Method for degumming and bleaching plant fibers

Abstract

The invention relates to a method for degumming and bleaching plant fibers, which comprises the steps of: a) contacting the plant fibers with a first natural deep eutectic solvent (NADES) having a pH equal to or greater than 12 and comprising a metal carbonate salt and a C2-C8 polyol; and b) contacting the plant fibers with a second natural deep eutectic solvent (NADES) comprising a quaternary ammonium compound and an acid compound selected from C2-C8 mono- or polycarboxylic acids optionally substituted by one or more hydroxy groups.

Description

[0001] METHOD FOR DEGUMMING AND BLEACHING PLANT FIBERS

[0002] TECHNICAL FIELD

[0003] The invention relates to the field of plant fiber treatments. More particularly, the invention relates to a method for degumming and bleaching plant fibers, such as hemps fibers and / or flax fibers.

[0004] TECHNICAL BACKGROUND

[0005] Plant fibers are lignocellulosic biomass which represent an abundant and widely available renewable resource.

[0006] For a number of years, plant fibers have attracted great interest because of their environmental value. Plant fibers represent a good alternative to the non-renewable resources in different fields such as textile, food or cosmetics industries. As a result, the global demand for plant fibers increases every year.

[0007] Plant fibers can be extracted from various plant materials such as stems, leaves, fruits and seeds and from different plant species. Plant fibers of high interest are the so-called “bast fibers”, and are characterized by their softness and flexibility. Bast fibers are generally extracted from the stems of plants such as flax, hemp, jute, and kenaf by retting process. The resulting raw bast fibers are mainly composed of cellulose, hemicellulose, and lignin. The resulting raw bast fibers may also contain remaining pectin and “gummy compounds” absorbed thereon. Gummy compounds mainly derive from the cuticle (e.g. cutin, cutan, cuticular wax), and / or from other cellular components such as proteins and secondary metabolites (e.g. phenolic compounds, flavonoids).

[0008] The non-cellulosic components (i.e. hemicellulose, lignin, pectin and other gummy compounds) should be removed to obtain high-quality plant fibers with appropriate mechanical properties. The step of removing the non-cellulosic components from raw plant fibers is usually referred to a “degumming” step.

[0009] In addition, plant fibers may need to be bleached, particularly for the textile industry.

[0010] Current methods for degumming and bleaching plant fibers use strong bases, such as sodium or potassium hydroxide, combined with oxidizing agents, such as hydrogen peroxide. Moreover, these methods are usually carried out at high temperatures (i.e. above 100 °C), even under high pressure, and generate toxic effluents.

[0011] In other words, the current degumming methods have several limitations such as high energy input, high water consumption and non-reusable or hardly reusable, toxic, effluents.More ecological and efficient degumming and bleaching methods for plant fibers are therefore sought. Several options are currently assessed, among which treatments of the plant fibers with Deep Eutectic Solvents (DES).

[0012] Deep Eutectic Solvents (DES) have gained a lot of attention for many different applications, including for extraction of plant biomass. They rank among the most promising alternative to conventional organic solvents.

[0013] DES are a subtype of ionic liquid formed by mixing one or more hydrogen bond acceptors (HBA) with one or more hydrogen bond donors (HBD) in a specific molar ratio that corresponds to, or is close to, the eutectic point. Hydrogen bonds between HBA and HBD are therefore formed, resulting in a significant lowering of the melting point of the DES compared to that of its individual components. DES can therefore be used as liquid at room temperature and exhibit unique properties of solvation.

[0014] Several studies have been reported on the assessment of DES in degumming plant fibers. The most widely used DES in the literature for degumming purpose consist of a mixture of choline chloride and urea. Of note, the treatment of plant fibers with such DES was shown to be insufficient to provide a proper degumming without using high extraction temperature and / or without being combined with another more drastic treatment.

[0015] For example, SongY. eta / . (Cellulose 2019, 26, 8047-8057) describe a method for degumming Apocynum venetum bast fibers, in which the fibers are treated with a DES consisting of a mixture of choline chloride and urea, under microwaves and at a temperature of about 110 °C. Such a treatment was insufficient to degum the Apocynum venetum bast fibers alone, and an additional treatment of the bast fibers, namely a cooking in a 1% NaOH solution at high temperature, was necessary to obtain the desired degumming effect.

[0016] Thus, the method proposed by Song Y. et al. requires the use of a strong base as well as high temperatures, and thus cannot be seen as an eco-friendly method. Besides, the use of microwaves may complicate the implementation of the process on an industrial scale.

[0017] There is thus a need for more sustainable and environmentally -friendly methods for degumming and bleaching plant fibers.

[0018] SUMMARY OF THE INVENTION

[0019] The present invention pertains to a method for degumming and bleaching plant fibers. The method of the invention comprises the steps of:

[0020] a) contacting the plant fibers with a first natural deep eutectic solvent (NADES) having a pH equal to or greater than 12 and comprising a metal carbonate salt and a C2-C8 polyol; andb) contacting the plant fibers with a second natural deep eutectic solvent (NADES) comprising a quaternary ammonium compound and an acid compound selected from C2-C8 mono- or poly carboxylic acids optionally substituted by one or more hydroxy groups.

[0021] Steps a) and b) may be carried out in any order. Preferably step a) is performed before step b). In some embodiments, the first NADES has a pH of at least 13, preferably equal to or greater than 14.

[0022] In some embodiments, in step a), i) the metal carbonate salt is potassium carbonate and / or ii) the C2-C8 polyol is selected from the group consisting of glycerol, ethylene glycol, triethylene glycol, propylene glycol, butane- 1,4-diol, sorbitol, xylitol, mannitol and combinations thereof. In some embodiments, in step a), i) the metal carbonate salt is potassium carbonate and / or ii) the C2-C8 polyol is selected from the group consisting of glycerol, ethylene glycol, triethylene glycol, propylene glycol, butane- 1,4-diol, sorbitol and combinations thereof, preferably glycerol or ethylene glycol.

[0023] In some embodiments, the first NADES has a molar ratio of the metal carbonate salt to the C2-Cs polyol from 0.2 to 0.4, such as 0.25 or 0.30. In some embodiments, the first NADES has a molar ratio of the metal carbonate salt to the C2-C8 polyol from 0.1 to 0.5.

[0024] In some embodiments, the first NADES further comprises water in an amount of 0.1% to 30% by weight relative to the total weight of said first NADES. Optionally, the second NADES further comprises water in an amount of 0.1% to 30% by weight relative to the total weight of said second NADES.

[0025] In some embodiments, in step b), i) the quaternary ammonium compound is selected from choline halide and a betaine and / or ii) the acid compound is selected from the group consisting of lactic acid, malic acid, oxalic acid, citric acid, acetic acid, malonic acid, succinic acid, tartaric acid, and combinations thereof, preferably lactic acid and / or malic acid. In some embodiments, in step b), i) the quaternary ammonium compound is selected from choline halide and a betaine and / or ii) the acid compound is selected from the group consisting of lactic acid, malic acid, oxalic acid, citric acid, acetic acid, malonic acid, succinic acid, tartaric acid, glycolic acid and combinations thereof, preferably lactic acid, citric acid, tartaric acid, oxalic acid, and / or glycolic acid.

[0026] In some embodiments, the second NADES has a molar ratio of the quaternary ammonium compound to the acid compound from 0.05 to 0.6, preferably from 0.1 to 0.5. In some embodiments, the second NADES has a molar ratio of the quaternary ammonium compound to the acid compound from 0.05 to 2.0, for example from 0.1 to 2.0 or from 0.1 to 0.5.In some embodiments, the first NADES comprises potassium carbonate as metal carbonate salt and glycerol or ethylene glycol as C2-C8 polyol, preferably in a molar ratio of 0.2 to 0.4, and / or the second NADES comprises choline chloride and lactic acid, preferably in a molar ratio of 0.1 to 0.5.

[0027] In some embodiments:

[0028] the first NADES consists essentially of potassium carbonate as metal carbonate salt, glycerol or ethylene glycol as C2-C8 polyol, and optionally water, wherein the metal carbonate salt / C2-Cs polyol molar ratio is preferably from 0.1 to 0.5, and wherein, when water is present in the first NADES, the potassium carbonate / water molar ratio is preferably from 0.2 to 1, and the second NADES consists essentially of:

[0029] - choline chloride, lactic acid and optionally water, or

[0030] - choline chloride, lactic acid, citric acid and optionally water, or

[0031] - choline chloride, tartaric acid and optionally water, or

[0032] - choline chloride, citric acid and optionally water, or

[0033] - choline chloride, glycolic acid and optionally water, or

[0034] - betaine, oxalic acid and optionally water, or

[0035] - betaine, lactic acid and optionally water, or

[0036] - betaine, citric acid and optionally water,

[0037] wherein the molar ratio of the quaternary ammonium compound to the acid compound in the second NADES is preferably from 0.1 to 2.0, for example from 0.1 to 0.5, and wherein, when water is present in the second NADES, the quaternary ammonium compound / water molar ratio is from 0.1 to 1.5.

[0038] In some embodiments, steps a) and b) are carried out at a temperature of at most 80 °C, for instance from 15 °C to 70 °C, or from 20 °C to 60 °C. In some embodiments, steps a) and b) are carried out at a temperature of at most 100°C, preferably at most 95°C, such as from 55°C to 95°C.

[0039] In some embodiments, at the end of step a) and / or step b), the plant fibers are recovered and then rinsed and / or washed with water.

[0040] In some embodiments, steps a) and b) are carried out for 2 hours to 24 hours, preferably for 4 hours to 16 hours.

[0041] In some embodiments, the method of the invention further comprises, after step b), a step c) for drying the plant fibers, preferably with an organic solvent, such as ethanol and / or acetone, and / or with a drying oven and / or by air-drying.In some embodiments, the method of the invention further comprises, after and / or prior to step c), a step d) of applying a mechanical action, such as combing, to the plant fibers.

[0042] In some embodiments:

[0043] step a) is carried out before step b);

[0044] in step a): the first NADES essentially consists of potassium carbonate as metal carbonate salt and glycerol or ethylene glycol as C2-C8 polyol in a molar ratio of 0.1 to 0.5, and water in an amount of 0.1% to 30% by weight (for example of 0.1% to 5% or of 5% to 30% by weight) of the total weight of the first NADES, and has a pH of at least 13, step a) being carried out by immersing the plant fibers in the first NADES, at a temperature of at most 70 °C, e.g. from 50 °C to 70 °C;

[0045] at the end of step a): the plant fibers are recovered and then washed with water; in step b): the second NADES essentially consists of choline chloride and lactic acid in a molar ratio of 0.1 to 0.5 and optionally further comprises water in an amount of 0.1% to 30% by weight (for example of 2% to 30% by weight) of the total weight of the second NADES, step b) being carried out by immersing the plant fibers in the second NADES, at a temperature of at most 70 °C, e.g. from 50 °C to 70 °C;

[0046] at the end of step b): the plant fibers are recovered and then washed with water; after step b): a step c) is carried out for drying the plant fibers followed by a step d) of combing the plant fibers.

[0047] In some embodiments:

[0048] - step a) is carried out before step b);

[0049] - in step a): the first NADES has a pH of at least 13 and essentially consists of potassium carbonate as metal carbonate salt and glycerol or ethylene glycol as C2-C8 polyol in a molar ratio of 0.1 to 0.5,

[0050] - step a) is carried out by immersing the plant fibers in the first NADES, at a temperature of at most 95°C, for example from 55°C to 95°C;

[0051] - at the end of step a): the plant fibers are recovered and then washed with water; - in step b): the second NADES essentially consists of:

[0052] • choline chloride and lactic acid in a molar ratio of 0.1 to 0.5, and optionally water in an amount of 0.1% to 30% by weight relative to the total weight of the second NADES, or

[0053] • choline chloride, lactic acid and citric acid, with a molar ratio of choline chloride to lactic acid of 0.1 to 0.5, and with a molar ratio of choline chloride to citric acid of 0.1 to 2.0, or• choline chloride and tartaric acid in a molar ratio of 0.1 to 2.0, or

[0054] • choline chloride and citric acid in a molar ratio of 0.1 to 0.5, or

[0055] • choline chloride and glycolic acid in a molar ratio of 0.1 to 2.0, or • betaine and oxalic acid in a molar ratio of 0.1 to 2.0, and optionally water in an amount of 0.1% to 5% by weight relative to the total weight of the second NADES, or

[0056] • betaine and lactic acid in a molar ratio of 0.1 to 0.5, or

[0057] • betaine and citric acid in a molar ratio of 0.1 to 2.0, and optionally water in an amount of 0.1% to 5% by weight relative to the total weight of the second NADES,

[0058] - step b) is carried out by immersing the plant fibers in the second NADES, at a temperature of at most 95°C, for example from 55°C to 95°C;

[0059] - at the end of step b): the plant fibers are recovered and then washed with water; - after step b): a step c) is carried out for drying the plant fibers followed by a step d) of combing the plant fibers.

[0060] In some embodiments:

[0061] - step a) is carried out before step b);

[0062] - in step a): the first NADES has a pH of at least 13 and essentially consists of potassium carbonate as metal carbonate salt and ethylene glycol as C2-C8 polyol in a molar ratio of 0.1 to 0.5;

[0063] - step a) is carried out by immersing the plant fibers in the first NADES, at a temperature of at most 95°C, for example from 55°C to 95°C;

[0064] - at the end of step a): the plant fibers are recovered and then washed with water; - in step b): the second NADES essentially consists of choline chloride and lactic acid in a molar ratio of 0.1 to 0.5;

[0065] - step b) is carried out by immersing the plant fibers in the second NADES, at a temperature of at most 95°C, for example from 55°C to 95°C;

[0066] - at the end of step b): the plant fibers are recovered and then washed with water; - after step b): a step c) is carried out for drying the plant fibers followed by a step d) of combing the plant fibers.

[0067] In some embodiments, the mass ratio of the plant fibers to the NADES is from 0.005 to 2.0, preferably from 0.01 to 1.0, such as from 0.01 to 0.1 or from 0.02 to 0.06.

[0068] In some embodiments, plant fibers are in the form of incomplete retted plant fibers, retted plant fibers or in the form of a tow.In some embodiments, plant fibers are bast fibers, leaf fibers, seed fibers or fruit fibers, preferably bast fibers.

[0069] In some embodiments, the plant fibers, particularly bast fibers, are hemp fibers, flax fibers, jute fibers, ramie fibers, kenaf fibers, mesta fibers, roselle fibers, nettle fibers or combination thereof, preferably hemps fibers and / or flax fibers.

[0070] The invention also relates to a use of a first NADES and then a different second NADES for degumming and bleaching plant fibers, the first NADES and the second NADES being as defined therein.

[0071] Another object of the invention is plant fibers directly obtained or obtainable by the method according to the invention.

[0072] Another object of the invention is an article made of plant fibers directly obtained or obtainable by the method according to the invention.

[0073] Finally, another object of the invention is a use of plant fibers directly obtained or obtainable by the method according to the invention, for the conception of an article.

[0074] In some embodiment, the article is a woven or a nonwoven material, for example a textile clothing, felt, thermal insulation material, sound insulation materials, or panels.

[0075] BRIEF DESCRIPTION OF THE FIGURES

[0076] Figure 1 shows the lightness L * measured on retted flax fibers treated according to the method of the invention (with the first and second NADES of Example 2) and on retted flax fibers treated with water (comparative).

[0077] Figure 2 shows the lightness L* measured on incomplete retted flax fibers treated according to the method of the invention (with the first and second NADES of Example 3) and on incomplete retted flax fibers treated with water (comparative).

[0078] Figure 3 shows the lightness L* measured on retted flax fibers according to the method of the invention (with the first and second NADES of Example 4) and on retted flax fibers treated with water (comparative).

[0079] Figure 4 shows the lightness L* measured on incomplete retted flax fibers according to the method of the invention (with the first and second NADES of Example 5) and on incomplete retted flax fibers treated with water (comparative).

[0080] Figure 5 shows the lightness L* measured on retted flax fibers according to the method of the invention (with the first and second NADES of Example 6) and on retted flax fibers treated with water (comparative).Figure 6 shows the lightness L* measured on incomplete retted flax fibers according to the method of the invention (with the first and second NADES of Example 7) and on incomplete retted flax fibers treated with water (comparative).

[0081] Figure 7 is a picture of plant fibers obtained after the method of the invention implemented during an industrial-scale pilot test.

[0082] DETAILED DESCRIPTION OF THE INVENTION

[0083] Definitions

[0084] Unless otherwise indicated, when a range is expressed using the expression “from... to... “of... to... “for... io..." or “at most... ” , the limit values are included within the range described. The term “about” is used herein to mean approximately, roughly, around or in the region of. When the term “about” is used in conjunction with a numerical value, it modifies that numerical value by extending it 10% above and 10% below the numerical value, preferably 5% above and 5% below the numerical value, more preferably 1% above and 1% below the numerical value. As used herein, the terms “consists essentially of means that the ingredients listed after “consists essentially of represent together more than 95% by weight, preferably more than 96%, 97% 98%, 99%, 99.5% or 99.9% by weight relative to the total weight of the composition under consideration (e.g. a NADES). In other words, the terms “essentially consists” may be similar to “comprises at least 95%”. In these cases, the remainder (up to 100% by weight) of the composition (e.g. the NADES) may be other components, for example the remainder of the composition may be water.

[0085] The term “plant fibers” refers to vegetable fibers obtained from plants, e.g. from plants grown for their fibers or from wild plants. In the context of the invention, plant fibers refer to a hairlike material with macroscopic dimensions, characterized by their long, narrow structure and significant length compared to their diameter. For instance, they are usually at least three times longer than they are wide. They are usually between a few millimeters and several centimeters (up to several tens or hundreds of centimeters) long, and generally between 20 and 200 micrometers in diameter. In other words, plant fibers, in the context of the invention, are not nanostructures. There are different types of plant fibers, e.g. bast fibers, leaf fibers, seed fibers and fruit fibers. In the context of the invention, preferred plant fibers are bast fibers. Bast fibers are generally collected from the phloem surrounding the stem of certain plants, e.g. cultivated plants such as flax, hemp, jute, kenaf, or ramie, and from wild plants, such as stinging nettle, and trees such as lime or linden, willow, oak, wisteria, and mulberry. Bast fibers are generallylocated in the phloem as bundles that are glued together by pectin and other compounds. Bast fibers can be separated from the central stem and / or the epidermis of the plant by different methods such as retting. Retting is a process combining the action of microorganisms and moistures to dissolve or rot away most of the cellular tissues and pectin. The resulting plant fibers are mainly composed of cellulose, hemicellulose and lignin. The resulting plant fibers may also contain residual pectin and residual gummy compounds absorbed thereon. The gummy compounds included derivatives from the cuticle (e.g. cutin, cutan, cuticular wax), and / or from other cellular components (e.g. proteins and secondary metabolites which may be phenolic compounds or flavonoids). Sometimes, residual epidermis may also be present on the surface of the plant fibers.

[0086] "Cellulose" is a polysaccharide consisting of a linear chain of several hundred to many thousands of P( 1— 4) linked D-glucose units. Cellulose is present in a high concentration in the plant fibers, giving them their strength. "Hemicellulose" are polysaccharides made up of a monosaccharides connected by P(l— 4) linkages, primarily xylose, mannose, glucose, and more or less ramified by side chains containing glucuronic acid, galactose, arabinose, fucose and partly substituted by methyl ether or / and phenolic acids. These complex polysaccharides form a network together with cellulose and pectin. “Zzgzi ” is a class of complex organic polymers made by cross-linking phenolic precursors called lignols. Heterogeneity arises from the diversity and degree of different types of crosslinking between these lignols. The lignols that crosslink are of three main types, all derived from phenylpropane: coniferyl alcohol (G radical), sinapyl alcohol (S radical), and -coumaryl alcohol (H radical).

[0087] As used herein, the term “method for degumming a plant fiber” or “step of degumming” refers to a process or a step wherein one or more non-cellulosic compounds are broke-down and / or come part and / or are removed from the cellulosic structure in the plant fibers. In some embodiments, a degumming method enables to increase the content of cellulose, preferably the content of crystalline cellulose, in the plant fibers while decreasing the amount of lignin and / or pectin and / or hemicellulose and / or gummy compounds. In some embodiments, such a method enables to obtain plant fibers with improved mechanical properties for subsequent uses e.g. plant fibers with improved fineness, suppleness and / or strength. A degumming method may also enable to decrease the color or bleach the plant fibers. One skilled in the art may be able to determine the level of a degumming step, for example by determining the mass loss of the plant fibers (i.e. the difference in mass of the plant fibers before and after the treatment) and / or by performing Infrared (IR) spectroscopy analyses.As used herein “non-cellulosic compounds" encompass, without being limited to, components that can be found in non-treated plant fibers which are not cellulose (in particular noncrystalline cellulose). Non-cellulosic compounds encompass, without being limited to, components of the plant cuticle (including cutin and / or cutan, epicuticular wax), lignin, hemicellulose, and pectin.

[0088] As used herein, the “cuticle” refers to a protecting film covering the outermost cellular layer (epidermidis) of the plant. The cuticle is composed of cutin (fatty acid polyesters), cutan (non-saponifiable hydrocarbon polymer) and epicuticular wax made of very-long-chain fatty acids (VLCFAs). Most of the so-called gummy compounds derive from the cuticle.

[0089] As used herein, the term “method for bleaching” or “step of bleaching” refers to a process or a step wherein the color of the plant fibers is decreased and / or the lightness and / or the degree of whiteness of the plant fibers is / are increased. One skilled in the art may be able to determine the level of a bleaching step, for example by comparing the lightness (especially the parameter L *) of the plant fibers before and after the treatment, for instance using a chromameter.

[0090] As mentioned above, a “Deep Eutectic solvent (DES)” is a subtype of ionic liquid formed by mixing one or more hydrogen bond acceptors (HBA) with one or more hydrogen bond donors (HBD) in a specific molar ratio which corresponds to, or is close to, the eutectic point. Hydrogen bonds between HBA and HBD are therefore formed, resulting in a significant lowering of the melting point of the DES compared to that of its individual components. DES can therefore be used as liquid at room temperature. Examples of DES encompass, without being limited to, (i) a solution comprising an organic cation and an inorganic metal salt, a hydroxy compound or an amide, (ii) a solution comprising an inorganic metal salt and a sugar or (iii) a solution comprising urea and a hydroxy compound.

[0091] A “natural deep eutectic solvent (NADES)” is a derivative of a DES but is considered as “natural” because of their components that are primary metabolite group, such as sugars, organics acids and bases, and amino acids. In the context of the invention, NADES is preferably either a solution comprising a metal carbonate salt and a polyol or a solution comprising a quaternary ammonium compound and a carboxylic acid. Examples of NADES encompass, but without being limited to, a solution comprising (i) potassium carbonate and (ii) glycerol, ethylene glycol, triethylene glycol, mannitol, xylitol, sorbitol, butane- 1,4-diol or propylene glycol; or a solution comprising (i) choline chloride or betaine and (ii) lactic, malic, oxalic, citric, acetic, malonic, succinic, tartaric, or glycolic acid.

[0092] A “metal carbonate salt” refers to a carbonate salt comprising CO? / 2' as anion and a metallic ion as counter-cation. In the context of the invention, a metal carbonate salt encompasses alkalimetal carbonate and alkaline earth metal carbonate. The general formula of an alkali metal carbonate is M2CO3, wherein M represents an alkali metal including lithium, sodium, potassium, rubidium and cesium. For example, an alkali metal carbonate may be a lithium carbonate (Li2COs), a sodium carbonate (Na2COs), a potassium carbonate (K2CO3), a rubidium carbonate (RfeCOs) or a cesium carbonate (CS2CO3). The general formula of an alkaline earth metal carbonate is MCO3, wherein M represent an alkaline earth metal including magnesium, calcium, strontium and barium. For example, an alkaline earth metal carbonate may be a magnesium carbonate (MgCOs), a calcium carbonate (CaCOs), a strontium carbonate (SrCOs) or a barium carbonate (BaCOs). In the context of the invention, preferred metal carbonate salts encompass sodium carbonate (Na2COs), potassium carbonate (K2CO3), and calcium carbonate (CaCO3).

[0093] A “C2-C8 polyol” refers to an organic aliphatic hydrocarbon chain substituted by two or more -OH groups (e.g. 2, 3, 4, 5, 6 or more -OH groups), and having at least 2 carbon atoms but no more than 8 carbon atoms (e.g. 2, 3, 4, 5, 6, 7 or 8 carbon atoms). The hydrocarbon chain may be saturated or may have one or more double bonds. Preferably, the hydrocarbon chain is saturated. The hydrocarbon chain may be linear or comprise one or more branches and may further be interrupted by one or more heteroatoms, such as oxygen. In the context of the invention, a C2-C8 polyol may be a polyhydroxyalkyl or a poly ether having two or more -OH groups. Examples of C2-C8 polyol encompass, but without being limited to, glycerol, ethylene glycol, tri ethylene glycol, propylene glycol, butane- 1 ,4-diol, sorbitol, xylitol or mannitol. A “quaternary ammonium compound” refers to a hydrocarbon group bearing a group of formula -N R1R2R3 wherein each of Ri, R2 and R3 is independently a C1-C12 alkyl group, preferably a Ci-Ce or C1-C3 alkyl, optionally substituted by a -OH. The hydrocarbon group is typically acyclic and has from 1 to 20 carbon atoms in its backbone, preferably from 1 to 12 carbon atoms and optionally one or more (e.g. 1, 2, 3, 4, 5, 6 or more) heteroatoms such as O or N in its backbone. The hydrocarbon group may further comprise one or several substituents in addition to -N Ri R2R3, such as a carboxylate, a phosphate, a sulfonate, a hydroxy, an oxo, a Ci-Ce hydroxyalkyl, Ci-Ce alkyl, a Ci-Ce alkoxy and -COH. In some embodiments, the “quaternary ammonium compound” is a saturated C1-C12 hydrocarbon chain bearing a group of formula -NFR1R2R3 (wherein each of Ri, R2 and R3 is as defined above, preferably a Ci-Ce alkyl) and which is optionally substituted by one or more groups selected from a carboxylate, a phosphate, a sulfonate, a hydroxy, a Ci-Ce hydroxyalkyl, a Ci-Ce alkyl, a Ci-Ce alkoxy. In the context of the invention, the quaternary ammonium compound may be in the form of a salt or a zwitterion.When the quaternary ammonium compound is in the form of a salt, the quaternary ammonium compound bears one single positive charge (due to the group -N R1R2R3) and the counter-ion is a counter-anion which may be a halide such as F’, Cl’, Br or I’. The quaternary ammonium compound may be a saturated C1-C12 hydrocarbon chain bearing a group of formula -N Ri R2R3 (wherein each of Ri, R2 and R3 is as defined above, preferably a Ci-Ce alkyl) and which is optionally substituted by one or more groups selected from a hydroxy, a Ci-Ce alkyl, a Ci-Ce alkoxy and a Ci-Ce hydroxyalkyl. An example of a quaternary ammonium salt is choline chloride.

[0094] When the quaternary ammonium compound is in the form of a zwitterion, the quaternary ammonium compound bears a -N Ri R2R3 as described above, and another substituent that can be negatively charged such as a carbonate, a sulfonate or a phosphate. In some embodiments, the quaternary ammonium compound may be a saturated C1-C12 hydrocarbon chain bearing a group of formula -N Ri R2R3 (wherein each of Ri, R2 and R3 is as defined above, preferably a Ci-Ce alkyl) and which is further substituted by a negative-bearing substituent such as a carboxylate, a phosphate or a sulphate. For example, the zwitterionic quaternary ammonium compound may be of the formula: RiR2R3-N+-(CH2)n-COO’, wherein n is an integer from 1 to 12. Examples of a zwitterionic quaternary ammonium compound encompass, but without being limited to, trimethylglycine (also called betaine).

[0095] As used herein, an “alkyl” refers to a saturated hydrocarbon radical which can be a straight or branched hydrocarbon group. Examples of C1-C12 alkyl group encompass, without being limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl. Examples of Ci-Ce alkyl group encompass, without being limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, and hexyl. A “C2-C8 mono- or polycarboxylic acids optionally substituted by one or more hydroxy groups ” refers to an organic acid, preferably a saturated or unsaturated, linear or branched hydrocarbon compound having one -COOH group (“C2-O monocarboxylic acid” or at least 2 -COOH groups (“C2-Cs polycarboxylic acid”,- e.g. 2, 3 or more -COOH groups), and having at least 2 carbon atoms but no more than 8 carbon atoms (e.g. 2, 3, 4, 5, 6, 7 or 8 carbon atoms). The hydrocarbon chain may be further substituted by one or more -OH groups. Examples of C2-C8 mono- or polycarboxylic acids optionally substituted by one or more hydroxy groups encompass, without being limited to, lactic acid, malic acid, oxalic acid, citric acid, acetic acid, malonic acid, succinic acid, tartaric acid, or glycolic acid.Method for degumming and bleachins, plant fibers

[0096] The Inventors have surprisingly showed that the treatment of plant fibers with two different natural deep eutectic solvents (NADES), one alkaline and the other acidic, allows to efficiently degum and bleach plant fibers. Surprisingly, the Inventors showed that the treatment with a specific alkaline NADES followed by the treatment with a specific acidic NADES according to the invention lead to better results in terms of degumming and bleaching compared to one single NADES treatment step.

[0097] The treatment of the plant fibers with the two different NADES can be performed in gentle conditions, in particular at a temperature of at most 100 °C, e.g. of at most 95°C or at most 80 °C. This notably helps to prevent plant fibers deterioration. The resulting plant fibers show appropriate mechanical properties in terms of strength and flexibility, evidencing an efficient removal of non-cellulosic compounds without alteration of the cellulosic structure. Of note, the resulting plant fibers were shown to have an improved lightness over plant fibers treated with ethanolic KOH at pH 14 and at 25 °C. No pre-treatment or later step in drastic conditions (e.g. temperature over 100 °C, high pressure and / or with sodium hydroxide) was necessary.

[0098] In other words, the combined use of an alkaline NADES and an acid NADES as described herein provides an efficient and gentle degumming and bleaching method based on renewable reagents. Such a combination enables to avoid high energy input, high water consumption, and toxic effluents. It also enables to highly limit the production of effluent wastes that are difficult to treat. Besides, the NADES solvents can be reused and valuable by-products, such as lignin, can be recovered from the effluents. The method of the invention may advantageously be implemented on an industrial scale. The Inventors have succeeded, in an industrial-scale pilot test, in obtaining degummed and bleached plant fibers (see Example 9). The obtained plant fibers were advantageously more robust than plant fibers obtained by a conventional degumming and bleaching process using harsh conditions with NaOH and hydrogen peroxide. Thus, in a first aspect, the invention relates to a method for degumming and bleaching plant fibers wherein the plant fibers are treated with two different NADES, one of the NADES being an alkali NADES (also called hereafter first NADES) and the other NADES being an acidic NADES (also called hereafter second NADES).

[0099] In some embodiments, the method of the invention comprises the steps of:

[0100] a) contacting the plant fibers with a first NADES having a pH equal to or greater than 12 and comprising, as hydrogen bond acceptor (HBA), a metal carbonate salt and, as hydrogen bond donor (HBD), a C2-C8 polyol; andb) contacting the plant fibers with a second NADES comprising, as HBA, a quaternary ammonium compound and, as HBD, an acid compound selected from C2-C8 mono- or poly carboxylic acids optionally substituted by one or more hydroxy groups.

[0101] At the end of the method of the Invention, degummed and bleached plant fibers are advantageously obtained.

[0102] According to the invention, steps a) and b) may be performed in any order. For example, step a) may be carried out before step b), or step b) may be carried out before step a).

[0103] In some preferred embodiments, step a) is carried out before step b).

[0104] In some embodiments, the plant fibers are put in contact with an aqueous solution, preferably with water, e.g. deionized or distilled water, between steps a) and b) or between steps b) and a), depending on the order in which they are carried out. This contacting step enables to rinse and / or wash the plant fibers e.g. for removing residual amounts of NADES and / or for rebalancing the pH near pH 7 on the surface of the plant fibers.

[0105] The step of contacting plant fibers with water is performed as defined in the sections “Step a)” and “Step b)” below. In some embodiments, the plant fibers may be subjected to a hydration step prior to steps a) and b). The hydration step can be performed by contacting the plant fibers with an aqueous solution, typically with water at a neutral pH, e.g. by immersion or by rinsing. The hydration step may enable to avoid the addition of water in the subsequent NADES step. In some other embodiments, water is directly added to the first and / or second NADES. In that case, a prior hydration step may not be required. The addition of water in a NADES may be performed in order to hydrate plant fibers and / or decrease the viscosity of the NADES, as defined in the sections “Step a)” and “Step b)” below.

[0106] In some preferred embodiments, step a) is carried out before step b), water is added to the first NADES in step a), plant fibers are further be put in contact with water between steps a) and b) and, optionally, water is also added to the second NADES in step b). In some other preferred embodiments, step a) is carried out before step b), plant fibers are further be put in contact with water between steps a) and b) and, optionally, water is added to the second NADES in step b) (i.e. in these preferred embodiments, no water is added to the first NADES in step a)).

[0107] According to the invention, the contacting steps a) and b) may be carried out by any appropriate method known in the art. Contacting the plant fibers with a NADES in step a) and / or step b) can be performed by circulating or percolating the solvent through the plant fibers. Alternatively, the step of contacting the plant fibers with a NADES in step a) and / or step b) can be performed in a batch mode, e.g. by plunging or immersing the plant fibers in the solvent. In some embodiments, both steps a) and b) are carried out by immersion.As used herein, the terms “immersing” , "immersion" . "immersed" or the like mean that the plant fibers are immersed or plunged in the NADES. As described further below, the plant fibers are immersed in the NADES solvent during a time sufficient to obtain the sought effects (namely the removal and / or the breaking down of at least a part of the non-cellulosic compounds). Such an immersion (that can be called also maceration) is performed during few minutes to several hours depending on the NADES and / or the plant fibers to treat, preferably at a temperature of at most 100 °C, preferably of at most 90 °C, 80 °C or 70 °C.

[0108] In each step, the volume of the solvent to be used may depend on the particular NADES to be used and / or the type of plant fibers to be treated and / or the device used to perform the contacting steps. Typically, when the contacting steps a) and b) are carried out by immersion, the volume of the NADES is such that it enables to recover the plant fibers almost totally or totally.

[0109] Typically, the mass ratio of the plant fibers to the NADES is from 0.005 to 2.0, preferably from 0.01 to 1.0, such as from 0.01 to 0.1 or from 0.02 to 0.06. For instance, the mass ratio of the plant fibers to the NADES is about 0.025.

[0110] It goes without saying that the mass ratio can be the same or can be different in steps a) and b).

[0111] Step a)

[0112] Step a) aims at breaking down and / or making come part and / or removing one or more non-cellulosic compounds from the cellulosic structure in the plant fibers, more particularly, the non-cellulosic compounds present in the outermost layer of the plant fiber, such as gummy compounds from the cuticle. In other words, step a) may aim at degumming and decolorizing the plant fibers.

[0113] In some embodiments, this step enables to disassemble and / or remove at least a part of the cuticle components such as cutin (namely fatty acid polyesters), cutan and / or cuticular wax. In some embodiments, this step also enables to disassemble and / or remove at least a part of the cuticle and / or the epidermis, if any, from the cellulosic layer.

[0114] In some embodiments, this step contributes to disassemble and / or remove, at least in part, pectin.

[0115] In some embodiments, this step enables to disassemble and / or remove at least a part of, or all, the gummy compounds, and particularly the cuticle components, the pectin and the epidermis, if any from the plant fibers. Preferably, this step makes it possible to remove at least a part (e.g. at least 50%, 60%, 70%, 80% or 90%) of the gummy compounds, and particularly the cuticle components, the pectin and the epidermis if any initially present in the plant fibers. A part ofthe other non-cellulosic compounds (i.e. hemicellulose and lignin) may also be broken down and / or removed and / or disassemble from the plant fibers.

[0116] As mentioned above, step a) comprises contacting the plant fibers with a first NADES. Preferably, the plant fibers are immersed in the first NADES with a pH of at least 12, e.g. from 12 to 14. The first NADES may have a pH of at least 13, for example from 13 to 14. In some embodiments, the pH of the first NADES may be about 14.

[0117] As mentioned above, the first NADES comprises a metal carbonate salt and a C2-C8 polyol. The C2-C8 polyol and the metal carbonate salt present in the first NADES are as defined in the section entitled “Definitions”.

[0118] The molar ratio of the metal carbonate salt to the C2-C8 polyol is selected so as to obtain a NADES with an appropriate pH value. Typically, the molar ratio of the metal carbonate salt to the C2-C8 polyol may be from 0.05 to 10, for instance from 0.1 to 1.0, from 0.1 to 0.5, or from 0.2 to 0.4, such as 0.25 or 0.30. In some embodiments, the molar ratio of the metal carbonate salt to the C2-C8 polyol may be from 0.1 to 0.5, preferably from 0.1 to 0.4, such as about 0.1, 0.125, 0.14, 0.17, 0.25, 0.33, preferably about 0.14.

[0119] In some embodiments, the metal carbonate salt in the first NADES is either an alkali metal carbonate or an alkaline earth metal carbonate.

[0120] In some embodiments, the metal carbonate salt in the first NADES is an alkali metal carbonate. In some preferred embodiments, the metal carbonate salt in the first NADES is potassium carbonate.

[0121] In some embodiments, the C2-C8 polyol in the first NADES is selected from the group consisting of glycerol, ethylene glycol, tri ethylene glycol, propylene glycol, butane- 1,4-diol, sorbitol, xylitol, mannitol and combinations thereof, preferably glycerol or ethylene glycol. In some embodiments, the C2-C8 polyol in the first NADES, is selected from the group consisting of glycerol, ethylene glycol, tri ethylene glycol, propylene glycol, butane- 1,4-diol, sorbitol, and combinations thereof, preferably glycerol or ethylene glycol.

[0122] In some embodiments, the C2-C8 polyol in the first NADES, is selected from the group consisting of glycerol and ethylene glycol.

[0123] For example, the first NADES may comprise potassium carbonate as HBA and glycerol or ethylene glycol as HBD.

[0124] For illustration only, the first NADES comprises potassium carbonate as metal carbonate salt and glycerol or ethylene glycol as C2-C8 polyol. For example, the molar ratio of potassium carbonate to glycerol or ethylene glycol is from 0.2 to 0.4, such as about 0.25 or about 0.30. The molar ratio of potassium carbonate to glycerol or ethylene glycol may otherwise be from0.1 to 0.5, for instance from 0.1 to 0.4, such as about 0.1, 0.125, 0.14, 0.17, 0.25, 0.33, preferably about 0.14.

[0125] In some embodiments, the first NADES comprises, essentially consists or consists of potassium carbonate as metal carbonate salt and ethylene glycol as C2-C8 polyol, preferably in a molar ratio of 0.1 to 0.5, preferably of 0.1 to 0.4, for instance about 0.14.

[0126] The first NADES may essentially consist or consist of a metal carbonate salt and a C2-C8 polyol. Alternatively, the first NADES may further comprise water in order to hydrate plant fibers and / or decrease the viscosity of the first NADES if necessary.

[0127] It goes without saying that water is present in an amount so that the solvent remains a NADES (e.g. does not dissociate and shift to a mere aqueous or hydro-alcoholic solution). The amount of water that can be present in the NADES may depend on the HBA and the HBD. Typically, the amount of water in the NADES is at most about 30% by weight, relative to the total weight of the NADES.

[0128] In some embodiments, the first NADES has a water amount from about 0.1% to about 30% by weight relative to the total weight of the first NADES.

[0129] The range from about 0.1% to about 30% of water includes 0.1% to 5%, 5% to 10%, 10% to 15%, 15% to 20%, 20% to 25% and 25% to 30%.

[0130] The amount of water may vary depending on the viscosity of the C2-C8 polyol.

[0131] For instance, when the C2-C8 polyol is ethylene glycol, the water amount can be from 0.1% to 15%, for instance from 0.1% to 10% or 0.1% to 5.0% by weight relative to the total weight of the first NADES.

[0132] When the C2-C8 polyol is glycerol, the water amount can be from 0.1% to 30%, for instance from 2% to 30% by weight relative to the total weight of the first NADES. When the C2-C8 polyol is glycerol, the water amount can be from 0.1% to 10%, e.g. from 0.1% to 5% or from 5% to 10% by weight relative to the total weight of the first NADES.

[0133] For example, the first NADES has a water amount from about 0.1% to about 5% or from about 5% to 30% by weight relative to the total weight of the first NADES.

[0134] In some embodiments, the first NADES has a water amount from about 2% to about 30% or from about 5% to 30% by weight relative to the total weight of the first NADES.

[0135] For example, the first NADES may comprise water in an amount of about 28% or about 30% by weight relative to the total weight of the first NADES. In another example, the first NADES may comprise water in an amount of about 10% by weight relative to the total weight of the first NADES. In another example, the first NADES may comprise water in an amount of about 5% by weight relative to the total weight of the first NADES.In a preferred embodiment, the first NADES may comprise water in an amount of at most 5% by weight, for instance from 0% to 5%, preferably from 0.1% to 5% or from 0.1% to 3% by weight relative to the total weight of the first NADES.

[0136] In a particular embodiment, the first NADES in step a) comprises, essentially consists or, consists of:

[0137] potassium carbonate,

[0138] glycerol or ethylene glycol and

[0139] optionally water in an amount of 0.1% to 30% by weight, for example from 0.1% to 5% or from 5% to 30% by weight, relative to the total weight of the first NADES.

[0140] Preferably, the molar ratio of the potassium carbonate to the glycerol or to the ethylene glycol is from 0.1 to 0.5, such as from 0.2 to 0.4 and / or the pH of the first NADES is at least 13. For instance, the first NADES may comprise, essentially consist or consist of potassium carbonate and glycerol in a molar ratio equal to about 0.25 or about 0.30, and about 28% by weight of water relative to the total weight of the first NADES. In other embodiments, the first NADES may comprise, essentially consist or consist of potassium carbonate, glycerol (in a molar ratio equal to about 0.25) and water in an amount of about 5% by weight relative to the total weight of the first NADES.

[0141] As another example, the first NADES may otherwise comprise, essentially consist or consist of potassium carbonate and ethylene glycol in a molar ratio equal to about 0.25 or about 0.30, and about 10% by weight of water relative to the total weight of the first NADES. In other embodiments, the first NADES may comprise, essentially consists or consist of potassium carbonate and ethylene glycol in a molar ratio from 0.1 to 0.5, preferably from 0.1 to 0.4, such as about 0.1, 0.14, 0.17, 0.125 or 0.33, and water in an amount of at most 5% by weight, for instance from 0% to 5%, preferably from 0.1% to 5% or from 0.1% to 3% by weight relative to the total weight of the first NADES.

[0142] In some embodiments, the first NADES may comprise a molar ratio of potassium carbonate to water of 0.2 to 1.

[0143] The first NADES may be prepared by any conventional methods known by the skilled artisan, e.g. merely by mixing the desired compounds (i.e. metal carbonate salt and the C2-C8 polyol) with the desired molar ratio. The preparation of the first NADES may be carried out without or with stirring. It may further be carried out with a temperature, for example, of at most 100 °C, for instance from 20 °C to 90 °C, for instance from 30°C to 80°C. If necessary, an amount of water may be added to the mixing solution.As mentioned above, the method of the invention does not require harsh conditions.

[0144] Indeed, in some embodiments, step a) (e.g. the immersion of the plant fibers in the first NADES) is carried out at a temperature of at most 100 °C, preferably of at most 80 °C or 70 °C, such as from 15 °C to 70 °C or from 20 °C to 60 °C or from 40 °C to 70 °C or from 50 °C to 70 °C. In some embodiments, step a) is carried out at a temperature of at most 100°C, preferably at most 95°C or at most 90°C.

[0145] For instance, the step a) is carried out at about 60 °C. Step a) may also be carried out at a temperature from 55°C to 95°C e.g. at about 90°C, at about 75°C or about 60°C. In preferred embodiments, step a) is carried out at about 90°C.

[0146] When step a) is performed by immersion, step a) may be carried out with or without stirring, for example by using a manual stirring, a mechanical stirring or a vibratory platform shaker. Preferably, step a) is carried out with mechanical stirring (e.g. with paddle or a magnetic stirrer), e.g. at a rate from 50 revolutions per minute (or “rpm”) to 300 rpm, e.g. 180 rpm.

[0147] According to the invention, step a) may be carried out for few minutes to few hours, notably depending on the particular first NADES to be used and / or the type of plant fibers to be treated and / or the device used to perform step a).

[0148] For example, step a) may be carried out for 5 min to 24 hours, e.g. from 30 min to 24 hours, from 2 hours to 24 hours or from 4 hours to 16 hours. In some embodiments, step a) may be carried out for 30 min to 16 hours, for instance for 30 min to 5 hours, preferably for 30 min to 4 hours. For instance, step a) may be carried out for about 30 min, 1 hour, 1.5 hour, 2 hours, 2.5 hours, 3 hours, or 4 hours, preferably about 2.5 hours.

[0149] At the end of step a), the plant fibers are typically recovered from the first NADES before to be treated with the second NADES in step b). The plant fibers may be recovered from the first NADES by carrying out any known methods in the art. For example, plant fibers may be recovered by filtration, decantation or centrifugation, preferably by filtration.

[0150] In addition, after having been recovered, the plant fibers, may be put in contact with water so as to rinse and / or wash them. This rinsing and / or washing step aims at removing residual amounts of the first NADES on the plant fibers and / or rebalancing the pH near pH 7 on the surface of the plant fibers.

[0151] This rinsing and / or washing step may be carried out by any appropriate methods, e.g. by a mere rinsing e.g. with a water flow, by plunging or by immersion, preferably by immersion of the plant fibers. For example, the rinsing and / or washing step may be carried out by immersing the plant fibers in water, preferably deionized water. This rinsing and / or washing step may be carried out for several minutes to several hours, for example for 5 min to 6 hours e.g. from10 min to 2 hours, e.g. 1 hour or 30 min. It may be carried out without or with stirring. This rinsing and / or washing step may be carried out at room temperature or under a slight heating. Typically, the step of rinsing and / or washing is carried out at a temperature of at most 80 °C, for instance from 15 °C to 70 °C or from 20 °C to 60 °C. For instance, the rinsing and / or washing step may be carried out at about 60 °C.

[0152] Then, the plant fibers may be recovered from water by any known method in the art, for example, by filtration, decantation or centrifugation, preferably by filtration.

[0153] The rinsing and / or washing step may be repeated several times, e.g. 1, 2, 3 or more times. The step of contacting the plant fibers with the first NADES can be also repeated e.g. before or after the rinsing and / or washing step.

[0154] Step b)

[0155] Step b), aims at breaking down and / or making come part and / or removing one or more non-cellulosic compounds from the cellulosic structure in the plant fibers, more particularly, the non-cellulosic compounds that are deeper in the plant fibers than those present in the outermost layer of the plant fibers.

[0156] In some embodiments, this step enables to disassemble and / or remove at least a part of the hemicellulose and lignin. More particularly, step b) may provide delignification of the plant fibers.

[0157] In some embodiments, this step also enables to remove and / or disassemble the residual gummy compounds and pectin, if any, that have not been removed during step a).

[0158] In some embodiments, this step also enables to remove and / or disassemble at least a part of the possible residual cuticle and / or the epidermis if any from the cellulosic layer.

[0159] In some embodiments, this step enables to disassemble and / or remove at least a part of, or all of, the hemicellulose and lignin and, if any, residual gummy compounds, residual cuticle and residual epidermis from the plant fibers

[0160] Step b) makes it possible to improve (or complete) the degumming and bleaching step carried out in step a).

[0161] In step b) the plant fibers are contacted with an acid NADES, preferably by immersion. The pH of the second NADES is preferably chosen so as not to degrade the structure of the plant fibers. For example, the second NADES may have a pH of at most 4, preferably of at most 3 such as from 0 to 2.The second NADES comprises, essentially consists or consists of a quaternary ammonium compound and an organic acid compound selected from C2-C8 mono- or poly carboxylic acids optionally substituted by one or more hydroxy groups.

[0162] Said quaternary ammonium compound and said organic acid compound are as defined in the above section entitled “Definitions”

[0163] The molar ratio of the quaternary ammonium compound to the acid compound is selected so as to obtain a NADES with an appropriate pH. The molar ratio of the quaternary ammonium compound to the acid compound may be from 0.01 to 1.0, such as from 0.05 to 0.8, 0.5 to 0.6, e.g. from 0.1 to 0.5, such as about 0.1 or about 0.5. In some embodiments, the molar ratio of the quaternary ammonium compound to the acid compound may be from 0.01 to 2.0, such as from 0.05 to 2.0, or from 0.1 to 2.0, or from 0.1 to 1.0, or from 0.1 to 0.5. For instance, the molar ratio of the quaternary ammonium compound to the acid compound may be about 0.1, 0.5, 0.67, 1.0 or 2.0.

[0164] The quaternary ammonium compound may be selected from choline halide and a betaine compound of formula: RiR.2R3-N -(CH2)n-COO', wherein n is an integer from 1 to 12 as defined above. More particularly, the quaternary ammonium compound may be selected from choline chloride and betaine (also known as trimethylglycine). Advantageously, the quaternary ammonium compound is chosen for its stability and its ability to be associated with C2-C8 mono- or poly carboxy lie acids.

[0165] The acid compound may be a C2-C8 mono-, di- and / or tricarboxylic acid optionally substituted by one or more -OH. The acid compound may be selected from the group consisting of lactic acid, malic acid, oxalic acid, citric acid, acetic acid, malonic acid, succinic acid, tartaric acid, and combinations thereof, preferably lactic acid and / or malic acid. The acid compound may otherwise be selected from the group consisting of lactic acid, malic acid, oxalic acid, citric acid, acetic acid, malonic acid, succinic acid, tartaric acid, glycolic acid and combinations thereof. In preferred embodiments, the acid compound may be selected from the group consisting of lactic acid, citric acid, tartaric acid, oxalic acid, glycolic acid and combinations thereof.

[0166] The second NADES may comprise, consist of, or essentially consist of, (i) choline chloride or betaine as HBA and (ii) lactic acid or oxalic acid as HBD. In some embodiments, the second NADES may comprise, consist of, or essentially consist of (i) choline chloride or betaine as HBA and (ii) lactic acid, citric acid, tartaric acid, oxalic acid and / or glycolic acid as HBD. In some embodiments, the second NADES comprises, essentially consists, or consists of:

[0167] - choline chloride and lactic acid, or- choline chloride, lactic acid and citric acid, or

[0168] - choline chloride and tartaric acid, or

[0169] - choline chloride and citric acid, or

[0170] - choline chloride and glycolic acid, or

[0171] - betaine and oxalic acid, or

[0172] - betaine and lactic acid, or

[0173] - betaine and citric acid,

[0174] for example, with a molar ratio of quaternary ammonium compound to the acid compound of 0.1 to 2.0, e.g. from 0.1 to 0.5.

[0175] In some embodiments, the second NADES comprises (or even consists of) choline chloride and lactic acid e.g. in a molar ratio of 0.1 to 0.5, for example equal to about 0.1 or about 0.5. In some embodiments, the second NADES comprises (or even consists of) choline chloride, lactic acid and citric acid, e.g. with a molar ratio of choline chloride to lactic acid of 0.1 to 0.5, for example about 0.1, and with a molar ratio of choline chloride to citric acid of 0.1 to 2.0, for example about 1.0.

[0176] In some embodiments, the second NADES comprises (or even consists of) choline chloride and tartaric acid, e.g. in a molar ratio of 0.1 to 2.0, for example about 2.0.

[0177] In some embodiments, the second NADES comprises (or even consists of) choline chloride and citric acid, e.g. in a molar ratio of 0.1 to 0.5, for example about 0.33.

[0178] In some embodiments, the second NADES comprises (or even consists of) choline chloride and glycolic acid, e.g. in a molar ratio of 0.1 to 2.0, for example about 0.5.

[0179] In some embodiments, the second NADES comprises (or even consists of) betaine and oxalic acid, e.g. in a molar ratio of 0.1 to 2.0, for example about 1.0.

[0180] In some embodiments, the second NADES comprises (or even consists of) betaine and lactic acid, e.g. in a molar ratio of 0.1 to 0.5, for example about 0.1.

[0181] In some embodiments, the second NADES comprises (or even consists of) betaine and citric acid, e.g. in a molar ratio of 0.1 to 1.0, for example about 0.67.

[0182] In some embodiments, the second NADES further comprises water. The water may be present in order to hydrate plant fibers and / or decrease the viscosity of the second NADES if necessary. It goes without saying that water is present in an amount so that the solvent remains a NADES (e.g. does not dissociate and shift to a mere acid aqueous solution). The amount of water that can be present in the NADES may depend on the HBA and the HBD. Typically, the amount of water in the NADES is at most about 30% by weight, relative to the total weight of the NADES.In some embodiments, the second NADES has a water amount from about 0.1% to about 30%, by weight, relative to the total weight of the second NADES.

[0183] The range from about 0.1% to about 30% of water includes 0.1% to 5%, 5% to 10%, 10% to 15%, 15% to 20%, 20% to 25% and 25% to 30%.

[0184] For example, the second NADES has a water amount from about 0.1% to about 5% or from about 5% to 30% by weight relative to the total weight of the second NADES.

[0185] In some embodiments, the second NADES has a water amount from about 2% to about 30% or from about 5% to 15% by weight relative to the total weight of the second NADES.

[0186] In a preferred embodiment, the second NADES may comprise water in an amount of at most 5% by weight, for instance from 0% to 5%, preferably from 0.1% to 5% or from 0.1% to 3% by weight relative to the total weight of the second NADES.

[0187] In some embodiments, the second NADES may comprise a molar ratio of a quaternary ammonium compound (e.g. choline chloride or betaine) to water of 0.1 to 1.5, preferably of 0.25 to 1.5 or of 0.3 to 1.0, for instance about, 0.4, 0.5 or 1.0.

[0188] In some embodiments, the second NADES may comprise a molar ratio of choline chloride to water of 0.5 to 1.5. In other embodiments, the second NADES may comprise a molar ratio of choline chloride to water of 0.1 to 1.5, preferably of 0.25 to 1.5. For instance, the second NADES may comprise a molar ratio of choline chloride to water of about 0.4 or about 1.0. In some embodiments, the second NADES may comprise a molar ratio of betaine to water of 0.1 to 1.5, preferably of 0.5 to 1.5, for instance about 0.5 or about 1.0.

[0189] In some embodiments, the second NADES may comprise (or consist of) choline chloride, lactic acid and water, e.g. with a molar ratio of choline chloride to lactic acid of 0.1 to 0.5, for example about 0.5, and with a molar ratio of choline chloride to water of 0.1 to 1.5, preferably of 0.5 to 1.5, for example about 1.0.

[0190] In some embodiments, the second NADES may comprise (or consist of) betaine, citric acid and water, e.g. with a molar ratio of betaine to citric acid of 0.1 to 2.0, for example about 0.67, and with a molar ratio of betaine to water of 0.1 to 1.5, preferably of 0.5 to 1.5, for example about 1.0.

[0191] In some embodiments, the second NADES may comprise (or consist of) betaine, oxalic acid and water, e.g. with a molar ratio of betaine to oxalic acid of 0.1 to 2.0, for example about 1.0, and with a molar ratio of betaine to water of 0.1 to 1.5, preferably of 0.5 to 1.5, for example about 0.5.

[0192] The second NADES may be prepared merely by mixing the desired compounds (the quaternary ammonium compound and the acid compound) in the appropriate molar ratio. The preparationof the second NADES may be carried out without or with stirring at room temperature or with heating of at most 100 °C, for instance from 80 °C to 90 °C. If necessary, an amount of water may be added to the mixing solution.

[0193] In some embodiments, step b) (e.g. the immersion of the plant fibers in the second NADES) is carried out at a temperature of at most 100 °C, preferably of at most 80 °C or 70 °C, such as from 15 °C to 70 °C or from 20 °C to 60 °C or from 40 °C to 70 °C or from 50 °C to 70 °C. In some embodiments, step b) is carried out at a temperature of at most 100°C, preferably at most 95°C or at most 90°C.

[0194] For instance, step b) may be carried out at about 60 °C. In some embodiments, step b) may be carried out at a temperature from 55°C to 95°C, e.g. at about 90°C, about 75°C or about 60°C. Preferably, step b) is carried out at about 60°C. A temperature of about 60°C advantageously prevents plant fibers from being damaged while achieving satisfactory results in terms of bleaching and / or degumming.

[0195] The temperature used in steps a) and b) may be the same or may be different.

[0196] In addition, step b) may be carried out without or with stirring, for example by using a manual stirring, a mechanical stirring or a vibratory platform shaker. Preferably, step b) is carried out with mechanical stirring, e.g. from 50 rpm to 300 rpm, preferably at 180 rpm.

[0197] According to the invention, step b) may be carried out for few minutes to few hours, notably depending on the particular second NADES to be used and / or the type of plant fibers to be treated and / or the device used to perform step b).

[0198] For example, step b) may be carried out for 5 min to 24 hours, for instance from 10 min to 16 hours, from 30 min to 12 hours, from 30 min to 6 hours e.g. from 1 hour to 6 hours or from 3 hours to 5 hours. In some embodiments, step b) may be carried out for 30 min to 12 hours, for instance for 30 min to 10 hours, preferably for 30 min to 5 hours. For instance, step b) may be carried out for about 30 min, 1 hour, 2.5 hours, or 3 hours, preferably about 30 min.

[0199] It goes without saying that steps a) and b) may be carried out for different durations, for example step a) may be carried out for 24 hours while step b) may be carried out for 3 hours or 5 hours. At the end of step b), the plant fibers are typically recovered from the second NADES. The plant fibers may be recovered from the second NADES by carrying out any methods known in the art. For example, plant fibers may be recovered by filtration, decantation or centrifugation, preferably by filtration.In addition, after the recovery, the plant fibers may be washed. In some embodiments, the plant fibers recovered in step b) are put in contact with water so as to rinsed and / or washed them to remove residual trace of NADES and / or non-cellulosic compounds at the surface of the plant fibers. This rinsing and / or washing step also enables to rebalance the pH near pH 7 on the surface of the plant fibers and / or hydrate plant fibers.

[0200] This rinsing and / or washing step may be carried using different processes, e.g. with a solvent flow or by immersion, preferably by immersion. For example, the rinsing and / or washing step may be carried out by immersing the plant fibers in water, preferably deionized water. This rinsing and / or washing step may be carried out for several minutes to several hours, for example for 1 hour or 30 min. It may be carried out without or with stirring, for example by using a manual stirring, a mechanical stirring or a vibratory platform shaker. Preferably this step is carried out with mechanical stirring, for example from 50 rpm to 300 rpm, preferably at 180 rpm. This rinsing and / or washing step may be carried out with a temperature, for example, of at most 100 °C, preferably of at most 80 °C, for instance from 15 °C to 70 °C or from 20 °C to 60 °C. For instance, the rinsing and / or washing step may be carried out at about 60 °C. Then, the plant fibers may be recovered from water by any known method in the art, for example, by filtration, decantation or centrifugation, preferably by filtration.

[0201] The rinsing and / or washing step may be repeated several times, e.g. 1, 2, 3 or more times. The step of contacting the plant fibers with the second NADES can be repeated before or after the rinsing and / or washing step.

[0202] - Additional steps

[0203] The method of the invention may comprise one or several additional steps, e.g. selected from:

[0204] - a step of wringing out the plant fibers, and / or

[0205] - a step of hydrating the plant fibers, and / or

[0206] - a step of drying the plant fibers, and / or

[0207] - a step of removing the possible remaining cuticle and / or epidermis, and / or

[0208] - a step of recovering and recycling the first and / or the second NADES, and / or

[0209] - a step of recovering the lignin extracted from the plant fibers, and / or

[0210] - a step of pre-treating the plant fibers, and / or

[0211] - a step of repeating step a) and / or step b).

[0212] For example, at the end of step a) and / or step b), the plant fibers can be (roughly) wrung out, e.g. with metal tongs, in order to remove excess NADES.For example, prior to steps a) and b), regardless the order in which they are carried out, a hydration step of the plant fiber can be performed, in particular when the starting plant fibers are dry.

[0213] For example, after steps a) and b) regardless the order in which they are carried out, a step c) of drying the plant fibers may be implemented. Step c) may be performed by any methods known in the art, e.g. by rinsing or immersing the plant fibers with / in an anhydrous organic solvent, such as ethanol and / or acetone. In addition or alternatively to the use of an anhydrous organic solvent, the plant fibers may be subjected to air-drying (e.g. with an air flow) and / or heating (e.g. in a drying oven).

[0214] Furthermore, it is possible that the cuticle and / or the epidermis if any, may remain on the surface of the plant fibers, but only slightly attached to the plant fibers. The possible remaining cuticle and / or epidermis can be easily separated from the plant fibers, for example by a mere application of a mechanical action.

[0215] Thus, in order to remove the possible remaining cuticle and / or epidermis, a step d) of applying a mechanical action to the plant fibers may be implemented after and / or prior to step c). Preferably, the possible remaining cuticle and / or epidermis can be removed from the plant fibers by combing and / or stirring and / or shaking and / or handling, more preferably by combing.

[0216] The plant fibers obtained with the method of the Invention are enriched in crystalline cellulose as compared to the starting (untreated) plant fibers. In some embodiments, the plant fibers obtained by the method of the invention may be depleted in non-cellulosic compounds (e.g. gummy compounds, hemicellulose and lignin). The plant fibers obtained are further lighter than the starting plant fibers.

[0217] The plant fibers obtained at the end of the method of the invention show appropriate color and mechanical properties in terms of strength and flexibility and can be used in many different fields such as textile, biomaterials, food or cosmetics industries. For example, the obtained degummed and bleached plant fibers may subsequently be spun into yams and thus used in woven textiles. The obtained degummed and bleached plant fibers may otherwise subsequently be transformed into (or use in) building materials, such as thermal and sound insulation materials, panels, etc.

[0218] In addition, at the end of the method of the invention, the first and the second NADES may advantageously be recycled and used again for degumming and bleaching other plant fibers. For example, the first and the second NADES can each be used at least twice for degummingand bleaching plant fibers. These NADES can be recycled directly after use. Alternatively, they can be purified prior being recycled.

[0219] In some embodiments, the by-products present in the effluents, e.g. the lignin extracted from the plant fibers, may be recovered for valorization and use in further processing.

[0220] Plant fibers

[0221] The plant fibers which are treated with the method of the invention may be of any type e.g. bast fibers, leaf fibers, seed fibers or fruit fibers. The plant fibers may be obtained or isolated from the starting plant of interest by any methods known in the art and including trimming (leaves release) and / or decortication and / or retting and / or scutching.

[0222] Preferably, the plant fibers are bast fibers.

[0223] Bast fibers encompass without being limited to hemp fibers, flax fibers, jute fibers, ramie fibers, kenaf fibers, mesta fibers, roselle fibers, nettle fibers or combination thereof, preferably hemps fibers and / or flax fibers.

[0224] In some embodiments, the harvested plant fiber or any part thereof (e.g. the stems) may be directly subjected to the method of the invention, i.e. without any pre-treatment.

[0225] Otherwise, prior to being subjected to the method of the invention, the harvested plant fiber may be subjected to one or more pre-treatments so as to help the isolation of the plant fibers. For example, prior to being subjected to the method of the invention, the harvested plants may be dried and, thus, the method of the invention may be implemented on dried plants or dried parts thereof, e.g. on dried stems. For instance, the method of the invention may be implemented on dried hemp, flax or nettle stems which have not been subjected to any retting and / or scutching step.

[0226] The method of the invention may otherwise be implemented on a tow, i.e. on plant fibers obtained by scutching and / or retting. In some embodiments, before step a), the method of the invention may comprise a step of retting and / or scutching the harvested plants so as to obtain tow plant fibers.

[0227] The step of retting employs the action of micro-organisms and moisture to dissolve or rot away much of the cellular tissues and pectins surrounding the plant fibers in the plant part of interest (e.g. in the stem). The aim of this step is to make it easier to extract the fibers.

[0228] The retting step may be carried out by the so-called dew retting wherein the harvested fiber plants are spread evenly in grassy fields. The combined action of bacteria, sun, rain, air, and dew produces fermentation, dissolving much of the material surrounding the plant fibers. This step, depends on climatic conditions and may be carried out up to two or three weeks.The retting step may also be carried out by the so-called water retting wherein the harvested plants are immersed in water, such as rivers or lakes where pectinolytic microbial communities develop. The water can penetrate into the plant structures, increase the moisture absorption of the plant fibers, and boost the proliferation of micro-organisms. This step may be carried out up to one or two weeks.

[0229] The retted plant fibers, called straw, may then be dried in open air or by mechanical means. After what a method can be carried out for breaking the brittle woody portion of the straw, either by hand or by passing through roller, followed by the scutching step of removing the broken woody portion of the straw, by beating or scraping. A tow is then obtained and may be subjected to the method of the invention.

[0230] The method of the invention may be implemented on incomplete retted plant fibers. In that case, plant fibers are subjected to an incomplete retting step.

[0231] - Particular embodiments of the method of the invention

[0232] According to the invention, the method may be implemented with one, several or all of the following features:

[0233] - step a) is carried out before step b),

[0234] - the first NADES comprises potassium carbonate as metal carbonate salt and glycerol or ethylene glycol as C2-C8 polyol in a molar ratio from 0.1 to 0.5,

[0235] - the first NADES further has a water content from 0.1% to 30% by weight, for example from 0.1% to 5.0% by weight or from 5% to 30% by weight of the total weight of the first NADES,

[0236] - the first NADES has a pH of at least 13, e.g. of about 14,

[0237] - the second NADES comprises:

[0238] • choline chloride and lactic acid in a molar ratio from 0.05 to 0.6 or from 0.1 to 0.5 and optionally further comprises water preferably in an amount of 0.1% to 30% by weight, for example in an amount of 2% to 30% by weight of the total weight of the second NADES, or

[0239] • choline chloride, lactic acid and citric acid, with a molar ratio of choline chloride to lactic acid of 0.1 to 0.5, and with a molar ratio of choline chloride to citric acid of 0.1 to 2.0, or

[0240] • choline chloride and tartaric acid, in a molar ratio of 0.1 to 2.0, or • choline chloride and citric acid, in a molar ratio of 0.1 to 0.5, or

[0241] • choline chloride and glycolic acid, in a molar ratio of 0.1 to 2.0, or• betaine and oxalic acid, in a molar ratio of 0.1 to 2.0, optionally further comprises water preferably in an amount of 0.1% to 5% by weight of the total weight of the second NADES, or

[0242] • betaine and lactic acid, in a molar ratio of 0.1 to 0.5, or

[0243] • betaine and citric acid, in a molar ratio of 0.1 to 2.0, optionally further comprises water preferably in an amount of 0.1% to 5% by weight of the total weight of the second NADES,

[0244] - in step a) and / or in step b), the plant fibers are immersed in the NADES,

[0245] - in step a) and / or in step b), the immersion of the plant fibers is performed at a temperature (i) of at most 80 °C, preferably of at most 70 °C such as from 40 °C to 70 °C, or (ii) of at most 100°C, preferably at most 95°C, for example from 55°C to 95°C, such as about 60°C or about 90°C,

[0246] - at the end of steps a) and b), the plant fibers are recovered, preferably by filtration, and then rinsed and / or washed with water,

[0247] - a step c) of drying the plant fibers is implemented at the end of step b),

[0248] - a step d) of removing the possible remaining cuticle and / or epidermis is implemented, step d) being preferably carried out by combing the plant fibers, and / or

[0249] - the plant fibers are hemp, nettle, or flax fibers and, preferably, in the form of incomplete retted plant fibers, retted plant fibers or in the form of a tow.

[0250] For instance, an example of a method according to the invention is as follows:

[0251] - step a) is carried out before step b);

[0252] - in step a): the first NADES essentially consists of potassium carbonate as metal carbonate salt and glycerol or ethylene glycol as C2-C8 polyol in a molar ratio of 0.1 to 0.5, water in an amount of 0.1% to 30% by weight (for example of 0.1% to 5% or of 5% to 30% by weight) of the total weight of the first NADES, and has a pH of at least 13 (e.g. of about 14), step a) being carried out by immersion, at a temperature of about 60 °C;

[0253] - at the end of step a): the plant fibers are recovered, preferably by filtration, and then rinsed and / or washed with water;

[0254] - in step b): the second NADES comprises choline chloride and lactic acid in a molar ratio of 0.1 to 0.5 and optionally further comprises water in an amount of 0.1% to 30% by weight (for example in an amount of 2% to 30% by weight) of the total weight ofthe second NADES, step b) being carried out by immersion, at a temperature of about 60 °C;

[0255] - at the end of step b): the plant fibers are recovered, preferably by filtration, and then rinsed and / or washed with water;

[0256] - after step b): a step c) is carried out for drying the plant fibers, e.g. with anhydrous solvent such as ethanol and acetone and / or with a drying oven and / or by air-drying, followed by a step d) of combing the plant fibers so as to remove the possible remaining cuticle and / or epidermis.

[0257] Another example of the method of the invention is as follows:

[0258] - step a) is carried out before step b);

[0259] - in step a): the first NADES has a pH of at least 13 (e.g. of about 14) and essentially consists of potassium carbonate as metal carbonate salt and glycerol or ethylene glycol as C2-C8 polyol in a molar ratio of 0.1 to 0.5,

[0260] - step a) is carried out by immersing the plant fibers in the first NADES, at a temperature of at most 95°C, for example from 55°C to 95°C, such as about 60 °C or about 90°C; - at the end of step a): the plant fibers are recovered, preferably by filtration, and then rinsed and / or washed with water;

[0261] - in step b): the second NADES comprises or essentially consists of:

[0262] • choline chloride and lactic acid in a molar ratio of 0.1 to 0.5, and optionally water in an amount of 0.1% to 30% by weight relative to the total weight of the second NADES, or

[0263] • choline chloride, lactic acid and citric acid, with a molar ratio of choline chloride to lactic acid of 0.1 to 0.5, and with a molar ratio of choline chloride to citric acid of 0.1 to 2.0, or

[0264] • choline chloride and tartaric acid, in a molar ratio of 0.1 to 2.0, or • choline chloride and citric acid, in a molar ratio of 0.1 to 0.5, or

[0265] • choline chloride and glycolic acid, in a molar ratio of 0.1 to 2.0, or • betaine and oxalic acid, in a molar ratio of 0.1 to 2.0, and optionally water preferably in an amount of 0.1% to 5% by weight relative to the total weight of the second NADES, or

[0266] • betaine and lactic acid, in a molar ratio of 0.1 to 0.5, or

[0267] • betaine and citric acid, in a molar ratio of 0.1 to 2.0, optionally water preferably in an amount of 0.1% to 5% by weight relative to the total weight of the second NADES;- step b) is carried out by immersing the plant fibers in the second NADES, at a temperature of at most 95°C, for example from 55°C to 95°C, such as about 60 °C or about 90°C;

[0268] - at the end of step b): the plant fibers are recovered, preferably by filtration, and then rinsed and / or washed with water;

[0269] - after step b): a step c) is carried out for drying the plant fibers, e.g. with anhydrous solvent such as ethanol and acetone and / or with a drying oven and / or by air-drying, followed by a step d) of combing the plant fibers so as to remove the possible remaining cuticle and / or epidermis.

[0270] Another example of the method of the invention is as follows:

[0271] - step a) is carried out before step b);

[0272] - in step a): the first NADES has a pH of at least 13 (e.g. of about 14) and essentially consists of potassium carbonate as metal carbonate salt and ethylene glycol as C2-C8 polyol in a molar ratio of 0.1 to 0.5,

[0273] - step a) is carried out by immersing the plant fibers in the first NADES, at a temperature of at most 95°C, for example from 55°C to 95°C, such as about 90 °C, preferably for 2.5 hours;

[0274] - at the end of step a): the plant fibers are recovered, preferably by filtration, and then rinsed and / or washed with water;

[0275] - in step b): the second NADES comprises or essentially consists of choline chloride and lactic acid in a molar ratio of 0.1 to 0.5;

[0276] - step b) is carried out by immersing the plant fibers in the second NADES, at a temperature of at most 95°C, for example from 55°C to 95°C, such as about 60 °C or about 90°C, preferably for 30 min;

[0277] - at the end of step b): the plant fibers are recovered, preferably by filtration, and then rinsed and / or washed with water;

[0278] - after step b): a step c) is carried out for drying the plant fibers, e.g. with anhydrous solvent such as ethanol and acetone and / or with a drying oven and / or by air-drying, followed by a step d) of combing the plant fibers so as to remove the possible remaining cuticle and / or epidermis.

[0279] In these embodiments, step a) is preferably carried out at a temperature comprised between 55°C and 95°C, more preferably between 85°C and 95°C and / or step b) is preferably carried out at a temperature comprised between 55°C and 95°C, more preferably between 55°C and 65°C.In these embodiments, the plant fibers are preferably bast fibers and, more particularly, hemp and / or flax fibers. Preferably the plant fibers have been obtained by retting and / or scutching steps. The plant fibers may therefore be in the form of incomplete retted plant fibers, retted plant fibers or in the form of a tow.

[0280] Other objects of the invention

[0281] Another object of the invention is a use of a first NADES and then a different second NADES for degumming and bleaching plant fibers.

[0282] According to the invention, the first and second NADES used to degum and bleach plant fibers are as defined above.

[0283] The invention also relates to plant fibers directly obtained or obtainable by the method of the invention.

[0284] The invention also relates to an article made of plant fibers directly obtained or obtainable from the method of the invention. In some embodiments, the article is a woven or a nonwoven material, e.g. a textile clothing, felt, thermal insulation material, sound insulation materials, panels, and the like.

[0285] Finally, the invention also relates to a use of plant fibers directly obtained or obtainable from the method of the invention, e.g. for the conception of an article e.g. in the textile industry. In some embodiments, the article is a woven or a nonwoven material, e.g. a textile clothing, felt, thermal insulation material, sound insulation materials, panels, and the like.

[0286] EXAMPLES

[0287] Example 1

[0288] Preparation of the first NADES

[0289] Potassium carbonate was dispersed in glycerol to obtain a molar ratio of potassium carbonate to glycerol of about 0.29. Water (28% by weight) was then added to the mixture.

[0290] The dispersion and the addition of water were both carried out with stirring and at a temperature of 80-90 °C, with an IKA™ C-MAG HS7 hotplate stirrer.

[0291] The solution was stirred and heated to 80-90 °C until a clear solution was obtained.

[0292] The first NADES was therefore obtained and had a pH of about 14.

[0293] Preparation of the second NADES

[0294] By using an IKA™ C-MAG HS7 hotplate stirrer, choline chloride was dispersed in lactic acid to obtain a molar ratio of choline chloride to lactic acid of about 0.1. The resulting solution was stirred and heated to 80-90 °C until a clear solution was obtained.The second NADES was therefore obtained.

[0295] - Method for degumming and bleaching tow flax fibers

[0296] In an Erlenmeyer flask, 1 g of tow flax fibers was dispersed in 90 mL of the first NADES. The Erlenmeyer flask was placed in a water bath (Jubulo™ SW 20C) and was stirred at 180 rpm and heated to 60 °C for 24 hours.

[0297] The tow flax fibers was then separated from the first NADES by filtration with a Buchner funnel G2.

[0298] The tow flax fibers was then dispersed in 100 mL of deionized water, with stirring (180 rpm), and was heated to 60 °C for 1 hour.

[0299] The tow flax fibers was separated from water by using a Buchner funnel G2, and was then dispersed in 100 mL of the second NADES, with stirring (180 rpm) and at a temperature of 60 °C for 3 hours.

[0300] The tow flax fibers was then separated from the second NADES by using a Buchner funnel G2. Still with the Buchner funnel G2, the tow flax fibers was rinsed with 100 mL of deionized water. Afterwards, the tow flax fibers was dried with 50 mL of ethanol 96% and then with 25 mL of acetone before being dried by air-drying.

[0301] At that stage, about 83% of the fibrous material were recovered.

[0302] Then, in order to remove the possible remaining cuticle and / or epidermis, the tow flax fibers was combed.

[0303] The color of the resulting tow flax fibers was measured with a Konica Minolta™ chromameter. As a result, lightness L* had increased from 53.2 to 73.1. Yellowness a* had also increased from 8.1 to 9.9 as compared to the starting, untreated tow flax fibers.

[0304] Example 2

[0305] Preparation of the first NADES

[0306] Potassium carbonate was mixed with water and ethylene glycol so as to obtain a solution with a molar ratio of potassium carbonate to ethylene glycol of about 0.25 and a water content of about 10% by weight. In other words, the solution had a potassium carbonate: ethylene glycokwater molar ratio of 1 :4:2.4.

[0307] The solution was stirred, heated to 60 °C for 2 hours and then cooled to room temperature. The first NADES was therefore obtained and had a pH of about 14.

[0308] Preparation of the second NADESCholine chloride was mixed with lactic acid and water so as to obtain a solution with a molar ratio of choline chloride to lactic acid of about 0.5 and a water content of about 5.33% by weight. In other words, the solution had a choline chloride:lactic acid:water molar ratio of 1:2:1. The solution was manually stirred at room temperature for 20 minutes.

[0309] The second NADES was therefore obtained and had a pH of about 0.

[0310] - Method for degumming and bleaching flax fibers

[0311] In an Erlenmeyer flask, 0.5 g of retted flax fibers was dispersed in 20 g of the first NADES. The Erlenmeyer flask was heated to 60 °C under stirring for 16 hours.

[0312] The fibers were recovered from the first NADES and then roughly wrung out with metal tongs. The fibers were then rinsed within 20 g of deionized water at 60 °C and under stirring (180 rpm) for 30 minutes twice.

[0313] The fibers were then dispersed in 20 g of the second NADES of Example 2, under stirring (180 rpm) and at a temperature of 60 °C for 3 hours.

[0314] The fibers were recovered from the second NADES and then roughly wrung out with metal tongs.

[0315] The fibers were rinsed within 20 g of deionized water at 60 °C and under stirring (180 rpm) for 30 minutes twice.

[0316] Afterwards, the fibers were dried by air-drying for 72 hours and then in a drying oven at 40 °C for 1 hour.

[0317] Then, in order to remove the possible remaining cuticle and / or epidermis, a gentle mechanical action was applied on the fibers.

[0318] Comparative assay: in the control process, the retted flax fibers were submitted to the same steps except that the first and second NADES were replaced by deionized water.

[0319] The color of the resulting retted flax fibers (those treated with NADES and those treated with water) was measured with a Konica Minolta™ chromameter.

[0320] The measured lightness L * is shown in figure 1. This figure shows that the lightness L * had increased from 61.96 to 70.50 for the retted flax fibers treated with the first and second NADES while, for the retted flax fibers treated with water, L* had only increased from 61.96 to 64.76.

[0321] The same conditions as in Example 2 were used for Example 3, but the degumming and bleaching method was carried out on incomplete retted flax fibers.

[0322] The color of the resulting incomplete retted flax fibers (those treated with NADES and those treated with water) was measured with a Konica Minolta™ chromameter.The measured lightness L* is shown in figure 2. This figure shows that the lightness L* had increased from 54.90 to 71.33 for the incomplete retted flax fibers treated with the first and second NADES while, for the incomplete retted flax fibers treated with water, L * had only increased from 54.90 to 62.56.

[0323] Therefore, the retted flax fibers and incomplete retted flax fibers obtained at the end of Example 2 and Example 3 had an equivalent lightness L *.

[0324] Other examples are carried out according to the following parameters:

[0325] Table 1

[0326]

[0327]

[0328] The color of the resulting treated plant fibers according to the table above was measured with a Konica Minolta™ chromameter. For each of the resulting treated plant fibers a comparative assay was performed with deionized water instead of the first and second NADES.

[0329] The measured lightness L * of the resulting treated plant fibers of Examples 4-7 is shown in figures 3-6 respectively.

[0330] These figures confirm that the method of the invention increased the lightness L * of the plant fibers.

[0331] Example 8

[0332] - Materials

[0333] Flax rovings were obtained from Linificio e Capanificio Nazionale (Bergamo, Italia). Potassium carbonate (CAS: 584-08-7, purity > 99.0 %), betaine (CAS: 107-43-7, purity >= 98 %), glycolic acid (CAS: 79-14-1, purity = 99 %), oxalic acid dihydrate (CAS: 6153-56-6, purity = 99.5 %) and choline chloride (CAS: 67-48-1, purity > 98 %) were purchased from Sigma-Aldrich. Ethylene glycol (CAS: 107-21-1, d = 1.113 kg / L) was purchase from Supelco. Lactic acid (CAS: 79-33-4, purity > 92 %) was purchased from Carlo Erba reagents. Glycerol (CAS: 56-81-5, anhydrous 99.0-101.0 % (alkalimetric)) was purchased from Honeywell. Tartaric acid (CAS: 87-69-4, purity = 99 %) was purchased from RECAPTURTM. The chemical reagents used in present study were analytical grade.

[0334] General degumming and bleaching method

[0335] - Step 1: First NADES (alkaline)160 cm of flax roving (more or less 500 mg) were placed into an Erlenmeyer flask, 20 g of first NADES were added to obtain the weight ratio of 1:40. Then flasks were screw-capped and placed into a shaked water-bath, shaking speed was about 180 r.p.m. (Julabo SW 20C).

[0336] The composition of the first NADES, the treatment temperature and duration for each sample are provided in Tables 2 and 3 below.

[0337] Following the treatment, roving pieces were wringed out with a metallic spatula.

[0338] Then, the roving pieces were rinsed by dispersing them in 20 g of Milli-Q water at 60 °C for 30 minutes. The roving pieces were then wringed out with a metallic spatula. A second rinse was completed in the same conditions with fresh Milli-Q water and wringed as described above. For comparative experiments (first series see below): the roving pieces were air-dried on absorbing paper during 72 h and then analysed for colour change, and weight loss.

[0339] For the experiments according to the invention (second series see below): the roving pieces were subjected to a step 2 with a second NADES.

[0340] - Step 2: Second NADES (acidic)

[0341] The wringed rovings were suspended into 20 g of the second NADES. The screw-capped flasks were heated in a shaked bath-water.

[0342] The composition of the second NADES, the treatment temperature and duration for each sample are provided in Table 3 below.

[0343] Following the treatment, rovings were wringed out with a metallic spatula. Samples were rinsed twice with Mili-Q water as described above.

[0344] After the full treatment, rovings were air-dried on absorbing paper during 72 h and then analysed for colour change, and weight loss.

[0345] Treatment method with the first NADES only (comparative)

[0346] A first series of experiments was carried out for comparative purposes. In this series, the flax rovings were subjected to a single NADES step, namely to the alkaline (first) NADES step only as described above (see Step 1) and in the conditions shown in Table 2:

[0347] Table 2 (Comparative - one single step)

[0348]

[0349]

[0350] Treatment method with the first and second NADES (method of the invention)

[0351] A second series of experiments was carried out according to the method of the invention, by subjecting the rovings to Step 1 with the alkaline (first) NADES and then to Step 2 with the acidic (second) NADES as described above and in the conditions shown in Table 3:

[0352] Table 3 (Invention)

[0353]

[0354] In Tables 2 and 3 above; “K” means carbonate potassium, “EG” means ethylene glycol, “CC” means choline chloride, “B” means betaine, “LA” means lactic acid, “CA” means citric acid, “TA” means tartaric acid, “GA” means glycolic acid, “OA” means oxalic acid, and “W” means water.

[0355] For comparative purposes, the following experiments were also conducted:

[0356] Control experiment: the flax rovings were subjected to a two steps protocol in which the flax rovings were subjected to two treatments with water at 90°C during one hour instead of treatments with the first and the second NADES; this experiment is noted no.21 hereinafter;

[0357] Comparative experiment 2: the flax rovings were subjected to a two steps protocol in which the first NADES was Betaine:Urea: Water (1:2:0.7) (step 1) and the second NADES was CC:LA (1:10) (step 2). Step 1) was carried out during 1 hour at 90°C and step 2) was carried out during 1 hour at 60°C); this experiment is noted no. 22 hereinafter.

[0358] Colour change (bleaching)

[0359] Colour of treated flax rovings (samples no. 1-22) was measured using a Minolta chromameter (CR-400 Minolta®) through the assessment of L * parameter to determine the whiteness of treated flax rovings (the higher the L* value, the whiter the fiber is). Five different sections of each sample were measured.

[0360] For comparative purposes, untreated plant fibers were also analysed.

[0361] The obtained I * of each sample is shown in Table 4 below:

[0362] Table 4

[0363]

[0364]

[0365] These results show that the method of the invention increases the lightening of the plant fibers as compared to untreated plant fibers, plant fibers treated with hot water (no. 21) or plant fibers treated with an alternative NADES system (no. 22). The method of the invention is also significantly more effective at bleaching plant fibers than a method based on a single alkaline NADES step (no. 1-4). In other words, step 2) with the acidic (second) NADES completes and improves the bleaching initiated by the alkaline (first) NADES.

[0366] Non-cellulosic component removal - Mass loss (degumming)

[0367] The overall removal of material during the treatments was measured as the mass loss of the samples. The samples were weighed before and after the treatment (after drying). Mass loss was determined as follows:

[0368] 100

[0369]

[0370] with mi = initial mass and mf = final mass.

[0371] The mass loss was determined for samples no. 1-22. The results are shown in Table 5 below:

[0372] Table 5

[0373]

[0374]

[0375] These results show that the method of the invention not only improves the degumming as compared to plant fibers treated with hot water (no. 21) or with an alternative NADES system (no. 22), but also improves the degumming as compared to plant fibers treated with an alkaline (first) NADES only. In other words, step 2) with acidic (second) NADES exerts an effective degumming action on plant fibers pre-treated with an alkaline NADES.

[0376] Example 9

[0377] A pilot test, in an industrial scale, was carried out on flax rovings (800 g) under the following conditions:

[0378] Table 6

[0379]

[0380] The first NADES was prepared into a preparation tank with 30 kg of ethylene glycol and 9,54 kg of potassium carbonate. Components were heated at 50 °C and stirred during 30 min.

[0381] The second NADES was prepared into a preparation tank with 16.94 kg of choline chloride and 27.32 kg of hydrated lactic acid (20 % of water content). Components were heated at 60 °C and stirred during 30 min.

[0382] Figure 7 is a picture of the obtained plant fibers.

[0383] The obtained fibers were lighter than before the treatment. Moreover, they were more degummed than fibers obtained by a conventional industrial process (i.e. under harsh conditions using NaOH and hydrogen peroxide).The obtained plant fibers were then spun: the resulting yam was finer than that obtained using the industrial process and was more robust (less breakage was observed). This suggests that the obtained elementary fibers were better separated and that there was better slippage between them compared to fibers obtained using the conventional industrial process.

Claims

43CLAIMS1. A method for degumming and bleaching plant fibers, which comprises the steps of: a) contacting the plant fibers with a first natural deep eutectic solvent (NADES) having a pH equal to or greater than 12 and comprising a metal carbonate salt and a C2-C8 polyol; and b) contacting the plant fibers with a second natural deep eutectic solvent (NADES) comprising a quaternary ammonium compound and an acid compound selected from C2-C8 mono- or poly carboxylic acids optionally substituted by one or more hydroxy groups.

2. The method according to claim 1, wherein the first NADES has a pH of at least 13, preferably equal to or greater than 14.

3. The method according to claim 1 or 2, wherein in step a), i) the metal carbonate salt is potassium carbonate and / or ii) the C2-C8 polyol is selected from the group consisting of glycerol, ethylene glycol, triethylene glycol, propylene glycol, butane- 1,4-diol, sorbitol and combinations thereof, preferably glycerol or ethylene glycol.

4. The method according to any one of claims 1 to 3, wherein the first NADES has a molar ratio of the metal carbonate salt to the C2-C8 polyol from 0.1 to 0.5.

5. The method according to any one of claims 1 to 4, wherein the first NADES further comprises water in an amount of 0.1% to 30% by weight relative to the total weight of said first NADES and / or wherein the second NADES further comprises water in an amount of 0.1% to 30% by weight relative to the total weight of said second NADES.

6. The method according to any one of claims 1 to 5, wherein in step b), i) the quaternary ammonium compound is selected from choline halide and a betaine and / or ii) the acid compound is selected from the group consisting of lactic acid, malic acid, oxalic acid, citric acid, acetic acid, malonic acid, succinic acid, tartaric acid, glycolic acid and combinations thereof, preferably lactic acid, citric acid, tartaric acid, oxalic acid, and / or glycolic acid.

7. The method according to any one of claims 1 to 6, wherein the second NADES has a molar ratio of the quaternary ammonium compound to the acid compound from 0.05 to 2.0, for example from 0.1 to 2.0 or from 0.1 to 0.5.

448. The method according to any one of claims 1 to 7, wherein the first NADES comprises potassium carbonate as metal carbonate salt and glycerol or ethylene glycol as C2-C8 polyol, preferably in a molar ratio of 0.2 to 0.4, and / or the second NADES comprises choline chloride and lactic acid, preferably in a molar ratio of 0.1 to 0.5.

9. The method according to any one of claims 1 to 7, wherein:the first NADES consists essentially of potassium carbonate as metal carbonate salt, glycerol or ethylene glycol as C2-C8 polyol, and optionally water, wherein the metal carbonate salt / C2-Cs polyol molar ratio is preferably from 0.1 to 0.5, and wherein, when water is present in the first NADES, the potassium carbonate / water molar ratio is preferably from 0.2 to 1.0, and the second NADES consists essentially of:- choline chloride, lactic acid and optionally water, or- choline chloride, lactic acid, citric acid and optionally water, or- choline chloride, tartaric acid and optionally water, or- choline chloride, citric acid and optionally water, or- choline chloride, glycolic acid and optionally water, or- betaine, oxalic acid and optionally water, or- betaine, lactic acid and optionally water, or- betaine, citric acid and optionally water,wherein the molar ratio of the quaternary ammonium compound to the acid compound in the second NADES is preferably from 0.1 to 2.0, for example from 0.1 to 0.5, and wherein, when water is present in the second NADES, the quaternary ammonium compound / water molar ratio is from 0.1 to 1.5.

10. The method according to any one of claims 1 to 9, wherein steps a) and b) are carried out at a temperature of at most 100°C, preferably at most 95°C, such as from 55°C to 95°C.

11. The method according to any one of claims 1 to 10, wherein, at the end of step a) and / or step b), the plant fibers are recovered and then rinsed and / or washed with water.

12. The method according to any one of claims 1 to 11, further comprising, after step b), a step c) of drying the plant fibers, preferably with an organic solvent, such as ethanol and / or acetone, and / or with a drying oven and / or by air-drying.4513. The method according to claim 12, further comprising, after and / or prior to step c), a step d) of applying a mechanical action, such as combing, to the plant fibers.

14. The method according to claim 1, wherein:- step a) is carried out before step b);- in step a): the first NADES has a pH of at least 13 and essentially consists of potassium carbonate as metal carbonate salt, glycerol or ethylene glycol as C2-C8 polyol, and water, wherein the molar ratio of the metal carbonate salt to the C2-C8 polyol is from 0.1 to 0.5 and wherein water is present at an amount of 0.1% to 30% by weight of the total weight of the first NADES;- step a) is carried out by immersing the plant fibers in the first NADES, at a temperature of at most 70 °C, e.g. from 50 °C to 70 °C;- at the end of step a): the plant fibers are recovered and then washed with water; - in step b): the second NADES essentially consists of choline chloride, lactic acid, and optionally water, wherein the choline chloride / lactic acid molar ratio is from 0.1 to 0.5 and wherein the optional water accounts for 0.1% to 30% by weight of the total weight of the second NADES;- step b) is carried out by immersing the plant fibers in the second NADES, at a temperature of at most 70 °C, e.g. from 50 °C to 70 °C;- at the end of step b): the plant fibers are recovered and then washed with water; - after step b): a step c) is carried out for drying the plant fibers followed by a step d) of combing the plant fibers.

15. The method according to claim 1, wherein:- step a) is carried out before step b);- in step a): the first NADES has a pH of at least 13 and essentially consists of potassium carbonate as metal carbonate salt and glycerol or ethylene glycol as C2-C8 polyol in a molar ratio of 0.1 to 0.5;- step a) is carried out by immersing the plant fibers in the first NADES, at a temperature of at most 95°C, for example from 55°C to 95°C;- at the end of step a): the plant fibers are recovered and then washed with water; - in step b): the second NADES essentially consists of:• choline chloride and lactic acid in a molar ratio of 0.1 to 0.5, and optionally water in an amount of 0.1% to 30% by weight relative to the total weight of the second NADES, or• choline chloride, lactic acid and citric acid, with a molar ratio of choline chloride to lactic acid of 0.1 to 0.5, and with a molar ratio of choline chloride to citric acid of 0.1 to 2.0, or• choline chloride and tartaric acid in a molar ratio of 0.1 to 2.0, or• choline chloride and citric acid in a molar ratio of 0.1 to 0.5, or• choline chloride and glycolic acid in a molar ratio of 0.1 to 2.0, or • betaine and oxalic acid in a molar ratio of 0.1 to 2.0, and optionally water in an amount of 0.1% to 5% by weight relative to the total weight of the second NADES, or• betaine and lactic acid in a molar ratio of 0.1 to 0.5, or• betaine and citric acid in a molar ratio of 0.1 to 2.0, and optionally water in an amount of 0.1% to 5% by weight relative to the total weight of the second NADES,- step b) is carried out by immersing the plant fibers in the second NADES, at a temperature of at most 95°C, for example from 55°C to 95°C;- at the end of step b): the plant fibers are recovered and then washed with water; - after step b): a step c) is carried out for drying the plant fibers followed by a step d) of combing the plant fibers.

16. The method according to claim 1, wherein:- step a) is carried out before step b);- in step a): the first NADES has a pH of at least 13 and essentially consists of potassium carbonate as metal carbonate salt and ethylene glycol as C2-C8 polyol in a molar ratio of 0.1 to 0.5;- step a) is carried out by immersing the plant fibers in the first NADES, at a temperature of at most 95°C, for example from 55°C to 95°C;- at the end of step a): the plant fibers are recovered and then washed with water; - in step b): the second NADES essentially consists of choline chloride and lactic acid in a molar ratio of 0.1 to 0.5;- step b) is carried out by immersing the plant fibers in the second NADES, at a temperature of at most 95°C, for example from 55°C to 95°C;at the end of step b): the plant fibers are recovered and then washed with water; after step b): a step c) is carried out for drying the plant fibers followed by a step d) of combing the plant fibers.

17. The method according to any one of claims 1 to 16, wherein the mass ratio of the plant fibers to the NADES is from 0.005 to 2.0, preferably from 0.01 to 1.0, such as from 0.01 to 0.1 or from 0.02 to 0.06.

18. The method according to any one of claims 1 to 17, wherein the plant fibers are in the form of incomplete retted plant fibers, retted plant fibers or in the form of a tow.

19. The method according to any one of claims 1 to 18, wherein the plant fibers are bast fibers, leaf fibers, seed fibers or fruit fibers, preferably bast fibers.

20. The method according to claim 19, wherein the bast fibers are hemp fibers, flax fibers, jute fibers, ramie fibers, kenaf fibers, mesta fibers, roselle fibers, nettle fibers or combination thereof, preferably hemps fibers and / or flax fibers.

21. Use of a first NADES and then a different second NADES for degumming and bleaching plant fibers, the first NADES and the second NADES being as defined in any one of claims 1 to 9.

22. Plant fibers directly obtained or obtainable by the method according to any one of claims 1 to 20.

23. An article made of plant fibers according to claim 22.

24. Use of plant fibers according to claim 22 for the conception of an article.

25. The article according to claim 23, or the use according to claim 24, wherein the article is a woven or a nonwoven material, for example a textile clothing, felt, thermal insulation material, sound insulation materials, or panels.

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