Preparation method of hyperelastic cellulose aerogel

Abstract

The invention discloses a preparation method of hyperelastic cellulose aerogel. According to the method, firstly, cellulose crystal form transformation is induced through molecular chain rearrangement, and the accessibility and reaction activity of hydroxyl on the fiber surface are remarkably improved; and then introducing a gas phase or in-situ mediated covalent cross-linking reaction into the three-dimensional porous aerogel skeleton, and constructing a uniform and continuous polymer topology network on the fiber surface. The formed covalent cross-linked structure effectively shields the hydrogen-bond interaction between fibers while keeping the fiber rigidity, so that the aerogel still has excellent elastic recovery and fatigue resistance under the condition of large deformation. The obtained cellulose aerogel has superelasticity, high strength and structural stability, and is applicable to flexible sensing, buffer protection and extreme environments.

Description

Technical Field

[0001] This invention belongs to the field of cellulose-based porous materials and aerogel preparation technology, specifically relating to a method for preparing superelastic cellulose aerogels by improving the surface reactivity of fibers and constructing a highly efficient covalent cross-linked network. Background Technology

[0002] Cellulose aerogels, due to their low density, large specific surface area, and high structural designability, have broad application prospects in fields such as flexible sensing, buffering and energy absorption, and thermal insulation. However, existing cellulose aerogels generally suffer from insufficient mechanical properties, especially under conditions of large deformation or repeated cyclic compression, which easily leads to structural collapse, irreversible deformation, or performance degradation, severely limiting their practical applications.

[0003] The main reason for the above problems lies in the numerous strong hydrogen bonds between cellulose molecules. During aerogel compression, the fibers on the pore walls are prone to irreversible adhesion, making structural recovery difficult. To improve elastic properties, existing techniques have attempted to weaken the inter-fiber interactions by introducing elastic polymers, physical coating, or non-covalent modification. However, these methods often suffer from uneven cross-linking, insufficient interfacial bonding, or shedding during cycling, making it difficult to achieve long-term stable hyperelasticity while maintaining material strength. Therefore, there is an urgent need for a preparation method that can construct a stable, uniform, and efficient covalently cross-linked structure within cellulose aerogels, thereby simultaneously achieving strength, elasticity, and structural stability. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing superelastic cellulose aerogels based on efficient covalent crosslinking. By improving the surface reactivity of the fibers and constructing a continuous covalent crosslinking network in the aerogel skeleton, the cellulose aerogel achieves high elastic recovery and mechanical stability under large deformation and multiple cycles.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for preparing superelastic cellulose aerogel, comprising the following steps:

[0007] S1. Using cellulose nanofibers as raw materials, their dispersion is directionally frozen to allow ice crystals to grow in an oriented manner, resulting in a cryogel with an oriented pore structure. After freeze-drying, a cellulose aerogel with a three-dimensional porous structure is obtained.

[0008] S2. The cellulose aerogel obtained in step S1 is immersed in anhydrous ethylenediamine (EDA) to induce cellulose molecular chain rearrangement and crystal transformation, thereby improving the reactivity of hydroxyl groups on the fiber surface and obtaining activated cellulose aerogel.

[0009] S3. The activated cellulose aerogel obtained in step S2 is placed in a closed reactor containing water vapor and methyltrimethoxysilane vapor. Through gas-phase hydrolysis-condensation reaction, a polysiloxane crosslinking network is generated in situ at the pore walls and fiber connection nodes of the aerogel to construct a continuous and uniform polymer topology.

[0010] S4. After drying, a superelastic cellulose aerogel is obtained.

[0011] Furthermore, the cellulose nanofibers mentioned in step (1) are cellulose nanofibers prepared by the TEMPO oxidation method, and the mass fraction of the dispersion is 1%.

[0012] Further, in step (1), liquid nitrogen at -196°C is used for directional freezing, and the freeze-drying temperature is -28°C.

[0013] Furthermore, the soaking treatment in step (2) is carried out at room temperature for 8 hours.

[0014] Furthermore, the molar ratio of water vapor to methyltrimethoxysilane in step (3) is 1:1.

[0015] Furthermore, the temperature of the gas-phase hydrolysis-condensation reaction in step (3) is 85°C and the time is 6 hours.

[0016] Furthermore, the drying process in step (4) is carried out at a temperature of 105°C for 1 hour.

[0017] The superelastic cellulose aerogel prepared by this invention still maintains a deformation recovery rate of more than 90% after 20,000 compression cycles.

[0018] The superelastic cellulose aerogel prepared by this invention can be used for flexible sensing, buffering and energy absorption, or extreme environment applications. These extreme environments include high humidity environments, organic solvent environments, or alternating high and low temperature environments.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] (1) By constructing an efficient and stable covalent cross-linking network, irreversible adhesion between fibers can be effectively suppressed;

[0021] (2) Significantly improves the elastic recovery properties of aerogel while maintaining the strength of the cellulose skeleton;

[0022] (3) The obtained aerogel still has good structural integrity and mechanical stability after multiple cycles of compression;

[0023] (4) The method is highly versatile and applicable to a variety of cellulose raw materials, and has good application prospects. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the preparation process of a superelastic cellulose aerogel according to the present invention.

[0025] Figure 2 The stress-strain curve of the superelastic cellulose aerogel prepared in Example 1 after 20,000 cycles of compression is shown. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the invention. Simple modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and substance thereof are all within the scope of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0027] Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0028] Example 1

[0029] (1) A cellulose nanofiber dispersion with a mass fraction of 1% (prepared by TEMPO oxidation method) was injected into a copper bottom mold and directionally frozen in liquid nitrogen at -196℃ to control the directional growth of ice crystals along the temperature gradient direction to obtain a cryogel with an oriented pore structure; after the cryogel was freeze-dried (-28℃), a cellulose aerogel with a three-dimensional porous structure was obtained.

[0030] (2) The obtained cellulose aerogel was placed in anhydrous ethylenediamine and soaked at 25°C for 8 hours to induce cellulose molecular chain rearrangement and crystal transformation (I type → III type) to improve the reactivity of hydroxyl groups on the fiber surface. After washing with ethanol to remove residual ethylenediamine, activated cellulose aerogel was obtained.

[0031] (3) The activated cellulose aerogel was placed in a closed reactor and a mixture of water vapor and methyltrimethoxysilane (MTMS) vapor (molar ratio of water to MTMS is 1:1) was introduced. The mixture was reacted at 85°C for 6 hours to allow MTMS to undergo hydrolysis-condensation reaction, and polysiloxane cross-linked network was generated in situ at the aerogel pore walls and fiber connection nodes to construct a continuous and uniform polymer topology.

[0032] (4) After the reaction is completed, the aerogel is dried at 105°C for 1 hour to obtain superelastic cellulose aerogel.

[0033] Test results show that the obtained aerogel can quickly recover its original shape after 50% compression deformation, and exhibits excellent elastic recovery rate during 20,000 compression cycles, maintaining a deformation recovery rate of more than 90% after 20,000 compression cycles. Figure 2 ).

Claims

1. A method for preparing superelastic cellulose aerogel, characterized in that, Includes the following steps: S1. Using cellulose nanofibers as raw materials, their dispersion is directionally frozen to allow ice crystals to grow in an oriented manner, resulting in a cryogel with an oriented pore structure. After freeze-drying, a cellulose aerogel with a three-dimensional porous structure is obtained. S2. The cellulose aerogel obtained in step S1 is immersed in anhydrous ethylenediamine to induce cellulose molecular chain rearrangement and crystal transformation, thereby improving the reactivity of hydroxyl groups on the fiber surface and obtaining activated cellulose aerogel. S3. The activated cellulose aerogel obtained in step S2 is placed in a closed reactor containing water vapor and methyltrimethoxysilane vapor. Through gas phase hydrolysis-condensation reaction, a polysiloxane crosslinking network is generated in situ at the pore walls and fiber connection nodes of the aerogel. S4. After drying, a superelastic cellulose aerogel is obtained.

2. The method according to claim 1, characterized in that, The cellulose nanofibers mentioned in step (1) are cellulose nanofibers prepared by TEMPO oxidation method, and the mass fraction of the dispersion is 1%.

3. The method according to claim 1, characterized in that, Step (1) involves directional freezing using liquid nitrogen at -196℃, and the freeze-drying temperature is -28℃.

4. The method according to claim 1, characterized in that, The soaking treatment in step (2) is carried out at room temperature for 8 hours.

5. The method according to claim 1, characterized in that, The molar ratio of water vapor to methyltrimethoxysilane in step (3) is 1:

1.

6. The method according to claim 1, characterized in that, The temperature of the gas-phase hydrolysis-condensation reaction in step (3) is 85°C and the time is 6 hours.

7. The method according to claim 1, characterized in that, The drying process in step (4) is carried out at a temperature of 105°C for 1 hour.

8. The method according to claim 1, characterized in that, The resulting superelastic cellulose aerogel still maintains a deformation recovery rate of more than 90% after 20,000 compression cycles.

9. The method according to claim 1, characterized in that, Applications of the superelastic cellulose aerogel in flexible sensing, buffering and energy absorption, or extreme environment applications; the extreme environment includes high humidity environment, organic solvent environment, or high and low temperature alternating environment.

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