Preparation process of meta-aramid spinning dope

Abstract

The present invention relates to the technical field of spinning dope, and particularly to a preparation process of meta-aramid spinning dope, which comprises the following steps: S1. Feed m-phenylenediamine into a tower kettle, and perform decolorization treatment through vacuum rectification. Remove high-boiling tar-like impurities by total reflux separation to obtain decolorized m-phenylenediamine; S2. First dissolve the decolorized m-phenylenediamine in dimethylacetamide, and then feed isophthaloyl chloride into a reactor through a pipeline for pre-polymerization reaction; S3. Continuously add isophthaloyl chloride to the filtered oligomer, introduce a composite catalyst, and perform post-polycondensation reaction to obtain a neutralized polymer slurry. After pressure filtration, meta-aramid spinning dope is obtained. The preparation process of the present invention can improve the quality and performance of the dope while improving production efficiency, thereby improving the quality of meta-aramid fibers.

Description

Technical Field

[0001] The present invention relates to the technical field of spinning dope, and particularly to a preparation process of meta-aramid spinning dope. Background Art

[0002] Meta-aramid, also known as poly(m-phenylene isophthalamide) fiber, is formed by the polycondensation of isophthaloyl chloride (IPC) and m-phenylenediamine (MPD). As a high-temperature resistant fiber developed early, widely used, mass-produced and rapidly developing, it has occupied an important position in the field of special fibers, and its total output ranks second. The molecular structural formula of meta-aramid fiber is:

[0003]

[0004] Meta-aramid is a linear macromolecule composed of amide groups connecting m-phenyl groups. In its crystal, hydrogen bonds exist on two planes and are arranged in a lattice-like pattern, thus forming a three-dimensional structure of hydrogen bridges. Due to the strong action of hydrogen bonds, meta-aramid has a stable chemical structure, superior heat resistance, excellent flame retardancy, chemical corrosion resistance, electrical insulation and mechanical properties, etc., and is an indispensable basic material in high-tech industrial fields such as aerospace, military fire protection, electronic communication, energy conservation and environmental protection, petrochemical industry, etc. The glass transition temperature Tg of meta-aramid fiber is 270 °C, and below 350 °C, no significant decomposition or carbonization occurs. In addition, when the environmental temperature exceeds 400 °C, the fiber will gradually lose its toughness, carbonize and finally decompose, but during this process, it will not produce molten droplets, thus reducing the fire risk. The production process of meta-aramid mainly includes two production processes: spinning dope preparation (polymerization process) and spinning, and the quality and stability of the spinning dope directly affect the stability of the spinning process and the fiber quality.

[0005] The invention patent with the publication number CN109400873A discloses a continuous polymerization method for preparing high-performance poly(m-phenylene isophthalamide), including pre-polymerization, neutralization, polymerization, neutralization, and filtration processes, and performing continuous low-temperature solution polymerization, which has the advantages of stable polymerization conditions, low energy consumption, and small investment. The invention patent with the publication number CN116813902A discloses a poly(m-phenylene isophthalamide) solution, a meta-aramid spinning dope and a preparation method thereof. By using another compound instead of dimethylacetamide (DMAC) as a solvent, low viscosity can also be achieved, allowing continuous production, and it can be used as a meta-aramid spinning dope. However, in the prior art, usually no catalyst or only a single catalyst, such as an acidic catalyst, a basic catalyst or a metal complex, etc., is used, resulting in a slow reaction rate, requiring a longer time to reach the required conversion rate, reducing the production efficiency, and also causing unnecessary side reactions, thereby affecting the properties of the spun fibers. Summary of the Invention

[0006] In order to solve the problems of lack of composite catalyst system and poor fiber properties mentioned in the above background technology, the present invention provides a preparation process of meta-aramid spinning dope.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A preparation process of meta-aramid spinning dope, comprising the following steps:

[0009] S1. Feed m-phenylenediamine (MPD) into the tower kettle, start the vacuum unit, slowly start the heat transfer oil, heat the tower kettle to the specified temperature. When the light component storage tank reaches 30% liquid level, start the bottom liquid pump to reflux to the tower, control the reflux flow rate for total reflux, remove high-boiling tar-like impurities, observe the color of the material in the tower discharge sight glass, open the discharge valve to feed the finished product metering storage tank. If the purity of MPD ≥ 99.98%, continue to discharge, and pump the decolorized MPD into the storage tank. If not, return it to the tower kettle for continuous decolorization. Among them, the waste gas generated by the decolorization of m-phenylenediamine is mainly m-phenylenediamine. After the decolorization waste gas is collected under negative pressure, it enters the tail gas treatment system at the front section of the polymerization workshop and the spinning workshop, and is discharged into the air after treatment. The residue generated by vacuum distillation is mainly composed of m-phenylenediamine and organic impurities, which are collected and disposed of centrally;

[0010] S2. Transport the decolorized m-phenylenediamine from the storage tank to the blending tank through a pipeline, first add dimethylacetamide (DMAC) for dissolution and then feed it into the reactor, and then put isophthaloyl chloride into the reactor through a pipeline. Under a nitrogen atmosphere, control the reaction conditions to carry out a prepolymerization reaction to generate oligomers and hydrogen chloride, carry out the first neutralization of hydrogen chloride, and carry out the first pressure filtration with a plate and frame filter press;

[0011] S3. Continuously add isophthaloyl chloride to the filtered oligomers, introduce a composite catalyst under the same conditions as the prepolymerization reaction, carry out a post-polycondensation reaction to generate poly(m-phenylene isophthalamide) and a small amount of hydrogen chloride, carry out the second neutralization of hydrogen chloride to obtain a neutralized polymer slurry, enter the spinning dope storage tank through a plate and frame filter press, recover DMAC and the catalyst, and obtain meta-aramid spinning dope.

[0012] Preferably, in the step S1, the temperature of the tower kettle is 190 - 200 °C, the pressure is (-0.09) - (-0.1) MPa, and when the color of the material becomes grayish white, carry out total reflux for 2 - 3 h.

[0013] Preferably, in the step S2, the pressure of the prepolymerization reaction is normal pressure, and the reaction temperature is (-10) - 30 °C.

[0014] Further, during both the first neutralization and the second neutralization, the pH value of the system is controlled to be < 7. Ammonia vapor is used for the first neutralization. The ammonia vapor is directly introduced into the pipeline after vaporizing the liquid ammonia in the steel cylinder. Hydrogen chloride reacts with the ammonia vapor to form microcrystalline ammonium chloride. After separating the ammonium chloride crystals by the first plate-and-frame filtration using a plate-and-frame filter press, the ammonium chloride is collected and dried and recovered in the closed room of the post-treatment workshop. Diethylamine is used for the second neutralization. The barreled diethylamine is pumped into the blending tank and then into the neutralization kettle. After neutralization, a small amount of diethylamine salt is dissolved in the DMAC solution. The diethylamine is recovered and used for the preparation of the composite catalyst. The incompletely filtered ammonium chloride is filtered out by the second plate-and-frame filtration using a plate-and-frame filter press.

[0015] Preferably, in step S3, the molar ratio of the oligomer to isophthaloyl chloride is 1:(0.8 - 1), and the content of the composite catalyst is 2 - 5 wt%.

[0016] Further, the composite catalyst in step S3 is prepared by the following steps:

[0017] A1. Under an inert atmosphere, dissolve the phenolic compound in excess ethanol, add ferric chloride, and stir and react at 60 - 70 °C for 4 - 10 h. Remove the solvent by rotary evaporation to obtain a polyphenol polymer, and its average molecular weight is determined by gel permeation chromatography to be 4000 - 7000 g / mol;

[0018] A2. Add the polyphenol polymer to excess tetrahydrofuran, add polydimethylsiloxane and an isocyanate coupling agent, stir and react at 70 - 80 °C for 2 - 4 h. While it is still hot, add ethylenediamine and 4-dimethylaminopyridine, stir and react at room temperature for 24 - 48 h, remove impurities, wash with ethanol 3 - 5 times, vacuum dry at 60 - 80 °C for 12 - 48 h, and heat-treat at 200 - 300 °C for 1 - 4 h under an inert atmosphere to obtain the composite catalyst.

[0019] Preferably, the mass ratio of the phenolic compound to ferric chloride is (5 - 7):(0.8 - 1.2).

[0020] Preferably, the phenolic compound is one of indane bisphenol, phloroglucinol, catechol, xylenol, 3-isopropylphenol, and p-cresol.

[0021] Preferably, the mass ratio of the polyphenol polymer, polydimethylsiloxane, and the isocyanate coupling agent is (10 - 15):(4 - 8):(1 - 3), and the mass ratio of ethylenediamine to 4-dimethylaminopyridine is (8 - 13):(2 - 4).

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. In the technical solution of the present invention, the polyphenol polymer backbone is mainly composed of phenolic hydroxyl (-OH) groups, which form abundant active sites on the molecular chain and can undergo chemical reactions with polydimethylsiloxane (PDMS) and isocyanate coupling agents to construct a stable composite structure. The specific reactions include the reactions between hydroxyl groups and ethylenediamine and isocyanate (-NCO), generating urethane (-NHCOO-) bonds, thereby enhancing the stability of the polymer backbone. The reaction equations are as follows:

[0024] Ar-OH + R-NCO → Ar-NHCOOR

[0025] NH2R + R'-NCO → NHCOOR′

[0026] The urethane bonds formed by the reaction of phenolic hydroxyl groups and ethylenediamine of the polyphenol polymer with isocyanate, as well as the introduction of PDMS segments, constitute a three-dimensional cross-linked network. This enhances the mechanical strength and thermal stability of the catalyst, and also provides abundant active sites, promoting the adsorption and activation of reactants. As a flexible segment, PDMS enhances the flexibility and solubility of the catalyst through silicon-oxygen bonds (Si-O-Si), contributing to the uniform dispersion of the catalyst in the reaction system and improving the overall catalytic efficiency.

[0027] 2. The composite catalyst forms an intermediate complex with m-phenylenediamine and m-phthaloyl chloride, reducing the activation energy of the reaction through coordination. The specific process is as follows:

[0028] Ar-NH2 + ClCO-Ar-COCl → Ar-NH-CO-Ar-CO-NH-Ar

[0029] Among them, the ligand stabilizes the intermediate complex, reduces the free energy barrier of the reaction, and accelerates the polymerization reaction. In addition, the unique structure on the catalyst surface guides the reactants to arrange in a specific direction. The specific structure is as follows: -(Ar-NH-CO-Ar-CO-) n , which helps to form regular polymer chains and improve the molecular weight of the polymer and the uniformity of its distribution. At the same time, the PDMS segments stabilize the reaction intermediates and transition states through steric hindrance effects and coordination, preventing side reactions from occurring. One of the reaction equations is:

[0030] Ar-NH-CO-Ar-CO-NH-Ar + Ar-NH2 → Ar-NH-CO-Ar-CO-NH-Ar-NH2

[0031] In this process, the PDMS segments provide effective spatial protection, avoiding unnecessary side reactions and improving selectivity and efficiency.

[0032] 3. By performing decolorization treatment on m-phenylenediamine, high-boiling tar-like impurities are effectively removed, significantly improving the purity of the raw material. This not only facilitates the subsequent polymerization reaction but also enhances the quality of the final product. High-purity m-phenylenediamine can reduce side reactions during the polymerization process, making the polymerization reaction more controllable, and thus obtaining meta-aramid with more excellent properties.

[0033] 4. The effective recovery and utilization of DMAC, ethylenediamine, and the catalyst not only reduce production costs but also decrease environmental pollution. The recovered DMAC and catalyst can be reused in the polymerization reaction, and the recovered ethylenediamine can be used in the production of the catalyst, realizing the recycling of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0035] Figure 1 It is a process flow chart for preparing meta-aramid spinning dope. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the present invention are all conventional products purchased from the market.

[0037] Preparation Example 1

[0038] The composite catalyst is prepared through the following steps:

[0039] A1. Under an inert atmosphere, 5 kg of p-cresol is dissolved in an excessive amount of ethanol, 0.8 kg of ferric chloride is added, and the mixture is stirred and reacted at 60°C for 4 h. The solvent is removed by rotary evaporation to obtain a polyphenol polymer.

[0040] A2. 10 kg of the polyphenol polymer is added to an excessive amount of tetrahydrofuran, 4 kg of polydimethylsiloxane and 1 kg of toluene diisocyanate are added, and the mixture is stirred and reacted at 70°C for 2 h. While it is still hot, 8 kg of ethylenediamine and 2 kg of 4-dimethylaminopyridine are added, and the mixture is stirred and reacted at room temperature for 24 h. Impurities are removed, and it is washed 3 times with ethanol, vacuum dried at 60°C for 12 h, and heat-treated at 200°C for 1 h under an inert atmosphere to obtain the composite catalyst.

[0041] Preparation Example 2

[0042] The composite catalyst was prepared by the following steps:

[0043] A1. Under an inert atmosphere, 6 kg of p-cresol was dissolved in an excessive amount of ethanol, 1 kg of ferric chloride was added, and the mixture was stirred and reacted at 65 °C for 7 h. The solvent was removed by rotary evaporation to obtain a polyphenol polymer;

[0044] A2. 12.5 kg of the polyphenol polymer was added to an excessive amount of tetrahydrofuran, 6 kg of polydimethylsiloxane and 2 kg of toluene diisocyanate were added, and the mixture was stirred and reacted at 75 °C for 3 h. While it was still hot, 10.5 kg of ethylenediamine and 3 kg of 4-dimethylaminopyridine were added, and the mixture was stirred and reacted at room temperature for 36 h. Impurities were removed, and it was washed 4 times with ethanol, vacuum dried at 70 °C for 24 h, and heat-treated at 250 °C for 2.5 h under an inert atmosphere to obtain the composite catalyst.

[0045] Preparation Example 3

[0046] The composite catalyst was prepared by the following steps:

[0047] A1. Under an inert atmosphere, 7 kg of xylenol was dissolved in an excessive amount of ethanol, 1.2 kg of ferric chloride was added, and the mixture was stirred and reacted at 70 °C for 10 h. The solvent was removed by rotary evaporation to obtain a polyphenol polymer;

[0048] A2. 15 kg of the polyphenol polymer was added to an excessive amount of tetrahydrofuran, 8 kg of polydimethylsiloxane and 3 kg of toluene diisocyanate were added, and the mixture was stirred and reacted at 80 °C for 4 h. While it was still hot, 13 kg of ethylenediamine and 4 kg of 4-dimethylaminopyridine were added, and the mixture was stirred and reacted at room temperature for 48 h. Impurities were removed, and it was washed 5 times with ethanol, vacuum dried at 80 °C for 48 h, and heat-treated at 300 °C for 4 h under an inert atmosphere to obtain the composite catalyst.

[0049] Example 1

[0050] A preparation process for meta-aramid spinning dope includes the following steps:

[0051] S1. 3 tons of MPD was introduced into the tower kettle, the vacuum unit was started, and the negative pressure was pumped to -0.09 MPa. The heat transfer oil was slowly turned on, and the tower kettle was heated to 190 °C. When the light component storage tank reached 30% liquid level, the bottom liquid pump was started to reflux to the tower, and the reflux flow rate was controlled for total reflux to remove high-boiling tar-like impurities. Observe the color of the material in the tower discharge sight glass. When the color of the material becomes grayish white, perform total reflux for another 2 h. Open the discharge valve to feed the finished product metering storage tank. If the purity of MPD ≥ 99.98%, continue to discharge, and pump the decolorized MPD into the storage tank. If it does not reach the requirement, return it to the tower kettle for continuous decolorization;

[0052] S2. Transfer the decolorized m-phenylenediamine from the storage tank to the blending tank through a pipeline. First, add an excessive amount of dimethylacetamide (DMAC) for dissolution and then introduce it into the reactor. Then, add 10 wt% of isophthaloyl chloride into the reactor through a pipeline. Under a nitrogen atmosphere, control the reaction temperature at -10 °C and carry out a prepolymerization reaction under normal pressure to generate oligomers and hydrogen chloride. Use ammonia vapor to neutralize the hydrogen chloride for the first time, and perform the first pressure filtration with a plate and frame filter press.

[0053] S3. Continuously add isophthaloyl chloride to the filtered oligomers with a molar ratio of 1:0.8. Under the same conditions as the prepolymerization reaction, introduce 2 wt% of the composite catalyst prepared in Preparation Example 1 and carry out a post-polycondensation reaction to generate poly(m-phenylene isophthalamide) and a small amount of hydrogen chloride. Use ethylenediamine to neutralize the hydrogen chloride for the second time to obtain a neutralized polymer slurry, which enters the stock solution storage tank through a plate and frame filter press to obtain the m-aramid spinning dope.

[0054] Example 2

[0055] A preparation process for m-aramid spinning dope, comprising the following steps:

[0056] S1. Feed 3 tons of MPD into the bottom of the tower, start the vacuum unit, evacuate to -0.097 MPa under negative pressure, slowly turn on the heat transfer oil, and heat the bottom of the tower to 198 °C. When the light component storage tank reaches 30% liquid level, start the bottom liquid pump to reflux to the tower, control the reflux flow rate for total reflux, remove high-boiling tar-like impurities, observe the color of the material in the tower discharge sight glass. When the color of the material becomes grayish white, carry out total reflux for another 2.5 h. Open the discharge valve to feed the finished product into the metering storage tank. If the purity of MPD ≥ 99.98%, continue to discharge, and pump the decolorized MPD into the storage tank. If it does not meet the requirement, return it to the bottom of the tower for continuous decolorization;

[0057] S2. Transfer the decolorized m-phenylenediamine from the storage tank to the blending tank through a pipeline. First, add an excessive amount of dimethylacetamide (DMAC) for dissolution and then introduce it into the reactor. Then, add 15 wt% of isophthaloyl chloride into the reactor through a pipeline. Under a nitrogen atmosphere, control the reaction temperature at 5 °C and carry out a prepolymerization reaction under normal pressure to generate oligomers and hydrogen chloride. Use ammonia vapor to neutralize the hydrogen chloride for the first time, and perform the first pressure filtration with a plate and frame filter press.

[0058] S3. Continuously add isophthaloyl chloride to the filtered oligomers with a molar ratio of 1:0.9. Under the same conditions as the prepolymerization reaction, introduce 3.5 wt% of the composite catalyst prepared in Preparation Example 2 and carry out a post-polycondensation reaction to generate poly(m-phenylene isophthalamide) and a small amount of hydrogen chloride. Use ethylenediamine to neutralize the hydrogen chloride for the second time to obtain a neutralized polymer slurry, which enters the stock solution storage tank through a plate and frame filter press to obtain the m-aramid spinning dope.

[0059] Example 3

[0060] A preparation process of meta-aramid spinning dope, comprising the following steps:

[0061] S1. Feed 3 tons of MPD into the tower kettle, start the vacuum unit, evacuate to -0.99 MPa under negative pressure, slowly turn on the heat-conducting oil, heat the tower kettle to 199 °C. When the light component storage tank reaches 30% liquid level, start the bottom liquid pump to reflux to the tower, control the reflux flow rate for total reflux, remove high-boiling tar-like impurities, observe the color of the material in the tower discharge sight glass. When the color of the material becomes grayish-white, conduct total reflux for another 3 h. Open the discharge valve to feed the finished product metering storage tank. If the purity of MPD ≥ 99.98%, continue discharging, pump the decolorized MPD into the storage tank, if not reached, return it to the tower kettle for continuous decolorization;

[0062] S2. Transfer the decolorized m-phenylenediamine from the storage tank to the blending tank through a pipeline. First, add an excessive amount of dimethylacetamide (DMAC) for dissolution and then feed it into the reactor. Then, put 18 wt% of isophthaloyl chloride into the reactor through a pipeline. Under a nitrogen atmosphere, control the reaction temperature at 10 °C and carry out a pre-polymerization reaction at atmospheric pressure to generate oligomers and hydrogen chloride. Use ammonia steam to conduct the first neutralization of hydrogen chloride, and conduct the first pressure filtration with a plate and frame filter press;

[0063] S3. Continuously add isophthaloyl chloride to the filtered oligomers with a molar ratio of 1:0.98. Under the same conditions as the pre-polymerization reaction, feed 4 wt% of the composite catalyst prepared in Preparation Example 3 to carry out a post-polycondensation reaction to generate poly(m-phenylene isophthalamide) and a small amount of hydrogen chloride. Use ethylenediamine to conduct the second neutralization of hydrogen chloride to obtain a neutralized polymer slurry, which enters the dope storage tank through a plate and frame filter press to obtain meta-aramid spinning dope.

[0064] Example 4

[0065] A preparation process of meta-aramid spinning dope, comprising the following steps:

[0066] S1. Feed 3 tons of MPD into the tower kettle, start the vacuum unit, evacuate to -0.1 MPa under negative pressure, slowly turn on the heat-conducting oil, heat the tower kettle to 200 °C. When the light component storage tank reaches 30% liquid level, start the bottom liquid pump to reflux to the tower, control the reflux flow rate for total reflux, remove high-boiling tar-like impurities, observe the color of the material in the tower discharge sight glass. When the color of the material becomes grayish-white, conduct total reflux for another 3 h. Open the discharge valve to feed the finished product metering storage tank. If the purity of MPD ≥ 99.98%, continue discharging, pump the decolorized MPD into the storage tank, if not reached, return it to the tower kettle for continuous decolorization;

[0067] S2. Transfer the decolorized m-phenylenediamine from the storage tank to the blending tank through a pipeline. First, add an excessive amount of dimethylacetamide (DMAC) for dissolution and then introduce it into the reactor. Next, add 20 wt% of isophthaloyl chloride into the reactor through a pipeline. Under a nitrogen atmosphere, control the reaction temperature at 30 °C and carry out a prepolymerization reaction under normal pressure to generate oligomers and hydrogen chloride. Use ammonia vapor to neutralize the hydrogen chloride for the first time and perform the first pressure filtration with a plate and frame filter press.

[0068] S3. Continuously add isophthaloyl chloride to the filtered oligomers with a molar ratio of 1:1. Under the same conditions as the prepolymerization reaction, introduce 5 wt% of the composite catalyst prepared in Preparation Example 3 and carry out a post-polycondensation reaction to generate poly(m-phenylene isophthalamide) and a small amount of hydrogen chloride. Use ethylenediamine to neutralize the hydrogen chloride for the second time to obtain a neutralized polymer slurry, which enters the stock solution storage tank through a plate and frame filter press to obtain the m-aramid spinning dope.

[0069] Comparative Example 1

[0070] The difference between this comparative example and Preparation Example 1 is that phenolic compounds are not added, and the remaining steps are the same as those in Example 1.

[0071] Comparative Example 2

[0072] The difference between this comparative example and Preparation Example 2 is that polydimethylsiloxane is not added, and the remaining steps are the same as those in Example 2.

[0073] Comparative Example 3

[0074] The difference between this comparative example and Preparation Example 3 is that isocyanate coupling agents are not added, and the remaining steps are the same as those in Example 3.

[0075] Comparative Example 4

[0076] The difference between this comparative example and Preparation Example 1 is that ethylenediamine is not added, and the remaining steps are the same as those in Example 1.

[0077] Comparative Example 5

[0078] The difference between this comparative example and Example 1 is that the composite obtained in Comparative Example 1 is used, and the remaining steps are the same as those in Example 1.

[0079] Comparative Example 6

[0080] The difference between this comparative example and Example 2 is that the composite obtained in Comparative Example 2 is used, and the remaining steps are the same as those in Example 2.

[0081] Comparative Example 7

[0082] The difference between this comparative example and Example 3 is that the composite obtained in Comparative Example 3 is used, and the remaining steps are the same as those in Example 3.

[0083] Comparative Example 8

[0084] The difference between this comparative example and Example 4 is that the composite prepared in Comparative Example 4 is used, and the remaining steps are the same as those in Example 4.

[0085] According to the preparation methods of Examples 1-4 and Comparative Examples 5-8, continuous production of meta-aramid spinning dope was carried out for 12 h. 500 g was randomly selected as a sample for performance testing, and the results are shown in Table 1:

[0086] Table 1. Test Results of the Dope Properties of Examples 1-4 and Comparative Examples 5-8

[0087]

[0088] Among them, the viscosity was measured with a viscometer, the molecular weight distribution was measured by gel permeation chromatography (Waters Alliancee2695 GPC / SEC system), and the thermal stability was measured by thermogravimetric analysis (TGA PT1600).

[0089] Each sample was spun, and the product specifications were 3.56 dtex × 69 mm. Referring to GB / T 31889-2015 "Meta-aramid Staple Fibers", the spun fibers were evaluated for quality, and the results are shown in Table 2:

[0090] Table 2. Test Results of the Fiber Properties of Examples 1-4 and Comparative Examples 5-8

[0091]

[0092] As can be seen from Table 1, the viscosities of the examples are generally higher than those of the comparative examples. This may be because the addition of the composite catalyst increases the molecular weight of the polymer, thereby increasing the viscosity of the dope. Viscosity is an important factor affecting spinning performance, and a higher viscosity usually means better spinning performance. The molecular weight distribution (Mw / Mn) of the examples is relatively narrower, indicating that the polymer molecular chains are more uniform, which helps to improve the quality and performance of the spun fibers. The molecular weight distribution in the comparative examples is wider, probably due to the lack of the regulatory effect of the composite catalyst. The thermal stability temperature of the examples is higher, indicating that the composite catalyst may improve the thermal stability of the polymer, which is very important for the heat resistance during the spinning process.

[0093] As can be seen from Table 2, the breaking strength of the examples is significantly higher than that of the comparative examples, which may be due to the addition of the composite catalyst enhancing the strength and uniformity of the polymer chains. The linear density deviation rate and length deviation rate of the examples are better than those of the comparative examples, indicating that the uniformity and consistency of the fibers are improved after using the composite catalyst. The ultra-long fiber rate and the content of double-length fibers in the examples are relatively low, indicating that the fiber lengths are more uniform, which is beneficial to improving the processing performance of the fibers and the quality of the final products. The difference in the defect content among the samples is not significant, but the examples are slightly better than the comparative examples, indicating that the composite catalyst may be helpful in reducing defects. The dry heat shrinkage rate of the examples is significantly lower than that of the comparative examples, indicating that the composite catalyst may improve the thermal stability of the fibers.

[0094] The composite catalyst added in Examples 1-4 may have improved the molecular weight and the uniformity of the molecular weight distribution of the polymer by promoting the uniformity and efficiency of the polymerization reaction, thereby enhancing the mechanical properties and thermal stability of the fibers. Components such as polyphenol polymer, polydimethylsiloxane, toluene diisocyanate, and ethylenediamine in the composite catalyst may have produced a synergistic effect, jointly promoting the growth and uniformity of the polymer chains. Due to the improvement of the spinning dope properties, the uniformity and consistency of the fibers during the spinning process are improved, thus affecting the various performance indicators of the final fiber products. In addition, in the comparative examples, it may be that the reaction was not sufficient within the specified time, resulting in a significant difference in performance compared with the examples.

[0095] In summary, by comparing and analyzing the spinning dope properties and fiber property data of the examples and the comparative examples, it can be inferred that the meta-aramid spinning dope prepared in Examples 1-4 has good properties and can improve the quality and performance of the fibers while increasing the production efficiency.

[0096] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered by the protection scope of the present invention.

Claims

1. A process for preparing a meta-aramid spinning solution, characterized in that: It includes the following steps: S1. Feed m-phenylenediamine into the bottom of the column, perform decolorization treatment by vacuum distillation, and separate and remove high-boiling tar-like impurities by total reflux to obtain decolorized m-phenylenediamine with a purity ≥99.98%; S2. First dissolve the decolorized m-phenylenediamine in dimethylacetamide, then feed isophthaloyl chloride into the reactor through a pipeline, and under an inert atmosphere, control the reaction conditions to carry out a prepolymerization reaction and perform the first neutralization of hydrogen chloride; S3. Continuously add isophthaloyl chloride to the filtered oligomer, introduce a complex catalyst under the same conditions as the prepolymerization reaction to carry out a post-polycondensation reaction, perform the second neutralization of hydrogen chloride to obtain a neutralized polymer slurry, and enter the stock solution storage tank through a filter press to obtain meta-aramid spinning stock solution; The complex catalyst in step S3 is prepared by the following steps: A1. Under an inert atmosphere, dissolve a phenolic compound in excessive ethanol, add ferric chloride, stir and react at 60 - 70°C for 4 - 10 h, remove the solvent by rotary evaporation to obtain a polyphenol polymer; A2. Add the polyphenol polymer to excessive tetrahydrofuran, add polydimethylsiloxane and an isocyanate coupling agent, stir and react at 70 - 80°C for 2 - 4 h, add ethylenediamine and 4-dimethylaminopyridine while it is hot, stir and react at room temperature for 24 - 48 h, remove impurities, wash with ethanol 3 - 5 times, vacuum dry at 60 - 80°C for 12 - 48 h, and heat-treat at 200 - 300°C for 1 - 4 h under an inert atmosphere to obtain the complex catalyst.

2. The preparation process of the meta-aramid spinning dope according to claim 1, characterized in that, In step S1, the temperature of the bottom of the column is 190 - 200°C, the pressure is (-0.09) - (-0.1) MPa, and when the color of the material turns grayish white, perform total reflux for 2 - 3 h.

3. The preparation process of a meta-aramid spinning dope according to claim 1, characterized in that, In step S2, the pressure of the prepolymerization reaction is normal pressure, and the reaction temperature is (-10) - 30°C.

4. The preparation process of the meta-aramid spinning dope according to claim 1, characterized in that, During both the first neutralization and the second neutralization, control the pH value of the system <7. The first neutralization uses ammonia vapor, and the second neutralization uses diethylamine.

5. The preparation process of a meta-aramid spinning dope according to claim 1, characterized in that, In step S3, the molar ratio of the oligomer to isophthaloyl chloride is 1:(0.8 - 1), and the content of the complex catalyst is 2 - 5 wt%.

6. The preparation process of a meta-aramid spinning dope according to claim 1, characterized in that, The mass ratio of the phenolic compound to ferric chloride is (5 - 7):(0.8 - 1.2).

7. A preparation process of meta-aramid spinning dope according to claim 1, characterized in that, The phenolic compound is one of indane bisphenol, phloroglucinol, catechol, xylenol, 3-isopropylphenol, and p-cresol.

8. The preparation process of the meta-aramid spinning dope according to claim 1, characterized in that, The mass ratio of the polyphenol polymer, polydimethylsiloxane, and the isocyanate coupling agent is (10 - 15):(4 - 8):(1 - 3), and the mass ratio of ethylenediamine to 4-dimethylaminopyridine is (8 - 13):(2 - 4).

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