Super-hydrophobic modification method of basic magnesium sulfate whisker

Abstract

The invention relates to a super-hydrophobic modification method of basic magnesium sulfate whiskers. The method comprises the following steps: adding anhydrous propionic acid into a water-alcohol solution to obtain an acidic water-alcohol solution with the pH value of 4-6; adding POTS into the acidic water-alcohol solution, and mixing to obtain an acidic POTS solution; sealing the acidic POTS solution, magnetically stirring the acidic POTS solution, and stirring the acidic POTS solution at a constant temperature of 40-50 DEG C for 1-6 hours to obtain a hydrolyzed acidic POTS solution; dropwise adding the hydrolyzed acidic POTS solution into the basic magnesium sulfate whisker aqueous solution, and after dropwise adding is completed, continuously stirring and modifying for 1-5 hours to obtain a modified basic magnesium sulfate whisker solution; and carrying out suction filtration on the modified basic magnesium sulfate whisker solution obtained in the previous step, and drying to obtain the modified basic magnesium sulfate whisker. The use of a large amount of organic solvents is avoided, the method is more environment-friendly, and the obtained basic magnesium sulfate whisker has excellent super-hydrophobicity and is beneficial to wide application in the field of plastics.

Description

Technical Field

[0001] This invention relates to the field of inorganic powder whisker material modification technology, and in particular to a superhydrophobic modification method for basic magnesium sulfate whiskers. Background Technology

[0002] Basic magnesium sulfate whiskers, also known as magnesium oxysulfate whiskers, have the molecular composition xMg(OH)2·yMgSO4·zH2O (x, y, and z represent quantities). They are an inorganic non-metallic powder, most commonly found in types 512, 513, and 517. Their low cost, environmental friendliness, and unique fibrous whisker structure have led to their widespread application in various fields. On one hand, the tightly packed and highly ordered internal atomic arrangement of the whisker structure endows them with excellent mechanical properties such as high strength and high modulus, making them frequently used as a reinforcing matrix. On the other hand, basic magnesium sulfate whiskers possess thermal stability, with an initial decomposition temperature exceeding 200 °C, and their final thermal decomposition product is MgO, with a decomposition temperature reaching as high as 1000 °C. Therefore, they are often used as inorganic flame retardants and added as a matrix to various polymer materials, particularly popular in the field of engineering plastics.

[0003] However, some problems exist in the practical application of doping. Engineering plastics are organic polymers with strong oleophilicity, while basic magnesium sulfate whiskers, as inorganic materials, contain a large number of hydroxyl groups on their surface, making them a strong hydrophilic substance. When basic magnesium sulfate whiskers are used as a matrix and mixed with plastics, insolubility or repulsion occurs at the interface, resulting in poor interfacial compatibility. Furthermore, in this environment surrounded by oleophilic molecules, the basic magnesium sulfate whiskers, which already have a large number of hydroxyl groups, are more likely to aggregate, leading to severe agglomeration. This agglomeration phenomenon results in a severely uneven distribution of the matrix in the plastic, which in turn leads to unsatisfactory flame retardant and mechanical properties of the doped composite material.

[0004] To address this issue and improve the interfacial compatibility between plastics and basic magnesium sulfate whiskers, the proposed method is to surface modify the basic magnesium sulfate whiskers. The aim is to coat the surface of the particles with a layer of oleophilic substance, which can reduce the repulsion between the inorganic powder and the plastic interface and effectively prevent the agglomeration of basic magnesium sulfate whiskers. The traditional surface modification process uses surfactants or coupling agents, which are first hydrolyzed with an alcohol solution, and then the basic magnesium sulfate whiskers are directly added to the prepared modifier solution for surface modification. The disadvantages of this process are: (1) In this oleophilic environment, the direct addition of basic magnesium sulfate whiskers may cause slight agglomeration, resulting in incomplete modification. (2) A large amount of organic solvent is required, and after the modification reaction is completed, the modifier may remain, which can easily cause pollution. For example, patent CN108276608A discloses a modification method that uses the bifunctional molecular structure of KH-570 (containing both hydrophilic and hydrophobic ends) to modify basic magnesium sulfate whiskers. Although this avoids the use of large amounts of organic solvents, the whiskers are prone to internal aggregation, and the hydrophobicity of the modifier's functional groups is insufficient, resulting in an oleophilic index generally below 30%, a contact angle generally around 110°, a relatively small interaction force with plastics, weak surface polymerization, and the final step requires high-temperature activation. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a superhydrophobic surface modification method for basic magnesium sulfate whiskers. This method uses a perfluorooctylsilane coupling agent (POTS) with lower surface energy to modify the basic magnesium sulfate whiskers. During the modification process, a POTS aqueous alcohol solution is added dropwise to the whisker aqueous solution, which effectively improves whisker agglomeration and reduces incomplete modification. This method not only effectively avoids the use of large amounts of organic solvents but also ensures successful superhydrophobic modification of the basic magnesium sulfate whisker surface, enhancing interfacial polymerization and compatibility with plastics.

[0006] The technical solution of this invention is as follows: A method for superhydrophobic modification of basic magnesium sulfate whiskers, comprising the following steps: (1) Add anhydrous propionic acid to the aqueous alcohol solution to obtain an acidic aqueous alcohol solution with a pH of 4 to 6; In the aqueous alcohol solution, the volume ratio of anhydrous ethanol to deionized water is 75~95:5~25. (2) Preparation: Add POTS to the water-alcohol solution and mix to obtain an acidic POTS solution; For each 10 mL of acidic aqueous alcoholic solution, add 0.015~0.15 g of POTS; (3) Seal the acidic POTS solution and stir it magnetically. Stir it at a constant temperature of 40~50℃ for 1~6 h to obtain the hydrolyzed acidic POTS solution. (4) At a modification temperature range of 40~80 ℃, the hydrolyzed acidic POTS solution was added dropwise to the basic magnesium sulfate whisker aqueous solution. After the addition was completed, the modification was continued by stirring for 1~5 h to obtain the modified basic magnesium sulfate whisker solution. In the hydrolyzed acidic POTS solution and the aqueous solution of basic magnesium sulfate whiskers, the mass of POTS is 3-30% of the mass of basic magnesium sulfate whiskers, that is, in the case of 1 g of basic magnesium sulfate whiskers, the amount of POTS added is 0.03-0.3 g. The dripping time is 35~150 min; (5) The modified basic magnesium sulfate whisker solution obtained in the previous step is filtered and dried to obtain modified basic magnesium sulfate whiskers.

[0007] The preparation method of the basic magnesium sulfate whisker aqueous solution is as follows: after mixing basic magnesium sulfate whiskers with water, the mixture is ultrasonically dispersed and mechanically stirred to obtain a basic magnesium sulfate whisker aqueous solution. The mass ratio of basic magnesium sulfate whiskers to water is 1:30~60; the stirring rate is 400~600 r / min.

[0008] The optimal quality ratio of basic magnesium sulfate whiskers to deionized water is 40-50:1.

[0009] In step (1), the optimal volume ratio of water to alcohol solution is 1:9.

[0010] In step (1), the optimal hydrolysis pH for the aqueous alcohol solution is 4.5 to 5.5.

[0011] In step (2), 0.035~0.05 g of POTS is added to every 10 mL of acidic aqueous alcohol solution.

[0012] In step (3), the hydrolysis stirring rate is 150~200 rpm, and the optimal hydrolysis time is 3~4 h.

[0013] In step (4), the optimal modification temperature is 50~60℃ and the stirring modification time is 3~3.5 h.

[0014] In step (5), the drying temperature is 70~80 ℃ and the drying time is 4~5 h.

[0015] The essential features of this invention are: In existing surface modification processes, basic magnesium sulfate whisker solids are usually added directly to a prepared modifier solution. Because there are a large number of hydroxyl groups on the surface of basic magnesium sulfate whiskers, hydrogen bonds are easily formed. In lipophilic organic solutions, agglomeration is more likely to occur, and the concentration is uneven in some areas during the modification reaction. The whisker surface will be repeatedly adsorbed and covered, thus affecting the surface modification effect of the whiskers. In addition, this method requires the use of a large amount of organic solvent to hydrolyze the whiskers and to ensure that the whiskers are uniformly dispersed in the solution. In this invention, the selected modifier is perfluorooctylsilane coupling agent (POTS). This substance has a lower surface energy and contains F groups in addition to hydrophobic silanols, giving it superhydrophobicity. During the modification process, a basic magnesium sulfate whisker-water solution is first prepared to ensure that the whiskers can be uniformly dispersed in water and to avoid whisker agglomeration. Then, the modifier solution is added dropwise to the whisker-water solution so that the modifier can be fully adsorbed on the uniformly dispersed whisker surface. This avoids the use of a large amount of organic solvent and results in a lower surface energy, better hydrophobic effect, and enhanced surface polymerization force with plastics.

[0016] The beneficial effects of this invention are as follows: In summary, this invention provides a novel method for superhydrophobic surface modification of basic magnesium sulfate whiskers. This method successfully avoids the use of large amounts of organic solvents by providing a new surface modification process, making it more environmentally friendly. By selecting POTS, a modifier with lower surface energy, the basic magnesium sulfate whiskers achieve superior superhydrophobicity (30.6%~37.5%, contact angle range of 130°~136°), which is beneficial for its widespread application in the plastics field. Attached Figure Description

[0017] Figure 1 A process flow diagram for the superhydrophobic modification of basic magnesium sulfate whiskers; Figure 2 The XRD patterns of basic magnesium sulfate whiskers before modification and after modification in Example 1 are shown. Figure 3 FTIR spectra of basic magnesium sulfate whiskers before modification and after modification in Example 1; Figure 4 The images show the contact angle measurements of basic magnesium sulfate whiskers before and after modification according to Example 1. Figure 5 This is a SEM image of the basic magnesium sulfate whiskers obtained in Example 1. Detailed Implementation

[0018] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0019] The basic magnesium sulfate whiskers involved in this invention are a known material. The specific preparation method of the whiskers used in the following examples is referenced in the literature (DOI: 10.1016 / j.matchemphys.2004.06.021): Prepare 30 ml of magnesium sulfate heptahydrate solution (1.6~2 mol / L) and 10 ml of sodium hydroxide solution (1~3 mol / L); mix and react the two solutions, then transfer them to a reaction vessel and carry out a hydrothermal reaction at a high temperature of 160~220 °C for 1~6 h, thereby obtaining the basic magnesium sulfate whisker product, which is then filtered, dried, and used in the following experiments. However, this method is not limited to this.

[0020] Example 1: First, 1 g of basic magnesium sulfate whiskers was mixed with 50 mL of water and sonicated for 1 h. Then, the mixture was transferred to a reactor and stirred at a constant temperature of 60 °C for 3 h to obtain solution a. Next, 18 mL of anhydrous ethanol and 2 mL of water were mixed to obtain a hydro-alcohol solution. An appropriate amount of anhydrous propionic acid was added to adjust the pH to 5.5. Then, 0.1 g of POTS was added to the adjusted acidic hydro-alcohol solution and placed in a sealed water bath at 40 °C with magnetic stirring for 3 h at a magnetic stirring speed of 150 rpm. Finally, the mixture was added dropwise to solution a at a rate of 1.5 mL / min using a peristaltic pump. After the addition was complete, the mixture was stirred continuously for 3 h. After completion, the mixture was removed and dried at 70 °C for 4 h.

[0021] In the above reaction, since POTS is a fluorosilane coupling agent, it needs to be added to an acidic aqueous alcohol solution first to fully hydrolyze its triethoxysilane into silanol and ethanol. Then, this solution is added dropwise to the whisker aqueous solution for modification. This ensures sufficient contact between POTS and basic magnesium sulfate whiskers. One end of the silanol molecule can form a chemical bond with the hydroxyl groups on the whisker surface (Si-O-Mg bond), and the F group can form a weak coordination bond (F-Mg bond). The other end is highly hydrophobic, meaning it is exposed on the whisker surface after covering it, thus making the modified whiskers superhydrophobic. The two types of chemical bonds formed by this molecule make its interaction with whiskers stronger than that of general silane coupling agents, resulting in better stability in high-temperature or high-humidity environments.

[0022] Example 2: All other steps are the same as in Example 1, except that the modification temperature is set to 50 °C.

[0023] Example 3: All other steps are the same as in Example 1, except that the hydrolysis pH is adjusted to 5.

[0024] Example 4: The other steps are the same as in Example 1, except that the mass of basic magnesium sulfate whiskers remains unchanged and the amount of POTS added is changed to 0.07 g.

[0025] Example 5: All other steps are the same as in Example 1, except that the hydrolysis time is 4 hours.

[0026] Example 6: All other steps are the same as in Example 1, except that the stirring time is 3.5 h after the addition is completed.

[0027] Comparative Example 1: All other steps are the same as in Example 1, except that the modification temperature is set to 30 °C.

[0028] Comparative Example 2: All other steps are the same as in Example 1, except that the hydrolysis pH is adjusted to 2.

[0029] Comparative Example 3: All other steps are the same as in Example 1, except that the hydrolysis time is 1 h.

[0030] Comparative Example 4: All other steps are the same as in Example 1, except that the drip rate of the peristaltic pump is 5 ml / min.

[0031] Comparative Example 5: All other steps are the same as in Example 1, except that the stirring time is 1 hour after the addition is completed.

[0032] Comparative Example 6: The other steps are the same as in Example 1, except that the amount of POTS added is 3% of the mass of basic magnesium sulfate whiskers in the reaction.

[0033] The contact angle and oleophilic index of the products obtained in the above examples were measured, and the results are shown in Table 1.

[0034] Contact angle testing method: The sample powder was pressed into circular tablets with a diameter of 20 mm and a thickness of approximately 2 mm using an FYD type benchtop electric tablet press. The pressure was 20 kPa, and the holding time was 3 min. The wetting contact angle of the tablets was measured using a DSA30 type contact angle meter. The water droplet volume was 5 μL, and the residence time was 20 s. At least 4 different locations were selected for each tablet, and the result was the average of 4 measurements.

[0035] Method for determining the oleophilic index: Add the modified whisker sample to 50 mL of water, stir, and let stand; after the suspension separates into layers, add methanol dropwise until the sample floating on the water surface is completely wetted and settles, and record the amount of methanol consumed, V, according to the formula: The lipophilicity index was calculated.

[0036] Table 1. Modification process and effects of basic magnesium sulfate whiskers

[0037] As shown in Table 1, the optimal modification process with the best hydrophobic effect and highest oleophilic index is as follows: a basic magnesium sulfate whisker-water mixture ratio of 50:1, a modification temperature of 60 ℃, a mechanical stirring rate of 500 r / min, a water-alcohol solution ratio of 18:2, a POTS addition amount of 10 wt%, a hydrolysis pH of 5.5, a hydrolysis time of 3 h, a POTS solution drop rate of 1.5 ml / min, and a modification time of 3 h. Using the superhydrophobic modification method for basic magnesium sulfate whiskers of this invention, the contact angle can reach a maximum of 136°, with most contact angles around 130°, and the oleophilic index exceeding 30%. This method demonstrates excellent hydrophobicity and significant modification effect.

[0038] As can be seen from the above embodiments, this invention selects POTS as the surface modifier for basic magnesium sulfate whiskers and explores the optimal parameters and range of the related processes. The modification effect is outstanding and significant, avoiding the use of large amounts of organic solvents. After superhydrophobic modification of basic magnesium sulfate whiskers, the repulsion between inorganic whisker materials and oleophilic materials is reduced, and the interfacial compatibility between the two is optimized. The superhydrophobic modified basic magnesium sulfate whiskers have a wider range of applications and broader application prospects.

[0039] The modifiers and related modification processes used in this invention have not yet been reported.

[0040] The above description is merely an enumeration of specific embodiments of the present invention. Any parts not described in detail should be understood as being implemented using the same equipment and methods already existing in the art. Any non-inventive modifications made by those skilled in the art based on the present invention are within the scope of protection of this invention.

[0041] Matters not covered in this invention are common knowledge.

Claims

1. A method for superhydrophobic modification of basic magnesium sulfate whiskers, characterized in that, The method includes the following steps: (1) Add anhydrous propionic acid to the aqueous alcohol solution to obtain an acidic aqueous alcohol solution with a pH of 4 to 6; In the aqueous alcohol solution, the volume ratio of anhydrous ethanol to deionized water is 75~95:5~25. (2) Add POTS to an acidic aqueous alcohol solution and mix to obtain an acidic POTS solution; For each 10 mL of acidic aqueous alcoholic solution, add 0.015~0.15 g of POTS; (3) Seal the acidic POTS solution and stir it magnetically. Stir it at a constant temperature of 40-50℃ for 1-6 h to obtain the hydrolyzed POTS solution. (4) At 40~80 ℃, the hydrolyzed POTS solution was added dropwise to the basic magnesium sulfate whisker aqueous solution. After the addition was completed, the mixture was stirred and modified for 1~5 h to obtain the modified basic magnesium sulfate whisker solution. The mass of POTS is 3-30% of the mass of basic magnesium sulfate whiskers; (5) The modified basic magnesium sulfate whisker solution obtained in the previous step is filtered and dried to obtain modified basic magnesium sulfate whiskers.

2. The method for superhydrophobic modification of basic magnesium sulfate whiskers as described in claim 1, characterized in that, The preparation method of the basic magnesium sulfate whisker aqueous solution is as follows: after mixing basic magnesium sulfate whiskers with water, the mixture is ultrasonically dispersed and mechanically stirred to obtain a basic magnesium sulfate whisker aqueous solution. The mass ratio of basic magnesium sulfate whiskers to water is 1:30~60; the stirring rate is 400~600 r / min.

3. The method for superhydrophobic modification of basic magnesium sulfate whiskers as described in claim 1, characterized in that, In step (1), the optimal volume ratio of water to alcohol solution is 1:9; the optimal hydrolysis pH of water to alcohol solution is 4.5~5.

5.

4. The method for superhydrophobic modification of basic magnesium sulfate whiskers as described in claim 1, characterized in that, In step (2), 0.035~0.05 g of POTS is added to every 10 mL of acidic aqueous alcohol solution.

5. The method for superhydrophobic modification of basic magnesium sulfate whiskers as described in claim 1, characterized in that, In step (3), the hydrolysis stirring rate is 150~200 rpm, and the hydrolysis time is 3~4 h; In step (4), the modification temperature is 50~60℃ and the stirring modification time is 3~3.5 h; In step (5), the drying temperature is 70~80 ℃ and the drying time is 4~5 h.

6. The method for superhydrophobic modification of basic magnesium sulfate whiskers as described in claim 1, characterized in that, In step (4), the dripping time is 35~150 min.

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