Asymmetric pore structure PVDF nanofiber membrane and preparation process

Abstract

The application discloses an asymmetric pore structure PVDF nanofiber membrane and a preparation process, relates to the field of membrane technology, and is formed by stacking first electrostatic spinning nanofibers and second electrostatic spinning nanofibers; the diameter of the first electrostatic spinning nanofibers is not equal to the diameter of the second electrostatic spinning nanofibers; compared with the prior art, the application has the beneficial effect that when the water bubble point of the symmetric pore nanofiber membrane and the asymmetric pore nanofiber membrane is 10KPa-12KPa after being wetted by ethanol, the pure water flow of the asymmetric pore nanofiber membrane is more than 50% higher than that of the symmetric pore nanofiber membrane formed by stacking electrostatic spinning nanofibers with the same diameter; after filtering the same ferrosol aqueous solution, the flow of the asymmetric nanofiber membrane is still much higher than that of the symmetric nanofiber membrane, which indicates that the asymmetric nanofiber membrane has better porosity, flow capacity and pollution capacity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of membrane, in particular to an asymmetric pore structure PVDF nanofiber membrane and a preparation process thereof. BACKGROUND

[0002] Nanofiber membrane is a kind of filtration material formed by stacking nanofibers as basic units, which has the characteristics of high specific surface area, high porosity and interpenetrating pore structure. The common production technology of polymer nanofiber is electrospinning, which is a process in which a polymer solution forms a Taylor cone under the action of electrostatic force and is then collected to form nanofibers. The fiber diameter of the nanofiber membrane produced by the existing electrospinning process can be adjusted, but the macrostructure is uniform, that is, the nanofibers produced by electrospinning have uniform diameters, which makes the pores of the nanofiber membrane symmetrical, and the filtration flux and the amount of pollutants of the nanofiber membrane are further improved. The filtration flux and the amount of pollutants of the current nanofiber membrane are still insufficient.

[0003] Therefore, it is necessary to develop an asymmetric pore structure PVDF nanofiber membrane and a preparation process thereof to further improve the filtration flux and the amount of pollutants of the nanofiber membrane. SUMMARY

[0004] The purpose of the present application is to disclose an asymmetric pore structure PVDF nanofiber membrane and a preparation process thereof, which forms a nanofiber membrane by optimizing the stacking design of electrospun nanofibers with different diameters, so as to improve the filtration flux and the amount of pollutants of the nanofiber membrane.

[0005] To achieve the first application purpose, the present application provides an asymmetric pore structure PVDF nanofiber membrane, which is stacked by first electrospun nanofibers and second electrospun nanofibers; the diameter of the first electrospun nanofibers is not equal to the diameter of the second electrospun nanofibers.

[0006] Preferably, the diameter of the first electrospun nanofibers is equal to twice the diameter of the second electrospun nanofibers.

[0007] Preferably, the first electrospun nanofibers and the second electrospun nanofibers are stacked to form a nanofiber membrane.

[0008] Preferably, the first electrospun nanofibers and the second electrospun nanofibers are mixed and stacked to form a nanofiber membrane.

[0009] Preferably, it comprises a first nanofiber layer, a second nanofiber layer, a third nanofiber layer and a fourth nanofiber layer.

[0010] The first nanofiber layer and the third nanofiber layer are respectively stacked by the first electrospun nanofibers;

[0011] The second nanofiber layer and the fourth nanofiber layer are respectively stacked by the second electrospun nanofibers.

[0012] Preferably,

[0013] The thickness of the first nanofiber layer and the third nanofiber layer is respectively 3-10 microns, and the diameter of the first electrospun nanofiber is 0.5-1.5 microns;

[0014] The thickness of the second nanofiber layer is 3-10 microns, the thickness of the fourth nanofiber layer is respectively 10-20 microns, and the diameter of the second electrospun nanofiber is 0.2-0.8 microns.

[0015] Based on the same inventive principle, in order to achieve the above-mentioned second object, the present application provides a preparation process of a non-symmetrical pore structure PVDF nanofiber membrane, comprising the following steps: dissolving PVDF material in a mixed solvent of dimethylformamide and acetone with a volume ratio of 1:1, and preparing a spinning solution with a mass content of 5%-12%;

[0016] The spinning solution is prepared into the non-symmetrical pore structure PVDF nanofiber membrane of the first invention by an electrospinning process, the voltage of the electrospinning is 24000-28000V, the spinning distance is 150-200mm, the production speed of the nanofiber membrane is 400mm / min, the spinning head of the electrospinning is composed of two different types of stainless steel needles for medical injectors, and the type of the stainless steel needle for the medical injector is 7-14.

[0017] Preferably, the spinning head of the electrospinning includes a first group of spinning heads and a second group of spinning heads;

[0018] The type of the spinning head of the first group of spinning heads is a stainless steel 12 needle for medical injectors, the arrangement mode of the spinning head of the first group of spinning heads is 4 rows*10 per row, and the first group of spinning heads uses a spinning solution with a mass content of 10%;

[0019] The type of the spinning head of the second group of spinning heads is a stainless steel 9 needle for medical injectors, the arrangement mode of the spinning head of the second group of spinning heads is 4 rows*10 per row, and the second group of spinning heads uses a spinning solution with a mass content of 7%.

[0020] Preferably, the nanofiber membrane is electrospun thickened by the first group of spinning heads, the second group of spinning heads, the first group of spinning heads and the second group of spinning heads in sequence.

[0021] Preferably, the nanofiber membrane is electrospun thickened by two groups of the first group of spinnerets, four groups of the second group of spinnerets, two groups of the first group of spinnerets and eight groups of the second group of spinnerets in sequence.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] When the symmetric-pore nanofiber membrane and the asymmetric-pore nanofiber membrane are wetted by ethanol and the water bubble point is 10 KPa-12 KPa, the asymmetric-pore nanofiber membrane has a water flow rate that is 50% higher than that of the symmetric-pore nanofiber membrane made of electrospun nanofibers of the same diameter; after filtering the same ferrosol aqueous solution, the flow rate of the asymmetric-pore nanofiber membrane is still much higher than that of the symmetric-pore nanofiber membrane, indicating that the asymmetric-pore nanofiber membrane has better porosity, flow rate and pollutant removal capacity. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a cross-sectional view of the asymmetric-pore PVDF nanofiber membrane of the present application.

[0025] Figure 2 is a flow rate comparison chart of the asymmetric-pore nanofiber membrane and the symmetric-pore nanofiber membrane of the present application.

[0026] Figure 3 is a flow rate comparison chart of the asymmetric-pore nanofiber membrane and the symmetric-pore nanofiber membrane of the present application after filtering ferrosol aqueous solution.

[0027] Figure 4 is a spinneret distribution chart of the electrospinning of the present application.

[0028] Figure 5 is a nanofiber membrane winding roller circuit chart of the present application.

[0029] 1, first nanofiber layer; 2, second nanofiber layer; 3, third nanofiber layer; 4, fourth nanofiber layer; 5, electrospinning spinneret; 51, first group of spinnerets; 52, second group of spinnerets.

[0030] 52, second group of spinnerets. DETAILED DESCRIPTION

[0031] The present application will be described in detail below in conjunction with the embodiments shown in the drawings, but it should be noted that these embodiments are not limiting to the present application, and equivalent transformations or substitutions of function, method or structure made by those skilled in the art based on these embodiments are within the protection scope of the present application.

[0032] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0033] The specific implementation process of the present application is described below through multiple embodiments.

[0034] Example One:

[0035] The present embodiment discloses an asymmetric pore structure PVDF nanofiber membrane, which is stacked by first electrospun nanofibers and second electrospun nanofibers; the diameter of the first electrospun nanofibers is not equal to the diameter of the second electrospun nanofibers. Specifically, the existing electrospinning process uses several stainless steel needles of the same model for spinning, and finally forms a nanofiber membrane with substantially the same diameter. The pores of such a membrane have symmetry, that is, the pores of each layer of the nanofiber membrane are substantially consistent. Such a membrane is called a symmetric pore nanofiber membrane, which results in insufficient filtration flux and pollution quantity of the current symmetric pore nanofiber membrane. To further improve the filtration flux and pollution quantity of the nanofiber membrane, the present embodiment uses first electrospun nanofibers and second electrospun nanofibers with different diameters to form an asymmetric pore nanofiber membrane, so that the filtration flux of the asymmetric pore nanofiber membrane is higher than that of the symmetric pore nanofiber membrane, and the pollution quantity is larger.

[0036] It should be further explained that the stacking of the first electrospun nanofibers and the second electrospun nanofibers has two forms. One is that the first electrospun nanofibers and the second electrospun nanofibers are stacked in layers to form a nanofiber membrane. In this stacking form, the diameters of the electrospun nanofibers in the same layer are substantially consistent, and several layers of electrospun nanofibers are stacked to form a nanofiber membrane. According to the requirements of the nanofiber membrane for filtration flux and pollution quantity, different diameter electrospun nanofibers are stacked in layers, as shown in Figure 1, the nanofiber membrane comprises a first nanofiber layer 1, a second nanofiber layer 2, a third nanofiber layer 3 and a fourth nanofiber layer 4; the first nanofiber layer 1 and the third nanofiber layer 3 are respectively stacked by the first electrospinning nanofiber; the second nanofiber layer 2 and the fourth nanofiber layer 4 are respectively stacked by the second electrospinning nanofiber; the second is: the first electrospinning nanofiber and the second electrospinning nanofiber are mixed and stacked to form a nanofiber membrane, in this stacking form, the diameters of the electrospinning nanofibers in the same layer are different, more accurately, in this stacking form, there is no obvious layered structure, that is, different diameter electrospinning nanofibers are mixed and formed according to a certain proportion, and the specific mixing proportion is closely related to the required filtration flux and the number of pollutants, for example, according to weight, the mixing proportion of the first electrospinning nanofiber and the second electrospinning nanofiber is 7:3-3:7, by mixing and stacking the electrospinning nanofibers with different diameters, the porosity and the void size can be adjusted, so as to adjust the filtration flux and the number of pollutants.

[0037] Example Two:

[0038] On the basis of example one, in example two, the diameter of the first electrospinning nanofiber is equal to 2 times the diameter of the second electrospinning nanofiber, see Figure 1 , the thickness of the first nanofiber layer 1 and the third nanofiber layer 3 is 5μm respectively, the diameter of the first electrospinning nanofiber is 1.0μm; the thickness of the second nanofiber layer 2 is 5μm respectively, the thickness of the fourth nanofiber layer 4 is 10μm-20μm respectively, and the diameter of the second electrospinning nanofiber is 0.5μm.

[0039] Referring to Table 1, which is a layered structure and performance parameter of the asymmetric nanofiber membrane, the asymmetric nanofiber membrane with serial number 1 comprises a first nanofiber layer 1, a second nanofiber layer 2, a third nanofiber layer 3 and a fourth nanofiber layer 4; the first nanofiber layer 1 and the third nanofiber layer 3 are respectively stacked by the first electrospinning nanofiber with a diameter of 1 μm, and the stacking thickness of the first nanofiber layer 1 and the third nanofiber layer 3 is 5 μm respectively; the second nanofiber layer 2 and the fourth nanofiber layer 4 are respectively stacked by the second electrospinning nanofiber with a diameter of 0.5 μm, wherein the stacking thickness of the second nanofiber layer 2 is 5 μm, and the stacking thickness of the fourth nanofiber layer 2 is 20 μm, and the total thickness of the asymmetric nanofiber membrane with serial number 1 finally stacked is 31 μm, which is slightly less than the sum of the thicknesses of each layer, because the fibers between each layer will be crossed and the stacking material is fluffy material; the difference between the asymmetric nanofiber membrane with serial number 1 and the asymmetric nanofiber membrane with serial number 2 is that the thickness of the fourth nanofiber layer 4 of the asymmetric nanofiber membrane with serial number 2 is 15 μm, and the total thickness of the asymmetric nanofiber membrane with serial number 2 is 28 μm; the difference between the asymmetric nanofiber membrane with serial number 1 and the asymmetric nanofiber membrane with serial number 3 is that the thickness of the fourth nanofiber layer 4 of the asymmetric nanofiber membrane with serial number 3 is 10 μm, and the total thickness of the asymmetric nanofiber membrane with serial number 3 is 25 μm.

[0040] Table 1 Layered structure and performance parameter of asymmetric nanofiber membrane

[0041]

[0042] Referring to Figure 2 , the pure water flow of the asymmetric nanofiber membrane with serial number 1 and the symmetric nanofiber membrane is compared, and the water bubble point of the asymmetric nanofiber membrane and the symmetric nanofiber membrane after ethanol wetting is 10 KPa-12 KPa, and the pure water flow of the asymmetric nanofiber membrane and the symmetric nanofiber membrane is 0.5 L / m2·h-0.6 L / m2·h. Figure 2 It can be seen from the comparison of the results that the pure water flow of the asymmetric nanofiber membrane is 85% higher than that of the symmetric nanofiber membrane at a pressure of 1.5 KPa; the pure water flow of the asymmetric nanofiber membrane is 92% higher than that of the symmetric nanofiber membrane at a pressure of 3 KPa; the pure water flow of the asymmetric nanofiber membrane is 80% higher than that of the symmetric nanofiber membrane at a pressure of 5 KPa; the pure water flow of the asymmetric nanofiber membrane is 67% higher than that of the symmetric nanofiber membrane at a pressure of 10 KPa; the pure water flow of the asymmetric nanofiber membrane is 59% higher than that of the symmetric nanofiber membrane at a pressure of 15 KPa. It can be seen that the asymmetric nanofiber membrane of the present embodiment has a larger pure water flow at the same pressure, which can represent that the asymmetric nanofiber membrane of the present embodiment has higher porosity.

[0043] Referring to Figure 3, the flow rate attenuation of the asymmetric nanofiber membrane with serial number 1 and the symmetric nanofiber membrane with the aqueous ferric sol solution is compared, the water bubble point of the asymmetric nanofiber membrane and the symmetric nanofiber membrane after being wetted by ethanol is 10 KPa-12 KPa, the average flow rate of four different positions of the asymmetric nanofiber membrane is taken as the basis, the average flow rate of four different positions of the symmetric nanofiber membrane is taken as the basis, and the results are compared from Figure 3 The comparison of the results can see that when 5 L of the aqueous ferric sol solution is filtered, the flow rates of the asymmetric nanofiber membrane and the symmetric nanofiber membrane are 1300 and 680 respectively, the flow rate of the symmetric nanofiber membrane is 52% of that of the asymmetric nanofiber membrane; when 20 L of the aqueous ferric sol solution is filtered, the flow rates of the asymmetric nanofiber membrane and the symmetric nanofiber membrane are 970 and 530 respectively, the flow rate of the symmetric nanofiber membrane is 55% of that of the asymmetric nanofiber membrane; when 35 L of the aqueous ferric sol solution is filtered, the flow rates of the asymmetric nanofiber membrane and the symmetric nanofiber membrane are 788 and 432 respectively, the flow rate of the symmetric nanofiber membrane is 55% of that of the asymmetric nanofiber membrane; when 50 L of the aqueous ferric sol solution is filtered, the flow rates of the asymmetric nanofiber membrane and the symmetric nanofiber membrane are 593 and 294 respectively, the flow rate of the symmetric nanofiber membrane is 50% of that of the asymmetric nanofiber membrane. It can be seen that after the same amount of impurities is intercepted, the flow rate of the asymmetric nanofiber membrane is much higher than that of the symmetric nanofiber membrane, that is, after the same aqueous ferric sol solution is filtered, the flow rate of the asymmetric nanofiber membrane is still much higher than that of the symmetric nanofiber membrane, which indicates that the asymmetric nanofiber membrane has higher porosity, flow rate and pollution capacity.

[0044] Example Three:

[0045] The preparation process of the asymmetric pore structure PVDF nanofiber membrane in the embodiment one or the embodiment two includes the following steps:

[0046] Step S1: the PVDF material is dissolved in a mixed solvent of dimethylformamide and acetone with a volume ratio of 1:1, and a spinning solution with a mass content of 5%-12% is prepared;

[0047] Step S2: the spinning solution is used to prepare the asymmetric pore structure PVDF nanofiber membrane in the embodiment one or the embodiment two through an electrospinning process, the voltage of the electrospinning is 24000 V-28000 V, the spinning distance is 150 mm-200 mm, and the production speed of the nanofiber membrane is 400 mm / min, the spinning head of the electrospinning is composed of two different types of stainless steel needles for medical injectors, and the type of the stainless steel needle for the medical injector is 7-14. It needs to be further explained that the size and inner diameter of the stainless steel needle for the medical injector with the type of 7-14 are definite, the spinning inner diameter of the stainless steel needle for the medical injector with different types is different, and the diameter of the electrospun nanofiber is also different.

[0048] To realize the layered accumulation of the first electrospinning nanofiber and the second electrospinning nanofiber to form the nanofiber membrane, referring to Figure 4 , the nanofiber membrane is driven along several rollers, the electrospinning spinneret 5 includes a first group of spinnerets 51 and a second group of spinnerets 52, the first group of spinnerets 51 and the second group of spinnerets 52 are aligned to spin the nanofiber membrane, so as to continuously thicken the nanofiber membrane; the spinneret type of the first group of spinnerets 51 is stainless steel No. 12 needle for medical syringe (No. 12 in Figure 4 ), the arrangement mode of the spinneret of the first group of spinnerets 51 is 4 rows * 10 per row, that is, the number of spinnerets of each first group of spinnerets 51 is 40, and the first group of spinnerets 51 uses a spinning solution with a mass content of 10%; the spinneret type of the second group of spinnerets 52 is stainless steel No. 9 needle for medical syringe (No. 9 in Figure 4 ), the arrangement mode of the spinneret of the second group of spinnerets 52 is 4 rows * 10 per row, that is, the number of spinnerets of each second group of spinnerets 52 is 40, and the second group of spinnerets 52 uses a spinning solution with a mass content of 7%.

[0049] The nanofiber membrane is formed by accumulating several layers of electrospinning nanofibers, according to the requirements of the nanofiber membrane on the filtration flux and the number of pollutants, different diameter electrospinning nanofibers are layered and accumulated, in the specific accumulation, the nanofiber membrane is sequentially driven through several groups of the first group of spinnerets (to form the first nanofiber layer), several groups of the second group of spinnerets (to form the second nanofiber layer), several groups of the first group of spinnerets (to form the third nanofiber layer) and several groups of the second group of spinnerets (to form the fourth nanofiber layer), by adjusting the number and position of the first group of spinnerets, the nanofiber membrane with different filtration flux and different number of pollutants is formed.

[0050] Referring to Figure 4 , Figure 4 is a schematic diagram of preparing the asymmetric nanofiber membrane with serial number 1 in Example 2, Figure 5 is Figure 4The winding roller line diagram of the middle nanofiber membrane, the nanofiber membrane successively passes through two groups of the first group of spinnerets 51, four groups of the second group of spinnerets 52, two groups of the first group of spinnerets 51 and eight groups of the second group of spinnerets 52; two groups of the first group of spinnerets 51 are used for preparing the first nanofiber layer 1, the first nanofiber layer 1 is stacked by the first electrospinning nanofiber with a diameter of 1 μm, and the stacking thickness is 5 μm; four groups of the second group of spinnerets 52 are used for preparing the second nanofiber layer 2, the second nanofiber layer 2 is stacked by the second electrospinning nanofiber with a diameter of 0.5 μm, and the stacking thickness is 5 μm; two groups of the first group of spinnerets 51 are used for preparing the third nanofiber layer 3, the third nanofiber layer 3 is stacked by the first electrospinning nanofiber with a diameter of 1 μm, and the stacking thickness is 5 μm; eight groups of the second group of spinnerets 52 are used for preparing the fourth nanofiber layer 4, the fourth nanofiber layer 4 is stacked by the second electrospinning nanofiber with a diameter of 0.5 μm, and the stacking thickness is 20 μm.

Claims

1. An asymmetrically-structured PVDF nanofiber membrane, characterized in that, The first nanofiber layer, the second nanofiber layer, the third nanofiber layer and the fourth nanofiber layer are included. The nanofiber membrane is stacked by the first electrospun nanofiber and the second electrospun nanofiber, both of which are prepared by electrospinning process from PVDF spinning solution with mass content of 5%-12%. The diameter of the first electrospun nanofiber is not equal to the diameter of the second electrospun nanofiber. The first nanofiber layer and the third nanofiber layer are stacked by the first electrospun nanofiber respectively. The second nanofiber layer and the fourth nanofiber layer are stacked by the second electrospun nanofiber respectively. The thickness of the first nanofiber layer and the third nanofiber layer is 3-10μm respectively, the diameter of the first electrospun nanofiber is 0.5-1.5μm. The thickness of the second nanofiber layer is 3-10μm, the thickness of the fourth nanofiber layer is 10-20μm respectively, the diameter of the second electrospun nanofiber is 0.2-0.8μm.

2. A process for the preparation of asymmetrically structured PVDF nanofiber membranes, characterized in that, The steps include: The PVDF material is dissolved in the mixed solvent of dimethylformamide and acetone with volume ratio of 1:1 to prepare the PVDF spinning solution with mass content of 5%-12%. The spinning solution is prepared by electrospinning process to prepare the asymmetric pore structure PVDF nanofiber membrane of claim 1, the voltage of electrospinning is 24000-28000V, the spinning distance is 150-200mm, the production speed of nanofiber membrane is 400mm / min, the spinning head of electrospinning is composed of two different types of stainless steel needles for medical syringe, the type of stainless steel needle for medical syringe is 7-14.

3. The asymmetric pore structure PVDF nanofiber membrane preparation process of claim 2, wherein, The spinning head of electrospinning includes the first group of spinning heads and the second group of spinning heads. The type of the first group of spinning heads is stainless steel 12 needle for medical syringe, the arrangement of the first group of spinning heads is 4 rows*10 per row, the first group of spinning heads uses the PVDF spinning solution with mass content of 10%. The type of the second group of spinning heads is stainless steel 9 needle for medical syringe, the arrangement of the second group of spinning heads is 4 rows*10 per row, the second group of spinning heads uses the spinning solution with mass content of 7%.

4. The process for the preparation of asymmetrically structured PVDF nanofiber membranes according to claim 3, wherein, The nanofiber membrane is electrospun thickened by the first group of spinning heads, the second group of spinning heads, the first group of spinning heads and the second group of spinning heads in turn.

5. The process for the preparation of asymmetrically structured PVDF nanofiber membranes according to claim 4, wherein, The nanofiber membrane is electrospun thickened by two groups of the first group of spinning heads, four groups of the second group of spinning heads, two groups of the first group of spinning heads and eight groups of the second group of spinning heads in turn.

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