A charged hydrophilic polymer porous membrane, a preparation method thereof and application thereof in concentration and purification of polysaccharides in Chinese herbal medicines

Abstract

The application discloses a kind of charged hydrophilic polymer porous membrane, its preparation method and application in polysaccharide concentration purification in Chinese herbal medicine, belong to porous membrane technical field.It includes: while the non-solvent phase separation of film-forming polymer solution and the formation of separation layer on the outer surface of polymer membrane, simultaneously coating water-soluble coating layer polymer solution on the surface of separation layer, obtain charged hydrophilic polymer porous membrane;Film-forming polymer solution uses fluorine-containing polymer as film-forming base material, uses nitrogen-containing small molecule as first solvent, uses macromolecular organic matter as pore-forming agent.The application is applied to polysaccharide concentration purification in Chinese herbal medicine, solve the problem that the membrane surface opening rate is low, hydrophilic and poor negative charge of existing non-solvent phase separation technology is not applicable to polysaccharide concentration purification in Chinese herbal medicine, the opening rate of charged hydrophilic polymer porous membrane prepared is high, cutting molecular weight is 10-1000kDa, and can realize membrane forming, improve surface opening rate and surface hydrophilic negative charge modification simultaneously.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of porous membranes, and particularly relates to a charged hydrophilic polymer porous membrane, a preparation method thereof and application thereof in concentration and purification of polysaccharides in Chinese herbal medicines. BACKGROUND

[0002] Membrane separation technology is a technology that can realize high selective separation, and fluorine-containing polymers are currently widely used in the preparation of porous membranes. The porous membranes prepared from fluorine-containing polymers can be used for concentration and purification of Chinese herbal medicine systems containing polysaccharides with different molecular weights. Common polysaccharides in Chinese herbal medicines include astragalus polysaccharides, lentinan, ganoderma polysaccharides, medlar polysaccharides, bamboo cane polysaccharides, cordyceps polysaccharides, polygonatum polysaccharides, and radix codonopsis polysaccharides, etc. The molecular weight range of these polysaccharides is widely distributed in the range of 10-1000 kDa. The commonly used technology for Chinese herbal medicine extraction is hot water extraction, but the polysaccharide aqueous solution obtained has a low concentration and needs to be concentrated. Although mature evaporation technology can achieve concentration, it has high energy consumption and may damage the polysaccharides. Membrane technology has the advantages of realizing deep separation and concentration at room temperature, and is suitable for the concentration and purification of polysaccharides in Chinese herbal medicines. The membrane has a suitable pore size, a high flux, and a low polysaccharide adsorption capacity, which are the prerequisite conditions for the practical value of the polysaccharide concentration membrane in Chinese herbal medicines. A suitable pore size can efficiently intercept polysaccharides in Chinese herbal medicine solution. The lower the filtration resistance, the higher the membrane flux. Good membrane pore connectivity and high surface opening rate are the main factors to reduce the membrane filtration resistance. In addition, giving the membrane strong hydrophilicity and strong negative surface charge can significantly reduce the adsorption of polysaccharides (polysaccharides are usually negatively charged and are easily repelled by negatively charged membrane surfaces), and also reduces the membrane filtration resistance to some extent.

[0003] The non-solvent induced phase technique is the mainstream technology for preparing fluorine-containing polymer porous membranes at present. The principle of this technology is that the polymer, pore-forming agent and solvent form a polymer solution at a certain temperature. When the polymer solution and the coagulation bath (usually water) are in contact, mass transfer occurs between the solvent and the additive and the coagulation bath due to the concentration gradient. When the water content in the polymer solution reaches a certain level, the amount of remaining solvent is insufficient to dissolve the polymer, and the polymer solidifies and precipitates. The space previously occupied by the solvent and the additive in the polymer solution forms pores.

[0004] The ideal structure of separation membrane is good mechanical properties, high surface porosity and suitable pore size, and cross-section of mesh pore structure. However, the ternary solution of "polymer / pore-forming agent / solvent" usually forms instantaneous phase separation due to the fast phase separation speed, and finally forms a thick and dense skin layer with a cross-section of a finger-shaped pore structure, which is not suitable for long-term operation of concentrating and purifying polysaccharides in Chinese herbal medicine. Literature research shows that the reverse thermal induced phase separation technology can prepare polyvinylidene fluoride porous membrane with cross-section of sponge pores and thin skin layer. However, the reverse thermal induced phase separation technology is difficult to form a stable solution at room temperature, but a metastable dispersion system, which is very sensitive to environmental temperature. The system becomes more unstable when the environmental temperature rises, so the batch repeatability of the microstructure of the prepared membrane is poor. In addition, the concentration of the polymer solution prepared by the reverse thermal induced phase separation technology is only 12%, and it is also difficult to obtain a membrane with a molecular weight cut-off of less than 500 kDa, and the surface porosity is not high.

[0005] Because the non-solvent induced phase separation technology is relatively simple, the control requirements of process parameters are not very harsh, therefore, in addition to exploring convenient and effective surface hydrophilic modification method, it is particularly necessary to study the preparation of simple and convenient porous polymer membrane for concentrating and purifying polysaccharides in Chinese herbal medicine by non-solvent induced phase separation technology, which has good cross-linking, thin skin layer, high surface porosity, pore size of 10-1000 kDa and good hydrophilicity.

[0006] The current methods for improving the surface open porosity of membranes prepared by non-solvent induced phase separation technology mainly include the following: (1) adding a template agent (such as inorganic nano-particles such as nano calcium carbonate, nano silicon dioxide, etc.) to the casting solution, and then removing the template agent with a strong alkali or strong acid solution after film formation. However, the prepared membrane has uneven pore size due to the poor compatibility between the inorganic nano-particles and the polymer, which makes it difficult to disperse the template agent uniformly in the casting solution system, thereby significantly reducing the separation precision. In addition, a certain amount of waste acid or alkali solution is generated during the removal of the template agent; (2) adding a certain proportion of a solvent such as N,N-dimethylacetamide (DMAC) to the coagulation bath water. The presence of the solvent reduces the solidification rate of the polymer, thereby slowing down the formation of a dense skin layer and finger-like pore structure due to the rapid solidification of the polymer. However, this method can only reduce the skin layer thickness and improve the surface pore size and open porosity to a certain extent, and the effect of improving the surface open porosity is not significant; (3) increasing the air humidity. The water vapor in the air adheres to the surface of the casting film before the casting solution enters the coagulation bath, which can greatly slow down the diffusion speed between water and solvents and additives in the subsequent casting solution entering the coagulation bath, thereby reducing the skin layer thickness, eliminating the cross-sectional finger-like pores, and improving the membrane surface open porosity and pore size. However, this process requires the air humidity to be supersaturated, which not only greatly increases the equipment process, but also requires a very high humidity control. The water in the supersaturated air will condense and precipitate, changing the humidity of the air, making it difficult to achieve the required membrane pore size and limiting the degree of improvement of the membrane surface open porosity; (4) simultaneous coating of polymer solution. A composite membrane is prepared by using a double doctor blade (from top to bottom, polymer coating solution, film-forming polymer solution) on the surface of a plastic film support. The result is that the bottom membrane skin layer thickness is reduced and the finger-like pores are eliminated. However, the coating solution also forms a thin layer of polymer attached to the underlying polymer membrane, thereby reducing the membrane surface open porosity and pore size. In addition, the polymer used in the coating solution is a non-water-soluble polymer with weak hydrophilicity and no negative charge.

[0007] However, since the surface simultaneous coating method is simple, efficient, and easy to industrialize, it is an ideal technology for effectively controlling the surface microstructure of the membrane. Therefore, whether the simultaneous coating can significantly improve the open porosity, hydrophilicity, and negative charge of the membrane surface is the key. SUMMARY

[0008] In view of the deficiencies of the prior art, the technical problem to be solved by the present application is that the existing non-solvent induced phase separation technology has low surface opening rate, poor hydrophilicity and negative charge, and is not suitable for concentrating and purifying polysaccharides in Chinese herbal medicines, and a charged hydrophilic polymer porous membrane with high opening rate, a molecular weight of 10-1000 kDa, and capable of simultaneously realizing membrane forming, improving surface opening rate, and surface hydrophilic and negative charge modification, a preparation method thereof, and application thereof in concentrating and purifying polysaccharides in Chinese herbal medicines are provided.

[0009] To solve the technical problem, the technical solution adopted by the present application is:

[0010] The present application provides a preparation method of a charged hydrophilic polymer porous membrane, comprising: synchronously coating a water-soluble coating layer polymer solution on the surface of a separation layer while the non-solvent induced phase separation of a film-forming polymer solution occurs and the separation layer is formed on the outer surface of the polymer membrane, to obtain a charged hydrophilic polymer porous membrane; the film-forming polymer solution takes a fluorine-containing polymer as a film-forming base material, a small-molecule nitrogen-containing compound as a first solvent, and a high-molecular organic compound as a pore-forming agent; the coating layer polymer solution is negatively charged, and has a viscosity of 800-3000 mPa·s.

[0011] In some embodiments, the coating layer polymer solution comprises a negatively charged water-soluble polymer containing carboxyl and hydroxyl groups, and the negatively charged water-soluble polymer is selected from at least one of polyhydroxyethyl methacrylate, sodium alginate, and sodium carboxymethyl cellulose.

[0012] In some embodiments, the mass fraction of the negatively charged water-soluble polymer in the coating layer polymer solution is 1-2.5%.

[0013] In some embodiments, the coating layer polymer solution comprises a negatively charged water-soluble polymer and a second solvent, and the second solvent is water or ethanol that can dissolve the negatively charged water-soluble polymer but cannot dissolve the fluorine-containing polymer.

[0014] In some embodiments, the mass ratio of the fluorine-containing polymer, the pore-forming agent, and the first solvent in the film-forming polymer solution is 18-26:3-8:66-79; and the fluorine-containing polymer is a homopolymer or copolymer of polyvinylidene fluoride with a weight average molecular weight of 700-900 kDa.

[0015] In some embodiments, the first solvent in the film-forming polymer solution is N,N-dimethylacetamide or N-methylpyrrolidone, and the pore-forming agent is polyvinylpyrrolidone with a molecular weight of 30-45 kDa.

[0016] In some embodiments, the method comprises:

[0017] S1, uniformly mix the fluorine-containing polymer, the pore-forming agent, and the first solvent at 50-70 DEG C, and then vacuum degas to obtain a film-forming polymer solution for preparing a polymer membrane;

[0018] S2, the negatively charged water-soluble polymer is mixed with a second solvent at 50 DEG C, and then vacuum degassing to obtain a coating layer polymer solution for preparing a coating layer;

[0019] S3, the coating layer polymer solution and the film forming polymer solution are simultaneously flowed out through a liquid tank containing a doctor blade with a thickness of 0.2 mm at 50-60 DEG C by using a double doctor blade, so that the film forming polymer solution is coated on a plastic film substrate of polyethylene terephthalate with a thickness of 0.4 mm, and the coating layer polymer solution is coated on the film forming polymer solution, and then cooled and solidified to form a film;

[0020] S4, the film is immersed and washed with a deionized water extractant at 25 DEG C to obtain a charged hydrophilic polymer porous film.

[0021] In some embodiments, the air gap length in S3 is 30-60 cm, and the doctor blade speed is 2-4 m / min.

[0022] Another aspect of the present application provides a charged hydrophilic polymer porous film prepared by the preparation method of the charged hydrophilic polymer porous film provided in any of the above technical solutions, wherein the charged hydrophilic polymer porous film is a flat film, the pore size of the flat film is 5-100 nm, and the cut-off molecular weight is 10-1000 kDa.

[0023] The present application also provides an application of the charged hydrophilic polymer porous film provided in the above technical solutions in the concentration and purification of polysaccharides in Chinese herbal medicines.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] The application provides a preparation method of a charged hydrophilic polymer porous membrane, which comprises the following steps: using a fluoropolymer as a base material, and preparing a polymer flat membrane by using a non-solvent induced phase separation technology, and synchronously coating a water-soluble polymer aqueous solution with certain viscosity and adhesion on the surface of the fluoropolymer during the preparation of the fluoropolymer membrane, so as to obtain a polymer flat membrane with a required structure. The method utilizes the contact interface between the water-soluble polymer chains and the film-forming polymer chains in the synchronous coating forming process before solidification, and the strong adhesion of the water-soluble polymer chains and the film-forming polymer chains makes the water-soluble polymer chains and the film-forming polymer chains firmly adhere to the surface of the polymer membrane and not easy to fall off. In addition, the coating layer polymer has high viscosity, which slows down the double diffusion mass transfer between the film-forming polymer solution and the coagulation bath, so that the film-forming polymer solution system obviously delays the phase separation, thereby improving the surface opening rate of the membrane, increasing the membrane pore size and eliminating the finger-shaped pore structure. In addition, the high negative charge density on the surface of the membrane not only significantly improves the combination with water molecules and improves the hydrophilicity of the membrane, but also significantly improves the repulsive force of the membrane surface to the polysaccharide in the negatively charged Chinese herbal medicine, thereby improving the anti-pollution and interception of the polysaccharide in the Chinese herbal medicine. The charged hydrophilic polymer porous membrane has the characteristics of simple preparation process, good membrane pore connectivity, large pore size and high surface opening rate. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The surface morphology diagram of the charged hydrophilic polymer porous membrane provided in Example 1 of the application;

[0027] Figure 2 The surface morphology diagram of the charged hydrophilic polymer porous membrane provided in Comparative Example 1 of the application;

[0028] Figure 3 The cross-sectional morphology diagram of the charged hydrophilic polymer porous membrane provided in Example 1 of the application;

[0029] Figure 4 The cross-sectional morphology diagram of the charged hydrophilic polymer porous membrane provided in Comparative Example 1 of the application. DETAILED DESCRIPTION

[0030] The technical solutions in the specific embodiments of the application will be described in detail below. Obviously, the described embodiments are only part of the specific embodiments of the general technical solution of the application, but not all the embodiments. Based on the general concept of the application, all other embodiments obtained by those skilled in the art fall within the scope of protection of the application.

[0031] The application provides a preparation method of a charged hydrophilic polymer porous membrane, comprising the following steps: synchronously coating a water-soluble coating layer polymer solution on the surface of a separation layer while the non-solvent induced phase separation of a film-forming polymer solution occurs and the separation layer is formed on the outer surface of the polymer membrane, so as to obtain the charged hydrophilic polymer porous membrane; the film-forming polymer solution takes a fluorine-containing polymer as a film-forming base material, takes a small molecule containing nitrogen as a first solvent, and takes a high-molecular organic substance as a porogen; and the coating layer polymer solution is negatively charged and has a viscosity of 800-3000 mPa·s.

[0032] The preparation method utilizes the contact interface between the water-soluble polymer chains of the coating layer and the film-forming polymer chains in the synchronous coating forming process to be fully contacted before solidification, and the coating layer polymer diffuses to the side of the film-forming polymer solution due to the adhesive effect between the coating layer polymer solution and the film-forming polymer solution, so as to further strengthen the entanglement between the coating layer polymer and the film-forming polymer chains, and the strong adhesion makes the coating layer polymer firmly adhere to the upper surface of the polymer membrane and not easy to fall off. In addition, the coating layer polymer has high viscosity, which slows down the double diffusion mass transfer between the film-forming polymer solution and the coagulation bath, so that the film-forming polymer solution system obviously delays phase separation, thereby improving the opening rate of the membrane surface, effectively eliminating the finger-shaped pore structure, and appropriately increasing the membrane pore size. In addition, the high negative charge density on the membrane surface not only significantly improves the combination with water molecules and improves the hydrophilicity of the membrane, but also significantly improves the repulsive force of the negatively charged polysaccharide in Chinese herbal medicine on the membrane surface, thereby improving the anti-pollution and interception of polysaccharide in Chinese herbal medicine, and finally obtaining a polymer porous membrane that can be used for concentrating and purifying polysaccharide in Chinese herbal medicine.

[0033] The ternary solution of the general "polymer / porogen / solvent" formed in the non-solvent induced phase separation process occurs instantaneous phase separation due to the fast phase separation speed, and finally forms a skin layer with high thickness and density, and a cross-section with a finger-shaped pore structure that is not resistant to pressure. The above preparation method of the application overcomes the above problems, and the principle is as follows:

[0034] A thin layer of the same temperature, viscosity and adhesion and negatively charged water-soluble polymer solution (referred to as coating layer) is coated on the film-forming polymer solution. Since the coating layer polymer solution has a certain viscosity and can form a barrier between the coagulation bath and the film-forming polymer solution, the double diffusion mass transfer between the coagulation bath and the film-forming polymer solution can be greatly slowed down, and the solidification of the polymer in the film-forming polymer solution can be greatly slowed down, so that a dense thick skin layer is not formed, a porous skin layer structure is formed, the membrane surface opening rate is improved, the finger-like pore structure is effectively eliminated, and the membrane pore size is appropriately increased, so that the membrane cutting molecular weight is 10-1000 kDa. Since the contact interface between the coating layer water-soluble polymer chain and the film-forming polymer chain in the coating layer water-soluble polymer solution and the film-forming polymer solution is fully contacted before solidification during the synchronous coating forming process, and there is a concentration gradient between the coating layer polymer solution and the film-forming polymer solution, the coating layer polymer diffuses to the side of the film-forming polymer solution to further strengthen the entanglement between the film-forming polymer chains, and its strong adhesion makes it more firmly adhere to the surface of the polymer film and not easy to fall off. In addition, the high negative charge density on the surface of the membrane not only significantly improves the combination with water molecules and improves the hydrophilicity of the membrane, but also significantly improves the repulsive force of the negatively charged polysaccharide in Chinese herbal medicine on the surface of the membrane, thereby improving the anti-pollution and interception of polysaccharide in Chinese herbal medicine, which is very suitable for polysaccharide concentration and purification operation in the field of Chinese herbal medicine.

[0035] In some embodiments, the coating layer polymer solution includes a negatively charged water-soluble polymer containing carboxyl and hydroxyl groups, and the negatively charged water-soluble polymer is selected from at least one of poly(hydroxyethyl methacrylate), sodium alginate, and sodium carboxymethyl cellulose.

[0036] It is found that when glycerol, triethylene glycol, propylene glycol and polyethylene glycol 400 organic solvents are used in the coating layer polymer solution, their viscosity is very low, and controllability is poor in the synchronous film coating process, making it difficult to form a continuous coating layer. When using water-soluble solutions of polyethylene glycol and polyethylene oxide with a molecular weight of 10-100 kDa, the adhesion between the bottom film-forming polymer is not strong and is prone to fall off, and the surface of the membrane cannot be negatively charged, and the hydrophilic and surface negatively charged effects cannot be achieved.

[0037] In some embodiments, the mass fraction of the negatively charged water-soluble polymer in the coating layer polymer solution is 1-2.5%.

[0038] It is determined by experiment that the mass fraction of the negatively charged water-soluble polymer in the coating layer polymer solution is preferably 1-2.5%, and the viscosity of the coating layer polymer solution in the corresponding concentration range is 800-3000 mPa·s. When the viscosity is lower than 800 mPa·s, the controllability of the simultaneous blade coating is poor, and it is difficult to form a continuous coating layer. When the viscosity is higher than 3000 mPa·s, the high viscosity makes the blade coating of the coating layer polymer solution poor and uneven. The low concentration of the polymer does not significantly block the pores and reduce the open pore ratio of the polymer film below. The coated is a thin layer of water or ethanol solution, and the amount of solvent is very small, so it only causes the surface of the polymer solution below to phase separate and does not further expand. The phase separation of the fluorine-containing polymer chain on the surface and the polymer chain with strong adhesion in the coating solution further entangles and adheres, making it more difficult to fall off. It can be understood that the mass fraction of the negatively charged water-soluble polymer in the coating layer polymer solution can also be 1.5%, 2.0%, and any point value within the range.

[0039] In some embodiments, the coating layer polymer solution comprises a negatively charged water-soluble polymer and a second solvent, and the second solvent is water or ethanol that can dissolve the negatively charged water-soluble polymer but cannot dissolve the fluorine-containing polymer.

[0040] In some embodiments, the mass ratio of the fluorine-containing polymer, the pore-forming agent, and the first solvent in the film-forming polymer solution is 18-26:3-8:66-79; and the fluorine-containing polymer is a homopolymer or copolymer of polyvinylidene fluoride with a weight average molecular weight of 700-900 kDa.

[0041] If the weight average molecular weight of the fluorine-containing polymer is too low or the content of the fluorine-containing polymer in the film-forming polymer solution is too low, the viscosity of the film-forming polymer solution is too low, the formability is poor, and the strength is low. If the weight average molecular weight of the fluorine-containing polymer is too high or the content of the fluorine-containing polymer in the film-forming polymer solution is too high, the viscosity of the film-forming polymer solution is too large and not easy to process, and the pore size is too small to meet the pore size requirement of polysaccharide concentration and purification in the field of Chinese herbal medicines. It can be understood that the weight average molecular weight of the fluorine-containing polymer can also be 750 kDa, 800 kDa, 850 kDa, and any point value within the range.

[0042] In some embodiments, the first solvent in the film-forming polymer solution is N,N-dimethylacetamide or N-methylpyrrolidone, and the pore-forming agent is polyvinylpyrrolidone with a molecular weight of 30-45 kDa. It can be understood that the molecular weight of the polyvinylpyrrolidone can also be 32 kDa, 34 kDa, 36 kDa, 38 kDa, 40 kDa, 42 kDa, 44 kDa, and any point value within the range.

[0043] In some embodiments, the method comprises:

[0044] S1, uniformly mix fluorine-containing polymer, pore-forming agent and first solvent at 50-70°C, then vacuum degassing to obtain film-forming polymer solution for preparing polymer film;

[0045] S2, uniformly mix negatively charged water-soluble polymer and second solvent at 50°C, then vacuum degassing to obtain coating layer polymer solution for preparing coating layer;

[0046] S3, using double doctor blade, coating layer polymer solution and film-forming polymer solution are simultaneously discharged through liquid tank containing doctor blade with thickness of 0.2mm at 50-60°C, so that film-forming polymer solution is coated on plastic film substrate of polyethylene terephthalate with thickness of 0.4mm, and coating layer polymer solution is coated on film-forming polymer solution, forming flat membrane shape, then cooling, solidifying and forming into membrane;

[0047] S4, immerse membrane in deionized water extractant at 25°C to obtain charged hydrophilic polymer porous membrane.

[0048] In the preparation process of the above charged hydrophilic polymer porous membrane, coating layer polymer solution and film-forming polymer solution are synchronously coated, the former is on the top of the latter, and the latter is coated on plastic film with certain thickness. The preparation method has the following characteristics:

[0049] (1) The preparation process is simple. Only one scraper is added, the existing commercial non-solvent phase separation technology is used, one metering pump and one kettle containing the coating material are added, and the flat sheet membrane with the required structure can be prepared.(2) The effects of improving the membrane surface porosity, hydrophilicity and negative charge are remarkable and the method is simple: through the way of surface coating and simultaneous polymer film forming, the fluoropolymer film is formed at the same time, and the water-soluble polymer solution with certain viscosity, adhesion and negative charge is coated on the surface. The contact interface between the water-soluble polymer chain and the film-forming polymer chain in the coating layer is fully contacted before solidification during the synchronous coating and molding process, and its strong adhesion makes it firmly adhere to the surface of the polymer film and not easy to fall off. In addition, the coating layer polymer has high viscosity, which slows down the double diffusion mass transfer between the film-forming polymer solution and the coagulation bath, so that the film-forming polymer solution system obviously delays the phase separation, thereby improving the membrane surface porosity, increasing the membrane pore size and eliminating the finger-like pore structure. In addition, the high negative charge density on the surface of the membrane not only significantly improves the combination with water molecules to improve the hydrophilicity of the membrane, but also significantly improves the repulsion of the membrane surface to the negatively charged polysaccharides in Chinese herbal medicine, thereby improving the anti-pollution and retention of polysaccharides in Chinese herbal medicine.(3) The adjustment of the membrane pore size. By adjusting the composition of the coating layer and the composition of the film-forming polymer layer and the membrane preparation process parameters, the film-forming process can be effectively adjusted, which finally improves the membrane pore connectivity, effectively reduces the skin thickness, improves the membrane surface porosity, and realizes the hydrophilic modification and negative charge, thereby realizing the adjustment of the membrane microstructure, hydrophilicity and negative charge, which can effectively separate multiple polysaccharides in Chinese herbal medicine extract.

[0050] In some embodiments, the air gap length in S3 is 30-60 cm, and the casting rate is 2-4 m / min.

[0051] Since the coating layer polymer solution and the film forming polymer solution enter the coagulation bath together, first, the double diffusion mass transfer between the coating layer polymer solution and the coagulation bath and the double diffusion mass transfer between the coating layer polymer solution and the film forming polymer solution occur respectively, therefore, the contact interface between the coating layer polymer and the film forming polymer needs to be completed in the air gap time before the coating layer polymer enters the coagulation bath, the chain entanglement is completed to be integrated, and the coating layer polymer is fully adhered to the surface of the film forming polymer under the action of the concentration difference, and the peeling is not easy to occur. In addition, the high viscosity of the coating layer polymer solution effectively hinders the double diffusion between the water in the coagulation bath and the film forming polymer solution after the film forming polymer enters the coagulation bath, the significant delayed phase separation of the film forming polymer solution further increases the pore size of the film surface and eliminates the finger-shaped hole, and finally forms the pore size and the membrane surface with hydrophilic (hydroxyl) and negatively charged (carboxyl) that can be used for the concentration and purification of polysaccharides in Chinese herbal medicine. The time of the polymer solution in the air is closely related to the air gap length, the doctor blade speed, the membrane liquid thickness and the like. Experimental tests show that for the flat plate membrane with a thickness of 0.2 mm, the doctor blade thickness is 0.2 mm, the air gap length is 30-60 cm, and the doctor blade speed is 2-4 m / min, the above purpose can be achieved. If the air gap length is too short, the coating layer polymer solution thickness is too thin, or the doctor blade speed is too fast, it is difficult to ensure that the double-component pore-forming agent in the coating polymer solution layer effectively diffuses to the film forming polymer solution layer, and the required size of the pore size and the complete coating layer cannot be obtained. On the contrary, the pore size of the membrane is too large and the strength is reduced.

[0052] It can be understood that the air gap length can also be 35 cm, 40 cm, 45 cm, 50 cm, 55 cm and any point value in the range thereof, and the doctor blade speed can also be 2.5 m / min, 3.0 m / min, 3.5 m / min and any point value in the range thereof.

[0053] The above preparation process of the application: (1) for the polymer membrane layer, using a fluorine-containing polymer as a substrate, a non-solvent phase separation technology is used to prepare a polymer porous membrane with a sponge hole cross-section and a high open hole rate on the surface; (2) for the coating layer, a water-soluble polymer solution with certain viscosity and adhesion and negative charge is coated on the surface of the fluorine-containing polymer at the same time when the fluorine-containing polymer is formed into a film, and a polymer flat plate membrane with a required structure is obtained; (3) the film forming and surface coating, the hydrophilic modification and the negative charge are carried out at the same time. Specifically, the following steps are included:

[0054] 1) Preparation of polymer solution:

[0055] Preparation of the coating layer polymer solution: the water-soluble polymer with strong adhesion, higher viscosity and negative charge and the second solvent were mixed in a kettle stirrer at 50°C for 6h to form a polymer solution, and then vacuum degassed for 1h to obtain the coating layer polymer solution for preparing the coating layer, the viscosity of the coating layer polymer solution was in the range of 800-3000mPa·s;

[0056] Preparation of the coating layer polymer solution: the water-soluble polymer with strong adhesion, higher viscosity and negative charge and the second solvent were mixed in a kettle stirrer at 50°C for 6h to form a polymer solution, and then vacuum degassed for 1h to obtain the coating layer polymer solution for preparing the coating layer, the viscosity of the coating layer polymer solution was in the range of 800-3000mPa·s;

[0057] 2) Preparation of flat sheet membrane:

[0058] The coating layer polymer solution and the film-forming polymer solution obtained in step 1) were simultaneously flowed out through the liquid tank containing the scraper with a thickness of 0.2mm at 50-60°C using a double scraper, so that the film-forming polymer solution was coated on the plastic film substrate of polyethylene terephthalate with a thickness of 0.4mm, and the coating layer polymer solution was coated on the film-forming polymer solution to form the shape of flat sheet membrane; the coating layer polymer solution and the film-forming polymer solution were simultaneously passed through the air gap with a length of 30-60cm and then entered the coagulation bath composed of deionized water at room temperature, and the obtained nascent membrane was cooled by deionized water at a certain temperature, and then the solvent and the pore-forming agent were extracted from the membrane using deionized water at 25°C, and after 2 extractions, the membrane was dried in the shade to obtain the finished flat sheet membrane product, the cutting molecular weight of the membrane was in the range of 10-1000kDa, which met the use requirements; wherein:

[0059] The solvent in the film-forming polymer solution in step 1) was N,N-dimethylacetamide or N-methylpyrrolidone; the pore-forming agent was polyvinylpyrrolidone with a molecular weight in the range of 30-45kDa;

[0060] The solvent in the coating layer polymer solution in step 1) was ethanol or water;

[0061] The winding speed in the spinning process in step 2) was in the range of 2-4m / min.

[0062] Compared with the prior art, the present application uses a hydroxyl and carboxyl containing negatively charged water-soluble polymer with strong adhesion and high viscosity as a coating layer solution, simultaneously forms a surface on the film forming polymer film and synchronously coats the above coating layer polymer solution on the surface, obtains a required structure of polymer flat film, and through selecting a polymer with a suitable weight average molecular weight and content, a solvent and a pore forming agent, can easily obtain or control the formation of a surface hydrophilic negatively charged structure with a thin and porous skin layer and a cutting molecular weight of 10-1000 kDa by a non-solvent phase inversion film forming technology.

[0063] Compared with the prior art, the present application is different in coating method, used coating layer polymer, coating temperature, film forming effect, obtained film structure and air gap length. In the present application, the temperature of the coating layer polymer solution and the film forming polymer solution is the same, and the main functions are two: one is to hinder the double diffusion between the coagulation bath and the film forming polymer solution and greatly delay the phase separation process of the film forming polymer solution; the other is that the hydrophilic negatively charged polymer with strong adhesion and high viscosity in the coating layer polymer solution has a relatively sufficient contact between the chain and the film forming polymer chain before solidification in the synchronous coating forming process, so that it is firmly adhered to the upper surface of the polymer film and is not easy to fall off, and finally gives the film surface strong hydrophilicity and negative charge. The film forming polymer solution layer undergoes non-solvent phase separation, and the polymer film forming and the film surface coating are synchronously performed, which is different from the reported step-by-step coating (first film forming and then coating polymer on the film surface-the coating polymer is not washed away, which is to realize the shrinkage of the film), homogeneous composite (the coating layer and the film are the same polymer, the coating layer undergoes non-solvent phase separation, and the separated layer undergoes thermal phase separation-the coating polymer is not washed away, which is to realize the shrinkage of the film) and synchronous coating with styrene-maleic anhydride copolymer (the styrene-maleic anhydride copolymer has poor film forming property, poor adhesion with the polymer film and obvious shrinkage effect).

[0064] In the present application, the coating layer uses a polymer with high viscosity, strong adhesion, solubility in ethanol or water and carboxyl and hydroxyl groups, which can be adhered to the upper surface of the fluorine-containing polymer after film forming to improve the opening rate, hydrophilicity and negative charge of the film surface. The viscosity of substances such as tannic acid and dopamine dissolved in water used for coating is not high, and not only has no obvious opening effect, but also has poor doctor blade film forming effect, the film surface after polymerization has poor hydrophilicity and obvious pore blocking phenomenon. The cutting molecular weight of the obtained film is 10-1000 kDa, and the purpose of the coating technology reported in the literature and patents is to reduce the thickness of the skin layer or the surface pore size. In summary, the present application has good adaptability, is simple and easy to implement, has a wide source of materials, low cost, good effect, only needs to add a small amount of equipment, is easy to popularize, has good industrialization prospect and good industrialization prospect.

[0065] Another aspect of the present application provides a charged hydrophilic polymer porous membrane prepared by the method of any of the above technical solutions, wherein the charged hydrophilic polymer porous membrane is a flat membrane, the pore size of the flat membrane is 5-100 nm, and the molecular weight cut-off is 10-1000 kDa.

[0066] It can be understood that the pore size of the flat membrane can also be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, and any point value in the range thereof, and the molecular weight cut-off can also be 100 kDa, 200 kDa, 300 kDa, 400 kDa, 500 kDa, 600 kDa, 700 kDa, 800 kDa, 900 kDa, and any point value in the range thereof.

[0067] The present application also provides a charged hydrophilic polymer porous membrane provided by the above technical solutions for use in the concentration and purification of polysaccharides in Chinese herbal medicines.

[0068] In order to more clearly and specifically introduce the charged hydrophilic polymer porous membrane, its preparation method, and its application in the concentration and purification of polysaccharides in Chinese herbal medicines provided by the embodiments of the present application, the following will be described in combination with specific embodiments.

[0069] Embodiment 1

[0070] 1) Preparation of polymer solution:

[0071] Preparation of film-forming polymer solution: 18 parts of fluorine-containing polymer with a weight average molecular weight of 700 kDa after drying and 3 parts of polyvinylpyrrolidone with a molecular weight of 30 kDa after drying were mixed uniformly with 79 parts of N,N-dimethylacetamide in a kettle-type stirrer at 50℃ for 10 h to form a polymer solution, and then vacuum degassing was performed for 1 h to obtain a polymer solution for preparing a polymer membrane;

[0072] Preparation of coating layer polymer solution: 1 part of sodium carboxymethyl cellulose and 99 parts of deionized water were mixed uniformly in a kettle-type stirrer at 50℃ for 6 h to form a polymer solution, and then vacuum degassing was performed for 1 h to obtain a polymer solution for preparing a coating layer;

[0073] 2) Preparation of flat sheet membrane: using double doctor blade, the coating layer polymer solution and the film forming polymer solution obtained in step 1) are simultaneously flowed out through the liquid tank containing the doctor blade with thickness of 0.2 mm at 50℃, so that the film forming polymer solution is coated on the plastic film substrate of polyethylene terephthalate with thickness of 0.4 mm, and the coating layer polymer solution is coated on the film forming polymer solution to form the shape of flat sheet membrane; the coating layer polymer solution and the film forming polymer solution are simultaneously passed through the air gap with length of 60 cm at the winding speed of 2 m / min, and then enter the coagulation bath composed of deionized water at room temperature, cooled by deionized water at certain temperature, and the obtained nascent membrane is extracted with deionized water at 25℃ to extract the solvent and pore-forming agent, after 2 times of extraction, dried in the shade to obtain the finished product of flat sheet membrane;

[0074] The surface morphology of the membrane is shown in Figure 1 The membrane cross-section is sponge hole, the cut-off molecular weight is 1000 kDa, and the flux recovery rate is 86.2% (1 g / L bovine serum protein solution, pH = 7.4), as shown in Figure 3 The pore size of the membrane without coating layer is 78 nm, the cross-section is finger hole, and the flux recovery rate is 42.7%.

[0075] Example 2

[0076] 1) Preparation of polymer solution:

[0077] Preparation of film forming polymer solution: 26 parts of fluorine-containing polymer with weight average molecular weight of 900 kDa after drying and 8 parts of polyvinylpyrrolidone with molecular weight of 45 kDa after drying and 66 parts of N,N-dimethylacetamide are mixed uniformly in a kettle stirrer at 70℃ for 10 h to form a polymer solution, and then vacuum degassing for 1 h to obtain the polymer solution for preparing polymer membrane;

[0078] Preparation of coating layer polymer solution: 2.5 parts of sodium carboxymethyl cellulose and 97.5 parts of deionized water are mixed uniformly in a kettle stirrer at 50℃ for 6 h to form a polymer solution, and then vacuum degassing for 1 h to obtain the polymer solution for preparing coating layer;

[0079] 2) Preparation of flat sheet membrane: using double doctor blade, the coating layer polymer solution and the film forming polymer solution obtained in step 1) are simultaneously flowed out through the liquid tank containing doctor blade with thickness of 0.2 mm at 60 ℃, so that the film forming polymer solution is coated on the plastic film substrate of polyethylene terephthalate with thickness of 0.4 mm, and the coating layer polymer solution is coated on the film forming polymer solution to form the shape of flat sheet membrane; the coating layer polymer solution and the film forming polymer solution are simultaneously passed through the air gap with length of 30 cm at winding speed of 4 m / min, and then enter the coagulation bath composed of deionized water at room temperature, cooled by deionized water at certain temperature, and the obtained nascent membrane is extracted with deionized water at 25 ℃ to extract the solvent and pore-forming agent, and after extraction for 2 times, the flat sheet membrane product is obtained after drying in the shade.

[0080] It is determined (the test method is "Ultrafiltration Membrane Test Method" (GB / T 32360-2015)) that the cross section of the membrane is sponge hole, the cut-off molecular weight is 10 kDa, and the flux recovery rate is 97.2% (1 g / L bovine serum protein solution, pH = 7.4); the pore size of the membrane without coating layer is 47 nm, the cross section is finger hole, and the flux recovery rate is 44.8%.

[0081] Example 3

[0082] Preparation of film forming polymer solution: 20 parts of fluorine-containing polymer with oven-dried weight average molecular weight of 700 kDa, 5 parts of oven-dried polyvinylpyrrolidone with molecular weight of 30 kDa, and 75 parts of N,N-dimethylacetamide are uniformly mixed in a kettle stirrer at 50 ℃ for 10 h to form a polymer solution, and then vacuum degassing is performed for 1 h to obtain a polymer solution for preparing a polymer membrane;

[0083] Preparation of coating layer polymer solution: 2 parts of sodium alginate and 98 parts of deionized water are uniformly mixed in a kettle stirrer at 50 ℃ for 6 h to form a polymer solution, and then vacuum degassing is performed for 1 h to obtain a polymer solution for preparing a coating layer;

[0084] 2) Preparation of flat sheet membrane: using double doctor blade, the coating layer polymer solution and the film forming polymer solution obtained in step 1) are simultaneously flowed out through the liquid tank containing doctor blade with thickness of 0.2 mm at 50 ℃, so that the film forming polymer solution is coated on the plastic film substrate of polyethylene terephthalate with thickness of 0.4 mm, and the coating layer polymer solution is coated on the film forming polymer solution to form the shape of flat sheet membrane; the coating layer polymer solution and the film forming polymer solution are simultaneously passed through the air gap with length of 60 cm at winding speed of 3 m / min, and then enter the coagulation bath composed of deionized water at room temperature, cooled by deionized water at certain temperature, and the obtained nascent membrane is extracted with deionized water at 25 ℃ to extract the solvent and pore-forming agent, and after extraction for 2 times, the flat sheet membrane product is obtained after drying in the shade;

[0085] The membrane has sponge pores, a molecular weight cut-off of 220 kDa, and a flux recovery rate of 89.2% (1 g / L bovine serum albumin solution, pH = 7.4); the membrane without the coating layer has a pore size of 69 nm, finger-shaped pores, and a flux recovery rate of 43.5%.

[0086] Example 4

[0087] Preparation of the film-forming polymer solution: 20 parts of the fluorine-containing polymer with a weight average molecular weight of 700 kDa after drying, 5 parts of polyvinylpyrrolidone with a weight average molecular weight of 30 kDa after drying, and 75 parts of N-methylpyrrolidone were mixed uniformly in a kettle stirrer at 50°C for 10 h to obtain a polymer solution for preparing a polymer film, and then vacuum degassing was performed for 1 h;

[0088] Preparation of the coating polymer solution: 2 parts of hydroxyethyl methacrylate and 98 parts of ethanol were mixed uniformly in a kettle stirrer at 50°C for 6 h to obtain a polymer solution for preparing a coating layer, and then vacuum degassing was performed for 1 h;

[0089] 2) Preparation of the flat sheet membrane: the coating polymer solution and the film-forming polymer solution obtained in step 1) were simultaneously discharged through a liquid tank containing a doctor blade with a thickness of 0.2 mm at 50°C, so that the film-forming polymer solution was coated on a plastic film substrate of polyethylene terephthalate with a thickness of 0.4 mm, and the coating polymer solution was coated on the film-forming polymer solution, to form a flat sheet membrane; the coating polymer solution and the film-forming polymer solution were simultaneously passed through an air gap with a length of 50 cm at a winding speed of 3 m / min, and then entered a coagulation bath composed of deionized water at room temperature, and the obtained nascent membrane was cooled by deionized water at a certain temperature, and then the solvent and the pore-forming agent were extracted from the nascent membrane by deionized water at 25°C, and the extraction was performed twice, and then the nascent membrane was dried in the shade to obtain a flat sheet membrane product;

[0090] The membrane has sponge pores, a molecular weight cut-off of 310 kDa, and a flux recovery rate of 92.5% (1 g / L bovine serum albumin solution, pH = 7.4); the membrane without the coating layer has a pore size of 71 nm, finger-shaped pores, and a flux recovery rate of 42.7%.

[0091] Comparative Example 1

[0092] The same as in Example 1, except that no synchronous coating was performed, and the details are as follows:

[0093] 1) Preparation of the polymer solution:

[0094] Preparation of the film-forming polymer solution: 26 parts by mass of a fluorine-containing polymer having a weight average molecular weight of 900 kDa after drying, 8 parts by mass of polyvinylpyrrolidone having a weight average molecular weight of 45 kDa after drying, and 66 parts by mass of N,N-dimethylacetamide were mixed uniformly in a kettle stirrer at 70°C for 10 h to obtain a polymer solution, which was then vacuum degassed for 1 h to obtain a polymer solution for preparing a polymer film;

[0095] 2) Preparation of flat sheet membrane: using a single doctor blade, the film-forming polymer solution obtained in step 1) was made to flow out of a liquid tank containing a doctor blade having a thickness of 0.2 mm at 60°C, so that the film-forming polymer solution was coated on a plastic film substrate of polyethylene terephthalate having a thickness of 0.4 mm to form a flat sheet membrane shape; the film-forming polymer solution was passed through an air gap having a length of 30 cm at a winding speed of 4 m / min, and then entered a coagulation bath composed of deionized water at room temperature, and was cooled by deionized water at a certain temperature; the resulting nascent membrane was extracted with deionized water at 25°C to remove the solvent and pore-forming agent, and was extracted twice and then dried in the shade to obtain a flat sheet membrane product;

[0096] The surface morphology of the membrane is shown in Figure 2 The membrane without a coating layer has a pore size of 47 nm, as shown in Figure 4 The cross-section is a finger-shaped hole, and the flux recovery rate is 44.8%.

[0097] It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and are considered to be included in the spirit, scope and content of the present application. For example, changing the type of coating layer material, the type of polymer or diluent, the spinning temperature, the type and temperature of the quenching bath, the temperature and length of the air gap, different membrane shapes such as flat sheet, hollow fiber, tube, etc., and composite membranes scraped on high-temperature-resistant non-woven fabrics, etc.

[0098] The above only describes embodiments of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation using the content of the present application specification, or direct or indirect use of other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. A method for preparing a charged hydrophilic polymer porous membrane, characterized by, The application relates to a method for preparing a charged hydrophilic polymer porous membrane. The coating layer polymer solution is negatively charged and has a viscosity of 800-3000 mPa.s; The coating layer polymer solution comprises a negatively charged water-soluble polymer containing carboxyl and hydroxyl, and the negatively charged water-soluble polymer is selected from at least one of polyhydroxyethyl methacrylate, sodium alginate and sodium carboxymethyl cellulose; The mass ratio of the fluorine-containing polymer, the pore-forming agent and the first solvent in the film-forming polymer solution is 18-26:3-8:66-79; the fluorine-containing polymer is a homopolymer or copolymer of polyvinylidene fluoride with a weight average molecular weight of 700-900 kDa. The coating layer polymer solution and the film-forming polymer solution are simultaneously discharged through the liquid trough of the scraper.

2. The method of claim 1, wherein the method further comprises the step of: The mass fraction of the negatively charged water-soluble polymer in the coating layer polymer solution is 1-2.5%.

3. The method of claim 1, wherein the method further comprises the step of: The coating layer polymer solution comprises the negatively charged water-soluble polymer and a second solvent, and the second solvent is water or ethanol which can dissolve the negatively charged water-soluble polymer but cannot dissolve the fluorine-containing polymer.

4. The method of claim 1, wherein the hydrophilic porous membrane is a hydrogel- forming membrane. The first solvent in the film-forming polymer solution is N,N-dimethylacetamide or N-methylpyrrolidone, and the pore-forming agent is polyvinylpyrrolidone with a molecular weight of 30-45 kDa.

5. The method of claim 1, wherein the method further comprises the step of: The application relates to a method for preparing a charged hydrophilic polymer porous membrane. S1, uniformly mixing fluorine-containing polymer, the pore-forming agent and the first solvent at 50-70 DEG C, and vacuum degassing to obtain the film-forming polymer solution for preparing a polymer membrane; S2, uniformly mixing the negatively charged water-soluble polymer and a second solvent at 50 DEG C, and vacuum degassing to obtain the coating layer polymer solution for preparing a coating layer; S3, using double scrapers, simultaneously discharging the coating layer polymer solution and the film-forming polymer solution through the liquid troughs of the scrapers with a thickness of 0.2 mm at 50-60 DEG C, so that the film-forming polymer solution is coated on a plastic film substrate of polyethylene terephthalate with a thickness of 0.4 mm, and the coating layer polymer solution is coated above the film-forming polymer solution, forming a flat membrane shape, and then cooling and solidifying to form a membrane; S4, immersing and washing the membrane in a deionized water extracting agent at 25 DEG C to obtain the charged hydrophilic polymer porous membrane.

6. The method of claim 5, wherein the hydrophilic porous membrane is a hydrogel- forming membrane. The air gap length in S3 is 30-60 cm, and the scraping rate is 2-4 m / min.

7. The charged hydrophilic porous polymer membrane prepared according to the method of any one of claims 1-6, wherein, The charged hydrophilic polymer porous membrane is a flat membrane, the pore size of the flat membrane is 5-100 nm, and the cutting molecular weight is 10-1000 kDa.

8. Application of the charged hydrophilic polymer porous membrane according to claim 7 in polysaccharide concentration and purification in Chinese herbal medicines.

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