CN108176253B - Polypropylene microporous membrane and preparation method thereof - Google Patents
Polypropylene microporous membrane and preparation method thereof Download PDFInfo
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- CN108176253B CN108176253B CN201611122541.7A CN201611122541A CN108176253B CN 108176253 B CN108176253 B CN 108176253B CN 201611122541 A CN201611122541 A CN 201611122541A CN 108176253 B CN108176253 B CN 108176253B
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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
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Abstract
A polypropylene microporous membrane and a preparation method thereof relate to a high-molecular separation membrane and a preparation method thereof, in particular to a polypropylene microporous membrane prepared by adopting an environment-friendly diluent and a preparation method thereof. The preparation method solves the problem that the diluent generally has physiological toxicity when TIPS is adopted to prepare the polypropylene microporous membrane in the prior art, and the extracted extractant is recycled, so that green and clean production in the membrane preparation process is realized. The method is simple and suitable for industrial popularization and application. The polypropylene microporous membrane prepared by the method has a through spongy microporous structure. The prepared polypropylene microporous membrane can be applied to the fields of membrane distillation and membrane degassing.
Description
Technical Field
The invention belongs to the field of polymer material science, relates to a polymer separation membrane and a preparation method thereof, and particularly relates to a polypropylene microporous membrane and a preparation method thereof.
Background
The polypropylene is a highly crystalline thermoplastic resin mainly polymerized from propylene monomers, and has the excellent properties of high transparency, no toxicity, light specific gravity, easy processing, high impact strength, chemical corrosion resistance, flexibility resistance, good electrical insulation property and the like. Because of its excellent performance, large output and low price, it has great advantages as the membrane material for preparing microporous membrane.
In the technical field of preparing polypropylene microporous membranes by a TIPS (thermal induced phase separation) method, membrane preparation parameters are required to be fully adjusted to control the membrane structure and morphology so as to adjust the membrane performance, and the polymer type, the concentration in a membrane casting solution, the polymer molecular weight, the diluent type, the diluent concentration, the diluent molecular weight, the melting temperature and time of a system, additives, cooling conditions, extraction, drying and the like all influence the preparation of the polypropylene microporous membranes by the thermal induced phase separation method. Among them, the diluent plays an important role in the film formation process by the TIPS method.
The diluents used in the prior art are mostly phthalate-containing diluent systems (e.g. dibutyl phthalate) and diphenyl ether-containing irritant diluent systems. Such diluents are either generally physiologically toxic or have a strong irritating odor. The influence of carcinogenesis or fertility impairment on experimental animals or human is determined by the international cancer research organization. So far, most of solvents used in the film preparation process have reproductive and environmental toxicity, which causes adverse effects on human health and environmental safety.
Chinese patent 103785303 discloses a method for preparing hydrophobic membrane of hollow polypropylene fiber by thermally induced phase separation, which uses carcinogenic and teratogenic substances containing phthalate as coagulating bath medium. Patent CN101862601A discloses a polypropylene hollow fiber microporous membrane and a preparation method thereof, wherein one or more of dibutyl phthalate, fatty amine, calcium stearate, isopropyl alcohol, methyl propyl benzoate, vegetable oil or diphenyl ether is used as a diluent. Patent CN201210434202.8 discloses a preparation method and application of a polypropylene hollow fiber hydrophobic membrane, which adopts a mixture of vegetable oil and phthalate as a diluent. Patent CN1356410A discloses a method for preparing polypropylene microporous membrane by thermally induced phase separation, which uses vegetable oil, liquid paraffin, diphenyl ether and engine oil as diluent, adipic acid and benzoic acid as auxiliary agents to prepare homogeneous solution, and the homogeneous solution is spun into polypropylene hollow fiber filaments through a spinning nozzle, and the polypropylene hollow fiber filaments are solidified in water and extracted to prepare the polypropylene hollow fiber membrane. Patent 00802940.7 and patent 00802939.3 disclose a method for preparing an integral asymmetric polyolefin hydrophobic membrane for gas exchange by heat-induced liquid-liquid separation, using a mixed solvent system consisting of two compounds a and B, compound a being a weak solvent for the polymer and compound B being a non-solvent for the polymer. In the case of polypropylene, the compound A adopted in patent 00802940.7 is soybean oil, palm kernel oil, dioctyl phthalate, N-bis (2-hydroxyethyl) tallow amine or a mixture thereof. Compound B is dibutyl phthalate, diethyl phthalate, triacetin, castor oil, or a mixture thereof. Patent 00802939.3 uses N, N-bis (2-hydroxyethyl) tallow amine, dioctyl phthalate, soybean oil, palm kernel oil or mixtures thereof as compound A and dibutyl phthalate, diethyl phthalate, triethyl glyceride, castor oil or mixtures thereof as compound B for polypropylene.
The adverse environmental effects of these diluents have been appreciated in the manufacture of films, and strictly speaking, such a film process cannot be referred to as a green cleaning process. Especially, as the law of environmental protection becomes stricter, the demand for environmentally friendly green solvents or low-toxic and low-harmful solvents will become stronger. Therefore, the present inventors have studied to prepare a polypropylene microporous membrane by a TIPS method using an environmentally friendly diluent.
Disclosure of Invention
In order to overcome the technical problems in the prior art, the invention provides a polypropylene microporous membrane prepared by a TIPS method, which is prepared by controlling the composition of a membrane casting solution, including the concentration of a polymer, the type of a diluent, the composition and the content of the diluent, and thermally induced phase separation membrane forming conditions, including extrusion temperature, cooling conditions and extraction conditions.
The invention also provides a method for preparing the environment-friendly polypropylene microporous membrane by the thermally induced phase separation method, which comprises the steps of mixing the polypropylene resin and the environment-friendly diluent to prepare a membrane casting solution, filtering, extruding the membrane casting solution through a slit die head, cooling and solidifying to prepare a polypropylene microporous membrane precursor, rolling the polypropylene microporous membrane precursor by a winder, putting the wound precursor into a microporous membrane extraction device, extracting by using an extracting agent, and drying the extracted membrane by a freeze drying device to obtain the polypropylene microporous membrane. The cross section of the membrane prepared by the method has a through and spongy asymmetric homogeneous microporous structure, and the problem that a diluent generally has physiological toxicity or strong pungent smell when a polypropylene hollow fiber membrane is prepared by TIPS in the prior art is solved. After the extractant and the diluent are treated by the extraction device, the recovered extractant can be recycled. Also provides the application of the polypropylene microporous membrane in membrane distillation and membrane degassing.
In order to achieve the above purposes, the technical scheme adopted by the invention is as follows:
a polypropylene microporous membrane comprising: a polypropylene resin,
the contact angle of the polypropylene microporous membrane is 120-140 degrees, and the average pore size is 0.01-0.04 mu m.
The preparation method of the polypropylene microporous membrane comprises the following steps:
step a, mixing polypropylene resin and a diluent to prepare a membrane casting solution;
b, filtering the membrane casting solution by a filter;
step c, conveying the filtered casting solution to a slit die head, extruding the casting solution through the slit die head to obtain a flat membrane precursor, and then immersing the flat membrane precursor into a coagulating bath to cool the flat membrane precursor until the flat membrane precursor is solidified to obtain a polypropylene microporous membrane precursor;
d, winding the polypropylene microporous membrane precursor by using a winding machine, and then putting the wound precursor into a microporous membrane extraction device for extraction by using an extractant;
and e, drying the extracted microporous membrane precursor by a freeze drying device, and removing the extractant to obtain the polypropylene microporous membrane.
In step a, after mixing the polypropylene resin and the diluent, heating and stirring the mixture under a vacuum condition, standing and defoaming the mixture to prepare the casting solution.
On the basis of the scheme, the conditions for preparing the casting solution are as follows: the heating temperature is 175-200 ℃, the pressure is-0.095 MPa, the stirring time is 0.5-12 h, and the defoaming time is 0.5-12 h.
On the basis of the scheme, in the casting solution in the step a, the content of the polypropylene resin is 20-35 wt%, preferably 22.5-27.5 wt%, and the content of the diluent is 65-80 wt%, preferably 72.5-77.5 wt%.
On the basis of the scheme, the diluent in the step a is a mixture consisting of A and B, the content of A in the diluent is 10 wt% -45 wt%, A and B are liquid and mutually soluble at the heating temperature, wherein A is a poor solvent of the polypropylene resin, B is a good solvent of the polypropylene resin, and B adjusts the interaction parameters of the polypropylene resin and A.
On the basis of the scheme, the A is extracted from natural plants or animal products and is one of carnauba wax, candelilla wax or beeswax; and B is one of soybean oil or peanut oil.
On the basis of the scheme, the slit gap distance of the slit die head in the step c is 2-10 mm, the die head temperature is 140-175 ℃, and the preferable temperature is 145-165 ℃.
On the basis of the scheme, the flat membrane precursor in the step c is firstly cooled by air cooling, then is wound on a cooling roller, and is then immersed in a coagulating bath to be cooled to be solidified, so that the polypropylene microporous membrane precursor is obtained.
On the basis of the scheme, the coagulation bath is a double-stage coagulation bath; and extruding the casting film liquid through a slit die head and then performing two-stage coagulation bath.
On the basis of the scheme, the first-stage coagulation bath in the two-stage coagulation bath is air-cooled, the temperature of the second-stage coagulation bath in the two-stage coagulation bath is 0-25 ℃, the components of the second-stage coagulation bath are similar to or compatible with the diluent, and the components of the second-stage coagulation bath are air or vegetable oil.
On the basis of the scheme, the vegetable oil is one of soybean oil, castor oil, corn oil or palm kernel oil, and is preferably soybean oil.
On the basis of the scheme, the extracting agent in the step d is a boiling alcohol substance or warm chloroform, the alcohol substance is preferably ethanol or isopropanol, and the warm chloroform is heated at the temperature of 30-50 ℃.
On the basis of the scheme, the extraction time in the step d is 3-8 h, and the extracting agent can be recycled.
In one embodiment of the invention, boiling ethanol is adopted in a microporous membrane extraction device for extraction for 3-8 hours, and the extracted membrane is taken out and dried by a freeze dryer to remove an extractant, so that the polypropylene microporous membrane is prepared. The recovery rate of the ethanol after extraction is 99 percent.
In the film-making process of thermally induced phase separation, the process control conditions also include the type temperature of the coagulating bath (affecting the outer surface of the film) and the selection of the cooling rate thereof, which all affect the phase separation of the casting solution and further affect the structural morphology of the film.
In the prior art, when TIPS is adopted to prepare the polypropylene hollow fiber membrane, the diluent generally has physiological toxicity or strong pungent smell. The invention provides a brand new method and a brand new way for preparing the polypropylene microporous membrane by adopting a thermally induced phase separation method by adopting an environment-friendly diluent for membrane preparation.
Has the advantages that:
compared with the prior art, the invention has the following improvements that the polypropylene microporous membrane with better hydrophobicity is prepared by selecting a class of environment-friendly diluents and adopting a thermally induced phase separation process, and the environment-friendly polypropylene microporous membrane is obtained by controlling the composition of the membrane casting solution, including the concentration of the polymer, the composition and the content of the diluents, and the thermally induced phase separation membrane forming conditions, including extrusion temperature, cooling medium, cooling temperature, extraction and treatment conditions. The preparation method solves the problem that the diluent generally has physiological toxicity when TIPS is adopted to prepare the polypropylene hollow fiber membrane in the prior art, and the extracted extractant is recycled, so that green and clean production in the membrane preparation process is realized. The polypropylene microporous membrane prepared by the method has a through surface with a spongy microporous structure section and uniformly distributed micropores. The prepared polypropylene microporous membrane can be applied to the fields of membrane distillation and membrane degassing. The method is simple and suitable for industrial popularization and application.
Drawings
The invention has the following drawings:
FIGS. 1 to 3 are scanning electron micrographs of cross sections of films obtained in example 4.
Wherein the magnification of fig. 1 is 500, the magnification of fig. 2 is 2000, and the magnification of fig. 3 is 5000;
FIGS. 4 to 6 are scanning electron micrographs of cross sections of the film obtained in comparative example 1.
Wherein the magnification of fig. 4 is 400, the magnification of fig. 5 is 2000, and the magnification of fig. 6 is 5000.
Detailed Description
In order that the present invention may be more readily understood, the following detailed description of the invention is given, with reference to the accompanying drawings and examples, which are given by way of illustration only and are not intended to limit the scope of the invention, and the following examples are given without reference to specific experimental procedures, which are generally conducted in accordance with routine experimentation.
A polypropylene microporous membrane comprising: a polypropylene resin,
the contact angle of the polypropylene microporous membrane is 120-140 degrees, and the average pore size is 0.01-0.04 mu m.
The preparation method of the polypropylene microporous membrane comprises the following steps:
step a, mixing polypropylene resin and a diluent to prepare a membrane casting solution;
b, filtering the membrane casting solution by a filter;
step c, conveying the filtered casting solution to a slit die head, extruding the casting solution through the slit die head to obtain a flat membrane precursor, and then immersing the flat membrane precursor into a coagulating bath to cool the flat membrane precursor until the flat membrane precursor is solidified to obtain a polypropylene microporous membrane precursor;
d, winding the polypropylene microporous membrane precursor by using a winding machine, and then putting the wound precursor into a microporous membrane extraction device for extraction by using an extractant;
and e, drying the extracted microporous membrane precursor by a freeze drying device, and removing the extractant to obtain the polypropylene microporous membrane.
In step a, after mixing the polypropylene resin and the diluent, heating and stirring the mixture under a vacuum condition, standing and defoaming the mixture to prepare the casting solution.
On the basis of the scheme, the conditions for preparing the casting solution are as follows: the heating temperature is 175-200 ℃, the pressure is-0.095 MPa, the stirring time is 0.5-12 h, and the defoaming time is 0.5-12 h.
On the basis of the scheme, in the casting solution in the step a, the content of the polypropylene resin is 20-35 wt%, preferably 22.5-27.5 wt%, and the content of the diluent is 65-80 wt%, preferably 72.5-77.5 wt%.
On the basis of the scheme, the diluent in the step a is a mixture consisting of A and B, the content of A in the diluent is 10 wt% -45 wt%, A and B are liquid and mutually soluble at the heating temperature, wherein A is a poor solvent of the polypropylene resin, B is a good solvent of the polypropylene resin, and B adjusts the interaction parameters of the polypropylene resin and A.
On the basis of the scheme, the A is extracted from natural plants or animal products and is one of carnauba wax, candelilla wax or beeswax; and B is one of soybean oil or peanut oil.
On the basis of the scheme, the slit gap distance of the slit die head in the step c is 2-10 mm, the die head temperature is 140-175 ℃, and the preferable temperature is 145-165 ℃.
On the basis of the scheme, the flat membrane precursor in the step c is firstly cooled by air cooling, then is wound on a cooling roller, and is then immersed in a coagulating bath to be cooled to be solidified, so that the polypropylene microporous membrane precursor is obtained.
On the basis of the scheme, the coagulation bath is a double-stage coagulation bath; and extruding the casting film liquid through a slit die head and then performing two-stage coagulation bath.
On the basis of the scheme, the first-stage coagulation bath in the two-stage coagulation bath is air-cooled, the temperature of the second-stage coagulation bath in the two-stage coagulation bath is 0-25 ℃, the components of the second-stage coagulation bath are similar to or compatible with the diluent, and the components of the second-stage coagulation bath are air or vegetable oil.
On the basis of the scheme, the vegetable oil is one of soybean oil, castor oil, corn oil or palm kernel oil, and is preferably soybean oil.
On the basis of the scheme, the extracting agent in the step d is a boiling alcohol substance or warm chloroform, the alcohol substance is preferably ethanol or isopropanol, and the warm chloroform is heated at the temperature of 30-50 ℃.
On the basis of the scheme, the extraction time in the step d is 3-8 h, and the extracting agent can be recycled.
Example 1
A polypropylene microporous membrane has an average pore diameter of 0.04 mu m and a contact angle of 125.6 degrees, and is prepared by the following steps: the heating temperature is 175-200 ℃, the pressure is-0.095 MPa, the stirring time is 0.5-12 h, and the defoaming time is 0.5-12 h.
And c, setting the slit gap distance of the slit die head to be 2-10 mm, setting the die head temperature to be 140-175 ℃, and preferably setting the temperature to be 145-165 ℃.
The alcohol substance is preferably ethanol or isopropanol, and the heating temperature of the warm chloroform is 30-50 ℃.
(1) 20 wt% of polypropylene resin and 80wt% of mixed diluent of carnauba wax and soybean oil are added into a kettle with a stirring device, and the content of the carnauba wax in the diluent is 10 wt%. Heating to 175 ℃, stirring for 1.5h under the pressure of-0.095 MPa, stopping stirring, standing at constant temperature and defoaming for 1.5h under the pressure of-0.095 MPa to obtain a casting solution;
(2) filtering the casting solution with the temperature of 175 ℃ by a stainless steel filter screen of 100 meshes, extruding the casting solution by a slit type die head, wherein the distance between slits is 2mm, the temperature of the die head is 160 ℃, cooling the extruded flat membrane precursor by air cooling, rolling the flat membrane precursor on a cooling roller, immersing the flat membrane precursor into a two-stage solidification bath for cooling, wherein the first-stage solidification bath in the two-stage solidification bath is air cooling, the component of the second-stage solidification bath is air, the temperature is 0 ℃, and cooling to obtain the polypropylene flat microporous membrane precursor.
(3) Winding the polypropylene flat microporous membrane precursor by a winding machine, and then putting the precursor into a microporous membrane extraction device for extraction by using boiling ethanol as an extractant for 3 hours;
(4) and taking out the wet membrane obtained after extraction, drying the membrane by a freeze dryer, and removing the extractant to obtain the polypropylene microporous membrane. The ethanol recovery rate is 90 percent.
(5) Drying to obtain the polypropylene plate microporous membrane.
Contact angle test method: a contact angle tester is adopted, the measurement range is 1-180 degrees, the resolution ratio is +/-0.1 degrees, a static sitting drop method is adopted, deionized water with the volume of 2 mu L is fixed every time and is dropped on a membrane wire, the calculated initial contact angle is taken as the contact angle measurement value of the hollow fiber membrane wire, the parallel measurement is carried out for 6 times, and the average value is calculated.
Membrane distillation water production flux (J) test method: taking 10 hollow fiber membrane filaments to prepare a membrane component, adopting 1 wt% sodium chloride aqueous solution to perform vacuum membrane distillation test, and performing cross flow filtration at the feed temperature of 80 ℃, the vacuum operation pressure of-0.09 MPa and the flow rate of 0.62 cm/s. The produced water obtained in a certain period of time was collected, the flux of produced water by membrane distillation was calculated by the following formula (1), measured 3 times, and the average value was calculated.
Wherein W, A, and t represent the water production weight, the effective membrane area, and the interval water production time, respectively. Salt rejection (R) test method: measuring the conductivity of the raw material liquid and the produced water by a conductivity meter, and calculating by the formula (2)
Wherein, Cp、CbRepresenting the conductivity of the produced water and feed solution.
Minimum pore size and air permeability (P, unit cm)3/(cm2∙ s ∙ bar), test method: and (4) testing by a bubble pressure method membrane aperture analyzer.
The test shows that the water flux produced by vacuum membrane distillation is 5.55L/(m)2H), salt rejection 99.83%. Air permeability of 0.88cm3/(cm2∙s∙bar)。
Example 2
A polypropylene microporous membrane has an average pore diameter of 0.033 mu m and a contact angle of 140.0 degrees, and is prepared by the following method:
(1) 30 wt% of polypropylene resin and 70 wt% of mixed diluent of carnauba wax and soybean oil are added into a kettle with a stirring device, and the content of the carnauba wax in the diluent is 20 wt%. Heating to 180 ℃, stirring for 0.5h under the pressure of-0.095 MPa, stopping stirring, standing at constant temperature and defoaming for 0.5h under the pressure of-0.095 MPa to obtain a casting solution;
(2) filtering the casting solution with the temperature of 180 ℃ by a stainless steel filter screen of 100 meshes, extruding the casting solution by a slit type die head, wherein the distance between slits is 4mm, the temperature of the die head is 140 ℃, cooling the extruded flat membrane precursor by air cooling, rolling the flat membrane precursor on a cooling roller, immersing the flat membrane precursor into a two-stage solidification bath for cooling, wherein the first-stage solidification bath in the two-stage solidification bath is air cooling, the second-stage solidification bath comprises soybean oil, the temperature is 25 ℃, and cooling to obtain the polypropylene flat microporous membrane precursor.
(3) Winding the polypropylene flat microporous membrane precursor by a winding machine, and then putting the precursor into a microporous membrane extraction device to extract for 4 hours by using boiling isopropanol as an extractant;
(4) and drying the wet material obtained after extraction by a freeze dryer, and removing the extractant to obtain the polypropylene microporous membrane. The recovery rate of the isopropanol is 90 percent.
(5) Drying to obtain the polypropylene plate microporous membrane.
The test shows that the water flux produced by vacuum membrane distillation is 9.84L/(m)2H), salt rejection 99.78%. Air permeability of 0.88cm3/(cm2∙s∙bar)。
Example 3
A polypropylene microporous membrane, the average pore diameter is 0.033 mu m, the contact angle is 129.9 degrees, and the preparation method is as follows:
(1) 22.5 wt% of polypropylene resin and 77.5 wt% of mixed diluent of carnauba wax and soybean oil were added to a kettle equipped with a stirring device, and the content of carnauba wax in the diluent was 30 wt%. Heating to 190 ℃, stirring for 2h under the pressure of-0.095 MPa, stopping stirring, standing and defoaming for 2h under the pressure of-0.095 MPa at constant temperature to obtain a casting solution;
(2) filtering the casting solution with the temperature of 190 ℃ by a stainless steel filter screen of 100 meshes, extruding the casting solution by a slit type die head, wherein the distance between slits is 6mm, the temperature of the die head is 150 ℃, cooling the extruded flat membrane precursor by air cooling, rolling the flat membrane precursor on a cooling roller, immersing the flat membrane precursor into a two-stage solidification bath for cooling, wherein the first-stage solidification bath in the two-stage solidification bath is air cooling, the second-stage solidification bath is composed of castor oil, the temperature is 15 ℃, and cooling to obtain the polypropylene flat microporous membrane precursor.
(3) Winding the polypropylene flat microporous membrane precursor by a winding machine, and then putting the precursor into a microporous membrane extraction device to extract by using chloroform with the temperature of 50 ℃ as an extractant for 5 hours;
(4) and taking out the wet membrane obtained after extraction, drying the membrane by a freeze dryer, and removing the extractant to obtain the polypropylene microporous membrane. The chloroform recovery rate is 90%.
(5) Drying to obtain the polypropylene plate microporous membrane.
The test shows that the water flux produced by vacuum membrane distillation is 5.85L/(m)2H), salt rejection 98.15%. Air permeability of 0.88cm3/(cm2∙s∙bar)。
Example 4
A polypropylene microporous membrane has an average pore diameter of 0.03 mu m and a contact angle of 125.7 degrees, and is prepared by the following steps:
(1) 30 wt% of polypropylene resin and 70 wt% of mixed diluent of carnauba wax and soybean oil are added into a kettle with a stirring device, and the content of the carnauba wax in the diluent is 35 wt%. Heating to 185 ℃, stirring for 1.5h under the pressure of-0.095 MPa, stopping stirring, and standing and defoaming for 1.5h under the pressure of-0.095 MPa at constant temperature to obtain a casting solution;
(2) filtering the casting solution with the temperature of 185 ℃ by a stainless steel filter screen of 100 meshes, extruding the casting solution by a slit type die head, wherein the distance between slits is 8mm, the temperature of the die head is 145 ℃, cooling the extruded flat membrane precursor by air cooling, rolling the flat membrane precursor on a cooling roller, immersing the flat membrane precursor into a two-stage solidification bath for cooling, wherein the first-stage solidification bath in the two-stage solidification bath is air cooling, the second-stage solidification bath is corn oil, the temperature is 15 ℃, and cooling to obtain the polypropylene flat microporous membrane precursor.
(3) Winding the polypropylene flat microporous membrane precursor by a winding machine, and then putting the precursor into a microporous membrane extraction device to extract by using chloroform with the temperature of 40 ℃ as an extractant for 6 hours;
(4) and taking out the wet membrane obtained after extraction, drying the membrane by a freeze dryer, and removing the extractant to obtain the polypropylene microporous membrane. The chloroform recovery rate is 90%.
(5) Drying to obtain polypropylene plate microporous membrane, and SEM pictures of membrane cross section are shown in figures 1-3.
The test shows that the water flux produced by vacuum membrane distillation is 7.47L/(m)2H), salt rejection 99.91%. Air permeability of 1.13cm3/(cm2∙s∙bar)。
Example 5
A polypropylene microporous membrane has an average pore diameter of 0.01 mu m and a contact angle of 128.4 degrees, and is prepared by the following steps:
(1) 35wt% of polypropylene resin and 65 wt% of mixed diluent of carnauba wax and soybean oil are added into a kettle with a stirring device, and the content of the carnauba wax in the diluent is 40 wt%. Heating to 200 ℃, stirring for 6h under the pressure of-0.095 MPa, stopping stirring, standing and defoaming for 4h under the pressure of-0.095 MPa at constant temperature to obtain a casting solution;
(2) filtering the casting solution with the temperature of 200 ℃ by a stainless steel filter screen of 100 meshes, extruding the casting solution by a slit type die head, wherein the distance between slits is 10mm, the temperature of the die head is 165 ℃, cooling the extruded flat membrane precursor by air cooling, rolling the flat membrane precursor on a cooling roller, immersing the flat membrane precursor into a two-stage solidification bath for cooling, wherein the first-stage solidification bath in the two-stage solidification bath is air cooling, the second-stage solidification bath is palm kernel oil, the temperature is 25 ℃, and cooling to obtain the polypropylene flat microporous membrane precursor.
(3) Winding the polypropylene flat microporous membrane precursor by a winding machine, and then putting the precursor into a microporous membrane extraction device to extract by using chloroform with the temperature of 30 ℃ as an extractant for 7 hours;
(4) and taking out the wet membrane obtained after extraction, drying the membrane by a freeze dryer, and removing the extractant to obtain the polypropylene microporous membrane. The chloroform recovery rate is 90%.
(5) Drying to obtain the polypropylene plate microporous membrane.
The test shows that the water flux produced by vacuum membrane distillation is 9.22L/(m)2H), salt rejection 99.94%. Air permeability of 2.00cm3/(cm2∙s∙bar)。
Example 6
A polypropylene microporous membrane has an average pore diameter of 0.04 mu m and a contact angle of 120 degrees, and is prepared by the following steps:
(1) 27.5 wt% of polypropylene resin and 72.5 wt% of mixed diluent of carnauba wax and soybean oil were added to a kettle equipped with a stirring device, and the content of carnauba wax in the diluent was 45 wt%. Heating to 195 ℃, stirring for 8 hours under the pressure of-0.095 MPa, stopping stirring, standing and defoaming for 5 hours at constant temperature under the pressure of-0.095 MPa to obtain a casting solution;
(2) filtering the casting solution with the temperature of 195 ℃ by a stainless steel filter screen of 100 meshes, extruding by a slit die head, wherein the distance between slits is 2mm, the temperature of the die head is 170 ℃, cooling the extruded flat membrane precursor by air cooling, rolling on a cooling roller, immersing into a two-stage solidification bath for cooling, wherein the first-stage solidification bath in the two-stage solidification bath is air cooling, the second-stage solidification bath comprises soybean oil, the temperature is 15 ℃, and cooling to obtain the polypropylene flat microporous membrane precursor.
(3) Winding the polypropylene flat microporous membrane precursor by a winding machine, and then putting the precursor into a microporous membrane extraction device for extraction by using boiling ethanol as an extractant for 8 hours;
(4) and taking out the wet membrane obtained after extraction, drying the membrane by a freeze dryer, and removing the extractant to obtain the polypropylene microporous membrane. The ethanol recovery rate is 90 percent.
(5) Drying to obtain the polypropylene plate microporous membrane.
The test shows that the water flux produced by vacuum membrane distillation is 7.31L/(m)2H), salt rejection of 99.98%. Air permeability of 0.94cm3/(cm2∙s∙bar)。
Example 7
A polypropylene microporous membrane has an average pore diameter of 0.03 mu m and a contact angle of 128 degrees, and is prepared by the following steps:
(1) 30 wt% of polypropylene resin and 70 wt% of beeswax and peanut oil mixed diluent are added into a kettle with a stirring device, and the content of beeswax in the diluent is 30 wt%. Heating to 185 ℃, stirring for 5h under the pressure of-0.095 MPa, stopping stirring, standing and defoaming for 6h under the pressure of-0.095 MPa at constant temperature to obtain a casting solution;
(2) filtering the casting solution with the temperature of 185 ℃ by a stainless steel filter screen of 100 meshes, extruding the casting solution by a slit type die head, wherein the distance between slits is 2mm, the temperature of the die head is 175 ℃, cooling the extruded flat membrane precursor by air cooling, rolling the flat membrane precursor on a cooling roller, immersing the flat membrane precursor into a two-stage solidification bath for cooling, wherein the first-stage solidification bath in the two-stage solidification bath is air cooling, the second-stage solidification bath comprises soybean oil, the temperature is 0 ℃, and cooling to obtain the polypropylene flat microporous membrane precursor.
(3) Winding the polypropylene flat microporous membrane precursor by a winding machine, and then putting the precursor into a microporous membrane extraction device for extraction by using boiling ethanol as an extractant for 3 hours;
(4) and taking out the wet membrane obtained after extraction, drying the membrane by a freeze dryer, and removing the extractant to obtain the polypropylene microporous membrane. The ethanol recovery rate is 90 percent.
(5) Drying to obtain the polypropylene plate microporous membrane.
The test shows that the water flux produced by vacuum membrane distillation is 7.88L/(m)2H), salt rejection of 99.98%. Air permeability of 1.86cm3/(cm2∙s∙bar)。
Example 8
A polypropylene microporous membrane has an average pore diameter of 0.038 μm and a contact angle of 133 degrees, and is prepared by the following steps:
35wt% of polypropylene resin and 65 wt% of mixed diluent of small candle number wax and soybean oil are added into a kettle with a stirring device, wherein the content of the small candle number wax in the diluent is 45 wt%. Heating to 185 ℃, stirring for 12h under the pressure of-0.095 MPa, stopping stirring, standing and defoaming for 12h under the pressure of-0.095 MPa at constant temperature to obtain a casting solution;
the other steps are the same as example 7, and the polypropylene flat microporous membrane is obtained.
The test shows that the water flux produced by vacuum membrane distillation is 8.25L/(m)2H), salt rejection 99.58%. Air permeability of 1.36cm3/(cm2∙s∙bar)。
Comparative example 1
A polypropylene microporous membrane, the average pore diameter is 0.063 mu m, the contact angle is 114 degrees, and the preparation method comprises the following steps:
30 wt% of polypropylene resin and 70 wt% of soybean oil diluent were added to a kettle equipped with a stirring device. Heating to 185 ℃, stirring for 1.5h under the pressure of-0.095 MPa, stopping stirring, and standing and defoaming for 1.5h under the pressure of-0.095 MPa at constant temperature to obtain a casting solution; the other steps are the same as example 4, and the polypropylene flat microporous membrane is obtained. The resulting film was rugged in shape, hard and brittle. SEM photographs of the film sections are shown in FIGS. 4-6.
Those not described in detail in this specification are within the skill of the art.
Claims (6)
1. A preparation method of a polypropylene microporous membrane is characterized by comprising the following steps: a polypropylene microporous membrane comprising: the contact angle of the polypropylene microporous membrane is 120-140 degrees, the average pore size is 0.03-0.04 mu m,
the method specifically comprises the following steps:
step a, mixing polypropylene resin and a diluent to prepare a membrane casting solution;
b, filtering the membrane casting solution by a filter;
step c, conveying the filtered casting solution to a slit die head, extruding the casting solution through the slit die head to obtain a flat membrane precursor, and then immersing the flat membrane precursor into a coagulating bath to cool the flat membrane precursor until the flat membrane precursor is solidified to obtain a polypropylene microporous membrane precursor;
d, winding the polypropylene microporous membrane precursor by using a winding machine, and then putting the wound precursor into a microporous membrane extraction device for extraction by using an extractant;
e, drying the extracted microporous membrane precursor by a freeze drying device, and removing an extracting agent to obtain a polypropylene microporous membrane;
in the step a, mixing polypropylene resin and a diluent, heating and stirring the mixture under a vacuum condition, and standing and defoaming the mixture to prepare a casting solution;
the conditions for preparing the casting solution are as follows: the heating temperature is 175-200 ℃, the pressure is-0.095 MPa, the stirring time is 0.5-12 h, and the defoaming time is 0.5-12 h;
in the step a, the diluent is a mixture consisting of A and B, wherein A is one of carnauba wax, candelilla wax or beeswax, the content of A in the diluent is 10-45 wt%, and B is one of soybean oil or peanut oil; a and B are liquid and mutually soluble at the heating temperature, wherein A is a poor solvent of the polypropylene resin.
2. The method for preparing a polypropylene microporous membrane according to claim 1, wherein: in the film casting solution in the step a, the content of the polypropylene resin is 20-35 wt%, and the content of the diluent is 65-80 wt%.
3. The method for preparing a polypropylene microporous membrane according to claim 1, wherein: and c, setting the slit gap distance of the slit die head to be 2-10 mm and setting the die head temperature to be 140-175 ℃.
4. The method for preparing a polypropylene microporous membrane according to claim 1, wherein: and c, firstly cooling the flat membrane precursor by air cooling, then rolling the flat membrane precursor on a cooling roller, and then soaking the flat membrane precursor into a coagulating bath to cool the flat membrane precursor to be solidified to obtain the polypropylene microporous membrane precursor.
5. The method for preparing a polypropylene microporous membrane according to claim 1, wherein: the coagulation bath is a two-stage coagulation bath; the air cooling is adopted in the first-stage coagulation bath in the two-stage coagulation bath, the temperature of the second-stage coagulation bath in the two-stage coagulation bath is 0-25 ℃, the components of the second-stage coagulation bath are air or vegetable oil, and the vegetable oil is one of soybean oil, castor oil, corn oil or palm kernel oil.
6. The method for preparing a polypropylene microporous membrane according to claim 1, wherein: and d, the extractant is a boiling alcohol substance or warm chloroform, the heating temperature of the warm chloroform is 30-50 ℃, the extraction time is 3-8 h, and the extractant can be recycled.
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