Fiber and preparation method therefor

Abstract

The present application relates to the technical field of textile printing and dyeing, and relates to a fiber and a preparation method therefor. The preparation method comprises: selecting a dihydrazide monomer, a first monomer, and a second monomer for reaction to prepare a polymeric intermediate containing hydrazide acyl chloride segments and aryl amide segments; subjecting the polymeric intermediate to spinning treatment to obtain nascent fibers; and performing heating post-treatment on the nascent fibers to obtain fibers containing oxadiazole groups. Compared with the existing aramid fibers which have the problems such as poor high-temperature dimensional stability, poor wearing comfort, and poor dyeability, the fiber in the present application has a great improvement, and can maintain dimensional stability under high-temperature conditions.

Description

Fiber and preparation method thereof Technical Field

[0001] The present application relates to the field of textile printing and dyeing technology, and in particular to a fiber and a preparation method thereof. Background Art

[0002] Poly(m-phenylene isophthalamide), hereinafter referred to as PMIA, has a fiber decomposition temperature of up to 500°C, a long-term operating temperature greater than 230°C, a limiting oxygen index greater than 29, and excellent high-temperature acid and alkali resistance, electrical insulation, and good textile processing properties. It is widely used in protective clothing, high-temperature filter materials, electrical industry, and composite materials, and is an indispensable strategic material for national economic development. However, the meta-aramid fiber molecules are arranged in a zigzag pattern, and the amide groups therein are flexible connection points that will vibrate, rotate, and rearrange themselves at high temperatures. This causes the aramid fiber molecules to have significant thermal shrinkage when the temperature changes, which is not conducive to the dimensional stability of the aramid fiber molecules at high temperatures, further limiting the improvement of the high-temperature resistance of the aramid fiber molecules.

[0003] At the same time, due to the regular molecular structure, high crystallinity and lack of active functional groups on the molecular chain of aramid fiber, it is difficult for dye or pigment molecules to penetrate into its structure. The polymerized aramid fiber molecules are difficult to combine with dye or pigment molecules, which makes it difficult to dye itself and the prepared fabrics, making the application of aramid modified fiber in the field of high-temperature protection a "short board".

[0004] In addition, meta-aramid fiber has the disadvantages of low water absorption (4-5%) and poor wearing comfort.

[0005] Therefore, the prior art needs to further improve the high temperature dimensional stability, wearing comfort and dyeability of meta-aramid. Summary of the Invention

[0006] In view of the above analysis, the present application aims to provide a fiber and a preparation method thereof, so as to improve at least one of the problems of existing fibers, such as poor high-temperature dimensional stability, poor wearing comfort, and poor dyeability.

[0007] The purpose of this application is mainly achieved through the following technical solutions:

[0008] A fiber preparation method comprising:

[0009] Step 1: Select a dihydrazide monomer, a first monomer, and a second monomer to react to prepare a polymer intermediate comprising a hydrazide chloride segment and an arylamide segment;

[0010] Step 2: Spinning the polymer intermediate to obtain nascent fibers;

[0011] Step 3: The as-spun fibers are heated and post-treated to obtain fibers containing oxadiazole groups.

[0012] Preferably, the first monomer contains an amino group, and the second monomer contains a formyl group; preferably, the first monomer is an aromatic diamine monomer, and the second monomer is a dibasic acid chloride monomer.

[0013] Preferably, the first monomer is one or more of m-phenylenediamine, p-phenylenediamine, and 3,4-diaminodiphenyl ether; and / or the second monomer is isophthaloyl chloride or a mixture of isophthaloyl chloride and terephthaloyl chloride.

[0014] Preferably, the dihydrazide monomer is an aromatic compound containing two primary hydrazides; preferably, the dihydrazide monomer is an aromatic dihydrazide; further preferably, the dihydrazide monomer is one or more of isophthaloyl dihydrazide and terephthaloyl dihydrazide.

[0015] Preferably, the monomers with meta-structured substituents in the first monomer and the dihydrazide monomer account for 80-100% of the total molar amount of the first monomer and the dihydrazide monomer, and the monomers with para-structured substituents in the first monomer and the dihydrazide monomer account for 0-20% of the total molar amount of the first monomer and the dihydrazide monomer.

[0016] Preferably, the molar proportion of the para-structured monomers in the first monomer and the dihydrazide monomer is ≤10%.

[0017] Preferably, the proportion of the meta-structure monomer of the substituent in the second monomer does not exceed 5%.

[0018] Preferably, the step 1 of adding the second monomer two or more times comprises the following steps:

[0019] S101: dissolving a dihydrazide monomer and a first monomer in a polar organic solvent;

[0020] S102: Adding the second monomer to the mixed system in S101 multiple times to perform multiple prepolymerizations, adding an acid binder after the prepolymerization, precipitating and separating the reaction product of the acid binder and the prepolymerization byproducts, and then continuing to add the second monomer and perform postpolymerization to obtain a polymer intermediate containing hydrazide chloride chain segments and arylamide chain segments.

[0021] Preferably, the polar organic solvent in step 101 is any one of N-dimethylacetamide, dimethylformamide, and N-methylpyrrolidone.

[0022] A fiber prepared by the above fiber preparation method comprises an aromatic structure and a heterocyclic structure for connecting the aromatic structure.

[0023] Preferably, the fiber comprises the following structure (I):

[0024] Compared with the prior art, this application can achieve at least one of the following beneficial effects:

[0025] (1) The fiber of the present application has a low thermal shrinkage rate, which is less than 2% at 400°C, much lower than the 4-7% thermal shrinkage rate of meta-aramid, thereby improving the dimensional stability of protective fabrics under high temperature conditions.

[0026] (2) The fiber of the present application has strong hygroscopicity and good hydrophilicity, reaching 6-12%, which is higher than the 4-5% of meta-aramid. When people wear fabrics made of this fiber, the comfort is improved.

[0027] (3) The heat resistance of the product of the present application is such that the glass transition temperature is greater than 280°C, so the long-term use temperature can reach 250°C, which is higher than the 220°C of meta-aramid.

[0028] (4) The product of the present application has high flame retardancy, with a limiting oxygen index of 30-32%, which is further improved compared to the 28-29% of meta-aramid.

[0029] (5) The product of the present application does not reduce the relative strength and elongation at break of the fiber compared to meta-aramid, nor does it reduce the processing performance in the downstream processing field, and is very suitable for processing such as spinning.

[0030] (6) The dyeability K / S value of the product of the present application is significantly improved relative to that of meta-aramid, which is convenient for printing and dyeing after weaving. The K / S value can reach above 1, preferably 1-8.

[0031] In this application, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of this application will be described in the subsequent description, and some advantages may become obvious from the description or be understood by practicing this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered as limiting the present application. Like reference symbols denote like components throughout the drawings.

[0033] FIG1 is a flow chart of a fiber preparation process in one embodiment of the present application. DETAILED DESCRIPTION

[0034] The preferred embodiments of the present application are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present application and are used together with the embodiments of the present application to illustrate the principles of the present application, and are not used to limit the scope of the present application.

[0035] In view of one aspect of the defects in the prior art, the present application discloses a fiber comprising an aromatic structure and a heterocyclic structure for connecting the aromatic structure.

[0036] Specifically, the fiber can be obtained by introducing a heterocyclic structure into the aramid molecule.

[0037] It can be understood that the present application introduces a heterocyclic structure into the traditional aramid molecule to improve the high temperature resistance, thermal stability, high temperature mechanical strength and dyeability of the fiber molecule.

[0038] Specifically, the heterocyclic ring structure is a rigid structure in which all atoms are coplanar.

[0039] Specifically, the heterocyclic structure has ≥5 constituent atoms and contains at least two double bonds.

[0040] Specifically, the heterocyclic structure may be an oxadiazole structure.

[0041] Preferably, the heterocyclic structure may be a connecting structure of benzene rings in the modified aramid molecule.

[0042] Specifically, fibers include:

[0043] It can be understood that the benzene rings in (I) are connected by the oxadiazole structure, and all atoms in the oxadiazole are coplanar. When the temperature changes, all atoms in the oxadiazole vibrate and rotate in the same plane, and its degree of freedom is significantly reduced compared to traditional aramid fibers.

[0044] In another aspect, the present application discloses a method for preparing a fiber, comprising:

[0045] An aromatic polymer intermediate containing hydrazide chloride chain segments is prepared; and the aromatic polymer intermediate is spun and then subjected to heating treatment to obtain fibers containing oxadiazole groups.

[0046] It is understandable that fibers containing oxadiazole groups are highly rigid and difficult to spin. The present application overcomes the defect of difficulty in spinning fibers containing oxadiazole groups by introducing softer hydrazide chloride chain segments into the spinning raw materials and processing the hydrazide chloride chain segments after spinning to obtain oxadiazole groups.

[0047] Specifically, the preparation of the fiber includes the following steps:

[0048] Step 1: Select a dihydrazide monomer, a first monomer, and a second monomer to react to prepare a polymer intermediate comprising a hydrazide chloride segment and an arylamide segment;

[0049] Step 2: Spinning the polymer intermediate to obtain nascent fibers;

[0050] Step 3: The as-spun fibers are heated and post-treated to obtain fibers containing oxadiazole groups.

[0051] During implementation, step 1 generates the corresponding hydrazide chloride segment through the reaction of hydrazide and acyl chloride; and simultaneously the first monomer reacts with acyl chloride to generate an arylamide segment;

[0052] Step 2: spinning the polymer intermediate prepared in step 1 to obtain nascent fibers;

[0053] Step 3: The hydrazide chloride chain segments in the nascent fiber are heated and converted into oxadiazole groups to obtain fibers.

[0054] Specifically, step 1 is carried out in a polar organic solvent.

[0055] Specifically, the polar organic solvent may be any one of N-dimethylacetamide, dimethylformamide (DMF), and N-methylpyrrolidone, which has good solubility for the raw material monomers and does not react with any raw material monomers.

[0056] Preferably, the preparation in step 1 includes: conducting a prepolymerization according to the insufficient amount of the second monomer, separating the impurity products after each prepolymerization to promote the forward reaction, and further adding the second monomer according to the complete reaction stoichiometric ratio or a near complete reaction stoichiometric ratio and then polymerizing to prepare a polymer intermediate.

[0057] It should be noted that when the dihydrazide monomer, the first monomer, and the second monomer react to form a synthesis, reaction byproducts are simultaneously generated. When the reaction byproducts accumulate to a certain level in the system, they will inhibit the forward reaction, affecting the polymer chain growth and the final fiber properties. This application adopts a pre-polymerization-post-polymerization process in which the second monomer is added twice or more. After the pre-polymerization, an acid binding agent is added to bind to the reaction byproducts, and the combined products are separated from the solution system to achieve the purpose of promoting the forward reaction binding.

[0058] Specifically, the acid binding agent includes inorganic acid binding agents and organic acid binding agents.

[0059] Preferably, the acid binding agent is an inorganic acid binding agent.

[0060] Specifically, the inorganic acid-binding agent is one or more of ammonia, calcium hydroxide, calcium oxide, ammonium carbonate and ammonium bicarbonate.

[0061] Specifically, the organic acid-binding agent includes any one of diethylamine and triethylamine.

[0062] It should be noted that inorganic acid binders have significant advantages over organic acid binders: on the one hand, organic acid binders are soluble in synthetic solvent systems and are relatively difficult to separate; on the other hand, the reaction between organic acid binders and hydrochloric acid is a reversible reaction, which is unstable at high temperatures and decomposes during heating and polymerization, making it difficult to achieve a good acid binding effect; in addition, due to the good crystallinity of the polymer itself, the fiber surface is regular and dense after the polymer is precipitated into silk, making it difficult to thoroughly clean the interior, resulting in some organic acid binders easily remaining inside the fiber and affecting its performance.

[0063] The difference is that the inorganic acid-binding agent contains ammonia or its decomposition product is ammonia. On the one hand, ammonia and the like are insoluble in the solvent system, and excess raw material heating produces ammonia or carbon dioxide which can be easily separated by heating and reducing pressure. While fully reacting with hydrogen chloride, excess ammonia residue and the introduction of raw material impurities are avoided. On the other hand, ammonia is insoluble in the hydrogen chloride product ammonium chloride and the organic polar solvent system and can be easily removed by precipitation, thereby avoiding the introduction of new impurities.

[0064] In addition, multiple additions of the second monomer can avoid decomposition of the more active second monomer, reaction with impurities, and volatilization loss. On the other hand, multiple additions facilitate control of the reaction rate and reduce uneven reaction levels of the polymerization reaction caused by uneven mass transfer.

[0065] Specifically, the first monomer includes an amino group, and the second monomer includes a formyl group.

[0066] Preferably, the first monomer is an aromatic diamine monomer, and the second monomer is a dibasic acid chloride monomer.

[0067] Preferably, the first monomer may be one or more of m-phenylenediamine, p-phenylenediamine, and 3,4-diaminodiphenyl ether.

[0068] Specifically, the dihydrazide monomer is an aromatic compound containing two primary hydrazides.

[0069] Preferably, the dihydrazide monomer is an aromatic dihydrazide.

[0070] Preferably, the dihydrazide monomer is one or more of isophthalic acid hydrazide and terephthalic acid hydrazide.

[0071] Preferably, the monomers with meta-structured substituents in the first monomer and the dihydrazide monomer account for 80-100% of the total molar amount of the first monomer and the dihydrazide monomer, and the monomers with para-structured substituents in the first monomer and the dihydrazide monomer account for 0-20% of the total molar amount of the first monomer and the dihydrazide monomer.

[0072] Preferably, the molar proportion of the para-structured monomers in the first monomer and the dihydrazide monomer is ≤10%.

[0073] Preferably, the second monomer is isophthaloyl chloride or a mixture of isophthaloyl chloride and terephthaloyl chloride.

[0074] Preferably, the proportion of the substituent meta-structure monomer in the second monomer does not exceed 5%.

[0075] Specifically, the molar ratio of the first monomer to the dihydrazide monomer is 0-100:0-100.

[0076] Preferably, the molar ratio of the total molar amount of the first monomer and the dihydrazide monomer to the molar amount of the second monomer is 1:(0.95-1.05).

[0077] For example, NH2NHCO-Aq-CONHNH2 is used as the general formula of the dihydrazide monomer, m-phenylenediamine is used as the first monomer, isophthaloyl chloride is used as the second monomer, isophthaloyl hydrazide is the dihydrazide monomer, and the overall reaction of the dihydrazide monomer, the first monomer, and the second monomer is as follows:

[0078] Where n represents the number of polymer components; (I) represents a polymer constituent unit formed by the reaction of the first monomer and the second monomer, represents a polymer intermediate component unit formed by the reaction of a dihydrazide monomer and a second monomer, a represents the number of polymer structural units formed by the reaction of the dihydrazide monomer, na represents the number of polymer structural units formed by the reaction of the first monomer, and Aq represents either a phenyl group or a naphthyl group in the aromatic group; the two structural units (I) and (II) in the polymer structural unit are randomly distributed:

[0079] Specifically, the quantitative ratio of the two structural units (I) and (II) in the polymer intermediate is: 0-99.99:0.01-100.

[0080] Specifically, adding the second monomer twice or more in step 1 comprises the following steps:

[0081] S101: dissolving a dihydrazide monomer and a first monomer in a polar organic solvent;

[0082] S102: Adding the second monomer to the mixed system in S101 multiple times to perform multiple prepolymerizations, adding an acid binder after the prepolymerization, precipitating and separating the reaction product of the acid binder and the prepolymerization byproducts, and then continuing to add the second monomer and perform postpolymerization to obtain a polymer intermediate containing hydrazide chloride chain segments and arylamide chain segments.

[0083] Specifically, the polar organic solvent in step 101 is any one of N-dimethylacetamide, dimethylformamide, and N-methylpyrrolidone.

[0084] Specifically, the prepolymerization in step S102 is mainly the reaction of the first monomer, the dihydrazide monomer and the second monomer to generate a small molecule prepolymer and the random copolymerization of the small molecule prepolymer to generate a long chain prepolymer. Taking the second monomer as isophthaloyl chloride as an example, the main reaction equation of the prepolymer satisfies:

[0085] Wherein, R represents the structure after removing two primary amino groups from the first monomer or dihydrazide monomer; for example, taking toluenediamine as the first monomer and isophthalic acid hydrazide as the dihydrazide monomer, then R represents the benzene ring or m represents the number of polyisophthaloyl structures in the long-chain prepolymer or the amount of the second monomer consumed in the first stage.

[0086] Specifically, in step S102, the post-polymerization is mainly to react with the first monomer or the dihydrazide monomer end group of the prepolymer molecule to achieve long-chain prepolymer connection and long-chain growth as the second monomer is continuously added; taking isophthaloyl chloride as an example, the main reaction equation of the post-polymerization satisfies:

[0087] Where n represents the number of structural units of the polymer intermediate; p represents the number of second monomers consumed in the post-polymerization stage to prepare a PMIA molecule with n structural units; R p+1 represents the p+1th long-chain prepolymer, and the number of polyisophthaloyl structures in different long-chain prepolymers may be the same or different; R represents the structure after removing two primary amino groups from the first monomer or dihydrazide monomer.

[0088] Preferably, the prepolymerization reaction temperature is -20°C to 20°C, for example, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, or 20°C.

[0089] In this range, the product has a larger viscosity-average molecular weight and better mechanical strength; the reaction time is 0.05h~1h.

[0090] More preferably, the prepolymerization reaction temperature is -15°C to 10°C.

[0091] Preferably, the post-polymerization reaction temperature is 20° C. to 50° C., for example, 25° C., 30° C., 35° C., 40° C., 45° C., or 50° C.; and the reaction time is 0.05 h to 2 h.

[0092] It should be noted that when the prepolymerization temperature is lower than -20°C, the reaction rate is low, which will reduce the efficiency of the entire process; when the prepolymerization temperature is higher than 20°C or the post-polymerization temperature is higher than 50°C, side reactions increase, the linearity of the polymer molecules is destroyed, the molecular weight is lower, the viscosity is lower, the spinnability decreases, and the fiber strength and elongation at break decrease; the post-polymerization temperature is higher than the prepolymerization temperature.

[0093] Specifically, the amount ratio of the dihydrazide monomer in the dihydrazide monomer and the first monomer is in the range of 0.01% to 100%.

[0094] Specifically, the mass concentration of the polymer intermediate solution in step S102 is 13-25%.

[0095] Specifically, in step 1, the molar ratio of the dihydrazide monomer to the first monomer is in the range of 100-0.01:0-99.99.

[0096] Specifically, step 2 includes:

[0097] S201: using the prepared polar solvent solution of the polymer intermediate as a spinning solution, and performing a pre-spinning slurry pretreatment to remove impurities;

[0098] S202: Spinning the pretreated spinning solution to obtain spun fibers.

[0099] Specifically, the pretreatment of the spinning slurry in S201 includes: neutralization, filtration and degassing.

[0100] Neutralizing agent selection: any one of inorganic base and organic amine.

[0101] Preferably, the inorganic base is one or more of calcium oxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, and liquid ammonia.

[0102] The organic amine is one or more of diethylamine, triethylamine and tetraethylethylenediamine.

[0103] Specifically, the filtration pressure is 0.3 MPa to 0.8 MPa.

[0104] Specifically, the degassing adopts vacuum degassing with a vacuum degree of 0.1KPa to 20KPa.

[0105] Specifically, wet spinning is preferred in step 2, and the spinning pressure is set to 0.2 MPa to 2 MPa, for example, 0.2 MPa, 0.3 MPa, 0.5 MPa, 0.6 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, 1.2 MPa, 1.3 MPa, 1.5 MPa, 1.6 MPa, 1.8 MPa, 1.9 MPa, and 2.0 MPa.

[0106] Specifically, after the primary fibers are formed in step 2, post-processing is also included: plasticizing and stretching, washing, and drying.

[0107] Specifically, the specific method and process conditions of plasticizing and stretching are: the fiber passes through multiple rollers with different speeds in sequence, so that the speed of the fiber when leaving the stretching machine is greater than the speed when entering the stretching machine, thereby achieving the stretching effect.

[0108] Specifically, the fibers are immersed in the plasticizing liquid or washed by the plasticizing liquid when passing through two multi-roll machines at different speeds.

[0109] Specifically, the plasticizing liquid is a mixture of a polar solvent, an inorganic salt and water.

[0110] Preferably, the plasticizing liquid is an aqueous solution of DMAC (dimethylacetamide) and calcium chloride, and the mass ratio satisfies: DMAC: calcium chloride: water = (5-30): (0-20): (70-50).

[0111] It can be understood that the effect of plasticization and stretching is: the fiber is affected by the plasticizing liquid, and the polymer is affected by the solvent, and has a certain swelling. Under the action of external force, the polymer can slide against each other to a certain extent, thereby achieving the purpose of stretching the molecules in the fiber along the axial orientation of the fiber.

[0112] Specifically, during the plasticizing and stretching process, the fibers absorb the plasticizing liquid, resulting in residual polar solvents, inorganic salts and other substances in the plasticizing liquid; the presence of these substances affects the physical and mechanical properties of the fibers, and water washing is used to remove impurities, recover solvents, and reduce material consumption; specific methods of water washing include: using multi-stage water washing, and washing the fibers by multi-stage countercurrent immersion or elution.

[0113] Specifically, the specific method and process conditions of drying are: drying the fiber bundle by means of multi-stage hot rollers, hot plates or hot cavities, etc. When the fiber passes through the surface of the above-mentioned hot equipment, heat is transferred from the machine to the fiber, the temperature of the fiber bundle rises, and the moisture in the fiber bundle evaporates due to the heat, thereby achieving the drying effect; equipment such as hot rollers or hot plates can use electric thermal resistors or heat media (such as thermal oil) or steam for heating.

[0114] Specifically, the dynamic viscosity of the polymer intermediate solution in step 3 is 10,000 to 100,000 centipoise.

[0115] Specifically, the post-heating treatment in step 3 to obtain the modified aramid fiber containing oxadiazole groups can be performed by online heat treatment or continuous heat treatment.

[0116] Specifically, online heat treatment includes:

[0117] First, pre-treat and stretch the film at a temperature between 180°C and 280°C, with a stretching ratio between 100% and 550%.

[0118] Then, a setting treatment of 100% to 150% is carried out at a temperature within the range of 280°C to 400°C.

[0119] Specifically, intermittent heat treatment methods include:

[0120] The spun fibers are washed and dried, then cut and subjected to a relaxation heat treatment.

[0121] Specifically, the relaxation heat treatment includes heat treatment in a high-temperature heat treatment furnace, a blast or a vacuum environment.

[0122] Specifically, the relaxation heat treatment time is 20 minutes to 20 hours, and the temperature is 250 to 400°C.

[0123] Specifically, in step 3, the spun fiber is heated and post-treated to obtain the modified aramid fiber containing oxadiazole groups, which includes: removing water molecules from the hydrazide chloride chain segments in the spun fiber to generate oxadiazole groups.

[0124] The above reaction process satisfies:

[0125] Wherein, R' may be a benzene ring, and the position of the oxadiazole group to which R' is connected may be the meta position or the para position.

[0126] Compared with the prior art, in the post-heating treatment in step 3, the dihydrazide bonds in the polymer chain undergo a condensation reaction, each chain segment removes a water molecule, and the dihydrazide bonds simultaneously form oxadiazole rings. At the same time, the molecular chain segments are oriented along the fiber axis and regularly stacked with other molecular chain segments to crystallize, forming a perfect fiber structure, giving the fiber heat resistance and very good dry-heat shrinkage performance. Moreover, the introduction of the oxadiazole ring greatly improves the hydrophilicity of the fiber and improves the hygroscopicity of the fiber, thereby improving the wearing comfort of the fabric made of this fiber.

[0127] Specifically, the dynamic viscosity of the spinning solution of the fiber is 10,000 to 100,000 / centipoise; the glass transition temperature of the fiber is 270 to 390° C.; the relative strength of the fiber is 3.5 to 5 cN / dtex; the breaking elongation of the fiber is 10% to 40%; and the CV value of the fiber is 8% to 15%.

[0128] In order to better illustrate the present application, the following examples and comparative examples are further provided:

[0129] Example 1

[0130] This embodiment discloses a method for preparing a fiber:

[0131] (1) Preparation of polymer intermediate: The dihydrazide reaction monomer and the first monomer were added to an appropriate amount of N-dimethylacetamide solvent at a molar ratio of 50:50, and a set dosage of the second monomer was added. The polymerization reaction temperature and time were controlled at -10-0°C for 1 h in the prepolymerization stage and at 30-50°C for 2 h in the postpolymerization stage. The solute mass concentration in the polymer intermediate solution was 20%. The specific compositions of the dihydrazide reaction monomer, the first monomer, and the second monomer are shown in Tables 1a and 1b.

[0132] (2) Spinning the polymer intermediate solution:

[0133] The polymer intermediate solution was filtered at a pressure of 0.3 MPa and degassed. The solution was then wet-spun at a spinning pressure of 1 MPa. The spinning process was smooth and virtually free of lint, resulting in the precipitation of nascent fibers. The precipitate was a mixture of N-dimethylacetamide, calcium chloride, and water (mass ratio 45:25:30).

[0134] (3) Post-treatment of primary fibers:

[0135] The nascent fibers are plasticized, stretched, washed and dried.

[0136] (4) Fiber molding:

[0137] Online heat treatment was adopted, and the specific components are shown in Table 1a and Table 1b.

[0138] This embodiment discloses a fiber prepared by the above method, and the specific parameters are shown in Table 2.

[0139] Example 2

[0140] This embodiment discloses a method for preparing a fiber:

[0141] (1) Preparation of polymer intermediate: The dihydrazide reaction monomer and the first monomer were added to an appropriate amount of N-dimethylacetamide solvent at a molar ratio of 95:5, and a set dosage of the second monomer was added. The polymerization reaction temperature and time were controlled at 20°C for 0.05 h in the prepolymerization stage and at 30°C for 0.05 h in the postpolymerization stage. The solute mass concentration in the polymer intermediate solution was 20%. The specific compositions of the dihydrazide reaction monomer, the first monomer, and the second monomer are shown in Tables 1a and 1b.

[0142] (2) Spinning the polymer intermediate solution:

[0143] The polymer intermediate solution was filtered at a pressure of 0.3 MPa and degassed. The solution was then wet-spun at a spinning pressure of 1 MPa. The spinning process was smooth and virtually free of lint, resulting in the precipitation of nascent fibers. The precipitate was a mixture of N-dimethylacetamide, calcium chloride, and water (mass ratio 45:25:30).

[0144] (3) Post-treatment of primary fibers:

[0145] The nascent fibers are plasticized, stretched, washed and dried.

[0146] (4) Fiber molding:

[0147] Online heat treatment was adopted, and the specific components are shown in Table 1a and Table 1b.

[0148] This embodiment discloses a fiber prepared by the above method, and the specific parameters are shown in Table 2.

[0149] Example 3

[0150] This embodiment discloses a method for preparing a fiber:

[0151] (1) Preparation of polymer intermediate: The dihydrazide reaction monomer and the first monomer were added to an appropriate amount of N-dimethylacetamide solvent at a molar ratio of 20:80, and a set dosage of the second monomer was added. The polymerization reaction temperature and time were controlled at -5°C for 0.2 h in the prepolymerization stage and at 40°C for 1 h in the postpolymerization stage. The solute mass concentration in the polymer intermediate solution was 20%. The specific compositions of the dihydrazide reaction monomer, the first monomer, and the second monomer are shown in Tables 1a and 1b.

[0152] (2) Spinning the polymer intermediate solution:

[0153] The polymer intermediate solution was filtered at a pressure of 0.4 MPa and degassed. The solution was then wet-spun at a spinning pressure of 1 MPa. The spinning process was smooth and virtually free of lint, resulting in the precipitation of nascent fibers. The precipitate was a mixture of N-dimethylacetamide, calcium chloride, and water (mass ratio 45:25:30).

[0154] (3) Post-treatment of primary fibers:

[0155] The nascent fibers are plasticized, stretched, washed and dried.

[0156] (4) Fiber molding:

[0157] Online heat treatment was adopted, and the specific components are shown in Table 1a and Table 1b.

[0158] This embodiment discloses a fiber prepared by the above method, and the specific parameters are shown in Table 2.

[0159] The settings of Examples 4 to 9 and the comparative example are the same as those of Example 1 except for the parameters in Table 1a and Table 1b.

[0160] The main raw material compositions of the above examples and comparative examples are shown in Table 1a and Table 1b:

[0161] Table 1a Main raw material composition of some examples and comparative examples

[0162] Note: “-” in the table means the component does not exist or the process conditions are not implemented.

[0163] Table 1b Main raw material composition of some examples and comparative examples Note: “-” in the table means the component does not exist or the process conditions are not implemented.

[0164] The process parameters of the above examples and comparative examples are shown in Table 2:

[0165] Table 2 Process parameters of some examples and comparative examples Note: “-” in the table means the component does not exist or the process conditions are not implemented.

[0166] The polymer intermediates and fibers prepared in the above examples and comparative examples were tested, wherein dyeability, CV value, hydrophilicity, and limiting oxygen index were measured using known standards or methods. The viscosity of the spinning solution was measured using relative viscosity [η]: the ratio of the dynamic viscosity of the spinning solution to the dynamic viscosity of the pure solvent at the same temperature. The results are shown in Tables 3a and 3b:

[0167] Table 3a Part of the relevant data of spinning solution and fiber properties Note: “-” in the table means the component does not exist or the process conditions are not implemented.

[0168] Table 3b Part of the relevant data of spinning solution and fiber properties Note: “-” in the table means the component does not exist or the process conditions are not implemented.

[0169] The results show that the fiber of the present application has a low thermal shrinkage rate, which is less than 2% at 400°C, which is much lower than the thermal shrinkage rate of 4-7% of meta-aramid (such as Comparative Example 1), thereby improving the dimensional stability of protective fabrics under high temperature conditions.

[0170] The fiber of the present application has strong hygroscopicity, good hydrophilicity and high moisture regain, reaching 6-12%, which is higher than 4-5% of meta-aramid. When people wear fabrics made of the fiber, the comfort is improved.

[0171] The heat resistance of the product of this application is such that the glass transition temperature is greater than 280°C and the long-term use temperature reaches 250°C, which is higher than the 220°C of meta-aramid.

[0172] The product of the present application has high flame retardancy, with a limiting oxygen index of 30-32%, which is higher than the 28-29% of meta-aramid.

[0173] The dyeability K / S value of the product of the present application is significantly improved relative to that of meta-aramid, and can reach above 1, preferably 1-8.

[0174] By comparing Example 1 and Comparative Example 1, it can be seen that the CV value of the product of the present application is somewhat lower than that of meta-aramid, which is conducive to the stability of fiber performance.

[0175] The product of the present application does not reduce the relative strength and elongation at break of the fiber compared to meta-aramid, and does not reduce the processing performance in downstream processing fields, and is very suitable for processing such as spinning.

[0176] The above is only a preferred specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed in this application should be covered by the scope of protection of the present application.

Claims

1. A fiber preparation method, characterized in that: include: Step 1: Select a dihydrazide monomer, a first monomer, and a second monomer to react to prepare a polymer intermediate comprising a hydrazide chloride segment and an arylamide segment; Step 2: Spinning the polymer intermediate to obtain nascent fibers; Step 3: The as-spun fibers are heated and post-treated to obtain fibers containing oxadiazole groups.

2. The fiber preparation method according to claim 1, characterized in that: The first monomer contains an amino group, and the second monomer contains a formyl group; preferably, the first monomer is an aromatic diamine monomer, and the second monomer is a dibasic acid chloride monomer.

3. The fiber preparation method according to claim 2, characterized in that: The first monomer is one or more of m-phenylenediamine, p-phenylenediamine, and 3,4-diaminodiphenyl ether; and / or the second monomer is isophthaloyl chloride or a mixture of isophthaloyl chloride and terephthaloyl chloride.

4. The fiber preparation method according to claim 1, characterized in that: The dihydrazide monomer is an aromatic compound containing two primary hydrazides; preferably, the dihydrazide monomer is an aromatic dihydrazide; more preferably, the dihydrazide monomer is one or more of isophthaloyl dihydrazide and terephthaloyl dihydrazide.

5. The fiber preparation method according to claim 1, characterized in that: The monomers with meta-structure substituents in the first monomer and the dihydrazide monomer account for 80-100% of the total molar amount of the first monomer and the dihydrazide monomer, and the monomers with para-structure substituents in the first monomer and the dihydrazide monomer account for 0-20% of the total molar amount of the first monomer and the dihydrazide monomer.

6. The fiber preparation method according to claim 1, characterized in that: The molar proportion of the para-structured monomers in the first monomer and the dihydrazide monomer is ≤10%.

7. The fiber preparation method according to claim 1, characterized in that: The proportion of the meta-structure monomer of the substituent in the second monomer does not exceed 5%.

8. The fiber preparation method according to claim 1, characterized in that: Adding the second monomer twice or more in step 1 comprises the following steps: S101: dissolving a dihydrazide monomer and a first monomer in a polar organic solvent; S102: Adding the second monomer to the mixed system in S101 multiple times to perform multiple prepolymerizations, adding an acid binder after the prepolymerization, precipitating and separating the reaction product of the acid binder and the prepolymerization byproducts, and then continuing to add the second monomer and perform postpolymerization to obtain a polymer intermediate containing hydrazide chloride chain segments and arylamide chain segments.

9. A fiber, characterized in that The fiber is prepared by the fiber preparation method according to any one of claims 1 to 8, comprising an aromatic structure and a heterocyclic structure for connecting the aromatic structure.

10. The fiber according to claim 9, characterized in that It includes the following structure (I):

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