AU570508B2 - Hydrophyllic ultra filter - Google Patents

Description

TREATMENT OF POROUS MEMBRANES

FIELD OF INVENTION

This invention relates to porous membranes, particularly those having pores in the range of about 0.01 to 1 micron which are hereinafter called "fine pored filtration membranes".

BACKGROUND ART

Various types of fine pored filtration membranes have been developed, however, the cheaper and more useful types such as those made of polyolefines, polysulphones, ^• poly(vinylidenefluoride) , poly(dimethylphenyleneoxide) and poly(acrylonitrile) are normally hydrophobic and completely resist initial water permeation up to high pressures such as those above 10. Pa due to surface tension effects. The water permeation of the above-mentioned membranes can be substantially improved leading to hydraulic flow at low pressures, once the voids or pores have been wetted.

Although the voids or pores may be wetted by the addition of "surfactants" followed by continuous wet storage in water or humectant solutions, these procedures are not stable to washing, heating and drying as is required for heat sterilisation at 122°C. Such temporary wetting procedures fail with polypropylene.

There is a need for mechanically strong, highly stable membranes of controllable pore size and hydrophilicity and this need has been highlighted in recent symposia - see, for example, the chapter "Practical Aspects in the Development of a Polymer Matrix for Ultrafiltration" by Israel Cabasso in "Ultrafiltration Membranes and Application", editor A. R. Cooper (1979) ISBN 0-306-40548-2.

O The most recent approaches to the solution of this problem have involved preparing expensive hydrophilic special polymers. The cheaper hydrophilic polymers such as cellulose, hydrophilic nylons and cellulose esters do not resist hot, strong acids nor do they resist small concentrations of chlorine or hydrogen peroxide sterilants. Furthermore, some of these cheaper polymers do not even tolerate repeated wetting and drying. Many of them swell greatly in water and shrink on drying. Thus, the prior art is characterised by expensive experimental procedures to create a particular hydrophilicity for each new polymer and no stable post-formation control has been possible.

It is an object of this invention to provide hydrophilicity treatment systems for fine pored filtration membranes which are initially hydrophobic. It is a further object of the invention to provide treatment systems which permit continuous variations in hydrophilicity and in which pore size control extends beyond the surface to include selective spatial modification of the^'pores such as more hydrophilic small pores rather than larger pores or vice versa.

DISCLOSURE OF INVENTION

According to the invention there is provided a process of treating a hydrophobic porous membrane so as to render it hydrophilic in which a hydrophilic material is deposited on the walls of the pores of the membrane.

The invention also provides a method of treating a hydrophobic porous membrane so as to render it hydrophilic by coating the walls of the pores of the membrane with a hydrophilic material in which the hydrophilic material is deposited on the walls of the pores by the reaction of first and second components of the material within the membrane.

OMPI Preferably, the method of the invention includes the steps of:

(a) preparing a deposition formulation of the first component, (b) passing the deposition formulation through the membrane under conditions of humidity and temperature that will ensure that the selected material is deposited from the formulation on the walls of the pores of the membrane at the desired concentrations and form,

(c) passing the second component through the membrane so that it will react with the first component to form the selected material, and, if necessary,

(d) stabilising the so treated membrane.

The invention also provides a method of treating a^' hydrophobic porous membrane so as to render it hydrophilic which comprises the steps of:

(a) selecting a material from the group:

(1) Polyamides and polyimides (2) Polyesters

(3) Polyurethanes

(4) Phenol/aldehyde resins

(5) Polyamide/aldehyde resins

(6) Epoxy resins (7) Interpolymers of materials 1 to 6

(8) Mixtures of materials 1 to 6

which can be formed on or in the membrane by the reaction of first and second components whereby the material is deposited on the walls of the pores of the membrane to provide the required hydrophilicity. (b) preparing a deposition formulation of the first component,

(c) passing the deposition formulation through the membrane under conditions of humidity and temperature that will ensure that the selected material is deposited from the formulation on the walls of the pores of the membrane at the desired concentrations and form,

(d) passing the second component through the membrane so that it will react with the first component to form the selected material, and, if necessary, Ce) stabilising the so treated membrane.

Preferably, the deposition material is selected from:

(a) Polyamides and polyimides formed from a first component such as primary or secondary amines and a second component such as acid halides and in which at least one of the first and second components is aromatic or substituted aromatic. The acid halide is normally used in excess to give chemical resistance and the average functionality is above two so that there is considerable cross- linking.

(b) Polyesters formed from a first component such as an hydroxyaromatic and a second component such as aromatic or hetero-aromatic acid chlorides

(including sulphonylchlorides) reacted such that the average functionality is above or equal to t o.

(c) Polyurethanes formed from a first component having - a reactive hydrogen group such as alcohols, amines, acids, ureas, urethanes, phenols and thiols and a second component such as an isocyanate. (d) Phenol/aldehyde resins which react very rapidly in aqueous media to precipitate fine, porous solids. Gaseous acidic catalysts may be used to ensure reaction in a mixture of polyhydroxyaromatics and low volatile aldehydes or pre-polymers of these two components. The water solvent can be easily evaporated from the hydrophobic porous base. Dry hydrochloric acid, sulphur trioxide, boron trifluoride or sulphury1 chloride may be admitted to speed up the reaction.

(e) Polyamine/aldehyde resins which are the reaction products of aromatic and heterocyclic amines (such as melamine) with aldehydes.

(f) Epoxy resins include all epoxides and their reaction products with reactive hydrogen groups such as alcohols, amines, acids, ureas, urethanes, phenols and thiols.

Preferably, the stabilisation step includes dissolving any unco bined material and hydrolysing excess terminal groups or reacting them further as desired to secure specific surface effects as given below. In some instances, the two components may be passed through the membrane together provided that there is sufficient delay in the commencement of the reaction between the components to enable them to be properly disposed.

The invention also provides a method of treating a membrane of non-uniform pore size so as to provide a membrane having a predetermined porosity in which a blocking material is deposited within selected pores and on the walls of the other pores of the membrane by the reaction of first and second components of the material within the membrane. Preferably, the first component is an emulsion in which the size of the dispersed phase and its interfacial tension with the continuous phase are such as to cause exclusion of the dispersed phase from pores which are smaller than the predetermined pore size. The emulsion may be formed from a primary or secondary amine, which is converted into a polyamide by an acid halide as previously described.

The blocking material may also be formed from:

Ca) an alcohol such as polyvinylalcohol and an isocyanate,

(b) a phenol such as resorcinol and an aldehyde such _ as formaldehyde,

(c) an epoxy resin and an amine.

According to a further aspect of the invention there is provided a method of treating a membrane of non-uniform pore size so as to provide a membrane having a predetermined porosity comprising the steps of:

(a) selecting a material from the group defined above which can be formed on or in the membrane by the reaction of first and second components whereby the material is deposited within selected pores and on the walls of the other pores of the membrane,

(b) preparing an emulsion of the first component of predetermined size and of such interfacial tension with the continuous phase so as to cause exclusion from pores below the predetermined size but to allow entry into the pores above the predetermined size, (c) passing the emulsion through the membrane under conditions of humidity and temperature that will ensure that the emulsion is held in the pores above the predetermined size, and. <gTT_R£

O P (d) passing the second component through the membrane so that it will react with the first component to form the selected material, and, if necessary,

(e) stabilising the so treated membrane.

The above aspects of the invention may be combined if so required and they may be complemented, either singularly or together, by further steps in which desired chemical groups such as carboxylic acid, sulphonic acid, quaternary bases, reducing groups, aldehydes or isothiocyanates as may be required in particular electrical, biological and affinity chromatographic applications of the fine pored filtration membranes.

The methods of the invention permit the preparation of fine pored filtration membranes of desired physical and/or chemical characteristics without the need of expensive experimental procedures.

The coatings or materials deposited by the methods of the invention will sometimes be in themselves novel and the particular method of application of the material may itself be novel. For example, it may be necessary to introduce new techniques such as supplying gaseous catalysts to affect spatially selected areas. When selecting the particular material with which to treat the otherwise unsuitable fine pored filtration membrane certain considerations must be borne in mind.

In general terms the choice of the material will be in the decreasing order of polyamide or polyimide, polyesters, polyurethanes, phenol/aldehyde resins, polyamine/aldehyde resins, epoxy resins, interpolymers of the foregoing and mixtures of the foregoing. The reasons for this preferred order include the availability of a wide range of cheap. co mercial intermediates, chemical stability, controllability of deposition place, controllability of pore size, controllability of hydrophilicity, low cost due to minimum handling and safety of chemical handling.

The order of preference is one of average circumstance choice and those skilled in applied polymer chemistry and fine pored filtration will at once perceive whether some cheap chemical raw material will confer the required chemical or mechanical property on the membrane to be treated. For example, in the case of cation exchange necessitating -SO3H groups in a matrix resistant to 30% NaOH at 80°C the choice of material would not be polyamide or polyimide but rather a phenol/aldehyde resin.

When the treatment is for hydrophilicity, acid and chlorine resistance, polyamides would be the best choice.. Cross-linked polyamides (or polyimides if suitable acid chlorides are used) are particularly useful as they are resistant to hot hydrochloric acid and chlorine and pH 13 for at least a year. Many functional groups may be incorporated in their structure, for example, a -SO^H group may be incorporated by using sulfanilic acid. However, when incorporating such functional groups allowance must be made for the mono-functional nature of the single - H2 group.

The cheapest available aromatic acid chloride of functionality two is terephthaloylchloride and thus it would be the preferred material. Such a material will give resistant products with any diamine or polyamine but high hydrophilicity demands that there will be a limit to the ratio of hydrophobic carbon groups to the hydrophilic nitrogen group. Ethylene diamine or triethylene tetramine may be used. Also any polyamine containing up to 20 carbon atoms per nitrogen atom may be used to give a continuous spectrum of reliable hydrophilicity.

OMPΓ x^ The polyester treatment materials have advantages where phenolic functional groups or sulphonic functional groups are required. The phenolic hydroxyl groups are useful when reactions with epoxides are required. Such epoxides may be gaseous such as ethylene epichlorhydrin dilute vapour which produces highly hydroxylated surfaces. Ethyleneimine can also be used in such circumstances.

When the polyurethane materials are used the reaction is usually anhydrous and is most useful where very rapid homogeneous reactions precipitate fine polymeric substances. The products are stable and swell well in water so that the membranes are often useful f.or electrodialysis.

The phenol/aldehyde resins are useful for chelating metals and they also form good electrodialysis membranes. The polyamine/aldehyde resins tend to be most useful where excess aldehyde groups allow easy conversion to a wide range of other chemical groups or compounds. . For example, aldehydes are excellent for binding antibodies which are used in affinity chromatography to isolate useful or harmful biological products.

One of the main uses of the epoxy resins is to overcoat the phenol/aldehyde resins since the latter tend to be rather coarse. In some cases interpolymers and mixtures of the materials may be used.

The deposition formulation may bia prepared using a hydrophobic solvent such as hexane which is allowed to evaporate. In some cases, more uniform films are obtained if a small amount of surfactant is included in the formulation. Chemical considerations may suggest addition of a hydrochloric acid absorbing substance such as a tertiary amine to ensure complete reaction of the substitutable amines. Alternatively, the treatment material may be dissolved in water, ethanol or a hydrophilic solvent. The hydrophilic solvent may contain a small amount of surfactant and a small amount of non-volatile hydrophilic humectant substance such as glycerol. Such hydrophilic solvent mixtures usually need considerable pressure to ensure displacement of all air from the membrane. Complete displacement of the air is vital if all the surface of the membrane is to be made hydrophilic. Lesser pressures leave the smaller pores hydrophobic which may, in some instances, be desired.

Irrespective of the nature of the formulation, control of the water content of the residual material film is essential for uniform results. For example, the water controls the rate of diffusion of terephthaloylchloride from a hydrophobic solvent in which it is applied. Water content control may be obtained by the relative humidity and temperature of the drying atmosphere and the hydrophilicity of the deposited film depends greatly on the composition and amount of any surfactant or humectant used.

DESCRIPTION OF PREFERRED EMBODIMENTS

In order that the invention may be more readily understood reference will now be made to the following examples:

Example 1

A bundle of hydrophobic polypropylene hollow fibre porous membranes are to be treated so as to be easily wettable with aqueous biological media after being heat sterilised and dried at 100°C. The treated bundle of membranes must be clearable by back-blowing with water containing 10 ppm chlorine and soaking at 50°C in 20% hydrochloric acid to dissolve any protein clots therein. The pore sizes of the polypropylene fibres to be treated are from 0.05 to 0.5 microns but the use to which the bundle will be put indicates that some selective plugging of a small proportion of 1 to 5 micron large holes which undesirably allow the permeate to appear optically hazy.

The needs of hydrophilicity, acid and chlorine resistance can be readily met by a po^'lyamide as defined above. Terephthaloylchloride was chosen as the acid chloride (i.e. the second component of the polyamide) and bis (3-aminopropyl) amine was selected as the first component of the polyamide because of its solubility in hexane to provide the deposition formulation. With such components, polyamide deposition should be complete within an hour.

In order to ensure that the material deposited into the pores of 1 to 5 microns in size, a fine dilute emulsion was formed in which the dispersed phase was of a size about 1 micron and its interfacial tension with the continuous phase was such so as to cause exclusion of the dispersed phase from the smaller pores but to allow entry into the coarser pores. The emulsion was formed as a mixture of:

Bis (3-aminopropyl) amine 3.93 grams P-tertiaryoctylphenoxy- polyethyleneglycolether 0.1 grams

Petroleum spirit (b.p. 60-80°C) 950 millilitres Absolute ethanol - 50 millilitres

Water was added drop-by-drop until a distinct opalescent turbidity indicated that droplets above the wave length of visible light were present. These would, of course, be above 1 micron in size. Care was taken to apply the second component namely a 1% weight per volume terephthaloylchloride solution in petroleum spirit as soon as the amine solution had evaporated to the desired film with droplets in the larger pores. When the treated membrane was allowed to stand for 24 hours before fixing with the acid chloride (the second component) diffusion into the smaller pore occurred as is required for thermodynamic stability but that is to be avoided in order to produce the treated membrane required.

The treated membrane was washed in a 20% weight per volume aqueous hydrochloric acid to dissolve any uncro'ss- linked material and to hydrolyse the excess terminal acid chloride to carboxylic acid groups. A thorough water wash and drying at 60°C completed the treatment.

The properties of the treated membrane were excellent. Although the initial polypropylene had shown nil permeation rate of water at 125 kPa, the permeation rate of the treated membrane was 1800 litres per square metre per hour. Microfiltration was excellent since at 125 kPa suspension of extra-fine (i.e. under 1 micron) titanium oxide filtered at 1800 litres per square metre per hour gave a permeate which was optically clear at 650 nanometres. A 0.1% suspension of the cutting oil B.P. FEDARO M which is partly solubilised by wetting agent (i.e. the oil phase is not highly hydrophobic and has about zero interfacial surface tension between the suspended and continuous phases) at 125 kPa gave a permeate at 1080 litres per square metre per hour with 85% rejection of the turbidity at 650 nanometres. It should be noted that the oil is not a solid and that separation was determined by hydrophilicity. A coated polypropylene was so hydrophilic that it selectively passed the wetter solution rather than the hydrophilic micelles.

Example 2

In this example it was desired to treat an existing hydrophobic bundle of low-grade polypropylene hollow fibre porous membrane which was impermeable to water at 100 kPa

OMPI but which had 5 leaky tubes at 300 kPa. The treatment required a high level of hydrophilicity so that 100% rejection of solubilised cutting oil B.P. FEDARO M would occur. The membrane must have all the pores below 100 nanometres so as to reject over 50% of protein of molecular weight 43,000 (ovalbumin). Furthermore the treated membrane must be able to cope with a wide range of food industry wastes and must be able to produce optically clear permeates. It must also be able to withstand a hypochlorite sterilisation and a hot 20% hydrochloric acid clean.

Again, a polyamide system as described in Example 1 will meet the cleaning and chemical criteria. An initial effort was made to deposit a formulated (H^NtCE^^)₂NH film (the first component of the polyamide) using a solution of terephthaloylchloride (the second component of the polyamide). In order to obtain the required treated membrane all the pores will have to contain considerable fine pored filtration polyamide filling of the highest hydrophilicity. As polyamide fine pored filters absorb proteins to form a dynamic interactive pseudo-membrane, the pores may be larger than the radius of gyration of the ovalbumin. This requirement ensures that polyamides, polyesters and phenol/aldehyde resins are the main choices for the treatment material since they best absorb protein. A higher concentration of deposit than was the case with

Example 1 is necessary in order to give the finer porosity.

OMPI A deposition formulation was made from:

H ⁽-CH₂-CH2-CH2-NH₂ ⁾2 ¹⁰ gra s

Ethoxylated octylphenol 2 grams

Glycerol 20 grams NaOH 8 grams

Methylene blue 100 millilitres of 250 ppm solution

Sufficient water was added to make up 1000 millilitres of the solution which was forced through the fibres at 700 kPa to fill all the voids completely and to allow easy hydraulic flow. After draining, the fibres were dried at 22°C in a flow of 50 kPa air which was saturated with water at 15°C and 800 kPa before expansion to 50 kPa. The amine- coated ultrafilter was soaked in a 2% weight per volume terephthaloylchloride in hexane at 22°C -for 30 minutes. It was then freed of hexane by an air stream and electron scanning microscopy showed that the deposit was suitable.

The treated membrane was stabilised by washing with water at 400 kPa at a high rate of flow and it was then immersed in 7N hydrochloric acid overnight. It was then washed until neutral and its permeability tested with tap water. At 125 kPa the permeation rate was 864 litres per square metre per hour which confirmed a finer pore than that of Example 1. The 0.1% B.P. FEDARO M oil showed over 99.95% rejection which was the limit of instrumental detection. A faint haze in 40 cm thickness could just be detected and this was possibly due to wetter micelles. The ovalbumin showed 50% rejection. Biological wastes from a variety of food processes showed optical clarity. In a modification of this example another membrane was produced using a reaction time of one hour instead of 30 minutes. The resultant membrane was excellent in every way.

Example 3

A defective polypropylene hollow fibre porous membrane cartridge leaked in many tubes when water was applied at only 40 kPa. As such a cartridge should not leak at 300 kPa it was apparent that there were many over-sized pores present in the membranes. Thus the object of the example was to seal the defective larger pores by position. As there were over 30% leaks, heat sealing and blocking off each end of a tube was uneconomical. Other requirements of the finished cartridge were that it must withstand concentrated hydrochloric acid, it must wet readily and it must possess no pore over 0.5 micron in diameter. The emulsion process of the previous examples was used except that the emulsion was made coarser by using:

HN(CH₂-CH₂-CH₂-NH₂)₂ 3.93 grams

Absolute ethanol 50 millilitres Cyclohexane 950 millilitres

Water was added drop-by-drop at 22°C until a distinct emulsion was formed. The emulsion was poured down the inside of the fibres so that the fast flow through the large pores caused suitable sized droplets to fill them, finally blocking them with over-sized droplets. The cyclohexane was rapidly evaporated by 50 kPa air passing down the inside of the fibres at 22°C. A 1% weight per volume solution of terephthaloylchloride (the second component of the polyamide) in cyclohexane was then poured down the inside of the tubes and left for 45 minutes. The cyclohexane swelled the polypropylene about 10% in all dimensions. The cyclohexane was then removed by blowing in air at 50 kPa.

OMPI Hydrolysis overnight with ION hydrochloric acid followed by water washing showed that the relatively large holes were filled with the material but so much of the amine had been in the dispersed phase that insufficient had been left to confer the required hydrophilicity of the membranes. However after the drying step it was noted that there was no water leakage at 600 kPa.

In order to satisfy the other requirements of the membrane further treatment was necessary. Normally, treatment analogous to that set forth in Example 1 but without the emulsion formulation would have been used to secure overall hydrophilicity. With the view in mind of producing a fibre membrane that would reject over 90% commercial gelatin (preferably 95 - 98% rejection of high quality gelatin) it was decided to confer hydrophilicity by depositing an interstitial deposit of zirconyl or zirconium phosphate.

Before the phosphate treatment, the cartridge at 125 kPa gave an 80% rejection of 0.1% B.P. FEDARO M soluble cutting oil at 254 litres per square metre per hour. The cartridge was saturated with a 2% weight per volume aqueous solution sodium phosphate (Na₃P0₄.12H₂0) and 0.2% ethoxylated octylphenol and dried with air at 60°C. A 2% weight per volume aqueous solution of zirconium chloride (Zr0₂Cl₂.6H₂0) was then poured down the fibres under gravity and left for 30 minutes. The fibres were then washed with water and testing at 125 kPa with 0.1% FEDARO M cutting oil gave a permeation rate of 87 litres per square metre per hour but 100% rejection of visible oil.

Testing on 0.5% commercial gelatin at 22°C and pH 6.5 at 125 kPa gave a permeation rate of 12 litres per square metre per hour with an 80% rejection of all protein. Optimisation of the pH allowed 90% rejection of the protein. The zirconium phosphate was held on the

OMPI hydrophilic base. The phosphate was washed out from untreated polypropylene. The zirconium phosphates resist ION hydrochloric acid, chlorine and most chelating agents. They may be washed out with hydrofluoric solution and redeposited.

All the fibres used in the following examples 4 to 9 were from the same batch of polypropylene. Their internal diameter was 200 microns and their external diameter was 600 microns. The porous walls had an average pore size of 0.2 microns. Bubble points varied- between 220 and 320 kPa, when using air and water.

These fibres, when treated, were subjected to a sterility test in which they were boiled in a large amount - of water for 1 hour, rinsed, and then heated to 122°C for 4 minutes. The fibres were then rewetted, redried tested and classified as follows:

(a) excellent immediate wetting,

(b) good wetting at 100 to 200 kPa transmembrane pressure, or, (c) no wetting.

During these tests it is possible to- measure pore size and ascertain whether the larger pores have been selectively blocked.

Example 4 (Polyurethane)

The polypropylene fibres were soaked in a solution of 5% l,2-bis(3-aminopropylamino)ethane and 1% p- tertiaryoctylphenoxypolyethyleneglycolether (I.C.I. TERIC X10) in ether for 15 minutes. After drying in air for 3 minutes the fibre was soaked in a solution of 5% I.C.I. SUPRASEC 5005 (the first component of the polyurethane) in acetone for 1 hour. It was then dried for 15 minutes at r ONTI

. . WIPO 65°C and then soaked in a solution of 2% Texas Chemicals JEFFAMINE M2005 (the second component of the polyurethane) in acetone for 15 hours. The hydrophilicity was excellent. Since SUPRASEC 5005 is a commercial diphenylmethanediisocyanate and JEFFAMINE M2005 is a polyglycolether of monoethanolamine, the coating represents a polyurethane resin. In contrast a fibre treated with JEFFAMINE M2005 only (although a known wetting agent) was apparently removed by the sterility test cycle and failed to wet. Also no trace of JEFFAMINE was detected by a test sensitive to 1 part per million as a possible contaminant of the invention coated fibre proving that hydrophilicity was due to the polyurethane coating only.

Example 5 (Urea/aldehyde Resins)

5g of Urea (the first component of the resin) and 0.5g of diethylenegycol were dissolved in 5ml of a 40% formaldehyde solution (the second component of the resin) at 20°C. The polypropylene fibres were impregnated by forcing the solution through the pores, followed by 400 kPa air for 2 minutes via the fibre lumen. The fibres were then immersed at once in 7N hydrochloric acid for 15 minutes. They were dried at 65°C for 1 hour, soaked in a solution of 5% SUPRASEC 5005 in acetone and again dried. Finally they were soaked in a 2% solution of JEFFAMINE M2005 in acetone for 1 hour. The fibres showed excellent wetting after the standard sterility test cycle given above.

Excellent amine/aldehyde coatings were similarly obtained from urea/glutaraldehyde resin, treated with sodium hypochlorite as well as from melamine/formaldehyde/polyethyleneglycol (Molecular Weight 600).

C?..'PI_ Example 6 (Epoxy Resins)

The polypropylene porous, hollow fibres were soaked in 5% CIBA-GEIGY ARALDITE LCI91 (the first component of the resin) in acetone, dried in air for 3 minutes and then soaked for 2 hours in a solution of 5% l,2-bis(3- aminopropylamino) ethane and 1% TERIC X10 in ether. After the standard wet/dry sterility test hydrophilicity was good but a greater bubble-point test showed selective blocking of the larger pores. Selective blocking is against thermodynamic prediction and is economically more important when obtained simultaneously with hydrophilicity than either selective blocking or hydrophilicity.

A similar good coating was made from ARALDITE LCI91 and bis(3-aminopropyl)amine.

Example 7 (Phenol/aldehyde Resins)

Polypropylene fibres were soaked in a solution of 5g of resorcinol (the first component of the resin) and 2.5 ml of diethyleneglycol in 20 ml. of ethanol. They were dried at 65°C for 30 minutes and soaked for 1 hour in a 1:1 mixture of ION hydrochloric acid and 40% formaldehyde, (the second component of the resin) , redried as before, rinsed with 10% aqueous sodium hydroxide then water and then soaked for 2 hours in a solution of 5% chloroacetic acid in ethanol. The treated fibres were given the standard test and showed good hydrophilicity as well as the highly desirable increase in bubble-point without loss of much permeation rate. Similar coatings were obtained from:-

(a) Resorcinol/formaldehyde/sodium hydroxide/chloroacetic acid sequences

(b) Resorcinol/formaldehyde/hydrochloric acid/hexamethylenediisocyanate/JEFFAMINE M2005 sequences

(c) Resorcinol/gluta aldehyde/hydrochloric acid/sodium hypochlorite sequences

(d) Phenol/formaldehyde/hydrochloric acid/chloroacetic acid sequences

Example 8 (Polyamide Resins)

Polypropylene hollow fibres were soaked for 10 minutes in a solution of 5% l,2-bis(3-aminopropylamino)ethane (the first component of the polyamide) in ether and dried in air for 3 minutes. They were then soaked for 10 minutes in 5% terephthaloylchloride (the second component of the polyamide) in ether, again dried and soaked in a solution of 2% JEFFAMINE M2005 in acetone for 15 hours. After the standard test hydrophilicity was excellent.

Similar excellent results were obtained from the sequential series of reactions:-

(a) 1,2-bis(3-aminopropylamino)- ethane/sebacoylchloride/JEFFAMINE M2005

(b) l,2-bis(3-aminopropylamino)ethane/terephthaloylch- loride/JEFFAMINE M2005

(c) Bis(3-aminopropyl)amine/terephthaloylchloride/- JEFF MINE M2005

OMPI Example 9 (Polyvinylalcohol/Crosslinked Resin)

Polypropylene hollow fibres (prewetted with ethanol then water) were impregnated with a solution of 1.5% polyvinylalcohol (Molecular Weight 15,000) (the first component of the resin) in water by forcing the solution through the pores. They were dried at 65°C for 2 hours and soaked for 3 hours in a solution of 1% SUPRASEC 5005 (the second component of the resin) and 0.16% triethylenediamine in N-methyl-2-pyrrolidone. The chemical structure is a form of polyurethane. After the standard sterility cycle the hydrophilicity was good and the bubble-point was raised desirably, showing blocking of the larger pores.

In general terms the methods of the invention provide good control of pore size and distribution, good control of hydrophilic distribution and supply of functional groups can be obtained on cheap hydrophobic porous supports. Physical faults in such cheap porous supports can be corrected without recourse to monomolecular layers or surface chemical changes of the hydrophobic base.

The methods of the invention form adherent coatings, networks and interstitial porous precipitates and in so doing form novel membrane products.

Various modifications may be made in details of the deposition formulations, the method of treatment and the stabilisation treatments without departing from the scope and ambit of the invention.

Claims (23)

1. A method of treating a hydrophobic porous membrane so as to render it hydrophilic in which a hydrophilic material is deposited on the walls of the pores of the membrane.

2. A method of treating a hydrophobic porous membrane so as to render it hydrophilic by coating the walls of the pores of the membrane with a hydrophilic material in which the hydrophilic material is deposited on the walls of the pores by the reaction of first and second components of the material within the membrane.

3. A method according to claim 2 including the steps of:

(a) preparing a deposition formulation of the first component,

(b) passing the deposition formulation through the - membrane under conditions of humidity and temperature that will ensure that the selected material is deposited from the formulation in the on the walls of the pores of the membrane at the desired concentrations and form,

(c) passing the second component through the membrane so that it will react with the first component to form the selected material, and, if necessary,

(d) stabilising the so treated membrane.

4. A method of treating a hydrophobic porous membrane so as to render it hydrophilic comprising the steps of:

(a) selecting a material from the group consisting of:

(1) Polyamides and polyimides

(2) Polyesters

(3) Polyurethanes

(4) Phenol/aldehyde resins

OMFI (5) Polyamide/aldehyde resins

(6) Epoxy resins

(7) Interpolymers of materials 1 to 6

(8) Mixtures of materials 1 to 6

which can be formed on or in the membrane by the reaction of first and second components whereby the material is deposited on the walls of the pores of the membrane to provide the required hydrophilicity,

(b) preparing a deposition formulation of the first component,

(c) passing the deposition formulation through the membrane under conditions of humidity and temperature that will ensure that the selected material is deposited from the formulation on the walls of the pores of the membrane at the desired concentrations and form,

(d) passing the second component through the membrane so that it will react with the first component to form the selected material, and, if necessary,

(e) stabilising the so treated membrane.

5. A method according to claim 4, wherein

(i) the polyamides and polyimides are those formed from a first component which is a primary or secondary amine and a second component which is an acid halide and in which at least one of the first and second components is aromatic or substituted aromatic; —

(ii) the polyesters are those formed from a first component which is an hydroxyaromatic and a second component which is an aromatic or hetero- aromatic acid chloride reacted such that the average functionality is above or equal to two; (iii) the polyurethanes are those formed from a first component having a reactive hydrogen group, and a second component which is an isocyanate; (iv) the phenol/aldehyde resins are those which react very rapidly in aqueous media to precipitate fine, porous solids; Cv) the polyamide/aldehyde resins which are the reaction products of aromatic and heterocyclic amines with aldehydes; (vi) the epoxy resins include all epoxides and their reaction products with reactive hydrogen groups.

6. A method according to claim 4, wherein the hydrophobic porous membrane is made from the group consisting of polyolefines, polysulphones, poly(vinylidenefluoride) , poly(dimethylphenyleneoxide) or poly(acrylonitrile) .

7. A method according to claim 5, wherein the second component of the polyester includes sulphonyl chlorides.

8. A method according to claim 5, wherein the first component of the polyurethanes is chosen from the group comprising alcohols, amines, acids, ureas, urethanes, phenols, and thiols.

9. A method according to claim 5, wherein the aromatic and heterocyclic amines of the polyamide/aldehyde resins include melamine.

10. A method according to claim 5, wherein the reactive hydrogen group is chosen from the group consisting of alcohols, amines, acids, ureas, urethanes, phenols and thiols.

11. A method according to claim 3 or claim 4 where the stabilisation step includes dissolving any uncombined material and hydrolysing excess terminal groups.

12. A method according to claim 11 modified in that the excess terminal groups are further reacted to provide a specific surface effect.

13. A method of treating a membrane having non-uniform pore size so as to provide a membrane having a predetermined porosity in which a blocking material is deposited within selected pores and on the walls of the other pores of the membrane by the reaction of first and second components of the material within the membrane.

14. A method according to claim 13 wherein the first component is an emulsion in which the size of the dispersed phase and its interfacial tension with the continuous phase are such as to cause exclusion of the dispersed phase from pores which are smaller than the predetermined pore size.

15. A method according to claim 14 wherein the emulsion is formed from a primary or secondary amine which can be converted into a polyamide by an acid halide.

16. A method according to claim 13 wherein the first component is an alcohol and the second component is an isocyanate.

17. A method according to claim 13 wherein the first component is a phenol and the second component is an aldehyde.

18. A method according to claim 16 wherein the alcohol is a polyvinylalcohol.

19. A method according to claim 16 wherein the phenol is resorcinol and the aldehyde is formaldehyde.

20. A method according to claim 13 wherein the first component is an epoxy resin and the second component is an amine.

21. A method of treating a membrane of noή-uniform pore size so as to provide a membrane having a predetermined porosity comprising the steps of:

(a) selecting a material from the group defined in claim 4 which can be formed on or in the membrane by the reaction of first and second components whereby the material is deposited within selected pores and on the walls of the pores of the membrane,

(b) preparing an emulsion of the first component in which the size of the dispersed phase and its interfacial tension with the continuous phase are such as to cause exclusion of the dispersed phase from pores which are smaller than the predetermined size,

(c) passing the emulsion through the membrane under conditions of humidity and temperature that will ensure that the emulsion is held in the pores above the predetermined size,

(d) passing the second component through the membrane so that it will react with the first component to form the selected material, and, if necessary,

(e) stabilising the so treated membrane.

22. A method according to claim 21 where the stabilization step includes dissolving any uncombined material and hydrolysing excess terminal groups.

23. A method according to claim 21 modified in that the excess terminal groups are further reacted to provide specific surface effects.