Porous hollow hydrophilic polylactic acid nanofiber separation membrane and preparation method thereof

Abstract

The invention discloses a porous hollow hydrophilic polylactic acid nanofiber separation membrane and a preparation method thereof, and belongs to the technical field of oil-water separation materials, the porous hollow hydrophilic polylactic acid nanofiber separation membrane is prepared from biodegradable polylactic acid (PLA) and water-soluble polyvinyl alcohol (PVA) through a coaxial electrostatic spinning method, a shell layer of the porous hollow hydrophilic polylactic acid nanofiber separation membrane is PLA, and the shell layer of the porous hollow hydrophilic polylactic acid nanofiber separation membrane is a porous hollow hydrophilic polylactic acid nanofiber separation membrane. A core layer is water-soluble PVA, and then a layer of cellulose diacetate CDA nanofiber is spun on the surface through electrostatic spinning; finally, the prepared fiber membrane is immersed in deionized water to be subjected to ultrasonic treatment for 30 minutes, the porous hollow fiber membrane is obtained after drying, the prepared porous hollow hydrophilic polylactic acid nanofiber membrane has the advantages of being porous, high in specific surface area and hollow in structure, and the prepared membrane material is natural, degradable and non-toxic and harmless to the environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil-water separation materials, and particularly relates to a porous hollow hydrophilic polylactic acid nanofiber separation membrane and a preparation method thereof. BACKGROUND

[0002] In recent years, due to the increasing discharge of industrial oil-containing wastewater and the frequent occurrence of oil leakage accidents, the treatment of oil-containing wastewater has become a big problem. The membrane separation method has the advantages of simple preparation, low cost, high separation efficiency, etc., and is widely used in the field of oil-water separation. However, the traditional polymer membranes such as polystyrene, polyvinylidene fluoride and polyacrylonitrile have the problems of non-degradability and low separation efficiency, which will pollute the environment. Therefore, the application uses a biodegradable polylactic acid as the main raw material to prepare an oil-water separation material. According to the type of oil-water emulsion, the oil-water separation membrane mainly has two types: super-hydrophilic type and super-oleophilic type. Considering the problem that the membrane material will be contaminated by oil droplets, it is more challenging to design a super-hydrophilic membrane material. Therefore, it is of great significance to select a degradable material as the raw material to prepare a super-hydrophilic oil-water separation material.

[0003] Polylactic acid (PLA) is a bio-based polyester derived from renewable resources such as corn and starch. And PLA has biocompatibility, biodegradability and non-toxicity, and has been widely used in various fields. However, the mechanical properties and heat resistance of PLA are poor, and the prepared membrane filtration material has the problems of poor repeated use performance and inability to separate hot oil wastewater with high temperature. Water-soluble polyvinyl alcohol (PVA) is a water-soluble polymer with good water solubility and viscosity. Cellulose diacetate (CDA) is a regenerated cellulose fiber with biodegradability and hydrophilicity, and its hydrophilicity will vary greatly with the degree of substitution of its acetyl group. Therefore, the use of PLA / PVA / CDA to make oil-water separation membrane material has a wide application prospect.

[0004] At present, many researchers are very concerned about the hydrophilic modification of PLA membrane. Chinese patent CN109847598A discloses a super-hydrophilic self-cleaning oil-water separation membrane and its preparation method and application. The membrane is prepared by coating a super-hydrophilic coating containing carboxylate titanium coordination bond on the surface of a polymer membrane or a non-polymer membrane, which is prepared by reacting plant polyphenol and titanium dioxide precursor. The obtained oil-water separation membrane is super-hydrophilic, which can quickly separate various oil-water layered mixtures and surface-active oil-in-water emulsions. Meanwhile, the photocatalytic degradation property of titanium dioxide makes the membrane have excellent self-cleaning and antifouling performance. Chinese patent CN116036876A discloses a preparation method and application of a super-hydrophobic polylactic acid nanofiber membrane. The membrane with super-hydrophilic and biodegradable properties is produced by optimizing the molecular weight, optical isomer content and mixing ratio of PLA and polyglycolic acid, and spinning the PLA / polyglycolic acid blended fiber at a suitable spinning temperature and spinning speed. The fiber has uniform shape and size, and high orientation degree and crystallinity, and the super-hydrophilic and degradation resistance performance is significantly better than that of ordinary polyglycolic acid nanofiber. The super-hydrophilic coating preparation process of Chinese patent CN109847598A is relatively complicated, and the stability of the coating is insufficient. The molecular weight and mixing ratio of PLA and polyglycolic acid in Chinese patent CN116036876A are not easy to control, and it is difficult to achieve high oil-water separation efficiency. SUMMARY

[0005] Technical problems to be solved:

[0006] The present application solves the technical problems of the prior art, such as the non-degradable and low separation efficiency of traditional polymer membranes such as polystyrene, polyvinylidene fluoride and polyacrylonitrile, the poor mechanical properties and heat resistance of PLA, the poor repeated use performance of the prepared membrane filter material, and the inability to separate hot oil sewage at high temperature. A porous hollow hydrophilic polylactic acid nanofiber separation membrane and its preparation method are provided. The porous hollow hydrophilic polylactic acid nanofiber separation membrane prepared by the method has high hydrophilicity, underwater super-oleophobicity, high porosity, high specific surface area, nanoscale diameter, good mechanical properties, complete biodegradability, simple process, low cost, and is conducive to industrialization.

[0007] Technical scheme:

[0008] To achieve the above-mentioned purpose, the following technical scheme is adopted:

[0009] A method for preparing a porous hollow hydrophilic polylactic acid (PLA) nanofiber separation membrane, wherein the porous hollow hydrophilic PLA nanofiber separation membrane is prepared by coaxial electrospinning to form a core-shell structured nanofiber membrane using PLA as the shell layer solution and PVA as the core layer solution, followed by electrospinning CDA on the surface to obtain a composite fiber membrane, and finally immersing the prepared composite fiber membrane in deionized water for ultrasonic removal of the PVA core layer, and drying to obtain a porous hollow structure. The method specifically includes the following steps:

[0010] Step 1: Weigh 80-90 parts of chloroform and 8-10 parts of N,N dimethylformamide according to the mass ratio, mix them evenly to obtain a mixed solvent, weigh 6-8 parts of PLA and dissolve them in the mixed solvent, stir evenly at room temperature, and let it sit overnight to obtain the shell spinning solution;

[0011] Step 2: Dissolve 5-7 parts of PVA in 100 parts of deionized water according to the mass ratio, and heat in a water bath at 90°C to dissolve it, thus obtaining the core spinning solution;

[0012] Step 3: According to the mass ratio, connect 6-8 parts of shell spinning solution PLA and 5-7 parts of core spinning solution PVA to the outer and inner layers of the coaxial needle, connect the coaxial needle to the high voltage electrostatic generator for electrospinning, and obtain a core-shell structured nanofiber membrane.

[0013] Step 4: Mix 80-90 parts of chloroform and 8-10 parts of N,N dimethylformamide according to the mass ratio to obtain a mixed solvent. Weigh 4-6 parts of CDA and dissolve them in the mixed solvent. Stir evenly at room temperature and let it sit overnight to obtain the spinning solution.

[0014] Step 5: The spinning solution is spun onto a core-shell nanofiber membrane using electrospinning technology to obtain a hydrophilic core-shell nanofiber membrane;

[0015] Step 6: Immerse the hydrophilic core-shell nanofiber membrane in deionized water and sonicate for 30 minutes, then dry it to obtain a porous hollow hydrophilic polylactic acid nanofiber separation membrane.

[0016] Furthermore, in the first and fourth steps, the mass ratio of chloroform to N,N-dimethylformamide is 9:1.

[0017] Furthermore, the PLA mass concentration in the first-step shell spinning solution is 6-8 wt%, and the PVA mass concentration in the second-step core spinning solution is 5-7 wt%.

[0018] Furthermore, the electrospinning parameters in the third step are as follows: spinning voltage 16-20kV, spinning distance 20cm, core spinning speed 0.3mL / h, shell spinning speed 0.3-1.2mL / h, core-shell flow rate ratio controlled at 1-4, and rotation speed 65-80r / min.

[0019] Furthermore, the CDA mass concentration in the spinning solution of the fourth step is 4-6 wt%.

[0020] Furthermore, the electrospinning parameters in the fifth step are: spinning voltage 20kV, spinning distance 20cm, spinning speed 1mL / h, and spinning speed 65-80r / min.

[0021] Furthermore, in the sixth step, the hydrophilic core-shell nanofiber membrane is immersed in deionized water and placed in an ultrasonic cleaner for ultrasonic treatment for 30 minutes at a frequency of 40 kHz and a power of 240 W.

[0022] Furthermore, the hydrophilic core-shell nanofiber membrane after ultrasonic treatment in the sixth step is placed in a forced-air drying oven at 60°C for 180 minutes.

[0023] This application also discloses a porous hollow hydrophilic polylactic acid nanofiber separation membrane prepared by any of the above preparation methods. The shell material of the porous hollow hydrophilic polylactic acid nanofiber separation membrane is PLA and CDA, and the core layer is a hollow structure. The thickness of the porous hollow hydrophilic polylactic acid nanofiber separation membrane is 40-45 μm, the fiber diameter is 400-1270 nm, the outer diameter is 265-770 nm, and the inner diameter is 235-500 nm.

[0024] Furthermore, the porous hollow hydrophilic polylactic acid nanofiber separation membrane has a pore size of 2-6 μm and a specific surface area of ​​310-370 m². 2 / g, water contact angle is 0°, and tensile strength reaches 0.65-1.8MPa.

[0025] The principle of the above-mentioned porous hollow hydrophilic polylactic acid nanofiber separation membrane and its preparation method is as follows: First, a PLA / PVA core-shell structured fiber membrane is prepared. Then, the membrane is hydrophilically modified with hydrophilic CDA. Finally, it is immersed in deionized water and sonicated for 30 minutes. After drying, a hollow structured nanofiber membrane is obtained. Due to the evaporation of the solvent, pores will appear on the fiber surface, resulting in porous hollow structured nanofibers. Finally, a hydrophilic porous hollow PLA fiber membrane is obtained.

[0026] Beneficial effects:

[0027] This application provides a porous hollow hydrophilic polylactic acid nanofiber separation membrane and its preparation method, which has the following advantages compared with the prior art:

[0028] 1. The porous hollow hydrophilic polylactic acid nanofiber membrane separation membrane prepared by the present invention has high hydrophilicity, underwater oleophobicity, high specific surface area, and good mechanical properties;

[0029] 2. The porous hollow hydrophilic polylactic acid nanofiber membrane prepared by the present invention has a triple transport channel consisting of inter-fiber pores, fiber pores, and pores inside the fiber channels, which can achieve high throughput while maintaining high separation efficiency;

[0030] 3. The porous hollow hydrophilic polylactic acid nanofiber membrane prepared by this invention has a simple preparation process, significant modification effect, does not generate secondary pollutants, is environmentally friendly, and can be applied to industrial production;

[0031] 4. The porous hollow hydrophilic polylactic acid nanofiber membrane prepared by this invention has a thickness of 310-370 μm. 2 With a specific surface area of ​​ / g, it can stably separate oil-in-water emulsions, with an emulsion flux of 2500-3200 L / m³. 2 It has an alcohol content of 1.5 liters per hour and good oil stain resistance. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1:

[0034] A method for preparing a porous hollow hydrophilic polylactic acid nanofiber separation membrane specifically includes the following steps:

[0035] Step 1: Weigh 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio, mix them evenly to obtain a mixed solvent, weigh 6 parts of PLA and dissolve them in the mixed solvent, stir evenly at room temperature, and let it sit overnight to obtain the shell spinning solution;

[0036] Step 2: Dissolve 5 parts of water-soluble PVA in 100 parts of deionized water according to the mass ratio, and heat it at 90°C with a magnetic stirrer to dissolve it, thus obtaining the core spinning solution;

[0037] Step 3: According to the mass ratio, 6 parts of shell PLA spinning solution and 5 parts of core PVA spinning solution are connected to the outer and inner layers of the coaxial needle, respectively. The coaxial needle is connected to a high-voltage electrostatic generator for electrospinning. The shell spinning speed is 1.2 mL / h, the core spinning speed is 0.3 mL / h, the shell-core flow rate ratio is controlled at 4, the spinning voltage is 20 kV, the spinning distance is 20 cm, and the rotation speed is 65 r / min to obtain PLA / PVA core-shell structured nanofiber membrane.

[0038] Step 4: Mix 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio to obtain a mixed solvent. Weigh 4 parts of CDA and dissolve them in the mixed solvent. Stir evenly at room temperature and let it sit overnight to obtain the spinning solution.

[0039] Step 5: The spinning solution is spun onto a core-shell nanofiber membrane using electrospinning technology to obtain a hydrophilic core-shell nanofiber membrane; Electrospinning parameters: spinning voltage 20kV, spinning distance 20cm, spinning speed 1mL / h, rotation speed 65-80r / min.

[0040] Step 6: Immerse the hydrophilic core-shell nanofiber membrane in deionized water and sonicate for 30 minutes, then place it in a forced-air drying oven at 60℃.

[0041] The membrane was dried for 180 minutes to obtain a porous hollow hydrophilic polylactic acid nanofiber separation membrane.

[0042] The obtained porous hollow hydrophilic PLA nanofiber membrane has a thickness of 43 μm, an inner diameter of 240-360 nm, an outer diameter of 480-620 nm, and a specific surface area of ​​310 m². 2 / g, pore size 3.56μm, tensile strength 1.5MPa, emulsion separation flux 2497L / m 2 The emulsion separation efficiency was 94.7% at h.

[0043] Example 2:

[0044] A method for preparing a porous hollow hydrophilic polylactic acid nanofiber separation membrane specifically includes the following steps:

[0045] Step 1: Weigh 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio, mix them evenly to obtain a mixed solvent, weigh 6 parts of PLA and dissolve them in the mixed solvent, stir evenly at room temperature, and let it sit overnight to obtain the shell spinning solution;

[0046] Step 2: Dissolve 5 parts PVA in 100 parts deionized water according to the mass ratio, and heat at 90°C with a magnetic stirrer to dissolve it, thus obtaining the core spinning solution;

[0047] Step 3: According to the mass ratio, 6 parts of shell PLA spinning solution and 5 parts of core PVA spinning solution are connected to the outer and inner layers of the coaxial needle, respectively. The coaxial needle is connected to a high-voltage electrostatic generator for electrospinning. The shell spinning speed is 1.2 mL / h, the core spinning speed is 0.6 mL / h, the shell-core flow rate ratio is controlled at 2, the spinning voltage is 20 kV, the spinning distance is 20 cm, and the rotation speed is 65 r / min to obtain PLA / PVA core-shell structured nanofiber membrane.

[0048] Step 4: Mix 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio to obtain a mixed solvent. Weigh 4 parts of CDA and dissolve them in the mixed solvent. Stir evenly at room temperature and let it sit overnight to obtain the spinning solution.

[0049] Step 5: The spinning solution is spun onto a core-shell nanofiber membrane using electrospinning technology to obtain a hydrophilic core-shell nanofiber membrane; Electrospinning parameters: spinning voltage 20kV, spinning distance 20cm, spinning speed 1mL / h, rotation speed 65-80r / min.

[0050] Step 6: Immerse the hydrophilic core-shell nanofiber membrane in deionized water and sonicate for 30 minutes, then place it in a forced-air drying oven at 60°C for 180 minutes to obtain a porous hollow hydrophilic polylactic acid nanofiber separation membrane.

[0051] The obtained porous hollow hydrophilic PLA nanofiber membrane has a thickness of 40 μm, an inner diameter of 260-375 nm, an outer diameter of 465-730 nm, and a specific surface area of ​​330 m². 2 / g, pore size 3.2μm, tensile strength 1.24MPa, emulsion separation flux 2673L / m 2 •h, the emulsion separation efficiency is 95.1%.

[0052] Example 3:

[0053] A method for preparing a porous hollow hydrophilic polylactic acid nanofiber separation membrane specifically includes the following steps:

[0054] Step 1: Weigh 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio, mix them evenly to obtain a mixed solvent, weigh 6 parts of PLA and dissolve them in the mixed solvent, stir evenly at room temperature, and let it sit overnight to obtain the shell spinning solution;

[0055] Step 2: Dissolve 5 parts PVA in 100 parts deionized water according to the mass ratio, and heat at 90°C with a magnetic stirrer to dissolve it, thus obtaining the core spinning solution;

[0056] Step 3: According to the mass ratio, 6 parts of shell PLA spinning solution and 5 parts of core PVA spinning solution are connected to the outer and inner layers of the coaxial needle, respectively. The coaxial needle is connected to a high-voltage electrostatic generator for electrospinning. The shell spinning speed is 1.2 mL / h, the core spinning speed is 0.9 mL / h, the shell-core flow rate ratio is controlled at 4 / 3, the spinning voltage is 20 kV, the spinning distance is 20 cm, and the rotation speed is 65 r / min to obtain PLA / PVA core-shell structured nanofiber membrane.

[0057] Step 4: Mix 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio to obtain a mixed solvent. Weigh 4 parts of CDA and dissolve them in the mixed solvent. Stir evenly at room temperature and let it sit overnight to obtain the spinning solution.

[0058] Step 5: The spinning solution is spun onto a core-shell nanofiber membrane using electrospinning technology to obtain a hydrophilic core-shell nanofiber membrane; Electrospinning parameters: spinning voltage 20kV, spinning distance 20cm, spinning speed 1mL / h, rotation speed 65-80r / min.

[0059] Step 6: Immerse the hydrophilic core-shell nanofiber membrane in deionized water and sonicate for 30 minutes, then place it in a forced-air drying oven at 60°C for 180 minutes to obtain a porous hollow hydrophilic polylactic acid nanofiber separation membrane.

[0060] The obtained porous hollow hydrophilic PLA nanofiber membrane has a thickness of 42 μm, an inner diameter of 280-410 nm, an outer diameter of 490-740 nm, and a specific surface area of ​​330 m². 2 / g, pore size 3.05μm, tensile strength 1.4MPa, emulsion separation flux 2908L / m 2 •h, the emulsion separation efficiency is 95.5%.

[0061] Example 4:

[0062] A method for preparing a porous hollow hydrophilic polylactic acid nanofiber separation membrane specifically includes the following steps:

[0063] Step 1: Weigh 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio, mix them evenly to obtain a mixed solvent, weigh 6 parts of PLA and dissolve them in the mixed solvent, stir evenly at room temperature, and let it sit overnight to obtain the shell spinning solution;

[0064] Step 2: Dissolve 5 parts PVA in 100 parts deionized water according to the mass ratio, and heat at 90°C with a magnetic stirrer to dissolve it, thus obtaining the core spinning solution;

[0065] Step 3: According to the mass ratio, 6 parts of shell PLA spinning solution and 5 parts of core PVA spinning solution are connected to the outer and inner layers of the coaxial needle, respectively. The coaxial needle is connected to a high-voltage electrostatic generator for electrospinning. The shell spinning speed is 1.2 mL / h, the core spinning speed is 1.2 mL / h, the shell-core flow rate ratio is controlled at 1, the spinning voltage is 20 kV, the spinning distance is 20 cm, and the rotation speed is 65 r / min to obtain PLA / PVA core-shell structured nanofiber membrane.

[0066] Step 4: Mix 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio to obtain a mixed solvent. Weigh 4 parts of CDA and dissolve them in the mixed solvent. Stir evenly at room temperature and let it sit overnight to obtain the spinning solution.

[0067] Step 5: The spinning solution is spun onto a core-shell nanofiber membrane using electrospinning technology to obtain a hydrophilic core-shell nanofiber membrane; Electrospinning parameters: spinning voltage 20kV, spinning distance 20cm, spinning speed 1mL / h, rotation speed 65-80r / min.

[0068] Step 6: Immerse the hydrophilic core-shell nanofiber membrane in deionized water and sonicate for 30 minutes, then place it in a forced-air drying oven at 60°C for 180 minutes to obtain a porous hollow hydrophilic polylactic acid nanofiber separation membrane.

[0069] The obtained porous hollow hydrophilic PLA nanofiber membrane has a thickness of 41 μm, an inner diameter of 280-430 nm, an outer diameter of 470-760 nm, and a specific surface area of ​​360 m². 2 / g, pore size 2.97μm, tensile strength 1.48MPa, emulsion separation flux 3010L / m 2 •h, the emulsion separation efficiency is 96%.

[0070] Example 5:

[0071] A method for preparing a porous hollow hydrophilic polylactic acid nanofiber separation membrane specifically includes the following steps:

[0072] Step 1: Weigh 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio, mix them evenly to obtain a mixed solvent, weigh 6 parts of PLA and dissolve them in the mixed solvent, stir evenly at room temperature, and let it sit overnight to obtain the shell spinning solution;

[0073] Step 2: Dissolve 5 parts PVA in 100 parts deionized water according to the mass ratio, and heat at 90°C with a magnetic stirrer to dissolve it, thus obtaining the core spinning solution;

[0074] Step 3: According to the mass ratio, 6 parts of shell PLA spinning solution and 5 parts of core PVA spinning solution are connected to the outer and inner layers of the coaxial needle, respectively. The coaxial needle is connected to a high-voltage electrostatic generator for electrospinning. The shell spinning speed is 1.2 mL / h, the core spinning speed is 0.6 mL / h, the shell-core flow rate ratio is controlled at 2, the spinning voltage is 20 kV, the spinning distance is 20 cm, and the rotation speed is 65 r / min to obtain PLA / PVA core-shell structured nanofiber membrane.

[0075] Step 4: Mix 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio to obtain a mixed solvent. Weigh 4 parts of CDA and dissolve them in the mixed solvent. Stir evenly at room temperature and let it sit overnight to obtain the spinning solution.

[0076] Step 5: The spinning solution is spun onto a core-shell nanofiber membrane using electrospinning technology to obtain a hydrophilic core-shell nanofiber membrane; Electrospinning parameters: spinning voltage 20kV, spinning distance 20cm, spinning speed 1mL / h, rotation speed 65-80r / min.

[0077] Step 6: Immerse the hydrophilic core-shell nanofiber membrane in deionized water and sonicate for 30 minutes, then place it in a forced-air drying oven at 60°C for 180 minutes to obtain a porous hollow hydrophilic polylactic acid nanofiber separation membrane.

[0078] The obtained porous hollow hydrophilic PLA nanofiber membrane has a thickness of 45 μm, an inner diameter of 300-440 nm, an outer diameter of 465-770 nm, and a specific surface area of ​​365 m². 2 / g, pore size 2.9μm, tensile strength 1.56MPa, emulsion separation flux 3002L / m 2 The emulsion separation efficiency was 94.6% at h.

[0079] Example 6:

[0080] A method for preparing a porous hollow hydrophilic polylactic acid nanofiber separation membrane specifically includes the following steps:

[0081] Step 1: Weigh 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio, mix them evenly to obtain a mixed solvent, weigh 6 parts of PLA and dissolve them in the mixed solvent, stir evenly at room temperature, and let it sit overnight to obtain the shell spinning solution;

[0082] Step 2: Dissolve 5 parts PVA in 100 parts deionized water according to the mass ratio, and heat at 90°C with a magnetic stirrer to dissolve it, thus obtaining the core spinning solution;

[0083] Step 3: According to the mass ratio, 6 parts of shell PLA spinning solution and 5 parts of core PVA spinning solution are connected to the outer and inner layers of the coaxial needle, respectively. The coaxial needle is connected to a high-voltage electrostatic generator for electrospinning. The shell spinning speed is 1.2 mL / h, the core spinning speed is 0.6 mL / h, the shell-core flow rate ratio is controlled at 2, the spinning voltage is 20 kV, the spinning distance is 20 cm, and the rotation speed is 65 r / min to obtain PLA / PVA core-shell structured nanofiber membrane.

[0084] Step 4: Mix 90 parts of chloroform and 10 parts of N,N dimethylformamide according to the mass ratio to obtain a mixed solvent. Weigh 6 parts of CDA and dissolve them in the mixed solvent. Stir evenly at room temperature and let it sit overnight to obtain the spinning solution.

[0085] Step 5: The spinning solution is spun onto a core-shell nanofiber membrane using electrospinning technology to obtain a hydrophilic core-shell nanofiber membrane; Electrospinning parameters: spinning voltage 20kV, spinning distance 20cm, spinning speed 1mL / h, rotation speed 65-80r / min.

[0086] Step 6: Immerse the hydrophilic core-shell nanofiber membrane in deionized water and sonicate for 30 minutes, then place it in a forced-air drying oven at 60°C for 180 minutes to obtain a porous hollow hydrophilic polylactic acid nanofiber separation membrane.

[0087] The obtained porous hollow hydrophilic PLA nanofiber membrane has a thickness of 47 μm, an inner diameter of 300-460 nm, an outer diameter of 470-760 nm, and a specific surface area of ​​370 m². 2 / g, pore size 2.85μm, tensile strength 1.62MPa, emulsion separation flux 3200L / m 2 •h, the emulsion separation efficiency is 94%.

[0088] Comparative Example 1:

[0089] Weigh out the corresponding mass of PLA particles and dissolve them in a mixed solvent of chloroform and N,N-dimethylformamide to prepare a 7wt% spinning solution. Electrospin the solution to form a fiber membrane at a spinning voltage of 20 kV, a spinning distance of 20 cm, a spinning speed of 1 ml / h, and a spinning speed of 65 r / min. The resulting fiber membrane has a thickness of 40 μm, a fiber diameter of 650-1220 nm, and a specific surface area of ​​28 m². 2 / g, pore size of 5.07μm, tensile strength of 1.3MPa, emulsion separation efficiency of 67%.

[0090] Comparative Example 2:

[0091] Weigh out the corresponding mass of PVA, dissolve it in deionized water to prepare a 7wt% spinning solution, and electrospin it into a fiber membrane at a spinning voltage of 20kV, a spinning distance of 20cm, a spinning speed of 1ml / h, and a spinning speed of 65r / min. The resulting fiber membrane has a thickness of 36μm, a fiber diameter of 490-650nm, and a specific surface area of ​​36m². 2 / g, pore size of 5.2μm, tensile strength of 0.93MPa, emulsion separation efficiency of 64%.

[0092] Comparative Example 3:

[0093] The corresponding mass of CDA was weighed and dissolved in a mixed solvent of chloroform and N,N-dimethylformamide to prepare a 7 wt% spinning solution. Electrospinning was performed at a spinning voltage of 20 kV, a spinning distance of 20 cm, a spinning speed of 1 ml / h, and a spinning speed of 65 r / min to form a fiber membrane. The resulting fiber membrane had a thickness of 42 μm, a fiber diameter of 560-890 nm, and a specific surface area of ​​54 m². 2 / g, pore size of 4.95μm, tensile strength of 0.65MPa, emulsion separation efficiency of 76%.

[0094] Comparative Example 4:

[0095] A corresponding mass of PLA particles was dissolved in a mixed solvent of chloroform and N,N-dimethylformamide to prepare a 7 wt% shell spinning solution. A corresponding mass of PVA was then dissolved in deionized water to prepare a 7 wt% core spinning solution. The prepared shell PLA solution and core PVA solution were connected to the inner and outer layers of a coaxial needle, respectively. The coaxial needle was then connected to a high-voltage electrostatic generator for electrospinning. Electrospinning was performed at a spinning voltage of 20 kV, a spinning distance of 20 cm, a core spinning speed of 1 mL / h, a shell spinning speed of 1 mL / h, and a rotation speed of 65 r / min to form a PLA / PVA core-shell structured nanofiber membrane. The resulting fiber membrane had a thickness of 43 μm, a fiber diameter of 660-820 nm, and a specific surface area of ​​60 m². 2 / g, pore size of 4.6μm, tensile strength of 1.2MPa, emulsion separation efficiency of 72%.

[0096] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a porous hollow hydrophilic polylactic acid nanofiber separation membrane, characterized in that, The porous hollow hydrophilic polylactic acid nanofiber separation membrane is prepared by coaxial electrospinning to form a core-shell structured nanofiber membrane using PLA as the shell layer solution and PVA as the core layer solution. Then, CDA is electrospun on the surface to obtain a composite fiber membrane. Finally, the prepared composite fiber membrane is immersed in deionized water and ultrasonically removed to remove the PVA core layer. After drying, a porous hollow structure is obtained. The specific steps include the following: Step 1: Weigh 80-90 parts of chloroform and 8-10 parts of N,N dimethylformamide according to the mass ratio, mix them evenly to obtain a mixed solvent, weigh 6-8 parts of PLA and dissolve them in the mixed solvent, stir evenly at room temperature, and let it sit overnight to obtain the shell spinning solution; Step 2: Dissolve 5-7 parts of PVA in 100 parts of deionized water according to the mass ratio, and heat in a water bath at 90°C to dissolve it, thus obtaining the core spinning solution; Step 3: According to the mass ratio, connect 6-8 parts of shell spinning solution PLA and 5-7 parts of core spinning solution PVA to the outer and inner layers of the coaxial needle, connect the coaxial needle to the high voltage electrostatic generator for electrospinning, and obtain a core-shell structured nanofiber membrane. Step 4: Mix 80-90 parts of chloroform and 8-10 parts of N,N dimethylformamide according to the mass ratio to obtain a mixed solvent. Weigh 4-6 parts of CDA and dissolve them in the mixed solvent. Stir evenly at room temperature and let it sit overnight to obtain the spinning solution. Step 5: The spinning solution is spun onto a core-shell nanofiber membrane using electrospinning technology to obtain a hydrophilic core-shell nanofiber membrane; Step 6: Immerse the hydrophilic core-shell nanofiber membrane in deionized water and sonicate for 30 minutes, then dry it to obtain a porous hollow hydrophilic polylactic acid nanofiber separation membrane.

2. The method for preparing the porous hollow hydrophilic polylactic acid nanofiber separation membrane according to claim 1, characterized in that, In the first and fourth steps, the mass ratio of chloroform to N,N-dimethylformamide is 9:

1.

3. The method for preparing the porous hollow hydrophilic polylactic acid nanofiber separation membrane according to claim 1, characterized in that: The PLA mass concentration in the first-step shell spinning solution is 6-8 wt%, and the PVA mass concentration in the second-step core spinning solution is 5-7 wt%.

4. The method for preparing the porous hollow hydrophilic polylactic acid nanofiber separation membrane according to claim 1, characterized in that: The electrospinning parameters in the third step are as follows: spinning voltage is 16-20kV, spinning distance is 20cm, shell spinning speed is 1.2mL / h, core spinning speed is 0.3-1.2mL / h, shell-core flow rate ratio is controlled at 1-4, and rotation speed is 65-80r / min.

5. The method for preparing the porous hollow hydrophilic polylactic acid nanofiber separation membrane according to claim 1, characterized in that: The CDA mass concentration in the spinning solution of the fourth step is 4-6 wt%.

6. The method for preparing the porous hollow hydrophilic polylactic acid nanofiber separation membrane according to claim 1, characterized in that: The electrospinning parameters in the fifth step are: spinning voltage 20kV, spinning distance 20cm, spinning speed 1mL / h, and spinning speed 65-80r / min.

7. The method for preparing the porous hollow hydrophilic polylactic acid nanofiber separation membrane according to claim 1, characterized in that, In the sixth step, the hydrophilic core-shell nanofiber membrane is immersed in deionized water and placed in an ultrasonic cleaner for ultrasonic treatment for 30 minutes at a frequency of 40 kHz and a power of 240 W.

8. The method for preparing the porous hollow hydrophilic polylactic acid nanofiber separation membrane according to claim 1, characterized in that, The hydrophilic core-shell nanofiber membrane after ultrasonic treatment in step six is ​​placed in a forced-air drying oven at 60°C for 180 minutes.

9. A porous hollow hydrophilic polylactic acid nanofiber separation membrane prepared by any one of the preparation methods of claims 1-8, characterized in that, The shell material of the porous hollow hydrophilic polylactic acid nanofiber separation membrane is PLA and CDA, and the core layer is hollow. The thickness of the porous hollow hydrophilic polylactic acid nanofiber separation membrane is 40-45 μm, the fiber diameter is 400-1270 nm, the outer diameter is 265-770 nm, and the inner diameter is 235-500 nm.

10. The porous hollow hydrophilic polylactic acid nanofiber separation membrane according to claim 9, characterized in that, The porous hollow hydrophilic polylactic acid nanofiber separation membrane has a pore size of 2-6 μm and a specific surface area of ​​310-370 m². 2 / g, water contact angle is 0°, and tensile strength reaches 0.65-1.8MPa.