Flame-retardant polyarylate nanofiber and method for preparing the same

Abstract

The application provides a kind of flame-retardant polyarylate nanofiber and its preparation method, belong to polyarylate nanofiber field, wherein, by plasma treatment, activated PAR and activated flame retardant are obtained by respectively making PAR particles and flame retardant;After the activated PAR particles are melted, the activated flame retardant is added, and the blending melt is obtained by shearing mixing, extruded by spinneret, cools and winds, and the nascent fiber is obtained;The nascent fiber is sheared into short fibers, and the fiber suspension is obtained by ball milling with anhydrous ethanol as medium;Activated flame retardant and initiator are added to the fiber suspension for reaction, and the flame-retardant polyarylate nanofiber is obtained by suction filtration, washing and vacuum drying.The application adopts an innovative "plasma synergistic activation-melt blending-radical grafting" composite process and flame retardant molecular bonding formula, which effectively solves the problems of dispersion, migration and interface bonding strength of traditional physical blending flame-retardant fiber.

Description

Technical Field

[0001] This invention relates to the field of polyarylate nanofiber technology, specifically to a flame-retardant polyarylate nanofiber and its preparation method. Background Technology

[0002] Polyaryl aramid (PAR) fibers are widely used in aerospace, electronics, and automotive interiors due to their excellent mechanical properties, heat resistance, and chemical stability. However, the flammability of PAR fibers limits their application range; therefore, the development of flame-retardant PAR fibers has become a current research hotspot.

[0003] Currently, the commonly used flame retardant technologies for PAR fibers mainly have the following problems: (1) Uneven dispersion of flame retardants: Traditional physical blending methods are difficult to achieve uniform dispersion of flame retardants in the PAR matrix, resulting in uneven flame retardant effect and reduced flame retardant efficiency; (2) Easy migration at high temperature: Physically blended flame retardants are prone to migration and precipitation at high temperatures, resulting in a decrease in flame retardant effect over time and reduced flame retardant durability; (3) Weak interfacial bonding: The interfacial bonding force between the flame retardant and the PAR matrix is ​​weak, and interfacial debonding is easy to occur, reducing the stability and flame retardant effect of the flame retardant; (4) Unstable flame retardant effect: Traditional flame retardant technology is difficult to effectively control the amount and dispersion state of flame retardants, resulting in unstable flame retardant effect and difficulty in meeting the needs of different application fields; (5) Decreased fiber mechanical properties: The addition of flame retardants will have a negative impact on the mechanical properties of PAR fibers, reducing their tensile strength, modulus and other performance indicators.

[0004] In view of this, it is necessary to design an improved flame-retardant polyarylate nanofiber and its preparation method to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a flame-retardant polyarylate nanofiber and its preparation method, aiming to solve the technical problems existing in the flame-retardant treatment of PAR fibers, such as uneven dispersion of flame retardants, easy migration at high temperatures, weak interfacial bonding, unstable flame-retardant effect, and decreased fiber mechanical properties.

[0006] In a first aspect, this application provides a method for preparing flame-retardant polyarylate nanofibers, comprising the following steps:

[0007] S1. PAR particles and flame retardant are respectively subjected to plasma treatment to obtain activated PAR and activated flame retardant;

[0008] S2. After melting the activated PAR particles, add the activated flame retardant, shear and mix to obtain a blend melt, and then extrude it to obtain nascent fibers;

[0009] S3. The nascent fibers are cut into short fibers and ball-milled with anhydrous ethanol as the medium to obtain a fiber suspension.

[0010] S4. The activated flame retardant and initiator are added to the fiber suspension to react, and the mixture is then filtered, washed, and vacuum dried to obtain flame-retardant polyarylate nanofibers.

[0011] As a further improvement of this application, the flame retardant is obtained by mixing antimony trioxide and aluminum hydroxide in a mass ratio of 1:(0.8~1.2).

[0012] As a further improvement of this application, the power of the plasma treatment is 180~250W and the treatment time is 5~30min.

[0013] As a further improvement of this application, in step S2, the melting temperature is 320~430℃, the shearing speed is 200~300rpm, and the amount of activated flame retardant added is 2~15% of the mass of the activated PAR particles.

[0014] As a further improvement of this application, in step S3, the ball milling speed is 450~550 rpm, the ball milling time is 25~35 min, and the mass ratio of the nascent fiber to the anhydrous ethanol is 1:(8~10).

[0015] As a further improvement of this application, in step S4, the initiator is ammonium persulfate, and the amount of the initiator added is 0.5 to 1.5% of the mass of the nascent fiber.

[0016] As a further improvement to this application, the reaction temperature is 60~80℃ and the time is 1.5~2.5h.

[0017] As a further improvement of this application, in step S4, the amount of the activated flame retardant added is 10-20% of the mass of the nascent fiber.

[0018] As a further improvement of this application, in step S3, the ball milling is performed until the monofilament dispersion is >95%.

[0019] Secondly, this application provides a flame-retardant polyarylate nanofiber, which is prepared by the method for preparing flame-retardant polyarylate nanofibers described in the first aspect, wherein the diameter of the flame-retardant polyarylate nanofiber is 160~170nm.

[0020] The beneficial effects of this application are as follows:

[0021] This application provides a method for preparing flame-retardant polyarylate nanofibers. The method involves plasma-treating PAR particles and a flame retardant separately to obtain activated PAR and activated flame retardant. The activated PAR particles are melted, and the activated flame retardant is added. The mixture is sheared and mixed to obtain a blend melt, which is then extruded through a spinneret, cooled, and wound to obtain nascent fibers. The nascent fibers are sheared into short fibers and ball-milled using anhydrous ethanol as the medium to obtain a fiber suspension. The activated flame retardant and an initiator are added to the fiber suspension to react. The mixture is then filtered, washed, and vacuum-dried to obtain flame-retardant polyarylate nanofibers. This application employs an innovative "plasma-assisted activation-melt blending-free radical grafting" composite process and a molecular-level bonding formulation for the flame retardant, effectively solving the problems of dispersibility, migration, and interfacial bonding strength in traditional physically blended flame-retardant fibers.

[0022] This application achieves CO-Sb covalent bonding between the flame retardant and the PAR backbone through plasma pretreatment and free radical grafting reaction. The binding force is increased from 0.1~0.3 N / mm (physical adsorption) to 5~8 N / mm, the high-temperature mobility is reduced to <5%, and the flame retardant is dispersed to the submicron level, increasing the effective contact area by 3 times. When aluminum hydroxide is used in combination with PAR as a flame retardant, synergistic flame retardancy is achieved through multiple mechanisms, such as high-temperature dehydration and heat absorption, release of water vapor to dilute oxygen, formation of alumina for physical barrier, and combination with antimony trioxide to capture combustion free radicals. This achieves dual flame retardancy of "physical barrier (aluminum hydroxide endothermic water release) + chemical char formation (antimony trioxide catalytic coking)," reducing smoke density by 40% and exhibiting only 8% attenuation of hydroxyl groups under humid and hot conditions. This application provides an efficient, green, and scalable high-performance flame-retardant fiber preparation solution for multiple fields.

[0023] The core advantage of this application lies in overcoming the inherent defects of traditional physical blending flame retardant technology. Addressing the problems of weak bonding between flame retardants and polyarylate (PAR) matrices due to physical adsorption, easy migration at high temperatures, and uneven dispersion in existing processes, this application employs a plasma-assisted activation process. This process simultaneously constructs active sites such as hydroxyl, carboxyl, and ≡Sb-O・ free radicals on the surfaces of PAR particles and antimony trioxide. Stable CO-Sb covalent bonds are formed through free radical grafting reactions, transforming the flame retardant from a "loose mixture" to a "molecular-level bond," significantly increasing the bonding strength to 5-8 N / mm and effectively inhibiting flame retardant migration. In the melt blending stage, high-shear crushing and ball milling dispersion (monofilament dispersion > 95%) achieves a submicron-level uniform distribution of the flame retardant (< 10 μm), increasing the effective working area by three times compared to traditional agglomerated particles (> 50 μm).

[0024] This application employs a closed-loop design of "plasma activation-melt spinning-free radical grafting," integrating the synergistic effects of material surface modification, melt processing, and chemical grafting. Plasma treatment avoids high pollution issues, using only air / oxygen and recyclable anhydrous ethanol as the dispersion medium, reducing VOC emissions by 70%. The free radical grafting process simplifies the production flow, reducing two steps, shortening the production cycle by 30%, and lowering unit energy consumption to 8 kWh / kg, achieving 40% energy savings compared to traditional processes. The effective grafting rate of flame retardants is increased to over 75%, with a 40% reduction in usage. In aerospace, electronics, and electrical fields, this invention successfully achieves systematic optimization of flame retardant performance, mechanical strength, and weather resistance, demonstrating an efficient transformation from problem-oriented approaches to technological innovation.

[0025] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0027] Figure 1 This is a SEM image of the flame-retardant polyarylate nanofibers provided in Example 1 of this application;

[0028] Figure 2 The DTG and DSC images of the flame-retardant polyarylate nanofibers provided in Example 1 and Comparative Example 1 of this application are shown.

[0029] Figure 3 The stress-strain curves of the flame-retardant polyarylate nanofibers provided in Example 1 and Comparative Example 1 of this application are shown.

[0030] Figure 4 The thermal shrinkage diagrams of the flame-retardant polyarylate nanofibers provided in Example 1 and Comparative Example 1 of this application are shown.

[0031] Figure 5 The limiting oxygen index is the value of the flame-retardant polyarylate nanofibers provided in Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0032] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0034] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0037] Existing flame retardant technologies for PAR fibers mainly suffer from the following problems: Traditional physical blending methods struggle to achieve uniform dispersion of flame retardants in the PAR matrix, resulting in uneven flame retardant effects and reduced flame retardant efficiency; physically blended flame retardants are prone to migration and precipitation at high temperatures, causing the flame retardant effect to decline over time and reducing flame retardant durability; the interfacial bonding between the flame retardant and the PAR matrix is ​​weak, easily leading to interfacial debonding, which reduces the stability and flame retardant effect; traditional flame retardant technologies struggle to effectively control the amount and dispersion state of flame retardants, resulting in unstable flame retardant effects and difficulty in meeting the needs of different application fields; the addition of flame retardants negatively impacts the mechanical properties of PAR fibers, reducing their tensile strength, modulus, and other performance indicators.

[0038] To address the technical problems of weak bonding between flame retardants and polyarylate matrices due to physical adsorption, easy migration at high temperatures, and uneven dispersion in existing processes, this application provides a flame-retardant polyarylate nanofiber and its preparation method. In this method, chemical grafting can stabilize the flame-retardant groups, improve dispersion uniformity and interfacial compatibility, prevent migration and precipitation, and retain the mechanical properties of the fiber.

[0039] In a first aspect, embodiments of this application provide a method for preparing flame-retardant polyarylate nanofibers, comprising the following steps:

[0040] S1. PAR particles and flame retardant are respectively subjected to plasma treatment to obtain activated PAR and activated flame retardant;

[0041] S2. After melting the activated PAR particles, add the activated flame retardant, shear and mix to obtain a blend melt, and then extrude it to obtain nascent fibers;

[0042] S3. The nascent fibers are cut into short fibers and ball-milled with anhydrous ethanol as the medium to obtain a fiber suspension;

[0043] S4. Add an activating flame retardant and an initiator to the fiber suspension to react, and then filter, wash and vacuum dry to obtain flame retardant polyarylate nanofibers.

[0044] In the technical solution of this application embodiment, plasma synergistic activation technology is employed. High-energy plasma particles bombard PAR and flame retardants to generate polar groups such as hydroxyl and carboxyl groups, as well as oxygen vacancies, thereby enhancing interfacial affinity and reactivity. Through melt blending and spinning, submicron-level dispersion of the flame retardant is achieved under high temperature and twin-screw high-shear conditions, forming a physical flame-retardant "barrier network" and controlling the temperature to prevent decomposition. The fibers are dissociated into monofilaments through ball milling and anhydrous ethanol, exposing more active sites. Hydroxyl flame-retardant groups are grafted using free radical reactions, overcoming the defects of uneven dispersion, easy migration, and weak interfaces inherent in physical blending. Through optimization of all process parameters, a step-by-step modification process of "physical dispersion-chemical grafting" is achieved, improving the flame-retardant performance of PAR fibers while maintaining the tensile strength and thermal stability of the fibers, making it applicable to high-end fields such as aerospace and electronic packaging.

[0045] Furthermore, in some embodiments, in step S1, the flame retardant is obtained by mixing antimony trioxide and aluminum hydroxide at a mass ratio of 1:(0.8~1.2).

[0046] In the technical solution of this application embodiment, antimony trioxide melts at high temperature and covers the material surface, forming a glassy protective layer that isolates oxygen and heat, preventing the outward diffusion of combustible gases. Aluminum hydroxide decomposes at high temperature, absorbing a large amount of heat and generating high-melting-point alumina and water vapor. The alumina covering the material surface acts as a heat and oxygen barrier, while the generated water vapor dilutes the concentration of combustible gases and oxygen, and also has a certain cooling effect. Simultaneously, alumina can promote the formation of a denser carbon layer in the polymer matrix, effectively preventing the inward transfer of heat and oxygen, and the outward diffusion of combustible gases. By combining antimony trioxide and aluminum hydroxide, flame retardancy can be synergistically achieved from both the gas phase and condensed phase perspectives. If the proportion of aluminum hydroxide is too low, the heat absorption effect may be insufficient; if the proportion is too high, although the heat absorption effect is good, the gas-phase synergistic and covering effect of antimony trioxide may be weakened, and the negative impact of aluminum hydroxide itself on the material's mechanical properties (such as reduced toughness) will increase.

[0047] Furthermore, in some embodiments, the plasma treatment power is 180~250W, and the treatment time is 5~30min.

[0048] In the technical solution of this application embodiment, PAR particles and flame retardants are treated with plasma to generate hydroxyl / carboxyl groups on the PAR surface and form oxygen vacancy free radicals from antimony trioxide, thereby activating the matrix and flame retardant, solving interfacial compatibility issues, and providing grafting anchoring points. Specifically, the particle size of the PAR particles ranges from 20 to 40 mesh, the plasma reaction gas is air or oxygen, and the flow rate is 100 to 150 mL / min.

[0049] Furthermore, in some embodiments, in step S2, the melting temperature is 320~430℃, the shearing speed is 200~300rpm, and the amount of activated flame retardant added is 2~15% of the mass of the activated PAR particles.

[0050] In the technical solution of this application embodiment, a suitable melt temperature is beneficial for subsequent mixing and extrusion molding. Excessive temperature may lead to thermal degradation of PAR, affecting fiber properties. A suitable shear speed can generate sufficient shear force and turbulence to effectively disperse the activated flame retardant into the PAR melt, preventing agglomeration and making the flame retardant particles more uniformly distributed in the matrix. A suitable amount of activated flame retardant helps provide basic flame retardant properties in the extruded nascent fibers; excessive amounts may lead to a decrease in the mechanical properties of the fibers. Specifically, activated PAR particles are fed into a twin-screw extruder with a screw zone temperature of 320~380℃, a metering zone temperature of 380~400℃, and a box zone temperature of 400~430℃. After the PAR is completely melted, the activated flame retardant is added, and the mixture is sheared and mixed for 15~20 min until the particle size is <10μm. The blended melt is extruded through a 0.15~0.25mm spinneret, cooled by cold air at 0.8~1.2m / s, and wound and collected at 800m / min to obtain nascent fibers. Under three-stage temperature control, high shear dispersion to the submicron level retains 92% of the water of crystallization of aluminum hydroxide and achieves uniform dispersion, laying the foundation for synergistic flame retardancy.

[0051] Furthermore, in some embodiments, in step S3, the ball milling speed is 450~550 rpm, the ball milling time is 25~35 min, the mass ratio of nascent fiber to anhydrous ethanol is 1:(8~10), and the ball milling is performed until the monofilament dispersion is >95%.

[0052] In the technical solution of this application embodiment, the nascent fibers are uniformly refined to the nanoscale by ball milling dispersion, while maintaining the fiber morphology to the maximum extent and reducing thermal degradation and excessive damage. Specifically, the nascent fibers are cut into short fibers of 4-6 mm and treated with zirconia grinding balls (ball-to-material ratio of 5:1) using anhydrous ethanol as the medium until the monofilament dispersion is >95%.

[0053] Furthermore, in some embodiments, in step S4, the initiator is ammonium persulfate, and the amount of initiator added is 0.5 to 1.5% of the mass of the nascent fiber.

[0054] In the technical solution of this application embodiment, ammonium persulfate is used to initiate a free radical reaction, causing the carbon free radicals of the PAR backbone to combine with antimony trioxide (≡Sb-O・) to form CO-Sb covalent bonds. A suitable initiator can effectively decompose and provide sufficient free radicals, thereby optimizing the efficiency of the polymerization reaction. Too low an initiator addition may result in a slow reaction rate; while too high an addition may lead to a broadening of the molecular weight distribution, or even induce branching or cross-linking. By replacing physical blending with chemical bonding, the binding energy is significantly improved and the high-temperature mobility is reduced.

[0055] Furthermore, in some embodiments, in step S4, the reaction temperature is 60~80°C and the time is 1.5~2.5h.

[0056] In the technical solution of this application embodiment, suitable temperature and time help to graft hydroxyl flame-retardant groups onto the PAR surface, thereby improving the flame-retardant properties of the fiber. Specifically, after the reaction is completed, the fiber is filtered, washed three times each with ethanol and deionized water, and then vacuum dried at 50~60℃ for 10~14h to obtain modified PAR fiber.

[0057] Furthermore, in some embodiments, in step S4, the amount of the activated flame retardant added is 10-20% of the mass of the nascent fiber.

[0058] In the technical solution of this application embodiment, the activated flame retardant can provide a large number of active sites to effectively collide and react with the carbon free radicals on the PAR fiber, forming an effective flame retardant network. If the dosage is too low, the network will be discontinuous and the flame retardant effect will be limited; if the dosage is too high, the fiber performance may be damaged due to excessive cross-linking or flame retardant agglomeration.

[0059] Secondly, embodiments of this application provide a flame-retardant polyarylate nanofiber, which is prepared by the method for preparing flame-retardant polyarylate nanofibers described in the first aspect, and the diameter of the flame-retardant polyarylate nanofiber is 160-170 nm.

[0060] In the technical solution of this application embodiment, a high-performance flame-retardant polyarylate nanofiber is prepared by combining the endothermic water release of aluminum hydroxide, the film-forming barrier of antimony trioxide, and the char-promoting effect of grafted groups through a synergistic flame-retardant mechanism, while improving mechanical properties through interfacial covalent bonding. This improves the flame-retardant performance while maintaining the tensile strength and thermal stability of the fiber.

[0061] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0062] Example 1

[0063] This embodiment provides a method for preparing flame-retardant polyarylate nanofibers, including the following steps:

[0064] S1. Treat the PAR particles and flame retardant in air (100 mL / min) and 200 W plasma for 20 min respectively to generate hydroxyl groups, carboxyl groups and oxygen-containing defect sites on the surface of both, to obtain activated PAR and activated flame retardant, wherein the flame retardant is obtained by mixing antimony trioxide and aluminum hydroxide in a mass ratio of 1:1;

[0065] S2. 100g of activated PAR granules are fed into a twin-screw extruder at 350°C in the screw zone, 400°C in the metering zone, and 420°C in the box zone. After the PAR is completely melted, 5g of activated flame retardant is added. The mixture is sheared and mixed at 250rpm for 15min until the particle size is <10μm to obtain a blended melt. The melt is then extruded through a 0.2mm spinneret, cooled with cold air at 1.0m / s, and wound and collected at 800m / min to obtain nascent fibers.

[0066] S3. Cut 50g of nascent fiber into 5mm short fibers, and treat with 450g of anhydrous ethanol as medium, zirconium oxide grinding balls (ball-to-material ratio 5:1), at 500rpm for 30min until the monofilament dispersion is >95%, to obtain a fiber suspension.

[0067] S4. Transfer the fiber suspension to a three-necked flask, add 7.5g of activating flame retardant, heat to 70℃, prepare an aqueous solution of 0.5g of ammonium persulfate, add it dropwise to the fiber suspension to initiate the reaction for 2h, so that hydroxyl flame retardant groups are grafted onto the surface of PAR. After filtration, washing with ethanol and deionized water 3 times each, dry under vacuum at 55℃ for 12h to obtain flame retardant polyarylate nanofibers.

[0068] Example 2

[0069] This embodiment provides a method for preparing flame-retardant polyarylate nanofibers. Compared with Example 1, the only difference is that in step S2, the amount of activated flame retardant added is 2g.

[0070] Example 3

[0071] This embodiment provides a method for preparing flame-retardant polyarylate nanofibers. Compared with Example 1, the only difference is that in step S2, the amount of activated flame retardant added is 15g.

[0072] Example 4

[0073] This embodiment provides a method for preparing flame-retardant polyarylate nanofibers. Compared with Example 1, the only difference is that in step S2, the temperature of the screw zone is 320°C, the temperature of the metering zone is 380°C, and the temperature of the chamber zone is 400°C.

[0074] Example 5

[0075] This embodiment provides a method for preparing flame-retardant polyarylate nanofibers. Compared with Example 1, the only difference is that in step S2, the temperature of the screw zone is 380°C, the temperature of the metering zone is 400°C, and the temperature of the chamber zone is 430°C.

[0076] Example 6

[0077] This embodiment provides a method for preparing flame-retardant polyarylate nanofibers. Compared with Example 1, the only difference is that in step S4, the amount of activated flame retardant added is 5g.

[0078] Example 7

[0079] This embodiment provides a method for preparing flame-retardant polyarylate nanofibers. The only difference from Example 1 is that in step S4, the amount of activated flame retardant added is 10g.

[0080] Comparative Example 1

[0081] This comparative example provides a method for preparing flame-retardant polyarylate nanofibers. The only difference from Example 1 is that no activating flame retardant is added in step S2.

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing flame-retardant polyarylate nanofibers. The only difference from Example 1 is that, in step S2, the amount of activated flame retardant added is 20g.

[0084] Comparative Example 3

[0085] This comparative example provides a method for preparing flame-retardant polyarylate nanofibers. The only difference from Example 1 is that, in step S2, the temperature of the screw zone is 300°C, the temperature of the metering zone is 350°C, and the temperature of the chamber zone is 380°C.

[0086] Comparative Example 4

[0087] This comparative example provides a method for preparing flame-retardant polyarylate nanofibers. The only difference from Example 1 is that, in step S4, the amount of activated flame retardant added is 2.5g.

[0088] Comparative Example 5

[0089] This comparative example provides a method for preparing flame-retardant polyarylate nanofibers. The only difference from Example 1 is that, in step S4, the amount of activated flame retardant added is 15g.

[0090] The performance test results of the flame-retardant polyarylate nanofibers prepared in the examples and comparative examples are shown in Table 1.

[0091] Table 1. Performance test results of flame-retardant polyarylate nanofibers provided in the examples and comparative examples.

[0092]

[0093] As shown in Table 1, in terms of flame retardant performance (limiting oxygen index LOI), the LOI of Example 1 reached 32.5%, which was significantly higher than that of Comparative Example 1 (26.0%). This proves that the plasma activation and free radical grafting process greatly improved the flame retardant efficiency. Example 3 had a higher LOI (15g) due to the higher amount of flame retardant added during the melting stage, resulting in stronger flame retardancy, but the tensile strength decreased to 85.7MPa. In contrast, Comparative Example 2 had an excessive amount of flame retardant added (20g), resulting in a decrease in both LOI and tensile strength, indicating that increasing the amount of flame retardant added would sacrifice mechanical properties. Comparative Example 4 had an LOI of only 27.8% due to the addition of only 2.5g of flame retardant during the grafting stage, indicating that insufficient flame retardant during the grafting stage would lead to an incomplete flame retardant network. The LOI values ​​of Comparative Examples 2 and 5 (28.1% and 29.1%, respectively) were both lower than those of Example 1 (32.5%). This is because the excessive flame retardant did not effectively participate in the flame retardant effect. Instead, due to severe agglomeration and interfacial failure, it completely destroyed the uniformity and structural integrity of the material. In Comparative Example 2, the 20g of flame retardant added in step S2 far exceeded the dispersion limit of the twin-screw extruder, causing macroscopic agglomeration of antimony trioxide / aluminum hydroxide particles and forming defect points. These agglomerates not only became stress concentration points (leading to a decrease in tensile strength to 78.5MPa), but also failed to form a continuous and dense barrier layer during combustion. Oxygen and combustible gases could diffuse around them, causing the "physical barrier" mechanism to almost fail. In Comparative Example 5, the 15g of flame retardant in step S4 far exceeded the capacity of active sites that could be grafted onto the fiber surface. The excessive flame retardant could only be physically adsorbed onto the fiber surface because it could not obtain grafting sites. This loosely bound state was extremely prone to migration and detachment at high temperatures and could not participate in the synergistic flame retardant reaction. In contrast, in Example 1, although the amount of flame retardant mixed in step S2 was only 5g, the 7.5g of flame retardant in step S4 achieved effective bonding through CO-Sb covalent bonds, resulting in uniform distribution and extremely high thermal stability. During combustion, it can efficiently catalyze char formation and exert a multi-effect synergy of "endothermic-dilution-barrier," ultimately achieving a high LOI of 32.5%. Therefore, the contradictory data confirms that there is a critical addition threshold for flame retardants; exceeding this threshold leads to performance degradation rather than linear growth.

[0094] Regarding mechanical properties (tensile strength), the tensile strength of Example 1 was 93.3 MPa, which is close to that of pure PAR fiber. This is due to the effective reduction of the negative impact of flame retardant on mechanical properties by interfacial covalent bonding (CO-Sb). The tensile strengths of Comparative Example 2 (excess flame retardant in step S2) and Comparative Example 5 (excess flame retardant in step S4) decreased to 78.5 MPa and 74.3 MPa, respectively. It can be seen that flame retardant agglomeration or excessive cross-linking can damage the fiber structure.

[0095] Regarding thermal stability (thermal shrinkage rate), the thermal shrinkage rate of Example 1 was only 3.2%, far lower than that of Comparative Example 1 (8.5%). This is attributed to the reduction of flame retardant migration rate to <5% and the stabilizing effect of covalent bonds. Comparative Example 3 had a thermal shrinkage rate of 9.3% due to its excessively low melting temperature. The low temperature resulted in uneven dispersion of the flame retardant and insufficient dehydration of aluminum hydroxide, which weakened the barrier effect.

[0096] Figure 1 The flame-retardant polyarylate nanofibers exhibit uniform size, with a single filament dispersion of >95%, and no obvious entanglement or agglomeration. The flame retardant is uniformly distributed at the submicron level (<10μm), confirming the improvement in dispersibility brought about by the "plasma activation-melt blending" process. Figure 2 (The left figure is the DTG diagram, and the right figure is the DSC diagram.) In Example 1, the peak temperature of thermal decomposition is significantly later than that of Comparative Example 1, and the peak value of weight loss rate is reduced. A broad endothermic peak of aluminum hydroxide dehydration endothermic occurs in the 200-300℃ range, and the intensity of the exothermic peak decreases in the high temperature range. This reflects the role of flame retardant in delaying thermal decomposition and inhibiting combustion exothermic, and improving thermal stability. Figure 3 The stress-strain curves show that the tensile strength of Example 1 is close to that of Comparative Example 1, and the difference between the fracture strain and the initial slope is small. This indicates that the "plasma activation-free radical grafting" process enhances the interfacial bonding force through covalent bonds, thereby reducing the negative impact on mechanical properties. Figure 4 In the heat shrinkage diagram, the heat shrinkage of Example 1 (3.2%) is significantly lower than that of Comparative Example 1 (8.5%), and the shrinkage trend is more gradual. This is because the flame retardant is covalently bonded, the high temperature migration rate is <5%, and the alumina layer provides physical support, which improves the dimensional stability. Figure 5 (Limiting Oxygen Index Chart) shows that the LOI of Example 1 is 32.5%, which is significantly higher than that of Comparative Example 1 (26.0%). The synergistic effect of antimony trioxide and aluminum hydroxide compound achieves a dual flame retardant effect of physical barrier and chemical char formation.

[0097] This application significantly enhances the polarity between PAR particles and the antimony trioxide surface through plasma-assisted activation treatment, reducing the interfacial contact angle from 85° to 32°. This treatment not only reduces dispersion time by 40% but also enhances the reactivity of antimony trioxide by 60% and provides 10 times more reaction sites for grafting reactions. During melt blending spinning, by precisely controlling the high shear force and temperature gradient of the twin-screw extruder, the flame retardant was successfully dispersed to the submicron level, increasing the specific surface area to 3.8 m². 2 / g, thereby improving the physical flame retardant efficiency. Ball milling dispersion technology increases the density of active groups on the fiber surface, resulting in a grafting site density of 2×10⁻⁶. 14 pcs / cm 2This is four times the original amount. Furthermore, 60% of the internal flame retardant migrated to the fiber surface, enhancing the flame retardant effect. Using free radical grafting technology, the flame retardant formed covalent bonds with the PAR backbone, increasing the binding energy by seven times. This grafting method significantly reduced the migration rate at high temperatures to 4.2%, while extending the flame retardant duration by 50%.

[0098] This application utilizes the dehydration and heat absorption properties of molten blended aluminum hydroxide and the catalytic char formation and heat conduction blocking effects of grafted antimony trioxide to form a gas-solid synergistic flame retardant effect, achieving a 35% reduction in heat release rate and a 40% reduction in smoke density, and reaching the UL-94V-0 flame retardant rating.

[0099] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing flame-retardant polyarylate nanofibers, characterized in that, The method comprises the following steps: S1. Plasma treatment of PAR particles and flame retardant respectively to obtain activated PAR and activated flame retardant; the flame retardant is a mixture of antimony trioxide and aluminum hydroxide with a mass ratio of 1:(0.8-1.2); S2. After melting the activated PAR particles, the activated flame retardant is added, and a blending melt is obtained by shearing mixing, and then extrusion molding is performed to obtain primary fibers; the melting temperature is 320-430℃, the shearing rotation speed is 200-300rpm, and the addition amount of the activated flame retardant is 2-15% of the mass of the activated PAR particles; S3. The primary fibers are sheared into short fibers, and ball milling is performed in anhydrous ethanol as a medium to obtain a fiber suspension; S4. The activated flame retardant and an initiator are added to the fiber suspension for reaction, and then filtration, washing and vacuum drying are performed to obtain flame-retardant polyarylate nanofibers; the addition amount of the activated flame retardant is 10-20% of the mass of the primary fibers.

2. The method for preparing flame-retardant polyarylate nanofibers according to claim 1, characterized in that, The power of the plasma treatment is 180-250W, and the treatment time is 5-30min.

3. The method for preparing flame-retardant polyarylate nanofibers according to claim 1, characterized in that, In step S3, the rotation speed of the ball milling is 450-550rpm, the ball milling time is 25-35min, and the mass ratio of the primary fibers to the anhydrous ethanol is 1:(8-10).

4. The method for preparing flame-retardant polyarylate nanofibers according to claim 1, characterized in that, In step S4, the initiator is ammonium persulfate, and the addition amount of the initiator is 0.5-1.5% of the mass of the primary fibers.

5. The method of claim 4, wherein the polyarylate nanofiber is prepared by a method comprising: (a) dissolving the polyarylate in a solvent to prepare a solution; (b) electrospinning the solution to prepare a nanofiber; and (c) drying the nanofiber. The reaction temperature is 60-80℃, and the reaction time is 1.5-2.5h.

6. The method for preparing flame-retardant polyarylate nanofibers according to claim 1, characterized in that, In step S3, the ball milling is performed until the single fiber dispersity is >95%.

7. A flame-retardant polyarylate nanofiber, characterized by, The flame-retardant polyarylate nanofibers are prepared by the method of any one of claims 1-6, and the diameter of the flame-retardant polyarylate nanofibers is 160-170nm.

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