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

Abstract

The invention provides a preparation method of composite whiskers of calcium sulfate and basic magnesium salt, and belongs to the field of whisker preparation. The method comprises the following steps: respectively treating dihydrate gypsum, thiomagnesium acid and magnesium hydroxide into micron-sized powder, weighing gypsum powder, magnesium sulfate powder, magnesium hydroxide powder, water, a crystal form control agent and an ion regulator, and adding into a high-temperature and high-pressure reaction kettle for hydrothermal reaction to obtain a composite whisker crude product; centrifugally dewatering, washing and drying to obtain composite crystal whiskers of calcium sulfate and basic magnesium salt; the crystal form control agent adopts at least one of aluminum salt, dodecyl trimethyl ammonium bromide and sodium dodecyl sulfate; the ion regulator comprises a calcium ion regulating aid and a magnesium ion regulating aid. The calcium sulfate and the basic magnesium salt grow to form the composite whisker under the same condition through specific conditions and auxiliaries, the two different crystal form states of the composite whisker form a special folding stool bridging structure, and therefore the composite whisker shows more excellent mechanical performance when being applied to high polymer materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of whisker preparation, and particularly relates to a composite whisker of calcium sulfate and basic magnesium salt and a preparation method thereof. Background Art

[0002] Calcium sulfate whisker is a calcium sulfate fibrous single crystal synthesized from gypsum as raw material through a specific process and formula. It has a uniform cross-section, a complete shape, and a highly perfect internal structure. It is a non-metallic material with many special properties and is a microcrystalline columnar fiber that almost reaches an ideal state. The main preparation methods of calcium sulfate whisker are mineral autoclaving method and hydrothermal method, among which the hydrothermal method is the most widely used. After grinding natural dihydrate gypsum ore into powder, it forms hemihydrate calcium sulfate whisker or anhydrous calcium sulfate whisker with water and a crystal conversion agent under the conditions of a high-temperature and high-pressure reaction kettle, and becomes anhydrous calcium sulfate whisker after dehydration and calcination. The anhydrous calcium sulfate whisker prepared by this method has three disadvantages: one is that the diameter and aspect ratio are not easy to control; the second is that the functionality is not strong, especially the strengthening and toughening functions are not strong, and the strengthening effect is not as good as that of talcum powder; the third is that when applied in polymer materials, its bridging function is not firm, so the influence on the thermal deformation and dimensional shrinkage of polymer materials is not obvious.

[0003] The crystal form of basic magnesium sulfate whisker is an umbrella structure, and its molecular formula is xMgSO4·yMg(OH)2·zH2O, which can be abbreviated as xyz-type basic magnesium sulfate whisker. With the continuous research on basic magnesium sulfate whisker, the currently prepared structural types of basic magnesium sulfate whisker also include 138-type, 165-type, 153-type, 213-type, 235-type, 115-type, among which the most studied are 152-type and 153-type. Basic magnesium sulfate whisker is an additive with excellent performance and is widely used as an additive for polymers such as resins and plastics; for example, when basic magnesium sulfate whisker is added to crystalline polymers such as PP, the tensile strength, flexural strength, and flexural modulus are effectively improved; in addition, since basic magnesium sulfate whisker decomposes to generate water when heated, it can play a flame-retardant effect, and when added to plastics, it can reduce the toxic gases generated by combustion, which is an ideal environmentally friendly flame-retardant material and significantly improves the heat distortion temperature and dimensional stability of polymer materials. However, as a functional additive, basic magnesium sulfate whisker has technical defects such as instability and high cost.

[0004] To solve the above problems, calcium sulfate whisker and basic magnesium salt whisker can be combined to form a composite whisker. It has been found through research that when calcium sulfate whisker and basic magnesium salt whisker are conventionally mixed as a composite whisker, there are disadvantages of uneven mixing and still not firm bridging function. When it is used as a functional additive for polymer materials, the influence on thermal deformation and dimensional shrinkage is not obvious. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a composite whisker of calcium sulfate and basic magnesium salt and a preparation method thereof, aiming to solve at least one technical problem in the background art.

[0006] The present invention is implemented as follows: A preparation method of a composite whisker of calcium sulfate and basic magnesium salt, the preparation method comprising the following steps: Gypsum dihydrate, industrial grade magnesium sulfate, and industrial grade magnesium hydroxide are pretreated respectively to obtain micron-sized gypsum powder, magnesium sulfate powder, and magnesium hydroxide powder; Weigh raw materials in a preset ratio, the raw materials 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 reaction kettle for hydrothermal reaction to obtain a crude product of the composite whisker; Centrifugal dehydration, washing with water, and drying are carried out to obtain a composite whisker of calcium sulfate and basic magnesium salt; Among them, the crystal form control agent adopts at least one of aluminum salts, dodecyltrimethylammonium bromide, and sodium dodecylsulfonate; The ion regulator includes a calcium ion regulating auxiliary agent and a magnesium ion regulating auxiliary agent.

[0007] Preferably, the raw materials contain the following components in weight percentages: Gypsum powder 2% - 10%; 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%.

[0008] Preferably, the calcium ion regulating auxiliary agent adopts at least one of calcium citrate and EDTA calcium; the magnesium ion regulating auxiliary agent adopts at least one of magnesium citrate and EDTA magnesium.

[0009] Preferably, D90 of the gypsum powder, magnesium sulfate powder, and magnesium hydroxide powder ≤ 2 μm.

[0010] Preferably, the specific steps of the hydrothermal reaction are: heating to 200°C - 230°C within a predetermined time for heat preservation treatment; stirring operations are carried out during both the heating and heat preservation processes; stop stirring and release gas after the heat preservation ends; Among them, the time used for heating is 1h - 2h, and the stirring speed during heating is 2500rpm - 3000rpm; The heat preservation time is 1h - 3h, and the stirring speed during heat preservation is 1000rpm - 1500rpm; The gas release time is 3h - 5h.

[0011] Preferably, the water content of the composite whiskers after centrifugal dehydration treatment is less than 2%.

[0012] Preferably, flash drying is used for the drying, and the water content of the composite whiskers after flash drying is less than 0.3%.

[0013] The second aspect of the present invention provides a composite whisker of calcium sulfate and basic magnesium salt, which is prepared by the above preparation method.

[0014] The present invention adds gypsum powder with D90≤2um, magnesium sulfate with D90≤2um, magnesium hydroxide with D90≤2um, water, crystal form control agent and ion regulator into a high-temperature and high-pressure reaction kettle, and directly reacts at a specific temperature and time to obtain a composite whisker of calcium sulfate and basic magnesium salt, and after dehydration by a centrifuge, washing with water, and drying by a flash dryer, a composite whisker of calcium sulfate and basic magnesium salt is obtained.

[0015] The present invention enables calcium sulfate and basic magnesium salt to grow under the same conditions through specific conditions and additives, forming a composite whisker of calcium sulfate and basic magnesium salt. Its two different crystal forms form a special "maza bridging" structure, so that it shows more excellent mechanical properties when applied in polymer materials. The composite whisker prepared by the present invention makes a significant contribution to the improvement of the tensile strength, bending strength and bending modulus of polymer materials, promotes the obvious improvement of the heat distortion temperature and dimensional stability of polymer materials, and also reduces the cost. Detailed implementation mode

[0016] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific implementation cases described here are only used to explain the present invention and are not used to limit the present invention.

[0017] A preparation method of a composite whisker of calcium sulfate and basic magnesium salt, which comprises the following steps: S1. Sort, grind and classify natural dihydrate gypsum to obtain gypsum powder with D90≤2um; grind and classify industrial grade magnesium sulfate to obtain magnesium sulfate powder with D90≤2um; grind and classify industrial grade magnesium hydroxide to obtain magnesium hydroxide powder with D90≤2um.

[0018] S2. Weigh a preset proportion of raw materials, the raw materials include gypsum powder, magnesium sulfate powder, magnesium hydroxide powder, water, crystal form control agent and ion regulator, and add them into a high-temperature and high-pressure reaction kettle for hydrothermal reaction to obtain a crude composite whisker; The raw materials contain the following components in weight percentage: Gypsum powder 2%-10%; Magnesium sulfate powder 5%-15%; Magnesium hydroxide powder: 2% - 8%; Water: 70% - 90%; Crystal form control agent: 0.1% - 2%, which is at least one of aluminum salts (such as aluminum sulfate), dodecyl trimethyl ammonium bromide (DTAB), and sodium dodecyl sulfonate (SDS); Ion regulator: 0.2% - 0.8%, which includes calcium ion regulating aids (calcium citrate, calcium EDTA) and magnesium ion regulating aids (magnesium citrate, magnesium EDTA).

[0019] The hydrothermal reaction is specifically as follows: Heat up to 200°C - 230°C within 1 h - 2 h, and the stirring speed during heating is 2500 rpm - 3000 rpm; keep warm for 1 h - 3 h, and the stirring speed during heat preservation is 1000 rpm - 1500 rpm; stop stirring and vent after heat preservation, and the time for venting to complete is 3 h - 5 h.

[0020] S3. Centrifugal dehydration, water washing, and drying to obtain the composite whiskers of calcium sulfate and basic magnesium salt; Pour the crude composite whiskers prepared in S2 into a continuous centrifugal dehydrator for dehydration to make the moisture content less than 2%, and transport the dehydrated composite whiskers into a continuous flash dryer for drying to make the moisture content less than 0.3%.

[0021] Example 1 A preparation method of composite whiskers of calcium sulfate and basic magnesium salt, which includes the following steps: S1. Sort, grind, and classify natural dihydrate gypsum to obtain gypsum powder with D90 ≤ 2 μm; grind and classify industrial grade magnesium sulfate to obtain magnesium sulfate powder with D90 ≤ 2 μm; grind and classify industrial grade magnesium hydroxide to obtain magnesium hydroxide powder with D90 ≤ 2 μm.

[0022] S2. Weigh 2 g of gypsum powder, 5 g of magnesium sulfate powder, 3 g of magnesium hydroxide powder, 89.7 g of water, 0.1 g of aluminum sulfate, 0.1 g of calcium citrate, and 0.1 g of magnesium citrate, add them to a high-temperature and high-pressure reaction kettle for hydrothermal reaction, where the heating time is 1 h and the stirring speed during heating is 2500 rpm; heat up to 200°C and keep warm for 3 h, and the stirring speed during heat preservation is 1000 rpm; stop stirring and vent after heat preservation, and it takes about 3 h to complete venting to obtain crude composite whiskers.

[0023] S3. Pour the crude composite whiskers prepared in S2 into a continuous centrifugal dehydrator for dehydration to make the moisture content less than 2%, and transport the dehydrated composite whiskers into a continuous flash dryer for drying to make the moisture content less than 0.3% to obtain the composite whiskers of calcium sulfate and basic magnesium salt.

[0024] Example 2

[0025] A preparation method of composite whiskers of calcium sulfate and basic magnesium salt, comprising the following steps: S1. Sort, grind, and classify natural dihydrate gypsum to obtain gypsum powder with D90 ≤ 2 μm; grind and classify industrial-grade magnesium sulfate to obtain magnesium sulfate powder with D90 ≤ 2 μm; grind and classify industrial-grade magnesium hydroxide to obtain magnesium hydroxide powder with D90 ≤ 2 μm.

[0026] S2. Weigh 6 g of gypsum powder, 10 g of magnesium sulfate powder, 8 g of magnesium hydroxide powder, 74.2 g of water, 1 g of aluminum sulfate, 0.25 g of calcium citrate, and 0.25 g of magnesium citrate, add them to a high-temperature and high-pressure reaction kettle for hydrothermal reaction. The heating-up time is 2 h, and the stirring speed during heating-up is 3000 rpm; heat up to 230 °C and keep warm for 1 h, and the stirring speed during heat preservation is 1500 rpm; stop stirring and deflate after heat preservation, and it takes about 5 h to complete deflation to obtain crude composite whiskers.

[0027] S3. Pour the crude composite whiskers obtained in S2 into a continuous centrifugal dehydrator for dehydration to make the moisture content less than 2%, and transport the dehydrated composite whiskers into a continuous flash dryer for drying to make the moisture content less than 0.3% to obtain composite whiskers of calcium sulfate and basic magnesium salt.

[0028] Example 3 A preparation method of composite whiskers of calcium sulfate and basic magnesium salt, comprising the following steps: S1. Sort, grind, and classify natural dihydrate gypsum to obtain gypsum powder with D90 ≤ 2 μm; grind and classify industrial-grade magnesium sulfate to obtain magnesium sulfate powder with D90 ≤ 2 μm; grind and classify industrial-grade magnesium hydroxide to obtain magnesium hydroxide powder with D90 ≤ 2 μm.

[0029] S2. Weigh 10 g of gypsum powder, 8 g of magnesium sulfate powder, 2 g of magnesium hydroxide powder, 78 g of water, 1.2 g of aluminum sulfate, 0.4 g of calcium citrate, and 0.4 g of magnesium citrate, add them to a high-temperature and high-pressure reaction kettle for hydrothermal reaction. The heating-up time is 1.5 h, and the stirring speed during heating-up is 2700 rpm; heat up to 220 °C and keep warm for 2 h, and the stirring speed during heat preservation is 1300 rpm; stop stirring and deflate after heat preservation, and it takes about 4 h to complete deflation to obtain crude composite whiskers.

[0030] S3. Pour the crude composite whiskers obtained in S2 into a continuous centrifugal dehydrator for dehydration to make the moisture content less than 2%, and transport the dehydrated composite whiskers into a continuous flash dryer for drying to make the moisture content less than 0.3% to obtain composite whiskers of calcium sulfate and basic magnesium salt.

[0031] Example 4 A preparation method of composite whiskers of calcium sulfate and basic magnesium salt, which comprises the following steps: S1. Sort, grind and classify natural dihydrate gypsum to obtain gypsum powder with D90 ≤ 2 μm; grind and classify industrial grade magnesium sulfate to obtain magnesium sulfate powder with D90 ≤ 2 μm; grind and classify industrial grade magnesium hydroxide to obtain magnesium hydroxide powder with D90 ≤ 2 μm.

[0032] S2. Weigh 7 g of gypsum powder, 15 g of magnesium sulfate powder, 5 g of magnesium hydroxide powder, 70.8 g of water, 2 g of aluminum sulfate, 0.1 g of calcium citrate and 0.1 g of magnesium citrate, add them into a high-temperature and high-pressure reactor for hydrothermal reaction. The heating time is 3 h, and the stirring speed during heating is 2500 rpm; heat up to 210 °C and keep it for 3 h, and the stirring speed during heat preservation is 1500 rpm; stop stirring and release gas after heat preservation, and it takes about 4 h to complete gas release to obtain crude composite whiskers.

[0033] S3. Pour the crude composite whiskers prepared in S2 into a continuous centrifugal dehydrator for dehydration to make the moisture content less than 2%, and transport the dehydrated composite whiskers into a continuous flash dryer for drying to make the moisture content less than 0.3% to obtain composite whiskers of calcium sulfate and basic magnesium salt.

[0034] Example 5

[0035] This example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt, in which the crystal form control agent aluminum sulfate is replaced by dodecyltrimethylammonium bromide on the basis of Example 1; other steps and reaction conditions are the same as those in Example 1.

[0036] Example 6

[0037] This example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt, in which the crystal form control agent aluminum sulfate is replaced by sodium dodecyl sulfonate on the basis of Example 1; other steps and reaction conditions are the same as those in Example 1.

[0038] Example 7

[0039] This example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt, in which calcium citrate in the ion regulator is replaced by EDTA calcium on the basis of Example 1; other steps and reaction conditions are the same as those in Example 1.

[0040] Example 8 This example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt, in which magnesium citrate in the ion regulator is replaced by EDTA magnesium on the basis of Example 1; other steps and reaction conditions are the same as those in Example 1.

[0041] Example 9

[0042] This example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt. On the basis of Example 1, calcium citrate in the ionic regulator is replaced by calcium EDTA, and magnesium citrate is replaced by magnesium EDTA; other steps and reaction conditions are the same as those in Example 1.

[0043] Comparative Example 1 This comparative example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt. On the basis of Example 1, aluminum sulfate as the crystal form control agent is deleted; other steps and reaction conditions are the same as those in Example 1.

[0044] Comparative Example 2 This comparative example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt. On the basis of Example 1, calcium citrate in the ionic regulator is deleted; other steps and reaction conditions are the same as those in Example 1.

[0045] Comparative Example 3 This comparative example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt. On the basis of Example 1, magnesium citrate in the ionic regulator is deleted; other steps and reaction conditions are the same as those in Example 1.

[0046] Comparative Example 4 This comparative example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt. On the basis of Example 3, the heat preservation temperature in S2 is adjusted to 190 °C; other steps and reaction conditions are the same as those in Example 3.

[0047] Comparative Example 5 This comparative example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt. On the basis of Example 3, the heat preservation temperature in S2 is adjusted to 240 °C; other steps and reaction conditions are the same as those in Example 3.

[0048] Comparative Example 6 This comparative example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt. On the basis of Example 3, the heat preservation rotation speed in S2 is adjusted to 900 rpm; other steps and reaction conditions are the same as those in Example 3.

[0049] Comparative Example 7 This comparative example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt. On the basis of Example 3, the heat preservation rotation speed in S2 is adjusted to 1600 rpm; other steps and reaction conditions are the same as those in Example 3.

[0050] Comparative Example 8 This comparative example is a preparation method of composite whiskers of calcium sulfate and basic magnesium salt. On the basis of Example 3, the heating-up rotation speed in S2 is adjusted to 2400 rpm; other steps and reaction conditions are the same as those in Example 3.

[0051] Comparative Example 9 This comparative example is a method for preparing a composite whisker of calcium sulfate and basic magnesium salt. On the basis of Example 3, the heating rotation speed in S2 was adjusted to 3100 rpm; other steps and reaction conditions were the same as those in Example 3.

[0052] Comparative Example 10 This comparative example is a method for preparing calcium sulfate whiskers, which includes the following steps: S1. Sort, grind, and classify natural dihydrate gypsum to obtain gypsum powder with D90 ≤ 2 μm.

[0053] S2. Weigh 2 g of gypsum powder, 89.7 g of water, 0.1 g of aluminum sulfate, and 0.1 g of calcium citrate, add them to a high-temperature and high-pressure reaction kettle for hydrothermal reaction. The heating time is 1 h, and the stirring rotation speed during heating is 2500 rpm; heat up to 200 °C and keep it warm for 3 h, and the stirring rotation speed during heat preservation is 1000 rpm; stop stirring and deflate after heat preservation, and it takes about 3 h to complete deflation to obtain crude whiskers.

[0054] S3. Pour the crude whiskers obtained in S2 into a continuous centrifuge for dehydration to make the water content less than 2%, and convey the dehydrated whiskers into a continuous flash dryer for drying to make the water content less than 0.3% to obtain calcium sulfate whiskers.

[0055] Comparative Example 11 This comparative example is a method for preparing basic magnesium sulfate whiskers, which includes the following steps: S1. Grind and classify industrial-grade magnesium sulfate to obtain magnesium sulfate powder with D90 ≤ 2 μm; grind and classify industrial-grade magnesium hydroxide to obtain magnesium hydroxide powder with D90 ≤ 2 μm.

[0056] S2. Weigh 8 g of magnesium sulfate powder, 2 g of magnesium hydroxide powder, 78 g of water, 1.2 g of aluminum sulfate, and 0.4 g of magnesium citrate, add them to a high-temperature and high-pressure reaction kettle for hydrothermal reaction. The heating time is 1 h, and the stirring rotation speed during heating is 2500 rpm; heat up to 200 °C and keep it warm for 3 h, and the stirring rotation speed during heat preservation is 1000 rpm; stop stirring and deflate after heat preservation, and it takes about 3 h to complete deflation to obtain crude whiskers.

[0057] S3. Pour the crude whiskers obtained in S2 into a continuous centrifuge for dehydration to make the water content less than 2%, and convey the dehydrated whiskers into a continuous flash dryer for drying to make the water content less than 0.3% to obtain basic magnesium sulfate whiskers.

[0058] The whiskers (20 wt%) prepared in Examples 1 to 9 and Comparative Examples 1 to 11 were mixed with a polyolefin polymer material (80 wt% PP7726), and then melt-blended and pelletized in a J25 co-rotating parallel twin-screw extruder. The process conditions included: the temperature in zones 1 - 8 of the J25 co-rotating parallel twin-screw extruder was set at 200 °C, the extrusion speed was set at 200 rpm, the feeding speed was set at 12 rpm, the traction and pelletizing speed was set at 12 rpm, and then water cooling was carried out. After air drying, the pellet product was obtained; the pellet product was injection molded at 220 °C through an injection molding machine to obtain samples. The corresponding mechanical properties and thermal stability of the test samples and the PP7726 raw material were tested to detect the strengthening effect of the whiskers on the properties of the polymer material. The results are shown in Table 1. Among them, the test standard for tensile strength is: GB / T 1040.2 - 2022 Plastics - Determination of tensile properties - Part 2: Test conditions for moulding and extrusion plastics; the test standard for dimensional shrinkage rate is: GB / T 17037.4 - 2003 Plastics - Preparation of specimens for injection moulding of thermoplastic materials - Part 4: Determination of moulding shrinkage rate; the test standards for flexural strength and flexural modulus are: GB / T 9341 - 2008 Plastics - Determination of flexural properties; the test standard for notched impact strength is: GB / T 1843 - 2008 Plastics - Method for cantilever beam impact test; the test standard for heat distortion temperature is: GB / T 1634.2 - 2019 Plastics - Determination of Vicat softening temperature and heat distortion temperature - Part 2: Plastics and ebonite. The size specifications of the test samples were adjusted according to the requirements of the test standards.

[0059] Table 1

[0060] As can be seen from the data in Table 1, adding the composite whiskers prepared in the examples of the present invention to the polyolefin polymer material PP7726 has a significant strengthening effect on its mechanical properties and thermal stability.

[0061] Comparing Comparative Examples 1 to 3 with Example 1 respectively, it can be seen that for the composite whiskers prepared without any one of the crystal form control agent and the ionic regulator, the strengthening effect on the mechanical properties and thermal stability of the polymer material will be reduced. Especially for the tensile strength and notched impact strength, there is almost no positive strengthening effect and even a negative reduction effect, and the strengthening effect on other mechanical properties and thermal stability is significantly weaker than that of Example 1. The reason is that during the production process of the two kinds of whiskers, their crystal forms are not effectively controlled, resulting in a relatively complex multi-morphological and irregular inorganic powder material.

[0062] Comparing Comparative Example 4 and Comparative Example 5 with Example 1 respectively, it can be seen that the composite whiskers prepared at too low or too high hydrothermal reaction temperatures have reduced enhancement effects on the mechanical properties and thermal stability of polymer materials. In particular, the tensile strength and notched impact strength have almost no positive enhancement effect and even have a negative reduction effect, and the enhancement effect on other mechanical properties and thermal stability is significantly weaker than that of Example 1. The reason is that at too low a temperature, magnesium sulfate hydroxide does not grow into whiskers; at too high a temperature, its ionic regulator completely fails and effective whiskers cannot grow.

[0063] Comparing Comparative Example 6 to Comparative Example 9 with Example 1 respectively, it can be seen that the composite whiskers prepared with too high / too low holding rotation speed / heating-up rotation speed in the hydrothermal reaction have reduced enhancement effects on the mechanical properties and thermal stability of polymer materials. In particular, the positive enhancement effect on the tensile strength is very weak, and the notched impact strength is weakened. The enhancement effect on other mechanical properties and thermal stability is significantly weaker than that of Example 1. The reason is that too low a holding rotation speed / heating-up rotation speed makes the whiskers grow too long and cannot be dispersed, while too high a holding rotation speed / heating-up rotation speed causes the whiskers to be continuously broken during production.

[0064] Comparing Comparative Example 10 and Comparative Example 11 with Example 1 respectively, it can be seen that the single calcium sulfate whiskers or single magnesium sulfate hydroxide whiskers are not as good as the composite whiskers of Example 1 in terms of their enhancement effects on the mechanical properties, thermal stability of polymer materials. The reason is that calcium sulfate crystals are single columnar crystals and it is difficult to form a relatively firm inorganic bridging structure during the blending modification of polymer materials. Although magnesium sulfate hydroxide whiskers contribute significantly to the mechanical properties of polypropylene, when their single fan-shaped structure is mixed into polymer materials, their influence on the mechanical properties of polymer materials is not as good as that of composite whiskers.

[0065] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A preparation method of a composite whisker of calcium sulfate and basic magnesium salt, characterized in that, The preparation method includes the following steps: Gypsum dihydrate, industrial grade magnesium sulfate, and industrial grade magnesium hydroxide are pretreated respectively to obtain micron-sized gypsum powder, magnesium sulfate powder, and magnesium hydroxide powder; Weigh raw materials in a preset ratio. The raw materials include 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 reaction kettle for hydrothermal reaction to obtain crude composite whiskers; Centrifugal dehydration, water washing, and drying are carried out to obtain composite whiskers of calcium sulfate and basic magnesium salt; Among them, the crystal form control agent uses at least one of aluminum salts, dodecyl trimethyl ammonium bromide, and sodium dodecyl sulfonate; The ion regulator includes a calcium ion regulation assistant and a magnesium ion regulation assistant; The specific steps of the hydrothermal reaction are as follows: heat up to 200°C - 230°C within a predetermined time and carry out heat preservation treatment; stirring operations are carried out during both the heating-up and heat preservation processes; stop stirring and release gas after the heat preservation ends; Among them, the time used for heating up is 1h - 2h, and the stirring speed during heating up is 2500rpm - 3000rpm; The heat preservation time is 1h - 3h, and the stirring speed during heat preservation is 1000rpm - 1500rpm; The gas release time is 3h - 5h.

2. The preparation method of a composite whisker of calcium sulfate and basic magnesium salt according to claim 1, characterized in that, The raw materials contain the following components by weight percentage: Gypsum powder 2% - 10%; 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 preparation method of a composite whisker of calcium sulfate and basic magnesium salt according to claim 1, characterized in that, The calcium ion regulation assistant uses at least one of calcium citrate and EDTA calcium; the magnesium ion regulation assistant uses at least one of magnesium citrate and EDTA magnesium.

4. The preparation method of a composite whisker 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 ≤ 2um.

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

6. The preparation method of a composite whisker of calcium sulfate and basic magnesium salt according to claim 1, characterized in that, The drying uses 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 preparation method of the composite whiskers of calcium sulfate and basic magnesium salt according to any one of claims 1 to 6.

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