Preparation method of porous multi-scale fiber with core-shell structure

Abstract

The invention relates to the technical field of electrostatic spinning, in particular to a preparation method of a porous multi-scale fiber with a core-shell structure. The problem that the air permeability and the antibacterial property of the porous multi-scale fiber prepared by the traditional production method cannot be considered at the same time is solved. According to the preparation method, polyvinyl alcohol with proper temperature and proper molecular weight is selected when a core layer polymer melt is prepared, so that tetrabutyl titanate, polyvinyl alcohol and SiO2 sol are promoted to form a uniform cross-linked structure; the middle-layer fiber takes sugarcane fibril as a main raw material, impurities are removed through a mixed solution, and components for improving a gap structure are added to form a fine fiber network; the two closely cooperate to improve the air permeability of the material; the core-shell fibers are uniformly distributed in combination with dissolution and electrostatic spinning parameters of polylactic acid; the core-shell structure porous multi-scale fiber obtained by dipping treatment with a silver nitrate solution keeps a good breathable structure while enhancing the antibacterial property, and the breathable and antibacterial properties of the core-shell structure porous multi-scale fiber are synergistically enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of electrospinning, and particularly to a method for preparing porous multi-scale fibers with a core-shell structure. Background Art

[0002] After modification, the physical and chemical properties of the fibers change. For example, after surface modification of polyester fibers, they are more widely used in fields such as automotive engineering and construction; secondly, some modified fibers can enhance specific properties. For example, after modification with graphene and high-density polyethylene, the mechanical and heat resistance properties of polypropylene fibers are significantly improved; in addition, modified fibers may also increase biocompatibility. For example, when modified PP fibers are used as biological carriers, the number of fixed bacteria is far more than that of unmodified fibers.

[0003] Fibers with a core-shell structure possess the excellent properties of both the core layer and the shell layer. For example, the mechanical strength and good thermal conductivity coefficient can be controllably obtained; secondly, the special structure greatly improves the use value of the fibers and broadens the application fields; furthermore, in the field of biomedicine, core-shell structure magnetic fibers can provide a good microenvironment for cell growth and have excellent biocompatibility; in short, by controlling the internal structure and surface morphology of the fibers, composite fibers with a porous structure inside and a protective shell layer outside can be prepared, which have broad application prospects in fields such as health protection, materials science, oil-water separation, and electromagnetic protection.

[0004] Existing methods for preparing porous multi-scale fibers with a core-shell structure, such as the solution spinning method, dissolve different polymers in a solvent, stretch the solution into slender fibers by means of a spinning process, and form different core-shell structures by adjusting the solvent evaporation rate or the fiber cooling rate. This method is simple to operate and easy to achieve large-scale production, but often faces problems such as uneven fiber morphology and great difficulty in structure control, resulting in a complex structure of the prepared porous multi-scale fibers with a core-shell structure, which causes hindered gas flow and thus affects their air permeability; while the phase separation method forms a porous structure by using phase separation of two immiscible polymers in a solvent. During the spinning process, fibers with different pore sizes and multi-scale characteristics can be formed by adjusting the phase separation temperature and the solvent selection. This method can effectively control the pore structure of the fibers, but has high requirements for the fiber size and the uniformity of the core-shell structure. Uneven porosity and core-shell ratio of the fibers during the preparation process will affect the loading amount and release rate of the antibacterial agent, thus affecting their antibacterial performance.

[0005] In summary, it is difficult for the porous multi-scale fibers manufactured by traditional methods to maintain good air permeability while meeting high antibacterial performance.

[0006] Therefore, a method for preparing porous multi-scale fibers with a core-shell structure is proposed. Summary of the Invention

[0007] The object of the present invention is to provide a method for preparing porous multi-scale fibers with a core-shell structure. In the present invention, when preparing the core-layer polymer melt, appropriate temperature and appropriate molecular weight polyvinyl alcohol are selected to promote the formation of a uniform cross-linked structure of tetrabutyl titanate, polyvinyl alcohol and SiO2 sol; the intermediate-layer fibers use sugarcane fibrils as the main raw material, are decontaminated by a mixed solution and added with components to improve the pore structure to form a fine fiber network; the two work closely together to improve the air permeability of the material; by combining the dissolution of polylactic acid and the electrospinning parameters, the core-shell fibers are evenly distributed; the core-shell structure porous multi-scale fibers obtained by impregnation treatment with silver nitrate solution maintain a good air-permeable structure while enhancing the antibacterial performance, and synergistically enhance the air permeability and antibacterial performance of the core-shell structure porous multi-scale fibers.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] The present invention provides a method for preparing porous multi-scale fibers with a core-shell structure, and the preparation method is as follows:

[0010] The core-layer polymer melt and the shell-layer polymer solution are respectively ejected and spun on the upper layer and the lower layer of the base layer by a coaxial electrospinning machine to form core-shell nanofibers; wherein, the intermediate-layer fibers serve as the base layer of the coaxial electrospinning; the core-layer polymer melt is prepared from polyvinyl alcohol, a cross-linking agent, distilled water and SiO2 sol; the shell-layer polymer solution is obtained by stirring and mixing polylactic acid and a solvent;

[0011] The core-shell nanofibers are impregnated with a silver nitrate solution to obtain the core-shell structure porous multi-scale fibers;

[0012] The core-shell structure includes a core-layer polymer melt, intermediate-layer fibers and a shell-layer polymer solution.

[0013] Preferably, the preparation method of the core-layer polymer melt is as follows: 30 parts of polyvinyl alcohol (PVA) with a concentration of 5% is used as the matrix, 0.3 parts of tetrabutyl titanate (TBT) is used as the cross-linking agent, 40 parts of distilled water is added, and 3 parts of SiO2 sol is slowly added, and stirred evenly at 75-85 °C by a magnetic stirrer to form the core-layer polymer melt; the molecular weight of polyvinyl alcohol (PVA) is 1600-1900.

[0014] Preferably, the preparation method of the core-layer polymer melt is as follows: 30 parts of polyvinyl alcohol with a concentration of 5% is used as the matrix, 0.3 parts of the cross-linking agent, 40 parts of distilled water is added, and 3 parts of SiO2 sol is slowly added, and stirred evenly at 75-85 °C by a magnetic stirrer to form the core-layer polymer melt; the molecular weight of polyvinyl alcohol is 1600-1900; the cross-linking agent is tetrabutyl titanate.

[0015] Preferably, the SiO2 sol is prepared as follows: tetraethyl orthosilicate (TEOS) is added to distilled water, where the ratio of tetraethyl orthosilicate (TEOS) to distilled water is 3-5:1; 0.1 part of ammonia water is slowly added, and the mixture is stirred at room temperature for 1.5 h to form a uniform SiO2 sol; the concentration of ammonia water is 25%.

[0016] Preferably, the intermediate layer fiber is prepared as follows: bagasse is crushed to obtain bagasse powder with a particle size of 80 mesh; 100 parts of bagasse powder are placed in a water bath at 60 °C and stirred for 2 h, and the bagasse raw fiber is obtained after filtration and washing; the bagasse raw fiber is placed in a mixed solution of zinc chloride and sodium hydroxide with a ratio of 1-3:1, and stirred at 75 °C for 1 h to remove the xylan component and impurities in the bagasse raw fiber, and the bagasse fiber is obtained by filtration; 60 parts of bagasse fiber, 15 parts of chitosan, 15 parts of activated carbon, and 10 parts of polyvinyl alcohol are put into a beaker, and distilled water is added and stirred for 1 h to obtain the first intermediate layer mixture; the first intermediate layer mixture is filtered through a vacuum funnel with a pressure of 0.5-0.7 MPa and a screen pore size of 50 mesh to obtain a preliminary intermediate layer; the preliminary intermediate layer is placed in a vacuum drying oven at 60 °C and dried for 24 h, and then hot-pressed into an intermediate layer fiber; the concentration of the zinc chloride aqueous solution in the mixed aqueous solution is 1%, and the concentration of the sodium hydroxide aqueous solution is 3%.

[0017] Preferably, the shell polymer solution is prepared as follows: a solvent is added to 50 parts of polylactic acid (PLA), and the mixture is stirred in a magnetic stirrer at a temperature of 45 °C and a rotation speed of 600 rpm for 3 h to form a shell polymer solution; where the ratio of polylactic acid (PLA) to the solvent is 1:0.9, and the concentration of polylactic acid (PLA) is 10%.

[0018] Preferably, the solvent is any one of 1,4-dioxane (1,4-Dioxane), ethyl acetate (EA), dichloromethane (DCM), and ethanol (ET).

[0019] Preferably, the core-shell nanofibers (NFs) are prepared as follows: the core layer polymer melt and the shell polymer solution are respectively pumped into the inner needle and the outer needle, and the intermediate layer fiber is placed on the collecting plate of a coaxial electrospinning machine as the base layer of coaxial electrospinning. Then, the distance from the nozzle to the collecting plate is set to 18 cm, the rotation speed of the collecting plate is 2500 rpm, and under the conditions of a DC voltage of 25-30 kV and a liquid supply rate of 0.3-0.5 mL / h, the core layer polymer melt and the shell polymer solution are sprayed and spun on the upper layer and the lower layer of the base layer by the coaxial electrospinning machine to form core-shell nanofibers (NFs).

[0020] Preferably, the method for preparing the porous multi-scale fibers with a core-shell structure is as follows: Immerse the core-shell nanofibers (NFs) in a silver nitrate solution for 1 h at room temperature. After loading silver nanoparticles (AgNPs), wash the sample in distilled water and dry it in an oven at 45 °C for 2 h to obtain the porous multi-scale fibers with a core-shell structure.

[0021] Preferably, the concentration of the silver nitrate solution is 15-18 mmol / L.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. During the preparation of the porous multi-scale fibers with a core-shell structure, a moderate concentration and molecular weight of polyvinyl alcohol in the core layer polymer melt will promote the formation of a uniformly dispersed cross-linked structure of tetrabutyl titanate, polyvinyl alcohol, and SiO2 sol; when preparing the intermediate layer fibers, use a mixed solution of zinc chloride and sodium hydroxide to remove impurities and purify the sugarcane raw fibers and add an appropriate amount of polyvinyl alcohol to form a fine fiber network with a fiber diameter of 2.09-2.25 μm in the prepared material; the two work together to further improve the air permeability of the porous multi-scale fibers with a core-shell structure.

[0024] 2. Using DCM as the solvent for dissolving polylactic acid, selecting tetrabutyl titanate as a mild cross-linking agent to prepare the core layer polymer melt, and controlling the ratio of the number of parts of tetraethyl orthosilicate (TEOS) to distilled water within the range of 3-5:1, and maintaining the ammonia water concentration at 25%, the prepared porous multi-scale fibers have a uniform thickness. Tetrabutyl titanate interacts with polyvinyl alcohol and SiO2 sol through hydrolysis and condensation reactions to generate a stable network structure of PVA / SiO2-TiO2 melt. The porous multi-scale fibers with a core-shell structure prepared through the subsequent electrospinning process are soft to the touch and have good air permeability.

[0025] 3. By using an appropriate electrospinning voltage, liquid supply rate, and precisely adjusting the structure of the core and shell layer materials, the electric field force received by the solution after it is ejected from the nozzle is uniform. The tensile force and traction force of the electric field on the core layer polymer melt and the shell layer polymer solution make the core layer fibers and the shell layer fibers evenly distributed on both sides of the base layer fibers; the diameter of the prepared core-shell nanofibers is moderate, and the uniformity is increased. The porous multi-scale fibers with a core-shell structure obtained after impregnation treatment have the performance of resisting external bacteria.

[0026] 4. During the impregnation treatment, the core-shell nanofibers are immersed in a silver nitrate solution with a concentration of 15 - 18 mmol / L, and the concentration of the silver nitrate solution and the immersion time are coordinated with each other; silver nitrate can enable the core-shell nanofibers to carry silver nanoparticles, enhancing the resistance of the porous multi-scale fibers with a core-shell structure to bacteria. At the same time, during the loading process, the overall structure of the material is not damaged, and the pore structure that is beneficial to air permeability formed before is still maintained, enabling the air permeability and antibacterial properties of the porous multi-scale fibers with a core-shell structure to be enhanced simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the porous multi-scale fiber structure with a core-shell structure of the present invention.

[0028] In the figure: 1. Core layer fiber; 2. Intermediate layer fiber; 3. Shell layer fiber. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] Please refer to Figure 1 , the present invention provides a preparation method for porous multi-scale fibers with a core-shell structure, and the technical solution is as follows:

[0031] The substances involved in the present invention are as follows:

[0032] Tetrabutyl titanate CAS: 5593 - 70 - 4; Tetraethyl orthosilicate CAS: 78 - 10 - 4; Ammonia water CAS: 12336 - 21 - 6; Zinc chloride CAS: 7646 - 85 - 7; Sodium hydroxide CAS: 1310 - 73 - 2; Chitosan CAS: 9012 - 76 - 4; 1,4 - Dioxane CAS: 123 - 91 - 1; Ethyl acetate CAS: 141 - 78 - 6; Dichloromethane CAS: 75 - 09 - 2; Ethanol CAS: 64 - 17 - 5; Silver nitrate CAS: 7761 - 88 - 8; Polyvinyl alcohol is purchased from Anhui Wanwei High - tech Materials Co., Ltd.; Polylactic acid model is PLA - 6252D; Coaxial electrospinning machine is purchased from Shanghai Chubo Laboratory Equipment Co., Ltd.

[0033] Among them, the ratio of polylactic acid (PLA) to dichloromethane (DCM) is the "volume ratio"; in addition, the "ratio" mentioned in the present invention is the "mass ratio" unless otherwise specified.

[0034] Example 1

[0035] The preparation method of SiO2 sol is as follows: Add tetraethyl orthosilicate into distilled water, where the ratio of tetraethyl orthosilicate to distilled water is 5:1; Slowly add 0.1 part of ammonia water, stir and react at room temperature for 1.5 h to form a uniform SiO2 sol; The concentration of ammonia water is 25%.

[0036] The preparation method of the core layer polymer melt is as follows:

[0037] Take 30 parts of polyvinyl alcohol with a concentration of 5% as the matrix, 0.3 part of tetrabutyl titanate as the cross-linking agent, add 40 parts of distilled water, and slowly add 3 parts of SiO2 sol, and stir evenly at 75 - 85 °C with a magnetic stirrer to form the core layer polymer melt; The molecular weight of polyvinyl alcohol (PVA) is 1600 - 1900; The obtained core layer polymer melt is PVA / SiO2 - TiO2 melt.

[0038] The preparation method of the intermediate layer fiber is as follows: Crush bagasse and select bagasse powder with a particle size of 80 mesh; Place 100 parts of bagasse powder in a water bath at 60 °C and stir for 2 h, and obtain raw bagasse fibers after filtration and washing; Place the raw bagasse fibers in a mixed solution of zinc chloride and sodium hydroxide with a ratio of 1:1, stir at 75 °C for 1 h to remove the xylan component and impurities in the raw bagasse fibers, and filter to obtain bagasse fibers; Put 60 parts of bagasse fibers, 15 parts of chitosan, 15 parts of activated carbon, and 10 parts of polyvinyl alcohol into a beaker, add distilled water and stir for 1 h to obtain the first intermediate layer mixture; Filter the first intermediate layer mixture with a vacuum funnel with a pressure of 0.7 MPa and a sieve pore size of 50 mesh to obtain the preliminary intermediate layer; Place the preliminary intermediate layer in a vacuum drying oven at 60 °C and dry for 24 h, and then hot press to form the intermediate layer fiber; The concentration of zinc chloride aqueous solution in the mixed aqueous solution is 1%, and the concentration of sodium hydroxide aqueous solution is 3%.

[0039] The preparation method of the shell layer polymer solution is as follows: Add ethyl acetate to 50 parts of polylactic acid and stir in a magnetic stirrer at a temperature of 45 °C and a rotation speed of 600 rpm for 3 h to form the shell layer polymer solution; Among them, the ratio of polylactic acid to ethyl acetate is 1:0.9, and the concentration of polylactic acid is 10%.

[0040] Pump the core layer polymer melt and the shell layer polymer solution into the inner needle and the outer needle respectively, place the intermediate layer fiber on the collecting plate of the coaxial electrospinning machine as the base layer of coaxial electrospinning, then set the distance from the nozzle to the collecting plate to 18 cm, the rotation speed of the collecting plate to 2500 rpm, and under the conditions of a DC voltage of 25 - 30 kV and a liquid supply rate of 0.3 - 0.5 mL / h, spray and spin the core layer polymer melt and the shell layer polymer solution on the upper and lower layers of the base layer through the coaxial electrospinning machine to make core - shell nanofibers.

[0041] The core-shell nanofibers were immersed in a silver nitrate solution with a concentration of 15 mmol / L for 1 h at room temperature. After loading AgNPs, the samples were washed in distilled water and dried in an oven at 45 °C for 2 h to obtain the porous multi-scale fibers with a core-shell structure. As Figure 1 shown, the porous multi-scale fiber structure of the core-shell structure of the present invention includes a core layer fiber 1, an intermediate layer fiber 2, and a shell layer fiber 3.

[0042] Example 2-11

[0043] Compared with Example 1, the parameters were adjusted, and the specific summary is shown in Table 1; the temperature in Table 1 is the temperature of the magnetic stirrer in the preparation method of the core layer polymer melt; the pressure is the pressure of filtering the intermediate layer mixture 1 with a vacuum funnel.

[0044] Table 1 Process parameter adjustment of Examples 1-11

[0045] Example Temperature / °C PVA Molecular Weight <![CDATA[TEOS:H2O / parts]]> <![CDATA[ZnCl2: NaOH / parts]]> Pressure / MPa Example 1 75 1650 5.0：1.0 1.0：1.0 0.70 Example 2 76 1750 3.6：1.0 1.2：1.0 0.58 Example 3 77 1600 4.8：1.0 1.4：1.0 0.56 Example 4 78 1690 4.6：1.0 1.6：1.0 0.68 Example 5 79 1700 4.4：1.0 1.8：1.0 0.66 Example 6 80 1790 4.2：1.0 2.0：1.0 0.63 Example 7 81 1870 4.0：1.0 2.2：1.0 0.60 Example 8 82 1900 3.2：1.0 2.4：1.0 0.50 Example 9 83 1890 3.4：1.0 2.6：1.0 0.52 Example 10 84 1850 3.8：1.0 2.8：1.0 0.55 Example 11 85 1780 3.0：1.0 3.0：1.0 0.65

[0046] Examples 12-20

[0047] Referring to the process flow and preparation method of Example 11, but some of the parameters were changed, and the specific summary is shown in Table 2; the DC voltage and the liquid supply rate in Table 2 are the DC voltage and the liquid supply rate of the coaxial electrospinning machine in the preparation method of the core-shell nanofibers.

[0048] Table 2 Process parameter adjustment of Examples 11-20

[0049]

[0050] In order to verify the necessity of some technical solutions in the present invention for achieving the technical effects of the present invention, some comparative examples of the present invention will be shown and described below.

[0051] Comparative Example 1

[0052] Different from Example 1, when preparing the core layer polymer melt, 30 parts of polyvinyl alcohol (PVA) with a concentration of 10% was used as the matrix, and the molecular weight of polyvinyl alcohol (PVA) was 13000, and other process parameters were the same.

[0053] Comparative Example 2

[0054] Different from Example 1, when preparing the core layer polymer melt, glutaraldehyde was used as the cross-linking agent, and the temperature of the magnetic stirrer was set at 100 °C, and other process parameters were the same.

[0055] Comparative Example 3

[0056] Different from Example 1, when preparing the SiO2 sol, the ratio of tetraethyl orthosilicate (TEOS) to distilled water is 1:1, and the concentration of ammonia water added is 15%. All other process parameters are the same.

[0057] Comparative Example 4

[0058] Different from Example 1, when preparing the intermediate layer fiber, polyvinyl alcohol is not added, and the pressure of the vacuum funnel is 0.3 MPa. All other process parameters are the same.

[0059] Comparative Example 5

[0060] Different from Example 1, when preparing the intermediate layer fiber, the sugarcane raw fiber (SF) is placed in distilled water. All other process parameters are the same.

[0061] Comparative Example 6

[0062] Different from Example 1, when preparing the core-shell nanofibers (NFs), the DC voltage is 15 kV and the liquid supply rate is 0.1 mL / h. All other process parameters are the same.

[0063] Comparative Example 7

[0064] Different from Example 1, the shell layer polymer solution is electrospun on the upper layer of the substrate, and the core layer polymer melt is electrospun on the lower layer of the substrate. All other process parameters are the same.

[0065] Comparative Example 8

[0066] Different from Example 1, the core-shell nanofibers (NFs) are immersed in a silver nitrate solution with a concentration of 25 mmol / L at room temperature for 10 h. All other process parameters are the same.

[0067] Experimental Example 1 Air Permeability Test

[0068] The porosity was measured according to the GB / T 42697-2023 standard; the specific test results are shown in Table 3.

[0069] Table 3 Air Permeability of the Core-Shell Structured Porous Multi-Scale Fibers Prepared in Examples 2-5, Example 11, Examples 15-17 and Comparative Example 1, Comparative Examples 4-5

[0070] Example Fiber Diameter / μm Porosity / % Example 2 2.14 85.87 Example 3 2.25 86.26 Example 4 2.09 85.02 Example 5 2.13 85.83 Example 6 2.15 85.96 Example 11 2.28 86.37 Example 15 2.12 85.89 Example 16 2.15 86.05 Example 17 2.13 85.91 Comparative Example 1 50.2 - Comparative Example 4 8.27 98.2 Comparative Example 5 1.23 65.4

[0071] Table 3 shows the test results of the fiber diameter, porosity, and air permeability of the porous multi-scale fibers with a core-shell structure prepared in Examples 2-6, Example 11, Examples 15-17, and Comparative Examples 1, 4-5. According to the test results, it can be seen that the fiber diameters measured in Examples 2-4, Example 11, and Examples 15-17 are uniform, and the porosity of the material is stable between 85.03% and 86.37%. In Comparative Example 1, when preparing the core-layer polymer melt, 30 parts of polyvinyl alcohol with a concentration of 10% was used as the matrix, and the molecular weight of polyvinyl alcohol was 13,000; the concentration and molecular weight of polyvinyl alcohol were much higher than those in the above examples. As the concentration and molecular weight of polyvinyl alcohol increased, the viscosity of the prepared core-layer polymer melt increased, resulting in tetrabutyl titanate being unable to form a cross-linked structure with the high-viscosity polyvinyl alcohol, and polyvinyl alcohol could not be dispersed in the core-layer polymer melt, thus unable to form a stable solution; at the same time, the high-viscosity solution led to insufficient fiber stretching during the electrospinning process, making it difficult to form a fine fiber network; too high viscosity also caused difficulties in nozzle spraying, resulting in thicker fibers and clogging of the spinneret holes, thereby making it impossible to accurately measure the porosity of the prepared material. In Comparative Example 4, when preparing the intermediate-layer fibers, no polyvinyl alcohol was added, and the pressure of the vacuum funnel was 0.3 MPa; polyvinyl alcohol acts as a cross-linking agent during the preparation process. When no polyvinyl alcohol is added, the bonding between sugarcane fibers, chitosan, and activated carbon becomes weaker, the structure of the generated material becomes loose, the gap between fibers increases, and the fiber diameter becomes larger, resulting in an increase in porosity. However, this structure obviously does not improve the air permeability of the material. On the contrary, it will lead to poorer connectivity between pores, restricting the path of air circulation, thereby resulting in a decrease in air permeability. Since distilled water was used instead of the mixed solution of zinc chloride and sodium hydroxide in Comparative Example 5, a large amount of xylan components and impurities were contained in the sugarcane fibers; the xylan components reacted with the chitosan added during the preparation of the intermediate-layer fibers, and the charcoal physically adsorbed the impurities, thus seriously affecting the preparation process of the intermediate-layer fibers, resulting in a decrease in the crystallinity of the prepared intermediate-layer fibers, more smaller-diameter fibers becoming amorphous, and the smaller-diameter fibers swelling faster, thereby leading to a decrease in the porosity and air permeability of the prepared porous multi-scale fibers with a core-shell structure, and the air permeability performance of the material becoming worse. In summary, during the preparation of the porous multi-scale fibers with a core-shell structure, a moderate concentration and molecular weight of polyvinyl alcohol in the core-layer polymer melt will promote the formation of a uniformly dispersed cross-linked structure of tetrabutyl titanate, polyvinyl alcohol, and SiO2 sol; when preparing the intermediate-layer fibers, using the mixed solution of zinc chloride and sodium hydroxide to remove impurities and purify the sugarcane raw fibers and adding an appropriate amount of polyvinyl alcohol can enable the prepared material to form a fine fiber network with a fiber diameter of 2.09-2.25 μm; the two work together to further improve the air permeability performance of the porous multi-scale fibers with a core-shell structure.

[0072] Experimental Example 2 Air Permeability Test

[0073] The air permeability rate was measured with reference to the standard of GB / T 24218.15-2017; the specific test results are shown in Table 4.

[0074] Table 4 Air Permeability of the Core-Shell Structured Porous Multiscale Fibers Prepared in Examples 8-15 and Comparative Examples 2-3

[0075]

[0076]

[0077] The thickness, mass per unit area and air permeability rate of the core-shell structured porous multiscale fibers prepared in Examples 8-15 and Comparative Examples 2-3 were tested according to the data in Table 4. According to the test results, it can be seen that the core-shell structured porous multiscale fiber measured in Example 15 has the thinnest thickness, with a thickness of 0.383 mm and a mass per unit area of 49.28 g·m -2 , and its air permeability rate can reach 1324.6 L / m 2·s. This is because different solvents are added in the preparation of the shell polymer solution, and the evaporation rates of various solvents from fast to slow are arranged as DCM > ET > EA > 1,4 - Dioxane. When using DCM as the solvent to dissolve polylactic acid, the evaporation rate of DCM is relatively fast at 45°C. During the preparation of the core - shell structure, the polymer is rapidly stretched during the electrospinning process, and the rapidly volatilized DCM will cause the shell polymer solution to quickly concentrate and solidify on the surface of the substrate, resulting in a smaller fiber diameter. The formed material has a uniform thickness and is thinner than the materials formed by ET, EA, and 1,4 - Dioxane solvents, with a smaller mass per unit area, thereby improving the air permeability of the porous multi - scale fibers of the core - shell structure and having better air - permeable performance. In Comparative Example 2, when preparing the core - layer polymer melt, glutaraldehyde was used as the cross - linker, and the temperature of the magnetic stirrer was set at 100°C. Due to the too high temperature, the acetal reaction rate between glutaraldehyde and the hydroxyl groups in the polyvinyl alcohol molecules through the aldehyde groups was too fast, resulting in a rapid cross - linking reaction. The SiO2 sol locally aggregated in the system, causing uneven cross - linking of the core - layer polymer melt, reducing the flexibility of the prepared material, becoming brittle and hard during the electrospinning process, and showing fracture phenomena; the material thickness and mass per unit area increased, and the air permeability decreased significantly, and the air - permeable performance decreased significantly. In Comparative Example 3, when preparing the SiO2 sol, the ratio of the number of parts of tetraethyl orthosilicate to distilled water was 1:1, and the concentration of ammonia water added was 15%; since the role of ammonia water is that the hydroxide ions in ammonia water attack the silicon - ethoxy groups in the tetraethyl orthosilicate molecules, promoting its hydrolysis reaction and accelerating the formation of intermediate products containing silanol groups; when the concentration of ammonia water decreases, the concentration of hydroxide ions decreases, and the ability to attack the silicon - ethoxy bonds in the tetraethyl orthosilicate molecules becomes weak, resulting in the hydrolysis reaction not being able to proceed quickly and effectively; at the same time, the insufficient water content causes the tetraethyl orthosilicate molecules not to be able to fully contact enough water molecules for hydrolysis, resulting in a low content of the generated SiO2 sol and containing more tetraethyl orthosilicate impurities inside, causing an increase in the product of the thickness and mass per unit area of the porous multi - scale fibers of the formed core - shell structure and a significant decrease in the air permeability. In summary, when using DCM as the solvent to dissolve polylactic acid, selecting tetrabutyl titanate as a mild cross - linker to prepare the core - layer polymer melt and controlling the ratio of the number of parts of tetraethyl orthosilicate to distilled water within the range of 3 - 5:1, and maintaining the ammonia water concentration at 25%, the prepared porous multi - scale fibers have a uniform thickness. Tetrabutyl titanate interacts with polyvinyl alcohol and SiO2 sol through hydrolysis and condensation reactions to form a stable network - structured PVA / SiO2 - TiO2 melt. The porous multi - scale fibers of the core - shell structure prepared through the subsequent electrospinning process have a soft hand feeling and good air - permeable performance.

[0078] Experimental Example 3 Antibacterial Performance Test

[0079] After a gentle washing, the number of Escherichia coli colonies and the antibacterial rate of Escherichia coli on the porous multi-scale fibers with a core-shell structure were measured in a relatively dry and clean environment. The number of Escherichia coli colonies and the antibacterial rate of Escherichia coli on the porous multi-scale fibers with a core-shell structure were measured according to the standard of GB / T 20944.2-2007. The specific test results are shown in Table 5.

[0080] Table 5 Antibacterial properties of the porous multi-scale fibers with a core-shell structure prepared in Examples 8-11, Examples 19-20 and Comparative Examples 6-7 against Escherichia coli

[0081] Example Escherichia coli Colony Count / CFU Escherichia coli Antibacterial Rate / % Example 8 13 96.2 Example 9 10 96.5 Example 10 8 97.4 Example 11 3 98.6 Example 19 4 98.5 Example 20 6 97.6 Comparative Example 6 33 87.6 Comparative Example 7 134 57.3

[0082] The data in Table 5 tested the number of Escherichia coli colonies and the antibacterial rate of Escherichia coli on the porous multi-scale fibers with a core-shell structure prepared in Examples 8-11, Examples 19-20 and Comparative Examples 6-7 after a gentle washing. According to the test results, after one washing, the number of Escherichia coli colonies in Examples 8-11 and Examples 19-20 was maintained within the range of 3-13 CFU, and the antibacterial rate of Escherichia coli was between 96.2% and 98.6%, proving that the prepared porous multi-scale fibers with a core-shell structure all had good anti-Escherichia coli performance. In Comparative Example 6, when preparing the core-shell nanofibers, the DC voltage of the coaxial electrospinning machine was set to 15 kV and the feeding rate was 0.1 mL / h. Due to the low DC voltage and feeding rate, the tensile force and traction force of the electric field on the core-layer polymer melt and the shell-layer polymer solution were weakened, and the electric field force received by the solution after spraying from the nozzle was uneven, prompting the stretched fibers to be in a finer state. The diameter of the prepared core-shell nanofibers increased and the non-uniformity increased, resulting in a significant reduction in the antibacterial performance of the porous multi-scale fibers with a core-shell structure obtained after impregnation treatment. In Comparative Example 7, the shell-layer polymer solution was spray-spun on the upper layer of the base layer, and the core-layer polymer melt was spray-spun on the lower layer of the base layer. The prepared porous multi-scale fibers with a core-shell structure showed that the density and viscosity of the core layer were greater than those of the shell layer, and the pores of the porous multi-scale fibers with a core-shell structure became larger, unable to achieve physical barrier to bacteria. Bacteria were more likely to penetrate the shell layer and enter the material interior, resulting in the ineffectiveness of the impregnation treatment and a significant reduction in the antibacterial timeliness. In summary, by using appropriate electrospinning voltage, feeding rate and the structure of the core and shell materials, the electric field force received by the solution after spraying from the nozzle is uniform, and the tensile force and traction force of the electric field on the core-layer polymer melt and the shell-layer polymer solution make the core-layer fibers and the shell-layer fibers evenly distributed on both sides of the base-layer fibers; the diameter of the prepared core-shell nanofibers is moderate and the uniformity increases, and the porous multi-scale fibers with a core-shell structure obtained after impregnation treatment have the performance of resisting external bacteria.

[0083] Experimental Example 4 Antibacterial performance test

[0084] After a mild washing, the number of Staphylococcus aureus colonies and the antibacterial rate of Staphylococcus aureus of the core-shell structured porous multi-scale fibers were measured in a relatively dry and clean environment. The number of Staphylococcus aureus colonies and the antibacterial rate of Staphylococcus aureus of the core-shell structured porous multi-scale fibers were measured with reference to the standard of GB / T 20944.2-2007. The specific test results are shown in Table 6.

[0085] Table 6 Antibacterial properties of the core-shell structured porous multi-scale fibers prepared in Examples 15-20 and Comparative Example 8 against Staphylococcus aureus

[0086] Example Staphylococcus aureus Colony Count / CFU Staphylococcus aureus Antibacterial Rate / % Example 15 18 87.5 Example 16 17 87.7 Example 17 16 88.6 Example 18 15 89.8 Example 19 12 91.3 Example 20 13 90.2 Comparative Example 8 65 63.4

[0087] The data in Table 6 tested the number of Staphylococcus aureus colonies and the antibacterial rate of Staphylococcus aureus of the core-shell structured porous multi-scale fibers prepared in Examples 15-20 and Comparative Example 8 after a mild washing. According to the test results, after one washing, the number of Staphylococcus aureus colonies in Examples 15-20 was maintained within the range of 12-18 CFU, and the antibacterial rate of Staphylococcus aureus was 87.5-91.3%, proving that the prepared core-shell structured porous multi-scale fibers all had good anti-Staphylococcus aureus performance. In Comparative Example 8, the core-shell nanofibers were immersed in a 25 mmol / L silver nitrate solution at room temperature for 10 h. Due to the increase in the concentration of the silver nitrate solution, the amount of AgNPs loaded on the core-shell nanofibers increased, and the antibacterial performance against Staphylococcus aureus would be enhanced in a short time. However, with the prolongation of time, excessive AgNPs would diffuse into the interior and surface of the fibers and continue to aggregate to form larger particles in the adsorbed areas, resulting in an excessive AgNPs loading amount in some areas, affecting the stability of the fibers and reducing the antibacterial and air permeability of the fibers. In summary, selecting an appropriate silver nitrate solution concentration and impregnation time can enhance the resistance of the core-shell structured porous multi-scale fibers to bacteria.

[0088] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a porous multi-scale fiber with a core-shell structure, characterized in that: The preparation method is as follows: The core-shell nanofibers are prepared by respectively ejecting and spinning the core-layer polymer melt and the shell-layer polymer solution onto the upper layer and the lower layer of the base layer through a coaxial electrospinning machine; wherein, the intermediate-layer fibers serve as the base layer of the coaxial electrospinning; the core-layer polymer melt is prepared from polyvinyl alcohol, a crosslinking agent, distilled water and SiO2 sol; the shell-layer polymer solution is obtained by stirring and mixing polylactic acid and a solvent; The core-shell nanofibers are impregnated with a silver nitrate solution to obtain the porous multi-scale fibers with a core-shell structure; The core-shell structure includes the core-layer polymer melt, the intermediate-layer fibers and the shell-layer polymer solution.

2. The preparation method of a porous multi-scale fiber with a core-shell structure according to claim 1, characterized in that: The preparation method of the core-layer polymer melt is as follows: 30 parts of the polyvinyl alcohol with a concentration of 5% is used as the matrix, 0.3 part of the crosslinking agent is added, 40 parts of the distilled water is added, and 3 parts of the SiO2 sol is slowly added, and the mixture is stirred evenly at 75-85 °C by a magnetic stirrer to form the core-layer polymer melt; the molecular weight of the polyvinyl alcohol is 1600-1900; the crosslinking agent is tetrabutyl titanate.

3. The preparation method of a porous multi-scale fiber with a core-shell structure according to claim 2, characterized in that: The preparation method of the SiO2 sol is as follows: tetraethyl orthosilicate is added to the distilled water, wherein the ratio of the number of parts of tetraethyl orthosilicate to the distilled water is 3-5:1; 0.1 part of ammonia water is slowly added, and the mixture is stirred and reacted at room temperature for 1.5 h to form the uniform SiO2 sol; the concentration of the ammonia water is 25%.

4. The preparation method of a porous multi-scale fiber with a core-shell structure according to claim 1, characterized in that: The preparation method of the intermediate-layer fibers is as follows: bagasse is crushed, and sugarcane powder with a particle size of 80 mesh is selected; 100 parts of the sugarcane powder is placed in a water bath at 60 °C and stirred for 2 h, and the sugarcane raw fibers are obtained after filtration and washing; the sugarcane raw fibers are placed in a mixed solution of zinc chloride and sodium hydroxide with a ratio of 1-3:1, and stirred at 75 °C for 1 h to remove the xylan components and impurities in the sugarcane raw fibers, and the sugarcane fibers are obtained by filtration; 60 parts of the sugarcane fibers, 15 parts of chitosan, 15 parts of activated carbon and 10 parts of polyvinyl alcohol are put into a beaker, and distilled water is added and stirred for 1 h to obtain the first intermediate-layer mixture; the first intermediate-layer mixture is filtered through a vacuum funnel with a pressure of 0.5-0.7 MPa and a sieve pore size of 50 mesh to obtain the preliminary intermediate layer; the preliminary intermediate layer is placed in a vacuum drying oven at 60 °C and dried for 24 h and then hot-pressed into the intermediate-layer fibers; the concentration of the zinc chloride aqueous solution in the mixed solution is 1%, and the concentration of the sodium hydroxide aqueous solution is 3%.

5. The preparation method of a porous multi-scale fiber with a core-shell structure according to claim 1, characterized in that: The preparation method of the shell-layer polymer solution is as follows: the solvent is added to 50 parts of the polylactic acid, and the mixture is stirred at 45 °C and a rotation speed of 600 rpm by a magnetic stirrer for 3 h to form the shell-layer polymer solution; wherein, the ratio of the number of parts of the polylactic acid to the solvent is 1:0.9, and the concentration of the polylactic acid is 10%.

6. The preparation method of a porous multi-scale fiber with a core-shell structure according to claim 5, characterized in that: The solvent is any one of 1,4-dioxane, ethyl acetate, dichloromethane and ethanol.

7. The preparation method of a porous multi-scale fiber with a core-shell structure according to claim 1, characterized in that: The preparation method of the core-shell nanofibers is as follows: Pump the core-layer polymer melt and the shell-layer polymer solution into the inner needle and the outer needle respectively. Place the intermediate-layer fiber on the collection plate of the coaxial electrospinning machine as the base layer for coaxial electrospinning. Then set the distance from the nozzle to the collection plate to 18 cm and the rotation speed of the collection plate to 2500 rpm. Under the conditions of a DC voltage of 25 - 30 kV and a liquid supply rate of 0.3 - 0.5 mL / h, jet-spin the core-layer polymer melt and the shell-layer polymer solution through the coaxial electrospinning machine on the upper layer and the lower layer of the base layer to form the core-shell nanofibers.

8. A method for preparing a porous multi-scale fiber with a core-shell structure according to claim 1, characterized in that: The impregnation treatment method is as follows: Immerse the core-shell nanofibers in a silver nitrate solution and soak for 1 h at room temperature; after loading AgNPs, wash the sample in distilled water and dry it in an oven at 45 °C for 2 hours to obtain the porous multi-scale fibers with a core-shell structure.

9. A method for preparing a porous multi-scale fiber having a core-shell structure according to claim 8, characterized in that: The concentration of the silver nitrate solution is 15 - 18 mmol / L.

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