Composite film and preparation method thereof

Abstract

The invention relates to the technical field of composite membrane materials, in particular to a composite membrane and a preparation method thereof. The composite membrane comprises a fluorine-containing polymer membrane, a styrene-maleic anhydride copolymer layer is deposited on the surface of the fluorine-containing polymer membrane to form a fiber membrane, and polysaccharide is crosslinked on the surface of the styrene-maleic anhydride copolymer layer; the molecular weight of the polysaccharide is 342-1120Da, the thickness of the fiber membrane is equal to or greater than 0.3 mm, and the removal rate of silicate on the surface of the composite membrane is 84-94%. Therefore, the problems that pollutants in sewage are easily attached to the filter membrane and the filter membrane is not easy to clean are solved, and the filter membrane disclosed by the invention has a retarding effect on silicate inorganic matters, so that the silicate inorganic matters form a loose pollution layer on the surface of the filter membrane, and the pollution layer is easy to clean.

Description

Technical Field

[0001] The present invention relates to the technical field of composite membrane materials, in particular to a composite membrane and a preparation method thereof. Background Art

[0002] Membrane separation technology has been developed in recent years as a high-precision separation technology. Fluoropolymers, represented by polyvinylidene fluoride, are currently widely used to prepare porous membranes and are widely used in water treatment, biopurification, the electronics industry, and membrane contactors. Prerequisites for the practical value of water treatment membranes are that the membrane has good anti-fouling properties and is effective in removing pollutants after cleaning. The more hydrophilic the membrane surface is, the more pollutants form a loose scale layer with weak adhesion to the membrane surface, and the less likely the fouling layer is to adhere to the membrane surface and harden. Grafting suitable hydrophilic groups on the membrane surface is a convenient means to achieve the above goals. Non-solvent-induced phase separation technology and thermally induced phase separation technology are currently commonly used technologies for preparing polymer porous membranes. Compared with non-solvent-induced phase separation technology, thermally induced phase separation technology has the advantages of easy control of pore structure, high membrane mechanical properties, and a convenient preparation process. It is particularly suitable for the preparation of polymer porous membranes without solvents at room temperature.

[0003] Silicates are ubiquitous in natural water bodies, both surface and underground. These water bodies are weakly acidic to alkaline, with a pH of 6-8. Due to their strong adhesion, silicates are easily adsorbed, deposited, and hardened on membrane surfaces during long-term membrane water treatment processes, ultimately becoming irreversibly contaminated inorganic foulants. This in turn leads to reduced flux and shortened membrane life. Since inorganic silicate foulants are insoluble in acids and alkalis and strongly adhere to the membrane surface, they are difficult to clean with simple water, making membrane fouling a particularly prominent problem.

[0004] The membrane formation principle of thermally induced phase separation technology is: a polymer and a specific diluent are formed into a polymer solution at high temperature. When the temperature drops to a certain level, the polymer solution undergoes solid-liquid or liquid-liquid phase separation. After the diluent is extracted, the space occupied by the diluent in the system forms micropores.

[0005] Fluoropolymers are often used to prepare wastewater treatment membranes. Moreover, polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) in fluoropolymers easily entangles with styrene-maleic anhydride copolymer (SMA) chains, preventing SMA from falling off. SMA is deposited on the surface of PVDF, causing the membrane surface to be loaded with reactive groups such as maleic anhydride (MA).

[0006] In the construction industry, sugar is used as a retarder for Portland cement. Sugar slows down the hydration process of Portland cement through various actions, including adsorption, complex salt formation, control of calcium hydroxide crystal growth, and formation of a solvated water film, thereby disrupting the hardening of the cement. Summary of the Invention

[0007] In order to solve the problem that pollutants in sewage are easily attached to the filter membrane and the filter membrane is not easy to be cleaned, the present invention provides a composite membrane and a preparation method thereof.

[0008] According to a first aspect of the present invention, the present invention provides a composite film comprising:

[0009] A fluoropolymer membrane, wherein a styrene-maleic anhydride copolymer layer is deposited on the surface of the fluoropolymer membrane to form a fiber membrane, and the surface of the styrene-maleic anhydride copolymer layer is cross-linked with polysaccharide;

[0010] The molecular weight of the polysaccharide is 342 to 1120 Da, the thickness of the fiber membrane is equal to or greater than 0.3 mm, and the silicate removal rate on the surface of the composite membrane is 84% to 94%.

[0011] Preferably, the molecular weight of the polysaccharide is 342-505 Da.

[0012] Preferably, the polysaccharide comprises sucrose, raffinose or maltose.

[0013] Preferably, the fluoropolymer membrane is a fluoropolymer hollow membrane, a styrene-maleic anhydride copolymer layer is deposited on the surface of the fluoropolymer hollow membrane to form a hollow fiber membrane, the thickness of the hollow fiber membrane is 0.3 to 0.4002 mm, the thickness of the fluoropolymer hollow membrane is 0.3 to 0.4 mm, and the thickness of the styrene-maleic anhydride copolymer layer is 100 to 200 nm.

[0014] Preferably, the outer diameter of the obtained hollow fiber membrane is 1.2 to 1.3 mm, and the inner diameter is 0.6 to 0.7 mm.

[0015] Preferably, the pore size of the composite membrane is 20-29 nm, and the porosity is 70%-75%.

[0016] Preferably, the fluorine-containing polymer comprises a homopolymer or copolymer of polyvinylidene fluoride.

[0017] Preferably, the weight average molecular weight of the fluorine-containing polymer is 500-700 kDa, the weight average molecular weight of the styrene-maleic anhydride copolymer is 100-120 kDa, and the content of maleic anhydride in the styrene-maleic anhydride copolymer is 20-25%.

[0018] According to a second aspect of the present invention, the present invention provides a method for preparing the above-mentioned composite membrane, comprising the following steps:

[0019] The fluorine-containing polymer and the styrene-maleic anhydride copolymer are blended and then phase-separated to obtain a fiber membrane. The styrene-maleic anhydride copolymer on the surface of the fiber membrane is modified and then cross-linked with a polysaccharide by a cross-linking agent to obtain a composite membrane.

[0020] Preferably, the step of phase separation of the fluoropolymer and the styrene-maleic anhydride copolymer comprises: mixing the fluoropolymer, the styrene-maleic anhydride copolymer, a diluent and an antioxidant at a temperature of 170-180° C., extruding and granulating the mixture through an extruder to obtain mixture particles;

[0021] The mixture particles are sequentially melted, spun and cooled to obtain primary membrane fibers;

[0022] The diluent in the primary membrane fibers is removed by an extractant to obtain a fiber membrane with a hollow structure.

[0023] Preferably, the diluent comprises diethyl sebacate, γ-butyrolactone, sulfolane or tributyl citrate;

[0024] The antioxidant includes β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate;

[0025] The extractant includes ethanol.

[0026] Preferably, the step of modifying the styrene-maleic anhydride copolymer on the upper surface of the fiber membrane comprises: immersing the fiber membrane in a solution containing a catalyst and a diol-containing modifier at a temperature of 50 to 65° C. for 1 to 4 hours.

[0027] Preferably, the step of cross-linking the polysaccharide with a cross-linking agent comprises: immersing the fiber membrane with the modified styrene-maleic anhydride copolymer on the surface in an aqueous solution containing a dialdehyde cross-linking agent at a temperature of 50-60°C for 20-40 minutes under acidic conditions of pH 2-4.

[0028] Preferably, the glycol-containing modifier comprises polyethylene glycol or triethylene glycol.

[0029] Preferably, the step of cross-linking the polysaccharide with a cross-linking agent comprises: soaking the fiber membrane containing the cross-linking agent in an aqueous solution containing polysaccharide at a temperature of 50-60° C. for 1-2 hours under acidic conditions of pH 2-4 to obtain a composite membrane.

[0030] Preferably, the dialdehyde-containing cross-linking agent includes glutaraldehyde or succinaldehyde.

[0031] Preferably, the mass ratio of the fluorine-containing polymer, the styrene-maleic anhydride copolymer, the diluent and the antioxidant is 25-30:5-10:49.5-64.9:0.1-0.5.

[0032] The principles upon which the present invention is based are as follows:

[0033] (1) When preparing the "fluoropolymer / styrene-maleic anhydride copolymer" ultrafiltration membrane using the thermally induced phase separation technology, the different solidification and precipitation temperatures of styrene-maleic anhydride and fluoropolymer in the diluent coagulation bath (usually water) during the cooling process are utilized to make the fluoropolymer solidify and precipitate from the diluent first during the cooling process, while the other styrene-maleic anhydride copolymer solidifies and precipitates from the diluent during the subsequent extraction and continuously deposits on the surface of the fluoropolymer hollow membrane, thereby loading the membrane surface with anhydride functional groups with reactive effects. The anhydride on the membrane surface is then used to react with polyethylene glycol, glutaraldehyde, and a polysaccharide with a retarding effect on silicate inorganic substances in turn, thereby loading the membrane surface with a polysaccharide with a retarding effect on silicate inorganic substances. When the styrene-maleic anhydride copolymer blending amount is appropriate, due to the certain compatibility between the styrene-maleic anhydride copolymer and the fluoropolymer, the two polymer long chains at the interface are firmly physically entangled with each other, so that the styrene-maleic anhydride copolymer does not fall off.

[0034] (2) The polysaccharide molecular chains that have a slow-setting effect on silicate fouling not only improve the hydrophilicity of the membrane, but also slow down the adsorption and deposition of silicate inorganic fouling on the membrane surface. Moreover, the slow-setting effect of the polysaccharide molecular chains on silicate fouling makes it difficult for the sediment to further harden on the membrane surface and develop into irreversible fouling. Instead, it forms reversible fouling with only a weak binding force and a loose structure on the membrane surface. It can be easily washed away by the raw liquid or washing water of the cross-flow operation, so that silicate fouling can be effectively removed. Therefore, by grafting the hydrophilic long-chain polysaccharide groups that have a slow-setting effect on silicate fouling on the membrane surface, it is possible to prepare a polymer ultrafiltration membrane with high efficiency and resistance to silicate inorganic fouling. In addition, it also has the following characteristics:

[0035] 1) Requirements for polymer content, molecular weight, and ratio are required to ensure the membrane has good mechanical properties and ultrafiltration membrane characteristics, the appropriate density of maleic anhydride functional groups on the membrane surface, and that the styrene-maleic anhydride copolymer does not detach. The total polymer content (fluoropolymer + SMA) should be between 30-40%, including 25-30 parts of fluoropolymer with a weight-average molecular weight of 500-700 kDa and 5-10 parts of styrene-maleic anhydride copolymer with a weight-average molecular weight of 100-120 kDa and a maleic anhydride ratio of 20%-25% in the styrene-maleic anhydride copolymer.

[0036] 2) Requirements for the diluent: the diluent is one of diethyl sebacate, γ-butyrolactone, cyclopentane, and tributyl citrate, which is soluble in ethanol but insoluble in water and cannot dissolve styrene-maleic anhydride copolymer at room temperature.

[0037] 3) Requirements for grafting conditions. Since it is difficult to directly graft hydroxyl-containing polysaccharides on the surface of fluoropolymer hollow membranes, it is necessary to first introduce acid anhydrides on the surface of fluoropolymer hollow membranes, and then the acid anhydrides undergo a ring-opening grafting reaction with polyethylene glycol under anhydrous conditions, and then undergo aldol condensation and aldehyde group-polysaccharide grafting reaction in sequence to graft the polysaccharide with retarding effect onto the membrane surface.

[0038] 4) The retarding effect of the membrane is related to the grafting degree and the molecular weight of the grafted polysaccharide. The preferred styrene-maleic anhydride copolymer has a weight-average molecular weight of 100-120 kDa and a maleic anhydride content of 20%-25%. The preferred addition level is 5-10 parts per million. If the addition level is too high, interfacial defects increase, reducing the retention effect. Furthermore, a thick styrene-maleic anhydride copolymer layer forms on the membrane surface, causing it to fall off. If the addition level is too low, the surface maleic anhydride density is too low, the grafted polysaccharide content is too low, and the retarding effect is ineffective.

[0039] 5) Polysaccharides are polysaccharides with good retarding effect, such as sucrose, raffinose, and maltose.

[0040] 6) The core liquid used in spinning is hot high-purity nitrogen at 100-120°C rather than other liquid organic solvents.

[0041] 7) The extractant is ethanol at 25-40°C, which further improves the pressure resistance of the membrane fibers and ensures that the membrane fibers can withstand a pressure of 4 bar after external pressure testing.

[0042] The present invention has the following beneficial effects:

[0043] 1. The present invention achieves different solidification and precipitation temperatures of the blended polymers during the cooling process of the diluent, so that the fluorine-containing polymer solidifies and precipitates from the diluent first during the cooling process, while the other polymer solidifies and precipitates from the diluent later and is deposited on the surface of the fluorine-containing polymer hollow membrane, thereby loading the membrane surface with anhydride functional groups with reactive efficacy, increasing the density of the reactive functional groups anhydride on the membrane surface, and thereby improving the subsequent grafting density.

[0044] 2. The present invention has a slow-coagulation effect on silicate fouling by grafting polysaccharide molecular chains on the membrane, making it difficult for the sediment to further harden on the membrane surface and develop into irreversible fouling. Instead, it forms reversible fouling with a loose structure that has only weak binding force with the membrane surface. It can be easily washed away by the raw liquid or washing water of the cross-flow operation, so that silicate fouling can be effectively removed. The composite membrane filter flux recovery rate reaches 93.4%.

[0045] 3. The composite membrane of the present invention not only has a strong hydrophilicity on the membrane surface to slow down the adsorption and deposition of pollutants on the membrane surface, but also can effectively prevent the inorganic dirt from becoming dense and hardened and turning into irreversible pollution, and finally makes the inorganic dirt have a loose structure and the force between the membrane surface and the inorganic dirt is weakened.

[0046] 4. The composite membrane of the present invention has good adaptability, is suitable for promotion and application, and has good industrialization prospects. The composite membrane preparation method of the present invention is simple and easy to implement, the material source is widely available, the cost is low, and the anti-silicate pollution effect is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Shows an SEM image of the hollow fiber membrane of the present invention;

[0048] Figure 2 The SEM image of the polysaccharide composite membrane ultrafiltration membrane of the present invention is shown. DETAILED DESCRIPTION

[0049] The present disclosure will now be discussed with reference to several exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the present disclosure, rather than to imply any limitation on the scope of the present disclosure.

[0050] As used herein, the term "including" and its variations are to be interpreted as open-ended terms meaning "including but not limited to." The term "based on" is to be interpreted as "based at least in part on." The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment." The term "another embodiment" is to be interpreted as "at least one other embodiment." In addition, the terms "first," "second," etc. are primarily used to distinguish different devices, elements, or components (the specific types and configurations may be the same or different), and are not intended to indicate or imply the relative importance and quantity of the indicated devices, elements, or components. Unless otherwise specified, "plurality" means two or more.

[0051] According to a first aspect of the present invention, this embodiment provides a composite film, comprising:

[0052] A fluoropolymer membrane, wherein a styrene-maleic anhydride copolymer layer is deposited on the surface of the fluoropolymer membrane to form a fiber membrane, and the surface of the styrene-maleic anhydride copolymer layer is cross-linked with polysaccharide;

[0053] The molecular weight of the polysaccharide is 342 to 1120 Da, the thickness of the fiber membrane is equal to or greater than 0.3 mm, and the silicate removal rate on the surface of the composite membrane is 84% to 94%.

[0054] Preferably, the molecular weight of the polysaccharide is 342-505 Da.

[0055] Preferably, the polysaccharide comprises sucrose, raffinose or maltose.

[0056] Preferably, the molecular weight of sucrose is 342.3 Da, the molecular weight of raffinose is 360.3 Da, and the molecular weight of maltose is 504.5 Da.

[0057] Preferably, the fluoropolymer membrane is a fluoropolymer hollow membrane, a styrene-maleic anhydride copolymer layer is deposited on the surface of the fluoropolymer hollow membrane to form a hollow fiber membrane, the thickness of the hollow fiber membrane is 0.3 to 0.4002 mm, the thickness of the fluoropolymer hollow membrane is 0.3 to 0.4 mm, and the thickness of the styrene-maleic anhydride copolymer layer is 100 to 200 nm.

[0058] Preferably, the outer diameter of the obtained hollow fiber membrane is 1.2 to 1.3 mm, and the inner diameter is 0.6 to 0.7 mm.

[0059] Preferably, the pore size of the composite membrane is 20-29 nm, and the porosity is 70%-75%.

[0060] Preferably, the fluorine-containing polymer comprises a homopolymer or copolymer of polyvinylidene fluoride.

[0061] Preferably, the weight average molecular weight of the fluorine-containing polymer is 500-700 kDa, the weight average molecular weight of the styrene-maleic anhydride copolymer is 100-120 kDa, and the content of maleic anhydride in the styrene-maleic anhydride copolymer is 20-25%.

[0062] Preferably, the weight average molecular weight of the fluorine-containing polymer is 500 kDa, the weight average molecular weight of the styrene-maleic anhydride copolymer is 120 kDa, and the content of maleic anhydride in the styrene-maleic anhydride copolymer is 25%.

[0063] According to the second aspect of the present invention, this embodiment provides a method for preparing the above-mentioned composite membrane, comprising the following steps:

[0064] The fluorine-containing polymer and the styrene-maleic anhydride copolymer are blended and then phase-separated to obtain a fiber membrane. The styrene-maleic anhydride copolymer on the surface of the fiber membrane is modified and then cross-linked with a polysaccharide by a cross-linking agent to obtain a composite membrane.

[0065] In this embodiment, the requirements for preparing the composite membrane are relatively low, and the grafted polymer has strong hydrophilicity and significant pH responsiveness.

[0066] Preferably, the step of phase separation of the fluorine-containing polymer and the styrene-maleic anhydride copolymer comprises:

[0067] The fluorine-containing polymer, styrene-maleic anhydride copolymer, diluent and antioxidant are mixed at a temperature of 170-180° C., and then extruded and granulated by an extruder to obtain mixture particles;

[0068] The mixture particles are sequentially melted, spun and cooled to obtain primary membrane fibers;

[0069] The diluent in the primary membrane fibers is removed by an extractant to obtain a fiber membrane with a hollow structure.

[0070] In this embodiment, the primary membrane filaments prepared by spinning have a hollow structure, and then a fiber membrane with a hollow structure is obtained subsequently. The thickness of the fluoropolymer is 0.3-0.4 mm; the thickness of the thin deposition layer of styrene-maleic anhydride copolymer is 100-200 nm; in the straightened state, the total length of the diol-containing modifier, the dialdehyde-containing cross-linking agent and the polysaccharide does not exceed 0.2 μm.

[0071] In some embodiments, the primary membrane filaments can be prepared as flat plates or other non-hollow structures, so that the subsequently obtained fiber membranes are also flat plates or other non-hollow structures, that is, the present invention can also prepare other types of membranes through fluoropolymers, styrene-maleic anhydride copolymers and polysaccharides.

[0072] Preferably, the diluent comprises diethyl sebacate, γ-butyrolactone, sulfolane or tributyl citrate;

[0073] The antioxidant includes β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate;

[0074] The extractant includes ethanol.

[0075] Preferably, the step of modifying the styrene-maleic anhydride copolymer on the upper surface of the fiber membrane includes: immersing the fiber membrane in a solution containing a catalyst and a diol-containing modifier at a temperature of 50 to 65°C for 1 to 4 hours to obtain a fiber membrane containing a styrene-maleic anhydride copolymer and a diol-containing modifier binary copolymer.

[0076] Preferably, the fiber membrane is immersed in a solution containing a catalyst and a diol-containing modifier at a temperature of 65° C. for 1 hour.

[0077] Preferably, the glycol-containing modifier comprises polyethylene glycol or triethylene glycol.

[0078] Preferably, the polyethylene glycol includes polyethylene glycol 200 or polyethylene glycol 400.

[0079] Preferably, the catalyst comprises triethylamine.

[0080] Preferably, the step of cross-linking the polysaccharide with a cross-linking agent comprises: immersing the fiber membrane with the modified styrene-maleic anhydride copolymer on the surface in an aqueous solution containing a dialdehyde-containing cross-linking agent at a temperature of 50 to 60°C for 20 to 40 minutes under acidic conditions of pH 2 to 4, to obtain a fiber membrane containing a ternary copolymer of styrene-maleic anhydride copolymer, a diol-containing modifier and a dialdehyde-containing cross-linking agent.

[0081] Preferably, the fiber membrane with the modified styrene-maleic anhydride copolymer on the surface is immersed in an aqueous solution containing a dialdehyde-containing cross-linking agent at a temperature of 60° C. for 20 minutes.

[0082] Preferably, the step of cross-linking the fiber membrane with the polysaccharide by a cross-linking agent comprises: soaking the fiber membrane containing the cross-linking agent in an aqueous solution containing polysaccharide at a temperature of 50-60°C for 1-2 hours under acidic conditions of pH 2-4 to obtain a composite membrane with polysaccharide grafted on the surface.

[0083] Preferably, the fiber membrane containing the cross-linking agent is immersed in an aqueous solution containing polysaccharide at a temperature of 50° C. for 2 hours.

[0084] Preferably, the dialdehyde-containing cross-linking agent includes glutaraldehyde or succinaldehyde.

[0085] Preferably, the mass ratio of the fluorine-containing polymer, the styrene-maleic anhydride copolymer, the diluent and the antioxidant is 25-30:5-10:49.5-64.9:0.1-0.5.

[0086] Preferably, the mass ratio of the fluorine-containing polymer, the styrene-maleic anhydride copolymer, the diluent and the antioxidant is 30:5-10:59.9-64.9:0.1.

[0087] Preferably, the mass ratio of the fluorine-containing polymer, the styrene-maleic anhydride copolymer, the diluent and the antioxidant is 30:10:59.9:0.1.

[0088] In the present invention, styrene-maleic anhydride copolymer (SMA) and polyethylene glycol (PEG) are reacted under the catalysis of triethylamine (TEA) to obtain SMA-PEG binary copolymer, and the reaction equation is shown in formula (1).

[0089] Formula (1):

[0090] .

[0091] The SMA-PEG binary copolymer reacts with glutaraldehyde (GA) to obtain the SMA-PEG-GA ternary copolymer, and the reaction equation is shown in formula (2).

[0092] Formula (2):

[0093] .

[0094] The SMA-PEG-GA ternary copolymer reacts with raffinose to obtain a surface-grafted raffinose polysaccharide ultrafiltration membrane with a slow-coagulation effect on silicate inorganic substances. The reaction equation is shown in Equation (3).

[0095] Formula (3):

[0096] .

[0097] The SMA-PEG-GA ternary copolymer reacts with sucrose to obtain a surface-grafted sucrose polysaccharide ultrafiltration membrane with a slow-coagulation effect on silicate inorganic substances. The reaction equation is shown in Equation (4).

[0098] Formula (4):

[0099] .

[0100] Example 1

[0101] A method for preparing a polymer ultrafiltration membrane with high efficiency and resistance to silicate inorganic fouling comprises the following steps:

[0102] 1) 25 parts by mass of polyvinylidene fluoride having a weight-average molecular weight of 700 kDa, 10 parts of styrene-maleic anhydride copolymer having a weight-average molecular weight of 120 kDa (the maleic anhydride content in the styrene-maleic anhydride copolymer being 25%), and 0.1 part of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate were dried separately, and then thoroughly mixed with 64.9 parts of diethyl sebacate in a mixer (700 rpm for 10 minutes). The mixture was then extruded through an extruder (a twin-screw extruder with a length-to-diameter ratio of 40 and a temperature of 170°C), and cooled in air to obtain mixture pellets;

[0103] 2) The core liquid used for spinning is hot high-purity nitrogen at 100°C, with a flow rate of 2.5 L / h. The resulting material pellets are melted and then spun through an extruder at 170°C at a flow rate of 8 L / h. After passing through a 5 cm air gap, they enter a coagulation bath consisting of deionized water, are cooled with deionized water, and wound into filaments (winding speed of 30 m / min). The resulting nascent membrane filaments are extracted with ethanol with a purity of not less than 99% at 40°C for 1 hour to remove the diluent. After two extraction cycles, a hollow fiber membrane with an outer diameter of 1.3 mm and an inner diameter of 0.7 mm is obtained.

[0104] 3) The hollow fiber membrane was immersed in a 0.1 g triethylamine catalyst + 25 g polyethylene glycol (PEG) 200 solution and reacted at 65°C for 1 hour. After washing with water, the hollow fiber membrane grafted with PEG200 was immersed in a 0.5% dilute H2SO4 and 4% glutaraldehyde (GA) aqueous solution and reacted at 60°C for 20 minutes. After washing with water, the hollow fiber membrane was immersed in a 0.2% dilute H2SO4 raffinose aqueous solution and reacted at 50°C for 1 hour. The membrane was then removed to obtain a surface-grafted raffinose polysaccharide composite membrane ultrafiltration membrane having a retarding effect on silicate inorganic substances.

[0105] Example 2

[0106] A method for preparing a polymer ultrafiltration membrane with high efficiency and resistance to silicate inorganic fouling comprises the following steps:

[0107] 1) Calculated by mass, 30 parts of polyvinylidene fluoride having a weight-average molecular weight of 700 kDa, 10 parts of styrene-maleic anhydride copolymer having a weight-average molecular weight of 120 kDa (the maleic anhydride content in the styrene-maleic anhydride copolymer being 25%), and 0.1 parts of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid octadecyl were dried separately, and then thoroughly mixed with 59.9 parts of sulfolane in a mixer (700 rpm, time 10 min), and then extruded through an extruder (the extruder was a twin-screw extruder with a length-to-diameter ratio of 40, temperature 180°C), and cooled in air to granulate to obtain mixture pellets;

[0108] 2) The core liquid used for spinning was hot, high-purity nitrogen at 120°C, with a flow rate of 2.5 L / h. The resulting granules were melted and then spun through an extruder at 180°C at a flow rate of 0.8 L / h. After passing through a 5 cm air gap, they entered a coagulation bath consisting of deionized water, were cooled with deionized water, and wound into filaments (at a winding speed of 30 m / min). The resulting nascent membrane filaments were extracted with ethanol (at a purity of not less than 99%) at 40°C for 1 hour to remove the diluent. After two extraction cycles, a hollow fiber membrane with an outer diameter of 1.3 mm and an inner diameter of 0.7 mm was obtained.

[0109] 3) The hollow fiber membrane was immersed in a 0.1g triethylamine catalyst + 25g PEG200 solution and reacted at 65°C for 1 hour. After washing with water, the hollow fiber membrane grafted with PEG200 was immersed in a 0.5% dilute H2SO4 and 4% GA aqueous solution and reacted at 60°C for 20 minutes. After washing with water, the hollow fiber membrane was immersed in a 0.5% dilute H2SO4 raffinose aqueous solution and reacted at 50°C for 1 hour to obtain a surface-grafted raffinose polysaccharide composite membrane ultrafiltration membrane with a retarding effect on silicate inorganic substances.

[0110] Example 3

[0111] A method for preparing a polymer ultrafiltration membrane with high efficiency and resistance to silicate inorganic fouling comprises the following steps:

[0112] 1) Calculated by mass, 30 parts by weight of a polyvinylidene fluoride-hexafluoropropylene copolymer having a weight-average molecular weight of 500 kDa, 10 parts by weight of a styrene-maleic anhydride copolymer having a weight-average molecular weight of 120 kDa (the maleic anhydride content in the styrene-maleic anhydride copolymer being 25%), and 0.1 parts by weight of octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate were dried separately, and then thoroughly mixed with 59.9 parts by weight of tributyl citrate in a mixer (700 rpm for 10 minutes). The mixture was then extruded through an extruder (a twin-screw extruder having a length-to-diameter ratio of 40 and a temperature of 170°C), and cooled in air to obtain mixture pellets.

[0113] 2) The core liquid used for spinning was hot, high-purity nitrogen at 100°C, with a flow rate of 1.5 L / h. The resulting granules were melted and then spun through an extruder at 170°C at a flow rate of 0.8 L / h. After passing through a 5 cm air gap, they entered a coagulation bath consisting of deionized water, were cooled with deionized water, and wound into filaments (at a winding speed of 30 m / min). The resulting nascent membrane filaments were extracted with ethanol (at a purity of not less than 99%) at 25°C for 1 hour to remove the diluent. After two extraction cycles, a hollow fiber membrane with an outer diameter of 1.2 mm and an inner diameter of 0.6 mm was obtained.

[0114] 3) The hollow fiber membrane was immersed in a 0.1g triethylamine catalyst + 25g PEG200 solution and reacted at 65°C for 1h. After washing with water, the hollow fiber membrane grafted with PEG200 was immersed in a 0.5% dilute H2SO4 and 4% GA aqueous solution and reacted at 60°C for 20min. After washing with water, the hollow fiber membrane was immersed in a 0.5% dilute H2SO4 maltose aqueous solution and reacted at 50°C for 2h to obtain a surface-grafted maltose polysaccharide composite membrane ultrafiltration membrane with a retarding effect on silicate inorganic substances.

[0115] Example 4

[0116] A method for preparing a polymer ultrafiltration membrane with high efficiency and resistance to silicate inorganic fouling comprises the following steps:

[0117] 1) Calculated by mass, 30 parts of polyvinylidene fluoride having a weight-average molecular weight of 600 kDa, 5 parts of styrene-maleic anhydride copolymer having a weight-average molecular weight of 120 kDa (the maleic anhydride content in the styrene-maleic anhydride copolymer is 25%), and 0.1 parts of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate are dried separately, and then thoroughly mixed with 64.9 parts of γ-butyrolactone in a mixer (700 rpm, time 10 min), and then extruded through an extruder (the extruder is a 40 twin-screw extruder with a length-to-diameter ratio, temperature 175°C), and cooled in air to granulate to obtain mixture pellets;

[0118] 2) The core liquid used for spinning was hot, high-purity nitrogen at 110°C, with a flow rate of 2 L / h. The resulting granules were melted and then spun through an extruder at 175°C at a flow rate of 6 L / h. After passing through a 5 cm air gap, they entered a coagulation bath consisting of deionized water, were cooled with deionized water, and wound into filaments (at a winding speed of 30 m / min). The resulting nascent membrane filaments were extracted with ethanol (purity not less than 99%) at 30°C for 1 hour to remove the diluent. After two extraction cycles, a hollow fiber membrane with an outer diameter of 1.3 mm and an inner diameter of 0.7 mm was obtained.

[0119] 3) The hollow fiber membrane was immersed in a 0.1g triethylamine catalyst + 25g PEG200 solution and reacted at 65°C for 1h. After washing with water, the hollow fiber membrane grafted with PEG200 was immersed in a 0.5% dilute H2SO4 and 4% GA aqueous solution and reacted at 60°C for 20min. After washing with water, the hollow fiber membrane was immersed in a 0.4% dilute H2SO4 sucrose aqueous solution and reacted at 50°C for 1h to obtain a surface-grafted sucrose polysaccharide composite membrane ultrafiltration membrane with a retarding effect on silicate inorganic substances.

[0120] Example 5

[0121] A method for preparing a polymer ultrafiltration membrane with high efficiency and resistance to silicate inorganic fouling comprises the following steps:

[0122] 1) 28 parts by mass of polyvinylidene fluoride having a weight-average molecular weight of 700 kDa, 5 parts of styrene-maleic anhydride copolymer having a weight-average molecular weight of 120 kDa (the maleic anhydride content in the styrene-maleic anhydride copolymer being 25%), and 0.1 part of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid octadecyl, were dried separately, and then thoroughly mixed with 66.9 parts of sulfolane in a mixer (700 rpm, time 10 min), extruded through an extruder (twin-screw extruder with an aspect ratio of 40, temperature 178°C), and cooled in air to obtain mixture pellets;

[0123] 2) The core liquid used for spinning was hot, high-purity nitrogen at 118°C, with a flow rate of 2.5 L / h. The resulting granules were melted and then spun through an extruder at 178°C at a flow rate of 8 L / h. After passing through a 5 cm air gap, they entered a coagulation bath consisting of deionized water, were cooled with deionized water, and wound into filaments (at a winding speed of 30 m / min). The resulting nascent membrane filaments were extracted with ethanol (at a purity of not less than 99%) at 40°C for 1 hour to remove the diluent. After two extraction cycles, a hollow fiber membrane with an outer diameter of 1.3 mm and an inner diameter of 0.7 mm was obtained.

[0124] 3) The hollow fiber membrane was immersed in a 0.1g triethylamine catalyst + 25g PEG200 solution and reacted at 65°C for 1 hour. After washing with water, the hollow fiber membrane grafted with PEG200 was immersed in a 0.5% dilute H2SO4 and 4% GA aqueous solution and reacted at 60°C for 20 minutes. After washing with water, the hollow fiber membrane was immersed in a 0.5% dilute H2SO4 raffinose solution and reacted at 50°C for 1 hour to obtain a surface-grafted raffinose polysaccharide composite membrane ultrafiltration membrane with a retarding effect on silicate inorganic substances.

[0125] A polyvinylidene fluoride / styrene-maleic anhydride copolymer base film was used as Comparative Example 1.

[0126] The hydrophilic non-retarding ultrafiltration membrane grafted with PEG200 was used as comparative example 2.

[0127] The pore sizes of the filter membranes of Comparative Example 1-2 and Examples 1-5 are compared, as shown in Table 1.

[0128] Table 1 Pore diameter of filter membranes in Examples 1-5

[0129]

[0130] As shown in Table 1, the minimum pore size of the filter membrane of the present invention is 20 nm and the maximum pore size is 29 nm. The pore size of the filter membrane prepared by the method of the present invention is 20-29 nm, which is smaller than the pore size of the comparative example of 34-36 nm. The porosity of the filter membrane of the present invention is 70%-75%.

[0131] The filter membranes of Examples 1-5 and Comparative Examples 1-2 were contaminated for 1 hour using a solution containing 7 mM CaCl2 and 0.5 mM Na2SiO3 as a model contaminant. The contaminated filter membranes were cleaned under pressure, and the flux recovery rates of the membranes were measured after cleaning. A comparison of the flux recovery rates of the contaminated filter membranes of Comparative Examples 1-2 and Examples 1-5 is shown in Table 2.

[0132] Table 2 Flux recovery rate after membrane contamination in Examples 1-5

[0133]

[0134] As can be seen from Table 1, after the filter membrane prepared by the method of the present invention is contaminated by pollutants containing 7 mM CaCl2 and 0.5 mM Na2SiO3 solution, the flux recovery rate of the present invention is 83.9% to 93.4%, and the highest flux recovery rate reaches 93.4%, that is, the removal rate of silicate inorganic pollutants on the surface of the polysaccharide composite membrane filter membrane of the present invention reaches 93.4%. The minimum flux recovery rate of the filter membrane prepared by the present invention is 83.9%, which is significantly higher than that of comparative examples 1-2, indicating that the filter membrane of the present invention has good silicate pollutant retarding and silicate pollution resistance effects.

[0135] like Figure 1 , which shows a SEM image of the hollow fiber membrane of the present invention, wherein the fiber membrane has a hollow structure.

[0136] like Figure 2 FIG. 4 shows an SEM image of the polysaccharide composite membrane filter of the present invention, where the scale is 100 μm, wherein:

[0137] Z1 is the PVDF / SMA base membrane of Comparative Example 1;

[0138] Z2 is the PVDF / SMA-based membrane grafted with polyethylene glycol, glutaraldehyde, and sucrose membrane of Example 4;

[0139] Z3 is the PVDF / SMA-based membrane grafted with polyethylene glycol, glutaraldehyde, and maltose membrane of Example 3;

[0140] Z4 is the PVDF / SMA base membrane grafted with polyethylene glycol, glutaraldehyde and raffinose membrane of Example 2;

[0141] a is the filter membrane before contamination, b is the filter membrane after contamination with 7 mM CaCl2 and 0.5 mM Na2SiO3 solution as model contaminants, and c is the filter membrane after cleaning.

[0142] Depend on Figure 2 It can be seen that after the polysaccharide ultrafiltration membrane of Examples 2-4 was contaminated by pollutants containing 7 mM CaCl2 and 0.5 mM Na2SiO3 solution, the area of the filter membrane surface in contact with silicate reached more than 90%, and the SEM image of the polysaccharide ultrafiltration membrane after cleaning was close to the SEM image before contamination. The removal rate of silicate inorganic pollutants on the filter membrane surface reached 93.4%, indicating that the pollutants were easy to clean. However, the cleaning effect of Comparative Example 1 after contamination was not obvious, and obvious pollutants still existed, further indicating that the polysaccharide composite membrane filter membrane of the present invention has high efficiency in retarding the coagulation of silicate pollutants and has obvious anti-silicate pollution effect.

[0143] Sugar can be used as a retarder for Portland cement, a pollutant. Sugar molecules contain multiple hydroxyl groups, which can be adsorbed on the surface of cement particles (especially active minerals such as tricalcium silicate and tricalcium aluminate) to form a stable protective film, preventing cement particles from contacting with water, thereby delaying the hydration reaction of cement. At the same time, the hydroxyl groups of sugar can react with Ca2+ released during cement hydration. 2+ Combine to form a soluble complex. This complexation reduces the free Ca in the solution 2+ The concentration of Ca 2+ It is the key ion for the hydration of tricalcium silicate to form hydrated calcium silicate. 2+ The concentration of tricalcium silicate decreases, and thus the hydration rate of tricalcium silicate slows down. Furthermore, sugar molecules adsorb on the growth sites of hydration products (such as hydrated calcium silicate and calcium hydroxide crystals), hindering the orderly arrangement of crystals and the formation of a three-dimensional network structure. This process prolongs the transition time of the cement slurry from a plastic state to a hardened state, thereby achieving the purpose of slow setting. Therefore, the present invention grafts sugars with slow-release properties onto the membrane surface, effectively delaying the scaling and hardening process of silicates in wastewater on the membrane surface, thereby effectively weakening the bonding force between the dirt and the membrane surface, making it easily cleaned away by cross-flowing raw liquid or cleaning fluid. This gives the membrane a strong resistance to silicates in the water.

[0144] The high-efficiency silicate-resistant inorganic fouling polymer ultrafiltration membrane of the present invention not only has a strong hydrophilicity on the membrane surface to slow down the adsorption and deposition of pollutants on the membrane surface, but also can effectively prevent the inorganic fouling from becoming dense and hardened and turning into irreversible fouling, thereby ultimately making the inorganic fouling have a loose structure and weakening the force between the membrane surface and the inorganic fouling.

[0145] Those skilled in the art will appreciate that the above-mentioned embodiments are specific examples for implementing the present disclosure, and that in actual applications, various changes may be made thereto in form and detail without departing from the scope of the present disclosure.

Claims

1. A composite membrane, characterized in that include: A fluoropolymer membrane, wherein a styrene-maleic anhydride copolymer layer is deposited on the surface of the fluoropolymer membrane to form a fiber membrane, and the surface of the styrene-maleic anhydride copolymer layer is cross-linked with polysaccharide; The molecular weight of the polysaccharide is 342 to 1120 Da, the thickness of the fiber membrane is equal to or greater than 0.3 mm, and the silicate removal rate on the surface of the composite membrane is 84% to 94%.

2. A composite membrane according to claim 1, characterized in that The polysaccharide includes sucrose, raffinose or maltose.

3. A composite membrane according to claim 1, characterized in that The fluoropolymer membrane is a fluoropolymer hollow membrane, and a styrene-maleic anhydride copolymer layer is deposited on the surface of the fluoropolymer hollow membrane to form a hollow fiber membrane. The thickness of the hollow fiber membrane is 0.3 to 0.4002 mm, the thickness of the fluoropolymer hollow membrane is 0.3 to 0.4 mm, and the thickness of the styrene-maleic anhydride copolymer layer is 100 to 200 nm.

4. A composite membrane according to claim 1, characterized in that: The composite membrane has a pore size of 20-29 nm and a porosity of 70%-75%.

5. A composite membrane according to claim 1, characterized in that: The fluorine-containing polymer includes a homopolymer or copolymer of polyvinylidene fluoride.

6. A composite membrane according to claim 1, characterized in that: The weight average molecular weight of the fluorine-containing polymer is 500-700 kDa, the weight average molecular weight of the styrene-maleic anhydride copolymer is 100-120 kDa, and the content of maleic anhydride in the styrene-maleic anhydride copolymer is 20-25%.

7. The method for preparing a composite membrane according to any one of claims 1 to 6, characterized in that: The steps include: The fluorine-containing polymer and the styrene-maleic anhydride copolymer are blended and then phase-separated to obtain a fiber membrane. The styrene-maleic anhydride copolymer on the surface of the fiber membrane is modified and then cross-linked with a polysaccharide by a cross-linking agent to obtain a composite membrane.

8. The method for preparing a composite membrane according to claim 7, characterized in that: The step of phase separation of the fluorine-containing polymer and the styrene-maleic anhydride copolymer comprises: The fluorine-containing polymer, styrene-maleic anhydride copolymer, diluent and antioxidant are mixed at a temperature of 170-180° C., and then extruded and granulated by an extruder to obtain mixture particles; The mixture particles are sequentially melted, spun and cooled to obtain primary membrane fibers; The diluent in the primary membrane fibers is removed by an extractant to obtain a fiber membrane with a hollow structure.

9. The method for preparing a composite membrane according to claim 8, characterized in that: The diluent includes diethyl sebacate, γ-butyrolactone, sulfolane or tributyl citrate; The antioxidant includes β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; The extractant includes ethanol.

10. The method for preparing a composite membrane according to claim 7, characterized in that: The step of modifying the styrene-maleic anhydride copolymer on the upper surface of the fiber membrane comprises: immersing the fiber membrane in a solution containing a catalyst and a diol-containing modifier at a temperature of 50-65° C. for 1-4 hours.

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