Preparation method of spiropyrane labeled chitosan for manufacturing fluorescent anti-counterfeiting fiber

Abstract

The invention relates to the technical field of preparation of textile raw materials, in particular to a preparation method of spiropyrane labeled chitosan for manufacturing fluorescent anti-counterfeiting fibers. The preparation method comprises the following steps: dispersing chitosan powder, a catalyst 4-dimethylaminopyridine (DMAP) and a dehydrating agent N, N '-dicyclohexylcarbodiimide (DCC) into a dimethylacetamide (DMAc) / LiCl solvent system, and after the chitosan is completely dissolved, adding a catalyst 4-dimethylaminopyridine (DMAP) and a dehydrant N, N'-dicyclohexylcarbodiimide (DCC) into the DMAc / LiCl solvent system; adding a 3-(3 ', 3'-dimethyl-6-nitro-spiro [benzopyran-2, 2 '-indoline]-1'-yl) propionic acid (SP-COOH) DMAc solution to start a reaction, fully stirring for a period of time, then stopping the reaction, carrying out suction filtration to remove solid impurities, then adding ethanol to separate out an SP-labeled chitosan product, repeatedly washing with ethanol, and centrifuging to remove impurities; and dissolving the obtained SP-labeled chitosan with dilute acetic acid, dialyzing in distilled water for 24-48 hours, and freeze-drying to obtain the SP-labeled chitosan. The preparation process is simple, and the obtained SP-labeled chitosan has a dynamic color-changing fluorescent effect under ultraviolet light and can be used for manufacturing fluorescent anti-counterfeiting fibers.

Description

Technical Field

[0001] The invention relates to the technical field of textile raw material preparation, in particular to a method for preparing spiropyran-labeled chitosan for manufacturing fluorescent anti-counterfeiting fibers. Background Art

[0002] Fluorescent anti-counterfeiting fiber, also known as security fiber, is currently the most widely used anti-counterfeiting method, and has been used in products such as banknotes, passports, stamps, securities, anti-counterfeiting paper and clothing fabrics. At present, fluorescent anti-counterfeiting fibers are mainly synthetic fibers such as PP, PET, PVA, PMMA, etc., and the development of bio-based fiber raw materials is still in its infancy.

[0003] Chitosan (CS) is a natural polysaccharide with abundant sources, biodegradability and good biocompatibility. It has been applied in textile, printing and dyeing, papermaking, food, medicine and other fields. my country has a vast sea area, and there are sufficient sources of chitosan production raw materials such as shrimp skin and crab shell. However, the shells of aquatic products such as shrimp and crab are often treated as solid waste after being processed for consumption, resulting in a huge waste of chitosan resources. Therefore, if chitosan extracted from fishery by-products can be used as a substrate and properly chemically modified to obtain functional fibers with good general and fluorescent properties, a large amount of modified chitosan fiber raw materials with high added value can be obtained, and the adverse effects on the environment caused by landfilling fishery waste can be avoided.

[0004] At present, there are some public documents on the preparation of fluorescent chitosan; for example: the invention patent application with application publication number CN109988254 A discloses a method for preparing a perylenetetracarboxylic acid labeled chitosan fluorescent slurry. The patent disperses chitosan powder, catalyst DMAP, and dehydrating agent DCC in a DMAc / LiCl solvent system, and after the chitosan is completely dissolved, perylenetetracarboxylic acid (PTCA) DMAc solution is added to start the reaction, and the reaction is stopped after being fully stirred for a period of time, and solid impurities are removed by suction filtration, and methanol is added to precipitate the PTCA labeled chitosan product. After centrifugation, washing and dialysis, vacuum freeze drying is performed to obtain the PTCA labeled fluorescent chitosan slurry.

[0005] For another example, the invention patent application with application publication number CN110220873 A discloses a method for preparing a FITC-labeled chitosan fluorescent slurry. The patent disperses chitosan powder in a dilute acetic acid aqueous solution, and after it is completely dissolved, adds an equal volume of methanol, and then adds a FITC methanol solution. After being fully stirred for a period of time in a light-proof place, the reaction is stopped, and the pH is adjusted to 7-8 to precipitate the FITC-labeled chitosan product. After centrifugation, washing and dialysis, the FITC-labeled fluorescent chitosan slurry is obtained by vacuum freeze-drying.

[0006] Although the above-mentioned research can prepare modified chitosan materials with fluorescence effects, there are still two main problems in using them for fluorescent anti-counterfeiting fibers. First, the manufacturing technology of chitosan with single-wavelength static fluorescence properties has become increasingly mature, but there is still little research on the preparation of chitosan with dynamic color-changing fluorescence effects, and it is not very difficult for counterfeiters to imitate. Second, most of the fluorescent groups used to label chitosan are molecules with serious aggregation-induced fluorescence quenching (ACQ) properties, resulting in the inability of the prepared modified chitosan to have a high labeling rate. This means that the fluorescence intensity of chitosan products is not high and the light bleaching resistance is not good. It is okay to use it in functional textile sizing to measure the penetration rate and coverage rate of the sizing on the yarn. However, when it comes to using it for anti-counterfeiting fibers, neither the fluorescence intensity nor the fluorescence durability can meet the usage requirements.

[0007] Spiropyran (SP) and its derivatives, as a representative photochromic molecular switch, have attracted the interest of many researchers. The photoresponsive fluorescence molecular switch constructed by SP has been widely used in fields such as anti-counterfeiting encryption, bioluminescence imaging, drug carriers, and optical information storage. Under ultraviolet light, the molecular switch of SP can be triggered to isomerize from the closed-ring SP form to the open-ring merocyanine (MC) form. The open-ring MC can emit bright fluorescence with a long wavelength (such as red or orange). In addition, the fluorescence color can change dynamically with the continuation of the ultraviolet light irradiation time, and the bright and variable fluorescence after ultraviolet irradiation is easily recognizable by the naked eye. This characteristic makes SP and its derivatives have broad application potential in the field of anti-counterfeiting.

[0008] At present, the literature has disclosed methods for manufacturing photoluminescent and color-changing microcapsules using chitosan and SP as raw materials. For example, the invention patent application with the application publication number CN103962076 B discloses a preparation method of polyurethane-chitosan double-shell photochromic microcapsules. This patent prepares polyurethane-chitosan double-shell photochromic microcapsules by in-situ polymerization, using photochromic compounds such as SP as the core material, polyurethane as the inner wall material, and chitosan as the outer wall material. Another example is the invention patent application with the application publication number CN115228399A, which discloses a highly fatigue-resistant modified chitosan / SP photochromic microcapsule and its preparation method. This invention synthesizes SP using indole and nitrobenzaldehyde, uses the synthesized SP as the core material and chitosan as the shell material to prepare microcapsules, dissolves the antioxidant in an organic solvent, adds a coupling reagent, stirs, and then adds the chitosan / SP microcapsules to react with triethylamine for a certain time, and filters to obtain the product modified microcapsules.

[0009] Although the chitosan / SP microcapsules prepared in the above literature have a photoluminescent color-changing effect, chitosan and SP are only used as the shell material and core material of the microcapsules respectively. The relationship between the two is a coating and being coated, which is a physical combination, so this kind of microcapsules cannot be spun into fibers for use. Therefore, only by exploring a method to label SP onto chitosan molecules so that the two can be chemically bonded to form SP-labeled chitosan with dynamic color-changing fluorescence effects can it be spun into textile fibers with good general properties and fluorescent properties. This chemically modified chitosan material lays the foundation for the manufacture of fluorescent anti-counterfeiting fibers that are easy for consumers to identify and difficult to imitate. Summary of the invention

[0010] The present invention provides a method for preparing spiropyran (SP) labeled chitosan for manufacturing fluorescent anti-counterfeiting fibers. The modified chitosan prepared by the method has high fluorescence intensity and can change color dynamically under ultraviolet light excitation. The method specifically comprises the following steps:

[0011] (1) Dispersing chitosan powder, catalyst 4-dimethylaminopyridine (DMAP) and dehydrating agent N,N'-dicyclohexylcarbamide (DCC) in a dimethylacetamide (DMAc) / LiCl solvent system with a mass fraction of 8% to prepare a chitosan solution with a mass fraction of 0.30-1.30%, wherein the mass fraction of DMAP / chitosan is 4.00-6.00%, and the mass fraction of DCC / chitosan is 40.0-60.0%, and stirring at 70-80°C until the chitosan is completely dissolved;

[0012] (2) adding a certain volume of 0.70-1.90% by mass DMAc solution of 3-(3',3'-dimethyl-6-nitrospiro[benzopyran-2,2'-indoline]-1'-yl) propionic acid (SP-COOH) to the chitosan solution obtained in step (1) to start the reaction, wherein the volume ratio of the SP-COOH DMAc solution to the chitosan solution is 1:12, stirring at 70-90° C. for 1.0-3.0 h before the reaction is terminated, and filtering to remove solid impurities to obtain an SP-labeled chitosan solution;

[0013] (3) Add ethanol to the solution obtained in step (2) to precipitate the SP-labeled chitosan product, place the precipitated product in a centrifuge tube and centrifuge at 10,000 rpm for 15 minutes, wash with ethanol and centrifuge at least 5 times, then dissolve the SP-labeled chitosan product with distilled water and place it in a dialysis bag, dialyze with distilled water for 24 to 48 hours, and freeze-dry the dialyzed product to obtain SP-labeled chitosan.

[0014] In step (1), the particle size of the chitosan powder is between 50 and 300 meshes, the deacetylation degree of the chitosan is between 60% and 100%, and the molecular weight is between 10,000 and 800,000.

[0015] In step (3), the cut-off molecular weight of the dialysis bag is 8000.

[0016] Under suitable reaction conditions, the present invention enables the SP fluorescent molecule containing a carboxyl group to undergo esterification and amidation reactions with the hydroxyl and amino groups on the chitosan molecular chain to obtain SP-labeled fluorescent chitosan. The obtained chitosan has high fluorescence intensity and can dynamically change color under ultraviolet light excitation, and can be used for manufacturing fluorescent anti-counterfeiting fibers.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention utilizes the unique fluorescence property of SP to fluorescently label chitosan macromolecules. Under ultraviolet light excitation, the chemical bond in the SP group on the modified chitosan molecule will break, forming a ring-opening structure MC, thereby presenting red fluorescence. However, the chemical bonds in different SP groups break gradually rather than simultaneously. Therefore, the fluorescence color of the SP-labeled chitosan will change dynamically with the continuation of the ultraviolet light irradiation time under ultraviolet light excitation, and the red light gradually becomes stronger (see the appendix Figure 5 ), which is easy to be recognized by the naked eye and greatly increases the counterfeiting difficulty for counterfeiters.

[0019] (2) Compared with common organic fluorescent molecules (such as FITC, perylene derivatives), the SP derivative does not show significant ACQ properties. Therefore, the labeling rate of the SP-labeled chitosan with good fluorescence effect prepared by the present invention can reach more than 0.50 mol%. The main reason for the fluorescence quenching of ACQ luminescent materials during aggregation is that their planar conjugated structures are prone to π-π stacking during aggregation. Taking perylene derivatives as an example, existing studies have shown that when the distance between perylene groups is 70 nm, π-π stacking will occur, resulting in fluorescence quenching. In order to avoid the ACQ phenomenon, the labeling rates of FITC-labeled and perylene-labeled fluorescent chitosan with practical value usually need to be controlled below 0.10 mol%, which is much lower than the labeling rate of the SP-labeled chitosan. In other words, the number of effective fluorescent groups in the chitosan labeled with common ACQ molecules with practical value is much less than that of the SP-labeled chitosan. Therefore, the fluorescence intensity emitted by the SP-labeled chitosan prepared by the present invention can be significantly higher than that of the chitosan labeled with common ACQ molecules (compare the fluorescence intensity data of perylene-labeled and SP-labeled chitosan in the appendix Figure 3 ), and it is easier for consumers to identify and recognize. Description of the Drawings

[0020] Figure 1 It is a reaction schematic diagram of chitosan and SP-COOH of the present invention (taking Example 1 as an example);

[0021] Figure 2Infrared spectra of unmodified chitosan (CS 0#) and CS-SP (1# - 5#) of the present invention;

[0022] Figure 3 Fluorescence spectra of perylene-labeled fluorescent chitosan (CS-perylene) 1# - 3# (a) and CS-SP 1# - 3# (b) of the present invention (Note: The labeling rates of CS-perylene 1# - 3# are 0.02, 0.07, and 0.11 mol%, respectively; the labeling rates of CS-SP 1# - 3# are 0.08, 0.19, and 0.50 mol%, respectively);

[0023] Figure 4 Photographs of electrospun fiber membranes of unmodified chitosan / PVA (0#) and CS-SP 1# - 3# / PVA (1# - 3#) of the present invention under visible light (a) and 365 nm ultraviolet light (b) (Note: The ultraviolet light irradiation time is 30 s);

[0024] Figure 5 Photographs of the electrospun fiber membrane of CS-SP 3# / PVA of the present invention under visible light (a) and 365 nm ultraviolet light when irradiated for 5 s (b), 10 s (c), 20 s (d), and 30 s (e). Detailed implementation manners

[0025] The present invention will be further described below in conjunction with specific embodiments. The following are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The particle size of the chitosan powder used in the following examples is between 50 and 300 mesh, the deacetylation degree of chitosan is 60% - 100%, and the molecular weight is 10,000 - 800,000.

[0026] Example 1

[0027] (1) Dispersed chitosan powder, catalyst DMAP, and dehydrating agent DCC in a DMAc / LiCl solvent system with a mass fraction of 8% to prepare a chitosan solution with a mass fraction of 0.87%. Among them, the mass fraction of DMAP / chitosan is 4.52%, and the mass fraction of DCC / chitosan is 45.8%. Stir at 70 °C until the chitosan is completely dissolved;

[0028] (2) Add a DMAc solution of SP-COOH with a mass fraction of 0.78% to the chitosan solution obtained in step (1) to start the reaction. The volume ratio of the SP-COOH DMAc solution to the chitosan solution is 1:12. Stir thoroughly at 70 °C for 2.0 h and then end the reaction. Filter to remove solid impurities to obtain an SP-labeled chitosan solution;

[0029] (3) Add ethanol to the solution obtained in step (2) to precipitate the SP-labeled chitosan product, place the precipitated product in a centrifuge tube and centrifuge at 10,000 rpm for 15 min, wash with ethanol and centrifuge 5 times, then dissolve the SP-labeled chitosan product with distilled water and place it in a dialysis bag, dialyze with distilled water for 24 h, and freeze-dry the dialyzed product to obtain SP-labeled chitosan 1# (abbreviated as CS-SP 1#).

[0030] Example 2

[0031] (1) Dispersing chitosan powder, catalyst DMAP and dehydrating agent DCC in a DMAc / LiCl solvent system with a mass fraction of 8% to prepare a chitosan solution with a mass fraction of 1.05%, wherein the mass fraction of DMAP / chitosan is 4.97% and the mass fraction of DCC / chitosan is 50.4%, and stirring at 75° C. until the chitosan is completely dissolved;

[0032] (2) adding a 1.25% by mass SP-COOH DMAc solution to the chitosan solution obtained in step (1) to start the reaction, wherein the volume ratio of the SP-COOH DMAc solution to the chitosan solution is 1:12, stirring at 75° C. for 1.5 h before the reaction is terminated, and filtering to remove solid impurities to obtain an SP-labeled chitosan solution;

[0033] (3) Add ethanol to the solution obtained in step (2) to precipitate the SP-labeled chitosan product, place the precipitated product in a centrifuge tube and centrifuge at 10,000 rpm for 15 min, wash with ethanol and centrifuge 5 times, then dissolve the SP-labeled chitosan product with distilled water and place it in a dialysis bag, dialyze with distilled water for 30 h, and freeze-dry the dialyzed product to obtain SP-labeled chitosan 2# (abbreviated as CS-SP 2#).

[0034] Example 3

[0035] (1) Dispersing chitosan powder, catalyst DMAP and dehydrating agent DCC in a DMAc / LiCl solvent system with a mass fraction of 8% to prepare a chitosan solution with a mass fraction of 1.22%, wherein the mass fraction of DMAP / chitosan is 5.42% and the mass fraction of DCC / chitosan is 55.0%, and stirring at 75° C. until the chitosan is completely dissolved;

[0036] (2) adding a 1.81% by mass SP-COOH DMAc solution to the chitosan solution obtained in step (1) to start the reaction, wherein the volume ratio of the SP-COOH DMAc solution to the chitosan solution is 1:12, stirring at 80° C. for 2.0 h before the reaction is terminated, and filtering to remove solid impurities to obtain an SP-labeled chitosan solution;

[0037] (3) Add ethanol to the solution obtained in step (2) to precipitate the SP-labeled chitosan product, place the precipitated product in a centrifuge tube and centrifuge at 10,000 rpm for 15 min, wash with ethanol and centrifuge 5 times, then dissolve the SP-labeled chitosan product in distilled water and place it in a dialysis bag, dialyze with distilled water for 36 h, and freeze-dry the dialyzed product to obtain SP-labeled chitosan 3# (abbreviated as CS-SP 3#).

[0038] Example 4

[0039] (1) Dispersing chitosan powder, catalyst DMAP and dehydrating agent DCC in a DMAc / LiCl solvent system with a mass fraction of 8% to prepare a chitosan solution with a mass fraction of 0.70%, wherein the mass fraction of DMAP / chitosan is 5.88% and the mass fraction of DCC / chitosan is 59.5%, and stirring at 80° C. until the chitosan is completely dissolved;

[0040] (2) adding a 1.25% by mass SP-COOH DMAc solution to the chitosan solution obtained in step (1) to start the reaction, wherein the volume ratio of the SP-COOH DMAc solution to the chitosan solution is 1:12, stirring at 85° C. for 3.0 h before the reaction is terminated, and filtering to remove solid impurities to obtain an SP-labeled chitosan solution;

[0041] (3) Add ethanol to the solution obtained in step (2) to precipitate the SP-labeled chitosan product, place the precipitated product in a centrifuge tube and centrifuge at 10,000 rpm for 15 min, wash with ethanol and centrifuge 5 times, then dissolve the SP-labeled chitosan product with distilled water and place it in a dialysis bag, dialyze with distilled water for 42 h, and freeze-dry the dialyzed product to obtain SP-labeled chitosan 4# (abbreviated as CS-SP 4#).

[0042] Example 5

[0043] (1) Dispersing chitosan powder, catalyst DMAP and dehydrating agent DCC in a DMAc / LiCl solvent system with a mass fraction of 8% to prepare a chitosan solution with a mass fraction of 0.87%, wherein the mass fraction of DMAP / chitosan is 4.97% and the mass fraction of DCC / chitosan is 50.4%, and stirring at 80° C. until the chitosan is completely dissolved;

[0044] (2) adding a 1.81% by mass SP-COOH DMAc solution to the chitosan solution obtained in step (1) to start the reaction, wherein the volume ratio of the SP-COOH DMAc solution to the chitosan solution is 1:12, stirring at 90° C. for 3.0 h before the reaction is terminated, and filtering to remove solid impurities to obtain an SP-labeled chitosan solution;

[0045] (3) Add ethanol to the solution obtained in step (2) to precipitate the SP-labeled chitosan product. Place the precipitated product in a centrifuge tube and centrifuge at 10,000 rpm for 15 min. Wash and centrifuge with ethanol 5 times. Then dissolve the SP-labeled chitosan product in distilled water and place it in a dialysis bag. Dialyze with distilled water for 48 h. Freeze-dry the dialyzed product to obtain SP-labeled chitosan 5# (abbreviated as CS-SP 5#).

[0046] Detect the labeling rates of the SP-labeled chitosan prepared in Examples 1-5. The results are shown in Table 1.

[0047] Table 1 Labeling rates of CS-SP under different treatment processes

[0048] CS-SP number 1# 2# 3# 4# 5# Labeling rate (mol%) 0.08 0.19 0.50 0.72 1.06

[0049] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing spiropyran-labeled chitosan for making fluorescent anti-counterfeiting fibers, characterized in that: The following steps are involved: (1) dispersing chitosan powder, catalyst 4-dimethylaminopyridine and dehydrating agent N,N'-dicyclohexylcarbocyanine in a dimethylacetamide / LiCl solvent system, stirring until the chitosan is completely dissolved to obtain a chitosan solution; (2) adding a certain volume of DMAc solution of 3-(3',3'-dimethyl-6-nitrospiro[benzopyran-2,2'-indoline]-1'-yl)propionic acid to the chitosan solution obtained in step (1) to start the reaction, stirring thoroughly to terminate the reaction, and filtering to remove solid impurities to obtain an SP-labeled chitosan solution; (3) Add ethanol to the solution obtained in step (2) to precipitate the SP-labeled chitosan product. Place the precipitated product in a centrifuge tube for centrifugation, wash with ethanol, and centrifuge at least 5 times. Dissolve the SP-labeled chitosan product in distilled water and place it in a dialysis bag. Dialyze with distilled water for 24 to 48 hours. After lyophilizing the dialyzed product, the SP-labeled chitosan can be obtained.

2. The method for preparing spiropyran-labeled chitosan for making fluorescent anti-counterfeiting fibers according to claim 1, characterized in that: The mass fraction of the dimethylacetamide / LiCl solvent system in step (1) is 8%.

3. The method for preparing spiropyran labeled chitosan for making fluorescent anti-counterfeiting fiber according to claim 1, characterized in that: The mass fraction of the catalyst 4-dimethylaminopyridine / chitosan powder in the step (1) is 4.00-6.00%.

4. The method for preparing spiropyran labeled chitosan for making fluorescent anti-counterfeiting fiber according to claim 1, characterized in that: In the step (1), the mass fraction of the dehydrating agent N,N'-dicyclohexylcarboximide / chitosan powder is 40.0-60.0%.

5. The method for preparing spiropyran labeled chitosan for making fluorescent anti-counterfeiting fiber according to claim 1, characterized in that: The stirring temperature in step (1) is 70-80°C.

6. The method for preparing spiropyran labeled chitosan for manufacturing fluorescent anti-counterfeiting fiber according to claim 1, characterized in that: In the step (1), the particle size of the chitosan powder is between 50 and 300 meshes, the degree of deacetylation is between 60% and 100%, and the molecular weight is between 10,000 and 800,000.

7. The method for preparing spiropyran labeled chitosan for making fluorescent anti-counterfeiting fiber according to claim 1, characterized in that: In the step (2), the volume ratio of the DMAc solution of 3-(3',3'-dimethyl-6-nitrospiro[benzopyran-2,2'-indoline]-1'-yl)propionic acid to the chitosan solution is 1:

12.

8. The method for preparing spiropyran labeled chitosan for making fluorescent anti-counterfeiting fiber according to claim 1, characterized in that: The mass fraction of the DMAc solution of 3-(3',3'-dimethyl-6-nitrospiro[benzopyran-2,2'-indoline]-1'-yl)propanoic acid in step (2) is 0.70-1.90%.

9. The method for preparing spiropyran labeled chitosan for making fluorescent anti-counterfeiting fiber according to claim 1, characterized in that: The stirring temperature in step (2) is 70-90°C.

10. The method for preparing spiropyran labeled chitosan for manufacturing fluorescent anti-counterfeiting fiber according to claim 1, characterized in that: The molecular weight cut-off of the dialysis bag in step (3) is 8000.

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