Modified aramid short fiber and preparation method thereof

Abstract

The invention discloses a modified aramid short fiber and a preparation method thereof, and belongs to the field of non-fiber weaving. According to the preparation method, a one-step impregnation process and plasma treatment are combined, the nano whiskers are grafted to the surfaces of the aramid fibers, the physical binding force between the aramid fibers and resin is improved, meanwhile, the coating resin reacts to the surfaces of the aramid fibers and the nano whiskers, and the dispersity and the chemical binding force of the aramid fibers are improved; therefore, the mechanical interlocking effect and the chemical bonding effect of the aramid fiber and the resin are improved, meanwhile, the dispersity of the aramid fiber in the resin can be improved, the wear resistance and the mechanical property of the aramid fiber can be greatly improved after the aramid fiber is mixed with the resin, and the method is low in energy consumption, non-toxic and easy for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of non-fiber weaving, specifically relating to a modified aramid staple fiber and its preparation method. Background Technology

[0002] Aramid fiber, also known as aromatic polyamide fiber, is a new type of high-tech synthetic fiber with excellent properties such as ultra-high strength, high modulus, high temperature resistance, acid and alkali resistance, and light weight. Its strength is 5-6 times that of steel wire, its modulus is 2-3 times that of steel wire or glass fiber, and its toughness is twice that of steel wire, while its weight is only about 1 / 5 that of steel wire. It does not decompose or melt at 560 degrees Celsius. It has good insulation and anti-aging properties and a long lifespan. Currently, it is widely used in various fields such as life protection, aerospace, composite materials, fiber optic communication, electrical insulation, and the automotive industry.

[0003] Structurally, aramid fibers have a smooth surface, a high degree of orientation, and lack active groups, making it difficult to form chemical bonds with other atoms or groups. To improve the compatibility of aramid fibers with other materials, it is necessary to modify or treat the aramid fibers.

[0004] Chinese patent document CN113463396A discloses an aramid staple fiber for nylon resin products and its preparation method. The method involves surface modification of aramid fibers using water-based epoxy and isocyanate treatment agents to obtain modified aramid fibers; modification of nylon using phenolic resin to obtain modified nylon; carding and splitting the modified aramid fibers; attaching modified nylon to the surface; and cutting to obtain aramid staple fibers for nylon resin products. The aramid staple fibers prepared by this method have improved dispersion in nylon due to the surface coating of modified nylon resin. However, this method requires two impregnation and coating processes, each requiring drying, resulting in significant energy consumption. This method is only suitable for nylon matrices or resins with similar structures to nylon; it is less effective for resins with significant structural differences and a lack of active groups in their molecular chains.

[0005] Chinese patent document CN114059347A discloses a surface modification method to improve the bonding strength between ultra-high molecular weight polyethylene (UHMWPE) fibers and matrix resins. This method utilizes plasma to introduce functional groups onto the surface of UHMWPE fibers, followed by the use of silane coupling agents and inorganic nanoparticles to increase the fiber roughness, thereby increasing the bonding strength between UHMWPE and the material. However, the introduction of inorganic nanoparticles onto the fiber surface leads to increased fiber rigidity, making the fibers more prone to breakage during melt mixing. Furthermore, the increased surface roughness makes it difficult for the fibers to disperse in the resin, resulting in a decrease in the tensile and flexural properties of the material after resin addition. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing modified aramid short fibers, which can effectively improve the dispersibility and chemical bonding of aramid fibers. This method is simple, energy-efficient, non-toxic, and easy to industrialize.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for preparing modified aramid staple fibers, comprising the following steps: (1) The aramid fiber is subjected to plasma treatment to obtain activated aramid fiber; (2) Dissolve the coating resin, coupling agent, chain extender, penetrant, and nanocrystals in water, stir until completely dissolved, and let stand for 20-40 minutes to obtain the impregnating agent; (3) The activated aramid fiber in step (1) is impregnated with the impregnating agent in step (2) and dried to obtain modified aramid fiber.

[0008] (4) Cut the modified aramid fiber in step (3) to obtain modified aramid short fiber.

[0009] Preferably, in step (1), the plasma treatment time is 30-120s, the treatment gas is one or two of air, argon, and nitrogen, the gas flow rate is 2-4L / min, and the power is 800-2000W.

[0010] Preferably, in step (2), the coating resin is one or more of polyethylene oxide, waterborne polyurethane, waterborne epoxy resin, and acrylic resin; the chain extender is one of blocked isocyanate and epoxy chain extender; and the penetrant is one of penetrant T, penetrant M, and penetrant SFC.

[0011] Preferably, in step (2), the coupling agent is one of Woland coupling agent, silane coupling agent, and titanate coupling agent; the nano whiskers are one of nano silicon carbide whiskers, nano calcium carbonate whiskers, and nano calcium sulfate whiskers.

[0012] Preferably, in step (2), the mass ratio of water, coating resin, chain extender, coupling agent, penetrant, and nano whiskers is 54-83:10-30:1-3:2-5:2-3:3-8.

[0013] Preferably, in step (3), the soaking time is 10-30s; the drying process is pre-drying at 80-100℃ for 30-40s and drying at 120-150℃ for 10-20s.

[0014] Preferably, in step (3), the weight increase of the modified aramid fiber is 2%-5% of that of the activated aramid fiber in step (1).

[0015] Another object of the present invention is to provide a modified aramid short fiber prepared by the above method, the surface of which comprises a composite layer of nanofibers and a coating resin.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The technical solution of the present invention uses plasma technology in combination with coupling agent to achieve resin coating in one impregnation step. The combination of nano whiskers and aramid can significantly reduce the energy consumption of the drying process, thereby saving energy and shortening the processing time.

[0017] (2) The technical solution of the present invention adopts plasma treatment, with a limited treatment time of 30-120s, a gas flow rate of 2-4L / min, and a power of 800-2000W. By coordinating the gas flow rate and power, the degree of etching on the fiber surface is controlled, which avoids excessive damage to the fiber structure and ensures that the active sites are fully exposed.

[0018] (3) The technical solution of the present invention introduces nanofibers with a high aspect ratio on the surface of aramid fibers. After mixing with resin, the bonding force between aramid fibers and resin can be greatly improved. At the same time, the aramid fibers with introduced nanofibers can transmit stress well. After adding resin, the wear resistance and tensile and bending properties of the material can be greatly improved.

[0019] (4) The technical solution of the present invention is to coat the surface of the nano whiskers with resin. When the modified aramid fiber is added to the plastic for melt blending, the coating resin can melt and play a lubricating and isolating role, so as to avoid the nano whiskers from breaking during the melt blending process due to the increased rigidity after being grafted to the fiber.

[0020] (5) The technical solution of the present invention improves the bonding force between aramid and resin through the mechanical interlocking effect between fiber and resin. At the same time, the surface-coated resin can also play a chemical bonding role with resin with similar structure. Therefore, the modified aramid fiber prepared by the technical solution of the present invention has stronger universality.

[0021] (6) In this invention, nano-whiskers and coating resin are introduced on the fiber surface. The coating resin is melted by segmented drying and grafted onto the nano-whiskers and aramid fiber surface by reaction with chain extender. The thermoplasticity of the resin is ensured by controlling the amount of chain extender. Therefore, the resin on the surface can play a role in structural protection and promoting dispersion during melt blending. Compared with the prior art of directly grafting nanoparticles onto the aramid fiber surface, the modified aramid obtained is easier to disperse in the resin and its structure is not easily destroyed.

[0022] (7) The present invention uses segmented drying to fully dry the water in the impregnating agent so that the coating resin melts and reacts with the chain extender. Compared with the existing single drying technology, it can prevent the water from reacting with the chain extender at excessively high temperatures or the coating resin from wrapping the water on the surface of the aramid fiber, which would affect the performance of the modified fiber. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. The plasma treatment equipment used in the embodiments of the present invention is the NE-VRL500 plasma cleaner from Ninebot. Example 1

[0024] (1) Aramid fibers were activated by plasma treatment in air atmosphere. The treatment time was 120s, the gas flow rate was 2L / min, and the treatment power was 800W.

[0025] (2) Weigh water, coating resin, chain extender, coupling agent, penetrant, and nano whiskers in a mass ratio of 83:10:1:2:2:3. Dissolve the weighed coating resin, chain extender, coupling agent, penetrant, and nano whiskers in water and stir until completely dissolved. Let stand for 20 minutes to obtain an impregnating agent. The coating resin is a mixture of waterborne epoxy resin and waterborne polyurethane resin in a 2:1 ratio. The chain extender is a blocked isocyanate, the coupling agent is a silane coupling agent, the penetrant is penetrant M, and the nano whiskers are nano silicon carbide whiskers.

[0026] (3) The activated aramid fiber was impregnated for 10 seconds; it was pre-dried at 80°C for 30 seconds and then dried at 120°C for 10 seconds to obtain the modified aramid fiber. The weight increase of the modified aramid fiber was 2% of that of the activated aramid fiber.

[0027] (4) The modified aramid fiber is cut to obtain modified aramid short fiber. Example 2

[0028] (1) Aramid fibers were activated by plasma treatment under a mixture of argon and nitrogen. The mixing ratio of argon and nitrogen was 3:1, the treatment time was 30s, the gas flow rate was 4L / min, and the treatment power was 2000W.

[0029] (2) Weigh water, coating resin, chain extender, coupling agent, penetrant, and nano whiskers in a mass ratio of 54:30:3:5:3:8. Dissolve the weighed coating resin, coupling agent, penetrant, chain extender, and nano whiskers in water and stir until completely dissolved. Let stand for 40 minutes to obtain an impregnating agent. The coating resin is acrylic resin, the chain extender is epoxy chain extender, the coupling agent is titanate coupling agent, the penetrant is penetrant T, and the nano whiskers are nano calcium carbonate whiskers.

[0030] (3) The activated aramid fiber was impregnated for 30 seconds; it was pre-dried at 100℃ for 40 seconds and dried at 150℃ for 20 seconds to obtain the modified aramid fiber. The weight increase of the modified aramid fiber was 5% of that of the activated aramid fiber.

[0031] (4) The modified aramid fiber is cut to obtain modified aramid short fiber. Example 3

[0032] (1) Aramid fibers were activated by plasma treatment in a mixture of air and nitrogen, wherein the mixing ratio of air and nitrogen was 3:1, the treatment time was 95s, the gas flow rate was 3L / min, and the treatment power was 1700W.

[0033] (2) Weigh water, coating resin, chain extender, coupling agent, penetrant, and nano whiskers in a mass ratio of 68:20:2:4:2.5:5.5. Dissolve the weighed coating resin, chain extender, coupling agent, penetrant, and nano whiskers in water and stir until completely dissolved. Let stand for 25 minutes to obtain an impregnating agent. The coating resin is polyethylene oxide, the chain extender is blocked isocyanate, the coupling agent is Wolan coupling agent, the penetrant is penetrant T, and the nano whiskers are nano calcium sulfate whiskers.

[0034] (3) The activated aramid fiber was impregnated for 15 seconds; it was pre-dried at 87°C for 37 seconds and then dried at 130°C for 15 seconds to obtain the modified aramid fiber. The weight increase of the modified aramid fiber was 4% of that of the activated aramid fiber.

[0035] (4) The modified aramid fiber is cut to obtain modified aramid short fiber. Example 4

[0036] (1) Aramid fibers were activated by plasma treatment under a mixture of argon and nitrogen. The mixing ratio of argon and nitrogen was 1:3, the treatment time was 75s, the gas flow rate was 3.5L / min, and the treatment power was 1100W.

[0037] (2) Weigh water, coating resin, chain extender, coupling agent, penetrant, and nano whiskers in a mass ratio of 75.5:15:1.5:3:2:4.5. Dissolve the weighed coating resin, chain extender, coupling agent, penetrant, and nano whiskers in water and stir until completely dissolved. Let stand for 35 minutes to obtain an impregnating agent. The coating resin is a mixture of waterborne polyurethane, acrylic resin, and waterborne epoxy resin in a ratio of 2:1:1. The chain extender is an epoxy chain extender, the coupling agent is a titanate coupling agent, the penetrant is penetrant T, and the nano whiskers are nano silicon carbide whiskers. (3) The activated aramid fiber was impregnated for 20s; it was pre-dried at 95℃ for 35s and dried at 138℃ for 17s to obtain the modified aramid fiber. The weight increase of the modified aramid fiber was 3% of that of the activated aramid fiber.

[0038] (4) Cut the modified aramid fiber to obtain aramid short fiber. Comparative Example 1

[0039] 1) Activated aramid fibers were obtained by plasma treatment of aramid fibers in an air atmosphere. The treatment time was 120 s, the gas flow rate was 2 L / min, and the treatment power was 800 W. (2) Weigh water, coating resin, chain extender, coupling agent, and penetrant in a mass ratio of 83:10:1:2:2. Dissolve the weighed coating resin, chain extender, coupling agent, and penetrant in water and stir until completely dissolved. Let stand for 20 minutes to obtain an impregnating agent. The coating resin is a mixture of waterborne epoxy resin and waterborne polyurethane resin in a 2:1 ratio. The chain extender is a blocked isocyanate, the coupling agent is a silane coupling agent, and the penetrant is penetrant M. (3) The activated aramid fiber was impregnated for 10 seconds; it was pre-dried at 80°C for 30 seconds and then dried at 120°C for 10 seconds to obtain the modified aramid fiber. The weight increase of the modified aramid fiber was 2% of that of the activated aramid fiber.

[0040] (4) The modified aramid fiber is cut to obtain modified aramid short fiber. Comparative Example 2

[0041] (1) Aramid fibers were activated by plasma treatment in air atmosphere. The treatment time was 120 s, the gas flow rate was 2 L / min, and the treatment power was 800 W.

[0042] (2) Weigh water, coupling agent, chain extender, penetrant and nano whiskers in a mass ratio of 83:1:2:2:3. Dissolve the weighed coupling agent, chain extender, penetrant and nano whiskers in water and stir until completely dissolved. Let stand for 20 minutes to obtain impregnating agent. Among them, the chain extender is blocked isocyanate, the coupling agent is silane coupling agent, the penetrant is penetrant M and the nano whiskers are nano silicon carbide whiskers.

[0043] (3) The activated aramid fiber was impregnated for 10 seconds; it was pre-dried at 80°C for 30 seconds and then dried at 120°C for 10 seconds to obtain the modified aramid fiber. The weight increase of the modified aramid fiber was 2% of that of the activated aramid fiber.

[0044] (4) The modified aramid fiber is cut to obtain modified aramid short fiber. Comparative Example 3

[0045] (1) Aramid fibers were activated by plasma treatment in air atmosphere. The treatment time was 120s, the gas flow rate was 2L / min, and the treatment power was 800W.

[0046] (2) Weigh water, coating resin, chain extender, coupling agent, penetrant, and nano whiskers in a mass ratio of 83:10:1:2:2:3. Dissolve the weighed coating resin, chain extender, coupling agent, penetrant, and nano whiskers in water and stir until completely dissolved. Let stand for 20 minutes to obtain an impregnating agent. The coating resin is a mixture of waterborne epoxy resin and waterborne polyurethane resin in a 2:1 ratio. The chain extender is a blocked isocyanate, the coupling agent is a silane coupling agent, the penetrant is penetrant M, and the nano whiskers are nano silicon carbide whiskers.

[0047] (3) The activated aramid fiber was impregnated for 10 seconds and dried at 120°C for 50 seconds. The weight increase of the modified aramid fiber was 2% of that of the activated aramid fiber.

[0048] (4) The modified aramid fiber is cut to obtain modified aramid short fiber. Comparative Example 4

[0049] (1) Aramid fibers were activated by plasma treatment in air atmosphere. The treatment time was 120s, the gas flow rate was 2L / min, and the treatment power was 800W.

[0050] (2) Weigh water, coating resin, chain extender, coupling agent, penetrant, and nano whiskers in a mass ratio of 83:10:0.2:2:2:3. Dissolve the weighed coating resin, chain extender, coupling agent, penetrant, and nano whiskers in water and stir until completely dissolved. Let stand for 20 minutes to obtain an impregnating agent. The coating resin is a mixture of waterborne epoxy resin and waterborne polyurethane resin in a 2:1 ratio. The chain extender is a blocked isocyanate, the coupling agent is a silane coupling agent, the penetrant is penetrant M, and the nano whiskers are nano silicon carbide whiskers.

[0051] (3) The activated aramid fiber was impregnated for 10 seconds; pre-dried at 80°C for 30 seconds and dried at 120°C for 10 seconds to obtain the modified aramid fiber. The weight increase of the modified aramid fiber was 2% of that of the activated aramid fiber.

[0052] (4) The modified aramid fiber is cut to obtain modified aramid short fiber. Comparative Example 5

[0053] (1) Aramid fibers were activated by plasma treatment in air atmosphere. The treatment time was 120s, the gas flow rate was 2L / min, and the treatment power was 800W.

[0054] (2) Weigh water, coating resin, chain extender, coupling agent, penetrant, and nano whiskers in a mass ratio of 83:10:5:2:2:3. Dissolve the weighed coating resin, chain extender (blocked isocyanate), coupling agent, penetrant, and nano whiskers in water, stir until completely dissolved, and let stand for 20 minutes to obtain an impregnating agent. The coating resin is a mixture of waterborne epoxy resin and waterborne polyurethane resin in a 2:1 ratio. The chain extender is blocked isocyanate, the coupling agent is silane coupling agent, the penetrant is penetrant M, and the nano whiskers are nano silicon carbide whiskers.

[0055] (3) The activated aramid fiber was impregnated for 10 seconds; pre-dried at 80°C for 30 seconds and dried at 120°C for 10 seconds to obtain the modified aramid fiber. The weight increase of the modified aramid fiber was 2% of that of the activated aramid fiber.

[0056] (4) The modified aramid fiber is cut to obtain modified aramid short fiber. Comparative Example 6

[0057] Tested using pure polyoxymethylene (1) Polyoxymethylene resin was extruded using a twin-screw extruder at a temperature of 180°C and a twin-screw speed of 60 r / min.

[0058] The modified aramid short fibers prepared in the examples and comparative examples were melt-mixed with polyoxymethylene resin at a mass ratio of 15:85 using a twin-screw extruder. The mixing conditions were a temperature of 180°C and a twin-screw speed of 60 r / min, resulting in aramid-modified polyoxymethylene composite materials. The aramid-modified polyoxymethylene composite materials prepared in each example and comparative example, as well as pure polyoxymethylene as comparative example 6, were prepared into test specimens according to the following relevant performance standards and tested: 1. Tensile strength test method: according to GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molding and extruded plastics". 2. Flexural strength test method: according to GB / T 9341-2008 "Determination of flexural properties of plastics". 3. Abrasion resistance test method: according to GBT 3960-2016 "Plastics - Test method for sliding friction and abrasion". The test results are shown in Table 1.

[0059] As can be seen from the data in the table above, the modified aramid short fibers prepared in Examples 1-5 have a better modification effect on polyoxymethylene.

[0060] As can be seen from the data in the table above, the modified aramid short fiber prepared in Comparative Example 1 has a worse modification effect than the aramid short fiber prepared in Examples 1-5. This is because in Comparative Example 1, the surface of the modified aramid fiber is only coated with a layer of resin. Although the surface coating resin can play a transitional role, the modification effect is limited due to the lack of active groups in the polyoxymethylene molecular chain. Furthermore, the resin coating on the surface of the aramid fiber makes it easier for the aramid fiber to be pulled out during the friction process, thus increasing the wear volume.

[0061] As can be seen from the data in the table above, the modified aramid short fiber prepared in Comparative Example 2 has a worse modification effect on the aramid short fiber for polyoxymethylene resin products than that prepared in Examples 1-5. This is because the surface of the aramid fiber is coated with nanofibers, which increases the rigidity and roughness of the aramid fiber. During the melt mixing process, the aramid fiber and the polyoxymethylene resin matrix are damaged by friction and shear, resulting in poor performance of the composite material.

[0062] As can be seen from the data in the table above, the modified aramid short fiber prepared in Comparative Example 3 has a worse modification effect on the aramid short fiber prepared in Examples 1-5 for polyoxymethylene resin products. This is because the chain extender reacts with water during the drying process, and some water is trapped under the resin layer, which weakens the bonding force between the resin and the aramid fiber.

[0063] As can be seen from the data in the table above, the modified aramid short fibers prepared in Comparative Example 4 have a worse modification effect on the aramid short fibers prepared in Examples 1-5 for polyoxymethylene resin products. This is because the content of chain extender is too low, which cannot effectively connect the coating resin to the surface of aramid and nanofibers. Therefore, the coating resin is easy to detach from the surface of aramid and distribute in polyoxymethylene during the mixing process, which leads to a decrease in material performance.

[0064] As shown in the table above, pure polyoxymethylene (POM) exhibits generally poor abrasion resistance and mechanical properties. However, the addition of modified aramid significantly improves its tensile and flexural properties. This is because the modified aramid has a good bonding effect with POM, effectively transferring stress and thus greatly enhancing the bending and tensile properties of POM. Furthermore, the presence of nanofibers on the surface of the modified aramid, along with the resin coating, effectively reduces fiber pull-out and POM powder generation during wear, thereby reducing the wear quality and significantly improving the material's abrasion resistance.

Claims

1. A method for preparing modified aramid staple fibers, characterized in that, Includes the following steps: (1) The aramid fiber is subjected to plasma treatment to obtain activated aramid fiber; (2) Dissolve the coating resin, chain extender, coupling agent, penetrant, and nanocrystals in water, stir until completely dissolved, and let stand for 20-40 minutes to obtain the impregnating agent; (3) The activated aramid fiber is impregnated with the impregnating agent of step (2) and dried in sections to obtain modified aramid fiber; (4) Cut the modified aramid fiber obtained in step (3) to obtain modified aramid short fiber.

2. The method for preparing modified aramid staple fiber according to claim 1, characterized in that, In step (1), the plasma treatment time is 30-120s, the treatment gas is one or two of air, argon, and nitrogen, the gas flow rate is 2-4L / min, and the power is 800-2000W.

3. The method for preparing modified aramid staple fibers according to claim 1, characterized in that, In step (2), the coating resin is one or more of polyethylene oxide, waterborne polyurethane, waterborne epoxy resin, and acrylic resin; the chain extender is one of blocked isocyanate and epoxy chain extender; and the penetrant is one of penetrant T, penetrant M, and penetrant SFC.

4. The method for preparing modified aramid staple fiber according to claim 1, characterized in that, In step (2), the coupling agent is one of Woland coupling agent, silane coupling agent, and titanate coupling agent; the nano whiskers are one of nano silicon carbide whiskers, nano calcium carbonate whiskers, and nano calcium sulfate whiskers.

5. The method for preparing modified aramid staple fiber according to claim 1, characterized in that, In step (2), the mass ratio of water, coating resin, chain extender, coupling agent, penetrant, and nano whiskers is 54-83:10-30:1-3:2-5:2-3:3-8.

6. The method for preparing modified aramid staple fiber according to claim 1, characterized in that, In step (3), the immersion treatment time is 10-30s; the segmented drying is: pre-drying at 80-100℃ for 30-40s, and drying at 120-150℃ for 10s-20s.

7. The method for preparing modified aramid staple fiber according to claim 1, characterized in that, In step (3), the weight increase of the modified aramid fiber is 2%-5% of that of the activated aramid fiber in step (1).

8. A modified aramid staple fiber, prepared by the method according to any one of claims 1-7, characterized in that, The surface of the modified aramid short fiber contains a composite layer of nanofibers and coated resin.

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