JP7292742B2 - Asymmetric composite membranes and modified substrates used in their preparation - Google Patents

Description

The present invention relates to durable water permeable asymmetric composite membranes with high levels of protein rejection and substrates for use in their preparation. In particular, the present invention relates to a durable water permeable asymmetric composite membrane consisting of a film of partially crosslinked poly(ethenol) adhered to a hydrophilized microporous sheet of poly(ethylene).

The use of grafts to modify the surface of films, sheets and moldings formed from polyolefins is well known. For example, Tasuke and Kimura (1978) (Non-Patent Document 1) describe poly(propylene), poly(ethylene), and several other Photografting onto polymer films is disclosed. This publication stated that the choice of solvent and sensitizer was very important.

Ang et al. (1980) reported that a sensitizer was dissolved in a monomer solution to photosensitize styrene, 4-vinylpyridine and methyl methacrylate to poly(propylene) in high yield. discloses an irradiation procedure that can be used for sensitive copolymerization. Again, this publication notes that the response was found to be highly specific for certain sensitizers.

Ogiwara et al. (1981) describes photografting onto presensitized poly(propylene) and low density poly(ethylene) (LDPE) films. is disclosed. Film-coated sensitizers allowed vinyl monomers such as methyl methacrylate, acrylic acid and methacrylic acid to be grafted easily and in high yields. The hydrophilic monomers acrylic acid and methacrylic acid were conveniently grafted with them in aqueous solutions of liquid-phase systems.

Allmer et al. (1988) (1988) discloses the surface modification of LDPE, high density polyethylene (HDPE) and polystyrene by grafting with acrylic acid. Grafting was done in the gas phase to increase the wettability of the polymer. It was observed that acetone can initiate grafting and either promote or induce grafting to the surface. A later publication by Allmer et al. (1989) discloses the surface grafting of LDPE with glycidyl acrylate and glycidyl methacrylate by photoinitiation. Acetone and ethanol were used as solvents, but acetone resulted in slightly more grafting to the surface.

Yao and Ranby, 1990a, 1990b and 1990c (1990a, 1990b and 1990c), inter alia, describe continuous photoinitiated grafting of acrylamide and acrylic acid onto the surface of HDPE tape films. A process for copolymerization is disclosed. This process is carried out under a nitrogen atmosphere using benzophenone as a photoinitiator. It was stated that pre-soaking is very important for efficient photografting within short irradiation times. Application of this pre-soak photografting method to poly(ethylene terephthalate) (PET) was also disclosed. Acetone was found to be a somewhat better solvent than methyl ethyl ketone and methyl propyl ketone in this situation. Optimal concentrations of monomers and initiators in the pre-dip solution when applied to a continuous process for photochemically induced graft polymerization of acrylamide and acrylic acid on poly(propylene) (PP) fiber surfaces under nitrogen atmosphere. was decided.

Kubota and Hata (1990a and 1990b) (Non-Patent Documents 9-10) describe the location of methacrylic acid chains introduced into poly(ethylene) films by liquid and gas phase photografting. Studies and comparative tests of the photografting behavior of benzyl, benzophenone and benzoin ethyl ether as sensitizers are disclosed. In these latter studies, poly(methacrylic acid) was grafted onto an initiator-coated LDPE membrane.

Edge et al. (1993) (Non-Patent Document 11) discloses the photochemical grafting of 2-hydroxyethyl methacrylate (HEMA) onto LDPE films. A liquid phase process is used to produce materials with enhanced wettability.

Singleton et al. (1993) discloses a method of making polymer sheets that are wettable by aqueous solvents and useful as electrode separators in electrochemical devices. Polymer sheets are formed from fibers comprising only poly(propylene) to distinguish them from membranes formed from microporous polymer sheets.

A publication by Zhang and Ranby (1993) discloses photochemically induced graft copolymerization of acrylamide onto the surface of a PP film. Acetone was shown to be the best solvent among the three aliphatic ketones tested.

Yang and Ranby (1996a and 1996b) (12-13) disclose factors affecting the photografting process, including the role of deep UV (200-300 nm). are doing. In these studies, benzophenone was used as the photoinitiator and LDPE film as the substrate. Added water was shown to favor photograft polymerization of acrylic acid on polyolefin surfaces, whereas acetone was shown to have a negative effect due to different solvation of poly(acrylic acid) (PAA). It had been.

Hirooka and Kawazu (1997) disclose alkaline separators prepared from unsaturated carboxylic acid grafted poly(ethylene)-poly(propylene) fiber sheets. Again, the sheets used as substrates in these studies are distinguished from membranes formed from microporous polymer sheets.

A publication by Xu and Yang (2000) (Non-Patent Document 14) discloses a study on the mechanism of vapor-phase photografting of acrylic acid onto LDPE.
Shentu et al. (2002) (Non-Patent Document 15) disclose a study of factors affecting photografting onto LDPE, including monomer concentration.

El Kholdi et al. (2004) (Non Patent Literature 16) discloses a continuous process for grafting acrylic acid onto LDPE from a monomer solution in water. Bai et al. (2011) (Non Patent Literature 17) discloses the preparation of grafted low density poly(ethylene) (LDPE) hot melt adhesives. Adhesives were prepared by surface UV photografting of acrylic acid onto LDPE using benzophenone as a photoinitiator.

A publication by Choi et al. (2001) states that graft polymerization is considered to be a general method for modifying the chemical and physical properties of polymeric materials.

Choi publication (2002) discloses a method of producing acrylic grafted polymer on the surface of a polyolefin article, which method comprises exposing the article to an initiator in a volatile solvent. immersing the article in a solution; allowing the solvent to evaporate; and then immersing the article in a solution of acrylic monomers before exposing the article to UV irradiation in air or an inert atmosphere. Acrylic acid is used as the acrylic acid monomer in each of the examples disclosed in the publication, although equivalent amounts of methacrylic acid, acrylamide and other acrylic monomers are contemplated.

Choi publication (2004) discloses the use of "ethylenically unsaturated monomers" in graft polymerization. These other monomers are polymerizable by addition polymerization to thermoplastic polymers, carboxyl groups (--COOH), hydroxyl groups (--OH), sulfonyl groups (SO ₃ ), sulfonic acid groups (--SO ₃ H). or as a monomer that is hydrophilic as a result of containing a carbonyl group (-CO). No experimental results regarding the chemical and physical properties of the grafted polymers prepared by methods using these other monomers are disclosed.

Choi publication (2005) discloses a nonwoven sheet of polyolefin fibers in which the opposing surfaces of the sheet are hydrophilic as a result of acrylic graft polymerization. The sheet properties were asymmetric and the ion exchange coefficients of the two surfaces were different. The method used to prepare these asymmetric acrylic acid grafted nonwoven polyolefin sheets includes the steps of soaking the substrate in a solution of benzophenone (a photoinitiator), drying, and then removing the substrate from the acrylic acid. followed by ultraviolet (UV) irradiation. Irradiation can be performed while the surface is in contact with either air or an inert atmosphere.

Gao et al. (2013) (Patent Document 5) discloses a method of preparing a radiation-crosslinked lithium-ion battery separator. In one example, a porous polyethylene membrane is soaked in a solution of benzophenone and triallyl cyanurate in dichloromethane. After drying the immersed film at room temperature, it is immersed in a water bath at 30° C. and irradiated on both sides for 3 minutes using a high-pressure mercury lamp.

A publication by Jaber and Gjoka (2016) (US Pat. No. 6,300,004) describes the production of ultra-high molecular weight polyethylene microporous membranes using monomers having one or more anionic, cationic or neutral groups. Grafting is disclosed. The publication states that the authors discovered that an ultraviolet energy source could be used to graft molecules onto the surface of an asymmetric porous ultra-high molecular weight polyethylene membrane. A grafted membrane is proposed for removing charged contaminants from liquids.

The goal of most of these prior art methods is to use photoinitiated polymerization to improve the adhesion, biocompatibility, printability or wettability of the surface of a substrate. These methods are distinguished from the use of UV-initiated grafting with exogenously prepared preformed polymers to modify the permeability to water of hydrophobic microporous polyolefin substrates. should.

The publication of Bolto et al. (2009) (Non-Patent Document 18) reviews what is disclosed in publications on the cross-linking of poly(ethenol), namely PVA. These publications include publications on cross-linking methods and grafting of PVA onto support membranes, including porous hydrophobic membranes such as poly(ethylene) and poly(propylene).

Linder et al., (1988) (US Pat. No. 5,700,001) discloses a semipermeable composite membrane comprising a film of modified PVA or PVA copolymer on a porous support. Suitable support materials should be water-insoluble and may be selected from, for example, polyacrylonitrile, polysulfone, polyamide, polyolefins such as poly(ethylene) and poly(propylene), or cellulose.

Exley publication (2016) discloses an asymmetric composite membrane consisting of a film of crosslinked poly(etheretherketone) adhered to a sheet of grafted microporous poly(ethylene). are doing. Microporous poly(ethylene) is obtained by photoinitiated grafting with an ethenyl monomer to provide a hydrophilic sheet.

The publication of Craft et al. (2017) (US Pat. No. 6,200,000) discloses an improvement on the asymmetric composite membrane disclosed in the publication of Exley (2016) (US Pat. No. 6,300,003). The improved asymmetric composite membrane is a poly(etheretherketone) crosslinked with a crosslinker (such as divinylbenzene) on a film of crosslinked poly(etheretherketone) adhered to a sheet of grafted microporous poly(ethylene). vinyl alcohol) polymer coating. The selectivity of the resulting asymmetric composite membrane is improved.

International Publication No. WO93/01622 U.S. Pat. No. 6,384,100 U.S. Pat. No. 6,680,144 U.S. Pat. No. 6,955,865 Chinese Patent Application Publication No. 103421208 International Publication No. WO2016/081729 U.S. Pat. No. 4,753,725 International Publication No. WO2016/103239 International Publication No. WO2017/056074

Tasuke and Kimura (1978), "Surface photography. I. Graft polymerization of hydrophilic monomers onto various polymer films", Journal of Polymer Science: Polymer Letters Edition, 16, 497-500 Ang et al. (1980), "Photosensitized grafting of styrene, 4-vinylpyridine and methyl methacrylate to polypropylene," Journal of Polymer Science: Polymer Letter s Edition, 18, 471-475 OGIWARA etc. (1981), "Photosensitized GRAFTING ON POLYOLEFING OF VAPOR AND LIQUID PHASES", JOURNAL OF POLYMER SCIENCE: POL: POL Ymer Letters Edition, 19, 457-462 Allmer et al. (1988), "Surface modification of polymers. I. Vapor-phase photography with acrylic acid," Journal of Polymer Science, Part A: Polymer Chem. 26(8), 2099-111 Allmer et al. (1989), "Surface modification of polymers. II. Grafting with glycidyl acrylates and the reactions of the grafted surfaces with amines", Journal of Polymer Science: Part A: Polymer Chemistry, 27, 1641-1652 Yao and Ranby (1990a), “Surface modification by continuous graft copolymerization. ce", Journal of Applied Polymer Science, 40, 1647-1661 Yao and Ranby (1990b), Surface modification by continuous graft copolymerization. III. surface,” Journal of Applied Polymer Science, 41, 1459-1467. Yao and Ranby (1990c), "Surface modification by continuous graft copolymerization. IV. Photoinitiated graft copolymerization onto a polypropylene fiber surface." , Journal of Applied Polymer Science, 41, 1469-1478 Kubota and Hata (1990a), "Distribution of methacrylic acid-grafted chains introduced into polyester film by photography," Journal of Applied Polymer Science, 41, 689-695 Kubota and Hata (1990b), "Benzil-sensitized photography of methacrylic acid on low-density polyester film", Journal of Applied Polymer Science, 40, 10 71-1075 Edge et al. (1993), "Surface modification of polyethylene by photochemical grafting with 2-hydroxyethylmethacrylate," Journal of Applied Polymer Science, 47, 1075-1082 Yang and Ranby (1996a), "The role of far UV radiation in the photographic process", Polymer Bulletin (Berlin), 37(1), 89-96 Yang and Ranby (1996b), "Bulk surface photography process and its applications. II. Principal factors affecting surface photography," Journal of Applied Polymer Science, 63(3), 545-555 Xu and Yang (2000), "Study on the mechanism of LDPE-AA vapor-phase photography system", Gaofenzi Xuebao (2000), 5, 594-598 Shentu et al. (2002), "Factors affecting photo-grafting on low density polyethylene", Hecheng Suzuki Ji Suliao 19(3), 5-8. El Kholdi et al. (2004), "Modification of adhesive properties of a polyethylene film by photography," Journal of Applied Polymer Science, 92(5), 2803-28. 11 Bai et al. (2011), "Surface UV photography of acrylic acid onto LDPE powder and its adhesion", Shenyang Huagong Daxue Xuebao 25(2), 121-125 Bolto et al. (2009), "Crosslinked poly(vinyl alcohol) membranes," Progress in Polymer Science, 34, 969-981

It is an object of the present invention to provide asymmetric composite membranes with improved levels of protein rejection while maintaining acceptable flux. It is an object of the present invention to provide a method for preparing asymmetric composite membranes. SUMMARY OF THE INVENTION It is an object of the present invention to provide a hydrophilized sheet of microporous polyolefin particularly suitable for use in a method of preparing an asymmetric composite membrane. It is an object of the present invention to provide asymmetric composite membranes and hydrophilized sheets of microporous polyolefin suitable for use in the extraction or recovery of water from feedstreams in the dairy beverage and food processing industries. be. These objectives should be read alternatively at least for providing useful choices in the selection of such methods, membranes, and sheets.

In a first aspect, the present invention provides a hydrophilicitized microporous sheet of polyolefin, wherein the microporous polyolefin comprises preformed poly(4-ethenylbenzenesulfonic acid) ( It is grafted with preformed poly (4-ethyl benzene sulfonic acid)).

Preferably, the polyolefin is selected from the group consisting of poly(ethylene), poly(propylene), poly(butylene) and poly(methylpentene). More preferably, the polyolefin is poly(ethylene) or poly(propylene). Most preferably, the polyolefin is poly(ethylene).

Preferably, the preformed poly(4-ethenylbenzenesulfonic acid) is equivalent to that provided in the working solution prepared according to Example 1.

In a second aspect, the present invention provides a polyolefin grafted with preformed poly(4-ethenylbenzenesulfonic acid) prior to adhesion of a film of partially crosslinked poly(ethenol). An asymmetric composite membrane is provided comprising a film of partially crosslinked poly(ethenol) adhered to a hydrophilized microporous sheet of polyolefin.

Preferably, the partially crosslinked poly(ethenol) is the partially crosslinked poly(ethenol) provided in vial 2 of Example 8 and the partially crosslinked poly(ethenol) provided in vial 4 of Example 8. Crosslinked to an extent comparable to crosslinked poly(ethenol). More preferably, the partially crosslinked poly(ethenol) is crosslinked to substantially the same extent as the partially crosslinked poly(ethenol) provided in vial 3 of Example 8.

Preferably, the polyolefin is selected from the group consisting of poly(ethylene), poly(propylene), poly(butylene) and poly(methylpentene). More preferably, the polyolefin is poly(ethylene) or poly(propylene). Most preferably, the polyolefin is poly(ethylene).

In a preferred embodiment of the second aspect, the invention provides an asymmetric composite membrane consisting essentially of a film of partially crosslinked poly(ethenol) adhered to a hydrophilized microporous sheet of poly(ethylene). provided, wherein the polyolefin is grafted with pre-formed poly(4-ethenylbenzenesulfonic acid) prior to bonding a film of partially crosslinked poly(ethenol).

In a most preferred embodiment of the second aspect, the present invention provides an asymmetric composite membrane consisting essentially of a film of partially crosslinked poly(ethenol) adhered to a hydrophilized microporous sheet of poly(ethylene). where the polyolefin is equivalent to that provided in the working solution prepared according to Example 1 prior to adhesion of the film of partially crosslinked poly(ethenol) preformed Poly(4-ethenylbenzenesulfonic acid) grafted and partially crosslinked poly(ethenol) was compared with that of the partially crosslinked poly(ethenol) provided in vial 3 of Example 8. crosslinked to substantially the same extent.

An asymmetric composite membrane is provided that can provide at least 99.9% total protein rejection at a flux of 5 LMH using milk as the feed stream.

In a third aspect, the present invention provides a method of preparing a hydrophilized microporous sheet of polyolefin according to the first aspect of the present invention, the method comprising the steps of:
1. contacting a polyolefin microporous sheet with a dispersion comprising preformed poly(4-ethenylbenzenesulfonic acid) in an aqueous solvent to provide a contacted microporous sheet;
2. Curing the contacted microporous sheet at a temperature and for a time sufficient to provide a cured microporous sheet in which at least a portion of the poly(4-ethenylbenzenesulfonic acid) is grafted onto the polyolefin substrate. and 3. washing the cured microporous sheet to provide a polyolefin hydrophilized microporous sheet;

Preferably, the polyolefin is selected from the group consisting of poly(ethylene), poly(propylene), poly(butylene) and poly(methylpentene). More preferably, the polyolefin is poly(ethylene) or poly(propylene). Most preferably, the polyolefin is poly(ethylene).

Preferably, the aqueous solvent is acetone-water.
Preferably, curing the contacted microporous sheet is at a sufficient intensity and temperature for a time sufficient to graft at least a portion of the poly(4-ethenylbenzenesulfonic acid) onto the polyolefin. It is done by irradiating with ultraviolet rays.

Preferably irradiation is carried out in the presence of a photoinitiator. More preferably irradiation is performed on acetophenone, anthraquinone, benzoin, benzoin ether, benzoin ethyl ether, benzyl, benzyl ketal, benzophenone, benzoyl peroxide, n-butyl phenyl ketone, isobutyl phenyl ketone, fluorenone, propiophenone, n-propyl It is carried out in the presence of a photoinitiator selected from the group consisting of phenyl ketone and isopropyl phenyl ketone. Most preferably, the irradiation is carried out in the presence of the photoinitiator benzophenone.

Preferably, the ultraviolet light has a broad spectrum centered at 250 nm and bandwidth limits of approximately 250 nm and 400 nm.
Washing is preferably done with water.

In a preferred embodiment of the third aspect, the present invention provides a method of preparing a hydrophilized microporous sheet of poly(ethylene) comprising the steps of:
1. polymerizing 4-ethenylbenzenesulfonic acid in the presence of a radical initiator to obtain a first dispersion of poly(4-ethenylbenzenesulfonic acid) in a first solvent;
2. contacting a microporous sheet of poly(ethylene) with a second dispersion of poly(4-ethenylbenzenesulfonic acid) in a second solvent to provide a contacted microporous sheet of poly(ethylene); ;
3. 3. curing the contacted microporous sheet at a temperature and for a time sufficient to graft at least a portion of the poly(4-ethenylbenzenesulfonic acid) onto the polyolefin substrate; washing the cured microporous sheet to obtain a hydrophilized microporous sheet of polyethylene, wherein the first solvent is water and the second solvent is acetone-water. do.

4-ethenylbenzenesulfonic acid can be provided in salt form, eg as its sodium salt (SSS).
Preferably, the radical initiator is selected from the group consisting of ammonium persulfate and sodium persulfate. More preferably, the radical initiator is sodium persulfate.

Preferably, the second solvent is 40-60% (w/w) acetone in water. Most preferably, the second solvent is 50% (v/v) acetone in water.
A second dispersion can be prepared by adding acetone to the first dispersion.

In a fourth aspect, the invention provides a hydrophilized microporous sheet of polyolefin prepared according to the method of the third aspect of the invention.
In a fifth aspect, the invention provides a method of preparing the asymmetric composite membrane of the second aspect of the invention, the method comprising the steps of:
1. contacting one side of the hydrophilized microporous sheet of the first or fourth aspect of the present invention with a solution of partially crosslinked poly(ethenol) in a first solvent in the presence of a radical initiator to obtain a contacting sheet;
2. Sufficient partially crosslinked poly(ethenol) adheres to one side of the hydrophilized microporous sheet of polyolefin to evaporate substantially all of the solvent to provide a dry contact sheet. 2. drying the contacted sheet at a suitable temperature and time; Washing the dried contacted sheet in a second solvent to obtain an asymmetric composite membrane.

Preferably, drying the contacted sheet is done by applying a positive temperature gradient across the thickness of the sheet from one contacted side of the hydrophilized microporous sheet to the other.

In the description and claims herein, the following abbreviations, acronyms, terms and phrases have the following meanings provided: "comprising", "including", "containing means "containing" or "characterized by", not excluding any additional elements, ingredients or steps; "consisting of" means free from impurities and other means excluding any unspecified element, ingredient, or step, except incidental; "consisting essentially of" means any element, ingredient, "crosslinker" means a substance that is incorporated into the crosslinks of the polymer network to be crosslinked; "flux" means permeate transported per unit membrane area (permeate) rate (volume per unit time); "graft polymer" means a polymer in which side chains of different structure than the main chain are attached at various points to a linear main chain; "Homopolymer" means a polymer formed by the polymerization of a single monomer; "hydrophilic" means having a tendency to be miscible with water, dissolved in water, or wetted by water. , "hydrophilicity", "hydrophilicitized" and "hydrophilicitizing" have corresponding meanings; "microporous" means the Means consisting of an essentially continuous matrix structure containing small pores or channels that are substantially uniform (such as can be produced using cast (wet) process techniques), especially discontinuities in woven or nonwoven fabrics The matrix is excluded; "partially cross-linked" means that only a portion of the sites available for cross-linking were utilized and the cross-linking reaction was limited by reagents, temperature, or duration; "Photoinitiator" means a photolabile compound that forms radicals upon irradiation; "poly(ethanol)" and "polyvinyl alcohol" are used synonymously; means a polymer that is partially or fully modified after the functional polymer backbone is formed; "preformed" means formed beforehand, i.e., prior to processing; "PSSS" or "pSSS" denotes SSS, the product of the polymerization of poly(4-ethenylbenzenesulfonic acid); "PVA" denotes poly(ethenol) (or polyvinyl alcohol); ' means sodium styrene sulfonate, ie the sodium salt of 4-ethenylbenzene sulfonic acid; 'UVA' means electromagnetic radiation at wavelengths between 320 and 400 nm; 'UVB' means between 290 and 320 nm "UVC" means electromagnetic radiation having a wavelength of 200-290 nm; and "xPVA" means at least partially crosslinked PVA.

When used in reference to the subject matter elements, features, or integers defined in the Summary of the Invention and the Claims, or when used in reference to alternative embodiments of the invention, the terms "first," "second," The terms "of", "third", etc. are not intended to imply a preferred order. The numbering of the Examples and Comparative Examples (if any) is not intended to imply that any pair of Examples and Comparative Examples are directly comparable. If the value is represented to one or less decimal places, standard rounding is applied. For example, 1.7 includes the range from 1.65000 to 1.74999. Where reagent or solvent concentrations or ratios are specified, the specified concentration or ratio is the initial concentration or ratio of the reagent or solvent. References to the use of 4-ethenylbenzenesulfonic acid include references to the use of salts of acids, including SSS. Without further limitation, the use of a single bond (if used) in depicting the structure of a compound encompasses diastereoisomers, enantiomers, and mixtures thereof of that compound.

FTIR spectra of monomeric 4-ethenylbenzenesulfonic acid (SSS) and poly(4-ethenylbenzenesulfonic acid) (PSSS) prepared according to the methods described in Example 1 (water) and Example 2 (DMSO). . Poly(4-ethenylbenzenesulfonic acid) (PSSS), photoinitiator benzophenone (BP), no-wash protocol (1), washed with water at a temperature of 45-50° C. before drying (2), acetone (3) and washed with water at a temperature of 45-50° C., dried and then washed with acetone (4). Photograph of a vial containing partially cross-linked poly(ethenol) (xPVA) prepared according to Example 8. From left to right: vial 1, vial 2, vial 3 and vial 4. Flux (LMH) (♦, dashed line), total solids (%) (▲ , dotted line) and protein exclusion (%) (■, solid line). Pressure series testing (0-20 bar (0-2.0 MPa)) of a sample of asymmetric composite membrane (030918Siii) prepared according to Example 9. Flux and protein exclusion were measured using milk as the feed stream. FTIR spectra (full range )comparison. FTIR spectra (stretch mode area) comparison. FTIR spectra (finger print area) comparison. Scanning electron micrographs of the surface of a sample of an asymmetric composite membrane prepared according to Example 9, before and after repeated cleaning-in-place (CIP) protocols.

The present invention will now be described with reference to embodiments or examples and figures on the accompanying drawing pages.
This invention relates, in part, to the selection of preformed polymers of 4-ethenylbenzenesulfonic acid as hydrophilizing agents used in preparing hydrophilized polyolefin substrates. This part of the invention is most advantageously applied to the hydrophilization of preformed sheets of microporous polyethylene. The use of poly(4-ethenylbenzenesulfonic acid) as a hydrophilicizing agent has been found to provide greater and more consistent hydrophilization of polyolefin substrates. This improvement is due, at least in part, to a reduction in the number of possible side reactions when compared to the use of monomers (described in Exley (2016) US Pat. method). This use is also expected to increase the likelihood that the preformed polymer will be grafted to the polyolefin substrate at multiple sites. Thus, structurally different forms of grafted polyolefin substrates can be obtained.

The improved performance of hydrophilized sheets of microporous poly(ethylene) prepared by the method of the present invention is disclosed in Exley (2016) US Pat. demonstrated by higher fluxes with water as the feed stream, while maintaining the desired durability, including resistance to chlorine and other cleaning agents, when compared to those prepared by . Hydrophilized sheets of microporous poly(ethylene) prepared by the method of the present invention also "wet out" at pressures lower than previously required. The method of preparing hydrophilized sheets of microporous poly(ethylene) also results in less waste of reagents, including photoinitiators, and does not require exclusion of oxygen during preparation. Polymers of 4-ethenylbenzenesulfonic acid are advantageously prepared as dispersions (“working solutions”) that can be used directly without the need to isolate the polymer. This advantage is demonstrated in the methods of the examples below.

The invention also relates, in part, to the use of hydrophilized sheets of microporous polyolefins to prepare asymmetric composite membranes. Providing a sheet of microporous polyolefin that is hydrophilized, i.e. wettable, promotes the formation of a film of partially crosslinked poly(ethenol) (xPVA) on the surface and its adhesion to the surface. make it easier. Persulfate is used as a cross-linking agent, in contrast to the preparation of asymmetric composite membranes disclosed in US Pat. The high level of protein exclusion exhibited by the asymmetric composite membrane is due in part to the choice of this crosslinker. A porosity that provides a reduced size exclusion from an estimated 160 kDa to an estimated 30 kDa is believed to be achieved (supported by an increase in total protein exclusion levels of >99.9%).

In drying a hydrophilized microporous sheet of polyolefin in contact with an aqueous dispersion of partially crosslinked poly(ethenol) (xPVA), positive heat is applied across the thickness of the sheet from the contacted side to the other side. Applying a gradient also helps maintain the porosity of the hydrophilized microporous sheet of polyolefin, thereby providing an asymmetric composite membrane with higher flux rates than otherwise achievable. Conceivable. In Example 9, the application of a positive temperature gradient is the result of the sheet being supported on the glass plate during the drying step. A positive temperature gradient is believed to limit the extent to which the dispersion in water penetrates the pores of the hydrophilized microporous sheet.

Accordingly, the asymmetric composite membrane provided by the present invention is proposed to be coated on a sheet of another membrane, for example a surface membrane of crosslinked PVA or PVA-copolymer, of a hydrophobic, i.e. water-repellent, microporous polyolefin. (1988) proposed membrane in US Pat.

Materials and Methods All microporous sheets used for sample preparation were prepared from virgin poly(ethylene), ie, poly(ethylene) of high purity.

FTIR
Sample spectra were recorded using a Thermo Electron Nicolet™ 8700 FTIR spectrometer equipped with a single reflection ATR and a diamond crystal. An average of 32 scans were taken for all samples at a resolution of 4 cm ⁻¹ .

Flux
Permeability was determined by measuring the flux using deionized water as the feed stream at various pressures using a filter assembly (Sterlitech). The flux _JV was then graphed against the effective pressure difference across the membrane p _eff and the slope of the permeability L _p .

The sample was attached to the filter assembly. Deionized water was fed to the apparatus at 2.5 L/min at 4-8°C. The time to collect a given amount of permeate was recorded. The flux rate (J) was calculated according to the following formula.

where V is the volume of permeate (L), t is the time to collect V (hours), A is the area of the sample (m ² ), and the area is 0.014 m ² was determined.
salt rejection
Rejection was measured using a 2 g/L aqueous solution of sodium chloride at a feed pressure of 16 bar (1.6 MPa). The feed and permeate conductivities were compared.

where σ _p is the conductivity of the permeate and σ _f is the conductivity of the feed.
Total Solids Exclusion Total milk sample rejection was measured by pouring a 20 mL sample from the feed into a petri dish and measuring the dry weight after 2 hours in an oven at 100°C.

where m _p,TS is the total milk solids in the permeate and m _f,TS is the mass of the total milk solids in the feed.
Protein Concentration Total protein and total whey protein concentrations in the permeate were calculated based on HPLC analysis with UV absorbance monitoring.

“Clean-in-Place” (CIP) Protocol To mimic commercial processing operations, samples of asymmetric composite membranes were repeatedly were subjected to an in situ cleaning protocol. Intermediate and subsequent flux rates were measured to assess the membrane's expected durability in commercial processing operations. The in situ cleaning protocol was based on that used in commercial processing operations, but the duration was modified to compensate for the greater exposure of the membranes to cleaning agents (caustic and acid) within the filter assembly. was done. Prior to the wash step, the membrane was rinsed by circulating water at an initial temperature of 65°C through the filter assembly for 3 minutes before draining the system.

The membrane was first washed ("caustic wash") by circulating a 2% (w/v) sodium hydroxide solution through the filter assembly for 5 minutes, then drained and water at an initial temperature of 65°C was passed through the filter assembly system for 5 minutes. The system was flushed by circulating for 1 minute. A second wash ("acid wash") of the membrane was performed by circulating a 2% (w/w) nitric acid solution through the filter assembly system for 10 minutes, followed by draining and circulating water for 10 minutes at an initial temperature of 65°C. The system was flushed by letting it run. A third wash of the membrane (“caustic wash”) was performed before water washing the system by circulating water for 5 minutes at an initial temperature of 65° C. before circulating cold water for 5 minutes to cool the system. . All rinsing and washing steps were performed without recording pressure on the pressure gauge of the filter assembly.

Preparation of poly(4-ethenylbenzenesulfonic acid) Example 1
An amount of 50 g of the monomer 4-ethenylbenzenesulfonic acid as sodium salt (SSS) was dissolved in a volume of 100 mL of distilled water to form a solution. An amount of 0.5 g of initiator sodium persulfate (SPS) was then dissolved in this solution and the initiator-monomer mixture was heated with stirring at a temperature of 80° C.-90° C. for about 20 minutes. A viscous solution with a total volume of about 125 mL was obtained. The viscous solution was diluted with an equal volume of distilled water to give a 250 mL working solution of poly(4-ethenylbenzenesulfonic acid).

An excess amount of acetone was added to this working solution to precipitate the polymer, which was collected by filtration through a Buchner funnel, then washed with acetone and easily ground into a powder using a pestle and mortar. A pale white solid was obtained.

Example 2
An amount of 5 g of the monomer 4-ethenylbenzenesulfonic acid (SSS) as the sodium salt was dissolved in a volume of 20 mL of dimethylsulfoxide (DMSO) to form a solution.

An amount of 0.05 g of initiator ammonium persulfate (APS) was then dissolved in this solution and the initiator-monomer mixture was heated with stirring at a temperature of 80° C.-90° C. for about 20 minutes. Poly(4-ethenylbenzenesulfonic acid) is precipitated by adding excess acetone to the cooled solution, collected by filtration on a Buchner funnel, washed with acetone, and can be obtained in Example 1. A pale white solid similar to that which can be easily ground into a powder was obtained.

The Fourier transform infrared (FTIR) spectra of the powders obtained by the preparation methods described in Example 1 (PSSS from water) and Example 2 (PSSS from DMSO) were compared with the monomer 4-ethenylbenzene of FIG. It was compared with the FTIR spectrum of sulfonic acid (SSS). A comparison of the spectra was consistent with the polymerization of the monomers in both preparation methods. The polymer, working solution, prepared by the method described in Example 1 was used as a hydrophilizing agent in the preparation of hydrophilized sheets of microporous poly(ethylene) according to the following examples.

Preparation of Hydrophilized Sheets of Microporous Poly(ethylene) Example 3
A 6 mL volume of the working solution obtained according to Example 1 was mixed with a 5 mL volume of distilled water in a vial to give an initial solution containing 1.2 g of poly(4-ethenylbenzenesulfonic acid) (pSSS). got A volume of 10 mL of acetone was added to the initial solution and clarified, then an amount of 0.2 g of photoinitiator benzophenone was added and dissolved in the solution to obtain a hydrophilicizing mixture. (13.5 cm x 18.5 cm) microporous poly(ethylene) (TARGRAY™ wet-process polyethylene separator, part number SW320H (Targray, Quebec, Canada) sized to fit the filter assembly (Sterlitech). Kirkland, State) sheet surface was contacted with the hydrophilizing mixture and irradiated with ultraviolet (UV) light (broad spectrum centered at 320 nm) for 2 minutes. The irradiated and contacted sheet was then rinsed with cold tap water before being placed in a water bath maintained at a temperature of 45°C to 50°C for about 5 minutes. The washed sheets were then air dried prior to testing or used to prepare asymmetric composite membranes.

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

Example 5
A one-step preparation method involving the monomer 4-ethenylbenzenesulfonic acid was evaluated.
A volume of 3 mL of the working solution obtained according to Example 1 is mixed in a vial with a volume of 8 mL of distilled water and an amount of 0.6 g of the monomer 4-ethenylbenzenesulfonic acid to give 0.6 g of poly(4 -ethenylbenzenesulfonic acid) was obtained. A volume of 10 mL of acetone was added to the volume of this initial solution and after clarification, a quantity of 0.4 g of photoinitiator benzophenone was added to obtain a hydrophilized mixture.

(13.5 cm x 18.5 cm) microporous poly(ethylene) (TARGRAY™ wet-process polyethylene separator, part number SW320H (Targray, Quebec, Canada) sized to fit the filter assembly (Sterlitech). Kirkland, State) sheet surface was brought into contact with the hydrophilizing mixture and irradiated with UV light (broad spectrum centered at 350 nm) for 2 minutes before washing with cold tap water and heating to a temperature of 45°C-50°C. Placed in a maintained water bath for about 5 minutes and then air dried.

Example 6
A two-step preparation method using only the monomer 4-ethenylbenzenesulfonic acid in the first of the two steps was evaluated.

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 monomer and a quantity of 0.4 g of photoinitiator benzophenone. , the mixture was shaken until all solids dissolved. A (13.5 cm x 18.5 cm) microporous poly(ethylene) (TARGRAY™ wet-process polyethylene separator, part number SW320H (Targray, Canada) sized to fit the filter assembly (Sterlitech, Inc.) of the test apparatus. Kirkland, Quebec) sheet surface was brought into contact with the mixture and irradiated with ultraviolet (UV) light (broad spectrum centered at 350 nm), followed by washing with cold tap water and heating at 45°C to 50°C. It was placed in a temperature-maintained water bath for about 5 minutes and then air dried.

In a 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 yield 1.2 g of poly(4-ethenylbenzenesulfonic acid). A containing amount of initial solution was obtained. A volume of 10 mL of acetone was added to the volume of the initial solution and after clarification, a quantity of 0.2 g of photoinitiator benzophenone was added and dissolved in the solution to obtain a hydrophilic mixture. The surface of the air-dried sheet obtained according to the first step was brought into contact with the hydrophilizing mixture and irradiated with UV light (broad spectrum centered at 350 nm) for 2 minutes before being washed with cold tap water at 45-50°C. for about 5 minutes and then air dried.

Observations Preformed poly(4-ethenylbenzenesulfonic acid) on sheets of microporous poly(ethylene) according to the preparation methods described in Examples 3, 4, 5 and 6. Grafting was confirmed by washing in acetone (solvent for photoinitiator benzophenone) and water (solvent for poly(4-ethenylbenzenesulfonic acid)). Four washing protocols (1, 2, 3, and 4) were employed, following the application of these washing protocols, the hydrophilization of microporous poly(ethylene) prepared according to the method described in Example 3. An FTIR spectrum recorded for a sample of the sheet is shown in FIG.

Preparation of Asymmetric Composite Membrane Example 7
A series of preliminary experiments were performed to evaluate methods of preparing films of crosslinked poly(ethenol) (xPVA) on surfaces. A radical initiator sodium persulfate solution (SPS) was prepared by adding an amount of 0.2 g sodium persulfate (SPS) to a volume consisting of 10 mL deionized water and 10 mL acetone. A solution of radical initiator was applied to the surface of each of three glass plates (Plate 1, Plate 2 and Plate 3). Plates 2 and 3 were transferred to an oven and dried at a temperature of 60° C. until all solvent had evaporated leaving a thin layer of initiator deposited on the surface. Solutions of poly(ethenol) (PVA) were prepared at a concentration of 1% (w/v) in either dimethylsulfoxide (DMSO) or deionized water. A solution of poly(ethenol) (PVA) in DMSO was sprayed onto the wet surface of plate 1, then the plate was transferred to an oven and dried at a temperature of 60°C. A solution of poly(ethenol) (PVA) in DMSO was also sprayed onto the dry surface of plate 2, then the plate was transferred to an oven and dried at a temperature of 60°C. A deionized aqueous solution of poly(ethenol) was sprayed onto the dry surface of plate 3, then the plate was transferred to an oven and dried at a temperature of 60°C. The desired film of crosslinked poly(ethenol) did not form on Plate 1. This failure was attributed to the presence of acetone which caused the polymer to crash out of solution. The film formed on plate 2 was brittle and not useful as an exclusion layer for the asymmetric composite membrane. A clear, peelable film was formed on the surface of plate 3 . The films were not brittle and this preparation method was adopted for use in preparing asymmetric composite membranes.

Example 8
A series of preliminary experiments were performed to evaluate the preparation of partially crosslinked poly(ethenol) (xPVA) membranes and thereby control the exclusion layer properties of the asymmetric composite membranes. A 10 mL volume of 1% (w/v) deionized aqueous solution of poly(ethenol) (PVA) containing 0.1 g of SPS was added to four vials (Vial 1, Vial 2, Vial 3, and Vial 4). Dispensed to each. 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 observed (and the vials were cooled):
- yellow solid crached out of solution (vial 1; 3-4 minutes);
- Formed a cloudy solution with some precipitation (vial 2, about 3 minutes);
- A cloudy solution formed (Vial 3; 1.5-2 min);
• A cloudy solution began to form (vial 4; 10-20 seconds).

Observations are also shown in FIG. The method of preparing partially crosslinked poly(ethenol) according to that formed in vial 3 was adapted for use in membrane preparation.
Example 9
A 20 mL volume of radical initiator sodium persulfate solution (SPS) was prepared according to Example 7. A aliquot solution of partially crosslinked poly(ethenol) (xPVA) was prepared according to Example 8 (vial 3).

A solution of radical initiator was applied to one surface of a hydrophilized sheet of microporous poly(ethylene) prepared according to Example 3. The sheet was then placed on a glass plate, transferred to an oven and dried at a temperature of 60°C. A solution of partially crosslinked poly(ethenol) was applied to the same surface of the dry sheet and then the sheet was returned to the oven and dried at 60°C. The dried membranes were then washed with cold water, air dried and evaluated for flux, total solids and salt rejection using different feed streams (water and milk).

Evaluation of Samples of Asymmetric Composite Membranes Replicate samples of membranes prepared according to Example 9 (240818Si, 240818Sii, 240818Siii, 030918Si, 030918Sii, 030918Siii) were evaluated. The results of this evaluation are summarized in Table 1. After initial wetting with a 20% (v/v) aqueous solution of isopropanol, at a pressure of 10 bar (1.0 MPa), 7.8 to 10.9 liters/square meter/hour ( LMH) flux was obtained. Similarly, salt solutions with salt rejection greater than 20%, if not, gave slightly higher fluxes. For the whole milk feed stream, the flux was reduced, but the total solids rejection was over 50% and the protein rejection was well over 99%.

Table 1: Evaluation of samples of asymmetric composite membranes prepared according to Example 9. The sample that showed the highest salt rejection (240818Siii) was also evaluated for total solids and protein rejection with milk as the feed stream, along with two other samples (030918Sii and 030918Siii).

One of the samples (030918Sii) was further evaluated for its resistance to cleaning-in-place (CIP) protocols. One of the samples (030918Siii) was also further evaluated in a series of pressure tests to see how flux and protein rejection were affected. The results of these further evaluations are summarized in Tables 2 and 3 and Figures 4 and 5.

Table 2: Flux, total solids and protein rejection during repeated cleaning-in-place (CIP) protocols of a sample of asymmetric composite membrane (030918Sii) prepared according to Example 9.

Table 3: Pressure test series (0-20 bar (0-2.0 MPa)) of a sample of asymmetric composite membrane (030918Siii) prepared according to Example 9. Flux and protein rejection were measured using milk as the feed stream.

Although 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 there are known equivalents to particular elements, features or integers, such equivalents are incorporated herein as if specifically referred to. In particular, variations and modifications to the embodiments disclosed in the referenced publications and including elements, features, or integers selected from the referenced publications are within the scope of the invention unless specifically disclaimed. is. The advantages provided by the invention and discussed in the detailed description may be provided alternatively or in combination in these different embodiments of the invention.

Durable asymmetric composite membranes with high levels of protein rejection are provided while maintaining high fluxes in feedstreams such as whole milk.
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Claims (8)

A microporous sheet of polyolefin grafted with preformed poly(4-ethenylbenzenesulfonic acid). A microporous sheet according to claim 1, wherein said polyolefin is poly(ethylene). An asymmetric composite membrane comprising a film of partially crosslinked poly(ethenol) adhered to one side of a preformed poly(4-ethenylbenzenesulfonic acid) grafted polyolefin microporous sheet. 4. The asymmetric composite membrane of claim 3, wherein said polyolefin is poly(ethylene). A method of preparing a hydrophilized microporous sheet of polyolefin, said method comprising:
a) contacting a microporous sheet of polyolefin with a dispersion comprising preformed poly(4-ethenylbenzenesulfonic acid) in an aqueous solvent to provide a contacted microporous sheet;
b) subjecting said contacted microporous sheet to a temperature and time sufficient to provide a cured microporous sheet in which at least a portion of poly(4-ethenylbenzenesulfonic acid) is grafted onto the polyolefin substrate; and then curing with
c) washing the cured microporous sheet to provide a polyolefin hydrophilized microporous sheet;
method including. 6. The method of claim 5, wherein said polyolefin is poly(ethylene). A method according to claim 5 or 6, wherein said aqueous solvent is acetone-water. A method according to any one of claims 5 to 7, wherein curing the contacted microporous sheet is by irradiation with ultraviolet light in the presence of a photoinitiator.

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