Rod-like magnesium hydroxide, its preparation method and application

Abstract

The application relates to the technical field of inorganic material preparation, in particular to rod-shaped magnesium hydroxide as well as a preparation method and application thereof. The method comprises the following steps: mixing a magnesium source, water, a precipitating agent and a crystal growth control agent to obtain a mixed reaction solution; the crystal growth control agent comprises sodium citrate; and the mixed reaction solution is subjected to hydrothermal reaction to obtain the rod-shaped magnesium hydroxide. By introducing sodium citrate as the crystal growth control agent and combining with optimized process parameters, the rod-shaped magnesium hydroxide with regular morphology, high specific surface area and high thermal stability is successfully prepared, and the technical problems of irregular morphology, small specific surface area and poor thermal stability of traditional magnesium hydroxide are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of inorganic material preparation technology, and in particular to a rod-shaped magnesium hydroxide, its preparation method, and its application. Background Technology

[0002] Magnesium hydroxide (Mg(OH)2), as an important environmentally friendly inorganic flame retardant, is widely used in the flame-retardant modification of polymer materials due to its good thermal stability, smoke suppression, non-toxicity, and non-corrosiveness. Currently, the industrial preparation of magnesium hydroxide mainly employs the conventional precipitation method, which uses soluble magnesium salts as raw materials and obtains them through a precipitation reaction under the action of an alkaline precipitant. The products obtained from this traditional process typically exhibit hexagonal flake or irregular granular morphology.

[0003] However, in practical applications, magnesium hydroxide prepared by traditional methods has the following two technical defects: First, due to the irregular morphology of the product, it is difficult to disperse it uniformly in the polymer matrix and build a continuous and effective flame retardant network, thus limiting the full realization of flame retardant efficiency; Second, the specific surface area of ​​traditional products is small, resulting in insufficient thermal stability, and it is prone to premature decomposition during high-temperature processing or long-term use, thereby affecting the flame retardant modification effect of the material.

[0004] The root cause is that the traditional preparation process failed to effectively control the growth direction of magnesium hydroxide crystals. The crystals tend to grow isotropically, resulting in irregular product morphology. The irregular crystals are densely packed, which not only results in a low specific surface area, but also makes the crystal structure easily destroyed under high temperature conditions, further exacerbating the lack of thermal stability. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing a rod-shaped magnesium hydroxide, its preparation method, and its application. By introducing sodium citrate as a crystal growth regulator and combining it with optimized process parameters, rod-shaped magnesium hydroxide with regular morphology, high specific surface area, and high thermal stability was successfully prepared.

[0006] To achieve the above objectives, the present invention provides a method for preparing rod-shaped magnesium hydroxide, comprising the following steps: S1. Mix magnesium source, water, precipitant, and crystal growth regulator to obtain a mixed reaction solution; the crystal growth regulator includes sodium citrate; S2. The mixed reaction solution is subjected to a hydrothermal reaction to obtain the rod-shaped magnesium hydroxide.

[0007] In this invention, sodium citrate, as a crystal regulator, can selectively adsorb onto specific crystal planes of magnesium hydroxide crystals, inducing the orderly stacking of plate-like units along the (001) crystal plane, thereby forming a rod-shaped morphology.

[0008] In an optional embodiment, in S1, the magnesium source includes magnesium chloride; the precipitant includes ammonia; and the concentration of the ammonia is 0.5-1.5 mol / L, preferably 1 mol / L.

[0009] In an optional implementation, in S1, the mixing process includes: The magnesium source was dissolved in water to prepare a magnesium source solution; the precipitant was slowly added dropwise to the magnesium source solution and stirred until homogeneous to obtain a mixed solution; finally, a crystal growth regulator was added to the mixed solution and stirred until the solution was homogeneous to obtain a mixed reaction solution.

[0010] In an optional embodiment, in S1, the molar ratio of magnesium ions to hydroxide ions in the mixed reaction solution is 1:(2-3). Preferably, in S1, the molar ratio of magnesium ions to hydroxide ions in the mixed reaction solution is 1:2.3. When the molar ratio of magnesium ions to hydroxide ions is 1:2.3, the resulting product has the most regular morphology and the highest aspect ratio.

[0011] In an optional embodiment, in S1, the concentration of the crystal growth regulator in the mixed reaction solution is 5-20 g / L.

[0012] In an optional embodiment, in step S2, the hydrothermal reaction temperature is 135-145°C and the time is 11-13 hours. Preferably, in step S2, the hydrothermal reaction temperature is 140°C and the time is 12 hours. Under these preferred conditions, the regulating effect of sodium citrate can be fully utilized, promoting the growth of magnesium hydroxide crystals along a specific direction to form a rod-shaped structure with a high aspect ratio.

[0013] In an optional embodiment, in S2, after the hydrothermal reaction is completed, the mixture is naturally cooled to room temperature, and solid-liquid separation is performed. The obtained solid is washed alternately with water and anhydrous ethanol 3-5 times, and finally filtered, dried and ground in sequence to obtain rod-shaped magnesium hydroxide.

[0014] The present invention also provides a rod-shaped magnesium hydroxide, which is prepared according to the method for preparing rod-shaped magnesium hydroxide.

[0015] In an optional embodiment, the specific surface area of ​​the rod-shaped magnesium hydroxide is ≥43 m². 2 / g.

[0016] In an optional embodiment, the 5% mass loss temperature (T0) of the rod-shaped magnesium hydroxide is... 5% ≥362℃, 10% mass loss temperature (T) 10% ≥382℃, the temperature at which the decomposition rate is maximum (T) max ≥402℃.

[0017] T 5% This refers to the temperature at which the sample loses 5% of its mass during thermal decomposition; T 10% This refers to the temperature at which the sample loses 10% of its mass during thermal decomposition; T max This refers to the temperature at which the decomposition rate reaches its maximum during the thermal decomposition process of a sample.

[0018] This invention also provides the application of the aforementioned rod-shaped magnesium hydroxide in the flame-retardant modification of polymer materials.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) By introducing sodium citrate as a crystal growth regulator, the present invention utilizes its directional induction effect on the growth of magnesium hydroxide crystals to transform the originally isotropic plate-like or granular products into rod-like structures with regular morphology, effectively overcoming the technical defect of irregular product morphology in traditional methods.

[0020] (2) The rod-shaped magnesium hydroxide prepared by the present invention has a regular morphology, which effectively avoids the problem of small specific surface area caused by the dense stacking of traditional sheet products, thus greatly improving the specific surface area of ​​the product and enhancing its interfacial interaction with the polymer matrix.

[0021] (3) The rod-shaped magnesium hydroxide crystal structure prepared by the present invention is more regular and has fewer defects. The decomposition process is significantly delayed in the high temperature environment, and the thermal stability is significantly better than that of traditional sheet magnesium hydroxide, which can better meet the needs of high temperature processing and application of polymer materials.

[0022] (4) The raw materials used in this invention, such as magnesium chloride, ammonia, and sodium citrate, are all common chemical raw materials with low cost. The preparation process only involves conventional steps such as mixing, hydrothermal reaction, washing, and drying. The operation is simple, the process conditions are mild, and it is easy to achieve large-scale industrial production.

[0023] (5) The rod-shaped magnesium hydroxide prepared by the present invention has a high aspect ratio rod structure, which makes it easier to build stress transmission network and flame retardant barrier in polymer matrix, and can significantly improve the mechanical properties and flame retardant effect of composite material, and has broad application prospects in the field of flame retardant modification of polymer material.

[0024] In summary, by introducing sodium citrate as a crystal growth regulator and combining it with optimized process parameters, this invention successfully prepared rod-shaped magnesium hydroxide with regular morphology, high specific surface area, and high thermal stability, effectively solving the technical problems of irregular morphology, small specific surface area, and poor thermal stability of traditional magnesium hydroxide. Attached Figure Description

[0025] Figure 1These are X-ray diffraction patterns of rod-shaped magnesium hydroxide in Examples 1-4 of this invention and magnesium hydroxide in Comparative Example 1; Figure 2 These are SEM characterization images of rod-shaped magnesium hydroxide in Examples 1-4 and magnesium hydroxide in Comparative Example 1 at a scale bar of 2 micrometers. Figure 2 In the image, 'a' is the SEM characterization image of magnesium hydroxide in Comparative Example 1. Figure 2 In the image, b is the SEM characterization image of the rod-shaped magnesium hydroxide from Example 2. Figure 2 In the image, c represents the SEM characterization image of the rod-shaped magnesium hydroxide from Example 3. Figure 2 In the image, d represents the SEM characterization image of the rod-shaped magnesium hydroxide from Example 4. Figure 2 In this image, 'e' represents the SEM characterization image of the rod-shaped magnesium hydroxide from Example 1. Figure 3 These are SEM characterization images of rod-shaped magnesium hydroxide in Example 1 and magnesium hydroxide in Comparative Example 1 at different scales in this invention; Figure 3 In the image, 'a' represents the SEM image of magnesium hydroxide in Comparative Example 1 at a scale bar of 5 micrometers. Figure 3 b in Example 1 is a SEM image of the rod-shaped magnesium hydroxide at a scale bar of 30 micrometers; Figure 4 This is the TG-DTG curve of the rod-shaped magnesium hydroxide in Example 1 of this invention; Figure 5 This is the TG-DTG curve of magnesium hydroxide in Comparative Example 1 of this invention; Figure 6 This is a comparison chart of the specific surface area of ​​rod-shaped magnesium hydroxide in Example 1 and magnesium hydroxide in Comparative Example 1 of the present invention. Detailed Implementation

[0026] The following embodiments are provided to better understand the present invention and are not limited to the described embodiments. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0027] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0028] Example 1 This embodiment provides a method for preparing rod-shaped magnesium hydroxide, including the following steps: 1.904 g of magnesium chloride was dissolved in 20 mL of water to prepare a magnesium source solution. Ammonia solution with a concentration of 1 mol / L was slowly added dropwise to the magnesium source solution, and the mixture was stirred until homogeneous, yielding a mixed solution. Finally, sodium citrate was added to the mixed solution, and stirring continued until the solution was homogeneous, yielding a mixed reaction solution. In the mixed reaction solution, the molar ratio of magnesium ions to hydroxide ions was 1:2.3, and the concentration of sodium citrate was 15 g / L.

[0029] The mixed reaction solution was transferred to a high-temperature and high-pressure reactor and subjected to a constant-temperature hydrothermal reaction at 140°C for 12 hours. After the reaction was completed, the mixture was naturally cooled to room temperature and solid-liquid separation was performed. The obtained solid was washed four times alternately with water and anhydrous ethanol. Finally, it was filtered, dried and ground in sequence to obtain rod-shaped magnesium hydroxide.

[0030] Example 2 This embodiment provides a method for preparing rod-shaped magnesium hydroxide, which differs from Example 1 only in that the concentration of sodium citrate in the mixed reaction solution is adjusted to 5 g / L.

[0031] Example 3 This embodiment provides a method for preparing rod-shaped magnesium hydroxide, which differs from Example 1 only in that the concentration of sodium citrate in the mixed reaction solution is adjusted to 10 g / L.

[0032] Example 4 This embodiment provides a method for preparing rod-shaped magnesium hydroxide, which differs from Example 1 only in that the concentration of sodium citrate in the mixed reaction solution is adjusted to 20 g / L.

[0033] Comparative Example 1 This comparative example provides a method for preparing magnesium hydroxide, which differs from Example 1 in that the addition of crystal growth regulator (sodium citrate) is omitted.

[0034] Experimental Example 1 X-ray diffraction analysis was performed on the rod-shaped magnesium hydroxide in Examples 1-4 and the magnesium hydroxide in Comparative Example 1, respectively, and the X-ray diffraction patterns of the rod-shaped magnesium hydroxide in Examples 1-4 and the magnesium hydroxide in Comparative Example 1 were obtained, as follows: Figure 1 As shown. By Figure 1It can be seen that the X-ray diffraction peaks of the products obtained in Examples 1-4 and Comparative Example 1 are in good agreement with the characteristic diffraction peaks of the magnesium hydroxide standard card PDF#74-2220. Characteristic diffraction peaks corresponding to the (001), (100), (101), (102), (110), and (111) crystal planes of hexagonal magnesium hydroxide appear at 2θ angles of approximately 18.6°, 32.9°, 38.0°, 50.9°, 58.7°, and 62.1°, respectively. The sharp diffraction peaks of all products indicate good crystallinity; and the absence of characteristic peaks from other impurity phases indicates that all products are pure-phase magnesium hydroxide. This result also shows that the addition of sodium citrate and different addition amounts (5-20 g / L) do not change the crystal structure of magnesium hydroxide, and the products maintain high phase purity, indicating that sodium citrate only plays a role in morphology regulation without introducing impurity phases or changing the crystal form.

[0035] Experiment Example 2 The rod-shaped magnesium hydroxide from Examples 1-4 and the magnesium hydroxide from Comparative Example 1 were characterized by scanning electron microscopy (SEM). The SEM images of the rod-shaped magnesium hydroxide from Examples 1-4 and the magnesium hydroxide from Comparative Example 1 at a scale bar of 2 micrometers were obtained, as shown below. Figure 2 As shown; Figure 2 In the image, 'a' is the SEM characterization image of magnesium hydroxide in Comparative Example 1. Figure 2 In the image, b is the SEM characterization image of the rod-shaped magnesium hydroxide from Example 2. Figure 2 In the image, c represents the SEM characterization image of the rod-shaped magnesium hydroxide from Example 3. Figure 2 In the image, d represents the SEM characterization image of the rod-shaped magnesium hydroxide from Example 4. Figure 2 In the figure, 'e' represents the SEM characterization image of the rod-shaped magnesium hydroxide in Example 1. The SEM characterization images of the rod-shaped magnesium hydroxide in Example 1 and the magnesium hydroxide in Comparative Example 1 at different scales are shown below. Figure 3 As shown; Figure 3 In the image, 'a' represents the SEM image of magnesium hydroxide in Comparative Example 1 at a scale bar of 5 micrometers. Figure 3 b in the figure is the SEM characterization image of the rod-shaped magnesium hydroxide in Example 1 at a scale bar of 30 micrometers.

[0036] from Figure 2 As can be seen, the product obtained in Comparative Example 1 (without sodium citrate) has an irregular plate-like structure with tightly packed crystals and an irregular morphology. The products obtained in Examples 2-4 and Example 1 (with sodium citrate) all exhibit a regular rod-like structure, indicating that the addition of sodium citrate successfully induced magnesium hydroxide crystals to grow along a specific direction, forming a rod-like morphology. Figure 3 This further demonstrates intuitively that the rod-shaped magnesium hydroxide prepared by the method of the present invention has a regular morphology and a significant aspect ratio advantage.

[0037] Experimental Example 3 Thermogravimetric analysis (TG-DTG) was performed on the rod-shaped magnesium hydroxide in Example 1 and the magnesium hydroxide in Comparative Example 1, respectively. The TG-DTG curve of the rod-shaped magnesium hydroxide in Example 1 was obtained, as shown in the figure. Figure 4 As shown; the TG-DTG curve of magnesium hydroxide in Comparative Example 1, as shown. Figure 5 As shown. From Figure 4-5 It can be seen that the thermal decomposition curve of the product of Example 1 shifts towards higher temperatures, indicating that its thermal stability is better than that of the product of Comparative Example 1.

[0038] In addition, the thermal decomposition data of the rod-shaped magnesium hydroxide in Example 1 and the magnesium hydroxide in Comparative Example 1 are recorded in Table 1.

[0039] Table 1 Thermal decomposition data

[0040] Based on the data in Table 1, the T of the rod-shaped magnesium hydroxide prepared in Example 1 is as follows: 5% The temperature was 362.98℃, an increase of 30.51℃ compared to Comparative Example 1; T 10% The temperature was 382.29℃, an increase of 35.67℃ compared to Comparative Example 1; T max The temperature was 402.51℃, which is 40.11℃ higher than that of Comparative Example 1. These results indicate that the rod-shaped magnesium hydroxide prepared in this invention has superior thermal stability.

[0041] Experiment Example 4 The specific surface area of ​​the rod-shaped magnesium hydroxide in Example 1 and the magnesium hydroxide in Comparative Example 1 was characterized, and a comparison chart of the specific surface area of ​​the rod-shaped magnesium hydroxide in Example 1 and the magnesium hydroxide in Comparative Example 1 was obtained, as shown in the figure. Figure 6 As shown. Figure 6 The results show that the specific surface area of ​​the rod-shaped magnesium hydroxide prepared in Example 1 reaches 43.5789 m². 2 / g, while the specific surface area of ​​the flake magnesium hydroxide prepared in Comparative Document 1 is only 9.5369m². 2 / g. The specific surface area of ​​the product of this invention is approximately 4.6 times that of conventional products, a significant improvement. This is mainly attributed to the fact that the rod-shaped morphology effectively avoids the dense packing of crystals, resulting in more surface exposure and a porous structure.

[0042] In summary, this invention successfully prepared magnesium hydroxide with a regular rod-shaped morphology by introducing sodium citrate as a crystal growth regulator during the preparation process. This rod-shaped magnesium hydroxide not only exhibits a significantly increased specific surface area but also demonstrates excellent thermal stability, showing promising application prospects in the field of flame-retardant modification of polymer materials.

[0043] Finally, it should be noted that the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing rod-shaped magnesium hydroxide, characterized in that, Includes the following steps: S1. Mix magnesium source, water, precipitant, and crystal growth regulator to obtain a mixed reaction solution; the crystal growth regulator includes sodium citrate; S2. The mixed reaction solution is subjected to a hydrothermal reaction to obtain the rod-shaped magnesium hydroxide.

2. The method for preparing rod-shaped magnesium hydroxide according to claim 1, characterized in that, In S1, the magnesium source includes magnesium chloride; the precipitant includes ammonia; and the concentration of the ammonia is 0.5-1.5 mol / L.

3. The method for preparing rod-shaped magnesium hydroxide according to claim 1, characterized in that, In S1, the molar ratio of magnesium ions to hydroxide ions in the mixed reaction solution is 1:(2-3).

4. The method for preparing rod-shaped magnesium hydroxide according to claim 3, characterized in that, In S1, the molar ratio of magnesium ions to hydroxide ions in the mixed reaction solution is 1:2.

3.

5. The method for preparing rod-shaped magnesium hydroxide according to claim 1, characterized in that, In S1, the concentration of the crystal growth regulator in the mixed reaction solution is 5-20 g / L.

6. The method for preparing rod-shaped magnesium hydroxide according to claim 1, characterized in that, In S2, the hydrothermal reaction is carried out at a temperature of 135-145℃ for 11-13 hours.

7. The method for preparing rod-shaped magnesium hydroxide according to claim 1, characterized in that, In S2, the hydrothermal reaction is carried out at a temperature of 140°C for 12 hours.

8. A rod-shaped magnesium hydroxide, characterized in that, The rod-shaped magnesium hydroxide was prepared according to any one of claims 1-7.

9. The rod-shaped magnesium hydroxide according to claim 8, characterized in that, The specific surface area of ​​the rod-shaped magnesium hydroxide is ≥43 m². 2 / g.

10. The application of the rod-shaped magnesium hydroxide according to claim 8 or 9 in the flame-retardant modification of polymer materials.

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