Asymmetric composite membranes and hydrophilicitized microporous sheets of polyolefin used in their preparation

Abstract

Composite membranes having a film of poly(ethenol) (polyvinyl alcohol; PVA) adhered to a microporous sheet of polyolefin are disclosed. The microporous sheet is made hydrophilic by grafting of the polyolefin, e.g. poly(ethylene), with a preformed polymer before adherence of the film of PVA. The composite membranes are chlorine tolerant with high levels of protein rejection making them particularly suitable for use in the extraction or recovery of water from feed streams in the beverage and food industries, including dairy.

Claims

1. A method of preparing an asymmetric composite membrane comprising: a) Wetting one side of a hydrophilicitized microporous sheet of polyolefin with a solution in an aqueous solvent comprising poly(ethenol) and a persulfate; b) Irradiating the wetted sheet to graft the poly(ethenol) to the sheet; and then c) Washing and drying the sheet to provide the asymmetric composite membrane, where the microporous sheet has been hydrophilicitized by grafting of the polyolefin with a preformed polymer.

2. The method of claim 1 where the preformed polymer is poly(4-ethenyl benzene sulfonic acid) or a poloxamer of the structure:
HO(ethylene oxide).sub.m-(propylene oxide).sub.n-(ethylene oxide).sub.mH where m is in the range 15 to 25 and n is in the range 50 to 90.

3. The method of claim 2 where the aqueous solvent is water.

4. The method of claim 3 where the persulfate is sodium persulfate (SPS).

5. The method of claim 4 where the polyolefin is poly(ethylene).

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1. Exploded view of the filter assembly (Sterlitech Corp.) used in the flux testing of samples of composite membranes and hydrophilicitized microporous sheets.

(2) FIG. 2. FTIR spectra of the monomer 4-ethenylbenzenesulfonic acid (SSS) and poly(4-ethenylbenzenesulfonic acid) (PSSS) prepared according to the method described in Example 1 (water) and Example 2 (DMSO).

(3) FIG. 3. FTIR spectra recorded for poly(4-ethenylbenzenesulfonic acid)(PSSS), the photoinitiator benzophenone (BP), no washing protocol (1), washed with water at a temperature of 45 to 50? C. before drying (2), washed with acetone (3) and washed with water at a temperature of 45 to 50? C., dried and then washed with acetone (4).

(4) FIG. 4. Photograph of vials containing partially crosslinked poly(ethenol) (xPVA) prepared according the Example 8. From left to right: Vial 1, Vial 2, Vial 3 and Vial 4.

(5) FIG. 5. Flux (LMH) (?, broken line), total solids (%) (?, dotted line) and protein rejection (%) (?, solid line) of a sample of an composite membrane (030918Sii) prepared according to Example 10 during repeated clean-in-place (C-i-P) protocols.

(6) FIG. 6. Pressure series testing (0 to 20 bar) of a sample (030918Siii) of a composite membrane prepared according to Example 10. Flux and protein rejection with milk as the feed stream were measured.

(7) FIG. 7. Comparison of the FTIR spectra (full range) recorded for samples (240818Si and 240818Sii) of a composite membrane prepared according to Example 10 and the poly(ethenol) (PVA) and cross-linked poly(ethenol) (xPVA) used in their preparation.

(8) FIG. 8. Comparison of the FTIR spectra (stretch mode region) recorded for samples (240818Si and 240818Sii) of a composite membrane prepared according to Example 10 and the poly(ethenol) (PVA) and cross-linked poly(ethenol) (xPVA) used in their preparation.

(9) FIG. 9. Comparison of the FTIR spectra (fingerprint region) recorded for samples (240818Si and 240818Sii) of a composite membrane prepared according to Example 10 and the poly(ethenol) (PVA) and cross-linked poly(ethenol) (xPVA) used in their preparation.

(10) FIG. 10. Scanning electron micrographs of the surface of samples of composite membrane prepared according to Example 10 before (A) and after (B) being subjected to repeated clean-in-place (CIP) protocols.

DETAILED DESCRIPTION

(11) Polyolefins are inherently hydrophobic, whereas poly(ethenol) (polyvinyl alcohol; PVA) is inherently hydrophilic and water soluble. The incompatible properties of the two polymers present an obstacle to the preparation of composite membranes consisting of poly(ethenol) adhered, e.g. by photoinitiated grafting, to a polyolefin substrate, such as a microporous sheet. The obstacle may be overcome by modification of the surface of the substrate to increase its hydrophilicity, i.e. wettability. It has been found that wettable, microporous sheets of polyolefin suitable for use in the manufacture of composite membranes comprising poly(ethenol) can be prepared by grafting the polyolefin substrate with certain preformed polymers. The use of the preformed polymers demonstrated here allows for the preparation of microporous sheets of polyolefin with differing degrees of hydrophilicity. Along with the selection of solvent, the degree of hydrophilicity can be used to control the extent to which the solution of poly(ethenol) permeates the microporous sheet of polyolefin during the preparation of the composite membranes. Such control can be advantageous for the continuous production of composite membranes. The use of microporous sheets of polyolefin grafted with a poloxamer is particularly advantageous as the degree of hydrophilicity imparted by these thermoresponsive polymers can additionally be controlled by temperature.

(12) Providing a hydrophilicitized, i.e. wettable, microporous sheet of polyolefin facilitates the formation of a film of at least partially crosslinked poly(ethenol) (xPVA) on the surface and adherence to that surface. In contrast with the preparation of the asymmetric composite membranes disclosed in the publication of Craft et al (2017) persulfate is used as an agent to promote cross-linking. The high levels of protein rejection demonstrated for these composite membranes is attributed in part to the selection of this crosslinking agent. A porosity providing a size exclusion reduced to an estimated 30 kDa from an estimated 160 kDa is believed to be achieved (and is supported by the increased levels of total protein rejection of greater than 99.9%).

(13) When drying the hydrophilicitized microporous sheet of polyolefin following contact with the dispersion in aqueous solvent of poly(ethenol) (PVA) applying a thermal gradient across the thickness of the sheet from the contacted side to the other side is also believed to assist in maintaining the porosity of the sheet and thereby provide a composite membrane with higher flux rates than might otherwise be achievable. In Example 10 the application of a positive thermal gradient is a consequence of the sheet being supported on a glass plate during the drying steps. The positive thermal gradient is believed to limit the extent to which the dispersion in water may permeate the pores of the hydrophilicitized microporous sheet.

(14) When the hydrophilicitized microporous sheet of polyolefin has been prepared using a poloxamer, as in Example 12, heating transiently alters the degree of hydrophilicity imparted by the graft. This phenomenon may also be utilised to promote formation of a thin film of poly(ethenol) at the surface of the sheet without loss of porosity of the substrate. The transient decrease in hydrophilicity favours exclusion of the aqueous solvent from the pores of the substrate.

(15) The composite membranes provided here are distinguished from other membranes, e.g. those suggested in the publication of Linder et al (1988), where a superficial film of cross-linked PVA or PVA-copolymer is proposed to be coated on a hydrophobic, i.e. water repelling, microporous sheet of polyolefin.

(16) Materials and Methods

(17) All microporous sheets of polyolefin used in the preparation of samples were prepared from virgin poly(ethylene), i.e. poly(ethylene) of high purity.

(18) FTIR

(19) Spectra of the samples were recorded using a Thermo Electron Nicolet 8700 FTIR spectrometer equipped with a single bounce ATR and diamond crystal. An average of 32 scans with a 4 cm.sup.?1 resolution was taken for all samples.

(20) Flux

(21) Permeability was determined using a filter assembly (Sterlitech Corp.) (FIG. 1) by measuring the flux with deionized water as the feed stream at various pressures. Flux J.sub.V was then graphed against effective pressure difference across the membrane, p.sub.eff, and the slope of the permeability L.sub.p.

(22) $L_p=\frac{J_V}{?p_{\mathrm{eff}}}$

(23) The samples were mounted in the filter assembly. Deionized water was fed into the rig at 2.5 L min.sup.?1 and 4 to 8? C. The time to collect a predetermined volume of permeate was noted. The flux rate (J) was calculated according to the following equation:

(24) $J=\frac{V}{t?A}$
where V is the permeate volume (L), t is the time (h) for the collection of V and A is area of the sample (m.sup.2) which was determined to be 0.014 m.sup.2.
Salt Rejection

(25) Rejection was measured using a 2 g/L solution in water of sodium chloride with a feed pressure of 16 bar. The conductivities from the feed and permeate were compared.

(26) $\%R_{\mathrm{NaCl}}=\left(1-\frac{{?}_p}{{?}_f}\right)?100$
where ?.sub.p is the conductivity of permeate and ?.sub.f is the conductivity of the feed.
Total Solids Rejection

(27) Rejection for whole milk samples was measured by pouring 20 mL of sample from the feed in a petri dish and measuring the dry weight after 2 hours in a 100? C. oven.

(28) $\%R_{TS}=\left(1-\frac{m_{p,\mathrm{TS}}}{m_{f,TS}}\right)?100$
where m.sub.p,Ts is total milk solids in the permeate and m.sub.f,Ts is the mass of milk total solids in the feed.
Protein Concentrations

(29) Total protein and total whey protein concentrations in permeate were calculated on the basis of HPLC analysis with UV absorbance monitoring.

(30) Clean-in-Place (CIP) Protocol

(31) To mimic commercial processing operations samples of the composite membrane was subjected to repeated in situ washing protocols) as described in Craft et al (2017). The intermediate and subsequent flux rates were determined to assess the likely durability of the membrane in commercial processing operations. The in situ washing protocol was based on that employed in a commercial processing operation but modified in duration to compensate for the greater exposure of the membrane to the cleaning agents (caustic and acid) in the filter assembly. Prior to the washing steps the membrane was rinsed by circulating water at an initial temperature of 65? C. through the filter assembly for a period of time of three minutes before draining the system.

(32) The membrane was subjected to a first wash by circulating a 2% (w/v) sodium hydroxide solution (caustic wash) through the filter assembly for a period of time of five minutes before draining and flushing the system by circulating water at an initial temperature of 65? C. through the filter assembly system for a period of time of five minutes. The membrane was subjected to a second wash by circulating a 2% (w/w) nitric acid solution (acid wash) through the filter assembly system for a period of time of ten minutes before draining and flushing the system of circulating water at an initial temperature of 65? C. for a period of time of ten minutes. The membrane was subjected to a third wash (a caustic wash) before flushing the system by circulating water at an initial temperature of 65? C. for a period of time of five minutes before circulating chilled water for a period of time of five minutes to cool the system. All rinsing and washing steps were performed with no pressure recorded on the pressure gauge of the filter assembly.

(33) Hydrophilicitized Macroporous Sheets of Polyolefin

Preparation of poly(4-ethenylbenzenesulfonic acid)

Example 1

(34) A quantity of 50 g of the monomer 4-ethenylbenzenesulfonic acid as its sodium salt (SSS) was dissolved in a volume of 100 mL of distilled water to provide a solution. A quantity of 0.5 g of the initiator sodium persulfate (SPS) was then dissolved in the solution and the initiator-monomer mixture heated with stirring at a temperature of 80 to 90? C. for a time of about 20 minutes. A viscous solution was obtained having a total volume of about 125 mL. The viscous solution was diluted with the same volume of distilled water to provide 250 mL of a working solution of poly(4-ethenylbenzenesulfonic acid).

(35) The polymer could be precipitated from this working solution by the addition of an excess volume of acetone, followed by collection of the precipitate by filtration through a Buchner funnel and then washing with acetone to provide a light white solid that could be readily ground to a powder using a pestle and mortar.

Example 2

(36) A quantity of 5 g of the monomer 4-ethenylbenzenesulfonic acid as its sodium salt (SSS) was dissolved in a volume of 20 mL of dimethylsulfoxide (DMSO) to provide a solution.

(37) A quantity of 0.05 g of the initiator ammonium persulfate (APS) was then dissolved in the solution and the initiator-monomer mixture heated with stirring at a temperature of 80 to 90? C. for a time of about 20 minutes. The poly(4-ethenylbenzenesulfonic acid) was precipitated from the cooled solution by addition of an excess volume of acetone, collected by filtration through a Buchner funnel and washed with acetone to provide the same light white solid that could be readily ground to a powder obtainable in Example 1.

(38) The Fourier transform infrared (FTIR) spectra of the powder obtained by the methods of preparation described in Example 1 (pSSS from water) and Example 2 (pSSS from DMSO) are compared with that of the FTIR spectrum of the monomer 4-ethenylbenzenesulfonic acid (SSS) in FIG. 2. A comparison of the spectra was consistent with the polymerisation of the monomer in both methods of preparation. The polymer prepared by the method described in Example 1, i.e. the working solution, was used as the hydrophilicitizing agent in the preparation of hydrophilicitized sheets of microporous poly(ethylene) according to the following examples.

Preparation of Hydrophilicitized Microporous Sheets of poly(ethylene) Using poly(4-ethenylbenzenesulfonic acid)

Example 3

(39) A volume of 6 mL of the working solution obtained according to Example 1 was mixed with a volume of 5 mL of distilled water in a vial to provide a volume of initial solution containing 1.2 g of poly(4-ethenylbenzenesulfonic acid)(pSSS). A volume of 10 mL acetone was added to the volume of initial solution and allowed to become transparent before adding and dissolving in the solution a quantity of 0.2 g of the photoinitiator benzophenone (BP) to provide a hydrophilicitizing mixture. The surface of a microporous sheet of poly(ethylene)(TARGRAY? wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) dimensioned (13.5 cm?18.5 cm) to fit the filter assembly (Sterlitech Corp.) was contacted with the hydrophilicitizing mixture and irradiated with ultraviolet (UV) light (250 nm) for a period of time of 2 minutes. The irradiated contacted sheets were then washed with cold tap water before being placed in a water bath maintained at a temperature of 45 to 50? C. for a time of about 5 minutes. The washed sheets were then air dried before testing or use in the preparation of a composite membrane.

Example 4

(40) The method of preparation described in Example 3 was repeated with the volume of initial solution containing 1.7 g of poly(4-ethenylbenzenesulfonic acid). This quantity of the polymer was close to the maximum that could be dissolved in the solvent system used.

Example 5

(41) A one step method of preparation including the monomer 4-ethenylbenzenesulfonic acid was evaluated.

(42) A volume of 3 mL of the working solution obtained according to Example 1 was mixed with a volume of 8 mL of distilled water and a quantity of 0.6 g of the monomer 4-ethenylbenzenesulfonic acid in a vial to provide a volume of initial solution containing 0.6 g of poly(4-ethenylbenzenesulfonic acid). A volume of 10 mL acetone was added to the volume of this initial solution and allowed to become transparent before adding a quantity of 0.4 g of the photoinitiator benzophenone to provide a hydrophilicitizing mixture.

(43) The surface of a microporous sheet of poly(ethylene)(TARGRAY? wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) dimensioned (13.5 cm?18.5 cm) to fit the filter assembly (Sterlitech Corp.) was contacted with the hydrophilicitizing mixture and irradiated with UV light (250 nm) for a period of time of 2 minutes before being washed with cold tap water and placed in a water bath maintained at a temperature of 45 to 50? C. for about 5 minutes and then air dried.

Example 6

(44) A two-step method of preparation using only the monomer 4-ethenylbenzenesulfonic acid in the first of the two steps was evaluated.

(45) In the first step a volume of 10 mL of distilled water followed by a volume of 10 mL of acetone was added to a foil wrapped vial containing a quantity of 2.4 g of the monomer and a quantity of 0.4 g of the photoinitiator benzophenone and the mixture shaken until all solids had dissolved. The surface of a microporous sheet of poly(ethylene)(TARGRAY? wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) dimensioned (13.5 cm?18.5 cm) to fit the filter assembly of a test rig (Sterlitech Corp.) was contacted with the mixture and irradiated with ultraviolet (UV) light (250 nm) before washing with cold tap water and placing in a water bath maintained at a temperature of 45 to 50? C. for a time of 5 minutes before being air dried.

(46) In the second step a volume of 6 mL of the working solution obtained according to Example 1 was mixed with a volume of 5 mL of distilled water in a vial to provide a volume of initial solution containing 1.2 g of poly(4-ethenylbenzenesulfonic acid). A volume of 10 mL acetone was added to the volume of initial solution and allowed to become transparent before adding and dissolving in the solution a quantity of 0.2 of the photoinitiator benzophenone to provide a hydrophilicitizing mixture. The surface of the air dried sheet obtained according to the first step was contacted with the hydrophilicitizing mixture and irradiated with UV light (250 nm) for a period of time of 2 minutes before washing with cold tap water and placing in a water bath maintained at a temperature of 45 to 50? C. for a period of time of about 5 minutes and then air dried.

(47) Observations

(48) Grafting of the preformed poly(4-ethenylbenzenesulfonic acid) onto the microporous sheet of poly(ethylene) according to the methods of preparation described in Example 3, Example 4, Example 5 and Example 6 was confirmed by washing in acetone (solvent for the photoinitiator benzophenone) and water (solvent for poly(4-ethenylbenzenesulfonic acid)). Four washing protocols (1, 2, 3 and 4) were adopted and the FTIR spectra recorded for samples of hydrophilicitized sheets of microporous poly(ethylene) prepared according to the method described in Example 3 following application of these washing protocols are presented in FIG. 3.

Preparation of Hydrophilicitized Microporous Sheets of poly(ethylene) Using Poloxamer (High Hydrophilicity)

Example 7

(49) A volume of 10 mL of a solution in water of 10% (w/v) triblock copolymer (PLURONIC? P-123; lot #MKCC2305, Sigma-Aldrich) was mixed with an equal volume of deionised water. A quantity of 0.2 g of the photoinitiator benzophenone (diphenylmethanone; Ph.sub.2O) was dissolved in a separate volume of 10 mL of ethanol before being added to the diluted solution of the triblock copolymer. This working solution was stored in the dark until use.

(50) Samples (13.5?18.5 cm) were cut from a microporous sheet of poly(ethylene) (TARGRAY? wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) and each sample coated with a volume of the working solution using the rollers from a developmental continuous production line. The coated samples were then irradiated with ultraviolet (UV) light (250 nm) for a period of time of two minutes before rinsing with water and air-drying at room temperature.

(51) The three replicate samples prepared according to this method were designated 040918Wiv, 040918Wv and 040918Vi. A small piece of the sample designated 040918Wiv was excised from the edge of the sample and submitted to scanning electronic microscopy (SEM).

(52) Each of the samples was readily wetted with water.

(53) Composite Membranes

Preparation of Composite Membrane Using Microporous Sheet of poly(ethylene) Grafted with Poly(4-ethenyl benzene sulfonic acid (Low Hydrophilicity)

Example 8

(54) A series of preliminary experiments were performed to evaluate methods of preparing a film of cross-linked poly(ethenol) (xPVA) on a surface. A solution of the radical initiator sodium persulfate (SPS) was prepared by adding a quantity of 0.2 g of SPS to a volume consisting of 10 mL deionised water and 10 mL acetone. The solution of radical initiator was applied onto the surface of each of three glass plates (Plate 1, Plate 2 and Plate 3). Plate 2 and Plate 3 were transferred to an oven and dried at a temperature of 60? C. until all solvent had evaporated to leave a thin layer of the initiator deposited on the surface. Solutions of poly(ethenol) (PVA) were prepared at a concentration of 1% (w/v) in either dimethyl sulfoxide (DMSO) or deionised water. The solution of poly(ethenol) (PVA) in DMSO was sprayed onto the wet surface of Plate 1 and the plate then transferred to an oven and dried at a temperature of 60? C. The solution of poly(ethenol)(PVA) in DMSO was also sprayed onto the dry surface of Plate 2 and the plate then transferred to an oven and dried at a temperature of 60? C. The solution of poly(ethenol) in deionised water was sprayed onto the dry surface of Plate 3 and the plate then transferred to an oven and dried at a temperature of 60? C. The desired film of cross-linked poly(ethenol) was not formed on Plate 1. The failure attributed to the presence of acetone causing the polymer to crash out of solution. The film formed on Plate 2 was too frangible to be useful as a rejection layer of an asymmetric composite membrane. A clear, peelable film formed on the surface of Plate 3. The film was not brittle and this method of preparation was adopted for use in the preparation of the asymmetric composite membrane.

Example 9

(55) A series of preliminary experiments were performed to evaluate methods of preparing a film of partially cross-linked poly(ethenol) (xPVA) and thereby control the properties of the rejection layer of the composite membrane. Volumes of 10 mL of a 1% (w/v) solution of poly(ethenol)(PVA) in deionised water containing a quantity of 0.1 g of SPS were dispensed into each four vials (Vial 1, Vial 2, Vial 3 and Vial 4). The solution in each vial was heated to a temperature of 75? C. and maintained at this temperature with stirring until the following observations were made (and the vials then cooled): A yellow solid crashed out of solution (Vial 1; 3 to 4 minutes) A cloudy white solution with some precipitation formed (Vial 2, around 3 minutes) A cloudy white solution formed (Vial 3; 1.5 to 2 minutes) A cloudy solution started to form (Vial 4; 10 to 20 seconds)

(56) The observations are also presented in FIG. 3. The method of preparing partially cross-linked poly(ethenol) according to that formed in Vial 3 was adapted for use in the preparation of the membrane.

Example 10

(57) A volume of 20 mL of the solution of the radical initiator sodium persulfate (SPS) was prepared according to Example 8. A volume of the solution of partially cross-linked poly(ethenol) (xPVA) was prepared according to Example 9 (Vial 3).

(58) The solution of the radical initiator was applied to one surface of a hydrophilicitized microporous sheet of poly(ethylene) prepared according to Example 3. The sheet was then placed on a glass plate and transferred to an oven and dried at a temperature of 60? C. The solution of partially cross-linked poly(ethenol) was applied to the same surface of the dried sheet and the sheet then returned to the oven and dried at 60? C. The dried membrane was then washed with cool water and air dried before evaluation for flux, total solids and salts rejection with different feed streams (water and milk).

Example 11

(59) To facilitate use in the continuous production of membranes on a developmental continuous production line a more viscous solution of partially cross-linked poly(ethenol) (xPVA) was required. Solutions having a final concentration of 5, 8 and 10% (w/v) were therefore prepared and evaluated.

(60) A volume of 11.5 mL of a solution in distilled water of 0.1 g sodium persulfate (SPS) was mixed with a volume of 8.5 mL of a solution in water of 12% (w/v) poly(ethenol) to provide a total volume of 20 mL at a final concentration of 5% (w/v).

(61) A volume of 6.5 mL of a solution in distilled water of 0.2 g sodium persulfate (SPS) was mixed with a volume of 13.5 mL of a solution in water of 12% (w/v) poly(ethenol) to provide a total volume of 20 mL at a final concentration of 8% (w/v).

(62) A volume of 3.5 mL of a solution in distilled water of 0.2 g sodium persulfate (SPS) was mixed with a volume of 16.5 mL of a solution in water of 12% (w/v) poly(ethenol) to provide a total volume of 20 mL at a final concentration of 10% (w/v).

(63) A portion of each of the volumes at a final concentration of 5, 8 and 10% (w/v) poly(ethenol) (PVA) was transferred to a vial and each stirred with heating to 75? C. until the solution turned a pale yellow (cf. Vial 3 of Example 9). These vials containing partially cross-linked poly(ethenol) (xPVA) were then cooled to room temperature.

(64) The volume containing 10% (w/v) partially cross-linked poly(ethenol)(xPVA) was applied to one surface of a hydrophilicitized microporous sheet of poly(ethylene) prepared according to Example 3 using the rollers of the developmental continuous production line before being placed on a glass plate and transferred to an oven and dried at a temperature of 60? C. The composite membrane was then washed with cool water and air dried before evaluation for flux and protein rejection with different feed streams (water and milk) (Table 4).

Preparation of Composite Membrane Using Microporous Sheet of poly(ethylene) Grafted with a Poloxamer (High Hydrophilicity)

Example 12

(65) A volume of a solution in water of 1% (w/w) of the radical initiator sodium persulfate (SPS) and 8% (w/w) partially cross-linked poly(ethenol) (xPVA) prepared according to Example 11 was applied to one surface of a hydrophilicitized microporous sheet of poly(ethylene) prepared according to Example 7. The sheet was then irradiated at a wavelength of 250 nm for a period of time of two minutes before being placed on a glass plate and transferred to an oven and dried at a temperature of 60? C.

Example 13

(66) A volume of a solution in water of 1% (w/w) of the radical initiator sodium persulfate (SPS) and 5% (w/w) poly(ethenol) (PVA) prepared according to Example 11 was applied directly, i.e. without crosslinking, to one surface of a hydrophilicitized microporous sheet of poly(ethylene) prepared according to Example 7. The sheet was then irradiated at a wavelength of 250 nm for a period of time of two minutes before being placed on a glass plate and transferred to an oven and dried at a temperature of 60? C. The composite membrane was then washed with cool water and air dried before evaluation for flux and protein rejection with different feed streams (water and milk) (Table 4).

Example 14

(67) A volume of a solution in water of 1% (w/w) of the radical initiator sodium persulfate (SPS) and 8% (w/w) poly(ethenol) (PVA) prepared according to Example 11 was applied directly, i.e. without crosslinking, to one surface of a hydrophilicitized microporous sheet of poly(ethylene) prepared according to Example 7. The sheet was then irradiated at a wavelength of 250 nm for a period of time of two minutes before being placed on a glass plate and transferred to an oven and dried at a temperature of 60? C. The composite membrane was then washed with cool water and air dried before evaluation for flux and protein rejection with different feed streams (water and milk) (Table 4).

(68) Evaluation of Samples of Composite Membrane

(69) Replicate samples (240818Si, 240818Sii, 240818Siii, 030918Si, 030918Sii, 030918Siii) of membrane prepared according to Example 10 were evaluated. The results of this evaluation are summarised in Table 1. Following an initial wetting with 20% (v/v) isopropanol in water, fluxes in the range 7.8 to 10.9 litres per square meter per hour (LMH) were obtainable for a feed stream of water at a pressure of 10 bar. Similar, if not slightly greater fluxes were obtained for a solution of salts with salt rejection in excess of 20%. For a feed stream of whole milk, fluxes were reduced but provided in excess of 50% total solids rejection and well in excess of greater than 99% protein rejection.

(70) TABLE-US-00001 TABLE 1 Evaluation of samples of asymmetric composite membrane prepared according to Example 10. The sample (240818Siii) demonstrating the highest salt rejection was also evaluated along with two other samples (030918Sii and 030918Siii) for total solids and protein rejection with milk as a feed stream. Salt Total solids Protein Initial flux Salt flux rejection Milk flux rejection rejection Sample (LMH) (LMH) (%) (LMH) (%) (%) 240818Si 10.9 at 11.7 at 20.3 10 bar 10 bar 240818Sii 7.8 at 10.7 at 21.3 10 bar 10 bar 240818Siii 8.9 at 10.3 at 28.4 4.5 at 63.0 99.95 10 bar 10 bar 10 bar 030918Si 2.1 at 1.3 at 99.83 5 bar 10 bar 030918Sii 0.7 at 62.4 99.99 5 bar 030918Siii 0.6 at 55.7 100.00 5 bar

(71) TABLE-US-00002 TABLE 2 Flux, total solids and protein rejection of a sample of an asymmetric composite membrane (030918Sii) prepared according to Example 10 during repeated clean-in-place (CIP) protocols. Number Milk flux Total solids Protein of CIPs (LMH) rejection (%) rejection (%) 0 0.7 62.4 99.99 1 2.3 55.9 99.94 2 2.0 99.94 3 4.7 50.7 99.93 4 5.0 46.3 99.88 5 5.7 42.0 99.84 10 5.7 49.0 99.87

(72) One of the samples (030918Sii) was further evaluated for its tolerance to clean-in-place (CIP) protocols. One of the samples (030918Siii) was also further evaluated in a pressure series test to see how the flux and protein rejection were affected. The results of these further evaluations are summarised in Tables 2 and 3 and FIGS. 4 and 5.

(73) TABLE-US-00003 TABLE 3 Pressure series testing (0 to 20 bar) of a sample (030918Siii) of an asymmetric composite membrane prepared according to Example 10. Flux and protein rejection with milk as the feed stream were measured. Milk flux Protein Pressure (LMH) rejection (%) 0 99.99 5 0.6 99.94 10 3.3 99.94 15 5.1 99.93 20 7.1 99.88

(74) Samples of composite membrane prepared according to Example 11, Example 13 and Example 14 were evaluated. A protein rejection above 99.9% was observed for all samples. Increases in the concentration of poly(ethenol) (PVA) used to prepare the rejection layer were observed to reduce the flux for both water and milk as the feed stream. This is attributed to the increasing concentrations increasing the viscosity of the solution applied to the hydrophilicitized microporous sheet of polyolefin and reduced ease of application on the developmental continuous production line. For example, the viscosity of solutions prepared at a concentration of 10% (w/v) or more of poly(ethenol) is too high, limiting the facility with which a thin, consistent coating can be achieved. By contrast, the viscosity of solutions prepared at a concentration of 5% (w/v) or less of poly(ethenol) is too low, again limiting the facility with which a thin, consistent coating can be achieved. A concentration around 8% (w/v) appears to be optimal as this scale of continuous production.

(75) TABLE-US-00004 TABLE 4 Evaluation of samples of membrane prepared according to Example 11, Example 13 and Example 14. (*indicates sample of membrane evaluated after clean-in-place protocol and drying). Average water Average milk flux at flux at Protein Membrane 5 bar (LMH) 5 bar (LMH) rejection 8% xPVA adhered to 11.7 7.8 99.97% poloxamer-?PE Example 14*) 10% xPVA adhered 3.8 1.8 99.96% to pSSS-?PE (Example 11) 5% xPVA adhered to 32.2 11.6 99.92% poloxamer-?PE Example 13) 8% xPVA adhered to 7.0 3.8 99.91% poloxamer-?PE (Example 14) poloxamer-?PE 826 20.6 99.56% (Example 7)

(76) Although the invention has been described with reference to embodiments or examples it should be appreciated that variations and modifications may be made to these embodiments or examples without departing from the scope of the invention. Where known equivalents exist to specific elements, features or integers, such equivalents are incorporated as if specifically referred to in this specification. In particular, variations and modifications to the embodiments or examples that include elements, features or integers disclosed in and selected from the referenced publications are within the scope of the invention unless specifically disclaimed. The advantages provided by the invention and discussed in the description may be provided in the alternative or in combination in these different embodiments of the invention.

INDUSTRIAL APPLICABILITY

(77) A durable composite membrane with high levels of protein rejection whilst maintaining a high flux with feed streams such as whole milk is provided.

INCORPORATION BY REFERENCE

(78) Where the claims, description or drawings of this specification are missing in their entirety or part, the corresponding portion of the specification accompanying the most recently filed application from which priority is claimed is to be incorporated by reference so as to complete this specification in accordance with Rules 4.18, 20.5 and 20.6 of the PCT Regulations (as in force from 1 Jul. 2015 or subsequently amended).

(79) For the purposes of 37 C.F.R. 1.57 of the United States Code of Federal Regulations the disclosures of the following publications (as more specifically identified under the heading Referenced Publications) are incorporated by reference: Jones et al (2008) and Schmolka (1973).

REFERENCED PUBLICATIONS

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