Water-wettable filtration membrane and its manufacture

Abstract

A filtration membrane prepared by adhering a poloxamer to a preformed sheet of microporous polyolefin is described. In one embodiment, the poloxamer is supplied under the trade name PLURONIC® P-123, and the sheet is microporous poly(ethylene). This membrane offers the advantage of being resistant to cleaning agents used in clean-in-place protocols.

Description

[Technical Field]

[0001] The present invention relates to durable filtration membranes, filtration membrane assemblies including such membranes, and their use in recovering water from feed streams. In particular, the present invention relates to durable filtration membranes and their use in recovering water from feed streams where periodic in-situ cleaning of the membranes is required. [Background technology]

[0002] Patent Document 1 discloses the preparation of polyoxyethylene-polyoxypropylene block polymers represented by the following formula: HO(C2H4O) b (C3H6O) a (C2H4O) b H where a is an integer, represented by (CHO), such that the molecular weight of the hydrophobic base is at least 2,250, and b is an integer between about 8 and 180 or greater. These block polymers are used to prepare solid or semisolid colloids containing significant amounts of liquid, such as "gels" or "hydrosols" (where the liquid is water), which are particularly useful in formulating topically applied cosmetic and pharmaceutical compositions. These nonionic triblock copolymers, called poloxamers, are available under a number of trade names, including ACCLAIM®, ADEKANOL®, ANTAROX®, BASOROL™, BLAUNON®, ETHOX®, KOLLIPHOR®, LUTROL™, MEROXAPOL™, PLURIOL®, PLURONIC®, and SYNPERONIC®. The properties of poloxamers are determined both by the ratio of the integers a and b and by their size. Triblock copolymers in which the order of the polyoxyethylene and polyoxypropylene blocks is reversed are also supplied under these trade names. These "reverse" triblock copolymers may be identified by the use of the letter "R" and should not be called "poloxamers."

[0003] (2003) discloses the formation of membranes from blends of polyethersulfone and other triblock copolymers by a phase inversion method. The water flux determined for the membranes was observed to depend on the triblock copolymer structure, not the content. For example, the water flux of the membrane formed from the blend with PLURONIC® 123 (50.161 LMH) was observed to be lower than the water flux observed for the polyethersulfone control membrane (109.081 LMH). The water flux of the membrane formed from the blend with PLURONIC® F68 (218.28 LMH) was observed to be higher than the water flux of the control membrane.

[0004] Patent document 2 (machine translation) discloses the preparation of microporous membranes with microstructured surfaces for use in separating oil from water in oil / water emulsions. In this membrane preparation method, polyoxyethylene-polyoxypropylene-polyoxyethylene (F127) is used as an additive in the preparation of a homogeneous solution of the polymer in a solvent. The polymer is selected from the group consisting of polyvinylidene fluoride (PVDF), polysulfone (PSf), polyethersulfone (PES), polyacrylonitrile (PAN), polyvinyl chloride (PVC), polylactic acid (PLA), polyimide (PI), polypropylene (PP), or cellulose acetate, and the solvent is selected from the group consisting of chloroform (CHCl), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), triethyl phosphate (TEP), trimethyl phosphate (TMP), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), dibutyl phthalate (DBP), dioxane, propiophenone, diphenyl ether, and mixtures of one or more thereof.

[0005] Non-Patent Document 2 discloses a composite polymer electrolyte for use in lithium polymer batteries. The composite material consisted of mesoporous modified silica fillers dispersed in a poly(vinylidene fluoride-hexafluoropropylene) matrix. The triblock copolymer PLURONIC® 123 (Aldrich) was used to prepare the mesoporous silica fillers.

[0006] Patent Document 3 discloses a microporous material for use in micro- and ultrafiltration membranes. The microporous material contains finely divided particles, such as water-insoluble silica fillers, dispersed throughout a matrix, such as poly(ethylene). This material further contains a network of interconnected pores and can be further processed depending on the desired application. In such further processing, triblock copolymers based on poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) can be used as a hydrophilic coating, although polymers containing tertiary amine functional groups are preferred. Without intending to be bound by theory, it is stated that components of the coating may interact with the silica particles in the microporous material filler, adjusting the surface energy and affecting wettability. Covalent bonding of the hydrophilic coating, such as that achievable by grafting, is not disclosed.

[0007] Patent Document 4 (machine translation) discloses the use of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers as "structure directing agents" in the preparation of mesoporous composite films. The structure directing agents are used in conjunction with catalysts and precursor compounds such as tetraethyl orthosilicate, titanium tetrachloride, titanium n-butyl acetate, isopropyl titanium, dizinc acetate phthalate, tin esters, and one or more niobates to provide mesoporous composite films.

[0008] (2003) discloses the evaluation of the triblock copolymer PLURONIC® L64 as a solvent for pore-filling regenerated cellulose membranes during initiator immobilization. In this context, glycerol was determined to be a more efficient pore-filling solvent.

[0009] Fouling due to nonspecific protein adsorption or deposition requires periodic cleaning of filtration membranes. Being able to clean filtration membranes in place improves plant operating efficiency. Filtration membranes that are resistant to the chemicals used in these cleaning-in-place (CIP) protocols (acids, alkalis, hypochlorite) are desirable.

[0010] It is an object of the present invention to provide filtration membranes suitable for use in these and other situations, or at least to provide useful options in the selection of filtration membranes for use in these and other situations. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] U.S. Patent No. 3,740,421 [Patent Document 2] Chinese Patent No. 103611437 [Patent Document 3] International Publication No. 2015 / 073161 [Patent Document 4] Chinese Patent No. 106731886 [Non-patent literature]

[0012] [Non-Patent Document 1] Wang et al (2006), Journal of Membrane Science, 283, 440-447 [Non-patent document 2] Yang et al(2014),Electrochimica Acta 134,258-265 [Non-patent document 3] Carter et al(2018), Journal of Membrane Science, 554, 109-116 Summary of the Invention

[0013] In a first embodiment, a water-wettable filtration membrane is provided, comprising a poloxamer attached to a substrate consisting of a microporous polyolefin sheet. The poloxamer is attached to a preformed microporous polyolefin sheet. The poloxamer is attached to the polyolefin matrix of the preformed microporous sheet by forming a covalent bond between the two polymers. The covalent bond may be formed directly between the poloxamer and the polyolefin or indirectly via a crosslinker.

[0014] Preferably, the poloxamer is attached to the matrix by grafting. Most preferably, the poloxamer is attached to the matrix by photoinitiated grafting. In this context, photoinitiated grafting will be understood to include the formation of covalent bonds initiated by irradiation with ultraviolet (UV) light in the presence of a suitable photoinitiator. Suitable photoinitiators are type II photoinitiators such as benzophenone (diphenylmethanone; BP). Photoinitiated grafting is advantageously carried out in the presence of a crosslinking agent. Suitable crosslinking agents are low molecular weight diethenyl compounds. Low molecular weight diethenyl compounds are compounds with a molecular weight of 150 gmol, such as divinylbenzene (DVB). -1 It is a compound of less than

[0015] Preferably, the poloxamer is a polymer of the following structure: HO (ethylene oxide) m -(propylene oxide) n -(ethylene oxide) m H where m is in the range of 15 to 25 and n is in the range of 50 to 90. Most preferably, the poloxamer is equivalent to the triblock copolymer supplied under the trade name PLURONIC® P-123 (Sigma-Aldrich). It is understood that for the polymer sold under the trade name PLURONIC® P-123 (Sigma-Aldrich), m is 20 and n is 70.

[0016] Preferably, the polyolefin is poly(ethylene) or poly(propylene). More preferably, the polyolefin is poly(ethylene). Most preferably, the polyolefin is virgin poly(ethylene).

[0017] In a first embodiment of the first aspect, there is provided a water-wettable filtration membrane consisting of a microporous sheet of grafted poly(ethylene), the graft comprising a poloxamer of the following structure: HO (ethylene oxide) m -(propylene oxide) n -(ethylene oxide) m H Here, m is in the range of 15 to 25, and n is in the range of 50 to 90.

[0018] In a second embodiment of the first aspect, there is provided a water-wettable filtration membrane consisting of a microporous sheet of grafted poly(ethylene), the graft comprising divinylbenzene and a poloxamer of the following structure: HO (ethylene oxide) m -(propylene oxide) n -(ethylene oxide) m H Here, m is in the range of 15 to 25, and n is in the range of 50 to 90.

[0019] It is anticipated that in both the first and second embodiments of the first aspect, poly(propylene) may be used in place of poly(ethylene). Preferably, the filtration membrane is a semi-permeable membrane.

[0020] In a second aspect, there is provided a method of preparing a water-wettable filtration membrane, the method comprising: 1. contacting a microporous sheet of polyolefin with a solution of poloxamer in a solvent to provide a contacted sheet; 2. providing an irradiated sheet by irradiating the contacted sheet with ultraviolet light in the presence of a photoinitiator; and thereafter 3. Washing and drying the irradiated sheet to provide a membrane.

[0021] Preferably, the polyolefin is poly(ethylene) or poly(propylene). More preferably, the polyolefin is poly(ethylene). Most preferably, the polyolefin is virgin poly(ethylene).

[0022] Preferably, the solution includes a photoinitiator. More preferably, the solution further includes a crosslinker. Preferably, the poloxamer is a polymer of the following structure: HO (ethylene oxide) m -(propylene oxide) n -(ethylene oxide) m H where m is in the range of 15 to 25 and n is in the range of 50 to 90. Most preferably, the poloxamer is equivalent to the triblock copolymer supplied under the trade name PLURONIC® P-123 (Sigma-Aldrich). It is understood that for the polymer sold under the trade name PLURONIC® P-123 (Sigma-Aldrich), m is 20 and n is 70.

[0023] Preferably, the solvent is water-alcohol or water-acetone, with the ratio of water to alcohol or acetone (v / v) ranging from 1:1 to 3:1. More preferably, the ratio of water to alcohol or acetone (v / v) ranging from 1:1 to 2:1. Most preferably, the solvent is water-ethanol.

[0024] Preferably, the photoinitiator is a Type II photoinitiator. Most preferably, the photoinitiator is benzophenone (diphenylmethanone; BP). Preferably, the cross-linking agent has a molecular weight of 150 gmol -1 Most preferably, the crosslinker is divinylbenzene (DVB).

[0025] Preferably, the wavelength of the ultraviolet light is in the range of 250 to 360 nm, more preferably in the range of 250 to 280 nm, and most preferably, the wavelength of the ultraviolet light is 250 nm.

[0026] Preferably, the irradiation is for a period of between 1.5 and 2.5 minutes, more preferably for a period of 2 minutes ±10 seconds. In one embodiment of the second aspect, there is provided a method for preparing a water-wettable membrane, comprising irradiating at a wavelength of 250 nm a microporous sheet of poly(ethylene) impregnated with a solution of 3-5% (w / v) poloxamer supplied as PLURONIC® P-123, 0.5-1% (w / v) benzophenone, and 0-0.5% (w / v) divinylbenzene in 30-50% (v / v) ethanol in water.

[0027] In this embodiment of the second aspect, it is anticipated that poly(propylene) may be used in place of poly(ethylene). In a third aspect, there is provided a water-wettable filtration membrane prepared according to the second aspect.

[0028] In a fourth aspect, there is provided a method for recovering water from a feed stream comprising contacting a first side of a filtration membrane of the first or third aspect with the feed stream at a pressure sufficient to provide a permeate.

[0029] Preferably, the feed stream is selected from the group consisting of milk and wastewater. More preferably, the feed stream is selected from the group consisting of wastewater containing particulate matter and skim milk. Most preferably, the feed stream is selected from the group consisting of wastewater containing particulate matter in suspension. The particulate matter may be of abiotic or biological origin.

[0030] Preferably, the filtration membrane is in the form of a filtration membrane assembly or filter element. More preferably, the membrane is in the form of a spiral wound filtration membrane assembly or filter element.

[0031] Preferably, the method comprises at least periodically contacting the filtration membrane with an acid, alkali or chlorite. In a fifth aspect, the present invention provides a spiral wound filtration membrane assembly or filter element comprising the filtration membrane of the first or third aspect.

[0032] In the description and claims herein, the following abbreviations, acronyms, phrases, and terms have the meanings indicated: "Block" means a portion of a polymer containing many structural units. A structural unit has at least one structural or compositional feature that is not present in adjacent portions. "CAS RN" means a Chemical Abstracts Service (CAS, Columbus, Ohio) registration number. "Comprising" means "including," "containing," or "characterized by" and does not exclude any additional elements, components, or steps. "Consisting essentially of" means excluding any element, component, or step that is a material limitation. "Consisting of" means excluding any unspecified element, component, or step, except impurities or other incidentals. "Crosslinking" means a reaction involving sites or groups on, or an interaction between, existing polymers that results in the formation of small regions, such as crosslinked bridges, where at least four chains are generated within the polymer. "Crosslinking agent" means a substance incorporated into the crosslinked bridges of a crosslinked polymer network. "Curing" refers to a chemical process that converts a prepolymer or polymer into a polymer of higher molecular weight and higher connectivity, ultimately resulting in a network. "Filter" refers to the removal of particles from a fluid by passing it through a porous substrate, and "filtration" has a corresponding meaning. "Graft molecule" or "graft polymer molecule" refers to a macromolecule having one or more species blocks attached to the main chain as side chains with structural or compositional features different from those of the main chain. "Grafting" refers to a reaction in which one or more species blocks are attached to the main chain of a macromolecule by side chains with compositional structural features different from those of the main chain, and "grafted" has a corresponding meaning. "LMH" refers to liters per square meter per hour. "Impregnation" refers to the infiltration of a substrate with, for example, a solution of a reagent in a solvent. "Macromolecule" or "polymer" refers to a molecule of high relative molecular weight, the structure of which essentially, actually or conceptually, comprises multiple repeating units derived from molecules of lower relative molecular weight. "Monomer molecule" refers to a molecule capable of undergoing polymerization, thereby contributing a building block to the essential structure of a macromolecule."Monomer unit," "monomer unit," or "mer" refers to the largest building block of a polymer, where a single monomer molecule contributes to its structure. "Permeable" means allowing a solvent, e.g., water, to pass through. "Permeate" means permeating throughout. "Poloxamer" refers to a symmetric nonionic triblock copolymer composed of a central chain of poly(propylene oxide) flanked by two chains of poly(ethylene oxide). "Semipermeable" means allowing certain substances to pass through while blocking others, particularly allowing a solvent such as water to pass through while blocking certain solutes (e.g., proteins, salts, sugars, etc.). "Wettable" means allowing penetration by a solvent such as water upon contact under standard laboratory conditions (i.e., 25°C, 100 kPa). "Water-wettable" means capable of being wetted with water.

[0033] Cognates of all defined terms have the corresponding meaning. In the event of uncertainty regarding the meaning of an undefined abbreviation, acronym, phrase, or term related to polymer terminology and nomenclature, the meaning set forth in the Jones et al. (2008) publication shall prevail.

[0034] It is recognized that the porosity determined for a substrate will depend, at least in part, on the method employed to determine the porosity. The term "microporous" is used herein to refer to a polyolefin sheet porosity equivalent to that of TARGRAY™ wet-process polyethylene separator, product number SW320H (Targray, Kirkland, Quebec, Canada). In this context, the term "equivalent" means that the porosity determined for the polyolefin sheet is 75-125% of the porosity determined for TARGRAY™ wet-process polyethylene separator, product number SW320H (Targray, Kirkland, Quebec, Canada) using the same method.

[0035] The terms "first," "second," "third," etc., when used with reference to an aspect, element, feature, or integer described in the description of the invention or defined in the claims, or when used with reference to alternative aspects or embodiments of the invention, are not intended to imply any order of priority.

[0036] When a reagent concentration or ratio is specified, the specified concentration or ratio is the initial concentration or ratio of the reagent. When values ​​are expressed with one or more decimal places, standard rounding applies. For example, 1.7 includes the range 1.650 to 1.74999...

[0037] The present invention will now be described with reference to embodiments or examples and the accompanying drawings. In the brief description of the drawings and elsewhere in the following description, references to the "front" (C-front, E-front, etc.) of a filtration membrane or polyolefin microporous sheet prepared according to laboratory methods refer to the face or side of the membrane or sheet that contacts the working solution. References to the "back" (C-back, E-back, etc.) or "backing layer" refer to the opposite face or side. It will be understood that due to the attachment of the membrane or sheet to the filtration membrane assembly, not the entire face or side is exposed to the feed stream. A description of this filtration membrane assembly (Sterlitech Corp.) and its use is provided on page 24, lines 24 et seq., of the accompanying specification of International Application No. PCT / NZ2015 / 050034 [Publication No. WO2015 / 147657A1]. [Brief explanation of the drawings]

[0038] [Figure 1] Exploded view of the filtration membrane assembly (Sterlitech Corp.) used in flux testing of filtration membrane sheet samples. [Figure 2]Comparison of spectra (3800 cm-1 to 525 cm-1) recorded for untreated microporous poly(ethylene) (TARGRAY™ wet-process polyethylene separator, product number SW320H (Targray, Kirkland, Quebec, Canada)) (PE virgin), the triblock copolymer (PLURONIC® P-123, lot #MKCC2305, Sigma-Aldrich) used to prepare sample (P123), and the front (E-front) and backing layer (E-back) sides of each sample, designated 040918Wiv, 040918Wv, and 040918Wvi. [Figure 3] Comparison of spectra extended over the "fingerprint region" (1800 cm-1 to 600 cm-1) recorded for untreated microporous poly(ethylene) (TARGRAY™ wet-process polyethylene separator, product number SW320H, Targray, Kirkland, Quebec, Canada) (PE virgin), the triblock copolymer (PLURONIC® P-123, lot #MKCC2305, Sigma-Aldrich) used to prepare sample (P123), and the front (E-front) and backing layer (E-back) sides of each sample, designated 040918Wiv, 040918Wv, and 040918Wvi. [Figure 4] Comparison of spectra (3800 cm-1 to 525 cm-1) recorded for a region of the sample designated 040918Wvi with (C-front and C-back) and without (E-front and E-back) exposure to the feed stream. [Figure 5] Scanning electron micrographs of the front (E-front) side of the sample designated 040918Wiv at magnifications of 250,000x (A), 35,000x (B), and 10,000x (C). [Figure 6] Scanning electron micrographs at 100,000x magnification of two areas on the front (E-front) side of the sample designated 040918Wiv. [Figure 7]Comparison of the flux (LMH) maintained in samples of filtration membranes (180419Wi and 230419Wii (■); 180419Wii and 230419Wiii (●)) prepared with (solid line) and without (dashed line) cross-linking agent (DVB). [Figure 8] Schematic of a prototype production line used to prepare water-wettable filtration membranes according to Example C. DETAILED DESCRIPTION OF THE INVENTION

[0039] Filtration membranes are used in a variety of industrial processes, including food processing, to recover or remove water from feed streams. In some applications, the goal may be to separate water from contaminant particles. In other applications, the goal may be to concentrate high-value solutes.

[0040] In both applications, efficiency is improved by contacting the feed stream with the large surface area of ​​the filtration membrane. For this purpose, filtration membranes are often assembled into spiral-wound filter elements, which are then installed in industrial plants. Such spiral-wound membrane assemblies (or "filter elements") are supplied by manufacturers such as Synder Filtration (Vacaville, California, USA).

[0041] Further efficiencies would be realized if cleaning could be performed in-place without requiring removal and reinstallation of the filter element. Clean-in-place protocols use chemically aggressive solutions such as acids, alkalis, and hypochlorites. Alternatively, the feed streams to which the membrane is exposed can be chemically aggressive, and durability under these conditions would reduce the frequency with which filter elements need to be replaced.

[0042] Microporous sheets of polyolefins such as poly(ethylene) are commercially available from suppliers such as Celgard (Charlotte, NC, USA) and Targray (Kirkland, Quebec, Canada). One obstacle to using these substrates as filtration membranes in the applications suggested above is their inherent hydrophobicity. They may also lack the necessary rejection properties if the goal is to provide a semipermeable membrane for use in concentrating high-value solutes.

[0043] Grafting microporous sheets of poly(ethylene) with poloxamer, available under the trade name PLURONIC®-P123, has been found to provide filtration membranes that are readily wettable by water and provide high flux rates at relatively low pressures (500 kPa or 5 bar). Filtration membranes so produced have also been demonstrated to possess desirable durability when exposed to chemically aggressive fluids.

[0044] The retention of these desirable properties due to grafting is enhanced by including a cross-linking agent in the working solution used in the preparation method. Without wishing to be bound by theory, low molecular weight cross-linking agents are preferred so as not to destroy the desirable blocking properties of the membranes demonstrated.

[0045] The method for preparing filtration membranes is easily adaptable to continuous production processes. According to the described method, a working solution of the following composition is used to impregnate a microporous substrate, which is then irradiated with ultraviolet light at a wavelength in the range of 250 nm to 360 nm. Wavelengths at or near the lower end of this range (250 nm) are preferred.

[0046] Working solution: 3-5% (w / v) poloxamer 0.5 to 1% (w / v) photoinitiator 0-0.5% (w / v) crosslinker 30-50% (v / v) alcohol or acetone in water A preferred poloxamer for use in the working solution is that supplied under the trade name PLURONIC® P-123. A preferred photoinitiator for use in the working solution is benzophenone. A preferred crosslinker for use in the working solution is divinylbenzene.

[0047] Example A Preparation of filtration membrane (laboratory method) Five mL of a 10% (w / v) aqueous solution of triblock copolymer (PLURONIC® P-123; lot #MKCC2305, Sigma-Aldrich) was mixed with an equal volume of deionized water. A 0.1 g quantity of the photoinitiator benzophenone (diphenylmethanone; PhO) was dissolved in another 5 mL of ethanol and then added to the diluted solution of triblock copolymer. The working solution was stored in the dark until use.

[0048] Samples (13.5 x 18.5 cm) were cut from a sheet of microporous poly(ethylene) (TARGRAY™ wet-process polyethylene separator, product number SW320H (Targray, Kirkland, Quebec, Canada)), and each sample was coated with 5 mL of working solution. The coated samples were then irradiated with ultraviolet (UV) light in the 250-360 nm range for 2 minutes, rinsed with water, and air-dried in a warm oven.

[0049] Four replicate samples prepared according to this method were designated 040918Wiv, 040918Wv, 040918Wvi, and 151018Wi. A small piece of the sample designated 040918Wiv was cut from the edge of the sample and subjected to scanning electron microscopy (SEM).

[0050] Each sample was observed to wet readily with water and become uniformly translucent upon contact with this solvent. Durability, flux and protein inhibition The flux (LMH) of each sample, designated 040918Wiv, 040918Wv, and 040918Wvi, was measured using a membrane filter assembly (Sterlitech) as shown in Figure 1. The samples were individually mounted in the membrane filter assembly, and the flux was measured at 0 and 500 kPa (5 bar). The time to collect a given amount of permeate at a specified pressure and temperature was recorded, and the flux (J) was calculated according to the following formula:

[0051]

number

[0052] where V is the volume of permeate (L), t is the time for collection of V (h), and A is the area of ​​the sample exposed to the feed stream (water or skim milk) (m 2 The results are summarized in Table 1.

[0053] [Table 1]

[0054] To assess durability, flux was also measured after repeated cleaning-in-place (CIP) protocols. The CIP protocols were based on those employed in commercial reverse osmosis (RO) membrane treatment operations (Anon (2014)) and are summarized in Table 2.

[0055] [Table 2]

[0056] For each sample, several CIP protocols were alternated using water or skim milk as the feed stream. The measured flux and protein rejection (using skim milk as the feed stream) for samples designated 040918Wv and 040918Wvi are shown in Table 3. The total protein concentration in the permeate was calculated based on HPLC analysis using UV absorbance monitoring.

[0057] [Table 3]

[0058] The durability of the filtration membrane was further evaluated by contacting a sample designated 151018Wi with 2% (w / v) sodium hydroxide (NaOH) for 7 days. The measured flux and protein rejection (using skim milk as the feed stream) for these samples are shown in Table 4.

[0059] [Table 4]

[0060] Fourier transform infrared (FTIR) spectroscopy A Thermo Electron Nicolet 8700 FTIR spectrometer equipped with a single bounce ATR and a diamond crystal was used to record the spectra of each sample, designated 040918Wiv, 040918Wv, and 040918Wvi. For each sample, a 4 cm -1 Thirty-two scans were averaged at a resolution of 3800 cm. Spectra were recorded for (i) untreated microporous poly(ethylene) (TARGRAY™ wet-process polyethylene separator, product number SW320H (Targray, Kirkland, Quebec, Canada)) ("PE Virgin"); (ii) the triblock copolymer (PLURONIC® P-123; lot #MKCC2305, Sigma-Aldrich) used to prepare sample ("P123"); and (iii) the front (E-front) and back (E-back) sides of each sample, designated 040918Wiv, 040918Wv, and 040918Wvi. -1 From 525cm -1 ) is compared in Figure 2.

[0061] The symmetric stretching mode of the COC fragment (1108 cm ) present in the spectrum of the triblock copolymer (PLURONIC® P-123) -1) and CH stretching mode of CH3 (2970 cm -1 ) were also present in the spectra recorded for each sample. Many signals characteristic of the triblock copolymer (PLURONIC® P-123) were also observed at low intensity in the "fingerprint" region of the spectrum shown in Figure 3. Signals characteristic of the triblock copolymer (PLURONIC® P-123) were retained in the spectrum recorded after exposure to the feed stream (water) in the region of the sample labeled 040918Wiv, as shown in Figure 4.

[0062] SEM Scanning electron micrographs of a small piece cut from the edge of the sample designated 040918Wiv are shown in Figures 5 and 6. The microporous sheet appears to be coated with poly(ethylene) fibers.

[0063] Observations from FTIR spectroscopy and SEM appeared to indicate the grafting of poloxamer to the polyolefin matrix of the microporous sheet, resulting in the transformation of the inherently hydrophobic microporous sheet of polyolefin into a water-wettable, permeable membrane.

[0064] Example B Preparation of filtration membrane (laboratory method) A 10 mL aqueous solution of 10% (w / v) triblock copolymer (PLURONIC® P-123; Lot #MKCC2305, Sigma-Aldrich) was mixed with an equal volume of deionized water. 0.2 g of the photoinitiator benzophenone (diphenylmethanone; PhO) and 0 or 0.1 g of the crosslinker divinylbenzene (DVB) were dissolved in separate 10 mL portions of ethanol (methanol-denatured spirit) and then added to 10 mL of the diluted triblock copolymer solution. These working solutions (with or without the crosslinker DVB) were stored in the dark until use.

[0065] Samples (13.5 × 18.5 cm) were cut from a sheet of microporous poly(ethylene) (TARGRAY™ wet-process polyethylene separator, product number SW320H (Targray, Kirkland, Quebec, Canada)) and each sample was coated with one of the working solutions. The coated samples were then exposed to ultraviolet (UV) light in the range of 250–360 nm for 2 minutes, rinsed with water, and air-dried outdoors.

[0066] Three replicate samples prepared according to this method using a working solution excluding DVB were designated 110419Wi, 180419Wi, and 180419Wii. Three replicate samples prepared according to this method using a working solution containing DVB were designated 230419Wi, 230419Wii, and 230419Wiii. Each sample was observed to wet readily with water and become uniformly translucent upon contact with this solvent.

[0067] The water flux of each sample was measured using deionized water as the feed stream (DI1). The samples were then allowed to dry completely, and the water flux was measured again using deionized water as the feed stream (DI2). Each sample was then subjected to a clean-in-place (CIP) protocol, after which the water flux was measured two more times using deionized water as the feed stream (DI3 and DI4), with the sample allowed to dry in between. Each sample was still easily wetted with water. The results are summarized in Tables 5 and 6 and compared in Figure 7.

[0068] [Table 5]

[0069] [Table 6]

[0070] Example C Preparation of filtration membrane (prototype method) A 300 mL solution of 10% (w / v) triblock copolymer (PLURONIC® P-123; lot #MKCC2305, Sigma-Aldrich) in distilled water was dispensed into a reservoir protected from exposure to light. An additional 300 mL of distilled water was then added to provide an initial solution of 5% (w / v) triblock copolymer (PLURONIC® P-123; lot #MKCC2305, Sigma-Aldrich) in the reservoir. A solution of 1.5% (w / v) benzophenone in ethanol (methanol-denatured spirit) was separately prepared, and an amount of the crosslinker divinylbenzene (DVB) was added to a final concentration of 0.75% (v / v) DVB. 400 mL of this separately prepared solution was then mixed with a solution of triblock copolymer (PLURONIC® P-123; Lot #MKCC2305, Sigma-Aldrich) in a reservoir to provide the working solution.

[0071] Referring to Figure 7 of the accompanying drawings, peristaltic pumps (1, 2) were used to pump the working solution from the reservoir (3, 4) into two semi-cylindrical troughs (5, 6) of the prototype production line. During operation of the prototype production line, the reservoir was periodically replenished with working solution.

[0072] A width of continuous microporous poly(ethylene) sheet (7) was fed from a stock dispense roll to a first impregnation station containing an idler roller (8) coaxially mounted in the first of two semi-cylindrical troughs (5). The difference in radius between the roller (8) and the trough (5) was sufficient to allow the sheet (7) to pass freely around the roller and through the trough, but not so great as to promote evaporation of the working solution within the trough. The surface of the roller (8) over which the sheet (7) passed may be spirally grooved to promote the passage of the working solution along the length of its surface.

[0073] The sheet (7) exiting the first impregnation station was then fed vertically into a first irradiation station comprising a slotted chamber (9) containing two opposing arrays (10, 11) of ultraviolet light sources. The sheet (7) passed between the opposing arrays (10, 11) so that it was illuminated on both sides. The speed at which the sheet (7) was fed was adjusted to provide the required residence time within the slotted chamber (9).

[0074] The irradiated sheet (7) then passed through a second impregnation station (12) and a second irradiation station (13), which were identical in configuration to the first impregnation station and first irradiation station. Following these repeated steps, the irradiated sheet (7) was fed around several idler rollers (14, 15, 16) submerged in water in a washing station (17). The water in the washing station (17) was circulated by an external pump (18), and the water depth was controlled by a combination of a level transmitter and a solenoid valve (19). The combination of the several idler rollers (14, 15, 16) and the water depth ensured sufficient residence time for the water-washed sheet (7) before it was fed to the drying station.

[0075] The drying station was a forced air dryer containing two plenum chambers (20, 21) with opposing perforated faceplates through which the substrate sheet passed. Hot air blowers (22, 23) mounted on the wall of each chamber forced air through the perforated faceplates. The dried substrate sheet (7) was then wound onto a receiving roll (not shown).

[0076] filter element The membranes can be used to manufacture assemblies of various configurations. In one embodiment, the membranes are used to manufacture spiral wound filter elements. The manufacture of such filter elements is well known in the art.

[0077] While the present invention has been described with reference to embodiments or examples, it should be understood that changes and modifications can be made to these embodiments or examples without departing from the scope of the present invention. Where known equivalents exist for specific elements, features, or integers, such equivalents are incorporated as if specifically referenced herein. Changes and modifications to the embodiments or examples that include elements, features, or integers disclosed in and selected from referenced publications are within the scope of the present invention, unless otherwise noted. The advantages provided by the present invention and described in this specification may be provided alternatively or in combination in these different embodiments of the present invention. [Industrial Applicability]

[0078] Methods for preparing filtration membranes and their use in recovering or removing water from feed streams are provided. Filtration membranes are advantageously used to recover or remove water from feed streams when it is desirable to clean the membrane in situ to increase plant operating efficiency.

[0079] Incorporation by Reference If all or part of the claims, specification, or drawings of this application are missing, the corresponding portions of the specification accompanying the most recently filed application to which priority is claimed are incorporated by reference to complete this specification pursuant to PCT Rules 4.18, 20.5, and 20.6 (in effect on July 1, 2015, or as subsequently amended).

[0080] For purposes of 37 CFR 1.57, the disclosures of the following publications (more specifically identified under the heading "References") are incorporated by reference: Jones et al. (2008) and Schmolka (1973).

[0081] References

[0082] [Table 7]

Claims

1. A water-wettable filtration membrane comprising a microporous sheet of grafted polyolefin, said graft being formed by photoinitiated grafting; HO (ethylene oxide) ｍ - (propylene oxide) ｎ - (ethylene oxide) ｍ H wherein m is in the range of 15 to 25 and n is in the range of 50 to 90.

2. The membrane of claim 1 , wherein the polyolefin is poly(ethylene).

3. 3. The membrane of claim 1, wherein m is 20 and n is 70.

4. The membrane of any one of claims 1 to 3, wherein the graft comprises a cross-linking agent.

5. The crosslinker was 150 gmol －１ 5. The membrane of claim 4 having a molecular weight of less than 1000 .mu.m.

6. 6. The membrane of claim 5, wherein the cross-linking agent is divinylbenzene.

7. A membrane assembly comprising the membrane according to any one of claims 1 to 6.

8. The membrane assembly of claim 7 , wherein the membrane is spirally wound.

9. 1. A method for preparing a water-wettable filtration membrane, comprising: (a) contacting a microporous sheet of polyolefin with a solution of poloxamer in a solvent to provide a contacted sheet; (b) irradiating the contacted sheet with ultraviolet light in the presence of a photoinitiator to provide an irradiated sheet; and (c) drying and washing the irradiated sheet to provide a membrane; The poloxamer is HO (ethylene oxide) ｍ - (propylene oxide) ｎ - (ethylene oxide) ｍ H wherein m is in the range of 15 to 25 and n is in the range of 50 to 90.

10. 10. The method of claim 9, wherein the polyolefin is poly(ethylene).

11. 11. The method of claim 9 or 10, wherein m is 20 and n is 70.

12. The method of any one of claims 9 to 11, wherein the solution comprises the photoinitiator.

13. The method of any one of claims 9 to 12, wherein the photoinitiator is a Type II photoinitiator.

14. The method of any one of claims 9 to 13, wherein the photoinitiator is benzophenone.

15. The method of any one of claims 9 to 14, wherein the solution comprises a low molecular weight cross-linking agent.

16. 16. The method of claim 15, wherein the crosslinking agent is divinylbenzene.

17. 17. The method according to any one of claims 9 to 16, wherein the solvent is 30-50% (v / v) alcohol or acetone in water.

18. The method according to any one of claims 9 to 14, wherein the solvent is 30-50% (v / v) ethanol in water.

19. 7. A method for recovering or removing water from a feed stream comprising contacting a first side of the membrane of any one of claims 1 to 6 with the feed stream at a pressure sufficient to provide a permeate.

20. 20. The method of claim 19, wherein the pressure is less than 1 MPa (10 bar) and the flux is greater than 500 LMH.

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