Method for producing a liquid cellulose composite from bacterial nanocellulose and carboxymethylcellulose, cellulose composite and its use

Abstract

Method for producing a liquid cellulose composite from bacterial nanocellulose and carboxymethylcellulose, comprising a) Treating bacterial nanocellulose, which is present in the form of water-containing pieces, with carboxymethylcellulose in an aqueous medium, wherein the carboxymethylcellulose is incorporated into the bacterial nanocellulose and a cellulose composite comprising bacterial nanocellulose and the carboxymethylcellulose is formed, b) Mechanical comminution of the cellulose composite in the presence or with the addition of water, whereby the cellulose composite is brought into a liquid form and an aqueous liquid gel is obtained.

Description

[0001] The invention relates to a process for producing a liquid cellulose composite from bacterial nanocellulose and carboxymethylcellulose, a liquid cellulose composite in the form of an aqueous liquid gel which can be produced by this process, and its use.

[0002] Bacterial nanocellulose (BNC) is a cellulose synthesized by Gram-negative bacteria. BNC differs significantly in its morphology from cellulose of plant origin. It consists of fibers with a diameter in the nanometer range (20–100 nm), which are 100 times finer than conventional plant cellulose fibers (cellulose). The natural nanofiber network exhibits a scaffold structure comparable to human tissue (collagen). It contains up to 99% water and is capable of intensive interactions with its environment. BNC is mechanically stable even when moist. BNC is a highly pure polymer, free of accompanying plant components such as lignin, pectin, and hemicelluloses. It is characterized by a high molecular weight (degree of polymerization of approximately 4,000–10,000) and high crystallinity (80–90%).BNC is not degraded in the human and mammalian organism, does not trigger any immune reactions of the body and is effectively colonized by the body's own cells (Klemm D, Kramer F, Moritz S, Lindström T, Ankerfors M, Gray D, Dorris A: Nanocelluloses: a new family of nature-based materials. Angew. Chem. Int. Ed. (2011) 50, 5438-5466).

[0003] BNC has potential applications in medicine, pharmacy, cosmetics, and technology, for example, as a base material or excipient for the production of cosmetic, technical, or medical formulations. One problem with the use of BNC is its network structure, which makes it difficult to produce homogeneous compositions. When BNC is ground in the presence of water, it produces a fiber pulp that is difficult to process and handle.

[0004] WO 2020 / 136629A1 proposes the preparation of a powdered formulation of BNC and an additive that is redispersible.

[0005] CN 112773941 A relates to a composite material made of chitosan microspheres and bacterial cellulose, as well as its preparation and application. The composite material made of chitosan microspheres and bacterial cellulose has a three-dimensional network structure, and the surface and the network of nanofibers are loaded with chitosan microspheres.

[0006] The review article by Khalid M., Rashid A., Arif Z., Ahmed W., and Arshad H., "Recent advances in nanocellulose-based different biomaterials: types, properties, and emerging applications." Journal of Materials Research and Technology 2021, 14, 2601. ISSN 2238-7854. https: / / doi.org / 10.1016 / j.jmrt.2021.07.128, focuses on green composites based on nanocellulose. Current developments, results, and findings are comprehensively presented. The properties of nanocellulose are influenced by various factors, including fiber type, environmental conditions, manufacturing methods, and any modification of the fiber surface. Finally, future challenges and opportunities in the field of nanocellulose materials are discussed.

[0007] Shahriari-Khalaji, M.; Hong, S.; Hu, G.; Ji, Y.; Hong, FF Bacterial Nanocellulose-Enhanced Alginate Double-Network Hydrogels Cross-Linked with Six Metal Cations for Antibacterial Wound Dressing. Polymers 2020, 12, 2683. https: / / doi.org / 10.3390 / polym12112683 report that alginate and bacterial nanocellulose (BNC) have great potential for biomedical applications, especially for wound dressings. BNC is described as a natural biopolymer that brings great advances to current and future biomedical materials. The results showed that fabricated composites not only exhibit pH-responsive antibacterial activities but also enhanced mechanical properties, making them suitable for use as smart dressings.

[0008] The object of the invention is to provide BNC in a homogeneous, flowable formulation, which should preferably be suitable as a component for medical, technical or cosmetic formulations.

[0009] The object is achieved according to the independent claims by a method for producing a liquid cellulose composite from bacterial nanocellulose and carboxymethylcellulose, a liquid cellulose composite in the form of an aqueous liquid gel which can be produced by this method, and the use of the liquid cellulose composite.

[0010] According to the basic idea of ​​the invention, bacterial nanocellulose is treated with carboxymethylcellulose. This process incorporates carboxymethylcellulose into the structure of the bacterial nanocellulose, creating a composite.

[0011] It has been found that this composite can be converted into a homogeneous and flowable form in the presence of water and upon comminution. After incorporation of the carboxymethylcellulose into the BNC structure, the composite can be easily mechanically comminuted. The resulting product is referred to according to the invention as an aqueous liquid gel. The product according to the invention is ready for use without further treatment, for example as a flowable base material or excipient for medical, technical, and cosmetic applications, and can be refilled. Available moist BNC starting materials, such as layers, cubes, or spheres, can be used as starting materials in the process according to the invention. They do not require prior preparation, such as comminution.

[0012] Before use in the process, the bacterial nanocellulose can be purified, if desired, preferably with an aqueous alkaline solution, such as sodium hydroxide solution. In its raw form, bacterial nanocellulose is often present in an aqueous, acetic acid medium. Washing with an alkaline solution destroys any remaining microorganisms. After washing with an alkaline solution, a further washing step with neutral water can be performed until a neutral pH value is reached. Before use in the process, the washed BNC can be pressed to reduce the water content. In the preferred variant of the process, the bacterial nanocellulose contains water.

[0013] The process according to the invention preferably does not comprise a drying step, in particular an intermediate step.

[0014] The process according to the invention preferably does not comprise a step, in particular an intermediate step, of producing a powder.

[0015] The treatment in a) can be carried out by placing the bacterial nanocellulose in the aqueous medium containing the carboxymethylcellulose.

[0016] An example treatment time for a) is 1-4 days. Treatment in a) can take place at elevated temperatures, particularly 30 to 80°C, and / or with stirring, which can shorten the treatment time.

[0017] In the process, in b) a viscosity of the liquid cellulose composite can be adjusted by the amount of water, whereby a lower viscosity is achieved by adding more water

[0018] In one embodiment, the method further comprises: the removal of excess carboxymethylcellulose that is not incorporated into the bacterial nanocellulose. This step preferably takes place after treating the bacterial nanocellulose with carboxymethylcellulose and before mechanically comminuting the cellulose composite. Removed carboxymethylcellulose can be recovered, in particular for further use in the process according to the invention.

[0019] In one embodiment of the method, excess carboxymethylcellulose is removed after treating the bacterial nanocellulose with carboxymethylcellulose by washing with water. Excess carboxymethylcellulose that is not incorporated into the bacterial nanocellulose is washed away. Non-incorporated carboxymethylcellulose is washed away from the surface of the bacterial nanocellulose structure.

[0020] For mechanical comminution of the cellulose composite, a dispersing rod, a strainer rod, a mixer, a mill or a combination thereof can be used, without the tools being limited to these. A preferred carboxymethylcellulose is sodium carboxymethylcellulose.

[0021] According to the invention, the bacterial nanocellulose is in the form of pieces, for example flat pieces (sheets), cubes or spheres, before treatment with the carboxymethylcellulose.

[0022] In one embodiment of the process, in a), the concentration of carboxymethylcellulose in the aqueous medium is 0.1 to 2% (w / v). In other words, BNC can be treated with an aqueous solution of carboxymethylcellulose, with the concentration preferably being within the stated range.

[0023] In one embodiment of the process, the mass ratio of carboxymethylcellulose to bacterial nanocellulose in the cellulose composite is 0.35:1 to 0.85:1. In the process according to the invention, a cellulose composite with this mass ratio is produced in this embodiment. The mass ratio can be adjusted, for example, by the duration of the treatment in a), by the concentration of the water-soluble ionic polysaccharide in the aqueous medium, by the choice of temperature, or by a combination thereof.

[0024] The viscosity of the carboxymethylcellulose in solution (solution viscosity) is preferably 50 to 200 mPas at a concentration of 4% (w / v) in water. For use in the process, the solution can be brought to a concentration as previously stated. Other applicable solution viscosities are 100-160 mPas at 2% (w / v), 550-900 mPas at 2% (w / v), or 1500-3000 cps at 1% (w / v).

[0025] In a further aspect, the invention relates to a liquid cellulose composite in the form of an aqueous liquid gel comprising bacterial nanocellulose, carboxymethylcellulose, and water. This composite is obtained by a process according to the invention.

[0026] In one embodiment of the liquid cellulose composite, the mass ratio of carboxymethylcellulose to bacterial nanocellulose in the cellulose composite is 0.35:1 to 0.85:1.

[0027] In another aspect, the invention relates to the use of a liquid cellulose composite, as described above, as a component in medical, technical, or cosmetic formulations. Exemplary technical fields in which the liquid cellulose composite according to the invention can be advantageously used are electronics and electrical engineering, for example in electronic components or parts such as batteries, accumulators, or capacitors. Another technical field is surface treatment, where the composite can be used, for example, as a base or additive in paints or primers.

[0028] In another aspect, the invention relates to the use of the composite as a dispersion base material.

[0029] The invention is illustrated below using exemplary embodiments. Example 1: 1. In a washing section, the commercially available BNC raw material is washed with an aqueous solution of an alkaline, medically approved detergent and then with water, and excess water is removed by pressing. 2. In a homogenization section, the purified product obtained in (1) is mixed with an aqueous solution of an ionic cellulose ether. The resulting composite is then homogenized with a dispersing rod. Example 2:

[0030] In a wash vessel, the commercially available BNC raw material containing acetic acid (pH 3.5) is boiled with 1N aqueous NaOH solution for 20 minutes. After removing the wash solution (which mainly contains amino acids from the cleavage products of the killed bacteria, sodium acetate, and excess NaOH), excess water is removed by pressing, and the product is then washed with water until pH neutral.

[0031] In a mixing container, the purified product obtained above is mixed with the aqueous solution of carboxymethylcellulose (CMC) and allowed to stand for 24 hours at room temperature. Excess CMC solution is then separated and collected for reuse. The mixture is then rinsed with running water.

[0032] The composite is then homogenized with a dispersing rod. The resulting liquid gel can be either steam sterilized or treated with a sterilizing additive. Example 3:

[0033] The invention involves the production of a liquid nanocellulose hydrogel for use as a dispersion base and viscosity regulator for cosmetics, pharmaceuticals, medicine, and technology. It was found that purified bacterial nanocellulose (BNC) of various shapes (sheets, cubes, tubes, spheres), including commercially available BNC starting materials, can be directly converted into the target product by adding aqueous ionic polysaccharide derivatives and subsequent mechanical disintegration, regardless of the shape of the starting material and without further pretreatment. Procedure: 1. Cleaned BNC fleece: Pressing to a solids content of 5-50%, in this case: cube 10 x 10 x 10 mm, solids content 9% 2. Placement in an aqueous solution of polysaccharides and polysaccharide derivatives, preferably ionic, namely in this example carboxymethylcellulose sodium salt (CMC) Concentration of 0.1 - 2% Stand at RT for at least 24 h or stir for 0.5-1 h or heat for 30 min until complete swelling In this example, 250 g of wet BNC cubes are treated with 2 L of aqueous CMC solution (1%, w / v, specific CMC: 4% solution has a viscosity of 50 - 200 cps): Stand for 4 d at RT) 3. Drain the polysaccharide derivative solution from the treated solid. 4. Rinse with water to remove excess polysaccharide derivative. In this example: Rinse once with running water. 5. Drain off excess water 6. Mechanical comminution with a dispersing rod, mixer, mill, etc., with the addition of a defined amount of water to adjust the gel viscosity. In this example: transfer portion by portion into dispersing beakers (volume of approx. 150ml swollen BNC-CMC cubes), add approx. 50ml water per portion and homogenize 3x for 1 min with a blender, 7. Optionally, sterilize (e.g., autoclave, gamma irradiation, biocide) and fill. In this example: combine gel portions, steam sterilize, and pack sterilely.

[0034] The CMC content in the hydrogel depends on the molar mass of the CMC, the concentration of the CMC solution, and the duration and type of exposure (e.g., standing, stirring, heating). It varies between 0.35 g and 0.85 g in the product (dry mass) based on 1 g of BNC from point 1 (dry mass).

[0035] The solutions from points 3 to 5 are combined, the concentration is determined, enriched to the initial concentration and returned to the process.

Claims

[1] Process for the preparation of a liquid cellulose composite from bacterial nanocellulose and carboxymethylcellulose, comprising a) treating bacterial nanocellulose, which is in the form of water-containing pieces, with carboxymethylcellulose in an aqueous medium, whereby the carboxymethylcellulose is incorporated into the bacterial nanocellulose and a cellulose composite comprising bacterial nanocellulose and the carboxymethylcellulose is formed, b) Mechanical comminution of the cellulose composite in the presence or addition of water, whereby the cellulose composite is brought into a liquid form and an aqueous liquid gel is obtained. [2] The method according to claim 1, wherein in b) a viscosity of the liquid cellulose composite is adjusted by the amount of water. [3] The method according to claim 1 or 2, further comprising, preferably after a) and before b), removing excess carboxymethylcellulose which is not incorporated into the bacterial nanocellulose. [4] Process according to claim 3, wherein the removal of the excess carboxymethylcellulose after a) is carried out by washing with water. [5] Process according to one of the preceding claims, wherein in a) the concentration of carboxymethylcellulose in the aqueous medium is 0.1 to 2% (w / v). [6] Liquid cellulose composite in the form of an aqueous liquid gel comprising bacterial nanocellulose, carboxymethylcellulose and water, and obtained by a process according to any one of claims 1-5. [7] The liquid cellulose composite according to claim 6, wherein in the cellulose composite the mass ratio of the carboxymethylcellulose to the bacterial nanocellulose is 0.35:1 to 0.85:

1. [8] Use of a liquid cellulose composite according to any one of claims 6-7, or obtained by a process according to any one of claims 1-5, as a component in medical, technical or cosmetic formulations. [9] Use of a liquid cellulose composite according to any one of claims 6-7, or obtained by a process according to any one of claims 1-5, as a dispersion base material.