Multistage branched thermotropic liquid crystalline polyarylate nanofiber and method of making same

Abstract

The application provides a kind of multistage bifurcation thermotropic liquid crystal polyarylate nanofiber and its preparation method, belong to nanofiber field, wherein, by surface activation to eutectic gallium-indium alloy liquid metal, grafting agent is added to carry out grafting reaction, obtain modified liquid metal;The modified liquid metal is melt blended with thermotropic liquid crystal polyarylate resin to prepare composite master batch;Melt spinning and hot drawing are carried out on the composite master batch to obtain composite fiber;Mechanical cleavage, separation and purification are carried out on the composite fiber to obtain multistage bifurcation thermotropic liquid crystal polyarylate nanofiber.The application establishes a new, solvent-free, continuous production nanofiber preparation platform, by combining interface chemistry, liquid crystal polymer physics and advanced melt processing technology, not only fundamentally solves the problems existing in traditional method in environmental protection, efficiency and structure singleness, but also opens up a new way for preparing high-performance nanomaterials with complex configuration.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanofiber, and particularly relates to a multi-level branched thermotropic liquid crystal polyarylate nanofiber and a preparation method thereof. BACKGROUND

[0002] Thermotropic liquid crystal polyarylate (TLCP-PAR) is a kind of top-notch high-performance polymer material, and the molecular chain thereof can spontaneously form a highly ordered liquid crystal phase in a molten state. This characteristic enables the molecular chain to be highly oriented during a melt processing process only by using a low shear force or a stretching force, thereby endowing the final product with super-high mechanical strength, modulus and excellent thermal stability. However, it still faces great challenges to prepare the TLCP-PAR into nanofibers with a complex three-dimensional network structure and fully exert the high orientation advantage thereof.

[0003] The prior art, such as the electrospinning method, is not only limited by the environmental and safety problems caused by the use of solvents and the low production efficiency, but more importantly, the electric field stretching process is difficult to fully induce the high orientation degree of the liquid crystal polymer, and the performance potential of the material cannot be fully exerted. Although the traditional melt spinning method can obtain highly oriented fibers, it can only prepare single one-dimensional linear fibers and cannot construct a multi-level branched structure with higher specific surface area and application value.

[0004] In addition, the introduction of inorganic functional phases such as liquid metal into the highly ordered TLCP-PAR matrix faces more severe interfacial incompatibility problems than ordinary polymers. The existence of the inorganic phase can easily destroy the ordered arrangement of the liquid crystal phase, resulting in a serious decrease in the mechanical properties of the material. At the same time, the large interfacial tension between the two phases makes the liquid metal easily aggregate in the TLCP-PAR melt, and cannot form the nanoscale dispersion required for subsequent templating. Therefore, how to overcome the interface barrier and skillfully use the unique rheological behavior of TLCP-PAR in the melt processing to construct a new nanostructure is a challenging and urgent technical problem in the field.

[0005] Therefore, it is necessary to design a multi-level branched thermotropic liquid crystal polyarylate nanofiber and a preparation method thereof to solve the above problems. SUMMARY

[0006] In view of the technical problems in the background art, the present application provides a multi-level branched thermotropic liquid crystal polyarylate nanofiber and a preparation method thereof, which aims to solve the technical problem that the structural complexity of high-performance nanofibers, the high orientation of molecular chains and the difficulty in coordinating and unifying the green and efficient production process are difficult to be coordinated and unified. By using a surface-functionalized liquid metal as a deformable sacrificial template, the self-orientation effect of the thermotropic liquid crystal polyarylate in the melt spinning process is utilized to cooperatively induce the deformation of the template, and finally the multi-level branched structure nanofiber is prepared by mechanical cleavage.

[0007] In a first aspect, the embodiments of the present application provide a preparation method of multi-level branched thermotropic liquid crystal polyarylate nanofibers, comprising the following steps:

[0008] S1. After surface activation of the eutectic gallium-indium alloy liquid metal, a grafting agent is added for grafting reaction to obtain a modified liquid metal;

[0009] S2. The modified liquid metal is melt-blended with a thermotropic liquid crystal polyarylate resin to prepare a composite master batch;

[0010] S3. The composite master batch is melt-spun and hot-drawn to obtain a composite fiber;

[0011] S4. The composite fiber is mechanically cracked, separated and purified to obtain multi-level branched thermotropic liquid crystal polyarylate nanofibers.

[0012] As a further improvement of the present application, in step S1, the mass ratio of gallium to indium in the eutectic gallium-indium alloy liquid metal is (70-80):(20-30).

[0013] As a further improvement of the present application, the grafting agent is (3-phenylpropyl)trimethoxysilane; the mass ratio of the eutectic gallium-indium alloy liquid metal to the grafting agent is 1:(0.15-0.25).

[0014] As a further improvement of the present application, the temperature of the grafting reaction is 45-80℃, and the time is 7-9h.

[0015] As a further improvement of the present application, in step S2, the mass ratio of the modified liquid metal to the thermotropic liquid crystal polyarylate resin is (5-15):(85-95).

[0016] As a further improvement of the present application, the temperature of the melt-blending is 290-380℃, and the time is 5-30min.

[0017] As a further improvement of the present application, in step S3, the temperature of the melt-spinning is 300-420℃, and the draw ratio is 8-12; the temperature of the hot-drawing is 80-240℃, and the draw multiple is 1-3 times.

[0018] As a further improvement of the present application, in step S4, the mechanical cracking is performed by shearing the composite fiber into 1-2mm short fibers, dispersing the short fibers in water at a solid content of 1-3%, using a high-pressure homogenizer to perform cyclic treatment at a pressure of 800-1100bar for 14-18 times, and cracking for 20-40min.

[0019] As a further improvement of the present application, in step S1, the surface activation method is: adding the eutectic gallium-indium alloy liquid metal into a hydrochloric acid solution, washing with deionized water and anhydrous ethanol for three to five times after ultrasonic treatment, and transferring to anhydrous toluene under nitrogen protection.

[0020] In a second aspect, the embodiments of the present application provide a multi-level branched thermotropic liquid crystal polyarylate nanofiber prepared by the preparation method of the first aspect.

[0021] The present application has the following beneficial effects:

[0022] The present application provides a multi-level branched thermotropic liquid crystal polyarylate nanofiber and a preparation method thereof. After surface activation of the eutectic gallium-indium alloy liquid metal, a grafting agent is added for grafting reaction to obtain a modified liquid metal. The modified liquid metal is melt blended with a thermotropic liquid crystal polyarylate resin to prepare a composite master batch. The composite master batch is melt spun and hot drawn to obtain a composite fiber. The composite fiber is mechanically cracked, separated and purified to obtain a multi-level branched thermotropic liquid crystal polyarylate nanofiber. The present application establishes a brand-new, solvent-free and continuous production nanofiber preparation platform. By combining interfacial chemistry, liquid crystal polymer physics and advanced melt processing technology, not only the environmental protection, efficiency and structural simplicity problems of traditional methods are fundamentally solved, but also a new way for preparing high-performance nanomaterials with complex structure is opened up.

[0023] The present application realizes two kinds of "order" cooperation: one is to construct an ordered interface layer through chemical means, and the other is to utilize the inherent molecular chain order arrangement of liquid crystal polymers through physical processing. The double-order cooperation makes it possible to accurately control the morphology of liquid metal templates at the nanoscale in the macroscopic processing process, and finally convert into the complex and regular topological structure of polyarylate nanofibers.

[0024] The multi-level branched thermotropic liquid crystal polyarylate nanofiber prepared by the present application has double advantages: (1) structural advantage: the multi-level branched morphology gives it a large specific surface area and a highly connected pore structure, which has excellent performance in the fields of filtration, adsorption and catalysis; (2) performance advantage: due to inheriting the high molecular orientation formed in the processing of the thermotropic liquid crystal matrix, the mechanical properties (strength and modulus) of the single nanofiber are far superior to those of the same kind of nanofibers prepared by other methods, showing excellent performance potential.

[0025] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, the specific embodiments of the present application can be implemented in accordance with the content of the description, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the present application, the drawings used in the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0027] Figure 1 SEM image of the multi-stage branched thermotropic liquid crystal polyarylate nanofiber obtained in Example 1 of the present application. DETAILED DESCRIPTION

[0028] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, but cannot limit the protection scope of the present application.

[0029] 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 the present application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0030] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0031] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to each other. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] At present, it still faces great challenges to prepare TLCP-PAR into nanofibers with complex three-dimensional network structure and fully exert its high orientation advantage. It is difficult to simultaneously realize structural complexity, high molecular chain orientation and green and efficient production in the prior art: electrospinning relies on solvent, has low efficiency and insufficient orientation; melt spinning has high orientation but single structure; liquid metal and liquid crystal polyarylate interface are not compatible, which easily destroys ordered arrangement and leads to agglomeration, and cannot meet the preparation requirements of high-performance nanofibers.

[0033] To solve the technical problem that structure complexity, high molecular chain orientation and green and efficient production process are difficult to be coordinated in high-performance nanofiber preparation, the application provides a multi-stage branched thermotropic liquid crystal polyarylate nanofiber and a preparation method thereof, wherein, by realizing the interface strong coupling of liquid metal and thermotropic liquid crystal polyarylate matrix, and utilizing the self-orientation behavior of liquid crystal phase in the flow field to cooperatively induce the controllable nanoscale deformation of the liquid metal template, the polyarylate nanofiber with multi-stage branched complex structure and high molecular chain orientation is finally prepared.

[0034] In the first aspect, the application provides a preparation method of a multi-stage branched thermotropic liquid crystal polyarylate nanofiber, comprising the following steps:

[0035] S1. After surface activation of the eutectic gallium-indium alloy liquid metal, a grafting agent is added for grafting reaction to obtain a modified liquid metal;

[0036] S2. The modified liquid metal is melt-blended with the thermotropic liquid crystal polyarylate resin to prepare a composite master batch;

[0037] S3. The composite master batch is melt-spun and hot-drawn to obtain a composite fiber;

[0038] S4. The composite fiber is mechanically cracked, separated and purified to obtain the multi-stage branched thermotropic liquid crystal polyarylate nanofiber.

[0039] In the technical scheme of the application, a benzene ring organic long chain layer which is affinity with the TLCP-PAR matrix is constructed on the surface of the liquid metal. Through the π-π stacking effect, the organic layer and the aromatic backbone of the TLCP-PAR produce strong interaction, realizing the strong coupling of the inorganic liquid droplet and the organic liquid crystal phase, not only solving the problem of phase separation, but also enabling the liquid metal droplet to perceive and respond to the flow and orientation of the liquid crystal matrix. Instead of relying on the external applied mechanical force to stretch the liquid metal, the application skillfully utilizes the inherent and spontaneous orientation behavior of the thermotropic liquid crystal polymer in the flow field. The highly ordered liquid crystal domains form a micro and efficient stress transmission and morphology induction field, which can stretch and shape the liquid metal droplet into a fine nanometer network consistent with the orientation of the liquid crystal domains with much higher efficiency than ordinary amorphous polymers. The final mechanical cracking step utilizes the pre-set weak path inside the material. The liquid metal / polyarylate interface is a mechanical weak point relative to the highly crystalline and oriented polyarylate fibrils themselves. The high-strength mechanical energy preferentially acts on the interface, so that the polyarylate fibrils are accurately torn along the complex profile of the liquid metal template, thereby perfectly reproducing the multi-stage branched structure of the template.

[0040] Further, in some embodiments, in step S1, the mass ratio of gallium to indium in the eutectic gallium-indium alloy liquid metal is (70-80):(20-30).

[0041] In the technical scheme of the embodiments of the present application, the eutectic gallium-indium alloy (EGaIn) is a typical eutectic alloy, and the composition ratio directly affects its physical and chemical properties, such as melting point, surface tension, viscosity, oxidation characteristics, and flowability. The ratio of EGaIn in the high-temperature molten state is not easy to volatilize or decompose, and matches well with the processing temperature range of liquid crystal polyarylate, ensuring the stability of the blending process. In the melt spinning process, the liquid metal can be deformed controllably in the shear field, laying a foundation for the subsequent formation of a multi-stage branched structure.

[0042] Further, in some embodiments, the grafting agent is (3-phenylpropyl)trimethoxysilane; and the mass ratio of the eutectic gallium-indium alloy liquid metal to the grafting agent is 1:(0.15-0.25).

[0043] In the technical scheme of the embodiments of the present application, (3-phenylpropyl)trimethoxysilane (C6H5-(CH2)3-Si(OCH3)3) contains a benzene ring structure, which can form a π-π interaction with the aromatic ring structure in the molecular chain of the thermotropic liquid crystal polyarylate (TLCP-PAR), enhancing the interface compatibility. By specific surface modification of the liquid metal, i.e., covalently grafting organic molecules with a specific structure of “anchoring group-flexible chain-benzene ring” on the surface of the liquid metal, the interface repulsion problem between the liquid metal and the highly ordered liquid crystal polyarylate matrix is solved, which is the basis for subsequent physical deformation. An appropriate amount of grafting agent can fully cover the surface of the liquid metal, forming a monolayer modification. Insufficient amount of grafting agent will result in insufficient interface modification, poor dispersibility of the liquid metal in the polymer matrix, and easy agglomeration, affecting the structural uniformity and mechanical properties of the nanofiber; too much grafting agent may cause self-aggregation, forming multiple layers or disordered organic molecular layers, which in turn hinders the effective combination of the liquid metal and the polymer matrix, reducing the interface coupling strength. In addition, unreacted grafting agent remaining in the system may affect the stability of the subsequent melt blending and spinning process.

[0044] Further, in some embodiments, the temperature of the grafting reaction is 45-80℃, and the time is 7-9h.

[0045] In the technical scheme of the embodiment of the present application, the silane molecules form stable Ga-O-Si covalent bonds on the surface of the liquid metal through hydrolysis and condensation, thereby firmly grafting the benzene ring organic long chain. The process has a relatively optimal reaction rate and stability at 45-80°C, which can ensure sufficient formation of the interface chemical bonding and a sufficient time range to ensure that the above reaction is completed, so that the grafting agent forms a uniform and dense modification layer on the surface of the liquid metal. After the reaction is completed, the product is collected by centrifugation, washed repeatedly with toluene to remove physically adsorbed and unreacted molecules, and finally vacuum dried to obtain a modified liquid metal coated with an organic molecular layer on the surface.

[0046] Further, in some embodiments, the mass ratio of the modified liquid metal to the thermotropic liquid crystalline polyarylate resin is (5-15):(85-95).

[0047] In the technical scheme of the embodiment of the present application, the modified liquid metal can form good interfacial compatibility with the thermotropic liquid crystalline polyarylate resin after surface modification. The mass ratio is controlled within the range of (5-15):(85-95), which can ensure uniform dispersion of the liquid metal in the resin matrix and avoid agglomeration due to too high content, thereby improving the mechanical properties and electrical conductivity of the composite material. The thermotropic liquid crystalline polyarylate resin is an aromatic copolyester copolymerized from p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA), wherein the molar ratio of HBA to HNA is within the range of 60:40 to 85:15, and the number average molecular weight (Mn) is within the range of 15,000 g / mol to 35,000 g / mol.

[0048] Further, in some embodiments, the temperature of melt blending is 290-380°C, and the time is 5-30 min.

[0049] In the technical scheme of the embodiment of the present application, the melt blending temperature ensures that the thermotropic liquid crystalline polyarylate resin reaches a fully molten state, thereby promoting uniform dispersion of the modified liquid metal in the matrix. Within this temperature range, the resin has good flowability, which is beneficial to the smooth progress of the blending process. As the blending time is prolonged, the particle size of the dispersed phase gradually decreases, and the particle size distribution tends to be uniform, thereby improving the mechanical properties and electrical conductivity of the composite material. Specifically, a co-rotating twin-screw extruder is used, and the screw rotation speed is 450-550 rpm. The strong shearing action breaks and uniformly disperses the modified liquid metal into the liquid crystalline polyarylate melt, obtaining a composite master batch.

[0050] Further, in some embodiments, in step S3, the temperature of melt spinning is 300-420°C, and the draw ratio is 8-12; the temperature of hot drawing is 80-240°C, and the draw ratio is 1-3 times.

[0051] In the technical scheme of the embodiment of the present application, the thermotropic liquid crystal polyarylate resin has high melting point and high viscosity characteristics, and in the temperature range of 300-420℃, the resin can be fully melted and keep appropriate melt flowability, which is beneficial to form continuous fibers by extruding through a spinneret. If the temperature is lower than 300℃, the melt viscosity is too high, which easily leads to spinning breakage and uneven fiber diameter; if the temperature is higher than 420℃, the resin may be thermally degraded, which affects the mechanical properties and surface quality of the fiber. When the composite melt passes through the spinning orifice and the drawing zone, the strong shearing and stretching flow field makes the rigid rod-like molecular chains of the thermotropic liquid crystal polyarylate spontaneously highly oriented, forming a highly ordered nematic phase domain. This strong orientation field formed by the self-arrangement of the molecular chains exerts a strong, cooperative tensile deformation force on the internal liquid metal droplets through strong interface coupling, forcing them to be elongated, broken and interconnected along the orientation direction of the liquid crystal domain, forming a nanoscale network template embedded in the highly oriented fibrillated polyarylate matrix. Too low stretching ratio leads to insufficient molecular orientation and poor fiber mechanical properties; too high stretching ratio may cause fiber breakage or increase internal defects. The thermal drawing further improves the fibrillation degree of the polyarylate and the deformation and orientation degree of the liquid metal template. Different from conventional passive stretching, the liquid crystal domain formed by the spontaneous orientation of the thermotropic liquid crystal polyarylate molecular chains in the flow field actively and efficiently exerts a cooperative deformation force on the internal liquid metal through the above-mentioned strong interface, shaping it into a fine nanometer network, which is the key physical principle of the method to construct a complex structure.

[0052] The obtained composite fiber structure is characterized by highly oriented thermotropic liquid crystal polyarylate fibrils as the matrix, and the same highly oriented nanoscale filamentous or networked surface modified liquid metal template embedded in the matrix along the axial direction. The intermediate is a key material for realizing the final product, and itself has a novel composite structure.

[0053] Further, in some embodiments, in step S4, the mechanical cleavage is achieved by shearing the composite fiber into 1-2 mm short fibers, dispersing them in water at a solid content of 1-3%, and using a high-pressure homogenizer to process them under a pressure of 800-1100 bar for 14-18 cycles, with a cleavage time of 20-40 min.

[0054] In the technical scheme of the embodiment of the present application, through the synergistic effect of shearing, dispersion, high-pressure homogenization and other processes, the composite fiber can be efficiently cleaved into multi-stage branched nanofibers while maintaining its structural integrity and performance stability. The slurry after cleavage is centrifuged at 7500-8500 rpm for 8-15 min, and the supernatant is the dispersion of multi-stage branched nanofibers. The supernatant is recovered, washed, filtered and freeze-dried to obtain the final product.

[0055] Further, in some embodiments, in step S1, the surface activation is performed by adding the eutectic gallium-indium alloy liquid metal into a hydrochloric acid solution, washing with deionized water and anhydrous ethanol for three to five times after ultrasonic treatment, and transferring to anhydrous toluene under nitrogen protection.

[0056] In the technical scheme of the embodiments of the present application, the surface oxide layer is completely removed by ultrasonic treatment in a hydrochloric acid solution to expose the fresh metal surface. Specifically, the concentration of the hydrochloric acid solution is 1-1.5 mol / L, and the ultrasonic treatment time is 10-20 min.

[0057] In a second aspect, the embodiments of the present application provide a multi-level branched thermotropic liquid crystal polyarylate nanofiber prepared by the preparation method of the first aspect.

[0058] The multi-level branched thermotropic liquid crystal polyarylate nanofiber provided by the present application is a nanofiber product with both "complex morphology" and "high orientation". This product has unique combined features that cannot be simultaneously achieved by the prior art: (a) the chemical composition is thermotropic liquid crystal polyarylate; (b) the micro-morphology is a multi-level branched (or dendritic) structure; (c) the internal structure is a high molecular chain orientation along the fiber axis.

[0059] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application and cannot be understood as a limitation of the present application. If the specific technology or condition is not specified in the examples, it is performed according to the technology or condition described in the literature in the art or according to the product instruction. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0060] Example 1

[0061] The present embodiment provides a preparation method of a multi-level branched thermotropic liquid crystal polyarylate nanofiber, comprising the following steps:

[0062] S1. Take 10 g of eutectic gallium indium alloy liquid metal (the mass ratio of gallium to indium is 75.5:24.5), add 100 mL of 1 mol / L hydrochloric acid solution, ultrasonic treatment for 15 min, the power is set to 200 W, the frequency is 20 kHz, to completely remove the surface oxide layer, expose the fresh metal surface, then wash with deionized water and anhydrous ethanol each three times, and transfer to 200 mL of anhydrous toluene under nitrogen protection; 2 g of (3-phenylpropyl) trimethoxysilane is added to the above system, heated to 75°C and continuously stirred at 500 rpm for 8 hours, in this process, the silane molecules form stable Ga-O-Si covalent bonds on the surface of the liquid metal through hydrolysis and condensation, and the surface is grafted with an organic molecular layer containing a benzene ring; After the reaction is completed, the product is collected by centrifugation (5000 rpm, 5 min), washed repeatedly with toluene to remove physically adsorbed and unreacted molecules, and finally dried under vacuum to obtain modified liquid metal coated with an organic molecular layer on the surface;

[0063] S2. Pre-mix 10 parts by mass of modified liquid metal with 90 parts by mass of dry thermotropic liquid crystal polyarylate resin, use a co-rotating twin-screw extruder, set the barrel partition temperature to 290°C, 320°C, 350°C, 340°C in turn, and the screw rotation speed to 500 rpm; The modified liquid metal is broken and uniformly dispersed into the liquid crystal state polyarylate melt by strong shearing to obtain a composite master batch; wherein the thermotropic liquid crystal polyarylate resin is copolymerized from p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, and the molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid is 70:30;

[0064] S3. The composite master batch is extruded through a double screw spinning machine at 360°C, the screw rotation speed is 500 rpm, the spinneret hole diameter is 0.6 mm, and the die stretching ratio is 10 to obtain the as-spun fiber; The as-spun fiber is subjected to 3 times of hot drawing through multi-stage heating rollers at a temperature of 220°C, and the orientation behavior of the liquid crystal phase is used to induce the deformation of the liquid metal template to form a composite fiber with a nano-scale network structure;

[0065] S4. The drawn composite fiber is cut into 2 mm short fibers, dispersed in water at a solid content of 2%, and treated with a high-pressure homogenizer at a pressure of 1000 bar for 15 cycles, with a total limited cracking time of 30 min; The cracked slurry is centrifuged at 8000 rpm for 10 min, and the supernatant is the dispersion liquid of the multi-stage branched nanofiber, which is recovered, washed, filtered, and freeze-dried at -80°C under a pressure of less than 10 Pa for 48 hours to obtain a multi-stage branched thermotropic liquid crystal polyarylate nanofiber, as shown in Figure 1 , which has a multi-stage branched structure and the molecular chains are highly oriented along the fiber axis.

[0066] Example 2

[0067] The embodiment provides a preparation method of multi-level branched thermotropic liquid crystal polyarylate nanofibers, and only differs from the embodiment 1 in that 1.5g of (3-phenylpropyl)trimethoxysilane is added in the step S1, and other experimental parameters and conditions are basically the same as those of the embodiment 1, which will not be repeated here.

[0068] Embodiment 3

[0069] The embodiment provides a preparation method of multi-level branched thermotropic liquid crystal polyarylate nanofibers, and only differs from the embodiment 1 in that 2.5g of (3-phenylpropyl)trimethoxysilane is added in the step S1, and other experimental parameters and conditions are basically the same as those of the embodiment 1, which will not be repeated here.

[0070] Embodiment 4

[0071] The embodiment provides a preparation method of multi-level branched thermotropic liquid crystal polyarylate nanofibers, and only differs from the embodiment 1 in that 5 parts of modified liquid metal are premixed with 95 parts of dry thermotropic liquid crystal polyarylate resin in the step S2, and other experimental parameters and conditions are basically the same as those of the embodiment 1, which will not be repeated here.

[0072] Embodiment 5

[0073] The embodiment provides a preparation method of multi-level branched thermotropic liquid crystal polyarylate nanofibers, and only differs from the embodiment 1 in that 15 parts of modified liquid metal are premixed with 85 parts of dry thermotropic liquid crystal polyarylate resin in the step S2, and other experimental parameters and conditions are basically the same as those of the embodiment 1, which will not be repeated here.

[0074] Comparative Example 1

[0075] The comparative example 1 provides a preparation method of multi-level branched thermotropic liquid crystal polyarylate nanofibers, and only differs from the embodiment 1 in that no (3-phenylpropyl)trimethoxysilane is added in the step S1, and other experimental parameters and conditions are basically the same as those of the embodiment 1, which will not be repeated here.

[0076] Comparative Example 2

[0077] The comparative example 2 provides a preparation method of multi-level branched thermotropic liquid crystal polyarylate nanofibers, and only differs from the embodiment 1 in that 3g of (3-phenylpropyl)trimethoxysilane is added in the step S1, and other experimental parameters and conditions are basically the same as those of the embodiment 1, which will not be repeated here.

[0078] Comparative Example 3

[0079] Comparative Example 3 provides a preparation method of a multi-level branched thermotropic liquid crystal polyarylate nanofiber, which is different from Example 1 only in that, in step S2, a common non-liquid crystal polyarylate resin is used, and other experimental parameters and conditions are basically the same as those of Example 1, which will not be repeated here.

[0080] The multi-level branched thermotropic liquid crystal polyarylate nanofibers obtained in the examples and comparative examples were tested for performance, and the results are shown in Table 1.

[0081] Table 1 Performance test results of examples and comparative examples

[0082]

[0083] As can be seen from Table 1, Comparative Example 1 is not surface modified, resulting in a very low specific surface area of the fiber, indicating that the fiber structure is not multi-level branched, the mechanical properties are poor, the interface bonding is weak, the structure is disordered, and the molecular orientation degree cannot be measured; Comparative Example 2 adds an excess of a grafting agent, resulting in an excessively thick interface layer or self-polymerization, which weakens the interface bonding and stress transfer efficiency, and the mechanical properties and orientation degree are poor; Comparative Example 3 uses a common non-liquid crystal polyarylate, and the performance is significantly reduced, the specific surface area, mechanical properties, and orientation degree are much lower than those of Example 1, indicating that the self-orientation behavior of the thermotropic liquid crystal polymer is the key to achieving a high orientation structure and synergistic deformation.

[0084] The multi-level branched thermotropic liquid crystal polyarylate nanofiber prepared in the present application has a high specific surface area, is suitable for use in filtration, catalysis, adsorption, and the like; excellent mechanical properties, far exceeding conventional nanofibers; a high orientation degree (≥88%), indicating that the molecular chains are highly ordered and the structure is regular; a high porosity (≥88.5%), which is conducive to mass transfer and interfacial reactions; and a controllable elongation at break, indicating that the material has a certain toughness and is not prone to brittle fracture.

[0085] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, and other ways constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a multi-stage branched thermotropic liquid crystalline polyarylate nanofiber, characterized in that, The preparation method comprises the following steps: S1. After surface activation of eutectic gallium-indium alloy liquid metal, a grafting agent is added for grafting reaction to obtain modified liquid metal; the grafting agent is (3-phenylpropyl) trimethoxysilane; the mass ratio of the eutectic gallium-indium alloy liquid metal to the grafting agent is 1: (0.15-0.25); S2. The modified liquid metal is melt blended with thermotropic liquid crystal polyarylate resin to prepare a composite master batch; S3. The composite master batch is melt spun and hot drawn to obtain a composite fiber; S4. The composite fiber is mechanically cracked, separated and purified to obtain multi-stage branched thermotropic liquid crystal polyarylate nanofiber.

2. The method for preparing multi-level branched thermotropic liquid crystal polyarylate nanofibers according to claim 1, characterized in that, In step S1, the mass ratio of gallium to indium in the eutectic gallium-indium alloy liquid metal is (70-80): (20-30).

3. The method for preparing multi-level branched thermotropic liquid crystal polyarylate nanofibers according to claim 2, characterized in that, The grafting reaction is carried out at a temperature of 45-80℃ for 7-9h.

4. The method for preparing multi-level branched thermotropic liquid crystal polyarylate nanofibers according to claim 1, characterized in that, In step S2, the mass ratio of the modified liquid metal to the thermotropic liquid crystal polyarylate resin is (5-15):(85-95).

5. The method for preparing multi-level branched thermotropic liquid crystal polyarylate nanofibers according to claim 4, characterized in that, The melt blending is carried out at a temperature of 290-380℃ for 5-30min.

6. The method for preparing multi-level branched thermotropic liquid crystal polyarylate nanofibers according to claim 1, characterized in that, In step S3, the melt spinning is carried out at a temperature of 300-420℃ with a draw ratio of 8-12; the hot drawing is carried out at a temperature of 80-240℃ with a draw ratio of 1-3 times.

7. The method for preparing multi-level branched thermotropic liquid crystal polyarylate nanofibers according to claim 1, characterized in that, In step S4, the mechanical cracking is carried out by shearing the composite fiber into 1-2mm short fibers, dispersing the short fibers in water at a solid content of 1-3%, and using a high-pressure homogenizer to treat the mixture under a pressure of 800-1100bar for 14-18 cycles for 20-40min.

8. The method for preparing multi-level branched thermotropic liquid crystal polyarylate nanofibers according to claim 1, characterized in that, In step S1, the surface activation is carried out by adding the eutectic gallium-indium alloy liquid metal into a hydrochloric acid solution, ultrasonic treatment, washing with deionized water and anhydrous ethanol for three to five times, and transferring the mixture to anhydrous toluene under nitrogen protection.

9. A multi-stage branched thermotropic liquid crystalline polyarylate nanofiber, characterized in that, The preparation method is prepared by any one of claims 1-8.

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