A method for preparing a composite fiber membrane with high ultraviolet light absorption capacity based on electrospinning

Abstract

The application relates to the field of functional materials and discloses a method for preparing a composite fiber membrane with high ultraviolet light absorption capacity based on electrostatic spinning, which comprises the following steps: (1) extraction of silk fibroin; (2) preparation of a silk fibroin / photoreactive polymer solution; and (3) preparation of an electrostatic spinning composite fiber membrane. The method uses a compound solution containing azobenzene photoreactive polymer and silk fibroin as a spinning solution, and a uniform and stable spinning solution with a proper viscosity can be obtained; then, the jetting action in electrostatic spinning is used to induce the orientation of the molecular chains of the azobenzene photoreactive polymer, and the cis-trans isomerization conversion rate of azobenzene is significantly improved, so that the composite fiber membrane with excellent ultraviolet light absorption capacity can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of functional materials, in particular to a method for preparing a composite fiber membrane with high ultraviolet light absorption capacity based on electrospinning. BACKGROUND

[0002] In recent years, due to the continuous destruction of the ozone layer of the atmosphere, the ultraviolet rays on the earth's surface are increasing, which has a great impact on human life. Excessive ultraviolet radiation can cause human skin to darken, age, and even cause skin cancer, so people need to protect themselves from ultraviolet rays in daily life.

[0003] Due to the cis-trans isomerization of azobenzene under the condition of ultraviolet light and visible light, fabrics containing azobenzene polymers can achieve ultraviolet light absorption. The specific principle is as follows:

[0004]

[0005] In the above reaction, trans-azobenzene is converted from trans-structure to cis-structure under the irradiation of ultraviolet light, which shows that the Π-Π* transition is weak and the n-Π* intensity is enhanced. Cis-azobenzene is converted to trans-structure under visible light or dark conditions, so that ultraviolet light absorption can be achieved through continuous structural transformation.

[0006] However, the above cis-trans isomerization of azobenzene usually requires a long time, so its ultraviolet light absorption capacity is limited. If the cis-trans isomerization rate of azobenzene can be improved, the ultraviolet light absorption capacity of fabrics containing azobenzene can be further increased, thereby achieving better ultraviolet light protection effect. SUMMARY

[0007] In order to solve the above technical problems, the present application provides a method for preparing a composite fiber membrane with high ultraviolet light absorption capacity based on electrospinning. The present application uses a compound solution of azobenzene-containing photoresponsive polymer and silk fibroin as a spinning solution, so that a uniform and stable spinning solution with appropriate viscosity can be obtained. Then, the jetting action in electrospinning is used to induce the orientation of the molecular chain of the azobenzene-containing photoresponsive polymer, thereby significantly improving the cis-trans isomerization rate of azobenzene, and obtaining a composite fiber membrane with excellent ultraviolet light absorption capacity.

[0008] The specific technical scheme of the present application is as follows: a method for preparing a composite fiber membrane with high ultraviolet light absorption capacity based on electrospinning, comprising the following steps:

[0009] (1) Extraction of silk fibroin.

[0010] (2) Preparation of silk fibroin / photore sponsive polymer solution: 2-methyl-2-propenoic acid-2-(2-methoxyethoxy)ethyl ester ((MEO2) (molecular formula ), polyethylene glycol methyl ether methacrylate (OEG 300 ) (molecular formula ), 6-(4-phenylazophenyl) hexyl methacrylate (AHMA) (molecular formula ), CuBr, Me6TREN, solvent, initiator were added to a reaction vessel, and oxygen was removed by freezing extraction; then the polymerization reaction was carried out by heating, and the reaction was stopped by cooling; the obtained mixed solution was eluted with tetrahydrofuran on an alumina column to remove excess CuBr, and the obtained solution was repeatedly precipitated and dissolved in n-hexane; finally, the obtained precipitated product was vacuum dried to obtain the azobenzene-containing photore sponsive polymer P(MEO2-co-OEG 300 -co-AHMA) (molecular formula

[0011] ) in the form of a yellow-brown viscous gel; the azobenzene-containing photore sponsive polymer and silk fibroin were dissolved in a formic acid solution and heated and stirred to obtain a spinning solution.

[0012] (3) Preparation of electrospun composite fiber membrane: the spinning solution was moved into a syringe installed on a syringe pump, a voltage was applied at the needle, small droplets in the form of a conical jet were sprayed from the needle, and a collector was used for collection; after the electrospinning was completed, drying was performed to obtain a composite fiber membrane with high ultraviolet light absorption capacity.

[0013] In polymers, the molecular chains generally present a disordered aggregation state, which is generally described by a "random coil model". Due to the random arrangement of the molecular chains, the side groups of the molecular chains are relatively close to each other, which limits the cis-trans isomerization movement of the azobenzene groups on the molecular side chains. It is found in the present application that the molecular chain orientation of the azobenzene-containing photore sponsive polymer can be induced by means of the jetting action in electrospinning. Specifically, under the action of an electric field force, the polymer chains present a high degree of orientation and a relatively regular arrangement. When the orientation degree of the polymer molecular chains is increased, the distance between the side groups of the molecular chains is relatively increased, the relative force is reduced, and the molecular movement is relatively easy. Under the irradiation of ultraviolet light, the photore sponsive groups will react more quickly, the trans-azobenzene will be converted into cis-azobenzene, and under the irradiation of visible light, the cis-azobenzene will be converted into trans-azobenzene, and the cis-trans isomerization conversion rate is improved. Under the condition of rapid conversion, repeated absorption of ultraviolet light is realized, and therefore the ultraviolet light has a stronger absorption capacity.

[0014] However, the applicant found in the experiment that although the photoresponsive polymer containing azobenzene has the advantages of being sensitive to light and fast response speed, the spinnability of the photoresponsive polymer containing azobenzene is not ideal, and the photoresponsive polymer containing azobenzene cannot be directly used as a spinning solution for electrospinning. Therefore, the silk fibroin with high spinnability is selected for compounding with the photoresponsive polymer containing azobenzene, so that a spinning solution with uniform stability and suitable viscosity can be formed, and the composite fiber membrane can be successfully obtained by electrospinning.

[0015] As preferred, in step (1), first, the cocoon is degummed by using a sodium carbonate solution, and then the degummed product is rinsed and dried, and then added into a lithium bromide solution for heating and complete dissolution, and then dialysis, centrifugation, collection of supernatant, and finally freeze-drying are performed to obtain the silk fibroin.

[0016] As preferred, in step (1), the concentration of the sodium carbonate solution is 0.04-0.06 mol / L -1 ; the concentration of the lithium bromide solution is 8-10 mol / L -1 ; the rinsing time is 8-15 min; the heating temperature is 50-70 DEG C; the centrifugation speed is 8000-12000 rpm, and the centrifugation time is 10-20 min; and the freeze-drying temperature is -40 to -50 DEG C.

[0017] As preferred, in step (2), the amount ratio of 2-methyl-2-propenoic acid-2-(2-methoxyethoxy) ethyl ester, polyethylene glycol methyl ether methacrylate, 6-(4-phenylazobenzene) methyl hexyl methacrylate, CuBr, Me6TREN, solvent and initiator is (1-5) mL:(1-3) mL:(1-2) mg:(10-100) mg:(60-100) muL:(30-50) mL:(30-50) muL.

[0018] As preferred, in step (2), the mass ratio of the photoresponsive polymer containing azobenzene and the silk fibroin is (0.1-0.5):(0.5-1), and the total mass fraction of the two in the spinning solution is 5-25%.

[0019] The reason why the present application controls the ratio of the photoresponsive polymer and the silk fibroin within the above range is that the absorption capacity of the ultraviolet light is mainly related to the content of the azobenzene in the photoresponsive polymer, and under the above ratio, the photoresponsive polymer and the silk fibroin can form a uniform solution under certain conditions, and the composite fiber membrane with ultraviolet absorption shielding effect can be formed through the electrospinning technology, and the composite fiber membrane with the above ratio can better realize the ultraviolet absorption effect, if the photoresponsive polymer is too much, it is difficult to form the composite fiber membrane due to the poor spinnability, and if the content of the photoresponsive polymer is too low, the content of the azobenzene is too low, which can weaken the ultraviolet absorption shielding.

[0020] Preferably, in step (2), the solvent is anisole, and the initiator is methyl 2-chloropropionate.

[0021] Preferably, in step (2), the temperature of the polymerization reaction is 60-80 DEG C, and the reaction time is 2-5 h.

[0022] Preferably, in step (2), the temperature of the vacuum drying is 30-50 DEG C.

[0023] Preferably, in step (3), the electrospinning parameters are as follows: the extrusion rate is set to 0.5-1.0 mL / h, the distance between the injector tip and the collection surface is fixed to 6-10 cm, and the working voltage applied to the needle tip is 8-9 kV.

[0024] The present application finds that the electrospinning parameters have a significant influence on the ultraviolet light absorption capacity of the composite fiber membrane. Therefore, in order to further obtain the composite fiber membrane with high ultraviolet light absorption capacity, the present application needs to strictly control the extrusion rate, the distance between the injector and the collection surface, and the working voltage. Finally, the present application finds that the above parameters are controlled within the above range, which can improve the molecular chain orientation degree of the polymer during the electrospinning process, and further improve the ultraviolet light absorption capacity of the composite fiber membrane.

[0025] Preferably, in step (3), the drying temperature is 40-60 DEG C.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] (1) The present application induces the molecular chain of the photoresponsive polymer containing azobenzene to be oriented by means of the spinning effect in the electrospinning, and further significantly improves the cis-trans isomerization conversion rate of the azobenzene, which can enhance the repeated ultraviolet light absorption capacity under the condition of rapid conversion.

[0028] (2) The application uses a compound solution of a photoresponsive polymer containing azobenzene and silk fibroin as a spinning solution, so that a uniform and stable spinning solution with appropriate viscosity can be obtained, and a composite fiber membrane can be smoothly obtained by electrospinning.

[0029] (3) The application optimizes the electrospinning parameters to improve the molecular chain orientation degree of the polymer in the electrospinning process, thereby improving the ultraviolet light absorption capacity of the electrospinning composite fiber membrane. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Fig. 2: Absorption spectra of electrospun composite fiber membranes prepared in Example 3 (the ratio of photoresponsive polymer and silk fibroin is 0.5:0.5) under ultraviolet light and visible light at different times;

[0031] Figure 2 Fig. 3: Scanning electron microscope images of electrospun composite fiber membranes prepared in Example 3 (the ratio of photoresponsive polymer and silk fibroin is 0.5:0.5) under different voltages;

[0032] Figure 3 Fig. 4: Scanning electron microscope images of electrospun composite fiber membranes prepared in Example 4 (the ratio of photoresponsive polymer and silk fibroin is 1:0.5) under a voltage of 9kV;

[0033] Figure 4 Fig. 5: Absorption spectra of electrospun composite fiber membranes prepared in Example 3 (the ratio of photoresponsive polymer and silk fibroin is 0.5:0.5) and blended films (the ratio of photoresponsive polymer and silk fibroin is 0.5:0.5) under ultraviolet light and visible light at different times;

[0034] Figure 5 Fig. 6: Absorption values at 356nm of electrospun composite fiber membranes prepared in Example 3 (the ratio of photoresponsive polymer and silk fibroin is 0.5:0.5) and blended films (the ratio of photoresponsive polymer and silk fibroin is 0.5:0.5) under alternating ultraviolet light and visible light;

[0035] Figure 6Zn-MOF@WO3 / TPU composite fiber membranes with UV color-changing ability were prepared by electrospinning composite fiber membranes (light-responsive polymer and silk fibroin ratio of 0.5:0.5) or blending membranes prepared by Example 3, and the K / S value diagram of Zn-MOF@WO3 / TPU composite fiber membranes after alternating UV light 1 min and visible light 10 min irradiation (light brown: K / S value of the membrane covered by the blending film, light green: K / S value of the membrane covered by the electrospun composite fiber membrane) wherein the abscissa "0" is the K / S value of the membrane not irradiated by UV light, the abscissa "1" is the K / S value of the membrane after the first UV light irradiation, then visible light irradiation for 10 min, the abscissa "2" is the K / S value of the membrane after the second UV light irradiation, then visible light irradiation for 10 min, the abscissa "3" is the K / S value of the membrane after the third UV light irradiation, then visible light irradiation for 10 min, and the abscissa "4" is the K / S value of the membrane after the fourth UV light irradiation, then visible light irradiation for 10 min. DETAILED DESCRIPTION

[0036] The application will be further described below in conjunction with examples.

[0037] The UV absorption ability test uses the color-changing degree of Zn-MOF@WO3 / TPU composite fiber membranes with UV color-changing ability to characterize, and the composite fiber membranes are prepared as follows: 0.714 g of zinc nitrate hexahydrate ((Zn(NO3)2-6H2O)) is weighed and added to 120 mL of deionized water, stirred and dissolved for about 30 minutes to produce a uniform clear solution (I). 3.9 g of 2-methylimidazole (2-MIM) is weighed and added to 120 mL of deionized water, stirred and dissolved for about 30 minutes to produce another uniform transparent liquid (II). Then, solution I is added to solution II, and the stirring time is 15 minutes. The mixed solution is kept at room temperature for 24 hours. After that, centrifugation is performed at a speed of 7000 rpm for 30 minutes, and finally washed with deionized water three times. 0.2 g of (poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) is weighed and added to a mixed solution containing 0.5 g of deionized water and 13 g of ethanol, and stirred for 30 minutes, then 0.4 g of WCl6 (tungsten chloride) and 200 mg of Zn-MOF are added to the above-mentioned mixed solution of ethanol and deionized water, and stirred again for 30 minutes to prepare a uniform suspension. Finally, the suspension is transferred to an autoclave and heated at 110°C for 1 hour. After heating, it is cooled to room temperature, and then the suspension is washed with deionized water three times. The product Zn-MOF@WO 3。The electrospinning solution was mixed with a syringe installed on a syringe pump. The electrospinning solution was added to a syringe (5 mL) installed on a syringe pump, and a voltage of 15 kv was applied to the needle, and the receiving surface was an MFNF (polyurethane microfiber nonwoven fabric) with a thickness of 2 mm. After the electrospinning was completed, a Zn-MOF@WO3 / TPU composite fiber membrane was finally obtained, which showed color under ultraviolet light irradiation. The fiber membrane was responsive to ultraviolet light, and the longer the ultraviolet light irradiation time, the deeper the degree of change from white to blue-violet of the membrane. The Zn-MOF@WO3 / TPU composite fiber membrane was used to verify the anti-ultraviolet ability of the electrospun composite fiber membrane in the application.

[0038] In order to further characterize the orientation-induced enhancement of ultraviolet absorption ability, a blended film without high molecular chain orientation was also prepared. The preparation method is as follows: first, silk fibroin was extracted, and the cocoon was cut into small pieces. In order to remove sericin, the cocoon was placed in a heated Na2CO3 solution with a concentration of 0.047 mol / L -1 , and then the silk fibroin was repeatedly rinsed with distilled water for 10 min. Then the silk fibroin was placed in an oven for drying. After drying, it was completely dissolved in a LiBr solution at 60℃, and then the solution was moved into a dialysis bag for dialysis. After dialysis, centrifugation was performed at 10,000 rpm for 15 min. The supernatant was collected, and finally placed in a freeze dryer at a temperature of -45℃ to obtain white silk fibroin.

[0039] 2-methoxy-2-propenoic acid-2-(2-methoxyethoxy) ethyl ester (MEO2) (molecular formula ), polyethylene glycol methyl ether methacrylate (OEG 300 ) (molecular formula ), 6-(4-phenylazophenyl) hexyl methacrylate (AHMA) (molecular formula ), CuBr, Me6TREN, anisole, methyl 2-chloropropionate were added to the reaction bottle in the order of 3.70 mL: 1.52 mL: 1.840 mg: 50 mg: 80 μL: 40 mL: 40 μL according to the amount ratio, and the oxygen in the reaction bottle was removed by freezing and pumping. Then the reaction was carried out at 75℃ for 3 h. The reaction was stopped in an ice bath. In order to remove excess CuBr, the mixed solution was eluted with tetrahydrofuran on an alumina column. The obtained solution was precipitated and dissolved in n-hexane three times. Finally, the obtained product was dried in a vacuum drying oven at 40℃ to obtain an azobenzene-containing photoresponsive polymer P(MEO2-co-OEG300 co-AHMA) (molecular formula ) was mixed with silk fibroin in a mass ratio of 0.5:0.5, added to 2 mL of formic acid, and a mixed solution was obtained. Barium sulfate was added to the mixed solution, and then the solution was heated and stirred at 40°C for 6 h to ensure that the solutes were completely and uniformly mixed. The solution was then placed in a vacuum drying oven at 40°C to obtain a blend film. The blend film was used to compare the UV shielding ability with the electrospun composite fiber film.

[0040] Example 1

[0041] First, silk fibroin was extracted. The cocoon was cut into small pieces, and the cocoon was placed in a heated Na2CO3 solution having a concentration of 0.047 mol / L -1 to remove sericin. The silk fibroin was then repeatedly rinsed with distilled water for 10 min, and then the silk fibroin was placed in an oven to dry. After drying, the silk fibroin was completely dissolved in a LiBr solution at 60°C, and then the solution was moved to a dialysis bag. After dialysis, centrifugation was performed at 10,000 rpm for 15 min. The supernatant was collected, and then the collected solution was placed in a freeze dryer at -45°C to obtain white silk fibroin.

[0042] 2-methoxyethyl 2-methacrylate (MEO2) (molecular formula ), polyethylene glycol methyl ether methacrylate (OEG 300 ) (molecular formula ), 6-(4-phenylazophenyl) hexyl methacrylate (AHMA) (molecular formula ), CuBr, Me6TREN, anisole, methyl 2-chloropropionate were sequentially added to a reaction bottle in a ratio of 3.70 mL:1.52 mL:1.840 mg:50 mg:80 μL:40 mL:40 μL. Oxygen in the reaction bottle was removed by freeze-thawing, and then the reaction was performed at 75°C for 3 h. The reaction was stopped in an ice bath. To remove excess CuBr, the mixed solution was eluted with tetrahydrofuran on an alumina column. The obtained solution was precipitated and dissolved in n-hexane three times. Finally, the obtained product was dried in a vacuum drying oven at 40°C to obtain the azobenzene-containing photoresponsive polymer P(MEO2-co-OEG 300 -co-AHMA) (molecular formula The photoresponsive polymer containing azobenzene and silk fibroin were mixed at a mass ratio of 0:1 and added to 2 mL of formic acid to obtain a mixture. The mixture was heated at 40°C for 6 hours to ensure homogeneous solute mixing, and then transferred to a syringe mounted on an injection pump. A voltage was applied to the needle tip to eject small, cone-shaped droplets. Aluminum foil was used as the receiving surface. After spinning, the fabric was dried in a 50°C oven until constant weight, finally obtaining an electrospun composite fiber membrane. The extrusion rate was set to 0.1 mL / h, and the distance between the syringe tip and the collector was fixed at 7 cm. The working voltage applied to the needle tip was 9 kV.

[0043] Test data for electrospinning using different operating voltages are as follows: Figure 2 and Figure 3 As shown; Regarding the extrusion rate, the experiment found that a rate of around 0.1 mL / h resulted in a suitable amount of spinning liquid being extruded. If the rate was too high, too much spinning liquid would be extruded and unable to form complete filaments, leading to liquid dripping. If the rate was too low, too little spinning liquid would be extruded, causing discontinuity in the spinning process. Regarding the spinning distance, the experiment found that a distance of around 7 cm ensured that the fibers would fall almost entirely onto the receiving surface. If the distance was too large, the fibers would not fall completely onto the receiving surface.

[0044] Example 2

[0045] First, silk fibroin was extracted by cutting silkworm cocoons into small pieces. To remove sericin, the cocoons were placed in heated Na₂CO₃ solution with a concentration of 0.047 mol / L. -1 The silk fibroin was then repeatedly rinsed with distilled water for 10 minutes in a solution, followed by drying in an oven. After drying, it was completely dissolved in LiBr solution at 60°C, and then the solution was transferred to a dialysis bag for dialysis. After dialysis, it was centrifuged at 10,000 rpm for 15 minutes. The supernatant was collected and finally freeze-dried at -45°C to obtain white silk fibroin.

[0046] 2-Methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester (MEO2) (molecular formula: ), polyethylene glycol methyl ether methacrylate (OEG) 300 (Molecular formula is) ), 6-(4-phenylazobenzene)hexyl methacrylate (AHMA) (molecular formula is ), CuBr, Me6TREN, anisole, methyl 2-chloropropionate were added into a reaction bottle in the order of 3.70 mL: 1.52 mL: 1.840 mg: 50 mg: 80 μL: 40 mL: 40 μL, and oxygen was removed by freezing and thawing. Then, the reaction was carried out at 75°C for 3 h. The reaction was stopped in an ice bath. In order to remove excess CuBr, the mixed solution was eluted with tetrahydrofuran on an alumina column. The obtained solution was precipitated and dissolved in n-hexane three times. Finally, the obtained product was dried in a vacuum drying oven at 50°C to obtain an azobenzene-containing photoresponsive polymer P(MEO2-co-OEG 300 -co-AHMA) (molecular formula: ) with a yellow-brown sticky gel. The azobenzene-containing photoresponsive polymer and the silk fibroin were mixed in a mass ratio of 0.1:1, added to 2 mL of formic acid, heated at 40°C for 6 h to ensure uniform mixing of the solutes, and then transferred into a syringe installed on a syringe pump. A voltage was applied at the needle tip to cause the needle to eject small droplets with a conical shape, and aluminum foil paper was used as a receiving surface. After spinning, the fabric was placed in an oven at 50°C for drying until a constant weight was obtained, and finally an electrospun composite fiber membrane was obtained. The extrusion rate was set to 0.1 mL / h, and the distance between the tip of the syringe and the collector was fixed at 7 cm. The working voltage applied at the needle tip was 9 kV.

[0047] Example 3

[0048] First, the silk fibroin was extracted, and the cocoon was cut into small pieces. In order to remove sericin, the cocoon was placed in a heated Na2CO3 solution with a concentration of 0.047 mol / L -1 , and then the silk fibroin was repeatedly rinsed with distilled water for 10 min. Then, the silk fibroin was placed in an oven for drying. After drying, it was completely dissolved in a LiBr solution at 60°C, and then the solution was transferred into a dialysis bag for dialysis. After dialysis, centrifugation was performed at 10,000 rpm for 15 min, and the supernatant was collected. Finally, the white silk fibroin was obtained by freeze-drying at a temperature of -45°C.

[0049] 2-methoxy-2-propenoic acid-2-(2-methoxyethoxy) ethyl ester (MEO2) (molecular formula: ), polyethylene glycol methyl ether methacrylate (OEG 300 ) (molecular formula: ), and 6-(4-phenylazobenzene) methyl methacrylate (AHMA) (molecular formula: ), CuBr, Me6TREN, anisole, methyl 2-chloropropionate were added into a reaction bottle in the order of 3.70 mL: 1.52 mL: 1.840 mg: 50 mg: 80 μL: 40 mL: 40 μL, oxygen was removed by freezing and thawing, and then the reaction was carried out at 75°C for 3 h. The reaction was stopped in an ice bath. In order to remove excess CuBr, the mixed solution was eluted with tetrahydrofuran on an alumina column. The obtained solution was precipitated and dissolved in n-hexane three times. Finally, the obtained product was dried in a vacuum drying oven at 50°C to obtain an azobenzene-containing photoresponsive polymer P(MEO2-co-OEG 300 -co-AHMA) (molecular formula is ) with brownish yellow sticky gel. The azobenzene-containing photoresponsive polymer and the silk fibroin were mixed in a mass ratio of 0.5:0.5, added to 2 mL of formic acid, heated at 40°C for 6 h to ensure uniform mixing of the solutes, and then transferred into a syringe installed on a syringe pump. A voltage was applied at the needle tip to make the needle eject small droplets with a conical shape, and aluminum foil paper was used as a receiving surface. After spinning, the fabric was placed in an oven at 50°C for drying until a constant weight was obtained, and finally an electrospun composite fiber membrane was obtained. The extrusion rate was set to 0.1 mL / h, and the distance between the tip of the syringe and the collector was fixed at 7 cm. The working voltage applied at the needle tip was 9 kV.

[0050] Example 4

[0051] First, the silk fibroin was extracted, and the cocoon was cut into small pieces. In order to remove sericin, the cocoon was placed in a heated Na2CO3 solution with a concentration of 0.047 mol / L -1 , and then the silk fibroin was repeatedly rinsed with distilled water for 10 min. Then, the silk fibroin was placed in an oven for drying. After drying, it was completely dissolved in a LiBr solution at 60°C, and then the solution was transferred into a dialysis bag for dialysis. After dialysis, centrifugation was performed at 10,000 rpm for 15 min, and the supernatant was collected. Finally, the white silk fibroin was obtained by freeze-drying at a temperature of -45°C.

[0052] 2-methoxy-2-propenoic acid-2-(2-methoxyethoxy) ethyl ester (MEO2) (molecular formula is ), polyethylene glycol methyl ether methacrylate (OEG 300 ) (molecular formula is ), and 6-(4-phenylazobenzene) methyl methacrylate (AHMA) (molecular formula is ), CuBr, Me6TREN, anisole, methyl 2-chloropropionate were added into a reaction flask in the order of 3.70 mL: 1.52 mL: 1.840 mg: 50 mg: 80 μL: 40 mL: 40 μL, respectively, and oxygen was removed by freezing and thawing. Then, the reaction was carried out at 75 °C for 3 h. The reaction was stopped in an ice bath. In order to remove excess CuBr, the mixed solution was eluted with tetrahydrofuran on an alumina column. The resulting solution was precipitated in n-hexane three times. Finally, the obtained product was dried in a vacuum oven at 50 °C to obtain the azobenzene-containing photoresponsive polymer P(MEO2-co-OEG 300 -co-AHMA) (molecular formula ) with brownish yellow sticky gel. The azobenzene-containing photoresponsive polymer and silk fibroin were mixed in a mass ratio of 1:0.5, added to 2 mL of formic acid, heated at 40 °C for 6 h to ensure uniform mixing of the solutes, and then transferred into a syringe installed on a syringe pump. A voltage was applied at the needle tip to cause the needle to eject small droplets of conical shape, and aluminum foil was used as the receiving surface. After spinning, the fabric was placed in an oven at 50 °C for drying until a constant weight was obtained, and finally an electrospun composite fiber membrane was obtained. The extrusion rate was set to 0.1 mL / h, and the distance between the tip of the syringe and the collector was fixed at 7 cm. The working voltage applied at the needle tip was 9 kV.

[0053] Performance test

[0054] (1) The electrospun fiber membrane prepared in Example 1 (the ratio of photoresponsive polymer to silk fibroin was 0:1) and the electrospun composite fiber membrane prepared in Example 2 (the ratio of photoresponsive polymer to silk fibroin was 0.1:1) were irradiated with ultraviolet light and visible light for different times. The ultraviolet-visible absorption spectra are shown in Figure 1 . Figure 1 In Fig. a) and b), the fiber membrane with a ratio of photoresponsive polymer to silk fibroin of 0:1 showed no response to ultraviolet light and visible light, and a peak appeared in the range of 200-300 nm, which was the absorption peak of silk fibroin. Figure 1 In Fig. c) and d), the electrospun composite fiber membrane (the ratio of photoresponsive polymer to silk fibroin was 0.1:1) showed a response to both ultraviolet light and visible light, in addition to the silk fibroin absorption peak at 200-300 nm, an azobenzene absorption peak at 350 nm was also found, and the maximum absorbance was about 0.37. Figure 4 In Fig. c) and d), the maximum absorbance was about 0.78, which was due to the different contents of azobenzene, resulting in different response intensities to ultraviolet light. In order to highlight the better test results of the electrospun composite fiber membrane compared to the blended film, the electrospun composite fiber membrane with a ratio of photoresponsive polymer to silk fibroin of 0.5:0.5 was selected.

[0055] (2) The electrospun composite fiber membranes prepared in Example 3 with different working voltages (the ratio of photoresponsive polymer and silk fibroin is 0.5:0.5) were observed under a scanning electron microscope as shown in Figure 2 , it was found that the surface morphology of the composite fiber membrane was better when the voltage was 9 kV, so the voltage of electrospinning was selected as 9 kV.

[0056] (3) The electrospun composite fiber membrane prepared in Example 4 (the ratio of photoresponsive polymer and silk fibroin is 1:0.5) (the voltage of electrospinning is 9 kV) was observed under a scanning electron microscope as shown in Figure 3 , it was found that the morphology of the electrospun composite fiber membrane was not good, the main reason was that the content of photoresponsive polymer was too high, which led to too large viscosity of the spinning solution, and the liquid was not easy to volatilize, causing adhesion between fibers, so the electrospun composite fiber membrane in this ratio range was not preferred.

[0057] (4) The blended film and the electrospun composite fiber membrane prepared in Example 3 (the ratio of photoresponsive polymer and silk fibroin is 0.5:0.5) were irradiated with ultraviolet light and visible light. From the black curves in (a) and (c) of Figure 4 , it can be seen that the absorption peak near 350 nm of the blended film and the composite fiber membrane decreases, and the absorption peak near 450 nm increases under the irradiation of ultraviolet light, because the azobenzene changes from trans structure to cis structure, when irradiated under visible light conditions, as shown in (b) and (d) of Figure 4 , with the increase of light irradiation time, the absorption peak near 350 nm increases, and the absorption peak near 450 nm decreases, because the cis structure of azobenzene changes to trans structure. Under the irradiation of visible light for 20 minutes, the absorbance of the blended film is about 82% of the original state powder (as shown in Figure 4 b), indicating that a part of azobenzene changes from cis structure to trans structure, while the electrospun composite fiber membrane under the same time of visible light irradiation, its absorption peak near 350 nm is about 96% of the original state fiber membrane (as shown in Figure 4 d), the conversion efficiency of azobenzene from cis structure to trans structure is improved by about 15%, which is mainly due to the orientation of polymer molecular chains caused by electrospinning, thereby accelerating the isomerization conversion efficiency of azobenzene, realizing the recycling of the prepared electrospun composite fiber membrane with anti-ultraviolet performance.

[0058] (5) The blended film and the electrospun composite fiber membrane prepared in Example 3 (the ratio of photoresponsive polymer and silk fibroin is 0.5:0.5) were tested for their absorbance under the irradiation of alternating ultraviolet light and visible light. As shown in Figure 5As can be seen on the right, the absorbance of the blend film at 356 nm changed by a maximum of about 0.2 after 20 minutes of visible light irradiation, while the absorbance of the composite fiber film at 356 nm changed by only about 0.35 after 10 minutes of visible light irradiation. Figure 5 (Left) This shows that the composite fiber membrane has a higher efficiency in cis-trans isomerization and the conversion time is significantly reduced compared to the blended film. This is because the polymer molecular chains are given orientation under the action of electrospinning, which significantly improves the repeated absorption of ultraviolet light by the fabric.

[0059] (6) The Zn-MOF@WO3 / TPU composite fiber membrane was covered on its surface by a blended film and the electrospun composite fiber membrane prepared in Example 3 (the ratio of photoresponsive polymer to silk fibroin was 0.5:0.5), and then placed under ultraviolet light for 1 min and visible light for 10 min, and its K / S value was measured. Figure 6 It can be seen that the K / S ratios of both the Zn-MOF@WO3 / TPU composite fiber membrane covered by electrospun composite fiber membrane and the Zn-MOF@WO3 / TPU composite fiber membrane covered by blend film increase continuously with ultraviolet light irradiation. This is because WO3 in the Zn-MOF@WO3 / TPU composite fiber membrane responds to ultraviolet light and undergoes a significant color change under ultraviolet light irradiation. Under ultraviolet light irradiation, the photochemical absorption of WO3 changes, and the color changes from colorless to blue. As the irradiation time increases, the color of the film deepens continuously, so the K / S ratio increases continuously. Furthermore, the Zn-MOF@WO3 / TPU composite fiber membrane covered by the blend film exhibits a greater change in K / S ratio, indicating that under the same UV irradiation conditions, the electrospun composite fiber membrane provides better UV shielding than the blend film. Under UV irradiation, azobenzene transforms from a trans to a cis configuration, and this structure gradually reverts to its original state under visible light irradiation. This difference in K / S ratio is due to the orientation of the molecular chains in the electrospun composite fiber membrane. Under the same conditions, the transformation from a cis to a trans configuration in azobenzene occurs faster than in the blend film. Therefore, upon subsequent UV irradiation, the electrospun composite fiber membrane absorbs more UV light, while the blend film, due to its slower cis-trans isomerization, absorbs less UV light upon re-irradiation. This demonstrates that electrospinning can achieve more efficient UV absorption in composite fiber membranes.

[0060] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0061] The above is only the preferred embodiment of the present application, and does not limit the present application, and any simple modification, change and equivalent transformation of the above embodiment according to the technical essence of the present application still belongs to the protection scope of the technical scheme of the present application.

Claims

1. A method for preparing composite fiber membranes with high ultraviolet light absorption capacity based on electrospinning, characterized in that... Includes the following steps: (1) Extraction of silk fibroin; (2) Preparation of silk fibroin / photoresponsive polymer solution: 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, polyethylene glycol methyl ether methacrylate, 6-(4-phenylazobenzene) methyl methacrylate, CuBr, Me6TREN, solvent, and initiator were added to a reaction vessel, and oxygen was removed by freeze-drying; then the polymerization reaction was carried out by heating, and the reaction was stopped by cooling; the resulting mixed solution was eluted with tetrahydrofuran in an alumina column to remove excess CuBr, and the resulting solution was repeatedly precipitated and dissolved in n-hexane; finally, the obtained precipitate was dried under vacuum to obtain the photoresponsive polymer P(MEO2-) containing azobenzene. co -OEG 300 - co -AHMA); The photoresponsive polymer containing azobenzene and silk fibroin are dissolved in formic acid solution and heated and stirred to obtain a spinning solution; (3) Preparation of composite fiber membrane: The spinning solution is transferred into a syringe installed on the injection pump. A voltage is applied to the needle to make the needle spray out small droplets in the shape of a spindle cone. The droplets are collected on the collection surface. After electrospinning, the membrane is dried to obtain a composite fiber membrane with high ultraviolet light absorption capacity.

2. The method according to claim 1, characterized in that: In step (1), the silkworm cocoons are first degummed using sodium carbonate solution. After the degummed product is rinsed and dried, it is added to lithium bromide solution and heated to dissolve completely. Then, it is dialyzed, centrifuged, and the supernatant is collected. Finally, it is freeze-dried to obtain silk fibroin.

3. The method according to claim 2, characterized in that: In step (1), The concentration of the sodium carbonate solution is 0.04-0.06 mol / L. -1 ; The concentration of the lithium bromide solution is 8-10 mol / L. -1 ; The rinsing time is 8-15 minutes; The heating temperature is 50-70 ℃; The centrifugation speed is 8000-12000 rpm, and the centrifugation time is 10-20 min; The freeze-drying temperature is -40 to -50°C.

4. The method according to claim 1, characterized in that: In step (2), the ratio of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, polyethylene glycol methyl ether methacrylate, 6-(4-phenylazobenzene) methyl methacrylate, CuBr, Me6TREN, solvent, and initiator is (1~5) mL: (1~3) mL: (1~2) mg: (10~100) mg: (60~100) μL: (30~50) mL: (30~50) μL.

5. The method according to claim 1 or 4, characterized in that: In step (2), the mass ratio of the azobenzene-containing photoresponsive polymer to silk fibroin is (0.1-0.5):(0.5-1), and the total mass fraction of both in the spinning solution is 5-25%.

6. The method according to claim 1 or 4, characterized in that: In step (2), the solvent is anisole and the initiator is methyl 2-chloropropionate.

7. The method according to claim 1 or 4, characterized in that: In step (2), the polymerization reaction is carried out at a temperature of 60-80°C for 2-5 hours.

8. The method according to claim 1 or 4, characterized in that: In step (2), the temperature of vacuum drying is 30-50℃.

9. The method according to claim 1, characterized in that: In step (3), the parameters of the electrospinning are: the extrusion rate is set to 0.1-0.3 mL / h, the distance between the syringe tip and the collection surface is fixed to 6-10 cm, and the working voltage applied to the needle tip is 8-9 kV.

10. The method according to claim 1 or 9, characterized in that: In step (3), the drying temperature is 40-60℃.

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