Selective depolymerization of cellulose

Abstract

According to an example aspect of the present invention, there is provided a selective method for producing cellulose The method comprising the steps of providing cellulose, reducing crystallinity of the cellulose by pretreatment to obtain a pretreated cellulose, oxidizing the pretreated cellulose, and subjecting the oxidized cellulose to depolymerization. Further, the present invention concerns a cellulose obtained by such method and a cellulose having controlled molecular weight, as well as uses of such celluloses.

Description

Selective depolymerization of celluloseFIELD OF INVENTION

[0001] The present invention relates to a selective method for depolymerizing cellulose, and more generally to a selective method for producing cellulose. In particular, the invention relates to method of depolymerizing cellulose with controlled molecular weight and polydispersity. Further, the present invention concerns cellulose obtained by such method, as well as cellulose having a controlled molecular weight / degree of polymerization, in particular cellulose having low degree of polymerization.

[0002] In addition, the present invention relates to the use of such cellulose.BACKGROUND

[0003] Oligosaccharides and other low DP (degree of polymerization) polymeric fractions, derived from cellulose, have great potential as building blocks in the synthesis of renewable materials or as chemicals.

[0004] Cello-oligosaccharides (COS) are oligosaccharides made from D-glucose units (anhydroglucose units) bonded to each other with P-l,4-glucosidic linkages, forming short linear chain polymers. These short polymers typically are consisting of 2-20 glucose units, which determine the degree of polymerization (DP) for the polymer. Depending on the degree of polymerization, COS have varying solubility in water, leading to partially or totally insoluble polymers with DP 6-20, and soluble when DP is 2-6. The center of activity of those molecules is associated with the hydroxyl groups found on the glucose units, and new properties can be identified after selected modifications are implemented.

[0005] One of the most valuable properties of cellulose oligomers is their prebiotic activity, which is the main reason for the incorporation of these materials in food, as well as in animal food products, supporting the human or animal health. Due to their bacteriostatic activity, they could be utilized in medical, pharmaceutical, and cosmetic industry. Further, their ability to improve the rheological properties of a product can be fully utilized in the generation of new materials with refined formulations. Recently, it was also discovered that cellulose oligomers can effectively stabilize oil in water systems and form stable Pickering emulsions. Moreover, new bio-based amphiphilic compounds havebeen obtained when cellulose oligomers underwent a functionalization reaction and a subsequent coupling reaction step.

[0006] Even though COS have many distinct characteristics like good physicalchemical, and rheological properties that make them valuable materials with various potential applications, they haven’t been fully assessed regarding their properties and their potential applications, because of the existing challenges in their bulk production.

[0007] Cellulose oligomers’ synthesis has been attempted with various methodologies, including enzymatic or chemical synthesis, and depolymerization of cellulose through enzymatic or chemical hydrolysis of recalcitrant cellulose. Their synthesis, starting from a cellobiose or glucose unit, is possible by employing a glycosylation reaction, but control of reaction topochemistry has been quite challenging. A similar synthetic approach which employs phosphorylase enzymes as catalysts, has been studied; however, upscaling of such method is not yet readily available. In the physicalchemical methods, cellulose is hydrolyzed either heterogeneously or homogeneously, in the presence of a catalyst, to produce cellulose oligomers. Between the acid hydrolysis procedures, one effective and scalable method that has been utilized is the acidic hydrolysis of cellulose with H3PO4, which produced oligomers in a moderate yield due to the formation of side products and increased time for the fractionation process. Improved results have also been obtained with heterogeneous catalysis in the hydrolysis step, using solid catalysts such as metal oxides, since they allow formation of products in good yield with easy recovery of the water-soluble products. Concerning enzymatic depolymerization, cellulases and LPMOs (lytic polysaccharide monooxygenases) are two distinct types of enzymes that catalyze the hydrolytic and oxidative cleavage of cellulose respectively. Moreover, some alternative methods that have been utilized for the same target molecules, include mechanocatalysis and sonochemical degradation, where mechanical forces are applied on the samples to yield fragmented cellulose products.

[0008] However, a selective straightforward synthesis of cellulose oligomers or other low DP (degree of polymerization) polymeric fractions of the desired length, in sufficient amount and without long fragmentation procedures, has not been previously reported. Thus, there is still a need for further improvements producing cellulose with controlled molecular weight and polydispersity.SUMMARY OF THE INVENTION

[0009] The present invention aims at solving at least some of the problems of the prior art. In particular, the present invention provides a novel method for selective depolymerization of cellulose. In more particular, the present invention provides a novel method of depolymerizing cellulose with controlled molecular weight / degree of polymerization and polydispersity. Further, the present invention provides a novel method for production of cellulose, referring to a method of producing cellulose derivatives or products from selectively depolymerized cellulose, often using targeted methods or catalysts. This can involve converting cellulose into valuable chemicals or materials through controlled reactions.

[0010] It is an objective of the present invention to provide a selective method for depolymerizing / producing cellulose, wherein molecular weight and poly dispersity of cellulose can be controlled.

[0011] Thus, the present invention relates to a method for depolymerizing and / or producing cellulose, the method comprising the steps of providing cellulose, reducing crystallinity of the cellulose by pretreatment to obtain a pretreated cellulose, oxidizing the pretreated cellulose, and subjecting the oxidized cellulose to depolymerization, such as beta-elimination. Such cellulose can further be subjected to fractionation, chemical conjugation, solvent or mechanical processing, or any combination of these.

[0012] Further, it is an object of the present invention to provide cellulose obtained by such method.

[0013] Further, it is an object of the present invention to provide cellulose having a low degree of polymerization, in particular cellulose having a degree of polymerization in the range of 5 to 50, and preferably having a poly dispersity index in the range of 1 to 3. Thus, the present invention also relates to a cellulose having controlled molecular weight and polydispersity.

[0014] Further, it is an object of the present invention to provide uses of such cellulose.

[0015] The present invention is at least partially based on the concept of selective depolymerization of cellulose with defined polymer lengths by combining crystallinityreducing pretreatment with controlled oxidation, followed by depolymerization, preferably through beta-elimination. Thus, the method of the present invention provides a selective depolymerization method of cellulose based on controlled oxidation of cellulose having reduced crystallinity. Without being bound by a theory, generally oxidation methods are known to only work on the surface of the fibres / fibrils in technical cellulose, i.e. there is not a statistical oxidation of the polymer but a heterogenous one, whereas reduced crystallinity of cellulose allows for a more statistical access to the cellulose molecule, and not just on the crystalline surface of cellulose fibrils. In addition to reduced crystallinity obtained by pretreatment, pretreatment improves reactivity of cellulose by causing separation and / or swelling of cellulose fibers. When native cellulose fibers go into solution through solid-liquid interface, they are swelling heterogeneously in specific areas, a phenomenon known as ballooning. Solvent passes into the fibres through the primary wall, then the cellulose in secondary wall swells and cause primary wall to expand, However, because primary wall is not fully permeable, it is not expanding uniformly along fiber, forming structures like balloons. Such swelling enables even more efficient reaction with the oxidizing agent in the oxidation step, through cell wall fragmentation. Improved statistical access thus basically increases reactivity of cellulose by maximizing the availability of the polymer for reaction and enables production of more uniform products, thereby enabling control over polydispersity. Thus, in the present invention, controlled oxidation of cellulose having reduced crystallinity is used to tune the chain-lengths and their distribution, obtained from depolymerization. In other words, the present invention is based on a method providing control over degree of polymerization and poly dispersity through amorphization (reduced crystallinity) and oxidative fragmentation of cellulose.

[0016] Various embodiments of the present invention may comprise one or more features from the following bulleted list:• The pretreatment comprises treating the cellulose pulp with a cellulose solvent (dissolving or non-dissolving).• The pretreatment comprises treating the cellulose pulp with a cellulose solvent (dissolving or non-dissolving) selected from concentrated alkali, ionic liquids, deep eutectic solvents, molten salt hydrates, N-oxide based solvents and combinations thereof.• The pretreatment comprises treating the cellulose pulp with a reagent comprising NaOH, in particular the mixture of NaOH and urea, lithium bromide trihydrate (LiBr 3H2O), an ionic liquid, such as tetrabutylphosphonium acetate, or N- methylmorpholine-N-oxide (NMMO) hydrate.• The pretreatment comprises a non-dissolving pretreatment.• The obtained pretreated cellulose has a crystallinity index (CI) that is at least 50 %, 60 %, 70 %, 80 % or 90 %, preferably 100 %, lower than the CI of the cellulose before pretreatment.• An oxidizing agent used in the oxidation step includes at least one of sodium chlorite (NaCICh), TEMPO, periodate or nitrogen dioxide, oxygen, ozone, air, chlorite, chlorine, hydrogen peroxide, periodate, nitrogen dioxide, such as TEMPO, nitroxyl radicals, hypochlorite, DMD, hypervalent iodine regents, bromate, bromide, nitrite, nitrate, persulphates, permanganate, dichromate sulphuric acid, hypohalites and combinations thereof.• The stoichiometric ratio of the pretreated cellulose anhydroglucose unit and an oxidizing agent in the oxidation step is in the range 1:0.5 to 1:0.01, preferably in the range 1:0.05: to 1:0.02, such as in the range of 1:0.1 to 1:0.05.• The beta-elimination is performed in an alkaline aqueous solution, preferable having a pH in the range of 8 to 14, more preferably in the range of 9-12.• The beta-elimination is performed in an acidic aqueous solution, preferably having a pH in the range of 1 to 6, more preferably in the range of 2 to 4.• The beta-elimination is performed in an acidic alcohol solution, such as in acidic methanol solution.• The cellulose obtained by beta-elimination is fractionated.• The cellulose obtained by beta-elimination is fractionated by water soluble / insoluble fractionation.The cellulose obtained by beta-elimination is, after optional fractionation, chemically conjugated.The conjugation of the cellulose obtained by beta-elimination is performed with primary amine and / or alcohol.• The cellulose has a degree of polymerization in the range of 5 to 50.• The cellulose has a poly dispersity index in the range of 1 to 3, preferably in the range of 1 to 2.• The cellulose is obtained by the method of the present invention.• The cellulose is used as surfactant and / or emulsion stabilizer.

[0017] In particular, the present invention is characterized by what is stated in the independent claims. Some specific embodiments are defined in the dependent claims.

[0018] Several advantages are reached using the present invention. Above all, the present invention provides a novel, improved and scalable, method to synthesize cellulose with controlled molecular weight, in particular with controlled molecular weight and polydispersity. Especially, the present invention enables providing cellulose with low degree of polymerization. Thus, the method enables providing novel cellulose having a degree of polymerization in the range of 5 to 50. In particular, the method enables selective production of oligosaccharides and other low DP (degree of polymerization) polymeric fractions, derived from cellulose. The products are suitable starting compounds in the synthesis of high value materials from biobased sources and could contribute in the development of novel sustainable solutions for global challenges.

[0019] Thus, the method improves efficiency of producing oligosaccharides and other low DP (degree of polymerization) polymeric fractions, derived from cellulose. In particular, the invention lies in providing very defined fractions of cellulose, thereby minimizing the need for additional steps of fractionation.

[0020] The present invention also provides an effective method for generally tuning molecular weight and poly dispersity of cellulose. Thus, the method of the present invention is suitable for producing cellulose with varying molecular weight and polydispersity, especially low polydispersity.

[0021] Next, embodiments will be examined more closely with the aid of a detailed description with reference to the appended drawing.BRIEF DESCRIPTION OF THE DRAWING

[0022] Some results of the Examples are presented with reference to the attached drawings in which:

[0023] FIGURE 1 illustrates one embodiment of the present invention, wherein the pretreatment reduces crystallinity of cellulose.

[0024] FIGURE 2 illustrates the swelling during the pretreatment according to one embodiment of the present invention.

[0025] FIGURE 3 illustrates one embodiment of the present invention, wherein the pretreatment doesn't affect the degree of polymerization of cellulose and beta-elimination of oxidized pretreated cellulose enables narrower poly dispersity compared to nonpretreated cellulose.

[0026] FIGURE 4 illustrates HSQC NMR spectrum from acidic methanolysis of TEMPO oxidized CNF according to one embodiment of the present invention.

[0027] FIGURE 5 illustrates formation of a, 0- unsaturated uronate groups and functionalization thereof according to one embodiment of the present invention.

[0028] FIGURE 6 illustrates one embodiment of the present invention, wherein the pretreatment reduces crystallinity of cellulose.

[0029] FIGURE 7 illustrates one embodiment of the present invention, wherein the pretreatment doesn't affect the degree of polymerization of cellulose and beta-elimination of oxidized pretreated cellulose enables narrower polydispersity compared to nonpretreated cellulose.

[0030] FIGURE 8 illustrates WAXS diffractograms for the wet and dry samples according to one embodiment of the present invention.

[0031] FIGURE 9 illustrates SAXS diffractograms (log I vs Q) for the wet and dry samples according to one embodiment of the present invention.

[0032] FIGURE 10 illustrates Kratky plots for the wet and dry samples according to one embodiment of the present invention.

[0033] FIGURE 11 illustrates Correlations between PDI and the structural ordering parameters from SAXS and WAXS analysis according to one embodiment of the present invention.

[0034] FIGURE 12 illustrates pulp before / after each treatment step observed by optical microscopy according to one embodiment of the present invention.DETAILED DESCRIPTION OF EMBODIMENTS

[0035] The present invention concerns a method, in particular, a selective method, for depolymerizing and / or producing cellulose, the method comprising the steps of reducing crystallinity of cellulose, oxidizing such cellulose and subjecting the oxidized cellulose to beta-elimination.

[0036] Thus, according to one embodiment the present invention concerns a method for producing cellulose, the method preferably comprising the steps of:- providing a cellulose,- reducing crystallinity of the cellulose by pretreatment to obtain a pretreated cellulose,- oxidizing the pretreated cellulose, and- subjecting the oxidized cellulose to beta-elimination.

[0037] In one embodiment, the first step of the method is providing cellulose. Cellulose is an organic compound with the formula (CeHwOs), a polysaccharide consisting of a linear chain of several hundred to many thousands of P-(l,4)-linked glucose units. The cellulose of the present invention can be derived from any existing source of cellulose. Thus, the cellulose may be from various sources and in the form of various cellulose materials, such as pulp, waste, by-product, non-fibrous and bacterial cellulose.

[0038] In particular embodiment, the cellulose is in the form of a pulp, wherein the first step comprises providing cellulose pulp. In one embodiment the cellulose is selected from the group consisting of chemical pulp, mechanical pulp, thermo mechanical pulp, chemical thermomechanical pulp, and a mixture thereof.

[0039] In a further embodiment, the chemical pulp is selected from the group consisting of organosolv pulp, soda pulp, dissolving pulp, kraft pulp, sulphite pulp, hot water extraction pulp, and a mixture thereof. In embodiments, paper grade pulp is used. In further embodiments dissolving grade pulp is used. Recycled pulps such as deinked pulpare also useful in embodiments. In a particular embodiment the cellulose is a dried dissolving pulp.

[0040] In an embodiment the cellulose is obtained from recycled cellulose selected from the group consisting of paper, board, cotton, cotton linter, wheat straw, rice straw, corn stover, hemp, kenaf, bagasse, bamboo, flax, jute and a mixture thereof. Similarly, virgin sources of cellulose are equally suitable. Thus, in an embodiment the cellulose is obtained from virgin cotton, virgin cotton linter, virgin wheat straw, virgin rice straw, virgin com stover, virgin hemp, virgin kenaf, virgin bagasse, virgin bamboo, virgin flax, virgin jute and a mixture thereof.

[0041] In one embodiment, the cellulose is derived from waste materials, such as recycled cellulose, in particular non-fibrous, textile waste, sugarcane bagasse or any combination thereof.

[0042] According to one embodiment the cellulose source is purified before providing it as a starting material to the method of present invention, for removing impurities, such as hemicellulose, polyester and / or lignin. Typical purification methods might include hydra pulping, aqueous acid hydrolysis, Kraft pulping, cold caustic extraction, bleaching and / or mechanical processing

[0043] Typically, cellulose is present in nature with high proportion of cellulose I crystalline allomorphs, which limits its chemical reactivity and general transformation into value-added chemicals. In one embodiment, the present invention aims to provide cellulose having improved reactivity through reduced crystallinity by transforming the cellulose I form mainly into the more thermodynamically stable and more accessible crystalline form denominated cellulose II.

[0044] Thus, according to one embodiment, the next step of the method is pretreatment of cellulose, especially chemical pretreatment. In particular, the pretreatment comprises processing of cellulose in a way that enables reducing crystallinity of cellulose, thereby increasing statistical molecular accessibility of cellulose. Thus, in one embodiment, the method comprises the step of reducing crystallinity of the cellulose by pretreatment to obtain pretreated cellulose. Such pretreated cellulose is typically characterized by increased hydrophilicity, reactivity and enzymatic digestibility. In the context of the present invention the pretreated cellulose having reduced crystallinity is alsoreferred as amorphous cellulose. In a particular embodiment, the pretreated cellulose, i.e. amorphous cellulose, has at least 50 % lower crystallinity index (CI) than the CI of the cellulose before the pretreatment. Thus, in one embodiment, the pretreatment reduces crystallinity of cellulose by at least 50 %.

[0045] According to one embodiment, the obtained pretreated cellulose has a crystallinity index (CI) that is at least 50 %, 60 %, 70 %, 80 %, 90 % or 99 % lower than CI of the cellulose before the pretreatment. In one embodiment, the obtained pretreated cellulose has a crystallinity index (CI) that is at least 50 %, preferably 100 %, lower than CI of the cellulose before pretreatment. Such relative reduction of CI can be calculated by any known method since the relative reduction should remain constant despite of what method is used. In general, crystallinity index is highly dependent on the used cellulose source, but also depends on the used measurement and calculation methods of the index. It is acknowledged that ‘amorphous’ cellulose still contains some degree of short-range ordering but that the common analytical protocols set artificial limits and give relative values. Thus, there is no absolute scale and each method gives a roughly relative CI, wherein it is not totally appropriate, in a science reporting context, to set certain limits on CI. Degree of crystallinity can for example be determined by experimental techniques based on X-ray diffraction, solid-state NMR spectroscopy, calorimetry, density measurement, Raman spectroscopy or infrared spectroscopy, such as13C CP MAS NMR (carbon- 13 nuclear magnetic resonance) spectroscopy or WAXS (wide-angle X-ray scattering), and it can be expressed in terms of mass fraction or volume fraction. As an example, untreated kraft pulp can have a crystallinity index in the range of about 60 to 80 %, whereas a corresponding pretreated pulp has a crystallinity index in the range of 20 to 40 % [as calculated by deconvolution (amorphous contribution, background and pseudoVoight peak fitting for key Miller index diffraction peaks) of ID X-ray diffractograms (Rico del Cerro et al.)].

[0046] According to one embodiment, the pretreated cellulose has a crystallinity index in the range of 0 to 60 %, preferably 0 to 40 %, such as 0 to 20 %, more preferably 0 to 10 %, such as 1 to 10 %, most preferably 0 %, calculated using13C-CPMAS NMR spectroscopy.

[0047] According to one embodiment, any known method of reducing crystallinity can be used, that is commonly used in peer reviewed publications.

[0048] According to one embodiment the pretreatment may be based on a dissolving or non-dissolving method. In a dissolving pretreatment, dissolution of cellulose is followed by rapid regeneration through a precipitation mechanism by using a non-solvent, reagent and / or temperature change, whereas, in the non-dissolving (heterogeneous) method (e.g. Mercerisation utilising aqueous NaOH) regeneration, i.e. precipitation by washing, is not required. Thus, in the non-dissolving method, cellulose is present in a heterogeneous solidliquid phase, form which the cellulose may be obtained simply by pressing and / or filtering the pretreated cellulose, whereas the dissolving method requires recovery of the solvents, typically by distillation, crystallisation or other more expensive purification methods. Thus, non-dissolving method allows easier cellulose recovery and solvent recycling. Further, addition of a non-solvent, that is typically water, in the dissolving method often results in gelation, which complicates the biomass recovery due to limited mass transfer. Thus, in a preferred embodiment, the pretreatment comprises a non-dissolving pretreatment and optional washing step.

[0049] In a non-dissolving method, a non-derivatizing solvent is used, wherein none of the polymer molecules are, actually, chemically modified during dissolution, but induced polymer separation and / or swelling generates alteration in the crystalline structure from cellulose I to cellulose II and / or amorphous cellulose, rather than actual dissolution. Whether a dissolving or non-dissolving method is used, is determined by the used solvent as well as the pretreatment conditions. Cellulose dissolution is thus highly affected by temperature, molecular weight and solvent / non-solvent concentrations. Thus, for example ionic liquids, can be used in either method.

[0050] According to one embodiment, the pretreatment may be based on reactive dissolution and regeneration, wherein there is a chemical modification of cellulose followed by a return to the unmodified cellulose polymer. One example of such derivatising solvents are organic solvents with sulfur dioxide and amines (DMSO / SO2 / di ethylamine) .

[0051] In a preferred embodiment, a direct dissolving method is used.

[0052] According to one embodiment, the pretreatment may be based on mechanical treatment, such as milling, that is also able to reduce crystallinity of cellulose by using mechanical force to fragment the cell walls of cellulose, thus making cellulose more accessible to following treatments. In one embodiment, the mechanical treatment cancomprise milling, grinding, refining, fluidisation, ultrasonication, extrusion or any mixture thereof, preferably milling. In one embodiment, mechanical pretreatment is combined with any other pretreatment method.

[0053] According to one embodiment, the pretreatment comprises treating the cellulose pulp with a cellulose solvent, in particular, treating the cellulose pulp with a cellulose solvent in dissolving or non-dissolving conditions. Any suitable solvent can be used. In one embodiment, the solvent is selected from the group of aqueous transitionmetal complexes (e.g., Cuprammonium hydroxide), aqueous alkali (e.g., LiOH or NaOH) solutions, aqueous concentrated salt solutions (e.g., ZnCh, ammonium, or sodium thiocyanate solutions), molten inorganic / organic salt hydrates ((e.g. LiCICU • 3H2O), inorganic salts dissolved in organic solvents (e.g., LiCl / N,N-dimethylacetamide (DMAc), ammonia / sodium or ammonium salt, or tetrabutylammonium fluoride (TBAF) / dimethyl sulfoxide (DMSO)), mixtures of organic solvents with sulfur dioxide and amines (DMSO / SCh / diethylamine), amine oxides (e.g., N-methylmorpholine-N-oxide (NMMO)), ionic liquids (e.g. l-butyl-3-methylimidazolium chloride ([Bmim]Cl), l-allyl-3-methylimidazolium chloride ([Amim]Cl), l-ethyl-3-methylimidazolium acetate ([emim][0Ac]) or 7-methyl-l,5,7-triazabicyclo[4.4.0]dec-5-enium acetate ([mTBDH][OAc])) and deep eutectic solvents. These are all solvent systems that can directly dissolve cellulose.

[0054] Aqueous alkali solutions are one of the most research solvent systems for cellulose dissolution, in particular in a non-dissolving method. In particular concentrated NaOH solutions have been actively researched, such as solutions having NaOH content of about 5 to 20 wt.%, for example about 10 wt.%, calculated from the total weight of the solution. In the context of aqueous alkali solution, it has been found that addition of chemical in NaOH / water system shows improved quality of solution / dissolution yield and reduces the gelation of cellulose. Suitable chemicals are for example urea, thiourea, PEG and metal oxides. However, also here, every solvent system is totally dependent of the solution conditions.

[0055] Ionic liquids are relatively new solvents for cellulose dissolution, whose chemical and physical properties can be tuned by varying the cations. Ionic liquids have low vapor pressure (allowing wide processing conditions), they are non-flammable andprovide low-toxicity options. NMMO, in turn, is a well-known low-cost and low-toxicity bulk solvent for cellulose.

[0056] In a preferred embodiment, the solvent is selected from the group of aqueous alkali solutions, ionic liquids, deep eutectic solvents, molten salt hydrates, N-oxide based solvents and combinations thereof.

[0057] In particular embodiment, the pretreatment comprises treating the cellulose with a reagent comprising NaOH, in particular the mixture of NaOH and urea, lithium bromide trihydrate (LiBr • 3H2O), lithium chloride trihydrate (LiCl • 3H2O), an ionic liquid, such as tetrabutylphosphonium acetate, or N-methylmorpholine-N-oxide (NMMO) hydrate (wide range).

[0058] Typically, pretreatment occurs in an aqueous solution. According to one embodiment, the water content of the aqueous solution has effect on “amorphization” of cellulose and / or solvent recovery, wherein the properties of the obtained cellulose can be adjusted by varying the water content.

[0059] According to one embodiment, the pretreatment comprises mixing cellulose with a solvent. In the context of the present invention, in particular in the context of the pretreatment, the term “solvent” includes solvents used both in dissolving and nondissolving pretreatment, further it includes so called dissolving solvents as well as partially separating / swelling solvents, such as molten salt hydrates.

[0060] In one embodiment, the mixing temperature depends on the cellulose and the used solvent, and whether a dissolving or non-dissolving method is used. Typically, the mixing is performed at room temperature, i.e. at about 20 °C, wherein heating is preferably not required. In a preferred embodiment, the mixture is homogenized, for example in a rotary homogenizer. The homogenization is preferably performed for 0.5 to 5 hours, such as 2 to 4 hours. In one embodiment, the homogenized mixture is washed, filtered and / or dried. Optional washing can be made with distilled water, for example. In a preferred embodiment, the homogenized mixture, i.e. the pretreated cellulose, is not dried, but used directly in the next step of the process. Without being bound by a theory, drying may collapse the structure and reintroduce some crystallinity.

[0061] According to one embodiment, the method comprises, before and / or after, the pretreatment mechanical treatment(s) that may further improve the ‘accessibility’ of thecellulose towards oxidation. Such mechanical treatment step may be any step that uses mechanical force to fragment the cell walls of cellulose making cellulose more accessible to following treatments. In one embodiment, the mechanical treatment can comprise milling, grinding, refining, fluidisation, ultrasonication, extrusion or any mixture thereof, preferably milling.

[0062] In one embodiment, the pretreated cellulose is subjected for oxidation, in particular for controlled and / or selective oxidation. In particular, the oxidation of the present invention concerns oxidation of cellulose having reduced crystallinity. In general, oxidation is a chemical reaction that takes place when a substance comes into contact with oxygen or another oxidizing substance, typically called as an oxidizing agent. Cellulose oxidation is a commonly employed reaction in various applications.

[0063] In one embodiment, the oxidation is performed by contacting the pretreated cellulose with an oxidizing agent. Oxidation is highly dependent on the applied oxidizing condition; thus, it is not convenient for the present invention to define any specific oxidization conditions since those are selected depending on the desired outcome and used cellulose and oxidizing agent. For example, in one embodiment cellulose oxidation is associated with degradation of cellulose, which already as such shortens its chain length and produces new reducing end groups. Whereas some other oxidation may only occur as a change in functional groups of cellulose without affecting the chain length, such as oxidation of hydroxyl group. Reactions of the oxidation step determines the outcome of the following beta-elimination step.

[0064] Typically, oxidation is performed at room temperature, i.e. at about 20 °C. In one embodiment, oxidation is performed at a temperature in the range of 15 to 80 °C, preferably in the range of 20 to 60 °C, such as in the range of 20 to 40 °C. Preferably, the oxidation is performed under aqueous conditions.

[0065] In one embodiment, oxidation can also introduce additional chemical functionalities, such as a,P-unsaturated uronate groups, to the cellulose that may be leveraged in possible further modification steps of cellulose.

[0066] There exist various oxidizing agents that can be used in the present invention, to mention few; oxygen, ozone, air, chlorite, such as sodium chlorite, chlorine, hydrogen peroxide, periodate, nitrogen dioxide, such as TEMPO, nitroxyl radicals, hypochlorite,DMD, hypervalent iodine regents, bromate, bromide, nitrite, nitrate, persulphates, permanganate, dichromate sulphuric acid, hypohalites and combinations thereof.

[0067] According to one embodiment, the pretreated cellulose is subjected for selective oxidation. Selective oxidation enables optimizing the chemical structure of the oxidized cellulose, thereby affecting it further reactions. In particular embodiment, selective oxidation enables controlling carbonyl moieties of the oxidized cellulose, thereby affecting the following beta-elimination step. Selective oxidation is based on selecting an oxidizing agent that enables certain kind of oxidation reaction(s). Oxidation at different positions of cellulose gives differences in reactivity of cellulose, i.e. faster or slower under given conditions. Typically, oxidation occurs at 2, 3 and / or 6 positions (to aldehyde, ketone or carboxylate) of cellulose, that introduce instability towards depolymerization. Generally, 6-carboxylates are the most stable oxidised species. Thus, in particular embodiment, selective oxidation enables control over the oxidized positions.

[0068] According to one embodiment, controlled oxidation allows control over the stoichiometry of the oxidized cellulose.

[0069] According to one embodiment, an oxidizing agent used in the oxidation step includes at least one of sodium chlorite (NaCICh), TEMPO (2,2,6,6-tetramethylpiperidin-l-yl)oxyl), periodate or nitrogen dioxide.

[0070] For example, TEMPO oxidation employing stable nitroxyl radicals provides high selectivity, short reaction time, mild reaction conditions and limited side reactions. In particular, TEMPO allows a significant number of C6 hydroxyl groups to be transformed into carboxylate moieties. Also, periodate provides selective oxidation by cleaving C2-C3 bonds in monomer units of cellulose and oxidize the newly formed vicinal hydroxyl groups into 2,3 dialdehyde moieties.

[0071] According to one embodiment, an oxidation agent used in the oxidation step is periodate or nitroxyl radical (as catalysts).

[0072] According to one embodiment, the stoichiometric ratio of the pretreated cellulose anhydroglucose unit to the oxidation agent is in the range 1:0.5 to 1:0.01, preferably in the range 1:0.05 to 1:0.02, such as in the range of 1:0.1 to 1:0.05. In one embodiment, the stoichiometric ratio can be calculated based on the following equation 1.

[0073] wherein R is the relative molar amount of the depolymerizing reagent (normalized to cellulose units), DPSis the starting degree of polymerization and DPa is the desired degree of polymerization. Equation 1 assumes that a 1 to 1 stoichiometry of oxidant is required to break each linkage, however, this is variable between different oxidant systems and conditions. Thus, such equation provides a good starting point for roughly stoichiometric reaction.

[0074] According to one embodiment, the stoichiometric ratio of the pretreated cellulose anhydroglucose unit to the oxidation agent is in the range 1:0.5 to 1:0.01, preferably in the range 1:0.05 to 1:0.02, such as in the range of 1:0.1 to 1:0.05. In one embodiment, the stoichiometric ratio can be calculated based on the following equation 2.

[0075] wherein DPs is the starting DPN of the feedstock, DPp is the desired DPN of r the depolymerized material and Req is the molar ratio of the stoichiometric oxidant to the monomer unit (in molar quantities). Equation 2 assumes that a 1 to 1 stoichiometry of oxidant is required to break each linkage, however, this is variable between different oxidant systems and conditions. Thus, such equation provides a good starting point for roughly stoichiometric reaction.

[0076] According to one embodiment, the oxidation is followed by a depolymerization step, such as beta-elimination step. In general, depolymerization is a process where polymer breaks down into monomer, oligomers and / or polymers with reduced chain lengths. Any known depolymerization method can be applied in the present invention. However, in a preferred embodiment, beta-elimination is applied.

[0077] Beta-alkoxy-elimination reaction of oxidized cellulose results in cleavage of polyglycosidic bonds in P-position, and thus chain scission. Thus, by applying controlled and / or selective oxidation for cellulose, it is possible to adjust the amount of polyglycosidic bond in the cellulose and thereby affect the outcome of the beta-elimination. Therefore, in one embodiment, degree of oxidation is used to control the molecular weight of the obtained cellulose since each oxidation point is cleaved during the beta-elimination. For example, by applying only minor oxidation, only a few oxidation points, may be introduced to the cellulose molecule, wherein such cellulose molecule is fragmented to a few cellulose molecules during beta-elimination. Whereas when applying more harsh oxidizing conditions, more oxidation points are formed and further eliminated during beta-elimination, thereby ending with more cellulose factions. Same principle applies also to other depolymerization methods.

[0078] Beta-elimination is preferably performed under aqueous conditions. Typically, the aqueous solution comprises a catalyst, such as acid or base. In one embodiment, beta-elimination can occur under alkaline of acidic conditions, with water and / or alcohols. However, in one embodiment, beta-elimination may also occur under aprotic conditions, i.e. water or alcohol are not required.

[0079] Typically, beta-elimination is performed in an alkaline aqueous solution. Such aqueous solution preferably having a pH in the range of 8 to 14, more preferably in the range of 9-12. However, according to one embodiment, the beta-elimination step is performed in an acidic aqueous solution, preferably having a pH in the range of 1 to 6, more preferably in the range 2 to 4. Further, in one embodiment, the beta-elimination step is performed in an acidic alcohol solution, such as acidic methanol solution. According to one embodiment, beta-elimination may even occur thermally or autocatalytically in water, with minimal addition of acid or base. Overall, there are wide range of conditions to be applied for beta-elimination, by selection of which the chemistry of the cellulose obtained by the present invention can be further tuned.

[0080] According to one embodiment, the cellulose fraction obtained from depolymerization, such as beta-elimination, is a defined fraction with low poly dispersity index. Thus, fractionation is not necessarily required. Fractionation means separation of fractions having different molecular weight ranges. However, according to one embodiment, the obtained cellulose fraction, i.e. the cellulose obtained by beta-elimination, is fractionated. In one embodiment, the fractionation is rather simple water solubleinsoluble fractionation. However, also other fractionation method(s) can be used.

[0081] Typically, the cellulose obtained by the present method is subjected for further reaction(s) in order to modify cellulose for different applications. Thus, accordingto one embodiment, the cellulose obtained by beta-elimination is, after optional fractionation, chemically conjugated. Such chemical conjugation can be any chemical reaction in which the cellulose participates. Conjugation can be used for varying the properties of the obtained cellulose, such HLB (hydrophilic and lipophilic balance), solubility, surface interactions, complexation, etc. Appropriate conjugation reactions depend on the obtained cellulose. In one embodiment, the depolymerization, in particular beta-elimination, may, for example, yield reducing end groups (such as aldehydes), uronate groups or lactones, depending on used oxidant and conditions. According to one embodiment, these can be further reacted with nucleophilic reagents, such as alcohols, amines and / or thiols, to yield glycosides, ethers, esters, amides, amines, thioethers and thioesters, for example.

[0082] In a preferred embodiment, the cellulose obtained by depolymerization, inp articular beta-elimination, is conjugated with amines and / or alcohols.

[0083] The present invention also concerns a cellulose obtained by the present method described by any of the above embodiments.

[0084] The present invention also concerns a cellulose having a degree of polymerization in the range of 5 to 50. The degree of polymerization can be determined for example by following the method of Fliri et al. (Equation 1). In particular, present invention concerns a cellulose, degree of polymerization, and preferably poly dispersity, of which can be controlled to a desired range. In one embodiment, the cellulose has a poly dispersity index in the range of 1 to 3, preferably in the range of 1 to 2, more preferably in the range of 1 to 1.5. Poly dispersity index can be determined by GPC / SEC (gel permeation chromatography / size-exclusion chromatography).

[0085] According to one embodiment, the cellulose obtained by the present invention is microcrystalline cellulose (MCC). In particular, such MCC has high surface area, is insoluble, highly dispersible and finds applications especially in composites, tabletting (pharma industry / medical application) and formation of emulsions. Traditional MCC retains the cellulose I allomorph and is highly crystalline, whereas the MCC formed by the method of the present invention is highly crystalline but will have tuneable crystallinity between cellulose I and cellulose II. Thus, the MCC of the present invention has quite similar properties to traditional MCC, but also provides new properties that may provide new applications for MCC.

[0086] According to one embodiment, the cellulose obtained by the method of the present invention can be in form of a dispersion or a solid, in particular of as solid of high consistency, i.e. low water content. In one embodiment, different types of solids may be provided using different drying methods, such as freeze-drying, spray drying, supercritical solvent exchange. Such dry materials may have different particle size distributions or reactive accessibilities. Further mechanical milling may also be applied to further increase the accessibility and modify particle sizes of the cellulose powder. In the case of cellulose dispersion, in turn, a high shear mixing or fluidisation may for example be applied to the dispersion of the particles in different solvents. This may change the dispersibility properties, such as surfactant properties, emulsion formation, particle size distributions and Pickering stabilisation. Further, in one embodiment, the obtained cellulose may dissolve completely in certain solvents, such as DMSO, over a temperature range, facilitating further chemical reaction or formation of shaped objects, e.g. fibres or films.

[0087] The present invention also concerns use of the cellulose of the present invention. According to one embodiment, the cellulose of the present invention can be used especially as a surfactant and / or emulsion stabilizer.

[0088] EXAMPLES

[0089] Example 1

[0090] 1. Pretreatment of cellulose

[0091] A solvent system was prepared by mixing 7 % NaOH and 12 % urea solutions in deionised water at 0 °C. 5g of softwood sulphite pulp was subjected for pretreatment by dissolving the pulp in 100 ml of the solvent system while stirring occasionally for 1 hour in an ice-salt bath. The formed solution was left in a freezer (-25 °C) overnight. Once the frozen solution was thawed at room temperature, 1 L of deionised water was added and mixed into the solution to form a slurry texture. The mixture was filtered through a Buchner funnel under vacuum to recover the pretreated cellulose pulp. The pretreated pulp was acidified with 1 % HC1 solution and washed several times with deionised water. The obtained pretreated pulp was stored in a fridge as never dried pulp. Dry matter content of the sample was calculated after an overnight oven drying at 105 ± 3 °C and found to be around 10 %.

[0092] 2. Characterization of pretreated cellulose

[0093] The NaOH / urea pretreated cellulose was characterized, using13C crosspolarisation (CP) magic-angle spinning (MAS) nuclear magnetic resonance (NMR, Agilent 600 MHz solid-state NMR spectrometer) spectroscopy, to determine its crystallinity index (CI). Following the established protocol for crystallinity determination (Zuckerstatter et al.) and by comparing the obtained peaks in the C4 region, it was possible to identify the transformation from the cellulose I to the cellulose II crystalline allomorph content and calculate the CI from the fitted area (Figure 1). Among the different methodologies that have been utilized to study the morphology and crystalline phase composition of cellulose,13C CP MAS NMR spectroscopy is a widely recognized method, due to cellulose’s distinct spectral resolution for the C4 and C6 species (crystalline and amorphous) in the anhydroglucose units (AGUs) of technical cellulosics.

[0094] Because of the fine resolution of signal at C4 region, with wide chemical shift range, this area is typically used for crystallinity determination of cellulose. In the current work, deconvolution of signals was applied. The assignment for cellulose I, its allomorphs a and P, and other crystallinity contributions was done according to Larsson and his coworkers (Wickholm et al.) by application of Gaussian functions on the C4 area. For cellulose II the peak fitting was performed based on the work of Ibbett et al..

[0095] In contrast with original untreated pulp (softwood sulfite pulp), with 44% crystallinity index, the pretreated pulp was calculated to have around 17% crystallinity index, as shown in Table 1.

[0096] Table 1. Crystallinity of original and pretreated pulp.

[0097] Swelling effect during the pretreatment causing ballooning on the fibers was also observed by optical microscopy as shown by Figure 2.

[0098] 3. Oxidation of pretreated cellulose

[0099] The pretreated cellulose (obtained in step 1 of pretreatment of cellulose) was put in a glass vial and diluted to the appropriate volume of distilled water and stirred with a magnetic stirrer at 45 °C, for 15 minutes. The relevant volume / molarity of NaICU (solution pre-dissolved to 0.1 M) was added to the cellulose dispersion. The vial was covered with aluminium foil to avoid contact with light. The mixture was then left to stir for an appropriate time and temperature (oil bath heating). Solid fraction was then recovered by centrifugation. Wet sample was washed with water and recovered by centrifugation (in Eppendorf AG Centrifugate) for further three times. The sample was then freeze-dried (using Micro Modulyo freeze dryer) and characterized.

[0100] 4. Beta-elimination of the oxidized cellulose

[0101] Freeze-dried oxidized cellulose (250 mg) (obtained in step 3 of oxidation of pretreated cellulose) was added to a sample vial. NaOH solution (25 ml, 0.01 M in water) was added to the solid and the mixture was magnetically stirred at room temperature for 1.5 hours. The solid fraction was then recovered by centrifugation. The sample was then freeze-dried and characterized.

[0102] 5. Characterization of oxidized and depolymerized cellulose

[0103] 5a. NMR spectroscopy:

[0104] The average degree of polymerization (DP) was derived from solution state 'H-NMR spectroscopy (Bruker AVANCE III 500 MHz spectrometer), after peak fitting and the polymeric proton was compared with non-reducing end proton, reducing end protons a and P at position 1 of AGU unit. Different samples obtained by the present method, as well as a reference sample comprising oxidized cellulose without pretreatment were analyzed. Each NMR sample was prepared by first dissolving the sample in an electrolyte solvent system, more specifically, tetra-n-butylphosphonium acetate [P4444][OAC]: DMSO-de , (1:4 wt%), reaching 5 % consistency (concentration). Initially, the dry samples (25-50mg) were put into a 4 ml screw cap vial, with magnetic stirrer and electrolyte solvent system was added, to have 1 g final solution weight. The solution was stirred at 65 °C until the solution become homogenous and transferred to a 5 mm NMR tube for the analysis. The NMRs were run according to the protocol of Fliri et al.

[0105] The average DPs of different samples are shown in Tables 2 and 3. The DPs of Table 2 are calculated based on equation 1, whereas the DPs of Table 3 are calculated based on equation 2, both equations being presented on page 16. Both pretreated oxidized samples, as well as further depolymerized samples were examined. Also reference samples without pretreatment were examined for comparison. It can be observed in the first reactions of pretreated cellulose with varying oxidant concentration (samples A and B), that an increase from 1 to 3 eq clearly affects the degree of oxidation, which further leads to more extended depolymerization. In an attempt to identify the effect of temperature on the degree of oxidation of pretreated cellulose, the reaction temperature was changed to 70 °C, while keeping the smaller concentration of oxidant. It is shown in Table 2 (sample A vs. sample D), that DP was decreased in comparison to reaction at lower temperature, which illustrates that utilization of higher temperature had a positive effect on the conversion. When (un-pretreated) softwood pulp was used as a substrate in a 5g scale reaction (3 eq) as a reference sample, as expected, it was observed that degree of polymerization was much higher compared to the corresponding pretreated sample (sample C). Thus, pretreatment of the initial pulp leads to easier penetration of cellulose from the oxidant, promoting the oxidation reaction and allowing control over the dialdehyde group distribution on the cellulose backbone.

[0106] Samples F and G illustrate the difference in DP between pretreated and unpretreated cellulose, after beta-elimination. Un-pretreated oxidized sample (sample F) having significantly higher DP compared to pretreated oxidized sample G.

[0107] Table 2. Average DP (DPn) of cellulose samples after periodate oxidation according to equation 1.

[0108] Table 3. Number-average degree of polymerisations for the starting material (DPs) and products (DPp) after periodate oxidation according to equation 2.

[0109] Samples 3 and 5 of Table 3 illustrate the difference in DP between pretreated and un-pretreated cellulose, after beta-elimination. Un-pretreated oxidized sample (sample 5) having significantly higher DP compared to pretreated oxidized sample (sample 3).

[0110] 5b. Gel permeation chromatography (GPC)

[0111] The effect of amorphization / decreased crystallinity on the DP of obtained products and the molecular weight distribution of those were further examined by GPC analysis for selected samples, including initial sulfite softwood (SW) pulp, pretreated pulp, and their oxidized samples that have been recovered after alkaline wash, i.e. betaelimination. The cellulose samples were prepared for analysis by dissolution in a LiCl / DMAc solvent system. The dissolution of cellulosic samples was made through a solvent exchange process. A 50 ±5 mg sample was first put into a tube and 4 mL of milliQ water was added and left overnight to activate the sample. After the water was removed from the tube, the sample was rinsed with acetone and excess of solvent was removed. Acetone, 4 mL, was added to the tube and left overnight to activate the sample. Removalof acetone took place and 4 mL of DMAc solvent was used for washing and immersion of sample for 16 hours. Filtration of solution followed, and the samples were transferred to glass bottles and 5 ml of 90g LiCl / DMAc solvent system were added to the residue, where they were left to stir constantly until it was dissolved. To prepare the sample for analysis, 0.5 ml of sample was further diluted with 4.5 ml of DMAc to adjust the concentration at l.Omg / mL. Sample was filtered and put into the glass vials for GPC analysis.

[0112] Results of the GPC analysis are summarized in Table 4. It can be concluded from the graph in Figure 3 that amorphization of starting pulp doesn’t affect the degree of polymerization. Instead, it is only inducing a decrease in the crystallinity of cellulose, as it is calculated based on13C CPMAS NMR spectroscopy (Figure 1). Furthermore, the betaelimination of the oxidized original pulp resulted in depolymerized cellulose of similar size with the oxidized amorphous pulp, but the poly dispersity is narrower for the amorphous pulp, which showcases that the reaction is more specific and oxidizes cellulose in a more controlled manner.

[0113] Table 4. DP and poly dispersity of selected samples.

[0114] Example 2

[0115] 0.5 g of dry TEMPO-CNF was dispersed in methanol (10 ml). A catalytic amount of concentrated H2SO4 (0.145 ml 98 % H2SO4 / IOO ml methanol) was added and the reaction was stirred at room temperature for 24 hours. The product was recovered by centrifugation (3 times MeOH wash) followed by freeze-drying. The sample was then analysed by NMR, according to the procedure of Fliri et al., see Figure 4. Formation of a,P-unsaturated uronate groups, and functionalization (with O, S or NH-containing reagents) thereof, is demonstrated in Figure 5.

[0116] Example 3

[0117] 1. Pretreatment of cellulose

[0118] LiBr • 3H2O solution was prepared in a separate flask by mixing 1 mol of anhydrous LiBr with 3 mol of milliQ water at room temperature for 2 hours. 8g of softwood sulphite pulp was dissolved in approximately 240 g of the LiBr • 3H2O solution and left to mix for 1 hour at room temperature for pretreatment. The obtained suspension was filtrated and the solids were washed with milliQ water until the condutctivity of the filtrate was below 10 pS cm'1. The pretreated pulp was stored in a refrigerator (4 °C) as never dried pulp (Zhang et al., 2023). The dry matter content of this sample after oven drying at 105 ± 3 °C and calculated to be around 23 %.

[0119] 2 Characterization of pretreated cellulose

[0120] The LiBr • 3H2O pre-treated cellulose sample was characterized by solid state NMR spectroscopy similar to step 2 of Example 1. Following the established protocol for crystallinity determination (Zuckerstatter et al.) and by comparing the obtained peaks in the C4 region, it was possible to identify the transformation from the cellulose I to the cellulose II crystalline allomorph content and calculate the CI from the fitted area (Figure 6). Figure 6 also showing for comparison the NMR spectra of the original untreated pulp and NaOH / urea pretreated pulp according to Example 1.

[0121] The LiBr»3H2O pretreated pulp was calculated to have around 0 % crystallinity index, as shown in Table 5 together with the results of Table 1 (crystallinity index of original untreated pulp and NaOH / urea pretreated pulp). Thus, it was evidenced that both NaOH / urea and LiBr»3H2O pretreatments lead to highly amorphous materials.

[0122] Table 5. Crystallinity of original and pretreated pulps.

[0123] 3. Oxidation of pretreated cellulose

[0124] The LiBr»3H2O pretreated cellulose was oxidized similar to step 3 of Example 1.

[0125] 4. Beta-elimination of the oxidized cellulose

[0126] The oxidized cellulose was subjected for beta-elimination similar to step 4 of Example 1.

[0127] 5. Characterization of oxidized and depolymerized cellulose

[0128] 5a. NMR spectroscopy:

[0129] The number-average degree of polymerization (DP) of the LiBr»3H2O pretreated, oxidized and alkaline washed (beta-elimination step) cellulose was derived from solution state 'H-N R spectroscopy similar to step 5a of Example 1.

[0130] The average DP of said cellulose, together with the DP of oxidized and alkaline washed sulphite pulp and NaOH / urea pretreated pulp according to Table 2 for comparison, is shown in Table 6.

[0131] Table 6. Average DPN of cellulose samples after periodate oxidation and beta-elimination.

[0132] 5b. Gel permeation chromatography (GPC)

[0133] The effect of amorphization / decreased crystallinity on the DP of obtained product and the molecular weight distribution of that was further examined by GPC analysis for LiBr«3H2O pretreated and oxidized pulp that has been recovered after alkaline wash, i.e. beta-elimination. The cellulose sample for the analysis was prepared similar to step 5b of Example 1.

[0134] Results of the GPC analysis are summarized in Table 7, together with the GPC results of Table 4 for comparison.

[0135] Table 7. DP and poly dispersity of selected samples.

[0136] Further, Figure 7 present molar mass distribution of selected cellulose samples using GPC. All oxidized samples have undergone the beta-elimination step prior to analysis. Based on the GPC results, it is clear that both pre-treated samples result in much lower polydispersity compared to the untreated sample, giving proof of concept for increased statistical access to the polymer by a crystallinity reduction pre-treatment.

[0137] Example 4

[0138] 1. WAXS Processing

[0139] Identification of the presence of residual polymorphs was determined through WAXS (wide-angle X-ray scattering) analysis. Rough crystallite sizes for key polymorph reflection planes were determined, using the Scherrer relationship. Both wet and dry samples prepared according to the pretreatment processes of Examples 1 and 3 [LiBrGEEO / NaOH-Urea pre-treated pulp (never dried / freeze-dried)], freeze-dried samples obtained after beta-elimination steps of Examples 1 and 3 [LiBrGEEO / NaOH-Urea pre-treatment MCC oligomers (freeze-dried)], as well as original dry pulp as a reference, were used for measurements. Further, The WAXS diffractograms of different samples are shown in Figure 8, showing the transition from cellulose II hydrate to cellulose II.

[0140] WAXS diffractograms for the recovered dried cello-oligomer materials also indicate that an MCC-like material can be recovered, where the amorphous content can be varied between cellulose II and amorphous material, based on the kinetics of conversion from cellulose Iamorphouscellulose II (involving parallel to anti-parallel chain reorientation) during the ‘amorphisation’ step. Control over these kinetics seems to be easier using LiBr»3H2O, compared to NaOH-Urea pre-treatments.

[0141] 2 SAXS Processing

[0142] The samples similar to WAXS processing were also subjected for SAXS (small-angle X-ray scattering) analysis. The SAXS diffractograms (log I vs. Q) for wet (never-dried) and dry (freeze-dried) samples are shown in Figure 9, and the Kratky plots are shown Figure 10.

[0143] Multiple parameters were extracted from the SAXS data: A) the low-c / ‘Porod’ exponent (n) is related to the 3D surface fractal dimension; related to the relative surface area to volume, after drying. B) the high-t / ‘Lorentzian’ exponent is related to the molecular chain to aggregate ‘smoothness’ (degree of branching), with highest contrast in the water-swollen (never-dried) state. C) the correlation length (Lmeasured in A) is a measure of crystallite / aggregate separation, mainly used to parametrise gels with maximised aggregate separation through solvent-swollen regions (e.g., never-dried). The parameters are shown in Table 8 and the DPN, PDI and crystallinity analytics thereof are shown in Table 9. Crystallite sizes of Table 9 are calculated from peak-fitting of the WAXS diffractograms, using the Scherrer relationship. Further in Table 9, NT refers to non-treated, ND refers to never-dried and FD refers to freeze-dried.

[0144] Table 8. Parameters extracted from SAXS data.

[0145] Table 9. DPN, PDI and crystallinity analytics (CI and Lx) for the never-dried (ND) and freeze-drie (FD) samples. L(i-io) indicating crystallite sizes.a before / after the P-elimination step

[0146] Correlations between PDI and the structural ordering parameters from SAXS and WAXS analysis are presented in Figure 11.

[0147] It was observed that crystallinity index (CI), correlation length ( L), crystallite sizes (L), surface area fractal dimensions (n) and aggregate branching (m) are all correlated according to crystallinity of the samples. As crystallinity is decreased, upon pretreatment: hydrogel correlation length decreases, due to the reduction in crystallite size into more branched (less aggregated) species. Upon drying these samples give higher surface areas. The resulting conclusion is that there is higher statistical access to the polymer, especially in the never-dried state, which is demonstrated by production of low poly dispersity (PDI) cello-oligomers, after oxidation and b-elimination.

[0148] 3. Optical microscopy

[0149] Pulp was also observed by optical microscopy before / after each treatment step as shown by Figure 12 a) dry softwood sulphite pulp, b) rewetted softwood sulfite pulp c) wet amorphous (NaOH-urea pre-treated) pulp, d) freeze-dried amorphous pulp, e) freeze-dried alkaline washed oxidised amorphous pulp, f) rewetted alkaline washed oxidised amorphous pulp. The optical microscopy further evidences that there is a transition from fibrous form of the pulp to a microcrystalline form for the recovered oligoMCC material.

[0150] Numerous other variations and modifications in the invention as illustrated in the specific examples will be apparent to those skilled in the art, and hence it is not intended that the invention be limited to the examples but only as required by the spirit and scope of the appended claims.

[0151] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0152] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0153] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0154] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0155] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0156] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.ACRONYMS LISTAGU anhydroglucose unitCI crystallinity indexCNF cellulose nanofiberCOS cello-oligosaccharidesDMAc dimethylacetamideDMSO dimethyl sulfoxideDP degree of polymerizationHLB hydrophilic and lipophilic balanceLiBr3H2O lithium bromide trihydrateLPMO lytic polysaccharide monooxygenasesNMMO N-methylmorpholine-N-oxideNMR nuclear magnetic resonanceMCC microcrystalline cellulosePDI poly dispersity indexTBAF tetrabutylammonium fluorideTEMPO 2,2,6,6-Tetramethylpiperidine-l-oxylWAXS wide-angle X-ray scattering[Amim]Cl 1 -ally 1 -3 -methylimidazolium chloride[Bmim]Cl 1 -butyl-3 -methylimidazolium chloride [emim][0Ac] 1 -ethyl-3 -methylimidazolium acetate [mTBDH][OAc] 7 -methyl -1,5,7 -tri azabi cy cl o [4.4.0] dec-5 -enium acetateREFERENCESFliri L. et al, “Solution-state nuclear magnetic resonance spectroscopy of crystalline cellulosic materials using a direct dissolution ionic liquid electrolyte”, Nature Protocols, 18, pp. 2084-2123, 2023.Ibbett, R.N., Domvoglou, D. and Fasching, M., “Characterisation of the supramolecular structure of chemically and physically modified regenerated cellulosic fibres by means of high-resolution Carbon-13 solid-state NMR”, Polymer, 48(5), pp. 1287-1296, 2007.Rico del Cerro et al., “Crystallinity reduction and enhancement in the chemical reactivity of cellulose by non-dissolving pre-treatment with tetrabutylphosphonium acetate”, Springer, Volume 27, pages 5545-5562, 2020.Wickholm, K., Larsson, P.T. and Iversen, T., “Assignment of non-crystalline forms in cellulose I by CP / MAS13C NMR spectroscopy”, Carbohydrate Research, 312(3), pp. 123— 129, 1998.Zuckerstatter et al., “The elucidation of cellulose supramolecular structure by13C CP -MAS NMR”, Lenzinger Berichte, Volume 87, pages 38-46, 2009.

Claims

CLAIMS:

1. A selective method for producing cellulose, the method comprising the steps of:- providing cellulose,- reducing crystallinity of the cellulose by pretreatment to obtain a pretreated cellulose,- oxidizing the pretreated cellulose, and- subjecting the oxidized cellulose to beta-elimination.

2. The method according to claim 1, wherein the pretreatment comprises treating the cellulose pulp with a cellulose solvent (dissolving or non-dissolving).

3. The method according to claim 2, wherein the solvent is selected from concentrated alkali, ionic liquids, deep eutectic solvents, molten salt hydrates, N-oxide based solvents and combinations thereof.

4. The method according to any of the preceding claims, wherein the pretreatment comprises treating the cellulose pulp with a reagent comprising NaOH, in particular the mixture of NaOH and urea, lithium bromide trihydrate (LiBr 3H2O), an ionic liquid, such as tetrabutylphosphonium acetate, or N-methylmorpholine-N-oxide (NMMO) hydrate.

5. The method according to any of the preceding claims, wherein the pretreatment comprises a non-dissolving pretreatment.

6. The method according to any of the preceding claims, wherein the obtained pretreated cellulose has a crystallinity index (CI) that is at least 50 %, 60 %, 70 %, 80 % or 90 %, preferably 100 %, lower than CI of the cellulose before pretreatment.

7. The method according to any of the preceding claims, wherein an oxidizing agent used in the oxidation step includes at least one of sodium chlorite (NaCICh), TEMPO, periodate, nitrogen dioxide, oxygen, ozone, air, chlorite, chlorine, hydrogen peroxide, periodate, nitrogen dioxide, such as TEMPO, nitroxyl radicals, hypochlorite, DMD, hypervalent iodine regents, bromate, bromide, nitrite, nitrate, persulphates, permanganate, dichromatesulphuric acid, hypohalites and combinations thereof, preferably periodate or nitroxyl radical.

8. The method according to any of the preceding claims, wherein the stoichiometric ratio of the pretreated cellulose anhydroglucose unit and an oxidizing agent in the oxidation step is in the range 1:0.5 to 1:0.01, preferably in the range 1:0.05: to 1:0.02, such as in the range of 1:0.1 to 1:0.05.

9. The method according to any of the preceding claims, wherein the beta-elimination is performed in an alkaline aqueous solution, preferable having a pH in the range of 8 to 14, more preferably in the range of 9-12.

10. The method according to any of claim 1 to 8, wherein the beta-elimination is performed in an acidic aqueous solution, preferably having a pH in the range of 1 to 6, more preferably in the range of 2 to 4.

11. The method according to claims 1 to 9 or 10, wherein the beta-elimination is performed in an acidic alcohol solution, such as in acidic methanol solution.

12. The method according to any of the preceding claims, wherein the cellulose obtained by beta-elimination is fractionated, preferably by water soluble / insoluble fractionation.

13. The method according to any of the preceding claims, wherein the cellulose obtained by beta-elimination is, after optional fractionation, chemically conjugated, wherein the conjugation is preferably performed with primary amine and / or alcohol.

14. Cellulose having a degree of polymerization in the range of 5 to 50 and having a poly dispersity index in the range of 1 to 3.

15. The cellulose according to claim 14, wherein the cellulose is microcrystalline cellulose.

16. The cellulose according to claim 14 or 15, wherein the cellulose is obtained by the method according to any of claims 1 to 13.

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