阅读说明：本技术 一种聚对苯撑苯并二噁唑纤维的制备方法 (Preparation method of poly (p-phenylene-benzobisoxazole) fibers ) 是由 陈湘栋 刘群 刘薇 钟蔚华 郭程 刘宗法 张晓光 张殿波 孟昭瑞 于 2021-01-27 设计创作，主要内容包括：本发明属于高性能纤维领域,尤其涉及一种聚对苯撑苯并二噁唑纤维的制备方法。以冷冻多聚磷酸粉末、五氧化二磷、4,6-二氨基间苯二酚盐酸盐和对苯二甲酸为原料,将五氧化二磷选择合适时间段以合理的比例分步投入到反应体系中,并对预聚过程物料表观粘度实时检测和调控,确保得到表观粘度均一的预聚物,然后经过后聚合得到PBO纺丝浆液,经过干喷湿纺和后纺获得成品PBO纤维。该方法解决了传统固体原料与溶剂混合分散效果差,易团聚、不能均匀反应的缺点,而且保证了预聚反应终点的一致性,减少工艺误差。同一批次不同时间段聚合物特性粘度变化小,特性粘度高,纤维力学性能可明显提高,质量稳定性也得到提高。(The invention belongs to the field of high-performance fibers, and particularly relates to a preparation method of poly (p-phenylene benzobisoxazole) fibers. The preparation method comprises the steps of taking frozen polyphosphoric acid powder, phosphorus pentoxide, 4, 6-diaminoresorcinol hydrochloride and terephthalic acid as raw materials, putting the phosphorus pentoxide into a reaction system step by step in a reasonable proportion in a proper time period, detecting and regulating apparent viscosity of materials in a prepolymerization process in real time to ensure that a prepolymer with uniform apparent viscosity is obtained, then carrying out post-polymerization to obtain PBO spinning slurry, and carrying out dry-jet wet spinning and post-spinning to obtain the finished PBO fiber. The method overcomes the defects of poor mixing and dispersing effects, easy agglomeration and non-uniform reaction of the traditional solid raw materials and solvents, ensures the consistency of the prepolymerization reaction end point and reduces process errors. The intrinsic viscosity of the polymer in the same batch and different time periods is small in change, the intrinsic viscosity is high, the mechanical property of the fiber can be obviously improved, and the quality stability is also improved.)

1. A preparation method of poly-p-phenylene benzobisoxazole fiber is characterized by comprising the following steps: the method comprises the following steps:

(1) mixing and degassing:

freezing polyphosphoric acid at low temperature to obtain solid, and pulverizing into fine powder; phosphorus pentoxide is added in the steps of mixing, degassing and prepolymerization step by step according to a certain proportion; adding polyphosphoric acid solid powder, 4, 6-diaminoresorcinol hydrochloride, terephthalic acid, part of phosphorus pentoxide and antioxidant stannous chloride into a stirring kettle, keeping low temperature, stirring and dispersing uniformly, transferring to a reaction kettle, and continuously mixing and degassing;

(2) pre-polymerization:

after the mixing and degassing step is finished, under the protection of inert gas, heating to 100 ℃, preserving heat and reacting for 2-4 h at 120 ℃, preserving heat and reacting for 3-5 h at 135 ℃, preserving heat and reacting for 2-7 h at 155 ℃, wherein phosphorus pentoxide is replenished when the temperature is raised to 100 ℃ and 135 ℃ respectively; reacting to obtain PBO prepolymer;

(3) post-polymerization:

the prepolymer is further polymerized after being processed by a double-screw extruder to finally obtain poly (p-phenylene benzobisoxazole) spinning slurry;

(4) spinning:

PBO spinning slurry is filtered, a spinning assembly and a hot air channel form spinning trickle, and the spinning trickle sequentially passes through a coagulating bath, water washing and drying to obtain the final poly-p-phenylene benzobisoxazole fiber.

2. The method for preparing polyparaphenylene benzobisoxazole fiber according to claim 1, characterized in that:

wherein in the step (1), the terephthalic acid is subjected to pre-crushing treatment, the particle size of the treated terephthalic acid reaches 2-15 mu m, the freezing temperature of the polyphosphoric acid is-50 to-30 ℃, and the particle size of the powder of the frozen polyphosphoric acid after crushing treatment reaches 50-100 mu m.

3. The method for preparing polyparaphenylene benzobisoxazole fiber according to claim 1, characterized in that:

the mixing and degassing process in the step (1) comprises the following steps: the mixed material is vacuumized at 80-95 ℃, the vacuum degree is-0.06-0.095 MPa, and the degassing time is 6-10 h.

4. The method for preparing polyparaphenylene benzobisoxazole fiber according to claim 1, characterized in that:

the phosphorus pentoxide dosage in the steps (1) and (2) is as follows: the mass of phosphorus pentoxide put into the mixing and degassing stage is as follows: adding phosphorus pentoxide when the temperature is raised to 100 ℃: when the temperature is raised to 135 ℃, 70-85% of phosphorus pentoxide is added: 10% -20%: 5 to 10 percent.

5. The method for preparing polyparaphenylene benzobisoxazole fiber according to claim 1, characterized in that:

in the steps (1) and (2), the mass of the 4, 6-diaminoresorcinol hydrochloride accounts for 14-23 wt% of the mass of the PBO prepolymer, and the molar ratio of the input amount of the terephthalic acid to the 4, 6-diaminoresorcinol hydrochloride is 1: the mass of polyphosphoric acid accounts for 50.6-57.2 wt% of the mass of the PBO prepolymer, the total input mass of phosphorus pentoxide accounts for 21.4-26.7 wt% of the mass of the PBO prepolymer, and the mass of stannous chloride added accounts for 0.2-1.5 wt% of the mass of the PBO prepolymer.

6. The method for preparing polyparaphenylene benzobisoxazole fiber according to claim 1, characterized in that:

and (3) detecting the apparent viscosity in the prepolymerization process in real time in the prepolymerization in the step (2), and stopping the prepolymerization reaction to obtain the prepolymer when the apparent viscosity of the PBO prepolymer is detected to be 450-750 Pa.s in the heat preservation reaction process at 155 ℃.

7. The method for preparing polyparaphenylene benzobisoxazole fiber according to claim 1, characterized in that:

in the step (3), the material retention time of the extruder is 60-130 min, the temperature of the double-screw extruder is divided into 9 zones, the temperature is set from the direction of the feed inlet, and the first zone is as follows: 150-160 ℃, and a second region and a third region: 160-175 ℃, fourth-sixth zone: 175-195 ℃, seventh-ninth zones: 195-225 ℃; obtaining final polymer spinning slurry; the intrinsic viscosity of the polymer is 35-41 dL/g.

8. The method for preparing p-phenylene benzobisoxazole fiber as claimed in claim 1, wherein the spinning dope before entering the spinning assembly is sampled at intervals of 2.5h in the step (4), the intrinsic viscosity of the PBO polymer is measured, and the change of the intrinsic viscosity of the polymer at different time periods is detected.

9. The method for preparing polyparaphenylene benzobisoxazole fiber according to claim 1, characterized in that:

in the step (4), the drying is carried out by adopting heat pipe non-contact heating, the residence time of the fiber in the heat pipe is 8-30 s, and the drying temperature of the fiber is 160-220 ℃.

Technical Field

The invention belongs to the field of high-performance fibers, and particularly relates to a preparation method of poly (p-phenylene-benzobisoxazole) fibers.

Background

The poly-p-Phenylene Benzobisoxazole (PBO) (cis and trans conformations) benzene ring and oxazole ring are almost coplanar with a chain axis, and are bilaterally symmetrical rigid rod-shaped molecular structures which are one form with the lowest energy. Due to the use of liquid crystal spinning technology, macromolecular chains, crystals and microfibrils/fibrils are all arranged along the axial direction of the fiber in an almost completely oriented manner, and a highly oriented ordered structure is formed. Therefore, the unique structure of the PBO fiber determines the excellent and outstanding performance of the PBO fiber, has the characteristics of high strength, high modulus, high heat resistance and good flame retardance, has good dimensional stability and high chemical resistance stability, and is the best comprehensive performance in all the organic fibers at present. The method is not only widely applied to the fields of science and technology, war industry and national defense such as aerospace, bullet-resistant armor protection and the like, but also widely applied to the civil fields such as sports equipment, protective clothing and the like. PBO fibers were produced industrially in the last 90 s by eastern japan textile company (trade name Zylon), which currently produces 2000 tons per year.

At present, many countries in the world still consume a great deal of manpower, material resources and financial resources to research and prepare the PBO fiber, but only a few companies can carry out industrial production. There are many methods and process routes for preparing PBO fiber at home and abroad, the main flow comprises monomer synthesis, polymer preparation, fiber forming and post-treatment, and in the industrial process preparation process, many technical problems still exist and cannot be solved.

(1) Polyphosphoric acid is used as a solvent or an initiator in a PBO polymerization system, but is viscous at normal temperature and has high density. The densities of the 4, 6-diaminoresorcinol hydrochloride, the terephthalic acid and the phosphorus pentoxide raw materials are greatly different, the raw materials are difficult to obtain good dispersion and mixing in the PPA solvent, the phenomenon that the raw materials cannot react uniformly and cause local agglomeration is easy to occur, and the requirement on stirring reaction equipment is high.

(2) Secondly, in many patents and documents, spinning slurry is obtained by two steps of prepolymerization and postpolymerization, but the condition control of the reaction process in the prepolymerization process and the end point of the prepolymerization end are not explicitly indicated, and the optimization and the stability of subsequent process parameters can be realized only by ensuring the batch consistency of the prepolymer in the prepolymerization process, so that the quality stability of fiber batches is ensured.

The PBO polymerization reaction can be completed only after long-time high-frequency shearing under the high-temperature condition, meanwhile, the difficulty of conveying high-viscosity materials is overcome, the PBO polymer with high relative molecular mass is the main reason for obtaining the high-mechanical-property fiber, and therefore how to obtain the PBO polymer with a high intrinsic viscosity range is also an important problem to be solved in the field.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a preparation method of poly (p-phenylene-benzobisoxazole) fiber. The preparation method comprises the steps of taking frozen polyphosphoric acid powder, phosphorus pentoxide, 4, 6-diaminoresorcinol hydrochloride and terephthalic acid as raw materials, putting the phosphorus pentoxide into a reaction system step by step in a reasonable proportion in a proper time period, detecting and regulating apparent viscosity of materials in a prepolymerization process in real time to ensure that a prepolymer with uniform apparent viscosity is obtained, then carrying out post-polymerization to obtain PBO spinning slurry, and carrying out dry-jet wet spinning and post-spinning to obtain the finished PBO fiber. The method overcomes the defects of poor mixing and dispersing effects, easy agglomeration and non-uniform reaction of the traditional solid raw materials and solvents, ensures the consistency of the prepolymerization reaction end point and reduces process errors. The intrinsic viscosity of the polymer in the same batch and different time periods is small in change, the intrinsic viscosity is high, the mechanical property of the fiber can be obviously improved, and the quality stability is also improved.

The specific technical scheme of the invention is as follows:

a preparation method of poly-p-phenylene benzobisoxazole fibers comprises the following steps:

(1) mixing and degassing:

freezing polyphosphoric acid at low temperature to obtain solid, and pulverizing into fine powder; phosphorus pentoxide is added in the steps of mixing, degassing and prepolymerization step by step according to a certain proportion; adding polyphosphoric acid solid powder, 4, 6-diaminoresorcinol hydrochloride, terephthalic acid, part of phosphorus pentoxide and antioxidant stannous chloride into a stirring kettle, keeping low temperature, stirring and dispersing uniformly, transferring to a reaction kettle, and continuously mixing and degassing;

(2) pre-polymerization:

after the mixing and degassing step is finished, under the protection of inert gas, heating to 100 ℃, preserving heat and reacting for 2-4 h at 120 ℃, preserving heat and reacting for 3-5 h at 135 ℃, preserving heat and reacting for 2-7 h at 155 ℃, wherein phosphorus pentoxide is replenished when the temperature is raised to 100 ℃ and 135 ℃ respectively; reacting to obtain PBO prepolymer;

in the step (1), the terephthalic acid is subjected to pre-crushing treatment, and the particle size of the treated terephthalic acid is 2-15 microns. The freezing temperature of the polyphosphoric acid is-50 to-30 ℃, and the particle size of the powder of the frozen polyphosphoric acid after being crushed reaches 50 to 100 mu m;

the mixing and degassing process in the step (1) comprises the following steps: vacuumizing the mixed material at 80-95 ℃, wherein the vacuum degree is-0.06-0.095 MPa, and the degassing time is 6-10 h;

in the steps (1) and (2), the dosage of the phosphorus pentoxide is as follows: the mass of phosphorus pentoxide put into the mixing and degassing stage is as follows: adding phosphorus pentoxide when the temperature is raised to 100 ℃: when the temperature is raised to 135 ℃, 70-85% of phosphorus pentoxide is added: 10% -20%: 5% -10%;

in the steps (1) and (2), the mass of the 4, 6-diaminoresorcinol hydrochloride accounts for 14-23 wt% of the mass of the PBO prepolymer, and the molar ratio of the input amount of the terephthalic acid to the 4, 6-diaminoresorcinol hydrochloride is 1: 1, the mass of polyphosphoric acid accounts for 50.6-57.2 wt% of the mass of the PBO prepolymer, the total input mass of phosphorus pentoxide accounts for 21.4-26.7 wt% of the mass of the PBO prepolymer, and the mass of stannous chloride added accounts for 0.2-1.5 wt% of the mass of the PBO prepolymer;

and (3) in the prepolymerization in the step (2) in the reaction process, detecting the apparent viscosity in the prepolymerization reaction process in real time, and stopping the prepolymerization reaction when the apparent viscosity of the PBO prepolymer is detected to be 450-750 pas in the heat preservation reaction process at 155 ℃ to obtain the prepolymer.

(3) Post-polymerization:

the prepolymer is further subjected to post-polymerization by a double-screw extruder to finally obtain poly (p-phenylene benzobisoxazole) spinning slurry, and the final intrinsic viscosity of the polymer is 35-41 dL/g;

and (4) the material retention time of the extruder in the step (3) is 60-130 min. The temperature of the twin-screw extruder is divided into 9 zones, the temperature is set from the direction of the feed inlet, and the first zone: 150-160 ℃, and a second region and a third region: 160-175 ℃, fourth-sixth zone: 175-195 ℃, seventh-ninth zones: 195-225 ℃. The spinning slurry before entering the spinning assembly is sampled every 2.5h, the intrinsic viscosity of the PBO polymer is measured, and the change of the intrinsic viscosity of the polymer in different time periods is detected.

The main advantages of the twin-screw extruder polymerization are that the polymerization temperature is higher than that of the conventional process, the lower temperature of the first zone is used for promoting the further mixing and dispersion of the prepolymer material, the polymerization temperature of the later zones is set to be higher, and the high-viscosity PBO polymer can be obtained more easily.

(4) Spinning:

PBO spinning slurry is filtered, a spinning assembly and a hot air channel form spinning trickle, and the spinning trickle is subjected to coagulating bath, water washing and drying to obtain final poly (p-phenylene benzobisoxazole) fiber;

the drying is carried out in a heat pipe in a non-contact manner, the residence time of the fibers in the heat pipe is 8-30 s, and the drying temperature of the fibers is 160-220 ℃;

the heat pipe non-contact heating has the advantages that the heat pipe non-contact heating can be avoided from being in direct contact with a hot roller, the phenomenon that drying of the whole bundle of fibers is influenced due to uneven heating of each fiber is avoided, the generation of broken filament phenomenon can be reduced, and the quality of the fibers is improved.

In addition, the other technical schemes of the invention all adopt the conventional prior art, and the inventor does not need to describe any more.

Compared with the prior art, the method has the main improvements that:

(1) from the production process, it is conventional to mix all or part of the monomers in a precisely metered amount into the PPA solvent, and to obtain a prepolymer by degassing and polymerizing by gradually increasing the temperature and stirring or directly obtain a polymer. The method mainly adopts the steps of fully mixing frozen polyphosphoric acid powder with other monomer particles, and then gradually heating and stirring to complete prepolymerization. On one hand, the method is more beneficial to uniformly mixing raw materials and reducing the material gathering condition. On the other hand, the method is favorable for realizing uniform reaction, greatly reduces the existence of monomers in the prepolymer, is favorable for obtaining more stable prepolymer, and reduces the dispersion coefficient of the intrinsic viscosity of the same batch of polymer obtained in different time periods. Practice proves that the viscosity dispersion coefficient of the polymer obtained by the method of the invention in the same batch and different time periods is 1.3% -3.4%.

(2) Different from the traditional method of feeding phosphorus pentoxide all at one time, the method of the invention feeds the phosphorus pentoxide three times, realizes reasonable control of the feeding ratio by controlling the mass proportion of each feeding, and achieves the final phosphorus pentoxide content of the system. By changing the feeding mode of phosphorus pentoxide, the viscosity of the system can be reduced at the early stage, the degassing is facilitated, the degassing time is reduced from the existing 10-15 h to 6-10 h, the degassing efficiency is obviously improved, and the degassing time is reduced; in addition, the inventive method promotes further thorough mixing and dispersion of the raw materials with the solvent.

(3) The method provided by the invention can be used for detecting the apparent viscosity of the prepolymerization material in the whole prepolymerization reaction process in real time, effectively controlling the prepolymerization process and the end point according to the time-viscosity curve data by efficiently monitoring a prepolymerization reaction system, greatly improving the batch consistency of the prepolymer and directly influencing the subsequent polymer intrinsic viscosity and fiber quality batch stability. Compared with the prior art, the method provided by the invention controls the apparent viscosity of the prepolymer at the end point of the prepolymerization reaction, so that the dispersion coefficient of the intrinsic viscosity of different batches of polymers is reduced from 11% to 5%.

(4) The intrinsic viscosity value of PBO polymer used for producing fiber conventionally in China is 20-30 dL/g, the PBO polymer with the intrinsic viscosity of 35-41 dL/g can be obtained by the method, the PBO fiber can obtain a better aggregation state structure, and the mechanical property of the fiber can be obviously improved.

In conclusion, the technical scheme of the invention overcomes the defects of poor mixing and dispersing effects and easy agglomeration of the traditional solid raw materials and solvents, ensures the consistency of the prepolymerization reaction end point and reduces process errors. The intrinsic viscosity dispersion coefficient of the polymer at different time of the same batch is small (1.3-3.4%), the intrinsic viscosity of the polymer is high (35-41 dL/g), the mechanical property of the fiber can be obviously improved, the quality stability is also improved, the high-strength poly (p-phenylene benzobisoxazole) fiber can be prepared in the enlarged production process, and the method is suitable for industrial production.

Detailed Description

The present invention is further illustrated below with reference to examples, which will enable those skilled in the art to more fully understand the present invention, but which are not intended to limit the invention in any way;

example 1:

a preparation method of poly-p-phenylene benzobisoxazole fibers comprises the following steps:

(1) mixing and degassing: the air in the mixing kettle was replaced with nitrogen, 240g of 4, 6-diaminoresorcinol hydrochloride, 187g of terephthalic acid with a particle size of 13 μm, 977.1g of frozen polyphosphoric acid powder, 322.3g of phosphorus pentoxide and 7.8g of stannous chloride were stirred and mixed, and then the mixture was put into a reaction kettle, the temperature of the reaction kettle was raised to 93 ℃, vacuum pumping was started to degas, the vacuum degree was-0.06 MPa, and the degassing time was 6 hours.

(2) Pre-polymerization: and (2) introducing nitrogen into the reaction kettle to change the negative pressure into the positive pressure of 0.01MPa, continuing to finish prepolymerization, heating the material obtained by degassing in the step (1) to 100 ℃, adding 60.4g of phosphorus pentoxide, preserving heat for 3 hours, then preserving heat for 3.5 hours at 120 ℃, adding 20.1g of phosphorus pentoxide, preserving heat for 4 hours, heating to 135 ℃, and finally, heating to 155 ℃ and preserving heat. And (3) detecting the viscosity of the material in real time by an apparent viscosity detector in the prepolymerization process, detecting that the apparent viscosity of the prepolymerization material reaches 500 Pa.s in the heat preservation process at 155 ℃, and finishing the prepolymerization reaction.

(3) Post-polymerization: the pre-polymerized material is conveyed into a screw reactor for post polymerization, and the material stays in an extruder for 65 min. The temperature of the double-screw extruder is set from the direction of the feed inlet, and the temperature of the double-screw extruder is set in a first area: 155 ℃, second, third region: 170 ℃, fourth to sixth zones: 185 ℃, seventh to ninth zones: at 210 ℃. The intrinsic viscosity of the polymer was measured by an Ubbelohde viscometer to be 35 dL/g.

(4) Spinning: and filtering the spinning slurry, forming a spinning trickle by a spinning assembly, shaping the stretched fiber by a coagulating bath, removing a large amount of phosphoric acid by washing, drying at the temperature of 200 ℃ for 12s, and winding to obtain the nascent PBO fiber.

Through detection, the intrinsic viscosity dispersion coefficient of the polymer prepared by the scheme of the embodiment in different time periods is 1.9%, and the strength and the modulus of the prepared nascent PBO fiber can reach 5.42GPa and 168GPa respectively.

Example 2:

a preparation method of poly-p-phenylene benzobisoxazole fibers comprises the following steps:

(1) mixing and degassing: the air in the mixing kettle is replaced by nitrogen, 325.6g of 4, 6-diaminoresorcinol hydrochloride, 253.8g of terephthalic acid with the particle size of 8 mu m, 1325.6g of frozen polyphosphoric acid powder, 409.9g of phosphorus pentoxide and 15.8g of stannous chloride are stirred, mixed and then put into a reaction kettle, the temperature of the reaction kettle is raised to 88 ℃, the reaction kettle starts to be vacuumized and degassed, the vacuum degree is-0.08 MPa, and the degassing time is 7.2 h.

(2) Pre-polymerization: and (2) introducing nitrogen into the reaction kettle to change the negative pressure into the positive pressure of 0.01MPa, continuing to finish prepolymerization, heating the degassed material obtained in the step (1) to 100 ℃, adding 92.9g of phosphorus pentoxide, preserving heat for 3 hours, then preserving heat for 4 hours at 120 ℃, adding 43.7g of phosphorus pentoxide, preserving heat for 5 hours when the temperature is raised to 135 ℃, and finally heating to 155 ℃ for heat preservation. And (3) detecting the viscosity of the material in real time by an apparent viscosity detector in the prepolymerization process, detecting that the apparent viscosity of the prepolymerization material reaches 620 Pa.s in the heat preservation process at 155 ℃, and finishing the prepolymerization reaction.

(3) Post-polymerization: the pre-polymerized material is conveyed into a screw reactor for post polymerization, and the material stays in an extruder for 78 min. The temperature of the double-screw extruder is set from the direction of the feed inlet, and the temperature of the double-screw extruder is set in a first area: 152 ℃, second, third zone: 166 ℃, fourth to sixth zones: 190 ℃, seventh to ninth zones: at 210 ℃. The intrinsic viscosity of the polymer was measured by an Ubbelohde viscometer to be 38 dL/g.

(4) Spinning: filtering the post-polymerization material, forming spinning trickle by a spinning assembly, shaping the stretched fiber by a coagulating bath, removing a large amount of phosphoric acid by washing, drying at 160 ℃ for 27s, and winding to obtain the nascent PBO fiber.

The intrinsic viscosity coefficient of variation of the polymer over different time periods produced according to the embodiment of this example was determined to be 2.3%. The strength and modulus of the prepared nascent PBO fiber can reach 5.49GPa and 168GPa respectively.

Example 3:

a preparation method of poly-p-phenylene benzobisoxazole fibers comprises the following steps:

(1) mixing and degassing: the air in the mixing kettle was replaced with nitrogen, 434g of 4, 6-diaminoresorcinol hydrochloride, 338g of terephthalic acid with a particle size of 8 μm, 1767g of frozen polyphosphoric acid powder, 509.5g of phosphorus pentoxide and 17.7g of stannous chloride were stirred and mixed, and then the mixture was put into a reaction kettle, the temperature of the reaction kettle was raised to 82 ℃, vacuum pumping was started to degas, the vacuum degree was-0.093 MPa, and the degassing time was 9.8 hours.

(2) Pre-polymerization: and (2) introducing nitrogen into the reaction kettle to change the negative pressure into the positive pressure of 0.01MPa, continuing to finish prepolymerization, heating the degassed material obtained in the step (1) to 100 ℃, adding 145.7g of phosphorus pentoxide, keeping the temperature for 4h, then keeping the temperature for 4h at 120 ℃, heating to 135 ℃, adding 72.9g of phosphorus pentoxide, keeping the temperature for 5h, and finally heating to 155 ℃ and keeping the temperature. And (3) detecting the viscosity of the material in real time by an apparent viscosity detector in the prepolymerization process, detecting that the apparent viscosity of the prepolymerization material reaches 730 pas in the heat preservation process at 155 ℃, and finishing the prepolymerization reaction.

(3) Post-polymerization: the pre-polymerized material is conveyed into a screw reactor for post polymerization, and the material stays in an extruder for 92 min. The temperature of the double-screw extruder is set from the direction of the feed inlet, and the temperature of the double-screw extruder is set in a first area: 155 ℃, second, third region: 175 ℃, fourth to sixth zones: 188 ℃, seventh to ninth zones: 215 ℃ is adopted. The intrinsic viscosity of the polymer was measured by an Ubbelohde viscometer to be 41 dL/g.

(4) Spinning: filtering the post-polymerization material, forming spinning trickle by a spinning assembly, shaping the stretched fiber by a coagulating bath, removing a large amount of phosphoric acid by washing, drying at 180 ℃ for 20s, and winding to obtain the nascent PBO fiber.

The intrinsic viscosity coefficient of variation of the polymer over different time periods produced according to the embodiment of this example was determined to be 1.5%. The strength and modulus of the prepared nascent PBO fiber can reach 5.6GPa and 170GPa respectively.

Comparative example:

the comparative example provides a traditional method for preparing poly (p-phenylene benzobisoxazole) fiber, and comprises the following steps:

(1) mixing and degassing: 1216.5g of polyphosphoric acid liquid was charged into a reaction kettle purged with nitrogen, 13.4g of stannous chloride was added, and 298.8g of 4, 6-diaminoresorcinol hydrochloride, 232.9g of terephthalic acid having a particle size distribution of 3 μm and 501.5g of phosphorus pentoxide were mixed with stirring. And putting the mixture into a reaction kettle, heating the reaction kettle to 95 ℃, vacuumizing to degas at the vacuum degree of-0.093 MPa for 12 h.

(2) Pre-polymerization: and (3) introducing nitrogen into the reaction kettle to change the negative pressure into the positive pressure of 0.01MPa, continuing to finish prepolymerization, heating the material obtained by degassing in the step (1) to 100 ℃, preserving heat for 2h, preserving heat for 3h at 120 ℃, heating to 135 ℃, preserving heat for 4h, and heating to 155 ℃ and preserving heat for 3 h. The prepolymerization reaction time is taken as the end point of the prepolymerization.

(3) Post-polymerization: the pre-polymerized material is conveyed into a screw reactor for post polymerization, and the material stays in an extruder for 48 min. The temperature of the double-screw extruder is set from the direction of the feed inlet, and the temperature of the double-screw extruder is set in a first area: 150 ℃, second, third zone: 166 ℃, fourth to sixth zones: 180 ℃, seventh to ninth zones: 190 ℃. The intrinsic viscosity of the polymer was measured by an Ubbelohde viscometer to be 27.4 dL/g.

(4) Spinning: filtering the post-polymerization material, forming spinning trickle by a spinning assembly, shaping the stretched fiber by a coagulating bath, removing a large amount of phosphoric acid by washing, drying at the temperature of 170 ℃ for 20s, and winding to obtain the nascent PBO fiber.

Through detection, the strength and the modulus of the PBO fiber prepared by the scheme of the comparative example can respectively reach 5.0GPa and 150 GPa. The intrinsic viscosity coefficient of variation for the polymer prepared according to this comparative example protocol was 5.2% for different time periods.

From the above results, it can be seen that the comparative examples are substantially identical to the process steps of examples 1-3, but the related properties of the nascent PBO fibers obtained from the comparative examples are lower than those of examples 1-3. The inventors analyzed that this is because phosphorus pentoxide was not added in portions at the early stage of the prepolymerization reaction in the comparative examples, the early stage viscosity was high, the effect of dispersing and mixing the starting materials was poor, and the dehydrochlorination time was prolonged; moreover, the dispersion of the intrinsic viscosity of the polymer in the same batch at different time periods is high, and the intrinsic viscosity of the whole polymer is low. The fiber spun by the polymer has the disadvantages of overall reduction of fiber strength, increase of yarn evenness, increase of broken filaments of the fiber and reduction of fiber quality.

Therefore, the technical scheme of the invention solves the problems of poor dispersion effect of raw materials and easy agglomeration. In addition, the invention adopts a more accurate detection means to ensure the consistency of the prepolymerization reaction process and the end point, and is beneficial to the industrial continuous preparation of the poly (p-phenylene benzobisoxazole) fiber.