Non-woven fabric with nano-porous fibers

Abstract

The present invention relates to a method for preparing a nonwoven fabric having nanoporous fibers. The invention relates to a method for producing fibrils (20), comprising at least the following steps: providing (10) a spinning solution comprising a fibrous raw material, in particular a polymer, and a solvent, producing (12) fibrils (20) from the spinning solution, in particular by extruding the spinning solution through capillaries; accelerating (14) the produced fibrils (20) by means of an accelerating fluid flow; laying (16) the accelerated fibrils (20) with a fluid as a wet nonwoven precursor (26); and drying (18) the non-woven fabric precursor (26) in a liquid state bypassing the wet non-woven fabric precursor (26) in which the liquid has a capillary action in order to produce the non-woven fabric having nanoporous fibers. The invention also relates to a non-woven fabric and a preparation device.

Description

Technical Field

[0001] This invention relates to a method for preparing nonwoven fabrics with nanoporous fibers, particularly aerosol fibers. Furthermore, this invention relates to a nonwoven fabric with nanoporous fibers and an apparatus for preparing such a fabric. Background Technology

[0002] Aerosols are porous solids, in which, for example, more than 99% of the volume is composed of pores. The pore size is, for example, in the nanometer range. Aerosols can be formed, for example, based on silicates. Aerosols are very lightweight and possess excellent thermal insulation and filtration properties. However, the industrial-scale preparation of aerosols is extremely expensive, and using them as monolithic solids is costly, difficult, or even impossible for some applications.

[0003] Aerosol fiber materials, their preparation methods, and their applications are described in DE 10 2006 049 179. Thus, aerosols can be processed into nonwoven fabrics, for example. However, the preparation of aerosol fibers is very costly. Drying the fibers during preparation is particularly expensive and only fibers with significant thickness can be produced. Further processing of thick fibers into nonwoven fabrics can result in significant fiber breakage. The flexibility of the nonwoven fabric can be very low.

[0004] Jens Mroszczok's 2019 paper, "Preparation of Aerosol Nonwovens," describes the production of cellulose-based aerosol nonwovens. However, this method only allows for the production of fibers with large thicknesses, and the drying of the nonwovens remains a costly process.

[0005] Methods and apparatus for forming directly shaped cellulose strips are described in EP3529405 A1. Summary of the Invention

[0006] A first aspect of the invention relates to a method for preparing a nonwoven fabric having nanoporous fibers. The nonwoven fabric can be a nonwoven material. The nonwoven fabric can be a structure formed from fibers already combined into fiber layers or nonwoven fabric layers. These fibers can be arranged non-uniformly and / or partially randomly oriented in the nonwoven fabric. These fibers can, for example, have a randomly distributed orientation within a preferred orientation. The nanoporous fibers can, for example, be formed as aerosol fibers. The nanoporous fibers can be elastically deformable. These fibers can, for example, be formed as fibers with a finite length or continuous fibers. The corresponding pores of the fibers can be open or closed. These pores can be filled with a gas, such as air or CO2.

[0007] The method includes providing a spinning solution. The spinning solution includes a fiber raw material. The fiber raw material may be, for example, a polymer. The spinning solution includes a solvent. The fiber raw material can be dissolved in the solvent. During fiber preparation, fibers can be formed solely from the fiber raw material, and the solvent can be removed later. The solvent may be a processing aid. The fiber raw material may, for example, exist in a solid form and can be dissolved and thus liquefied in the solvent to provide the spinning solution. The spinning solution may consist of the fiber raw material and the solvent. However, the spinning solution may also include additives. In addition to the solvent, the spinning solution may also include water, as long as the water does not form the solvent. The spinning solution may also contain multiple fiber raw materials and solvents. The spinning solution may be a high-viscosity fluid.

[0008] The method includes the step of producing fibrils from the spinning solution. For example, the fibrils can be formed by extruding the spinning solution through capillary tubes. The extrusion process can also be used here to mix and / or generally provide the spinning solution. For example, the fiber material, as a solid, and the solvent can be fed separately into the extruder and mixed only during the extrusion process used to form the spinning solution. The fibrils can, for example, be formed from partially cross-linked fiber material. The fibrils can also include a solvent. The fibrils can, for example, have a gel-like consistency. The fibrils can be formable and correspond to a state in which the respective fiber components are not yet fully solidified into fibers. Multiple fibrils can be produced in parallel. A spinning block can, for example, have 10,000, 20,000, 50,000, or more capillaries, through which one fibril is simultaneously formed at the outlet during extrusion. The fibrils can, for example, be formed as continuous fibers. The fibrils may already have a nanoporous structure, which remains substantially unchanged in further method steps. The nanoporous structure can also be produced at a later point in time.

[0009] The method includes the step of accelerating the produced fibrils by means of an accelerating fluid flow. The accelerating fluid flow may, for example, include water and / or air. The accelerating fluid may be the same as or different from the solvent. For example, a non-solvent may be selected as the accelerating fluid flow. The accelerating fluid flow may be oriented substantially parallel to the extrusion direction of the fibrils. By accelerating the fibrils, their diameter can be reduced and / or their length can be stretched. The fibrils can be stretched by acceleration. Due to the finer cross-section, the nonwoven fabric thus prepared can have significantly better flexibility. Additionally, drying can be carried out in a particularly rapid and / or low-energy manner. For example, unlike other measures to reduce cross-section, acceleration only slightly reduces or even does not reduce nanoporosity at all. The risk of fibril breakage is also lower when accelerated by means of the accelerating fluid flow. Furthermore, acceleration by means of the accelerating fluid flow can facilitate the formation of the nonwoven fabric due to the eddies in the fibrils. The fibrils may be accelerated unevenly. The accelerating fluid flow may, for example, act on both sides of the spinning block. For example, the fibrils facing the outer side of the fluid flow are accelerated more significantly than the fibrils facing the inner side. Therefore, the bonds between fibers in the nonwoven fabric can be stronger and / or the fiber density of the nonwoven fabric can be increased. The accelerating fluid flow can initially solidify the fibrils and / or act as an antisolvent. The accelerating fluid flow can also act on the fibrils in the gaps between the corresponding capillary openings. Fiber preparation with an accelerating process as described herein can also be referred to as a solution blown process. The accelerating fluid flow can be captured and reused. The accelerating fluid flow can, for example, flow at near-sonic speeds. For example, the accelerating fluid can be directed to the fibrils at about Mach 0.8.

[0010] The method includes the step of laying accelerated fibrils as a wet nonwoven fabric precursor with a fluid. The fluid may exist in a liquid aggregated state. In the nonwoven fabric precursor, the fibrils may already be arranged in a nonwoven-like manner. This nonwoven-like arrangement may be a woven layer. The fibers in the nonwoven fabric precursor may, for example, be partially attached to each other, wound around each other, or even partially form a uniform structure. The nonwoven fabric precursor may also contain a significant proportion of solvent and / or accelerating fluid, particularly placed within the pores of the fibers. Other fluids may be added for storage purposes and / or to prevent environmental impact. Before a subsequent drying step, all fibers in the nonwoven fabric precursor may be, for example, wetted and / or completely or almost completely covered by the liquid. Alternatively or additionally, the fluid used to wet the nonwoven fabric precursor may be stored within the fiber structure. That is, for example, at a process time point prior to the explicitly stated drying step, the fibrils are not dried. The liquid in the pores of the corresponding fibers may, for example, be retained until drying. However, the liquid may also be replaced by another liquid before drying. Laying can be done, for example, by trapping, especially on a conveyor belt. The fibers in the nonwoven precursor can be oriented arbitrarily or have a preferred orientation. In a preferred orientation, the nonwoven fabric can withstand a higher load in one direction and / or be more easily bent in one direction.

[0011] The method includes the step of drying the nonwoven precursor. During drying, the fluid in the wet nonwoven precursor is bypassed in a state where the liquid exhibits capillary action. For example, a state without capillary action is achieved before significant removal of the liquid from the fibers, for example, by increasing the temperature simultaneously with increasing the pressure. This produces the nonwoven fabric with nanoporous fibers. Under capillary action, the fluid in the wet nonwoven precursor has a variable interface with the surrounding atmosphere. Capillary action corresponds, for example, to the surface tension of the fluid. For example, water or alcohol does not exhibit capillary action in a frozen or supercritical state. Then, by bypassing the liquid phase, this state can be converted to a vapor phase, for example, by sublimation or superheating. In the vapor phase, the fluid, which has been pre-liquidized in the fibers, can escape from the fibers. The fibers may be completely cured during drying or may have been pre-completely cured.

[0012] During drying, the process can be initiated from the liquid phase with little or no drying (i.e., with minimal removal of fluid from the nonwoven precursor). Upon reaching this phase, sublimation or superheating can occur, transforming the frozen or supercritical aggregated state into a vapor-like aggregated state. Consequently, the remaining fluid cannot cause the corresponding pores of the fibers to shrink and collapse through capillary action. Thus, the nanoporosity can remain largely unchanged, or even entirely, during drying. This drying process is highly efficient and can be meaningfully used on an industrial scale due to the smaller diameter resulting from the accelerated passage of the corresponding fibers. Drying can be carried out, for example, in a closed space, such as an autoclave.

[0013] For example, due to its drapier barkeit (cuttable design), nonwoven fabrics with nanoporous fibers can be prepared inexpensively and are easy to process and apply. These nonwoven fabrics can be used, for example, as filling materials in insulating clothing, especially as a down substitute. They can also be used as barrier materials in aircraft manufacturing, vehicle manufacturing, and construction. Furthermore, they can be biodegradable. Thus, in the textile industry, they can be used not only as functional materials but also as hygiene products. They can also be used as bandage materials or wound dressings. Finally, they can be used as filter cloths in, for example, catalysts or water filters.

[0014] In one embodiment of the method, the drying process includes supercritical drying. The drying can, for example, be carried out solely in a supercritical manner. In the case of supercritical drying, the atmosphere surrounding the nonwoven precursor can be brought into its supercritical aggregated state. For this purpose, pressure and / or temperature can be increased. For example, CO2 (i.e., carbon dioxide) can be introduced to reduce the required pressure and / or temperature. In the case of supercritical drying, the fluid in the nonwoven precursor can be replaced from the pores of the fibers by CO2 or other gases. In the case of supercritical drying, the nanoporosity of the nonwoven fibers can be particularly high.

[0015] In one embodiment of the method, the drying includes freeze-drying. The drying can, for example, be carried out solely by freeze-drying. In the case of freeze-drying, the atmosphere surrounding the nonwoven precursor and / or the liquid in the wet nonwoven precursor can be transformed into its solid aggregated state. For this purpose, the pressure can be increased and / or the temperature decreased. The pressure can then be reduced to allow drying by sublimation, for example, while maintaining the reduced temperature. Freeze-drying can be carried out on an industrial scale at particularly low cost.

[0016] In one embodiment of the method, CO2 is introduced for the drying process. Introducing CO2 reduces the energy intensity of the drying process. Furthermore, this allows CO2 to be primarily stored within the pores of the fibers, resulting in favorable nonwoven fabric properties. For example, drying can be carried out in an autoclave by essentially replacing air with CO2. After drying, the CO2 can be captured and reused.

[0017] In one embodiment of the method, the solvent is washed out after the production of the fibrils. For example, the solvent can be washed out using non-solvent or inexpensive methods such as water. This stabilizes the fibrils. The accelerated fluid flow can aid in the washing process. Alternatively or additionally, the washing can be performed separately, for example, during or after the laying process and before the drying process. This prevents the fibers from being damaged by the solvent during drying. The washed-out solvent can be collected and reused.

[0018] In one embodiment of the method, it is proposed that the fluid in the wet nonwoven precursor be replaced prior to the drying process. This allows the selection of a fluid with particularly favorable energy for the drying. For example, isopropanol and / or ethanol can be used to replace water. The replacement liquid can also be a liquid mixture. This replacement allows for supercritical drying, for example, at lower temperatures and / or pressures. The replacement liquid can, for example, enable the drying at temperatures harmless to the fiber or fibrous material. Otherwise, materials such as cellulose may decompose under excessively high pressures and temperatures. At the temperatures at which cellulose decomposes, water may, for example, require supercritical drying. The replacement can simultaneously clean the nonwoven precursor. Here, the alcohol can form a phase with CO2, which also improves the drying process. The replacement liquid can be a non-solvent for the fibrous raw material. In this replacement, the solvent, the accelerating fluid, and / or the cleaning liquid can be replaced. For example, this replacement can be performed by simply rinsing the nonwoven precursor with the replacement liquid.

[0019] In one embodiment of the method, the fiber raw material is cellulose. Cellulose is inexpensive, biodegradable, human-acceptable, and highly flexible at small fiber thicknesses, exhibiting only a low tendency to break. Thus, barrier materials can be produced, for example, in a simple manner that is acceptable to handle without protective equipment. Cellulose fibers can be treated with additives (such as flame retardants) after the drying process. Additives can also be added in other steps.

[0020] In one embodiment of the method, the solvent is NMMO. N-methylmorpholine-N-oxide is a readily treatable solvent for cellulose. Furthermore, NMMO can be easily recovered for reuse, thus allowing for lower costs.

[0021] Other suitable combinations of fiber raw materials and solvents for preparing nonwoven fabrics from the spinning solution include PAN (polyacrylonitrile) with DMSO (dimethyl sulfoxide) and TEOS (tetraethyl orthosilicate) with ethanol. In such combinations, nonwoven fabrics with high-porosity fibers can be prepared with lower consumption. Other examples of suitable organic or inorganic polymers as fiber raw materials are PUR (polyurethane), PET (polyethylene terephthalate), lignin, PHA (polyhydroxyalkanoate), para- and meta-aramids, dextran, and protein fibers. Suitable solvents can be, for example, alcohols, i.e., organic solvents. Depending on the fiber raw material selected, suitable solvents can be acetone, water, and NaSCn (sodium thiocyanate). Examples of organic solvents are DMSO (dimethyl sulfoxide), DMF (dimethylformamide), and DMAC (dimethylacetamide).

[0022] In one embodiment of the method, the accelerating fluid comprises water, a non-solvent for the fiber material, and / or air. Thus, the accelerating fluid can be reused very inexpensively and easily. Furthermore, the accelerating fluid can then exchange the solvent and / or clean the fibrils. The accelerating fluid may also consist of water, a non-solvent for the fiber material, and / or air.

[0023] In one embodiment of the method, the accelerating fluid flow is formed as an aerosol. The accelerating fluid can, for example, be formed as a flowing water mist or solvent mist. This allows the fibrils to be well wetted and prevents complete drying. Simultaneously, it also allows for a smaller volume of liquid required to provide the fluid flow.

[0024] A second aspect of the invention relates to a nonwoven fabric having nanoporous fibers, particularly aerosol fibers. The nonwoven fabric is prepared using the method according to the first aspect. This can be identified, for example, by the different diameters of the fibers in the nonwoven fabric, the highly nanoporous structure of the fibers, and / or their very small diameters. The corresponding features and advantages of the first aspect can also form the features and advantages of the second aspect, and vice versa. The nonwoven fabric can be composed of the nanoporous fibers. The nonwoven fabric can also have other fibers and layers. For example, more than 30%, particularly more than 50%, 75%, or 95% of the nonwoven fabric can be formed as nanoporous fibers.

[0025] In one embodiment of the method, it is proposed that the cross-section of the nanoporous fiber is formed by more than 30%, particularly more than 50%, 60%, 70%, 90%, or 95%, nanopores. The cross-section can be orthogonal to the longitudinal extension. The nanopores can be, for example, openings or cavities in the fiber, and have a diameter of less than 1500 nm, particularly less than 1000 nm, 750 nm, or 500 nm. Due to the high proportion of nanopores in the cross-section, the nonwoven fabric can have particularly strong thermal resistance. A high proportion can be achieved, for example, by the preparation method described in detail above.

[0026] In one embodiment of the method, the nanoporous fibers have a diameter of less than 100 µm, particularly less than 75 µm, 50 µm, 25 µm, 20 µm, 15 µm, or less than 10 µm. A smaller diameter can be achieved by accelerating the fabrication of the fibrils. A smaller diameter allows for efficient and rapid drying and can contribute to greater flexibility of the nonwoven fabric. The diameter can be the minimum, maximum, or average diameter of the fiber. Some fibers may be randomly coarser or finer. The diameter of the nanoporous fibers, for example, as an average of all fibers, can be less than 100 µm, particularly less than 75 µm, 50 µm, 25 µm, 20 µm, 15 µm, or less than 10 µm. However, at least 90%, particularly at least 95%, 97%, or 99% of the diameter of all fibers in the nonwoven fabric can be less than 100 µm, particularly less than 75 µm, 50 µm, 25 µm, 20 µm, 15 µm, or less than 10 µm. Other fibers in the nonwoven fabric can be coarser. Some of these fibers can even be significantly finer. At least 0.1%, particularly at least 0.5%, 1%, 5%, or 10% of all fibers can, for example, have a diameter of less than 5 µm, particularly even less than 2 µm, 1 µm, or 0.8 µm. The diameter of the corresponding fibers in the nonwoven fabric can, for example, be significantly smaller than the diameter of the capillary at the spinneret. Most fiber diameters are in the lower micrometer range, for example less than 10 µm, and the higher nanometer range, for example greater than 800 nm. The fibers can, for example, have a minimum thickness in the double-digit nanometer range, for example at least greater than 10 nm, 50 nm, or 75 nm.

[0027] In one embodiment of the method, it is proposed that the nonwoven fabric has a layer thickness of less than 5 mm, particularly less than 4 mm, 3 mm, 2 mm, 1.5 mm, or 1 mm. This smaller layer thickness can be achieved, for example, by a correspondingly smaller fiber diameter. The layer thickness can be the thickness of a single nonwoven fabric layer. The thickness can be orthogonal to the planar extension. A smaller layer thickness allows for simpler further processing because a smaller thickness can be easily provided. If a larger thickness is desired, multiple nonwoven fabric layers can be used.

[0028] In one embodiment of the method, the nonwoven fabric has a bending radius of less than 5 mm, particularly less than 4 mm, 3 mm, 2 mm, 1.5 mm, 1 mm, 0.5 mm, or 0.1 mm. The nonwoven fabric can be, for example, a handkerchief or thin napkin. No noticeable fiber breakage occurs. For example, when bending or folding without auxiliary tools, no debris or broken edges are visible in the nonwoven fabric. The nonwoven fabric can then be easily processed.

[0029] In one embodiment of the method, the nonwoven fabric has a weight per unit area of ​​less than 100 gsm, particularly less than 75 gsm, 50 gsm, or 30 gsm, at a layer thickness of 1 mm. Depending on the layer thickness, the weight per unit area can be proportionally smaller or larger. The weight per unit area can be expressed in grams per square meter. Although the nonwoven fabric has excellent barrier properties, it is very lightweight. Low weight is particularly desirable in aircraft manufacturing or functional textiles.

[0030] A third aspect of the invention relates to a preparation apparatus for preparing a nonwoven fabric having nanoporous fibers. The preparation apparatus can be configured to prepare the nonwoven fabric according to the second aspect and / or perform the method according to the first aspect. The corresponding features and advantages of the first or second aspect can also form the features and advantages of the third aspect, and vice versa.

[0031] The preparation equipment may include a production unit configured to produce fibrils from a spinning solution containing fiber raw material and a solvent. The preparation equipment may, for example, include an extruder and a spinning head with capillary tubes. The preparation equipment may also include a mixing unit for providing the spinning solution. This mixing unit may be part of the production unit. The extruder may also form part of the mixing unit.

[0032] The fabrication apparatus may include an acceleration device configured to accelerate the fibrils by means of an accelerating fluid flow. The acceleration device may, for example, include a fluid reservoir, a pump, and at least one nozzle. The nozzle may be arranged adjacent to the spinning head, and its opening may be oriented in the same direction as the capillary. The nozzle may also be integrated into the spinning head.

[0033] The preparation equipment may include a laying device configured to lay accelerated fibrils as a wet nonwoven fabric precursor with liquid. The laying device may, for example, include a conveyor belt on which the wet nonwoven fabric precursor is laid. The laying device may be configured to prevent the nonwoven fabric precursor from drying out.

[0034] The preparation apparatus may include a cleaning device. The cleaning device may be configured to remove residual solvent from the wet nonwoven fabric precursor. The preparation apparatus may also include a fluid exchange device. The fluid exchange device may be configured to replace the solvent and optionally other fluids in the wet nonwoven fabric precursor, particularly in the pores of the fibers of the nonwoven fabric precursor. This replacement may be performed with alcohol and / or without drying the wet nonwoven fabric precursor. The cleaning device and the fluid exchange device may be comprised of a single, shared unit.

[0035] The preparation equipment may include a drying device configured to dry the wet nonwoven fabric precursor while passing through a liquid phase in which the liquid exhibits capillary action. The drying device may include an autoclave. The drying device may also include a freezing device. Furthermore, the drying device may include a means for introducing CO2 into a closed atmosphere surrounding the wet nonwoven fabric precursor. The drying process produces the finished nonwoven fabric.

[0036] The preparation equipment may include a recycling device. This recycling device may, for example, capture solvents after fibril preparation, capture accelerating fluids after nonwoven fabric precursor laying, capture exchanged and / or washed-out liquids, capture introduced CO2, and / or capture liquids escaping from the wet nonwoven fabric precursor during drying, and provide them for reuse and / or processing. This allows for particularly low material consumption during preparation. Attached Figure Description

[0037] Figure 1 A method for preparing nonwoven fabrics with nanoporous fibers is demonstrated.

[0038] Figure 2 This schematically illustrates a method for performing based on Figure 1 The preparation equipment for the method.

[0039] Figure 3 The cross-section of a fiber with high macroporosity and low nanoporosity is shown.

[0040] Figure 4 The cross-section of the fiber with high nanoporosity is shown. Detailed Implementation

[0041] Figure 1 A method for preparing nonwoven fabrics with nanoporous fibers is demonstrated. This method can be achieved by... Figure 2 The preparation equipment shown is used to perform the procedure.

[0042] In step 10, a spinning solution containing a fibrous raw material (cellulose in this case) and a solvent (NMMO in this case) is provided. In step 12, multiple fibrils 20 are produced from the spinning solution. For this purpose, the preparation equipment includes an extruder 22. In the extruder, cellulose and NMMO are mixed into a viscous solution and extruded through the capillary of a spinneret 24. The fibrils 20 exit the spinneret 24 vertically downwards and are wet, because the solvent has been trapped in the pores of the fibrils 20.

[0043] The produced fibrils are accelerated in step 14, either upon exiting the spinneret 24 or subsequently, by means of an accelerating fluid flow. Water, air, or a water-air-aerosol mixture is used as the accelerating fluid. This acceleration stretches the fibrils, making their diameter significantly smaller than the capillary diameter or the diameter at which they exit the capillary from the spinneret 24. The preparation equipment correspondingly includes an accelerating device configured to accelerate the fibrils by means of the accelerating fluid flow. In the example shown, the accelerating device has nozzles integrated into or disposed on the spinneret 24 at both sides. Details of the accelerating device are described in... Figure 2 Not shown in the image.

[0044] In step 16, the accelerated or stretched fibrils 20 are laid as a wet nonwoven fabric precursor 26. For this purpose, the preparation equipment has a laying device, which is here formed as a conveyor belt 28 with a collection basin 30. The wet nonwoven fabric precursor solidifies on the conveyor belt 28 due to agglomeration, but the nonwoven fabric precursor and its fibers are not dried. Excess deposited mixture formed from the solvent or NMMO and the accelerating fluid is captured in the collection basin 30 and can thus be reused.

[0045] The wet nonwoven precursor 26 is then optionally wound up in the winding device 32 of the preparation apparatus. The nonwoven precursor 26 may optionally be cleaned before winding, for example, to reduce the amount of solvent in the nonwoven precursor. For cleaning, water or other non-solvents for cellulose may be used, for example. However, the wound wet nonwoven precursor 26 is cured while still wet because the corresponding pores of the fibers in the nonwoven precursor 26 still contain water and any possible NMMO residue.

[0046] The liquids trapped in the pores of the fibers of the nonwoven precursor 26 are then optionally exchanged via a fluid exchange device 34. A non-solvent is chosen here as the replacement liquid, which allows for supercritical drying of the wet fibers of the nonwoven precursor 26 without decomposition (e.g., due to high temperatures). In the detailed example, isopropanol and / or ethanol are used, which expel water and NMMO from the pores. In another embodiment, a fluid suitable for supercritical drying is used for cleaning and / or acceleration, thus eliminating the need for liquid exchange in the pores.

[0047] Subsequently, the wet nonwoven fabric precursor 26 is dried in step 18. This removes the liquid from the pores of the fibers. The drying is performed here as supercritical drying, but freeze-drying can also be used. In the case of supercritical drying, the liquid in the pores of the fibers enters a supercritical aggregated state, in which the liquid does not have capillary action. In the supercritical state, the fluid in the pores of the fibers has no surface tension. Therefore, as the amount of fluid in the pores decreases, the pore walls do not shrink, and the nanopores in the fibers can remain completely or largely unchanged. In the case of supercritical drying, and alternatively, in the case of freeze-drying, the capillary action of the liquid in the wet nonwoven fabric precursor 26 or the pores of the fibers is bypassed. After drying, the nonwoven fabric with nanoporous fibers is complete.

[0048] For drying, the preparation apparatus includes a drying unit 36. The drying unit includes an autoclave. CO2 is introduced into the autoclave to reduce the pressure and temperature to achieve a supercritical aggregation state. Thus, ethanol or isopropanol in the pores can be supercritically dried at a temperature of approximately 50°C and a pressure of approximately 92 bar. Any residual water and NMMO that may be present are also dried here.

[0049] Figure 3Fibers with a low proportion of nanopores are shown. The fibers are prepared without stretching under ambient drying and have PAN as the fiber material. The non-solvent in the wet fibers is water, where other non-solvents can also produce this result without supercritical drying. The nanopores are almost exclusively present in the edge regions 40 of the fibers. Conversely, in the central region 42, the fibers have significantly larger macropores. Nonwovens with such fibers have poor insulating properties. In the central region 42, the nanopores collapse because capillary action has already occurred during drying. Drying is typically carried out simply by heating or storing at room temperature. Figure 3 The cross-section of the fiber is shown here as circular, but may also be flattened due to the collapse of the nanopores in the central region 42.

[0050] Figure 4 The nonwoven fibers prepared using the previously detailed method are shown, and correspondingly supercritically dried without solvent (here, a combination of ethanol and isopropanol). The fibers have regularly distributed, finely spaced nanopores throughout their entire cross-section. More than 80% of the cross-section of the nanoporous fibers here consists of nanopores. Only small defects exist in the form of shrinkage pores 44, where the nanopores have collapsed.

[0051] List of reference numerals 10. Steps for providing spinning solution 12 Steps in the production of fibrils 14. Steps to accelerate the production of fibrils 16. Steps for laying accelerated fibrils 18. Steps for drying nonwoven fabric precursors 20 fibrils 22 Extruder 24 spinning heads 26 Nonwoven Fabric Precursors 28 conveyor belts 30 catch basin 32 winding device 34 fluid exchange devices 36 Drying Equipment 40 edge areas 42 Central Region 44 Shrinkage holes

Claims

1. A method for preparing a nonwoven fabric having nanoporous fibers, particularly aerosol fibers, wherein the method comprises at least the following steps: Provided (10) a spinning solution, said spinning solution having fiber raw material, particularly a polymer, and a solvent, (12) fibrils (20) are produced from the spinning solution, particularly by extruding the spinning solution from a capillary tube; The production of fibrils (20) is accelerated by means of accelerated fluid flow (14); Accelerated fibrils (20) are used as wet nonwoven fabric precursors (26) and fluid is laid (16). The nonwoven precursor (26) is dried (18) in a liquid state bypassing the wet nonwoven precursor (26), in which the liquid has capillary action, to produce the nonwoven fabric with nanoporous fibers.

2. The method according to claim 1, wherein the drying (18) comprises supercritical drying, and / or wherein the drying comprises freeze drying.

3. The method according to any one of the preceding claims, wherein CO2 is introduced to perform the drying (18).

4. The method according to any one of the preceding claims, wherein the solvent is washed out after the production of (12) fibrils (20).

5. The method according to any one of the preceding claims, wherein the fluid in the wet nonwoven precursor (26) is replaced prior to the drying (18), particularly wherein the replacement liquid is a non-solvent for the fiber raw material, and / or particularly wherein the solvent, the accelerating fluid and / or the cleaning liquid are replaced.

6. The method according to any one of the preceding claims, wherein the fiber raw material is cellulose, and / or the solvent is NMMO.

7. The method according to any one of the preceding claims, wherein the accelerating fluid comprises water, a non-solvent for the fiber raw material, and / or air, and / or wherein the accelerating fluid flow is formed as an aerosol.

8. A nonwoven fabric having nanoporous fibers, particularly aerosol fibers. The nonwoven fabric is prepared using the method according to any one of claims 1 to 7.

9. The nonwoven fabric according to claim 8, wherein the cross-section of the nanoporous fibers is formed by more than 30% nanopores, particularly more than 50%, 60%, 70%, 90%, and 95% nanopores. and / or The nanoporous fibers have a diameter of less than 100 µm, particularly less than 75 µm, 50 µm, 25 µm, 20 µm, 15 µm or less than 10 µm.

10. The nonwoven fabric according to claim 8 or 9, wherein the nonwoven fabric has a layer thickness of less than 5 mm, particularly less than 4 mm, 3 mm, 2 mm, 1.5 mm or 1 mm. and / or The nonwoven fabric has a bending radius of less than 5 mm, especially less than 4 mm, 3 mm, 2 mm, 1.5 mm, 1 mm, 0.5 mm or 0.1 mm. and / or The nonwoven fabric has a unit area weight of less than 100 gsm, particularly less than 75 gsm, 50 gsm, and 30 gsm, at a layer thickness of 1 mm.

11. An apparatus for preparing a nonwoven fabric having nanoporous fibers, the apparatus being particularly configured for preparing a nonwoven fabric according to any one of claims 8 to 10 and / or configured for performing the method according to any one of claims 1 to 7, wherein the apparatus comprises a production device (22) configured for producing (12) fibrils (20) from a spinning solution having fiber raw material and solvent, an acceleration device configured for accelerating (14) the fibrils by means of an acceleration fluid flow, a laying device (28, 30) configured for laying (16) the accelerated fibrils (20) as a wet nonwoven fabric precursor (26) with a liquid, and a drying device (36) configured for drying (18) the wet nonwoven fabric precursor (26) in the presence of a liquid phase bypassing the wet nonwoven fabric precursor (26), wherein the liquid has capillary action.

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