WO2018234838A1 - Filtration medium, processes to produce it and uses thereof - Google Patents

Filtration medium, processes to produce it and uses thereof Download PDF

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Publication number
WO2018234838A1
WO2018234838A1 PCT/IB2017/000750 IB2017000750W WO2018234838A1 WO 2018234838 A1 WO2018234838 A1 WO 2018234838A1 IB 2017000750 W IB2017000750 W IB 2017000750W WO 2018234838 A1 WO2018234838 A1 WO 2018234838A1
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WO
WIPO (PCT)
Prior art keywords
filtration medium
medium according
filtration
polymer matrix
composition
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PCT/IB2017/000750
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French (fr)
Inventor
Leonardo CECCHINI
Renata REDONDO BONALDI
Tarcis BASTOS
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Rhodia Poliamida E Especialidades S.A.
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Application filed by Rhodia Poliamida E Especialidades S.A. filed Critical Rhodia Poliamida E Especialidades S.A.
Priority to PCT/IB2017/000750 priority Critical patent/WO2018234838A1/en
Publication of WO2018234838A1 publication Critical patent/WO2018234838A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
    • B01D65/08—Prevention of membrane fouling or of concentration polarisation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
    • B01D39/1607—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous
    • B01D39/1623—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous of synthetic origin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
    • B01D39/1692—Other shaped material, e.g. perforated or porous sheets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0079—Manufacture of membranes comprising organic and inorganic components
    • B01D67/00793—Dispersing a component, e.g. as particles or powder, in another component
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/26—Polyalkenes
    • B01D71/261—Polyethylene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/26—Polyalkenes
    • B01D71/262—Polypropylene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/48—Polyesters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
    • B01D2239/04—Additives and treatments of the filtering material
    • B01D2239/0442—Antimicrobial, antibacterial, antifungal additives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/15—Use of additives
    • B01D2323/21—Fillers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/48—Antimicrobial properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/56—Polyamides, e.g. polyester-amides

Definitions

  • the present invention is in the field of anti-microbial filtration media, notably of flexible polymeric anti-microbial filtration media, processes for manufacturing them and uses thereof for liquid and/or gas phase treatments, in particular for water-based phases treatments to prevent biofouling.
  • filtration systems are intended to retain, remove or neutralize microorganisms coming from air, gas or liquids.
  • Applications of filtration media can be found in industrial wastewater treatments, in ultrapure water production used for medical purposes, in electronics and in food processing, in drinkable water production processes, in ocean desalination processes, in industrial gases treatments and in residential air purification, among others.
  • Biofouling, biofilm or biological fouling is the gradual accumulation of microorganisms, plants, animals, algae, barnacles and protozoa on filtration wetted surfaces.
  • the main microorganisms responsible for biofouling are Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli but also algae, fungi, protozoa and viruses.
  • Membrane biofouling is a major problem encountered in membrane filtration processes, and it is a major factor in determining their practical application in water and wastewater treatment and in desalination in terms of technology and economics. Membrane biofouling leads to higher maintenance costs, lower efficiency and shorter service life. Membranes with high flux, high rejection, and low tendency for biofouling are most desired for use in emerging and conventional treatment processes that provide consistently high process performance, require few chemicals, and produce little waste.
  • MF microfiltration
  • UF ultrafiltration
  • NF nanofiltration
  • RO reverse osmosis
  • RO desalination is currently the most efficient and widely adopted process. However, it requires a great deal of energy to create the high pressures necessary to overcome the osmotic pressure of saline waters and there are often significant issues with disposal of brine resulting from the process. Therefore, technological advances in biofilm formation are needed to improve the energy efficiency, contaminant removal, and environmental impacts of the processes, as the biofilm formation interferes in the pressure of the membrane and increases the use of harmful chemicals to prevent and remove the biofilm.
  • a major challenge during operation of RO membranes is the deposition of colloidal materials and organic macromolecules on the membrane surface and the growth of microbes. This deposition leads to cake formation, irreversible adsorption, and growth of persistent biofilms, collectively referred to as biofouling. Fouling can cause a substantial increase in power consumption due to additional resistance to flow.
  • the conventional anti-fouling strategy has been to dose feed water continuously with biocides or antimicrobial substances. Biocide treatment must be followed by high velocity detergent cleaning and flushing to remove the organic debris.
  • Chlorine is the most widely used disinfectant in water and wastewater treatment. In many cases, chlorine (either as a gas or in the hypochlorite form) cannot be used for membrane treatment because most commercially available polymeric membranes are sensitive to chlorine; and due to the production of a large amount of Assimilable Organic Carbons (AOC) which leads to bacterial growth.
  • AOC Assimilable Organic Carbons
  • Hydraulic cleaning such as flushing and backwashing/back pulsing is the most common technique for mitigating fouling. Regular intermittent backwashing will lift the foulants off the membrane surface and minimize the extent of concentration polarization.
  • US2012168367A describes a water filter for treating tap water from a water supply, comprising a water inlet; a water outlet; and a filter cartridge.
  • the filter cartridge comprises several mixtures and layers based on mineral powders.
  • Far Infrared (FIR) ore powder is used to remove odor, color and organic contaminants.
  • Other layers have the role of reducing bacteria content (germanite layer) or to remove large particles and floating solids.
  • FIR Far Infrared
  • Other layers have the role of reducing bacteria content (germanite layer) or to remove large particles and floating solids.
  • This kind of filter does not suffer from biofilm formation as it is made of large ceramic grains which are not incorporated in a polymeric matrix. Therefore, it is not a thin flexible membrane and the performance is not impacted.
  • it has the drawback of not being applicable to small particle filtration such as UF, NF, MF and RO, where the biofilm formation causes above mentioned issues.
  • CN1460533A discloses an additive of multifunctional filter material that has the functions of resisting bacteria and decomposing harmful gas and organic pollutant, and can release negative ions. It is a liquid composition comprising a mineral mixture and a small amount of adhesive (10-20%), applied via spray in the filter medium to eliminate bacteria from the air. This solution is not appropriate for antibiofouling prevention because it is intended to reduce bacteria from the air and not to reduce the bacteria growing in the filter media. In addition, it has the drawback of being applied as a spray onto the filter, thus suffering from durability issues and prone to leakage, hence reducing the effectiveness.
  • the object of the present invention is to provide a flexible polymeric filtration layer, such as fabric, membrane or film, composed of aliphatic polymers like polyamide, polypropylene and polyesters, exhibiting water permeability and biofouling resistance, while maintaining good mechanical properties, to be suitably used as filtration medium for treating liquid and/or gas phases.
  • the invention described hereunder prolongs the service life of the filtration medium, and reduces maintenance costs. Furthermore, the invention also reduces the current use of biocides in this industry, thereby contributing to the respect of the environment.
  • the present invention thus relates to a filtration medium comprising at least one filtration layer consisting of a composition (C) comprising:
  • At least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 ⁇ , dispersed in the aliphatic polymer matrix (P).
  • the present invention also relates to processes for producing the filtration medium of the invention.
  • the filtration medium of the invention advantageously exhibits improved biofouling resistance, while preserving the mechanical properties, to be suitably used as anti-microbial and anti-fouling filtration media for various liquid, air and/or gas phases, in particular water-based phases.
  • the filtration media of the invention advantageously exhibits good wettability to be suitably used as filtration membrane for water-based phases.
  • filtration medium in the sense of the present invention is the generic term including the following articles: membranes, fabrics, films, nonwoven, fibers and composites.
  • filtration layer means any layer, generally thin or interface that moderates the permeation of chemical species in contact with it, said interface may contain pores of finite dimensions, as for porous membranes or fabrics, or even dense non-porous membranes or films, in which the selectivity is affected by the chemical molecular affinity.
  • aliphatic polymer in the sense of the invention excludes any aromatic polymers, fluoropolymers, or polysulfones.
  • the term "dispersed in the aliphatic polymer matrix" in the sense of the present invention means that the mineral compound(s) (M) are homogeneously distributed inside the polymeric material, and are not present at the surface only, like for coatings. Of course, some particles can be found at the surface but the probability to find them at the surface is equivalent to the probability to find them in the core of the polymer. Therefore, the mineral compounds(s) (M) are not removable and do not detach from the matrix during the service life.
  • the invention uses a polymeric composition (C) comprising an aliphatic polymer matrix (P).
  • the aliphatic polymer matrix (P) is selected from the group consisting of polyamides, polyolefins such as polypropylene and polyethylene, polyketones, polyesters such as polylacticacid, polyhydroxybutyrate; and also cellulose esters such as cellulose acetate. These polymers are widely available in the market for engineering applications. They are also cheaper and require less sophisticated processing steps than the specialty polymers such as polysulfone (PSU), fluoropolymers (eg. PVDF) and etc.
  • PSU polysulfone
  • PVDF fluoropolymers
  • Preferred polyamides are polyhexamethylene adipamide (PA66), polycaproamide (PA6), PA6.10, PA10.10 and PA12, copolymers in any proportions of these polymers, and blends between any of these polymers.
  • the polymer matrix consists of polypropylene, polyester or polyamide, most preferably polyamide.
  • Polyamide is preferably selected from polyamide 6, polyamide 66 and copolymers of polyamide 6/polyamide 66 in any proportions. Those polymers are commercially available. Those polymers allow higher amounts of mineral fillers to be incorporated in their matrix while maintaining good mechanical properties compared to aromatic polymers, fluoropolymers and polysulfones.
  • the polymeric composition according to the invention comprises at least one mineral compound (M) having properties of absorption and/or emission in the far infrared region ranging from 2 to 20 Mm.
  • the mineral compound(s) has (have) properties of absorption and/or emission in the far infrared region ranging from 3 to 20 ⁇ , and even more preferentially from 3 to 15 m.
  • the mineral compound(s) usable according to the invention can be chosen in particular from oxides, sulfates, carbonates, phosphates and silicates.
  • the oxide(s) is (are) chosen from titanium dioxide, silicon dioxide and magnesium oxide, more preferably titanium dioxide.
  • the sulfate(s) can advantageously be chosen from alkali metal and alkaline-earth metal sulfates, preferably from barium sulfate, calcium sulfate and strontium sulfate, more preferably barium sulfate.
  • the carbonate(s) is (are) advantageously chosen from calcium carbonate and sodium carbonate.
  • the silicate(s) is (are) chosen from actinolite, tourmaline, serpentine, kaolinite, and zirconium silicate, more preferably tourmaline.
  • the phosphate(s) can be chosen from zirconium phosphates, cerium phosphate and apatite, and mixtures thereof.
  • the composition (C) comprises an total amount of mineral compound (M) ranging from 1 % to 20%, preferably from 2% to 10%, more preferably from 3% to 6% by weight based on the total weight of the at least one aliphatic polymer matrix (P).
  • the composition (C) comprises at least two mineral fillers (M) dispersed in the aliphatic polymer matrix (P).
  • the composition (C) can comprise two or three mineral fillers (M) dispersed in the aliphatic polymer matrix (P).
  • At least one mineral compound (M) is a silicate, preferably selected from the group consisting of tourmaline, actinolite, serpentine, muscovite and kaolin, more preferably tourmaline.
  • at least a silicate is used in combination with at least one other mineral compound (M) that can be one or more oxides and/or one or more sulfates and/or one or more carbonates the total amount of this "at least one other mineral compound (M)" is comprised between 40% and 95% by weight, based on the total weight of the silicate.
  • composition (C) comprises two mineral fillers (M) being tourmaline and titanium dioxide.
  • This preferred composition has improved water permeability.
  • tourmaline and titanium dioxide are present in a mass ratio ranging from 40/60 to 95/5.
  • the mineral filler(s) (M) have advantageously a particle size ranging from 0.05 to 6 pm, preferably from 0.1 to 3 pm, most preferably 0.2 to 1 pm.
  • the advantages of particle size less than 1 ⁇ are less filtering media defects, less impact in the mechanical properties, better dispersion, higher surface active area, hence optimizing the amount needed to achieve the same benefit.
  • composition (C) may contain one or more additional components such as pore forming agents, nucleating agents, fillers, latent organic solvents, surfactants and the like.
  • Pore forming agents are typically added to the composition (C) when porous filtration layer is targeted in amounts usually ranging from 0.1 % to 30% by weight, preferably from 0.5% to 5% by weight.
  • Suitable pore forming agents are for instance polyvinylpyrrolidone (PVP) and polyethyleneglycol (PEG), with PVP being preferred.
  • Filtration media according to the invention can be a mono- or multi-layer system. It means it can be made from the filtration layer only plus optionally a substrate layer (mono), or the filtration layer of the filtration media can be associated to several other layers, such as substrate layer, optionally further intermediate layers and top layers (multi).
  • the filtration layer can be porous or dense.
  • porous means any physical path that moderates the permeation of liquids or gases, such as physical pores (e.g. voids) with finite dimensions, for instance in the case of fabrics or porous membranes.
  • a “porous” filtration layer is a permeable medium, where fluids or molecules can move through holes.
  • ⁇ or “non-porous” means any chemical path that moderates the permeation of liquids or gases and use the molecular porosity as a diffusion pathway, for instance in the case of dense membranes or films.
  • a “non-porous” filtration layer is as a permeable medium, where fluids or molecules can have mobility through the molecules/chains of the films or membranes.
  • the filtration medium according to the invention can further comprise at least one substrate layer.
  • the filtration medium according to the invention can comprise:
  • - at least one substrate layer - at least one top layer made of a polymer selected from the group consisting of polyamides, polyimides, polyacrylonitriles, polybenzimidazoles, cellulose acetates and polyolefins, and
  • composition (C) - between said at least one substrate layer and said at least one top layer, at least one filtration layer consisting of composition (C).
  • substrate layers, further intermediate and top layers can be made of fabric, porous or dense membrane or film compositions, and are composed of polymers such as fluorinated polymers, aromatic polymers, aliphatic polymers, most notably PVDF, PS, PES, PET, PP, PA, PE and so on.
  • polymers such as fluorinated polymers, aromatic polymers, aliphatic polymers, most notably PVDF, PS, PES, PET, PP, PA, PE and so on.
  • the intermediate and top layers are most frequently membrane or film media, whereas the substrate layer is most frequently fabric media.
  • the membrane technologies are classified as follows:
  • the pore size of a microfiltration membrane ranges from 0.1 to 5 pm, and has the largest pore size of the four main membrane types. Its pores are large enough to filter out bacteria, blood cells, flour, talc and many other kinds of fine dust in solution. Because its pores are relatively large compared to other membranes, it can be operated under low pressures and therefore low energy.
  • Ultrafiltration has a pore size ranging from 0.1 to 0.01 ⁇ .
  • UF membranes reject particles such as silica, viruses, endotoxins, proteins, plastics and smog/fumes such as ZnO. Due to the decrease in pore size, the osmotic pressure required is higher than that of MF.
  • Nanofiltration has a pore size ranging from 0.001 to 0.01 pm.
  • NF membranes can filter particles up to and including some salts, synthetic dies and sugars, however it is unable to remove most aqueous salts and metallic ions, as such, NF is generally confined to specialist uses.
  • Reverse Osmosis has a pore size ranging from 0.0001 to 0.001 pm. It is by far the finest separation material available to industry. It is used on a large scale for the desalination and purification of water as it filters out everything but water molecules, with pore sizes approaching the radius of some atoms in many cases. This pore size means it is the only membrane that can reliably filter out salt and metallic ions from water. The small pore size of RO membranes means that a significant amount of osmotic pressure is required to force filtration.
  • the support layers can be made of fabrics such as woven, knitted and non-woven fabric. Nonwoven fabrics are the most common fabric used.
  • Non-woven fabrics can be produced mostly be one of the following methods: dry-laid methods; wet-laid methods; or spun melt processes.
  • Dry-laid nonwovens are fibrous webs formed from staple fibres. They are classified as air-laid (randomly oriented short staple fibers) or carded (oriented long staple fibers).
  • the staple fibers are dispersed into a fast moving air stream that condenses them onto a moving screen by means of pressure or vacuum.
  • Carded nonwovens are produced by mechanically separating, aligning and disposing the staple fibers in a flat sheet or web. The webs are then bonded either by mechanical, thermal or chemical means, such as needlepunching, heated calender rollers, or hydroentanglement (spunlace), respectively.
  • Wetlaid non-woven are non-wovens made by a modified papermaking process. That is, the fibres to be used are suspended in water.
  • a major objective of wet laid nonwoven manufacturing is to produce structures with textile-fabric characteristics, primarily flexibility and strength, at speeds approaching those associate with papermaking.
  • Spun melt nonwovens are webs made directly from filaments spun or extruded directly from polymer pellets. They are classified as spunbound and melt-blown, and are produced by depositing extruded, spun filaments onto a collection belt in a uniform random manner followed by bonding the fibers.
  • the filtration layer can either be a porous membrane, a woven, non- woven or knitted fabric or a dense film or membrane.
  • the porous membrane of the invention typically has a gravimetric porosity comprised between 5% and 90%, preferably between 10% and 85% by volume, more preferably between 50% and 80%, based on the total volume of the membrane.
  • the term “gravimetric porosity” is intended to denote the fraction of voids over the total volume of the porous membrane. Depending on the final form of the membrane, it may be either flat, when flat membranes are required or tubular in shape, when tubular or hollow fiber membranes are required.
  • the process for manufacturing a porous membrane is carried out in liquid phase.
  • liquid medium (L) comprising at least one solvent
  • step (iii) precipitating the film provided in step (ii) thereby providing a porous membrane.
  • the liquid composition (C) is advantageously a homogeneous solution.
  • solvent is used herein in its usual meaning that is it indicates a substance capable of dissolving another substance (solute) to form a uniformly dispersed mixture at the molecular level.
  • solvent it is common practice to refer to a solution of the polymer in a solvent when the resulting mixture is transparent and no phase separation is visible in the system. Phase separation is taken to be the point, often referred to as “cloud point", at which the solution becomes turbid or cloudy due to the formation of polymer aggregates.
  • the medium (L) typically comprises at least one solvent selected from the group consisting of: hydrochloric acid, formic acid or sulphuric acid, in particular for polyamide matrix P.
  • solvent selected from the group consisting of: hydrochloric acid, formic acid or sulphuric acid, in particular for polyamide matrix P.
  • Halogenated hydrocarbons, higher aliphatic esters and ketones above 80°C can be used to dissolve polyesters and polyolefins.
  • the medium (L) typically comprises at least 50% by weight of at least one solvent.
  • the medium (L) may further comprise at least one non-solvent medium (NS).
  • the medium (NS) may comprise water up to 50% by weight based on the total weight of liquid medium (L).
  • the liquid composition (C) is typically manufactured by any conventional techniques.
  • the medium (L) may be added to the polymer matrix (P) or, preferably, the polymer (P) may be added to the medium (L) or even the polymer (P) and the medium (L) may be simultaneously mixed.
  • any suitable mixing equipment may be used.
  • the mixing equipment is selected to reduce the amount of air entrapped in the liquid composition (C) which may cause defects in the final membrane.
  • the mixing time during stirring required to obtain a clear homogeneous liquid composition (C) can vary widely depending upon the rate of dissolution of the components, the temperature, the efficiency of the mixing apparatus, the viscosity of the liquid composition (C) and the like.
  • the liquid composition (C) is typically processed in liquid phase.
  • the liquid composition (C) is typically processed by casting thereby providing a film.
  • Casting generally involves solution casting, wherein typically a casting knife, a draw-down bar or a slot die is used to spread an even film of a liquid composition comprising a suitable medium (L) across a suitable support.
  • the temperature at which the liquid composition (C) is processed by casting may be or may be not the same as the temperature at which the liquid composition (C) is mixed under stirring.
  • the liquid composition (C) is cast as a film over a flat supporting substrate, typically a plate, a belt or a fabric, or another microporous supporting membrane, typically by means of a casting knife, a draw-down bar or a slot die.
  • a flat supporting substrate typically a plate, a belt or a fabric, or another microporous supporting membrane, typically by means of a casting knife, a draw-down bar or a slot die.
  • the liquid composition (C) is processed by casting onto a flat supporting substrate thereby providing a flat film.
  • the liquid composition (C) is processed by casting thereby providing a tubular film.
  • the tubular film is manufactured using a spinneret.
  • spinneret is hereby understood to mean an annular nozzle comprising at least two concentric capillaries: a first outer capillary for the passage of the liquid composition (C) and a second inner one for the passage of a supporting fluid, generally referred to as "lumen”.
  • Hollow fibers and capillary membranes may be manufactured by the so-called spinning process according to this variant of the second embodiment of the invention.
  • the liquid composition (C) is generally pumped through the spinneret.
  • the lumen acts as the support for the casting of the liquid composition (C) and maintains the bore of the hollow fiber or capillary precursor open.
  • the lumen may be a gas, or, preferably, a medium (NS) or a mixture of the medium (NS) with a medium (L).
  • the selection of the lumen and its temperature depends on the required characteristics of the final membrane as they may have a significant effect on the size and distribution of the pores in the membrane.
  • the hollow fiber or capillary precursor is precipitated thereby providing the hollow fiber or capillary membrane.
  • the supporting fluid forms the bore of the final hollow fiber or capillary membrane.
  • Tubular membranes because of their larger diameter, are generally manufactured using a different process from the one employed for the production of hollow fiber membranes.
  • the filtration medium can be a woven, non- woven or knitted fabric.
  • the porosity for such materials is given by the voids created by the interface between interlaced or bound-together yarns.
  • the process for manufacturing the filtration medium comprises:
  • step (ii) processing the solid composition (C) provided in step (i) by melt-extrusion or solvent- extrusion, thereby producing filaments;
  • step (ii) disposing the filaments provided in step (ii) to form a nonwoven layer (N) or
  • step (ii) knitting the filaments provided in step (ii) to form a knitted fabric (K).
  • non-woven fabrication Under step of non-woven fabrication, conventional extrusion and spinning techniques can be used for processing the composition (C) thereby providing a non-woven layer (N).
  • the at least aliphatic polymer (P) and at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 ⁇ , to be dispersed in the aliphatic polymer matrix (P) can be supplied in powder or granule form, pre-dried and then melt spun in an extruder with melt filters. The resulting filaments are then interlaced using proper machinery.
  • the at least aliphatic polymer (P) and at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 m, to be dispersed in the aliphatic polymer matrix (P) can be supplied in powder or granule form, pre-dried and then melt spun in an extruder with melt filters and looped together with a set of needles.
  • the filtration medium can be a dense film.
  • the process for manufacturing the filtration medium comprises:
  • step (ii) processing the solid composition (C) provided in step (i) by extrusion thereby producing a film.
  • melt forming is commonly used to make dense films by film extrusion, preferably by flat cast film extrusion or by blown film extrusion.
  • the solid composition (C) is extruded through a die so as to obtain a molten tape, which is then calibrated and stretched in the two directions until obtaining the required thickness and wideness.
  • the solid composition (C) is melt compounded for obtaining a molten composition.
  • melt compounding is carried out in an extruder.
  • the solid composition (C) is typically extruded through a die at temperatures of generally lower than 250°C, preferably lower than 200°C thereby providing strands which are typically cut thereby providing pellets.
  • Twin screw extruders are preferred devices for accomplishing melt compounding of the solid composition (C).
  • Films can then be manufactured by processing the pellets so obtained through traditional film extrusion techniques.
  • Film extrusion is preferably accomplished through a flat cast film extrusion process or a hot blown film extrusion process. Film extrusion is more preferably accomplished by a hot blown film extrusion process.
  • the filtrating medium according to the invention above described in all the possible preferred embodiments that can be combined in all the possible ways is useful for filtrating any liquid or gas phase.
  • the invention also aims at a process comprising filtrating a liquid phase or a gas phase comprising one or more solid contaminants through the filtration medium according to the invention.
  • such a filtration medium according to the invention has the property of being flexible, of exhibiting water permeability and biofouling resistance, while maintaining good mechanical properties. It can also prolong the service life of the filtration medium, and reduces maintenance costs. Furthermore, the invention also reduces the current use of biocides in this industry, thereby contributing to the respect of the environment.
  • the liquid phase is a water-based phase comprising one or more microorganisms selected from the group consisting of bacteria such as E.coli, Staphylococcus aureus and Pseudomonas aeruginosa, Klebsiella pneumoniae, algae, fungi, protozoa and viruses.
  • bacteria such as E.coli, Staphylococcus aureus and Pseudomonas aeruginosa
  • Klebsiella pneumoniae Klebsiella pneumoniae
  • algae fungi, protozoa and viruses.
  • the membrane thickness was measured using a digital micrometer. At least four different samples were taken from different parts of different membranes to have a significant result. The thickness measurement is relevant because during the phase inversion it is expected a shrinkage during the membrane consolidation. The thickness is also important to calculate the membrane porosity, as it is used to determine the membrane volume (sample area x thickness). Measurement of Hydrophilicity (contact angle, CA)
  • the contact angle test aims to determine the hydrophilicity of the membrane surface.
  • the angle measured is the angle between the liquid-gas tangent and membrane-liquid boundary. The smaller the angle between the droplet and the membrane surface, more hydrophilic is the membrane and lower the tendency to fouling.
  • the methodology used for these trials was recommended by ISO 15989/2004 Plastics - Film and sheeting - Measurement of water- contact angle of corona-treated films (2004). 20 to 30 measurements were performed on a minimum of three different samples of each membrane and contact angle measurements were determined with a goniometer Kino SL150E.
  • the evaluation of mechanical strength considers three major parameters: The Young Modulus, the Tension at Rupture and the Elongation at Rupture.
  • the Young Modulus is a parameter that helps to evaluate the elasticity of the tested sample for a specific applied tension. This behaviour is considered linear during the elastic deformation of the sample (condition in which after releasing the stress over the sample, it returns to its initial state). The higher the Young Modulus, higher is the tension needed to deform a sample, hence, stiffer is the material. Samples with low Young Modulus are easily deformed by lower tensions, being more elastic. Standard Test Method for Tensile Properties of Thin Plastic Sheet - as a methodology for performing these tests to ASTM D 882 was used. At least three samples were evaluated for each membrane type being calculated the average modulus.
  • the test consists of applying tension in a specimen of defined dimensions until their elongation and subsequent rupture.
  • the tension applied is plotted in the function of deformation, providing a curve whose linear coefficient provides the elastic modulus.
  • the mechanical resistance tests were completed on the Shimadzu Compact Table-top Universal Testing Machine EZTest EZ-LX at 25 °C with a crosshead speed of 5 mm min "1 .
  • the dimensions of the samples used by this test were 5 x 15 mm x the membrane thickness. At least 3 samples were analysed for average tensile strength, Young's modulus, and elongation at break.
  • the apparent porosity evaluation was performed by analyzing the difference between membranes wet and dry weights.
  • the wet weight was measured after removing the superficial water with Synthesis and Characterization of Polyamide membrane using additives two polyester/cellulose wipers (VWR International) and the dry weight was measured after drying the samples.
  • Test and control samples are inoculated with the test organisms. After 24 hr of contact, the bacteria are removed from the samples by shaking in known amounts of neutralizing solution. The number of bacteria present in this liquid is determined, and the percentage reduction by the treated sample is calculated.
  • the antimicrobial activity of a substrate-bound, non-leaching antimicrobial agent is dependent upon direct contact of microbes with the active chemical agent. This test determines the antimicrobial activity of a treated specimen by shaking samples of surface-bound materials in a concentrated bacterial suspension for a one hour contact time. The suspension is serially diluted both before and after contact and cultured. The number of viable organisms from the suspension is determined and the percent reduction (or log 10 reduction) is calculated by comparing retrievals from appropriate controls.
  • Treated substrates used in this test method can be subjected to a wide variety of physical/chemical stresses or manipulations and allows for the versatility of testing the effect of contamination.
  • the microbial culture is diluted in a sterile buffer solution and microbial cultures are grown and harvested in a soy broth. Microbial concentrations from the bacterial suspension-only flasks are identified at "time zero.”
  • Concentration of microorganisms in the flask that contained the antimicrobial product are compared to either the flask that contained only microbial suspension or the flask that contained the untreated control, depending on certain circumstances specified by the method.
  • a product is said to be "antimicrobial” if it produces a substantial reduction relative to either the inoculum or untreated controls.
  • a Solution Test is conducted per the method to determine leaching of the antimicrobial agent. If the post-test shows the presence of a "leaching antimicrobial,” then the results are deemed unreliable until it confirmed that the active ingredient was successfully neutralized.
  • a polymer solution (1000 g) was prepared by dissolving 100 grams of polyamide in 900 g of concentrated H 2 S0 4 (98%).
  • compositions comprising the mineral FIR compounds with a total mass concentration of 10% based on the polyamide mass for membranes according to Examples 1 , 2 and 3 indicated below.
  • the polyamide was added gradually (a quarter of the total mass every 20 minutes). The solutions were stirred for 24 hours at 180 rpm to ensure the polyamide was dissolved. For examples 1 , 2 and 3, the mineral compounds were slowly added in the form of water suspensions after the polymer became soluble and under stirring to avoid phase inversion. Prior to the membrane casting, the solutions were degassed in an ultrasonic bath (Branson 2100) for 30 minutes to eliminate air bubbles that could interfere with the final membrane structure.
  • Branson 2100 ultrasonic bath
  • the glass plate was quickly immersed ( ⁇ 10 s) into the coagulation bath containing deionized water at room temperature and the membranes were formed via phase inversion. After immersion in the coagulation bath, the membranes were placed in a second demineralized water bath at room temperature (> 24 hours) to remove any residual solvent. For membrane characterization, the membranes were kept in isopropyl alcohol for 24 hours, then covered by absorbent paper towels and left to dry naturally inside a fume hood to prevent pore collapse.
  • Example 1 sulphuric acid, 90% polyamide + 10% Tourmaline
  • Example 2 sulphuric acid, 90% polyamide + 10% Titanium Dioxide
  • Example 3 sulphuric acid, 90% polyamide + 5% Tourmaline + 5% Titanium Dioxide Control
  • Example 1 sulphuric acid, 100% polyamide
  • the increase in porosity is also associated with better membrane permeability and low flow resistance.
  • the membrane obtained with the FIR mineral compounds resulted in a decrease of the contact angle, indicating the membrane hydrophilicity was improved.
  • the results obtained indicate that the FIR mineral compounds present a high potential to be used for the production of filtration media with anti-biofouling properties for water and gas applications.
  • Resin was dried for 15 hours under 85 °C in presence of dissecant.
  • the process was carried out using a pilot line for melt spun nonwovens with a heating profile from 250 to 280 °C per zone.
  • the melt filters were type PG8 which have 67 micron pores.
  • each sample was tested from the base condition (pure PA66) to 4 % and 8 % of Tourmaline and weight varying from 25 to 100 g / m 2 .
  • Each sample weighted at least 2 g with a 10 cm 2 area meeting the minimum amount to material required for the analysis.
  • AATCC100 results also present anti-microbial resistance due to the presence of FIR mineral facing the micro-organisms tested.

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Abstract

The present invention is in the field of anti-microbial filtration media, notably of flexible polymeric anti-microbial filtration media, processes for manufacturing them and uses thereof for liquid and/or gas phase treatments, in particular for water-based phases treatments to prevent biofouling.

Description

FILTRATION MEDIUM, PROCESSES TO PRODUCE IT AND USES THEREOF Abstract
The present invention is in the field of anti-microbial filtration media, notably of flexible polymeric anti-microbial filtration media, processes for manufacturing them and uses thereof for liquid and/or gas phase treatments, in particular for water-based phases treatments to prevent biofouling.
Description
Background
Among other functionalities, filtration systems are intended to retain, remove or neutralize microorganisms coming from air, gas or liquids. Applications of filtration media can be found in industrial wastewater treatments, in ultrapure water production used for medical purposes, in electronics and in food processing, in drinkable water production processes, in ocean desalination processes, in industrial gases treatments and in residential air purification, among others.
Biofouling - definition and challenges
During usage, microorganisms tend to accumulate in filtration media, which leads to the formation of biofouling or biofilm, mainly in liquid-based filtration systems. Biofouling, biofilm or biological fouling is the gradual accumulation of microorganisms, plants, animals, algae, barnacles and protozoa on filtration wetted surfaces.
The main microorganisms responsible for biofouling are Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli but also algae, fungi, protozoa and viruses.
In addition, the deposition of colloidal materials and organic macromolecules on the filtration surface causes further growth and proliferation of microbes.
Biofouling happens in filtration media in general, such as in membrane, fabric and film processes. However, it is most prominent in membrane processes, due to the low size porosity and high media flux.
Membrane biofouling is a major problem encountered in membrane filtration processes, and it is a major factor in determining their practical application in water and wastewater treatment and in desalination in terms of technology and economics. Membrane biofouling leads to higher maintenance costs, lower efficiency and shorter service life. Membranes with high flux, high rejection, and low tendency for biofouling are most desired for use in emerging and conventional treatment processes that provide consistently high process performance, require few chemicals, and produce little waste.
Examples of membrane processes are microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO). Nanofiltration and reverse osmosis media are the most affected by biofouling formation, notably, reverse osmosis.
One of the most important applications of RO is the ocean desalination. RO desalination is currently the most efficient and widely adopted process. However, it requires a great deal of energy to create the high pressures necessary to overcome the osmotic pressure of saline waters and there are often significant issues with disposal of brine resulting from the process. Therefore, technological advances in biofilm formation are needed to improve the energy efficiency, contaminant removal, and environmental impacts of the processes, as the biofilm formation interferes in the pressure of the membrane and increases the use of harmful chemicals to prevent and remove the biofilm.
A major challenge during operation of RO membranes is the deposition of colloidal materials and organic macromolecules on the membrane surface and the growth of microbes. This deposition leads to cake formation, irreversible adsorption, and growth of persistent biofilms, collectively referred to as biofouling. Fouling can cause a substantial increase in power consumption due to additional resistance to flow.
Current approaches to solve the problem
The conventional anti-fouling strategy has been to dose feed water continuously with biocides or antimicrobial substances. Biocide treatment must be followed by high velocity detergent cleaning and flushing to remove the organic debris.
Chlorine is the most widely used disinfectant in water and wastewater treatment. In many cases, chlorine (either as a gas or in the hypochlorite form) cannot be used for membrane treatment because most commercially available polymeric membranes are sensitive to chlorine; and due to the production of a large amount of Assimilable Organic Carbons (AOC) which leads to bacterial growth.
Hydraulic cleaning such as flushing and backwashing/back pulsing is the most common technique for mitigating fouling. Regular intermittent backwashing will lift the foulants off the membrane surface and minimize the extent of concentration polarization.
Otherwise, in literature, various filtration media using mineral based technology have been studied. For instance, US2012168367A describes a water filter for treating tap water from a water supply, comprising a water inlet; a water outlet; and a filter cartridge. The filter cartridge comprises several mixtures and layers based on mineral powders. In one of the layers Far Infrared (FIR) ore powder is used to remove odor, color and organic contaminants. Other layers have the role of reducing bacteria content (germanite layer) or to remove large particles and floating solids. This kind of filter does not suffer from biofilm formation as it is made of large ceramic grains which are not incorporated in a polymeric matrix. Therefore, it is not a thin flexible membrane and the performance is not impacted. In addition, it has the drawback of not being applicable to small particle filtration such as UF, NF, MF and RO, where the biofilm formation causes above mentioned issues.
Also, CN1460533A discloses an additive of multifunctional filter material that has the functions of resisting bacteria and decomposing harmful gas and organic pollutant, and can release negative ions. It is a liquid composition comprising a mineral mixture and a small amount of adhesive (10-20%), applied via spray in the filter medium to eliminate bacteria from the air. This solution is not appropriate for antibiofouling prevention because it is intended to reduce bacteria from the air and not to reduce the bacteria growing in the filter media. In addition, it has the drawback of being applied as a spray onto the filter, thus suffering from durability issues and prone to leakage, hence reducing the effectiveness.
Proposed solution
In spite of the already existing solutions, it remains a need to provide polymeric filtration media exhibiting water permeability and (bio)fouling resistance, while maintaining good mechanical properties and flexibility, to be suitably used for filtration of various liquid and/or gas phases. Therefore, the object of the present invention is to provide a flexible polymeric filtration layer, such as fabric, membrane or film, composed of aliphatic polymers like polyamide, polypropylene and polyesters, exhibiting water permeability and biofouling resistance, while maintaining good mechanical properties, to be suitably used as filtration medium for treating liquid and/or gas phases. The invention described hereunder prolongs the service life of the filtration medium, and reduces maintenance costs. Furthermore, the invention also reduces the current use of biocides in this industry, thereby contributing to the respect of the environment.
Most of related patents and papers describe the use of minerals as such or as coatings compositions, and it has been surprisingly found that when a mineral filler with Far Infra-red emission/absorption properties is used in the form of a dispersion in an aliphatic polymeric matrix, that enable and provide more efficiency and flexibility in applications where coatings and compositions are not suitable. Summary of invention
The present invention thus relates to a filtration medium comprising at least one filtration layer consisting of a composition (C) comprising:
at least one aliphatic polymer matrix (P), and
at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 μητι, dispersed in the aliphatic polymer matrix (P).
The present invention also relates to processes for producing the filtration medium of the invention.
It is also an object of the present invention a process comprising filtrating a liquid phase or a gas phase comprising one or more solid contaminants through the filtration medium according to the invention.
It has been now surprisingly found that the filtration medium of the invention advantageously exhibits improved biofouling resistance, while preserving the mechanical properties, to be suitably used as anti-microbial and anti-fouling filtration media for various liquid, air and/or gas phases, in particular water-based phases.
Also, it has been found that the filtration media of the invention advantageously exhibits good wettability to be suitably used as filtration membrane for water-based phases.
Detailed description
Definitions
The expression "filtration medium" in the sense of the present invention is the generic term including the following articles: membranes, fabrics, films, nonwoven, fibers and composites. The term "filtration layer" means any layer, generally thin or interface that moderates the permeation of chemical species in contact with it, said interface may contain pores of finite dimensions, as for porous membranes or fabrics, or even dense non-porous membranes or films, in which the selectivity is affected by the chemical molecular affinity.
The expression "aliphatic polymer" in the sense of the invention excludes any aromatic polymers, fluoropolymers, or polysulfones.
The term "dispersed in the aliphatic polymer matrix" in the sense of the present invention means that the mineral compound(s) (M) are homogeneously distributed inside the polymeric material, and are not present at the surface only, like for coatings. Of course, some particles can be found at the surface but the probability to find them at the surface is equivalent to the probability to find them in the core of the polymer. Therefore, the mineral compounds(s) (M) are not removable and do not detach from the matrix during the service life.
Aliphatic polymer matrix
The invention uses a polymeric composition (C) comprising an aliphatic polymer matrix (P). The aliphatic polymer matrix (P) is selected from the group consisting of polyamides, polyolefins such as polypropylene and polyethylene, polyketones, polyesters such as polylacticacid, polyhydroxybutyrate; and also cellulose esters such as cellulose acetate. These polymers are widely available in the market for engineering applications. They are also cheaper and require less sophisticated processing steps than the specialty polymers such as polysulfone (PSU), fluoropolymers (eg. PVDF) and etc.
Preferred polyamides are polyhexamethylene adipamide (PA66), polycaproamide (PA6), PA6.10, PA10.10 and PA12, copolymers in any proportions of these polymers, and blends between any of these polymers.
According to one preferential embodiment, the polymer matrix consists of polypropylene, polyester or polyamide, most preferably polyamide. Polyamide is preferably selected from polyamide 6, polyamide 66 and copolymers of polyamide 6/polyamide 66 in any proportions. Those polymers are commercially available. Those polymers allow higher amounts of mineral fillers to be incorporated in their matrix while maintaining good mechanical properties compared to aromatic polymers, fluoropolymers and polysulfones.
Mineral compound M
The polymeric composition according to the invention comprises at least one mineral compound (M) having properties of absorption and/or emission in the far infrared region ranging from 2 to 20 Mm.
Preferably, the mineral compound(s) has (have) properties of absorption and/or emission in the far infrared region ranging from 3 to 20 μηι, and even more preferentially from 3 to 15 m.
The mineral compound(s) usable according to the invention can be chosen in particular from oxides, sulfates, carbonates, phosphates and silicates.
Preferably, the oxide(s) is (are) chosen from titanium dioxide, silicon dioxide and magnesium oxide, more preferably titanium dioxide. The sulfate(s) can advantageously be chosen from alkali metal and alkaline-earth metal sulfates, preferably from barium sulfate, calcium sulfate and strontium sulfate, more preferably barium sulfate. The carbonate(s) is (are) advantageously chosen from calcium carbonate and sodium carbonate. Preferably, the silicate(s) is (are) chosen from actinolite, tourmaline, serpentine, kaolinite, and zirconium silicate, more preferably tourmaline. The phosphate(s) can be chosen from zirconium phosphates, cerium phosphate and apatite, and mixtures thereof.
All those mineral compounds (M) having properties of absorption and/or emission in the far infrared region ranging from 2 to 20 μηι are commercially available.
According to one embodiment, the composition (C) comprises an total amount of mineral compound (M) ranging from 1 % to 20%, preferably from 2% to 10%, more preferably from 3% to 6% by weight based on the total weight of the at least one aliphatic polymer matrix (P).
Within this specific range, both mechanical properties for processing/application and antimicrobial effect are particularly satisfying.
According to a preferred embodiment, the composition (C) comprises at least two mineral fillers (M) dispersed in the aliphatic polymer matrix (P). In some cases, the composition (C) can comprise two or three mineral fillers (M) dispersed in the aliphatic polymer matrix (P).
According to a particularly preferred embodiment, at least one mineral compound (M) is a silicate, preferably selected from the group consisting of tourmaline, actinolite, serpentine, muscovite and kaolin, more preferably tourmaline. According to this embodiment, when at least a silicate is used in combination with at least one other mineral compound (M) that can be one or more oxides and/or one or more sulfates and/or one or more carbonates the total amount of this "at least one other mineral compound (M)" is comprised between 40% and 95% by weight, based on the total weight of the silicate.
It is advantageous when the composition (C) comprises two mineral fillers (M) being tourmaline and titanium dioxide. This preferred composition has improved water permeability. In this particular embodiment, tourmaline and titanium dioxide are present in a mass ratio ranging from 40/60 to 95/5.
The mineral filler(s) (M) have advantageously a particle size ranging from 0.05 to 6 pm, preferably from 0.1 to 3 pm, most preferably 0.2 to 1 pm. The advantages of particle size less than 1 μηη are less filtering media defects, less impact in the mechanical properties, better dispersion, higher surface active area, hence optimizing the amount needed to achieve the same benefit.
The composition (C) may contain one or more additional components such as pore forming agents, nucleating agents, fillers, latent organic solvents, surfactants and the like.
Pore forming agents are typically added to the composition (C) when porous filtration layer is targeted in amounts usually ranging from 0.1 % to 30% by weight, preferably from 0.5% to 5% by weight. Suitable pore forming agents are for instance polyvinylpyrrolidone (PVP) and polyethyleneglycol (PEG), with PVP being preferred.
Preferred embodiments can be combined together in all the possible ways.
Filtration layer
Filtration media according to the invention can be a mono- or multi-layer system. It means it can be made from the filtration layer only plus optionally a substrate layer (mono), or the filtration layer of the filtration media can be associated to several other layers, such as substrate layer, optionally further intermediate layers and top layers (multi).
The filtration layer can be porous or dense.
The term "porous" according to the present invention, means any physical path that moderates the permeation of liquids or gases, such as physical pores (e.g. voids) with finite dimensions, for instance in the case of fabrics or porous membranes. A "porous" filtration layer is a permeable medium, where fluids or molecules can move through holes.
The term "dense" or "non-porous" means any chemical path that moderates the permeation of liquids or gases and use the molecular porosity as a diffusion pathway, for instance in the case of dense membranes or films. A "non-porous" filtration layer is as a permeable medium, where fluids or molecules can have mobility through the molecules/chains of the films or membranes.
The filtration medium according to the invention can further comprise at least one substrate layer.
According to a specific embodiment, the filtration medium according to the invention can comprise:
- at least one substrate layer, - at least one top layer made of a polymer selected from the group consisting of polyamides, polyimides, polyacrylonitriles, polybenzimidazoles, cellulose acetates and polyolefins, and
- between said at least one substrate layer and said at least one top layer, at least one filtration layer consisting of composition (C).
These substrate layers, further intermediate and top layers can be made of fabric, porous or dense membrane or film compositions, and are composed of polymers such as fluorinated polymers, aromatic polymers, aliphatic polymers, most notably PVDF, PS, PES, PET, PP, PA, PE and so on.
The intermediate and top layers are most frequently membrane or film media, whereas the substrate layer is most frequently fabric media.
The membrane technologies are classified as follows:
Microfiltration (MF)
The pore size of a microfiltration membrane ranges from 0.1 to 5 pm, and has the largest pore size of the four main membrane types. Its pores are large enough to filter out bacteria, blood cells, flour, talc and many other kinds of fine dust in solution. Because its pores are relatively large compared to other membranes, it can be operated under low pressures and therefore low energy.
Ultrafiltration (UF)
Ultrafiltration has a pore size ranging from 0.1 to 0.01 μηη. UF membranes reject particles such as silica, viruses, endotoxins, proteins, plastics and smog/fumes such as ZnO. Due to the decrease in pore size, the osmotic pressure required is higher than that of MF.
Nanofiltration (NF)
Nanofiltration has a pore size ranging from 0.001 to 0.01 pm. NF membranes can filter particles up to and including some salts, synthetic dies and sugars, however it is unable to remove most aqueous salts and metallic ions, as such, NF is generally confined to specialist uses.
Reverse Osmosis (RO)
Reverse Osmosis has a pore size ranging from 0.0001 to 0.001 pm. It is by far the finest separation material available to industry. It is used on a large scale for the desalination and purification of water as it filters out everything but water molecules, with pore sizes approaching the radius of some atoms in many cases. This pore size means it is the only membrane that can reliably filter out salt and metallic ions from water. The small pore size of RO membranes means that a significant amount of osmotic pressure is required to force filtration. The support layers can be made of fabrics such as woven, knitted and non-woven fabric. Nonwoven fabrics are the most common fabric used. It is typically manufactured by putting small fibers together in the form of a sheet or web, and then binding them either mechanically (as in the case of felt, by interlocking them with serrated needles such that the inter-fiber friction results in a stronger fabric), with an adhesive, or thermally (by applying binder (in the form of powder, paste, or polymer melt) and melting the binder onto the web by increasing temperature). Non-woven fabrics can be produced mostly be one of the following methods: dry-laid methods; wet-laid methods; or spun melt processes.
Dry-laid nonwovens are fibrous webs formed from staple fibres. They are classified as air-laid (randomly oriented short staple fibers) or carded (oriented long staple fibers). In the air-laid process, the staple fibers are dispersed into a fast moving air stream that condenses them onto a moving screen by means of pressure or vacuum. Carded nonwovens are produced by mechanically separating, aligning and disposing the staple fibers in a flat sheet or web. The webs are then bonded either by mechanical, thermal or chemical means, such as needlepunching, heated calender rollers, or hydroentanglement (spunlace), respectively.
Wetlaid non-woven are non-wovens made by a modified papermaking process. That is, the fibres to be used are suspended in water. A major objective of wet laid nonwoven manufacturing is to produce structures with textile-fabric characteristics, primarily flexibility and strength, at speeds approaching those associate with papermaking.
Spun melt nonwovens are webs made directly from filaments spun or extruded directly from polymer pellets. They are classified as spunbound and melt-blown, and are produced by depositing extruded, spun filaments onto a collection belt in a uniform random manner followed by bonding the fibers.
According to the invention, the filtration layer can either be a porous membrane, a woven, non- woven or knitted fabric or a dense film or membrane.
Porous Membranes
The porous membrane of the invention typically has a gravimetric porosity comprised between 5% and 90%, preferably between 10% and 85% by volume, more preferably between 50% and 80%, based on the total volume of the membrane.
For the purpose of the present invention, the term "gravimetric porosity" is intended to denote the fraction of voids over the total volume of the porous membrane. Depending on the final form of the membrane, it may be either flat, when flat membranes are required or tubular in shape, when tubular or hollow fiber membranes are required.
According to a first embodiment of the invention, the process for manufacturing a porous membrane is carried out in liquid phase.
The process according to this first embodiment of the invention typically comprises:
(i) providing a liquid composition (C) comprising:
- at least one aliphatic polymer matrix (P), and
- at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 pm, to be dispersed in the aliphatic polymer matrix (P).
- a liquid medium (L) comprising at least one solvent;
(ii) processing the liquid composition (C) provided in step (i) thereby providing a film; and
(iii) precipitating the film provided in step (ii) thereby providing a porous membrane.
Each of the preferred embodiments developed above for the nature of polymer (P) and mineral compounds (M) is applicable to the above process according to the invention. Preferred embodiments can be combined together in all the possible ways.
The liquid composition (C) is advantageously a homogeneous solution.
The term "solvent" is used herein in its usual meaning that is it indicates a substance capable of dissolving another substance (solute) to form a uniformly dispersed mixture at the molecular level. In the case of a polymeric solute, it is common practice to refer to a solution of the polymer in a solvent when the resulting mixture is transparent and no phase separation is visible in the system. Phase separation is taken to be the point, often referred to as "cloud point", at which the solution becomes turbid or cloudy due to the formation of polymer aggregates.
The medium (L) typically comprises at least one solvent selected from the group consisting of: hydrochloric acid, formic acid or sulphuric acid, in particular for polyamide matrix P. Halogenated hydrocarbons, higher aliphatic esters and ketones above 80°C can be used to dissolve polyesters and polyolefins.
The medium (L) typically comprises at least 50% by weight of at least one solvent. The medium (L) may further comprise at least one non-solvent medium (NS). The medium (NS) may comprise water up to 50% by weight based on the total weight of liquid medium (L).
Under step (i) of the process for manufacturing a porous membrane according to the first embodiment of the invention, the liquid composition (C) is typically manufactured by any conventional techniques. For instance, the medium (L) may be added to the polymer matrix (P) or, preferably, the polymer (P) may be added to the medium (L) or even the polymer (P) and the medium (L) may be simultaneously mixed.
Any suitable mixing equipment may be used. Preferably, the mixing equipment is selected to reduce the amount of air entrapped in the liquid composition (C) which may cause defects in the final membrane.
Under step (i) of the process for manufacturing a porous membrane according to the first embodiment of the invention, the mixing time during stirring required to obtain a clear homogeneous liquid composition (C) can vary widely depending upon the rate of dissolution of the components, the temperature, the efficiency of the mixing apparatus, the viscosity of the liquid composition (C) and the like.
Under step (ii) of the process for manufacturing a porous membrane according to this first embodiment of the invention, the liquid composition (C) is typically processed in liquid phase. Under step (ii) of the process for manufacturing a porous membrane according to this first embodiment of the invention, the liquid composition (C) is typically processed by casting thereby providing a film.
Casting generally involves solution casting, wherein typically a casting knife, a draw-down bar or a slot die is used to spread an even film of a liquid composition comprising a suitable medium (L) across a suitable support.
Under step (ii) of the process for manufacturing a porous membrane according to this first embodiment of the invention, the temperature at which the liquid composition (C) is processed by casting may be or may be not the same as the temperature at which the liquid composition (C) is mixed under stirring.
Different casting techniques are used depending on the final form of the membrane to be manufactured.
When the final product is a flat membrane, the liquid composition (C) is cast as a film over a flat supporting substrate, typically a plate, a belt or a fabric, or another microporous supporting membrane, typically by means of a casting knife, a draw-down bar or a slot die. According to a first embodiment of the invention, under step (ii) of the process for manufacturing a porous membrane according to this first embodiment of the invention, the liquid composition (C) is processed by casting onto a flat supporting substrate thereby providing a flat film.
According to a second embodiment of the invention, under step (ii) of the process for manufacturing a porous membrane according to this first embodiment of the invention, the liquid composition (C) is processed by casting thereby providing a tubular film.
According to a variant of this second embodiment of the invention, the tubular film is manufactured using a spinneret.
The term "spinneret" is hereby understood to mean an annular nozzle comprising at least two concentric capillaries: a first outer capillary for the passage of the liquid composition (C) and a second inner one for the passage of a supporting fluid, generally referred to as "lumen".
Hollow fibers and capillary membranes may be manufactured by the so-called spinning process according to this variant of the second embodiment of the invention. According to this variant of the second embodiment of the invention, the liquid composition (C) is generally pumped through the spinneret. The lumen acts as the support for the casting of the liquid composition (C) and maintains the bore of the hollow fiber or capillary precursor open. The lumen may be a gas, or, preferably, a medium (NS) or a mixture of the medium (NS) with a medium (L). The selection of the lumen and its temperature depends on the required characteristics of the final membrane as they may have a significant effect on the size and distribution of the pores in the membrane. At the exit of the spinneret, after a short residence time in air or in a controlled atmosphere, under step (iii) of the process for manufacturing a porous membrane according to this first embodiment of the invention, the hollow fiber or capillary precursor is precipitated thereby providing the hollow fiber or capillary membrane.
The supporting fluid forms the bore of the final hollow fiber or capillary membrane.
Tubular membranes, because of their larger diameter, are generally manufactured using a different process from the one employed for the production of hollow fiber membranes.
Fabrics
According to a second embodiment of the invention, the filtration medium can be a woven, non- woven or knitted fabric. The porosity for such materials is given by the voids created by the interface between interlaced or bound-together yarns. In this case, the process for manufacturing the filtration medium comprises:
(i) providing a solid composition (C) comprising:
- at least one aliphatic polymer matrix (P), and - at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 μιη to be dispersed in the aliphatic polymer matrix (P),
(ii) processing the solid composition (C) provided in step (i) by melt-extrusion or solvent- extrusion, thereby producing filaments; and
(iii) either
- disposing the filaments provided in step (ii) to form a nonwoven layer (N) or
- interlacing the filaments provided in step (ii) to form a woven layer (W) or
- knitting the filaments provided in step (ii) to form a knitted fabric (K).
Non-Woven
Under step of non-woven fabrication, conventional extrusion and spinning techniques can be used for processing the composition (C) thereby providing a non-woven layer (N).
Woven
Under the process of manufacturing a woven layer (W), the at least aliphatic polymer (P) and at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 μηι, to be dispersed in the aliphatic polymer matrix (P) can be supplied in powder or granule form, pre-dried and then melt spun in an extruder with melt filters. The resulting filaments are then interlaced using proper machinery.
Knitted
Under the process of manufacturing a knitted layer (K), the at least aliphatic polymer (P) and at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 m, to be dispersed in the aliphatic polymer matrix (P) can be supplied in powder or granule form, pre-dried and then melt spun in an extruder with melt filters and looped together with a set of needles.
Dense Films or Membranes
For dense membranes or films, the pore size is extremely small, then its diameter is the same size as or smaller than the mean free path of the molecules. Diffusion through such pores is governed by Knudsen diffusion. The membrane pores are of the order 5-20 A, and the separation process is governed by molecular sieving. Transport through this type of membrane is complex and includes both diffusion and adsorbed species on the surface of the pores (surface diffusion). According to a third embodiment of the invention, the filtration medium can be a dense film. In this case, the process for manufacturing the filtration medium comprises:
(i) providing a solid composition (C) comprising:
- at least one aliphatic polymer matrix (P), and
- at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 pm to be dispersed in the aliphatic polymer matrix (P),
(ii) processing the solid composition (C) provided in step (i) by extrusion thereby producing a film.
Melt forming is commonly used to make dense films by film extrusion, preferably by flat cast film extrusion or by blown film extrusion. According to this technique, the solid composition (C) is extruded through a die so as to obtain a molten tape, which is then calibrated and stretched in the two directions until obtaining the required thickness and wideness. The solid composition (C) is melt compounded for obtaining a molten composition. Generally, melt compounding is carried out in an extruder. The solid composition (C) is typically extruded through a die at temperatures of generally lower than 250°C, preferably lower than 200°C thereby providing strands which are typically cut thereby providing pellets.
Twin screw extruders are preferred devices for accomplishing melt compounding of the solid composition (C).
Films can then be manufactured by processing the pellets so obtained through traditional film extrusion techniques. Film extrusion is preferably accomplished through a flat cast film extrusion process or a hot blown film extrusion process. Film extrusion is more preferably accomplished by a hot blown film extrusion process.
Uses
The filtrating medium according to the invention above described in all the possible preferred embodiments that can be combined in all the possible ways is useful for filtrating any liquid or gas phase. The invention also aims at a process comprising filtrating a liquid phase or a gas phase comprising one or more solid contaminants through the filtration medium according to the invention.
Advantageously, such a filtration medium according to the invention has the property of being flexible, of exhibiting water permeability and biofouling resistance, while maintaining good mechanical properties. It can also prolong the service life of the filtration medium, and reduces maintenance costs. Furthermore, the invention also reduces the current use of biocides in this industry, thereby contributing to the respect of the environment.
In a preferred embodiment, the liquid phase is a water-based phase comprising one or more microorganisms selected from the group consisting of bacteria such as E.coli, Staphylococcus aureus and Pseudomonas aeruginosa, Klebsiella pneumoniae, algae, fungi, protozoa and viruses.
EXPERIMENTAL PART
Raw Materials
Polymeric matrix:
- Polyamide PA66 commercialized by Rhodia Poliamida e Especialidades SA under STABAMID® 26 AE1 B2 name to prepare the porous membranes of part A.
- Semidull Polyamide PA66 commercialized by Rhodia Poliamida and Especialidades SA to prepare the nonwoven fabrics of part B.
- Masterized Polyamide PA66 with 8 % of tourmaline FIR Mineral compounds produced by incorporation of the appropriate amount of water suspension of tourmaline (below) in a previously melt Semidull polyamide 66 referenced above, to prepare the nonwoven fabrics of part B.
- Tourmaline water suspension with D90 < 0.7 pm was prepared as described in WO 2010/013107 (RHODIA POLIAMIDA E ESPECIALIDADES LTDA) 2/4/2010
- Titanium Dioxide water suspension with D90 < 0.7 pm was prepared as described in WO 2010/013107 (RHODIA POLIAMIDA E ESPECIALIDADES LTDA) 2/4/2010
Solvents
- Sulphuric Acid 98 %
- Formic Acid 85 %
- Demineralized water with conductivity < 1 pS
Methods of measurement
Measurement of Thickness
The membrane thickness was measured using a digital micrometer. At least four different samples were taken from different parts of different membranes to have a significant result. The thickness measurement is relevant because during the phase inversion it is expected a shrinkage during the membrane consolidation. The thickness is also important to calculate the membrane porosity, as it is used to determine the membrane volume (sample area x thickness). Measurement of Hydrophilicity (contact angle, CA)
The contact angle test aims to determine the hydrophilicity of the membrane surface. The angle measured is the angle between the liquid-gas tangent and membrane-liquid boundary. The smaller the angle between the droplet and the membrane surface, more hydrophilic is the membrane and lower the tendency to fouling. The methodology used for these trials was recommended by ISO 15989/2004 Plastics - Film and sheeting - Measurement of water- contact angle of corona-treated films (2004). 20 to 30 measurements were performed on a minimum of three different samples of each membrane and contact angle measurements were determined with a goniometer Kino SL150E.
Mechanical Properties Testing
The evaluation of mechanical strength considers three major parameters: The Young Modulus, the Tension at Rupture and the Elongation at Rupture. The Young Modulus is a parameter that helps to evaluate the elasticity of the tested sample for a specific applied tension. This behaviour is considered linear during the elastic deformation of the sample (condition in which after releasing the stress over the sample, it returns to its initial state). The higher the Young Modulus, higher is the tension needed to deform a sample, hence, stiffer is the material. Samples with low Young Modulus are easily deformed by lower tensions, being more elastic. Standard Test Method for Tensile Properties of Thin Plastic Sheet - as a methodology for performing these tests to ASTM D 882 was used. At least three samples were evaluated for each membrane type being calculated the average modulus. The test consists of applying tension in a specimen of defined dimensions until their elongation and subsequent rupture. The tension applied is plotted in the function of deformation, providing a curve whose linear coefficient provides the elastic modulus. The mechanical resistance tests were completed on the Shimadzu Compact Table-top Universal Testing Machine EZTest EZ-LX at 25 °C with a crosshead speed of 5 mm min"1. The dimensions of the samples used by this test were 5 x 15 mm x the membrane thickness. At least 3 samples were analysed for average tensile strength, Young's modulus, and elongation at break.
Measurement of gravimetric porosity
The apparent porosity evaluation was performed by analyzing the difference between membranes wet and dry weights. The wet weight was measured after removing the superficial water with Synthesis and Characterization of Polyamide membrane using additives two polyester/cellulose wipers (VWR International) and the dry weight was measured after drying the samples.
Determination of anti-microbial property
AATCC 100
This test method provides a quantitative procedure for the evaluation of the degree of antibacterial activity. Test and control samples are inoculated with the test organisms. After 24 hr of contact, the bacteria are removed from the samples by shaking in known amounts of neutralizing solution. The number of bacteria present in this liquid is determined, and the percentage reduction by the treated sample is calculated.
ASTM E2149
The antimicrobial activity of a substrate-bound, non-leaching antimicrobial agent is dependent upon direct contact of microbes with the active chemical agent. This test determines the antimicrobial activity of a treated specimen by shaking samples of surface-bound materials in a concentrated bacterial suspension for a one hour contact time. The suspension is serially diluted both before and after contact and cultured. The number of viable organisms from the suspension is determined and the percent reduction (or log10 reduction) is calculated by comparing retrievals from appropriate controls.
Treated substrates used in this test method can be subjected to a wide variety of physical/chemical stresses or manipulations and allows for the versatility of testing the effect of contamination.
The microbial culture is diluted in a sterile buffer solution and microbial cultures are grown and harvested in a soy broth. Microbial concentrations from the bacterial suspension-only flasks are identified at "time zero."
Concentration of microorganisms in the flask that contained the antimicrobial product are compared to either the flask that contained only microbial suspension or the flask that contained the untreated control, depending on certain circumstances specified by the method.
A product is said to be "antimicrobial" if it produces a substantial reduction relative to either the inoculum or untreated controls.
A Solution Test is conducted per the method to determine leaching of the antimicrobial agent. If the post-test shows the presence of a "leaching antimicrobial," then the results are deemed unreliable until it confirmed that the active ingredient was successfully neutralized. EXAMPLES
PART A - POROUS MEMBRANES
Step (i) Solution preparation
A polymer solution (1000 g) was prepared by dissolving 100 grams of polyamide in 900 g of concentrated H2S04 (98%).
This base solution was used:
- Alone to prepare the membrane of control example 1
- To prepare compositions comprising the mineral FIR compounds with a total mass concentration of 10% based on the polyamide mass for membranes according to Examples 1 , 2 and 3 indicated below.
In order to avoid pellet agglomeration when adding the polyamide pellets in sulphuric acid, the polyamide was added gradually (a quarter of the total mass every 20 minutes). The solutions were stirred for 24 hours at 180 rpm to ensure the polyamide was dissolved. For examples 1 , 2 and 3, the mineral compounds were slowly added in the form of water suspensions after the polymer became soluble and under stirring to avoid phase inversion. Prior to the membrane casting, the solutions were degassed in an ultrasonic bath (Branson 2100) for 30 minutes to eliminate air bubbles that could interfere with the final membrane structure.
Step (ii) Porous membrane preparation
After mixing, stirring, and degassing, the solutions were cast into membranes. The polyamide solution was carefully applied to a glass plate using an automatic film applicator (Elcometer 4340 Automatic Film Applicator) with a casting bar at a fixed height (150 pm) and application speed of 1.0 cm. s~1.
Step (iii) precipitation
After the membrane casting, the glass plate was quickly immersed (< 10 s) into the coagulation bath containing deionized water at room temperature and the membranes were formed via phase inversion. After immersion in the coagulation bath, the membranes were placed in a second demineralized water bath at room temperature (> 24 hours) to remove any residual solvent. For membrane characterization, the membranes were kept in isopropyl alcohol for 24 hours, then covered by absorbent paper towels and left to dry naturally inside a fume hood to prevent pore collapse.
Example 1 : sulphuric acid, 90% polyamide + 10% Tourmaline
Example 2: sulphuric acid, 90% polyamide + 10% Titanium Dioxide
Example 3: sulphuric acid, 90% polyamide + 5% Tourmaline + 5% Titanium Dioxide Control Example 1 : sulphuric acid, 100% polyamide
Table 1
Figure imgf000020_0001
Conclusion:
The increase in porosity is also associated with better membrane permeability and low flow resistance. The membrane obtained with the FIR mineral compounds resulted in a decrease of the contact angle, indicating the membrane hydrophilicity was improved.
There was a significant reduction in bacteria population with the samples containing the FIR mineral filler composition.
The presence of FIR mineral compounds resulted in more rigid membranes, what was expected since there are inorganic. Nevertheless, the mechanical properties are still maintained and considered suitable for its use as filtration media.
The results obtained indicate that the FIR mineral compounds present a high potential to be used for the production of filtration media with anti-biofouling properties for water and gas applications.
PART B - NONWOVEN FABRICS
20 linear meters of melt blown polyamide samples were successfully produced at three FIR mineral concentrations and three basis weights (9 samples in total - see table 2). For control samples, only semidull polyamide was melt-spun.
For samples with 4% and 8% of tourmaline - a mix of 50% (w/w) of semidull and masterized polyamide containing 8% of tourmaline was melt spun.
For samples with 8% of tourmaline - only the masterized polyamide containing 8% of tourmaline was melt spun.
Calendering the as-spun web through a heated nip resulted in samples with good balance of tensile strength and a fibrous, porous structure. Mineral used was tourmaline only.
Step (i) drying of polymer chips
Resin was dried for 15 hours under 85 °C in presence of dissecant.
Step (ii) melt-extrusion
The process was carried out using a pilot line for melt spun nonwovens with a heating profile from 250 to 280 °C per zone. The spinneret used had 250μηα capillaries with IJD=5. The melt filters were type PG8 which have 67 micron pores.
Different basis weights were achieved by varying the nip speed from 0.67 to 2.80 m / min.
Step (iii) Bonding: heated calender
Thermally bonding a web of loose fibers by passing them through the nip of a pair of Calender rollers, of which one or both are heated. One or both rolls are heated internally to a temperature that usually exceeds the melting point temperature of the binder fibers to ensure there is sufficient hear transfer to induce softening at the prevailing line speed. As the web passes between the calender nip, fibers are heated and compressed.
As it is summarized in table 2 below, each sample was tested from the base condition (pure PA66) to 4 % and 8 % of Tourmaline and weight varying from 25 to 100 g / m2. Each sample weighted at least 2 g with a 10 cm2 area meeting the minimum amount to material required for the analysis.
Table 2
CS1 S1.1 S1.2 CS2 S2.1 S2.2 CS3 S3.1 S3.2
Additive contents 0 % 4 % 8 % 0 % 4 % 8 % 0 % 4 % 8 %
Basis Weight [g / m2] 100 101 101 52 51 52 26 26 26
Filaments Diameter [mm] 18.1 17.3 14.9 18.1 17.3 14.9 18.1 17.3 14.9
Thickness [mm] 0.17 0.24 0.26 0.09 0.12 0.13 0.06 0.07 0.07
Load [kgf] 4.10 2.51 2.49 2.20 1.75 1.07 0.85 0.64 0.90
Elongation [%] 17.14 6.67 6.67 16.91 10.39 5.41 27.03 10.65 15.89
Tension [kgf/cm2] 8.208 5.028 4.98 4.4 3.508 2.13 1.706 1.274 1.794 % of Reduction E. coli None 60.40 63.70 None 54.29 55.71 None 55.45 58.18 (ASTM E 2149)
% of Reduction P. None 61.16 64.07 None 57.39 58.79 None 59.58 60.42 aeruginosa
(ASTM E 2149)
% of Reduction S. aureus None 57.39 59.13
(AATCC100)
% of Reduction Klebsiella None 60.4 61.2 - - - - - - pneumoniae (AATCC 00)
CS: control sample / S: sample
Conclusion:
For the non-woven samples, some mechanical properties such as Elongation at Break and Load Resistance tend to decrease as the amount of filler increases but still remain acceptable for the application. In addition, there is significant decrease in bacteria when mineral fillers are incorporated into the medium. The higher the basis weight, more resistant is the material.
AATCC100 results also present anti-microbial resistance due to the presence of FIR mineral facing the micro-organisms tested.

Claims

Claims
1. A filtration medium comprising at least one filtration layer consisting of a composition (C) comprising:
- at least one aliphatic polymer matrix (P), and
- at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 μηι, dispersed in the aliphatic polymer matrix (P).
2. The filtration medium according to claim 1 , wherein the aliphatic polymer matrix (P) is selected from the group consisting of polyolefin, polyamides, polypropylenes and polyesters, preferably polyamide.
3. The filtration medium according to claim 1 or 2, wherein the composition (C) comprises an total amount of mineral compound (M) ranging from 1% to 20%, preferably from 2% to 10%, more preferably from 3% to 6% by weight based on the total weight of the at least one aliphatic polymer matrix (P).
4. The filtration medium according to claim 1 to 3, wherein the at least one mineral compound (M) is selected from the group consisting of silicates, oxides, sulfates, phosphates and carbonates.
5. The filtration medium according to any one of claims 1 to 4, wherein the at least one mineral filler (M) is selected from the group consisting of:
- silicates selected from the group consisting of tourmaline, actinolite, serpentine, muscovite and kaolin, preferably tourmaline,
- oxides selected from the group consisting of titanium oxide, magnesium oxide, aluminium oxide, potassium oxide, zirconium oxide, preferably titanium dioxide,
- sulfates selected from the group consisting of barium sulfate, calcium sulphate strontium sulfate, preferably barium sulfate,
- phosphates selected from the group consisting of zirconium phosphates, cerium phosphate and apatite, and
- carbonates selected from the group consisting of calcium carbonate and sodium carbonate.
6. The filtration medium according to any one of claim 1 to 5, wherein the composition (C) comprises at least two mineral fillers (M) dispersed in the aliphatic polymer matrix (P).
7. The filtration medium according to claim 1 to 6, wherein at least one mineral compound (M) is a silicate, preferably selected from the group consisting of tourmaline, actinolite, serpentine, muscovite and kaolin, more preferably tourmaline.
8. The filtration medium according to any one of claims 1 to 7, wherein the composition (C) comprises two mineral fillers (M) being tourmaline and titanium dioxide.
9. The filtration medium according to any one of claims 1 to 7, wherein the mineral filler(s) (M) has a particle size ranging from 0.05 to 6 μηη, preferably from 0.2 to 1 pm.
10. The filtration medium according to any one of claims 1 to 9, further comprising at least one substrate layer.
11. The filtration medium according to any one of claims 1 to 10, said filtration medium comprising:
- at least one substrate layer,
- at least one top layer made of a polymer selected from the group consisting of polyamides, polyimides, polyacrylonitriles, polybenzimidazoles, cellulose acetates and polyolefins, and
- between said at least one substrate layer and said at least one top layer, at least one filtration layer consisting of composition (C).
12. The filtration medium according to any one of claims 1 to 11, wherein the filtration layer is a porous membrane.
13. The filtration medium according to any one of claims 1 to 11, wherein the filtration layer is a woven, non-woven or knitted fabric.
14. The filtration medium according to any one of claims 1 to 11 , wherein the filtration layer is a dense membrane or film.
15. A process for manufacturing the filtration medium according to claim 12, said process comprising:
(i) providing a liquid composition (C) comprising:
- at least one aliphatic polymer matrix (P),
- at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 μηη to be dispersed in the aliphatic polymer matrix (P), and
- a liquid medium (L) comprising at least one solvent;
(ii) processing the liquid composition (C) provided in step (i) thereby providing a film; and
(iii) precipitating the film provided in step (ii) thereby providing a porous membrane.
16. A process for manufacturing the filtration medium according to claim 13, said process comprising:
(i) providing a solid composition (C) comprising:
- at least one aliphatic polymer matrix (P), and
- at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 μιτι to be dispersed in the aliphatic polymer matrix (P),
(ii) processing the solid composition (C) provided in step (i) by melt-extrusion or solvent-extrusion, thereby producing filaments; and
(iii) either
- disposing the filaments provided in step (ii) to form a nonwoven layer N or
- interlacing the filaments provided in step (ii) to form a woven layer W or
- knitting the filaments provided in step (ii) to form a knitted fabric K.
17. A process for manufacturing the filtration medium according to claim 14, said process comprising:
(i) providing a solid composition (C) comprising:
- at least one aliphatic polymer matrix (P), and
- at least one mineral compound (M) which has properties of absorption and/or emission of radiation in the far infrared region 2-20 m to be dispersed in the aliphatic polymer matrix (P),
(ii) processing the solid composition (C) provided in step (i) by extrusion thereby producing a film.
18. A process comprising filtrating a liquid phase or a gas phase comprising one or more solid contaminants through the filtration medium according to any one of claims 1 to 14.
19. The process according to claim 18, wherein the liquid phase is a water-based phase ' comprising one or more microorganisms selected from the group consisting of bacteria such as E.coli, Staphylococcus aureus and Pseudomonas aeruginosa, Klebsiella pneumoniae, algae, fungi, protozoa and viruses.
PCT/IB2017/000750 2017-06-20 2017-06-20 Filtration medium, processes to produce it and uses thereof WO2018234838A1 (en)

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