CN112458551A

CN112458551A - Method for spinning polybenzazole fibers

Info

Publication number: CN112458551A
Application number: CN202011326118.5A
Authority: CN
Inventors: 范新年; 许伟; 付兴伟; 赵亮; 黄治川; 冉茂强
Original assignee: Zhonglan Chenguang Chemical Co ltd; China Bluestar Chengrand Research Institute of Chemical Industry Co Ltd
Current assignee: Zhonglan Chenguang Chemical Co ltd; China Bluestar Chengrand Research Institute of Chemical Industry Co Ltd
Priority date: 2020-11-23
Filing date: 2020-11-23
Publication date: 2021-03-09

Abstract

The invention discloses a method for spinning polybenzazole fibers, which comprises the steps of firstly passing a polybenzazole spinning stock solution through a spinneret plate with an angle theta of less than or equal to 25 degrees in a transition cone before a capillary or a spinneret plate with smooth contraction of arc shape in front of the capillary, spraying the polybenzazole spinning stock solution under the pressure drop of less than or equal to 13MPa, and stretching, solidifying, washing, drying and rolling the sprayed filaments. The spinneret plate has at least 2 sections of front transition cone cylinders of capillaries or smooth arc transition cone cylinders, the angle theta of the transition cone cylinders is small, and proper capillary diameter, length-diameter ratio and pressure drop are selected in a matching manner, so that the spinning stability is high, the spinning speed and production efficiency can be greatly improved, the spinneret plate is very suitable for industrial production, the mechanical property of fibers can be fully guaranteed, and the spinneret plate is suitable for preparing high-strength polybenzoxazole fibers.

Description

Method for spinning polybenzazole fibers

Technical Field

The invention belongs to the technical field of industrial production of polybenzazole fibers, and particularly relates to a spinning method for preparing high-strength polybenzazole fibers with high production efficiency and good stability.

Background

Polybenzazole fibers are aromatic heterocyclic fibers in which the heterocyclic ring may be oxazole, thiazole or imidazole, etc., and the main representative species are poly (p-Phenylenebenzobisoxazole) (PBO) fibers, poly [2, 5-dihydroxy-1, 4-phenylenepyridobisimidazole ] (PIPD) fibers and Polybenzimidazole (PBI) fibers. Generally, polybenzazole fibers are prepared by dry-jet wet spinning techniques, and have the advantages of high strength, high modulus and heat resistance. However, since the polybenzazole polymer has a very rigid molecular structure, the viscosity of a polybenzazole-containing dope is very high, and it has a great influence on the spinning part of the spinning process, such as: 1. too high a viscosity of the polybenzazole polymer dope causes too high a pressure of a spinning pack, and material leakage is likely to occur during spinning. In order to avoid material leakage, higher requirements are put forward on the sealing performance of the assembly, so that the requirements on the processing precision of the spinning assembly are high, and the requirements on assembly operation are very strict. 2. Since the spinning dope of polybenzazole polymer generally exhibits liquid crystallinity, its flow behavior in the spinning section during the preparation of fibers by dry-jet wet spinning has an important influence on the spinning stability and fiber properties. Like polymer melt in melt spinning, when the viscosity of polybenzazole spinning solution is too high, the surface of sprayed filament is sharkskin-like, and even cracks occur in severe cases. The unstable rheological behavior can also cause the problems of plate sticking, plate overflowing, wire breakage and the like at a spinneret plate, seriously affect the spinning process and cause poor processability. In general, since spinning equipment is expensive, it is economically desirable to increase the spinning speed as much as possible. In addition, in order to prepare polybenzazole fibers with high performance (i.e., high strength, high modulus, flame retardancy, heat resistance, etc. of the fibers), it is generally necessary to achieve fine denier of the fibers during spinning to improve the uniformity and homogeneity of the inside and outside of the fibers. This places a high demand on the stability of the polybenzazole fiber in the high speed spinning process.

JP05304112 discloses a preparation method of polybenzazole fiber, which adopts a spinneret plate with an angle of a transition cone cylinder in front of a capillary tube being below 30 degrees, can realize stable spinning at a speed of 150m/min, and the single fiber diameter of the obtained fiber can reach 18 μm. However, when the flow rate of the spinning solution is increased to further increase the spinning speed, the yarn breakage frequency at the spinneret plate is increased, which leads to the reduction of the spinning stability; meanwhile, the mechanical properties of the prepared polybenzazole fiber such as strength and the like are reduced. This is because the dope of polybenzazole polymer in the form of a rigid rod has a very high viscosity, and its rheological behavior is not only related to the angle of the transition cone in front of the capillaries of the spinneret, but also to the length and diameter of the capillaries, the pressure drop across the spinneret, and the like. Therefore, at present, the technical scheme disclosed by the prior art (JP05304112) only improves the angle of the transition cone barrel in front of the capillary of the spinneret plate, the obtained spinning speed can only reach 150m/min, and the economical efficiency is low; when the flow of the spinning solution is continuously increased and the spinning speed is increased, the stability of spinning becomes poor, and the mechanical property of the obtained fiber is obviously reduced, which is about reduced by 0.5-2 GPa.

Disclosure of Invention

The invention aims to provide a method for spinning polybenzazole fibers, which has high production efficiency and good spinning stability and does not influence the mechanical strength of the prepared fibers.

The specific technical scheme adopted for realizing the purpose of the invention is as follows:

a method for spinning polybenzazole fibers, which is characterized by comprising the following process steps and conditions:

(1) the polybenzazole spinning stock solution with the mass percentage concentration of 10-15% is sprayed out through a spinneret plate with the angle theta of a transition cone cylinder in front of a capillary tube being not more than 25 degrees or a spinneret plate with smooth contraction being arc-shaped in front of the capillary tube under the pressure drop of not more than 13 MPa;

(2) the sprayed spinning solution filaments enter a stretching area which is filled with inert gas or air and has the temperature of 40-90 ℃ and are stretched under the condition that the stretching ratio is 20-100 times to form primary tows;

(3) and (3) sequentially allowing the nascent fiber bundle to enter a coagulating bath for coagulation, washing, drying and rolling to complete preparation.

The polybenzazole spinning solution in the step (1) of the method is a spinning solution formed by any one of polybenzoxazole, polybenzothiazole, polybenzimidazole or random copolymer, alternating copolymer and block copolymer thereof and a solvent, and the mass percentage concentration of the polybenzazole spinning solution is 10-15%. The structural unit contained in these polymers is a polymer structural unit capable of forming a lyotropic liquid crystal, and the structural unit is preferably a structural unit represented by a to g below, more preferably a structural unit represented by a to c below:

a

b

c

d

e

f

g

in general, a dope comprising a polymer containing the above-mentioned structural unit and a solvent exhibits liquid crystallinity within the concentration range defined in the present invention. Liquid crystallinity means that the microstructure thereof exhibits locally ordered heterogeneity, and the arrangement direction of rigid molecular chains is uniform in each part. However, the polyphosphoric acid and other solvents can solvate molecular chains of the polybenzazole, so that the acting force between polymer molecules (eutectic formed by the solvent and the solute) is reduced, the arrangement directions of the polymer molecules tend to be consistent, the local boundaries gradually disappear, and finally the polymer molecules become spinning solution with a uniform structure, thereby laying a good foundation for obtaining fine denier fibers through spinning.

The solvent described in step (1) of the above method is preferably any one of polyphosphoric acid, methanesulfonic acid, or trifluoroacetic acid, and more preferably polyphosphoric acid.

The transition cone before the capillary of the spinneret plate in the step (2) of the method preferably has not less than 2 sections, and the angle theta is preferably 10-25 degrees, more preferably 10-20 degrees; the aspect ratio L/D of the capillary is 0.5 to 3, more preferably L/D is 0.5 to 2; the pressure drop is preferably 4 to 13MPa, more preferably 6 to 10 MPa.

The stretching in the step (2) is achieved by means of a roller device, and the preferred stretching ratio is 30-100 times, and more preferably 35-100 times. The macromolecules of the polybenzazole polymer can realize high orientation by high-power drawing to prepare high-performance fibers. However, when the draw ratio is too high, slippage between macromolecules occurs, and even yarn breakage occurs, so that the draw ratio is not too high. In order to achieve stable drawing, inert gas is generally passed through the drawing zone, and the cooling rate of the filaments can be controlled by adjusting the temperature of the inert gas. The inert gas is usually air, nitrogen, carbon dioxide or argon.

The primary tow after high-power stretching needs the procedures of solidification, washing, drying and rolling in sequence to form the fiber with compact aggregation structure.

The coagulating bath in the step (3) of the above method is a dilute solution of a corresponding solvent having a mass concentration of 0 to 35%.

The washing described in the step (3) of the above method is washing by neutralizing with alkali and water in sequence. The alkali neutralization is carried out by using 0.5-20%, preferably 2-15% sodium hydroxide, potassium hydroxide or triethylamine, and washing until the residual amount of the solvent is less than or equal to 5000 ppm.

The drying described in step (3) of the above method is carried out at a temperature of 100 ℃ and 250 ℃ until the moisture content of the fibers is less than 10%, preferably less than 5%, more preferably until the equilibrium moisture content is reduced to about 2%.

The average tensile strength of the poly-p-Phenylene Benzobisoxazole (PBO) fiber prepared by the method is more than or equal to 5GPa, better more than or equal to 5.5GPa, and most better more than or equal to 5.8 Gpa; the strength and tensile strength of the poly [2, 5-dihydroxy-1, 4-phenylene pyridobisimidazole ] fiber are more than or equal to 4GPa, better more than or equal to 4.5GPa, and most better more than or equal to 5.0 GPa.

The speed of the filaments as they exit the drawing zone is at least 270m/min, preferably 270-900m/min, more preferably 400-815 m/min. When the spinneret plate is used for spinning, the stability of high-speed spinning is higher. By selecting parameters such as transition cone angle, capillary diameter, length-diameter ratio, spinning temperature and the like, the average breaking point of the filaments can be not higher than 1 time/10 km, preferably not higher than 1 time/100 km, and most preferably not higher than 1 time/1000 km.

The invention has the following beneficial technical effects:

1. because the front transition cone cylinder of the capillary tube of the spinneret plate adopted in the spinning method provided by the invention is more than or equal to 2 sections or is a smooth arc transition cone cylinder, and when the transition cone cylinder is adopted, the angle theta is much smaller than that of the prior art, the turbulent flow of spinning stock solution near the symmetric axis of a spinneret orifice can be greatly reduced, the occurrence of melt fracture is avoided, on the basis, the spinning speed can be greatly improved, the stability of high-speed spinning is higher, and the mechanical property of fibers can be fully guaranteed.

2. The spinneret plate adopted in the spinning method provided by the invention is matched with the spinneret plate to select proper technical measures such as capillary diameter, length-diameter ratio, pressure drop and the like, so that the average breaking point of the filaments can be at least not higher than 1 time/10 km, the best breaking point can be not higher than 1 time/1000 km, the spinning stability is high, the highest spinning speed can be up to more than 800m/min, and the production efficiency is greatly improved.

3. The spinning method provided by the invention can realize the stability under high-speed spinning, greatly reduce the yarn breaking frequency, and has good operability and good spinning state, thereby being very suitable for industrial production.

4. The spinning method provided by the invention can be used for preparing high-strength polybenzazole fibers under the condition of high-speed stable spinning without losing the strength of the fibers, so that the polybenzazole fibers are particularly suitable for preparing high-strength polybenzazole fibers, and particularly, when the polybenzazole fibers are spun at a high speed of 815m/min, the spinning state is good, the average breaking point of filaments is not higher than 1 time/1000 km, and the strength of the fibers can reach 5.95GPa at most.

Drawings

FIG. 1 is a schematic structural view of a transition cone at the front of a section 1 of a capillary tube of a single spinneret orifice in a spinneret plate in the prior art;

FIG. 2 is a schematic structural diagram of a transition cone in front of 2 sections of capillaries of a single spinneret orifice in a spinneret plate adopted in the embodiment of the invention;

FIG. 3 is a schematic structural diagram of a spinneret plate according to the present invention, wherein the front capillary portion of a single spinneret hole is a spinneret hole which is smoothly contracted into an arc shape.

In the figure: 1-a transition cone; 2-capillary front transition cone angle 2 theta; 3-a capillary tube; l-capillary length; d-capillary diameter.

Detailed Description

The invention is further illustrated by the following examples. It should be noted that the examples given are not to be construed as limiting the scope of the invention, and that those skilled in the art, on the basis of the teachings of this invention, will be able to make numerous insubstantial modifications and adaptations of the invention without departing from its scope.

It is worth mentioning that: 1) the concentrations in the following examples and comparative examples are mass percent concentrations; 2) the mechanical properties of the fibers prepared in the following examples and comparative examples were measured by using an Instron universal tensile tester according to the GJB348-87 immersion method for tensile Properties of aramid multifilament.

Example 1

Firstly, preparing a polyparaphenylene benzobisoxazole polymer with the intrinsic viscosity of 28dL/g and the kinetic viscosity of 8000 kilo-centipoise into polyphosphoric acid spinning stock solution with the concentration of 15 percent, and spraying out by using a spinneret plate with the hole number of 330, the 2-section transition cone 1 in front of a spinneret orifice capillary 3, the angle theta of 20 degrees, the diameter of the capillary of 0.18mm and the length-diameter ratio L/D of 2.00 under the conditions that the spinning temperature is 185 ℃ and the flow rate is 76mL/min, wherein the pressure drop is 8.0 MPa. The spun dope filament entered the stretching zone filled with air at a temperature of 80 ℃ and was stretched at a draw ratio of 44.6 to form a nascent strand, and exited the stretching zone at a spinning speed of 404 m/min. And (3) putting the nascent fiber bundle into a coagulating bath for coagulation, wherein the coagulating bath is a dilute phosphoric acid aqueous solution with the mass concentration of 20%. And (3) neutralizing the strand wires leaving the coagulation bath by using sodium hydroxide with the mass concentration of 5% in sequence, fully washing the strand wires with water until the residual amount of the solvent is less than or equal to 5000ppm, then drying the strand wires in a roller at the temperature of 220 ℃, and rolling the strand wires to obtain the fiber with the water content of 3%.

The yarn breaking frequency in the spinning process is 1 time/800 km, and the spinning state is good; the fineness of the obtained fiber was 56.5tex, and the tensile strength was 5.85 GPa.

Example 2

Firstly, preparing a polyparaphenylene benzobisoxazole polymer with the intrinsic viscosity of 27.5dL/g and the kinetic viscosity of 6500 kilo-centipoise into a polyphosphoric acid spinning stock solution with the concentration of 10 percent, and spraying a spinneret plate with the hole number of 330, the 2-section transition cone 1 in front of a spinneret orifice capillary 3, the angle theta of 25 degrees, the capillary diameter D of 0.18mm and the length-diameter ratio L/D of 2.00 under the conditions of the spinning temperature of 185 ℃ and the flow rate of 76mL/min, wherein the pressure drop is 8.2 MPa. The spun dope filament entered the stretching zone charged with nitrogen at a temperature of 40 ℃ and was stretched at a draw ratio of 30 to form a nascent strand and exited the stretching zone at a spinning speed of 270 m/min. And (3) putting the nascent fiber bundle into a coagulating bath for coagulation, wherein the coagulating bath is a dilute phosphoric acid aqueous solution with the mass concentration of 35%. And (3) neutralizing the strand wires leaving the coagulation bath by using 10% by mass of potassium hydroxide in sequence and fully washing the neutralized strand wires with water until the residual amount of the solvent is less than or equal to 5000ppm, then drying the neutralized strand wires in a roller at the temperature of 250 ℃, and rolling the dried strand wires to obtain the fiber with the water content of 2.2%.

The yarn breaking frequency in the spinning process is 1 time/850 km, and the spinning state is good; the fineness of the obtained fiber was 56.5tex, and the tensile strength was 5.83 GPa.

Example 3

Firstly, preparing a polyparaphenylene benzobisoxazole polymer with the intrinsic viscosity of 30dL/g and the kinetic viscosity of 7800 kilo-centipoise into a polyphosphoric acid spinning stock solution with the concentration of 12 percent, and spraying out by using a spinneret plate with the hole number of 330, 3 sections of transition cone cylinders in front of a spinneret orifice capillary, the angle theta of 20 degrees, the diameter of the capillary of 0.18mm and the length-diameter ratio L/D of 3.00 under the conditions that the spinning temperature is 185 ℃ and the flow rate is 76mL/min, wherein the pressure is reduced to 12.6 MPa. The spun dope filament entered the drawing zone charged with carbon dioxide at a temperature of 90 ℃ and was drawn at a draw ratio of 35.5 to form a nascent strand and exited the drawing zone at a spinning speed of 322 m/min. And (3) putting the nascent fiber bundle into a coagulating bath for coagulation, wherein the coagulating bath is a dilute phosphoric acid aqueous solution with the mass concentration of 25%. And (3) neutralizing and fully washing the strand wires leaving the coagulation bath by using triethylamine with the mass concentration of 15% in sequence and using water until the residual amount of the solvent is less than or equal to 5000ppm, then drying the strands in a contact manner on a roller at the temperature of 180 ℃, and rolling to obtain the fiber with the water content of less than 5%.

The broken yarn frequency in the spinning process is 1 time/950 km, and the spinning state is good; the fineness of the obtained fiber was 56.6tex, and the tensile strength was 5.83 GPa.

Example 4

Firstly, preparing a polyparaphenylene benzobisoxazole polymer with the intrinsic viscosity of 29dL/g and the dynamic viscosity of 9000 kilo-centipoise into a polyphosphoric acid spinning stock solution with the concentration of 13 percent, and spraying a spinneret plate with the hole number of 330, 2 sections of transition cone cylinders in front of a spinneret hole capillary, the angle theta of 20 degrees, the diameter of the capillary of 0.20mm and the length-diameter ratio L/D of 2.00 under the conditions that the spinning temperature is 190 ℃ and the flow rate is 112.5mL/min, wherein the pressure is reduced to 10.0MPa at the moment. The spun dope filament entered the stretching zone filled with air at a temperature of 65 ℃ and was stretched at a draw ratio of 50 to form a nascent strand and exited the stretching zone at a spinning speed of 540 m/min. And (3) putting the nascent fiber bundle into a coagulating bath for coagulation, wherein the coagulating bath is a dilute phosphoric acid aqueous solution with the mass concentration of 30%. And (3) neutralizing the strand wires leaving the coagulation bath by using sodium hydroxide with the mass concentration of 20% in sequence, fully washing the strand wires with water until the residual amount of the solvent is less than or equal to 5000ppm, then drying the strand wires in a contact manner on a roller at the temperature of 100 ℃, and rolling the strand wires to obtain the fiber with the water content of 2.5%.

The broken yarn frequency in the spinning process is 1 time/900 km, and the spinning state is good; the fineness of the obtained fiber was 54.2tex, and the tensile strength was 5.83 GPa.

Example 5

Firstly, preparing a polyparaphenylene benzobisoxazole polymer with the intrinsic viscosity of 30dL/g and the dynamic viscosity of 8500 kilo-centipoise into polyphosphoric acid spinning stock solution with the concentration of 13 percent, and spraying out by using a spinneret plate with the hole number of 330, 4 sections of transition cone cylinders in front of a spinneret orifice capillary, the angle theta of 15 degrees, the diameter of the capillary of 0.30mm and the length-diameter ratio L/D of 0.50 under the conditions that the spinning temperature is 195 ℃ and the flow rate is 190mL/min, wherein the pressure drop is 6.3 MPa. The spun dope filament entered the stretching zone filled with air at a temperature of 90 ℃ and was stretched at a draw ratio of 100 to form a nascent strand and exited the stretching zone at a spinning speed of 815 m/min. And (3) putting the nascent fiber bundle into a coagulating bath for coagulation, wherein the coagulating bath is a dilute phosphoric acid aqueous solution with the mass concentration of 25%. And (3) neutralizing the strand wires leaving the coagulation bath by adopting 13% of sodium hydroxide in sequence, fully washing the strand wires with water until the residual amount of the solvent is less than or equal to 5000ppm, then drying the strand wires in a contact manner on a roller at the temperature of 240 ℃, and rolling the strand wires to obtain the fiber with the water content of less than 2.3%.

The yarn breaking frequency in the spinning process is 1 time/1000 km, and the spinning state is good; the fineness of the obtained fiber was 55.0tex, and the tensile strength was 5.95 GPa.

Example 6

Firstly, preparing a poly [2, 5-dihydroxy-1, 4-phenylene pyridine diimidazole ] polymer with the intrinsic viscosity of 32dL/g and the dynamic viscosity of 9200 kilo-centipoise into polyphosphoric acid spinning stock solution with the concentration of 11%, and spraying out by using a spinneret plate with the hole number of 330, 4 sections of transition cones in front of a spinneret orifice capillary, the angle theta of 10 degrees, the diameter of the capillary of 0.30mm and the length-diameter ratio L/D of 1.50 under the conditions that the spinning temperature is 200 ℃ and the flow rate is 195mL/min, wherein the pressure is reduced to 10.0 MPa. The spun dope filament entered the stretching zone filled with air at a temperature of 90 ℃ and was stretched at a draw ratio of 95.6 to form a nascent strand and exited the stretching zone at a spinning speed of 800 m/min. And (4) putting the nascent fiber bundle into a coagulating bath for coagulation, wherein the coagulating bath is deionized water. And (3) neutralizing the strand wires leaving the coagulation bath by sequentially adopting 2% sodium hydroxide by mass concentration and fully washing the strand wires with water until the residual amount of the solvent is less than or equal to 5000ppm, then drying the strands in a contact manner on a roller at the temperature of 180 ℃, and rolling the strands to obtain the fiber with the water content of 10%.

The yarn breaking frequency in the spinning process is 1 time/880 km, and the spinning state is good; the fineness of the obtained fiber was 53.6tex, and the tensile strength was 5.10 GPa.

Example 7

Firstly, preparing a poly [2, 5-dyhydroxy-1, 4-phenylene pyridine diimidazole ] polymer with the intrinsic viscosity of 29.1dL/g and the dynamic viscosity of 8200 kilo-centipoise into polyphosphoric acid spinning stock solution with the concentration of 11%, and spraying a spinneret plate with the hole number of 330, 3 sections of transition cones in front of a spinneret hole capillary, the angle theta of 18 degrees, the capillary diameter of 0.30mm and the length-diameter ratio L/D of 0.50 under the conditions that the spinning temperature is 200 ℃ and the flow rate is 195mL/min, wherein the pressure is reduced to 4.1 MPa. The spun dope filament entered the stretching zone filled with air at a temperature of 90 ℃ and was stretched at a draw ratio of 95.6 to form a nascent strand and exited the stretching zone at a spinning speed of 800 m/min. And (3) putting the nascent fiber bundle into a coagulating bath for coagulation, wherein the coagulating bath is a dilute phosphoric acid aqueous solution with the mass concentration of 10%. And (3) neutralizing the strand wires leaving the coagulation bath by using sodium hydroxide with the mass concentration of 0.5% in sequence, fully washing the strand wires with water until the residual amount of the solvent is less than or equal to 5000ppm, then carrying out contact drying on a roller at the temperature of 180 ℃, and rolling to obtain the fiber with the water content of 8%.

The yarn breaking frequency in the spinning process is 1 time/880 km, and the spinning state is good; the fineness of the obtained fiber was 53.8tex, and the tensile strength was 4.52 GPa.

Comparative example 1

Firstly, preparing a polyphosphoric acid spinning stock solution with the intrinsic viscosity of 28.2dL/g and the dynamic viscosity of 7500 kilo-centipoise (poly-p-phenylene benzobisoxazole polymer is prepared into polyphosphoric acid spinning stock solution with the concentration of 13 percent under the conditions that the spinning temperature is 185 ℃ and the flow rate is 76mL/min, spraying out by using a spinneret plate with the hole number of 330, 2 sections of transition cones in front of a spinneret hole capillary, the angle theta of 30 degrees, the diameter of the capillary of 0.18mm and the length-diameter ratio L/D of 2.00, reducing the pressure to 7.9MPa, feeding the sprayed spinning stock solution filaments into a stretching area filled with air and the temperature of 80 ℃, stretching to form primary filaments under the stretching ratio of 38, leaving the stretching area at the spinning speed of 350m/min, entering a coagulation bath for coagulation, washing the filaments leaving the coagulation bath by using dilute aqueous solution of 20 percent by mass concentration of sodium hydroxide and water to fully wash the filaments leaving the coagulation bath until the residual amount of the solvent is less than or equal to 5000ppm, and (3) after the contact drying is carried out on a roller at the temperature of 130 ℃, rolling to prepare the fiber with the water content of 2.6 percent.

The yarn breaking frequency in the spinning process is 1 time/7 km, and the spinning state is poor; the fineness of the obtained fiber was 56.5tex, and the tensile strength was 5.50 GPa.

Comparative example 2

Firstly, preparing a polyparaphenylene benzobisoxazole polymer with the intrinsic viscosity of 29dL/g and the dynamic viscosity of 8000 ten thousand centipoises into polyphosphoric acid spinning stock solution with the concentration of 13 percent, and spraying out by using a spinneret plate with the hole number of 330, 2 sections of transition conical cylinders in front of a spinneret orifice capillary, the angle theta of 20 degrees, the diameter of the capillary of 0.18mm and the length-diameter ratio L/D of 4.00 under the conditions that the spinning temperature is 185 ℃ and the flow rate is 76mL/min, wherein the pressure drop is 12.8 MPa. The spun dope filament entered the stretching zone filled with air at a temperature of 80 ℃ and was stretched at a draw ratio of 38 to form a nascent strand and exited the stretching zone at a spinning speed of 350 m/min. And (3) putting the nascent fiber bundle into a coagulating bath for coagulation, wherein the coagulating bath is a dilute phosphoric acid aqueous solution with the mass concentration of 20%. And (3) neutralizing the strand wires leaving the coagulation bath by using 10% by mass of sodium hydroxide in sequence, fully washing the strand wires with water until the residual amount of the solvent is less than or equal to 5000ppm, then drying the strand wires in a contact manner on a roller at the temperature of 160 ℃, and rolling the strand wires to obtain the fiber with the water content of 2.8%.

The broken yarn frequency in the spinning process is 1 time/750 km, and the spinning state is good; the fineness of the obtained fiber was 56.4tex, and the tensile strength was 5.75 GPa.

Comparative example 3

Firstly, preparing a poly-p-phenylene benzobisoxazole polymer with the intrinsic viscosity of 28.8dL/g and the dynamic viscosity of 10000 kilo-centipoise into a polyphosphoric acid spinning stock solution with the concentration of 13 percent, and spraying out by using a spinneret plate with the hole number of 330, 2 sections of transition cone cylinders in front of a spinneret orifice capillary, the angle theta of 20 degrees, the diameter of the capillary of 0.18mm and the length-diameter ratio L/D of 2.00 under the conditions that the spinning temperature is 188 ℃ and the flow rate is 95mL/min, wherein the pressure is reduced to 13.5 MPa. The spun dope filament entered the stretching zone filled with air at a temperature of 85 ℃ and was stretched at a draw ratio of 40 to form a nascent strand and exited the stretching zone at a spinning speed of 450 m/min. And (3) putting the nascent fiber bundle into a coagulating bath for coagulation, wherein the coagulating bath is a dilute phosphoric acid aqueous solution with the mass concentration of 30%. And (3) neutralizing the strand wires leaving the coagulation bath by using 10% by mass of sodium hydroxide in sequence, fully washing the strand wires with water until the residual amount of the solvent is less than or equal to 5000ppm, then drying the strand wires in a contact manner on a roller at the temperature of 170 ℃, and rolling the strand wires to obtain the fiber with the water content of 3.2%.

The yarn breaking frequency in the spinning process is 1 time/8 km, and the spinning state is poor; the fineness of the obtained fiber was 56.4tex, and the tensile strength was 5.75 GPa.

Comparative example 1 compared with examples 1 and 2, the filament lines ejected from the spinneret holes were observed to be disordered during the spinning process due to the large angle of 30 ° of the transition cone before the capillary of comparative example 1, and about 10 holes resulted in irregular filament breakage. The broken filament frequency is obviously increased and is about 1 time/7 km; at the same time, the strength of the prepared fiber is reduced.

The effect of the capillary aspect ratio L/D can be illustrated from a comparison of examples 1, 3 and comparative example 2. When the L/D exceeds 3, the strength of the fiber tends to be lowered. After passing through a long capillary, the drawing flow velocity distribution of the spinning solution develops into a parabola shape due to the viscous resistance of the tube wall; after ejection, the molecules of the inner layer and the outer layer are oriented differently during the stretching process.

A comparison of examples 1 and 4 with comparative example 3 shows the effect of excessive shearing of the spinneret part. The pressure drop of the spinneret plate exceeds 13MPa, the sprayed filaments are disordered and are easy to break, and the strength of the prepared fiber is reduced.

Through the embodiments 1,4 and 5, it can be shown that the increase of the spinning speed can be realized through the control of parameters such as the angle of the transition cone before the capillary, the length-diameter ratio of the capillary, the pressure drop of the spinneret plate and the like, the spinning stability is good, and the prepared fiber has high strength.

Claims

1. A method for spinning polybenzazole fibers, which is characterized by comprising the following process steps and conditions:

(1) the polybenzazole spinning stock solution with the mass percentage concentration of 10-15% passes through a spinneret plate with the angle theta of a transition cone cylinder in front of a capillary tube being less than or equal to 25 degrees or a spinneret plate with smooth contraction being arc-shaped in front of the capillary tube, and is sprayed out when the pressure drop is less than or equal to 13 MPa;

2. The process for spinning polybenzazole fibers according to claim 1, wherein the polybenzazole dope in step (1) of the process is a dope formed by any of polybenzoxazole, polybenzothiazole, polybenzimidazole or their random copolymer, alternating copolymer, block copolymer and solvent.

3. The process for spinning polybenzazole fibers according to claim 2, characterized in that the solvent in step (1) of the process is any one of polyphosphoric acid, methanesulfonic acid or trifluoroacetic acid.

4. The process for spinning polybenzazole fibers according to any of claims 1 to 3, wherein the transition cone before the capillary of the spinneret in step (2) of the process is not less than 2 transition cones, the angle θ is 10 to 25 °, the aspect ratio L/D of the capillary is 0.5 to 3, and the pressure drop is 4 to 13 MPa.

5. The process for spinning polybenzazole fibers according to any one of claims 1 to 3, characterized in that the drawing in step (2) of the process is carried out by means of a roller apparatus at a draw ratio of 30 to 100 times.

6. The process for spinning polybenzazole fibers according to claim 4, wherein said drawing in step (2) is carried out by means of a roller apparatus at a drawing ratio of 30 to 100 times.

7. A process for spinning polybenzazole fibers according to any one of claims 1 to 3, characterized in that the coagulation bath in step (3) of the process is a dilute solution of the corresponding solvent with a mass concentration of 0 to 35%; the washing is carried out by sequentially adopting alkali neutralization water, wherein the alkali neutralization adopts 0.5-20% of sodium hydroxide, potassium hydroxide or triethylamine, and the washing is carried out until the residual amount of the solvent is less than or equal to 5000 ppm; the drying is carried out at the temperature of 100 ℃ and 250 ℃ until the water content of the fiber is lower than 10 percent.

8. The process for spinning polybenzazole fibers according to claim 4, characterized in that the coagulation bath in step (3) of the process is a dilute solution of 0 to 35% by mass of the corresponding solvent; the washing is carried out by sequentially adopting alkali neutralization water, wherein the alkali neutralization adopts 0.5-20% of sodium hydroxide, potassium hydroxide or triethylamine, and the washing is carried out until the residual amount of the solvent is less than or equal to 5000 ppm; the drying is carried out at the temperature of 100 ℃ and 250 ℃ until the water content of the fiber is lower than 10 percent.

9. The process for spinning polybenzazole fibers according to claim 6, characterized in that the coagulation bath in step (3) of the process is a dilute solution of 0-35% by mass of the corresponding solvent; the washing is carried out by sequentially adopting alkali neutralization water, wherein the alkali neutralization adopts 0.5-20% of sodium hydroxide, potassium hydroxide or triethylamine, and the washing is carried out until the residual amount of the solvent is less than or equal to 5000 ppm; the drying is carried out at the temperature of 100 ℃ and 250 ℃ until the water content of the fiber is lower than 10 percent.