Process for the production of photochromic fibers by wet spinning

Abstract

The application provides a method for preparing photochromic fibers by wet spinning. The method prepares WO3 powder suitable for spinning by controlling pH value and adding an appropriate amount of CuBr; then the WO3 powder is uniformly mixed with a spinning solution, and spinning is performed in a coagulation bath by selecting a suitable spinning needle, and photochromic fibers are prepared by adding different polymer spinning solutions and selecting corresponding coagulation baths. The process of preparing photochromic fibers by wet spinning is simple, non-toxic and harmless, and can be prepared in large quantities; the mechanical properties of the fibers can be improved by adding different polymers, the fibers have strong plasticity, and the photochromic fibers have flexibility, good mechanical properties and excellent color changing properties. The prepared fibers can be woven into textiles at will, and have potential applications in smart textiles.

Description

Technical Field

[0001] This invention relates to the field of photochromic fiber technology, and more particularly to a method for preparing photochromic fibers by wet spinning. Background Technology

[0002] In recent years, textiles have moved beyond their initial basic functions of comfort, warmth, and aesthetics, gradually moving towards intelligence and functionality, such as waterproofing, luminescence, UV sensitivity, and energy storage. By incorporating functional materials into textiles, smart textiles with various functions can be achieved. As a fundamental component of textiles, the strategy of developing smart fibers may offer a promising approach to manufacturing smart wearable devices.

[0003] Polyvinyl alcohol (PVA) is a water-soluble, low-cost synthetic polymer with a huge global production volume. PVA possesses excellent mechanical properties, film-forming properties, adhesiveness, chemical stability, biocompatibility, and biodegradability, making its applications widespread across various aspects of life. Thermoplastic polyurethane rubber (TPU), a commonly used wet spinning solution, is also widely used in the textile industry. Mixing TPU with photochromic particles (WO3) and spinning it yields photochromic fibers with a certain degree of flexibility, showing potential applications in smart textiles. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing photochromic fibers using wet spinning. This method is simple, low-cost, non-toxic, and allows for large-scale production. The addition of an appropriate amount of CuBr significantly improves the color bleaching efficiency and enhances the color-changing properties. The added polymer improves the mechanical properties of the fiber and increases its plasticity. The photochromic fibers prepared by this invention possess both flexibility and good mechanical properties, allowing them to be woven into textiles in any way, and have potential applications in smart textiles.

[0005] To achieve the above objectives, the present invention provides a method for preparing photochromic fibers by wet spinning, comprising the following steps:

[0006] S1, Prepare a sodium tungstate solution of a predetermined concentration and add oxalic acid, then stir until homogeneous to obtain a mixed solution;

[0007] S2, add hydrochloric acid to the mixed solution obtained in step S1 to adjust the pH value to 1.2-1.6;

[0008] S3, Add cuprous bromide to the solution obtained in step S2 and stir to react;

[0009] S4. After the solution obtained in step S3 is allowed to stand for 24-48 hours, it is centrifuged and filtered to obtain the lower precipitate. After heating and drying, it is ground to obtain amorphous WO3 powder.

[0010] S5. Add the WO3 powder obtained in step S4 to the prepared polyvinyl alcohol solution or thermoplastic polyurethane rubber solution, stir, and obtain the spinning solution.

[0011] S6. Prepare the corresponding coagulation bath according to the type of solution selected in step S5 for preparing the spinning solution.

[0012] S7. Using a spinning needle, the spinning solution obtained in step S5 is extracted into the coagulation bath prepared in step S6, and the spinning rate is controlled to spin the fiber to obtain photochromic fiber.

[0013] As a further improvement of the present invention, in step S5, a PVA solution with a mass fraction of 10-20% is prepared by using an aqueous solution or a TPU solution with a mass fraction of 10-25% is prepared by using dimethylformamide, and then WO3 powder with a mass fraction of 2-5% is added and mechanically stirred for 4-8 hours to obtain a uniform spinning solution.

[0014] As a further improvement of the present invention, in step S6, when the polyvinyl alcohol solution is selected as the spinning solution in step S5, a saturated solution of sodium sulfite and borax is prepared as the coagulation bath of PVA.

[0015] As a further improvement of the present invention, in step S6, when the spinning solution in step S5 is a thermoplastic polyurethane rubber solution, deionized water is used as the coagulation bath for TPU.

[0016] As a further improvement of the present invention, in step S3, the mass fraction of cuprous bromide added relative to the mass fraction of sodium tungstate added is 2-5%, and the stirring reaction time is 5-10 min.

[0017] As a further improvement of the present invention, in step S1, the concentration of the sodium tungstate solution is 0.05-0.1 mol / L; and the mass fraction of the added oxalic acid relative to the added sodium tungstate is 2-5 wt%.

[0018] As a further improvement of the present invention, in step S2, the concentration of the added hydrochloric acid is 3-5 mol / L, and the stirring reaction time is 20-30 min.

[0019] As a further improvement of the present invention, in step S4, the solution obtained in step S3 is placed at room temperature for 24-48 hours, centrifuged and filtered 2-3 times with deionized water, and the precipitate is dried at 60-70°C for 8-10 hours and then ground into powder for later use.

[0020] As a further improvement of the present invention, in step S7, the outer diameter of the spinning needle is 0.8-1.0 mm; the spinning rate is controlled at 15-30 mm / min; and the spinning solution becomes photochromic fiber after passing through the coagulation bath.

[0021] The beneficial effects of this invention are:

[0022] 1. The wet spinning method for preparing photochromic fibers provided by this invention synthesizes the spinning solution at room temperature, does not produce toxic or harmful substances, is environmentally friendly and pollution-free, and is simple to operate with low cost. When preparing the spinning solution, the pH is adjusted to 1.2-1.6 with hydrochloric acid to obtain smaller WO3 particles and a more uniform spinning solution; an appropriate amount of CuBr is added, because Cu... + It has strong reproducibility and can directly reproduce the W from WO3. 6+ Restore to W 5+ This caused a chemical change in the system. When the solution remained standing for an extended period, the Cl- ions in the hydrochloric acid reacted with Cu... 2+ The resulting tetrachlorocopper complex ion [CuCl4] is formed. 2- The addition of CuBr results in a pale yellow color, making the obtained powder lighter and providing greater contrast in subsequent color changes. Without the addition of CuBr, it is difficult to obtain WO3 powder, and the resulting powder is pale blue with very low yield.

[0023] 2. This invention improves the mechanical properties of the resulting fiber by adding a high molecular polymer (polyvinyl alcohol or thermoplastic polyurethane rubber) to the spinning solution and selecting a corresponding coagulation bath. The prepared photochromic fiber combines the flexibility and mechanical strength of the fiber, and can be woven into textiles at will. In addition, the fiber has excellent color-changing properties and a fast response to UV. After being irradiated by ultraviolet light, it can change from grayish-white to blue with obvious color. It has potential applications in smart textiles.

[0024] 3. The wet spinning method used in this invention can produce uniform and fine fibers with good mechanical properties and chemical stability, making it suitable for manufacturing high-performance fibers. The solvent selection and spinning conditions during the spinning process can be adjusted to meet the performance requirements of different fibers; by adjusting the solution concentration and spinning conditions, fibers of different diameters can be produced to meet the needs of different applications. The entire process is relatively environmentally friendly. Attached Figure Description

[0025] Figure 1 The front and cross-sectional SEM images are of the photochromic fiber prepared in Example 1.

[0026] Figure 2 The image shown is a photograph of the fiber obtained in Example 1, with the inset in the lower left corner showing the color-changed image.

[0027] Figure 3 The front and cross-sectional SEM images are of the photochromic fiber prepared in Example 2.

[0028] Figure 4This is a photograph of the color change of the photochromic fiber prepared in Example 3.

[0029] Figure 5 Stress-strain curves for fibers with different PVA contents.

[0030] Figure 6 Photographs of the color change of the photochromic fiber obtained by spinning in Example 4.

[0031] Figure 7 This is a photograph of the fiber obtained in Comparative Example 6. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0034] This invention provides a method for preparing photochromic fibers by wet spinning, comprising the following steps:

[0035] S1, Prepare a sodium tungstate solution of a predetermined concentration and add oxalic acid, then stir until homogeneous to obtain a mixed solution;

[0036] Specifically, prepare a sodium tungstate solution with a concentration of 0.05–0.1 mol / L using deionized water as the solvent, and stir for 5–10 minutes; add oxalic acid at a mass fraction of 2–5 wt% relative to the added sodium tungstate, and continue stirring for 5–10 minutes.

[0037] S2, add hydrochloric acid to the mixed solution obtained in step S1 to adjust the pH value to 1.2-1.6;

[0038] Specifically, the concentration of hydrochloric acid added is 3-5 mol / L, and the stirring reaction time is 20-30 min.

[0039] By adjusting the pH to 1.2-1.6 with hydrochloric acid, the resulting WO3 particles are smaller and the spinning solution is more uniform, which facilitates subsequent wet spinning.

[0040] S3, Add cuprous bromide to the solution obtained in step S2 and stir to react;

[0041] Specifically, the mass fraction of cuprous bromide added relative to sodium tungstate added is 2-5%, and the stirring reaction time is 5-10 minutes.

[0042] Add a small amount of cuprous bromide because Cu + It has strong reproducibility and can directly reproduce the W from WO3. 6+ Restore to W 5 + This caused a chemical change in the system. When the solution remained standing for an extended period, the Cl- in the hydrochloric acid... - With Cu 2+ The resulting tetrachlorocopper complex ion [CuCl4] is formed. 2- The addition of CuBr results in a pale yellow color, making the obtained powder lighter in color and providing greater contrast in subsequent color changes. Without the addition of CuBr, it is difficult to obtain WO3 powder, and the obtained powder is pale blue in color with very low yield, which is not conducive to collecting WO3 powder for preparing spinning solutions.

[0043] S4. After the solution obtained in step S3 is allowed to stand for 24-48 hours, it is centrifuged and filtered to obtain the lower precipitate. After heating and drying, it is ground to obtain amorphous WO3 powder.

[0044] Specifically, the solution obtained in step S3 is placed at room temperature for 24-48 hours, centrifuged and filtered 2-3 times with deionized water, and the precipitate is dried at 60-70℃ for 8-10 hours and then ground into powder for later use.

[0045] S5. Add the WO3 powder obtained in step S4 to the prepared polyvinyl alcohol solution or thermoplastic polyurethane rubber solution, stir, and obtain the spinning solution.

[0046] Specifically, a PVA solution with a mass fraction of 10-20% or a TPU solution with a mass fraction of 10-25% is prepared using an aqueous solution, and then WO3 powder with a mass fraction of 2-5% is added and mechanically stirred for 4-8 hours to obtain a uniform spinning solution.

[0047] S6. Prepare the corresponding coagulation bath according to the type of solution selected in step S5 for preparing the spinning solution.

[0048] Specifically, when polyvinyl alcohol solution is selected as the spinning solution in step S5, a saturated solution of sodium sulfite and borax is prepared as the coagulation bath for PVA.

[0049] When a thermoplastic polyurethane rubber solution is selected as the spinning solution in step S5, deionized water is used as the coagulation bath for the TPU.

[0050] S7. Using a spinning needle, the spinning solution obtained in step S5 is extracted into the coagulation bath prepared in step S6, and the spinning rate is controlled to spin the fiber to obtain photochromic fiber.

[0051] The outer diameter of the spinning needle is 0.8-1.0 mm, corresponding to specifications of 21G-19G. The spinning rate is controlled at 15-30 mm / min, and the spinning solution becomes photochromic fiber after passing through the coagulation bath.

[0052] This method involves uniformly mixing WO3 powder with a spinning solution, then selecting a suitable spinning needle and spinning in a coagulation bath to form the fibers. By adding different polymers to the spinning solution and selecting the corresponding coagulation bath, photochromic fibers can be obtained. The entire process is simple, non-toxic, and harmless, and can produce photochromic fibers in large quantities. The prepared photochromic fibers respond quickly to UV light, changing from grayish-white to blue after being irradiated with ultraviolet light, exhibiting a clear color change and showing potential applications in smart textiles.

[0053] The method for preparing photochromic fibers by wet spinning provided by the present invention will be described below with reference to specific embodiments.

[0054] Example 1

[0055] This embodiment provides a method for preparing photochromic fibers by wet spinning, including the following steps:

[0056] S1, prepare a 0.1 mol / L sodium tungstate solution with deionized water, add 2% oxalic acid and stir for 10 min;

[0057] S2, add 5 mol / L hydrochloric acid to the solution obtained in step S1, adjust the pH of the solution to 1.5, and continue stirring for 20 min;

[0058] S3, add 2% CuBr to the solution obtained in step S2 and stir for 5 min;

[0059] S4. The solution obtained from S3 was left at room temperature for 24 hours, centrifuged and filtered 2-3 times with deionized water, and the precipitate was dried at 60℃ for 8 hours and then ground into powder for later use.

[0060] S5. Prepare a 10% PVA solution with an aqueous solution, then add 2% WO3 powder and mechanically stir for 4 hours to obtain a uniform spinning solution.

[0061] S6. Prepare a saturated solution of sodium sulfite and borax as a coagulation bath, and use a 19G spinning needle at a spinning rate of 15 mm / min to wet spin photochromic fibers.

[0062] Please see Figure 1 The image shown is a front and cross-sectional SEM image of the photochromic fiber prepared in Example 1.

[0063] As can be seen from the figure, the WO3 particles on the fiber surface are evenly distributed and small in size (50-70nm), with the fiber diameter being around 330μm.

[0064] Please see Figure 2 The image shown is a photograph of the fiber obtained in Example 1. It can be seen that a relatively long fiber length is obtained through spinning, and the fiber as a whole is uniformly fine. Experiments show that the prepared fiber rapidly changes color from white to blue after exposure to light, with a coloring time of only about 30 seconds. The fading process can also be completed within a few hours. Compared to traditional spun color-changing fibers that require 12-24 hours to fade, its fading performance is significantly improved. The color-changing effect is shown in the illustration in the lower left corner, demonstrating its obvious color change.

[0065] Comparative Example 1

[0066] Comparative Example 1 provides a method for preparing photochromic fibers by wet spinning. The difference from Example 1 is that CuBr is not added in step S3. The rest is roughly the same as in Example 1 and will not be repeated here.

[0067] Experiments revealed that in step S3, without the addition of CuBr, in step S4 of powder preparation, it is difficult to obtain WO3 powder from the solution obtained in step S3 under natural conditions, and the powder is pale blue in color with extremely low yield; after adding CuBr, due to Cu... + It has strong reproducibility and can directly reproduce the W from WO3. 6+ Restore to W 5+ This caused another chemical change in the system. When the solution remained standing for an extended period, the Cl- in the hydrochloric acid... - With Cu 2+ The resulting tetrachlorocopper complex ion [CuCl4] is formed. 2- The pale yellow color makes the resulting powder lighter in color, resulting in greater contrast in subsequent color changes.

[0068] Comparative Example 2

[0069] Comparative Example 2 provides a method for preparing photochromic fibers by wet spinning. The difference from Example 1 is that hydrochloric acid is added in step S2 to adjust the pH value to 2.0. The rest is roughly the same as Example 1 and will not be described again here.

[0070] Experiments show that the amount of hydrochloric acid added under these acid-base conditions is significantly reduced, and the prepared tungstic acid solution is clearer. It is possible that some sodium tungstate did not participate in the reaction, resulting in less product obtained from the continued reaction and decomposition process, which is not conducive to the collection of WO3 powder.

[0071] Examples 2-5 and Comparative Examples 3-5

[0072] The methods for preparing photochromic fibers by wet spinning provided in Examples 2-5 and Comparative Examples 3-5 are mainly different from those in Example 1 in that the type and amount of the spinning solution used in step S5, as well as the mass fraction of WO3 powder added, are changed, as shown in the table below; the rest are roughly the same as in Example 1, and will not be repeated here.

[0073]

[0074]

[0075] Please see Figure 3 The image shown is a front and cross-sectional SEM image of the photochromic fiber prepared in Example 2.

[0076] As shown in the figure, with the increase of WO3 powder dosage, the number and size of particles on the fiber surface increase, and the diameter of the prepared fiber is 179 μm. This may be related to the stretching after spinning, but the cross-section shows that a void structure appears inside the fiber. This is attributed to the large number of WO3 particles, which formed a network with the PVA colloid during the preparation of the spinning solution. When the fiber is stretched after spinning, some particles move, forming the void structure shown in the cross-section.

[0077] Experiments show that the prepared fibers change color rapidly from white to blue after being exposed to light, with a coloring time of only about 30 seconds and a fading time of 3-5 hours.

[0078] This indicates that the increase in WO3 content has a significant impact on the morphology of the fiber, but little impact on the color-changing properties. This is because color change only shows the color change on the fiber surface, and the WO3 particles on the surface are the main reason for the color development.

[0079] Please see Figure 4 The image shown is a photograph of the color change of the photochromic fiber obtained by spinning in Example 3. As can be seen from the image, the fiber spun from PVA is white in color, but turns blue after being irradiated with ultraviolet light. The coloring time is only about 30 seconds, and the fading time is 3-5 hours. Compared to the 12-24 hours required for fading of traditional spun color-changing fibers, its fading performance is significantly improved, and its color-changing performance is stable.

[0080] As shown in the table above, in Comparative Example 3, the amount of WO3 added was further increased.

[0081] According to the experimental results of Comparative Example 3, when the amount of WO3 continues to increase to 10%, it is easy to form particle deposits in the PVA spinning solution, resulting in uneven spinning solution, poorer fiber toughness, and obvious powdery roughness.

[0082] Comparative Example 4

[0083] Comparative Example 4 provides a method for preparing photochromic fibers by wet spinning. The difference from Example 1 is that in step S5, a 25% PVA solution is prepared using an aqueous solution. The rest is roughly the same as in Example 1 and will not be repeated here.

[0084] Experiments have shown that when the PVA content is too high, the spun fibers are lighter in color and closer to transparent. However, due to the excessive coating of WO3 particles, the PVA layer thickness increases, which is not conducive to the color change of the fibers. Under ultraviolet light irradiation, it takes more than 10 minutes to color the fibers and the color change is not obvious.

[0085] Please see Figure 5 As shown in the figure, the tensile properties of fibers with different PVA contents are illustrated. Fibers with 10% PVA exhibit significantly better tensile properties (Example 2). However, when the PVA content increases to 25%, the mechanical properties decrease, the elastic properties deteriorate significantly, and the dry fibers are prone to breakage. Therefore, the mass fraction of PVA should not exceed 20%.

[0086] Example 4

[0087] This embodiment provides a method for preparing photochromic fibers by wet spinning. Compared with Example 1, the difference is that in step S5, a 10% TPU solution is prepared with DMF, and then 2% WO3 powder is added and mechanically stirred for 4 hours to obtain a uniform spinning solution; in step S6, water is used as a coagulation bath, and the rest is roughly the same as in Example 1, and will not be described again here.

[0088] Please see Figure 6 The image shows a photograph of the photochromic fiber obtained from spinning in Example 4. It can be seen that the spun TPU fiber is white and somewhat transparent, but turns a distinct blue after being irradiated with ultraviolet light, indicating that using TPU as a spinning solution does not affect the photochromic properties of the WO3 powder.

[0089] Example 5

[0090] This embodiment provides a method for preparing photochromic fibers by wet spinning. Compared with Example 1, the difference is that in step S5, a 25% TPU solution is prepared with DMF, and then 5% WO3 powder is added and mechanically stirred for 4 hours to obtain a uniform spinning solution; in step S6, water is used as a coagulation bath, and the rest is roughly the same as in Example 1, and will not be described again here.

[0091] Experiments showed that when the TPU concentration increased to 25%, the mechanical properties of the spun fibers improved due to TPU's good elasticity and stretchability. However, when the fibers were irradiated with ultraviolet light while stretched, the depth of color change varied slightly. This may be because the increased concentration of the spinning solution affected the dispersion of WO3 particles, leading to localized agglomeration. Nevertheless, the color-changing ability remained good, and uniform fibers could still be obtained by using a larger diameter spinning needle.

[0092] Comparative Example 5

[0093] Comparative Example 5 provides a method for preparing photochromic fibers by wet spinning. Compared with Example 1, the difference is that in step S5, a 10% TPU solution is prepared with DMF, and then 10% WO3 powder is added and mechanically stirred for 4 hours to obtain a uniform spinning solution; in step S6, water is used as a coagulation bath, and the rest is roughly the same as in Example 1, and will not be repeated here.

[0094] It can be seen that when the amount of WO3 continues to increase to 10%, uneven spinning solution also appears in TPU spinning solution, resulting in coarse fibers.

[0095] In summary, in step S5, the amount of WO3 powder should be controlled between 2% and 5%.

[0096] The mass fraction of PVA is controlled at 10-20%, and the mass fraction of TPU solution is controlled at 10-25%.

[0097] Comparative Example 6

[0098] Comparative Example 6 provides a method for preparing photochromic fibers by wet spinning. The difference from Example 1 is that in step S6, the spinning needle 19G (outer diameter 1.0 mm) is replaced with 22G (outer diameter 0.7 mm). The rest is roughly the same as in Example 1 and will not be described again here.

[0099] Please see Figure 7 As shown, due to the reduced diameter of the spinning needle, the needle is prone to clogging and the fiber diameter becomes thinner, resulting in less noticeable color change.

[0100] In summary, this invention provides a method for preparing photochromic fibers by wet spinning. The spinning solution can be synthesized at room temperature, without producing toxic or harmful substances, making it environmentally friendly and pollution-free. The method is simple to operate and has low cost. Adjusting the pH to 1.2-1.6 with hydrochloric acid results in smaller WO3 particles and a more uniform spinning solution. Adding an appropriate amount of CuBr further enhances the effect of Cu... + It has strong reproducibility and can directly reproduce the W from WO3. 6+ Restore to W 5+This caused a chemical change in the system. When the solution remained standing for an extended period, the Cl- in the hydrochloric acid... - With Cu 2+ The resulting tetrachlorocopper complex ion [CuCl4] is formed. 2- The pale yellow color makes the resulting powder lighter in color, resulting in greater contrast in subsequent color changes; it also improves the color-changing ability of the fiber.

[0101] Photochromic fibers with both flexibility and good mechanical properties were obtained by preparing spinning solutions using polyvinyl alcohol (PVA) or thermoplastic polyurethane rubber (TPU). The prepared photochromic fibers change color from grayish-white to blue upon exposure to ultraviolet light, exhibiting a clear color change. They can be woven into textiles in any way and have potential applications in smart textiles.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing photochromic fibers by wet spinning, characterized in that, Includes the following steps: S1, Prepare a sodium tungstate solution of a predetermined concentration and add oxalic acid, then stir until homogeneous to obtain a mixed solution; S2, add hydrochloric acid to the mixed solution obtained in step S1 to adjust the pH value to 1.2-1.6; S3, Add cuprous bromide to the solution obtained in step S2 and stir to react; the mass fraction of the added cuprous bromide relative to the added sodium tungstate is 2~5%; S4. After the solution obtained in step S3 is allowed to stand at room temperature for 24-48 h, it is centrifuged and filtered to obtain the lower precipitate. After heating and drying, it is ground to obtain amorphous WO3 powder. S5. Add the WO3 powder obtained in step S4 to the prepared polyvinyl alcohol solution or thermoplastic polyurethane rubber solution, stir, and obtain the spinning solution. S6. Prepare the corresponding coagulation bath according to the type of solution selected in step S5 for preparing the spinning solution. S7. Using a spinning needle, the spinning solution obtained in step S5 is extracted into the coagulation bath prepared in step S6, and the spinning rate is controlled to spin the fiber to obtain photochromic fiber.

2. The method for preparing photochromic fibers by wet spinning according to claim 1, characterized in that: In step S5, a PVA solution with a mass fraction of 10-20% is prepared using an aqueous solution or a TPU solution with a mass fraction of 10-25% is prepared using dimethylformamide. Then, WO3 powder with a mass fraction of 2-5% is added and mechanically stirred for 4-8 hours to obtain a uniform spinning solution.

3. The method for preparing photochromic fibers by wet spinning according to claim 1, characterized in that: In step S6, when polyvinyl alcohol solution is selected as the spinning solution in step S5, a saturated solution of sodium sulfite and borax is prepared as the coagulation bath for PVA.

4. The method for preparing photochromic fibers by wet spinning according to claim 1, characterized in that: In step S6, when the thermoplastic polyurethane rubber solution is selected as the spinning solution in step S5, deionized water is used as the coagulation bath for TPU.

5. The method for preparing photochromic fibers by wet spinning according to claim 1, characterized in that: In step S3, the stirring reaction time is 5-10 min.

6. The method for preparing photochromic fibers by wet spinning according to claim 1, characterized in that: In step S1, the concentration of the sodium tungstate solution is 0.05~0.1 mol / L; the mass fraction of the added oxalic acid relative to the added sodium tungstate is 2-5 wt%.

7. The method for preparing photochromic fibers by wet spinning according to claim 1, characterized in that: In step S2, the concentration of the added hydrochloric acid is 3-5 mol / L, and the stirring reaction time is 20-30 min.

8. The method for preparing photochromic fibers by wet spinning according to claim 1, characterized in that: In step S4, the solution obtained in step S3 is left to stand for 24-48 hours, centrifuged and filtered 2-3 times with deionized water, and the precipitate is dried at 60-70℃ for 8-10 hours and then ground into powder for later use.

9. The method for preparing photochromic fibers by wet spinning according to claim 1, characterized in that: In step S7, the outer diameter of the spinning needle is 0.8-1.0 mm; the spinning rate is controlled at 15-30 mm / min; and the spinning solution becomes photochromic fiber after passing through the coagulation bath.

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