A type of ultra-high molecular weight polyethylene fiber and its preparation process

Abstract

This application relates to the field of polyethylene fiber technology, specifically disclosing an ultra-high molecular weight polyethylene (UHMWPE) fiber and its preparation process. The UHMWPE fiber comprises the following raw materials: UHMWPE powder, solvent, copolymer flame retardant, hydrotalcite, modified nano-silica, and antioxidant; the UHMWPE powder has a viscosity-average molecular weight of 2 million to 8 million; the copolymer flame retardant is obtained by free radical graft copolymerization of hyperbranched polyethylene and vinyl-containing DOPO derivatives. The UHMWPE fiber of this application exhibits excellent flame retardant properties, meeting the application requirements of polyethylene fibers in aerospace, rail transportation, and other fields with stringent fire safety requirements.

Description

Technical Field

[0001] This application relates to the field of polyethylene fiber technology, and more specifically, to an ultra-high molecular weight polyethylene fiber and its preparation process. Background Technology

[0002] Polyethylene fiber is a type of synthetic fiber made from polyethylene resin through spinning. Ordinary polyethylene fiber, due to its low molecular weight and poor molecular chain orientation, suffers from low strength, insufficient heat resistance, and susceptibility to creep, limiting its application to conventional fields such as textiles and packaging. Ultra-high molecular weight polyethylene fiber, as a third-generation high-performance synthetic fiber, is prepared from linear polyethylene with a viscosity-average molecular weight of 1 million to 5 million through gel spinning and ultra-high thermal stretching processes. Its macromolecular chains are highly straightened and crystalline, exhibiting excellent properties such as low density, high specific strength, chemical corrosion resistance, impact resistance, and abrasion resistance. Along with carbon fiber and aramid fiber, it is considered one of the world's three major high-performance fibers, widely used in high-end fields such as machinery and chemical engineering, marine engineering, safety protection, and sports equipment.

[0003] In existing technologies, ultra-high molecular weight polyethylene (UHMWPE) fibers are mostly prepared using pure UHMWPE resin as the main raw material, combined with solvents such as decahydronaphthalene and white oil, and a small amount of antioxidants, employing a gel spinning process. For example, patent application CN107841796A discloses a method for preparing UHMWPE fibers and the UHMWPE fibers prepared therefrom. The preparation method includes the following steps: selecting UHMWPE powder with a viscosity-average molecular weight of 2 million to 5 million, adding solvent oil, antioxidants, and modifiers; feeding the spinning solution into a twin-screw extruder for co-extrusion; feeding the spinning solution into a filter, and then through a metering pump and extruding it through a spinneret; sequentially performing extraction, drying, and primary drawing. The UHMWPE fibers are obtained according to this preparation method. The above technical solution increases the rheological properties of the spinning solution and reduces its viscosity by adding a modifier to the spinning solution, thereby improving the spinnability of the product. In the subsequent drafting process, using single-stage drafting instead of the traditional three-stage drafting can ensure that the product inspection indicators meet the requirements while also reducing energy consumption, saving space and costs, and saving time and effort.

[0004] However, when using ultra-high molecular weight polyethylene fiber, due to its non-polar saturated alkane structure and high crystallinity, its oxygen index is only about 17.5%. It is extremely easy to melt and burn in high temperature or open flame environments. The combustion process is not self-extinguishing and is accompanied by melting and dripping. It cannot form a dense char layer to block heat and oxygen transfer. Therefore, it has the defect of poor flame retardant performance, which limits its application in fields with strict fire safety requirements such as aerospace, rail transportation, special protection and building flame retardancy. Summary of the Invention

[0005] To enhance the flame retardant properties of ultra-high molecular weight polyethylene (UHMWPE) fibers, this application provides an UHMWPE fiber and its preparation process.

[0006] This application provides a type of ultra-high molecular weight polyethylene fiber using the following technical solution: An ultra-high molecular weight polyethylene fiber comprises the following raw materials in parts by weight: 100-120 parts of ultra-high molecular weight polyethylene powder; Solvent 600-800 parts; 5-15 parts of copolymer flame retardant; 5-10 parts of hydrotalcite; 1-6 parts of modified nano-silica; Antioxidant 0.1-1.5 parts; The viscosity-average molecular weight of the ultra-high molecular weight polyethylene powder is 2 million to 8 million. The copolymer flame retardant is prepared by free radical graft copolymerization of hyperbranched polyethylene and vinyl-containing DOPO derivatives.

[0007] By adopting the above technical solution and introducing a copolymer flame retardant, which is prepared by free radical graft copolymerization of hyperbranched polyethylene and vinyl-containing DOPO derivatives, the modification paradigm of simple physical blending in the prior art is broken, and molecular-level fusion of flame-retardant groups and polymer matrix is ​​achieved. Hyperbranched polyethylene has abundant terminal alkenyl reaction sites, which can covalently graft vinyl-containing DOPO derivatives onto its own backbone, so that the flame-retardant groups exist in a molecularly dispersed state in the ultra-high molecular weight polyethylene matrix. This fundamentally solves the problems of agglomeration, migration and precipitation of traditional flame retardants, ensuring the long-term flame-retardant effect. At the same time, hyperbranched polyethylene and ultra-high molecular weight polyethylene have similar chemical structures, and the two can achieve molecular-level entanglement and partial co-crystallization, effectively avoiding the damage to fiber mechanical properties caused by flame-retardant modification, and achieving synergistic improvement of flame-retardant performance and mechanical properties.

[0008] Furthermore, the aforementioned technical solution further enhances the flame-retardant effect by introducing hydrotalcite and modified nano-silica to form a ternary synergistic flame-retardant system with the copolymer flame retardant. Hydrotalcite, as a layered inorganic material, can decompose and absorb heat at high temperatures, releasing inert gases while simultaneously forming a layered metal oxide barrier to help block heat and oxygen transfer. Modified nano-silica can improve the density and stability of the char layer, suppress melting and dripping, and also provide mechanical reinforcement, preventing the fiber from experiencing a decline in mechanical properties due to flame-retardant modification. The synergistic effect of the various raw material components effectively solves the defects of existing ultra-high molecular weight polyethylene fibers, such as poor flame-retardant performance and easy dripping during combustion, broadening its application scope in fields with stringent fire safety requirements.

[0009] Meanwhile, the selected ultra-high molecular weight polyethylene powder has a viscosity-average molecular weight of 2 million to 8 million. This molecular weight range can ensure that the fiber has a good mechanical property foundation, providing a guarantee for the super-stretching and molecular chain orientation in the subsequent spinning process, and ensuring that the fiber can maintain excellent tensile strength and elastic modulus while achieving high flame retardancy.

[0010] Optionally, the copolymer flame retardant is prepared by the following method: A1. Mix DOPO, formaldehyde solution and p-toluenesulfonic acid, reflux at 70-100℃ for 4-8 hours, and then neutralize, extract and recrystallize to obtain hydroxymethylated DOPO intermediate; A2. The hydroxymethylated DOPO intermediate was mixed with acryloyl chloride, triethylamine was added, and the mixture was reacted at 0-30℃ for 6-12 hours. After washing and purification, the vinyl-containing DOPO derivative was obtained. A3. Hyperbranched polyethylene is mixed with vinyl-containing DOPO derivatives, benzoyl peroxide is added, and a melt grafting reaction is carried out at 100-120℃ for 1-3 hours. After purification and drying, a copolymer flame retardant is obtained.

[0011] By employing the above-mentioned technical solution, a vinyl-containing DOPO derivative is precisely synthesized through a three-step reaction and then melt-grafted copolymerized with hyperbranched polyethylene. This ensures the structural stability and flame-retardant efficiency of the copolymer flame retardant, specifically addressing the problems of complex preparation processes and unstable flame-retardant effects in existing flame retardants. In this preparation method, the first step, hydroxymethylation, introduces hydroxyl active sites into the DOPO derivative, providing a foundation for subsequent vinyl functionalization. Simultaneously, the hydroxymethyl group can dehydrate during thermal decomposition to form a stable cross-linked network, enhancing the density of the char layer. The second step, vinyl esterification, endows the DOPO derivative with a polymerizable double-bond structure, enabling it to covalently graft with the terminal alkenyl groups of hyperbranched polyethylene, achieving molecular-level fixation of the flame-retardant groups. The third step, melt grafting, ensures the sufficiency of the grafting reaction, avoiding the residual unreacted flame-retardant monomers that could lead to a decrease in flame-retardant effect or mechanical properties. The resulting copolymer flame retardant possesses excellent compatibility, flame retardancy, and processability, providing a reliable guarantee for improving the overall performance of the fiber.

[0012] Optionally, in step A1, the mass concentration of the formaldehyde solution is 37%-40%, and the mass ratio of DOPO, formaldehyde solution and p-toluenesulfonic acid is 10:(3.5-4.5):(0.05-0.15).

[0013] By adopting the above technical solution, the formaldehyde solution concentration of 37%-40% is the appropriate concentration for the hydroxymethylation reaction. This ensures the full reaction between DOPO and formaldehyde while avoiding side reactions caused by excessive formaldehyde. A reasonable raw material ratio can control the reaction rate, reduce the generation of by-products, and improve the purity and yield of the hydroxymethylated DOPO intermediate. This lays the foundation for the smooth progress of subsequent vinyl functionalization and graft copolymerization reactions, ensuring that the copolymer flame retardant can play a stable flame retardant role, thereby improving the overall flame retardant performance of the fiber.

[0014] Optionally, in step A2, the mass ratio of hydroxymethylated DOPO intermediate, acryloyl chloride, and triethylamine is 1:(0.4-0.5):(0.45-0.55).

[0015] Optionally, in step A3, the mass ratio of hyperbranched polyethylene, vinyl-containing DOPO derivative, and benzoyl peroxide is 1:(0.5-2):(0.01-0.05).

[0016] The modified nano-silica was prepared by the following method using the above technical solution: B1. Disperse nano-silica in an ethanol solution, add γ-methacryloxypropyltrimethoxysilane, adjust the pH to 3-5 with acetic acid, stir the reaction at 40-80℃ for 2-6 h, centrifuge, wash with ethanol and vacuum dry to obtain silane-modified nano-silica. B2. Silane-modified nano-silica was dispersed in toluene, and glycidyl methacrylate and azobisisobutyronitrile were added. The mixture was polymerized at 70-90℃ for 4-12 hours under nitrogen protection. After centrifugation, the nano-silica was washed three times each with toluene and ethanol, and then dried under vacuum to obtain modified nano-silica.

[0017] Optionally, a two-step modification process improves the compatibility of nano-silica with the ultra-high molecular weight polyethylene matrix and copolymer flame retardants, solving the problems of unmodified nano-silica's tendency to agglomerate and its weak bonding with the matrix, leading to decreased fiber mechanical properties and insufficient char layer stability. Step B1 involves modifying the nano-silica with a silane coupling agent to introduce active groups on its surface, improving its surface polarity and enhancing its interaction with hyperbranched polyethylene and DOPO derivatives. Step B2 involves a polymerization reaction to coat the silane-modified nano-silica with a polymer layer, further improving its compatibility with the non-polar ultra-high molecular weight polyethylene matrix. This ensures that the nano-silica can be uniformly dispersed, fully exerting its mechanical reinforcement and char layer hardening effects. This enhances the tensile strength and creep resistance of the fiber, improves the density and stability of the char layer, inhibits melt dripping, and further optimizes the flame retardant effect and mechanical properties of the fiber.

[0018] Optionally, in step B1, the mass concentration of the ethanol solution is 40%-50%; the mass concentrations of the nano-silica, the ethanol solution, and γ-methacryloyloxypropyltrimethoxysilane are 1:(20-30):(0.1-0.3).

[0019] Optionally, in step B2, the mass ratio of silane-modified nano-silica, toluene, glycidyl methacrylate, and azobisisobutyronitrile is 1:(30-50):(1.2-2):(0.02-0.06).

[0020] Optionally, the average particle size D50 of the hydrotalcite is 100-300 nm.

[0021] By adopting the above technical solution, hydrotalcite within this particle size range can be uniformly dispersed in the fiber matrix. Its layered structure can fully decompose at high temperatures, releasing inert gases and absorbing heat, while forming a uniform metal oxide layered barrier. This barrier works synergistically with the copolymer flame retardant and modified nano-silica to effectively block heat and oxygen transfer and inhibit melt dripping. At the same time, the appropriate particle size can reduce the influence of hydrotalcite on the orientation of ultra-high molecular weight polyethylene molecular chains, avoiding a decline in fiber mechanical properties and ensuring that the fiber maintains excellent mechanical properties while achieving high-efficiency flame retardancy.

[0022] This application also provides a process for preparing ultra-high molecular weight polyethylene fiber, which adopts the following technical solution: A process for preparing ultra-high molecular weight polyethylene fiber includes the following steps: S1. Add copolymer flame retardant, hydrotalcite, and modified nano silica to a solvent, emulsify by high-speed shearing and disperse by ultrasonication to obtain a dispersion slurry. Add ultra-high molecular weight polyethylene powder and antioxidant to the dispersion slurry, swell at 75-90℃ for 3-5 hours, and then blend and dissolve in a twin-screw extruder to obtain a spinning solution. S2. The spinning solution is regulated by a metering pump and extruded through a spinneret. It is then stretched through a 7-12cm air layer and quenched in a 5-15℃ water bath to form gel fiber. The gel fiber is extracted with dichloromethane at 40-50℃ for 30-50 minutes and then dried until the water content is ≤0.03% to obtain dried fiber. S3. The dried precursor fiber is subjected to three-stage drawing in a gradient drawing box: first stage drawing temperature 120-130℃, drawing ratio 3-8 times; second stage drawing temperature 130-140℃, drawing ratio 6-15 times; third stage drawing temperature 140-155℃, drawing ratio 2-6 times; the stretched fiber is then heat-set in a nitrogen atmosphere at 140-150℃ for 2-4 minutes to obtain ultra-high molecular weight polyethylene fiber.

[0023] By adopting the above-mentioned technical solution and employing a three-step core process, combining next-generation gel spinning and ultra-high gradient drawing technology, this process specifically addresses the problems of uneven dispersion of flame-retardant components and insufficient molecular chain orientation in existing preparation processes, which makes it difficult to simultaneously achieve both flame-retardant and mechanical properties of fibers. The first step, raw material dispersion and spinning solution preparation, ensures that the copolymer flame retardant, hydrotalcite, and modified nano-silica are uniformly dispersed in the ultra-high molecular weight polyethylene matrix, avoiding agglomeration. The second step, gel spinning and extraction drying, uses low-temperature water bath quenching to form uniformly structured gel fibers, combined with efficient extraction and drying to ensure complete solvent removal, laying the foundation for subsequent ultra-high gradient drawing. The third step, three-stage gradient drawing and heat setting, precisely controls the drawing temperature and ratio to promote high orientation of ultra-high molecular weight polyethylene molecular chains, while simultaneously oriented the flame-retardant components along the fiber axis, further enhancing the synergistic effect of flame retardancy and fiber mechanical properties. Ultimately, this produces ultra-high molecular weight polyethylene fibers that possess both high flame retardancy and excellent mechanical properties, completely solving the core defects of existing technologies and meeting the application needs of high-end fields.

[0024] In summary, this application has the following beneficial effects: 1. This application uses a copolymer flame retardant as the core flame retardant component, fundamentally solving the technical defects of poor flame retardant performance and easy agglomeration and migration of existing ultra-high molecular weight polyethylene fibers. This copolymer flame retardant is prepared by free radical graft copolymerization of hyperbranched polyethylene and vinyl-containing DOPO derivatives, breaking the traditional simple physical blending modification mode and achieving molecular-level fusion of flame retardant groups and the polymer matrix. Hyperbranched polyethylene itself has abundant terminal alkenyl reaction sites, which can covalently graft DOPO-type flame retardant groups onto its backbone, allowing the flame retardant groups to be uniformly distributed in a molecularly dispersed state within the ultra-high molecular weight polyethylene matrix. This effectively avoids the problems of agglomeration, migration, and precipitation of traditional flame retardants, ensuring the long-lasting flame retardant effect. Meanwhile, hyperbranched polyethylene and ultra-high molecular weight polyethylene have similar chemical structures, and the two can achieve molecular-level entanglement and partial co-crystallization, effectively avoiding the damage to the mechanical properties of fibers caused by flame retardant modification. This successfully achieves a synergistic improvement in flame retardant performance and mechanical properties, solving the problem of difficulty in balancing flame retardancy and mechanical properties in existing technologies, and improving the defects of fibers such as easy melting and burning at high temperatures, lack of self-extinguishing properties, and easy dripping.

[0025] 2. The modified nano-silica prepared using a specific method in this application effectively solves the problems of poor compatibility and easy agglomeration between unmodified nano-silica and the ultra-high molecular weight polyethylene matrix, leading to decreased fiber mechanical properties and insufficient char layer stability. The modified nano-silica is prepared through a two-step modification process. First, it is modified with a silane coupling agent to introduce active groups, improving its surface polarity and enhancing its interaction with the copolymer flame retardant. Then, it is coated with a polymer layer through a polymerization reaction, further improving its compatibility with the non-polar ultra-high molecular weight polyethylene matrix and ensuring its uniform dispersion within the matrix. The uniformly dispersed modified nano-silica not only provides mechanical reinforcement, enhancing the tensile strength and creep resistance of the fiber, but also improves the density and stability of the char layer during fiber combustion, effectively suppressing melt dripping and further enhancing the flame retardant effect. It also forms a synergistic effect with the copolymer flame retardant and hydrotalcite, further optimizing the overall performance of the fiber and providing important support for achieving a balance between high-efficiency flame retardancy and excellent mechanical properties.

[0026] 3. The overall technical solution of this application, through reasonable raw material ratios and suitable preparation processes, comprehensively solves the core technical problems of poor flame retardant performance and limited application range of existing ultra-high molecular weight polyethylene fibers. In the raw material system, the copolymer flame retardant, hydrotalcite, and modified nano-silica form a ternary synergistic flame retardant system, constructing a multi-layered flame retardant defense from the molecular scale to the microstructure level, effectively blocking heat and oxygen transfer, inhibiting melt dripping, and significantly improving the flame retardant performance of the fiber. This successfully broadens the application range of ultra-high molecular weight polyethylene fibers in fields with stringent fire safety requirements such as aerospace and rail transportation, and has significant practical value and technical advantages. Detailed Implementation

[0027] The present application will be further described in detail below with reference to the embodiments.

[0028] The hyperbranched polyethylene used in this application embodiment was prepared by the following method: Under inert gas protection, α-diimide nickel palladium and methylaluminoxane activator were added to a dry high-pressure reactor at a molar ratio of 1:250. Then, anhydrous toluene was added as a solvent (100 mL / mmol α-diimide nickel palladium). The temperature was raised to 25°C, and ethylene gas was introduced to a pressure of 0.8 MPa. The mixture was stirred and polymerized for 18 hours. After the reaction was completed, methanol was added to terminate the polymerization. The reaction solution was poured into 5-8 times the volume of methanol to precipitate the product. The product was filtered and dried under vacuum at 60°C for 24 hours to obtain hyperbranched polyethylene.

[0029] Preparation example of copolymer flame retardants Preparation Example 1 The copolymer flame retardant was prepared by the following method: A1. DOPO, a 37% formaldehyde solution, and p-toluenesulfonic acid were mixed in a mass ratio of 10:3.5:0.05 and refluxed at 70°C for 4 hours. After neutralization, extraction, and recrystallization, the hydroxymethylated DOPO intermediate was obtained. A2. The hydroxymethylated DOPO intermediate was mixed with acryloyl chloride and triethylamine in a mass ratio of 1:0.4:0.45 and reacted at 0°C for 6 hours. After washing and purification, a vinyl-containing DOPO derivative was obtained. A3. Hyperbranched polyethylene, vinyl-containing DOPO derivative, and benzoyl peroxide were mixed at a mass ratio of 1:0.5:0.01 and subjected to a melt grafting reaction at 100°C for 1 hour. After purification and drying, a copolymer flame retardant was obtained.

[0030] Preparation Example 2 The copolymer flame retardant was prepared by the following method: A1. DOPO, 38% formaldehyde solution and p-toluenesulfonic acid were mixed at a mass ratio of 10:4.0:0.10 and refluxed at 85°C for 6 hours. After neutralization, extraction and recrystallization, hydroxymethylated DOPO intermediate was obtained. A2. The hydroxymethylated DOPO intermediate was mixed with acryloyl chloride and triethylamine at a mass ratio of 1:0.45:0.50 and reacted at 15°C for 9 hours. After washing and purification, a vinyl-containing DOPO derivative was obtained. A3. Hyperbranched polyethylene, vinyl-containing DOPO derivative, and benzoyl peroxide were mixed at a mass ratio of 1:1.25:0.03 and subjected to a melt grafting reaction at 110°C for 2 hours. After purification and drying, a copolymer flame retardant was obtained.

[0031] Preparation Example 3 The copolymer flame retardant was prepared by the following method: A1. DOPO, 40% formaldehyde solution and p-toluenesulfonic acid were mixed in a mass ratio of 10:4.5:0.15 and refluxed at 100℃ for 8 hours. After neutralization, extraction and recrystallization, hydroxymethylated DOPO intermediate was obtained. A2. The hydroxymethylated DOPO intermediate was mixed with acryloyl chloride and triethylamine in a mass ratio of 1:0.5:0.55 and reacted at 30°C for 12 hours. After washing and purification, a vinyl-containing DOPO derivative was obtained. A3. Hyperbranched polyethylene, vinyl-containing DOPO derivative, and benzoyl peroxide were mixed at a mass ratio of 1:2:0.05 and subjected to a melt grafting reaction at 120°C for 3 hours. After purification and drying, a copolymer flame retardant was obtained.

[0032] Preparation example of modified nano silica Preparation Example 4 Modified nano-silica was prepared using the following method: B1. Disperse nano-silica in a 40% (w / w) ethanol solution, add γ-methacryloxypropyltrimethoxysilane, the mass ratio of nano-silica, ethanol solution, and γ-methacryloxypropyltrimethoxysilane is 1:20:0.1; adjust the pH to 3 with acetic acid, stir the reaction at 40℃ for 2 h, centrifuge, wash with ethanol and vacuum dry to obtain silane-modified nano-silica; B2. Silane-modified nano-silica was dispersed in toluene, and glycidyl methacrylate and azobisisobutyronitrile were added. The mass ratio of silane-modified nano-silica, toluene, glycidyl methacrylate, and azobisisobutyronitrile was 1:30:1.2:0.02. The polymerization reaction was carried out at 70°C for 4 hours under nitrogen protection. After centrifugation, the nano-silica was washed three times each with toluene and ethanol, and then dried under vacuum to obtain modified nano-silica.

[0033] Preparation Example 5 Modified nano-silica was prepared using the following method: B1. Disperse nano-silica in a 45% (w / w) ethanol solution, add γ-methacryloxypropyltrimethoxysilane, the mass ratio of nano-silica, ethanol solution, and γ-methacryloxypropyltrimethoxysilane is 1:25:0.2; adjust the pH to 4 with acetic acid, stir the reaction at 60℃ for 4 h, centrifuge, wash with ethanol and vacuum dry to obtain silane-modified nano-silica; B2. Silane-modified nano-silica was dispersed in toluene, and glycidyl methacrylate and azobisisobutyronitrile were added. The mass ratio of silane-modified nano-silica, toluene, glycidyl methacrylate, and azobisisobutyronitrile was 1:40:1.6:0.04. The polymerization reaction was carried out at 80°C for 8 hours under nitrogen protection. After centrifugation, the nano-silica was washed three times each with toluene and ethanol, and then dried under vacuum to obtain modified nano-silica.

[0034] Preparation Example 6 Modified nano-silica was prepared using the following method: B1. Disperse nano-silica in a 50% (w / w) ethanol solution, add γ-methacryloxypropyltrimethoxysilane, the mass ratio of nano-silica, ethanol solution, and γ-methacryloxypropyltrimethoxysilane is 1:30:0.3; adjust the pH to 5 with acetic acid, stir the reaction at 80℃ for 6 h, centrifuge, wash with ethanol and vacuum dry to obtain silane-modified nano-silica; B2. Silane-modified nano-silica was dispersed in toluene, and glycidyl methacrylate and azobisisobutyronitrile were added. The mass ratio of silane-modified nano-silica, toluene, glycidyl methacrylate, and azobisisobutyronitrile was 1:50:2:0.06. The polymerization reaction was carried out at 90°C for 12 h under nitrogen protection. After centrifugation, the nano-silica was washed three times each with toluene and ethanol, and then dried under vacuum to obtain modified nano-silica.

[0035] Example Example 1 A type of ultra-high molecular weight polyethylene fiber, the raw material composition and formulation of which are shown in Table 1, wherein the viscosity-average molecular weight of the ultra-high molecular weight polyethylene powder is 2 million, the solvent is paraffin oil, the copolymer flame retardant is the copolymer flame retardant prepared in Preparation Example 1, the average particle size D50 of the hydrotalcite is 100 nm, the modified nano silica is the modified nano silica prepared in Preparation Example 4, and the antioxidant is antioxidant 1010.

[0036] A process for preparing ultra-high molecular weight polyethylene fiber includes the following steps: S1. Add copolymer flame retardant, hydrotalcite, and modified nano silica to a solvent, emulsify by high-speed shearing and disperse by ultrasonication to obtain a dispersion slurry. Add ultra-high molecular weight polyethylene powder and antioxidant to the dispersion slurry, swell at 75°C for 5 hours, and then blend and dissolve in a twin-screw extruder to obtain a spinning solution. S2. The spinning solution is regulated by a metering pump and extruded through a spinneret. It is then stretched through a 7cm air layer and quenched in a 5℃ water bath to form gel fiber. The gel fiber is extracted with dichloromethane at 40℃ for 50min and then dried to a water content of ≤0.03% to obtain dried fiber. S3. The dried precursor fiber is subjected to three-stage drawing in a gradient drawing box: first stage drawing temperature 120℃, drawing ratio 8 times; second stage drawing temperature 130℃, drawing ratio 15 times; third stage drawing temperature 140℃, drawing ratio 6 times; the stretched fiber is then heat-set at 140℃ in a nitrogen atmosphere for 4 minutes to obtain ultra-high molecular weight polyethylene fiber.

[0037] Example 2 A type of ultra-high molecular weight polyethylene fiber, the raw material composition and formulation of which are shown in Table 1, wherein the viscosity-average molecular weight of the ultra-high molecular weight polyethylene powder is 5 million, the solvent is paraffin oil, the copolymer flame retardant is the copolymer flame retardant prepared in Preparation Example 2, the average particle size D50 of the hydrotalcite is 200 nm, the modified nano silica is the modified nano silica prepared in Preparation Example 5, and the antioxidant is antioxidant 168.

[0038] A process for preparing ultra-high molecular weight polyethylene fiber includes the following steps: S1. Add copolymer flame retardant, hydrotalcite, and modified nano silica to a solvent, emulsify by high-speed shearing and disperse by ultrasonication to obtain a dispersion slurry. Add ultra-high molecular weight polyethylene powder and antioxidant to the dispersion slurry, swell at 85°C for 4 hours, and then blend and dissolve in a twin-screw extruder to obtain a spinning solution. S2. The spinning solution is regulated by a metering pump and extruded through a spinneret. It is then stretched through a 10cm air layer and quenched in a 10℃ water bath to form gel fiber. The gel fiber is extracted with dichloromethane at 45℃ for 40min and then dried to a water content ≤0.03% to obtain dried fiber. S3. The dried precursor fiber is subjected to three-stage drawing in a gradient drawing box: first stage drawing temperature 125℃, drawing ratio 5 times; second stage drawing temperature 135℃, drawing ratio 10 times; third stage drawing temperature 150℃, drawing ratio 4 times; the stretched fiber is then heat-set at 145℃ in a nitrogen atmosphere for 3 minutes to obtain ultra-high molecular weight polyethylene fiber.

[0039] Example 3 A type of ultra-high molecular weight polyethylene fiber, the raw material composition and formulation of which are shown in Table 1, wherein the viscosity-average molecular weight of the ultra-high molecular weight polyethylene powder is 8 million, the solvent is paraffin oil, the copolymer flame retardant is the copolymer flame retardant prepared in Preparation Example 3, the average particle size D50 of the hydrotalcite is 300 nm, the modified nano silica is the modified nano silica prepared in Preparation Example 6, and the antioxidant is antioxidant 1010.

[0040] A process for preparing ultra-high molecular weight polyethylene fiber includes the following steps: S1. Add copolymer flame retardant, hydrotalcite, and modified nano silica to a solvent, emulsify by high-speed shearing and disperse by ultrasonication to obtain a dispersion slurry. Add ultra-high molecular weight polyethylene powder and antioxidant to the dispersion slurry, swell at 90℃ for 3 hours, and then blend and dissolve in a twin-screw extruder to obtain a spinning solution. S2. The spinning solution is regulated by a metering pump and extruded through a spinneret. It is then stretched through a 12cm air layer and quenched in a 15℃ water bath to form gel fiber. The gel fiber is extracted with dichloromethane at 50℃ for 30min and then dried to a water content ≤0.03% to obtain dried fiber. S3. The dried precursor fiber is subjected to three-stage drawing in a gradient drawing box: first stage drawing temperature 130℃, drawing ratio 3 times; second stage drawing temperature 140℃, drawing ratio 6 times; third stage drawing temperature 155℃, drawing ratio 2 times; the stretched fiber is then heat-set at 150℃ in a nitrogen atmosphere for 2 minutes to obtain ultra-high molecular weight polyethylene fiber.

[0041] Table 1. Raw material composition and proportions (kg) of ultra-high molecular weight polyethylene fiber in Examples 1-3

[0042] Example 4 An ultra-high molecular weight polyethylene fiber, which differs from Example 3 in that the viscosity-average molecular weight of the ultra-high molecular weight polyethylene powder in this example is 6 million.

[0043] Example 5 An ultra-high molecular weight polyethylene fiber, which differs from Example 3 in that the copolymer flame retardant used in this example is the copolymer flame retardant prepared in Preparation Example 2.

[0044] Example 6 An ultra-high molecular weight polyethylene fiber, which differs from Example 3 in that the modified nano-silica in this example is the modified nano-silica prepared in Preparation Example 4.

[0045] Example 7 The ultra-high molecular weight polyethylene fiber differs from that in Example 3 in that the preparation process step S3 is different. Specifically, step S3 of this example is as follows: The dried precursor fiber is subjected to three stages of drawing in a gradient drawing box: first stage drawing temperature 130℃, drawing ratio 8 times; second stage drawing temperature 140℃, drawing ratio 15 times; third stage drawing temperature 155℃, drawing ratio 6 times; the stretched fiber is then heat-set at 150℃ in a nitrogen atmosphere for 2 minutes to obtain ultra-high molecular weight polyethylene fiber.

[0046] Example 8 An ultra-high molecular weight polyethylene fiber, which differs from Example 3 in that the average particle size D50 of the hydrotalcite in this example is 50 nm.

[0047] Comparative Example Comparative Example 1 An ultra-high molecular weight polyethylene fiber was prepared according to Example 1 in the patent application document with publication number CN107841796A entitled "An ultra-high molecular weight polyethylene fiber and its preparation method".

[0048] Comparative Example 2 An ultra-high molecular weight polyethylene fiber, which differs from Example 3 in that no copolymer flame retardant was added in this comparative example.

[0049] Comparative Example 3 An ultra-high molecular weight polyethylene fiber, which differs from Example 3 in that an equal amount of melamine cyanurate is used instead of the copolymer flame retardant in this comparative example.

[0050] Comparative Example 4 An ultra-high molecular weight polyethylene fiber, which differs from Example 3 in that unmodified nano-silica is used instead of modified nano-silica in this comparative example.

[0051] Comparative Example 5 A type of ultra-high molecular weight polyethylene fiber, which differs from Example 3 in that hydrotalcite was not added in this comparative example.

[0052] Performance testing 1. Limiting Oxygen Index (LOI) Detection The procedure shall be performed in accordance with GB / T 5454-1997 "Test for Burning Performance of Textiles - Oxygen Index Method", and the specific operation is as follows: (1) The ultra-high molecular weight polyethylene fibers prepared in each embodiment and comparative example are made into samples with a specification of 150mm×10mm×0.5mm. Five parallel samples are prepared in each group. Impurities on the sample surface are removed and the fiber orientation is straightened. (2) Fix the sample vertically on the sample clamp of the oxygen index tester, adjust the mixing ratio of oxygen and nitrogen, start from a low oxygen concentration, and gradually increase the oxygen concentration until the sample can burn continuously for 30 seconds or the burning length reaches 50 mm. (3) Record the oxygen concentration at this time, which is the limiting oxygen index of the sample. Take the average value of 5 parallel samples as the final test result, accurate to 0.1%.

[0053] 2. Vertical flammability rating (UL-94) testing The vertical burning test method in GB / T 2408-2021 "Determination of Burning Performance of Plastics - Horizontal and Vertical Methods" shall be followed. The specific operation is as follows: (1) Prepare standard specimens of 127mm×12.7mm×0.5mm, and prepare 5 parallel specimens for each group. The specimen surface is free of damage and wrinkles. (2) Fix the sample vertically, with the lower end 300mm away from the degreased cotton pad. Use a Bunsen burner flame (20mm high) to vertically burn the lower end of the sample for 10s. Remove the flame and record the burning time of the sample, whether it self-extinguishes, whether there is melting dripping, and whether the dripping material ignites the degreased cotton. (3) The combustion level is determined according to the combustion phenomenon. The levels are divided into V-0, V-1 and V-2. Among them, V-0 has the best flame retardant performance (no dripping and short self-extinguishing time), and V-2 is the worst (dripping and easy to ignite degreased cotton). If the V-2 level is not reached, it is recorded as "non-compliant".

[0054] 3. Fracture strength testing The procedure shall be performed in accordance with GB / T 14344-2008 "Test Method for Tensile Properties of Chemical Fiber Filaments", and the specific operation is as follows: (1) Cut the ultra-high molecular weight polyethylene fibers prepared in each example and comparative example into 300 mm long samples, prepare 10 parallel samples in each group, adjust the ambient temperature to 23±2℃ and the relative humidity to 65±5%, and place the samples in this environment for 24 h to equilibrate. (2) Using an electronic universal testing machine, set the tensile speed to 50 mm / min and the clamping distance to 200 mm. Clamp both ends of the sample on the upper and lower clamps of the testing machine to ensure that the sample is not skewed or under tension. (3) Start the testing machine until the specimen breaks, record the breaking load of each specimen, calculate the breaking strength based on the cross-sectional area of ​​the specimen (breaking strength = breaking load / cross-sectional area of ​​the specimen), and take the average value of 10 parallel specimens as the final test result, accurate to 0.1cN / dtex.

[0055] The performance test results of each embodiment and comparative example are shown in Table 2.

[0056] Table 2 Detection Results

[0057] As shown in Table 2, from the perspective of the limiting oxygen index (LOI), a core indicator of flame retardant performance, the LOI of Examples 1-8 is between 31.2% and 35.1%, which is much higher than the 17.5% of conventional ultra-high molecular weight polyethylene fiber and significantly better than the comparative examples. Among them, Examples 3 and 7 have the best performance, with LOIs of 34.8% and 35.1% respectively. This is because they use the optimal raw material ratio and drawing process, which allows the ternary synergistic flame retardant system formed by the copolymer flame retardant, hydrotalcite, and modified nano-silica to fully exert its effect. Example 1, as the basic ratio, has an LOI of 31.2%, which is still higher than that of Comparative Example 4 (29.8%) and Comparative Example 5 (30.3%). The core reason is that Example 1 has complete components, and the ternary synergistic flame retardant effect is effectively exerted. In contrast, Comparative Examples 4 and 5 lack the modification effect of modified nano-silica and hydrotalcite, respectively, and cannot form a complete synergistic system. Even with a higher amount of copolymer flame retardant added, the flame retardant effect is still not as good as that of Example 1 with complete components. Comparative Examples 1 and 2 had oxygen indices of only 17.8%-18.2%, which could not improve the flammability of polyethylene fibers because they did not use the copolymer flame retardant of this application. Comparative Example 3 used MCA to replace the copolymer flame retardant, and the oxygen index was only 25.3%, which proved the superiority of the copolymer flame retardant of this application over traditional physical blend flame retardants.

[0058] As shown in Table 2, the vertical burning rating test results further confirm the flame-retardant advantages of this application. Examples 1-8 all achieved the UL-94 V-0 rating, with no melting drips during combustion and excellent self-extinguishing properties. In contrast, comparative examples 1 and 2 did not reach the V-2 rating, exhibiting no self-extinguishing properties and accompanied by a large amount of melting drips. Comparative example 3 was at the V-2 rating, with melting drips that easily ignited absorbent cotton, indicating that traditional physical blend flame retardants cannot effectively suppress melting drips. Comparative examples 4 and 5 were at the V-1 rating, with slight drips and prolonged self-extinguishing time. This is because they lacked key synergistic components, and the layered barrier effect of hydrotalcite or the carbon layer strengthening effect of modified nano-silica could not be exerted, making it difficult to achieve the excellent flame-retardant effect of the V-0 rating. This further proves that the ternary synergistic effect of copolymer flame retardant, hydrotalcite, and modified nano-silica is indispensable.

[0059] Regarding mechanical properties, the fracture strength of Examples 1-8 is all above 28.2 cN / dtex, reaching a maximum of 33.4 cN / dtex, indicating that the technical solution of this application can achieve a synergistic improvement in flame retardant performance and mechanical properties. Comparative Examples 3 and 4 show a significant decrease in fracture strength, primarily due to the poor compatibility between traditional physically blended flame retardants, unmodified nano-silica, and the matrix. Agglomeration disrupts the molecular chain entanglement, leading to impaired mechanical properties.

[0060] In summary, this application achieves molecular-level fusion of flame-retardant groups and the matrix through copolymer flame retardants, and forms a ternary synergistic flame-retardant system by combining hydrotalcite and modified nano-silica. With a suitable preparation process, it not only significantly improves the flame-retardant performance of ultra-high molecular weight polyethylene fibers and solves the core defects of flammability and dripping, but also avoids the damage to mechanical properties caused by flame-retardant modification, thus broadening its application scope in the high-end flame-retardant field and highlighting the technical advantages and practical value of the solution proposed in this application.

[0061] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A type of ultra-high molecular weight polyethylene fiber, characterized in that, The raw materials include the following parts by weight: 100-120 parts of ultra-high molecular weight polyethylene powder; Solvent 600-800 parts; 5-15 parts of copolymer flame retardant; 5-10 parts of hydrotalcite; 1-6 parts of modified nano-silica; Antioxidant 0.1-1.5 parts; The viscosity-average molecular weight of the ultra-high molecular weight polyethylene powder is 2 million to 8 million. The modified nano silica is prepared by modifying nano silica with γ-methacryloxypropyltrimethoxysilane, and then modifying it with glycidyl methacrylate and azobisisobutyronitrile. The copolymer flame retardant was prepared using the following method: A1. Mix DOPO, formaldehyde solution and p-toluenesulfonic acid, reflux at 70-100℃ for 4-8 hours, and then neutralize, extract and recrystallize to obtain hydroxymethylated DOPO intermediate; A2. The hydroxymethylated DOPO intermediate was mixed with acryloyl chloride, triethylamine was added, and the mixture was reacted at 0-30℃ for 6-12 hours. After washing and purification, the vinyl-containing DOPO derivative was obtained. A3. Hyperbranched polyethylene is mixed with vinyl-containing DOPO derivatives, benzoyl peroxide is added, and a melt grafting reaction is carried out at 100-120℃ for 1-3 hours. After purification and drying, a copolymer flame retardant is obtained.

2. The ultra-high molecular weight polyethylene fiber according to claim 1, characterized in that: In step A1, the mass concentration of the formaldehyde solution is 37%-40%, and the mass ratio of DOPO, formaldehyde solution and p-toluenesulfonic acid is 10:(3.5-4.5):(0.05-0.15).

3. The ultra-high molecular weight polyethylene fiber according to claim 1, characterized in that: In step A2, the mass ratio of hydroxymethylated DOPO intermediate, acryloyl chloride, and triethylamine is 1:(0.4-0.5):(0.45-0.55).

4. The ultra-high molecular weight polyethylene fiber according to claim 1, characterized in that: In step A3, the mass ratio of hyperbranched polyethylene, vinyl-containing DOPO derivative, and benzoyl peroxide is 1:(0.5-2):(0.01-0.05).

5. The ultra-high molecular weight polyethylene fiber according to claim 1, characterized in that, The modified nano-silica was prepared using the following method: B1. Disperse nano-silica in an ethanol solution, add γ-methacryloxypropyltrimethoxysilane, adjust the pH to 3-5 with acetic acid, stir the reaction at 40-80℃ for 2-6 h, centrifuge, wash with ethanol and vacuum dry to obtain silane-modified nano-silica. B2. Silane-modified nano-silica was dispersed in toluene, and glycidyl methacrylate and azobisisobutyronitrile were added. The mixture was polymerized at 70-90℃ for 4-12 hours under nitrogen protection. After centrifugation, the nano-silica was washed three times each with toluene and ethanol, and then dried under vacuum to obtain modified nano-silica.

6. The ultra-high molecular weight polyethylene fiber according to claim 5, characterized in that: In step B1, the ethanol solution has a mass concentration of 40%-50%; the mass ratio of the nano-silica, ethanol solution and γ-methacryloyloxypropyltrimethoxysilane is 1:(20-30):(0.1-0.3).

7. The ultra-high molecular weight polyethylene fiber according to claim 5, characterized in that: In step B2, the mass ratio of silane-modified nano-silica, toluene, glycidyl methacrylate, and azobisisobutyronitrile is 1:(30-50):(1.2-2):(0.02-0.06).

8. The ultra-high molecular weight polyethylene fiber according to claim 1, characterized in that: The average particle size D50 of the hydrotalcite is 100-300 nm.

9. A process for preparing ultra-high molecular weight polyethylene fiber according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Add copolymer flame retardant, hydrotalcite, and modified nano silica to a solvent, emulsify by high-speed shearing and disperse by ultrasonication to obtain a dispersion slurry. Add ultra-high molecular weight polyethylene powder and antioxidant to the dispersion slurry, swell at 75-90℃ for 3-5 hours, and then blend and dissolve in a twin-screw extruder to obtain a spinning solution. S2. The spinning solution is regulated by a metering pump and extruded through a spinneret. It is then stretched through a 7-12cm air layer and quenched in a 5-15℃ water bath to form gel fiber. The gel fiber is extracted with dichloromethane at 40-50℃ for 30-50 minutes and then dried until the water content is ≤0.03% to obtain dried fiber. S3. The dried precursor fiber is subjected to three-stage drawing in a gradient drawing box: first stage drawing temperature 120-130℃, drawing ratio 3-8 times; second stage drawing temperature 130-140℃, drawing ratio 6-15 times; third stage drawing temperature 140-155℃, drawing ratio 2-6 times; the stretched fiber is then heat-set in a nitrogen atmosphere at 140-150℃ for 2-4 minutes to obtain ultra-high molecular weight polyethylene fiber.

Images