Preparation method for and use of quaternized chitin nanofiber

Abstract

A preparation method for and a use of a quaternized chitin nanofiber, relating to the field of natural polymers. The preparation method comprises the following steps: adding chitin to a mixed solution containing a low concentration of alkali, urea, and water, and performing low-temperature freezing treatment, wherein the treated chitin is in a swollen state; adding a quaternization reagent to a chitin suspension obtained by thawing, after the reaction is carried out, using deionized water to dialyze same to neutrality, performing ultrasonic dispersion to obtain a chitin nanofiber dispersion, performing centrifugation to obtain a uniform chitin nanofiber supernatant, and performing freeze-drying to obtain a quaternized chitin nanofiber. Also disclosed is a use of the prepared quaternized chitin nanofiber for antibacterial and bacteriostatic purposes. The preparation method is simple to operate, involves mild and efficient reaction, and can be used for producing a series of quaternized chitin nanofibers with different lengths, diameters, and degrees of substitution, exhibiting broad‑spectrum antibacterial activity.

Description

Preparation method of quaternary ammonium chitin nanofiber and application thereof TECHNICAL FIELD

[0001] The present application belongs to the field of natural polymers, and particularly relates to a preparation method of quaternary ammonium chitin nanofiber and application thereof. BACKGROUND

[0002] Chitin is mainly derived from the exoskeleton of marine crustaceans and is the second most abundant biopolymer in nature after cellulose. According to the different orientation of microprotoplast fibers, chitin exists in three forms of alpha, beta and gamma chitin in nature. Chitin has good biocompatibility, biodegradability and non-toxicity. In addition to inheriting the advantages of chitin, nanochitin has a large surface-to-volume ratio, small pore size and high porosity due to its nano structure, which endows it with unique physical and chemical properties, and thus is widely used in biomedical, agricultural, food and cosmetic fields.

[0003] Due to the high crystallinity between chitin molecular chains and the strong intermolecular and intramolecular hydrogen bond interactions, their solubility in ordinary solvents is poor, and they are difficult to be easily dispersed into nanofibers, which hinders their application in various fields. Considering the good biocompatibility of natural polymers, researchers have gradually developed a series of chemical modification methods such as carboxymethylation, hydroxypropylation, sulfation and quaternization, and introduced multifunctional groups to improve their solubility and physicochemical properties, so as to have specific functions and enhance application value. Among them, quaternization is a common method for modification of natural polysaccharides. However, the existing methods for preparing quaternary ammonium chitin nanofiber mostly rely on high-concentration alkali or organic solvents, which have certain shortcomings and limitations. For example, in the process of preparing quaternary ammonium chitin nanofiber by using high-concentration sodium hydroxide (NaOH) solution, although the solubility of chitin can be effectively improved, the use of high-concentration alkali may lead to partial degradation of chitin and cause corrosion and safety hazards to equipment and operators. In addition, although organic solvents such as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) can dissolve chitin and carry out quaternization reaction under relatively mild conditions, these solvents have potential pollution risk to the environment, and their recovery and treatment cost is high.

[0004] In addition, Cai et al. demonstrated the uniform synthesis of cationic quaternary ammonium beta-chitin derivatives from KOH / urea aqueous solution, which can be used for wound infection treatment. Patent No. 201610145653.8 discloses a method for homogeneously preparing water-soluble alpha-chitin and beta-chitin derivatives. However, the existing preparation methods all have unavoidable problems, such as using high-concentration KOH to completely dissolve chitin molecular chains and then self-assembling into micelles.

[0005] SUMMARY

[0006] In order to overcome the defects of the prior art, the application provides a method for preparing quaternary ammonium chitin nanofiber and application thereof. The application uses a relatively low concentration of alkali / urea aqueous solution to swell the chitin molecular chain, and 2,3-epoxypropyltrimethylammonium chloride (EPTMAC) as a quaternary ammonium reagent to prepare chitin nanofiber. Compared with dissolving chitin and preparing nanomaterials by using a high-concentration alkali / urea mixed solution, the application uses a relatively low concentration of alkali and urea mixed solution as a treatment solvent for chitin, thereby reducing the environmental pollution caused by high-concentration alkali.

[0007] In addition, the low-concentration alkali / urea mixed solution can effectively swell the chitin, promote the quaternary ammonium reaction, improve the reaction efficiency, reduce the energy consumption, and achieve unexpected substantial effects. Finally, the method can control the morphology and degree of substitution of the chitin nanofiber by simply controlling the alkali concentration and reaction conditions, so that the chitin nanofiber is suitable for various application fields.

[0008] In order to achieve the above-mentioned purpose, the application provides the following scheme:

[0009] The application first provides a method for preparing quaternary ammonium chitin nanofiber, which specifically comprises the following steps:

[0010] (1) adding alkali and urea into water and stirring uniformly to obtain a mixed solution, which is denoted as solution A; the concentration of the alkali in the solution A is 2-10 wt%, the concentration of the urea is 0-5 wt%, and the balance is water;

[0011] (2) adding chitin into the solution A prepared in step (1) to form a mixed solution, which is denoted as solution B; then, the solution B is subjected to low-temperature freezing pretreatment to obtain a pretreated chitin mixture;

[0012] (3) thawing the pretreated chitin mixture to obtain a chitin suspension, adding a quaternary ammonium reagent for reaction, and then dialyzing with deionized water until the pH is neutral, and then performing ultrasonic dispersion treatment to obtain a chitin nanofiber suspension; centrifuging to collect the supernatant, which is a chitin nanofiber supernatant; and finally, performing freeze-drying to obtain chitin nanofiber.

[0013] Preferably, the concentration of the alkali in step (1) is 3-7 wt%, and the concentration of the urea is 1-2 wt%.

[0014] Preferably, the alkali in step (1) includes any one of potassium hydroxide, sodium hydroxide, or lithium hydroxide.

[0015] Preferably, the chitin in step (2) includes β-chitin and α-chitin.

[0016] Preferably, the concentration of chitin in the solution B in step (2) is 1-3 wt%.

[0017] Preferably, the temperature of the low-temperature freezing pretreatment in step (2) is -40 to -20℃, and the time is 4-24 hours.

[0018] Further, the low-temperature freezing pretreatment is performed by freezing at -40 to -20℃ for 1.5 hours to form a slush, stirring uniformly, and then continuing to freeze for 2.5-22.5 hours.

[0019] Preferably, the quaternary ammonium reagent in step (3) includes 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl triethyl ammonium chloride, 2,3-epoxypropyl trimethyl ammonium chloride, or 2,3-epoxypropyl triethyl ammonium chloride; and the molar ratio of the quaternary ammonium reagent to chitin monomers in the chitin suspension is (4-9):1.

[0020] Preferably, the temperature of the reaction in step (3) is 0-15℃, and the time is 10-36 hours.

[0021] More preferably, the molar ratio of the quaternary ammonium reagent to chitin monomers in the chitin suspension is 4:1, the reaction temperature is 15℃, and the reaction time is 24 hours.

[0022] The main chemical reactions involved in the present application are as follows:

[0023] The chitin nanofiber prepared according to the present application can be used for antibacterial and bacteriostatic purposes.

[0024] The present application has the following technical effects:

[0025] (1) The present application uses a relatively low concentration of alkali, which causes less damage to the chitin molecular chain, and reduces the environmental pollution caused by high-concentration alkali.

[0026] (2) The present application uses a low-concentration alkali-urea mixed solution to effectively swell chitin and promote the quaternary ammonium reaction; through the swelling treatment of chitin, the efficiency of preparing quaternized chitin nanofiber is greatly improved.

[0027] (3) The method of the present application is simple, easy to operate, low in cost, environmentally friendly, and high in yield.

[0028] (4) The quaternized chitin nanofiber of the present application has a broad-spectrum antibacterial ability, and the morphology and degree of substitution of the chitin nanofiber can be adjusted by simply controlling the alkali concentration and reaction conditions, so that it is suitable for various application fields and can be widely used in food, biological medicine, tissue engineering, and other fields, and has good application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a nuclear magnetic resonance spectrum 1 HNMR chart; wherein (a) is chitin, (b)-(f) are quaternized chitin nanofibers of Example 2-Example 6.

[0030] Figure 2 is an infrared spectrum chart; wherein (a) is chitin, (b), (c), (d) are quaternized chitin nanofibers of Example 2, Example 3 and Example 5 respectively.

[0031] Figure 3 is a transmission electron microscope photo; wherein (a) is chitin, (b), (c), (d) are quaternized chitin nanofibers of Example 2, Example 3 and Example 5 respectively.

[0032] Figure 4 is a picture of antibacterial experiment; wherein (a) and (b) are quaternized chitin nanofibers of Example 2, Example 5 respectively. DETAILED DESCRIPTION

[0033] The detailed description particularly prefers certain aspects, features and embodiments of the present application, but it is to be understood that the detailed description is not to be taken as limiting the scope of the present application. The detailed description includes specific details for the purpose of providing a thorough understanding of the present application.

[0034] It should be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0035] Although preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in further detail the methods and / or materials associated with the documents. In the event of conflict between the present specification and any incorporated document, the present specification controls.

[0036] Various modifications and changes can be made to the specific embodiments of the present application described herein without departing from the scope or spirit of the application.

[0037] Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only.

[0038] Example 1:

[0039] KOH, urea were added into water, and stirred to obtain a mixture, wherein the concentration of KOH was 5wt%, and the concentration of urea was 1wt%;

[0040] Take 98g of the mixed solution to add 2g of β-chitin, stir evenly to get chitin mixed solution; freeze at -35℃ for 1.5 hours to ice slurry, then fully stir evenly with glass rod, continue to freeze for 13.5 hours to get pretreated chitin mixture;

[0041] Take the pretreated chitin mixture to naturally thaw to get chitin suspension, mechanically stir at 15℃ for 24 hours. After the reaction is completed, dialyze with deionized water until the pH is neutral, ultrasonic dispersion to get chitin nanofiber suspension, centrifugal treatment to obtain uniform chitin nanofiber supernatant, freeze-drying to get white powder quaternized chitin nanofiber. Figure 3(a) is the transmission electron microscope graph of the quaternized chitin nanofiber obtained in this example.

[0042] Example 2:

[0043] Add KOH and urea into water, stir evenly to get mixed solution, wherein the concentration of KOH is 5wt%, the concentration of urea is 1wt%;

[0044] Take 98g of the mixed solution to add 2g of β-chitin, stir evenly to get chitin mixed solution; freeze at -35℃ for 1.5 hours to ice slurry, then fully stir evenly with glass rod, continue to freeze for 13.5 hours to get pretreated chitin mixture;

[0045] Take the pretreated chitin mixture to naturally thaw to get chitin suspension. According to the molar ratio of 2,3-epoxypropyl trimethyl ammonium chloride to β-chitin monomer is 4:1, add 5.97g of 2,3-epoxypropyl trimethyl ammonium chloride powder to the chitin suspension, mechanically stir at 15℃ for 24 hours; after the reaction is completed, dialyze with deionized water until the pH is neutral, ultrasonic dispersion to get chitin nanofiber suspension, centrifugal treatment to obtain uniform chitin nanofiber supernatant, freeze-drying to get white powder quaternized chitin nanofiber.

[0046] Figure 1(b) curve and Figure 3(b) are the nuclear magnetic resonance spectrum and transmission electron microscope graph of the quaternized chitin nanofiber obtained in this example. The degree of substitution of the obtained quaternized chitin nanofiber is 0.24, and the degree of deacetylation is 0.86, which is determined by 1H NMR. Transmission electron microscope observation found that the average length of the nanofiber is about 300nm, and the average diameter is about 30nm.

[0047] Figure 2(b) curve is the infrared spectrum of the quaternized chitin nanofiber obtained in this example. From Figure 2(b), it can be seen that the characteristic absorption peak of chitin in the infrared spectrum is 1650cm -1 and 1548cm -1, relative to the original chitin infrared spectrum, quaternary chitin nanofiber at 1480 cm -1 absorption peak of the amino group in the quaternary chitin nanofiber.

[0048] As can be seen from Figure 1(b), the absorption peaks at 1.90 ppm and 3.05 ppm correspond to the acetyl group (-COCH3) and quaternary ammonium group (-N+(CH3)3) in the quaternary chitin nanofiber, respectively, which is consistent with the conclusion of infrared spectrum, indicating that chitin has reacted with the modifier 2,3-epoxypropyl trimethyl ammonium chloride.

[0049] Example 3:

[0050] KOH, urea were added to water to obtain a mixture, wherein the concentration of KOH was 5wt%, and the concentration of urea was 1wt%;

[0051] 98g of the mixture was taken and 2g of β-chitin was added and stirred uniformly to obtain a chitin mixture solution; the chitin mixture solution was frozen at -35℃ for 1.5 hours to form ice slurry, then it was stirred uniformly with a glass rod and further frozen for 13.5 hours to obtain a pretreated chitin mixture;

[0052] The pretreated chitin mixture was naturally thawed to obtain a chitin suspension; 10.45g of 2,3-epoxypropyl trimethyl ammonium chloride powder was added to the above chitin suspension according to a molar ratio of 2,3-epoxypropyl trimethyl ammonium chloride to β-chitin monomer of 7:1, and the mixture was mechanically stirred at 15℃ for 24 hours. After the reaction was completed, the mixture was dialyzed with deionized water until the pH was neutral, and then ultrasonic dispersion was performed to obtain a chitin nanofiber suspension. The chitin nanofiber suspension was centrifuged to obtain a uniform chitin nanofiber supernatant, which was freeze-dried to obtain white powder quaternary chitin nanofiber.

[0053] The (c) curve in Figure 1 and Figure 3(c) are the nuclear magnetic resonance spectrum and transmission electron microscope image of the quaternary chitin nanofiber obtained in this example, respectively. The degree of substitution of the quaternary chitin nanofiber obtained was 0.36, and the degree of deacetylation was 0.84, as determined by 1H NMR. Transmission electron microscopy observation found that the average length of the nanofiber was about 150 nm, and the average diameter was about 10 nm. The (c) curve in Figure 2 is the infrared spectrum of the quaternary chitin nanofiber obtained in this example.

[0054] Example 4:

[0055] KOH, urea were added to water to obtain a mixture, wherein the concentration of KOH was 5wt%, and the concentration of urea was 1wt%;

[0056] Take 98 g of the mixed solution to add 2 g of β-chitin, stir evenly to get chitin mixed solution; freeze at -35 ℃ for 1.5 hours to ice slurry, then fully stir evenly with a glass rod, continue to freeze for 13.5 hours to get pretreated chitin mixture;

[0057] Take the pretreated chitin mixture to naturally thaw to get chitin suspension; according to the molar ratio of 2,3-epoxypropyl trimethyl ammonium chloride to β-chitin monomer is 9:1, add 13.43 g of 2,3-epoxypropyl trimethyl ammonium chloride powder to the above mixed solution, mechanically stir at 15 ℃ for 24 hours. After the reaction is completed, dialysis with deionized water until the pH is neutral, ultrasonic dispersion to get chitin nanofiber suspension, centrifugal treatment to obtain uniform chitin nanofiber supernatant, freeze-drying to get white powder quaternized chitin nanofiber. The (d) curve in FIG. 1 is the nuclear magnetic resonance spectrum of the quaternized chitin nanofiber obtained in this example. The degree of substitution of the quaternized chitin nanofiber obtained is 0.48 and the degree of deacetylation is 0.78 by 1H NMR determination.

[0058] Example 5:

[0059] Add KOH and urea to water to stir evenly to get a mixed solution, wherein the concentration of KOH is 7wt%, and the concentration of urea is 1wt%;

[0060] Take 98 g of the mixed solution to add 2 g of β-chitin, stir evenly to get chitin mixed solution; freeze at -35 ℃ for 1.5 hours to ice slurry, then fully stir evenly with a glass rod, continue to freeze for 13.5 hours to get pretreated chitin mixture;

[0061] Take the pretreated chitin mixture to naturally thaw to get chitin suspension; according to the molar ratio of 2,3-epoxypropyl trimethyl ammonium chloride to β-chitin monomer is 4:1, add 5.97 g of 2,3-epoxypropyl trimethyl ammonium chloride powder to the above mixed solution, mechanically stir at 15 ℃ for 24 hours. After the reaction is completed, dialysis with deionized water until the pH is neutral, ultrasonic dispersion to get chitin nanofiber suspension, centrifugal treatment to obtain uniform chitin nanofiber supernatant, freeze-drying to get white powder quaternized chitin nanofiber.

[0062] The (e) curve in FIG. 1 and (d) in FIG. 3 are the nuclear magnetic resonance spectrum and transmission electron microscope diagram of the quaternized chitin nanofiber obtained in this example, respectively. The degree of substitution of the quaternized chitin nanofiber obtained is 0.29 and the degree of deacetylation is 0.86 by 1H NMR determination. The (b) curve in FIG. 2 and (b) in FIG. 4 are the infrared spectrum and antibacterial experiment diagram of the quaternized chitin nanofiber obtained in this example, respectively.

[0063] As can be seen from Fig. 4(b), the quaternary ammonium chitin nanofiber has good antibacterial property and shows significant bacteriostatic effect on E. coli and S. aureus.

[0064] Example 6:

[0065] KOH and urea were added to water to obtain a mixed solution, wherein the concentration of KOH was 14wt%, and the concentration of urea was 1wt%;

[0066] 98g of the mixed solution was taken and 2g of β-chitin was added and stirred uniformly to obtain a chitin mixed solution; the chitin mixed solution was frozen at a low temperature of-35℃ for 1.5 hours to a slush state, then uniformly stirred with a glass rod, and continuously frozen for 13.5 hours to obtain a pretreated chitin mixture;

[0067] The pretreated chitin mixture was naturally thawed to obtain a chitin suspension; 5.97g of 2,3-epoxypropyltrimethylammonium chloride powder was added to the above mixed solution according to a molar ratio of 2,3-epoxypropyltrimethylammonium chloride to β-chitin monomer of 4:1, and mechanically stirred at 15℃ for 24 hours. After the reaction was completed, the product was dialyzed with deionized water until the pH was neutral, and ultrasonic dispersion was performed to obtain a chitin nanofiber suspension. Centrifugal treatment was performed to obtain a uniform chitin nanofiber supernatant, and freeze-drying was performed to obtain white powder quaternary ammonium chitin nanofiber.

[0068] Fig. 1(f) is the nuclear magnetic resonance spectrum of the quaternary ammonium chitin nanofiber obtained in the present example. The degree of substitution of the obtained quaternary ammonium chitin nanofiber was 0.27, and the degree of deacetylation was 0.86, which were determined by 1H NMR.

[0069] Example 7:

[0070] KOH and urea were added to water to obtain a mixed solution, wherein the concentration of KOH was 2wt%, and the concentration of urea was 1wt%;

[0071] 98g of the mixed solution was taken and 2g of β-chitin was added and stirred uniformly to obtain a chitin mixed solution; the chitin mixed solution was frozen at a low temperature of-20℃ for 1.5 hours to a slush state, then uniformly stirred with a glass rod, and continuously frozen for 2.5 hours to obtain a pretreated chitin mixture;

[0072] The pretreated chitin mixture was naturally thawed to obtain a chitin suspension; 2.98 g of 2,3-epoxypropyl trimethylammonium chloride was added to the above mixture according to a molar ratio of 2,3-epoxypropyl trimethylammonium chloride to β-chitin monomer of 4:1, and mechanically stirred at 15 °C for 36 hours. After the reaction was completed, deionized water was used for dialysis until the pH was neutral, ultrasonic dispersion was performed to obtain a chitin nanofiber suspension, centrifugal treatment was performed to obtain a uniform chitin nanofiber supernatant, and freeze-drying was performed to obtain white powder quaternized chitin nanofibers.

[0073] Example 8:

[0074] KOH and urea were added to water to obtain a mixture, wherein the concentration of KOH was 7 wt%, and the concentration of urea was 1 wt%;

[0075] 97 g of the mixture was taken and 3 g of β-chitin was added and stirred uniformly to obtain a chitin mixed solution; the solution was frozen at -40 °C for 1.5 hours to ice slurry, then uniformly stirred with a glass rod, and then continuously frozen for 22.5 hours to obtain a pretreated chitin mixture;

[0076] The pretreated chitin mixture was naturally thawed to obtain a chitin suspension; 2.98 g of 2,3-epoxypropyl trimethylammonium chloride was added to the above mixture according to a molar ratio of 2,3-epoxypropyl trimethylammonium chloride to β-chitin monomer of 4:1, and mechanically stirred at 15 °C for 36 hours. After the reaction was completed, deionized water was used for dialysis until the pH was neutral, ultrasonic dispersion was performed to obtain a chitin nanofiber suspension, centrifugal treatment was performed to obtain a uniform chitin nanofiber supernatant, and freeze-drying was performed to obtain white powder quaternized chitin nanofibers.

[0077] Example 9:

[0078] KOH and urea were added to water to obtain a mixture, wherein the concentration of KOH was 7 wt%, and the concentration of urea was 5 wt%;

[0079] 98 g of the mixture was taken and 2 g of β-chitin was added and stirred uniformly to obtain a chitin mixed solution; the solution was frozen at -35 °C for 1.5 hours to ice slurry, then uniformly stirred with a glass rod, and then continuously frozen for 13.5 hours to obtain a pretreated chitin mixture;

[0080] The pretreated chitin mixture was naturally thawed to obtain a chitin suspension; 5.97 g of 2,3-epoxypropyl trimethylammonium chloride was added to the above mixture according to a molar ratio of 2,3-epoxypropyl trimethylammonium chloride to a-chitin monomer of 4:1, and mechanically stirred at 15°C for 24 hours. After the reaction was completed, deionized water was used for dialysis until the pH was neutral, ultrasonic dispersion was performed to obtain a chitin nanofiber suspension, centrifugal treatment was performed to obtain a uniform chitin nanofiber supernatant, and freeze-drying was performed to obtain white powder quaternized chitin nanofibers.

[0081] Example 10:

[0082] LiOH and urea were added to water to obtain a mixture, wherein the concentration of KOH was 7wt%, and the concentration of urea was 1wt%;

[0083] 98 g of the mixture was taken and 2 g of β-chitin was added and stirred uniformly to obtain a chitin mixed solution; the chitin mixed solution was frozen at -35°C for 1.5 hours to form ice slurry, then a glass rod was used for uniform stirring, and then the ice slurry was continuously frozen for 13.5 hours to obtain a pretreated chitin mixture;

[0084] The pretreated chitin mixture was naturally thawed to obtain a chitin suspension; 5.97 g of 2,3-epoxypropyl trimethylammonium chloride was added to the above mixture according to a molar ratio of 2,3-epoxypropyl trimethylammonium chloride to a-chitin monomer of 4:1, and mechanically stirred at 15°C for 24 hours. After the reaction was completed, deionized water was used for dialysis until the pH was neutral, ultrasonic dispersion was performed to obtain a chitin nanofiber suspension, centrifugal treatment was performed to obtain a uniform chitin nanofiber supernatant, and freeze-drying was performed to obtain white powder quaternized chitin nanofibers.

[0085] As can be seen from Examples 1-6, after the alkaline and urea system low-temperature freezing treatment, the chitin can react with the modifying agent 2,3-epoxypropyl trimethylammonium chloride to obtain a series of quaternized chitin nanofibers with different lengths, diameters and degrees of substitution.

[0086] When the concentrations of the alkaline and urea are the same, it is found by 1H NMR that a higher proportion of 2,3-epoxypropyl trimethylammonium chloride is added, and the quaternized chitin nanofibers obtained have a higher degree of substitution. This result is consistent with the infrared spectrum, indicating that the increase of the concentration of the modifying agent 2,3-epoxypropyl trimethylammonium chloride can increase the degree of substitution of the quaternized chitin nanofibers.

[0087] When the proportion of 2,3-epoxypropyl trimethyl ammonium chloride added is the same, the nuclear magnetic resonance spectrum shows that, compared with 5% and 14% alkali, the degree of substitution of quaternary ammonium chitin nanofiber is the highest when the alkali concentration is 7%, indicating that the concentration of alkali also affects the degree of substitution of quaternary ammonium chitin nanofiber, and the concentration of 7% is the best.

[0088] Transmission electron microscopy observation found that when no modified reagent 2,3-epoxypropyl trimethyl ammonium chloride is added, the prepared fiber has a larger particle size and is intertwined and aggregated. After adding 2,3-epoxypropyl trimethyl ammonium chloride and chitin monomer at a molar ratio of 4:1, the prepared nanofiber has a smaller particle size and is more dispersed. When the ratio is increased to 7:1, the average length of the obtained nanofiber is reduced from 300 nm to 150 nm, and the average diameter is reduced from 30 nm to 10 nm, indicating that the increase of the concentration of 2,3-epoxypropyl trimethyl ammonium chloride is conducive to reducing the average particle size of the nanofiber.

[0089] When the molar ratio of 2,3-epoxypropyl trimethyl ammonium chloride to chitin monomer is fixed at 4:1 and the alkali concentration is increased to 7%, the obtained nanofiber is uniformly dispersed and has an average diameter of less than 10 nm, which is more conducive to further application.

[0090] In addition, it can be seen from the optical picture of the antibacterial experiment that the experimental groups with the addition of 2,3-epoxypropyl trimethyl ammonium chloride all have good antibacterial properties and show significant bacteriostatic effect on Escherichia coli and Staphylococcus aureus. This result shows that when the molar ratio of 2,3-epoxypropyl trimethyl ammonium chloride to chitin monomer is 4:1, the nanofiber exhibits broad-spectrum antibacterial ability, and the change of alkali concentration has no effect. In summary, when the alkali concentration is 7% and the molar ratio of 2,3-epoxypropyl trimethyl ammonium chloride to chitin monomer is 4:1, the prepared quaternary ammonium chitin nanofiber has the best performance and is more suitable for further functional application.

[0091] The degree of substitution and the degree of deacetylation of the quaternary ammonium chitin nanofiber obtained in Examples 1-6 were measured by the following method:

[0092] In the formula, DS is the degree of substitution of quaternary ammonium group in quaternary ammonium chitin nanofiber, and DA is the degree of deacetylation of quaternary ammonium chitin nanofiber; I-N + (CH3)3 is the integral area of methyl protons in quaternary ammonium trimethyl, denoted as C; I H-Acetyl is the integral area of methyl protons in acetylamino group, denoted as E; H-1 proton integral is denoted as A.

[0093] Since the integral value of A in (1) and (2) has an important influence on DS and DA, a calibration formula is needed to make the integral value of A more accurate. In the formula, IH-2-D D is the integral of the proton on C2 which is connected with amino group in quaternary ammonium chitin nanofiber; B is the integral of all protons on C2-C6 in acetyl amino sugar ring and other protons in quaternary ammonium group.

[0094] Therefore, the following equation should be satisfied: B-5DS = 6 (4)

[0095] The D+E / 3 value of different quaternary ammonium chitin nanofibers calculated by the above method is basically around 1, which is consistent with formula (3), and the integral area B and DS value also satisfy formula (4).

[0096] These data show that the proton nuclear magnetic resonance signal accurately quantitatively characterizes the structure of uniformly synthesized quaternary ammonium chitin nanofiber.

[0097] The method provided by the application promotes the quaternary ammonium reaction, improves the reaction efficiency, reduces the energy consumption, and achieves unexpected substantial effects. Moreover, the method can control the morphology and degree of substitution of chitin nanofiber by simply controlling the alkali concentration and reaction conditions, so that it is suitable for various application fields and has wide application prospect.

[0098] Description: The above examples are only used to illustrate the technical solutions described in the application and not to limit the application; therefore, although the application has been described in detail with reference to the above examples, those skilled in the art should understand that the application can still be modified or replaced equivalently; and all technical solutions and improvements which do not deviate from the spirit and scope of the application should be covered in the scope of the claims of the application.

Claims

1. A method for preparing quaternized chitin nanofibers, characterized by, The steps are as follows: (1) adding alkali and urea into water, stirring to obtain a mixed solution, which is recorded as solution A; the concentration of alkali in the solution A is 2-10 wt%, the concentration of urea is 0-5 wt%, and the rest is water; (2) adding chitin into the solution A prepared in step (1) to form a mixed solution, which is recorded as solution B; then the solution B is subjected to low-temperature freezing pretreatment to obtain a pretreated chitin mixture; (3) after thawing the pretreated chitin mixture to obtain a chitin suspension, adding a quaternary ammonium reagent for reaction, after the reaction, dialyzing with deionized water until the pH is neutral, and then performing ultrasonic dispersion treatment to obtain a chitin nanofiber suspension, centrifuging to collect the supernatant, which is a chitin nanofiber supernatant, and finally freeze-drying to obtain chitin nanofibers.

2. The method for preparing quaternized chitin nanofibers according to claim 1, characterized in that, In step (1), the concentration of alkali is 3-7 wt%, and the concentration of urea is 1-2 wt%; the alkali includes any one of potassium hydroxide, sodium hydroxide or lithium hydroxide.

3. The method for preparing quaternized chitin nanofibers according to claim 1, characterized in that, In step (2), the chitin includes β-chitin and α-chitin; the concentration of chitin in the solution B is 1-3 wt%.

4. The method for preparing quaternized chitin nanofibers according to claim 1, characterized in that, In step (2), the low-temperature freezing pretreatment is performed at a temperature of-40 to-20℃ for 4-24 hours.

5. The method for preparing quaternized chitin nanofibers according to claim 4, characterized in that, The low-temperature freezing pretreatment is performed by freezing at-40 to-20℃ for 1.5 hours to form a slush, stirring uniformly, and then continuing to freeze for 2.5-22.5 hours.

6. The method for preparing quaternized chitin nanofibers according to claim 1, characterized in that, In step (3), the quaternary ammonium reagent includes 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl triethyl ammonium chloride, 2,3-epoxypropyl trimethyl ammonium chloride or 2,3-epoxypropyl triethyl ammonium chloride; the molar ratio of the quaternary ammonium reagent to chitin monomers in the chitin suspension is (4-9):

1.

7. The method for preparing quaternized chitin nanofibers according to claim 6, characterized in that, The molar ratio of the quaternary ammonium reagent to chitin monomers in the chitin suspension is 4:

1.

8. The method for preparing quaternized chitin nanofibers according to claim 1, characterized in that, In step (3), the reaction is performed at a temperature of 0-15℃ for 10-36 hours.

9. The method for preparing quaternized chitin nanofibers according to claim 8, characterized in that, The reaction is performed at a temperature of 15℃ for 24 hours.

10. The use of the quaternized chitin nanofibers prepared by the method of any one of claims 1-9 for antibacterial and bacteriostatic purposes.

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