Polylactic acid porous film and method for preparing the same

Abstract

This invention relates to the field of polymer materials and discloses a polylactic acid porous membrane and its preparation method. The method includes: (1) mixing a left-handed lactic acid copolymer and a right-handed lactic acid copolymer with a solvent to obtain a casting solution; (2) coating the casting solution to obtain a thin film; (3) atomizing the thin film and then allowing it to stand in a non-solvent of polylactic acid to obtain a polylactic acid porous membrane. The polylactic acid porous membrane of this invention has high heat resistance and mechanical strength.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, specifically to a polylactic acid porous membrane and its preparation method. Background Technology

[0002] Polylactic acid (PLA) porous membranes are widely used in filtration, packaging, protection, tissue engineering, and drug delivery due to their excellent biocompatibility and degradation properties. While the porous structure endows PLA with high application potential, the large-area defects caused by the dense pores also reduce the strength and thermal stability of porous PLA, making it difficult to meet diverse application requirements. To improve the low strength and poor heat resistance of PLA porous membranes, long-chain branching modification and blending with petroleum-based polymers or fillers are commonly used methods. Although these methods have achieved significant results, they destroy PLA's unique degradability and biocompatibility. Therefore, achieving the manufacture of high-strength, heat-resistant PLA films without introducing any additives remains a challenge. Summary of the Invention

[0003] The purpose of this invention is to overcome the problem that polylactic acid porous membranes in the prior art cannot simultaneously achieve high strength and high heat resistance, and to provide a polylactic acid porous membrane and its preparation method, wherein the polylactic acid porous membrane has high heat resistance and mechanical strength.

[0004] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a polylactic acid porous membrane, wherein the method includes:

[0005] (1) Mix the L-lactic acid copolymer and the D-lactic acid copolymer with a solvent to obtain a casting solution;

[0006] (2) The casting solution is coated to obtain a thin film;

[0007] (3) After atomizing the film, it is placed in a non-solvent bath of polylactic acid to obtain a polylactic acid porous membrane.

[0008] A second aspect of the present invention provides a polylactic acid porous membrane prepared by the above method.

[0009] Through the above technical solutions, the polylactic acid porous membrane and its preparation method provided by the present invention have the following beneficial effects.

[0010] This invention uses L-lactic acid copolymer and D-lactic acid copolymer as raw materials to prepare a casting solution, and then places the atomized film in a non-solvent bath of polylactic acid. The resulting polylactic acid porous membrane not only has high heat resistance, but also high mechanical strength. Attached Figure Description

[0011] Figure 1This is an electron microscope image of the polylactic acid porous membrane prepared in Example 1.

[0012] Figure 2 This is an electron microscope image of the polylactic acid porous membrane prepared in Example 2.

[0013] Figure 3 This is an electron microscope image of the polylactic acid porous membrane prepared in Comparative Example 1.

[0014] Figure 4 This is an electron microscope image of the polylactic acid porous membrane prepared in Comparative Example 2. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] The first aspect of this invention provides a method for preparing a polylactic acid porous membrane, wherein the method includes:

[0017] (1) Mix the L-lactic acid copolymer and the D-lactic acid copolymer with a solvent to obtain a casting solution;

[0018] (2) The casting solution is coated to obtain a thin film;

[0019] (3) After atomizing the film, it is placed in a non-solvent bath of polylactic acid to obtain a polylactic acid porous membrane.

[0020] This invention uses L-lactic acid copolymer and D-lactic acid copolymer as raw materials to prepare a casting solution, and then places the atomized film in a non-solvent bath of polylactic acid. The resulting polylactic acid porous membrane not only has high heat resistance, but also high mechanical strength.

[0021] According to the present invention, in step (1), the number-average molecular weights of the L-lactic acid copolymer and the D-lactic acid copolymer are each independently greater than or equal to 20,000 g / mol.

[0022] In this invention, when the number-average molecular weight of the L-lactic acid copolymer and / or the number-average molecular weight of the D-lactic acid copolymer meet the above-mentioned ranges, the polylactic acid porous membrane prepared has good mechanical strength.

[0023] Furthermore, in step (1), the number-average molecular weights of the L-lactic acid copolymer and the D-lactic acid copolymer are each independently greater than or equal to 50,000 g / mol.

[0024] According to the present invention, in step (1), the molar ratio of the L-lactic acid copolymer and the D-lactic acid copolymer is 1:0.5-2.

[0025] In this invention, when the molar ratio of L-lactic acid copolymer and D-lactic acid copolymer meets the above-mentioned range, the polylactic acid porous membrane prepared has high heat resistance and mechanical strength.

[0026] Further, in step (1), the molar ratio of the L-lactic acid copolymer and the D-lactic acid copolymer is 1:0.7-1.5.

[0027] According to the present invention, in step (1), the solid content of the casting solution is 5-30 wt%.

[0028] In this invention, when the solid content of the casting solution meets the above-mentioned range, it is more beneficial to the subsequent coating operation.

[0029] Further, in step (1), the solid content of the casting solution is 10-20 wt%.

[0030] According to the present invention, in step (1), the solvent is selected from at least one of 1,4-dioxane, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, ethyl acetate, chloroform and dichloromethane.

[0031] In this invention, the solvent in step (1) is a solvent for polylactic acid.

[0032] Furthermore, the solvent is selected from 1,4-dioxane and / or chloroform.

[0033] In this invention, step (1) further includes removing air bubbles from the casting solution. There are no particular limitations on the method for removing air bubbles from the casting solution in this invention; conventional methods in the art can be used. For example, the casting solution can be allowed to stand under vacuum conditions.

[0034] According to the present invention, in step (2), the thickness of the film is 100-800 μm.

[0035] In this invention, the thickness of the film refers to the coating thickness.

[0036] Furthermore, in step (2), the thickness of the film is 300-500 μm.

[0037] According to the present invention, in step (3), the atomization conditions include: the shortest distance between any position I on the film and the atomizer is 5-30cm.

[0038] According to the present invention, in step (3), the atomization time is greater than or equal to 1 min.

[0039] According to the present invention, the atomization temperature is 40-70°C.

[0040] According to the present invention, the atomizing medium is at least one of air, nitrogen and argon.

[0041] In this invention, when any one of the following conditions is met: the shortest distance between any position I on the film and the atomizer, the atomization time, the atomization temperature, and the atomization medium, the polylactic acid porous film produced has a better pore size, higher porosity, and stronger mechanical strength and toughness.

[0042] Furthermore, in step (3), the atomization conditions include: the shortest distance between any position I on the film and the atomizer is 8-15cm.

[0043] Furthermore, in step (3), the atomization time is 5-30 minutes.

[0044] Furthermore, the atomization temperature is 50-60℃.

[0045] Furthermore, the atomizing medium is air.

[0046] According to the present invention, in step (3), the non-solvent of the polylactic acid is selected from at least one of distilled water, methanol, ethanol and N-methylpyrrolidone.

[0047] Furthermore, in step (3), the non-solvent for the polylactic acid is distilled water.

[0048] According to the present invention, in step (3), the conditions for standing include: standing time ≥ 1h, and standing temperature 10-40℃.

[0049] Furthermore, in step (3), the conditions for settling include: settling time of 4-8 hours and settling temperature of 20-30°C.

[0050] A second aspect of the present invention provides a polylactic acid porous membrane prepared by the above method.

[0051] According to the present invention, the thickness of the polylactic acid porous membrane is 20-500 μm, preferably 50-200 μm, and more preferably 80-150 μm;

[0052] According to the present invention, the polylactic acid porous membrane has a melting point T. H and optional melting point T L .

[0053] In this invention, the L-lactic acid copolymer and the D-lactic acid copolymer can form a stereocomplex, and the melting point of the stereocomplex is T. HFurthermore, the polylactic acid porous membrane of the present invention may also contain a L-lactic acid copolymer and / or a D-lactic acid copolymer, the melting point of which is T. L .

[0054] According to the present invention, the melting point T H The temperature range is 160-185℃, preferably 165-180℃.

[0055] According to the present invention, the melting point T L The temperature is greater than or equal to 210℃, preferably 215-230℃.

[0056] According to the present invention, the average pore size of the polylactic acid porous membrane is 5-30 μm, preferably 10-20 μm;

[0057] According to the present invention, the porosity of the polylactic acid porous membrane is 40-70%, preferably 45-60%.

[0058] In this invention, when the thickness of the polylactic acid porous membrane is 20-500 μm, the elastic modulus of the polylactic acid porous membrane is greater than or equal to 900 MPa, preferably greater than or equal to 1100 MPa.

[0059] In this invention, when the thickness of the polylactic acid porous membrane is 20-500 μm, the elongation at break of the polylactic acid porous membrane is greater than or equal to 8%, preferably greater than or equal to 11%.

[0060] In this invention, when the thickness of the polylactic acid porous membrane is 20-500 μm, the tensile strength of the polylactic acid porous membrane is greater than or equal to 17 MPa, preferably greater than or equal to 30 MPa.

[0061] The present invention will be described in detail below through embodiments.

[0062] The thickness of the polylactic acid porous membrane was measured three times in different areas using vernier calipers, and the average value was taken.

[0063] The average pore size of the polylactic acid porous membrane was determined using the PEG solute transfer method, the detailed steps of which are as follows:

[0064] (1) Test the retention rate of polylactic acid porous membrane for PEG of different molecular sizes;

[0065] (2) Linear fitting of PEG size and retention rate in log-probability coordinate system, the PEG size corresponding to 50% retention rate is the average pore size of polylactic acid porous membrane.

[0066] Porosity of polylactic acid (PLA) porous membranes: The thickness of the PLA porous membrane is measured using vernier calipers, and its volume is calculated as V0 (unit: cm). 3The weight of the polylactic acid porous membrane was measured (denoted as m0, in g), and its content in alcohol (density 0.79 g / cm³) was also measured. 3 The weight (denoted as m1, in grams) after soaking in the solution for 2 hours. The porosity of the polylactic acid porous membrane is calculated using the following formula:

[0067] Porosity (%) = (m1 - m0) / (0.79 × V0).

[0068] Elastic modulus, elongation at break and tensile strength of polylactic acid porous membrane: The elastic modulus, elongation at break and tensile strength were tested at room temperature (room temperature 20℃, sample clamping distance 30mm) using an INSTRON 5965 tensile tester. The long strip film sample (30mm long and 10mm wide) was tested according to GB / T1040.3-2006 standard at a tensile rate of 50mm / min.

[0069] Melting point of polylactic acid porous membrane: measured using differential scanning calorimetry (DSC).

[0070] The raw materials used in the examples and comparative examples were all commercially available products.

[0071] Example 1

[0072] Step 1, add 7.5g PLLA (M n =10 5 g / mol) and 7.5 g PDLA (M n =10 5 The casting solution was prepared by dissolving (g / mol) in 85g of 1,4-dioxane. The casting solution was then placed in a vacuum drying oven and left under vacuum for 12 hours to remove air bubbles. The molar ratio of L-lactic acid copolymer to D-lactic acid copolymer was 1:1; the solid content of the casting solution was 15wt%.

[0073] Step 2: Pour the casting solution onto a glass plate and use a four-sided coating apparatus to coat the solution into a thin film with a thickness of 400 μm.

[0074] Step 3: Place the film 10cm above the atomizer and atomize for 20 minutes at a temperature of 55℃. The atomizing medium is air.

[0075] Step 4: Place the atomized membrane in distilled water and let it stand for 6 hours (at 25℃). After drying, a polylactic acid porous membrane is obtained. The test results of the polylactic acid porous membrane are shown in Table 1. Electron microscope images of the polylactic acid porous membrane are shown below. Figure 1 As shown, the surface of the polylactic acid porous membrane has a microporous structure, indicating that the above atomization conditions effectively promote the formation of micropores.

[0076] Example 2

[0077] Step 1, add 7.5g PLLA (M n =10 5 g / mol) and 7.5 g PDLA (M n =10 5 The casting solution was prepared by dissolving (g / mol) in 85g of 1,4-dioxane. The casting solution was then placed in a vacuum drying oven and left under vacuum for 12 hours to remove air bubbles. The molar ratio of L-lactic acid copolymer to D-lactic acid copolymer was 1:1; the solid content of the casting solution was 15wt%.

[0078] Step 2: Pour the casting solution onto a glass plate and use a four-sided coating apparatus to coat the solution into a thin film with a thickness of 400 μm.

[0079] Step 3: Place the film 10cm above the atomizer and atomize for 5 minutes at a temperature of 55℃. The atomizing medium is air.

[0080] Step 4: Place the atomized membrane in distilled water and let it stand for 6 hours (at 25℃). After drying, a polylactic acid porous membrane is obtained. The test results of the polylactic acid porous membrane are shown in Table 1. Electron microscope images of the polylactic acid porous membrane are shown below. Figure 2 As shown, the surface of the polylactic acid porous membrane has a microporous structure, but the pore size is smaller than that of Example 1, indicating that shortening the atomization time reduces the pore size of the polylactic acid porous membrane.

[0081] Example 3

[0082] Polylactic acid porous membranes were prepared according to the method in Example 1, except that in step 3, the membrane was placed 25 cm above the atomizer and atomized for 2 min.

[0083] Example 4

[0084] Polylactic acid porous membranes were prepared according to the method in Example 1, except that in step 3, the membrane was placed 35 cm above the atomizer and atomized for 50 seconds.

[0085] Example 5

[0086] Polylactic acid porous membranes were prepared according to the method in Example 1, except that in step 3, the membrane was placed 25 cm above the atomizer and atomized for 2 min at a temperature of 45°C.

[0087] Example 6

[0088] Polylactic acid porous membranes were prepared according to the method of Example 1, except that in step 1, the molar ratio of L-lactic acid copolymer to D-lactic acid copolymer was 1:1.75.

[0089] Example 7

[0090] Polylactic acid porous membranes were prepared according to the method of Example 1, except that in step 1, the molar ratio of L-lactic acid copolymer to D-lactic acid copolymer was 1:1.75; and in step 3, the membrane was placed 25 cm above the atomizer and atomized for 2 min.

[0091] Example 8

[0092] Polylactic acid porous membranes were prepared according to the method of Example 1, except that in step 1, the molar ratio of L-lactic acid copolymer to D-lactic acid copolymer was 1:1.75, and in step 4, the atomized membrane was placed in distilled water and allowed to stand for 2 hours at a standing temperature of 15°C.

[0093] Example 9

[0094] Polylactic acid porous membranes were prepared according to the method of Example 1, except that in step 1, the molar ratio of L-lactic acid copolymer to D-lactic acid copolymer was 1:5.

[0095] Comparative Example 1

[0096] Step 1, add 15g of PLLA (M n =10 5 (g / mol) was dissolved in 85g of 1,4-dioxane to obtain a casting solution. The casting solution was placed in a vacuum drying oven and left under vacuum for 12 hours to remove air bubbles. The solid content of the casting solution was 15wt%.

[0097] Step 2: Pour the casting solution onto a glass plate and use a four-sided coating apparatus to coat the solution into a thin film with a thickness of 400 μm.

[0098] Step 3: Place the film 10cm above the atomizer and atomize for 20 minutes at a temperature of 55℃. The atomizing medium is air.

[0099] Step 4: Place the atomized membrane in distilled water and let it stand for 6 hours (at 25℃). After drying, a polylactic acid porous membrane is obtained. The test results of the polylactic acid porous membrane are shown in Table 1. Electron microscope images of the polylactic acid porous membrane are shown below. Figure 3 As shown, the surface of the polylactic acid membrane has a microporous structure. Compared with Example 1, the pores are shallower and the edges are not obvious, indicating that the mixing of L-lactic acid copolymer and D-lactic acid copolymer is beneficial to the formation of micropores in the polylactic acid porous membrane.

[0100] Comparative Example 2

[0101] Step 1, add 7.5g PLLA (M n =10 5 g / mol) and 7.5 g PDLA (M n =10 5The casting solution was prepared by dissolving (g / mol) in 85g of 1,4-dioxane. The casting solution was then placed in a vacuum drying oven and left under vacuum for 12 hours to remove air bubbles. The molar ratio of L-lactic acid copolymer to D-lactic acid copolymer was 1:1; the solid content of the casting solution was 15wt%.

[0102] Step 2: Pour the casting solution onto a glass plate and use a four-sided coating apparatus to coat the solution into a thin film with a thickness of 400 μm.

[0103] Step 3: The un-atomized membrane was placed in distilled water and allowed to stand for 6 hours (at 25°C). After drying, a polylactic acid porous membrane was obtained. The test results of the polylactic acid porous membrane are shown in Table 1. Electron microscope images of the polylactic acid porous membrane are shown below. Figure 4 As shown, the number of pores on the polylactic acid membrane surface is reduced and the pore size is significantly decreased, indicating that atomization is a necessary condition for the formation of micropores.

[0104] Table 1

[0105]

[0106] As can be seen from the results in Table 1, the embodiments of the present invention have higher melting point, pore size, porosity, elastic modulus, elongation at break and fracture strength, indicating that the polylactic acid porous membrane formed has better heat resistance, higher mechanical strength and toughness.

[0107] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing polylactic acid porous membranes, characterized in that, The method includes: (1) Mix the L-lactic acid copolymer and the D-lactic acid copolymer with a solvent to obtain a casting solution; (2) The casting solution is coated to obtain a thin film; (3) After atomizing the film, it is left to stand in a non-solvent of polylactic acid to obtain a polylactic acid porous membrane.

2. The method according to claim 1, wherein, In step (1), the number-average molecular weights of the L-lactic acid copolymer and the D-lactic acid copolymer are each independently greater than or equal to 20,000 g / mol, preferably greater than or equal to 50,000 g / mol.

3. The method according to claim 1 or 2, wherein, In step (1), the molar ratio of the L-lactic acid copolymer and the D-lactic acid copolymer is 1:0.5-2, preferably 1:0.7-1.

5.

4. The method according to any one of claims 1-3, wherein, In step (1), the solid content of the casting solution is 5-30 wt%, preferably 10-20 wt%.

5. The method according to any one of claims 1-4, wherein, In step (1), the solvent is selected from at least one of 1,4-dioxane, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, ethyl acetate, chloroform, and dichloromethane.

6. The method according to any one of claims 1-5, wherein, In step (2), the thickness of the film is 100-800 μm, preferably 300-500 μm.

7. The method according to any one of claims 1-6, wherein, In step (3), the atomization conditions include: the shortest distance between any position I on the film and the atomizer is 5-30cm, preferably 8-15cm; Preferably, the atomization temperature is 40-70℃, and more preferably 50-60℃; Preferably, the atomizing medium is at least one of air, nitrogen, and argon, with air being the most preferred.

8. The method according to any one of claims 1-7, wherein, In step (3), the atomization time is greater than or equal to 1 minute, preferably 5-30 minutes.

9. The method according to any one of claims 1-8, wherein, In step (3), the non-solvent for the polylactic acid is selected from at least one of distilled water, methanol, ethanol and N-methylpyrrolidone; Preferably, in step (3), the conditions for settling include: settling time ≥ 1h, preferably 4-8h, and settling temperature 10-40℃, preferably 20-30℃.

10. A polylactic acid porous membrane prepared by the method according to any one of claims 1-9; Preferably, the thickness of the polylactic acid porous membrane is 20-500 μm, more preferably 50-200 μm; Preferably, said polylactic acid porous film has a melting point T H and optionally a melting point T L ; Preferably, said melting point T H is comprised between 160 and 185 °C, preferably between 165 and 180 °C; Preferably, the melting point T L ≥210℃, preferably 215-230℃; Preferably, the polylactic acid porous membrane has an average pore size of 5-30 μm, and more preferably 10-20 μm; Preferably, the porosity of the polylactic acid porous membrane is 40-70%, more preferably 45-60%.

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