A method for rapidly preparing chitosan nanofibers with controllable morphology and multi-solvent dispersibility

Abstract

This invention discloses a rapid method for preparing chitosan nanofibers with controllable morphology and good multi-solvent dispersibility, belonging to the field of fiber preparation technology. The method involves first pretreating chitosan with lithium salt or lithium alkali, then adding it to an acetic acid solution containing polyol and stirring to dissolve it. A dilute alkali solution is then added dropwise to the completely dissolved chitosan solution until the solution becomes weakly alkaline, resulting in a dispersion of single, branchless regenerated chitosan nanofibers. Alternatively, a dilute alkali solution containing a nonionic surfactant is added dropwise to the completely dissolved chitosan solution until the solution becomes weakly alkaline, resulting in a dendritic regenerated chitosan nanofiber dispersion. Alternatively, by adjusting the order of adding the completely dissolved chitosan solution and the dilute alkali solution, a network-structured regenerated chitosan nanofiber dispersion is obtained. The chitosan regenerated nanofibers of this invention exhibit controllable fiber size and morphology, a relatively constant degree of polymerization, and good multi-solvent dispersibility.

Description

Technical Field

[0001] This invention relates to a method for rapidly preparing chitosan nanofibers with controllable morphology and multi-solvent dispersibility, belonging to the field of fiber preparation technology. Background Technology

[0002] Chitosan, a natural cationic polysaccharide derived from crustacean waste such as shrimp and crab shells and fungal cell walls, has a molecular chain rich in amino and hydroxyl groups. It possesses excellent biocompatibility, biodegradability, antibacterial activity, and cell affinity, showing broad application prospects in biomedicine, environmental remediation, and food packaging. Chitosan nanofibers, with their three-dimensional microstructure similar to the extracellular matrix, high specific surface area, and controllable porosity, can directionally regulate cell adhesion, proliferation, and differentiation, while enhancing adsorption and sustained-release functions. They have become a research hotspot in the field of bio-based nanomaterials, especially in tissue engineering scaffolds, antibacterial dressings, thermal insulation materials, and pollutant adsorption materials, where they possess irreplaceable advantages.

[0003] Currently, the main methods for preparing chitosan nanofibers include electrospinning, self-assembly, and template methods. Electrospinning is the most widely used, but it relies on high-voltage equipment. The viscosity and conductivity of the pure chitosan spinning solution are difficult to balance, leading to bead-like defects. It requires the addition of synthetic auxiliaries such as polyvinyl alcohol to reduce product biocompatibility, and residual acids and crosslinking agents pose biotoxic risks. Furthermore, the process is sensitive to environmental temperature and humidity, making it difficult to control product quality stability in large-scale production. Self-assembly does not require complex equipment, but it suffers from low preparation efficiency, poor fiber size control, and easy dissociation of the product in electrolyte solutions. While carboxymethylation modification improves redispersibility, it still struggles to precisely control fiber morphology uniformity. Template methods, although capable of producing uniformly sized fibers, suffer from difficulties in template removal, high costs, and limited fiber length, hindering industrial application.

[0004] To address the drawbacks of the aforementioned methods, alkali-induced regeneration has gradually become a research hotspot, for example:

[0005] Patent CN113336977A, based on the low-temperature dissolution mechanism of chitosan in an alkali / urea aqueous solvent system, describes the formation of nanofibers through the thermally induced parallel self-assembly of chitosan molecular chains. Physically regenerated chitosan nanofiber microspheres are then constructed using an emulsion method. The patent mentions that the nanofiber structure can be effectively controlled by altering the initial solution concentration and the thermal induction temperature. However, in terms of process efficiency and operability, this method is highly dependent on repeated "freeze-thaw" processes. This cyclical operation not only significantly extends the production cycle, leading to high time costs, but also results in low production efficiency in industrial-scale production, making it difficult to meet the demands of continuous and large-scale industrial production. Furthermore, the prepared fibers are entangled and bound within the microspheres, making it impossible to obtain single, independent nanofibers with controllable aspect ratios.

[0006] Patent CN110093683A discloses a method for preparing chitosan nanofibers. First, chitosan with a certain molecular weight and degree of deacetylation is dissolved in an acid solution. Then, it is degraded with hydrogen peroxide at a certain temperature to obtain degraded chitosan with a smaller molecular weight. Finally, the degraded chitosan is homogenized under high pressure to obtain nano-chitosan fibers. However, hydrogen peroxide, as a strong oxidant, not only destroys the regularity of the chitosan macromolecular chain, thereby reducing the degree of polymerization of chitosan, but also brings certain safety hazards, such as personnel health, equipment corrosion, and even explosions.

[0007] Although existing alkali-induced technologies have made some progress, key technical bottlenecks still exist: fiber size and morphology are uncontrollable; chitosan is difficult to dissolve, the dissolution process is slow, and problems such as a decrease in the degree of polymerization are easy to occur during the dissolution process; and the regenerated chitosan nanofibers are difficult to disperse stably in a variety of solvent systems.

[0008] Efficient preparation, controllable morphology, and multi-solvent dispersion are core requirements for the application of chitosan nanofibers in biomedicine, tissue engineering, food packaging, daily chemical care, and environmental remediation. Therefore, finding a rapid, morphology-controllable, and multi-solvent-dispersible chitosan nanofiber and its preparation method has broad market application prospects. Summary of the Invention

[0009] [Technical Issues]

[0010] The preparation of regenerated chitosan nanofibers faces challenges such as uncontrollable fiber size and morphology, slow chitosan dissolution rate, decreased degree of polymerization, and poor dispersibility in multiple solvents.

[0011] [Technical Solution]

[0012] To address the aforementioned problems, this invention provides a method for rapidly preparing chitosan nanofibers with controllable morphology and multi-solvent dispersibility. Specifically, this invention first pretreats chitosan with lithium salt or lithium alkali, then adds it to an acetic acid solution containing polyol, stirs to dissolve, and obtains a completely dissolved chitosan solution. A dilute alkali solution is then added dropwise to the completely dissolved chitosan solution until the solution becomes weakly alkaline, resulting in a dispersion of single, branchless regenerated chitosan nanofibers. Alternatively, a dilute alkali solution containing a nonionic surfactant is added dropwise to the completely dissolved chitosan solution until the solution becomes weakly alkaline, resulting in a dendritic regenerated chitosan nanofiber dispersion. Alternatively, by adjusting the order of adding the completely dissolved chitosan solution and the dilute alkali solution, a network-structured regenerated chitosan nanofiber dispersion is obtained. The chitosan regenerated nanofibers prepared by this invention exhibit controllable fiber size and morphology, rapid chitosan dissolution rate, essentially unchanged degree of polymerization, and good multi-solvent dispersibility.

[0013] The first objective of this invention is to provide a method for rapidly preparing chitosan nanofibers with controllable morphology and multi-solvent dispersibility, the method comprising the following three approaches:

[0014] Method 1: Single root without branches

[0015] (1) Chitosan is dispersed in lithium salt or lithium alkali solution for pretreatment to obtain pretreated chitosan;

[0016] (2) Add the pretreated chitosan to an acetic acid solution containing polyols, stir to dissolve, and obtain a completely dissolved chitosan solution;

[0017] (3) Add dilute alkaline aqueous solution dropwise to the completely dissolved chitosan solution until the solution is weakly alkaline to obtain a single, branchless chitosan regenerated nanofiber dispersion.

[0018] Method 2: Tree-like

[0019] (1) Chitosan is dispersed in lithium salt or lithium alkali solution for pretreatment to obtain pretreated chitosan;

[0020] (2) Add the pretreated chitosan to an acetic acid solution containing polyols, stir to dissolve, and obtain a completely dissolved chitosan solution;

[0021] (3) Add the dilute alkaline aqueous solution containing nonionic surfactant dropwise to the completely dissolved chitosan solution until the solution is weakly alkaline to obtain a dendritic chitosan regenerated nanofiber dispersion.

[0022] Method 3: Mesh

[0023] (1) Chitosan is dispersed in lithium salt or lithium alkali solution for pretreatment to obtain pretreated chitosan;

[0024] (2) Add the pretreated chitosan to an acetic acid solution containing polyols, stir to dissolve, and obtain a completely dissolved chitosan solution;

[0025] (3) The completely dissolved chitosan solution is added dropwise to a dilute alkaline aqueous solution until the solution is weakly alkaline, thus obtaining a network-like chitosan regenerated nanofiber dispersion.

[0026] In one embodiment of the present invention, in step (1) of method one, the lithium salt or lithium alkali solution is one or both of LiCl aqueous solution and LiOH aqueous solution, and the mass concentration of the solution is 8-12%.

[0027] In one embodiment of the present invention, the mass ratio of chitosan to (lithium salt or lithium alkali) solution in step (1) of method one is 10-30:400.

[0028] In one embodiment of the present invention, the pretreatment in step (1) of method one is to stir at 35-75°C and 100-500 rpm for 0.2-1 h, and then take it out and wash it with water.

[0029] In one embodiment of the present invention, step (2) of method one contains a polyol that is one or both of isopropanol and tert-butanol; the method for preparing the acetic acid solution containing the polyol is as follows:

[0030] Add water to glacial acetic acid and mix well to obtain an acetic acid solution with a volume fraction of 1-3%; then add polyol to the acetic acid solution and stir well to obtain an acetic acid solution containing polyol; wherein the volume ratio of polyol to acetic acid solution is 30-50 mL: 1 L.

[0031] In one embodiment of the present invention, the ratio of the amount of pretreated chitosan to the acetic acid solution containing polyol in step (2) of method one is 400-500g: 1000-1100mL.

[0032] In one embodiment of the present invention, the stirring and dissolving in step (2) of method one is carried out at 55-65°C and 100-500 rpm for 30-120 min.

[0033] In one embodiment of the present invention, the dilute alkaline aqueous solution in step (3) of method one is a NaOH aqueous solution with a mass concentration of 0.5-3%.

[0034] In one embodiment of the present invention, the dripping rate in step (3) of method one is 20-40 mL / min; the dripping process is accompanied by stirring, and the stirring speed is 300-500 rpm.

[0035] In one embodiment of the present invention, the weakly alkaline pH in step (3) of method one is 8.5-9.5.

[0036] In one embodiment of the present invention, steps (1) and (2) of method two are the same as those of method one.

[0037] In one embodiment of the present invention, the dilute alkaline aqueous solution containing nonionic surfactant in step (3) of method two is a NaOH aqueous solution containing nonionic surfactant, and the ratio of nonionic surfactant, NaOH and water is 10-30mL: 15-25g: 1900-2000mL.

[0038] In one embodiment of the present invention, the nonionic surfactant in step (3) of method two is one or both of AEO-9 and APG.

[0039] In one embodiment of the present invention, the dripping rate in step (3) of method two is 20-40 mL / min; the dripping process is accompanied by stirring, and the stirring speed is 300-500 rpm.

[0040] In one embodiment of the present invention, the weakly alkaline pH in step (3) of method two is 8.5-9.5.

[0041] In one embodiment of the present invention, steps (1) and (2) of method three are the same as those of method one.

[0042] In one embodiment of the present invention, the dilute alkaline aqueous solution in step (3) of method three is a NaOH aqueous solution with a mass concentration of 0.5-3%.

[0043] In one embodiment of the present invention, the dripping rate in step (3) of method three is 20-40 mL / min; the dripping process is accompanied by stirring, and the stirring speed is 300-500 rpm.

[0044] In one embodiment of the present invention, the weakly alkaline pH in step (3) of method three is 8.5-9.5.

[0045] The second objective of this invention is to obtain chitosan nanofibers with controllable morphology and multi-solvent dispersibility prepared by the method described in this invention.

[0046] In one embodiment of the present invention, the fineness of single, unbranched chitosan regenerated nanofibers is 10-80 nm; the fineness of dendritic chitosan regenerated nanofibers is 20-80 nm; and the fineness of network-like chitosan regenerated nanofibers is 30-60 nm.

[0047] The third objective of this invention is the application of the chitosan nanofibers described herein, which have controllable morphology and multi-solvent dispersibility, in the fields of drug preparation, tissue engineering, food packaging, daily chemical products, or functional materials.

[0048] The fourth objective of this invention is to provide a method for improving the stability of chitosan fibers in a multi-solvent system while maintaining the degree of polymerization, which employs chitosan nanofibers with controllable morphology and multi-solvent dispersibility as described in this invention.

[0049] The fifth objective of this invention is to provide an aerogel that utilizes chitosan nanofibers with controllable morphology and multi-solvent dispersibility as described in this invention.

[0050] The sixth objective of this invention is to provide a heat-insulating and warm-keeping material that utilizes chitosan nanofibers with controllable morphology and multi-solvent dispersibility as described in this invention.

[0051] [Beneficial Effects]

[0052] (1) The present invention uses (lithium hydroxide or lithium chloride) pretreatment and polyol (isopropanol or tert-butanol) to assist in dissolution. By adjusting the effect of intramolecular and intermolecular hydrogen bonds of chitosan, the dissolution rate of chitosan is greatly improved, and chitosan can be dissolved within 30 minutes, which shortens the time for fiber preparation and is more efficient.

[0053] (2) The present invention accelerates the dissolution process and effectively inhibits the degradation reaction during the dissolution process, so that the degree of polymerization of the regenerated chitosan decreases less and the excellent properties of the raw material are preserved.

[0054] (3) The present invention can achieve precise control of the morphology of nanofibers, and the resulting fiber products have the advantages of good size uniformity and high structural stability, providing an efficient and controllable preparation path for the large-scale application of chitosan nanomaterials.

[0055] (4) The chitosan regenerated nanofiber dispersion prepared by the present invention has a zeta potential between 20-35mV and good dispersibility; the degree of polymerization is basically consistent with that of the chitosan raw material itself, and it is well dispersed in water, alcohol, alkali and DMF systems. Attached Figure Description

[0056] Figure 1 The images show the infrared spectra of chitosan raw material and regenerated chitosan nanofibers; where sample CS is chitosan raw material, sample A is Example 1, sample B is Example 5, and sample C is Example 7.

[0057] Figure 2The image shows the zeta potential distribution of the chitosan regenerated nanofiber dispersion; sample A is Example 1, sample B is Example 5, and sample C is Example 7.

[0058] Figure 3 The particle size distribution diagram is shown for the chitosan regenerated nanofiber dispersion; among them, sample A is Example 1, sample B is Example 5, and sample C is Example 7.

[0059] Figure 4 The images are transmission electron microscopy (TEM) images of chitosan regenerated nanofibers; where a is Example 1, b is Example 5, and c is Example 7.

[0060] Figure 5 These are actual photos of the chitosan nanofiber dispersion after standing for two months; from left to right, they are Example 1, Example 3, Example 5, and Example 7.

[0061] Figure 6 The images show chitosan nanofibers dispersed in an alkaline system and left to stand for two months; from left to right, they are Example 1 and Comparative Example 3.

[0062] Figure 7 The images shown are of chitosan nanofiber dispersion in Example 1, dispersed in different systems and left to stand for two months. From left to right, the systems are water, alkali, alcohol, and DMF.

[0063] Figure 8 This is a scanning electron microscope image of an axial section of chitosan nanofiber aerogel from Example 8. Detailed Implementation

[0064] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0065] Test method:

[0066] The chemical structure and functional groups of chitosan raw materials and chitosan nanofibers were analyzed using Fourier transform infrared spectroscopy.

[0067] The zeta potential and particle size distribution of chitosan nanofiber dispersion were tested using a laser particle size analyzer.

[0068] The morphology of chitosan nanofibers was observed using transmission electron microscopy.

[0069] The morphology of chitosan nanofiber aerogel was observed using scanning electron microscopy.

[0070] Chitosan nanofiber dispersion performance test:

[0071] The prepared chitosan nanofiber dispersion was placed into a sample bottle and left to stand at room temperature (20-30℃) for two months to observe its aggregation.

[0072] All systems tested used nanofiber dispersions with a solid content of 2 wt%. The solvent for the aqueous system was deionized water, the solvent for the alkaline system was 4% NaOH solution, the solvent for the alcohol system was anhydrous ethanol, and the solvent for the organic system was DMF. The dispersion was observed after standing at room temperature (20-30℃). The standardization was based on the following: good dispersion of nanofibers in the corresponding system for 2 months or more, fair dispersion for 1 week to 2 months, and poor dispersion due to aggregation and sedimentation within 1 week.

[0073] Raw materials used in the examples:

[0074] Chitosan: Molecular weight 50,000-200,000, degree of deacetylation 75%-85%;

[0075] LiOH powder: 300-500µm;

[0076] LiCl powder: 300-500µm;

[0077] Water: Deionized water;

[0078] AEO-9: Fatty alcohol polyoxyethylene ether;

[0079] APG: Alkyl glycoside;

[0080] Glacial acetic acid: 99.5%.

[0081] Example 1: Single root without branches

[0082] A method for preparing single, branchless chitosan nanofibers includes the following steps:

[0083] (1) Add 40g of LiOH powder to 360mL of water and stir at 100rpm until completely dissolved to obtain a LiOH aqueous solution with a mass concentration of 10%;

[0084] 20g of chitosan was dispersed in 400g of 10% LiOH aqueous solution, heated to 60℃, stirred at 150rpm for 0.5h, removed, and washed with water until the pH of the water was close to 7 to obtain pretreated chitosan.

[0085] (2) Add 980 mL of water to 20 mL of 99.5% glacial acetic acid and stir at 100 rpm to obtain 1 L of acetic acid solution with a volume fraction of 2%; then add 40 mL of isopropanol to the acetic acid solution and stir at 100 rpm to obtain acetic acid solution containing isopropanol.

[0086] (3) Add the pretreated chitosan to an acetic acid solution containing isopropanol, heat the solution in a water bath to 60°C, and stir at 200 rpm for 30 min to obtain a completely dissolved chitosan solution.

[0087] (4) Add 20 g of NaOH powder to 1980 mL of water and stir at 100 rpm until completely dissolved to obtain a 1% NaOH dilute alkaline solution.

[0088] (5) Under stirring at 400 rpm, dilute NaOH solution was added dropwise (dropping rate 30 mL / min) to the completely dissolved chitosan solution until the solution was weakly alkaline (pH about 9) to obtain a single, branchless chitosan regenerated nanofiber dispersion (fiber fineness 10-30 nm).

[0089] Example 2: Single root without branches

[0090] Adjust step (4) of Example 1 as follows:

[0091] (4) Add 40 g of NaOH powder to 1960 mL of water and stir at 100 rpm until completely dissolved to obtain a 2% NaOH dilute alkaline solution.

[0092] Everything else remained the same as in Example 1, resulting in a coarser, single-stranded, branchless chitosan regenerated nanofiber dispersion (fiber fineness of 40-80 nm).

[0093] Example 3: Single root without branches

[0094] The LiOH aqueous solution in step (1) of Example 1 is adjusted to a LiCl aqueous solution; specifically as follows:

[0095] Add 40g of LiCl powder to 360mL of water and stir at 100rpm until completely dissolved to obtain a 10% LiCl aqueous solution.

[0096] The stirring time in step (3) is 60 minutes;

[0097] Everything else remained the same as in Example 1, resulting in a single, branchless chitosan regenerated nanofiber dispersion (fiber fineness of 10-30 nm).

[0098] Example 4: Single root without branches

[0099] The isopropanol in step (2) of Example 1 was changed to tert-butanol; the rest remained the same as in Example 1, and a single chitosan regenerated nanofiber dispersion without branches was obtained.

[0100] Example 5: Dendritic

[0101] A method for preparing dendritic chitosan nanofibers, wherein the method is based on Example 1, with the addition of AEO-9 in step (4);

[0102] Specifically, the steps include the following:

[0103] (1) Add 40g of LiOH powder to 360mL of water and stir at 100rpm until completely dissolved to obtain a LiOH aqueous solution with a mass concentration of 10%;

[0104] 20g of chitosan was dispersed in 400g of 10% LiOH aqueous solution, heated to 60℃, stirred at 150rpm for 0.5h, removed, and washed with water until the pH of the water was close to 7 to obtain pretreated chitosan.

[0105] (2) Add 980 mL of water to 20 mL of 99.5% glacial acetic acid and stir at 100 rpm to obtain 1 L of acetic acid solution with a volume fraction of 2%; then add 40 mL of isopropanol to the acetic acid solution and stir at 100 rpm to obtain acetic acid solution containing isopropanol.

[0106] (3) Add the pretreated chitosan to an acetic acid solution containing isopropanol, heat the solution in a water bath to 60°C, and stir at 200 rpm for 30 min to obtain a completely dissolved chitosan solution.

[0107] (4) Add 20 g of NaOH powder to 1980 mL of water and stir at 100 rpm until completely dissolved. Then add 20 mL of surfactant AEO-9 to obtain a dilute NaOH alkaline solution containing surfactant.

[0108] (5) Under stirring at 400 rpm, add the dilute NaOH solution containing surfactant dropwise (dropping rate 30 mL / min) to the completely dissolved chitosan solution until the solution is weakly alkaline (pH about 9) to obtain a dendritic chitosan regenerated nanofiber dispersion (fiber fineness 20-40 nm).

[0109] Example 6 Dendritic

[0110] In Example 5, AEO-9 was replaced with APG, while other aspects remained the same as in Example 5, resulting in a chitosan regenerated nanofiber dispersion.

[0111] Example 7: Mesh

[0112] A method for preparing a network of chitosan nanofibers, wherein the method is based on Example 1, but the order of adding the completely dissolved chitosan solution and the dilute NaOH alkali solution in step (5) is adjusted;

[0113] Specifically, the steps include the following:

[0114] (1) Add 40g of LiOH powder to 360mL of water and stir at 100rpm until completely dissolved to obtain a LiOH aqueous solution with a mass concentration of 10%;

[0115] 20g of chitosan was dispersed in 400g of 10% LiOH aqueous solution, heated to 60℃, stirred at 150rpm for 0.5h, removed, and washed with water until the pH of the water was close to 7 to obtain pretreated chitosan.

[0116] (2) Add 980 mL of water to 20 mL of 99.5% glacial acetic acid and stir at 100 rpm to obtain 1 L of acetic acid solution with a volume fraction of 2%; then add 40 mL of isopropanol to the acetic acid solution and stir at 100 rpm to obtain acetic acid solution containing isopropanol.

[0117] (3) Add the pretreated chitosan to an acetic acid solution containing isopropanol, heat the solution in a water bath to 60°C, and stir at 200 rpm for 30 min to obtain a completely dissolved chitosan solution.

[0118] (4) Add 20 g of NaOH powder to 1980 mL of water and stir at 100 rpm until completely dissolved to obtain a 1% NaOH dilute alkaline solution.

[0119] (5) Under stirring at 400 rpm, the completely dissolved chitosan solution is added dropwise (dropping rate 30 mL / min) to a dilute NaOH solution until the solution is weakly alkaline (pH about 9) to obtain a network of regenerated chitosan nanofiber dispersion (fiber fineness 30-60 nm).

[0120] Comparative Example 1

[0121] Step (1) in Example 1 is omitted, that is, no pretreatment is performed on chitosan; everything else is the same as in Example 1, and a single, branchless chitosan regenerated nanofiber dispersion is obtained.

[0122] Comparative Example 2

[0123] Isopropanol in step (2) of Example 1 is omitted; everything else remains the same as in Example 1, resulting in a single, branchless chitosan regenerated nanofiber dispersion.

[0124] Comparative Example 3

[0125] The NaOH powder in step (4) of Example 1 was changed to Na2CO3 powder; the rest remained the same as in Example 1, and a microparticle-shaped regenerated chitosan dispersion was obtained.

[0126] Comparative Example 4

[0127] The isopropanol in step (2) of Example 1 was changed to anhydrous ethanol; the rest remained the same as in Example 1, and a single chitosan regenerated nanofiber dispersion without branches was obtained.

[0128] Comparative Example 5

[0129] Isopropanol in step (2) of Example 1 is omitted. Then chitosan and isopropanol are added together to an acetic acid solution. Everything else is the same as in Example 1 to obtain a single, branchless chitosan regenerated nanofiber dispersion.

[0130] Comparative Example 6

[0131] In Example 5, AEO-9 was replaced with SDBS (sodium dodecylbenzenesulfonate), while other aspects remained the same as in Example 5, resulting in a microparticle chitosan regenerated nanofiber dispersion.

[0132] The obtained fibers were subjected to performance tests, and the test results are as follows:

[0133] Figure 1 The images show the infrared spectra of chitosan raw material and recycled chitosan nanofibers; sample CS is chitosan raw material, sample A is from Example 1, sample B is from Example 5, and sample C is from Example 7. Figure 1 It can be seen that there are no significant changes in the chemical structure of the different chitosan regenerated nanofibers.

[0134] Figure 2 The image shows the zeta potential distribution of the chitosan regenerated nanofiber dispersion; sample A is from Example 1, sample B is from Example 5, and sample C is from Example 7. Figure 2 It can be seen that the Zeta potential of the chitosan regenerated nanofiber dispersion is between 20-35 mV, indicating good dispersibility; the Zeta potentials of the regenerated chitosan nanofibers prepared in Examples 1, 5, and 7 are specifically 24.32 mV, 28.43 mV, and 20.91 mV, respectively.

[0135] Figure 3 This is a particle size distribution diagram of the chitosan regenerated nanofiber dispersion; sample A is from Example 1, sample B is from Example 5, and sample C is from Example 7. Figure 3 It can be seen that the particle size distribution of the regenerated chitosan nanofibers is between 2 and 12 μm. The particle sizes of the regenerated chitosan nanofibers prepared in Examples 1, 5, and 7 are specifically 3.58 μm, 7.81 μm, and 10.59 μm, respectively.

[0136] Figure 4 The images show transmission electron microscopy (TEM) images of chitosan-regenerated nanofibers; where a represents Example 1, b represents Example 5, and c represents Example 7. Figure 4It can be seen that: the morphology of the chitosan regenerated nanofibers prepared in Example 1 is single and without branches; the morphology of the chitosan regenerated nanofibers prepared in Example 5 is dendritic; and the morphology of the chitosan regenerated nanofibers prepared in Example 7 is network.

[0137] Table 1 shows the test results of the chitosan regenerated nanofibers obtained in the examples and comparative examples. As can be seen from Table 1, the morphology of the chitosan regenerated nanofibers obtained from different pretreatment materials, different polyols, and different alkali systems differs, and these pretreatments also have a certain impact on the solubility of chitosan.

[0138] Table 1. Morphological and structural characteristics of chitosan nanofibers prepared in the examples and comparative examples.

[0139]

[0140] Tables 2 and 3 compare the chitosan dissolution rate and degree of polymerization in the examples and comparative examples. As can be seen from Tables 2 and 3, the treatment methods of Examples 1-7 do not significantly damage the degree of polymerization of chitosan.

[0141] Table 2 Comparison of chitosan dissolution rate and degree of polymerization in the examples

[0142]

[0143] Table 3 Comparison of chitosan dissolution rate and degree of polymerization in comparative examples

[0144]

[0145] Tables 4 and 5 compare the dispersion performance of chitosan nanofibers in the examples and comparative examples. As can be seen from Tables 4 and 5, the chitosan regenerated nanofibers prepared in Examples 1-7 are well dispersed in water, alcohol, alkali and DMF systems; it is difficult to achieve multi-solvent dispersion by changing the parameters.

[0146] Table 4 Comparison of Chitosan Nanofiber Dispersion Performance in Examples

[0147]

[0148] Table 5. Comparison of Chitosan Nanofiber Dispersion Performance in Comparative Examples

[0149]

[0150] Figure 5 These are actual photos of the chitosan nanofiber dispersion after standing for two months; from left to right, they are Example 1, Example 3, Example 5, and Example 7. Figure 5 It can be seen that after two months of standing, the chitosan nanofiber dispersion did not show any aggregation, indicating that it has good dispersibility.

[0151] Figure 6 These are actual photos taken after chitosan nanofibers have been dispersed in an alkaline system and left to stand for two months; from left to right, they are Example 1 and Comparative Example 3. Figure 6 It is evident that the sample in Example 1, when dispersed in the alkaline system and left to stand for 2 months, remained uniformly dispersed, while the sample in Comparative Example 3 showed signs of aggregation and sedimentation.

[0152] Figure 7 These are actual photos taken after the chitosan nanofiber dispersion from Example 1 has been dispersed in different systems and allowed to stand for two months. From left to right, the systems are: water, alkali, alcohol, and DMF. Figure 7 It is evident that the sample from Example 1 is well dispersed in aqueous systems, alkaline systems, alcohol systems, and organic solvents (DMF).

[0153] Example 8 Aerogel

[0154] Chitosan nanofiber dispersion (hereinafter referred to as dispersion) prepared in Example 1 was used to prepare chitosan nanofiber aerogel using the one-way ice template method.

[0155] Specifically, the steps include the following:

[0156] (1) Filter the dispersion using a 1000-mesh filter bag and rinse repeatedly with deionized water until the dispersion is neutral (pH=7); then redisperse with deionized water until the solid content of the dispersion is 2.5%;

[0157] (2) A bottom cold source needs to be built first using a foam box, liquid nitrogen, and a thermally conductive copper block. A silicone mold is placed on top of the thermally conductive copper block. The redispersed dispersion is slowly injected into the silicone mold to freeze and solidify, thus obtaining the aerogel precursor.

[0158] (3) The aerogel precursor was placed in a freeze dryer and freeze-dried for 48 hours to obtain chitosan nanofiber aerogel.

[0159] The obtained chitosan aerogel was subjected to performance testing, and the test results are as follows:

[0160] Figure 8 This is a scanning electron microscope (SEM) image of an axial section of chitosan nanofiber aerogel from Example 8. From... Figure 8 As can be seen, the scanning electron microscope image of chitosan nanofiber aerogel shows a parallel and regularly arranged layered structure. This structure can effectively enhance the thermal insulation performance of the aerogel. The thermal conductivity of the chitosan nanofiber aerogel prepared by this method is 0.033 W / mK. Moreover, the aerogel structure is intact and does not easily shed.

[0161] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for rapidly preparing a chitosan nanofiber dispersion liquid having a controllable morphology and a multi-solvent dispersibility, characterized by, The method includes the following three approaches: Method 1: Single root without branches (1) Chitosan is dispersed in lithium salt or lithium alkali solution for pretreatment to obtain pretreated chitosan; wherein the mass ratio of chitosan to lithium salt solution is 10-30:400; the mass ratio of chitosan to lithium alkali solution is 10-30:400; (2) Add the pretreated chitosan to an acetic acid solution containing one or both of isopropanol and tert-butanol, stir to dissolve, and obtain a completely dissolved chitosan solution. (3) Add dilute alkaline aqueous solution dropwise to the completely dissolved chitosan solution until the solution is weakly alkaline to obtain a single, branchless chitosan regenerated nanofiber dispersion. Method 2: Tree-like (1) Chitosan is dispersed in lithium salt or lithium alkali solution for pretreatment to obtain pretreated chitosan; wherein the mass ratio of chitosan to lithium salt solution is 10-30:400; the mass ratio of chitosan to lithium alkali solution is 10-30:400; (2) Add the pretreated chitosan to an acetic acid solution containing one or both of isopropanol and tert-butanol, stir to dissolve, and obtain a completely dissolved chitosan solution. (3) Add the dilute alkaline aqueous solution containing nonionic surfactant dropwise to the completely dissolved chitosan solution until the solution is weakly alkaline to obtain a dendritic chitosan regenerated nanofiber dispersion. Among them, the dilute alkaline aqueous solution containing nonionic surfactant is a NaOH aqueous solution containing nonionic surfactant, and the ratio of nonionic surfactant, NaOH and water is 10-30mL: 15-25g: 1900-2000mL. Method 3: Mesh (1) Chitosan is dispersed in lithium salt or lithium alkali solution for pretreatment to obtain pretreated chitosan; wherein the mass ratio of chitosan to lithium salt solution is 10-30:400; the mass ratio of chitosan to lithium alkali solution is 10-30:400; (2) Add the pretreated chitosan to an acetic acid solution containing one or both of isopropanol and tert-butanol, stir to dissolve, and obtain a completely dissolved chitosan solution. (3) The completely dissolved chitosan solution is added dropwise to a dilute alkaline aqueous solution until the solution is weakly alkaline, thus obtaining a network-like chitosan regenerated nanofiber dispersion.

2. The method of claim 1, wherein, In step (1) of Method 1, the pretreatment is to stir at 35-75℃ and 100-500rpm for 0.2-1h, and then take it out and wash it with water.

3. The method of claim 1, wherein, In step (2) of Method 1, the stirring and dissolving process involves stirring at 55-65℃ and 100-500rpm for 30-120 minutes.

4. The method of claim 1, wherein, In step (3) of Method 1, the dilute alkaline aqueous solution is a NaOH aqueous solution with a mass concentration of 0.5-3%.

5. The method of claim 1, wherein, In step (3) of Method 1, the dripping rate is 20-40 mL / min; the dripping process is accompanied by stirring, and the stirring speed is 300-500 rpm.

6. The method of claim 1, wherein, In step (3) of Method 2, the dripping rate is 20-40 mL / min; the dripping process is accompanied by stirring, and the stirring speed is 300-500 rpm.

7. The method of claim 1, wherein, In step (3) of Method 3, the dripping rate is 20-40 mL / min; the dripping process is accompanied by stirring, and the stirring speed is 300-500 rpm.

8. The method according to claim 1, characterized in that, In step (3) of Method 2, the nonionic surfactant is one or both of AEO-9 and APG.

9. The chitosan nanofiber dispersion with controllable morphology and multi-solvent dispersibility prepared by the method according to any one of claims 1-8.

10. The application of the chitosan nanofiber dispersion with controllable morphology and multi-solvent dispersibility as described in claim 9 in the fields of drug preparation, tissue engineering preparation, food packaging preparation, daily chemical product preparation, or functional material preparation.

11. A method of improving the stability of chitosan fibers in a multi-solvent system while maintaining the degree of polymerization, characterized by, The chitosan nanofiber dispersion with controllable morphology and multi-solvent dispersibility as described in claim 9 was used.

12. An aerogel, characterized in that, The chitosan nanofiber dispersion with controllable morphology and multi-solvent dispersibility as described in claim 9 was used.

13. A heat-insulating and heat-preserving material, characterized in that, The chitosan nanofiber dispersion with controllable morphology and multi-solvent dispersibility as described in claim 9 was used.

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