CN-122006515-A - Nanofiber composite ultrafiltration membrane and gradient pore diameter preparation method thereof

CN122006515ACN 122006515 ACN122006515 ACN 122006515ACN-122006515-A

Abstract

The invention belongs to the technical field of membrane separation, and discloses a nanofiber composite ultrafiltration membrane and a gradient pore diameter preparation method thereof, wherein the nanofiber composite ultrafiltration membrane comprises a nanofiber network formed by PVDF-HFP polymer matrixes containing amino or hydroxyl functional groups, and surface-modified SiO 2 nano particles connected with the matrixes through Si-O-C covalent bonds; the pore diameter of the membrane is continuously distributed in a gradient along the thickness direction. The method comprises the steps of preparing a functionalized spinning solution and a modified nanoparticle dispersion solution, forming an initial structure gradient film through electrostatic spinning of gradient voltage and gradient receiving speed, sequentially carrying out gradient crosslinking shrinkage, gradient heat and humidity regulation and control and ultraviolet-induced interface covalent grafting on line, and finally washing and drying. The invention realizes the precise regulation and control of the membrane structure and the cooperative promotion of multiple performances, and remarkably improves the flux, the rejection rate, the pollution resistance and the mechanical stability.

Inventors

ZENG MING
MENG FANMING
ZHOU MINGJING
FAN SHIXIN
CHEN YONGMING
LI XUEYAN
Xin Hongguo

Assignees

辽宁智泽源科技有限公司

Dates

Publication Date: 20260512
Application Date: 20260409

Claims (9)

1. The nanofiber composite ultrafiltration membrane is characterized by comprising the following components: a three-dimensional nanofiber network structure comprised of a polymer matrix; and inorganic nano particles which are uniformly distributed in the three-dimensional nano fiber network structure and are chemically connected with the polymer matrix through covalent bonds; The nano fiber composite ultrafiltration membrane comprises a polymer matrix, inorganic nano particles, a silane coupling agent and a silane coupling agent, wherein the pore diameter of the nano fiber composite ultrafiltration membrane is continuously distributed in gradient along the thickness direction of the nano fiber composite ultrafiltration membrane, and the pore diameter is gradually increased from the outer surface of the nano fiber composite ultrafiltration membrane to the inner surface of the nano fiber composite ultrafiltration membrane; the covalent bond is a Si-O-C covalent bond formed by the reaction of a side chain active functional group of the polymer matrix with a functional group of the silica nanoparticle surface, thereby establishing a molecular-level interfacial connection between the polymer matrix and the inorganic nanoparticle.
2. The nanofiber composite ultrafiltration membrane of claim 1, wherein the continuous gradient pore size distribution is embodied as: Controlling the average pore size to be in the range of 5-20 nanometers in the outer surface area of the nanofiber composite ultrafiltration membrane; and continuing to increase in average pore size during the transition from the outer surface to the inner surface until a range of 80 nm to 150nm is reached at the inner surface region.
3. The nanofiber composite ultrafiltration membrane of claim 1, wherein the diameter of the nanofibers constituting the three-dimensional nanofiber network structure ranges from 50 nanometers to 500 nanometers, and the nanofiber composite ultrafiltration membrane has a porosity of not less than 80%.
4. The nanofiber composite ultrafiltration membrane according to claim 1, wherein the mechanical tensile strength of the nanofiber composite ultrafiltration membrane is not less than 5MPa and the elongation at break thereof is not less than 100%.
5. The nanofiber composite ultrafiltration membrane according to claim 1, wherein the pure water flux of the nanofiber composite ultrafiltration membrane is not lower than 500L m -2 ·h -1 under a transmembrane pressure difference of 0.1 MPa, and the rejection rate of proteins with molecular weight of 10 kDa is not lower than 98%.
6. A method for preparing a gradient pore size of a nanofiber composite ultrafiltration membrane according to any one of claims 1 to 5, comprising the following steps: step 1, preparing functionalized polymer spinning solution and surface modified inorganic nano particle dispersion liquid; step 2, adopting an electrostatic spinning technology, and preparing a nanofiber membrane with an initial structural gradient by carrying out gradient regulation and control on technological parameters in a spinning process; step 3, introducing the nanofiber membrane with the initial structural gradient into an integrated online treatment cavity, and continuously performing gradient crosslinking shrinkage, gradient heat treatment, gradient humidity regulation and ultraviolet-induced graft copolymerization treatment; And 4, carrying out online cleaning and online drying on the treated nanofiber membrane.
7. The method for preparing the gradient pore diameter of the nanofiber composite ultrafiltration membrane according to claim 6, wherein the step 1 is specifically as follows: Dissolving polyvinylidene fluoride-hexafluoropropylene copolymer containing 0.5-5% of side chain amino or hydroxyl functional groups in a molar fraction in a mixed solvent consisting of N, N-dimethylformamide and acetone according to a mass ratio of 7:3 to form a functionalized polymer spinning solution with a mass percentage concentration of 10-20%; dispersing silica nanoparticles with the particle size ranging from 10 nanometers to 50 nanometers in a solvent, adding a silane coupling agent, and reacting under a weak alkaline condition to introduce active functional groups for subsequent graft copolymerization on the surfaces of the silica nanoparticles, thereby preparing the surface-modified silica nanoparticles; Uniformly dispersing the surface-modified silica nanoparticles in the functionalized polymer spinning solution, wherein the mass of the silica nanoparticles accounts for 1-5% of the total mass of the polymer.
8. The method for preparing a gradient pore size of a nanofiber composite ultrafiltration membrane according to claim 6, wherein in the step 2, the step of preparing a nanofiber membrane having an initial structural gradient specifically comprises: providing an electrostatic spinning device which comprises a programmable high-voltage power supply, a multi-needle spinning jet head and a rotary receiving roller with adjustable rotating speed; By synchronously and programmatically controlling the voltage applied between the spinning jet and the rotating receiving roller and the linear velocity of the rotating receiving roller, a nanofiber membrane with a preset initial porosity gradient, in which the fiber stacking density continuously varies in the thickness direction, is deposited on the rotating receiving roller.
9. The method for preparing the gradient pore diameter of the nanofiber composite ultrafiltration membrane according to claim 6, wherein in the step 3, the treatments for continuously performing gradient cross-linking shrinkage, gradient heat treatment and gradient humidity control specifically comprise: Exposing the nanofiber membrane to glutaraldehyde vapor at a concentration of 0.5% to 2.0% (w/v) in a gradient crosslinking shrinkage zone of the integrated in-line processing chamber, reacting at a temperature of 25 ℃ to 40 ℃ to form preliminary crosslinks between nanofibers of the polymer matrix and induce a preset shrinkage of the fiber network; Subsequently, the crosslinked and contracted nanofiber membrane is fed to a gradient heat treatment and humidity control zone, in which a linear temperature gradient continuously rising from 40 ℃ to 80 ℃ and a linear humidity gradient continuously rising from 30% relative humidity to 70% are cooperatively applied along the traveling direction of the membrane, and a continuous gradient pore size distribution from a dense pore structure of the outer surface to a loose pore structure of the inner surface is driven by precisely controlling the kinetics of solvent evaporation and polymer segment relaxation.

Description

Nanofiber composite ultrafiltration membrane and gradient pore diameter preparation method thereof Technical Field The invention belongs to the technical field of membrane separation, and particularly relates to a nanofiber composite ultrafiltration membrane and a gradient pore diameter preparation method thereof. Background The ultrafiltration membrane technology can effectively intercept macromolecular substances, colloid, bacteria, viruses and the like at normal temperature and normal pressure, and becomes a core unit in the water treatment process. With the continuous evolution of material science, the nanofiber composite ultrafiltration membrane prepared by electrostatic spinning and other technologies has the advantages of extremely high specific surface area, three-dimensional through porous structure, functional design and the like, and has more excellent permeation flux and pollution resistance compared with the traditional phase inversion membrane, so that the nanofiber composite ultrafiltration membrane becomes the research front edge and development focus in the field. In the prior art, multilayer composite structural films and surface-functionalized modified films are common technical paths. For example, the patent publication No. CN105032202B discloses a multi-layer composite ultrafiltration membrane, which adopts PET or PP non-woven fabrics as a matrix, forms a polymer nanofiber membrane layer through electrostatic spinning, and introduces a cellulose nanofiber membrane layer into the middle layer to form a five-layer symmetrical structure. According to the technology, the hydrophilicity and the pollution resistance of the membrane are improved through a physical lamination mode, but the layers are combined mainly through physical adsorption, molecular level interface connection is lacked, continuous gradient distribution of pore diameters cannot be realized, interlayer stripping is easy to occur in long-term operation of the membrane, and cooperative promotion of flux and retention rate is limited. The invention patent with publication number CN107081078B discloses a preparation method of a nano-structure composite ultrafiltration membrane, which comprises the steps of coating hydrophilic polymer solution on an electrostatic spinning nanofiber membrane base layer, uniformly spraying and pressing a porous functional material (such as active carbon) on the surface of the coating layer by an air-jet method, and finally forming the composite membrane by dipping and opening treatment. The method avoids the use of chemical cross-linking agents, but the binding force between the functional layer and the base layer mainly depends on physical bonding, functional materials are easy to fall off under the scouring of high-pressure water flow, and the uniformity and thickness control difficulty of a coating layer are high, so that the long-term stability of the film is influenced. The common characteristic of the above technical paths is that the technical paths are essentially to induce the spontaneous and integral phase separation of the polymer chains by regulating and controlling a macroscopic and homogeneous thermodynamic and kinetic environment, thereby forming a micro-porous structure. In a specific historical development stage, the initial problems of low flux, easy pollution and the like of the symmetrical porous membrane are successfully solved based on a film forming mechanism of a statistical mechanical average effect, and the large-scale application of the membrane technology is promoted. However, with increasing complexity of application scenarios, for example, in the treatment of high turbidity industrial wastewater containing multi-scale particle pollutants or in the separation of high precision biomacromolecules, the requirement on membrane separation performance is no longer a single index improvement, but a synergistic optimization on multi-dimensional performance such as flux, retention rate, pollution resistance, mechanical stability and the like. Some inherent limitations of the prior art fabrication technology in underlying logic are increasingly pronounced. Both solvent and non-solvent diffusion exchange and polymer chain precipitation aggregation represent an unpredictable, randomly occurring process on a microscopic scale. The randomness results in a high tortuosity of the internal pore channels of the membrane and non-uniformity of pore size distribution, and although the average pore size can be regulated by the process parameters, it is difficult to realize an accurate and programmed gradient design of the pore size along the film thickness direction. The direct consequence is that the surface and inner layers of the membrane lack effective functional partitioning in the filtering behaviour. In the filtration process, large particle pollutants rapidly cover the surface of the membrane to form a compact filter cake layer, and small particle pollutants easily invade the inside