阅读说明：本技术 一种高伸长低模量对位芳纶纤维及其制备方法 (High-elongation low-modulus para-aramid fiber and preparation method thereof ) 是由 高殿飞 马千里 邱召明 杜志林 孙宇 孙德卫 尚晴 于 2020-12-09 设计创作，主要内容包括：本发明公开了一种高伸长低模量对位芳纶纤维及其制备方法,属于芳纶纤维及其制备方法领域。采用低温溶液缩聚、干喷湿纺工艺,主要解决聚合分子量分布不均匀性问题,实现聚合分子量在更窄范围内分布；对位芳纶纺丝过程设计优化以及凝固浴温度的工艺设定,实现生产连续性,并对纤维取向度及初生纤维力学性能等参数的控制,优化生产工艺；对位芳纶洗涤、干燥等后处理过程中温度的工艺设定,控制纤维拉伸过程中纤维结晶参数,提升产品性能。基于上述制备方法得到的对位芳纶纤维断裂伸长率≥3.5％,初始弹性模量80～88Gpa,断裂强度≥20.5cN/dtex,满足对位芳纶在汽车胶管、轮胎、输送带领域的应用需求。(The invention discloses a high-elongation low-modulus para-aramid fiber and a preparation method thereof, belonging to the field of aramid fibers and preparation methods thereof. The low-temperature solution polycondensation and dry-jet wet spinning process is adopted, the problem of non-uniformity of the distribution of the polymerization molecular weight is mainly solved, and the distribution of the polymerization molecular weight in a narrower range is realized; optimizing the design of the para-aramid spinning process and setting the process of the coagulation bath temperature, realizing the production continuity, controlling the parameters such as the fiber orientation degree, the mechanical property of nascent fiber and the like, and optimizing the production process; the temperature is set in the post-treatment processes of para-aramid washing, drying and the like, the fiber crystallization parameters in the fiber stretching process are controlled, and the product performance is improved. The para-aramid fiber obtained by the preparation method has the elongation at break of more than or equal to 3.5 percent, the initial elastic modulus of 80-88 Gpa and the breaking strength of more than or equal to 20.5cN/dtex, and meets the application requirements of the para-aramid fiber in the fields of automobile rubber tubes, tires and conveying belts.)

1. A preparation method of high-elongation low-modulus para-aramid fiber is characterized by comprising the following steps:

dispersing poly-p-phenylene terephthamide in a solvent to obtain a polymer mixed solution, and defoaming the obtained polymer mixed solution to obtain a spinning solution; carrying out dry-jet wet spinning on the obtained spinning solution to obtain high-elongation low-modulus para-aramid fibers;

wherein, the dry-jet wet spinning process specifically comprises the following steps: extruding and pushing the obtained spinning solution to a metering pump to obtain a primary yarn solution, treating the obtained primary yarn solution through a pore spinneret plate and a coagulating bath to obtain primary yarns, sequentially carrying out shaping treatment on the obtained primary yarns to obtain shaped fiber yarns, and oiling and winding the shaped fiber yarns to obtain the high-elongation low-modulus para-aramid fibers.

2. The preparation method of the high-elongation low-modulus para-aramid fiber according to claim 1, characterized in that the mass percentage of the polymer mixed solution is 15-20%.

3. The method for preparing the high-elongation low-modulus para-aramid fiber according to claim 1, wherein the polymer mixed solution is prepared by: the preparation method comprises the steps of firstly mixing poly-p-phenylene terephthalamide and concentrated sulfuric acid with the mass concentration of 99% -101% according to the mass ratio of 1: 4-4.5, and then pushing the mixture into a dissolving machine, so that the poly-p-phenylene terephthalamide is dissolved in the concentrated sulfuric acid for 1-4 hours to obtain a polymer mixed solution.

4. The preparation method of the high-elongation low-modulus para-aramid fiber according to claim 1, wherein the pressure of extrusion pushing is 5-20 MPa; the temperature of the coagulating bath treatment is 10-30 ℃.

5. The method for preparing the high-elongation low-modulus para-aramid fiber according to claim 1, wherein the sizing treatment comprises: washing the obtained primary filament, then carrying out alkali washing neutralization, washing, drying, and then carrying out multi-stage heating drying to obtain a shaped fiber filament;

wherein, multistage heating stoving adopts tertiary warming mill, and the temperature of tertiary warming mill is respectively: 100-150 ℃, 160-200 ℃ and 210-240 ℃.

6. The method for preparing the high-elongation low-modulus para-aramid fiber according to claim 1, wherein the intrinsic viscosity of the poly (p-phenylene terephthalamide) is 6.0 to 7.5 dL/g.

7. The preparation method of the high-elongation low-modulus para-aramid fiber according to claim 1, wherein the winding speed of the winding forming is 280-320 m/min.

8. The method for preparing the high-elongation low-modulus para-aramid fiber according to claim 1, wherein the poly (p-phenylene terephthalamide) is obtained by low-temperature solution polycondensation, and comprises the following steps:

(1) uniformly mixing anhydrous calcium chloride and N-methyl pyrrolidone according to a weight ratio of 4-20: 100, and then adding p-phenylenediamine for uniform mixing to obtain a premixed system;

(2) cooling the obtained premixed system to-15-0 ℃, adding terephthaloyl chloride to obtain a one-stage reaction mixed system, and reacting the obtained reaction mixed system for 30min to obtain a one-stage system; wherein, the addition amount of the paraphthaloyl chloride in the first-stage reaction is 20 to 40 percent of the total mass of the paraphthaloyl chloride;

(3) cooling the obtained first-stage system to-15-0 ℃, adding paraphthaloyl chloride to obtain a second-stage reaction mixed system, and stopping the reaction after the obtained second-stage reaction system is in a state of gel, rod climbing and crushed again to obtain poly (p-phenylene terephthalamide); wherein the addition amount of the paraphthaloyl chloride in the two-stage reaction is 60-80% of the total mass of the paraphthaloyl chloride;

wherein the mass ratio of the p-phenylenediamine used in the step (1) to the total mass of the terephthaloyl chloride used in the steps (2) and (3) is 1: 1-1.05.

9. The high-elongation low-modulus para-aramid fiber prepared by the preparation method of any one of claims 1 to 8.

10. The high-elongation low-modulus para-aramid fiber as claimed in claim 9, wherein the high-elongation low-modulus para-aramid fiber has a fiber elongation at break of 3.5% or more, an initial elastic modulus of 80-88 GPa, and a breaking strength of 20.5cN/dtex or more.

Technical Field

The invention belongs to the field of aramid fibers and preparation methods thereof, and relates to a high-elongation low-modulus para-aramid fiber and a preparation method thereof.

Background

Para-aramid is fully called poly (p-phenylene terephthalamide) (PPTA), is an organic synthetic fiber with high strength and high modulus, is widely applied to the important fields of bulletproof, tires, rubber products (automobile rubber tubes and conveyor belts), outdoor optical cables, advanced composite materials and the like, and is an important basic material for aerospace and national defense and military industry construction. The reinforcing materials adopted in the manufacturing industry of the traditional rubber tube, tire and conveyer belt are steel wire, polyester, rayon, nylon and the like. These reinforcing materials have not been able to meet the requirements of products to withstand higher pressure and temperature and harsh working environment, so that the reinforcing layer thereof is required to have not only high temperature and high pressure resistance, but also more excellent comprehensive properties. Aramid fiber is the best choice for rubber reinforcing materials due to its unique properties.

The high-elongation low-modulus para-aramid fiber not only has the characteristics of low density, high strength, high and low temperature resistance and chemical corrosion resistance which are peculiar to para-aramid fiber, but also has higher toughness and fatigue resistance than conventional fibers, has wide application requirements in the fields of automobile rubber tubes, tires and conveying belts, and has an important promotion effect on the healthy, stable and orderly development of national economy. The project researches and develops domestic high-elongation low-modulus para-aramid mainly according to the development trend and market demand of para-aramid industry and the international leading level of the standard, and the product performance index reaches that the elongation at break is more than or equal to 3.5 percent, the initial elastic modulus is 80-88 Gpa, and the breaking strength is more than or equal to 20.5cN/dtex (standard para-aramid)119) The rubber belt is mainly applied to mechanical rubber commodities such as tires, automobile safety belts, rubber tubes, conveying belts and the like, and industrialization in the rubber field is realized. However, at present, the stable mass production of para-aramid fibers with high elongation and low modulus material characteristics has not been realized. Aiming at the problem of low productivity caused by insufficient development of the conventional high-elongation low-modulus para-aramid fiber process, the important problem to be solved by technical personnel is to develop a process method for solving the problem of unstable control of fiber elongation and modulus index by the conventional dry-jet wet spinning process.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a high-elongation low-modulus para-aramid fiber and a preparation method thereof. The mass stable production of the para-aramid fiber with the characteristics of the high-elongation low-modulus material is realized, and the mechanical property stability of the high-elongation low-modulus para-aramid fiber is enhanced.

In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:

the invention discloses a preparation method of high-elongation low-modulus para-aramid fiber, which comprises the following steps:

dispersing poly-p-phenylene terephthamide in a solvent to obtain a polymer mixed solution, and defoaming the obtained polymer mixed solution to obtain a spinning solution; carrying out dry-jet wet spinning on the obtained spinning solution to obtain high-elongation low-modulus para-aramid fibers;

wherein, the dry-jet wet spinning process specifically comprises the following steps: extruding and pushing the obtained spinning solution to a metering pump to obtain a primary yarn solution, treating the obtained primary yarn solution through a pore spinneret plate and a coagulating bath to obtain primary yarns, sequentially carrying out shaping treatment on the obtained primary yarns to obtain shaped fiber yarns, and oiling and winding the shaped fiber yarns to obtain the high-elongation low-modulus para-aramid fibers.

Preferably, the mass percentage of the polymer mixed solution is 15 to 20 percent.

Preferably, the polymer mixed solution is prepared by: the preparation method comprises the steps of firstly mixing poly-p-phenylene terephthalamide and concentrated sulfuric acid with the mass concentration of 99% -101% according to the mass ratio of 1: 4-4.5, and then pushing the mixture into a dissolving machine, so that the poly-p-phenylene terephthalamide is dissolved in the concentrated sulfuric acid for 1-4 hours to obtain a polymer mixed solution.

Preferably, the pressure of extrusion pushing is 5-20 MPa.

Preferably, the temperature of the coagulation bath treatment is 10-30 ℃.

Preferably, the setting treatment comprises: and washing the obtained primary filament, then carrying out alkali washing neutralization, washing, drying, and then carrying out multi-stage heating drying to obtain the shaped cellosilk.

Further preferably, the multistage heating, drying and shaping adopt three-stage heating rollers, and the temperatures of the three-stage heating rollers are respectively as follows: 100-150 ℃, 160-200 ℃ and 210-240 ℃.

Preferably, the poly (p-phenylene terephthalamide) used has an intrinsic viscosity of 6.0 to 7.5 dL/g.

Preferably, the viscosity average molecular weight of the poly-p-phenylene terephthalamide is 40000-49000.

Preferably, the winding speed of the winding forming is 280-320 m/min.

Preferably, the poly (p-phenylene terephthalamide) is obtained by low temperature solution polycondensation, comprising:

(1) uniformly mixing anhydrous calcium chloride and N-methyl pyrrolidone according to a weight ratio of 4-20: 100, and then adding p-phenylenediamine for uniform mixing to obtain a premixed system; (2) cooling the obtained premixed system to-15-0 ℃, adding terephthaloyl chloride to obtain a one-stage reaction mixed system, and reacting the obtained reaction mixed system for 30min to obtain a one-stage system; wherein, the addition amount of the paraphthaloyl chloride in the first-stage reaction is 20 to 40 percent of the total mass of the paraphthaloyl chloride;

(3) cooling the obtained first-stage system to-15-0 ℃, adding paraphthaloyl chloride to obtain a second-stage reaction mixed system, and stopping the reaction after the obtained second-stage reaction system is in a state of gel, rod climbing and crushed again to obtain poly (p-phenylene terephthalamide); wherein the addition amount of the paraphthaloyl chloride in the two-stage reaction is 60-80% of the total mass of the paraphthaloyl chloride;

wherein the mass ratio of the p-phenylenediamine used in the step (1) to the total mass of the terephthaloyl chloride used in the steps (2) and (3) is 1: 1-1.05.

The invention also discloses the high-elongation low-modulus para-aramid fiber prepared by the preparation method.

Preferably, the high-elongation low-modulus para-aramid fiber is subjected to a performance test according to FZ/T54076-2014, wherein the fiber elongation at break of the high-elongation low-modulus para-aramid fiber is more than or equal to 3.5%, the initial elastic modulus is 80-88 Gpa, and the breaking strength is more than or equal to 20.5 cN/dtex.

More preferably, the high-elongation low-modulus para-aramid fiber has a fiber elongation at break of 3.5-4.5%, an initial elastic modulus of 80-88 Gpa, and a breaking strength of 20.5-24 cN/dtex.

Compared with the prior art, the invention has the following beneficial effects:

the invention discloses a preparation method of high-elongation low-modulus para-aramid fiber, which adopts a dry-jet wet spinning process to solve the problems of tension and temperature control in the processes of washing and drying post-treatment in the spinning process of para-aramid polymer, thereby solving the problem of unstable elongation control of the conventional para-aramid fiber, enhancing the mechanical property of the high-elongation low-modulus para-aramid fiber and realizing stable batch production.

Further, the poly-p-phenylene terephthalamide as the raw material is prepared by adopting low-temperature solution polycondensation, the stability in the polymerization reaction process is improved through the improvement of a polymerization sectional prepolymerization process, the condition of local excessive polymerization in the prepolymerization process is effectively reduced, the generation of gel byproducts is reduced, the condition that a low-molecular-weight polymer is separated out from a solvent system in advance is reduced in the subsequent polycondensation process, the uniformity of molecular weight distribution can be effectively improved, the molecular weight of the polymer is integrally improved, the intrinsic viscosity of the polymer is improved, the problem of non-uniformity of the distribution of the molecular weight of the polymer is solved, and the distribution of the molecular weight of the polymer in a narrower range is realized.

Furthermore, the spinning process realizes the control of parameters such as fiber orientation degree, mechanical property of nascent fiber and the like through the process of the temperature of the coagulating bath, and optimizes the production process. The temperature of the coagulation bath is suitably increased during the coagulation molding, and the temperature of the coagulation bath is set to 10 to 30 ℃. The phase separation speed is accelerated, and the compactness of the fiber is properly reduced, so that the toughness of the fiber is improved.

Furthermore, the temperature of the para-aramid fiber is set in the post-treatment processes of washing, drying and the like, fiber crystallization parameters in the fiber stretching process are controlled, the product performance is improved, and the temperature of the three-stage heating roller is increased in a primary mode and is respectively 100-150 ℃, 160-190 ℃ and 210-240 ℃.

Furthermore, in the hot drawing step of the fiber post-treatment, the degree of fiber orientation is increased, fiber crystal grains are increased, the elongation at break of the fiber is greatly reduced, and the toughness of the fiber is poor, so that in the high-elongation and low-modulus para-aramid post-treatment, the fiber needs to be in a low-tensile state as much as possible, and the winding speed is controlled within the range of 280-320 m/min.

The invention also discloses the high-elongation low-modulus para-aramid fiber, which has the fiber elongation at break of more than or equal to 3.5%, the initial elastic modulus of 80-88 Gpa and the breaking strength of more than or equal to 20.5cN/dtex according to the performance test requirements of the para-aramid fiber in the standard FZ/T54076-2014.

Detailed Description

In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It is to be understood that the description and claims of the present invention are for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

The invention discloses a preparation method of high-elongation low-modulus para-aramid fiber, which comprises the following steps:

(a) preparing a polymer mixed solution with the mass percent of 15-20% by taking concentrated sulfuric acid as a solvent from a poly-p-phenylene terephthalamide (PPTA) raw material, standing for 1-4 hours for dissolution, and standing for 2-6 hours under a vacuum condition for deaeration to obtain a spinning solution;

(b) extruding and pushing the spinning solution under the pressure of more than 5MPa, filtering, passing through a spinneret plate with the aperture of 0.080mm, and performing dry-jet wet spinning on the sprayed filaments to obtain the high-elongation low-modulus para-aramid fibers;

preferably, the pressure of extrusion pushing is 5-20 MPa.

Preferably, the viscosity average molecular weight of the PPTA raw material in the step (a) of preparing the high-elongation low-modulus para-aramid fiber is 40000-49000, and the intrinsic viscosity is 6.0-7.5 dL/g;

the PPTA raw material is prepared by the following low-temperature solution polycondensation steps:

adding anhydrous calcium chloride and N-methylpyrrolidone (NMP) into a reactor according to the weight ratio of 4-20: 100, adding a proper amount of p-phenylenediamine (PPD), and stirring at room temperature for 30 min;

secondly, cooling a reactor jacket by introducing a refrigerant to reduce the temperature of the system to-15-0 ℃, adding a first batch of paraphthaloyl chloride (TPC) accounting for 20-40% of the total amount, and continuously stirring for 30 min;

thirdly, reducing the temperature of the system to-15-0 ℃ again, adding 60-80% of TPC (thermoplastic vulcanizate) in the second batch, quickly stirring, stopping reaction after the reaction system is gelled, climbed and crushed again, and preparing PPTA;

the mole ratio of the PPD added in the step I to the TPC added in the step II to the TPC added in two batches in the step III is 1: 1-1.05.

Preferably, the dry-jet wet spinning process of the preparation step (b) of the high-elongation low-modulus para-aramid fiber comprises the steps of solidification, spinning, washing, drying and shaping, oiling and winding.

Preferably, the coagulation in the dry-jet wet-spinning process in the step (b) of preparing the high-elongation low-modulus para-aramid fiber is a coagulation bath operation, and the temperature of the coagulation bath is set to be 10-30 ℃.

More preferably, the temperature of the coagulation bath is set to 20 to 30 ℃.

Preferably, the dry-jet wet-spinning process in the fiber preparation step (b) is characterized in that in the drying process, the temperature of the three-stage heating roller is increased in a primary mode, and the temperature is 100-150 ℃, 160-190 ℃ and 220-230 ℃ respectively.

Preferably, the dry-jet wet-spinning process in the fiber preparation step (b) comprises a whole set of dry-jet wet-spinning process, and the winding speed is 280-320 m/min.

The high-elongation low-modulus para-aramid fiber obtained by the preparation method is subjected to a performance test of FZ/T54076-2014, and the performance of the para-aramid fiber meets the following requirements: the breaking elongation of the fiber is more than or equal to 3.5 percent; the initial elastic modulus is 80-88 Gpa; the breaking strength is more than or equal to 20.5 cN/dtex.

Specifically, in the specific embodiment of the invention, the fiber elongation at break of the high-elongation low-modulus para-aramid fiber is 3.5-4.5%, the initial elastic modulus is 80-88 Gpa, and the breaking strength is 20.5-24 cN/dtex.

The present invention will be described in detail with reference to the following specific examples:

example 1

A preparation method of high-elongation low-modulus para-aramid fiber comprises the following steps:

(1) adding anhydrous calcium chloride and N-methylpyrrolidone (NMP) into a reactor according to the weight ratio of 4:100, adding a proper amount of p-phenylenediamine (PPD), and stirring for 30min at room temperature;

(2) cooling the jacket of the reactor by introducing a cooling medium to reduce the temperature of the system to-15 ℃, adding a first batch of paraphthaloyl chloride (TPC) accounting for 20 percent of the total amount, and continuously stirring for 30 min;

(3) and (3) reducing the temperature of the system to-15 ℃, adding 80% of TPC in the second batch, quickly stirring, stopping the reaction after the reaction system is gelled and climbed and is crushed again to obtain PPTA, wherein the molar ratio of PPD added in the step (1) to TPC added in the two batches in the steps (2) and (3) is 1:1. Finally, poly-p-phenylene terephthamide (PPTA) with the viscosity-average molecular weight of 49000 and the intrinsic viscosity of 7.5dL/g is prepared;

(4) adding a PPTA raw material and concentrated sulfuric acid with the concentration of 99% into a double-screw extruder according to the proportion of 1:4, primarily mixing the PPTA raw material and the concentrated sulfuric acid by the extruder, pushing the mixture into a dissolving machine to complete the full dissolution of the PPTA in the concentrated sulfuric acid for 3 hours to obtain a polymer mixed solution with the PPTA mass fraction of 15%, and carrying out vacuum defoaming on the polymer mixed solution for 3 hours to ensure that the dissolution performance and the degradation performance are consistent to obtain a spinning solution.

(5) The spinning solution which is fully mixed, well temperature-regulated and completely bubble-removed is extruded and pushed at high pressure and is transmitted to a metering pump (the pressure of extrusion and pushing is 10MPa), and the spinning solution is filtered and then is sent to a fine-hole spinneret plate. Wherein the temperature of the coagulating bath is set to be 25 ℃, the spinning solution is sprayed out of a spinneret plate to form filaments, the spun filaments are subjected to primary washing, alkali washing neutralization, washing and drying processes, and then are subjected to multistage heating, drying and shaping, and the temperature of a three-stage heating roller is set to be 100 ℃, 160 ℃ and 210 ℃. In the whole set of dry-jet wet-spinning process, the winding speed is 300m/min, oil is applied after cooling, and winding forming is carried out, so that the high-elongation low-modulus para-aramid fiber is obtained.

Example 2

A preparation method of high-elongation low-modulus para-aramid fiber comprises the following steps:

(1) adding anhydrous calcium chloride and N-methylpyrrolidone (NMP) into a reactor according to the weight ratio of 20:100, adding a proper amount of p-phenylenediamine (PPD), and stirring for 30min at room temperature;

(2) cooling the jacket of the reactor by introducing a cooling medium to reduce the temperature of the system to 0 ℃, adding a first batch of terephthaloyl chloride (TPC) accounting for 40 percent of the total amount, and continuously stirring for 30 min;

(3) and (3) reducing the temperature of the system to 0 ℃, adding 60 percent of TPC in the second batch, quickly stirring, stopping the reaction after the reaction system is gelled, climbed and crushed again to obtain PPTA, wherein the molar ratio of PPD added in the step (1) to TPC added in the two batches in the steps (2) and (3) is 1: 1.05. Finally obtaining poly-p-phenylene terephthamide (PPTA) with viscosity-average molecular weight of 46000 and intrinsic viscosity of 7.0 dL/g;

(4) adding a PPTA raw material and concentrated sulfuric acid with the concentration of 100% into a double-screw extruder according to the proportion of 1:4.5, primarily mixing the PPTA raw material and the concentrated sulfuric acid by the extruder, pushing the mixture into a dissolving machine to complete the full dissolution of the PPTA in the concentrated sulfuric acid for 4 hours to obtain a polymer mixed solution with the mass fraction of the PPTA of 20%, and carrying out vacuum defoaming on the polymer mixed solution for 4 hours to ensure that the dissolving performance and the degradation performance are consistent to obtain a spinning solution.

(5) The spinning solution which is fully mixed, well temperature-regulated and completely bubble-removed is extruded and pushed at high pressure and is transmitted to a metering pump (the pressure of extrusion and pushing is 15MPa), and the spinning solution is filtered and then is sent to a fine hole spinneret plate. Wherein the temperature of the coagulating bath is set to be 30 ℃, the spinning solution is sprayed out of a spinneret plate to form filaments, the spun filaments are subjected to primary washing, alkali washing neutralization, washing and drying processes, and then are subjected to multistage heating, drying and shaping, and the temperature of a three-stage heating roller is set to be 150 ℃, 200 ℃ and 240 ℃. In the whole set of dry-jet wet-spinning process, the winding speed is 320m/min, oil is applied after cooling, and winding forming is carried out, so that the para-aramid fiber is obtained.

Example 3

A preparation method of high-elongation low-modulus para-aramid fiber comprises the following steps:

(1) adding anhydrous calcium chloride and N-methylpyrrolidone (NMP) into a reactor according to the weight ratio of 10:100, adding a proper amount of p-phenylenediamine (PPD), and stirring for 30min at room temperature;

(2) cooling the jacket of the reactor by introducing a cooling medium to reduce the temperature of the system to 0 ℃, adding a first batch of terephthaloyl chloride (TPC) accounting for 35 percent of the total amount, and continuously stirring for 30 min;

(3) and (3) reducing the temperature of the system to 0 ℃, adding 65% of TPC in the second batch, quickly stirring, stopping the reaction after the reaction system is gelled, climbed and crushed again to obtain the PPTA, wherein the molar ratio of the PPD added in the step (1) to the TPC added in the two batches in the steps (2) and (3) is 1: 1.02. Finally, the poly-p-phenylene terephthalamide (PPTA) with viscosity-average molecular weight of 40000 and intrinsic viscosity of 6.0dL/g is prepared;

(4) adding a PPTA raw material and concentrated sulfuric acid with the concentration of 101% into a double-screw extruder according to the proportion of 1:4.2, initially mixing the PPTA raw material and the concentrated sulfuric acid by the extruder, pushing the mixture into a dissolving machine to complete the full dissolution of the PPTA in the concentrated sulfuric acid for 2 hours to obtain a polymer mixed solution with the mass fraction of 18% of the PPTA, and carrying out vacuum defoaming on the polymer mixed solution for 3.5 hours to ensure that the dissolution performance and the degradation performance are consistent to obtain a spinning solution.

(5) The spinning solution which is fully mixed, well temperature-regulated and completely bubble-removed is extruded and pushed at high pressure and is transmitted to a metering pump (the pressure of extrusion and pushing is 20MPa), and the spinning solution is filtered and then is sent to a fine-hole spinneret plate. Wherein the temperature of the coagulating bath is set to be 25 ℃, the spinning solution is sprayed out of a spinneret plate to form filaments, the spun filaments are subjected to primary washing, alkali washing neutralization, washing and drying processes, and then are subjected to multistage heating, drying and shaping, and the temperature of a three-stage heating roller is set to be 120 ℃, 180 ℃ and 220 ℃. In the whole set of dry-jet wet-spinning process, the winding speed is 310m/min, oil is applied after cooling, and winding forming is carried out, so that the high-elongation low-modulus para-aramid fiber is obtained.

Example 4

A preparation method of high-elongation low-modulus para-aramid fiber comprises the following steps:

(1) adding anhydrous calcium chloride and N-methylpyrrolidone (NMP) into a reactor according to the weight ratio of 8:100, adding a proper amount of p-phenylenediamine (PPD), and stirring for 30min at room temperature;

(2) cooling the jacket of the reactor by introducing a cooling medium to reduce the temperature of the system to-10 ℃, adding a first batch of terephthaloyl chloride (TPC) accounting for 30 percent of the total amount, and continuously stirring for 30 min;

(3) and (3) reducing the temperature of the system to-10 ℃, adding 70% of TPC in the second batch, quickly stirring, stopping the reaction after the reaction system is gelled and climbed and is crushed again to obtain PPTA, wherein the molar ratio of PPD added in the step (1) to TPC added in the two batches in the steps (2) and (3) is 1: 1.01. Finally, the poly-p-phenylene terephthamide (PPTA) with the viscosity-average molecular weight of 47000 and the intrinsic viscosity of 7.2dL/g is prepared;

(4) adding a PPTA raw material and concentrated sulfuric acid with the concentration of 101% into a double-screw extruder according to the proportion of 1:4.4, initially mixing the PPTA raw material and the concentrated sulfuric acid by the extruder, pushing the mixture into a dissolving machine to complete the full dissolution of the PPTA in the concentrated sulfuric acid for 3.5 hours to obtain a polymer mixed solution with the mass fraction of 19% of the PPTA, and carrying out vacuum defoaming on the polymer mixed solution for 6 hours to ensure that the dissolving performance and the degradation performance are consistent to obtain a spinning solution.

(5) The spinning solution which is fully mixed, well temperature-regulated and completely bubble-removed is extruded and pushed at high pressure and is transmitted to a metering pump (the pressure of extrusion and pushing is 5MPa), and the spinning solution is filtered and then is sent to a fine hole spinneret plate. The coagulating bath temperature is set to 10 ℃, the spinning solution is sprayed out of a spinneret plate to form filaments, the spun filaments are subjected to primary washing, alkali washing neutralization, washing and drying processes, then multi-stage heating drying and shaping are carried out, and the temperature of a three-stage heating roller is set to 135 ℃, 190 ℃ and 235 ℃. In the whole set of dry-jet wet-spinning process, the winding speed is 290m/min, oil is applied after cooling, and winding forming is carried out, so that the high-elongation low-modulus para-aramid fiber is obtained.

The fiber elongation at break of the high-elongation low-modulus para-aramid fiber is 4.50%, the initial elastic modulus is 88Gpa, and the breaking strength is 20.50cN/dtex through the test of FZ/T54076-2014.

Example 5

A preparation method of high-elongation low-modulus para-aramid fiber comprises the following steps:

(1) adding anhydrous calcium chloride and N-methylpyrrolidone (NMP) into a reactor according to the weight ratio of 5.5:100, adding a proper amount of p-phenylenediamine (PPD), and stirring for 30min at room temperature;

(2) cooling the jacket of the reactor by introducing a cooling medium to reduce the temperature of the system to-5 ℃, adding a first batch of terephthaloyl chloride (TPC) accounting for 37 percent of the total amount, and continuously stirring for 30 min;

(3) and (3) reducing the temperature of the system to-5 ℃, adding 63% of TPC in the second batch, quickly stirring, stopping the reaction after the reaction system is gelled and climbed and is crushed again to obtain PPTA, wherein the molar ratio of PPD added in the step (1) to TPC added in the two batches in the steps (2) and (3) is 1: 1.04. Finally, the poly-p-phenylene terephthamide (PPTA) with viscosity-average molecular weight of 43000 and intrinsic viscosity of 6.5dL/g is prepared;

(4) adding a PPTA raw material and concentrated sulfuric acid with the concentration of 100% into a double-screw extruder according to the proportion of 1:4.3, initially mixing the PPTA raw material and the concentrated sulfuric acid by the extruder, pushing the mixture into a dissolving machine to complete the full dissolution of the PPTA in the concentrated sulfuric acid, wherein the dissolving time is 1 hour, obtaining a polymer mixed solution with the mass fraction of the PPTA of 16.5%, and carrying out vacuum defoaming on the polymer mixed solution for 2 hours, so that the dissolving performance and the degradation performance are consistent, and obtaining a spinning solution.

(5) The spinning solution which is fully mixed, well temperature-regulated and completely bubble-removed is extruded and pushed at high pressure and is transmitted to a metering pump (the pressure of extrusion and pushing is 8MPa), and the spinning solution is filtered and then is sent to a fine hole spinneret plate. The coagulating bath temperature is set to be 20 ℃, the spinning solution is sprayed out of a spinneret plate to form filaments, the spun filaments are subjected to primary washing, alkali washing neutralization, washing and drying processes, then multi-stage heating drying and shaping are carried out, and the temperature of a three-stage heating roller is set to be 110 ℃, 170 ℃ and 215 ℃. In the whole set of dry-jet wet-spinning process, the winding speed is 280m/min, and the para-aramid fiber is obtained after cooling, oiling and winding forming.

The fiber elongation at break of the high-elongation low-modulus para-aramid fiber is 3.50%, the initial elastic modulus is 80Gpa, and the breaking strength is 24.00cN/dtex through the test of FZ/T54076-2014.

Comparative example 1

The spinning solution which is fully mixed, well temperature-regulated and completely bubble-removed is delivered under high pressure, passes through a metering pump and is filtered, and then is sent into a fine-hole spinneret plate. Wherein the coagulation bath temperature was set to 5 ℃. The rest is the same as in example 1.

Comparative example 2

Spinning solution is sprayed out of a spinneret plate to form filaments, the spun filaments are subjected to primary washing, alkali washing neutralization, washing and drying processes, and then are subjected to multi-stage heating, drying and shaping, and the temperature of a three-stage heating roller is set to be 90 ℃, 155 ℃ and 245 ℃. The rest is the same as in example 1.

Comparative example 3

In the whole set of dry-jet wet-spinning process, the winding speed is 260m/min, and the para-aramid fiber is obtained after oil application and winding forming after cooling. The rest is the same as in example 1.

The aramid fibers prepared in the above examples and comparative examples were subjected to performance tests, the test method adopted FZ/T54076-2014, and the results are shown in Table 1.

TABLE 1 Performance test results of aramid fibers of examples and comparative examples

In conclusion, the invention discloses a preparation method of high-elongation low-modulus para-aramid fiber, which adopts the processes of low-temperature solution polycondensation and dry-jet wet spinning, mainly solves the problem of non-uniformity of the distribution of the polymeric molecular weight, and realizes the distribution of the polymeric molecular weight in a narrower range; optimizing the design of the para-aramid spinning process and setting the process of the coagulation bath temperature, realizing the production continuity, controlling the parameters such as the fiber orientation degree, the mechanical property of nascent fiber and the like, and optimizing the production process; the temperature is set in the post-treatment processes of para-aramid washing, drying and the like, the fiber crystallization parameters in the fiber stretching process are controlled, and the product performance is improved. Based on the para-aramid fiber obtained by the preparation method, the performance test of FZ/T54076-2014 shows that the test result of the high-elongation low-modulus para-aramid fiber prepared by the invention is in accordance with: the fiber elongation at break is more than or equal to 3.5 percent, the initial elastic modulus is 80-88 Gpa, the breaking strength is more than or equal to 20.5cN/dtex, and the application requirements of the para-aramid in the fields of automobile rubber tubes, tires and conveying belts are met.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.