PBO fiber surface modification method for treating synergistic copolymer coating through plasma

Abstract

The invention belongs to the field of macromolecules, and particularly relates to a PBO fiber surface modification method for a synergistic copolymer coating through plasma treatment. According to the method, modification is designed by adopting a synergistic mechanism of plasma treatment and a functional coating: firstly, the PBO fiber is treated by oxygen plasma, a microstructure and an active group are formed on the surface of the PBO fiber, and the surface activity of the PBO fiber is rapidly improved; then coating a monomer solution containing a photoinitiator, exciting light to initiate free radical polymerization through ultraviolet irradiation, forming a random copolymer coating on the surface of the PBO fiber, and repairing the damage of oxygen plasmas to the PBO fiber structure while introducing active groups into the coating; and active groups formed by oxygen plasma treatment can enhance the adhesive force between the coating and the PBO fiber. Finally, the invention provides an environment-friendly and controllable PBO fiber surface synergistic modification technology, the intrinsic performance of the PBO fiber and the interface bonding strength are improved for a long time, and a support is provided for engineering application of the high-performance PBO fiber.

Description

Technical Field

[0001] The invention belongs to the field of polymers, and in particular relates to a method for modifying the surface of a PBO fiber by plasma-treated synergistic copolymer coating. Background Art

[0002] Poly-p-phenylene benzobisoxazole (PBO) fiber is a third-generation high-performance organic fiber. With its excellent specific strength (5.8 GPa / g·cm -3 ), specific modulus (280GPa / g·cm - 3) Thermal stability (decomposition temperature greater than or equal to 650°C) and flame retardancy (limited oxygen index 68%) have important application value in the fields of aerospace structural reinforcement, bulletproof armor materials, special protective equipment and advanced composite materials. However, the surface of PBO fiber is highly chemically inert. Its benzene ring conjugated structure and smooth surface lead to low surface energy and poor interface wettability (contact angle greater than 100°), and poor bonding performance with the resin matrix, which seriously restricts its stress transfer efficiency as a reinforcement phase and directly affects the interlaminar toughness and fatigue life of the composite material.

[0003] Existing surface modification technologies mainly include three categories: (1) Chemical etching method: polar groups are introduced through strong acid (such as concentrated sulfuric acid / nitric acid mixture) or strong alkali treatment, but it will cause the fiber body strength loss and produce toxic waste liquid; (2) Physical roughening method: mechanical grinding or high-energy radiation (such as gamma rays) is used to change the surface morphology, but the treatment depth is difficult to control and it is easy to cause defects such as microcracks; (3) Traditional coating method: silane coupling agent or epoxy resin is used for coating, which has problems such as weak coating bonding (peel strength less than 5N / cm) and poor thermal stability (decomposition temperature less than 300°C). Especially for ultra-high modulus materials such as PBO fibers, conventional treatment is difficult to achieve a breakthrough improvement in interface performance while maintaining the fiber body performance.

[0004] In recent years, plasma surface treatment technology has attracted attention due to its non-contact, environmentally friendly and efficient characteristics. Low-temperature plasma can form nanoscale grooves (Ra is about 50-200nm) on the fiber surface and introduce oxygen-containing polar groups (such as -C=O, -OH) through the dual mechanisms of physical sputtering and chemical grafting. However, the timeliness problem of single plasma treatment is significant, and the modification effect decays with the extension of storage time (the surface energy decreases by about 40% after 72 hours). Although synchronous coating technology can prolong the modification effect, it is difficult for traditional coating processes to form chemical bonds with plasma-activated surfaces, resulting in limited interface enhancement effects.

[0005] Based on this, there is an urgent need to develop a green and controllable surface modification technology for PBO fibers, which can achieve a long-term improvement in interfacial bonding strength while avoiding damage to the intrinsic properties of the fibers, providing a basis for the engineering application of high-performance PBO fiber composites. Summary of the Invention

[0006] In view of the above existing problems or deficiencies, in order to solve the problem that the traditional modification methods of existing PBO fibers cannot effectively improve the interfacial properties of PBO fibers, the present invention provides a surface modification method for PBO fibers by plasma treatment in combination with copolymer coating. By treating PBO fibers with oxygen plasma, the surface activity of the fibers is increased. Subsequently, a copolymer coating is formed on the fiber surface by photoinitiated free radical polymerization, introducing active functional groups while repairing the surface structure defects caused by oxygen plasma treatment, and significantly enhancing the surface activity of PBO fibers.

[0007] The specific technical solution of the present invention is as follows:

[0008] A surface modification method for PBO fibers by plasma treatment in combination with copolymer coating, the specific steps are as follows:

[0009] Step 1: Modify PBO fibers with oxygen plasma;

[0010] Bombard the surface of PBO fibers with oxygen plasma to remove surface pollutants on the PBO fibers by physical sputtering and form a micro-nano rough structure, improving the surface roughness and providing active oxygen and dangling bonds.

[0011] Step 2: Modify PBO fibers by oxygen plasma treatment in combination with copolymer coating;

[0012] Dissolve the copolymer monomer in an acetonitrile solution and add a photoinitiator, stir until completely dissolved to obtain solution A.

[0013] Step 3: Immerse the PBO fibers treated with oxygen plasma in step 1 in solution A prepared in step 2 for at least 10 min, and maintain the pulling speed at 1-4 mm / s to form a uniform liquid film; then keep warm at 80-110 °C until the solvent is completely removed.

[0014] Step 4: Use ultraviolet light to irradiate the PBO fibers obtained in step 3 to complete free radical polymerization, then take out the PBO fibers and ultrasonically clean them with absolute ethanol and deionized water for at least 10 min to remove residual solvents; finally, dry them completely at 80-110 °C to obtain PBO fibers modified by plasma treatment in combination with copolymer coating.

[0015] Furthermore, the tensile strength of the PBO fibers treated with oxygen plasma in step 1 is not less than 3.2 GPa.

[0016] Further, the copolymer monomer is glycidyl methacrylate GMA and ethylene glycol dimethacrylate EGDMA with a molar ratio of 5:1.

[0017] Further, the photoinitiator is photoinitiator 2959.

[0018] Further, the purity of glycidyl methacrylate, ethylene glycol dimethacrylate and photoinitiator is ≥99.5%.

[0019] Further, the oxygen purity of the oxygen plasma treatment in step 1 is ≥99.99%, the vacuum degree of the treatment chamber is less than 3.3 KPa, the power is 300 W, and the treatment time is 20 min.

[0020] In the present invention, the PBO fiber is first treated by oxygen plasma to form microstructures and active groups on the surface of the PBO fiber, rapidly improving the surface activity of the PBO fiber; then a monomer solution containing a photoinitiator is coated on the surface of the PBO fiber treated by oxygen plasma, and free radical polymerization is excited by ultraviolet light irradiation to form a random copolymer coating on the surface of the PBO fiber treated by oxygen plasma. The coating introduces active groups (such as epoxy groups) and repairs to a certain extent the damage to the PBO fiber structure caused by oxygen plasma; while the active groups formed on the surface of the PBO fiber by oxygen plasma treatment can enhance the adhesion between the coating and the PBO fiber and strengthen the coating structure. The two work together to improve the surface activity of the PBO fiber.

[0021] In summary, the present invention provides a green and controllable surface synergistic modification technology for PBO fibers. Through the design of the synergistic action mechanism of plasma treatment and functional coating, the structural damage caused by oxygen plasma treatment to PBO fibers is repaired to a certain extent, and at the same time the coating is more firmly anchored on the surface of the PBO fiber, improving the surface activity of the PBO fiber, providing key technical support for the engineering application of high-performance PBO fiber composites. Description of the Drawings

[0022] Figure 1 SEM images of the comparative example and the examples;

[0023] Figure 2 Tensile strength of the comparative example and the examples;

[0024] Figure 3 Surface free energy of the comparative example and the examples. Specific Embodiments

[0025] The following further describes the present invention in detail with reference to the drawings and embodiments.

[0026] Comparative Example 1:

[0027] Cut the PBO fibers (with a diameter of 12 μm) into lengths of 50 mm and arrange them in parallel and fix them on a glass substrate. Then, immerse them successively in acetone and ethanol (analytical grade) and ultrasonically clean each for 15 min to remove surface impurities. Then dry them in a vacuum drying oven at 60 °C for 2 hours with a humidity < 5%. Place the treated fibers in a desiccator (25 °C, relative humidity < 10%) for standby to avoid environmental oxidation or contamination.

[0028] Comparative Example 2:

[0029] Follow the same cutting, cleaning, and drying procedures as in Comparative Example 1.

[0030] Oxygen plasma modification: The rated power of the plasma processor is 300 W, and high-purity oxygen is used as the treatment gas. Fix the cleaned and dried PBO fibers on a wire mesh frame to ensure sufficient contact between the oxygen plasma and the fiber surface during treatment, while preventing the fibers from clogging the vacuum valve. Set the treatment power to 300 W and the treatment time to 20 min, and open the oxygen valve to perform oxygen plasma treatment on the PBO fibers. After completion, seal and dry the fibers for storage.

[0031] Example:

[0032] A method for surface modification of PBO fibers by plasma treatment synergistic copolymer coating, the specific steps are as follows:

[0033] Perform oxygen plasma treatment on the PBO fibers following the same oxygen plasma treatment procedure as in Comparative Example 2.

[0034] Mix glycidyl methacrylate GMA and ethylene glycol dimethacrylate EGDMA in a molar ratio of 5:1. Add 2 wt% photoinitiator 2959 and ultrasonically disperse for 30 minutes until homogeneous and transparent to obtain Solution A. Then immerse the oxygen plasma-treated PBO fibers in the monomer solution A for 10 min with a pulling speed of 2 mm / s to form a uniform liquid film. Subsequently, place it in an oven at 85 °C for 5 min to remove the solvent.

[0035] Then use an ultraviolet lamp at a distance of 5 cm for illumination for 3 min to complete free radical polymerization. Subsequently, take out the PBO fibers and ultrasonically clean them successively with absolute ethanol and deionized water for 10 min to remove the residual solvent, and dry them in an oven at 60 °C for 2 h, then take them out, seal them, and store them in a dry place.

[0036] Test and characterize the samples prepared in the above comparative examples and examples:

[0037] The SEM morphology diagrams of the surfaces of the PBO fibers prepared in the comparative examples and examples are as Figure 1 shown.

[0038] It can be seen that the surface of the fiber of Comparative Example 1 after cleaning is smooth, which is due to its special rigid rod-like structure and spinning process. After the fiber of Comparative Example 2 is treated with oxygen plasma at a power of 300 W for 20 minutes, a large number of oxidation particles and island-like protrusions appear on the surface. This is because the high-energy oxygen plasma bombards the surface of the PBO fiber, causing oxidation and even partial dissolution and swelling of the fiber surface. After the PBO fiber of the example is treated with the copolymer coating, the surface defects left by the oxygen plasma treatment are filled and compensated. A large number of random copolymer particles appear on the surface and are scattered, which is beneficial to the improvement of the surface roughness and activity of the fiber.

[0039] The tensile strength of the PBO fibers prepared in the comparative examples and examples is as Figure 2 shown.

[0040] The tensile strength of the PBO fiber of Comparative Example 1 is as high as 4.65 GPa. After the fiber sample of Comparative Example 2 is treated with oxygen plasma, the tensile strength rapidly drops to 3.2 GPa, a decrease of 31.18%. After the coating treatment, the tensile strength of the fiber sample of the example rises to 3.47 GPa. This is because the copolymer coating has the function of repairing some surface defects, thereby improving the mechanical properties of the PBO fiber.

[0041] The surface free energy of the PBO fibers prepared in the comparative examples and examples is as Figure 3 shown.

[0042] The PBO fiber in unmodified Comparative Example 1 has a smooth surface and lacks polar functional groups, which results in poor surface activity and a surface free energy of only 12.46 mN / m. After the oxygen plasma treatment, the surface free energy of the PBO fiber sample in Comparative Example 2 rapidly increases to 31.8 mN / m, an increase of 155.22%. This is because the oxygen plasma treatment brings rich active oxygen and dangling bonds to the PBO fiber, thus rapidly improving the surface activity of the PBO fiber. The surface free energy of the PBO fiber sample in the example after further coating treatment is 43.73 mN / m. This is because the copolymer coating contains rich epoxy functional groups. By combining the oxygen plasma treatment with the copolymer coating, while repairing the damage to the mechanical properties of the PBO fiber caused by the oxygen plasma treatment to a certain extent, the surface activity of the PBO fiber is significantly improved.

[0043] As can be seen from the above experiments, in the present invention, the PBO fiber is first treated with oxygen plasma to form microstructures and active groups on the surface of the PBO fiber, rapidly improving the surface activity of the PBO fiber; then, a monomer solution containing a photoinitiator is coated on the surface of the PBO fiber treated with oxygen plasma, and free radical polymerization is initiated by ultraviolet light irradiation to form a random copolymer coating on the surface of the PBO fiber treated with oxygen plasma. The coating introduces active groups (such as epoxy groups) while repairing to a certain extent the damage to the PBO fiber structure caused by oxygen plasma; and the active groups formed on the surface of the PBO fiber by oxygen plasma treatment can enhance the adhesion between the coating and the PBO fiber and strengthen the coating structure. The present invention provides an effective, green and controllable surface synergistic modification technology for PBO fibers, with long-term improvement of both the intrinsic properties of PBO fibers and the interfacial bonding strength, providing key technical support for the engineering application of high-performance PBO fiber composites.

Claims

1. A method for surface modification of PBO fibers coated with plasma-treated synergistic copolymers, characterized in that: The specific steps are as follows: Step 1, oxygen plasma modification of PBO fiber; The PBO fiber is bombarded with oxygen plasma to remove the surface pollutants of the PBO fiber through physical sputtering and form a micro-nano rough structure, thereby improving the surface roughness and providing active oxygen and dangling bonds; Step 2, oxygen plasma treatment of the synergistic copolymer coating modified PBO fiber; Dissolve the copolymer monomer in acetonitrile solution, add the photoinitiator and stir until it is completely dissolved to obtain solution A; Step 3, immersing the PBO fiber treated with oxygen plasma in step 1 in solution A prepared in step 2 for at least 10 minutes, and maintaining a pulling speed of 1-4 mm / s to form a uniform liquid film; then keeping the temperature at 80-110° C. until the solvent is completely removed; Step 4, using ultraviolet light to irradiate the PBO fiber obtained in step 3 to complete free radical polymerization, then taking out the PBO fiber and using anhydrous ethanol and deionized water ultrasonic cleaning for at least 10 minutes in turn to remove residual solvent; finally drying it completely at 80-110° C. to obtain a plasma-treated synergistic copolymer-coated modified PBO fiber.

2. The method for surface modification of PBO fiber by plasma treatment of synergistic copolymer coating as claimed in claim 1, characterized in that: The tensile strength of the PBO fiber after the oxygen plasma treatment in step 1 is not less than 3.2 GPa.

3. The method for surface modification of PBO fiber by plasma treatment of synergistic copolymer coating as claimed in claim 1, characterized in that: The copolymer monomers are glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDMA) in a molar ratio of 5:

1.

4. The method for surface modification of PBO fiber by plasma treatment of synergistic copolymer coating as claimed in claim 1, characterized in that: The photoinitiator is photoinitiator 2959.

5. The method for surface modification of PBO fiber by plasma treatment of synergistic copolymer coating as claimed in claim 1, characterized in that: The purity of the glycidyl methacrylate, ethylene glycol dimethacrylate and photoinitiator is ≥99.5%.

6. The method for surface modification of PBO fiber by plasma treatment of synergistic copolymer coating as claimed in claim 1, characterized in that: In the step 1, the oxygen purity of the oxygen plasma treatment is ≥99.99%, the vacuum degree of the treatment chamber is less than 3.3 KPa, the power is 300 W, and the treatment time is 20 min.

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