WO2013114297A1

WO2013114297A1 - Uv polymerization of specific acrylic monomers on reverse osmosis membranes for improved bio-fouling resistance

Info

Publication number: WO2013114297A1
Application number: PCT/IB2013/050790
Authority: WO
Inventors: Edoardo Menozzi; Jaleh Mansouri; Matthias Häussler; Jana Habsuda
Original assignee: Polymers Crc Ltd.; Basf (China) Company Limited
Priority date: 2012-01-31
Filing date: 2013-01-30
Publication date: 2013-08-08
Also published as: AR095650A1

Abstract

Provided is a UV polymerization method for the preparation of coated thin-film composite (TFC) membranes on a microporous substrate with specific acrylic monomers and optionally additional bio active compounds to yield membranes having antifouling and/or anti-bacterial properties. Further aspects of the present invention are a polymer coating composition on thin-film composite (TFC) membranes, a coated thin-film composite (TFC) membrane on the microporous substrate itself and the use of such membranes in water purification systems which may be exposed to microbial contamination.

Description

UV Polymerization of Specific Acrylic Monomers on Reverse Osmosis Membranes for Improved Bio-Fouling Resistance

Description

The present invention relates to a UV polymerization method for the preparation of coated thin-film composite (TFC) membranes on a microporous substrate with specific acrylic monomers and optionally additional bio active compounds to yield membranes having antifouling and or anti-bacterial properties. Further aspects of the invention are a polymer coating composition on a thin-film composite (TFC) membrane, a coated thin-film composite (TFC) membrane on the microporous substrate itself and the use of such membranes in water purification systems which may be exposed to microbial contamination. The current worldwide expansion and diverse application of Reverse Osmosis (RO) technology has resulted from the introduction of thin-film-composite (TFC) membranes by interfacial polymerization. Interfacial polymerization is copolymerization of two reactive monomers dissolved in two immiscible solutions respectively. The monomers can meet and react only at the interface of the solutions when two solutions are contained in a reaction chamber. As the reaction continues, polymer film is formed at the interface. The film is usually very thin because the growing interfacial polymer behaves as a barrier to diffusion of the two monomers, and the polymerization levels off at a limiting thickness, typically of the order of a micrometer or less. To provide durability to the fragile films, the interfacial polymerization was frequently carried out at the surface of a microporous substrate, in which case the result is called a thin-film composite membrane. This is for example described by Wamser et al., J. Am. Chem. Soc. 1 1 1 , 1989, 8485-8491 .

The problem of biofouling is pronounced in semipermeable membranes used for sepa- ration purposes like reverse osmosis and/or ultra and micro filtration. Membranes may be classified according to their pore dimension in most of the application profiles. For example, in water filtration applications ultrafiltration membranes (approximate pore diameter: 100 - 1000 nm) are used for wastewater treatment retaining organic and bioorganic material. Much smaller diameters are required in desalination applications (reverse osmosis; approximate pore diameter 1 nm) for retaining ions. In both applications, the ambient medium is an aqueous phase, where potential blockage may occur by adhesion of microorganisms and bio-film formation. As a consequence, a membrane with anti-adhesion properties is desired, which would reduce bio-film formation and thus require less cleaning cycles.

Thus, fouling is currently one of the major remaining problems for aromatic polyamide reverse osmosis (RO) membranes. Fouling causes deterioration of the membrane per- formance and shortens membrane lifetime, limiting further application of RO membrane technology. It is thus desirable to improve antifouling and antibacterial properties of RO membranes without impairing their transport characteristics as a result of higher membrane resistance.

Preparation methods and use of thin film composite membranes are principally known and, for example described by R. J. Petersen in Journal of Membrane Science 83 (1993) 81 -150. Commercial RO membranes are available as thin-film-composite (TFC) membranes, which generally consist of a woven polyester support layer (80-1 ΟΟμηη thickness), a polysulfone or polyethersulfone ultrafiltration/nanofiltration (UF/NF) layer (40μηη) and a thin, densely cross-linked polyamide (PA) top-coating (0.1 -0.2μηη). This PA top-layer is prone to fouling by organic (e.g. proteins and bacteria) and inorganic matters (e.g. sili- ca scale). Strategies to combat fouling include the deposition of anti-adhesive hydro- philic polymer coatings such as polyethylene glycol (PEG) and polyvinyl alcohol (PVA). These coatings have also been reported to reduce fouling through reduction of the surface roughness. However, the application of such a hydrophilic polymer layer often involves thermally induced cross-linking of the polymer chains in order to stabilize the coating and to render it insoluble under cleaning conditions (standard cleaning conditions consist mainly of dilute acid and base treatment of the RO membrane filtration device). In one aspect the instant invention relates to a method for the preparation of a hydrophilic anti-fouling coating onto commercial RO membranes by UV-induced photo- polymerization of suitable anti-adhesive polymers and monomers. Optionally further antimicrobial agents may be added to the coating.

Bacteria contained in the influent water are accumulated by the membranes and consequently accumulate on their surfaces. The rapid growth of bacteria results in fouling of the membrane which reduces the flow of water through the membrane and can ad- versely affect the filtering properties of the membrane.

As a result of bacterial growth on the membrane, a gelatinous biofilm is formed on the upstream side of the membrane that is very difficult to remove except through the use of aggressive cleaning. This can compromise membrane lifetime as well as incur signif- icant costs.

One aspect of the invention is a method for imparting decreased adhesion of biological material to the surface of a reverse osmosis thin-film composite membrane on a mi- croporous substrate comprising providing a composition of

a1 ) hydroxyethyl-methacrylate or ethyleneglycol-methacrylate or a compound of formulae

, or MA-EDMAPS a2) 0.1 % to 10% by weight of ethyleneglycol-dimethacrylate, based on the weight of component a1 );

a3) 0.5% to 5% by weight of glycidyl-methacrylate

(GMA), based on the weight of component a1 );

and

a4) 0.1 % to 10% by weight of a radical photoinitiator, based on the weight of component a1 ); b) coating the surface of the reverse osmosis thin-film composite membrane on a mi- croporous substrate with said composition; and

c) exposing the surface of the coated reverse osmosis thin-film composite membrane on a microporous substrate to UV light to form a cured coating layer.

The compounds MA-TMEA, MAA-TMEA and MA-DMP are cations, which are added as salts with an appropriate anion. Typical anions are CI -, Br -, or I -.

The term anti-fouling is used in the context of the present invention as a synonym for prevention of adhesion of biological material.

Biological material can be proteins, spores, nucleic acids, viruses or biological cells as well as fragments or extracts of biological cells.

Examples of proteins are fibrous proteins such as actin and tubulin, globular proteins such as albumin, fibrin, thrombin and immunoglobulin, enzymes such as oxidoreduc- tases, transferases and hydrolases, and prions.

Examples of spores are spores of fungi, ferns and fern allies.

Examples of nucleic acids are deoxyribonucleic acid and ribonucleic acid. Examples of viruses are adenovirus, AIDS virus, lambda phage, T4 phage and T7 phage.

Examples of biological cells are archaea, bacterial cells or eukaryotic cells.

Examples of bacterials cells are cells from the phyla Actinobactena, Chlamydia, Cya- nobacteria, Firmicutes, Proteobacteria and Spirochaetes. Examples of genera of the phylum Actinobactena are Actinomyces, Arthrobacter, Corynebacterium, Nocardia and Streptomyces. Examples of genera of the phylum Firmicutes are Bacillus, Enterococ- cus, Lactobacillus, Lactococcus, Streptococcus, Acetobacterium, Clostridium, Eubac- trium and Heliobacterium. Examples of genera of the phylum Proteobacteria are Enter- obacter, Escherichia, Klebsiella, Salmonella, Pseudomonas, Vibrio, Burkholdria, Helicobacter and Campylobacter. Cells of the species Escherichia coli are particular preferred bacterial cells.

Examples of eukaryotic cells are fungal cells, human cells, animal cells and plant cells.

Examples of fungal cells are molds, mushrooms and yeast cells. Examples of yeast cells are cells of generae Saccharomyces and Candida. Cells of the species Saccha- romyces cerevisae and Candida albicans are particular preferred yeast cells.

The degree of adhesion of biological matter to the surface of a substrate can be determined, for example, by comparing the flux and the retention parameters of the membrane after a period of time.

In a specific embodiment of the invention silver lactate is additionally added to the composition.

Typically silver lactate is added when component a1 ) is hydroxyethyl-methacrylate or ethyleneglycol-methacrylate.

Silver, in particular silver in the form of nano-scale silver is a powerful biocide (as for example described in Water Research, (2008), 42(18), 4591 -4602). Silver particles in nano-form have preferably a particle size of 10-100 nm, more preferably 30-80 nm.

The amount of silver lactate added is typically from 0.1 % to 10% by weight, preferably from 0.5% to 6% by weight, based on the weight of component a1 ), for example hy- droxyethyl-methacrylate.

For example the top layer of the thin-film composite membrane is a polyamide layer. Polyamides can be polymers formed from at least one monomer having an amide group or an amino as well as a carboxy group or from at least one monomer having two amino groups and at least one monomer having two carboxy groups. An example of a monomer having an amide group is caprolactam. An example of a diamine is 1 ,6- diaminohexane. Examples of dicarboxylic acids are adipic acid, terephthalic acid, isophthalic acid and 1 ,4-naphthalenedicarboxylic acid. Examples of polyamides are polyhexamethylene adipamide and polycaprolactam.

In a specific embodiment of the invention one or more conventional biocides different from those mentioned above are additionally added to the coating before exposing it to UV-light.

Examples of conventional biocides are 5-chloro-2-(2,4-dichlorophenoxy)phenol, which is sold, for example, under the tradename Irgasan® DP300, N'-feri-butyl-N-cyclopropyl- 6-(methylthio)-1 ,3,5-triazine-2,4-diamine, which is sold under the tradename Irga- rol® 1051 , 2-thiazol-4-yl-1 H-benzoimidazole, which is sold under the tradename Irg- aguard® F3000, chlorhexidine, gallic acid, mucobromic acid, itaconic acid and 3-iodo- 2-propynyl butyl carbamate, which is sold under the tradename Maguard™ 1-100. Other quaternary ammonium compounds carrying one or more ethylenically unsaturated groups are given below. Usually these compounds have biocidal activity. The quaternary ammonium compounds carrying one or more ethylenically unsaturated groups can be of formula

wherein

R⁵⁸, R⁵⁹ and R⁶⁰ can be the same or different and are hydrogen, halogen or Ci-6-alkyl, R⁶¹, R⁶² and R⁶³ can be the same or different and are Ci-30-alkyl, C2-3o-alkenyl, C3-8- cycloalkyl, aryl, or R⁶¹ and R⁶² together with the N of the ammonium group form a 4 to 8 membered cycle, wherein one CH2 group of the cycle may be replaced with NH or O,

Q and Y can be the same or different and are Ci-15-alkylene,

M is a bridging group,

n and m can be the same or different and are 0 or 1 ,

J- is an anion, wherein Ci-30-alkyl, C2-3o-alkenyl, C3-8-cycloalkyl or Ci-15-alkylene can be unsubstituted or substituted with one or more aryl, OC2-6-alkenyl, halogen, CN, C(0)OR⁶⁴, C(0)NR⁶⁵R⁶⁶, OR⁶⁷, NR⁶⁸R⁶⁹, NHC(O)C(R⁷⁰)=C(R⁷¹)R⁷², OC(0)C(R⁷³)=C(R⁷⁴)R⁷⁵ or C(0)OC(R⁷⁶)=C(R⁷⁷)R⁷⁸; wherein aryl can be unsubstituted or substituted with one or more Ci-6-alkyl, C2-6- alkenyl, OC₂-₆-alkenyl, halogen, CN, C(0)OR⁶⁴, C(0)NR⁶⁵R⁶⁶, OR⁶⁷, NR⁶⁸R⁶⁹,

NHC(O)C(R⁷⁰)=C(R⁷¹)R⁷², OC(0)C(R⁷³)=C(R⁷⁴)R⁷⁵ or C(0)OC(R⁷⁶)=C(R⁷⁷)R⁷⁸; wherein R⁶⁴, R⁶⁵, R⁶⁶, R⁶⁷, R⁶⁸, R⁶⁹, R⁷⁰, R⁷ , R⁷², R⁷³, R⁷⁴, R⁷⁵, R⁷⁶, R⁷⁷ and R⁷⁸ can be the same or different and are hydrogen or Ci-6-alkyl, and one or more Chb-groups of Ci-15-alkylene can be replaced by N-CH2-CH=CH2, CH-CH=CH₂, NH and/or O.

Ci-3o-Alkyl can be branched or unbranched. Examples of Ci-30-alkyl are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, fert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tetradecyl, pentadecyl, hexadecyl, octadecyl, eicosyl, heneico- syl, docosyl, tetracosyl and triacontyl.

Examples of Ci-15-alkylene are methylene, propylene and butylene.

Examples of bridging groups M are C3-8-cycloalkylene, arylene, polymer, OC(O), C(0)0, NH(CO) and C(0)NH. Arylene can be phenylene. An example of a polymer is polyethyleneimine. J^" can be any anion, for example sulfate, sulfite, carbonate, phosphate or halogenide. Halogenide can be fluoride, chloride, bromide or iodide.

Examples of quaternary ammonium compounds carrying one or more ethylenically unsaturated group are trimethylaminoethyl acrylate chloride, trimethylaminoethyl meth- acrylate chloride, trimethylaminotetradecyl acrylate chloride, trimethylaminohexadecyl acrylate chloride, trimethylaminooctadecyl acrylate chloride and diallyldimethylammo- nium chloride and the compounds of formulae

More quaternary ammonium compounds carrying one or more ethylenically unsaturated group are of formula

wherein

R⁵⁸, R⁵⁹ and R⁶⁰ can be the same or different and are hydrogen or Ci-6-alkyl,

R⁶¹, R⁶² and R⁶³ can be the same or different and are Ci-30-alkyl or C2-3o-alkenyl, Q and Y can be the same or different and are Ci-15-alkylene,

M is a bridging group selected from the group consisting of arylene, polymer, OC(O) and C(0)0,

n and m can be the same or different and are 0 or 1 ,

J- is a halogenide, wherein Ci-30-alkyl, C2-3o-alkenyl or Ci-15-alkylene can be unsubstituted or substituted with one or more OC₂-₆-alkenyl, C(0)OR⁶⁴, C(0)NR⁶⁵R⁶⁶, OR⁶⁷, NR⁶⁸R⁶⁹,

Preferred quaternary ammonium compounds carrying one or more ethylenically un- saturated groups are of formula

wherein

R⁶¹, R⁶² and R⁶³ can be the same or different and are Ci-30-alkyl,

Q and Y can be the same or different and are Ci-6-alkylene,

M is a bridging group selected from the group consisting of polymer and OC(O), n and m can be the same or different and are 0 or 1 ,

J^" is a halogenide, wherein Ci-30-alkyl or Ci-6-alkylene can be unsubstituted or substituted with one or more OR⁶⁷, wherein R⁶⁷ can be hydrogen or Ci-6-alkyl, and one or more Chb-groups of Ci-6-alkylene can be replaced by N-CH2-CH=CH2.

Examples of Ci-6-alkylene are methylene, propylene and butylene.

Compounds 3A and 3B are especially preferred quaternary ammonium compounds carrying one or more ethylenically unsaturated groups.

Compound 3A can be prepared by reacting polyethyleneimine with A/-3-chloro-2- hydroxypropyl-A/-lauryl-dimethylammonium chloride and allyl bromide. Compound 3B can be prepared by reacting A/,A/-dimethylaminoethyl methacrylate with dodecyl bro- mide as described in S.M. Hamid and D.C. Sherrington, Polymer 1987, 28, 325 to 331.

When additional biocides are added to the coating composition they are added in an amount of from 0.1 % to 10% by weight, based on the weight of component a1 ), for example hydroxyethyl-methacrylate.

For example the porous substrate is a polymer selected from the group consisting of a polyester, polysulfone, polycarbonate, polypropylene, polyamide and polyether sulfone. Polyolefins, such as polypropylene can be polymers formed from at least one olefin monomer or from at least one olefin monomer and maleic monomer. Examples of poly- olefines are low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), biaxially orientated polypropylene (BOPP), polybutadiene, polytetraflu- oroethylene (Teflon-PTFE), chlorinated polyethylene and isopropylene-maleic anhydride copolymer.

Polyamides can be polymers formed from at least one monomer having an amide group or an amino as well as a carboxy group or from at least one monomer having two amino groups and at least one monomer having two carboxy groups. An example of a monomer having an amide group is caprolactam. An example of a diamine is 1 ,6- diaminohexane. Examples of dicarboxylic acids are adipic acid, terephthalic acid, isophthalic acid and 1 ,4-naphthalenedicarboxylic acid. Examples of polyamides are polyhexamethylene adipamide and polycaprolactam.

Polyesters can be polymers formed from at least one monomer having a hydroxy as well as a carboxy group or from at least one monomer having two hydroxy groups and at least one monomer having two carboxy groups or a lactone group. An example of a monomer having a hydroxy as well as a carboxy group is adipic acid. An example of a diol is ethylene glycol. An example of a monomer having a lactone group is carprolac- tone. Examples of dicarboxylic acids are terephthalic acid, isophthalic acid and 1 ,4- naphthalenedicarboxylic acid. An example of a polyester is polyethylene terephthalate (PET). So-called alkyd resins are also regarded to belong to polyester polymers. Examples of polycarbonates are poly(aromatic carbonates) and poly(aliphatic carbonates). Poly(aliphatic carbonates) can be formed from carbon dioxide and at least one epoxide.

Examples of sulfone-based polymers are polyarylsulfone, polyethersulfone (PES), poly- phenylsulfone (PPS) and polysulfone (PSF). Polysulfone (PSF) is a polymer formed from 4,4-dichlorodiphenyl sulfone and bisphenol A.

For example, the weight ratio between ethyleneglycol-dimethacrylate, component a2) and glycidyl-methacrylate, component a3) is from 10:1 to 1 :5, preferably 2:1 to 1 :2 and more preferably 1 :1 .

As outlined above the thin-film composite membrane on a microporous substrate is coated with the composition mentioned under a1 ) to a4). In some cases it is convenient to dilute the monomers with an organic solvent and/or water. Examples of organic solvents are Ci-4-alkanols, C2-4-polyols, C3-6-ketones, C4-6-ethers, C2-3-nitriles, nitromethane, dimethylsulfoxide, dimethylformamide, dimethylacetamide, A/-methylpyrolidone and sulfolane, whereby Ci-4-alkanols and C2-4-polyols may be substituted with Ci-4-alkoxy. Examples of Ci-4-alkanols are methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol and feri-butanol. Examples of Ci-4-alkoxy- derivatives thereof are 2-ethoxyethanol and 1 -methoxy-2-propanol. Examples of C2-4-polyols are glycol and glycerol. Examples of C3-6-ketones are acetone and methyl ethyl ketone. Examples of C4-6-ethers are dimethoxyethane, diisopropylether and tetra- hydrofurane. An example of a C2-3-nitrile is acetonitrile. Preferably, the organic solvent is selected from the group consisting of Ci-4-alkanols, C2-4-polyols, C3-6-ketones, dimethylformamide and dimethylacetamide, whereby Ci-4-alkanols and C2-4-polyols may be substituted with Ci-4-alkoxy. More preferably, the organic solvent is a Ci-4-alkanol.

As outlined above the thin-film composite membrane on a microporous substrate is coated with the composition mentioned above. The coating may be applied from a so- lution of the components. The solvent may be an organic solvent or a mixture of water with an organic solvent. Examples for suitable organic solvents are outlined above.

In some cases the solvent is a mixture of water and an alcohol, such as ethanol or propanol. Typically the ratio between organic solvent and water is from 80:20 to 20:80 by volume, preferably from 80:20 to 40:60.

The concentration of the total components in the solution may be in the range of 1 % to 50%, preferably from 5% to 20% by weight, based on the weight of the total solution. The coating may be applied by any coating technique, such as in the form of a draw down with a doctor blade or a spiral coater or by spin coating. Typically the wet thickness of the coating is in the range of 1 μηη to 500 μηη, preferably from 10 μηη to 100 μΠΊ. For example the cured coating layer has a thickness in the range of from 0.1 to 50 μηη, preferably, from 1 to 10 μηη.

Typically the exposure to UV light is carried out under inert gas atmosphere.

Examples for inert gases are Argon, Xenon, Helium and Nitrogen. Nitrogen is preferred

The composition to be coated comprises one or more radical photoinitiators.

The photoinitiator can be of formula

wherein L can be hydrogen or

wherein Ci-6-alkylene can be unsubstituted or substituted with hydroxyl, and

R²⁷, R²⁸ and R²⁹ can be the same or different and can be hydrogen, halogen, hydroxyl, Ci-6-alkyl, aryl, 0-Ci_-6-alkyl, O-aryl, S-Ci_-6-alkyl, S-aryl or NR³⁰R³¹, wherein R³⁰ and R³¹ can be the same or different and can be hydrogen or Ci-6-alkyl, or together with the nitrogen form a five to seven membered cycle, wherein a Chb group of the cycle can be replaced with -0-, and Ci-6-alkyl, O-Ci-6-alkyl and S-Ci-6-alkyl can be unsubstituted or substituted with one or more hydroxyl, C2-3o-alkenyl, OC(0)C2-3o- alkenyl or aryl, and X can be

wherein E and G can be -0-, -S- or NR⁴⁰, wherein R⁴⁰ can be hydrogen or Ci-6-alkyl, or R⁴⁰ and R³², respectively, R³⁵ can, together with the nitrogen, form a five to seven membered cycle, wherein a Chb group of the cycle can be replaced with -0-, NH, NC(0)C(R⁴¹)C=C(R⁴²)R⁴³ and/or

R³², R³⁵ and R³⁹ can be the same or different and can be hydrogen, Ci-100-alkyl, C3-8- cycloalkyl, C₂-₃o-alkenyl, aryl or C(0)R⁴⁴,

R³⁶, R³⁷ and R³⁸ can be the same or different and can be hydrogen, Ci-100-alkyl, O-C1- 100-alkyl, S-Ci-100-alkyl, NR⁴⁵Ci-ioo-alkyl, C₃-₈-cycloalkyl, C₂-₃o-alkenyl, aryl or C(0)R⁴⁴, wherein R⁴⁵ can have the same meaning as R³² and R⁴⁴ can have the same meaning as R³⁶,

R³³ and R³⁴ can have the same meaning as R³⁶ and in addition can, together with the linking carbon atom, form a five to seven membered cycle,

Ci-100-alkyl and C2-3o-alkenyl can be unsubstituted or substituted with one or more Cs-s-cycloalkyl, aryl, halogen, amino, hydroxyl, CN, COOH, C(0)R⁴⁶, C(0)OR⁴⁷, C(0)NR⁴⁸R⁴⁹, OR⁵⁰, OC(0)R⁵¹, OC(0)C(R⁵²)=C(R⁵³)R⁵⁴, C(0)OC(R⁵⁵)=C(R⁵⁶)R⁵⁷,

aryl can be unsubstituted or substituted with one or more Ci-4-alkyl, C3-8-cycloalkyl, C₂-3o-alkenyl, halogen, hydroxyl, CN , COOH , C(0)R⁴⁶, C(0)OR⁴⁷, C(0)N R ⁸R⁴⁹, OR⁵⁰, OC(0)R⁵¹ , OC(0)C(R⁵²)=C(R⁵³)R⁵⁴ or C(0)OC(R⁵⁵)=C(R⁵⁶)R⁵⁷; wherein R⁴ , R⁴², R⁴³, R⁴⁶, R⁴⁷, R⁴⁸, R⁴⁹, R⁵⁰, R⁵¹ , R⁵², R⁵³, R⁵⁴, R⁵⁵, R⁵⁶ and R⁵⁷ can be the same or different and can be hydrogen or Ci-6-alkyl, and one or more Chb-groups of Ci-100-alkyl or C2-3o-alkenyl can be replaced with -O- , -N and/or phenylene, and one Chb-group of C3-8-cycloalkyl can be replaced with -0-. Examples of Ci-6-alkylene are methylene, propylene and butylene. Examples of photoinitiators of formula 2 are benzoin ethers such as benzoin ethyl ether, benzyl monoketals such as 2,2-diethoxy-1 -phenylethanon and 2,2-diethoxy-1 ,2- diphenylethanon, alpha-substituted acetophenone derivatives such as 2-hydroxy-2- methylpropiophenone, 1 -hydroxycyclohexyl phenyl ketone, 2-methyl-4'-(methylthio)-2- morpholino-propiophenone and 2-benzyl-2-(dimethylamino)-4'- morpholinobutyrophenone, acylphosphine oxides such as diphenyl(2,4,6- trimethylbenzoyl)-phosphine oxide or phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide, alpha-acyloximester such as 1-[4-(phenylthio)phenyl]-2-(0-benzoyloxim)octan-1 ,2- dione, and phenylglyoxalic acid esters such as diethyleneglycol di(phenylglyoxylate), triethyleneglycol di(phenylglyoxylate), polyethylene glycol (150) di(phenylglyoxylate), polyethylene glycol (300) di(phenylglyoxylate), polyethylene glycol (400)

di(phenylglyoxylate) and polyethylene glycol (600) di(phenylglyoxylate).

In preferred compounds of formula 2, R²⁷, R²⁸ and R²⁹ can be the same or different and are hydrogen, hydroxyl, Ci-6-alkyl, O-Ci-6-alkyl, S-Ci-6-alkyl, S-aryl or NR³⁰R³¹ , wherein R³⁰ and R³¹ can be the same or different and can be hydrogen or Ci-6-alkyl, or together with the nitrogen form a five to seven membered cycle, wherein a Chb group of the cycle can be replaced with -0-, and Ci-6-alkyl and O-Ci-6-alkyl can be unsubstituted or substituted with one or more hydroxyl, C2-3o-alkenyl or aryl, and X is

wherein E and G are -O- or NR⁴⁰, wherein R⁴⁰ can be hydrogen or Ci-6-alkyl, or R⁴⁰ and R³², respectively, R³⁵ can, together with the nitrogen, form a five to seven membered cycle, wherein a Chb group of the cycle can be replaced with -0-, NH,

NC(0)C(R⁴¹)C=C(R⁴²)R⁴³ and/or

R³², R³⁵ and R³⁹ can be the same or different and are hydrogen, Ci-100-alkyl, C2-30- alkenyl, aryl or C(0)R⁴⁴; R³⁶, R³⁷ and R³⁸ can be the same or different and are hydrogen, Ci-100-alkyl, O-Ci-100-alkyl or C(0)R⁴⁴; R³³ and R³⁴ can have the same meaning as R³⁶ and in addition can, together with the linking carbon atom, form a five to seven membered cycle, R⁴⁴ has the same meaning as R³⁶,

Ci-100-alkyl and C2-3o-alkenyl can be unsubstituted or substituted with one or more aryl, amino, hydroxyl, OC(0)C(R⁵²)=C(R⁵³)R⁵⁴, C(0)OC(R⁵⁵)=C(R⁵⁶)R⁵⁷,

wherein R⁴¹, R⁴², R⁴³, R⁵², R⁵³, R⁵⁴, R⁵⁵ and R⁵⁶ and R⁵⁷ can be the same or different and are hydrogen or Ci-6-alkyl, aryl can be unsubstituted or substituted with one or more Ci-4-alkyl, and one or more Chb-groups of Ci-100-alkyl or C2-3o-alkenyl can be replaced with -O- and/or -NR⁴⁰-. In more preferred compounds of formula 2, R²⁷, R²⁸ and R²⁹ can be the same or different and are hydrogen, hydroxyl, Ci-e-alkyl, O-Ci-6-alkyl, S-Ci-6-alkyl or NR³⁰R³¹, wherein R³⁰ and R³¹ can be the same or different and are hydrogen or Ci-6-alkyl; wherein C1-6- alkyl and O-Ci-6-alkyl can be unsubstituted or substituted with one or more hydroxyl, C2-3o-alkenyl or aryl, and

X is

G- R wherein G is -O- or NR⁴⁰, wherein R⁴⁰ can be hydrogen, or R⁴⁰ and R³⁵ can, together with the nitrogen, form a five to seven membered cycle, wherein a Chb group of the cycle can be replaced with NH, NC(0)C(R⁴¹)C=C(R⁴²)R⁴³ and/or

R³⁵ is hydrogen, Ci-100-alkyl or C2-3o-alkenyl, wherein Ci-100-alkyl and C2

be unsubstituted or substituted with one or more amino, hydroxyl,

OC(0)C(R⁵²)=C(R⁵³)R⁵⁴ and/or

wherein R⁴¹, R⁴², R⁴³, R⁵², R⁵³ and R⁵⁴ can be the same or different and are hydrogen or Ci-6-alkyl, and one or more Chb-groups of Ci-100-alkyl or C2-3o-alkenyl can be replaced with -O- and/or -NR⁴⁰-.

In the most preferred compounds of formula 2, R²⁷, R²⁸ and R²⁹ are hydrogen or C1-6- alkyl, and

X is

wherein G is -0-; R³⁵ is Ci-100-alkyl, wherein Ci-100-alkyl can be unsubstituted or substituted with one or more

one or more Chb-groups of Ci-100-alkyl can be replaced with -O- Especially preferred photoinitiators of formula 2 are diethyleneglycol

di(phenylglyoxylate), triethyleneglycol di(phenylglyoxylate), polyethylene glycol (150) di(phenylglyoxylate), polyethylene glycol (300) di(phenylglyoxylate), polyethylene glycol (400) di(phenylglyoxylate) and polyethylene glycol (600) di(phenylglyoxylate). Polyeth- ylene glycol (600) di(phenylglyoxylate) is especially preferred.

The photoinitiator can also be a titanocene or combinations of a benzophenone as well as thioxanthon-derivative with a coinitiator, for example a tertiary amine. But preferably, the photoinitiator is a compound of formula 2.

The photoinitiators are mostly items of commerce and supplied, for example, by BASF SE.

The photoinitiators are added in an amount of from 0.1 % to 10% by weight, preferably 0.5% to 5% by weight based on the weight of component a1 ), for example hydroxyeth- yl-methacrylate.

The UV lamps suitable for this process are known in the art and commercially available. Typically medium or high pressure mercury lamps are used. However, it is also possible to use laser light in the UV region.

A further aspect of the invention is a composition comprising

a) a reverse osmosis thin-film composite membrane on a microporous substrate;

b1 ) hydroxyethyl-methacrylate, ethyleneglycol-methacrylate or a compound of formulae

b2) 0.1 % to 10% by weight of ethyleneglycol-dimethacrylate, based on the weight of component b1 );

b3) 0.5% to 5% by weight of glycidyl-methacrylate

(GMA), based on the weight of component b1 );

and b4) 0.1 % to 10% by weight of a radical photoinitiator, based on the weight of component b1 ).

For instance the composition contains one or more further biocides, different from those mentioned in claim 1 or 2.

In a preferred embodiment component b) of the above composition is as a cured film on the thin-film composite membrane on a microporous substrate. Yet a further aspect of the invention is the use of a composition as described above as separating membrane which has antifouling properties in a reverse osmosis process.

Also an aspect of the invention is a coated thin-film composite membrane on a microporous substrate obtainable as described above.

The above definitions, explanations and preferences apply equally for all aspects of the invention.

The following examples illustrate the invention.

Experimental

Chemicals and Measurements

Chemicals

All monomers (HEMA, GMA, EGDMA, MA-TMEA and MA-EDMAPS) were obtained from Sigma-Aldrich and passed through a short alumina column to remove the inhibitors before use. Silver lactate was purchased from Fluka and used as received. All solvents used were obtained from Merck and were of ACS reagent or HPLC grade. Da- rocur 1 173 was purchased from CIBA (now BASF) and used as received.

Equipment

The UV coating experiments are carried out inside a UV cabinet with a power output of the lamp of 10 mW/cm². The performances of the membranes are tested in two stirred dead-end cells at constant pressure: Sterlitech HP 4750 stirred cell operated at 15 bar with a membrane area of 14.6 cm² and a home-made stainless steel stirred cell operated at 24.1 bar with a membrane area of 21 .2 cm².

Coating of LE membranes with acrylic monomers

LE membranes (DOW-Filmtec) are washed with water/iso-propanol (70:30 v/v) solvent mixture to remove stabilizers and other impurities from the surface. A solution consisting of 0.6 g HEMA, 6 mg (1 wt% based on HEMA) EGDMA, 6 mg (1 wt% based on HEMA) GMA, 6 mg (1 wt% based on HEMA) Darocur 1 173, 5.8 g i-propanol and 13.6 g distilled water is prepared. 2ml_ of this coating solution is spread over the LE membrane and coated to an even thickness with a draw down spiral coater bar (24 or 50μηη). The membranes are placed between two plastic sheets inside a sealable plastic bag and flushed with nitrogen for 15 min. After 30 min of UV curing, the membranes are washed with the water/i-propanol solvent mixture and kept in Dl water until testing. Coated membranes PolyPEG-MA, PolyMA-TMEA (QA) and PolyMA-EDMAPS (ZW) are prepared in the same way by substituting the HEMA monomer with 0.6 g PEG-MA, 0.6 g MA-TMEA or 0.6 g MA-ED MAPS, respectively. Coating of LE membranes with HEMA and silver lactate

To the HEMA-containing coating mixture described above is added a solution of 24mg silver lactate, 57 mg Λ/,Λ/,Λ/',Λ/'-tetramethylethylenediamine (TEMED) in 54mg water/i- propanol (70:30 v/v) and stirred thoroughly. The coating, polymerization and purification steps are then carried out in the same manner as described above.

Application Data

Stability of commercial RO membranes under UV treatment

A fast and efficient way to apply polymer coatings to various applications is by UV photo-polymerization of monomers and photo-crosslinkable polymers. The effect of UV irradiation on the performance of commercial RO membranes is therefore investigated (Table 1 )

The salt rejection is found to be very stable, over different irradiation time; also the flux in all membranes is comparable to the values obtained previously for DOW-LE membranes and it is slightly higher for the UV-exposed membranes compared to the con- trol.

Table 1 : Effect of UV irradiation on the performance of commercial RO membranes (DOW-LE)

a Power output of UV lamp: 10 mW/cm²; ^b Conditions of testing: 10g/L NaCI in Dl water; These results are given as an average of two tested membranes.

UV photopolymerization of acrylic monomers Hydrophilic monomer, hydroxyethyl-methacrylate (HEMA), is used as anti-adhesive layer to coat commercial TFC-RO membranes via UV photopolymerisation.

In addition ethylene glycol dimethacrylate (EGDMA) and glycidyl methacrylate (GMA) are used as crosslinker and surface binder, respectively (Figure 1 ).

2-Hydroxy-2-methyl-1 -phenylpropan-1 -one (Darocur 1 173) is chosen as photoinitiator.

Figure 1 : Monomers and components used during the photopolymerization.

Anti-foulin coating Anti-microbial additives

Acrylic, hydrophilic

monomer

Crosslinker

Surface binder

Photoinitiator

Membranes functionalization and contact angle analysis

Commercial RO membranes (DOW Filmtec LE) are coated by a draw-down coating using a 50μηι spiral coater bar. For coating solution: See experimental part

UV curing: Membranes are placed under nitrogen for at least 15 minutes before UV treatment. UV curing is carried for 30 minutes then membranes are washed with the water/i-propanol solvent mixture and kept in distilled water.

Contact angle (CA): membranes are dried in a stream of cold air before contact angle measurements (Table 2).

Table 2. Contact angle of PolyHEMA coated LE membranes

Membrane EGDMA Contact Angle

[wt%] [degree]

DOW-LE (reference) / 60 ± 7

PolyHEMA 1 0.1 32 ± 7

PolyHEMA 2 1 .0 31 ± 4 PolyHEMA 3 10.0 33 ± 14

The contact angle (CA) of dried surfaces is determined by measuring CA of three spots as an average of 6 values after removing first two values when equilibration between a water droplet and the membrane surface s reached. Uncoated DOW-LE membrane exhibits a contact angle around 60°; applying the PolyHEMA coating reduces the contact angle to about 30°, suggesting the successful deposition of hydrophilic PolyHEMA on the surface. Independent of the EGDMA content, the contact angles does not vary significantly. UV photopolymerization of acrylic monomers and Ag nanoparticles

Membrane functionalisation with Ag nanoparticles

Commercial RO membranes (DOW Filmtec LE) are coated by a draw down coating using a 50μηη spiral coater bar.

Coating solution: See experimental part.

The silver-containing membrane films were analysed by transmission electron micros- copy (TEM. UV irradiation produced well dispersed silver nanoparticles (AgNP) in the size range of 5-10 nm. Additional treatment of the PolyHEMA-AgNP films with a reducing solution (0.01 M NaBH₄) did not cause much change to the particles inside the films and the size remains in the range of 5-10 nm. Performance of DOW-LE-coated RO membranes in dead-end cell

Dead-end cell filtration (Testing conditions: 24.1 bar, 10g/L NaCI, Table 3)

Table 3: Performance of coated LE membranes in dead-end cell

EGDMA Permeate Flux Salt Rejection

Membrane

[wt%] [LMH] [%]

DOW-LE (reference

/ 128.3 98.3

no coating)

BW-30FR (refe¬

/ 65.8 100

rence, coated)

PolyHEMA 1 0.1 97.9 100

PolyHEMA 2 1.0 74.7 100

PolyHEMA 3 10.0 71 .9 100

PolyHEMA-Ag 1 0.1 108.6 100

PolyHEMA-Ag 2 1.0 1 12.6 100 Table 3 shows the results of the PolyHEMA coated membranes with and without AgNPs. If no AgNPs are present the permeate flux decreases with increasing cross- linker concentration from 97.9 to 71.9 LMH but it is still higher compared to BW30FR, a commercial fouling resistant membrane.

Incorporation of AgNPs into the coating layer increases the flux to a permeate flux of about 1 10 LMH similar to standard non coated RO membranes (DOW-LE).

Performance of DOW-LE antimicrobial coated RO membranes in dead-end cell

Antimicrobial compounds like Quarternary amines (QA) such as 2-(methacryloyloxy)- Ν,Ν,Ν-trimethylethanaminium (MA-TMEA) and zwitterionic methacrylates (ZW) such as 3-((2-(methacryloyloxy)ethyl) dimethylammonio) propanesulfonate (MA-EDMAPS), see Chart 1 , are used to coat DOW-LE membranes under the same above conditions above (1wt% EGDMA as cross-linker) using a 24μηη draw-down coater bar. Additionally, coatings using HEMA as well as PEG-MA as anti-adhesive monomers are prepared. Flux and flux recovery in a dead-end cell of these functionalized membranes is studied (Table 4).

Testing conditions: 0.2g/L sodium alginate in 2000ppm salt (2g/L NaCI), 15 bar; Rins- ing: 30mL MilliQ water stirred for 5 min. Pure water flux

PolyHEMA and PolyPEG-MA coated membranes show a slightly lower rinsed water flux than uncoated DOW-LE. The flux is, however, higher than commercial anti-fouling membrane BW-30FR (pure water flux of 44 LMH). The QA and ZW membranes show higher pure water flux.

Water flux during fouling solution (2000ppm NaCI solution with 0.2g/L sodium alginate) For all membranes the flux drops significantly mainly due to the increase in membrane resistance caused by the fouling of the alginate salt. Again, the QA and ZW together with the PEG-MA coated membranes show the highest flux. Fouling cleaning (30ml_ MilliQ water for 5 min) and flux recovery

All the coated membranes show much higher flux recovery (>85%) than uncoated DOW-LE, which exhibits only a flux recovery of -74%.

BW-30FR shows the best recovery with 100%, which, however, has to be put in relation to its lowest value for the initial water flux.

Claims

1. A method for imparting decreased adhesion of biological material to the surface of a reverse osmosis thin-film composite membrane on a microporous substrate comprising providing a composition of

a1 ) hydroxyethyl-methacrylate, ethyleneglycol-methacrylate or a compound of formulae

a2) 0.1 % to 10% by weight of ethyleneglycol-dimethacrylate, based on the weight of component a1 );

a3) 0.5% to 5% by weight of glycidyl-methacrylate

(GMA), based on the weight of component a1 );

and

2. A method according to claim 1 wherein silver lactate is additionally added to the composition.

3. A method according to claim 1 wherein the top layer of the thin-film composite membrane is a polyamide layer.

4. A method according to claims 1 or 2 wherein one or more further biocides different from those of claim 1 or 2 are additionally added to the composition.

5. A method according to claims 1 to 4 wherein the porous substrate is a polymer selected from the group consisting of a polyester, polysulfone, polycarbonate, polypropylene, polyamide and polyether sulfone.

6. A method according to any preceding claim wherein the cured coating layer has a thickness in the range of from 0.1 to 50 μηη, preferably, from 1 to 10 μηη.

7. A method according to any preceding claim wherein the exposure to UV light is carried out under inert gas atmosphere.

8. A composition comprising

a) a reverse osmosis thin-film composite membrane on a microporous substrate;

b3) 0.5% to 5% by weight of glycidyl-methacrylate

(GMA), based on the weight of component b1 );

and

b4) 0.1 % to 10% by weight of a radical photoinitiator, based on the weight of component b1 ).

9. A composition according to claim 8 which additionally contains one or more further biocides different from those of claim 1 or 2.

10. A composition according to claims 8 or 9 wherein component b) is as a cured film on the reverse osmosis thin-film composite membrane on a microporous substrate.

1 1 . Use of a composition according to claims 8 to 10 as separating membrane which has antifouling properties in a reverse osmosis process.

12. A coated thin-film composite membrane on a microporous substrate obtainable according to claim 1 .