CN110711430A

CN110711430A - Composite filter material and preparation method thereof

Info

Publication number: CN110711430A
Application number: CN201910993213.1A
Authority: CN
Inventors: 吴龙涛; 王亚飞; 宋宝祥; 刘欣; 邓波; 张小宇; 陈凯
Original assignee: Jiangsu Yimao Filter Co Ltd
Current assignee: Jiangsu Yimao Filter Co Ltd
Priority date: 2019-10-18
Filing date: 2019-10-18
Publication date: 2020-01-21
Anticipated expiration: 2039-10-18
Also published as: CN110711430B

Abstract

The invention provides a composite filter material and a preparation method thereof. The composite filter material is prepared by sequentially depositing and compounding micron-to-submicron-to-nanometer-sized fiber filter layers, and comprises a non-woven fabric primary filter layer, a porous micro-nano fiber medium-effect filter layer, a cobweb nano fiber high-efficiency filter layer and a composite layer formed by mutually inserting fibers in adjacent filter layers between the adjacent filter layers. The preparation method of the composite filter material comprises the following steps: firstly, a non-woven fabric primary filter layer is prepared by a plane receiving type centrifugal spinning process, then an electrostatic spinning process is adopted, a deposited porous micro-nanofiber medium-effect filter layer and a cobweb nanofiber high-efficiency filter layer are sequentially received and deposited on the surface of the non-woven fabric primary filter layer, and the multi-stage structure composite filter material with the pore diameter changing in a gradient manner along the thickness direction is prepared. The composite filter material has excellent air filtering performance, and also has photocatalysis and antibacterial performance.

Description

Composite filter material and preparation method thereof

Technical Field

The invention relates to the field of preparation of filter materials, in particular to a composite filter material and a preparation method thereof.

Background

The traditional filtering material has the problems of low filtering effect, difficult realization of high efficiency and low resistance and the like on micro nano particles. The electrostatic spinning nanofiber material has the advantages of small fiber diameter, large specific surface area, small pore diameter, high porosity, good connectivity of pores inside a fiber membrane and the like, can effectively intercept tiny particles in air, and improves the air filtration performance of the fiber material to a great extent. At present, researches find that the air filtration performance of the material can be remarkably improved by further refining the fiber diameter, but the fiber diameter is more than 100nm, the further refining is difficult, the large improvement of the filtration performance of the material is seriously limited, and the bottleneck problem of insufficient filtration efficiency of particles with ultra-small particle size (less than or equal to 0.3 mu m) still exists.

Research reports that micro-nano fibers and nano fibers with various surface morphologies and rich pore structures have higher specific surface areas and pore volumes, so that the trapping capacity of the fibers on fine particles can be improved, and the resistance pressure drop can be reduced. Therefore, the micro-nano fiber and the nano fiber with various surface and pore structures have very wide application prospects in the field of high-efficiency low-resistance air filter materials.

However, electrospun nanofibers have the disadvantages of low molecular chain orientation, low strength, etc., which make nanofibers unusable alone and must be deposited on a nonwoven substrate.

The invention patent with the application number of CN201810341627.1 discloses a high-efficiency low-resistance micro-nanofiber micro-gradient structure filter material and a preparation method thereof, wherein the filter material comprises a nano fine filter layer, a micro support primary filter layer and a protection surface layer; the nano fine filter layer is of a grid structure and consists of a planar matrix fiber layer and a cone structure, the micro-nano fiber layer forms a locally oriented 3D stereo structure, and the filter material which is locally oriented and multistage and comprises a transition structure is formed by nano and micron, so that the filter resistance can be reduced, and the service life of the filter material can be prolonged; and the air passes through the primary filtration of the micron fiber layer, and the fine filtration of the nanometer fiber layer, so that a high filtration effect is achieved, the non-woven fabric surface layer provides the support protection of the core layer filter material, and the mechanical property of the core layer filter material is improved.

The invention patent with the application number of CN201810980066.X discloses a four-layer composite micro-nanofiber air filtering membrane and application thereof, wherein the four-layer composite micro-nanofiber air filtering membrane comprises a non-woven fabric substrate layer, an electrostatic spinning micron-sized fiber layer, an electrostatic spinning bead nanofiber layer and an electrostatic spinning superfine nanofiber layer which are arranged from bottom to top; sequentially depositing three layers of fiber filtering membranes with different scales and different appearances on the surface of a non-woven fabric substrate by adopting an electrostatic spinning technology; from bottom to top, the fiber diameter and the pore size of each layer of fiber membrane are gradually reduced and are distributed in a gradient manner, the filtering effect is better, but the fiber structure of the filtering membrane prepared by the method is single.

Centrifugal spinning is a novel spinning technology which is suitable for both solution spinning and melt spinning, wherein a high molecular polymer solution is thrown out through a spinneret orifice by means of centrifugal force to form jet flow, and the jet flow is rapidly attenuated, solidified and formed into superfine fibers under the combined action of inertia force, viscous force and air resistance and rapidly moves towards a collector. The centrifugal spinning process has high yield, and the prepared non-woven fabric product can be applied to the fields of biomedicine, air filtration, energy and the like. At present, fibers prepared by centrifugal spinning are mainly collected in an annular mode at home and abroad, but the collection mode is not beneficial to the industrialization of the centrifugal spinning, and the obtained fibers are discontinuous short fibers.

The invention patent with the application number of CN201910431025.X discloses automatic production equipment and a method for plane receiving centrifugal spinning, spinning solution sprayed out by a spinning sprayer when the spinning sprayer rotates at a high speed descends in a spiral line and is collected on a collecting device which is arranged below the spinning sprayer and continuously conveys, continuous collection of fibers is realized, and the problem of preparation of continuous filaments is solved.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a composite filter material with high-efficiency and multi-level filtering function and a preparation method thereof.

In order to achieve the aim, the invention provides a composite filter material, which comprises a non-woven fabric primary filter layer, a porous micro-nanofiber middle-effect filter layer and a cobweb nanofiber high-efficiency filter layer which are deposited and compounded from bottom to top in sequence, wherein a first composite layer and a second composite layer which are formed by mutually inserting fibers in adjacent filter layers are arranged between the adjacent filter layers;

wherein the non-woven fabric primary filter layer is a micron-sized fiber non-woven fabric, the fiber diameter is 1-10 mu m, the average pore diameter is 1-10 mu m, and the thickness is 0.5-1.5 mm; the porous micro-nano fiber middle-effect filtering layer is a micro-nano fiber membrane with a fiber surface provided with a nano-pore and nano-particle protrusion mixed structure, the fiber diameter is 100 nm-1.0 mu m, the average pore diameter is 0.5-3 mu m, and the thickness is 0.05-0.2 mm; the efficient filter layer of the spider-web nano fibers is a two-dimensional spider-web structure nano-sized fiber membrane, the fiber diameter is 20-100 nm, the average pore diameter is 0.3-1 mu m, and the thickness is 0.05-0.2 mm.

Preferably, at the wind speed of 0.05m/s, the filtering efficiency of the composite filtering material on PM0.3 NaCl aerosol is 99.999%, the resistance pressure drop is less than 60Pa, and the function of efficient air filtering and purifying can be realized.

In order to achieve the above object, the present invention further provides a preparation method of the composite filter material, comprising the following steps:

s1, preparing a first polymer spinning solution with a preset concentration, injecting the first polymer spinning solution into a plane receiving type centrifugal spinning device for centrifugal spinning, and collecting by a collecting device of the plane receiving type centrifugal spinning device to obtain a non-woven fabric primary filter layer;

s2, preparing a dichloromethane/N, N-dimethylacetamide mixed organic solvent with a predetermined mass ratio, and then respectively adding titanium dioxide nanoparticles and second polymer particles, stirring and performing ultrasonic treatment to obtain a polymer/titanium dioxide/organic solvent mixed spinning solution; finally, preparing porous micro-nano fibers by adopting an electrostatic spinning process, collecting and depositing the porous micro-nano fibers on the surface of the non-woven fabric primary filter layer to obtain a porous micro-nano fiber medium-efficiency filter layer;

s3, preparing a third polymer/dodecyl trimethyl ammonium bromide/N, N-dimethylacetamide mixed spinning solution with a preset concentration, preparing the nano fibers with the cobweb structure by adopting an electrostatic spinning process, and collecting and depositing the nano fibers on the surface of the porous micro-nanofiber medium-efficiency filter layer to obtain the cobweb nano fiber high-efficiency filter layer;

s4, post-processing: and (3) sequentially depositing the three fiber filter layers to form a multilayer superposed fiber membrane, carrying out hot air forming treatment, and carrying out vacuum drying at 80-100 ℃ to prepare the composite filter material.

Preferably, in step S1, the mass fraction of the first polymer is 15 to 40%.

Preferably, the plane receiving type centrifugal spinning device further comprises a spinning device arranged above the collecting device; in the centrifugal spinning process, the spinning device rotates at a high speed to enable the spinning solution to be ejected out of a spinning needle of the spinning device and descend to the collecting device in a spiral line, and the non-woven fabric primary effect filter layer is prepared under the action of centrifugal force.

Preferably, the collecting device is a planar conveyor belt, and the continuous collection of the fibers is performed.

Preferably, in step S2, the mass ratio of dichloromethane to N, N-dimethylacetamide in the organic solvent is 12:1 to 6: 1; in the mixed spinning solution, the mass fraction of the second polymer is 5-20 wt%, and the mass fraction of the titanium dioxide nanoparticles is 0.5-2.0 wt%.

Preferably, in the step S2, in the electrostatic spinning process, the relative humidity is 30 to 55%, the aperture of the spinneret needle is 0.64 to 1mm, the receiving distance is 10 to 15cm, the spinning voltage is 10 to 20kV, and the spinning speed is 0.5 to 1.5 ml/h.

Preferably, in step S3, in the spinning solution, the mass fraction of the third polymer is 5 to 20 wt%, and the mass fraction of the dodecyltrimethylammonium bromide is 0.1 to 0.5 wt%.

Preferably, in step S3, the electrospinning process is an electrostatic screen-spraying process; wherein the spinning voltage is 40-60 kV, the relative humidity is 25-40%, and the receiving distance is 15-25 cm.

Preferably, the first polymer is one of polybutylene terephthalate, polyethylene terephthalate and polyimide; the second polymer is one of polylactic acid, polyacrylonitrile, polyamide, polyvinyl alcohol and polystyrene; the third polymer is one of polyacrylic acid, polyisophthaloyl metaphenylene diamine, polyurethane and polyamide.

Preferably, the first polymer is polyimide; the second polymer is polystyrene; the third polymer is a polyurethane.

Advantageous effects

1. The invention provides a preparation method of a composite filter material, which prepares a multi-stage structure composite air filter material with the aperture distributed along the thickness direction in a gradient way by sequentially depositing fiber membranes with the diameter ranging from micron to submicron to nanometer, and in the composite filter material, a non-woven fabric primary filter layer, a porous micro-nanofiber middle-effect filter layer and a spider web nanofiber high-effect filter layer are tightly combined together, and fibers are interpenetrated and inserted together at the junction of the fiber membranes of different layers to form a composite layer formed by mutually interpenetration of fibers in adjacent filter layers, so as to realize the high-efficiency filtration of the cooperation of different filter layers, namely, the filter adsorption of particles with different sizes is realized by the cooperation of different filter layers, the interception efficiency of the particles is improved, the air permeability is ensured, the air permeability is prevented from being deteriorated due to the single increase of the interception of the particles, or simply increasing the permeability to air, resulting in poor interception capability of the particles.

2. According to the preparation method of the composite filter material, titanium dioxide nano particles are added into an electrostatic spinning solution to endow a fiber filter layer with photocatalysis and antibacterial properties; and the introduction of titanium dioxide nano particles in the fiber material improves the micro-nano structure of the medium-efficiency filter layer, a titanium dioxide nano-shaped protrusion structure is formed on the surface of the fiber and is mixed with the nano-porous structure on the surface of the fiber, the filtering performance of the fiber filter layer is synergistically increased, the specific surface area and the nano-pore volume are increased to a great extent, the pore structure of the fiber medium-efficiency filter layer is further adjusted, the probability of collision and adhesion of particles in the medium-efficiency filter layer and the fiber is improved, and the resistance pressure drop of the fiber membrane is reduced.

3. According to the preparation method of the composite filter material, the nanometer cobweb structure of the high-efficiency filter layer fiber is regulated, controlled and optimized by adding the dodecyl trimethyl ammonium bromide surfactant, so that the nanometer fiber forms a cobweb structure with extremely high coverage rate, and the composite filter material is promoted to realize a high-efficiency filter function; and the fiber membrane in the high-efficiency filter layer has a two-dimensional nano spider-web structure, so that a large number of bonding points exist among fibers, and the fiber membrane has better mechanical property.

4. The composite filter material prepared by the invention has a multistage pore size and a multi-form fiber structure, so that three fiber filter layers with different scales are deposited and compounded to obtain the composite filter material with three-dimensional multistage structure distribution, has excellent filtering performance, antibacterial performance and photocatalytic performance, and has great application potential in the field of air filtration.

5. According to the invention, the non-woven fabric prepared by centrifugal spinning is used as a primary filter layer, so that particles with larger particle size can be primarily filtered to achieve the primary filtering function; on the other hand, the non-woven fabric fiber prepared by the plane receiving type centrifugal spinning process is continuous filament, has better mechanical property and larger strength, and can provide framework support for medium and high efficiency filter layers prepared by electrostatic spinning.

Drawings

Fig. 1 is a schematic structural view of a planar receiving centrifugal spinning apparatus used in the present invention.

Fig. 2 is a schematic structural view of the spinning device in fig. 1.

Fig. 3 is a schematic structural view of the collecting device in fig. 1.

Fig. 4 is a schematic diagram of a porous micro-nanofiber with a hybrid structure of nano-pores and nano-particle protrusions on the surface of an intermediate-efficiency filter layer.

Fig. 5 is a schematic diagram of a high efficiency filtration layer spider-web structured nanofiber.

Fig. 6 is a schematic structural view of a composite filter material.

Reference numerals:

1. a frame; 2. a spinning device; 201. a buffer tank; 202. a material guide pipe; 203. a spinneret; 204. a spinneret needle; 205. a traversing device; 3. a collection device; 301. a horizontal support plate; 302. a collection belt; 303. a traction device; 4. a feeding device; 5. a temperature control device; 6. a control system; 10. the cobweb nanofiber high-efficiency filtering layer; 20. a first composite layer; 30. a porous micro-nano fiber medium effect filtering layer; 40. a second composite layer; 50. a non-woven fabric primary filter layer; 400. porous micro-nanofibers of the middle effect filter layer; 401. a nanopore; 402. a nanoparticle protrusion; 500. the high-efficiency filter layer is made of spider-web structure nano fibers; 501. a nanofiber; 502. a spider web structure.

Detailed Description

The technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without any inventive step, are within the scope of the present invention.

Referring to fig. 1, the planar receiving centrifugal spinning device of the present invention includes a frame 1, a spinning device 2, a collecting device 3, a feeding device 4, a temperature control device 5, and a control system 6; the collecting device 3 is arranged below the spinning device 2 and extends along the horizontal direction; negative pressure is formed on the surface of the collecting device 2, and the centrifugal spinning fibers are adsorbed on the collecting device 2 by the negative pressure.

Referring to fig. 2, the spinning device 2 includes a buffer tank 201, a material guiding pipe 202 and a spinning device 203, and the spinning solution in the buffer tank 201 enters the spinning device 203 through the material guiding pipe 202; the spinneret 203 is provided with a spinneret needle 204, and the spinning solution in the spinneret 203 is ejected through the spinneret needle 204. The spinning device 2 further comprises a traversing device 205 fixedly mounted on the rack 1, and the traversing device 205 drives the spinning device 2 to horizontally reciprocate above the collecting device 3, so that the wide-width non-woven production is realized.

Referring to fig. 3, the collecting device 3 includes a horizontal supporting plate 301, a collecting belt 302 and a traction device 303; the supporting plate 301 is used for supporting the collecting belt 302 in a horizontal state; the collecting belt 302 is an annular belt and is sleeved on the transmission traction device 303 to perform coiling and collecting; the transmission traction device 303 drives the collection belt 302 to perform a cyclic conveying motion in a fixed direction, so as to continuously collect fibers.

In the centrifugal spinning process, the spinning device 2 rotates at a high speed to make the spinning solution jet out from the spinning needle 204 of the spinning device 2 and descend to the collection belt 302 of the collection device 3 in a spiral line to prepare the fiber non-woven fabric.

Referring to fig. 4-6, the present invention provides a method for preparing a composite filter material, comprising the following steps:

s1, preparing a first polymer spinning solution with a preset concentration, injecting the first polymer spinning solution into a plane receiving type centrifugal spinning device, carrying out centrifugal spinning, and collecting by a collecting device to obtain a non-woven fabric primary filter layer;

s3, preparing a third polymer/dodecyl trimethyl ammonium bromide/N, N-dimethylacetamide mixed spinning solution with a preset concentration, preparing two-dimensional cobweb-structured nanofibers by adopting an electrostatic spinning process, and collecting and depositing the two-dimensional cobweb-structured nanofibers on the surface of the porous micro-nanofiber medium-efficiency filter layer to obtain the cobweb-structured nanofiber high-efficiency filter layer;

Referring to fig. 6, the composite filter material prepared by the present invention includes a non-woven fabric primary filter layer 50, a porous micro-nanofiber middle-effect filter layer 30, and a spider-web nanofiber high-effect filter layer 10 deposited and compounded in sequence from bottom to top, and a first composite layer 20 and a second composite layer 40 formed by mutually inserting fibers in adjacent filter layers are disposed between adjacent filter layers, so as to realize high-efficiency filtration by cooperation of different filter layers, that is, through effective gradient cooperation of different filter layers, to realize filtration and adsorption of particles of different sizes, and to improve the interception efficiency of the particles.

The preparation of the composite filter material according to the invention is described below with reference to examples 1 to 17:

example 1

A preparation method of a composite filter material comprises the following steps:

s1, dissolving polyimide polymer particles in N, N-dimethylacetamide, preparing a polyimide spinning solution with the mass fraction of 25 wt%, injecting the polyimide spinning solution into a plane receiving type centrifugal spinning device, carrying out centrifugal spinning, and collecting by a collecting device to obtain a non-woven fabric primary filter layer; wherein, in the centrifugal spinning process, the aperture of a spinning needle is 0.41mm, the collection distance is 10cm, and the spinning temperature is 80 ℃; the spinning speed is 8000 r/min.

S2, preparing a dichloromethane/N, N-dimethylacetamide (DCM/DMAC) mixed organic solvent with a mass ratio of 10:1, adding titanium dioxide particles, fully stirring at room temperature by using a constant-temperature magnetic stirrer, and performing ultrasonic treatment; then adding polystyrene particles, fully stirring until the polystyrene particles are completely dissolved, and then carrying out ultrasonic treatment to finally obtain uniform polystyrene/titanium dioxide/organic solvent mixed spinning solution; finally, injecting the spinning solution into an injector by adopting an electrostatic spinning process to prepare porous micro-nano fibers, and collecting and depositing the porous micro-nano fibers on the surface of the non-woven fabric primary filter layer to obtain a porous micro-nano fiber intermediate filter layer;

wherein in the spinning solution, the mass fraction of polystyrene is 10 wt%, and the mass fraction of titanium dioxide is 1.0 wt%; in the electrostatic spinning process, the spinning voltage is 25kV, the flow rate of the spinning solution is 1ml/h, the receiving distance is 15cm, the relative humidity is 45 percent, and the aperture of a spinning needle head is 0.81 mm.

S3, adding Dodecyl Trimethyl Ammonium Bromide (DTAB) into an N, N-Dimethylacetamide (DMAC) organic solution, fully dissolving, then adding Polyurethane (PU) particles, and magnetically stirring under a heating condition of 80 ℃ to obtain a polyurethane/dodecyl trimethyl ammonium bromide/N, N-dimethylacetamide mixed spinning solution; then preparing two-dimensional cobweb-structured nano fibers by adopting an electrostatic net spraying process, and collecting and depositing the two-dimensional cobweb-structured nano fibers on the surface of the middle-effect filtering layer of the porous micro-nano fibers to obtain the high-effect filtering layer of the cobweb-structured nano fibers;

wherein in the spinning solution, the mass fraction of polyurethane is 15 wt%, and the mass fraction of dodecyl trimethyl ammonium bromide is 0.1 wt%; in the electrostatic net spraying process, the spinning voltage is 40kV, the relative humidity is 25%, and the receiving distance is 20 cm.

S4, post-processing: and (3) sequentially depositing the three fiber filter layers to form a multilayer superposed fiber membrane, carrying out hot air forming treatment, and carrying out vacuum drying at 85 ℃ to prepare the composite filter material.

The composite filter material prepared in example 1 was subjected to a filtration performance test: at the wind speed of 0.05m/s, the composite filter material is used for filtering PM_0.3The filtering efficiency of NaCl aerosol is 99.999%, the resistance pressure drop is less than 60Pa, and the function of high-efficiency air filtering and purifying can be realized. In addition, the antibacterial rate of the composite filter material to staphylococcus aureus reaches 99.5%.

Examples 2 to 10

The difference from example 1 is that: the mass fractions of polystyrene and titanium dioxide, the mass ratio of dichloromethane/N, N-dimethylacetamide (DCM/DMAC) and the relative humidity are different, and other steps are basically the same and are not repeated herein.

Table 1 shows the mass fractions of polystyrene and titanium dioxide, the mass ratio of dichloromethane/N, N-dimethylacetamide (DCM/DMAC) and the setting of the relative humidity in examples 1 to 10

Examples	Polystyrene	Titanium dioxide	DCM/DMAC	Relative humidity
					Example 1	10wt％	1.0wt％	10:1	45％
Example 2	5wt％	1.0wt％	10:1	45％
					Example 3	20wt％	1.0wt％	10:1	45％
Example 4	7wt％	0.5wt％	10:1	45％
					Example 5	7wt％	1.5wt％	10:1	45％
Example 6	7wt％	2.0wt％	10:1	45％
					Example 7	7wt％	1.0wt％	8:1	45％
Example 8	7wt％	1.0wt％	12:1	45％
					Example 9	7wt％	1.0wt％	10:1	30％
Example 10	7wt％	1.0wt％	10:1	55％

In examples 1 to 10, the present invention produced a hybrid fiber medium efficiency filter layer in which both nanopores and titania nanoparticles protrusions were formed on the fibers, as shown in fig. 4. The main mechanism is liquid phase separation pore-forming, namely in a high-voltage electrostatic field, spinning solution is stretched into jet flow, an organic solvent is quickly volatilized to reduce the jet flow temperature, the components of the spinning solution are changed to form a liquid phase separation area, and when the jet flow is solidified into fibers, the area rich in the organic solvent forms a porous structure.

Influence of polymer mass fraction on the effective filtration layer of the composite filter material: the change in polystyrene concentration determines the viscosity of the spinning dope. As the mass fraction of the polystyrene solution increases, the diameter of the fiber also gradually increases. The fiber surface of the polystyrene medium-efficiency filter layer prepared by the invention forms a nano-pore structure, and the quantity of the nano-pore structure is gradually increased and increased along with the increase of the mass fraction of the polystyrene, so that the filtering effect of the medium-efficiency filter layer is remarkably increased.

Influence of titanium dioxide mass fraction on the middle-effect filtering layer of the composite filtering material: along with the increase of the mass fraction of the titanium dioxide in the spinning solution, the diameter of the fiber is gradually increased, the morphological structure of the fiber is greatly changed, the surface of the fiber is provided with titanium dioxide nano-particle protrusions besides a nano-pore structure, and the titanium dioxide nano-particle protrusions are mixed with the nano-pore structure on the surface of the fiber, so that the filtering performance of the fiber filtering layer is synergistically increased, the specific surface area and the nano-pore volume are increased to a great extent, the pore structure of the fiber medium-efficiency filtering layer is further adjusted, the chances of collision and adhesion of particles and the fiber in the medium-efficiency filtering layer are improved, and the resistance pressure drop of the fiber membrane is. In addition, titanium dioxide nanoparticles are subjected to a photocatalytic reaction under the irradiation of light, hydroxyl radicals are generated to cause the oxidation reaction of polyunsaturated phospholipids of bacteria and the loss of respiratory activity, and finally the bacteria are killed, so that the composite filter material prepared by the invention has excellent antibacterial performance.

Influence of dichloromethane/N, N-dimethylacetamide (DCM/DMAC) mass ratio on the effective filtration layer in the composite filter material: dichloromethane is a highly volatile, low conductivity solvent, and N, N-dimethylacetamide is a low volatile solvent in the solvent system. When the content of dichloromethane in the mixed organic solvent is increased, the volatilization rate of the mixed solvent is increased, the number of the nano-pore structures in the fiber is gradually increased, the diameter of the fiber is gradually reduced, and the filtering effect of the medium-efficiency filtering layer is further promoted to be remarkably increased. This is because dichloromethane is a benign solvent for polystyrene, and N, N-dimethylacetamide is a poor solvent for polystyrene, and an increase in dichloromethane in the mixed organic solvent reduces the viscosity of the polystyrene solution, contributing to the formation of a nanoporous structure; meanwhile, under benign solvent conditions, polymer molecular chains are fully swelled, so that the concentration of molecular chain entanglement is low, and the fiber diameter is reduced.

Influence of relative humidity on the effective filtering layer of the composite filtering material: with the increase of relative humidity, the diameter of the fiber is gradually increased, the nano-pore structure on the surface of the fiber is obviously increased, and the protrusions of the titanium dioxide nano-particles are gradually reduced. This is mainly due to the fact that during the electrospinning process, the higher relative humidity can cause water vapor in the air to be condensed into more small water drops which are gathered on the surface of the jet; the increase of the relative humidity is also beneficial to the phase separation of the solution jet flow and the formation of the nano-pore structure on the surface of the fiber; in addition, the gradually increasing fiber diameter allows more titanium dioxide nanoparticles to be encapsulated inside the fiber reducing the formation of protrusions, and thus the nano-protrusion structure gradually decreases.

It should be noted that, as will be understood by those skilled in the art, in the electrostatic spinning process, the setting of the process parameters (the diameter of the spinneret needle, the receiving distance, the spinning voltage, and the spinning speed) all affect the middle effect filter layer of the composite filter material prepared by the present invention, and therefore, the setting of the electrostatic spinning process parameters for preparing the middle effect filter layer according to the present invention is as follows: the aperture of the spinneret needle is 0.64-1 mm, the receiving distance is 10-15 cm, the spinning voltage is 10-20 kV, and the spinning speed is 0.5-1.5 ml/h.

Examples 11 to 17

The difference from example 1 is that: the mass fractions and relative humidities of PU and DTAB are different, and other steps are basically the same, and are not described again.

Table 2 shows the mass fractions of PU and DTAB and the relative humidity settings in examples 11 to 17

In example 1 and examples 11-17, the present invention produced a fibrous high efficiency filtration layer with a two-dimensional spider-web nanostructure formed on the fibers, as shown in fig. 5. With the increase of the spider web coverage, the filtration efficiency of the polyurethane nano spider web structure fiber membrane is obviously increased.

Influence of the polymer on the high-efficiency filtering layer of the composite filtering material: the polyurethane nano-fibers are deposited on the medium-effect filter layer in a disordered and staggered manner to form a nano-aperture spider-web structure, and the fibers at the boundary of the medium-effect filter layer are mutually staggered and interpenetrated together, and the crossed structure can provide a bent multistage channel for air to pass through and particulate matter to intercept. As the concentration of polyurethane increases, the fiber diameter increases and the fibers are uniform and smooth. The nano-cobweb fiber membrane has many open and unobstructed channels formed by a two-dimensional cobweb-shaped pore structure, so that the nano-cobweb fiber membrane has lower pressure resistance. Due to the two-dimensional nano spider-web structure, a large number of bonding points exist among the fibers, and the fiber membrane of the high-efficiency filter layer is promoted to have better mechanical property.

Influence of Dodecyl Trimethyl Ammonium Bromide (DTAB) on the high efficiency filtration layer of the composite filter material: in the preparation process of the composite filter material provided by the invention, the surface tension and the conductivity of the spinning solution can be regulated and controlled by using the surfactant DTAB so as to increase the capability of the spinning solution for forming liquid drops and optimize and regulate and control the spider-web structure of the high-efficiency filter layer. The regulation and control of the polyurethane fiber spider-web coverage rate can be realized by regulating the concentration of DTAB, and the nano spider-web fiber membrane with high coverage rate can be obtained. With the increase of the DTAB concentration, the coverage rate of the two-dimensional spider-web nano structure of the high-efficiency filter layer tends to increase firstly and then decrease. This is mainly due to the fact that when the DTAB concentration is too high, the spinning dope conductivity is too high, resulting in excessive charge remaining on the droplets, thereby increasing the stretching effect of the electric field, causing a partial spider-web destruction of the fibers during phase separation.

Influence of relative humidity on the high-efficiency filter layer of the composite filter material: relative humidity is closely related to solvent evaporation and charge dissipation of the charged fluid. With increasing relative humidity, the spider web structure in the fibrous layer gradually decreases.

It should be noted that, as will be understood by those skilled in the art, in the electrostatic spinning process, the setting of the electrostatic spraying process parameters (receiving distance, spinning voltage) will all affect the high efficiency filter layer of the composite filter material prepared by the present invention, and therefore, the setting of the electrostatic spraying process parameters of the medium efficiency filter layer prepared by the present invention is as follows: the spinning voltage is 40-60 kV, and the receiving distance is 15-25 cm.

In addition, it will be understood by those skilled in the art that the first polymer may also be one of polybutylene terephthalate, polyethylene terephthalate, polyamide, polypropylene, polyethylene; the second polymer can also be one of polyacrylonitrile, polyamide, polyvinyl alcohol and polylactic acid; the third polymer can also be one of polyacrylic acid, polyisophthaloyl metaphenylene diamine and polyamide.

In summary, the invention provides a composite filter material and a preparation method thereof. The composite filter material is prepared by sequentially depositing and compounding micron-to-submicron-to-nanometer-sized fiber filter layers, and comprises a non-woven fabric primary filter layer, a porous micro-nanofiber medium-effect filter layer and a cobweb nanofiber high-efficiency filter layer. The preparation method of the composite filter material comprises the following steps: firstly, a non-woven fabric primary filter layer is prepared by a plane receiving type centrifugal spinning process, then an electrostatic spinning process is adopted, a deposited porous micro-nanofiber medium effect filter layer and a cobweb nanofiber high effect filter layer are sequentially received on the surface of the non-woven fabric primary filter layer, a composite layer formed by mutually inserting fibers in adjacent filter layers is arranged between the adjacent filter layers, and the multi-stage structure composite filter material with the pore diameter changing along the thickness direction in a gradient manner is prepared. In addition, in the composite filter material, the three filter layers are tightly combined together, and fibers at the junctions of the different fiber membranes are mutually interpenetrated together, so that the different filter layers cooperatively perform high-efficiency filtration, namely, the different filter layers are matched to realize filtration and adsorption of particles with different sizes, and the interception efficiency of the particles is improved.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims

1. A composite filter material characterized by: the composite filter material comprises a non-woven fabric primary filter layer, a porous micro-nanofiber medium filter layer and a cobweb nanofiber high-efficiency filter layer which are sequentially deposited and compounded from bottom to top, and a first composite layer and a second composite layer which are formed by mutually inserting fibers in adjacent filter layers are arranged between the adjacent filter layers;

2. A method of preparing the composite filter material of claim 1, wherein: the method comprises the following steps:

s2, preparing a dichloromethane/N, N-dimethylacetamide mixed organic solvent with a predetermined mass ratio, and then preparing a second polymer/titanium dioxide/organic solvent mixed spinning solution; finally, preparing micro-nano fibers with a hybrid structure by adopting an electrostatic spinning process, collecting and depositing the micro-nano fibers on the surface of the non-woven fabric primary filter layer to obtain a porous micro-nano fiber medium-efficiency filter layer;

s4, post-processing: and sequentially depositing and superposing the three fiber filter layers to form a multilayer fiber membrane, carrying out hot air forming treatment, and carrying out vacuum drying at 80-100 ℃ to prepare the composite filter material.

3. The method for producing a composite filter material according to claim 2, characterized in that: in step S1, the mass fraction of the first polymer is 15-40%; the plane receiving type centrifugal spinning device also comprises a spinning device arranged above the collecting device; in the centrifugal spinning process, the spinning device rotates at a high speed to enable the spinning solution to be ejected out of a spinning needle of the spinning device and descend to the collecting device in a spiral line, and a non-woven fabric primary effect filter layer is prepared under the action of centrifugal force; the collecting device is a plane type conveyor belt and is used for continuously collecting the fibers.

4. The method for producing a composite filter material according to claim 2, characterized in that: in step S2, the mass ratio of dichloromethane to N, N-dimethylacetamide in the organic solvent is 12: 1-6: 1; in the mixed spinning solution, the mass fraction of the second polymer is 5-20 wt%, and the mass fraction of the titanium dioxide nanoparticles is 0.5-2.0 wt%.

5. The method for producing a composite filter material according to claim 2, characterized in that: in step S2, in the electrostatic spinning process, the relative humidity is 30-55%, the receiving distance is 10-15 cm, and the spinning voltage is 10-20 kV.

6. The method for producing a composite filter material according to claim 2, characterized in that: in step S3, in the spinning solution, the mass fraction of the third polymer is 5 to 20 wt%, and the mass fraction of the dodecyl trimethyl ammonium bromide is 0.1 to 0.5 wt%.

7. The method for producing a composite filter material according to claim 2, characterized in that: in step S3, the electrospinning process is an electrostatic screen-spraying process; wherein the spinning voltage is 40-60 kV, the relative humidity is 25-40%, and the receiving distance is 15-25 cm.

8. The method for producing a composite filter material according to claim 2, characterized in that: the first polymer is one of polybutylene terephthalate, polyethylene terephthalate, polyimide, polyamide, polypropylene and polyethylene; the second polymer is one of polylactic acid, polyacrylonitrile, polyamide, polyvinyl alcohol and polystyrene; the third polymer is one of polyacrylic acid, polyisophthaloyl metaphenylene diamine, polyurethane and polyamide.

9. The method for producing a composite filter material according to claim 8, characterized in that: the first polymer is polyimide; the second polymer is polystyrene; the third polymer is a polyurethane.

10. A composite filter material according to claim 1 or produced by the production method according to any one of claims 2 to 9, characterized in that: at the wind speed of 0.05m/s, the composite filter material is used for filtering PM_0.3The filtering efficiency of NaCl aerosol is 99.999%, the resistance pressure drop is less than 60Pa, and the function of high-efficiency air filtering and purifying can be realized.