A microporous polyurethane membrane for fabrics and method of manufacture thereof

Abstract

The present invention provides for a method of manufacturing a microporous polymer membrane having pore size of 5nm to 10μm, comprising the steps of: (a) providing a dispersion comprising: at least one organic (non-toxic and biodegradable) solvent; at least one polymer in the amount of 13wt% or 17wt% with respect to said at least one organic solvent; Graphene Nanoplatelets (GNP) in an amount of 0.1wt% to 0.5wt% with respect to said at least one polymer, and at least one pore forming agent in an amount of 10wt% to 20wt% with respect to said at least one polymer; and the additional steps of (b) coating a substrate with said dispersion; (c) inducing phase inversion (phase separation) by immersion precipitation in a non-solvent coagulation bath at a predetermined coagulation bath temperature (CBT); and (d) optionally, removing said obtained microporous polymer membrane from said substrate.

Description

[0001] A MICROPOROUS POLYURETHANE MEMBRANE FOR FABRICS AND METHOD OF MANUFACTURE THEREOF

[0002] Technical Field of Invention

[0003] The present invention generally relates to microporous composite materials, and in particular to a breathable, hydrophobic microporous layer or membrane and respective laminates for a structure of fabric useful in protective garments (e.g. clothing, footwear) and other applications. Furthermore, the present invention relates to the manufacturing processes for waterproof and breathable polymer membranes and textiles containing such membranes.

[0004] Background

[0005] Waterproof breathable fabrics (WBF) and materials have been around for over 40 years. In inclement weather, a user’s outerwear must be windproof and waterproof, as it is expected to provide protection against both wind and precipitation. The waterproof material is designed to fully shield a wearer from rain, snow and wind by preventing the penetration and absorption of liquid water. Typically, waterproof textiles act as a barrier between the wearer’s body and the environmental humidity. While waterproof fabrics offer excellent protection from the elements, by their very nature they are unable to effectively transport the perspiration from the inside of the clothing to the outside, potentially causing moisture buildup and making the wearer feel damp.

[0006] One possible solution to this problem is provided by the so-called waterproof breathable fabrics (WBFs). The technology for manufacturing waterproof breathable textiles has been continuously developing and improving since its introduction in the 1970s (Gore- Tex). Garments made of waterproof breathable textiles are typically utilized by sports and outdoor enthusiasts, as well as, professionals in any weather conditions. Here, the waterproof and breathable fabric combines two mutually contradictory distinct functions, i.e. waterproofness and breathability. The fabric is required to provide protection from the rain, snow, wind, and cold, but also maintain comfort just below the fabric layer by allowing internal water vapor to escape.

[0007] Waterproof breathable fabrics (WBFs) can be categorized into three main types based on their structure. The first type is a tightly woven fabric made of long fibre cotton, which allows minimal gaps and provides breathability. The second type is a microporous layer or membrane, either laminated or coated, featuring very small gaps or holes throughout the fabric that allow water vapor to escape while preventing water from permeating from the outside. The third type is composed of nonporous structures and is developed as hydrophilic films. These films can absorb water vapor on one side and re-evaporate it from the other side, effectively preventing liquid water penetration. Other types of WBFs are usually combinations of two or more of these structures.

[0008] For microporous membranes, the main principle is based on the fact that water drops cannot penetrate through the membrane, because the pores are much smaller than the waterdrop, while perspiration (vapour) can evaporate through the pores since they are much larger than the vapor molecules. Further, microporous membranes for outdoor clothing are often hydrophobic, which has the advantage of adding to the comfort feeling of the wearer, as the hydrophobicity of the base material means that the membrane does not get saturated with water, in contrast to a hydrophilic nonporous membrane.

[0009] Currently, the manufacture of porous or microporous membrane systems in clothing (or other applications) is predominantly based on fluorine chemistry. For example, Per- and Polyfluorinated Alkyl Substances (PFAS) are a group of organic chemicals containing a very strong carbon-fluorine bond. Accumulation of both long chain and short chain PFAS has been observed in human and environment due to their persistency and high mobility in air and water. Exposure of human beings to such chemicals results in an increase in health problems such as decreased immune system and cancer. Some of the few well studied PFAs are already considered as moderately to highly toxic.

[0010] Consequently, there is a huge demand for alternative environmentally-friendly materials (without the use of PFAS or other fluorinated materials, such as PTFE and PVDF) that have the capability to deliver the required performance without harming the environment and having potential toxicity.

[0011] One process for manufacturing these non-PFC-type microporous membranes typically requires solvents such as dimethylformamide (DMF) and N-Methyl-2-pyrrolidone (NMP), both of which belong to the family of solvents known as polar aprotic solvents, which are generally toxic and, thus, pose serious health concerns. Hence, the European Chemicals Agency (ECHA) has classified these solvents on the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) list of substances of very high concern.

[0012] Another common process or method for preparing non-PFC-type microporous membranes is via a process known as Thermally Induced Phase Separation (TIPS). Though, these membranes are also often based on application of a combination of hazardous solvents and specific temperatures, resulting in a considerable increase of energy usage due to the need for heating and cooling.

[0013] In yet another manufacturing process or method, polymer melt or a polymer solution is spun, though, this method still has negative environmental impacts, as the same hazardous solvents are used. Also, when spinning melt polymer, a considerable amount of energy is required in order to melt the polymer (often at temperatures at around 180- 200°C). In addition, the resulting nanofibrous membranes (e.g. Electrospun Nanofibrous Membrane ENMs) commonly suffer from relatively low durability and mechanical strength.

[0014] Other common methods or processes for preparing microporous membranes include the well known non-solvent induced phase separation (i.e. NIPS, see examples in Figure 1 ), often used for the manufacture of filtration membranes. However, the majority of such membranes for filtration applications are still based on PFC-type materials (e.g. PVDF and PTFE) and utilise toxic solvents such as D F.

[0015] The NIPS process typically involves the formation of two phases through an exchange of the solvent from the polymer solution through a non-solvent from a precipitation bath. One of the phases contains a high polymer solution and is responsible for the formation of the membrane matrix, whereas the second phase contains only a very small proportion of the polymer and is washed out during the membrane formation process. This causes the development of the pore network within the matrix of the membrane until structure solidification sets in.

[0016] For controlling the membrane morphology, many factors have to be considered. Apart from the process conditions the composition of the initial polymer solution has a major impact on the thermodynamics and kinetics of the membrane formation process. In this context, different membrane-forming polymers, different solvents and various non-solvent or polymeric additives can be used to alter the fundamental progress of phase inversion.

[0017] In order to prepare a membrane casting solution, the polymer and potential non-solvent or polymeric additives have to be dissolved in an appropriate solvent. As mentioned earlier, common solvents used for preparing membrane casting solutions include N-methyl-2- pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF) and dioxane, which are known to bring up several issues regarding safety, health and environmental sustainability during transport, storage and handling. Another concern with these solvents is their disposal. They often cannot be reused due to certain quality requirements and regulatory demands. So, in order to keep the production of microporous membranes as environmentally friendly, cost effective and simple as possible, a solvent-based process is still one of the best options, if not essential.

[0018] Also, membranes that are applied in textile fabrication are typically very thin (i.e. in the order of micrometer, pm, depending on the specific application) and often suffer from low mechanical strength, which in turn leads to limited lifetime and durability. However, less durable apparel usually turns into unwanted waste, potentially polluting the environment. When creating laminate fabrics with a membrane (typically 2-layered, or 3-layered), for example, to increase the strength and durability, additional adhesive material (e.g. thermoplastic adhesives) may be required to secure the membrane to the fabric or textile layer, again, using up resources and potentially create further waste that can pollute the environment.

[0019] It is therefore an object of the invention to mitigate at least some of the drawbacks of the prior art, by providing an improved microporous membrane and manufacturing process thereof. In particular, it is an object of the present invention to provide a microporous membrane with improved performance characteristics, such as, waterproofness and breathability, as well as, improved durability and thermal conductivity (optimised removal of thermal energy from hot spots to cold spot within the microclimate next to the skin).

[0020] Summary of the Invention

[0021] An aspect of the invention is set out in the independent claim(s). Dependent claims describe optional features.

[0022] In one first aspect of the invention, there is provided a method of manufacturing a microporous polymer membrane having pore size of 5nm to 10pm, comprising the steps of:

[0023] (a) providing a dispersion comprising: at least one organic (non-toxic and biodegradable) solvent; at least one polymer in the amount of 13wt% or 17wt% with respect to said at least one organic solvent;

[0024] Graphene Nanoplatelets (GNP) in an amount of 0.1 wt% to 0.5wt% with respect to said at least one polymer, and at least one pore forming agent in an amount of 10wt% to 20wt% with respect to said at least one polymer;

[0025] (b) coating a substrate with said dispersion;

[0026] (c) inducing phase inversion (phase separation) by immersion precipitation in a nonsolvent coagulation bath at a predetermined coagulation bath temperature (CBT);

[0027] (d) optionally, removing said obtained microporous polymer membrane from said substrate.

[0028] This provides the advantage of manufacturing a microporous membrane or laminate that has improved breathability and waterproofness, durability and thermal distribution characteristics. By using the so called “green” solvents a suitable environmentally friendly alternative is provided for the manufacture of microporous membranes based on non-PFA substances.

[0029] In one example embodiment, said dispersion comprises:

[0030] Dimethyl Sulfoxide (DMSO) as said at least one organic (non-toxic and biodegradable) solvent; a polyurethane-based polymer as said at least one polymer, in the amount of 17wt% with respect to said DMSO solvent; said GNP in an amount of 0.5wt% with respect to said polyurethane-based polymer, and

[0031] Polyethylene Glycol 300 as said at least one pore forming agent, in an amount of 10wt% with respect to said DMSO solvent.

[0032] Advantageously, said polyurethane-based polymer comprises [Poly[4,4 - methylenebis(phenylisocyanate)-alt-1 ,4-butanediol / di(propyleneglycol) / polycaprolactone].

[0033] In another example embodiment, said dispersion comprises:

[0034] Dihydrolevoglucosenone (Cyrene™) as said at least one organic (non-toxic and biodegradable) solvent; a polyurethane-based polymer as said at least one polymer, in the amount of 13wt% with respect to said Dihydrolevoglucosenone (Cyrene™) solvent; said GNP in an amount of 0.5wt% with respect to said polyurethane-based polymer, and Polyethylene Glycol 300 as said at least one pore forming agent, in an amount of 10wt% with respect to said Dihydrolevoglucosenone (Gyrene™) solvent.

[0035] In yet another example embodiment, said dispersion comprises:

[0036] Dihydrolevoglucosenone (Cyrene™) as said at least one organic (non-toxic and biodegradable) solvent; a polyurethane-based polymer as said at least one polymer, in the amount of 15wt% with respect to said Dihydrolevoglucosenone (Cyrene™) solvent; said GNP in an amount of 0.1 wt% with respect to said polyurethane-based polymer, and

[0037] Polyethylene Glycol 300 as said at least one pore forming agent, in an amount of 20wt% with respect to said Dihydrolevoglucosenone (Cyrene™) solvent.

[0038] Preferably, the polyurethane-based polymer comprises a polycarbonate-based polyurethane (Chronosil®).

[0039] Advantageously, said GNP has a platelet thickness in the region of 1 nm to 15 nm (nanometer), and a platelet mean diameter in the region of 2 pm to 25 pm (micrometer).

[0040] Advantageously, said non-solvent coagulation bath is a water bath.

[0041] In a second aspect of the invention, there is provided a dispersion for manufacturing a microporous polymer membrane, comprising: at least one organic (non-toxic and biodegradable) solvent; at least one polymer in the amount of 13wt% or 17wt% with respect to said at least one organic diluent;

[0042] Graphene Nanoplatelets (GNP) in an amount of 0.1wt% to 0.5wt% with respect to said at least one polymer, and at least one pore forming agent in an amount of 10wt% to 20wt% with respect to said at least one polymer.

[0043] In a third aspect of the invention there is provided a microporous polymer membrane for at least one layer of functional fabric, obtainable by a method according to the method of the first aspect of the invention.

[0044] Advantageously, the membrane comprises a polymer and Graphene Nanoplatelets (GNP) in an amount of 0.1 wt% to 0.5wt% with respect to said polymer. Preferably, said GNP has a platelet thickness in the region of 1 nm to 15nm (nanometer), and a platelet mean diameter in the region of 2pm to 25pm (micrometer).

[0045] Advantageously, said polymer is a polyurethane-base polymer. Preferably, said polyurethane-base polymer is any one of a polycarbonate-based polyurethane (Chronosil®) and [Poly[4,4'-methylenebis(phenyl isocyanate)-alt-1 ,4-butanediol / di(propylene glycol) / polycaprolactone]

[0046] Advantageously, said membrane has a network of pores with a pore size in the region of 5nm to 10pm, a water vapor flux in the region of 3000 to 4000 [g / m2per hour], a porosity in the region of 60 to 70%.

[0047] According to a fourth aspect of the invention, there is provided a textile material comprising a microporous polymer membrane according to the third aspect of the invention, wherein said membrane is directly coated or transferred onto at least one textile substrate without an additional adhesive so as to form a two layer textile material.

[0048] Advantageously, said membrane is adhered between two textile substrates without an additional adhesive so as to form a three layer textile material.

[0049] Brief Description of the Drawings

[0050] An exemplary embodiment of the invention is explained in more detail hereinbelow with reference to the figures:

[0051] Figure 1 (a) and (b) shows two different schematic illustrations of the known NIPS method;

[0052] Figure 2 shows an illustration (table) comparing water vapour flux [g / m2per hour] and salt rejection factor [%] of PU [(Poly[4,4'-methylenebis(phenylisocyanate)-alt-1 ,4- butanediol / di(propylene glycol) / polycaprolactone] membranes obtained from different dispersions;

[0053] Figure 3 shows an illustration (table) comparing water vapour flux [g / m2per hour] and salt rejection factor [%] of ChronoSil based membranes (and the optimal PU based of Figure 2) obtained from different dispersions;

[0054] Figure 4 illustrates the effect of GNP and PEG content on the porosity of the test membranes (PU based); Figure 5 illustrates the effect of GNP and PEG content on the porosity of the test membranes (ChronoSil based);

[0055] Figure 6 shows SEM (Scanning Electron Microscope) images illustrating the porosity of PU based membranes containing 0.5wt% GNP increased upon addition of 10wt% PEG, (a) without PEG and (b) with PEG;

[0056] Figure 7 shows SEM images illustrating the porosity of ChronoSil based membranes containing (a) 1 Owt% ChronoSil in Cyrene and (b) 1 Owt% ChronoSil in Cyrene with 20wt% PEG;

[0057] Figure 8 shows SEM images illustrating the porosity of ChronoSil based membranes containing 15wt% ChronoSil, 15wt% ChronoSil with 0.1wt% GNP, and 15wt% ChronoSil with 0.1wt% GNP and 20wt% PEG, respectively;

[0058] Figure 9 shows an illustration (table) comparing Ultimate Tensile Strength (UTS) [ Pa] of coated fabrics with different additions of GNP and PEG;

[0059] Figure 10 shows an illustration (table) comparing elongation at break [%] of coated fabrics with different additions of GNP and PEG, and

[0060] Figure 11 shows an illustration (droplet pictures) comparing the water contact angle of PU-based membranes with different additions of GNP.

[0061] Detailed Description

[0062] Unless otherwise stated, the following definitions / characterisations (membrane) shall apply in this specification:

[0063] Polymer: The term "polymer" is known in the field. The term refers to a material of repeating structural units ("monomers"), particularly to synthetic polymers (synthetic monomers). The term thus includes homo-polymers, co-polymers and blends thereof. Polymers may be cross-linked.

[0064] Particle / T em pl ate / fi II er: The term "particle" is known in the field and includes crystalline or amorphous materials. The term includes uncoated particles and coated particles as well as treated particles and untreated particles.

[0065] Pore size: The "pore size" of a material as described herein is the middle size of the pore size distribution throughout the membranes. A particularly suitable method in the context of this invention is the optical analysis of the membranes' surface thereby providing information on pore mouth size.

[0066] Permeability: The "permeability" of a material as described herein is defined as the flux of a fluid (i.e. a liquid medium or a gaseous medium) through interconnected pores of the material. Permeability can be determined by measuring the liquid or gas volume which passes a defined membrane area in a defined time at an applied pressure. Here an example for illustrative purpose only:

[0067] (i) For gaseous medium, the water vapor transmission rate (VWTR) is a suitable parameter to determine permeability also referred to as "breathability" in this work. VWTR is measured according to the ASTM Standard E96 B in gram per square meter per day (g I m2per day). This method, also known as upright cup method with water, consisted of a cup with water that is covered by the test specimen. The prepared sample was weighed before it was placed in an oven, which controlled temperature (23°C), relative humidity (50% RH) and ventilation (1 m / s). Alternative measures are covered in standards ASTM E96 BW for the inverted cup, or ISO 11092 for the sweating hot plate method. The Desiccant method of the upright cup test is also described in the ASTM E96 standard.

[0068] (ii) For liquid medium, the waterproofing is a relevant parameter. In determining water proofing, the relevant driving force is pressure. The water column (WC) in meter (m) is determined in compliance with ISO 811 . Briefly, water may be pressed onto the sample at constant pressure increase (600 mmWC per minute) over time. The dry side of the sample is observed optically and the third penetrating water droplet is defined as the breakthrough of the sample and the pressure represents the water column (WC).

[0069] Cyrene™: The synthesis of Cyrene is based on a two-step process using renewable cellulose waste. Water is the main biproduct of the synthesis process and the final product has very low toxicity, well below the hazard thresholds defined by the Globally Harmonized System of Classification and Labelling of Chemicals (GHS). Similarly, there is no GHS symbol known for DMSO.

[0070] The described method and obtained membrane is believed to be the first example for preparing a PU-based waterproof breathable microporous membrane that exploits the benefits of hydrophobic graphene (i.e. graphene nanoplatelets (GNP), not to be confused with Graphene Oxide (GO)), and a pore forming agent (i.e. polyethylene glycol, PEG300) as a textile coating. SEM: Surface and cross sectional SEM images (50 °C) of the membranes were prepared using a QUANTA FEG250 SEM instrument at an accelerating voltage ranging from 10 to 15kV.

[0071] Water contact angle: T o get information about the hydrophobicity of the membranes, water contact angle measurements were done using an Attention Theta optical tensiometer (Biolin Scientific, UK) via the sessile drop method. A drop of water was deposited onto the membrane surface using a microsyringe with a stainless-steel needle (Hamilton microsyringe) at room temperature and the contact angle was immediately measured.

[0072] Porosity: The membrane porosity, E, was measured based on the gravimetric method. In brief, circular samples with dimater of 1cm were cut from each membrane and were immersed in IPA for 24h at room temperature. Then, the samples were removed and gently daubed with tissue to remove excess IPA (Isopropyl Alcohol) from the surfaces. These wet samples were then weighed, Ww. The samples were then fully dried at vacuum oven for 12h at 50°C and were weighed again to obtain the dry weight, Wd. Five coupons of each membrane were tested, and the average weight change and standard deviation were calculated. Porosity was then measured using Eguation below:

[0073] Where peis the density of IPA (786 kg m"3) and ppis the density of PU (1180 kg m"3).

[0074] Mechanical properties: Tensile strength and elongation at break of the polymeric films were calculated according to the standard ASTM D882 for thin plastic sheeting with thickness of less than 1 mm. Five strips of samples with effective length of 60mm and a width of 10 mm were tested using an Instron 5542 tensiometer (Instron, USA), equipped with Bluehill 3 software and a 10N (Newton) load cell.

[0075] UTS is defined by the maximum stress that the samples can withstand. Young’s modulus is a measure of the samples’ stiffness and is calculated as the gradient of the stress to strain curve in the elastic region of the deformation. Finally, elongation at break, sbreak, is the ratio between the change in length and the initial length of the specimen at break and is calculated using the Equation below: where l0is the initial length and l£breakis the length at break point.

[0076] The nominal tensile strength is measured by dividing the maximum force to the original sectional area of the membranes and is reported in megapascals or force per unit area.

[0077] Thermal properties: Effect of GNP loading on glass transition temperature and specific heat capacity of PU-based membranes was studied using differential scanning calorimetry, DSC, and modulated DSC, MDSC (Q100, TA instruments). The films were cut into small pieces to provide an approximate mass of 6 mg and Aluminium hermetic pans were used. Standard DSC with Heat / Cool / Heat method was performed at the start before MDSC experiments to get an idea of the Tg and decomposition temperature. In short: samples were equilibrated at 20 °C, then ramped at 10 °C / min to 200 °C, then ramped at 5 °C / min to -70 °C and then again ramped at 10 °C / min to 200 °C.

[0078] MDSC tests were conducted between -70 °C to 50 °C (starting parameters for MDSC: ±1 °C, 60 second period, 3 °C / min).

[0079] Water vapour flux: An air gap membrane distillation (AGMD) rig was used to measure the water vapour flux of microporous membranes.

[0080] The water vapour flux, J, was calculated using Equation below (three values were averaged for each membrane sample):

[0081] Where Am is the mass of the collected permeate, A is the membrane surface area (9.1 cm2) and At is time required to collect the permeate mass. Usually, tests were done for a total of 2h.

[0082] The salt rejection, SR, was calculated based on the difference in the conductivity of the feed water and the permeate using the following equation:

[0083] SR= 100

[0084] Where apand afare the conductivities of the permeate and the feed water.

[0085] Breathability: Also, additional breathability tests were conducted following JISL 1099 (2012), B-1 method. The apparatus consists of a permeable cup containing a desiccant solution and a water tank. The permeating cup is approximately 2 / 3 full and is sealed with a PTFE microporous membrane (0.2 pm, Cole Parmer). The specimen (membrane to be tested) was placed on top of the PTFE membrane and was held in place using elastic bands (following the standard method). The permeable cup and the specimen, with the specimen side facing down, was placed in water carefully so that the entire membrane surface is in contact with water. Any water vapour molecule that permeates from the front surface of the membrane, where the membrane is in direct contact with DI water at 30°C, get absorbed by the desiccant solution on the other side of the membrane. The change in weight of the desiccant over 15 min test was measured and was used to calculate water vapour flux (breathability) of the membrane using the same equation as above. At least three coupons were tested for each membrane sample. To prepare the desiccant solution, potassium acetate was used as a moisture absorbing media on the back side of the membrane. The desiccant solution was prepared by dissolving 300 g potassium acetate in 100 g DI water using a magnetic stirrer at 35°C for 24h to. membrane. The water bath temperature was controlled at 23 ±4°C and the test was conducted in an oven at 30 ±3°C.

[0086] Membrane fabrication:

[0087] Referring now to Figure 1 , two examples are shown to illustrate the well-known NIPS method.

[0088] In brief, and in addition to the description of NIPS in the introduction (hereby incorporated by reference), a polyurethane based solution containing GNP particles (Graphene Nanoplatelets) was prepared in a desired solvent (DMSO or Cyrene). Pore forming agent PEG300 was used to help improve the porosity and breathability of the final microporous membrane. After optimisation of the membrane formulation by testing various loadings (see tables), the following formulations were chosen for the optimum performing membrane in terms of breathability, porosity, mechanical performance, as well as, thermal properties:

[0089] PU-based with DMSO

[0090] 17 wt.% PU [(Poly[4,4'-methylenebis(phenyl isocyanate)-alt-1 ,4-butanediol / di(propylene glycol) / polycaprolactone], Sigma Aldrich), 0.5 wt.% GNP-M5 (XGSciences, USA) with respect to the polymer content, 10 wt.% PEG300 with respect to the polymer content and the rest being DMSO as the main solvent.

[0091] ChronoSil based with Cyrene

[0092] 13 wt.% ChronoSil polycarbonate-based PU (thermoplastic silicone polycarbonate elastomer with 5% Silica, AdvanSource Biomaterials, USA), 0.5 wt.% GNP-M5 (XGSciences) with respect to the polymer content, 10 wt.% PEG300 with respect to the polymer content and the rest being Gyrene as the main solvent.

[0093] In this set of experiments, a polyurethane with higher hydrophobicity was used. This polyurethane is a polycarbonate-based material which offers better mechanical strength, and also contains silica which is responsible for its softness and higher hydrophobicity.

[0094] The membranes that are typically applied in textile are very thin (in the order of micrometres depending on the specific application) and suffer from low mechanical strength. The present invention utilises the benefits of adding graphene-based nanoparticles in order to improve the durability of microporous PU-based membranes. Further, the comfort feeling of a coated fabric is intrinsically connected to its breathability (water vapor flux) as well as its thermal conductivity (efficiency in removal of thermal energy from hot to cold spots in the microclimate next to the skin). The present invention is able to provide membranes containing GNP (one of the most thermally conductive materials known) in the membrane structure in order to improve the thermal properties of the base membrane and subsequent fabric textiles. All of the manufacturing process is based on stable GNP based dispersions using greener solvents such as DMSO and Cyrene.

[0095] The trade-off for utilising GNP nanoparticles, although improving durability and thermal properties, is a reduced water vapor flux (i.e. breathability), which is mitigated by using pore forming agent PEG in the formulation of the dispersion.

[0096] In addition, because the invention is principally based on a thermoplastic PU, the membranes can be readily adhered to a textile fabric without the need to add any additional layer (adhesives). This reduces the time required to form the final structure of the textile fabric (2-layer, 3-layer, x-layer,...) because membranes can be directly coated on the textile fabric of interest. For example, three-layer structures can be formed without the need for any lamination. The lining is directly applied to a wet coated fabric immediately after membrane coating and prior to the immersion of the coated structure into a water bath (phase inversion), hence, securing the lining to the membrane before the final membrane structure is formed in water bath. This means the cost and energy required for the final product is reduced significantly.

[0097] Membrane formulation

[0098] A variety of different formulations were prepared to study the effect of GNP on the membrane structure and performance. Table 1 summarises different formulations that were prepared based on the first type of PU (Poly[4,4'-methylenebis(phenyl isocyanate)- alt-1 ,4-butanediol / di(propylene glycol) / polycaprolactone]) and DMSO:

[0099] (Table 1)

[0100] For the membranes based on ChronoSil and Cyrene, table below shows some of the formulations that were tried:

[0101] (Table 2)

[0102] It was first attempted to see the maximum concentration of ChronoSil that can be dissolved in Cyrene. Then PEG was added to increase porosity of the membranes.

[0103] Results of the tests and membrane characteristics are illustrated in Figures 2, 3, 4, 5, 9, 10 and 11. As can be seen particularly in Figures 2 and 3 (Breathability (AGMD)), the addition of GNP from 0.1 to 2 wt.% reduces the water vapour flux of the membranes. Membrane with 0.1 wt.% GNP had higher water vapour flux than the pure PU membrane (no GNP addition).

[0104] Further, the addition of 10 wt.% PEG dramatically improved the water vapour flux of the membrane containing 0.5wt.% GNP (nearly 10 fold increase from around 400 to nearly 3400 g / m2per hour). This membrane formulation was produced at pilot scale by either direct coating on a fabric of interest or coating on release paper.

[0105] Also, the membrane with ChronoSil showed a good moisture vapour transmission rate. An addition of 20 wt.% PEG to the ChronoSil-based membranes also improved the water vapour flux drastically. Although addition of GNP (0.1 wt.%) reduced vapour flux, addition of PEG mitigated that effect. So the best performing membrane with PU and ChronoSil both have similar vapour flux.

[0106] With regards to Figures 4 and 5, the porosity results are generally consistent with breathability (moisture vapour flux) data. The addition of PEG increased the breathability and porosity of the membranes and mitigated the effect of GNP on porosity.

[0107] Referring now particularly to Figures 6, 7 and 8, SEM (Scanning Electron Microscope) images show the porosity of the membrane containing 0.5 wt.% GNP increased upon addition of 10 wt.% PEG, (a) without PEG, (b) with PEG, and the SEM images in Figure 7 and 8 show a clear increase in the surface porosity of the ChronoSil based membranes after addition of 20wt% PEG. Here again, it can be seen that addition of PEG (20 wt.%) to the membranes containing 15wt.% ChronoSil and 0.1wt.%GNP, increase the surface porosity.

[0108] Thus, the invention provides a successful formation of microporous membranes (based on a green solvent(Cyrene), a hydrophobic non-PFC PU(ChronoSil), graphene (GNP) and pore former(PEG)) for application in waterproof breathable coatings.

[0109] Referring now to Figures 9 and 10, the tensile strength and elongation of coated textile fabrics has been tested. Here, an addition of 0.5 wt.% GNP increased the ultimate tensile strength (UTS) in [MPa] and elongation [%] at break. Addition of 10wt.% PEG did not reduce those values considerably (sample M15 compared to M11 ).

[0110] Figure 11 shows the water contact angle of the membranes and the effect of GNP on hydrophobicity. In particular, the addition of GNP to PU increased the water contact angle of the membranes from an average of 89° to 104°, meaning, a higher hydrophobicity of the membranes, because of the presence of GNP.

[0111] It will be appreciated by persons skilled in the art that the above embodiment(s) have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departing from the scope of the invention as defined by the appended claims. Various modifications to the detailed designs as described above are possible.

Claims

CLAIMS1. A method of manufacturing a microporous polymer membrane having pore size of 5nm to 10pm, comprising the steps of:(a) providing a dispersion comprising: at least one organic (non-toxic and biodegradable) solvent; at least one polymer in the amount of 13wt% or 17wt% with respect to said at least one organic solvent;Graphene Nanoplatelets (GNP) in an amount of 0.1wt% to 0.5wt% with respect to said at least one polymer, and at least one pore forming agent in an amount of 10wt% to 20wt% with respect to said at least one polymer;(b) coating a substrate with said dispersion;(c) inducing phase inversion (phase separation) by immersion precipitation in a non-solvent coagulation bath at a predetermined coagulation bath temperature (CBT);(d) optionally, removing said obtained microporous polymer membrane from said substrate.

2. A method according to claim 1 , wherein said dispersion comprises:Dimethyl Sulfoxide (DMSO) as said at least one organic (non-toxic and biodegradable) solvent; a polyurethane-based polymer as said at least one polymer, in the amount of 17wt% with respect to said DMSO solvent; said GNP in an amount of 0.5wt% with respect to said polyurethane-based polymer, andPolyethylene Glycol 300 as said at least one pore forming agent, in an amount of 10wt% with respect to said DMSO solvent.

3. A method according to claim 2, wherein said polyurethane-based polymer comprises [Poly[4,4'-methylenebis(phenyl isocyanate)-alt-1 ,4-butanediol / di(propylene glycol) / polycaprolactone].

4. A method according to claim 1 , wherein said dispersion comprises:Dihydrolevoglucosenone (Cyrene™) as said at least one organic (non-toxic and biodegradable) solvent; a polyurethane-based polymer as said at least one polymer, in the amount of 13wt% with respect to said Dihydrolevoglucosenone (Cyrene™) solvent; said GNP in an amount of 0.5wt% with respect to said polyurethane-based polymer, andPolyethylene Glycol 300 as said at least one pore forming agent, in an amount of 10wt% with respect to said Dihydrolevoglucosenone (Cyrene™) solvent.

5. A method according to claim 1 , wherein said dispersion comprises:Dihydrolevoglucosenone (Cyrene™) as said at least one organic (non-toxic and biodegradable) solvent; a polyurethane-based polymer as said at least one polymer, in the amount of 15wt% with respect to said Dihydrolevoglucosenone (Cyrene™) solvent; said GNP in an amount of 0.1 wt% with respect to said polyurethane-based polymer, andPolyethylene Glycol 300 as said at least one pore forming agent, in an amount of 20wt% with respect to said Dihydrolevoglucosenone (Cyrene™) solvent.

6. A method according to any one of claims 4 and 5, wherein said polyurethane-based polymer comprises a polycarbonate-based polyurethane (Chronosil®).

7. A method according to any one of the preceding claims, wherein said GNP has a platelet thickness in the region of 1 nm to 15 nm (nanometer), and a platelet mean diameter in the region of 2 pm to 25 pm (micrometer).

8. A method according to any one of the preceding claims, wherein said non-solvent coagulation bath is a water bath.

9. A dispersion for manufacturing a microporous polymer membrane, comprising: at least one organic (non-toxic and biodegradable) solvent; at least one polymer in the amount of 13wt% or 17wt% with respect to said at least one organic diluent;Graphene Nanoplatelets (GNP) in an amount of 0.1 wt% to 0.5wt% with respect to said at least one polymer, and at least one pore forming agent in an amount of 10wt% to 20wt% with respect to said at least one polymer.

10. A microporous polymer membrane for at least one layer of functional fabric, obtainable by a method according to any one of claims 1 to 9.

11. A microporous polymer membrane according to claim 10, comprising a polymer and Graphene Nanoplatelets (GNP) in an amount of 0.1wt% to 0.5wt% with respect to said polymer.

12. A microporous polymer membrane according to claim 11 , wherein said GNP has a platelet thickness in the region of 1 nm to 15nm (nanometer), and a platelet mean diameter in the region of 2pm to 25pm (micrometer).

13. A microporous polymer membrane according to any one of claims 11 and 12, wherein said polymer is a polyurethane-base polymer.

14. A microporous polymer membrane according to claim 13, wherein said polyurethane-base polymer is any one of a polycarbonate-based polyurethane (Chronosil®) and [Poly[4,4'-methylenebis(phenyl isocyanate)-alt-1 ,4-butanediol / di(propylene glycol) / polycaprolactone]15. A microporous polymer membrane according to any one of claims 10 to 15, wherein said membrane has a network of pores with a pore size in the region of 5nm to 10pm, a water vapor flux in the region of 3000 to 4000 [g / m2per hour], a porosity in the region of 60 to 70%.

16. A textile material comprising a microporous polymer membrane according to any one of claims 10 to 15, wherein said membrane is directly coated or transferred onto at least one textile substrate without an additional adhesive so as to form a two layer textile material.

17. A textile material according to claim 16, wherein said membrane is adhered between two textile substrates without an additional adhesive so as to form a three layer textile material.

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