HOLLOW FIBER MEMBRANE FOR FILTRATION OF LIQUIDS

Abstract

The present invention provides an intrinsically anti-microbial hollow fiber membrane for filtration of liquids. The membrane comprises a plurality of porous hollow bilayer membrane fibers wherein the liquid enters from outside of the fiber, passing through the porous membrane into the lumen of the fiber and coming out from the hollow ending of the fiber, wherein this configuration provides a liquid outside-in arrangement and retains the filtrate outside. It means that membrane of the invention has built in characteristics to act against microbes in order to provide the use with a safe liquid free from microbes. The outer side or outer wall of the hollow fibers may be configured to become hydrophobic whereas inner side or inner wall of the hollow fiber membrane may be configured to become hydrophilic to enhance the water permeability to a great extent. The hollow fiber membrane may be configured to give it an intrinsic anti-microbial capability. A device containing above said membrane has also been disclosed.

Claims

1-44. (canceled)

45. An intrinsically anti-microbial hollow fiber membrane for filtration of liquids comprising a plurality of porous hollow membrane fibers, wherein liquid enters from outside of the fiber membrane and passes through the porous membrane fibers into and along a lumen of the fibers, thereby retaining filtrate outside of the membrane and filtered liquid flows out from a hollow end of the fiber.

46. The intrinsically anti-microbial hollow fiber membrane of claim 45, wherein the hollow fibers are: (a) formed from a polymer or a polymer mixture; and/or (b) intrinsically antimicrobial in nature.

47. The intrinsically anti-microbial hollow fiber membrane of claim 45, wherein the fibers comprise: (a) 12% to 25% polyethersulfone, of from 5 to 20% polyvinylpyrrolidone, of from 70% to 90% N-methyle pyrrolidone solution and of from 10% to 45% polyethylene glycol; (b) 10%-25% polysulfon and from 5% to 15% polyvinyl pyrrolidone; (c) 3%-25% polyethersulfon and from 5% to 15% polyvinyl pyrrolidone; or (d) the fibers comprise polycarbonates, polyamides, and aqueous isopropyl or any combination thereof.

48. The intrinsically anti-microbial hollow fiber membrane of claim 45, wherein the fibers form: (a) a single layer membrane, the single layer membrane being either hydrophobic or hydrophilic; (b) a membrane comprising more than one layer; or (c) a double layer membrane, the double layer membrane being either hydrophobic or hydrophilic.

49. The intrinsically anti-microbial hollow fiber membrane of claim 48, wherein the outer side or wall of the membrane layer is hydrophobic and the inner side layer or wall is hydrophilic.

50. The intrinsically anti-microbial hollow fiber membrane according to claim 45, wherein the hydrophobic layer: (a) reduces air trappings and suction pressure requirements; (b) increases liquid flux; and/or (c) maintains a capillary action of the liquid through the pores on fiber walls towards the hollow cavity of the fibers and decreases suction pressure or passage pressure or gravitational head requirements.

51. The intrinsically anti-microbial hollow fiber membrane according to claim 45, wherein the liquid flows with: (a) outside-in orientation; or (b) inside-out orientation.

52. The intrinsically anti-microbial hollow fiber membrane according to claim 45, wherein the filtrate is retained outside of the membrane.

53. The intrinsically anti-microbial hollow fiber membrane according to claim 45, wherein the membrane: (a) is washable; (b) comprises fibers having a porosity range from 80% to 90% by volume of fiber wall; (c) comprises pores ranging from 0.1 nm to 25 nm in diameter; and/or (d) comprises pores having a diameter ranging from 50 nm to 150 nm for usage under suction.

54. The intrinsically anti-microbial hollow fiber membrane according to claim 45, wherein the hollow fibers form a U-shaped membrane module with open ends where liquid enters the membrane for filtration and filtered liquid comes out through the open ends of fibers.

55. The intrinsically anti-microbial hollow fiber membrane according to claim 54, wherein: (a) substantially all or all of the externally facing surface of each fiber includes an anti-microbial substance within the substance of the polymer or polymer mix; or (b) substantially all or all of the luminal facing surface of each fiber is free of an anti-microbial substance within the substance of the polymer or polymer mix.

56. The intrinsically anti-microbial hollow fiber membrane according to claim 55, wherein: (a) the antimicrobial substance comprises a metal oxide, metal salt or metal; (b) the antimicrobial substance is embedded in the polymer or polymer mix; (c) an embedded polymer or polymer mix is from 2-5% by weight of the fiber.

57. A process of making an intrinsically anti-microbial hollow fiber membrane comprising the steps of: I) a) mixing a polymer or a polymer mix with a pore former comprising polyethylene glycol (PEG); and b) passing the mixture produced in step a) through a spinneret together with a non-solvent for the polymers; or comprising the steps of; II) a) mixing an antimicrobial substance embedded polymer or antimicrobial substance embedded polymer mix with a polymer or a polymer mix absent of an antimicrobial substance and with a solvent for both polymers; and b) passing the mixture produced in step II) a) through a spinneret together with a nonsolvent for the polymers.

58. A process according to claim 57, wherein: (i) step b) is carried out at a temperature of from 25 to 80 C.; and/or (ii) the spinneret operates at a speed of from 350 rpm to 600 rpm.

59. A process according to claim 57, wherein: (a) the antimicrobial substance is a metal oxide, metal salt or meta; and/or (b) the embedded polymer or polymer mix is from 2-5% by weight of total polymers in the mixture formed in step a).

60. The intrinsically anti-microbial hollow fiber membrane according to claim 55, wherein: (a) the polymer or polymer mix absent of an antimicrobial substance is from 95-98% by weight of the fiber; and/or (b) the antimicrobial substance embedded polymer is polyethersulfon and the polymer or a polymer mix absent of an antimicrobial substance is polyethersulfon, the polymers being provided in a 3% to 97% weight ratio.

61. A process according to any of claim 57, wherein: (a) the polymer or polymer mix with the anti-microbial substance and absent the anti-microbial substance is the same polymer or polymer mix; (b) the antimicrobial substance has metal oxide particles embedded therein through cross-linking between polymeric chains; and/or (c) the process produces intrinsically anti-microbial hollow fiber membranes comprising a plurality of porous hollow membrane fibers wherein liquid enters from outside of the fiber membrane and passes through the porous membrane into and along a lumen of the fibers, thereby retaining filtrate outside of the membrane and filtered liquid flows out from a hollow end of the fiber.

62. A device for liquid filtration comprising a hollow fiber membrane as claimed in claim 45, wherein the membrane is placed in a housing with: (a) at least one feed channel and at least one drain channel; wherein the hydrophilic layer of membrane maintains a capillary action of the liquid through the holes on fiber walls towards the hollow cavity of fibers and decreases suction pressure or passage pressure or gravitational head requirements; or (b) multiple openings for inlet, outlet, and backflush drains, wherein the hydrophilic layer of the membrane maintains a capillary action of the liquid through the holes on fiber walls towards the hollow cavity of fibers and decreases suction pressure or passage pressure or gravitational head requirements.

63. The process of making an intrinsically anti-microbial hollow fiber membrane according to claim 57, wherein: (a) the polymer or a polymer mix absent of an antimicrobial substance is from 95-98% by weight of the fiber; and/or (b) the antimicrobial substance embedded polymer is polyethersulfon and the polymer or a polymer mix absent of an antimicrobial substance is polyethersulfon, the polymers being provided in a 3% to 97% weight ratio.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The present invention is now described, by way of example only, and with reference to the following figures

[0078] FIG. 1 depicts hollow fibers (2), fibers ends sealed and potted (3), and potting module (4).

[0079] FIG. 2 depicts nano pores on a fiber wall and through which a liquid enters the lumen of the hollow fiber (1), and hollow fibers (2).

[0080] FIG. 3 depicts nano pores on a fiber wall and through which a liquid enters the lumen of the hollow fiber (1), filtered liquid (5), cavities in fiber walls (6), hydrophilic layer (7), meeting point of both layers (8), space created between liquid and fiber due to hydrophobic layer (9), coarse particles, impurities, contaminations (10), hydrophobic layer facing unfiltered liquid (11), and unfiltered liquid (12)

[0081] FIG. 4 depicts nano pores on fiber walls through which a liquid is entered (1), hollow fibers (2), fibers ends sealed and potted (3), potting module (4), filtered liquid (5), cavities in fiber walls (6), ,hydrophilic layer (7), meeting point of both layers (8), space created between liquid and fiber due to hydrophobic layer (9), coarse particles, impurities, contaminations (10), hydrophobic layer facing unfiltered liquid (11), and unfiltered liquid (12).

[0082] FIG. 5 depicts ends of hollow fibers from which filtered liquid comes out (13), potting module wall (14), and the sealant between the fiber ends (15).

[0083] FIG. 6 depicts a SEM Picture of the fiber wall thickness close-up.

[0084] FIG. 7 depicts a SEM Picture of the fiber wall thickness in whole cross section.

[0085] FIG. 8 depicts a chart of the water flux over time derived from a study of 10 membranes made according to the present invention

[0086] FIG. 9 depicts the results of an antibacterial study of the fiber material of the present invention.

[0087] FIG. 10 depicts representation of the Flux behavior of the membrane sample-1 corresponding to the data in Table named under column HF Membrane Flux summary, the sample was tested for PWP and CWF, the graph is extracted from for FIG. 8 for the purpose of clarity. The graph shows that the initial PWP reading was recorded at 2400 LMH and then normalizing at 800 LMH.

[0088] FIG. 11 depicts representation of the Flux behavior of the membrane sample-2 corresponding to the data in Table named under column HF Membrane-2 Flux summary, the sample was tested for PWP and CWF, the graph is extracted from for FIG. 8 for the purpose of clarity. The graph shows that the initial PWP reading was recorded around 1800 LMH and then normalizing at a reading a little above 900 LMH.

[0089] FIG. 12 depicts representation of the Flux behavior of the membrane sample-3 corresponding to the data in Table named under column HF Membrane-3 Flux summary, the sample was tested for PWP and CWF, the graph is extracted from for FIG. 8 for the purpose of clarity. The graph shows that the initial PWP reading was recorded at 1900 LMH and then normalizing at 900 LMH.

[0090] FIG. 13 depicts representation of the Flux behavior of the membrane sample-4 corresponding to the data in Table named under column HF Membrane-4 Flux summary, the sample was tested for PWP and CWF, the graph is extracted from for FIG. 8 for the purpose of clarity. The graph shows that the initial PWP reading was recorded around 1800 LMH and then normalizing at a reading at around 880 LMH.

[0091] FIG. 14 depicts representation of the Flux behavior of the membrane sample-5 corresponding to the data in Table named under column HF Membrane-5 Flux summary, the sample was tested for PWP and CWF, the graph is extracted from for FIG. 8 for the purpose of clarity. The graph shows that the initial PWP reading was recorded around 2200 LMH and then normalizing at a reading a little above 700 LMH.

[0092] FIG. 15 depicts representation of the Flux behavior of the membrane sample-6 corresponding to the data in Table named under column HF Membrane-6 Flux summary, the sample was tested for PWP and CWF, the graph is extracted from for FIG. 8 for the purpose of clarity. The graph shows that the initial PWP reading was recorded around 1800 LMH and then normalizing at a reading around 1000 LMH.

[0093] FIG. 16 depicts representation of the Flux behavior of the membrane sample-7 corresponding to the data in Table named under column HF Membrane-7 Flux summary, the sample was tested for PWP and CWF, the graph is extracted from for FIG. 8 for the purpose of clarity. The graph shows that the initial PWP reading was recorded around 1930 LMH and then normalizing at a reading around 920 LMH.

[0094] FIG. 17 depicts representation of the Flux behavior of the membrane sample-8 corresponding to the data in Table named under column HF Membrane-8 Flux summary, the sample was tested for PWP and CWF, the graph is extracted from for FIG. 8 for the purpose of clarity. The graph shows that the initial PWP reading was recorded around 2100 LMH and then normalizing at a reading around 780 LMH.

[0095] FIG. 18 depicts representation of the Flux behavior of the membrane sample-9 corresponding to the data in Table named under column HF Membrane-9 Flux summary, the sample was tested for PWP and CWF, the graph is extracted from for FIG. 8 for the purpose of clarity. The graph shows that the initial PWP reading was recorded around 2370 LMH and then normalizing at a reading a little above 800 LMH.

[0096] FIG. 19 depicts representation of the Flux behavior of the membrane sample-10 corresponding to the data in Table named under column HF Membrane-10 Flux summary, the sample was tested for PWP and CWF, the graph is extracted from for FIG. 8 for the purpose of clarity. The graph shows that the initial PWP reading was recorded around 1800 LMH and then normalizing at a reading of 900 LMH.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0097] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The aspects and features of the present invention and methods for achieving the aspects and features will be apparent by referring to exemplary embodiments to be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the exemplary embodiments disclosed hereinafter but can be implemented in various forms. The matters defined in the description, such as the detailed construction and elements, are nothing but specific details provided to assist those of ordinary skill in the art in a comprehensive understanding of the invention, and the exemplary embodiments are only defined within the scope of the appended claims. In the drawings, sizes and relative sizes of layers and areas may be exaggerated for clarity in explanation.

[0098] The term on that is used to designate that an element is on another element located on a different layer or a layer includes both a case where an element is located directly on another element or a layer and a case where an element is located on another element via another layer or still another element. By contrast, the term directly on means that an element is directly on another element or a layer without the intervention of any other element or layer. In the entire description of the present invention, the same drawing reference numerals are used for the same elements across various figures. Also, the term and/or includes the respective described items and combinations thereof.

[0099] Spatially relative wordings below, beneath, lower, above, upper, and so forth, as illustrated in the drawings, may be used to facilitate the description of relationships between an element or constituent elements and another element or other constituent element. The spatially relative wordings should be understood as wordings that include different directions of the element in use or operation in addition to the direction illustrated in the drawings.

[0100] In the following description of the present invention, an exemplary embodiment of the present invention will be described with reference to plane views and sectional views which are ideal schematic views. The form of exemplary views may be modified due to manufacturing techniques and/or allowable errors. Accordingly, the exemplary embodiments of the present invention are not limited to their specified form as illustrated but include changes in the form being produced according to manufacturing processes. Accordingly, areas exemplified in the drawings have rough properties, and the shapes of areas in the drawings are to exemplify specified forms of areas of elements but do not limit the scope of the present invention.

[0101] Hereinafter, A representative example of the structure of the hollow fiber filter membrane (hereinafter sometimes referred to as merely membrane) of the present invention will be explained referring to the accompanying drawings. FIG. 1 is an enlarged photograph of a cross section perpendicular to the lengthwise direction of the membrane, and FIG. 2 is an enlarged photograph of the inner surface of the membrane.

[0102] The membrane of the present invention is formed from a number of hollow fibers, each having an inner surface and an outer surface, and comprises a network structure which integrally continues from one surface (e.g., the inner surface) to another surface (e.g., the outer surface) as shown in FIG. 3. The network structure in the membrane has no vacant portions of the polymer such as a finger-shaped structure layer having cavities and a void layer.

[0103] The membrane of the present invention comprises a network structure having an anisotropy in pore diameter, such that the membrane has a layer with a lower average pore diameter of pores present therein (hereinafter referred to as average pore diameter of the outer surface) in the outer surface or near the outer surface compared to the average pore diameter of pores present in the inner surface of the membrane (hereinafter referred to as average pore diameter of inner surface). The pore diameter generally becomes gradually greater toward the inner surface of the membrane form that towards the outer surface of the membrane. According to an embodiment of the invention, it is ensured that more than 99% of the pores are of the size of mentioned diameter on the outer surface (hereinafter referred to as average pore diameter of outer surface).

[0104] The membrane of the present invention has a void content of 70-90% when the material of the membrane is polyethersulfone and depending on the void content, the breaking stress IS in the range of 2 to 3.5bar and the breaking elongation is up to 70%.

[0105] As materials which constitute the hollow fiber membrane of the present invention, mention may be made of, for example, polysulfone polymers, polyethersulfone, polyvinylidene fluoride polymers, polyacrylonitrile polymers, polymethacrylic acid polymers, polyamide polymers, polyimide polymers, polyetherimide polymers, and cellulose acetate polymers. Especially preferred are aromatic polysulfones, polyacrylonitrile copolymers, polyvinylidene fluoride, and aromatic polyetherimides. A type polyethersulfone is especially preferred.

[0106] In a further aspect of the present invention, there is also described a filtering device for liquid filtration comprising a hollow fiber membrane of the invention wherein the membrane is placed in a housing with at least one feed channel and at least one drain channel. According to the device of the invention, the hydrophilic layer of membrane maintains a capillary action of the liquid through the holes on the fiber walls towards the hollow cavity of fibers and decreases the requirement of suction pressure or passage pressure or gravitational head.

[0107] The intrinsically anti-microbial hollow fiber membrane is produced by spinning the polymer mixture at high speed revolutions to place the said polymer mixture at the circumference of the base polymers, wherein the polymer mixture comprising of 3% of antimicrobial embedded polyethersulfon 6020 p in base polyethersulfon that does not include an antimicrobial substance which gives around 99.9% surface area of the finished product as antimicrobial. As the antimicrobial embedded polymer has higher density, the centrifugal force pushes it out-wards and places it at the circumference of the base polymer which reduces the cost of production of a product. The antimicrobial polymer is chemically developed by embedding the metal oxide particles in polymers through cross-linking between the polymeric chains. This produces an intrinsically antimicrobial polymer where the susbtances imparting antimicrobial properties never leach out and never migrate from the polymer to any other substance in contact.

[0108] Examples of the present invention will be shown below, but the present invention is not limited to these examples. Methods for the measurement of properties are as follows:

[0109] The hollow fiber membranes used as samples for measurement are all in the state of being sufficiently impregnated with water. As for the membrane obtained by using polyvinyl pyrrolidone as an additive, the membrane was dipped in an aqueous sodium hypochlorite solution and then washed with hot water to make a membrane in which substantially no polyvinyl pyrrolidone was present.

[0110] Water permeation of the hollow fiber membrane was expressed by the amount of filtered water when ultrafiltration water of 25.degree. C. was allowed to permeate through a sample of the hollow fiber.

EXAMPLE 1

[0111] Although preferred embodiments of the present invention have been described for illustrative purposes, it will be apparent to those skilled in the art that various modifications, additions and substitutions can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

[0112] The device of the present invention is an intrinsic anti-microbial hollow fiber membrane. The membrane received an intrinsic change on a micrometrical scale which results in antiseptic and antibacterial characteristics. The adhesion and proliferation of bacteria on the surface of the object are slowed down and the microbes and bacteria count is being strongly reduced. This antiseptic/anti-microbial nature of the material is the intrinsic property of the membrane polymer and never migrates/leaches with filtered liquid and never diminishes with use/time.

[0113] The hollow fiber consists of two layers. The outer layer is hydrophobic and the inner layer is hydrophilic by nature. The hydrophobic layer never allows the water to come in physical contact with membrane hence stops any adherence of any kind on it. Hydrophobic layer makes the air trappings minimum as the outside-in passage of air is facilitated by the absence of water layer on the outside hence decreasing the suction pressure requirement and increasing the flux of liquid. While the inner hydrophilic layer maintains a capillary action of the liquid through the holes on fiber walls towards the hollow cavity of fibers hence decreasing the requirement of suction pressure or passage pressure or gravitational head. The liquid flows in outside-in orientation i.e. filtration happens when liquid from the outside of the fiber wall passes through its hole and filtered liquid comes out of the hollow ending of the fiber. Hence keeping the unfiltered liquid outside the fiber walls and retaining the filtered liquid inside the hollow fiber. Making it the only membrane used with outside-in direction of flow while having a hydrophobic layer on its outside and a hydrophilic layer on its inside.

[0114] Fibers can have pores ranging from 0.1 nm to 25 nm in its walls. The liquid especially water is filtered when it passes to the hollow cavity of fiber from the holes in its walls from the outside of the fiber. The fibers make U-shaped membrane modules with open ends sealed and supported in such a way that U-shaped side always faces the liquid coming for filtration and filtered liquid always comes out through the open ends of fibers. The porosity of the fibers ranges from 70% to 90%.

[0115] The anti-microbial embedded polymer is developed by chemically bonding metal oxide particles in polymer ultrason Polyethersulfon (A BASF brand), which produces an intrinsically antimicrobial polymer in which the antimicrobicity never leaches out and never migrates from the polymer to any other substance come in contact with the surface of the polymer unlike the existing antimicrobial membranes on which antimicrobicity has been created by coating the surface with an antimicrobial substance which may leaches out and contaminate the substance which comes into contact with it. Polyethersulfon is the polymer of which the hollow fibers of the membrane are made.

[0116] The porosity is achieved during the hollow fiber membrane manufacturing process. The process involves the use of 2 tanks connected to the spinneret via gear-pump assisted flow tubes. The dope solution tank and the bore solution tank. The polymers are mixed with a solvent where they totally dissolve in the dope solution tank. As soon as the flow of both dope and bore solution (also called as the non-solvent) starts through the spinneret of the spinning machine the process of phase inversion starts (the polymer that was dissolved in the solvent now will start to solidify). This phenomenon can be explained by the simple process of mass-transfer, as soon as the non-solvent and solvent come in contact the interaction between them acts as the driving force to push the dissolved base polymer out of the solvent and hence it starts to solidify again. During this process the pores are created because the instantaneous (very short, takes less than a second) de-mixing the time period too short for the polymer to solidify completely and hence as the polymer starts to come out of the solvent and solidify, the instantaneous nature of de-mixing renders some discontinuities in the solidifying polymeric structure and these discontinuities (spaces) are ultimately the pores and all these pores combined to give the porosity to the fiber. The process of fiber formation is carried out at 50 degrees Celsius at atmospheric pressure with the spinneret operating at 500 rpm. 3% by weight of the total polymer is formed from the antimicrobial embedded polymer, whilst 97% is antimicrobial substance absent polymer.

EXAMPLE 2:PORE FORMATION

[0117] A dope solution/polymer solution was made by combining the components in the table below. To this, the below described bore solution/inner solution was added and the combination thoroughly mixed. This mixture was then passed through a spinneret along with water in order to form hollow fibers. [0118] 1. In the process of making dope solution, low molecular weight additives (such as LiCl etc) should be added first in the solvent with constant agitation and at 50 C. [0119] 2.Gradually, additives with the higher molar masses (such as PEG, PVP etc) should be introduced into the solvent at constant stirring. [0120] 3. Lastly, the base polymer (such as PES, PSU etc.) will be introduced in the dope solution under the constant stirring and at 80 C. for approx. three hours. [0121] 4. Dope solution will only be considered ready for spinning, until all the additives and the base polymer is homogenously dissolved in the solvent. The dope solution should be in one phase before spinning along with the absence of any air bubbles and foreign particles. [0122] 5. Dope solution should be left overnight or for sufficient amount of time, without agitation, in order to remove the air bubbles, generate during stirring. [0123] 6. The spinneret temperature should be at room temperature but the temperature of the coagulant liquid should be at 50 C. [0124] 7. The bore liquid can be either pure PEG or a mixture of PEG:Water 9:1 or NMP:Water 9:1.

TABLE-US-00001 Dope Solution/Polymer Solution (% by Bore Solution/Inner volume) Solution Coagulant PES 15% PEG:Water 100% Water Polyethersulone (9:1) (Ultrason E6020P) PEG 38% (Polyethylene glycol) LiCl (Lithium Chloride) 1.5% H2O 2% NMP (N-methyl-2- Pyrrolidone) 43.5%

[0125] It has been found that fibers produced according to the above process, through testing and benchmarking the performance of these fibers, are superior as compared to the fibers available currently at disposal or cited in the prior arts. The PWP and CWF values are higher then what usually are reported for such fibers in the published literature. PWP value of 1800 Lmh and CWF value of 900 Lmh for fibers with 20 nm pore size is higher than those compared to the Hollow fiber membranes for ultra-filtration.

[0126] When PEG is used as the bore solution and as a pore former in the dope, it is believed due to its high viscosity and flowing behavior, it has been observed to impart properties to the nascent fibers in terms of morphology. In particular, the fibers tend to have a well pronounced finger-like pore structures, hence having straight and well-pronounced channels along the thickness of the fiber as seen in the FIG. 6 and FIG. 7, the picture of the wall thickness taken with a Scanning Electron Microscope (SEM) when the fiber is observed with the instrument with its cross-section facing the observer.

[0127] The Pure Water Permeation and Critical Water Flux for the fibers made according to the above method were then established.

[0128] Pure Water Permeability (PWP): The pure water permeability, also known as the pure water flux is defined as the volume of water that passes through a membrane per unit time, per unit area and pre-unit of transmembrane pressure. This property indicates the effort required to generate permeate for a membrane and can be used to compare the initial performance of a membrane. This analysis does not, however, provide any guidance as to the performance of the material for extended periods of time and so it is also useful to look at Critical Water Flux.(see Persson, Kenneth M., Vassilis Gekas, and Gun Trgrdh. Study of membrane compaction and its influence on ultrafiltration water permeability. Journal of membrane science 100, no. 2 (1995): 155-162.)

[0129] Critical Water Flux (CWF): Either as the flux at which the transmembrane pressure (TMP) starts to deviate from the pure water line (the strong form of critical flux) or as the first permeate flux for which irreversible fouling appears on the membrane surface. The critical flux can be generally defined as the first permeate flux for which fouling becomes predominant; being then well differentiated from limiting flux (the last flux reachable). (see Bacchin, Patrice, Pierre Aimar, and Robert W. Field. Critical and sustainable fluxes: theory, experiments, and applications. Journal of membrane science 281, no. 1-2 (2006): 42-69).

[0130] 10 separate samples of the fibers made according to the above methodology were created and used to form 10 separate membranes. The membranes were tested to establish their PWP and CWF. The membranes formed were tested for their PWP and CWF by: Pure water flux experiments were performed using deionized water. Each module was immersed in deionized water for 24 h, and run in the test system for 1 h, to eliminate the effect of the residual glycerol on the hollow-fiber membranes before any sample collection. A UF experimental unit designed to evaluate the PWP and protein rejection is shown in detail (Please see: C. S. Feng, B. Shi, G. Li, Y. Wu, Preparation and properties of microporous membrane from polyvinylidene fluoride cotetrafluoroethylene) (F2.4) for membrane distillation, J. Membr. Sci. 237 (2004) 15-24.). A transmembrane pressure of 1 bar and feed solution temperature of 20 C., all experiments were performed in hollow-fiber modules with crossflow mode. Two modules were prepared for each hollow-fiber sample. Pure water permeation fluxes (PWP) were obtained as follows:

[0131] When the pure water is passed through the membrane and readings calculated using the equation above each value is tabulated and a graph between time and the readings is plotted. For the prolonged or extended period of time (in our case more than 5 hours) the PWP value begins to stabilize signifying the CWF value for the membrane at this point. The apparatus used for carrying out the PWP tests on the fibers can be represented by the following schematic:

[0132] The results and essential conditions for the test are provided in Table 1 below. The test was carried out at STP.

TABLE-US-00002 TABLE 1 The table enlists the data recorded during for the PWP test performed on the 10 hollow fiber membrane samples prepared. Flux Tables -5 pairs from 10 samples PakVitae's lab in Singapore HF membrane flux summary Unit No Date 05.03.2019 Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-1 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14 Length of Fibers (mm) 180 180 180 180 180 ID (Reading under NUS x5, NUS Lab) 15 15 15 15 15 OD (Reading under NUS x5, NUS Lab) 25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.500 0.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.00396 0.00396 Total Duration Time (mins) 0 30 60 90 120 PUB water permeability g/m 785 507 355 303 270 (g/min) Times mins 5 5 5 5 5 PUB Water Flux LMH 2380 1540 1080 920 820 (LMH-Bar) Average Water Flux (LMH-Bar) 1350 PakVitae's lab in Singapore HF membrane 2 flux summary Unit No Date 05.03.2019 Inlet Pressure (bar) 1 1 1 1 Fiber ID Fiber-2 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 Length of Fibers (mm) 180 180 180 180 ID (Reading under NUS x5, NUS Lab) 15 15 15 15 OD (Reading under NUS x5, NUS Lab) 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.00396 Total Duration Time (mins) 0 60 90 120 PUB water permeability g/m 589 406 352 308 (g/min) Times mins 5 5 5 5 PUB Water Flux LMH 1790 1230 1070 930 (LMH-Bar) Average Water Flux (LMH-Bar) 1260 PakVitae's lab in Singapore HF membrane 3 flux summary Unit No Date 10.03.2019 Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-3 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14 Length of Fibers (mm) 180 180 180 180 180 eading under NUS x5, NUS Lab) 15 15 15 15 15 eading under NUS x5, NUS Lab) 25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.500 0.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.00396 0.00396 Total Duration ime (mins 0 30 60 90 120 PUB water permeab g/m 630 545 466 392 295 Times mins 5 5 5 5 5 PUB Water Flux (LM LMH 1910 1655 1415 1190 895 Average Water Flux (LMH-Bar) 1415 PakVitae's lab in Singapore HF membrane 4 flux summary Unit No Date 10.03.2019 Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-4 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14 Length of Fibers (mm) 180 180 180 180 180 eading under NUS x5, NUS Lab) 15 15 15 15 15 eading under NUS x5, NUS Lab) 25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.500 0.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.00396 0.00396 Total Duration ime (mins 0 30 60 90 120 PUB water permeab g/m 596 522 443 374 286 Times mins 5 5 5 5 5 PUB Water Flux (LM LMH 1810 1585 1345 1135 870 Average Water Flux (LMH-Bar) 1350 PakVitae's lab in Singapore HF membrane 5 flux summary Unit No Date 15.03.2019 Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-5 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14 Length of Fibers (mm) 180 180 180 180 180 eading under NUS x5, NUS Lab) 15 15 15 15 15 eading under NUS x5, NUS Lab) 25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.500 0.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.00396 0.00396 Total Duration ime (mins 0 30 60 90 120 PUB water permeab g/m 730 645 524 409 240 Times mins 5 5 5 5 5 PUB Water Flux (LM LMH 2215 1955 1590 1240 730 Average Water Flux (LMH-Bar) 1550 PakVitae's lab in Singapore HF membrane 6 flux summary Unit No Date 15.03.2019 Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-6 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14 Length of Fibers (mm) 180 180 180 180 180 eading under NUS x5, NUS Lab) 15 15 15 15 15 eading under NUS x5, NUS Lab) 25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.500 0.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.00396 0.00396 Total Duration ime (mins 0 30 60 90 120 PUB water permeab g/m 598 425 409 366 324 Times mins 5 5 5 5 5 PUB Water Flux (LM LMH 1815 1290 1240 1110 985 Average Water Flux (LMH-Bar) 1290 PakVitae's lab in Singapore HF membrane 7 flux summary Unit No Date 20.03.2019 Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-7 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14 Length of Fibers (mm) 180 180 180 180 180 eading under NUS x5, NUS Lab) 15 15 15 15 15 eading under NUS x5, NUS Lab) 25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.500 0.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.00396 0.00396 Total Duration ime (mins 0 30 60 90 120 PUB water permeab g/m 643 518 416 372 312 Times mins 5 5 5 5 5 PUB Water Flux (LM UMH 1950 1570 1260 1130 945 Average Water Flux (LMH-Bar) 1370 PakVitae's lab in Singapore HF membrane 8 flux summary Unit No Date 20.03.2019 Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-8 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14 Length of Fibers (mm) 180 180 180 180 180 eading under NUS x5, NUS Lab) 15 15 15 15 15 eading under NUS x5, NUS Lab) 25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.500 0.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.00396 0.00396 Total Duration ime (mins 0 30 60 90 120 PUB water permeab g/m 707 556 416 325 251 Times mins 5 5 5 5 5 PUB Water Flux (LM UMH 2140 1690 1260 990 760 Average Water Flux (LMH-Bar) 1360 PakVitae's lab in Singapore HF membrane 9 flux summary Unit No Date 25.03.2019 Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-9 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14 Length of Fibers (mm) 180 180 180 180 180 eading under NUS x5, NUS Lab) 15 15 15 15 15 eading under NUS x5, NUS Lab) 25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.500 0.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.00396 0.00396 Total Duration ime (mins 0 30 60 90 120 PUB water permeab g/m 784 406 354 303 275 Times mins 5 5 5 5 5 PUB Water Flux (LM LMH 2370 1230 1070 920 830 Average Water Flux (LMH-Bar) 1290 PakVitae's lab in Singapore HF membrane 10 flux summary Unit No Date 25.03.2019 Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-10 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14 Length of Fibers (mm) 180 180 180 180 180 eading under NUS x5, NUS Lab) 15 15 15 15 15 eading under NUS x5, NUS Lab) 25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.500 0.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.00396 0.00396 Total Duration ime (mins 0 30 60 90 120 PUB water permeab g/m 674 515 364 305 292 Times mins 5 5 5 5 5 PUB Water Flux (LM LMH 2040 1560 1100 920 890 Average Water Flux (LMH-Bar) 1300 indicates data missing or illegible when filed

[0133] Table 2 provides a summary of the Pure Water Flux established over 5-minute intervals over a 120 minute period for each of the membranes. The results are also charted in FIG. 8

TABLE-US-00003 TABLE 2 Sample-3 Sample-4 Sample-5 Sample-6 Sample-7 Sample-8 Sample-9 Sample-10 Sample-1 LMH Sample-2 LMH LMH LMH LMH LMH LMH LMH LMH LMH 2380 1790 1910 1810 2215 1815 1950 2140 2370 2040 1540 1270 1655 1585 1955 1290 1570 1690 1230 1560 1080 1230 1415 1345 1590 1240 1260 1260 1070 1100 920 1070 1190 1135 1240 1110 1130 990 920 920 820 930 895 870 730 985 945 760 830 890

[0134] From these results, it can be seen that there is a good level of consistency across each of the samples. It can also be concluded that the initial PWP readings are higher as compared to the conventional fibers, although over the prolonged testing the PWP readings tend to decline and stabilize at a point (where the graph tends to become straight and have a constant slope) which is designated as the CWF for the respective membrane and CWF is the parameters which is used as the design factor when such membranes are used in their practictal applications. However it can be seen that for all the samples the CWF is in the range of 800 to 900 Lmh, which again is an advantageous property of the fibers describes in the present invention, as it will require less pressure to permeate the same amount of water through these fiber as compared to the conventional ones, hence saving costs.

EXAMPLE 3: TESTING FOR THE ANTIMICROBIAL NATURE OF THE MEMBRANE FIBER SURFACE

[0135] A membrane was provided with hollow fibers made according to Example 2, but with zinc salt embedded within the polymer. The principal polymer for fiber making, in our case polyethersulfuone is modified using the salts of Zinc such as Zinc Pyrithione and etc. The modification is done based on the methods described in the patent U.S. Pat. No. 9,527,918.

[0136] The membrane was then tested for its ability to inhibit two types of bacterial strains (Escherichia Coli ATCC 8739 (Gram) and Staphylococcus Aureus 6538 (Gram+)) using the standard international method for evaluating the antibacterial of the polymer surfaces.

[0137] The results can be found in the images of bacterial cultures grown on the Petri dishes and shown in the FIG. 9. The results are provided below.

[0138] The membrane was then tested for its ability to inhibit two types of bacterial strains (Escherichia Coli ATCC 8739(Gram) and Staphylococcus Aureus 6538 (Gram+)) using the standard international method for evaluating the antibacterial of the polymer surfaces. The results can be found in the images of bacterial cultures grown on the Petri dishes and shown in the FIG. 9. The results are provided below.

TABLE-US-00004 TABLE 3 Initial Incubation Control Spun Microbial inoculum at 37 inoculum polymeric Reduction Strains (cfu/ml) degree (cfu/ml) fiber log Reduction % Escherichia Coli 2.5 10.sup.6 Celsius for 6.2 10.sup.7 1.0 10.sup.4 3.1 99.9 Staphylococcus 1.7 10.sup.6 24 hours 2.5 10.sup.7 1.4 10.sup.4 2.9 99.9

[0139] As can be seen, the zone of inhibition for the tests carried out on the spun polymeric fiber (ie the polymer with zinc salt embedded therein) match the geometry of the fiber sample placed on the petri dish; representing an almost complete kill of the bacteria on the portions of the disk to which the fiber was applied. This is confirmed by the CFU/ml reduction presented in Table 3 for the initial inoculum compared to that calculated for the spun polymer fiber.

Test Method

[0140] A hollow fiber obtained by spinning the antibacterial polymer Polyethersulfone prepared as described above was tested to evaluate the effectiveness of the polymer against the main microbial strains defined by current legislation regarding plastic products intended to come into contact with the skin.

[0141] The product was tested for 2 types of bacterial strains (Escherichia Coli ATCC 8739 (Gram) and Staphylococcus Aureus ATCC 6538 (Gram+)) using the standard international method for evaluating the antibacterial activity of non-porous plastic surfaces. Moulded Initial Incubation Control polymer MICROBIAL inoculum at 37 C. inoculum item Reduction STRAINS (cfu/ml) for 24 h (cfu/ml) (cfu/ml) log Reduction % Escherichia 2.510.sup.66.210.sup.71.010.sup.70.79 83.87% coli Staphylococcus 1.710.sup.62.310.sup.71.410.sup.61.2 93.91% Aureus

[0142] The initial bacterial suspensions were diluted so as to obtain a known bacterial concentration expressed in colony forming units-cfu/ml. The fibers analyzed were duly sectioned in order to produce pieces of optimal dimensions for conducting the tests. These were treated with the reference microbial strains, covered with sterile polyethylene film and placed in an incubator at a temperature of 371 C. for 24 hours. At the end of the incubation period the samples were washed with neutralizing solution, on which the residual microbial count was determined.

[0143] The results obtained show that after 24 hours of incubation at 37 C. the polymer treated with zinc reduces the bacterial count by 83.870 (in the case of Escherichia coli) and 93.91% (in the case of Staphylococcus aureus).

FIG. 9. Explanation

[0144] As can be seen from the figure that there are 6 petri dishes in total in two sets of 3 each. The 3 on top have a substance impregnated with silver Nano-particles to give the substance a biocidal property and the 3 below have the sample extracted from the fiber surface of the present invention (spun hollow fiber membranes). It can be seen that the Nano-particles have leached out in the above 3 petri dishes migrating/leaching out of the substance to kill the bacteria around the sample. However the bacterial growth in the lower 3 petri dishes is only inhibited at the surface if the sample which substantiates the claim that the substance responsible for imparting antimicrobial property does not leach out of the material of the present invention.