CN112473401A - Polyethylene microporous membrane, polyethylene nanofiltration membrane and preparation method thereof - Google Patents
Polyethylene microporous membrane, polyethylene nanofiltration membrane and preparation method thereof Download PDFInfo
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Abstract
The invention relates to the technical field of nanofiltration membranes, and particularly discloses a polyethylene microporous membrane capable of being used for preparing a nanofiltration membrane, a polyethylene-based nanofiltration membrane and a preparation method thereof. Compared with the nanofiltration membrane prepared by the commercial polyethylene membrane on the market, the nanofiltration membrane prepared by the polyethylene microporous membrane with the limited range of physical property parameters has the advantages of high flux, high divalent salt rejection rate, high monovalent salt rejection rate, high tap water rejection rate and more excellent overall filtering performance, can be applied to scenes of various solvents, keeps the flux stable, does not have damage or breakage on the membrane surface, reaches the tolerance limit only after 70 ℃, has excellent tolerance performance, long service life, has strong market competitiveness and very considerable application prospect.
Description
Technical Field
The invention relates to the technical field of nanofiltration membranes, in particular to a polyethylene microporous membrane capable of being used for preparing a nanofiltration membrane, a polyethylene-based nanofiltration membrane and a preparation method thereof.
Background
Since the last century into industrial production, new technologies are emerging continuously and widely applied in more and more fields, which show great economic benefits, and the explanation of the process on the concept of green sustainable development will be the main melody of the current and future industrial civilization development.
Although the membrane has high filtration efficiency, economy and environmental protection, the traditional high polymer material has poor strength and pollution resistance and short service life, so that the membrane element is replaced too fast, and the material waste phenomenon is very serious. The polyvinyl nanofiltration membrane can greatly reduce the cost of the membrane material, shows great market competitiveness, and is a high-quality substitute which can replace the traditional polysulfone material in the future.
The polyethylene microporous membrane is a new hot spot for preparing nanofiltration and reverse osmosis membranes, but the quality of the polyethylene material directly influences the performance of the prepared nanofiltration membrane, so that the problems of poor membrane strength, short service life and the like are caused. Although the economic advantages are obvious, under the situation of resource conservation and sustainable development, the development of new technology and the improvement of the service life and the utilization rate of products are the current necessary trends.
Therefore, on the basis of meeting the filtering and separating capacity, a high-quality polyethylene microporous membrane is needed, and a high-performance nanofiltration membrane is prepared by using the high-quality polyethylene microporous membrane so as to meet the market demand.
Disclosure of Invention
In view of the above, the present invention is intended to provide a polyvinyl nanofiltration membrane having excellent mechanical strength, environmental resistance, and long-term stability.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the invention provides a polyethylene microporous membrane for preparing a nanofiltration membrane, which is characterized in that: selecting ultra-high molecular weight polyethylene and high density polyethylene to blend, wherein the molecular weight of the ultra-high molecular weight polyethylene is 1.0 x 106～10.0×106The density of the high-density polyethylene is between 0.94 and 0.98g/cm3Wherein the ratio of the ultra-high molecular weight polyethylene to the total mass of the blended polyethylene is 10-50%; the thickness of the polyethylene microporous membrane is between 5 and 30 mu m, the average pore diameter is between 0.01 and 0.15 mu m, and the porosity is between 25 and 75 percent.
Further, the ultra-high molecular weightThe polyethylene has a molecular weight of 3.0X 106～8.0×106The density of the high-density polyethylene is between 0.95 and 0.97g/cm3Wherein the ratio of the ultra-high molecular weight polyethylene to the total mass of the blended polyethylene is 20-30%.
Furthermore, the thickness of the polyethylene microporous membrane is between 8 and 22 mu m, the average pore diameter is between 0.03 and 0.06 mu m, and the porosity is between 30 and 55 percent.
Further, the surface water contact angle of the polyethylene microporous membrane is between 105 and 130 DEG, and the pure water flux is between 100 and 350L/m2H/bar.
Furthermore, the surface water contact angle of the polyethylene microporous membrane is 115-125 DEG, and the pure water flux is 150-250L/m2H/bar.
Further, the surface density of the polyethylene microporous membrane is 5-15 g/m2The air permeability is 100-200 s/100ml, the shrinkage at 105 ℃ is 2.5-6% in MD direction and 1-3% in TD direction.
Furthermore, the surface density of the polyethylene microporous membrane is 8-12 g/m2The air permeability is 120-160 s/100ml, the shrinkage at 105 ℃ is 3.0-4.5% in MD direction and 1.5-2.5% in TD direction.
Further, the microporous polyethylene membrane has a tensile strength of 1550 to 1900kgf/cm in the MD direction2The tensile strength in the TD direction is 1500 to 1850kgf/cm2In the meantime.
Further, the microporous polyethylene membrane has a tensile strength of 1650 to 1800kgf/cm in the MD direction2Between about 1600 and 1750kgf/cm in TD tensile strength2In the meantime.
Further, the microporous polyethylene membrane has an elongation in the MD direction of 20 to 50% and an elongation in the TD direction of 50 to 80%.
Further, the microporous polyethylene membrane has an elongation in the MD direction of 20 to 40% and an elongation in the TD direction of 60 to 70%.
The invention also provides a polyvinyl nanofiltration membrane, which comprises any one of the polyethylene microporous membranes used for preparing the nanofiltration membrane and a functional nano separation layer; the functional nano separation layer is supported on the polyethylene microporous membrane in any one of the above aspects; the polyethylene microporous membrane is formed by interfacial polymerization of polyamine water-phase monomers and polyacyl chloride oil-phase monomers, and the polyethylene nanofiltration membrane with a functional nano separation layer is formed.
The invention also provides a preparation method of the polyvinyl nanofiltration membrane, which is characterized by comprising the following steps:
immersing the polyethylene microporous membrane in any one of the above schemes in a polyamine aqueous phase solution;
taking out the membrane from the water phase, removing the redundant water phase solution, and then soaking the membrane into an oil phase solution containing a polyacyl chloride monomer;
taking out after interface polymerization reaction, and removing redundant oil phase solution to obtain a polyvinyl primary nanofiltration membrane with a functional nano separation layer;
and (3) carrying out heat treatment on the nascent nanofiltration membrane obtained in the step, and cleaning to obtain the polyvinyl nanofiltration membrane.
The invention has the following beneficial effects:
1) the invention provides a polyethylene microporous membrane, and a polyethylene nanofiltration membrane is prepared by using the polyethylene microporous membrane as a substrate. The polyethylene microporous membrane prepared by the invention has the advantages of excellent performance, uniform and stable physical parameters, concentrated pore size distribution, high porosity and good permeability; the polyethylene microporous membrane prepared by the melting-extruding-stretching process shows excellent mechanical properties under a thinner thickness, and lays a foundation for preparing a nanofiltration membrane with stable performance;
2) compared with the nanofiltration membrane prepared by adopting the commercial polyethylene membrane on the market, the nanofiltration membrane prepared by adopting the polyethylene microporous membrane with the limited physical property parameter range has high flux, high divalent salt rejection rate, high monovalent salt rejection rate, high tap water rejection rate and more excellent overall filtration performance;
3) compared with the nanofiltration membrane prepared by adopting the commercial polyethylene membrane on the market, the nanofiltration membrane prepared by adopting the polyethylene microporous membrane with the limited range of physical property parameters can be applied to scenes of various solvents, the flux is stable, and no damage or breakage occurs on the membrane surface;
4) compared with the nanofiltration membrane prepared by a commercial polyethylene membrane on the market, the nanofiltration membrane prepared by the polyethylene microporous membrane with the limited physical property parameter reaches the tolerance limit only after the temperature of the nanofiltration membrane is 70 ℃, and the tolerance performance is superior;
5) compared with the nanofiltration membrane prepared by commercial polyethylene membranes on the market, the polyethylene nanofiltration membrane provided by the invention is more stable in long-term use, long in service life, extremely strong in market competitiveness and very considerable in application prospect.
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Detailed Description
The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The specific embodiment of the invention provides a polyethylene microporous membrane for preparing a nanofiltration membrane, which is prepared by blending ultra-high molecular weight polyethylene and high density polyethylene, wherein the molecular weight of the ultra-high molecular weight polyethylene is 1.0 multiplied by 106～10.0×106The density of the high-density polyethylene is between 0.93 and 0.97g/cm3Wherein the ratio of the ultra-high molecular weight polyethylene to the total mass of the blended polyethylene is 10-50%. The ultrahigh molecular weight polyethylene and the high density polyethylene are selected and blended according to the proportion selected by the invention, and the polyethylene can be obtainedThe microporous film has good crystallization, high mechanical property and good chemical stability resistance. In order to more effectively exhibit the above-mentioned effects, it is further preferable that the molecular weight of the ultrahigh molecular weight polyethylene is 3.0 × 106～8.0×106The density of the high-density polyethylene is between 0.95 and 0.97g/cm3Wherein the ratio of the ultra-high molecular weight polyethylene to the total mass of the blended polyethylene is 20-30%.
In the specific embodiment of the invention, the thickness of the microporous polyethylene film is between 5 and 30 μm, the average pore diameter is between 0.01 and 0.15 μm, and the porosity is between 25 and 75 percent. Thinner membrane thickness reduces the resistance of the fluid transport process, while larger pore size, higher porosity improves the permeability of the membrane, thereby increasing water production efficiency. However, for the requirement of strength, the membrane thickness should not be too thin, the pore diameter should not be too large, the porosity should not be too high, and the defect caused by the damage of the membrane structure is avoided, so that the separation performance of the membrane is not influenced. In order to more effectively exhibit the above effects, the inventors of the present invention have conducted a lot of experiments, and further preferably have a microporous polyethylene film thickness of 8 to 22 μm, an average pore diameter of 0.03 to 0.06 μm, and a porosity of 30 to 55%.
In the specific embodiment of the invention, the surface water contact angle of the polyethylene microporous membrane is between 105 and 130 DEG, and the pure water flux is between 100 and 350L/m2H/bar. Further preferably, the surface water contact angle of the polyethylene microporous membrane is 115-125 DEG, and the pure water flux is 150-250L/m2H/bar.
In the specific embodiment of the invention, the surface density of the polyethylene microporous membrane is 5-15 g/m2The air permeability is 100-200 s/100ml, and the shrinkage at 105 ℃ is 2.5-6% in MD direction and 1-3% in TD direction. The surface density is low, the air permeability value is low, the more effective holes of the membrane main body are, the better the permeability is, but when the surface density and the air permeability value are too low, the mechanical strength of the membrane main body is deteriorated, the performance and the service life are influenced, and therefore, an optimal range is provided for the selection of the membrane main body. The smaller the shrinkage at 105 ℃ is, the lower the sensitivity of the film matrix segment to heat is, and therefore the longer the life and durability of the film are, the wider the applicable range is. To make moreThe above effects are effectively exhibited, and the surface density of the polyethylene microporous membrane is more preferably 8 to 12g/m2The air permeability is 120-160 s/100ml, the shrinkage at 105 ℃ is 3.0-4.5% in MD direction and 1.5-2.5% in TD direction.
In the embodiment of the invention, the tensile strength of the microporous polyethylene membrane in the MD direction is 1550 to 1900kgf/cm2The tensile strength in the TD direction is 1500 to 1850kgf/cm2In the meantime.
In the embodiment of the invention, the elongation of the polyethylene microporous membrane in the MD direction is between 20 and 50 percent, and the elongation in the TD direction is between 50 and 80 percent.
The tensile strength and the elongation are important indexes for representing the mechanical property of the film, and the film has the advantages of high tensile strength, high breaking strength, good rigidity and difficult breaking; on the other hand, the elongation is high and the toughness of the film is good, but the film is easily deformed to cause deformation of the film pores and lose the functionality, so that it is desired that the tensile strength is high and the elongation is low.
In order to more effectively exhibit the above-mentioned effects, it is further preferable that the microporous polyethylene membrane has a tensile strength of 1650 to 1800kgf/cm in the MD direction2Between about 1600 and 1750kgf/cm in TD tensile strength2In the meantime. Further preferably, the microporous polyethylene membrane has an elongation in the MD of 20 to 40% and an elongation in the TD of 60 to 70%.
The specific embodiment of the invention also provides a method for preparing the polyethylene microporous membrane capable of being used for preparing the nanofiltration membrane, which comprises the following steps:
melting a certain amount of polyethylene, a diluent and an antioxidant according to a certain proportion at high temperature to obtain a uniform molten casting solution; the mass of the polyethylene accounts for 10-35% of the total mass of the melt-casting liquid; the diluent is paraffin oil and accounts for 60-85% of the total mass; the antioxidant is dibutyl hydroxy toluene, phosphite ester or 2-tert-butyl-6-methylphenol, and accounts for 0.5-10% of the total mass; the melting temperature is between 150 and 250 ℃;
extruding the melt casting liquid through a double-screw extruder, cooling and casting the melt casting liquid into a strip-shaped object, then, enabling the strip-shaped object to enter a stretcher for asynchronous stretching, and preparing a strip-shaped primary film in the MD direction and the TD direction; the cooling temperature is 50-110 ℃; the stretching ratio is 6-10 times;
then immersing the mixture into an extracting agent dichloromethane for extraction to remove the diluent; cleaning, heat setting and finally rolling to obtain the polyethylene microporous membrane; the heat setting temperature is 50-100 ℃.
The specific embodiment of the invention also provides a polyvinyl nanofiltration membrane, which comprises any one of the polyethylene microporous membrane and the functional nano separation layer which can be used for preparing the nanofiltration membrane; the functional nano separation layer is supported on the polyethylene microporous membrane which can be used for preparing the nanofiltration membrane in any scheme; the polyethylene microporous membrane is formed by interfacial polymerization of polyamine water-phase monomers and polyacyl chloride oil-phase monomers, and the polyethylene nanofiltration membrane with a functional nano separation layer is formed.
The specific embodiment of the invention also provides a preparation method of the polyvinyl nanofiltration membrane, which comprises the following steps:
immersing the polyethylene microporous membrane which can be used for preparing the nanofiltration membrane and is prepared in any scheme in a polyamine aqueous phase solution;
taking out the immersed membrane from the water phase, removing the redundant water phase solution, and then immersing the membrane into an oil phase solution containing the polyacyl chloride monomer;
taking out after interface polymerization reaction, and removing redundant oil phase solution to obtain a polyvinyl primary nanofiltration membrane with a functional nano separation layer;
and (3) carrying out heat treatment on the nascent nanofiltration membrane obtained in the step, and cleaning to obtain the polyvinyl nanofiltration membrane.
Further, the polyamine aqueous phase solution comprises a polyfunctional amine monomer, an acid acceptor and a surfactant.
Furthermore, the mass fraction of the polyfunctional amine monomer in the aqueous phase solution is 1.0-4.0%, and the mass fraction of the acid acceptor in the aqueous phase solution is 0.1-10%; the mass fraction of the surfactant in the aqueous phase solution is 0.05-0.5%.
Specifically, the multifunctional amine monomer is one or more of piperazine, homopiperazine, N-methylpiperazine, 1-amino-4-methylpiperazine, 2, 3-dimethylpiperazine, m-phenylenediamine, p-phenylenediamine, o-phenylenediamine and ethylenediamine.
Specifically, the acid acceptor is one or more of triethylamine, sodium acetate, pyridine and potassium carbonate.
The surfactant comprises one or more of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, polyoxyethylene octylphenol ether, polyoxyethylene nonylphenol ether, polyoxyethylene fatty alcohol ether, Tween 20, Tween 80 and Dynol series.
Further, the mass fraction of the polybasic acyl chloride monomer in the oil phase solvent is 0.01-1%, and the immersion time is 5-120 seconds.
Specifically, the polybasic acyl chloride monomer is one of trimesoyl chloride, paraphthaloyl chloride, isophthaloyl chloride, phthaloyl chloride and cyclohexanetricarboxylic acid chloride.
Specifically, the oil phase solvent is one of n-hexane, cyclohexane, Isopar G, Isopar E and Isopar L.
Specifically, the mass fraction of the polybasic acyl chloride monomer in the oil phase solvent is 0.05-0.5%.
Further, the heat treatment temperature is 30-90 ℃, and the heat treatment time is 0.5-15 minutes.
The present invention will be described in detail below by way of examples.
In the following examples and comparative examples, the performance parameters were determined as follows:
(1) thickness: the thickness of the plastic film and the sheet is measured by using a German Mark film thickness gauge C1216 according to the measuring method of GB/T6672-2001, the same sample is tested for 5 times, and the average value is taken as the thickness.
(2) Average pore diameter and porosity: the average pore size and porosity of the polyethylene separation membrane were obtained by testing with a fully automatic water press of type AAQ-3K-a-1, manufactured by american Porous Materials inc. The water pressure of the full-automatic water pressure instrument is controlled at 1500psi of 100 and 1500psi, the surface tension of water is 72dyn/cm, and the contact angle between water and the polyethylene separation membrane is 115 degrees.
(3) Water contact angle: the surface contact angle was measured by the sitting drop method using a model DSA25 contact angle tester manufactured by KRUSS, germany.
(4) Air permeability value: the determination was carried out according to the GB/T1037 Plastic film and sheet Water vapor permeability test method using a Gurley air Permeability tester 4110.
(5) Surface density: samples were taken at ambient temperature (23 ℃) and formed into 0.10M by 0.10M squares, and M was weighed, and the areal density ρ was M/0.01.
(5) Shrinkage rate: measuring the distance L0 between two points on the diaphragm under the test environment of normal temperature (23 ℃), adding stainless steel in an oven with the temperature of 120 +/-1 ℃ to the sample, keeping the temperature for 1h, taking out the sample, measuring the distance L1 between the two points on the diaphragm when the diaphragm is cooled to the test environment of normal temperature, and calculating the shrinkage ratio S according to the following formula: s ═ L0-L1)/L0 × 100%.
(6) Mechanical properties: the tensile strength and elongation were tested according to the plastic tensile test method of GB1040-79 using an AGX-V electronic Universal tensile tester from Shimadzu corporation.
(7) Pure water flux and rejection:
pure water flux: and (3) measuring by adopting a nanofiltration tester (self-made).
Retention rate: measured using a conductivity meter (HQ30d, hash, usa).
Flux and rejection: pure water flux is an important parameter for representing the water permeability of the separation membrane, and the membrane is pre-pressed for 1 hour by using deionized water as feed liquid under the pressure of 0.48MPa to ensure that the effluent is stable; then, a pure water flux test was carried out, and the effective membrane area of the test apparatus was 32cm2. The calculation formula is as follows:
wherein Q is the volume (L) of pure water passing therethrough, Δ t is the time (h) of passing therethrough, and A is the effective area (cm) of the permeable membrane2)。
Retention performance: interceptionThe rate (R) is an important indicator for characterizing the separation capacity of the membrane. After the membrane pre-compaction is finished, the MgSO with 2000mg/L of MgSO4And 500mg/L NaCl and 150mg/L tap water as test solutions, and tested at room temperature and 25 ℃. The calculation formula is as follows:
CPand CFThe permeate and feed concentrations (mg/L), respectively, are generally considered to be linearly related to the salt concentration, and thus the salt cut-off R can be calculated using conductivity instead of concentration.
Example 1
Polyethylene with the mass fraction of 32 percent is taken as a raw material (wherein the high molecular weight polyethylene accounts for 40 percent of the blended polyethylene raw material), 67 percent of paraffin oil is added as a diluent, 1 percent of dibutyl hydroxy toluene is taken as an antioxidant, the mixture is mixed and melted at the temperature of 200 ℃, and then the mixture is extruded by a double screw, and is cast to be cooled and mixed at the temperature of 100 ℃. The film was stretched 8.2 times in the transverse direction and 6.8 times in the longitudinal direction. And (3) extracting the membrane in dichloromethane, then performing heat setting at 80 ℃, and rolling to obtain the polyethylene microporous membrane 1. Immersing a polyethylene microporous membrane into a polyamine aqueous phase solution, wherein the solution contains piperazine (with the mass concentration of 2%), an acid acceptor, triethylamine (with the mass concentration of 0.75%) and sodium dodecyl sulfate (with the mass concentration of 0.1%); taking out, removing the redundant liquid on the surface, immersing into a polybasic acyl chloride oil phase solution, wherein the polybasic acyl chloride monomer is trimesoyl chloride (the mass concentration is 0.11 percent), the used solvent is ethylcyclohexane, immersing for 45 seconds, and taking out; and then, the mixture enters an oven for heat treatment at 60 ℃ for 2 minutes to obtain the polyvinyl nanofiltration membrane A1.
Example 2
Polyethylene with the total mass fraction of 28 percent is used as a raw material (wherein the high molecular weight polyethylene accounts for 20 percent of the raw material of the blended polyethylene), phosphite ester with the total mass of 2 percent is used as an antioxidant, and the rest of the diluent is paraffin oil, is mixed and melted at the temperature of 240 ℃, is extruded by a double screw, and is extended to be cooled and mixed at the temperature of 80 ℃. The film was stretched 8.8 times in the transverse direction and 7.4 times in the longitudinal direction, respectively. And (3) extracting the membrane in dichloromethane, then performing heat setting at 80 ℃, and rolling to obtain the polyethylene microporous membrane 2.
The polyvinyl nanofiltration membrane B2 was prepared according to the method for preparing polyvinyl nanofiltration membranes as in example 1.
Example 3
Polyethylene accounting for 25 percent of the total mass is taken as raw material (wherein, the high molecular weight polyethylene accounts for 33 percent of the blended polyethylene raw material), the rest of the diluent paraffin oil is mixed and melted at 210 ℃, and then is extruded by a double screw, and is extended to be cooled and mixed at 110 ℃. The film was stretched 9.0 times in the transverse direction and 7.7 times in the longitudinal direction, respectively. And (3) extracting the membrane in dichloromethane, then performing heat setting at 65 ℃, and rolling to obtain the polyethylene microporous membrane 3.
The polyvinyl nanofiltration membrane C3 was prepared according to the method for preparing polyvinyl nanofiltration membranes as in example 1.
Example 4
Polyethylene with the total mass fraction of 24 percent is used as a raw material (wherein the high molecular weight polyethylene accounts for 25 percent of the blended polyethylene raw material), dibutyl hydroxy toluene with the total mass of 1 percent is used as an antioxidant, and the rest of diluent paraffin oil is mixed and melted at the temperature of 200 ℃, extruded by a double screw, and cast to be cooled and mixed at the temperature of 90 ℃. The film was stretched 9.5 times in the transverse direction and 7.5 times in the longitudinal direction. And (3) extracting the membrane in dichloromethane, performing heat setting at 80 ℃, and rolling to obtain the polyethylene microporous membrane 4.
The polyvinyl nanofiltration membrane D4 was prepared according to the method for preparing polyvinyl nanofiltration membranes as described in example 1.
The physical properties of the microporous polyethylene membrane 1-4 are shown in Table 2.
TABLE 1 Property parameter Table of base film
Comparative examples 1 to 3
Three commercial polyethylene microporous membranes of R1, P2 and Q3 were purchased from the market, and the polyethylene nanofiltration membranes R11, P22 and Q33 were prepared according to the method for preparing polyethylene nanofiltration membranes in example 1.
TABLE 2 physical Properties of commercial microporous polyethylene Membrane
The results of the filtration performance test of comparative examples 1 to 3 and examples 1 to 4 are shown in table 3 below:
table 3 test results of pure water flux and inorganic salt rejection rate for examples and comparative examples
As can be seen from table 3: the flux of the nanofiltration membrane prepared by the commercial polyethylene membrane in the comparative example is low, even if the aperture of the R1 basal membrane is large, the porosity is low, and the flux measured is still less than 60L/m2H, and the flux of the prepared nanofiltration membrane is only 36L/m because the base membrane of the Q33 has small aperture and low porosity2H. Interception tests show that the nanofiltration membrane prepared by the commercial polyethylene membrane in the comparative example has the divalent salt content of less than 99 percent and the monovalent salt content of about 50 to 60 percent; in the embodiment of the polyvinyl nanofiltration membrane, the flux reaches nearly 70L/m2H, meanwhile, the retention rate of divalent salt is about 99%, and the retention rate of monovalent salt is slightly lower but is more than 60%; after the tap water is changed, the test shows that the comparative example can keep about 60 percent of interception, and the example can reach more than 70 percent.
The results of the long-term stability tests conducted on comparative examples 1 to 3 and examples 1 to 4 are shown in Table 4 below:
TABLE 4 Long term stability test
As can be seen from table 4: long-term stability tests show that R11 and P22 in the comparative example have higher flux, the attenuation reaches 25 percent after 30 days, and Q33 has lower flux and the attenuation is 13 percent; in the example, the attenuation of the test in 30 days is 13-18%, and the attenuation is smaller than that of the comparative example. The base membranes of R11 and P22 have large pore diameters, are easy to be polluted and blocked after long-term use, and cause serious flux attenuation.
Example 5
Two films, D4 and R11, were tested for their resistance in different solution environments, and the results are shown in Table 5 below:
TABLE 5 tolerance test
As can be seen from table 5: the flux is kept stable in the tolerance test of the embodiment to various solvents, and the integrity test also proves that no damage or breakage occurs on the membrane; in various solvent tests, the commercial membrane R11 has relatively poor alkali resistance and oxidation resistance, and has the phenomena of flux increase and membrane surface dead spots; the flux of the two membranes in the acid solution is slightly low, and the flux is slightly improved due to the expansion of the high molecular chain segment in the alkali solution, which are normal phenomena; the examples showed good performance in the alkaline and oxidizing agent tests, with little increase in flux, but no defect on the membrane surface, and excellent solvent resistance. In the comparative example, the R11 has low areal density and poor tensile strength, and the membrane surface is easy to deform, so that the functional skin layer is damaged, and the problem of intolerance to alkali and oxidizing agents is solved.
The polyethylene nanofiltration membrane E5 and the commercial membrane R11 were subjected to different temperature tests, and the results are shown in the following Table 6:
TABLE 6 high temperature resistance test
As can be seen from table 6: the membrane E5 has excellent temperature tolerance, and has stable flux below 50 ℃ and flux change of about 10 percent; the flux starts to obviously increase at 60 ℃, and the flux increases by nearly 30 percent until 70 ℃, and the film surface has defects at the moment, so that the film surface is considered to reach tolerance limit; and the flux change of R11 is small below 40 ℃, and after the flux changes to exceed 50 ℃, the flux rises obviously, and the film surface has dead spots. Comparative example No. R11 is sensitive to heat due to poor heat shrinkage, and is deformed by heat, the skin layer is broken, and the flux is remarkably increased.
The above matters related to the common general knowledge are not described in detail and can be understood by those skilled in the art.
The above description is only exemplary of the present invention and should not be construed as limiting the present invention, and any modification, equivalent replacement, or improvement made without departing from the spirit and principle of the present invention should be included in the scope of the present invention (e.g., another prior art method is used to prepare the polyethylene microporous membrane according to the present invention). The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.
Claims (13)
1. A polyethylene microporous membrane for preparing a nanofiltration membrane is characterized in that: selecting ultra-high molecular weight polyethylene and high density polyethylene to blend, wherein the molecular weight of the ultra-high molecular weight polyethylene is 1.0 x 106～10.0×106The density of the high-density polyethylene is between 0.94 and 0.98g/cm3Wherein the ratio of the ultra-high molecular weight polyethylene to the total mass of the blended polyethylene is 10-50%; the thickness of the polyethylene microporous membrane is between 5 and 30 mu m, the average pore diameter is between 0.01 and 0.15 mu m, and the porosity is between 25 and 75 percent.
2. The polyethylene microporous membrane used for preparing nanofiltration membranes according to claim 1, wherein the polyethylene microporous membrane comprises: the molecular weight of the ultra-high molecular weight polyethylene is 3.0 x 106～8.0×106Said high density polyethyleneThe density of (a) is 0.95 to 0.97g/cm3Wherein the ratio of the ultra-high molecular weight polyethylene to the total mass of the blended polyethylene is 20-30%.
3. The polyethylene microporous membrane used for preparing nanofiltration membranes according to claim 1, wherein the polyethylene microporous membrane comprises: the thickness of the polyethylene microporous membrane is between 8 and 22 mu m, the average pore diameter is between 0.03 and 0.06 mu m, and the porosity is between 30 and 55 percent.
4. The polyethylene microporous membrane used for preparing nanofiltration membranes according to claim 1, wherein the polyethylene microporous membrane comprises: the surface water contact angle of the polyethylene microporous membrane is 105-130 DEG, and the pure water flux is 100-350L/m2H/bar.
5. The polyethylene microporous membrane used for preparing nanofiltration membranes according to claim 4, wherein the polyethylene microporous membrane comprises: the surface water contact angle of the polyethylene microporous membrane is 115-125 DEG, and the pure water flux is 150-250L/m2H/bar.
6. The polyethylene microporous membrane used for preparing nanofiltration membranes according to claim 1, wherein the polyethylene microporous membrane comprises: the surface density of the polyethylene microporous membrane is 5-15 g/m2The air permeability is 100-200 s/100ml, the shrinkage at 105 ℃ is 2.5-6% in MD direction and 1-3% in TD direction.
7. The polyethylene microporous membrane used for preparing nanofiltration membranes according to claim 6, wherein the polyethylene microporous membrane comprises: the surface density of the polyethylene microporous membrane is 8-12 g/m2The air permeability is 120-160 s/100ml, the shrinkage at 105 ℃ is 3.0-4.5% in MD direction and 1.5-2.5% in TD direction.
8. The polyethylene microporous membrane used for preparing nanofiltration membranes according to claim 1, wherein the polyethylene microporous membrane comprises: the microporous polyethylene membrane has tensile strength in the MD directionBetween 1550 and 1900kgf/cm2The tensile strength in the TD direction is 1500 to 1850kgf/cm2In the meantime.
9. The polyethylene microporous membrane used for preparing nanofiltration membranes according to claim 8, wherein the polyethylene microporous membrane comprises: the microporous polyethylene membrane has a tensile strength of 1650 to 1800kgf/cm in the MD direction2Between about 1600 and 1750kgf/cm in TD tensile strength2In the meantime.
10. The polyethylene microporous membrane used for preparing nanofiltration membranes according to claim 1, wherein the polyethylene microporous membrane comprises: the microporous polyethylene membrane has an elongation in the MD of 20 to 50% and an elongation in the TD of 50 to 80%.
11. The polyethylene microporous membrane used for preparing nanofiltration membranes according to claim 10, wherein the polyethylene microporous membrane comprises: the polyethylene microporous membrane has an elongation in the MD direction of 20-40% and an elongation in the TD direction of 60-70%.
12. A polyvinyl nanofiltration membrane is characterized in that: the polyethylene microporous membrane used for preparing the nanofiltration membrane, and the functional nano separation layer, wherein the polyethylene microporous membrane is as claimed in any one of claims 1 to 11; the functional nano separation layer is supported on the polyethylene microporous membrane; the polyethylene microporous membrane is formed by interfacial polymerization of polyamine water-phase monomers and polyacyl chloride oil-phase monomers, and the polyethylene nanofiltration membrane with a functional nano separation layer is formed.
13. The preparation method of the polyvinyl nanofiltration membrane is characterized by comprising the following steps:
immersing the polyethylene microporous membrane used for preparing the nanofiltration membrane of any one of claims 1 to 11 in a polyamine aqueous phase solution;
taking out the membrane from the water phase, removing the redundant water phase solution, and then soaking the membrane into an oil phase solution containing a polyacyl chloride monomer;
taking out after interface polymerization reaction, and removing redundant oil phase solution to obtain a polyvinyl primary nanofiltration membrane with a functional nano separation layer;
and (3) carrying out heat treatment on the nascent nanofiltration membrane obtained in the step, and cleaning to obtain the polyvinyl nanofiltration membrane.
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