A super-tough cellulose aerogel fiber, its preparation method and application

Abstract

The present invention provides a super-tough cellulose aerogel fiber, a preparation method thereof and an application thereof. Specifically, it includes using a wet spinning technology to prepare a cellulose molecular-level solution with cellulose polymers as raw materials; using the cellulose molecular-level solution as a spinning solution, and in the spinning process, the cellulose polymers undergo in-situ self-assembly and hydrogen bond cross-linking reactions to form a multi-level nanofiber structure; the nanofiber structure is a continuous three-dimensional multi-level pore network structure. The cellulose aerogel fiber prepared by the technical solution of the present invention not only has excellent physical properties such as high strength and high toughness, but also, due to its multi-level pore structure, it has good adsorption and heat preservation properties, enabling it to be applied not only in the field of knitting technology, but also in the technical fields of air purification, heavy metal adsorption, atmospheric inhalable particulate matter adsorption, indoor harmful gas adsorption, filter materials or heat insulation materials, and can be widely applied.

Description

Technical Field

[0001] The present invention relates to the technical field of nanoporous materials and functional fibers, and particularly relates to super-tough cellulose aerogel fibers, a preparation method thereof, and an application thereof. Background Art

[0002] An aerogel is a material with a three-dimensional porous network structure. It is a porous material formed by using a sol-gel process to form a disordered and continuous colloidal network in a solution and then drying it. Its unique pore structure and surface chemical properties make it have broad application prospects in many fields. Compared with other porous materials, the aerogel material has more uniform pore size and distribution, a larger surface area, a higher porosity, and extremely low density and thermal conductivity. The preparation process of the aerogel material usually requires methods such as supercritical drying or freeze-drying to convert the liquid in the wet gel into a gas to maintain the shape and network structure of the gel. At present, the aerogel material has developed from traditional inorganic aerogels to organic aerogels, and the building units of its framework structure have also expanded from traditional nanoparticles to one-dimensional nanofibers and two-dimensional nanosheets, etc., greatly expanding its application fields and functions. The aerogel material has broad application prospects in the fields of environmental protection, energy storage and conversion, heat insulation, etc. For example, in the environmental protection field, the aerogel material can be used for water treatment and air purification to purify the environment by adsorbing and catalytically decomposing harmful substances. In the energy field, the aerogel material can be used for the preparation of batteries and supercapacitors to improve the energy density and energy storage efficiency. In the fields of architecture and aviation, the aerogel material can be used for the preparation of heat insulation materials to improve the energy utilization efficiency.

[0003] The aerogel material has received more and more attention and research from scientific researchers due to its unique properties and broad application prospects. Currently, most of the aerogel research mainly focuses on bulk, thin film, and microsphere aerogels, and relatively few studies have been conducted on aerogel fibers. Although the aerogel material has unique properties such as low density and thermal conductivity, high porosity, and large specific surface area, traditional aerogel materials generally have defects such as poor mechanical properties, fragility, and low toughness, which seriously limit the development of aerogel materials in practical applications. Due to the low skeleton strength of the aerogel and its porous network structure, it is challenging to prepare it into a fibrous shape and endow it with slender and flexible characteristics.

[0004] At present, with the efforts of researchers, the preparation and application of aerogel fibers have achieved certain development. Aerogel fibers based on materials such as cellulose (CN105970325A), aramid (CN115073803A), graphene (CN113215828A), etc. have been successively developed. The current preparation methods of aerogel fibers mainly involve first preparing nanomaterial dispersions of corresponding materials, such as aramid nanofiber dispersions, graphene dispersions, cellulose nanocrystal dispersions, etc., and then using the nanomaterial dispersions as spinning solutions for spinning. After obtaining gel fibers, they are dried to obtain aerogel fibers. Although this method can prepare aerogel fibers of different materials, since the connection between nanomaterials is usually achieved through hydrogen bond forces or simple physical lap joints, the connection of nanomaterials inside the fiber is fragile. Therefore, the obtained aerogel fibers mainly exhibit the characteristics of rigid materials, are easily damaged and broken in practical applications, and are difficult to be applied in the textile field. For example, the invention patent with the patent publication number CN105970325A proposes a continuous cellulose aerogel fiber and its preparation method. This method first disperses cellulose in a dispersant formed by dissolving NaOH and thiourea in water to form a cellulose nanocrystal spinning stock solution, and then spins and dries to obtain aerogel fibers. Another example is Chinese invention patents CN105970326A and CN106012107A. Compared with the patent publication number CN105970325A, the former is different in that the solid cellulose aerogel fiber is transformed into a hollow cellulose aerogel fiber, while the latter is different in that the cellulose aerogel fiber is subjected to high-temperature carbonization treatment. Obviously, although the prior art can obtain cellulose aerogel fibers, the hydrogen bond strength between cellulose nanocrystals is very weak, and the cellulose aerogel fibers cannot obtain strong strength and toughness.

[0005] In summary, although the preparation of aerogel fibers has achieved great development at present, high-strength and tough cellulose aerogel fibers have not been developed so far, which limits the popularization of cellulose aerogel fibers in practical applications.

[0006] Therefore, it is very necessary to develop a high-strength and super-tough cellulose aerogel fiber and its preparation method. Summary of the Invention

[0007] In view of this, to solve the above problems, the present invention provides a super-tough cellulose aerogel fiber, its preparation method and application, aiming to solve the thorny problems of low mechanical properties, poor toughness, difficult solvent recovery and high cost of the aerogel fibers prepared by the prior art, and further expand the practical scope of the aerogel fibers.

[0008] To achieve the above object, the present invention provides a super-tough cellulose aerogel fiber, which includes using a wet spinning technique to prepare a cellulose molecular-level solution with cellulose macromolecules as raw materials; using the cellulose molecular-level solution as a spinning solution, and in the spinning process, the cellulose macromolecules undergo in-situ self-assembly and hydrogen bond cross-linking reactions to form a multi-level nanofiber structure; the nanofiber structure is a continuous three-dimensional multi-level pore network structure; when subjected to external force stretching, the pore structure in the three-dimensional multi-level pore network structure becomes smaller, and as the stretching progresses, the degree of orientation of the three-dimensional multi-level pore network structure in the length direction gradually becomes higher, so that the strength of the connection points between nanofibers constitutes the strength of the fiber body, forming the cellulose gel fiber with super-tough properties;

[0009] Among them, the cellulose molecular-level solution is a polymer solution.

[0010] Preferably, the toughness of the cellulose aerogel fiber is not less than 5 MJ / m 3 .

[0011] Based on the technical problems existing in the prior art, the cellulose aerogel fiber proposed by the present invention is a technology for constructing high-strength and high-toughness aerogel fibers through an integrated method of in-situ self-assembly and hydrogen bond cross-linking of cellulose macromolecules. This technology uses a cellulose molecular-level solution as a spinning solution, and in the spinning process, the cellulose macromolecules undergo in-situ self-assembly and hydrogen bond cross-linking to form a continuous three-dimensional network structure; this three-dimensional network structure is a uniform nanofiber network structure with multi-level pores and no obvious network defects. When subjected to external force stretching, the strength of numerous connection points between nanofibers constitutes the strength of the fiber body. Therefore, when the overall network is deformed to the limit, slip failure occurs, making it have the characteristics of super toughness, and the toughness of the aerogel fiber is improved by an order of magnitude compared with the aerogel fiber obtained by simply assembling nanostructures.

[0012] The beneficial technical effects obtained by the present invention:

[0013] 1. The technical solution of the present invention is a technology for preparing high-strength and high-toughness aerogel fibers through an integrated method of in-situ self-assembly and hydrogen bond cross-linking of cellulose macromolecules. The prepared super-tough cellulose aerogel fiber has the characteristics of high strength, ultra-high toughness, low thermal conductivity, high porosity, continuous spinnability, good flexibility, strong weavability, and excellent skeleton structure stability.

[0014] 2. The cellulose aerogel fiber prepared by adopting the technical solution of the present invention not only has excellent physical properties, but also, due to its multi-level pore structure, has good adsorption and heat preservation properties, so that it can not only be applied to the field of weaving technology, but also be applied to the technical fields of air purification, heavy metal adsorption, atmospheric inhalable particulate matter adsorption, indoor harmful gas adsorption, filter materials or heat insulation materials, and can be widely used.

[0015] 3. By adopting the technical solution of the present invention and utilizing the cellulose molecular binding wet spinning technology, the raw materials are widely available and easy to obtain. The raw materials used are not limited to degreased cotton balls, and directly using cellulose and other cellulose-rich materials can also obtain super-tough cellulose aerogel fibers, which are inexpensive and have high economic benefits. In particular, the solvent used can be recycled nearly 100%, thus greatly reducing the raw material cost, and the process is an existing technology, and industrial production can be carried out on the basis of existing processing equipment without prior equipment investment, meeting the conditions for industrial production.

[0016] 4. By adopting the technical solution of the present invention, the preparation process of the super-tough cellulose aerogel fiber is simple, the reaction conditions are mild, it can be continuously prepared, the energy consumption is low, it is green and environmentally friendly, and the cost is relatively low, and it is applicable to industrial production as well as mass production and promotion.

[0017] 5. By adopting the technical solution of the present invention, using ionic liquid as the solvent, it can be recycled nearly 100% after production, and the whole process does not involve organic solvents that are extremely harmful to the ecological environment and human health. In addition, the dissolution process is relatively fast, the cellulose source is wide and the price is low, greatly shortening the preparation cycle and reducing the production cost. Description of the Drawings

[0018] Figure 1 is the optical photograph of the cellulose gel fiber prepared in Example 1 of the present invention.

[0019] Figure 2 is the optical photograph of the cellulose aerogel fiber prepared in Example 1 of the present invention.

[0020] Figure 3 is the surface scanning electron micrograph of the cellulose aerogel fiber prepared in Example 1 of the present invention.

[0021] Figure 4a and Figure 4b are respectively the cross-section ( Figure 4a ) of the cellulose aerogel fiber prepared in Example 1 of the present invention and its partial enlarged ([[]] Figure 4b ) scanning electron micrograph.

[0022] Figure 5a and Figure 5b are respectively the surface ( Figure 5a ) of the cellulose aerogel fiber prepared in Example 1 of the present invention after knotting and its partial enlarged ([[]] Figure 5b ) scanning electron micrograph.

[0023] Figure 6 is the nitrogen adsorption and desorption curve graph of the cellulose aerogel fiber prepared in Example 1 of the present invention..

[0024] Figure 7 It is the pore size distribution diagram of the cellulose aerogel fiber prepared in Example 1 of the present invention.

[0025] Figure 8 It is the tensile stress-strain curve diagram of the cellulose aerogel fiber prepared in Example 1 of the present invention.

[0026] Figure 9 It is the cross-sectional scanning electron microscope images of the cellulose aerogel fiber prepared in Example 1 of the present invention before and after stretching.

[0027] Figure 10 It is the infrared curve diagram of the cellulose aerogel fiber prepared in Example 1 of the present invention before and after stretching.

[0028] Figure 11 It is the XRD patterns of the cellulose aerogel fiber and cellulose prepared in Example 1 of the present invention.

[0029] Figure 12 It is the TG curve diagrams of the cellulose aerogel fiber and cellulose prepared in Example 1 of the present invention.

[0030] Figure 13 It is the contact angle picture of the cellulose aerogel fiber prepared in Example 1 of the present invention before hydrophobization.

[0031] Figure 14 It is the contact angle pictures of the cellulose aerogel fiber prepared in Example 1 of the present invention at different times after hydrophobization.

[0032] Figure 15 It is the tensile stress-strain curve diagram of the cellulose aerogel fiber prepared in Example 6 of the present invention.

[0033] Figure 16 It is the optical picture of the cellulose aerogel fiber prepared in Example 1 of the present invention woven into a cloth.

[0034] Figure 17 It is the optical picture of the cellulose aerogel fiber prepared in Example 1 of the present invention woven into a net bag. Detailed implementation manners

[0035] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are some, but not all, of the embodiments of the present application.

[0036] The present invention provides a super-tough cellulose aerogel fiber. Using a cellulose molecular-level solution as the spinning solution, when it enters the coagulation bath, ionic liquid will diffuse into the coagulation bath, and free cellulose molecular chains can undergo in-situ self-assembly. At the same time, due to the presence of a large number of hydroxyl groups on the cellulose molecular chains, hydrogen bond cross-linking reactions can occur. Under the dual action of in-situ self-assembly and hydrogen bond cross-linking reactions of cellulose macromolecules, a nanofiber structure with multi-level pores is formed.

[0037] The nanofiber structure is a continuous three-dimensional multi-level pore network structure; when subjected to external tensile force, the pore structure in the three-dimensional multi-level pore network structure becomes smaller. As the stretching progresses, the orientation degree of the three-dimensional multi-level pore network structure along the length direction gradually increases, making the strength of the connection points between nanofibers constitute the strength of the fiber body, forming a cellulose gel fiber with super-tough properties.

[0038] Among them, the cellulose molecular-level solution is a cellulose macromolecule solution.

[0039] Preferably, the three-dimensional multi-level pore network structure includes micropores with a pore diameter of less than 2 nm, mesopores with a pore diameter of 2 - 50 nm, and macropores with a pore diameter of 50 nm - 100 nm.

[0040] Preferably, the toughness of the cellulose aerogel fiber is not less than 5 MJ / m 3 , and in some specific embodiments, the toughness of the cellulose aerogel fiber is 5 - 25 MJ / m 3 .

[0041] The fiber diameter is 0.1 μm - 1 mm, the specific surface area is 290 - 372 m 2 / g, the porosity is 80 - 90%, and the density is 0.18 - 0.25 g / cm 3 .

[0042] Compared with traditional inorganic, organic, and composite aerogel fibers, the super-tough cellulose aerogel fiber of the present invention has cellulose molecular chains undergoing in-situ self-assembly and hydrogen bond cross-linking, and then undergoing orientation treatment to obtain a multi-level nanofiber structure; specifically, its maximum tensile strength is 17 - 30 MPa, and the elongation at break is 82 - 110%.

[0043] On the other hand, the present invention also provides a preparation method for the above-mentioned super-tough cellulose aerogel fiber. This preparation method uses a cellulose macromolecule solution as the spinning solution, and through wet spinning technology, in-situ self-assembly and hydrogen bond cross-linking reactions are carried out. Based on the obtained cellulose gel fiber, cellulose aerogel fiber can be obtained through solvent replacement and drying treatment. The in-situ self-assembly and hydrogen bond cross-linking reactions in this method.

[0044] The specific steps include:

[0045] (1) Dissolve the cellulose polymer in a solvent to obtain a cellulose molecular solution;

[0046] (2) Pass the cellulose molecular solution through wet spinning technology to cause in-situ self-assembly and hydrogen bond cross-linking reactions of the cellulose polymer, and combine with orientation treatment to obtain cellulose gel fibers;

[0047] (3) Perform solvent replacement and drying treatment on the cellulose gel fibers to obtain super-tough cellulose aerogel fibers.

[0048] In some preferred embodiments, the cellulose polymer and its sources include any one or two or more combinations of natural plant materials such as polycellulose, lignin fiber, cellulose ether, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, cotton, linen, wood materials, straw, husk, bamboo, etc.

[0049] In some preferred embodiments, the solvent includes but is not limited to ionic liquid, or any one or two or more combinations of DMSO, NMP, DMAC, or deionized water and ionic liquid.

[0050] In some more preferred embodiments, the ionic liquid includes but is not limited to liquids composed entirely of ions, including imidazole-based ionic liquids, pyridine-based ionic liquids, quaternary ammonium salt-based ionic liquids, etc.

[0051] In some preferred embodiments, when the ionic liquid is used in combination with other reagents, the mass ratio of the ionic liquid to other reagents is 1:1; other reagents include one or two or more combinations of DMSO, NMP, DMAC, or deionized water.

[0052] In some preferred embodiments, the cellulose molecular solution is composed of a cellulose polymer and an ionic liquid; wherein, the concentration of the cellulose polymer in the cellulose molecular solution is 0.1-20 wt%; preferably 4-6 wt%.

[0053] In some preferred embodiments, the degree of polymerization of the cellulose polymer is 6000-11000.

[0054] In some preferred embodiments, the temperature for dissolving the cellulose polymer in the solvent is 50-100 °C, preferably 70-80 °C.

[0055] In some preferred embodiments, the time for dissolving the cellulose polymer in the solvent is 0.3-96 h, preferably 72 h. The dissolution time depends on the cellulose content in the polymer solution. The less the cellulose content, the shorter the required dissolution time.

[0056] In some preferred embodiments, the wet spinning technique is achieved by adding a coagulation bath. Specifically, based on water, absolute ethanol, and a mixed solution of any ratio between them, a good solvent or a poor solvent is added or not added to adjust the coagulation rate.

[0057] In some preferred embodiments, the wet spinning technique includes providing a cellulose molecular solution with a selected concentration as the spinning solution, using absolute ethanol as the coagulation bath, extruding the spinning solution through an injection pump so that it flows into the coagulation bath, causing in-situ self-assembly and hydrogen bond cross-linking reactions of the cellulose macromolecules in the cellulose molecular solution, and then performing an orientation treatment to obtain cellulose gel fibers.

[0058] Furthermore, the process conditions adopted in the wet spinning technique include: the concentration of the cellulose molecular solution is 0.1 - 20 wt%, the diameter of the extrusion needle is 0.1 μm - 1 cm, and the extrusion speed ranges from 0.1 - 1000 mL / min.

[0059] In some preferred embodiments, the orientation methods adopted in the wet spinning technique include any one or a combination of two or more of flow orientation, drawing orientation, and directional freezing orientation.

[0060] In some preferred embodiments, the solvent replacement in the preparation method includes first using an easily dried solvent to replace the not easily dried solvent in the cellulose gel fibers, and then performing a drying treatment on the replaced cellulose gel fibers to obtain cellulose aerogel fibers.

[0061] In some preferred embodiments, the easily dried solvent includes any one or a combination of two or more of water, methanol, ethanol, tert-butanol, acetone, cyclohexane, and n-hexane, etc., but is not limited thereto.

[0062] In some preferred embodiments, the drying treatment includes any one or a combination of two or more of supercritical fluid drying method, vacuum freeze-drying method, and reduced pressure drying method.

[0063] Through the above technical solutions, the preparation method proposed by the present invention has a high degree of orientation through orientation treatment, thereby obtaining greater mechanical strength and ultra-high toughness. This aerogel fiber combines the lightweight and mesoporous characteristics of aerogel with the flexible and slender characteristics of fibers, and has a wider application in the fields of smart fabrics, wearables, etc. Compared with the reported inorganic, organic, and composite aerogel fibers, the preparation method of the super-tough cellulose aerogel fiber proposed by the present invention has two obvious advantages: First, this method uses ionic liquid as a solvent, which can be recycled almost 100% after production, and the whole process does not involve organic solvents that are extremely harmful to the ecological environment and human health. This is because ionic liquid hardly volatilizes, and even when mixed with other solvents, it can be recycled almost 100% only by heating. In addition, the dissolution process is relatively fast, the cellulose source is wide and the price is low, which greatly shortens the preparation cycle and reduces the production cost; Second, the raw materials used in this method are not limited to degreased cotton balls, and super-tough cellulose aerogel fibers can also be obtained by directly using cellulose and other cellulose-rich materials.

[0064] Based on the cellulose aerogel fiber provided by the above technical solution, another aspect of the present invention also provides the application of the above-mentioned super-tough aerogel fiber in the fields of textile preparation, composite material preparation, air purification, heavy metal adsorption, atmospheric inhalable particulate matter adsorption, indoor harmful gas adsorption, filter materials, or heat insulation materials, etc.

[0065] The technical solutions of the present invention will be further described in detail below through specific examples.

[0066] Example 1

[0067] This example provides a preparation method of super-tough cellulose aerogel fiber, and the specific steps include:

[0068] (1) Preparation of spinning solution: Dissolve cellulose (degreased cotton) with ionic liquid (1-allyl-3-methylimidazolium chloride) at 80 °C, heat and stir slowly for 72 h to prepare a 5 wt% cellulose molecular solution; the degree of polymerization of cellulose macromolecules is ~9000;

[0069] (2) Wet spinning: Pass the 5 wt% cellulose molecular solution through the method of wet spinning, and obtain cellulose gel fiber through orientation treatment (flow orientation). Specifically, the cellulose molecular solution is extruded at a speed of 300 μL / min, flows through a catheter and a spinning needle (diameter 300 μm), and then enters an anhydrous ethanol coagulation bath to initially obtain cellulose gel fiber, and finally obtains cellulose gel fiber through orientation treatment (flow orientation);

[0070] (3) Preparation of super-tough cellulose aerogel fibers: After subjecting the cellulose gel fibers obtained in step (2) to solvent replacement (the easily dried solvent used is absolute ethanol), super-tough cellulose aerogel fibers are obtained by freeze-drying.

[0071] The specific physical properties of the super-tough cellulose aerogel fibers are shown in Table 1.

[0072] Figure 1 and Figure 2 are respectively the optical pictures of the cellulose gel fibers and the super-tough cellulose aerogel fibers obtained in this example through the above steps. As can be seen from the figure, the appearance of the super-tough cellulose aerogel fibers prepared in this example is uniform. Or rather, the aerogel fibers prepared by the method provided in this example are of uniform thickness and have the potential for batch preparation and production.

[0073] Figure 3 、 Figure 4a and Figure 4b are respectively the surface and cross-section scanning electron micrographs of the super-tough cellulose aerogel fibers prepared in this example. As can be seen from the figure, the surface of the super-tough cellulose aerogel fibers prepared in this example is uniform and crack-free, and the interior of the fibers is a continuous three-dimensional multi-level pore network structure.

[0074] Figure 5a and Figure 5b are respectively the surface and its partial enlarged scanning electron micrographs of the super-tough cellulose aerogel fibers prepared in this example after knotting. As can be seen from the figure, the super-tough cellulose aerogel fibers prepared in this example have good flexibility, and even after knotting, these fibers will not crack, enabling their practical application in fields such as weaving.

[0075] Figure 6 and Figure 7 are respectively the nitrogen adsorption-desorption isotherm curve and pore size distribution diagram of the super-tough cellulose aerogel fibers prepared in this example. From Figure 6 it can be seen that the curve has an obvious hysteresis loop, which is a typical type-IV adsorption-desorption isotherm, indicating that the cellulose aerogel fibers have a three-dimensional multi-level pore network structure composed of typical mesoporous structures, including micropores with pore diameters below 2 nm, mesopores with pore diameters of 2 - 50 nm, and macropores with pore diameters of 50 nm - 100 nm. Due to the multi-level pore network structure, the cellulose aerogel fibers can have excellent adsorption capacity.

[0076] From Figure 7 it can be seen that there is a very wide distribution in the mesopore size range with pore diameters above 10 nm, mainly concentrated in 15 - 30 nm.

[0077] Figure 8The tensile stress-strain curve of the super-tough cellulose aerogel fiber prepared in this example. As can be seen from the figure, the tensile strength of the super-tough aerogel fiber prepared in this example increases with the increase of tensile strain. Among them, its tensile strength can reach 20 MPa, and the fracture tensile strain can reach 84%.

[0078] Figure 9 The cross-sectional scanning electron microscope images of the super-tough cellulose aerogel fiber before and after being pulled in this example. As can be seen from the figure, during the process of the super-tough aerogel fiber prepared in this example being stretched by external force, its macropores gradually become smaller, and the degree of orientation of the fiber along the length direction gradually becomes higher. Specifically, the pore structure in the three-dimensional multi-level pore network structure becomes smaller. As the stretching progresses, the degree of orientation of the pore fiber along the length direction gradually becomes higher, making the strength of the connection points between nanofibers constitute the strength of the fiber body. Based on this, the cellulose aerogel fiber provided in this example has super-tough performance. That is to say, with the stretching of external force, the change in the degree of orientation of its pore fiber is that the orientation of the connection points of nanofibers tends to be consistent, forming the strength of the fiber body, and the orientation direction is as shown by the arrow in the figure.

[0079] Figure 10 The infrared curve graphs of the super-tough cellulose aerogel fiber before and after being pulled in this example. As can be seen from the figure, after the super-tough aerogel fiber prepared in this example is stretched, more hydrogen bonds are formed, and the O-H bond shows a blue shift phenomenon.

[0080] Figure 11 The XRD patterns of the super-tough cellulose aerogel fiber and cellulose prepared in this example. From the patterns, it can be seen that after dissolution in ionic liquid and regeneration in solvent, the diffraction peaks of cellulose change greatly. For the cellulose before dissolution, the main peaks are distributed at 15.05°, 16.76° and 22.76°, corresponding to the (101), (101) and (002) crystal planes of cellulose I crystal form. Therefore, the cellulose in the raw material degreased cotton mainly exists in the form of cellulose I crystal; while the main peak in the regenerated cellulose aerogel fiber is located at 20.45°, corresponding to the (200) crystal plane of cellulose II crystal form, indicating a transformation from the original cellulose I crystal form to the regenerated cellulose II crystal form.

[0081] Figure 12 The TG curve graphs of the super-tough cellulose aerogel fiber and cellulose prepared in this example. It can be seen from the figure that the decomposition temperature of the cellulose aerogel fiber is slightly lower than that of the raw material before dissolution, and its thermal stability is slightly reduced, but the residual mass is higher than that of the original fiber. This may be because during the preparation of the cellulose aerogel fiber, cellulose transforms from type I crystal to type II crystal, and the conformation of cellulose II crystal is more prone to conformational inversion than that of type I, and is more likely to dehydrate and decarboxylate to form residues, thus having a higher carbon residue content.

[0082] Figure 13Contact angle pictures of the super-tough cellulose aerogel fiber before hydrophobization prepared in this example. It can be seen from the figure that the super-tough cellulose aerogel fiber has good hydrophilicity, and its three-dimensional network structure is prone to collapse after water absorption.

[0083] Figure 14 Pictures of the changes in contact angle of the super-tough cellulose aerogel fiber at different times after hydrophobization prepared in this example. It can be seen from the figure that after the cellulose aerogel fiber is hydrophobized, it can have excellent hydrophobic properties. The hydrophobic modification method is as follows: Methyltrimethoxysilane is used as the cold plasma gas source. In the plasma equipment, the dry cellulose aerogel is placed in the cold plasma chamber and processed under the glow discharge system. When the vacuum degree reaches a constant value (the set value in the experiment is about 200 Pa ± 50 Pa), the discharge system is started. At a specific power (150 W in the experiment) and time (3 - 10 min in the experiment), hydrophobic cellulose aerogel fibers are finally obtained.

[0084] Example 2

[0085] This example provides a preparation method of super-tough cellulose aerogel fibers, and the specific steps include:

[0086] (1) Preparation of the spinning solution: Dissolve cellulose (degreased cotton) in an ionic liquid (1-allyl-3-methylimidazolium chloride) at 80 °C, and heat and stir slowly for 48 h to prepare a cellulose molecular solution with a concentration of 4 wt%; the cellulose molecular solution is a cellulose polymer solution, and the degree of polymerization of the cellulose polymer is -9500;

[0087] (2) Wet spinning: Pass the 4 wt% cellulose molecular solution through the wet spinning method and perform orientation treatment (flow orientation, etc.) to obtain cellulose gel fibers. Specifically, the cellulose molecular solution is extruded at a speed of 300 μL / min, flows through a catheter and a spinning needle (with a diameter of 300 μm), and then enters an anhydrous ethanol coagulation bath to initially obtain cellulose gel fibers, and finally, after orientation treatment, cellulose gel fibers are obtained;

[0088] (3) Preparation of super-tough cellulose aerogel fibers: After solvent replacement of the cellulose gel fibers in step (2) (the easy-to-dry solvent used is anhydrous ethanol), super-tough cellulose aerogel fibers are obtained by freeze-drying.

[0089] Through the above steps, the specific properties of the super-tough cellulose aerogel fibers obtained in this example are shown in Table 1.

[0090] Example 3

[0091] This example provides a preparation method of super-tough cellulose aerogel fibers, and the specific steps include:

[0092] (1) Preparation of spinning solution: Dissolve cellulose (degreased cotton) in ionic liquid (1-allyl-3-methylimidazolium chloride) at 80 °C, heat and stir slowly for 96 h to prepare a 6 wt% cellulose molecular solution; the degree of polymerization of the cellulose polymer is ~9000;

[0093] (2) Wet spinning: Pass the 6 wt% cellulose molecular solution through wet spinning, and after orientation treatment (flow orientation), obtain cellulose gel fibers. Specifically, the cellulose molecular solution is extruded at a speed of 300 μL / min, flows through a catheter and a spinning needle (with a diameter of 300 μm), and then enters an absolute ethanol coagulation bath to initially obtain cellulose gel fibers, and finally, after orientation treatment, cellulose gel fibers are obtained;

[0094] (3) Preparation of super-tough cellulose aerogel fibers: After solvent replacement of the cellulose gel fibers in step (2) (using absolute ethanol as the easily dried solvent), super-tough cellulose aerogel fibers are obtained by freeze-drying.

[0095] After the above steps, the stress-strain curve of the super-tough cellulose aerogel fibers obtained in this example is as Figure 15 shown, and the specific properties are shown in Table 1.

[0096] Example 4

[0097] This example provides a method for preparing super-tough cellulose aerogel fibers, and the specific steps include:

[0098] (1) Preparation of spinning solution: Dissolve cellulose (degreased cotton) in a mixed solution of ionic liquid (1-allyl-3-methylimidazolium chloride) and DMSO (mass ratio 1:1) at 80 °C, heat and stir slowly for 72 h to prepare a 5 wt% cellulose molecular solution; the degree of polymerization of the cellulose polymer is ~7000;

[0099] (2) Wet spinning: Pass the 5 wt% cellulose molecular solution through wet spinning, and after orientation treatment (flow orientation,), obtain cellulose gel fibers. Specifically, the cellulose molecular solution is extruded at a speed of 300 μL / min, flows through a catheter and a spinning needle (with a diameter of 300 μm), and then enters an absolute ethanol coagulation bath to initially obtain cellulose gel fibers, and finally, after orientation treatment, cellulose gel fibers are obtained;

[0100] (3) Preparation of super-tough cellulose aerogel fibers: After solvent replacement of the cellulose gel fibers in step (2) (using absolute ethanol as the easily dried solvent), super-tough cellulose aerogel fibers are obtained by freeze-drying.

[0101] After the above steps, the specific properties of the super-tough cellulose aerogel fibers obtained in this example are shown in Table 1.

[0102] Example 5

[0103] The difference between this example and Example 1 lies in Step 1. The steps of Step 1 include the preparation of the spinning solution: dissolving cellulose (degreased cotton) with ionic liquid (1-allyl-3-methylimidazolium chloride) at 80 °C, heating and slowly stirring for 20 h to prepare a cellulose molecular solution with a concentration of 5 wt%; the degree of polymerization of the cellulose polymer is ~9000.

[0104] Example 6

[0105] The difference between this example and Example 1 lies in Step 1. Step 1 includes the preparation of the spinning solution: dissolving cellulose (degreased cotton) with ionic liquid (1-allyl-3-methylimidazolium chloride) at 80 °C, heating and slowly stirring for 72 h to prepare a cellulose molecular solution with a concentration of 20 wt%; the degree of polymerization of the cellulose polymer is ~9300.

[0106] Example 7

[0107] The difference between this example and Example 1 lies in Step 1. The steps of Step 1 include the preparation of the spinning solution: dissolving cellulose (degreased cotton) with ionic liquid (1-allyl-3-methylimidazolium chloride) at 50 °C, heating and slowly stirring for 72 h to prepare a cellulose molecular solution with a concentration of 20 wt%; the degree of polymerization of the cellulose polymer is ~9200.

[0108] Example 8

[0109] The cellulose aerogel fibers prepared in Example 1 were woven into fabrics in a vertical and horizontal interlaced manner.

[0110] As Figure 16 shown, it can be applied to high-temperature heat insulation and low-temperature heat preservation.

[0111] Example 9

[0112] The cellulose aerogel fibers prepared in Example 1 were woven into a net bag in a vertical and horizontal interlaced manner.

[0113] As Figure 17 shown, it can be applied to catching objects from a height.

[0114] Comparative Example 1

[0115] This comparative example provides cellulose gel fibers prepared by using urea and thiourea as raw materials and adopting the technical solution of the present invention. The specific preparation steps include:

[0116] (1) Preparation of spinning solution: Dissolve cellulose in a solution formed by NaOH, urea, thiourea and water (mass ratios are 16:16:13:155 respectively) at 80 °C to prepare a 5 wt% cellulose spinning dope;

[0117] (2) Wet spinning: Pass the 5 wt% cellulose spinning dope through the wet spinning method, and after orientation treatment, obtain cellulose gel fibers. Specifically, the cellulose molecular solution flows through a catheter and a spinning needle (with a diameter of 300 μm) at an extrusion speed of 300 μL / min, and then enters an absolute ethanol coagulation bath to initially obtain cellulose gel fibers, and finally, after orientation treatment, cellulose gel fibers are obtained;

[0118] (3) Preparation of cellulose aerogel fibers: After solvent replacement of the cellulose gel fibers in step (2) (the easily dried solvent used is absolute ethanol), cellulose aerogel fibers are obtained by freeze-drying.

[0119] Through the above steps, compared with Example 1, the strength and toughness of the cellulose aerogel fibers obtained in this comparative example are far lower than those in Example 1 of the present invention, and their specific properties are shown in Table 1.

[0120] Refer to Table 1, which shows the structural and physical property parameters of the cellulose aerogel fibers obtained in Examples 1-7 and Comparative Example 1 of the present invention.

[0121] Table 1 Performance parameters of the cellulose aerogel fibers obtained in Examples 1-7 and Comparative Example 1

[0122]

[0123] As can be seen from Table 1, the toughness of Examples 1-7 is all above 5 MJ / m 3 and the highest can reach 22 MJ / m 3 , and compared with the prior art, its toughness has been greatly improved.

[0124] Furthermore, when comparing Example 1 and Comparative Example 1, the tensile strength, elongation at break and toughness are all significantly and greatly improved. That is to say, the cellulose aerogel fibers constructed by using the in-situ self-assembled hydrogen bond cross-linking integration technology of the cellulose molecular solution of the present invention are greatly improved in physical properties.

[0125] Examples 1-7 respectively used different cellulose molecular solutions and cellulose aerogel fibers prepared with different solidification rates, and all were able to achieve cellulose aerogel fibers with high strength and high toughness. In particular, by comparing Example 1 and Example 3, when the concentration of the cellulose molecular solution increased from 5 wt% to 6 wt%, the cellulose dissolution time extended from 72 h to 96 h, and its physical properties were significantly improved; further, by comparing Example 1 and Example 4, only the ionic liquid in Step 1 was changed. In Example 1, only 1-allyl-3-methylimidazolium chloride was used, while in Example 4, a mixture of 1-allyl-3-methylimidazolium chloride and DMSO was used. Their properties were relatively close, and the performance of Example 4 decreased slightly.

[0126] In summary, with the above technical solutions, a preparation method of a super-tough cellulose aerogel fiber provided by the present invention has a simple preparation process, few preparation steps, a relatively short preparation period, does not require harmful solvents that are difficult to recover, has a low cost, high economic benefits, and meets the conditions for industrial production.

[0127] In addition, this method can be continuously prepared, the solvent used can be almost 100% recycled, and the raw materials are widely sourced and inexpensive, having good industrialization prospects. The obtained super-tough aerogel fiber has characteristics such as high strength, ultra-high toughness, low thermal conductivity, high porosity, continuous spinnability, good flexibility, strong weavability, and excellent skeleton structure stability, etc., and can be woven and applied to extreme environments or special environments, further expanding the application range of this type of material.

Claims

1. A super-tough cellulose aerogel fiber, which includes using a wet spinning technique to prepare a cellulose molecular-level solution with cellulose polymers as raw materials; using the cellulose molecular-level solution as a spinning solution, and during the spinning process, in-situ self-assembly and hydrogen bond cross-linking reactions occur to form a multi-level nanofiber structure; the nanofiber structure is a continuous three-dimensional multi-level pore network structure; when subjected to external tensile force, the pore structure in the three-dimensional multi-level pore network structure becomes smaller, and as the stretching progresses, the degree of orientation of the three-dimensional multi-level pore network structure in the length direction gradually becomes higher, so that the strength of the connection points between nanofibers constitutes the strength of the fiber body, forming a cellulose aerogel fiber with super-tough properties. Among them, The cellulose molecular-level solution is a cellulose polymer solution. The toughness of the cellulose aerogel fiber is not less than 5 MJ / m 3 .

2. The super-tough cellulose aerogel fiber according to claim 1, characterized in that, The sources of the cellulose polymers include any one or two or more combinations of polycellulose, lignin fiber, cellulose ether, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, or natural plant materials.

3. The super-tough cellulose aerogel fiber according to claim 2, wherein The natural plant materials include any one or two or more combinations of cotton, linen, wood materials, straw, husk, bamboo.

4. The super-tough cellulose aerogel fiber according to claim 1, characterized in that, The degree of polymerization of the cellulose polymers is 6000 - 11000.

5. The super-tough cellulose aerogel fiber according to claim 2, characterized in that, Dissolve the cellulose polymers in a solvent to obtain a cellulose molecular-level solution. The solvent includes ionic liquid, or any one or two or more of DMSO, NMP, DMAC, deionized water and their mixtures with ionic liquid.

6. The super-tough cellulose aerogel fiber according to claim 5, characterized in that, The ionic liquid is a liquid composed entirely of ions, including at least one of imidazole-based ionic liquids, pyridine-based ionic liquids, quaternary ammonium salt-based ionic liquids.

7. The super-tough cellulose aerogel fiber according to claim 5, wherein The ionic liquid can be recycled and reused.

8. The super-tough cellulose aerogel fiber according to any one of claims 1-7, characterized in that, The three-dimensional multi-level pore network structure includes micropores with pore diameters below 2 nm, mesopores with pore diameters of 2 - 50 nm, and macropores with pore diameters of 50 nm - 100 nm.

9. The super-tough cellulose aerogel fiber according to any one of claims 1-7, characterized in that, The toughness of the cellulose aerogel fiber is not less than 5 MJ / m 3 , with a diameter of 0.1 μm to 1 mm, a specific surface area of 290~372 m 2 / g, a porosity of 80-90%, and a density of 0.18~0.25 g / cm 3 .

10. The super-tough cellulose aerogel fiber according to any one of claims 1-7, characterized in that, The maximum tensile strength of the cellulose aerogel fiber is 17 - 30 MPa, and the elongation at break is 82 - 110%. The toughness of the cellulose aerogel fiber is 5~25 MJ / m 3 .

11. A method for preparing a super-tough cellulose aerogel fiber according to any one of claims 1-10, characterized in that, The specific steps include: (1) Dissolve the cellulose polymers in a solvent to obtain a cellulose molecular solution. (2) Pass the cellulose molecular solution through a wet spinning technique to cause in-situ self-assembly and hydrogen bond cross-linking reactions of the cellulose polymers, and combine with orientation treatment to obtain a cellulose gel fiber. (3) Perform solvent replacement and drying treatment on the cellulose gel fiber to obtain a cellulose aerogel fiber.

12. The preparation method of the super-tough cellulose aerogel fiber according to claim 11, characterized in that, The wet spinning technique includes providing a cellulose molecular solution with a selected concentration as a spinning solution, using anhydrous ethanol as a coagulation bath, extruding the spinning solution through an injection pump so that it flows into the coagulation bath, causing in-situ self-assembly and hydrogen bond cross-linking reactions of the cellulose polymers in the cellulose molecular solution, and then performing orientation treatment to obtain the cellulose gel fiber.

13. The preparation method of the super-tough cellulose aerogel fiber according to claim 11, characterized in that, The concentration of the cellulose polymers in the cellulose molecular solution is 0.1 - 20 wt%.

14. The preparation method of the super-tough cellulose aerogel fiber according to claim 11, characterized in that The concentration of the cellulose polymers in the cellulose molecular solution is 4 - 6 wt%.

15. The preparation method of the super-tough cellulose aerogel fiber according to claim 11, characterized in that The temperature for dissolving the cellulose polymers in the solvent is 50 - 100 °C; the dissolution time is 0.3 - 96 h.

16. The preparation method of the super-tough cellulose aerogel fiber according to claim 11, wherein, The dissolution time of the cellulose polymer in the solvent is 72 to 96 h.

17. The preparation method of the super-tough cellulose aerogel fiber according to claim 11, wherein The process conditions adopted by the wet spinning technology include: the diameter of the extrusion needle of the injection pump is 0.1 μm to 1 cm, and the extrusion speed is 0.1 to 1000 mL / min.

18. The preparation method of the super-tough cellulose aerogel fiber according to claim 11, characterized in that, The method of the orientation treatment includes any one or a combination of two or more of flow orientation, drawing orientation, and directional freezing orientation.

19. The preparation method of the super-tough cellulose aerogel fiber according to any one of claims 11-18, characterized in that, The solvent replacement includes first replacing the solvent that is not easy to dry in the cellulose gel fiber with an easily dried solvent, and then drying the replaced cellulose gel fiber to obtain the cellulose aerogel fiber.

20. The preparation method of the super-tough cellulose aerogel fiber according to claim 19, wherein, The easily dried solvent includes any one or a combination of two or more of water, methanol, ethanol, tert-butanol, acetone, cyclohexane, and n-hexane.

21. The preparation method of the super-tough cellulose aerogel fiber according to any one of claims 11-18, characterized in that, The drying treatment includes any one or a combination of two or more of supercritical fluid drying method, vacuum freeze drying method, and reduced pressure drying method.

22. The application of the super-tough cellulose aerogel fiber according to any one of claims 1-10 in the fields of textile preparation, composite material preparation, air purification, heavy metal adsorption, atmospheric inhalable particulate matter adsorption, indoor harmful gas adsorption, filter material, or heat insulation material.

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