Coarse-diameter high-strength heterocyclic aramid fibers prepared by an air heat treatment method

Abstract

The present invention discloses a preparation method of thick-diameter high-strength heterocyclic aramid fibers prepared by an air heat treatment method. The present invention overcomes technical prejudices and uses an ethanol aqueous solution as the coagulation bath for the nascent fibers, providing a basis for the preparation of high-strength fibers; by adjusting the ethanol content, the polarity difference between the coagulation bath and the aramid polymer can be adjusted, thereby obtaining a higher draw ratio, which is helpful for the drawing of aramid fibers. Further, the present application combines multi-stage coagulation drawing and air heat treatment to achieve the strengthening of aramid fibers. The aramid fibers prepared by the present invention have a diameter of up to 36 μm, a breaking strength of up to 5.5 GPa, an elastic modulus of up to 122 GPa, an elongation at break of up to 4.5%, and a toughness of up to 123.7 MJ / m<supgt;3< / supgt>.

Description

Technical Field

[0001] The present invention relates to a method for preparing thick-diameter high-strength heterocyclic aramid fibers, which is an energy-saving, environment-friendly, low-cost and high-efficiency method for preparing thick-diameter high-strength, high-modulus and high-elongation-at-break aramid fibers. Background Art

[0002] Aramid fiber is fully called "aromatic polyamide fiber", and its English name is Aramid fiber. It is a new type of high-tech synthetic fiber with excellent properties such as ultra-high strength, high modulus, high temperature resistance, acid and alkali resistance, and light weight. Its strength is 5-6 times that of steel wire, the modulus is 2-3 times that of steel wire or glass fiber, the toughness is 2 times that of steel wire, and the weight is only about 1 / 5 of that of steel wire. At a temperature of 560 °C, it does not decompose or melt. It has good insulation and anti-aging properties and a long life cycle.

[0003] The preparation process of aramid usually is: degassing and filtering the heterocyclic aramid solution, and then performing wet spinning. The polymer solution is sprayed into a coagulation bath through a spinneret with a pore diameter of 0.05-0.2 mm to form nascent fibers. The coagulation bath is an aqueous solution of dimethylacetamide with a mass fraction of 40-65% at 10-40 °C. Then the nascent fibers enter a plasticizing and stretching bath, which is an aqueous solution of dimethylacetamide with a mass fraction of 10-25% at 20-70 °C. Then water washing is carried out, and deionized water at 80-98 °C is used for water washing. Then drying is carried out, and the drying is contact drum drying at a temperature of 90-160 °C. Then heat treatment is carried out, and the heat treatment is carried out at 320-420 °C for 0.5-4 minutes in a nitrogen atmosphere. The aramid fibers prepared by this method have a breaking strength of 25-34 cN / dtex (3.6-4.9 GPa), an elastic modulus of 900-1200 cN / dtex (129.6-172.8 GPa), and an elongation at break of 2.5-4.0%.

[0004] In the above method, there are at least the following disadvantages:

[0005] 1) The coagulation bath and the plasticizing and stretching bath are aqueous solutions of dimethylacetamide. Dimethylacetamide is a toxic solvent, which is not environmentally friendly and has a high cost.

[0006] 2) The water washing is with high-temperature deionized water, which has high energy consumption.

[0007] 3) The drying is high-temperature drying, which has high energy consumption.

[0008] 4) The heat treatment is carried out in a nitrogen atmosphere, which has a high cost.

[0009] 5) The pore diameter of the spinneret needs to be relatively fine to prepare aramid fibers with higher strength. Under a fine pore diameter, the fibers are relatively thin, which will seriously affect the spinning efficiency.

[0010] 6) The solid content of the polymer in the polymer solution is 2-10%, with a high viscosity. The bubbles generated by stirring are difficult to escape from the solution in a short time and need to be degassed, which reduces the production efficiency and increases the complexity of the spinning process. Summary of the Invention

[0011] The present invention aims at the problems in the background technology and provides a method for preparing thick-diameter high-strength heterocyclic aramid fibers.

[0012] First of all, in the preparation method of the present invention, ethanol is used as the coagulation bath for wet-spun aramid. Technically, the coagulation bath for wet spinning generally uses a coagulation bath similar to the solvent. For example, the solvent for para-aramid is concentrated sulfuric acid, and the coagulation bath will choose an aqueous sulfuric acid solution; the solvent for heterocyclic aramid is dimethylacetamide, and the coagulation bath will choose an aqueous dimethylacetamide solution. On the one hand, it is easy to adjust the polarity difference between the coagulation bath and the polymer to adjust coagulation and stretching, and on the other hand, it is convenient for the recovery and utilization of the solvent. The present invention overcomes the technical prejudice and uses an alcohol aqueous solution as the coagulation bath for the nascent fiber, which has the following advantages:

[0013] 1) By adjusting the alcohol content, the polarity difference between the coagulation bath and the aramid polymer can be adjusted, so as to obtain a higher draw ratio, which is helpful for the stretching of aramid fibers.

[0014] 2) By adjusting the alcohol content, the density of the coagulation bath can be adjusted to make its density equal to or slightly greater than the density of the aramid solution, so as to ensure that the nascent fiber maintains a good state and is pulled out of the coagulation bath with the least force, laying a foundation for subsequent high strength.

[0015] Secondly, this application adopts the combination of multi-stage coagulation stretching and heat treatment to achieve the strengthening of aramid fibers. To obtain high-strength, high-toughness and thick-diameter aramid fibers is the result of the close cooperation of various parameters. First, the primary coagulation bath should choose a low-temperature ethanol aqueous solution. The nascent fiber is coagulated to a certain extent while the structure is frozen, and is pulled out of the primary coagulation bath with the least stress to ensure a large draw ratio in the follow-up. Then, the second coagulation bath chooses deionized water with a large polarity. At this stage, a large proportion of stretching and good further coagulation are carried out. The third coagulation bath chooses medium-temperature deionized water. At this point, while carrying out a small amount of stretching, the fiber is washed and thoroughly coagulated. An appropriate temperature is very important. Then it is dried. The drying time should not be too long. It is dried at 60 degrees for 1-2 hours. Finally, heat treatment is carried out. The heat treatment adopts air stretching heat treatment in a tubular furnace. This heat treatment method is proposed and used for the first time in the industry. Compared with the traditional intermittent heat treatment in a nitrogen atmosphere, this heat treatment method has the following advantages:

[0016] 1) While performing heat treatment with slight stretching on the side, some solvents hydrogen-bonded to aramid molecules can be baked out during the heat treatment process. Due to the stretching effect, the space originally occupied by the solvents will be instantly occupied by aramid molecules, and at the same time, the aramid molecules will obtain better orientation, thereby obtaining dense and highly oriented fibers.

[0017] 2) Since the fibers continuously pass through the tube furnace, the fibers can obtain more uniform heat treatment, and due to continuous production, the efficiency will be higher.

[0018] 3) Since it is air heat treatment and does not require nitrogen, the cost will be lower.

[0019] Specifically, the technical solution adopted in the present invention at least includes the following steps:

[0020] (1) Using a dimethylacetamide solution of a heterocyclic aramid polymer with a mass fraction of 1.5 - 2.0% as the spinning solution, which is sprayed into a coagulation bath through a spinneret with a pore diameter of 0.38 - 1.0 mm to form nascent fibers; the coagulation bath is an aqueous alcohol solution with a volume fraction of 30% - 40%; the alcohol is one or more of methanol, ethanol, propanol, sec-butanol, and isobutanol;

[0021] In this application, the heterocyclic aramid polymer refers to poly(p-phenylenebenzimidazole terephthalamide). In some embodiments of this application, the heterocyclic aramid polymer is poly(p-phenyleneterephthalamide) containing 2-(4-aminophenyl)-5-aminobenzimidazole, which can be prepared by the method described in 201010108545.6, and its structural formula is:

[0022]

[0023] where the ratio of m to n is less than or equal to 1, the breaking strength is 25 - 34 cN / dtex, the elastic modulus is 900 - 1200 cN / dtex, and the breaking elongation is 2.5 - 4.0%;

[0024] (2) Introducing the nascent fibers obtained in step 1 into a primary stretching bath and a secondary stretching bath in sequence for stretching treatment; where the primary stretching bath is deionized water at 2 - 40°C, and the stretching ratio is 1.8 - 2.0 times; the secondary stretching bath is deionized water at 70 ± 10°C, and the stretching ratio is 1.03 - 1.05 times;

[0025] (3) Traction the stretched fibers to a continuous tube furnace for air heat treatment, and apply a stretching ratio of 1.01 - 1.02 times; the heat treatment temperature is 340 - 440°C, and the travel time of the fibers in the tube furnace is 1 - 20 minutes.

[0026] Through the present invention, the obtained aramid fiber has a breaking strength of 4.4 - 5.5 GPa, an elastic modulus of 110 - 150 GPa, and a breaking elongation at break of 3.0 - 4.5%.

[0027] In some more preferred embodiments of the present invention, the fiber after the stretching treatment in step 2 is dried at 60 - 70 °C, which can further improve its mechanical properties. Generally, the drying time is less than 4 hours. This drying treatment can also be carried out by continuous drying using a low-temperature tube furnace.

[0028] The present invention also provides a continuous production device for high-strength, high-modulus, and high-breaking-elongation heterocyclic aramid fibers, which at least includes:

[0029] A spinneret with a pore diameter of 0.38 - 1.0 mm;

[0030] A coagulation bath, a primary stretching bath, and a secondary stretching bath;

[0031] And, a continuous tube furnace;

[0032] A solution of a heterocyclic aramid polymer in dimethylacetamide with a mass fraction of 1.5 - 2.0% is sprayed through a spinneret with a pore diameter of 0.38 - 1.0 mm into the coagulation bath to form nascent fibers;

[0033] The nascent fibers are introduced into the primary stretching bath through the first traction roller and led out through the second traction roller. The rotational speed of the second traction roller is 1.8 - 2.0 times that of the first traction roller;

[0034] The fibers stretched in the primary stretching bath are introduced into the secondary stretching bath through the third traction roller and led out through the fourth traction roller. The rotational speed of the fourth traction roller is 1.03 - 1.05 times that of the third traction roller;

[0035] The fibers stretched in the secondary stretching bath are introduced into the continuous tube furnace through the fifth traction roller and led out through the sixth traction roller. The rotational speed of the sixth traction roller is 1.01 - 1.02 times that of the fifth traction roller.

[0036] Compared with the prior art, when the aramid fiber prepared by the present invention has a diameter of 36 μm, its breaking strength reaches 5.5 GPa, the elastic modulus reaches 122 GPa, the breaking elongation at break reaches 4.5%, and the toughness reaches 124 MJ / m 3 . In addition,

[0037] 1) The coagulation bath is an aqueous alcohol solution, which is non-toxic and harmless; the stretching bath is deionized water, and the cost is extremely low.

[0038] 2) The water washing temperature is relatively low, and the energy consumption is less.

[0039] 3) High-strength aramid fibers can be produced without drying, with a strength of 5 GPa. If drying is required, only low-temperature drying is needed, resulting in low energy consumption, high efficiency, and low cost.

[0040] 4) No inert gas is required during heat treatment. Heat treatment can be carried out in air, and it is a continuous heat treatment, which is highly efficient and low-cost. After heat treatment, the fibers are slightly carbonized, which helps to improve the strength.

[0041] 5) The diameter of the spinneret holes can be relatively large. The resulting aramid fibers have a diameter of more than 30 microns, and the strength of a single fiber is high, which can greatly accelerate the spinning speed and thus significantly improve the spinning efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 : Schematic structural diagram of the continuous production equipment of the present invention.

[0043] Figure 2 : Schematic diagram of the load test of the heterocyclic aramid fiber obtained by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0044] The present invention will be described in detail below in conjunction with specific embodiments. These examples are purely illustrative and are only used to specifically describe the present invention, rather than limiting the present invention.

[0045] As Figure 1 shown, a continuous production equipment for high-strength, high-modulus, and high-elongation-at-break heterocyclic aramid fibers of the present invention is provided, which includes:

[0046] A spinneret tube 1 with a pore diameter of 0.38 - 1.0 mm;

[0047] A coagulation bath 2, a primary stretching bath 3, and a secondary stretching bath 4;

[0048] And, two continuous tube furnaces 5;

[0049] Among them, the first tube furnace is used for drying, and the second tube furnace is used for heat treatment.

[0050] A dimethylacetamide solution of a heterocyclic aramid polymer with a mass fraction of 1.5 - 2.0% is sprayed into the coagulation bath through a spinneret tube with a pore diameter of 0.38 - 1.0 mm to form nascent fibers;

[0051] The nascent fibers are introduced into the primary stretching bath through the first traction roller and led out through the second traction roller. The rotational speed of the second traction roller is 1.8 - 2.0 times that of the first traction roller;

[0052] The fiber after being stretched in the first-stage stretching bath is introduced into the second-stage stretching bath through the third drawing roller and led out through the fourth drawing roller, and the rotational speed of the fourth drawing roller is 1.03 to 1.05 times that of the third drawing roller;

[0053] The fiber after being stretched in the second-stage stretching bath is introduced into a continuous tubular furnace through the fifth drawing roller and led out through the sixth drawing roller, and the rotational speed of the sixth drawing roller is 1.01 to 1.02 times that of the fifth drawing roller.

[0054] The present invention will be further described below in conjunction with embodiments.

[0055] In the following embodiments, unless otherwise specified, percentages are all mass percentages.

[0056] In the following embodiments, unless otherwise specified, the structural formula of poly(p-phenylbenzimidazole terephthalamide) used is:

[0057]

[0058] The ratio of m to n is less than or equal to 1.

[0059] Example 1:

[0060] Prepare a poly(p-phenylbenzimidazole terephthalamide) solution with a polymer solid content of 4.0%, dilute it with dimethylacetamide to make its solid content 2%, stir for 30 minutes, and carry out wet spinning after standing for 5 minutes.

[0061] During spinning, the polymer solution is sprayed into the coagulation bath through a spinneret with a pore diameter of 0.38 mm to form nascent fibers. The coagulation bath is an aqueous ethanol solution with a volume fraction of 30% at 10°C. Then the nascent fibers enter the plasticizing stretching bath, which is deionized water at 2 - 5°C. By adjusting the rotational speeds of the front and rear rollers, the stretching ratio is controlled to be 2.0 times. Then it is washed with deionized water at 70 ± 10°C, and a stretching ratio of 1.03 times is applied. Then it directly enters the heat treatment, which is air heat treatment in a continuous tubular furnace at a temperature of 340°C for 20 minutes, and by adjusting the rotational speeds of the front and rear rollers, the stretching ratio is controlled to be 1.01 times.

[0062] The aramid fiber prepared by this method has a diameter of 30 μm, a breaking strength of 5.0 GPa, an elastic modulus of 125 GPa, and an elongation at break of 4.0%.

[0063] Example 2:

[0064] Prepare a poly(p-phenylene benzobisoxazole terephthalamide) solution with a polymer solid content of 4.0%, dilute it with dimethylacetamide to a solid content of 1.5%, stir for 30 minutes, let it stand for 5 minutes, and then perform wet spinning. During spinning, the polymer solution is sprayed through a spinneret with a pore diameter of 1.0 mm into a coagulation bath to form nascent fibers. The coagulation bath is an aqueous methanol solution with a volume fraction of 30% at 10°C. Then the nascent fibers enter a plasticizing and stretching bath, which is deionized water at 40°C, and the stretching ratio is 1.8 times. Then perform water washing, using deionized water at 70 ± 10°C, and apply a stretching ratio of 1.05 times. Then dry in an oven at a temperature of 60°C for 2 hours. Then enter heat treatment, which is continuous tube furnace air heat treatment at a temperature of 340°C for 20 minutes, and control the stretching ratio to be 1.01 times by adjusting the rotation speeds of the front and rear rollers.

[0065] The aramid fibers prepared by this method have a diameter of 70 μm, a breaking strength of 4.5 GPa, an elastic modulus of 100 GPa, and an elongation at break of 4.5%.

[0066] Example 3:

[0067] Prepare a poly(p-phenylene benzobisoxazole terephthalamide) solution with a polymer solid content of 4.0%, dilute it with dimethylacetamide to a solid content of 2.0%, stir for 30 minutes, let it stand for 5 minutes, and then perform wet spinning. During spinning, the polymer solution is sprayed through a spinneret with a pore diameter of 0.5 mm into a coagulation bath to form nascent fibers. The coagulation bath is an aqueous propanol solution with a volume fraction of 40% at 0°C. Then the nascent fibers enter a plasticizing and stretching bath, which is deionized water at 2°C, and the stretching ratio is 1.8 times. Then perform water washing, using deionized water at 70°C, and apply a stretching ratio of 1.03 times. Then perform non-contact oven drying at a temperature of 60°C for 1 hour. Then enter heat treatment, which is continuous tube furnace air heat treatment at a temperature of 350°C for 16 minutes, and control the stretching ratio to be 1.01 times by adjusting the rotation speeds of the front and rear rollers.

[0068] The aramid fibers prepared by this method have a diameter of 36 μm, a breaking strength of 5.5 GPa, an elastic modulus of 120 GPa, and an elongation at break of 4.5%.

[0069] Example 4:

[0070] Prepare a poly(p - phenylene benzobisoxazole terephthalamide) solution with a polymer solid content of 4.0%, dilute it with dimethylacetamide to a solid content of 2.0%, stir for 30 minutes, let it stand for 5 minutes, and then perform wet spinning. During spinning, the polymer solution is sprayed through a spinneret with a pore diameter of 0.5 mm into a coagulation bath to form nascent fibers. The coagulation bath is an aqueous ethanol solution with a volume fraction of 30% at - 15°C. Then the nascent fibers enter a plasticizing and stretching bath, which is deionized water at 2°C, and the stretching ratio is 2.0 times. Then perform water washing, using deionized water at 70°C and applying a stretching ratio of 1.03 times. Then perform non - contact oven drying at a temperature of 60°C for 1 hour. Then enter heat treatment, which is continuous tube furnace air heat treatment at a temperature of 400°C for 1 minute, and control the stretching ratio to be 1.01 times by adjusting the rotation speeds of the front and rear rollers.

[0071] The aramid fiber prepared by this method has a diameter of 36 μm, a breaking strength of 5.0 GPa, an elastic modulus of 125 GPa, and an elongation at break of 4.0%.

[0072] Example 5:

[0073] Prepare a poly(p - phenylene benzobisoxazole terephthalamide) solution with a polymer solid content of 4.0%, dilute it with dimethylacetamide to a solid content of 2.0%, stir for 30 minutes, let it stand for 5 minutes, and then perform wet spinning. During spinning, the polymer solution is sprayed through a spinneret with a pore diameter of 0.5 mm into a coagulation bath to form nascent fibers. The coagulation bath is an aqueous ethanol solution with a volume fraction of 30% at 0°C. Then the nascent fibers enter a plasticizing and stretching bath, which is deionized water at 2°C, and the stretching ratio is 2.0 times. Then perform water washing, using deionized water at 70°C and applying a stretching ratio of 1.03 times. Then perform non - contact oven drying at a temperature of 60°C for 1 hour. Then enter heat treatment, which is continuous tube furnace air heat treatment, and the heat treatment temperature is 400°C for 5 minutes, and control the stretching ratio to be 1.01 times by adjusting the rotation speeds of the front and rear rollers.

[0074] The aramid fiber prepared by this method has a diameter of 38 μm, a breaking strength of 4.6 GPa, an elastic modulus of 146.6 GPa, and an elongation at break of 3.0%.

[0075] Example 6:

[0076] Prepare a poly(p - phenylene benzobisoxazole terephthalamide) solution with a polymer solid content of 4.0%, dilute it with dimethylacetamide to a solid content of 2%, stir for 30 minutes, let it stand for 5 minutes, and then perform wet spinning. During spinning, the polymer solution is sprayed through a spinneret with a pore size of 0.5 mm into a coagulation bath to form nascent fibers. The coagulation bath is an aqueous ethanol solution with a volume fraction of 40% at -20°C. Then the nascent fibers enter a plasticizing and stretching bath, which is deionized water at 40°C, and the stretching ratio is 2.0 times. Then perform water washing with deionized water at 70°C and apply a stretching ratio of 1.03 times. Then perform non - contact oven drying at a temperature of 60°C for 1 hour. Then enter heat treatment, which is continuous tube furnace air heat treatment, with a heat treatment temperature of 340°C for 20 minutes, and control the stretching ratio to be 1.01 times by adjusting the rotation speeds of the front and rear rollers.

[0077] The aramid fiber prepared by this method has a breaking strength of 4.4 GPa, an elastic modulus of 125.7 GPa, and an elongation at break of 3.5%.

[0078] Comparative Example 1

[0079] Prepare a poly(p - phenylene benzobisoxazole terephthalamide) solution with a polymer solid content of 4.0%, dilute it with dimethylacetamide to a solid content of 2%, stir for 30 minutes, let it stand for 5 minutes, and then perform wet spinning. During spinning, the polymer solution is sprayed through a spinneret with a pore size of 0.5 mm into a coagulation bath to form nascent fibers. The coagulation bath is an aqueous ethanol solution with a volume fraction of 30% at 30°C. Then the nascent fibers enter a primary stretching bath, which is deionized water at room temperature, and the stretching ratio is 2.6 times. Then perform a secondary stretching bath, which uses deionized water at 70°C and applies a stretching ratio of 1.04 times. Then perform non - contact oven drying at a temperature of 60°C for 1 hour. Then enter heat treatment, which is continuous tube furnace air heat treatment, with a heat treatment temperature of 400°C for 5 minutes, and control the stretching ratio to be 1.01 times by adjusting the rotation speeds of the front and rear rollers.

[0080] The aramid fiber prepared by this method has a breaking strength of 2.7 GPa, an elastic modulus of 90 GPa, and an elongation at break of 3.0%.

[0081] Comparative Example 2

[0082] Prepare a poly(p - phenylene benzobisoxazole terephthalamide) solution with a polymer solid content of 4.0%, dilute it with dimethylacetamide to a solid content of 2%, stir for 30 minutes, let it stand for 5 minutes, and then perform wet spinning. During spinning, the polymer solution is sprayed through a spinneret with a pore diameter of 0.5 mm into a coagulation bath to form nascent fibers. The coagulation bath is an ethanol - aqueous solution with a volume fraction of 50% at room temperature. Then the nascent fibers enter the first - stage stretching bath, which is deionized water at 40°C, and the stretching ratio is 2.6 times. Then they enter the second - stage stretching bath, which uses deionized water at 70°C and applies a stretching ratio of 1.03 times. Then perform non - contact oven drying at a temperature of 60°C for 1 hour. Then enter heat treatment, which uses continuous tube - furnace air heat treatment at a heat treatment temperature of 350°C for 16 minutes, and by adjusting the rotation speeds of the front and rear rollers, control the stretching ratio to be 1.01 times.

[0083] The aramid fiber prepared by this method has a breaking strength of 2.2 GPa, an elastic modulus of 66 GPa, and an elongation at break of 3.4%.

[0084] Comparative Example 3

[0085] Prepare a poly(p - phenylene benzobisoxazole terephthalamide) solution with a polymer solid content of 4.0%, dilute it with dimethylacetamide to a solid content of 2%, stir for 30 minutes, let it stand for 5 minutes, and then perform wet spinning. During spinning, the polymer solution is sprayed through a spinneret with a pore diameter of 0.5 mm into a coagulation bath to form nascent fibers. The coagulation bath is an ethanol - aqueous solution with a volume fraction of 30% at 10°C. Then the nascent fibers enter the first - stage stretching bath, which is deionized water at room temperature, and the stretching ratio is 2.6 times. Then perform non - contact oven drying at a temperature of 60°C for 2 hours. Then enter heat treatment, which uses continuous tube - furnace air heat treatment at a heat treatment temperature of 330°C for 20 minutes, and by adjusting the rotation speeds of the front and rear rollers, control the stretching ratio to be 1.01 times.

[0086] The aramid fiber prepared by this method has a breaking strength of 3.2 GPa, an elastic modulus of 91.4 GPa, and an elongation at break of 3.5%.

[0087] Comparative Example 4

[0088] Prepare a poly(p-phenylene benzobisoxazole terephthalamide) solution with a polymer solid content of 4.0%, dilute it with dimethylacetamide to a solid content of 2%, stir for 30 minutes, let it stand for 5 minutes, and then perform wet spinning. During spinning, the polymer solution is sprayed through a spinneret with a pore size of 0.5 mm into a coagulation bath to form nascent fibers. The coagulation bath is an aqueous solution of ethanol with a volume fraction of 30% at 10°C. Then the nascent fibers enter the first-stage stretching bath, which is deionized water at room temperature, and the stretching ratio is 2.67 times. Then it enters the second-stage stretching bath, which uses deionized water at 70°C and applies a stretching ratio of 1.03 times. Then it undergoes non-contact oven drying at a temperature of 60°C for 4 hours. Then it enters heat treatment, which uses continuous tube furnace air heat treatment. The heat treatment temperature is 420°C for 2 minutes, and by adjusting the rotation speeds of the front and rear rollers, the stretching ratio is controlled to be 1.01 times.

[0089] The aramid fiber prepared by this method has a breaking strength of 1.8 GPa, an elastic modulus of 72 GPa, and an elongation at break of 2.5%.

[0090] Comparative Example 5

[0091] Prepare a poly(p-phenylene benzobisoxazole terephthalamide) solution with a polymer solid content of 4.0%, dilute it with dimethylacetamide to a solid content of 2%, stir for 30 minutes, let it stand for 5 minutes, and then perform wet spinning. During spinning, the polymer solution is sprayed through a spinneret with a pore size of 0.5 mm into a coagulation bath to form nascent fibers. The coagulation bath is an aqueous solution at 10°C. Then the nascent fibers enter the first-stage stretching bath, which is deionized water at room temperature, and the stretching ratio is 2.4 times. Then it enters the second-stage stretching bath, which uses deionized water at 70°C and applies a stretching ratio of 1.03 times. Then it undergoes non-contact oven drying at a temperature of 60°C for 1 hour. Then it enters heat treatment, which uses continuous tube furnace air heat treatment. The heat treatment temperature is 350°C for 16 minutes, and by adjusting the rotation speeds of the front and rear rollers, the stretching ratio is controlled to be 1.01 times.

[0092] The aramid fiber prepared by this method has a breaking strength of 2.6 GPa, an elastic modulus of 65.3 GPa, and an elongation at break of 3.98%.

Claims

1. A high-strength heterocyclic aramid fiber with a large diameter prepared by air heat treatment, It is characterized in that Prepared by the following steps: (1) A dimethylacetamide solution of heterocyclic aramid with a mass fraction of 1.5-2.0% is used as a spinning solution, and is sprayed into a coagulation bath through a spinneret with a pore size of 0.38-1.0 mm to form nascent fibers; the coagulation bath is an alcohol aqueous solution with a volume fraction of 30%-40%; the alcohol is one or more of methanol, ethanol, propanol, sec-butanol, and isobutanol; (2) introducing the spun fiber obtained in step 1 into a primary stretching bath and a secondary stretching bath in sequence for stretching treatment; wherein the primary stretching bath is deionized water at 2-40° C., and the stretching ratio is 1.8-2.0 times; the secondary stretching bath is deionized water at 70±10° C., and the stretching ratio is 1.03-1.05 times; (3) The stretched fiber is drawn into a continuous tubular furnace for air heat treatment, and a stretching ratio of 1.01 to 1.02 is applied; the heat treatment temperature is 340 to 440° C., and the fiber travel time in the tubular furnace is 1 to 20 minutes.

2. The heterocyclic aramid fiber according to claim 1, It is characterized in that The fiber after the stretching treatment in step 2 is dried at 60°C.

3. The heterocyclic aramid fiber according to claim 1, It is characterized in that The heterocyclic aramid is a copolymerized aromatic polyamide containing a heterocyclic ring.

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