Water washable photochromic fibers and methods for making the same

Abstract

The application provides a washable photochromic fiber and a preparation method thereof. The preparation method synthesizes a tungstic acid solution at room temperature, and obtains a WO3 solution at room temperature; the fiber is soaked in the prepared solution, and the photochromic fiber is obtained after being taken out and naturally dried; the fiber is coated with a certain concentration of polydimethylsiloxane, so that the fiber has a certain hydrophobicity and washing stability. The preparation method is simple in operation, harmless and non-toxic, and can be prepared in large quantities. The prepared photochromic fiber has good flexibility and stable photochromic performance. By adding an appropriate amount of CuCl, rapid coloring and bleaching are realized, and the color bleaching efficiency is greatly improved. By using polydimethylsiloxane coating, the washing and recycling are realized. The prepared photochromic fiber has weaving property and direct wearability, and can be used for future smart clothing and implantable display applications.

Description

Technical Field

[0001] This invention relates to the field of photochromic fiber technology, and more particularly to a washable photochromic fiber and its preparation method. Background Technology

[0002] Photochromism refers to the phenomenon where certain materials undergo changes in molecular structure or electronic activity under light of a specific wavelength and intensity, resulting in different color changes. While the number of photochromic materials has gradually increased over the years, the main drawbacks of organic materials include toxicity, poor light fatigue resistance, high cost, and complex synthesis routes. In contrast, inorganic materials offer significantly improved performance.

[0003] WO3 has been extensively studied due to its excellent electrochromic and photochromic properties. The crystallinity and size of WO3 have a significant impact on its photochromic performance. Photochromic WO3 is characterized by its crystalline structure and large size, and can be triggered by ultraviolet light to achieve color changes; however, rapid bleaching remains a major challenge. Summary of the Invention

[0004] To address the shortcomings of the existing technology, the present invention aims to provide a washable photochromic fiber and its preparation method. This preparation method uses the fiber as a substrate, synthesizes a photochromic solution at room temperature, and significantly improves the color bleaching efficiency by adding an appropriate amount of CuCl. Furthermore, a layer of PDMS is coated on the fiber surface, making the fiber hydrophobic, enabling the photochromic fiber to be washed and reused repeatedly, while maintaining color stability above 95%. The washable photochromic fiber prepared by this invention can be sewn into clothing as an ultraviolet display material, greatly enhancing its application in wearable and smart display fields.

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

[0006] S1, perform surface cleaning treatment on the fibers;

[0007] S2, prepare a sodium tungstate dihydrate solution of a predetermined concentration and add oxalic acid, then stir until homogeneous to obtain a mixed solution;

[0008] S3, add hydrochloric acid to the mixed solution obtained in step S2 to adjust the pH value to 1.0-1.3;

[0009] S4. Add nickel nitrate hexahydrate to the solution obtained in step S3 and stir to react.

[0010] S5, add cuprous chloride to the solution obtained in step S4 and stir to react;

[0011] S6, the fiber after the cleaning treatment in step S1 is soaked in the solution obtained in step S5 to react, and then taken out and air-dried under natural conditions to obtain photochromic fiber.

[0012] S7. Prepare a polydimethylsiloxane solution of a predetermined concentration and add a curing agent; immerse the photochromic fiber obtained in step S6 in the polydimethylsiloxane solution once, remove it and air dry it at room temperature to obtain a water-washable photochromic fiber.

[0013] As a further improvement of the present invention, in step S5, the mass fraction of cuprous chloride is 1-4%, and the stirring reaction time is 5-10 min.

[0014] As a further improvement of the present invention, in step S7, the volume fraction of PDMS is 10-20%, the solvent is n-hexane, and the amount of curing agent added accounts for 10 wt% of PDMS.

[0015] As a further improvement of the present invention, in step S2, the concentration of the sodium tungstate dihydrate solution is 0.1-0.2 mol / L, the solvent used is deionized water, and the mass fraction of the added oxalic acid relative to the added sodium tungstate dihydrate is 6.7-13.4 wt%.

[0016] As a further improvement of the present invention, in step S3, the concentration of the added hydrochloric acid is 2-3 mol / L, and the stirring reaction time is 10-15 min.

[0017] As a further improvement of the present invention, in step S4, the mass fraction of nickel nitrate hexahydrate is 10-20 wt%, and the stirring reaction time is 20-30 min.

[0018] As a further improvement of the present invention, in step S7, the curing agent is butyl fluorinated silane (BFS), hydrosilane, or organic peroxide, etc.

[0019] As a further improvement of the present invention, in step S1, the surface cleaning treatment of the fiber is to place the fiber in a solution with a volume ratio of ethanol:water = 7:3 and sonicate for 20 minutes to remove dust and oil stains from the fiber surface.

[0020] As a further improvement of the present invention, the fiber is a hydrophilic flexible fiber such as cotton fiber, polyester blended fiber, hemp fiber, or bamboo fiber.

[0021] To achieve the above objectives, the present invention also provides a washable photochromic fiber, which is prepared by the preparation method described in any of the foregoing technical solutions. The washable photochromic fiber includes a fiber substrate, a color-changing layer coated on the fiber substrate, and a waterproof coating formed by polydimethylsiloxane.

[0022] The beneficial effects of this invention are:

[0023] 1. The method for preparing washable photochromic fibers provided by this invention allows for the synthesis of photochromic solutions at room temperature, saving energy and reducing costs. Adding an appropriate amount of CuCl accelerates the recovery and bleaching process of the WO3 membrane. The introduction of Cu ions increases the average size of the nanoparticles in the membrane, while a considerable number of smaller nanoparticles (≈1-2 nm) remain around the larger nanoparticles. This results in rapid coloring after UV irradiation and a quick return to colorless after the UV light source is removed. Simultaneously, the combination of chloride ions and divalent copper ions forms a tetrachlorocopper complex ion [CuCl4]. 2 - This process makes the color lighter and the color change more pronounced, significantly shortening the fading time after WO3 color change. A certain concentration of PDMS is coated onto the surface of the original photochromic fiber, making the fiber hydrophobic and enabling repeated washing and reuse of the photochromic fiber, while maintaining color stability above 95%. Simultaneously, it does not alter the fiber's flexibility and mechanical strength, allowing for free weaving and patterning, and can be sewn into clothing as a UV display material, greatly enhancing its application in wearable and smart display fields.

[0024] 2. This invention uses cotton fibers as a substrate and obtains photochromic fibers by soaking, which is not only simple to operate but also allows for mass production.

[0025] 3. The washable photochromic fiber prepared by this invention not only has a fast UV response but also a significantly improved bleaching rate, and can be washed and recycled multiple times, greatly improving its application performance in wearables and displays. After irradiating the photochromic fiber with a 365nm ultraviolet lamp for 3-5 seconds, the fiber changes from white to light blue; after irradiation for 20-30 seconds, the fiber color deepens to dark blue.

[0026] 4. The washable photochromic fiber prepared by this invention can be rapidly bleached back to its initial white color under natural conditions after coloring; light blue to white takes only 30-60 seconds; dark blue to white takes only 3-5 minutes. Compared with existing WO3 photochromic materials, this significantly improves the color bleaching efficiency.

[0027] 5. The washable photochromic fiber prepared by the present invention, after being washed 10 times, shows almost no change in stability when the fiber is dyed and faded again, indicating that the PDMS layer on its surface improves its hydrophobicity and gives it washable stability. Attached Figure Description

[0028] Figure 1 SEM image of the photochromic fiber prepared in Example 1.

[0029] Figure 2 The image shows the actual photos of the color change and washability of the photochromic fiber prepared in Example 1.

[0030] Figure 3 A physical color-changing illustration of the sample from Example 1.

[0031] Figure 4 The stress-strain curves are for different photochromic fibers prepared in Example 1.

[0032] Figure 5 SEM image of the photochromic fiber prepared in Comparative Example 1 without Ni(NO3)2·6H2O.

[0033] Figure 6 This is a diagram showing the color-changing ability of the photochromic fiber prepared without CuCl, as shown in Comparative Example 2.

[0034] Figure 7 The images show the color changes of the photochromic fibers prepared without PDMS in Comparative Example 4 before and after 10 washes.

[0035] Figure 8 SEM image of the photochromic fiber prepared in Example 2.

[0036] Figure 9 SEM image of the photochromic fiber prepared in Example 3.

[0037] Figure 10 SEM image of the photochromic fiber prepared in Example 4.

[0038] Figure 11 SEM image of the photochromic fiber prepared in Example 5.

[0039] Figure 12 The image shows the coloring properties of the photochromic fiber prepared in Comparative Example 5 before and after 10 washes. Detailed Implementation

[0040] 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.

[0041] 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.

[0042] This invention provides a method for preparing washable photochromic fibers, comprising the following steps:

[0043] S1, perform surface cleaning treatment on the fibers;

[0044] The fiber was placed in a solution with a volume ratio of ethanol:water = 7:3 and sonicated for 20 minutes to remove dust, oil, and other contaminants from the fiber surface.

[0045] The fibers are hydrophilic flexible fibers such as cotton, polyester blended fibers, hemp fibers, and bamboo fibers.

[0046] S2, prepare a sodium tungstate dihydrate solution of a predetermined concentration and add oxalic acid, then stir until homogeneous to obtain a mixed solution;

[0047] Specifically, prepare a sodium tungstate dihydrate solution with a concentration of 0.1–0.2 mol / L, using deionized water as the solvent, and stir for 5–10 min; the oxalic acid added should have a mass fraction of 6.7–13.4 wt% relative to the added sodium tungstate dihydrate, and continue stirring for another 5–10 min.

[0048] S3, add hydrochloric acid to the mixed solution obtained in step S2 to adjust the pH value to 1.0-1.3;

[0049] Specifically, the concentration of hydrochloric acid added is 2-3 mol / L, and the stirring reaction time is 10-15 min.

[0050] S4. Add nickel nitrate hexahydrate to the solution obtained in step S3 and stir to react.

[0051] Specifically, the mass fraction of nickel nitrate hexahydrate added is 10-20 wt%, and the stirring reaction time is 20-30 min.

[0052] S5, add cuprous chloride to the solution obtained in step S4 and stir to react;

[0053] Specifically, the mass fraction of cuprous chloride is 1-4 wt%, and the stirring reaction time is 5-10 min.

[0054] The addition of cuprous chloride accelerates the recovery bleaching process of the WO3 membrane. The introduction of Cu ions increases the average size of the nanoparticles in the membrane, while a considerable number of smaller nanoparticles (≈1-2 nm) remain around the larger ones. These smaller nanoparticles color quickly after UV irradiation and rapidly revert to colorless after the UV light source is removed. Simultaneously, the combination of chloride ions and divalent copper ions forms a tetrachlorocopper complex ion [CuCl4]. 2 - (Pale yellow) makes the color lighter and the color change more obvious, and significantly shortens the fading time of WO3 after the color change.

[0055] S6, the fiber after the stain removal treatment in step S1 is immersed in the solution obtained in step S5 for reaction, and then air-dried under natural conditions to obtain photochromic fiber; the immersion time is 1 to 2 minutes.

[0056] S7. Prepare a polydimethylsiloxane solution of a predetermined concentration and add a curing agent; immerse the photochromic fiber obtained in step S6 in the polydimethylsiloxane solution once, remove it and air dry it at room temperature to obtain a water-washable photochromic fiber.

[0057] Specifically, the volume fraction of PDMS is 10-20%, the solvent is n-hexane, and the amount of curing agent added accounts for 10 wt% of PDMS.

[0058] The curing agent is butyl fluorinated silane (BFS), hydrogenated silane, or peroxide (such as organic peroxide).

[0059] The washable photochromic fiber prepared according to the aforementioned method includes a fiber substrate, a color-changing layer coated on the fiber substrate, and a waterproof coating formed by polydimethylsiloxane.

[0060] The preparation method of the washable photochromic fiber provided by the present invention will be described below with reference to specific embodiments.

[0061] Example 1

[0062] This embodiment provides a method for preparing washable photochromic fibers, including the following steps:

[0063] S1. Take 10cm of cotton fiber and place it in a solution with a volume ratio of ethanol:water = 7:3. Sonicate for 20 minutes to remove dust, oil, etc. from the surface of the fiber.

[0064] S2, prepare a 0.18 mol / L sodium tungstate dihydrate solution with deionized water and stir for 5 min; then add 6.7 wt% oxalic acid dihydrate and stir for another 5 min;

[0065] S3. Add 3 mol / L hydrochloric acid to the solution obtained in step S2 to adjust the pH of the solution to 1.2 ± 0.05, and continue stirring for 10 min to obtain a light yellow transparent solution.

[0066] S4. Add 20 wt% nickel nitrate hexahydrate to the solution obtained in step S3, stir for 20 min, and obtain a green transparent solution.

[0067] S5. Add 3 wt% cuprous chloride to the solution obtained in step S4 and stir for 5 min to obtain a dark blue solution.

[0068] S6. The fiber that has been treated with stain removal in step S1 is immersed in the dark blue solution obtained in step S5 for 1 minute. After being taken out, it is naturally dried at room temperature to obtain white fiber with photochromic response.

[0069] S7. Prepare a 10% (v / v) PDMS solution using n-hexane, add a curing agent (PDMS:curing agent = 10:1), immerse the fiber obtained in step S6 in the PDMS solution once, remove it, and air dry it naturally at 25°C to obtain a washable photochromic fiber. The curing agent is butyl fluorinated silane (BFS).

[0070] Please see Figure 1 The image shown is a SEM image of the photochromic fiber after adding 20 wt% Ni(NO3)2·6H2O and 3 wt% CuCl in Example 1, and after using 10% PDMS as a sealant.

[0071] As can be seen from the figure, the cotton fiber surface is uniformly covered with a photochromic layer with a certain thickness. It can be seen that there are obvious WO3 particles attached to the fiber photochromic coating and they are evenly distributed. Furthermore, the PDMS film at this concentration has little effect on the thickness of the film on the fiber surface, thus maintaining the good flexibility of the cotton fiber.

[0072] Please see Figure 2 The image shows a photograph of the photochromic fiber prepared in Example 1, illustrating its color change and washability. As can be seen, the cotton fiber prepared in Example 1 was initially white; after irradiation with a 365nm UV lamp for 30 seconds, it reached its maximum coloration state, clearly turning bluish-black; after being left to stand naturally for 3 minutes, the color faded completely, and the fiber returned to white. This is due to the addition of a small amount of Cu. + Ions accelerate the reduction and natural oxidation processes of WO3.

[0073] After the fiber was washed 10 times, it was dyed and faded again. Its stability remained almost unchanged, indicating that the PDMS layer on its surface improved its hydrophobicity and gave it washable stability.

[0074] Please see Figure 3 The image shown is a physical demonstration of the color-changing properties of the sample from Example 1. It can be seen that the pattern sewn from this color-changing fiber changes from white to a distinct deep blue after about 20 seconds of exposure to ultraviolet light. It also exhibits good flexibility and weavability, showing promising application prospects in pattern design.

[0075] Please see Figure 4 The figure shows the stress-strain curves of different photochromic fibers in Example 1. The tensile strength of the original cotton yarn was 210 MPa. After absorbing the color-changing solution, its tensile strength became 195 MPa. After coating its surface with a 10% PDMS film, its tensile strength increased significantly to 380 MPa, and its elongation at break also increased significantly.

[0076] This demonstrates that the photochromic fiber prepared in Example 1 improved the mechanical properties of the original fiber.

[0077] Comparative Example 1

[0078] Comparative Example 1 provides a method for preparing washable photochromic fibers. The difference from Example 1 is that Ni(NO3)2·6H2O is not added in step S4. The rest is roughly the same as Example 1 and will not be repeated here.

[0079] Please see Figure 5 The image shown is a SEM image of the photochromic fiber prepared in Comparative Example 1 without Ni(NO3)2·6H2O. Without Ni, the film thickness on the fiber surface is small, and no obvious WO3 particles are observed. The flaky appearance may be due to the uneven coating of PDMS. However, due to the small number of effective particles on its surface, the coloring time is significantly increased, requiring 5 minutes to color to a deep blue.

[0080] Comparative Example 2

[0081] Comparative Example 2 provides a method for preparing washable photochromic fibers. The difference from Example 1 is that CuCl is not added in step S5. The rest is roughly the same as Example 1 and will not be repeated here.

[0082] Please see Figure 6 The image shown is a diagram illustrating the color-changing ability of the photochromic fiber prepared without CuCl in Comparative Example 2. Compared to Example 1, without CuCl, the photochromic fiber changed from white to bluish-black after 60 seconds of UV irradiation, but the bleaching time increased significantly. Under natural conditions, the color faded to light blue after 10 minutes, and complete fading required more than 20 minutes. This indicates that adding a certain concentration of CuCl can greatly improve the efficiency of the fiber's color-to-fading transition.

[0083] Comparative Example 3

[0084] Comparative Example 3 provides a method for preparing washable photochromic fibers. The difference from Example 1 is that Ni(NO3)2·6H2O and CuCl are not added in steps S4 and S5. The rest is roughly the same as in Example 1, and will not be repeated here.

[0085] Experiments show that when the system does not contain Ni 2+ and Cu + When using pure WO3 film for coloring and fading, the effect is poor. The coloring time of this sample is 3-5 minutes, and the natural fading time is about 30 minutes.

[0086] Comparative Example 4

[0087] Comparative Example 4 provides a method for preparing washable photochromic fibers. The difference from Example 1 is that in step S7, PDMS is not used to encapsulate the photochromic fibers. The rest is roughly the same as Example 1 and will not be described again here.

[0088] Please see Figure 7 The image shown is a photograph of the photochromic fiber prepared without PDMS in Comparative Example 4, before and after 10 washes.

[0089] As can be seen, before washing, the fiber color ranged from white to dark blue; after 10 washes, not only did the fiber surface become rougher, but its maximum color intensity also only reached blue-gray. Compared to Example 1, its color change stability was poor. Therefore, the PDMS coating on its surface is crucial for achieving washability.

[0090] Examples 2-5 and Comparative Example 5

[0091] The preparation methods of washable photochromic fibers provided in Examples 2-5 and Comparative Example 5 differ from those in Example 1 in that the mass fraction of Ni(NO3)2·6H2O in step S4, the mass fraction of CuCl in step S5, and the volume fraction of PDMS in step S7 are changed, as shown in the table below; the rest are roughly the same as in Example 1 and will not be repeated here.

[0092]

[0093] Please see Figure 8 The image shown is a SEM image of the photochromic fiber prepared in Example 2.

[0094] As can be seen, when the content of Ni(NO3)2·6H2O is reduced to 10%, larger aggregates appear on the fiber surface, and the WO3 layer on its surface becomes significantly thicker. Although this photochromic fiber can still achieve photochromism, its coloring time increases by 5-10 seconds compared to Example 1, but its coloring and fading abilities remain good. This may be due to the Ni content... 2+ The doping amount affects the crystal structure of WO3, thereby changing the morphology of WO3.

[0095] When the content of Ni(NO3)2·6H2O is further reduced to 8%, the stability of the precursor solution obtained in step S5 decreases, resulting in large particles accumulating on the surface of the fibers soaked in the solution, which affects the bleaching rate of the discolored fibers after discoloration.

[0096] Please see Figure 9 The image shown is a SEM image of the photochromic fiber prepared in Example 3.

[0097] As can be seen from the figure, WO3 particles and Cu are uniformly distributed on the fiber surface. + The content of Cu has little effect on the structure and morphology of WO3. The coloring and fading ability of this sample are similar to those of Example 1. + Bleaching and fading time will be longer when the content is low compared to when 3wt% Cu is added. + The sample fading time increases by 5-10 seconds.

[0098] Example 4

[0099] This embodiment provides a method for preparing washable photochromic fibers. Compared with Example 1, the difference is that 4 wt% CuCl is added in step S5. The rest is roughly the same as in Example 1 and will not be described again here.

[0100] Please see Figure 10 The image shown is a SEM image of the photochromic fiber prepared in Example 4. When the CuCl content increased to 4%, a rice-grain-like granular structure appeared in the WO3 layer on the fiber surface, with a small amount of Cu... + It can accelerate the bleaching of colored WO3 layers, but when Cu... + Excessive concentration can affect the achievement of the deepest color in the coloring state, but its bleaching time is shorter than that of low-concentration Cu. + It can shorten the time by 20-30 seconds. Compared with Example 1, the color reaching the maximum color state is lighter, but the maximum color absorption value differs by only 0.05; this color change is within the normal error range.

[0101] When the CuCl content is further increased to 5%, the coloring time of the color-changing fiber increases to over 60 seconds, and the maximum color achieved is higher than that of low-concentration CuCl. + The sample is light in color, and the color contrast before and after coloring decreases, indicating a reduction in coloring efficiency and a deterioration in color-changing performance.

[0102] Example 5

[0103] This embodiment provides a method for preparing washable photochromic fibers. Compared with Example 1, the difference is that in step S7, the photochromic fibers obtained in step S6 are coated with a 20% PDMS solution. The rest is roughly the same as in Example 1, and will not be described again here.

[0104] Please see Figure 11 The image shown is a SEM image of the photochromic fiber prepared in Example 5.

[0105] As shown in the figure, increasing the PDMS content only affects the degree of particle aggregation on the fiber surface, but the WO3 particles are still clearly visible. The content of other particles remains unchanged, and it does not affect its coloring and bleaching abilities.

[0106] Please see Figure 12 The image shows the coloring properties of the photochromic fiber prepared in Comparative Example 5 (coated with a 5% PDMS solution obtained in step S6) before and after 10 washes. As can be seen from the image, before washing, the photochromic fiber could change from white to bluish-black under UV light, but after 10 washes, its maximum color state only reached bluish-gray. This is because the concentration of PDMS was too low, resulting in poor coating on the fiber surface and an insignificant hydrophobic modification effect.

[0107] In summary, this invention provides a method for preparing washable photochromic fibers. The photochromic solution can be synthesized at room temperature, saving energy and reducing costs. By adding an appropriate amount of CuCl, the switching efficiency from coloring to fading of the fiber is greatly improved. A certain concentration of PDMS is coated onto the surface of the original photochromic fiber, making the fiber hydrophobic and enabling repeated washing and reuse of the photochromic fiber, while maintaining color stability above 95%. Simultaneously, the fiber's flexibility and mechanical strength are not altered, allowing for arbitrary weaving and patterning. It can be sewn into clothing as a UV display material, significantly enhancing its application in wearable and smart display fields.

[0108] The above description is only 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 a washable photochromic fiber, characterized in that, Includes the following steps: S1, perform surface cleaning treatment on the fibers; S2, prepare a sodium tungstate dihydrate solution of a predetermined concentration and add oxalic acid, then stir until homogeneous to obtain a mixed solution; S3, add hydrochloric acid to the mixed solution obtained in step S2 to adjust the pH value to 1.0-1.3; S4. Add nickel nitrate hexahydrate to the solution obtained in step S3 and stir to react. S5, add cuprous chloride to the solution obtained in step S4 and stir to react; S6, the fiber after the cleaning treatment in step S1 is soaked in the solution obtained in step S5 to react, and then taken out and air-dried under natural conditions to obtain photochromic fiber. S7, prepare polydimethylsiloxane of a predetermined concentration and add curing agent; The photochromic fiber obtained in step S6 is immersed once in a polydimethylsiloxane solution, then removed and air-dried at room temperature to obtain a washable photochromic fiber; and after washing 10 times, the color stability of the washable photochromic fiber remains above 95%.

2. The method for preparing washable photochromic fibers according to claim 1, characterized in that: In step S5, the mass fraction of cuprous chloride is 1-4%, and the stirring reaction time is 5-10 min.

3. The method for preparing washable photochromic fibers according to claim 1, characterized in that: In step S7, the volume fraction of the polydimethylsiloxane is 10-20%, the solvent is n-hexane, and the amount of the added curing agent accounts for 10 wt% of the polydimethylsiloxane.

4. The method for preparing washable photochromic fibers according to claim 1, characterized in that: In step S2, the concentration of the sodium tungstate dihydrate solution is 0.1~0.2 mol / L, and the solvent used is deionized water; the mass fraction of oxalic acid added relative to the added sodium tungstate dihydrate is 6.7-13.4 wt%.

5. The method for preparing washable photochromic fibers according to claim 1, characterized in that: In step S3, the concentration of the added hydrochloric acid is 2-3 mol / L, and the stirring reaction time is 10-15 min.

6. The method for preparing washable photochromic fibers according to claim 1, characterized in that: In step S4, the mass fraction of the nickel nitrate hexahydrate is 10-20 wt%, and the stirring reaction time is 20-30 min.

7. The method for preparing washable photochromic fibers according to claim 1, characterized in that: In step S7, the curing agent is butyl fluorinated silane, hydrosilane, or organic peroxide.

8. The method for preparing washable photochromic fibers according to claim 1, characterized in that: In step S1, the surface cleaning treatment of the fiber involves placing the fiber in a solution with a volume ratio of ethanol:water = 7:3 and sonicating it for 20 minutes to remove dust and oil from the fiber surface.

9. The method for preparing washable photochromic fibers according to claim 1, characterized in that: The fiber is a hydrophilic flexible fiber.

10. A washable photochromic fiber, characterized in that: The washable photochromic fiber is prepared by the preparation method according to any one of claims 1-9; the washable photochromic fiber includes a fiber substrate, a color-changing layer coated on the fiber substrate, and a waterproof coating formed by polydimethylsiloxane; and after washing 10 times, the color stability of the washable photochromic fiber remains above 95%.

Images