Description

Porous membrane and method of making

Cross-Reference to Related Application

[0001] This application claims priority to European application 17192099.4 filed on September 20, 2017, the whole content of this application being

incorporated herein by reference for all purposes.

Technical Field

[0002] The present invention relates to a porous membrane of fluorinated

thermoplastic elastomers, to methods for the manufacture of the same, and to the use thereof in a variety of fields of use.

Background Art

[0003] Fluorinated polymers based on vinylidene fluoride are widely used in the preparation of porous structures comprising voids, generically referred to as porous membranes.

[0004] Fluorinated polymer porous membranes have found large use for e.g. microfiltration and ultrafiltration for separating liquid or gases, due to their good thermal stability, chemical resistance, excellent processability and convenience in controlling the porosity and the morphology of said membranes.

[0005] Further, fluoropolymers porous membranes have been included in

breathable fabrics, i.e. fabrics designed for use in garments that provide protection from wind, rain and loss of body heat, which are simultaneously waterproof (and hence referred to as waterproof breathable fabrics, WBF), in order to prevent the penetration and absorption of liquid water, but which passively allows water vapour due to perspiration from the body to diffuse through the fabric, yet still preventing the penetration of liquid water from the outside.

[0006] Still, porous fluoropolymer-based membranes have been used as

reinforcement support for creating composite separation/conduction layers, by filling porosity with appropriate active material conferring e.g.

ion-conductivities or other properties.

[0007] In all the mentioned applications field of use, porous fluoropolymer

membranes, either during their use (e.g. as fabrics) or during their processing and integration into final parts/devices, may be subjected to deformation and be required to possess a certain flexibility, so as to retain their integrity and porous structure upon bending or other mechanical deformation.

[0008] Further, especially when porous membranes are to be used as fabrics' components, it is essential that the said mechanical properties are maintained both when the porous membrane is in dry state and when the same is in wet state.

[0009] There is hence a need in the art for providing flexible porous structures which can withstand deformation without detrimentally affect their mechanical integrity and their permeability, in both dry and wet state.

[0010] Further, manufacturing techniques for industrial production of porous

membranes generally include the preparation of solutions of vinylidene fluoride polymers in suitable solvents, possibly in combination with specific pore forming agents. According to these techniques, a clear polymer solution, often referred to as a dope or a dope solution, is precipitated into two phases: a solid, polymer-rich phase that forms the matrix of the membrane, and a liquid, polymer-poor phase that forms the membrane pores. Polymer precipitation from a solution can be induced in several ways, such as cooling, solvent evaporation, precipitation by immersion in water, or imbibition of water from the vapour phase; nevertheless, a step of contacting the dope with a non-solvent, causing hence polymer to bring to completion coagulation is generally part of most of industrial techniques.

[001 1] If precipitation is rapid, the pore-forming liquid droplets tend to be small and the membranes formed are markedly asymmetric. If precipitation is slow, the pore-forming liquid droplets tend to agglomerate while the casting solution is still fluid, so that the final pores are relatively large and the membrane structure is more symmetrical. [0012] When a pore forming adjuvant is used, this agent is generally leached during the fluoropolymer polymer precipitation, although other techniques can be used for its removal. It may happen, nonetheless, that residues of pore forming agent can remain trapped in the porous membrane, leading to e.g. thermal stability issues or other degradation phenomena, or even possible long-term leaching during actual porous membrane

operations/uses.

[0013] In all these techniques, it remains nevertheless key to provide for methods whereas solutions of the fluorinated polymer, which are able, when exposed to precipitation conditions, as above detailed, to coagulate in a uniform and regular manner, so as to deliver a structure characterized by high porosity in the form of very small pores, homogeneously distributed throughout the entire membrane section, so enabling high fluxes.

[0014] The present invention thus provides fluoropolymer-based porous

membranes, possessing high porosity, delivering high fluxes, which combines the advantageous properties typical of fluoropolymers (chemical resistance, hydrophobicity, stain-resistance, oleophobicity, anti-fouling performances, thermal resistance) combined with advantageous mechanical properties, in particular good flexibility, and resistance to deformation/bending/crumpling up, i.e. outstanding mechanical properties, both in dry and wet state.

[0015] The invention further pertains to methods of making such porous

membranes, said method delivering membranes with voids of small size, good water permeability and good mechanical properties, yet deprived of non-porous skins, even when no adjuvant for forming pores is used during manufacture.

Brief description of drawings

[0016] Figure 1 is a simplified scheme of the hollow fibre spinning machine used for manufacturing hollow fibre membrane.

[0017] Figure 2 is a schematic cut of the spinneret (annular die), through a plane parallel to the fibre extrusion flow. [0018] Figure 3 is a schematic cut of the spinneret (annular die), through a plane perpendicular to the fibre extrusion flow.

Summary of invention

[0019] The invention thus pertains to a porous membrane possessing a

gravimetric porosity (£ _m ) of 20 to 95 %, said porous membrane comprising at least one fluorinated thermoplastic elastomer [polymer (F-TPE)] comprising:

(i) at least one elastomeric block (A) consisting of a sequence of recurring units, said sequence comprising recurring units derived from at least one fluorinated monomer, said block (A) possessing a glass transition temperature of less than 25°C, as determined according to ASTM D3418, and

(ii) at least one thermoplastic block (B) consisting of a sequence of recurring units, said sequence comprising recurring units derived from at least one fluorinated monomer,

wherein the crystallinity of said block (B) and its weight fraction in the polymer (F-TPE) are such to provide for a heat of fusion of the polymer (F-TPE) of at least 2.5 J/g, when determined according to ASTM D3418.

[0020] The invention further pertains to a method of making a porous membrane, as above detailed, the method comprising:

(i) providing a composition (C) comprising at least one fluorinated thermoplastic elastomer [polymer (F-TPE)], as detailed above;

(ii) processing the composition (C) provided in step (i) thereby providing a film; and

(iii) processing the film provided in step (ii) thereby providing a porous membrane.

[0021] Still, the invention additionally pertains to a method of making a porous membrane, as above detailed, the method comprising:

(j) providing a composition (C) comprising at least one fluorinated thermoplastic elastomer [polymer (F-TPE)], as detailed above;

(jj) processing the composition (C) provided in step (i) thereby providing a plurality of fibres; and (jjj) assembling the said plurality of fibres provided in step (ii) thereby providing a porous membrane.

[0022] The Applicant has found that the porous membrane of the invention can withstand deformation without detrimentally affecting its mechanical integrity and its permeability, in both dry and wet state.

[0023] Further, porous membranes of the invention can be easily manufactured, including from dope solutions, with no need of pore forming adjuvants, hence avoiding use of possibly leachable/contaminant components.

[0024] This and other objects, advantages, and features of the invention will be more readily understood and appreciated by reference to the detailed description of the invention.

[0025] The porous membrane

[0026] A first object of the invention is hence a porous membrane comprising a polymer (F-TPE), as above detailed, said membrane possessing a gravimetric porosity (£ _m ) of 20 to 95 % v/v.

[0027] The term "membrane" is used herein in its usual meaning, that is to say it refers to a discrete, generally thin, interface that moderates the permeation of chemical species in contact with it. This interface may be molecularly homogeneous, that is, completely uniform in structure (dense membrane), or it may be chemically or physically heterogeneous, for example containing voids, holes or pores of finite dimensions (porous membrane).

[0028] The membranes of the present invention are porous membranes,

possessing well-defined porosity, that is to say are membranes comprising pores.

[0029] Porous membranes can be generally characterized by their average pore diameter and the porosity, i.e. the fraction of the total membrane that is porous.

[0030] Membranes having a uniform structure throughout their thickness,

containing pores homogeneously distributed throughout their thickness are generally known as symmetric (or isotropic) membranes; membranes having pores which are not homogeneously distributed throughout their thickness are generally known as asymmetric membranes. Asymmetric membranes may include a thin selective layer (0.1-1 μηη thick) and a highly porous thick layer (100-200 μηη thick) which acts as a support and has little effect on the separation characteristics of the membrane.

[0031] The porous membrane of the invention may be either a symmetric

membrane or an asymmetric membrane.

[0032] The porous membrane of the invention typically possesses a gravimetric porosity (£ _m ) comprised between 20% and 95% v/v, preferably between 25% and 92 % v/v, more preferably between 30% and 90% v/v.

[0033] As explained, the term "gravimetric porosity" is intended to denote the volume fraction of voids over the total volume of the porous membrane.

[0034] Suitable techniques for the determination of the gravimetric porosity in the porous membranes of the invention are described for instance in

SMOLDERS K., et al. Terminology for membrane distillation. Desalination. 1989, vol.72, p.249-262.

[0035] The porous membrane of the invention may be either a self-standing

porous membrane or can be assembled in a multi-layer assembly.

[0036] When assembled into a multi-layer assembly, the porous membrane of the invention may be notably supported onto a substrate layer, which may be partially or fully interpenetrated by the porous membrane of the invention, or may be not interpenetrated.

[0037] The nature of the substrate is not particularly limited. The substrate

generally consists of materials having a minimal influence on the selectivity of the porous membrane. The substrate layer preferably consists of non-woven materials, glass fibres and/or polymeric material such as for example polypropylene, polyethylene and polyethyleneterephthalate.

[0038] Membranes can be in the form of a flat sheet or in the form of tubes.

Tubular membranes are classified based on their dimensions in:

- tubular membranes having a diameter greater than 3 mm;

- capillary membranes, having a diameter comprised between 0.5 mm and 3 mm; and

- hollow fibres having a diameter of less than 0.5 mm. Oftentimes capillary membranes are also referred to as hollow fibres. [0039] Flat sheet membranes are generally preferred when high fluxes are required whereas hollow fibres are particularly advantageous in

applications where compact modules with high surface areas are required.

[0040] The porous membrane of the invention generally has an average pore diameter of at least 0.001 μηη, more preferably of at least 0.005 μηη, and even more preferably of at least 0.01 μηη. The porous membrane of the invention preferably has an average pore diameter of at most 50 μηη, more preferably of at most 20 μηη, even more preferably of at most 15 μηη, most preferably of at most 5 μηη.

[0041] Suitable techniques for the determination of the average pore diameter in the porous membranes of the invention are described for instance in Handbook of Industrial Membrane Technology . Edited by PORTER. Mark C. Noyes Publications, 1990. p.70-78. Average pore diameter is preferably determined by scanning electron microscopy (SEM).

[0042] According to this method, average diameter of pores (also referred to as "voids") can be measured taking SEM picture from surfaces of fractured sections of the porous membrane. Fractured sections are obtained fracturing the porous membrane in liquid nitrogen, generally in a parallel direction to the intended direction of flow through the porous membrane; fracturing in the said conditions is efficient in ensuring geometry and morphology to be preserved and avoiding any ductile deformation.

[0043] Manual or automated analysis of SEM pictures taken at suitable

magnification/resolution enables delivering data regarding average diameter of pores.

[0044] The expression "average diameter" is meant to indicate that for pore

three-dimensional shapes having non-circular cross-sections, an averaged diameter is computed considering average between longest axis and shortest axis perpendicular thereto, while for pore three-dimensional shapes having circular cross-sections, the actual geometrical diameter is to be taken as average diameter.

[0045] Thickness of the porous membrane of the invention can be tuned

depending on the target field of use. Generally, porous membranes of the invention possess a thickness of at least 10 μηη, preferably of at least 15 μηη, more preferably at least 20 μηη, and/or of at most 500 μηη, preferably at most 350 μηη, even more preferably at most 250 μηη.

[0046] The porous membrane of the invention generally possesses a water flux permeability, at a pressure of 1 bar and at a temperature of 23°C, of at least 300, preferably at least 400, more preferably at least 500 I /(h x m ² ).

[0047] Further, the porous membrane of the invention generally possesses an air flux permeability, at a pressure of 0.1 bar and at a temperature of 23°C, of at least 0.1 , preferably at least 1 , more preferably at least 10 I /(min x cm ² ), and/or of at most 100, preferably at most 70, more preferably at most 50 I /(min x cm ² ). Porous membranes of the present invention, thanks to their air permeability, are specifically useful for use as breathable fabrics, whereas ability of the porous membrane to allow air to pass through it generally entails high moisture vapour transmission, which is key to offer body moisture to be permeated.

[0048] The polymer (F-TPE)

[0049] For the purpose of the present invention, the term "elastomeric", when used in connection with the "block (A)" is hereby intended to denote a polymer chain segment which, when taken alone, is substantially amorphous, that is to say, has a heat of fusion of less than 2.0 J/g, preferably of less than 1.5 J/g, more preferably of less than 1.0 J/g, as measured according to ASTM D3418.

[0050] For the purpose of the present invention, the term "thermoplastic", when used in connection with the "block (B)", is hereby intended to denote a polymer chain segment which, when taken alone, is semi-crystalline, and possesses a detectable melting point, with an associated heat of fusion of exceeding 10.0 J/g, as measured according to ASTM D3418.

[0051] The fluorinated thermoplastic elastomer of the composition (C) of the

invention is advantageously a block copolymer, said block copolymer typically having a structure comprising at least one block (A) alternated to at least one block (B), that is to say that said fluorinated thermoplastic elastomer typically comprises, preferably consists of, one or more repeating structures of type (B)-(A)-(B). Generally, the polymer (F-TPE) has a structure of type (B)-(A)-(B), i.e. comprising a central block (A) having two ends, connected at both ends to a side block (B).

[0052] The block (A) is often alternatively referred to as soft block (A); the block

(B) is often alternatively referred to as hard block (B).

[0053] The term "fluorinated monomer" is hereby intended to denote an

ethylenically unsaturated monomer comprising at least one fluorine atom.

[0054] The fluorinated monomer may further comprise one or more other halogen atoms (CI, Br, I).

[0055] Any of block(s) (A) and (B) may further comprise recurring units derived from at least one hydrogenated monomer, wherein the term "hydrogenated monomer" is intended to denote an ethylenically unsaturated monomer comprising at least one hydrogen atom and free from fluorine atoms.

[0056] The polymer (F-TPE) typically comprises, preferably consists of:

- at least one elastomeric block (A) selected from the group consisting of: (1) vinylidene fluoride (VDF)-based elastomeric blocks (AVDF) consisting of a sequence of recurring units, said sequence comprising recurring units derived from VDF and recurring units derived from at least one fluorinated monomer different from VDF, said fluorinated monomer different from VDF being typically selected from the group consisting of:

(a) C2-C8 perfluoroolefins such as tetrafluoroethylene (TFE),

hexafluoropropylene (HFP);

(b) hydrogen-containing C2-C8 fluoroolefins different from VDF, such as vinyl fluoride, trifluoroethylene (TrFE), hexafluoroisobutylene (HFIB), perfluoroalkyl ethylenes of formula CH2=CH-Rfi, wherein Rfi is a C1-C6 perfluoroalkyl group;

(c) C2-C8 chloro- and/or bromo-containing fluoroolefins such as

chlorotrifluoroethylene (CTFE);

(d) perfluoroalkylvinylethers (PAVE) of formula CF2=CFORfi, wherein Rfi is a C1-C6 perfluoroalkyl group, such as CF3 (PMVE), C2F5 or C3F7;

(e) perfluorooxyalkylvinylethers of formula CF2=CFOXo, wherein Xo is a a C1-C12 perfluorooxyalkyl group comprising one or more than one ethereal oxygen atom, including notably perfluoromethoxyalkylvinylethers of formula CF2=CFOCF2ORf2, with Rf2 being a C1-C3 perfluoro(oxy)alkyl group, such as -CF2CF3, -CF2CF2-O-CF3 and

(f) (per)fluorodioxoles of formula:

wherein each of Rf3, Rf4, Rts and Rf6, equal to or different from each other, is independently a fluorine atom, a C1-C6 perfluoro(oxy)alkyl group, optionally comprising one or more oxygen atoms, such as -CF3, -C2F5, -C3F7, -OCF3 or -OCF2CF2OCF3; and

(2) tetrafluoroethylene (TFE)-based elastomeric blocks (ATFE) consisting of a sequence of recurring units, said sequence comprising recurring units derived from TFE and recurring units derived from at least one fluorinated monomer different from TFE, said fluorinated monomer being typically selected from the group consisting of those of classes (b), (c), (d), (e) as defined above;

- at least one thermoplastic block (B) consisting of a sequence of recurring units derived from at least one fluorinated monomer.

[0057] Any of block(s) (AVDF) and (ATFE) may further comprise recurring units

derived from at least one hydrogenated monomer, which may be selected from the group consisting of C2-C8 non-fluorinated olefins such as ethylene, propylene or isobutylene.

[0058] The elastomeric block (A) is preferably a block (AVDF), as above detailed, said block (AVDF) typically consisting of a sequence of recurring units comprising, preferably consisting of:

- from 45% to 80% by moles of recurring units derived from vinylidene fluoride (VDF),

- from 5% to 50% by moles of recurring units derived from at least one fluorinated monomer different from VDF,

- optionally, up to 1.0 % by moles of recurring units derived from at least one bis-olefin (OF), as above detailed; and

- optionally, up to 30% by moles of recurring units derived from at least one hydrogenated monomer, with respect to the total moles of recurring units of the sequence of block (AVDF).

[0059] The elastomeric block (A) may further comprise recurring units derived from at least one bis-olefin [bis-olefin (OF)] of formula:

wherein RA, RB, RC, RD, RE and RF, equal to or different from each other, are selected from the group consisting of H, F, CI, C1-C5 alkyl groups and C1-C5 (per)fluoroalkyl groups, and T is a linear or branched C1-C18 alkylene or cycloalkylene group, optionally comprising one or more than one ethereal oxygen atom, preferably at least partially fluorinated, or a

(per)fluoropolyoxyalkylene group.

[0060] The bis-olefin (OF) is preferably selected from the group consisting of

those of any of formulae (OF-1 ), (OF-2) and (OF-3):

(OF-1 )

wherein j is an integer comprised between 2 and 10, preferably between 4 and 8, and R1 , R2, R3 and R4, equal to or different from each other, are selected from the group consisting of H, F, C1-C5 alkyl groups and C1-C5 (per)fluoroalkyl groups;

(OF-2)

wherein each of A, equal to or different from each other and at each occurrence, is independently selected from the group consisting of H, F and CI; each of B, equal to or different from each other and at each occurrence, is independently selected from the group consisting of H, F, CI and ORB, wherein RB is a branched or straight chain alkyl group which may be partially, substantially or completely fluorinated or chlorinated, E is a divalent group having 2 to 10 carbon atoms, optionally fluorinated, which may be inserted with ether linkages; preferably E is a -(CF2) _m - group, wherein m is an integer comprised between 3 and 5; a preferred bis-olefin of (OF-2) type is F ₂ C=CF-O-(CF ₂ )5-O-CF=CF ₂ ;

(OF-3)

wherein E, A and B have the same meaning as defined above, R5, R6 and R7, equal to or different from each other, are selected from the group consisting of H, F, C1-C5 alkyl groups and C1-C5 (per)fluoroalkyl groups.

[0061 ] Should the block (A) consist of a recurring units sequence further

comprising recurring units derived from at least one bis-olefin (OF), said sequence typically comprises recurring units derived from the said at least one bis-olefin (OF) in an amount comprised between 0.01 % and 1 .0% by moles, preferably between 0.03% and 0.5% by moles, more preferably between 0.05% and 0.2% by moles, based on the total moles of recurring units of block (A).

[0062] Block (B) may consist of a sequence of recurring units, said sequence comprising:

- recurring units derived from one or more than one fluoromonomer, preferably selected from the group consisting of:

(a) C2-C8 perfluoroolefins such as tetrafluoroethylene (TFE),

hexafluoropropylene (HFP);

(b) hydrogen-containing C2-C8 fluoroolefins, such as vinylidene fluoride (VDF), vinyl fluoride, trifluoroethylene (TrFE), hexafluoroisobutylene (HFIB), perfluoroalkyl ethylenes of formula CH2=CH-Rfi , wherein Rfi is a C1-C6 perfluoroalkyl group;

(c) C2-C8 chloro- and/or bromo-containing fluoroolefins such as

chlorotrifluoroethylene (CTFE);

(d) perfluoroalkylvinylethers (PAVE) of formula CF2=CFORfi , wherein Rfi is a C1-C6 perfluoroalkyl group, such as CF3 (PMVE), C2F5 or C3F7;

(e) perfluorooxyalkylvinylethers of formula CF2=CFOXo, wherein Xo is a a C1-C12 perfluorooxyalkyl group comprising one or more than one ethereal oxygen atom, including notably perfluoromethoxyalkylvinylethers of formula CF2=CFOCF2ORf2, with F½ being a C1-C3 perfluoro(oxy)alkyl group, such as -CF2CF3, -CF2CF2-O-CF3 and -CF ₃ ; and

(f) (per)fluorodioxoles of formula:

wherein each of Rf3, Rf4, Rts and Rf6, equal to or different from each other, is independently a fluorine atom, a C1-C6 perfluoro(oxy)alkyl group, optionally comprising one or more oxygen atoms, such as -CF3, -C2F5, -C3F7, -OCF3 or -OCF2CF2OCF3; and

- optionally, recurring units derived from one or more than one

hydrogenated monomer, as above detailed, including notably ethylene, propylene, (meth)acrylic monomers, styrenic monomers.

[0063] More specifically, block (B) may be selected from the group consisting of:

- blocks (BVDF) consisting of a sequence of recurring units derived from vinylidene fluoride and optionally from one or more than one additional fluorinated monomer different from VDF, e.g. HFP, TFE or CTFE, and optionally from a hydrogenated monomer, as above detailed, e.g. a (meth)acrylic monomer, whereas the amount of recurring units derived from VDF is of 85 to 100 % moles, based on the total moles of recurring units of block (BVDF);

- blocks (BTFE) consisting of a sequence of recurring units derived from tetrafluoroethylene, and optionally from an additional perfluorinated monomer different from TFE, whereas the amount of recurring units derived from TFE is of 75 to 100 % moles, based on the total moles of recurring units of block (B);

- blocks (BE/(C)TFE) consisting of a sequence of recurring units derived from ethylene and recurring units derived from CTFE and/or TFE, possibly in combination with an additional monomer.

[0064] The weight ratio between blocks (A) and blocks (B) in the fluorinated

thermoplastic elastomer is typically comprised between 95:5 and 10:90. [0065] According to certain preferred embodiments, the polymers (F-TPE) comprise a major amount of blocks (A); according to these embodiment's, the polymer (F-TPE) used in the method of the present invention is characterized by a weight ratio between blocks (A) and blocks (B) of 95:5 to 65:35, preferably 90: 10 to 70:30.

[0066] The crystallinity of block (B) and its weight fraction in the polymer (F-TPE) are such to provide for a heat of fusion (AHf ) of the polymer (F-TPE) of advantageously at most 20 J/g, preferably at most 18 J/g, more preferably at most 15 J/g, when determined according to ASTM D3418, to provide for suitable flexibility and elastic recovery after deformation in the porous membrane; on the other side, polymer (F-TPE) used in the porous membrane of the invention combines thermoplastic and elastomeric character, so as to possess a certain crystallinity, delivering a heat of fusion of at least 2.5 J/g, preferably at least 3.0 J/g, which ensure that porosity is maintained e.g. when applying the required pressure for generating appropriate fluxes throughout the membrane.

[0067] Preferred polymers (F-TPE) for the porous membrane of the invention are those comprising:

- at least one elastomeric block (AVDF), as above detailed, and

- at least one thermoplastic block (BVDF), as above detailed, and

wherein the crystallinity of said block (B) and its weight fraction in the polymer (F-TPE) are such to provide for a heat of fusion of the polymer (F-TPE) of at most 20.0 J/g, and/or of at least 5.0 J/g, when determined according to ASTM D3418.

[0068] The polymers (F-TPE) used in the method of the present invention may be manufactured by a manufacturing process comprising the following sequential steps:

(a) polymerizing at least one fluorinated monomer, and possibly at least one bis-olefin (OF), in the presence of a radical initiator and of an iodinated chain transfer agent, thereby providing a pre-polymer consisting of at least one block (A) containing one or more iodinated end groups; and

(b) polymerizing at least one fluorinated monomer, in the presence of a radical initiator and of the pre-polymer provided in step (a), thereby providing at least one block (B) grafted on said pre-polymer through reaction of the said iodinated end groups of the block (A).

[0069] The manufacturing process above detailed is preferably carried out in

aqueous emulsion polymerization according to methods well known in the art, in the presence of a suitable radical initiator.

[0070] The radical initiator is typically selected from the group consisting of:

- inorganic peroxides such as, for instance, alkali metal or ammonium persulphates, perphosphates, perborates or percarbonates, optionally in combination with ferrous, cuprous or silver salts or other easily oxidable metals;

- organic peroxides such as, for instance, disuccinylperoxide,

tertbutyl-hydroperoxide, and ditertbutylperoxide; and

- azo compounds (see, for instance, US 2515628 (E. I. DU PONT DE NEMOURS AND CO.) 7/18/1950 and US 2520338 (E. I. DU PONT DE NEMOURS AND CO.) 8/29/1950 ).

[0071] It is also possible to use organic or inorganic redox systems, such as

persulphate ammonium/sodium sulphite, hydrogen

peroxide/aminoiminomethansulphinic acid.

[0072] In step (a) of the manufacturing process as above detailed, one or more iodinated chain transfer agents are added to the reaction medium, typically of formula R _x l _n , wherein R _x is a C1-C16, preferably a Ci-Cs (per)fluoroalkyl or a (per)fluorochloroalkyl group, and n is 1 or 2. It is also possible to use as chain transfer agents alkali or alkaline-earth metal iodides, as described in US 5173553 (AUSIMONT S.P.A.) 12/22/1992. The amount of the chain transfer agent to be added is established depending on the molecular weight which is intended to be obtained and on the effectiveness of the chain transfer agent itself.

[0073] In any of steps (a) and (b) of the manufacturing process as above detailed, one or more surfactants may be used, preferably fluorinated surfactants of formula: wherein R _y is a C5-C16 (per)fluoroalkyl or a (per)fluoropolyoxyalkyl group, X- is -COO ^" or -SO3 ^" , and M ⁺ is selected from the group consisting of H ⁺ , NH ₄ ⁺ , and an alkali metal ion.

[0074] Among the most commonly used surfactants, mention can be made of

(per)fluoropolyoxyalkylenes terminated with one or more carboxyl groups.

[0075] In the manufacturing process, when step (a) is terminated, the reaction is generally discontinued, for instance by cooling, and the residual monomers are removed, for instance by heating the emulsion under stirring. The second polymerization step (b) is then advantageously carried out, feeding the new monomer(s) mixture and adding fresh radical initiator. If necessary, under step (b) of the process for the manufacture of the polymer (F-TPE), one or more further chain transfer agents may be added, which can be selected from the same iodinated chain transfer agents as defined above or from chain transfer agents known in the art for use in the manufacture of fluoropolymers such as, for instance, ketones, esters or aliphatic alcohols having from 3 to 10 carbon atoms, such as acetone, ethylacetate, diethylmalonate, diethylether and isopropyl alcohol;

hydrocarbons, such as methane, ethane and butane;

chloro(fluoro)carbons, optionally containing hydrogen atoms, such as chloroform and trichlorofluoromethane; bis(alkyl)carbonates wherein the alkyl group has from 1 to 5 carbon atoms, such as bis(ethyl) carbonate and bis(isobutyl) carbonate. When step (b) is completed, the polymer (F-TPE) is generally isolated from the emulsion according to conventional methods, such as by coagulation by addition of electrolytes or by cooling.

[0076] Alternatively, the polymerization reaction can be carried out in mass or in suspension, in an organic liquid where a suitable radical initiator is present, according to known techniques. The polymerization temperature and pressure can vary within wide ranges depending on the type of monomers used and based on the other reaction conditions. Step (a) and/or step (b) of process for the manufacture of the polymer (F-TPE) is typically carried out at a temperature of from -20°C to 150°C; and/or typically under pressures up to 10 MPa.

[0077] The manufacturing process as above detailed is preferably carried out in aqueous emulsion polymerization in the presence of a microemulsion of perfluoropolyoxyalkylenes, as described in US 4864006 (AUSIMONT S.P.A.) 9/5/1989 , or in the presence of a microemulsion of

fluoropolyoxyalkylenes having hydrogenated end groups and/or hydrogenated recurring units, as described in EP 625526 A (AUSIMONT S.P.A.) 1 1/23/1994

[0078] The method of making a porous membrane of first embodiment

[0079] The invention further pertains to a process for manufacturing a porous membrane, as above detailed, the method comprising:

(i) providing a composition (C) comprising at least one fluorinated thermoplastic elastomer [polymer (F-TPE)], as detailed above;

(ii) processing the composition (C) provided in step (i) thereby providing a film; and

(iii) processing the film provided in step (ii) thereby providing a porous membrane.

[0080] In step (i) of the process for manufacturing a porous membrane according to the invention, the composition (C) is typically manufactured by any conventional techniques, by mixing polymer (F-TPE) with any additional ingredient(s).

[0081] Similarly, in step (ii) of the process for manufacturing a porous membrane according to the invention, conventional techniques can be used for processing the composition (C) thereby providing a film.

[0082] The term "film" is used herein to refer to a layer of composition (C)

obtained after processing of the same under step (ii) of the process of the invention. The term "film" is used herein in its usual meaning, that is to say that it refers to a discrete, generally thin, dense layer. This film may be a " wet" film, i.e. a film made of a layer of a liquid composition, or maybe a " solid" film, i.e. a film made of a solid composition.

[0083] Depending on the final form of the membrane, the film may be either flat, when flat porous membranes are to be manufactured, or tubular in shape, when tubular or hollow fibre porous membranes are to be produced.

[0084] According to a first embodiment of the invention, the process for

manufacturing a porous membrane involves using a liquid composition. [0085] The process according to this first embodiment preferably comprises: (i ^A ) providing a liquid composition [composition (C ^L )] comprising:

- at least one polymer (F-TPE) as defined above, and

- a liquid medium [medium (L)];

(ϋ ^Λ ) processing composition (C ^L ) provided in step (i) thereby providing a wet film; and

(iii ^A ) precipitating the wet film provided in step (ii) thereby providing a porous membrane.

[0086] The term "solvent" is used herein in its usual meaning, that is it indicates a substance capable of dissolving another substance (solute) to form an 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.

[0087] The medium (L) preferably comprises at least one organic solvent. Suitable examples of organic solvents which are able to solubilize polymer (F-TPE) are:

- aliphatic hydrocarbons including, more particularly, the paraffins such as, in particular, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane or cyclohexane, and naphthalene and aromatic hydrocarbons and more particularly aromatic hydrocarbons such as, in particular, benzene, toluene, xylenes, cumene, petroleum fractions composed of a mixture of alkylbenzenes;

- aliphatic or aromatic halogenated hydrocarbons including more particularly, perch lorinated hydrocarbons such as, in particular,

tetrachloroethylene, hexachloroethane;

- partially chlorinated hydrocarbons such as dichloromethane, chloroform, 1 ,2-dichloroethane, 1 ,1 ,1 -trichloroethane, 1 ,1 ,2,2-tetrachloroethane, pentachloroethane, trichloroethylene, 1 -chlorobutane, 1 ,2-dichlorobutane, monochlorobenzene, 1 ,2-dichlorobenzene, 1 ,3-dichlorobenzene,

1 ,4-dichlorobenzene, 1 ,2,4-trichlorobenzene or mixture of different chlorobenzenes;

- aliphatic, cycloaliphatic or aromatic ether oxides, more particularly, diethyl oxide, dipropyl oxide, diisopropyl oxide, dibutyl oxide, methylterbutyl ether, dipentyl oxide, diisopentyl oxide, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether benzyl oxide; dioxane, tetrahydrofuran (THF);

- dimethylsulfoxide (DMSO);

- glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether;

- glycol ether esters such as ethylene glycol methyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate;

- alcohols, including polyhydric alcohols, such as methyl alcohol, ethyl alcohol, diacetone alcohol, ethylene glycol;

- ketones such as acetone, methylethylketone, methylisobutyl ketone, diisobutylketone, cyclohexanone, isophorone;

- linear or cyclic esters such as isopropyl acetate, n-butyl acetate, methyl acetoacetate, dimethyl phthalate, γ-butyrolactone;

- linear or cyclic carboxamides such as Ν,Ν-dimethylacetamide (DMAc), Ν,Ν-diethylacetamide, dimethylformamide (DMF), diethylformamide or N-methyl-2-pyrrolidone (NMP);

- organic carbonates for example dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, ethylmethyl carbonate, ethylene carbonate, vinylene carbonate;

- phosphoric esters such as trimethyl phosphate, triethyl phosphate (TEP);

- ureas such as tetramethylurea, tetraethylurea;

- methyl-5-dimethylamino-2-methyl-5-oxopentanoate (commercially available under the tradename Rhodialsov Polarclean®).

Preferably, said at least one organic solvent is selected from polar aprotic solvents and even more preferably in the group consisting of: N-methyl-pyrrolidone (NMP), dimethyl acetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), methyl-5-dimethylamino-2-methyl-5- oxopentanoate (commercially available under the tradename Rhodialsov Polarclean®) and

triethylphosphate (TEP).

[0089] The medium (L) preferably comprises at least 40 wt.%, more preferably at least 50 wt.% based on the total weight of said medium (L), of at least one organic solvent. Medium (L) preferably comprises at most 100 wt.%, more preferably at most 99 wt.% based on the total weight of said medium (L), of at least one organic solvent.

[0090] The medium (L) may further comprise at least one non-solvent medium [medium (NS)]. The medium (NS) may comprise water.

[0091] Under step (i ^A ), composition (C ^L ) is manufactured by any conventional techniques. For instance, the medium (L) may be added to the polymer (F-TPE), or, preferably, the polymer (F-TPE) may be added to the medium (L), or even the polymer (F-TPE) and the medium (L) may be

simultaneously mixed.

[0092] Any suitable mixing equipment may be used. Preferably, the mixing

equipment is selected to reduce the amount of air entrapped in composition (C ^L ) which may cause defects in the final membrane. The mixing of the polymer (F-TPE) and the medium (L) may be conveniently carried out in a sealed container, optionally held under an inert atmosphere. Inert atmosphere, and more precisely nitrogen atmosphere has been found particularly advantageous for the manufacture of composition (C ^L ).

[0093] Under step (i ^A ), the mixing time during stirring required to obtain a clear homogeneous composition (C ^L ) can vary widely depending upon the rate of dissolution of the components, the temperature, the efficiency of the mixing apparatus, the viscosity of composition (C ^L ) and the like.

[0094] The composition (C ^L ) may contain additional components, such as pore forming agents, nucleating agents, fillers and the like.

[0095] The use of a pore forming agent is not mandatory for delivering appreciable fluxes through the porous membrane of polymer (F-TPE), which is particularly advantageous, when residues thereof may detrimentally affect purity or cause contamination during use.

[0096] Without being bound by this theory, the Applicant is of the opinion that the peculiar microstructure of the polymer (F-TPE), comprising soft and hard interconnected blocks, is such that when processing the composition (C ^L ) into a wet film, and then precipitating the polymer (F-TPE) for providing the porous membranes, the kinetic of precipitation/crystallization is slow enough to avoid formation of a continuous skin, responsible of inhibiting flux.

[0097] Nevertheless, a pore forming agent may be used, in particular when the polymer (F-TPE) is intended for the manufacture of a hollow fibre membrane. Suitable pore forming agents are notably polyvinylpyrrolidone (PVP), and polyethyleneglycol (PEG) having a molecular weight of at least 200.

[0098] The pore forming agent, if added to the composition (C ^L ), is present in amounts typically ranging from 0.1 to 40% by weight, preferably from 0.5 to 40% by weight.

[0099] When PEG pore forming agents are used, their amounts are generally of from 15 to 40 % wt, with respect to the total weight of composition (C ^L ); when PVP pore forming agents are employed, their amounts is generally of 2 to 10 % wt, with respect to the total weight of composition (C ^L ).

[0100] Besides, composition (C ^L ) generally comprises polymer (F-TPE) in an

amount of at least 3 % wt, preferably at least 5 % wt, more preferably at least 10 % wt and/or of at most 40 % wt, preferably of at most 35 % wt, even more preferably at most 30 % wt, with respect to the total weight of composition (C ^L ).

[0101] Under step (ϋ ^Λ ), composition (C ^L ) is typically processed in liquid phase.

[0102] Under step (ϋ ^Λ ), composition (C ^L ) is typically processed by casting thereby providing a wet film.

[0103] 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. [0104] Under step (ϋ ^Λ ), the temperature at which composition (C ^L ) is processed by casting may be or may be not the same as the temperature at which composition (C ^L ) is mixed under stirring.

[0105] Different casting techniques are used depending on the final form of the membrane to be manufactured.

[0106] When the final product is a flat membrane, composition (C ^L ) is cast as a wet 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.

[0107] According to a first embodiment of step (ϋ ^Λ ), composition (C ^L ) is processed by casting onto a flat supporting substrate to provide a flat film.

[0108] According to a second embodiment of step (ϋ ^Λ ), composition (C ^L ) is

processed to provide a tubular wet film.

[0109] According to a variant of this second embodiment of step (ϋ ^Λ ), the tubular wet film is manufactured using a spinneret.

[01 10] 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 composition (C ^L ) and a second inner one for the passage of a supporting fluid, generally referred to as "lumen".

[01 1 1] Hollow fibres and capillary porous membranes may be manufactured by the so-called spinning process according to this variant of the second embodiment of step (ϋ ^Λ ). According to this variant of the second

embodiment of the invention, composition (C ^L ) is generally pumped through the spinneret. The lumen acts as the support for the casting of composition (C ^L ) and maintains the bore of the hollow fibre 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.

[01 12] At the exit of the spinneret, after a short residence time in air or in a

controlled atmosphere, under step (iii ^A ) of the process for manufacturing a porous membrane according to this first embodiment of the invention, the wet film in the form of hollow fibre precursor or capillary precursor is precipitated thereby providing the hollow fibre or capillary membrane.

[01 13] The supporting fluid forms the bore of the final hollow fibre or capillary

membrane.

[01 14] Figure 1 is a simplified scheme of the hollow fibre spinning machine which can be used for manufacturing hollow fibre membrane, wherein 1 is the dope solution tank equipped with a feeding pump, 2 is the bore fluid tank, equally equipped with an injection pump, 3 is the spinneret or annular die, 4 is the nascent hollow fibre, 5 is the air gap, 6 is the coagulation bath and 7 is the so obtained hollow fibre.

[01 15] Figure 2 is a schematic cut of the spinneret (annular die), through a plane parallel to the fibre extrusion flow, wherein 1 is the bore fluid die, and 2 is the annular die feeding the dope solution.

[01 16] Figure 3 is a schematic cut of the spinneret (annular die), through a plane perpendicular to the fibre extrusion flow, wherein 1 is the extruded/spin ned bore fluid, 2 is the extruded/spinned dope solution, and 3 is the body of the spinneret/annular die.

[01 17] Tubular membranes, because of their larger diameter, are generally

manufactured using a different process from the one employed for the production of hollow fibre membranes.

[01 18] The Applicant has found that use of solvent/non-solvent mixtures at a given temperature, in any one of steps (ϋ ^Λ ) and (iii ^A ) of the process according to the invention, advantageously allows controlling the morphology of the final porous membrane including its average porosity.

[01 19] The temperature gradient between the film provided in any one of steps (ϋ ^Λ ) and (iii ^A ) of the process according to the first embodiment of the invention and the medium (NS) may also influence the pore size and/or pore distribution in the final porous membrane as it generally affects the rate of precipitation of the polymer (F-TPE) from composition (C ^L ).

[0120] According to a first variant of the first embodiment of the invention, the

process for manufacturing a porous membrane comprises:

(i ^A* ) providing a liquid composition [composition (C ^L )] comprising:

- at least one polymer (F-TPE), and - a liquid medium comprising at least one organic solvent [medium (L)]; (ϋ ^Λ* ) processing composition (C ^L ) provided in step (i ^A* ) thereby providing a wet film; and

(iii ^A* ) precipitating the wet film provided in step (ϋ ^Λ* ) in a non-solvent medium [medium (NS)] thereby providing a porous membrane.

[0121] Under step (i ^A* ), the medium (L) comprising at least one organic solvent, such as those detailed above, preferably further comprises water.

[0122] Under step (iii ^A* ), the medium (NS) preferably comprises water and,

optionally, at least one organic solvent.

[0123] According to a second variant of the first embodiment of the invention, the process for manufacturing a porous membrane comprises:

(i ^A** ) providing a liquid composition [composition (C ^L )] comprising:

- at least one polymer (F-TPE), and

- a liquid medium comprising at least one organic solvent [medium (L)]; (ii ^A** ) processing composition (C ^L ) provided in step (i ^A** ) thereby providing a wet film; and

(iii ^A** ) precipitating the wet film provided in step (ii ^A** ) by cooling thereby providing a porous membrane.

[0124] Under step (i ^A** ), the medium (L) of composition (C ^L ) advantageously

comprises at least one latent organic solvent.

[0125] For the purpose of the present invention, the term "latent" is intended to denote an organic solvent which behaves as an active solvent only when heated above a certain temperature.

[0126] Under step (ii ^A** ), the composition (C ^L ) is typically processed into a wet film at a temperature high enough to maintain composition (C ^L ) as a

homogeneous solution.

[0127] Under step (ii ^A** ), the wet film is typically processed at a temperature

comprised between 60°C and 250°C, preferably between 70°C and 220°, more preferably between 80°C and 200°C.

[0128] Under step (iii ^A** ), the wet film provided in step (ii ^A** ) is typically

precipitated by cooling to a temperature below 100°C, preferably below 60°

C, more preferably below 40°C, typically using any conventional techniques. [0129] Under step (iii ^A** ), cooling is typically carried out by contacting the wet film provided in step (ϋ ^Λ** ) with a liquid medium [medium (L')].

[0130] Under step (iii ^A** ), the medium (U) preferably comprises, and more

preferably consists of, water.

[0131] Alternatively, under step (iii ^A** ), cooling is carried out by contacting the film provided in step (ϋ ^Λ** ) with air.

[0132] Under step (iii ^A** ), either the medium (U) or air is typically maintained at a temperature below 100°C, preferably below 60°C, more preferably below

40°C.

[0133] According to a third variant of the first embodiment of the invention, the process for manufacturing a porous membrane comprises:

(i ^A*** ) providing a liquid composition [composition (C ^L )] comprising:

- at least one polymer (F-TPE), and

- a liquid medium comprising at least one organic solvent [medium (L)]; (ϋ ^Λ*** ) processing composition (C ^L ) provided in step (i ^A*** ) thereby providing a wet film; and

(iii ^A*** ) precipitating the wet film provided in step (ϋ ^Λ*** ) by absorption of a non-solvent medium [medium (NS)] from a vapour phase thereby providing a porous membrane.

[0134] Under step (iii ^A*** ), the wet film provided in step (ϋ ^Λ*** ) is preferably

precipitated by absorption of water from a gas phase comprising water vapour.

[0135] Under step (iii ^*** ), the wet film provided in step (ϋ ^Λ*** ) is preferably

precipitated under air, typically having a relative humidity higher than 10%, preferably higher than 50%.

[0136] According to a fourth variant of the first embodiment of the invention, the process for manufacturing a porous membrane comprises:

(i ^A**** ) providing a liquid composition [composition (C ^L )] comprising:

- at least one polymer (F-TPE), and

- a liquid medium comprising at least one organic solvent [medium (L)]; (ii ^A ****) processing composition (C ^L ) provided in step (j ****) to provide a wet film; and (ίϋ ^Λ**** ) evaporating the medium (L) from the said wet film, thereby providing a porous membrane.

[0137] Preferably, when the medium (L) comprise more than one organic solvents, step (ϋ ^Λ**** ) comprises processing composition (C ^L ) to provide a wet film, which is then precipitated in step (ίϋ ^Λ**** ) by evaporation of the medium (L) at a temperature above the boiling point of the organic solvent having the lowest boiling point.

[0138] According to a preferred embodiment, step (ϋ ^Λ**** ) is performed by

processing composition (C ^L ) with a high voltage electric field.

[0139] For the purpose of the present invention, by the term "non-solvent medium

[medium (NS)]" it is meant a medium consisting of one or more liquid substances incapable of dissolving the polymer (F-TPE) at a given temperature.

[0140] The medium (NS) typically comprises water and, optionally, at least one organic solvent selected from alcohols or polyalcohols, preferably aliphatic alcohols having a short chain, for example from 1 to 6 carbon atoms, more preferably methanol, ethanol, isopropanol and ethylene glycol.

[0141] The medium (NS) is generally selected among those miscible with the

medium (L) used for the preparation of composition (C ^L ).

[0142] The medium (NS) may further comprise the medium (L).

[0143] More preferably, the medium (NS) consists of water. Water is the most inexpensive non-solvent medium and can be used in large amounts.

[0144] The medium (L) is advantageously soluble in water, which is an additional advantage of the process of the present invention.

[0145] The process for manufacturing a porous membrane according to the first embodiment may comprise any combination of the first, second, third and fourth variants as defined above. For instance, the porous membrane according to the present invention may be obtainable by the process according to the second variant of the first embodiment of the invention followed by the process according to the first variant of the first

embodiment of the invention. [0146] The porous membrane obtainable by the process according to the first embodiment may undergo additional post treatment steps, for instance rinsing and/or stretching.

[0147] The porous membrane obtainable by the process according to the first embodiment of the invention is typically rinsed using a liquid medium miscible with the medium (L).

[0148] The porous membrane obtainable by the process according to the first embodiment of the invention may be advantageously stretched so as to increase its average porosity.

[0149] According to a second embodiment of the invention, the process for

manufacturing a porous membrane comprises processing the composition

(C) from the molten phase.

[0150] The process according to the second embodiment of the invention

preferably comprises the following steps:

(ί ^ΛΛ ) providing a solid composition [composition (C ^s )] comprising at least one polymer (F-TPE), as defined above, and optionally one or more than one additional ingredient;

(ϋ ^ΛΛ ) processing the composition (C ^s ) provided in step (ί ^ΛΛ ) thereby providing a solid film and

(ίϋ ^ΛΛ ) stretching the solid film provided in step (ϋ ^ΛΛ ) thereby providing a porous membrane.

[0151] Under step (ϋ ^ΛΛ ), composition (C ^s ) is processed in molten phase.

[0152] Melt forming is commonly used to make dense films by film extrusion, preferably by flat cast film extrusion or by blown film extrusion.

[0153] According to this technique, composition (C ^s ) 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. Composition (C ^s ) is melt compounded for obtaining a molten composition. Generally, melt compounding is carried out in an extruder. Composition (C ^s ) 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. [0154] Twin screw extruders are preferred devices for accomplishing melt compounding of composition (C ^s ).

[0155] Solid 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.

[0156] Under step (ίϋ ^ΛΛ ), the solid film provided in step (ϋ ^ΛΛ ) may be stretched either in molten phase or after its solidification upon cooling.

[0157] When composition (C ^s ) comprises a leachable pore-forming ingredient, the solid film is advantageously treated with a suitable solvent, causing the said pore-forming ingredient to be leached out, and hence contributing to creating porosity throughout the porous membrane.

[0158] The porous membrane obtainable by the process of the invention is

typically dried, preferably at a temperature of at least 30°C.

[0159] Drying can be performed under air or a modified atmosphere, e.g. under an inert gas, typically exempt from moisture (water vapour content of less than 0.001 % v/v). Drying can alternatively be performed under vacuum.

[0160] The method of making a porous membrane of second embodiment

[0161] As said, the invention further pertains to a method of making a porous

membrane, as above detailed, the method comprising:

(j) providing a composition (C) comprising at least one fluorinated thermoplastic elastomer [polymer (F-TPE)], as detailed above;

(jj) processing the composition (C) provided in step (i) thereby providing a plurality of fibres; and

(jjj) assembling the said plurality of fibres provided in step (ii) thereby providing the said porous membrane.

[0162] All embodiment's described above in connection with polymer (F-TPE) are features applicable to specific embodiment's of the method of this embodiment.

[0163] Composition (C) may comprise, in addition to polymer (F-TPE), additional ingredients, including additional polymeric components, and/or additives or fillers. Generally, composition (C) may comprise additives selected from the group consisting of stabilizers, pigments, processing aids, and the like.

[0164] Depending on the technology used in step (jj), composition (C) may be a liquid composition, i.e. a composition (C'L). All embodiment's described above in connection with composition (CL) are applicable to composition (C 'L), mutatis mutandis.

[0165] According to certain embodiment's, fibres are produced in step (jj) from processing composition (C'L) comprising polymer (F-TPE) and an organic solvent able to solubilize polymer (F-TPE) at the processing temperature; the composition (C'L) comprising solubilized polymer (F-TPE) is spun through orifices, and the wet precursors of the fibres are

coagulated/solidified either by immersion in a non-solvent bath or by evaporation of the solvent.

[0166] According to other preferred embodiment's, fibres are produced in step (jj) from processing composition (C) from the molten state. Generally, these techniques comprise processing composition (C) in the molten state in an extrusion device to provide for a molten composition, and forcing the molten composition through a die comprising a plurality of orifices.

Generally, a pump is positioned between the extruder barrel and the die; such pump may be a metering pump comprising intermeshing

counter-rotating toothed gears, although other types of pumps may be used.

[0167] A variety of dies may be used, which generally include a polymer feed distribution section and a spinneret, i.e. a block of metal having a plurality of drilled orifices.

[0168] Fibres obtained from step (jj) may be under the form of staple fibres or may be under the form of continuous filaments.

[0169] Fibres may be assembled to create an assembly processed into a porous membrane by a variety of techniques. These assembling techniques may lead to knitted fabrics (e.g. weft-knit and warp-knit fabrics) or woven fabrics, which may provide the porous membrane or which may be assembled to provide the said porous membrane; as an alternative, fibres may be assembled as a non-woven fabric, which can provide the porous membrane or which may be assembled to provide the said porous membrane.

[0170] In case of assembly as a non-woven fabric, the fibres are generally

entangled and bonded in step (jjj).

[0171] Entanglement of fibres may be achieved using different techniques,

including the use of mechanical and pneumatic fibres oscillators, rotating deflectors, electrostatic charging, compressed air flow, etc.

[0172] Bonding may be achieved e.g. by hydro-entangle bonding,

needle-punching bonding, thermal bonding, chemical bonding, stich bonding, ultrasonic fusing, etc.

[0173] According to a first variant of the method of this second embodiment, the method is a spun-bond process, comprising:

(j') providing a composition (C ^s"b ) comprising at least one fluorinated thermoplastic elastomer [polymer (F-TPE)], as detailed above;

(jj') extruding through a spinneret die from the molten state a plurality of filament fibres, and drawing the same, to provide for continuous filament fibres having a diameter of 1 to 50 μηη, preferably of 15 to 35 μηη; and (jjj') entangling and deposing the filament fibres under the form of a web on a moving suctioned belt, so as to provide a spun web; and

(jv') bonding at least a portion of the spun web, to provide the porous membrane.

[0174] The composition (C ^s"b ) may consist essentially of polymer (F-TPE), or may comprise the said polymer (F-TPE° in combination with other

melt-processable ingredients. Generally, composition (C ^s"b ) will comprise polymer (F-TPE) as major component, and may comprise minor amounts (e.g. of up to 10 % wt, preferably up to 5 % wt) of usual additives and formulation aids for polymer (F-TPE).

[0175] Filament fibres are formed in step (jj') as the molten composition (C ^s"b ) exits the spinneret, and is generally quenched by hot air. Drawing the filament fibres to attenuate the same is achieved generally by stretching the same immediately after exiting the spinneret; in practice, the fibres are accelerated either mechanically or pneumatically to effect drawing and attenuation: a drawing channel (or Venturi tube) is generally used for drawing using aero-dynamical forces to attenuate the filament fibres.

[0176] In step (jjj') the web is formed by the pneumatic deposition of the filament fibres onto a moving belt, while filaments are separated and entangled by electrostatic, mechanical or aero-dynamic forces.

[0177] The conveyor belt is generally moving transversally with respect to the direction of lay-down, and generally deposition occurs in a zig-zag pattern on the surface of the moving belt.

[0178] Bonding can be achieved by any of the methods described above, and can be effected either on large regions or small regions of the so formed web.

[0179] According to a second variant of the method of this second embodiment, the method is a melt-blown process, comprising:

(j") providing a composition (C ^m"b ) comprising at least one fluorinated thermoplastic elastomer [polymer (F-TPE)], as detailed above;

(jj") extruding from the molten state, through a die including capillaries surrounded by high speed blowing gas manifolds, a plurality of molten extrudates, and blow high velocity hot air through said feeders so as to provide for attenuated discontinuous fibres; and

(jjj") entangling the said attenuated discontinuous fibres and collecting the same onto a collecting device, so as to form a melt-blown web; and (jv') bonding at least a portion of the melt-blown web, to provide the porous membrane.

[0180] The composition (C ^m"b ) may consist essentially of polymer (F-TPE), or may comprise the said polymer (F-TPE° in combination with other

melt-processable ingredients. Generally, composition (C ^m"b ) will comprise polymer (F-TPE) as major component, and may comprise minor amounts (e.g. of up to 10 % wt, preferably up to 5 % wt) of usual additives and formulation aids for polymer (F-TPE).

[0181] The high speed blowing gas manifolds supply high velocity hot air through the slots on to the molten extrudates; high velocity hot air is generally generated by air compressor and passed through a heat exchange unit to heat the air to desired processing temperatures. Typical air temperatures range from 230°C-360°C, and are generally selected depending upon melt temperature of the polymer (F-TPE); high velocity hot air is blown at velocities of 0.3 to 1 %, preferably 0.5 to 0.8% of the speed of sound.

[0182] As soon as the molten composition (C ^m"b ) is extruded from the capillaries, high velocity hot air stream (exiting from the said manifolds) attenuate the extrudates to form micro-fibres.

[0183] Melt-blown micro-fibres generally have an average fibre diameter range of

2 to 4 μηη, although they may be as low as 0.3-0.6 μηη and as high as 15-

20 Mm.

[0184] As the hot air stream containing the micro-fibres progresses toward the collector, it generally draws in a large amount of surrounding air (also called secondary air) that cools and solidifies the fibres, while, at the same time, entangling the same. The solidified fibres generally get laid randomly and entangle themselves onto the collecting screen, forming a self-bonded nonwoven web due to the turbulence of secondary air.

[0185] The collecting device may be in the form of a suctioned rotating screen.

The collecting device speed and the distance from the die can be varied to produce a variety of melt-blown webs. A vacuum is generally applied to the inside of the collector screen to withdraw the hot air and enhance the fibre laying process.

[0186] The melt-blown web is usually wound onto a cardboard core and

processed according to the end-use requirement.

[0187] Additional bonding over the fibre adhesion and fibre entanglement that occurs at lay down is generally employed to alter web characteristics. Thermal bonding is the most commonly used technique. The bonding can be either overall (area bonding) or spot (pattern bonding). Bonding is usually used to increase web strength and abrasion resistance.

[0188] According to a third variant of the method of this second embodiment, the method is an electrospinning process, comprising:

(j'") providing a composition (C ^e-S ) comprising at least one fluorinated thermoplastic elastomer [polymer (F-TPE)], as detailed above, and optionally at least one organic solvent, as detailed above;

(jj") spinning charged jets from said composition (C ^e-S ) using a high voltage electric field, and drying/solidifying said jets to provide for electrostatically charged fibres; and

(jjj") entangling and collecting said electrostatically charged fibres onto a collecting device having opposite electrostatic charge, so as to form an electro-spun web; and

(jv') bonding at least a portion of the electro-spun web, to provide the porous membrane.

[0189] Fibre diameter of electrostatically charged fibres can easily be below 1 μηη, and being generally in the range of hundreds of nm or even down to 100 nm or less.

[0190] Uses of the porous membrane

[0191] The porous membrane according to the present invention can be used in several technical fields, notably for the filtration of liquid and/or gas phases or can be embedded or laminated into multi-layered assemblies, such as those which are used as 'breathable fabric'.

[0192] Thus, in another aspect, the present invention pertains to a method of separating components of a liquid and/or gas medium comprising contacting the said medium with at least one porous membrane, as above detailed.

[0193] Generally, the liquid and/or gas medium which will be submitted to the

separation method of the invention comprises one or more contaminant(s). Liquid and gas phases comprising one or more solid contaminants are also referred to as "suspensions", i.e. heterogeneous mixtures comprising at least one solid particle (the contaminant) dispersed into a continuous phase (or "dispersion medium", which is in the form of liquid or gas or in the form of a liquid comprising dispersed gas).

[0194] Said at least one solid contaminant preferably comprises comprising

microorganisms, preferably selected from the group consisting of bacteria such as Staphylococcus aureus and Pseudomonas aeruginosa, algae, fungi, protozoa and viruses.

[0195] In one embodiment, two or more porous membranes according to the

present invention can be used in series for the filtration of a liquid and/or gas medium. Advantageously, a first filtration step is performed by contacting liquid and/or gas medium comprising one or more solid contaminants with a porous membrane according to the present invention having an average pore diameter higher than 5 μηη; and a second filtration step is performed after said first filtration step, by contacting the same liquid and/or gas phase with a porous membrane according to the present invention having an average pore diameter of from 0.001 to 5 μηη.

[0196] Alternatively, at least one porous membrane according to the present invention is used in series with at least one porous membrane other than the porous membrane of the present invention.

[0197] In a further aspect, the present invention relates to a breathable fabric comprising at least one layer consisting of a porous membrane according to the present invention.

[0198] Breathable fabrics are typically provided as continuous rolls of 1.5 to 2 meters wide and 100 to 5000 meters long.

[0199] Generally, the breathable fabric of the invention comprises at least one additional layer, and more specifically comprises the porous membrane of the present invention as inner layer comprised between an outer layer and an inner layer.

[0200] In connection with a breathable fabric, the expression "outer" is used for designating the surface side which is intended to be exposed to the outside environment, while the expression "inner" is the surface side directed to the body.

[0201] The inner layer of the breathable fabrics generally include non-absorbent materials, e.g. in the form of woven or non-woven substrates, which are advantageously designed to provide a comfortable soft touch/hand. While natural fibres such as cotton fibres can be used, polyester-type, and more particularly polyethylene terephthalates are generally used, often processed in shapes possessing many narrow capillaries, such as microfibers, are ideal for moisture transport as these materials are more keen to a dry contact surface between the human body and the breathable fabric.

[0202] The outer layer is not particularly limited, although it is generally recognized that sufficient water repellency would be needed for avoiding this layer becoming soaked, and suppressing breathability. Nylon or polyester (e.g. PET) fabrics maybe used, as they provide adequate strength; water repellent surface treatment may be applied, in case water repellence of base material is not sufficient.

[0203] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0204] The invention will be now described in more details with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.

[0205] Raw materials

[0206] Dimethyl acetamide (DMAc) was supplied from Sigma Aldrich and used as received.

[0207] Isopropyl alcohol (IPA) from Sigma Aldrich

[0208] SOLEF ^® 1015 PVDF is a VDF homopolymer commercially available from Solvay Specialty Polymers Italy S.p.A. (PVDF-1 , herein after)

[0209] PVP K15, polyvinylpyrrolidone with K-value of about 15, was supplied from Sigma Aldrich.

[0210] Preparative Example 1 - Manufacture of fluorinated thermoplastic

elastomer (F-TPE-1)

[021 1] In a 7.5 liters reactor equipped with a mechanical stirrer operating at 72 rpm, 4.5 I of demineralized water and 22 ml of a microemulsion, previously obtained by mixing 4.8 ml of a perfluoropolyoxyalkylene having acidic end groups of formula CF ₂ CIO(CF2-CF(CF3)O)n(CF2O)mCF ₂ COOH, wherein n/m = 10, having an average molecular weight of 600, 3.1 ml of a 30% v/v NH4OH aqueous solution, 1 1.0 ml of demineralized water and 3.0 ml of GALDEN® D02 perfluoropolyether of formula

CF ₃ O(CF2CF(CF3)O)n(CF2O)mCF ₃ , wherein n/m = 20, having an average molecular weight of 450, were introduced.

The reactor was heated and maintained at a set-point temperature of 80°C; a mixture of vinylidene fluoride (VDF) (78.5% moles) and

hexafluoropropylene (HFP) (21.5% moles) was then added to reach a final pressure of 20 bar. Then, 8 g of 1 ,4-diiodoperfluorobutane (C ₄ Fsl2) as chain transfer agent were introduced, and 1.25 g of ammonium persulfate (APS) as initiator were introduced. Pressure was maintained at a set-point of 20 bar by continuous feeding of a gaseous mixture of vinylidene fluoride (VDF) (78.5% by moles) and hexafluoropropylene (HFP) (21.5% by moles) up to a total of 1600 g.

[0212] Once 1600 g of monomer mixture were fed to the reactor, the reaction was discontinued by cooling the reactor to room temperature. The residual pressure was then discharged and the temperature brought to 80°C. VDF was then fed into the autoclave up to a pressure of 20 bar, and 0.14 g of ammonium persulfate (APS) as initiator were introduced. Pressure was maintained at a set-point of 20 bar by continuous feeding of VDF up to a total of 690 g. Then, the reactor was cooled, vented and the latex recovered. The latex was treated with aluminum sulphate, separated from the aqueous phase, washed with demineralized water and dried in a convection oven at 90°C for 16 hours.

[0213] Thermal properties have been determined by differential scanning

calorimetry pursuant to ASTM D3418 standard.

[0214]

Table 1

[0215] Solution preparation

Solutions were prepared by adding the appropriate amount of polymer and solvent (DMAC) (optionally with other ingredients) and stirring with a mechanical anchor for several hours at room temperature.

[0216] Table 1

[0217] Porous membrane preparation

Flat sheet porous membranes were prepared by filming the dope solution over a suitable smooth glass support by means of an automatized casting knife. Membrane casting was performed by keeping dope solutions, the casting knife and the support temperatures at 25°C, so as to prevent premature precipitation of the polymer. The knife gap was set to 250 μηη. After casting, polymeric films were immediately immersed in a coagulation bath in order to induce phase inversion. The coagulation bath consisted of pure de-ionized water. After coagulation the membranes were washed several times in pure water during the following days to remove residual traces of solvent. The membranes were stored (wet) in water.

[0218] Water flux permeability measurements:

[0219] Water flux (J) through each membrane at given pressure, is defined as the volume which permeates per unit area and per unit time. The flux is

calculated by the following equation: A- to

whereas V (I) is the volume of permeate, A (m ² ) is the membrane area, and At (H) is the operation time. J is hence measured in l/(h x m ² ), and this unit is otherwise referred as LMH.

Water flux measurements were conducted on circular specimens cut off from flat porous membranes (diameter: 47 mm) at room temperature (23° C) using a dead end configuration under a constant pressure of 1 bar. Data summarized in table 2 are provided as the average of measurements performed on at least 5 different specimens. [0220] Air flux permeability measurements

[0221] Air permeability of a substrate is a property which characterize how well the said substrate allows the passage of air though it, and is a common determination for characterizing fabrics. Air permeability determinations were performed using the Porometer "Porolux 1000" (POROMETER Belgium). Under air, a pressure of 0.1 bar was applied on dry circular specimens with a diameter of 10.2 mm and the corresponding air flux measured at room temperature (23°C). The values reported are the average of at least 5 measurements. Air permeability is expressed as the ratio between the air volume permeated V _a ir (I), and the product of permeation area A (cm ² ) by permeation time At (minutes). Air permeability is hence measured in l/(min x cm ² ).

Measurement of gravimetric porosity on porous membranes

[0222] Gravimetric porosity of the membrane is defined as the volume of the pores divided by the total volume of the membrane. The porosities were measured using pure IPA as wetting fluid according to the procedure described, for instance, in the Appendix of SMOLDERS, K., et al.

Terminology for membrane distillation. Desalination. 1989, vol.72, p.249-262. Perfectly dry membrane pieces were weighed and impregnated in isopropyl alcohol (IPA) for 24h; after this time, the excess of the liquid was removed with tissue paper, and membranes weight was measured again. Finally, from the dry and the wet weight of the sample, it is possible to evaluate the porosity of the membrane using the following formula:

w _w - w _d

'w Pd

wherein:

Ww is the weight of the wet membrane,

Wd is the weight of the dry membrane,

Pw is the IPA density (0.785 g/cm ³ ) and

Pd is the polymer density (1.76 g/cm ³ for polymer F-TPE-1 and PVDF-1) [0223] Mechanical (Tensile) test

[0224] Porous membranes were submitted to tensile determination according to ASTM D 638 standard procedure (type V, grip distance = 25.4 mm, initial length Lo = 21.5 mm). Velocity was between 1 and 50 mm/min. For "wet" measurements, tested membranes were stored in water without any supplementary treatment; "dry" measurements were carried out on membranes which have been dried at room temperature for 2 days.

Measurements were repeated on at least 5 specimens.

[0225] Data are collected in Table below, inclusive of standard deviations,

whereas:

E is the apparent modulus;

Ob is the stress at break;

£b is the elongation at break.

[0226] Crumpling test

[0227] To assess flexibility and resistance to bending/deformation, a crumpling test was performed. It was conducted on squared specimens (4x4cm ² ) of dry membranes. The procedure is as follows: 1) the dry sample under testing was gently rolled into a tube shape to reduce its dimensions to approximately a diameter of 1 cm; 2) The specimen so obtained was crumpled up under a fixed force of 100N for 45 seconds (applied on one of the bases of the cylinder); 3) The force was then released and a) the aspect of the specimen was inspected, and b) possible wrinkles, flaw or defects were detected.

[0228] The test is considered passed only when: a) the sample recovered its

original dimensions within 15 seconds; b) no more than two defects or wrinkles are observed on the surface; and c) no cuts or flaws were present on the surface.

[0229] Test was fully passed only by porous membrane of Ex. 2 made from

F-TPE-1 which recovered its dimension in few seconds without showing any apparent defect. PVDF porous membranes (EX 3C-4C-5C) never recovered the original dimensions even after minutes and showed several defects and wrinkles on the surface.

[0230] Table 2

Data summarized in Table above clearly demonstrate that high

permeability can be achieved with the porous membranes of the present invention, even when the same are manufactured in the absence of porous-forming agents. In the case of traditional PVDF materials, no flux is obtained in similar manufacturing conditions, unless a pore forming agent is suitably added.

Table 3

[0232] ( ^* ): determinations made on "wet" membrane; ( ^** ): determinations made on "dry" membranes.

[0233] Data listed in Table above clearly demonstrate that porous membranes of the present invention are more flexible and withstand higher deformations before critical failure (ε_>) both in their wet and dry status than

corresponding PVDF porous membranes. Further, while dry status in PVDF membranes causes stiffness and brittle behaviour, with dramatic loss in elongation at break, porous membranes of the invention are not significantly sensitive to the moisture content, and hence can be used both in their dry and wet forms.