Heterocyclic aramid fibrid as well as preparation method and application thereof

Abstract

The invention relates to the technical field of heterocyclic aramid fibrids, in particular to a heterocyclic aramid fibrid and a preparation method and application thereof.The preparation method comprises the steps that p-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole are dissolved in a polar solvent to obtain a diamine mixed solution; adding a part of paraphthaloyl chloride into the diamine mixed solution to carry out pre-polycondensation reaction to obtain an initial polymerization solution, then adding the rest of paraphthaloyl chloride to carry out chain extension polycondensation reaction, and after the reaction is finished, adjusting the pH value to alkalescence to obtain a homogeneous polymer solution containing a heterocyclic aramid polymer; the heterocyclic aramid polymer is subjected to precipitation forming in a polar solvent aqueous solution containing glycerin, and the heterocyclic aramid fibrid is obtained. The heterocyclic aramid fibrid has heat-resistant stability and excellent mechanical property, and aramid paper prepared from the heterocyclic aramid fibrid has excellent tensile property and heat stability.

Description

Technical Field

[0001] The invention relates to a heterocyclic aramid fibrid and a preparation method and application thereof, belonging to the technical field of heterocyclic aramid fibrid. Background Art

[0002] Aramid precipitated fiber, as a differentiated product of aramid fiber, is a special fiber with excellent comprehensive performance. This product has excellent properties such as high specific surface area, high temperature resistance, chemical stability and insulation. It is widely used in high-performance sealing materials, friction materials, battery separators, composite material reinforcement, special paper and high-temperature filter materials.

[0003] At present, aramid fibrils are mainly meta-aramid fibrils (MAF). MAF inherently has good high-temperature resistance and mechanical properties. However, in the process of processing MAF into aramid paper, in order to form a dense structure and improve the mechanical strength of the paper, it is necessary to perform hot pressing treatment under high temperature conditions. Under such treatment conditions, MAF is prone to thermal oxidative aging, yellowing, and decreased mechanical properties.

[0004] In the prior art, inorganic additives are added to polymer solutions to improve the heat resistance of fibrids. For example, patent application publication number CN113789583A discloses an anti-yellowing meta-aramid fibrid, a preparation method, and an application thereof. In this technology, the heat resistance of fibrids is improved by adding an inorganic additive, bismuth hydroxide, to a polymer solution. However, the inorganic additive has poor compatibility with the polymer and is prone to sedimentation during the production process, resulting in poor uniformity of the produced fibrids, unstable performance indicators, and affected fiber mechanical properties. In addition, the agglomerated additive particles during the production process are prone to clogging equipment and are easily precipitated during the subsequent washing process due to bonding strength issues. This results in low utilization of the inorganic additive and unstable product performance. By introducing heterocyclic molecules into the molecular chain system, the heat resistance, mechanical performance and other performance indicators of aramid fibrils can be effectively improved. However, when using conventional aramid fibrils preparation process to prepare heterocyclic aramid fibrils, many other problems are likely to arise. For example, the prepared fibrils have a broken morphology and the beating degree cannot meet the application of downstream products. This is because the introduction of heterocyclic molecules increases the rigidity of the molecular chain, and the fibrils are easily brittle during the precipitation process, resulting in problems such as fibrils breaking. Summary of the Invention

[0005] The present invention addresses the deficiencies in the prior art and provides a heterocyclic aramid fibrid, a preparation method, and an application thereof. The invention improves the heat resistance and mechanical properties of the fibrid by subjecting the molecular chain to heterocyclic modification without changing the basic properties of the fibrid itself. Aramid paper prepared using the heterocyclic aramid fibrid has excellent tensile properties and thermal stability.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: a heterocyclic aramid fiber, wherein the polymer molecular chain of the heterocyclic aramid fiber contains monomer segments of diamine and terephthaloyl chloride, and the diamine includes 2-(4-aminophenyl)-5-aminobenzimidazole and p-diphenylamine; when preparing the heterocyclic aramid fiber, a polar solvent aqueous solution containing glycerol is used for precipitation and molding.

[0007] Furthermore, the polymer structural formula of the heterocyclic aramid fibrid is:

[0008]

[0009] The number average molecular weight of the heterocyclic aramid fibrid is 160,000-230,000.

[0010] Furthermore, the molar ratio of the 2-(4-aminophenyl)-5-aminobenzimidazole to p-diphenylamine is 1:(1-3);

[0011] The molar ratio of the total mole of the diamine to the terephthaloyl chloride is 1:(0.90-1.00).

[0012] The present invention also discloses a method for preparing heterocyclic aramid fibrids, which comprises:

[0013] S1, dissolving p-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole in a polar solvent to obtain a diamine mixed solution;

[0014] S2, adding a portion of terephthaloyl chloride to the diamine mixed solution for a pre-polycondensation reaction to obtain an initial polymer solution, and then adding the remaining portion of terephthaloyl chloride for a chain extension polycondensation reaction. After the reaction is completed, adjusting the pH to a weakly alkaline state to obtain a homogeneous polymer solution containing a heterocyclic aramid polymer;

[0015] S3. The heterocyclic aramid polymer is precipitated in a polar solvent aqueous solution containing glycerol to obtain the heterocyclic aramid fibrid.

[0016] Furthermore, in step S2, the temperature of the pre-polycondensation reaction is -10 to 5°C; the temperature of the chain extension polycondensation reaction is -10 to 5°C;

[0017] During the pre-polycondensation reaction, the amount of terephthaloyl chloride added is 90%-97.5% of the total amount of terephthaloyl chloride used in step S2; during the chain extension polycondensation reaction, the amount of terephthaloyl chloride added is 2.5%-10% of the total amount of terephthaloyl chloride used in step S2.

[0018] Furthermore, in step S2, during the pre-polycondensation reaction, the addition rate of terephthaloyl chloride is 30-45 kg / h; during the chain extension polycondensation reaction, the addition rate of terephthaloyl chloride is 5-15 kg / h.

[0019] Furthermore, the mass concentration of the heterocyclic aramid polymer in the homogeneous polymer solution is 5-7 wt %, the viscosity of the homogeneous polymer solution at 25° C. is 50-200 Po, and the pH of the homogeneous polymer solution is 8-10.

[0020] Furthermore, in step S3, the homogeneous polymer solution is diluted with a polar solvent to obtain a polymer dilution solution, the polymer dilution solution and a polar solvent aqueous solution containing glycerol are subjected to high-speed shearing, and then subjected to countercurrent water washing to obtain the heterocyclic aramid fibrid;

[0021] The mass concentration of the heterocyclic aramid polymer in the polymer diluent is 3-4wt%, and the viscosity of the polymer diluent at 25°C is 40-80CP.

[0022] Furthermore, the mass ratio of the polymer diluent to the glycerol-containing polar solvent aqueous solution is 1:(6-8);

[0023] In the polar solvent aqueous solution containing glycerol, the mass content of the polar solvent is 20-40%, and the mass ratio of the polar solvent to the glycerol is 1:(1-1.4);

[0024] The high-speed shearing speed is 4000-8500 rpm, and the diameter of the stock solution gun is 0.05-0.07 mm.

[0025] The invention also discloses an application of heterocyclic aramid fibrids, and the heterocyclic aramid fibrids are applied to aramid paper.

[0026] The beneficial effects of the present invention are:

[0027] The heterocyclic aramid fibrids of the present invention are prepared by modifying the original aramid fibers through a third monomer modification technique so that the molecular chains contain heterocyclic groups, thereby achieving modification of the molecular structure without changing the properties of the aramid fibrids themselves. As a result, the fibrids produced using the modified aramid polymers have higher mechanical properties during the production process. When the heterocyclic aramid fibrids are applied to the downstream product aramid paper, the comprehensive properties of the aramid paper can be comprehensively improved.

[0028] In addition, the presence of heterocyclic diamines in polymer molecular chains can effectively enhance hydrogen bonding between molecular chains, improving their stability under high temperature conditions. Unlike physical doping, this method forms covalent bonds between molecules, effectively preventing the heat-resistant groups from becoming ineffective due to release during processing and subsequent use. At the same time, based on the strong rigidity of the polymer chain, the introduction of glycerol in a certain proportion into the original DMAC aqueous solution can effectively reduce the problem of heterocyclic aramid fibrils being broken and unformed during fiber precipitation due to excessive molecular chain rigidity and decreased inter-chain plasticity, ultimately resulting in a heterocyclic aramid fibril product with both high mechanical properties and heat resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is an electron microscope image of the heterocyclic aramid fiber prepared in Example 1. DETAILED DESCRIPTION

[0030] The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0032] A heterocyclic aramid fibrid, wherein the polymer molecular chain of the heterocyclic aramid fibrid contains monomer segments of diamine and terephthaloyl chloride, wherein the diamine includes 2-(4-aminophenyl)-5-aminobenzimidazole and p-diphenylamine; and the heterocyclic aramid fibrid is prepared by precipitation and molding using a polar solvent aqueous solution containing glycerol.

[0033] Specifically, the polymer structural formula of the heterocyclic aramid fibrid is:

[0034]

[0035] The number average molecular weight of the heterocyclic aramid fibrid is 160,000-230,000. In the above structural formula, n and m are natural numbers greater than 0, representing a repeating unit structure in the polymer.

[0036] Specifically, the molar ratio of 2-(4-aminophenyl)-5-aminobenzimidazole to p-diphenylamine is 1:(1-3);

[0037] The molar ratio of the total mole of the diamine to the terephthaloyl chloride is 1:(0.90-1.00).

[0038] The present invention also discloses a method for preparing heterocyclic aramid fibrids, which comprises:

[0039] S1, dissolving p-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole in a polar solvent to obtain a diamine mixed solution;

[0040] S2, adding a portion of terephthaloyl chloride to the diamine mixed solution for a pre-polycondensation reaction to obtain an initial polymer solution, and then adding the remaining portion of terephthaloyl chloride for a chain extension polycondensation reaction. After the reaction is completed, adjusting the pH to a weakly alkaline state to obtain a homogeneous polymer solution containing a heterocyclic aramid polymer;

[0041] S3. The heterocyclic aramid polymer is precipitated in a polar solvent aqueous solution containing glycerol to obtain the heterocyclic aramid fibrid.

[0042] More specifically, the operations of step S1 and step S2 are both performed under the protection of an inert gas.

[0043] More specifically, the polar solvent is dimethylformamide, dimethylacetamide or N-methylpyrrolidone.

[0044] Preferably, the polar solvent is dimethylacetamide or N-methylpyrrolidone. Compared with dimethylformamide, dimethylacetamide has higher thermal stability and hydrolytic stability, and is less corrosive and toxic. Therefore, the use of dimethylacetamide is better than dimethylformamide.

[0045] Specifically, in step S2, the temperature of the pre-polycondensation reaction is -10 to 5°C; the temperature of the chain extension polycondensation reaction is -10 to 5°C;

[0046] During the pre-polycondensation reaction, the amount of terephthaloyl chloride added is 90%-97.5% of the total amount of terephthaloyl chloride used in step S2; during the chain extension polycondensation reaction, the amount of terephthaloyl chloride added is 2.5%-10% of the total amount of terephthaloyl chloride used in step S2.

[0047] Specifically, in step S2, during the pre-polycondensation reaction, the addition rate of terephthaloyl chloride is 30-45 kg / h; during the chain extension polycondensation reaction, the addition rate of terephthaloyl chloride is 5-15 kg / h.

[0048] Specifically, the mass concentration of the heterocyclic aramid polymer in the homogeneous polymer solution is 5-7 wt %, the viscosity of the homogeneous polymer solution at 25° C. is 50-200 Po, and the pH of the homogeneous polymer solution is 8-10.

[0049] Specifically, in step S2, a pH regulator is used to adjust the pH, and the pH regulator is any one of an alkaline earth metal hydroxide or an organic amine.

[0050] More specifically, the alkaline earth metal hydroxide is lithium hydroxide or calcium hydroxide.

[0051] Specifically, in step S3, the homogeneous polymer solution is diluted with a polar solvent to obtain a polymer dilution solution, the polymer dilution solution and a polar solvent aqueous solution containing glycerol are subjected to high-speed shearing, and then subjected to countercurrent water washing to obtain the heterocyclic aramid fibrid;

[0052] The mass concentration of the heterocyclic aramid polymer in the polymer diluent is 3-4wt%, and the viscosity of the polymer diluent at 25°C is 40-80CP.

[0053] Specifically, the mass ratio of the polymer diluent to the glycerol-containing polar solvent aqueous solution is 1:(6-8);

[0054] In the polar solvent aqueous solution containing glycerol, the mass content of the polar solvent is 20-40%, and the mass ratio of the polar solvent to the glycerol is 1:(1-1.4);

[0055] The high-speed shearing speed is 4000-8500 rpm, and the diameter of the stock solution gun is 0.05-0.07 mm.

[0056] More specifically, the polar solvent aqueous solution containing glycerol used in the embodiment of the present invention is a DMAC glycerol aqueous solution.

[0057] The invention also discloses an application of heterocyclic aramid fibrids, and the heterocyclic aramid fibrids are applied to aramid paper.

[0058] The following are specific examples of preparing heterocyclic aramid fibrids, wherein the amounts of the various raw materials used in the examples are all molar fractions.

[0059] Example 1

[0060] S1. In an inert gas environment, at a temperature of 25° C., add 1 part of p-phenylenediamine and 1 part of 2-(4-aminophenyl)-5-aminobenzimidazole to 60 parts of dimethylacetamide and dissolve them;

[0061] S2. After the dissolution is complete, the system temperature is controlled at -5°C under nitrogen protection, and 1.8 parts of terephthaloyl chloride are added to carry out polymerization reaction to obtain an initial polymerization solution, wherein the addition rate of terephthaloyl chloride is 35 kg / h;

[0062] 0.2 parts of terephthaloyl chloride was added to the initial polymerization solution (the addition rate of terephthaloyl chloride was 5 kg / h), and the temperature in the system was controlled at -5°C. After the reaction was completed, lithium hydroxide was used for neutralization and the pH was adjusted to 8.5 to obtain a homogeneous polymer solution with a viscosity of 150 Po (25°C). The solution was diluted with DMAC solvent to obtain a polymer dilution solution with a viscosity of 80 CP.

[0063] S3. The polymer dilution liquid and the DMAC glycerol aqueous solution (the mass concentration of DMAC in the DMAC glycerol aqueous solution is 20%, wherein the weight ratio of the organic solvent DMAC and glycerol is 1:1) are transported to a precipitator at a mass ratio of 1:6 for high-speed shearing at a shear speed of 4000 rpm and a stock liquid gun diameter of 0.05 mm, and then countercurrent water washing is performed to obtain the heterocyclic aramid fibrid.

[0064] Example 2

[0065] S1. In an inert gas environment, 1.5 parts of p-phenylenediamine and 0.7 parts of 2-(4-aminophenyl)-5-aminobenzimidazole were added to 60 parts of dimethylacetamide and dissolved at 25°C.

[0066] S2. After the dissolution is complete, the system temperature is controlled at -10°C under nitrogen protection, and 1.9 parts of terephthaloyl chloride are added to carry out polymerization reaction to obtain an initial polymerization solution, wherein the addition rate of terephthaloyl chloride is 30 kg / h;

[0067] 0.1 parts of terephthaloyl chloride was added to the initial polymerization solution (the addition rate of terephthaloyl chloride was 10 kg / h), and the temperature in the system was controlled at -10°C. After the reaction was completed, calcium hydroxide was used for neutralization and the pH was adjusted to 8.5 to obtain a homogeneous polymer solution with a viscosity of 100 Po (25°C). The solution was diluted with DMAC solvent to obtain a polymer dilution solution with a viscosity of 80 CP.

[0068] S3. The polymer dilution solution and the DMAC glycerol aqueous solution (the mass concentration of DMAC in the DMAC glycerol aqueous solution is 30%, wherein the weight ratio of the organic solvent DMAC and glycerol is 1:1.2) are transported to a precipitator at a mass ratio of 1:7 for high-speed shearing at a shear speed of 5000 rpm and a stock liquid gun diameter of 0.06 mm, and then countercurrent water washing is performed to obtain the heterocyclic aramid fibrid.

[0069] Example 3

[0070] S1. In an inert gas environment, 1.5 parts of p-phenylenediamine and 0.5 parts of 2-(4-aminophenyl)-5-aminobenzimidazole were added to 60 parts of dimethylacetamide and dissolved at 25°C.

[0071] S2. After the dissolution is complete, the system temperature is controlled at 0°C under nitrogen protection, and 1.95 parts of terephthaloyl chloride are added to carry out polymerization reaction to obtain an initial polymerization solution, wherein the addition rate of terephthaloyl chloride is 40 kg / h;

[0072] 0.05 parts of terephthaloyl chloride was added to the initial polymerization solution (the addition rate of terephthaloyl chloride was 15 kg / h), and the temperature in the system was controlled to 0°C. After the reaction was completed, it was neutralized with ethylenediamine and the pH was adjusted to 8.5 to finally obtain a homogeneous polymer solution with a viscosity of 50 Po (25°C). The solution was diluted with DMAC solvent to obtain a polymer dilution solution with a viscosity of 80 CP.

[0073] S3. The polymer dilution solution and the DMAC glycerol aqueous solution (the mass concentration of DMAC in the DMAC glycerol aqueous solution is 40%, wherein the weight ratio of the organic solvent DMAC and glycerol is 1:1.4) are transported to a precipitator at a mass ratio of 1:8 for high-speed shearing at a shear speed of 6500 rpm and a stock gun diameter of 0.07 mm, and then countercurrent water washing is performed to obtain the heterocyclic aramid fibrid.

[0074] Comparative Example 1

[0075] Aramid fibrids were prepared using the same method as in Example 1, except that no heterocyclic aramid monomer was added, and the diamine and diacyl chloride monomers used were m-phenylenediamine and isophthaloyl chloride, respectively. The specific preparation process was as follows:

[0076] S1. Add 2 parts of m-phenylenediamine to 60 parts of dimethylacetamide and dissolve them;

[0077] S2. After the dissolution is complete, the system temperature is controlled at -5°C under nitrogen protection, and 1.8 parts of isophthaloyl chloride are added to carry out polymerization reaction to obtain an initial polymerization solution, wherein the addition rate of isophthaloyl chloride is 35 kg / h;

[0078] 0.2 parts of isophthaloyl chloride was added to the initial polymerization solution (the addition rate of isophthaloyl chloride was 5 kg / h), and the temperature in the system was controlled at -5°C. After the reaction was completed, it was neutralized with lithium hydroxide and the pH was adjusted to 8.5 to finally obtain a homogeneous polymer solution with a viscosity of 150 Po (25°C). The solution was diluted with DMAC solvent to obtain a polymer dilution solution with a viscosity of 80 CP.

[0079] S3. The polymer dilution liquid and the DMAC aqueous solution (the mass concentration of DMAC in the DMAC aqueous solution is 20%) are transported to a precipitator in a mass ratio of 1:6 for high-speed shearing at a shear speed of 4000 rpm and a stock liquid gun diameter of 0.05 mm, and then countercurrent water washing is performed to obtain meta-aramid fiber precipitates.

[0080] Comparative Example 2

[0081] Aramid fibrids were prepared using the same method as in Example 1, except that no heterocyclic aramid monomer was added. The specific preparation process was as follows:

[0082] S1. In an inert gas environment, add 2 parts of p-phenylenediamine to 60 parts of dimethylacetamide at a temperature of 25°C and dissolve them;

[0083] S2. After the dissolution is complete, the system temperature is controlled at -5°C under nitrogen protection, and 1.8 parts of terephthaloyl chloride are added to carry out polymerization reaction to obtain an initial polymerization solution, wherein the addition rate of terephthaloyl chloride is 35 kg / h;

[0084] 0.2 parts of terephthaloyl chloride was added to the initial polymerization solution (the addition rate of terephthaloyl chloride was 5 kg / h), and the temperature in the system was controlled at -5°C. After the reaction was completed, lithium hydroxide was used for neutralization and the pH was adjusted to 8.5 to obtain a homogeneous polymer solution with a viscosity of 150 Po (25°C). The solution was diluted with DMAC solvent to obtain a polymer dilution solution with a viscosity of 80 CP.

[0085] S3. The polymer dilution solution and the DMAC glycerol aqueous solution (the mass concentration of DMAC in the DMAC glycerol aqueous solution is 20%, wherein the weight ratio of the organic solvent DMAC and glycerol is 1:1) are transported to a precipitator at a mass ratio of 1:6 for high-speed shearing at a shear speed of 4000 rpm and a stock liquid gun diameter of 0.05 mm, and then countercurrent water washing is performed to obtain para-aramid fibrid.

[0086] Comparative Example 3

[0087] Aramid fibrids were prepared using the same method as in Example 1, except that in step S3, DMAC aqueous solution was used for fiber precipitation without adding glycerol. The specific preparation process is as follows:

[0088] S1. In an inert gas environment, at a temperature of 25° C., add 1 part of p-phenylenediamine and 1 part of 2-(4-aminophenyl)-5-aminobenzimidazole to 60 parts of dimethylacetamide and dissolve them;

[0089] S2. After the dissolution is complete, the system temperature is controlled at -5°C under nitrogen protection, and 1.8 parts of terephthaloyl chloride are added to carry out polymerization reaction to obtain an initial polymerization solution, wherein the addition rate of terephthaloyl chloride is 35 kg / h;

[0090] 0.2 parts of terephthaloyl chloride was added to the initial polymerization solution (the addition rate of terephthaloyl chloride was 5 kg / h), and the temperature in the system was controlled at -5°C. After the reaction was completed, lithium hydroxide was used for neutralization and the pH was adjusted to 8.5 to obtain a homogeneous polymer solution with a viscosity of 150 Po (25°C). The solution was diluted with DMAC solvent to obtain a polymer dilution solution with a viscosity of 80 CP.

[0091] S3. The polymer dilution solution and the DMAC aqueous solution (the mass concentration of DMAC in the DMAC aqueous solution is 20%) are transported to a precipitator in a mass ratio of 1:6 for high-speed shearing at a shear speed of 4000 rpm and a stock solution gun diameter of 0.05 mm, and then countercurrent water washing is performed to obtain the heterocyclic aramid fibrid.

[0092] Comparative Example 4

[0093] Aramid fibrids were prepared using the same method as in Example 1, except that the amount of glycerol used in this comparative example 4 was increased. In the DMAC glycerol aqueous solution, the weight ratio of the organic solvent DMAC to glycerol was 1:2. The specific preparation process was as follows:

[0094] S1. In an inert gas environment, at a temperature of 25° C., add 1 part of p-phenylenediamine and 1 part of 2-(4-aminophenyl)-5-aminobenzimidazole to 60 parts of dimethylacetamide and dissolve them;

[0095] S2. After the dissolution is complete, the system temperature is controlled at -5°C under nitrogen protection, and 1.8 parts of terephthaloyl chloride are added to carry out polymerization reaction to obtain an initial polymerization solution, wherein the addition rate of terephthaloyl chloride is 35 kg / h;

[0096] 0.2 parts of terephthaloyl chloride was added to the initial polymerization solution (the addition rate of terephthaloyl chloride was 5 kg / h), and the temperature in the system was controlled at -5°C. After the reaction was completed, lithium hydroxide was used for neutralization and the pH was adjusted to 8.5 to obtain a homogeneous polymer solution with a viscosity of 150 Po (25°C). The solution was diluted with DMAC solvent to obtain a polymer dilution solution with a viscosity of 80 CP.

[0097] S3. The polymer dilution solution and the DMAC glycerol aqueous solution (the mass concentration of DMAC in the DMAC glycerol aqueous solution is 20%, wherein the weight ratio of the organic solvent DMAC and glycerol is 1:2) are transported to a precipitator at a mass ratio of 1:6 for high-speed shearing at a shear speed of 4000 rpm and a stock liquid gun diameter of 0.05 mm, and then countercurrent water washing is performed to obtain the heterocyclic aramid fibrid.

[0098] The aramid fibrids prepared in the above examples and comparative examples were subjected to performance tests, and corresponding aramid papers were made and subjected to performance tests. The specific data are shown in Table 1. The test methods involved are as follows:

[0099] (1) Aramid paper heat loss test method: The product is treated at 285°C and 2MPa, and then the tensile strength test is performed according to the GB / T455-2002 test method.

[0100] (2) Limiting oxygen index test method: Test according to GB / T2406 test method.

[0101] (3) Test method for tensile strength of aramid paper: Test according to GB / T455-2002 test method.

[0102] (4) Test method for beating degree of fibrillation: The test was conducted according to the test method of GB / T 3332-2004.

[0103] In order to test the performance of aramid paper, the aramid fibrids prepared in the above examples and comparative examples were made into corresponding aramid paper in the same manner. The preparation method and process conditions are as follows:

[0104] Meta-aramid chopped fibers (fiber breaking strength 3.5 cN / dtex, fiber breaking elongation 40%, fiber breaking modulus 60 cN / dtex) and aramid fibrids are mixed in deionized water at a mass ratio of 3:4. After mechanical stirring or ultrasonic treatment, the dispersed fiber mixture is fed into a papermaking machine. A cylinder-shaped forming process is used to evenly interweave the fibers on the screen to form a wet paper web. After dehydration by pressing, the paper is dried with hot air to form a nascent aramid base paper. The base paper is then hot-pressed under high pressure of 5 MPa, twice at 200°C and 300°C, to produce an aramid paper product (48 μm thick).

[0105] Table 1 Performance test data

[0106]

[0107] From the experimental data of Examples 1 to 3, it can be seen that the use of the technical solution of the present invention can obtain heterocyclic aramid fibrid products with high tear strength and high heat resistance. Comparative Example 1 is a meta-aramid fibrid prepared by a conventional preparation method, which has a tear strength of 286cN and a secondary hot pressing tensile loss of 146cN, while the aramid fibrid prepared by the method of the present invention in Example 1 has a secondary hot pressing tensile loss of only 34cN. Comparison of the data of Example 1 and Comparative Example 1 shows that the use of the technical solution of the present invention improves the tensile strength of the meta-aramid fibrid by 17% compared with the conventional one, and the secondary hot pressing tensile loss performance is improved by nearly 5 times. In addition, Figure 1 This is an electron microscope image of the heterocyclic aramid fiber prepared in Example 1. Figure 1 It can be seen that the fibrils prepared in Example 1 have a stable morphology, are small and film-like in shape. When the fibrils with this morphology are applied to downstream aramid paper products, it is beneficial to improve the stability of the fibrils in the aramid paper products.

[0108] Comparison of the data of Comparative Example 2 and Example 1 shows that the secondary hot pressing tensile loss of Comparative Example 2 is 134 cN, which is significantly lower than the heat loss resistance of Example 1. This is because the polymerization system is not modified by the addition of heterocyclic diamine molecules, which reduces the direct hydrogen bonding force of the molecular chain, resulting in a decrease in the tensile strength and thermal stability of the product. The use of heterocyclic diamine to modify the molecular chain in the technical solution of the present invention greatly improves the direct interaction between the polymer chains, enhances the tensile strength and thermal stability of the downstream products, and the presence of heterocyclic diamine molecules in the system in the form of covalent bonds stabilizes the molecular structure and does not cause functional degradation due to the preparation process.

[0109] From the comparison of the experimental results of Comparative Examples 3, 4 and Example 1, it can be seen that if the components and ratios of the molding reagents are changed during the precipitation molding process, the beating degree of the fibrils will be too high or too low, the morphology of the fibrils will change, and the production stability of the downstream papermaking process will be reduced, thereby affecting the tensile strength and heat stability of the downstream products. This is because in Comparative Example 3, when no glycerol component is added, the shaping between the heterocyclic polymer chains is poor, which is not conducive to the formation of long ribbon-shaped fibrils. At the same time, it can be seen from Comparative Example 4 that when the glycerol ratio is too high, the phase separation process is too slow, and the high beating degree affects the application of downstream products. Therefore, the precipitation molding process conditions defined by the present invention are more conducive to obtaining heterocyclic aramid fibrils with excellent performance. It provides raw materials with better performance for downstream product applications, and improves the tensile strength and secondary hot pressing tensile loss capacity of downstream products.

[0110] The technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0111] For those skilled in the art, several variations and improvements may be made without departing from the scope of the present invention, which all fall within the scope of protection of the present invention. The scope of protection of the present invention shall be based on the appended claims.

Claims

1. A heterocyclic aramid fiber, characterized in that: The polymer molecular chain of the heterocyclic aramid fibrid contains monomer segments of diamine and terephthaloyl chloride, wherein the diamine includes 2-(4-aminophenyl)-5-aminobenzimidazole and p-diphenylamine. The heterocyclic aramid fibrid is prepared by precipitation and molding using a polar solvent aqueous solution containing glycerol.

2. The heterocyclic aramid fiber according to claim 1, characterized in that: The polymer structural formula of the heterocyclic aramid fibrid is: The number average molecular weight of the heterocyclic aramid fibrid is 160,000-230,000.

3. The heterocyclic aramid fiber according to claim 1, characterized in that: The molar ratio of the 2-(4-aminophenyl)-5-aminobenzimidazole to p-diphenylamine is 1:(1-3); The molar ratio of the total mole of the diamine to the terephthaloyl chloride is 1:(0.90-1.00).

4. A method for preparing a heterocyclic aramid fibrid according to any one of claims 1 to 3, characterized in that: The preparation method is: S1, dissolving p-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole in a polar solvent to obtain a diamine mixed solution; S2, adding a portion of terephthaloyl chloride to the diamine mixed solution for a pre-polycondensation reaction to obtain an initial polymer solution, and then adding the remaining portion of terephthaloyl chloride for a chain extension polycondensation reaction. After the reaction is completed, adjusting the pH to a weakly alkaline state to obtain a homogeneous polymer solution containing a heterocyclic aramid polymer; S3. The heterocyclic aramid polymer is precipitated in a polar solvent aqueous solution containing glycerol to obtain the heterocyclic aramid fibrid.

5. The method for preparing heterocyclic aramid fibrid according to claim 4, characterized in that: In step S2, the temperature of the pre-polycondensation reaction is -10 to 5°C; the temperature of the chain extension polycondensation reaction is -10 to 5°C; During the pre-polycondensation reaction, the amount of terephthaloyl chloride added is 90%-97.5% of the total amount of terephthaloyl chloride used in step S2; during the chain extension polycondensation reaction, the amount of terephthaloyl chloride added is 2.5%-10% of the total amount of terephthaloyl chloride used in step S2.

6. The method for preparing heterocyclic aramid fibrid according to claim 4, characterized in that: In step S2, during the pre-polycondensation reaction, the addition rate of terephthaloyl chloride is 30-45 kg / h; during the chain extension polycondensation reaction, the addition rate of terephthaloyl chloride is 5-15 kg / h.

7. The method for preparing heterocyclic aramid fibrid according to claim 4, characterized in that: The mass concentration of the heterocyclic aramid polymer in the homogeneous polymer solution is 5-7wt%, the viscosity of the homogeneous polymer solution at 25° C. is 50-200 Po, and the pH of the homogeneous polymer solution is 8-10.

8. The method for preparing heterocyclic aramid fibrid according to claim 4, characterized in that: In step S3, the homogeneous polymer solution is diluted with a polar solvent to obtain a polymer dilution solution, the polymer dilution solution and a polar solvent aqueous solution containing glycerol are subjected to high-speed shearing, and then subjected to countercurrent water washing to obtain the heterocyclic aramid fibrid; The mass concentration of the heterocyclic aramid polymer in the polymer diluent is 3-4wt%, and the viscosity of the polymer diluent at 25°C is 40-80CP.

9. The method for preparing heterocyclic aramid fibrid according to claim 8, characterized in that: The mass ratio of the polymer diluent to the glycerol-containing polar solvent aqueous solution is 1:(6-8); In the polar solvent aqueous solution containing glycerol, the mass content of the polar solvent is 20-40%, and the mass ratio of the polar solvent to the glycerol is 1:(1-1.4); The high-speed shearing speed is 4000-8500 rpm, and the diameter of the stock solution gun is 0.05-0.07 mm.

10. Use of a heterocyclic aramid fibrid according to any one of claims 1 to 3, characterized in that: The heterocyclic aramid fibrid is used in aramid paper.

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