Solvent-resistant, hydrophilic, lamellar composite polylactic acid membrane for oil-water separation and method of making same

Abstract

The application belongs to the technical field of oil-water separation materials, and discloses a solvent-resistant hydrophilic stereocomplex polylactic acid oil-water separation membrane and a preparation method thereof. The preparation method is as follows: stereocomplex polylactic acid (sc-PLA) nanofiber membranes are obtained by electrospinning after biodegradable poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA) are polymerized by a solution method; and the sc-PLA membranes are subjected to phase separation treatment by using cellulose diacetate (CDA) and silicon dioxide (SiO2). The solvent-resistant hydrophilic sc-PLA membrane material prepared by the application has the characteristics of porous, high specific surface area and nanoscale diameter; meanwhile, the hydrophilic sc-PLA membrane has excellent mechanical properties and good solvent stability, and the modified sc-PLA membrane can be completely biodegraded and is an environment-friendly material.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of oil-water separation materials, and particularly relates to a solvent-resistant hydrophilic stereocomplex polylactic acid oil-water separation membrane and a preparation method thereof. BACKGROUND

[0002] The treatment of oily wastewater has attracted worldwide attention. Membrane separation technology has been widely used in the field of oil-water separation due to its low energy consumption and high separation efficiency. Various inorganic and organic membranes have been developed and used for oil-water separation. Considering the source and recycling of membrane materials, it is necessary to introduce the use of widely available and biodegradable materials. Oil-water separation membranes can be divided into two types: superhydrophobic and superoleophobic. In the filtration and separation of oil-in-water emulsions, superoleophobic membranes have more advantages. Therefore, it is of great significance to choose biodegradable materials as raw materials to prepare superoleophobic oil-water separation materials.

[0003] Polylactic acid (PLA) is a biobased polymer, and the raw material mainly comes from biomass materials such as grains. PLA has excellent biodegradability, biocompatibility, non-toxicity and renewability. The molecular chain of PLA has high regularity, which makes it have the disadvantages of high brittleness, slow crystallization rate and poor mechanical properties. PLLA and PDLA have good crystallization properties. When PLLA and PDLA are blended in a certain proportion, the molecular chains of PLLA and PDLA are complementary in structure, and sc-PLA is formed under certain conditions. However, the hydrophilicity of sc-PLA is poor. To improve its hydrophilicity, hydrophilic substances can be added for modification. Cellulose diacetate (CDA) is an environmentally friendly and biodegradable modified regenerated cellulose material with high hydrophilicity, and the raw material is widely available, which has been widely used in the field of oil-water separation. Therefore, it has wide application prospects to use green and environmentally friendly PLLA / PDLA and CDA to prepare oil-water separation membranes.

[0004] At present, many researchers are very concerned about the hydrophilic modification of PLA membrane. A high-efficiency oil-water separation iron-based polymeric polylactic acid super-hydrophilic microporous membrane is disclosed in Chinese patent CN110559690A, which is composed of non-woven fabric as support layer and PLA membrane. The sc-PLA membrane layer is modified by dopamine and polyethylene polyamine to have rich iron ion adsorption sites, and the sc-PLA membrane is modified in hydrophilicity by iron-based nanoparticles to obtain a super-hydrophilic layer surface. A temperature-sensitive hydrophilic PLA membrane is prepared by using N-isopropyl acrylamide and vinyl acetate as raw materials, using azobis isobutyronitrile as initiator, and blending hydrophilic adjusting filler with PLA through solution casting method. The preparation process of the polylactic acid membrane prepared by the above method is relatively complicated, and the surface modification in Chinese patent CN110559690A may affect the stability and recycling number of the membrane. The hydrophilicity improvement of PLA in Chinese patent CN113831561A is limited, and the oil-water separation effect cannot be achieved. SUMMARY

[0005] In view of the defects and shortcomings of the prior art, the present application provides a solvent-resistant hydrophilic stereocomplex polylactic acid oil-water separation membrane and a preparation method thereof. The solvent-resistant hydrophilic stereocomplex polylactic acid oil-water separation membrane prepared by the method has high hydrophilicity, underwater super-oleophobicity, multiple pores, high specific surface area, nanoscale diameter, good mechanical properties, complete biodegradability, simple process, low cost, and is conducive to industrialization.

[0006] To achieve the above-mentioned purpose, the present application realizes the following technical scheme:

[0007] A preparation method of a solvent-resistant hydrophilic stereocomplex polylactic acid oil-water separation membrane, wherein the oil-water separation membrane is prepared by polymerizing PLLA and PDLA through a solution method, then electrospinning to form a film, and then performing phase separation treatment with cellulose diacetate (CDA), and the preparation method comprises the following preparation steps:

[0008] S1. Dissolve PLLA and PDLA particles in a mixed solvent of chloroform (CHL) and hexafluoroisopropanol (HFIP) to obtain a PLLA / PDLA spinning solution, and electrospin to obtain a sc-PLA fiber membrane.

[0009] S2. The sc-PLA fiber membrane obtained in step S1 is first treated at 120°C for 10-30 minutes, and then treated at 180°C for 10-30 minutes.

[0010] S3. The sc-PLA fiber membrane obtained in step S2 is immersed in an acetone solution containing CDA and SiO2 for treatment, then immersed in a coagulation bath for treatment, then washed with deionized water until neutral, and then dried to obtain an oil-water separation membrane.

[0011] Preferably, the sc-PLA membrane has a single fiber diameter of 430-1350 nm and a thickness of 34-40 μm.

[0012] Preferably, in step S1, the mass ratio of CHL to HFIP in the mixed solvent of chloroform (CHL) and hexafluoroisopropanol (HFIP) is 7 / 3.

[0013] Preferably, in step S1, the mass concentration of PLLA and PDLA in the PLLA / PDLA spinning solution is 7%-13%.

[0014] Preferably, in step S1, the conditions for electrospinning are: spinning voltage 20kV, spinning distance 20cm, spinning speed 1ml / h, and spinning speed 65-80r / min.

[0015] Preferably, in step S3, the concentration of CDA in the acetone solution containing CDA and SiO2 is 1-4 wt%.

[0016] Preferably, in step S3, the coagulation bath is water, and the immersion in the coagulation bath treatment is: immersing the sc-PLA fiber membrane in water for 60 minutes.

[0017] Preferably, in step S3, the drying process involves placing the PLA fiber membrane in a forced-air drying oven at 60°C for 180 minutes.

[0018] The present invention also provides an oil-water separation membrane prepared by the above preparation method.

[0019] The solvent-resistant hydrophilic stereocomposite polylactic acid oil-water separation membrane of the present invention has the following advantages and beneficial effects:

[0020] (1) The stereocomposite polylactic acid oil-water separation membrane of the present invention has the characteristics of superhydrophilicity, superoleophobicity underwater, good mechanical properties and recyclability, and complete biodegradability.

[0021] (2) The preparation process is simple and low-cost, and it has good application prospects in the field of environmentally friendly oil-water separation membrane materials, meeting the production needs of the oil-water separation membrane industry. Attached Figure Description

[0022] Figure 1 The images are SEM images of the sc-PLA oil-water separation membranes obtained in Examples 1-6 (af corresponds to CDA concentrations of 1%, 2%, 2.5%, 3%, 3.5%, and 4%, respectively).

[0023] Figure 2The underwater oil contact angle diagrams of the sc-PLA oil-water separation membranes obtained in Examples 1-6 are shown (af corresponds to CDA concentrations of 1%, 2%, 2.5%, 3%, 3.5%, and 4%, respectively). Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] (1) Weigh the corresponding mass of PLLA particles and PDLA particles, and use CHL and HFIP mixed solvent as solvent to prepare 7wt% PLLA solution and 13wt% PDLA solution respectively. Then, the two are mixed to prepare a spinning solution. Electrospinning is carried out at a spinning voltage of 20kv, a spinning distance of 20cm, a spinning speed of 1ml / h, and a rotation speed of 65-80r / min to form sc-PLA fiber membrane.

[0027] (2) Treat the sc-PLA fiber membrane obtained in step (1) at 120°C for 20 minutes, and then at 180°C for 10 minutes.

[0028] (3) The sc-PLA fiber membrane obtained in step (2) is immersed in an acetone solution of CDA (1 wt%) and SiO2 (5 wt%).

[0029] (4) Immerse the membrane obtained in step (3) in a coagulation bath (water) at a temperature of 25°C for 60 minutes.

[0030] (5) After removing the membrane from step (4), rinse it with deionized water until it is neutral.

[0031] (6) The membrane from step (5) was thoroughly dried in a 60°C forced-air oven. A solvent-resistant hydrophilic sc-PLA oil-water separation membrane was obtained. The resulting sc-PLA oil-water separation membrane had a thickness of 40 μm, a fiber diameter of 740-850 nm, a tensile strength of 3.26 MPa, an elongation at break of 33%, and a water flux of 7985 L / m³. 2 / h, the sc-PLA oil-water separator is insoluble in chloroform.

[0032] Example 2

[0033] (1) Weigh the corresponding mass of PLLA particles and PDLA particles, and use CHL and HFIP mixed solvent as solvent to prepare 7wt% PLLA solution and 13wt% PDLA solution respectively. Then, the two are mixed to prepare a spinning solution. Electrospinning is carried out at a spinning voltage of 20kv, a spinning distance of 20cm, a spinning speed of 1ml / h, and a rotation speed of 65-80r / min to form sc-PLA fiber membrane.

[0034] (2) Treat the sc-PLA fiber membrane obtained in step (1) at 120°C for 10 minutes, and then at 180°C for 10 minutes.

[0035] (3) The sc-PLA fiber membrane obtained in step (2) is immersed in an acetone solution of CDA (2wt%) and SiO2 (2wt%).

[0036] (4) Immerse the membrane obtained in step (3) in a coagulation bath (water) at a temperature of 25°C for 60 minutes.

[0037] (5) After removing the membrane from step (4), rinse it with deionized water until it is neutral.

[0038] (6) The membrane from step (5) was thoroughly dried in a 60°C forced-air oven. A solvent-resistant hydrophilic sc-PLA oil-water separation membrane was obtained. The resulting sc-PLA oil-water separation membrane had a thickness of 39 μm, a fiber diameter of 740-850 nm, a tensile strength of 3.18 MPa, an elongation at break of 36%, and a water flux of 4534 L / m³. 2 / h, the fiber membrane does not dissolve in chloroform.

[0039] Example 3

[0040] (1) Weigh the corresponding mass of PLLA particles and PDLA particles, and use CHL and HFIP mixed solvent as solvent to prepare 7wt% PLLA solution and 13wt% PDLA solution respectively. Then, the two are mixed to prepare a spinning solution. Electrospinning is carried out at a spinning voltage of 20kv, a spinning distance of 20cm, a spinning speed of 1ml / h, and a rotation speed of 65-80r / min to form sc-PLA fiber membrane.

[0041] (2) Treat the sc-PLA fiber membrane obtained in step (1) at 120°C for 20 minutes, and then at 180°C for 10 minutes.

[0042] (3) The sc-PLA fiber membrane obtained in step (2) is immersed in an acetone solution of CDA (2.5 wt%) and SiO2 (2 wt%).

[0043] (4) Immerse the membrane obtained in step (3) in a coagulation bath (water) at a temperature of 25°C for 60 minutes.

[0044] (5) After removing the membrane from step (4), rinse it with deionized water until it is neutral.

[0045] (6) The membrane from step (5) was thoroughly dried in a 60°C forced-air oven. A solvent-resistant hydrophilic sc-PLA oil-water separation membrane was obtained. The resulting sc-PLA oil-water separation membrane had a thickness of 38 μm, a fiber diameter of 740-850 nm, a tensile strength of 2.85 MPa, an elongation at break of 30%, and a water flux of 4643 L / m³. 2 / h, the fiber membrane does not dissolve in chloroform.

[0046] Example 4

[0047] (1) Weigh the corresponding mass of PLLA particles and PDLA particles, and use CHL and HFIP mixed solvent as solvent to prepare 10wt% PLLA solution and 10wt% PDLA solution respectively. Then, the two are mixed to form a spinning solution. Electrospinning is carried out at a spinning voltage of 20kv, a spinning distance of 20cm, a spinning speed of 1ml / h, and a rotation speed of 65-80r / min to form sc-PLA fiber membrane.

[0048] (2) Treat the sc-PLA fiber membrane obtained in step (1) at 120°C for 20 minutes, and then at 180°C for 20 minutes.

[0049] (3) The sc-PLA fiber membrane obtained in step (2) is immersed in an acetone solution of CDA (3wt%) and SiO2 (1wt%).

[0050] (4) Immerse the membrane obtained in step (3) in a coagulation bath (water) at a temperature of 25°C for 60 minutes.

[0051] (5) After removing the membrane from step (4), rinse it with deionized water until it is neutral.

[0052] (6) The membrane from step (5) was thoroughly dried in a 60°C forced-air oven. A solvent-resistant hydrophilic sc-PLA oil-water separation membrane was obtained. The resulting PLA oil-water separation membrane had a thickness of 37 μm, a fiber diameter of 740-850 nm, a tensile strength of 2.76 MPa, an elongation at break of 31%, and a water flux of 2109 L / m³. 2 / h, the fiber membrane does not dissolve in chloroform.

[0053] Example 5

[0054] (1) Weigh the corresponding mass of PLLA particles and PDLA particles, and use CHL and HFIP mixed solvent as solvent to prepare 7wt% PLLA solution and 13wt% PDLA solution respectively. Then, the two are mixed to prepare a spinning solution. Electrospinning is carried out at a spinning voltage of 20kv, a spinning distance of 20cm, a spinning speed of 1ml / h, and a rotation speed of 65-80r / min to form sc-PLA fiber membrane.

[0055] (2) Treat the sc-PLA fiber membrane obtained in step (1) at 120°C for 20 minutes, and then at 180°C for 30 minutes.

[0056] (3) The sc-PLA fiber membrane obtained in step (2) is immersed in an acetone solution of CDA (3.5 wt%) and SiO2 (8 wt%).

[0057] (4) Immerse the membrane obtained in step (3) in a coagulation bath (water) at a temperature of 25°C for 60 minutes.

[0058] (5) After removing the membrane from step (4), rinse it with deionized water until it is neutral.

[0059] (6) The membrane from step (5) was thoroughly dried in a 60°C forced-air oven. A solvent-resistant hydrophilic sc-PLA oil-water separation membrane was obtained. The resulting PLA oil-water separation membrane had a thickness of 39 μm, a fiber diameter of 740-850 nm, a tensile strength of 2.64 MPa, an elongation at break of 35%, and a water flux of 1986 L / m³. 2 / h, the fiber membrane does not dissolve in chloroform.

[0060] Example 6

[0061] (1) Weigh the corresponding mass of PLLA particles and PDLA particles, and use CHL and HFIP mixed solvent as solvent to prepare 13wt% PLLA solution and 7wt% PDLA solution respectively. Then, the two are mixed to prepare a spinning solution. Electrospinning is carried out at a spinning voltage of 20kv, a spinning distance of 20cm, a spinning speed of 1ml / h, and a rotation speed of 65-80r / min to form sc-PLA fiber membrane.

[0062] (2) Treat the sc-PLA fiber membrane obtained in step (1) at 120°C for 30 minutes, and then at 180-200°C for 10 minutes.

[0063] (3) The sc-PLA fiber membrane obtained in step (2) is immersed in an acetone solution of CDA (4 wt%) and SiO2 (10 wt%).

[0064] (4) Immerse the membrane obtained in step (3) in a coagulation bath (water) at a temperature of 25°C for 60 minutes.

[0065] (5) After removing the membrane from step (4), rinse it with deionized water until it is neutral.

[0066] (6) The membrane from step (5) was thoroughly dried in a 60°C forced-air oven. A hydrophilic and robust SC-PLA oil-water separation membrane was obtained. The resulting PLA oil-water separation membrane had a thickness of 38 μm, a fiber diameter of 740-850 nm, a tensile strength of 2.53 MPa, an elongation at break of 29%, and a water flux of 1310 L / m³. 2 / h, the fiber membrane does not dissolve in chloroform.

[0067] Comparative Example 1

[0068] Weigh corresponding masses of PLLA and PDLA particles and prepare 7wt% and 10wt% spinning solutions in a CHL and HFIP mixed solution. After dissolving the PLLA and PDLA particles separately, blend the spinning solutions and electrospin the mixtures at a spinning voltage of 20 kV, a spinning distance of 20 cm, a spinning speed of 1 ml / h, and a spinning speed of 65 r / min to form an sc-PLA fiber membrane. The resulting sc-PLA oil-water separation membrane has a thickness of 35 μm, a fiber diameter of 430-570 nm, a tensile strength of 1.85 MPa, an elongation at break of 44%, and a water flux of 27 L / m³. 2 / h, the fiber membrane is dissolved in chloroform.

[0069] Comparative Example 2

[0070] Weigh corresponding masses of PLLA and PDLA particles and prepare 7wt% and 10wt% spinning solutions in a CHL and HFIP mixed solution. Dissolve the PLLA and PDLA particles separately, then blend the spinning solutions. Electrospin the sc-PLA fiber membrane at a spinning voltage of 20 kV, a spinning distance of 20 cm, a spinning speed of 1 ml / h, and a spinning speed of 65 r / min. Treat the sc-PLA fiber membrane at 120℃ for 30 minutes, then at 180-200℃ for 10 minutes. The resulting sc-PLA oil-water separation membrane has a thickness of 36 μm, a fiber diameter of 490-650 nm, a tensile strength of 1.93 MPa, an elongation at break of 37%, and a water flux of 16 L / m³. 2 / h, the fiber membrane does not dissolve in chloroform.

[0071] Comparative Example 3

[0072] Weigh corresponding masses of PLLA and PDLA particles and prepare spinning solutions of 7wt% and 13wt% in a CHL and HFIP mixed solution. Dissolve the PLLA and PDLA particles separately, then blend the spinning solutions. Electrospin the sc-PLA fiber membrane at a spinning voltage of 20kV, a spinning distance of 20cm, a spinning speed of 1ml / h, and a spinning speed of 65r / min. Treat the sc-PLA fiber membrane at 120℃ for 30 minutes, then at 180℃ for 20 minutes. Immerse the obtained sc-PLA fiber membrane in an acetone solution of CDA (4wt%), then immerse the membrane in a coagulation bath (water) at 25℃ for 60 minutes. Wash with deionized water until neutral and dry thoroughly in a 60℃ forced-air oven. The resulting sc-PLA oil-water separation membrane has a thickness of 36μm, a fiber diameter of 740-850nm, a tensile strength of 2.86MPa, an elongation at break of 28%, and a water flux of 468L / m³. 2 / h, the fiber membrane does not dissolve in chloroform.

[0073] Comparative Example 4

[0074] (1) Weigh the corresponding mass of PLLA particles and prepare a 7wt% spinning solution in a mixed solvent of CHL and HFIP. Electrospin the solution to form an sc-PLA fiber membrane at a spinning voltage of 20kV, a spinning distance of 20cm, a spinning speed of 1ml / h, and a spinning speed of 65r / min. Treat the PLLA fiber membrane at 120℃ for 30 minutes. Immerse the obtained PLLA fiber membrane in an acetone solution of CDA (4wt%), then immerse the membrane in a coagulation bath (water) at 25℃ for 60 minutes. Then wash it with deionized water until neutral and dry it thoroughly in a forced-air oven at 60℃. The resulting PLLA oil-water separation membrane has a thickness of 34μm, a fiber diameter of 690-760nm, a tensile strength of 2.14MPa, an elongation at break of 32%, and a water flux of 490L / m. 2 / h, the fiber membrane is dissolved in chloroform.

[0075] SEM images of the sc-PLA oil-water separation membranes obtained in Examples 1-6 are shown below. Figure 1 As shown, according to Figure 1 It can be observed that the addition of CDA alters the surface morphology of the sc-PLA fiber membrane. With increasing CDA concentration, the roughness of the sc-PLA oil-water separation membrane increases, and the porosity decreases, which is beneficial for achieving the oil-water separation function. However, excessively high CDA concentrations can clog the fiber membrane pores, thereby reducing the oil-water separation performance.

[0076] The underwater oil contact angle diagrams of the sc-PLA oil-water separation membranes obtained in Examples 1-6 are shown below. Figure 2 As shown, according to Figure 2It is known that the addition of CDA endows sc-PLA fiber membranes with superoleophobic properties, which is beneficial to the realization of the oil-water separation function of the fiber membrane.

Claims

1. A method for preparing a solvent-resistant hydrophilic stereocomposite polylactic acid oil-water separation membrane, characterized in that, Includes the following steps: S1. Dissolve PLLA and PDLA particles in a mixed solvent of chloroform and hexafluoroisopropanol to obtain a PLLA / PDLA spinning solution, and electrospin to obtain an sc-PLA fiber membrane. In the PLLA / PDLA spinning solution, the mass concentration of PLLA and PDLA is 7%-13%. S2. The sc-PLA fiber membrane obtained in step S1 is first treated at 120°C for 10-30 minutes, and then treated at 180°C for 10-30 minutes; S3. The sc-PLA fiber membrane obtained in step S2 is immersed in an acetone solution containing cellulose diacetate (CDA) and SiO2. After being removed, it is immersed in a coagulation bath. After being removed, it is washed with deionized water until neutral and dried to obtain an oil-water separation membrane. The acetone solution containing cellulose diacetate (CDA) and SiO2 has a CDA concentration of 1-4 wt% and a SiO2 mass concentration of 1%-10 wt%.

2. The preparation method according to claim 1, characterized in that, In step S1, the single fiber diameter of the sc-PLA fiber membrane is 430-1350 nm and the thickness is 34-40 μm.

3. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of CHL to HFIP in the mixed solvent of chloroform and hexafluoroisopropanol is 7:

3.

4. The preparation method according to claim 1, characterized in that, In step S1, the conditions for electrospinning are: spinning voltage 20kV, spinning distance 20cm, spinning speed 1ml / h, and spinning speed 65-80r / min.

5. The preparation method according to claim 1, characterized in that, In step S3, the coagulation bath is water, and the immersion in the coagulation bath treatment is: immersing the sc-PLA fiber membrane in water for 60 minutes.

6. The preparation method according to claim 1, characterized in that, In step S3, the drying process involves placing the PLA fiber membrane in a forced-air drying oven at 60°C for 180 minutes.

7. The oil-water separation membrane prepared by the preparation method according to any one of claims 1-6.

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