CN115007000A - A kind of modified attapulgite polylactic acid separation membrane, preparation method and use - Google Patents

Abstract

The invention proposes a modified attapulgite polylactic acid separation membrane, a preparation method and an application, and uses attapulgite as a multi-reaction site modification carrier and the concept of composite modification of a polylactic acid membrane. Mixing porogen PEG 4000 and PVP K30 makes the water flux of attapulgite composite PLA film twice as high as that of pure PLA film. Through the co-precipitation method, nano-silver was loaded on the surface and inside of the pores of attapulgite with the help of the adhesion and strong reducibility of dopamine, and the separation membrane of bio-based polymer combined with natural minerals was obtained. The flux recovery rate of the polylactic acid/attapulgite/silver nanocomposite membrane increased from 40.99% to 89.41%, and the antibacterial rate of the composite membrane reached 98.0%.

Description

A kind of modified attapulgite polylactic acid separation membrane, preparation method and use

technical field

The invention relates to a functional attapulgite composite polylactic acid membrane and a preparation method thereof, belonging to the technical field of membrane separation materials.

Background technique

Biodegradable bio-based polymer materials are mainly based on renewable resources such as starch, soybean, vegetable oil, etc., and have the characteristics of "originating from nature and belonging to nature". Polylactic acid (PLA) is the second largest bio-based polymer material that is fully biodegradable. Compared with traditional petroleum-based polymer materials, the energy loss and _CO emissions during PLA production are only half of those of fossil resources. Not only that, PLA synthetic raw materials are readily available, have good biocompatibility, easy processing and other characteristics, and are easily degraded after disposal without causing secondary pollution. Based on these characteristics, PLA is a good choice to replace traditional polymer membrane materials for membrane separation. However, the film-forming properties of PLA are weak, and it is necessary to adjust the film-forming conditions to improve the film-forming properties. Moreover, the thermal stability of PLA films is poor, the mechanical strength is low, and brittle fractures tend to occur, which limits its practical production and application.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is the problems of low mechanical strength and poor film-forming property in the process of preparing polymer separation membrane from polylactic acid material. The technical means adopted in this patent is to use attapulgite as a carrier and use the abundant hydrophilic groups on its surface to improve the compatibility with polylactic acid and improve the mechanical properties after film formation; mix PEG 4000 and PVP K30 It can be used as a porogen to improve the film-forming properties of polylactic acid; at the same time, silver nanoparticles are loaded on the surface of ATP to give it bacteriostatic properties and improve the anti-fouling ability of the film.

A modified attapulgite polylactic acid separation membrane is compounded by a mixture of attapulgite and polylactic acid.

The surface of the attapulgite is also loaded with nano silver.

The mass ratio range of the attapulgite and polylactic acid is 1-15:100.

The molecule of the polylactic acid has been modified with an alkyl sulfonate.

The preparation method of modified attapulgite polylactic acid separation membrane comprises the following steps:

Step 1, dispersing attapulgite in an organic solvent, adding a porogen;

In step 2, polylactic acid is added to the suspension obtained in step 1, and after mixing uniformly, a membrane casting solution is obtained, and a separation membrane is prepared by a phase inversion method.

The weight of the attapulgite is 1-10% of the polylactic acid.

In the step 1, the surface of the attapulgite is also loaded with silver, and the preparation method includes the following steps: dispersing the attapulgite powder in a Tris buffer solution, adjusting the pH to alkaline, adding dopamine hydrochloride to react, The reactant is washed and dried; then it is placed in a silver nitrate solution for reduction reaction, and the reaction product is washed and dried.

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 dopamine hydrochloride is 10-40h.

The concentration of the silver nitrate solution is 0.01-0.05M, the reduction reaction is protected from light, and the reaction time is 5-30h.

The phase inversion method described is a non-solvent induced phase inversion method.

The porogen is one or both of polyethylene glycol or polyvinylpyrrolidone.

The molecular weight of the polyethylene glycol is 2000-8000Da, and the molecular weight of the polyvinylpyrrolidone is 30000-60000Da.

The concentration of the porogen in the 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 an alkyl sulfonate, and the preparation method is as follows: in an organic solvent in which polylactic acid is dissolved, an aqueous solution containing an alkyl sulfonate is added dropwise, stirred to form an emulsion, and the solvent is evaporated under reduced pressure. , and the remaining product is washed with water and dried 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 aqueous solution containing the alkyl sulfonate is 0.2-2%.

The volume ratio of organic solvent to aqueous solution is 10:1-5.

In the said step 2, mixing evenly refers to mixing for 5-30 hours under the condition of 60-100°C.

The organic solvent is N-methylpyrrolidone.

Application of the above-mentioned modified attapulgite polylactic acid separation membrane in liquid filtration.

The application of polylactic acid in improving the mechanical strength and retention rate of attapulgite polylactic acid separation membrane.

Application of the above-mentioned modified attapulgite polylactic acid separation membrane in antibacterial.

beneficial effect

The present invention utilizes attapulgite, a natural biocompatible natural magnesium aluminum silicate clay mineral, to modify the degradable polylactic acid membrane to prepare a bio-based composite membrane with high flux, high retention rate and high mechanical properties. The polymer membrane can be used for antifouling and antibacterial applications in water treatment.

The surface of the natural porous magnesium aluminosilicate clay mineral attapulgite (ATP) is rich in hydrophilic groups, such as hydroxyl (-OH), which is beneficial to improve the biocompatibility with polymers, and the surface of ATP has reactive Si The -OH group can effectively achieve the in-situ loading of silver nanoparticles through the self-crosslinking and reduction reactions of dopamine, and achieve antibacterial properties on its surface.

The nano-silver generated in situ on the surface of attapulgite has a positive charge. By modifying the surface of polylactic acid with sodium alkyl sulfonate, the surface has a negative charge. When it is formulated into a casting liquid, polylactic acid can be electrostatically charged. It is embedded in the surface porous structure of attapulgite, which on the one hand enhances the physical strength after phase inversion into the film, and on the other hand reduces the film pore, so that the retention rate of macromolecules is improved.

Description of drawings

Fig. 1 is the infrared spectrum characterization result;

Figure 2 is the XRD characterization results;

Figure 3 is the SEM characterization results;

Figure 4 is the characterization result of the antibacterial experiment.

Detailed ways

Attapulgite (ATP) is a clay mineral with a layered chain crystal structure. Its basic structure is composed of two layers of indirectly inversely arranged silicon-oxygen tetrahedron and one layer of non-continuously arranged magnesium (aluminum)-oxygen octahedron layer. connected. The ideal chemical structure is Si ₈ Mg ₅ O ₂₀ (OH) ₂ (H2O) ₄ 4H ₂ O. The basic structure is as follows:

The polylactic acid used in the present invention is obtained by direct polycondensation of lactic acid monomers or by ring-opening polymerization of lactide.

Comparative Example 1 Preparation of Polylactic Acid Film (different porogens)

(1) Dissolve polylactic acid (PLA), single porogen (polyethylene glycol 4000 (PEG), polyvinylpyrrolidone (PVPK30), mixed porogen (different proportions) in N-methyl methacrylate according to a certain mass ratio In the pyrrolidone (NMP) solvent, the mass ratio of polylactic acid, porogen and solvent is 18:6:76, and mechanical stirring is carried out at a high temperature of 80 ° C for 18 to 24 hours. A uniform casting solution was obtained; the concentration of polylactic acid was 7 wt.%, and the concentration of porogen was 6% (respectively, PEG4000, PVP K30, and a 1:1 mixture of the two were used).

(2) Set the temperature of the scraper to 80°C, control the thickness of the scraper to be 200μm, scrape the casting liquid on the glass plate, control the volatilization time for 5 to 10s, and then immerse it in a water coagulation bath, phase inversion and solidification into a film After soaking for 10min, take out the wet polylactic acid film, the prepared film is stored in deionized water, the water is changed every 12h, and the residual water on the film surface is removed with absorbent paper. The film from which the moisture on the film surface was removed was placed in an oven to dry at 30° C. for 40 min to obtain a polylactic acid dry film.

The prepared polylactic acid film was used for comparison in the following examples. Unless otherwise specified, the polylactic acid film in this comparative example mentioned below refers to PEG4000/PVP K30 under the condition of 1:1

Comparative Example 1 Preparation of Polylactic Acid/Attapulgite Composite Film

(1) Sieve the attapulgite (ATP) powder into powders with a size of 400 meshes, weigh a certain amount of ATP powder (7 wt.% of the mass of PLA) and disperse it in a solvent N-methylpyrrolidone (NMP) with continuous ultrasonic dispersion 5-10min to obtain a uniformly dispersed ATP suspension; polylactic acid (PLA), polyethylene glycol 4000 (PEG) and polyvinylpyrrolidone (PVP K30) were dissolved in the ATP suspension. Taking 7 wt.% ATP (relative to the mass of PLA) as an example, the mass ratio of PLA, ATP, PEG 4000/PVP K30 and NMP was 16.74:1.26:3:3:76, and mechanical stirring was carried out at a high temperature of 80 °C for 18-24 h , after it is completely dissolved, let it stand for defoaming for 8-12 hours to obtain a uniform casting liquid;

(2) Set the temperature of the scraper to 80°C, control the thickness of the scraper to be 200μm, scrape the casting liquid on the glass plate, control the volatilization time for 5 to 10s, and then immerse it in a water coagulation bath, phase inversion and solidification into a film After soaking for 10min, take it out to obtain wet polylactic acid/attapulgite composite membrane. The prepared membrane is stored in deionized water, the water is changed every 12h, and the residual moisture on the membrane surface is removed with absorbent paper. The film with the moisture removed from the film surface was dried in an oven at 30° C. for 40 min to obtain a polylactic acid/attapulgite composite dry film.

Example 2 Preparation of polylactic acid/attapulgite/silver nanocomposite film

(1) Weigh a certain amount of ATP powder, put it in 100ml of deionized water and ultrasonically disperse it for 30min to make the ATP dispersed evenly, weigh an appropriate amount of Tris standard substance into the ATP suspension (0.01M Tris standard buffer solution), stir magnetically for 1h , and adjust the pH of the solution with hydrochloric acid and sodium hydroxide until its value is 8.5, add an appropriate amount of dopamine hydrochloride, stir magnetically at 800 r/min for 24 h at room temperature, and then centrifuge at 10,000 r/min for 10 min. The ionized water was repeatedly washed and centrifuged until the solution was clear, and the final precipitate was placed in a vacuum drying oven at 60 °C for 24 h to obtain ATP/PDa powder.

Weigh an appropriate amount of ATP/PDa powder and put it in 100ml of 0.03M silver nitrate solution. The mixed solution is stirred at room temperature with a magnetic force of 400rmp for 12h (in the dark), and the fully reacted ATP/Ag suspension is centrifuged at 10,000r/min. For 10 min, the centrifuged precipitate was repeatedly centrifuged and washed with deionized water until the solution was clear, placed in a vacuum drying oven at 40 °C for 12 h, and then placed in a brown bottle to obtain ATP/Ag powder.

(2) Sieve the ATP/Ag powder into powders with a size of 400 meshes, weigh a certain amount of ATP/Ag powder (7 wt.% of the mass of PLA) and disperse it in the solvent N-methylpyrrolidone (NMP) with continuous ultrasonic waves 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.% ATP (relative to the mass of PLA) as an example, the mass ratio of PLA, ATP/Ag, PEG 4000, PVP K30 and NMP is 16.74:1.26:3:3:76, mechanically stirred at a high temperature of 80 °C for 18 ~24h, after it is completely dissolved, stand for deaeration for 8~12h to obtain a uniform casting liquid;

(3) Set the temperature of the scraper to 80°C, control the thickness of the scraper to be 200μm, scrape the casting liquid on the glass plate, control the volatilization time for 5-10s, and then immerse it in a water coagulation bath, phase inversion and solidification into a film After soaking for 10min, take it out to obtain wet polylactic acid/attapulgite/silver nanocomposite film. The membrane from which the moisture on the membrane surface was removed was dried in an oven at 30° C. for 40 min to obtain a polylactic acid/attapulgite/silver nanocomposite dry membrane.

Example 3 Preparation of polylactic acid/attapulgite/silver nanocomposite film

(1) 100ml of ethyl acetate solution containing 2% polylactic acid was prepared, and 20ml of 0.5% sodium dodecylbenzenesulfonate aqueous solution was slowly added dropwise. , the remaining product was washed with water and dried in vacuum to obtain PLA with a positively charged surface;

(2) Weigh a certain amount of ATP powder, put it in 100ml of deionized water and ultrasonically disperse it for 30min to make the ATP disperse evenly. Weigh an appropriate amount of Tris standard substance into ATP suspension (0.01M Tris standard buffer solution) and stir magnetically for 1h , and adjust the pH of the solution with hydrochloric acid and sodium hydroxide until its value is 8.5, add an appropriate amount of dopamine hydrochloride, stir magnetically at 800 r/min for 24 h at room temperature, and then centrifuge at 10,000 r/min for 10 min. The ionized water was repeatedly washed and centrifuged until the solution was clear, and the final precipitate was placed in a vacuum drying oven at 60 °C for 24 h to obtain ATP/PDa powder.

Weigh an appropriate amount of ATP/PDa powder and put it in 100ml of 0.03M silver nitrate solution. The mixed solution is stirred at room temperature with a magnetic force of 400rmp for 12h (in the dark), and the fully reacted ATP/Ag suspension is centrifuged at 10,000r/min. For 10 min, the centrifuged precipitate was repeatedly centrifuged and washed with deionized water until the solution was clear, placed in a vacuum drying oven at 40 °C for 12 h, and then placed in a brown bottle to obtain ATP/Ag powder.

(3) Sieve the ATP/Ag powder into powders with a size of 400 meshes, weigh a certain amount of ATP/Ag powder (7 wt.% of the mass of PLA) and disperse it in the solvent N-methylpyrrolidone (NMP) with continuous ultrasonic dispersion 5 ~10 min to obtain a uniformly dispersed ATP/Ag suspension; surface positively charged PLA, polyethylene glycol 4000 (PEG) and polyvinylpyrrolidone (PVPK30) were dissolved in the ATP/Ag suspension. Taking 7 wt.% ATP (relative to the mass of PLA) as an example, the mass ratio of PLA, ATP/Ag, PEG4000, PVP K30 and NMP was 16.74:1.26:3:3:76, and mechanical stirring was carried out at a high temperature of 80 °C for 18~ 24h, after it is completely dissolved, let it stand for defoaming for 8-12h to obtain a uniform casting liquid;

(4) Set the temperature of the scraper to 80°C, control the thickness of the scraper to be 200 μm, scrape the casting liquid on the glass plate, control the volatilization time for 5 to 10s, and then immerse it in a water coagulation bath, phase inversion and solidification into a film After soaking for 10min, take it out to obtain wet polylactic acid/attapulgite/silver nanocomposite film. The membrane from which the moisture on the membrane surface was removed was dried in an oven at 30° C. for 40 min to obtain a polylactic acid/attapulgite/silver nanocomposite dry membrane.

Infrared Characterization

1 is the infrared spectrum of the composite films prepared in Example 2 and Example 3. The characteristic peak at 1650-1660 cm ^-1 is assigned to the absorption peak of the catechol group of polydopamine, the absorption peak at 3410 cm ^-1 is assigned to the characteristic peak of ATP, and the characteristic peak at 2850-2900 cm ^-1 is assigned to the twelve Methyl and methylene HCH antisymmetric stretching vibrations and symmetric stretching vibration peaks of sodium alkylbenzene sulfonates. It can be seen that dopamine, sulfonate, etc. successfully form a composite membrane with ATP.

XRD characterization

Figure 2 is the XRD pattern of powder ATP, ATP/PDa and ATP/Ag. The position of the characteristic reflection peaks of ATP/PDa is consistent with that of ATP, indicating that its crystal structure has not changed, while the characteristic reflection peaks of AgNPs appeared in ATP/Ag, indicating that AgNPs were successfully synthesized. When loaded on polydopamine, it will also occupy free sites in its pores by ATP adsorption, reducing the free volume of ATP, thereby weakening the characteristic reflection peak of ATP.

SEM characterization

FIG. 3 is the SEM images of the pure polylactic acid film and its modified film prepared in Comparative Example 1, Example 1 and Example 2 under different magnifications. The unmodified membrane was named PLA, the membrane modified by ATP was named PLA/ATP/Ag, and the membrane modified by ATP/Ag was named PLA/ATP/Ag. It can be seen from the figure that the surface of the PLA pure membrane is a porous structure, and the cross-sectional structure is also composed of a finger-like pore structure and a macroporous structure. The surface of the PLA/ATP composite membrane is still porous, and many pore structures also appear. The PLA/ATP/Ag composite membrane is the same as the PLA/ATP composite membrane.

Pure Water Flux and Bovine Serum Retention Assays

The pure water flux and bovine serum albumin (BSA) retention test results of the composite membranes prepared in the control example and the embodiment are shown in the following table, wherein the BSA retention test adopts a BSA solution with a concentration of 1 g/L (the retention rate is 1 g/L). The experimental test pressure is 1 bar, the membrane area is 0.001256m ² , and the test temperature is 25±1°C).

The data show that the PLA membrane obtained by the mixed porogen has higher flux and BSA rejection rate. After incorporating ATP, the composite membrane flux and BSA rejection rate increased from 89.7% to 96.72%. After incorporating ATP/Ag, the membrane flux was increased. was improved, while the BSA rejection rate did not change significantly and remained at 90.46%; when the composite membrane was prepared with positively charged PLA and negatively charged ATP, the pure water flux decreased slightly, while the BSA rejection rate The improvement is mainly attributable to the formation of smaller membrane pores due to the electrostatic interaction of PLA and ATP during the phase inversion process, although the water flux decreases and the rejection increases.

Membrane Strength Characterization

The table and table are the mechanical strength test data of the composite films prepared in the comparative examples and the examples. (The size of the test film sample was 1 cm x 8 cm).

table 3

As can be seen from the above table, the tensile strength of PLA obtained by mixing the porogen is 46%. The elongation at break of the composite film prepared in Example 2 was increased to 45.07%, and the film tensile strength of the film was increased from 2.00 MPa to 2.61 MPa, mainly due to the addition of ATP, which can significantly improve the composite film. Mechanical properties; while in Example 3 by preparing the casting solution, the positive charge on the surface of the silver nanoparticles obtained by in-situ growth on the surface of ATP and the negative charge on the PLA surface can be electrostatically charged, so that the nanopores on the surface of ATP can accommodate With more accommodating and incorporating PLA, the resulting composite films exhibited better mechanical strength and elongation at break after the phase inversion process.

Anti-pollution experiment

To study the anti-fouling performance of the membrane surface, a 1g/LBSA solution was used as a simulated pollutant, which mainly went through two water-BSA cycles. In order to eliminate the influence of concentration polarization, the experiment needs to be carried out under the operation of magnetic stirring. A complete dynamic fouling experiment consists of three stages. The first stage filters pure water for 30 minutes, the second stage filters BSA solution for 1 hour, and the third stage mechanically rinses and backwashes the membrane and then filters pure water for 30 minutes. The composite membrane obtained in the control example and the example was used for testing, and the flux changes with time were recorded. The data showed that after two cycles, the flux of the composite membrane recovered more obviously than that of the pure membrane.

The following table shows the flux recovery rate data of PLA pure membrane, PLA/ATP composite membrane and PLA/ATP/Ag composite membrane.

The data show that the flux recovery rate of the composite membrane prepared by the composite of the present invention is increased from 38.21% to 78% or higher than that of the polylactic acid membrane.

The following is the fouling resistance analysis data of PLA pure membrane, PLA/ATP composite membrane and PLA/ATP/Ag composite membrane.

table 5

The total fouling resistance to the membrane surface is mainly based on irreversible fouling, because irreversible fouling cannot be easily removed, and the fouling has blocked the membrane pores and become part of the membrane module, so it is more intuitive to judge the anti-fouling ability of the membrane based on irreversible fouling. The data show that the composite membrane prepared in the example has a smaller irreversible fouling ratio than the common PLA membrane, indicating that the anti-fouling ability of the PLA/ATP/Ag membrane surface is significantly better than the first two membranes.

Antibacterial test

Figure 4 is the antibacterial effect diagram of ATP and its modified materials and PLA film and its modified film. It can be directly reflected that AgNPs loaded on the surface of ATP has obvious antibacterial effect. The bacteriostatic rate of pure PLA membrane was -10%, that of PLA/ATP composite membrane was 18%, and that of PLA/ATP/Ag composite membrane was 98%. The antibacterial properties of the composite membranes were derived from ATP and ATP/Ag composite materials, and the antibacterial properties of the materials themselves were consistent with the antibacterial properties of the composite membranes.

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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