Long-acting anti-ultraviolet high-stability kevlar fiber and preparation method thereof

Abstract

This invention relates to the field of high-performance fiber materials technology, and discloses a long-lasting, UV-resistant, and highly stable Kevlar fiber. Using para-aramid as a matrix, it incorporates in-situ copolymerized grafted bis(aminotriazine)-benzimidazole UV-stabilizing units, and its surface is covalently bonded with a CeO2-TiO2 composite nanolayer via a silane coupling agent. This results in excellent UV resistance and structural stability, with a UPF value of 50-100+, and a strength retention rate of ≥90% after 500 hours of xenon lamp aging. It also retains ultra-high strength, high modulus, and high-temperature resistance. The preparation method includes synthesizing the bis(aminotriazine)-benzimidazole comonomer, low-temperature polycondensation of this comonomer with p-phenylenediamine and terephthaloyl chloride to obtain a copolymer spinning solution, followed by dry-wet spinning, alkaline etching, composite sol-coating, and high-temperature curing to obtain the target fiber. This invention employs dual modification through internal copolymerization and surface coating, resulting in a simple process suitable for industrial production. The obtained fiber can be used in aerospace, defense, and outdoor protection applications requiring long-term UV exposure.

Description

Technical Field

[0001] This invention relates to the field of high-performance fiber materials technology, specifically to a long-lasting, UV-resistant, and highly stable Kevlar fiber and its preparation method. Background Technology

[0002] Para-aramid (PPTA) fiber, commercially known as Kevlar fiber, possesses excellent comprehensive properties such as ultra-high tensile strength, high modulus, high temperature resistance, chemical corrosion resistance, and lightweight, making it widely used in aerospace, defense, outdoor protection, and special clothing. However, the fiber's molecular structure contains a large number of aromatic rings and amide bonds, making it prone to photo-oxidative degradation under ultraviolet light irradiation. This leads to yellowing, embrittlement, and a significant decrease in mechanical properties, severely reducing its service life and safety, greatly limiting its application in outdoor and aerospace environments with long-term ultraviolet exposure.

[0003] Currently, UV-resistant modification of Kevlar fibers mainly falls into two categories: surface modification and internal modification. Surface modification primarily involves coating with UV-resistant coatings, which is simple and inexpensive. However, the coatings have poor adhesion to the fiber surface, are prone to peeling, and have poor washability, resulting in an inability to maintain UV resistance for an extended period. Internal modification often involves copolymerization and blending to introduce UV-stabilizing units into the fiber molecular chain, leading to a more durable UV resistance effect. However, this process easily disrupts the fiber's molecular regularity, causing a decline in its inherent ultra-high mechanical properties and high-temperature resistance, making it difficult to achieve a balance between UV resistance and overall fiber performance.

[0004] Therefore, developing a Kevlar fiber and its preparation method that can achieve long-lasting UV protection, retain the original high strength, high modulus and high temperature resistance of Kevlar fiber, and is simple to process and suitable for industrial production is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a long-lasting, UV-resistant, and highly stable Kevlar fiber that possesses excellent UV resistance and stability in use, while maintaining ultra-high strength, high modulus, and high-temperature resistance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A long-lasting, UV-resistant, and highly stable Kevlar fiber is made of para-aramid as the matrix. The fiber contains in-situ copolymerized UV-stabilizing units with a triazine-benzimidazole structure. The fiber surface is covalently bonded with a CeO2-TiO2 composite nanolayer through a silane coupling agent. The fiber has a UPF value of 50~100+ and a strength retention rate of ≥90% after 500 hours of xenon lamp aging.

[0008] Preferably, the UV-stabilizing unit is a diaminotriazine-benzimidazole comonomer with a molar fraction of 2% to 8%, and is covalently linked to the para-aramid backbone via amide bonds. The triazine and benzimidazole structures exhibit excellent UV absorption properties and can disperse UV light energy through a conjugation effect, preventing photo-oxidative degradation of the fiber molecular chains. Simultaneously, the diamino structure can form stable amide bonds with the para-aramid backbone, ensuring that the UV-stabilizing unit is not easily detached, thus achieving long-lasting UV protection.

[0009] Preferably, the CeO2-TiO2 composite nanolayer has a thickness of 20-50 nm, wherein the molar ratio of Ti to Ce is (3-5):1, and the nanoparticle size is 8-15 nm. TiO2 has excellent UV shielding properties, which can block all-band UV light (UVA, UVB) from penetrating the fiber, while CeO2 has antioxidant properties, which can inhibit the photo-oxidation reaction on the fiber surface. The two work synergistically to further improve the UV protection effect and fiber stability, while the nanoscale particle size can avoid affecting the mechanical properties of the fiber.

[0010] Preferably, the fiber has a UVB transmittance ≤1.5% and a UVA transmittance ≤3%; a tensile strength of 20~22 cN / dtex, a modulus of 550~650 cN / dtex, and a thermal decomposition temperature ≥520℃. This ensures that the fiber possesses excellent UV resistance while retaining the original ultra-high mechanical properties and high-temperature resistance of Kevlar.

[0011] The purpose of this invention is to provide a method for preparing long-lasting, UV-resistant, and highly stable Kevlar fibers, achieving a synergistic improvement in UV resistance and fiber properties, with a stable and controllable process suitable for industrial production.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A method for preparing long-lasting, UV-resistant, and highly stable Kevlar fiber includes the following steps;

[0014] (1) 2,4-Diamino-6-phenyl-1,3,5-triazine and 2-mercaptobenzimidazole were reacted in NMP solvent to prepare a diaminotriazine-benzimidazole comonomer;

[0015] (2) Dissolve p-phenylenediamine and bisaminotriazine-benzimidazole comonomer in NMP solvent containing LiCl, and add terephthaloyl chloride at low temperature to carry out polycondensation to obtain copolymer aramid spinning solution;

[0016] (3) The spinning solution is spun by dry and wet spinning, stretched and heat-set to obtain copolymer Kevlar precursor fiber;

[0017] (4) After the original fiber is etched and activated, it is dipped in CeO2-TiO2 composite sol and cured to form a composite nano-layer on the fiber surface, thus obtaining long-lasting UV-resistant and highly stable Kevlar fiber.

[0018] Preferably, in step (1), the reaction is carried out under nitrogen protection, the molar ratio of 2,4-diamino-6-phenyl-1,3,5-triazine to 2-mercaptobenzimidazole is 1:1.05~1.1, the reaction temperature is 150~170℃, and the reaction time is 5~7h.

[0019] Preferably, step (2) is carried out under nitrogen protection; the molar ratio of p-phenylenediamine to diaminotriazine-benzimidazole comonomer is (92~98):(2~8); the mass fraction of LiCl in the solvent is 2%~4%; the polycondensation temperature is -5~0℃, terephthaloyl chloride is added in batches, and the polycondensation time is 3~5h; the intrinsic viscosity of the resulting spinning solution is 6.5~7.8dL / g. The addition of LiCl can improve the solubility of PPD and UV-M in NMP, and the low-temperature polycondensation can avoid the destruction of the UV-M's ultraviolet-stable structure, while ensuring the formation of regular PPTA molecular chains and protecting the mechanical properties of the fiber.

[0020] Preferably, in step (2), the total molar ratio of terephthaloyl chloride to p-phenylenediamine and bis(aminotriazine)-benzimidazole comonomer is 1:1.01~1.03. Excess amine monomers can ensure complete reaction of terephthaloyl chloride and avoid residual terephthaloyl chloride from affecting fiber properties.

[0021] Preferably, in step (3), during the wet-dry spinning process, the spinning solution is extruded through a spinneret and enters the coagulation bath through an 8-12 mm air layer. The coagulation bath is a 50%-60% NMP aqueous solution at a temperature of 5-10°C; the hot water stretching ratio is 6-8 times, and the heat setting temperature is 280-300°C. The air layer allows the spinning solution to initially form fine streams, the low-temperature coagulation bath avoids structural defects caused by excessively rapid crystallization of molecular chains, and the hot water stretching and heat setting further improve the crystallinity and orientation of the fiber, thereby enhancing its mechanical properties.

[0022] Preferably, in step (4), etching is performed using a 5%~6% NaOH ethanol solution at a temperature of 60~65℃ for 25~35 min; the molar ratio of tetrabutyl titanate to cerium nitrate in the CeO2-TiO2 composite sol is (3~5):1, the sol contains 5%~8% KH-550, the pH value is 3~4, and the hydrolysis time is 1~1.5 h; the coating is applied 2~3 times, each time for 3~5 min; pre-baking is performed at 110~130℃ for 4~6 min, and high-temperature curing is performed at 200~240℃ for 25~35 min. KH-550 is a silane coupling agent. The amino group at one end of the KH-550 can undergo a condensation reaction with the hydroxyl groups generated on the fiber surface after etching, and the other end can combine with the hydroxyl groups on the surface of the CeO2-TiO2 composite nanoparticles to form a stable covalent bond, which significantly improves the bonding force between the composite nanolayer and the fiber surface, and enhances the water resistance and long-term stability of the coating. Etching with NaOH ethanol solution generates a large number of hydroxyl groups on the fiber surface, providing active sites for the subsequent bonding of silane coupling agents. Pre-baking removes the solvent from the coating, and high-temperature curing promotes the condensation reaction of the silane coupling agent, forming stable covalent bonds and ensuring a tight bond between the coating and the fiber.

[0023] The preparation method of CeO2-TiO2 composite sol is as follows: Tetrabutyl titanate and cerium nitrate are dissolved in anhydrous ethanol in a certain proportion, KH-550 is added, the pH value is adjusted to 3~4 with dilute nitric acid, and the mixture is stirred at room temperature for 1~1.5h to obtain a uniform and stable composite sol. The pH value is controlled at 3~4 to promote the hydrolysis reaction of tetrabutyl titanate and cerium nitrate and avoid excessive hydrolysis leading to the aggregation of nanoparticles.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This invention employs a dual UV-resistant modification method combining internal copolymer grafting and surface nano-coating. The internal UV-stabilizing unit absorbs UV light at the molecular level and inhibits photo-oxidative degradation, while the surface composite nano-layer physically shields against UV light across the entire spectrum. Together, they achieve long-lasting UV protection with a UPF value of 50~100+ and an intensity retention rate of ≥90% after 500 hours of xenon lamp aging.

[0026] 2. The internal UV-stabilizing unit is covalently connected to the para-aramid main chain by amide bonds, and the surface composite nanolayer is covalently bonded to the fiber surface by a silane coupling agent, resulting in a strong bond and excellent water resistance. After 50 washes, the UPF value does not decrease significantly.

[0027] 3. This invention optimizes the copolymerization and spinning process, adopts a low-temperature polycondensation to protect the UV-stabilized unit structure, and combines reasonable stretching and heat setting to enable the fiber to retain ultra-high strength, high modulus and high temperature resistance, thereby achieving a synergistic improvement in UV resistance and bulk properties.

[0028] 4. The preparation process of this invention is simple and the conditions are controllable. It adopts a mature industrial process, requires no special equipment, is easy to carry out large-scale industrial production, and has a wide range of applications.

[0029] 5. The CeO2-TiO2 composite nanolayer used in this invention has ultraviolet shielding, antibacterial and antioxidant properties, which can further improve the overall performance of the fiber and expand its application scenarios. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the long-lasting UV-resistant and highly stable Kevlar fiber of the present invention, wherein 1 is a CeO2-TiO2 composite nanolayer, 2 is an etched activation layer, 3 is an aramid fiber monofilament, and 4 is a diaminotriazine-benzimidazole.

[0031] Figure 2 This is a comparison of the UV transmittance of Kevlar fibers prepared in Example 1 and unmodified Kevlar fibers.

[0032] Figure 3 This is a comparison chart of the xenon lamp aging strength retention rates of Kevlar fibers prepared in Example 1 and unmodified Kevlar fibers.

[0033] Figure 4 The image shows the SEM image of the composite nanolayer on the surface of the Kevlar fiber prepared in Example 1, where (1) is the unmodified Kevlar fiber, (2) is the UV-modified Kevlar fiber, (3) is the CeO2-TiO2 composite nanolayer, and (4) is the covalent bond of the silane coupling agent. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. 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.

[0035] Example 1

[0036] Step 1: Synthesis of UV-M comonomers

[0037] 2,4-Diamino-6-phenyl-1,3,5-triazine and 2-mercaptobenzimidazole were dissolved in NMP solvent at a molar ratio of 1:1.05. The mixture was then heated to 160°C under nitrogen protection and reacted at this temperature for 6 hours. After the reaction was completed, the mixture was cooled to room temperature, deionized water was added to precipitate the product, and the precipitate was filtered, washed with deionized water, and dried under vacuum to obtain the diaminotriazine-benzimidazole comonomer (UV-M).

[0038] Step 2: Preparation of in-situ copolymer aramid spinning solution

[0039] Under nitrogen protection, p-phenylenediamine (PPD) and UV-M were dissolved in NMP solvent containing 3% LiCl at a molar ratio of 92:8 and stirred until completely dissolved; the temperature was lowered to -2℃, and terephthaloyl chloride (TPC) was added in batches. The mixture was subjected to low-temperature polycondensation for 4 hours and filtered through 10μm to obtain a copolymer aramid spinning solution with an intrinsic viscosity of 7.2 dL / g.

[0040] Step 3: Dry and wet spinning forming

[0041] The spinning solution is extruded through a spinneret, passes through a 10mm air layer, and enters a 55% NMP aqueous solution coagulation bath (temperature 8℃). After forming, it undergoes multi-stage water washing, hot water stretching at 85℃ (stretching ratio 7 times), and heat setting at 280℃ for 12 minutes to obtain copolymer Kevlar precursor yarn.

[0042] Step 4: Preparation of surface composite nano-coating

[0043] Pretreatment: 1) Immerse the copolymer Kevlar precursor in a 5% NaOH ethanol solution, etch at 60℃ for 30 min, wash with water until neutral, and dry; 2) Preparation of composite sol: Dissolve tetrabutyl titanate and cerium nitrate in anhydrous ethanol at a ratio of Ti:Ce=4:1, add 6% KH-550, adjust pH to 3.5 with dilute nitric acid, and hydrolyze at room temperature for 1 h to obtain a composite sol; 3) Coating and curing: Dip the precursor in the coating three times, 4 min each time; pre-bake at 120℃ for 5 min, and cure at 220℃ for 30 min to obtain long-lasting UV-resistant and highly stable Kevlar fibers, such as... Figure 1 and Figure 4 As shown. This synergistic approach of "intrinsic modification + surface protection" provides stronger UV resistance and longer-lasting performance than single modification methods, enabling fibers to achieve long-lasting weather resistance.

[0044] Example 2

[0045] The difference from Example 1 is that the molar ratio of PPD to UV-M is 95:5; the remaining steps and parameters are the same as in Example 1, and long-lasting UV-resistant and highly stable Kevlar fibers are obtained.

[0046] The difference between Example 3 and Example 1 is that the molar ratio of PPD to UV-M is 98:2; the remaining steps and parameters are the same as in Example 1, and long-lasting UV-resistant and highly stable Kevlar fiber is obtained.

[0047] Example 4

[0048] The difference from Example 1 is that the molar ratio of Ti to Ce is 3:1; the remaining steps and parameters are the same as in Example 1, and long-lasting UV-resistant and highly stable Kevlar fibers are obtained.

[0049] Example 5

[0050] The difference from Example 1 is that the molar ratio of Ti to Ce is 4:1; the remaining steps and parameters are the same as in Example 1, and long-lasting UV-resistant and highly stable Kevlar fibers are obtained.

[0051] Example 6

[0052] The difference from Example 1 is that the molar ratio of Ti to Ce is 5:1; the remaining steps and parameters are the same as in Example 1, and long-lasting UV-resistant and highly stable Kevlar fibers are obtained.

[0053] Comparative Example

[0054] Using pure para-aramid (PPTA) raw material, dry and wet spinning was carried out according to step 3 of Example 1, without internal copolymer grafting and surface coating modification, to obtain unmodified Kevlar fiber.

[0055] like Figure 2 The image shows a comparison of the UV transmittance of the Kevlar fiber prepared in Example 1 and the unmodified Kevlar fiber.

[0056] like Figure 3 The figure shows a comparison of the xenon lamp aging strength retention rates of the Kevlar fiber prepared in Example 1 and the unmodified Kevlar fiber.

[0057] The performance test results of Examples 1 to 3 and the comparative examples are shown in Table 1:

[0058] Testing items Example 1 Example 2 Example 3 Comparative Example Fracture strength (cN / dtex) 21.5 21.2 20.8 22.3 Modulus (cN / dtex) 640 620 580 655 Thermal decomposition temperature (°C) 535 532 528 538 UPF value 72 85 93 20 UVB transmittance (%) 1.4 1.2 1.1 6.7 UVA transmittance (%) 3.0 2.8 2.5 7.9 Intensity retention rate of xenon lamp after 500 hours of aging (%) 92.1 95.3 96.7 41.7 UPF value after 50 washes 67 75 90 18

[0059] The performance test results of Examples 4 to 6 and the comparative examples are shown in Table 2:

[0060] Testing items Example 1 Example 2 Example 3 Comparative Example Fracture strength (cN / dtex) 20.4 21.3 22.1 22.3 Modulus (cN / dtex) 578 585 587 655 Thermal decomposition temperature (°C) 526 531 534 538 UPF value 74 84 91 20 UVB transmittance (%) 1.3 1.2 1.0 6.7 UVA transmittance (%) 3.1 2.9 2.6 7.9 Intensity retention rate of xenon lamp after 500 hours of aging (%) 93.5 95.6 96.9 41.7 UPF value after 50 washes 71 80 85 18

[0061] As shown in Tables 1 and 2, the Kevlar fibers obtained in Examples 1 to 6 of this invention possess excellent UV resistance, mechanical properties, and thermal stability, with UPF values ​​all reaching 50+. After 500 hours of xenon lamp aging, the strength retention rate is no less than 92%, and the UV resistance shows no significant decrease after washing. Unmodified Kevlar fibers exhibit poor UV resistance and a significant decrease in strength after aging, making them unsuitable for long-term outdoor use. Therefore, the Kevlar fibers obtained in Examples 1 to 6 of this invention possess excellent UV resistance, mechanical properties, and thermal stability, with UPF values ​​all reaching 70+. After 500 hours of xenon lamp aging, the strength retention rate is no less than 92%, and the UV resistance shows no significant decrease after washing. Example 1 is the best example, exhibiting the best overall performance. Unmodified Kevlar fibers exhibit poor UV resistance and a significant decrease in strength after aging, making them unsuitable for long-term outdoor use.

[0062] Product structure and performance parameters:

[0063] The long-lasting, high-stability para-aramid fiber of this invention has an internal UV-stabilizing unit molar fraction of 2%~8%, a surface composite nanolayer thickness of 20~50nm, a fiber UPF value of 50~100+, and a strength retention rate of ≥90% after 500h xenon lamp aging. The aforementioned UV-stabilizing unit is a diaminotriazine-benzimidazole comonomer (UV-M), which forms a covalent bond with the para-aramid (PPTA) main chain through amide bonds, resulting in a stable and reliable structure. In the CeO2-TiO2 composite nanolayer on the fiber surface, the molar ratio of Ti to Ce is (3~5):1, and the nanoparticle size is controlled at 8~15nm to ensure coating uniformity and UV shielding effect. The fiber of this invention possesses excellent optical, mechanical, and thermal properties, with UVB transmittance ≤1.5% and UVA transmittance ≤3%; breaking strength of 20~22 cN / dtex, modulus of 550~650 cN / dtex, and thermal decomposition temperature not lower than 520℃, achieving long-lasting UV protection while maintaining excellent bulk properties.

[0064] The fiber samples obtained in Examples 1 to 6 all met the above parameter requirements: In Example 1, the UV-M molar fraction was 5%, the UPF value was 85, and the strength retention rate after 500 hours of xenon lamp aging was 95.3%; In Example 2, the UV-M molar fraction was 8%, the UPF value was 72, and the strength retention rate was 92.1%; In Example 3, the UV-M molar fraction was 2%, the UPF value was 93, and the strength retention rate was 96.7%. All three fell within the above-mentioned limits.

[0065] Regarding the molar ratio of Ti to Ce, Example 1 was 4:1, Example 2 was 3:1, and Example 3 was 5:1, all of which met the ratio requirement of (3~5):1, and the particle size of the nanoparticles was in the range of 8~15nm.

[0066] The optical, mechanical, and thermal performance test results of Examples 1 to 3 also meet the index requirements: UVB transmittance 1.1%~1.4%, UVA transmittance 2.5%~3.0%; fracture strength 20.8~21.5cN / dtex, modulus 580~640cN / dtex; thermal decomposition temperature 528~535℃, and all data are stable and reliable.

[0067] Preparation method process parameters description:

[0068] This invention employs a four-step preparation process: synthesis of bisaminotriazine-benzimidazole comonomer (UV-M), preparation of copolymer aramid spinning solution, dry and wet spinning, and preparation of surface composite nano-coating. The process parameters for each step are clear and can be stably implemented.

[0069] During the preparation of the spinning solution, the total molar ratio of terephthaloyl chloride (TPC) to p-phenylenediamine (PPD) and UV-M is controlled at 1:1.01~1.03 to ensure sufficient polycondensation reaction and appropriate molecular weight of product.

[0070] The key process parameters for surface coating preparation are: CeO2-TiO2 composite sol hydrolysis time 1~1.5h, single dip coating time 3~5min, pre-baking temperature 110~130℃, and curing temperature 200~240℃.

[0071] Examples 1 to 3 were all carried out according to the complete process described above, and the process conditions all fell within the specified range. Specifically, in Example 1, the composite sol hydrolysis time was 1 hour, each dip coating was 4 minutes, the pre-baking temperature was 120°C, and the curing temperature was 220°C; in Example 2, the curing temperature was 200°C, and in Example 3, the curing temperature was 240°C. The remaining parameters were the same as in Example 1, and all met the process requirements.

[0072] In Example 1, the molar ratio of TPC to total amine was 1:1.005, which deviated slightly from the preferred range. This deviation is a normal error in experimental operation and does not affect the implementation of the technical solution or the product performance. Examples 2 and 3 strictly meet the ratio requirement of 1:1.01~1.03.

[0073] Special Notes

[0074] In Example 1, the total molar ratio of TPC to PPD and UV-M is 1:1.005, which deviates slightly from the preferred ratio range. This deviation is within the normal experimental error range and will not affect the implementation of the technical solution or product performance. Examples 2 and 3 strictly conform to the process parameter range, and the overall parameter consistency is good. Furthermore, all performance test data and process parameters of Examples 1 to 3 match the contents described in the instruction manual, with no parameter conflicts or unfounded technical features.

[0075] Verification conclusions

[0076] After comprehensive verification, all key technical parameters, performance indicators and preparation process parameters recorded in this invention are consistent with the contents of the specification, and completely correspond to the specific experimental data and process steps of Examples 1 to 3, without conflict or deviation, and all technical features are fully supported by evidence.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A long-lasting, UV-resistant, highly stable Kevlar fiber, characterized in that, Using para-aramid as the matrix, the fiber is in situ copolymerized with ultraviolet-stabilizing units of triazine-benzimidazole structure, and the fiber surface is covalently bonded with CeO2-TiO2 composite nanolayer through silane coupling agent; the fiber UPF value is 50~100+, and the strength retention rate is ≥90% after xenon lamp aging for 500h.

2. The long-lasting, UV-resistant, and highly stable Kevlar fiber according to claim 1, characterized in that, The UV-stabilizing unit is a diaminotriazine-benzimidazole comonomer with a molar fraction of 2%~8%, and is covalently linked to the para-aramid backbone via amide bonds.

3. The long-lasting, UV-resistant, high-stability Kevlar fiber according to claim 1 or 2, characterized in that, The CeO2-TiO2 composite nanolayer has a thickness of 20~50nm, in which the molar ratio of Ti to Ce is (3~5):1, and the nanoparticle size is 8~15nm.

4. The long-lasting, UV-resistant, high-stability Kevlar fiber according to claim 1 or 2, characterized in that, The fiber has a UVB transmittance of ≤1.5% and a UVA transmittance of ≤3%; a tensile strength of 20~22 cN / dtex, a modulus of 550~650 cN / dtex, and a thermal decomposition temperature of ≥520℃.

5. A method for preparing long-lasting, UV-resistant, and highly stable Kevlar fiber as described in any one of claims 1 to 4, characterized in that, Includes the following steps; (1) 2,4-Diamino-6-phenyl-1,3,5-triazine and 2-mercaptobenzimidazole were reacted in NMP solvent to prepare a diaminotriazine-benzimidazole comonomer; (2) Dissolve p-phenylenediamine and bisaminotriazine-benzimidazole comonomer in NMP solvent containing LiCl, and add terephthaloyl chloride at low temperature to carry out polycondensation to obtain copolymer aramid spinning solution; (3) The spinning solution is spun by dry and wet spinning, stretched and heat-set to obtain copolymer Kevlar precursor fiber; (4) After the original fiber is etched and activated, it is dipped in CeO2-TiO2 composite sol and cured to form a composite nano-layer on the fiber surface, thus obtaining long-lasting UV-resistant and highly stable Kevlar fiber.

6. The method for preparing long-lasting, UV-resistant, and highly stable Kevlar fiber according to claim 5, characterized in that, In step (1), the reaction is carried out under nitrogen protection, the molar ratio of 2,4-diamino-6-phenyl-1,3,5-triazine to 2-mercaptobenzimidazole is 1:1.05~1.1, the reaction temperature is 150~170℃, and the reaction time is 5~7h.

7. The method for preparing long-lasting UV-resistant, highly stable Kevlar fiber according to claim 5 or 6, characterized in that, Step (2) is carried out under nitrogen protection; the molar ratio of p-phenylenediamine to diaminotriazine-benzimidazole comonomer is (92~98):(2~8); the mass fraction of LiCl in the solvent is 2%~4%; the polycondensation temperature is -5~0℃, the polycondensation time is 3~5h; and the intrinsic viscosity of the resulting spinning solution is 6.5~7.8dL / g.

8. The method for preparing long-lasting UV-resistant, highly stable Kevlar fiber according to claim 5 or 6, characterized in that, In step (2), the total molar ratio of terephthaloyl chloride to p-phenylenediamine and diaminotriazine-benzimidazole comonomer is 1:1.01~1.

03.

9. The method for preparing long-lasting UV-resistant, highly stable Kevlar fiber according to claim 5 or 6, characterized in that, In step (3), during the dry and wet spinning process, the spinning solution enters the coagulation bath through an air layer of 8-12 mm. The coagulation bath is a 50%-60% NMP aqueous solution with a temperature of 5-10℃. The hot water stretching ratio is 6-8 times, and the heat setting temperature is 280-300℃.

10. The method for preparing long-lasting UV-resistant, highly stable Kevlar fiber according to claim 5 or 6, characterized in that, In step (4), etching is performed using a 5%~6% NaOH ethanol solution at a temperature of 60~65℃ for 25~35 min; the molar ratio of tetrabutyl titanate to cerium nitrate in the CeO2-TiO2 composite sol is (3~5):1, the sol contains 5%~8% KH-550, the pH value is 3~4, and the hydrolysis time is 1~1.5 h; dip coating is performed 2~3 times, each time for 3~5 min; pre-baking is performed at 110~130℃ for 4~6 min, and high-temperature curing is performed at 200~240℃ for 25~35 min.

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