DELIGNIFICATION OF MATERIALS IN DEEP EUTECTIC SOLVENTS

Abstract

Embodiments of the present disclosure pertain to methods of removing lignin from a material by associating the material with a deep eutectic solvent (DES) that includes at least one hydrogen bond acceptor (HBA) and at least one hydrogen bond donor (HBD). The methods of the present disclosure may also include one or more steps of heating the solvent-associated material, separating the material from the solvent, drying the material, washing the material, and/or processing the material. Additional embodiments of the present disclosure pertain to delignified materials that are formed in accordance with the methods of the present disclosure.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 63/456,184, filed on Mar. 31, 2023. The entirety of the aforementioned patent application is incorporated herein by reference.

BACKGROUND

Current methods of delignifying materials have numerous limitations. Various embodiments of the present disclosure aim to address the aforementioned limitations.

SUMMARY

In some embodiments, the present disclosure pertains to methods of removing lignin from a material by associating the material with a solvent that is operational to dissolve the lignin associated with the material. In some embodiments, the solvent includes a deep eutectic solvent (DES) that includes at least one hydrogen bond acceptor (HBA) and at least one hydrogen bond donor (HBD). In some embodiments, the methods of the present disclosure also include one or more steps of heating the solvent-associated material, separating the material from the solvent, drying the material, washing the material, and/or processing the material. In some embodiments, the processing of the material includes one or more steps of: opening the material, carding the material, blending the material with another material, yarn production from the material, and/or fiber production from the material.

Additional embodiments of the present disclosure pertain to delignified materials that are formed in accordance with the methods of the present disclosure. In some embodiments, the delignified material is in a form that includes, without limitation, a yarn, a fiber, a cellulosic fiber, or combinations thereof. In some embodiments, the delignified material is smoother relative to the untreated material. In some embodiments, the delignified material is softer relative to the untreated material. In some embodiments, the delignified material is stronger relative to the untreated material.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method of removing lignin from materials in accordance with various embodiments of the present disclosure.

FIG. 2 is a graph showing the composition of raw fibers (untreated).

FIGS. 3A-3D show the spatial distribution of cellulose, hemicellulose, and lignin in hemp bast characterization using Fourier-Transform Infrared (FT-IR) spectroscopy.

FIG. 4 is a graph showing the crystallinity assessment of hemp bast fiber.

FIGS. 5A-5B show CIELAB color spaces of deep eutectic solvent system (DES)-treated fibers (FIG. 5A) and raw fibers (FIG. 5B).

FIGS. 6A-6B illustrate an example of thermal delignification reactions (FIG. 6A) and the appearances of delignified fibers (FIG. 6B). The left panels of FIGS. 6A-6B represent reactions where the fibers were pre-treated with potassium hydroxide (KOH), and the DES included choline chloride and urea ([Cho]Cl:Urea). The right panels of FIGS. 6A-6B represent reactions where the fibers were not pre-treated, and the DES included choline chloride and lactic acid ([Cho]Cl:Lactic Acid).

FIGS. 7A-7B illustrate an example of microwave-assisted delignification reactions using [Cho]Cl:Urea as the DES. The top images in FIGS. 7A-7B show the reactions while the bottom images in FIGS. 7A-7B show the appearance of delignified fibers. FIG. 7A shows the delignification reaction of raw hemp fiber (Ø ˜60 μm) to form DES-treated hemp fiber (Ø ˜20 μm). FIG. 7B shows the delignification reaction of cotton fiber.

FIGS. 8A-8C show scanning electron microscopic (SEM) images of raw hemp fibers (Ø ˜60 μm) (FIG. 8A), DES-treated hemp fiber (Ø ˜20 μm) (FIG. 8B), and cotton fibers (FIG. 8C).

FIGS. 9A-9C show fiber analyses of raw hemp fiber (FIG. 9A), DES-treated hemp fiber (FIG. 9B), and KOH-pretreated and DES-treated hemp fiber (FIG. 9C) using MDTA 3 Microdust and Trash Analyzer.

FIG. 10 shows an image of open fibers (carded).

FIGS. 11A-11B show flow diagrams of yarn formation.

FIGS. 12A-12B show images of formed cotton-hemp yarns at a weight ratio of 50:50.

FIG. 13 shows an image of a dyed hemp fiber.

DETAILED DESCRIPTION

It is to be understood that both the foregoing general description and the following detailed description are illustrative and explanatory, and are not restrictive of the subject matter, as claimed. In this application, the use of the singular includes the plural, the word “a” or “an” means “at least one”, and the use of “or” means “and/or”, unless specifically stated otherwise. Furthermore, the use of the term “including”, as well as other forms, such as “includes” and “included”, is not limiting. Also, terms such as “element” or “component” encompass both elements or components comprising one unit and elements or components that include more than one unit unless specifically stated otherwise.

The section headings used herein are for organizational purposes and are not to be construed as limiting the subject matter described. All documents, or portions of documents, cited in this application, including, but not limited to, patents, patent applications, articles, books, and treatises, are hereby expressly incorporated herein by reference in their entirety for any purpose. In the event that one or more of the incorporated literature and similar materials defines a term in a manner that contradicts the definition of that term in this application, this application controls.

Lignocellulosic materials have gained significant interest as renewable natural resources for bioenergy production and biomaterials due to the wide availability of the raw materials, the cost-effectiveness of processing, and the already large-scale manufacturing. These materials can be obtained from plants and downstream residues of energy and pulp production. They are considered the most sustainable resource for substrates and precursors for a broad range of applications, from biofuels to value-added chemicals, such as bioethanol production, biocomposite materials, food additives, paper, board industry, biotechnology, and pharmaceutical products.

Hemp is a lignocellulosic material that is recognized as a source of extraordinarily tensile and durable textile fibers. The material is not susceptible to shrinkage, highly resistant to pilling, very soft, and highly durable. For example, a hemp shirt typically lasts two or three times longer than cotton.

Hemp provides many benefits to other materials. However, hemp's properties, such as coarseness, lack of uniform length, and high stiffness present challenges to using hemp to produce materials on traditional cotton spinning systems.

Moreover, textile applications of hemp require transformation of hemp fiber to yarn and yarn to fabric. However, the surface characteristics and other properties of hemp make it difficult to process hemp on cotton spinning systems. In order to have a yarn from fiber, the yarn needs to be spun by using cotton-spinning methods, such as rings and rotors.

Furthermore, in order to produce fine quality yarn, special physical and mechanical characteristics are required for hemp fibers: strength, softness, uniform staple length, fineness (e.g., as represented by micronaire value), and single entity fiber. For hemp, lack of individual fiber entity, fiber thickness (>8 micronaire), coarseness, lack of uniform length, and high stiffness make it difficult to be spun on cotton spinning systems.

Among these parameters, the fiber coarseness is one of the major hindrances to hemp's extensive production as it requires higher investments for specialized machinery. The reason for this coarseness is that the outer part of the plant, long phloem fibers (also called bast), contains not only cellulose (57-77%), but also hemicellulose (9-14%), and lignins (5-9%). High amount of lignins binds plant fibers, providing rigidity to the cell wall. The quantity, constitution, and structure of lignins may differ throughout the fiber.

To be able to use hemp in textile products either alone or in combination with cotton, the process called “delignification” is required. Delignification is the process of degumming (i.e., removal of lignins, pectins, gums, and some of hemicellulose from the bast), which softens natural fibers in order to bring them as much as possible to the properties of cotton. Different parts of a fiber show different susceptibility to delignification. Once delignified, hemp fibers could be spun on the cotton machinery alone or blended with other fibers.

While significant research efforts have been made on delignification of other biomasses, these efforts have used heavy chemical treatment and/or did not produce fiber of desired properties. The current delignification practices of hemp employ various processes that have numerous limitations.

For instance, processes exist for delignification of hemp using hydrogen peroxide (H₂O₂), sodium sulfite (Na₂SO₃), alkali metasilicates, Na₅P₃O, and urea. See, e.g., Yu et al., “Hemp fiber and preparation method thereof.” Chinese Pat. No. CN101831715A. In many instances, such processes use caustic solutions (e.g., pH=11) containing the following chemicals (in various ratios): hydrogen peroxide (H₂O₂), sodium sulfite (Na₂SO₃), alkali metasilicates, Na₅P₃O, urea, and a penetrating agent. Moreover, such processes are typically carried out under high temperature and (often) pressure, which damage fiber strength and necessitate the use of expensive, specialized equipment. Such processes also produce large amounts of liquid waste, involve processing difficulties, and present serious environmental concerns. Additionally, such processes are not feasible in view of sustainable production.

Additional delignification processes involve Kraft (alkaline) pulping. See, e.g., Wool et al., “Lignin polymers and composites.” In: Bio-Based Polymers and Composites, Wool, R. P.; Sun, X. S. (Eds), Academic Press, 2005, 551-598. However, the Kraft pulping process uses a hot mixture of water, sodium hydroxide (NaOH), and sodium sulfide (Na₂S), and requires a lot of energy to reduce sulfides-containing black liquor waste emissions.

Similarly, OrganoSolv (i.e., solvent-based) processes use catalysts in organic solvents for delignification. See, e.g., Moradbak et al., “Effects of alkaline sulfite anthraquinone and methanol pulping conditions on the mechanical and optical paper properties of bamboo.” BioRes. 2016, 11, 5994-6005. There are many processes that belong to the OrganoSolv family. While this process is environmentally friendlier than Kraft pulping, OrganoSolv pulping has high capital and processing costs associated with extensive recycling of the solvents. Moreover, the OrganoSolv process has not been permanently applied at the industrial scale.

Ionic liquids (ILs)-based methods also exist for delignification. See, e.g., Miranda et al., “Pineapple crown delignification using low-cost ionic liquid based on ethanolamine and organic acids.” Carbohydr. Polym. 2019, 206, 302-308. For instance, many ILs-based methods use 1,3-dialkylimidazolium ionic liquids with moderate to strong hydrogen-bonding anions such as trifluoromethanesulfonate (triflate, [OTf]⁻), methyl sulfate ([MeSO₄]⁻), chloride, bromide, and acetate anions. However, such methods suffer from the necessity of recycling the costly solvents, which may not be practical in view of the current state of recycling technologies.

Many methods also rely on microbial and enzymatic delignification processes. For instance, an enzymatic delignification process followed by a mechanical carding has been reported. See, e.g., Sedelnik et al., “Properties of hemp fiber cottonised by biological modification of hemp hackling noils.” Fibres Textiles East. Eur. 2004, 12 (1), 58-60. As a result of treating hemp bundles with enzymatic pectoenzyme cocktail, the content of hemicelluloses, lignin, and pectin decreased by 28%, 23%, and 98%, respectively. Subsequent mechanical processing resulted in the bundles' separation into smaller units, producing soft, easily separable hemp fibers. The enzymatic treatment reduced the fiber linear density by 30-40% and mean length by 5.5 times. However, this hemp has not been used for yarn production.

Various commercial and non-commercial enzymatic cocktails have also been utilized for delignification (e.g., enzymes produced by Röhm Enzyme GmbH and Novozymes AS/Bayer AG). Dreyer et al., “Comparison of enzymatically separated hemp and nettle fiber to chemically separated and steam exploded hemp fiber.” Journal of Industrial Hemp 2001, 7 (1), 43-59. When such enzymatic treatments were compared to alkaline treatment, it was found that the enzymatic separation was capable of producing comparably fine and strong fibers suitable for textile production, and that changes in fiber fineness and strength were similar to those obtained after alkaline treatments. However, such enzymatic treatment processes are slow, cost-prohibitive, and, most importantly, result in loosening a fibers' tenacity by more than 90%. The fibers therefore become unsuitable for cotton spinning systems. In addition, there exists a disagreement about the effect of enzymatic treatment on the strength of hemp fibers.

Many studies also utilize a combination of enzymatic and chemical treatment approaches. See, e.g., Fischer et al., “Enzymatic Modification of Hemp Fibres for Sustainable Production of High Quality Materials”, J. Natur. Fibers 2006, 3, 39-53. For instance, the study in Fischer et al. combined chemical pretreatment (using sodium hydroxide NaOH, ethylenediaminetetraacetic acid EDTA, and sodium hydrogen carbonate NaHCO₃) with enzymatic treatment (using Lyvelin™ and Texazym™ pectinases) and investigated the effect on the resulting fibers' quality. The results showed that treatment with NaOH of low concentrations had a limited effect on fiber quality, EDTA treatment had no effect, and NaHCO₃ treatment improved the efficiency of the subsequent enzymatic step. Lignin content (expressed in kappa-number) decreased from 18 in raw fibers to 7 in fibers that were treated chemically.

Another study investigated the chemical composition of a hemp fiber and its properties (morphology, fineness, flexibility, tensile strength, and moisture absorption) after a combination of enzymatic pretreatment (using Scourzyme301L enzyme) with a chemical treatment. See, e.g., Jinqiu et al., “Effect of refined processing on the physical and chemical properties of hemp bast fibers.” Textile Res. J. 2010, 80 (8), 744-753. Chemical treatment included alkali boiling (NaOH, 0.6 wt. %), alkali refinement (NaOH, 2 wt. %) and bleaching (hypochlorite solution, NaClO₂). The study reported that the removal of lignins and pectins was at least 93%. While the fiber strength was insignificantly reduced, fiber fineness increased, and the number of fibers in a given fiber count increased proportionally.

Another study reported pure alkaline (sodium hydroxide, NaOH) boiling for cottonization of hemp fibers, and determined that this process was 100% effective for removing pectin but not lignin. See, e.g., Wang et al., “Removing pectin and lignin during chemical processing of hemp for textile applications.” Textile Res. J. 2003, 73 (8), 664-669. While lignin in the middle lamella could be removed fully by pure alkali treatment, the lignin from the cell secondary layers could not be accessed and/or degraded during alkali boiling. It was also found that the concentration of NaOH had significant effects on lignin removal, and that addition of sodium sulfite (NaSO₃) to the process facilitated the delignification.

However, many of the aforementioned processes utilize conditions that damage fibers and reduce fiber strength. Additionally, such conditions necessitate the use of expensive and specialized equipment. Moreover, the aforementioned processes produce large amounts of liquid waste, involve processing difficulties, and present serious environmental concerns. Numerous embodiments of the present disclosure aim to address the aforementioned limitations.

In some embodiments, the present disclosure pertains to methods of removing lignin from a material. In some embodiments illustrated in FIG. 1, the methods of the present disclosure include associating the material with a solvent that is operational to dissolve the lignin associated with the material (step 10). In some embodiments, the methods of the present disclosure also include a step of heating the material (step 12). In some embodiments, the methods of the present disclosure also include one or more steps of: separating the material from the solvent (step 14); drying the material (step 16); washing the material (step 18); and/or processing the material (step 20). In some embodiments, the processing of the material includes one or more steps of: opening the material (step 22); carding the material (step 24); blending the material with another material (step 26); yarn production from the material (step 28); and/or fiber production from the material (step 30).

Additional embodiments of the present disclosure pertain to delignified materials. In some embodiments, the delignified materials are formed in accordance with the methods of the present disclosure.

As set forth in more detail herein, the methods of the present disclosure can delignify various materials for various purposes. As also set forth in more detail herein, the delignified materials of the present disclosure can have numerous structures and advantageous properties.

Materials

The methods of the present disclosure may be utilized to delignify various materials. Additionally, the delignified materials of the present disclosure may be derived from various materials. For instance, in some embodiments, the materials include, without limitation, lignocellulosic materials, biomass, woody biomass, untreated wood, fibers, lignocellulosic fibers, hemp, hemp bast fibers, kenaf, jute, sisal, flax, ramie or combinations thereof. In some embodiments, the materials include hemp. In some embodiments, the materials include hemp bast fibers.

Association of Materials with Solvents

The present disclosure may utilize various methods to associate materials with solvents. For instance, in some embodiments, the associating occurs by a method that includes, without limitation, mixing, immersing, sonicating, embedding, incubating, or combinations thereof.

Solvents

The present disclosure may utilize various solvents to delignify materials. For instance, in some embodiments, the solvent is operational to completely dissolve the lignin associated with the material. In some embodiments, the solvent is operational to substantially dissolve the lignin associated with the material. In some embodiments, the solvent dissolves at least 60% of the lignin associated with the material. In some embodiments, the solvent dissolves at least 80% of the lignin associated with the material. In some embodiments, the solvent dissolves at least 90% of the lignin associated with the material. In some embodiments, the solvent dissolves at least 95% of the lignin associated with the material. In some embodiments, the solvent dissolves at least 99% of the lignin associated with the material. In some embodiments, the solvent dissolves at least 100% of the lignin associated with the material.

In some embodiments, the solvent includes a deep eutectic solvent (DES). In some embodiments, the DES solvent includes two or more components. In the context of the present disclosure, a DES solvent consisting of two or more components is meant, in particular at least a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBO) interacting therebetween by associating and forming a eutectic mixture with a melting temperature much lower than that of its components. In some embodiments, it is assumed that the self-association occurs through interactions of hydrogen bond, even if it is assumed that even Van der Waals forces can play a relevant role. DES solvents generally refer to solvents formed from a eutectic mixture of Lewis or Brønsted acids and bases. In some embodiments, the DES solvents can contain a variety of anionic and/or cationic species. In some embodiments, DES solvents can form a eutectic point in a two-component phase system.

In some embodiments, the DES solvent includes at least one HBA and at least one HBD. In some embodiments, the HBAs and HBDs non-covalently interact with one another in the DES solvent. In some embodiments, the interaction of HBDs with HBAs in the DES solvent reduces the DES solvent's electrostatic force, thereby decreasing the melting point of the DES solvent.

HBAs generally refer to compounds that are operational to accept an electron pair. The DES solvents of the present disclosure can include various HBAs. For instance, in some embodiments, the HBA includes, without limitation, a quaternary ammonium salt selected in the group consisting of choline, betaine, proline, carnitine, acetylcholine, carnitine, ethyl ammonium chloride, diethyl ammonium chloride, a salt of a neutral compound with a positively charged cationic functional group, imidazolium, a substituted imidazolium salt, a quaternary ammonium compound, a substituted ammonium compound, pyridinium, a substituted pyridinium compound, a phosphonium compound, a morpholinium compound, or combinations thereof.

In some embodiments, the HBA includes a neutral compound with a positively charged cationic functional group. In some embodiments, the positively charged cationic functional group includes, without limitation, choline, betaine, carnitine, imidazolium, a substituted imidazolium, a quaternary ammonium, a substituted ammonium, pyridinium, a substituted pyridinium, phosphonium, morpholinium, or combinations thereof.

HBDs generally refer to compounds with at least one functional group that possesses an electron pair. The DES solvents of the present disclosure can also include various HBDs. For instance, in some embodiments, HBDs include, without limitation, urea, amide, a carboxylic acid, an amino acid, an amine, an amide, an alcohol, or combinations thereof.

In some embodiments, the HBDs include, without limitation, one or more amino acids. In some embodiments, the one or more amino acids include, without limitation, proline, serine, glycine, alanine, glutamic acid.

In some embodiments, the HBDs include, without limitation, urea. In some embodiments, the urea includes, without limitation, thiourea, methyl urea, dimethyl urea, trifluoromethyl urea.

In some embodiments, the HBD includes one or more amides. In some embodiments, the one or more amides include, without limitation, acetamide, trifluoroacetamide, or combinations thereof.

In some embodiments, the HBD includes a carboxylic acid. In some embodiments, the carboxylic acid includes, without limitation, lactic acid, oxalic acid, formic acid, glycolic acid, levulinic acid, malic acid, malonic acid, glutaric acid, succinic acid, tartaric acid, benzoic acid, itaconic acid, citric acid, isocitric acid, or combinations thereof.

In some embodiments, the HBD includes an alcohol. In some embodiments, the alcohol includes, without limitation, propylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, ethylene glycol, triethylene glycol, sorbitol, xylitol, ribitol, erytritol, maltitol, mannitol, lactitol, inositol, butanediol, glycerol, or combinations thereof.

The DES solvents of the present disclosure can include various ratios of HBAs and HBDs. For instance, in some embodiments, the molar ratio of HBA to HBD includes a value ranging from about 3:1 to about 1:3. In some embodiments, the molar ratio of HBA to HBD includes value ranging from about 0.1 to about 3. In some embodiments, the molar ratio of HBA to HBD includes a value of about 0.5. In some embodiments, the molar ratio of HBA to HBD includes, without limitation, a value of 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:2, 1:1, 1:0.9, 1:0.8, 1:0.7, 1:0.6, 1:0.5, 1:0.4, 1:0.3, 1:0.2, or 1:0.1.

The DES solvents of the present disclosure can include various combinations of HBAs and HBDs. For instance, in some embodiments, the HBA includes choline chloride, and the HBD includes urea. In some embodiments, the DES solvents of the present disclosure include choline chloride and urea at a molar ratio of 1:2. In some embodiments, the HBA includes choline chloride and the HBD includes lactic acid. In some embodiments, the DES solvents of the present disclosure include choline chloride and lactic acid at a molar ratio of 1:2.

Heating

In some embodiments, the methods of the present disclosure also include a step of heating a material of the present disclosure. In some embodiments, the heating step and the solvent associating step occur simultaneously. In some embodiments, the solvent associating step occurs prior to the heating step.

The heating of the materials of the present disclosure can occur in various manners. For instance, in some embodiments, the heating step includes thermal heating, microwave heating, or combinations thereof. In some embodiments, the heating step includes applying heat from a heat source. In some embodiments, the heat source includes a microwave radiation source.

In some embodiments, the heating of a material includes microwave radiation of a material of the present disclosure. Microwave radiation of a material may occur for various periods of time. For instance, in some embodiments, the microwave radiation occurs from about 1 minute to about 10 minutes. In some embodiments, the microwave radiation occurs for at least about 1 minute. In some embodiments, the microwave radiation occurs for at least about 2 minutes. In some embodiments, the microwave radiation occurs for at least about 3 minutes. In some embodiments, the microwave radiation occurs for at least about 5 minutes.

Microwave radiation of a material may occur at various frequencies. For instance, in some embodiments, the microwave radiation frequency includes at least 1 GHz. In some embodiments, the microwave radiation frequency includes at least 1.5 GHZ. In some embodiments, the microwave radiation frequency includes at least 2.0 GHz. In some embodiments, the microwave radiation frequency includes at least 2.5 GHz.

In some embodiments, the heating of a material includes thermal heating. Thermal heating may occur at various temperatures. For instance, in some embodiments, thermal heating occurs at a temperature above room temperature. In some embodiments, thermal heating occurs at a temperature above 25° C. In some embodiments, thermal heating occurs at a temperature above 50° C. In some embodiments, thermal heating occurs at a temperature above 75° C. In some embodiments, thermal heating occurs at a temperature above 80° C. In some embodiments, thermal heating occurs at a temperature above 90° C. In some embodiments, thermal heating occurs at a temperature of at least 100° C. In some embodiments, thermal heating occurs at a temperature ranging from about 100° C. to about 160° C. In some embodiments, thermal heating occurs at a temperature ranging from about 90° C. to about 150° C. In some embodiments, thermal heating occurs at a temperature of about 135° C.

Thermal heating may occur for various periods of time. For instance, in some embodiments, thermal heating occurs for at least about 1 minute. In some embodiments, thermal heating occurs for at least about 5 minutes. In some embodiments, thermal heating occurs for at least about 10 minutes. In some embodiments, thermal heating occurs for at least about 15 minutes. In some embodiments, thermal heating occurs for at least about 30 minutes. In some embodiments, thermal heating occurs for at least about 45 minutes. In some embodiments, thermal heating occurs for at least about 1 hour. In some embodiments, thermal heating occurs for at least about 2 hours. In some embodiments, thermal heating occurs for at least about 4 hours. In some embodiments, thermal heating occurs from about 1 hour to about 4 hours. In some embodiments, the thermal heating occurs for about 2 hours.

Solvent Separation

In some embodiments, the methods of the present disclosure also include a step of separating a material of the present disclosure from a solvent. In some embodiments, the solvent separation step occurs after the solvent associating step. In some embodiments, the solvent separation step occurs after the solvent associating and heating steps.

Various methods may be utilized to separate a material of the present disclosure from a solvent. For instance, in some embodiments, the separation occurs by a method that includes, without limitation, centrifugation, evaporation, decantation, or combinations thereof.

Drying

In some embodiments, the methods of the present disclosure also include a step of drying a material of the present disclosure. In some embodiments, the drying occurs after the solvent associating step. In some embodiments, the drying occurs after the solvent associating and heating steps. In some embodiments, the drying occurs after separating the material from the solvent.

In some embodiments, the drying occurs by incubating the material at room temperature for a certain amount of time. In some embodiments, the drying occurs by incubating the material in a heated environment above room temperature for a certain amount of time.

Washing

In some embodiments, the methods of the present disclosure also include a step of washing a material of the present disclosure. In some embodiments, the washing occurs after the solvent associating step. In some embodiments, the washing occurs after the solvent associating and heating steps. In some embodiments, the washing occurs after separating the material from the solvent.

The materials of the present disclosure may be washed in various manners. For instance, in some embodiments, the washing step includes washing a solvent-treated material of the present disclosure with water until the solvent is fully or substantially removed. In some embodiments, the materials may then be dried.

Processing

In some embodiments, the methods of the present disclosure also include a step of processing a material of the present disclosure. In some embodiments, the processing occurs after the solvent associating step. In some embodiments, the processing occurs after the solvent associating and heating steps.

The materials of the present disclosure may be processed in various manners. For instance, in some embodiments, the processing occurs by a method that includes, without limitation, opening the material, carding the material, blending the material with another material, yarn production from the material, fiber production from the material, or combinations thereof.

In some embodiments, the processing includes blending the material with another material. In some embodiments, the other material includes, without limitation, polymer fiber, cotton, polyester, wool, or combinations thereof. In some embodiments, the other material includes cotton.

In some embodiments, the processing includes yarn production from the material. In some embodiments, the processing further includes fiber production from the yarn.

Pre-Treatment

In some embodiments, the methods of the present disclosure also include a step of pre-treating a material of the present disclosure. In some embodiments, the pretreatment step occurs prior to the solvent associating step. In some embodiments, the pretreatment step occurs prior to the solvent associating and heating steps.

The materials of the present disclosure can be pre-treated in various manners. For instance, in some embodiments, the pre-treatment step includes pre-treating the material with an alkali metal, such as potassium hydroxide (KOH), sodium hydroxide (NaOH).

The pre-treatment steps of the present disclosure can occur for various periods of time. For instance, in some embodiments, the pre-treatment step occurs for at least about 15 minutes. In some embodiments, the pre-treatment step occurs for at least about 30 minutes. In some embodiments, the pre-treatment step occurs for at least about 45 minutes. In some embodiments, the pre-treatment step occurs for at least about 1 hour. In some embodiments, the pre-treatment step occurs for at least about 1.5 hours. In some embodiments, the pre-treatment step occurs for at least about 2 hours.

The pre-treatment step can occur at various temperatures. For instance, in some embodiments, the pre-treatment step occurs at a temperature above room temperature. In some embodiments, the pre-treatment step occurs at a temperature above 25° C. In some embodiments, the pre-treatment step occurs at a temperature above 50° C. In some embodiments, the pre-treatment step occurs at a temperature above 65° C. In some embodiments, the pre-treatment step occurs at a temperature above 75° C.

Delignified Materials

The methods of the present disclosure may be utilized to form various types and forms of delignified materials. Additional embodiments of the present disclosure pertain to such delignified materials.

In some embodiments, the methods of the present disclosure substantially remove lignin, pectins, gums, and hemicellulose from a material. For instance, in some embodiments, the methods of the present disclosure remove at least 60% of lignin from a material. In some embodiments, the methods of the present disclosure remove at least 80% of lignin from a material. In some embodiments, the methods of the present disclosure remove 100% of lignin from a material.

The delignified materials of the present disclosure may be in various forms. For instance, in some embodiments, the delignified material is in a form that includes, without limitation, a yarn, a fiber, a cellulosic fiber, or combinations thereof.

The delignified materials formed by the methods of the present disclosure can have various advantageous properties. For instance, in some embodiments, the delignified material is smoother relative to the untreated material. In some embodiments, the delignified material is softer relative to the untreated material. In some embodiments, the delignified material is stronger relative to the untreated material. In some embodiments, the delignified material is lighter in color relative to the untreated material.

Advantages

The methods and materials of the present disclosure have numerous advantages. For instance, in some embodiments, the methods of the present disclosure do not require destruction of material components other than lignin. Moreover, in some embodiments, the methods of the present disclosure occur in an expedited manner while being environmentally friendly. Additionally, the methods of the present disclosure can be scaled for the treatment of various materials. Furthermore, the materials formed by the methods of the present disclosure are generally smooth, soft, and strong.

As such, the methods and materials of the present disclosure can have numerous advantageous applications. For instance, in some embodiments, the methods of the present disclosure provide a microwave-based method for processing raw hemp into easily manipulated fiber for hemp-based materials. In some embodiments, the methods of the present disclosure may be utilized to produce soft and strong hemp fibers. In some embodiments, the methods of the present disclosure may allow hemp to be spun on traditional cotton machines without the use of harsh chemicals or sophisticated machinery, thereby decreasing costs and expanding the broad applications of the material.

ADDITIONAL EMBODIMENTS

Reference will now be made to more specific embodiments of the present disclosure and experimental results that provide support for such embodiments. However, Applicants note that the disclosure below is for illustrative purposes only and is not intended to limit the scope of the claimed subject matter in any way.

Example 1. Transformation of Lignocellulosic Fiber to Yarn and Fabric Via Delignification, Fiber Formation and Yarn Production

This Example provides for a method for producing yarn from hemp bast fibers or other lignocellulosic materials (e.g., kenaf, jute, flax) through (1) delignification using deep eutectic solvents (also called deep eutectic systems), (2) fiber opening/carding, and (3) spinning steps. This Example is based on a new and useful method for removing lignin from lignocellulosics such as hemp bast fibers and other natural lignocellulosic materials in various deep eutectic solvents under thermal or microwave heating, affecting the critical spinning properties of hemp fiber, and production of yarn from hemp fiber on cotton spinning systems.

In this Example, lignin is removed from lignocellulosic materials in one-step using deep eutectic solvent (DES) treatment, at elevated temperatures (e.g., 90-150° C.) for 1-4 h. Heating can also be provided using microwave heating (0.1-15 min).

Example 1.1. Assessment of ‘Original’ Hemp Bast Properties

Five different samples of raw long phloem fibers, bast, were obtained from supplier, and the composition was assessed (Table 1 and FIG. 2). The cellulose content in biomass was determined in accordance with the TAPPI T203 cm-99 method, and the cellulose, hemicellulose and lignin contents were determined using a modified TAPPI T222om-06 method. The composition was found to be as follows: 61.2±6.6% cellulose, 17.4±3.38% hemicellulose, and 21.4±4.03% lignin, average on 5 cultivars. While the amount of cellulose in fibers was in line with reported literature data (57-77 wt. %), the amount of hemicellulose and lignin were higher than those reported (Lit: 9-14 wt. % for hemicellulose and 5-9 wt. % for lignin). Four different types of hemp bast fibers were analyzed for composition.

TABLE 1
Composition of hemp bast fibers. Samples from B1 through
B5. B1 = Preliminary sample, B2 = Mason Fane Farms
(SS Delta 19′), B3 = Mason Lane Farms (Bialobrzeskie
21′), B4 = Mason Lane Farms (Futura 75 20′), B5 = Ziegler (Jinma 20′).
	Holocellulose	Lignin	Hemicellulose	Cellulose
Samples	(%)	(%)	(%)	(%)
B1	77 ± 0	23	22 ± 0	55 ± 0
B2	79 ± 2.83	21 ± 2.83	14 ± 0	65 ± 2.83
B3	84 ± 0.71	16 ± 0.71	13 ± 1.41	71 ± 0.71
B4	81 ± 0	19 ± 0	19 ± 0	62 ± 0
B5	72 ± 1.41	28 ± 1.41	19 ± 1.41	53 ± 2.83

The morphological structures were observed using scanning electron microscope (SEM) (Hitachi™-1000, Japan) with an accelerating voltage of 15 kV. The fiber thickness was found to be in the range of 60-80 μm. The raw hemp fibers that contained cellulose, lignin, hemicellulose, and pectin demonstrated a rough surface.

The spatial distribution of cellulose, hemicellulose, and lignin in hemp biomass was assessed through characterization using Fourier-Transform Infrared (FT-IR) spectroscopy, and showed peaks associated with all three biopolymers: cellulose, hemicellulose, and lignin, respectively (FIGS. 3A-3D). The crystalline structures were identified using powder X-ray diffraction (pXRD) on the SmartLab system and was determined to be 63% (FIG. 4).

Example 1.2. Delignification of Fibers

Several delignification trials of raw (and also KOH-pretreated) fibers using deep eutectic solvent systems (DESs) under different conditions (e.g., type of DES, time, and temperature) were conducted. The best systems involved included choline chloride:lactic acid ([Ch]Cl:LA) and choline chloride:urea ([Ch]Cl:Urea) (FIGS. 6A-6B, and 7A-7B). Various eutectic compositions (from 1:1 to 10:1), at different temperatures (90° C.-135° C.), for different reaction times (0.5 h-3 h) were employed. After the treatment, fibers appeared off-white, became soft on touch, and the surface of fibers appeared to be smooth and round without fibers being destroyed.

Similarly, microwave heating (1-10 min) as an alternative to temperature heating was successfully conducted. Microwaving remarkably reduced the energy required for the treatment, because of partially ionized nature of deep eutectic solvents. For the trials that resulted in strong and/or soft fibers, resulting fibers were analyzed through morphological evaluation using scanning electron microscopy (SEM), chemical characterization using Fourier-Transform Infrared (FT-IR) spectroscopy, weight loss after treatment, “feel” (soft or brittle), color, and extent of fiber breakage after the treatment. It appeared that the choline chloride/urea DES-system is less destructive than other systems.

Example 1.2.1. Fiber Appearance. Fibers that were Treated with [Ch]Cl:Urea (1:2) for 2 h at 135° C., or (alternatively) for 5 min in microwave showed a smooth and clean surface, comparable with alkali-treated fiber surfaces. The fibers were soft to the touch, strong, and lost 18-25% weight due to delignification.

Example 1.2.2. Change of color. Bast fibers after the treatment were assessed using X-rite Ci7600 benchtop spectrophotometer, which allowed one to measure color and appearance on a wide range of samples. The spectrophotometer used a CIELAB color space diagram principle, which represents quantitative relationship of colors on three axes: lightness, and chromaticity coordinates. The results are shown in FIGS. 5A-5B, where a change of color was observed after treatment.

Example 1.2.3. Scanning electron microscopy (SEM) of raw cotton and delignified hemp fibers. As shown in FIGS. 8A-8C, SEM of the fibers were conducted and showed significant difference between raw and treated fibers. While raw cotton exhibits natural convolution to the fiber axis (FIG. 8C), hemp fibers do not have such twists (FIGS. 8A-8B). Comparison of raw hemp (FIG. 8A), delignified hemp, and KOH-treated delignified hemp using DESs (FIG. 8B) side-by-side with raw cotton, with cotton shown in FIG. 8C, show comparable diameter of delignified fibers with cotton fibers. Raw hemp fiber appears rough and thick (FIG. 8A), whereas hemp delignified and treated with [Ch]Cl:Urea (1:2) appears round, smooth, and fine (FIG. 8B). The fibers also appeared as individual fibers. Such noticeably cleaner surface of the DES-treated hemp fibers was due to the removal of lignin from the fiber structure.

Example 1.2.4. Fiber analysis using MDTA 3 microdust and trash analyzer. As shown in FIGS. 9A-9C, analysis of the delignified hemp fibers was conducted using the QUICKSPIN Module 1, Microdust and Trash Analyzer (MDTA 3, SDL ATLAS, Textile Testing Solution, SC, US), which delivers valuable information regarding different raw materials: cleanability, opening behavior, fiber cohesion, processing behavior, and contamination. Testing a sample on the microdust and trash analyzer (MDTA 3) machine allowed determination of the trash content, and dust and fiber fragments vs. clean fiber weight, while evaluating fibers' cleanability. Module 1 requires fibers to be placed on a conveyor and transported with unidirectional feed to the opening roller for fiber opening. Dust particles and fiber fragments were separated from the fibers, collected in the dust channel, and gravimetrically measured. By testing a sample on the MDTA 3, the trash content, dust and fiber fragments were determined (Table 2). Additionally, the cleaning efficiency and cleanability was calculated. While raw hemp fibers were harsh to the touch, delignified fibers were soft, brighter in color, and lighter than the raw fibers. The amount of “trash” determined by the machine is shown in Table 2.

TABLE 2
Fiber Analysis using MDTA 3 Microdust and Trash Analyzer.
	Total	Sliver
Fiber types	weight (g)	weight (g)	Waste %
Raw hemp (no treatment)	7.30	3.00	61
DES-hemp (as prepared),	5.5	4.90	11
MDTA-3 Analysis
DES-hemp (after carding	6	5.82	3
w/o flats)
DES-hemp (after carding	6	4.26	29 (9% licker-
w/flats)			in, 18% stripper,
			2% other)

Example 1.2.5. Scale-up delignification. The reactor (10 L) was filled with DES, and fibers were added. The oil was set to run through a reactor jacket, and heated. After 1.5-2 h, the reactor temperature reached 135° C. After this moment, the reaction continued for 2 h. After that, the reactor was allowed to cool down, fibers were taken from a reactor and washed with water. Fibers were dried in the oven at 50° C. overnight. Due to washing with water, the fibers appeared clustered and harsh, and had to be opened afterwards.

Example 1.2.6. Fiber opening by hand. The individual fibers after washing and drying were tightly entangled. Before the fibers can be spun into a yarn, the high-density entangled fibers must be separated to a fiber-to-fiber state. Such reduction of the bulk density into progressively smaller and smaller tufts of fibers is commonly referred to as “fiber opening”. The degree and method of fiber opening is extremely important to the textile industry, because it is well known that fibers cannot be properly blended or carded until they have been separated into very small tufts. Fibers initially were opened by hand. As illustrated in FIG. 10, the volume occupied by a given weight of fibers significantly increased after opening.

Example 1.2.7. Determination of the trash content, and dust and fiber fragments vs. clean fiber weight. Testing a sample on the microdust and trash analyzer (MDTA 3) machine allowed determination of the trash content, and dust and fiber fragments vs. clean fiber weight, while evaluating fibers' cleanability (Table 2).

Example 1.2.8. Fiber carding by mini-carding equipment. After fibers were opened by hand, they were carded by mini-carding equipment (Platt Bros & Co Ltd, Werneth, Oldham, England), of two different types: 1) “without flats” and 2) “with flats” (for gentler and less gentle opening, respectively). First, fibers were processed using more gentle opening, using “without flats” carding machine (Platt Bros & Co Ltd, Werneth, Oldham, England), resulting in essentially no waste. Then the carded fibers obtained from “without flats” carding machine were fed into the mini-carding machine “with flats” (Platt Bros & Co Ltd, Werneth, Oldham, England), to remove course and short fibers (29% waste). After mini carding no web formation was observed however fiber opening was sufficient for further processing into blend.

Example 1.2.9. Yarn Formation. As illustrated in FIGS. 11A-11B, Applicants attempted a small amount (2 g) of delignified fibers for yarn formation. Applicants used 50/50: cotton/hemp. (Cotton mic value: 4.9, hemp mic value: 6.5, assessed by the conventional micronaire measurement tester). Hemp fibers were blended with cotton using MDTA 3 (SDL ATLAS, Textile Testing Solution, SC, US), avoiding draw frame, although the draw frame might provide more uniform slivers. The MDTA 3 produced cotton/hemp blended sliver (60 grain/yard) without forming any trash. The sliver was fed into a rotor spinning machine (Quickspin, SDL ATLAS, Textile Testing Solution, SC, US), using the following settings: face plate 400 mm, large spiral nable, and 40 mm rotor. As shown in FIGS. 12A-12B and 13, rotor-spun yarn was produced without any problems.

Example 1.3. Assessment of Hemp Bast Composition

Example 1.3.1. Lignin removal by bleaching. Ground bast (2 g) was weighed using a balance (XS 104, Mettler Toledo, Switzerland) and placed into a 100 mL round bottom flask equipped with a condenser and a magnetic stir bar. Then, 75 mL DI water was placed into the flask. Next, the flask was shaken by hand until the hemp materials dipped into the water, and the flask was placed into a silicon oil heating bath. The heating and mixing (Isotemp, Fisher Scientific, Waltham, MA, US) continued until the temperature reached 75° C., at which point, 0.5 mL acetic acid and 0.6 g sodium chlorite were added consecutively. After 1 hour of heating and mixing, the addition of 0.5 mL acetic acid and 0.6 g sodium chlorite was repeated. This was done two more times every 1 h, for a total of 4 times.

After 4 h of chlorite treatment, the material was cooled down to 5° C. in an ice bath. After cooling, the solids were filtered using a Buchner funnel (Whatman filter paper, Buckinghamshire, UK). The remaining solids were washed using DI water (3×150 mL) until the yellow color was completely removed. The material was then additionally washed with acetone (2×25 mL). After washing, solids were kept in a 50° C.-temperature oven overnight. Percent loss was reported as lignin content.

Example 1.3.2. Hemicellulose removal by NaOH treatment. The dried residue from the previous step was placed in a 50 mL beaker equipped with a magnetic stir bar, and 5 wt. % NaOH solution was added to bast (liquid:solid ratio of 30:1 w/w). The beaker was heated at 60° C. for 4 h on a hot plate (Isotemp, Fisher Scientific, Hampton, NH). Upon completing this step, the beaker was cooled down to RT. Solid was then filtered using the Buchner funnel (Whatman filter paper, Buckinghamshire UK).

Finally, the filtered solid was placed into 17 wt. % NaOH (liquid:solid ratio of 30:1 w/w) and stirred in NaOH solution for 45 min, at RT. Then the material was filtered and washed using DI water (3×150 mL), 10% acetic acid (2×25 mL), and acetone (2×25 mL). Resulting solid was in 50° C.-temperature oven overnight. The percent loss was reported as hemicellulose content.

As summarized in Table 3, the cellulose content was determined by the difference between weight of raw fibers and lignin and hemicellulose content. All experiments were conducted in triplicates.

TABLE 3
Composition of hemp bast fibers.
	Biomass	Biomass	Holocellulose	Holocellulose	Lignin	Lignin	Hemicellulose	Hemicellulose	Cellulose	Cellulose
Sample	(g)	(%)	(g)	(%)	(g)	(%)	(g)	(%)	(g)	(%)
Bast
B - 1	2	100	1.531	77	0.469	23	0.426	22	1.105	55
B - 1	2	100	1.536	77	0.464	23	0.431	22	1.106	55
Avg.				77		23		22		55
STD				0		0		0		0
B - 2	2	100	1.533	77	0.467	23	0.270	14	1.264	63
B - 2	2	100	1.611	81	0.388	19	0.263	14	1.3485	67
Avg.				79		21		14		65
STD				2.83		2.83		0		2.83
B - 3	2	100	1.691	85	0.309	15	0.266	14	1.424	71
B - 3	2	100	1.679	84	0.321	16	0.236	12	1.443	72
Avg.				84		16		13		71
STD				0.71		0.71		1.41		0.71
B - 4	2	100	1.618	81	0.382	19	0.373	19	1.246	62
B - 4	2	100	1.617	81	0.384	19	0.373	19	1.245	62
Avg.				81		19		19		62
STD				0		0		0		0
B - 5	2	100	1.413	71	0.588	29	0.397	20	1.016	51
B - 5	2	100	1.452	73	0.548	27	0.344	18	1.108	55
Avg.				72		28		19		53
STD				1.41		1.41		1.41		2.83
Samples from B1 through B5.
B1 = Preliminary sample, B2 = Mason Fane Farms (SS Delta 19′), B3 = Mason Lane Farms (Bialobrzeskie 21′), B4 = Mason Lane Farms (Futura 75 20′), B5 = Ziegler (Jinma 20′).

Example 1.4. Preparation of [Ch]Cl:Urea Deep Eutectic Systems

Deep eutectic system [Ch]Cl:Urea (10:1 through 1:10) were prepared by mixing choline chloride and urea, at a desired molar ratio. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution.

Example 1.5. Preparation of [Ch]Cl:Lactic Acid Deep Eutectic Systems

Deep eutectic systems [Ch]Cl:Lactic Acid (10:1 through 1:10) were prepared by mixing choline chloride and lactic acid, at a desired molar ratio. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution.

Example 1.6. Delignification (Thermal Treatment) Using [Ch]Cl:Urea (1:2) with No Fibers Pretreatment

The heating conditions used in this Example were 140° C. for 1 h. Fibers were treated with [Ch]Cl:Urea (1:2) for 2 h at 140° C. [Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea, at a molar ratio of 1:2. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution. The hemp fiber sample was placed into DES (2 wt %) and heated until 140° C. was achieved, and for 1 h afterwards. After reaction, fibers were washed with tap water, oven-dried, and kept for further characterization. The reaction resulted in strong soft fibers of off-white color. The weight loss (lignin loss) was determined to be 25% by weight.

Example 1.7. Delignification (Thermal Treatment) Using [Ch]Cl:Urea (1:2) with KOH-Pretreatment

The heating conditions used in this Example were 140° C. for 1 h. Prior to the delignification, half of the fibers were pretreated using 5 wt. % of KOH for 90 min at 70° C. Pretreated fibers appear brighter in color than raw fibers, slightly softer in feel, and lost 20 wt. % during a pretreatment.

Next, KOH-pre-treated fibers were treated with [Ch]Cl:Urea (1:2) for 1 h at 140° C. [Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea, at a molar ratio of 1:2. The mixture was heated in at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution. The hemp fiber sample was placed into DES (2 wt %) and heated until 140° C. was achieved and for 2 h afterwards. After reaction, fibers were washed with tap water, oven-dried, and kept for further characterization. The reaction resulted in strong soft fibers of off-white color. The weight loss (lignin loss) was determined to be 8% by weight. Total weight loss during pretreatment and delignification was found to be 28%.

Example 1.8. Delignification (Thermal Treatment) Using [Ch]Cl:Urea (1:2) with No Fibers Pretreatment

The heating conditions used in this Example were 140° C. for 2 h. Fibers were treated with [Ch]Cl:Urea (1:2) for 2 h at 140° C. [Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea, at a molar ratio of 1:2. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution. The hemp fiber sample was placed into DES (2 wt %) and heated until 140° C. was achieved, and for 2 h afterwards. After reaction, fibers were washed with tap water, oven-dried, and kept for further characterization. The reaction resulted in strong soft fibers of off-white color. The weight loss (lignin loss) was determined to be 28% by weight.

Example 1.9. Delignification (Thermal Treatment) Using [Ch]Cl:Urea (1:2) with KOH-Pretreatment

The heating conditions used in this Example were 140° C. for 2 h. Prior to the delignification, half of the fibers were pretreated using 5 wt. % of KOH for 90 min at 70° C. Pretreated fibers appear brighter in color than raw fibers, slightly softer in feel, and lost 20 wt. % during a pretreatment.

KOH-pre-treated fibers were treated with [Ch]Cl:Urea (1:2) for 2 h at 140° C. [Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea, at a molar ratio of 1:2. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution. The hemp fiber sample was placed into DES (2 wt %) and heated until 140° C. was achieved and for 2 h afterwards. After reaction, fibers were washed with tap water, oven-dried, and kept for further characterization. The reaction resulted in strong soft fibers of off-white color. The weight loss (lignin loss) was determined to be 13% by weight; total weight loss during pretreatment and delignification was found to be 33%.

Example 1.10. Delignification (Thermal Treatment) Using [Ch]Cl:Urea (1:2) with No Fibers Pretreatment

The heating conditions used in this Example were 140° C. for 3 h. Fibers were treated with [Ch]Cl:Urea (1:2) for 3 h at 140° C. [Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea, at a molar ratio of 1:2. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution. The hemp fiber sample was placed into DES (2 wt %) and heated until 140° C. was achieved, and for 3 h afterwards. After reaction, fibers were washed with tap water, oven-dried, and kept for further characterization. The reaction resulted in strong soft fibers of off-white color. The weight loss (lignin loss) was determined to be 28% by weight.

Example 1.11. Delignification (Thermal Treatment) Using [Ch]Cl:Urea (1:2) with KOH-Pretreatment

The heating conditions used in this Example were 140° C. for 3 h. Prior to the delignification, half of the fibers were pretreated using 5 wt. % of KOH for 90 min at 70° C. Pretreated fibers appear brighter in color than raw fibers, slightly softer in feel, and lost 20 wt. % during a pretreatment.

KOH-pre-treated fibers were treated with [Ch]Cl:Urea (1:2) for 3 h at 140° C. [Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea, at a molar ratio of 1:2. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution. The hemp fiber sample was placed into DES (2 wt %) and heated until 140° C. was achieved and for 3 h afterwards. After reaction, fibers were washed with tap water, oven-dried, and kept for further characterization. The reaction resulted in strong soft fibers of off-white color. The weight loss (lignin loss) was determined to be 13% by weight. The total weight loss during pretreatment and delignification was found to be 33%.

Example 1.12. Delignification (Thermal Treatment) Using [Ch]Cl:Lactic Acid (1:2) with No Pretreatment

The heating conditions used in the Example were 135° C. for 1 h. Fibers were treated with [Ch]Cl:Lactic Acid (1:2) for 2 h at 135° C. [Ch]Cl:Lactic Acid (1:2) was prepared by mixing choline chloride and lactic acid, at a molar ratio of 1:2. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution. The hemp fiber sample was placed into DES (2 wt %) and heated until 135° C. was achieved and for 1 h afterwards. After reaction, fibers were washed with tap water, oven-dried, and kept for further characterization. The reaction resulted in strong soft fibers of off-white color. The weight loss (lignin loss) was determined to be 18% by weight.

Example 1.13. Delignification Using [Ch]Cl:Urea (1:2) with No Pretreatment

The heating conditions used in this Example were microwave heating for 5 minutes. [Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea, at a molar ratio of 1:2. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution. Fibers (2 wt. %) were placed into a 250 mL Erlenmeyer flask and heated via microwave irradiation (household microwave Emerson MW8999SB, Emerson Radio Corp., Moonachie, NJ) using 2 s pulses (to avoid overheating of the mixture). Between each pulse, the Erlenmeyer flask was removed from microwave, the mixture manually stirred with a glass stirring rod to ensure uniform dispersion of fibers in the DES, and the flask returned to the microwave. The mixture was heated for a total of 5 min (150 pulses). After reaction, fibers were washed with tap water, oven-dried, and kept for further characterization. The reaction resulted in strong soft fibers of off-white color. The weight loss (lignin loss) was determined to be 25% by weight.

Example 1.14. Delignification Using [Ch]Cl:Urea (1:2) with KOH-Pretreatment

The heating conditions used in this Example were microwave for 5 min. Prior to the delignification, half of the fibers were pretreated using 5 wt. % of KOH for 90 min at 70° C. Pretreated fibers appear brighter in color than raw fibers, slightly softer in feel, and lost 20 wt. % during a pretreatment.

[Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea, at a molar ratio of 1:2. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution. Fibers (2 wt. %) were placed into a 250 mL Erlenmeyer flask and heated via microwave irradiation (household microwave Emerson MW8999SB, Emerson Radio Corp., Moonachie, NJ) using 2 s pulses (to avoid overheating of the mixture). Between each pulse, the Erlenmeyer flask was removed from microwave, the mixture manually stirred with a glass stirring rod to ensure uniform dispersion of fibers in the DES, and the flask returned to the microwave. The mixture was heated for a total of 5 min (150 pulses). After reaction, fibers were washed with tap water, oven-dried, and kept for further characterization. The reaction resulted in strong soft fibers of off-white color. The weight loss (lignin loss) was determined to be 9% by weight. Total weight loss 29%.

Example 1.15. Delignification Using [Ch]Cl:Urea (1:2) with No Pretreatment

The heating conditions used in this Example were microwave heating for 8 min. [Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea at a molar ratio of 1:2. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution. Fibers (2 wt. %) were placed into a 250 mL Erlenmeyer flask and heated via microwave irradiation (household microwave Emerson MW8999SB, Emerson Radio Corp., Moonachie, NJ) using 2 s pulses (to avoid overheating of the mixture). Between each pulse, the Erlenmeyer flask was removed from microwave, the mixture was manually stirred with a glass stirring rod to ensure uniform dispersion of fibers in the DES, and the flask was returned to the microwave. The mixture was heated for a total of 5 min (150 pulses). After reaction, fibers were washed with tap water, oven-dried, and kept for further characterization. The reaction resulted in strong soft fibers of off-white color. The weight loss (lignin loss) was determined to be 30% by weight

Example 1.16. Delignification Using [Ch]Cl:Urea (1:2) with KOH-Pretreatment

The heating conditions used in this Example were microwave heating for 6 min. Prior to the delignification, half of the fibers were pretreated using 5 wt. % of KOH for 90 min at 70° C. Pretreated fibers appear brighter in color than raw fibers, slightly softer in feel, and lost 20 wt. % during a pretreatment.

[Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea, at a molar ratio of 1:2. The mixture was heated at 100° C. in an oven for 12 h, until fully melted, with occasional mechanical stirring using a glass rod. DES appeared as a transparent and homogenous viscous solution. Fibers (2 wt. %) were placed into a 250 mL Erlenmeyer flask and heated via microwave irradiation (household microwave Emerson MW8999SB, Emerson Radio Corp., Moonachie, NJ) using 2 s pulses (to avoid overheating of the mixture).

Between each pulse, the Erlenmeyer flask was removed from microwave, the mixture manually stirred with a glass stirring rod to ensure uniform dispersion of fibers in the DES, and the flask returned to the microwave. The mixture was heated for a total of 5 min (150 pulses). After reaction, fibers were washed with tap water, oven-dried, and kept for further characterization. The reaction resulted in strong soft fibers of off-white color. The weight loss (lignin loss) was determined to be 9% by weight. Total weight loss was 29%.

Example 1.17. Delignification (10 L Reactor, 2 wt. % Load)

[Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea, at a molar ratio of 1:2, in the amount of 5 kg. The reactor inner vessel was filled with DES system. The inner vessel was surrounded by a jacket which contained heat-transfer liquid (silicon oil). To control the temperature of a reactor, the temperature control system was used which continuously pumped the oil through the jacket of the reactor. The temperature control system, setup to 135° C. to afford 125° C. temperature inside the reactor, forced oil to travel against gravity through the jacket, heating the reactor content. Once the temperature in the reactor reached 125° C., 100 g of bast fibers were added, and reaction continued for 2 h. After that the heating was turned off, and after cooling down, fibers were taken off the reactor, washed with tap water, oven-dried, and kept for further characterization. Weight loss was found to be 18%.

Example 1.18. Delignification (10 L Reactor, 4 wt. % Load)

[Ch]Cl:Urea (1:2) was prepared by mixing choline chloride and urea, at a molar ratio of 1:2, in the amount of 5 kg. The reactor inner vessel was filled with DES system. The inner vessel was surrounded by a jacket which contained heat-transfer liquid (silicon oil). To control the temperature of a reactor, the temperature control system was used which continuously pumped the oil through the jacket of the reactor. The temperature control system, setup to 135° C. to afford 125° C. temperature inside the reactor, forced oil to travel against gravity through the jacket, heating the reactor content. Once the temperature in the reactor reached 125° C., 200 g of bast fibers were added, and reaction continued for 2 h. After that the heating was turned off, and after cooling down, fibers were taken out off the reactor, washed with tap water, oven-dried, and kept for further characterization. Weight loss was found to be 21%.

In sum, the Examples presented herein provide a process for a complete or substantially complete delignification of hemp bast fibers, woody biomass, and other lignocellulosic materials in deep eutectic solvents with use of thermal and/or microwave heating. In particular, the Examples provide practical and operationally simple delignification processes of hemp bast fibers. The Examples include a method for removing lignin from lignocellulosic biomass (hemp bast fibers) by mixing the lignocellulosic material with a deep eutectic solvent under microwave heating and/or under temperature, to completely dissolve the lignin fraction in biomass. The Examples also include a step of microwave heating to assist in dissolution. It is also possible to apply temperature to assist in delignification (e.g., 100-160° C.). The solution is agitated until complete dissolution of lignin takes place (e.g., 1 to 2 h with thermal heating, and 5 min with microwave heating).

Without further elaboration, it is believed that one skilled in the art can, using the description herein, utilize the present disclosure to its fullest extent. The embodiments described herein are to be construed as illustrative and not as constraining the remainder of the disclosure in any way whatsoever. While the embodiments have been shown and described, many variations and modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims, including all equivalents of the subject matter of the claims. The disclosures of all patents, patent applications and publications cited herein are hereby incorporated herein by reference, to the extent that they provide procedural or other details consistent with and supplementary to those set forth herein.

Claims

1. A method of removing lignin from a material, said method comprising:

associating the material with a deep eutectic solvent comprising at least one hydrogen bond acceptor (HBA) and at least one hydrogen bond donor (HBD), wherein the solvent is operational to dissolve lignin associated with the material; and

heating the material.

2. The method of claim 1, wherein the material is selected from the group consisting of lignocellulosic materials, biomass, woody biomass, untreated wood, fibers, lignocellulosic fibers, hemp, hemp bast fibers, kenaf, jute, sisal, flax, ramie, or combinations thereof.

3. The method of claim 1, wherein the material comprises hemp.

4. The method of claim 1, wherein the associating occurs by a method selected from the group consisting of mixing, immersing, sonicating, embedding, incubating, or combinations thereof.

5. The method of claim 1, wherein the HBA comprises a quaternary ammonium salt selected in the group consisting of choline, betaine, proline, carnitine, acetylcholine, carnitine, ethyl ammonium chloride, diethyl ammonium chloride, a salt of a neutral compound with a positively charged cationic functional group, imidazolium, a substituted imidazolium salt, a quaternary ammonium compound, a substituted ammonium compound, pyridinium, a substituted pyridinium compound, a phosphonium compound, a morpholinium compound, or combinations thereof.

6. The method of claim 1, wherein the HBA comprises a neutral compound comprising a positively charged cationic functional group, wherein the positively charged cationic functional group is selected from the group consisting of choline, betaine, carnitine, imidazolium, substituted imidazolium, a quaternary ammonium, a substituted ammonium, pyridinium, a substituted pyridinium, phosphonium, morpholinium, or combinations thereof.

7. The method of claim 1, wherein the HBD is selected from the group consisting of urea, amide, a carboxylic acid, an amino acid, an amine, an amide, an alcohol, or combinations thereof.

8. The method of claim 1, wherein the HBD comprises a carboxylic acid selected from the group consisting of lactic acid, oxalic acid, formic acid, glycolic acid, levulinic acid, malic acid, malonic acid, glutaric acid, succinic acid, tartaric acid, benzoic acid, itaconic acid, citric acid, isocitric acid, or combinations thereof.

9. The method of claim 1, wherein the HBD comprises an alcohol selected from the group consisting of propylene glycol, 1,2-propanediol,1,3-propanediol, glycerol, ethylene glycol, triethylene glycol, sorbitol, xylitol, ribitol, erytritol, maltitol, mannitol, lactitol, inositol, butanediol, glycerol, or combinations thereof.

10. The method of claim 1, wherein the HBA comprises choline chloride and the HBD comprises urea.

11. The method of claim 1, wherein the HBA comprises choline chloride and the HBD comprises lactic acid.

12. The method of claim 1, wherein the heating comprises thermal heating.

13. The method of claim 1, wherein the heating comprises microwave radiation.

14. The method of claim 1, further comprising a step of separating the material from the solvent, wherein the separating occurs after the solvent associating and heating steps.

15. The method of claim 1, further comprising a step of drying the material, wherein the drying occurs after the solvent associating and heating steps.

16. The method of claim 1, further comprising a step of washing the material, wherein the washing occurs after the solvent associating and heating steps.

17. The method of claim 1, further comprising a step of processing the material.

18. The method of claim 17, wherein the processing comprises at least one of opening the material, carding the material, blending the material with another material, yarn production from the material, fiber production from the material, or combinations thereof.

19. The method of claim 17, wherein the processing comprises blending the material with another material.

20. The method of claim 19, wherein the other material is selected from the group consisting of polymer fibers, cotton, polyester, wool, or combinations thereof.

21. The method of claim 17, wherein the processing comprises yarn production from the material.

22. The method of claim 21, wherein the processing further comprises fiber production from the yarn.

23. The method of claim 1, further comprising a step of pre-treating the material prior to the solvent associating step.

24. The method of claim 23, wherein the pre-treatment step comprises pre-treating the material with an alkali metal.

25. The method of claim 24, wherein the alkali metal is selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH), or combinations thereof.