Synthesis method of hexagonal flaky magnesium hydroxide and flame-retardant application of hexagonal flaky magnesium hydroxide

Abstract

The invention belongs to the technical field of synthesis of magnesium hydroxide flame retardants, and provides a synthesis method and flame-retardant application of hexagonal flaky magnesium hydroxide, and the synthesis method comprises the following steps: step 1, dissolving a mineralizer, a crystal form control agent and magnesium chloride in water in proportion; step 2, putting a certain amount of the mixed solution into a high-pressure reaction kettle for hydrothermal reaction; step 3, after the reaction is finished, taking out the cooled solution from the high-pressure reaction kettle, and filtering and separating out a white product; 4, drying the sample, and grinding to obtain pure magnesium hydroxide powder; through reasonable process design and optimization, the prepared magnesium hydroxide not only has regular morphology and better dispersity, but also has excellent performance in the field of flame retardance of high polymer materials, meets the requirement of environmental protection, has the production advantages of low cost and high efficiency, and is suitable for industrial production. The method not only can effectively improve the overall utilization rate of salt lake resources, but also has remarkable economic and application values, and has wide industrial application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium hydroxide flame retardant synthesis, in particular to an efficient and green synthesis method for preparing hexagonal flaky magnesium hydroxide flame retardant, and is applied to the flame retardant field of polymer materials. Background Art

[0002] my country's salt lake resources are rich and widely distributed. More than 1,500 salt lakes have been discovered, containing more than 200 kinds of mineral resources. The Chaerhan Salt Lake in the Qaidam Basin of Qinghai is the largest chloride-type potassium-magnesium salt deposit in my country, famous for its large reserves, high grade and complete types. The Chaerhan Salt Lake is rich in salt resources, storing more than 55.5 billion tons of sodium chloride, which can be consumed by the world's population for nearly 1,000 years; the reserves of potassium chloride, magnesium chloride and lithium chloride are all ranked first in China; at present, the focus of my country's salt lake resource development is mainly on the extraction of potassium and lithium to meet the domestic demand for potash fertilizers and the rapid development of the new energy industry. The Chaerhan Salt Lake discharges a large amount of magnesium chloride brine every year. Therefore, improving the comprehensive utilization rate of high-magnesium brine in salt lakes and realizing waste resource utilization have become key issues that need to be urgently addressed by the Qinghai salt lake industry.

[0003] In this context, the efficient utilization of magnesium chloride has become one of the research focuses, especially its conversion into high value-added magnesium-based functional materials, such as magnesium hydroxide. Magnesium hydroxide is widely used in the flame retardancy of polymer materials such as ethylene-vinyl acetate copolymer (EVA), linear low-density polyethylene (LLDPE) and polyvinyl chloride (PVC) due to its excellent flame retardant properties, including low smoke, non-toxicity, non-corrosiveness and high decomposition temperature. The magnesium chloride resources in the old brine of Qinghai Salt Lake have the characteristics of high purity and excellent quality, which provides an ideal raw material for the preparation of industrial-grade magnesium hydroxide. The development of this high value-added material can not only effectively improve the overall utilization rate of salt lake resources, but also has significant economic and application value. Therefore, in-depth research on the preparation and application of magnesium hydroxide is crucial to promote the comprehensive utilization and sustainable development of Qinghai Salt Lake resources.

[0004] Common methods for preparing magnesium hydroxide include precipitation, solvent thermal method, mechanical grinding method, vapor deposition method and electrolysis method, but these methods usually result in irregular shapes, non-uniform particle sizes and poor dispersibility of synthesized magnesium hydroxide particles, which require further treatment to improve product performance; At present, most of the magnesium hydroxide flame retardants prepared in industry are in the form of irregular particles. Because of their large polarity, strong hydrophilicity and easy agglomeration, their dispersibility and flame retardant effect in polymer materials still need to be further improved; In industry, magnesium hydroxide is usually modified secondary to improve its dispersibility in polymer materials, but this process increases costs and complicates the process. Therefore, how to use salt lake magnesium chloride resources to synthesize magnesium hydroxide flame retardants with regular morphology and good compatibility with polymer materials in one step is a problem that needs to be solved at present.

[0005] For this reason, those skilled in the art have proposed a method for synthesizing hexagonal flake magnesium hydroxide and its flame retardant application to solve the problems raised in the background art. Summary of the Invention

[0006] In order to address the deficiencies of irregular morphology, strong hydrophilicity, and easy agglomeration of magnesium hydroxide, the purpose of the present invention is to provide a method for preparing hexagonal flake magnesium hydroxide by a one-step hydrothermal method using magnesium chloride resources in salt lakes. This method has a simple process, low cost, and the obtained product has regular morphology, good dispersibility, and significant flame retardant effect, and is particularly suitable for flame retardant applications in polymer materials.

[0007] The present invention is achieved through the following technical solutions.

[0008] A method for preparing a hexagonal flake magnesium hydroxide flame retardant, comprising:

[0009] Step 1: Dissolve a mineralizer, a crystal form control agent, and magnesium chloride in water in proportion, adding while stirring until a uniform reaction solution is formed;

[0010] Step 2: Put a certain amount of the mixed solution into a high-pressure reaction kettle and carry out a hydrothermal reaction at a certain temperature and pressure to gradually form a hexagonal flake structure of magnesium hydroxide;

[0011] Step 3: After the reaction is completed, take out the cooled solution from the high-pressure reaction kettle, filter and separate the white product, and carry out multiple washing and filtering;

[0012] Step 4: Dry the sample and obtain pure magnesium hydroxide powder after grinding.

[0013] Furthermore, in Step 1, the mineralizer includes but is not limited to one of sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia water, or several in any proportion; the crystal form control agent includes but is not limited to potassium carbonate, potassium bicarbonate, sodium carbonate, anhydrous sodium carbonate, sodium bicarbonate, urea, polyvinylpyrrolidone, sodium dodecyl sulfate, ethylenediamine, sodium citrate, potassium citrate.

[0014] Furthermore, in Step 1, the molar concentration of the mineralizer is 1-4 mol / L, the molar concentration of the crystal form control agent is 1-4 mol / L, and the molar concentration of magnesium chloride is 1-2 mol / L.

[0015] Furthermore, in Step 1, the mineralizer, the crystal form control agent, and magnesium chloride are dissolved in deionized water, and the stirring speed at room temperature is 200-800 r / min.

[0016] Furthermore, in Step 2, the filling rate of the reaction kettle is 20-80%.

[0017] Further, the volume of the autoclave in step 2 is 50 mL - 5000 mL.

[0018] Further, in step 2, the reaction temperature is 120 - 200 °C, and the reaction time is 2 - 6 h.

[0019] Further, in step 3, vacuum filtration is used for filtration.

[0020] Further, in step 3, deionized water and absolute ethanol are used for filtration 3 - 4 times until the filtrate is neutral.

[0021] Further, in step 4, the drying temperature is 60 - 100 °C, and the drying time is 6 - 24 h.

[0022] The present invention makes full use of the rich magnesium chloride resources in salt lake brine to prepare magnesium hydroxide, realizes the efficient utilization of waste magnesium chloride, achieves the purpose of turning waste into treasure and eliminating "magnesium harm", and effectively promotes the high-value development of salt lake resources; meanwhile, in the hydrothermal reaction process, different crystal form control agents (such as anhydrous sodium carbonate, etc.) are added, and the nucleation and growth of magnesium hydroxide are promoted by regulating the alkalinity of the solution and the reaction environment, thereby preparing a magnesium hydroxide flame retardant with regular hexagonal platelet morphology.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The method for preparing hexagonal platelet magnesium hydroxide by hydrothermal method adopted in the present invention, through reasonable process design and optimization, the prepared magnesium hydroxide not only has a regular morphology and good dispersibility, but also has excellent performance in the field of flame retardancy of polymer materials, meets the environmental protection requirements, has the production advantages of low cost and high efficiency, can not only effectively improve the overall utilization rate of salt lake resources, but also has significant economic and application values, and has a wide industrial application prospect.

[0025] Specifically, the present invention has the following advantages:

[0026] 1. The present invention makes full use of the magnesium chloride resources in Qinghai Salt Lake, synthesizes magnesium hydroxide by hydrothermal method, the process is very simple, the cost is low, effectively improves the comprehensive utilization rate of salt lake resources, reduces resource waste, can be mass-produced industrially, and has significant economic value.

[0027] 2. Using potassium carbonate, potassium bicarbonate, sodium carbonate, anhydrous sodium carbonate, sodium bicarbonate, urea, etc. as crystal form control agents, by adjusting the reaction conditions, the morphology of magnesium hydroxide can be precisely controlled to form a regular hexagonal platelet structure; the hexagonal platelet structure is beneficial to improving the dispersibility and stability of the material, and further enhancing its performance in practical applications.

[0028] 3. The hexagonal flake magnesium hydroxide prepared by the invention has good dispersibility in polymer materials, can be evenly distributed in the matrix, and effectively prevents the spread of fire. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is the X-ray diffraction pattern of the hexagonal flake magnesium hydroxide prepared in Example 1 of the present invention;

[0030] Figure 2 It is the electron micrograph of the hexagonal flake magnesium hydroxide prepared in Example 2 of the present invention;

[0031] Figure 3 It is the electron micrograph of the hexagonal flake magnesium hydroxide prepared in Example 4 of the present invention;

[0032] Figure 4 It is the electron micrograph of the cross-section of the EVA composite material prepared in Comparative Example 1 and Comparative Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] The embodiments of the present invention will be further described in detail below with reference to the drawings and examples. The following examples are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0034] Example 1

[0035] Step 1: Dissolve 8 g of potassium hydroxide, 5.3 g of sodium bicarbonate and 9.5 g of magnesium chloride in 100 mL of deionized water, set the rotation speed to 500 r / min, and add and stir at room temperature until a uniform reaction solution is formed;

[0036] Step 2: Put the mixed solution in Step 1 into a 100 mL high-pressure reaction kettle with a filling amount of 50%, the reaction temperature is 180 °C, and the reaction time is 3 h;

[0037] Step 3: After the reaction is completed, take out the cooled reaction solution in Step 2 from the high-pressure reaction kettle, filter and separate the white product with a vacuum pump, and wash and filter it with deionized water and absolute ethanol for many times until the filtrate is neutral;

[0038] Step 4: Put the filter cake obtained in Step 3 into an oven at 100 °C and dry it for 6 h, then take it out and grind it to finally obtain pure magnesium hydroxide powder; through weighing and calculation, the yield is about 88%.

[0039] Figure 1X-ray diffraction pattern of the magnesium hydroxide flame retardant prepared in Example 1; it can be seen from the pattern that the characteristic diffraction peaks at 2θ of 18.89°, 38.25°, 50.93°, 58.71°, 62.11°, 68.33°, and 71.92° correspond to the (001), (101), (102), (110), (111), (103), and (201) crystal planes of magnesium hydroxide respectively; the comparison result with the standard card (PDF#07-0239) shows that its crystal structure is consistent with it, indicating that magnesium hydroxide has been successfully prepared; the peak shape of the pattern is sharp and there are no impurity peaks, which indicates that the prepared magnesium hydroxide has high crystallinity.

[0040] Example 2

[0041] Step 1: Dissolve 8 g of potassium hydroxide, 10.6 g of anhydrous sodium carbonate, and 9.5 g of magnesium chloride in 100 mL of deionized water. Set the rotation speed to 500 r / min and stir while adding at room temperature until a uniform reaction solution is formed.

[0042] Step 2: Put the mixed solution in Step 1 into a 100 mL high-pressure reactor with a filling amount of 80%, the reaction temperature is 180 °C, and the reaction time is 3 h.

[0043] Step 3: After the reaction is completed, take out the cooled reaction solution in Step 2 from the high-pressure reactor, filter and separate the white product with a vacuum pump, and wash and filter it with deionized water and anhydrous ethanol multiple times until the filtrate is neutral.

[0044] Step 4: Put the filter cake obtained in Step 3 into an oven at 100 °C and dry it for 6 h, then take it out and grind it to finally obtain pure magnesium hydroxide powder; the yield is about 91% by weighing and calculating.

[0045] Figure 2 The electron microscope image of the magnesium hydroxide prepared in Example 2 shows that hexagonal flake magnesium hydroxide with good dispersion and a thickness of about 50 nm has been successfully prepared by the preparation method of the present invention.

[0046] Example 3

[0047] Step 1: Dissolve 20 g of sodium hydroxide, 39.75 g of potassium carbonate, and 23.75 g of magnesium chloride in 250 mL of deionized water. Set the rotation speed to 400 r / min and stir while adding at room temperature until a uniform reaction solution is formed.

[0048] Step 2: Put the mixed solution in Step 1 into a 300 mL high-pressure reactor with a filling amount of 50%, the reaction temperature is 180 °C, and the reaction time is 3 h.

[0049] Step 3: After the reaction is completed, take out the cooled reaction solution in Step 2 from the high-pressure reactor, filter and separate the white product with a vacuum pump, and wash and filter it several times with deionized water and absolute ethanol until the filtrate is neutral.

[0050] Step 4: Put the filter cake obtained in Step 3 into an oven at 100 °C and dry it for 6 h, then take it out and grind it to finally obtain pure magnesium hydroxide powder; the yield is about 87% through weighing and calculation.

[0051] Example 4

[0052] Step 1: Dissolve 20 g of sodium hydroxide, 26.5 g of anhydrous sodium carbonate and 23.75 g of magnesium chloride in 250 mL of deionized water, set the rotation speed to 500 r / min, and add and stir at room temperature until a uniform reaction solution is formed.

[0053] Step 2: Put the mixed solution in Step 1 into a 300 mL high-pressure reactor with a filling amount of 80%, the reaction temperature is 180 °C, and the reaction time is 3 h.

[0054] Step 3: After the reaction is completed, take out the cooled reaction solution in Step 2 from the high-pressure reactor, filter and separate the white product with a vacuum pump, and wash and filter it several times with deionized water and absolute ethanol until the filtrate is neutral.

[0055] Step 4: Put the filter cake obtained in Step 3 into an oven at 100 °C and dry it for 6 h, then take it out and grind it to finally obtain pure magnesium hydroxide powder; the yield is about 91% through weighing and calculation.

[0056] Figure 3 It is the electron microscope image of the hexagonal flake magnesium hydroxide prepared in Example 4; it can be seen from the electron microscope image that the morphology of magnesium hydroxide becomes very regular due to the addition of the crystal form control agent anhydrous sodium carbonate, and it is hexagonal flakes with good dispersion and a thickness of about 50 nm.

[0057] Example 5

[0058] Step 1: Dissolve 120 g of sodium hydroxide, 159 g of anhydrous sodium carbonate and 142.5 g of magnesium chloride in 2000 mL of deionized water in turn, set the rotation speed to 600 r / min, and add and stir at room temperature until a uniform reaction solution is formed.

[0059] Step 2: Put the mixed solution in Step 1 into a 2000 mL high-pressure reactor with a filling amount of 70%, the reaction temperature is 180 °C, and the reaction time is 3 h.

[0060] Step 3: After the reaction is completed, take out the cooled reaction solution in Step 2 from the autoclave, filter it with a vacuum pump to separate the white product, and wash and filter it several times with deionized water and absolute ethanol until the filtrate is neutral.

[0061] Step 4: Put the filter cake obtained in Step 3 into an oven at 100 °C and dry it for 6 h, then take it out and grind it to finally obtain pure magnesium hydroxide powder; the yield can be calculated to be about 87% by weighing.

[0062] Combined with the experimental results, we decided to conduct further research on the flame retardancy of the magnesium hydroxide flame retardant prepared in Example 4; for this purpose, we found a commercially available magnesium hydroxide flame retardant with good performance as a comparative study.

[0063] Comparative Example 1

[0064] We selected the magnesium hydroxide flame retardant (MHk) provided by Shanghai Kaibo Cable Special Materials Co., Ltd. and added it to EVA at the addition amounts of 50 wt% and 60 wt% respectively with the magnesium hydroxide (Mhz) prepared in Example 4; the mixing temperature was set at 140 °C, the mixing time was set at 10 min, and the rotation speed was set at 60 r / min; during the tablet pressing process, the hot pressing temperature was 140 °C, the hot pressing time was 10 min, and the cold pressing time was 5 min; the prepared EVA composites were named EVA / MHk50, EVA / MHk60, EVA / MHz50, and EVA / MHz60 respectively.

[0065] Comparative Example 2

[0066] We selected the magnesium hydroxide flame retardant (MHy) produced by Albemarle Corporation, which is popular in the market and has good flame retardancy, and the preparation conditions of the composite material were exactly the same as those in Comparative Example 1; MHk was added to EVA at the addition amounts of 50 wt% and 60 wt%; the mixing temperature was set at 140 °C, the mixing time was set at 10 min, and the rotation speed was set at 60 r / min; during the tablet pressing process, the hot pressing temperature was 140 °C, the hot pressing time was 10 min, and the cold pressing time was 5 min; the prepared EVA composites were named EVA / MHy50 and EVA / MHy60 respectively.

[0067] Table 1 shows the flame retardancy data of the EVA composites prepared in Comparative Example 1 and Comparative Example 2.

[0068] Table 1

[0069]

[0070] As can be seen from the above table, the magnesium hydroxide prepared by the method of the present invention has very excellent flame retardant properties; among them, the oxygen index of EVA / MHz50 is 31.2%, and the vertical burning rating reaches V-2 level; when the addition amount of MHz is 60wt%, the oxygen index of the composite material is as high as 49.2%, and the vertical burning rating reaches V-0 level; Figure 4 For the SEM images of the cross-section of the EVA composites with 60wt% magnesium hydroxide prepared in Comparative Example 1 and Comparative Example 2, it can be found that for the magnesium hydroxide prepared by the method of the present invention, almost no obvious particle edges can be seen in the EVA matrix, indicating better compatibility and dispersibility with the matrix.

[0071] Application Example: The application of this method in industry includes the following steps:

[0072] S1. Raw material preparation:

[0073] Magnesium chloride: Magnesium chloride in Qinghai Salt Lake brine is used as the raw material, which has high purity and excellent quality;

[0074] Mineralizer: One or more of sodium hydroxide, potassium hydroxide, lithium hydroxide or ammonia water are selected as the mineralizer;

[0075] Crystal form control agent: Potassium carbonate, potassium bicarbonate, sodium carbonate, anhydrous sodium carbonate, sodium bicarbonate, urea, etc. are selected as the crystal form control agent to control the morphology of magnesium hydroxide;

[0076] S2. Synthesis process:

[0077] The mineralizer, crystal form control agent and magnesium chloride are dissolved in deionized water in proportion, and stirred while adding to form a uniform reaction solution;

[0078] The reaction solution is put into a high-pressure reaction kettle and subjected to hydrothermal reaction at a certain temperature and pressure; by adjusting the reaction conditions (such as reaction temperature, time, filling rate, etc.), magnesium hydroxide gradually forms a hexagonal flake structure;

[0079] After the reaction is completed, the cooled solution is taken out from the high-pressure reaction kettle, the white product is separated by filtration, and washed and filtered repeatedly until the filtrate is neutral;

[0080] The washed product is dried and ground to obtain pure hexagonal flake magnesium hydroxide powder;

[0081] S3. Product application:

[0082] The prepared hexagonal flake magnesium hydroxide powder is added as a flame retardant to polymer materials such as ethylene-vinyl acetate copolymer (EVA), linear low-density polyethylene (LLDPE) and polyvinyl chloride (PVC);

[0083] Through processes such as mixing and hot pressing, a polymer composite material with excellent flame retardant properties is prepared.

[0084] As can be seen from the above, the hexagonal flake magnesium hydroxide flame retardant prepared by the method of the present invention has good dispersibility and stability in polymer materials, can be evenly distributed in the matrix, and effectively prevents the spread of flames; the test results show that the polymer composite material added with this flame retardant has a high oxygen index and vertical burning rating, and its flame retardant performance is significantly better than that of traditional irregular granular magnesium hydroxide flame retardants.

[0085] The embodiments of the present invention are given for the purpose of illustration and description. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limitations on the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a hexagonal flaky magnesium hydroxide flame retardant, characterized in that: include: Step 1, dissolving the mineralizer, the crystal form control agent and magnesium chloride in water in proportion, adding and stirring until a uniform reaction solution is formed; Step 2, placing a certain amount of the mixed solution into a high-pressure reactor, and performing a hydrothermal reaction at a certain temperature and pressure, so that the magnesium hydroxide gradually forms a hexagonal sheet structure; Step 3: After the reaction is completed, the cooled solution is taken out from the autoclave, the white product is separated by filtration, and then washed and filtered for multiple times; Step 4: Dry the sample and grind it to obtain pure magnesium hydroxide powder.

2. A method for preparing a hexagonal flaky magnesium hydroxide flame retardant as claimed in claim 1, characterized in that: The mineralizer in step 1 includes but is not limited to one of sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonia water, or a mixture of several of them in any proportion; the crystal form control agent includes but is not limited to potassium carbonate, potassium bicarbonate, sodium carbonate, anhydrous sodium carbonate, sodium bicarbonate, urea, polyvinyl pyrrolidone, sodium dodecyl sulfate, ethylenediamine, sodium citrate, and potassium citrate.

3. A method for preparing a hexagonal flaky magnesium hydroxide flame retardant as claimed in claim 1, characterized in that: In step 1, the molar concentration of the mineralizer is 1-4 mol / L, the molar concentration of the crystal form control agent is 1-4 mol / L, and the molar concentration of magnesium chloride is 1-2 mol / L.

4. A method for preparing a hexagonal flaky magnesium hydroxide flame retardant as claimed in claim 1, characterized in that: In the step 1, the mineralizer, the crystal form control agent and the magnesium chloride are dissolved in deionized water, and the stirring speed at room temperature is 200-800 r / min.

5. A method for preparing a hexagonal flaky magnesium hydroxide flame retardant as claimed in claim 1, characterized in that: The filling rate of the reaction kettle in step 2 is 20-80%.

6. A method for preparing a hexagonal flaky magnesium hydroxide flame retardant as claimed in claim 1, characterized in that: The volume of the high-pressure reactor in step 2 is 50 mL-5000 mL.

7. A method for preparing a hexagonal flaky magnesium hydroxide flame retardant as claimed in claim 1, characterized in that: In step 2, the reaction temperature is 120-200° C. and the reaction time is 2-6 hours.

8. A method for preparing a hexagonal flaky magnesium hydroxide flame retardant as claimed in claim 1, characterized in that: In the step 3, a vacuum pump is used for filtration.

9. A method for preparing a hexagonal flaky magnesium hydroxide flame retardant as claimed in claim 1, characterized in that: In step 3, deionized water and anhydrous ethanol are used for filtration 3-4 times respectively until the filtrate is neutral.

10. The method for preparing a hexagonal flaky magnesium hydroxide flame retardant according to claim 1, characterized in that: In step 4, the drying temperature is 60-100° C. and the drying time is 6-24 hours.

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