CN115007000A - Modified attapulgite polylactic acid separation membrane, preparation method and application - Google Patents
Modified attapulgite polylactic acid separation membrane, preparation method and application Download PDFInfo
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Abstract
The invention provides a modified attapulgite polylactic acid separation membrane, a preparation method and application thereof, and the concept of composite modification of a polylactic acid membrane by taking attapulgite as a multi-reaction-site modified carrier. The pore-foaming agents PEG4000 and PVP K30 are mixed, so that the water flux of the attapulgite composite polylactic acid membrane is 2 times of that of a pure polylactic acid membrane. The nanometer silver is loaded on the surface and the inside of a pore channel of the attapulgite by a coprecipitation method by virtue of the adhesiveness and strong reducibility of dopamine, so that the antifouling and antibacterial integrated bio-based polymer and natural mineral combined separation membrane is obtained. The flux recovery rate of the polylactic acid/attapulgite/silver nano composite membrane is increased from 40.99% to 89.41%, and the bacteriostasis rate of the composite membrane reaches 98.0%.
Description
Technical Field
The invention relates to a functional attapulgite composite polylactic acid film and a preparation method thereof, belonging to the technical field of film separation materials.
Background
The degradable bio-based high polymer material mainly takes starch, soybean, vegetable oil and other renewable resources as raw materials, and has the characteristics of 'natural origin and nature attribution'. Polylactic acid (PLA) is the second largest fully biodegradable bio-based polymer material, and compared with the traditional petroleum-based polymer material, the energy loss and the emission of CO in the production process of PLA are reduced 2 The exhaust gas is only half of fossil resources. Furthermore, the PLA synthetic raw material is easy to obtain, has the characteristics of good biocompatibility, easy processing and the like, is easy to degrade after being discarded, and cannot generate secondary pollution. Based on these characteristics, PLA is a good alternative to traditional polymeric membrane materials for membrane separation applications. However, the film forming property of PLA is weak, the film forming condition needs to be regulated to improve the film forming property, and the PLA film has poor thermal stability and low mechanical strength, and is often brittle and broken, which limits the practical production and application thereof.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the problems of low mechanical strength and poor film forming property exist in the process of preparing the polymer separation film by the polylactic acid material. The technical means adopted by the method is that attapulgite is used as a carrier, and abundant hydrophilic groups on the surface of the attapulgite are used, so that the compatibility of the attapulgite and polylactic acid is improved, and the mechanical property of the attapulgite after film forming is improved; PEG4000 and PVP K30 are mixed to be used as pore-foaming agents to improve the film-forming property of the polylactic acid; meanwhile, the ATP surface is endowed with bacteriostatic activity by loading silver nanoparticles, so that the anti-pollution capability of the membrane is improved.
A modified attapulgite polylactic acid separation membrane is prepared by compounding attapulgite and polylactic acid mixture.
The surface of the attapulgite is also loaded with nano silver.
The mass ratio of the attapulgite to the polylactic acid is 1-15: 100.
the molecule of the polylactic acid is modified by alkyl sulfonate.
The preparation method of the modified attapulgite polylactic acid separation membrane comprises the following steps:
and 2, adding polylactic acid into the suspension obtained in the step 1, uniformly mixing to obtain a casting solution, and preparing the separation membrane by a phase inversion method.
The weight of the attapulgite is 1-10% of that of the polylactic acid.
In the step 1, silver is loaded on the surface of the attapulgite, and the preparation method comprises the following steps: dispersing attapulgite powder in a Tris buffer solution, adjusting the pH value to be alkaline, adding dopamine hydrochloride for reaction, washing and drying reactants; then placing the reaction product in silver nitrate solution to carry out reduction reaction, and washing and drying the reaction product.
The concentration of the Tris buffer solution is 0.005-0.03M; adjusting the pH to alkaline means that the pH is 8.0-10.0; the reaction time of the dopamine hydrochloride is 10-40 h.
The concentration of the silver nitrate solution is 0.01-0.05M, the reduction reaction is carried out in a dark condition, and the reaction time is 5-30 h.
The phase inversion method is a non-solvent induced phase inversion method.
The pore-foaming agent is one or two of polyethylene glycol or polyvinylpyrrolidone.
The molecular weight of the polyethylene glycol is 2000-8000Da, and the molecular weight of the polyvinylpyrrolidone is 30000-60000 Da.
The concentration of the pore-foaming agent in the membrane casting solution is 4-8%.
The concentration of the organic solvent in the casting solution is 70-78%.
The concentration of the polylactic acid in the casting solution is 15-20%.
The surface of the polylactic acid is modified by alkyl sulfonate, and the preparation method comprises the following steps: dropping water solution containing alkyl sulfonate into organic solvent with polylactic acid dissolved, stirring to form emulsion, decompressing and steaming to remove solvent, washing residual product with water, drying to obtain modified polylactic acid.
The concentration of the polylactic acid in the organic solvent is 0.5-5%.
The organic solvent is one or a mixture of ester solvents, benzene solvents and hydrocarbon solvents.
The concentration of the water solution containing the alkyl sulfonate is 0.2-2%.
The volume ratio of the organic solvent to the aqueous solution is 10: 1-5.
In the step 2, the step of uniformly mixing refers to mixing for 5-30h at the temperature of 60-100 ℃.
The organic solvent is N-methyl pyrrolidone.
The modified attapulgite polylactic acid separation membrane is applied to liquid filtration.
The polylactic acid is applied to improving the mechanical strength and the retention rate of the attapulgite polylactic acid separation membrane.
The modified attapulgite polylactic acid separation membrane is applied to antibiosis.
Advantageous effects
The invention utilizes the natural magnesium aluminum silicate clay mineral with biocompatibility-attapulgite to modify the degradable polylactic acid film to prepare the bio-based composite film with high flux, high retention rate and high mechanical property, and the polymer film can be used for pollution resistance and antibacterial application in water treatment.
The natural porous magnesium aluminum silicate clay mineral Attapulgite (ATP) contains abundant hydrophilic groups such as hydroxyl (-OH) on the surface, so that the biocompatibility with a polymer is improved, and the ATP has reactive Si-OH groups on the surface, so that the nano silver can be effectively loaded in situ through self-crosslinking and reduction reaction of dopamine, and the antibacterial property of the surface of the attapulgite is realized.
The nano silver generated in situ on the surface of the attapulgite has positive charge, the surface of the polylactic acid is provided with negative charge after being modified by sodium alkyl sulfonate, and when the polylactic acid is prepared into a casting solution, the polylactic acid can be embedded into a porous structure on the surface of the attapulgite through electrostatic interaction, so that the physical strength after phase inversion film forming is enhanced, the film pores are reduced, and the retention rate of macromolecules is improved.
Drawings
FIG. 1 shows the results of IR spectroscopy;
FIG. 2 is a XRD characterization result;
FIG. 3 is SEM characterization results;
FIG. 4 shows the results of the antibacterial test.
Detailed Description
Attapulgite (ATP) is a clay mineral with layer chain crystal structure, and its basic structure is formed by two layers of indirect reactionsThe rotary silica tetrahedron is connected with a layer of non-continuous magnesium (aluminum) oxygen octahedron. The ideal chemical structural formula is Si 8 Mg 5 O 20 (OH) 2 (H2O) 4 4H 2 And (O). The basic structure is as follows:
the polylactic acid adopted by the invention is prepared by direct polycondensation of lactic acid monomers or ring-opening polymerization of lactide.
Comparative example 1 preparation of polylactic acid film (different pore-foaming agent)
(1) Dissolving polylactic acid (PLA), a single pore-forming agent (polyethylene glycol 4000(PEG), polyvinylpyrrolidone (PVP K30) and a mixed pore-forming agent (different proportions) in an N-methylpyrrolidone (NMP) solvent according to a certain mass ratio, mechanically stirring the polylactic acid, the pore-forming agent and the solvent at a high temperature of 80 ℃ for 18-24 h, standing and defoaming for 8-12 h after the polylactic acid, the pore-forming agent and the solvent are completely dissolved to obtain a uniform membrane casting solution, wherein the concentration of the polylactic acid is 7 wt%, and the concentration of the pore-forming agent is 6% (respectively adopting PEG4000, PVP K30 and a mixture of the PEG4000 and the PVP K30 in a ratio of 1: 1).
(2) Setting the temperature of a film scraping machine to 80 ℃, controlling the thickness of a scraper to be 200 mu m, scraping the casting film liquid on a glass plate, controlling the volatilization time to be 5-10 s, immersing the glass plate into a water coagulation bath, carrying out phase conversion curing to form a film, immersing for 10min, taking out to obtain a wet polylactic acid film, storing the prepared film in deionized water, changing water every 12h, and removing residual water on the film surface by absorbent paper. And (3) drying the film with the moisture removed from the film surface in an oven at 30 ℃ for 40min to obtain a polylactic acid dry film.
The resulting polylactic acid film was prepared for comparison in the following examples. Unless otherwise specified, the following references to polylactic acid films in this comparative example all refer to PEG4000/PVP K30 as per 1: 1 condition(s)
Comparative example 1 preparation of polylactic acid/Attapulgite composite Membrane
(1) Screening Attapulgite (ATP) powder into powder with the size of 400 meshes, weighing a certain amount of ATP powder (7 wt.% of PLA mass) and continuously ultrasonically dispersing in N-methylpyrrolidone (NMP) as a solvent for 5-10 min to obtain uniformly dispersed ATP suspension; polylactic acid (PLA), polyethylene glycol 4000(PEG) and polyvinylpyrrolidone (PVP K30) were dissolved in the ATP suspension. Taking 7 wt.% of ATP (relative to the mass of PLA) as an example, the mass ratio of PLA to ATP to PEG4000/PVP K30 to NMP is 16.74:1.26:3:3:76, mechanically stirring at 80 ℃ for 18-24 h, standing and defoaming for 8-12 h after the materials are completely dissolved, and obtaining a uniform casting solution;
(2) setting the temperature of a film scraping machine to 80 ℃, controlling the thickness of a scraper to be 200 mu m, scraping the casting film liquid on a glass plate, controlling the volatilization time to be 5-10 s, immersing the glass plate into a water coagulation bath, carrying out phase inversion curing to form a film, immersing for 10min, taking out to obtain a wet polylactic acid/attapulgite composite film, storing the prepared film in deionized water, changing water every 12h, and removing residual water on the film surface by using absorbent paper. And (3) placing the membrane with the membrane surface moisture removed in an oven to be dried for 40min at 30 ℃ to obtain the polylactic acid/attapulgite composite dry membrane.
Example 2 preparation of polylactic acid/Attapulgite/silver nanocomposite film
(1) Weighing a certain amount of ATP powder, placing the ATP powder in 100ml of deionized water for ultrasonic dispersion for 30min to uniformly disperse ATP, weighing a proper amount of Tris standard substance in an ATP suspension (0.01M Tris standard buffer solution), magnetically stirring for 1h, adjusting the pH value of the solution to 8.5 by using hydrochloric acid and sodium hydroxide, adding a proper amount of dopamine hydrochloride, magnetically stirring for 24h at the room temperature at 800r/min, then centrifuging for 10min at the rotating speed of 10,000r/min, repeatedly washing and centrifuging the centrifuged precipitate by using deionized water until the solution is clear, and placing the final precipitate in a vacuum drying box at the temperature of 60 ℃ for 24h to obtain ATP/PDa powder.
Weighing an appropriate amount of ATP/PDa powder, placing the ATP/PDa powder in 100ml of 0.03M silver nitrate solution, magnetically stirring the mixed solution at the room temperature for 12h at 400rmp (under the condition of keeping out of the sun), centrifuging the ATP/Ag suspension liquid completely reacted for 10min at 10,000r/min, repeatedly centrifuging and washing the centrifuged precipitate by using deionized water until the solution is clear, placing the solution in a vacuum drying oven at the temperature of 40 ℃ for 12h, and placing the solution in a brown bottle to obtain the ATP/Ag powder.
(2) Sieving the ATP/Ag powder into powder with the size of 400 meshes, weighing a certain amount of ATP/Ag powder (7 wt.% of PLA mass) and continuously ultrasonically dispersing the ATP/Ag powder in a solvent N-methylpyrrolidone (NMP) for 5-10 min to obtain a uniformly dispersed ATP/Ag suspension; polylactic acid (PLA), polyethylene glycol 4000(PEG) and polyvinylpyrrolidone (PVP K30) were dissolved in the ATP/Ag suspension. Taking 7 wt.% of ATP (relative to the mass of PLA) as an example, the mass ratio of PLA, ATP/Ag, PEG4000, PVP K30 and NMP is 16.74:1.26:3:3:76, mechanically stirring at the high temperature of 80 ℃ for 18-24 h, standing and defoaming for 8-12 h after the materials are completely dissolved, and obtaining a uniform membrane casting solution;
(3) setting the temperature of a film scraping machine to be 80 ℃, controlling the thickness of a scraper to be 200 mu m, scraping and coating the film casting solution on a glass plate, controlling the volatilization time to be 5-10 s, then immersing the glass plate into a water coagulation bath for phase inversion solidification to form a film, taking out the film after immersing for 10min to obtain the wet polylactic acid/attapulgite/silver nano composite film, storing the prepared film in deionized water, changing water every 12h, and removing residual moisture on the film surface by using absorbent paper. And (3) placing the membrane with the membrane surface moisture removed in an oven to be dried for 40min at 30 ℃ to obtain the polylactic acid/attapulgite/silver nano composite dry membrane.
Example 3 preparation of polylactic acid/Attapulgite/silver nanocomposite film
(1) Preparing 100ml of ethyl acetate solution containing 2% polylactic acid, slowly dropwise adding 20ml of 0.5% sodium dodecyl benzene sulfonate aqueous solution, stirring at high speed for 4 hours after dropwise adding to form emulsion, evaporating under reduced pressure to remove a solvent, washing the residual product with water, and drying in vacuum to obtain PLA with positive charge on the surface;
(2) weighing a certain amount of ATP powder, placing the ATP powder in 100ml of deionized water for ultrasonic dispersion for 30min to uniformly disperse ATP, weighing a proper amount of Tris standard substance in an ATP suspension (0.01M Tris standard buffer solution), magnetically stirring for 1h, adjusting the pH value of the solution to 8.5 by using hydrochloric acid and sodium hydroxide, adding a proper amount of dopamine hydrochloride, magnetically stirring for 24h at the room temperature at 800r/min, then centrifuging for 10min at the rotating speed of 10,000r/min, repeatedly washing and centrifuging the centrifuged precipitate by using deionized water until the solution is clear, and placing the final precipitate in a vacuum drying box at the temperature of 60 ℃ for 24h to obtain ATP/PDa powder.
Weighing an appropriate amount of ATP/PDa powder, placing the ATP/PDa powder in 100ml of 0.03M silver nitrate solution, magnetically stirring the mixed solution at the room temperature for 12h at 400rmp (under the condition of keeping out of the sun), centrifuging the ATP/Ag suspension liquid completely reacted for 10min at 10,000r/min, repeatedly centrifuging and washing the centrifuged precipitate by using deionized water until the solution is clear, placing the solution in a vacuum drying oven at the temperature of 40 ℃ for 12h, and placing the solution in a brown bottle to obtain the ATP/Ag powder.
(3) Sieving the ATP/Ag powder into powder with the size of 400 meshes, weighing a certain amount of ATP/Ag powder (7 wt.% of PLA mass) and continuously ultrasonically dispersing the ATP/Ag powder in a solvent N-methylpyrrolidone (NMP) for 5-10 min to obtain a uniformly dispersed ATP/Ag suspension; PLA, polyethylene glycol 4000(PEG) and polyvinylpyrrolidone (PVP K30) with surface positive charge treatment were dissolved in the ATP/Ag suspension. Taking 7 wt.% of ATP (relative to the mass of PLA) as an example, the mass ratio of PLA, ATP/Ag, PEG4000, PVP K30 and NMP is 16.74:1.26:3:3:76, mechanically stirring at the high temperature of 80 ℃ for 18-24 h, standing and defoaming for 8-12 h after the materials are completely dissolved, and obtaining a uniform casting solution;
(4) setting the temperature of a film scraping machine to be 80 ℃, controlling the thickness of a scraper to be 200 mu m, scraping and coating the film casting solution on a glass plate, controlling the volatilization time to be 5-10 s, then immersing the glass plate into a water coagulation bath for phase inversion solidification to form a film, taking out the film after immersing for 10min to obtain the wet polylactic acid/attapulgite/silver nano composite film, storing the prepared film in deionized water, changing water every 12h, and removing residual moisture on the film surface by using absorbent paper. And (3) placing the membrane with the membrane surface moisture removed in an oven to be dried for 40min at 30 ℃ to obtain the polylactic acid/attapulgite/silver nano composite dry membrane.
Infrared characterization
Fig. 1 is an infrared spectrum of the composite films prepared in examples 2 and 3. 1650-1660cm -1 Is attributed to the absorption peak of the catechol group of polydopamine, 3410cm -1 The absorption peak at the position belongs to the characteristic peak of ATP and is at 2850-2900cm -1 The characteristic peak of the compound is attributed to the methyl and methylene H-C-H antisymmetric stretching vibration and symmetric stretching vibration peak of the sodium dodecyl benzene sulfonate. It can be seen that dopamine, sulfonate, etc. successfully form ATP into a composite membrane.
Characterization of XRD
FIG. 2 is an XRD pattern of powdered ATP, ATP/PDa and ATP/Ag. The position of the characteristic reflection peak of the ATP/PDa is consistent with that of the ATP, which shows that the crystal structure of the ATP/PDa is not changed, but the ATP/Ag has the characteristic reflection peak of AgNPs, which shows that the AgNPs are successfully synthesized, and the characteristic peaks are weakened through comparison, which shows that the AgNPs not only are loaded on polydopamine, but also occupy free sites in pore channels by virtue of the ATP adsorption effect, so that the free volume of the ATP is reduced, and the characteristic reflection peak of the ATP is weakened.
SEM characterization
Fig. 3 is SEM images of the polylactic acid pure films prepared in comparative example 1, example 1 and example 2, and the modified films thereof at different magnifications. The unmodified membrane is named PLA, the membrane modified by ATP is named PLA/ATP/Ag, and the membrane modified by ATP/Ag is named PLA/ATP/Ag. As can be seen from the figure, the surface of the PLA pure film is a porous structure, and the section structure is also composed of a finger-shaped pore structure and a large pore structure. The surface of the PLA/ATP composite membrane is still in a porous structure, a plurality of pore structures also appear, and the section of the PLA/ATP composite membrane is changed from a structure formed by finger-shaped pores and macropores into a through finger-shaped pore structure. The PLA/ATP/Ag composite membrane has a porous structure and a pore structure on the surface, and the cross section of the PLA/ATP/Ag composite membrane is a through finger-shaped pore structure.
Pure water flux and bovine serum rejection test
The pure water flux and Bovine Serum Albumin (BSA) retention test results of the composite membranes prepared in the control examples and examples are shown in the following table, wherein the BSA retention test employs a BSA solution having a concentration of 1g/L (the retention test pressure is 1bar, and the membrane area is 0.001256m 2 The test temperature is 25 +/-1 ℃).
Data show that the PLA membrane flux obtained by mixing the pore-foaming agent is higher, the BSA retention rate is increased, the composite membrane flux and the BSA retention rate after ATP is doped are improved from 89.7% to 96.72%, the membrane flux is improved after ATP/Ag is doped, and the BSA retention rate is not obviously changed and still remains at 90.46%; when the composite membrane is prepared by using the PLA modified by positive charge and the ATP modified by negative charge, the pure water flux is slightly reduced, and the retention rate of BSA (bovine serum albumin) is improved mainly because smaller membrane pores can be formed due to the electrostatic action of the PLA and the ATP in the phase inversion process, although the water flux is reduced, the retention rate is improved.
Film Strength characterization
The comparative example and the composite films prepared in examples were subjected to mechanical strength test. (the test film sample had dimensions of 1 cm. times.8 cm).
TABLE 3
As can be seen from the above table, the tensile strength of PLA resulting from mixing the porogen was 46%. The elongation at break of the composite film prepared in the embodiment 2 is improved to 45.07%, and the tensile strength of the composite film is increased from 2.00MPa to 2.61MPa, mainly due to the fact that after ATP is added, the mechanical property of the composite film can be obviously improved; in example 3, when the casting solution is prepared, the positive charge of the surface of the nano silver and the negative charge of the PLA obtained by the in-situ growth on the surface of ATP can accommodate more PLA in the nano pore channel on the surface of ATP through electrostatic interaction, and after the phase inversion process, the obtained composite film shows better mechanical strength and elongation at break.
Anti-pollution experiment
The anti-pollution performance of the membrane surface is researched by adopting 1g/LBSA solution as a simulated pollutant, and the simulated pollutant is mainly subjected to two water-BSA circulating processes. To eliminate the effect of concentration polarization, experiments were performed under magnetic stirring. A complete dynamic pollution experiment comprises three stages, wherein the first stage filters pure water for 30min, the second stage filters BSA solution for 1h, and the third stage filters pure water for 30min after mechanical washing and backwashing of the membrane. The composite membranes obtained in the comparative example and the example are used for testing, the change of the flux is recorded along with the time, and the data shows that the flux of the composite membrane is recovered more obviously compared with the flux of a pure membrane after two cycles.
The following table shows the flux recovery data of PLA pure film, PLA/ATP composite film and PLA/ATP/Ag composite film.
The data show that the flux recovery rate of the composite membrane prepared by the method is improved from 38.21% to 78% or higher compared with that of the polylactic acid membrane.
The following is the pollution resistance analysis data of PLA pure film, PLA/ATP composite film and PLA/ATP/Ag composite film.
TABLE 5
The total pollution resistance to the membrane surface is mainly based on irreversible pollution, because the irreversible pollution cannot be simply removed, the pollution blocks the membrane pores and becomes a part of the membrane module, and the anti-pollution capability of the membrane is judged more visually according to the irreversible pollution. The data show that the composite membrane prepared in the embodiment has smaller irreversible pollution ratio compared with the common PLA membrane, and the anti-pollution capability of the PLA/ATP/Ag membrane is obviously superior to that of the two membranes.
Antibacterial experiments
FIG. 4 is a diagram showing the antibacterial effect of ATP and its modified material and PLA film and its modified film, from which it can be intuitively reflected that AgNPs loaded on the ATP surface have obvious antibacterial effect. The bacteriostatic rate of the pure PLA film is-10%, the bacteriostatic rate of the PLA/ATP composite film is 18%, and the bacteriostatic rate of the PLA/ATP/Ag composite film is 98%. The antibacterial activity of the composite membrane is derived from ATP and ATP/Ag composite materials, and the antibacterial activity of the materials is consistent with the antibacterial activity trend of the composite membrane.
Claims (10)
1. A modified attapulgite polylactic acid separation membrane is characterized by being compounded by a mixture of attapulgite and polylactic acid.
2. The modified attapulgite polylactic acid separation membrane according to claim 1, wherein the surface of the attapulgite is also loaded with nano silver;
the mass ratio of the attapulgite to the polylactic acid is 1-15: 100;
the molecule of the polylactic acid is modified by alkyl sulfonate.
3. The preparation method of the modified attapulgite polylactic acid separation membrane according to claim 1, characterized by comprising the following steps:
step 1, dispersing attapulgite in an organic solvent, and adding a pore-foaming agent;
and 2, adding polylactic acid into the suspension obtained in the step 1, uniformly mixing to obtain a casting membrane liquid, and preparing the casting membrane liquid into the separation membrane by a phase inversion method.
4. The preparation method of the modified attapulgite polylactic acid separation membrane according to claim 3, wherein the weight of the attapulgite is 1-10% of the weight of the polylactic acid;
in the step 1, silver is loaded on the surface of the attapulgite, and the preparation method comprises the following steps: dispersing attapulgite powder in a Tris buffer solution, adjusting the pH value to be alkaline, adding dopamine hydrochloride for reaction, washing and drying reactants; then placing the mixture in silver nitrate solution for reduction reaction, and washing and drying a reaction product;
the concentration of the Tris buffer solution is 0.005-0.03M; adjusting the pH to alkaline means that the pH is 8.0-10.0; the reaction time of the dopamine hydrochloride is 10-40 h;
the concentration of the silver nitrate solution is 0.01-0.05M, the reduction reaction is carried out in a dark condition, and the reaction time is 5-30 h.
5. The method for preparing the modified attapulgite polylactic acid separation membrane according to claim 3, wherein the phase inversion method is a non-solvent induced phase inversion method;
the pore-foaming agent is one or two of polyethylene glycol or polyvinylpyrrolidone;
the molecular weight of the polyethylene glycol is 2000-8000Da, and the molecular weight of the polyvinylpyrrolidone is 30000-60000 Da.
6. The preparation method of the modified attapulgite polylactic acid separation membrane according to claim 3, wherein the concentration of the pore-foaming agent in the membrane casting solution is 4-8%;
the concentration of the organic solvent in the casting solution is 70-78%;
the concentration of the polylactic acid in the casting solution is 15-20%.
7. The preparation method of the modified attapulgite polylactic acid separation membrane according to claim 3, wherein the surface of the polylactic acid is modified by alkyl sulfonate, and the preparation method comprises the following steps: dripping an aqueous solution containing alkyl sulfonate into an organic solvent in which polylactic acid is dissolved, stirring to form an emulsion, evaporating under reduced pressure to remove the solvent, washing and drying the residual product to obtain modified polylactic acid;
the concentration of the polylactic acid in the organic solvent is 0.5 to 5 percent
The organic solvent is one or a mixture of ester solvent, benzene solvent and hydrocarbon solvent
The concentration of the water solution containing the alkyl sulfonate is 0.2-2%;
the volume ratio of the organic solvent to the aqueous solution is 10: 1-5.
8. The preparation method of the modified attapulgite polylactic acid separation membrane according to claim 3, wherein in the step 2, the uniform mixing refers to mixing for 5-30h at 60-100 ℃;
the organic solvent is N-methyl pyrrolidone.
9. The use of the modified attapulgite polylactic acid separation membrane of claim 1 in liquid filtration.
10. The polylactic acid is applied to improving the mechanical strength and the retention rate of the attapulgite polylactic acid separation membrane.
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