Method for producing charged ultrafiltration membranes and their use in dairy applications - Patent Application 20070122997

Abstract

Charged UF membranes are synthesized by thermally initiated free-radical polymerization and grafting of sodium styrene sulfonate onto the pores of an UF precursor membrane. The resulting grafted chains of the charged UF membrane provide a significant negative charge to maintain near-complete protein rejection with significant superflux.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application was filed as a PCT international patent application on January 11, 2024, and claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 479,560, filed January 12, 2023, the disclosure of which is incorporated herein by reference in its entirety. [Background technology]

[0002] The present invention relates generally to the use of ultrafiltration membranes to fractionate aqueous streams containing proteins, sugars, and minerals, with the proteins being retained by the membrane while the sugars, minerals, and water permeate the membrane. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] IUPAC Compendium of Chemical Terminology, 2nd Ed (1997) Summary of the Invention [Problem to be solved by the invention]

[0004] This Summary is provided to introduce a selection of concepts in a simplified form that are further described herein. This Summary is not intended to identify essential or essential features of the claimed subject matter, nor is this Summary intended to be used to limit the scope of the claimed subject matter.

[0005] In accordance with an aspect of the present invention, a method for producing an ultrafiltration membrane is disclosed herein, which may include: (a) contacting a precursor membrane comprising polyethersulfone (PES) and / or polysulfone (PSF) with an aqueous mixture comprising sodium styrenesulfonate, a free radical initiator, a crosslinker, and water; and (b) curing the precursor membrane to form an ultrafiltration membrane having sulfonated polystyrene covalently bonded to the pores and / or on the outer surface of the ultrafiltration membrane. Optionally, the aqueous mixture may further contain a cosolvent (e.g., methanol, n-butanol, etc.) and / or a pore wetting agent (e.g., glycerin).

[0006] Ultrafiltration membranes are also included herein. Generally, ultrafiltration membranes may include (I) polyethersulfone (PES) and / or polysulfone (PSF) membranes, and (II) sulfonated polystyrene covalently bonded to the pores of the ultrafiltration membrane and / or on the outer surface of the ultrafiltration membrane. More often, ultrafiltration membranes further include a mechanical support layer disposed below (and attached to) the membrane. The mechanical support layer may include polypropylene (PP) or polyester (PET), for example, nonwoven PP or PET.

[0007] In accordance with other aspects of the present invention, ultrafiltration modules and milk fractionation systems are provided herein. An exemplary ultrafiltration module can include (1) an inlet for a feed stream (e.g., a dairy product such as whole milk or skim milk), (2) one or more of the ultrafiltration membranes disclosed herein in any suitable configuration, such as a hollow fiber configuration, a tubular configuration, or a spiral-wound configuration, (3) a first outlet for a UF retentate stream, and (4) a second outlet for a UF permeate stream. An exemplary milk fractionation system can include (A) one or more of the ultrafiltration modules disclosed herein, (B) a nanofiltration module, and (C) a reverse osmosis module.

[0008] Also encompassed herein are methods for producing a dairy composition. One such method may include (i) ultrafiltering a milk product using any of the ultrafiltration membranes disclosed herein (or any of the ultrafiltration modules disclosed herein) to produce a UF permeate fraction and a UF retentate fraction, (ii) nanofiltering the UF permeate fraction to produce an NF permeate fraction and an NF retentate fraction, (iii) subjecting the NF permeate fraction to a reverse osmosis step to produce an RO permeate fraction and an RO retentate fraction, and (iv) combining at least two of the UF retentate fraction, the RO permeate fraction, the RO retentate fraction, and the fat-enriched fraction to form the dairy composition.

[0009] Both the foregoing general description and the following detailed description are exemplary and explanatory only. Accordingly, the foregoing general description and the following detailed description should not be construed as limiting. Furthermore, features or variations may be provided in addition to those described herein. For example, certain aspects may be directed to combinations and subcombinations of various features described in the detailed description.

[0010] definition The following definitions are provided to more clearly define terms used herein. Unless otherwise indicated, the following definitions apply to this disclosure. If a term used in this disclosure is not specifically defined herein, it is assumed that the definition will be in accordance with the IUPAC Compendium of Chemical Terminology, 2000, unless such definition contradicts other disclosures or definitions applicable herein and would not obscure or invalidate any claim to which such definition is applicable. nd (IUPAC Handbook of Chemical Terminology, 2nd Edition) (1997) definitions are applicable. To the extent that a definition or usage provided by a document incorporated herein by reference conflicts with a definition or usage provided herein, the definition or usage provided herein shall control.

[0011] The subject features are described herein such that combinations of different features may be envisioned within particular embodiments. For any and all aspects and / or features disclosed herein, all combinations that do not adversely affect the systems, compositions, processes, and / or methods described herein, with or without the explicit description of a specific combination, are contemplated. Furthermore, unless expressly recited otherwise, all aspects and / or features disclosed herein may be combined to describe inventive systems, compositions, processes, and / or methods consistent with the present invention.

[0012] In this disclosure, compositions and methods and systems are often described in terms of "comprising" various materials or steps or components, but unless otherwise specified, the compositions and methods and systems can also "consist essentially of" or "consist of" various materials or steps or components.

[0013] The terms "a," "an," and "the" are intended to include plural alternatives, e.g., at least one, unless otherwise specified. For example, disclosure of an "ultrafiltration membrane" is meant to encompass one or more ultrafiltration membranes unless otherwise specified.

[0014] In the disclosed methods, the terms "combining" and "contacting" include combining or contacting materials in any order, in any manner, and for any length of time, unless otherwise specified. For example, materials can be blended, mixed, treated, impregnated, submerged, soaked, dipped, etc.

[0015] The present invention discloses several types of ranges. When any type of range is disclosed or claimed, the intent is to individually disclose or claim each possible numerical value that such range may reasonably encompass, including the endpoints of the range, and any subranges and combinations of subranges encompassed therein. For example, in an embodiment of the present invention, the aqueous mixture of step (a) can contain 1 to 60 wt.% sodium styrene sulfonate. By disclosing that the aqueous mixture contains 1 to 60 wt.% sodium styrene sulfonate, the intent is to describe that the weight percent can be any amount within the range, for example, any range or combination of ranges from 1 to 60 wt.% sodium styrene sulfonate, such as, for example, 2 to 45 wt.%, 3 to 25 wt.%, 5 to 25 wt.%, 7 to 23 wt.%, or 10 to 30 wt.%. Similarly, all other ranges disclosed herein should be interpreted in a similar manner.

[0016] In general, any amount, size, formulation, parameter, range, or other quantity or characteristic is "about" or "approximately," whether or not expressly stated as such. Whether or not modified by the term "about" or "approximately," the claims include the equivalent of the quantity or characteristic.

[0017] Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, exemplary methods, devices, and materials are described herein.

[0018] All publications and patents mentioned herein are incorporated by reference in their entirety for the purpose of describing and disclosing, for example, the compositions and methodologies described in the publications and patents, which may be used in connection with the invention(s) described herein.

[0019] Disclosed herein are ultrafiltration membranes comprising polyethersulfone (PES) and / or polysulfone (PSF) membranes and sulfonated polystyrene covalently bonded to the pores of the ultrafiltration membrane and / or on the outer surface thereof; methods for producing the ultrafiltration membranes; ultrafiltration modules containing a plurality of ultrafiltration membranes; milk fractionation systems containing a plurality of ultrafiltration modules; and methods for producing dairy compositions utilizing the ultrafiltration membranes and ultrafiltration modules.

[0020] Ultrafiltration (UF) membranes are typically described by their molecular weight cut-off (MWCO, the molecular weight or size of molecules that are retained by the membrane). For example, when separating and concentrating proteins in the dairy industry, an ultrafiltration membrane may have a MWCO of 10 kDa, thus retaining at least 90% of material with a molecular weight above 10,000 daltons (retentate), while lower molecular weight species pass through (permeate).

[0021] The goal of the present invention is to produce an ultrafiltration membrane that maintains a high level of protein rejection while maintaining a higher overall flux. Thus, the membrane retains the same amount of protein at a higher throughput. For example, the charged ultrafiltration membranes disclosed herein can retain proteins at the same level as a standard 10 kDa MWCO ultrafiltration membrane, but with a significantly higher flux (e.g., 10-50% higher). This is achieved by modifying precursor PES or PSF membranes with covalently attached sulfonated polystyrene functional groups to form a charged polymer membrane that rejects proteins based on both molecular size and charge.

[0022] Because the primary component is protein, this focus is primarily directed to dairy applications, e.g., milk-based beverages and related products. However, the methods, techniques, membranes, etc. described herein are not limited to milk or dairy applications, but may also be applied to non-alcoholic and alcoholic beverages in general, including, but not limited to, beer, wine, water, wastewater treatment, juice, oat, almond / nut, pea, rice, seeds, grain, and other plant material processing, as well as end-use applications and products based on these materials.

[0023] Another object of the present invention is to form charged polymer membranes using a free radical polymerization process instead of a cationic polymerization process, which creates ionic bonds between the polymer chains and the precursor membrane. While any curing method can be used, in certain embodiments, a thermal initiator is used for the thermal cure of the free radical polymerization process, thereby forming a charged UF membrane.

[0024] It is yet another object of the present invention to form charged polymer membranes using a simple synthetic scheme with a limited number of process steps, in this case directly using sodium styrene sulfonate. Additionally, glycerin may be included in the aqueous mixture along with sodium styrene sulfonate to promote and maintain wetting of the substrate membrane and pores.

[0025] Although the present invention has been described in detail in connection with ultrafiltration (UF) membranes and methods for producing same, the methods and techniques disclosed herein are also applicable to microfiltration (MF) membranes, as well as nanofiltration (NF), reverse osmosis (RO) and forward osmosis (FO) membranes, and thus MF membranes—and NF membranes and RO and FO membranes—having covalently bonded sulfonated polystyrene moieties are encompassed herein.

[0026] In addition to the food processing applications mentioned above, other non-limiting uses of charged membranes (e.g., charged UF membranes, charged MF membranes) can include bacterial removal, viral removal, fermentation processes, ion exchange, rare element isolation, and charged paint particle isolation, among other end-use applications. [Means for solving the problem]

[0027] Ultrafiltration Membrane Various methods for producing ultrafiltration membranes are provided herein. For example, a method for producing an ultrafiltration membrane can include (or consist essentially of, or consist of) (a) contacting a precursor membrane comprising polyethersulfone (PES) and / or polysulfone (PSF) with an aqueous mixture comprising sodium styrenesulfonate, a free radical initiator, a crosslinker, and water, and (b) curing the precursor membrane to form an ultrafiltration membrane having sulfonated polystyrene covalently bonded to the pores and / or on the outer surface of the ultrafiltration membrane.

[0028] The following figures form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to these figures in combination with the detailed description and examples. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a scanning electron microscope (SEM) photograph of a precursor membrane containing upper and lower mechanical support layers of PSF. [Figure 2] FIG. 1 shows a diagram of polystyrene covalently bonded to the pores of an ultrafiltration membrane. [Figure 3] 1 shows a representative schematic of the diffusion of an aqueous mixture or solution into the pores of a precursor film before curing. [Figure 4] 1 shows a bar graph of the water permeability of the precursor membranes of Comparative Examples 5 and 6 and the charged ultrafiltration membranes of Examples 4A and 4B. [Figure 5] 1 is a plot of absorbance at a wavelength of 280 nm versus milk concentration. [Figure 6] 1 shows a bar graph of skim milk process flux for precursor membranes of Comparative Examples 5-6 and charged ultrafiltration membranes of Examples 3A and 4A. [Figure 7] 1 shows a bar graph of the skim milk permeability of the precursor membranes of Comparative Examples 5 and 6 and the charged ultrafiltration membranes of Examples 3A and 4A. [Figure 8] 1 shows a bar graph of protein rejection for the precursor membranes of Comparative Examples 5-6 and the charged ultrafiltration membranes of Examples 3A-3B and 4A. [Figure 9] 1 shows a bar graph of skim milk process flux for the precursor membrane of Comparative Example 5 and the charged ultrafiltration membranes of Examples 3A-3B. [Figure 10] 1 shows a bar graph of the skim milk permeability of the precursor membrane of Comparative Example 5 and the charged ultrafiltration membranes of Examples 3A and 3B. [Figure 11] 1 shows a bar graph of the protein rejection rates of the precursor membranes of Comparative Examples 5 and 6 and the charged ultrafiltration membranes of Examples 3A and 3B. [Figure 12] 1 is a plot of absorbance versus wavenumber (cm −1 ) for the precursor membrane of Comparative Example 6 before and after the CIP cleaning procedure. [Figure 13] 1 is a plot of absorbance versus wavenumber (cm −1 ) for the ultrafiltration membrane of Example 2A before and after the CIP cleaning procedure. [Figure 14] 1 is a plot of absorbance versus wavenumber (cm −1 ) for the ultrafiltration membrane of Example 7 before and after the CIP cleaning procedure. [Figure 15] 1 is a plot of absorbance versus wavenumber (cm −1 ) for the ultrafiltration membrane of Example 8 before and after the CIP cleaning procedure. [Figure 16] 16 shows bar graphs of the integrated areas under the ATR-FTIR curves of FIGS. 13-15 before and after the CIP cleaning procedure for the ultrafiltration membranes described in Examples 2A and 7-8. DETAILED DESCRIPTION OF THE INVENTION

[0030] Generally, any feature of the methods disclosed herein (e.g., the PES polymer, the PSF polymer, the composition of the aqueous mixture, the curing process, and the temperature and time conditions under which any steps are carried out, etc.) are described independently herein, and these features can be combined in any combination to further describe the disclosed methods. Furthermore, unless otherwise specified, other process steps can be performed before, during, and / or after any step recited in the disclosed methods. Furthermore, any ultrafiltration membrane produced according to any of the disclosed methods is within the scope of this disclosure and is encompassed herein.

[0031] Referring to step (a), any suitable precursor membrane comprising a polyethersulfone (PES) polymer material and / or a polysulfone (PSF) polymer material can be utilized. Generally, precursor PES and PSF membranes have a pure water permeability at least 20% greater than that of a standard 10 kDa MWCO PES membrane, a non-limiting example of which is a 20 kDa MWCO PES membrane. The precursor membrane may be fully wet, partially dried, or fully dried, with or without glycerin, prior to contacting with the aqueous mixture in step (a). The precursor membrane may be unsupported or supported, and if supported, is typically supported on a PP or PET nonwoven material.

[0032] The aqueous mixture of step (a) contains a monomer, typically sodium styrene sulfonate, a free radical initiator, a crosslinker, and water. While not limited thereto, the aqueous mixture often contains 1 to 60 wt.% sodium styrene sulfonate in one embodiment, 2 to 45 wt.% sodium styrene sulfonate in another embodiment, 3 to 25 wt.% sodium styrene sulfonate in another embodiment, 5 to 25 wt.% sodium styrene sulfonate in another embodiment, 7 to 23 wt.% sodium styrene sulfonate in yet another embodiment, and 10 to 30 wt.% sodium styrene sulfonate in still yet another embodiment. The amount of sodium styrene sulfonate present in the aqueous mixture of step (a) may often be limited by the desired amount of diffusion into pores or the desired extent of reaction. For example, too much graft polymer may result in excessive flux loss.

[0033] Similarly, the amount of free radical initiator in the aqueous mixture is not particularly limited. Typical ranges include, but are not limited to, 0.1 to 5 wt.%, 0.1 to 1.5 wt.%, 0.2 to 3 wt.%, 0.2 to 1.5 wt.%, or 0.2 to 1 wt.% of the free radical initiator, based on the weight of the aqueous mixture. The amount of free radical initiator can often vary depending on, among other considerations, the amount of sodium styrene sulfonate present in the mixture, the type of cure used in step (b), and the prevailing temperature.

[0034] Any suitable free radical initiator can be used in the aqueous mixture, although the type of initiator may vary depending on the type of cure used in step (b). For thermal cure, a representative, non-limiting example of a suitable curing agent is potassium persulfate, which is advantageously heat-activated and water-soluble. Other suitable alternatives include sodium persulfate and ammonium persulfate, both of which are water-soluble. Water-insoluble initiators such as azobisisobutyronitrile (AIBN) can also be used, but are generally used with a suitable cosolvent, typically a water-soluble alcohol.

[0035] The amount of cross-linking agent in the aqueous mixture in step (a) is not particularly limited. Typical ranges include, but are not limited to, 0.1 to 8 wt.%, 0.2 to 6 wt.%, 0.3 to 4 wt.%, 0.4 to 3 wt.%, or 0.5 to 2 wt.% of the cross-linking agent, based on the weight of the aqueous mixture. Any suitable cross-linking agent can be used, and illustrative, non-limiting examples include divinylacetylene, divinylsulfone, 5-hexadiene, divinylbenzene, substituted divinylbenzenes, and the like, as well as combinations thereof.

[0036] Although the initial combination of components in step (a) is described as a mixture, it is often a solution, for example, a single-phase solution, before polymer formation or when the concentrations of the components (monomer, initiator, crosslinker) are low. In such cases, the aqueous mixture in step (a) may further include a cosolvent to increase the solubility of sodium styrenesulfonate, the crosslinker, and / or the free radical initiator in the aqueous mixture (or solution, if desired). Representative, non-limiting examples of suitable cosolvents include methanol, n-butanol, etc. (e.g., other water-soluble alcohols), and combinations thereof. Any suitable amount of cosolvent can be used.

[0037] Optionally, the aqueous mixture (or solution) may further comprise a pore wetting agent such as glycerin. Without being bound by theory, it may be advantageous to have a small amount of pore wetting agent (e.g., glycerin) in the aqueous mixture, typically with a maximum amount ranging from 0.1 wt.% to a maximum of 25 wt.%, to improve pore wetting and prevent the pores from drying out (or becoming blocked or collapsing). More often, the aqueous mixture contains 0.5-20 wt.%, 1-15 wt.%, 2-8 wt.%, 5-25 wt.%, or 10-20 wt.% of the pore wetting agent (e.g., glycerin). Other suitable pore wetting agents, such as polyols, may also be used, a non-limiting example of which is propylene glycol.

[0038] The aqueous mixture (or solution) in step (a) often contains water as a major component in addition to sodium styrene sulfonate, a free radical initiator, a crosslinker, an optional cosolvent, and an optional pore wetting agent. While not limited thereto, the aqueous mixture (or solution) contains 20 to 80 wt.% water, for example, 30 to 70 wt.%, 30 to 45 wt.%, 35 to 50 wt.%, or 40 to 65 wt.% water.

[0039] Step (a) can be carried out at any suitable temperature, such as, but not limited to, 10°C to 90°C, 20°C to 70°C, 15°C to 55°C, 20°C to 45°C, or 20°C to 30°C. In these and other embodiments, these temperature ranges are meant to encompass situations where step (a) is carried out at a series of different temperatures, rather than at a single fixed temperature, with at least one temperature within each range. Although not required, the temperature in step (a) is often low to prevent incomplete reaction of the sodium styrene sulfonate, free radical initiator, and crosslinker, and thus premature polymer formation, prior to step (b).

[0040] The pressure at which step (a) is performed is not particularly limited and can be high pressure (e.g., 5 psig to 100 psig), atmospheric pressure, or any suitable subatmospheric pressure. In some cases, step (a) is performed at atmospheric pressure, thereby eliminating the need for a pressurized vessel and its associated cost and complexity. Step (a) can be performed for any period sufficient to allow the aqueous mixture (or solution) to diffuse and / or wick into the pores of the precursor membrane. Exemplary, non-limiting periods include a wide range of periods, such as 2 seconds to 6 hours, 2 seconds to 2 minutes, 10 seconds to 6 hours, 10 seconds to 2 minutes, 15 seconds to 5 hours, 30 seconds to 2 hours, 1 minute to 24 hours, 1 minute to 1 hour, 5 minutes to 6 hours, 15 minutes to 5 hours, or 30 minutes to 2 hours, but are not limited to these periods alone. Other suitable temperature, pressure, and time ranges will be readily apparent from this disclosure.

[0041] Any suitable vessel or container can be used for step (a), as long as the vessel or container can, for example, allow the precursor membrane to be contacted (e.g., immersed) in the aqueous mixture (or solution) for a period of time sufficient for the aqueous mixture (or solution) to diffuse and / or be wicked into the pores of the precursor membrane. Step (a) can be carried out batchwise or continuously. Furthermore, during step (a), the aqueous mixture (or solution) can be subjected to agitation to improve the uniformity of the reactive components (or any polymer that may have formed) in the aqueous mixture (or solution) during pore diffusion.

[0042] In one embodiment of the invention, the precursor film may be dry prior to step (a), while in another embodiment, the precursor film may be wet prior to step (a), and in yet another embodiment, the precursor film may be dry prior to step (a) but may be further wetted with water prior to step (a).

[0043] After performing step (a)—where the precursor membrane is in full contact with the aqueous mixture or solution—the precursor membrane may be partially dried before step (b). In particular, excess water or excess aqueous mixture / solution may be removed from the precursor membrane before step (b). The precursor is only partially dried, leaving a suitable amount of water (and sodium styrene sulfonate monomer, initiator, and crosslinker) in the pores.

[0044] Referring to step (b), the precursor membrane is cured to form an ultrafiltration membrane, which thus contains sulfonated polystyrene covalently bonded to the pores and / or on the outer surface of the ultrafiltration membrane (i.e., covalently bonded to the pores or on the outer surface, or covalently bonded to both the pores and the outer surface). Sulfonated polystyrene is used herein to encompass substituted styrene moieties, such as methylated polystyrene groups.

[0045] Any suitable curing method can be utilized in step (b), such as subjecting the precursor film to UV irradiation (UV photoinitiated) or electron beam irradiation. However, it has been found herein that the precursor film can be conveniently cured with heat. Accordingly, in one embodiment of the present invention, curing in step (b) can include subjecting the precursor film to an elevated temperature, typically, but not limited to, within the range of 70-200°C. Other suitable temperature ranges include 70-150°C, 95-180°C, or 80-130°C. In these and other embodiments, these temperature ranges are intended to encompass situations where thermal curing is carried out at a series of different temperatures, rather than at a single fixed temperature, with at least one temperature within each range. The maximum curing temperature often depends on the melting or softening point of the polyethersulfone (PES) and / or polysulfone (PSF) used in the precursor film, as well as the melting or softening point of any supporting layer (which may be, for example, PP- or PET-based). Exemplary, non-limiting curing times include broad ranges such as 1 minute to 24 hours, 1 minute to 1 hour, 5 minutes to 6 hours, 15 minutes to 5 hours, or 30 minutes to 2 hours, but are not limited to these. Other suitable temperature and time ranges will be readily apparent from this disclosure. The curing process can be carried out batchwise or continuously.

[0046] In one embodiment, after step (b), the ultrafiltration membrane may be rinsed with water, which may be performed in the same location as step (b) or at a different location. In another embodiment, after step (b), the ultrafiltration membrane may be rinsed with water, contacted with an aqueous glycerin solution, and then dried.

[0047] According to an embodiment of the present invention, the precursor membrane and the ultrafiltration membrane may further contain a mechanical support layer disposed under (and attached to) each membrane. This additional layer is generally present before step (a). The mechanical support layer can be composed of any suitable material, but is often PP- or PET-based, e.g., nonwoven PP or nonwoven PET. As mentioned above, depending on the composition of the mechanical support layer and its melting point or softening temperature, the curing temperature in step (b) can vary. PP can often be used as the support layer to achieve a wide pH range during use of the membrane.

[0048] Also included herein are (I) polyethersulfone (PES) and / or polysulfone (PSF) membranes, and (II) ultrafiltration membranes that may include sulfonated polystyrene covalently bonded to the pores of the ultrafiltration membrane and / or to the outer surface of the ultrafiltration membrane (i.e., covalently bonded to the pores or to the outer surface, or to both the pores and the outer surface). These ultrafiltration membranes can be produced according to any of the methods and processes described herein. Furthermore, ultrafiltration membranes may, and often do, contain a mechanical support layer disposed below (and attached to) the membrane. As noted above, suitable PP or PET nonwoven materials are typically used as the mechanical support layer. A photograph of a representative precursor membrane is shown in Figure 1, with the top layer being a PES or PSF mechanical support layer and the bottom layer being a PP or PET mechanical support layer. Generally, the layers are interconnected, and the two-layer structure does not delaminate. FIG. 2 shows polystyrene covalently bonded to the pores of an ultrafiltration membrane (no sulfonic acid or sulfonate groups are explicitly shown, only the polystyrene grafts are shown).

[0049] In certain embodiments, the disclosed ultrafiltration membranes may be characterized by a water permeability (or skim milk permeability) that is at least 10% greater than a 10 kDa molecular weight cutoff (MWCO) membrane, and in some cases at least 15% greater, at least 20% greater, at least 30% greater, at least 50% greater, at least 100% greater, or at least 200% greater. Additionally or alternatively, the ultrafiltration membranes disclosed herein may have a water permeability (or skim milk permeability) of at least 120 L / m 2 -time-bar, for example at least 140, at least 160, at least 180, at least 200, at least 250, or at least 500 L / m 2 The water permeability test may be characterized by a water permeability rate of 100-150 bar (hours). These are minimum thresholds because no maximum value is generally established, provided the minimum threshold is exceeded. The water permeability test and the skim milk permeability test are further described in the examples below.

[0050] In certain embodiments, the disclosed ultrafiltration membranes are characterized by a percent protein rejection equal to or greater than that of a 10 kDa MWCO membrane. Additionally or alternatively, the disclosed ultrafiltration membranes may be characterized by a percent protein rejection equal to or greater than that of a 20 kDa MWCO membrane. Additionally or alternatively, the disclosed ultrafiltration membranes may be characterized by a percent protein rejection in skim milk of at least 90%, and in some cases at least 92%, at least 95%, or at least 97%. Protein rejection testing is further described in the Examples below.

[0051] To determine whether the sulfonated polystyrene grafts were covalently bonded within the membrane pores, the membranes were subjected to the clean-in-place (CIP) cleaning procedure described in the Examples section below, followed by ATR-FTIR at a wavenumber of 1036 cm. -1 The membrane can be analyzed at a wavenumber of 1036 cm. After the CIP cleaning procedure, the non-covalently bonded sulfonated polystyrene moieties are removed. -1 There is no significant peak in

[0052] In contrast, the disclosed ultrafiltration membrane (with covalently bonded sulfonated polystyrene) exhibits a wavelength of 1036 cm using ATR-FTIR. -1 Herein, after the CIP cleaning procedure, the peak at wavenumber 1036 cm -1 A (charged) ultrafiltration membrane is considered to have covalently bound sulfonated polystyrene if the integrated absorbance area under the ATR-FTIR curve at a wavenumber of 1036 cm is 0.05 or greater. In some embodiments, after a CIP cleaning procedure, the ultrafiltration membranes described herein have a covalently bound sulfonated polystyrene. -1 Alternatively, the integrated absorbance area under the ATR-FTIR curve at 0.08 or greater; alternatively, 0.1 or greater; alternatively, 0.2 or greater; alternatively, 0.3 or greater; alternatively, 0.5 or greater; or alternatively, 0.7 or greater. These integrated absorbance areas are minimum thresholds because, as long as the minimum threshold is exceeded, there is generally no maximum value.

[0053] In one aspect, the disclosed ultrafiltration membranes can be cleaned in place (CIP) using the CIP cleaning procedure described in the Examples below. Due to the covalent bond, the charged membranes described herein are generally stable during the CIP procedure. Cleaning may be necessary when the flux through the membrane drops to a certain level, e.g., when the flux drops by more than 5-10% of the initial flux. Thus, the membrane can be reused after being subjected to the CIP cleaning procedure.

[0054] In one embodiment, the disclosed ultrafiltration membranes can have a lifespan of at least 1 month, at least 3 months, at least 6 months, or at least 1 year. It is believed that the sulfonated polystyrene moieties covalently bonded to the pores of the UF membrane improve membrane lifespan over similarly modified membranes in which covalent bonding is not achieved.

[0055] Systems and processes using ultrafiltration membranes The disclosed UF membranes contain sulfonated polystyrene covalently bonded to the pores and / or on the outer surface of the UF membrane and can be utilized in a variety of devices, systems, and processes. One such device is an ultrafiltration module that can include (1) a feed stream inlet, (2) one or more of any of the ultrafiltration membranes disclosed herein in any suitable configuration, such as a hollow fiber, tubular, or spiral-wound configuration, (3) a first outlet for a UF retentate stream, and (4) a second outlet for a UF permeate stream. The feed stream entering the ultrafiltration module at the inlet can be any suitable dairy product, such as, but not limited to, whole milk or skim milk. Typically, an ultrafiltration module uses multiple ultrafiltration membranes in, for example, a spiral-wound configuration.

[0056] An exemplary milk fractionation system can include (A) one or more of the ultrafiltration modules disclosed herein, (B) a nanofiltration module, and (C) a reverse osmosis module. Other milk fractionation systems encompassed herein can include one or more of any of the ultrafiltration modules disclosed herein, a nanofiltration module, and a forward osmosis module; or one or more of any of the ultrafiltration modules disclosed herein and a nanofiltration module; or one or more of any of the ultrafiltration modules disclosed herein and a reverse osmosis module; or alternatively, one or more of any of the ultrafiltration modules disclosed herein and a forward osmosis module. Typically, milk fractionation systems use multiple ultrafiltration modules.

[0057] Also provided herein are methods for producing dairy compositions using ultrafiltration membranes. Exemplary methods can include the following steps: (i) ultrafiltering a dairy product using any of the ultrafiltration membranes disclosed herein (or any of the ultrafiltration modules disclosed herein) to produce a UF permeate fraction and a UF retentate fraction; (ii) nanofiltering the UF permeate fraction to produce an NF permeate fraction and an NF retentate fraction; (iii) subjecting the NF permeate fraction to a reverse osmosis process to produce an RO permeate fraction and an RO retentate fraction; and (iv) combining at least two of the UF retentate fraction, the RO permeate fraction, the RO retentate fraction, and the fat-rich fraction to form the dairy composition. For example, in one aspect, the dairy composition can contain at least a UF retentate fraction and an RO retentate fraction; in another aspect, the dairy composition can contain at least a UF retentate fraction, an RO retentate fraction, and a fat-rich fraction (cream). [Example]

[0058] The present invention is further illustrated by the following examples, which should not be construed as limiting the scope of the present invention in any way. After reading the description herein, those skilled in the art may suggest various other embodiments, modifications, and equivalents without departing from the spirit of the present invention or the scope of the appended claims.

[0059] In Example 1, a first 100 mL solution was prepared by mixing the following components in a beaker at room temperature: 50 mL of deionized (DI) water, 1 mL of divinylbenzene (DVB), 20 mL of n-butanol, 20 mL of methanol, 12 g of sodium styrenesulfonate, and 0.4 g of potassium persulfate (KSO). The total mass of this first 100 mL solution was 95.31 g, and the approximate contents of each component (by mass) were 52.5 wt.% DI water, 0.95 wt.% DVB, 16.8 wt.% n-butanol, 16.8 wt.% methanol, 12.6 wt.% sodium styrenesulfonate, and 0.42 wt.% potassium persulfate (KSO).

[0060] Once this first solution was homogeneous, it was diluted with a 2:1:1:1.7 solution of water:methanol:butanol:glycerin, doubling the volume to 200 mL, and stirred for 5 minutes to ensure homogeneity. The total mass of this diluted 200 mL solution was 196.31 g, and the approximate contents of each component (by mass) were 43.3 wt.% DI water, 0.47 wt.% DVB, 15.3 wt.% n-butanol, 15.3 wt.% methanol, 6.1 wt.% sodium styrenesulfonate, 0.2 wt.% potassium persulfate (KSO), and 19.4 wt.% glycerin.

[0061] Dry precursor PE20 membranes with a 20 kDa MWCO were obtained from Solecta. These membranes were polyethersulfone (PES) on a polypropylene (PP) backing. Two 5.5 in x 7.5 in samples of the precursor PE20 membrane were cut from the same vertical region of the membrane.

[0062] The first membrane sample (Example 1A) was submerged and immersed in 200 mL of the diluted solution at room temperature for 2 hours, while the solution was continuously stirred. Without being bound by theory, it is believed that no or significant amounts of polymer are formed before the curing process. A representative schematic of the diffusion of the aqueous reaction solution into the pores of the precursor membrane before curing is shown in Figure 3. While diffusion is one mechanism for the monomer to enter the pores, another mechanism is for the aqueous reaction solution to wick up into the open, dried pores. The dried pores may also be partially filled with glycerin from the drying process. The first membrane sample was removed from the solution, and excess solution was drained from the membrane.

[0063] A second membrane sample (Example 1B) was quickly and briefly immersed in the diluted 200 mL solution for a period ranging from a few seconds to a maximum of 10-30 seconds, then removed from the solution and excess solution drained from the membrane. Both membrane samples were placed on a glass plate with the PP backing facing the glass, with the edges trimmed to prevent curling, but with a polypropylene mesh between them to prevent direct contact with the glass and allow evaporation from the backside of the membrane. The glass plate and clamped membrane were then inverted and placed in a 100°C oven (PP backing facing up, PES facing the bottom of the oven) and heat-cured for 1 hour. The cured membrane samples were removed from the oven and allowed to cool at room temperature for 5 minutes before cleaning and / or testing the membranes.

[0064] In Example 2, a first solution was prepared by mixing the following ingredients in a beaker at room temperature: 25 mL of deionized (DI) water, 1.5 mL of divinylbenzene (DVB), 10 mL of n-butanol, 10 mL of methanol, 18 g of sodium styrenesulfonate, and 0.6 g of potassium persulfate (KSO). Once this first solution was homogeneous, it was diluted with 50 mL of a 2:1:1:1.7 solution of water:methanol:butanol:glycerin and stirred for 5 minutes to ensure homogeneity. Thus, the diluted solution in Example 2 contained approximately 2.5 times the concentrations of DVB, sodium styrenesulfonate, and potassium persulfate (KSO) as in Example 1. The approximate amounts of each component, by mass, were 38.1 wt.% DI water, 1.2 wt.% DVB, 13.5 wt.% n-butanol, 13.5 wt.% methanol, 16.1 wt.% sodium styrenesulfonate, 0.5 wt.% potassium persulfate (KSO), and 17 wt.% glycerin. Submerged / immersed (Example 2A) and short-immersed (Example 2B) membrane samples were prepared from the diluted solution of Example 2 in a manner similar to that of Example 1.

[0065] In Example 3, a first solution was prepared by mixing the following ingredients in a beaker at room temperature: 25 mL of deionized (DI) water, 3 mL of divinylbenzene (DVB), 10 mL of n-butanol, 10 mL of methanol, 36 g of sodium styrenesulfonate, and 1.2 g of potassium persulfate (KSO). Once this first solution was homogeneous, it was diluted with 50 mL of a 2:1:1:1.7 solution of water:methanol:butanol:glycerin and stirred for 5 minutes to ensure homogeneity. Because the diluted solution was not homogeneous, 10 mL of DI water was added and stirred for 10 minutes. The diluted solution in Example 3 contained approximately 4-4.5 times the concentrations of DVB, sodium styrenesulfonate, and potassium persulfate (KSO) compared to Example 1. The approximate amounts of each component, by mass, were 37.1 wt.% DI water, 1.9 wt.% DVB, 10.6 wt.% n-butanol, 10.6 wt.% methanol, 25.5 wt.% sodium styrenesulfonate, 0.9 wt.% potassium persulfate (KSO), and 13.4 wt.% glycerin. Submerged / immersed (Example 3A) and short-immersed (Example 3B) membrane samples were prepared from the diluted solution of Example 3 in a manner similar to that of Example 1.

[0066] In Example 4, a first solution was prepared by mixing the following ingredients in a beaker at room temperature: 25 mL of deionized (DI) water, 3 mL of divinylbenzene (DVB), 10 mL of n-butanol, 10 mL of methanol, 18 g of sodium styrenesulfonate, and 1.2 g of potassium persulfate (KSO). Once this first solution was homogeneous, it was diluted with 50 mL of a 2:1:1:1.7 solution of water:methanol:butanol:glycerin and stirred for 5 minutes to ensure homogeneity. In this case, the diluted solution was not homogeneous, so 10 mL of n-butanol was added and stirred for 10 minutes. The diluted solution in Example 4 contained approximately 5 times the concentrations of DVB and potassium persulfate (KSO) and 2.5 times the concentration of sodium styrenesulfonate as in Example 1. The approximate amounts of each component, by mass, were 35 wt.% DI water, 2.3 wt.% DVB, 18.9 wt.% n-butanol, 12.4 wt.% methanol, 14.8 wt.% sodium styrenesulfonate, 1 wt.% potassium persulfate (KSO), and 15.6 wt.% glycerin. Submerged / immersed (Example 4A) and short-immersed (Example 4B) membrane samples were prepared from the diluted solution of Example 4 in a manner similar to that of Example 1.

[0067] Comparative Example 5 was a 10 kDa MWCO PE10 membrane (PES on a PET backing) obtained from Solecta, Inc. Comparative Example 6 was a 20 kDa MWCO PE20 membrane (PES on a PP backing) obtained from Solecta, Inc., prior to any of the modifications described in Examples 1-4.

[0068] Flux, permeability, and protein inhibition experiments Pure water permeability was measured in a dead-end cell equipped with a stainless steel membrane holder. Water permeability was measured after a 2-minute ramp to 90 psig. Skim milk permeability and process flux and protein rejection tests were also performed using the same dead-end cell equipped with a stainless steel membrane holder after a 2-minute ramp to 25 psig.

[0069] Figure 4 summarizes the results of water permeability testing of the precursor membranes of Comparative Examples 5 and 6 and the charged ultrafiltration membranes of Examples 4A and 4B. Flux was measured using a stainless steel dead-end cell fed from a stainless steel tank pressurized with compressed air. The feed pressure was initially spiked to 90 psig for 2 minutes to ensure complete wetting of the membrane. Flux data was collected at five pressure measurements, 5 psig apart, over 60 seconds, with each pressure measurement repeated three times. The permeability of the precursor membrane of Comparative Example 5 (PE10) and the charged ultrafiltration membranes of Examples 4A and 4B is shown as a single bar graph in Figure 4, while two separate samples of Comparative Example 6 (PE20) were tested. The PE20 membrane of Comparative Example 6 had a much higher pure water permeability (before reaction / impregnation) than the PE10 membrane of Comparative Example 5. Examples 4A and 4B in Figure 4 demonstrate the effect of pore-bound sulfonated polystyrene on the membrane pore size and, therefore, the reduced water permeability relative to the precursor PE20 membrane. Unexpectedly and advantageously, the charged ultrafiltration membranes of Examples 4A-4B after reaction / impregnation had significantly higher water permeabilities than the PE10 membrane of Comparative Example 5, at least 150 L / m 2 The water permeability was surprisingly high at -100 bar for -100 hours.

[0070] Next, tests were performed on various membranes using skim milk. Figure 5 shows a milk calibration curve plotting absorbance at 280 nm versus milk concentration. This technique is based on the absorbance of amino acids, which are part of milk proteins. A calibration curve was constructed using three known concentrations of skim milk (e.g., dilution factors of 200 to 1000) in solutions with absorbances near or below 1. Using this calibration curve and a regression equation, the protein concentration of the permeate was determined from the absorbance readings of the permeate.

[0071] Figures 6-7 summarize the results of skim milk process flux and skim milk permeability tests for the precursor membranes of Comparative Examples 5-6 and the charged ultrafiltration membranes of Examples 3A and 4A. Flux and permeability were measured similarly to the water tests described above, but using skim milk instead at 25 psig. The skim milk nominally contained 91 wt.% water, 0.75 wt.% minerals, 5 wt.% carbohydrates / lactose, 3.3 wt.% protein, and 0.1 wt.% fat. Similar to Figure 4, the skim milk process flux and skim milk permeability of the charged ultrafiltration membranes of Examples 3A and 4A generally fell between those of the PE20 membrane of Comparative Example 6 and the PE10 membrane of Comparative Example 5, as shown in Figures 6-7. The large error bars were likely the result of insufficient sample collection time and flow rate differences between the two different flow cells due to the stir plate.

[0072] Figure 8 summarizes the protein rejection of the precursor membranes of Comparative Examples 5-6 and the charged ultrafiltration membranes of Examples 3A-3B and 4A. The percent protein rejection of the various membranes using skim milk was determined in a dead-end cell equipped with a stainless steel membrane holder filled with approximately 25 mL of skim milk, with the agitator set at 3 and a pressure of 25 psig. Protein concentration was determined using a UV-visible spectrophotometer at 280 nm and the calibration curve in Figure 5, and the percent reduction was determined by calculating the milk concentration in the permeate and comparing it to a 100% skim milk feed. With the exception of Example 4A, the protein rejection of each of the other membranes was approximately 95%.

[0073] Figures 9-11 are similar to Figures 6-8, but tests were run with a new stir plate to improve consistency and reduce error bars. As shown in Figures 9-10, the charged ultrafiltration membrane of Example 3A (submerged / immersed) had slightly lower process flux and permeability than the precursor membrane of Comparative Example 5, while the charged ultrafiltration membrane of Example 3B (short-time immersion) did not perform as well. Without being bound by theory, it is believed that the membrane of Example 3B (short-time immersion) did not perform as well as the membrane of Example 3A (submerged / immersed), possibly because the impregnation solution required less time to fully diffuse and wet the pores, potentially resulting in pore clogging.

[0074] 11 , the protein rejection (97.3%) of the charged ultrafiltration membranes of Examples 3A-3B was unexpectedly the same as that of the precursor membrane of Comparative Example 5 and better than that of the precursor membrane of Comparative Example 6. Given the excellent protein rejection performance of the charged ultrafiltration membranes of Examples 3A-3B, increasing or decreasing the monomer / reactant concentration can increase the flux or permeability to be equal to or better than that of, for example, the PE10 membrane of Comparative Example 5.

[0075] Covalent bonding experiments In these experiments, the charged ultrafiltration membrane (submerged / soaked) of Example 2A and the precursor PE20 membrane of Comparative Example 6 were soaked in water overnight to remove glycerin.

[0076] Example 7 was prepared from the precursor PE20 membrane in the same manner as Example 3A. Submerged / immersed membrane samples of Example 7 were prepared from the impregnation solution of Example 7 in the same manner as Example 1. The charged ultrafiltration membrane of Example 7 was then immersed in water overnight to remove glycerin.

[0077] In Example 8, an aqueous reaction solution was prepared by mixing 50 mL of DI water, 1 mL of divinylbenzene (DVB), 20 mL of n-butanol, 20 mL of methanol, 12 g of sodium styrenesulfonate, and 0.4 g of potassium persulfate (KSO) in a round-bottom flask. This reaction solution was heated under reflux for 75 minutes and then cooled / quenched with a 2:1:1:1.7 solution of water:methanol:butanol:glycerin to a total volume of 200 mL and stirred for 1 hour. Next, 0.8 mL of divinylbenzene (DVB) and 0.8 g of potassium persulfate (KSO) were added and stirred at room temperature until homogeneous. Submerged / immersed membrane samples of Example 8 were prepared from this mixture at room temperature (over a 2-hour time interval) in a manner similar to that of Example 1, except that a subsequent curing step was not used. The charged ultrafiltration membrane of Example 8 was then immersed in water overnight to remove the glycerin.

[0078] The precursor membrane of Comparative Example 6 and the ultrafiltration membranes of Examples 2A and 7-8 were then analyzed using ATR-FTIR both before and after the following rigorous clean-in-place (CIP) cleaning procedure, which was carried out in a dead-end cell at pressures ranging from 20 to 30 psig. The operating sequence of the CIP cleaning procedure was as follows: 1) Caustic solution for 1 hour 2) DI water 5 min 3) HCl in DI water (pH 3) for 30 min 4) DI water 5 min 5) Caustic solution 30 minutes 6) DI water 5 min

[0079] The caustic solution consisted of 1000 mL of DI water, 0.8 mL of Apollo 8 surfactant, 0.25 mL of bleach, and NaOH to reach a pH equivalent to 10. The purpose of the CIP cleaning procedure was to remove non-covalently bound chemicals from the membrane surface / pores. Simply washing or rinsing the modified membrane with water is not sufficient to remove the sulfonated polystyrene moieties from the membrane surface / pores.

[0080] ATR-FTIR was performed using a Perkin Elmer Spectrum Two FT-IR spectrometer with 8 scans and a 4cm -1 Resolution: 400-4000 cm -1 The main absorbance wavenumber of the sulfonated polystyrene moiety was 1036 cm. -1 The wavenumbers were selected. For each example, five samples were tested (and then averaged) for different positions on each film surface. The dry film surface was placed face down on top of the optical crystal of the ATR-FTIR instrument.

[0081] 12 to 15 show the absorbance versus wavenumber (cm) for the precursor membrane of Comparative Example 6, the ultrafiltration membrane of Example 2A, the ultrafiltration membrane of Example 7, and the ultrafiltration membrane of Example 8, both before and after the CIP cleaning procedure. -1 12, in Comparative Example 6, the wavenumber of 1036 cm was 1036 cm before and after the CIP cleaning procedure. -1 No peak was observed at wavenumber 1036 cm, which was expected since no polymer was grafted / coated onto the PE20 membrane surface / pores. Referring to Figure 15, in Example 8, no peak was observed at wavenumber 1036 cm before the CIP cleaning procedure. -1 A small peak was observed at 1000 nm, but no peak was observed after the CIP cleaning procedure (i.e., the polymer was not covalently attached to the membrane surface / pores).

[0082] In FIG. 13, Example 2A shows a wavenumber of 1036 cm both before the CIP cleaning procedure and, more importantly, after the CIP cleaning procedure. -1 A prominent peak is observed at 1036 cm. Thus, in Example 2A, sulfonated polystyrene was covalently bonded to the membrane surface / pores. In Figure 14, in Example 7, before the CIP cleaning procedure, a prominent peak is observed at 1036 cm. -1 A prominent peak was observed at 1000 kJ / cm2, and a smaller peak was observed after the CIP cleaning procedure. Thus, in Example 7, the sulfonated polystyrene was covalently bonded to the membrane surface / pores, but it is likely that excess monomer was removed during the CIP cleaning procedure.

[0083] Figure 16 shows a quantitative analysis of the integrated area under the ATR-FTIR curves of Figures 13 to 15 before and after the CIP cleaning procedure for the ultrafiltration membranes of Examples 2A and 7 to 8. The error bars shown are the integrated area of ​​the curve for PE20 Comparative Example 6 shown in Figure 12 and are believed to be due to variations in instrumentation and testing. The integrated area is 1036 cm -1 Below the peak of 1036cm -1 From the trough / minimum at wavenumbers less than 1036 cm -1 The integrated area is the area above a line drawn to the valley / minimum at wavenumbers above 0. After the CIP cleaning procedure, the integrated area for Example 8 was approximately 0.025 (likely due to instrumentation and test variability), while the integrated areas for Example 7 and Example 2A were unexpectedly 0.11 and 0.68, respectively.

[0084] These examples demonstrate that the CIP cleaning procedure, as in Example 8, results in a wavenumber of 1036 cm for the non-covalently bound sulfonated polystyrene moiety. -1 As shown in Examples 2A and 7, the membranes containing covalently bonded sulfonated polystyrene exhibited a peak at 1036 cm even after rigorous CIP cleaning procedures. -1 The peak of

Claims

1. 1. A method for producing an ultrafiltration membrane, the method comprising: (a) contacting a precursor membrane comprising polyethersulfone (PES) and / or polysulfone (PSF) with an aqueous mixture comprising sodium styrenesulfonate, a free radical initiator, a crosslinker, and water; and (b) curing the precursor membrane to form the ultrafiltration membrane, wherein the ultrafiltration membrane has sulfonated polystyrene covalently bonded to its pores and / or on its outer surface.

2. The precursor film is dried prior to step (a); or the precursor membrane is wet prior to step (a); or The method of claim 1 , wherein the precursor film is dry prior to step (a) and is wetted with water prior to step (a).

3. 3. The method of claim 1 or 2, wherein the aqueous mixture comprises 1 to 60 wt.%, 2 to 45 wt.%, 3 to 25 wt.%, 5 to 25 wt.%, 7 to 23 wt.%, or 10 to 30 wt.% sodium styrenesulfonate.

4. 4. The method of claim 1, wherein the aqueous mixture comprises 0.1 to 5 wt.%, 0.1 to 1.5 wt.%, 0.2 to 3 wt.%, 0.2 to 1.5 wt.%, or 0.2 to 1 wt.% of the free radical initiator.

5. 5. The method of any one of claims 1 to 4, wherein the free radical initiator comprises potassium persulfate, sodium persulfate, ammonium persulfate, azobisisobutyronitrile (AIBN), or any combination thereof.

6. 6. The method of claim 1, wherein the aqueous mixture comprises 0.1 to 8 wt.%, 0.2 to 6 wt.%, 0.3 to 4 wt.%, 0.4 to 3 wt.%, or 0.5 to 2 wt.% of the cross-linking agent.

7. 7. The method of any one of claims 1 to 6, wherein the crosslinking agent comprises divinylacetylene, divinylsulfone, 5-hexadiene, divinylbenzene, substituted divinylbenzene, or any combination thereof.

8. 8. The method of claim 1, wherein the aqueous mixture comprises a co-solvent.

9. 9. The method of claim 8, wherein the co-solvent comprises methanol, n-butanol, or a combination thereof.

10. 10. The method of claim 1, wherein the aqueous mixture further comprises a pore wetting agent, such as glycerin.

11. 11. The method of claim 10, wherein the aqueous mixture comprises 0.1 to 25 wt.%, 0.5 to 20 wt.%, 1 to 15 wt.%, 2 to 8 wt.%, 5 to 25 wt.%, or 10 to 20 wt.% of the pore wetting agent, such as glycerin.

12. 12. The method of any one of claims 1 to 11, wherein the aqueous mixture comprises 20 to 80 wt.%, 30 to 70 wt.%, 30 to 45 wt.%, 35 to 50 wt.%, or 40 to 65 wt.% water.

13. 13. The method of claim 1, wherein step (a) is carried out for a time sufficient for the aqueous mixture to diffuse and / or wick into the pores of the precursor membrane.

14. 14. The method of any one of claims 1 to 13, wherein the aqueous mixture is subjected to stirring in step (a).

15. 15. The method of any one of claims 1 to 14, wherein the aqueous mixture is a solution.

16. 16. The method of claim 1, wherein the precursor film is partially dried before step (b).

17. The curing in step (b) comprises: subjecting the precursor film to an elevated temperature in the range of 70 to 200°C; or 17. The method of claim 1, comprising subjecting the precursor film to UV irradiation or electron beam irradiation.

18. The ultrafiltration membrane after step (b) is subjected to: Rinse with water; or 18. The method of any one of claims 1 to 17, comprising rinsing with water, contacting with an aqueous glycerin solution, and drying.

19. 19. The method of any one of claims 1 to 18, wherein the precursor membrane and the ultrafiltration membrane comprise a mechanical support layer disposed beneath (and attached to) the respective membrane.

20. 20. An ultrafiltration membrane prepared by the method of any one of claims 1 to 19.

21. (I) polyethersulfone (PES) and / or polysulfone (PSF) membranes; and (II) An ultrafiltration membrane comprising sulfonated polystyrene covalently bonded to the pores and / or on the outer surface of the ultrafiltration membrane.

22. 22. The membrane of claim 21, wherein the ultrafiltration membrane comprises a mechanical support layer disposed beneath (and attached to) the membrane.

23. 23. The membrane of any one of claims 20 to 22, wherein the ultrafiltration membrane is characterized by a water permeability (or skim milk permeability) that is at least 10% greater, at least 15% greater, at least 20% greater, at least 30% greater, at least 50% greater, at least 100% greater, or at least 200% greater than a 10 kDa molecular weight cut-off (MWCO) membrane.

24. The ultrafiltration membrane has a flow capacity of at least 120, at least 140, at least 160, at least 180, at least 200, at least 250, or at least 500 L / m 2 24. The membrane of any one of claims 20 to 23, characterized by a water permeability of -hour-bar.

25. 25. The membrane of any one of claims 20 to 24, wherein the ultrafiltration membrane is characterized by a percent protein rejection that is equal to or greater than the percent protein rejection of a 10 kDa MWCO membrane (or a 20 kDa MWCO membrane).

26. 26. The membrane of any one of claims 20 to 25, wherein the ultrafiltration membrane is characterized by a percent rejection of proteins in skim milk of at least 90%, at least 92%, at least 95%, or at least 97%.

27. After the CIP cleaning procedure, the ultrafiltration membrane had a wave number of 1036 cm -1 27. The membrane of any one of claims 20 to 26, characterized by an integrated absorbance area under the ATR-FTIR curve at 0.05 or more, 0.08 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.5 or more, or 0.7 or more.

28. (1) Feed stream inlet; (2) one or more of the ultrafiltration membranes of any one of claims 20 to 27 in a hollow fiber configuration, a tubular configuration, or a spiral wound configuration; (3) a first outlet for the UF retentate stream; and (4) a second outlet for the UF permeate stream.

29. (A) one or more ultrafiltration modules according to claim 28; (B) a nanofiltration module; and (C) A milk fractionation system including a reverse osmosis module.

30. 1. A method for producing a dairy composition, comprising: (i) ultrafiltering a milk product using an ultrafiltration membrane according to any one of claims 20 to 27 (or a module according to claim 28) to produce a UF permeate fraction and a UF retentate fraction; (ii) nanofiltering the UF permeate fraction to produce an NF permeate fraction and an NF retentate fraction; (iii) subjecting the NF permeate fraction to a reverse osmosis step to produce an RO permeate fraction and an RO retentate fraction; and (iv) combining at least two of the UF retentate fraction, the RO permeate fraction, the RO retentate fraction, and a fat-enriched fraction to form the dairy composition.

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