CN104911896B - A kind of aramid III fiber of resistance to ultraviolet and preparation method thereof - Google Patents

Abstract

The ultraviolet-resistant aramid fiber III disclosed by the invention is prepared by putting the spun aramid fiber III into a low-concentration acidic solution prepared by inorganic acid or organic acid, immersing and drying. After treatment, acidic molecules are complexed on the benzimidazole ring unit of the main chain of the fiber macromolecule, which can produce a fluorescence enhancement effect to dissipate ultraviolet light energy, thus making the aramid III fiber obtain excellent UV resistance. Performance, after the fiber is irradiated by ultraviolet rays, the retention rate of its tensile strength and initial modulus is 75-95%, which is 26-60% higher than the ultraviolet resistance of the aramid fiber III without complexing acid molecules. The preparation method provided by the invention is simple and easy, has low cost and is beneficial to industrialized production.

Description

A kind of ultraviolet resistant aramid fiber III and preparation method thereof

technical field

The invention belongs to the technical field of ultraviolet-resistant aramid fiber III and its preparation, and in particular relates to an ultraviolet-resistant aramid fiber III in which a benzimidazole unit is complexed with an acidic small molecule in a macromolecular chain and a preparation method thereof.

Background technique

Aramid III fiber (called Armos fiber in Russia) is a high-strength and high-modulus aramid fiber, which has become a reinforcing fiber for the preparation of advanced composite materials for aerospace. Specifically, it is made of p-phenylenediamine, terephthaloyl chloride and 5(6)-amino-2-(4-aminophenyl)benzimidazole as raw materials, and dimethylacetamide/ Lithium chloride is used as a solvent to obtain spinning stock solution through low-temperature copolymerization, and then high-strength and high-modulus aramid III fibers are obtained through processes such as filtration, defoaming, spinning, washing, drying, winding and heat treatment. However, aromatic polyamide fibers (aramid fibers for short) including aramid III fibers are prone to photoaging degradation under ultraviolet irradiation, resulting in a gradual decline in the mechanical properties of the product, resulting in brittleness, cracking, and yellowing, and even complete destruction and failure to use. .

At present, the way to improve the aging resistance of aramid fiber is to add UV-resistant shielding agent. There are two types of specific implementation methods; one is the coating method, that is, a layer of UV-resistant shielding agent is coated on the surface of the aramid fiber. Such as a kind of _TiO disclosed in CN1837455A Anti-ultraviolet finishing solution, this finishing solution adopts sol-gel technology, and nano-titanium dioxide is coated on the surface of aramid fiber III by soaking or padding, thereby improving its UV resistance . The second is the mixed spinning method, that is, adding an ultraviolet absorber to the aramid spinning solution, and then mixing and spinning to obtain aramid III fiber. Such as Xing Zhe et al. (Xing Zhe, Xia Yanzhi, Wang Chuan. Preparation and mechanical properties of UV-resistant aramid fiber 1313[J]. Journal of Shaanxi University of Science and Technology: Natural Science Edition, 2008,25(5):67-70.) The benzotriazoles, benzophenones and triazines small molecule ultraviolet absorbers are mixed into the aramid fiber 1313 solution, and the UV-resistant aramid fiber III fiber is obtained through mixed spinning and heat treatment. However, these two UV-resistant methods have their disadvantages when applied to aramid III fibers. The disadvantage of the first method is that the surface adhesion of the coated UV-resistant agent to the aramid III fiber is poor. With the use of the aramid III fiber and the change of the environment, the UV-resistant agent is easy to fall off, and the protective layer outside the fiber It will slowly wear out, and finally make the fiber lose its protection. The disadvantage of the second method is that the mixed small molecule ultraviolet absorber is easy to degrade during the high-temperature heat treatment (above 340°C) of the aramid III fiber, which will cause the decomposition of the macromolecular chain of the aramid III fiber and damage the aramid III fiber. Mechanical and thermal properties.

Contents of the invention

The object of the present invention is to aim at the defects existing in the existing methods of UV resistance of aramid III fibers, and firstly provide a method capable of preparing aramid III fibers with excellent UV resistance.

Another object of the present invention is to provide a UV-resistant aramid III fiber prepared by the above method, which not only has strong UV resistance, but also can last.

In order to achieve the purpose of the present invention, the inventor has carried out in-depth analysis and research to the benzimidazole structure, and found that the protonated benzimidazole structure (see Fig. 1, 2) can produce a kind of unexpected effect: promptly when acidity After the molecule is complexed to the benzimidazole unit on the macromolecular chain of the aramid fiber III, it can inhibit the transfer effect of the intramolecular charge, thereby producing a fluorescence enhancement effect (see Figure 3), which can dissipate the energy of ultraviolet light , thereby reducing the ability of ultraviolet light to damage fibers and improving the ultraviolet resistance of aramid III fibers. A kind of method that can prepare the aramid fiber III fiber with excellent UV-resisting performance that research and development provides is thus:

First use deionized water to prepare inorganic acid or organic acid into a low-concentration acidic solution with a mass fraction of 0.05-5%, then put the whole tube of spun and wound aramid fiber III into the acidic solution, and place it at a temperature of 10-5%. Static immersion treatment at 80°C for 5-30 minutes, or the aramid fiber III after spinning and winding is exported by a traction roller and then dynamically and continuously immersed in the acid solution at a temperature of 40-80°C for 0.5-5 minutes, or After the thermal stretching in the fiber spinning process, the aramid III fiber is directly and continuously immersed in the acidic solution at a temperature of 40-80°C for 0.5-5 minutes, and finally the impregnated aramid III fiber is in the whole cylinder Static or dynamic continuous drying at the temperature of 80 ~ 120 ℃.

The inorganic acid used in the above method is at least one of sulfuric acid, hydrochloric acid, phosphoric acid and nitric acid; the organic acid is at least one of formic acid, acetic acid and oxalic acid.

The mass fraction of the low-concentration acidic solution used in the above method is preferably 0.1-1%.

The static immersion temperature of the whole cylinder described in the above method is preferably 30-60° C.; the immersion time is preferably 10-20 minutes.

In the dynamic continuous impregnation process described in the above method, the immersion temperature is preferably 60-70° C.; the immersion time is preferably 1-3 minutes.

In the drying step described in the above method, the drying time of the whole cylinder after static immersion is 30-120 minutes, and the drying time after dynamic continuous immersion is 5-10 minutes.

A kind of ultraviolet resistant aramid fiber III prepared by the above method provided by the present invention is characterized in that acidic molecules are complexed on the benzimidazole unit of the fiber macromolecular chain, and the fiber uses a 1500W ultraviolet light with a wavelength of 365nm After being irradiated by a high-pressure mercury lamp for 1000 hours, the retention rate of its tensile strength is 75-95%, and the retention rate of its initial modulus is 78.6-95.7%; Increased by 26-60%.

The acidic molecule complexed on the benzimidazole unit of the fiber macromolecular chain is an inorganic acid or an organic acid molecule, and the inorganic acid is at least one of sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid; the organic acid is at least one of formic acid, acetic acid, and oxalic acid. at least one.

Compared with the prior art, the present invention has the following positive effects:

1. Since the method provided by the present invention is to use acidic molecules to be complexed to the benzimidazole unit to form a protonated benzimidazole structure capable of dissipating ultraviolet light energy to obtain excellent ultraviolet resistance of the aramid fiber III, thus not only It provides a new solution for the UV resistance of aramid III fiber, and because the acid-base ionic bond formed is a chemical bond, the interaction force is strong, and it will not fall off during use, which avoids the existing solution by coating UV-resistant agents. problems posed by the method.

2. Since the aramid III fiber provided by the present invention is obtained by the fluorescence enhancement effect generated in situ by the newly formed protonated benzimidazole unit on its macromolecular chain, its UV resistance is not only long-lasting , and can well maintain its own excellent tensile strength and initial modulus.

3. Since the acidic molecules complexed on the aramid fiber III fiber provided by the present invention will fall off at a temperature above 280°C (see Figure 4), even if it falls off, it will not have a negative impact on its macromolecular chain, so it is not only resistant to The UV modification effect is stable and will not affect its own excellent mechanical properties.

4. Since the preparation method provided by the present invention only needs to immerse the aramid fiber III in a low-concentration acidic solution to obtain excellent ultraviolet resistance, the process is simple, the cost is low, and it is beneficial to industrial production.

Description of drawings

Fig. 1 is the infrared spectrogram of the aramid III fiber not impregnated with acid solution (curve a, dotted line) and the aramid III fiber impregnated with acid solution by the method of the present invention (curve b, solid line). Among them, the curve b shows that there is an obvious N ⁺ -H vibration peak at 2500-2900 cm ^-1 , which proves that the acidic molecules are complexed on the macromolecular chain of the aramid fiber III.

Fig. 2 is a schematic diagram of the reaction of benzimidazole units complexing acidic molecules in the macromolecular chain of aramid fiber III fibers impregnated with the acidic solution by the method of the present invention, wherein the acidic molecules are represented by HR.

Fig. 3 is a test diagram of the fluorescence enhancement effect of the aramid III fiber impregnated with the acidic solution and complexed with the acidic molecules by the method of the present invention. The solid line in the figure is the fluorescence curve of the uncomplexed acid molecule aramid fiber, and the dotted line is the fluorescence curve of the aramid fiber complexed with the acid molecule. It can be seen that the fluorescence intensity of the latter is 6-7 times that of the former.

Fig. 4 is a thermal analysis (TGA) test chart of the aramid III fiber impregnated with an acidic solution and complexed with hydrochloric acid at a heating rate of 10° C./min by the method of the present invention. The weight loss at around 100°C in the figure is caused by the removal of water in the aramid III fiber; the weight loss (280-320°C) in the part surrounded by the dotted circle in the figure is the area where the complexed acidic molecules are removed.

detailed description

Examples are given below to further illustrate the present invention. It is necessary to point out that the following examples cannot be interpreted as limiting the protection scope of the present invention, if those skilled in the art make some non-essential improvements and adjustments to the present invention according to the above-mentioned content of the present invention, they still belong to the protection scope of the present invention.

In addition, it is worth noting that;

1) the following examples and comparative examples are 1500W high-pressure mercury lamps used for the ultraviolet irradiation of the obtained aramid fiber III fiber, wherein the ultraviolet light wavelength is 365nm, and the irradiation time is 1000h;

2) The ultraviolet resistance of the aramid fiber III fiber obtained in the following examples and comparative examples is characterized by the tensile strength retention rate of the aramid fiber III fiber before and after ultraviolet irradiation, and its calculation formula is as follows:

Tensile strength retention W=σ ₂ /σ ₁

Wherein σ ₁ is the tensile strength of the aramid fiber III before ultraviolet irradiation, and σ ₂ is the tensile strength of the aramid fiber III after ultraviolet irradiation, and the higher the tensile strength retention rate of the aramid fiber III is, the stronger the ultraviolet resistance is;

3) The tensile strength of the aramid III fiber obtained in the following examples and comparative examples is to adopt the British Instron4302 type strength meter, according to the method of ASTM D 885-2007, according to the clamp spacing 215mm, the clamp moving speed 25mm/min, one-way tension stretch test.

Example 1

First use deionized water to prepare concentrated hydrochloric acid into a hydrochloric acid aqueous solution with a mass fraction of 0.1%, then put the whole tube of spun and wound aramid III fiber into the hydrochloric acid aqueous solution, and statically immerse it at a temperature of 50°C for 10 minutes, then take it out , and then statically dry the whole cylinder in a blast oven at 100°C for 60 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 27.2cN/dt, and the initial modulus is 845cN/dt. The tensile strength and initial modulus retention rates were 90.7% and 91.8%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acid solution, its UV resistance performance was improved by 53%.

Example 2

First use deionized water to prepare concentrated sulfuric acid into a sulfuric acid aqueous solution with a mass fraction of 0.5%, then put the whole tube of the spun and wound aramid fiber III into the sulfuric acid aqueous solution, and statically immerse it at a temperature of 30°C for 25 minutes. , and then statically dry the whole cylinder in a blast oven at 100°C for 30 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 28.5cN/dt, and the initial modulus is 880cN/dt. The tensile strength and initial modulus retention rates were 95% and 95.7%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acid solution, its UV resistance performance was improved by 60%.

Example 3

First prepare concentrated nitric acid with deionized water to make a nitric acid aqueous solution with a mass fraction of 0.05%, then put the whole tube of spun and wound aramid fiber III into the nitric acid aqueous solution, and statically immerse it at a temperature of 40°C for 5 minutes, and take it out , and then statically dry the whole cylinder in a blast oven at 80°C for 120 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 24.0cN/dt, and the initial modulus is 770cN/dt. The tensile strength and initial modulus retention rates were 80% and 83.7%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acid solution, its UV resistance performance was improved by 34.9%.

Example 4

First use deionized water to prepare concentrated phosphoric acid into a phosphoric acid aqueous solution with a mass fraction of 0.08%, then put the whole tube of spun and wound aramid III fiber into the phosphoric acid aqueous solution, and statically immerse it at a temperature of 60°C for 8 minutes, and take it out , and then statically dry the whole cylinder in a blast oven at 80°C for 80 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 25.0cN/dt, and the initial modulus is 790cN/dt. The tensile strength The retention rates of initial modulus and initial modulus were 83.3% and 85.9%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acidic solution, its UV resistance performance was improved by 40.5%.

Example 5

First use deionized water to prepare formic acid into a formic acid aqueous solution with a mass fraction of 2%, then put the whole tube of spun and wound aramid fiber III fiber into the formic acid aqueous solution, and statically immerse it at a temperature of 20°C for 8 minutes, then take it out. Then dry the whole cylinder statically in a blast oven at 90°C for 70 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 25.5cN/dt, and the initial modulus is 806cN/dt. The tensile strength The retention rates of initial modulus and modulus were 85% and 87.6%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acid solution, its UV resistance performance was improved by 43.3%.

Example 6

First prepare oxalic acid with deionized water to make an aqueous oxalic acid solution with a mass fraction of 2%, then put the whole tube of the spun and wound aramid III fiber into the aqueous oxalic acid solution, and statically immerse it at a temperature of 10°C for 30 minutes, then take it out. Then dry the whole cylinder statically in a blast oven at 100°C for 50 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 25.8cN/dt, and the initial modulus is 814cN/dt. The tensile strength and initial modulus retention rates were 86% and 88.5%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acid solution, its UV resistance performance was improved by 45.0%.

Example 7

First use deionized water to prepare acetic acid into an acetic acid aqueous solution with a mass fraction of 5%, then put the whole tube of spun and wound aramid fiber III fiber into the acetic acid aqueous solution, and statically immerse it at a temperature of 80°C for 15 minutes, then take it out. Then dry the whole cylinder statically in a blast oven at 100°C for 60 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 26.5cN/dt, and the initial modulus is 825cN/dt. The tensile strength and initial modulus retention rates were 88.3% and 89.7%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acidic solution, its UV resistance performance was improved by 48.9%.

Example 8

First, use deionized water to prepare concentrated sulfuric acid into a sulfuric acid aqueous solution with a mass fraction of 0.1%, and then take out the spun and wound aramid fiber III with a traction roller, and then dynamically and continuously immerse it in the sulfuric acid aqueous solution at a temperature of 80°C. 1 minute, and finally dry the impregnated aramid III fiber online on a heating roller at 120°C for 5 minutes.

The tensile strength of gained fiber is 30cN/dt, and initial modulus is 920cN/dt, it is 25cN/dt to test its tensile strength after this fiber is irradiated with ultraviolet light, and initial modulus is 782cN/dt, then tensile strength and The retention rates of the initial modulus were 83.3% and 85%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acidic solution, its UV resistance performance was improved by 40.5%.

Example 9

First use deionized water to prepare concentrated hydrochloric acid into a hydrochloric acid aqueous solution with a mass fraction of 0.2%, and then take out the spun and wound aramid fiber III using a traction roller and then dynamically and continuously immerse it in the hydrochloric acid aqueous solution at a temperature of 70°C. 2 minutes, and finally dry the impregnated aramid III fiber online on a heating roller at 120°C for 8 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 26.1cN/dt, and the initial modulus is 807cN/dt. The tensile strength and the retention rate of initial modulus were 87% and 87.7%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acidic solution, its UV resistance performance was improved by 51.8%.

Example 10

First prepare phosphoric acid with deionized water to make a phosphoric acid aqueous solution with a mass fraction of 0.2%, and then take out the spun and wound aramid fiber III with a traction roller, and then dynamically and continuously immerse it in the phosphoric acid aqueous solution at a temperature of 60°C. Minutes, and finally dry the impregnated aramid III fiber online for 10 minutes on a heating roller at 120°C.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 25.5cN/dt, and the initial modulus is 788cN/dt. The tensile strength and initial modulus retention rates were 85% and 85.7%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acid solution, its UV resistance performance was improved by 43.3%.

Example 11

First prepare nitric acid with deionized water to make a nitric acid aqueous solution with a mass fraction of 0.08%, and then take out the spun and wound aramid fiber III with a traction roller and then dynamically and continuously immerse it in the nitric acid aqueous solution at a temperature of 75°C for 0.5 Minutes, and finally dry the impregnated aramid III fiber online for 10 minutes on a heating roller at 120°C.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 22.5cN/dt, and the initial modulus is 725cN/dt. The tensile strength and the retention rate of initial modulus were 75% and 78.8%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acid solution, its UV resistance performance was improved by 26%.

Example 12

First use deionized water to prepare oxalic acid solution with a mass fraction of 1.5% oxalic acid solution, and then take out the spun and wound aramid fiber III with a traction roller and then dynamically and continuously immerse it in the oxalic acid solution at a temperature of 50°C for 5 minutes, and finally dry the impregnated aramid III fiber in a common oven at 110°C for 8 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 24.5cN/dt, and the initial modulus is 775cN/dt. The tensile strength and initial modulus retention rates were 81.7% and 84.2%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acid solution, its UV resistance performance was improved by 37.8%.

Example 13

First use deionized water to prepare formic acid into a formic acid aqueous solution with a mass fraction of 2.5%, and then take out the spun and wound aramid III fiber with a traction roller and then dynamically and continuously immerse it in the formic acid aqueous solution at a temperature of 65°C. Minutes, and finally the impregnated aramid III fibers are dried on-line on a heating roller at 120°C for 6 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 24.0cN/dt, and the initial modulus is 755cN/dt. The tensile strength and initial modulus retention rates were 80% and 82.1%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acid solution, its UV resistance performance was improved by 34.9%.

Example 14

First use deionized water to prepare hydrochloric acid into a hydrochloric acid aqueous solution with a mass fraction of 0.1%, and then take out the spun and wound aramid fiber III using a traction roller and then dynamically and continuously immerse it in the hydrochloric acid aqueous solution at a temperature of 40°C for 0.8 Minutes, and finally dry the impregnated aramid III fiber online for 10 minutes on a heating roller at 110°C.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 23.3cN/dt, and the initial modulus is 735cN/dt. The tensile strength The retention rates of initial modulus and initial modulus were 77.7% and 79.9%, respectively. Compared with the fiber obtained in Comparative Example 1 without acid solution immersion treatment, its UV resistance performance was improved by 31%.

Example 15

First use deionized water to prepare concentrated hydrochloric acid and concentrated sulfuric acid into a hydrochloric acid/sulfuric acid aqueous solution with a mass fraction of 0.08%, and then directly pass the aramid III fiber after thermal stretching in the fiber spinning process under the action of the traction roller. The temperature is The hydrochloric acid/sulfuric acid aqueous solution at 45°C is impregnated for 1.8 minutes, and finally the impregnated aramid III fiber is dried on-line on a heating roller at 110°C for 10 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 23.1cN/dt, and the initial modulus is 723cN/dt. The tensile strength and initial modulus retention were 77.0% and 78.6%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acidic solution, its UV resistance performance was improved by 29.8%.

Example 16

First, use deionized water to prepare acetic acid and oxalic acid into a 3% acetic acid/oxalic acid aqueous solution, and then directly pass the aramid III fiber after thermal stretching in the fiber spinning process under the action of the traction roller at a temperature of 65°C. The acetic acid/oxalic acid aqueous solution is impregnated for 1.8 minutes, and finally the impregnated aramid fiber III fiber is dried in a blast oven at 100° C. for 60 minutes.

The tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 920cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 25.1cN/dt, and the initial modulus is 785cN/dt. The tensile strength and the retention rate of initial modulus were 83.7% and 85.3%, respectively. Compared with the fiber obtained in Comparative Example 1 without dipping treatment in acidic solution, its UV resistance performance was improved by 41.1%.

comparative example

The aramid III fiber is directly irradiated with ultraviolet light, the tensile strength of the obtained fiber is 30cN/dt, and the initial modulus is 556cN/dt. After the fiber is irradiated with ultraviolet light, the tensile strength is 17.8cN/dt. When the modulus is 785cN/dt, the retention rates of tensile strength and initial modulus are 59.3% and 60.4%, respectively.

Claims (8)

1. a preparation method of UV-resistant aramid fiber III fiber is characterized in that the processing steps and conditions of the method are as follows: First use deionized water to prepare inorganic acid or organic acid into a low-concentration acidic solution with a mass fraction of 0.05-5%, and then put the whole tube of spun and wound aramid fiber III into the low-concentration acidic solution. Static dipping treatment at 10-80°C for 5-30 minutes, or take out the spun and wound aramid III fiber with a traction roller and then dynamically and continuously dip it in the low-concentration acidic solution at a temperature of 40-80°C for 0.5-30 minutes 5 minutes, or after the thermal stretching of the fiber spinning process, the aramid III fiber is directly and continuously immersed in the low-concentration acidic solution at a temperature of 40-80°C for 0.5-5 minutes, and finally the impregnated The whole drum of aramid III fiber can be dried statically or dynamically at a temperature of 80-120°C. 2. the preparation method of the UV-resistant aramid fiber III according to claim 1 is characterized in that the inorganic acid used in the method is at least one of sulfuric acid, hydrochloric acid, phosphoric acid and nitric acid; the organic acid is formic acid, acetic acid and at least one of oxalic acid. 3. The method for preparing UV-resistant aramid fiber III according to claim 1 or 2, characterized in that the mass fraction of the low-concentration acidic solution used in the method is 0.1-1%. 4. The method for preparing UV-resistant aramid III fiber according to claim 1 or 2, characterized in that the static immersion temperature of the whole cylinder described in the method is 30-60°C; the immersion time is 10-20 minutes. 5 . The method for preparing UV-resistant aramid III fiber according to claim 3 , characterized in that the static immersion temperature of the whole cylinder described in the method is 30-60° C.; the immersion time is 10-20 minutes. 6. The preparation method of the UV-resistant aramid fiber III according to claim 1 or 2, characterized in that in the dynamic continuous dipping process described in the method, the dipping temperature is 60 to 70°C; the dipping time is 1 to 70°C. 3 minutes. 7. The preparation method of UV-resistant aramid fiber III according to claim 3, characterized in that in the dynamic continuous dipping process described in the method, the dipping temperature is 60-70°C; the dipping time is 1-3 minutes . 8. a kind of ultraviolet resistant aramid fiber III fiber prepared by the method claimed in claim 1, it is characterized in that on the benzimidazole unit of this fiber macromolecular chain complex has acidic molecule, and this fiber uses ultraviolet light wavelength to be 365nm After being irradiated by a 1500W high-pressure mercury lamp for 1000 hours, the retention rate of its tensile strength is 75-95%, and the retention rate of its initial modulus is 78.6-95.7%; The UV performance is improved by 26-60%.