High-ductility oxidation-resistant microporous hydrophobic membrane and preparation method and application thereof
阅读说明：本技术 一种高延展性耐氧化微孔疏水膜及其制备方法和应用 (High-ductility oxidation-resistant microporous hydrophobic membrane and preparation method and application thereof ) 是由 唐娜 高一方 项军 田桂英 程鹏高 张蕾 杜威 王松博 张建平 于 2021-09-23 设计创作，主要内容包括：本发明公开了一种高延展性耐氧化微孔疏水膜及其制备方法和应用,该共混膜包括平板膜、中空纤维膜两种形式。其中,聚合物组成主要由聚丙烯、乙烯丙烯共聚物和抗氧剂共混组成,成膜过程中上述聚合物相互交联,通过场发射扫描电镜(SEM)表征,发现上述聚合物均匀分布于断面。所述聚合物由质量分数59％～89％的聚丙烯、10％～40％的乙烯丙烯共聚物、0.4％～5％的抗氧剂。本发明所制备的平板膜和中空纤维膜采用热致相分离法制备。通过对聚丙烯进行乙烯丙烯共聚物和抗氧剂共混改性,制得的疏水膜具有更好的机械性能和耐氧化能力,在未提高成本的前提下极大地提高了聚丙烯膜在实际应用过程中的使用寿命,突破了聚丙烯疏水膜在膜蒸馏领域应用实际使用寿命短的瓶颈问题。(The invention discloses a high-ductility oxidation-resistant microporous hydrophobic membrane, and a preparation method and application thereof. The polymer is mainly formed by blending polypropylene, ethylene-propylene copolymer and antioxidant, the polymers are mutually crosslinked in the film forming process, and the polymers are found to be uniformly distributed on the cross section by the characterization of a field emission Scanning Electron Microscope (SEM). The polymer comprises 59-89% of polypropylene, 10-40% of ethylene-propylene copolymer and 0.4-5% of antioxidant by mass. The flat membrane and the hollow fiber membrane prepared by the invention are prepared by a thermally induced phase separation method. By blending modification of the ethylene-propylene copolymer and the antioxidant to the polypropylene, the prepared hydrophobic membrane has better mechanical property and oxidation resistance, greatly prolongs the service life of the polypropylene membrane in the actual application process on the premise of not increasing the cost, and breaks through the bottleneck problem that the practical service life of the polypropylene hydrophobic membrane in the membrane distillation field is short.)
1. A high ductility oxidation-resistant microporous hydrophobic membrane is characterized in that: the film-forming polymer of the microporous hydrophobic membrane comprises the following raw materials in percentage by weight:
59 to 89 percent of polypropylene
10 to 40 percent of ethylene-propylene copolymer
0.4 to 5 percent of antioxidant.
The hydrophobic polypropylene microporous membrane can be a flat membrane and a hollow fiber membrane;
the pore diameter of the microporous hydrophobic membrane is 0.1-0.3 micron.
2. The high ductility, oxidation resistant microporous hydrophobic membrane of claim 1, wherein the ethylene propylene copolymer is not limited to one or more of ethylene propylene rubber, ethylene propylene diene rubber or other high molecular weight resins of ethylene propylene polymers in varying mass concentrations.
3. The highly ductile oxidation-resistant microporous hydrophobic membrane according to claim 1, wherein the antioxidant is 1,3, 5-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) s-triazine-2, 4,6- (1H,3H5H) trione, pentaerythrityl tetrakis [ β - (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ], 2, 4-bis (dodecylthiomethyl) -6-methylphenol, N '-bis- (3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine, 2' -thiobis [3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ], diethylene glycol bis [ β - (3-tert-butyl-4-hydroxy-5-methylphenyl) Propionate ], bis (2, 4-di-tert-butylphenol) pentaerythritol diphosphite, distearyl pentaerythritol diphosphite, a copolymer of p-cresol and dicyclopentadiene, 2' -methylenebis (4-methyl-6-tert-butylphenol).
4. The high-ductility oxidation-resistant microporous hydrophobic membrane according to claim 1, wherein the melt index of the ethylene-propylene copolymer is equal to or slightly less than that of the selected polypropylene polymer, and the mass concentration of the ethylene-propylene copolymer is 1/3-1/8 mass concentration of polypropylene, preferably 1/6.
5. The high-ductility oxidation-resistant microporous hydrophobic membrane is characterized in that the microporous hydrophobic membrane polymer raw material is prepared by sequentially mixing, melting, extruding and granulating polypropylene, ethylene-propylene copolymer and an antioxidant serving as membrane forming polymer materials of the microporous hydrophobic membrane through a stirrer, a single screw and a double screw.
6. The method for preparing the high-ductility oxidation-resistant microporous hydrophobic membrane according to claim 1, wherein the hydrophobic polypropylene microporous membrane is a hollow fiber membrane, and the method comprises the following steps:
(1) and (3) mixing PP granules and ethylene propylene rubber granules according to the mass ratio of 8: 1-3: 1, adding 0.4 to 2.5 percent of antioxidant, and uniformly mixing in a stirrer;
(2) melting and extruding the mixed material obtained in the step (1) through a single-screw extruder and granulating to obtain a hollow fiber membrane modified polymer material;
(3) preparing a diluent and a core liquid used in the film making process, wherein the diluent is obtained by mixing dibutyl phthalate and soybean oil in a mass ratio of 4: 6-8: 2 (preferably 7:3), and the core liquid is obtained by mixing liquid paraffin and soybean oil in a mass ratio of 2: 8-9: 1 (preferably 5: 5);
(4) adding the polymer material and the diluent into a double-screw extruder through a solid material feeding system and a liquid feeding system respectively, and quickly forming uniform membrane casting liquid by the mixture through rotation and tangential force between screws. The solid-liquid feeding amount is controlled by the frequency of a motor and a pump, so that the proportion of the polymer material and the diluent is controlled, and the solid content is controlled by 26-45 percent (preferably 28-31 percent);
(5) feeding the casting solution obtained by the double-screw extruder in the step (4) into a spinning nozzle through a metering pump, wherein the feeding rate is controlled by pressure, the control range is 0.2-0.6 MPa, the core solution enters the spinning nozzle through a core solution metering pump, and the control flow rate range is 8-35 ml/min;
(6) the spinneret structure is single-hole spinning, and the discharging speed is controlled to be 40 g/min. The hot film filaments enter a coagulating bath water tank to be subjected to a phase separation process, and are automatically collected onto rollers under the stretching and drawing action of certain rollers to form original film filaments;
(7) and (3) placing the solidified hollow fiber membrane in an extracting agent (normal hexane) for extraction for 12h, then placing the hollow fiber membrane in ethanol for extraction for 12h, and mutually and alternately extracting for 72 h. And (3) taking out the membrane which is completely extracted until the diluent is completely removed, placing the membrane in a constant-temperature drying oven at 60 ℃ to remove the residual volatile extracting agent in the extraction process for 12 hours at constant temperature, and then obtaining a PP/EPR (EPDM) blended high-ductility oxidation-resistant hydrophobic microporous hollow fiber membrane sample.
7. The method for preparing the high-ductility oxidation-resistant microporous hydrophobic membrane according to claim 1, wherein the hydrophobic polypropylene microporous membrane is a flat plate membrane, and the method comprises the following steps:
(1) and (3) mixing PP granules and ethylene propylene rubber granules according to the mass ratio of 8: 1-3: 1, adding 0.4 to 2.5 percent of antioxidant, and uniformly mixing in a stirrer;
(2) melting and extruding the mixed material obtained in the step (1) through a single-screw extruder and granulating to obtain a hollow fiber membrane modified polymer material;
(3) stirring and mixing the modified polymer material obtained in the step (2) and a diluent in a reactor according to the mass fraction of 20-45%, wherein the diluent is prepared by mixing dibutyl phthalate and soybean oil in a mass ratio of 4: 6-8: 2 (preferably 7: 3);
(4) introducing nitrogen into the reactor for protection, heating to 160-240 ℃, fully stirring, standing for more than 2 hours for deaeration, and obtaining a homogeneous casting solution;
(5) coating the casting solution obtained in the step (4) on the surface of a polyester non-woven fabric, scraping into a flat shape, and then cooling and curing in a water bath/oil bath for coating the casting solution;
(6) and (3) placing the solidified flat membrane into an extracting agent (normal hexane) for extraction for 12h, then placing the flat membrane into ethanol for extraction for 12h, and mutually and alternately extracting for 72 h. And (3) taking out the membrane which is completely extracted until the diluent is completely removed, placing the membrane in a constant-temperature drying oven at 60 ℃ to remove the residual volatile extractant in the extraction process at constant temperature for 12h, and then obtaining a PP/EPR (EPDM) blended high-ductility oxidation-resistant microporous hydrophobic flat membrane sample.
8. Use of a high ductility, oxidation resistant microporous hydrophobic membrane of any one of claims 1-5 for a membrane distillation process.
9. A method for improving ductility and oxidation resistance of a polypropylene film, which is characterized in that an ethylene-propylene copolymer and an antioxidant are added into raw materials of the polypropylene film, and the high-ductility oxidation-resistant microporous hydrophobic film is prepared by the preparation method of any one of claims 6 to 7.
10. A method for maintaining ductility of a polypropylene film after oxidation, characterized in that an ethylene-propylene copolymer and an antioxidant are added to the raw material of the polypropylene film, and a highly ductile oxidation-resistant microporous hydrophobic film is prepared by the preparation method according to any one of claims 6 to 7.
Technical Field
The invention belongs to the technical field of high polymer material science and membrane separation, relates to a preparation method of a high polymer separation membrane, and more particularly relates to a preparation method and application of a polypropylene/ethylene-propylene copolymer blended high-ductility oxidation-resistant microporous hydrophobic membrane.
Background
The microporous hydrophobic membrane can be used as a transmission medium of a membrane contactor to be applied to various novel membrane separation processes, including membrane distillation, membrane extraction, membrane absorption, membrane stripping, membrane adsorption and the like. Membrane Distillation (MD) is a process of evaporating solvent or solute in solution, and compared with other membrane separation technologies, the technology has the advantages of being capable of operating at low temperature and normal pressure, and effectively utilizing cheap energy sources (such as solar energy, industrial waste heat and waste heat) to have great competitiveness in the modern society with increasingly tense energy sources. MD has great advantages in the industrial process of concentrating high-salt aqueous solution, and can concentrate the high-salt aqueous solution to a nearly saturated solution, and in addition, the membrane distillation process has the advantages of energy consumption and operation and maintenance cost which are incomparable with the traditional evaporation process in a multi-element aqueous solution system for separating volatile acid, water and salt.
The core component of the MD process is a separation membrane, which can be generally classified into a flat sheet membrane and a hollow fiber membrane in terms of membrane morphology. The preparation of the flat membrane and the hollow fiber membrane prepared by the thermotropic phase method is simple, the polymer is dissolved in the diluent at a certain temperature in experiments to form a homogeneous membrane casting solution, the homogeneous membrane casting solution is quantitatively input into a die head (a slit, a double-layer or multi-layer hollow tube) with a specific size through a metering pump and extruded, the temperature drop speed of the membrane casting solution is controlled to crystallize the polymer into a membrane, the diluent in the membrane is extracted by a solvent after the membrane is formed, and the required polypropylene hydrophobic membrane is obtained after drying.
Polytetrafluoroethylene, polyvinylidene fluoride and polypropylene (PP) are hydrophobic membrane materials commonly used in membrane distillation at present, wherein polypropylene is a nonpolar plastic with higher crystallinity, has good chemical stability, acid and alkali resistance, high hydrophobicity and strong thermal stability, is low in price, and has wide research at home and abroad. However, the polypropylene film has insufficient mechanical properties and poor toughness after being formed, and the defects of the polypropylene are particularly prominent particularly for the film form of the hollow fiber film. In practical application, the PP hollow fiber membrane with the service life of more than 1 year is generally found to be unusable due to the reduced toughness and reduced mechanical strength of the PP membrane after being used for 6 months in the process of treating seawater by MD, which limits the application of the PP hollow fiber membrane in the MD field. For analysis reasons, the assembly of the hollow fiber membrane module is usually to pack a 2-6 m fiber membrane bundle into a shell, a port is bonded and sealed by epoxy resin with a special formula, the junction of the fiber membrane and the epoxy resin is the weakest part of the membrane, and the hardness of the cured epoxy resin is far greater than that of the membrane material and has certain deformation, so that the epoxy resin can be embedded into the membrane material to a certain depth after the assembly and the sealing of the membrane module are completed, and the membrane is damaged. In addition, the curing process of epoxy resin releases a large amount of heat, which undoubtedly puts higher demands on the mechanical properties and oxidation resistance of the film. Also, although the PP polymer is thermally compounded on the surface of the nonwoven fabric, after oxidation, the polymer is pulverized or a lot of cracks appear, and the hydrophobicity is reduced, which seriously affects the separation performance of the hydrophobic membrane.
Therefore, it is desirable to improve the ductility and oxidation resistance of polypropylene films.
The present invention has been made to solve the above problems.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a preparation method of a polypropylene/ethylene propylene rubber blended high-ductility oxidation-resistant microporous hydrophobic membrane. The hydrophobic membrane prepared by the invention has higher toughness and elongation at break, has oxidation resistance, and still has very long service life when used under the oxidation condition. The membrane has the pore diameter of 0.1-0.3 mu m, narrow pore diameter distribution, uniform membrane pore diameter, porosity of 55-75 percent, high air permeability and stable hydrophobic angle of 118-123 degrees, and is an excellent MD separation membrane. More importantly, the hydrophobic membrane prepared by the invention adopts the following membrane materials: the polypropylene and the ethylene propylene rubber have wide application, low cost and simple and convenient operation in the preparation process. The invention greatly prolongs the service life of the PP hydrophobic microporous membrane in the actual application process on the premise of not increasing the cost, and breaks through the bottleneck problem of the application of the hydrophobic membrane of the PP material in the MD field.
The invention provides a high-ductility oxidation-resistant microporous hydrophobic membrane, wherein a membrane-forming polymer of the microporous hydrophobic membrane comprises the following raw materials in percentage by weight:
59 to 89 percent of polypropylene
10 to 40 percent of ethylene-propylene copolymer
0.4 to 5 percent of antioxidant.
The hydrophobic polypropylene microporous membrane can be a flat membrane and a hollow fiber membrane;
the pore diameter of the microporous hydrophobic membrane is 0.1-0.3 micron.
Preferably, the ethylene-propylene copolymer is not limited to one or more of ethylene-propylene-diene rubber, ethylene-propylene-diene rubber or other high molecular resins of ethylene-propylene polymers with different mass concentrations.
Preferably, the antioxidant is 1,3, 5-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) s-triazine-2, 4,6- (1H,3H5H) trione, pentaerythritol tetrakis [ beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ], 2, 4-bis (dodecylthiomethyl) -6-methylphenol, N '-bis- (3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine, 2' -thiobis [3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ], diethylene glycol bis [ beta- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionate ], (a salt thereof), One or more of bis (2, 4-di-tert-butylphenol) pentaerythritol diphosphite, pentaerythritol distearyl diphosphite, a copolymer of p-cresol and dicyclopentadiene, 2' -methylenebis (4-methyl-6-tert-butylphenol).
Preferably, the melt index of the ethylene-propylene copolymer is equal to or slightly less than that of the selected polypropylene polymer, and the mass concentration of the melt index is 1/3-1/8 of the mass concentration of polypropylene, preferably 1/6.
Preferably, the film-forming polymer materials of the microporous hydrophobic film, namely polypropylene, ethylene-propylene copolymer and antioxidant, are mixed, melted, extruded and granulated sequentially by a stirrer, a single screw and a double screw to obtain the raw material for preparing the microporous hydrophobic film polymer. The key point of the invention is that the stirrer, the single screw and the double screw are stirred and mixed in three steps, and in the preparation process of the high-ductility oxidation-resistant microporous hydrophobic membrane, the raw material for preparing the membrane is granular material, the antioxidant is powder material, and the problem of uneven mixing exists. Therefore, the invention adopts a stirrer for mixing, then uses a single-screw extruder for blending granulation, and finally uses a double-screw extruder for melting and diluting for film preparation, so that the problem of uneven material mixing can be solved more favorably; melting, mixing and granulating polypropylene, ethylene-propylene copolymer and antioxidant by a single-screw extruder to obtain a polymer material required by film making; and melting and mixing the granules obtained by the single-screw extruder and the diluent by using a double-screw extruder to obtain the casting solution. In the three-step mixing, each step has a strong mixing effect and has different functions.
In a second aspect of the present invention, there is provided a high-ductility oxidation-resistant microporous hydrophobic membrane according to the first aspect of the present invention, and the steps of the thermotropic phase method for preparing the PP/epr (epdm) blended high-ductility oxidation-resistant microporous hollow fiber membrane are as follows:
(1) and (3) mixing PP granules and ethylene propylene rubber granules according to the mass ratio of 8: 1-3: 1, adding 0.4 to 2.5 percent of antioxidant, and uniformly mixing in a stirrer;
(2) melting and extruding the mixed material obtained in the step (1) through a single-screw extruder and granulating to obtain a hollow fiber membrane modified polymer material;
(3) preparing a diluent and a core liquid used in the film making process, wherein the diluent is obtained by mixing dibutyl phthalate and soybean oil in a mass ratio of 4: 6-8: 2 (preferably 7:3), and the core liquid is obtained by mixing liquid paraffin and soybean oil in a mass ratio of 2: 8-9: 1 (preferably 5: 5);
(4) adding the polymer material and the diluent into a double-screw extruder through a solid material feeding system and a liquid feeding system respectively, and quickly forming uniform membrane casting liquid by the mixture through rotation and tangential force between screws. The solid-liquid feeding amount is controlled by the frequency of a motor and a pump, so that the proportion of the polymer material and the diluent is controlled, and the solid content is controlled by 26-45 percent (preferably 28-31 percent);
(5) feeding the casting solution obtained by the double-screw extruder in the step (4) into a spinning nozzle through a metering pump, wherein the feeding rate is controlled by pressure, the control range is 0.2-0.6 MPa, the core solution enters the spinning nozzle through a core solution metering pump, and the control flow rate range is 8-35 ml/min;
(6) the spinneret structure is single-hole spinning, and the discharging speed is controlled to be 40 g/min. The hot film filaments enter a coagulating bath water tank to be subjected to a phase separation process, and are automatically collected onto rollers under the stretching and drawing action of certain rollers to form original film filaments;
(7) and (3) placing the solidified hollow fiber membrane in an extracting agent (normal hexane) for extraction for 12h, then placing the hollow fiber membrane in ethanol for extraction for 12h, and mutually and alternately extracting for 72 h. And (3) taking out the membrane which is completely extracted until the diluent is completely removed, placing the membrane in a constant-temperature drying oven at 60 ℃ to remove the residual volatile extracting agent in the extraction process for 12 hours at constant temperature, and then obtaining a PP/EPR (EPDM) blended high-ductility oxidation-resistant hydrophobic microporous hollow fiber membrane sample.
In a third aspect of the present invention, there is provided a high-ductility oxidation-resistant microporous hydrophobic membrane according to the first aspect of the present invention, and the steps of the thermotropic phase method for preparing the PP/epr (epdm) blended high-ductility oxidation-resistant hydrophobic microporous flat membrane according to the present invention are as follows:
(1) and (3) mixing PP granules and ethylene propylene rubber granules according to the mass ratio of 8: 1-3: 1, adding 0.4 to 2.5 percent of antioxidant, and uniformly mixing in a stirrer;
(2) melting and extruding the mixed material obtained in the step (1) through a single-screw extruder and granulating to obtain a hollow fiber membrane modified polymer material;
(3) stirring and mixing the modified polymer material obtained in the step (2) and a diluent in a reactor according to the mass fraction of 20-45%, wherein the diluent is prepared by mixing dibutyl phthalate and soybean oil in a mass ratio of 4: 6-8: 2 (preferably 7: 3);
(4) introducing nitrogen into the reactor for protection, heating to 160-240 ℃, fully stirring, standing for more than 2 hours for deaeration, and obtaining a homogeneous casting solution;
(5) and (4) coating the casting solution obtained in the step (4) on the surface of a polyester non-woven fabric, scraping into a flat shape, and then cooling and curing in a water bath/oil bath for coating the casting solution obtained in the step (0).
(6) And (3) placing the solidified flat membrane into an extracting agent (normal hexane) for extraction for 12h, then placing the flat membrane into ethanol for extraction for 12h, and mutually and alternately extracting for 72 h. And (3) taking out the membrane which is completely extracted until the diluent is completely removed, placing the membrane in a constant-temperature drying oven at 60 ℃ to remove the residual volatile extractant in the extraction process at constant temperature for 12h, and then obtaining a PP/EPR (EPDM) blended high-ductility oxidation-resistant microporous hydrophobic flat membrane sample.
The antioxidant is 1,3, 5-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) s-triazine-2, 4,6- (1H,3H5H) trione, pentaerythrityl tetrakis [ beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ], 2, 4-bis (dodecylthiomethyl) -6-methylphenol, N '-bis- (3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine, 2' -thiobis [3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ], diethylene glycol bis [ beta- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionate ] (a), One or more of bis (2, 4-di-tert-butylphenol) pentaerythritol diphosphite, tris [2, 4-di-tert-butylphenyl ] phosphite, pentaerythritol distearyl diphosphite, a copolymer of p-cresol and dicyclopentadiene, 2' -methylenebis (4-methyl-6-tert-butylphenol).
In a fourth aspect, the present invention provides the use of a high ductility, oxidation resistant microporous hydrophobic membrane according to the first aspect of the invention in a membrane distillation process.
The fifth aspect of the invention provides a method for improving the ductility and oxidation resistance of a polypropylene film, wherein an ethylene-propylene copolymer and an antioxidant are added into the raw materials of the polypropylene film, and the high-ductility oxidation-resistant microporous hydrophobic film is prepared by adopting the preparation method of the second aspect or the third aspect of the invention.
In the sixth aspect of the present invention, a method for maintaining ductility of a polypropylene film after oxidation is provided, wherein an ethylene-propylene copolymer and an antioxidant are added to raw materials of the polypropylene film, and the high-ductility oxidation-resistant microporous hydrophobic film is prepared by the preparation method according to the second aspect or the third aspect of the present invention.
The antioxidant mainly plays a role in functional group sacrifice and substitution in the oxidation process of the hydrophobic membrane, but does not influence the hydrophilic and hydrophobic properties of the hydrophobic membrane, a large number of functional groups such as hydroxyl, sulfydryl or ester bonds and the like replace H on a C-H bond after the blended polymer is oxidized, and the hydrophilic and hydrophobic properties of the hydrophobic membrane are kept unchanged; after the ethylene propylene copolymer is oxidized or in the oxidation process of the hydrophobic microporous membrane, the ethylene propylene copolymer also participates in the oxidation process, and after the ethylene propylene copolymer is oxidized, H on a C-H bond in a chemical formula of the ethylene propylene copolymer is captured and substituted by functional groups such as hydroxyl, sulfydryl or ester bonds in antioxidant molecules; the ethylene propylene copolymer maintains the ductility of the hydrophobic microporous membrane before and after oxidation.
Ethylene-propylene copolymers, represented by ethylene-propylene rubber, are synthetic rubbers with ethylene and propylene as main monomers, and are classified into ethylene-propylene-diene rubber, which is a copolymer of ethylene and propylene and is represented by EPM, and ethylene-propylene-diene rubber, which is a copolymer of ethylene, propylene and a small amount of a third monomer of a non-conjugated diene and is represented by EPDM, according to the difference in monomer composition in a molecular chain. Both are commonly referred to as ethylene propylene rubber, Ethylene Propylene Rubber (EPR). The ethylene propylene rubber has excellent weather resistance, ozone resistance, heat resistance, acid and alkali resistance, water vapor resistance and color stability. Ethylene-propylene rubber lacks polarity and has low unsaturation degree, so that the ethylene-propylene rubber has better resistance to various polar chemicals such as alcohol, acid, alkali, oxidant, refrigerant, detergent, animal and vegetable oil, ketone, grease and the like. Because the molecular structure of the ethylene propylene rubber has no polar substituent, the molecular cohesive energy is low, the molecular chain can keep flexibility in a wider range, is second to natural rubber and cis-butadiene rubber, and can still keep the flexibility at low temperature. Isotactic polypropylene is blended with EPR and EPDM, and the composition ratio and the difference in melt index between the two determine the morphology of the blend. When the PP and the EPR or the EPDM have similar melt indexes, the blend has a uniform morphological structure, and the two components are continuous phases within the PP/EPR blending ratio of 60/40-40/60.
In order to solve the problem that the practical service life of a PP hollow fiber membrane is greatly reduced after the PP hollow fiber membrane is filled into a membrane component, PP and EPR (EPDM) with close melt indexes are selected, PP is blended and modified by the EPR (EPDM), an antioxidant component is added, and the PP/EPR (EPDM) blended high-ductility oxidation-resistant microporous hydrophobic membrane is prepared. The hydrophobic microporous hollow fiber membrane has high toughness and elongation at break, the tensile strength reaches 6MPa, the maximum elongation reaches 300 percent, the pore size distribution is narrow, the air permeability is good, the contact angle is stable at 118-123 degrees, and the hydrophobic microporous hollow fiber membrane is an excellent MD separation membrane.
Because PP is insoluble in any solvent at normal temperature, the invention adopts a thermally induced phase separation method to prepare PP/EPR (EPDM) modified hollow fiber and flat membrane. The thermally induced phase separation method is that polymer is dissolved in solvent with high boiling point and low volatility at high temperature to form homogeneous solution, then the homogeneous solution is cooled to cause solution phase separation, and volatile reagent is selected to extract out the solvent, so as to obtain the macromolecule microporous membrane with a certain structural shape. The microporous membrane prepared by the method has the advantages of high strength, high porosity, narrow pore size distribution and the like, and can be applied to a plurality of crystalline polymers which can not be prepared into a membrane by a common solution method due to poor solubility at normal temperature.
Compared with the prior art, the hollow fiber membrane and the flat membrane prepared by blending the polypropylene and the ethylene propylene rubber and adding the antioxidant have more excellent chemical resistance and good flexibility and mechanical strength, the actual service life is greatly prolonged after the hollow fiber membrane and the flat membrane are filled into the membrane module, and the hollow fiber membrane and the flat membrane are applied to the membrane distillation process, stable in operation and excellent in separation effect. The vacuum membrane distillation and direct contact membrane distillation processes are tested at present, and the PP/EPR (EPDM) blended high-ductility oxidation-resistant microporous hydrophobic membrane prepared by the method is proved to be an excellent membrane distillation separation membrane, so that the application of the polypropylene material in the field of membrane distillation is widened.
The polypropylene/ethylene-propylene copolymer blended high-ductility oxidation-resistant hydrophobic microporous membrane mainly comprises polypropylene, ethylene-propylene copolymer and an antioxidant, wherein the polymers are crosslinked with each other in a membrane forming process, and are found to be uniformly distributed on a cross section through the characterization of a field emission Scanning Electron Microscope (SEM). The polymer comprises 35-80% of polypropylene, 6-14% of ethylene-propylene copolymer and 0.8-5% of antioxidant by mass. The flat membrane and the hollow fiber membrane prepared by the invention are prepared by a thermally induced phase separation method. By blending modification of the ethylene-propylene copolymer and the antioxidant to the polypropylene, the prepared hydrophobic membrane has better mechanical property and oxidation resistance, greatly prolongs the service life of the polypropylene membrane in the actual application process on the premise of not increasing the cost, and breaks through the bottleneck problem that the practical service life of the polypropylene hydrophobic membrane in the membrane distillation field is short.
Drawings
FIG. 1 is an SEM photograph of a cross section of a flat sheet membrane prepared by the TIPS method;
FIG. 2 is a SEM photograph of the surface of a flat membrane prepared by the TIPS method;
FIG. 3 is an SEM photograph of a cross section of a hollow fiber membrane prepared by the TIPS method;
FIG. 4 is an SEM photograph of the surface of a hollow fiber membrane prepared by the TIPS method;
FIG. 5 is an SEM photograph of the inner wall of a hollow fiber membrane prepared by the TIPS method;
FIG. 6 SEM photograph of a cross-section of the film of example 1.
Detailed Description
The present invention will be described below with reference to specific examples, but the embodiments of the present invention are not limited thereto. The experimental methods not specified in the examples are generally commercially available according to the conventional conditions and the conditions described in the manual, or according to the general-purpose equipment, materials, reagents and the like used under the conditions recommended by the manufacturer, unless otherwise specified. The starting materials required in the following examples and comparative examples are all commercially available.
Example 1
Uniformly mixing PP granules and ethylene propylene rubber granules with 1,3, 5-tri (3, 5-di-tert-butyl-4-hydroxybenzyl) s-triazine-2, 4,6- (1H,3H5H) trione according to the mass ratio of 17:3 and the addition amount of 0.4 percent by using a stirrer, melting and extruding the mixture by using a single-screw extruder, granulating the mixture, and adding the mixture into a solid material feeding system of a double-screw extruder; mixing dibutyl phthalate and soybean oil in a mass ratio of 7:3, and adding the mixture into a liquid feeding system of a double-screw extruder; and mixing the liquid paraffin and the soybean oil in a mass ratio of 5:5, and adding the mixture into a core liquid storage tank of the spinning nozzle. The temperature of the extruder is 180 ℃, the temperature of the spinning jet is 170 ℃, the temperature of the core liquid is 80 ℃, and the temperature of the coagulating bath is 70 ℃. Starting the double-screw extruder, the solid material and liquid feeding system, starting the membrane casting liquid metering pump and the core liquid metering pump, enabling the membrane casting liquid to form initial hollow fibers through an annular spinning nozzle, further cooling and solidifying and forming in a solidification bath water tank, and finally drawing and winding the filaments at 19m/min through a roller to obtain the original membrane filaments. The original membrane filaments are extracted by absolute ethyl alcohol for 12 hours after being processed by normal hexane for 12 hours, are mutually and alternately extracted for 72 hours, are dried and are placed in a constant temperature drying oven at 60 ℃ for 12 hours. Finally obtaining the modified polypropylene hollow fiber membrane, wherein the outer diameter of membrane filaments is 1.8mm, the inner diameter is 0.9mm, the average pore diameter of membrane pores is 0.2 micron, the surface contact angle is 119 degrees, the maximum elongation is 300 percent, the tensile strength is 6.2MPa, and the air permeability is 0.52L cm under the air pressure of 1bar-2·min-1。
Soaking the hollow fiber membrane into a 2% sodium hypochlorite solution, keeping the pH value of the solution at 6-7, and keeping the temperature at 60 ℃. The oxidation resistance of the membrane was judged by subjecting the membrane to extreme oxidation conditions to accelerate its oxidation. And dipped into a commercial polypropylene hollow fiber membrane as a control. When the hollow membrane is immersed for 52 hours, the contact angle of the outer surface of the membrane wire of the control group is 85 degrees, the maximum elongation is reduced from 95 percent to 65 percent, the contact angle of the outer surface of the hollow membrane prepared by the invention is 110 degrees, and the maximum elongation is 300 percent. The membrane material is soaked in water for a long time, and the halogen absorbent calcium stearate added in the polypropylene synthesis process is precipitated, so that the membrane contact angle is greatly reduced. Research shows that halogen catalyst is required to be added in the polypropylene synthesis process to improve the polymerization degree, so calcium stearate is required to be added as a halogen absorbent to eliminate the adverse effects of residual catalyst on color and stability, and the calcium stearate can be separated out in water for a long time. Experiments show that the surface contact angle of the modified polypropylene hollow fiber membrane can be recovered along with time, and the surface contact angle of the commercial polypropylene hollow fiber membrane can not be recovered. At 480h, the contact angle of the outer surface of the hollow membrane prepared by the method is 115 degrees, the maximum elongation is 275 percent, the contact angle of the outer surface of the membrane filament of the control group is 87 degrees, and the maximum elongation is 30 percent.
The hollow fiber membrane prepared by the invention is filled into a membrane component for vacuum membrane distillation, the vacuum degree of the permeation side is 0.09MPa, the feeding temperature is 80 ℃, the feeding flow rate is 180L/h, the hollow fiber membrane is used for separating and concentrating nitric acid from nitric acid waste liquid, and when the hollow fiber membrane is stably operated for 6 months, the flux is still stable at 22 kg.m-2·h-1。
Example 2
Uniformly mixing PP granules and ethylene propylene rubber granules according to the mass ratio of 4:1 and 0.8% of 2, 4-bis (dodecyl sulfur methyl) -6-methylphenol by using a stirrer, carrying out melt extrusion granulation by using a single-screw extruder, and adding the mixture into a solid material feeding system of a double-screw extruder; mixing dibutyl phthalate and soybean oil in a mass ratio of 7:3, and adding the mixture into a liquid feeding system of a double-screw extruder; and mixing the liquid paraffin and the soybean oil in a mass ratio of 5:5, and adding the mixture into a core liquid storage tank of the spinning nozzle. The temperature of the extruder is 175 ℃, the temperature of the spinning jet is 170 ℃, the temperature of the core liquid is 65 ℃, the temperature of the coagulating bath is water, and the temperature is 60 ℃. Starting the double-screw extruder, the solid material and liquid feeding system, starting the membrane casting liquid metering pump and the core liquid metering pump, enabling the membrane casting liquid to form initial hollow fibers through an annular spinning nozzle, further cooling and solidifying and forming in a solidification bath water tank, and finally drawing and winding the filaments at 19m/min through a roller to obtain the original membrane filaments. The original membrane filaments are extracted by absolute ethyl alcohol for 12 hours after being processed by normal hexane for 12 hours, are mutually and alternately extracted for 72 hours, are dried and are placed in a constant temperature drying oven at 60 ℃ for 12 hours. Finally obtaining the modified polypropylene hollow fiber membrane, the outer diameter of the membrane filament is 1.5mm, the inner diameter is 0.8mm, the average pore diameter of the membrane pore is 0.22 micron, the surface contact angle is 118 degrees,maximum elongation of 310%, tensile strength of 6.0MPa, and air permeability of 0.59L cm under 1bar pressure-2·min-1。
Soaking the hollow fiber membrane into a 2% sodium hypochlorite solution, and keeping the temperature at 60 ℃ at a pH of 6-7. The oxidation resistance of the membrane was judged by subjecting the membrane to extreme oxidation conditions to accelerate its oxidation. And dipped into a commercial polypropylene hollow fiber membrane as a control. When the hollow membrane is immersed for 52 hours, the contact angle of the outer surface of the membrane wire of the control group is 85 degrees, the maximum elongation is reduced from 95 percent to 65 percent, the contact angle of the outer surface of the hollow membrane prepared by the invention is 110 degrees, the maximum elongation is 310 percent, and when the contact angle of the outer surface of the hollow membrane prepared by the invention is 480 hours, the contact angle of the outer surface of the hollow membrane prepared by the invention is 115 degrees, the maximum elongation is 300 percent, the contact angle of the outer surface of the membrane wire of the control group is 87 degrees, and the maximum elongation is 30 percent.
The hollow fiber membrane prepared by the invention is filled into a membrane component for vacuum membrane distillation, the vacuum degree of a permeation side is 0.09MPa, the feeding temperature is 80 ℃, the feeding flow rate is 48L/h, the hollow fiber membrane is used for separating and concentrating nitric acid from nitric acid waste liquor, and when the hollow fiber membrane is stably operated for 240h, the flux is still stable at 20 kg.m-2·h-1。
Example 3
Mixing PP granules and ethylene propylene rubber granules with 2,2' -thiobis [3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate according to the mass ratio of 4:1]Uniformly mixing the components by using a stirrer according to the addition of 0.55 percent, performing melt extrusion granulation by using a single-screw extruder, adding the mixture into a reactor, mixing the dibutyl phthalate and the soybean oil according to the mass ratio of 7:3, and adding the mixture into the reactor, wherein the mass ratio of the granules to the diluent in the reactor is 3: 7. And introducing nitrogen into the reactor for protection, heating to 180 ℃, stirring, stopping stirring after 5 hours, standing for 3 hours, and defoaming to obtain the homogeneous casting solution. Coating the casting film liquid on the surface of a polyester non-woven fabric, scraping the polyester non-woven fabric into a flat plate shape at the film scraping temperature of 180 ℃, and then cooling and solidifying the polyester non-woven fabric in a 30 ℃ water tank. And (3) placing the solidified flat membrane into an extracting agent (normal hexane) for extraction for 12h, then placing the flat membrane into ethanol for extraction for 12h, and mutually and alternately extracting for 72 h. And (3) taking out the membrane which is completely extracted until the diluent is completely removed, and placing the membrane in a constant-temperature drying oven at 60 ℃ to remove the residual volatile extractant in the extraction process for 12 hours at constant temperature, thus preparing the PP/EPR (EPDM) blended high-ductility oxidation-resistant microporous hydrophobic flat membrane. The membrane has average poresThe diameter is 0.25 micrometer, the contact angle is 120 degrees, the porosity is 70 percent, and the air permeability is 0.71L cm under the air pressure of 1bar-2·min-1。
The flat membrane prepared by the method is filled into a membrane component for vacuum membrane distillation, the vacuum degree of a permeation side is 0.05MPa, the feeding temperature is 40 ℃, the feeding flow rate is 1.2m/s of the membrane surface flow rate, the flat membrane is used for deammoniation treatment of garbage percolate with 120mg/L ammonia nitrogen, the continuous stable operation lasts more than 1200h, the ammonia removal rate is 93.3 percent, and the pure water flux is 6.3L/(. square meter.h).