Carboxylated cnf@ punicalagin / chitosan core-shell fibers, preparation and application thereof

Abstract

The application discloses a kind of carboxylated CNF@ punicalagin / chitosan core-shell fibers and preparation and application thereof, belong to functional fiber preparation technical field.The application uses punicalagin as biological base functional component, and introduces negative carboxylated CNF (carboxylated cellulose nanofiber) as reinforcing framework, synergistic effect, improve chitosan fiber mechanical property and water resistance, and give it antioxidant, antibacterial and other functional properties.The application makes full use of crop waste resources, while reducing the introduction of toxic crosslinking agent.At the same time, the application provides a coaxial spinning method by core-shell blending, positively charged chitosan in shell layer and negatively charged carboxylated CNF in core layer diffuse and form wrapping by ion complexation, improve the swelling fracture of fiber, realize water absorption effect with its surface wrinkle and internal pore, and is expected to be applied in surgical suture, wound hemostatic dressing and other fields.

Description

Technical Field

[0001] This invention relates to a carboxylated CNF@punicaloside / chitosan core-shell fiber, its preparation and application, belonging to the field of functional fiber preparation technology. Background Technology

[0002] Chitosan is a natural polycationic polysaccharide with excellent biocompatibility, biodegradability, antibacterial properties, and hemostatic activity, making it widely used in biomedicine, textiles, and environmental materials. However, chitosan molecules are rigid and have significant intermolecular hydrogen bonding, resulting in brittle, low-strength, and poorly flexible chitosan fibers that are prone to swelling and degradation, severely limiting the expansion of its applications.

[0003] Punic glycosides have significant biological activity, and studies have shown that they possess various pharmacological potentials, including antioxidant, anti-inflammatory, antitumor, antiviral, and broad-spectrum inhibition of foodborne pathogens.

[0004] Currently, researchers have combined pomegranate peel extract or punicalin with chitosan to prepare bio-based materials. For example: Nishant Kumar et al. (KUMAR N, PRATIBHA, PETKOSKA AT, et al. ChitosanEdible 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 pomegranate peel extract at different concentrations as a reinforcing agent into chitosan-based edible films, and the tensile strength, antioxidant activity, and antibacterial properties of the prepared films were all improved. Mirella RV Bertolo et al. (BERTOLO MRV, DE OLIVEIRA FILHO JG, LAMONICA GC, 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 pomegranate peel extract on chitosan / gelatin-based coating materials. Duraiarasan Surendhira et al. (SURENDHIRAN D, LI CZ, CUI HY, LIN L. Fabrication of high stability active nanofibers encapsulated with pomegranatepeel 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 a highly stable active nanofiber membrane of chitosan / polyethylene glycol / pomegranate peel extract using electrospinning technology. The membrane has good mechanical properties, antibacterial and antioxidant activities, and can be used for meat preservation.

[0005] However, these studies mainly focus on coatings and food preservation films, primarily studying the tensile strength, antioxidant activity, and antibacterial properties of the films; while there are very few studies on the preparation of composite fibers by wet methods, and little attention is paid to properties such as anti-swelling performance and thermal stability. Summary of the Invention

[0006] [Technical Issues] Chitosan fibers have problems such as poor mechanical properties, high brittleness, and insufficient flexibility; Chitosan fibers have poor water resistance and are prone to swelling. Their mechanical properties decrease and their dimensions become unstable in humid environments, limiting their widespread application.

[0007] [Technical Solution] To address the aforementioned issues, this invention provides a carboxylated CNF@punicaloside / chitosan core-shell fiber, its preparation, and its applications. Specifically, this invention uses punicaloside as a bio-based functional component and introduces negatively charged carboxylated CNF (carboxylated cellulose nanofibers) as a reinforcing framework, synergistically improving the mechanical properties and water resistance of chitosan fibers, and endowing them with antioxidant and antibacterial functional properties. This invention fully utilizes agricultural waste resources while reducing the introduction of toxic crosslinking agents. Furthermore, this invention provides a coaxial spinning method using core-shell blending, where the positively charged chitosan in the shell layer and the negatively charged carboxylated CNF in the core layer diffuse through ionic complexation to form an encapsulation, improving fiber swelling and breakage. Its surface wrinkles and internal pores achieve water absorption, making it promising for applications in surgical sutures, wound hemostatic dressings, and other fields.

[0008] The first objective of this invention is to provide a method for preparing carboxylated CNF@punicaloside / chitosan core-shell fibers, 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.

[0009] In one embodiment of the present invention, the preparation method of the chitosan / punical glycoside mixed solution is as follows: Add the pungent glycoside solution to the chitosan solution and mix well to obtain a chitosan / pungent glycoside mixed solution; Among them, the pungent glycoside solution is an aqueous solution of pungent glycoside, and the amount of water used is just enough to dissolve the pungent glycoside; In the chitosan / punical glycoside mixed solution, the mass concentration of chitosan is 1-3%, the mass concentration of acetic acid is 1-3%, and the amount of punical glycoside is 2.5-10% of the mass of chitosan. Chitosan solution is an aqueous solution of chitosan and acetic acid; during preparation, it is necessary to mechanically stir at a rate of 300-500 rpm for 3-8 hours under a water bath at 35-45℃ to ensure that the chitosan is fully dissolved. The mixture is thoroughly mixed by mechanical stirring at a rate of 300-500 rpm for 1-4 hours under a water bath at 35-45℃.

[0010] In one embodiment of the present invention, the core spinning solution and the shell spinning solution have the same flow rate in coaxial spinning, which is 0.8-1.2 mL / min.

[0011] In one embodiment of the present invention, the needle specifications in coaxial spinning are 14-19G, with an inner diameter of 0.70 mm and an outer diameter of 1.60 mm. The carboxylated cellulose nanofiber suspension, which serves as the core layer, has high fluidity, and an excessively large inner diameter of the needle can easily cause core layer leakage. The chitosan / punicin mixed solution has high viscosity, and an excessively small outer diameter can easily cause needle blockage during spinning, affecting the coating of the core layer and the uniformity of the fibers.

[0012] In one embodiment of the present invention, the syringe containing the chitosan / punicin mixed solution in coaxial spinning is connected to the outer diameter of a 14-19G coaxial needle; the syringe containing the carboxylated cellulose nanofiber suspension is connected to the inner diameter of the needle. Both syringes are placed on a micro-injection pump and injected into the coagulation bath through the coaxial spinning needle.

[0013] In one embodiment of the present invention, the coagulation bath is obtained by mixing a 5-8% sodium hydroxide aqueous solution with anhydrous ethanol at a mass ratio of 2.5-3.5:1. Since the carboxylated cellulose nanofiber suspension cannot be formed in the coagulation bath, the chitosan / punicin mixed solution serves as the shell layer during coaxial spinning, and its diameter increases, requiring faster coagulation. According to preliminary experiments, the mass concentration of the sodium hydroxide aqueous solution in the coagulation bath needs to be increased to 5% to ensure smooth spinning.

[0014] In one embodiment of the present invention, the cleaning is performed using water.

[0015] In one embodiment of the present invention, the glycerol solution is an aqueous glycerol solution with a mass fraction of 0.8-1.2%; the immersion is performed at 20-30°C (room temperature) for 0.5-2 hours.

[0016] In one embodiment of the present invention, freeze drying is performed by freezing at -80°C for 20-30 hours or by freezing in a freeze dryer for 40-50 hours.

[0017] The second objective of this invention is to prepare carboxylated CNF@pungentinin / chitosan core-shell fibers using the method described herein.

[0018] In one embodiment of the present invention, the carboxylated CNF@punicaloside / chitosan core-shell fiber has a core-shell structure.

[0019] The third objective of this invention is the application of the carboxylated CNF@pungentinin / chitosan core-shell fiber described herein in the preparation of functional materials.

[0020] In one embodiment of the present invention, the functional material includes materials for preparing medical products, such as surgical sutures and wound hemostatic dressings.

[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 carboxylated cellulose nanofiber suspension 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). From... 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 for preparing carboxylated CNF@punicaloside / chitosan core-shell fibers, characterized in that, Includes the following steps: Using a carboxylated cellulose nanofiber suspension with a mass concentration of 1-4% as the core spinning solution and a chitosan / punicin mixed solution as the shell spinning solution, the nanofibers were obtained by coaxial spinning, coagulation in a coagulation bath, washing, immersion in glycerol solution, removal, and freeze-drying. In the chitosan / punical glycoside mixed solution, the mass concentration of chitosan is 1-3%, and the amount of punical glycoside is 2.5-10% of the mass of chitosan. The coagulation bath is obtained by mixing a 5-8% sodium hydroxide aqueous solution with anhydrous ethanol at a mass ratio of 2.5-3.5:

1.

2. The method according to claim 1, characterized in that, The preparation method of the chitosan / punical glycoside mixed solution is as follows: Add the pungent glycoside solution to the chitosan solution and mix well to obtain a chitosan / pungent glycoside mixed solution.

3. The method according to claim 1, characterized in that, In coaxial spinning, the core spinning solution and the shell spinning solution have the same flow rate, which is 0.8-1.2 mL / min.

4. The method according to claim 1, characterized in that, The glycerol solution is an aqueous solution of glycerol with a mass fraction of 0.8%-1.2%.

5. The method according to claim 1, characterized in that, The specifications for needles used in coaxial spinning are 14-19G.

6. The carboxylated CNF@punicaloside / chitosan core-shell fiber prepared by the method according to any one of claims 1-5.

7. The application of the carboxylated CNF@punicaloside / chitosan core-shell fiber as described in claim 6 in the preparation of functional materials.

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