Carboxylated CNF (punicalagin / chitosan core-shell fiber as well as preparation and application thereof

Abstract

The invention discloses a carboxylated CNF (punicalagin / chitosan core-shell fiber as well as preparation and application thereof, and belongs to the technical field of functional fiber preparation. The punicalagin is used as a bio-based functional component, and carboxylated CNF (carboxylated cellulose nanofiber) with negative electricity is introduced as a reinforcing skeleton for synergistic interaction, so that the mechanical property and water resistance of the chitosan fiber are improved, and the chitosan fiber is endowed with functional characteristics of oxidation resistance, bacteria resistance and the like. According to the invention, crop waste resources are fully utilized, and introduction of toxic cross-linking agents is reduced. Meanwhile, the invention provides a coaxial spinning method adopting core-shell blending, chitosan with positive electricity in a shell layer and carboxylated CNF with negative electricity in a core layer are mutually diffused and wrapped through ion complexing, swelling fracture of the fiber is improved, the water absorption effect is achieved through surface wrinkles and internal pores, and the water absorption effect is improved. The material is expected to be applied to the fields of surgical sutures, wound hemostatic dressings and the

Description

TECHNICAL FIELD

[0001] The present application relates to a carboxylated CNF@ punicalagin / chitosan core-shell fiber and its preparation and application, and belongs to the technical field of functional fiber preparation. BACKGROUND

[0002] Chitosan is a natural polycationic polysaccharide, which has excellent biocompatibility, biodegradability, antibacterial property and hemostatic activity, and is widely used in biomedical, textile and environmental materials fields. However, the chitosan molecular chain has strong rigidity and significant intermolecular hydrogen bonding, so the chitosan fiber has high brittleness, low strength and poor flexibility, and is easily swollen and degraded, which seriously restricts the expansion of application fields.

[0003] Punicalagin has significant biological activity, and studies have shown that it has multiple pharmacological potentials such as antioxidant, anti-inflammatory, antitumor, antiviral and broad-spectrum inhibition of foodborne pathogenic bacteria.

[0004] At present, some researchers have combined pomegranate peel extract or punicalagin with chitosan to prepare bio-based materials. For example: Nishant Kumar et al. (KUMAR N, PRATIBHA, PETKOSKA A T, et al. Chitosan Edible Films Enhanced with Pomegranate Peel Extract: Study on Physical, Biological, Thermal, and Barrier Properties [J]. Materials, 2021, 14(12). http: / / doi.org / 10.3390 / ma14123305.) incorporated different concentrations of pomegranate peel extract as reinforcing agent into chitosan-based edible film, and the tensile strength, antioxidant activity and antibacterial property of the prepared film were improved; Mirella R.V. Bertolo et al. (BERTOLO M R V, DE OLIVEIRA FILHO J G, LAMONICA G C, et al. Improvement of the physical chemical, microbiological, volatiles and sensory quality of strawberries covered with chitosan / gelatin / pomegranate peel extract-based coatings [J]. Food Chemistry, 2025, 471: 142755. http: / / doi.org / 10.1016 / j.foodchem.2025.142755.) studied the improvement of the rheological properties and antibacterial properties of chitosan / gelatin-based coating materials with pomegranate peel extract; Duraiarasan Surendhira et al. (SURENDHIRAN D, LI C Z, CUI H Y, LIN L. Fabrication of high stability active nanofibers encapsulated with pomegranate peel extract using chitosan / PEO for meat preservation [J]. Food Packaging and Shelf Life, 2020, 23. http: / / doi.org / 10.1016 / j.fpsl.2019.100439.) prepared chitosan / polyethylene glycol / pomegranate peel extract high-stability active nanofiber membranes by electrospinning technology, which had good mechanical properties, antibacterial and antioxidant activity, and could be used for meat preservation.

[0005] However, these studies mainly focus on coatings, food preservation films, etc., mainly studying the tensile strength, antioxidant activity, antibacterial properties, etc. of the film; and there are few studies on the preparation of composite fibers by wet method, and there are few concerns about the anti-swelling properties, thermal stability, etc. SUMMARY

[0006] [TECHNICAL PROBLEM] Chitosan fibers have poor mechanical properties, high brittleness and insufficient flexibility, etc. Chitosan fibers have poor water stability and are easily swollen, with decreased mechanical properties and unstable size in a wet environment, which limits their wide application.

[0007] [Technical scheme] To solve the above problems, the application provides a carboxylated CNF@ punicalagin / chitosan core-shell fiber and a preparation and application thereof. Specifically, the application takes punicalagin as a bio-based functional component and introduces a negatively charged carboxylated CNF (carboxylated cellulose nanofiber) as a reinforced framework to improve the mechanical properties and water resistance of chitosan fibers, and to endow them with functional properties such as antioxidant and antibacterial properties. The application makes full use of crop waste resources while reducing the introduction of toxic cross-linking agents. Meanwhile, the application provides a coaxial spinning method of core-shell blending, and the positively charged chitosan in the shell layer and the negatively charged carboxylated CNF in the core layer are diffused and wrapped through ionic complexation, improving the swelling and breaking of the fiber, and realizing the water absorption effect through the surface wrinkles and internal pores, which is expected to be applied in surgical sutures, wound hemostatic dressings and other fields.

[0008] The first object of the application is to provide a method for preparing a carboxylated CNF@ punicalagin / chitosan core-shell fiber, comprising the following steps: The carboxylated CNF@ punicalagin / chitosan core-shell fiber is obtained by using a carboxylated cellulose nanofiber suspension with a mass concentration of 1-4% as the core layer spinning solution, using a chitosan / punicalagin mixed solution as the shell layer spinning solution, through coaxial spinning, coagulation in a coagulation bath, washing, immersion in a glycerol solution, taking out, and freeze-drying.

[0009] In an embodiment of the application, the preparation method of the chitosan / punicalagin mixed solution is as follows: The punicalagin solution is added to the chitosan solution and mixed uniformly to obtain a chitosan / punicalagin mixed solution; The punicalagin solution is a punicalagin aqueous solution, and the amount of water is sufficient to ensure the dissolution of punicalagin; The mass concentration of chitosan in the chitosan / punicalagin mixed solution is 1-3%, the mass concentration of acetic acid is 1-3%, and the amount of punicalagin is 2.5-10% of the mass of chitosan; The chitosan solution is a chitosan acetic acid aqueous solution; during the preparation process, the chitosan needs to be mechanically stirred at a speed of 300-500 rpm for 3-8 h under the condition of a 35-45℃ water bath to ensure that the chitosan is fully dissolved; The uniform mixing is carried out by mechanical stirring at a speed of 300-500 rpm for 1-4 h under the condition of a 35-45℃ water bath.

[0010] In an embodiment of the application, the flow rates of the core layer spinning solution and the shell layer spinning solution in the coaxial spinning are the same, and are 0.8-1.2 mL / min.

[0011] In an embodiment of the present application, the gauge of the needle in the coaxial spinning is 14-19G, the inner diameter of the needle is 0.70 mm, and the outer diameter of the needle is 1.60 mm; the carboxylated cellulose nanofiber suspension as the core layer has strong fluidity, and the inner diameter of the needle is too large to easily cause leakage of the core layer; the chitosan / punicalagin mixed solution has high viscosity, and the outer diameter is too small to easily cause needle blockage in the spinning process, affecting the wrapping of the core layer and the uniformity of the fiber.

[0012] In an embodiment of the present application, the syringe of the chitosan / punicalagin mixed solution is connected with the outer diameter of the 14-19G coaxial needle in the coaxial spinning; the syringe containing the carboxylated cellulose nanofiber suspension is connected with the inner diameter of the needle, and the two syringes are placed on the micro-injection pump, and then injected into the coagulation bath through the coaxial spinning needle.

[0013] In an embodiment of the present application, the coagulation bath is obtained by mixing a sodium hydroxide aqueous solution with anhydrous ethanol in a mass ratio of 2.5-3.5:1; since the carboxylated cellulose nanofiber suspension cannot be formed in the coagulation bath, the chitosan / punicalagin mixed solution as the shell layer increases in diameter during the coaxial spinning, and needs to be coagulated and formed faster, and through the pre-experiment, the mass concentration of the sodium hydroxide aqueous solution in the coagulation bath needs to be increased to 5%, which can ensure the smooth spinning.

[0014] In an embodiment of the present application, the cleaning is water cleaning.

[0015] In an embodiment of the present application, the glycerol solution is a glycerol aqueous solution with a mass fraction of 0.8-1.2%; the immersion is 0.5-2 h at 20-30℃ (room temperature).

[0016] In an embodiment of the present application, the freeze-drying is freezing at-80℃ for 20-30 h, and freeze-drying in the freeze-drying machine for 40-50 h.

[0017] The second object of the present application is the carboxylated CNF@ punicalagin / chitosan core-shell fiber prepared by the method of the present application.

[0018] In an embodiment of the present application, the carboxylated CNF@ punicalagin / chitosan core-shell fiber has a core-shell structure.

[0019] The third object of the present application is the application of the carboxylated CNF@ punicalagin / chitosan core-shell fiber of the present application in the preparation of functional materials.

[0020] In an embodiment of the present application, the functional materials include medical supplies, and the medical supplies include surgical sutures, wound hemostatic dressings, etc.

[0021] The fourth objective of this invention is to provide a method for improving the mechanical properties, water absorption properties, and thermal stability of chitosan, comprising the following steps: Using a 1-4% (w / w) carboxylated cellulose nanofiber suspension as the core spinning solution and a chitosan / punicin mixed solution as the shell spinning solution, coaxial spinning, coagulation in a coagulation bath, washing, immersion in a glycerol solution, removal, and freeze-drying were performed to obtain carboxylated CNF@punicin / chitosan core-shell fibers.

[0022] [Beneficial Effects] (1) The breaking strength of CNF-C@CS / PL fiber shows a trend of first increasing and then decreasing with the increase of CNF-C suspension concentration. The strength of 2% CNF-C@CS / PL fiber is the highest compared with CS / PL hollow fiber, increasing by 200%.

[0023] (2) The weight loss rate and mass loss rate of 2% CNF-C@CS / PL fiber are much smaller than those of CS / PL hollow fiber. The weight loss rate of 2% CNF-C@CS / PL fiber is 1 / 3 that of CS / PL hollow fiber, and the mass loss rate is 1 / 4 that of CS / PL hollow fiber. The temperature corresponding to the maximum thermal decomposition rate of 2% CNF-C@CS / PL fiber is 13% higher than that of CS / PL hollow fiber, and the heat resistance stability is enhanced.

[0024] (3) The water absorption rates of 1%, 2%, and 3% CNF-C @CS / PL fibers are all around 400%, mainly due to water absorption from surface wrinkles and internal pores. No excessive swelling has occurred, leading to breakage. They are expected to be used in wound dressings and other fields. Attached Figure Description

[0025] Figure 1 The diagram shows the preparation process and diffusion mechanism of Examples 1-4 and Comparative Example 1.

[0026] Figure 2 The results show the test results of breaking strength (a) and breaking elongation (b) of the fibers prepared in Examples 1-4 and Comparative Example 1.

[0027] Figure 3 SEM images of the fiber surfaces of Comparative Example 1(a) and Example 1(b).

[0028] Figure 4 The images show the cross-sectional SEM images (a) and cross-sectional SEM images (b) of the fiber in Comparative Example 1, as well as a magnified view of a portion thereof.

[0029] Figure 5 The images show cross-sectional SEM images (a) and cross-sectional SEM images (b) of the fiber in Example 1, as well as a magnified view of a portion thereof.

[0030] Figure 6SEM images of cross-sections of fibers prepared in Examples 2(a), 1(b), 3(c), and 4(d).

[0031] Figure 7 This is an EDS image of the cross-section of the fiber in Comparative Example 1.

[0032] Figure 8 This is an EDS image of the cross-section of the fiber in Example 1.

[0033] Figure 9 The X-ray diffraction patterns are for the fibers of Comparative Example 1 and Example 1.

[0034] Figure 10 The thermogravimetric (a) and mass loss rate (b) curves of fibers for Comparative Example 1 and Example 1 are shown.

[0035] Figure 11 The fiber water absorption rate is for Comparative Example 1.

[0036] Figure 12 This is a comparison of the fiber before and after water absorption in Examples 1-4.

[0037] Figure 13 The fiber water absorption rate curves are for Examples 1-4.

[0038] Figure 14 The results are for Comparative Example 5. Detailed Implementation

[0039] 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.

[0040] Test method: 1. SEM: After gold sputtering, the samples were examined using scanning electron microscopy (SEM) and cold field emission scanning electron microscopy (CFE) to observe the surface, cross-section, and microstructure of the fibers. The scanning voltage was 5 kV.

[0041] 2. X-ray diffraction: The crystallization properties of the fibers were analyzed using X-ray diffraction. The scanning rate was 4° / min, and the scanning range was 5°–80° (2θ).

[0042] 3. Mechanical properties: The mechanical properties of fibers were tested using a YG004 electronic single-fiber tensile testing machine.

[0043] The experimental parameters were: tensile speed: 20 mm / min, clamping distance: 20 mm, and 20 tests per sample.

[0044] 4. Water absorption rate: Using deionized water as the medium, completely dried fibers were immersed in a certain amount of deionized water at room temperature to absorb water. The samples were carefully removed from the liquid at different times within 30 minutes. The deionized water on the sample surface was then wiped clean with filter paper, and the weight was recorded as W. t The water absorption rate is denoted as Q and is calculated using the following formula.

[0045] In the formula: Q is the water absorption rate, W t The mass of the sample after water absorption is expressed in g; W o The mass of the sample when it is dried is in grams. Each sample was tested three times.

[0046] 5. Thermogravimetric analysis: The thermal stability of fibers was measured using a fully automated thermogravimetric analyzer.

[0047] The experiment was conducted under nitrogen atmosphere, with a temperature range of 25℃-700℃ and a heating rate of 10℃ / min.

[0048] Raw materials used in the examples: Chitosan: Deacetylation degree ≥85%, viscosity 1150 mPa·s, purchased from Qingdao Yunzhou Biotechnology Co., Ltd. Punic glycoside: Pomegranate peel extract, content 40.5%, purchased from Shaanxi Haochen Biotechnology Co., Ltd.; Carboxylated cellulose nanofibers: diameter: 4-10nm, length: 200nm; purchased from Suzhou Great Medical Technology Co., Ltd.

[0049] Example 1 A method for preparing carboxylated CNF@punicaloside / chitosan core-shell fibers includes the following steps: (1) Preparation of chitosan / punicin mixed solution: Chitosan (CS) and an aqueous acetic acid solution were mixed and mechanically stirred at 400 rpm for 4 hours in a 40°C water bath to fully dissolve the chitosan, thus obtaining a chitosan solution. Dissolve pungent glycoside (PL) in a very small amount of water to obtain a pungent glycoside solution; then add the pungent glycoside solution to the above chitosan solution, and mechanically stir at a rate of 400 rpm for 2 h under a water bath at 40°C to make the two uniformly mixed, thus obtaining a chitosan / pungent glycoside mixed solution. In the chitosan / punical glycoside mixed solution, the mass concentration of chitosan was 2%, and the mass concentration of acetic acid was 2%. The mass ratio of punicalin to chitosan was 5:100, and the amount of punicalin used was 5% of the mass of chitosan. (2) Preparation of carboxylated cellulose nanofiber (CNF-C) suspension: Carboxylated cellulose nanofibers were dispersed in water and mechanically stirred at 500 rpm for 3 hours at 40°C using a water bath to obtain a suspension of carboxylated cellulose nanofibers with a mass concentration of 2%. (3) Coaxial spinning: Using a carboxylated cellulose nanofiber suspension as the core spinning solution and a chitosan / punicalloside mixed solution as the shell spinning solution, a syringe containing the chitosan / punicalloside mixed solution was connected to the outer diameter of a 14-19G coaxial needle (needle inner diameter 0.70 mm, needle outer diameter 1.60 mm), and a syringe containing the carboxylated cellulose nanofiber suspension was connected to the inner diameter of the needle. Both syringes were placed on a microinjection pump, and the injection was carried out at a rate of 1... Two spinning solutions were injected into a coaxial spinning needle at a flow rate of mL / min into a coagulation bath (a mixture of 5% sodium hydroxide aqueous solution and anhydrous ethanol at a mass ratio of 3:1). After washing with deionized water, the solution was immersed in a 1% glycerol aqueous solution at 25°C for 1 hour. Then, it was first frozen in an ultra-low temperature freezer at -80°C for 24 hours, and then dried in a freeze dryer for 48 hours to obtain carboxylated CNF@punicaloside / chitosan core-shell fiber (labeled as 2% CNF-C@CS / PL according to the concentration of the carboxylated cellulose nanofiber suspension).

[0050] Example 2 The mass concentration of the carboxylated cellulose nanofiber suspension in Example 1 was adjusted to 1%, while other aspects remained the same as in Example 1, to obtain carboxylated CNF@pungillin / chitosan core-shell fibers (labeled as 1%CNF-C@CS / PL according to the concentration of the carboxylated cellulose nanofiber suspension).

[0051] Example 3 The mass concentration of the carboxylated cellulose nanofiber suspension in Example 1 was adjusted to 3%, while other aspects remained the same as in Example 1, to obtain carboxylated CNF@punicaloside / chitosan core-shell fibers (labeled as 3%CNF-C@CS / PL according to the concentration of the carboxylated cellulose nanofiber suspension).

[0052] Example 4 The mass concentration of the carboxylated cellulose nanofiber suspension in Example 1 was adjusted to 4%, while other aspects remained the same as in Example 1, to obtain carboxylated CNF@punicaloside / chitosan core-shell fibers (labeled as 4%CNF-C@CS / PL according to the concentration of the carboxylated cellulose nanofiber suspension).

[0053] Comparative Example 1 In Example 1, the carboxylated cellulose nanofiber suspension was changed to deionized water, while other aspects remained the same as in Example 1, resulting in hollow fibers (CS / PL hollow fibers).

[0054] The obtained fibers were subjected to performance tests, and the test results are as follows: Figure 1 The diagram shows the preparation process and diffusion mechanism of Examples 1-4 and Comparative Example 1. Fibers were prepared and collected using wet spinning with a coaxial needle, followed by freeze-drying. In the coagulation bath, CS / PL diffused into the inner layer due to concentration and the attraction of positive and negative charges, while CNF-C diffused into the outer layer. The two diffused towards each other and formed ion complexes internally. The outermost layer rapidly solidified and formed an encapsulation under the action of the coagulation bath.

[0055] Figure 2 The results show the breaking strength (a) and breaking elongation (b) of the fibers prepared in Examples 1-4 and Comparative Example 1. Figure 2 It can be seen that as the concentration of CNF-C suspension in the core layer increases, the tensile strength of CNF-C@CS / PL fiber shows a trend of first increasing and then decreasing. The strength of 2% CNF-C@CS / PL fiber is the highest compared with that of CS / PL hollow fiber, increasing by 200%. At this point, the theoretical mass ratio of the shell layer to the core layer of CNF-C@CS / PL fiber reaches 1:1, and the fiber mechanical properties reach the best, with a tensile strength of 6.20 MPa and a tensile elongation of 23.16%.

[0056] Figure 3 SEM images of the fiber surfaces of Comparative Example 1(a) and Example 1(b). Figure 4 The images show the cross-sectional SEM images (a) and cross-sectional SEM images (b) of the fiber in Comparative Example 1, as well as a magnified view of a portion thereof. Figure 5 The images show cross-sectional SEM images (a) and cross-sectional SEM images (b) of the fiber from Example 1, as well as a magnified view of a portion thereof. Figures 3-5 It can be seen that both CS / PL hollow fibers and 2%CNF-C@CS / PL fibers have wrinkled structures on their surfaces, while the rest of the surface is smooth. The cross-sectional microstructure of the CS / PL hollow fibers reveals a distinct hollow structure, with the outer shells converging towards the center due to external pressure during the cutting process. The 2%CNF-C@CS / PL fibers exhibit a network-like structure internally, with the CNF-C core layer and chitosan shell layer linked by ionic complexation, which supports their strength. The external pressure during cutting did not cause significant outer shell aggregation, indicating that the internal connections within the fiber provide support. Irregular nanoscale pores also form during the freeze-drying process.

[0057] Figure 6 Cross-sectional SEM images of the fibers prepared in Examples 2(a), 1(b), 3(c), and 4(d). Figure 6It can be seen that when the CNF-C concentration in the core layer increases to more than 3%, the porosity of CNF-C@CS / PL fibers increases. This may be because the CNF-C concentration is too high, and the theoretical ratio of CNF-C to chitosan dry weight reaches 3:2. This can easily cause core layer leakage and reduce the complexation rate during spinning. Furthermore, the CS / PL shell is not tightly wrapped. This also verifies the strength law of CNF-C@CS / PL fibers.

[0058] Figure 7 and Figure 8 EDS images of cross-sections of the fibers from Comparative Example 1 and Example 1. From Figure 7 and Figure 8 It can be seen that there is no N element distribution inside the hollow CS / PL fiber, forming a distinct hollow structure; while the N, C, and O elements are clearly distributed inside the CNF-C@CS / PL fiber, indicating that the positively charged chitosan in the outer shell of the core-shell fiber is ionically complexed with the negatively charged carboxylated cellulose nanofibers in the core layer, and the solvent is replaced in the coagulation bath, so that the shell and core layers not only form an encapsulation, but also form a tight internal connection.

[0059] Figure 9 X-ray diffraction patterns of the fibers from Comparative Example 1 and Example 1 are shown. Figure 9 It can be seen that CS / PL hollow fibers and 2%CNF-C@CS / PL fibers have significant characteristic absorption peaks at 2θ=20.3° and 20.5°, respectively, with the 2%CNF-C@CS / PL fiber exhibiting a sharper absorption peak at this location. This indicates that the orderliness of the molecular chain arrangement within the fiber increases due to ion complexation. The X-ray diffraction peaks of both fibers are similar, and no new phase is formed.

[0060] Figure 10 The thermogravimetric (a) and mass loss rate (b) curves for Comparative Example 1 and Example 1 are shown. From... Figure 10 It can be seen that the TG(a) and DTG(b) curves of CS / PL hollow fiber and 2% CNF-C@CS / PL fiber exhibit three stages: The first stage is around 30-100℃, which mainly removes physically adsorbed water and bound water. In this stage, the weight loss rate and mass loss rate of 2%CNF-C@CS / PL fiber are much smaller than those of CS / PL hollow fiber. The weight loss rate of 2%CNF-C@CS / PL hollow fiber is 1 / 3 of that of CS / PL hollow fiber, and the mass loss rate is 1 / 4 of that of CS / PL hollow fiber. The second stage, at 200-300℃, involves sugar ring dehydration, polymer backbone degradation, and glycosidic bond breakage. The 2% CNF-C@CS / PL fiber and CS / PL hollow fiber reached their maximum thermal decomposition rates at 247.5℃ and 218.3℃, respectively, with the temperature corresponding to the maximum thermal decomposition rate increasing by 13%. This is because strong electrostatic interactions and ionic complexes form between chitosan and carboxylated CNF, essentially creating "molecular bridges" between the shells. This strengthens the network structure of the entire system and also restricts the movement of molecular chains when heated, requiring even higher temperatures for the molecular backbone to begin breaking. In the third stage, after reaching 400℃, the residual carbon in chitosan slowly decomposes, and the remaining substances undergo further oxidation and pyrolysis. The residual weight ratio of 2% CNF-C@CS / PL fiber is higher than that of CS / PL hollow fiber.

[0061] Figure 11 The fiber water absorption rate is for Comparative Example 1. Figure 12 This is a comparison of the fiber before and after water absorption in Examples 1-4. Figure 13 The fiber water absorption rate curves are for Examples 1-4. From... Figure 11 , Figure 12 , Figure 13 It can be seen that CS / PL hollow fibers exhibit rapid water absorption within 30 seconds, with a water absorption rate exceeding 3500%, leading to excessive swelling and breakage. The surface of CS / PL hollow fibers has numerous wrinkles and lacks a porous structure, primarily exhibiting high-swelling failure. CNF-C@CS / PL fibers completely overcome the shortcomings of high-speed swelling and breakage in CS / PL hollow fibers. The introduced carboxylated CNF acts as a nanofiber reinforcing network in the core layer, achieving a transformation towards "tough swelling." The water absorption rates of 1% CNF-C@CS / PL and 2% CNF-C@CS / PL fibers increased due to the presence of more and more stable pores. The water absorption rate of 3% CNF-C@CS / PL fiber was lower due to a poorer internal network structure. All three fibers maintained a water absorption rate of around 400% (367%, 428%, and 316% for 1%, 2%, and 3% CNF-C@CS / PL fibers, respectively). 4% CNF-C@CS / PL fiber exhibited the highest water absorption rate and showed a macroscopic swelling effect. This was due to the addition of excessive carboxylated CNF. SEM results also revealed a large hollow structure within the fiber, resulting in a less compact internal network structure, where shell swelling dominated the effect.

[0062] Comparative Example 2 The order of the core and shell layers in Example 1 was adjusted, and a carboxylated cellulose nanofiber suspension was used as the shell spinning solution, while a chitosan / punicin mixed solution was used as the core spinning solution. Everything else remained the same as in Example 1.

[0063] The results showed that spinning was impossible, and the carboxylated cellulose nanofibers in the shell would escape into the coagulation bath and could not form a coating.

[0064] Comparative Example 3 The mass concentration of the carboxylated cellulose nanofiber suspension in Example 1 was adjusted to 5%, while other aspects remained the same as in Example 1.

[0065] The results showed that the core layer leaked, affecting fiber quality.

[0066] Comparative Example 4 In Example 1, pungent glycoside (PL) was replaced with tea polyphenols (purity 50%+, RG, Shanghai Titan Technology Co., Ltd.), while other aspects remained the same as in Example 1.

[0067] The results showed that insufficient shell viscosity led to poor shell solidification and incomplete encapsulation.

[0068] Comparative Example 5 The core spinning solution and the chitosan / punicin mixed solution from Example 1 were mixed evenly at a mass ratio of 1:1 to form a composite spinning solution; Everything else remains the same as in Example 1.

[0069] The results showed that during the mixing process, the positive charge of chitosan and the negative charge of carboxylated CNF interacted violently, resulting in high agglomeration of the composite spinning solution, making wet spinning impossible. Figure 14 .

[0070] Comparative Example 6 The coagulation bath in Example 1 was replaced with a 3% sodium hydroxide aqueous solution and anhydrous ethanol mixed at a mass ratio of 3:1. Everything else remains the same as in Example 1.

[0071] The results showed that the shell solidification rate was too slow, which affected the shell's encapsulation of the core and fiber formation.

[0072] 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 of preparing carboxylated CNF@punicalagin / chitosan core-shell fibers, characterized by, It comprises the following steps: The carboxylated CNF@ punicalin / chitosan core-shell fiber is obtained by the following steps: taking the carboxylated cellulose nanofiber suspension with a mass concentration of 1-4% as the core layer spinning solution, taking the chitosan / punicalin mixed solution as the shell layer spinning solution, performing coaxial spinning, solidifying in a coagulation bath, cleaning, immersing in a glycerol solution, taking out, and freeze-drying.

2. The method of claim 1, wherein, The preparation method of the chitosan / punicalin mixed solution is as follows: The punicalin solution is added into the chitosan solution and uniformly mixed to obtain the chitosan / punicalin mixed solution.

3. The method of claim 2, wherein, The mass concentration of chitosan in the chitosan / punicalin mixed solution is 1-3%, and the amount of punicalin is 2.5-10% of the mass of chitosan.

4. The method of claim 1, wherein, In the coaxial spinning, the flow rates of the core layer spinning solution and the shell layer spinning solution are the same, being 0.8-1.2 mL / min.

5. The method of claim 1, wherein, The coagulation bath is obtained by mixing a sodium hydroxide aqueous solution with a mass fraction of 5-8% and anhydrous ethanol according to a mass ratio of 2.5-3.5:

1.

6. The method of claim 1, wherein, The glycerol solution is a glycerol aqueous solution with a mass fraction of 0.8-1.2%.

7. The method of claim 1, wherein, In the coaxial spinning, the gauge of the needle is 14-19G.

8. The carboxylated CNF@ punicalin / chitosan core-shell fiber prepared by the method of any one of claims 1-7.

9. The carboxylated CNF@ punicalin / chitosan core-shell fiber of claim 8 in the preparation of functional materials.

10. A method for improving the mechanical properties, water absorption properties, and thermal stability of chitosan, characterized by, It comprises the following steps: The carboxylated CNF@ punicalin / chitosan core-shell fiber is obtained by the following steps: taking the carboxylated cellulose nanofiber suspension with a mass concentration of 1-4% as the core layer spinning solution, taking the chitosan / punicalin mixed solution as the shell layer spinning solution, performing coaxial spinning, solidifying in a coagulation bath, cleaning, immersing in a glycerol solution, taking out, and freeze-drying.

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