Fiber and process for spinning a fiber with improved thermal insulation properties

Abstract

The invention relates to a fiber with improved thermal insulation properties comprising a polymeric fiber base material and a microporous material in particle form, wherein the microporous material comprises an agglomerate of precipitated insoluble amorphous metal silicates, in particular precipitated silicon dioxide. The invention further includes a method for producing a fiber with improved thermal insulation properties.

Description

[0001] The invention relates to a method for producing a fiber with improved insulation properties, as well as a fiber and a product with fibers produced accordingly.

[0002] It is known from the prior art, as described, for example, in document CN1129811575A, to produce an aerogel fiber composite material by dispersing aerogel particles in a suitable polymer solvent to obtain an aerogel dispersion fluid. A polymer raw material is also dissolved in the suitable polymer solvent to obtain a polymer solution. Finally, the polymer solution is mixed with the aerogel dispersion fluid to obtain a composite dispersion fluid, and a spinning process is carried out with the composite dispersion fluid to obtain the aerogel composite fiber material.According to the specifications of CN1129811575A, the aerogel composite fiber material, which is intended to fully maintain the microscopic aerogel skeleton, should fully retain the thermal insulation performance of the aerogel, exhibit certain flame-retardant properties and a carbon dioxide adsorption effect, and accordingly be suitable for use in military, industrial and civilian applications such as high-performance fabrics, flame-retardant products and the like.

[0003] A well-known solution for providing a fiber with improved insulation properties lies in the use of aerogel particles, which, due to their highly dendritic structure—that is, a branching of particle chains with numerous spaces in the form of open pores—are highly porous solids in which up to 99.98% of the volume consists of pores. Because of this specific property, they are regularly used as thermal insulation or filter material.

[0004] However, a problem with the use of aerogels is that the manufacturing process and the materials used must be specifically designed to prevent the highly porous structure from being destroyed during further processing. Therefore, the selection of usable materials and processing methods is at least severely limited.

[0005] Aerogels are produced by drying a gel of a gel-like substance, usually silica (SiO2 n H2O), under extreme conditions.

[0006] In the Kistner aerogel manufacturing process, sodium silicate is mixed with water to create a solution, to which hydrochloric acid, acting as a precipitation reagent, is added. Over time Silica particles precipitate (precipitation reaction), which, due to Brownian molecular motion, distribute themselves uncoordinatedly in the solution and collide. Na2SiO3 + 2 HCl → 2 NaCl + H2SiO3 H2SiO3 → H2O + SiO2 or: Na2H2SiO4 + 2 HCl → 2 NaCl + H4 SiO4 H4SiO4 → 2 H2O + SiO2

[0007] Due to gradual adhesion, these particles aggregate over time, and within approximately one day a gel with a network-like structure results. The sodium chloride and excess hydrochloric acid must then be rinsed out of this gel with water (aquagel), followed by the addition of alcohol (alcogel).

[0008] This step is necessary because otherwise, the water would destroy the gel structure again later in the process. If the alcohol evaporates slowly, menisci form due to the surface forces acting upon it. These menisci "burrow" into the gel, creating a channel-like structure. This would lead to shrinkage of the gel and, consequently, a porous structure with only about 50% porosity, which is precisely what must be avoided. Drying is carried out as supercritical drying at elevated temperature and pressure beyond the critical point of alcohol, resulting in a supercritical fluid. This eliminates the phase boundary between gas and liquid; the surface forces that would otherwise lead to the formation of menisci no longer exist. The supercritical fluid can then be blown off, causing the product to dry and ultimately form an aerogel.

[0009] However, the Kistler manufacturing method has the disadvantage of being long and complex, especially with regard to the solvent exchange before the alcohol evaporates.

[0010] Another method is the sol-gel process, which is now used as the standard method. The starting material here is the toxic tetramethyl orthosilicate (TMOS), which, according to the reaction equation below, slowly hydrolyzes with a defined amount of water to orthosilicic acid and methanol after the addition of a catalyst. (H3CO)4 Si + 4 H2O → H4SiO4 + 4 CH3OH

[0011] Water is subsequently released from the silica, forming SiO₂ tetrahedra. These then cross-link to form a gel. The drying of the resulting aerogel is carried out again via supercritical drying (as described above), with the methanol exhibiting critical values ​​of 239.4 °C and 80.9 bar. The properties of the aerogel formed in this way, especially its structure and density, can be controlled by the choice of catalyst, pH value, or the ratio of the substances used, particularly the methanol.

[0012] Due to the specific manufacturing process of aerogels and aerogel particles (using supercritical drying), most aerogels react to water or moisture and can lose their typical structure and thus their specific properties when in contact with water or other liquids.

[0013] To address this problem, CN108754630A describes a specific process for wet spinning polymer fibers with aerogel particles: the polymer can be, for example, polyacrylonitrile (PAN), polyvinyl acetate (PVA), or cellulose. Any solvent used in the conventional solution spinning process for these polymers can be used for dissolving, and any process parameters used in the conventional solution spinning process for these polymers are suitable for wet spinning.

[0014] The solvents used for wet spinning of PAN can include aqueous sodium thiocyanate, aqueous nitric acid, dimethylformamide, dimethylacetamide, acetone, ethylene carbonate, and the concentration in the spinning liquid is 15-25%.

[0015] The solvent for wet spinning of PVA includes water, but is not limited to it, and the concentration in the spinning liquid is 14%-18%.

[0016] The solvent used for wet spinning of cellulose includes, among other things, N-methylmorpholine N-oxide (NMMO), dilute sodium hydroxide solution, copper hydroxide or alkaline copper salt solution with concentrated ammonia, with the concentration in the spinning liquid being 10% to 38%.

[0017] In a preferred embodiment of CN108754630A, the particle size of the aerogel is 10 nm–100 µm and the porosity is 40%–99.9%. Preferably, the weight percentage of the aerogel in the aerogel-modified polymer fiber is 0.1% to 3.0%, more preferably 2.2% to 3.0%. In this way, the density of the fiber is lower and the thermal insulation performance is improved.

[0018] According to another aspect of CN108754630A, an aerogel-modified polymer fiber is also provided, which is produced according to the above process. Accordingly, the aerogel-modified polymer fiber produced by this process has a lower density and better thermal insulation performance.

[0019] In practice, however, it has been shown that the production of polymer fibers with aerogel particles could not be achieved with the desired reproducibility. Furthermore, large-scale production is expensive and therefore does not represent an economically viable alternative to the media discussed above.

[0020] Hydrophilic aerogels produced using known methods are at risk of disintegrating when they come into contact with liquid, especially water or similar substances in the spinning solution, and are subsequently dried using conventional methods. Hydrophobic aerogels, on the other hand, are difficult to disperse and can clog the nozzles. Furthermore, experiments have shown that these aerogels can also lose their specific properties, particularly their thermal insulating properties, during spinning due to the process conditions.

[0021] Therefore, there remains a great need for a polymer fiber with improved thermal, especially thermally insulating, properties, as well as for a method to manufacture it.

[0022] The problem is solved by a method having the features of claim 1 and a fiber having the features of claim 1. Furthermore, the invention also relates to a product having the features of claim 9.

[0023] Accordingly, a fiber with improved thermal insulation properties is proposed, comprising a polymeric fiber base material and a microporous material in particle form. According to the invention, the microporous material comprises an agglomerate of precipitated insoluble amorphous metal silicates, in particular precipitated silicon dioxide.

[0024] In addition to the proven improved thermal insulation properties, the fiber according to the invention can also have other properties, for example flame-retardant properties.

[0025] In the prior art sol-gel technique described above, which is commonly used to produce homogeneous gels and powders with a large surface area, e.g., aerogels, a gel is an intermediate product of the manufacturing process. During gelation, particles are linked together in branched chains that fill the entire volume of the solution, so that there is no increase in silica concentration in any macroscopic region of the medium; that is, the silica is (on a macroscopic level) uniformly distributed throughout the medium. This makes the entire medium viscous, and it subsequently solidifies, forming a cohesive particle network that retains the liquid by capillary action.

[0026] The microporous material used in the present invention is produced by a precipitation reaction in which an alkali silicate solution is brought into contact with a salt solution containing divalent or polyvalent metal cations. When a soluble silicate is mixed with salt solutions containing metals other than those of the alkali group, insoluble amorphous metal silicates precipitate. This process can be described as a coagulation process in which the particles assemble into relatively densely packed aggregates in which the silica is more concentrated than in the original solution, so that the coagulate settles as a relatively dense precipitate.

[0027] The resulting precipitated coagulum is then rinsed in water until the remaining reaction products and excess components are removed. This slurry is then dehydrated by vacuum or centrifugal filtration until a fairly stiff paste with, for example, approximately 15% dry matter is obtained.

[0028] The microporous material can be impregnated if required, as described in more detail below. Such impregnation can be achieved by a final rinse of the coagulate with a solution containing the necessary impregnating chemicals in a suitable concentration. If impregnation is not carried out in conjunction with the final rinse, the required chemicals can be added after the final rinse and dehydration step and mixed with the paste.

[0029] In embodiments where the microporous material is preferably in pellet form, such pellets are produced using a standard paste extrusion system. If spherical or rounded particles are required, the pellets can subsequently be spherized / marumerized in a separate step. Finally, the resulting material must be dried either in a fluidized bed, a rotary dryer, or another conventional and suitable drying system, with the shaping and drying of the impregnated coagulum being carried out to a dry matter content of > 75%, preferably > 90%, even more preferably > 95%, and most preferably > 97%.

[0030] In summary, the microporous material used in the solution according to the invention, instead of aerogel particles, is formed by mixing alkali silicate with a salt solution as a precipitate, and the precipitate is processed in various ways to obtain the desired end product. An agglomerate of precipitated silica as a microporous material has a highly porous surface.

[0031] In contrast, precipitated and pyrogenic silica are also known in the prior art. While these substances also possess good insulating properties as pure substances and are used for this purpose, they cannot be used for the desired fiber according to the invention or in the process according to the invention because they do not have a porous structure.

[0032] A significant advantage of the microporous material used for the desired fiber according to the invention or in the method according to the invention instead of aerogel particles is that it does not disintegrate or dissolve when exposed to both saturated water vapor and liquid water.

[0033] Alkali silicates suitable for the production of the material used in the process according to the present invention are available in various types, depending on the alkali metal involved and the molar ratio of the main components of the alkali silicate, namely SiO2 and, in the case of sodium silicate, Na2. Commercially available alkali silicates are offered in molar ratios between 3.9 and 1.6. The most common alkali silicate is based on sodium, Na, but also on potassium, K, and to some extent on lithium, Li.

[0034] To obtain the coagulation reaction, a dilute alkali silicate solution, typically at a concentration of 1.5 M based on SiO2, mixed with a concentrated or even saturated solution of Mg and / or Ca salts, can be used. The most readily available salts for this purpose are MgCb and CaCb. However, any other readily soluble salt, such as nitrates and acetates, can also be used within the scope of the invention. Although Mg and Ca are the most accessible cations, other divalent and polyvalent ions can also be used, such as Cu, Zn, Mn, Cd, Pb, Ni, Fe, Cr, Ag, Al, Ti, V, Co, Mo, Sn, Sb, Sr, Ba, and W.

[0035] When a dilute solution of sodium silicate is mixed with Mg and / or Ca chloride under vigorous stirring, the mixture coagulates immediately. The reaction is assumed to proceed according to the following formula: Na2O · nSiO2 (1) + ½Mg 2+ + ½Ca 2+→ (Mg, Ca)O · nSiO2 (s) + Na + (1)

[0036] The silica particles enriched with Mg and Ca coagulate as loose aggregates in the aqueous medium, are collected on a filter, washed, shaped, and dried as previously described. In this state, the resulting precipitated silicon dioxide can be used as an absorbent for certain types of pollutants due to its affinity for these gas molecules. Some examples of possible reaction formulas are shown below for the active sites of the medium: (Mg, Ca)O (s) + SO2 (g) + ½O2 (g) → (Mg, Ca)SO4 (s) (2) (Mg, Ca)O (s) + CO2 (g)→ (Mg, Ca)CO3 (s) (3) (Mg, Ca)O (s) + H2S (g)→ (Mg, Ca)S (s) + H2O (g) (4)

[0037] In this way, a microporous material is provided that comprises agglomerates of precipitated silicon dioxide (silica) and corresponds to the following formula: MeOx · mSiO2

[0038] Me denotes any metal or any mixture of metals including Ca, Mg, Cu, Zn, Mn, Cd, Pb, Ni, Fe, Cr, Ag, Al, Ti, V, Co, Mo, Sn, Sb, Sr, Ba and W, wherein x denotes the molar ratio of oxygen to metallic components, and wherein m denotes the molar ratio of Si / Me, and wherein the agglomerates are composed of porous particles, wherein the agglomerates have a size in the range of 0.5 - 500 µm, preferably 5 - 200 µm, particularly preferably 10 - 100 µm.

[0039] The microporous material used in the production of the fiber according to the invention can have a molar ratio m = Si / Me in the range of 1 to 4, preferably 2 to 3.5, particularly preferably 2.5 to 3.

[0040] Furthermore, in a further development of the invention, the fiber can comprise 0.1 to 70 wt%, for example 10 to 40 wt%, of the microporous material in particle form and 30 to 99.9 wt%, for example 60 to 90 wt%, of the fiber base material. Furthermore, the particles of the microporous material can have, in particular, a minimum diameter of 0.01 to 200 µm, more specifically a minimum diameter of 0.1 to 15 µm, for example 0.5 to 10 µm, advantageously 0.5 to 5 µm.

[0041] The particles do not necessarily have to be spherically shaped, but can have a wide variety of forms. Accordingly, the minimum diameter, for example, denotes the smallest extent through a cross-section of the particle such that the particle can pass through a sieve with a sieve opening diameter corresponding to the minimum diameter in at least one orientation (sieve analysis). As is known, depending on the sample material and the specific question being addressed, the analysis of the particle size distribution to determine a minimum diameter can also employ methods other than sieve analysis, such as laser diffraction, dynamic image analysis, or dynamic light scattering.

[0042] Furthermore, the microporous material can be a so-called polydisperse system, meaning that the particles are not all the same size, but vary in size. A particle size distribution indicates the percentage of particles of a specific size (or within a specific size interval). These intervals are also called size classes or fractions. They can be expressed in percentile notation, where percentiles are statistical values ​​that can be directly derived from the cumulative particle size distribution and indicate the size x below which a certain quantity, for example, 10%, 50%, or 90% of all particles are found. Percentiles thus answer questions such as:The question "Below what size are the 90% (or other freely selectable percentages) of the smallest particles?" Percentiles are denoted by the letter d, followed by the % value, for example d90= 10 µm thus means that 90% of all considered particles are smaller than 10 µm.

[0043] Furthermore, according to a further development of the invention, the particles of the microporous material can be homogeneously distributed in the polymeric fiber base material. A homogeneous distribution here refers to a uniform or nearly uniform distribution such that the properties of the fiber do not differ significantly from one another along the length of the fiber.

[0044] Alternatively or additionally, the microporous material can be loaded with additional active ingredients to modify the fiber's properties. These active ingredients can be introduced into the fiber, for example, through an impregnation process. The microporous material can be impregnated with an impregnating agent content of 0–20%, preferably 5–20%, and particularly preferably 10–20%.

[0045] To increase the thermal insulation efficiency or other properties of the fiber produced using this process, additional substances can be incorporated into the microporous material, such as fragrances, pharmaceutical active substances, antibacterial substances, or similar materials. These substances can enhance wearing comfort, provide specific effectiveness (e.g., in skin contact), act as catalysts and pH buffers, or act as scavengers for certain gas components.

[0046] The polymeric fiber base material includes, for example, viscose, lyocell, acrylic, aramid, Pyrotex, and / or polytetrafluoroethylene. Table 1 lists some examples of polymeric fiber base materials below: Table 1: Examples of a polymeric fiber base material Polymer fiber base material based on naturally occurring polymers Polymer fiber base material based on synthetically produced polymers viscose Acrylic Lyocell (CLY) Acrylonitrile Modal Polyacrylonitrile (PAN) Rayon Polymethyl methacrylate (PMMA) Aramid (Aromatic Polyamide) Polytetrafluoroethylene (PTFE) Polybenzimidazole (PBI) Melamine resin (melamine-formaldehyde condensation resin: MF) Phenoplast (Phenol-Formaldehyde: PF) Pyrotex

[0047] Depending on the choice of polymeric fiber base material, which may also contain pyrone and / or silicon dioxide compounds, both the thermal insulation properties and other properties of the fiber, such as flame retardant properties, can be further improved.

[0048] Many fibers are formed from naturally occurring polymers. Various processing steps may be required to convert these natural polymers into fibers, and the resulting fibers can also be referred to as regenerated fibers.

[0049] A significant class of regenerated fibers comprises fibers formed from cellulose. Cellulose is a major component of plant material such as leaves, wood, bark, and cotton. A solution spinning process is conventionally used to form fibers from cellulose. A wet solution spinning process can be used to form rayon and lyocell fibers, while a dry solution spinning process is used to form acetate fibers. Rayon and lyocell fibers often contain cellulose that has the same chemical structure as naturally occurring cellulose. However, the cellulose in these fibers often has a shorter molecular chain length relative to naturally occurring cellulose. Acetate fibers often contain a chemically modified form of cellulose in which various hydroxyl groups are replaced by acetyl groups.

[0050] There are numerous applications for fibers made from cellulose. For example, these fibers can be used to create knitted, woven, or nonwoven fabrics that are incorporated into products such as clothing or footwear. Fabrics made from these fibers are generally classified as comfort fabrics due to their ability to absorb moisture and their low heat retention. These properties make the fabric desirable in warm weather, as they allow the wearer to feel cooler. However, these same properties can make the fabric undesirable in cold weather. In cold and damp weather, the fabric may be undesirable due to the rapid loss of body heat when wet. For this reason, the addition of the microporous material according to the invention, with its thermally insulating properties, is particularly advantageous.

[0051] In addition to so-called regenerated fibers, fibers made from synthetic polymers are also conceivable (see Table 1), such as polyacrylic (PAN) fibers (also known as acrylic fibers), aramid fibers, and polytetrafluoroethylene (PTFE).

[0052] A characteristic of the fiber according to the invention and the associated manufacturing process is that, as already indicated above, the fiber can furthermore be produced by means of a wet spinning process, a dry spinning process, or a matrix spinning process of a starting material such as cellulose-based, protein-containing, natural, regenerated, and / or synthetic materials. However, all fibers produced by melt spinning processes are excluded from the invention.

[0053] Because the microporous material according to the present invention has a thermo-insulating effect, a textile surface structure or textile spatial structure made from the fiber according to the invention, such as knitted fabric, woven fabric or non-woven fabric (fleece, wadding, felt and the like), can be perceived as comfortable even at cooler temperatures.

[0054] Furthermore, the present invention relates to a method for producing a fiber with improved thermal insulation properties, comprising at least the following steps: providing a spinning solution with a starting material and a solvent, providing a microporous material, mixing the microporous material with the spinning solution to form a spinning mass, and spinning the spinning mass. According to the invention, the microporous material comprises an agglomerate of precipitated insoluble amorphous metal silicates, in particular precipitated silicon dioxide.

[0055] The spinning solution may also include a solvent, depending on the starting material of the fiber stock. The composition of the solvent used can vary depending on the starting material and the desired application of the resulting fibers. For example, when using a cellulose solution as the spinning solution, granules of cellulose xanthate can be dissolved in a base solution (such as sodium hydroxide or 2.8% sodium hydroxide solution) to form a viscous solution. Alternatively, precipitated flakes, as described above, can be dissolved in acetone to form a viscous solution. Various other types of solvents can be used, such as a solution of amine oxide or cuprammonium hydroxide. In some cases, the resulting viscous solution can be filtered to remove undissolved cellulose stock.

[0056] Prior to selecting a suitable solvent for dissolving the starting material and spinning a polymeric fiber base material, the preparation of a spinning solution involves selecting a starting material from a group of materials, including: cellulose-based, protein-containing, natural, regenerated and / or synthetic materials, for spinning, for example, viscose, lyocell, acrylic, aramid, Pyrotex and / or polytetrafluoroethylene or other fibers according to Table 1.

[0057] Alternatively or additionally, the step of providing a microporous material includes providing the microporous material in particle form, wherein the particles of the microporous material have a minimum diameter of 0.01 to 200 µm, in particular a minimum diameter of 0.1 to 15 µm, for example 0.5 to 10 µm, advantageously 0.5 to 5 µm.

[0058] Furthermore, the step of providing a microporous material includes the preparation of a preparation solution comprising at least the microporous material in particle form, as well as a solvent and optionally an aqueous medium, and / or a catalyst.

[0059] Such a preparation solution is commonly referred to as a "slurry." Considering the small particle size of the microporous material, its advantage lies in the simplified introduction of the microporous material into the spinning solution. Furthermore, the preparation solution can be mixed more easily and effectively with the spinning solution, resulting in a homogeneous distribution of the microporous material within the fiber substrate. However, a potential disadvantage is that a slurry must be processed relatively quickly, whereas, for example, microporous material in powder or particle form can be stored for a very long time.

[0060] The ability to provide the microporous material in a slurry or a so-called preparation solution is a particular advantage of the invention, since the use of a microporous material comprising an agglomerate of precipitated insoluble amorphous metal silicates makes it possible to mix it with an aqueous medium or solvent without the microporous material losing its advantageous thermally insulating properties.

[0061] Alternatively or additionally, it may be provided that the spinning of the spinning mass includes spinning the fiber using a wet spinning process, a dry spinning process or a matrix spinning process.

[0062] Alternatively or additionally, the microporous material can be produced in particle form by at least the following steps: preparing a solution of at least two metal salts (Me), wherein the metal ions are divalent or polyvalent; preparing a solution of alkali metal (M) silicate with a silicate / alkali metal oxide molar ratio of 1 to 4, preferably 2 to 3.7, more preferably 3 to 3.7, most preferably 3 to 3.5; mixing the solutions while stirring the mixture, whereby a coagulum is formed; rinsing the coagulum in water; collecting the coagulum;Processing the coagulum to obtain a material with a dry matter content of >15 or about 15% dry mass, and optionally impregnating the material with an impregnating agent by adding and mixing the impregnating agent and the coagulate before drying, the impregnating agent being selected from the following: KMnO4, C2H2O4, C6H8O7, Na2S2O3, NaClO, KOH, NaOH, KI, Nal, K2CO3, Na2CO3, NaHCO3, KHCO3. Following the processing of the coagulum or the optional impregnation of the material, the steps of forming and drying the impregnated coagulum to a dry matter content of > 75%, for example > 90%, preferably > 95%, particularly preferably > 97%, wherein the drying of the coagulate takes place at a temperature of 50°–250°C, for example 70°–175°C, preferably 70°–130°C, particularly preferably 90°–115°C, in one case 105°C.

[0063] Finally, the invention also relates to a fiber product comprising a fiber with the aforementioned features, wherein the fiber product may comprise a yarn, a textile surface or spatial structure (comprising knitted fabric, woven fabric or non-woven fabric) or an insulating material, wherein the fiber product comprises a microporous material in particle form comprising an agglomerate of precipitated insoluble amorphous metal silicates, in particular precipitated silicon dioxide.

[0064] It should also be noted that terms such as "comprehensive," "exhibit," or "with" do not exclude other characteristics or steps. Furthermore, terms like "a" or "that," which indicate a singular set of steps or characteristics, do not exclude a plurality of characteristics or steps, and vice versa.

[0065] Further features and advantages of the invention will become apparent from the following description of an exemplary embodiment of the invention and from the dependent claims.

[0066] The invention is described in more detail below with reference to the accompanying figures. The figures show several features of the invention in combination with one another. Of course, a person skilled in the art can also consider these features separately and, if necessary, combine them into further meaningful sub-combinations without having to make an inventive step.

[0067] They show schematically: Fig. 1 an example of a spinning process for fibers according to the invention; and Fig. 2 a method according to the invention as a flowchart.

[0068] The following example is intended as a guide for an ordinary practitioner in this field. The example should not be considered as limiting the invention, as it merely provides a specific procedure for understanding and practicing one embodiment of the invention.

[0069] The terms used in the figures are better known and more common in English in the professional world, which is why they are also used in this German-language application for better understanding.

[0070] In the exemplary process for producing a viscose fiber according to Fig. 1. In a first step, S100 (see below) will be used. Fig.2) A viscose spinning solution is prepared. For this purpose, a starting material of cellulose 10 (wood pulp) is soaked with the addition of sodium hydroxide Na4OH to improve the breakdown of the cellulose material, and alkali cellulose 12 is formed (sub-step S101). In a further sub-step S102, a carbon disulfide, for example carbon disulfite SC2, is added and forms cellulose xanthate 14 (xanthate). In sub-step S103, the cellulose xanthate is dissolved in an added aqueous sodium hydroxide solution NaOH and forms the desired viscose spinning solution 16.

[0071] In a second process step S200, the microporous material 20 is added to the viscose spinning solution. For this purpose, a microporous material can first be produced (sub-step S201) and optionally further processed into a preparation solution 22 (slurry) (sub-step S202).

[0072] Whether as a preparatory solution or as powder or particle-shaped material, the microporous material is then added to the spinning solution (partial step S203) and mixed with the spinning solution (S300) in order to achieve the most homogeneous distribution possible of the microporous material in the fiber base material.

[0073] The actual fiber is formed when the solution described above, containing the microporous material, is forced or extruded through dies into an acidic precipitation bath (S400). The size of the dies determines the thickness of the fiber and varies, for example, between 25 and 250 µm. The precipitation bath contains sulfuric acid (H₂SO₄) and, if necessary, other additives such as sodium sulfate and small amounts of zinc sulfate. Through the chemical reactions in the precipitation bath, the dissolved cellulose regenerates and coagulates into the desired fiber.

[0074] In a further step (S500), the fiber is removed from the coagulation bath and prepared for further processing. While still soft, it is stretched at least once (sub-step S501), thus permanently elongating it. This makes the fibers more resistant to abrasion and tensile strength. Optionally, the fiber can be washed as shown (sub-step S502) and stretched a second time (sub-step S503) before being cut (sub-step S504). The fiber is also chemically washed to remove any chemical residues (sub-step S505), dried (sub-step S506), and, if necessary, softened by applying soap-like substances (sub-step S507) (opening). Finally, the fibers produced in this way can be wound onto bales or similar containers and transported for further processing into knitted fabrics, woven fabrics, or nonwovens (sub-step S508).

[0075] The described process is only an example. Accordingly, a cellulose material can initially be provided in any number of different forms, such as cellulose sheets, wood pulp, cotton linters, and other sources of essentially purified cellulose. Typically, a cellulose material is dissolved in a solvent before passing through the spinneret openings. In some cases, the cellulose material can be processed (for example, chemically treated) before dissolving in the solvent. For instance, the cellulose material can be immersed in a base solution (for example, sodium hydroxide), pressed through rollers, and then crushed to form granules. The granules can then be treated with carbon disulfide to form cellulose xanthate.As another example, the cellulose material can be mixed with a solution of glacial acetic acid, acetic anhydride and a catalyst and then aged to form a cellulose acetate which can precipitate from the solution in the form of flakes.

[0076] The composition of a solvent used to dissolve cellulose material can vary depending on the desired application of the resulting cellulose fibers. For example, granules of cellulose xanthate, as described above, can be dissolved in a base solution (such as sodium hydroxide or 2.8% sodium hydroxide solution) to form a viscous solution. Alternatively, precipitated flakes, as described above, can be dissolved in acetone to form a viscous solution. Various other types of solvents can be used, such as a solution of amine oxide or cuprammonium hydroxide. In some cases, the resulting viscous solution can be filtered to remove undissolved cellulose material.

[0077] During the formation of cellulose fibers, a microporous material can be mixed with a cellulose base material to create a blend that improves the thermal insulation properties of the cellulose fiber. As a result of this mixing, the microporous material can be distributed within, and at least partially enclosed by, the cellulose base material, particularly homogeneously. The microporous material can be mixed with the cellulose base material at various stages of fiber formation. Typically, the microporous material is mixed with the cellulose base material before it passes through the spinneret openings. In particular, the microporous material can be mixed with the cellulose base material before or after it has been dissolved in a solvent. In some cases, the microporous material can be mixed with the viscous solution immediately before it passes through the spinneret openings.

[0078] According to some embodiments of the invention, cellulose fibers can be formed using the microporous material in powder or particle (pellet) form. For example, the cellulose fibers can be formed using powders or pellets made from the microporous material. During the formation of the cellulose fibers, the powder or pellets can be mixed with a cellulose material at various stages of fiber formation to create a mixture. Typically, the powder or pellets are mixed with the cellulose material before passing through the openings of the spinneret.

[0079] According to some embodiments of the invention, the microporous material can also be provided in a preparatory dispersion, a slurry. This slurry can, in addition to the microporous material, also include, for example, a dispersing agent (e.g., phosphate ester, hexanol), a solvent (e.g., DMF, ionic liquids, NMMO), and optionally an aqueous medium and / or a catalyst, which are mixed to form a preparatory solution before being introduced into the spinning solution.

[0080] For certain applications, the fibers can also be formed as multi-component fibers. For example, a first cellulose material can be mixed with a microporous material to form a blend. This blend and a second cellulose material can be combined and dispensed through the spinneret openings in a specific arrangement to form elongated cellulose fiber elements. The blend can be dispensed through the openings to form so-called core or island elements, while the second cellulose material can be dispensed through the openings to form sheath elements that at least partially surround the core or island elements. Before passing through the openings, the first and second cellulose materials can be dissolved in the same or different solvents.Portions of the microporous material not enclosed by the first cellulose material can be enclosed by the second cellulose material after exiting the spinneret to reduce or prevent loss of the microporous material from the resulting cellulose fibers. It is considered that the first cellulose material need not be used for certain applications. Naturally, such an arrangement can also be applied to other fiber feedstocks.

[0081] After exiting the spinneret, one or more cellulose materials typically solidify to form cellulose fibers. In a wet solution spinning process, the spinneret can be immersed in a coagulation or spinning bath (for example, a chemical bath), allowing one or more cellulose materials to precipitate and form solid cellulose fibers upon exiting the spinneret. The composition of a spinning bath can vary depending on the desired application of the resulting cellulose fibers. For example, the spinning bath can be water, an acidic solution (for example, a weakly acidic solution with sulfuric acid), or a solution of amine oxide. In a dry solution spinning process, one or more cellulose materials can exit the spinneret into warm air and solidify upon exiting due to a solvent (for example, acetone).

[0082] After exiting the spinneret, cellulose fibers can be drawn or stretched using a gusset or suction device. For example, exiting spinneret cellulose fibers can form a vertically oriented curtain of downward-moving fibers, which are drawn between gusset rollers at variable speed before being wound onto a bobbin or cut into staple fibers. Exiting spinneret cellulose fibers can also form a horizontally oriented curtain within a spinning bath and can be drawn between gusset rollers at variable speed. As another example, exiting spinneret cellulose fibers can be at least partially compressed before entering a long, slotted air suction device positioned below the spinneret.The suction device can introduce a rapid, downward-moving stream of air generated by compressed air from one or more air intake nozzles. The airflow can exert a pulling force on the cellulose fibers, causing them to be drawn between the spinneret and the air stream, thus thinning the cellulose fibers. During this stage of fiber formation, one or more of the cellulose materials forming the cellulose fibers may solidify. It is considered that the drawing or stretching of cellulose fibers can occur before or after drying.

[0083] Once the cellulose fibers are formed, they can be further processed for various other fiber applications. In particular, cellulose fibers can be used or integrated into different products in accordance with different embodiments of the invention to provide thermal insulation properties in these products.Cellulose fibers can be used, for example, in textiles (e.g., woven fabrics), clothing (e.g., outdoor clothing, drysuits, and protective suits), footwear (e.g., socks, boots, and shoe insoles), medical products (e.g., thermal blankets, therapy pads, incontinence pads, and hot / cold packs), containers and packaging (e.g., beverage / food containers, food warmers, seat cushions, and printed circuit board laminates), buildings (e.g., insulation in walls or ceilings, wallpaper, curtain linings, pipe coverings, carpets, and tiles), appliances (e.g., insulation in home appliances), and other products (e.g., automotive lining material, fixtures, sleeping bags, and upholstery).

[0084] In some cases, cellulose fibers can undergo weaving, nonwoven, knitting, or braiding processes to form various types of interlaced, braided, twisted, or nonwoven fabrics. For example, cellulose fibers can be wound onto a spool or spun into yarn and then used in various conventional knitting or weaving processes. Alternatively, cellulose fibers can be randomly laid onto a forming surface (such as a moving conveyor belt like a Fourdrinier screen) to form a continuous web of cellulose fibers. In some cases, cellulose fibers can be cut into short staple fibers before the web is formed.A potential advantage of using staple fibers is that a nonwoven web with higher isotropy can be formed, since the staple fibers can be arranged more randomly in the web than longer or uncut fibers (for example, continuous fibers). The web can then be bound using any binding process (for example, a spunbond process) to form a stable nonwoven fabric for use in the manufacture of various textiles. An example of a binding process involves lifting the web from a moving conveyor belt and passing the web through two heated calender rolls. One or both rolls may have a relief to cause the web to be bound at numerous points. Air-combed or spun-laid webs can be formed from cellulose fibers in accordance with some embodiments of the invention.

[0085] It is considered that fabrics can be formed from cellulose fibers comprising two or more different microporous materials. According to some embodiments of the invention, this combination of microporous materials can exhibit other different properties in addition to its thermally insulating properties, for example, by impregnating one microporous material and not the other.

[0086] Additionally, fabrics can be made from two or more types of fibers, for example, two or more types of cellulose fibers that differ in some way (for example, with different arrangements, or that include other microporous materials and / or other materials, such as temperature-regulating materials, phase-change materials, or the like). This combination of cellulose fibers can provide the fabric with improved thermal insulation properties as well as improved thermoregulation properties in different environments (for example, cold and warm environments).

[0087] It is also possible to further process the fibers produced in the described manner (or other fibers which comprise a microporous material in accordance with the invention) in order to change their properties.

[0088] It is conceivable that these could be carbonized to carbon in a subsequent pyrolysis process to produce carbon fibers. By stretching (applying tensile stress) during this heat treatment step, the orientation of the atomic structure in the fibers can be altered in such a way that higher strengths and stiffnesses of the fibers are achieved during carbonization.

[0089] The inventive method is described above by way of example using a manufacturing process for producing cellulose fibers with microporous material. Of course, a method for producing alternative fibers with an alternative polymeric fiber base material and a microporous material, as well as fibers produced accordingly, also fall within the scope of protection of the invention.

[0090] In a first series of experiments, two sets of cellulose fibers were formed. One set of cellulose fibers was used as a control set (without the addition of microporous material).

[0091] Both sets of cellulose fibers underwent an identical viscose process according to the specifications and process parameters of Kelheim Fibres GmbH.

[0092] For a second batch of cellulose fibers, a microporous material in the form of an agglomerate of precipitated silicon dioxide (in powder form with an average minimum particle diameter of 10 µm) was added to the identical viscous spinning solution used for the first batch of cellulose fibers during the ongoing process (as with the first batch) via a metering pump at a ratio of 20%. The spinning process was identical to that of the first batch; no other machine parameters or formulations were changed when switching from the first to the second batch of cellulose fibers.

[0093] The two sets of cellulose fibers were filtered and dried identically, and measurements of fiber density and the distribution of microporous material within the fibers were performed using light microscopy. Tables 2 to 4 below present the results of these measurements, along with further analyses and measurements for the two sets of cellulose fibers.

[0094] A comparison of the fibers (see Table 2 below) revealed that, with otherwise identical manufacturing parameters, the fibers from the first batch exhibited a lower fiber density, which consequently resulted in lower thermal conductivity and improved insulation. Furthermore, even after subsequent treatment (pyrolysis), only a slight decrease in the microporous material detected in the fiber was measurable, meaning that the thermally insulating properties of the fiber were not significantly impaired. Table 2: Comparison of fiber sets 1 and 2 Fiber set 1 Fiber set 2 Fiber fineness [dtex] determined according to DIN EN ISO 1973) 7,3 7,1 Fiber density [g / cm³] 3 Determined using a light microscope 1,5 1,1 Percentage of microporous material in fiber [%] 0 20 Determined proportion of microporous material in fiber after pyrolysis [%] determined according to DIN 51903 0 15,4 D90 value of the particle size distribution of microporous material [µm] 0 10 Fiber strength [cN / tex] determined according to DIN EN ISO 5079 19,4 9,6 Strain [%] determined according to DIN EN ISO 5079 25 20 LOI (ASTM D2863 Procedure B) 19,5 24,7

[0095] Since the insulation properties of the fibers themselves cannot be determined, non-woven fabrics were produced from the fibers.

[0096] For the first product (thermally bonded cotton wool), 900g of fibers were mixed with 100g of PLA melt fibers. Bonding took place at 140°C. The cotton wool had a weight of 250g / m². 2 and a thickness of 2.5 cm. The results are shown in Table 3 below: Table 3: Comparison of the cotton wool from fiber sets 1 and 2 Cotton wool made from fiber set 1 Cotton wool made from fiber set 2 Thickness [mm] 25 25 RCT [m 2 *K / W] determined according to DIN EN ISO11092 0,404 0,543 TOG (BS 4745: 20005) 2,85 3,41

[0097] Furthermore, needle felt was produced from the fibers. The felt had a weight of 150g / m². 2 The thickness of the two felts differs slightly, as can be seen in Table 4 below: Table 4: Comparison of felts from fiber sets 1 and 2 Felt made from fiber set 1 Felt made from fiber set 2 Thickness [mm] 3 2 RCT [m 2 *K / W] (DATE 11092) 0,143 0,151

[0098] In summary, the fibers according to the invention, which, in addition to a polymeric fiber base material, comprise a microporous material in particle form consisting of an agglomerate of precipitated insoluble amorphous metal silicates, in particular precipitated silicon dioxide, have a lower density and thus a larger cross-section for the same weight. Consequently, this results in higher thermal resistance and therefore better insulation as well as improved sound absorption. The increased LOI value of the fiber according to the invention (sentence 2) also indicates improved flame retardancy.

[0099] Although the invention has been described with reference to its specific embodiments, those skilled in the art should understand that various modifications can be made without altering the scope of protection of the invention as defined by the accompanying claims. Furthermore, adjustments or modifications can be made to adapt a particular situation, material, composition of elements, method, process step or steps to the problem and scope of the invention. All such modifications shall remain within the scope of the claims accompanying this document.In particular, it will be understood that although the methods disclosed in this document are described with reference to specific operations carried out in a particular sequence, these operations can be combined, subdivided, or rearranged to form an equivalent method without departing from the teachings of the invention. Accordingly, the sequence and grouping of the described steps and operations are not limitations of the invention, unless specifically stated in this document. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] CN 1129811575A

[0002] CN 108754630A [0013, 0017, 0018]

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