratio of 20: 1; the stainless steel grinding ball comprises large balls and small balls in a number ratio of 2: 1; the diameter of the big ball is 20mm, and the diameter of the small ball is 5 mm; the ball milling adopts an upright ball mill with the rotating speed of 350 r/min; the mass ratio of the magnesium hydroxide to the stearic acid is 90: 1. Through detection, D of the modified magnesium hydroxide₅₀1.56 um; the oxygen index of the composite material prepared by compounding the modified magnesium hydroxide and nylon 66 is 29 percent;

comparative example 1:

a production process of magnesium hydroxide comprises the following steps:

step one, adding magnesium chloride into water, preparing a magnesium chloride solution, adding the magnesium chloride solution into a reactor, adding a crystal form control agent, and performing ultrasonic treatment; obtaining a mixed material; the mass ratio of the magnesium chloride to the water is 1: 5; the frequency of the ultrasonic wave is 35 KHz;

the addition amount of the crystal form control agent is as follows: adding 0.5g of crystal form control agent into each liter of magnesium chloride solution; the preparation method of the crystal form control agent comprises the following steps: mixing inulin 5kg, ethylene glycol 3kg, phytic acid 1kg, 1-ethyl-3-methylimidazolium lactic acid 0.5kg and water 40kg, heating to 55 ℃, and stirring at 800r/min for 90min to obtain a crystal form control agent;

step two, placing the ethanol aqueous solution in an ultrasonic atomizer for ultrasonic atomization to obtain ethanol atomized matter, and introducing the ethanol atomized matter into the mixed material in the reactor through carrier gas; the volume ratio of ethanol to water in the ethanol water solution is 2: 1; the power of the ultrasonic atomization is 5kW, the frequency is 2.5MHz, and the atomization rate is 100 mL/min; the carrier gas is inert gas, and the flow rate of the carrier gas is 5L/min; the mass ratio of the magnesium chloride to the ethanol aqueous solution is 1: 8;

thirdly, under the stirring condition of 300r/min, introducing ammonia gas into the mixed material in the reactor at the speed of 350mL/min until the precipitate is stable, stopping introducing the ammonia gas, filtering and washing to obtain magnesium hydroxide; the purity of the magnesium hydroxide is 98.95 percent by detection, and D₅₀＝2.75um；

Adding magnesium hydroxide into a ball milling tank, simultaneously adding stearic acid and stainless steel grinding balls, introducing liquid nitrogen into the ball milling tank, completely immersing the magnesium hydroxide, the stearic acid and the stainless steel grinding balls in the liquid nitrogen, carrying out ball milling for 2 hours, heating the ball-milled materials to 80 ℃, and carrying out heat preservation for 90-120 min; adding the heated and heat-preserved material into the ball milling tank again, introducing liquid nitrogen into the ball milling tank, completely immersing the material in the liquid nitrogen, and performing ball milling for 3 hours to obtain modified magnesium hydroxide; adding stainless steel grinding balls into a ball-milling tank according to the ball material mass ratio of 20: 1; the stainless steel grinding ball comprises large balls and small balls in a number ratio of 2: 1; the diameter of the big ball is 15mm, and the diameter of the small ball is 3 mm; the ball milling adopts an upright ball mill with the rotating speed of 350 r/min; the mass ratio of the magnesium hydroxide to the stearic acid is 100: 1. Through detection, D of the modified magnesium hydroxide₅₀1.60 um; the oxygen index of the composite material prepared by compounding the modified magnesium hydroxide and nylon 66 is 27 percent;

comparative example 2:

a production process of magnesium hydroxide comprises the following steps:

adding magnesium chloride into water, preparing a magnesium chloride solution, purifying the magnesium chloride solution, adding the purified magnesium chloride solution into a reactor, and performing ultrasonic treatment; obtaining a mixed material; the mass ratio of the magnesium chloride to the water is 1: 5; the frequency of the ultrasonic wave is 35 KHz;

the method for purifying the magnesium chloride solution comprises the following steps: adjusting the pH value of the magnesium chloride solution to 4 by adopting hydrochloric acid with the concentration of 0.5 mol/L; then adding barium chloride and polyvinylpyrrolidone into the magnesium chloride solution, and carrying out pressure ultrasound for 60 min; filtering to obtain filtrate, namely the purified magnesium chloride solution; the molar concentration of the barium chloride is 0.8 percent greater than the molar concentration of sulfate ions in the magnesium chloride solution; the pressure of the pressurized ultrasound is 3MPa, and the frequency is 55 KHz; the mass ratio of the barium chloride to the polyvinylpyrrolidone is 1: 0.02;

step two, placing the ethanol aqueous solution in an ultrasonic atomizer for ultrasonic atomization to obtain ethanol atomized matter, and introducing the ethanol atomized matter into the mixed material in the reactor through carrier gas; the volume ratio of ethanol to water in the ethanol water solution is 2: 1; the power of the ultrasonic atomization is 5kW, the frequency is 2.5MHz, and the atomization rate is 100 mL/min; the carrier gas is inert gas, and the flow rate of the carrier gas is 5L/min; the mass ratio of the magnesium chloride to the ethanol aqueous solution is 1: 8;

thirdly, under the stirring condition of 300r/min, introducing ammonia gas into the mixed material in the reactor at the speed of 350mL/min until the precipitate is stable, stopping introducing the ammonia gas, filtering and washing to obtain magnesium hydroxide; the purity of the magnesium hydroxide is 99.68 percent by detection, and D₅₀＝4.58um；

Adding magnesium hydroxide into a ball milling tank, simultaneously adding stearic acid and stainless steel grinding balls, introducing liquid nitrogen into the ball milling tank, completely immersing the magnesium hydroxide, the stearic acid and the stainless steel grinding balls in the liquid nitrogen, carrying out ball milling for 2 hours, heating the ball-milled materials to 80 ℃, and carrying out heat preservation for 90-120 min; adding the heated and heat-preserved material into the ball milling tank again, introducing liquid nitrogen into the ball milling tank, completely immersing the material in the liquid nitrogen, and performing ball milling for 3 hours to obtain modified magnesium hydroxide; adding stainless steel grinding balls into a ball-milling tank according to the ball material mass ratio of 20: 1; the stainless steel grinding ball comprises large balls and small balls in a number ratio of 2: 1; the diameter of the big ball is 15mm, and the diameter of the small ball is 3 mm; the ball milling adopts an upright ball mill with the rotating speed of 350 r/min; the mass ratio of the magnesium hydroxide to the stearic acid is 100: 1. Through detection, D of the modified magnesium hydroxide₅₀2.45 um; the oxygen index of the composite material prepared by compounding the modified magnesium hydroxide and nylon 66 is 25 percent;

comparative example 3:

a production process of magnesium hydroxide comprises the following steps:

adding magnesium chloride into water, preparing a magnesium chloride solution, purifying the magnesium chloride solution, adding the purified magnesium chloride solution into a reactor, adding a crystal form control agent, and performing ultrasonic treatment; obtaining a mixed material; the mass ratio of the magnesium chloride to the water is 1: 5; the frequency of the ultrasonic wave is 35 KHz;

the method for purifying the magnesium chloride solution comprises the following steps: adjusting the pH value of the magnesium chloride solution to 4 by adopting hydrochloric acid with the concentration of 0.5 mol/L; then adding barium chloride and polyvinylpyrrolidone into the magnesium chloride solution, and carrying out pressure ultrasound for 60 min; filtering to obtain filtrate, namely the purified magnesium chloride solution; the molar concentration of the barium chloride is 0.8 percent greater than the molar concentration of sulfate ions in the magnesium chloride solution; the pressure of the pressurized ultrasound is 3MPa, and the frequency is 55 KHz; the mass ratio of the barium chloride to the polyvinylpyrrolidone is 1: 0.02;

the addition amount of the crystal form control agent is as follows: adding 0.5g of crystal form control agent into each liter of magnesium chloride solution; the preparation method of the crystal form control agent comprises the following steps: mixing inulin 5kg, ethylene glycol 3kg, phytic acid 1kg, 1-ethyl-3-methylimidazolium lactic acid 0.5kg and water 40kg, heating to 55 ℃, and stirring at 800r/min for 90min to obtain a crystal form control agent;

step two, placing the ethanol aqueous solution in an ultrasonic atomizer for ultrasonic atomization to obtain ethanol atomized matter, and introducing the ethanol atomized matter into the mixed material in the reactor through carrier gas; the volume ratio of ethanol to water in the ethanol water solution is 2: 1; the power of the ultrasonic atomization is 5kW, the frequency is 2.5MHz, and the atomization rate is 100 mL/min; the carrier gas is inert gas, and the flow rate of the carrier gas is 5L/min; the mass ratio of the magnesium chloride to the ethanol aqueous solution is 1: 8;

thirdly, under the stirring condition of 300r/min, introducing ammonia gas into the mixed material in the reactor at the speed of 350mL/min until the precipitate is stable, stopping introducing the ammonia gas, filtering and washing to obtain magnesium hydroxide;

stirring and mixing magnesium hydroxide and stearic acid at the speed of 350 revolutions per minute for 2 hours, heating the mixed material to 80 ℃, and preserving heat for 90-120 min; stirring and mixing the heated and heat-preserved materials for 3 hours at the speed of 350 revolutions per minute to obtain modified magnesium hydroxide; the mass ratio of the magnesium hydroxide to the stearic acid is 100: 1; through detection, D of the modified magnesium hydroxide₅₀3.85 um; subjecting the modified hydrogen to hydrogenationThe oxygen index of the composite material prepared by compounding the magnesium oxide and the nylon 66 is 22 percent.

In the invention, the process of preparing the composite material by compounding the modified magnesium hydroxide and the nylon 66 comprises the following steps: vacuum drying nylon 6 at 90 deg.C for 12 hr, mixing nylon 6 and modified magnesium hydroxide at a ratio of 20:1 in a high-speed mixer for 30min, discharging, extruding and granulating with a twin-screw extruder, wherein the temperatures of screw sections are 220 deg.C, 230 deg.C, 235 deg.C, 240 deg.C, 235 deg.C and 230 deg.C, and the neck mold temperature is 230 deg.C; drying at 80 deg.C for 24 h. The oxygen index was determined according to ASTM D2863-77.

While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable to various fields of endeavor for which the invention may be embodied with additional modifications as would be readily apparent to those skilled in the art, and the invention is therefore not limited to the details given herein and to the examples shown and described without departing from the generic concept as defined by the claims and their equivalents.