A polyamide-imide fiber, a method for preparing the same, and an application thereof

Abstract

The present application relates to a kind of polyamide-imide fibers and its preparation method and application, with the quick reaction of isocyanate under the action of weak organic base catalyst and trimellitic anhydride monomer, and the amine monomer containing disulfide bond is added, the high solid content polyamide-imide spinning solution is realized by microreactor quick synthesis, and directly transported to dry spinning system to prepare the polyamide-imide fiber based on disulfide bond with self-repairing characteristics.It avoids the problems of low efficiency, high cost and other problems in traditional batch process, and the continuous synthesis of microreactor is beneficial to the preparation of high molecular weight polyamide-imide fiber, with excellent mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of fiber technology, and specifically relates to a polyamide-imide fiber, its preparation method, and its application. Background Technology

[0002] Polyamide-imide (PAI) was first developed as a molding compound by Amoco in the United States in 1972 and commercialized under the brand name Torlon in 1976. The main chain of PAI contains both amide and imide rings as structural units. In terms of performance, it possesses some of the advantages of both PA and PI, such as high temperature resistance, corrosion resistance, wear resistance, excellent mechanical properties, and the ability to be compounded with various materials. Therefore, polyamide-imide fiber (PAI fiber) is a high-performance fiber with wide applications in aerospace, electrical and electronic industries, high-temperature cables, the automotive industry, high-temperature filtration, and marine engineering.

[0003] Currently, there is considerable research on PAI fibers, but limited research on their self-healing properties. Improving the self-healing ability of these fibers, building upon their excellent heat resistance and acid / alkali corrosion resistance, would be of significant value in expanding their application areas. In the field of self-healing based on dynamic covalent bonds, disulfide bonds are an effective approach. A disulfide bond is a dynamic covalent bond formed by the coupling of two thiol groups. Due to the extreme instability of disulfide bonds, their exchange reactions can be initiated by various stimuli (heat, light, and external free radicals, etc.), causing them to recombine with other sulfur atoms. This leads to self-healing through redox reactions between the disulfide bond and thiol groups. By copolymerizing with monomers containing disulfide bonds, PAI fibers can be efficiently prepared and endowed with a certain degree of self-healing ability, offering advantages for expanding the fiber's application areas.

[0004] For the preparation of polyamide-imide spinning solutions, the traditional isocyanate method uses trimellitic anhydride (TMA) and diisocyanate as raw materials to perform polycondensation in a high-boiling-point solvent to prepare PAI materials. This method directly reacts equimolar amounts of TMA and diisocyanate in a high-boiling-point solvent to synthesize PAI with a high degree of polymerization. The polymerization process is direct and has a high degree of polymerization, but the cyclization reaction in the polymerization stage involves a seven-membered ring intermediate, requiring not only higher temperatures but also more time. Therefore, a polymerization reactor is needed to prepare the spinning solution, and the requirements for the polymerization reactor are relatively high.

[0005] Microreactors are miniature reaction systems with characteristic dimensions at the micrometer level, fabricated using precision microfabrication technology. These reactors are not simply miniaturized devices, but rather, through their unique microstructure, they can fundamentally alter the heat transfer, mass transfer, and mixing characteristics during the reaction process, thereby achieving more efficient, safer, and more precise chemical synthesis. At the same time, their extremely high specific surface area enables extremely high heat and mass transfer efficiency during polymerization reactions, and therefore they have been widely used in the polymerization reactions of many polymer materials. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a polyamide-imide fiber, its preparation method and application, and particularly relates to a polyamide-imide fiber and its continuous preparation method and application.

[0007] This invention provides a method for preparing polyamide-imide fibers, comprising:

[0008] Step (1) Prepare solutions A, B and C respectively;

[0009] Solution A includes monomer A and solvent; solution B includes monomer B, solvent and catalyst; solution C includes monomer C and solvent; wherein monomer A includes one or more of carboxylic acids and carboxylic acid derivatives; monomer B includes isocyanate; monomer C includes amine monomers containing disulfide bonds; the catalyst is an organic weak base catalyst; and the solvents are all selected from polar aprotic solvents.

[0010] Step (2) Inject solutions A, B and C into the microreactor to react and obtain spinning solution. Spinning is performed directly to obtain nascent fibers. After segmented thermal stretching, polyamide-imide fibers are obtained. The microreactor is equipped with three temperature sections, with the first section temperature being 20-25℃, the second section temperature being 45-55℃ and the third section temperature being 75-85℃.

[0011] Preferably, monomer A in step (1) includes , , One or more of them.

[0012] Preferably, monomer B in step (1) includes , , , , , One or more of them.

[0013] Preferably, the monomer C includes , , One or more of them.

[0014] Preferably, the organic weak base catalyst in step (1) is one or more of triethylenediamine, 4-dimethylaminopyridine, and 1,2-dimethylimidazole.

[0015] In step (1), the mass fraction of the catalyst in solution B is 0.3-0.5 wt%.

[0016] Preferably, the polar aprotic solvent in step (1) includes one or more of N-methylpyrrolidone (NMP) and N,N-dimethylacetamide (DMAc).

[0017] In step (1), the mass fraction of the reaction system is 15-40 wt%, which is the mass percentage of the overall monomer.

[0018] In step (2), the injection rate ratio of solution A, solution B and solution C is 1:(0.9-0.8):(0.2-0.1).

[0019] The molar ratio of monomers is controlled by adjusting the delivery rate.

[0020] In step (2), the microreactor is equipped with a three-stage temperature system, which means the microreactor is in a segmented oil bath heating system.

[0021] The microreactor has a pore size of 500 μm.

[0022] In step (2), the injection rate of solution A into the microreactor is controlled at 100-200 ml / min.

[0023] In step (2), the transport time of the microreactor is 5-25 min, which is also the reaction time of 5-25 min.

[0024] Step (2) involves spinning to obtain nascent fibers, where the spinning solution enters the dry spinning channel through a spinneret and is extruded and wound to obtain nascent fibers. The channel is heated in three sections, with the first section having a temperature of 100-140 ℃, the second section having a temperature of 150-190 ℃, and the third section having a temperature of 200-240 ℃. The total residence time of the spinning solution in the channel is 3-6 s.

[0025] The tunnel is heated in three sections from the top.

[0026] Furthermore, the spinning solution is fed into the dry spinning tunnel through the spinneret and then into the dry spinning tunnel.

[0027] The extrusion rate of the spinning solution is 50-300 ml / min.

[0028] The winding speed is 200-500 m / min.

[0029] In step (2), the molecular weight of the spinning solution reaches 50,000-100,000 and the apparent viscosity is 150,000-300,000 mPa·s.

[0030] In step (2), the segmented stretching is a two-stage stretching process, with the first stage at 160-190 ℃ and a stretching of 1.0-2.25 times, followed by the second stage at 200-300 ℃ and a stretching of 1.25-2.25 times for 3-5 seconds.

[0031] The two-stage drawing process involves the nascent fibers passing through two drawing furnaces and undergoing two-stage heating.

[0032] This invention provides a polyamide-imide fiber prepared by the method described above.

[0033] The polyamide-imide fiber has a tensile strength of 6-15 cN / dtex, a modulus of 150-500 cN / dtex, and an elongation at break of 30%-70%.

[0034] The polyamide-imide fiber has a self-healing efficiency of ≥85% at 150 °C.

[0035] This invention provides an application of the polyamide-imide fiber in the fields of aerospace, electrical and electronic industries, high-temperature cables, automotive industry, high-temperature filtration, and marine engineering.

[0036] This invention is based on the rapid reaction of isocyanates with trimellitic anhydride monomers under the action of a weak organic base catalyst, and incorporates amine monomers containing disulfide bonds. A high-solids-content polyamide-imide spinning solution is rapidly synthesized via a microreactor and directly transported to a dry spinning system to prepare polyamide-imide fibers with self-healing properties based on disulfide bonds. This method avoids the problems of low efficiency and high cost associated with traditional batch processes. Furthermore, the continuous synthesis using a microreactor facilitates the preparation of high-molecular-weight polyamide-imide fibers with excellent mechanical properties. Simultaneously, the self-healing ability of the fibers enhances their service safety, making them promising for applications in aerospace, electrical and electronic industries, high-temperature cables, the automotive industry, high-temperature filtration, and marine engineering.

[0037] Beneficial effects: (1) By copolymerizing monomers containing disulfide bonds, the present invention enables polyamide-imide PAI fibers to have a certain self-repair function, which also enhances the strength of the fibers. After the broken polyamide-imide PAI fibers are self-repaired at 150°C for 24 hours, the repair efficiency can reach more than 85%, which is of great help to expand the application field of polyamide-imide PAI fibers.

[0038] (2) The present invention carries out the polymerization reaction in a microreactor and directly delivers the solution to the spinneret through micron-sized channels. By using a microreactor reaction, the reaction temperature is reduced from the traditional 150 ℃ to segmented temperatures of 20-25 ℃, 45-55 ℃ and 75-85 ℃. The microreactor transport time replaces the polymerization kettle reaction time, which reduces the requirements for the polymerization reaction. At the same time, the storage process is eliminated, reducing the degradation and water absorption of the spinning solution during storage, making continuous production possible.

[0039] (3) The present invention heats the spinning solution in stages through multiple spinning channels, so that the spinning solution is heated in a stepwise manner. The organic weak base catalyst added to the system undergoes a catalytic reaction in the first channel at 100-120 ℃ and the second channel at 140-160 ℃. In particular, in the first channel, it effectively promotes the removal of CO2 from the seven-membered ring intermediate in the polyamide-imide spinning solution, turning it into a stable five-membered ring, stabilizing the molecular chain structure, and improving the strength of the fiber when it is solidified and formed. Attached Figure Description

[0040] Figure 1 The reaction flow chart is for the preparation in Example 1.

[0041] Figure 2 Photograph of the polyamide-imide fiber prepared in Example 1.

[0042] Figure 3 The stress-strain curves of the polyamide-imide fiber prepared in Example 1 before and after self-healing are shown. Detailed Implementation

[0043] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0044] Trimeric triglyceride was provided by Shanghai Titan Co., Ltd.; diisocyanate was provided by Shandong Baiqian Chemical Co., Ltd.; disulfide bond-containing monomers were provided by Shanghai Haohong Biomedical Technology Co., Ltd.; and organic weak base catalysts were provided by Shanghai Yien Chemical Technology Co., Ltd.

[0045] Mechanical properties were tested using an XD-1 fineness tester and an XQ-1C monofilament tensile tester. The clamping distance of the tensile tester was 20 mm, the tensile speed was 20 mm / min, and each sample was tested ten times. The maximum and minimum values ​​were removed, and the average value was taken.

[0046] Example 1

[0047] Under nitrogen protection, trimellitic anhydride (TMA), diphenylmethane diisocyanate (MDI) stored at 47.5℃, and 2,2'-dithiodiethylamine (L-1591) were dissolved in DMAc, respectively. The extrusion rate ratio of TMA / MDI / L-1591 was controlled at 1:0.9:0.1, and the mass fraction of the reaction system was 30 wt%. Triethylenediamine (0.3 wt%) was added to the MDI solution. The three monomer solutions were injected into the microreactor system, with the TMA injection rate at 150 ml / min. After injection, the solution was conveyed to the spinneret assembly and heated in a three-stage oil bath at 20℃, 50℃, and 80℃ for 20 min. The polyamide-imide spinning solution in the microreactor was conveyed to the spinneret assembly, extruded from the spinneret into the channel, and nascent fibers were obtained through extrusion and winding. The temperatures of the three sections of the channel were controlled at 100℃, 160℃, and 220℃, respectively. The polyamide-imide spinning solution was kept in the tunnel for a total residence time of 4 s at ℃, and the winding speed was 300 m / min. The nascent fibers were then subjected to two-stage drawing in a drawing furnace, with drawing ratios of 1.25 and 2.25, and drawing temperatures of 180 ℃ and 240 ℃, respectively, to obtain polyamide-imide fibers.

[0048] Example 2

[0049] Under nitrogen protection, TMA and MDI stored at 47.5℃, L-1591 were dissolved in DMAc, respectively. The extrusion rate ratio of TMA / MDI / L-1591 was controlled at 1:0.85:0.15, and the mass fraction of the reaction system was 25 wt%. Triethylenediamine (TDI) with a mass fraction of 0.5 wt% was added to the MDI solution. The three monomer solutions were injected into the microreactor system, with the TMA injection rate at 175 ml / min. After injection, the solution was conveyed to the spinneret and heated in a three-stage oil bath at 20℃, 50℃, and 80℃ for 18 min. The polyamide-imide spinning solution in the microreactor was then conveyed to the spinneret and extruded into the channel through the spinneret. After extrusion and winding, nascent fibers were obtained. The temperatures of the three sections of the channel were controlled at 100℃, 150℃, and 200℃, and the total residence time of the polyamide-imide spinning solution in the channel was 3 minutes. The nascent fibers were wound at a speed of 500 m / min. The nascent fibers were then subjected to two-stage drawing in a drawing furnace, with drawing ratios of 1.25 and 2.00, and drawing temperatures of 160℃ and 200℃, respectively, to obtain polyamide-imide fibers.

[0050] Example 3

[0051] Under nitrogen protection, TMA and toluene diisocyanate (TDI) L-1591 stored at 40°C were dissolved in DMAc, respectively. The extrusion rate ratio of TMA / TDI / L-1591 was controlled at 1:0.9:0.1, and the mass fraction of the reaction system was 30 wt%. Triethylenediamine (TDI) with a mass fraction of 0.3 wt% was added to the TDI solution. The three monomer solutions were injected into the microreactor system, with the TMA injection rate at 150 ml / min. After injection, the solution was conveyed to the spinneret assembly and heated in a three-stage oil bath at 20°C, 55°C, and 80°C for 20 min. The polyamide-imide spinning solution in the microreactor was then conveyed to the spinneret assembly, extruded from the spinneret into the channel, and nascent fibers were obtained through extrusion and winding. The temperatures of the three sections of the channel were controlled at 100°C, 160°C, and 220°C, and the total residence time of the polyamide-imide spinning solution in the channel was 4 minutes. The nascent fibers were wound at a speed of 300 m / min. The nascent fibers were then subjected to two-stage drawing in a drawing furnace, with drawing ratios of 1.25 and 2.25, and drawing temperatures of 160℃ and 220℃, respectively, to obtain polyamide-imide fibers.

[0052] Example 4

[0053] Under nitrogen protection, TMA and MDI stored at 47.5℃, L-1591 were dissolved in DMAc, respectively. The extrusion rate ratio of TMA / MDI / L-1591 was controlled at 1:0.8:0.2, and the mass fraction of the reaction system was 25 wt%. 0.3 wt% of 4-dimethylaminopyridine was added to the MDI solution. The three monomer solutions were injected into the microreactor system, with the TMA injection rate at 125 ml / min. After injection, the solution was conveyed to the spinneret assembly and heated in a three-stage oil bath at 25℃, 55℃, and 85℃ for 30 min. The polyamide-imide spinning solution in the microreactor was then conveyed to the spinneret assembly, extruded from the spinneret into the channel, and nascent fibers were obtained through extrusion and winding. The temperatures of the three sections of the channel were controlled at 140℃, 180℃, and 220℃, and the total residence time of the polyamide-imide spinning solution in the channel was 5 minutes. The nascent fibers were wound at a speed of 300 m / min. The fibers were then subjected to two-stage drawing in a drawing furnace with drawing ratios of 1.00 and 1.75, and drawing temperatures of 180 °C and 240 °C, respectively, to obtain polyamide-imide fibers.

[0054] Example 5

[0055] Under nitrogen protection, TMA and TDI stored at 40℃, L-1591 were dissolved in DMAc, respectively. The extrusion rate ratio of TMA / TDI / L-1591 was controlled at 1:0.9:0.1, and the mass fraction of the reaction system was 30 wt%. 0.5 wt% of 4-dimethylaminopyridine was added to the TDI solution. The three monomer solutions were injected into the microreactor system, with the TMA injection rate at 125 ml / min. After injection, the solution was conveyed to the spinneret assembly and heated in a three-stage oil bath at 20℃, 50℃, and 80℃ for 30 min. The polyamide-imide spinning solution in the microreactor was conveyed to the spinneret assembly, extruded from the spinneret into the channel, and nascent fibers were obtained through extrusion and winding. The temperatures of the three sections of the channel were controlled at 120℃, 180℃, and 240℃, and the total residence time of the polyamide-imide spinning solution in the channel was 3 minutes. The nascent fibers were wound at a speed of 500 m / min. The nascent fibers were then subjected to two-stage drawing in a drawing furnace, with drawing ratios of 1.05 and 2.25, and drawing temperatures of 160 ℃ and 220 ℃, respectively, to obtain polyamide-imide fibers.

[0056] Comparative Example 1

[0057] Under nitrogen protection, MDI and TMA were dissolved in NMP solvent, and the other steps were the same as in Example 1.

[0058] Comparative Example 2

[0059] Without adding catalysts such as triethylenediamine, the other steps are the same as in Example 1.

[0060] Comparative Example 3

[0061] The material is collected and stored in the microreactor, but not directly fed into the spinning assembly. It is then metered and fed into the spinning tank, and the other steps are the same as in Example 1.

[0062] Comparative Example 4

[0063] The fiber underwent only one thermal stretching process, with a stretching ratio of 1.75 and a stretching temperature of 200°C. The other steps were the same as in Example 1.

[0064] Comparative Example 5

[0065] The fibers were not thermally stretched, and the other steps were the same as in Example 1.

[0066] Table 1. Performance Comparison of Polyamide-Imide Fibers

[0067]

[0068] The polyamide-imide fibers prepared in Examples 1-5 have excellent mechanical properties and self-healing properties.

[0069] Compared to Example 1, Comparative Example 1 added NMP components with higher boiling points, resulting in increased solvent residue during spinning and poor fiber performance. Comparative Example 2 did not add an organic alkaline catalyst, leading to a higher number of seven-membered ring intermediates, structural instability during spinning, and ultimately poor fiber mechanical properties and reduced self-repair efficiency. Comparative Example 3 involved storing the spinning solution before adding it to the spinning process, resulting in some water absorption and degradation of the fiber, which affected its mechanical properties. Comparative Example 4 only involved one stage of hot drawing, leaving some solvent residue and incomplete CO2 removal, resulting in incomplete fiber orientation and lower fiber mechanical properties compared to Example 1, along with lower self-repair efficiency. Comparative Example 5 lacked a hot drawing process, leaving more residual solvent and only initial orientation during spinning, leading to significantly lower fiber mechanical properties than Example 1.

Claims

1. A method for preparing polyamide-imide fibers, characterized in that, include: Step (1) Prepare solutions A, B and C respectively; Solution A includes monomer A and solvent; solution B includes monomer B, solvent and catalyst; solution C includes monomer C and solvent; wherein monomer A includes one or more of carboxylic acids and carboxylic acid derivatives; monomer B is a diisocyanate monomer; monomer C is a diamine monomer containing disulfide bonds; the catalyst is an organic weak base catalyst; and the solvents are all selected from polar aprotic solvents. Monomer A includes , , One or more of them; Step (2) Inject solutions A, B, and C into a microreactor to react and obtain a spinning solution, which is then directly transported to a spinning system for spinning to obtain nascent fibers. After segmented thermal drawing, polyamide-imide fibers are obtained. The microreactor has three temperature sections: the first section is 20-25℃, the second section is 45-55℃, and the third section is 75-85℃. The segmented drawing consists of two stages: 160-190℃ with a drawing ratio of 1.0-2.25 times, followed by 200-300℃ with a drawing ratio of 1.25-2.25 times. The spinning process to obtain nascent fibers involves the spinning solution entering a dry spinning channel through a spinneret, and then being extruded and wound to obtain nascent fibers. The channel is heated in three stages: the first stage is 100-140℃, the second stage is 150-190℃, and the third stage is 200-240℃. ℃, the total residence time of the spinning solution in the channel is 3-6 s; the injection rate ratio of solution A, solution B and solution C in step (2) is 1:(0.9-0.8):(0.2-0.1).

2. The preparation method according to claim 1, characterized in that, In step (1), monomer B includes , , , , , One or more of them; The monomer C includes , One or more of them.

3. The preparation method according to claim 1, characterized in that, The organic weak base catalyst in step (1) is one or more of triethylenediamine, 4-dimethylaminopyridine, and 1,2-dimethylimidazole; The polar aprotic solvent in step (1) includes one or more of N-methylpyrrolidone (NMP) and N,N-dimethylacetamide (DMAc). In step (1), the mass fraction of the catalyst in solution B is 0.3-0.5 wt%.

4. The preparation method according to claim 1, characterized in that, The transport time of the microreactor in step (2) is 5-25 minutes.

5. The preparation method according to claim 1, characterized in that, The winding speed in step (2) is 200-500 m / min.

6. A polyamide-imide fiber prepared by the method of claim 1.

7. The application of the polyamide-imide fiber of claim 6 in the aerospace, electrical and electronic, automotive, and marine engineering fields.

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