Waterproof breathable membrane

Abstract

A waterproof breathable porous membrane (10) is formed from, or comprises, a first polymeric material. The first polymeric material is a polyolefin elastomer. The membrane further comprises a second polymeric material which is different to the first polymeric material. A method (100) for creating the waterproof breathable porous membrane is also provided. The method comprises providing (100) a polymer mixture comprising a first polymeric material and a second polymeric material, where the first polymeric material is, or comprises, a polyolefin elastomer. The method further comprises using the polymer mixture to form a pre-membrane (120). The method also comprises forming a plurality of pores in the pre-membrane to form the membrane (130).

Description

[0001] WATERPROOF BREATHABLE MEMBRANE

[0002] The invention relates generally to a waterproof breathable membrane and a method for creating said membrane. More particularly, but not exclusively, the invention relates to waterproof breathable membranes formed from polyolefin elastomers with improved heat-resistance properties.

[0003] Background

[0004] Waterproof breathable membranes enable the passage of gases therethrough whilst inhibiting the passage of water. Waterproof breathable membranes are used in a wide variety of applications, such as in waterproof breathable textiles, which are often used in waterproof garments, such as shoes and clothes, as well as waterproof gear such as tents.

[0005] Waterproof breathable membranes fall into two general categories - porous and non- porous. Porous membranes are hydrophobic and employ micron-sized to sub-micronsized pores to prevent the passage of liquid (e.g., raindrops) through the membrane whilst allowing small gaseous molecules (e.g., water vapour molecules) to permeate through the membrane. The material of the porous membrane will also have an intrinsic permeability for respective gaseous molecules, which may allow gaseous molecules to also pass through the membrane material itself in addition to through the pores in the membrane. However, the primary transport mechanism for gaseous molecules through a porous membrane is typically through the pores in the membrane. In contrast, non- porous membranes are hydrophilic, and the primary transport mechanism for water vapour molecules is along hydrophilic polymer chains through the membrane.

[0006] Porous waterproof breathable membranes need to be made from a hydrophobic material. Traditional porous waterproof breathable membranes are made from Polytetrafluoroethylene (PTFE), which is a type of Polyfluorinated Substance (PFAS). PTFE has high hydrophobicity, high temperature resistance, and good physical properties, such as a high tensile strength. However, PFAS’s are not good for public health or the environment and are subject to regulation. It is expected that PFAS will be phased out and, as such, PTFE will not be usable in waterproof breathable membranes. Typical alternatives to PTFE are hydrophobic crystalline or semi-crystalline materials, such as polyethylene and polypropylene. When these materials are melt-extruded and stretched to form membranes, the lamellar nano-structures in the semi-crystalline and crystalline material separate, resulting in pore creation. However, the resulting membranes are brittle and have low melting temperatures.

[0007] An alternative method for making porous waterproof breathable membranes is to add filler particles to the base material. After addition of filler particles, pores can be created by subsequent stretching of the extruded membrane and / or via subsequent removal of the filler particles. However, current membranes formed via this method have low temperature resistance and are brittle.

[0008] The present invention was devised with the foregoing problems in mind.

[0009] Summary of Invention

[0010] According to a first aspect, there is provided a waterproof breathable porous membrane. The waterproof breathable porous membrane may be formed from, or comprise, a first polymeric material. The first polymeric material may be a polyolefin elastomer.

[0011] The use of an elastomer to form a membrane improves its robustness and makes it less brittle. The elastomer provides the membrane with greater flexibility and elongation before breaking.

[0012] The membrane may further comprise a second polymeric material which is different to the first polymeric material. The use of a second material may improve the characteristics of the membrane. For example, membranes formed from elastomers typically have a low melting temperature and poor hydrophobicity. By using a second polymeric material with a high melting temperature and high hydrophobicity, the characteristics of the membrane can be improved without losing the elastomer properties provided by the first polymer material.

[0013] The first polymeric material may have a melting temperature above 90°C. The first polymeric material may have a melting temperature above 100°C. The first polymeric material may have a melting temperature above 110°C. The first polymeric material may have a melting temperature above 120°C. The first polymeric material may have a melting temperature above 130°C. The first polymeric material may have a melting temperature above 140°C. The first polymeric material may have a melting temperature above 150°C. The first polymeric material may have a melting temperature above 160°C.

[0014] The first polymeric material may be, or comprise, an ethylene a-olefins interpolymer. The one or more a-olefins may each comprise between 2 and 20 carbon atoms. For example, the first polymeric material may be: an ethylene propylene interpolymer or copolymer; an ethylene butene interpolymer or copolymer; an ethylene pentene interpolymer or copolymer; an ethylene hexene interpolymer or copolymer; an ethylene heptene interpolymer or copolymer; an ethylene octene interpolymer or copolymer; or any other ethylene a-olefins interpolymer or copolymer.

[0015] The first polymeric material may be, or comprise, an interpolymer or copolymer of polybutylene. The first polymeric material may be, or comprise, an interpolymer or copolymer of polypropylene.

[0016] The second polymeric material may be, or comprise, an ethylene a-olefins interpolymer. The one or more a-olefins may each comprise between 2 and 20 carbon atoms. For example, the first polymeric material may be: an ethylene propylene interpolymer or copolymer; an ethylene butene interpolymer or copolymer; an ethylene pentene interpolymer or copolymer; an ethylene hexene interpolymer or copolymer; an ethylene heptene interpolymer or copolymer; an ethylene octene interpolymer or copolymer; or any other ethylene a-olefins interpolymer or copolymer. The second polymeric material may be, or comprise, an interpolymer or copolymer of polybutylene. The second polymeric material may be, or comprise, an interpolymer or copolymer of polypropylene.

[0017] The first polymeric material may be, or comprise, a polymer, interpolymer, or copolymer of polybutene. The first polymeric material may be, or comprise, a polymer, interpolymer, or copolymer of polybutylene.

[0018] The second polymeric material may be, or comprise, a polymer, interpolymer, or copolymer of polybutene. The second polymeric material may be, or comprise, a polymer, interpolymer, or copolymer of polybutylene.

[0019] The first polymeric material may be, or comprise, a propylene a-olefins interpolymer. The one or more a-olefins may each comprise between 2 and 20 carbon atoms. For example, the first polymeric material may be: a propylene ethylene interpolymer or copolymer; a propylene butene interpolymer or copolymer; a propylene pentene interpolymer or copolymer; a propylene hexene interpolymer or copolymer; a propylene heptene interpolymer or copolymer; a propylene octene interpolymer or copolymer; or any other propylene a-olefins interpolymer or copolymer.

[0020] The first polymeric material may be, or comprise: a diene polymer or a diene a-olefins interpolymer. The one or more a-olefins may each comprise between 2 and 20 carbon atoms (e.g. polybutadiene, polyisoprene and its copolymers, ethylene propylene diene terpolymer).

[0021] The first polymeric material may be, or comprise: a butene polymer or a butene a-olefins interpolymer. The one or more a-olefins may each comprise between 2 and 20 carbon atoms, (e.g. polybutene, polyisobutene and its copolymers).

[0022] The first polymeric material may be, or comprise, an ethylene-based elastomer with nano-crystal structure. The first polymeric material may be, or comprise, a propylene- based elastomer with nano-crystal structure. The first polymeric material may be, or comprise, a butene-based elastomer with nano-crystal structure.

[0023] The first polymeric material may be, or comprise: a styrene polyolefin. The first polymeric material may be, or comprise, a styrenic block copolymer, such as SEBS (polystyrene saturated polybutadiene-polystyrene), SBS (polystyrene-polybutadiene- polystyrene), SEPS (polystyrene-saturated polyisoprene-polystyrene) or SIS (polystyrene-polyisoprene 50 polystyrene).

[0024] The first polymeric material may be, or comprise, a thermoplastic vulcanizate.

[0025] The first polymeric material may be a propylene-olefinic copolymer, an ethylene propylene copolymer plastomer, polyethylene octene elastomer, or any similar variation.

[0026] The second polymeric material may have a greater melting temperature than the first polymeric material.

[0027] Having a first and / or second polymeric material with a high melting point may enable the use of higher melting point adhesives, thereby broadening the available range to choose from for lamination.

[0028] The second material may be hydrophobic. The second material may have greater hydrophobicity than the first material.

[0029] The second polymeric material may be, or comprise, a polyolefin. The second polymeric material may be, or comprise, polymethylpentene or a copolymer thereof. The second polymeric material may be, or comprise, a copolymer of 4-methyl-l -pentene with one or more a-olefins. The one or more a-olefins may each comprise between 2 and 20 carbon atoms.

[0030] The ratio by weight of the first polymeric material to the second polymeric material may be between 1 :9 and 9: 1. The ratio by weight of the first polymeric material to the second polymeric material may be between 1 :5 and 5: 1. The ratio by weight of the first polymeric material to the second polymeric material may be between 1 :2 and 2: 1. The ratio by weight of the first polymeric material to the second polymeric material may be 1 : 1.

[0031] The membrane may comprise a plurality of filler particles dispersed throughout. The filler particles may have properties, such as high hydrophobicity, which improve the overall characteristics of the membrane. The filler particles may be calcium carbonate particles. The presence of filler particles may increase the porosity of the membrane, thereby leading to greater gas permeability. The filler particles in the membrane may account for 50% of the weight of the membrane. The filler particles in the membrane may account for 60% of the weight of the membrane.

[0032] The membrane may be resistant to melting up to temperatures of at least 130°C. The membrane may be resistant to melting up to temperatures of at least 140°C. The membrane may be resistant to melting up to temperatures of at least 150°C. The membrane may be resistant to melting up to temperatures of at least 160°C. The membrane may be resistant to melting up to temperatures of at least 170°C. The membrane may be resistant to melting up to temperatures of at least 180°C. The membrane may be resistant to melting up to temperatures of at least 190°C. The membrane may be resistant to melting up to temperatures of at least 200°C. The membrane may be resistant to melting up to temperatures of at least 210°C. The membrane may be resistant to melting up to temperatures of at least 220°C. The membrane may be resistant to melting up to temperatures of at least 230°C.

[0033] The membrane may be resistant to melting up to a temperature exceeding 160°C.

[0034] The membrane may be resistant to heat shrinkage by up to 10% in a machine direction when exposed to temperatures of at least 90°C. The membrane may be resistant to heat shrinkage by up to 15% in a machine direction when exposed to temperatures of at least 90°C. The membrane may be resistant to heat shrinkage by up to 20% in a machine direction when exposed to temperatures of at least 90°C. The membrane may be resistant to heat shrinkage by up to 25% in a machine direction when exposed to temperatures of at least 90°C.

[0035] The membrane may be resistant to heat shrinkage by up to 10% in a machine direction when exposed to temperatures of at least 120°C. The membrane may be resistant to heat shrinkage by up to 15% in a machine direction when exposed to temperatures of at least 120°C. The membrane may be resistant to heat shrinkage by up to 20% in a machine direction when exposed to temperatures of at least 120°C. The membrane may be resistant to heat shrinkage by up to 25% in a machine direction when exposed to temperatures of at least 120°C.

[0036] The membrane may have an elongation at break of at least 30%. The membrane may have an elongation at break of at least 40%. The membrane may have an elongation at break of at least 50%. The membrane may have an elongation at break of at least 60%.

[0037] The membrane may have an elastic modulus greater than 50MPa in the transverse direction. The membrane may have an elastic modulus between 50-80MPa in the transverse direction.

[0038] The membrane may have an elastic modulus greater than 180MPa in the machine direction. The membrane may have an elastic modulus between 180-360MPa in the machine direction.

[0039] Having a lower elastic modulus in the transverse direction may result in the membrane being softer and / or more flexible to a user’s touch.

[0040] The polymer chains within the membrane may be cross-linked. Cross-linking of the polymer chains within the membrane may improve the thermal properties (i.e increase the melting temperature and reduce the heat shrinkage) of the membrane. Cross-linking of the polymer chains within the membrane may improve the mechanical properties, including, but not limited to, the tensile strength, tear strength, and puncture resistance of the membrane. Cross-linking of the polymer chains within the membrane may improve the chemical resistance of the cross-linked material against different liquids and chemicals. Cross-linking of the polymer chains within the membrane may provide the membrane with form setting capabilities at temperature above its original melting point.

[0041] The membrane may be waterproof up to pressures of at least 1000 mmH20. The membrane may be waterproof up to pressures of at least 1500 mmH20. The membrane may be waterproof up to pressures of at least 2000 mmH20. The membrane may be waterproof up to pressures of at least 2500 mmH20. The membrane may be waterproof up to pressures of at least 3000 mmH20. The membrane may be waterproof up to pressures of at least 3500 mmH20. The membrane may be waterproof up to pressures of at least 4000 mmH20.

[0042] The membrane may have a water vapour transmission rate of at least 1000 g / m2 / 24h.

[0043] The membrane may have a water vapour transmission rate of at least 2000 g / m2 / 24h.

[0044] The membrane may have a water vapour transmission rate of at least 3000 g / m2 / 24h.

[0045] The membrane may have a water vapour transmission rate of at least 4000 g / m2 / 24h.

[0046] The membrane may have a water vapour transmission rate of at least 5000 g / m2 / 24h.

[0047] The membrane may have a water vapour transmission rate of at least 6000 g / m2 / 24h.

[0048] The membrane may have a water vapour transmission rate of at least 7000 g / m2 / 24h.

[0049] The membrane may have a water vapour transmission rate of at least 8000 g / m2 / 24h.

[0050] The membrane may have a water vapour transmission rate of at least 9000 g / m2 / 24h.

[0051] The membrane may have a water vapour transmission rate of at least 10000 gm_2d-1. The membrane may have a water vapour transmission rate of at least 11000 gm_2d-1.

[0052] The membrane may have a melt flow rate between 1-40 grams over a period of 10 minutes. The membrane may have a melt flow rate between 3-37 grams over a period of 10 minutes.

[0053] Lower melt flow rates may be more suitable for a parallel extrusion orientation. Higher melt flow rates may be more suitable for a perpendicular extrusion orientation.

[0054] The membrane may have a glass transition temperature between -30°C to +20°C. The first polymeric material may have a glass transition temperature between -30°C to +20°C. The second polymeric material may have a glass transition temperature between -30°C to +20°C.

[0055] According to a second aspect of the invention, there is provided a method for creating a waterproof breathable porous membrane. The method of the second aspect of the invention may be used to create the membrane of the first aspect of the invention.

[0056] The method may comprise providing a polymer mixture comprising a first polymeric material and a second polymeric material. The first polymeric material may be, or comprises, a polyolefin elastomer. The method may comprise using the polymer mixture to form a pre-membrane. The method may comprise forming a plurality of pores in the pre-membrane to form the membrane.

[0057] The method may comprise adding a plurality of filler particles to the polymer mixture prior to formation of the pre-membrane. The addition of filler particles to the polymer mixture may help to encourage debonding between the polymers within the polymer mixture during pore formation, leading to increased porosity in the final membrane. The addition of filler particles having beneficial characteristics, such as high hydrophobicity, may improve the overall characteristics of the membrane.

[0058] The filler particles may be template particles. In such cases, forming the plurality of pores in the pre-membrane to form the membrane may comprise removing the template particles. Removing the template particles may comprise exposing the template particles to a solvent. The use of template particles may increase the porosity of the membrane.

[0059] The filler particles may be formed from, or comprise, calcium carbonate. The filler particles may be hydrophobic.

[0060] Using the polymer mixture to form a porous membrane may comprise extruding the polymer mixture into a film.

[0061] Forming the plurality of pores may comprise stretching the pre-membrane. Stretching the pre-membrane may comprise uniaxial stretching or bi-axial stretching. Uniaxial stretching and / or biaxial stretching may be performed along a machine direction and / or a transverse direction defined during extrusion of the polymer mixture into the premembrane.

[0062] Stretching the pre-membrane may comprise stretching the pre-membrane whilst maintaining the pre-membrane at a pre-determined temperature. Maintaining the premembrane at a pre-determined temperature during stretching may comprise stretching the pre-membrane using one or more heated rollers. The pre-membrane may be maintained above an activation temperature during stretching. Maintaining a minimum temperature of the pre-membrane during stretching may enable debonding between the polymers and the filler particles, thereby leading to increased pore formation.

[0063] The method may comprise irradiating the membrane with an electron beam. Irradiating the membrane with an electron beam may encourage cross-linking between polymers, thereby leading to improved heat resistance properties. Additionally, or alternatively, a cross-linking agent may be added to the polymer mixture to encourage cross-linking.

[0064] Cross-linking the membrane may improve the melting temperature of the membrane. The cross-linking of the membrane may enable the subsequent form setting of the membrane, as it may enable the membrane to be heated to the required temperatures for form setting without melting.

[0065] The method may comprise form setting the membrane. Form setting the membrane may reduce heat shrinkage of the membrane when it is subsequently exposed to high temperatures.

[0066] Optional features of any of the above aspects may be combined with the features of any other aspect, in any combination. For example, features described in connection with the membrane of the first aspect may have corresponding features definable with respect to the method of the second aspect, and vice versa, and these embodiments are specifically envisaged. Features which are described in the context or separate aspects and embodiments of the invention may be used together and / or be interchangeable wherever possible. Similarly, where features are, for brevity, described in the context of a single embodiment, those features may also be provided separately or in any suitable sub-combination.

[0067] Brief description of the drawings

[0068] The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0069] Figure 1 shows a schematic view of a membrane according to an embodiment of the invention; Figure 2 shows a flowchart representing steps of a method for creating a membrane according to an embodiment of the invention;

[0070] Figure 3 shows a flowchart representing steps of a method for creating a membrane according to an embodiment of the invention;

[0071] Figures 4(a) and (b) respectively show a photograph and a SEM image of a membrane according to an embodiment of the invention; and

[0072] Figures 5(a) and (b) respectively show a photograph and a SEM image of a membrane according to another embodiment of the invention.

[0073] Detailed description

[0074] Figure 1 shows a schematic view of a membrane 10. The membrane 10 is a waterproof porous membrane.

[0075] The membrane 10 comprises a body 12. A plurality of pores 14 are formed throughout the body 12. The pores 14 within the body 12 enable the passage of gases (e.g., water vapour molecules) therethrough. The pores 14 are sufficiently small to prevent the passage of liquid water droplets therethrough. For this reason, the membrane 10 may be referred to as “waterproof’ and “breathable”.

[0076] The body 12 of the membrane 10 is hydrophobic and is formed of a first polymeric material. The first polymeric material is a polyolefin. In some embodiments, the first polymeric material is a polyolefin elastomer.

[0077] In some embodiments, the first polymeric material has a melting temperature above 100°C. In some embodiments, the first polymeric material has a melting temperature above 110°C. In some embodiments, the first polymeric material has a melting temperature above 120°C. In some embodiments, the first polymeric material has a melting temperature above 130°C. In some embodiments, the first polymeric material has a melting temperature above 140°C. In some embodiments, the first polymeric material has a melting temperature above 150°C. In some embodiments, the first polymeric material has a melting temperature above 160°C.

[0078] In some embodiments, the first polymeric material is a polyolefin elastomer which is capable of being cross-linked.

[0079] In some embodiments, the first polymeric material is an ethylene a-olefins polymer or interpolymer. For example, in some embodiments, the first polymeric material may be, or comprise, an ethylene hexene copolymer. In other embodiments, the first polymeric material may be, or comprise, an ethylene octene copolymer.

[0080] In some embodiments, the first polymeric material is a propylene a-olefins polymer or interpolymer. For example, in some embodiments, the first polymeric material may be, or comprise, a propylene butylene copolymer. In other embodiments, the first polymeric material may be, or comprise, a propylene ethylene copolymer.

[0081] In some embodiments, the first polymeric material is, or comprises, a methylpentene a- olefins copolymer or interpolymer.

[0082] The term “interpolymer” used herein refers to a polymer prepared by the polymerization of at least two different types of monomers. For example, the term “interpolymer” encompasses copolymers (polymers comprising two discrete monomers) and terpolymers (polymers comprising three discrete monomers).

[0083] In some embodiments, the first polymeric material is, or comprises, Linear Low-Density Polyethylene (LLDPE) - Linear poly(ethylene) with short-chain branching from alphaolefin co-monomers. In some embodiments, the first polymeric material comprises Very-Low-Density Polyethylene (VLDPE). In some embodiments, the first polymeric material comprises Ultra-Low-Density Polyethylene (ULDPE).

[0084] In some embodiments, the first polymeric material is, or comprises, Ethylene-Propylene Rubber (EPR) or Ethylene Propylene Diene Monomer (EPDM) Rubber.

[0085] In some embodiments, the first polymeric material is, or comprises, Poly(isobutylene).

[0086] In some embodiments, the first polymeric material is, or comprises, Poly(butene-l). In some embodiments, the first polymeric material is, or comprises, a styrenic interpolymer, such as: SEBS (polystyrene saturated polybutadiene-polystyrene), SBS (polystyrene-polybutadiene-polystyrene), SEPS (polystyrene-saturated polyisoprenepolystyrene), SIS (polystyrene-polyisoprene- 50 polystyrene), and SEPSEP.

[0087] In some embodiments, the first polymeric material is, or comprises, a thermoplastic vulcanizate.

[0088] In some embodiments, the first polymeric material is a polyolefin elastomer which has an elongation at break of at least 300%. In some embodiments, the polymeric material is a polyolefin elastomer which has an elongation at break of at least 400%.

[0089] In some embodiments, the body 12 further comprises a second polymeric material. In such embodiments, the second polymeric material is a different material to the first polymeric material.

[0090] In some embodiments, the second polymeric material is a polyolefin. However, in other embodiments, the second polymeric material is not a polyolefin.

[0091] In some embodiments, the second polymeric material has a higher melting temperature than the first polymeric material. In some embodiments, the second polymeric material has a higher hydrophobicity than the first polymeric material. In some embodiments, the second polymeric material has higher chemical resistance than the first polymeric material.

[0092] In some embodiments, the second polymeric material is, or comprises, a polymethylpentene polymer or interpolymer. In some embodiments, the second polymeric material is, or comprises, a copolymer of 4-methyl-l -pentene with one or more a-olefins. In some embodiments, the one or more a-olefins each comprise between 2 and 20 carbon atoms, although that is not essential. The molecular chain of the one or more a-olefins may be linear or branched. Specific examples of such a-olefins include ethylene, propylene, 1 -butene, 1 -pentene, 1 -hexene, 1 -octene, 1 -decene, 1 -dodecene, 1- tetradecene, 1-dexadecene, 1-octadecene, 1-eicosene, 3 -methyl- 1 -butene, 3-methyl-l- pentene, 3-ethyl-l-pentene, 3-ethyl-l- hexene and the like. In other embodiments, the second polymeric material is a polymer or co-polymer of a different polyolefin, such as polypropylene, polyethylene, polystyrene, polybutylene, or polybutene.

[0093] In some embodiments, the first and second polymeric materials are present in a 1 : 1 ratio by weight. In other embodiments, the first and second polymeric material are present in a ratio by weight ranging between 1 :9 and 9: 1. In some embodiments, the first and second polymeric material are present in a ratio by weight ranging between 1 :5 and 5: 1. In some embodiments, the first and second polymeric material are present in a ratio by weight ranging between 1 :2 and 2: 1.

[0094] In some embodiments, the membrane 10 has a melting temperature which is greater than the melting temperature of the first polymeric material. In some embodiments, the membrane 10 has a melting temperature of at least 130°C. That is to say, the membrane 10 is resistant to melting up to temperatures of at least 130°C. In some embodiments, the membrane 10 has a melting temperature of at least 160°C.

[0095] In some embodiments, the membrane 10 is resistant to heat shrinkage up to temperatures of at least 90°C. That is to say, the membrane 10 is resistant to heat shrinkage up to temperatures of at least 90°C. In some embodiments, the membrane 10 is resistant to heat shrinkage such that the membrane 10 shrinks by less than 20% when heated to temperatures of at least 90°C. In some embodiments, the membrane 10 is resistant to heat shrinkage such that the membrane 10 shrinks by less than 15% when heated to temperatures of at least 90°C. In some embodiments, the membrane 10 is resistant to heat shrinkage such that the membrane 10 shrinks by less than 10% when heated to temperatures of at least 90°C. In some embodiments, the membrane 10 is resistant to heat shrinkage such that the membrane 10 shrinks by less than 5% when heated to temperatures of at least 90°C.

[0096] In some embodiments, the membrane 10 is resistant to heat shrinkage up to temperatures of at least 120°C. That is to say, the membrane 10 is resistant to heat shrinkage up to temperatures of at least 120°C. In some embodiments, the membrane 10 is resistant to heat shrinkage such that the membrane 10 shrinks by less than 20% when heated to temperatures of at least 120°C. In some embodiments, the membrane 10 is resistant to heat shrinkage such that the membrane 10 shrinks by less than 15% when heated to temperatures of at least 120°C. In some embodiments, the membrane 10 is resistant to heat shrinkage such that the membrane 10 shrinks by less than 10% when heated to temperatures of at least 120°C. In some embodiments, the membrane 10 is resistant to heat shrinkage such that the membrane 10 shrinks by less than 5% when heated to temperatures of at least 120°C.

[0097] The "porosity" of a material as described herein is the volumetric percentage of pores of the total material. Porosity can be determined by porosimetry, by measuring the apparent material density, BET analysis, or by microscope images.

[0098] In some embodiments, the membrane 10 has a porosity of at between 1-90%. In some embodiments, the membrane 10 has a porosity between 30-70%. In some embodiments, the membrane 10 has a porosity of at between 40-50%.

[0099] In some embodiments, the membrane 10 has an average pore 14 size in the range of Inm to 100pm. In some embodiments, the membrane 10 has an average pore 14 size in the range of 0.01 m to 10pm. In some embodiments, the membrane 10 has an average pore 14 size in the range of 0.05pm to 1pm.

[0100] The "permeability" of a material as described herein is defined as the flux of a gaseous medium through interconnected pores of the material. Permeability can be determined by measuring the gas volume which passes a defined membrane area in a defined time at an applied pressure.

[0101] The water vapor transmission rate (WVTR) is one suitable parameter to determine permeability. WVTR is measured according to the ASTM Standard E96 B in grams of water per square metre per day (gm_2d-1)

[0102] In some embodiments, the membrane 10 has a water vapour transmission rate of at least 100 gm_2d-1. In some embodiments, the membrane 10 has a water vapour transmission rate of at least 1000 gm_2d-1. In some embodiments, the membrane 10 has a water vapour transmission rate of at least 2500 gm_2d-1. In some embodiments, the membrane 10 has a water vapour transmission rate of at least 5000 gm_2d-1. In some embodiments, the membrane 10 has a water vapour transmission rate of at least 7500 gm_2d-1. In some embodiments, the membrane 10 has a water vapour transmission rate of at least 10000 gm^d1.

[0103] In some embodiments, the membrane 10 is waterproof up to pressures of at least 100 mmltO. In some embodiments, the membrane 10 is waterproof up to pressures of at least 1000 mmltO. In some embodiments, the membrane 10 is waterproof up to pressures of at least 2000 mmltO. In some embodiments, the membrane 10 is waterproof up to pressures of at least 3000 mmltO. In some embodiments, the membrane 10 is waterproof up to pressures of at least 4000 mmltO. In some embodiments, the membrane 10 is waterproof up to pressures of at least 5000 mmltO. In some embodiments, the membrane 10 is waterproof up to pressures of at least 6000 mmltO. In some embodiments, the membrane 10 is waterproof up to pressures of at least 7000 mmltO. In some embodiments, the membrane 10 is waterproof up to pressures of at least 8000 mmltO. In some embodiments, the membrane 10 is waterproof up to pressures of at least 9000 mmltO. In some embodiments, the membrane 10 is waterproof up to pressures of at least 10000 mmltO. As will be recognised by the skilled person, the mmltO is a unit a pressure defined as the pressure exerted by a column of water of 1mm in height.

[0104] Figure 2 shows a flowchart 100 representing a method for forming a porous membrane. The method of Figure 2 can be used to form any of the porous membranes described herein, including the membrane 10 of Figure 1.

[0105] The method comprises: providing 110 a polymer mixture; using 120 the polymer mixture to form a pre-membrane; and forming 130 a plurality of pores in the pre-membrane to form the membrane.

[0106] Figure 3 shows a flowchart 200 representing another method for forming a porous membrane. The method of Figure 3 is more detailed and includes additional steps which are not essential to all embodiments of the invention. The method of Figure 3 can be used to form any of the porous membranes described herein, including the membrane 10 of Figure 1.

[0107] The method of flowchart 200 comprises: providing 210 a polymer mixture; adding 215 filler particles to the polymer mixture; using 220 the polymer mixture to form a pre-membrane via extrusion of the polymer mixture; forming 230 a plurality of pores in the pre-membrane, via stretching of the premembrane, to form the membrane; cross-linking 235 the membrane; and form-setting 240 the membrane.

[0108] The polymer mixture comprises a first polymeric material. In some embodiments, the first polymeric material is, or comprises, a polyolefin. In some embodiments, the first polymeric material is, or comprises, a polyolefin elastomer. The first polymeric material in the polymer mixture can be any of the first polymeric materials described herein with respect to the membrane 10 of Figure 1.

[0109] In some embodiments, the body 12 further comprises a second polymeric material. In such embodiments, the second polymeric material is a different material to the first polymeric material. The second polymeric material in the polymer mixture can be any of the second polymeric materials described herein with respect to the membrane 10 of Figure 1.

[0110] In some embodiments, the step of providing 110, 210 the polymer mixture may comprise creating the polymer mixture. Creating the polymer mixture comprises mixing the first polymeric material with the second polymeric material.

[0111] In some embodiments, mixing the first and second polymeric materials together to form the polymer mixture comprises using an extruder, such as a twin-screw extruder. However, the person skilled in the art will recognise that any other suitable method or machinery for uniformly mixing two polymeric materials together can be used.

[0112] In some embodiments, the first and second polymeric materials are mixed at a temperature exceeding the melting temperature of both the first and second polymeric materials. As such, the temperature at which the polymeric materials should be mixed depends on the choice of first and second polymers. In some embodiments, the first and second polymeric materials are mixed uniformly in a 1 : 1 ratio by weight. In other embodiments, the first and second polymeric material are mixed with a ratio by weight ranging between 1 :9 and 9: 1. In some embodiments, the first and second polymeric material are mixed with a ratio by weight ranging between 1 :5 and 5: 1. In some embodiments, the first and second polymeric material are mixed with a ratio by weight ranging between 1 :2 and 2: 1.

[0113] In some embodiments, such as in Figure 3, the method further comprises the step of adding 215 filler particles to the polymer mixture. In some embodiments, the filler particles are mixed into the polymer mixture, prior to the formation of the premembrane. In some embodiments, the filler particles are mixed into the polymer mixture such that they are evenly dispersed throughout the polymer mixture.

[0114] In some embodiments, the filler particles are “template particles” which are subsequently removed to create pores. The use of the term “template particle” herein refers specifically to filler particles which are used to form pores via their subsequent removal.

[0115] The skilled person will recognise that a wide variety of materials can be used as filler particles. A non-exhaustive list of example filler particles is discussed below.

[0116] In some embodiments, the filler particles comprise one or more inorganic materials. For example, filler particles can include ceramics, such as titania, Zirconia, alumina, silica, ruthenium oxide, and tin oxide. One or more metallic materials can also be used as filler particles, such as titanium, Zirconium, aluminium, chromium, iron, Zinc, nickel, gold, silver, and platinum. In other embodiments, the filler particles comprise metal salts (e.g., calcium carbonate, sodium chloride). In other embodiments, Cermets (material / ceramic composites) are used as filler particles.

[0117] In other embodiments, the filler particles comprise various polymers or copolymers. The filler particles can be formed from thermoplastic or thermosetting copolymers. A variety of polymers may be used. Non-limiting examples include polystyrene, polyamide, polyethylene, polypropylene, polycarbonate, polyester, polyacrylates and related polymers (e.g., polymethylmethacrylates); polyacetals, polybutenes, polyacryamides, polyalkylene glycols, polysiloxanes, polyphenylene Sulfides, polylactides, and polysaccharides (e.g., cellulosic polymers). The polymers may be in the form of homopolymers or copolymers (e.g., branch- or graft-copolymers). Physical mixtures of such materials are also possible. In some specific embodiments, the polymer is in latex form, e.g., a stable dispersion of polymer microparticles. A variety of polymers can be used to form latex particles, e.g., vinyl acetate, styrene, styrenebutadiene, and (meth)acrylates.

[0118] It should also be noted that, in some embodiments, the filler particles comprise combinations of organic and inorganic materials.

[0119] The size of the filler particles used depends on the desired size for the pores within the membrane. In some embodiments, the filler particles have an average diameter in the range of about 1 nm to about 100 pm. In some embodiments, the filler particles have an average diameter in the range of about 50 nm to about 50 pm. In some embodiments, the filler particles have an average diameter in the range of about 100 nm to about 5 pm. In some embodiments, the filler particles have an average diameter in the range of about 500 nm to about 1pm.

[0120] In some particular embodiments, the filler particles are calcium carbonate filler particles with an average diameter between Inm - 100pm. In some particular embodiments, the filler particles are calcium carbonate filler particles with an average diameter between 500nm - 5pm. In some particular embodiments, the filler particles are calcium carbonate filler particles with an average diameter of substantially 1.3pm.

[0121] In some embodiments, the filler particles (for example, the calcium carbonate filler particles) comprise a coating. The use of coatings on filler particles are aimed to stabilise the dispersion of the filler particles in the polymer matrix, thereby reducing particle agglomeration. Depending on coating wettability, coatings can also aid in other properties, such as hydrophobicity and contact angle measurements

[0122] In some embodiments, using 120, 220 the polymer mixture to form the pre-membrane comprises extruding the polymer mixture. In some embodiments, the polymer mixture (comprising the first polymeric material, second polymeric material, and filler particles) is compounded to form a plurality of pellets, and these pellets are subsequently extruded to create a film, which is the pre-membrane. There are several methods for extruding the polymer mixture to create the film (pre-membrane). For example, the method may comprise one or more of: melt extrusion, cast extrusion, blow film extrusion; or solvent cast extrusion.

[0123] After the pre-membrane is formed via step 120, 220, the membrane is formed by forming 130, 230 a plurality of pores in the pre-membrane.

[0124] In some embodiments, forming 130, 230 pores to create the membrane comprises stretching the pre-membrane.

[0125] In some embodiments, stretching 230 comprises uniaxial stretching. In other embodiments, stretching 230 comprises biaxial stretching. Stretching the pre-membrane leads to separation between polymers, thereby creating pores.

[0126] In some embodiments, during the stretching 230 process (uniaxial or biaxial), the temperature of the pre-membrane plays an important role in activating porosity. If stretching is performed whilst the pre-membrane is below an activation temperature, stretching causes the polymers within the pre-membrane to elongate without debonding from the filler particles. If stretching is performed whilst the pre-membrane is above the activation temperature, debonding occurs between the polymers and the filler particles, and hence the formation of pores occurs. The activation temperature for formation of pores during stretching is specific to the polymer mixture used to form the pre-membrane.

[0127] In embodiments wherein filler particles are added to the polymer mixture, forming 220 the pre-membrane via extrusion, and forming the membrane 230 via stretching, should be performed at a temperature which is below the melting temperature of the material of the filler particles.

[0128] In some embodiments, filler particles are removed from the polymer during the formation of pores. In some embodiments, filler particles are removed from the polymer in order to form the pores (i.e., pores are formed in the gaps left by the particles). In some embodiments, filler particles are removed from the polymer following the formation of pores. Solvents, such as hydrochloric acid or sodium hydroxide, can be used to remove the filler particles from the membrane. The choice of solvent depends on the material of the filler particles, as different filler particles will dissolve upon exposure to different solvents. However, removal of the filler particles is not essential and can be omitted is some embodiments.

[0129] In some embodiments, filler particles remain dispersed throughout the membrane. For example, in embodiments wherein calcium carbonate filler particles are used, the filler particles remain and enhance the hydrophobicity of the membrane.

[0130] In other embodiments, the stretching 230 process is performed without the presence of filler particles.

[0131] In other embodiments, the stretching process 230 is omitted entirely, and the pores are formed by removal of template particles from the pre-membrane alone.

[0132] In some embodiments, the method further comprises cross-linking 235 the membrane to improve the temperature resistance of the membrane. Cross-linking 235 of the membrane can refer to any process which results in the crossing-linking (i.e., formation of chemical bonds between polymer chains) of polymer chains within the membrane. In some embodiments, cross-linking 235 is performed after creation of the pores within the membrane.

[0133] In some embodiments, the cross-linking of the polymer mixture comprises radiation cross-linking, such as cross-linking using electron beam radiation. In other embodiments, the cross-linking of the polymer mixture comprises addition of a crosslinking agent to the polymer mixture.

[0134] In some embodiments, electron beam irradiation is used to cross-link the membrane. In some embodiments, the acceleration voltage used for the electron beam irradiation is between 0-200kV. In some embodiments, the acceleration voltage used for the electron beam irradiation is between 50-150kV. In some embodiments, the absorbed dose for the electron beam irradiation is between 0-250kGy. In some embodiments, the absorbed dose for the electron beam irradiation is between 50-200kGy. In some embodiments, the method further comprises a final step of form setting 240 the membrane. In some embodiments, form setting 240 is performed to prevent heat shrinkage of the membrane.

[0135] In some embodiments, the step of form setting 240 is performed via an annealing process (wherein the membrane is exposed to heat and then cooled) or a heat setting process (wherein the membrane is exposed to heat and cooled while held in place).

[0136] In some embodiments, form setting 240 is performed using an air-circulating fan- assisted oven. In some embodiments, the form setting is performed at a temperature less than the crystallisation temperature of the polymer mixture (below the crystallisation temperature of the polymer in the mixture with the highest melting point). In some embodiments, after exposing the membrane during form setting to the high temperatures, the membrane is removed from the oven and left to cool to room temperature.

[0137] Figures 4(a) and (b) respectively show a photograph and a scanning electron microscope image (SEM) of a membrane 10. The membrane 10 of Figures 4(a) and 4(b) was formed from a pre-membrane which was extruded from a polymer mixture comprising an elastomeric co-polymer of 4-methyl-l -pentene and a-olefin monomer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The membrane was formed by providing a mix ratio between the first and second polymer materials of 2: 1 by weight in the polymer mixture. Calcium carbonate (CaCCE) particles were used as filler particles which were added to polymer mixture and remained dispersed throughout the membrane. The proportion of calcium carbonate particles used was 50% by weight.

[0138] Figures 5(a) and (b) respectively show a photograph and a scanning electron microscope image (SEM) of a membrane 10. The membrane 10 of Figures 5(a) and 5(b) was formed from a pre-membrane which was extruded from a polymer mixture comprising an elastomeric ethylene octene copolymer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The membrane was formed by providing a mix ratio between the first and second polymer materials of 2: 1 by weight in the polymer mixture. Calcium carbonate (CaCCE) particles were used as filler particles which were added to polymer mixture and remained dispersed throughout the membrane. The proportion of calcium carbonate particles used was 50% by weight.

[0139] Various membranes and their properties are discussed below with reference to Tables 1-6. These membranes describe various embodiments of the invention.

[0140] Table 1 below shows various measured characteristics for three different membranes.

[0141] The three different membranes were formed using different polymer mixtures.

[0142] Table 1 - Properties of membranes formed using different elastomers in the polymer mixtures.

[0143] Membrane 1 was formed from a polymer mixture comprising an elastomeric propylene butylene co-polymer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The first and second polymeric materials were mixed in a 2: 1 ratio by weight.

[0144] Membrane 2 was formed from a polymer mixture comprising an elastomeric ethylene octene co-polymer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The first and second polymeric materials were mixed in a 2: 1 ratio by weight. Membrane 3 was formed from a polymer mixture comprising an elastomeric propylene ethylene co-polymer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The first and second polymeric materials were mixed in a 2: 1 ratio by weight.

[0145] For each of the three membranes, calcium carbonate (CaCCE) particles were used as filler particles which were added to polymer mixture and remained dispersed throughout the membrane. The proportion of calcium carbonate particles used in the polymer mixture was 50% by weight. For all membranes discussed in relation to tables 1-6, the calcium carbonate filler particles used had an average diameter of 1.3pm.

[0146] The abbreviations “MD” and “TD” stand for stretching in a Machine direction and a Transverse direction, respectively. The “Machine direction” refers to the direction in which the polymer mixture was extruded to form the pre-membrane. The “Transverse direction” is perpendicular to the machine direction.

[0147] Table 2 below shows the measured characteristics of three different membranes. Each of the three membranes were formed from the same first and second polymeric materials, but the mixing ratio of the materials in the polymer mixture was different for each of the membranes. Table 2 - Properties of membranes formed using different mixing ratios in the polymer mixtures.

[0148] The three membranes tested in table 2 were each formed from a polymer mixture comprising an elastomeric ethylene octene co-polymer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The membranes were formed by providing mix ratios between the first and second polymer materials of 2: 1, 1 : 1, and 1 :2, respectively. For each of the three membranes, calcium carbonate (CaCCh) particles were used as filler particles which were added to polymer mixture and remained dispersed throughout the membrane. The proportion of calcium carbonate particles used was 50 by weight%.

[0149] Table 3 below compares the measured characteristics of two different membranes formed by varying the amount of filler particles within the polymer mixture. The filler particles were added to polymer mixture and remained dispersed throughout the membrane.

[0150] Table 3 - Properties of membranes formed using different amount of filler particles in the polymer mixture.

[0151] Each of the membranes in Table 3 were formed from the same materials, but the percentage by weight of CaCCE filler particles within the polymer mixture varied between the membranes. The first membrane used 50% by weight filler particles in the polymer mixture, whereas the second membrane used 60% by weight filler particles in the polymer mixture, meaning the second membrane was more porous. Both membranes were formed from a polymer mixture comprising an elastomeric ethylene octene co-polymer as the first polymeric material and polymethylpentene copolymer as the second polymeric material. The membranes were formed by providing mix ratios between the first and second polymer materials of 2: 1. Table 4 below compares the measured characteristics of membranes formed using alternative stretching methods.

[0152] For each of the membranes, a pre-membrane was formed via extrusion of a polymer mixture. Each pre-membrane was formed from a polymer mixture comprising an elastomeric ethylene octene co-polymer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The membranes were formed by providing mix ratios by weight between the first and second polymer materials of 2: 1. For each of the three membranes, calcium carbonate (CaCCE) particles were used as filler particles which were added to polymer mixture and remained dispersed throughout the membrane. The proportion of calcium carbonate particles used was 50% by weight.

[0153] The first three membranes in the table were stretched uniaxially (i.e ., in one direction) along the y-axis. Herein, the y-axis refers to the machine direction and the x-axis refers to the transverse direction. The first three membranes were stretched to 3x, 4x, and 5x the original length of the pre-membrane respectively (i.e., by 300%, 400%, and 500% respectively).

[0154] The fourth membrane in the table was stretched biaxially (i.e., in two directions). The membrane was stretched to 4x the original length of the pre-membrane (i.e., it was stretched by 400%) in the machine direction and was stretched to 2x the original width of the pre-membrane (i.e., it was stretched by 200%) in the transverse direction.

[0155] For each of the stretching techniques described above in relation to table 4, the membrane was maintained at 75°C during the stretching process.

[0156] In some embodiments of the invention, the membrane has an elastic modulus greater than 50MPa in the transverse direction. In some embodiments of the invention, the membrane has an elastic modulus between 50-80MPa in the transverse direction. In some embodiments of the invention, the membrane has an elastic modulus greater than 180MPa in the machine direction. In some embodiments of the invention, the membrane has an elastic modulus between 180-360MPa in the machine direction.

[0157] Table 5 below compares the liquid repellency of membranes formed using different stretching methods.

[0158] Table 5 - Results for liquid repellency tests for membrane formed using different stretching methods.

[0159] For each of the membranes tested in table 5, the pre-membrane was formed via extrusion of an identical polymer mixture. Each pre-membrane was formed from a polymer mixture comprising an elastomeric co-polymer of 4-methyl-l -pentene and a- olefin monomer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The membranes were formed by providing mix ratios between the first and second polymer materials of 2: 1. For each of the membranes, calcium carbonate (CaCCE) particles were used as filler particles which were added to polymer mixture and remained dispersed throughout the membrane. The proportion of calcium carbonate particles used was 60% by weight.

[0160] The first four membranes were formed by stretching the pre-membrane by 4x, 5.5x, 6.5x, and 8.5x (i.e., by 400%, 550%. 650% and 850% respectively) in the machine direction. The fifth membrane was formed by stretching the pre-membrane by 7.5x (i.e., by 750%) in the machine direction and by 2.2x (i.e., by 220%) in the transverse direction.

[0161] For each membrane, water repellency was tested using the AATCC TM193 protocol. Water / Alcohol mixtures with various surface tensions were used to characterise liquid repellency. The lower the surface tension of the mixture being repelled, the greater the liquid repellency properties of the membrane. Each test was classified as a pass or fail dependent on whether the water / alcohol solution was successfully repelled or not.

[0162] Table 6 below compares the water vapour transmission rate for various membranes formed via stretching at different temperatures. membranes at different temperatures.

[0163] For the first two membranes in the table, the pre-membrane was formed via extrusion of an identical polymer mixture. Each pre-membrane for the first two membranes was formed from a polymer mixture comprising an elastomeric co-polymer of 4-methyl-l- pentene and a-olefin monomer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The membranes were formed by providing mix ratios between the first and second polymer materials of 2: 1. For each of the three membranes, calcium carbonate (CaCCE) particles were used as filler particles which were added to polymer mixture and remained dispersed throughout the membrane. The proportion of calcium carbonate particles used was 60% by weight.

[0164] Both the first and the second membranes in the table were stretched to 7x the original length of the pre-membrane (i.e stretched by 700%) in the machine direction. However, the first membrane was maintained at a temperature of 55 °C during stretching, whilst the second membrane was maintained at a temperature of 95 °C. The second membrane, which was stretched at the higher temperature, has a significantly greater measured value for WVTR. The data in Table 6 demonstrates that the activation temperature for the first two membranes is in the region of 95°C.

[0165] For the second two membranes in the table, the pre-membrane was formed via extrusion of an identical polymer mixture. Each pre-membrane for the second two membranes was formed from a polymer mixture comprising an elastomeric ethylene octene co-polymer as the first polymeric material and polymethylpentene as the second polymeric material. The membranes were formed by providing mix ratios between the first and second polymer materials of 2: 1. For each of the membranes, calcium carbonate (CaCCE) particles were used as filler particles which were added to polymer mixture and remained dispersed throughout the membrane. The proportion of calcium carbonate particles used was 50% by weight.

[0166] Both the third and the fourth membranes in the table were stretched to 5x the original length of the pre-membrane (i.e., stretched by 500%) in the machine direction. However, the first membrane was maintained at a temperature of 35 °C during stretching, whilst the second membrane was maintained at a temperature of 75 °C. The second membrane, which was stretched at the higher temperature, has a significantly greater measured value for WVTR. The data in Table 6 demonstrates that the activation temperature for the first two membranes is in the region of 75°C.

[0167] The temperatures for the various membranes were maintained using heated rollers.

[0168] The results in table 6 show that, during the stretching process, the temperature plays an important role in activating porosity. When stretching is performed below an activation temperature, stretching causes the polymer matrix to elongate without debonding from the filler particles. When stretching is performed above the activation temperature, debonding occurs leading to the formation of pores, thereby providing high WVTR values. The activation temperature during stretching is specific to the polymer mixture used to form the membrane.

[0169] In some embodiments of the invention, stretching is performed at temperatures between 30-190°C. In some embodiments of the invention, stretching is performed at temperatures between 90-120°C.

[0170] In some embodiments of the invention, the stretching line speed is in the range of 0.1- 25m / min. In some embodiments of the invention, the stretching line speed is in the range of 5-15m / min.

[0171] The waterproof rating (hydrostatic head pressure) and breathability (WVTR) of the membrane are contradictory properties. A lower porosity allows for a stronger and therefore more waterproof membrane but will not allow high levels of water vapour transmission. For a waterproof breathable membrane, both these values must be high.

[0172] Tables 7 and 8 below show the measured shrinkage for membranes which were form set at different temperatures and for different lengths of time. Table 7 shows the measured shrinkage for membranes which were form set at temperatures of 125°C. Table 8 shows the measured shrinkage for membranes which were form set at temperatures of 180°C. Table 7 - Measured heat shrinkage for membranes form set at 125 °C for various periods of time.

[0173] Table 8 - Measured heat shrinkage for membranes form set at 180°C for various periods of time.

[0174] The membranes being tested in tables 7 and 8 were formed via extrusion of a premembrane. Each pre-membrane was formed from a polymer mixture comprising an elastomeric co-polymer of 4-methyl-l -pentene and a-olefin monomer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The membranes were formed by providing mix ratios between the first and second polymer materials of 2: 1 by weight. For each of the three membranes, calcium carbonate (CaCCE) particles were used as filler particles which were added to polymer mixture and remained dispersed throughout the membrane. The proportion of calcium carbonate particles used was 50% by weight.

[0175] The results in tables 7 and 8 demonstrate that form setting reduces the heat shrinkage as a result of heating in both the machine and transverse directions. Form setting at 180°C reduced the heat shrinkage more than form setting at 125°C.

[0176] Table 9 below shows the measured heat shrinkage for membranes without and without form setting, and with and without electron beam irradiation.

[0177] Table 9 - Measured heat shrinkage with and without form-setting and cross-linking.

[0178] For each of the membranes tested in Table 9, the pre-membrane was formed via extrusion of a polymer mixture. Each pre-membrane was formed from a polymer mixture comprising an elastomeric ethylene octene co-polymer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The membranes were formed by providing mix ratios between the first and second polymer materials of 2: 1 by weight. For each of the three membranes, calcium carbonate (CaCCE) particles were used as filler particles which were added to polymer mixture and remained dispersed throughout the membrane. The proportion of calcium carbonate particles used was 50w% by weight.

[0179] In table 9, “TBT” refers to measurements which have not yet been obtained. “NM” refers to measurements which were unobtainable due to the membrane splitting. The blank squares in the table indicate where measurements were unobtainable. Negative values refer to elongation, rather than shrinkage.

[0180] The cross-linking was performed via electron beam irradiation. The absorbed dose for the electron beam irradiation for each membrane is indicated in Table 9. The electron beam radiation was provided using an acceleration voltage of 150kV. In some embodiments, heat setting is performed at temperatures between 50-220°C. In some embodiments, heat setting is performed at temperatures between 100-120°C.

[0181] In some embodiments, the line speed of the heat setting is in the range of O. lm / min to lOOm / min. In some embodiments, the heat setting occurs by conveying the membrane through a heated zone. In some embodiments, the line speed is set such that the membrane is within the heated zone for between 5-100 seconds.

[0182] Table 10 below shows the measured thermal characteristics for membranes formed using different polymer mixture ratios. polymer mixture ratios. For each of the membranes tested in Table 10, the pre-membrane was formed via extrusion of a polymer mixture. Each pre-membrane was formed from a polymer mixture comprising an elastomeric co-polymer of 4-methyl-l -pentene and a-olefin monomer as the first polymeric material and a polymethylpentene copolymer as the second polymeric material. The membranes were formed by providing mix ratios between the first and second polymer materials of 1 : 1, 2: 1, and 3: 1 by weight. For each of the three membranes, calcium carbonate (CaCCE) particles were used as filler particles which were added to polymer mixture and remained dispersed throughout the membrane. The proportion of calcium carbonate particles used was 50% by weight.

[0183] The measurements of Table 10 were obtained using differential scanning calorimetry (DSC). Two temperatures are shown for melting and crystallisation because, when measuring a polymer blend using DSC, thermal characteristics, and hence peaks on the heating / cooling curves, arise from each of the first and second polymeric components. So, for the two columns, the lowest of the two values corresponds to the thermal response from the first polymeric material, and the higher value is from the second polymeric material. Herein, the lower temperature measured as the as melting temperature may be referred to as the melting temperature of the membrane.

[0184] For the characteristics and properties of the membranes discussed above, the tests were performed using the following protocols and standards:

[0185] • Hydrostatic pressure at fracture was measured based on BS EN ISO 811 :2018

[0186] • Water vapour transmission rate (WVTR) was measured based on ASTM E96

[0187] • Elongation at break was measured based on ASTM D882

[0188] • Tensile stress at break / fracture was measured based on ASTM D882

[0189] • Melting and degradation temperature was measured based on ISO 11357-1 :2023.

[0190] • Liquid repellency was measured based on AATCC TM193.

[0191] In some embodiments, the membrane may have a melt flow rate between 1-40 grams over a period of 10 minutes when tested at 230°C under 2.16kg. In some embodiments, the membrane may have a melt flow rate between 3-37 grams over a period of 10 minutes when tested at 230°C under 2.16kg.

[0192] In some embodiments, the membrane has a glass transition temperature between -30°C to +20°C.

[0193] From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art of waterproof breathable membranes, and which may be used instead of, or in addition to, features already described herein.

[0194] Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention.

[0195] Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The applicant hereby gives notice that new claims may be formulated to such features and / or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

[0196] For the sake of completeness, it is also stated that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude a plurality, a single processor or other unit may fulfil the functions of several means recited in the claims and any reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

CLAIMS1. A waterproof breathable porous membrane formed from, or comprising, a first polymeric material, wherein the first polymeric material is a polyolefin elastomer; and wherein the membrane further comprises a second polymeric material which is different to the first polymeric material.

2. The waterproof breathable porous membrane of claim 1, wherein the first polymeric material has a melting temperature above 100°C.

3. The waterproof breathable porous membrane of claim 1 or claim 2, wherein the second polymeric material has a greater melting temperature than the first polymeric material.

4. The waterproof breathable porous membrane of any preceding claim, wherein the first polymeric material is, or comprises: a polymethyl pentene a-olefin copolymer, an ethylene octene copolymer, a propylene butylene copolymer, a propylene ethylene copolymer, or an ethylene hexene copolymer.

5. The waterproof breathable porous membrane of any preceding claim, wherein the second polymeric material is, or comprises, a polyolefin.

6. The waterproof breathable porous membrane of claim 5, wherein the second polymeric material is, or comprises, polymethylpentene or a copolymer thereof.

7. The waterproof breathable porous membrane of claims 6, wherein the second polymeric material is, or comprises, a copolymer of 4-methyl-l -pentene with one or more a-olefins.

8. The waterproof breathable porous membrane of claim 7, wherein the one or more a-olefins each comprise between 2 and 20 carbon atoms.

9. The waterproof breathable porous membrane of any preceding claim, wherein the ratio by weight of the first polymeric material to the second polymeric material is between 1 :9 and 9: 1.

10. The waterproof breathable membrane of any preceding claim, wherein the membrane comprises a plurality of filler particles dispersed throughout.

11. The waterproof breathable porous membrane of any preceding claim, wherein the membrane is resistant to melting up to temperatures of at least 160°C.

12. The waterproof breathable porous membrane of any preceding claim, wherein the membrane is resistant to heat shrinkage by up to 10% in the machine direction when exposed to temperatures of at least 90°C.

13. The waterproof breathable porous membrane of any preceding claim, wherein the membrane has an elongation at break of at least 30%.

14. The waterproof breathable porous membrane of any preceding claim, wherein the polymer chains within the membrane are cross-linked.

15. The waterproof breathable porous membrane of any preceding claim, wherein the membrane is waterproof up to pressures of at least 3000 mmH20.

16. The waterproof breathable porous membrane of any preceding claim, wherein the membrane has a water vapour transmission rate of at least 1000 g / m2 / 24h.

17. A method for creating the waterproof breathable porous membrane of any of claims 1-16, the method comprising: providing a polymer mixture comprising a first polymeric material and a second polymeric material, wherein the first polymeric material is, or comprises, a polyolefin elastomer; using the polymer mixture to form a pre-membrane; and forming a plurality of pores in the pre-membrane to form the membrane.

18. The method of claim 17, further comprising: adding a plurality of filler particles to the polymer mixture prior to formation of the pre-membrane.

19. The method of any preceding method claim, wherein using the polymer mixture to form a pre-membrane comprises extruding the polymer mixture into a film.

20. The method of claim 18 or 19, wherein the filler particles are template particles; and wherein forming the plurality of pores in the pre-membrane to form the membrane comprises removing the template particles.

21. The method of any of claims 18-20, wherein the filler particles are formed from, or comprise, calcium carbonate.

22. The method of any preceding method claim, wherein forming the plurality of pores comprises stretching the pre-membrane.

23. The method of claim 22, wherein stretching the pre-membrane comprises stretching the pre-membrane whilst maintaining the pre-membrane at a pre-determined temperature.

24. The method of any preceding method claim, further comprising: irradiating the membrane with an electron beam.

25. The method of any preceding method claim, further comprising: form setting the membrane.