阅读说明：本技术 一种内支撑聚偏氟乙烯中空干膜及其制备方法 (Internal support polyvinylidene fluoride hollow dry film and preparation method thereof ) 是由 陈慧英 方富林 洪昱斌 蓝伟光 于 2020-04-27 设计创作，主要内容包括：本发明公开了一种内支撑聚偏氟乙烯中空干膜及其制备方法。该中空干膜包括内支撑管和膜层,所述膜层覆盖于内支撑管的表面,膜层的厚度为0.1～0.15mm,且膜层具有若干膜孔,其中膜孔的平均孔径大于0.5μm。其制备方法为将聚偏氟乙烯、表面活性剂、有机亲水成孔剂、有机溶剂混合制备铸膜液,并将控制粘度在32000～38000mpa·s的铸膜液涂覆在钩编管上,控制第一凝固浴温度大于60℃,利用钩编管的自支撑结构,使得膜大孔结构层在膜丝干燥即使形成少量崩塌也能保持需要通量的孔径结构,本发明制得的内支撑中空膜可实现干燥保存并且可有效的恢复通量,无需再进行后处理,节约了成本。(The invention discloses an inner support polyvinylidene fluoride hollow dry film and a preparation method thereof. The hollow dry film comprises an inner supporting tube and a film layer, wherein the film layer covers the surface of the inner supporting tube, the thickness of the film layer is 0.1-0.15 mm, the film layer is provided with a plurality of film holes, and the average pore diameter of the film holes is larger than 0.5 mu m. The preparation method comprises the steps of mixing polyvinylidene fluoride, a surfactant, an organic hydrophilic pore-forming agent and an organic solvent to prepare a membrane casting solution, coating the membrane casting solution with the viscosity controlled to be 32000-38000 mpa · s on a crochet tube, controlling the temperature of a first coagulation bath to be higher than 60 ℃, and keeping a pore diameter structure with required flux even if a membrane wire is dried and collapsed in a small amount by utilizing a self-supporting structure of the crochet tube.)

1. An interior support polyvinylidene fluoride cavity dry film which characterized in that: the membrane comprises an inner supporting tube and a membrane layer, wherein the membrane layer covers the surface of the inner supporting tube, the thickness of the membrane layer is 0.1-0.15 mm, the membrane layer is provided with a plurality of membrane pores, the average pore diameter of the membrane pores is 0.5-5 mu m, and the effective porosity is more than or equal to 80%.

2. The internal support polyvinylidene fluoride hollow dry film of claim 1, characterized in that: the membrane casting solution of the membrane layer comprises the following components in percentage by weight:

the organic hydrophilic pore-forming agent is at least one of polyethylene oxide, polyethylene glycol and polyvinylpyrrolidone;

the surfactant is at least one of tween, OP phosphate, alkylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether and polyoxyethylene alkyl benzene sulfonic acid ammonium salt.

3. The internal support polyvinylidene fluoride hollow dry film according to claim 2, characterized in that: the polymerization degree of the polyvinylidene fluoride is 25000-50000.

4. The internal support polyvinylidene fluoride hollow dry film according to claim 2, characterized in that: the organic solvent is at least one of dimethylformamide, dimethylacetamide and N-methylpyrrolidone.

5. The internal support polyvinylidene fluoride hollow dry film of claim 1, characterized in that: the inner support pipe comprises a crochet pipe, the inner diameter of the crochet pipe is 0.5-2.2 mm, and the outer diameter of the crochet pipe is 1.2-3.2 mm.

6. The preparation method of the internal support polyvinylidene fluoride hollow dry film according to any one of claims 2 to 4, characterized by comprising the following steps: the method comprises the following steps:

(1) weighing the components according to the corresponding weight percentage, stirring uniformly, standing for defoaming, stirring uniformly at 40-70 ℃, standing at 40 ℃ for removing bubbles, and obtaining a casting solution with viscosity of 32000-38000 mpa.s;

(2) coating the casting solution prepared in the step (1) on the surface of the inner support tube with the roughened surface through a spinning nozzle, controlling the thickness of the coating film layer to be 0.1-0.15 mm through an air bath, and immersing the inner support tube in a coagulating bath at the temperature of 60-80 ℃ for coagulation forming to obtain a formed piece;

(3) and (3) soaking the formed part obtained in the step (2) in pure water at 15-35 ℃ for 40-60 h, and airing the membrane wires to obtain the internal support polyvinylidene fluoride hollow dry film.

7. The method for preparing an internal support polyvinylidene fluoride hollow dry film according to claim 6, characterized in that: in the step (2), the surface roughening treatment is to perform sodium hydroxide aqueous solution treatment and drying on the inner supporting tube, and increase the roughness through corona.

8. The method for preparing an internal support polyvinylidene fluoride hollow dry film according to claim 6, characterized in that: the air bath vertically travels downwards for 8-10 cm in the air.

9. The method for preparing an internal support polyvinylidene fluoride hollow dry film according to claim 6, characterized in that: the medium of the coagulating bath is water or a mixture of water and the organic solvent.

10. The method for preparing an internal support polyvinylidene fluoride hollow dry film according to claim 6, characterized in that: the temperature of the coagulating bath is controlled to be 60-70 ℃.

Technical Field

The invention relates to an internal support polyvinylidene fluoride hollow dry film and a preparation method thereof.

Background

When the hollow membrane is used for water treatment, the chemical stability and hydrophilicity of the material are two most important properties. Chemical stability determines the lifetime of the material under the action of acids and bases, oxidants, microbes, etc., and it is also directly related to the method that can be taken for cleaning; the hydrophilicity determines the adsorption degree of the membrane material on organic pollutants in water, and influences the flux of the membrane. The hydrophilic substance is added in the production process of the hollow membrane, so that the surface of the membrane presents hydrophilicity in water, but once the membrane is dried, the hydrophilicity is lost, the membrane becomes waterproof, the hollow membrane filaments become brittle and are easy to break and damage, and the flat membrane sheet is also curled due to drying and even peeled and separated from the non-woven fabric. Therefore, in order to maintain the performance of the membrane in the production process, the ultrafiltration membrane is usually kept in a wet state by sealing and adding a moisture absorbing agent, and in the last few years of technology, substances such as glycerin, a surfactant, a preservative, a hydrophilic agent, RO water and the like are mainly used for post-treatment of membrane filaments so as to keep the membrane filaments wet or store the membrane filaments in a pseudo-dry state (after-treatment liquid is treated and dried), so that the main problems caused by assembly manufacturing and transportation are that:

(1) in the post-treatment, due to the addition of the glycerol and the surfactant, the post-treatment liquid has abundant foam, so that a plurality of bubbles are generated in the operation process of the membrane component, the operation of a pump is difficult, and the application of a subsequent membrane is difficult;

(2) natural dehydration and drying of hollow membranes will lead to collapse of membrane pores, thus severely influencing the permeability and mechanical strength of the membranes;

(3) biological pollution (even membrane hole blockage) and biodegradation of the wet membrane caused by microbial proliferation are caused, the wet membrane is not beneficial to processing, manufacturing and transportation of the membrane component and has high requirement on glue in the membrane component manufacturing engineering, and the membrane component cost is increased;

(4) in the MBR off-line cleaning process, the membrane filaments need to be kept moist at any time to keep the membrane filament flux, so that the cleaning difficulty and the workload are increased.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides an internal support polyvinylidene fluoride hollow dry film and a preparation method thereof, and solves the problems in the background art.

The technical scheme adopted by the invention for solving the technical problems is as follows: an inner support polyvinylidene fluoride hollow dry film comprises an inner support tube and a film layer, wherein the film layer covers the surface of the inner support tube, the thickness of the film layer is 0.1-0.15 mm, a plurality of film holes are distributed in the film layer in a staggered mode, the average pore diameter of each film hole is 0.5-5 mu m, the effective porosity is larger than or equal to 80%, and the effective porosity refers to the ratio of the sum of pore volumes which are communicated with each other and can allow fluid to flow in the film holes to the total volume of a sample under the common pressure condition.

In a preferred embodiment of the present invention, the film casting solution of the film layer comprises the following components by weight:

the organic hydrophilic pore-forming agent is at least one of polyethylene oxide, polyethylene glycol and polyvinylpyrrolidone;

the surfactant is at least one of tween, OP phosphate, alkylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether and polyoxyethylene alkyl benzene sulfonic acid ammonium salt.

In a preferred embodiment of the present invention, the polymerization degree of the polyvinylidene fluoride is 25000 to 50000.

In a preferred embodiment of the present invention, the organic solvent is at least one of dimethylformamide, dimethylacetamide and N-methylpyrrolidone.

In a preferred embodiment of the present invention, the inner support tube comprises a crochet knitted tube having an inner diameter of 0.5 to 2.2mm and an outer diameter of 1.2 to 3.2 mm.

The invention also provides a preparation method of the internal support polyvinylidene fluoride hollow dry film, which comprises the following steps:

(1) weighing the components according to the corresponding weight percentage, stirring uniformly, standing for defoaming, stirring uniformly at 40-70 ℃, standing at 40 ℃ for removing bubbles, and obtaining a casting solution with viscosity of 32000-38000 mpa.s; the defoaming temperature needs to be strictly controlled to be 40 ℃, and when the temperature is lower than the temperature, the defoaming time is too long, the defoaming is not thorough, so that the coating film layer is not uniform, and the size and the effective porosity of a formed part and subsequent apertures are influenced; temperatures above this temperature can result in partial volatilization of the casting solution components, which is detrimental to controlling the effective viscosity of the formulation.

(2) Coating the casting solution prepared in the step (1) on the surface of the inner support tube with the roughened surface through a spinning nozzle, controlling the thickness of the coating film layer to be 0.1-0.15 mm through an air bath, and immersing the inner support tube in a coagulating bath at the temperature of 60-80 ℃ for coagulation forming to obtain a formed piece;

(3) and (3) soaking the formed part obtained in the step (2) in pure water at 15-35 ℃ for 40-60 h, and airing the membrane wires to obtain the internal support polyvinylidene fluoride hollow dry film.

In a preferred embodiment of the present invention, in the step (2), the surface roughening treatment is to perform sodium hydroxide aqueous solution treatment drying on the inner supporting tube, and increase roughness through corona.

In a preferred embodiment of the present invention, the air bath vertically travels downward 8-10 cm in the air.

In a preferred embodiment of the present invention, the medium of the coagulation bath is water or a mixture of water and the organic solvent.

In a preferred embodiment of the present invention, the temperature of the coagulation bath is controlled to be 60-70 ℃.

Compared with the background technology, the technical scheme has the following advantages:

by utilizing the self-supporting structure of the inner supporting tube (crocheted tube), the surface of the membrane is enabled to form a macroporous structure with the thickness of 0.1-0.15 mm by controlling the viscosity of the membrane casting solution and the spinning process parameters, the effective porosity is more than or equal to 80%, even if the macroporous structure layer of the membrane forms a small amount of collapse in the drying process of membrane yarns, the macroporous structure layer of the membrane can keep a proper pore diameter structure to maintain the required flux, the prepared inner supporting hollow membrane can realize drying preservation and can effectively recover the flux, no post-treatment is needed, and the cost is saved.

Drawings

Fig. 1 is a surface electron microscope image of the internal support polyvinylidene fluoride hollow dry film prepared in example 1.

Detailed Description

Example 1

Under high-speed stirring, adding 1000 g of polyvinylidene fluoride powder (with the polymerization degree of 30,000) and 7000 g of dimethylacetamide, stirring and dissolving uniformly, after stirring uniformly, adding 1,200 g of N-methyl pyrrolidone and 300g of polyethylene glycol as organic hydrophilic pore-forming agents and 500g of Tween-20, stirring at 70 ℃, standing and defoaming at 40 ℃ for 24 hours, and detecting the viscosity of the casting solution to be 33149 mpa.s; the outer coagulating bath is water of 60 ℃, the casting film liquid is extruded and coated on an inner supporting tube with the outer diameter of 1.9mm and the inner diameter of 0.8mm together with the core liquid by a spinning nozzle after passing through a filter screen, the inner supporting tube is soaked and dried by 20 percent sodium hydroxide and then is subjected to corona treatment, and after the inner supporting tube travels 10cm in the air, the inner supporting tube enters the outer coagulating bath for forming and is wound by a winding wheel. After the internal support polyvinylidene fluoride hollow fiber membrane obtained by the method is soaked in pure water (room temperature is 15-35 ℃) for 48 hours, the external diameter of the obtained internal support polyvinylidene fluoride hollow fiber membrane is 2.2mm, the internal diameter is 0.8mm, the coating thickness is 0.15mm, and the pure water flux of the hollow fiber membrane is 2850L/m measured at 25 DEG C²H (0.1MPa), an overall burst strength of 0.4MPa, an average pore diameter of 0.8 μm, an effective porosity of 95%, a flux of 2680L/m after repeated water drying²H (0.1MPa), flux recovery: 94.0 percent.

Example 2

Under high-speed stirring, adding 1500 g of polyvinylidene fluoride powder (with the polymerization degree of 45,000) and 7000 g of dimethylacetamide, stirring and dissolving uniformly, after stirring uniformly, adding 1,000 g of polyethylene glycol, 300g of Tween-20 and 200g of glycerol as surfactants, stirring at 70 ℃, standing and defoaming at 40 ℃ for 24 hours, and detecting the viscosity of the casting solution to be 36256 mpa.s; the external coagulating bath is 70 deg.C water, and the casting solution is filtered by filter screenAnd then, the inner support tube and core liquid are extruded and coated on an inner support tube with the outer diameter of 1.9mm and the inner diameter of 0.8mm through a spinning nozzle, the inner support tube is soaked and dried by 20% of sodium hydroxide, then is subjected to corona treatment, travels in the air for 10cm, enters an outer coagulation bath for forming, and is wound by a winding wheel. After the internal support polyvinylidene fluoride hollow fiber membrane obtained in the way is soaked in pure water (room temperature is 15-35 ℃) for 48 hours, the outer diameter of the obtained internal support polyvinylidene fluoride hollow fiber membrane is 2.15mm, the inner diameter is 0.8mm, the coating thickness is 0.105mm, and the pure water flux of the hollow fiber membrane is 2630L/m measured at 25 DEG C²H (0.1MPa), the overall bursting strength is 0.4MPa, the average pore diameter is 0.6 mu m, the effective porosity is 90 percent, and the flux is 2521L/m after repeated water drying²H (0.1MPa), flux recovery: 95.8 percent.

Comparative example 1

Under high-speed stirring, adding 1000 g of polyvinylidene fluoride powder (with the polymerization degree of 25,000) and 7300 g of dimethylacetamide, stirring and dissolving uniformly, after stirring uniformly, adding 1,200 g of N-methyl pyrrolidone and 500g of Tween-20, stirring at 70 ℃, standing and defoaming at 40 ℃ for 24 hours, and detecting the viscosity of the casting solution to be 31022 mpa.s; the outer coagulating bath is 50 deg.C water, the casting solution is filtered by a filter screen, extruded together with core solution by a spinning nozzle and coated on an inner support tube with an outer diameter of 1.9mm and an inner diameter of 0.8mm, the inner support tube is soaked and dried by 20% sodium hydroxide, then corona treated, and after the inner support tube travels 10cm in air, the inner support tube enters the outer coagulating bath for forming and is wound by a winding wheel. After the internal support polyvinylidene fluoride hollow fiber membrane obtained by the method is soaked in pure water (room temperature is 15-35 ℃) for 48 hours, the outer diameter of the obtained internal support polyvinylidene fluoride hollow fiber membrane is 2.1mm, the inner diameter is 0.8mm, the coating thickness is 0.1mm, the effective porosity is 52%, and the pure water flux of the hollow fiber membrane is 3200L/m measured at 25 DEG C²H (0.1MPa), an overall burst strength of 0.2MPa, an average pore diameter of 0.8 μm, a flux of 425L/m after repeated water-drying²H (0.1MPa), flux recovery: 13.3 percent.

Comparative example 2

1500 g of polyvinylidene fluoride powder (degree of polymerization: 50,000) and 7000 g of dimethylacetamide were added under high-speed stirring,stirring to dissolve uniformly, adding 1,000 g of polyethylene glycol, 300g of tween-20 and 200g of glycerol after stirring uniformly, stirring at 70 ℃, standing and defoaming at 40 ℃ for 24 hours, and detecting the viscosity of the casting solution to be 39478 mpa.s; the outer coagulating bath is 50 deg.C water, the casting solution is filtered by a filter screen, extruded together with core solution by a spinning nozzle and coated on an inner support tube with an outer diameter of 1.9mm and an inner diameter of 0.8mm, the inner support tube is soaked in 20% sodium hydroxide, dried, corona treated, and formed in the outer coagulating bath after traveling 8cm in air, and wound by a winding wheel. After the internal support polyvinylidene fluoride hollow fiber membrane obtained by the method is soaked in pure water (room temperature is 15-35 ℃) for 48 hours, the outer diameter of the obtained internal support polyvinylidene fluoride hollow fiber membrane is 2.3mm, the inner diameter is 0.8mm, the coating thickness is 0.20mm, the effective porosity is 47%, and the pure water flux of the hollow fiber membrane is 1400L/m measured at 25 DEG C²H (0.1MPa), an overall burst strength of 0.4MPa, an average pore diameter of 0.35 μm, and a flux of 524L/m after repeated water-drying²H (0.1MPa), flux recovery: 37.4 percent.

The above description is only a preferred embodiment of the present invention, and therefore should not be taken as limiting the scope of the invention, which is defined by the appended claims and their equivalents.