Cellulose tube and preparation method thereof

Abstract

The invention discloses a cellulose tube and a preparation method thereof, and belongs to the technical field of natural polymer materials. The preparation method comprises the following steps: S1, dissolving cellulose in an organic alkali aqueous solution to obtain a cellulose solution; s2, immersing a glass rod into the cellulose solution obtained in the step S1, taking out the glass rod, and immersing the glass rod into a poor solvent for regeneration; s3, taking out, washing and drying to obtain a layer of regenerated cellulose hydrogel; and S4, repeating the steps S1-S3, finally immersing the glass rod into the poor solvent for soaking, removing the glass rod to obtain cellulose hydrogel, immersing the cellulose hydrogel into the poor solvent for soaking, taking out the cellulose hydrogel, and drying to obtain the cellulose tube. The method is simple in preparation process, free of freeze drying, low in production cost and environmentally friendly, and the obtained cellulose tube has good mechanical properties and structural stability.

Description

Technical Field

[0001] The invention belongs to the technical field of natural polymer materials, and particularly relates to a cellulose tube and a preparation method thereof. Background Art

[0002] In the context of global energy restructuring and sustainable development, the non-renewable nature of traditional fossil fuels and the resulting environmental pollution have catapulted the development and utilization of green, renewable resources into the global spotlight. Biomass resources such as cellulose, starch, chitosan, alginate, and lignin, as natural polymers synthesized through photosynthesis, demonstrate significant competitive potential within sustainable development strategies due to their core advantages: renewability, abundance, environmental friendliness, and biocompatibility. In this context, scientifically advancing the efficient conversion and utilization of biomass resources is crucial for alleviating global resource shortages and environmental pollution.

[0003] Among numerous biomass resources, cellulose, the most abundant natural polymer on Earth, is widely found in natural plant fibers such as cotton and wood pulp. Its unique molecular structure and physicochemical properties make it a promising alternative to traditional energy sources and materials. Cellulose, in particular, has attracted considerable attention due to its combination of low density, high porosity, low thermal conductivity, customizable surface functional groups, and biodegradability. In recent years, it has demonstrated broad application prospects in areas such as adsorption, thermal insulation, sensing, and energy storage.

[0004] Cellulose materials can be prepared from cellulose solutions or dispersions. Currently, the main methods for preparing cellulose materials with three-dimensional morphological structures are: machine rolling method, extrusion method, and hot pressing and winding method. For example, Chinese patent CN202411901270.X discloses a wood cellulose straw with a high bamboo powder content and a preparation method thereof. The invention is to compound bamboo, cellulose, protective additives, etc. in proportion and then dehydrate them under negative pressure. A winder is used to make straws. After drying, the straws are immersed in a protective agent, dried, and finally cut into straws of specified lengths using a pipe cutter. However, this method requires customized machinery and equipment, and has high cost and energy consumption. Chinese patent CN202411393214.X discloses a cellulose-based straw and a preparation method thereof. The invention mixes and cross-links a cellulose solution, cellulose powder, cellulose nanofibers, and nanocrystals, and then places them in a vacuum at low temperature and heats up for aging. The straws are formed using a twin-screw or single-screw extruder. The straws are placed in a sulfuric acid / sodium sulfate solution for solidification, washed with water, and then dried. However, this method is complex, requires high equipment requirements, and increases costs. Low-temperature pre-cooling, vacuum treatment, and high-temperature drying steps consume a lot of energy. Chinese patent CN202111683390.3 discloses a bacterial cellulose-based edible straw and its preparation method. This invention produces a bacterial cellulose hydrogel through a biosynthetic process, which is then sterilized by bleaching with hydrogen peroxide. The hydrogel is then dried by hot pressing to form a film. A sodium alginate aqueous solution is coated on the film surface and rolled into a tube. Cross-linking is carried out in the presence of a cross-linking agent (such as calcium lactate or calcium chloride), followed by washing away the cross-linking agent and drying to produce the straw. However, this method is complex, requires multiple steps, and has a long production cycle (four days of fermentation). It also requires biofermentation equipment, cross-linking agents, and hot pressing equipment, resulting in high costs. Consequently, existing methods for preparing cellulose materials with three-dimensional morphologies often involve cumbersome processes, complex steps, and a high reliance on equipment. This leads to high energy consumption and increased production costs, severely hindering large-scale production.

[0005] Therefore, developing a preparation process for cellulose materials with three-dimensional morphology that is simple, environmentally friendly and economical has become a key issue in promoting their industrial application. Summary of the Invention

[0006] In view of the above shortcomings of the prior art, one of the objectives of the present invention is to provide a method for preparing cellulose tubes. The method of the present invention has a simple preparation process, does not require freeze-drying, has low production costs, is green and environmentally friendly, and the obtained cellulose tubes have good mechanical properties and structural stability.

[0007] To achieve the above purpose, the specific technical solutions of the present invention are as follows:

[0008] A method for preparing a cellulose tube comprises the following steps:

[0009] S1. Dissolving cellulose in an aqueous organic base solution to obtain a cellulose solution;

[0010] S2. The glass rod is immersed in the cellulose solution obtained in step S1, removed and then immersed in a poor solvent for regeneration;

[0011] S3 was removed and washed and dried to obtain a layer of regenerated cellulose hydrogel;

[0012] S4. Repeat steps S1 to S3, and finally immerse the glass rod in a poor solvent, remove the glass rod to obtain a cellulose hydrogel, and then immerse the cellulose hydrogel in a poor solvent, remove it, and dry it to obtain the cellulose tube.

[0013] The present invention uses an aqueous organic base solution to dissolve cellulose. A glass rod is then repeatedly immersed in a cellulose solution, regenerated in a poor solvent, and then washed with water to form a multilayer cellulose hydrogel on the rod. Finally, the glass rod with the multilayer hydrogel on its surface is immersed in a poor solvent for a period of time. After the glass rod is successfully removed, the multilayer cellulose hydrogel is obtained. The resulting multilayer cellulose hydrogel is then immersed in a poor solvent for a period of time to solidify the cellulose tube. After removal, the tube is naturally dried in air to form the cellulose tube. Compared to existing methods for preparing cellulose tubes, the present method is simpler and easier to operate, operates under mild conditions, does not require freeze-drying, has low production costs, and is environmentally friendly.

[0014] Preferably, the concentration of the organic base aqueous solution is 1-2 mol / L.

[0015] Preferably, the organic base includes at least one of benzyltrimethylammonium hydroxide, benzyltriethylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0016] Preferably, the mass fraction of the cellulose solution is 3-6%.

[0017] Preferably, the method further comprises the following step: adding epichlorohydrin to the cellulose solution in an ice-water bath to carry out a cross-linking reaction.

[0018] Preferably, in step S2, the glass rod is immersed in the poor solvent for 2 to 6 minutes.

[0019] Preferably, the poor solvent includes at least one of ultrapure water, ethanol, tert-butanol, and acetic acid.

[0020] Preferably, in step S3, the glass rod is washed with ultrapure water, and the liquid on the surface of the glass rod is absorbed with filter paper.

[0021] Preferably, the diameter of the glass rod is 2-40 mm.

[0022] Preferably, the number of repetitions in step S4 is ≥ 3 times; more preferably, the number of repetitions in step S4 is 3 to 9 times.

[0023] Preferably, in step S4, the glass rod is immersed in the poor solvent for 6 to 24 hours, and after the glass rod is removed, the cellulose hydrogel is immersed in the poor solvent for 6 to 24 hours.

[0024] Another object of the present invention is to provide a cellulose tube prepared by the method.

[0025] Compared with the prior art, the present invention is beneficial in that:

[0026] (1) Compared with the preparation method of cellulose tubes in the prior art, the preparation process of the method of the present invention is simple and easy to operate, the conditions are mild, no freeze-drying is required, the production cost is low, and it is green and environmentally friendly.

[0027] (2) The present invention forms a cellulose tube with a multi-layer structure by multiple regeneration on a glass rod. The mechanical properties of the cellulose tube can be controlled by adjusting the number of layers and whether or not the cellulose tube is cross-linked.

[0028] (3) The present invention obtains multilayer cellulose hydrogel on the glass rod by repeatedly immersing the glass rod in cellulose solution, regenerating the poor solvent, and washing with water. The multilayer cellulose structure can form a dense network through interlayer hydrogen bonds (-OH groups) and van der Waals forces, thereby enhancing the mechanical properties. The cellulose tube prepared by the method of the present invention has good mechanical properties and structural stability, and the compressive strength is as high as 4.96 MPa (10 layers). It has good application prospects in the field of degradable daily necessities such as straws.

[0029] (4) The present invention successfully removes the glass rod by regeneration through soaking in a poor solvent, solidifies and shapes it by soaking in a poor solvent, and removes organic alkali residues at the same time, thereby obtaining a transparent hollow tubular cellulose tube with a smooth surface and a hard texture. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a physical picture of a layer of cellulose hydrogel prepared in Example 1;

[0031] Figure 2 This is a physical picture of the cellulose tube prepared in Example 1;

[0032] Figure 3 This is a scanning electron microscope image of the cellulose tube prepared in Example 1;

[0033] Figure 4 This is a physical picture of the cellulose tube prepared in Example 2;

[0034] Figure 5This is a microscope image of the cellulose tube prepared in Example 2;

[0035] Figure 6 This is a comparison chart of the mechanical properties of the cellulose tubes prepared in Examples 2, 3, and 4. DETAILED DESCRIPTION

[0036] The technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] The present invention provides a method for preparing a cellulose tube, comprising the following steps:

[0038] S1. Dissolving cellulose in an aqueous organic base solution to obtain a cellulose solution;

[0039] S2. The glass rod is immersed in the cellulose solution obtained in step S1, removed and then immersed in a poor solvent for regeneration;

[0040] S3 was removed and washed and dried to obtain a layer of regenerated cellulose hydrogel;

[0041] S4. Repeat steps S1 to S3, and finally immerse the glass rod in a poor solvent, remove the glass rod to obtain a cellulose hydrogel, and then immerse the cellulose hydrogel in a poor solvent, remove it, and dry it to obtain the cellulose tube.

[0042] In step S1 , the concentration of the organic base aqueous solution may be 1-2 mol / L, for example, 1 mol / L, 1.4 mol / L, 1.88 mol / L, 2 mol / L, etc.

[0043] The organic base may be selected from at least one of benzyltrimethylammonium hydroxide, benzyltriethylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0044] The mass fraction of cellulose in the cellulose solution obtained in step S1 is 3% to 6%.

[0045] In step S2, the poor solvent can be selected from at least one of ultrapure water, ethanol, tert-butanol, and acetic acid; the glass rod is immersed in the poor solvent for 2 to 6 minutes, for example, 2 minutes, 3 minutes, 5 minutes, or 6 minutes.

[0046] The diameter of the glass rod can be 2-40 mm.

[0047] The number of repetitions in step S4 is ≥ 3 times.

[0048] In step S4, the glass rod may be immersed in the poor solvent for 6 to 24 hours. After the glass rod is removed, the cellulose hydrogel may be immersed in the poor solvent for 6 to 24 hours.

[0049] Example 1

[0050] This embodiment provides a method for preparing a cellulose tube, comprising the following steps:

[0051] S1. Cotton linters with an average molecular weight of 108,000 were dissolved in a 1.88 mol / L aqueous solution of benzyltrimethylammonium hydroxide, frozen at -24°C, and then thawed at room temperature to obtain a 4 wt% cellulose solution.

[0052] S2. Immerse a 5.80 mm diameter glass rod in the cellulose solution, remove it, and then immerse it in ultrapure water for 3 minutes.

[0053] S3. After removing the glass rod, wash it with ultrapure water for 3 minutes to remove the solvent, and then dry the surface liquid with filter paper to obtain a layer of regenerated cellulose hydrogel;

[0054] S4. Repeat steps S1-S3 three times. Finally, immerse the glass rod in ethanol for 12 hours. Remove the glass rod to obtain the cellulose hydrogel. Soak the cellulose hydrogel in ethanol for another 12 hours. Remove the cellulose hydrogel and air dry it for 12 hours to obtain the cellulose tube.

[0055] The core of the present invention is to realize the controllable construction of the layered structure on the glass rod by subjecting the glass rod to a cyclic operation of "cellulose solution immersion-poor solvent regeneration-water washing".

[0056] Figure 1 This is a physical picture of a layer of cellulose hydrogel prepared in this example. As can be seen from the figure, the sample is milky white and translucent, with a smooth surface without defects, indicating that the casting process of the cellulose solution on the glass rod has good uniformity. Figure 2 This is a physical picture of the cellulose tube prepared in this example. As can be seen from the figure, it is a transparent hollow tubular structure with a slightly light yellow color, a smooth surface and significantly improved hardness, and the structure has not collapsed. This may be due to the dense hydrogen bond network structure formed by the cellulose molecular chains between single layers and multiple layers during the regeneration and drying process. Figure 3 This is a scanning electron microscope image of the cellulose tubes prepared in this example. It can be observed that the cellulose tubes present a clear and orderly layered structure, and the thickness of a single layer is about 19 μm, indicating the multi-layer physical structure of the cellulose tubes.

[0057] Example 2

[0058] The preparation method of the cellulose tube in this embodiment is basically the same as that in Example 1, except that in step S2, a glass rod with a diameter of 5.80 mm is immersed in the cellulose solution, taken out, and then immersed in ethanol for regeneration for 3 minutes.

[0059] Figure 4 This is a photo of the cellulose tube prepared in this example, which is also a transparent hollow tube with a slightly light yellow color and a hard texture. Figure 5 This microscopic image of the cellulose tubes prepared in this example clearly shows a four-layer structure, with each layer approximately 50-54 μm thick, a slight increase compared to Example 1. This thickness variation can be attributed to the polarity of the solvent: Ethanol accelerates the conformational reorganization and regeneration of cellulose molecular chains compared to ultrapure water, causing the solution to gel before it is fully cast on the substrate surface, resulting in a thicker monolayer structure.

[0060] Example 3

[0061] The method for preparing the cellulose tubes of this embodiment is substantially the same as that of embodiment 2, with the only difference being that in step S4, steps S1 to S3 are repeated nine times.

[0062] Example 4

[0063] The preparation method of the cellulose tubes in this embodiment is basically the same as that in Example 2, except that step S1 further includes the following operations: adding epichlorohydrin to the cellulose solution in an ice-water bath (adding 200 μL of epichlorohydrin to 30 g of cellulose solution), stirring for 15 minutes to carry out a cross-linking reaction, and then centrifuging at 0°C and 8000 rpm to remove bubbles.

[0064] Figure 6The following is a comparison of the mechanical properties of the cellulose tubes prepared in Examples 2, 3, and 4. As shown, the four-layer cellulose tube has a compressive strength of 1.37 MPa and a compression modulus of 18.76 MPa, while the ten-layer cellulose tube has a compressive strength of 4.96 MPa and a compression modulus of 133.13 MPa, demonstrating a significant layer-strengthening effect. This mechanical strengthening effect is primarily due to two mechanisms: first, the interlayer interface forms a cooperative load-bearing network through physical entanglement and hydrogen bonding; second, the water washing process effectively reduces stress concentration between the layers. Furthermore, a comparison of the data from Example 2 (uncrosslinked) and Example 4 (crosslinked) reveals that the crosslinked four-layer cellulose tube has a compressive strength of 1.96 MPa and a compression modulus of 59.25 MPa, both higher than the uncrosslinked cellulose tube. This demonstrates that crosslinking effectively enhances interlayer interactions, thereby improving the overall mechanical properties of the cellulose tube. In summary, the present invention successfully prepared cellulose tubes with adjustable mechanical properties and structural stability by repeatedly immersing in cellulose solution-poor solvent regeneration-water washing process, combined with a natural drying process, highlighting the unique advantages of this preparation method in constructing high-strength and lightweight cellulose materials.

[0065] In addition, the inventors found that the mechanical properties of a single-layer cellulose tube were very poor and it was very easy to collapse during compression testing, making it impossible to measure effective compressive strength and compression modulus data.

[0066] Example 5

[0067] This embodiment provides a method for preparing a cellulose tube, comprising the following steps:

[0068] S1. Cotton linters with an average molecular weight of 108,000 were dissolved in a 1.88 mol / L aqueous solution of benzyltrimethylammonium hydroxide, frozen at -24°C, and then thawed at room temperature to obtain a 5 wt% cellulose solution.

[0069] S2. Immerse a 5.80 mm diameter glass rod in the cellulose solution, remove it, and then immerse it in acetic acid for 2 minutes.

[0070] S3. After removing the glass rod, wash it with ultrapure water for 4 minutes to remove the solvent, and then dry the surface liquid with filter paper to obtain a layer of regenerated cellulose hydrogel;

[0071] S4. Repeat steps S1-S3 four times. Finally, immerse the glass rod in ethanol for 6 h. Remove the glass rod to obtain the cellulose hydrogel. Soak the cellulose hydrogel in ethanol for another 6 h. Remove the cellulose hydrogel and air dry it for 6 h to obtain the cellulose tube.

[0072] Example 6

[0073] This embodiment provides a method for preparing a cellulose tube, comprising the following steps:

[0074] S1. Cotton linters with an average molecular weight of 108,000 were dissolved in a 1.88 mol / L aqueous solution of benzyltrimethylammonium hydroxide, frozen at -24°C, and then thawed at room temperature to obtain a 4 wt% cellulose solution.

[0075] S2. Immerse a glass rod with a diameter of 8.10 mm in the cellulose solution, remove it, and then immerse it in ethanol for 4 minutes.

[0076] S3. After removing the glass rod, wash it with ultrapure water for 4 minutes to remove the solvent, and then dry the surface liquid with filter paper to obtain a layer of regenerated cellulose hydrogel;

[0077] S4. Repeat steps S1-S3 nine times. Finally, immerse the glass rod in ethanol for 18 hours. Remove the glass rod to obtain the cellulose hydrogel. Then, immerse the cellulose hydrogel in ethanol for 6 hours. After removing the cellulose hydrogel, air dry it for 12 hours to obtain the cellulose tube.

[0078] Example 7

[0079] This embodiment provides a method for preparing a cellulose tube, comprising the following steps:

[0080] S1. Cotton linters with an average molecular weight of 108,000 were dissolved in a 1.88 mol / L aqueous solution of benzyltrimethylammonium hydroxide, frozen at -24°C, and then thawed at room temperature to obtain a 5 wt% cellulose solution.

[0081] S2. Immerse a glass rod with a diameter of 8.10 mm in the cellulose solution, remove it, and then immerse it in acetic acid for 4 minutes;

[0082] S3. After removing the glass rod, wash it with ultrapure water for 6 minutes to remove the solvent, and then dry the surface liquid with filter paper to obtain a layer of regenerated cellulose hydrogel;

[0083] S4. Repeat steps S1-S3 three times. Finally, immerse the glass rod in acetic acid for 12 hours. Remove the glass rod to obtain the cellulose hydrogel. Then, immerse the cellulose hydrogel in ethanol for 12 hours. Remove the cellulose hydrogel and air-dry it for 12 hours to obtain the cellulose tube.

[0084] Comparative Example 1

[0085] The preparation method of the cellulose tubes in this comparative example is basically the same as that in Example 1, except that step S4 is as follows: repeating the operations of steps S1 to S3 three times to obtain the cellulose tubes.

[0086] In this comparative example, the curing operation was omitted and drying was performed directly, and the obtained cellulose tubes could not be completely removed from the glass rod.

[0087] Comparative Example 2

[0088] The preparation method of the cellulose tubes in this comparative example is basically the same as that in Example 1, except that step S4 is as follows: repeat the operations of steps S1 to S3 three times, and finally immerse the glass rod in ethanol for 1 hour, remove the glass rod to obtain a cellulose hydrogel, and then immerse the cellulose hydrogel in ethanol for 1 hour. After taking out, the cellulose hydrogel is placed in air to dry naturally for 12 hours to obtain a cellulose tube.

[0089] The second immersion time of the poor solvent in this comparative example was too short, resulting in the sample not being completely cured and having weak mechanical properties.

[0090] Comparative Example 3

[0091] The preparation method of the cellulose tubes in this comparative example is basically the same as that in Example 1, except that step S4 is as follows: repeat the operations of steps S1 to S3 three times, and finally immerse the glass rod in an aqueous solution of benzyltrimethylammonium hydroxide for 12 hours. After removing the glass rod, the cellulose hydrogel is obtained, and then immersed in an aqueous solution of benzyltrimethylammonium hydroxide for 12 hours. After removing, the cellulose hydrogel is placed in air to dry naturally for 12 hours to obtain the cellulose tubes.

[0092] Since the benzyltrimethylammonium hydroxide aqueous solution can dissolve the cellulose solution, in this comparative example, when the glass rod soaked in the cellulose solution is immersed in the benzyltrimethylammonium hydroxide aqueous solution, the cellulose will swell and cannot regenerate into a membrane, resulting in the inability to regenerate and form the cellulose tube.

[0093] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a cellulose tube, characterized in that: The following steps are involved: S1. Dissolving cellulose in an aqueous organic base solution to obtain a cellulose solution; S2. The glass rod is immersed in the cellulose solution obtained in step S1, removed and then immersed in a poor solvent for regeneration; S3 was removed and washed and dried to obtain a layer of regenerated cellulose hydrogel; S4. Repeat steps S1 to S3, and finally immerse the glass rod in a poor solvent, remove the glass rod to obtain a cellulose hydrogel, and then immerse the cellulose hydrogel in a poor solvent, remove it, and dry it to obtain the cellulose tube.

2. The method for preparing a cellulose tube according to claim 1, characterized in that: The concentration of the organic base aqueous solution is 1-2 mol / L; And / or, the organic base includes at least one of benzyltrimethylammonium hydroxide, benzyltriethylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

3. The method for preparing a cellulose tube according to claim 1, characterized in that: The mass fraction of the cellulose solution is 3% to 6%.

4. The method for preparing a cellulose tube according to claim 1, characterized in that: The following steps are also included: Epichlorohydrin is added to the cellulose solution in an ice-water bath to carry out a cross-linking reaction.

5. The method for preparing a cellulose tube according to claim 1, characterized in that: In step S2, the glass rod is immersed in the poor solvent for 2 to 6 minutes.

6. The method for preparing a cellulose tube according to claim 1, characterized in that: The poor solvent includes at least one of ultrapure water, ethanol, tert-butanol, and acetic acid.

7. The method for preparing a cellulose tube according to claim 1, characterized in that: The diameter of the glass rod is 2-40 mm.

8. The method for preparing a cellulose tube according to claim 1, characterized in that: The number of repetitions in step S4 is ≥ 3 times.

9. The method for preparing a cellulose tube according to claim 1, characterized in that: In step S4, the glass rod is immersed in the poor solvent for 6 to 24 hours. After the glass rod is removed, the cellulose hydrogel is immersed in the poor solvent for 6 to 24 hours.

10. A cellulose tube prepared by the method according to any one of claims 1 to 9.

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