NL7905816A - MEMBRANE WITH POROUS SURFACE. - Google Patents

Description

* I A GW 1843

Membrane with porous surface.

! The invention relates to a membrane in the form of a flat film, tubular film or hollow wire from synthetic polymers, to a method of manufacturing the membrane, and to the use thereof, in particular as a filter or membrane support for separation purpose i | ends.

Membranes in the form of a flat film, tubular film or hollow wire have been known for a long time. A variety of methods are available to those skilled in the art to to manufacture such membranes from the most diverse polymers.

i s; Hollow threads can be processed in the manufacture of textile products, but are also used for filtration, ultrafiltration, micro-filtration, dialysis, reverse osmosis, etc. · | j i i • When using membranes in the form of flat films, tubular films or | 1: hollow wires in separators, the permeability and the selectivity of the membranes are decisive, since the membrane | 15 | branes must, on the one hand, retain certain substances and, on the other hand, other substances, e.g. the solvent of a solution should be as soon as possible:! let through. j; ! ; Films with a microporous or porous structure have long been known. So j; In German Offenlegungsschrift 27 37 745 methods of working are described. I have described the manufacture of films having a porous or microporous structure. The structures described therein are undoubtedly valuable! i products which are used in many fields.

After finishing the teaching described therein, however, it was found that the films thus obtained generally have a closed surface. In the 25! in particular, it appears to be impossible to obtain films which have pores on both sides which are known as openings directly on the surface. There is therefore a need for improved processes for the production of such membranes, in particular for processes in which porous films with both good permeability and high 3 µ selectivity are obtained, which additionally have open pores on both sides and yet have a smooth and flat surface structure .

For example, a method of manufacturing hollow fibers with selective permeability is described in German Auslegeschrift 14 94 579, 7 9 Q..5 8 1 6 i -2- whereby hollow threads are obtained from a homogeneous mixture of a thermoplastic polymer and a plasticizer by melt-spinning, from which the plasticizer is subsequently removed. One of the requirements is that the plasticizer can be easily and practically completely removed from the spun fiber. Often, however, the removal of the plasticizer requires a rather time-consuming treatment of the wire and it is not always possible to remove the plasticizer as a whole. In addition, the hollow fibers obtained by this method have a relatively low permeability. Finally, it is not possible to vary the plasticizer-polymer ratio within a wide range. This is because filament formation does not occur with a high plasticizer percentage, while too low a permeability is obtained with a plasticizer percentage that is too low. In addition, there is a risk of the plasticizer not being adequately distributed over the thermoplastic polymer during mixing, resulting in build-up which, when washed out, creates holes or pores that are too large, rendering the hollow fibers useless for many purposes.

Another method for manufacturing hollow wires is described in German Auslegeschrift No. 2 346 011. Here a solution of an i | copolymer from acrylonitrile spun in an aqueous solution of 20! mineral salts. It is thereby required that, with a view to the coagulation in the core, coagulation liquid is also injected therein. However, the method described in this Auslegeschrift is rather complicated, while it is moreover difficult to obtain hollow wires with constant properties.

US-A-3 674 628 discloses a method according to which first a solution of a fiber-forming polymer is spun, then the outer and optionally also the inner zone is gelled, and then, or simultaneously, both zones are coagulated. This produces a hollow fiber, which has a skin-shaped structure internally and externally. However, the method according to this US patent is also rather complicated, while moreover the permeability of the obtained hollow wire leaves something to be desired.

Although many membranes in the form of flat films, tubular films or hollow wires are already known, there is still a need for improved membranes, especially those that can be easily produced from a simple spinning mass without the use of wrapped spinning baths. There is also a need for improved membranes which are porous and which are distinguished, inter alia, by good permeability coupled with a high selectivity.

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The object of the invention is to provide porous membranes which are advantageously distinguished from the known membranes by an open surface; flat and of which both the outer and inner walls have an open-pored, yet smooth structure.

Another object of the invention is to provide membranes which, in addition to | in the textile sector also in the technical and medical sector, e.g. when separating j | theses processes can find application and are especially suitable as a filter, 10 1 micro filter, membrane support and substrate for certain substances.

i [! This is achieved by membranes in the form of flat films, tubular films or hollow threads of synthetic polymers, which are characterized by this; that they contain 10 to 90% by volume of interconnected pores and have a smooth open pore surface, these open pores occupying 10 to 90% of the surface. The apparent density of the hollow wire is between about 10 and 90% of the actual density of: the polymer used; the permeability coefficient is at least,

1 -12 2! : 10. 10 cm. I

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; (; The membranes can be used as a filter, especially in microfiltration.

20! The membranes can also serve as a membrane support, which means that a layer is applied to the membrane which also acts as a membrane, optionally * with other permeabilities and selectivities.

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The membranes can also be used as a substrate, which means that they are soaked with certain substances to be released later. They can also be used as oxygenators.

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Another object of the invention is to provide a method in which polymers can be converted into a spinning mass in a simple manner and spinning thereof can also take place without having to use complicated spinning techniques or spinning baths. Another object of the invention is to provide a method in which it is possible to obtain membranes of different porosity and permeability merely by varying process conditions.

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This object is achieved by a method of manufacturing hollow wires, which is characterized in that a homogeneous mixture of at least two components, one of which is formed by a meltable polymer and the other by a liquid inert to the polymer. And which together form a binary system having in the liquid state an area of complete miscibility and an area of incomplete miscibility, spun at a temperature above the demixing point in a bath containing the same inert liquid as the mixture to be spun and whose temperature is below the demixing point and that the formed membrane solidifies in the form of a flat film, tubular film or hollow wire.

Subsequently, the solid membrane thus obtained can be washed with (I) using a solvent, to which in particular acetone lends itself.

It is advantageous if there is an air gap between the exit surface of the extruder 15 and the surface of the spin bath. This air gap can be heated.

It is also possible to spin the homogeneous mixture directly into the bath.

In a special embodiment of the method according to the invention, a bath with a determined temperature profile is used. The bath can consist of one or more parts which exhibit a temperature gradient such that the temperature decreases continuously from start to finish of the spin bath.

It is also possible to use two or more separate baths of different temperatures.

It is advantageous if the temperature of the bath is at least 100 ° C below the demixing point of the binary composition used. In the case of tubular film and hollow wires in particular, the homogeneous mixture can also first be passed through a spinning housing placed in front of the spinning bath and filled with spinning bath liquid.

According to the invention, homogeneous mixtures of 10 to 90 wt. % and 90-10 wt. % inert liquid are spun.

7905816 i -5- i ί> i Preferably polypropylene as polymer and inert liquid i | NN-bis- (2-hydroxyethyl) -hexadecylamine is used.

Preferably, the two components, i.e. molten polymer and inert liquid, are continuously mixed before extrusion, it being advantageous that the mixing only takes place immediately before spinning. The | obtained mixture can still be homogenized before spinning. For | the mixing can in particular use a pen mixer.

i s | For the manufacture of the membranes according to the invention, use can be made of customary per se, in particular fiber-forming, macromolecular substances, in particular synthetic polymers obtained by polymerization, polyaddition or polycondensation, provided that these are: fusible, ie without decomposing into the liquid state, ji can transition and with the inert liquid to them form a binary system ji which, in the liquid state, adjoins an area of completely miscible | exhibits an area of incomplete miscibility. j i i i. In the liquid state, such systems display a phase diagram such as:! ; for example in the Textbook of Physical Chemistry by S. Glasstone, i Macmillian and Co. Ltd, St. Martin's Street, London, 1953, at page 724 j; for the aniline hexane system is shown. For t 20j this diagram shows both components above the curve full miscibility, while below i the curve the two liquid phases are in balance.

It is not absolutely necessary for the practicability of the invention! j that in the 2-phase region the two components still show a considerable solubility with respect to each other, as shown in the diagram above-j. Usually it is sufficient if a certain minimum solubility still exists in the liquid 2-phase region. However, it is essential that the two components form two liquid phases next to each other in the liquid state. This distinguishes the systems which can be used according to the invention from those systems in which the dissolved polymer immediately changes to a solid state when the temperature decreases without first going through the liquid state during cooling.

Within the scope of the invention, the conventional fusible poly- mers are used such as the polymers obtained by polymerization 79058-1-6-polyethylene, polypropylene, polyvinyl chloride, polyacrylates, polycaprolactam as well as corresponding copolymers; polycondensation polymers such as polyethylene terephthalate, polybutylene terephthalate, polyamide-6.6, polyphenylene oxide and polyaddition polymers such as polyurethane and polyurea.

Within the scope of the invention, in principle, all liquids which form a binary system of the above-mentioned type with the polymer in the liquid state are suitable for use as an inert liquid. Inert with respect to the polymer means that the liquid does not cause a significant degradation of the polymer or reacts with the poly-10 itself within a short time.

| Even though the aforementioned diagram for the aniline hexane system gives the! ! for a binary system consisting only of two essentially pure, stand-alone substances, the term binary | system within the scope of the invention is not to be strictly construed as referring to mixtures of only two pure, by themselves. i.

j standing fabrics. The person skilled in the art knows that a polymeric substance is composed of a large number of molecules of different molecular weight, which is why such polymers are to be regarded as a single component within the scope of the invention. The same is true for mixed polymers. Under certain conditions, polymer blends may even behave as a single component, form a one-phase mixture with the inert solvent, and divide into two liquid phases under the critical temperature. Preferably, however, only one polymer is used.

Also the inert liquid need not be completely pure and only form a single stand-alone substance. For example, it often does not produce any objection if it contains small amounts of impurities and possibly a certain percentage of homologous compounds, such as large-scale manufacturing entails.

For the practical implementation of the process, a homogeneous mixture is prepared from the two components at the required temperature. This can be done in such a way that the inert liquid is mixed with the finely divided polymer and heated to the correct temperature, ensuring appropriate mixing.

790 5 8 1 6 --- “1 I -7- i I Another suitable method is that the two components | separately brought to the required temperature and only mixed briefly before the extrusion in the required ratio.

ί | This mixing can take place in a pin mixer placed between the metering pumps of the individual 5 I components and the spin pump. It may then be desirable to carry out a homogenization.

ί | It is often recommended to adjust the homogeneous mixture by setting! vent a suitable vacuum before extrusion.

| . The polymer / inert liquid ratio in the spinning mass can be varied within wide 10: limits. By varying this ratio the pore volume in the interior, the surface structure and the number of open pores on the surfaces of the membrane obtained can be strongly influenced. As a result, membranes suitable for a wide variety of purposes can be obtained.

J: 15 In general, it is sufficient if the temperature of the homogeneous mixture before spinning is only a few degrees above the critical temperature; temperature, i.e. above the demixing point of the respective composition.

! i; However, by increasing the difference between the temperature of the homogeneous mixture to be spun and the demixing point, interesting

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Effects on the structure of the membrane obtained are obtained. got.

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The homogeneous spinning mass is extruded in a bath containing the inert liquid of the extruded component mixture, the temperature of which is below the demixing point. Preferably, the bath consists wholly or largely of the inert liquid which is also present in the mixture to be extruded.

The bath temperature is below the demixing point of the binary mixture used, i.e. below the temperature above which the two components are completely homogeneously miscible. Preferably the temperature of the bath is at least 100 ° C below the demixing point of the binary mixture used.

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The temperature may also already be so low that, according to the phase diagram applicable to the binary system, one is already within the range in which a solid state occurs.

If the temperature of the bath is so high that it is still in the liquid 2-phase region, then it is required to bring the forming membrane structure to the solid state as soon as possible, which can take place because, after a certain distance has traveled within the bath, the temperature is lowered accordingly.

Importantly, before reaching the bath, the extruded mixture is still in one phase, i.e. essentially no two-phase separation has taken place.

It has been found that the advantage, especially when the membrane is to take the form of a tubular film or hollow wire, is in certain cases to provide a spinning housing before the bath, which is also filled with the bath liquid and reaches into the spinning bath. This spinning housing may be provided with a conventional spinning funnel at its inlet opening and bent at its lower end to facilitate transport of the membrane through the bath.

The filling of the spinning housing can take place via an overflow vessel surrounding this. For a complete filling of the spin house and the maintenance of the level therein, it is necessary that more liquid is supplied to the overflow vessel from a main reservoir than flows out through the spin house. The excess spin bath liquid can be returned to the main reservoir via a second overflow from the overflow vessel. Main reservoir and overflow vessel 25 can be equipped with a thermostatic control.

After leaving the spin bath, the membrane can be washed with a suitable extractant. A large number of solvents, such as e.g. acetone, cyclohexane, ethanol etc. as well as mixtures thereof are used.

In some cases, washing out of the membrane is not required, especially in those cases in which the inert liquid used must itself impart to the thread certain additional properties which are relevant for the later field of application, or to have its own function. For example, e.g. liquids which have an antistatic effect are used 7905816 ..11 I I I. .......... .1 I I II · I I ... M - I — I I, .1 .... I ... -. For example, it has been found particularly useful for a range of application areas between the exit face of the extruder, i.e., the exit face of the extruder. For example, provide a spinneret and the surface of the bath to provide an air gap. It is possible to change the size of the air gap mainly influence the structure of the obtained membrane from its surface. For example, it was established that by extension resp. shortening the air gap, the number of open pores in the surface decreases resp. increases.

| As the air gap increases, the diameter of the pores decreases.

j [! 10! The air gap can be heated, for example at a temperature above:; i • the demixing point of the mixture to be spun. j s

In general, the size of the air gap (the length of the

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[path over which the extrusion product moves through the air) at least! ί:; about 1 mm. Depending on the circumstances, the air gap size may vary; 15 ί rise to about 10 cm. It is important that, before reaching the bath, no or at least no noticeable separation in two liquid phases occurs in the air gap. As already stated, this can be done by controlling the length of the path to be followed. or be controlled by heating, but it is also possible to prevent premature segregation by increasing the outflow rate from the extruder.

j; j j; According to a special embodiment of the method according to the invention! - 1; However, the homogeneous mixture is extruded directly into the bath; », F whereby open pores with a maximum diameter are created on the surface. j

The membranes obtained are very suitable for use as a filter, especially in microfiltration and ultrafiltration. They are especially suitable for application in the medical field, where they e.g. because of their selectivity for the secretion of bacteria, in blood filtration e.g. can be used to separate platelets. They are also very suitable as oxygenators, the oxygen flowing on one side of the membrane 30 and the blood on its other side.

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For a number of application purposes, the membranes can also serve as a support for other membrane layers. Because of their very smooth, open-pore surface structure, they can be extremely well covered with a highly adhesive thin layer of a membrane-serving material, which often takes place by brushing or spraying with suitable film-forming solutions. Because of the excellent surface properties, the membrane layer that forms thereby adheres very well to the membrane. The solution can be applied as a thin skin without penetration or seepage into the hollow wire, allowing the realization of highly effective membrane associations for a wide variety of application areas.

Due to their excellent internal and external structure, the membranes are also particularly suitable for use as a substrate for certain substances. It is also possible to apply such substances in the internally continuous hollow space of a hollow wire membrane.

In this way, objects in the form of a flat film, tube film or hollow wire, possibly parts thereof, can be obtained, which slowly release the absorbed material again. The membranes according to the invention can also be used for adsorption of substances.

According to the invention, films of the usual dimensions, e.g. with a thickness of 20 µm to a few mm. The films can be flat or tubular. They can also be used for isolation purposes, e.g. thermal insulation or soundproofing are applied.

According to the invention, hollow wires of very different dimensions can be obtained. External diameters of several mm are thus possible, while the wall thickness can also be varied within very wide limits, e.g. from 20 Um to 1 to 2 mm.

The pores in the membranes according to the invention can have the most diverse shapes. For example, they can e.g. be round or oblong. They are in communication with one another, partly by means of small hollow spaces, partly because they merge directly into one another. Even with membranes obtained from mixtures with a polymer content of only about 30%, the polymer can still form the matrix into which the individual pores are divided and still more or less discrete, but interconnected hollow 7905816 Ί! '1711! i: form spaces. Conversely, structures can also arise in which the hollow spaces form the matrix in the same way as with membranes and the polymer substance has a quasi-fibrillated structure. These two structures merge smoothly and partly also appear mixed.

However, the structure forms can also be processed by further process conditions such as | transport speed, cooling speed, stretching after spinning, affected turn into.

The membranes according to the invention are characterized in particular by a high permeability to gases such as nitrogen or air. This permeability can be achieved by means of the so-called permeability coefficient. cient K, as explained in more detail on p. 10 of it! i I book Flow of Fluids through Porous Materials by R.E. Collins, published! i by Reinhold Publishing Corp., New York 1961. K is defined by,

i K = Q. η, where Q is the flow rate (e.g. in m ^ / s) and η is the viscosity of; i A (Δ P / h) I

15 i is the flowing medium (Pa.s), A is the average area through which the gas | j j emerges, Δ P is the differential pressure (Pa) and h is the wall thickness. i i 't; :

The permeability coefficient of the membranes according to the invention is at least 10. 10 cm, preferably at least 22. 10 cm! -12 2 -i while values above 100. 10 cm can be reached.

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! j: 20 | For membranes in the form of flat films or tube films, the measurement i! I of the permeability coefficient takes place using nitrogen, which is a f; pressurized flange-mounted film. Using a flow rate; j · | meters the air leaving the film was measured. !

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| Films according to the invention, which were made from a mixture of 30 wt.% Polypropylene and 70 wt.% NN-bis (2-hydroxyethyl) hexadecylamine using an air gap between extruder and bath, were able to determine the following values: -12 2 K (x 10 cm) Air gap 52 5 30 27 10 «

Measurement was performed as follows for hollow wire membranes:

A 5 cm long PVC hose was placed around each end of a bundle of 31 cm long hollow wires. The hollow wires were then embedded in a curable polyurethane mass at 7905816''T ends. After the polyurethane has cured, one of the PVC hoses is cut and the exposed openings of the hollow wires are connected to a nitrogen bottle by means of a pipe. The end of the other hose is closed with a 5 stopper. The gas emerging from the wires is measured using a flow meter. The bundle of wires is located in a measuring chamber. For hollow filament membranes according to the invention, which were obtained from a mixture of 30 wt% polypropylene and 70 wt% NN-bis (2-hydroxyethyl) hexadecylamine using an air gap between extruder 10 and spin bath, the following values were used determined: -12 2 K (x 10 cm) Air gap (mm) 99 3 22 20 iThe hollow wire membranes according to the invention can also be used for insulation purposes.

A device suitable for the production of hollow membrane wires according to the invention is explained in more detail with reference to Figure 1. Herein 1 is a vessel with a thermostatic temperature control, from which the inert liquid is supplied to the mixer 8 via a double-plunger pump 3 and a heating device 4. Preheating of the liquid takes place by means of the heating device 2. From the pellet vessel 5, polypropylene is supplied via an extruder 6 and a gear pump 7 to the mixer 8, after which the resulting mixture is fed via a gear pump 9 to a spinneret 10 for making of hollow wires, which is supplied with the required amount of nitrogen by means of a rotameter 17. The outflowing mass enters via an air gap into a spinning housing 12 provided with a spinning funnel 11, which is supplied with inert liquid from the main reservoir 14 via an overflow vessel. The spinning housing has a curvature at its lower end. When leaving the bath 15, the wires are led to a winding device 16.

The invention is further illustrated by the following examples.

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Example 1

In an extruder, at heating temperatures of 260 to 280 ° C, poly-35 propylene with a melt index of 1.5 g / 10 min is melted, after which the melted 7905816> * s [! -13- "becomes mass via an gear pump to an intensively mixing pen mixer! supplied.

i; At the same time, NN-bis- (2-hydroxyethyl) hexadecylamine, which is used

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of a flow heater is preheated to 135 C, by means of a \ 5 j pump with double plunger via a separate pipe also on the | mixer supplied.

The mixing ratio of polypropylene: amine is 30:70 many of the mixer is set to 400 rpm.

! After passing through the mixer, the two become a homogeneous mass molded fabrics pressed into a spinneret at a speed of 15 g / min for manufacturing hollow wires, which cap has an annular gap of; 1200 ym internal diameter and 2000 ym external diameter. With the addition of 4 1 / h nitrogen to the gas capillaries of the spinneret, the hollow thread is formed. After a free fall of 3 mm, the freshly spun liquid thread enters the spinning funnel filled with amine as spinning bath liquid and then flows; with this liquid through a 400 mm long spinning housing of 8 mm 0 to the 1 m long spinning bath and after it has been run through at a speed of 7 m / min: is wound up on a rinsing device.

20; The resulting hollow wire is extracted with alcohol and stripped of amine.

! The hollow wire has a diameter of 2200 µm and an internal diameter. of 1400 ym.

Example 2 25 j Polypropylene granules are melted in an extruder and fed to a pin mixer via a gear pump.

At the same time, liquid NN-bis- (2-hydroxyethyl) hexadecylamine at a temperature of 40 ° C is pumped from a heatable storage reservoir through a double plunger pump to an electric heating device 30 and then passed into the mixer at a temperature of about 150 ° C . A pin mixer is used as a mixer. After homogeneous mixing of the two components, the molten mass is forced through a measuring pump through a spinner head with slit and immediately extruded into the bath, which consists of pure ij NN-bis- (2-hydroxyethyl) hexadecylamine and has a temperature of 50 ° C. C.

After passing through the bath, the length of which is 50 cm, the film obtained is extracted with ethanol and then dried. The resulting 7905816 -14 foil exhibits excellent membrane properties and has a particularly good surface texture.

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Claims (4)

Membrane in the form of a flat film, tubular film or hollow thread of synthetic polymers, characterized in that it contains 10 to 90% by volume of interconnected pores and has a smooth open-pore surface, these open pores Take up 10 to 90% of the 5 surface. Membrane according to claim 1, characterized in that the apparent density thereof is between 10 and 90% of the actual density of the polymer used. f Membrane according to claim 1 or 2, characterized in that it has a permeability coefficient of at least 10. Possesses 10 cm. 4. Method for manufacturing a membrane in the form of a flat ί! film, tubular film or hollow wire according to any one of claims 1 to 3, characterized in that a homogeneous mixture of at least two [components, one of which is formed by a meltable polymer 15 'and the other by one with respect to the polymer inert liquid and which together form a binary system which in the liquid state has an area of complete miscibility and an area of incomplete miscibility, is extruded at a temperature above the demixing point in a bath containing the same inert liquid as the one to be extruded mixture 20. the temperature of which is below the demixing point, and the membrane becomes solid in the form of a flat film, tubular film or hollow wire [I]. i A method according to claim 4, characterized in that the formed membrane is washed with a solvent after solidification. Method according to claim 5, characterized in that acetone is used for washing out. A method according to any one of claims 4 to 6, characterized in that an air gap is provided between the exit surface of the extruder and the surface of the spin bath. 7905816 -; - Method according to claim 7, characterized in that the air gap is heated. Process according to any one of claims 4 to 6, characterized in that the homogeneous mixture is extruded directly into the bath. Method according to any one of claims 4 to 8, characterized in that the temperature of the bath is at least 100 ° C below the demixing point of the binary mixture used. 11. A method according to any one of claims 4 to 9, characterized in that the homogeneous mixture is first passed through a spinning housing placed in front of the spinning bath and filled with spinning bath liquid. Method according to any one of claims 4 to 11, characterized in that polypropylene is used as the polymer. 13. Process according to any one of claims 4 to 12, characterized in that NN-bis- (2-hydroxyethyl) hexadecylamine is used as the inert liquid. Method according to any one of claims 4 to 13, characterized in that a bath with a defined temperature profile is used. 15. A method according to any one of claims 4 to 14, characterized in that a homogeneous mixture of 10-90 wt.% Polymer and 90-10 wt.% Inert liquid is used. A method according to any one of claims 4 to 15, characterized in that the two components are continuously mixed before extrusion. Method according to claim 16, characterized in that a pen mixer is used for mixing. A filter formed by a membrane according to any one of claims 1 to 3, respectively. through a membrane obtained by the method according to any one of claims 4 to 17. 7905815 j -17-t i! Filter for microfiltration formed by a membrane according to any one of claims 1 to 3 or by a membrane obtained by the method according to any one of claims 4 to 17. Membrane support formed by a membrane according to any one of claims 1 to 3, respectively by a membrane obtained by the method j according to any one of claims 4 to 17. t Substrate formed by a membrane according to any one of claims 1 to 3 or by a membrane obtained by the method according to any one of claims 4 to 17. Oxygenator formed by a membrane according to any one of claims 1 to 3, respectively a membrane obtained by the method according to any one of claims 4 to 17. t! t = i i] \ ί *. I i 7905816 * Tl xJ - V 'T71 T 6 0 Li_ 4 Y_I-1 CD '"’ 8 Hvïïïïïïï�H | | Al [l | l | l | l | hL 9 Φ Hin 10 τΦ pl v 13 17:::; _; » ^ -15 _ - w 16 ^ 790 5 8 1 6