Preparation method of antibacterial water-soluble betaine-modified chitosan and its film

Abstract

The present invention relates to the field of natural polymer material preparation, discloses a kind of antibacterial water-soluble betaine modified chitosan and preparation method of its film, comprise the following steps: preparation of S1 chloropropyl betaine, N, N-dimethylamino chloropropane hydrochloride aqueous solution is reacted with tert-butyl bromoacetate after desalting treatment, after reaction terminates, dichloromethane is added to dissolve, then reacted with trifluoroacetic acid, after reaction terminates, dichloromethane is drained, and the reaction product is added dropwise to ethyl acetate for sedimentation separation, vacuum filtration obtains chloropropyl betaine. S2 betaine modified chitosan, chitosan powder is dispersed in alkali / urea aqueous solution to obtain clear chitosan solution, chloropropyl betaine is added to chitosan solution to react, after reaction terminates, dialyze and lyophilize to obtain betaine modified chitosan. After betaine modified chitosan prepared by the present invention is prepared into film, there is biosafety, degradability, bactericidal property, washability.

Description

Technical Field

[0001] The present invention relates to the field of natural polymer material preparation, in particular to a method for preparing antibacterial water-soluble betaine-modified chitosan and a film thereof. Background Art

[0002] Betaine, chemically known as N,N,N-trimethylglycine, has a chemical structure similar to amino acids and is a quaternary ammonium alkaloid. It is widely found in plants and animals. Among plants, goji berries and legumes contain betaine, with beet molasses being the primary source. Betaine is also found in the liver, spleen, and amniotic fluid of mollusks (such as octopus, cuttlefish, and shrimp), as well as vertebrates (including humans). Betaine is stable over a wide pH range and is not easily destroyed by acids or bases. Its zwitterionic nature allows it to react with both acids and bases, making it widely used in biochemistry, nutritional supplements, food additives, and corrosion prevention.

[0003] Chitosan, a cationic polysaccharide, is a random copolymer composed of N-acetyl-D-glucosamine and D-glucosamine units linked by β-1,4-glycosidic bonds. In the industrial field, it can be obtained by removing some acetyl groups from the natural polysaccharide chitin. Due to its biocompatibility, biodegradability, film-forming properties, and antimicrobial activity, chitosan has been widely used in biomedicine, cosmetics, pharmaceuticals, agriculture, textiles, food, and other fields. However, chitosan is only soluble in acidic aqueous solutions or alkaline / urea aqueous solutions, which to some extent limits its scope of application.

[0004] In recent years, numerous researchers have published papers on the chemical modification of chitosan via its N-amino functionality. For example, a Chinese invention patent application with publication number CN109485747A discloses a water-soluble antimicrobial chitosan derivative and its preparation method. The derivative comprises a chitosan backbone and bifunctional groups that modify the amino groups on the chitosan backbone: guanidine groups and carbonyl polyethylene glycol monomethyl ether. This invention simultaneously modifies the chitosan side chains with guanidine groups and short-chain polyethylene glycol, imparting excellent antimicrobial properties and enhanced biosafety to the chitosan. The preparation method involves first reacting chitosan with carboxyl polyethylene glycol monomethyl ether and then reacting it with thiourea trioxide.

[0005] For example, a Chinese invention patent application with publication number CN117343214A discloses a method for preparing a water-soluble and antibacterial chitosan derivative and its application in fruit and vegetable preservation, comprising the following steps: (1) reacting chitosan with phthalic anhydride to produce N-phthaloyl chitosan, thereby protecting the amino group at C2 of chitosan; (2) reacting the chitosan with N-bromosuccinimide (NBS) and triphenylphosphine (PPh3) to produce 6-bromo-6-deoxy-N-phthaloyl chitosan; and (3) reacting the chitosan with an aminoglycoside antibiotic and removing the phthalic anhydride at C2 with hydrazine hydrate to obtain a water-soluble and antibacterial chitosan derivative. The chitosan derivative has a large number of amino groups grafted onto the C6 position, which improves the water solubility and antibacterial properties of chitosan while also taking into account its biosafety and reducing drug resistance. The chitosan derivative can be compounded with polymers such as pullulan, gelatin, starch, cellulose or alginic acid, and sprayed or coated on the surface of food or fruits and vegetables to form a transparent coating that effectively inhibits the infection of pathogenic microorganisms.

[0006] However, there is no related research on the modification of chitosan with betaine in the prior art. In view of this, the present invention proposes for the first time to chemically modify chitosan with betaine, aiming to enhance its water solubility and antibacterial properties, so as to broaden its application value in natural polymer materials. Summary of the Invention

[0007] The present invention aims to provide a method for preparing antibacterial water-soluble betaine-modified chitosan and a film thereof. The betaine-modified chitosan is prepared by a substitution reaction between organic compounds, thereby providing a new approach for the modification of chitosan. Furthermore, the present invention provides at least a beneficial option or creates conditions for solving one or more technical problems existing in the prior art.

[0008] To achieve the above objectives, the present invention adopts the following technical solutions.

[0009] A preparation method of antibacterial water-soluble betaine-modified chitosan, comprising the following steps: 1) preparing chloropropyl betaine, adding sodium hydroxide solution to an N,N-dimethylaminochloropropane hydrochloride aqueous solution under ice bath conditions for desalination treatment; adding ethyl acetate for extraction after desalination treatment, and drying the extract with anhydrous magnesium sulfate; after drying, performing vacuum filtration to obtain a solution, and then adding tert-butyl bromoacetate to the solution for stirring reaction; after the reaction, adding dichloromethane to dissolve, and then adding trifluoroacetic acid for stirring reaction; after the reaction, draining the dichloromethane, and The reaction product is added to ethyl acetate for sedimentation separation and vacuum filtration to obtain chloropropyl betaine; 2) betaine-modified chitosan: chitosan powder is dispersed in an alkali / urea aqueous solution to form a suspension; then, the suspension is placed in a refrigerator until completely frozen, then stirred and thawed at room temperature, and centrifuged to obtain a clear and transparent chitosan solution; chloropropyl betaine is added to the chitosan solution, first reacted at low temperature for a period of time, and then reacted at room temperature for a period of time; after the reaction, the pH value is adjusted to 7 with a hydrochloric acid solution, dialyzed, and freeze-dried to obtain betaine-modified chitosan.

[0010] More preferably, in step 1), the desalting treatment time is 30±10 min.

[0011] More preferably, in step 1), the stirring reaction time of adding tert-butyl bromoacetate is 6-8 hours.

[0012] More preferably, in step 1), the temperature for stirring the reaction with adding trifluoroacetic acid is 50±5° C., and the reaction time is 3-5 hours.

[0013] More preferably, in step 1), the ratio of N,N-dimethylaminopropane chloride hydrochloride, sodium hydroxide and tert-butyl bromoacetate is 12-18:3-5:25-35.

[0014] More preferably, in step 2), the alkali / urea aqueous solution is an aqueous solution of KOH, LiOH and urea, and the alkali / urea aqueous solution has a KOH content of 5-8 wt %, a LiOH content of 8-10 wt %, and a urea content of 8-10 wt %.

[0015] More preferably, in step 2), the reaction time at low temperature is 12-18 hours, and the reaction time at room temperature is 12-18 hours.

[0016] More preferably, in step 2), the molar ratio of chitosan to chloropropyl betaine is 1:3-1:9.

[0017] On the other hand, the present invention also provides a method for preparing an antibacterial water-soluble betaine-modified chitosan film, comprising dissolving the betaine-modified chitosan prepared as above in pure water to prepare a film-forming liquid, degassing the film-forming liquid by centrifugation, pouring the liquid into a culture dish, and drying the liquid. Finally, the film is peeled off to obtain the betaine-modified chitosan film.

[0018] More preferably, the concentration of the membrane-forming solution is 1-5 wt %, the drying temperature is 40-60° C., and the drying time is 20-30 hours.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects.

[0020] 1. The present invention provides a betaine-modified chitosan process, and the reaction conditions do not require strict anhydrous and anaerobic conditions, and no oxidants or catalysts are involved. The operating conditions are relatively mild, which reduces the difficulty and cost of preparation. The water-solubility and antibacterial properties of the modified chitosan are enhanced.

[0021] 2. After the betaine-modified chitosan prepared by the present invention is prepared into a film, it has biological safety, degradability, bactericidal properties, and water washability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Shown is the synthetic route of betaine-modified chitosan.

[0023] Figure 2 Shown is the H NMR spectrum of betaine-modified chitosan.

[0024] Figure 3 Infrared image of betaine-modified chitosan.

[0025] Figure 4 Graph of the water solubility of betaine-modified chitosan.

[0026] Figure 5 Figure 2. Adhesion and film-forming properties of betaine-modified chitosan.

[0027] Figure 6 Coating simulated washability plot of betaine-modified chitosan.

[0028] Figure 7 Macroscopic image and electron microscopy (SME) image of betaine-modified chitosan film.

[0029] Figure 8 Figure 2. In vitro antibacterial test of betaine-modified chitosan. DETAILED DESCRIPTION

[0030] The following further describes the specific embodiments of the present invention to make the technical solutions and beneficial effects of the present invention clearer and more specific. The following embodiments are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0031] Additional aspects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention.

[0032] Reference Figure 1 As shown, the present invention provides a method for preparing antibacterial water-soluble betaine-modified chitosan, including: 1) preparing chloropropyl betaine, wherein an aqueous solution of N,N-dimethylaminochloropropane hydrochloride is desalted and then reacted with tert-butyl bromoacetate. After the reaction, dichloromethane is added to dissolve the solution, followed by reaction with trifluoroacetic acid. After the reaction, the dichloromethane is removed, and the reaction product is added dropwise to ethyl acetate for sedimentation separation and vacuum filtration to obtain chloropropyl betaine. 2) preparing betaine-modified chitosan, wherein chitosan powder is dispersed in an alkali / urea aqueous solution to obtain a clear and transparent chitosan solution. chloropropyl betaine is then added to the chitosan solution for reaction. After the reaction, the chitosan solution is dialyzed and freeze-dried to obtain the betaine-modified chitosan.

[0033] Specifically, the process of preparing chloropropyl betaine in step 1) is as follows: adding sodium hydroxide solution to an aqueous solution of N,N-dimethylaminochloropropane hydrochloride under ice bath conditions for desalting; then adding ethyl acetate to complete extraction, and drying with anhydrous magnesium sulfate; after drying, vacuum filtration is performed to obtain a solution; then tert-butyl bromoacetate is added to the solution for magnetic stirring reaction; after the reaction is completed, dichloromethane is added for dissolution, and trifluoroacetic acid is added for magnetic stirring reaction; after the reaction is completed, the dichloromethane is drained, and the reaction product is dropwise added to ethyl acetate for sedimentation separation and vacuum filtration, thereby obtaining chloropropyl betaine.

[0034] Step 2) The process of betaine-modified chitosan is as follows: chitosan powder is dispersed in an alkali / urea aqueous solution to form a suspension; the suspension is then placed in a refrigerator until completely frozen, then stirred and thawed at room temperature, and centrifuged to obtain a clear and transparent chitosan solution. Chloropropyl betaine is then added to the chitosan solution, and the reaction is first carried out at a low temperature and then at room temperature. After the reaction is completed, the pH value is adjusted to 7 with a hydrochloric acid solution, and dialyzed and freeze-dried to obtain the betaine-modified chitosan.

[0035] When preparing the betaine modified chitosan film, the betaine modified chitosan prepared above was dissolved in pure water to prepare a film-forming solution, the film-forming solution was centrifuged and degassed, then poured into a culture dish and dried, and finally the film was peeled off to obtain the betaine modified chitosan film. Example

[0036] A method for preparing antibacterial water-soluble betaine-modified chitosan comprises the following steps.

[0037] Step 1 S1: Preparation of chloropropyl betaine. 15.8g of N,N-dimethylaminochloropropane hydrochloride was dissolved in water to form an aqueous solution. Under ice bath conditions, 4.0g of sodium hydroxide solution was added dropwise to the N,N-dimethylaminochloropropane hydrochloride aqueous solution for desalination for 30 minutes. Ethyl acetate was then added to complete the extraction, and anhydrous magnesium sulfate was used for drying for 12 hours. After drying, vacuum filtration was performed to obtain a solution. Then 29.26g of tert-butyl bromoacetate was added dropwise to the solution and magnetic stirring was performed for 6 hours. After the reaction was completed, dichloromethane was added to dissolve, and trifluoroacetic acid was slowly added dropwise, and the reaction was magnetically stirred at 50°C for 3 hours. Finally, after the reaction was completed, the dichloromethane was drained, and the reaction product was added dropwise to ethyl acetate for sedimentation separation and vacuum filtration to obtain chloropropyl betaine.

[0038] Step 2 (S2): Betaine-modified chitosan. First, 0.58 g of chitosan powder was dispersed in an alkaline / urea aqueous solution containing 7 wt% KOH, 8 wt% LiOH, and 8 wt% urea to form a suspension. The suspension was then placed in a -30°C freezer until completely frozen, then thawed with stirring at room temperature and centrifuged at 3000 rpm for 15 minutes to obtain a clear chitosan solution. Next, 4.18 g of chloropropyl betaine was added to the chitosan solution, followed by a 12-hour low-temperature reaction and a 12-hour room-temperature reaction. Following the reaction, the pH was adjusted to 7 with 1 mol / L hydrochloric acid solution, followed by dialysis and freeze-drying to obtain betaine-modified chitosan LBM-CS. Example

[0039] A method for preparing antibacterial water-soluble betaine-modified chitosan comprises the following steps.

[0040] Step 1 S1: Preparation of chloropropyl betaine. 15.8g of N,N-dimethylaminochloropropane hydrochloride was dissolved in water to form an aqueous solution. Under ice bath conditions, 4.0g of sodium hydroxide solution was added dropwise to the N,N-dimethylaminochloropropane hydrochloride aqueous solution for desalination for 30 minutes. Ethyl acetate was then added to complete the extraction, and anhydrous magnesium sulfate was used for drying for 12 hours. After drying, vacuum filtration was performed to obtain a solution. Then 29.26g of tert-butyl bromoacetate was added dropwise to the solution and magnetic stirring was performed for 6 hours. After the reaction was completed, dichloromethane was added to dissolve, and trifluoroacetic acid was slowly added dropwise, and the reaction was magnetically stirred at 50°C for 3 hours. Finally, after the reaction was completed, the dichloromethane was drained, and the reaction product was added dropwise to ethyl acetate for sedimentation separation and vacuum filtration to obtain chloropropyl betaine.

[0041] Step 2 (S2): Betaine-modified chitosan. First, 0.58 g of chitosan powder was dispersed in an alkaline / urea aqueous solution containing 7 wt% KOH, 8 wt% LiOH, and 8 wt% urea to form a suspension. The suspension was then placed in a -30°C freezer until completely frozen, then thawed with stirring at room temperature and centrifuged at 3000 rpm for 15 minutes to obtain a clear chitosan solution. Next, 8.37 g of chloropropyl betaine was added to the chitosan solution, followed by a 12-hour low-temperature reaction and a further 12-hour room-temperature reaction. Following the reaction, the pH was adjusted to 7 with 1 mol / L hydrochloric acid solution, followed by dialysis and freeze-drying to obtain betaine-modified chitosan MBM-CS. Example

[0042] A method for preparing antibacterial water-soluble betaine-modified chitosan comprises the following steps.

[0043] Step 1 S1: Preparation of chloropropyl betaine. 15.8g of N,N-dimethylaminochloropropane hydrochloride was dissolved in water to form an aqueous solution. Under ice bath conditions, 4.0g of sodium hydroxide solution was added dropwise to the N,N-dimethylaminochloropropane hydrochloride aqueous solution for desalination for 30 minutes. Ethyl acetate was then added to complete the extraction, and anhydrous magnesium sulfate was used for drying for 12 hours. After drying, vacuum filtration was performed to obtain a solution. Then 29.26g of tert-butyl bromoacetate was added dropwise to the solution and magnetic stirring was performed for 6 hours. After the reaction was completed, dichloromethane was added to dissolve, and trifluoroacetic acid was slowly added dropwise, and the reaction was magnetically stirred at 50°C for 3 hours. Finally, after the reaction was completed, the dichloromethane was drained, and the reaction product was added dropwise to ethyl acetate for sedimentation separation and vacuum filtration to obtain chloropropyl betaine.

[0044] Step 2 (S2): Betaine-modified chitosan. First, 0.58 g of chitosan powder was dispersed in an alkaline / urea aqueous solution containing 7 wt% KOH, 8 wt% LiOH, and 8 wt% urea to form a suspension. The suspension was then placed in a -30°C freezer until completely frozen, then thawed with stirring at room temperature and centrifuged at 3000 rpm for 15 minutes to obtain a clear chitosan solution. Next, 12.56 g of chloropropyl betaine was added to the chitosan solution, and the reaction was carried out at low temperature for 12 hours, followed by another 12 hours at room temperature. After the reaction, the pH was adjusted to 7 with 1 mol / L hydrochloric acid solution, and the mixture was dialyzed and freeze-dried to obtain betaine-modified chitosan HBM-CS. Example

[0045] A method for preparing a betaine-modified chitosan film comprises the following steps: dissolving the betaine-modified chitosan prepared in step 2 (S2) of Example 1 in pure water to prepare a 2% by weight film-forming solution. The film-forming solution is centrifugally degassed and then poured into a plastic Petri dish. The solution is then placed in an oven and dried at 45°C. Finally, the film is removed to produce the betaine-modified chitosan film.

[0046] Among them, the culture dish is a plastic culture dish with a diameter of 90 mm, the film-forming liquid poured in is 25 mL, and the drying time is 24 h.

[0047] In order to verify the structure of betaine-modified chitosan, the present invention conducted nuclear magnetic 1H NMR characterization on LBM-CS, MBM-CS, and HBM-CS. The results are as follows Figure 2 As shown. Figure 2 As can be seen, the chemical shifts of CONH- are 1.97-2.08 ppm, and the chemical shifts of the methyl and methylene groups on the quaternary ammonium salt are 3.10-3.30 ppm. The DS of the betaine-modified chitosans was calculated using the peak area. The DS of LBM-CS, MBM-CS, and HBM-CS were 40.29%, 45.65%, and 50.43%, respectively. The 1H NMR spectra indicate that betaine-modified chitosans were successfully synthesized in all examples.

[0048] In order to further verify the structure of betaine-modified chitosan, the present invention also characterized the infrared spectrum of betaine-modified chitosan by infrared method, such as Figure 3 As shown, for chitosan, at 3400 cm -1 The absorption peak at 1629cm is attributed to the stretching vibration peak of hydroxyl (-OH) and amino (-NH2). -1 The absorption peak at 1000-1300 cm is attributed to the stretching vibration peak of the amide bond (-CONH-) in the chitosan molecule. -1 The absorption peak near 1523cm is for CN stretching vibration. -1 The absorption peak at is the stretching vibration peak of the methyl group (-CH3) in the introduced chloropropyl betaine molecule. The infrared results show that the substitution reaction between chitosan and chloropropyl betaine is completed, and the product is betaine-modified chitosan.

[0049] In order to determine the water solubility of betaine-modified chitosan, 0.1g chitosan, 0.1g LBM-CS, 0.1g MBM-CS and 0.1g HBM-CS were added to the corresponding glass bottles, and 2mL pure water was added to each glass bottle to observe its dissolution in 10 minutes. The results are shown in Figure 2. Figure 4As shown in the figure, at 10 min, chitosan did not dissolve in 2 mL of pure water, while LBM-CS, MBM-CS and HBM-CS were completely dissolved in 2 mL of pure water, indicating that chitosan is not water-soluble, while the synthesized LBM-CS, MBM-CS and HBM-CS are water-soluble.

[0050] In order to determine the adhesion and film-forming ability of betaine-modified chitosan on hydrophobic surfaces, 1 mL of 1 wt% LBM-CS, MBM-CS, and HBM-CS solutions were added dropwise to 75 mm × 25 mm hydrophobic surfaces (glass and plastic). After drying at room temperature for 24 h, the adhesion and film-forming properties were observed. Figure 5 As shown. Figure 5 As can be seen, LBM-CS, MBM-CS, and HBM-CS solutions spread easily on hydrophobic surfaces and formed uniform films after drying. The resulting coatings peeled easily from plastic substrates but not from glass. This demonstrates that LBM-CS, MBM-CS, and HBM-CS possess film-forming properties on hydrophobic surfaces, and that betaine-modified chitosan adheres better to glass than to plastic substrates.

[0051] In order to verify the washability of betaine-modified chitosan coating, the coating was immersed in tap water and washed by friction in a way that simulated washing fruit, and the coating was observed to fall off from the substrate into the water. Figure 6 As shown, after rubbing and washing the LBM-CS, MBM-CS, and HBM-CS films in tap water for 4 minutes, the entire coating fell off the substrate into the water. This demonstrates that the LBM-CS, MBM-CS, and HBM-CS films prepared by the present invention are washable, allowing betaine-modified chitosan to be used as an antibacterial coating for fruit and vegetable preservation, ensuring that the coating can be easily removed from the fruit surface before consumption.

[0052] Figure 7 The macroscopic image and electron microscope (SME) image of the betaine modified chitosan film prepared in Example 4 are shown; Figure 7 It can be seen intuitively that the surfaces of LBM-CS, MBM-CS and HBM-CS membranes are flat, smooth and transparent, without obvious cracks and holes, with dense cross-sections and no voids, and have good air tightness and light transmittance.

[0053] In order to verify the antibacterial activity of betaine-modified chitosan, the present invention also conducted an in vitro antibacterial test: S. aureus (Staphylococcus aureus) and E. coli (Gram-negative bacteria) were used as antibacterial targets to test the in vitro antibacterial performance of betaine-modified chitosan membrane. LBM-CS, MBM-CS, HBM-CS with mass concentrations of 1×1%, 1 / 2×1%, 1 / 4×1%, 1 / 8×1%, 1 / 16×1%, 1 / 32×1%, 1 / 64×1% and blank control group were respectively mixed with 1x10 6 CFU / mL of S. aureus and E. coli bacteria were co-cultured for 3 hours, and 100 μL of the co-culture solution was spread on agar for 24 hours to observe the colony growth. Figure 8 As shown. Figure 8 It can be seen that LBM-CS, MBM-CS, and HBM-CSQ-CS have strong antimicrobial activity, which is mainly generated by the electrostatic interaction between cationic quaternary ammonium salts and negatively charged cell or bacterial membranes. These results indicate that betaine-modified chitosan can effectively inhibit or retard microbial growth and has good prospects for future antimicrobial applications.

[0054] It should be noted that the various technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0055] The above embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art could make numerous modifications and improvements without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention. Any portions not described in the specific embodiments represent prior art or common knowledge.

[0056] It should also be noted that, in the description of the present invention, the content of the present invention can be more easily understood by referring to the above detailed description of the preferred embodiment of the present invention and the included embodiments. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those of ordinary skill in the art to which the present invention belongs. In the event of a conflict, the definitions in this specification shall prevail.

[0057] As used herein, the term "prepared from" is used synonymously with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0058] In the present invention, when amount, concentration or other value or parameter is expressed as a range, preferred range or a series of upper preferred values and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including a range of "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When a numerical range is described in the present invention, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

[0059] In addition, the indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirement (i.e., the number of times the elements or components appear). Therefore, "a" or "an" should be interpreted as including one or at least one, and elements or components in the singular also include plural forms, unless the number is obviously intended to be singular.

Claims

1. A method for preparing antibacterial water-soluble betaine-modified chitosan, characterized in that: Here are the steps: 1) preparing chloropropyl betaine by adding a sodium hydroxide solution to an aqueous solution of N,N-dimethylaminochloropropane hydrochloride under ice bath conditions for desalting; after the desalting treatment is completed, ethyl acetate is added for extraction, and the extract is dried using anhydrous magnesium sulfate; after the drying is completed, vacuum filtration is performed to obtain a solution, and then tert-butyl bromoacetate is added to the solution for stirring and reacting; after the reaction is completed, dichloromethane is added for dissolution, and then trifluoroacetic acid is added for stirring and reacting; after the reaction is completed, the dichloromethane is drained, and the reaction product is added to ethyl acetate for sedimentation separation and vacuum filtration, thereby obtaining chloropropyl betaine; 2) Betaine-modified chitosan: chitosan powder is dispersed in an alkaline / urea aqueous solution to form a suspension; the suspension is then placed in a refrigerator until completely frozen, then thawed by stirring at room temperature, and centrifuged to obtain a clear and transparent chitosan solution; chloropropyl betaine is added to the chitosan solution, reacted at low temperature for a period of time, and then at room temperature for a period of time; after the reaction, the pH is adjusted to 7 with hydrochloric acid solution, dialyzed, and freeze-dried to obtain betaine-modified chitosan; The low-temperature reaction time is 12-18 hours, the room-temperature reaction time is 12-18 hours, and the molar ratio of chitosan to chloropropyl betaine is 1:3-1:

9.

2. The method for preparing an antibacterial water-soluble betaine-modified chitosan according to claim 1, wherein: In step 1), the desalting time is 30±10 min.

3. The method for preparing an antibacterial water-soluble betaine-modified chitosan according to claim 1, wherein: In step 1), tert-butyl bromoacetate is added and stirred for reaction for 6-8 hours.

4. The method for preparing an antibacterial water-soluble betaine-modified chitosan according to claim 1, wherein: In step 1), the temperature for adding trifluoroacetic acid and stirring the reaction is 50±5° C., and the reaction time is 3-5 hours.

5. The method for preparing an antibacterial water-soluble betaine-modified chitosan according to claim 1, wherein: In step 1), the ratio of N,N-dimethylaminopropane chloride hydrochloride to tert-butyl bromoacetate is 12-18:25-35.

6. The method for preparing an antibacterial water-soluble betaine-modified chitosan according to claim 1, wherein: In step 2), the alkali / urea aqueous solution is an aqueous solution of KOH, LiOH and urea, wherein the content of KOH in the alkali / urea aqueous solution is 5-8 wt %, the content of LiOH is 8-10 wt %, and the content of urea is 8-10 wt %.

7. A method for preparing an antibacterial water-soluble betaine-modified chitosan film, characterized in that: The betaine-modified chitosan prepared by the method for preparing an antibacterial water-soluble betaine-modified chitosan as described in any one of claims 1 to 6 is dissolved in pure water to prepare a film-forming liquid, the film-forming liquid is centrifuged and degassed, then poured into a culture dish and dried, and finally the film is peeled off to obtain a betaine-modified chitosan film.

8. The method for preparing an antibacterial water-soluble betaine-modified chitosan film according to claim 7, characterized in that: The concentration of the film-forming liquid is 1-5wt%, the drying temperature is 40-60°C, and the drying time is 20-30 hours.

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