High-strength and high-toughness modified p-aramid fiber and preparation method thereof

Abstract

The present application relates to the technical field of para-aramid fiber preparation, and discloses a high-strength and high-toughness modified para-aramid fiber and a preparation method thereof. The present application introduces a chlorine-containing diamine monomer with a molar ratio of 0.05-0.15 to the diamine into the para-heterocyclic aramid structure in the form of block copolymerization through a two-pot method, so that when the fiber is heat-treated, the chlorine side groups on the chlorine-containing block are broken and dechlorinated to generate phenyl radicals at high temperature, local chemical coupling reactions are achieved between macromolecular chains to expand the chains and increase the molecular weight. At the same time, the ratio of the polymerization degree of the chlorine-free block to the chlorine-containing block is controlled to be 4.0-9.0 to maintain the movement ability of the overall macromolecular chain, thereby preparing the high-strength and high-toughness modified para-aramid fiber. The high-strength and high-toughness modified para-aramid fiber prepared by the present application has a tensile strength of 33-40 cN / dtex, an elongation at break of 4.5-8.0%, a toughness of 100-130 MJ / m 3 2, and good composite performance, with a strength of 5.5-7.0 GPa.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of para-aramid preparation, in particular to a high-strength and high-toughness modified para-aramid fiber and a preparation method thereof. BACKGROUND

[0002] Para-aramid is a typical high-performance organic fiber, which is widely used in aerospace, national defense and military industry, automobile electronics and sports equipment fields. Heterocyclic aramid is a modified para-aramid prepared by introducing asymmetric benzimidazole ring structure into the structure of para-aramid (PPTA). The regularity of the molecular chain is reduced, but the tensile strength is higher, which has attracted much attention. Compared with PPTA and PBO organic fibers, and carbon fibers and other inorganic fibers, the heterocyclic modified para-aramid has better comprehensive strength and toughness, so it has important application in the field of impact-resistant materials, especially as bulletproof materials and rubber reinforcing materials. With the development of modern industrial technology, it is necessary to further improve the strength and toughness of the heterocyclic aramid. However, there is an essential contradiction between strength and toughness, and it is a great challenge to simultaneously improve the strength and toughness of the heterocyclic aramid.

[0003] To improve the toughness of heterocyclic aramid fiber, it is necessary to improve its fracture resistance, i.e. to increase the elongation at break. The common method is to introduce meta-connection, flexible structure and side groups into the molecular structure of the fiber to destroy the rigidity and regularity of the molecular chain, so as to reduce the crystallinity and orientation of the fiber and increase the deformation ability of the fiber under stress. Although these modification methods can improve the elongation at break of the fiber, the tensile strength will be significantly reduced, and the toughness will not be improved. Chinese Patent No. 202010402998.3 discloses a high-strength and high-elongation heterocyclic aromatic polyamide fiber and its preparation process, which specifically discloses introducing chlorine side groups, cyano side groups, meta-phenyl structures and ether bonds into the molecular chain of heterocyclic aramid fiber. The elongation at break of the prepared heterocyclic aramid fiber can reach 4.5-10.0%, but the tensile strength has not been improved. Chinese Patent No. 201410656733.0 discloses a chlorine-containing high-performance heterocyclic aramid fiber and its preparation method and application, which specifically discloses introducing chlorine side groups into the molecular chain of heterocyclic aramid fiber to improve the adhesion of the fiber to epoxy resin, but the tensile strength and elongation at break of the fiber are not high, the tensile strength is 24-32 cN / dtex, and the elongation at break is 2.3-4.0%. Chinese Patent No. 201711091330.6 discloses a preparation method of chlorine-containing high-performance heterocyclic aromatic polyamide fiber, which specifically discloses introducing chlorine side groups into the molecular chain of heterocyclic aramid fiber. The modified fiber has improved surface activity and improved flame retardancy, with an limiting oxygen index of 30-50%, but its mechanical properties are not high, with a breaking strength of 3.50-5.0 GPa. In addition, Chinese Patent No. 202110871051.1 also discloses introducing chlorine side groups into the molecular chain of heterocyclic aramid fiber by copolymerizing p-phenylenediamine, 2-(4-aminophenyl)-5-aminobenzimidazole, 4,4'-diamino-2'-chloro-benzanilide and terephthaloyl chloride. The composite performance of the modified fiber with epoxy resin is also improved, with a tensile strength of 5.0-6.5 GPa for the dipped yarn and a dry yarn breaking strength of 27-36 cN / dtex, but the elongation at break of the fiber is only 2.5-4.2%, and the toughness is not high. Chinese Patent No. 201710694853.3 discloses a high-strength aromatic copolyamide fiber and its preparation method, which specifically discloses introducing cyano side groups into the molecular chain of heterocyclic aramid fiber. The prepared fiber has a tensile strength of 3.5-5.5 GPa, but the elongation at break is only 2.5-4.5%. Therefore, simple chemical modification methods cannot simultaneously improve the strength and toughness of heterocyclic aramid fiber.

[0004] Another method to improve the breaking resistance of heterocyclic aramid is to increase its molecular weight, but due to the greater rigidity of the molecular chain of heterocyclic aramid, its solubility in composite solvents is limited, and increasing the molecular weight will sharply increase the dynamic viscosity of the spinning solution, reduce the spinnability, and thus significantly reduce the mechanical strength. In order to increase the molecular weight of heterocyclic aramid without affecting its glue solution spinnability, a method for preparing heterocyclic aramid fiber based on high-temperature post-chain extension reaction is disclosed in Chinese patent No. 201710256235.0, which uses amino-terminated oligomer and carboxyl-terminated oligomer to blend spinning, and uses the condensation reaction of amino and carboxyl at high temperature to increase the molecular weight of heterocyclic aramid in the later stage. However, this method greatly sacrifices the molecular weight of heterocyclic aramid in the polymerization stage, and the molecular weight increases limitedly in the later stage, and the tensile strength of the prepared fiber is only 26-31 cN / dtex.

[0005] The existing preparation methods for modifying heterocyclic aramid fibers all focus on improving the composite performance, mechanical strength and production efficiency of heterocyclic aramid, and there are few reports on solving the contradictory problem of simultaneously improving the strength and toughness of heterocyclic aramid. SUMMARY

[0006] The purpose of the present application is to solve the problem that the strength and toughness of para-heterocyclic aramid fiber are difficult to be improved simultaneously, and to provide a preparation method for simultaneously significantly improving the strength and toughness of para-heterocyclic aramid fiber. The appropriate chlorine-containing diamine monomer is introduced into the structure of heterocyclic aramid in the form of block copolymerization through the traditional "two-pot method", and the polymerization degree ratio of the chlorine-free block to the chlorine-containing block is simultaneously controlled. The chlorine side group on the chlorine-containing block is removed to produce phenyl radicals during heat treatment, which initiates local coupling reaction between macromolecular chains to extend the chain, and the molecular weight increases. At the same time, the appropriate length of non-coupling chlorine-free block maintains the mobility of the overall macromolecular chain, thereby significantly improving the strength and toughness of heterocyclic aramid.

[0007] To achieve the above-mentioned purpose, on the one hand, the present application provides a preparation method of high-strength and high-toughness modified para-aramid fiber, which comprises the following steps:

[0008] S1, under the protection of dry nitrogen, the diamine monomer is dissolved in the N,N-dimethylacetamide composite solvent of lithium chloride, the reaction temperature is reduced to 0-10℃, and then 75-97% of the equivalent of the diamine is added to the reaction with terephthaloyl chloride to obtain an amino-terminated chlorine-free block oligomer with a polymerization degree of 7.0-65.7, wherein the diamine monomer is 2-(4-aminophenyl)-5-aminobenzimidazole, or 2-(4-aminophenyl)-5-aminobenzimidazole and p-phenylenediamine;

[0009] S2, under the protection of dry nitrogen, the chlorine-containing diamine monomer is added to the lithium chloride N,N-dimethylacetamide complex solvent to dissolve, the reaction temperature is reduced to 0-10℃, then 115-400% of the equivalent of chlorine-containing diamine is added to the terephthaloyl chloride to react, and a chlorine-containing block oligomer capped with acyl chloride with a polymerization degree of 1.7-14.3 is obtained, wherein the amount of chlorine-containing diamine accounts for 0.05-0.15 of the molar ratio of all diamines in steps S1 and S2;

[0010] S3, the total chlorine-free block oligomer of step S1 is blended with the total chlorine-containing block oligomer of step S2, and the temperature is raised to 20-40℃ for reaction, to obtain a polymer solution with a solid content of 3-4.5wt%, and a kinetic viscosity of 3-100 million centipoise at 25℃, wherein the polymerization degree ratio of chlorine-free block oligomer to chlorine-containing block oligomer is 4.0-9.0;

[0011] S4, the polymer solution of step S3 is obtained by a wet spinning process to obtain a modified para-aramid fiber, and the fiber is then subjected to static heat treatment at 340-380℃ or continuous heat stretching treatment at 390-420℃, so that the degree of breakage and removal of chlorine side groups is 7-20%, and finally a modified para-aramid fiber is prepared.

[0012] In the above steps S1 and S2, the amino group has very high reactivity with acyl chloride, which will release a large amount of heat, in order to prevent local overheating and polymerization, the reaction temperature is reduced to 0-10℃, and further preferably to 0-5℃. In addition, after the blending of the oligomers in steps S1 and S2, the mixed solution in step S3 has a certain viscosity, and the concentration of acyl chloride and amino end groups is not as high as directly adding monomers, so the temperature needs to be raised to 20-40℃ to promote sufficient reaction, and further preferably the temperature is 30-40℃.

[0013] The chemical structures of the above 2-(4-aminophenyl)-5-aminobenzimidazole, p-phenylenediamine and terephthaloyl chloride are as follows:

[0014]

[0015] As a further preferred technical solution of the present application, in step S1, the molar ratio of 2-(4-aminophenyl)-5-aminobenzimidazole to p-phenylenediamine is 0.65-0.95:0-0.25.

[0016] As a further preferred technical solution of the present application, in steps S1 and S2, the mass fraction of lithium chloride in the N,N-dimethylacetamide complex solvent is 3-5%.

[0017] As a further preferred technical solution of the present application, in steps S1 and S2, the total amount of terephthaloyl chloride added twice accounts for 0.995-1.005 of the molar ratio of all diamines.

[0018] As a further preferred technical solution of the present application, the chlorine-containing diamine is at least one of 2-chloro-1, 4-phenylenediamine, 2, 5-dichloro-1, 4-phenylenediamine, 3, 3'-dichlorobenzidine, 2-chloro-4, 4'-diaminobenzanilide, 2, 6-dichloro-4, 4'-diaminobenzanilide, 2-(2-chloro-4-aminophenyl)-5-aminobenzimidazole and 2-(2-chloro-4-aminophenyl)-5-aminobenzoxazole. The chemical structures are as follows:

[0019]

[0020] As a further preferred technical solution of the present application, in step S4, the static heat treatment process adopts a mode of vacuum extraction < 200 Pa, or nitrogen protection at 0.5-5 L / min.

[0021] As a further preferred technical solution of the present application, in step S4, the continuous heat stretching process is protected by nitrogen at 0.5-5 L / min.

[0022] As a further preferred technical solution of the present application, in step S4, the tension of the continuous heat stretching is 0.05-0.5 cN / dtex.

[0023] According to another aspect of the present application, the present application also provides a modified para-aramid fiber prepared by the above method.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] (1) The present application introduces chlorine-containing diamine monomers in the form of block copolymerization through "two-pot method" on the basis of the conventional diamine monomers 2-(4-aminophenyl)-5-aminobenzimidazole and p-phenylenediamine used in heterocyclic aramid, and the modified para-heterocyclic aramid has the characteristics of different block structures, including chlorine-free block and chlorine-containing block. The regularity of chlorine-free block structure is better, and the regularity of chlorine-containing block structure is reduced. By adjusting the length ratio of the two, the synergy of the two blocks not only effectively transfers stress and converts energy, but also avoids the influence of chlorine side groups on the overall regularity of the modified para-aramid macromolecules, thereby improving the orientation degree of the modified para-aramid.

[0026] (2) Due to the principle of "similar compatibility", the chlorine-containing block is more likely to aggregate, and the chlorine side groups thereon break to produce phenyl radicals during high-temperature treatment, and local coupling reactions occur between macromolecular chains to expand the chain. Therefore, compared with the existing preparation technology of chlorine-containing heterocyclic aramid, the present application can effectively increase the molecular weight of the modified heterocyclic aramid by introducing a smaller amount of chlorine-containing diamine monomers during heat treatment.

[0027] (3) The present application controls the ratio of polymerization degree of the non-chlorine block and the chlorine block to be 4.0-9.0, and the intermolecular coupling reaction only occurs in the chlorine block. The non-coupling non-chlorine block with appropriate length keeps the mobility of the whole macromolecular chain, so that the fiber mechanical strength and toughness are simultaneously improved.

[0028] (4) The present application controls the removal of only 7-20% of the chlorine side groups to initiate the coupling reaction chain extension in the heat treatment, which does not cause defects in the fiber. In addition, the majority of the remaining chlorine side groups increase the surface polarity of the fiber, so that the composite performance of the fiber is also significantly improved.

[0029] (5) The high-strength and high-toughness modified para-aramid fiber prepared by the present application has a tensile strength of 33-40 cN / dtex, an elongation at break of 4.5-8.0%, a toughness of 100-130 MJ / m 3 , and good composite performance with a gel-coated yarn strength of 5.5-7.0 GPa. BRIEF DESCRIPTION OF DRAWINGS

[0030] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Figure 1 The infrared spectra of the modified para-aramid precursor fiber and the finished fiber after heat treatment in Example 1 of the present application are shown in the figure. In the figure: 1-precursor fiber; 2-finished fiber after heat treatment.

[0032] Figure 2 The stress (cN / dtex)-strain (%) curve of the modified para-aramid fiber prepared in Example 1, Example 2 and Example 3 of the present application is shown in the figure. In the figure, the curves: 1-Example 1; 2-Example 2; 3-Example 3.

[0033] The purpose of the present application, functional characteristics and advantages will be further described with reference to the accompanying drawings. DETAILED DESCRIPTION

[0034] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0035] Unless otherwise defined, the technical terms used in the following examples have the same meaning as generally understood by those skilled in the art to which the present application belongs. The test reagents used in the following examples, unless otherwise specified, are conventional biochemical reagents; the experimental methods, unless otherwise specified, are conventional methods.

[0036] In the preparation process of the high-strength and high-toughness modified para-aramid fiber proposed in the application, chlorine-containing side groups need to be introduced into the macromolecular chains of the heterocyclic aramid. Although the prior art (such as Chinese patents with application numbers 201410656733.0, 201711091330.6 and 202110871051.1) discloses introducing chlorine-containing side groups into the molecular structure of the heterocyclic aramid, so as to improve the composite performance, flame retardance or strength of the fiber. However, the present application provides a new preparation process and a chlorine-containing modified heterocyclic aramid with a new structural feature, so as to simultaneously improve the strength and toughness.

[0037] In the present application, the control of the block polymerization degree length is realized by changing the feeding ratio of diamine and acyl chloride, r is the group number ratio of amino group to acyl chloride, or acyl chloride to amino group in the reaction system, 0 < r < 1; p is the reaction degree, since the reaction activity of amino group and acyl chloride is very high, therefore p ≈ 1.

[0038]

[0039] In the present application, the process of dechlorination of chlorine-containing side groups on the modified para-aramid fiber in the heat treatment to initiate the chain extension of local coupling reaction is as follows:

[0040] (1)

[0041] (2)

[0042] (3)

[0043] In the present application, the degree of rupture and removal of chlorine-containing side groups on the molecular chain of the modified para-aramid fiber can be calculated by the change of the infrared absorption characteristic peak intensity of the chlorine-containing side groups before and after heat treatment. 1052cm -1 is the infrared stretching vibration absorption peak of C-Cl bond, I0 is the C-Cl bond absorption peak intensity of the modified para-aramid fiber, and I1 is the C-Cl bond absorption peak intensity of the modified para-aramid fiber after heat treatment.

[0044]

[0045] The technical scheme of the present application for preparing high-strength and high-toughness modified para-aramid fiber is further described in detail through specific examples.

[0046] Example 1

[0047] A, in the first reaction kettle, under the protection of dry nitrogen, according to the molar ratio of 0.7:0.15, diamine monomer 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ, 50.253g) and p-phenylenediamine (PDA, 5.193g) were added to the lithium chloride mass fraction of 3.5% N,N-dimethylacetamide composite solvent, stirring until the diamine was completely dissolved, the temperature in the reaction kettle was reduced to 5℃, then the equivalent of 97% of the diamine terephthaloyl chloride (TPC, 53.585g) was added at one time, after 1h of reaction, an amino-terminated non-chlorine-containing block oligomer solution was obtained, and the polymerization degree was 65.7;

[0048] B, in another reaction kettle, under the protection of dry nitrogen, 2-chloro-1,4-phenylenediamine (Cl-PDA, 6.846g) was added to the lithium chloride mass fraction of 3.5% N,N-dimethylacetamide composite solvent, stirring until the diamine was completely dissolved, the temperature was reduced to 5℃, then the equivalent of 120% of Cl-PDA TPC (11.731g) was added at one time, after 0.5h of reaction, an acyl chloride-terminated chlorine-containing block oligomer was obtained, and the polymerization degree was 10.8;

[0049] C, according to the molar ratio of the diamine monomers PABZ, PDA and Cl-PDA in steps A and B, 0.7:0.15:0.15, the acyl chloride-terminated chlorine-containing block oligomer of step B was all poured into the first reaction kettle and stirred with the amino-terminated non-chlorine-containing block oligomer solution, and the temperature was raised to 30℃ for 2h of reaction to obtain a polymer solution with a solid content of 3.5wt% and a kinematic viscosity of 730,000 centipoises at 25℃.

[0050] D, the polymer solution of step C was spun using a conventional wet spinning method, first poured into a spinning storage tank for degassing and filtration, and then passed through a metering pump and a spinneret cap (150 holes, 0.1mm pore size) into a first coagulation bath of water and N,N-dimethylacetamide in a mass ratio of 1:1 to coagulate and form, drawn into a second coagulation bath of water and N,N-dimethylacetamide in a mass ratio of 5.6:1 to be plasticized and stretched at a rate of 2.3 times, then washed with water, oiled, dried and wound into a cylinder to obtain modified para-aramid filaments, the filament fineness was 480±5dtex; the filaments were placed in an atmosphere with a vacuum degree of 100Pa, and heat treated at 360℃ for 40min to prepare modified para-aramid fibers.

[0051] From Figure 1As can be seen from the above table, the modified para-aramid fiber obtained in the embodiment has a lower intensity of the C-Cl bond infrared stretching vibration absorption peak than the para-aramid fiber, which indicates that the content of the chloro side group is reduced after the heat treatment, because the chloro side group is broken and removed to a certain extent during the heat treatment, and the phenyl free radical is generated to initiate the local coupling reaction. The calculation shows that the dechlorination degree of the modified para-aramid fiber is 13%. The fiber performance is shown in Table 1.

[0052] Example 2

[0053] The modified para-aramid fiber is prepared by using the modified para-aramid fiber prepared in Example 1, and the difference is that, in step D, the static treatment process is changed to static heat treatment at 400℃ for 20 min, and the modified para-aramid fiber is finally prepared, and the dechlorination degree is 57%. The fiber performance is shown in Table 1.

[0054] Example 3

[0055] The modified para-aramid fiber is prepared by using the modified para-aramid fiber prepared in Example 1, and the difference is that, in step D, the static treatment process is changed to static heat treatment at 320℃ for 30 min, and the modified para-aramid fiber is prepared, and the dechlorination degree is <1%. The fiber performance is shown in Table 1.

[0056] Example 4

[0057] A. In the first reaction kettle, under the protection of dry nitrogen, PABZ (58.317 g) and PDA (10.816 g) are added to the N,N-dimethylacetamide composite solvent with a lithium chloride mass fraction of 4.5% according to a molar ratio of 0.65:0.25, and stirred until the diamine is completely dissolved. The internal temperature is lowered to 4℃, and then an equivalent of 95% TPC (69.444 g) is added at one time. After 1 h of reaction, an amino-terminated chloro-free block oligomer solution is obtained, and the polymerization degree is 39.0;

[0058] B. In another reaction kettle, under the protection of dry nitrogen, 3,3'-dichlorobenzidine (DCl-BPDA, 10.127 g) is added to the N,N-dimethylacetamide composite solvent with a lithium chloride mass fraction of 4.5%, and stirred until the diamine is completely dissolved. The internal temperature is lowered to 4℃, and then an equivalent of 145% TPC (11.777 g) is added at one time. After 0.5 h of reaction, an acyl chloride-terminated chloro-containing block oligomer is obtained, and the polymerization degree is 5.4.

[0059] C. The molar ratio of the diamine monomers PABZ, PDA and DCl-BPDA charged in steps A and B was 0.65:0.25:0.10. The acyl chloride-terminated chloro-containing block oligomer of step B was all poured into the first reactor to stir and blend with the amino-terminated non-chloro-containing block oligomer solution. The temperature was raised to 40°C and the reaction was continued for 1 h to obtain a polymer solution with a solid content of 4.5 wt% and a kinematic viscosity of 89,000 centipoises at 25°C.

[0060] D. The polymer solution of step C was subjected to a wet spinning process identical to that of Example 1 to obtain modified para-aramid filaments. The filaments were then subjected to a continuous heat stretching treatment at 390°C for 3 min at a stretching tension of 0.5 cN / dtex and a nitrogen flow rate of 0.5 L / min to prepare modified para-aramid fibers with a dechlorination degree of 8%. The fiber properties are shown in Table 1.

[0061] Example 5

[0062] A. In the first reactor, PABZ (60.428 g) and PDA (4.371 g) were added to a lithium chloride mass fraction of 5% N,N-dimethylacetamide composite solvent under the protection of dry nitrogen according to a molar ratio of 0.80:0.12. The mixture was stirred until the diamines were completely dissolved. The internal temperature was then lowered to 2°C, and then an equivalent of 88% TPC (55.361 g) was added at once. After 0.7 h of reaction, an amino-terminated non-chloro-containing block oligomer solution was obtained, and the degree of polymerization was 15.7.

[0063] B. In another reactor, 2-chloro-4,4'-diaminobenzanilide (Cl-DABA, 7.052 g) was added to a lithium chloride mass fraction of 5% N,N-dimethylacetamide composite solvent under the protection of dry nitrogen. The mixture was stirred until the diamine was completely dissolved. The internal temperature was then lowered to 2°C, and then an equivalent of 238% TPC (13.020 g) was added at once. After 0.5 h of reaction, an acyl chloride-terminated chloro-containing block oligomer was obtained, and the degree of polymerization was 2.4.

[0064] C. The molar ratio of the diamine monomers PABZ, PDA and Cl-DABA charged in steps A and B was 0.80:0.12:0.08. The acyl chloride-terminated chloro-containing block oligomer of step B was all poured into the first reactor to stir and blend with the amino-terminated non-chloro-containing block oligomer solution. The temperature was raised to 20°C and the reaction was continued for 3 h to obtain a polymer solution with a solid content of 4.0 wt% and a kinematic viscosity of 54,000 centipoises at 25°C.

[0065] D, the polymer solution in step C was obtained by the same wet spinning process as example 1 to obtain the modified para-aramid precursor, then the precursor was heated to 380℃ under nitrogen flow of 5L / min for static heat treatment for 20min, to obtain the modified para-aramid fiber, the dechlorination degree was 16%. The fiber properties are shown in Table 1.

[0066] Example 6

[0067] A, in the first reaction kettle, the diamine monomer PABZ (62.853g) was added to the N,N-dimethylacetamide composite solvent with a lithium chloride mass fraction of 3.5% under the protection of dry nitrogen, and stirred until the diamine was completely dissolved. The internal temperature was reduced to 0℃, then 80% of TPC (45.520g) equivalent to the diamine was added at one time, and the reaction was carried out for 1h to obtain an amino-terminated non-chlorine-containing block oligomer solution with a polymerization degree of 9.0;

[0068] B, in another reaction kettle, 2,6-dichloro-4,4'-diaminobenzanilide (DCl-DABA, 9.224g) was added to the N,N-dimethylacetamide composite solvent with a lithium chloride mass fraction of 3.5% under the protection of dry nitrogen, and stirred until the diamine was completely dissolved. The internal temperature was reduced to 0℃, then 280% of TPC (17.702g) equivalent to DCl-DABA was added at one time, and the reaction was carried out for 0.5h to obtain a chloro-containing block oligomer terminated by acyl chloride with a polymerization degree of 2.1;

[0069] C, the molar ratio of diamine monomer PABZ and DCl-DABA in steps A and B was 0.90:0.10, the acyl chloride-terminated chloro-containing block oligomer in step B was all poured into the first reaction kettle to stir and blend with the amino-terminated non-chlorine-containing block oligomer solution, and the temperature was raised to 30℃ for continuous reaction for 2h to obtain a polymer solution with a solid content of 4.0wt% and a dynamic viscosity of 34 million centipoise at 25℃.

[0070] D, the polymer solution in step C was obtained by the same wet spinning process as example 1 to obtain the modified para-aramid precursor, then the precursor was heated to 380℃ under nitrogen flow of 5L / min for static heat treatment for 20min, to obtain the modified para-aramid fiber, the dechlorination degree was 16%. The fiber properties are shown in Table 1.

[0071] Example 7

[0072] A, in the first reactor, under the protection of dry nitrogen, diamine monomer PABZ (78.451 g) and PDA (9.187 g) were added to the lithium chloride mass fraction of 4% N, N-dimethylacetamide composite solvent in a molar ratio of 0.70:0.17, stirring until the diamine was completely dissolved, the internal temperature was reduced to 10℃, then the equivalent of 92% TPC (81.207 g) was added at one time, after 1h reaction, the amino-terminated non-chlorine-containing block oligomer solution was obtained, and the polymerization degree was 24.0;

[0073] B, in another reactor, under the protection of dry nitrogen, 2-(2-chloro-4-aminophenyl)-5-aminobenzoxazole (Cl-BOA, 16.872 g) was added to the lithium chloride mass fraction of 4% N, N-dimethylacetamide composite solvent, stirring until the diamine was completely dissolved, the internal temperature was reduced to 10℃, then the equivalent of 155% TPC (20.454 g) was added at one time, after 0.5h reaction, the acyl chloride-terminated chlorine-containing block oligomer was obtained, and the polymerization degree was 4.6;

[0074] C, the molar ratio of diamine monomers PABZ, PDA and Cl-BOA in steps A and B was 0.70:0.17:0.13, the acyl chloride-terminated chlorine-containing block oligomer of step B was all poured into the first reactor to stir and blend with the amino-terminated non-chlorine-containing block oligomer solution, and the temperature was raised to 30℃ for 1h to obtain a polymer solution with a solid content of 3.5wt% and a kinetic viscosity of 96 million centipoise at 25℃.

[0075] D, the polymer solution in step C was obtained by the same wet spinning process as in example 1 to obtain modified para-aramid filaments, then the filaments were protected by nitrogen gas with a flow rate of 1L / min, and the temperature was raised to 370℃ for static heat treatment for 30min to prepare modified para-aramid fibers, and the dechlorination degree was 14%. The fiber properties are shown in Table 1.

[0076] Example 8

[0077] A, in the first reactor, under the protection of dry nitrogen, diamine monomer PABZ (68.931 g) was added to the lithium chloride mass fraction of 3.0% N, N-dimethylacetamide composite solvent, stirring until the diamine was completely dissolved, the internal temperature was reduced to 8℃, then the equivalent of 87% TPC (54.290 g) was added at one time, after 1h reaction, the amino-terminated non-chlorine-containing block oligomer solution was obtained, and the polymerization degree was 14.4;

[0078] B. In another reaction kettle, 2-(2-chloro-4-aminophenyl)-5-aminobenzimidazole (Cl-PABZ, 4.185 g) was added into the lithium chloride mass fraction of 3.0% N,N-dimethylacetamide complex solvent under the protection of dry nitrogen, and stirred until the diamine was completely dissolved. The internal temperature was reduced to 8°C, and then an equivalent of 343% of the acyl chloride (11.265 g) of Cl-PABZ was added at one time. After 0.5 h of reaction, an acyl chloride-terminated chloro-containing block oligomer with a polymerization degree of 1.8 was obtained;

[0079] C. The molar ratio of the diamine monomers PABZ and Cl-PABZ in steps A and B was 0.95:0.05. The acyl chloride-terminated chloro-containing block oligomer of step B was all poured into the first reaction kettle and stirred and blended with the amino-terminated non-chloro-containing block oligomer solution. The temperature was raised to 30°C and the reaction was continued for 2 h to obtain a polymer solution with a solid content of 4.0 wt% and a kinematic viscosity of 46,000 centipoises at 25°C.

[0080] D. The polymer solution in step C was obtained by the same wet spinning process as in Example 1 to obtain modified para-aramid filaments. The filaments were then subjected to continuous heat stretching treatment at 410°C for 2 min with a stretching tension of 0.2 cN / dtex and a nitrogen flow rate of 3 L / min to prepare modified para-aramid fibers with a dechlorination degree of 9%. The fiber properties are shown in Table 1.

[0081] Example 9

[0082] A. In the first reaction kettle, diamine monomers PABZ (55.786 g) and PDA (9.607 g) were added into the lithium chloride mass fraction of 4.0% N,N-dimethylacetamide complex solvent under the protection of dry nitrogen according to a molar ratio of 0.7:0.25, and stirred until the diamine was completely dissolved. The internal temperature was reduced to 8°C, and then an equivalent of 89% of TPC (61.205 g) of the diamine was added at one time. After 1 h of reaction, an amino-terminated non-chloro-containing block oligomer solution with a polymerization degree of 17.7 was obtained;

[0083] B. In another reaction kettle, 2,5-dichloro-1,4-phenylenediamine (DCl-PDA, 3.146 g) was added into the lithium chloride mass fraction of 4.0% N,N-dimethylacetamide complex solvent under the protection of dry nitrogen, and stirred until the diamine was completely dissolved. The internal temperature was reduced to 8°C, and then an equivalent of 303% of TPC (10.941 g) of DCl-PDA was added at one time. After 0.6 h of reaction, an acyl chloride-terminated chloro-containing block oligomer with a polymerization degree of 2.0 was obtained;

[0084] C. The molar ratio of the diamine monomers PABZ, PDA and DCl-PDA charged in step A and B is 0.7:0.25:0.05, the acyl chloride end-capped chloro-containing block oligomer of step B is all poured into the first reaction kettle to stir and blend with the amino end-capped non-chloro-containing block oligomer solution, and the temperature is raised to 30°C to continue to react for 2h to obtain a polymer solution with a solid content of 4.0wt% and a kinetic viscosity of 82,000 centipoises at 25°C.

[0085] D. The polymer solution of step C is obtained by the same wet spinning process as in example 1 to obtain modified para-aramid filaments, and then the filaments are placed in an atmosphere with a vacuum degree of 50Pa, and the temperature is raised to 340°C for static heat treatment for 60min to prepare modified para-aramid fibers with a dechlorination degree of 10%. The fiber properties are shown in Table 1.

[0086] Comparative Example 1

[0087] The same process as in example 9 is used, except that:

[0088] The TPC charging distribution in step A and step B is changed to change the degree of polymerization. In step A, the TPC charging amount is 92% of the equivalent of diamine (63.056g), and the degree of polymerization of the non-chloro-containing block is 24.0. In step B, the TPC charging amount is 252% of the equivalent of DCl-PDA (9.090g), and the degree of polymerization of the chloro-containing block is 2.3. The final modified para-aramid product fiber has a dechlorination degree of 6%. The fiber properties are shown in Table 1.

[0089] Comparative Example 2

[0090] The same process as in example 9 is used, except that:

[0091] The TPC charging distribution in step A and step B is changed to change the degree of polymerization. In step A, the TPC charging amount is 65% of the equivalent of diamine (44.550g), and the degree of polymerization of the non-chloro-containing block is 4.7. In step B, the TPC charging amount is 765% of the equivalent of DCl-PDA (27.596g), and the degree of polymerization of the chloro-containing block is 1.3. The final modified para-aramid product fiber has a dechlorination degree of 5%. The fiber properties are shown in Table 1.

[0092] Comparative Example 3

[0093] The same molar ratio of diamine monomers as in example 9 is used, i.e. the molar ratio of PABZ, PDA and DCl-PDA is 0.7:0.25:0.05. The specific preparation process is as follows:

[0094] The chloro-containing para-modified aramid was prepared by random copolymerization. PABZ (55.786 g), PDA (9.607 g) and DCl-PDA (3.146 g) were added into the composite solvent of N,N-dimethylacetamide with 3.5% lithium chloride under the protection of dry nitrogen, and stirred until the diamines were completely dissolved. The internal temperature was reduced to 5°C, and 90% of TPC (64.932 g) based on the molar amount of diamines was added first. After 1 h of reaction, the temperature was increased to 30°C, and the remaining 10% of TPC (7.215 g) was added in two portions. The stirring reaction was continued for 2 h to obtain a chloro-containing para-modified aramid polymer solution by random copolymerization, with a solid content of 4.0 wt% and a dynamic viscosity of 81,000 centipoise at 25°C.

[0095] The wet spinning process and heat treatment process were the same as in Example 9. The final chloro-containing modified para-aramid product fiber had a dechlorination degree of 4%. The fiber properties are shown in Table 1.

[0096] Comparative Example 4

[0097] A. In the first reaction kettle, the diamine monomers PABZ (61.238 g) and PDA (5.062 g) were added into the composite solvent of N,N-dimethylacetamide with 4.0% lithium chloride under the protection of dry nitrogen, and stirred until the diamines were completely dissolved. The internal temperature was reduced to 8°C, and then 98% of TPC (63.643 g) equivalent to the diamines was added at once. After 1 h of reaction, an amino-terminated chloro-free block oligomer solution was obtained, with a polymerization degree of 99.0;

[0098] B. In another reaction kettle, DCl-PDA (12.431 g) was added into the composite solvent of N,N-dimethylacetamide with 4.0% lithium chloride under the protection of dry nitrogen, and stirred until the diamines were completely dissolved. The internal temperature was reduced to 8°C, and then 109% of TPC (15.554 g) equivalent to DCl-PDA was added at once. After 0.6 h of reaction, an acyl chloride-terminated chloro-containing block oligomer was obtained, with a polymerization degree of 23.0;

[0099] C. The acyl chloride-terminated chloro-containing block oligomer of step B was poured into the first reaction kettle and stirred with the amino-terminated chloro-free block oligomer solution. The temperature was increased to 30°C and the reaction was continued for 2 h to obtain a polymer solution with a solid content of 4.0 wt% and a dynamic viscosity of 78,000 centipoise at 25°C. The molar ratio of diamine monomers PABZ, PDA and DCl-PDA in the polymer was 0.7:0.12:0.18.

[0100] D. The wet spinning process and heat treatment process were the same as in Example 9. The final chloro-containing modified para-aramid product fiber had a dechlorination degree of 22%. The fiber properties are shown in Table 1.

[0101] Comparative Example 5

[0102] Under nitrogen protection, PABZ (82.712 g) and PDA (17.093 g) were weighed according to a molar ratio of 0.7:0.3, and were added to a composite solvent of N,N-dimethylacetamide with a lithium chloride mass fraction of 3.5%. After stirring until the diamine was completely dissolved, the internal temperature was reduced to 5°C. 90% of the TPC (96.272 g) based on the molar amount of the diamine was first added, and after 1 h of reaction, the temperature was increased to 30°C. The remaining 10% of the TPC (10.697 g) was added in two portions, and the stirring reaction was continued for 2 h. A common heterocyclic aramid polymer solution was obtained, with a solid content of 3.5 wt% and a kinetic viscosity of 650,000 centipoise. The wet spinning process and heat treatment process were the same as those of Example 9, and finally a common hybrid aramid finished yarn was obtained. The fiber properties are shown in Table 1.

[0103] The modified para-aramid fibers prepared by the methods provided in Examples 1-9 and Comparative Examples 1-5 were tested for tensile properties, toughness, and epoxy impregnated yarn strength, according to the following test methods:

[0104] Tensile property test: A British Instron 4302 strength tester was used according to the GB / T 19975-2005 standard, with a clamping distance of 500 mm and a tensile speed of 250 mm / min.

[0105] Toughness test: The toughness of the modified para-aramid fiber was calculated by the integral area under the fiber stress (cN / dtex) - strain (%) curve. The toughness (cN / dtex) was calculated according to the following formula: Figure 2 It can be seen that the higher the tensile strength and elongation at break, the greater the toughness.

[0106] Epoxy impregnated yarn strength test: A British Instron 4302 strength tester was used according to the GJB 348-87 standard.

[0107] The test results are shown in Table 1.

[0108] Table 1 Tensile property, toughness, and epoxy resin impregnated yarn strength test results

[0109]

[0110]

[0111] From the data in Table 1, it can be seen that, compared with the existing common hybrid aramid in Comparative Example 5, the strength and toughness of the modified para-aramid fibers in Examples 1, 4, 5, 6, 7, 8 and 9 are significantly improved by introducing the chlorine-containing diamine monomer through block copolymerization, and then initiating local chain extension of the chlorine-containing block after dechlorination by heat treatment, and the fibers have better composite performance. In addition, using the same raw fibers as in Example 1, static heat treatment at a higher temperature (400℃) is carried out in Example 2, so that the dechlorination degree is increased from 13% in Example 1 to 57%, and structural defects are generated due to the escape of a large amount of dechlorination gas and thermal degradation of the molecular chain, etc. Figure 2 It can be seen from the above that the tensile strength and elongation at break of the modified fibers are significantly deteriorated, and the toughness is decreased; while in Example 3, the dechlorination degree of the chlorine side groups is <1% due to the too low heat treatment temperature (320℃), chain extension is not initiated, and the tensile strength and toughness of the fibers are also low. After a large number of experiments, it is found that the suitable static heat treatment temperature is 340-380℃, or the continuous heat stretching treatment temperature is 390-420℃. The ratio of the polymerization degree of the chlorine-free block to the chlorine-containing block has a key influence on the performance of the fibers. Compared with Example 9, the polymerization degree ratio in Comparative Example 1 is too large (10.4), and the polymerization degree ratio in Comparative Example 2 is too small (3.6), so the tensile strength and toughness of the fibers are not high. In Comparative Example 3, the chlorine-containing modified para-aramid fibers are prepared by using the conventional random copolymerization method, and it can be found that the strength and toughness of the fibers are significantly lower than those of Example 9. In Comparative Example 4, a higher content of DCl-PDA is used for block copolymerization, and the molar ratio of DCl-PDA in the diamine is 18%, although the polymerization degree ratio of the chlorine-free block to the chlorine-containing block is 4.3, the dechlorination degree of the chlorine side groups reaches 22%, and compared with Example 9, the strength and toughness of the fibers in Comparative Example 4 are also decreased. After a large number of experiments, it is found that the molar ratio of the chlorine-containing diamine to all diamines is 0.05-0.15, and the fibers have good strength and toughness.

[0112] Although the specific embodiments of the present application are described above, those skilled in the art should understand that these are only illustrative, and various changes or modifications can be made to the embodiments without departing from the principles and essence of the present application, and the protection scope of the present application is only defined by the appended claims.

Claims

1. A method for preparing high-strength, high-toughness modified para-aramid fiber, characterized in that, Includes the following steps: S1. Under the protection of dry nitrogen, the diamine monomer is dissolved in a lithium chloride N,N-dimethylacetamide composite solvent. The reaction temperature is lowered to 0-10℃, and then 75-97% terephthaloyl chloride (equivalent to diamine) is added to react with it to obtain an amino-terminated, chlorine-free block oligomer with a degree of polymerization of 7.0-65.

7. The diamine monomer is 2-(4-aminophenyl)-5-aminobenzimidazole, or 2-(4-aminophenyl)-5-aminobenzimidazole and p-phenylenediamine. S2. Under the protection of dry nitrogen, the chlorinated diamine monomer is dissolved in a lithium chloride N,N-dimethylacetamide composite solvent. The reaction temperature is lowered to 0-10°C. Then, terephthaloyl chloride with an equivalent amount of 115-400% of the chlorinated diamine is added to react and a chlorinated block oligomer with an acyl chloride end-capped polymer degree of polymerization of 1.7-14.3 is obtained. The amount of chlorinated diamine used accounts for 0.05-0.15 of the molar ratio of all diamines in steps S1 and S2. S3. Blend all the chlorine-free block oligomers from step S1 with all the chlorine-containing block oligomers from step S2, and heat to 20-40°C to react, to obtain a polymer solution with a solid content of 3-4.5 wt% and a kinetic viscosity of 3-100,000 centipoise at 25°C, wherein the degree of polymerization ratio of the chlorine-free block oligomers to the chlorine-containing block oligomers is 4.0-9.

0. S4. The polymer solution from step S3 is used to obtain modified para-aramid precursor fibers through a wet spinning process. The modified para-aramid precursor fibers are then subjected to static heat treatment at 340–380°C or continuous hot stretching treatment at 390–420°C to reduce the degree of removal of chlorine side groups to 7–20%, and finally modified para-aramid fibers are obtained.

2. The method for preparing high-strength, high-toughness modified para-aramid fiber according to claim 1, characterized in that, In step S1, the molar ratio of 2-(4-aminophenyl)-5-aminobenzimidazole to p-phenylenediamine is 0.65–0.95:0–0.

25.

3. The method for preparing high-strength, high-toughness modified para-aramid fiber according to claim 1, characterized in that, In steps S1 and S2, the mass fraction of lithium chloride in the N,N-dimethylacetamide composite solvent is 3-5%.

4. The method for preparing high-strength, high-toughness modified para-aramid fiber according to claim 1, characterized in that, In steps S1 and S2, the total amount of terephthaloyl chloride added in both steps accounts for 0.995 to 1.005 of the total molar ratio of all diamines added.

5. The method for preparing high-strength, high-toughness modified para-aramid fiber according to claim 1, characterized in that, The chlorinated diamine is at least one of 2-chloro-1,4-phenylenediamine, 2,5-dichloro-1,4-phenylenediamine, 3,3'-dichlorobenzidine, 2-chloro-4,4'-diaminobenzonitridine, 2,6-dichloro-4,4'-diaminobenzonitridine, 2-(2-chloro-4-aminophenyl)-5-aminobenzimidazole, and 2-(2-chloro-4-aminophenyl)-5-aminobenzoxazole.

6. The method for preparing high-strength, high-toughness modified para-aramid fiber according to claim 1, characterized in that, In step S4, the static heat treatment process is carried out by vacuuming <200Pa or by introducing nitrogen gas at a rate of 0.5 to 5 L / min.

7. The method for preparing high-strength, high-toughness modified para-aramid fiber according to claim 1, characterized in that, In step S4, nitrogen gas is introduced at a rate of 0.5–5 L / min for protection during the continuous hot stretching process.

8. The method for preparing high-strength, high-toughness modified para-aramid fiber according to claim 1, characterized in that, In step S4, the tension of the continuous hot stretching is 0.05 to 0.5 cN / dtex.

9. A modified para-aramid fiber, characterized in that, It is prepared by the method described in any one of claims 1-8.

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