A composite film and a method for preparing the same

Abstract

The present application relates to the technical field of composite membrane material, in particular to a kind of composite membrane and preparation method thereof.The composite membrane includes fluoropolymer film, and the surface of fluoropolymer film is deposited with styrene-maleic anhydride copolymer layer to form fiber membrane, and the surface of styrene-maleic anhydride copolymer layer is crosslinked with polysaccharide;The molecular weight of polysaccharide is 342-1120Da, the thickness of fiber membrane is equal to or greater than 0.3mm, and the removal rate of silicate on the surface of composite membrane is 84%-94%.Thus, the problem that pollutants in sewage are easily attached to the filter membrane and the filter membrane is not easy to be cleaned is solved, and the filter membrane has a retarding effect on silicate inorganic matter, so that silicate inorganic matter forms a loose pollution layer on the surface of the filter membrane and is easily cleaned.

Description

TECHNICAL FIELD

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

[0002] Membrane separation technology is a high-precision separation technology developed in recent years. Fluorine-containing polymers represented by polyvinylidene fluoride are widely used to prepare porous membranes and are widely used in water treatment, biological purification, electronic industry, and membrane contactor fields. The good anti-fouling property and good removal effect of pollutants after cleaning are the prerequisite for the practical value of the membrane used for water treatment. The better the hydrophilicity of the membrane surface, the looser the scale layer of the pollutants, and the weaker the bonding force between the scale layer and the membrane surface, the more difficult the scale layer is to adhere to the membrane surface and harden. Grafting appropriate hydrophilic groups on the membrane surface is a convenient means to achieve the above goals. Non-solvent induced phase technology and thermal induced phase separation technology are commonly used technologies for preparing polymer porous membranes. Compared with non-solvent induced phase membrane preparation technology, thermal induced phase separation membrane preparation technology has the advantages of easy control of pore structure, high mechanical property of membrane, and convenient preparation process, and is especially suitable for the preparation of polymer porous membranes without solvent at room temperature.

[0003] Silicates are ubiquitous in natural water bodies on the ground and underground, which are weakly acidic to weakly alkaline with a pH of 6-8. Due to the strong adhesion of silicates, adsorption, deposition, and hardening of silicates on the membrane surface are easy to occur during long-term operation of membrane water treatment process, which eventually become irreversible inorganic scale pollution, and further lead to flux decline and reduced membrane life. Since the silicate inorganic scale is insoluble in acid and alkali, and the bonding force between the silicate inorganic scale and the membrane surface is strong, it is difficult to clean with pure water alone, thus the membrane pollution problem caused by silicates is particularly prominent.

[0004] The principle of thermal induced phase separation technology for membrane formation is that the polymer and a specific diluent form a polymer solution at high temperature. When the temperature decreases to a certain value, 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] Fluorine-containing polymers are commonly used to prepare sewage treatment membranes. Moreover, polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) in the fluorine-containing polymer is easy to entangle with styrene-maleic anhydride copolymer (SMA) chains, so that SMA does not fall off, and SMA is deposited on the surface of PVDF to load reactive groups maleic anhydride (MA) on the membrane surface.

[0006] In the construction industry, sugar is used as a retarder for Portland cement. That is, sugar retards the hydration process of Portland cement by adsorption, complex formation, control of calcium hydroxide crystal growth, and formation of a solvated water film, etc., thereby destroying the hardening of cement. SUMMARY

[0007] 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 application provides a composite membrane and a preparation method thereof.

[0008] According to a first aspect of the application, the application provides a composite membrane, comprising:

[0009] The fluoropolymer membrane has a surface deposited with a layer of styrene-maleic anhydride copolymer to form a fiber membrane, and the surface of the layer of styrene-maleic anhydride copolymer is crosslinked with polysaccharide;

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

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

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

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

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

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

[0016] Preferably, the fluoropolymer includes a homopolymer or a copolymer of polyvinylidene fluoride.

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

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

[0019] The fluoropolymer and the styrene-maleic anhydride copolymer are phase separated to obtain a fiber membrane, the styrene-maleic anhydride copolymer on the surface of the fiber membrane is modified, and the modified fiber membrane is crosslinked with a polysaccharide by using a crosslinking agent to obtain the composite membrane.

[0020] Preferably, the step of phase separating 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, and then extruding and granulating the mixture by using an extruder to obtain mixture particles;

[0021] The mixture particles are sequentially subjected to melting, spinning and cooling to obtain nascent membrane filaments;

[0022] The diluent in the nascent membrane filaments is removed by using 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 comprises β-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate;

[0025] The extractant comprises ethanol.

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

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

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

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

[0030] Preferably, the di-aldehyde group-containing crosslinking agent comprises glutaraldehyde or succinaldehyde.

[0031] Preferably, the fluoropolymer, styrene-maleic anhydride copolymer, diluent and antioxidant are in a mass ratio of 25-30:5-10:49.5-64.9:0.1-0.5.

[0032] The principle on which the present application is based is as follows:

[0033] (1) In the preparation of "fluoropolymer / styrene-maleic anhydride copolymer" ultrafiltration membrane by heat-induced phase separation technology, the solidification precipitation temperature of styrene-maleic anhydride and fluoropolymer in the diluent coagulation bath (usually water) during cooling is different, so that the fluoropolymer is first solidified and precipitated from the diluent during cooling, while the other styrene-maleic anhydride copolymer is then extracted from the diluent and continuously deposited on the surface of the fluoropolymer hollow membrane, so that the membrane surface is loaded with anhydride functional groups with reaction efficacy. Then the anhydride on the membrane surface reacts in turn with polyethylene glycol, glutaraldehyde and polysaccharides with setting retardation efficacy for silicate inorganic substances to load the membrane surface with polysaccharides with setting retardation efficacy for silicate inorganic substances. When the blending amount of styrene-maleic anhydride copolymer is moderate, due to the certain compatibility between styrene-maleic anhydride copolymer and fluoropolymer, the long chains of the two polymers 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 chain with setting retardation efficacy for silicate dirt not only improves the hydrophilicity of the membrane, but also slows down the adsorption and deposition of silicate inorganic dirt on the membrane surface. Moreover, the setting retardation efficacy of the polysaccharide molecular chain for silicate dirt makes it difficult for the deposit to further harden on the membrane surface to develop into irreversible pollution, but forms reversible pollution with weak binding force and loose structure on the membrane surface, which can be easily cleaned by the original solution or washing water under cross-flow operation, so that silicate dirt can be effectively removed. Therefore, grafting hydrophilic long-chain groups of polysaccharides with setting retardation efficacy for silicate dirt on the membrane surface can realize the preparation of polymer ultrafiltration membrane with high efficiency of anti-silicate inorganic dirt. In addition, it also has the following characteristics:

[0035] 1) Requirements for polymer content, molecular weight and ratio to ensure that the membrane has good mechanical properties and the characteristics of ultrafiltration membrane, the maleic anhydride functional groups on the membrane surface have a suitable density, and the styrene-maleic anhydride copolymer does not fall off. The total polymer content (fluoropolymer + SMA) is between 30-40%, of which 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 content of 20%-25% in the styrene-maleic anhydride copolymer.

[0036] 2) the requirement for a diluent, which is one of diethyl sebacate, gamma-butyrolactone, sulfolane, tributyl citrate, which is soluble in ethanol at room temperature but not in water and also not soluble in styrene-maleic anhydride copolymer.

[0037] 3) the requirement for grafting conditions, since it is difficult to directly graft the hydroxyl-containing polysaccharide on the surface of the fluoropolymer hollow membrane, for this purpose, it is necessary to first introduce anhydride on the surface of the fluoropolymer hollow membrane, then the anhydride undergoes ring-opening grafting reaction with polyethylene glycol under anhydrous conditions, and then sequentially undergoes hydroxy aldehyde condensation and aldehyde group grafting reaction with polysaccharide, so as to graft the polysaccharide with the retarding effect on 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 type of styrene-maleic anhydride copolymer is 100-120kDa, the proportion of maleic anhydride in the styrene-maleic anhydride copolymer is 20%-25%, and the preferred addition amount is 5-10 parts. If the addition amount is too high, on the one hand, the interface defect increases and the retention effect decreases; on the other hand, the over-thick styrene-maleic anhydride copolymer layer formed on the membrane surface will fall off. If the addition amount is too small, the surface maleic anhydride density is low, the amount of grafted polysaccharide is small, and the retarding effect is not obvious.

[0039] 5) the polysaccharide is a polysaccharide with good retarding effect, such as sucrose, raffinose and maltose.

[0040] 6) the core liquid used in spinning is hot high-purity nitrogen gas at 100-120℃ instead of other liquid organic solvents.

[0041] 7) the extracting agent is 25-40℃ ethanol, which further improves the pressure resistance of the membrane wire, and can ensure that the membrane wire can withstand 4bar pressure in the external pressure test.

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

[0043] 1) the present application makes the fluoropolymer first solidify and precipitate from the diluent in the cooling process, and the other polymer is then deposited on the surface of the fluoropolymer hollow membrane, so that the membrane surface is loaded with anhydride functional groups with reaction effect, the density of the anhydride functional groups on the membrane surface is increased, and the subsequent grafting density is improved.

[0044] 2) the present application grafts polysaccharide molecular chains on the membrane, which has a retarding effect on silicate dirt, so that the deposit is difficult to further harden on the membrane surface to develop into irreversible pollution, but forms reversible pollution with weak binding force and loose structure on the membrane surface, which can be easily cleaned by the original solution or washing water in cross-flow operation, so that the silicate dirt can be effectively removed, and the recovery rate of the composite membrane filter membrane flux reaches 93.4%.

[0045] 3、The composite membrane of the present application has strong hydrophilicity on the membrane surface, which can slow down the adsorption and deposition of pollutants on the membrane surface, and can effectively prevent inorganic dirt from becoming dense and hardened to change into irreversible pollution, so that the inorganic dirt is finally in a loose structure and has weak interaction with the membrane surface.

[0046] 4、The composite membrane of the present application has good adaptability, is suitable for popularization and application, and has good industrialization prospect. The preparation method of the composite membrane of the present application is simple and easy to realize, the material source is wide and easy to obtain, the cost is low, and the anti-silicate pollution effect is good. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 The SEM image of the hollow fiber membrane in the present application is shown;

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

[0049] The present disclosure will now be discussed with reference to a number of example embodiments. It should be appreciated that these embodiments are discussed solely for the purpose of enabling those with ordinary skill in the art to better understand and therefore practice the present disclosure, and are not intended to imply any limitations of the scope of the present disclosure.

[0050] As used herein, the term "includes" and its variants are to be read as meaning "comprising, but not limited to," an open term. The term "based on" is to be read as "based, at least in part, on." The terms "one embodiment" and "an embodiment" are to be read as "at least one embodiment." The term "another embodiment" is to be read as "at least one other embodiment." Furthermore, the terms "first," "second," etc. are used merely as labels, and are not intended to impose numerical or sequential order unless specifically indicated. The term "plurality" means two or more, unless otherwise specified.

[0051] According to a first aspect of the present application, the present embodiment provides a composite membrane, comprising:

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

[0053] The molecular weight of the polysaccharide is 342-1120 Da, the thickness of the fiber membrane is equal to or greater than 0.3 mm, and the silicate removal rate of the surface of the composite membrane is 84%-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 fluorine-containing polymer film is a fluorine-containing polymer hollow membrane, a layer of styrene-maleic anhydride copolymer is deposited on the surface of the fluorine-containing polymer hollow membrane to form a hollow fiber membrane, the thickness of the hollow fiber membrane is 0.3-0.4002 mm, the thickness of the fluorine-containing polymer hollow membrane is 0.3-0.4 mm, and the thickness of the layer of styrene-maleic anhydride copolymer is 100-200 nm.

[0058] Preferably, the outer diameter of the obtained hollow fiber membrane is 1.2-1.3 mm, and the inner diameter is 0.6-0.7 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 the 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 the maleic anhydride in the styrene-maleic anhydride copolymer is 25%.

[0063] According to a second aspect of the present application, the embodiment provides a preparation method of the composite membrane described above, comprising the following steps:

[0064] The fluorine-containing polymer is blended with the styrene-maleic anhydride copolymer, and then phase separation is performed 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 through a cross-linking agent to obtain a composite membrane.

[0065] In the embodiment, the requirements for the preparation of the composite membrane are low, 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 to obtain mixture particles;

[0068] The mixture particles are sequentially subjected to melting, spinning and cooling to obtain primary film filaments;

[0069] The diluent in the primary film filaments is removed by an extracting agent to obtain a fibrous membrane with a hollow structure.

[0070] In the embodiment, the primary film filaments are prepared by spinning to have a hollow structure, and then a fibrous membrane with a hollow structure is obtained. The thickness of the fluorine-containing polymer is 0.3-0.4 mm. The thickness of the thin deposition layer of the styrene-maleic anhydride copolymer is 100-200 nm. In the straightened state, the total length of the diol group-containing modifier, dialdehyde group-containing crosslinking agent and polysaccharide is not more than 0.2 μm.

[0071] In some embodiments, the primary film filaments can be prepared as flat plates or other non-hollow structures, and then the fibrous membrane obtained subsequently is also a flat plate or other non-hollow structure. That is, the fluorine-containing polymer, styrene-maleic anhydride copolymer and polysaccharide can also be prepared as other types of membranes.

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

[0073] The antioxidant includes β-(3,5-di-tert-butyl-4-hydroxyphenyl)propyl octadecanoate.

[0074] The extracting agent includes ethanol.

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

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

[0077] Preferably, the diol group-containing modifier includes polyethylene glycol or triethylene glycol.

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

[0079] Preferably, the catalyst includes triethylamine.

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

[0081] Preferably, the fiber membrane with the styrene-maleic anhydride copolymer on the surface modified is immersed in an aqueous solution containing the cross-linking agent containing a dialdehyde group and having a temperature of 60℃ for 20 min.

[0082] Preferably, the step of cross-linking the polysaccharide by the cross-linking agent comprises: immersing the fiber membrane with the styrene-maleic anhydride copolymer on the surface modified in an aqueous solution containing the cross-linking agent containing a dialdehyde group and having a temperature of 50-60℃ for 20-40 min under acidic conditions with a pH of 2-4 to obtain the fiber membrane containing the ternary copolymer of the styrene-maleic anhydride copolymer, the diol group-containing modifier and the cross-linking agent containing a dialdehyde group.

[0083] Preferably, the fiber membrane with the styrene-maleic anhydride copolymer on the surface modified is immersed in an aqueous solution containing the cross-linking agent containing a dialdehyde group and having a temperature of 60℃ for 20 min.

[0084] Preferably, the cross-linking agent containing a dialdehyde group comprises glutaraldehyde or succendialdehyde.

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

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

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

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

[0089] Formula (1):

[0090] .

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

[0092] Formula (2):

[0093] .

[0094] SMA-PEG-GA ternary copolymer and raffinose (raffinose) reaction, get surface grafting silicate inorganic material has the retarding effect of raffinose polysaccharide ultrafiltration membrane, the reaction equation is shown as formula (3).

[0095] Formula (3):

[0096] .

[0097] SMA-PEG-GA ternary copolymer and sucrose (sucrose) reaction, get surface grafting silicate inorganic material has the retarding effect of sucrose polysaccharide ultrafiltration membrane, the reaction equation is shown as formula (4).

[0098] Formula (4):

[0099] .

[0100] Example 1

[0101] A method for preparing a polymer ultrafiltration membrane with high efficiency anti-silicate inorganic dirt, comprising the following steps:

[0102] 1) According to the mass fraction, 25 parts of polyvinylidene fluoride with a weight average molecular weight of 700 kDa, 10 parts of styrene-maleic anhydride copolymer (the content of maleic anhydride in styrene-maleic anhydride copolymer is 25%) with a weight average molecular weight of 120 kDa and 0.1 part of β-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate are respectively dried, then mixed with 64.9 parts of diethyl sebacate in a mixer (700 rpm, time 10 min), then extruded through an extruder (the extruder is a double screw extruder with a length-diameter ratio of 40, the temperature is 170°C), and cooled in air to obtain granules;

[0103] 2) The core liquid used in spinning, with temperature 100℃ hot high-purity nitrogen as cavity forming fluid, the flow rate is 2.5L / h. The obtained material particles are melted and spun through the extruder at 170℃, the flow rate is 8L / h; After passing through an air gap with a length of 5cm, it enters the coagulation bath composed of deionized water, cools in deionized water and winds into a yarn (winding speed is 30m / min), the obtained primary membrane yarn is extracted with ethanol with a purity of not less than 99% at 40℃ for 1h to extract the diluent, after 2 times of extraction, a hollow fiber membrane with an outer diameter of 1.3mm and an inner diameter of 0.7mm is obtained.

[0104] 3) The hollow fiber membrane is immersed in 0.1 g triethylamine catalyst + 25 g PEG200 solution at 65°C for 1 h, and then washed with water. The PEG200 grafted hollow fiber membrane is immersed in 0.5% dilute H2SO4 and 4% glutaraldehyde (GA) aqueous solution at 60°C for 20 min, and then washed with water. The hollow fiber membrane is immersed in 0.5% dilute H2SO4 raffinose solution at 50°C for 1 h, and then taken out to obtain a raffinose polysaccharide composite membrane ultrafiltration membrane with surface grafted silicate inorganic material with a retarding effect.

[0105] Example 2

[0106] A method for preparing a polymer ultrafiltration membrane with high efficiency against silicate inorganic dirt, comprising the following steps:

[0107] 1) According to the mass fraction, 30 parts of polyvinylidene fluoride with a weight average molecular weight of 700 kDa, 10 parts of styrene-maleic anhydride copolymer (the content of maleic anhydride in the styrene-maleic anhydride copolymer is 25%) with a weight average molecular weight of 120 kDa, and 0.1 part of β-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate are dried respectively, then mixed with 59.9 parts of sulfolane in a mixer (700 rpm, time 10 min), extruded through an extruder (the extruder is a double screw extruder with a length-diameter ratio of 40, the temperature is 180°C), and cooled and granulated in air to obtain mixture particles;

[0108] 2) The core liquid used in spinning is hot high-purity nitrogen gas with a temperature of 120°C as a cavity forming fluid, and the flow rate is 2.5 L / h. The obtained material particles are melted and spun through an extruder at 180°C with a flow rate of 0.8 L / h; after passing through an air gap with a length of 5 cm, they enter a coagulation bath composed of deionized water, are cooled by deionized water, and are wound into a yarn (the winding speed is 30 m / min). The obtained primary membrane yarn is extracted with ethanol with a purity of not less than 99% at 40°C for 1 h to remove the diluent. After 2 extractions, hollow fiber membranes with an outer diameter of 1.3 mm and an inner diameter of 0.7 mm are obtained.

[0109] 3) The hollow fiber membrane is immersed in 0.1 g triethylamine catalyst + 25 g PEG200 solution at 65°C for 1 h, and then washed with water. The PEG200 grafted hollow fiber membrane is immersed in 0.5% dilute H2SO4 and 4% glutaraldehyde (GA) aqueous solution at 60°C for 20 min, and then washed with water. The hollow fiber membrane is immersed in 0.5% dilute H2SO4 raffinose solution at 50°C for 1 h, and then taken out to obtain a raffinose polysaccharide composite membrane ultrafiltration membrane with surface grafted silicate inorganic material with a retarding effect.

[0110] Example 3

[0111] A preparation method of a polymer ultrafiltration membrane with high-efficiency resistance to silicate inorganic dirt, comprising the following steps:

[0112] 1) After drying 30 parts of polyvinylidene fluoride-hexafluoropropylene copolymer with a weight average molecular weight of 500 kDa, 10 parts of styrene-maleic anhydride copolymer (the content of maleic anhydride in the styrene-maleic anhydride copolymer is 25%) with a weight average molecular weight of 120 kDa and 0.1 part of β-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate respectively, they are mixed with 59.9 parts of tributyl citrate in a mixer (700 rpm, time 10 min), then extruded through an extruder (the extruder is a double-screw extruder with a length-diameter ratio of 40, the temperature is 170°C), and cooled and granulated in air to obtain granules of the mixture;

[0113] 2) The core liquid used in spinning, with hot high-purity nitrogen gas at a temperature of 100°C as a cavity-forming fluid, the flow rate is 1.5 L / h. The obtained material granules are melted and spun through an extruder at 170°C, the flow rate is 0.8 L / h; after passing through an air gap with a length of 5 cm, they enter a coagulation bath composed of deionized water, are cooled by deionized water, and are wound into a yarn (the winding speed is 30 m / min), the obtained primary membrane yarn is extracted with ethanol with a purity of not less than 99% at 25°C for 1 h to extract the diluent, and after 2 extractions, a hollow fiber membrane with an outer diameter of 1.2 mm and an inner diameter of 0.6 mm is obtained.

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

[0115] Example 4

[0116] A preparation method of a polymer ultrafiltration membrane with high-efficiency resistance to silicate inorganic dirt, comprising the following steps:

[0117] 1) 30 parts of polyvinylidene fluoride with a weight average molecular weight of 600 kDa, 5 parts of styrene-maleic anhydride copolymer with a weight average molecular weight of 120 kDa (the content of maleic anhydride in the styrene-maleic anhydride copolymer is 25%) and 0.1 part of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid octadecyl ester are respectively dried, then 64.9 parts of γ-butyrolactone is fully mixed (700 rpm, time 10 min) in a mixer, then extruded through an extruder (40 double screw extruder with a length-diameter ratio of 40, temperature 175°C), and cooled and granulated in air to obtain mixture particles;

[0118] 2) The core liquid used in spinning is hot high-purity nitrogen gas with a temperature of 110°C as a cavity-forming fluid, and the flow rate is 2 L / h. The obtained material particles are melted and spun through an extruder at 175°C with a flow rate of 6 L / h; after passing through an air gap with a length of 5 cm, they enter a coagulation bath composed of deionized water, are cooled by deionized water, and are wound into a yarn (winding speed is 30 m / min). The obtained primary membrane yarn is extracted with ethanol with a purity of not less than 99% at 30°C for 1 h to extract the diluent. After 2 extractions, a hollow fiber membrane with an outer diameter of 1.3 mm and an inner diameter of 0.7 mm is obtained.

[0119] 3) The hollow fiber membrane is immersed in a solution of 0.1 g of triethylamine catalyst + 25 g of PEG200 for 1 h at 65°C, washed with water, then immersed in a solution containing 0.5% dilute H2SO4 and 4% GA aqueous solution, reacted at 60°C for 20 min, washed with water, then immersed in a solution containing 0.4% dilute H2SO4 and sucrose aqueous solution, reacted at 50°C for 1 h, and then taken out to obtain a sucrose polysaccharide composite membrane ultrafiltration membrane with a surface grafted with silicate inorganic matter having a retarding effect.

[0120] Example 5

[0121] A method for preparing a polymer ultrafiltration membrane with high-efficiency anti-silicate inorganic dirt, comprising the following steps:

[0122] 1) 28 parts of polyvinylidene fluoride with a weight average molecular weight of 700 kDa, 5 parts of styrene-maleic anhydride copolymer with a weight average molecular weight of 120 kDa (the content of maleic anhydride in the styrene-maleic anhydride copolymer is 25%) and 0.1 part of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid octadecyl ester are respectively dried, then 66.9 parts of sulfolane is fully mixed (700 rpm, time 10 min) in a mixer, then extruded through an extruder (40 double screw extruder with a length-diameter ratio of 40, temperature 178°C), and cooled and granulated in air to obtain mixture particles;

[0123] 2) The core liquid used in spinning, with hot high-purity nitrogen gas at a temperature of 118℃ as the cavity-forming fluid, a flow rate of 2.5 L / h. The obtained material particles are melted and spun through an extruder at 178℃, a flow rate of 8 L / h; after passing through an air gap of 5 cm, they enter a coagulation bath composed of deionized water, are cooled by deionized water, and are wound into a yarn (winding speed of 30 m / min); the obtained nascent membrane yarn is extracted with ethanol with a purity of not less than 99% at 40℃ for 1 h to extract the diluent, and after 2 extractions, a hollow fiber membrane with an outer diameter of 1.3 mm and an inner diameter of 0.7 mm is obtained.

[0124] 3) The hollow fiber membrane is immersed in a 0.1 g triethylamine catalyst + 25 g PEG200 solution and reacted at 65℃ for 1 h; after being washed with water, the hollow fiber membrane grafted with PEG200 is immersed in a 0.5% dilute H2SO4 and 4% GA aqueous solution, and reacted at 60℃ for 20 min; after being washed with water, the hollow fiber membrane is immersed in a 0.5% dilute H2SO4 raffinose solution, and reacted at 50℃ for 1 h; the obtained raffinose polysaccharide composite membrane ultrafiltration membrane has a retarding effect on the surface grafting of silicate inorganic matter.

[0125] The polyvinylidene fluoride / styrene-maleic anhydride copolymer base membrane is used as Comparative Example 1.

[0126] The hydrophilic non-retarding effect ultrafiltration membrane grafted with PEG200 is used as Comparative Example 2.

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

[0128] Table 1 Pore size of the filter membranes of Examples 1-5

[0129]

[0130] As shown in Table 1, the minimum pore size of the filter membrane of the present application 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 application is 20-29 nm, which is smaller than the pore size of 34-36 nm of the comparative examples. The porosity of the filter membrane of the present application is 70%-75%.

[0131] The filter membranes of Examples 1-5 and Comparative Examples 1-2 are contaminated with a solution containing 7 mM CaCl2 and 0.5 mM Na2SiO3 as a model contaminant for 1 h. The contaminated filter membranes are cleaned under pressure driving, and the flux recovery rate of the filter membranes after cleaning is tested. The flux recovery rates of the filter membranes of Comparative Examples 1-2 and Examples 1-5 after contamination are compared, as shown in Table 2.

[0132] Table 2 Flux recovery rate of the filter membranes of Examples 1-5 after contamination

[0133]

[0134] As shown in Table 1, the flux recovery rate of the filter membrane prepared by the method of the application is 83.9% to 93.4% after the filter membrane is polluted by the pollutants containing 7 mM CaCl2 and 0.5 mM Na2SiO3 solution, and the highest flux recovery rate reaches 93.4%, that is, the polysaccharide composite membrane filter membrane surface silicate inorganic pollutant removal rate reaches 93.4%, and the minimum flux recovery rate of the filter membrane prepared by the application is 83.9%, which is significantly higher than that of Comparative Example 1-2, indicating that the filter membrane of the application has good silicate pollutant retarding effect and anti-silicate pollution effect.

[0135] As shown in FIG. 1, the SEM image of the hollow fiber membrane of the application is shown, and the fiber membrane has a hollow structure. Figure 1

[0136] As shown in FIG. 2, the SEM image of the polysaccharide composite membrane filter membrane of the application is shown, and the scale in the figure is 100 μm, wherein: Figure 2 Z1 is the PVDF / SMA base membrane of Comparative Example 1;

[0137] Z2 is the PVDF / SMA base membrane of Example 4 grafted with polyethylene glycol, glutaraldehyde and sucrose membrane;

[0138] Z3 is the PVDF / SMA base membrane of Example 3 grafted with polyethylene glycol, glutaraldehyde and maltose membrane;

[0139] Z4 is the PVDF / SMA base membrane of Example 2 grafted with polyethylene glycol, glutaraldehyde and raffinose membrane;

[0140] a is before the filter membrane is polluted, b is after being polluted by 7 mM CaCl2 and 0.5 mM Na2SiO3 solution as a model pollutant, and c is after cleaning after pollution.

[0141] As shown in Table 1, the polysaccharide ultrafiltration membrane of Examples 2-4 is polluted by the pollutants containing 7 mM CaCl2 and 0.5 mM Na2SiO3 solution, and the area of the filter membrane surface in contact with silicate reaches more than 90%, and the SEM image of the polysaccharide ultrafiltration membrane after cleaning is close to the SEM image before pollution, and the silicate inorganic pollutant removal rate of the filter membrane surface reaches 93.4%, indicating that the pollutants are easy to be cleaned, and the cleaning effect of Comparative Example 1 after pollution is not obvious, and there is still obvious pollutants, further indicating that the polysaccharide composite membrane filter membrane of the application has high silicate pollutant retarding effect and obvious anti-silicate pollution effect.

[0142] Figure 2 As shown in Table 1, the polysaccharide ultrafiltration membrane of Examples 2-4 is polluted by the pollutants containing 7 mM CaCl2 and 0.5 mM Na2SiO3 solution, and the area of the filter membrane surface in contact with silicate reaches more than 90%, and the SEM image of the polysaccharide ultrafiltration membrane after cleaning is close to the SEM image before pollution, and the silicate inorganic pollutant removal rate of the filter membrane surface reaches 93.4%, indicating that the pollutants are easy to be cleaned, and the cleaning effect of Comparative Example 1 after pollution is not obvious, and there is still obvious pollutants, further indicating that the polysaccharide composite membrane filter membrane of the application has high silicate pollutant retarding effect and obvious anti-silicate pollution effect.

[0143] ​​Sugar can be used as a retarder for silicate cement in the contaminant. Sugar molecules contain multiple hydroxyl groups, which can be adsorbed on the surface of cement particles (especially tricalcium silicate, tricalcium aluminate and other active minerals) to form a stable protective film, preventing the cement particles from contacting water, thereby delaying the hydration reaction of the cement. At the same time, the hydroxyl groups of sugar can form soluble complexes with Ca 2+ ions released during the hydration of cement. This complexation reduces the concentration of free Ca 2+ ions in the solution, and Ca 2+ ions are the key ions for the hydration of tricalcium silicate to form hydrated calcium silicate. The decrease in Ca 2+ concentration, in turn, reduces the tricalcium silicate, slowing down the hydration rate of tricalcium silicate. In addition, sugar molecules are adsorbed on the growth sites of hydration products (such as hydrated calcium silicate, calcium hydroxide crystals), hindering the ordered arrangement of crystals and the formation of three-dimensional network structure. This process prolongs the transition time of the cement paste from the plastic state to the hardened state, thereby achieving the purpose of retarding. Therefore, the sugar with sustained-release effect is grafted to the film surface in the present application, effectively delaying the hardening process of silicate on the membrane surface in the sewage, thereby effectively weakening the binding force between the dirt and the membrane surface, making it easy to be cleaned by the original solution or cleaning solution flowing in cross flow. Thus, the membrane has strong resistance to silicate in water.

[0144] The high-efficiency anti-silicate inorganic dirt polymer ultrafiltration membrane of the present application exhibits not only strong hydrophilicity on the membrane surface to slow down the adsorption and deposition of pollutants on the membrane surface, but also effectively prevents the hardening of inorganic dirt to irreversible pollution, so that the inorganic dirt is in a loose structure and has weak interaction with the membrane surface.

[0145] Those skilled in the art can understand that the above-mentioned embodiments are specific cases for implementing the present disclosure, and in actual application, various changes can be made in form and details 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%; 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 pore size of the composite membrane is 20-29 nm, and the porosity is 70%-75%.

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 thickness of the hollow fiber membrane is 0.3-0.4002 mm, the thickness of the fluorine-containing polymer hollow membrane is 0.3-0.4 mm, and the thickness of the styrene-maleic anhydride copolymer layer is 100-200 nm.

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

5. 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%.

6. The method for preparing a composite membrane according to any one of claims 1 to 5, 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.

7. The method for preparing a composite membrane according to claim 6, wherein: 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.

8. The method for preparing a composite membrane according to claim 7, 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.

9. The method for preparing a composite membrane according to claim 6, 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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