A cellulose-based hydrogel satisfying 3D printing and sensing performance, and a preparation method and application thereof

Abstract

The present application relates to the field of hydrogel 3D printing, flexible sensor, wearable electronic device, in particular to a cellulose-based hydrogel meeting 3D printing and sensing performance, and a preparation method and application thereof.The cellulose-based hydrogel contains zinc salt, lithium salt, water and alkali pretreated cellulose;in the cellulose-based hydrogel, the content of the alkali pretreated cellulose is 1%-6% based on 100% of the total mass of the zinc salt, lithium salt and water, the molar ratio of the total amount of zinc salt and lithium salt to water is 1:(3-4), the molar ratio of zinc salt to lithium salt is 1:(0.4-2.4), and the molar amount of zinc salt and lithium salt is calculated based on the content of zinc element and lithium element.The present application uses alkali pretreated cellulose, combines the ratio of alkali pretreated cellulose and metal salt solution (containing the above-mentioned zinc salt, lithium salt and water) with a specific content, and the composition of the metal salt solution, to obtain a cellulose-based hydrogel meeting sensing and 3D printing performance, and having better anti-freezing performance, higher conductivity and better mechanical performance, achieving unexpected technical effects.

Description

Technical Field

[0001] This invention relates to the fields of hydrogel 3D printing, flexible sensors, and wearable electronic devices, specifically to a cellulose-based hydrogel that meets 3D printing and sensing performance requirements, its preparation method, and its applications. Background Technology

[0002] Hydrogels are three-dimensional hydrophilic or water-soluble polymeric network systems formed through chemical or physical cross-linking. They can absorb large amounts of water, maintain a certain soft material shape, and possess characteristics such as high water content, excellent biocompatibility, good environmental sensitivity, functional designability, and good structural controllability. However, traditional polymeric hydrogels are not easily degraded, lack biological functions, and their petrochemical raw materials are not renewable in the short term.

[0003] Existing technologies indicate that cellulose is a renewable resource and contains a large number of hydroxyl groups, making it suitable for preparing hydrogels. CN 109942838A discloses a method for preparing a cellulose conductive hydrogel that can be used for 3D printing. The method includes: preparing a mixed solution of ZnCl2 and CaCl2; adding cellulose; and dissolving the cellulose solution by magnetic stirring at 50℃ to 90℃ for 10 min to 90 min until completely dissolved, to obtain a cellulose solution; adding water or a small molecule alcohol to the cellulose solution; and stirring the solution by magnetic stirring at 50℃ to 90℃ for 5 min to 30 min until homogeneous; and degassing and cooling to obtain a cellulose conductive hydrogel. This cellulose hydrogel exhibits certain advantages in electrical conductivity, but its antifreeze properties are limited. The mechanical properties of the hydrogel decrease significantly at low temperatures. For example, at -20℃, the elongation at break is only 80% of that at room temperature, and at -60℃, it is only 54%. This indicates that the hydrogel undergoes partial crystallization and freezing at -20℃ and -60℃, affecting its performance and lifespan in low-temperature environments. Its antifreeze properties need further improvement, limiting its application in flexible sensors, electric vehicles, and other fields. Its tensile strength at room temperature is also low (only 0.35 MPa). Cellulose-based hydrogels are soft materials, and mechanical properties are a crucial factor influencing their application development. Improving its tensile strength can provide better deformability and shape memory properties in the field of flexible sensors, making them more flexible and durable. In the biomedical field, it can improve delivery efficiency and tissue repair capabilities.

[0004] Therefore, how to provide a cellulose-based hydrogel with good electrical conductivity and superior antifreeze and mechanical properties is a technical problem that needs to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a cellulose-based hydrogel that meets the requirements for 3D printing and sensing performance, along with its preparation method and applications. The cellulose-based hydrogel of this invention overcomes the shortcomings of existing technologies in terms of lack of freeze resistance and possesses excellent freeze resistance, exhibiting no crystallization behavior at temperatures as low as -80°C. In addition to its excellent freeze resistance, the cellulose-based hydrogel of this invention also has good electrical conductivity and mechanical properties.

[0006] The first aspect of the present invention is to provide a cellulose-based hydrogel containing zinc salt, lithium salt, water and alkali-pretreated cellulose; wherein, based on the total mass of zinc salt, lithium salt and water being 100%, the content of the alkali-pretreated cellulose is 1%-6%, the molar ratio of the total amount of zinc salt and lithium salt to water is 1:(3-4), the molar ratio of zinc salt to lithium salt is 1:(0.4-2.4), and the molar amounts of zinc salt and lithium salt are both based on the content of zinc and lithium elements.

[0007] As mentioned earlier, the antifreeze properties of cellulose-based hydrogels in the prior art need further improvement. Cellulose is difficult to dissolve in common salt solutions, and even if it does dissolve, it is difficult to obtain cellulose-based hydrogels with high conductivity, good mechanical properties, and superior antifreeze properties. This invention uses alkali-pretreated cellulose, combined with a specific ratio of alkali-pretreated cellulose to a metal salt solution (containing the aforementioned zinc salt, lithium salt, and water), and the composition of the metal salt solution, to obtain a cellulose-based hydrogel that meets the requirements for sensing and 3D printing performance, and exhibits superior antifreeze properties, while also possessing high conductivity and good mechanical properties, achieving unexpected technical results.

[0008] The inventors believe that the technical effects achieved by this invention are due to the following reasons, based on their research:

[0009] This invention refines and shortens cellulose microfiber bundles by pre-treating cellulose with alkali, making cellulose easier to dissolve in the metal salt solution of this invention.

[0010] By adjusting the cellulose content, it has good 3D printing performance;

[0011] By adjusting the ratio of metal salts (zinc salt, lithium salt), the dissolution of cellulose and good conductive sensing performance can be achieved. The metal cations first enter the cellulose network structure and swell, and then form coordination bonds with the cellulose hydroxyl groups. The hydrogen bonds inside and between cellulose molecules are broken, and finally the cellulose solution is dissolved into a transparent and homogeneous solution.

[0012] If the zinc salt content is too high, the strength of the final cellulose-based conductive hydrogel will be weakened, and salt precipitation will easily occur at low temperatures. If the zinc salt content is too low, the cellulose will be difficult to dissolve.

[0013] The strength and toughness of cellulose-based conductive hydrogels also increase with increasing lithium salt content. This may be because the mechanical properties of cellulose-based conductive hydrogels depend to some extent on the coordination bonds formed between metal salt ions and cellulose molecules through chelation. When the contents of zinc and lithium salts change, the coordination balance between cellulose and metal salt ions is disrupted, and its mechanical properties change accordingly.

[0014] The cellulose-based conductive hydrogel system prepared by dissolving cellulose pretreated according to the present invention in a metal salt solvent system (i.e., metal salt solution) contains free ions. These ions can move in the three-dimensional network system of the cellulose-based conductive hydrogel, providing ion carriers for the conductivity of the cellulose-based hydrogel and effectively improving the conductivity and sensing performance of the cellulose-based conductive hydrogel.

[0015] This invention optimizes the ionized structure of cellulose and the solvent / dispersant system to influence its rheological properties, meeting the requirements of 3D printing and constructing a cellulose-based conductive hydrogel material with a designable structure. Building upon the aforementioned properties, the cellulose-based conductive hydrogel of this invention exhibits excellent antifreeze properties. This invention improves the antifreeze and mechanical properties of cellulose-based hydrogels, broadening their application prospects.

[0016] According to the present invention, the cellulose-based hydrogel contains zinc salt, lithium salt, water, and alkali-pretreated cellulose. In the cellulose-based hydrogel, based on the total mass of zinc salt, lithium salt, and water as 100%, the content of the alkali-pretreated cellulose is 1%-6%, the molar ratio of the total amount of zinc salt and lithium salt to water is 1:(3-4), and the molar ratio of zinc salt to lithium salt is 1:(0.4-2.4). The molar amounts of zinc salt and lithium salt are calculated based on the content of zinc and lithium elements. The composition of the above-mentioned cellulose-based hydrogel can be calculated by the amount of materials fed in the preparation method, or its composition can be detected using existing detection methods. For example, the water content can be detected by a moisture analyzer, the cellulose content by a cellulose analyzer, and the zinc and lithium salt contents by atomic absorption spectrometry.

[0017] According to some preferred embodiments of the present invention, in the cellulose-based hydrogel, the content of the cellulose in the alkalization pretreatment is 2%-5%, more preferably 3%-5%, based on the total mass of zinc salt, lithium salt and water of 100%.

[0018] According to some preferred embodiments of the present invention, the total amount of zinc salt and lithium salt to water has a molar ratio of 1:(3-3.5).

[0019] According to some preferred embodiments of the present invention, the molar ratio of zinc salt to lithium salt is 1:(0.6-1.5), preferably 1:(0.8-1.2).

[0020] According to some preferred embodiments of the present invention, the zinc salt is selected from at least one of Zn(NO3)2, ZnBr2, and ZnSO4.

[0021] According to some preferred embodiments of the present invention, the lithium salt is selected from at least one of LiBr, LiCl, and Li2SO4.

[0022] According to some preferred embodiments of the present invention, the method for preparing the alkalized pretreated cellulose includes:

[0023] Cellulose is alkalized in an alkaline solution, then washed until neutral, dissolved in a mixed solvent, and freeze-dried to obtain alkalized pretreated cellulose.

[0024] According to some more preferred embodiments of the present invention, in the method for preparing cellulose with alkalization pretreatment:

[0025] The cellulose is selected from at least one of cotton pulp cellulose, hemp fiber, and lignin fiber; and / or,

[0026] The alkali in the alkaline solution is selected from at least one of a weak base and a strong base, preferably the weak base is selected from at least one of Na₂CO₃ and K₂CO₃, and preferably the strong base is selected from at least one of KOH and NaOH; and / or,

[0027] The mass ratio of alkali to water in the alkaline solution is 1:(15-25); and / or,

[0028] The amount of alkaline solution used is 80-120 mL relative to 1 g of cellulose.

[0029] According to some preferred embodiments of the present invention, in the method for preparing cellulose through alkalization pretreatment:

[0030] The alkalization treatment conditions include: a temperature of 20-30°C, a time of 1-3 hours, and / or, the pretreatment is carried out under mixed conditions, preferably using a high-speed homogenizer for stirring; and / or,

[0031] The method of washing to neutral is as follows: repeatedly rinsing the pretreated cellulose with water until it is neutral; and / or,

[0032] The mixed solvent is a mixed solution of alcohol and water, preferably the alcohol is selected from at least one of anhydrous ethanol and propylene glycol; and / or the volume ratio of alcohol to water is (2:8) to (4:6).

[0033] According to the present invention, the water may be conventional laboratory water, including but not limited to deionized water.

[0034] According to the present invention, preferably, the freeze-drying process is carried out in a freeze dryer.

[0035] A second aspect of the present invention is to provide a method for preparing the cellulose-based hydrogel described in the first aspect, comprising:

[0036] The alkalized cellulose was dissolved in an aqueous solution containing zinc and lithium salts to obtain a cellulose-based hydrogel.

[0037] According to some preferred embodiments of the present invention, the amount of cellulose used in the alkalization pretreatment is 1%-6%, preferably 2%-5%, and more preferably 3%-5%, based on the total mass of zinc salt, lithium salt and water as 100%.

[0038] According to some preferred embodiments of the present invention, in an aqueous solution containing zinc salt and lithium salt:

[0039] The total amount of zinc salt and lithium salt in the molar ratio of water is 1:(3-4), preferably 1:(3-3.5); and / or, the molar ratio of zinc salt and lithium salt is 1:(0.4-2.4), preferably 1:(0.6-1.5), more preferably 1:(0.8-1.2, and the molar amounts of zinc salt and lithium salt are calculated based on the content of zinc and lithium elements.

[0040] According to some preferred embodiments of the present invention, the zinc salt is selected from at least one of Zn(NO3)2, ZnBr2, and ZnSO4.

[0041] According to some preferred embodiments of the present invention, the lithium salt is selected from at least one of LiBr, LiCl, and Li2SO4.

[0042] According to some preferred embodiments of the present invention, the dissolution conditions include: a temperature of 90-120°C and / or a time of 3-5 hours; preferably, a temperature of 90-100°C and / or a time of 3-4 hours. Under these preferred dissolution conditions, cellulose can be dissolved more effectively while ensuring that cellulose does not degrade.

[0043] According to the present invention, the process of dissolving cellulose is carried out under mixing conditions, and the mixing method can be conventional methods such as stirring, including but not limited to magnetic stirring.

[0044] According to some preferred embodiments of the present invention, the preparation method further includes:

[0045] After dissolving the alkalized pretreated cellulose in an aqueous solution containing zinc and lithium salts to obtain a cellulose-based hydrogel, the cellulose-based hydrogel is injected into a container and then degassed. Preferably, the container is placed in a centrifuge for degassed treatment.

[0046] According to the present invention, the preparation method further includes the step of preparing an aqueous solution containing zinc salt and lithium salt according to the raw material composition. For example, zinc salt, lithium salt and water are directly mixed and stirred until the salt dissolves to obtain an aqueous solution containing zinc salt and lithium salt (also known as a metal salt solution). In order to accelerate the dissolution rate during the mixing process, the solution can be heated appropriately, for example, heated to 90-120°C. Alternatively, higher concentrations of zinc salt aqueous solution and lithium salt aqueous solution can be prepared separately first, and then appropriate amounts of zinc salt aqueous solution and lithium salt aqueous solution can be taken according to the raw material composition and optionally some water can be added to obtain an aqueous solution containing zinc salt and lithium salt.

[0047] A third aspect of the present invention is to provide an application of the cellulose-based hydrogel described in the first aspect or the cellulose-based hydrogel prepared by the preparation method described in the second aspect in the fields of 3D printing, flexible sensors, and wearable electronic devices.

[0048] According to some preferred embodiments of the present invention, when using the cellulose-based hydrogel for 3D printing, the moving speed of the 3D printing nozzle is 80-130 mm / min; and / or, the injection speed of the injection pump containing the cellulose-based hydrogel is 30-60 μL / min.

[0049] For 3D printing, this is an existing technology. For example, you can first use CAD to model the target graphic, and then use Simply 3D slicing software to slice the model and import it into a 3D printer for printing. I will not go into details here.

[0050] This invention prepares a cellulose-based conductive hydrogel. The cellulose molecule is rich in hydroxyl groups, which can form numerous hydrogen bonds, cross-linking to form a three-dimensional network structure, and creating intermolecular interactions with the hydrogel. This allows for the construction of a green and environmentally friendly cellulose hydrogel with good degradability, biocompatibility, flexibility, and water absorption, which has wide applications in biomedicine, flexible electronic devices, and many other fields.

[0051] Compared with traditional synthetic polymer hydrogels, cellulose-based hydrogels are non-toxic, biodegradable, biocompatible, environmentally friendly, and renewable.

[0052] The cellulose-based conductive hydrogel of the present invention has the following advantages:

[0053] As mentioned earlier, the antifreeze properties of cellulose-based hydrogels in the prior art need further improvement. Cellulose is difficult to dissolve in common salt solutions, and even if it does dissolve, it is difficult to obtain cellulose-based hydrogels with high conductivity, good mechanical properties, and superior antifreeze properties. This invention uses alkali-pretreated cellulose, combined with a specific ratio of alkali-pretreated cellulose to a metal salt solution (containing the aforementioned zinc salt, lithium salt, and water), and the composition of the metal salt solution, to obtain a cellulose-based hydrogel that meets the requirements for sensing and 3D printing performance, and exhibits superior antifreeze properties, while also possessing high conductivity and good mechanical properties, achieving unexpected technical results.

[0054] In addition to the advantages mentioned above, the cellulose-based conductive hydrogel of the present invention also has the following characteristics:

[0055] Analysis of its storage modulus (G') and loss modulus (G") shows that as the shear force increases, the storage modulus of the cellulose-based hydrogel of the present invention is generally less than the loss modulus, indicating that it is more like a viscoelastic liquid. It also shows that the cellulose-based hydrogel has the property of transforming from a shear-thinned fluid to a solid-like substance during the printing process. Therefore, it can maintain good shape fidelity, indicating that the cellulose-based hydrogel prepared by the present invention meets the requirements of good 3D printing performance.

[0056] The conductivity of the cellulose-based conductive hydrogel of the present invention is 6-7.5 S / m. The conductivity of most hydrogels is generally less than 1 S / m. This indicates that there are free ions in the cellulose-based conductive hydrogel system prepared by dissolving cellulose in a metal salt solvent system. These ions can move in the three-dimensional network system of the cellulose-based conductive hydrogel, providing ion carriers for the conductivity of the cellulose-based hydrogel and effectively improving the conductivity of the cellulose-based conductive hydrogel.

[0057] Thin sheets of cellulose-based conductive hydrogel were fixed onto the fingers, wrists, and arms of the human body. An electrochemical workstation was used to collect changes in electrochemical signals when these parts were periodically bent. When the human body parts underwent periodic changes, the rate of change of current through the hydrogel also showed periodic changes over time. This indicates that cellulose-based conductive hydrogel has good sensing performance and can be applied in sensors, especially in wearable flexible electronic devices, to monitor human movement and health. Attached Figure Description

[0058] Figure 1 The image shows a scanning electron microscope image of the untreated cellulose used in Comparative Example 1 at 100x magnification.

[0059] Figure 2 Scanning electron microscope image of cellulose pretreated with alkali in Example 1 at 100x magnification.

[0060] Figure 3 The graphs show the antifreeze properties of the cellulose-based conductive hydrogels in Examples 1-4 at -80℃ to 20℃, as determined by differential scanning calorimetry.

[0061] Figure 4(a) shows the change in current over time when the hydrogel sheet in Example 1 is attached to a human finger and the finger is bent regularly.

[0062] Figure 4(b) shows the change in current over time when the hydrogel sheet in Example 1 is attached to the wrist of a human body and the wrist is bent regularly.

[0063] Figure 4(c) shows the change in current over time when the hydrogel sheet in Example 1 is attached to the arm of a human body and the arm is bent regularly. Detailed Implementation

[0064] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0065] Among the following raw materials:

[0066] The cotton pulp cellulose was purchased from Xinxiang Chemical Fiber Co., Ltd.

[0067] Unless otherwise specified, the devices in the following embodiments are all commercially available conventional devices in the art.

[0068] Unless otherwise specified, room temperature in the following examples refers to 25°C.

[0069] In the following examples and comparative examples, the molar ratio of zinc salt and lithium salt is expressed in terms of the molar amounts of zinc and lithium, respectively; the molar ratio of the total amount of metal salt to deionized water is also expressed in terms of the total amount of metal salt, expressed in terms of the total molar amounts of zinc and lithium.

[0070] Example 1

[0071] Preparation method of cellulose-based hydrogels:

[0072] Step 1: Prepare an alkaline solution by mixing Na2CO3 and deionized water at a mass ratio of 1:20, then add cotton pulp cellulose. The volume of the alkaline solution is 100 mL relative to 1 g of cellulose. Stir the solution using a high-speed homogenizer at room temperature (25°C) for 1 hour. After stirring, rinse the cellulose repeatedly with deionized water until the pH of the cellulose is neutral. Then add the cellulose to a solution of anhydrous ethanol and deionized water at a volume ratio of 3:7 and freeze-dry it to obtain a pretreated cellulose sample.

[0073] Step 2: Prepare a metal salt solution. The molar ratio of zinc salt to lithium salt (based on the molar amount of metal elements) is 1:1, and the molar ratio of the total amount of metal salt (based on the molar amount of metal elements) to deionized water is 1:3. Mix Zn(NO3)2, LiBr, and deionized water, stir at 90°C for 1 hour, and then stir at room temperature for 1 hour to obtain the metal salt solution.

[0074] Step 3: The alkalized cellulose is gradually added to the prepared metal salt solution. The amount of cellulose added is 5% of the mass of the solvent (i.e., the metal salt solution). The dissolution temperature is 90℃. The dissolution process is carried out by magnetic stirring for 4 hours to obtain a completely dissolved cellulose-based hydrogel with a transparent and uniform texture.

[0075] 3D printing cellulose-based hydrogels

[0076] Step a: The cellulose-based hydrogel obtained in this embodiment, which is completely dissolved and has a transparent and uniform texture, is poured into a syringe and then placed in a centrifuge for degassing treatment at a speed of 7000 r / min for 10 min.

[0077] Step b: Place the syringe on the extrusion equipment and adjust the injection device;

[0078] Step c: Model the target graphic using CAD, then slice the model using Simply 3D slicing software and import it into the 3D printer for printing. The 3D printing nozzle moves at a speed of 100 mm / min, and the injection pump injection speed is set to 40 uL / min.

[0079] Example 2

[0080] Step 1: Prepare an alkaline solution by mixing Na2CO3 and deionized water at a mass ratio of 1:20, then add cotton pulp cellulose. The volume of the alkaline solution is 100 mL relative to 1 g of cellulose. Stir the solution using a high-speed homogenizer at room temperature (25°C) for 1 hour. After stirring, rinse the cellulose repeatedly with deionized water until the pH of the cellulose is neutral. Then add the cellulose to a solution of anhydrous ethanol and deionized water at a volume ratio of 3:7 and freeze-dry it to obtain a pretreated cellulose sample.

[0081] Step 2: Prepare a metal salt solution. The molar ratio of zinc salt to lithium salt (based on the molar amount of metal elements) is 1:1, and the molar ratio of the total amount of metal salt (based on the molar amount of metal elements) to deionized water is 1:3. Mix Zn(NO3)2, LiBr, and deionized water, stir at 90°C for 1 hour, and then stir at room temperature for 1 hour to obtain the metal salt solution.

[0082] Step 3: The alkalized cellulose is gradually added to the prepared metal salt solution. The amount of cellulose added is 4% of the mass of the solvent (i.e., the metal salt solution). The dissolution temperature is 90℃. The dissolution process is magnetically stirred for 4 hours to obtain a completely dissolved cellulose-based hydrogel with a transparent and uniform texture.

[0083] The method for 3D printing cellulose-based hydrogels is the same as in Example 1.

[0084] Example 3

[0085] Step 1: Prepare an alkaline solution by mixing Na2CO3 and deionized water at a mass ratio of 1:20, then add cotton pulp cellulose. The volume of the alkaline solution is 100 mL relative to 1 g of cellulose. Stir the solution using a high-speed homogenizer at room temperature (25°C) for 1 hour. After stirring, rinse the cellulose repeatedly with deionized water until the pH of the cellulose is neutral. Then add the cellulose to a solution of anhydrous ethanol and deionized water at a volume ratio of 3:7 and freeze-dry it to obtain a pretreated cellulose sample.

[0086] Step 2: Prepare a metal salt solution. The molar ratio of zinc salt to lithium salt (based on the molar amount of metal elements) is 1:1, and the molar ratio of the total amount of metal salt (based on the molar amount of metal elements) to deionized water is 1:3. Mix Zn(NO3)2, LiBr, and deionized water, stir at 90°C for 1 hour, and then stir at room temperature for 1 hour to obtain the metal salt solution.

[0087] Step 3: The alkalized cellulose is gradually added to the prepared metal salt solution. The amount of cellulose added is 3% of the mass of the solvent (i.e., the metal salt solution). The dissolution temperature is 90℃. The dissolution process is carried out by magnetic stirring for 4 hours to obtain a cellulose-based hydrogel that is completely dissolved and has a transparent and uniform texture.

[0088] The method for 3D printing cellulose-based hydrogels is the same as in Example 1.

[0089] Example 4

[0090] Step 1: Prepare an alkaline solution by mixing Na2CO3 and deionized water at a mass ratio of 1:20, then add cotton pulp cellulose. The volume of the alkaline solution is 100 mL relative to 1 g of cellulose. Stir the solution using a high-speed homogenizer at room temperature (25°C) for 1 hour. After stirring, rinse the cellulose repeatedly with deionized water until the pH of the cellulose is neutral. Then add the cellulose to a solution of anhydrous ethanol and deionized water at a volume ratio of 3:7 and freeze-dry it to obtain a pretreated cellulose sample.

[0091] Step 2: Prepare zinc salt and lithium salt solutions. The molar ratio of zinc salt and lithium salt (based on the molar amount of metal elements) is 1:1, and the molar ratio of the total amount of metal salt (based on the molar amount of metal elements) to deionized water is 1:3. Mix Zn(NO3)2, LiBr and deionized water, stir at 90℃ for 1 hour, and then stir at room temperature for 1 hour to obtain the metal salt solution.

[0092] Step 3: The alkalized cellulose is gradually added to the prepared metal salt solution. The amount of cellulose added is 2% of the mass of the solvent (i.e., the metal salt solution). The dissolution temperature is 90℃. The dissolution process is carried out by magnetic stirring for 4 hours to obtain a cellulose-based hydrogel that is completely dissolved and has a transparent and uniform texture.

[0093] The method for 3D printing cellulose-based hydrogels is the same as in Example 1.

[0094] Example 5

[0095] Cellulose-based hydrogels were prepared according to the method in Example 1, except that the molar ratio of zinc salt to lithium salt was 1:1.5.

[0096] The obtained cellulose-based hydrogel still has a relatively uniform texture, which can meet the requirements for sensing and 3D printing performance. However, when the cellulose dissolution time is increased to 5 hours, the cellulose-based hydrogel turns pale yellow, indicating that the cellulose undergoes slight degradation due to the increased heating time.

[0097] Example 6

[0098] Cellulose-based hydrogels were prepared according to the method in Example 1, except that the molar ratio of zinc salt to lithium salt was 1:0.6.

[0099] The resulting cellulose-based hydrogel has a uniform texture and can meet the requirements for sensing and 3D printing performance, but its strength is weaker than that of Example 1.

[0100] Example 7

[0101] Cellulose-based hydrogels were prepared according to the method in Example 1, except that the dissolution temperature in step 3 was 110°C.

[0102] The obtained cellulose-based hydrogel has a uniform texture and can meet the requirements for sensing and 3D printing performance. However, the dissolution rate is accelerated, and the hydrogel turns pale yellow after dissolution, indicating that the dissolution temperature is slightly high and cellulose degradation has occurred.

[0103] Example 8

[0104] Cellulose-based hydrogels were prepared according to the method in Example 1, except that NaOH was used instead of Na2CO3 in step 1, while the rest was the same as in Example 1.

[0105] The results showed that the antifreeze properties, electrical conductivity, and mechanical properties of the obtained cellulose-based hydrogel were similar to those of Example 1.

[0106] Comparative Example 1

[0107] Cellulose-based hydrogels were prepared according to the method in Example 1, except that step 1 in Example 1 was not performed, i.e., the cellulose was not pretreated, while other conditions were the same as in Example 1.

[0108] Under the same conditions, the amount of cellulose dissolved in Comparative Example 1 was reduced, the dissolution difficulty was increased, its tensile strength was lower than that of Example 1, and the reduced content of dissolved cellulose made it difficult for the hydrogel to be stacked and formed, thus failing to meet the 3D printing performance requirements.

[0109] Scanning electron microscopy analysis was performed on cellulose before and after alkalization pretreatment. The results are shown in the figure. Figure 1 , Figure 2 . Figure 1 The image shows a scanning electron microscope image of the untreated cellulose used in Comparative Example 1 at 100x magnification. Figure 2 Scanning electron microscope image of cellulose pretreated with alkali in Example 1 at 100x magnification.

[0110] Depend on Figure 1 , Figure 2 As can be seen from the comparison, the alkali pretreatment of cellulose can reduce the length and diameter of cellulose microfiber bundles to a certain extent, and the surface of the cellulose microfiber bundles is damaged to a certain extent, which can refine and shorten the cellulose microfiber bundles. The finer and shorter the cellulose microfiber bundles, the easier it is for cellulose to dissolve. Therefore, the alkali pretreatment of cellulose can destroy the dense structure of cellulose, making it easier to dissolve in the metal salt solution of this invention.

[0111] Comparative Example 2

[0112] Cellulose-based hydrogels were prepared according to the method in Example 1. Only zinc salt was used as the metal salt solution. The strength of the cellulose-based hydrogels was severely weakened, as shown in Table 2. They were difficult to stack and form, and salt precipitation occurred at room temperature (20°C).

[0113] Comparative Example 3

[0114] Cellulose-based hydrogels were prepared according to the method in Example 1. Only lithium salt was used in the metal salt solution, and cellulose was difficult to dissolve. As the amount of cellulose dissolved decreased, its tensile strength also decreased, as shown in Table 2. Cellulose-based hydrogels that meet the requirements for sensing and 3D printing performance could not be obtained.

[0115] Comparative Example 4

[0116] Cellulose-based hydrogels were prepared according to the method in Example 1, except that the molar ratio of zinc salt to lithium salt in the metal salt solution was 1:0.2. The tensile strength of the dissolved cellulose-based hydrogels was significantly lower than that in Example 1. When stacking was simulated using syringes, it could not be stacked and formed, and there was no shape fidelity, which did not meet the 3D printing performance requirements.

[0117] Detection Example 1

[0118] The cellulose-based hydrogels in Examples 1-8 were tested using the following methods:

[0119] The rheological properties of the cellulose-based conductive hydrogels prepared in Examples 1-8 were tested using a steady-state rheometer to determine their printability at room temperature (25°C). In steady-state mode, with a shear rate of 0-100 s, the viscosity of the ink was measured as a function of the shear rate. Simultaneously, a strain scan of 0.01-100% was performed on the cellulose-based conductive hydrogels at a fixed frequency of 1 Hz to analyze the viscosity changes with shear rate, storage modulus (G'), and loss modulus (G"). Analysis of the storage modulus (G') and loss modulus (G") showed that as the shear force increased, the storage modulus of the cellulose-based hydrogel was generally lower than the loss modulus, indicating that it tends towards a viscoelastic liquid state. This also indicates that the cellulose-based hydrogel has the property of transforming from a shear-thinned fluid to a solid-like state during printing, thus maintaining good shape fidelity. Therefore, the cellulose-based hydrogel prepared in this invention meets the requirements for good 3D printing performance.

[0120] Detection Example 2

[0121] Differential scanning calorimetry (DSC) was used to determine the freeze-thaw resistance of the cellulose-based conductive hydrogels in Examples 1-4 at -80°C. Temperature variations were controlled to investigate the relationship between heat flow between the sample and the reference material as a function of temperature. A DSC was also used to examine whether the hydrogels exhibited crystallization behavior at low temperatures, thus exploring the freeze-thaw resistance of the cellulose-based conductive hydrogels. In this invention, a differential scanning calorimeter was used to test the glass transition temperature of the cellulose-based conductive hydrogels. Sample mass was 5-10 mg, test temperature was -80 to 20°C, heating rate was 10°C / min, and a nitrogen atmosphere was used for protection. Results are shown below. Figure 3 .

[0122] pass Figure 3 It was found that within the temperature range of -80℃ to 20℃, the curves of the cellulose-based conductive hydrogels in Examples 1-4 all tended to be stable, with no crystallization peaks appearing. This indicates that the cellulose-based conductive hydrogels did not freeze within this temperature range, which shows that the prepared cellulose-based conductive hydrogels have excellent antifreeze properties and can still maintain stable performance at low temperatures (-80 to -20℃).

[0123] Similarly, it has been verified that the cellulose-based conductive hydrogels in Examples 5-8 also have excellent antifreeze properties and can maintain stable performance at low temperatures (down to -80°C, such as -78°C, -76°C, -75°C and above).

[0124] Detection Example 3

[0125] The conductivity of the cellulose-based hydrogels in the examples was tested using the following method: A four-probe tester was used to test the conductivity of the cellulose-based conductive hydrogels from Examples 1-4 (sample size: 10mm*10mm*2mm) at room temperature, and the conductivity was measured. The tensile strength of the cellulose-based conductive hydrogels at room temperature (25℃) was tested using an electronic universal testing machine (sample size: 65mm in length, gauge length: 35mm), and the results are shown in Table 1.

[0126] Table 1

[0127] project Tensile strength Conductivity S / m Example 1 1.3MPa 6.2672 Example 2 0.8MPa 6.3699 Example 3 0.5MPa 6.5219 Example 4 0.4MPa 7.4486 Example 5 1.6MPa - Example 6 0.3MPa - Comparative Example 2 0.1MPa - Comparative Example 3 0.1MPa - Comparative Example 4 0.2MPa -

[0128] As can be seen from Comparative Example 1, even when using the same metal salt solution as in Example 1 of the present invention, without the pretreatment of cellulose according to the present invention, the amount of cellulose dissolved in Comparative Example 1 is reduced, the dissolution difficulty is increased, its tensile strength is lower than that of Example 1, and the reduced content of dissolved cellulose makes it difficult for the hydrogel to be stacked and formed, thus failing to meet the 3D printing performance requirements.

[0129] In Comparative Example 2, using only zinc salt in the metal salt solution resulted in a significantly weakened cellulose-based hydrogel that was difficult to stack and form, failing to meet 3D printing performance requirements.

[0130] In Comparative Example 3, only lithium salt was used in the metal salt solution, which made it difficult to dissolve cellulose. As the amount of cellulose dissolved decreased, its tensile strength also decreased, and a cellulose-based hydrogel that met the requirements for sensing and 3D printing performance could not be obtained.

[0131] Although zinc salt and lithium salt were used in the metal salt solution in Comparative Example 4, the ratio of zinc salt and lithium salt is not within the scope of this invention. The tensile strength of the dissolved cellulose-based hydrogel is greatly reduced compared with Example 1. When using syringes for stacking simulation, it is impossible to stack and form, there is no shape fidelity, and it does not meet the 3D printing performance requirements.

[0132] For the cellulose-based hydrogels in Comparative Examples 1-4, their conductivity was not tested because none of them met the 3D printing performance requirements.

[0133] As can be seen from the embodiments of the present invention and the above comparative examples, only by using the pretreatment steps of the present invention on cellulose can a cellulose-based hydrogel with good performance be obtained by the method of the present invention; only metal salt solutions with the combined action of zinc salt and lithium salt can construct a cellulose-based hydrogel with uniform texture and good performance.

[0134] As can be seen from the embodiments of the present invention, the present invention uses alkali-pretreated cellulose, combined with a specific ratio of alkali-pretreated cellulose and metal salt solution, as well as the composition of the metal salt solution, to obtain a cellulose-based hydrogel that meets the requirements of sensing and 3D printing performance, achieving unexpected technical effects.

[0135] Furthermore, as shown in Table 1, the conductivity of the cellulose-based conductive hydrogel of the present invention is 6-7.5 S / m, while the conductivity of most hydrogels in the prior art is generally below 1 S / m. Therefore, the cellulose-based conductive hydrogel of the present invention exhibits superior conductivity. This indicates that the cellulose-based conductive hydrogel system prepared by dissolving cellulose in the metal salt solvent system of the present invention contains free ions (e.g., Br⁻). - (etc.) Free ions can move in the three-dimensional network system of cellulose-based conductive hydrogels, providing ion carriers for the conductivity of cellulose-based hydrogels and effectively improving the conductivity of cellulose-based conductive hydrogels.

[0136] As shown in Examples 1-6 of Table 1, under the same solvent conditions, the tensile strength of the cellulose-based hydrogel increases with increasing cellulose content. Under the same cellulose content conditions, the tensile strength of the cellulose-based hydrogel increases with increasing lithium salt content. As shown in Example 5, although the tensile strength of the cellulose-based hydrogel increases with increasing lithium salt content, the difficulty of dissolving cellulose increases when the lithium salt content increases and the zinc salt content decreases. Therefore, preferably, the molar ratio of zinc salt to lithium salt is more preferably 1:(0.8-1.2). Within this preferred range, the tensile strength of the cellulose-based hydrogel is higher, and the dissolution process of cellulose is easier to control. It has been verified that the conductivity of the cellulose-based hydrogels in Examples 5 and 6 is close to that in Example 1. Specifically, the conductivity in Example 5 is slightly lower than that in Example 1, approximately 6.1 S / m, while the conductivity of the cellulose-based hydrogel in Example 6 is slightly higher than that in Example 1.

[0137] As shown in Examples 1-4, the conductivity of the cellulose-based hydrogel obtained in Example 4 is higher than that in Examples 1-3. A decrease in cellulose content increases the conductivity of the cellulose-based hydrogel, but its tensile strength decreases compared to Examples 1-3. This indicates that the increased cellulose content in Examples 1-3 resulted in a denser three-dimensional network structure of the hydrogel. More preferably, the cellulose content in the alkali pretreatment is 3%-5% of the solvent (i.e., the metal salt solution) mass, and even more preferably 4%-5%. The resulting cellulose-based hydrogel possesses both high strength and superior conductivity.

[0138] As can be seen from the test examples 2 and 3, the cellulose-based hydrogel of the present invention overcomes the disadvantage of non-freezing in the prior art and has excellent antifreezing performance. In addition to its excellent antifreezing performance, the cellulose-based hydrogel of the present invention also has good electrical conductivity and mechanical properties, achieving unexpected technical effects.

[0139] Detection Example 4

[0140] The hydrogel from Example 1 was cut into thin slices of 10mm×20mm×2mm and applied to the fingers, wrists, and arms of the human body. The fingers, wrists, and arms were bent regularly, and the change in current over time was detected by an electrochemical workstation. The voltage was 3V and the sensitivity (A / V) was 0.01. The sensing performance of the cellulose-based conductive hydrogel was studied, and the results are shown in Figures 4(a), 4(b), and 4(c).

[0141] As can be seen from Figures 4(a), 4(b), and 4(c), when the human body undergoes periodic changes, the rate of change of current through the hydrogel also exhibits periodic changes over time. This indicates that cellulose-based conductive hydrogels have good sensing performance and can be applied in sensors, especially in wearable flexible electronic devices, to monitor human movement and health.

[0142] Similarly, it has been verified that the cellulose-based conductive hydrogels in Examples 1-8 also have good sensing performance and can be applied to sensors.

[0143] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0144] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0145] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0146] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0147] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0148] Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas shall be regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination to be obviously unreasonable.

Claims

1. A cellulose-based hydrogel, comprising a zinc salt, a lithium salt, water and an alkali pretreated cellulose; wherein the content of the alkali pretreated cellulose in the cellulose-based hydrogel is 1%-6%, the molar ratio of the total amount of the zinc salt and the lithium salt to the water is 1:(3-4), and the molar ratio of the zinc salt to the lithium salt is 1:(0.4-2.4), wherein the molar amount of the zinc salt and the lithium salt is calculated based on the content of zinc element and lithium element. 2.The cellulose-based hydrogel according to claim 1, wherein: the content of the alkali pretreated cellulose in the cellulose-based hydrogel is 2%-5%; and / or, the molar ratio of the total amount of the zinc salt and the lithium salt to the water is 1:(3-3.5); and / or, the molar ratio of the zinc salt to the lithium salt is 1:(0.6-1.5); and / or, the zinc salt is selected from at least one of Zn(NO 3) 2, ZnBr 2 and ZnSO 4; and / or, the lithium salt is selected from at least one of LiBr, LiCl and Li 2 SO 4. 3.The cellulose-based hydrogel according to claim 1, wherein: the content of the alkali pretreated cellulose in the cellulose-based hydrogel is 3%-5%; and / or, the molar ratio of the zinc salt to the lithium salt is 1:(0.8-1.2). 4.A method for preparing an alkali pretreated cellulose, comprising: alkali treatment of cellulose in an alkali solution, washing to neutral, dissolving in a mixed solvent, and freeze-drying to obtain the alkali pretreated cellulose. 5.The cellulose-based hydrogel according to claim 4, wherein: in the method for preparing the alkali pretreated cellulose, the cellulose is selected from cotton pulp cellulose and / or hemp fiber. 6.The cellulose-based hydrogel according to claim 4, wherein: the alkali in the alkali solution is selected from at least one of a weak alkali and a strong alkali. 7.The cellulose-based hydrogel according to claim 6, wherein: the strong alkali is selected from at least one of KOH and NaOH. 8.The cellulose-based hydrogel according to claim 4, wherein: the mass ratio of alkali to water in the alkali solution is 1:(15-25); and / or, the amount of the alkali solution is 80-120 mL per 1 g of cellulose. 9.The cellulose-based hydrogel according to claim 4, wherein: in the method for preparing the alkali pretreated cellulose, the alkali treatment conditions include a temperature of 20-30℃, a time of 1-3 h, and / or the pretreatment is carried out under mixing conditions. 10.The cellulose-based hydrogel according to claim 4, wherein: the alkali treatment conditions include stirring using a high-speed homogenizer. 11.The cellulose-based hydrogel according to claim 4, wherein: the washing to neutral is carried out by repeatedly washing the pretreated cellulose to neutral with water.

4. The cellulose-based hydrogel according to any one of claims 1 to 3, characterized in that, 12.The cellulose-based hydrogel according to claim 4, wherein: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The mixed solvent is a mixed solution of alcohol and water.

13. The cellulose-based hydrogel according to claim 12, wherein: The alcohol is selected from at least one of anhydrous ethanol and propylene glycol; and / or, the volume ratio of alcohol to water is (2:8)~(4:6).

14. A method for preparing the cellulose-based hydrogel according to any one of claims 1-13, comprising: dissolving the alkali pretreated cellulose in an aqueous solution containing zinc salt and lithium salt to obtain the cellulose-based hydrogel.

15. The method according to claim 14, wherein: The amount of the alkali pretreated cellulose is 1%-6% based on the total mass of zinc salt, lithium salt and water being 100%.

16. The method according to claim 14, wherein: The amount of the alkali pretreated cellulose is 2%-5% based on the total mass of zinc salt, lithium salt and water being 100%.

17. The method according to claim 14, wherein: The amount of the alkali pretreated cellulose is 3%-5% based on the total mass of zinc salt, lithium salt and water being 100%.

18. The method according to claim 14, wherein: In the aqueous solution containing zinc salt and lithium salt: The molar ratio of the total amount of zinc salt and lithium salt to water is 1:(3-4); and / or, the molar ratio of zinc salt to lithium salt is 1:(0.4-2.4), the molar amount of zinc salt and lithium salt is based on the content of zinc element and lithium element.

19. The method according to claim 14, wherein: In the aqueous solution containing zinc salt and lithium salt: The molar ratio of the total amount of zinc salt and lithium salt to water is 1:(3-3.5); and / or, the molar ratio of zinc salt to lithium salt is 1:(0.6-1.5), the molar amount of zinc salt and lithium salt is based on the content of zinc element and lithium element.

20. The method according to claim 14, wherein: In the aqueous solution containing zinc salt and lithium salt: The molar ratio of zinc salt to lithium salt is 1:(0.8-1.2), the molar amount of zinc salt and lithium salt is based on the content of zinc element and lithium element.

21. The method according to claim 14, wherein: The zinc salt is selected from at least one of Zn(NO3)2, ZnBr2 and ZnSO4; and / or, The lithium salt is selected from at least one of LiBr, LiCl and Li2SO4.

22. The method according to claim 14, wherein: The dissolving condition includes: temperature of 90-120℃, and / or, time of 3-5h.

23. The method according to claim 14, wherein: The dissolving condition includes: temperature of 90-100℃, and / or, time of 3-4h.

24. The method according to claim 14, wherein: The method further comprises: After dissolving the alkali pretreated cellulose in the aqueous solution containing zinc salt and lithium salt to obtain the cellulose-based hydrogel, the step of injecting the cellulose-based hydrogel into a container and then performing defoaming treatment.

25. The method according to claim 24, wherein: The container is placed in a centrifuge for defoaming treatment.

26. Use of the cellulose-based hydrogel according to any one of claims 1-13 or prepared by the method according to any one of claims 14-25 in the field of 3D printing, flexible sensors, wearable electronics.

27. The use according to claim 26, wherein: when the cellulose-based hydrogel is used for 3D printing, the moving speed of the 3D printing nozzle is 80-130 mm / min; and / or the injection speed of the injection pump containing the cellulose-based hydrogel is 30-60 μL / min.

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