CN109550411B - Polytetrafluoroethylene hollow fiber composite membrane and low-temperature wrapping preparation method - Google Patents
Polytetrafluoroethylene hollow fiber composite membrane and low-temperature wrapping preparation method Download PDFInfo
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- CN109550411B CN109550411B CN201811525075.6A CN201811525075A CN109550411B CN 109550411 B CN109550411 B CN 109550411B CN 201811525075 A CN201811525075 A CN 201811525075A CN 109550411 B CN109550411 B CN 109550411B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/30—Polyalkenyl halides
- B01D71/32—Polyalkenyl halides containing fluorine atoms
- B01D71/36—Polytetrafluoroethene
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D67/0002—Organic membrane manufacture
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/08—Hollow fibre membranes
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/12—Composite membranes; Ultra-thin membranes
- B01D69/125—In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction
Abstract
The invention discloses a polytetrafluoroethylene hollow fiber composite membrane and a low-temperature wrapping preparation method, and aims to overcome the defects that the polytetrafluoroethylene hollow fiber membrane is high in sintering temperature, high in energy consumption, easy in damage of a microporous structure and influenced in porosity. The polytetrafluoroethylene hollow fiber microporous membrane comprises a polytetrafluoroethylene hollow fiber microporous membrane and a polytetrafluoroethylene flat microporous membrane which is wrapped on the outer surface of the polytetrafluoroethylene hollow fiber microporous membrane and is partially overlapped, and crosslinked polyvinyl alcohol is contained between the polytetrafluoroethylene hollow fiber microporous membrane and the polytetrafluoroethylene flat microporous membrane and between the overlapped parts of the polytetrafluoroethylene flat microporous membrane. The stable wrapping and bonding of the polytetrafluoroethylene flat sheet membrane on the surface of the polytetrafluoroethylene hollow fiber membrane under the low-temperature condition can be realized, the energy consumption is low, the microporous structure of the composite membrane is not damaged, and the porosity is not influenced.
Description
Technical Field
The invention relates to the field of preparation of polymer hollow fiber membranes, in particular to a polytetrafluoroethylene hollow fiber composite membrane and a low-temperature wrapping preparation method.
Background
The regeneration of sewage is one of the keys of the sustainable utilization of water resources in the future, and relates to the purification and reuse of sewage in various fields of industry, agriculture, municipal administration, rural areas and the like. With the gradual development of separation technology, membrane separation is becoming the core technology for sewage reuse and water quality purification and upgrading. As one of hearts of membrane separation technology, hollow fiber membranes have received high attention and popularity in the industry due to their large integration area and small footprint. At present, common hollow fiber membranes mainly made of polyvinylidene fluoride, polysulfone, polyvinyl chloride and the like are limited by the material defects, and the hollow fiber membranes are often poor in physical and chemical stability and short in service life, and are difficult to bear use in harsh environments such as acid, alkali, oxidation and the like.
With the research, the polytetrafluoroethylene has excellent chemical stability, thermal stability and corrosion resistance, and the hollow fiber membrane prepared from the polytetrafluoroethylene not only has high strength and high porosity, but also has excellent acid and alkali resistance, oxidation resistance, high and low temperature resistance and the like. For example, in the patent (201210554647. X), alginate is taken as a carrier, a nascent polytetrafluoroethylene hollow fiber membrane is prepared by adopting dry-wet spinning, and then the polytetrafluoroethylene hollow fiber membrane is prepared by sintering, stretching and other processes; the patent (201310033443.6) prepares a polytetrafluoroethylene hollow fiber membrane by mixing polytetrafluoroethylene dispersion resin powder with an extrusion aid and the like, and performing processes such as blank pressing, extrusion, longitudinal stretching, heat setting and the like. However, the preparation processes of the polytetrafluoroethylene hollow fiber membranes have the following common points: and (2) longitudinal hot stretching, wherein the porosity and the pore size of the membrane depend on the longitudinal hot stretching multiplying power, the pore size is small and the porosity is low when the stretching multiplying power is low, the pore size is large and the porosity is large when the stretching multiplying power is high, and the production and preparation of the polyvinylidene fluoride hollow fiber membrane with small pore size and high porosity are difficult to realize. In the patent (201210051801.1), polyacrylonitrile is used as a carrier, and a composite pore-forming agent is combined to spin polytetrafluoroethylene hollow fibers, and the polytetrafluoroethylene hollow fiber membrane is further prepared through high-temperature preoxidation, high-temperature sintering and extraction washing processes. However, the method has the disadvantages of high difficulty in spinning and subsequent extraction and washing processes, and low porosity of the prepared polytetrafluoroethylene hollow fiber membrane.
Then, the patent (201310248985.5) prepares a polytetrafluoroethylene flat membrane with small aperture and high porosity through the processes of extrusion, rolling, stretching, sintering and the like, then cuts the polytetrafluoroethylene flat membrane into strips and wraps the strips on a polytetrafluoroethylene hollow fiber supporting layer with large aperture and high porosity, and finally prepares the polytetrafluoroethylene hollow fiber membrane with small aperture and high porosity on the surface through sintering. In the patent (201410119738. X), a polytetrafluoroethylene flat membrane is wound on an organic fiber sleeve such as aramid fiber and poly (p-phenylene terephthalamide), and then a polytetrafluoroethylene heterogeneous hollow fiber membrane is prepared by a sintering process. However, the preparation process of the polytetrafluoroethylene hollow fiber membrane needs to realize the stable coating of the polytetrafluoroethylene flat membrane on the supporting tube through a high-temperature sintering process, the sintering temperature is higher than 300 ℃, the production energy consumption is very high, and meanwhile, the high-temperature sintering process tends to cause irreversible loss on the surface micropores of the polytetrafluoroethylene flat membrane. .
In conclusion, the polytetrafluoroethylene hollow fiber membrane commonly used at present has high sintering temperature and large energy consumption, and the microporous structure is easy to damage, thereby influencing the porosity.
Disclosure of Invention
The invention overcomes the defects of high sintering temperature, large energy consumption, easy damage of a microporous structure and influence on porosity of the polytetrafluoroethylene hollow fiber membrane, and provides the polytetrafluoroethylene hollow fiber composite membrane and the low-temperature wrapping preparation method, which can realize stable wrapping and bonding of the polytetrafluoroethylene flat membrane on the surface of the polytetrafluoroethylene hollow fiber membrane under the low-temperature condition, have low energy consumption, do not damage the microporous structure of the composite membrane and do not influence on porosity.
In order to solve the technical problems, the invention adopts the following technical scheme: a polytetrafluoroethylene hollow fiber composite membrane comprises a polytetrafluoroethylene hollow fiber microporous membrane and a polytetrafluoroethylene flat microporous membrane which is wrapped on the outer surface of the polytetrafluoroethylene hollow fiber microporous membrane and is partially overlapped, and crosslinked polyvinyl alcohol is contained between the polytetrafluoroethylene hollow fiber microporous membrane and the polytetrafluoroethylene flat microporous membrane and between overlapped parts of the polytetrafluoroethylene flat microporous membrane.
The polytetrafluoroethylene flat microporous membrane is wrapped on the outer surface of the polytetrafluoroethylene hollow microporous membrane, crosslinked polyvinyl alcohol is contained between the polytetrafluoroethylene hollow microporous membrane and the polytetrafluoroethylene flat microporous membrane and between the overlapped parts of the polytetrafluoroethylene flat microporous membrane, stable adhesion of the polytetrafluoroethylene flat microporous membrane on the surface of the polytetrafluoroethylene hollow microporous membrane under a low-temperature condition can be realized, the energy consumption is low, the microporous structure of the composite membrane is not damaged, and the porosity is not influenced. The polytetrafluoroethylene hollow fiber microporous membrane and the polytetrafluoroethylene flat microporous membrane prepared by the stretching and sintering processes form a unique fibril-node microstructure and a microporous structure consisting of the fibril-node microstructure in the stretching process, and polyvinyl alcohol molecules are adsorbed in a polytetrafluoroethylene membrane body, particularly on surfaces of fibrils and nodes of the polytetrafluoroethylene membrane body; the wrapped polytetrafluoroethylene flat membrane and fibrils and nodes between the wrapped polytetrafluoroethylene flat membrane and polytetrafluoroethylene hollow fiber membranes are in close contact, and polyvinyl alcohol is distributed among the corresponding fibrils and fibrils, fibrils and nodes, and nodes which are in close contact with the surfaces of the flat membrane and the hollow fiber membranes; when the cross-linking agent is cross-linked with the polyvinyl alcohol adsorbed on the polytetrafluoroethylene fibrils and nodes, the fibrils and the fibrils, the fibrils and the nodes, and the nodes which are in close contact with the surfaces of the flat membrane and the hollow fiber membrane form a micro-lap joint structure, and macroscopically, the micro-lap joint structure is shown as greatly enhancing the bonding strength of the polytetrafluoroethylene flat membrane and the polytetrafluoroethylene hollow fiber membrane.
Preferably, the pore diameter of the polytetrafluoroethylene hollow fiber microporous membrane is 0.5-10 microns. The pore diameter of the polytetrafluoroethylene flat microporous membrane is 0.05-1 micron, and the thickness is 5-50 microns. The aperture of the polytetrafluoroethylene flat microporous membrane is smaller than that of the polytetrafluoroethylene hollow fiber microporous membrane, so that the blockage phenomenon of the wrapped polytetrafluoroethylene hollow fiber microporous membrane is prevented. The method is favorable for ensuring higher porosity of the polytetrafluoroethylene hollow fiber composite membrane, and simultaneously obtains good support performance and less fluid resistance.
A low-temperature wrapping preparation method of a polytetrafluoroethylene hollow fiber composite membrane comprises the following steps:
s1, slitting the polytetrafluoroethylene flat microporous membrane to obtain a strip-shaped polytetrafluoroethylene flat microporous membrane with the width of 5-15 mm;
s2, soaking the strip polytetrafluoroethylene flat microporous membrane into 1-5% polyvinyl alcohol aqueous solution by mass;
s3, soaking a polytetrafluoroethylene hollow fiber microporous membrane into a polyvinyl alcohol solution with the mass fraction of 1-5%;
s4, wrapping the impregnated banded polytetrafluoroethylene flat microporous membrane on the outer surface of the impregnated polytetrafluoroethylene hollow fiber membrane microporous membrane to form a polytetrafluoroethylene hollow fiber composite membrane;
s5, placing the wrapped polytetrafluoroethylene hollow fiber composite membrane in a cross-linking agent solution at the temperature of 20-100 ℃ for treatment for 10-60 minutes to obtain the polytetrafluoroethylene hollow fiber composite membrane.
The invention firstly adopts polyvinyl alcohol aqueous solution to respectively soak a polytetrafluoroethylene hollow fiber microporous membrane and a polytetrafluoroethylene flat plate microporous membrane, then a polytetrafluoroethylene flat plate membrane is continuously and tightly wrapped on the polytetrafluoroethylene hollow fiber membrane through a wrapping process, and finally the wrapped composite membrane is soaked in a cross-linking agent solution, thus realizing the stable adhesion of the polytetrafluoroethylene flat plate membrane on the surface of the polytetrafluoroethylene hollow fiber membrane under the low temperature condition. The reason is that the polytetrafluoroethylene hollow fiber microporous membrane and the polytetrafluoroethylene flat microporous membrane prepared by the stretching and sintering processes form a unique fibril-node microstructure and a microporous structure formed by the fibril-node microstructure in the stretching process. When the microporous membrane is soaked in the polyvinyl alcohol solution, polyvinyl alcohol molecules are adsorbed in the polytetrafluoroethylene membrane body, particularly to the surfaces of fibrils and nodes of the polytetrafluoroethylene membrane body; then through the wrapping process, fibrils and nodes between the polytetrafluoroethylene flat membranes and the polytetrafluoroethylene hollow fiber membranes are in close contact, and polyvinyl alcohol is distributed among the corresponding fibrils and fibrils, fibrils and nodes which are in close contact with the surfaces of the flat membranes and the hollow fiber membranes; furthermore, when the wrapped composite membrane is soaked in a cross-linking agent solution, polyvinyl alcohol adsorbed on polytetrafluoroethylene fibrils and nodes is cross-linked, so that fibrils, fibrils and nodes, and nodes which are in close contact with the surface of the flat membrane and the hollow fiber membrane form a micro-lap joint structure, the bonding strength of the polytetrafluoroethylene flat membrane and the polytetrafluoroethylene hollow fiber membrane is greatly enhanced macroscopically, and the bonding strength of the wrapped polytetrafluoroethylene hollow fiber membrane can reach more than 0.3 MPa.
Meanwhile, the crosslinked polyvinyl alcohol has good structural stability, and compared with the uncrosslinked polyvinyl alcohol, the crosslinked polyvinyl alcohol has good water resistance and medicament performance, and can prevent the polyvinyl alcohol from being dissolved in water or being corroded and falling off by chemical medicaments in the use process, thereby reducing the bonding strength of the composite polytetrafluoroethylene hollow fiber membrane.
The mass fraction of the polyvinyl alcohol aqueous solution is 1-5%, the concentration is low, so that the polyvinyl alcohol is mainly present in the specific fibril and node microstructure of the polytetrafluoroethylene microporous membrane in the cross-linking process, the original pore structure of the microporous membrane is not influenced, the surface microstructure of the microporous membrane is not damaged, and the pore size of the polytetrafluoroethylene hollow fiber composite membrane can be regulated and controlled only by selecting a polytetrafluoroethylene flat membrane and a hollow fiber membrane with proper pore size and porosity before the wrapping process. The temperature of the cross-linking agent and the cross-linking process thereof is preferably 20-100 ℃, and compared with the sintering temperature of nearly 300 ℃ in the existing high-temperature sintering technology, the energy consumption of the composite membrane making process can be greatly reduced, and the production cost is reduced.
Preferably, the cross-linking agent solution is an aldehyde aqueous solution, wherein the mass fraction of aldehyde is 1% -10%. Is favorable for ensuring better bonding strength and porosity of the polytetrafluoroethylene hollow fiber composite membrane.
Preferably, the aldehyde is one or more of glutaraldehyde, glyoxal, succinaldehyde, adipaldehyde, formaldehyde, acetaldehyde, butyraldehyde. The pH value of the cross-linking agent solution is 1-5. Is favorable for ensuring the bonding strength and the porosity of the polytetrafluoroethylene hollow fiber composite membrane.
Preferably, the polyvinyl alcohol is a polyvinyl alcohol polymer having a polymer main chain containing vinyl alcohol units, and the molar ratio of the vinyl alcohol repeating units is more than 50%.
Compared with the prior art, the invention has the beneficial effects that: the stable wrapping and bonding of the polytetrafluoroethylene flat sheet membrane on the surface of the polytetrafluoroethylene hollow fiber membrane under the low-temperature condition can be realized in the preparation process of the polytetrafluoroethylene hollow fiber composite membrane, the energy consumption is low, the microporous structure of the composite membrane is not damaged, and the porosity is not influenced.
Drawings
FIG. 1 is a microscopic morphology representation of a polytetrafluoroethylene hollow fiber composite membrane according to example 1;
FIG. 2 is a microscopic topography representation of the combination of the surface of the PTFE hollow fiber microporous membrane of example 1 with the surface of the PTFE flat microporous membrane;
FIG. 3 is a microscopic morphology characterization diagram of the polytetrafluoroethylene hollow fiber composite membrane of comparative example 1.
Detailed Description
The technical scheme of the invention is further described in detail by the following specific embodiments in combination with the attached drawings:
the invention provides a polytetrafluoroethylene hollow fiber composite membrane, which comprises a polytetrafluoroethylene hollow fiber microporous membrane and a polytetrafluoroethylene flat microporous membrane wrapped on the outer surface of the polytetrafluoroethylene hollow fiber microporous membrane and partially overlapped with the polytetrafluoroethylene flat microporous membrane, wherein cross-linked polyvinyl alcohol is contained between the polytetrafluoroethylene hollow fiber microporous membrane and the polytetrafluoroethylene flat microporous membrane and between the overlapped parts of the polytetrafluoroethylene flat microporous membrane. The pore diameter of the polytetrafluoroethylene hollow fiber microporous membrane is 0.5-10 microns. The pore diameter of the polytetrafluoroethylene flat microporous membrane is 0.05-1 micron, and the thickness is 5-50 microns.
A low-temperature wrapping preparation method of a polytetrafluoroethylene hollow fiber composite membrane comprises the following steps:
s1, slitting the polytetrafluoroethylene flat microporous membrane to obtain a strip-shaped polytetrafluoroethylene flat microporous membrane with the width of 5-15 mm;
s2, soaking the strip polytetrafluoroethylene flat microporous membrane into 1-5% polyvinyl alcohol aqueous solution by mass;
s3, soaking a polytetrafluoroethylene hollow fiber microporous membrane into a polyvinyl alcohol solution with the mass fraction of 1-5%;
s4, wrapping the impregnated banded polytetrafluoroethylene flat microporous membrane on the outer surface of the impregnated polytetrafluoroethylene hollow fiber membrane microporous membrane to form a polytetrafluoroethylene hollow fiber composite membrane; the number of layers of the polytetrafluoroethylene flat membrane wrapping is preferably 1-3;
s5, placing the wrapped polytetrafluoroethylene hollow fiber composite membrane in a cross-linking agent solution at the temperature of 20-100 ℃ for treatment for 10-60 minutes to obtain the polytetrafluoroethylene hollow fiber composite membrane. The cross-linking agent solution is an aldehyde aqueous solution, wherein the mass fraction of aldehyde is 1-10%. The aldehyde is one or more of glutaraldehyde, glyoxal, succinaldehyde, adipaldehyde, formaldehyde, acetaldehyde and butyraldehyde. The pH value of the cross-linking agent solution is 1-5.
The polyvinyl alcohol is a polyvinyl alcohol polymer with a polymer main chain containing vinyl alcohol units, and the molar ratio of the vinyl alcohol repeating units is more than 50%.
In step S1, in order to provide the polytetrafluoroethylene hollow fiber composite membrane with better surface pore size distribution and separation performance, the polytetrafluoroethylene flat microporous membrane preferably has a pore size of 0.05 to 1 micron and a thickness of 5 to 50 microns; in order to optimize the wrapping process, the strip-shaped width of the slit polytetrafluoroethylene flat membrane is preferably 5-15 mm.
In steps S2 and S3, the polyvinyl alcohol solution with high concentration can provide higher adhesive strength to the polytetrafluoroethylene hollow fiber composite membrane, which of course also causes poor blocking of the micro-pores of the composite membrane, resulting in decreased porosity; while low polyethylene concentrations result in low composite film bond strengths. In order to provide better adhesive strength and porosity to the polytetrafluoroethylene hollow fiber composite membrane, the mass fraction of the polyvinyl alcohol aqueous solution is preferably 1-5%.
In step S3, in order to provide the polytetrafluoroethylene hollow fiber composite membrane with higher porosity, good support performance and less fluid resistance, the pore size distribution of the polytetrafluoroethylene hollow fiber microporous membrane is preferably 0.5 to 10 μm.
In step S4, the number of layers wrapped by the ptfe flat sheet membrane is preferably 1 to 3 in order to obtain superior retention performance and separation throughput.
In step S5, the crosslinking process is an acetal reaction between polyvinyl alcohol and an aldehyde crosslinking agent in an aqueous environment, and a high concentration of the crosslinking agent, a high crosslinking temperature, and a low pH can increase the crosslinking reaction speed and further shorten the crosslinking time, which, of course, can also cause poor adhesion such as particles due to excessive reaction, resulting in roughness of the film surface and reduced porosity; low crosslinker concentration, low crosslinking temperature and high pH result in a reduced crosslinking reaction rate, resulting in longer crosslinking time and higher process time consumption. In order to optimize the crosslinking process and integrate the requirements of the adhesion strength and the porosity of the polytetrafluoroethylene hollow fiber composite membrane, the mass percentage of aldehyde in the crosslinking agent solution is preferably 1-10%, the pH value is 1-5, the crosslinking temperature is 20-100 ℃, and the crosslinking treatment time is 10-60 minutes.
Of course, in the present invention, the core performance index of the polytetrafluoroethylene hollow fiber composite membrane is the overlapping portion of the wrapped flat membrane and the adhesion strength of the flat membrane and the hollow fiber membrane support layer. The method for testing the wrapping adhesion strength of the composite film is as follows:
step 1, two polytetrafluoroethylene hollow fiber composite membranes are extracted and bent into a U shape, the effective length of a membrane wire is taken to be 30 cm, the opening end of the membrane wire is packaged by an adhesive, the opening of the membrane wire is kept, and the membrane element for testing the bonding strength is manufactured.
Step 2, fixing the test membrane element, putting the effective length section of the hollow fiber composite membrane into water, slowly introducing high-pressure gas into the inner cavity of the hollow fiber composite membrane through a pressure reducing valve, slowly increasing the gas inlet pressure, wherein the process is that the pressure per liter is 0.05MPa, keeping the pressure for 1min, and simultaneously observing whether the hollow fiber composite membrane has a rupture phenomenon; the air inlet pressure when the outer surface of the hollow fiber composite membrane is cracked is selected as the bonding strength of the hollow fiber composite membrane.
Example 1: a low-temperature wrapping preparation method of a polytetrafluoroethylene hollow fiber composite membrane comprises the following steps:
s1, selecting a biaxially oriented polytetrafluoroethylene flat microporous membrane with the average pore size of 0.1 micron and the thickness of 30 microns, and slitting to obtain a strip-shaped polytetrafluoroethylene flat microporous membrane with the width of 10 millimeters;
s2, dipping the banded polytetrafluoroethylene flat microporous membrane obtained in the step S1 into a polyvinyl alcohol aqueous solution with the mass fraction of 3%;
s3, selecting a polytetrafluoroethylene hollow fiber microporous membrane with the average pore diameter of 1 micron, wherein the inner diameter and the outer diameter are respectively 1 mm and 2 mm, and soaking in a polyvinyl alcohol solution with the mass percentage of 3%;
s4, wrapping the impregnated strip polytetrafluoroethylene flat microporous membrane obtained in the step S2 on the outer surface of the impregnated polytetrafluoroethylene hollow fiber microporous membrane obtained in the step S3, wherein the number of wrapping layers is 1;
and S5, treating the wrapped polytetrafluoroethylene composite membrane obtained in the step S4 in glutaraldehyde aqueous solution with the temperature of 60 ℃, the mass fraction of 5% and the pH value of 2 for 40 minutes to obtain the polytetrafluoroethylene hollow fiber composite membrane.
And performing microscopic morphology characterization on the obtained polytetrafluoroethylene hollow fiber composite membrane. The results are shown in FIGS. 1 and 2.
As can be seen from fig. 1, the surface of the resulting polytetrafluoroethylene hollow fiber composite membrane is provided with intact fibrils and nodes, which can provide excellent rejection performance and high separation flux of the composite membrane. As can be seen from FIG. 2, the surface of the polytetrafluoroethylene hollow fiber microporous membrane of the resulting polytetrafluoroethylene hollow fiber composite membrane is tightly bonded to the surface of the polytetrafluoroethylene flat microporous membrane.
Tests show that the bonding strength of the polytetrafluoroethylene hollow fiber composite membrane is about 0.35MPa, and the pure water flux of the prepared polytetrafluoroethylene hollow fiber composite membrane reaches 2100
。
Comparative example 1
Step (1), selecting a biaxially oriented polytetrafluoroethylene flat microporous membrane with the average pore diameter of 0.1 micron and the thickness of 30 microns, and slitting to obtain a strip-shaped polytetrafluoroethylene flat microporous membrane with the width of 10 millimeters;
step (2), selecting a polytetrafluoroethylene hollow fiber microporous membrane with the average pore diameter of 1 micron, wherein the inner diameter and the outer diameter are respectively 1 mm and 2 mm, wrapping the belt-shaped polytetrafluoroethylene flat microporous membrane in the step (1) on the outer surface of the polytetrafluoroethylene hollow fiber microporous membrane, and wrapping the outer surface by 1 layer;
and (3) sintering the wrapped polytetrafluoroethylene composite membrane obtained in the step (2) for 30 seconds at 360 ℃ to obtain the polytetrafluoroethylene hollow fiber composite membrane.
Tests show that the polytetrafluoroethylene hollow fiber composite membrane has the adhesive strength of about 0.3MPa and the pure water flux of about1500 
。
As can be seen from fig. 3, the surface of the ptfe hollow fiber composite membrane has a large area of pore fusion due to high-temperature melting, and the porosity of the membrane surface is low.
Example 2: a low-temperature wrapping preparation method of a polytetrafluoroethylene hollow fiber composite membrane comprises the following steps:
s1, selecting a biaxially oriented polytetrafluoroethylene flat microporous membrane with the average pore size of 0.2 micron and the thickness of 30 microns, and slitting to obtain a strip-shaped polytetrafluoroethylene flat microporous membrane with the width of 10 millimeters;
s2, soaking the band-shaped polytetrafluoroethylene flat microporous membrane obtained in the step S1 in a polyvinyl alcohol aqueous solution with the mass fraction of 5%;
s3, selecting a polytetrafluoroethylene hollow fiber microporous membrane with the average pore diameter of 1.5 microns, wherein the inner diameter and the outer diameter are respectively 1 mm and 2 mm, and soaking the polytetrafluoroethylene hollow fiber microporous membrane in a polyvinyl alcohol solution with the mass percentage of 5%;
s4, wrapping the impregnated banded polytetrafluoroethylene flat microporous membrane obtained in the step S2 on the outer surface of the impregnated polytetrafluoroethylene hollow fiber microporous membrane obtained in the step S3, wherein the number of wrapping layers is 1;
and S5, treating the wrapped polytetrafluoroethylene composite membrane obtained in the step S4 in a formaldehyde aqueous solution with the temperature of 40 ℃, the mass fraction of 3% and the pH value of 3 for 50 minutes to obtain the polytetrafluoroethylene hollow fiber composite membrane.
Tests show that the bonding strength of the polytetrafluoroethylene hollow fiber composite membrane is about 0.40MPa, and the pure water flux reaches 2500
。
Example 3: a low-temperature wrapping preparation method of a polytetrafluoroethylene hollow fiber composite membrane comprises the following steps:
s1, selecting a biaxially oriented polytetrafluoroethylene flat microporous membrane with the average pore diameter of 0.4 micron and the thickness of 10 microns, and slitting to obtain a strip-shaped polytetrafluoroethylene flat microporous membrane with the width of 10 millimeters;
s2, impregnating the banded polytetrafluoroethylene flat microporous membrane obtained in the step S1 with a polyvinyl alcohol aqueous solution with the mass fraction of 1%;
s3, selecting a polytetrafluoroethylene hollow fiber microporous membrane with the average pore diameter of 2 microns, wherein the inner diameter and the outer diameter are respectively 1 mm and 2 mm, and soaking the polytetrafluoroethylene hollow fiber microporous membrane in a polyvinyl alcohol solution with the mass percentage of 1%;
s4, wrapping the impregnated banded polytetrafluoroethylene flat microporous membrane obtained in the step S2 on the outer surface of the impregnated polytetrafluoroethylene hollow fiber microporous membrane obtained in the step S3, wherein the number of wrapping layers is 3;
and S5, treating the wrapped polytetrafluoroethylene composite membrane obtained in the step S4 in an aqueous solution with the mass fraction of 3% acetaldehyde and 7% hexanedial and the pH value of 3 at the temperature of 80 ℃ for 10 minutes to obtain the polytetrafluoroethylene hollow fiber composite membrane.
Tests show that the bonding strength of the polytetrafluoroethylene hollow fiber composite membrane is about 0.45MPa, and the pure water flux reaches 3600
。
Example 4: a low-temperature wrapping preparation method of a polytetrafluoroethylene hollow fiber composite membrane comprises the following steps:
s1, selecting a biaxially oriented polytetrafluoroethylene flat microporous membrane with the average pore diameter of 0.5 micron and the thickness of 50 microns, and slitting to obtain a strip-shaped polytetrafluoroethylene flat microporous membrane with the width of 15 millimeters;
s2, impregnating the banded polytetrafluoroethylene flat microporous membrane obtained in the step S1 with a polyvinyl alcohol aqueous solution with the mass fraction of 4%;
s3, selecting a polytetrafluoroethylene hollow fiber microporous membrane with the average pore diameter of 3 microns, wherein the inner diameter and the outer diameter are respectively 1 mm and 2 mm, and soaking the polytetrafluoroethylene hollow fiber microporous membrane in a polyvinyl alcohol solution with the mass percentage of 4%;
s4, wrapping the impregnated banded polytetrafluoroethylene flat microporous membrane obtained in the step S2 on the outer surface of the impregnated polytetrafluoroethylene hollow fiber microporous membrane obtained in the step S3, wherein the number of wrapping layers is 1;
and S5, treating the wrapped polytetrafluoroethylene composite membrane obtained in the step S4 in a glyoxal aqueous solution with the temperature of 20 ℃, the mass fraction of 1% and the pH value of 1 for 30 minutes to obtain the polytetrafluoroethylene hollow fiber composite membrane.
Tests show that the bonding strength of the polytetrafluoroethylene hollow fiber composite membrane is about 0.35MPa, and the pure water flux reaches 4300
。
Example 5: a low-temperature wrapping preparation method of a polytetrafluoroethylene hollow fiber composite membrane comprises the following steps:
s1, selecting a biaxially oriented polytetrafluoroethylene flat microporous membrane with the average pore diameter of 0.2 micron and the thickness of 40 microns, and slitting to obtain a strip-shaped polytetrafluoroethylene flat microporous membrane with the width of 12 millimeters;
s2, impregnating the banded polytetrafluoroethylene flat microporous membrane obtained in the step S1 with a polyvinyl alcohol aqueous solution with the mass fraction of 2.5%;
s3, selecting a polytetrafluoroethylene hollow fiber microporous membrane with the average pore diameter of 2 microns, wherein the inner diameter and the outer diameter are respectively 1 mm and 2 mm, and soaking the polytetrafluoroethylene hollow fiber microporous membrane in a polyvinyl alcohol solution with the mass percentage of 2.5%;
s4, wrapping the impregnated banded polytetrafluoroethylene flat microporous membrane obtained in the step S2 on the outer surface of the impregnated polytetrafluoroethylene hollow fiber microporous membrane obtained in the step S3, wherein the number of wrapping layers is 1;
and S5, treating the wrapped polytetrafluoroethylene composite membrane obtained in the step S4 in an aqueous solution with the mass fraction of 3% of succinaldehyde and 4% of butyraldehyde and the pH value of 5 at the temperature of 50 ℃ for 20 minutes to obtain the polytetrafluoroethylene hollow fiber composite membrane.
Tests show that the bonding strength of the polytetrafluoroethylene hollow fiber composite membrane is about 0.30MPa, and the pure water flux reaches 3100
。
Example 6: a low-temperature wrapping preparation method of a polytetrafluoroethylene hollow fiber composite membrane comprises the following steps:
s1, selecting a biaxially oriented polytetrafluoroethylene flat microporous membrane with the average pore diameter of 0.4 micron and the thickness of 10 microns, and slitting to obtain a strip-shaped polytetrafluoroethylene flat microporous membrane with the width of 9 millimeters;
s2, impregnating the banded polytetrafluoroethylene flat microporous membrane obtained in the step S1 with a polyvinyl alcohol aqueous solution with the mass fraction of 1%;
s3, selecting a polytetrafluoroethylene hollow fiber microporous membrane with the average pore diameter of 3 microns, wherein the inner diameter and the outer diameter are respectively 1 mm and 2 mm, and soaking the polytetrafluoroethylene hollow fiber microporous membrane in a polyvinyl alcohol solution with the mass percentage of 1%;
s4, wrapping the impregnated banded polytetrafluoroethylene flat microporous membrane obtained in the step S2 on the outer surface of the impregnated polytetrafluoroethylene hollow fiber microporous membrane obtained in the step S3, wherein the number of wrapping layers is 2;
and S5, treating the wrapped polytetrafluoroethylene composite membrane obtained in the step S4 in a glutaraldehyde aqueous solution with the temperature of 100 ℃, the mass fraction of 8% and the pH value of 4 for 60 minutes to obtain the polytetrafluoroethylene hollow fiber composite membrane.
Tests show that the bonding strength of the polytetrafluoroethylene hollow fiber composite membrane is about 0.40MPa, and the pure water flux reaches 3200
。
The above-described embodiments are merely preferred embodiments of the present invention, which is not intended to be limiting in any way, and other variations and modifications are possible without departing from the scope of the invention as set forth in the appended claims.
Claims (7)
1. A polytetrafluoroethylene hollow fiber composite membrane is characterized by comprising a polytetrafluoroethylene hollow fiber microporous membrane and a polytetrafluoroethylene flat microporous membrane wrapped on the outer surface of the polytetrafluoroethylene hollow fiber microporous membrane and partially overlapped with the polytetrafluoroethylene hollow fiber microporous membrane, wherein cross-linked polyvinyl alcohol is contained between the polytetrafluoroethylene hollow fiber microporous membrane and the polytetrafluoroethylene flat microporous membrane and between the overlapped parts of the polytetrafluoroethylene flat microporous membrane; the adhesive strength of the polytetrafluoroethylene hollow fiber membrane can reach more than 0.3 MPa; the polytetrafluoroethylene hollow fiber composite membrane is prepared by a low-temperature wrapping preparation method, and the preparation process comprises the following steps:
s1, slitting the polytetrafluoroethylene flat microporous membrane to obtain a strip-shaped polytetrafluoroethylene flat microporous membrane with the width of 5-15 mm;
s2, soaking the strip polytetrafluoroethylene flat microporous membrane into 1-5% polyvinyl alcohol aqueous solution by mass;
s3, soaking a polytetrafluoroethylene hollow fiber microporous membrane into a polyvinyl alcohol solution with the mass fraction of 1-5%;
s4, wrapping the impregnated banded polytetrafluoroethylene flat microporous membrane on the outer surface of the impregnated polytetrafluoroethylene hollow fiber membrane microporous membrane to form a polytetrafluoroethylene hollow fiber composite membrane;
s5, placing the wrapped polytetrafluoroethylene hollow fiber composite membrane in a cross-linking agent solution at the temperature of 20-100 ℃ for treatment for 10-60 minutes to obtain the polytetrafluoroethylene hollow fiber composite membrane.
2. The polytetrafluoroethylene hollow fiber composite membrane according to claim 1, wherein the pore size of the polytetrafluoroethylene hollow fiber microporous membrane is 0.5 to 10 microns.
3. The polytetrafluoroethylene hollow fiber composite membrane according to claim 1, wherein the polytetrafluoroethylene flat microporous membrane has a pore size of 0.05 to 1 micron and a thickness of 5 to 50 microns.
4. The polytetrafluoroethylene hollow fiber composite membrane according to claim 1, wherein the cross-linking agent solution is an aldehyde aqueous solution, wherein the mass fraction of aldehyde is 1-10%.
5. A polytetrafluoroethylene hollow fiber composite membrane according to claim 4, wherein the aldehyde is one or more of glutaraldehyde, glyoxal, succinaldehyde, adipaldehyde, formaldehyde, acetaldehyde, and butyraldehyde.
6. A polytetrafluoroethylene hollow fiber composite membrane according to claim 1 or 4 or 5, wherein the pH of the crosslinking agent solution is in the range of 1 to 5.
7. A polytetrafluoroethylene hollow fiber composite membrane according to claim 1 or 4 or 5, wherein the polyvinyl alcohol is a polyvinyl alcohol polymer having a polymer main chain containing vinyl alcohol units, and the molar ratio of the vinyl alcohol repeating units is more than 50%.
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| CN110394068B (en) * | 2019-06-21 | 2021-12-10 | 苏州智能制造研究院有限公司 | Janus polytetrafluoroethylene hollow fiber membrane and preparation method thereof |
| CN111359442B (en) * | 2020-03-16 | 2022-10-14 | 中国科学院宁波材料技术与工程研究所 | PTFE composite membrane for MABR and preparation method thereof |
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| CN102266725A (en) * | 2011-06-09 | 2011-12-07 | 浙江东大环境工程有限公司 | Polytetrafluoroethylene hollow fiber membrane and preparation method thereof |
| CN103191654B (en) * | 2013-04-27 | 2015-02-25 | 中材科技股份有限公司 | Lasting hydrophilic modification method of polytetrafluoroethylene microporous membrane |
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