Method of improving membrane coating properties for ion exchange membrane applications and woven mesh fabric for ion exchange membrane applications having improved membrane coating properties

Abstract

The invention relates to a method for improving the membrane coating properties of a woven mesh fabric as a reinforcing fabric for ion exchange membrane applications, said woven mesh fabric comprising warp and weft monofilament fibers of at least one of the following polymers: polyphenylene sulfide, polyether ether ketone and liquid crystalline polyester, wherein one monofilament fiber is made of only one of said polymers. The method comprises a fixation step after weaving the woven mesh fabric, wherein said woven mesh fabric is subjected to at least one heat treatment to fix the mesh openings to a desired size and to stabilize the monofilament fibers of the woven mesh fabric as well as to remove surface contaminants from the monofilament fibers, and one or more preparation steps, including a plasma pretreatment step and / or a plasma etching step. The method further comprises a subsequent coating step of depositing a plasma coating on the woven mesh fabric by means of a plasma polymerization introducing functional groups selected from at least one of the following: hydroxyl, carboxyl, amino and sulfonate.

Description

Technical Field

[0001] The present invention relates to a method for improving the properties of membrane coatings used in ion exchange membrane applications by using a woven mesh fabric as a reinforcing fabric, the woven mesh fabric comprising warp and weft monofilament fibers.

[0002] Furthermore, the present invention also relates to a woven mesh fabric with improved membrane coating properties for use as a reinforcing fabric in ion exchange membrane applications, wherein the woven mesh fabric comprises warp and weft monofilament fibers. Background Technology

[0003] Given the premise of anthropogenic climate change, we are facing significant challenges in the energy and environment sectors, making the search for alternative energy strategies crucial to ensuring the world's energy needs in the future.

[0004] Hydrogen, as an inexpensive and abundant energy source, contributes to a sustainable energy future with zero carbon emissions. In terms of compatibility, it can be produced using renewable energy sources, making it a viable alternative to fossil fuels. This energy source is crucial in the transition to a greener energy system and in addressing the challenges of climate change. It has important applications in various industries, enhancing energy security and reducing dependence on traditional fuels.

[0005] Hydrogen is gaining increasing recognition for its versatility and potential to decarbonize a wide range of industrial and commercial applications. Its primary uses span several sectors, including energy, chemicals, and metallurgy, and significantly contribute to the transition to a low-carbon economy. In many applications, hydrogen is being used in industrial sectors such as oil and ammonia production due to market demand. It can also enable decarbonization in transportation, construction, and heating, and is used for energy storage in the power sector. Despite the numerous opportunities offered by hydrogen, its interactions with metals present risks that require careful management.

[0006] Hydrogen production for large-scale industrial applications is developing, with several promising methods emerging. The most noteworthy technologies include steam methane reforming, electrochemical water splitting, biomass gasification, and marine renewable energy systems. Given that the footprint of hydrogen technology depends on its production methods and energy sources, water electrolysis is a particularly promising and desirable method due to its compatibility with different types of power generation.

[0007] Conventional alkaline electrolysis is not very efficient, and proton exchange membranes (PEMs) have shown cost issues. Anion exchange membrane (AEM) water electrolyzers are a promising technology, constructed with solid polymer membrane stacks to provide high volumetric energy density, and are compatible with non-precious metal catalyst electrodes to reduce hydrogen production costs. Cation exchange membranes (CEMs) are also known.

[0008] All these PEM and AEM processes utilize ion-exchange membranes (IEMs), and membrane performance is crucial for ensuring long-term operation in electrochemical separation applications. A major challenge with ion-exchange membranes is their low chemical and thermal stability. Therefore, they are combined with a polymer backbone, i.e., a woven polymer fabric serving as a base or stabilizing layer. Degradation of the polymer backbone used leads to chain breakage, molecular weight reduction, and increased membrane brittleness, especially under alkaline conditions. Membrane performance is profoundly influenced by the supporting structure and the ionomer polymer that together form the composite material.

[0009] Industrial PEM coating processes involve numerous methods to apply protective and functional coatings to materials, particularly for applications in fuel cells. This approach is crucial for enhancing the performance and durability of components used in a variety of industrial applications. The transition from batch to continuous processes is necessary for large-scale production, ensuring that the coating retains its performance characteristics under industrial conditions. The method depends on several parameters, and key parameters such as current and time require careful control to achieve the desired coating properties in terms of thickness and adhesion.

[0010] The production of ion exchange membranes (PEM, CEM, or AEM) typically involves polymer synthesis, casting, and functionalization, usually as a coating. Various application techniques, such as spraying, roller coating, and dip coating or impregnation, are employed to ensure a uniform coating. Typically, ionomer coatings comprise a combination of polymers and conductive materials such as graphite to enhance conductivity and corrosion resistance. In the case of impregnation processes, the membrane passes through an impregnation chamber to enhance its chemical properties. In a later stage, the coated membrane is passed through a tunnel oven for curing to ensure proper adhesion of the coating and enhance the overall properties of the membrane.

[0011] The basic ionomer polymer can be dissolved or processed into a solution and applied directly to a support material, such as a porous or inert substrate. This support provides mechanical support, but the functionalized polymer itself forms an active ionic conductive layer. Ionic groups, such as sulfonic acids for PEM or quaternary ammonium compounds for AEM, are introduced into the polymer to ensure conductivity. The resulting product is a supported membrane, where the support is merely a supporting structure, not a functional component of the membrane itself.

[0012] Therefore, the terms "ion exchange membrane," "membrane," "electrolyte membrane," and "ion exchange matrix" are used interchangeably in this interpretation. Furthermore, the terms "membrane coating," "ionomer coating," and "ionomer material" are used interchangeably.

[0013] Incorporating reinforcing fabrics into ion exchange membranes significantly improves their mechanical stability and durability. Several studies have demonstrated the benefits of these reinforcing materials in reducing mechanical stress and improving performance under operating conditions.

[0014] Regarding improved mechanical and dimensional stability, reinforced membranes, such as those with woven mesh layers, have been shown to exhibit improved resistance to mechanical failure during operation, ensuring no failure under normal conditions. Furthermore, the use of porous polyethylene as a support layer in tandem sulfonated polyphenylene membranes has demonstrated a significant increase in tensile strength (up to 453%) and durability, withstanding 20,000 cycles in accelerated testing.

[0015] Sulfonated polyether ether ketone (sPEEK) reinforced membranes have been found to be particularly susceptible to chemical degradation during electrolysis due to reactions with hydroxyl radicals. This interaction can lead to polymer cationization, followed by bond breaking reactions, which adversely affect the membrane structure. Variations in the humid and hot operating conditions of the membrane assembly also affect its mechanical properties. Elevated temperatures exacerbate this problem, leading to microstructural damage and reduced mechanical properties. Consequently, the lifespan of PEEK reinforced membranes is significantly reduced. Without optimal processing conditions during the manufacture of PEEK composites, high porosity and poor consolidation can be achieved, indicating degradation and impacting the overall performance of the composite membrane.

[0016] Other recent innovations focus on non-fluorinated polymers, specialized structures, and methods for assessing membrane integrity.

[0017] Various ionomer polymers and their respective backbones have been researched and developed to overcome challenging problems and ensure membrane integrity, such as polystyrene (PS), polyphenylene ether (PPO), polysulfone or fluorinated polymers, polyethylene-co-tetrafluoroethylene (ETFE), polyetherimide (PEI), polyvinyl alcohol (PVA), polyether ether ketone (PEEK), poly(arylene ether ketone), and polycarbazole.

[0018] On the other hand, researchers also investigated the degradation mechanisms of enhanced membranes, particularly in fuel cell applications. This is crucial for improving the durability and performance of these membranes in harsh environments.

[0019] Woven monofilament fabrics made from polymers such as PEEK, polyphenylene sulfide (PPS), perfluoroalkoxyalkane (PFA), fluorinated ethylene propylene (FEP), or liquid crystal polyester (LCP) are an excellent choice due to their unique and superior properties, such as well-defined geometry (including mesh openings or porosity and fiber diameter), chemical and temperature stability, and high mechanical strength. The fabric can have regular openings in a square or rectangular configuration. Proper embedding of these woven webs results in more physically and ionicly stable composite membranes. However, literature data on the adequate preparation of woven polymer support structures, which are crucial for the proper functioning and optimal consolidation of membrane reinforcement, are very limited. Conventional woven fabrics made from these polymers are generally unsuitable for these applications due to incompatibility with ion exchange matrices.

[0020] Despite their advantages, the development of composite reinforced ion exchange membranes faces several technical hurdles. The difficulty in properly embedding the woven fabric with the ion exchange membrane remains a major problem, which in turn reduces ionic conductivity. Due to its hydrophobic and inert properties, the reinforcing material can act as an incompatible barrier throughout the composite, leading to ionomer filling problems in the pores. As a result, various interfacial problems arise, such as bubbles, coating defects, and interfacial cracks and fractures. Summary of the Invention

[0021] Therefore, one object of the present invention is to provide a method for improving the membrane coating properties for ion exchange membrane applications using a woven mesh fabric as a reinforcing fabric, and to provide a woven mesh fabric with improved membrane coating properties for use as a reinforcing fabric in ion exchange membrane applications.

[0022] According to the present invention, this objective is achieved, on the one hand, by a method having the features of claim 1 and by a woven mesh fabric having the features of claim 17.

[0023] Preferred embodiments of the invention are set forth in their respective dependent claims.

[0024] According to the method of the present invention, the woven mesh fabric comprises warp and weft monofilament fibers of at least one of the following polymers: polyphenylene sulfide (PPS), polyetheretherketone (PEEK), perfluoroalkoxyalkane (PFA), fluorinated ethylene propylene (FEP), and liquid crystal polyester (LCP), wherein a single monofilament fiber is made from only one of said polymers. Other family members of PPS polymers are polyethersulfone (PESU), polysulfone (PSU), and polyphenylene sulfone (PPSU). Polyaryletherketone (PAEK) is also a member of the PEEK family.

[0025] Based on the present invention, after the weaving of the woven mesh fabric, a fixing step is performed, wherein the woven mesh fabric is subjected to at least one heat treatment at a temperature between 240°C and 350°C to fix the mesh opening to the desired size and stabilize the monofilament fibers of the woven mesh fabric and remove surface contaminants from the monofilament fibers.

[0026] Perform one or more of the following preparatory steps, including: performing a plasma pretreatment step on the woven mesh fabric to further finely clean the surface of the woven mesh fabric, especially by removing impurities, strongly adhering dust particles and organic, inorganic and microbial contaminants from the filament surface, and / or exposing the woven mesh fabric to plasma to etch the surface of the monofilament fibers of the woven mesh fabric to an average roughness of 30 nm to 200 nm.

[0027] Following one or more preparation steps, a subsequent coating step is performed to deposit a plasma coating on the woven mesh fabric using plasma polymerization that introduces at least one functional group selected from the group consisting of hydroxyl, carboxyl, amino, and sulfonate groups. Both the preparation steps and the coating step are carried out in a plasma chamber having multiple rollers in a roll-to-roll system operating at approximately 13.56 MHz, a first electrode group, and a second electrode group within the plasma chamber, and the woven mesh fabric is passed through a plasma zone between the electrode groups, thereby treating both sides of the woven mesh fabric.

[0028] According to the present invention, the woven mesh fabric comprises a filament diameter between 10 µm and 60 µm and a mesh opening of more than 20 µm, and has a fabric thickness between 20 µm and 80 µm.

[0029] One of the basic ideas of this invention is to provide a basic structure that is robust to application and environmental conditions, and on which a membrane or membrane coating can be firmly fixed without affecting the electrolysis itself.

[0030] In this regard, it has been recognized that fabrics made of polyphenylene sulfide, polyetheretherketone and liquid crystal polyester are particularly suitable as base or carrier materials because they can withstand harsh environmental conditions well.

[0031] It is preferable to use only monofilament fibers. Woven fabrics with monofilament fibers having only one of the aforementioned polymers can be used, or woven fabrics with monofilament fibers made of different polymers can be used, i.e., woven fabrics with warp PPS monofilament fibers and weft PEEK monofilament fibers. The type of monofilament fibers in one direction can also be changed.

[0032] However, in order to manufacture high-performance ion exchange membranes, the present invention provides a surface treatment of the fabric to provide a good and durable bond between the fabric and the ion exchange membrane. Furthermore, it has been recognized that providing the largest possible mesh size is advantageous for this application, which in turn reduces the stability of the fabric during the ion exchange coating process.

[0033] The inventors recognized that a good chemical bond and sufficient adhesion between the woven porous structure and the ionomer of the ion exchange membrane are essential to overcoming interface problems. Furthermore, the compatibility between the reinforcing material and the ionomer is often limited, which affects the overall efficiency of the fuel cell and its tolerance to harsh chemical environments. To address this issue, many researchers have attempted to functionalize the fibers directly during spinning, but success has been very limited due to spinnability and the difficulty of setting functional groups on the filament surface. Moreover, the functional groups may ultimately be affected during the washing and fixing of the woven fabric. The inventors discovered that post-functionalization of a pre-fixed and dimensionally stable woven web using low-temperature plasma is a simple and scalable technique to eliminate these problems. Therefore, the concept of this invention is to design and fabricate a precise woven web structure that will be compatible with the membrane coating at a later stage.

[0034] The fundamental insight of this invention is to identify the influence of fabric geometry and surface properties to achieve an ideal enhancement or foundation for membrane coatings. The structure and construction of textiles or fabrics depend on many factors, such as weave type, fiber content type, fiber fineness, and mesh size, i.e., the number of threads per centimeter. Compared to flat surfaces (membranes, polymer solids, etc.), fabrics have a complex structure, essentially consisting of two surfaces: one macroscopic and visible to the naked eye, and the other an actual inner surface composed of the spaces between filaments and the pore size distribution. Ion exchange capacity has been found to be closely related to textile structure, such as mesh size, filament diameter, and weave structure, such as plain weave and twill weave. Plain weave structures with larger mesh openings are more effective because they reduce the physical barrier to ion exchange. Furthermore, in addition to plasma process parameters and plasma coating properties, capillary action is also strongly influenced by mesh geometry, particularly the mesh opening (the space between two adjacent filaments) and yarn (filament) diameter.

[0035] In this specification, the term "woven fabric" is used as a synonym for "net" or "textile" or "reinforcing fabric" or "fabric" or "woven structure" according to the invention, all of which describe the woven monofilament fabric of the invention as a functional reinforcing material for ion exchange membranes.

[0036] It has been found that the plain weave structure of woven fabrics with relatively large mesh openings is beneficial for achieving higher performance in ion exchange membranes. On the other hand, this combination makes the woven fabric less dimensionally stable. Therefore, one objective is to fix and dimensionally stabilize the woven mesh fabric through heat treatment. Thus, the woven mesh fabric is subjected to at least one heat treatment between 240°C and 350°C, which fixes the monofilament fibers of the woven mesh fabric together and stabilizes its dimensions. In other words, the heat treatment fixes the individual monofilament fibers together at their contact points. These contact points are particularly located where the weft and warp yarns overlap. The woven mesh fabric can be stretched or overfed in both length (warp) and width (weft) directions under appropriate heat setting to bring the mesh geometry, i.e., the mesh opening or aperture, to a predetermined size. Therefore, valuable mesh sizes can be obtained and stabilized to accommodate process parameters such as temperature, contact time (material linear velocity), stretching, or tension.

[0037] Heat treatment further removes contaminants, such as spinning oils, from the filament surface. Spinning oils are applied during the spinning and weaving processes of monofilament fibers and monofilament woven fabrics.

[0038] It has been found that, considering the further preparation and coating steps and for the effectiveness of the resulting ion exchange membrane, the woven mesh fabric should contain a filament diameter between 10 µm and 60 µm, preferably between 20 µm and 50 µm, a mesh opening of more than 20 µm, preferably between 75 µm and 225 µm, and a fabric thickness between 20 µm and 80 µm, preferably between 30 µm and 70 µm. The fabric can have any geometric mesh opening, but a regular opening with a square or rectangular configuration is preferred.

[0039] In principle, a classic washing process can be used prior to the heat treatment. However, the washing process has some drawbacks due to the displacement of monofilaments in the fabric, making it impossible to maintain the required mesh size. Therefore, the heat treatment can be optimized to serve as an alternative to wet washing. Besides saving energy, this avoids the use of chemicals that are extremely dangerous to humans and the aquatic world in wet washing processes.

[0040] This invention further proposes one or more preparation steps based on plasma pretreatment and / or plasma etching, and a subsequent coating step of depositing a plasma coating on a woven mesh fabric. These steps are techniques for improving the surface properties of fibers and fabrics without altering their overall properties. They are used to enhance surface properties by improving adhesion and wettability. Wetting plays a key role in enhancing the adhesive strength in ion exchange membranes by improving the interaction between the fibers and the ion exchange matrix. This is achieved through various mechanisms, including surface modification, chemical interactions, and mechanical interlocking, which collectively contribute to stronger interfacial adhesion. However, for some ion exchange membranes, specific functional groups in the plasma coating play a major role in achieving the final membrane performance rather than wettability.

[0041] Plasma pretreatment aims to further refine the cleaning of the surface of woven mesh fabrics, especially by removing impurities, strongly adhering dust particles, and organic, inorganic, and microbial contaminants from the filament surface. It also activates molecular groups on the surface of monofilament fibers.

[0042] Plasma etching exposes woven mesh fabrics to plasma to etch the surface of the monofilament fibers to an average roughness between 30 nm and 200 nm. This roughness creates an anchoring effect on the ion exchange membrane by providing a better surface for bonding with membrane chemicals. The etched and textured surface can be characterized using atomic force microscopy (AFM) to determine the average surface roughness.

[0043] The coating step, which involves depositing a plasma coating on a woven mesh fabric using plasma polymerization and thereby introducing at least one functional group selected from the group consisting of hydroxyl, carboxyl, amino, and sulfonate groups, is designed to prepare the surface for better chemical bonding with membrane chemicals. This also improves the wettability imparted by the increased surface energy. Through this step, functional groups are formed embedded in the coating. These ionic groups further enhance the ion exchange capacity of the ion exchange membrane.

[0044] To mitigate adhesion problems in ion exchange or electrolyte membranes, several inventive strategies have been provided, focusing on enhancing performance and durability. This invention offers a solution involving modifications to the properties of the reinforcing / supporting woven structure used for membrane reinforcement. This solution is based on a plasma coating process that can form functional surfaces that promote stronger bonding, reducing the likelihood of delamination. This involves depositing an ultrathin plasma polymer layer on this surface, such as reducing the contact angle of the supporting woven monofilament fabric surface. This hydrophilic property ultimately stimulates ion selectivity and mass transfer, as well as water management.

[0045] The one or more preparation and coating steps can be performed in a plasma chamber having multiple rollers and / or expanders in a roll-to-roll system operating preferably at a radio frequency of approximately 13.56 MHz. The chamber further includes a first and a second electrode group within the plasma chamber, and the woven mesh fabric is passed through a plasma zone between the electrode groups, thereby treating both sides of the woven mesh fabric. The chamber itself can be a ground electrode for these methods.

[0046] In a preferred embodiment, the coating step is a plasma-enhanced chemical vapor deposition (PECVD) process. Specific functionalization of the woven web can be achieved through various pathways, such as wet chemical methods, plasma treatment, PECVD, ion beam implantation, and combinations thereof. While permanent chemical functional groups can be introduced using conventional methods other than PECVD, micron-thick coatings adversely affect the ion exchange properties of the composite material. Coating thickness cannot be reduced during conventional wet chemical treatments due to low functional group density and uniformity issues. Furthermore, conventional coatings may lack the versatility and adaptability offered by nano-coatings, potentially limiting their effectiveness in advanced applications.

[0047] In the field of textile finishing, PECVD technology exhibits significant advantages due to its drying and environmentally friendly nature. Furthermore, the wide variety of feed gases available for achieving diverse surface chemistry allows for the incorporation of various chemical functionalities onto textile surfaces to obtain different chemical and physical properties. Non-thermal plasma has been widely adopted for practical industrial requirements, providing high-quality, high-productivity, low-cost, and environmentally clean surface treatment processes.

[0048] Quite noticeable is that plasma treatment improves the crosslinking degree of plasma polymers compared to classical polymerization. To explain the plasma polymerization method further: a vaporized monomer precursor is pumped into a plasma chamber that creates a vacuum. The energy input then generates excited electrons during a glow discharge, causing the molecules to decompose into free electrons, ions, radicals, and excited molecules. These radicals and excited molecules then recombine, condense, and polymerize on the substrate, while the ions and electrons crosslink or form chemical bonds with the already deposited polymer. Therefore, the properties of plasma polymers depend not only on the precursor but also on the deposition parameters. This highly controlled polymerization process ensures pinhole-free, crosslinked, and dry-deposited polymers through plasma polymerization, avoiding difficulties encountered in wet chemical polymerization, such as uneven coatings and solvent-induced impurities leading to defective coatings due to the presence of solvents.

[0049] Plasma polymer coatings, such as the nano-coatings of this invention, differ from conventional polymers in that they exhibit a high density of functional groups per unit volume, a highly cross-linked and branched plasma polymer network, a coating thickness of only nanometers (<100 nm), high adhesion of the coating to the substrate, and no change in the overall properties of the substrate. Retaining functional groups in the resulting plasma polymer during plasma polymerization is one of the key challenges in achieving high functionality. Therefore, new and unique properties can be introduced into polymer substrate materials, such as high-precision woven fabrics suitable for further processing with ion-exchange membrane coatings. Depending on the membrane type and application, different functional ionic groups, such as sulfonate (SO3), amine (NH2), carboxyl (COOH), and hydroxyl (OH), are embedded in the nanoscale plasma polymer coating. In addition to reinforcement, the modified filaments can also act as ion exchangers. The modified woven web exhibits lower internal resistance, resulting in higher ionic conductivity and process efficiency. These proposed groups are suitable for long-term coating stability. Furthermore, it is advantageous to form the functional layer without additional tempering or post-treatment steps. According to the method of the present invention, a nanoscale plasma polymer coating is deposited on a fabric by plasma polymerization of a mixture of halogen-free precursor monomers and / or hydrocarbons and reactive gases using a PECVD method. The halogen-free precursor monomers and gases are, for example, ammonia, acrylic acid, carbon dioxide, 3-allyloxy-1,2-propanediol and / or hydrocarbon precursors.

[0050] According to the method of the present invention, it is proposed to prepare woven fabrics that impart enhanced properties to ion exchange membranes. These properties can be observed on the one hand at the functional level to improve ion exchange capacity, and on the other hand at the physical level to enhance or strengthen the ion exchange membrane and prevent dimensional changes during application by improving mechanical properties.

[0051] Preferably, at least one functional group is selected to match the ionic groups of the ion exchange membrane and / or improve the wettability of the woven mesh fabric to the ion exchange membrane during the coating process. The selection of the ionomer material used for the ion exchange membrane and the corresponding adequate functionalization of the woven mesh fabric or textile are related to the performance of the battery, and its performance is often a key bottleneck. The functionalization of the woven mesh fabric should be compatible with the ionic groups present in the membrane chemistry. Therefore, surface functionalization with specific functional groups should address compatibility issues and thus improve ion exchange capacity. In fact, cation exchange membranes (CEMs) contain negatively charged functional groups, such as... , Furthermore, it allows cations to pass through while repelling anions. On the other hand, anion exchange membranes (AEMs) contain positively charged functional groups, such as... , Furthermore, it allows anions to pass through while rejecting cations. Therefore, ion exchange membranes with reinforced fabrics should be designed to provide excellent properties in terms of ion exchange performance and physical properties specific to each application.

[0052] Preferably, the one or more preparation steps are performed under a protective atmosphere and low-pressure plasma conditions, and / or the coating step is a low-pressure plasma polymerization process. These steps may also be low-temperature and low-pressure plasma processes. Low-temperature and / or low-pressure plasma processes are preferred because these processes are relatively tension-free for woven mesh fabrics. In connection with the invention, the low-pressure plasma is performed in the range of 0.02 mbar to 0.5 mbar, and the low-temperature plasma is performed in the range of 20°C to 50°C.

[0053] In a preferred embodiment, the plasma pretreatment step is performed using an inert gas or a reactive gas or a mixture thereof, and / or the plasma etching step is performed using oxygen or a fluorinated etchant gas or a mixture thereof.

[0054] The cleanliness of the woven mesh fabric, serving as a reinforcing and support layer, is a crucial factor for the successful and uniform deposition of ion-exchange membrane polymers and for ensuring consistent overall adhesion. Plasma pretreatment using inert gases such as argon and helium, and reactive gases such as nitrogen, carbon dioxide, and oxygen, and / or mixtures thereof, removes surface contaminants and impurities from the polymer and simultaneously introduces oxidized polar groups directly onto the surface. This results in enhanced hydrophilicity and negative charge density, significantly improving adhesion properties. The combination of adhesion and cohesion determines the overall integrity and performance of the composite material.

[0055] The improved fiber surface roughness achieved through plasma etching increases the number of potential anchoring points for the film coating, resulting in higher adhesion strength. Mixtures of different plasma process gases can be used to etch textile polymers such as PEEK, PPS, LCP, PSU, PESU, PAEK, PFA, and FEP. Oxygen and fluorinated gases, such as tetrafluoromethane (CF4), when mixed together for plasma etching, form oxyfluoride ions (OF-). OF-ions are strong etchants for polymers. These ions are particularly adept at cleaving carbon-carbon bonds in the polymer backbone and rapidly removing molecules.

[0056] Plasma etching processes are required to produce patterns ranging from nanometers to micrometers with consistent efficiency. Very stringent requirements are placed on plasma etching processes in terms of etching rate, selectivity, contour control, and surface damage. Key parameters of plasma-surface interaction vary with each material's gas mixture, bias voltage, and ion bombardment. Typically, the dominant parameter is the ratio of neutral flux to ion energy flux.

[0057] One of the main problems with composite reinforced ion exchange membranes, also known as ion exchange membranes, is delamination of the fabric layer caused by mechanical stress and operating conditions due to poor adhesion between the fabric layer and the ion exchange matrix. To improve adhesion, plasma treatments such as O2 ablation / etching are used to increase surface roughness, resulting in an increased contact area between the membrane coating and the reinforcing substrate. This facilitates mechanical adhesion between the ionomer polymer of the reinforced ion exchange membrane and the woven fabric. Furthermore, the increased O2 content on the plasma-treated fabric surface makes the surface more polar and more wettable. This can facilitate better penetration of the ion exchange matrix within the woven fabric that acts as the reinforcing layer.

[0058] In the coating step of plasma deposition of plasma coatings using plasma polymerization with the introduction of functional groups, it is advantageous to use a reactive gas mixture, such as nitrogen, carbon dioxide, and / or a mixture of ammonia and hydrocarbons. Alternatively, monomer vapors composed of monomers, such as acrylic acid, 3-allyloxy-1,2-propanediol, and / or hydrocarbon precursors, or a mixture of monomers with helium or argon can be used.

[0059] The one or more preparation steps and subsequent coating steps are performed in one processing stage or in two processing stages that are staggered in time. A processing stage according to this disclosure can be understood as different steps being performed one after another, preferably in the same reaction chamber. Two or more processing stages can be understood as meaning there is a time offset between different processing steps. For example, the fabric may be transferred from one processing chamber to another.

[0060] Preferably, the plasma power during the plasma pretreatment step is less than 5 W / cm² electrode surface, more preferably less than 3 W / cm² electrode surface, or even more preferably less than 2 W / cm² electrode surface.

[0061] In a preferred embodiment, the plasma power during the plasma etching step is less than 1 W / cm² electrode surface, preferably less than 1000 mW / cm² electrode surface, or more preferably less than 500 mW / cm² electrode surface.

[0062] The plasma power during the plasma coating process can be less than 1 W / cm² electrode surface, preferably less than 500 mW / cm² electrode surface, or more preferably less than 200 mW / cm² electrode surface.

[0063] Machine-woven mesh fabrics can be calendered on one or both sides using a calendering process.

[0064] To calender the mesh fabric prior to the one or more of the aforementioned preparation steps, a roll-to-roll calender can be used to raise the temperature of the woven web between 120°C and 200 N / mm². 2 Up to 450 N / mm 2 The material passes between the two rollers at a pressure and a velocity between 1 m / min and 4 m / min.

[0065] Calendering is a thermomechanical finishing method that compresses and smooths woven fabrics under controlled conditions of time, temperature, and pressure. A calendering mill essentially consists of two or more rollers stacked on top of each other, through which the woven fabric is passed, heated and pressurized. Different calendering effects can be achieved on woven fabrics: - Controlled fabric thickness - Single-sided calendering effect - Double-sided calendering effect - Smoothing / Roughening Depending on the application of ion exchange membranes, the physical properties of woven monofilament fabrics, such as thickness, density, pore size, and shape, can be further adjusted through calendering processes. This involves considering parameters such as roll temperature, roll gap pressure, and residence time (i.e., linear velocity) to obtain the desired properties with a defined solidity. Furthermore, the properties of woven fabrics can be affected by the calendering conditions used. For example, air permeability may decrease, and the filament shape may become flattened.

[0066] In a preferred embodiment, the woven mesh fabric after the coating step has a water contact angle between 20° and 90°, preferably between 40° and 80°, and more preferably between 50° and 70° when hydroxyl or carboxyl groups are introduced, and between 80° and 145°, preferably between 110° and 135°, when sulfonate and amino groups are introduced. The water contact angle is determined according to DIN EN ISO 19403:2020-04 for a woven fabric P (explained in detail later with reference to Table 1) having a filament diameter of 38 µm (warp or weft), a mesh opening of 195 µm (warp or weft), and a fabric thickness of 60 µm. As explained above, wettability is an important characteristic of the substrate woven fabric for depositing ion exchange membranes. It has been found that the above values ​​improve adhesion to the substrate and thus improve the efficiency of the resulting ion exchange membrane.

[0067] Preferably, the average roughness after the plasma etching step is between 50 nm and 120 nm. This average roughness provides good properties for subsequent deposition steps.

[0068] Preferably, the plasma coating has a thickness of 10 nm to 200 nm, more preferably 20 nm to 80 nm. For the end use of the electrolytic membrane, as already explained, it is desirable for the fabric to have the largest possible mesh openings and the smallest possible area (specific surface area / volume ratio). The preferred coating thickness takes this into account, as they are thin enough to increase the total area of ​​the membrane coating and thus result in a higher ion exchange capacity. Preferably, the average roughness is higher than the thickness of the plasma coating.

[0069] The processing time for the coating and pretreatment steps can be less than approximately 4 minutes per step, and for the plasma etching step, less than approximately 8 minutes. These durations are sufficient to achieve the desired results for each step without affecting, or only minimally affecting, the overall properties of the woven fabric.

[0070] It has been found advantageous to control the temperature of the electrodes of the electrode assembly and / or the walls defining the plasma chamber between 30°C and 100°C, preferably between 35°C and 80°C. These parameters are also sufficient to achieve the desired results for each step without damaging or only minimally damaging the fibers of the woven fabric.

[0071] Based on the method of the present invention, woven mesh fabrics with improved membrane coating properties can be produced as reinforcing fabrics for ion exchange membrane applications, wherein the woven mesh fabric comprises warp and weft monofilaments of at least one of the following polymers: polyphenylene sulfide, polyetheretherketone, perfluoroalkoxyalkane, fluorinated ethylene propylene, and liquid crystal polyester, and wherein one monofilament is made of only one of these polymers, wherein the woven mesh fabric comprises a filament diameter between 10 µm and 60 µm and a mesh opening of more than 20 μm, and has a fabric thickness between 10 μm and 80 μm.

[0072] After weaving, the woven mesh fabric is heat-treated at a temperature between 240°C and 350°C to remove surface contaminants, thereby fixing the monofilaments of the woven mesh fabric together and stabilizing its dimensions.

[0073] The woven mesh fabric is prepared by one or more preparation steps, including: a plasma pretreatment step of the woven mesh fabric to further finely clean the surface of the woven mesh fabric, especially by removing impurities, strongly adhering dust particles and organic, inorganic and microbial contaminants from the filament surface, and a plasma etching step of exposing the woven mesh fabric to plasma to etch the surface of the monofilament fibers of the woven mesh fabric to an average roughness of 30 nm to 200 nm.

[0074] According to the invention, the woven mesh fabric is subsequently coated by plasma polymerization to deposit a plasma coating on the woven mesh fabric using at least one functional group selected from the group consisting of hydroxyl, carboxyl, amino, and sulfonate groups. These groups act as ion exchangers and promote overall ion exchange efficiency.

[0075] In a preferred embodiment, the woven mesh fabric, when hydroxyl or carboxyl groups are introduced, has a water contact angle between 20° and 90°, preferably between 40° and 80°, more preferably between 50° and 70°; and when sulfonate and amino groups are introduced, it has a water contact angle between 80° and 145°, preferably between 110° and 135°. The water contact angle is determined according to DIN EN ISO 19403:2020-04. Attached Figure Description

[0076] The invention is further described below with reference to preferred exemplary embodiments schematically illustrated in the accompanying drawings: Figure 1 An illustration showing the fabric before the processing according to the present invention; Figure 2 An illustration showing the fabric after plasma pretreatment; Figure 3 An illustration and magnified view of the fabric after subsequent plasma etching. Figure 4 An illustration and magnified view of the fabric after the subsequent plasma coating step. Figure 5 Display SEM images of machine-woven webs; Figure 6 Two AFM images showing etched PEEK fabric; and Figure 7 Showing two SEM images of the untreated fabric P subsequently coated with Nafion, and the fabric P coated with SO3 plasma and subsequently coated with Nafion.

[0077] Figures 1 to 4 The illustration shows the same fabric before, during, and after the method of the present invention, wherein, for clarity, only a single monofilament fiber of the polymer material is shown.

[0078] Figure 1 The image shows the fabric prior to treatment by the method of the present invention. Unidentified particles are shown as impurities, strongly adhering dust particles, and organic, inorganic, and microbial contaminants on the surface of the monofilament fibers.

[0079] Figure 2 Displayed after plasma pretreatment Figure 1The fabric is treated to remove unidentified particles. The goal of this treatment is to clean the fabric surface so that subsequent polymer deposition can be easier.

[0080] Figure 3 Shown after the plasma etching step Figure 2 The fabric. The plasma etching step roughens the surface of the substrate or fiber to make subsequent layers adhere more easily. Sometimes this roughening is viewed as forming nano / micro grooves on the filament surface. A magnified view of the fiber surface is shown on the right. Irregularities and roughness are shown here.

[0081] at last, Figure 4 Displayed after subsequent PECVD steps Figure 3 The fabric is plasma-polymerized to form a very thin coating incorporating at least one functional group selected from the group consisting of hydroxyl, carboxyl, amino, and sulfonate groups. Due to the size and roughness of the irregularities and the very thin coating, the fiber material remains partially uncoated after coating. This has the advantage that, when the ion exchange membrane material is applied to the fabric, it is chemically bonded to the plasma coating on the fabric, while the relatively high roughness compared to the thin plasma coating also enables mechanical interlocking. Detailed Implementation

[0082] The following consideration of different fabrics further illustrates the invention. Table 1 summarizes the technical characteristics of fabrics with plain weave structures. This information helps in understanding their behavior and the reinforcing woven structure of the ion exchange membrane of the present invention.

[0083] Table 1. Exemplary fabric properties.

[0084] To illustrate these dimensions, Figure 5 SEM image showing the woven mesh visible in fabric P, with a mesh opening of 195 µm (3) (weft or warp), a filament diameter of 38 µm (4) (weft or warp), and a thickness of 60 μm. Weft (1) and warp (2) are also indicated, but they are interchangeable for this fabric.

[0085] calendering process To obtain a suitable thickness for the woven web later used as a reinforcing and support layer for the ion exchange membrane, fabric P was exposed to a calendering process, thereby compressing the fabric by passing it between two rollers under controlled conditions of time, temperature, and pressure. A two-step process was performed sequentially, first on the front side of the fabric and then on the back side, applying a pressure of 300 N / mm² and a linear velocity of 2 m / min at 160°C. Thus, a reduction in thickness was achieved while maintaining a constant open area of ​​the fabric. Table 2. Fabrics before and after calendering.

[0086] Cleaning process In polymer ion exchange membrane applications, insufficient cleanliness of the woven reinforcement layer can lead to significant performance degradation and reduced service life. Contaminants, particularly cations, can displace protons in the membrane, adversely affecting ionic conductivity and overall cell efficiency. In fact, contaminants can occupy active sites in the catalyst layer, reducing the electrochemical surface area and hindering reaction kinetics. Therefore, high cleanliness is required. As shown in Table 3, the woven PEEK fabric P has been exposed to different treatments, such as washing followed by heat curing, heat curing only, and heat curing followed by low-pressure plasma cleaning. Prior to treatment, the fabric was hydrophilic due to the addition of spinning oil during its processing. The treated fabrics have been studied according to the standard DIN EN ISO 11354:2012-06 using extraction with 96% ethanol and petroleum ether.

[0087] Clearly, heat curing alone achieves a better level of cleanliness compared to two-step processes such as washing and heat curing. Even higher levels of cleanliness can be achieved for woven fabrics through a suitable combination of heat curing and subsequent plasma cleaning. During the plasma cleaning process, high-energy ions collide with the filament surface and remove residual fine contaminants. In addition to the fine cleaning effect, plasma cleaning promotes the formation of active polar groups on the fabric surface, as evidenced by a lower water contact angle (Table 3). Contact angles were measured according to DIN EN ISO 19403:2020-04.

[0088] Table 3. Different cleaning treatments.

[0089] Plasma etching Plasma etching is performed using a suitable gas mixture. Examples include oxygen and tetrafluoromethane (CF4), which, when mixed together during plasma etching, produce oxyfluoride ions (OF-), a powerful etchant that removes solids from polymer surfaces by chemically converting them into small volatile molecules. The etched surfaces have been characterized using atomic force microscopy (AFM). Two different power sources, direct bias and remote plasma, were used to improve the root mean square roughness Rq and average roughness Ra. Direct bias plasma with a power of 500 V showed the best results on fabric P, achieving Rq of 130 nm and Ra of 105 nm.

[0090] Further investigation of the morphological changes caused by the etching process was conducted using AFM images. It can be seen that, compared with the untreated fabric, the etching conditions resulted in uniform texturing and roughening of the PEEK surface.

[0091] exist Figure 6 The image shows two AFM images of PEEK fabric P, where a) is unprocessed and b) is obtained by remote plasma etching at 1300 W.

[0092] Water contact angles were measured on two different fabric types, one using direct bias and the other using remote plasma etching, according to DIN EN ISO 19403:2020-04. In addition to the etching effect, the introduction of chemical functional groups on the filament surface alters the surface energy, particularly for the remote plasma etching process. Regardless of fabric type, the water contact angle was significantly reduced, demonstrating a trend towards achieving higher wettability for film coatings.

[0093] Table 5. Examples of water contact angles measured on etched PEEK fabric.

[0094] Ion exchange membrane Uncharged and inert woven fabrics act as a physical barrier in ion exchange membranes. This physical barrier is advantageous when there is good compatibility between the membrane coating and the woven fabric. Therefore, functionalizing the reinforcing material with suitable ionic groups can significantly enhance its thermal stability and resistance to degradation in the final application. This improvement is primarily attributed to better interfacial interactions between the reinforcing material and the polymer matrix, resulting in higher coating uniformity and better integrity of the woven fabric within the ion exchange matrix. Consequently, enhanced mechanical and thermal properties can be obtained on the reinforced ion exchange membrane.

[0095] Fabric P has been SO3 functionalized and coated with a Nafion film, and its performance is compared with that of uncoated P. For example... Figure 7 As can be seen in the images, Nafion-coated samples A and B have been studied using scanning electron microscopy (SEM). As can be seen in image A, the film coating on the untreated fabric leads to defects (pores, cracks) and bubble formation. This is attributed to lower affinity and poor pore filling by the polymer in the incompatible fabric. Conversely, image B shows very uniform penetration and swelling of the coating material, indicating uniform coating application and good adhesion between the functionalized fabric and the Nafion coating.

[0096] Clearly, the functionalization of the reinforcing layer of the ion exchange membrane significantly improves the consolidation and properties of the resulting composite material (Photo B). Conversely, as can be seen in Photo A, the loss of adhesion of the coating to the untreated woven mesh surface results in coating defects and inhomogeneities.

[0097] Plasma nanocoatings offer significant advantages over conventional coatings in enhancing the interfacial properties of composite materials. These advanced coatings utilize nanoscale effects to improve mechanical properties, durability, and functionality. In this sense, three fabrics, P, Q, and T, have been functionalized with hydroxyl groups to prepare them for subsequent ionomer coating. As shown in Table 6, the water contact angle decreased sharply after plasma nanocoating. This implies a higher surface energy on the fabric surface, leading to enhanced wettability, adhesion, and reactivity.

[0098] Table 6. Examples of water contact angles measured on plasma-coated fabrics.

[0099] According to ASTM F1980-16 (55℃ / 20% RH, 10 days), the durability of the coating, i.e., its self-life, was studied using real-time aging and accelerated aging tests. As can be seen in Table 7, the water contact angle remained almost unchanged for both aging types.

[0100] Table 7. Examples of water contact angles on plasma-coated and aged fabric P.

[0101] Based on the present invention, a method for preparing a woven mesh fabric as a reinforcing fabric for ion exchange membrane applications can be provided, wherein the fabric has improved membrane coating properties for ion exchange membrane applications.

Claims

1. A method for improving the properties of membrane coatings for ion exchange membrane applications using a woven mesh fabric as a reinforcing fabric, said woven mesh fabric comprising warp and weft monofilaments of at least one of the following polymers: Polyphenylene sulfide, polyetheretherketone, perfluoroalkoxyalkane, fluorinated ethylene propylene, and liquid crystal polyester, wherein a single monofilament fiber is made from only one of the polymers. The method includes: A fixing step performed after the weaving of the woven mesh fabric, wherein the woven mesh fabric is subjected to at least one heat treatment at a temperature between 240°C and 350°C to fix the mesh openings to the desired size, stabilize the monofilament fibers of the woven mesh fabric, and remove surface contaminants from the monofilament fibers. Perform one or more preparatory steps, including: • A plasma pretreatment step is performed on the woven mesh fabric to further refine the surface cleaning of the woven mesh fabric, especially by removing impurities, strongly adhering dust particles, and organic, inorganic, and microbial contaminants from the filament surface. • A plasma etching step that exposes the woven mesh fabric to plasma to etch the surface of the monofilament fibers of the woven mesh fabric to an average roughness of 30 nm to 200 nm; A subsequent coating step involves depositing a plasma coating on the woven mesh fabric using plasma polymerization that introduces at least one functional group selected from the group consisting of hydroxyl, carboxyl, amino, and sulfonate groups. One or more of the preparation and coating steps are performed in a plasma chamber having multiple rollers in a roll-to-roll system operating at approximately 13.56 MHz radio frequency, a first electrode group and a second electrode group within the plasma chamber, and the woven mesh fabric is passed through a plasma zone between the electrode groups, thereby treating both sides of the woven mesh fabric. The woven mesh fabric comprises filament diameters between 10 µm and 60 µm and mesh openings of more than 20 µm, and has a fabric thickness between 20 µm and 80 µm.

2. The method according to claim 1, Its features Select at least one functional group to match the ionic groups of the ion exchange membrane and / or improve the wettability of the woven mesh fabric to the ion exchange membrane during the coating process.

3. The method according to claim 1 or 2, Its features One or more of the preparation steps are performed under a protective atmosphere and low-pressure plasma conditions, and / or The coating step is a low-pressure plasma polymerization process.

4. The method according to any one of claims 1 to 3, Its features The plasma pretreatment step is performed using an inert gas or a reactive gas or a mixture thereof, and / or The plasma etching step is performed using oxygen or fluorinated etchant gas, or a mixture thereof.

5. The method according to any one of claims 1 to 4, Its features In the coating step of plasma polymerization deposition of plasma coatings by introducing functional groups, using • Reactive gas mixtures, or • Monomer vapor, which is composed of monomers, It may be composed of a monomer and a mixture of helium or argon.

6. The method according to any one of claims 1 to 5, Its features The one or more preparation steps and the subsequent coating steps are performed in one processing stage or in two processing stages that are staggered in time.

7. The method according to any one of claims 1 to 6, Its features During the plasma pretreatment step, the plasma power is less than 5 W / cm² electrode surface, preferably less than 3 W / cm² electrode surface, or more preferably less than 2 W / cm² electrode surface.

8. The method according to any one of claims 1 to 7, Its features During the plasma etching step, the plasma power is less than 1 W / cm² of the electrode surface, preferably less than 1000 mW / cm² of the electrode surface, or more preferably less than 500 mW / cm² of the electrode surface.

9. The method according to any one of claims 1 to 8, Its features During the plasma coating step, the plasma power is less than 1 W / cm² electrode surface, preferably less than 500 mW / cm² electrode surface, or more preferably less than 200 mW / cm² electrode surface.

10. The method according to any one of claims 1 to 9, Its features The woven mesh fabric is a calendered mesh fabric.

11. The method according to any one of claims 1 to 10, Its features Prior to one or more of the preparation steps, the woven mesh fabric is subjected to an elevated temperature between 120°C and 200°C and 200 N / mm using a roll-to-roll calender. 2 Up to 450 N / mm 2 The material passes between the two rollers at a pressure and a speed between 1 m / min and 4 m / min.

12. The method according to any one of claims 1 to 11, Its features The water contact angle of the woven mesh fabric after the coating step corresponds to • When hydroxyl or carboxyl groups are introduced, the angle is between 20° and 90°, preferably between 40° and 80°, more preferably between 50° and 70°, and • When sulfonate and amino groups are introduced, the angle is between 80° and 145°, preferably between 110° and 135°. The water contact angle was determined according to DIN EN ISO 19403:2020-04.

13. The method according to any one of claims 1 to 12, Its features The average roughness after the plasma etching step is between 50 nm and 120 nm.

14. The method according to any one of claims 1 to 13, Its features The plasma coating has a thickness of 10 nm to 200 nm, preferably 20 nm to 80 nm.

15. The method according to any one of claims 1 to 14, Its features The coating step and the pretreatment step each take approximately 4 minutes or less, and the plasma etching step takes approximately 8 minutes or less.

16. The method according to any one of claims 1 to 15, The temperature of the electrodes of the electrode assembly and / or the walls defining the plasma chamber is controlled between 30°C and 100°C, preferably between 35°C and 80°C.

17. A woven mesh fabric with improved membrane coating properties for use as a reinforcing fabric in ion exchange membrane applications, wherein the woven mesh fabric comprises warp and weft monofilament fibers of at least one of the following polymers: Polyphenylene sulfide, polyetheretherketone, perfluoroalkoxyalkane, fluorinated ethylene propylene, and liquid crystal polyester, One of the monofilament fibers is made from only one of the polymers. After weaving, the woven mesh fabric is heat-treated at a temperature between 240°C and 350°C to remove surface contaminants, thereby fixing the monofilament fibers of the woven mesh fabric together and stabilizing its dimensions. The woven mesh fabric is prepared through one or more preparation steps, including: • A plasma pretreatment step is performed on the woven mesh fabric to further refine the surface cleaning of the woven mesh fabric, especially by removing impurities, strongly adhering dust particles, and organic, inorganic, and microbial contaminants from the filament surface. • A plasma etching step that exposes the woven mesh fabric to plasma to etch the surface of the monofilament fibers of the woven mesh fabric to an average roughness of 30 nm to 200 nm; Subsequently, coating is performed by depositing a plasma coating on the woven mesh fabric using plasma polymerization that introduces at least one functional group selected from the group consisting of hydroxyl, carboxyl, amino, and sulfonate groups. The woven mesh fabric comprises filament diameters between 10 µm and 60 µm and mesh openings of more than 20 µm, and has a fabric thickness between 10 µm and 80 µm.

18. The woven mesh fabric according to claim 17, Its features Its water contact angle corresponds to • When hydroxyl or carboxyl groups are introduced, the angle is between 20° and 90°, preferably between 40° and 80°, more preferably between 50° and 70°, and • When sulfonate and amino groups are introduced, the angle is between 80° and 145°, preferably between 110° and 135°. The water contact angle was determined according to DIN EN ISO 19403:2020-04.

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