A heterocyclic polyaramide-polyhydroxyaromatic amide cast fiber, a method for preparing the same, and a heterocyclic polyaramide-polybenzoxazole paper

Abstract

This invention discloses a heterocyclic polyarylamide-polyhydroxyarylamide precipitated fiber, its preparation method, and a heterocyclic polyarylamide-polybenzodioxazole paper, belonging to the technical field of high-performance organic fiber and paper preparation. The preparation method of the precipitated fiber includes the following steps: A. Preparation of the polymerization solution: 3,3'-dihydroxybenzyl diamine (DHB) and 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) are dissolved in an organic solvent containing a solubilizing salt, and then terephthaloyl chloride is added to react and obtain a polymer solution with a solid content of 1-10%; B. Precipitation: After degassing, filtering, metering, and spinning, the polymer solution is mixed with a coagulation bath and precipitated to obtain the heterocyclic polyarylamide-polyhydroxyarylamide precipitated fiber. A heterocyclic polyarylamide-polybenzodioxazole paper prepared from this precipitated fiber is also provided. This invention introduces a heterocyclic polyaromatic amide structure through copolymerization, which not only improves the strength and composite properties of the cyclized PBO paper, but also maintains a decomposition temperature comparable to that of pure PBO fiber, exceeding 600℃, demonstrating excellent thermal stability. Furthermore, this method is simple and easy to implement, making it suitable for industrial production applications.

Description

Technical Field

[0001] This invention relates to a heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber, its preparation method, and heterocyclic polyaromatic amide-polybenzodioxazole paper, belonging to the technical field of high-performance organic fiber and paper preparation. Background Technology

[0002] High-temperature resistant organic fiber paper is made by mixing chopped fibers and precipitated fibers. Chopped fibers are obtained by cutting long filaments to a few millimeters and serve as the "skeleton" material of the paper. Precipitated fibers are obtained by injecting a large amount of coagulant into a strongly stirred dilute polymer solution, or by injecting the polymer solution in the form of a thin stream into a high-speed stirred coagulation bath for precipitation. They are thin films with a thickness of one to several micrometers and a length ranging from tens of micrometers to several millimeters. As a "filler" material for paper, their unique surface structure greatly improves adhesion, thus significantly increasing the strength of the paper.

[0003] Poly(p-phenylenebenzodioxazole) (PBO) is obtained by polymerizing and cyclizing terephthalic acid and 4,6-diaminoresorcinol hydrochloride in polyphosphoric acid. It possesses excellent high-temperature resistance and flame retardant properties, making it the best-performing organic fiber in terms of heat resistance to date, with a decomposition temperature exceeding 650℃. It represents an important development direction for novel high-temperature resistant paper-based materials. However, PBO has a rigid structure and poor solubility, dissolving only in a few strong acid solvents such as fuming sulfuric acid, polyphosphoric acid, and methanesulfonic acid. Not only are the solutions extremely viscous, but the strong acid solutions also release a large amount of heat during precipitation, making it difficult to process into precipitable fibers using a one-step method. Patents CN101802302A, CN107207726A, CN109354684A, CN113882185A and literature Thermal Rearrangement of Poly(o-hydroxyimide)s Synthesized from 4,6-DiaminoresorcinolDihydrochloride (Polymer Journal, 2003, 35(2): 208-212) report a two-step method for preparing PBO fiber filaments, precipitated fibers or membranes. The method involves synthesizing PBO precursors such as polyhydroxyamides, polyhydroxyimides or ortho-functionalized polyimides in organic solvents such as N-methylpyrrolidone, then processing the precursors into shapes, and finally heat-treating the precursor products at high temperatures to cyclize them, thereby converting small molecules into PBO structured products through structural rearrangement. While PBO precursors exhibit good solubility in organic solvents and are easily processed, the thermal rearrangement process of this method releases small molecule products, resulting in numerous structural defects in PBO fibers and paper products. This significantly impacts their mechanical properties, thus limiting its industrial application. Furthermore, the complete cyclization of the precursor into PBO results in a lack of polar functional groups, leading to poor composite properties with resins and hindering the application prospects of this method in preparing PBO precipitated fibers and paper. Summary of the Invention

[0004] This invention aims to solve the aforementioned technical problems by providing a heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber, its preparation method, and a heterocyclic polyaromatic amide-polybenzodioxazole paper. This invention introduces a heterocyclic polyaromatic amide structure through copolymerization. The prepared heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber exhibits excellent papermaking adaptability. Furthermore, after hot pressing at high temperatures of 280℃ to 500℃ for 15 to 60 minutes, the mechanical properties of the paper show minimal change. The cyclized PBO paper not only possesses excellent thermal stability but also good mechanical and composite properties. Simultaneously, the method is simple and suitable for industrial production applications.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A heterocyclic polyaromatic amide-polyhydroxyaromatic precipitable fiber, the molecular structure of which is formed by the arbitrary connection of repeating units of the following two structural formulas:

[0007] ..................Repeating Unit (Ⅰ)

[0008] ...Repeating Unit (II)

[0009] The molar percentage of repeating unit (Ⅰ) is 50-95%, and the molar percentage of repeating unit (Ⅱ) is 5-50%.

[0010] In this invention, the repeating unit (Ⅰ) is the main structure of a heterocyclic polyaromatic amide-polyhydroxyaromatic amide, possessing numerous polar hydroxyl groups, which helps improve hydrophilicity, making the precipitated fibers easily dispersed in water during papermaking and improving the uniformity and strength of the paper. During high-temperature treatment, the amide bonds and hydroxyl groups in this structure undergo a dehydration cyclization reaction, transforming into a high-temperature resistant benzoxazole structure.

[0011] In this invention, the repeating unit (II) is a modified structure of heterocyclic polyaromatic amide-polyhydroxyaromatic amide. This structure is rigid and regular, which helps to improve mechanical properties. The structure does not change during high-temperature treatment, and the -NH- structure of the imidazole ring is retained, which helps to improve the composite properties and mechanical properties of the cyclized PBO paper.

[0012] The present invention provides a method for preparing heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers, comprising the following steps:

[0013] A. Preparation of the polymerization solution: 3,3'-dihydroxybenzyl diamine (DHB) and 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) are dissolved in an organic solvent containing a solubilizing salt, and then terephthaloyl chloride is added. The reaction is carried out under inert gas protection with stirring to obtain a polymer solution. The polymer mass of the polymer solution accounts for 1-10% of the total mass of the solution, and the dynamic viscosity at room temperature is 0.5-200,000 centipoise.

[0014] B. Precipitation: The polymer solution from step A is transferred to a degassing tank, and after degassing, filtration, metering, and spinning, it enters a coagulation precipitation device with a rotation speed of 2000–20000 rpm. It is mixed with the coagulation bath at a mass ratio of 1:1 to 1:10 and precipitated for 1–30 seconds. After the precipitated fibers and the suspension from the coagulation bath flow out of the precipitation device, they are separated, washed, and dehydrated to obtain fibers with an average length of 0.2–3.0 mm and an average specific surface area of ​​4–36 m². 2 / g of heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber finished product.

[0015] Further, in step A, the organic solvent is one of N,N-dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone; the co-solvent is at least one of LiCl or CaCl2, and the solid content of the co-solvent in the organic solvent is 1.0 to 7.5%.

[0016] Furthermore, in step A, the polymer solution preferably comprises 2-4% of the total mass of the solution and has a dynamic viscosity of 10,000-30,000 centipoise at room temperature.

[0017] Further, in step B, the coagulation bath uses an aqueous solution of N,N-dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone with a mass concentration of 0-60%.

[0018] The present invention also provides a heterocyclic polyarylamide-polybenzodioxazole paper prepared using the above-mentioned heterocyclic polyarylamide-polyhydroxyarylamide precipitated fibers. It is prepared by using known conventional papermaking processes to form a paper base material by mixing heterocyclic polyarylamide-polyhydroxyarylamide precipitated fibers, or heterocyclic polyarylamide-polyhydroxyarylamide precipitated fibers with one or more of chopped fibers, pulp fibers, and other precipitated fibers, and then converting them into heterocyclic polyarylamide-polybenzodioxazole paper through a heat treatment process.

[0019] Furthermore, the chopped fibers include meta-aramid chopped fibers, para-aramid chopped fibers, heterocyclic aramid (aramid III) chopped fibers, PBO chopped fibers, polyimide chopped fibers, polysulfonamide chopped fibers, etc.; the pulp fibers include para-aramid pulp fibers, PBO pulp fibers, etc.; the other precipitated fibers include meta-aramid precipitated fibers, para-aramid precipitated fibers, heterocyclic aramid (aramid III) precipitated fibers, polyimide precipitated fibers, polysulfonamide precipitated fibers, etc.

[0020] The heat treatment temperature is 280℃~500℃, the heat treatment time is 15~60min, and the heat treatment atmosphere is an inert gas atmosphere or vacuum conditions.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] (1) Conventional high-strength PBO fibers are obtained by polymerizing 4,6-diaminoresorcinol dihydrochloride (DAR) and terephthalic acid in polyphosphoric acid, as shown in reaction formula 1. The structure is symmetrical and regular, and after polymerization, it forms a liquid crystal solution in polyphosphoric acid. After spinning, ultra-high-strength PBO fibers can be obtained. Since 4,6-diaminoresorcinol is easily oxidized in air, its hydrochloride structure must be used as the polymerization monomer.

[0023] Existing patent CN113882185A uses 4,6-diaminoresorcinol dihydrochloride and terephthaloyl chloride in an organic solvent (such as DMAc or NMP) to prepare polyhydroxy aromatic amide precipitated fibers. However, due to the presence of the complex salt, 4,6-diaminoresorcinol dihydrochloride has low reactivity, requiring large amounts of alkaline solvents such as pyridine, triethylamine, and isoquinoline as acid-binding agents to participate in the polymerization, as shown in reaction formula 2. Despite the addition of acid-binding agents, the molecular weight of the resulting polyhydroxy aromatic amide (PHA) remains low. Furthermore, acid-binding agents such as pyridine and isoquinoline are toxic, have an odor, and are difficult to separate from the solvent, leading to difficulties in solvent recovery and low industrial feasibility.

[0024] Existing patent CN101802302A uses 3,3'-diaminobiphenyldiamine (DHB) to react with terephthaloyl chloride, as shown in reaction formula three. Due to the presence of the biphenyl structure, 3,3'-diaminobiphenyldiamine is more stable, does not require complexation with hydrochloride, and readily reacts with terephthaloyl chloride to produce high molecular weight polyhydroxy aromatic amides. However, the introduction of the biphenyl structure leads to poor molecular structure regularity and low mechanical properties after cyclization.

[0025] This invention introduces an appropriate amount of 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) structure, which has high reactivity, rigidity, and symmetry, and can effectively improve the mechanical properties of cyclized PBO fiber paper.

[0026]

[0027] Reaction Formula 1: PBO Polymerization Reaction

[0028]

[0029] Reaction Formula 2: Polymerization Reaction of Polyhydroxy Aromatic Amides

[0030]

[0031] Reaction Formula 3: Polymerization reaction of biphenyl-type polyhydroxy aromatic amides

[0032] (2) The heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber prepared by the present invention has 2-(4-aminophenyl)-5-aminobenzimidazole introduced into its structure. After cyclization to form PBO structure, the molecular structure still contains -NH- groups (as shown in Formula 4), which helps to improve the composite performance of PBO paper and resin after cyclization.

[0033]

[0034] Formula 4: The molecular structure of heterocyclic polyarylamide-polybenzodioxazole after cyclization of heterocyclic polyarylamide-polyhydroxyarylamide according to the present invention.

[0035] (3) The heterocyclic polyaromatic amide-polyhydroxy amide paper prepared by the heterocyclic polyaromatic amide-polyhydroxy amide precipitated fiber of the present invention has little change in mechanical properties after hot pressing for 15 to 60 minutes at a high temperature of 280℃ to 500℃. The heterocyclic polyaromatic amide-polybenzoxazole paper obtained after cyclization has excellent thermal stability and a decomposition temperature above 600℃. Attached Figure Description

[0036] Figure 1 This is an electron microscope image of the heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers prepared in Example 1;

[0037] Figure 2 This is an electron microscope image of the precipitated fibers prepared in Comparative Example 1;

[0038] Figure 3 This is an electron microscope image of the precipitated fibers prepared in Comparative Example 2;

[0039] Figure 4 This is a thermogravimetric curve of the DAR-type polyhydroxyaramid precipitated fiber prepared in Comparative Example 1;

[0040] Figure 5 This is a thermogravimetric curve of conventional high-strength PBO fiber;

[0041] Figure 6 This is a thermogravimetric curve of the heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber prepared in Example 3;

[0042] Figure 7 These are comparison images of the heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers prepared in Example 4 before and after thermal cyclization.

[0043] Where a represents the area before cyclization and b represents the area after cyclization. Detailed Implementation

[0044] To better explain the present invention, the following detailed description is provided in conjunction with embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention still fall within the scope of protection of the present invention.

[0045] Note: The morphology, properties, and length distribution of the precipitated fibers obtained through the following examples and comparative examples are detailed in Table 1. The experimental methods and standards used are as follows:

[0046] 1) The average length and distribution of precipitated fibers were determined by a fiber analyzer in accordance with the national standard GB / T 29779-2013 Determination of pulp fiber length - non-polarized light method;

[0047] 2) The average specific surface area of ​​the precipitated fibers was measured using a specific surface area meter according to the national standard GB / T 19587-2004, which specifies the specific surface area of ​​solid materials by gas adsorption BET method.

[0048] 3) The morphology of the precipitated fibers was obtained by observation using optical microscopy and electron microscopy (SEM);

[0049] 4) The mechanical properties of paper-based materials were determined in accordance with GB / T 12914-2018.

[0050] (I) Preparation of Precipitated Fibers

[0051] The molecular structure of the heterocyclic polyaromatic amide-polyhydroxyaromatic amide involved in the following examples is formed by the arbitrary connection of repeating units of the following two structural formulas:

[0052] ..................Repeating Unit (Ⅰ)

[0053] ...Repeating Unit (II)

[0054] The molar percentage of repeating unit (Ⅰ) is 50-95%, and the molar percentage of repeating unit (Ⅱ) is 5-50%.

[0055] Example 1

[0056] A heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber is prepared according to the following steps:

[0057] A. Preparation of the polymerization solution: 83.6141 g (0.3867 mol) of 3,3'-dihydroxybenzyl diamine (DHB) and 21.6788 g (0.0967 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) were dissolved in 4000 g of N,N-dimethylacetamide containing 2.0% lithium chloride. Then, 98.1278 g (0.4833 mol) of terephthaloyl chloride was added in batches. The reaction was carried out under nitrogen protection and stirred to obtain a polymer solution with a polymer mass of 4% of the total solution mass and a dynamic viscosity of 28,000 centipoise at room temperature.

[0058] B. Precipitation: The polymer solution from step A is transferred to a degassing vessel, and after degassing, filtration, and metering, it is extruded into a precipitator with a rotation speed of 10,000 rpm and mixed with a 15% N,N-dimethylacetamide aqueous solution. The mass flow ratio of the polymer solution to the coagulation bath is 1:5. The solution stream is dispersed and coagulated in the coagulation bath to obtain a mixture of precipitated fibers and the coagulation bath. The precipitation time is 1 second. The mixture flows out of the precipitator outlet and enters a centrifuge. After separation and washing, heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers are obtained, wherein the molar percentage of repeating unit (I) is 80% and the molar percentage of repeating unit (II) is 20%.

[0059] Approximately 10 g (octane-dry weight) of the heterocyclic polyaramid-polyhydroxyaramid precipitated fiber obtained in Example 1 was weighed as a sample, designated A-1. The morphology of the fiber was observed using scanning electron microscopy, and its specific surface area and average length were measured. The results are shown in Table 1. Figure 1 .

[0060] Example 2

[0061] A heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber is prepared according to the following steps:

[0062] A. Preparation of the polymerization solution: 46.7070 g (0.2160 mol) of 3,3'-dihydroxybenzyl diamine (DHB) and 48.4393 g (0.2160 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) were dissolved in 3600 g of N,N-dimethylacetamide containing 3.5% lithium chloride. Then, 87.7031 g (0.4320 mol) of terephthaloyl chloride was added in batches. The reaction was carried out under nitrogen protection and stirred to obtain a polymer solution with a polymer mass of 4% of the total solution mass and a dynamic viscosity of 36,000 centipoise at room temperature.

[0063] B. Precipitation: The polymer solution from step A is transferred to a degassing tank, and after degassing, filtration, and metering, it is extruded into a precipitator with a rotation speed of 20,000 rpm and mixed with a 30% N,N-dimethylacetamide aqueous solution. The mass flow ratio of the polymer solution to the coagulation bath is 1:10. The solution stream is dispersed and coagulated in the coagulation bath to obtain a mixture of precipitated fibers and the coagulation bath. The precipitation time is 5 seconds. The mixture flows out of the precipitator outlet and enters a centrifuge. After separation and washing, heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers are obtained, wherein the molar percentage of repeating unit (I) is 50% and the molar percentage of repeating unit (II) is 50%.

[0064] Approximately 10 g (octane-dry weight) of the heterocyclic polyaramid-polyhydroxyaramid precipitated fiber obtained in Example 2 above was weighed as a sample, numbered A-2. The morphology of the fiber was observed by scanning electron microscopy, and its specific surface area and average length were measured. The results are shown in Table 1.

[0065] Example 3

[0066] A heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber is prepared according to the following steps:

[0067] A. Preparation of the polymerization solution: 153.3611 g (0.7092 mol) of 3,3'-dihydroxybenzyl diamine (DHB) and 8.3710 g (0.0373 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) were dissolved in 4000 g of N-methylpyrrolidone containing 7.5% lithium chloride. Then, 151.5634 g (0.7465 mol) of terephthaloyl chloride was added in batches. The reaction was carried out under nitrogen protection and stirred to obtain a polymer solution with a polymer mass of 6% of the total solution mass and a dynamic viscosity of 83,000 centipoise at room temperature.

[0068] B. Precipitation: The polymer solution from step A is transferred to a degassing vessel, and after degassing, filtration, and metering, it is extruded into a precipitator with a rotation speed of 20,000 rpm and mixed with pure water. The mass flow ratio of the polymer solution to the coagulation bath is 1:7. The solution stream is dispersed and coagulated in the coagulation bath to obtain a mixture of precipitated fibers and the coagulation bath. The precipitation time is 10 s. The mixture flows out of the precipitator outlet and enters a centrifuge. After separation and washing, heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers are obtained, wherein the molar percentage of repeating unit (I) is 95% and the molar percentage of repeating unit (II) is 5%.

[0069] Approximately 10 g (octane-dry weight) of the heterocyclic polyaramid-polyhydroxyaramid precipitated fiber obtained in Example 3 above was weighed as a sample, numbered A-3. The morphology of the fiber was observed by scanning electron microscopy, and its specific surface area and average length were measured. The results are shown in Table 1.

[0070] Example 4

[0071] A heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber is prepared according to the following steps:

[0072] A. Preparation of the polymerization solution: 72.9925 g (0.3376 mol) of 3,3'-dihydroxybenzyl diamine (DHB) and 32.4427 g (0.1447 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) were dissolved in 4000 g of N,N-dimethylacetamide containing 3.5% lithium chloride. Then, 97.9001 g (0.4822 mol) of terephthaloyl chloride was added in batches. The reaction was carried out under nitrogen protection and stirred to obtain a polymer solution with a polymer mass of 4% of the total solution mass and a dynamic viscosity of 57,000 centipoise at room temperature.

[0073] B. Precipitation: The polymer solution from step A is transferred to a degassing tank, and after degassing, filtration, and metering, it is extruded into a precipitator with a rotation speed of 2000 rpm and mixed with a 15% N,N-dimethylacetamide aqueous solution. The mass flow ratio of the polymer solution to the coagulation bath is 1:5. The solution stream is dispersed and coagulated in the coagulation bath to obtain a mixture of precipitated fibers and the coagulation bath. The precipitation time is 30 s. The mixture flows out of the precipitator outlet and enters a centrifuge. After separation and washing, heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers are obtained, wherein the molar percentage of repeating unit (I) is 70% and the molar percentage of repeating unit (II) is 30%.

[0074] Approximately 10 g (octane-dry weight) of the heterocyclic polyaramid-polyhydroxyaramid precipitated fiber obtained in Example 4 above was weighed as a sample, numbered A-4. The morphology of the fiber was observed by scanning electron microscopy, and its specific surface area and average length were measured. The results are shown in Table 1.

[0075] Example 5

[0076] A heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber is prepared according to the following steps:

[0077] A. Preparation of the polymerization solution: 176.1882 g (0.8148 mol) of 3,3'-dihydroxybenzyl diamine (DHB) and 45.6807 g (0.2037 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) were dissolved in 4000 g of N,N-dimethylacetamide containing 3.0% lithium chloride. Then, 206.7710 g (1.0185 mol) of terephthaloyl chloride was added in batches. The reaction was carried out under nitrogen protection and stirred to obtain a polymer solution with a polymer mass of 8% of the total solution mass and a dynamic viscosity of 137,000 centipoise at room temperature.

[0078] B. Precipitation: The polymer solution from step A is transferred to a degassing tank, and after degassing, filtration, and metering, it is extruded into a precipitator with a rotation speed of 10,000 rpm and mixed with a 45% N,N-dimethylacetamide aqueous solution. The mass flow ratio of the polymer solution to the coagulation bath is 1:10. The solution stream is dispersed and coagulated in the coagulation bath to obtain a mixture of precipitated fibers and the coagulation bath. The precipitation time is 8 seconds. The mixture flows out of the precipitator outlet and enters a centrifuge. After separation and washing, heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers are obtained, wherein the molar percentage of repeating unit (I) is 80% and the molar percentage of repeating unit (II) is 20%.

[0079] 10g (octane-dry weight) of the heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber obtained in Example 5 above was weighed as a sample, numbered A-5. The morphology of the fiber was observed by scanning electron microscopy, and its specific surface area and average length were measured. The results are shown in Table 1.

[0080] Example 6

[0081] A heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber is prepared according to the following steps:

[0082] A. Preparation of the polymerization solution: 226.2978 g (1.0465 mol) of 3,3'-dihydroxybenzyl diamine (DHB) and 58.6727 g (0.2616 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) were dissolved in 4000 g of N-methylpyrrolidone containing 6.0% calcium chloride. Then, 265.5786 g (1.3081 mol) of terephthaloyl chloride was added in batches. The reaction was carried out under nitrogen protection with stirring to obtain a polymer solution with a polymer content of 10% of the total solution mass. The dynamic viscosity at room temperature was 200,000 centipoise.

[0083] B. Precipitation: The polymer solution from step A is transferred to a degassing vessel, and after degassing, filtration, and metering, it is extruded into a precipitator with a rotation speed of 20,000 rpm and mixed with a 60% N-methylpyrrolidone aqueous solution. The mass flow ratio of the polymer solution to the coagulation bath is 1:8. The solution stream is dispersed and coagulated in the coagulation bath to obtain a mixture of precipitated fibers and the coagulation bath. The precipitation time is 8 seconds. The mixture flows out of the precipitator outlet and enters a centrifuge. After separation and washing, heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers are obtained, wherein the molar percentage of repeating unit (I) is 80% and the molar percentage of repeating unit (II) is 20%.

[0084] Approximately 10 g (octane-dry weight) of the heterocyclic polyaramid-polyhydroxyaramid precipitated fiber obtained in Example 6 was weighed as a sample, numbered A-6. The morphology of the fiber was observed by scanning electron microscopy, and its specific surface area and average length were measured. The results are shown in Table 1.

[0085] Example 7

[0086] A heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber is prepared according to the following steps:

[0087] A. Preparation of the polymerization solution: 17.5780 g (0.0813 mol) of 3,3'-dihydroxybenzyl diamine (DHB) and 7.8128 g (0.0348 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) were dissolved in 4000 g of N,N-dimethylacetamide containing 1.0% lithium chloride. Then, 23.5762 g (0.1161 mol) of terephthaloyl chloride was added in batches. The reaction was carried out under nitrogen protection and stirred to obtain a polymer solution with a polymer mass of 1.0% of the total solution mass and a dynamic viscosity of 0.5 kPa at room temperature.

[0088] B. Precipitation: The polymer solution from step A is transferred to a degassing tank, and after degassing, filtration, and metering, it is extruded into a precipitator rotating at 8000 rpm and mixed with a 10% N,N-dimethylacetamide aqueous solution. The mass flow ratio of the polymer solution to the coagulation bath is 1:1. The solution stream is dispersed and coagulated in the coagulation bath to obtain a mixture of precipitated fibers and the coagulation bath. The precipitation time is 15 s. The mixture flows out of the precipitator outlet and enters a centrifuge. After separation and washing, precipitated fibers are obtained, wherein the molar percentage of repeating unit (I) is 70% and the molar percentage of repeating unit (II) is 30%.

[0089] Approximately 10 g (octane-dry weight) of the heterocyclic polyaramid-polyhydroxyaramid precipitated fiber obtained in Example 7 was weighed as a sample, numbered A-7. The morphology of the fiber was observed by scanning electron microscopy, and its specific surface area and average length were measured. The results are shown in Table 1.

[0090] Example 8

[0091] A heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber is prepared according to the following steps:

[0092] A. Preparation of the polymerization solution: 35.5916 g (0.1646 mol) of 3,3'-dihydroxybenzyl diamine (DHB) and 15.8193 g (0.0705 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) were dissolved in 4000 g of N,N-dimethylformamide containing 2.5% lithium chloride. Then, 47.7367 g (0.2351 mol) of terephthaloyl chloride was added in batches. The reaction was carried out under nitrogen protection and stirred to obtain a polymer solution with a polymer mass of 2.0% of the total solution mass and a dynamic viscosity of 10,000 centipoise at room temperature.

[0093] B. Precipitation: The polymer solution from step A is transferred to a degassing tank, and after degassing, filtration, and metering, it is extruded into a precipitator with a rotation speed of 15000 rpm and mixed with a 15% N,N-dimethylformamide aqueous solution. The mass flow ratio of the polymer solution to the coagulation bath is 1:3. The solution stream is dispersed and coagulated in the coagulation bath to obtain a mixture of precipitated fibers and the coagulation bath. The precipitation time is 20 s. The mixture flows out of the precipitator outlet and enters a centrifuge. After separation and washing, precipitated fibers are obtained, wherein the molar percentage of repeating unit (I) is 70% and the molar percentage of repeating unit (II) is 30%.

[0094] Approximately 10 g (octane-dry weight) of the heterocyclic polyaramid-polyhydroxyaramid precipitated fiber obtained in Example 8 was weighed as a sample, numbered A-8. The morphology of the fiber was observed by scanning electron microscopy, and its specific surface area and average length were measured. The results are shown in Table 1.

[0095] Comparative Example 1

[0096] This comparative example is a comparison with Example 4, except that DHB and DAPBI in Example 4 are replaced with DAR, while other conditions are the same as in Example 4. However, the DAR used in this comparative example has low reactivity due to the presence of the complex salt, making it difficult to achieve a molecular weight (dynamic viscosity) similar to that of Example 4. The specific method is as follows:

[0097] A polyhydroxyaramid precipitated fiber is prepared according to the following steps:

[0098] A. Preparation of the polymerization solution: 134.5048 g (0.6313 mol) of 4,6-diaminoresorcinol dihydrochloride (DAR) was dissolved in 4000 g of N,N-dimethylacetamide containing 3.5% lithium chloride. Then, 128.1665 g (0.6313 mol) of terephthaloyl chloride and 3.0 g of isoquinoline were added. The reaction was carried out under nitrogen protection and stirred to obtain a polymer solution with a polymer mass of 4.0% of the total solution mass and a dynamic viscosity of 0.2 kPa at room temperature.

[0099] B. Precipitation: The polymer solution from step A is transferred to a degassing tank. After degassing, filtration, and metering, it is extruded into a precipitator rotating at 2000 rpm and mixed with a 15% N,N-dimethylacetamide aqueous solution. The mass flow ratio of the polymer solution to the coagulation bath is 1:5. The solution stream is dispersed and coagulated in the coagulation bath to obtain a mixture of precipitated fibers and the coagulation bath. The precipitation time is 30 seconds. The mixture flows out of the precipitator outlet and enters a centrifuge. After separation and washing, the precipitated fibers are obtained.

[0100] Approximately 10 g (octane-dry weight) of the polyhydroxyaramid precipitated fiber obtained in Comparative Example 1 was weighed as a sample, designated A-9. The morphology of the fiber was observed using scanning electron microscopy, and its specific surface area and average length were measured. The results are shown in Table 1. Figure 2 .

[0101] Comparative Example 2

[0102] This comparative example is a comparison with Example 1. In this comparative example, only DHB and TPC were used for polymerization, and the prepared precipitated fibers contained only repeating unit (Ⅰ) structure. Other conditions were the same as in Example 1. The specific method is as follows:

[0103] A polyhydroxyaramid precipitated fiber is prepared according to the following steps:

[0104] A. Preparation of the polymerization solution: 105.0060 g (0.4856 mol) of 3,3'-dihydroxybenzidine (DHB) was dissolved in 4000 g of N,N-dimethylacetamide containing 2.0% lithium chloride. Then, 98.5864 g (0.4856 mol) of terephthaloyl chloride was added in batches. The reaction was carried out under nitrogen protection and stirred to obtain a polymer solution with a polymer mass of 4.0% of the total solution mass and a dynamic viscosity of 30,000 centipoise at room temperature.

[0105] B. Precipitation: The polymer solution from step A is transferred to a degassing tank. After degassing, filtration, and metering, it is extruded into a precipitator running at 10,000 rpm and mixed with a 15% N,N-dimethylacetamide aqueous solution. The mass flow ratio of the polymer solution to the coagulation bath is 1:5. The solution stream is dispersed and coagulated in the coagulation bath to obtain a mixture of precipitated fibers and the coagulation bath. The precipitation time is 1 second. The mixture flows out of the precipitator outlet and enters a centrifuge. After separation and washing, the precipitated fibers are obtained.

[0106] Approximately 10 g (octane-dry weight) of the polyhydroxyaramid precipitated fiber obtained in Comparative Example 2 was weighed as a sample, designated A-10. The morphology of the fiber was observed using scanning electron microscopy, and its specific surface area and average length were measured. The results are shown in Table 1. Figure 3 .

[0107] Comparative Example 3

[0108] This comparative example is a comparison with Example 1. In this comparative example, only DAPBI and TPC were used for polymerization, and the prepared precipitated fibers contained only repeating unit (II) structures. Other conditions were the same as in Example 1. The specific methods are as follows:

[0109] A heterocyclic polyaromatic amide precipitated fiber is prepared according to the following steps:

[0110] A. Preparation of the polymerization solution: 106.4140 g (0.4745 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) was dissolved in 4000 g of N,N-dimethylacetamide containing 2.0% lithium chloride. Then, 96.3330 g (0.4745 mol) of terephthaloyl chloride was added in batches. The reaction was carried out under nitrogen protection and stirred to obtain a polymer solution with a polymer mass of 4.0% of the total solution mass and a dynamic viscosity of 33,000 centipoise at room temperature.

[0111] B. Precipitation: The polymer solution from step A is transferred to a degassing tank. After degassing, filtration, and metering, it is extruded into a precipitator running at 10,000 rpm and mixed with a 15% N,N-dimethylacetamide aqueous solution. The mass flow ratio of the polymer solution to the coagulation bath is 1:5. The solution stream is dispersed and coagulated in the coagulation bath to obtain a mixture of precipitated fibers and the coagulation bath. The precipitation time is 1 second. The mixture flows out of the precipitator outlet and enters a centrifuge. After separation and washing, the precipitated fibers are obtained.

[0112] Approximately 10 g (octane-dry weight) of the heterocyclic polyarylamide precipitated fiber obtained in Comparative Example 3 was weighed as a sample, designated A-11. The morphology of the fiber was observed by scanning electron microscopy, and its specific surface area and average length were measured. The results are shown in Table 1.

[0113]

[0114] From the test results in Table 1 and Figures 1-3 It can be seen that the heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers prepared by the embodiments of the present invention are membrane-like with abundant surface hairs, making them suitable for papermaking; while the polyhydroxyaromatic amide precipitated fibers prepared in Comparative Example 1 have a larger specific surface area, a significantly smaller average length than those in the embodiments, and a much smaller aspect ratio, as can be seen from the electron micrographs ( Figure 2As can be seen from the example, the fibers are in the form of fine particles, which are not suitable for papermaking. This is because the DAR has low reactivity due to the presence of complexed hydrochloride. Although isoquinoline is added as an acid-binding agent, the polymer molecular weight is still low, and the fibers are easily sheared into powder during precipitation. The polyhydroxy aromatic amide precipitated fiber prepared in Comparative Example 2 is in the form of a film, which can meet the needs of papermaking. However, compared with the example, the surface is smoother. The lack of fine hairs is not conducive to improving the paper uniformity and strength. The main reason is that the polymer strength is low, and it is easy to form a smooth sheet. Comparative Example 3 is a heterocyclic polyaromatic amide precipitated fiber, which contains only repeating units (II) and no repeating units (I) that can cyclize to form a benzoxazole structure. Although it can be used for papermaking, it cannot be further thermally cyclized at high temperature to form a benzoxazole structure. Its high temperature resistance is worse than that of the example of this invention.

[0115] (ii) Papermaking from precipitated fibers

[0116] Example 9

[0117] The precipitated fibers prepared in Examples 1-8 and Comparative Examples 1-3 were delaminated using a Lorentzen & Wettre 260 standard disperser and then wet-formed on an ERNSTHAAGEBBS-3 sheeter with a basis weight of 40 g·m³. -2 The hand-made paper base material was heat-dried at 90℃ for 15 minutes to obtain the base paper. The fiber composition of the paper base material and the properties of the base paper are shown in Table 2 below.

[0118]

[0119] As can be seen from Table 2, the base paper (numbered B-1 to B-2, B-6 to B-8) made solely using the heterocyclic polyaromatic amide-polyhydroxyaromatic precipitated fibers of the present invention has a tensile strength of 3.28 to 4.28 kN / m, an elongation of 1.07 to 3.11%, and a modulus of 3541 to 6011 MPa, exhibiting superior mechanical properties. This is because the precipitated fibers prepared by the present invention not only have a suitable appearance and structure for papermaking but also possess a large number of polar groups and high intermolecular bonding.

[0120] The base paper (numbered B-3 to B-5) produced by compounding heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers and 6mm PBO chopped fibers according to the present invention has a tensile strength of 1.22 to 2.35 kN / m, an elongation of 0.63 to 1.89%, and a modulus of 1280 to 1349 MPa, which can meet the requirements for use in high-temperature honeycomb and other fields. As the proportion of PBO chopped fibers increases, the mechanical properties of the paper decrease, mainly due to the smooth surface structure of PBO chopped fibers.

[0121] Compared to the examples, the B-9 base paper prepared from the comparative example A-9 precipitated fibers has lower mechanical properties, with a strength of only 0.82 kN / m. This is mainly because the A-9 precipitated fibers are granular and have a small aspect ratio. The B-10 and B-11 base papers prepared from the comparative examples A-10 and A-11 precipitated fibers have higher mechanical strength, comparable to the examples. However, after thermal cyclization, the mechanical properties of the B-10 paper decrease significantly, and thermal cyclization treatment is necessary for its use as a high-temperature resistant paper (see Table 3 below).

[0122] (III) Heat treatment of paper

[0123] Example 10

[0124] The base paper B1-B11 from Example 9 was hot-pressed at 280℃~500℃ for 15~60min under an inert gas atmosphere or vacuum conditions. The heat treatment conditions and the properties of the paper after heat treatment are shown in Table 3 below.

[0125]

[0126] 1. From the perspective of the thermal weight loss of each fiber:

[0127] Depend on Figure 4 The thermogravimetric curves show that the DAR-type polyhydroxyaramid precipitated fiber prepared in Comparative Example 1 has three weight loss ranges. The weight loss below 200℃ is caused by the loss of adsorbed free water. The weight loss in the range of 300℃ to 400℃ is caused by the cyclization and dehydration of hydroxyl and amide bonds to form an oxazole ring. The weight loss above 600℃ is the weight loss due to polymer decomposition. The temperature corresponding to the maximum decomposition rate is 675℃.

[0128] Depend on Figure 5 The thermogravimetric curves show that the temperature corresponding to the maximum decomposition rate of conventional high-strength PBO fibers is 700℃.

[0129] Depend on Figure 6 The thermogravimetric analysis (TGA) curves show that the heterocyclic polyarylamide-polyhydroxyarylamide precipitated fibers prepared in this invention also exhibit three weight loss ranges. The weight loss below 150°C is due to the loss of adsorbed free water by the precipitated fibers. The weight loss in the range of 300°C to 400°C is due to the cyclization and dehydration of hydroxyl groups and amide bonds to form oxazole rings. The weight loss above 600°C is due to polymer decomposition. The temperature corresponding to the maximum decomposition rate is 675°C. Compared with Comparative Example 1, the introduction of biphenyl structure and heterocyclic polyarylamide segments in this invention does not significantly reduce thermal stability and still exhibits excellent thermal stability.

[0130] Depend on Figure 7 It can be seen that the heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fibers prepared by the present invention still maintain a good morphological structure after thermal cyclization, without obvious shrinkage or deformation.

[0131] 2. From the perspective of paper properties after heat treatment:

[0132] Combined with the above figures and Table 3, it can be further verified that: after heat treatment (numbered C-1 to C-2, C-6 to C-8), the base paper obtained by using the heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber of the present invention has a tensile strength of 2.89 to 4.11 kN / m, an elongation of 1.33 to 2.99%, and a modulus of 2398 to 5749 MPa, it still has good mechanical properties.

[0133] The base paper made by combining the heterocyclic polyaromatic amide-polyhydroxyaromatic amide precipitated fiber of the present invention with 6mm PBO short chopped fiber, after heat treatment (numbered C-3 to C-5), has a tensile strength of 1.11 to 2.31 kN / m, an elongation of 0.59 to 1.85%, and a modulus of 1295 to 1344 MPa, with little change in mechanical properties.

[0134] The mechanical properties of base paper B-9, made using comparative example A-9 precipitated fiber, and base paper B-10, made using comparative example A-10 precipitated fiber, decreased significantly after heat treatment (C-9 and C-10) compared to before heat treatment. The main reason is that after heat treatment, the polar groups (hydroxyl and amide bonds, etc.) in the structure of B-9 and B-10 are transformed into oxazole ring structures, resulting in a lack of polar groups in the molecule and a reduction in interaction forces. The molecular structure of comparative example A-11 precipitated fiber consists entirely of repeating units (Ⅰ) and does not contain polyhydroxyamide structures (repeating units (Ⅱ)). The B-11 base paper made from it does not undergo cyclization reaction during heat treatment. As shown in Table 3, its mechanical properties decreased less after heat treatment, indicating that the heterocyclic polyaromatic amide structure (repeating units (Ⅰ)) in the comparative example and the embodiments of the present invention does not degrade during heat treatment.

[0135] In summary, this invention introduces a heterocyclic polyaromatic amide structure through copolymerization, and the cyclized paper still retains high mechanical properties and low decomposition temperature. Figure 6 (>600℃), after cyclization, it also has more polar groups, which helps to improve the composite performance with resin and expand the application prospects of PBO precipitated fibers and paper.

[0136] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A heterocyclic polyaramide Process for the preparation of polyhydroxy aramide spun fibers, characterized in that: Includes the following steps: A. Preparation of the polymerization solution: 3,3'-dihydroxybenzyl diamine and 2-(4-aminophenyl)-5-aminobenzimidazole are dissolved in an organic solvent containing a co-solvent, and then terephthaloyl chloride is added. The reaction is carried out under inert gas protection with stirring to obtain a polymer solution. The polymer mass of the polymer solution accounts for 1-10% of the total mass of the solution, and the dynamic viscosity at room temperature is 0.5-200,000 centipoise. B. precipitation: the polymer solution of step A is transferred into a deaeration kettle, deaerated, filtered, metered, and spun into a coagulation precipitation device with a rotation speed of 2000-20000 rpm, mixed with a coagulation bath at a mass ratio of 1:1-1:10, and precipitated for 1-30 s, the suspension of precipitated fibers and coagulation bath flows out of the precipitation device, and the precipitated fibers are separated, washed, and dehydrated to obtain a heterocyclic polyaramid with an average length of 0.2-3.0 mm, an average specific surface area of 4-36 m 2 / g of heterocyclic polyaramide Polyhydroxy aramide precipitated fiber product; Heterocyclic polyarylamide The molecular structure of polyhydroxy aramide is formed by the arbitrary connection of the following two structural formulas: ..................repeat unit I ...........repeating unit II The molar percentage of repeating unit I is 50-95%, and the molar percentage of repeating unit II is 5-50%.

2. A heterocyclic polyaramide according to claim 1 Process for the preparation of polyhydroxy aramide spun fibers, characterized in that: In step A, the organic solvent is one of N,N-dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone.

3. A heterocyclic polyaramide according to claim 1 Process for the preparation of polyhydroxy aramide spun fibers, characterized by the fact that: In step A, the co-solubilizing salt is at least one of LiCl or CaCl2, and the solid content of the co-solubilizing salt in the organic solvent is 1.0 to 7.5%.

4. A heterocyclic polyaramide according to claim 1 Process for the preparation of polyhydroxy aramide spun fibers, characterized by the fact that: In step A, the polymer mass of the polymer solution accounts for 2-4% of the total mass of the solution, and the dynamic viscosity at room temperature is 10,000-30,000 centipoise.

5. A heterocyclic polyaramide according to claim 1 Process for the preparation of polyhydroxy aramide spun fibers, characterized by the fact that: In step B, the coagulation bath uses an aqueous solution of N,N-dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone with a mass concentration of 15-60%.

6. A heterocyclic polyaramide Polybenzoxazole paper made from the heterocyclic polyaramide prepared according to any one of claims 1 to 5 Polyhydroxyaromatic amide spun fibers are produced, characterized in that: polyhydroxy aromatic polyamides polyhydroxy aromatic polyamide as-spun fibers, or heterocyclic polyaromatic polyamides polyhydroxy aromatic polyamide as-spun fibers are mixed with one or more of chopped fibers, pulp fibers, other as-spun fibers, and then converted into paper-based materials by a heat treatment process to yield heterocyclic polyaromatic polyamides polybenzoxazole paper.

7. A heterocyclic polyaramide according to claim 6 Polybenzoxazole paper, characterized by The other precipitation fibers include meta-aramid precipitation fibers, para-aramid precipitation fibers, heterocyclic aramid precipitation fibers, polyimide precipitation fibers, and polysulfone amide precipitation fibers.

8. A heterocyclic polyaramide according to claim 6 Polybenzoxazole paper, characterized by: The heat treatment temperature is 280℃~500℃, the heat treatment time is 15~60min, and the heat treatment atmosphere is an inert gas atmosphere or vacuum conditions.

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