Modification method and application of double-layer impregnated modified aramid fiber

Abstract

The invention discloses a modification method and application of double-layer impregnated modified aramid fiber, and the double-layer impregnated modified aramid fiber is prepared by the following steps: reacting hexamethylene diisocyanate and glycerol triglycidyl ether in a water phase to form a first-layer impregnation liquid, and carrying out first-layer impregnation modification on aramid fiber; and forming a second-layer impregnation liquid from ethylene glycol diglycidyl ether, diethylenetriamine, glycidyl methacrylate and butadiene-vinylpyridine rubber latex, performing second-layer impregnation modification on the aramid fibers, drying after double-layer modification to obtain double-layer impregnation modified aramid fibers, and blending and vulcanizing the double-layer impregnation modified aramid fibers and rubber to obtain the rubber-modified aramid fibers. The modified aramid fiber reinforced butadiene styrene rubber composite material can be prepared. By designing a two-step dipping treatment system containing isocyanate and epoxy bifunctional groups, efficient chemical modification of the aramid fiber surface is realized, and a good reaction interface with a rubber matrix is endowed.

Description

Technical Field

[0001] This invention relates to the field of high-performance fiber surface modification technology, and in particular to a method for modifying aramid fibers by double-layer impregnation and its application, which is suitable for constructing reinforcing interfaces in rubber matrices. Background Technology

[0002] Aramid fibers are widely used in high-performance composite materials due to their high modulus, high strength, and excellent thermal stability. However, the strong chemical inertness of the amide groups in the aramid molecular chain leads to poor compatibility with polymer matrices such as rubber, resulting in weak interfacial adhesion and limiting their further application in rubber-reinforced materials. To improve the interfacial bonding strength of aramid / rubber, researchers have developed various surface modification methods, including oxidation, plasma treatment, and solvent grafting. However, these methods generally suffer from problems such as unstable modified layers, low grafting density, or poor industrial adaptability.

[0003] To address the above issues, this invention modifies aramid fibers by designing a two-step impregnation system containing isocyanate and epoxy bifunctional groups. This achieves efficient chemical modification of the aramid fiber surface, improving the interfacial bonding strength between aramid and rubber. The modification method is simple, water-based, environmentally friendly, and suitable for continuous processing, demonstrating promising industrialization prospects. Summary of the Invention

[0004] The purpose of this invention is to provide a modification method for aramid fibers by double-layer impregnation and its application. By designing a two-step impregnation treatment system containing isocyanate and epoxy bifunctional groups, efficient chemical modification of the aramid fiber surface is achieved, and a good reaction interface with the rubber matrix is ​​given to it.

[0005] The technical solution of this invention is as follows: A method for modifying double-layer impregnated modified aramid fibers, wherein the double-layer impregnated modified aramid fibers are first impregnated with a first layer of impregnation solution formed by reacting hexamethylene diisocyanate and glycerol triglycidyl ether in an aqueous phase, and then the aramid fibers are first impregnated with a second layer of impregnation solution composed of ethylene glycol diglycidyl ether, diethylenetriamine, glycidyl methacrylate and butadiene-pyridine latex, and then the aramid fibers are second impregnated with a second layer of impregnation solution. After double-layer modification, the fibers are dried to obtain double-layer impregnated modified aramid fibers. The double-layer impregnated modified aramid fibers are then blended and vulcanized with rubber to obtain modified aramid-reinforced styrene-butadiene rubber composite materials.

[0006] The aforementioned method for modifying aramid fibers by double-layer impregnation is carried out according to the following steps: (1) Preparation of GH impregnation solution: Take 96.5-96.2g of deionized water and stir at 300-400rpm for 8-12 minutes to form a homogeneous system. Then, slowly add 1.3-1.4g of hexamethylene diisocyanate and 2.2-2.4g of glycerol triglycidyl ether at room temperature and maintain stirring for 35-45 minutes to obtain the first impregnation solution containing isocyanate and silane structures. GH impregnation solution: (2) Preparation of EDGV impregnation solution: At room temperature, 2g of ethylene glycol diglycidyl ether and 0.2g of glycidyl methacrylate were added to 47.65-47.56g of deionized water and stirred for 8-12 minutes. Then, 0.15-0.24g of diethylenetriamine was gradually added and stirred for 7-9 minutes. Finally, 50g of butadiene-pyridine latex was slowly added and stirred for 8-12 minutes to obtain the second impregnation solution, which is the EDGV impregnation solution. (3) Impregnation and drying treatment: First, 3.8-4.2g of aramid fiber is impregnated in 98-102g of GH impregnation solution for 1.5-2.5 minutes. After removal, the excess liquid is scraped off along the fiber direction with a scraper for 0.5-1.5 minutes. Then, the fiber is placed in an oven at 75-85℃ and dried for 8-12 minutes. Then, the dried aramid fiber is impregnated again in 98-102g of EDGV impregnation solution for 1.5-2.5 minutes. After removal, the excess liquid is scraped off along the fiber direction with a scraper for 0.5-1.5 minutes. Then, it is dried again at 75-85℃ for 8-12 minutes to complete the double impregnation treatment and obtain double impregnated modified aramid fiber.

[0007] In step (1) above, the preparation of GH impregnation solution is as follows: 96.31g of deionized water is taken and stirred at 300-400rpm for 10 minutes to form a homogeneous system. Then, 1.36g of hexamethylene diisocyanate and 2.33g of glycerol triglycidyl ether are slowly added at room temperature and stirred for 40 minutes to obtain the first layer of impregnation solution containing isocyanate and silane structure, GH impregnation solution.

[0008] In step (2) above, the preparation of EDGV impregnation solution is as follows: at room temperature, 2g of ethylene glycol diglycidyl ether and 0.2g of glycidyl methacrylate are added to 47.59g of deionized water and stirred for 10 minutes. Then, 0.21g of diethylenetriamine is gradually added and stirred for 8 minutes. Finally, 50g of butadiene-pyridine latex is slowly added and stirred for another 10 minutes to obtain the second impregnation solution, which is the EDGV impregnation solution.

[0009] In the aforementioned step (3), the impregnation and drying process is as follows: 4g of aramid fiber is first impregnated in 100g of GH impregnation solution for 2 minutes. After removal, excess liquid is scraped off along the fiber direction with a scraper for 1 minute. Then, the fiber is placed in an 80℃ oven and dried for 10 minutes. After drying, the aramid fiber is impregnated again in 100g of EDGV impregnation solution for 2 minutes. After removal, excess liquid is scraped off along the fiber direction with a scraper for 1 minute. Then, it is dried again at 80℃ for 10 minutes to complete the double-layer impregnation process and obtain double-layer impregnated modified aramid fiber.

[0010] The aforementioned application of double-layer impregnated modified aramid fiber in the preparation of rubber composite materials, wherein the rubber composite material is obtained by mixing double-layer impregnated modified aramid fiber and styrene-butadiene rubber matrix through internal mixing, open milling, and vulcanization.

[0011] The raw materials of the aforementioned modified aramid-reinforced styrene-butadiene rubber composite material, calculated by weight composition, include 180-220 parts of styrene-butadiene rubber, 3-5 parts of double-layer impregnated modified aramid fiber, 35-45 parts of silica, 14-17 parts of rubber compounding agent, and 3-4 parts of sulfur vulcanizing agent. The rubber compounding agent is composed of 5 parts zinc oxide, 4 parts stearic acid, 2.21 parts accelerator M, 0.5 parts accelerator D, 1.96 parts accelerator DM, 0.32 parts accelerator TMTD and 1.5 parts antioxidant 4010.

[0012] The raw materials of the aforementioned modified aramid-reinforced styrene-butadiene rubber composite material, calculated by weight, include 200 parts of styrene-butadiene rubber, 4 parts of double-layer impregnated modified aramid fiber, 80 parts of silica, 30.1 parts of rubber compounding agent, and 6.8 parts of sulfur vulcanizing agent.

[0013] The aforementioned rubber compounding agent consists of 5 parts zinc oxide, 4 parts stearic acid, 2.21 parts accelerator M, 0.5 parts accelerator D, 1.96 parts accelerator DM, 0.32 parts accelerator TMTD and 1.5 parts antioxidant 4010.

[0014] The specific preparation method of the aforementioned modified aramid-reinforced styrene-butadiene rubber composite material is as follows: Weigh the raw materials according to the proportions. First, put the styrene-butadiene rubber, silica, and double-layer impregnated modified aramid fiber into a mixer at 110-140℃ and mix for 6-8 minutes. Then, mix on a two-roll mill at 60-80℃, add sulfur vulcanizing agent and rubber compounding agent, and pass through a thin mill 4-6 times to obtain the compound. Vulcanize the compound according to the positive vulcanization time tc90 measured by the vulcanizer to prepare the modified aramid reinforced styrene-butadiene rubber composite material.

[0015] Compared with the prior art, the present invention has the following beneficial effects: In the first impregnation solution, the isocyanate groups react with the aramid bonds to form urea bonds, thereby achieving stable grafting and improving the interfacial bonding strength. 2. The second impregnation solution introduces a highly reactive epoxy / amine / latex system, which causes the epoxy groups to co-vulcanize and cross-link with the rubber, thereby enhancing the interfacial toughness. 3. The synergistic effect of the two-step reaction enables the interface layer to have both strong adhesion and cross-linking flexibility, achieving molecular-level fusion between aramid fibers and rubber; 4. The modification method is simple, water-based and environmentally friendly, suitable for continuous processing, and has good prospects for industrialization. Attached Figure Description

[0016] Figure 1 Comparison of mechanical properties of composite materials before and after modification; Figure 2 Comparison of H-extraction performance test results before and after composite material modification; Figure 3 Comparison chart of fatigue performance tests of composite materials; Figure 4 Photo of double-layer impregnated modified aramid fiber. Detailed Implementation

[0017] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention.

[0018] Reagents and raw materials: aramid fiber, glycerol triglycidyl ether (GTE), hexamethylene diisocyanate (HDI), ethylene glycol diglycidyl ether (EDGE), diethylenetriamine (DETA), glycidyl methacrylate (GMA), deionized water and butyl-butadiene rubber latex (VP latex), styrene-butadiene rubber, silica, zinc oxide, stearic acid, accelerator M (2-mercaptobenzothiazole), accelerator D (diphenylguanidine), accelerator DM (dibenzothiazole disulfide), accelerator TMTD (tetramethylthiuram disulfide), antioxidant 4010 (4-isopropylaminodiphenylamine), sulfur vulcanizing agent.

[0019] Example 1: 1. Preparation of double-layer impregnated modified aramid fibers: (1) Preparation of GH impregnation solution: Weigh out 1.36g of GTE, 2.33g of HDI, and 96.31g of deionized water, for a total of 100g.

[0020] Stir 96.31g of deionized water at 300-400rpm for 10 minutes to form a homogeneous system. Then, slowly add 1.36g of GTE and 2.33g of HDI at room temperature and maintain stirring for 40 minutes to obtain the first impregnation solution containing the urethane structure.

[0021] (2) Preparation of EDGV impregnation solution: Weigh out 2g of EDGE, 0.15g of DETA, 0.2g of GMA, 47.65g of deionized water and 50g of butyl-pyridine latex, for a total of 100g.

[0022] At room temperature, 2g of EDGE and 0.2g of GMA were added to 47.6g of deionized water and stirred for 10 minutes. Then, 0.15g of DETA was gradually added and stirred for 8 minutes. Finally, 50g of butyl-pyridine latex was slowly added and stirred for another 10 minutes to obtain the second impregnation solution.

[0023] (2) Impregnation and drying treatment: 4g of aramid fiber was first impregnated in 100g of GH impregnation solution for 2 minutes. After removal, excess liquid was scraped off along the direction of aramid fiber with a scraper for 1 minute. Then, the aramid fiber was placed in an 80°C oven to dry for 10 minutes. Then, the dried aramid fiber was impregnated again in EDGV impregnation solution for 2 minutes. The excess liquid was scraped off for 1 minute. The fiber was then dried again at 80°C for 10 minutes to complete the double impregnation treatment and obtain double impregnated modified aramid fiber.

[0024] 2. Preparation of modified aramid-reinforced styrene-butadiene rubber composites: Weigh out 200g of styrene-butadiene rubber, 80g of silica, 31g of rubber compounding agents (composed of 10g zinc oxide, 8g stearic acid, 4.42g accelerator M, 1g accelerator D, 3.92g accelerator DM, 0.64g accelerator TMTD and 3g antioxidant 4010), and 3.4g of sulfur vulcanizing agent.

[0025] Styrene-butadiene rubber, silica, and double-layer impregnated modified aramid fibers are mixed in a mixer at 110–140°C for 6–8 minutes, then mixed on a two-roll mill at 60–80°C. Sulfur vulcanizing agent and compounding agent are added, and the mixture is passed through a thin mill 4–6 times to obtain a compound. The compound is vulcanized according to the positive vulcanization time tc90 determined by the vulcanizer to prepare a modified aramid-reinforced styrene-butadiene rubber composite material.

[0026] Example 2: 1. Preparation of double-layer impregnated modified aramid fibers: (1) Preparation of GH impregnation solution: Weigh 1.36g GTE and 2.33g HDI, and 96.31g deionized water, for a total of 100g. Stir the deionized water at low speed for 10 minutes to form a homogeneous system. Then, slowly add HDI and GTE at room temperature and maintain stirring for 40 minutes to obtain the first impregnation solution containing the carbamate structure.

[0027] (2) Preparation of EDGV impregnation solution: Weigh 2g of EDGE, 0.18g of DETA, 0.2g of GMA, 47.62g of deionized water, and 50g of VP latex, for a total of 100g. Add EDGE and GMA to deionized water at room temperature and stir for 10 minutes. Then gradually add DETA and stir for 8 minutes. Finally, slowly add butyl-butadiene rubber latex (VP latex) and continue stirring for 10 minutes to obtain the second impregnation solution.

[0028] (3) Impregnation and drying treatment: 4g of aramid fiber was first impregnated in GH impregnation solution for 2 minutes. After taking it out, the excess liquid was scraped off along the fiber direction with a scraper for 1 minute. Then the fiber was placed in an 80°C oven to dry for 10 minutes. Then the dried aramid fiber was impregnated in EDGV impregnation solution again for 2 minutes. The excess liquid was scraped off for 1 minute. The fiber was dried again at 80°C for 10 minutes to complete the double impregnation treatment and obtain double impregnated modified aramid fiber.

[0029] 2. Preparation of modified aramid-reinforced styrene-butadiene rubber composite material: Weigh 200g styrene-butadiene rubber, 80g silica, 31g rubber compounding agent (composed of 10g zinc oxide, 8g stearic acid, 4.42g accelerator M, 1g accelerator D, 3.92g accelerator DM, 0.64g accelerator TMTD and 3g antioxidant 4010), and 3.4g sulfur vulcanizing agent. Add the styrene-butadiene rubber, silica, and modified aramid fiber to a mixer at 110–140℃ and mix for 6–8 minutes. Then, mix on a two-roll mill at 60–80℃, adding the sulfur vulcanizing agent and compounding agent, and pass through a thin mill 4–6 times to obtain a compound. Vulcanize the compound according to the positive vulcanization time tc90 determined by the vulcanizer to prepare the modified aramid-reinforced styrene-butadiene rubber composite material.

[0030] Example 3: 1. Preparation of double-layer impregnated modified aramid fibers: (1) Preparation of GH impregnation solution: Weigh 1.36g GTE and 2.33g HDI, and 96.31g deionized water, for a total of 100g. Stir the deionized water at low speed for 10 minutes to form a homogeneous system. Then, slowly add HDI and GTE at room temperature and maintain stirring for 40 minutes to obtain the first impregnation solution containing the carbamate structure.

[0031] (2) Preparation of EDGV impregnation solution: Weigh 2g of EDGE, 0.21g of DETA, 0.2g of GMA, 47.59g of deionized water, and 50g of VP latex, for a total of 100g. Add EDGE and GMA to deionized water at room temperature and stir for 10 minutes. Then gradually add DETA and stir for 8 minutes. Finally, slowly add butyl-butadiene rubber latex (VP latex) and continue stirring for 10 minutes to obtain the second impregnation solution.

[0032] (3) Impregnation and drying treatment: 4g of aramid fiber was first impregnated in GH impregnation solution for 2 minutes. After taking it out, the excess liquid was scraped off along the fiber direction with a scraper for 1 minute. Then the fiber was placed in an 80°C oven to dry for 10 minutes. Then the dried aramid fiber was impregnated in EDGV impregnation solution again for 2 minutes. The excess liquid was scraped off for 1 minute. The fiber was dried again at 80°C for 10 minutes to complete the double impregnation treatment and obtain double impregnated modified aramid fiber.

[0033] 2. Preparation of modified aramid-reinforced styrene-butadiene rubber composite material: Weigh 200g styrene-butadiene rubber, 80g silica, 31g rubber compounding agent (composed of 10g zinc oxide, 8g stearic acid, 4.42g accelerator M, 1g accelerator D, 3.92g accelerator DM, 0.64g accelerator TMTD and 3g antioxidant 4010), and 3.4g sulfur vulcanizing agent. Add the styrene-butadiene rubber, silica, and modified aramid fiber to a mixer at 110–140℃ and mix for 6–8 minutes. Then, mix on a two-roll mill at 60–80℃, adding the sulfur vulcanizing agent and compounding agent, and pass through a thin mill 4–6 times to obtain a compound. Vulcanize the compound according to the positive vulcanization time tc90 determined by the vulcanizer to prepare the modified aramid-reinforced styrene-butadiene rubber composite material.

[0034] Example 4: 1. Preparation of double-layer impregnated modified aramid fibers: (1) Preparation of GH impregnation solution: Weigh 1.36g GTE and 2.33g HDI, and 96.31g deionized water, for a total of 100g. Stir the deionized water at low speed for 10 minutes to form a homogeneous system. Then, slowly add HDI and GTE at room temperature and maintain stirring for 40 minutes to obtain the first impregnation solution containing the carbamate structure.

[0035] (2) Preparation of EDGV impregnation solution: Weigh 2g of EDGE, 0.24g of DETA, 0.2g of GMA, 47.56g of deionized water, and 50g of VP latex, for a total of 100g. Add EDGE and GMA to deionized water at room temperature and stir for 10 minutes. Then gradually add DETA and stir for 8 minutes. Finally, slowly add butyl-butadiene rubber latex (VP latex) and continue stirring for 10 minutes to obtain the second impregnation solution.

[0036] (3) Impregnation and drying treatment: 4g of aramid fiber was first impregnated in GH impregnation solution for 2 minutes. After taking it out, the excess liquid was scraped off along the fiber direction with a scraper for 1 minute. Then the fiber was placed in an 80°C oven to dry for 10 minutes. Then the dried aramid fiber was impregnated in EDGV impregnation solution again for 2 minutes. The excess liquid was scraped off for 1 minute. The fiber was dried again at 80°C for 10 minutes to complete the double impregnation treatment and obtain double impregnated modified aramid fiber.

[0037] 2. Preparation of modified aramid-reinforced styrene-butadiene rubber composite material: Weigh 200g styrene-butadiene rubber, 80g silica, 31g rubber compounding agent (composed of 10g zinc oxide, 8g stearic acid, 4.42g accelerator M, 1g accelerator D, 3.92g accelerator DM, 0.64g accelerator TMTD and 3g antioxidant 4010), and 3.4g sulfur vulcanizing agent. Add the styrene-butadiene rubber, silica, and modified aramid fiber to a mixer at 110–140℃ and mix for 6–8 minutes. Then, mix on a two-roll mill at 60–80℃, adding the sulfur vulcanizing agent and compounding agent, and pass through a thin mill 4–6 times to obtain a compound. Vulcanize the compound according to the positive vulcanization time tc90 determined by the vulcanizer to prepare the modified aramid-reinforced styrene-butadiene rubber composite material.

[0038] Comparative Example 1: Preparation method of pure styrene-butadiene rubber composite material: Weigh out 200g of styrene-butadiene rubber (SBR), 80g of silica, 31g of rubber compounding agents (composed of 10g zinc oxide, 8g stearic acid, 4.42g accelerator M, 1g accelerator D, 3.92g accelerator DM, 0.64g accelerator TMTD, and 3g antioxidant 4010), and 3.4g of sulfur vulcanizing agent. Mix the SBR and silica in a Banbury mixer at 110–140℃ for 6–8 minutes, then mix on a two-roll mill at 60–80℃, adding the sulfur vulcanizing agent and compounding agents, and passing through a thin mill 4–6 times to obtain a compound. Vulcanize the compound according to the positive vulcanization time tc90 determined by a vulcanizing apparatus to prepare the SBR composite material.

[0039] Comparative Example 2: Preparation method of unmodified aramid fiber / styrene-butadiene rubber composite material: Weigh out 200g of styrene-butadiene rubber (SBR), 80g of silica, 4g of aramid fiber, 31g of rubber compounding agents (composed of 10g zinc oxide, 8g stearic acid, 4.42g accelerator M, 1g accelerator D, 3.92g accelerator DM, 0.64g accelerator TMTD, and 3g antioxidant 4010), and 3.4g of sulfur vulcanizing agent. Mix the SBR, silica, and aramid fiber in a Banbury mixer at 110–140℃ for 6–8 minutes, then mix on a two-roll mill at 60–80℃, adding the sulfur vulcanizing agent and compounding agents, and passing through a thin mill 4–6 times to obtain a compound. Vulcanize the compound according to the positive vulcanization time tc90 determined by a vulcanizing apparatus to prepare an aramid-reinforced SBR composite material.

[0040] This invention tested the mechanical properties, extraction properties, and fatigue properties of various styrene-butadiene rubber composites prepared by methods 1-4 and Comparative Examples 1-2. The results of the experimental research of this invention are as follows: 1. Mechanical property testing: such as Figure 1 Samples 1, 2, 3, 4, 5, and 6 represent Comparative Example 1, Comparative Example 2, Example 1, Example 2, Example 3, and Example 4, respectively. Compared to Comparative Example 1 and Comparative Example 2, the overall mechanical properties of the experimental examples were improved, showing a trend of first increasing and then decreasing. After modification with a double-layer impregnation system, the 100% and 300% tensile stresses of the styrene-butadiene rubber composites continuously increased with the increase of amine content, with Experiment 4 exhibiting the highest tensile stress, indicating that the crosslinking density of the composite material was continuously increasing. However, the tensile strength and tear strength of the experimental examples showed a trend of first increasing and then decreasing, with Experiment 3 showing the best performance, while Experiment 4 experienced a decline in performance due to material embrittlement caused by excessive crosslinking. In summary, through the impregnation modification designed in this experiment, Experiment 3 and Experiment 4 showed the best overall mechanical properties.

[0041] 2. H extraction performance test: such as Figure 2 Samples 1, 2, 3, 4, and 5 represent Comparative Example 2, Example 1, Example 2, Example 3, and Example 4, respectively. It can be seen that compared to Comparative Example 2, the H-pull-out force of the modified styrene-butadiene rubber composite material is significantly improved, indicating that the double-layer impregnation system prepared in this experiment has better interfacial adhesion. Among them, Example 3 achieved the highest H-pull-out performance of 183.2 N.

[0042] 3. Fatigue performance testing: such as Figure 3Samples 1, 2, 3, 4, 5, and 6 are Comparative Example 1, Comparative Example 2, Example 1, Example 2, Example 3, and Example 4, respectively. A dynamic fatigue testing machine was used under load control conditions, with an initial load of 25 N, an amplitude of 10 N, and a frequency of 5 Hz, using a sinusoidal loading method. The fatigue tensile test data for each group of composite materials were obtained under the above conditions. Compared to Comparative Examples 1 and 2, the fatigue life of the modified styrene-butadiene rubber composite material increased significantly. This is because the fibers were not modified, the aramid fiber surface is chemically inert, and styrene-butadiene rubber is a polar rubber. There is a significant difference in interfacial compatibility between the aramid fiber and the rubber matrix, resulting in poor interfacial bonding and a very short fatigue life, making it prone to rapid failure under cyclic stress. The fatigue lives of samples in Examples 1, 2, 3, and 4 were 23,637, 28,754, 31,213, and 24,559 cycles, respectively. With increasing DETA gradient, the fatigue life of the composite material also increased accordingly. This is because the principle behind the composite material with superior fatigue performance obtained through impregnation treatment is that the impregnation treatment creates a gradient modulus interface layer at the fiber-rubber bonding interface, enhancing stress transmission and dissipating strain energy during fatigue cycles, thus inhibiting rapid crack propagation. However, when the DETA content reaches 0.24g, the fatigue life of the composite material decreases compared to Example 3. This is due to the increased curing agent content in the impregnation solution, leading to excessive cross-linking of the impregnated material.

Claims

1. A method for modifying aramid fibers by double-layer impregnation, characterized in that: The double-layer impregnated modified aramid fiber is first impregnated with a first layer of impregnation solution formed by reacting hexamethylene diisocyanate and glycerol triglycidyl ether in an aqueous phase. The aramid fiber is then impregnated with a second layer of impregnation solution composed of ethylene glycol diglycidyl ether, diethylenetriamine, glycidyl methacrylate, and butadiene-pyridine latex. After double-layer modification, the fiber is dried to obtain the double-layer impregnated modified aramid fiber. The double-layer impregnated modified aramid fiber is then blended and vulcanized with rubber to produce a modified aramid-reinforced styrene-butadiene rubber composite material.

2. The modification method for double-layer impregnation modified aramid fibers according to claim 1, characterized in that: The modification method is carried out according to the following steps: (1) Preparation of GH impregnation solution: Take 96.5-96.2g of deionized water and stir at 300-400rpm for 8-12 minutes to form a homogeneous system. Then, slowly add 1.3-1.4g of hexamethylene diisocyanate and 2.2-2.4g of glycerol triglycidyl ether at room temperature and maintain stirring for 35-45 minutes to obtain the first impregnation solution containing isocyanate and silane structures. GH impregnation solution: (2) Preparation of EDGV impregnation solution: At room temperature, 2g of ethylene glycol diglycidyl ether and 0.2g of glycidyl methacrylate were added to 47.65-47.56g of deionized water and stirred for 8-12 minutes. Then, 0.15-0.24g of diethylenetriamine was gradually added and stirred for 7-9 minutes. Finally, 50g of butadiene-pyridine latex was slowly added and stirred for 8-12 minutes to obtain the second impregnation solution, which is the EDGV impregnation solution. (3) Impregnation and drying treatment: First, 3.8-4.2g of aramid fiber is impregnated in 98-102g of GH impregnation solution for 1.5-2.5 minutes. After removal, the excess liquid is scraped off along the fiber direction with a scraper for 0.5-1.5 minutes. Then, the fiber is placed in an oven at 75-85℃ and dried for 8-12 minutes. Then, the dried aramid fiber is impregnated again in 98-102g of EDGV impregnation solution for 1.5-2.5 minutes. After removal, the excess liquid is scraped off along the fiber direction with a scraper for 0.5-1.5 minutes. Then, it is dried again at 75-85℃ for 8-12 minutes to complete the double impregnation treatment and obtain double impregnated modified aramid fiber.

3. The modification method for double-layer impregnation modified aramid fibers according to claim 2, characterized in that: In step (1), the preparation of GH impregnation solution is as follows: 96.31g of deionized water is taken and stirred at 300-400rpm for 10 minutes to form a homogeneous system. Then, 1.36g of hexamethylene diisocyanate and 2.33g of glycerol triglycidyl ether are slowly added at room temperature and stirred for 40 minutes to obtain the first layer of impregnation solution containing isocyanate and silane structure, GH impregnation solution.

4. The modification method for double-layer impregnation modified aramid fibers according to claim 2, characterized in that: In step (2), the EDGV impregnation solution is prepared as follows: at room temperature, 2g of ethylene glycol diglycidyl ether and 0.2g of glycidyl methacrylate are added to 47.59g of deionized water and stirred for 10 minutes. Then, 0.21g of diethylenetriamine is gradually added and stirred for 8 minutes. Finally, 50g of butadiene-pyridine latex is slowly added and stirred for another 10 minutes to obtain the second impregnation solution, which is the EDGV impregnation solution.

5. The modification method for double-layer impregnation modified aramid fibers according to claim 2, characterized in that: In step (3), the impregnation and drying process is as follows: 4g of aramid fiber is first impregnated in 100g of GH impregnation solution for 2 minutes. After removal, excess liquid is scraped off along the fiber direction with a scraper for 1 minute. Then, the fiber is placed in an 80℃ oven to dry for 10 minutes. After drying, the aramid fiber is impregnated again in 100g of EDGV impregnation solution for 2 minutes. After removal, excess liquid is scraped off along the fiber direction with a scraper for 1 minute. Then, it is dried again at 80℃ for 10 minutes to complete the double-layer impregnation process and obtain double-layer impregnated modified aramid fiber.

6. The application of the double-layer impregnated modified aramid fiber according to any one of claims 1-5 in the preparation of rubber composite materials, characterized in that: The rubber composite material is obtained by mixing, open milling, and vulcanization of double-layer impregnated modified aramid fibers and styrene-butadiene rubber matrix.

7. The application according to claim 6, characterized in that: The raw materials of the modified aramid-reinforced styrene-butadiene rubber composite material, calculated by weight, include 180-220 parts of styrene-butadiene rubber, 3-5 parts of double-layer impregnated modified aramid fiber, 35-45 parts of silica, 14-17 parts of rubber compounding agent, and 3-4 parts of sulfur vulcanizing agent. The rubber compounding agent is composed of 5 parts zinc oxide, 4 parts stearic acid, 2.21 parts accelerator M, 0.5 parts accelerator D, 1.96 parts accelerator DM, 0.32 parts accelerator TMTD and 1.5 parts antioxidant 4010.

8. The application according to claim 7, characterized in that: The raw materials of the modified aramid-reinforced styrene-butadiene rubber composite material, calculated by weight, include 200 parts of styrene-butadiene rubber, 4 parts of double-layer impregnated modified aramid fiber, 80 parts of silica, 30.1 parts of rubber compounding agent, and 6.8 parts of sulfur vulcanizing agent.

9. The application according to claim 7, characterized in that: The rubber compounding agent is composed of 5 parts zinc oxide, 4 parts stearic acid, 2.21 parts accelerator M, 0.5 parts accelerator D, 1.96 parts accelerator DM, 0.32 parts accelerator TMTD and 1.5 parts antioxidant 4010.

10. The application according to any one of claims 7-9, characterized in that: The specific preparation method of modified aramid-reinforced styrene-butadiene rubber composite material is as follows: Weigh the raw materials according to the proportions. First, put the styrene-butadiene rubber, silica, and double-layer impregnated modified aramid fiber into a mixer at 110-140℃ and mix for 6-8 minutes. Then, mix on a two-roll mill at 60-80℃, add sulfur vulcanizing agent and rubber compounding agent, and pass through a thin mill 4-6 times to obtain the compound. Vulcanize the compound according to the positive vulcanization time tc90 measured by the vulcanizer to prepare the modified aramid reinforced styrene-butadiene rubber composite material.

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