Composite whisker of calcium sulfate and basic magnesium salt and preparation method thereof

Abstract

This invention provides a method for preparing composite whiskers of calcium sulfate and basic magnesium salt, belonging to the field of whisker preparation. The method includes: treating gypsum dihydrate, magnesium sulfate, and magnesium hydroxide into micron-sized powders; weighing gypsum powder, magnesium sulfate powder, magnesium hydroxide powder, water, a crystal form control agent, and an ion regulator; adding these to a high-temperature, high-pressure reactor for hydrothermal reaction to obtain crude composite whiskers; centrifuging, dehydration, washing, and drying to obtain composite whiskers of calcium sulfate and basic magnesium salt; the crystal form control agent is at least one of aluminum salt, dodecyltrimethylammonium bromide, and sodium dodecyl sulfonate; the ion regulator includes calcium ion regulating aids and magnesium ion regulating aids. This invention, through specific conditions and aids, enables calcium sulfate and basic magnesium salt to grow into composite whiskers under the same conditions. Their two different crystal states form a special "bridging" structure, thus exhibiting superior mechanical properties when used in polymer materials.

Description

Technical Field

[0001] This invention belongs to the field of whisker preparation technology, and specifically relates to a composite whisker of calcium sulfate and basic magnesium salt and its preparation method. Background Technology

[0002] Calcium sulfate whiskers are fibrous single crystals of calcium sulfate synthesized from raw gypsum through specific processes and formulations. They possess a uniform cross-section, a complete shape, and a highly refined internal structure, making them a non-metallic material with many special properties. They are microcrystalline columnar fibers that have almost reached an ideal state. The main methods for preparing calcium sulfate whiskers are the mineral autoclaving method and the hydrothermal method, with the hydrothermal method being the most widely used. In this method, natural dihydrate gypsum ore is ground into powder and then reacted with water and a crystal-transforming agent in a high-temperature, high-pressure reactor to form hemihydrate or anhydrous calcium sulfate whiskers. After dehydration and calcination, anhydrous calcium sulfate whiskers are obtained. Anhydrous calcium sulfate whiskers prepared by this method have three main drawbacks: firstly, the diameter and aspect ratio are difficult to control; secondly, their functionality is weak, especially their reinforcing and toughening properties, with a reinforcing effect even less than talc; and thirdly, when used in polymer materials, their bridging function is not strong, resulting in a negligible impact on the thermal deformation and dimensional shrinkage of polymer materials.

[0003] Basic magnesium sulfate whiskers have an umbrella-shaped crystal structure and their molecular formula is xMgSO4·yMg(OH)2·zH2O, which can be abbreviated as xyz-type basic magnesium sulfate whiskers. With continuous research on basic magnesium sulfate whiskers, the structural types of basic magnesium sulfate whiskers prepared today also include type 138, type 165, type 153, type 213, type 235, and type 115, among which type 152 and type 153 are the most studied. Basic magnesium sulfate whiskers are a high-performance additive widely used in polymers such as resins and plastics. For example, adding basic magnesium sulfate whiskers to crystalline polymers such as PP effectively improves tensile strength, flexural strength, and flexural modulus. Furthermore, because basic magnesium sulfate whiskers decompose upon heating to produce water, they can have a flame-retardant effect. Adding them to plastics can reduce toxic gases produced during combustion, making them an ideal environmentally friendly flame-retardant material. They also significantly improve the heat distortion temperature and dimensional stability of polymer materials. However, basic magnesium sulfate whiskers, as a functional additive, have technical drawbacks such as instability and high cost.

[0004] To address the aforementioned issues, calcium sulfate whiskers and basic magnesium salt whiskers can be combined to form composite whiskers. However, research has revealed that conventionally mixing calcium sulfate and basic magnesium salt whiskers to create composite whiskers suffers from uneven mixing and weak bridging properties. Furthermore, when used as a functional additive in polymer materials, it has little effect on thermal deformation and dimensional shrinkage. Summary of the Invention

[0005] Therefore, the present invention aims to provide a composite whisker of calcium sulfate and basic magnesium salt and its preparation method, in order to solve at least one technical problem in the background art.

[0006] This invention is implemented as follows:

[0007] A method for preparing composite whiskers of calcium sulfate and basic magnesium salt, the method comprising the following steps:

[0008] Dihydrate gypsum, industrial-grade magnesium sulfate, and industrial-grade magnesium hydroxide were pretreated to obtain micron-sized gypsum powder, magnesium sulfate powder, and magnesium hydroxide powder.

[0009] Weigh out the raw materials in a predetermined proportion, including gypsum powder, magnesium sulfate powder, magnesium hydroxide powder, water, crystal form control agent and ion regulator, and add them to a high temperature and high pressure reactor for hydrothermal reaction to obtain crude composite whiskers;

[0010] Centrifugation, dehydration, washing, and drying were performed to obtain composite whiskers of calcium sulfate and basic magnesium salt.

[0011] The crystal form control agent is at least one of aluminum salt, dodecyltrimethylammonium bromide, and sodium dodecyl sulfonate.

[0012] The ion regulator includes calcium ion regulating aid and magnesium ion regulating aid.

[0013] Preferably, the raw material comprises the following components by weight percentage:

[0014] 2%-10% gypsum powder;

[0015] Magnesium sulfate powder 5%-15%;

[0016] Magnesium hydroxide powder 2%-8%;

[0017] Water 70%-90%;

[0018] Crystal form control agent 0.1%-2%;

[0019] Ion regulator 0.2%-0.8%.

[0020] Preferably, the calcium ion regulating agent is at least one of calcium citrate and calcium EDTA; the magnesium ion regulating agent is at least one of magnesium citrate and magnesium EDTA.

[0021] Preferably, the D90 of the gypsum powder, magnesium sulfate powder, and magnesium hydroxide powder is ≤2µm.

[0022] Preferably, the specific steps of the hydrothermal reaction are as follows: heating to 200℃-230℃ within a predetermined time and holding at that temperature; stirring during both the heating and holding processes; stopping stirring and releasing gas after the holding period;

[0023] The heating time is 1-2 hours, and the stirring speed is 2500-3000 rpm during heating.

[0024] The heat preservation time is 1-3 hours, and the stirring speed is 1000-1500 rpm during the heat preservation.

[0025] The venting time is 3-5 hours.

[0026] Preferably, the water content of the composite whiskers after centrifugal dehydration is less than 2%.

[0027] Preferably, the drying is performed by flash drying, and the moisture content of the composite whiskers after flash drying is less than 0.3%.

[0028] A second aspect of the present invention provides a composite whisker of calcium sulfate and basic magnesium salt, which is prepared by the above-described preparation method.

[0029] This invention involves adding gypsum powder with a D90≤2um, magnesium sulfate with a D90≤2um, magnesium hydroxide with a D90≤2um, water, a crystal form control agent, and an ion regulator into a high-temperature and high-pressure reactor. The reaction is carried out directly at a specific temperature and time to obtain composite whiskers of calcium sulfate and basic magnesium salt. After dehydration by centrifuge, washing with water, and drying by flash evaporator, the composite whiskers of calcium sulfate and basic magnesium salt are obtained.

[0030] This invention utilizes specific conditions and additives to grow calcium sulfate and basic magnesium salts under identical conditions, forming composite whiskers of calcium sulfate and basic magnesium salts. The two different crystal states create a unique "masa bridging" structure, resulting in superior mechanical properties when used in polymer materials. The composite whiskers prepared by this invention significantly contribute to improving the tensile strength, flexural strength, and flexural modulus of polymer materials, and also promote a marked increase in the heat distortion temperature and dimensional stability of polymer materials, while simultaneously reducing costs. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] A method for preparing composite whiskers of calcium sulfate and basic magnesium salt, comprising the following steps:

[0033] S1. Natural dihydrate gypsum is sorted, ground, and graded to obtain gypsum powder with D90≤2um; industrial grade magnesium sulfate is ground and graded to obtain magnesium sulfate powder with D90≤2um; industrial grade magnesium hydroxide is ground and graded to obtain magnesium hydroxide powder with D90≤2um.

[0034] S2. Weigh the raw materials in a preset proportion, including gypsum powder, magnesium sulfate powder, magnesium hydroxide powder, water, crystal form control agent and ion regulator, and add them to a high temperature and high pressure reactor for hydrothermal reaction to obtain crude composite whiskers.

[0035] The raw material comprises the following components by weight percentage:

[0036] 2%-10% gypsum powder;

[0037] Magnesium sulfate powder 5%-15%;

[0038] Magnesium hydroxide powder 2%-8%;

[0039] Water 70%-90%;

[0040] The crystal form control agent is 0.1%-2%, which is at least one of aluminum salts (such as aluminum sulfate), dodecyltrimethylammonium bromide (DTAB), and sodium dodecyl sulfonate (SDS);

[0041] Ion regulators are 0.2%-0.8%, including calcium ion regulators (calcium citrate, calcium EDTA) and magnesium ion regulators (magnesium citrate, magnesium EDTA).

[0042] The hydrothermal reaction is as follows: the temperature is raised to 200℃-230℃ within 1-2 hours, and the stirring speed is 2500rpm-3000rpm during the temperature rise; the temperature is held for 1-3 hours, and the stirring speed is 1000rpm-1500rpm during the temperature holding period; after the temperature holding period is completed, the stirring is stopped and the gas is released, and the time for the gas release is completed is 3-5 hours.

[0043] S3. Centrifuge, dehydrate, wash and dry to obtain composite whiskers of calcium sulfate and basic magnesium salt;

[0044] The crude composite whisker obtained by S2 is poured into a continuous centrifugal dehydrator for dehydration to reduce its moisture content to less than 2%. The dehydrated composite whisker is then conveyed into a continuous flash evaporator for drying to reduce its moisture content to less than 0.3%.

[0045] Example 1

[0046] A method for preparing composite whiskers of calcium sulfate and basic magnesium salt, comprising the following steps:

[0047] S1. Natural dihydrate gypsum is sorted, ground, and graded to obtain gypsum powder with D90≤2um; industrial grade magnesium sulfate is ground and graded to obtain magnesium sulfate powder with D90≤2um; industrial grade magnesium hydroxide is ground and graded to obtain magnesium hydroxide powder with D90≤2um.

[0048] S2. Weigh 2g of gypsum powder, 5g of magnesium sulfate powder, 3g of magnesium hydroxide powder, 89.7g of water, 0.1g of aluminum sulfate, 0.1g of calcium citrate, and 0.1g of magnesium citrate, and add them to a high-temperature and high-pressure reactor for hydrothermal reaction. The heating time is 1 hour, and the stirring speed is 2500 rpm during heating. Heat to 200℃ and hold for 3 hours, and the stirring speed is 1000 rpm during holding. After holding, stop stirring and release the gas. The gas release is completed in about 3 hours to obtain crude composite whiskers.

[0049] S3. The crude composite whisker obtained in S2 is poured into a continuous centrifugal dehydrator for dehydration to reduce the moisture content to less than 2%. The dehydrated composite whisker is then conveyed into a continuous flash evaporator for drying to reduce the moisture content to less than 0.3%, thus obtaining a composite whisker of calcium sulfate and basic magnesium salt.

[0050] Example 2

[0051] A method for preparing composite whiskers of calcium sulfate and basic magnesium salt, comprising the following steps:

[0052] S1. Natural dihydrate gypsum is sorted, ground, and graded to obtain gypsum powder with D90≤2um; industrial grade magnesium sulfate is ground and graded to obtain magnesium sulfate powder with D90≤2um; industrial grade magnesium hydroxide is ground and graded to obtain magnesium hydroxide powder with D90≤2um.

[0053] S2. Weigh 6g of gypsum powder, 10g of magnesium sulfate powder, 8g of magnesium hydroxide powder, 74.2g of water, 1g of aluminum sulfate, 0.25g of calcium citrate, and 0.25g of magnesium citrate, and add them to a high-temperature and high-pressure reactor for hydrothermal reaction. The heating time is 2 hours, and the stirring speed is 3000 rpm during heating. Heat to 230℃ and hold for 1 hour, and the stirring speed is 1500 rpm during holding. After holding, stop stirring and release the gas. The gas release is completed in about 5 hours to obtain crude composite whiskers.

[0054] S3. The crude composite whisker obtained in S2 is poured into a continuous centrifugal dehydrator for dehydration to reduce the moisture content to less than 2%. The dehydrated composite whisker is then conveyed into a continuous flash evaporator for drying to reduce the moisture content to less than 0.3%, thus obtaining a composite whisker of calcium sulfate and basic magnesium salt.

[0055] Example 3

[0056] A method for preparing composite whiskers of calcium sulfate and basic magnesium salt, comprising the following steps:

[0057] S1. Natural dihydrate gypsum is sorted, ground, and graded to obtain gypsum powder with D90≤2um; industrial grade magnesium sulfate is ground and graded to obtain magnesium sulfate powder with D90≤2um; industrial grade magnesium hydroxide is ground and graded to obtain magnesium hydroxide powder with D90≤2um.

[0058] S2. Weigh 10g of gypsum powder, 8g of magnesium sulfate powder, 2g of magnesium hydroxide powder, 78g of water, 1.2g of aluminum sulfate, 0.4g of calcium citrate, and 0.4g of magnesium citrate, and add them to a high-temperature and high-pressure reactor for hydrothermal reaction. The heating time is 1.5h, and the stirring speed is 2700rpm during heating. Heat to 220℃ and hold for 2h, and the stirring speed is 1300rpm during holding. After holding, stop stirring and release gas. The gas release is completed in about 4h to obtain crude composite whiskers.

[0059] S3. The crude composite whisker obtained in S2 is poured into a continuous centrifugal dehydrator for dehydration to reduce the moisture content to less than 2%. The dehydrated composite whisker is then conveyed into a continuous flash evaporator for drying to reduce the moisture content to less than 0.3%, thus obtaining a composite whisker of calcium sulfate and basic magnesium salt.

[0060] Example 4

[0061] A method for preparing composite whiskers of calcium sulfate and basic magnesium salt, comprising the following steps:

[0062] S1. Natural dihydrate gypsum is sorted, ground, and graded to obtain gypsum powder with D90≤2um; industrial grade magnesium sulfate is ground and graded to obtain magnesium sulfate powder with D90≤2um; industrial grade magnesium hydroxide is ground and graded to obtain magnesium hydroxide powder with D90≤2um.

[0063] S2. Weigh 7g of gypsum powder, 15g of magnesium sulfate powder, 5g of magnesium hydroxide powder, 70.8g of water, 2g of aluminum sulfate, 0.1g of calcium citrate, and 0.1g of magnesium citrate, and add them to a high-temperature and high-pressure reactor for hydrothermal reaction. The heating time is 3 hours, and the stirring speed is 2500 rpm during heating. The temperature is raised to 210℃ and held for 3 hours, with the stirring speed at 1500 rpm during the holding period. After the holding period, the stirring is stopped and the gas is released. The gas release is completed in about 4 hours, and the crude composite whisker product is obtained.

[0064] S3. The crude composite whisker obtained in S2 is poured into a continuous centrifugal dehydrator for dehydration to reduce the moisture content to less than 2%. The dehydrated composite whisker is then conveyed into a continuous flash evaporator for drying to reduce the moisture content to less than 0.3%, thus obtaining a composite whisker of calcium sulfate and basic magnesium salt.

[0065] Example 5

[0066] This embodiment describes a method for preparing composite whiskers of calcium sulfate and basic magnesium salt. It is based on Example 1, except that the crystal form control agent aluminum sulfate is replaced with dodecyltrimethylammonium bromide; other steps and reaction conditions are the same as in Example 1.

[0067] Example 6

[0068] This embodiment describes a method for preparing composite whiskers of calcium sulfate and basic magnesium salt, which is based on Example 1, except that the crystal form control agent aluminum sulfate is replaced with sodium dodecyl sulfonate; other steps and reaction conditions are the same as in Example 1.

[0069] Example 7

[0070] This embodiment describes a method for preparing composite whiskers of calcium sulfate and basic magnesium salt, which is based on Example 1, except that calcium citrate in the ion regulator is replaced with calcium EDTA; other steps and reaction conditions are the same as in Example 1.

[0071] Example 8

[0072] This embodiment describes a method for preparing composite whiskers of calcium sulfate and basic magnesium salt, which is based on Example 1, except that magnesium citrate in the ion regulator is replaced with magnesium EDTA; other steps and reaction conditions are the same as in Example 1.

[0073] Example 9

[0074] This embodiment describes a method for preparing composite whiskers of calcium sulfate and basic magnesium salt. It is based on Example 1, except that calcium citrate is replaced with calcium EDTA and magnesium citrate is replaced with magnesium EDTA in the ion regulator; other steps and reaction conditions are the same as in Example 1.

[0075] Comparative Example 1

[0076] This comparative example is a method for preparing a composite whisker of calcium sulfate and basic magnesium salt, which is based on Example 1 by removing the crystal form control agent aluminum sulfate; other steps and reaction conditions are the same as in Example 1.

[0077] Comparative Example 2

[0078] This comparative example is a method for preparing a composite whisker of calcium sulfate and basic magnesium salt, which is based on Example 1 by removing calcium citrate from the ion regulator; other steps and reaction conditions are the same as in Example 1.

[0079] Comparative Example 3

[0080] This comparative example is a method for preparing a composite whisker of calcium sulfate and basic magnesium salt, which is based on Example 1 by removing magnesium citrate from the ion regulator; other steps and reaction conditions are the same as in Example 1.

[0081] Comparative Example 4

[0082] This comparative example is a method for preparing composite whiskers of calcium sulfate and basic magnesium salt, which is based on Example 3, except that the holding temperature in S2 is adjusted to 190°C; other steps and reaction conditions are the same as in Example 3.

[0083] Comparative Example 5

[0084] This comparative example is a method for preparing composite whiskers of calcium sulfate and basic magnesium salt, which is based on Example 3, except that the holding temperature in S2 is adjusted to 240°C; other steps and reaction conditions are the same as in Example 3.

[0085] Comparative Example 6

[0086] This comparative example is a method for preparing composite whiskers of calcium sulfate and basic magnesium salt. It is based on Example 3, except that the heating speed in S2 is adjusted to 900 rpm; other steps and reaction conditions are the same as in Example 3.

[0087] Comparative Example 7

[0088] This comparative example is a method for preparing a composite whisker of calcium sulfate and basic magnesium salt. It is based on Example 3, except that the holding speed in S2 is adjusted to 1600 rpm; other steps and reaction conditions are the same as in Example 3.

[0089] Comparative Example 8

[0090] This comparative example is a method for preparing a composite whisker of calcium sulfate and basic magnesium salt. It is based on Example 3, except that the heating speed in S2 is adjusted to 2400 rpm; other steps and reaction conditions are the same as in Example 3.

[0091] Comparative Example 9

[0092] This comparative example is a method for preparing a composite whisker of calcium sulfate and basic magnesium salt. It is based on Example 3, except that the heating speed in S2 is adjusted to 3100 rpm; other steps and reaction conditions are the same as in Example 3.

[0093] Comparative Example 10

[0094] This comparative example illustrates a method for preparing calcium sulfate whiskers, which includes the following steps:

[0095] S1. Natural dihydrate gypsum is sorted, ground, and graded to obtain gypsum powder with D90≤2um.

[0096] S2. Weigh 2g of gypsum powder, 89.7g of water, 0.1g of aluminum sulfate, and 0.1g of calcium citrate, and add them to a high-temperature and high-pressure reactor for hydrothermal reaction. The heating time is 1 hour, and the stirring speed is 2500 rpm during heating. Heat to 200℃ and hold for 3 hours, and the stirring speed is 1000 rpm during holding. After holding, stop stirring and release the gas. The gas release is completed in about 3 hours to obtain crude whisker product.

[0097] S3. Pour the crude whisker obtained in S2 into a continuous centrifugal dehydrator for dehydration to reduce the moisture content to less than 2%. Then, transfer the dehydrated whiskers into a continuous flash evaporator for drying to reduce the moisture content to less than 0.3% to obtain calcium sulfate whiskers.

[0098] Comparative Example 11

[0099] This comparative example illustrates a method for preparing basic magnesium sulfate whiskers, which includes the following steps:

[0100] S1. Industrial-grade magnesium sulfate is ground and classified to obtain magnesium sulfate powder with D90≤2um; industrial-grade magnesium hydroxide is ground and classified to obtain magnesium hydroxide powder with D90≤2um.

[0101] S2. Weigh 8g of magnesium sulfate powder, 2g of magnesium hydroxide powder, 78g of water, 1.2g of aluminum sulfate, and 0.4g of magnesium citrate, and add them to a high-temperature and high-pressure reactor for hydrothermal reaction. The heating time is 1 hour, and the stirring speed is 2500 rpm during heating. Heat to 200℃ and hold for 3 hours, and the stirring speed is 1000 rpm during holding. After holding, stop stirring and release the gas. The gas release is completed in about 3 hours, and crude whisker product is obtained.

[0102] S3. The crude whisker obtained in S2 is poured into a continuous centrifugal dehydrator for dehydration to reduce the moisture content to less than 2%. The dehydrated whiskers are then transferred to a continuous flash evaporator for drying to reduce the moisture content to less than 0.3%, thus obtaining basic magnesium sulfate whiskers.

[0103] Whiskers (20 wt%) obtained from Examples 1 to 9 and Comparative Examples 1 to 11 were mixed with polyolefin polymer material (80 wt% PP7726) and placed in a J25 co-rotating parallel twin-screw extruder for melt blending extrusion granulation. The process conditions included: the temperature of zones 1-8 in the J25 co-rotating parallel twin-screw extruder was set to 200°C, the extrusion speed was set to 200 rpm, the feeding speed was set to 12 rpm, and the traction pelletizing speed was set to 12 rpm. After water cooling and air drying, granules were obtained. The granules were then injection molded at 220°C to obtain samples. The mechanical properties and thermal stability of the samples and PP7726 raw material were tested, and the reinforcing effect of whiskers on the properties of the polymer material was detected. The results are shown in Table 1. The testing standards for tensile strength are as follows: GB / T 1040.2-2022 "Determination of Tensile Properties of Plastics - Part 2: Test Conditions for Molded and Extruded Plastics"; for dimensional shrinkage, GB / T 17037.4-2003 "Preparation of Injection Molded Specimens for Thermoplastic Materials - Part 4: Determination of Molding Shrinkage"; for flexural strength and flexural modulus, GB / T 9341-2008 "Determination of Flexural Properties of Plastics"; for notched impact strength, GB / T 1843-2008 "Plastics - Cantilever Beam Impact Test Method"; and for heat deflection temperature, GB / T 1634.2-2019 "Determination of Load Deflection Temperature of Plastics - Part 2: Plastics and Hard Rubber". The dimensions of the test samples are adjusted according to the requirements of the testing standards.

[0104] Table 1

[0105]

[0106] As shown in Table 1, adding the composite whiskers prepared in the embodiments of the present invention to the polyolefin polymer material PP7726 has a significant enhancing effect on its mechanical properties and thermal stability.

[0107] Comparing Comparative Examples 1 to 3 with Example 1, it is evident that the composite whiskers prepared without either the crystal form control agent or the ion regulator exhibit reduced enhancement effects on the mechanical properties and thermal stability of the polymer materials. In particular, tensile strength and notched impact strength show almost no positive enhancement effect and may even exhibit a negative reduction effect. The enhancement effect on other mechanical properties and thermal stability is significantly weaker than that of Example 1. This is because the crystal form of both whiskers was not effectively controlled during the production process, resulting in relatively complex, multi-morphological, irregular inorganic powder materials.

[0108] Comparing Comparative Examples 4 and 5 with Example 1, it is evident that composite whiskers prepared at excessively low or high hydrothermal reaction temperatures exhibit reduced enhancement effects on the mechanical properties and thermal stability of the polymer materials. In particular, tensile strength and notched impact strength show almost no positive enhancement effect and may even experience a negative reduction. The enhancement effect on other mechanical properties and thermal stability is significantly weaker than in Example 1. This is because at excessively low temperatures, basic magnesium sulfate fails to grow whiskers; at excessively high temperatures, its ion regulator completely fails, preventing the growth of effective whiskers.

[0109] Comparing Comparative Examples 6 to 9 with Example 1, it is evident that composite whiskers prepared with excessively high / low holding / heating speeds during the hydrothermal reaction exhibit reduced enhancement effects on the mechanical properties and thermal stability of the polymer material. In particular, the positive enhancement effect on tensile strength is very weak, and the notched impact strength is also weakened. The enhancement effects on other mechanical properties and thermal stability are significantly weaker than in Example 1. This is because excessively low holding / heating speeds cause the whiskers to grow too long and cannot be broken up, while excessively high holding / heating speeds cause the whiskers to be continuously broken during the production process.

[0110] Comparing Comparative Examples 10 and 11 with Example 1, it can be seen that single calcium sulfate whiskers or single basic magnesium sulfate whiskers do not have the same effect on the mechanical properties, thermal stability, and reinforcement of polymer materials as the composite whiskers of Example 1. This is because calcium sulfate crystals are single columnar crystals, which are difficult to form a relatively strong inorganic bridging structure when blended with polymer materials. Although basic magnesium sulfate whiskers contribute significantly to the mechanical properties of polypropylene, their single fan-shaped structure has less impact on the mechanical properties of polymer materials than that of composite whiskers when mixed into polymer materials.

[0111] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing composite whiskers of calcium sulfate and basic magnesium salt, characterized in that, The preparation method includes the following steps: Dihydrate gypsum, industrial-grade magnesium sulfate, and industrial-grade magnesium hydroxide were pretreated to obtain micron-sized gypsum powder, magnesium sulfate powder, and magnesium hydroxide powder. Weigh out the raw materials in a predetermined proportion, including gypsum powder, magnesium sulfate powder, magnesium hydroxide powder, water, crystal form control agent and ion regulator, and add them to a high temperature and high pressure reactor for hydrothermal reaction to obtain crude composite whiskers; Centrifugation, dehydration, washing, and drying were performed to obtain composite whiskers of calcium sulfate and basic magnesium salt. The crystal form control agent is at least one of aluminum sulfate, dodecyltrimethylammonium bromide, and sodium dodecyl sulfonate. The ion regulator includes a calcium ion regulating agent and a magnesium ion regulating agent; The specific steps of the hydrothermal reaction are as follows: heating to 200℃-230℃ within a predetermined time and holding at that temperature; stirring is performed during both the heating and holding processes; stirring is stopped and gas is released after the holding process is completed. The heating time is 1-2 hours, and the stirring speed is 2500-3000 rpm during heating. The heat preservation time is 1-3 hours, and the stirring speed is 1000-1500 rpm during the heat preservation. The venting time is 3-5 hours.

2. The method for preparing composite whiskers of calcium sulfate and basic magnesium salt according to claim 1, characterized in that, The raw material comprises the following components by weight percentage: 2%-10% gypsum powder; Magnesium sulfate powder 5%-15%; Magnesium hydroxide powder 2%-8%; Water 70%-90%; Crystal form control agent 0.1%-2%; Ion regulator 0.2%-0.8%.

3. The method for preparing composite whiskers of calcium sulfate and basic magnesium salt according to claim 1, characterized in that, The calcium ion regulating agent is at least one of calcium citrate and calcium EDTA; the magnesium ion regulating agent is at least one of magnesium citrate and magnesium EDTA.

4. The method for preparing composite whiskers of calcium sulfate and basic magnesium salt according to claim 1, characterized in that, The D90 of the gypsum powder, magnesium sulfate powder, and magnesium hydroxide powder is ≤2µm.

5. The method for preparing composite whiskers of calcium sulfate and basic magnesium salt according to claim 1, characterized in that, The moisture content of the composite whiskers after centrifugal dehydration treatment is less than 2%.

6. The method for preparing composite whiskers of calcium sulfate and basic magnesium salt according to claim 1, characterized in that, The drying process employs flash drying, and the moisture content of the composite whiskers after flash drying is less than 0.3%.

7. A composite whisker of calcium sulfate and basic magnesium salt, characterized in that, The composite whiskers are prepared by the method for preparing composite whiskers of calcium sulfate and basic magnesium salt as described in any one of claims 1 to 6.

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