Method for producing microcrystalline or nanocrystalline cellulose

Abstract

The present invention relates to a method for producing a micro- or nanocrystalline cellulose composition from virgin cellulose having amorphous and crystalline cellulose phases, the method comprising the following steps: (A) contacting virgin cellulose with a first solvent, the first solvent being an aqueous solution containing 40 to 65% by weight of ZnCl, based on the total weight of ZnCl and water; (B) dissolving the amorphous cellulose phase, thereby dissolving the amorphous cellulose phase preferentially over the crystalline cellulose phase; and (C) separating the dissolved amorphous cellulose from the crystalline cellulose. Preferably, the micro- or nanocellulose obtained in step C has an XRD-I structure, which can then be contacted with a second solvent containing 65 to 90% by weight of ZnCl in water to produce delaminated cellulose with an XRD-II structure. The present invention also relates to micro- or nanocrystalline cellulose with an XRD-I structure and nanocrystalline cellulose with an XRD-II structure, or mixtures thereof, which have high crystallinity and purity, and uses thereof.

Description

[Technical Field]

[0001] This invention relates to a method for producing microcrystalline or nanocrystalline cellulose with a high degree of crystallinity. The invention also relates to microcrystalline or nanocrystalline cellulose with a high degree of crystallinity and mixtures thereof, as well as their uses. [Background technology]

[0002] Cellulose is the most abundant natural polymer in nature and one of the most promising polymer resources. It is renewable, biodegradable, and biocompatible. However, due to its partially crystalline structure and dense chain packing via numerous intermolecular and intramolecular hydrogen bonds, cellulose does not melt and does not dissolve in water or common solvents, making chemical processing generally extremely difficult.

[0003] For the past several decades, several cellulose solvent systems have been available for dissolving or reacting cellulose, such as the viscose process (CS2), LiCl / N,N-dimethylacetamide (DMAc), DMSO / paraformaldehyde (PF), and aqueous solutions of some metal complexes.

[0004] However, these conventional cellulose solvent systems have drawbacks such as limited solubility, toxicity, high cost, solvent recovery issues, uncontrollable side reactions, and instability during cellulose processing and / or derivatization.

[0005] The lyocell process uses N-methylmorpholine-N-oxide (NMMO) to directly dissolve cellulose, but it also has several drawbacks, including the formation of by-products, cellulose degradation, and high costs.

[0006] In recent years, another method has been developed for dissolving cellulose in NaOH / urea aqueous solution, which allows for dissolution of cellulose within 2 minutes and pre-cooling to -12°C. However, this dissolution method is limited in terms of cellulose concentration and degree of polymerization (DOP).

[0007] Recently, ionic liquids (ILs) have attracted considerable attention due to their high electrochemical and thermal stability, non-flammability, and controllable solubility. Ionic liquids often represent a new class of highly polar solvents that are fluid at room temperature and composed entirely of ionic species. Due to their low vapor pressure and the absence of the formation of toxic or explosive gases, ionic liquids are considered "low-pollution solvents." Furthermore, ionic liquids exhibit excellent solubility in cellulose, thereby expanding its comprehensive use. After precipitation and / or solidification, molding materials exhibiting good physical strength, such as threads, fibers, sheets, films, and particles, can be formed from these solutions.

[0008] Ioelovich and Leykin, in their report in the Research Journal of Nanoscience and Engineering, Volume 2, Issue 4, 2018, pp. 10-13, describe a method for producing micro or nanocrystalline cellulose compositions, which involves contact between virgin cellulose and concentrated acid, followed by mechanical treatment.

[0009] Ioelovich and Leykin describe a method involving the treatment of cellulose with dilute boiling sulfuric acid followed by sonication in Cellulose Chemistry and Technology, 40(5), 2006, 313-317.

[0010] In Biomass and Bioenergy 81(2015)584-591, Tan et al. describe a method for producing nanocrystalline cellulose compositions, which involves contacting virgin cellulose with ionic liquid 1-butyl-3-methylimidazolium bisulfate (BmimHSO4) as a solvent.

[0011] The drawbacks of the prior art methods mentioned are that they use very expensive and novel solvents and require very long reaction times to complete. The Bmim ionic liquid of Tan and Ioelovich acid take up to 10 hours. The enzymatic pathway takes even longer; up to 20-40 hours.

[0012] WO2017 / 055407 describes that improved properties can be obtained from nanocrystalline cellulose compositions obtained by exfoliating virgin cellulose in an ionic liquid, such as hydrated zinc chloride, without dissolving it.

[0013] CN102433786 describes a method for producing micro-nanosellol by mechanical chemistry, which is obtained by mixing and grinding in a solution that can be a salt solution of zinc chloride.

[0014] CN102093484 describes a method for producing nanocrystalline cellulose, which involves dissociating a cellulose raw material in a zinc chloride solution, dispersing it rapidly and uniformly under heating conditions, adding a dilute acid to precipitate it, and then subjecting it to ultrasonic dispersion treatment or wet grinding to obtain nanocrystalline cellulose.

[0015] A drawback of this prior art method is that it does not produce highly crystallin and high-purity micro or nanocellulose. In cellulose dissolution, amorphous materials and oligomers with low aspect ratios and low degrees of polymerization present in virgin cellulose also dissolve and partially precipitate during the formation of regenerated cellulose and the subsequent molding process. This can lead to a decrease in the properties of the resulting product, such as chemical stability and mechanical properties.

[0016] Prior art dissolution methods can also lead to the irreversible conversion of cellulose XRD-I crystal structure to cellulose XRD-II structure, which is undesirable in certain applications (e.g., high-quality fibers) from the standpoint of the physical properties of the resulting cellulose product.

[0017] The fundamental problem of the present invention is to provide a method that does not have at least one of the aforementioned drawbacks, in particular a simple and inexpensive method, and a method that yields cellulose having improved properties, especially high crystallinity and purity. [Overview of the project]

[0018] The present invention provides a method for producing microcrystalline or nanocrystalline cellulose from virgin cellulose having an amorphous cellulose phase and a crystalline cellulose phase, comprising the following steps: (A) A step of contacting virgin cellulose with a first solvent, wherein the first solvent is an aqueous solution containing ZnCl2 in an amount of 40 to 65% by weight, preferably 40 to 60% by weight, more preferably 40 to 55% by weight, relative to the total weight of ZnCl2 and water, and preferably the amount of virgin cellulose is 1 to 10% by weight of the amount of the first solvent. (B) A step of dissolving the amorphous cellulose phase, thereby preferentially dissolving the amorphous cellulose phase over the crystalline cellulose phase. (C) Steps to separate dissolved amorphous cellulose from crystalline cellulose. These problems are addressed by providing methods that include [specific methods].

[0019] This method allows for the reduction of amorphous material (amorphous material and oligomers) content in natural cellulose while avoiding impact on the integrity and crystalline structure of cellulose. Because this method can be performed at low temperatures and is fast, it is cost-effective and environmentally friendly, yielding microcellulose and / or nanocellulose materials, specifically micro and nanocellulose materials with high purity and crystallinity (by XRD), high average degree of polymerization (DOP), and high crystal content exhibiting a high average aspect ratio. This results in improved physical properties of the cellulose product.

[0020] The features and advantages of the present invention will be understood by referring to the drawings below. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 is a schematic diagram of the method according to the invention, which comprises a first step ST-1 of contacting a cellulose-containing feedstock F comprising crystalline cellulose Cx and amorphous cellulose A with a first solvent Z1 to produce a product stream P1 comprising highly crystalline cellulose XRD-I type and a dissolved amorphous product stream [A], and the amorphous product stream [A] is subjected to a separation step SEP comprising the addition of an antisolvent Z3 to produce a product stream P3 comprising a precipitate comprising (poly)sugars, in particular sugar monomers and oligomers (e.g. glucose and C6 oligomers), and a spent solvent stream Z0, and the spent solvent stream Z0 is sent to a solvent purification / concentration step PUR. [Figure 2] Figure 2 is a schematic diagram of a second method embodiment, in which the product stream P1 in the method described in Figure 1a is contacted with a second solvent Z2 to produce a product stream [Cx] comprising dissolved cellulose. The dissolved cellulose stream [Cx] can subsequently be subjected to a shaping or particle formation step SP and a precipitation step for producing highly crystalline cellulose type II (product P2) before, during or after the shaping step SP. [Figure 3] Figure 3 is a schematic diagram of a third method embodiment, in which a third method step ST-3 is added to the method described in Figure 2, and the dissolved cellulose product stream [Cx] is contacted with an antisolvent Z3 to produce a product stream P2 comprising precipitated highly crystalline cellulose type II and a spent solvent stream Z0, and the spent solvent stream Z0 is sent to the solvent purification in step PUR. [Figure 4]Figure 4 is a schematic diagram of a fourth method embodiment, where the feedstock F contains crystalline cellulose Cx, amorphous cellulose A, hemicellulose HC, and lignin L. In this feedstock, ST-1 produces a product stream [Cx,L] containing undissolved crystalline cellulose CxI type and lignin L, and a product stream [A,HC] containing dissolved amorphous cellulose A and hemicellulose HC. The product stream [A,HC] is subjected to a separation step SEP by the addition of an antisolvent Z3, resulting in a product stream P4 containing xylose, C5 oligomers, glucose, and C6 oligomers, and the used solvent Z0 is sent to PUR. In step ST-2, the product stream [Cx,L] is contacted with a second solvent Z2 to produce dissolved crystalline cellulose [Cx] and undissolved lignin L. In ST-3, the dissolved crystalline cellulose Cx is contacted with an antisolvent Z3, resulting in a product stream P2 containing high XRD cellulose II and the used solvent Z0, and the used solvent Z0 is sent to PUR. [Figure 5] Figure 5 is a schematic diagram of a fifth method embodiment. In the method described in Figure 4A, in step ST-2, a basic solvent Z4 (e.g., NaOH, KOH) is used instead of the second solvent Z2 to produce a separated phase of dissolved lignin [L] and dissolved crystalline cellulose [Cx]. The dissolved lignin [L] can be separated, and the product stream containing dissolved cellulose [Cx] is converted in the next step to a product stream P1 containing high XRD cellulose I.

Embodiments for Carrying out the Invention

[0022] In the method according to the present invention, in step A (step ST-1 shown in Figure 1), virgin cellulose is contacted with a first solvent, and the first solvent is an aqueous solution containing 40 to 65% by weight, preferably 40 to 60% by weight, more preferably 40 to 55% by weight of ZnCl2 based on the total weight of ZnCl2 and water.

[0023] The first solvent is a ZnCl2-based molten salt diluted with water to be a mild solvent that effectively and preferentially dissolves the amorphous phase, meaning that dissolution can be achieved in a relatively short time without substantially dissolving the crystalline phase. A hydrated inorganic molten salt means a salt that, in its undiluted form, has a melting temperature of less than 100°C. The hydrated molten salt is preferably ZnCl2.nH2O, where n=2 to 6, preferably n=4, which is relatively inexpensive and very effective. This is diluted so that the diluted aqueous solution contains 40 to 65% by weight of ZnCl2 in water. For example, ZnCl2.4H2O can be diluted with 20 or 30% by weight of water to form solvents containing 52.4% and 45.8% by weight of ZnCl2. The required ZnCl2 concentration can also be obtained by adding a concentrated ZnCl2 solution to a recycled and more diluted ZnCl2 solution. Higher concentrations are advantageous for accelerating the dissolution of the amorphous cellulose phase, but the concentration should not exceed 65% by weight. Virgin cellulose has an XRD-I type crystalline structure. It was found that when the first solvent has a relatively low ZnCl2 concentration of less than 65% by weight, the XRD-I type crystalline structure of virgin cellulose is maintained, but the degree of crystallinity can be improved by selective removal of the amorphous phase. At ZnCl2 concentrations exceeding approximately 65% ​​by weight, a transition from the XRD-I type crystalline structure to the XRD-II type crystalline structure was observed.

[0024] Virgin cellulose refers to cellulose having an XRD-I type crystalline structure, as found in biomass. It can be very pure virgin cellulose, such as cotton linters, or a less pure bio-based material. Virgin cellulose may be contained in biomass further containing lignin and / or hemicellulose. In that case, the biomass containing virgin cellulose and lignin and / or hemicellulose is brought into contact with a first solvent and further treated as described below.

[0025] Virgin cellulose derived from biomass may contain free water. The amount of water in the ZnCl2 solvent specified herein must also take into account the free water in the biomass feedstock. Therefore, biomass containing free water can be brought into contact with a more concentrated ZnCl2 solution, but the ZnCl2 concentration in the water, including the water in the biomass, should not exceed 65% by weight. If the water content in the biomass is too high to obtain an appropriate ZnCl2 concentration, the biomass is dried. Drying is usually carried out at about 120°C until a residual amount of free water of 7% by weight or less, preferably 5% by weight or less, is achieved.

[0026] The amount of virgin cellulose in the first solution is preferably 1 to 10% by weight, preferably 2 to 9% by weight, and more preferably 3 to 8% by weight, of the amount of the first solvent. From the viewpoint of productivity, a large amount of cellulose is generally preferred, but if the amount is too large, a solution that is too viscous may be produced, making it difficult to handle, for example, for separating precipitated cellulose crystals. When using biomass containing cellulose and hemicellulose and / or lignin, the amount of biomass to be contacted with the first solvent in step A is preferably selected so that the amount of virgin cellulose therein is 1 to 10% by weight.

[0027] The term "preferential dissolution" in step B means dissolving substantially more cellulose from the amorphous phase than from the crystalline phase. The crystalline phase preferably remains substantially undissolved, and preferably maintains an XRD crystallinity of 70, 80, 85, or even 90% of that of virgin cellulose. Dissolution of crystalline cellulose is prevented by further dilution of the solvent, relatively low temperatures, quenching, and / or the addition of proton scavengers.

[0028] In this method, the temperature of step B is preferably below 80°C, more preferably below 70, 60, and even below 50°C. Lower temperatures result in milder conditions and a greater tendency to dissolve only the amorphous phase, but also increase the time required to complete the process. Typically, higher concentrations of ZnCl2 are preferably combined with lower temperatures, and vice versa. Alternatively, it may be preferable to carry out step A, the contact step, at a higher temperature, for example, 50-80°C, and then quench after a predetermined optimal contact time to prevent further dissolution of crystalline cellulose. Quenching means rapidly lowering the temperature. An alternative or additional measure is rapid dilution with water.

[0029] The first solvent is free of protic acids and more preferably also contains a proton scavenger. It has been found that the absence of protic acids and the presence of a proton scavenger prevent a decrease in the degree of polymerization of the product, prevent conversion to type II crystals, and / or allow the use of higher temperatures and higher concentrations of salt. Suitable proton scavengers include oxides and hydroxides of alkali metals and alkaline earth metals, and oxides and hydroxides of non-precious metal transition metals. The use of oxides or hydroxides of the corresponding molten salt is desirable. For example, when zinc chloride hydrate is used as an inorganic molten salt, preferred proton scavengers are ZnO and Zn(OH)2. It should be noted that the term "solution containing a proton scavenger" also includes solutions to which a proton scavenger has been added, since the addition of a proton scavenger, preferably ZnO or Zn(OH)2, may cause conversion upon contact with the ZnCl2 solution.

[0030] The micro or nanocrystalline cellulose obtained in step B or step C contains cellulose with an XRD-I structure and has higher purity and XRD crystallinity than the initial virgin cellulose material. The cellulose obtained in step B mainly contains cellulose with an XRD-I structure. In this specification, the term "mainly" means at least 50, 60, 70, 80, 85, and ideally 90%. Preferably, the XRD crystallinity of the obtained crystalline cellulose is at least 5, preferably at least 10%, higher than that of virgin cellulose, and more preferably, the XRD crystallinity of the obtained crystalline cellulose is at least 85%, preferably at least 90%. The resulting product is particularly useful for the production of fibers or sheets, for use in coatings, or for use as an excipient. It should be noted that in this specification, the terms micro or nanocellulose are used for the product obtained from step 1, and the term nanocellulose is used for the product obtained from step 2. The cellulose crystals with an XRD-I structure obtained in step 1 may also have nanoscale sizes and may be referred to as both microcellulose and nanocellulose in this document.

[0031] The size and shape of cellulose particles, particularly the aspect ratio (AR), can be investigated by scanning electron microscopy. The XRD crystallinity of the sample can be determined by the X-ray diffraction method described below. The average degree of polymerization (DP) can be measured by the viscosity method using a cadxene dilution solution of cellulose. Descriptions of the measurement methods mentioned can be found in the references listed in Research Journal of Nanoscience and Engineering Vol2, Issue4, 2018, PP10-13 (M. Ioelovich).

[0032] Preferably, the method further comprises step E (step SEP in Figure 1) in which a coagulant is added to the dissolved amorphous cellulose obtained in step C to precipitate the amorphous cellulose, and then optionally, preferably, the precipitated amorphous cellulose is separated. The separated product contains a polysaccharide containing oligomeric and monomeric sugars, optionally containing sugar oligomers and monomers of C5 in addition to C6. The present invention also relates to a polysaccharide containing oligomeric and monomeric sugars prepared from the precipitate of dissolved amorphous cellulose obtained in step E of the method. This polysaccharide can be used as a prebiotic food additive.

[0033] Suitable coagulants are reverse solvents; in particular, C1-C8 alcohols and ketones, especially linear and branched C1-C4 alcohols, such as methanol, ethanol, propanol, and isopropanol, can be used. Particularly preferred ketones include C3-C5 ketones, such as acetone and methyl ethyl ketone (MEK). Preferred coagulants are acetone, ethanol, and t-butyl alcohol. Separation and washing of the solids can be carried out by either centrifugation or filtration. Cold water can also be used, which is effective for precipitating polysaccharides but not so effective for completely precipitating small polysaccharides and sugar monomers.

[0034] As described, the micro or nanocrystals obtained in step 1 are useful in themselves, but can also be used as starting materials in the subsequent step 2 to produce nanocellulose with an XRD-II structure having very high purity and high crystallinity. In this embodiment, the method comprises a further step D (step ST-2 shown in Figure 2) in which the crystalline cellulose obtained in step C is contacted with a second solvent containing 65-90% by weight, preferably 70-85% by weight, of ZnCl2, preferably molten salt hydrate ZnCl2.nH2O (n=1-4) in water, the second solvent preferably does not contain protic acids, and most preferably also contains a proton scavenger as described above, preferably ZnO or Zn(OH)2.

[0035] In step D, the second solvent has a higher ZnCl2 concentration and therefore has a higher dissolving power than the first solvent, i.e., it is stronger than the first solvent. The microcellulose XRD-I structure is a microcrystalline structure with a low aspect ratio containing stacked layers, and it is thought that in step D, these layers are exfoliated to form nanocellulose crystals with a high aspect ratio. The exfoliated cellulose obtained in step D contains, preferably mainly, cellulose with an XRD-II structure. Nanocellulose having the XRD-II structure can be advantageously used, for example, in paper coatings. An advantage of the method of the present invention over the method of WO2017 / 055407 is that it produces nanocellulose XRD-II with higher purity and higher crystallinity, which leads to better mechanical properties and chemical stability.

[0036] During contact with the second solvent, delamination occurs while minimizing hydrolysis of sugars and low-DP oligomers and minimizing dissolution of cellulose nanocrystals. Hydrolysis of cellulose leads to the formation of sugars and low-DP oligomers, and molded articles from such compositions may consequently have degraded properties and develop a brownish color as a result of decomposition; therefore, it is preferable to minimize it. Accordingly, an acid-free second solvent and, most preferably, a proton scavenger are used. However, even when an acid-free solvent is used together with a proton scavenger, care must be taken to prevent dissolution and hydrolysis of cellulose by appropriately selecting the salt concentration in the second solvent, contact temperature, and contact time so that delamination is achieved while minimizing cellulose dissolution. Contact with the second solvent may be carried out at a higher temperature, for example, about 70°C, but quenching must be performed after a predetermined optimal contact time to prevent dissolution and / or hydrolysis of crystalline type II nanocellulose.

[0037] After dissolving type I cellulose in the second solvent, a clear liquid of dissolved and exfoliated type II nanocrystals is formed. The dissolved and exfoliated type II nanocrystals are preferably precipitated by adding a reverse solvent. Preferably, water is used as the reverse solvent, and is added in an amount that dilutes the ZnCl2 concentration to 10-30% by weight, preferably 15-25% by weight, and most preferably about 20% by weight. Preferably, water is added to dilute the solution to a concentration of at least 10%, preferably at least 15% by weight, in order to avoid precipitation of dissolved sugar oligomers and to facilitate the regeneration of the solution in the first or second solvent. Preferably, dilution is carried out to a concentration of 25 or 30% by weight or less, because if the concentration is higher than that, precipitation will be too slow and the yield of cellulose type II crystals will decrease. To allow the precipitation of type II crystals to occur, a sufficient time of at least 10 minutes should usually be allowed. The cellulose nanocrystals can be separated from the solution by filtration or centrifugation, and then washed with (deionized) water to remove ZnCl2.

[0038] Virgin cellulose is preferably derived from a bio-based material. The bio-based material may also contain lignin and / or hemicellulose in addition to virgin cellulose. Lignin and / or hemicellulose may be removed and separated from virgin cellulose before the method of the present invention, but the starting material used in this method may also be a bio-based material containing lignin and / or hemicellulose in addition to virgin cellulose. In that case, amorphous cellulose and optional hemicellulose are dissolved in step B, and in separation step C, the dissolved amorphous cellulose and optional hemicellulose are separated from the phase containing micro or nanocellulose and lignin, for example, by filtration. Lignin is substantially insoluble in aqueous ZnCl2 solvent and is separated as a solid in step C together with the resulting XRD-I type solid micro or nanocellulose.

[0039] When the objective is to produce pure micro or nanocellulose of the XRD-I type structure, lignin can be separated from the resulting cellulose. Therefore, in any step H, the crystalline cellulose and lignin are treated with a solvent in which lignin is dissolved but the crystalline cellulose phase is not, and the dissolved lignin is separated from the solid crystalline cellulose phase. The crystalline cellulose can then be treated as described above. Suitable solvents for dissolving lignin are basic solvents or organic solvents known in the art, preferably basic solvents containing KOH or NaOH in water. However, lignin can be left in the resulting cellulose if, for example, to produce a lignin-cellulose XRD-I type composite material, or if the subsequent step D is carried out as described below.

[0040] Nanocellulose having XRD-II type cellulose with high crystallinity and purity can be obtained from biomass containing virgin cellulose, lignin, and optional hemicellulose by the method described above, which includes step D, after step C, contacting the crystalline cellulose and lignin with a second solvent to produce exfoliated crystalline cellulose. Step D produces a clear solution of exfoliated nanocellulose crystals, allowing separation of the solution containing nanocellulose crystals from the undissolved lignin. In an optional step G, lignin can be separated from the exfoliated crystalline cellulose, preferably by centrifugation and / or filtration.

[0041] In this method, the first and second solvents used in steps A and D are preferably regenerated by removing impurities and / or diluents and recycling the regenerated solvent into the method. A particular advantage of this method is that zinc chloride is used at different concentrations in the two steps so that the first and second solutions can be easily regenerated in the same regeneration step.

[0042] The present invention also relates to a micro or nanocrystalline cellulose-containing product P1 that can be obtained by any of the above embodiments of the present invention, which has an XRD-I type crystalline structure, an XRD crystallinity of at least 85%, preferably at least 90%, and a (poly)sugar content of less than 10% by weight, preferably less than 5% by weight, more preferably less than 2% by weight, and preferably has a degree of polymerization DP of at least 200 and an aspect ratio of less than 10.

[0043] The present invention also relates to a nanocrystalline cellulose-containing product P2 that can be obtained by any of the above embodiments of the present invention, wherein it has an XRD-II type structure, an XRD crystallinity of at least 80%, preferably at least 85%, more preferably at least 90%, and a (poly)sugar content of less than 15% by weight, preferably less than 10% by weight, more preferably less than 5% by weight, most preferably less than 2% by weight, and preferably has a degree of polymerization DP of 100 to 200 and an aspect ratio of at least 20. It should be noted that the crystallinity values ​​of type I and type II crystals are not comparable. The crystallinity of type II products may be measured lower than that of type I products because type II products may contain very small crystals that escape XRD detection.

[0044] The present invention also relates to a cellulose composition comprising a mixture of type I microcrystalline or nanocrystalline cellulose and type II nanocrystalline cellulose obtained by the method of the present invention, wherein the mixture has high crystallinity and purity, and preferably the mixture is obtained by method A, which preferably comprises mixing XRD-I type microcrystalline or nanocrystalline cellulose obtained by the method of the present invention comprising steps A, B and C as described above, with XRD-II type nanocrystalline cellulose obtained by the method of the present invention comprising step D as described above. Alternatively, the mixture is obtained by method B, which comprises steps A, B, C and D as described above, in which step D a partial conversion from XRD-I type cellulose to XRD-II type cellulose is made, and the partial conversion is preferably made by choosing a lower temperature and / or a shorter contact time before the addition of the reverse solvent, or a combination thereof. A ZnCl2 concentration lower than about 65% by weight is undesirable because it does not result in type II conversion.

[0045] Optionally, the cellulose composition may further contain lignin. The lignin may be mixed separately with the above-described XRD-I type cellulose and XRD-II type cellulose, or, if starting from a bio-based material containing lignin as described above, it may be mixed by not separating or completely separating the lignin from the above-described method for producing type I and / or type II.

[0046] The present invention also relates to the use of a cellulose composition of the present invention, comprising high-purity micro or nanocellulose with a high degree of crystallinity of the XRD-I structure of the present invention, high-purity nanocellulose with a high degree of crystallinity of the XRD-II structure of the present invention, or a mixture thereof, as a coating material, an excipient, a material for manufacturing fibers or films preferably used in the manufacture of cellulose molded articles, preferably packaging films, yarns, and fabrics, or as a starting material for the preparation of carbon fibers.

[0047] Accordingly, the present invention has been described with reference to the specific embodiments discussed above. It should be recognized that these embodiments are open to various modifications and alternative forms well known to those skilled in the art.

[0048] In addition to the foregoing, further modifications may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Therefore, while specific embodiments have been described, these are merely examples and do not limit the scope of the invention. The invention will be further illustrated by the following embodiments. [Examples]

[0049] Experimental method Crystal type measurement by XRD The cellulose products obtained in the experiment are characterized by XRD. XRD measurements are performed according to the method described in J. Polym. Environ 19 (2011) 726-731: Preparation of cellulose nanocrystals using an Ionic liquid by Z. Man, N. Muhammand, A. Sarwono, MA Bustam, M. Vignesh Kumar, and S. Rafiq. The crystal is identified as either type I or type II by the peak position, where type I has a 2θ of 22.6° (

[0200] reflection) and type II has 2θ of 20° and 22° (

[0110] and

[0020] reflections).

[0050] XRD crystallinity measurement The crystallinity of the product (crystallinity index in the above literature) is expressed by Segull's formula: CrI=(I 002 -I am ) / I 002 (In the formula, I 002 This is the overall intensity of the peak at 2θ = 22.6° for type I cellulose or 22° for type II cellulose. am (This is the baseline intensity when 2θ is approximately 18°) It was calculated using [this method].

[0051] Measurement of Crystal Size by XRD The crystal size of cellulose is calculated from the Scherrer's equation:

[0052] [Number]

[0053] (where β is the microcrystal size, λ is the wavelength of the incident X-ray, τ is the full width at half maximum (FWHM) of the XRD peak, and θ is the diffraction angle corresponding to the plane) and is calculated from the XRD results.

[0054] Measurement of Cellulose Yield and Cellulose Hydrolysis The soluble (poly)saccharide is (Poly)saccharide mass balance % = 1 - M prec cel / M in cel (where M)<000001><0> cel is the weight of the dry micro or nanocellulose obtained in the experiment, and M in cel is the weight of the dry cellulose put into the reactor) and is measured based on this. The term (poly)saccharide means polysaccharides such as sugars and oligomeric sugars. The obtained cellulose was subjected to convective furnace drying of the biomass at 45 °C for 24 to 48 hours, checking the weight regularly (usually every 3 hours) until the dry biomass weight did not change by more than 1 wt% per hour according to the NREL laboratory procedure.

[0055] Materials Used In all the experiments described below, the cellulose substrate is cotton linter microcrystalline cellulose (MCC) ex-Sigma C6288. The characterization by XRD shows that the XRD-I type is ±≤80%. ZnCl2 and ZnO were also obtained from Sigma.

[0056] Example 1 Process 1 <00><00226>A first solvent was prepared by adding 0.5 g of ZnO powder to 100 g of a 60 wt% ZnCl2 aqueous solution, and the mixture was kept at room temperature overnight with stirring (120 rpm / min). The remaining unreacted ZnO solid was removed from the solution by filtration. The obtained 100 g of solvent was mixed with 5 g of cotton liner cellulose with stirring (480 rpm / min) and kept at room temperature for 30 minutes with stirring. The obtained cellulose crystals were separated from the solution by filtration through a glass filter and washed eight times with deionized water to remove ZnCl2. A 20 wt% suspension containing cellulose microcrystals in water was obtained.

[0057] Prior to XRD measurement, the product was vacuum-dried at room temperature. XRD measurements showed that the crystallinity of the XRD-I material was higher (>85%) compared to the initial cellulose (80%).

[0058] The amount of (poly)sugars was investigated by further washing the cellulose XRD-I material with water. Almost no (poly)sugars were present in the sample (less than 5% by weight), which is desirable because (poly)sugars may, and indeed do, decompose during subsequent processing.

[0059] Process 2 The second solvent used in step 2 was prepared by mixing 0.5 g of ZnO powder with 100 g of a 65% ZnCl2 aqueous solution and keeping it at room temperature overnight with stirring. The remaining solid was removed from the solution by filtration. 100 g of the liquid was mixed with 5 g of XRD-I phase material and stirred at room temperature for 30 minutes until the solution became clear. 225 g of deionized water was added to the solution with stirring to reduce the ZnCl2 concentration to 20% by weight, and cellulose was precipitated from the second solution. The sample was stirred for 20 minutes to precipitate cellulose nanocrystals. The cellulose nanocrystals were separated from the solution by centrifugation (6000 rpm / min; 10 min), washed with deionized water until no trace of ZnCl2 remained, and stored as a 20% by weight suspension of nanocellulose in water.

[0060] Prior to XRD measurement, the sample was dried overnight at room temperature by vacuum drying. XRD measurement showed that the cellulose XRD-I phase was converted to the cellulose XRD-II phase. obtained The crystallinity exceeded 80%, and the formation of (poly)sugars was less than 5% by weight. In the second step, the XRD-I phase material from step 1 is converted to XRD-II by treatment with a 65% ZnCl2 solvent. The yield of highly crystallinity type II cellulose is approximately 75-80% of the virgin cellulose.

[0061] Example 2 The procedure is the same as in Example 1, but steps 1 and 2 are performed at a higher temperature of T=70°C. Higher temperatures result in shorter processing times. At 70°C, the processing time for both steps 1 and 2 is reduced to 15 minutes, but the crystallinity of the product remains substantially unchanged. Also, at 70°C, type I cellulose was produced in step 1, and type II cellulose crystals were produced in step 2.

[0062] Example 3 The procedure is the same as in Example 1, but step 1 or 2 is performed at a higher temperature of T=70°C. The higher the temperature, the shorter the processing time; at 70°C, the processing time is reduced to 15 minutes, but the crystallinity of the product remains substantially unchanged.

[0063] Example 4 The procedure was the same as in Example 2, but the amounts of cellulose and cellulose XRD-I in steps 1 and 2 were set to 8 g. Although the viscosity of the mixture increased and the processing time was extended (30 minutes), the crystallinity of the product remained substantially unchanged.

[0064] High cellulose concentrations (over 10% by weight in step 1 and over 8% by weight in step 2) were undesirable in this experimental setup because the solution viscosity became too high, preventing proper mixing and separation. Furthermore, it was found that only a very small amount of cellulose dissolved at ZnCl2 concentrations below 62.5% by weight, almost no cellulose dissolved below 60% by weight, and dissolved within 30 minutes at concentrations above approximately 62.5–65% by weight. At concentrations above 75% by weight, the solvent viscosity became extremely high, making it difficult to mix and dissolve an appropriate amount of cellulose in this experimental setup.

[0065] Comparative Experiment A (Based on Example 5 of Prior Art CN102433786) A method for producing nanocellulose includes the following steps: 1 g of cotton linter microcrystalline cellulose (MCC) ex-Sigma C6288 is added to 20 g of 70% ZnCl2 aqueous solution, placed in a basket mill for 180 minutes, then 50 g of water is added to the cellulose / ZnCl2 mixture to precipitate the cellulose at a final ZnCl2 concentration of 20% by weight, and then... The result The mixture is centrifuged (centrifugation speed: 4000 rpm, 15 minutes), the upper layer solution is removed, and the lower layer of cellulose jelly is separated to obtain nanocellulose.

[0066] Comparative Experiment B (Based on Example 5 of Prior Art CN102093484) The method for producing nanocellulose in this comparative experiment includes the following steps: 5 g of cotton linters is added to 150 g of 65% ZnCl2 aqueous solution, the mixture is heated in an oil bath at 90°C for 1 hour and homogenized at high speed (12,000 rpm) to obtain a clear cellulose / ZnCl2 solution. Next, 450 ml of 0.5% hydrochloric acid is added to the cellulose / ZnCl2 solution to precipitate the cellulose, the layers are separated by centrifugation, the upper layer of ZnCl2 and acid solution is removed, the lower layer of cellulose gum is centrifuged eight times with water, and the lower layer is ground in a wet ball mill for 5 hours to obtain nanocrystalline cellulose.

[0067] The properties of the nanocellulose obtained in comparative experiments A and B were clarified using XRD. A transition from the XRD-I structure to the XRD-II crystalline structure of the cotton linter was observed. The crystallinity of the product was 40-50%. The product contained 10-25% by weight of (poly)sugar.

[0068] Comparative experiment C (based on prior art WO2017055407) The solvent was prepared by the following method: 0.5 g of ZnO powder was added to 100 g of a 70 wt% ZnCl2 aqueous solution, and the mixture was left at room temperature overnight with stirring (120 rpm / min). The remaining solid was removed from the solution by filtration. obtained 100 g of solvent was mixed with 5 g of cotton liner cellulose under stirring (480 rpm / min), and the mixture was stirred at room temperature for 30 minutes until the solution became clear. Then, 250 g of deionized water was added to the solution under stirring. The sample was stirred for 20 minutes to precipitate the cellulose nanocrystals. The cellulose nanocrystals were separated from the solution by centrifugation (6000 rpm / min; 10 min) and washed eight times with deionized water to remove ZnCl2. A 20 wt% suspension containing nanocellulose in water was obtained.

[0069] Before XRD measurement, the samples were vacuum-dried at room temperature. XRD measurement showed that XRD-I transitioned to the XRD-II crystalline structure. The degree of crystallinity was 50–70%. The amount of cotton liner converted to (poly)sugar was less than 10% by weight. The yield of relatively low-crystallinity type II cellulose was approximately 75–80% of virgin cellulose.

[0070] Comparative Experiment D Comparative experiment D was conducted in accordance with the prior art by Xiao Yun Tan, Sharifah Bee Abd Hamid, and Chin Wei Lai, Biomass and Bioenergy 81 (2015) 584-591; "Preparation of high crystallinity cellulose nanocrystals (CNCs) by ionic liquid solvolysis".

[0071] In the experiment, pure 1-butyl-3-methylimidazolium bisulfate (BmimHSO4) was used as the solvolysis catalyst and solvent. The experiment included adding 10% by mass of cotton linter to BmimHSO4 with vigorous stirring, heating at 90°C for 1.5 hours on a magnetic hot plate stirrer, and then quenching by adding 20 cm of cold deionized water to the reaction mixture. After an off-white precipitate of cellulose was formed, the mixture was sonicated at room temperature for 15 minutes, and the suspension was washed with deionized water by repeated centrifugation to isolate the nanocrystalline cellulose. The precipitate was freeze-dried and stored in a refrigerator at 4°C until use.

[0072] XRD measurements revealed type I crystals with an XRD crystallinity of 85%. Polysaccharides (oligomers) and sugars were hardly formed (less than 10%).

[0073] It was found that it is impossible to convert type I cellulose crystals to type II cellulose crystals in the BmimHSO4 solvent. The BmimHSO4 solvent was not pre-diluted, and when the temperature was raised to 120°C and 140°C, it turned brown, probably due to decomposition. The invention as described in the original claims of the patent application is listed below. [1] A method for producing microcrystalline cellulose from virgin cellulose having an amorphous cellulose phase and a crystalline cellulose phase, comprising the following steps: (A) Virgin cellulose, ZnCl 2 and 40-65% by weight of ZnCl relative to the total weight of water 2 A step of contacting with a first solvent, which is an aqueous solution containing the first solvent, preferably in which the amount of virgin cellulose is 1 to 10% by weight of the amount of the first solvent. (B) A step of preferentially dissolving the amorphous cellulose phase with respect to the crystalline cellulose phase, (C) A step of separating the dissolved amorphous cellulose from the crystalline cellulose. Methods that include... [2] The method according to [1], wherein the temperatures of steps A and B are less than 80°C, preferably less than 70°C, more preferably less than 60°C, and even more preferably less than 50°C. [3] The first solvent does not contain a protic acid and preferably contains a proton scavenger, preferably ZnO or Zn(OH) 2 The method described in [1] or [2], including the method described in [1] or [2]. [4] The method according to any one of [1] to [3], wherein the crystalline cellulose obtained in step B contains cellulose with an XRD-I structure. [5] The method according to any one of [1] to [4], wherein the XRD crystallinity of the crystalline cellulose obtained in step B or C is higher than that of the virgin cellulose, preferably at least 5, preferably at least 10%, higher than that of the virgin cellulose, and preferably at least 85%, preferably at least 90%. [6] The method according to any one of [1] to [5], further comprising step E of adding a coagulant to the dissolved amorphous cellulose obtained in step C to precipitate the amorphous cellulose, and preferably separating the precipitated amorphous cellulose, wherein the reverse solvent is preferably one or more selected from the group consisting of C1 to C8 alcohols, ketones or water. [7] The process further comprises step D, in which the crystalline cellulose obtained in step C is brought into contact with a second solvent to produce exfoliated cellulose, wherein the second solvent is 65-90% by weight, preferably 70-85% by weight of ZnCl in water. 2 The second solvent preferably does not contain a proton acid and preferably contains a proton scavenger, preferably ZnO or Zn(OH) 2 This also includes, preferably, the exfoliated cellulose being ZnCl 2 The method according to any one of [1] to [6], wherein the concentration of is separated from the second solvent by precipitation by adding a reverse solvent, preferably water, in an amount that dilutes it to 10 to 30% by weight, preferably 15 to 25% by weight. [8] The method according to [7], wherein the exfoliated cellulose obtained in step D comprises cellulose with an XRD-II structure. [9] The virgin cellulose is present in a biomass containing virgin cellulose and lignin and optionally hemicellulose. a) In step B, the amorphous cellulose and any hemicellulose are dissolved in the first solvent. b) In separation step C, the dissolved amorphous cellulose and arbitrary hemicellulose are separated from the crystalline cellulose and lignin. c) If necessary, in step H, the crystalline cellulose and lignin are treated with a solvent, preferably a basic solvent, to dissolve the lignin but not the crystalline cellulose phase, and the dissolved lignin and crystalline cellulose are separated, preferably by filtration. The method described in any of [1] to [6].

[10] The virgin cellulose is present in a biomass containing virgin cellulose and lignin and optionally hemicellulose. In step B, amorphous cellulose and any hemicellulose are dissolved in the first solvent. In separation step C, the dissolved amorphous cellulose and arbitrary hemicellulose are separated from the crystalline cellulose and lignin. In step D, the crystalline cellulose and lignin are brought into contact with the second solvent to produce exfoliated crystalline cellulose. If necessary, in step G, the lignin and the exfoliated crystalline cellulose are separated, preferably by centrifugation and / or filtration. The method described in any of [7] to [8]. A micro or nanocrystalline cellulose-containing product P1 having an XRD-I structure, which can be obtained by the method described in any of [1] to [6] or [9], wherein the XRD crystallinity is at least 85%, preferably at least 90%, the (poly)sugar content is less than 10% by weight, preferably less than 5% by weight, more preferably less than 2% by weight, the degree of polymerization DP is preferably at least 200, and the aspect ratio is less than 10. A nanocrystalline cellulose-containing product P2 having an XRD-II structure, which can be obtained by the method described in any of

[12] [7]~[8] or

[10] , wherein the XRD crystallinity is at least 80%, preferably at least 85%, more preferably at least 90%, the (poly)sugar content is less than 15% by weight, preferably less than 10% by weight, more preferably less than 5% by weight, most preferably less than 2% by weight, the degree of polymerization DP is preferably 100~200, and the aspect ratio is at least 20.

[13] A cellulose composition comprising a mixture of XRD-I type microcrystalline cellulose and XRD-II type nanocrystalline cellulose obtained by any of the methods in [7] to [8] or

[10] , preferably, - The mixture is preferably obtained by Method A, which involves mixing XRD-I type microcrystalline cellulose obtained by any of the methods in [1] to [6] or [9] with XRD-II type nanocrystalline cellulose obtained by any of the methods in [7] to [8] or

[10] , or - The mixture obtained by Method B is obtained in step D of the method described in any of [7] to

[10] , in which cellulose with an XRD-I structure is partially converted to cellulose with an XRD-II structure, and the partial conversion is preferably achieved by selecting a lower temperature and / or a shorter contact time before the addition of the reverse solvent, or a combination thereof. composition.

[14] The cellulose composition according to

[13] , further comprising lignin.

[15] Use of the XRD-I type micro or nanocellulose described in

[11] , the XRD-II type nanocellulose described in

[12] , or the cellulose composition described in

[13] or

[14] as a coating material, an excipient, a material for producing cellulose molded articles, preferably a material for producing fibers or films preferably used in the manufacture of packaging films, yarns, or fabrics, or as a starting material for producing carbon fibers.

[16] Polysaccharides comprising oligomeric sugars and monomeric sugars produced from the precipitate of dissolved amorphous cellulose obtained in step E of [6], preferably for use as a prebiotic food additive.

Claims

1. A method for producing microcrystalline or nanocrystalline cellulose from virgin cellulose having an amorphous cellulose phase and a crystalline cellulose phase, comprising the following steps: (A) Virgin cellulose, ZnCl ２ and 40-65% by weight of ZnCl relative to the total weight of water ２ A step of contacting with a first solvent, which is an aqueous solution containing the first solvent, preferably, the amount of virgin cellulose is 1 to 10% by weight of the amount of the first solvent. (B) A step of preferentially dissolving the amorphous cellulose phase with respect to the crystalline cellulose phase, Here, the temperatures in steps A and B are less than 80°C. (C) A step of separating the dissolved amorphous cellulose from the crystalline cellulose. Includes, A method wherein the crystalline cellulose obtained in step B contains cellulose with an XRD-I type structure.

2. The method according to claim 1, wherein the temperatures of steps A and B are less than 70°C, more preferably less than 60°C, and even more preferably less than 50°C.

3. The first solvent does not contain a proton acid and preferably contains a proton scavenger, preferably ZnO or Zn(OH) ２ The method according to claim 1 or 2, including the method described in claim 1 or 2.

4. The first solvent does not contain a proton acid, and the proton scavenger is preferably ZnO or Zn(OH) ２ The method according to claim 1 or 2, including the method described in claim 1 or 2.

5. The method according to any one of claims 1 to 4, wherein the XRD crystallinity of the crystalline cellulose obtained in step B or C is higher than that of the virgin cellulose, preferably the XRD crystallinity of the obtained crystalline cellulose is at least 5, preferably at least 10%, higher than that of the virgin cellulose, and preferably the XRD crystallinity of the obtained crystalline cellulose is at least 85%, preferably at least 90%.

6. The method according to any one of claims 1 to 5, further comprising step E of adding a coagulant to the dissolved amorphous cellulose obtained in step C to precipitate the amorphous cellulose, and preferably separating the precipitated amorphous cellulose, wherein preferably the coagulant is a reverse solvent, and the reverse solvent is one or more selected from the group consisting of C1 to C8 alcohols, ketones, or water.

7. The process further comprises step D, in which the crystalline cellulose obtained in step C is brought into contact with a second solvent to produce exfoliated cellulose, wherein the second solvent is 65 to 90% by weight, preferably 70 to 85% by weight of ZnCl in water. ２ The second solvent preferably does not contain a proton acid and preferably contains a proton scavenger, preferably ZnO or Zn(OH) ２ This also includes, preferably, the exfoliated cellulose being ZnCl ２ The method according to any one of claims 1 to 6, wherein the concentration of is separated from the second solvent by precipitation by adding a reverse solvent, preferably water, in an amount that dilutes it to 10 to 30% by weight, preferably 15 to 25% by weight.

8. The method according to claim 7, wherein the exfoliated cellulose obtained in step D contains cellulose with an XRD-II structure.

9. The virgin cellulose is present in a biomass containing virgin cellulose, lignin, and optionally hemicellulose. a) In step B, the amorphous cellulose and any hemicellulose are dissolved in the first solvent. b) In separation step C, the dissolved amorphous cellulose and arbitrary hemicellulose are separated from the crystalline cellulose and lignin. c) If necessary, in step H, the crystalline cellulose and lignin are treated with a solvent, preferably a basic solvent, to dissolve the lignin but not the crystalline cellulose phase, and the dissolved lignin and crystalline cellulose are separated, preferably by filtration. The method according to any one of claims 1 to 6.

10. The virgin cellulose is present in a biomass containing virgin cellulose, lignin, and optionally hemicellulose. In step B, amorphous cellulose and any hemicellulose are dissolved in the first solvent. In separation step C, the dissolved amorphous cellulose and arbitrary hemicellulose are separated from the crystalline cellulose and lignin. In step D, the crystalline cellulose and lignin are brought into contact with the second solvent to produce exfoliated crystalline cellulose. - If necessary, in step G, the lignin and the exfoliated crystalline cellulose are separated, preferably by centrifugation and / or filtration. The method according to any one of claims 7 to 8.

11. The method according to any one of claims 7 to 10, wherein a mixture of XRD-I type microcrystalline cellulose and XRD-II type nanocrystalline cellulose is produced by method B, and in step D, a partial conversion is made from XRD-I type cellulose to XRD-II type cellulose, the partial conversion is made preferably by selecting a lower temperature and / or a shorter contact time or a combination thereof before the addition of the reverse solvent.

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