Aramid fiber surface treatment method

Abstract

The invention belongs to the field of fiber modification, and discloses an aramid fiber surface treatment method, which uses supercritical carbon dioxide as a main treatment medium, and adds auxiliary reagents such as acetone to treat aramid fiber under the assistance of supercritical fluid. Active substances containing epoxy groups, hydroxyl or carboxyl and the like are introduced to the surfaces of the fibers through physical or chemical effects, so that the surface activity of the fibers is improved, the interface bonding performance of the aramid fibers and resin such as epoxy and the like is enhanced, the conditions of the treatment method are relatively mild, and the mechanical property of the fibers cannot be damaged.

Description

Technical Field

[0001] This invention belongs to the field of fiber material modification, and specifically provides a method for surface treatment of aramid fibers. Background Technology

[0002] Aramid refers to high-performance fibers containing more than 85% benzene rings in an aromatic rigid chain. It has excellent properties such as high strength, high modulus, high temperature resistance, chemical solvent resistance, and low specific gravity. It is widely used in advanced strategic weapons, such as aerospace engines, bulletproof protective devices for soldiers, aerospace, automobiles, optical fiber reinforcement, and cables, and is an important strategic material.

[0003] Aramid fibers contain highly oriented crystalline regions, have a smooth surface, and few active groups, resulting in poor interfacial bonding with resins. Current technologies typically employ hot stretching to further induce internal crystal orientation and increase the fiber's modulus. However, this method often involves excessively high stretching temperatures, sometimes exceeding 500°C. o C, molecular chains will break, reducing the tensile strength of the fiber.

[0004] Patent CN201210037329.6 describes a method for surface crosslinking polymerization modification of aramid fibers in supercritical CO2, which mainly utilizes the carrying and swelling effect of supercritical CO2 to crosslink and modify the aramid fibers. CN201310419414.3 describes a method for improving the mechanical properties of aramid fibers through stretching and orientation in supercritical fluids, which utilizes the carrying effect of supercritical CO2 to achieve stretching and orientation, thereby improving the orientation and crystallinity of the aramid fibers. Both methods mention using supercritical CO2 as a fluid-assisted method to directly carry the relevant solvents. However, these methods have relatively limited solvent options and require high solubility in supercritical CO2, making industrial application difficult.

[0005] Therefore, developing a new method for surface modification of aramid fibers using supercritical carbon dioxide technology has significant practical application value. Summary of the Invention

[0006] To address the problems existing in the above-mentioned technologies, this invention provides a method for surface treatment of aramid fibers. Using supercritical carbon dioxide as the main treatment medium, and adding auxiliary reagents such as acetone, the aramid fibers are treated under supercritical fluid assistance. Active substances containing epoxy groups, hydroxyl groups, or carboxyl groups are introduced onto the fiber surface through physical or chemical action, thereby improving the surface activity of the fibers and enhancing the interfacial bonding performance between the aramid fibers and resins such as epoxy resins. The above treatment method is relatively mild and will not damage the mechanical properties of the fibers. The strength retention rate of modified aramid fibers is increased by 9.3-26.7%, the modulus retention rate is increased by 4.4-19.6%, the surface energy of aramid fibers can be increased by up to 23.5%, and the interfacial shear strength of aramid fibers can be increased by up to 38%.

[0007] The main technical solutions of this invention are as follows: Aramid fibers or fabrics are cleaned and dried with acetone. The pretreated aramid fibers are placed in a supercritical fluid reactor. The active substance is dissolved in a co-solvent. The prepared co-solvent is placed in the supercritical fluid reactor, ensuring that the co-solvent does not directly contact the aramid fibers. The reactor is sealed, and a certain volume of carbon dioxide gas is added. After treatment at a certain temperature and pressure for a certain time, the reactor is depressurized. The surface of the treated fibers is then dried to obtain the treated fibers, which can then be analyzed and tested.

[0008] The more specific technical solutions are as follows: A method for surface treatment of aramid fibers, the specific steps of which are as follows: Step 1), clean and dry the aramid fiber or its fabric with acetone, and place the pretreated aramid on the support of the supercritical reactor. Step 2): Dissolve the active substance in the co-solvent, place the prepared co-solvent at the bottom of the supercritical reactor, and ensure that the co-solvent does not come into direct contact with the aramid fiber or its fabric on the support, and seal the reactor. Step 3) Add a certain volume of carbon dioxide gas, treat it at a certain temperature and pressure for a certain time, then depressurize the reactor and dry the treated fiber surface to obtain the modified aramid fiber.

[0009] Carbon dioxide gas is introduced into the supercritical reactor. When the pressure reaches 7.38 MPa and the temperature is higher than 31.1°C, the carbon dioxide gas becomes a third state with both gas and liquid characteristics. At this time, the active material permeates into the aramid fiber through the supercritical fluid and is then grafted onto the fiber surface. Compared with the prior art of directly dissolving the target material (active material) using supercritical carbon dioxide, this application uses the permeation of supercritical carbon dioxide to uniformly and appropriately graft the active material onto the surface without directly contacting the aramid fiber.

[0010] In the preferred step 1), the aramid fiber is para-aramid Kevlar, Nomex fiber, Twaron fiber, Technora fiber, aramid III fiber, or F-12 fiber; the aramid fiber fabric is aramid fiber cloth.

[0011] In step 1), the aramid fiber or its fabric is first cleaned and dried with acetone in an ultrasonic cleaner, wherein the mass ratio of aramid fiber to acetone is 1:10-30, more preferably 1:30, the treatment temperature is 80-90℃, and the treatment time is 1-2h; after the reaction, it is dried under vacuum at 80℃ for 2h.

[0012] The support can be any of the supports in the prior art. The purpose is to suspend the aramid fiber or its fabric in the air, increase its contact area with the supercritical medium, and improve the surface treatment effect. The aramid fiber or its fabric can be suspended on the horizontal support or wrapped around the support. The specific choice can be made according to the shape of the aramid fiber or its fabric, which will not be elaborated further by the inventor.

[0013] The aforementioned active substances refer to substances containing epoxy, carboxyl, and hydroxyl groups, as detailed below: Epoxy groups: selected from trimethylolpropane triglycidyl ether (EPG–134) or glycidyl methacrylate (GMA); Carboxyl groups: selected from succinic anhydride or pyromellitic dianhydride (PMDA); Hydroxyl groups: selected from polyvinyl alcohol (PVA) or hydroxyethyl cellulose (HEC); The above active substances account for 0.5–5 wt% of the total weight of the active substances and cosolvents.

[0014] The cosolvents mentioned above are at least one of acetone, ethanol, and ethyl acetate; for the active substances mentioned above, acetone and ethyl acetate are recommended for epoxy groups; ethanol and ethyl acetate are recommended for carboxyl groups; and ethanol, ethyl acetate, and acetone are recommended for hydroxyl groups.

[0015] Furthermore, the volume ratio of CO2 to co-solvent is 1:0.2-1:3, which is determined by pressure conversion within the supercritical reactor. The co-solvent does not damage the aramid fiber and can dissolve the active material, increasing its volatility, thereby facilitating the grafting of the active material onto the surface of the aramid fiber via supercritical fluid.

[0016] The supercritical treatment conditions and process in step 3) are as follows: treatment at 7.4-20 MPa and 35-65℃ for 0.5-4 hours; pressure gradient reduction to atmospheric pressure at a rate of 0.3-1 MPa / min; and drying at 60-80℃. The reaction vessel is heated by electric heating or oil bath heating.

[0017] In the above process, excessively high temperatures will damage the aramid structure, while excessively low temperatures and pressures will not meet the supercritical requirements. If the pressure is released too quickly, the active substances grafted onto the aramid surface will be stripped off. If the time is too short, the active substances will not be completely grafted onto the aramid, and if the time is too long, the aramid properties will also be damaged.

[0018] Step 3) Before introducing carbon dioxide gas into the supercritical reactor, exhaust and drainage treatment is performed. Specifically, the exhaust and drainage treatment is as follows: first, the reaction vessel is heated until all moisture is converted into water vapor; then, the reaction vessel is evacuated. The purpose of exhaust and drainage treatment is to remove air and moisture from the sealed container and eliminate the influence of reactive gases such as oxygen and moisture in the air on the experiment.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. Due to its high crystallinity and regular rigid molecular chain structure, aramid fiber has low surface reactivity. However, the strong penetration and carrying effect of supercritical fluid can carry small molecule compounds into the interior of aramid fiber and its surface.

[0020] 2. This invention utilizes supercritical fluid technology (supercritical carbon dioxide and co-solvent) to introduce active substances into the surface and interior of aramid fibers, thereby increasing the number of surface active groups and improving the interfacial bonding performance between the fibers and the resin, while maintaining mild reaction conditions.

[0021] 3. Compared with unmodified aramid fibers, the treated aramid fibers have a strength retention rate that is 9.3-26.7% higher, a modulus retention rate that is 4.4-19.6% higher, a surface energy that can be increased by up to 23.5%, and an interfacial shear strength that can be increased by up to 38%.

[0022] 4. This invention utilizes supercritical fluid technology to modify the surface of aramid fibers. By adding co-solvents such as acetone / ethanol, it can carry 5–20 wt% of active substances (such as epoxy resin) to achieve molecular-level penetration. It has the advantages of being economical and environmentally friendly, having controllable reactions, simple separation of solvent and product, and minimal impact on the mechanical properties of the fiber, and has significant industrial application value.

[0023] 5. Although both use a supercritical CO2 system, compared with CN201210037329.6 and CN201310419414.3 in the background technology, the technical solution of this application has the following advantages: (1) The present invention adds active substances in combination with a co-solvent, which is significantly different from the additives in the above-mentioned patents. It can be easily dissolved in the supercritical CO2 system and produce a more beneficial effect on aramid. (2) The active substances are brought into the surface and interior of the aramid fiber by using supercritical fluid in combination with a co-solvent for strong penetration and carrying effect, thereby increasing the surface active groups and improving the interfacial bonding performance between the fiber and the resin. At the same time, the reaction conditions are mild. (3) The cleaning preparation conditions and reaction treatment conditions are different. The method provided by the present invention is simple and convenient, and the conditions are well controlled and easy to be applied industrially, with better results. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments, which will enable those skilled in the art to have a more comprehensive understanding of the invention, but will not limit the invention in any way. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] Before introducing carbon dioxide gas into the supercritical reactor in the following embodiments, exhaust and drainage treatment is performed: the reaction vessel is first heated until the water is converted into water vapor; then the reaction vessel is evacuated, and then the gas in the reaction vessel is discharged by replacing it with carbon dioxide gas multiple times, generally twice, each time at 0.5 MPa.

[0026] Example 1: A method for surface treatment of aramid fibers, the specific steps of which are as follows: (1) Place 5g of F-12 fiber in 150g of acetone solvent and wash it in an ultrasonic cleaner at 80℃ for 1h. Take it out and vacuum dry it at 80℃ for 2h.

[0027] (2) Wrap the F-12 fiber that has been washed and dried in step (1) around a metal support and place it in a 1L supercritical reactor.

[0028] (3) First, inject 200 mL of a mixture of acetone and EPG-134 (EPG-134 concentration of 3 wt%) into the bottom of the supercritical reactor; then pump in liquid CO2 until the pressure inside the reactor reaches 15 MPa (25℃), and raise the temperature to 50℃ at 3℃ / min, with a pressure of 20 MPa. Keep the pressure constant and treat for 2 hours, then depressurize. Reduce the pressure to 5 MPa at 0.7 MPa / min, and then reduce the pressure to atmospheric pressure at 0.3 MPa / min.

[0029] (4) The fibers treated in the previous step were washed with acetone at 80°C for 1 hour until constant weight, and then vacuum dried at 80°C for 1 hour to obtain the target modified F-12 fiber.

[0030] (5) Mechanical properties of F-12 fiber and modified F-12 fiber were tested using a monofilament tensile tester: The tensile strength of F-12 fiber monofilament is 32.3 CN / dtex, and the modulus is 980.4 CN / dtex; the tensile strength of modified F-12 fiber is 32.8 CN / dtex, and the modulus is 990.6 CN / dtex. Compared with unmodified F-12 fiber, modified F-12 fiber has a tensile strength increased by 2.28%, a modulus increased by 2.95%, and mechanical properties are also improved.

[0031] Surface energy of F-12 fiber and modified F-12 fiber was tested using a contact angle meter. The surface energy of F-12 fiber is 34.7 mJ / m. 2 The surface energy of the modified F-12 fiber is 41.8 mJ / m². 2 Compared with unmodified F-12 fiber, the surface energy of modified F-12 fiber is increased by 20.4%.

[0032] The interfacial shear strength of F-12 fiber, modified F-12 fiber and epoxy resin was tested using micro-debonding: the interfacial shear strength of F-12 fiber was 35 MPa, and the interfacial shear strength of modified F-12 fiber was 47 MPa. Compared with unmodified F-12 fiber, the interfacial shear strength of modified F-12 fiber was increased by 34%.

[0033] Example 2: A method for surface treatment of aramid fibers, the specific steps of which are as follows: (1) Place 5.5g of Kevlar29 fiber in 160g of acetone solvent and wash it in an ultrasonic cleaner at 80°C for 1 hour. Remove it and vacuum dry it at 80°C for 2 hours.

[0034] (2) Wrap the Kevlar29 fibers that have been washed and dried in step (1) around a metal support and place them in a 1L supercritical reactor.

[0035] (3) Inject 150 mL of a mixture of ethanol and pyromellitic dianhydride (PMDA) (PMDA concentration 2 wt%) into the bottom of the supercritical reactor. Then pump in liquid CO2 until the pressure inside the reactor reaches 10 MPa (25 °C). Increase the temperature to 50 °C at 3 °C / min, and the pressure is 15 MPa. Keep the pressure constant and treat for 1.5 h, then depressurize. Reduce the pressure to 5 MPa at 0.5 MPa / min, and then reduce the pressure to atmospheric pressure at 0.5 MPa / min.

[0036] (4) The fibers treated in the previous step were washed with acetone at 80°C for 1 hour until constant weight, and then vacuum dried at 80°C for 1 hour to obtain the target modified Kevlar29 fiber.

[0037] (5) The mechanical properties of Kevlar 29 fiber and modified Kevlar 29 fiber were tested using a monofilament tensile tester: The tensile strength of Kevlar29 fiber monofilament is 18.9 CN / dtex, and the modulus is 450.2 CN / dtex; the tensile strength of modified Kevlar29 fiber is 19.5 CN / dtex, and the modulus is 490.2 CN / dtex. Compared with unmodified Kevlar29 fiber, modified Kevlar29 fiber has a tensile strength increased by 3.98%, a modulus increased by 2.16%, and mechanical properties are also improved.

[0038] The surface energy of Kevlar 29 fiber and modified Kevlar 29 fiber was tested using a contact angle meter: the surface energy of Kevlar 29 fiber was 30.2 mJ / m. 2 The surface energy of the modified Kevlar29 fiber is 37.3 mJ / m². 2 Compared with unmodified Kevlar29 fiber, the surface energy of modified Kevlar29 fiber is increased by 23.5%.

[0039] Micro-debonding was used to test the interfacial shear strength of Kevlar 29 fibers, modified Kevlar 29 fibers, and epoxy resin: The interfacial shear strength of Kevlar29 fiber is 29 MPa, while that of modified Kevlar29 fiber is 40 MPa. Compared with unmodified Kevlar29 fiber, the interfacial shear strength of modified Kevlar29 fiber is increased by 38%.

[0040] Example 3: A method for surface treatment of aramid fibers, the specific steps of which are as follows: (1) Place 6g of Tecnora fiber in 180g of acetone solvent and wash it in an ultrasonic cleaner at 80°C for 1 hour. Remove it and vacuum dry it at 80°C for 2 hours.

[0041] (2) The Tecnora fibers that have been washed and dried in step (1) are wound onto a metal support and placed in a 1L supercritical reactor.

[0042] (3) First, inject 100 mL of a mixture of acetone and glycidyl methacrylate (GMA) (GMA concentration 4 wt%) into the bottom of the supercritical reactor. Then, pump in liquid CO2 until the pressure inside the reactor reaches 12 MPa (25℃). Increase the temperature to 45℃ at 3℃ / min, and the pressure to 14 MPa. Keep the pressure constant and treat for 1.5 h before depressurizing. Reduce the pressure to 5 MPa at 0.6 MPa / min, and then reduce the pressure to atmospheric pressure at 0.4 MPa / min.

[0043] (5) The fibers treated in the previous step were washed with acetone at 80°C for 1 hour until constant weight, and then vacuum dried at 80°C for 1 hour to obtain the target modified Tecnora fibers.

[0044] (6) Testing Tecnora fibers and modified Tecnora fibers using a monofilament tensile tester: The tensile strength of a single filament of Tecnora fiber is 20.1 CN / dtex, and the modulus is 510.4 CN / dtex. The tensile strength of modified Tecnora fiber is 21.8 CN / dtex, and the modulus is 530.6 CN / dtex. Compared with unmodified Tecnora fiber, modified Tecnora fiber has a 2.97% increase in tensile strength, a 3.88% increase in modulus, and improved mechanical properties.

[0045] Surface energy of Tecnora fibers and modified Tecnora fibers was tested using a contact angle meter. The surface energy of Tecnora fiber is 31.8 mJ / m 2 The surface energy of the modified Tecnora fiber is 38.6 mJ / m². 2 Compared with unmodified Tecnora fibers, modified Tecnora fibers have a 21% higher surface energy.

[0046] Micro-debonding was used to test the interfacial shear strength of Tecnora fibers, modified Tecnora fibers, and epoxy resin: The interfacial shear strength of Tecnora fiber is 32 MPa, while that of modified Tecnora fiber is 42 MPa. Compared with unmodified Tecnora fiber, the interfacial shear strength of modified Tecnora fiber is increased by 31%.

[0047] Example 4: A method for surface treatment of aramid fibers, the specific steps of which are as follows: (1) Place 7g of aramid III fiber in 200g of acetone solvent and wash it in an ultrasonic cleaner at 80°C for 1 hour. Remove it and vacuum dry it at 80°C for 2 hours.

[0048] (2) Place the aramid III fiber that has been washed and dried in step (1) into a 1L high-pressure reactor and place the aramid III fiber on a metal frame.

[0049] (3) Inject 250 mL of a mixture of ethanol and polyvinyl alcohol (PVA) (PVA concentration 4 wt%) into the bottom of the supercritical reactor, then pump in 600 mL of liquid CO2 until the pressure inside the reactor reaches 13 MPa (25 °C). Increase the temperature to 45 °C at 3 °C / min, and the pressure is 18 MPa. Keep the pressure constant and treat for 1 hour, then depressurize. Reduce the pressure to 5 MPa at 0.7 MPa / min, and then reduce the pressure to atmospheric pressure at 0.5 MPa / min.

[0050] (5) The fibers treated in the previous step were washed with acetone at 80°C for 1 hour until constant weight, and then vacuum dried at 80°C for 1 hour to obtain the target modified aramid III fiber.

[0051] (6) Testing of aramid III fibers and modified aramid III fibers using a monofilament tensile tester: The tensile strength of aramid III fiber monofilament is 22.3 CN / dtex and the modulus is 643.2 CN / dtex. The tensile strength of modified aramid III fiber is 23.7 CN / dtex and the modulus is 672.6 CN / dtex. Compared with unmodified aramid III fiber, the tensile strength of modified aramid III fiber is increased by 3.08% and the modulus is increased by 3.47%, and the mechanical properties are also improved.

[0052] Surface energy of aramid III fibers and modified aramid III fibers was tested using a contact angle measuring instrument. The surface energy of aramid III fiber is 32.9 mJ / m. 2 The surface energy of the modified aramid III fiber is 39.4 mJ / m. 2 Compared with unmodified aramid III fibers, modified aramid III fibers have a 20% higher surface energy.

[0053] The interfacial shear strength of aramid III fibers, modified aramid III fibers, and epoxy resin was tested using micro-debonding. The interfacial shear strength of aramid III fiber is 34 MPa, while that of modified aramid III fiber is 45 MPa. Compared with unmodified aramid III fiber, the interfacial shear strength of modified aramid III fiber is increased by 32%.

[0054] In summary, compared with unmodified aramid fibers, the modified aramid fibers exhibit improved strength retention by 9.3-26.7%, improved modulus retention by 4.4-19.6%, improved surface energy by up to 23.5%, and improved interfacial shear strength by up to 38%.

[0055] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method of surface treatment of aramid fibers, characterized by, The specific steps are as follows: Step 1), the aramid fiber or its fabric is cleaned with acetone and dried, and the pretreated aramid is placed on the support of the supercritical reaction kettle; Step 2), the active substance is dissolved in the cosolvent, the prepared cosolvent is placed at the bottom of the supercritical reaction kettle, and the cosolvent is ensured not to directly contact the aramid fiber or its fabric on the support, and the reaction kettle is sealed; Step 3), a certain volume of carbon dioxide gas is added, and after a certain temperature and pressure treatment for a certain time, the reaction kettle is depressurized, and the treated fiber surface is dried to obtain the modified aramid fiber.

2. The method of claim 1, wherein the aramid fiber is treated on the surface. In step 1), the aramid fiber is one of para-aramid Kevlar, Nomex fiber, Twaron fiber, Technora fiber, Aramid III fiber or F-12 fiber; and the aramid fiber fabric is aramid fiber cloth.

3. The method of claim 1 or 2, wherein the surface treatment of aramid fibers is characterized by, In step 1), the aramid fiber or its fabric is first cleaned and dried in an ultrasonic cleaning machine with acetone, wherein the mass ratio of aramid fiber to acetone is 1:10-30, the treatment temperature is 80-90℃, the treatment time is 1-2h, and the reaction is dried at 80℃ under vacuum for 2h.

4. The method for surface treatment of aramid fibers according to claim 3, characterized in that, In step 1), the mass ratio of aramid fiber to acetone is 1:

30.

5. The method of claim 1, wherein the aramid fiber is treated on the surface. The active substance refers to a substance containing epoxy, carboxyl and hydroxyl groups.

6. The method for surface treatment of aramid fibers according to claim 5, characterized in that, The epoxy group is selected from trimethylolpropane triglycidyl ether or glycidyl methacrylate; the carboxyl group is selected from succinic anhydride or pyromellitic dianhydride; and the hydroxyl group is selected from polyvinyl alcohol or hydroxyethyl cellulose; the above active substance accounts for 0.5-5wt% of the total weight of the active substance and the cosolvent.

7. The method of claim 1, wherein the aramid fiber is treated on the surface. The cosolvent is at least one of acetone, ethanol and ethyl acetate; wherein the epoxy group uses acetone and ethyl acetate; the carboxyl group uses ethanol and ethyl acetate; the hydroxyl group uses ethanol, ethyl acetate and acetone; and the volume ratio of CO2 to cosolvent is 1:0.2-1:

3.

8. The method of claim 1, wherein the aramid fiber is treated on the surface. The supercritical treatment conditions and process in step 3) are as follows: 7.4-20MPa, 35-65℃ for 0.5-4 hours; the pressure is reduced to normal pressure at a rate gradient of 0.3-1MPa / min, and dried at 60-80℃.

9. The method of claim 1 or 8, wherein the aramid fiber is treated with a surface treatment comprising a silane coupling agent. Before the reaction container is filled with carbon dioxide gas in step 3), the exhaust and drainage treatment is carried out: first heat the reaction container until the water is converted into water vapor; then vacuumize the reaction container.