Calcium sulfate whisker high-orientation reinforced functional composite material and preparation method thereof

Abstract

The invention relates to a calcium sulfate whisker high-orientation reinforced functional composite material and a preparation method thereof, and belongs to the technical field of polymer and inorganic whisker modified composite materials. The preparation method comprises the following steps: uniformly dispersing calcium sulfate whiskers and sodium polyacrylate in water to form a sodium polyacrylate electrolyte aqueous solution, applying an electric field in the solution, enabling the calcium sulfate whiskers to be directionally arranged through a filter screen, then enabling the solution to become sodium polyacrylate gel through a cross-linking agent N, N '-methylene bisacrylamide and an initiator ammonium persulfate, and finally preparing the calcium sulfate whiskers / sodium polyacrylate composite hydrogel. And heating to remove moisture in the cross-linked polymer, and drying at high temperature to remove polymer components to form a compact and complete inorganic oriented calcium sulfate whisker composite material. The whisker composite material prepared by the method is low in cost, simple and easy to operate and convenient for industrial production, is a novel reinforcing material, and is mainly applied to the fields of toughening and reinforcing of engineering plastics, grinding wheel friction material reinforcing agents, automobile brake pad reinforcing agent materials, aerospace materials and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer and inorganic whisker modified composite materials, and particularly relates to a calcium sulfate whisker highly oriented reinforced functional composite material and a preparation method thereof. Background Art

[0002] Calcium sulfate whiskers are a high-strength single crystal with a high aspect ratio, uniform cross-section, complete shape, perfect internal structure, and stable size. Calcium sulfate whiskers are inexpensive and have a mature preparation process. They are currently mainly used for reinforcement, wear resistance, and high temperature resistant filling materials. However, the distribution of calcium sulfate whiskers currently produced is chaotic. Although the strength of whiskers is much higher than that of other chopped fibers, the reinforcement and wear resistance effects are far from being fully exerted. The chaotic arrangement of whiskers cannot fully exert the reinforcing effect of whiskers. If the whiskers can be highly oriented and distributed in a directional manner, the whiskers can maximize their high reinforcing effect. Summary of the invention

[0003] In order to prepare oriented whiskers with higher reinforcement effect, the present invention provides a directional distribution calcium sulfate whisker composite material, in which the whiskers as reinforcement materials are not randomly distributed inside the reinforced material, but are orderly and directional distributed in one direction. The preparation method is simple and easy to operate, has low preparation cost, can be used as the last process of calcium sulfate whisker production, and can be quickly industrialized and mass-produced.

[0004] The product prepared by the present invention is a powdered filler, a pure inorganic whisker reinforcement material, a new type of reinforcement material, and has special functions such as high strength, toughness, heat resistance, wear resistance, and corrosion resistance. It is mainly used in the fields of toughening and strengthening of engineering plastics, reinforcing agents for grinding wheel friction materials, reinforcing agents for automobile brake pads, and aerospace materials.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing a calcium sulfate whisker highly oriented reinforced functional composite material comprises the following steps:

[0007] first step:

[0008] Add calcium sulfate whiskers, sodium hexametaphosphate and water into a container equipped with a stirrer, a graphite electrode, a precision filter, a heater and a vacuum pump, heat it to 80°C, stir it thoroughly, and evenly disperse the calcium sulfate whiskers in the water; then lower the temperature of the container to room temperature, add sodium polyacrylate into the container, and stir it thoroughly;

[0009] Step 2:

[0010] Take another container, add N,N'-methylenebisacrylamide, 30% ethanol solution, and ammonium persulfate, stir thoroughly at room temperature until completely dissolved;

[0011] Step 3:

[0012] Take the solution of the second step and add it to the solution of the first step, and stir it thoroughly at room temperature;

[0013] Step 4:

[0014] In the container used in the first step, a 15V DC voltage is applied to the solution in the third step through a graphite electrode for 3-5 seconds, then the stirrer is taken out, the precision filter is started, the solution is filtered repeatedly in a direction for 10 times, then the pressure is stopped, the graphite power supply is disconnected, and the temperature is raised to 80°C after 1-2 minutes, and maintained for 5-10 minutes to allow the sodium polyacrylate to be fully cross-linked; then the temperature is continued to be raised to 140°C, dried for 10-15 minutes, and vacuumed to completely evaporate the water in the container;

[0015] Step 5:

[0016] Release the material from the fourth step and crush it into 300 mesh powder using a liquid nitrogen low-temperature crusher;

[0017] Step 6: Put the powder from step 6 into a large industrial high-temperature drying oven, heat it to 600°C, evacuate it and keep it for 15 minutes to carbonize the polymer to form a dense high-strength carbon skeleton layer. The carbon layer is tightly combined with the calcium sulfate whiskers to form a dense oriented calcium sulfate whisker composite material, which is the patented product of the present invention. The material is in powder form and is easy to package and transport.

[0018] Furthermore, in the first step, the mass ratio of calcium sulfate whisker, sodium hexametaphosphate, water and sodium polyacrylate is: 120-140: 0.8-1: 800-1000: 80-100.

[0019] Furthermore, in the first step, the calcium sulfate whiskers have an average diameter of 1-2 μm, a length of 300 μm, and an aspect ratio of 150-300.

[0020] Furthermore, in the second step, the mass ratio of N,N'-methylenebisacrylamide, 30% ethanol solution and ammonium persulfate is 15-20: 600-800: 27-36.

[0021] Furthermore, in the third step, the mass ratio of the solution in the first step to the solution in the second step is: 1000-1241:252-314.

[0022] Furthermore, in the fourth step, the pore size of the precision filter is 30-50 μm.

[0023] Furthermore, the calcium sulfate whisker composite material prepared by the above preparation method is used in the fields of toughening and strengthening of engineering plastics, reinforcing agent of grinding wheel friction material, reinforcing agent material of automobile brake pad, and aerospace material.

[0024] Description of the main raw materials used in the present invention:

[0025] Sodium hexametaphosphate: white crystalline powder, dispersant;

[0026] Sodium polyacrylate: white powder, high molecular weight polymer resin, polymer electrolyte solution solute;

[0027] N,N'-Methylenebisacrylamide: white powdery crystals, cross-linking agent;

[0028] Ammonium persulfate: white crystalline powder, cross-linking initiator.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The distribution of calcium sulfate whiskers in products produced by ordinary calcium sulfate whiskers is disorderly. Although it achieves a certain strengthening and toughening effect, it cannot fully exert the strengthening effect of whiskers. The technology of the present invention is to make the calcium sulfate whiskers orderly and directional, highly oriented, and can maximize the high strengthening and toughening effect of whiskers.

[0031] 2. The preparation technology of the present invention is to first evenly disperse calcium sulfate whiskers and sodium polyacrylate in an aqueous solution to form a polymer electrolyte solution. Under normal circumstances, the sodium polyacrylate polymer segments are entangled and curled with each other, and the calcium sulfate whiskers are randomly distributed around the sodium polyacrylate polymer segments in the solution. The solution viscosity is high and the fluidity of the solution is poor. However, when a voltage is applied in a container to form an electric field, under the action of the external electric field, the ionic groups in the sodium polyacrylate electrolyte solution will move and tend to be arranged along the direction of the electric field. This arrangement will lead to the orientation of the sodium polyacrylate chain, produce electric field orientation, and the sodium polyacrylate chain will be highly stretched, the rheological properties will increase, and the viscosity of the solution will be greatly reduced, similar to a low-molecular solution. At this time, the precision filter is started and moves back and forth left and right. The sodium polyacrylate macromolecules can pass through the filter smoothly, and the calcium sulfate whiskers are also oriented in one direction through the filter. The sodium polyacrylate macromolecules and the whiskers are oriented in the same direction.

[0032] 3. After the sodium polyacrylate macromolecules and calcium sulfate whiskers are aligned in one direction, the power is turned off and the electric field applied to the solution is removed. The sodium polyacrylate polymer chains will curl and entangle with each other. The viscosity of the sodium polyacrylate electrolyte solution will increase to the level before pressure is applied, while the calcium sulfate whiskers, which are inorganic substances, still maintain a highly oriented shape. Then the temperature is raised to allow the sodium polyacrylate macromolecules to undergo a cross-linking reaction to form a gel. A cross-linked network structure is formed between the macromolecules, and the highly oriented calcium sulfate whiskers are fixed in the network structure.

[0033] 4. The cross-linked gel is heated and dried continuously to remove the water in the gel. The water is heated and becomes water vapor and evaporates. The water vapor can pass through the cross-linked network structure of the hydrogel, and the hydrogel collapses and becomes solid. However, the cross-linked structure of the carboxymethyl cellulose resin is not destroyed. The cross-linked network structure of the polymer still maintains the original structure and is very stable. The internal calcium sulfate whiskers are arranged more closely. The added powder is dried continuously at a high temperature of 600°C to remove the organic polymer, carbonize the polymer, form a dense high-strength carbon layer, and bond the carbon skeleton. The carbon layer is tightly combined with the calcium sulfate whiskers to form a dense oriented calcium sulfate whisker composite material, which is a complete inorganic synthetic composite material, i.e., the product of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structure of the container used in the preparation method of the present invention;

[0035] 1. Container, 2. Graphite electrode, 3. Precision filter, 4. Agitator. DETAILED DESCRIPTION

[0036] The technical solution and effects of the present invention are further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0037] The present invention is further described in detail below with reference to specific embodiments.

[0038] Example 1

[0039] A method for preparing a calcium sulfate whisker highly oriented reinforced functional composite material comprises the following steps:

[0040] first step:

[0041] Take 120 kg of calcium sulfate whiskers, 0.8 kg of sodium hexametaphosphate, and 800 kg of water and add them into a rectangular container 1 with a stirrer 4, a graphite electrode 5, a precision filter 3, a heater, and a vacuum pump (see attached). Figure 1 ), heat to 80°C, stir thoroughly to disperse the calcium sulfate whiskers evenly in the water; then lower the temperature of the container to room temperature, add 80 kg of sodium polyacrylate into the container, and stir thoroughly.

[0042] Step 2:

[0043] Take another container, add 15Kg N,N'-methylenebisacrylamide, 600Kg 30% ethanol solution, and 27Kg ammonium persulfate, stir thoroughly at room temperature, and completely dissolve.

[0044] Step 3:

[0045] Take 1000 kg of the solution from the second step and add it to 252 kg of the solution from the first step, and stir thoroughly at room temperature.

[0046] Step 4:

[0047] In the container used in the first step, a DC voltage of 15V is applied to the solution in the third step through a graphite electrode for 5 seconds, then the stirrer is taken out, the precision filter is started, and the solution is filtered repeatedly in a directional manner (from right to left in this embodiment) for 10 times, then the pressure is stopped, the graphite power supply is disconnected, and the temperature is raised to 80°C after 1-2 minutes, and maintained for 5-10 minutes to allow the sodium polyacrylate to be fully cross-linked; then the temperature is continued to be raised to 140°C, dried for 10-15 minutes, and vacuumed to completely evaporate the water in the container;

[0048] Step 5:

[0049] Release the material from the fourth step and crush it into 300 mesh powder using a liquid nitrogen low-temperature crusher;

[0050] Step 6: Put the powder in step 6 into a large industrial high-temperature drying oven, heat it to 600°C, and evacuate it for 15 minutes to carbonize the polymer to form a dense and high-strength carbon layer. The carbon layer is tightly combined with the calcium sulfate whiskers to form a dense oriented calcium sulfate whisker composite material.

[0051] Example 2

[0052] Same as Example 1, except that:

[0053] first step:

[0054] Take 140Kg of calcium sulfate whiskers, 1Kg of sodium hexametaphosphate and 1000Kg of water and add them into container 1, heat it to 80°C, stir it thoroughly to make the calcium sulfate whiskers evenly dispersed in the water; then lower the temperature of the container to room temperature, add 100Kg of sodium polyacrylate into the container and stir it thoroughly.

[0055] Step 2:

[0056] Take another container, add 20 kg N, N'-methylenebisacrylamide, 800 kg 30% ethanol solution, and 36 kg ammonium persulfate, stir thoroughly at room temperature, and completely dissolve.

[0057] Step 3:

[0058] Take 1241 kg of the solution from the second step and add it to 314 kg of the solution from the first step, and stir thoroughly at room temperature.

[0059] Example 3

[0060] Same as Example 1, except that:

[0061] first step:

[0062] Take 130Kg of calcium sulfate whiskers, 0.9Kg of sodium hexametaphosphate and 900Kg of water and add them into container 1, heat it to 80°C, stir it thoroughly to make the calcium sulfate whiskers evenly dispersed in the water; then lower the temperature of the container to room temperature, add 90Kg of sodium polyacrylate into the container, and stir it thoroughly.

[0063] Step 2:

[0064] Take another container, add 17 kg of N,N'-methylenebisacrylamide, 700 kg of 30% ethanol solution with a mass concentration of 30%, and 31 kg of ammonium persulfate, stir thoroughly at room temperature, and dissolve completely.

[0065] Step 3:

[0066] Take 1121 kg of the solution from the second step and add it to 283 kg of the solution from the first step, and stir thoroughly at room temperature.

[0067] In order to verify the modification effect of the present invention, the following two groups of tests were carried out.

[0068] Test 1: The non-oriented calcium sulfate whiskers prepared by the conventional process (here referring to the atmospheric pressure acidification method) and the product of the present invention were compared and tested on the modification effect on the engineering plastic nylon 66. The test results are as follows.

[0069] The test performance comparison of the nylon 66 composite material prepared by adding the product of the present invention and adding ordinary calcium sulfate whiskers is shown in Table 1 below (the added mass ratio is 3%).

[0070] Table 1 Comparison results of test performance of nylon 66 composite materials prepared by adding the product of the present invention and adding ordinary calcium sulfate whiskers

[0071]

[0072] As can be seen from Table 1, in the prepared nylon 66 composite material, when the product of the present invention is added as a reinforcing and toughening material, the calcium sulfate whisker content is 3%, and the tensile strength, flexural strength, notched impact strength, heat deformation temperature, and wear resistance are much higher. The test performances of Example 1, Example 2, and Example 3 are basically the same. The main reason is that the different formula ratios and the polymer content are different, but in the end the polymers are all carbonized to form a bonded carbon skeleton and a dense high-strength carbon layer. The final products are all highly oriented whisker-reinforced materials with similar reinforcing effects.

[0073] Test 2: When the whisker addition amount in the brake pad is 5%, the test results are shown in Table 2 below.

[0074] Table 2 Test results when the whisker addition amount in the brake pad is 5%

[0075]

[0076] It can be seen from Table 2 that the brake pad to which the present invention is added has a lower wear rate.

[0077] By adopting the concept of the present invention, the sodium polyacrylate in Example 1 was replaced with carboxymethyl cellulose resin and acrylic acid, and the prepared materials were subjected to comparative tests on the modification effect on engineering plastic nylon 66. The test results are as follows.

[0078] Table 3 Comparison results

[0079]

[0080] As can be seen from Table 3, the performance of the products prepared by replacing sodium polyacrylate with carboxymethyl cellulose resin and acrylic acid is very different. The reason is that calcium sulfate whiskers are added as a common additive, and the reinforcement effect is the same as that of ordinary calcium sulfate whiskers, which proves that the whiskers are not oriented inside the material, but are distributed in a disorderly manner, further illustrating that sodium polyacrylate, as a polymer electrolyte solution, causes the whiskers to be oriented.

[0081] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a calcium sulfate whisker highly oriented reinforced functional composite material, characterized in that: The preparation method comprises the following steps: first step: Add calcium sulfate whiskers, sodium hexametaphosphate and water into a container equipped with a stirrer, a graphite electrode, a precision filter, a heater and a vacuum pump, heat it to 80°C, stir it thoroughly, and evenly disperse the calcium sulfate whiskers in the water; then lower the temperature of the container to room temperature, add sodium polyacrylate into the container, and stir it thoroughly; Step 2: Take another container, add N,N'-methylenebisacrylamide, 30% ethanol solution, and ammonium persulfate, stir thoroughly at room temperature until completely dissolved; Step 3: Take the solution of the second step and add it to the solution of the first step, and stir it thoroughly at room temperature; Step 4: In the container used in the first step, a 15V DC voltage is applied to the solution in the third step through a graphite electrode for 3-5 seconds, then the stirrer is taken out, the precision filter is started, the solution is filtered repeatedly in a direction for 10 times, then the pressure is stopped, the graphite power supply is disconnected, and the temperature is raised to 80°C after 1-2 minutes, and maintained for 5-10 minutes to allow the sodium polyacrylate to be fully cross-linked; then the temperature is continued to be raised to 140°C, dried for 10-15 minutes, and vacuumed to completely evaporate the water in the container; Step 5: Release the material from the fourth step and crush it into 300 mesh powder using a liquid nitrogen low-temperature crusher; Step 6: Put the powder from step 6 into a large industrial high-temperature drying oven, heat it to 600°C, evacuate it and keep it for 15 minutes to carbonize the polymer to form a dense high-strength carbon skeleton layer. The carbon layer is tightly combined with the calcium sulfate whiskers to form a dense oriented calcium sulfate whisker composite material, which is the patented product of the present invention. The material is in powder form and is easy to package and transport.

2. The method for preparing the calcium sulfate whisker highly oriented reinforced functional composite material according to claim 1, wherein: In the first step, the mass ratio of calcium sulfate whisker, sodium hexametaphosphate, water and sodium polyacrylate is: 120-140: 0.8-1: 800-1000: 80-100.

3. The method for preparing the calcium sulfate whisker highly oriented reinforced functional composite material according to claim 1, wherein: In the first step, the calcium sulfate whiskers have an average diameter of 1-2 μm, a length of 300 μm, and an aspect ratio of 150-300.

4. The method for preparing the calcium sulfate whisker highly oriented reinforced functional composite material according to claim 1, wherein: In the second step, the mass ratio of N,N'-methylenebisacrylamide, 30% ethanol solution and ammonium persulfate is 15-20: 600-800: 27-36.

5. The method for preparing the calcium sulfate whisker highly oriented reinforced functional composite material according to claim 1, characterized in that: In the third step, the mass ratio of the solution in the first step to the solution in the second step is: 1000-1241: 252-314.

6. The method for preparing the calcium sulfate whisker highly oriented reinforced functional composite material according to claim 1, characterized in that: In the fourth step, the pore size of the precision filter is 30-50 μm.

7. The method for preparing the calcium sulfate whisker highly oriented reinforced functional composite material according to claim 1, characterized in that: The calcium sulfate whisker composite material prepared by the preparation method is used in the fields of toughening and strengthening of engineering plastics, reinforcing agent of grinding wheel friction material, reinforcing agent material of automobile brake pad, and aerospace material.

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