A modified anhydrous calcium sulfate whisker and its preparation method

Abstract

The present invention discloses a modified anhydrous calcium sulfate whisker and a preparation method thereof, belonging to the technical field of calcium sulfate whisker preparation. The method includes: obtaining micron-sized gypsum powder after pretreatment of natural dihydrate gypsum; weighing gypsum powder with D90 ≤ 15 μm, water, a dehydration activation reaction assistant and a functional assistant, adding them into a high-temperature and high-pressure reaction kettle, and directly reacting at a certain temperature and for a certain time to obtain calcium sulfate whiskers, dehydrating with a centrifuge and drying with a flash dryer to obtain the modified anhydrous calcium sulfate whiskers; the dehydration activation reaction assistant is an organic compound having a silicon hydroxyl group; the functional assistant adopts an ultra-fine inorganic whisker or a nucleating agent having an enhancing function. By introducing the dehydration activation reaction assistant and the functional assistant, the present invention directly grows dihydrate gypsum in a high-temperature reaction kettle to obtain modified anhydrous calcium sulfate whiskers, which have the characteristics of slender fibers, uniform distribution, good compatibility and dispersibility with polyolefin polymer materials, and excellent mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of anhydrous calcium sulfate whiskers, and particularly relates to a modified anhydrous calcium sulfate whisker and a preparation method thereof. Background Art

[0002] Calcium sulfate whisker (CSW), with the chemical formula CaSO4, also known as gypsum whisker and gypsum fiber. Calcium sulfate whisker is a calcium sulfate fibrous single crystal synthesized from raw gypsum through a specific process and formula. It has a uniform cross-section, a complete outer shape, and a highly perfect internal structure. It is a non-metallic material with many special properties and is an almost ideal microcrystalline fiber. Its mechanical properties far exceed those of general granular fillers widely used at present, such as wollastonite, silica, calcium carbonate powder, calcium sulfate powder, talc powder, etc. It combines the advantages of reinforcing fibers and ultrafine inorganic fillers and is a new type of inorganic chemical new material with high comprehensive performance.

[0003] The production of calcium sulfate whisker is generally divided into two categories. One is the mineral autoclave method, and the other is the hydrothermal method. The mineral autoclave method is to form hemihydrate fibrous gypsum from natural dihydrate gypsum ore under high-temperature and high-pressure steam conditions, and then grind the fibrous gypsum into calcium sulfate whiskers with different aspect ratios through a special mill. After being calcined at 200°C - 800°C, anhydrous calcium sulfate whiskers are formed, and then modified anhydrous calcium sulfate whiskers are formed through two surface treatment methods, namely dry method and wet method. The modified anhydrous calcium sulfate whiskers prepared by this method are bonded together by multiple fibers, resulting in uneven diameters, and it is not easy to control the aspect ratio of the fibers during the processing. They are prone to powdering and water absorption, and are thus not easy to disperse when applied in organic polymer materials, forming structural defects and not contributing well to the mechanical properties of organic polymer materials. The hydrothermal method is to grind natural dihydrate gypsum ore into powder and form hemihydrate calcium sulfate whiskers under high-temperature and high-pressure reaction conditions of 130°C - 160°C with water and a crystal conversion agent. After being calcined at 200°C - 800°C, anhydrous calcium sulfate whiskers are formed, and then modified anhydrous calcium sulfate whiskers are formed through two surface treatment methods, namely dry method and wet method. The modified anhydrous calcium sulfate whiskers prepared by both methods have the following disadvantages: First, it is not easy to control the diameter and aspect ratio; second, the functionality is not strong, especially the reinforcement and toughening functions are relatively low; third, calcium sulfate whiskers are extremely prone to water absorption and have poor compatibility with most plastics; fourth, the process is complex, the equipment investment is large, and the product cost is high. Summary of the Invention

[0004] In view of this, the present invention provides a modified anhydrous calcium sulfate whisker and a preparation method thereof, aiming to solve the problems in the prior art such as difficult control of diameter and aspect ratio, weak functionality, especially relatively low reinforcement and toughening functions.

[0005] The present invention is implemented as follows:

[0006] The first aspect of the present invention provides a method for preparing modified anhydrous calcium sulfate whiskers, which includes:

[0007] Obtaining micron-sized gypsum powder after pretreatment of natural dihydrate gypsum;

[0008] Weighing raw materials in a preset ratio, the raw materials include gypsum powder, water, dehydration activation reaction aids, and functional aids, adding them to a high-temperature and high-pressure reactor for activation heat treatment to obtain calcium sulfate whiskers with free water;

[0009] Centrifugal dehydration and drying to obtain modified anhydrous calcium sulfate whiskers;

[0010] Among them, the dehydration activation reaction aid is an organic compound with silanol groups;

[0011] The functional aid uses inorganic whiskers or nucleating agents.

[0012] Preferably, the specific steps of the activation heat treatment are: heating to 140°C - 155°C within a predetermined time and holding for heat preservation; stirring operations are carried out during both the heating and heat preservation processes; stop stirring and release gas after the heat preservation ends;

[0013] Among them, the time used for heating is 1h - 3h, and the stirring speed during heating is 450rpm - 550rpm;

[0014] The heat preservation time is 0.5h - 1h, and the stirring speed during heat preservation is 50rpm - 150rpm;

[0015] The gas release time is 0.5h - 1h.

[0016] Preferably, the raw materials contain the following components in weight percentages:

[0017] Gypsum powder 5% - 20%;

[0018] Water 70% - 90%;

[0019] Dehydration activation reaction aid 1% - 5%;

[0020] Functional aid 2% - 8%.

[0021] Preferably, the specific steps of the pretreatment are: successively sorting, grinding, and classifying natural anhydrous gypsum to obtain gypsum powder with D90 ≤ 15μm.

[0022] Preferably, the water content of the calcium sulfate whiskers after the centrifugal dehydration treatment is less than 3%.

[0023] Preferably, the drying uses flash drying, and the water content of the calcium sulfate whiskers after the flash drying is less than 0.5%.

[0024] Preferably, the dehydration activation reaction auxiliary agent is hydroxy silicone oil.

[0025] Preferably, the functional additive is selected from at least one of ultrafine fumed silica, silicon carbide whiskers, nano calcium carbonate whiskers, and PP-PE composite organic nucleating agents.

[0026] The second aspect of the present invention provides a modified anhydrous calcium sulfate whisker prepared by the above method.

[0027] The present invention adds gypsum powder (D90≤15μm), water, dehydration activation reaction aid, and functional aid into a high-temperature and high-pressure reactor in a certain proportion, and directly obtains calcium sulfate whiskers with free water at a specific temperature and time. Finally, the calcium sulfate whiskers with free water are dehydrated by a centrifuge and dried by a flash evaporator to obtain modified anhydrous calcium sulfate whiskers.

[0028] In the process of calcium sulfate whisker growth and formation, hydroxy silicone oil is introduced as a dehydration activation reaction aid, and the silicon hydroxyl group (-Si-OH) reacts with the Ca on the surface of calcium sulfate. 2+ A coordination or condensation reaction occurs to form Si-O-Ca bonds, thereby generating anhydrous calcium sulfate whiskers with organic hydrophobic groups. The present invention introduces very stable organic hydrophobic groups and drives away half of the crystal water formed during the growth of the calcium sulfate whiskers, and then conventional drying means are used to obtain modified anhydrous calcium sulfate whiskers that have good compatibility with polymer materials and are not easy to absorb water, without the need for high-temperature calcination above 200°C, thereby reducing energy consumption and costs.

[0029] At the same time, the introduction of organic hydrophobic groups on the calcium sulfate whiskers increases the surface energy of the calcium sulfate whiskers, which can capture reinforcing and toughening functional additives under a certain temperature and high-speed stirring state, prompting the functional additives to be adsorbed on the whisker surface, thereby adding more functions to the calcium sulfate whiskers, such as: ultrafine fumed silica can increase strength, and nano calcium carbonate whiskers can more effectively improve the crystallization effect of polymer materials.

[0030] The present invention adopts a common calcium sulfate whisker hydrothermal process to directly obtain functional modified anhydrous calcium sulfate whiskers. The calcium sulfate whisker fiber morphology obtained by the process of the present invention is controllable, and its compatibility and dispersibility with polymer materials are greatly improved. At the same time, the present invention also greatly improves the strengthening and toughening effect of calcium sulfate whiskers on organic polymer materials.

[0031] The invention solves the problems in the prior art that the diameter and aspect ratio of calcium sulfate whiskers are difficult to control, the functionality is not strong, it is easy to absorb water, the compatibility with most plastics and other polymer materials is poor, the process is complex, the equipment investment is large, and the product cost is high. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0033] Example 1

[0034] A preparation method of modified anhydrous calcium sulfate whiskers, the method comprising the following steps:

[0035] S1. Sort natural anhydrous gypsum, then grind it through equipment such as air classifiers, vertical mills, and roller presses, and obtain gypsum powder with a D90 of about 10 μm after classification;

[0036] S2. Weigh 5 g of gypsum powder, 90 g of water, 2 g of hydroxy silicone oil, and 3 g of ultrafine fumed silica, add them to a high-temperature and high-pressure reaction kettle for heating, stirring and dispersion, and reaction crystallization. Among them, the heating time is 1 h, the heating and stirring speed is 1500 rpm, after heating to 145 °C, keep warm for 0.5 h, the stirring speed during heat preservation is 100 rpm, stop stirring after heat preservation, and complete deflation in about 0.5 h to obtain calcium sulfate whiskers with free water;

[0037] S3. Pour the calcium sulfate whiskers prepared in S2 into a continuous centrifuge for dehydration to make the moisture content less than 3%, and transport the dehydrated calcium sulfate whiskers into a continuous flash dryer for drying to make the moisture less than 0.5% to obtain modified anhydrous calcium sulfate whiskers.

[0038] Example 2

[0039] A preparation method of modified anhydrous calcium sulfate whiskers, the method comprising the following steps:

[0040] S1. Sort natural anhydrous gypsum, then grind it through an air classifier, and obtain gypsum powder with a D90 of about 10 μm after classification;

[0041] S2. Weigh 20 g of gypsum powder, 67 g of water, 5 g of hydroxy silicone oil, and 8 g of ultrafine fumed silica, add them to a high-temperature and high-pressure reaction kettle for heating, stirring and dispersion, and reaction crystallization. Among them, the heating time is 3 h, the heating and stirring speed is 1500 rpm, after heating to 155 °C, keep warm for 0.5 h, the stirring speed during heat preservation is 100 rpm, stop stirring after heat preservation, and complete deflation in about 0.5 h to obtain calcium sulfate whiskers with free water;

[0042] S3. Pour the calcium sulfate whiskers prepared in S2 into a continuous centrifuge for dehydration to make the moisture content less than 3%, and transport the dehydrated calcium sulfate whiskers into a continuous flash dryer for drying to make the moisture less than 0.5% to obtain modified anhydrous calcium sulfate whiskers.

[0043] Example 3

[0044] A preparation method of modified anhydrous calcium sulfate whiskers, the method comprising the following steps:

[0045] S1. Sort natural anhydrous gypsum, then grind it with a jet mill and classify it to obtain gypsum powder with a D90 of about 10 μm;

[0046] S2. Weigh 17 g of gypsum powder, 75 g of water, 3 g of hydroxy silicone oil, and 5 g of ultrafine fumed silica, add them to a high-temperature and high-pressure reactor for heating, stirring and dispersion, and reaction crystallization. Among them, the heating time is 1 h, the heating and stirring speed is 2000 rpm, after heating to 150 °C, keep warm for 1 h, the stirring speed during heat preservation is 100 rpm, stop stirring after heat preservation is over, and complete deflation in about 1 h to obtain calcium sulfate whiskers with free water;

[0047] S3. Pour the calcium sulfate whiskers prepared in S2 into a continuous centrifugal dehydrator for dehydration to make the moisture content less than 3%, and transport the dehydrated calcium sulfate whiskers into a continuous flash dryer for drying to make the moisture less than 0.5% to obtain modified anhydrous calcium sulfate whiskers.

[0048] Example 4

[0049] This example is a preparation method of modified anhydrous calcium sulfate whiskers, which replaces the functional additive ultrafine fumed silica with silicon carbide whiskers on the basis of Example 3; other steps and reaction conditions are the same as those in Example 3.

[0050] Example 5

[0051] This example is a preparation method of modified anhydrous calcium sulfate whiskers, which replaces the functional additive ultrafine fumed silica with nano calcium carbonate whiskers on the basis of Example 3; other steps and reaction conditions are the same as those in Example 3.

[0052] Example 6

[0053] This example is a preparation method of modified anhydrous calcium sulfate whiskers, which replaces the functional additive ultrafine fumed silica with a PP-PE composite organic nucleating agent on the basis of Example 3; other steps and reaction conditions are the same as those in Example 3.

[0054] Comparative Example 1

[0055] This comparative example is a preparation method of modified anhydrous calcium sulfate whiskers, which removes the dehydration activation reaction aid hydroxy silicone oil in S2 on the basis of Example 3; other steps and reaction conditions are the same as those in Example 3.

[0056] Comparative Example 2

[0057] This comparative example is a preparation method of modified anhydrous calcium sulfate whiskers. On the basis of Example 3, the dehydration activation reaction assistant hydroxyl silicone oil in S2 is replaced with a hydroxyl-free silicone oil (illustrated with methyl silicone oil as an example); other steps and reaction conditions are the same as those in Example 3.

[0058] Comparative Example 3

[0059] This comparative example is a preparation method of modified anhydrous calcium sulfate whiskers. On the basis of Example 3, the functional assistant ultrafine fumed silica in S2 is removed; other steps and reaction conditions are the same as those in Example 3.

[0060] Comparative Example 4

[0061] This comparative example is a preparation method of modified anhydrous calcium sulfate whiskers. On the basis of Example 3, the heat preservation temperature in S2 is adjusted to 130 °C; other steps and reaction conditions are the same as those in Example 3.

[0062] Comparative Example 5

[0063] This comparative example is a preparation method of modified anhydrous calcium sulfate whiskers. On the basis of Example 3, the heat preservation temperature in S2 is adjusted to 160 °C; other steps and reaction conditions are the same as those in Example 3.

[0064] Comparative Example 6

[0065] This comparative example is a preparation method of modified anhydrous calcium sulfate whiskers. On the basis of Example 3, the heat preservation rotation speed in S2 is adjusted to 200 rpm; other steps and reaction conditions are the same as those in Example 3.

[0066] Comparative Example 7

[0067] This comparative example is a preparation method of modified anhydrous calcium sulfate whiskers. On the basis of Example 3, the heating-up rotation speed in S2 is adjusted to 400 rpm; other steps and reaction conditions are the same as those in Example 3.

[0068] The sizes of the calcium sulfate whiskers prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were tested, and the test results are shown in Table 1.

[0069] In addition, the calcium sulfate whiskers (20 wt%) prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were mixed with a polyolefin polymer material (80 wt% PP7726) and granulated by twin-screw extrusion to obtain a product, and its corresponding mechanical properties and processing and dispersion properties were tested. The test method for the dispersion property was: referring to the "Filter Press Value Test in the Chinese Version of BS EN13900-5:2021 Standard", and the results are shown in Table 1.

[0070] Table 1

[0071]

[0072] As can be seen from the data in Table 1, the anhydrous calcium sulfate whiskers prepared in the embodiments of the present invention have controllable morphology, greatly improved compatibility with polymer materials, excellent dispersibility (the pressure filtration value is inversely proportional to the dispersibility), and obvious contributions to the improvement of mechanical properties such as enhancing and toughening of polymer materials.

[0073] By comparing Comparative Example 1 and Comparative Example 2 with Example 3 respectively, it can be seen that the mechanical properties and dispersibility of the anhydrous calcium sulfate whiskers prepared without dehydration activation reaction additives or conventional organic additives are lower than those of the anhydrous calcium sulfate whiskers prepared with the dehydration activation reaction additives of the present invention, and the particle size distribution of Example 3 of the present invention is more uniform than that of Comparative Example 1 and Comparative Example 2.

[0074] By comparing Comparative Example 3 with Example 3, it can be seen that the mechanical properties and dispersibility of the anhydrous calcium sulfate whiskers prepared without functional additives are lower than those of the anhydrous calcium sulfate whiskers prepared with functional additives, and the particle size distribution of Example 3 of the present invention is more uniform than that of Comparative Example 3.

[0075] By comparing Comparative Example 4 and Comparative Example 5 with Example 3 respectively, it can be seen that too low or too high activation temperature is not conducive to improving the mechanical properties and dispersibility of the anhydrous calcium sulfate whiskers, and the particle size distribution of Example 3 of the present invention is more uniform than that of Comparative Example 4 and Comparative Example 5.

[0076] By comparing Comparative Example 6 and Comparative Example 7 with Example 3 respectively, it can be seen that too low heating and stirring rate or too high heat preservation and stirring rate are not conducive to improving the mechanical properties and dispersibility of the anhydrous calcium sulfate whiskers, and the particle size distribution of Example 3 of the present invention is more uniform than that of Comparative Example 6 and Comparative Example 7.

[0077] The above embodiments only represent several implementation modes of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A preparation method of modified anhydrous calcium sulfate whiskers, characterized in that, The method includes: Obtaining micron-sized gypsum powder after pre-treating natural dihydrate gypsum; Weighing raw materials in a preset ratio, where the raw materials include gypsum powder, water, a dehydration activation reaction assistant, and a functional assistant, adding them to a high-temperature and high-pressure reactor for activation heat treatment to obtain calcium sulfate whiskers with free water; Centrifugal dehydration and drying to obtain modified anhydrous calcium sulfate whiskers; Among them, the dehydration activation reaction assistant is an organic compound with silanol groups; the dehydration activation reaction assistant uses hydroxyl silicone oil; The functional assistant uses inorganic whiskers or a nucleating agent; the functional assistant is selected from at least one of ultrafine fumed silica, silicon carbide whiskers, nano calcium carbonate whiskers, and a PP-PE composite organic nucleating agent; The specific steps of the activation heat treatment are: heating to 140°C - 155°C within a predetermined time and holding for heat preservation; 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 - 3h, and the stirring speed during heating is 1500rpm - 2000rpm; The heat preservation time is 0.5h - 1h, and the stirring speed during heat preservation is 50rpm - 150rpm; The gas release time is 0.5h - 1h.

2. The preparation method of a modified anhydrous calcium sulfate whisker according to claim 1, characterized in that, The raw materials contain the following components by weight percentage: Gypsum powder 5% - 20%; Water 70% - 90%; Dehydration activation reaction assistant 1% - 5%; Functional assistant 2% - 8%.

3. The preparation method of a modified anhydrous calcium sulfate whisker according to claim 1, characterized in that, The specific steps of the pre-treatment are: sequentially sorting, grinding, and classifying natural anhydrous gypsum to obtain gypsum powder with D90 ≤ 15μm.

4. The preparation method of the modified anhydrous calcium sulfate whisker according to claim 1, characterized in that, The moisture content of the calcium sulfate whiskers after the centrifugal dehydration treatment is less than 3%.

5. The preparation method of the modified anhydrous calcium sulfate whisker according to claim 1 or 4, characterized in that, The drying uses flash drying, and the moisture content of the calcium sulfate whiskers after the flash drying is less than 0.5%.

6. A modified anhydrous calcium sulfate whisker, characterized in that, The modified anhydrous calcium sulfate whiskers are prepared by the preparation method of the modified anhydrous calcium sulfate whiskers according to any one of claims 1 to 5.

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