Composite polyacrylonitrile-based graphite soft felt and preparation method thereof

Abstract

The application discloses a kind of composite polyacrylonitrile-based graphite soft felt and preparation method thereof, the present application is mainly through that the original silk is curled, short cut, opens, carded web, pre-oxidation, layer, needle punching formation, low-temperature carbonization, high-temperature carbonization, high-temperature graphitization, sizing, to prepare and obtain composite polyacrylonitrile-based graphite soft felt;In the present application, by pre-piercing, the size uniformity and tensile strength of the formed pre-oxidized fiber felt are greatly improved by the process of repeated piercing;The pre-oxidation treatment process is advanced to carding web, which greatly improves the production efficiency, and the production efficiency is improved by 200-300% compared with the traditional production process, and effectively avoids the problems such as ignition caused by heat accumulation in the pre-oxidation process due to insufficient heat dissipation of carbon fiber soft felt.

Description

Technical Field

[0001] This invention relates to the field of thermal insulation materials technology, specifically to a composite polyacrylonitrile-based graphite soft felt and its preparation method. Background Technology

[0002] Graphite felt is divided into two types based on the raw material used: polyacrylonitrile-based graphite felt and viscose-based graphite felt. Polyacrylonitrile-based graphite felt is stronger and has better oxidation resistance than viscose-based graphite felt, but it has poor flexibility, high bulk density, and good thermal insulation performance. In addition to the high purity, high temperature resistance, corrosion resistance, and non-melting properties of block graphite, graphite felt also has the advantages of elasticity, arbitrarily foldable and cuttable, and can be sewn with graphite yarn.

[0003] Currently, the main methods for manufacturing traditional polyacrylonitrile-based graphite felt are as follows:

[0004] I. Using PAN-based pre-oxidized fiber as the base material, and taking advantage of the crimping property of PAN-based pre-oxidized fiber, a needle-punching nonwoven process is used to produce a pre-fabricated felt with a certain thickness, width and length. Then, it is carbonized and graphitized to form a polyacrylonitrile-based graphite soft felt. The pre-oxidized PAN-based fiber has defects such as low strength, less crimping, fiber brittleness and poor interfiber cohesion, and poor spinnability. The mechanical strength of the pre-fabricated felt obtained by needle-punching nonwoven technology is uneven.

[0005] Second, organic fibers are first crimped and then chopped, combed into a web and laid in layers. A needle-punching nonwoven process is used to make a pre-fabricated felt with a certain thickness, width and length. Then, it is pre-oxidized, carbonized and graphitized to form polyacrylonitrile-based graphite soft felt. During the pre-oxidation process, the acrylonitrile white fiber felt needs to be kept in hot air at 180-300 degrees for 0.5-3 hours. The process needs to be strictly controlled, as it is easy to cause heat accumulation and ignite the felt. In addition, the fiber pre-oxidation is uneven and the energy consumption is high.

[0006] Chinese patent document CN110002888A discloses a method for preparing carbon fiber thermal insulation felt from short fibers. The method involves pretreatment to obtain a preform, followed by impregnation with atomized resin and curing to obtain a cured preform. After carbonization and graphitization, carbon fiber thermal insulation material is obtained. This process not only recycles scraps from the cutting of carbon fiber soft felt, but also significantly improves resin utilization through atomization, making it safe and environmentally friendly. The resulting product has high surface smoothness, controllable density, and good thermal insulation effect, making it worthy of widespread promotion. However, the above process has slow production efficiency and low pre-oxidation degree. During the pre-oxidation process, heat easily accumulates in the felt, leading to ignition, and the process is difficult to control. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a composite polyacrylonitrile-based graphite soft felt and its preparation method, thereby solving the problems of high processing difficulty, slow efficiency, uneven pre-oxidation degree, and high preparation cost in the traditional polyacrylonitrile-based graphite soft felt pre-oxidation stage. The prepared composite polyacrylonitrile-based graphite soft felt has good mechanical properties and thermal insulation properties.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a composite polyacrylonitrile-based graphite soft felt includes the following steps:

[0010] S1. Polyacrylonitrile filaments are bundled together, crimped and chopped, then opened and entered into a carding machine, carded into a web, laid up, and pre-oxidized to obtain a pre-oxidized fiber web.

[0011] S2. The pre-oxidized fiber web is pre-punched and re-punched by a needle punching machine to obtain a shaped pre-oxidized fiber felt;

[0012] S3, pre-oxidized fiber felt is subjected to low-temperature carbonization treatment, high-temperature carbonization treatment and high-temperature graphitization treatment in sequence to obtain polyacrylonitrile-based graphite soft felt.

[0013] S4. The polyacrylonitrile-based graphite soft felt is first pretreated, then immersed in the composite slurry for 2-4 hours at room temperature, then taken out and vacuum dried to obtain the composite polyacrylonitrile-based graphite soft felt, wherein the composite slurry includes waterborne epoxy resin, modified bentonite, calcium carbonate whiskers and ceramic powder.

[0014] Preferably, in step S1, the curl degree is 4-8 and the short cut length is 38-65mm.

[0015] Preferably, in step S1, the pre-oxidation treatment temperature is 200-280℃ and the pre-oxidation treatment time is 1-4h.

[0016] Preferably, in step S3, the low-temperature carbonization treatment temperature is 400-700℃ and the treatment time is 1-3h; the high-temperature carbonization treatment temperature is 1200-1400℃ and the treatment time is 1-3h; the high-temperature graphitization treatment temperature is 1800-2200℃ and the treatment time is 0.5-2h.

[0017] Preferably, in step S4, the modified bentonite is prepared as follows:

[0018] (1) Disperse bentonite in deionized water, then add hexadecyltrimethylammonium bromide to it, heat and stir at 80-90℃ for 4-8 hours, and wash, filter and dry the mixture to obtain pretreated bentonite;

[0019] (2) Add carrageenan to deionized water and stir to dissolve at 75-90℃. Then add pretreated bentonite, disperse evenly, pour into a mold, cool to room temperature, freeze dry and then pulverize to obtain modified bentonite.

[0020] Preferably, in step (1), the mass ratio of bentonite to hexadecyltrimethylammonium bromide is 8-12:1-3.

[0021] Preferably, in step (2), the mass ratio of carrageenan, deionized water and pretreated bentonite is 1-2:100:6-10.

[0022] Preferably, in step S4, the pretreatment process of polyacrylonitrile-based graphite soft felt is as follows: the polyacrylonitrile-based graphite soft felt is immersed in an ethanol aqueous solution, then KH560 is added to it, and the mixture is heated and stirred for 2-3 hours. After that, it is taken out, washed, and dried to obtain pretreated polyacrylonitrile-based graphite soft felt.

[0023] Preferably, in step S4, the mass ratio of waterborne epoxy resin, modified bentonite, calcium carbonate whiskers and ceramic powder is 80-100:5-10:3-5:1-2.

[0024] The present invention also provides a composite polyacrylonitrile-based graphite soft felt prepared by the above preparation method.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) This invention provides a method for preparing composite polyacrylonitrile-based graphite soft felt. The invention mainly involves the following steps: curling, shaving, opening, carding into a web, pre-oxidation, lay-up, needle punching, low-temperature carbonization, high-temperature carbonization, high-temperature graphitization, and sizing to prepare composite polyacrylonitrile-based graphite soft felt. In this invention, the pre-needling and re-needling processes significantly improve the dimensional uniformity and tensile strength of the pre-oxidized fiber felt. The pre-oxidation process is advanced to after carding into a web, which greatly improves production efficiency by 200-300% compared to the traditional production process. It also effectively avoids problems such as insufficient heat dissipation of carbon fiber soft felt leading to heat accumulation and fire during the pre-oxidation process.

[0027] (2) This invention utilizes hexadecyltrimethylammonium bromide to intercalate bentonite, thereby increasing the interlayer spacing of bentonite. Then, carrageenan aerogel is introduced into the interlayer and surface of bentonite. The layered structure of bentonite and the porous structure of carrageenan aerogel give the composite polyacrylonitrile-based graphite soft felt good thermal insulation ability. By pre-treating the polyacrylonitrile-based graphite soft felt, epoxy groups are introduced on the surface of the polyacrylonitrile-based graphite soft felt, which improves the adhesion of the composite slurry to the surface of the polyacrylonitrile-based graphite soft felt and avoids the problem of the slurry easily falling off during use. Detailed Implementation

[0028] The present invention will be further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments.

[0029] It should be noted that, unless otherwise specified, all chemical reagents involved in this invention were purchased through commercial channels.

[0030] A method for preparing a composite polyacrylonitrile-based graphite soft felt includes the following steps:

[0031] S1. Polyacrylonitrile filaments are bundled together, crimped, and chopped. After being opened, they are carded into a web and laid up. Then, they are pre-oxidized to obtain a pre-oxidized fiber web.

[0032] In this step, the processed polyacrylonitrile filament fibers range from 1.67 to 6.67 dtex; the crimp is 4-8; then the fiber bundles with a crimp of 4-8 are chopped to a length of 38-65 mm.

[0033] The opening process is as follows: the opened fibers are conveyed by airflow to the first mixing chamber for mixing, and then the material is vertically grasped by the material handling device for secondary opening and mixing. This ensures that the fiber raw materials are mixed evenly. After being finely opened by the fine opening machine, the fibers are distributed to the feeding box of the subsequent web forming equipment for subsequent web forming processing and combed into a uniform fiber web.

[0034] The carding and web forming process combines airflow web forming and carding web forming. The initial process uses airflow web forming, which causes the fibers to fall off the needle cloth teeth under the combined action of centrifugal force generated by high-speed rotation and airflow. The fibers are then transported by airflow and condensed on the web forming curtain (or dust cage) to form a three-dimensional randomly arranged fiber web, resulting in a fiber web uniformity value of 14-16. Then, the doffer in the carding machine continues to condense and output the fiber web, resulting in a fiber web uniformity value of 4-6.

[0035] The layup process is vertical web laying, which involves folding a single layer of fiber web up and down so that the fibers in the web are arranged in a nearly vertical manner. After folding, the fiber web tends to have a three-dimensional structure. The product is better than cross-layup and parallel layup in terms of fluffiness, heat insulation, and strength in all directions. The layup thickness is 5-40mm.

[0036] The pre-oxidation process involves placing the formed fiber web in multiple layers on a transmission screen in a pre-oxidation furnace. Pre-oxidation after the web is combed is one of the innovations of this invention. The pre-oxidation temperature is 200℃-280℃ and the treatment time is 1-4 hours.

[0037] S2. The pre-oxidized fiber web is pre-punched and re-punched by a needle punching machine to obtain a shaped pre-oxidized fiber felt.

[0038] In this step, the needle punching process adopts progressive needle punching. The preceding process uses two pre-needling machines to needle the pre-oxidized fiber web upward and downward respectively, ensuring that the highly fluffy pre-oxidized fiber web after oxidation is smoothly fed into the main needle punching area without causing congestion or excessive unexpected stretching. The main needle punching machine further reinforces the fiber web after pre-needling to obtain the pre-oxidized fiber felt.

[0039] S3 and pre-oxidized fiber felt are successively subjected to low-temperature carbonization, high-temperature carbonization, and high-temperature graphitization to obtain polyacrylonitrile-based graphite soft felt.

[0040] In this step, the low-temperature carbonization process is carried out at a temperature of 400-700℃, with nitrogen as the medium atmosphere, for a processing time of 1-3 hours and a heating rate of 50-150℃ / hour. As a preferred option, the process involves holding the carbonized fiber felt at 400-600℃ for 0.5-1.5 hours and at 600-700℃ for 0.5-1.5 hours. During the carbonization process, the pyrolysis gases generated by the fiber felt, such as water molecules, are evacuated, condensed, collected, and discharged using a vacuum pump, while maintaining the vacuum level below 12 Pa.

[0041] The high-temperature carbonization treatment temperature is 1200-1400℃, the medium atmosphere is nitrogen, the treatment time is 1-3h, the heating rate is 50-150℃ / h, and the pyrolysis gas generated by the fiber during the carbonization process is evacuated, condensed, collected and discharged by a vacuum pump.

[0042] The high-temperature graphitization treatment temperature is 1800℃-2200℃, the medium atmosphere is nitrogen or argon, the treatment time is 0.5-2h, and the heating rate is 200-400℃ / h. As a preferred method, the temperature is held at 1800℃-2000℃ for 0.5-1.5h and at 2000℃-2200℃ for 0.5-1.5h. During the high-temperature graphitization process, the process involves vacuum pumping, condensation, and collection to remove impurity elements in a timely manner, ensuring the purity of the final product. The vacuum degree is controlled below 12Pa.

[0043] S4. The polyacrylonitrile-based graphite soft felt is first pretreated, then immersed in the composite slurry for 2-4 hours at room temperature, then taken out and vacuum dried to obtain the composite polyacrylonitrile-based graphite soft felt, wherein the composite slurry includes waterborne epoxy resin, modified bentonite, calcium carbonate whiskers and ceramic powder.

[0044] In this step, the mass ratio of pretreated polyacrylonitrile-based graphite felt to composite slurry is 1:20-30.

[0045] The mass ratio of waterborne epoxy resin, modified bentonite, calcium carbonate whiskers and ceramic powder in the composite slurry is 80-100:5-10:3-5:1-2.

[0046] The preparation method of modified bentonite is as follows:

[0047] Bentonite was dispersed in deionized water, and then hexadecyltrimethylammonium bromide was added. The mixture was heated and stirred at 80-90℃ for 4-8 hours. The mixture was washed, filtered, and dried to obtain pretreated bentonite.

[0048] Carrageenan is added to deionized water and stirred at 75-90℃ to dissolve. Then, pretreated bentonite is added and dispersed evenly. The mixture is poured into a mold, cooled to room temperature, freeze-dried, and then pulverized to obtain modified bentonite.

[0049] The mass ratio of bentonite to hexadecyltrimethylammonium bromide is 8-12:1-3; more preferably, the mass ratio of bentonite to hexadecyltrimethylammonium bromide is 10:2.

[0050] The mass ratio of carrageenan, deionized water and pretreated bentonite is 1-2:100:6-10, and more preferably 2:100:8;

[0051] The pretreatment process of polyacrylonitrile-based graphite soft felt is as follows: immerse polyacrylonitrile-based graphite soft felt in an ethanol aqueous solution, then add KH560 to it, heat and stir for 2-3 hours, then take it out, wash and dry it to obtain pretreated polyacrylonitrile-based graphite soft felt.

[0052] The mass ratio of polyacrylonitrile-based graphite felt to KH560 is 10-15:1-3, more preferably 10-12:1-2;

[0053] The mass fraction of the ethanol aqueous solution is 60-80%, more preferably 70-80%.

[0054] The present invention will be further illustrated below through specific embodiments. The polyacrylonitrile filament was purchased from Shanghai Fuding New Material Technology Co., Ltd.; the waterborne epoxy resin was purchased from Dongguang County Jinda Chemical Co., Ltd.; the bentonite was purchased from Hubei Xingdongcheng Chemical Co., Ltd., CAS: 1302-78-8; the aspect ratio of the calcium carbonate whiskers was 20-30, CAS No.: 471-34-1; and the mesh size of the ceramic powder was 1250 mesh.

[0055] Example 1

[0056] A method for preparing a composite polyacrylonitrile-based graphite soft felt includes the following steps:

[0057] S1. After the polyacrylonitrile filament fibers are bundled, they are crimped and chopped. The crimping degree is 4 and the chopped length is 45mm. Then, after opening, they are sent to a carding machine, carded into a web, and laid up with a layup thickness of 20mm. They are then pre-oxidized at a temperature of 230℃ for 2 hours to obtain a pre-oxidized fiber web.

[0058] S2. The pre-oxidized fiber web is pre-punched and re-punched by a needle punching machine to obtain a shaped pre-oxidized fiber felt;

[0059] S3. Pre-oxidized fiber felt is subjected to low-temperature carbonization, high-temperature carbonization, and high-temperature graphitization in sequence to obtain polyacrylonitrile-based graphite soft felt. The low-temperature carbonization treatment temperature is 500℃, the medium atmosphere is nitrogen, the treatment time is 3h, and the heating rate is 100℃ / h. The high-temperature carbonization treatment temperature is 1200℃, the medium atmosphere is nitrogen, the treatment time is 3h, and the heating rate is 100℃ / h. The high-temperature graphitization treatment temperature is 1800℃, the medium atmosphere is nitrogen, the treatment time is 2h, and the heating rate is 200℃ / h.

[0060] S4. Immerse 10g of pretreated polyacrylonitrile-based graphite soft felt in 200g of composite slurry, soak at room temperature for 4h, then take it out and dry it under vacuum to obtain composite polyacrylonitrile-based graphite soft felt. The mass ratio of waterborne epoxy resin, modified bentonite, calcium carbonate whiskers and ceramic powder in the composite slurry is 90:5:3:2.

[0061] The preparation method of modified bentonite is as follows:

[0062] 8g of bentonite was dispersed in 150g of deionized water, and then 1g of hexadecyltrimethylammonium bromide was added. The mixture was heated and stirred at 80°C for 4 hours. The mixture was washed, filtered, and dried to obtain pretreated bentonite.

[0063] Add 1g of carrageenan to 100g of deionized water and stir to dissolve at 80℃. Then add 6g of pretreated bentonite, disperse evenly, pour into a mold, cool to room temperature, freeze dry, pulverize, and pass through an 80-mesh sieve to obtain modified bentonite.

[0064] The pretreatment process of polyacrylonitrile-based graphite soft felt is as follows: 10g of polyacrylonitrile-based graphite soft felt is immersed in 150g of 60wt% ethanol aqueous solution, then 1g of KH560 is added, heated and stirred for 2h, then taken out, washed and dried to obtain pretreated polyacrylonitrile-based graphite soft felt.

[0065] Example 2

[0066] A method for preparing a composite polyacrylonitrile-based graphite soft felt includes the following steps:

[0067] S1. After the polyacrylonitrile filament fibers are bundled, they are crimped and chopped. The crimping degree is 6 and the chopped length is 40mm. Then, after opening, they are sent to a carding machine, carded into a web, and laid up with a layer thickness of 25mm. They are then pre-oxidized at a temperature of 280℃ for 3 hours to obtain a pre-oxidized fiber web.

[0068] S2. The pre-oxidized fiber web is pre-punched and re-punched by a needle punching machine to obtain a shaped pre-oxidized fiber felt;

[0069] S3. Pre-oxidized fiber felt is subjected to low-temperature carbonization, high-temperature carbonization, and high-temperature graphitization in sequence to obtain polyacrylonitrile-based graphite soft felt. The low-temperature carbonization treatment temperature is 600℃, the medium atmosphere is nitrogen, the treatment time is 2h, and the heating rate is 100℃ / h. The high-temperature carbonization treatment temperature is 1400℃, the medium atmosphere is nitrogen, the treatment time is 2h, and the heating rate is 100℃ / h. The high-temperature graphitization treatment temperature is 2000℃, the medium atmosphere is nitrogen, the treatment time is 1h, and the heating rate is 200℃ / h.

[0070] S4. Immerse 10g of pretreated polyacrylonitrile-based graphite soft felt in 300g of composite slurry, soak at room temperature for 4h, then take it out and dry it under vacuum to obtain composite polyacrylonitrile-based graphite soft felt. The mass ratio of waterborne epoxy resin, modified bentonite, calcium carbonate whiskers and ceramic powder in the composite slurry is 84:10:4:2.

[0071] The preparation method of modified bentonite is as follows:

[0072] 10g of bentonite was dispersed in 150g of deionized water, and then 2g of hexadecyltrimethylammonium bromide was added. The mixture was heated and stirred at 90°C for 4 hours. The mixture was washed, filtered, and dried to obtain pretreated bentonite.

[0073] Add 2g of carrageenan to 100g of deionized water and stir to dissolve at 80℃. Then add 8g of pretreated bentonite, disperse evenly, pour into a mold, cool to room temperature, freeze dry, pulverize, and pass through an 80-mesh sieve to obtain modified bentonite.

[0074] The pretreatment process of polyacrylonitrile-based graphite soft felt is as follows: 12g of polyacrylonitrile-based graphite soft felt is immersed in 150g of 80wt% ethanol aqueous solution, then 2g of KH560 is added, heated and stirred for 2h, then taken out, washed and dried to obtain pretreated polyacrylonitrile-based graphite soft felt.

[0075] Example 3

[0076] A method for preparing a composite polyacrylonitrile-based graphite soft felt includes the following steps:

[0077] S1. After the polyacrylonitrile filament fibers are bundled, they are crimped and chopped to a crimp degree of 8 and a chopped length of 60 mm. Then, after opening, they are fed into a carding machine, carded into a web, and laid up with a web thickness of 15 mm. They are then pre-oxidized at a temperature of 200℃ for 4 hours to obtain a pre-oxidized fiber web.

[0078] S2. The pre-oxidized fiber web is pre-punched and re-punched by a needle punching machine to obtain a shaped pre-oxidized fiber felt;

[0079] S3. Pre-oxidized fiber felt is subjected to low-temperature carbonization, high-temperature carbonization, and high-temperature graphitization treatment in sequence to obtain polyacrylonitrile-based graphite soft felt. The low-temperature carbonization treatment temperature is 500℃, the medium atmosphere is nitrogen, the treatment time is 2h, and the heating rate is 100℃ / h. The high-temperature carbonization treatment temperature is 1300℃, the medium atmosphere is nitrogen, the treatment time is 2h, and the heating rate is 100℃ / h. The high-temperature graphitization treatment temperature is 2200℃, the medium atmosphere is nitrogen, the treatment time is 0.5h, and the heating rate is 200℃ / h.

[0080] S4. Immerse 10g of pretreated polyacrylonitrile-based graphite soft felt in 400g of composite slurry, soak at room temperature for 4h, then take it out and dry it under vacuum to obtain composite polyacrylonitrile-based graphite soft felt. The mass ratio of waterborne epoxy resin, modified bentonite, calcium carbonate whiskers and ceramic powder in the composite slurry is 85:10:3:2.

[0081] The preparation method of modified bentonite is as follows:

[0082] 12g of bentonite was dispersed in 150g of deionized water, and then 3g of cetyltrimethylammonium bromide was added. The mixture was heated and stirred at 90°C for 4 hours. The mixture was washed, filtered, and dried to obtain pretreated bentonite.

[0083] Add 2g of carrageenan to 100g of deionized water and stir to dissolve at 80℃. Then add 10g of pretreated bentonite, disperse evenly, pour into a mold, cool to room temperature, freeze dry, pulverize, and pass through an 80-mesh sieve to obtain modified bentonite.

[0084] The pretreatment process of polyacrylonitrile-based graphite soft felt is as follows: 10g of polyacrylonitrile-based graphite soft felt is immersed in 150g of 70wt% ethanol aqueous solution, then 2g of KH560 is added, heated and stirred for 2h, then taken out, washed and dried to obtain pretreated polyacrylonitrile-based graphite soft felt.

[0085] Example 4

[0086] A method for preparing a composite polyacrylonitrile-based graphite soft felt includes the following steps:

[0087] S1. After the polyacrylonitrile filament fibers are bundled, they are crimped and chopped. The crimping degree is 5 and the chopped length is 42mm. Then, after opening, they are sent to a carding machine, carded into a web, and laid up with a layup thickness of 20mm. They are then pre-oxidized at a temperature of 260℃ for 4 hours to obtain a pre-oxidized fiber web.

[0088] S2. The pre-oxidized fiber web is pre-punched and re-punched by a needle punching machine to obtain a shaped pre-oxidized fiber felt;

[0089] S3. Pre-oxidized fiber felt is subjected to low-temperature carbonization, high-temperature carbonization, and high-temperature graphitization treatment in sequence to obtain polyacrylonitrile-based graphite soft felt. The low-temperature carbonization treatment temperature is 700℃, the medium atmosphere is nitrogen, the treatment time is 1h, and the heating rate is 100℃ / h. The high-temperature carbonization treatment temperature is 1400℃, the medium atmosphere is nitrogen, the treatment time is 1h, and the heating rate is 100℃ / h. The high-temperature graphitization treatment temperature is 2200℃, the medium atmosphere is nitrogen, the treatment time is 1.5h, and the heating rate is 200℃ / h.

[0090] S4. Immerse 10g of pretreated polyacrylonitrile-based graphite soft felt in 300g of composite slurry, soak at room temperature for 4h, then take it out and dry it under vacuum to obtain composite polyacrylonitrile-based graphite soft felt. The mass ratio of waterborne epoxy resin, modified bentonite, calcium carbonate whiskers and ceramic powder in the composite slurry is 85:10:3:2.

[0091] The preparation method of modified bentonite is as follows:

[0092] 10g of bentonite was dispersed in 150g of deionized water, and then 3g of hexadecyltrimethylammonium bromide was added. The mixture was heated and stirred at 80°C for 6 hours. The mixture was washed, filtered, and dried to obtain pretreated bentonite.

[0093] Add 1.5g of carrageenan to 100g of deionized water and stir to dissolve at 80℃. Then add 10g of pretreated bentonite, disperse evenly, pour into a mold, cool to room temperature, freeze dry, pulverize, and pass through an 80-mesh sieve to obtain modified bentonite.

[0094] The pretreatment process of polyacrylonitrile-based graphite soft felt is as follows: 10g of polyacrylonitrile-based graphite soft felt is immersed in 150g of 70wt% ethanol aqueous solution, then 2g of KH560 is added, heated and stirred for 2h, then taken out, washed and dried to obtain pretreated polyacrylonitrile-based graphite soft felt.

[0095] Comparative Example 1

[0096] A method for preparing a composite polyacrylonitrile-based graphite soft felt includes the following steps:

[0097] S1. After the polyacrylonitrile filament fibers are bundled, they are crimped and chopped to a crimp degree of 8 and a chopped length of 60 mm. Then, after opening, they are fed into a carding machine, carded into a web, and laid up with a web thickness of 15 mm. They are then pre-oxidized at a temperature of 200℃ for 4 hours to obtain a pre-oxidized fiber web.

[0098] S2. The pre-oxidized fiber web is pre-punched and re-punched by a needle punching machine to obtain a shaped pre-oxidized fiber felt;

[0099] S3. Pre-oxidized fiber felt is subjected to low-temperature carbonization, high-temperature carbonization, and high-temperature graphitization treatment in sequence to obtain polyacrylonitrile-based graphite soft felt. The low-temperature carbonization treatment temperature is 500℃, the medium atmosphere is nitrogen, the treatment time is 2h, and the heating rate is 100℃ / h. The high-temperature carbonization treatment temperature is 1300℃, the medium atmosphere is nitrogen, the treatment time is 2h, and the heating rate is 100℃ / h. The high-temperature graphitization treatment temperature is 2200℃, the medium atmosphere is nitrogen, the treatment time is 0.5h, and the heating rate is 200℃ / h.

[0100] S4. Immerse 10g of pretreated polyacrylonitrile-based graphite soft felt in 400g of composite slurry, soak at room temperature for 4h, then take it out and dry it under vacuum to obtain composite polyacrylonitrile-based graphite soft felt. The mass ratio of waterborne epoxy resin, bentonite, calcium carbonate whiskers and ceramic powder in the composite slurry is 85:10:3:2.

[0101] The pretreatment process of polyacrylonitrile-based graphite soft felt is as follows: 10g of polyacrylonitrile-based graphite soft felt is immersed in 150g of 70wt% ethanol aqueous solution, then 2g of KH560 is added, heated and stirred for 2h, then taken out, washed and dried to obtain pretreated polyacrylonitrile-based graphite soft felt.

[0102] The graphite felts prepared in Examples 1-4 and Comparative Example 1 were made into 50mm×50mm×10mm specimens for testing. The thermal conductivity was tested according to GB / T 10294-2008 at 25℃. The tensile strength was tested according to GB / T 30804-2014 using a type B specimen structure at a test speed of 10mm / min. The test results are shown in Table 1.

[0103] Table 1

[0104]

[0105]

[0106] Finally, it should be noted that the above embodiments do not limit the present invention in any way. Those skilled in the art can make modifications and improvements based on the present invention. Therefore, any modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a composite polyacrylonitrile-based graphite soft felt, characterized in that, Includes the following steps: S1. Polyacrylonitrile filaments are bundled together, crimped and chopped, then opened and entered into a carding machine, carded into a web, laid up, and pre-oxidized to obtain a pre-oxidized fiber web. S2. The pre-oxidized fiber web is pre-punched and re-punched by a needle punching machine to obtain a shaped pre-oxidized fiber felt; S3, pre-oxidized fiber felt is subjected to low-temperature carbonization treatment, high-temperature carbonization treatment and high-temperature graphitization treatment in sequence to obtain polyacrylonitrile-based graphite soft felt. S4. The polyacrylonitrile-based graphite soft felt is pretreated and then immersed in the composite slurry for 2-4 hours at room temperature. After that, it is taken out and dried under vacuum to obtain the composite polyacrylonitrile-based graphite soft felt. The composite slurry includes waterborne epoxy resin, modified bentonite, calcium carbonate whiskers and ceramic powder. In step S4, the modified bentonite is prepared as follows: (1) Disperse bentonite in deionized water, then add hexadecyltrimethylammonium bromide to it, heat and stir at 80-90℃ for 4-8 hours, and wash, filter and dry the mixture to obtain pretreated bentonite; (2) Add carrageenan to deionized water and stir to dissolve at 75-90℃. Then add pretreated bentonite, disperse evenly, pour into a mold, cool to room temperature, freeze dry and then pulverize to obtain modified bentonite.

2. The method for preparing composite polyacrylonitrile-based graphite soft felt according to claim 1, characterized in that, In step S1, the curl degree is 4-8 and the short cut length is 38-65mm.

3. The method for preparing composite polyacrylonitrile-based graphite soft felt according to claim 1, characterized in that, In step S1, the pre-oxidation treatment temperature is 200-280℃, and the pre-oxidation treatment time is 1-4h.

4. The method for preparing composite polyacrylonitrile-based graphite soft felt according to claim 1, characterized in that, In step S3, the low-temperature carbonization treatment temperature is 400-700℃ and the treatment time is 1-3h; the high-temperature carbonization treatment temperature is 1200-1400℃ and the treatment time is 1-3h; the high-temperature graphitization treatment temperature is 1800-2200℃ and the treatment time is 0.5-2h.

5. The method for preparing composite polyacrylonitrile-based graphite soft felt according to claim 1, characterized in that, In step (1), the mass ratio of bentonite to hexadecyltrimethylammonium bromide is 8-12:1-3.

6. The method for preparing composite polyacrylonitrile-based graphite felt according to claim 1, characterized in that, In step (2), the mass ratio of carrageenan, deionized water and pretreated bentonite is 1-2:100:6-10.

7. The method for preparing composite polyacrylonitrile-based graphite soft felt according to claim 1, characterized in that, In step S4, the pretreatment process of polyacrylonitrile-based graphite soft felt is as follows: the polyacrylonitrile-based graphite soft felt is immersed in an ethanol aqueous solution, then KH560 is added to it, and the mixture is heated and stirred for 2-3 hours. After that, it is taken out, washed, and dried to obtain pretreated polyacrylonitrile-based graphite soft felt.

8. The method for preparing composite polyacrylonitrile-based graphite soft felt according to claim 1, characterized in that, In step S4, the mass ratio of waterborne epoxy resin, modified bentonite, calcium carbonate whiskers and ceramic powder is 80-100:5-10:3-5:1-2.

9. The composite polyacrylonitrile-based graphite felt prepared by the preparation method according to any one of claims 1-8.

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