Preparation method and application of high-throughput and high-strength polylactic acid separation membrane

Abstract

The present invention belongs to the technical field of polylactic acid separation membranes, and specifically relates to a method for preparing a high-throughput and high-strength polylactic acid separation membrane and its application. The method comprises: step 1, preparing a casting liquid containing polylactic acid, a diluent, a pore-forming agent and an organic solvent; step 2, preparing a continuous liquid film on a horizontal substrate, and subjecting it to a constant temperature and humidity treatment; step 3, immersing the liquid film together with the substrate in a pure water coagulation bath to solidify the film, thereby obtaining the high-throughput and high-strength polylactic acid separation membrane. The present invention introduces a liquid having a higher boiling point and viscosity than the organic solvent as a diluent into the casting liquid, and subjecting the liquid film to a constant temperature and humidity treatment, so that the concentration of polylactic acid on the surface of the liquid film is within an appropriate range, while inducing the liquid film to undergo full matrix gelation, thereby ensuring the high throughput and high strength of the polylactic acid separation membrane, and being able to prepare a high-performance polylactic acid separation membrane with an approximately symmetrical structure. The above technical solution is simple to operate and has low cost, and is easy to scale up industrially.

Description

Technical Field

[0001] The invention belongs to the technical field of polylactic acid separation membranes, and in particular relates to a preparation method of a high-flux and high-strength polylactic acid separation membrane and application thereof. Background Art

[0002] Polylactic acid (PLA) is a polyester-based green bioplastic that can be extracted from animals, plants and microorganisms. It has a wide range of sources and has good biocompatibility and degradability. In recent years, its application has gradually expanded to the field of separation membranes for the separation and purification of mixtures. Polylactic acid has physical properties similar to those of traditional separation membrane materials, can meet general processing requirements, and is a good alternative substrate for new separation membranes. From the chemical structure of polylactic acid, it can be seen that its polymer chain contains a large number of hydrophobic methyl and ester groups, which also leads to the poor hydrophilicity of polylactic acid membrane materials and low water flux. In addition, polylactic acid has low crystallinity, and the film is prone to brittle fracture and poor mechanical strength. The above disadvantages limit the application of polylactic acid separation membranes to a certain extent.

[0003] The intrinsic deficiencies of the membrane substrate can be compensated to a certain extent by optimizing the preparation process. In order to improve the flux of the polylactic acid separation membrane, technicians in this field often start by improving the hydrophilicity of the membrane material. Commonly used methods include active site grafting polymerization and plasma post-treatment, but these methods have complex preparation processes and low operability. The industry can improve the mechanical properties of the polylactic acid separation membrane through the electrospinning-annealing process, but compared with the conventional non-solvent induced phase separation method, this process belongs to random disordered film formation, and it is difficult to effectively regulate the membrane pores. Generally speaking, the non-solvent induced phase separation method often induces instantaneous phase separation of the polylactic acid casting liquid, and the formed asymmetric membrane has both a dense cortex and a sublayer with finger-like cavities: the dense cortex increases the permeation resistance of the membrane, while the finger-like cavities are widely considered to be the stress weak points of the membrane material. Therefore, it is particularly important to develop a new preparation method to solve the problems of poor flux and low strength of polylactic acid separation membranes. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for preparing a high-throughput and high-strength polylactic acid separation membrane.

[0005] The preparation method comprises the following steps:

[0006] (1) Preparation of casting solution: Mix the dried polylactic acid pellets, diluent, pore-forming agent and organic solvent, heat and stir to completely dissolve them, then cool to room temperature, and vacuum degas to obtain a uniform casting solution;

[0007] The diluent is a liquid having a higher boiling point and a higher viscosity than the organic solvent, rich in oxygen atoms in its chemical structure and soluble in water;

[0008] (2) Liquid film preparation: placing the casting liquid obtained in step (1) on a horizontal substrate to form a continuous liquid film with uniform thickness, and then subjecting it to constant temperature and humidity treatment;

[0009] (3) Thin film solidification: The liquid film treated at constant temperature and humidity in step (2) is immersed in a solidification bath together with the substrate, so that the liquid film is solidified and detached from the substrate, thereby obtaining the high-throughput and high-strength polylactic acid separation membrane.

[0010] Preferably, the diluent in step (1) is one or more of glycerol carbonate, glycerol monoacetate, glycerol diacetate, glycerol triacetate and sulfolane.

[0011] Preferably, the pore-forming agent in step (1) is one or more of Tween 80, Triton X-100, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate and Pluronic F127.

[0012] Preferably, the organic solvent in step (1) is one or more of 1,4-dioxane, N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone.

[0013] Preferably, in step (1), the mass fraction of the polylactic acid is 12% to 14%, the mass fraction of the diluent is 15% to 20%, and the mass fraction of the pore-forming agent is 4% to 6%.

[0014] Preferably, the temperature of the constant temperature and humidity treatment in step (2) is 60° C. to 80° C., the relative humidity is 35% to 80%, and the treatment time is 30 s to 60 s.

[0015] Preferably, the thickness of the continuous liquid film in step (2) is 250 μm.

[0016] Preferably, the coagulation bath in step (3) is pure water, and the temperature of the coagulation bath is 40°C.

[0017] The present invention also provides a high-throughput and high-strength polylactic acid separation membrane prepared by the preparation method described in the above technical solution, wherein the pure water flux of the high-throughput and high-strength polylactic acid separation membrane is not less than 200 L·m -2 ·h -1 bar -1 , tensile strength is not less than 3.0 MPa, and elongation at break is not less than 110%.

[0018] The present invention also provides the use of the high-throughput and high-strength polylactic acid separation membrane described in the above technical solution in any one of the following (a) to (d):

[0019] (a) Separation and purification of organic matter;

[0020] (b) filtration sterilization;

[0021] (c) hemodialysis;

[0022] (d) Wastewater treatment.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention introduces a liquid with a higher boiling point and viscosity than the organic solvent as a diluent in the casting liquid. The liquid is not easy to volatilize, so as to avoid the excessive concentration of polylactic acid after the volatile organic solvent on the surface of the liquid film is lost, forming an asymmetric film with a dense surface layer and a loose lower layer or cavities. In addition, the introduction of the diluent can increase the overall viscosity of the liquid film, slow down the double diffusion rate, and facilitate the delayed phase separation to form a nearly symmetrical membrane material.

[0025] 2. The present invention performs a constant temperature and humidity treatment on the liquid film on the horizontal substrate before the film is solidified. Treatment under a constant high temperature environment can promote the volatilization of organic solvents on the surface of the liquid film. Due to the presence of the diluent, the concentration of the surface polylactic acid is moderately increased, which helps to form uniform openings and avoids the formation of irregular large openings that affect the retention rate; the constant high humidity environment induces the casting liquid to undergo full matrix gelation. Since the chemical structure of the diluent is rich in oxygen atoms, it can induce the water molecules in the atmosphere to be fully embedded in the liquid film through hydrogen bonding, which helps to form a membrane material with a uniform upper and lower gradient. The constant temperature and humidity treatment of the liquid film and the introduction of the diluent into the casting liquid play a synergistic role and jointly promote the formation of a high-performance polylactic acid separation membrane.

[0026] 3. The pore-forming agent added to the casting liquid of the present invention is an amphiphilic surfactant, which can cause surface segregation during the solidification of the liquid film. The hydrophilic segments are orderly oriented toward the outside of the membrane, the pore walls and other areas directly in contact with the pure water coagulation bath, thereby improving the hydrophilicity of the polylactic acid membrane and further improving the flux of the membrane.

[0027] 4. The technical solution provided by the present invention is easy to operate, the process parameters are easy to adjust, and the cost is low, and it is easy to expand industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0029] Figure 1 These are scanning electron microscope images of the overall cross-section, near-surface and near-back morphologies of the high-throughput and high-strength polylactic acid separation membrane prepared in Example 5. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing a high-throughput and high-strength polylactic acid separation membrane, the preparation method comprising the following steps:

[0031] (1) Preparation of casting solution: Mix the dried polylactic acid pellets, diluent, pore-forming agent and organic solvent, heat and stir to completely dissolve them, then cool to room temperature, and vacuum degas to obtain a uniform casting solution;

[0032] The diluent is a liquid having a higher boiling point and a higher viscosity than the organic solvent, rich in oxygen atoms in its chemical structure and soluble in water;

[0033] (2) Liquid film preparation: placing the casting liquid obtained in step (1) on a horizontal substrate to form a continuous liquid film with uniform thickness, and then subjecting it to constant temperature and humidity treatment;

[0034] (3) Thin film solidification: The liquid film treated at constant temperature and humidity in step (2) is immersed in a solidification bath together with the substrate, so that the liquid film solidifies and falls off from the substrate, thereby obtaining a high-throughput and high-strength polylactic acid separation membrane.

[0035] The invention firstly mixes dried polylactic acid pellets, a diluent, a pore-forming agent and an organic solvent, heats and stirs to completely dissolve them, then cools them to room temperature, and vacuum degasses them to obtain a uniform film casting solution.

[0036] In the present invention, the mass fraction of the polylactic acid is preferably 12% to 14%, more preferably 12% or 13% or 14%; the mass fraction of the diluent is preferably 15% to 20%, more preferably 15% or 18% or 20%; the mass fraction of the pore former is preferably 4% to 6%, more preferably 4% or 5% or 6%.

[0037] The diluent in step (1) of the present invention is preferably one or more of glycerol carbonate, glycerol monoacetate, glycerol diacetate, glycerol triacetate and sulfolane; the pore-forming agent is preferably one or more of Tween 80, Triton X-100, hexadecyltrimethylammonium bromide, sodium dodecylsulfonate and Pluronic F127; the organic solvent is preferably one or more of 1,4-dioxane, N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone. The present invention uses a liquid with a higher boiling point and viscosity than the organic solvent as a diluent. Since the liquid is not volatile, it avoids the formation of an asymmetric membrane with a dense surface layer and a loose lower layer or a cavity after the volatile organic solvent on the surface of the liquid membrane is lost due to excessive concentration of polylactic acid.

[0038] After obtaining the casting liquid, the present invention places the casting liquid on a horizontal substrate to form a continuous liquid film with uniform thickness, and performs a constant temperature and humidity treatment on the horizontal substrate covered with the casting liquid.

[0039] After the casting liquid is placed on a horizontal substrate, a stainless steel scraper is preferably used to form a continuous liquid film with uniform thickness. In the present invention, the temperature of the constant temperature and humidity treatment is preferably 60°C to 80°C, more preferably 60°C or 70°C or 80°C; the relative humidity of the constant temperature and humidity treatment is preferably 35% to 80%, more preferably 35% or 50% or 80%; the treatment time of the constant temperature and humidity treatment is preferably 30 s to 60 s, more preferably 30 s or 45 s or 60 s. The thickness of the continuous liquid film of the present invention is preferably 250 μm. Treatment under a constant high temperature environment can promote the volatilization of organic solvents on the surface of the liquid film. Due to the presence of a diluent, the concentration of polylactic acid on the surface is moderately increased, which helps to form uniform openings and avoids the formation of irregular large openings that affect the interception rate; a constant high humidity environment induces the casting liquid to undergo full matrix gelation. Since the chemical structure of the diluent is rich in oxygen atoms, water molecules in the atmosphere can be induced to be fully pre-embedded in the liquid film through hydrogen bonding, which helps to form a membrane material with uniform upper and lower gradients.

[0040] Finally, the present invention immerses the liquid film after constant temperature and humidity treatment together with the substrate into a coagulation bath, so that the liquid film is solidified and shaped and falls off from the substrate, thereby obtaining the high-throughput and high-strength polylactic acid separation membrane.

[0041] In the present invention, the coagulation bath is preferably pure water, and the temperature of the coagulation bath is preferably 40°C.

[0042] The present invention also provides a high-flux and high-strength polylactic acid separation membrane prepared by the preparation method described in the above technical solution. The structure of the high-flux and high-strength polylactic acid separation membrane of the present invention is approximately symmetrical, and its pure water flux is preferably not less than 200 L·m -2 ·h -1 bar -1 , the tensile strength is preferably not less than 3.0 MPa, and the elongation at break is preferably not less than 110%.

[0043] The present invention also provides the use of the high-throughput and high-strength polylactic acid separation membrane described in the above technical solution in any one of the following (a) to (d):

[0044] (a) Separation and purification of organic matter;

[0045] (b) filtration sterilization;

[0046] (c) hemodialysis;

[0047] (d) Wastewater treatment.

[0048] In order to further illustrate the present invention, the preparation method of a high-throughput and high-strength polylactic acid separation membrane provided by the present invention and its application are described in detail below in combination with the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0049] Example 1

[0050] The preparation method of the high-throughput and high-strength polylactic acid separation membrane in this embodiment is as follows:

[0051] Step 1, preparing a casting solution: mixing dried polylactic acid pellets, diluent glycerol carbonate, pore-forming agent Triton X-100 and organic solvent 1,4-dioxane, heating and stirring to completely dissolve them, cooling to room temperature, and vacuum degassing to obtain a uniform casting solution; wherein the mass fraction of polylactic acid is 13%, the mass fraction of diluent glycerol carbonate is 18%, and the mass fraction of pore-forming agent Triton X-100 is 5%;

[0052] Step 2, liquid film preparation: the casting liquid obtained in step 1 is placed on a horizontal substrate, and a stainless steel scraper is used to form a continuous liquid film with a thickness of 250 μm. The horizontal substrate covered with the casting liquid is placed in a constant temperature and humidity environment at a temperature of 70°C and a relative humidity of 50% for 45 s;

[0053] Step 3, film solidification: immerse the liquid film treated with constant temperature and humidity in step 2 together with the substrate in a pure water coagulation bath at a temperature of 40°C, so that the liquid film is solidified and falls off from the substrate to obtain a high-throughput and high-strength polylactic acid separation membrane.

[0054] Example 2

[0055] The preparation method of the high-throughput and high-strength polylactic acid separation membrane in this embodiment is as follows:

[0056] Step 1, preparing a casting solution: mixing dried polylactic acid pellets, diluent glycerol monoacetate, pore-forming agent hexadecyltrimethylammonium bromide and a mixed organic solvent of 1,4-dioxane and N,N-dimethylacetamide (volume ratio of 3:1), heating and stirring to completely dissolve them, cooling to room temperature, and vacuum degassing to obtain a uniform casting solution; wherein the mass fraction of polylactic acid is 12%, the mass fraction of diluent glycerol monoacetate is 15%, and the mass fraction of pore-forming agent hexadecyltrimethylammonium bromide is 6%;

[0057] Step 2, liquid film preparation: the casting liquid obtained in step 1 is placed on a horizontal substrate, and a stainless steel scraper is used to form a continuous liquid film with a thickness of 250 μm. The horizontal substrate covered with the casting liquid is placed in a constant temperature and humidity environment at a temperature of 80°C and a relative humidity of 35% for 60 s;

[0058] Step 3, film solidification: immerse the liquid film treated with constant temperature and humidity in step 2 together with the substrate in a pure water coagulation bath at a temperature of 40°C, so that the liquid film is solidified and falls off from the substrate to obtain a high-throughput and high-strength polylactic acid separation membrane.

[0059] Example 3

[0060] The preparation method of the high-throughput and high-strength polylactic acid separation membrane in this embodiment is as follows:

[0061] Step 1, preparing a casting solution: mixing dried polylactic acid pellets, diluent glyceryl diacetate, pore-forming agent sodium dodecyl sulfate and a mixed organic solvent of 1,4-dioxane and N,N-dimethylformamide (volume ratio of 3:1), heating and stirring to completely dissolve them, cooling to room temperature, and vacuum degassing to obtain a uniform casting solution; wherein the mass fraction of polylactic acid is 14%, the mass fraction of diluent glyceryl diacetate is 20%, and the mass fraction of pore-forming agent sodium dodecyl sulfate is 4%;

[0062] Step 2, liquid film preparation: the casting liquid obtained in step 1 is placed on a horizontal substrate, and a stainless steel scraper is used to form a continuous liquid film with a thickness of 250 μm. The horizontal substrate covered with the casting liquid is placed in a constant temperature and humidity environment at a temperature of 60°C and a relative humidity of 80% for 30 s;

[0063] Step 3, film solidification: immerse the liquid film treated with constant temperature and humidity in step 2 together with the substrate in a pure water coagulation bath at a temperature of 40°C, so that the liquid film is solidified and falls off from the substrate to obtain a high-throughput and high-strength polylactic acid separation membrane.

[0064] Example 4

[0065] The preparation method of the high-throughput and high-strength polylactic acid separation membrane in this embodiment is as follows:

[0066] Step 1, preparing a casting solution: mixing dried polylactic acid pellets, diluent triacetin, pore-forming agent Pluronic F127 and a mixed organic solvent of 1,4-dioxane and N-methylpyrrolidone (volume ratio of 3:1), heating and stirring to completely dissolve them, cooling to room temperature, and vacuum degassing to obtain a uniform casting solution; wherein the mass fraction of polylactic acid is 13%, the mass fraction of diluent triacetin is 18%, and the mass fraction of pore-forming agent Pluronic F127 is 5%;

[0067] Step 2, liquid film preparation: the casting liquid obtained in step 1 is placed on a horizontal substrate, and a stainless steel scraper is used to form a continuous liquid film with a thickness of 250 μm. The horizontal substrate covered with the casting liquid is placed in a constant temperature and humidity environment at a temperature of 70°C and a relative humidity of 50% for 45 s;

[0068] Step 3, film solidification: immerse the liquid film treated with constant temperature and humidity in step 2 together with the substrate in a pure water coagulation bath at a temperature of 40°C, so that the liquid film is solidified and falls off from the substrate to obtain a high-throughput and high-strength polylactic acid separation membrane.

[0069] Example 5

[0070] The preparation method of the high-throughput and high-strength polylactic acid separation membrane in this embodiment is as follows:

[0071] Step 1, preparing a casting solution: mixing dried polylactic acid pellets, diluent sulfolane, pore-forming agent Tween 80 and a mixed organic solvent of 1,4-dioxane and N-methylpyrrolidone (volume ratio of 3:1), heating and stirring to completely dissolve them, cooling to room temperature, and vacuum degassing to obtain a uniform casting solution; wherein the mass fraction of polylactic acid is 13%, the mass fraction of diluent sulfolane is 18%, and the mass fraction of pore-forming agent Tween 80 is 5%;

[0072] Step 2, liquid film preparation: the casting liquid obtained in step 1 is placed on a horizontal substrate, and a stainless steel scraper is used to form a continuous liquid film with a thickness of 250 μm. The horizontal substrate covered with the casting liquid is placed in a constant temperature and humidity environment at a temperature of 70°C and a relative humidity of 50% for 45 s;

[0073] Step 3, film solidification: immerse the liquid film treated with constant temperature and humidity in step 2 together with the substrate in a pure water coagulation bath at a temperature of 40°C, so that the liquid film is solidified and falls off from the substrate to obtain a high-throughput and high-strength polylactic acid separation membrane.

[0074] Comparative Example 1

[0075] A polylactic acid film prepared without adding a diluent to the casting solution is used as comparative example 1, comprising the following steps:

[0076] Step 1, preparation of casting solution: dry polylactic acid pellets, pore-forming agent Tween 80 and a mixed organic solvent of 1,4-dioxane and N-methylpyrrolidone (volume ratio is 3:1) are mixed, heated and stirred to completely dissolve, then cooled to room temperature, and vacuum degassed to obtain a uniform casting solution; wherein the mass fraction of polylactic acid is 13%, and the mass fraction of pore-forming agent Tween 80 is 5%;

[0077] Step 2, liquid film preparation: the casting liquid obtained in step 1 is placed on a horizontal substrate, and a stainless steel scraper is used to form a continuous liquid film with a thickness of 250 μm. The horizontal substrate covered with the casting liquid is placed in a constant temperature and humidity environment at a temperature of 70°C and a relative humidity of 50% for 45 s;

[0078] Step 3, film solidification: immerse the liquid film treated with constant temperature and humidity in step 2 together with the substrate in a pure water coagulation bath at a temperature of 40°C, so that the liquid film is solidified and falls off from the substrate to obtain a polylactic acid separation membrane.

[0079] Comparative Example 2

[0080] Taking the polylactic acid film prepared without constant temperature and humidity treatment as comparative example 2, the method comprises the following steps:

[0081] Step 1, preparing a casting solution: mixing dried polylactic acid pellets, diluent sulfolane, pore-forming agent Tween 80 and a mixed organic solvent of 1,4-dioxane and N-methylpyrrolidone (volume ratio of 3:1), heating and stirring to completely dissolve them, cooling to room temperature, and vacuum degassing to obtain a uniform casting solution; wherein the mass fraction of polylactic acid is 13%, the mass fraction of diluent sulfolane is 18%, and the mass fraction of pore-forming agent Tween 80 is 5%;

[0082] Step 2, liquid film preparation: placing the casting liquid obtained in step 1 on a horizontal substrate, and forming a continuous liquid film with a thickness of 250 μm by using a stainless steel scraper;

[0083] Step 3, film solidification: the liquid film in step 2 together with the substrate is quickly immersed in a pure water coagulation bath at a temperature of 40°C, so that the liquid film is solidified and falls off from the substrate to obtain a polylactic acid separation membrane.

[0084] Comparative Example 3

[0085] A polylactic acid film prepared without adding a diluent to the casting liquid and without subjecting the liquid film to a constant temperature and humidity treatment is used as comparative example 3, comprising the following steps:

[0086] Step 1, preparation of casting solution: dry polylactic acid pellets, pore-forming agent Tween 80 and a mixed organic solvent of 1,4-dioxane and N-methylpyrrolidone (volume ratio is 3:1) are mixed, heated and stirred to completely dissolve, then cooled to room temperature, and vacuum degassed to obtain a uniform casting solution; wherein the mass fraction of polylactic acid is 13%, and the mass fraction of pore-forming agent Tween 80 is 5%;

[0087] Step 2, liquid film preparation: placing the casting liquid obtained in step 1 on a horizontal substrate, and forming a continuous liquid film with a thickness of 250 μm by using a stainless steel scraper;

[0088] Step 3, film solidification: the liquid film in step 2 together with the substrate is quickly immersed in a pure water coagulation bath at a temperature of 40°C, so that the liquid film is solidified and falls off from the substrate to obtain a polylactic acid separation membrane.

[0089] Test Example 1

[0090] 1. The polylactic acid membranes obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were used as samples to test separation performance. The test method is as follows:

[0091] The pure water flux test was carried out by cross-flow filtration. The flux was stabilized by running at 1 bar pressure for 1 h. Then, the amount of pure water permeating per unit membrane area per unit time was calculated at 1 bar pressure. The measured pure water flux data are shown in Table 1. The retention test was carried out by cross-flow filtration using a polyethylene glycol (PEG) aqueous solution with a concentration of 300 ppm and a molecular weight of 100 kDa as the feed liquid. The performance was stabilized by running at 1 bar pressure for 1 h. Then, the product liquid was collected and tested on a TOC tester. The measured PEG retention rate data are shown in Table 1.

[0092] 2. The high-throughput and high-strength polylactic acid separation membranes obtained in Examples 1 to 5 and the polylactic acid membranes obtained in Comparative Examples 1 to 3 were used as samples to perform mechanical property tests. The test methods are as follows:

[0093] The tensile strength and elongation at break of the membrane samples were measured using an electronic tensile testing machine. The sample size was 5 mm × 30 mm, the tensile rate was 10 mm / min, and the average value was taken after three parallel tests. The mechanical properties data are shown in Table 1.

[0094] The separation performance and mechanical property data of the high-flux and high-strength polylactic acid separation membranes prepared in Examples 1 to 5 were compared with those of the polylactic acid separation membranes prepared in Comparative Examples 1 to 3, and the results are shown in Table 1. At the same level of rejection, the higher the water flux of the membrane, the better its permeability; the higher the tensile strength and elongation at break of the membrane, the better the mechanical strength of the membrane.

[0095] Table 1 Separation performance and mechanical properties of polylactic acid membrane

[0096]

[0097] It can be seen from Table 1 that compared with the polylactic acid membrane prepared in Comparative Example 1 without adding a diluent to the casting solution, the high-throughput and high-strength polylactic acid separation membranes of Examples 1 to 5 have similar retention rates for PEG, but the pure water flux is increased by 127% to 167%, the tensile strength is increased by 76% to 100%, and the elongation at break is increased by 87% to 125%.

[0098] Compared with the polylactic acid membrane prepared in comparative example 2 without constant temperature and humidity treatment, the high-throughput and high-strength polylactic acid separation membranes of embodiments 1 to 5 have significantly better retention rates for PEG, and the relatively high pure water flux of comparative example 2 is at the expense of retention rate; in addition, the high-throughput and high-strength polylactic acid separation membranes of embodiments 1 to 5 have a tensile strength increased by 50% to 75% and an elongation at break increased by 43% to 71% compared with comparative example 2.

[0099] Compared with the polylactic acid membrane prepared in comparative example 3, in which no diluent was added to the casting liquid and the liquid membrane was not subjected to constant temperature and humidity treatment, the high-throughput and high-strength polylactic acid separation membranes of Examples 1 to 5 had similar retention rates for PEG, but the pure water flux was increased by 67% to 96%, the tensile strength was increased by 58% to 84%, and the elongation at break was increased by 46% to 76%.

[0100] Test Example 2

[0101] The high-throughput and high-strength polylactic acid separation membrane prepared in Example 5 was characterized by scanning electron microscopy. Figure 1 As shown, Figure 1 From top to bottom are scanning electron microscope images of the overall cross-section, near-surface, and near-back morphology.

[0102] Depend on Figure 1 It can be seen that the high-throughput and high-strength polylactic acid separation membrane prepared by the method provided by the present invention has a nearly symmetrical physical structure, a dense surface layer and a dense bottom layer, and a matrix without finger-like cavities.

[0103] It can be seen from the above embodiments that in the preparation process of polylactic acid separation membrane, a liquid with a boiling point and viscosity higher than that of organic solvents, rich in oxygen atoms in its chemical structure and soluble in water is introduced into the casting liquid as a diluent, and the liquid film is subjected to constant temperature and humidity treatment before it solidifies, which can significantly improve the flux and strength of the membrane.

[0104] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-throughput and high-strength polylactic acid separation membrane, characterized in that: The preparation method comprises the following steps: (1) Preparation of casting solution: Mix the dried polylactic acid pellets, diluent, pore-forming agent and organic solvent, heat and stir to completely dissolve them, then cool to room temperature, and vacuum degas to obtain a uniform casting solution; The diluent is a liquid having a higher boiling point and a higher viscosity than the organic solvent, rich in oxygen atoms in its chemical structure and soluble in water; the liquid having a higher boiling point and a higher viscosity than the organic solvent, rich in oxygen atoms in its chemical structure and soluble in water is one or more of glycerol carbonate, glycerol monoacetate, glycerol diacetate, glycerol triacetate and sulfolane; The pore-forming agent is one or more of Tween 80, Triton X-100, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate and Pluronic F127; The organic solvent is one or more of 1,4-dioxane, N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone; (2) Liquid film preparation: placing the casting liquid obtained in step (1) on a horizontal substrate to form a continuous liquid film of uniform thickness, and then subjecting it to a constant temperature and humidity treatment; the temperature of the constant temperature and humidity treatment is 60°C to 80°C, the relative humidity is 35% to 80%, and the treatment time is 30 s to 60 s; (3) Thin film solidification: The liquid film treated at constant temperature and humidity in step (2) is immersed in a solidification bath together with the substrate, so that the liquid film is solidified and detached from the substrate, thereby obtaining the high-throughput and high-strength polylactic acid separation membrane.

2. The preparation method according to claim 1, characterized in that In step (1), the mass fraction of the polylactic acid is 12% to 14%, the mass fraction of the diluent is 15% to 20%, and the mass fraction of the pore-forming agent is 4% to 6%.

3. The preparation method according to claim 1, characterized in that: The thickness of the continuous liquid film in step (2) is 250 μm.

4. The preparation method according to claim 1, characterized in that: The coagulation bath in step (3) is pure water, and the temperature of the coagulation bath is 40°C.

5. A high-throughput and high-strength polylactic acid separation membrane prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The pure water flux of the high-flux and high-strength polylactic acid separation membrane is not less than 200 L·m -2 ·h -1 bar -1 , tensile strength is not less than 3.0 MPa, and elongation at break is not less than 110%.

6. Use of the high-throughput and high-strength polylactic acid separation membrane according to claim 5 in any one of the following (a) to (d): (a) Separation and purification of organic matter; (b) filtration sterilization; (c) hemodialysis; (d) Wastewater treatment.

Images