Aramid solution manufacturing method

Abstract

The present invention provides a method for producing an aramid solution by combining ingredients including a base, a proton donor, an aramid, and an aprotic solvent, comprising: Dissolving a base in a proton donor to obtain a base solution; combining an aprotic solvent with an aramid to obtain an aramid-solvent mixture; combining the base solution with the aramid-solvent mixture to obtain a suspension; The suspension is mixed to obtain an aramid solution. Also claimed are methods for producing continuous aramid fibers, continuous aramid fibers, methods for producing aramid nanofibers, and materials comprising aramid nanofibers.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a solution of aramid, a method for producing continuous aramid fibers or aramid nanofibers from the solution, and materials comprising continuous aramid fibers and aramid nanofibers.

[0002] Methods for making solutions of aramids are known, particularly methods using strong bases and aprotic solvents, such as proton donor assisted dissolution methods.

[0003] In this method, aramid, especially para-aramid, is contacted with an alkaline aprotic solvent (e.g., KOH / DMSO system). In this case, the hydroxide groups react with the methyl groups of DMSO, thereby forming dimsyl ions. The dimsyl ions can break the hydrogen bonds of the aramid chains. Hydrogen bonds between carbonyl groups from different polymer chains and secondary amines (derived from amide bonds) usually ensure the crystalline structure of aramid fibers. The dimsyl ions generate negative charges, which break the hydrogen bonds. The negative charges cause the polymer chains to repel each other, thus causing the aramid, e.g., aramid fibers, to collapse.

[0004] Chinese Patent No. 112878036 discloses a method for preparing aramid nanofibers based on para-aramid deprotonation, which includes stirring and pre-treating a mixed system of aramid fibers, an organic solvent and an alkali to obtain an aramid fiber dispersion, and adding a proton donor and / or an ionic reaction aid to the aramid fiber dispersion to adjust and control the deprotonation degree to obtain an aramid nanofiber dispersion.

[0005] WO 2021 / 070042 relates to a method for producing fibers containing meta-aramid. A spin dope containing meta-aramid polymer and sulfuric acid is prepared and passed through a spinneret into a coagulation bath, with the spin dope having a meta-aramid concentration of at least 10% by weight. The resulting meta-aramid fibers have a tensile strength of at least 300 mN / tex and can have a high elongation at break, for example, 49%. This application does not relate to aramid nanofibers or para-aramid fibers.

[0006] U.S. Patent No. 3,817,941 relates to fully aromatic carbocyclic polycarbonamide fibers having an initial modulus of at least 170 gpd and an orientation angle of up to 40°. These fibers, such as PPTA (poly(para-phenylene terephthalamide)) fibers, are spun from spin dopes based on polymers and organic solvents, such as hexamethylphosphoramide and / or N-methylpyrrolidone (NMP). As-spun fibers (prepared using the toxic solvent hexamethylphosphoramide) can have elongations of 18 or 20%, while heat-treated fibers have elongations of up to 5.4%. This application does not relate to aramid nanofibers.

[0007] European Patent Application Publication No. 0309229 describes the preparation of isotropic and anisotropic polyamide anionic solutions using a base and a sulfoxide solvent. In this manner, aramid solutions with concentrations of 1.5 to 1.7% by weight can be prepared. By applying solvent evaporation or freeze-drying, the aramid concentration of the solution can be increased up to 12% by weight. In this method, DMSO is added to the base and stirred. Subsequently, dried aramid pulp is added to the solvent-base mixture. The resulting solution can be used to spin aramid fibers. Such aramid fibers have elongations in the range of 4.2 to 4.9%.

[0008] WO 2017 / 117376 describes a method for producing aramid nanofibers (ANFs) in which an aramid material is combined with a solution containing a base and an aprotic solvent. In various embodiments, the KOH / EtOK / DMSO-based reaction medium can contain water. The aramid material and base are present in relatively small amounts in the solution. WO 2017 / 117376 describes that the diameter and number of branches per nanofiber produced by this method can be controlled by adding water to the reaction. The concentration of aramid (e.g., 1%) and the concentration of base are low relative to the amount of solvent. Dissolution times are generally on the order of days or weeks.

[0009] Cao et al. (Av. Funct. Mater., 2017, n. 27:1701061, DOI: 10.1002 / adfm.201701061) described the preparation of ANF-coated carbon nanotube wires by adding potassium tert-butoxide and short-cut para-aramid fibers to DMSO. After initial stirring, methanol (as a proton donor) was added stepwise to the reaction. Dispersions with high aramid concentrations (8 wt%) could be prepared in this manner. Hollow fibers spun from ANF dispersions appear to have elongations at break (strains) of less than 3%. Similarly, Yang et al. (ACS Nano, 2019, 13, 7, pp. 7886-7897, DOI: 10.1021 / acsnano.9b02258) reported that proton donor-assisted deprotonation of para-aramid fibers (aramid concentration 0.2 wt%) yielded ANFs in 4 hours. In this method, para-aramid fibers and KOH were added to DMSO. Water was then added to the system at different water-to-DMSO volume ratios.

[0010] H. Chen et al. (Green Chem., 2021, v23 n19:7646-7658, DOI: 10.1039 / d1gc01805a) also describe the proton donor-assisted preparation of aramid nanofibers. An aqueous KOH solution is prepared and added to DMSO with stirring to obtain a KOH / HO / DMSO system. To this system, the aramid material is added. Chen notes that the addition of aqueous KOH improves the solubility of KOH in DMSO and the dissolution of the aramid fibers. The dissolution time is short (26 minutes) for a 0.2 wt% aramid solution and 10 hours for a 4 wt% aramid solution.

[0011] Although the prior art has shown that the addition of a proton donor to a dissolution system can reduce the time to dissolve aramid in systems based on aprotic solvents and strong bases, the dissolution time is still not suitable for industrial processes, and further improvement is desired. Furthermore, continuous aramid fibers, especially para-aramid fibers, are desired that have a high elongation to break, preferably at least 15%, more preferably at least 20%. Optimally, such fibers exhibit a high elongation to break combined with high tenacity.

[0012] These objects are achieved by the presently claimed method for producing an aramid solution by combining ingredients including a base, a proton donor, an aramid, and an aprotic solvent, the method comprising: Dissolving a base in a proton donor to obtain a base solution; combining an aprotic solvent with an aramid to obtain an aramid-solvent mixture; combining the base solution with the aramid-solvent mixture to obtain a suspension; The suspension is mixed to obtain an aramid solution. This is achieved by the method.

[0013] The aramid used to prepare the solution may include aramid fibers (including, but not limited to, continuous and discontinuous aramid fibers), aramid pulp, aramid film, aramid paper, aramid fibrids, aramid polymer particles (e.g., powder or crumb), and any combination thereof. The aramid may include aramid obtained from recycling, and thus based on post-consumer materials or manufacturing waste. Preferably, the aramid used as the starting material comprises discontinuous aramid fibers. The discontinuous aramid fibers preferably have a length (or maximum dimension) ranging from 0.1 mm to a maximum of 100 cm, preferably a maximum of 50 cm, more preferably a maximum of 20 cm, and even more preferably a maximum of 10 cm, or even a maximum of 5 cm.

[0014] Fibers are to be understood as relatively flexible units of material having a large ratio of length to width (perpendicular to their length, across their cross-sectional area).

[0015] In the context of this application, the term "length" refers to the length-weighted length (LL) for short fibers and the average length for longer fibers. For short fibers (pulp, fibrils and fibrids) up to 6 mm in length, the length-weighted length can be determined using a Pulp Expert™ FS (Metso) which includes particles less than 250 microns in length.

[0016] For larger fibers (greater than 6 mm), length refers to the number average fiber length (mean length, ML), which is

number

[0017] The aramid fibers may be in the form of short cuts.

[0018] Short cuts comprise short filaments and can be obtained, for example, by cutting continuous yarns, fabrics or woven materials.

[0019] In one embodiment, the aramid short cut fibers have a length in the range of 0.1 to 20 mm, preferably 1 to 10 mm, more preferably 3 to 8 mm.

[0020] Preferably, the aramid short cuts have a narrow length distribution.

[0021] In one embodiment, the length distribution of the aramid short cuts is such that at least 50% by weight of the filaments have a length within 30% of the length at the peak maximum of the length distribution curve. Preferably, at least 70% by weight of the filaments have a length within 30% of the length at the peak maximum of the length distribution curve.

[0022] The aramid short cut fibers can be further processed before being used as a starting material, for example, the aramid short cut fibers can be crushed or ground.

[0023] Aramids may contain pulp, which consists of short fibers subjected to shear forces that lead to the formation of fibrils, most of which remain connected to the "stem" of the original fiber, but thinner fibrils detach from thicker ones. These fibrils are curled, sometimes ribbon-like, and exhibit variations in length and thickness.

[0024] In the present context, aramid refers to an aromatic polyamide consisting of aromatic moieties directly connected to each other via amide fragments. Methods for synthesizing aramids are known to those skilled in the art and typically involve the polycondensation of aromatic diamines with aromatic diacid halides. Aramids can exist in meta and para forms. Preferably, the aramid (preferably in the form described above) used as the starting material for the present process is or consists of para-aramid.

[0025] Meta-aramids can be prepared by the polymerization of meta-type aromatic amines and meta-dicarboxylic acid halides.

[0026] Suitable aromatic metadiamines include metaphenylenediamine, 3,4'-diaminodiphenyl ether, and 3,4'-diaminodiphenyl sulfone, as well as derivatives thereof having substituents such as halogen atoms and / or alkyl groups having 1 to 3 carbon atoms attached to the aromatic ring structure. For example, 2,4-toluylenediamine, 2,6-toluylenediamine, 2,4-diaminochlorobenzene, and 2,6-diaminochlorobenzene can be used. Preferably, metaphenylenediamine or a mixed diamine containing metaphenylenediamine in an amount of 85 mol% or more, more preferably 90 mol% or more, and even more preferably 95 mol% or more is used.

[0027] Suitable aromatic metadicarboxylic acid dihalides include isophthalic acid halides, such as isophthalic acid chloride and isophthalic acid bromide, and their derivatives having substituents such as halogen atoms and / or alkoxy groups having 1 to 3 carbon atoms, such as 3-chloroisophthalic acid chloride and 3-methoxyisophthalic acid chloride. Preferably, isophthalic acid chloride and mixed carboxylic acid halides containing isophthalic acid chloride in an amount of 85 mol% or more, more preferably 90 mol% or more, and even more preferably 95 mol% or more are used.

[0028] For purposes of this application, the term para-aramid refers to a class of fully aromatic polyamide polymers and copolymers having at least 60%, preferably at least 80%, and more preferably at least 90% para-oriented bonds between aromatic moieties. In one embodiment, at least 95% or all (i.e., 100%) of the bonds are para-oriented. Examples of para-oriented aromatic diamines that can be used to prepare the para-aramids of the present invention include para-phenylenediamine, 4,4'-diaminobiphenyl, 2,6-naphthalenediamine, 1,5-naphthalene-diamine, and 4,4'-diaminobenzanilide. Up to 50 mole % substituted aromatic diamines, such as 2-methyl-para-phenylenediamine and 2-chloro-para-phenylenediamine, can be used. Examples of para-oriented aromatic dicarboxylic acid halides that can be used in the present invention include terephthaloyl dichloride, 4,4'-benzoyl dichloride, 2,6-naphthalene-dicarboxylic acid dichloride, and 1,5-naphthalenedicarboxylic acid dichloride.

[0029] Typical para-aramids are poly(para-phenylene terephthalamide) (PPTA), poly(4,4'-benzanilide terephthalamide), poly(para-phenylene-4,4'-biphenylenedicarboxamide), poly(para-phenylene-2,6-naphthalenedicarboxamide), 5,4'-diamino-2-phenylbenzimidazole, poly(para-phenylene-co-3,4'-oxydiphenylene terephthalamide), and copolymers thereof. Preferably, the aramid comprises or consists of poly(para-phenylene terephthalamide).

[0030] The solvent is an aprotic solvent, preferably a polar aprotic solvent.

[0031] In one embodiment, the solvent is selected from dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dichloromethane (DCM), dimethylacetamide (DMAc or DMA), tetramethylurea or N-methyl-2-pyrrolidone (NMP), or mixtures thereof. While DMAc, NMP, and DMF are technically suitable solvents, it is preferred to use DMSO as the solvent, as it is not considered to be carcinogenic, mutagenic, or reproductively toxic.

[0032] The solvent is not sulfuric acid. Preferably, the solvent is free of alkali chloride salts and alkaline earth chloride salts.

[0033] The base is preferably a strong base, preferably a base having a dissociation constant pKa (in water) of at least 10, more preferably a base having a dissociation constant pKa of at least 11. Such bases include, for example, oxides of alkali metals.

[0034] In one embodiment, potassium hydroxide (KOH), sodium hydroxide (NaOH), potassium ethoxide (EtOK), sodium hydride (NaH), potassium tert-butoxide (tBuOK), potassium hydride (KH) or sodium amide (NaNH) is used as the base.

[0035] In one embodiment, DMSO is used as the aprotic solvent and KOH as the base.

[0036] The proton donor provides protons to the amide groups of the aramid polyanions being formed. Such protons are required to achieve nanofibers with an integrated molecular structure. Traditionally, proton donors are added after the formation of the aramid solution to induce structural recovery of the aramid nanofibers. However, it may be advantageous to have a small amount of proton donor present during the formation of the solution. The proton donor may be selected from water and alcohol. The alcohol may be selected from ethanol, methanol, isopropanol, and ethylene glycol. The water may be demineralized water. Different proton donors may be used in combination. Ethylene glycol has been found to be a suitable proton donor, particularly when the aramid solution is to be further processed into continuous aramid fibers. When preparing an aramid solution using ethylene glycol as a proton donor, a higher degree of elongation can be applied during the spinning process, resulting in continuous aramid fibers with attractive mechanical properties.

[0037] In this method, the base solution and the aramid-solvent mixture are formed separately and then combined to form the suspension.

[0038] The base solution is formed by combining an amount of base with an amount of proton donor and dissolving the base in the proton donor. The concentration of the base in the base solution may vary and may range from 0.05 to 20 M. The concentration is selected depending on the solubility of the base, particularly to achieve a specific molar ratio of base to amide bonds in the suspension obtained by combining the base solution with the aramid solvent mixture, as described below. The final concentration of base in the suspension and aramid solution is preferably less than 2 M, more preferably less than 1 M, and may be less than 0.5 M.

[0039] Preferably, the base solution does not contain an aprotic solvent, and more preferably, the base solution consists of a base and a proton donor.

[0040] The aramid solvent mixture is formed by combining an amount of aramid with an amount of aprotic solvent, in which the aramid and solvent may form a slurry.

[0041] Preferably, the aramid solvent mixture is free of bases and proton donors, and more preferably, the aramid solvent mixture consists of aramid and an aprotic solvent.

[0042] The base solution and the aramid solvent mixture are then combined, which may be done in different ways, for example by adding the base solution to the aramid solvent mixture stepwise or all at once, or vice versa, or by adding both to a suitable container for mixing.

[0043] In one embodiment of this method, the weight ratio between the proton donor and the solvent is in the range of 1:5 to 1:1000, preferably 1:10 to 1:200, and more preferably 1:20 to 1:100. For example, the weight ratio between the proton donor and the solvent may be in the range of 1:15 to 1:50, with a weight ratio of 1:25 being preferred. By adjusting the ratio between the proton donor and the solvent, the amount of proton donor present in the reaction relative to the amount of solvent can be controlled. The weight ratios shown, particularly those between 1:15 and 1:40, have been found to result in shorter dissolution times and much less base (e.g., KOH) crystals observed by optical microscopy in the aramid solution.

[0044] In one embodiment, the molar ratio of base to amide bonds present in the suspension during the reaction ranges from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 2:1 to 1:2, and even more preferably from 1.5:1 to 1:1.5. Preferably, the molar ratio of base to amide bonds present in the suspension during the reaction is less than 4:1, more preferably less than 3:1. For example, when the aramid is PPTA, the repeating unit of the polymer containing two amide bonds has a molecular weight of 238 g / mol. When PPTA is used as the aramid and KOH (56 g / mol) is used as the base, preferably an equimolar amount of base KOH per amide bond in the aramid is used (thus, the weight ratio of base to aramid is less than 1). Even when higher concentrations of aramid are used, i.e., when the concentration of aramid in the final aramid solution exceeds 3% by weight, the molar ratio of base to amide bond is preferably 2:1 to 1:2, even more preferably 1.5:1 to 1:1.5, and most preferably an equimolar ratio is applied.

[0045] This differs from the disclosure of, for example, WO 2017 / 117376, where a stoichiometric excess of base relative to aramid can be applied (conveniently at a 1:1 weight ratio), but only at lower aramid concentrations. Chen et al. increase the amount of base when a higher aramid concentration is desired, for example, up to a 3:1 molar ratio of base to amide bonds.

[0046] Using a nearly equimolar ratio of base to amide bonds in the aramid is advantageous to avoid aramid degradation, reaction rate, and the presence of excess base crystals, especially in the case of highly concentrated aramid solutions.

[0047] Separately preparing the base solution and the aramid solvent mixture, followed by simply combining these components, improves the aramid polymer disintegration and dissolution process and shortens the dissolution time (also called reaction time). In particular, adding the base solution to an aprotic solvent already containing aramid is advantageous because it appears to reduce the crystallization of base particles, which occurs more frequently when the base solution is added to the solvent and only then the aramid is added.

[0048] In one embodiment, the suspension is subjected to shear, preferably strong shear, to improve, particularly accelerate, the disintegration and subsequent dissolution of the aramid. This can improve dissolution of the aramid. Shear can be applied by vigorously stirring, kneading, or sonicating the composition. Sonication can be performed at frequencies ranging from 10 kHz to 50 kHz, preferably from 15 kHz to 25 kHz.

[0049] The dissolution of the aramid is preferably carried out at room temperature or at an elevated temperature, but below 75° C. Preferably, the reaction is carried out at a temperature ranging from room temperature to 65° C., more preferably from room temperature to 60° C., to avoid degradation (hydrolysis) of the polymer. Preferably, the dissolution of the aramid material is carried out at a temperature of at least 15° C., preferably at least 18° C. Reaction temperatures of 40° C. and 60° C. have been found to result in aramid solutions free of particles and crystals, in particular free of base crystals.

[0050] In one embodiment, at least the mixing step is carried out in a high-shear mixer or high-speed mixer, such as a twin-screw kneader or twin-screw extruder, or a twin-screw kneader or mixer, a single-screw kneader or single-screw extruder, or a Drais mixer. Preferably, the step of combining the base solution with the aramid-solvent mixture is also carried out in such a high-shear mixer. More particularly, both steps are carried out in the same high-shear mixer, preferably the same twin-screw kneader or twin-screw extruder.

[0051] Particularly in large scale processes, the use of such equipment has been found to be advantageous in generating sufficient shear, using shorter mixing times, and allowing for continuous processing.

[0052] In an industrial-scale process, the following embodiment of the method can be used: A base solution is obtained by dissolving the amount of base in a proton donor in a vessel. The aprotic solvent and aramid are added (simultaneously or sequentially; if added sequentially, the aramid polymer should preferably be added first) to a high-shear mixer, such as a twin-screw extruder, and mixed to prepare an aramid-solvent mixture. The base solution is then added to the high-shear mixer. The high-shear mixer, such as a twin-screw extruder, may have separate inlets for adding the base solution and the aramid-solvent mixture, or the polymer and solvent, if added separately. Preferably, the base solution inlet is downstream of the aramid and aprotic solvent inlets. The base solution may be injected (e.g., under high pressure) and combined with the aramid-solvent mixture. The amount of aramid should be adjusted to result in a final polymer concentration of at least 5% by weight, preferably 7-20% by weight, more preferably 10-20% by weight, and even more preferably 12-18% by weight. Processing in a high-shear mixer, such as a twin-screw extruder, should preferably be carried out at temperatures ranging from 15 to 70°C, preferably up to 65°C, more preferably up to 60°C (cooling may be applied if necessary). Mixing time is adjusted by adjusting the feed input and the outlet flow (extrudate). Rotation speeds of up to 300 rpm, for example, can be used to achieve high shear. The extruder screw configuration can be constructed with several different elements, such as conveying elements, mixing elements, and kneading elements.

[0053] The following screw configurations are preferably used: The entry zone elements preferably have a length of 3-6D (D represents the screw diameter in mm), but can have a length of 6-9D, and are equipped with single- or double-flighted conveying elements. Single- and double-flighted elements are well-known conveying elements that do not cause compaction during conveying. The mixing and dissolving zone may have a length of 15-30D, preferably 20-23D, and can use elements without conveying properties (screw elements such as W&P Igel or Hedgehog and / or single- or multi-flighted mixing ZME; Berstorff single- or multi-flighted mixing ZB; and Clextral multi-flighted mixing BMEL) or elements with interrupted conveying properties (screw elements such as W&P type SME or Berstorff type EAZ-ME). Mixing elements without conveying properties do not cause conveying and are therefore completely filled with product, characterized by dispersive mixing properties. Mixing elements with interrupted conveying properties have channels with conveying properties. These elements have distributive mixing properties and do not necessarily need to be completely filled.

[0054] Alternatively, the following screw configuration may be used: The entry zone element has a length of 2 to 10D, preferably 5 to 7D (D represents the screw diameter in mm).

[0055] The mixing and dissolving zone may have a length of 10-20D, preferably 13-16D, and elements with conveying properties can be used. The degassing zone may have a length of 3-8D, preferably 2-4D, and negative conveying elements can be used as vacuum locks, and positive conveying elements can be used at the vacuum connections of the (twin-screw) extruder.

[0056] The mixing and compression zone may have a length of 10 to 30D, preferably 16 to 19D, and elements having conveying or compression properties can be used.

[0057] Optionally, a vacuum (negative pressure) can be applied to the extruder to remove any gases and obtain a gas-free aramid solution suitable for further processing.

[0058] Optionally, large undissolved particles, for example base particles having a size greater than 0.5 μm, can be removed (for example, by settling, decanting, or filtration) before injecting the base solution into the high shear mixer.

[0059] The advantage of this method is the short time required to obtain the aramid solution. The mixing step to obtain the aramid solution preferably takes between 3 minutes and 2 hours for aramid concentrations above 3% by weight, or even above 5% by weight, depending on the mixing device selected. Since the base is easily soluble in the proton donor, the step of preparing the base solution is very short, and the step of combining the aprotic solvent with the aramid is also very short, especially when a high-shear mixer is used.

[0060] The dissolution or reaction time indicates the time after mixing of the base solution with the aramid solvent mixture until no aramid particles are visible when the solution is viewed under an optical microscope (5x magnification using cross polarizing filters).

[0061] Preferably, the aramid concentration in the aramid solution is in the range of 1 to 20% by weight, preferably 2 to 18% by weight, more preferably 4 to 15% by weight. Preferably, these concentrations are achieved by first preparing a lower concentration solution and subsequently dissolving the aramid starting material to this concentration without removing the solvent. Preferably, the aramid solution exhibits optical anisotropy (liquid crystal behavior), i.e., the aramid molecules are densely packed and adopt an ordered arrangement.

[0062] The optical anisotropy of the solution may be examined under a polarized microscope (crossed polarizers, clear vision image) and / or may be seen as opalescence during stirring.

[0063] Typically, aramid solutions based on aprotic solvents and bases containing at least 3% by weight of aramid (at room temperature) exhibit optical anisotropy. Aramid solutions with higher concentrations (e.g., at least 4%, at least 5%, or at least 10% by weight) exhibit optical anisotropy. Optical anisotropy is sometimes referred to as birefringence. Solutions with high concentrations of aramid are subsequently more easily and efficiently processed into shaped articles (e.g., continuous fibers, aramid nanofibers, films, or coatings). Also, less solvent is used, which is generated as waste or needs to be recovered.

[0064] Thus, the method of the present invention provides a very rapid method for producing aramid solutions with high aramid concentrations that can be processed in many ways and result in products with attractive properties.

[0065] The present invention also relates to methods for processing the aramid solution into various shaped articles or materials, such as continuous aramid fibers, aramid nanofibers, aramid films, or coatings or composites comprising aramid.

[0066] In particular, the present invention provides a method for producing continuous aramid fibers, comprising the steps of: i) providing an aramid solution produced according to any of the present method embodiments; ii) passing the solution through a spinneret; iii) solidifying the solution to obtain fibers; iv) washing the fibers; The present invention relates to a method, comprising:

[0067] Preferably, the method for producing continuous aramid fiber spinning is a dry-wet spinning method, which means that after leaving the spinneret, the solution passes through a gaseous medium before entering the coagulation bath. Preferably, the solution passes through a gaseous medium. The gaseous non-coagulation medium is preferably air.

[0068] The gaseous medium (also called air gap) preferably has a length in the range of 2 to 20 mm, more preferably 3 to 15 mm, and even more preferably 5 to 10 mm. The aramid present in the solution is stretched in the gaseous medium through which the solution passes. However, it is also possible to process the solution into continuous fibers by a wet spinning method without using an air gap; thus, after leaving the spinneret, the solution enters the coagulation bath directly.

[0069] The degree of drawing, i.e., the ratio of the length of the filament as it leaves the coagulation bath to the average length of the solution as it leaves the spinning orifice of the spinneret, can range from 1.5 to 15, preferably from 2 to 6. Drawing the fibers in the air gap increases the molecular alignment within the fiber, increasing the mechanical properties and reducing the fiber diameter (in the case of multifilament yarns, this occurs at the filament level).

[0070] After coagulation, the formed continuous aramid fibers are typically removed from the coagulation bath, washed, dried, and taken up on bobbins (in any order). Optionally, after passing through the coagulation bath and / or after washing, the continuous aramid fibers are neutralized, for example by subjecting them to an acidic solution (for example, by spraying the fibers or passing the fibers through a bath). An optional drying step may be carried out after washing and / or neutralization and before winding. In another embodiment, the wet continuous aramid fibers are wound onto bobbins and subsequently washed and / or dried. The spinnerets used may be of a type known per se for wet-dry spinning.

[0071] Surprisingly, it has been found that spinning of an aramid solution, in particular spinning into low linear density filaments (e.g., 0.5 to 10 dtex / filament, preferably 1 to 6 dtex / filament or 1 to 3 dtex / filament), and subsequent washing of the filaments allows for efficient removal of the base.

[0072] When a para-aramid polymer that has not been previously processed or shaped is used as the aramid starting material to make the solution, the continuous para-aramid fiber obtained by this method does not contain sulfonic acid groups.

[0073] Alternatively, if the aramid comprises recycled para-aramid, the continuous para-aramid fibers obtained by this method may contain sulfonic acid groups (if the para-aramid has been previously treated with sulfuric acid).

[0074] Continuous aramid fibers produced in this way, i.e., based on the above-described aramid solutions, can have attractive mechanical properties, for example, exhibiting less fibrillation (higher abrasion resistance), and can have high elongation at break and / or high lateral compression resistance.

[0075] Preferably, the continuous para-aramid fibers (e.g., obtained by the present process) have an elongation at break of at least 15%, more preferably at least 20%, even more preferably at least 25%, or even at least 30%. Preferably, the continuous para-aramid fibers (e.g., obtained by the present process) have a burst toughness of at least 40 J / g, more preferably at least 50 J / g, and even more preferably at least 60 J / g.

[0076] Therefore, the present invention also relates to continuous para-aramid fibers having high elongation at break and high burst toughness.

[0077] The continuous para-aramid fibers produced by this method preferably combine high elongation to break with high burst toughness. In one embodiment, the continuous para-aramid fibers have an elongation to break of at least 15%, more preferably at least 20%, and a burst toughness of at least 40 J / g, preferably at least 45 J / g. The elongation to break and burst toughness are determined at the filament level according to ASTM D3822 using a test speed of 50 mm / min and a gauge length of 100 mm after conditioning at 20°C and 65% relative humidity.

[0078] Burst toughness is also called toughness, fracture toughness, or fracture toughness. Toughness is the ability of a fiber to resist breaking under stress. Toughness is the area under the stress-strain curve.

[0079] Preferably, the continuous para-aramid fibers have a breaking tensile of at least 150 mN / tex, preferably at least 200 mN / tex, more preferably at least 250 mN / tex, after conditioning at 20°C and 65% relative humidity, determined according to ASTM D3822-14 using a test speed of 50 mm / min and a gauge length of 100 mm.

[0080] Preferably, the continuous para-aramid fibers comprise at most 10% by weight, even more preferably at most 5% by weight, or even at most 2% by weight, of a polymer other than para-aramid. More preferably, the continuous aramid fibers comprise or consist of para-aramid, preferably poly-p-phenylene terephthalamide.

[0081] Continuous para-aramid fibers having such high elongation at break and such high tenacity cannot be produced by conventional spinning techniques in which para-aramid is dissolved in sulfuric acid or in conventional organic solvents (e.g., hexamethylphosphoramide, N,N-DMAc, and / or N-methylpyrrolidone in combination with salts such as LiCl or CaCl) without deprotonation. Such continuous para-aramid fibers are particularly suitable for tire and hose applications, such as, for example, vehicle tires and turbocharger hoses.

[0082] Continuous para-aramid fibers have a different crystalline structure than conventionally produced para-aramid fibers obtained by dissolving para-aramid polymer in sulfuric acid or conventional organic solvents and processing the resulting spin dope by wet-dry spinning. In particular, continuous para-aramid fibers produced by the present method appear to have less orientation and alignment of the polymer crystallites in the fibers, even when subjected to similar spinning conditions.

[0083] A further difference between the continuous para-aramid fibers described herein and para-aramid fibers conventionally produced by dissolving para-aramid polymer in organic solvents or sulfuric acid is the morphology and surface structure of the fibers. In one embodiment, continuous para-aramid fibers have a parallel nanofiber structure on at least a portion of their surface that can be observed by microscopy, particularly scanning electron microscopy (SEM).

[0084] 2a and 2b show SEM images of two examples of continuous para-aramid fibers according to the present invention, and FIG. 2c shows an SEM image of a conventionally produced para-aramid fiber (Twaron®, spun from sulfuric acid).

[0085] The parallel nanofiber structure visible on conventional continuous para-aramid fibers can be attributed to the fact that the aramid solution used to spin continuous aramid fibers contains deprotonated para-aramid and therefore contains larger molecular structures than para-aramid present in spin dopes dissolved in sulfuric acid or organic solvents without deprotonation.

[0086] In one embodiment, the continuous para-aramid fibers have an oriented crystallite fraction of less than 40%, preferably less than 35%, more preferably in the range of 20-30%, and even more preferably in the range of 25-30%.

[0087] In one embodiment, the continuous para-aramid fibers are characterized by an orientation parameter OA in the range of 40 to 60°, preferably in the range of 42 to 57°, and more preferably in the range of 48 to 55°.

[0088] In one embodiment, the continuous para-aramid fibers have a lateral crystallite size L200 of less than 40 Å, preferably in the range of 30 to 38 Å.

[0089] Conventionally produced para-aramid yarns, such as those available under the TWARON® trademark, generally have an oriented crystallite fraction greater than 90%, usually near 100%, an orientation parameter OA of less than 30°, preferably 5-20°, and a lateral crystallite size L200 greater than 50 Å, usually in the range of 50-80 Å.

[0090] The oriented crystallite fraction, orientation parameter and lateral crystallite size L200 are determined by X-ray diffraction (XRD), as further detailed in the experimental section.

[0091] The continuous aramid fibers may be multifilament yarns.

[0092] In another embodiment, the fibers may be nanofilaments having diameters in the nanometer range.

[0093] Preferably, the continuous para-aramid fibers have a high relative viscosity η rel Preferably, the continuous para-aramid fibers have a relative viscosity η in the range of 3 to 8, preferably in the range of 3.5 to 6, more preferably in the range of 4 to 5.5, as determined by a viscometer. rel It has.

[0094] Relative viscosity is determined by dissolving a fiber sample in sulfuric acid at room temperature. The flow time of the sample in a 96% sulfuric acid solution (0.25% mass / volume) is measured in an Ubbelohde viscometer at 25°C. The flow time of 96% sulfuric acid is also measured under the same conditions. The relative viscosity is then calculated as the ratio of the two observed flow times.

[0095] Relative viscosity η rel is different from the intrinsic viscosity described in the prior art. The intrinsic viscosity is determined by the formula ln(η rel ) (the natural logarithm of the relative viscosity) to C, where C represents the concentration of 0.5 grams of para-aramid polymer in 100 ml of solvent.

[0096] The relative viscosity, which is the basis for this calculation, is determined by dividing the flow time of a dilute solution of the polymer in a capillary viscometer by the flow time of the pure solvent. However, in this case (as described, for example, in U.S. Pat. No. 3,817,941), the dilute solution used to determine the relative viscosity has the concentration represented by (C) above (i.e., 0.5 g / 100 ml), and the flow time is determined at 30°C using concentrated sulfuric acid (95-98%) as the solvent.

[0097] For example, an intrinsic viscosity of 1.13 corresponds to a relative viscosity of 1.34, an intrinsic viscosity of 2.56 corresponds to a relative viscosity of 1.97, an intrinsic viscosity of 4.00 corresponds to a relative viscosity of 3.00, an intrinsic viscosity of 4.97 corresponds to a relative viscosity of 3.98, an intrinsic viscosity of 5.73 corresponds to a relative viscosity of 4.99, an intrinsic viscosity of 6.35 corresponds to a relative viscosity of 6.01, and an intrinsic viscosity of 6.87 corresponds to a relative viscosity of 7.03. Fibers with high relative viscosities have improved mechanical properties.

[0098] Preferably, the continuous para-aramid fibers are produced by using the above aramid solution in the above spinning method, although the invention is not limited thereto.

[0099] In a preferred embodiment, the continuous para-aramid fibers have a content of carcinogenic, mutagenic and reproductively toxic organic solvents of less than 250 ppm, preferably less than 100 ppm, more preferably less than 50 ppm, which corresponds to a content of less than 0.025% by weight (based on the weight of the fiber), preferably less than 0.01% by weight, more preferably less than 0.005% by weight, which means that the combined content of carcinogenic and reproductively toxic organic solvents, in particular NMP (N-methylpyrrolidone), DMF (dimethylformamide), DMAc (dimethylacetamide) and HMPA (hexamethylphosphoramide), is less than 250 ppm, preferably less than 100 ppm, more preferably less than 50 ppm.

[0100] The organic solvent content can be determined by different methods depending on the specific organic solvent. Generally, gas chromatography (GC), nuclear magnetic resonance (NMR), and mass spectrometry (MS) are suitable for determining the organic solvent content of fibers, such as NMP or DMAc content. In the context of the present invention, the organic solvent content is determined by gas chromatography. Approximately 10 mg of fiber is collected and heated in an electric furnace at above 500 °C. The amount of amide solvent evaporated from the fiber was measured using a gas chromatograph (Shimadzu Corporation, Model GC-2010). Subsequently, the residual solvent concentration in the fiber was calculated using a calibration curve prepared using an amide-based solvent as a standard sample.

[0101] Another object of the present invention is to provide a method for producing aramid nanofibers, comprising the steps of: i) providing a solution produced according to any of the present method embodiments; ii) adding to the solution an amount of a proton donor; The method includes:

[0102] The proton donor may be, for example, the same proton donor used in the process for producing the aramid solution, or a different proton donor. Preferably, the added proton donor is water. Alternatively, another coagulant, such as a ketone (e.g., acetone or methyl ethyl ketone), may be used instead of the proton donor.

[0103] After precipitation of the aramid nanofibers, the aprotic solvent can be removed, for example, by washing with water and / or evaporation.

[0104] The aramid nanofibers obtained by this method can be used to coat various substrates, particularly to modify or improve the substrate properties or at least the surface properties of the substrate. For example, a coating of aramid nanofibers can be used to improve the fire resistance of a substrate.

[0105] Additionally, the aramid nanofibers may be used to reinforce composite materials, and in particular, the aramid nanofibers may be added to the resin or matrix material of the composite material.

[0106] Alternatively, the aramid nanofibers may be used as a filler material (eg, in sheet-like materials such as paper or composite materials) or as an adhesive.

[0107] The present application therefore also relates to a material comprising aramid nanofibers, said material preferably being selected from coatings and composite materials.

[0108] Another object of the present invention is to provide a method for producing an aramid film, comprising the steps of: i) providing a solution produced according to any of the present method embodiments; ii) applying a solution to the surface; iii) solidifying the solution to form a film; The method includes:

[0109] In one embodiment, the solution may be combined with a solution of another polymer before being applied to the surface, and the combined solution may be used to produce an aramid film containing the other polymer.

[0110] The surface may be a support surface, or it may be part of an object that is to be coated with a film of the solution.

[0111] The solution can be supplied to the (support) surface, for example by casting from a die or by application by a roller.

[0112] Alternatively, the object to be coated with a film of the solution may be dipped into the solution or coated by other methods, including spraying or other well-known methods.

[0113] The solution is then solidified to form a film, which can be achieved by drying or coagulation, in which case the solution is subjected to an aqueous coagulating agent, such as water or an aqueous solution of a solvent.

[0114] Preferably, the film is rinsed or washed to remove residual solvent and / or base. Aprotic solvents and bases can be removed, for example, by washing with water and / or evaporation.

[0115] The washed film may be stretched and dried, and optionally, the dried film may be heat-treated.

[0116] The solution may also be used to make resin composites. The solution may be combined with or added to a resin solution (e.g., containing an epoxy resin) to improve the mechanical properties of the resin after curing.

[0117] Therefore, the present application also relates to aramid nanofibers, aramid films, and continuous aramid fibers obtained by any of the methods for processing aramid solutions. Furthermore, the present application relates to materials containing aramid nanofibers obtained by the above methods. The materials may be selected from coatings and composite materials. [Brief explanation of the drawings]

[0118] [Figure 1] An example of a calculation is shown, showing the orientation parameter OA, background line L, peak area (peak) and total area (sum). [Figure 2a] 1 shows an SEM image of an example of a continuous para-aramid fiber according to the present invention. [Figure 2b] 1 shows an SEM image of another example of a continuous para-aramid fiber according to the present invention. [Figure 2c] 1 shows an SEM image of conventionally produced para-aramid fibers.

[0119] The present invention is further illustrated by the following non-limiting examples.

[0120] method 1. X-ray diffraction (XRD) a) Sample preparation A small bundle of thread was wound around a sample holder (thickness of the sample holder is 0.55 mm) and measured at approximately 0.03 g / cm 2 The filaments are wound parallel to each other around the sample holder.

[0121] b) Determination of lateral crystallite sizes L110 and L200 by 1D wide-angle X-ray scattering (WAXS) i) Measurement conditions XRD measurements are performed using a Bruker D8 Advance diffractometer in θ / 2θ geometry with parallel beam optics and a point detector (scintillation counter). The optics consist of a primary 60 mm Göbel focusing mirror (parabolic Ni / C multilayer device) providing Cu-Kα radiation (Kα1 / Kα2 doublet, Kα wavelength = 1.5418 Å) and a 0.12° parallel beam attachment (i.e., a Soller slit parallel to the goniometer axis). Generator settings: 40 kV, 40 mA.

[0122] The sample is rotated (15 rpm) and measured in reflection mode. Measurements are performed from 2θ = 3° to 50°, with a step size (2θ) of 0.02° and a time / step of 4 seconds.

[0123] ii) calculation The lateral crystallite sizes L110 and L200 are determined with Bruker TOPAS P, version 4.1 software, using a four-peak fit model with a linear background. This model consists of two split Pearson VII (SPVII) peaks in the 2θ range 12–35° at 2θ = 20.5° and 22.8°, and two Pearson VII (PVII) peaks at 2θ = 18.5° and 28.4° (Note: SPVII is the asymmetric profile function, and PVII is the symmetric profile function).

[0124] The crystallite size is calculated according to the Scherrer formula using a Scherrer constant k=1 and a nominal instrument correction (β correction) of 0.1°.

[0125] c) Determination of the oriented crystallite fraction f and the orientation parameter OA by 2D WAXS measurements of the 200 reflection i) Measurement conditions XRD measurements were performed using a Bruker D8 Discover X-ray diffractometer. The instrument is based on a horizontal dual-axis goniometer and is equipped with Montel optics, an XYZ translation stage, and a Vantec-500 area detector. The X-ray source is a 2.2 kW Cu anode long fine focus ceramic X-ray tube (type KFL CU 2K90). The Montel optics (Montel-P, 6 cm long) consist of a pair of Göbel mirrors (parabolic Ni / C multilayer devices) positioned side-by-side at a 90° angle to each other, producing a highly parallel beam. The divergence of the primary X-ray beam is limited to less than 0.07° in both directions. The sample-to-detector distance, as determined using a corundum standard, is 8.2 cm. Generator settings: 40 kV, 40 mA.

[0126] The sample is mounted on the goniometer so that the maximum intensity of the 200 peaks is at an azimuthal angle Phi = 90 ± 10°.

[0127] The sample is measured on-axis (i.e., primary beam perpendicular to the detector) for 30 min. The 2D XRD patterns are corrected for inhomogeneity and spatial distortion using standard GADDS procedures (i.e., flood-field correction and unwarping), and the patterns are also corrected for air scattering.

[0128] ii) Data processing The 2θ(max) positions of the maxima of the 200 peaks are determined by Bruker GADDS software, version 4.1.44.

[0129] The azimuthal curve for the 200 reflection is found by 2θ integration of a 2D region within the 2θ range between 2θ(max) -0.5° and 2θ(max) +0.5° (i.e., the integration region has a width of 1° in 2θ). This integration results in a 1D Phi curve from 0 to 180°.

[0130] iii) calculation The sample consists of an oriented crystallite fraction f with orientation parameter OA and a non-oriented crystallite fraction (1-f). The sample parameters f and OA are determined as follows: Fraction f [%] = 100 × (A(peak) [cps × degrees]) / (A(total) [cps × degrees]) OA[°]=FWHM[°], where the total area, A(total), under the azimuthal curve (raw area, unit: cps × degree), the area of ​​the peak, A(peak) (net area, unit: cps × degree), and the full width at half maximum (FWHM) (unit: degree) of the peak in the azimuthal angle phi range 10° to 170° with a linear background line L are calculated from the smoothed azimuthal curve using Bruker EVA software, version 14.0. Figure 1 shows an example of the calculation, showing the orientation parameter OA, background line L, peak area (Peak), and total area (Total).

[0131] 2. Mechanical fiber properties The elongation at break, burst toughness and tensile strength of the fibers are measured at the filament level according to ASTM D3822-14 using a test speed of 50 mm / min and a gauge length of 100 mm after conditioning at 20°C and 65% relative humidity.

[0132] 3. Turbidity A HACH 2100Qis portable turbidity meter was used according to the manufacturer's instructions: the instrument was first calibrated with the manufacturer's calibration sample, then a glass cuvette containing the solution sample was placed in the instrument, and the turbidity (determined in nephelometric turbidity units, NTU) was measured after 10 seconds. Prior to the measurement, the glass cuvette containing the sample was placed in a vacuum oven (room temperature, 50 mbar, 10 min) to remove air bubbles.

[0133] 4. Microscopy Samples of the suspension or aramid solution were observed under an optical microscope equipped with a polarizing filter (e.g., Leica) to determine the presence of base crystals and / or aramid particles and the anisotropic / isotropic behavior. To increase the contrast of the image (especially to determine the anisotropic or isotropic behavior of the sample), the polarizing filters were crossed.

[0134] 5. Scanning Electron Microscopy (SEM) Sample preparation was performed on a 6 cm x 10 cm brass plate. Images of the samples were recorded by SEM (Zeiss Sigma VP) using an SE2 detector and the following settings: EHT parameters 5kV Detector SE2 Aperture 120μm Sputter coater 208 hours High resolution Coating Pt / Pd Supply current 40mA Timer 60 seconds

[0135] Example 1 Two para-aramid solutions with a concentration of 5 wt% were prepared based on either PPTA short-cut fiber or PPTA polymer powder (PPTA polymer powder with a relative viscosity greater than 5). The respective amounts of PPTA were weighed and combined with DMSO to obtain an aramid solvent mixture. In parallel, an aqueous KOH solution was prepared. The base solution was added to the aramid solvent mixture in a 1:25 water-to-DMSO weight ratio to obtain a final KOH concentration in the suspension of 0.49 M. The suspension was mixed in a high-speed mixer until the aramid was completely dissolved (4 min for the powder and 8 min for the short-cut fiber). The molar ratio of KOH per amide bond was 1. The solution was further liquefied using a high-speed mixer (DAC150) and transferred to a spinning tube. Spinning was carried out at 60 °C using a spinneret with six holes, each 300 μm in diameter. The solution was passed through a filter and then pressurized through the spinneret. The filaments were passed through an air gap, coagulated in a water bath, wound onto bobbins under tension, washed, and dried. By varying the winding tension, different degrees of stretch were achieved (the stretch is the ratio of the final length after stretching to the length before stretching).

[0136] Table 1 shows the sample information of the yarn. [Table 1]

[0137] The mechanical properties of the filaments were then measured (the results are shown in Table 2), and the crystallite properties of Samples 1-1 and 1-5 were analyzed by X-ray diffraction (Table 3). [Table 2] [Table 3]

[0138] As shown by the examples, this method allows for the rapid preparation of spinnable aramid solutions. The fibers obtained after spinning have high elongation at break combined with high tenacity. The fibers contain a relatively low oriented crystallite fraction, exhibiting lower crystallinity and lower orientation. This combination of properties cannot be achieved by conventional spinning of para-aramid from sulfuric acid spin dopes. In contrast, conventionally obtained para-aramid yarns (i.e., by spinning from sulfuric acid) have a much higher crystallinity, with the crystallites being highly ordered within the fiber.

[0139] Samples 1-1 and 1-5 were analyzed by scanning electron microscopy (SEM). Figure 2 shows images of both samples (Figures 2a and 2b). Both samples clearly show nanofiber structures on parts of their surfaces. Figure 2c shows an SEM image of a prior art para-aramid fiber spun from sulfuric acid. No nanofiber structures are visible on the surface of this fiber.

[0140] Example 2 Aramid solutions were prepared in the same manner as described in Example 1, but using an amount of either PPTA short-cut fiber or PPTA polymer powder to obtain a solution with a para-aramid concentration of 3 wt %. For all samples, a base solution was added to the aramid solvent mixture at a weight ratio of 1:25 between the proton donor HO and the solvent DMSO.

[0141] The amount of KOH was varied to achieve final concentrations between 0.28 and 1 M in the solution, as shown below. For samples using 0.28 M KOH, the molar ratio between the base KOH and the amide bond in the aramid material was 1:1. The solutions were prepared using either a high-temperature agitator (Samples 2-1 to 2-4) or a high-speed mixer, where high temperatures were generated by shear (Samples 2-5 and 2-6). The high-speed mixer was rotated at a speed of 3500 rpm (2 x 90 s at 3500 rpm, 1 x 45 s at 3500 rpm, Samples 2-5) or at increasing speeds (2 x 30 s at 2000 rpm, 2 x 30 s at 2500 rpm, 4 x 30 s at 3500 rpm, Samples 2-6). With this setup, the temperature in the high-speed mixer is estimated to reach approximately 60–65 °C. The disintegration of the aramid was controlled by microscopy. Under these conditions, aramid solutions could be prepared within 4–12 min.

[0142] Table 4 shows the respective reaction conditions, reaction times, and further notes regarding the degradation of the para-aramid material. [Table 4]

[0143] Example 3 - Comparative Example 0.2 g or 3 g of poly(para-phenylene terephthalamide) (PPTA) short-cut fibers were weighed on a balance and added to a glass container. Then, 100 ml of DMSO was added, and the slurry was stirred at 400 rpm in a mechanical stirrer to obtain an aramid solvent mixture.

[0144] In separate Erlenmeyer flasks, 0.1 g or 3 g of KOH was dissolved in 4 g of demineralized water. This base solution was gently added dropwise to the aramid-solvent mixture. Stirring was continued until the yellow fiber visually disappeared. In this way, Samples 3-1 and 3-3 were prepared.

[0145] Alternatively, the same base solution was added dropwise to 100 ml of DMSO, and then the indicated amount of short-cut fiber was added to the DMSO / KOH / water system and then stirred. In this way, comparative samples 3-2 and 3-4 were prepared.

[0146] From the resulting solution, a sample was taken and a drop was examined under an optical microscope to observe whether any fibrous material was still present that was visible under the microscope, and the turbidity was determined.

[0147] The results are shown in Table 5. At lower para-aramid concentrations, the method according to the invention (3-1) resulted in lower turbidity of the solution, i.e., the solution was clearer and contained fewer particles than the comparative solution (3-2). At higher concentrations, the turbidity could not be determined, but the solution according to the invention (3-3) had no visible fiber debris, in contrast to the visible fiber debris present in the comparative solution of sample 3-4. [Table 5]

[0148] Example 4 - Large-scale processing To test the process of the present invention on a larger scale, the process was tested as a continuous process in a twin-screw extruder.

[0149] PPTA powder was added to a twin-screw extruder, a Theysohn TSK 20 / 40D, at the first inlet. Subsequently, DMSO was added at a throughput of 1120 g / h at an inlet approximately one-quarter of the extruder length. Further downstream, approximately halfway through the extruder, a base solution of KOH and water was added to the aramid solvent mixture present at this point in the extruder. The weight ratio between the proton donor (water) and the solvent (DMSO) was 1:25. The molar ratio of KOH / amide bond was 1. At the PPTA powder inlet, the extruder temperature was set to 20°C, and the remaining zones in the extruder were heated to 60°C. In the first experiment, the final PPTA concentration in the aramid solution was 5 wt%.

[0150] After a few minutes, the PPTA underwent complete disintegration, resulting in an aramid solution with no visible PPTA or KOH particles upon microscopic analysis. Subsequently, the PPTA concentration was increased to 6 wt% and 7 wt%, and the KOH concentration was increased accordingly, still resulting in a molar ratio of KOH / amide bonds of 1, while other settings remained the same. For these runs, again, after a few minutes, the PPTA underwent complete disintegration, resulting in an aramid solution with no visible PPTA or KOH particles upon microscopic analysis.

[0151] An aramid solution with a PPTA concentration of 6 wt % was spun through a spinneret with six holes, each 125 μm in diameter, at a draw ratio of 2 in the same manner as described in Example 1. The mechanical properties of the filaments were determined, and the results are shown in Table 6. [Table 6]

[0152] This example demonstrates that the method according to the invention is suitable for industrial scale production and for obtaining highly concentrated aramid solutions that can be spun to obtain para-aramid yarns with attractive mechanical properties.

Claims

1. 1. A method for producing an aramid solution by combining ingredients including a base, a proton donor, an aramid, and an aprotic solvent, comprising: dissolving the base in the proton donor to obtain a base solution; combining the aprotic solvent with the aramid to obtain an aramid-solvent mixture; combining the base solution with the aramid-solvent mixture to obtain a suspension; mixing the suspension to obtain an aramid solution.

2. 2. The method of claim 1, wherein the weight ratio between the proton donor and the solvent is in the range of 1:5 to 1:1000, preferably in the range of 1:10 to 1:200, more preferably in the range of 1:20 to 1:

100.

3. 3. The method of claim 1 or 2, wherein the molar ratio of base to amide bonds in the aramid is in the range of 10:1 to 1:10, preferably 5:1 to 1:5, more preferably 2:1 to 1:2, even more preferably 1.5:1 to 1:1.

5.

4. 4. The method according to any one of claims 1 to 3, wherein the concentration of aramid in the aramid solution is in the range of 1 to 20% by weight, preferably 2 to 18% by weight, more preferably 4 to 15% by weight.

5. The method according to any one of claims 1 to 4, wherein the proton donor is selected from water and alcohol, more preferably ethanol, methanol, isopropanol or ethylene glycol.

6. The method according to any one of claims 1 to 5, wherein at least the mixing is carried out in a twin-screw kneader or a twin-screw extruder, and preferably the combining of the base solution with the aramid-solvent mixture is also carried out in a twin-screw kneader or a twin-screw extruder.

7. 1. A method for producing continuous aramid fibers, comprising: i) providing an aramid solution produced according to the method of any one of claims 1 to 6; ii) passing the solution through a spinneret; iii) coagulating the solution to obtain fibers; iv) washing the fibers; A method comprising:

8. Continuous para-aramid fibers having an elongation at break of at least 15%, preferably at least 20%, and a burst toughness of at least 40 J / g, preferably at least 45 J / g, as determined according to ASTM D3822-14.

9. 9. The continuous para-aramid fiber of claim 8, which is a multifilament yarn.

10. 10. A continuous para-aramid fiber according to claim 8 or 9, having a breaking tensile of at least 150 mN / tex, preferably at least 200 mN / tex, more preferably at least 250 mN / tex, determined according to ASTM D3822-14.

11. 11. The continuous para-aramid fiber of any one of claims 8 to 10, having an elongation at break of at least 20%, preferably at least 25%, more preferably at least 30%, determined according to ASTM D3822-14.

12. 12. The continuous para-aramid fiber of any one of claims 8 to 11, having an oriented crystallite fraction of less than 40%, preferably less than 35%, more preferably in the range of 20 to 30%, and even more preferably in the range of 25 to 30%.

13. 13. Continuous para-aramid fibers according to any one of claims 8 to 12, having an orientation parameter in the range of 40 to 60°, preferably in the range of 42 to 57°, more preferably in the range of 48 to 55°.

14. A relative viscosity η in the range of 3 to 8, preferably in the range of 3.5 to 6, more preferably in the range of 4 to 5.5, as determined by a viscometer ｒｅｌ The continuous para-aramid fiber according to any one of claims 8 to 13, having

15. 15. The continuous para-aramid fiber of any one of claims 8 to 14, produced by the method of claim 7.

16. 1. A method for producing aramid nanofibers, comprising: i) providing a solution prepared according to the method of any one of claims 1 to 6; ii) adding a further amount of a proton donor to the solution; A method comprising:

17. 17. A material comprising aramid nanofibers obtained by the method of claim 16, preferably selected from coatings and composites.

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