Preparation of regenerated polysaccharides

Abstract

The regenerated cellulose produced can be used in filter technology, for example, the films produced can be used as membranes for the selective purification of drinking water.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a regenerated polysaccharide, the regenerated polysaccharide produced by the method, and a product using the regenerated polysaccharide.

[0002] Polysaccharides are carbohydrate polymers consisting of at least 11 monosaccharides linked together via glycosidic bonds. The most abundant polysaccharide in nature is cellulose. It is used as a raw material in the paper, construction, textile, and chemical industries. Furthermore, cellulose and its derivatives have been used for decades in numerous fields, including environmental technology, filtration, and medical applications.

[0003] Cellulose is a biopolymer synthesized by plants. Natural crystalline cellulose is frequently converted to synthetic regenerated cellulose for processing and product manufacturing. In this specification, regenerated cellulose refers to cellulose that has been dissolved and reprecipitated. This involves altering the crystalline lattice of natural cellulose through a process of swelling and dissolution without altering the molecular structure of the cellulose. This conversion is irreversible, as regenerated cellulose is the thermodynamically most stable form of cellulose. Additionally, cellulose can also be chemically synthesized.

[0004] For over a century, cellulose processing to produce regenerated cellulose fibers and films has mainly been via the viscose route (cellophane cellulose) and the cupromane route (cuprophane cellulose). However, these manufacturing methods involve significant environmental pollution and have many economic problems. Therefore, more environmentally friendly, simpler, and energy-saving manufacturing methods are needed.

[0005] In recent years, industrial and non-industrial methods for producing regenerated cellulose have been developed. Solvents used include non-derivatized solvents such as lithium chloride / dimethylacetamide (DMAc), N-methylmorpholine N-oxide (NMMO, Lyocell method), and alkali / urea or thiourea. Similar to water-phobic ionic liquids, aqueous mixed solvents, such as sodium hydroxide (NaOH) combined with highly toxic carbon disulfide (CS2), are also used. However, most solvents have drawbacks, such as high toxicity, volatility, and / or high cost. In contrast, electrolyte solutions, such as quaternary onium hydroxides like tetrabutylammonium hydroxide (TBAH) or tetrabutylphosphonium hydroxide (TBPH), are environmentally acceptable due to their low toxicity and easy handling.

[0006] The standard method for producing membranes is to introduce the cellulose membrane into an antisolvent or to evaporate the solvent. Using an ammonium-based electrolyte such as TBAH, cellulose membranes can be produced by "aging" (for a specific long period) on a PTFE surface. These membranes cannot be peeled off from other surfaces (e.g., glass).

[0007] US 2014 / 0212670 A1 discloses a method for producing regenerated cellulose using a phosphonium-based electrolyte such as TBPH. In this method, cellulose is precipitated in the form of flakes, fibers, films, pellets, or particles using a solvent that is more volatile than the solvent used for dissolution. This displaces water from the TBPH. However, research by the applicant has shown that in practice, only a fine powder of regenerated cellulose is formed. Therefore, developing a reliable method for providing regenerated polysaccharides in various forms and products remains a challenge.

[0008] This problem is solved by a method having the features according to claim 1. Further advantageous embodiments and configurations of the invention will become apparent from the auxiliary and dependent claims, the figures and examples. The embodiments of the invention can be advantageously combined with one another. The prior art documents relevant to the invention of this application are as follows (including documents cited in the international phase after the international filing date and documents cited when the application entered the national phase in other countries). (Prior art document) (Patent document) (Patent Document 1) International Publication No. 2019 / 180321 (Patent Document 2) U.S. Patent No. 5,656,373 (Patent Document 3) U.S. Patent Application Publication No. 2014 / 212670 Summary of the Invention [Means for solving the problem]

[0009] A first aspect of the present invention relates to a method for producing a solid regenerated polysaccharide, S1) providing a polysaccharide; S2) dissolving the polysaccharide in at least one electrolytic solvent, the electrolytic solvent used being a quaternary onium hydroxide in water at a content of about 40-80% by weight; S3) contacting the polysaccharide solution with an electrophilic reagent to precipitate the polysaccharide in a gelled form, the electrophilic reagent being at least one organic carbonate, or a mixture of different organic carbonates, or at least one polymer of an organic carbonate, or a mixture of different polymers of an organic carbonate, or a mixture of at least one organic carbonate and at least one polymer of an organic carbonate; S4) washing the regenerated polysaccharides. [Brief explanation of the drawings]

[0010] The invention will be elucidated in detail by the figures, which are shown in the figures below: [Figure 1] FIG. 1 is a flow diagram of a general embodiment of the method for producing regenerated cellulose of the present invention. [Figure 2]FIG. 2 is a flow diagram of a further embodiment of the method of the present invention for producing a film. [Figure 3] FIG. 3 is a flow diagram of one embodiment of the method of the present invention for producing pelletized material. [Figure 4] FIG. 4 is a diagram for analyzing the permeability of the regenerated cellulose film produced according to FIG. [Figure 5] Figure 5 is a diagram for analyzing the quality and structure of regenerated cellulose in films produced according to Figure 2. Cmcell.—Commercially available microcrystalline cellulose. [Figure 6] FIG. 6 is a diagram for analyzing the pore size of the regenerated cellulose film produced according to FIG. [Figure 7] FIG. 7 is a diagram for the analysis of the structure of regenerated cellulose of the pelletized material produced according to FIG. 3 by A) FT-IR spectroscopy, B) X-ray diffraction, and C) nuclear magnetic resonance spectroscopy. [Figure 8] FIG. 8 shows a comparative analysis of the structure of regenerated cellulose pellets produced using four types of organic carbonates according to FIG. 3 by A) FT-IR and B) X-ray diffraction. [Figure 9] FIG. 9 is an optical microscope photograph of a cross section of a regenerated cellulose film produced according to FIG. [Figure 10] FIG. 10 is a transmission electron micrograph of a cross section of a regenerated cellulose film produced according to FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] "Regenerated polysaccharides" are polysaccharides that have been dissolved and reprecipitated, which alter the crystal lattice of native polysaccharides through a process of swelling and dissolution without altering the molecular structure of the polysaccharide.

[0012] The term "gelled form" in the context of the present invention is understood to mean a set form, also called a solidified form. In the process of the present invention, a solid is formed in step S3.

[0013] In the method of the present invention, an electrophilic reagent is advantageously used for precipitation. However, this does not involve solvent exchange (as is standard in industrial processes or in US2014 / 212670A1); instead, the polysaccharide is precipitated directly by reaction of the electrophilic reagent with hydroxide ions of the solvent. Once the polysaccharide is dissolved, the polysaccharide and the ion [TBP] + , and [OH] when TBPH was used as the solvent. - Hydrogen bonds are formed, and upon contact with electrophilic reagents, the polysaccharides are separated again by reaction with hydroxide groups. There is no reaction between the polysaccharides and the reagents. This method has the advantage that powders and films can be easily produced in a few seconds without using harmful chemicals. This means that it is economical in terms of time and materials, and is also environmentally friendly. Furthermore, the regenerated polysaccharides are highly pure. This means that a simple and rapid method is provided for producing regenerated polysaccharides using non-toxic, recyclable, and water-resistant chemicals.

[0014] The polysaccharides to be regenerated may be provided in microcrystalline form, but may also be in other forms, such as synthetic or amorphous forms, or produced from biomass.

[0015] The polysaccharide may be, for example, cellulose, starch, chitin, chitosan or glycogen.

[0016] The polysaccharide used in this method is preferably cellulose. Cellulose and its derivatives can be used in various ways. This method advantageously produces high-quality regenerated cellulose. The film produced by this method is very smooth both within the film and on the surface, showing extremely high homogeneity. This indicates that the organic carbonate penetrates the dissolved cellulose uniformly and quickly.

[0017] The cellulose to be regenerated may be provided in microcrystalline form, but may also be any other form of cellulose, such as synthetic or amorphous form, or produced from biomass.

[0018] The electrolytic solvent used in this method is a quaternary onium hydroxide in water at a content of about 40 to 80 weight percent (weight percent). It is preferable to use at least phosphonium- and / or ammonium-containing onium hydroxides. It is particularly preferable to use TBPH. It is also possible to use TBAH, but in this case the amount of dissolved polysaccharide is less than in the case of TBPH, and dissolution takes longer.

[0019] The quaternary onium hydroxide may be, for example, a quaternary onium hydroxide as described in US2014 / 212670A1.

[0020] The quaternary onium hydroxide may be, for example, a tetraalkylphosphonium hydroxide in which the alkyl component has 2 to 8 carbon atoms, such as tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, tetrabutylphosphonium hydroxide, tetrapentylphosphonium hydroxide, or tetrahexylphosphonium hydroxide. The quaternary onium hydroxide may be, for example, tetraphenylphosphonium hydroxide. The quaternary onium hydroxide may be, for example, a substituted or unsubstituted alkyltriphenylphosphonium hydroxide, such as ethyltriphenylphosphonium hydroxide, butyltriphenylphosphonium hydroxide, pentyltriphenylphosphonium hydroxide, 2-dimethylaminoethyltriphenylphosphonium hydroxide, or methoxymethyltriphenylphosphonium hydroxide.

[0021] The quaternary onium hydroxide may be, for example, a tetraalkylammonium hydroxide in which the alkyl moiety has 2 to 6 carbon atoms, such as tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, or tetrapentylammonium hydroxide.

[0022] The quaternary onium hydroxide is used, for example, at a content of 50% by weight in water.

[0023] The polysaccharide may be present in the solution at a proportion of, for example, 20% by weight.

[0024] The polysaccharide can be dissolved, for example, by stirring the polysaccharide solution at room temperature (23° C.) for about 30 minutes.

[0025] In step S2, an additional solvent is preferably used. Therefore, the solvent can be used in addition to at least one electrolysis solvent. The additional solvent may be added before dissolving the polysaccharide, simultaneously with the electrolysis solvent, or after dissolving the polysaccharide. The ratio of the additional solvent to the electrolysis solvent may be, for example, 1:1. Dimethyl sulfoxide (DMSO) is particularly preferred as the additional solvent. Adding DMSO reduces the viscosity of the regenerated polysaccharide solution, improving its coatability during film production. It also promotes coagulation. Films produced using DMSO are more flexible and transparent than those produced without DMSO.

[0026] In this method, the electrophilic reagent used is (i) at least one organic carbonate, or (ii) a mixture of different organic carbonates, or (iii) at least one polymer of organic carbonate, or (iv) a mixture of different polymers of organic carbonate, or (v) a mixture of at least one organic carbonate and at least one polymer of organic carbonate. Organic carbonates are particularly effective in the context of the present invention. They cause immediate solidification of the polysaccharide solution without destroying the overall structure. When the polysaccharide solution comes into contact with the organic carbonate, a chemical reaction occurs between the hydroxide anions of the solvent and the organic carbonate, releasing diol and carbon dioxide gas, some of which is dissolved in the form of carbonate. Theoretically, the solvent and diol can be recycled and recovered in the next step. There is no reaction with the polysaccharide. A regenerated polysaccharide is formed.

[0027] The organic carbonate may be, for example, propylene carbonate, vinyl ethylene carbonate, butyl carbonate or ethylene carbonate.

[0028] The organic carbonate may be a cyclic organic carbonate or an acyclic organic carbonate. The cyclic organic carbonate may be, for example, propylene carbonate, vinyl ethylene carbonate, butyl carbonate, ethylene carbonate, or vinyl carbonate. The acyclic organic carbonate may be, for example, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, dibenzyl carbonate, diphenyl carbonate, or tert-butyl phenyl carbonate.

[0029] The organic carbonate used in this process is preferably propylene carbonate. Propylene carbonate is particularly advantageous in that it is liquid at room temperature, is a carbonate that can be sustainably produced from biomass, and is therefore easy to use. Propylene carbonate is also inexpensive.

[0030] The polymer of organic carbonate can have, for example, 2 to 1,000,000 monomers.

[0031] An example of the organic carbonate polymer is polypropylene carbonate.

[0032] The mixture of at least one organic carbonate and at least one polymer of an organic carbonate may be, for example, a mixture of propylene carbonate and polypropylene carbonate.

[0033] Solid organic carbonates are preferably dissolved before use in this method, for example in DMSO. DMSO is particularly preferred here. This also applies to polymers of organic carbonates. The polymers are solid at room temperature.

[0034] In this method, it is preferred to use at least one organic carbonate or a mixture of different organic carbonates.

[0035] The electrophilic reagent is used in step S3 at a concentration of 10 to 100%, particularly 80 to 100%. Step S3 is preferably carried out at a temperature in the range of 0 to 100°C for 0.01 to 100 hours, particularly preferably at 23°C for 0.01 to 10 minutes, and even more preferably at 23°C for 0.01 to 6 minutes. This means that the method advantageously functions at room temperature. The method is also very rapid.

[0036] The purification of the regenerated polysaccharide carried out in step S4 is preferably carried out using water, which allows for the effective removal of impurities, especially water-soluble impurities, and organic compounds (propylene glycol) and solvents formed, which advantageously results in a particularly high purity and a very uniform, homogeneous structure of the regenerated polysaccharide.

[0037] In a preferred embodiment of this method, the polysaccharide solution after step S2 is coated onto a surface with a coating medium of defined height, e.g., a doctor blade, in an additional step S2a, to produce the regenerated polysaccharide as a film (also called a foil). This results in a polysaccharide-solvent layer with a defined, uniform layer thickness. After contact with an organic carbonate, e.g., propylene carbonate, in step S3, this layer is converted into a film, e.g., by immersion in a propylene carbonate bath. This results in a non-transparent, whitish film. As mentioned above, adding DMSO can produce a transparent membrane.

[0038] Films produced by this method exhibit an average surface potential (zeta potential) of -20 mV in the pH range of 5.0 to 9.0.

[0039] Upon introduction of electrophiles and elution of solvent from the polysaccharide solution, the regenerated polysaccharide membranes form permeable (porous) microfibrillar structures. The properties of these films are found to be comparable to those of conventionally produced membranes.

[0040] The film can be stored in neutral, slightly basic, or slightly acidic media. It has been found that the print stability of the film is maintained during this storage process. To this end, the print stability of the film at pressures of 1 to 3 bar was confirmed in a flow reactor.

[0041] The film can be stored, for example, in water, ethanol, or acetone. Preferably, the film is stored in water.

[0042] In a further preferred embodiment of this method, the regenerated polysaccharide is produced in pelletized form by mechanically grinding after step S4 in an additional step S4a. The solid material consisting of regenerated polysaccharide obtained after contacting the polysaccharide solution with an organic carbonate, e.g., propylene carbonate, can be ground in a subsequent washing procedure to obtain a highly pure polysaccharide material in pelleted, e.g., powder form.

[0043] A second aspect of the present invention relates to a regenerated polysaccharide produced by the method of the present invention according to the above-mentioned embodiment. The regenerated polysaccharide is preferably regenerated cellulose.

[0044] The regenerated polysaccharide is preferably provided as a film. It is also preferable to provide a film of regenerated cellulose. The film exhibits high homogeneity within the film and on the surface. The surface is very smooth. The distance between fibrils (pores) is very small, preferably 10 to 100 nm, and accordingly, it is selective for specific particle sizes. The film of the present invention can be used, for example, as a film or as a membrane for selective purification of drinking water. Furthermore, it is also possible to selectively separate negatively charged ions from positively charged ions. Furthermore, the film of the present invention can be used in the production of plies and nanotubes.

[0045] Also preferably, the regenerated polysaccharide is provided in the form of pellets, which can be used, for example in powder form, for example as an additive in nutritional and medical preparations, in the construction chemical industry and in ceramic applications.

[0046] Regenerated cellulose films and pellets produced according to the present invention have been characterized by methods such as Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, X-ray diffraction, thermal analysis, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, UV / VIS spectroscopy, and size exclusion chromatography.

[0047] A third aspect of the invention relates to products comprising the polysaccharides regenerated according to the invention, such as membranes, films, plies or nanotubes, or in combination with other materials.

[0048] The advantages of the regenerated polysaccharides produced by this process and of the products made from the regenerated polysaccharides correspond to the advantages of the process to the extent that they are not limited to purely process technology aspects.

[0049] 1. A method for producing a solid regenerated polysaccharide, comprising: S1) providing a polysaccharide; S2) dissolving the polysaccharide in at least one electrolytic solvent; S3) Precipitating the polysaccharide in a gelled form by contacting the polysaccharide solution with an electrophilic reagent, the electrophilic reagent having the formula [ka] or expression [ka] or a mixture of electrophiles having formula I and / or formula II, wherein X is a C=O, C=S, or C=NR functional group, Y and Z are the same or different and are selected independently of each other and consist of O, NH, NR, S, or CR groups, R is hydrogen and / or a substituted or unsubstituted hydrocarbyl radical, and M is a bridge consisting of 0 to 20 carbon atoms and a linear or branched, substituted or unsubstituted hydrocarbyl radical; S4) washing the regenerated polysaccharide; A method comprising: 2. The method according to 1, wherein the polysaccharide used is cellulose. 3. The method according to 1 or 2, wherein the electrolytic solvent used is a quaternary onium hydroxide in water at a content of about 40-80% by weight. 4. The method according to claim 3, wherein at least one phosphonium-containing and / or at least one ammonium-containing onium hydroxide is used. 5. The method according to 4, wherein tetrabutylphosphonium hydroxide is used. 6. Any of the preceding methods, wherein an additional solvent is used in step S2. 7. The method according to 6, wherein dimethyl sulfoxide is used as an additional solvent. 8. Any of the aforementioned methods, wherein the electrophilic reagent is used at a concentration of 80 to 100%. 9. Any of the preceding methods, wherein the electrophile used in step S3 is at least one organic carbonate or a mixture of different organic carbonates. 10. The method according to 9, wherein an organic carbonate is used in step S3. 11. The method according to any one of 1 to 8, wherein the electrophilic reagent used in step S3 is at least one polymer of an organic carbonate, or a mixture of different polymers of organic carbonate, or a mixture of at least one organic carbonate and at least one polymer of an organic carbonate. 12. A method according to any of the preceding claims, wherein in an additional step S2a, the regenerated polysaccharide is produced as a film by coating the polysaccharide solution onto a surface after step S2. 13. A method according to any one of 1 to 12, wherein in an additional step S4a, the regenerated polysaccharide is produced in a powder or pellet form by mechanically pulverizing the regenerated polysaccharide after step S4. 14. A regenerated polysaccharide produced by the method according to any one of 1 to 13. 15. The regenerated polysaccharide according to 14, provided in the form of a film. 16. The regenerated polysaccharide according to 14, provided in pellet form. 17. A product made from the regenerated polysaccharide according to any one of 14 to 16.

[0050] The features and examples described for the inventive methods for producing regenerated polysaccharides, the inventive regenerated polysaccharides produced by the methods, and the inventive products produced from the regenerated polysaccharides are equally applicable to the corresponding features of the disclosed aspects, unless otherwise indicated.

[0051] The substituted or unsubstituted hydrocarbyl radical covered by R is in particular an alkyl or aryl radical, for example an alkyl radical having 1 to 20 carbon atoms or an alkyl radical having 1 to 8 carbon atoms. R is preferably a methyl, ethyl or n-propyl radical.

[0052] Explicitly excluded for use as electrophiles are the compounds disclosed in Publication US2014 / 212670A1 for the precipitation of regenerated cellulose. This particularly relates to alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, and 2-propanol, as well as ketones such as acetone. In other words, the use of these compounds is excluded from the scope of the disclosure of 1.

[0053] "Electrolytic solvent," in the context of this disclosure, is understood to mean a dissolved solid consisting of ionic crystals composed of hydroxide ions as negatively charged anions and positively charged cations. The electrolytic solvent used in the disclosed method is preferably a quaternary onium hydroxide in water at a content of about 40 to 80 weight percent (wt. %). Additionally, other protic and aprotic solvents are acceptable, which may improve flowability and, therefore, processability.

[0054] 1. A method for producing a solid regenerated polysaccharide, comprising: S1) providing a polysaccharide; S2) dissolving the polysaccharide in at least one electrolytic solvent; S3) Precipitating the polysaccharide in gelled form by contacting the polysaccharide solution with an electrophilic reagent, the electrophilic reagent used being at least one reagent having formula (I), [ka] wherein X and Y are O, S or NR functional groups, X and Y are the same or different and are selected independently of each other, R is hydrogen and / or a linear or branched, substituted or unsubstituted hydrocarbyl radical, or or at least one reagent having formula (II): [ka] wherein X and Y are O, S or NR functional groups, X and Y are the same or different and are selected independently of each other, R is hydrogen and / or a linear or branched, substituted or unsubstituted hydrocarbyl radical, B is a bridge consisting of a linear or branched, substituted or unsubstituted hydrocarbyl radical having 1 to 20 carbon atoms, or or a mixture of reagents having formula I and / or II, or at least one polymer having 2 to 1,000,000 monomers, said monomers corresponding to reagents having formula I and / or formula II, or a mixture of polymers each having 2 to 1,000,000 monomers, said monomers corresponding to reagents having formula I and / or formula II; or a mixture of at least one reagent having formula I and / or formula II and at least one polymer having 2 to 1,000,000 monomers, wherein the monomers correspond to the reagent having formula I and / or formula II; S4) washing the regenerated polysaccharide; A method comprising: 2. The method according to 1, wherein the polysaccharide used is cellulose. 3. The method according to 1 or 2, wherein the electrolytic solvent used is a quaternary onium hydroxide in water at a content of about 40-80% by weight. 4. The method according to claim 3, wherein at least one phosphonium-containing and / or at least one ammonium-containing onium hydroxide is used. 5. The method according to 4, wherein tetrabutylphosphonium hydroxide is used. 6. Any of the preceding methods, wherein an additional solvent is used in step S2. 7. The method according to 6, wherein dimethyl sulfoxide is used as an additional solvent. 8. Any of the aforementioned methods, wherein the electrophilic reagent is used at a concentration of 80 to 100%. 9. The method according to any of the preceding claims, wherein the electrophile used in step S3 is at least one organic carbonate, or a mixture of different organic carbonates, or a polymer of at least one organic carbonate, or a mixture of polymers of different organic carbonates, or a mixture of at least one organic carbonate and at least one polymer of organic carbonate. 10. The method according to 9, wherein an organic carbonate is used in step S3. 11. The method according to claim 10, wherein the organic carbonate used in step S3 is propylene carbonate. 12. A method according to any of the preceding claims, wherein in an additional step S2a, the regenerated polysaccharide is produced as a film by coating the polysaccharide solution onto a surface after step S2. 13. The method according to any one of 1 to 12, wherein in an additional step S4a, the polysaccharide solution is produced in powder or pelletized form by mechanically grinding the polysaccharide solution after step S4. 14. A regenerated polysaccharide produced by the method according to any one of 1 to 13. 15. The regenerated polysaccharide according to 14, provided in the form of a film. 16. The regenerated polysaccharide according to 14, provided in pellet form. 17. A product made from the regenerated polysaccharide according to any one of 14 to 16.

[0055] The features and examples described for the inventive methods for producing regenerated polysaccharides, the inventive regenerated polysaccharides produced by the methods, and the inventive products produced from the regenerated polysaccharides are equally applicable to corresponding features of the disclosed aspects, unless otherwise indicated.

[0056] The substituted or unsubstituted hydrocarbyl radical covered by R is in particular an alkyl or aryl radical, for example an alkyl radical having 1 to 20 carbon atoms or an alkyl radical having 1 to 8 carbon atoms. R is preferably a methyl, ethyl or n-propyl radical.

[0057] Explicitly excluded for use as electrophiles are the compounds disclosed in Publication US2014 / 212670A1 for the precipitation of regenerated cellulose. This particularly relates to alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, and 2-propanol, as well as ketones such as acetone. In other words, the use of these compounds is excluded from the scope of the disclosure of 1.

[0058] "Electrolytic solvent," in the context of this disclosure, is understood to mean a dissolved solid consisting of ionic crystals composed of hydroxide ions as negatively charged anions and positively charged cations. The electrolytic solvent used in the disclosed process is preferably a quaternary onium hydroxide in water at a content of about 40 to 80 weight percent (wt. %). Additionally, other protic and aprotic solvents are acceptable, which may improve flowability and, therefore, processability.

[0059] The invention will be elucidated in detail by the figures, which are shown in the figures below: FIG. 1 is a flow diagram of a general embodiment of the method for producing regenerated cellulose of the present invention. FIG. 2 is a flow diagram of a further embodiment of the method of the present invention for producing a film. FIG. 3 is a flow diagram of one embodiment of the method of the present invention for producing pelletized material. FIG. 4 is a diagram for analyzing the permeability of the regenerated cellulose film produced according to FIG. Figure 5: Analysis of the quality and structure of regenerated cellulose in films produced according to Figure 2. Cmcell.—Commercially available microcrystalline cellulose. FIG. 6 is a diagram for analyzing the pore size of the regenerated cellulose film produced according to FIG. FIG. 7. Diagrams for analysis of the structure of regenerated cellulose of pelleted material produced according to FIG. 3 by A) FT-IR spectroscopy, B) X-ray diffraction, and C) nuclear magnetic resonance spectroscopy. FIG. 8 Comparative analysis of the structure of regenerated cellulose pellets produced using four types of organic carbonates according to FIG. 3 by A) FT-IR and B) X-ray diffraction. FIG. 9 is an optical microscope photograph of a cross section of a regenerated cellulose film produced according to FIG. FIG. 10 is a transmission electron microscope photograph of a cross section of the regenerated cellulose film produced according to FIG.

[0060] In a typical embodiment of the method of the present invention according to FIG. 1, regenerated cellulose is produced. To this end, in the first step S1, natural cellulose is provided in microcrystalline form. However, alternatively, cellulose may also be provided in any other possible form, for example, in synthetic or amorphous form, or produced from biomass. In the second step S2, 20% by weight (200 mg) of microcrystalline cellulose is dissolved in a suitable container in a 50% aqueous solution (1 ml) of TBPH. This involves stirring the resulting cellulose solution at room temperature (23°C) for approximately 30 minutes. In the third step S3, this liquid is coagulated by the addition of propylene carbonate, which immediately converts the cellulose-solvent layer into regenerated cellulose. In the fourth step S4, the regenerated cellulose is washed with water to remove the solvent and any organic compounds formed. High-purity regenerated cellulose is obtained.

[0061] In one embodiment of the method of the present invention for producing a regenerated cellulose film / foil according to FIG. 2, the method is carried out similarly to that of FIG. 1, except that in an additional step S2a, the transparent solution is coated onto a glass plate, for example, by a doctor blade. This results in a specific preset thickness of the cellulose-solvent layer (e.g., 300 μm). In the third step S3, the casting solution is immersed in a propylene carbonate bath to coagulate. This immediately converts the cellulose-solvent layer into a regenerated cellulose film. In the fourth step S4, the regenerated cellulose film is washed with water to remove the resulting solvent and organic compounds, resulting in a highly pure cellulose film. It is immediately peeled off from the glass plate. This film is then stored in water until use.

[0062] However, this conversion does not change the optical properties, and the cellulose membrane remains whitish and opaque, so the conversion of the cellulose-solvent layer to a cellulose membrane is not visually detectable. In a further embodiment of the method of the present invention, in step S2, DMSO is added as an additional solvent to the dissolved cellulose (a preferred solvent:DMSO ratio is 1:1). This results in a transparent cellulose membrane in step S3. This conversion is also not visually detectable. The use of DMSO also affects the membrane permeability. This can be demonstrated by water flow tests of films used as membranes according to Figure 4. The water flow rate depends, in principle, on the size and distribution of the membrane pores. Here, a first membrane (RC1) without DMSO and a second membrane (RC2) with DMSO were produced. The first membrane, RC1, had a water flow rate of 1.6 to 5.4 L at a pressure range of 0.5 to 2.1 bar. * m -2* h -1 A pressure-dependent increase in water permeability was observed (square data points). For the second film, RC2, the permeability increased from 3.7 to 7.8 L / min in the pressure range of 0.5 to 1.1 bar. * m -2* h -1 The water permeability increased in a pressure-dependent manner up to 1000 kJ / cm (circle data points). Such a high water permeability indicates a clear dilution effect of DMSO on the regenerated cellulose.

[0063] Figure 5 shows the purification effect of the new method and the improved quality of the resulting films. The abbreviation au stands for arbitrary unit. Impurities (sharp signals) are not present in the films. Furthermore, the chemical structures of films RC2 (film 2, top graph) and RC1 (film 1, second graph from the top) are consistent with commercially available microcrystalline cellulose (abbreviated as Cmcell, second graph from the bottom). The bottom graph is for the solvent (TBPH, 50%).

[0064] The pore size distribution of the two membranes is shown in Figure 6. The pore size is 10 to 70 nm, which is much smaller than that of commercially available regenerated cellulose membranes (200 to 500 nm).

[0065] In a further embodiment of the method of the present invention according to FIG. 3, pelletized material is produced from regenerated cellulose. Steps S1 and S2 are performed here in the same manner as in the method described according to FIG. 1. Propylene carbonate is added directly to the cellulose solution in step S3 (preferably a 10:1 excess of propylene carbonate). There is immediate gelation / solidification of the regenerated cellulose. The solidified regenerated cellulose can be washed with water in step S4, e.g., by repeated decantation or centrifugation of the supernatant, once the cellulose settles to the bottom of the container containing the cellulose and solvent. The regenerated cellulose is preferably dried at 30-100°C and stored in pellet form until further use. The pelleted material may optionally be mechanically crushed in step S4a, e.g., using a pestle or mortar. The size of the pellet particles formed in the method described with respect to FIG. 3 can be varied to produce powder or coarse pelleted material. The size of the pelleted material can be adjusted via appropriate crushing equipment and crushing intensity (applied force, crushing time).

[0066] The pelleted material was structurally examined. It was shown that the regenerated cellulose was not chemically modified by propylene carbonate, indicating that there was no chemical reaction between cellulose and propylene carbonate. Fourier transform infrared spectroscopy (FT-IR) analysis showed that propylene carbonate was not incorporated into the cellulose structure (Figure 7A). The top line represents propylene carbonate, the middle line represents regenerated cellulose, and the bottom line represents native microcrystalline cellulose. Thus, the dissolved cellulose is regenerated without changing its chemical structure. X-ray diffraction (XRD) analysis of the pelleted material revealed changes in the macroscopic structure. Compared with the bottom line (native cellulose, crystalline cellulose), new reflections at 12.1° and 20.6° were observed in the top line (regenerated cellulose), indicating the formation of a cellulose II structure (regenerated cellulose) (Figure 7B). Nuclear magnetic resonance (NMR) analysis also revealed no change in chemical structure, as evidenced by the similar progression of the top graph (regenerated cellulose) compared to the bottom graph (native cellulose) (Figure 7C). Note that the abbreviation "au" stands for arbitrary units.

[0067] It is also possible to obtain regenerated cellulose by using other organic carbonates instead of the propylene carbonate used here (Figure 8). FT-IR (Figure 8A) and X-ray diffraction (Figure 8B) showed that regenerated cellulose with the same structure as propylene carbonate (bottom of the graph) could be obtained using vinyl ethylene carbonate (top of the graph), butyl carbonate (second from the top of the graph), and ethylene carbonate (second from the bottom of the graph). Note that au is an abbreviation for arbitrary unit.

[0068] Figure 9 is a light microscope photograph of the cross section of a regenerated cellulose film produced according to Figure 2. This image shows a film (foil) produced without DMSO as an additional solvent (RC1). The film thickness is 200 μm. Excellent homogeneity within the film can be seen. Furthermore, the film is free of air bubbles.

[0069] Figure 10 is a high-resolution transmission electron micrograph (TEM image) of a cross section of a regenerated cellulose film prepared according to Figure 2. The image shows a film (foil) prepared without the use of DMSO as an additional solvent (RC1). The microfibrillar structure was visualized with uranyl acetate and lead citrate.

Claims

1. 1. A method for producing a solid regenerated polysaccharide, comprising: S1) providing a polysaccharide; S2) dissolving the polysaccharide in at least one electrolytic solvent, the electrolytic solvent used being a quaternary onium hydroxide in water at a content of about 40-80% by weight; S3) Precipitating the polysaccharide in gelled form by contacting the polysaccharide solution with an electrophilic reagent, the electrophilic reagent being at least one cyclic organic carbonate; S4) washing the regenerated polysaccharide; A method comprising:

2. 2. The method of claim 1, wherein the polysaccharide used is cellulose.

3. 3. The process according to claim 1, wherein at least one phosphonium-containing and / or at least one ammonium-containing onium hydroxide is used.

4. 4. The process according to claim 3, wherein tetrabutylphosphonium hydroxide is used.

5. 4. The process according to claim 3, wherein tetrabutylammonium hydroxide is used.

6. The method according to any one of claims 1 to 5, wherein an additional solvent is used in step S2.

7. 7. The process of claim 6, wherein dimethyl sulfoxide is used as an additional solvent.

8. The method according to any one of claims 1 to 7, wherein the electrophile is used at a concentration of 80 to 100%.

9. 2. The method of claim 1, wherein the cyclic organic carbonate is propylene carbonate, vinyl ethylene carbonate, butyl carbonate, ethylene carbonate, and / or vinyl carbonate.

10. 10. The method according to any one of claims 1 to 9, wherein in an additional step S2a, the regenerated polysaccharide is produced as a film by coating the polysaccharide solution onto a surface after step S2.

11. 11. The method according to any one of claims 1 to 10, wherein in an additional step S4a, the regenerated polysaccharide is produced in powder or pellet form by mechanically grinding the regenerated polysaccharide after step S4.

12. 12. The method of claim 1, further comprising providing the regenerated polysaccharide in the form of a film, the film having pores with a diameter of 10 to 100 nm.

13. The method of claim 12, further comprising providing the regenerated polysaccharide in the form of a film.

14. 13. The method of claim 12, including providing the regenerated polysaccharide in pellet form.

Images