Method for producing fibers

Abstract

The present invention relates to a method for producing fibers, comprising the steps of preparing a dope containing lignin dissolved in a dope solvent and an additive polymer, wherein the dope solvent contains an ionic liquid and water; and extruding the spinning dope into a coagulation bath to obtain one or more fibers.

Description

Technical Field

[0001] The present invention relates to a method for producing fibers, comprising the steps of preparing a spinning dope comprising lignin dissolved in a dope solvent and an additive polymer, wherein the dope solvent comprises an ionic liquid and water; and extruding the spinning dope into a coagulation bath to obtain one or more fibers.

Background Art

[0002] Carbon fiber (CF) is a robust material that can be used to produce carbon fiber reinforced composites, which are desirable lightweight building materials. Carbon fibers are produced by thermal decomposition of precursor fibers made from polyacrylonitrile (PAN) and mesophase petroleum pitch. However, these two main precursors are derived from petroleum and are therefore non-renewable. For PAN, the use of toxic spinning solvents such as DMF and the production of toxic by-products such as HCN during carbonization raise additional environmental and health concerns. The high costs associated with precursor production and the energy-intensive high-temperature treatment also limit the use of carbon fiber composites to high-end markets and are an obstacle to rapid market growth.

[0003] Lignin is an easily accessible biopolymer with a high carbon content and thus has the potential to be a lower-cost and renewable alternative precursor. Lignin is attractive due to its sustainable origin, low cost, and relatively high fiber yield after carbonization. More than 70 million tons of lignin are extracted annually during paper and pulp production. Commercial lignin-based carbon fibers, which are currently not value-added products, could support the economy of the developing renewable chemical industry by providing additional revenue to wood processing biorefineries that burn most of the lignin to generate heat and electricity.

[0004] Many studies on the production of lignin fibers have focused on melt spinning at approximately 200 °C, often using copolymers. The process is attractive as it avoids solvents, but it is difficult to control the thermal behavior of lignin to obtain suitable melt behavior, and oxidation stabilization is slow to maintain fiber shape.

[0005] Wet (coagulation) spinning of pure unmodified lignin has not been demonstrated, probably due to its low average molar weight. Wet spinning may be made possible by blending lignin with another fiber-forming polymer, such as cellulose. Solvents reported to date for wet spinning include DMSO (Foellmer, M. et al., Wet-Spinning and Carbonization of Lignin-Polyvinyl Alcohol Precursor Fibers. Advanced Sustainable Systems 2019; Lu, C. et al., ACS Sustainable Chemistry and Engineering 2017, 5(4), 2949 - 2959).

[0006] In addition, the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate, [Emim][OAc], has been used with pure water as a coagulation bath to form precursor lignin / cellulose fibers (Bengtsson, A. et al., Holzforschung 2018, 72(12), 1007 - 1016; Vincent, S. et al., ACS Sustainable Chemistry and Engineering 2018, 6(5), 5903 - 5910). The ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate [DBNH][OAc] has also been used to produce carbon fibers derived from 50 / 50% kraft lignin / cellulose precursor fibers (Ma, Y. et al., ChemSusChem 2015, 8(23), 4030 - 4039). However, these methods require expensive ILs that must be rigorously dried to dissolve cellulose, which is a challenge for commercialization. SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

[0007] Therefore, there is a need for a new method for spinning lignin fibers that enables the use of water and a non-toxic and low-cost solvent that is moisture-permissive. It is also desirable to produce lignin fibers having a higher carbon yield.

Means for Solving the Problems

[0008] In a first aspect, a method for producing fibers includes a step of preparing a spinning dope including a dope solvent, lignin dissolved in the dope solvent, and an additive polymer dissolved in the dope solvent, wherein the dope solvent includes an ionic liquid and water; and a step of extruding the spinning dope into a coagulation liquid to obtain one or more fibers, which is provided herein.

[0009] In a second aspect, fibers obtainable by the method of the first aspect are provided herein.

[0010] Embodiments of the present disclosure will now be described with reference to the drawings, which are merely examples.

Brief Description of the Drawings

[0011]

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DETAILED DESCRIPTION OF THE INVENTION

[0012] In a first aspect, a method for producing fibers, comprising the step of preparing a spinning dope comprising a dope solvent, lignin dissolved in the dope solvent, and an additive polymer dissolved in the dope solvent, wherein the dope solvent comprises an ionic liquid and water; and extruding the spinning dope into a coagulation bath to obtain one or more fibers, is provided herein.

[0013] The fibers produced by this method may also be referred to as lignin fibers. The fibers contain lignin and an additive polymer. The fibers can be used, for example, as precursor fibers for producing carbon fibers or as raw materials for other fiber-based materials.

[0014] The spinning dope contains lignin and an additive polymer both dissolved in a dope solvent. The spinning dope is preferably homogeneous and free of any undissolved components.

[0015] The dope solvent is a solvent in which lignin can be dissolved. Preferably, the dope solvent is a solvent in which cellulose has lower solubility than lignin. More preferably, the dope solvent does not dissolve cellulose.

[0016] The spinning dope preferably contains a cellulose loading rate of 10% or less based on the mass of the spinning dope excluding the masses of cellulose, lignin, and the additive polymer. Preferably, the cellulose loading rate is 5% or less, 2% or less, or 1% or less of cellulose. The spinning dope preferably does not substantially contain cellulose. Undissolved cellulose can be removed, for example, by filtration.

[0017] The dope solvent may have a water content of at least 5% by weight, such as 5 - 40% by weight, 10 - 40% by weight, or 20 - 40% by weight. The water content of the dope solvent is calculated based on the mass of water present relative to the total mass of the dope solvent (i.e., w / w%). The presence of water reduces the overall solvent cost and minimizes the energy requirements for drying the solvent. The dope solvent may further contain ethanol. The dope solvent may contain 0 - 20% by weight of ethanol, such as 1 - 20% by weight of ethanol, preferably 5 - 15% by weight of ethanol, calculated based on the total mass of the dope solvent (i.e., w / w%).

[0018] When the dope solvent contains ethanol, the ionic liquid:ethanol mass ratio may be 3:1 - 15:1, preferably 5:1 - 12:1.

[0019] The spinning dope may have a total loading rate of lignin and additive polymer of 6 to 60 wt%, 6 to 50 wt%, 6 to 40 wt% or 6 to 30 wt%, for example 8 to 23 wt%, preferably 11 to 20 wt%, more preferably 10 to 20 wt%, still more preferably 15 to 20 wt%, calculated based on the mass of the spinning dope excluding the mass of lignin and additive polymer. This may also be referred to as the solid loading rate. When the solid loading rate is even higher, the production cost can be reduced and the dope viscosity can be increased, which may be advantageous for high draw ratio spinning.

[0020] The weight ratio of lignin to polymer in the spinning dope may be at least 2:1 or at least 3:1, for example 2:1 to 10:1, preferably 3:1 to 9:1.

[0021] Lignin may be present in the spinning dope at a loading rate of at least 5 wt%, at least 7 wt% or at least 10 wt% based on the mass of the spinning dope excluding the mass of lignin and additive polymer. Lignin may preferably be present at a loading rate of 5 to 50 wt%, 5 to 40 wt%, 5 to 20 wt%, 5 to 30 wt% or 5 to 15 wt%. Lignin may preferably be present at a loading rate of 7 to 30 wt%, 7 to 20 wt%, or 7 to 15 wt% based on the mass of the spinning dope excluding the mass of lignin and additive polymer. Lignin may preferably be present at a loading rate of 10 to 50 wt%, 10 to 40 wt%, 10 to 30 wt%, 10 to 20 wt% or 10 to 15 wt% based on the mass of the spinning dope excluding the mass of lignin and additive polymer.

[0022] Lignin may be hardwood lignin, softwood lignin, grass lignin or other lignin (e.g., genetically modified lignin). Lignin may be hardwood lignin. Lignin may be ionoSolv lignin or kraft lignin, for example LignoBoost lignin.

[0023] The additive polymer may be present in the spinning dope at a loading rate of 1 to 10% by weight based on the weight of the spinning dope excluding the weights of the lignin and the additive polymer. The additive polymer may preferably be present at a loading rate of 1 to 5% by weight.

[0024] When calculated based on the mass of water present in the spinning dope with respect to the mass of the spinning dope excluding the masses of the lignin and the additive polymer, the spinning dope may have a water content of at least 5% by weight, for example 5 to 40% by weight, 10 to 40% by weight or 20 to 40% by weight.

[0025] The spinning dope may have a viscosity of 0.3 to 300,000, for example 0.3 to 100,000 or 0.3 to 2500 Pa·s at zero shear (when measured at the spinning temperature). The zero-shear rate viscosity is 3.00×10 -6 ~30 s -1 at a low shear rate, and can be measured using an AR 2000ex rheometer having a cone-and-plate geometry (cone tilt angle 2°, plate diameter 20 mm and gap 53 μm). The spinning dope may have a viscosity of 0.3 to 12 Pa·s in a shear range of 1 to 1000 s -1 when measured using an AR 2000ex rheometer having a cone-and-plate geometry (cone tilt angle 2°, plate diameter 20 mm and gap 53 μm) at a shear rate of 1 to 1000 s -1 and may have a viscosity of 0.3 to 6 Pa·s at a shear rate of about 183 s -1 The spinning temperature as referred to herein may refer to 25°C.

[0026] The additive polymer can be selected from poly(vinyl alcohol) (PVA), poly(vinyl acetate), poly(furfuryl alcohol), poly(acrylic acid), poly(ethylene oxide), poly(ethylene imine), poly(2-hydroxyethyl methacrylate), polyoxymethylene, and mixtures thereof. Preferably, the polymer is PVA. PVA can hydrogen bond with an ionic liquid, such as [DMBA][HSO4], to form a system-spanning PVA gel network. The network may include acid-catalyzed cross-linked polymer chains. The PVA network can act as a higher molecular weight structure and hydrogen bond with lignin to form a material that is no longer soluble in water. The mechanism of PVA gelation by hydrogen bonding in the presence of an ionic liquid, such as [DMBA][HSO4], has a great influence on the rheology of the dope solution and thus on the ability to wet-spin continuous fibers.

[0027] PVA may be partially hydrolyzed. For example, PVA may have a degree of hydrolysis (DH) of 72% or higher, such as 72 - 95% or 80 - 95%, preferably 85 - 90%, more preferably 86.7 - 88.7% hydrolyzed. PVA may be formed by the hydrolysis of poly(vinyl acetate) (PVAc). PVA may include partially hydrolyzed PVA in which some PVAc monomer units have not been hydrolyzed to PVA. The degree of hydrolysis is the mol% value of OH groups relative to the amount of PVA subunits (hydrolyzed and acetylated). The degree of hydrolysis can be measured by proton NMR spectroscopy.

[0028] The weight average molecular weight (M W ) of the additive polymer may be 60 - 200 kDa, preferably 80 - 190 kDa.

[0029] The ionic liquid can be any ionic liquid described herein. Preferably, the ionic liquid has a cation and C 1~20 alkyl sulfate ([alkylSO4] - )、C1~20 Alkyl sulfonate ([alkyl SO3] - ), hydrogen sulfate ([HSO4] - ), hydrogen sulfite ([HSO3] - ), dihydrogen phosphate ([H2PO4] - ), hydrogen phosphate ([HPO4] 2- ), chloride (Cl - ), bromide (Br - ), trifluoromethanesulfonate ([OTf] - ), formate ([HCOO] - ), and acetate ([MeCO2] - ), and contains an anion selected from. Preferably, the anion is [HSO4] - and [HCOO] - selected from.

[0030] The cation may be an aprotic cation or a protic cation, preferably a protic cation. The cation may contain a nitrogen-containing heterocyclic moiety, or a cation of formula I

[0031] [Chemical formula]

[0032] [wherein, A 1 ~ A 4 are each independently H, aliphatic, C 3~6 carbocyclic, C 6~10 aryl, alkylaryl, and heteroaryl selected from].

[0033] The ionic liquid may be an [alkylammonium][HSO4] or [alkylammonium][HCOO] ionic liquid.

[0034] The ionic liquid may be N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4]), 1-butylimidazolium hydrogen sulfate ([HBim][HSO4]), triethylammonium hydrogen sulfate ([TEA][HSO4]), N-methylbutylammonium hydrogen sulfate ([MBA][HSO4]), 1-methylimidazolium formate ([HMim][HCOO]), N,N-dimethylbutylammonium formate ([DMBA][HCOO]), or a mixture thereof.

[0035] The ionic liquid may be [DMBA][HSO4]. [DMBA][HSO4] has certain suitability in the extraction of lignin from lignocellulosic biomass fractions, while having a lower melting point (and thus viscosity) and an estimated production cost of approximately $1 / kg (similar to [TEA][HSO4]) compared to other ionic liquids containing hydrogen sulfate anions. Therefore, the production cost is lower than that of many ionic liquids and also lower than DMSO. Furthermore, ammonium-based hydrogen sulfate ILs may be recyclable.

[0036] In the method described herein, the fibers are formed using wet (coagulation) spinning. This involves extruding the spinning dope into a coagulation liquid to form the fibers. The coagulation liquid may be contained within a coagulation bath. The coagulation liquid may contain water, preferably deionized (DI) water. The coagulation liquid may consist essentially of water. Alternatively, the coagulation liquid may contain water and an ionic liquid. The ionic liquid may be any ionic liquid as described herein, preferably the same ionic liquid as that present in the dope solvent. The ionic liquid may be present in the coagulation liquid at 60 wt% or less, 30 wt% or less, or 15 wt% or less, preferably 1 - 60 wt%, 1 - 30 wt% or 1 - 15 wt%, more preferably 5 - 10 wt% (based on the total mass of the coagulation liquid). In a further alternative, the coagulation liquid contains water and sodium sulfate (Na2SO4). For example, the coagulation bath may contain an aqueous sodium sulfate solution at a concentration of 0.5 - 1.5 M, preferably about 1 M.

[0037] The methods described herein can utilize a coagulation time of at least 30 seconds, at least 45 seconds, at least 60 seconds, or at least 90 seconds, preferably at least 45 seconds. The coagulation time represents the residence time of the spinning dope in the coagulation liquid for forming the fibers. After the coagulation time, the fibers may be handled and / or collected from the coagulation liquid.

[0038] The spinning dope can be prepared by a process comprising: a) optionally preparing an ionic liquid as a mixture with water, adding an aqueous solution of an additive polymer, and optionally adding water to achieve a desired water content to prepare a solution of the additive polymer in the dope solvent; and b) adding lignin to the solution formed in step a) to dissolve the lignin and obtain the spinning dope.

[0039] The dissolution of lignin can be carried out at a temperature of 10°C to 200°C, preferably 10°C to 100°C, more preferably 20°C to 100°C, 20°C to 60°C, or 20°C to 30°C.

[0040] The method may further include the step of aging the spinning dope for at least 2 minutes, at least 5 minutes, at least 30 minutes, preferably 6 to 48 hours, more preferably 6 to 24 hours, prior to extrusion. The aging can be carried out at room temperature.

[0041] The spinning dope can be heated during aging, for example, at a temperature of 20°C to 90°C, 30°C to 90°C or 30°C to 60°C, or at least 30°C, at least 60°C, for example up to 150°C. The spinning dope can be heated for at least 2 minutes, at least 5 minutes, at least 30 minutes or 30 minutes to 10 hours, for example 1 to 6 hours, prior to extrusion (during aging). These heating periods may correspond to the aging period.

[0042] The method may further include a step of mixing the spinning dope for at least 2 minutes, at least 5 minutes, at least 30 minutes or from 30 minutes to 10 hours, such as 1 to 6 hours, during aging.

[0043] Mixing, heating and aging of the spinning dope before extrusion can be used to improve the spinnability of the spinning dope.

[0044] The fibers can be extruded using any suitable wet spinning process, for example using a continuous spinning line. The fibers can be extruded into a rotating bath. The rotating bath is a laboratory approach for spinning fibers from the dope and ensures continuous stretching. However, unlike a standard fiber spinning process using a continuous spinning line where different degrees of stretching can be achieved by varying the ratio of the spinning speed to the injection speed (stretching ratio), the use of a rotating bath limits the stretching because the maximum stretching obtained depends on the viscous force of the coagulating liquid.

[0045] When extended stretching can be achieved with a laboratory-type device, the size of the needle / 1-hole spinneret used to spin lignin fibers using a spinning line may be, for example, from 300 μm to 1 mm (inner diameter). When the stretching is limited, thinner needles (such as a 27G needle having an inner diameter of 210 μm) can be used to assist in the alignment of the polymer chains within the fiber and reduce the fiber diameter. For example, even thinner openings (such as needles) can be used in a continuous spinning line.

[0046] The spinning dope can be prepared by a process comprising: a) contacting a lignocellulosic biomass containing lignin and cellulose with a composition containing an ionic liquid and water to dissolve the lignin and produce cellulose pulp; b) separating the cellulose pulp to obtain a liquor containing the ionic liquid, water and lignin; and c) combining the liquor with an additive polymer to obtain the spinning dope. In step a), the lignin is dissolved while the cellulose is left undissolved to produce cellulose pulp. The ionic liquid is the same ionic liquid as that present in the dope solvent. Step c) of combining the liquor with the additive polymer may include combining the liquor with an aqueous solution of the additive polymer. The liquor produced in step b) may be concentrated before step c). The composition containing the ionic liquid and water (also referred to as the ionic liquid / water composition) mentioned in step (a) may contain a water content of 2 to 40 wt%, 5 to 40 wt%, 5 to 30 wt%, or 10 to 30 wt%. The ionic liquid / water composition may consist essentially of the ionic liquid and water. The water content mentioned in step (a) is calculated based on the mass of water present relative to the total mass of the ionic liquid / water composition. The biomass loading rate in step a) may be, for example, 10 to 50 wt% or 20 to 50 wt%, such as 30 to 40 wt%, relative to the mass of the ionic liquid / water composition. Steps (a) to (c) enable lignin extraction, spinning dope formation, and fiber formation without the need for another step to isolate and / or dry the lignin. This may be referred to as an integrated spinning process. This approach avoids the need to recycle the ionic liquid after lignin extraction. As a result, the ionic liquid only needs to be recycled once after fiber spinning. By avoiding lignin precipitation and drying the precipitated lignin and ionic liquid after the lignin precipitation step, this approach has the potential to reduce the cost of precursor fiber production.By completely solidifying lignin and the additive polymer onto the fibers, any residual hemicellulose components can be diffused from the lignin copolymer matrix, enabling the utilization of hemicellulose as acetic acid and furfural.

[0047] The lignocellulosic biomass contacted with the composition in step a) can be heated to a temperature of at least 70°C, preferably 100 - 180°C, more preferably 120 - 170°C. For example, the lignocellulosic biomass contacted with the composition can be heated to 120 - 150°C. The heating can be carried out for 1 minute to 22 hours, 10 minutes to 20 hours, 10 minutes to 10 hours, 15 minutes to 8 hours, or 30 minutes to 8 hours.

[0048] The biomass can be contacted with the composition and subjected to mechanical treatment, such as stirring or vortexing, to assist in the dissolution of lignin and the production of cellulose pulp. The mechanical treatment can be carried out before heating. Ethanol can be added to the mixture resulting from step a) before the separation of the cellulose pulp. The separation of the cellulose pulp can be carried out using filtration, such as vacuum filtration. The biomass can be subjected to mechanical treatment before being contacted with the composition.

[0049] The integrated spinning process results in the dissolution of lignin from the lignocellulosic biomass in the dope solvent, while avoiding the dissolution of cellulose. Other components of the lignocellulosic biomass, such as hemicellulose, can dissolve.

[0050] The spinning dope may contain additional solutes, which may be lignocellulosic biomass components, such as hemicellulose, or hemicellulose degradation products, such as furfural.

[0051] The method may further include a step of washing one or more fibers after extrusion. The washing can be carried out with water.

[0052] The method may further comprise the step of drying one or more fibers, preferably under mechanical tension. This step can be carried out after the washing step.

[0053] The method may further comprise the step of heating one or more fibers in air at 150 - 300 °C. This step can be carried out to thermally stabilize one or more fibers.

[0054] A fabric can be formed using the thermally stabilized fibers. Thus, the method may further comprise the step of weaving the thermally stabilized fibers to form a fabric.

[0055] The method may further comprise the step of carbonizing one or more fibers to obtain carbon fibers. Carbonization may include the step of heating one or more fibers to 800 - 3000 °C, preferably 1200 - 1800 °C, in an inert atmosphere. For example, carbonization can be carried out under nitrogen or argon, preferably nitrogen. Carbonization can be carried out using fibers under tension. Carbonization can be carried out after thermal stabilization.

[0056] In a second aspect, fibers obtainable by the method of the first aspect are provided herein. Ionic liquid The ionic liquids referred to herein may be, for example, ionic liquids as described in WO2012080702, WO2014140643 or WO2017085516, which are incorporated herein by reference.

[0057] As used herein, "ionic liquid" refers to ionized species (i.e., cations and anions). Ionic liquids typically have a melting point of less than about 100 °C. Any of the anions listed below can be used in combination with any of the cations listed below to produce ionic liquids for use in the present invention.

[0058] The ionic liquid may contain one of the listed anions, or a mixture thereof.

[0059] The anion is C 1~20 alkyl sulfate ([alkyl SO4] - ), C 1~20 alkyl sulfonate ([alkyl SO3] - ), hydrogen sulfate ([HSO4] - ), hydrogen sulfite ([HSO3] - ), dihydrogen phosphate ([H2PO4] - ), hydrogen phosphate ([HPO4] 2- ), chloride (Cl - ), bromide (Br - ), trifluoromethanesulfonate ([OTf] - ), formate ([HCOO] - ) and acetate ([MeCO2] - ), and may be selected from. For example, the anion is [MeSO4] - , [HSO4] - 、 [MeSO3] - , Cl - , [HCOO] - and [MeCO2] - , for example, chloride Cl - and hydrogen sulfate [HSO4] - , or from [MeSO4] - , [HSO4] - 、 [MeSO3] - , and [MeCO2] - , and may be selected from. Preferably the anion is selected from [HSO4] - and [HCOO] - . The ionic liquid may contain one of the listed anions, or a mixture thereof. The ionic liquid may contain any one of the cations identified herein, or a mixture thereof.

[0060] The cation is preferably a protonic cation ion. That is, the cation is a cation that can donate a proton (H + ).

[0061] The cation may be an ammonium or phosphonium derivative. These cations have the general formula

[0062]

Chemical formula

[0063] wherein [In the formula, X is N or P; A 1 ~A 4 are each independently selected from H, aliphatic, C 3~6 carbocyclic ring, C 6~10 aryl, alkylaryl, and heteroaryl. The aliphatic may be substituted with one or more -OH].

[0064]

[0065]

Chemical formula

[0066] wherein [In the formula, A 1 ~A 4 are each independently selected from H, aliphatic, C 3~6 carbocyclic ring, C 6~10 aryl, alkylaryl, and heteroaryl, and the aliphatic may be substituted with one or more -OH]. Preferably, at least one of A 1 ~A 4 is H. Preferably, at least one of A 1 ~A 4is independently selected from H and aliphatic. In one embodiment, A 1 ~A 4 at least one of is H, and the remaining three are each independently aliphatic. In another method, A 1 ~A 4 two of are each H, and the remaining two are each independently aliphatic. In another method, A 1 ~A 4 at least one of is aliphatic, and the remaining three are all H. Preferably, the cation is not ammonium (NH4 + ). That is, A 1 ~A 4 at least one of is not H. The aliphatic may be alkyl optionally substituted with one or more -OH, preferably C 1~6 alkyl. In some embodiments, the aliphatic is unsubstituted.

[0067] In one embodiment, the cation is alkylammonium or a mixture thereof (i.e., A 1 ~A 4 is independently selected from H or alkyl, A 1 ~A 4a cation of the above formula in which at least one of them is not H. Preferably, this is a protonated alkylammonium, but non-protonated alkylammonium can also be used. Optionally, one or more of the alkyl groups may be substituted with -OH to form an alkanolammonium, which may also be referred to as an alcoholammonium. For example, the cation may be choline. As used herein, "alkylammonium" includes trialkylammonium, dialkylammonium, monoalkylammonium, and alcoholammonium including trialkanolammonium, dialkanolammonium and monoalkanolammonium. Trialkylammonium includes trimethylammonium, triethylammonium, and triethanolammonium. Examples of dialkylammonium include diethylammonium, diisopropylammonium, and diethanolammonium. Monoalkylammonium includes methylammonium, ethylammonium, and monoethanolammonium. The ionic liquid may preferably be an [alkylammonium][HSO4] or [alkylammonium][HCOO] ionic liquid.

[0068] In one embodiment, the alkylammonium cation is selected from triethylammonium, diethylammonium, dimethylethylammonium, diethylmethylammonium, dimethylbutylammonium, diethanolammonium and choline. The alkylammonium cation may be selected from triethylammonium, diethylammonium, dimethylethylammonium, diethylmethylammonium, and dimethylbutylammonium, diethanolammonium. In another embodiment, the alkylammonium cation is selected from dimethylbutylammonium, triethylammonium and methylbutylammonium.

[0069] The cation may contain a nitrogen-containing heterocyclic moiety, which, as used herein, refers to a monocyclic or bicyclic ring system containing one nitrogen atom and optionally one or more additional heteroatoms selected from N, S, and O. The ring system contains 5 to 9 members, preferably 5 or 6 members, for a monocyclic group, and 9 or 10 members for a bicyclic group. The ring may be aromatic, partially saturated or saturated, and thus includes both "heteroalicyclic" groups meaning non-aromatic heterocycles and "heteroaryl" groups meaning aromatic heterocycles. The cation is

[0070]

Chemical formula

[0071] selected from [wherein R 1 and R 2 are independently a C 1~6 alkyl or a C 1~6 alkoxyalkyl group, and R 3 , R 4 , R 5 , R 6 , R 7 , R 8 and R 9 , when present, are independently H, a C 1~6 alkyl, a C 1~6 alkoxyalkyl group, or a C 2~6 alkyloxy group]. Preferably, R 1 and R 2 are C 1~4 alkyl, one of which is methyl, and R 3 to R 9 (R 3 , R 4 , R 5 , R 6 , R 7 , R 8 and R 9 ), when present, are H. In one embodiment, the cation ring is imidazolium or pyridinium.

[0072] In one embodiment, the cation may be an imidazolium-based cation or a mixture thereof, particularly a protonated imidazolium-based cation. In one embodiment, the imidazolium-based cation may be 1-butyl-3-methylimidazolium [BMim] + 、1-ethyl-3-methylimidazolium [EMim] + 、1-methylimidazolium [HMim] + 、1-butylimidazolium [HBim] + and mixtures thereof. For example, the imidazolium-based cation may be selected from 1-butyl-3-methylimidazolium [BMim] + 、1-methylimidazolium [HMim] + 、1-butylimidazolium [HBim] + and mixtures thereof, for example, 1-methylimidazolium [HMim] + 、1-butylimidazolium [HBim] + and mixtures thereof. In one embodiment, the imidazolium-based cation is selected from 1-butyl-3-methylimidazolium [BMim] + 、1-butylimidazolium [HBim] + and mixtures thereof.

[0073] In some embodiments, the cation includes protonated alkylammonium, protonated methylimidazolium, protonated pyridinium, aprotic tetraalkylammonium, and aprotic dialkylimidazolium ions.

[0074] The ionic liquid may preferably be N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4]), 1-butylimidazolium hydrogen sulfate ([HBim][HSO4]), triethylammonium hydrogen sulfate ([TEA][HSO4]), methylbutylammonium hydrogen sulfate ([MBA][HSO4]), 1-methylimidazolium formate ([HMim][HCOO]), N,N-dimethylbutylammonium formate ([DMBA][HCOO]), or a mixture thereof.

[0075] In one embodiment, the ionic liquid is not 1-ethyl-3-methylimidazolium acetate [EMim][OAc].

[0076] In another embodiment, the ionic liquid is selected from triethylammonium hydrogen sulfate ([TEA][HSO4]), N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4]), diethylammonium hydrogen sulfate ([DEA][HSO4]), N,N-dimethylethylammonium hydrogen sulfate ([DMEA][HSO4]), diethanolammonium chloride [DEtOHA]Cl, 1-methylimidazolium hydrogen chloride [HMim]Cl, 1-ethyl-3-methylimidazolium chloride [EMim]Cl, and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMim][OTf].

[0077] In another embodiment, the ionic liquid is selected from 1-butyl-3-methylimidazolium methyl sulfate [BMim][MeSO4], 1-butyl-3-methylimidazolium hydrogen sulfate [BMim][HSO4], 1-butyl-3-methylimidazolium methanesulfonate [BMim][MeSO3], 1-butylimidazolium hydrogen sulfate [HBim][HSO4], and 1-ethyl-3-methylimidazolium acetate [EMim][MeCO2].

[0078] Preferred ionic liquids are [alkylammonium][HSO4] ionic liquids, such as N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4]), triethylammonium hydrogen sulfate ([TEA][HSO4]), N-methylbutylammonium hydrogen sulfate ([MBA][HSO4]), diethylammonium hydrogen sulfate [DEA][HSO4], N,N-dimethylethylammonium hydrogen sulfate ([DMEA][HSO4]), and ethylammonium hydrogen sulfate [EA][HSO4].

[0079] The dope solvents referred to herein include ionic liquids and water. For use in the methods disclosed herein, an ionic liquid is provided such that the dope solvent can dissolve lignin. Preferably, cellulose has a lower solubility than lignin in the dope solvent. More preferably, the dope solvent does not dissolve cellulose.

[0080] An ionic liquid, optionally in a mixture with water, can be used to separate lignin and cellulose, for example, in preparing a spinning dope in an integrated spinning process, in the treatment of lignocellulosic biomass. Since the ionic liquid can dissolve the lignin in the biomass but not the cellulose, this treatment results in a cellulose pulp and a lignin solution. Thus, most of the cellulose, for example at least 70%, preferably at least 80% (weight % based on the oven-dry weight of the biomass), remains solid. The cellulose pulp can be easily removed mechanically from the lignin solution, for example, by filtration. Other components such as hemicellulose can also dissolve in the ionic liquid. For example, at least 70%, preferably at least 80% of the hemicellulose in the lignocellulosic biomass can dissolve in the ionic liquid.

[0081] When the ionic liquid is present as a mixture with water, this is x% / water y%It may be represented as, where the percentage is the mass of the component relative to the total mass of the mixture (i.e., w / w%). For example, [DMBA][HSO4] 60% / water 40% refers to a mixture of [DMBA][HSO4] and water in which [DMBA][HSO4] is present at 60% (w / w) (60% by weight) and water is present at 40% (w / w) (40% by weight).

[0082] Ionic liquids can be prepared by methods known to those skilled in the art or can be obtained commercially. For example, protonated ammonium-based ILs can be prepared in a one-step synthesis from simple alkylamines such as triethylamine and sulfuric acid, as described, for example, in George et al. (2015) "Design of low-cost ionic liquids for lignocellulosic biomass treatment" Green Chemistry 17: 1728-1739.

[0083] In ionic liquids, typically, the cations and anions are present in equimolar amounts. However, the ionic liquid may contain an excess of base, preferably a protonated base. As used herein, "base" refers to the base from which the cation is derived, such as an amine / imidazole. The ionic liquid may contain a 10% molar excess of base, for example, a 4-8%, 5-7.5% excess of base. The ionic liquid may contain a 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10% molar excess of base.

[0084] In another embodiment, the dope solvent further contains an acid in a 0.01-20% molar excess, preferably a 1-5% molar excess, as a percentage relative to the IL. The acid can be selected from any known strong acid, such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydroiodic acid, perchloric acid, and hydrobromic acid. Preferably the acid is sulfuric acid or hydrochloric acid or phosphoric acid. More preferably, the acid is the same acid used to synthesize the protonated IL.

[0085] It should be recognized that the features described throughout this disclosure can exist in any combination, provided the necessary modifications are made. For example, whenever a discussion of the components of a spinning dope or their loading rates is provided, these components can be present in any combination, and the loading rates can exist in any combination.

[0086] All publications, published patent documents, and patent applications cited herein are hereby incorporated by reference to the same extent as if each individual publication, published patent document, and patent application was specifically and individually indicated to be incorporated by reference. Definitions To make the present invention more readily understood, some terms are first defined below. Additional definitions for the following terms and other terms are set forth throughout this specification.

[0087] As used herein, the singular forms "a", "an", and "the" include the plural forms as well, unless the context clearly dictates otherwise. The use of the singular form includes the plural form unless specifically stated otherwise. The terms "comprising", "containing", and "including", and other forms (e.g., "include", "comprise", and "contain") are not limiting. Whenever the term "comprising" is referred to herein, this can also refer to "consisting essentially of" and "consisting of". For example, a dope solvent comprising an ionic liquid, water, and optionally ethanol can also be a dope solvent consisting essentially of an ionic liquid, water, and optionally ethanol.

[0088] As used herein, "dope solvent" refers to a solvent mixture in which lignin can dissolve. The dope solvent includes ionic liquids and water. This may include additional solvents, such as ethanol. All solvents present in the spinning dope can constitute the dope solvent (i.e., the spinning dope does not contain any solvents other than the dope solvent). The dope solvent may consist essentially of an ionic liquid, water, and optionally ethanol. Preferably, the dope solvent does not dissolve cellulose.

[0089] Various components are described as being present in the spinning dope at a certain percentage loading. The loading is a mass loading, which can be referred to as loading % or loading weight %. Usually, the loading is described relative to the mass of the spinning dope excluding the mass of lignin and additive polymers. The loading rate calculation for a spinning dope component (e.g., lignin or additive polymer) is: (Component mass / Mass of spinning dope excluding mass of lignin and additive polymers) × 100 In embodiments where the spinning dope consists essentially of a dope solvent (water, ionic liquid, and optionally ethanol), lignin, and additive polymers, the loading rate calculation is: (Mass of component / Dope solvent) × 100 As described herein, in some embodiments, the spinning dope may include additional solutes. In such embodiments, the loading rate calculation is: (Mass of component / Dope solvent + Additional solutes) × 100 is.

[0090] As used herein, "coagulant" is a liquid into which the spinning dope can be extruded. Extrusion of the spinning dope into the coagulant results in fiber formation.

[0091] As used herein, "additive polymer" is a polymer contained in a spinning dope to assist in the formation of lignin fibers. The additive polymer is not a polymer derived from lignocellulosic biomass. Thus, the additive polymer is not lignin, cellulose or hemicellulose, or a cellulose or hemicellulose derivative or degradation product (e.g., hemicellulose sugar).

[0092] As used herein, the term "solid loading" refers to the weight ratio of solids to solvent, expressed as a percentage. Thus, the solid loading of a spinning dope containing lignin and additive polymer dissolved in a dope solvent can be expressed as follows:

[0093] [Number]

[0094] [wherein, m lignin is the mass of lignin, m additive polymer is the mass of the additive polymer, and m dope solvent is the mass of the dope solvent].

[0095] Room temperature, as referred to herein, may refer to 25 °C.

[0096] As used herein, the term poly(vinyl alcohol) (PVA) includes fully hydrolyzed PVA and partially hydrolyzed PVA. The degree of hydrolysis is expressed as mol%. In the case of partially hydrolyzed PVA, some PVAc monomer units are not hydrolyzed to PVA. The degree of hydrolysis is the mol% value of OH groups relative to the amount of PVA subunits (hydrolyzed and acetylated). The degree of hydrolysis can be measured by proton NMR spectroscopy.

[0097] The molecular weight of the polymer can be defined as the weight average molecular weight (Mw) or the number average molecular weight (Mn). The molecular weight can be determined, for example, by gel permeation chromatography.

[0098] As used herein, the term "lignocellulosic biomass" refers to living or dead biomass and may include any cellulosic or lignocellulosic material, such as may contain cellulose, and optionally further hemicellulose, lignin, starch, oligosaccharides and / or monosaccharides, biopolymers, natural derivatives of biopolymers, mixtures thereof, and degradation products. This can also include additional components, such as proteins and / or lipids. The biomass may be derived from a single source or may include mixtures derived from more than one source. Some specific examples of biomass include, but are not limited to, bioenergy crops, agricultural residues, municipal solid waste, industrial solid waste, paper mill sludge, yard waste, wood and forestry waste. Additional examples of biomass include, but are not limited to, corn kernels, corn cobs, crop residues such as corn husks, corn stover, grasses including Miscanthus X giganteus, wheat, straw, hay, rice straw, switchgrass, paper waste, sugarcane bagasse, sorghum, soybeans, components obtained from the grinding of grains, trees (e.g., pine), branches, roots, leaves, wood chips, wood pulp, sawdust, shrubs and bushes, vegetables, fruits, flowers, animal manure, multi-component feeds, and crustacean biomass (i.e., chitinous biomass). It may be preferable to process the biomass before using it in the methods of the present invention. For example, the biomass can be mechanically processed, such as by grinding or crushing.

[0099] As used herein, "aging" refers to the period from after the spinning dope is prepared until before the dope is extruded. During aging, the dope can be maintained at room temperature or heated. During aging, the dope can be mixed. Aging can be carried out for at least 30 minutes, preferably up to 72 or 48 hours.

[0100] As used herein, the term "aliphatic" refers to straight-chain or branched-chain hydrocarbons that are either fully saturated or contain one or more unsaturated units. Thus, aliphatic can preferably be alkyl, alkenyl or alkynyl having 1 to 12 carbon atoms, preferably up to 6 carbon atoms, or more preferably up to 4 carbon atoms. Aliphatic can have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 carbon atoms.

[0101] As used herein, the term "alkyl" typically refers to a straight-chain or branched alkyl group or moiety containing 1 to 20 carbon atoms, such as 11, 12, 13, 14, 15, 16, 17, 18, or 19 carbon atoms. Preferably, the alkyl group or moiety contains 1 to 10 carbon atoms, i.e., 2, 3, 4, 5, 6, 7, 8, 9, or 10 carbon atoms, for example, C 1~4 alkyl or C 1~6 alkyl group or moiety, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl and t-butyl, n-pentyl, methylbutyl, dimethylpropyl, n-hexyl, 2-methylpentyl, 3-methylpentyl, 2,3-dimethylbutyl, and 2,2-dimethylbutyl.

[0102] As used herein, the term "carbocyclic ring" refers to a saturated or partially unsaturated cyclic group having 3 to 6 ring carbon atoms, i.e., 3, 4, 5, or 6 carbon atoms. The carbocyclic ring is preferably "cycloalkyl", which, as used herein, refers to a fully saturated hydrocarbon cyclic group. Preferably, the cycloalkyl group is a C3-C6 cycloalkyl group.

[0103] As used herein, the term "C 6~10 aryl group" means an aryl group composed of 6, 7, 8, 9, or 10 carbon atoms, and includes fused ring groups, such as monocyclic ring groups, or bicyclic ring groups and the like. Specifically, examples of "C 6~10 aryl group" include a phenyl group, an indenyl group, a naphthyl group, or an azulenyl group and the like. It should be noted that fused rings such as indane and tetrahydronaphthalene are also included in the aryl group.

[0104] As used herein, the term "alkylaryl" refers to an alkyl group as defined below, substituted with an aryl as defined above. The alkyl component of the "alkylaryl" group may be substituted with any one or more of the substituents listed above for aliphatic groups, and the aryl or heteroaryl component of the "alkylaryl" or "alkylheteroaryl" group may be substituted with any one or more of the substituents listed above for aryl, and carbocyclic groups. Preferably, the alkylaryl is benzyl.

[0105] As used herein, the term "heteroaryl" refers to a monocyclic or bicyclic aromatic ring system having 5 to 10 ring atoms, i.e., 5, 6, 7, 8, 9, or 10 ring atoms, and at least one ring atom is a heteroatom selected from O, N, or S.

[0106] When referred to in this specification, an aliphatic, aryl, heteroaryl, or carbocyclic group may be unsubstituted or substituted with one or more substituents independently selected from the group consisting of halo, C 1~6 alkyl, -NH2, -NO2, -SO3H, -OH, alkoxy, -COOH, or -CN.

[0107] As used herein, the term "halogen atom" or "halo" means a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, and the like, preferably a fluorine atom or a chlorine atom, more preferably a fluorine atom.

[0108] "C 2~6 Alkoxy" refers to an alkyl group of the above C that is bonded to an oxygen that is also bonded to a cationic ring. 1~6 "C 2~6 An alkoxyalkyl group" has the general formula X-O-Y (wherein X and Y are each independently C 1~5 alkyl, and the total number of carbon atoms is between 2 and 6, for example, 2, 3, 4, 5, or 6), and refers to an alkyl containing an ether group.

[0109] As used herein, the term "alkenyl" refers to a straight-chain or branched alkenyl group or moiety containing 2 to 20 carbon atoms, such as 11, 12, 13, 14, 15, 16, 17, 18, or 19 carbon atoms. Preferably, the alkenyl group or moiety contains 2 to 10 carbon atoms, that is, 2, 3, 4, 5, 6, 7, 8, 9, or 10 carbon atoms, for example, C 2~4 Alkenyl or C 2~6 An alkenyl group or moiety, for example, ethenyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, and 5-hexenyl.

[0110] As used herein, the term "alkynyl" refers to a straight or branched alkynyl group or moiety containing from 2 to 20 carbon atoms, for example, 11, 12, 13, 14, 15, 16, 17, 18, or 19 carbon atoms. Preferably, the alkynyl group or moiety contains from 2 to 10 carbon atoms, i.e., 2, 3, 4, 5, 6, 7, 8, 9, or 10 carbon atoms, for example, C 2~4 alkynyl or C 2~6 an alkynyl group or moiety, for example, ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl, 3-butynyl, 1-pentynyl, 2-pentynyl, 3-pentynyl, 4-pentynyl, 1-hexynyl, 2-hexynyl, 3-hexynyl, 4-hexynyl, and 5-hexynyl.

[0111] The present disclosure provides embodiments and implementations as presented in the following clauses: 1. A method for producing fibers, comprising: preparing a spinning dope comprising a dope solvent, lignin dissolved in the dope solvent, and an additive polymer dissolved in the dope solvent, wherein the dope solvent comprises an ionic liquid and water; extruding the spinning dope into a coagulation bath to obtain one or more fibers; and a method comprising the steps of. 2. The method according to clause 1, wherein the water content in the dope solvent is at least 5% by weight. 3. The method according to clause 1 or 2, wherein the water content in the dope solvent is from 5 to 40% by weight. 4. The method according to any one of the preceding clauses, wherein the water content in the dope solvent is from 10 to 40% by weight. 5. The method according to any one of the preceding clauses, wherein the water content in the dope solvent is from 20 to 40% by weight. 6. The method according to any one of the preceding clauses, wherein the spinning dope has a total loading rate of lignin and additive polymer of 6 to 60% by weight or 6 to 50% by weight based on the weight of the spinning dope excluding the weight of the lignin and additive polymer. 7. The method according to clause 6, wherein the total loading rate of lignin and the additive polymer is 6 to 40% by weight. 8. The method according to clause 6, wherein the total loading rate of lignin and the additive polymer is 6 to 30% by weight. 9. The method according to clause 6, wherein the total loading rate of lignin and the additive polymer is 8 to 23% by weight. 10. The method according to clause 6, wherein the total loading rate of lignin and the additive polymer is 11 to 20% by weight. 11. The method according to clause 6, wherein the total loading rate of lignin and the additive polymer is 10 to 20% by weight. 12. The method according to clause 6, wherein the total loading rate of lignin and the additive polymer is 15 to 20% by weight. 13. The method according to any one of the preceding clauses, wherein the weight ratio of lignin to the additive polymer in the spinning dope is at least 2:1. 14. The method according to clause 13, wherein the weight ratio of lignin to the additive polymer in the spinning dope is at least 2.5:1. 15. The method according to clause 14, wherein the weight ratio of lignin to the additive polymer in the spinning dope is at least 3:1. 16. The method according to clause 13, wherein the weight ratio of lignin to the additive polymer in the spinning dope is 2:1 to 15:1. 17. The method according to clause 16, wherein the weight ratio of lignin to the additive polymer in the spinning dope is 2:1 to 10:1. 18. The method according to clause 17, wherein the weight ratio of lignin to the additive polymer in the spinning dope is 2.5:1 to 10:1. 19. The method according to clause 18, wherein the weight ratio of lignin to the additive polymer in the spinning dope is 3:1 to 9:1. 20. The method according to any one of the preceding clauses, wherein lignin is present in the spinning dope at a loading rate of at least 5% by weight based on the mass of the spinning dope excluding the mass of lignin and the additive polymer. 21. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of at least 7% by weight. 22. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of at least 10% by weight. 23. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 5 to 50% by weight. 24. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 5 to 40% by weight. 25. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 5 to 30% by weight. 26. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 5 to 20% by weight. 27. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 5 to 15% by weight. 28. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 7 to 30% by weight. 29. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 7 to 20% by weight. 30. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 7 to 15% by weight. 31. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 10 to 50% by weight. 32. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 10 to 40% by weight. 33. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 10 to 30% by weight. 34. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 10 to 20% by weight. 35. The method according to clause 20, wherein lignin is present in the spinning dope at a loading rate of 10 to 15% by weight. 36. The method according to any of the preceding clauses, wherein the additive polymer is present in the spinning dope at a loading rate of 1 to 10% by weight based on the mass of the spinning dope excluding the mass of the lignin and the additive polymer. 37. The method according to clause 36, wherein the additive polymer loading rate is 1 to 5% by weight. 38. The method according to any of the preceding clauses, wherein the spinning dope has a water content of at least 5% by weight, calculated based on the mass of water present relative to the mass of the spinning dope excluding the masses of lignin and the additive polymer. 39. The method according to any of the preceding clauses, wherein the spinning dope has a water content of 5 - 40% by weight, calculated based on the mass of water present relative to the mass of the spinning dope excluding the masses of lignin and the additive polymer. 40. The method according to any of the preceding clauses, wherein the spinning dope has a water content of 5 - 40% by weight, calculated based on the mass of water present relative to the mass of the spinning dope excluding the masses of lignin and the additive polymer. 41. The method according to any of the preceding clauses, wherein the spinning dope has a water content of 10 - 40% by weight, calculated based on the mass of water present relative to the mass of the spinning dope excluding the masses of lignin and the additive polymer. 42. The method according to any of the preceding clauses, wherein the spinning dope has a water content of 20 - 40% by weight, calculated based on the mass of water present relative to the mass of the spinning dope excluding the masses of lignin and the additive polymer. 43. The method according to any of the preceding clauses, wherein the additive polymer is selected from poly(vinyl alcohol) (PVA), poly(vinyl acetate), polyfurfuryl alcohol, polyacrylic acid, polyethylene oxide, polyethyleneimine, poly(2-hydroxyethyl methacrylate), polyoxymethylene, and mixtures thereof. 44. The method according to any of the preceding clauses, wherein the additive polymer is PVA. 45. The method according to clause 44, wherein the PVA is partially hydrolyzed and has a degree of hydrolysis (DH) of 72% or higher. 46. The method according to clause 44, wherein the PVA is partially hydrolyzed and has a degree of hydrolysis (DH) of 72% - 95%. 47. The method according to clause 44, wherein the PVA is partially hydrolyzed and has a degree of hydrolysis (DH) of 80% - 95%. 48. The method according to clause 44, wherein the PVA is partially hydrolyzed and has a degree of hydrolysis (DH) of 85% to 90%. 49. The method according to clause 44, wherein the PVA is partially hydrolyzed and has a degree of hydrolysis (DH) of 86.7 to 88.7%. 50. The weight average molecular weight (M w ) of the additive polymer is 60 to 200 kDa, preferably 80 to 190 kDa, and the method according to any of the preceding clauses. 51. The weight average molecular weight (M w ) of the additive polymer is 80 to 190 kDa, and the method according to any of the preceding clauses. 52. The ionic liquid contains a cation and an anion, and the anion is C 1~20 alkyl sulfate ([alkylSO4] - ), C 1~20 alkyl sulfonate ([alkylSO3] - ), hydrogen sulfate ([HSO4] - ), hydrogen sulfite ([HSO3] - ), dihydrogen phosphate ([H2PO4] - ), hydrogen phosphate ([HPO4] 2- ), chloride (Cl - ), bromide (Br - ), trifluoromethanesulfonate ([OTf] - ), formate ([HCOO] - ) and acetate ([MeCO2] - ), and the method according to any of the preceding clauses. 53. The method according to clause 52, wherein the anion is selected from [HSO4] - and [HCOO] - . 54. The method according to any of the preceding clauses, wherein the ionic liquid contains a cation and an anion, and the cation is a protic cation. 55. The ionic liquid contains a cation and an anion, and the cation contains a nitrogen-containing heterocyclic moiety or the cation is a cation of formula I

[0112] [Chemical formula]

[0113] [wherein, A 1 ~A 4 are each independently H, aliphatic, C 3~6 carbocyclic ring, C 6~10 aryl, alkylaryl, and heteroaryl, respectively, selected from], the method according to any one of the preceding clauses. 56. The method according to any one of the preceding clauses, wherein the ionic liquid is an [alkylammonium][HSO4] or [alkylammonium][HCOO] ionic liquid. 57. The ionic liquid is triethylammonium hydrogen sulfate [TEA][HSO4], N,N-dimethylbutylammonium hydrogen sulfate [DMBA][HSO4], diethylammonium hydrogen sulfate [DEA][HSO4], N,N-dimethylethylammonium hydrogen sulfate ([DMEA][HSO4]), diethanolammonium chloride [DEtOHA]Cl, 1-methylimidazolium chloride [HMim]Cl, 1-ethyl-3-methylimidazolium chloride [EMim]Cl, and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMim][OTf], 1-butylimidazolium hydrogen sulfate ([HBim][HSO4]), methylbutylammonium hydrogen sulfate ([MBA][HSO4]), 1-methylimidazolium formate ([HMim][HCOO]), N,N-dimethylbutylammonium formate ([DMBA][HCOO]), N,N-dimethylethylammonium hydrogen sulfate ([DMEA][HSO4]), 1-butyl-3-methylimidazolium hydrogen sulfate [BMim][HSO4], or N,N-dimethylbutylammonium acetate ([DMBA][OAc]), or a mixture thereof, the method according to any one of the preceding clauses. 58. The method according to any of the preceding clauses, wherein the ionic liquid is N,N-dimethylethylammonium hydrogen sulfate ([DMEA][HSO4]), N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4]), 1-butylimidazolium hydrogen sulfate ([HBim][HSO4]), triethylammonium hydrogen sulfate ([TEA][HSO4]), methylbutylammonium hydrogen sulfate ([MBA][HSO4]), 1-methylimidazolium formate ([HMim][HCOO]), N,N-dimethylbutylammonium formate ([DMBA][HCOO]), 1-methylimidazolium hydrogen chloride [HMim]Cl, N,N-dimethylbutylammonium chloride [DMBA]Cl, 1-butyl-3-methylimidazolium hydrogen sulfate [BMim][HSO4], or N,N-dimethylbutylammonium acetate ([DMBA][OAc]), or a mixture thereof. 59. The method according to any of the preceding clauses, wherein the ionic liquid is N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4]), 1-butylimidazolium hydrogen sulfate ([HBim][HSO4]), triethylammonium hydrogen sulfate ([TEA][HSO4]), methylbutylammonium hydrogen sulfate ([MBA][HSO4]), 1-methylimidazolium formate ([HMim][HCOO]), N,N-dimethylbutylammonium formate ([DMBA][HCOO]), 1-methylimidazolium hydrogen chloride [HMim]Cl, N,N-dimethylbutylammonium chloride [DMBA]Cl, 1-butyl-3-methylimidazolium hydrogen sulfate [BMIM][HSO4], or N,N-dimethylbutylammonium acetate ([DMBA][OAc]), or a mixture thereof. 60. The method according to any of the preceding clauses, wherein the ionic liquid is N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4]), 1-butylimidazolium hydrogen sulfate ([HBim][HSO4]), triethylammonium hydrogen sulfate ([TEA][HSO4]), methylbutylammonium hydrogen sulfate ([MBA][HSO4]), 1-methylimidazolium formate ([HMim][HCOO]), or N,N-dimethylbutylammonium formate ([DMBA][HCOO]), or a mixture thereof. 61. The method according to any of the preceding clauses, wherein the ionic liquid is [DMBA]Cl, [DMBA][HSO4], [BMim][HSO4], [MBA][HSO4] or [HBim][HSO4], or a mixture thereof. 62. The method according to any of the preceding clauses, wherein the ionic liquid is [DMBA][HSO4]. 63. The method according to any of the preceding clauses, wherein the doping solvent further contains ethanol. 64. The method according to clause 63, wherein ethanol is present at 1 to 20% by weight based on the total weight of the doping solvent. 65. The method according to clause 64, wherein ethanol is present at 5 to 15% by weight. 66. The method according to any of clauses 63 to 65, wherein the mass ratio of ionic liquid:ethanol is 3:1 to 15:1. 67. The method according to clause 66, wherein the mass ratio of ionic liquid:ethanol is 5:1 to 12:1. 68. The method according to any of the preceding clauses, wherein the coagulation liquid contains water. 69. The method according to any of the preceding clauses, wherein the coagulation liquid contains water and an ionic liquid, and the ionic liquid is present at 60% by weight or less based on the total mass of the coagulation liquid. 70. The method according to any of the preceding clauses, wherein the coagulation liquid contains water and an ionic liquid, and the ionic liquid is present at 30% by weight or less based on the total mass of the coagulation liquid. 71. The method according to any of the preceding clauses, wherein the coagulation liquid contains water and an ionic liquid, and the ionic liquid is present at 15% by weight or less based on the total mass of the coagulation liquid. 72. The method according to any one of the preceding clauses, wherein the coagulating liquid contains water and an ionic liquid, and the ionic liquid is present in an amount of 1 to 60% by weight based on the total mass of the coagulating liquid. 73. The method according to any one of the preceding clauses, wherein the coagulating liquid contains water and an ionic liquid, and the ionic liquid is present in an amount of 1 to 30% by weight based on the total mass of the coagulating liquid. 74. The method according to any one of the preceding clauses, wherein the coagulating liquid contains water and an ionic liquid, and the ionic liquid is present in an amount of 1 to 15% by weight based on the total mass of the coagulating liquid. 75. The method according to any one of the preceding clauses, wherein the coagulating liquid contains water and an ionic liquid, and the ionic liquid is present in an amount of 5 to 15% or 5 to 10% by weight based on the total mass of the coagulating liquid. 76. The method according to any one of the preceding clauses, wherein the coagulating liquid contains water and sodium sulfate. 77. The method according to clause 76, wherein the coagulation bath contains an aqueous sodium sulfate solution at a concentration of 0.5 to 1.5 M. 78. The method according to any one of the preceding clauses, wherein the spinning dope is prepared by a process comprising: a) optionally preparing an ionic liquid with a mixture with water, adding an aqueous solution of an additive polymer, and optionally adding water to achieve a desired water content to prepare a solution of the additive polymer in the dope solvent; and b) adding lignin to the solution formed in step a) to dissolve the lignin and obtain the spinning dope. 79. The method according to clause 78, wherein the dissolution of lignin is carried out at a temperature of 10°C to 200°C, preferably 10°C to 100°C. 80. The method according to clause 78, wherein the dissolution of lignin is more preferably carried out at a temperature of 20°C to 100°C, 20°C to 60°C or 20°C to 30°C. 81. The method according to any one of the preceding clauses, wherein the spinning dope further comprises an aging step for at least 2 minutes before extrusion. 82. The method according to any one of the preceding clauses, wherein the spinning dope further comprises an aging step for at least 5 minutes before extrusion. 83. The method according to any of the preceding clauses, further comprising the step of aging the spinning dope for at least 30 minutes before extrusion. 84. The method according to any of the preceding clauses, further comprising the step of aging the spinning dope for 6 to 48 hours before extrusion. 85. The method according to any of the preceding clauses, further comprising the step of aging the spinning dope for 6 to 24 hours before extrusion. 86. The method according to any one of clauses 81 to 85, wherein the spinning dope is heated at a temperature of 20°C to 90°C during aging. 87. The method according to any one of clauses 81 to 85, wherein the spinning dope is heated at a temperature of 30°C to 90°C during aging. 88. The method according to any one of clauses 81 to 85, wherein the spinning dope is heated at a temperature of 30°C to 60°C during aging. 89. The method according to any one of clauses 81 to 85, wherein the spinning dope is heated at a temperature of at least 30°C during aging. 90. The method according to any one of clauses 81 to 85, wherein the spinning dope is heated at a temperature of at least 60°C during aging. 91. The method according to any one of clauses 81 to 90, wherein the spinning dope is heated at a temperature up to 150°C during aging. 92. The method according to any one of clauses 86 to 91, wherein the spinning dope is heated for at least 2 minutes. 93. The method according to any one of clauses 86 to 91, wherein the spinning dope is heated for at least 5 minutes. 94. The method according to any one of clauses 86 to 91, wherein the spinning dope is heated for at least 30 minutes. 95. The method according to any one of clauses 86 to 91, wherein the spinning dope is heated for 30 minutes to 6 hours. 96. The method according to any one of clauses 86 to 91, wherein the spinning dope is heated for 1 to 10 hours. 97. The method according to any one of clauses 81 to 96, wherein the spinning dope is mixed for at least 2 minutes before extrusion. 98. The method according to any one of clauses 81 to 96, wherein the spinning dope is mixed for at least 5 minutes before extrusion. 99. The method according to any one of clauses 81 to 96, wherein the spinning dope is mixed for at least 30 minutes before extrusion. 100. The method according to any one of clauses 81 to 96, wherein the spinning dope is mixed for 30 minutes to 10 hours before extrusion. 101. The method according to any one of clauses 81 to 96, wherein the spinning dope is mixed for 1 to 6 hours before extrusion. 102. The step of preparing the spinning dope comprises a) contacting a lignocellulosic biomass containing lignin and cellulose with a composition containing an ionic liquid and water to dissolve the lignin and produce cellulose pulp; b) separating the cellulose pulp to obtain a liquor containing the ionic liquid, water and lignin; c) combining the liquor with an additive polymer to obtain a spinning dope, the method according to any preceding clause. 103. The method according to clause 102, wherein step c) of combining the liquor with the additive polymer may include combining the liquor with an aqueous solution of the additive polymer. 104. The method according to clause 102, wherein the composition containing the ionic liquid and water has a water content of 5 to 40% by weight. 105. The method according to clause 102, wherein the composition containing the ionic liquid and water has a water content of 5 to 30% by weight. 106. The method according to clause 102, wherein the composition containing the ionic liquid and water has a water content of 10 to 30% by weight. 107. The method according to any one of clauses 102 to 106, wherein the lignocellulosic biomass contacted with the composition is heated to 100 to 180 °C. 108. The method according to any one of clauses 102 to 106, wherein the lignocellulosic biomass contacted with the composition is heated to 120 to 170 °C. 109. The method according to any one of clauses 102 to 106, wherein the lignocellulosic biomass contacted with the composition is heated to 120 to 150 °C. 110. The method according to any one of clauses 102 to 109, wherein the lignocellulosic biomass is contacted with the composition for 1 minute to 22 hours. 111. The method according to any one of clauses 102 to 109, wherein the lignocellulosic biomass is contacted with the composition for 10 minutes to 22 hours. 112. The method according to any one of clauses 102 to 109, wherein the lignocellulosic biomass is contacted with the composition for 10 minutes to 10 hours. 113. The method according to any one of clauses 102 to 109, wherein the lignocellulosic biomass is contacted with the composition for 15 minutes to 8 hours. 114. The method according to any one of clauses 102 to 109, wherein the lignocellulosic biomass is contacted with the composition for 30 minutes to 8 hours. 115. The method according to any preceding clause, further comprising a step of washing one or more fibers after extrusion, and optionally, the washing is carried out with water. 116. The method according to any preceding clause, further comprising a step of drying one or more fibers. 117. The method according to any preceding clause, further comprising a step of drying one or more fibers under mechanical tension. 118. The method according to any preceding clause, further comprising a step of heating one or more fibers in air. 119. The method according to clause 118, comprising a step of heating one or more fibers in air at 150 to 300 °C. 120. The method according to clause 118 or 119, further comprising a step of weaving the fibers to form a cloth. 121. The method according to any preceding clause, further comprising the step of carbonizing one or more fibers to obtain carbon fibers. 122. The method according to clause 121, wherein the carbonization comprises the step of heating one or more fibers to 800 - 3000 °C in an inert atmosphere. 123. The method according to clause 122, wherein the carbonization comprises the step of heating one or more fibers to 1200 - 1800 °C in an inert atmosphere. 124. The method according to any one of clauses 121 to 123, wherein the carbonization is carried out on fibers under tension. 125. The method according to any preceding clause, wherein the spinning dope comprises a cellulose loading rate of 10 wt% or less based on the mass of the spinning dope excluding the mass of cellulose, lignin and additive polymer. 126. The method according to any preceding clause, wherein the spinning dope comprises a cellulose loading rate of 5 wt% or less. 127. The method according to any preceding clause, wherein the spinning dope comprises a cellulose loading rate of 4 wt% or less. 128. The method according to any preceding clause, wherein the spinning dope comprises a cellulose loading rate of 1 wt% or less. 129. Fibers obtainable by the method according to any of the preceding clauses. 130. Fibers obtained by the method according to any of the preceding clauses. 131. A cloth comprising the fibers according to one or more of clauses 129 or 130.

[0114] Here, the present invention will be described with reference to the following examples and the accompanying drawings, which exist only for illustrative purposes and should not be construed as a limitation to the present invention.

Examples

[0115] Materials and Methods The wood of willow (cultivar Endurance) was obtained from Agri-food & Biosciences Institute, UK, and the wood of eucalyptus (Eucalyptus grandis, also known as Red Grandis) was purchased from W. L. West & Sons Ltd. The willow and eucalyptus biomass were ground to a particle size of less than 1 cm using a cutting mill (Retch SM 2000) and stored in plastic bags to protect from sunlight. The moisture content of the biomass was determined by measuring the mass loss in triplicate during drying at 105 °C for at least 24 hours.

[0116] Softwood kraft lignin was obtained from Research Institute of Sweden (described as softwood kraft lignin 1) and Sigma Aldrich (Lignin Alkali, described as softwood kraft lignin 2). N,N-dimethylbutylamine (purity >99%) was purchased from Sigma Aldrich, and 66.3% sulfuric acid solution was purchased from VWR. Poly(vinyl alcohol) (PVA) was purchased from Kuraray Poval (No.13-88, 88% hydrolysis, ~100 kDa). All reagents were used as received.

[0117] Optical microscopy (OM) Optical microscope images of the dopes were taken with a DM2500 microscope equipped with a Basler Ace acA1920 camera. Samples were prepared by drawing the solution into a syringe through a needle and subsequently depositing small drops from the needle onto a glass slide. The samples were covered with a cover glass and imaged. Cross polarizers were used to identify birefringent particles.

[0118] Viscosity The viscosity of the lignin / PVA solution was measured at room temperature using an AR 2000ex rheometer with a cone-and-plate geometry (cone angle 2°, plate diameter 20 mm and gap 53 μm) from 1 to 1000 s -1It was measured using a shear rate of

[0119] Scanning electron microscope (SEM) The SEM images of the lignin-PVA fibers were recorded with a JEOL JSM-6010LA. The fibers were disassembled one by one using tweezers and placed on an aluminum support using carbon adhesive tape. The sample was sputter-coated with chromium before imaging. The acceleration voltage used was 20 kV.

[0120] Tensile test The tensile strength and stiffness of the lignin-PVA precursor and carbon fiber samples were determined using the standard test method ISO BSI11566. A single filament was placed on a card template (15 mm gauge) using an epoxy adhesive (Araldite Rapid, Huntsman Corporation, US). The sample was tested at 16.7 μm s -1 using a tensile testing machine (Linkam Scientific Ltd. GB) equipped with a 20 M load cell until failure. The tensile modulus of elasticity was determined from the linear region between 0.2% and 0.5% strain. The cross-sectional area of the sample was measured using an optical microscope.

[0121] Thermogravimetric analysis (TGA) Thermogravimetric analysis (TGA) was performed using a thermogravimetric analyzer (Mettle Toledo TGA / DSC 1LF / UMX) to predict the carbon yield of the precursor fibers. To determine the carbon yield of the precursor fibers, the sample was heated in a platinum pan from 25 °C to 100 °C at 10 °C min -1 in a nitrogen flow, held at a constant temperature for 30 minutes at 100 °C to drive out the moisture, and then the temperature was ramped up to 900 °C at 10 °C min -1 The weight loss during thermal stabilization was also determined using a thermogravimetric analyzer (Mettle Toledo TGA / DSC 1LF / UMX). For carbonization, the sample was heated in a platinum pan at 10 °C min -1Heated from 25 °C to 100 °C with a nitrogen flow, held at a constant temperature of 100 °C for 30 minutes to drive off moisture, and the temperature was ramped to 900 °C at 10 °C / min -1 For thermal stabilization, the fiber samples were heated in air at 1 °C / min from 25 to 100 °C and at 0.2 °C / min from 100 to 250 °C, followed by holding at 250 °C for 1 hour. The air / N2 flow rate was 50 mL / min.

[0122] Raman spectroscopy The graphite order in lignin-derived CF was investigated by Raman spectroscopy using a Renishaw inVia micro-Raman spectrometer with a 532 nm (2.33 eV) DPSS diode laser. Raman spectra in the range of 80 - 3200 cm -1 were collected using software WiRE 4.1 and averaged for at least 5 different positions along the CF surface. The intensity ratio (IG / ID) of the D-mode (1350 cm -1 ) to the G-mode (1582 cm -1 ) was measured using Lorentzian fitting with WiRE 4.1 software after fitting the D- and G-bands.

[0123] [Example 1] Synthesis of ionic liquid The ionic liquid [DMBA][HSO4] was synthesized from N,N-dimethylbutylamine and 66.3% sulfuric acid solution in a custom-made flow reactor. All reagents were used as received. The precursors were cooled and pumped into the stirred flow reactor at a flow rate of 5 ml / min for the acid and 7.8 ml / min for the base. The acid / base ratio of the produced IL was checked in triplicate using an automatic titrator (Mettler Toledo G205), and the HSO4− anion was titrated with an aqueous NaOH solution. To correct the acid / base ratio, a calculated amount of dimethylbutylamine or 66.3% sulfuric acid was gradually added to the IL cooled in an ice bath. The water content of the IL was adjusted if necessary: first, the water content was reduced by a rotary evaporator and then measured in triplicate using a volumetric Karl Fischer titrator (Mettler Toledo V20). The final water content of the IL was confirmed using a Karl Fischer volumetric titrator.

[0124] [Example 2] ionoSolv lignin extraction Lignin extraction was carried out according to the ionoSolv pretreatment procedure (Gschwend, F. J. v. et al. Journal of Visualized Experiments 2016, 2016 (114), 4 - 9). 30 g (dry basis) of biomass was added to a 200 mL pressure tube (Ace Glass pressure tube, front sealing), followed by [DMBA][HSO4] 80% / water 20%150 g was added. The biomass and IL were thoroughly mixed with a vortex shaker (VWR) until all biomass particles were in contact with the IL. The pressure tube was placed in a preheated oven at 170 °C for 1 h. After the pretreatment, the mixture was transferred from the pressure tube to a 1000 mL glass bottle and subsequently mixed with 600 mL of anhydrous ethanol (EtOH), shaken well, and left to rest at room temperature for 1 h. After 1 h, the mixture was separated using vacuum filtration into a cellulose-rich solid and a liquid (liquor) containing the dissolved biomass components including the ionic liquid, water, ethanol, and lignin. The cellulose was air-dried. The washing step was repeated three times. Each time, the liquor was collected. Using a rotary evaporator, most of the water and EtOH contained in the IL solvent were evaporated from the combined liquor fractions. To precipitate the lignin, 400 mL of deionized water (acting as a poor solvent) was added to the re-concentrated liquid, the mixture was transferred to a 500 mL centrifuge tube (Corning (registered trademark)), shaken well using a vortex shaker, left to rest for 1 h, and then centrifuged (Megastar 3.0, VWR, UK; 3000 rpm, 50 min). The supernatant was decanted. The precipitate was washed three times with deionized water and then the lignin was lyophilized for 2 days. The dried lignin and air-dried cellulose pulp were weighed on aluminum foil to determine the lignin and pump yields (the water content of the pulp was measured separately and subtracted from the air-dried yield). The fractionation was performed in triplicate.

[0125] [Example 3] Preparation of the spinning dope Poly(vinyl alcohol) stock solution, PVA (水溶液) , and the spinning dope were prepared on the day of the fiber spinning experiment. The PVA (水溶液) weight fraction in the PVA depended on the desired solid loading, water content, and lignin / PVA weight ratio in the dope, as well as the water content in the ionic liquid. The required PVA loading in deionized (D.I.) water for preparing the PVA (水溶液) was calculated using Equation (1):

[0126] [Number]

[0127] [wherein, W p / w = weight ratio of PVA to water in the PVA solution (i.e., PVA loading rate); W sl / sv = desired weight ratio of the solid to the solvent (solid loading rate); W l / P = desired weight ratio of lignin to PVA; W w、IL = water fraction of water in IL; W w、sv = desired weight fraction of water in the solvent]. Note that in this case, the solvent is a mixture of IL and water with the desired water content.

[0128] The amounts of PVA (水) solution and lignin to be added to IL were calculated by the following formulas (2) and (3):

[0129] [Number]

[0130] [wherein,

[0131] [Number]

[0132] = weight of PVA (aqueous solution) to be added, WIL = weight of IL to be added];

[0133] [Number]

[0134] [wherein, W lig = weight of lignin to be added].

[0135] To prepare the PVA solution, PVA flakes were slowly added to a pre-weighed 50 ml round-bottom flask equipped with a stir bar, and then deionized water was added while stirring at room temperature. The solution was mixed at room temperature for 15 minutes, then the temperature was raised to 85 °C and stirred for 1 hour until the polymer flakes dissolved. The round-bottom flask was weighed again to monitor water loss. For example (by equations (2) and (3)), to prepare a spinning dope having a solids loading of 16% (lignin / PVA = 3:1), 1.5 g of IL (4 wt% water content) was added to a 10 mL round-bottom flask equipped with a stir bar. The newly prepared PVA (水) solution (1 g, 10.67 wt%) was added to the IL and mixed on a hot plate at 60 °C for 5 minutes while stirring at 700 rpm. 0.288 g of lignin was slowly added to the PVA / IL / water mixture and the solution was mixed at 60 °C for 1 hour. Three dopes with different lignin / PVA ratios were prepared to have different lignin contents in the fibers (see Table 1).

[0136] [Table 1]

[0137] [Example 4] Spinning of fibers The dope solution was aspirated using a 1 mL plastic syringe without a needle and added to a 1 mL glass syringe (Hamilton® syringe, 1000 series GASTIGHT®, PTFE luer lock) via the plunger tip with the plunger removed. The plunger was inserted, and the syringe was held vertically with the plunger down to remove any air bubbles through the upper opening, during which the plunger was carefully pushed. A Z-shaped 27-gauge (inner diameter 0.21 mm) cannula (Central Surgical UK) was attached to the syringe. The dope solution (about 0.5 mL) was extruded into a coagulation bath (1 M Na2SO4 solution or deionized water) placed on a rotating table at 9 RPM using a syringe pump (KDS LEGATO(TM) 100, KD Scientific, US). The extrusion rate was 0.6 mL / h or 1.5 mL / h. The bath was rotated at 7.5 cm / s at the injection point to obtain an elongational flow during fiber coagulation. The theoretical ratio of the rotational speed of the coagulant fluid (at the injection point) to the injection rate was 15.6. However, due to the limited viscous forces of the coagulant, the stretching was limited and not achieved without reaching the theoretical stretch ratio. This was because the fiber was pulled towards the center of the bath where the rotational speed was quite low. The fiber was immersed in a coagulation bath containing 1 M Na2SO4 or water for 30 minutes. The fiber coagulated in 1 M Na2SO4 was transferred to another water bath for 30 minutes for washing (this step is not required if the fiber is coagulated in water). The fiber was hung on a rod under a tension (about 4 mN) from a known weight attached to the lower end of the fiber and air-dried overnight at room temperature (25°C).

[0138] [Example 5] Stabilization and Carbonization For thermal stabilization, air-dried lignin-PVA precursor fibers were vertically hung under tension (a weight of approximately 5.5 mN) during thermal stabilization. The precursor fibers were heated in a convection oven (Memmert UNP-200) using air as the gas atmosphere at a rate of 1 °C / min from 25 to 100 °C and 0.2 °C / min from 100 to 250 °C, and then stabilized by holding at 250 °C for 1 hour. Carbonization was carried out in a quartz tube furnace (OTF-1200X-III-S-NT) under a N2 flow (50 mL / min) by heating at a rate of 1 °C / min from 25 to 1000 °C and then holding at 1000 °C for 2 hours.

[0139] [Example 6] Effect of Dope Preparation Temperature and Fiber Extrusion Rate Generally, the dope for lignin fiber spinning is prepared in the temperature range from room temperature to 60 °C. In this example, the dope was prepared at three different temperatures (30 °C, 45 °C, and 60 °C). Regardless of the preparation temperature, the dope was homogeneous. The dope preparation temperature affected the dope viscosity, and this effect was independent of the type of lignin. The viscosities of dopes containing eucalyptus ionoSolv lignin (extracted and isolated in the laboratory) or commercially available softwood kraft lignin were measured. As can be seen in Figure 1, as the dope preparation temperature increased, the dope viscosity increased. This was contrary to the prediction that heating of the solution would decrease the viscosity of the solution. This may be an indication of the condensation reaction between lignin and PVA catalyzed by the acidic environment (i.e., [DMBA][HSO4] 60% / water 40% ) during dope preparation. No such increase in viscosity was observed in control solutions such as lignin and PVA solutions.

[0140] During fiber spinning, the estimated shear rate generated by the dope flow through a 27G needle at 0.6 ml / h is approximately 183 s according to Equation 4 -1 assuming Newtonian behavior.

[0141] [Number]

[0142] [where γ w is the shear rate of the needle wall, Q is the volumetric flow rate through the needle, and r is the radius of the needle].

[0143] According to rheology measurements (Figure 1), at a shear rate of 183 s -1 , the dope containing eucalyptus ionoSolv lignin (hardwood lignin) undergoes observable shear thinning, while the dope containing softwood kraft lignin undergoes only Newtonian flow or slight shear thinning. This indicates that at the applied extrusion speed, the more viscous ionoSolv lignin-containing dope results in more polymer alignment, while less alignment was observed in the softwood kraft lignin-containing dope, because there was no measurable decrease in viscosity compared to a lower shear rate. An increase in the extrusion speed up to above 1.2 ml / h (equivalent to 366 s -1 ) could promote more polymer alignment during fiber spinning for the softwood kraft lignin dope, which could be advantageous.

[0144] Na2SO 4(水溶液) Stable fiber spinning was achieved at all tested temperatures (30, 45, and 60 °C) at different extrusion speeds (0.6 ml / h and 1.5 ml / h) in Na2SO, and almost no difference was observed in the fiber morphology when changing the dope preparation temperature and extrusion speed. All fibers extruded from dopes prepared at different temperatures show a smooth surface and a circular cross-section with a uniform diameter along the fiber. An increase in the dope preparation temperature was observed to increase the fiber diameter (Figure 2), which is due to the increase in viscosity of the dope prepared at a higher temperature (Figure 1). An increase in the extrusion speed also increased the fiber diameter because the effective draw ratio decreased (Figure 2).

[0145] A common strategy for enhancing the mechanical properties of fibers is to reduce the fiber diameter, as this decreases the number of defects that introduce a focus on early failure under tension in each fiber. In this study, the fiber diameter decreased when the dope was prepared at a lower temperature and the fibers were extruded at a lower extrusion rate, but there was little change in the fiber tensile strength (Figure 3). This indicates that fiber breakage is related not only to defect induction but also to the microstructure. At a higher extrusion rate of 1.5 ml / h, the shear rate calculated for the dope flow within the needle was approximately 458 s -1- -1, suggesting more significant shear thinning behavior than during extrusion at 0.6 ml / h (Figure 1). The faster the extrusion rate, the more the polymer aligns while flowing within the needle. The increase in alignment can account for the compensation of the strength decrease caused by the increase in fiber diameter.

[0146] When the dope was prepared at 60 °C, the elastic modulus of the precursor fibers increased regardless of the extrusion rate (Figure 3). When the dope was prepared at 60 °C, the elastic modulus of the fibers extruded at 0.6 mL / h reached 4.5 GPa. As can be seen in Figure 1, the increase in dope viscosity due to the higher dope preparation temperature led to an increase in shear thinning. This promotes polymer alignment, which results in an improvement in the fiber elastic modulus. Additionally, a high-viscosity dope can form denser fibers, which can also lead to an increase in the fiber elastic modulus. In this study, it was also observed that extruding the fibers at a lower rate improved the elastic modulus, particularly when the dope was prepared at a high temperature. Despite the low shear within the needle at a lower extrusion rate, the overall effect of the lower extrusion rate was positive in combination with the higher dope preparation temperature. In the following study, the dope preparation temperature was set at 60 °C and the extrusion rate was set at 0.01 ml / min. The preparation of the dope at 60 °C for 1 hour was used for different lignin species (both ionoSolv and kraft lignin).

[0147] [Example 7] Effect of Lignin Content and Dope Aging Time The carbon yield in lignin (about 40%) is higher than that in PVA (<10%). Therefore, by maximizing the lignin content in the precursor fiber, the carbon yield should be improved, and thus the cost should be reduced. The dopes were prepared at lignin / PVA ratios of 3:1 to 9:1 (corresponding to lignin contents in the fibers of 75 - 90%, Table 1). As confirmed by optical microscopy, the dopes were homogeneous at lignin / PVA ratios of 3:1 to 9:1. Compared to the molar weight of PVA used (Mw about 100 kDa), the lignin molar weight is lower than that of PVA n (ionoSolv eucalyptus lignin Mn about 1000 Da, Mw about 3000, willow lignin Mn about 1000 Da, Mw about 6000 Da). As predicted, the viscosity of the dope (Figure 4a) decreased as the PVA content decreased. For dopes containing 82.5% and 75% lignin (w / w based on the total polymer content), shear thinning was also observed when the shear rate exceeded about 20 s -1 . At 90% lignin, the response was essentially Newtonian within the range studied. At an extrusion rate of 0.6 mL / h (equivalent to the region of 183 s -1 ), dopes containing 75% and 82.5% lignin underwent shear thinning flow with a viscosity of about 1.5 Pa·s, while the 90% lignin dope was considered to exhibit Newtonian behavior with a viscosity of less than 0.5 Pa·s. A viscosity in the range of 0.5 - 6 Pa·s at a shear rate of about 183 s -1 (extruded at 0.6 mL / h using a 27G needle) was favorable for stable and continuous spinnability. A viscosity of at least 0.6 Pa·s was favorable for good handleability of the fibers (avoiding breakage during pulling from the coagulation bath).

[0148] The eucalyptus lignin - PVA spinning dope was successfully spun in a 1M Na2SO 4(水溶液) coagulation bath to produce well - formed gel - like proto - fibers. Even at a very high lignin content (90%), good gel - like fibers were formed. Continuous fibers containing 82.5% and 75% lignin were successfully taken out of the bath and dried under tension.

[0149] Although not bound by theory, it is proposed that the increase in dope viscosity with increasing dope preparation temperature is caused by the lignin / PVA reaction involving chemical crosslinking and hydrogen bonding between lignin and PVA in an acidic environment. This reaction is considered to be irreversible. In this case, dope aging should have the same effect on viscosity. Indeed, the dope viscosity increased over time even at room temperature (Figure 4b). Within 6 hours after the dope was prepared, the viscosity of the dope increased with stronger shear thinning behavior. At low shear rates where the dope showed Newtonian flow, the viscosity increased from 1.7 Pa·s to over 2 Pa·s after 6 hours (Figure 4), and further increased to 6 Pa·s after 24 hours. Spinning of the aged dope was carried out to improve the strength of lignin fibers with a very high lignin content (90%). Generally, the dope aged for 6 hours and 24 hours did not affect the stability of lignin / PVA fiber spinning. However, aging of the spinning dope for 6 hours or 24 hours improved the ease of removing fibers containing 90% lignin from the coagulation and water washing baths and enabled drying under tension. The observations on the ease of fiber spinning and drying are summarized in Table 2.

[0150]

Table 2

[0151] As observed by SEM, the dried fibers had a dense structure with a smooth surface and a circular cross-section with a uniform diameter. In previous studies on the spinning of lignin / PVA fibers, bean-shaped fibers were obtained when the lignin content was 70%. This indicates that all the fibers produced by this method had a circular cross-section and an appropriate coagulation rate in general, regardless of the lignin content and lignin species. As evidenced by the cross-section examination, the fibers were also considered to have a homogeneous microstructure without phase separation on the fiber surface and inside. This is [DMBA][HSO4] 60% / water 40%This is an indication of very good miscibility between lignin and PVA in the dope solvent. In some fiber cross-sections, pores were observed, which were due to small air bubbles that were not removed before dope extrusion. Degassing the dope to remove more bubbles should minimize the number of pores in the fiber and improve their mechanical properties.

[0152] The dried fibers extruded in this way, with lignin contents of 75% and 82.5%, had similar diameters of about 100 - 120 μm regardless of the aging time. The 90% lignin fibers had a smaller fiber diameter of about 50 μm, which increased when the dope was aged. Considering that the solid content of the dope was constant, the change in fiber diameter should be related to the draw applied at the injection point. The speed of the coagulation bath was 15.6 times higher than the linear injection speed of the dope, imposing axial acceleration on the fiber during coagulation. The more viscous (75% and 82.5% lignin, aged 90% lignin) dopes resisted this acceleration more, limiting the drawing process, while the more fluid dopes showed the maximum elongation. The dope with a lignin content of 90% (relative to the total polymer loading) in the solid had a lower viscosity and resulted in fibers with the thinnest diameter, while the dopes with 75% and 82.5% lignin content had similar viscosities and resulted in fibers with similar diameters.

[0153] The tensile modulus was consistent at about 4 - 5 GPa (Figure 6c) through the lignin fibers produced using this method and showed similar densities. The tensile strength (Figure 6b) was highest at about 30 - 40 MPa for the 75% lignin fibers. The 82% and 90% lignin fibers had lower strengths of about 25 MPa. Surprisingly, similar or slightly higher strengths were measured for the 90% lignin fibers; an observation that could be due to their smaller diameter and thus reduced defect size. However, there was some variability due to the tendency of the 90% lignin samples to break into shorter lengths during handling and the variable tensile weights used. The trend for the elongation at break (Figure 6d) follows that for the tensile strength.

[0154] [Example 8] Effect of lignin species To investigate the generality of the approach, dopes were prepared using four lignins (two ionosolv hardwood lignins and two commercially available softwood kraft lignins). The dope containing eucalyptus lignin was particle-free and homogeneous. The dope containing ionosolv willow lignin contained undissolved particles dispersed homogeneously. Many of the particles were thought to be undissolved lignin, as they also appeared in the control solution ([DMBA][HSO4] 60% / water 40% containing 12% lignin). A smaller number of birefringent particles were observed under polarized light and appeared to be residual cellulose crystals. Presumably these crystals could be removed later by filtration. The two dopes containing kraft softwood lignin showed complete lignin dissolution at 12% lignin and 4% PVA concentrations.

[0155] The steady-shear viscosities (as a function of shear rate) for dopes containing different lignins are shown in Figure 7. The lignin species affects the dope viscosity. The dopes containing the two softwood kraft lignins exhibited lower viscosities than the two hardwood ionoSolv lignins, which is probably a reflection of the different chemical and physical properties (e.g., average molecular weight, polydispersity, and density) of the lignins extracted from different feedstocks by different processes. Shear thinning was observed for the ionoSolv lignin-containing dope solutions. Over the range of shear rates tested, shear thinning was evident due to the high viscosity of the willow lignin dope, especially for ionoSolv willow lignin. For the dopes containing kraft lignin and PVA, significant shear thinning behavior was only observed when the shear rate increased above 400 s -1 and 100 s -1 for kraft lignin 1 and 2, respectively (Figure 8).

[0156] To compare the spinnability and demonstrate the robustness of the developed dope preparations and spinning methods, extrusion of dopes (75% lignin and 25% PVA) containing different types of industrial lignin was carried out. The data show that homogeneous dopes can be prepared from various lignins, which can be continuously spun and then washed and dried. SEM images (Figure 9) of precursor fibers containing different lignins have a smooth surface and a circular cross-section, indicating that various lignins have good miscibility with PVA in the [DMBA][HSO4] 60% / water 40% dope solvent and that coagulation is successful for all the lignin species tested. Fibers containing poplar lignin had the least smooth surface (small lumps), which was due to undissolved lignin particles in the dope. However, this did not impair the mechanical properties of the precursor fibers.

[0157] The mechanical properties of the lignin fibers were tested (Table 3). Fibers containing two types of kraft lignin had smaller diameters, which was due to the lower viscosities of their dopes. This led to higher average tensile strengths of the spun fibers. Fibers derived from IonoSolv lignin had higher stiffness and shorter elongation at break. This could be due to better orientation of the polymer since the shear rate during extrusion falls within the shear thinning viscosity region.

[0158]

Table 3

[0159] [Example 9] Optimization of the Coagulating Liquid The use of an aqueous solution of 1M sodium sulfate (Na2SO4) and water for coagulating lignin / PVA fibers was investigated. Assuming that it would improve coagulation, a 1M sodium sulfate (Na2SO4) solution was used first. Using only water as the coagulant would make the fiber spinning process more sustainable because the fiber washing step could be omitted, thereby simplifying the recycling of the IL (no need to separate the sodium ions introduced by Na2SO4). When water was used as the coagulant, continuous and stable fiber spinning was observed. SEM imaging of eucalyptus lignin / PVA fibers containing 75% lignin showed that the fibers had a smooth surface and a circular cross-section, with no difference compared to the fibers spun in 1M Na2SO4. Fiber coagulation in water was successful with different lignin types (ionoSolv and kraft) and different lignin contents. Table 4 shows the dimensions and mechanical properties of the fibers coagulated in water and 1M Na2SO4.

[0160]

Table 4

[0161] For the purpose of promoting the recycling of the dope solvent, the use of [DMBA][HSO4] 10% / water 90% as the coagulant was also investigated. The use of IL as part of the coagulant would reduce the energy required for solvent recycling because solvent recycling is achieved by evaporating H2O and recovering the IL. Therefore, the presence of IL in the coagulant reduces the amount of H2O that must be removed to reconstitute the dope solvent.

[0162] The spinning dope was prepared as described in Example 3, which consisted of lignin and PVA (weight ratio 3:1) dissolved in [DMBA][HSO4] 60% / water 40% 10% / water 90% ​When used as the coagulation liquid, long fibers were formed, which were considered to be uniform and flexible and could be taken out and hung under tension for drying. The fibers were not washed in water. The fibers did not shrink during the drying process; instead, their length doubled under tension. The elongation stopped only when the weight attached to the lower end of the fiber reached the bench top surface. After drying, the fibers were stable and did not elongate further. Fibers that do not shrink during drying are desirable because this facilitates winding and thus the continuous production of precursor fibers, which is important for industrial deployment.

[0163] [DMBA][HSO4] 10% / water 90% Dimensions and mechanical properties of the fibers coagulated in:

[0164]

Table 5

[0165] Optimization of the spinning in H2O and 1M Na2SO4 coagulation liquids is possible with respect to the coagulation time and other variables including the washing step. Thus, it would be possible to improve the fiber properties spun in the [DMBA][HSO4] and water mixture by varying the parameters of the dope preparation, fiber spinning, and / or fiber washing steps.

[0166] [Example 10] Carbon yields of lignin and precursor fibers An important motivation for using lignin as a precursor for renewable carbon fibers is the high carbon content of lignin, which results in a high carbon yield. The carbon yields of various lignins and of each precursor fiber having a lignin content of 75% and a PVA content of 25% (assuming the same lignin:PVA ratio in the spinning dope) were estimated by using thermogravimetric analysis (TGA). The predicted carbon yields are listed in Table 5. Interestingly, all precursor fibers resulted in a high carbon yield similar to that of lignin alone, although the lignin content was 75% in the precursor fibers and PVA itself had a very low carbon yield. This is another indicator of the chemical reaction between lignin and PVA in acidic IL during dope preparation. The measured carbon yield of the precursor fibers (about 40%) is higher than that of previously reported fibers having the same lignin content obtained by wet spinning from DMSO (Foellmer, M. et al., Advanced Sustainable Systems 2019). It should be noted that these DMSO-based dopes were not homogeneous.

[0167] [Table 6]

[0168] [Example 11] Carbonization of Precursor Fibers Using the conditions described in Example 5 (1000 °C, heating rate of 1 °C / min, held for 2 hours), after heat stabilizing the fibers as described in Example 5 (in air at 250 °C, from 100 °C to 250 °C at a heating rate of 0.2 °C / min, held for 1 hour), carbonization of the lignin fibers was carried out. The SEM image of the carbon fibers showed that the circular shape of the fibers was retained during carbonization.

[0169] The characteristics of the carbon fibers are shown in Table 6.

[0170] [Table 7]

[0171] [Example 12] Properties of Heat-Stabilized and Carbonized Fibers An aqueous solution of poly(vinyl alcohol) was prepared and mixed with [DMBA][HSO4]. After forming a homogeneous solution, LignoBoost lignin was added and the mixture was continuously stirred until a homogeneous solution was obtained. The composition of the dope is presented in Table 7.

[0172] [Table 8]

[0173] In a static deionized water coagulation bath, continuous free-flowing fibers were produced by extrusion of the lignin dope using a 30-gauge needle at a rate of 2.5 mL hr -1 . The extruded fibers were gently guided onto a mandrel made of acetal (Delrin®) and left to air dry. The continuous fiber line collected single fibers approximately 6 m in length, limited by the length of the take-up mandrel.

[0174] The precursor fibers (untreated extruded fibers) were heat-stabilized at 250 °C (heat-stabilized fibers) and carbonized between 900 and 2200 °C (carbonized fibers). The carbon yields of the precursor fibers and heat-stabilized fibers were estimated by TGA and are shown in Table 8 together with comparative values for precursor fibers made from polyacrylonitrile (PAN) and mesophase petroleum pitch. As shown in Figure 10, the mechanical properties of the lignin fibers differ between the precursor fibers, heat-stabilized fibers, and carbonized fibers. For example, the lignin-derived fibers show an increase in tensile strength after heat stabilization. While high tensile strength and high tensile modulus are desirable for carbon fibers, a lower modulus is desirable for textile fibers.

[0175] [Table 9]

[0176] [Example 13] Fiber spinning using high MW PVA High molecular weight 88% hydrolyzed PVA (Sigma Aldrich, M w 146,000 - 186,000 g / mol) purchased from Sigma Aldrich and softwood kraft lignin were used to conduct fiber spinning research.

[0177] Using the method described in Example 3, a spinning dope containing [DMBA][HSO4] 60% / water 40% with a solid loading of 16% and a lignin / PVA ratio of 3:1 was prepared.

[0178] The dope was cooled to room temperature and then transferred to a 1 mL plastic syringe (Injekt(™)-F Fine Dosage Syringe, B.Braun, Germany). The plunger was slowly pushed and pulled to expel any air bubbles that might be present in the dope. Using a syringe pump (LEGATO(®) 100, KD Scientific, US), the dope was extruded into a coagulation bath containing 1 M Na2SO4 at an extrusion rate between 0.1 and 0.4 mL / min.

[0179] Tweezers were used to pull out the fibers. The fibers were successfully formed, coagulated in the Na2SO4 coagulation bath for 60 seconds, and then transferred to a washing batch containing deionized water for 30 seconds to wash the salt off the fiber surface.

[0180] The fibers were dried by hanging them overnight with a suitable weight loading of aluminum foil attached to the lower end, which was used to stretch the fibers.

[0181] [Example 14] Integrated lignin extraction and lignin fiber spinning Biomass fractionation (lignin extraction into [DMBA][HSO4]) Lignin extraction was carried out according to the pretreatment procedure (Gschwend, F. J. V et al., J. Vis. Exp. 2016, 2016(114), 4 - 9). 9 or 12 g of biomass (oven-dried weight, ODW) was added to a 100 mL pressure tube (Ace Glass, Vineland, NJ, USA, front sealing), followed by 83% / water 17% about 30 g was added to obtain a suspension with a biomass loading rate of 30% or 40% and a water content of 20%. The biomass and ionic liquid solution were thoroughly mixed using a vortex shaker (VWR) until all biomass particles were in contact with the IL. The pressure tube was placed in a preheated oven at 150 °C for 1 hour. The mixture in the pressure tube was cooled and transferred to a 500 mL glass bottle, then mixed with 180 g of anhydrous ethanol (EtOH), shaken well, and allowed to rest at room temperature for 1 hour. After 1 hour, the mixture was separated into a cellulose-rich solid and a liquid (liquor) containing the ionic liquid, ethanol, and dissolved lignin using vacuum filtration. The cellulose was air-dried. The pulp was further washed 3 times with EtOH and then Soxhlet extracted in anhydrous ethanol for 24 hours. The liquor was collected, and water and most of the EtOH were evaporated from the combined liquor fractions using a rotary evaporator. Lignin extraction was performed in triplicate. The liquors obtained from lignin extraction at biomass loading rates of 30% and 40% were labeled as liquor 30 and liquor 40. Compositional analysis of wood biomass and cellulose pulp According to the published standard procedure, the National Renewable Energy Laboratory (NREL) (Sluiter, A. et al., Natl. Renew. Energy Lab. 2008, No. April 2008, 17) carried out a compositional analysis. Using a Soxhlet extractor for 24 hours, ethanol was used to remove extracts from eucalyptus biomass and quantified by measuring the weight difference (oven-dried basis). Approximately 300 mg of air-dried extract-free biomass (oven-dried weight basis, sieved to 180 - 850 μm) or the recovered pulp was weighed into a 100 ml pressure tube (Ace Glass), and the exact weight was recorded. 3 mL of 72% sulfuric acid (Fluka) was added, the sample was stirred with a Teflon stirring rod, and the pressure tube was placed in a water bath preheated to 30 °C. The samples were stirred again every 10 minutes for 1 hour. Then, they were diluted with 84 mL of distilled water and capped. The samples were autoclaved at 121 °C for 1 hour (Sanyo Labo Autoclave ML5 3020 U) and cooled until the pressure tube could be opened. The samples were filtered through filtering ceramic crucibles of known weight. The filtrate was filled into two Falcon tubes (to determine the acid-soluble lignin content and sugar content), and the remaining black solid was washed with distilled water. The crucibles were dried in a convection oven (VWR Venti-Line 115) at 105 °C for 24 ± 2 hours. They were placed in a desiccator for 15 minutes, and then their weights were recorded. The crucibles were placed in a muffle oven (Nabertherm + controller P 330) and ashed to a constant weight at 575 °C. They were placed in a desiccator again for 15 minutes, and then their weights were recorded again. The content of acid-insoluble lignin (AIL) was determined by Equation 1:

[0182] [Number]

[0183] [where Wcrusible plus AIR is the weight of the oven-dried crucible and the acid-insoluble residue, W crusible plus ash is the weight of the crucible after ashing to a constant temperature of 575 °C].

[0184] The acid-soluble lignin content (ASL) was determined by UV analysis (Perkin Elmer Lambda 650 UV / Vis spectrometer) of the autoclave filtrate at 286 nm. 200 μL of the sample and 800 μL of D.I. water were added to the cuvette (1:4 dilution), mixed well, and the absorbance A was recorded. ASL was calculated according to Equation 2:

[0185]

Equation

[0186] [where A is the absorbance at 286 nm, l is the path length of the cuvette in cm (in this case 1 cm), ε is the extinction coefficient (25 L / g cm), c is the concentration in mg / mL, ODW is the oven-dried weight of the sample in mg, Vfiltrate is the volume of the filtrate in mL, equal to 86.73 mL].

[0187] Calcium carbonate was added to the remaining filtrate until the solution pH reached 5. The liquid was filtered through a 0.2 μm PTFE syringe filter and subjected to HPLC analysis (Shimadzu, Aminex HPX-97P manufactured by Bio rad, 300×7.8 mm, purified water as the mobile phase at 0.6 ml / min, column temperature 85 °C) to determine the total sugar content. Calibration standards containing glucose, xylose, mannose, arabinose, and galactose at concentrations of 0.1, 1, 2, and 4 mg / mL were used. A sugar recovery standard was prepared as 10 mL of an aqueous solution close to the predicted sugar concentration of the sample and transferred to a pressure tube. 278 μL of 72% sulfuric acid was added, the pressure tube was closed, and it was subjected to an autoclave, and the sugar content was determined as described above. The sugar recovery coefficient (SRC) and the sugar content of the analyzed sample were determined according to Equation 3 and Equation 4, respectively:

[0188]

Number

[0189] [where cHPLC is the sugar concentration detected by HPLC, V is the initial volume in mL of the solution (10.00 mL for the sugar recovery standard and 86.73 mL for the sample), initial weight is the mass of the weighed sugar, corr anhydro is the correction value for the mass increase during hydrolysis of the polymeric sugar, obtained by dividing the molecular weight of one polymeric sugar by its monomer weight (0.90 for glucose, galactose and mannose of C6 sugars, and 0.88 for xylose and arabinose of C5 sugars), and ODW is the oven-dried weight of the sample in mg]. Determination of lignin loading rate in liquor The lignin loading rate for integrated spinning liquor, defined as the percentage weight ratio of lignin to the liquid fraction of liquor containing IL, water, ethanol and any additional unidentified solutes used for spinning, was calculated based on the difference in lignin content of the raw biomass and lignin content in ionosolv pulp (as determined by compositional analysis), pulp yield (oven-dried weight basis) and the weight of the liquor used to prepare the integrated spinning dope. The mass of the liquid fraction is the mass of the liquor minus the mass of lignin in that liquor). The equations used are shown below (Equations 5, 6 and 7):

[0190]

Number

[0191] [where W lignin(biomass) and W lignin(pulp) are the weights of lignin in the raw biomass and eucalyptus pulp, respectively; ODW biomass and ODW pulp are the oven-dried weights of the raw wood and pulp, respectively; %Lignin(lq) is the lignin concentration in weight percentage in the liquor, W liquoris the weight of the lyocell.

[0192] The water content in the dope for integrated spinning was determined using a coulometric Karl-Fischer titrator (Mettler Toledo). The ionic liquid and residual ethanol contents were determined using the 1 1H-NMR spectrum of the lyocell. The signals of the methyl groups on ethanol (δH (400 MHz, DMSO-d6) / ppm: 1.05, t) and the methyl groups on the butyl chain of [DMBA][HSO4] (δH (400 MHz, DMSO-d6) / ppm: 0.90, t) were used to calculate the molar ratio between the IL and EtOH, which was converted to a weight ratio by multiplying by the molecular weight of each molecule. In the formula, %IL(lq), %EtOH(lq) and %Water(lq) are the weight percentages of IL, EtOH and water in the lyocell, respectively. W %IL,Etoh is 1 the weight ratio of IL and EtOH calculated from the molar ratio obtained from 1H-NMR spectrum analysis.

[0193] Preparation of the dope solution for integrated spinning Aqueous PVA solutions at several concentrations were prepared based on the desired lignin / PVA weight ratio. The lignin:PVA ratios investigated in the fibers were 3:1 or 75:25 wt% and 4.71:1 or 82.5:17.5 wt%) and the final water content in the dope (20 wt%). Surprisingly, the presence of ethanol in the dope for integrated spinning allowed for a lower water content.

[0194] Examples After the eucalyptus wood fraction with a biomass loading rate of 40%, a dopant with a lignin loading rate of 11% and a water loading rate of 0.7% (the values are the percentage weight ratios of lignin and water to the liquid fraction of the dopant) was used, and an 8.48% (w / w) aqueous solution of PVA was added to prepare a dopant with a lignin:PVA = 82.5:17.5% by weight and a water content of 20%. The same dopant was used to prepare a 13.16% (w / w) PVA (aqueous solution) to prepare a dopant with a lignin:PVA = 75%:25% and a water content of 20%.

[0195] To prepare the spinning dopant, the PVA aqueous solution was mixed with the dopant at 60 °C with stirring at 700 rpm for 1 hour in a 10 mL round-bottom flask equipped with a stirring bar. The amount of PVA added to the dopant depends on the amount of dopant added to the round-bottom flask. For example, to prepare a dopant with a polymer ratio of 3:1 (lignin:PVA = 75%:25%) and a water content of 20%, 1.00 g of the above-mentioned dopant was added, followed by 0.28 g of a 13.16% PVA (aqueous) solution.

[0196] Fiber spinning The dope solution was aspirated using a 1 mL plastic syringe (Normject™ Disposable), and air was carefully expelled. The dope solution (about 0.5 mL) was extruded at an extrusion rate of 1.5 mL / h using a syringe pump (KDS LEGATO™ 100, KD Scientific, US) into a coagulation bath (deionized water) placed on a rotating table at 3.5 RPM. For spinning fibers containing 75% lignin, 27 g and 29 g needles (inner diameters 210 and 184 μm respectively) were used. For spinning fibers containing 82.5% lignin, a 29 g needle (inner diameter 184 μm) was used. The bath was rotated at about 3 cm / s at the injection point to obtain an elongational flow during fiber coagulation. The ratio of the rotation speed at the injection point to the injection rate was 2.5. The fibers were immersed in the coagulation bath (water) for 2 minutes and then removed. Fibers with a 75% lignin content were hung on a rod under tension (about 0.5 mN) from a known weight attached to the lower end of the fiber, and fibers with an 82.5% lignin content could be drawn under a tension of 0 - 0.1 mN. The fibers were dried overnight.

[0197] Results and Discussion Lignin Extraction and Characteristics of Ricar As described above, lignin was extracted in [DMBA][HSO4] at 150 °C for 1 h. From the compositional analysis of raw biomass and recovered pulp, when the biomass loading rates were 30% and 40%, respectively, the delignification rates (representing lignin extraction efficiency) were calculated to be 80.0% and 72.5% (Table 9). Although additional lignin could be extracted at a biomass loading rate of 40%, the delignification rate decreased, which can be explained by the reduced contact between the biomass matrix and the ionic liquid solution at higher biomass loading rates. The amount of lignin extracted in the lignin / IL mixture (lika) was calculated from the difference in lignin content in eucalyptus raw biomass and recovered pulp. According to this calculation, the lignin contents were 8.8% and 9% in BL30 and BL40, respectively. The other compositions (IL, water, and residual EtOH) are shown in Table 10. Lika was homogeneous according to optical micrographs, and no undissolved particles were observed. However, under crossed polarizers, some small crystalline birefringent particles were observed, which were probably cellulose crystals.

[0198]

Table 10

[0199]

Table 11

[0200] Lika without PVA demonstrated Newtonian flow behavior (Figure 11). At a higher biomass loading rate (40%), lika had a slightly higher viscosity (about 0.6 Pa·s) than the lika obtained at a biomass loading rate of 30% (0.4 Pa·s) in the shear rate range of 1 - 1000 / s.

[0201] Preparation of dope for spinning Lignin alone cannot be wet-spun due to its low molecular weight and branched structure. Therefore, a highly fiber-forming polymer (in this example, PVA) is added to the re-concentrated liquor in the same way as when preparing a dope from lignin isolated as in the previous examples.

[0202] Ethanol was found to be present in the re-concentrate, which was added during the washing step of the cellulose pulp. 1 The ethanol content was quantified using an 1H NMR spectrum. A concentrated aqueous solution of PVA was prepared to achieve a final water content of approximately 20% in the dope upon addition (when ethanol is included in the liquor, an auxiliary solvent content of approximately 30%), which is different from the auxiliary solvent content in the spinning method using isolated lignin (water content 40 wt%). Subsequently, the PVA aqueous solution was prepared based on the known liquor composition and the desired lignin / PVA ratio in the fiber. When the lignin / PVA ratio was increased up to 82.5 / 17.5 wt%, a more diluted PVA stock solution was prepared. The final dope composition used for spinning is shown in Table 11.

[0203]

Table 12

[0204] Dope Rheology The viscosity of the dope for integrated spinning was measured and compared with the viscosity of the liquor. Compared with the re-concentrated liquor, the dope for integrated spinning with a 75 / 25% lignin / PVA ratio had a viscosity of 1 - 1000 s -1A slightly higher viscosity was observed in the shear rate range. In that dope, while shear-thinning behavior was observed, the liquor without added PVA showed only Newtonian flow behavior. The addition of the PVA aqueous solution increases the water content, which is expected to decrease the dope viscosity, while the addition of the copolymer is expected to increase the viscosity. Figure 11 shows that when the target polymer ratio was 75 / 25% (lignin / PVA), the addition of the PVA aqueous solution generally increased the viscosity for both 30% and 40% biomass loading liquors, and typical shear-thinning behavior of the spinning solution was observed.

[0205] However, when the lignin / PVA ratio was increased to 82.5 / 17.5%, the dope viscosity decreased significantly to 0.3 Pa·s, and the viscosity of the dope was here lower than that of the re-concentrated liquor. The dope was considered to also exhibit Newtonian fluid-like behavior at shear rates below 800 s -1 This was due to the decrease in the amount of PVA (1.8%) in the dope, as shown in Table 11 (2.7% in dope BL30_75% and 2.9% in dope BL40_75%).

[0206] Fiber Spinning and Characterization Generally, the extrusion pressure can affect the coagulation rate. A low extrusion pressure, for example, a low-viscosity dope, can result in faster coagulation. To optimize coagulation and fiber formation, the extrusion parameters can be changed. For example, a needle with a smaller diameter can be used to increase the extrusion pressure, or the dope viscosity can be increased.

[0207] In this example, using a 27G and 29G needle (inner diameters 210 and 184 μm) at an extrusion rate of 1.5 mL / h with a dope containing 75% lignin and 25% PVA, stable and continuous fiber spinning was achieved at a rotational speed of 3.5 - 9 RPM. The fibers could be taken out and dried under a small weight (50 mg, about 0.5 mN). This was the case for dopes with a biomass loading of 30% or 40%.

[0208] Using a 29G needle, lignin 82.5% fibers could be spun in a stable and continuous manner. Fiber spinning was repeated with dopes aged for 24 hours and 48 hours, and dopes heated and stirred for 6 hours (instead of 1 hour). The spinning of the aged dopes was also continuous and stable, and an increase in wet fiber strength was observed. These fibers could also hold a small weight (10 mg) during drying.

[0209] Figures 12a and 12b show, as predicted, that the increase in aging and wet fiber strength corresponded to an increase in the dope viscosity for integrated spinning. Longer mixing of the lye and PVA aqueous solution could further increase the dope viscosity and thus the wet fiber strength.

[0210] Fiber morphology Fibers spun using the integrated process and containing 75% lignin had a uniform diameter and a circular cross-section as observed by SEM, which demonstrated that good coagulation existed during spinning. The fiber surface was smooth, but small particles appeared on the surface, which were not observed when spinning fibers containing isolated eucalyptus lignin. Effect of dope preparation time and needle size As can be seen in Table 12, fibers spun from dopes prepared for 1 hour and 6 hours had similar elastic moduli and breaking point strains. An increase in dope preparation time was thought to increase the fiber diameter, which led to an increase in dope viscosity. Interestingly, as the dope preparation time increased, the average tensile strength of the fibers also increased. Without being bound by theory, this could be due to higher shear during extrusion of the higher viscosity dope.

[0211] [Table 13]

[0212] Effect of biomass loading rate Lignin fibers prepared from liquor obtained at biomass loading rates of 30% and 40% had similar fiber diameters and mechanical properties.

[0213] [Table 14]

[0214] Carbon yield A high yield of carbon fiber is important for reducing the cost of carbon fiber production and is an important requirement for increasing the adoption of sustainable carbon fiber composites. This can be simulated on a small scale by thermogravimetric analysis. TGA showed that the carbon yield could be increased by increasing the doping preparation time. Fibers spun from dopes prepared from LQ30 heated for 1 hour resulted in a carbon yield of about 30%, while fibers spun from dopes heated for 6 hours resulted in a carbon yield of about 31%. Fibers spun from dopes prepared from LQ40 had higher carbon yields, about 32% for fibers from 1-hour dopes and 36% for fibers from 6-hour dopes. For lignin 82.5% fibers, the carbon yield was approximately about 37%. During industrial carbon fiber production, the precursor fibers are usually thermally stabilized in air before carbonization to prevent the fibers from melting and fusing during carbonization. The carbon yield of the thermally stabilized fibers was about 57% (Table 14).

[0215] [Table 15]

[0216] [Example 15] Study on lignin spinnability using different ionic liquids Using methods known in the art, the following ionic liquids were synthesized:

[0217] [Table 16]

[0218] Other drugs used PVA, 88% hydrolyzed (Kuraray Poval, No. 13-88, 100 kDa) Kraft lignin: softwood kraft lignin (alkali), purchased from Sigma-Aldrich. Ionosolv lignin: extracted from eucalyptus wood (hardwood) using [DMBA][HSO4] containing 20% water at 170 °C for 1 hour.

[0219] Solubility of lignin in ionic liquid-water mixtures To study the spinnability of lignin-PVA dope in the presence of different ionic liquids, the solubility of hardwood (ionosolv lignin) and softwood lignin (kraft lignin) was first investigated in various ionic liquid-water mixtures. The solubility of lignin in the dope solvent is an important prerequisite for producing wet-spun lignin fibers. Since PVA was found to be soluble in a wide range of ionic liquid-water mixtures (prepared by adding to a stock aqueous solution of PVA) in previous studies, no screening was performed.

[0220] To determine the lignin solubility, ionic liquid / H2O mixtures containing 20 wt% and 40 wt% H2O2 were prepared, stirred, and heated to 60 °C. Lignin (12 wt%) was added, the mixture was stirred for 1 hour, cooled to room temperature, and the lignin solubility was checked by polarized light microscopy. The solution was stirred again at 60 °C for 1 hour, and the solubility was checked again by polarized light microscopy.

[0221] Fiber spinning Basic spinnability tests were carried out using ionic liquid-water mixtures.

[0222] As described in Example 3, the dope was prepared. Complete dissolution of lignin in the dope was confirmed by polarized light microscopy. Fiber spinning was achieved by manual stretching using a syringe pump. The dope was injected into a coagulation bath containing either 1M aqueous Na2SO4 or deionized (DI) water to form fibers. This was tested at an extrusion rate between 0.01 mL / min and 0.1 mL / min.

[0223] To characterize the lignin fibers, they were dried overnight as described in Example 4. The use of a force to straighten the fibers during the drying process was applied to fibers strong enough to withstand it. Otherwise, they were dried without applying additional force.

[0224] Solubility of Lignin in Ionic Liquid-Water Mixtures The results of the solubility tests are provided in Table 15.

[0225]

Table 17

[0226] Some ionic liquids were only able to dissolve lignin at a low H2O content of 20 wt%. This can be explained by the poor solvent characteristics of water.

[0227] Comparing various ionic liquids, lignin has high solubility in [DMBA]Cl, [DMBA][HSO4], [Bmim][HSO4], [MBA][HSO4] and [Hbim][HSO4] and dissolves in the IL-water mixture even in the presence of 40 wt% H2O.

[0228] Previous reports state that the solubility of lignin is mostly determined by the anion of the ionic liquid, but the results show that the cation also has an influence.

[0229] The data collected suggests that the type of lignin has a lower influence on its solubility than the ionic liquid composition and water content.

[0230] Fiber Spinning and Composition of Ionic Liquids Fiber spinning tests were carried out with various IL / water dope solvents. The results are summarized in Table 16.

[0231]

Table 18

[0232]

Table 19

[0233] The dope prepared using [DMBA][HSO4] mixed with 40 wt% H2O, with kraft lignin and ionoSolv lignin, and using 1M aqueous Na2SO4 solution as the coagulation bath and further deionized H2O, resulted in the formation of high-quality lignin PVA fibers. None of the other ionic liquids tested showed such good fiber formation under the conditions used for screening, but it should be noted that the protocol was optimized for [DMBA][HSO4]. By optimizing the spinning protocol, for example, by using different pump systems that can tolerate higher viscosities, improvement in fiber formation with other ionic liquids can be obtained.

[0234] The above description has been created as an example and it will be understood that it is not a limitation of the appended claims, including any equivalents as defined within the scope of the claims. Various modifications are possible and will be readily apparent to those skilled in the art. Similarly, the features of the described embodiments can be combined with any suitable aspect described above, and any optional feature of any one aspect can be combined with any other suitable aspect.

Claims

1. A method for producing fibers, The step of preparing a spinning dope comprising a doping solvent, lignin dissolved in the doping solvent, and an additive polymer dissolved in the doping solvent, wherein the doping solvent comprises an ionic liquid and water; The step of extruding the spinning dope into a coagulation solution to obtain one or more fibers is included. A method wherein the water content of the doped solvent is 5 to 40% by weight.

2. The method according to claim 1, wherein the water content in the doped solvent is 10 to 40% by weight, preferably 20 to 40% by weight.

3. The method according to claim 1, wherein the spinning dope has a total load of lignin and additive polymers of 6 to 60% by weight, 6 to 50% by weight, 6 to 40% by weight, 6 to 30% by weight, 8 to 23% by weight, 11 to 20% by weight, 10 to 20% by weight, and 15 to 20% by weight, relative to the mass of the spinning dope excluding the mass of lignin and additive polymers.

4. The method according to claim 1, wherein the weight ratio of lignin to additive polymer in the spinning dope is at least 2:1 or at least 3:1, for example 2:1 to 10:1, preferably 3:1 to 9:

1.

5. The method according to claim 1, wherein lignin is present in the spinning dope at a loading rate of at least 5% by weight relative to the total mass of the doping solvent, preferably at a loading rate of 5 to 50% by weight, 5 to 40% by weight, 5 to 30% by weight, or 5 to 15% by weight relative to the total mass of the doping solvent.

6. The method according to claim 1, wherein the additive polymer is present in the spinning dope at a load of 1 to 10% by weight, preferably 1 to 5% by weight, relative to the mass of the spinning dope excluding the mass of lignin and the additive polymer.

7. The method according to claim 1, wherein the additive polymer is selected from poly(vinyl alcohol) (PVA), polyvinyl acetate, polyfurfuryl alcohol, polyacrylic acid, polyethylene oxide, polyethyleneimine, poly(2-hydroxyethyl methacrylate), polyoxymethylene, and mixtures thereof.

8. The method according to claim 7, wherein the polymer is PVA.

9. The method according to claim 8, wherein the PVA is partially hydrolyzed and has a degree of hydrolysis (DH) of 80-95%, preferably 85-90%, and more preferably 86.7-88.7% hydrolyzed.

10. The method according to claim 1, wherein the weight-average molecular weight (Mw) of the additive polymer is 60 to 200 kDa, preferably 80 to 190 kDa.

11. The ionic liquid contains a cation and an anion, and the anion is C ３ , ４ , － , － , － , ２－ , ４ , － alkyl sulfate ([alkyl SO ４ ), C － alkyl sulfonate ([alkyl SO １～２０ ), hydrogen sulfate ([HSO ３ ), hydrogen sulfite ([HSO － ), dihydrogen phosphate ([H ２ PO ４ ), hydrogen phosphate ([HPO ４ ), chloride (Cl － ), bromide (Br ２ ), trifluoromethanesulfonate ([OTf] ４ ), formate ([HCOO] － ), and acetate ([MeCO ４ ), and the method according to claim 1, which is selected from ２－ ), chloride (Cl － ), bromide (Br － ), trifluoromethanesulfonate ([OTf] － ), formate ([HCOO] － ), and acetate ([MeCO ２ ), and the method according to claim 1, which is selected from － ).​​

12. The aforementioned anion is [HSO ４ ] － and [HCOO] － The method according to claim 1, selected from the following.

13. The ionic liquid comprises a cation and anion, wherein the cation contains a nitrogen-containing heterocyclic moiety, or the cation is a cation of formula I. 【Chemistry 1】 [In the formula, A １ ~A ４ These are H, aliphatic, and C, respectively, independently. ３～６ carbocycle, C ６～１０ The method according to claim 1, wherein the selected element is aryl, alkylaryl, and heteroaryl.

14. The aforementioned ionic liquid is [alkylammonium] [HSO] ４ The method according to claim 1, wherein the liquid is either [alkylammonium] [HClOO] ionic liquid.

15. The ionic liquid is triethylammonium hydrogen sulfate [TEA] [HSO4] ４ ], N,N-dimethylbutylammonium hydrogen sulfide [DMBA] [HSO ４ ], diethylammonium hydrogen sulfate [DEA] [HSO ４ ], N,N-dimethylethylammonium hydrogen sulfate ([DMAA][HSO ４ ]), diethanolammonium chloride [DEtOHA]Cl, 1-methylimidazolium chloride [HMim]Cl, 1-ethyl-3-methylimidazolium chloride [EMim]Cl, and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMim][OTf], 1-butylimidazolium hydrogen sulfate ([HBim][HSO ４ ]), methylbutylammonium hydrogen sulfate ([MBA][HSO ４ ]), 1-methylimidazolium formate ([HMim][HCOO]), N,N-dimethylbutylammonium formate ([DMBA][HCOO]), N,N-dimethylethylammonium hydrogen sulfide ([DMAA][HSO ４ ]), 1-butyl-3-methylimidazolium hydrogen sulfate [BMim] [HSO ４ ] or N,N-dimethylbutylammonium acetate ([DMBA][OAc]), or a mixture thereof, preferably the ionic liquid is [DMBA][HSO4] ４ The method according to claim 1.

16. The method according to claim 1, wherein the doping solvent further contains ethanol, and the ethanol may be present in an amount of 1 to 20% by weight, preferably 5 to 15% by weight, relative to the total weight of the doping solvent.

17. The method according to claim 1, wherein the coagulation solution contains water.

18. The method according to claim 1, wherein the coagulation solution comprises water and an ionic liquid, and the ionic liquid is present in an amount of 60% by weight or less, 30% by weight or less, or 15% by weight or less, preferably 1 to 60% by weight, 1 to 30% by weight or 1 to 15% by weight, more preferably 5 to 10% by weight, based on the total mass of the coagulation solution.

19. The method according to claim 1, wherein the coagulation solution comprises water and sodium sulfate.

20. The method according to claim 1, further comprising the step of aging the spinning dope for at least 2 minutes, preferably at least 30 minutes, prior to the extrusion step.

21. The step of preparing the spinning dope is a) A step of contacting lignocellulosic biomass containing lignin and cellulose with a composition containing the ionic liquid and water (preferably 5 to 40% by weight of water) to dissolve the lignin and produce cellulose pulp; b) Separating the cellulose pulp to obtain a liquor containing the ionic liquid, water, and lignin; c) The method according to claim 1, comprising the step of combining the liquor with the additive polymer to obtain the spinning dope.

22. The method according to claim 21, wherein the lignocellulosic biomass is brought into contact with the composition at 100 to 180°C.

23. The method according to claim 1, further comprising the step of drying one or more fibers under mechanical tension.

24. The method according to claim 1, further comprising the step of drying the one or more fibers by heating them in air at a temperature which may be 150 to 300°C.

25. The method according to claim 24, further comprising the step of weaving the fibers to form a cloth.

26. The method according to claim 1, further comprising the step of carbonizing one or more of the fibers to obtain carbon fibers, wherein the carbonization may include the step of heating the one or more of the fibers to 800 to 3000°C, preferably 1200 to 1800°C, in an inert atmosphere.

27. A fiber that can be obtained by the method of claim 1, wherein the additive polymer is poly(vinyl alcohol) (PVA).

28. A cloth comprising one or more fibers according to claim 27.

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