Preparation method and application of bio-based polyester porous membrane

Abstract

The invention discloses a preparation method and application of a bio-based polyester porous membrane, an organic solvent is used as a poly-3-hydroxybutyrate-co-4-hydroxybutyrate solvent, water is used as a non-solvent, and a phase inversion method is adopted to prepare the porous membrane. By adjusting the concentration of the membrane casting solution and the temperature of the coagulating bath, the phase separation behavior in the membrane forming process is regulated and controlled, the poly-3-hydroxybutyrate-co-4-hydroxybutyrate porous membrane with a controllable structure is prepared, and the porous membrane is uniform in pore distribution and high in porosity. The preparation method of the green polymer porous membrane material, provided by the invention, has the advantages of low cost, simple method, easiness in operation, energy conservation, environment friendliness and the like, and has a wide application prospect in the fields of oil-water separation, lithium ion batteries and the like; the problems of non-uniform pore size distribution, poor repeatability and the like of the existing polyhydroxyalkanoate in the phase separation film forming process are solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of porous membrane preparation, and more particularly relates to a preparation method and application of a bio-based polyester porous membrane. BACKGROUND

[0002] Porous separation membranes are thin film materials with micro-nano pore size structures, and their separation principle is based on size screening, adsorption or charge effect, which can selectively intercept specific substances. At present, commonly used separation membrane materials mainly include petroleum-derived polymers such as polyvinylidene fluoride (PVDF), polypropylene (PP), polysulfone (PSF) and polyether sulfone (PES). However, these petroleum-based polymers have challenges in degradation after use and may cause environmental pollution.

[0003] Polyhydroxyalkanoates (PHAs) are a class of linear biopolymers with thermoplastic properties, with diverse structures and numerous types, and the R group of the side chain and the monomer chain length of the main chain can be varied. Poly-3-hydroxybutyrate-co-4-hydroxybutyrate (P34HB) is the latest generation of aliphatic polyester, composed of 3-hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB) segments, and its structural formula is as follows:

[0004]

[0005] P34HB has the characteristics of high strength, good ductility, controllable mechanical properties, excellent processing performance, etc. In addition, according to the different molar fractions of 4HB segments, P34HB has a wide range of material properties from hard crystalline plastics to good elastic rubber. Therefore, P34HB is considered to be a promising biobased degradable membrane substitute material. In CN101327345B ultrafine fiber porous membrane material and its preparation method, an electrospinning process is used, in which a high-voltage electric field is used to generate an electric current on the surface of the spinning solution, causing the spinning solution stream to be stretched and split multiple times during the spraying process and move along a spiral trajectory to the receiving device to solidify into nanofibers. A large number of fibers are interlaced to form a porous membrane. However, the production efficiency of the electrospinning method is relatively low, the production cost is high, and the pore size distribution is wide, resulting in a significant decrease in the tensile strength and elongation at break of the membrane, which limits its further application.

[0006] Phase separation technique is a physical or chemical method that makes different components in a material system spontaneously separate into multiple phases (such as liquid-liquid, solid-liquid or solid-solid phase) by regulating the compatibility difference of different components, so that the microstructure of the film can be adjusted by regulating the solvent ratio, the temperature of the coagulation bath, the polymer concentration and other parameters. For example, CN101164678A discloses a method for preparing a polyvinylidene fluoride porous membrane with controllable pore structure. The method uses a mixture of high-temperature solvent and low-temperature solvent as a diluent, and uses a low-temperature solvent and a non-solvent (such as water) as a cooling liquid. By changing the components and contents in the mixture, the internal heat-induced phase separation of the film occurs, and the surface of the film exchanges solvents because it contacts the cooling liquid, causing the surface solute to separate and form a porous structure, thereby preparing a polyvinylidene fluoride porous membrane with controllable internal and external pore structures. The phase separation technique can improve the production efficiency and control the film structure. Although the heat-induced phase separation can form a porous structure, the uniformity of the film pore size is poor, and the repeatability is poor, which makes it difficult to ensure the quality stability between batches. SUMMARY

[0007] The present application provides a method for preparing a biobased polyester porous membrane and its application to overcome the problems of uneven pore size distribution and poor repeatability of the existing polyhydroxyalkanoate using phase separation technology.

[0008] The present application is realized by the following technical solutions:

[0009] A method for preparing a biobased polyester porous membrane, comprising the following steps:

[0010] S1. Preparing a casting solution;

[0011] Dissolving poly-3-hydroxybutyrate-co-4-hydroxybutyrate in an organic solvent to prepare a casting solution with a mass fraction of 10-18%;

[0012] S2. Coating film;

[0013] Coating the casting solution on a substrate to obtain a wet film with a thickness of 100-500 μm;

[0014] S3. Phase separation and solidification to form a film;

[0015] Immersion of the wet film in a water bath at 30-80℃ for 1-3h for phase separation, and drying to obtain a polyester porous membrane.

[0016] Further, the organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and 1,4 dioxane.

[0017] Further, the solubility temperature of the poly-3-hydroxybutyrate-co-4-hydroxybutyrate is 50-80℃.

[0018] Further, the mass fraction of poly-3-hydroxybutyrate-co-4-hydroxybutyrate in the casting solution is 14%.

[0019] Further, the casting solution further comprises removing bubbles before coating the film.

[0020] Further, the substrate is one of a glass plate, a polytetrafluoroethylene plate, and a polypropylene plate.

[0021] Further, the phase separation temperature is 60 DEG C.

[0022] Further, the phase separation time is 2 hours.

[0023] Further, the drying temperature is 20-40 DEG C.

[0024] The polyester porous membrane prepared by the above method of preparing a bio-based polyester porous membrane is applied to the fields of oil-water separation, energy, and biological medicine.

[0025] Compared with the prior art, the beneficial effects are:

[0026] The concentration of the casting solution is controlled to be 10-18%, so that better film forming performance is ensured, and the pore size is uniform at the concentration, avoiding the problem of uneven distribution of micropores of the porous membrane. Meanwhile, the coagulation bath temperature is determined to be 30-80 DEG C, so that the mass transfer exchange between the non-solvent and the solvent in the casting solution is at a suitable rate, the organic solvent is replaced out of the casting solution, the morphology of the membrane is controlled, the solidification, phase separation, and exchange rate of the solvent and the non-solvent of the polymer are controlled by the coagulation bath temperature, so that the form and performance of the porous membrane are adjusted. While the microporous structure is controlled, the exchange time in the coagulation bath is reduced, the operation steps are simplified, the production time of the P34HB porous membrane is reduced, and the production efficiency is improved.

[0027] Drawings of the specification

[0028] Figure 1 are SEM images of the upper surfaces of P34HB porous membranes prepared by different concentration phase inversion methods, wherein, A is 10% concentration, B is 12% concentration, C is 14% concentration, D is 16% concentration, and E is 18% concentration.

[0029] Figure 2 are WAXD images of P34HB porous membranes with different concentrations, wherein (a) is a 2D-WAXD image, (b) is a 1D-WAXD curve, and (c) is a crystallinity.

[0030] Figure 3 are contact angles of P34HB porous membranes with different concentrations.

[0031] Figure 4 Figure is the cross-sectional morphology of P34HB porous membrane under different coagulation bath conditions, wherein A is the coagulation bath temperature of 30℃; B is the coagulation bath temperature of 45℃; C is the coagulation bath temperature of 60℃; D is the coagulation bath temperature of 80℃

[0032] Figure 5 Figure is the porosity of P34HB porous membrane under different coagulation bath conditions;

[0033] Figure 6 Figure is the contact angle of P34HB porous membrane under different coagulation bath conditions;

[0034] Figure 7 Figure is the mechanical property display of P34HB porous membrane with different concentrations under the coagulation bath of 60℃; DETAILED DESCRIPTION

[0035] The following examples are further explained and illustrated, but the specific examples do not have any form of limitation on the present application. If not specifically indicated, the methods and equipment used in the examples are conventional methods and equipment in the art, and the raw materials used are conventional commercially available raw materials.

[0036] Example 1

[0037] A preparation method of a bio-based polyester porous membrane, the steps comprising:

[0038] S1. Preparation of casting solution;

[0039] Poly-3-hydroxybutyrate-co-4-hydroxybutyrate is mixed with DMF, the concentration of P34HB is 10%, and it is fully dissolved and stirred for 2 hours in a magnetic stirrer, and then it is left to stand for defoaming to obtain the casting solution.

[0040] S2. Film coating;

[0041] The casting solution is poured onto a glass plate, and a doctor blade with a slit size of 500 microns is used for blade coating to obtain a wet film.

[0042] S3. Phase separation and coagulation to form a film;

[0043] The wet film is immersed in water at 30℃ for 2h for phase separation, and the solvent and non-solvent fully exchange, and the film is taken out and completely dried at room temperature to obtain a polyester porous membrane.

[0044] Examples 2-5

[0045] The process of this example is the same as that of Example 1, and the difference is that the concentration of the casting solution is 12%, 14%, 16%, and 18%, respectively.

[0046] The porous membranes prepared by casting solutions of different concentrations in Examples 1-5 were subjected to electron microscopy, X-ray diffraction, and hydrophobicity tests. The results are as follows:

[0047] like Figure 1 The images show the upper surface morphology of P34HB membranes at different concentrations. It is evident that the casting solution concentration significantly affects the morphology of the P34HB porous membrane's upper surface; the pore size gradually decreases with increasing polymer concentration. At low concentrations, the solvent volume fraction is high, making instantaneous liquid-liquid phase separation more likely when the casting solution is immersed in the coagulation bath. This results in a faster phase separation rate and a larger number and size of pores. As the polymer concentration increases, the solvent volume fraction decreases, and the exchange rate between solvent and non-solvent gradually slows down, leading to a delayed liquid-liquid phase separation process, thus reducing the number and size of membrane pores. Simultaneously, increasing the casting solution concentration also increases the viscosity of the casting solution system, causing a decrease in membrane pore size and an increase in the distance between adjacent micropores, i.e., an increase in pore wall thickness. The P34HB membranes prepared by the solvent-free phase separation method in this invention have pore sizes mainly distributed between 1 and 1.5 μm.

[0048] Depend on Figure 2 The crystallization behavior of porous membranes prepared with different concentrations of casting solution shows that the intensity of the diffraction rings gradually increases with the increase of polymer concentration. Strong diffraction peaks were found at 2θ = 13.5° and 17.1°, corresponding to the (020) and (110) crystal planes, respectively. At lower polymer concentrations, the solvent volume fraction is larger, and instantaneous liquid-liquid phase separation is more likely to occur during phase separation. The speed of molecular chain movement increases, the movement time is shortened, and there is not enough time for rearrangement, which leads to a decrease in the diffraction peaks of the curve, resulting in a lower crystallinity of the membrane. As the polymer concentration increases, the formation process of the polymer solid phase gradually slows down during phase separation, resulting in delayed liquid-liquid phase separation. This delayed liquid-liquid phase separation phenomenon is caused by the slowdown of the exchange rate between the solvent and non-solvent in the three-phase system. At a low exchange rate, the P34HB molecular chains have more time to arrange themselves in an orderly manner and form a regular structure. Therefore, with the increase of polymer concentration, the intensity of the diffraction peaks and the crystallinity will gradually increase.

[0049] Figure 3The wettability of the polymer membranes with different concentrations was demonstrated. The contact angle of P34HB membrane was mainly affected by the pore structure of the membrane. When the concentration of P34HB solution was 10%, the contact angle of the membrane was 87.3°. This was because the high porosity and large pore structure at low concentration were conducive to the penetration of liquid droplets into the internal pores of the membrane, thereby reducing the contact angle and exhibiting good hydrophilicity. When the concentration of the solution increased to 14%, the contact angle of the P34HB membrane increased to 93.3°, because the gap between the surface micropores became larger and the pore size decreased. Further increasing the concentration to 18%, the contact angle of the P34HB membrane increased to 102°. Therefore, as the concentration of the casting solution increased, the size and number of micropores decreased, resulting in a continuous decrease in the porosity of the membrane and a significant increase in the surface hydrophobicity and a decrease in the hydrophilicity.

[0050] Example 6

[0051] S1. Preparation of casting solution;

[0052] Poly-3-hydroxybutyrate-co-4-hydroxybutyrate was mixed with DMF, and the concentration of P34HB was 14%. The mixture was fully dissolved and stirred for 2 hours in a magnetic stirrer, and then was left to stand for defoaming to obtain a casting solution.

[0053] S2. Film coating;

[0054] The casting solution was poured onto a glass plate, and a doctor blade with a slit size of 500 microns was used for blade coating to obtain a wet film.

[0055] S3. Phase separation and solidification into a membrane;

[0056] The wet film was immersed in water at 45°C for 2h for phase separation, and the solvent and non-solvent were fully exchanged. After the membrane was taken out and completely dried at room temperature, a P34HB porous membrane was obtained.

[0057] Examples 7-8

[0058] The process of this example was the same as that of Example 6, except that the phase separation temperatures were 60°C and 80°C, respectively.

[0059] The cross-sectional structure of the P34HB porous membranes prepared at different coagulation bath temperatures was as follows: Figure 4As shown, at low coagulation bath temperatures, the P34HB membrane consists of a dense skin layer and a porous support layer. With increasing coagulation bath temperature, the dense structure of the membrane cross-section gradually disappears, exhibiting a structure where finger-like pores and sponge-like pores coexist. At low temperatures, the mass transfer rate between solvent and non-solvent is limited, and the exchange rate slows down. The lower layer, which contacts the glass plate first, undergoes rapid gelation and solidification at low coagulation bath temperatures, exhibiting a dense, compact structure. When the coagulation bath temperature is higher, solvent molecules are more easily separated from the polymer solution under the influence of the non-solvent, simultaneously inhibiting the rapid gelation process on the lower surface of the membrane. The connectivity of the pores in the porous membrane cross-section is enhanced, forming a pore structure with sponge-like pores as the main morphology. The formation of this sponge-like porous structure helps to increase the porosity.

[0060] like Figure 5 The porosity of the membrane at different coagulation bath temperatures is shown. At a low coagulation bath temperature (30℃), the solidification of the lower surface of the membrane is faster, which restricts the phase separation process and makes it difficult for a porous structure to form on the lower surface of the membrane, ultimately resulting in a membrane porosity of 39.2%. When the coagulation bath temperature is increased to 60℃, the temperature difference between the casting solution and the coagulation bath decreases, and the exchange rate between the solvent and non-solvent increases, causing the structure on the lower surface of the membrane to gradually transform into a network structure. The cross-sectional morphology changes from an asymmetrical structure to a porous structure dominated by a sponge-like structure. Therefore, the membrane porosity significantly increases to 76.5%. Increasing the coagulation bath temperature to 80℃ further accelerates the mass transfer rate between the solvent and non-solvent, thereby forming a larger porous structure and increasing the membrane porosity to 80.3%.

[0061] Depend on Figure 6 The contact angles of the membranes at different coagulation bath temperatures show that at low coagulation bath temperatures (30°C), the lower surface of the membrane solidifies rapidly, hindering the exchange between solvent and non-solvent components. The lower surface does not form a porous structure, exhibiting low porosity with a contact angle of 92°, demonstrating some hydrophobicity. As the coagulation bath temperature gradually increases, the membrane cross-section gradually transforms from an asymmetric bilayer structure to a uniform sponge-like pore structure, significantly increasing the porosity of the P34HB membrane. The surface contact angles decrease to 90.2°, 78.4°, and 71.2°, respectively. This indicates that increasing the pore structure can reduce the membrane's contact angle and effectively improve its hydrophilicity.

[0062] In summary, coagulation bath temperature is one of the important factors affecting the film formation process in non-solvent phase separation methods. By adjusting the coagulation bath temperature, the movement of polymer molecules and the diffusion rate of solvent can be controlled, thereby effectively controlling the stability of film pores and morphology.

[0063] Example 9

[0064] S1. Place P34HB in an oven to dry at 80℃ for 12 hours.

[0065] S2. Mix the above P34HB with DMF and allow it to swell fully in a magnetic stirrer. The concentrations of P34HB are 14%, 16%, and 18%. Stir at 80°C for 2 hours.

[0066] S3. The obtained P34HB solution was allowed to stand to degas, and then coated onto a glass plate with a doctor blade to obtain a wet film. The slit size of the doctor blade was 500 μm.

[0067] S4. Place the wet membrane in a coagulation bath and leave it at 60°C for 2 hours to allow sufficient exchange between the solvent and non-solvent. Remove the membrane and dry it completely at room temperature to obtain the porous membrane P34HB.

[0068] The mechanical properties of porous membranes prepared with casting solution concentrations of 14%, 16%, and 18% were tested. To test the flexibility of the membranes, various types of deformation stresses were applied to the porous membranes, such as... Figure 7 (I) shows that the porous membrane can be easily folded and twisted to 360° after being folded, twisted, and folded multiple times. When the applied stress is removed, the membrane also quickly returns to its original size, exhibiting good flexibility. The effect of casting solution concentration on the mechanical properties of the P34HB membrane is also discussed. Figure 7-II As shown, P34HB films exhibit good elongation but low tensile strength. The tensile strength and elongation of the 14% P34HB film are 1.04 MPa and 30%, respectively. With increasing polymer concentration, the tensile strength and elongation at break of the P34HB film gradually increase, with the tensile strength of the 16% P34HB film increasing to 52%. Furthermore, with a further increase in casting solution concentration to 18%, the tensile strength and elongation of the P34HB film increase to 1.4 MPa and 89%, respectively.

[0069] Comparative Example 1

[0070] This comparative example is the same as Example 1, except that the concentration of the casting solution in this comparative example is 5%.

[0071] Comparative Example 2

[0072] This comparative example is the same as Example 1, except that the concentration of the casting solution in this comparative example is 25%.

[0073] When the concentration of the polymer casting solution is below 10%, the film-forming properties are poor, making it difficult to detach from the substrate. When the solution viscosity exceeds 18%, the viscosity is too high, resulting in poor flowability and poor coating performance. Therefore, a casting solution with a viscosity between 10% and 18% exhibits suitable flowability and good film-forming properties.

[0074] Obviously, the above embodiments of the present application are only examples for clearly explaining the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to exhaust all the embodiments. Any modification, equivalent replacement and improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method for preparing a bio-based polyester porous membrane, characterized by the steps of The application relates to a preparation method of a bio-based polyester porous membrane. S1. Preparing a casting solution; Dissolving poly-3-hydroxybutyrate-co-4-hydroxybutyrate in an organic solvent to prepare a casting solution with a mass fraction of 10-18%; S2. Coating a film; Coating the casting solution on a substrate to obtain a wet film with a thickness of 100-500 mu m; S3. Phase separation and solidification to form a film; Immersing the wet film in a water bath at 30-80 DEG C for 1-3 h for phase separation, and drying to obtain a polyester porous membrane.

2. The method for preparing the bio-based polyester porous membrane according to claim 1, characterized in that, The organic solvent comprises one or more of N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone and 1, 4 dioxane.

3. The method for preparing the bio-based polyester porous membrane according to claim 1, characterized in that, The dissolving temperature of the poly-3-hydroxybutyrate-co-4-hydroxybutyrate is 50-80 DEG C.

4. The method for preparing the bio-based polyester porous membrane according to claim 1, characterized in that, The mass fraction of the poly-3-hydroxybutyrate-co-4-hydroxybutyrate in the casting solution is 14-18%.

5. The method for preparing the bio-based polyester porous membrane according to claim 1, characterized in that, The casting solution further comprises bubble removal before film coating.

6. The method for preparing the bio-based polyester porous membrane according to claim 1, characterized in that, The substrate is one of a glass plate, a polytetrafluoroethylene plate and a polypropylene plate.

7. The method for preparing the bio-based polyester porous membrane according to claim 1, characterized in that, The phase separation temperature is 60 DEG C.

8. The method for preparing the bio-based polyester porous membrane according to claim 1, characterized in that, The phase separation time is 2 h.

9. The method for preparing the bio-based polyester porous membrane according to claim 1, characterized in that, The drying temperature is 20-40 DEG C.

10. The polyester porous membrane prepared by the preparation method of the bio-based polyester porous membrane according to claim 1 is applied to oil-water separation, energy and biological medicine.

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