RU2795574C1 - Method for producing cellulose acetate membrane - Google Patents

Abstract

FIELD: polymer industry.

SUBSTANCE: production of porous polymer films, and in particular a method for obtaining microfiltration membranes used for filtering, analyzing and purifying various media in microbiological, biochemical, pharmaceutical and other industries. A method for producing a cellulose acetate membrane includes the preparation of a molding solution by dissolving cellulose acetates in a mixture of an organic solvent, a precipitant, water and a plasticizer, filtration, thermostatic control, applying a molding solution to a moving metal band, molding and drying. One type of cellulose acetate should be with a low content of associated acetic acid, ranging from 53 to 56 wt.%, and another type of cellulose acetate should be high in bound acetic acid, ranging from 57 to 62 wt.%, polysorbate Twin-80 is added to the molding solution, the molding solution is thermostated for 6 hours at a temperature in the range of 28-30°C, and the molding is carried out at the degree of substitution of the vapor-air mixture of solvents and precipitants with prepared air in the range of 15-20 zone molding volumes per hour.

EFFECT: reduction of the ratio of the maximum pore size to their minimum size to a value not exceeding 1.1-1.2, obtaining a uniform structure with a narrow pore size distribution, reducing the confluent growth of test strain colonies on the membrane surface when microorganisms are isolated from water.

2 cl, 1 dwg, 1 tbl, 1 ex

Description

The invention relates to the production of porous polymer films, and in particular to a method for obtaining microfiltration membranes and can be used for filtering, analyzing and purifying various media in microbiological, biochemical, pharmaceutical and other industries. The invention relates to a semi-permeable cellulose acetate membrane with improved performance due to obtaining a uniform structure with a narrow pore size distribution and reducing bacterial growth on its surface when diagnosing drinking water by microbiological, parasitological and virological parameters. [IPC B01D 67/00, B01D 71/00]

A known method of obtaining microfiltration membranes based on a mixture of cellulose acetates, allowing you to achieve a ratio of maximum size to the average pore size in the range of 1.1-1.5 (Patent No. 2152818, publ. 20.07.2000). In the proposed method, a mixture of cellulose acetates is dissolved in an organic solvent containing a precipitant and a plasticizer, then the resulting solution is filtered, deaerated and applied to the moving surface through the gap between the die knife and the moving surface, and the die knife is equipped with a screen that creates a mobile mini-camera , limiting the volume of the initial molding zone. The main disadvantage of this membrane is a fairly wide range of pore size spread, as a result of which confluent growth of microorganism colonies was observed, which prevents reliable analysis results.

Also known is the invention of a semi-permeable cellulose acetate membrane (Patent No. 2303481, publ. 27.07.2007), consisting of cellulose acetate or a mixture of cellulose acetate and cellulose hydrate in the following mass ratio of cellulose acetate: cellulose hydrate (wt.h.): ( 0.01-0.8):(99.99-99.2), while the ratio of the maximum pore size to the minimum pore size in the polymer working layer does not exceed 1.4. In the present invention, involving the preparation of a spinning solution by dissolving cellulose acetate in a mixture of an organic solvent, a precipitant, water and a plasticizer, the application of the spinning solution is carried out on a moving porous substrate, and a composite membrane is obtained. The disadvantage of the invention is that when using a composite membrane, confluent growth was also observed due to the heterogeneity of the pores and the presence of a porous substrate.

The closest technical solution to the claimed method is a method for obtaining microfiltration membranes, protected by RF patent No. 2296611 (publ. 12.04.2007). The invention aims to obtain a cellulose acetate membrane with a uniform porous structure, characterized by a narrow range of pore size distribution. In accordance with the decision of the prototype cellulose acetate is dissolved in a mixture of organic solvent, precipitant, water and plasticizer, thermostatic for 14-16 hours at a temperature of 23-26°C. Molding is carried out in a closed working space at a relative humidity of 15-50% additional evaporation of a mixture of substances that can be used as a precipitant and an organic solvent, taken in the ratio (wt.h.): (0.3-0.5): (0.5-1.0) in the amount of 1000-6000 mg per 1 m ³ of a closed working space. When implementing the invention, the following drawback is revealed, namely, the invention provides a reduction in the ratio of the maximum pore size to the minimum pore size to a value not exceeding 1.3, but the tests of the membrane obtained by this method did not show satisfactory results in preventing confluent growth of colonies test strain on individual sectors of the membrane.

The objective of the invention is to eliminate the disadvantages of the prototype.

When using membranes based on cellulose acetates in the processes of quality control of drinking water and the isolation of the studied microorganisms from it, there is a problem of the so-called confluent growth of test strain colonies on separate sectors of the membrane or in the form of a continuous lawn on the entire filter, which makes it impossible to take into account the results of control. In this regard, it is necessary to eliminate these disadvantages by narrowing the spread of pore sizes by introducing a substance that prevents confluent growth, which is observed on the reverse side of the membrane during analyzes due to the presence of pores in the membrane, the size of which is larger than the size of the retained microorganisms. The technical result of the studied technical solution is to reduce the ratio of the maximum pore size to their minimum size to an indicator not exceeding 1.1-1.2. Additional technical results are:

-obtaining a uniform structure with a narrow pore size distribution;

-reduction of confluent growth of colonies of the test strain on the surface of the membrane when microorganisms are isolated from water.

This technical result is achieved due to the fact that the invention includes: obtaining a semi-permeable cellulose acetate membrane by preparing a molding solution by dissolving cellulose acetates in a mixture of a precipitant, water, a plasticizer and an organic solvent, while one type of cellulose acetate should be with a low content of bound acetic acid , ranging from 53% to 56%, and another type of cellulose acetate should be with a high content of bound acetic acid, ranging from 57% to 62%, the introduction of Tween-80 polysorbate into the solution, which allows to reduce confluent growth of colonies of the test strain on the surface of the membrane during the release of microorganisms from water, thermostatting the molding solution for 6 hours at a temperature of 28-30°C, and molding, which is carried out at a degree of substitution of the vapor-air mixture of solvents and precipitants with prepared air of 15-20 volumes of the molding zone per hour. When implementing this method, the technical results are achieved by improving the structure of the membranes and reducing the ratio of the maximum pore size to the minimum size to a value not exceeding 1.1-1.2.

Brief description of the figure.

A flowchart of the method for obtaining a cellulose acetate membrane is shown in Figure 1. Figure 1 shows: 1 - the stage of preparing the molding solution, 2 - filtration and temperature control of the solution, 3 - the stage of membrane molding and drying.

Brief description of the table.

Table 1 reflects the conditions for obtaining and measurement results D _max / D _min (D _max - maximum pore size to minimum pore size)

Implementation of the invention.

The method for producing a cellulose acetate membrane is characterized by the fact that at stage 1 of the preparation of the molding solution, cellulose acetates are dissolved in a mixture of an organic solvent, a precipitant, water and a plasticizer (with the addition of Tween-80 polysorbate), at stage 2 - filtration and temperature control of the solution after filtration. Thermostating is carried out at certain temperature values. At step 3, the molding solution is applied by means of a die onto a moving metal belt (in a particular embodiment of the invention, the belt is made of stainless steel) on a drum-type machine and dried.

The method is carried out as follows:

- prepare a molding solution by dissolving cellulose acetates in a mixture of organic solvent, precipitant, water and plasticizer;

- add polysorbate "Tween-80" to the molding solution;

- carry out filtration and temperature control of the molding solution. It has been experimentally proved that in order to achieve a technical result, it is necessary to carry out temperature control for 6 hours at a temperature of 28-30°C;

- carry out molding and drying. During molding, a molding solution is applied to a moving metal band, such as stainless steel. Molding is carried out at a set air flow rate of 50-200 m ³ /h for 0.5-3.5 minutes. It has been experimentally proved that in order to achieve a technical result, it is necessary to maintain a flow rate - the degree of substitution of the vapor-air mixture of solvents and precipitators - to maintain 15-20 volumes of the molding zone per hour with prepared air. At the same time, for one revolution of the molding solution on a drum machine, the membrane becomes practically dry, since the solvent - methylene chloride, the boiling point of which is 34 ° C, is removed from the membrane in one revolution of the tape, as a result, an almost dry finished membrane is wound on a roll. Prepared rolls with a membrane are placed in a separate room where they are stored and dry naturally.

The applicant has conducted several laboratory tests, the results of which have identified several embodiments of the invention.

The following substances were used in the tests:

- cellulose acetate, one kind of cellulose acetate should be low in bound acetic acid, ranging from 53% to 56%%, and the other kind of cellulose acetate should be high in bound acetic acid, ranging from 57% to 62 %, according to TU 20.16.59-04507510508-19;

- organic solvent - methylene chloride;

- precipitants: aliphatic alcohols (ethanol, butanol, propanol or isopropanol) or a mixture of aliphatic alcohols;

- water;

- plasticizer: glycerin, polysorbate Twin 80 (at a ratio of 70:30 to 50:50).

When implementing the method, D _min - the minimum pore size (hereinafter - D _min ) and D _max - the maximum pore size (hereinafter - D _max ) were determined, necessary for passing through the pores of the semipermeable membrane of the first bubble and the maximum flow of air bubbles. Determination of D _min and D _max was carried out as follows. To do this, a sample of a semipermeable membrane was fixed on the drain at the bottom of the test cell, distilled water was poured in, and then air was slowly supplied through the branch pipe to the bottom of the cell. The manometer was used to measure the pressure at which the first air bubble penetrated through the pores of the semipermeable membrane, after which the pressure was continued to increase and the pressure was noted at which the maximum flow of air bubbles appeared on the surface. Next, D _max was calculated by the formula:

cos

/Р, (1)D _max =4

cos

/P, (1)

- поверхностное натяжение воды (дин/см) на границе раздела с воздухом; Р - давление, при котором проникает первый пузырек воздуха (дин/см²);

- краевой угол смачивания (угол

равен 180° и, соответственно,
cos угла

равен 1). Д_мин вычисляли по формуле (1), в которой в этом случае Р - давление, при котором на поверхности появлялся максимальный поток пузырьков воздуха (дин/см²). У полученной ацетатцеллюлозной мембраны определяли Д_мин и Д_макс, рассчитывали соотношение Д _макс/Д_мин и исследовали сливной рост. Сливной рост определяли по МУ 2.1.4.1057-01. Способ получения полупроницаемой ацетатцеллюлозной мембраны осуществляли путем приготовление формовочного раствора за счет растворения при постоянном перемешивании ацетата целлюлозы в смеси органического растворителя, осадителя, воды, пластификатора, фильтрации и термостатирования в течение 6-8 часов при температуре 28-30°С. Нанесение же формовочного раствора производят посредством фильеры на движущуюся металлическую ленту.where D _max is the maximum pore size,

- surface tension of water (dynes/cm) at the interface with air; P is the pressure at which the first air bubble penetrates (dynes/cm ² );

- contact angle of wetting (angle

is equal to 180° and, accordingly,
cos angle

equals 1). D _min was calculated by formula (1), in which in this case P is the pressure at which the maximum flow of air bubbles appeared on the surface (dynes/cm ² ). The obtained cellulose acetate membrane was determined by D _min and D _max calculated the ratio of D _max /D _min and investigated confluent growth. Confluent growth was determined according to MU 2.1.4.1057-01. The method for producing a semipermeable cellulose acetate membrane was carried out by preparing a molding solution by dissolving with constant stirring cellulose acetate in a mixture of an organic solvent, precipitant, water, plasticizer, filtration and thermostating for 6-8 hours at a temperature of 28-30°C. The application of the molding solution is carried out by means of a spinneret on a moving metal tape.

1 example.

In a particular embodiment of the method for producing a semi-permeable cellulose acetate membrane, a molding solution was prepared by dissolving 7.0-8.0 wt.h. cellulose acetate in a mixture of an organic solvent - methylene chloride (49.0-57.0 parts by weight); precipitant - isopropanol (8.4 wt.h.), ethyl alcohol (23.0-30.0 wt.h.), water (2.1 wt.h.) and plasticizer - glycerol (1.75 - 1.25 wt.h.) and Tween-80 (0.75-1.25 wt.h.), the conditions of temperature control of the molding solution - 6 hours at a temperature of 28-30°C. The obtained cellulose acetate membrane was determined by D _min and D _max calculated the ratio of D _max /D _min and investigated confluent growth. The results D _max /D _min were entered in table 1. All the results obtained confirm that when using the specified compositions of the casting solution, the stated technical results are achieved.

Example 2

In a particular embodiment of the method for producing a semi-permeable cellulose acetate membrane, a molding solution was prepared by dissolving 7.3 wt.h. cellulose acetate in a mixture of organic solvent - methylene chloride (56.6 parts by weight); precipitant - isopropanol (8.4 parts by weight), ethyl alcohol (23 parts by weight), water (2.2 parts by weight) and plasticizer - glycerol (1.3 parts by weight) and Tween-80 ( 1.2 wt.h.), the conditions of temperature control of the molding solution - 6 hours at a temperature of 30°C. The resulting semipermeable cellulose acetate membrane had D _cf =0.46 µm and D _max =0.51 µm; D _max /D _cf =1.1. At the same time, confluent growth was absent.

Thus, it has been experimentally proved that the conditions for thermostating the molding solution are 6 hours at a temperature of 28-30°C.

Table 1 No. The composition of the molding solution Conditions
temperature control. D _max / D _avg The presence of confluent growth AC, wt.% Methylene chloride wt% Isopropyl Sirt, wt.% Ethanol, wt.% Water, wt.% Glycerin, wt.% Twin-80, wt.% 1 7.0-8.0 49.0-57.0 8.4 23.0-30.0 2.1 1.75-1.25 0.75-1.25 6 h (28-30). °С 1.1- 1.2 No 2 7.3 56.6 8.4 23 2.2 1.3 1.2 6 h 30°С 1.1 No Known method (according to the prototype) 3 7.2 52.5 7.8 27.0 3.1 2.3 - 15 h 26°С 1.3 There is

It follows from the table (examples 1, 2) that the introduction of Tween-80 polysorbate into the solution eliminates confluent growth on the reverse side of the membrane by obtaining a narrower pore size distribution.

The use of the proposed production method provides, in comparison with known methods, the following advantages:

a more uniform membrane structure is achieved;

the time of temperature control of the solution is reduced;

expanding the scope of membranes in various microbiological assays.

Twin-80 (TWEEN-80) - polysorbate, monooleate, non-ionic surfactant. It is obtained from sorbitol and fatty acids of olive oil by a chemical method. Name synonyms: polysorbate-80, food additive E 433, polyoxyethylene (20) sorbitan monoaleate. The chemical formula is C64H26O124. From the point of view of chemistry, the reagent is an ethoxylated monoester of anhydrohexavites of fatty acids. [https://pcgroup.ru/blog/tvin-80-populyarnyj-emulgator-dlya-rastitelnyh-masel/, publ. November 25, 2014].

Claims (2)

1. A method for producing a cellulose acetate membrane, which includes preparing a molding solution by dissolving cellulose acetates in a mixture of an organic solvent, a precipitant, water and a plasticizer, filtration, temperature control, applying a molding solution to a moving metal tape, molding and drying, characterized in that one type of acetate cellulose should be low in bound acetic acid, ranging from 53 to 56 wt. %, and the other type of cellulose acetate should be high in bound acetic acid, ranging from 57 to 62 wt. %, polysorbate "Tween-80" is added to the molding solution, the molding solution is thermostated for 6 hours at a temperature in the range of 28-30°C, and the molding is carried out at the degree of substitution of the vapor-air mixture of solvents and precipitants with prepared air in the range of 15-20 zone volumes molding per hour. 2. A method for producing a cellulose acetate membrane according to claim 1, characterized in that a stainless steel metal strip is used.

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