Preparation method of nanoscale liquid crystal polyarylester fiber

Abstract

The invention relates to a preparation method of nanoscale liquid crystal polyarylester fiber, which comprises the following steps: mixing and extruding high molecular weight polyarylester and low molecular weight polyarylester in a mass ratio of 1: (10-20), and performing melt spinning through a spinning machine to obtain nascent fiber, and heating the nascent fiber in a protective atmosphere until the melting point of the high molecular weight polyarylester and the melting point of the low molecular weight polyarylester is between the melting point of the high molecular weight polyarylester and the melting point of the low molecular weight polyarylester, and passing through a filter screen to obtain filter residues, wherein the filter residues are the nanoscale liquid crystal polyarylester fiber. The preparation method is simple in process, expensive equipment does not need to be used, and the preparation method has high industrialization value; meanwhile, an alkaline reagent does not need to be used for carrying out long-time alkali dissolution treatment, so that the degradation of the nanofiber can be avoided, the recovery rate is improved, and meanwhile, relatively high environmental protection benefits are achieved.

Description

Technical Field

[0001] This application relates to the technical field of liquid crystal polyester fibers, and specifically relates to a method for preparing nanoscale liquid crystal polyarylate fibers. Background Art

[0002] Liquid crystal polyarylate fiber (LCP) is a special fiber with high strength and high modulus, which is composed of rigid aromatic rings and flexible linking groups. Nanoscale liquid crystal polyarylate fiber refers to a fiber material with a diameter within 1000 nm. Its extremely fine fiber diameter results in a large specific surface area, thus having high adsorption performance. The main method for preparing nanoscale liquid crystal polyarylate fibers is electrospinning, but its production efficiency is low, and it relies on a high-voltage electric field, making it difficult to produce on a large scale. The patent CN103160953A of Wuhan Textile University discloses a short-process preparation method for thermotropic liquid crystal polyarylate nanofibrils. Using an alkali-soluble polyester as the dissolving component, the thermotropic liquid crystal polyarylate is compounded and spun with a water-soluble polyester, so that the thermotropic liquid crystal polyarylate is fully oriented along the melt flow direction in a spinneret with a high aspect ratio to form nanofibrils. After dissolving and removing the alkali-soluble polyester with hot alkali solution, and then through separation and drying, thermotropic liquid crystal polyarylate nanofibrils with excellent comprehensive performance are obtained. This method can prepare thermotropic liquid crystal polyarylate nanofibrils in a short process. However, this method has some problems: 1. A large amount of alkaline solution is required to dissolve the as-spun fibers, causing environmental pollution, and the alkali-soluble polyester is difficult to recycle; 2. During the alkali dissolution treatment, the degradation of thermotropic liquid crystal polyarylate nanofibrils will occur, resulting in a low recovery rate, and at the same time, it will affect its structural strength.

[0003] Therefore, it is necessary to provide a method for preparing nanoscale liquid crystal polyarylate fibers. Summary of the Invention

[0004] In order to solve the problems of complex preparation process and serious pollution of nanoscale liquid crystal polyarylate fibers, it is necessary to provide a method for preparing nanoscale liquid crystal polyarylate fiber LCP.

[0005] The first aspect of this application provides a method for preparing nanoscale liquid crystal polyarylate fibers, which includes the following steps: mixing and extruding a high molecular weight polyarylate and a low molecular weight polyarylate with a mass ratio of 1:(5 - 20), and then performing melt spinning through a spinning machine to obtain as-spun fibers. Heating the as-spun fibers in a protective atmosphere to a temperature between the melting points of the high molecular weight polyarylate and the low molecular weight polyarylate and passing them through a filter screen to obtain filter residues, and the filter residues are the nanoscale liquid crystal polyarylate fibers.

[0006] This solution uses a mixture of low molecular weight polyarylate (LMW) and high molecular weight polyarylate (HMW) with a high mass ratio to form a uniform mixture through co-extrusion. Then, through a melt spinning process, the polymer chains of the polyarylate are oriented along the flow direction to obtain highly oriented as-spun fibers. LMW can also act as a plasticizer during this process to promote the molecular chain movement of HMW. The as-spun fibers are heated to a temperature between the melting points of the two polyarylates in a protective atmosphere, causing LMW to melt and form a viscous flow phase while the HMW component maintains a highly oriented solid state structure. At this time, filtration is carried out through a filter screen. LMW can pass through the filter screen while HMW has a certain size and is intercepted by the filter screen to form filter residue, namely nano-scale liquid crystal polyarylate fiber LCP. The above preparation method has a simple process, does not require the use of expensive equipment, and has high industrialization value. At the same time, it does not require the use of alkaline reagents for long-term alkali dissolution treatment, which can avoid the degradation of nanofibers caused thereby, improve the recovery rate, and has high environmental benefits.

[0007] Furthermore, the monomers of the high molecular weight polyarylate and the low molecular weight polyarylate are the same. Using polyarylates with the same monomers can avoid phase separation caused by chemical structure differences and ensure the formation of a homogeneous system during blending.

[0008] Furthermore, a compatibilizer is added during the co-extrusion process. Compatibilizers such as maleic anhydride copolymers can avoid phase separation when there are significant differences in the chemical structure or physical properties of the two polyarylates.

[0009] Furthermore, the mass ratio of the high molecular weight polyarylate to the low molecular weight polyarylate is 15:83. The above preferred ratio can balance good processing performance and production efficiency.

[0010] Furthermore, the aspect ratio of the spinneret holes of the spinning machine is 10 - 20. Spinneret holes with a high aspect ratio can extend the shear action time of the melt in the hole channel to further improve the orientation degree of the polyarylate molecular chains.

[0011] Furthermore, the melting point of the high molecular weight polyarylate is 270 - 275 °C, and the melting point of the low molecular weight polyarylate is 220 - 230 °C. The as-spun fibers are heated to 245 - 255 °C in a protective atmosphere. Within the above range, it can ensure that the low molecular weight polyarylate is fully melted while the high molecular weight polyarylate remains solid.

[0012] Furthermore, the temperature of the co-extrusion is 290 - 310 °C. The above temperature ensures that the high molecular weight polyarylate is fully melted to form a homogeneous structure with the low molecular weight polyarylate, while avoiding oxidation of the polyarylate due to excessive temperature.

[0013] Further, the parameters of the melt spinning are as follows: the feeding zone is 230 - 250 °C, the melting zone is 290 - 310 °C, the compression zone is 290 - 310 °C, and the cabinet temperature is 290 - 310 °C.

[0014] Further, the filter residue is subjected to alkali dissolution treatment. The low molecular weight polyarylate has certain alkali solubility, while the high molecular weight polyarylate has alkali resistance. Moreover, the low molecular weight polyarylate has been largely removed (content less than 5%) in the filtration step. Therefore, only a mild alkali dissolution treatment is needed to further improve the purity of the filter residue, without significantly affecting the performance of the nanoscale liquid crystal polyarylate fiber. Specifically, the alkali dissolution treatment time is 5 - 10 min, and the reagent is selected from solutions of sodium hydroxide and potassium hydroxide. Detailed implementation manners

[0015] To facilitate the understanding of this application, the following will provide a more comprehensive description of this application. This application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure content of this application more thorough and comprehensive.

[0016] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the application, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the description of this application, the meaning of "several" is at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0018] In this application, among the technically characterized descriptions in an open-ended manner, it includes a closed technical solution composed of the listed features, as well as an open technical solution including the listed features.

[0019] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as every value between such minimum and maximum values. Further, when the range refers to integers, it includes every integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0020] In this application, unless otherwise specified, the percentage content for solid-liquid mixtures and solid-solid mixtures refers to mass percentage, and for liquid-liquid mixtures refers to volume percentage.

[0021] In this application, unless otherwise specified, the percentage concentration refers to the final concentration. The final concentration refers to the proportion of the added component in the system after adding the component.

[0022] In this application, unless otherwise specified, the temperature parameter allows both isothermal treatment and treatment within a certain temperature range. The isothermal treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument.

[0023] The "particles" mentioned in this application, or substances with a defined particle size distribution, do not necessarily have a spherical shape and may be irregular. They can be primary particles or secondary particles. The particle size of irregular particles is calculated as the average of their maximum diameter and minimum diameter.

[0024] Example 1: This example provides a method for preparing nano-scale liquid crystal polyarylate fibers.

[0025] Synthesis of high molecular weight polyarylate: p-Hydroxybenzoic acid (PHB) and terephthalic acid (TA) are copolymerized at a molar ratio of 6:4 and prepared by melt polycondensation. The intrinsic viscosity (the intrinsic viscosity can be used as a measure of molecular weight) η = 4.5 dL / g, and the melting point is 272 °C (DSC test).

[0026] Synthesis of low molecular weight polyarylate: The monomers are the same as those of the high molecular weight polyarylate (PHB / TA = 6:4), and it is prepared by controlling the polycondensation time. The intrinsic viscosity η = 1.2 dL / g, and the melting point is 225 °C (DSC test).

[0027] Compatibilizer: 5-Hydroxy-2-benzoxazole carboxylic acid.

[0028] Mixing and extrusion: The raw materials of high molecular weight polyarylate, low molecular weight polyarylate, and compatibilizer are weighed according to a mass ratio of 15:83:2, added to a twin-screw extruder for mixing, and the extrusion temperature is 290 °C to obtain mixed particles.

[0029] Melt spinning: Place the above-mentioned mixed particles in a spinning machine for spinning, with temperature control in zones: the feeding zone is 220°C, the melting zone is 300°C, the compression zone is 300°C, and the box body temperature is 300°C. Then, through a spinneret hole with a length-to-diameter ratio of 20 (length 8 mm, diameter 0.4 mm), the as-spun fiber is obtained; the as-spun fiber is further cut into short fibers of 1 mm.

[0030] Heat treatment and filtration: Feed the as-spun fiber into a tubular furnace, heat it to 255°C (heating rate 10°C / min) under a nitrogen atmosphere, hold for 10 min, and then pass through a 3-μm filter screen to recover the filter residue and the filtrate. The filter residue is the nano-scale liquid crystal polyarylate fiber.

[0031] Immerse the filter residue in a 0.5 M NaOH solution (50°C) for 10 min to further remove the low-molecular-weight polyarylate on the surface of the filter residue, thus obtaining the nano-scale liquid crystal polyarylate fiber.

[0032] Example 2: This example provides a method for preparing nano-scale liquid crystal polyarylate fiber.

[0033] Synthesis of high-molecular-weight polyarylate: p-Hydroxybenzoic acid (PHB) and terephthalic acid (TA) are copolymerized at a molar ratio of 6:4 and prepared by melt polycondensation. The intrinsic viscosity (the intrinsic viscosity can be used as a measure of the molecular weight) η = 4.5 dL / g, and the melting point is 272°C (DSC test).

[0034] Synthesis of low-molecular-weight polyarylate: The monomers are the same as those of the high-molecular-weight polyarylate (PHB / TA = 6:4), and it is prepared by controlling the polycondensation time. The intrinsic viscosity η = 1.2 dL / g, and the melting point is 225°C (DSC test).

[0035] Compatibilizer: 5-Hydroxy-2-benzoxazolecarboxylic acid.

[0036] Mixing and extrusion: Weigh the raw materials of high-molecular-weight polyarylate, low-molecular-weight polyarylate, and compatibilizer according to a mass ratio of 4:80:2, add them to a twin-screw extruder for mixing, and obtain mixed particles at an extrusion temperature of 290°C.

[0037] Melt spinning: Place the above-mentioned mixed particles in a spinning machine for spinning, with temperature control in zones: the feeding zone is 220°C, the melting zone is 300°C, the compression zone is 300°C, and the box body temperature is 300°C. Then, through a spinneret hole with a length-to-diameter ratio of 20 (length 8 mm, diameter 0.4 mm), the as-spun fiber is obtained; the as-spun fiber is further cut into short fibers of 1 mm.

[0038] Heat treatment and filtration: Feed the as-spun fiber into a tubular furnace, heat it to 255°C (heating rate 10°C / min) under a nitrogen atmosphere, hold for 10 min, and then pass through a 3-μm filter screen to recover the filter residue and the filtrate. The filter residue is the nano-scale liquid crystal polyarylate fiber.

[0039] The filter residue was immersed in a 0.5 M NaOH solution (50 °C) for 10 min to further remove the low-molecular-weight polyarylate on the surface of the filter residue, and then the nano-scale liquid crystal polyarylate fiber was obtained.

[0040] Example 3: This example provides a method for preparing nano-scale liquid crystal polyarylate fiber.

[0041] Synthesis of high-molecular-weight polyarylate: p-Hydroxybenzoic acid (PHB) and terephthalic acid (TA) were copolymerized at a molar ratio of 6:4 and prepared by melt polycondensation. The intrinsic viscosity (the intrinsic viscosity can be used as a measure of the molecular weight) η = 4.5 dL / g, and the melting point was 272 °C (DSC test).

[0042] Synthesis of low-molecular-weight polyarylate: The monomers were the same as those of the high-molecular-weight polyarylate (PHB / TA = 6:4), and were prepared by controlling the polycondensation time. The intrinsic viscosity η = 1.2 dL / g, and the melting point was 225 °C (DSC test).

[0043] Compatibilizer: 5-Hydroxy-2-benzoxazolecarboxylic acid.

[0044] Mixing and extrusion: The raw materials of high-molecular-weight polyarylate, low-molecular-weight polyarylate and compatibilizer were weighed according to a mass ratio of 15:83:2, added to a twin-screw extruder for mixing, and the extrusion temperature was 290 °C to obtain mixed particles.

[0045] Melt spinning: The above-mentioned mixed particles were placed in a spinning machine for spinning. The temperature was controlled in zones: the feeding zone was 220 °C, the melting zone was 300 °C, the compression zone was 300 °C, and the temperature of the spinning box was 300 °C. Then, through a spinneret hole with a length-to-diameter ratio of 10 (length 4 mm, diameter 0.4 mm), the as-spun fiber was obtained.

[0046] Heat treatment and filtration: The as-spun fiber was sent into a tube furnace, heated to 255 °C (heating rate 10 °C / min) under a nitrogen atmosphere, held for 10 min, and then passed through a 3-μm filter screen to recover the filter residue and the filtrate. The filter residue was the nano-scale liquid crystal polyarylate fiber.

[0047] The filter residue was immersed in a 0.5 M NaOH solution (50 °C) for 10 min to further remove the low-molecular-weight polyarylate on the surface of the filter residue, and then the nano-scale liquid crystal polyarylate fiber was obtained.

[0048] Example 4: This example provides a method for preparing nano-scale liquid crystal polyarylate fiber.

[0049] Synthesis of high-molecular-weight polyarylate: p-Hydroxybenzoic acid (PHB) and terephthalic acid (TA) were copolymerized at a molar ratio of 6:4 and prepared by melt polycondensation. The intrinsic viscosity (the intrinsic viscosity can be used as a measure of the molecular weight) η = 4.5 dL / g, and the melting point was 272 °C (DSC test).

[0050] Synthesis of low molecular weight polyarylate: The monomers are the same as those of the high molecular weight polyarylate (PHB / TA = 6:4), prepared by controlling the polycondensation time, with an intrinsic viscosity η = 1.2 dL / g and a melting point of 225 °C (DSC test).

[0051] Compatibilizer: 5-hydroxy-2-benzoxazolecarboxylic acid.

[0052] Mixing and extrusion: Weigh the raw materials of high molecular weight polyarylate, low molecular weight polyarylate and compatibilizer according to a mass ratio of 15:83:2, add them to a twin-screw extruder for mixing, and obtain mixed pellets at an extrusion temperature of 290 °C.

[0053] Melt spinning: Place the above-mentioned mixed pellets in a spinning machine for spinning, with zone temperature control: the feeding zone is 230 °C, the melting zone is 310 °C, the compression zone is 310 °C, and the cabinet temperature is 310 °C. Then, through a spinneret with a length-to-diameter ratio of 20 (length 8 mm, diameter 0.4 mm), as-spun fibers are obtained; the as-spun fibers are further cut into short fibers of 1 mm.

[0054] Heat treatment and filtration: Feed the as-spun fibers into a tube furnace, heat up to 255 °C (heating rate 10 °C / min) under a nitrogen atmosphere, hold for 10 min, and then pass through a 3-μm filter screen to recover the filter residue and the filtrate. The filter residue is the nano-scale liquid crystal polyarylate fiber.

[0055] Immerse the filter residue in a 0.5 M NaOH solution (50 °C) for 10 min to further remove the low molecular weight polyarylate on the surface of the filter residue, and thus obtain the nano-scale liquid crystal polyarylate fiber.

[0056] Example 5: This example provides a method for preparing nano-scale liquid crystal polyarylate fibers.

[0057] Synthesis of high molecular weight polyarylate: p-Hydroxybenzoic acid (PHB) and terephthalic acid (TA) are copolymerized at a molar ratio of 6:4, prepared by melt polycondensation, with an intrinsic viscosity (intrinsic viscosity can be used as a measure of molecular weight) η = 4.5 dL / g and a melting point of 272 °C (DSC test).

[0058] Synthesis of low molecular weight polyarylate: The monomers are the same as those of the high molecular weight polyarylate (PHB / TA = 6:4), prepared by controlling the polycondensation time, with an intrinsic viscosity η = 1.2 dL / g and a melting point of 225 °C (DSC test).

[0059] Compatibilizer: Styrene-maleic anhydride copolymer.

[0060] Mixing and extrusion: Weigh the raw materials of high molecular weight polyarylate, low molecular weight polyarylate and compatibilizer according to a mass ratio of 15:83:2, add them to a twin-screw extruder for mixing, and obtain mixed pellets at an extrusion temperature of 290 °C.

[0061] Melt spinning: Place the above-mentioned mixed particles in a spinning machine for spinning, with temperature control in zones: the feeding zone is 220 °C, the melting zone is 300 °C, the compression zone is 300 °C, and the temperature of the spinning box is 300 °C. Then, through a spinneret hole with a length-to-diameter ratio of 20 (length 8 mm, diameter 0.4 mm), the as-spun fibers are obtained; the as-spun fibers are further cut into short fibers of 1 mm.

[0062] Heat treatment and filtration: Feed the as-spun fibers into a tubular furnace, heat up to 255 °C (heating rate 10 °C / min) under a nitrogen atmosphere, hold for 10 min, and then pass through a 3-μm filter screen to recover the filter residue and the filtrate. The filter residue is the nano-scale liquid crystal polyarylate fiber.

[0063] Immerse the filter residue in a 0.5 M NaOH solution (50 °C) for 10 min to further remove the low-molecular-weight polyarylate on the surface of the filter residue, and thus obtain the nano-scale liquid crystal polyarylate fiber.

[0064] Example 6: This example provides a method for preparing nano-scale liquid crystal polyarylate fibers. I

[0065] Synthesis of high-molecular-weight polyarylate: p-Hydroxybenzoic acid (PHB) and terephthalic acid (TA) are copolymerized at a molar ratio of 6:4 and prepared by melt polycondensation. The intrinsic viscosity (the intrinsic viscosity can be used as a measure of the molecular weight) η = 4.5 dL / g, and the melting point is 272 °C (DSC test).

[0066] Synthesis of low-molecular-weight polyarylate: The monomers are the same as those of the high-molecular-weight polyarylate (PHB / TA = 6:4), and are prepared by controlling the polycondensation time. The intrinsic viscosity η = 1.2 dL / g, and the melting point is 225 °C (DSC test).

[0067] Compatibilizer: 5-Hydroxy-2-benzoxazolecarboxylic acid.

[0068] Mixing and extrusion: Weigh the raw materials of high-molecular-weight polyarylate, low-molecular-weight polyarylate, and compatibilizer according to a mass ratio of 15:83:2, add them to a twin-screw extruder for mixing, and obtain mixed particles at an extrusion temperature of 290 °C.

[0069] Melt spinning: Place the above-mentioned mixed particles in a spinning machine for spinning, with temperature control in zones: the feeding zone is 220 °C, the melting zone is 300 °C, the compression zone is 300 °C, and the temperature of the spinning box is 300 °C. Then, through a spinneret hole with a length-to-diameter ratio of 20 (length 8 mm, diameter 0.4 mm), the as-spun fibers are obtained; the as-spun fibers are further cut into short fibers of 1 mm.

[0070] Heat treatment and filtration: Feed the as-spun fibers into a tubular furnace, heat up to 245 °C (heating rate 10 °C / min) under a nitrogen atmosphere, hold for 10 min, and then pass through a 3-μm filter screen to recover the filter residue and the filtrate.

[0071] The filter residue was immersed in a 0.5 M NaOH solution (50 °C) for 10 min to further remove the low-molecular-weight polyarylate on the surface of the filter residue, and then the nanoscale liquid crystal polyarylate fiber was obtained.

[0072] Comparative Example 1: This comparative example provided a method for preparing nanoscale liquid crystal polyarylate fiber.

[0073] Synthesis of high-molecular-weight polyarylate: p-Hydroxybenzoic acid (PHB) and terephthalic acid (TA) were copolymerized at a molar ratio of 6:4 and prepared by melt polycondensation. The intrinsic viscosity (the intrinsic viscosity can be used as a measure of the molecular weight) η = 4.5 dL / g, and the melting point was 272 °C (DSC test).

[0074] Synthesis of low-molecular-weight polyarylate: The monomers were the same as those of the high-molecular-weight polyarylate (PHB / TA = 6:4), and it was prepared by controlling the polycondensation time. The intrinsic viscosity η = 1.2 dL / g, and the melting point was 225 °C (DSC test).

[0075] Compatibilizer: 5-Hydroxy-2-benzoxazole carboxylic acid.

[0076] Mixing and extrusion: The raw materials of high-molecular-weight polyarylate, low-molecular-weight polyarylate, and compatibilizer were weighed according to a mass ratio of 83:15:2, added to a twin-screw extruder for mixing, and the extrusion temperature was 290 °C to obtain mixed particles.

[0077] Melt spinning: The above-mentioned mixed particles were placed in a spinning machine for spinning. The temperature was controlled in different zones: the feeding zone was 220 °C, the melting zone was 300 °C, the compression zone was 300 °C, and the temperature of the spinning box was 300 °C. Then, through a spinneret with a length-to-diameter ratio of 20 (length 8 mm, diameter 0.4 mm), the as-spun fiber was obtained; the as-spun fiber was further cut into short fibers with a length of 1 mm.

[0078] Heat treatment and filtration: The as-spun fiber was fed into a tubular furnace, heated to 255 °C (heating rate 10 °C / min) under a nitrogen atmosphere, held for 10 min, and then passed through a 3-μm filter screen to recover the filter residue and the filtrate. The filter residue was the nanoscale liquid crystal polyarylate fiber.

[0079] The filter residue was immersed in a 0.5 M NaOH solution (50 °C) for 10 min to further remove the low-molecular-weight polyarylate on the surface of the filter residue, and then the nanoscale liquid crystal polyarylate fiber was obtained.

[0080] Comparative Example 2: This comparative example provided a method for preparing nanoscale liquid crystal polyarylate fiber.

[0081] Synthesis of high molecular weight polyarylate: Copolymerization of p-hydroxybenzoic acid (PHB) and terephthalic acid (TA) with a molar ratio of 6:4, prepared by melt polycondensation, intrinsic viscosity (intrinsic viscosity can be used as a measure of molecular weight) η = 2.5 dL / g, melting point 252 °C (DSC test).

[0082] Synthesis of low molecular weight polyarylate: The monomers are the same as those of the high molecular weight polyarylate (PHB / TA = 6:4), prepared by controlling the polycondensation time, intrinsic viscosity η = 1.2 dL / g, melting point 225 °C (DSC test).

[0083] Compatibilizer: 5-hydroxy-2-benzoxazole carboxylic acid.

[0084] Mixing and extrusion: Weigh the raw materials of high molecular weight polyarylate, low molecular weight polyarylate and compatibilizer according to the mass ratio of 15:83:2, add them to a twin-screw extruder for mixing, and the extrusion temperature is 290 °C to obtain mixed pellets.

[0085] Melt spinning: Place the above mixed pellets in a spinning machine for spinning, with zone temperature control: feeding zone 220 °C, melting zone 300 °C, compression zone 300 °C, and spinneret body temperature 300 °C, and then pass through a spinneret hole with a length-to-diameter ratio of 20 (length 8 mm, diameter 0.4 mm) to obtain as-spun fibers; further cut the as-spun fibers into short fibers of 1 mm.

[0086] Heat treatment and filtration: Feed the as-spun fibers into a tube furnace, heat up to 255 °C in a nitrogen atmosphere (heating rate 10 °C / min), hold for 10 min, and then pass through a 3 μm filter screen to recover the filter residue and filtrate. The filter residue is the nano-scale liquid crystal polyarylate fiber.

[0087] Immerse the filter residue in a 0.5 M NaOH solution (50 °C) for 10 min to further remove the low molecular weight polyarylate on the surface of the filter residue, and thus obtain the nano-scale liquid crystal polyarylate fiber.

[0088] Detect the average length and recovery rate of the nano-scale liquid crystal polyarylate fibers in the above examples and comparative examples. Among them, the detection method for the recovery rate is: the ratio of the mass of the product nano-scale liquid crystal polyarylate fiber to the mass of the high molecular weight polyarylate in the raw materials.

[0089] Table 1 Test results of examples and comparative examples.

[0090] Project Average length (nm) Recovery rate (%) Example 1 812±68 95.3 Example 2 632±115 72.4 Example 3 950±182 93.8 Example 4 785±59 94.9 Example 5 845±71 95.1 Example 6 860±75 93.6 Comparative Example 1 1784±568 94.7 Comparative Example 2 1016±121 26.2

[0091] According to the results of the examples and comparative examples, the diameter distributions of Examples 1-6 are better than those of Comparative Examples 1-2. This is because in this solution, a uniform mixture is formed by mixing low molecular weight polyarylate (LMW) and high molecular weight polyarylate (HMW) with a high mass ratio and then extruding them. Then, through the melt spinning process, the polymer chains of polyarylate are oriented along the flow direction to obtain highly oriented nascent fibers. LMW can also play the role of a plasticizer in this process to promote the molecular chain movement of HMW. The nascent fibers are heated to a temperature between the melting points of the two polyarylates in a protective atmosphere, so that LMW melts to form a viscous mobile phase while the HMW component maintains a highly oriented solid state structure. At this time, filtration is carried out through a filter screen. LMW can pass through the filter screen while HMW has a certain size and is intercepted by the filter screen to form filter residue, that is, nano-scale liquid crystal polyarylate fiber LCP. The above preparation method has a simple process, does not require the use of expensive equipment, and has high industrialization value. At the same time, it does not require the use of alkaline reagents for long-term alkali dissolution treatment, which can avoid the degradation of nanofibers caused thereby (the conventional solution requires long-term alkali dissolution treatment of the whole nascent fiber), improve the recovery rate, and has high environmental benefits. Comparative Example 1 used a high proportion of high molecular weight polyarylate, the fluidity of the mixture was poor, the fibers were thick and had poor dispersion, and the fiber length deviation was large. Comparative Example 2 used a high molecular weight polyarylate with a lower molecular weight, and the melting point was close to the heat treatment temperature. Some liquid crystal polyester fibers passed through the filter screen during filtration, resulting in a low recovery rate.

[0092] The above embodiments only represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A preparation method of a nano liquid crystal polyarylate fiber, characterized in that, It includes the following steps: mixing and extruding a high molecular weight polyarylate and a low molecular weight polyarylate with a mass ratio of 1:(5 - 20), and then performing melt spinning through a spinning machine to obtain nascent fibers. Heating the nascent fibers in a protective atmosphere to a temperature between the melting points of the high molecular weight polyarylate and the low molecular weight polyarylate and passing them through a filter screen to obtain filter residues, and the filter residues are the nano-scale liquid crystal polyarylate fibers.

2. The preparation method according to claim 1, characterized in that, The monomers of the high molecular weight polyarylate and the low molecular weight polyarylate are the same.

3. The preparation method according to claim 1, characterized in that, A compatibilizer is added during the mixing and extrusion process.

4. The preparation method according to claim 1, characterized in that, The mass ratio of the high molecular weight polyarylate to the low molecular weight polyarylate is 15:

83.

5. The preparation method according to claim 1, characterized in that, The aspect ratio of the spinneret holes of the spinning machine is 10 - 20.

6. The preparation method according to claim 1, characterized in that, Cutting the nascent fibers into short fibers with a diameter of 1 - 3 mm.

7. The preparation method according to claim 1, characterized in that, The melting point of the high molecular weight polyarylate is 270 - 275 °C, the melting point of the low molecular weight polyarylate is 220 - 230 °C, and heating the nascent fibers in a protective atmosphere to 245 - 255 °C.

8. The preparation method according to claim 1, wherein The temperature of the mixing and extrusion is 290 - 310 °C.

9. The preparation method according to claim 1, characterized in that, The parameters of the melt spinning are: feed zone 230 - 250 °C, melting zone 290 - 310 °C, compression zone 290 - 310 °C, and housing temperature 290 - 310 °C.

10. The preparation method according to claim 1, wherein Performing alkali dissolution treatment on the filter residues.