A method for preparing double-network nanocellulose microgel-based porous material

Abstract

The present invention discloses a method for preparing a double-network nanocellulose microgel-based porous material, the method comprising the following steps: (1) preparing a double-network nanocellulose microgel using carboxyl nanocellulose, aldehyde nanocellulose and an EDC / NHS mixed solution; (2) preparing a Pickering emulsion gel; and (3) freeze-drying the Pickering emulsion gel to obtain a nanocellulose microgel-based porous material. The method of the present invention has simple process and strong operability. The prepared nanocellulose microgel-based porous material has the characteristics of multi-level pore structure, controllable pore size distribution and pore morphology, and has excellent interface stability and mechanical properties, good biocompatibility, and has broad application prospects in multiple fields such as filtration adsorption, energy storage and sound absorption, energy dissipation buffering, chemical sensors, and controlled release of drugs.

Description

Technical Field

[0001] The invention belongs to the technical field of preparing porous materials, and in particular is a method for preparing a double-network nano-cellulose microgel-based porous material. Background Art

[0002] Porous materials are lightweight functional materials with rich pore structures and gas channels. The pore structure and raw material properties affect the specific surface area, permeability, adsorption and other physical and chemical properties of porous materials, thus determining the performance and application of porous materials. Among them, porous materials with multi-level pore structure, pore size distribution and controllable pore morphology have more advantages in application. In addition, in terms of raw materials, biomass-based porous materials have the advantages of being environmentally friendly, renewable, degradable and biocompatible.

[0003] At present, there are many reports on the preparation methods of cellulose-based porous materials, and the commonly used methods include freeze drying, supercritical drying and emulsion template method. Among them, freeze drying is a commonly used method for obtaining cellulose-based porous materials. For example, in the technical schemes of Chinese patent application publication number CN108484965A and Chinese patent application publication number CN115109426A, cellulose is made into a suspension or hydrogel and then freeze-dried to obtain a cellulose-based porous material. However, since the pore size and morphology of the porous material obtained by the traditional freeze drying method are mainly affected by the freezing conditions and ice crystals, the traditional preparation method has the problem of difficult control of pore morphology and pore size. In contrast, the method of preparing cellulose porous materials by emulsion template method has the advantage of controllable pore size, because the size and shape of the pores in the foam obtained after removing the emulsion template are controlled by the dispersed phase in the emulsion. Therefore, the pore structure, pore size distribution and pore morphology of the porous material can be regulated by regulating the droplet size and distribution of the emulsion template dispersed phase. However, the traditional emulsion template method for preparing porous materials still has the following problems: (1) The template emulsion itself is not very stable. During the demolding and drying process, the emulsion will undergo different degrees of demulsification, which will affect the product pore structure, pore size distribution and pore morphology to a certain extent; (2) The preparation of template emulsions mostly uses traditional small molecule surfactants, which have shortcomings such as poor emulsion stability at low dosage, large amount of surfactant, and poor biocompatibility. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a double-network nanocellulose microgel-based porous material, which can solve the problems of low stability of the emulsion template and low environmental friendliness. The prepared double-network nanocellulose microgel-based porous material has the characteristics of multi-level pore structure, controllable pore size distribution and pore morphology, and also has excellent interface stability and mechanical properties and good biocompatibility.

[0005] The present invention solves the above technical problems with the following technical solutions:

[0006] The present invention provides a method for preparing a double-network nanocellulose microgel-based porous material, comprising the following steps:

[0007] (1) Preparation of double network nanocellulose microgel: carboxyl nanocellulose and aldehyde nanocellulose are mixed in a mass ratio of 1:1 to 3 to prepare a nanocellulose aqueous dispersion with a mass concentration of 1.0% to 3.0%; then, a 2.0% polyethyleneimine aqueous solution is added dropwise on top of the nanocellulose aqueous dispersion in an equal volume ratio, and the mixture is allowed to stand at room temperature for 24 hours to obtain a gel matrix; the gel matrix is ​​transferred to a 2.0% polyethyleneimine aqueous solution and soaked for aging for 12 hours, then taken out and soaked in an EDC / NHS mixed solution for reaction for 24 hours to obtain a nanocellulose hydrogel; the hydrogel is rinsed twice with deionized water of the same mass ratio, and then deionized water of the same mass ratio is added and treated at a mechanical shear rate of 10,000 rpm for 3 minutes to obtain a double network nanocellulose microgel;

[0008] (2) Preparing a Pickering emulsion gel: taking the double network nanocellulose microgel prepared in step (1), adding n-hexane dropwise thereto, stirring and mixing at 3000 rpm to obtain a Pickering emulsion gel, wherein the double network nanocellulose microgel and n-hexane are used in a weight ratio of 10 to 30 parts: 70 to 90 parts;

[0009] (3) Preparation of nanocellulose microgel-based porous material: The Pickering emulsion gel obtained in step (2) was placed in a fume hood and dried at room temperature for 24 hours to evaporate the n-hexane, then frozen at -18°C for 24 hours, and then moved to a freeze dryer with a cold trap temperature of -65°C and a vacuum degree of 1 Pa and dried for 48 hours to obtain a nanocellulose microgel-based porous material.

[0010] In step (1), when the carboxyl nanocellulose and the aldehyde nanocellulose are mixed, they are mechanically stirred at a rotation speed of 3000 rpm at room temperature for 5 minutes.

[0011] In step (1), the surface carboxyl content of the carboxyl nanocellulose is 1.0-1.4 mmol / g, the surface aldehyde content of the aldehyde nanocellulose is 1.0-3.0 mmol / g, and the molecular weight of the polyethyleneimine is 10 kDa-70 kDa.

[0012] In step (1), the mass ratio of EDC to NHS in the EDC / NHS mixed solution is 1.5-2.5:1.

[0013] The present invention utilizes the carboxyl groups on carboxyl nanocellulose and the amino groups on polyethyleneimine to react to form gel network one, and at the same time, the amino groups remaining on the surface of the gel network can react with the aldehyde groups on the aldehyde nanocellulose to form gel network two, thereby preparing a double-network nanocellulose microgel. The double-network nanocellulose microgel has excellent interfacial stability and mechanical properties. As a solid particle emulsifier for Pickering emulsions, the prepared oil-in-water emulsion has high stability and high internal phase advantages. At the same time, the double-network nanocellulose microgel particles contain dynamic covalent bonds. During the drying process of the emulsion, the microgel particles on the oil-water interface and the microgel particles remaining in the water phase are cross-linked to form a three-dimensional network skeleton, so that the prepared cellulose-based porous material has the characteristics of multi-level pore structure, pore size distribution and controllable pore morphology.

[0014] Compared with the prior art, the method of the present invention has the following beneficial effects:

[0015] 1) Compared with traditional surfactants, the present invention can significantly improve the stability of the emulsion template by introducing double-network nanocellulose microgel particles, and the particles themselves have the advantage of being environmentally friendly. The present invention utilizes the chemical bonding between carboxyl nanocellulose, polyethyleneimine, and aldehyde nanocellulose to prepare double-network nanocellulose microgels, and the obtained microgels have excellent interfacial stability and mechanical properties. The gel particles are used as emulsifiers for Pickering emulsions to obtain high-stability high-internal phase emulsions, which can significantly reduce the problem of difficult pore size control caused by template emulsion demulsification during the drying pore-forming process. It is beneficial to the control of pore size and the maintenance of shape in the process of preparing porous materials by emulsion template method, and the raw materials and processes used are environmentally friendly.

[0016] 2) The double-network nanocellulose microgel in the method of the present invention has the dual advantages of excellent interfacial stability and dynamic self-healing properties, which is conducive to the construction of a multi-level pore structure with a combination of micron circular pores and nanopores based on the Pickering emulsion template technology. Among them, the excellent interfacial stability of the microgel is conducive to the maintenance of the micron-scale droplet morphology in the template emulsion. At the same time, the microgel particles contain dynamic covalent bonds. During the emulsion drying process, the microgel particles on the oil-water interface and the microgel particles remaining in the water phase are cross-linked to form a three-dimensional network skeleton with self-healing properties, further ensuring the maintenance of the micron-scale pore size morphology. In addition, the micron-scale pore size distribution can be regulated by adjusting the oil-water ratio in the template emulsion gel, and the nanopore structure can be obtained by combining freeze-drying, so that the pore size and morphology can be controlled, which provides an efficient new method for constructing nanocellulose porous materials with multi-level pore structures.

[0017] 3) The double-network nanocellulose microgel-based porous material obtained by the preparation method of the present invention has the characteristics of multi-level pore structure, controllable pore size distribution and pore morphology, and has high application value in many fields such as filtration adsorption, energy storage and sound absorption, energy dissipation buffering, chemical sensors, and controlled release of drugs. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with specific examples, but the present invention is not limited to the following examples. The chemical reagents and raw materials used in the following examples are all of analytical grade.

[0019] Example 1

[0020] A method for preparing a double-network nanocellulose microgel-based porous material comprises the following steps:

[0021] (1) Preparation of double network nanocellulose microgel: carboxyl nanocellulose with a surface carboxyl content of 1.0 mmol / g and aldehyde nanocellulose with a surface aldehyde content of 1.7 mmol / g were mixed in a mass ratio of 1:1, and mechanically stirred at 3000 rpm for 5 min at room temperature to prepare a nanocellulose aqueous dispersion with a mass concentration of 3.0%; a polyethyleneimine aqueous solution with a mass concentration of 2.0% and a molecular weight of 10 kDa was added dropwise on the nanocellulose aqueous dispersion in an equal volume ratio, and the mixture was allowed to stand at room temperature for 24 h to obtain a gel matrix; the gel matrix was transferred to a polyethyleneimine aqueous solution with a mass concentration of 2.0%, immersed and aged for 12 h, then taken out, immersed in an EDC / NHS mixed solution (the mass ratio of EDC to NHS was 2.5:1) for reaction for 24 h to obtain a nanocellulose hydrogel; the hydrogel was rinsed twice with deionized water of the same mass ratio, and then deionized water of the same mass ratio was added and treated at a mechanical shear rate of 10000 rpm for 3 min to obtain a double network nanocellulose microgel;

[0022] (2) Preparing a Pickering emulsion gel: taking the double network nanocellulose microgel prepared in step (1), adding n-hexane dropwise thereto, stirring and mixing at 3000 rpm to obtain a Pickering emulsion gel, wherein the double network nanocellulose microgel and n-hexane are used in a weight ratio of 20 parts:80 parts;

[0023] (3) Preparation of nanocellulose microgel-based porous material: The emulsion gel obtained in step (2) was placed in a fume hood and dried at room temperature for 24 hours to evaporate the n-hexane, then frozen at -18°C for 24 hours, and then moved to a freeze dryer with a cold trap temperature of -65°C and a vacuum degree of 1 Pa and dried for 48 hours to obtain a nanocellulose microgel-based porous material.

[0024] The nanocellulose microgel-based porous material obtained in this example has a multi-level pore structure combining micron circular pores and nanopores, wherein the micron circular pores are concentrated between 24 and 40 μm, with an average pore size of 35.8 μm, which is basically consistent with the droplet size in the template emulsion; the nanopores are concentrated between 200 and 600 nm, with an average pore size of 357 nm, indicating that the method of the present invention effectively achieves controllable pore size distribution and pore morphology.

[0025] Example 2

[0026] A method for preparing a double-network nanocellulose microgel-based porous material comprises the following steps:

[0027] (1) Preparation of double network nanocellulose microgel: carboxyl nanocellulose with a surface carboxyl content of 1.4 mmol / g and aldehyde nanocellulose with a surface aldehyde content of 1.0 mmol / g were mixed in a mass ratio of 1:3, and stirred at 3000 rpm for 5 min at room temperature to prepare a nanocellulose aqueous dispersion with a mass concentration of 1.0%; a polyethyleneimine aqueous solution with a mass concentration of 2.0% and a molecular weight of 70 kDa was added dropwise on top of the nanocellulose aqueous dispersion in an equal volume ratio, and the mixture was allowed to stand at room temperature for 24 h to obtain a gel matrix; the gel matrix was transferred to a polyethyleneimine aqueous solution with a mass concentration of 2.0% and aged for 12 h, then taken out and immersed in an EDC / NHS mixed solution (the mass ratio of EDC to NHS was 1.5:1) for reaction for 24 h to obtain a nanocellulose hydrogel; the nanocellulose hydrogel was rinsed twice with deionized water of the same mass ratio, and then deionized water of the same mass ratio was added and treated at a mechanical shear rate of 10000 rpm for 3 min to obtain a double network nanocellulose microgel;

[0028] (2) Preparing a Pickering emulsion gel: taking the double network nanocellulose microgel prepared in step (1), adding n-hexane dropwise thereto, stirring and mixing at 3000 rpm to obtain a Pickering emulsion gel, wherein the double network nanocellulose microgel and n-hexane are used in a weight ratio of 30 parts:70 parts;

[0029] (3) Preparation of nanocellulose microgel-based porous material: The emulsion gel obtained in step (2) was placed in a fume hood and dried at room temperature for 24 hours to evaporate the n-hexane, then frozen at -18°C for 24 hours, and then moved to a freeze dryer with a cold trap temperature of -65°C and a vacuum degree of 1 Pa and dried for 48 hours to obtain a nanocellulose microgel-based porous material.

[0030] The nanocellulose microgel-based porous material obtained in this example has a multi-level pore structure combining micron circular pores and nanopores, wherein the micron circular pores are concentrated between 12 and 26 μm, with an average pore size of 19.5 μm, which is basically consistent with the droplet size in the template emulsion; the nanopores are concentrated between 200 and 600 nm, with an average pore size of 413 nm, indicating that the method of the present invention effectively achieves controllable pore size distribution and pore morphology.

[0031] Example 3

[0032] A method for preparing a double-network nanocellulose microgel-based porous material comprises the following steps:

[0033] (1) Preparation of double network nanocellulose microgel: carboxyl nanocellulose with a surface carboxyl content of 1.2 mmol / g and aldehyde nanocellulose with a surface aldehyde content of 3.0 mmol / g were mixed in a mass ratio of 1:2, and stirred at 3000 rpm for 5 min at room temperature to prepare a nanocellulose aqueous dispersion with a mass concentration of 2.0%; a polyethyleneimine aqueous solution with a mass concentration of 2.0% and a molecular weight of 50 kDa was added dropwise on the nanocellulose aqueous dispersion in an equal volume ratio, and the mixture was allowed to stand at room temperature for 24 h to obtain a gel matrix; the gel matrix was transferred to a polyethyleneimine aqueous solution with a mass concentration of 2.0% and immersed in aging for 12 h, then taken out and immersed in an EDC / NHS mixed solution (the mass ratio of EDC to NHS was 2:1) for reaction for 24 h to obtain a nanocellulose hydrogel; the nanocellulose hydrogel was rinsed twice with deionized water in an equal mass ratio, and then deionized water in an equal mass ratio was added and treated at a mechanical shear rate of 10000 rpm for 3 min to obtain a double network nanocellulose microgel;

[0034] (2) Preparing a Pickering emulsion gel: taking the double network nanocellulose microgel prepared in step (1), adding n-hexane dropwise thereto, stirring and mixing at 3000 rpm to obtain a Pickering emulsion gel, wherein the double network nanocellulose microgel and n-hexane are used in a weight ratio of 10 parts:90 parts;

[0035] (3) Preparation of nanocellulose microgel-based porous material: The emulsion gel obtained in step (2) was placed in a fume hood and dried at room temperature for 24 hours to evaporate the n-hexane, then frozen at -18°C for 24 hours, and then moved to a freeze dryer with a cold trap temperature of -65°C and a vacuum degree of 1 Pa and dried for 48 hours to obtain a nanocellulose microgel-based porous material.

[0036] The nanocellulose microgel-based porous material obtained in this example has a multi-level pore structure combining micron circular pores and nanopores, wherein the micron circular pores are concentrated between 32 and 44 μm, with an average pore size of 39.7 μm, which is basically consistent with the droplet size in the template emulsion; the nanopores are concentrated between 200 and 600 nm, with an average pore size of 385 nm, indicating that the method of the present invention effectively achieves controllable pore size distribution and pore morphology.

Claims

1. A method for preparing a double-network nanocellulose microgel-based porous material, characterized in that: The steps are as follows: (1) Preparation of double-network nanocellulose microgel: carboxyl nanocellulose and aldehyde nanocellulose are mixed in a mass ratio of 1:1 to 3 to prepare a nanocellulose aqueous dispersion having a total mass concentration of 1.0% to 3.0% of carboxyl nanocellulose and aldehyde nanocellulose; a 2.0% polyethyleneimine aqueous solution is then added dropwise on top of the nanocellulose aqueous dispersion in an equal volume ratio, and the mixture is allowed to stand at room temperature for 24 hours to obtain a gel matrix; the gel matrix is ​​transferred to a 2.0% polyethyleneimine aqueous solution, immersed and aged for 12 hours, and then taken out and immersed in an EDC / NHS mixed solution for reaction for 24 hours to obtain a nanocellulose hydrogel; the nanocellulose hydrogel is rinsed twice with an equal mass ratio of deionized water, and then an equal mass ratio of deionized water is added to the mixture and treated at a mechanical shear rate of 10,000 rpm for 3 minutes to obtain a double-network nanocellulose microgel; (2) Preparing a Pickering emulsion gel: taking the double network nanocellulose microgel prepared in step (1), adding n-hexane dropwise thereto, stirring and mixing at 3000 rpm to obtain a Pickering emulsion gel, wherein the double network nanocellulose microgel and n-hexane are used in a weight ratio of 10 to 30 parts: 70 to 90 parts; (3) Preparation of nanocellulose microgel-based porous material: The Pickering emulsion gel prepared in step (2) was placed in a fume hood and dried at room temperature for 24 hours to evaporate the n-hexane, then frozen at -18°C for 24 hours, and then moved to a freeze dryer with a cold trap temperature of -65°C and a vacuum degree of 1 Pa and dried for 48 hours to obtain a nanocellulose microgel-based porous material.

2. The method for preparing the double-network nanocellulose microgel-based porous material according to claim 1, characterized in that: In step (1), when the carboxyl nanocellulose and the aldehyde nanocellulose are mixed, they are mechanically stirred at 3000 rpm at room temperature for 5 minutes.

3. The method for preparing the double-network nanocellulose microgel-based porous material according to claim 1, characterized in that: In step (1), the surface carboxyl content of the carboxyl nanocellulose is 1.0 to 1.4 mmol / g, the surface aldehyde content of the aldehyde nanocellulose is 1.0 to 3.0 mmol / g, and the molecular weight of the polyethyleneimine is 10 kDa to 70 kDa.

4. The method for preparing the double-network nanocellulose microgel-based porous material according to claim 1, characterized in that: In step (1), the mass ratio of EDC to NHS in the EDC / NHS mixed solution is 1.5-2.5:1.