Method for the recovery of cellulose, method for the regeneration of cellulose, and method for the preparation of nanocellulose

Abstract

The present invention relates to a method for the recovery of cellulose in a material containing cellulose fibres comprising the step of putting the material containing cellulose fibres in contact with at least one ternary deep eutectic solvent (DES ) comprising at least one organic acid chosen from mono carboxylic acids, poly carboxylic acids and mixtures thereof, preferably hydroxylated, more preferably an organic alpha-hydroxy acid; at least one metallic salt; and water, thus obtaining a cellulose in the form of solution or dispersion in said ternary DES. The present invention also relates to a method for the regeneration of cellulose and a method for the preparation of nanocellulose using a ternary DES according to the invention. Finally, the invention refers to a ternary DES according to the invention and a method for preparation thereof.

Description

[0001] METHOD FOR THE RECOVERY OF CELLULOSE , METHOD FOR THE REGENERATION OF CELLULOSE , AND METHOD FOR THE PREPARATION

[0002] OF NANOCELLULOSE

[0003] This study was carried out within the framework of the MICS (Made in Italy - Circular and Sustainable ) Extended Partnership and was financed by the European Union Next- GenerationEU (NATIONAL RECOVERY AND RES ILIENCE PLAN (NRRP ) - MISS ION 4 COMPONENT 2 , INVESTMENT 1 . 3 - D . D . 1551 . 11- 10-2022 , PE00000004 ) .

[0004] Field of application

[0005] The present invention relates in general to the field of cellulose recovery with application, for example , in the textile , food, pharmaceutical , paper, packaging, and construction fields , as well as in plant engineering .

[0006] In particular, the invention relates to a method for the recovery of cellulose , a method for the regeneration of cellulose , and a method for the preparation of nanocellulose (NC ) . Prior art

[0007] Cellulose plays an important role among natural macromolecular substances . It is the most widespread biopolymer in the environment and constitutes the predominant part of plant biomass . Generally, in nature , cellulose is found in the cell wall of plants , where it forms a fibrous structure together with lignin and hemicellulose .

[0008] As known, cellulose is a linear polysaccharide composed of repeating units of glucose molecules linked by a 1 , 4- p-glycosidic bond . Cellulose molecules form hydrogen bonds between chains that can give rise either to crystalline domains characterised by strongly compact packing, or to amorphous zones , where hydrogen-bond mediated interactions are less intense . In the latter, the chains are more flexible and capable of dissipating external stresses . This structure results in a material that is flexible and strong at the same time. These characteristics of cellulose are exploited in the fields of textiles, paper production, food (e.g. as a food additive) , and medicine (e.g. for the production of medical devices in the form of hydrogels) , to name a few.

[0009] Cotton, which generally consists in 90% (by weight) cellulose, represents a primary source of cellulose fibres, mainly used in textiles.

[0010] However, it is well known that activities related to the production of high-purity cellulose, such as cotton plantations or extraction from lignocellulosic materials, have a high environmental impact as they are polluting, require the use of a lot of water, soil, fertilisers, pesticides and other resources, and are also expensive.

[0011] Other sources of cellulose are secondary cellulose (derived from agricultural waste products, such as straw, bagasse and other vegetation) and tertiary cellulose, which can be recovered from waste deriving, for example, from the building, textile, wastewater treatment and industrial processing of agricultural products industries .

[0012] There is therefore a need to develop environmentally friendly methods for the recovery of cellulose from the aforementioned cellulose sources, in particular from tertiary cellulose.

[0013] The textile sector, for example, has had in recent decades an increase in the production of low-cost garments and consequently an increase in waste thereof, also as a consequence of the "fast fashion" phenomenon, having a strong impact on the environment.

[0014] The textile sector was the third largest cause of water pollution and land use in 2020, and one of the sectors with the highest carbon dioxide emissions.

[0015] Therefore, this is the sector where the need to find solutions for managing waste useful for cellulose recovery is most felt. Chemical recycling currently involves the dissolution and regeneration of cellulose derivatives and subsequent spinning into regenerated fibres using the "wet spinning" process , which involves the use of solvents .

[0016] As mentioned above , cellulose is characterised by the presence of several hydrogen bonds , which give stability to the structure of the resulting polysaccharide . Only a limited number of solvents are capable of breaking these hydrogen bonds without simultaneously irreversibly af fecting the polymeric structure of cellulose .

[0017] Various methods for converting cellulose pulp into fibres are known in the field .

[0018] Among them there is the "Viscose process" , in which the cellulose material is treated with a NaOH solution, and then with CS2 , thus obtaining cellulose xanthate , an intermediate in the production of viscose rayon . However, this described process is highly polluting to the environment and harmful to human health . Furthermore , the cellulose chains thus obtained are shorter than the original cellulose , and the fibres are weaker, with obvious negative consequences on the mechanical properties , which are worse than with cotton-derived cellulose .

[0019] Another method is the production of lyocell , which involves dissolving wood pulp in N-Methylmorpholine N- oxide (NMMO) and subsequently coagulating it into cellulose fibres using a non-solvent ( for example water ) . However, this method also has drawbacks , as NMMO, in addition to being very expensive, can also involve risks to humans and the environment .

[0020] Deep eutectic solvents ( DESs ) are an emerging class of solvents . These are multi-component systems which comprise at least one hydrogen bond donor (HBD) and at least one hydrogen bond acceptor (HBA) . Hydrogen-bond mediated interactions between HBD and HBA result in melting point depression, so that the melting point of the eutectic mixture is considerably lower than the melting point of each component of the mixture taken individually . Many DESs are therefore in a liquid state at room temperature or at temperatures not much higher than room temperature .

[0021] DESs are particularly stable due to the complex network of hydrogen bonds forming between the components of the mixture . The variability of chemical interactions they have , together with their distinct chemical-physical properties , such as their low volatility and toxicity, make DESs suitable for applications in the field of sustainable chemistry, for example in "green" extraction techniques and in the pharmaceutical sector, to name a few . DESs are also simple and cost-ef fective to prepare , compared to , for example , ionic liquids ( IL ) . The latter, while sharing similar properties to DESs , are often composed of organic cations and inorganic anions characterised by a relatively complex molecular structure and require a speci fic, often laborious and expensive synthesis .

[0022] The HBDs and HBAs that can be used in the production of DESs are many and of di f ferent nature , making it possible to obtain DESs with very di f ferent physical and chemical properties .

[0023] One of the first DESs recognised as such is a mixture of choline chloride and urea in a 1 : 2 molar ratio . This and other choline-based DESs have been studied for cellulose dissolution . Many choline chloride-based DESs have shown promising results in the dissolution of cellulose , however, choline chloride is produced from toxic or foul-smelling synthetic precursors derived from petroleum ( trimethylamine and ethylene oxide ) as well as hydrochloric acid and therefore poses non-negligible environmental risks . Furthermore , choline chloride is hygroscopic and DESs containing it are highly viscous .

[0024] Therefore , there is a need to make available a method for the chemical processing of cellulose present , for example , in cotton or fabrics , including waste fabrics , particularly from the textile industry, that has a lower environmental impact than the prior art .

[0025] The technical problem underlying the present invention is therefore to provide a method for the recovery of cellulose , including both a method for the regeneration of cellulose and a method for the preparation of nanocellulose , that overcomes the drawbacks of the prior art .

[0026] A further technical problem underlying the present invention is to provide such a method that is environmentally friendly compared to the prior art , in other words that is , for example , less polluting and uses solvents with a relatively low toxicity compared to the prior art .

[0027] Summary of the invention

[0028] This problem has been solved according to the invention by a method for the recovery of cellulose in a material containing cellulose fibres comprising the step of putting the material containing cellulose fibres in contact with at least one ternary deep eutectic solvent ( DES ) comprising :

[0029] - at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof ;

[0030] - at least one metallic salt ; and

[0031] - water ; thus obtaining cellulose in the form of a solution or dispersion in the ternary DES .

[0032] Preferably, the aforementioned at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof is hydroxylated, more preferably it is an organic alpha-hydroxy acid .

[0033] Preferably, polycarboxylic acids are chosen from monocarboxylic acids , dicarboxylic acids , tricarboxylic acids and mixtures thereof .

[0034] Preferably, the aforementioned at least one organic acid is chosen from organic acids having a molecular weight below 250 g / mol .

[0035] Preferably, the aforementioned monocarboxylic acids are chosen from lactic acid, formic acid, pyruvic acid, glyoxylic acid, glycolic acid, gluconic acid, glyceric acid, and mandelic acid, more preferably chosen from lactic acid, formic acid and mixtures thereof , even more preferably lactic acid .

[0036] Preferably, the aforementioned dicarboxylic acids are chosen from tartaric acid, oxalic acid, fumaric acid, maleic acid, malonic acid, malic acid, phthalic acid, glutaric acid, itaconic acid, citraconic acid, mesaconic acid, oxalacetic acid and mixtures thereof , more preferably tartaric acid, oxalic acid and mixtures thereof , even more preferably tartaric acid .

[0037] Preferably, the aforementioned tricarboxylic acids are chosen from citric acid, isocitric acid, tricarbalicylic acid, aconitic acid, more preferably citric acid .

[0038] Preferably the aforementioned at least one organic alpha-hydroxy acid is chosen from lactic acid, tartaric acid, citric acid, glycolic acid, gluconic acid, glyceric acid, malic acid, isocitric acid, mandelic acid, and mixtures thereof , more preferably chosen from lactic acid, tartaric acid, citric acid, and mixtures thereof , even more preferably chosen from lactic acid, tartaric acid, and mixtures thereof , most preferably chosen from lactic acid and tartaric acid .

[0039] Preferably, the aforementioned at least one metallic salt is a metall ic salt in which the metal is divalent , more preferably a divalent metal chosen from zinc, calcium, magnesium, iron and aluminium, even more preferably chosen from zinc, calcium and magnesium, even more preferably chosen from zinc and calcium.

[0040] Preferably, the metallic salt is a metallic salt of a single metal.

[0041] Preferably, the aforementioned at least one metallic salt is chosen from ZnC12, CaC12, MgC12, CaS04, A1C13, FeCl3, FeCl2and mixtures thereof, more preferably chosen from ZnC12, CaC12, MgC12 and mixtures thereof, even more preferably chosen from ZnC12, CaC12 and mixtures thereof, most preferably chosen from among ZnC12 and CaC12.

[0042] Preferably, the aforementioned at least one organic acid, more preferably the above at least one organic alpha-hydroxy acid, is chosen from lactic acid, tartaric acid and mixtures thereof; and the aforesaid at least one metallic salt is chosen from ZnC12, CaC12 and mixtures thereof .

[0043] Water is preferably deionised water.

[0044] Preferably, the at least one ternary DES comprises only one organic acid, more preferably only one organic alpha-hydroxy acid, only one metallic salt and water.

[0045] Preferably, the aforementioned at least one organic acid, more preferably the aforementioned at least one organic alpha-hydroxy acid, is chosen from lactic acid and tartaric acid; and the aforementioned at least one metallic salt is chosen from ZnC12 and CaC12.

[0046] Herein, weights and molar ratios referring to organic acids, preferably organic alpha-hydroxy acids, and metallic salts take into account any hydration water present in the starting products.

[0047] Preferably, in the ternary DES the molar ratio of the at least one organic acid, more preferably the at least one organic alpha-hydroxy acid, to the at least one metallic salt is from 1:20 to 5:1, more preferably from 1:15 to 5:1, even more preferably from 1:10 to 3:1, most preferably from 1:6 to 2:1. Preferably, the ternary DES comprises the at least one organic acid, more preferably the at least one organic alpha-hydroxy acid, in an amount, as a weight percentage of the weight of the ternary DES, from 1 to 90%, more preferably from 3.5 to 85%, even more preferably from 5 to 80%, most preferably from 10 to 65%.

[0048] Preferably, in the ternary DES the molar ratio of the at least one metallic salt to water is from 1:30 to 2:1, more preferably from 1:20 to 1:1, even more preferably from 1:15 to 1:1, most preferably from 1:14 to 1:1.

[0049] Preferably, the sum by weight of the at least one organic acid, more preferably of the at least one organic alpha-hydroxy acid, the at least one metallic salt and water accounts for at least 90%, more preferably at least 95%, even more preferably at least 99%, even more preferably at least 99.9% of the ternary DES, most preferably 100%, by weight percentage of the weight of the ternary DES .

[0050] Preferably, the ternary DES consists essentially of said at least one organic acid, more preferably at least one organic alpha-hydroxy acid, at least one metallic salt and water.

[0051] Preferably, the ternary DES consists of said at least one organic acid, more preferably at least one organic alpha-hydroxy acid, at least one metallic salt and water.

[0052] Preferably, step a) of putting the material containing cellulose fibres in contact with at least one ternary DES is performed with only one ternary DES.

[0053] Preferably, the content of cellulose fibres as a weight percentage of the weight of the material containing cellulose fibres is from 20 to 100%, more preferably from 40 to 99.9%, even more preferably from 70 to 99.5%.

[0054] Preferably, the material containing cellulose fibres comprises natural textile fibre and / or artificial textile fibre .

[0055] Natural textile fibre means textile fibre of animal, plant or mineral origin that has not undergone chemical treatments which alter its chemical structure.

[0056] Preferably, the natural textile fibre is natural textile fibre of plant origin, more preferably chosen from natural textile fibre of cotton, linen, hemp, ramie, jute, bamboo and mixtures thereof, even more preferably cotton .

[0057] Artificial textile fibre means a natural textile fibre that has undergone chemical treatment which alters its chemical structure.

[0058] Preferably, the artificial textile fibre is chosen from fibre of viscose, lyocell, rayon, modal, cupro and mixtures thereof, more preferably chosen from fibre of viscose, lyocell, rayon and mixtures thereof.

[0059] In some embodiments, the material containing cellulose fibres may comprise synthetic fibre.

[0060] Synthetic textile fibre means textile fibre obtained from petroleum.

[0061] Preferably, the synthetic textile fibre is chosen from fibre of polyester, elastane, nylon, polypropylene and mixtures thereof, most preferably polyester.

[0062] Preferably, polyester is polyethylene terephthalate (PET) .

[0063] Preferably, the aforementioned natural textile fibre and the aforementioned artificial textile fibre comprise at least 60%, by weight of the weight of the fibre, of cellulose, more preferably from 65 to 99.9%, even more preferably from 75 to 99%.

[0064] The determination of cellulose content can be performed according to methods known to the person skilled in the art, such as ASTM-D1103, Method of Test for Alpha-Cellulose in Wood.

[0065] Preferably, the natural textile fibre and the arti ficial texti le fibre comprise a lignin content , as weight percentage of the weight of the textile fibre , lower than 35% , more preferably lower than 15% .

[0066] The determination of lignin content can be performed according to methods known to the person skilled in the art , such as Acid-insoluble lignin in wood and pulp , Test Method T 222 om- 02 .

[0067] Preferably, the material containing cellulose fibres comprises natural textile fibre of plant origin, more preferably natural textile fibre of cotton .

[0068] Preferably, the material containing cellulose fibres consists of natural textile fibre and / or arti ficial textile fibre , more preferably natural textile fibre of plant origin and / or arti ficial textile fibre , even more preferably natural textile fibre of plant origin, even more preferably natural textile fibre of cotton .

[0069] In a preferred embodiment , the material containing cellulose fibres consists of or essentially consists of pure cotton, such as medical grade cotton .

[0070] Preferably, the material containing cellulose fibres is a fabric, most preferably chosen from cotton, linen, lyocell , viscose , cupro , muslin, flannel , poplin, j ersey, denim, most preferably cotton and / or denim .

[0071] Denim is a cotton canvas fabric, usually diagonally woven with coloured threads , usually blue , and white filling threads ; it can also be woven with coloured stripes . Denim is usually yarn-dyed and factory- finished, and is usually 100% cotton, although mixtures of cotton and synthetic fibres exist .

[0072] In a preferred embodiment , the material containing cellulose fibres is a fabric chosen from raw cotton, combed cotton, and denim .

[0073] Preferably, the material comprising cellulose fibres is a waste product of the textile industry .

[0074] In the method according to the invention, the material comprising cellulose is preferably put in contact with the ternary DES in a weight ratio from 0.1:100 to 60:100, more preferably from 0.3:100 to 30:100, even more preferably from 0.5:100 to 20:100.

[0075] Preferably, the step of putting the material containing cellulose fibres in contact with at least one ternary DES is performed at a temperature from 20 to 200 °C for a time from 5 to 300 minutes, more preferably from 35 to 150 °C for a time from 15 to 140 minutes, even more preferably from 30 to 130 °C for a time from 30 to 100 minutes .

[0076] Preferably, the step of putting the material containing cellulose fibres in contact with at least one ternary DES is performed by immersing it in the ternary DES .

[0077] Preferably, in step a) of putting the material containing cellulose fibres in contact with at least one ternary DES, the temperature is reached according to heating methods known in the field, such as direct heating or by means of electromagnetic radiation (for example microwaves) .

[0078] Preferably, in the ternary DES the aforementioned at least one organic acid, more preferably the aforementioned at least one organic alpha-hydroxy acid is an HBD (hydrogen bond donor) while the aforementioned at least one metallic salt is an HBA (hydrogen bond acceptor) .

[0079] Preferably, the ternary DES is free of choline chloride .

[0080] Indeed, it was surprisingly found that the method according to the invention makes it possible to avoid the use of choline chloride, whose preparation can give rise to environmental problems, and which has the disadvantage of imparting excessive hygroscopicity and viscosity to DESs containing it. Moreover, choline chloride is relatively expensive.

[0081] Indeed, DESs according to the present invention have been found to have excellent cellulose solubilisation characteristics , making it possible to obtain excellent cellulose yields without the need for extreme treatments and the use of harmful / toxic substances . It was also found that , using ternary DESs according to the present invention, satis factory results can be achieved while using smaller quantities of the most expensive components , such as organic salts or acids (preferably hydroxy acids ) , compared to DESs comprising choline chloride , since part of the DES is replaced by water . The ternary DESs according to the present invention also have excellent chemical-physical characteristics , for example lower viscosity, which also make them easier to handle in the plant .

[0082] In particular, it has been observed that , unlike DESs which include choline chloride and various ionic liquids , the combination of organic acids , in particular organic alpha-hydroxy acids , and metallic salts described in the present invention makes it possible to limit the absorption of water by DESs , thus resulting in greater chemical stability of the composition .

[0083] Finally, also for some of the reasons set forth above , DESs of the present invention are cheaper than choline chloride-based DESs .

[0084] According to the present invention, the aforementioned method for the recovery of cellulose can be a method for the regeneration of cellulose or a method for the preparation of nanocellulose , as described below .

[0085] The present invention therefore also relates to a method for the regeneration of cellulose from a material containing cellulose fibres comprising the steps of : a ) putting the material containing cellulose fibres in contact with at least one ternary deep eutectic solvent (DES ) comprising :

[0086] - at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof ; at least one metallic salt ; and water ; thus obtaining cellulose in the form of solution in the ternary DES ; b ) addition of a non-solvent to the solution thus obtained, thus precipitating the dissolved cellulose ; and c ) optionally separation of cellulose .

[0087] Preferably, the aforementioned at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof is hydroxylated, more preferably it is an organic alpha-hydroxy acid .

[0088] Preferably, polycarboxylic acids are chosen from monocarboxylic acids , dicarboxylic acids , tricarboxylic acids and mixtures thereof .

[0089] Preferably, the aforementioned at least one organic acid is chosen from organic acids having a molecular weight below 250 g / mol .

[0090] Preferably, the aforementioned monocarboxylic acids are chosen from lactic acid, formic acid, pyruvic acid, glyoxylic acid, glycolic acid, gluconic acid, glyceric acid, and mandelic acid, more preferably chosen from lactic acid, formic acid and mixtures thereof , even more preferably lactic acid .

[0091] Preferably, the aforementioned dicarboxylic acids are chosen from tartaric acid, oxalic acid, fumaric acid, maleic acid, malonic acid, malic acid, phthalic acid, glutaric acid, itaconic acid, citraconic acid, mesaconic acid, oxalacetic acid and mixtures thereof , more preferably tartaric acid, oxalic acid and mixtures thereof , even more preferably tartaric acid .

[0092] Preferably, the aforementioned tricarboxylic acids are chosen from citric acid, isocitric acid, tricarbalicylic acid, aconitic acid, more preferably citric acid . Preferably the aforementioned at least one organic alpha-hydroxy acid is chosen from lactic acid, tartaric acid, citric acid, glycolic acid, gluconic acid, glyceric acid, malic acid, isocitric acid, mandelic acid, and mixtures thereof , more preferably chosen from lactic acid, tartaric acid, citric acid, and mixtures thereof , even more preferably chosen from lactic acid, tartaric acid, and mixtures thereof , most preferably lactic acid .

[0093] Preferably, the aforementioned at least one metallic salt is a metall ic salt in which the metal is divalent , more preferably a divalent metal chosen from zinc, calcium, magnesium, iron and aluminium, even more preferably chosen from zinc, calcium and magnesium, even more preferably zinc .

[0094] Preferably, the metallic salt is a metallic salt of a single metal .

[0095] Preferably, the aforementioned at least one metallic salt is chosen from ZnC12 , CaC12 , MgC12 , CaS04, A1C13, FeCl3, FeCl2and mixtures thereof , more preferably chosen from ZnC12 , CaC12 , MgC12 and mixtures thereof , even more preferably chosen from ZnC12 , CaC12 and mixtures thereof , most preferably ZnC12 .

[0096] Preferably, the aforementioned at least one organic acid, more preferably the above at least one organic alpha-hydroxy acid, is chosen from lactic acid, tartaric acid and mixtures thereof ; and the aforesaid at least one metallic salt is chosen from ZnC12 , CaC12 and mixtures thereof .

[0097] Water is preferably deionised water .

[0098] Preferably, the at least one ternary DES comprises only one organic acid, more preferably only one organic alpha-hydroxy acid, only one metallic salt and water .

[0099] Preferably, the aforementioned at least one organic acid, more preferably the aforementioned at least one organic alpha-hydroxy acid, is chosen from lactic acid and tartaric acid; and the aforementioned at least one metallic salt is chosen from ZnC12 and CaC12.

[0100] Preferably, the aforementioned at least one organic acid, more preferably the aforementioned at least one organic alpha-hydroxy acid, is lactic acid; and the at least one aforementioned metallic salt is ZnC12.

[0101] Preferably, in the ternary DES the molar ratio of the at least one organic acid, more preferably the at least one organic alpha-hydroxy acid, to the at least one metallic salt is from 1:20 to 5:1, more preferably from 1:10 to 5:1, even more preferably from 1:4 to 3:1, most preferably from 1:3 to 1:1.

[0102] In a preferred embodiment, in the ternary DES the molar ratio of the at least one organic acid, preferably the at least one organic alpha-hydroxy acid, to the at least one metallic salt is 1:2.

[0103] Preferably, the ternary DES comprises the at least one organic acid, more preferably the at least one organic alpha-hydroxy acid, in an amount, as weight percentage of the weight of the ternary DES, from 5 to 70%, more preferably from 7 to 60%, even more preferably from 8 to 55%, most preferably from 10 to 50%.

[0104] Preferably, in the ternary DES the molar ratio of the at least one metallic salt to water is from 1:20 to 2:1, more preferably from 1:15 to 1:1, even more preferably from 1:11 to 1:1, most preferably from 1:3 to 1:1.

[0105] In a preferred embodiment, in the ternary DES the molar ratio of at least one metallic salt to water is 1:2.

[0106] In a preferred embodiment, the aforementioned at least one organic acid, preferably the aforementioned at least one organic alpha-hydroxy acid, is lactic acid and the aforementioned at least one metallic salt is ZnC12.

[0107] In this embodiment, the molar ratio of lactic acid to zinc chloride is preferably 1:2.

[0108] In this embodiment, the molar ratio of zinc chloride to water is preferably 1:2.

[0109] In this embodiment, lactic acid, zinc chloride and water are preferably in a molar ratio of 1:2:4.

[0110] Preferably, the sum by weight of the at least one organic acid, more preferably of the at least one organic alpha-hydroxy acid, the at least one metallic salt and water accounts for at least 90%, more preferably at least 95%, even more preferably at least 99%, even more preferably at least 99.9% of DES, most preferably 100%, by weight percentage the weight of DES.

[0111] Preferably, DES consists essentially of said at least one organic acid, more preferably at least one organic alpha-hydroxy acid, at least one metallic salt and water.

[0112] Preferably, DES consists of said at least one organic acid, more preferably at least one organic alphahydroxy acid, at least one metallic salt and water.

[0113] Preferably, step a) of putting the material containing cellulose fibres in contact with at least one ternary DES is performed with only one ternary DES.

[0114] Preferably, the content of cellulose fibres as a weight percentage of the weight of the material containing cellulose fibres is from 20 to 100%, more preferably from 40 to 99.9%, even more preferably from 70 to 99.5%.

[0115] Preferably, the material containing cellulose fibres comprises natural textile fibre and / or artificial textile fibre .

[0116] Preferably, the natural textile fibre is natural textile fibre of plant origin, more preferably chosen from natural textile fibre of cotton, linen, hemp, ramie, jute, bamboo and mixtures thereof, even more preferably cotton .

[0117] Preferably, the artificial textile fibre is chosen from fibre of viscose, lyocell, rayon, modal, cupro and mixtures thereof, more preferably chosen from fibre of viscose, lyocell, rayon and mixtures thereof.

[0118] In some embodiments, the material containing cellulose fibres may comprise synthetic fibre.

[0119] Preferably, the synthetic textile fibre is chosen from polyester, elastane, nylon, polypropylene and mixtures thereof, most preferably polyester.

[0120] Preferably, polyester is polyethylene terephthalate (PET) .

[0121] Preferably, the aforementioned natural textile fibre and the aforementioned artificial textile fibre comprise at least 60%, by weight of the fibre, of cellulose, more preferably from 65 to 99%, even more preferably from 75 to 95%. The determination of cellulose content can be performed as described above.

[0122] Preferably, the natural textile fibre and the artificial textile fibre comprise a lignin content, as weight percentage of the weight of the textile fibre, lower than 35%, more preferably lower than 15%. The determination of lignin content can be performed as described above.

[0123] Preferably, the material containing cellulose fibres comprises natural textile fibre of plant origin, more preferably natural textile fibre of cotton.

[0124] Preferably, the material containing cellulose fibres consists of natural textile fibre and / or artificial textile fibre, more preferably natural textile fibre of plant origin and / or artificial textile fibre, even more preferably natural textile fibre of plant origin, even more preferably natural textile fibre of cotton.

[0125] In a preferred embodiment, the material containing cellulose fibres consists of or essentially consists of pure cotton, such as medical grade cotton.

[0126] Preferably, the material containing cellulose fibres is a fabric, most preferably chosen from cotton, linen, lyocell, viscose, cupro, muslin, flannel, poplin, jersey, denim, more preferably cotton and / or denim. In a preferred embodiment, the material containing cellulose fibres is a fabric chosen from raw cotton, combed cotton, and denim.

[0127] Preferably, the material comprising cellulose fibres is a waste product of the textile industry.

[0128] In the method according to the invention, the material comprising cellulose is preferably put in contact with the ternary DES in a weight ratio from 0.3:100 to 60:100, more preferably from 1:100 to 30:100, even more preferably from 4:100 to 20:100, most preferably from 5:100 to 15:100.

[0129] Preferably, the step of putting the material containing cellulose fibres in contact with at least one ternary deep eutectic solvent (DES) is performed at a temperature from 20 to 150 °C for a time from 5 to 150 minutes, more preferably from 35 to 80 °C for a time from 15 to 60 minutes, even more preferably from 50 to 70 °C for a time from 40 to 60 minutes.

[0130] Preferably, step a) of putting the material containing cellulose fibres in contact with at least one ternary DES is performed by immersing the material containing cellulose fibres in the ternary DES.

[0131] Preferably, in step a) of putting the material containing cellulose fibres in contact with at least one ternary DES, the temperature is reached according to heating methods known in the field, such as direct heating or by means of electromagnetic radiation (for example microwaves) .

[0132] Preferably, step a) is performed by stirring, more preferably by means of a magnetic stirrer.

[0133] The obtained solution is usually transparent. By means of FTIR analysis (as described for example in Example 3) , it is possible to check the preservation of the characteristic peaks of cellulose.

[0134] Preferably, in step b) of adding a non-solvent, the non-solvent is chosen from water and an alcohol, more preferably ethanol.

[0135] Preferably, water is deionised water.

[0136] Preferably, the alcohol is a monofunctional aliphatic primary alcohol (in other words, having only one -OH group) C1-C4, most preferably chosen from ethanol, propanol and mixtures thereof, more preferably chosen from ethanol, 2-propanol (isopropanol) and mixtures thereof, most preferably ethanol.

[0137] The definition of monofunctional aliphatic primary alcohol 03 or C4, in other words, propanol and butanol, comprises all isomers.

[0138] Preferably, in the cellulose separation step c) , separation is performed by centrifugation and subsequent washing with a non-solvent, more preferably with one to three repetitions of centrifugation and subsequent washing .

[0139] Preferably, the non-solvent is defined as above.

[0140] Preferably, the non-solvent is water.

[0141] Preferably, centrifugation is performed from 1000 to 50000 rpm for a time from 2 to 20 minutes, even more preferably from 7000 to 20000 rpm for a time from 3 to 15 minutes, even more preferably from 8000 to 12000 rpm for a time from 4 to 6 minutes.

[0142] Preferably, step c) of separating the dissolved cellulose is followed by a step of drying cellulose, more preferably performed by drying in an oven, even more preferably in a vacuum oven.

[0143] Preferably, drying is performed in a vacuum oven at a temperature from 60 to 140 °C for a time from 20 minutes to 48 hours, more preferably from 70 to 130 °C for a time from 40 minutes to 24 hours, even more preferably from 80 to 125 °C for a time from 60 minutes to 28 hours.

[0144] In fact, it was surprisingly found that the use of the ternary DES according to the invention for the regeneration of cellulose results in cellulose yields higher than 35% by weight , with a solubility higher than 10% of cotton weight on DES weight .

[0145] When the starting material is denim post-consumer waste , it has been observed that cotton retains its blue colour, the dye having remained in an insoluble form . This is particularly advantageous , in the case of solvent recycling, because it indicates the absence of solvent contamination .

[0146] It was also observed that any synthetic fibres (polyester ) do not undergo any dissolution . The method of the present invention is therefore selective in relation to cellulose and thus makes it possible to use waste containing synthetic fibres .

[0147] The present invention also relates to a method for the preparation of nanocellulose from a material containing cellulose fibres comprising the steps of : a ) putting the material containing cellulose fibres in contact with at least one ternary deep eutectic solvent (DES ) comprising :

[0148] - at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof ;

[0149] - at least one metallic salt ; and

[0150] - water ; thus obtaining cellulose in the form of dispersion in the ternary DES ; b ) addition of a non-solvent to the dispersion thus obtained; c ) homogenisation of cellulose , thus obtaining a nanocellulose suspension; d) optionally separation of the nanocellulose from the nanocellulose suspension .

[0151] Preferably, the aforementioned at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof is hydroxylated, more preferably it is an organic alpha-hydroxy acid . Preferably, polycarboxylic acids are chosen from monocarboxylic acids , dicarboxylic acids , tricarboxylic acids and mixtures thereof

[0152] Preferably, the aforementioned at least one organic acid is chosen from organic acids having a molecular weight below 250 g / mol .

[0153] Preferably, the aforementioned monocarboxylic acids are chosen from lactic acid, formic acid, pyruvic acid, glyoxylic acid, glycolic acid, gluconic acid, glyceric acid, and mandelic acid, more preferably chosen from lactic acid, formic acid and mixtures thereof , even more preferably lactic acid .

[0154] Preferably, the aforementioned dicarboxylic acids are chosen from tartaric acid, oxalic acid, fumaric acid, maleic acid, malonic acid, malic acid, phthalic acid, glutaric acid, itaconic acid, citraconic acid, mesaconic acid, oxalacetic acid and mixtures thereof , more preferably tartaric acid, oxalic acid and mixtures thereof , even more preferably tartaric acid .

[0155] Preferably, the aforementioned tricarboxylic acids are chosen from citric acid, isocitric acid, tricarbalicylic acid, aconitic acid, more preferably citric acid .

[0156] Preferably the aforementioned at least one organic alpha-hydroxy acid is chosen from lactic acid, tartaric acid, citric acid, glycolic acid, gluconic acid, glyceric acid, malic acid, isocitric acid, mandelic acid, and mixtures thereof , more preferably chosen from lactic acid, tartaric acid, citric acid, and mixtures thereof , even more preferably chosen from lactic acid, tartaric acid, and mixtures thereof , most preferably chosen from lactic acid and tartaric acid .

[0157] Preferably, the aforementioned at least one metallic salt is a metallic salt in which the metal is divalent , more preferably a divalent metal chosen from zinc, calcium, magnesium, iron and aluminium, even more preferably chosen from zinc, calcium and magnesium, even more preferably chosen from zinc and calcium .

[0158] Preferably, the metallic salt is a metallic salt of a single metal .

[0159] Preferably, the aforementioned at least one metallic salt is chosen from ZnC12 , CaC12 , MgC12 , CaS04, A1C13, FeCl3, FeCl2and mixtures thereof , more preferably chosen from ZnC12 , CaC12, MgC12 and mixtures thereof , even more preferably chosen from ZnC12 , CaC12 and mixtures thereof , most preferably chosen from among ZnC12 and CaC12 .

[0160] Preferably, the aforementioned at least one organic acid, more preferably the above at least one organic alpha-hydroxy acid, is chosen from lactic acid, tartaric acid and mixtures thereof ; and the aforesaid at least one metallic salt is chosen from ZnC12 , CaC12 and mixtures thereof .

[0161] Water is preferably deionised water .

[0162] Preferably, the at least one ternary DES comprises only one organic acid, more preferably only one organic alpha-hydroxy acid, only one metallic salt and water .

[0163] Preferably, the aforementioned at least one organic acid, more preferably the aforementioned at least one organic alpha-hydroxy acid, is chosen from lactic acid and tartaric acid; and the aforementioned metallic salt is chosen from ZnC12 and CaC12 .

[0164] Preferably, the aforementioned at least one organic acid, more preferably the aforementioned at least one organic alpha-hydroxy acid, is lactic acid and the aforementioned at least one metallic salt is CaC12 ,' the aforementioned at least one organic acid, more preferably the aforementioned at least one alpha organic hydroxy acid, is tartaric acid and the aforementioned at least one metallic salt is CaC12 ,' or the aforementioned at least one organic acid, more preferably the aforementioned at least one alpha organic hydroxy acid, is tartaric acid and the aforementioned at least one metallic salt is ZnC12.

[0165] Preferably, in the ternary DES the molar ratio of the at least one organic acid, more preferably the at least one organic alpha-hydroxy acid, to the at least one metallic salt is from 1:20 to 4:1, more preferably from 1:15 to 3:1, even more preferably from 1:10 to 2.5:1, most preferably from 1:5 to 1:1 or about 2:1.

[0166] In a preferred embodiment, in the ternary DES the molar ratio of the at least one organic acid, more preferably the at least one organic alpha-hydroxy acid, to the at least one metallic salt is 1:1.

[0167] In an alternative preferred embodiment, in the ternary DES the molar ratio of the at least one organic acid, preferably the at least one organic alpha-hydroxy acid, to the at least one metallic salt is 1:5.

[0168] In an alternative preferred embodiment, in the ternary DES the molar ratio of the at least one organic acid, preferably the at least one organic alpha-hydroxy acid, to the at least one metallic salt is 2:1.

[0169] Preferably, the ternary DES comprises the at least one organic acid, more preferably the at least one organic alpha-hydroxy acid, in an amount, as a weight percentage of the weight of the ternary DES, from 1 to 90%, more preferably from 5 to 85%, even more preferably from 10 to 80%, most preferably from 10 to 60%.

[0170] Preferably, in the ternary DES the molar ratio between the at least one metallic salt and water is from 1:30 to 2:1, more preferably from 1:20 to 1:1, even more preferably from 1:15 to 1:1, most preferably from 1:14 to 1:5.

[0171] In a preferred embodiment, in the ternary DES the molar ratio of at least one metallic salt to water is 1:6.

[0172] In an alternative preferred embodiment, in the ternary DES the molar ratio of at least one metallic salt to water is 1:12. In a preferred embodiment, the aforementioned at least one organic acid, preferably the aforementioned at least one organic alpha-hydroxy acid, is lactic acid and the aforementioned at least one metallic salt is CaC12.

[0173] In this preferred embodiment, the molar ratio of lactic acid to calcium chloride is preferably from 1:10 to 3:1, more preferably from 1:7 to 2:1, even more preferably from 1:3 to 1.5:1, most preferably 1:1.

[0174] In this preferred embodiment, the molar ratio of calcium chloride to water is preferably from 1:30 to 2:1, more preferably from 1:20 to 1:1, even more preferably from 1:12 to 1:1, most preferably 1:6.

[0175] In this preferred embodiment, lactic acid, calcium chloride and water are preferably in a molar ratio of 1:1:6.

[0176] Preferably, in this embodiment, the ternary DES comprises the at least one organic acid, more preferably the at least one organic alpha-hydroxy acid, in an amount, as a weight percentage of the weight of the ternary DES, from 4 to 55%, more preferably from 5 to 45%, even more preferably from 10 to 40%, most preferably 30% .

[0177] In an alternative preferred embodiment, the aforementioned at least one organic acid, preferably the at least one organic alpha-hydroxy acid, is tartaric acid and the aforementioned at least one metallic salt is CaCl2.

[0178] In this preferred embodiment, the molar ratio of tartaric acid to calcium chloride is preferably from 1:15 to 4:1, more preferably from 1:10 to 3:1, even more preferably from 1:3 to 2.5:1, even more preferably 1:1 or 2:1.

[0179] In this preferred embodiment, the molar ratio of calcium chloride to water is preferably from 1:30 to 2:1, more preferably from 1:20 to 1:1, even more preferably from 1:15 to 1:1, most preferably 1:12 or 1:6. In this preferred embodiment, tartaric acid, calcium chloride and water are preferably in a molar ratio of 1:1:6 or 1:0.5:6.

[0180] Preferably, in this embodiment, the ternary DES comprises the at least one organic acid, more preferably the at least one organic alpha-hydroxy acid, in an amount, as a weight percentage of the weight of the ternary DES, from 10 to 90%, more preferably from 15 to 85%, even more preferably from 30 to 80%, most preferably from 40 to 58%.

[0181] In an alternative preferred embodiment, the aforementioned at least one organic acid, preferably the aforementioned at least one organic alpha-hydroxy acid, is tartaric acid and the aforementioned at least one metallic salt is ZnC12.

[0182] In this preferred embodiment, the molar ratio of tartaric acid to zinc chloride is preferably from 1:20 to 1:1, more preferably from 1:15 to 1:3, even more preferably from 1:10 to 1:3, most preferably 1:5.

[0183] In this preferred embodiment, the molar ratio of zinc chloride to water is preferably from 1:30 to 2:1, more preferably from 1:20 to 1:1, even more preferably from 1:12 to 1:1, most preferably 1:6.

[0184] In this preferred embodiment, tartaric acid, zinc chloride and water are preferably in a molar ratio of 0.2:1:6.

[0185] Preferably, in this embodiment, the ternary DES comprises the at least one organic acid, more preferably the at least one organic alpha-hydroxy acid, in an amount, as a weight percentage of the weight of the ternary DES, from 2.5 to 35%, more preferably from 3.5 to 20%, even more preferably from 5 to 20%, most preferably 11% .

[0186] Preferably, the sum by weight of the at least one organic acid, more preferably of the at least one organic alpha-hydroxy acid, the at least one metallic salt and water accounts for at least 90%, more preferably at least 95%, even more preferably at least 99%, even more preferably at least 99.9% of DES, most preferably 100%, by weight percentage the weight of DES.

[0187] Preferably, DES consists essentially of said at least one organic acid, more preferably at least one organic alpha-hydroxy acid, at least one metallic salt and water.

[0188] Preferably, DES consists of said at least one organic acid, more preferably at least one organic alphahydroxy acid, at least one metallic salt and water.

[0189] Preferably, step a) of putting the material containing cellulose fibres in contact with at least one ternary DES is performed with only one ternary DES.

[0190] Preferably, the content of cellulose fibres as a weight percentage of the material containing cellulose fibres is from 60 to 100%, more preferably from 90 to 99.9%, even more preferably from 95 to 99.5%.

[0191] Preferably, the material containing cellulose fibres comprises natural textile fibre and / or artificial textile fibre .

[0192] Preferably, the natural textile fibre is natural textile fibre of plant origin, more preferably chosen from natural textile fibre of cotton, linen, hemp, ramie, jute, bamboo and mixtures thereof, even more preferably cotton .

[0193] Preferably, the artificial textile fibre is chosen from fibre of viscose, lyocell, modal rayon, cupro and mixtures thereof, more preferably chosen from fibre of viscose, lyocell, rayon and mixtures thereof.

[0194] Preferably, the aforementioned natural textile fibre and the aforementioned artificial textile fibre comprise at least 60%, by weight of the weight of the fibre, of cellulose, more preferably from 65 to 99.9%, even more preferably from 75 to 99%. The determination of cellulose content can be performed as described above. Preferably, the natural textile fibre and the artificial textile fibre comprise a lignin content, as weight percentage of the weight of the textile fibre, lower than 35%, more preferably lower than 15%. The determination of lignin content can be performed as described above.

[0195] Preferably, the material containing cellulose fibres comprises natural textile fibre of plant origin, more preferably natural textile fibre of cotton.

[0196] Preferably, the material containing cellulose fibres consists of natural textile fibre and / or artificial textile fibre, more preferably natural textile fibre of plant origin and / or artificial textile fibre, even more preferably natural textile fibre of plant origin, even more preferably natural textile fibre of cotton.

[0197] In a preferred embodiment, the material containing cellulose fibres consists of or essentially consists of pure cotton, such as medical grade cotton.

[0198] Preferably, the material containing cellulose fibres is a fabric, most preferably chosen from cotton, linen, lyocell, viscose, cupro, muslin, flannel, poplin, jersey, denim, most preferably cotton and / or denim.

[0199] In a preferred embodiment, the material containing cellulose fibres is a fabric chosen from raw cotton, combed cotton, and denim.

[0200] Preferably, the material comprising cellulose fibres is a waste product of the textile industry.

[0201] In the method according to the invention, the material comprising cellulose is preferably put in contact with the ternary DES in a weight ratio from 0.1:100 to 60:100, more preferably from 0.3:100 to 10:100, even more preferably from 0.5:100 to 5:100, most preferably from 2:100 to 4:100.

[0202] Preferably, step a) of putting the material containing cellulose fibres in contact with at least one ternary deep eutectic solvent (DES) is performed at a temperature from 20 to 200 ° C for a time from 20 to 300 minutes , more preferably from 80 to 150 ° C for a time from 40 to 120 minutes , even more preferably from 90 to 120 ° C for a time from 50 to 70 minutes .

[0203] Preferably, step a ) of putting the material containing cellulose fibres in contact with at least one ternary deep eutectic solvent ( DES ) is performed by immersing the material containing cellulose fibres in the ternary DES .

[0204] Preferably, in step a ) of putting the material containing cellulose fibres in contact with at least one ternary DES , the temperature is reached according to heating methods known in the field, such as direct heating or by means of electromagnetic radiation ( for example microwaves ) .

[0205] Preferably, step a ) is performed by stirring, more preferably with a magnetic stirrer .

[0206] The dispersion thus obtained is usually opaque or cloudy, a characteristic indicating that the hydrolysis of cellulose into nanocellulose has taken place .

[0207] Preferably, in step b ) of adding a non-solvent , the non-solvent is water .

[0208] Preferably, water is deionised water .

[0209] In a preferred embodiment , the homogenisation step c ) is performed by ultrasonication .

[0210] Preferably, ultrasonication is performed at a power of from 600 to 1100 W for a time from 1 minute to 60 minutes , more preferably at a power of from 800 to 1000 W for a time from 3 minutes to 20 minutes , even more preferably at a power of from 850 to 900 W for a time from 4 minutes to 6 minutes .

[0211] In an alternative preferred embodiment , the homogenisation step c ) is performed using an immersion homogeniser, preferably at from 1000 to 50000 rpm for a time from 2 to 20 minutes , even more preferably at from 2000 to 30000 rpm for a time from 3 to 15 minutes , even more preferably at from 3000 to 24000 rpm for a time from

[0212] 5 to 10 minutes .

[0213] A suitable homogeniser is for example the T25 digital ultra-turrax® homogeniser produced by IKA ( Stgaufen, Germany)

[0214] Preferably, in nanocellulose separation step d) , separation is performed by centri fugation and subsequent washing with non-solvent , more preferably with one to ten- fold repetition of centri fugation and subsequent washing, even more preferably with three-fold repetition of centri fugation and subsequent washing .

[0215] Preferably, the non-solvent is defined as above .

[0216] Preferably, the non-solvent chosen is the same as in step b ) .

[0217] Preferably, centri fugation is performed at from 1000 to 50000 rpm for a time from 2 to 20 minutes , even more preferably at from 7000 to 20000 rpm for a time from 3 to 15 minutes , even more preferably at from 8000 to 12000 rpm for a time from 4 to 6 minutes .

[0218] It is possible , for example for analysis purposes , to perform, after the nanocellulose separation step d) , a step of drying the nanocellulose , preferably performed by drying in an oven, more preferably in a vacuum oven .

[0219] Preferably, drying is performed in a vacuum oven at a temperature from 60 to 140 ° C for a time from 20 minutes to 48 hours , more preferably from 70 to 130 ° C for a time from 40 minutes to 24 hours , even more preferably from 80 to 125 ° C for a time from 60 minutes to 12 hours .

[0220] Preferably, the nanocrystals obtained have a length from 1 nm to 1pm, more preferably from 5 nm to 500 nm, even more preferably from 20 nm to 200 nm .

[0221] It was indeed found that the use of ternary DESs according to the present invention in the preparation of NC results in a yield of NC from medical grade cotton of between 70 and 85% by weight ( see Example 5 ) . The yield from denim was instead of between 70% and 75% by weight . The crystallinity index of the NC obtained is very high, above 85% for both cotton and denim .

[0222] NCs are materials of great potential due to their mechanical properties and relatively high speci fic surface area . In addition, NCs are biodegradable . Applications of NCs include medical applications , for example as drug carriers or in composites , as hydrogels , in textile engineering, for bioreactors or scaf folding .

[0223] The present invention also relates to a method for the preparation of a ternary DES as described in the above-described methods comprising the step of mixing at least one organic acid, preferably at least one organic alpha-hydroxy acid, at least one metallic salt and water at a temperature from 50 to 100 ° C for a time from 10 minutes to 4 hours , more preferably at a temperature from 60 to 90 ° C for a time from 30 minutes to 2 hours , even more preferably at a temperature from 75 to 85 ° C for a time from 40 minutes to 90 minutes .

[0224] Preferably, mixing is performed by stirring, more preferably by means of a magnetic stirrer .

[0225] The present invention also relates to a ternary DES comprising :

[0226] - at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof ;

[0227] - at least one metallic salt ; and

[0228] - water .

[0229] The aforementioned at least one organic acid, preferably at least one organic alpha-hydroxy acid, and at least one metallic salt may be in the non-hydrated or hydrated form, for example in the monohydrated or dihydrated form .

[0230] Preferably, the DES has the characteristics described above .

[0231] Brief description of the Figures Figure 1 shows the dissolution steps of the sample DOI from Example 3. In particular, are shown in a) intact fibres visible at time 0; in b) partially dissolved fibres, at time 30 min at 60 °C; in b) dissolved fibres, at time 45 min at 60 °C; in d) and e) regenerated cellulose DOI obtained after the addition of the nonsolvent deionised water.

[0232] Figure 2 shows a comparison between original and regenerated cellulose for a) CF (cotton fibres) and b) DOI (denim) in Example 3.

[0233] Figure 3 shows a comparison of cellulose recovered from cotton fibres (CF) : a) with carboxymethylcellulose (CMC) and the solvent ZnLA for reference; and b) the differences in the recovery step with ethanol, isopropanol or water, to emphasise the differences in the carbonyl zone, in Example 3.

[0234] Figure 4 shows: a) a comparison of before and after 60 minutes of DES treatment at 80 °C for solvent ZnLA and b) for collected SF_D02 fibres, for Example 4.

[0235] Figure 5 shows the FTIR spectrum of separate D02 fibres, in the following order from above: vertical fibres of the fabric (CF_D02) identified as cotton; horizontal fibres of the fabric (SF_D02) identified as synthetic fibre (PET) and a sample of polyethylene terephthalate (PET) for comparison, according to Example 4.

[0236] Figure 6 shows the preparation of NC according to Example 5: a) comparison of DES / CF solution before and after addition of water and ultrasonication in CaTA_CF; b) final NC suspension obtained by CaLA_CF and ZnTA_CF.

[0237] Figure 7 shows the thermograms for a) NC prepared from CF with DES CaTA in an air atmosphere (25.0 ml / min) and b) NC obtained from D01 with DES CaTA or CaLA in a nitrogen atmosphere (10.0 ml / min) according to Example 5.

[0238] Figure 8 shows X-ray dif f ractograms of nanocellulose obtained from a) white cotton fibres and b) blue denim. Figure 9 shows the X-ray dif f ractograms for microcrystalline cellulose (Sigma Aldrich) according to Example 5.

[0239] Figure 10 shows the spectra of the NC samples obtained with the corresponding source materials according to Example 5.

[0240] Figure 11 shows the TEM analysis for a) CaTA_CF, b) CaTAJDOl, c) CaLAjCF, d) CaLAJDOl, e) ZnTAjCF and f) ZnTA_D01 (Example 5) .

[0241] Figure 12: Rheological behaviour over time of CCTA and ZnLA at 25°C, with exposure to air, according to Example 6.

[0242] Figure 13: Rheological behaviour over time of CCTA and ZnLA, in logarithmic scale at 25°C, according to Example 6.

[0243] Detailed description of the invention

[0244] The invention will now be further described with reference to embodiments provided for illustrative and non-limiting purposes.

[0245] EXAMPLE 1

[0246] Preparation of ternary ZnLA DESs

[0247] Different DESs based on lactic acid, zinc chloride and water, with composition as shown in Table 1 were prepared for cellulose regeneration tests (Examples 3 and 4) and viscosity measurement (Example 6) .

[0248] The DESs were prepared by mixing the components at 80°C for 60 minutes in an oil bath under stirring with a magnetic stirrer.

[0249] Table 1 - Composition of ternary DESs and MCC solubility .

[0250] 1. Molar ratios are given net of lactic acid and zinc chloride hydration .

[0251] 2. Lactic acid (liquid) : lactic acid in 85% solution by weight in water;

[0252] 3. Zinc chloride: anhydrous;

[0253] 4. Water: deionised water;

[0254] 5. MCC = microcrystalline cellulose: indicated in terms of maximum solubility achieved expressed as weight percentage of MCC to weight percentage of DES.

[0255] Solubility was then tested by adding 1% w / w microcrystalline cellulose (MCC) . In all cases, dissolution occurred after 24 hours at 80°C (the solution was clear) . The numbers in the column "Microcrystalline cellulose solubility" indicate the maximum solubility achieved indicated as a weight percentage of MCC to DES weight . EXAMPLE 2

[0256] Preparation of ternary CaTA, CaLA, ZnTA DESs

[0257] Different DESs based on lactic acid, tartaric acid, zinc chloride, calcium chloride and water were prepared for the cellulose regeneration tests (Example 5) , with composition as shown in Table 2.

[0258] DESs were prepared by mixing the components at 80°C for 60 minutes in an oil bath under stirring with a magnetic stirrer.

[0259] Table 2 - Composition of ternary DESs.

[0260] 1. Molar ratios are given net of hydration of acids and salts.

[0261] 2. Tartaric acid: solid, anhydrous;

[0262] 3. Calcium chloride: anhydrous;

[0263] 4. Water: deionised water; 5. Lactic acid (liquid) : lactic acid in 85% solution by weight in water;

[0264] 6. Zinc chloride: anhydrous.

[0265] EXAMPLE 3

[0266] Production Process in the regeneration of cellulose from cotton.

[0267] 20 ml of DES no. 2 of Table 1 of Example 1 were prepared using the method described in Example 1. The ZnLA DES was prepared by combining lactic acid, zinc chloride and deionised water in a 1:2:4 molar ratio. The cellulose was regenerated by immersing cotton (CF) or denim (DOI) fibres (Figure la) in the ZnLA DES, maintaining a cotton / DES weight ratio of 1:10. The tested denim (the label stated 99% cotton and 1% elastane) was made of 99% cotton fibres, while the 1% synthetic fibres were removed. Cotton (CF) was medical cotton and contained no other cellulose source or fibre.

[0268] It was heated at 60°C for 45 minutes under continuous stirring with a magnetic stirrer using a silicone oil bath, thus obtaining a solution (Figure 1c for sample DOI. This treatment eased the dissolution of the cellulose chains, highlighted by the (blue) staining of the solvent in the case of samples prepared with denim (DOI) (Figure lb, 1c) .

[0269] At the end of the heat treatment, the samples were diluted with 10 ml of deionised water, ethanol or isopropanol to promote the dissolution of DES into its original components and interrupt the activity thereof. This step makes it possible to avoid excessive hydrolysis of the sample, which could occur with excessive reaction times or at high temperatures. A floc dispersed in a solvent was thus obtained, white or blue in colour depending on the type of fibre used (Figure Id and Figure le) .

[0270] Cellulose separation was performed by centrifugation at 10,000 rpm for 5 minutes. The liquid phase was removed, and the samples were washed with 10 ml deionised water, ethanol or isopropanol, depending on the nonsolvent used. The centrifugation and washing process was repeated for three cycles. Finally, the regenerated cellulose was dried at 80 °C under vacuum, thus obtaining a dry solid within 24 hours.

[0271] Different analytical techniques were used to characterise the cellulose obtained, renamed ZnLA_CF and ZnLA_D01 depending on whether it was prepared from medical cotton or denim, respectively.

[0272] Fourier transform infrared spectroscopy (FTIR) was used to examine the chemical composition of the cellulose obtained, obtaining information on the functional groups present and any impurities in the material by comparing cellulose samples. By comparing the functional groups of the cotton fibres and the resulting cellulose, it was possible to detect any changes following the DES treatment process.

[0273] Measurements were performed on liquid and solid samples using a Nicolet FT-IR Nexus instrument (Nexus Analytics) in ATR (Attenuated Total Reflectance) mode using a multipass cell equipped with a diamond crystal, while Omnic IR and Origin 2021 software were used to process the data. Spectra were recorded from 400 cm-1 to 4000 cm-1 in absorbance with a resolution of 4 cm-1 and one scan 32 or 64 per spectrum.

[0274] The FTIR spectra of regenerated cellulose rCELL_CF and rCELL_D01 (Figure 2) were compared with those of medical cotton and denim (OF and D01) , respectively, to assess any changes in functional groups. The absorption peaks observed at 3300, 2900, 1425, 1375, 1160, 1115, 1060 and 897 cm-1correspond to the typical characteristics of cellulose, confirming the cellulosic structure of cotton. In the spectrum of regenerated cellulose, a peak appears at about 1730 cm-1, signalling the presence of post-treatment carbonyl groups (C=O) , often present for this type of process with DES. These signals may result from residual carboxyl groups from the solvent, partial esterification or carboxylation of the hydroxyl functions of cellulose.

[0275] Table 4 and Figure 3 show the FTIR spectra and assignments for regenerated cellulose coagulated in different solvents (water, ethanol, isopropanol) , compared with the solvent and a highly carboxyl- functionalised compound: carboxymethyl cellulose (CMC) . Figure 3b highlights that coagulation in water involves a different functionalisation of cellulose compared to ethanol or isopropanol, with the emergence of active bonds at 1584 cm-1, associated with the stretching vibrations of the carboxylate anion (-COO-) , as shown in Table 4. Conversely, cellulose coagulated in ethanol does not exhibit this behaviour, highlighting instead a more pronounced peak at 1728 cm-1, indicative of a carbonyl stretching .

[0276] Table 4 - Band assignments referred to Figure 3a.

[0277] EXAMPLE 4

[0278] Selectivity test

[0279] 20 ml of DES no. 2 of Table 1 of Example 1 were prepared using the method described in Example 1. The ZnLA DES was prepared by combining lactic acid, zinc chloride and deionised water in a 1:2:4 molar ratio. The cellulose was regenerated using this solvent in a process as described in Example 3.

[0280] A sample of mixed denim fabric of known composition, named D02, was used to carry out the selectivity test. Sample D02 showed in the label a composition mainly consisting of natural fibres (61% cotton) and synthetic fibres (36% polyester, 3% elastane) . The D02 fabric was subjected to a manual separation process to isolate the two main fibrous components. Horizontally woven fibres were identified as polyethylene terephthalate (SF_D02) , while vertically woven fibres were identified as cotton (CF_D02) by FTIR analysis (Figure 5) . The FTIR analysis was carried out as described in Example 3.

[0281] The synthetic fibres SF_D02 were manually separated from the cellulosic part and submitted to a treatment with ZnLA, following the protocol of Example 3 with the difference that the heat treatment was carried out for 60 minutes at a temperature of 80°C, with the aim of assessing the selective ability of the ZnLA solvent in dissolving or chemically modifying the synthetic fibres.

[0282] At the end of the treatment, both the solvent and recovered SF_D02 (that will be named rSF_D02) were analysed by FTIR spectroscopy (Figure 4a, 4b, respectively) . The IR spectra of the solvent before and after the treatment, shown in Figure 4a, do not highlight the presence of any new signals, indicating that no new functional groups, hence no new dissolved substances, were detected. The IR spectra of the treated fibres (rSF_D02) compared with untreated synthetic fibres (Figure 4) again confirmed the absence of significant chemical changes in the material after treatment. If SF_D02 had reacted with ZnLA, new signals would have been detected in the FTIR spectrum. The absence of these signals confirms that no dissolved substances are present in the post-treatment solvent, specifically no SF_D02.

[0283] EXAMPLE 5

[0284] Production Process in the preparation of nanocellulose .

[0285] For this experiment, 20 ml of the four DESs Nos 1-4 shown in Table 2 in Example 2 were prepared.

[0286] Cotton (CF) or denim (DOI) fibres (composition as in Example 3) were immersed in the corresponding solvent (in other words CF and DOI were both treated with each of the four DESs) , maintaining a cotton:DES weight ratio of 3 : 100.

[0287] It was then heated at 100°C for 60 minutes, under continuous stirring on a magnetic stirrer, using a silicone oil bath. This treatment eased the hydrolysis of the amorphous regions of cellulose (Figure 6a) , resulting in a fragmentation visible to the naked eye of the fibres into particles between 0.5 and 1 mm in size.

[0288] Once the heat treatment was complete, the samples were allowed to cool at room temperature and were diluted with 10 ml of deionised water to allow the DES to dissolve into its original components. At this point, the samples were subjected to ultrasonication at 95% of maximum intensity with a power of 880 W for 5 minutes to stimulate further dispersion of nanocellulose (NC) . The result was an aqueous suspension containing solid nanocellulose, white or blue in colour depending on the type of fibre used (Figure 7b) . The preparation of nanocellulose was considered successful when the dispersion remained stable in solution for at least seven days, without showing signs of precipitation or coagulation. A decisive confirmation was obtained by verifying the nanometric dimensions by TEM.

[0289] To separate nanocellulose, the samples were centrifuged at 10,000 rpm for 5 minutes. The liquid phase was removed and the samples were washed with 10 ml deionised water. The centrifugation and washing process was repeated for three cycles. Finally, the nanocellulose was dried under vacuum, as described in Example 3, thus obtaining a dry solid within 24 hours.

[0290] Various analytical techniques were used to characterise the obtained nanocellulose (NC) , renamed: CaTA_CF and CaTAJDOl, CaLA_CF and CaLAJDOl, ZnTA_CF and ZnTA_D01 depending on the solvent used and on the starting fabric (CF or DOI) .

[0291] Transmission electron microscopy (TEM) was used to visually confirm the presence of nanometric-scale fragments in NC samples. To perform the measuring, a drop of NC-water suspension was deposited on a carbon-coated copper grid, after performing negative-staining with uranyl acetate to improve image contrast. TEM images were acquired using an FEI Tecnai G2 microscope (Department of Biology, University of Padua) , operating at 100 kV, equipped with 4 MP Olympus Veleta and TVIPS F114 cameras.

[0292] Thermogravimetric analysis (TGA) was used to study the thermal behaviour of NC, in particular the thermal stability and decomposition of DESs and NC . This technique was used to correlate the thermal behaviour of various DESs based on their chemical composition. A TGA Q5000IR instrument (TA instruments) was used, equipped with an infrared oven using four IR lamps and an enclosure of silicon carbide that absorbs IR radiation.

[0293] Samples weighing up to 15 mg were placed in a platinum pan. The samples were heated from 40 °C to 700 °C at a rate of 10 °C / min, in N2 (10 ml / min) for samples CF, and CaTA_CF; and in air (25 ml / min) for samples D01, CaTAJDOl and CaLAJDOl.

[0294] X-ray diffraction (XRD) analysis was performed to determine the crystallinity of the NC, making it possible to confirm the formation of nanocellulose and to determine the crystallinity index.

[0295] Diffraction measurements were carried out using a Bruker AXS D8 Advance Plus diffractometer equipped with a LYNEXEYE detector in ID mode. A CuKal,2 - Kai, 2 radiation source (XI = 1.54060 A, X2 = 1.54439 A, with relative intensity Ka2 / Kal = 0.5) was used as the anode.

[0296] X-rays were generated by the Cu anode supplied with 40 kV and a current of 40 mA. Data were collected with Bragg / Brentano geometry in the range 20 5° - 65, with a scan rate of 4° min-1. Crystalline phase identification was performed using Bruker Diffrac EVA software with a Search and Match procedure. The relative crystallinity index (Crl%) was estimated using Segal's method (119) as follows : ction intensity of the reflection (200) of the lattice at 20^22.6°, representing the sum of the signals of the crystalline and amorphous component, and lam is the diffraction intensity of the reflection relative to the amorphous fraction at 20^18° (in other words the maximum intensity reached by the signal of the amorphous curve) .

[0297] Table 5: Percentage yields (rCF / rDOl weight on initial CF / D01 weight) of NC obtained from medical cotton (CF) or commercial denim (D01) treated with DES.

[0298] All solvents produced a yield higher than 65% (Table 5) , indicating their general effectiveness.

[0299] Although all solvents showed satisfactory results, CaTA was the most efficient (as shown in Table 5) , followed by the CaLA formulation . In contrast , ZnTA produced lower yields , suggesting that calcium salt is more ef fective than zinc salt in NC preparation .

[0300] The NC obtained from DO I showed a trend of lower or very similar yields compared to that derived from CF . This di f ference is probably due to the fact that the cotton used for denim is usually less refined than medical grade cotton, which is often bleached and treated to be more hydrophilic . These less refined fibres may have a lower cellulose content , as they contain higher levels of other substances ( for example lignin, hemicellulose , waxes and insoluble compounds ) .

[0301] Table 6 - Degradation temperatures obtained from thermogravimetric analysis on the NC .

[0302] As part of the development of sustainable solvents , thermogravimetric analysis ( TGA) is used to assess thermal stability . The degradation onset temperature ( Tonset ) is defined as the point at which the sample shows signi ficant mass loss , indicating the onset of thermal degradation . In parallel , the peak temperature ( Tpeak ) represents the step at which the degradation rate reaches its maximum, visible on the thermogram as a marked decrease in sample weight . As shown in Figure 7a, thermograms of CF and CaTA_CF, prepared through CaTA and obtained in an air atmosphere , highlight two distinct degradation events. The first event shows similar peak temperatures for maximum decomposition rates, with 342 °C for CF and 339°C for CaTA_CF (Table 6) . The degradation onset temperature (Tonset) is 324°C for CF and 339°C for CaTA_CF. However, the main difference lies in the distribution of mass loss: CF loses 84% of its mass during the first degradation event, compared to 67% for CaTA_CF after chemo-mechanical treatment. This indicates that a significant fraction of CaTA_CF decomposes at higher temperatures.

[0303] Two possible explanations for this phenomenon are: (1) the removal of hemicellulose (a less thermally stable compound due to its amorphous and complex structure) and lignin (also less stable than cellulose) during the chemical process; and (2) the increase in crystallinity after thermal and ultrasonic treatment, which could lead to a more compact and ordered structure, potentially more resistant to thermal degradation.

[0304] Table 7 - Crystallinity index (Crl%) of nanocellulose obtained from different fabrics

[0305] Figure 8 shows the dif f ractograms of the nanocellulose samples. All the samples analysed show diffraction peaks at 20 = 14.6°, 16.6° and 22.6°, corresponding to the la (triclinic) crystal lattice, and a peak at 34.5°, attributable to the Ip (monoclinic) lattice, both characteristic of native cellulose of plant origin. These results indicate that the treatment increased the crystalline content of cellulose without altering its fundamental crystallographic structure (Table 7) . The increase in crystallinity was favoured by the dissolution and removal of primary cell wall components, such as lignin and hemicellulose, and selective hydrolysis in amorphous regions. The appearance of a new diffraction peak at 20 » 20°, observed in all NC samples, which is absent in natural cellulose but present in reference microcrystalline cellulose (Sigma Aldrich, SI, Figure 9) , further reinforces this conclusion.

[0306] Considering that the CrI of the starting materials is 25% lower than that of the nanocellulose obtained, it is reasonably possible to conclude that the treatment was successful in increasing the crystallinity of the native cellulose. By comparison, although the crystallinity of natural fibres can vary considerably depending on the plant species and cultivation conditions, a range between 50% and 70% (Table 7) can generally be found.

[0307] The FTIR spectra of the prepared nanocellulose, shown in Figure 10, are very similar to those of the source material, with the exception of some samples such as CaTA_CF (0.5: 1:6) and ZnTA_CF, which show a weak additional peak at 1730 cm-1, indicative of a partial carbonyl functionalisation.

[0308] TEM analyses were used to confirm the formation of nanometric-scale structures. In Figure 11, images reveal the presence of fragments ascribable to crystalline nanocellulose in the size range from 100 nm to 400 nm.

[0309] EXAMPLE 6

[0310] Measurement of viscosity

[0311] An experiment was performed to compare the viscosity of a DES, ZnLA, according to the invention and prepared according to Example 1 (DES no. 2) , with a DES prepared with choline chloride and tartaric acid ( CCTA) in a 2 : 1 molar ratio .

[0312] Viscosity in relation to time was measured using a Kinexus Lab+ rotational rheometer (Net zsch-Geratebau GmBH) in conj unction with the rSpace software , equipped with a Peltier cell to ensure temperature control . A 20 mm parallel plate geometry with a fixed gap of 0 . 3 mm was used .

[0313] As shown in Figure 12 , rheological analysis of DES CCTA highlighted a 16% decrease in viscosity upon exposure to air over the course of three hours , while no change in viscosity was observed for ZnLA. Figure 13 shows the same results on a logarithmic scale , from which it can be seen that the viscosity of ZnLA is at least two orders of magnitude lower than that of CCTA, an appreciable characteristic in a class of solvents that are often characterised by high viscosities that make their use complicated ( Table 8 ) .

[0314] Table 8 - Average viscosity values for some DESs prepared from choline chloride .

[0315] 1 . Ch=choline chloride

Claims

CLAIMS1 . A method for the recovery of cellulose in a material containing cellulose fibres that comprises the step of putting said material containing cellulose fibres in contact with at least one ternary deep eutectic solvent ( DES ) comprising :- at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof , preferably hydroxylated, more preferably an organic alpha-hydroxy acid;- at least one metallic salt ; and- water ; thus obtaining cellulose in the form of solution or dispersion in said ternary DES .2 . Method according to claim 1 , wherein said at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids , and mixtures thereof is an organic alpha-hydroxy acid, preferably an organic alpha-hydroxy acid chosen from lactic acid, tartaric acid, citric acid, glycolic acid, gluconic acid, glyceric acid, malic acid, isocitric acid, mandelic acid and mixtures thereof , more preferably chosen from lactic acid, tartaric acid, citric acid, and mixtures thereof , even more preferably chosen from lactic acid, tartaric acid and mixtures thereof , most preferably chosen from lactic acid and tartaric acid .3 . Method according to claim 1 or 2 , wherein said at least one metallic salt is a metallic salt in which the metal is divalent , preferably a divalent metal chosen from zinc, calcium, magnesium, iron and aluminium, more preferably chosen from zinc, calcium and magnesium, even more preferably chosen from zinc and calcium .4 . Method according to any one of the preceding claims , wherein said at least one metallic salt is chosen from ZnCl2, CaCl2, MgCl2, CaS04, A1C13, FeCl3, FeCl2and mixtures thereof , preferably chosen from ZnCl2, CaCl2,MgC12 and mixtures thereof , more preferably chosen from ZnC12 , CaC12 and mixtures thereof , most preferably chosen from ZnC12 e CaC12 .5 . Method according to any one of the preceding claims , wherein said at least one organic acid, preferably said at least one organic alpha-hydroxy acid, is chosen from lactic acid, tartaric acid and mixtures thereof ; and said at least one metallic salt is chosen from ZnC12 , CaC12 and mixtures thereof .6 . A method for the regeneration of cellulose from a material containing cellulose fibres compris ing the steps of : a ) putting said material containing cellulose fibres in contact with at least one ternary deep eutectic solvent ( DES ) comprising :- at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof , preferably hydroxylated, more preferably an organic alpha-hydroxy acid;- at least one metallic salt ; and- water ; thus obtaining cellulose in the form of solution in the ternary DES ; b ) addition of a non-solvent to the solution thus obtained, thus precipitating the dissolved cellulose ; and c ) optionally separation of the cellulose .7 . Method according to claim 6 , wherein said at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof is an organic alpha-hydroxy acid, preferably an organic alpha-hydroxy acid chosen from lactic acid, tartaric acid, citric acid, glycolic acid, gluconic acid, glyceric acid, malic acid, isocitric acid, mandelic acid and mixtures thereof , more preferably chosen from lactic acid, tartaric acid, citric acid, and mixtures thereof , even more preferably chosenfrom lactic acid, tartaric acid and mixtures thereof, most preferably lactic acid.

8. Method according to claim 6 or 7, wherein said at least one metallic salt is a metallic salt in which the metal is divalent, preferably a divalent metal chosen from zinc, calcium, magnesium, iron and aluminium, more preferably chosen from zinc, calcium and magnesium, even more preferably zinc.

9. Method according to any one of claims 6 to 8, wherein said at least one metallic salt is chosen from ZnCl2, CaCl2, MgCl2, CaS04, A1C13, FeCl3, FeCl2and mixtures thereof, preferably chosen from ZnCl2, CaCl2, MgCl2and mixtures thereof, more preferably chosen from ZnCl2, CaCl2and mixtures thereof, most preferably ZnCl2.

10. Method according to any one of claims 6 to 9, wherein said at least one organic acid, preferably said at least one organic alpha-hydroxy acid, is chosen from lactic acid, tartaric acid and mixtures thereof; and said at least one metallic salt is chosen from ZnCl2, CaCl2and mixtures thereof; preferably wherein said at least one organic acid, more preferably said at least one organic alpha-hydroxy acid, is lactic acid; and said at least one metallic salt is ZnCl2.

11. Method according to any one of claims 6 to 10, wherein in said ternary DES the molar ratio of said at least one organic acid, preferably said at least one organic alpha-hydroxy acid, to said at least one metallic salt is from 1:20 to 5:1, preferably from 1:10 to 5:1, more preferably from 1:4 to 3:1, even more preferably from 1:3 to 1:1.

12. A method for the preparation of nanocellulose from a material containing cellulose fibres comprising the steps of: a) putting said material containing cellulose fibres in contact with at least one ternary deep eutectic solvent (DES) comprising:- at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof , preferably hydroxylated, more preferably an organic alpha-hydroxy acid;- at least one metallic salt ; and- water ; thus obtaining cellulose in the form of dispersion in the ternary DES ; b ) addition of a non-solvent to the dispersion thus obtained; c ) homogenisation of the cellulose , thus obtaining a nanocellulose suspension; d) optionally separation of the nanocellulose from said nanocellulose suspension .13 . Method according to claim 12 , wherein said at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids , and mixtures thereof is an organic alpha-hydroxy acid, preferably an organic alpha-hydroxy acid chosen from lactic acid, tartaric acid, citric acid, glycolic acid, gluconic acid, glyceric acid, malic acid, isocitric acid, mandelic acid and mixtures thereof , more preferably chosen from lactic acid, tartaric acid, citric acid, and mixtures thereof , even more preferably chosen from lactic acid, tartaric acid and mixtures thereof , most preferably chosen from lactic acid and tartaric acid .14 . Method according to claim 12 or 13 , wherein said at least one metallic salt is a metallic salt in which the metal is divalent , preferably a divalent metal chosen from zinc, calcium, magnesium, iron and aluminium, more preferably chosen from zinc, calcium and magnesium, even more preferably chosen from zinc and calcium .15 . Method according to any one of claims 12 to 14 , wherein said at least one metallic salt is chosen from ZnCl2, CaCl2, MgCl2, CaS04, A1C13, FeCl3, FeCl2and mixtures thereof , preferably chosen from ZnCl2, CaCl2,MgC12 and mixtures thereof, more preferably chosen from ZnC12, CaC12 and mixtures thereof, most preferably chosen from ZnC12 and CaC12.

16. Method according to any one of claims 12 to 15, wherein said at least one organic acid, preferably said at least one organic alpha-hydroxy acid, is chosen from lactic acid, tartaric acid and mixtures thereof; and said at least one metallic salt is chosen from ZnC12, CaC12 and mixtures thereof; preferably wherein said at least one organic acid, more preferably said at least one organic alpha-hydroxy acid, is chosen from lactic acid and tartaric acid; and said metallic salt is chosen from ZnC12 and CaC12,' more preferably wherein said at least one organic acid, even more preferably said at least one organic alpha-hydroxy acid, is lactic acid and said at least one metallic salt is CaC12,- said at least one organic acid, even more preferably said at least one organic alpha-hydroxy acid, is tartaric acid and said at least one metallic salt is CaC12,- or said at least one organic acid, even more preferably said at least one organic alpha-hydroxy acid, is tartaric acid and said at least one metallic salt is ZnC12.

17. Method according to any one of claims 12 to 16, wherein in said ternary DES the molar ratio of said at least one organic acid, preferably said at least one organic alpha-hydroxy acid, to said at least one metallic salt is from 1:20 to 4:1, preferably from 1:15 to 3:1, more preferably from 1:10 to 2.5:1, even more preferably from 1:5 to 1:1 or about 2:1.

18. A method for the preparation of a ternary DES comprising :- at least one organic acid chosen from monocarboxylic acids, polycarboxylic acids and mixtures thereof, preferably hydroxylated, more preferably an organic alpha-hydroxy acid;- at least one metallic salt; andwater, comprising the step of mixing said at least one organic acid, preferably said at least one organic alpha-hydroxy acid, said at least one metallic salt and said water at a temperature from 50 to 100 ° C for a time from 10 minutes to 4 hours , preferably at a temperature from 60 to 90 ° C for a time from 30 minutes to 2 hours , more preferably at a temperature from 75 to 85 ° C for a time from 40 minutes to 90 minutes .19 . A ternary DES comprising :- at least one organic acid chosen from monocarboxylic acids , polycarboxylic acids and mixtures thereof , preferably hydroxylated, more preferably an organic alpha-hydroxy acid;- at least one metallic salt ; and- water .

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