Preparation method of tough and conductive cellulose / polyacrylic acid gel based on in-situ dissolution esterification strategy

Abstract

The invention discloses a preparation method of tough and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy, and belongs to the technical field of preparation of flexible cellulose-based composite gel. The invention aims to solve the problems of poor mechanical strength and complex preparation steps of the existing cellulose / PAA. The method comprises the following steps: 1, preparing a polymerizable eutectic solvent; 2, preparing a cellulose solution; 3, carrying out ultraviolet radiation; and 4, regenerating. The method is used for preparing tough and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of flexible cellulose-based composite gel. Background Art

[0002] Flexible gel materials have shown great application potential in the fields of electronic skin, flexible energy storage devices, wearable sensors and soft robots due to their excellent flexibility, deformability and adjustable three-dimensional network structure. Cellulose, as an abundant natural renewable polymer, has become an ideal choice for the preparation of flexible gels due to its wide range of raw material sources, excellent processability, degradability and good biocompatibility. Therefore, the development of cellulose-based functional gel materials with excellent mechanical properties has become a current research hotspot.

[0003] At present, many studies have combined cellulose with water-soluble polyacrylic acid polymers to prepare functional gel materials with excellent performance. For example, Wei et al. (Wei D, Lv S, Zuo J, et al. Engineering versatile bi-network ionic conductive hydrogels wearable sensors via on demand graft modification for real-time human movement monitoring [J]. Chemical Engineering Journal, 2024, 496: 154176.) dissolved the cellulose solution in epoxy imidazole ionic liquid at 85 ° C, and then added acrylic acid monomer (AA), crosslinker (N, N-methylenebisacrylamide, MBA) and initiator (ammonium persulfate, APS). Under ultraviolet light, the imidazolium ion cellulose / polyacrylic acid double network gel was successfully synthesized by free radical polymerization reaction. The tensile strength of the gel can reach 1.2 MPa. Yan et al. (Yan X, Lin X, Liu H, et al. Tough and temperature-tolerance cellulose / polyacrylic acid / bentonite hydrogel with high ionic conductivity enables self-powered triboelectric wearable electronic devices [J]. Carbohydrate Polymers, 2024, 344: 122552.) directly dissolved bacterial cellulose in 65 wt% ZnCl 2The AA monomer, APS initiator, MBA crosslinker and bentonite were then introduced into the solution one after another, and a cellulose / polyacrylic acid / bentonite hydrogel containing a large number of coordination bonds and hydrogen bonds was synthesized through free radical polymerization. The tensile fracture stress of the gel can reach 2.39 MPa, and it also has high ionic conductivity, which can be used in self-powered wearable electronic devices.

[0004] In the above studies, cellulose and polyacrylic acid (PAA) are mainly connected through physical cross-linking methods such as hydrogen bonds and ionic bonds, which leads to poor mechanical properties of the gel, thus limiting its application. Although strategies such as cellulose modification and double network structure can enhance its mechanical properties to a certain extent, these methods are relatively complicated and have limited toughening effects. In addition, due to the highly crystalline structure and strong solvent resistance of cellulose, it is difficult to mix it with acrylic acid solution. The preparation process may take hours or even days, and additional initiators and cross-linking agents are usually required during the polymerization process, which increases the complexity of the operation. Therefore, it is of great significance to develop a simple and efficient in situ polymerization method to prepare cellulose / PAA gels with excellent mechanical properties. Summary of the invention

[0005] The present invention aims to solve the problems of poor mechanical strength and complicated preparation steps of existing cellulose / PAA, and further provide a method for preparing strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy.

[0006] A method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy is carried out in the following steps:

[0007] 1. Preparation of polymerizable low eutectic solvent:

[0008] At room temperature, ZnCl 2 , water and acrylic acid are stirred and mixed uniformly to obtain a polymerizable low eutectic solvent;

[0009] The ZnCl 2 The mass ratio of ZnCl to water is 20:(5-9); 2 The mass ratio of acrylic acid is 20:(2-4);

[0010] 2. Preparation of cellulose solution:

[0011] The cellulose is crushed and added into a polymerizable low eutectic solvent, heated and stirred to dissolve, and then centrifuged to remove bubbles to obtain a cellulose solution;

[0012] 3. Ultraviolet irradiation:

[0013] Under ultraviolet light, the cellulose solution is polymerized with acrylic acid to obtain an intermediate gel;

[0014] 4. Regeneration:

[0015] The intermediate gel is placed in an ethanol solution for regeneration, thereby completing the preparation method of strong, conductive cellulose / polyacrylic acid gel based on the in situ dissolution esterification strategy.

[0016] The beneficial effects of the present invention are:

[0017] The present invention designs and synthesizes a polymerizable low eutectic solvent. Step 2 adopts an in-situ dissolution and esterification cellulose strategy. While efficiently dissolving cellulose, the acrylic acid monomer AA is grafted onto the cellulose in the form of a covalent ester bond. Without the need for an initiator or a cross-linking agent, the network formed by polymerization of acrylic acid interacts with the cellulose network regenerated from ethanol, achieving high mechanical properties in a short time, thereby forming a cellulose / PAA gel with excellent mechanical properties and high conductivity.

[0018] 1. The polymerizable low eutectic solvent used in the present invention can dissolve cellulose efficiently and completely dissolve pulp cellulose in 20 to 40 minutes. The mass of the dissolved cellulose is 6% to 8% of the mass of the polymerizable low eutectic solvent.

[0019] 2. In the process of dissolving cellulose, the acrylic acid monomer AA in the prepared polymerizable low eutectic solvent is grafted onto cellulose through ester bond action, which can increase the connection strength between the finally formed PAA network and the cellulose network.

[0020] 3. During the PAA polymerization process, the polymerization reaction can be completed without the addition of additional initiator.

[0021] 4. The polymerizable low eutectic solvent acts as a solvent in the reaction. All components play a certain role in forming the network. The acrylic acid monomer AA is used as a polymerizable monomer to form a network. After the network is formed, the zinc ions can form metal coordination bonds with cellulose and PAA and increase the ionic conductivity of the material.

[0022] 5. The cellulose / PAA conductive gel prepared by the present invention has excellent mechanical properties, with a tensile strength of 12.6MPa and a toughness of 4.24MJ / m 3 , the conductivity also reaches 0.47S / m. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The polarized light microscope images of the pulp cellulose and the prepared cellulose solution described in step 2 of Example 1, a is the pulp cellulose, and b is the cellulose solution;

[0024] Figure 2 FT-IR spectra of the pulp cellulose and the prepared cellulose solution after drying described in step 2 of Example 1;

[0025] Figure 3 The pulp cellulose and the prepared cellulose solution after drying described in step 2 of Example 1 13 C NMR spectrum;

[0026] Figure 4 The stress-strain curves of the cellulose / PAA double network conductive gels prepared in Example 1 and Comparative Examples 1 to 4;

[0027] Figure 5 This is a graph of the toughness of the cellulose / PAA double network conductive gel prepared in Example 1 and Comparative Example 1;

[0028] Figure 6 This is an EIS curve of the cellulose / PAA double network conductive gel prepared in Example 1;

[0029] Figure 7 This is the sensing performance diagram of the cellulose / PAA double network conductive gel prepared in Example 1. DETAILED DESCRIPTION

[0030] Specific embodiment 1: This embodiment is a method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy, which is carried out in the following steps:

[0031] 1. Preparation of polymerizable low eutectic solvent:

[0032] At room temperature, ZnCl 2 , water and acrylic acid are stirred and mixed uniformly to obtain a polymerizable low eutectic solvent;

[0033] The ZnCl 2 The mass ratio of ZnCl to water is 20:(5-9); 2 The mass ratio of acrylic acid is 20:(2-4);

[0034] 2. Preparation of cellulose solution:

[0035] The cellulose is crushed and added into a polymerizable low eutectic solvent, heated and stirred to dissolve, and then centrifuged to remove bubbles to obtain a cellulose solution;

[0036] 3. Ultraviolet irradiation:

[0037] Under ultraviolet light, the cellulose solution is polymerized with acrylic acid to obtain an intermediate gel;

[0038] 4. Regeneration:

[0039] The intermediate gel is placed in an ethanol solution for regeneration, thereby completing the preparation method of strong, conductive cellulose / polyacrylic acid gel based on the in situ dissolution esterification strategy.

[0040] The beneficial effects of this embodiment are:

[0041] In this embodiment, a polymerizable low eutectic solvent is designed and synthesized. Step 2 adopts an in-situ dissolution and esterification cellulose strategy. While efficiently dissolving cellulose, the acrylic acid monomer AA is grafted onto the cellulose in the form of a covalent ester bond. Without the need for an initiator or a cross-linking agent, the network formed by polymerization of acrylic acid interacts with the cellulose network regenerated from ethanol, achieving high mechanical properties in a short period of time, thereby forming a cellulose / PAA gel with excellent mechanical properties and high conductivity.

[0042] 1. The polymerizable low eutectic solvent used in this embodiment can dissolve cellulose efficiently and completely dissolve pulp cellulose in 20 to 40 minutes. The mass of the dissolved cellulose is 6% to 8% of the mass of the polymerizable low eutectic solvent.

[0043] 2. In the process of dissolving cellulose, the acrylic acid monomer AA in the prepared polymerizable low eutectic solvent is grafted onto cellulose through ester bond action, which can increase the connection strength between the finally formed PAA network and the cellulose network.

[0044] 3. During the PAA polymerization process, the polymerization reaction can be completed without the addition of additional initiator.

[0045] 4. The polymerizable low eutectic solvent acts as a solvent in the reaction. All components play a certain role in forming the network. The acrylic acid monomer AA is used as a polymerizable monomer to form a network. After the network is formed, the zinc ions can form metal coordination bonds with cellulose and PAA and increase the ionic conductivity of the material.

[0046] 5. The cellulose / PAA conductive gel prepared in this embodiment has excellent mechanical properties, with a tensile strength of 12.6 MPa and a toughness of 4.24 MJ / m 3 , the conductivity also reaches 0.47S / m.

[0047] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that the cellulose in step 2 is pulp cellulose and the pulp cellulose is wood pulp cellulose. The rest is the same as specific implementation method 1.

[0048] Specific embodiment 3: This embodiment is different from specific embodiment 1 or 2 in that: the heating, stirring and dissolving described in step 2 is specifically carried out at a temperature of 70°C to 80°C and a rotation speed of 400r / min to 450r / min for 20min to 40min. The rest is the same as specific embodiment 1 or 2.

[0049] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the centrifugal degassing in step 2 is performed at a rotation speed of 8500 r / min to 9500 r / min for 15 to 20 minutes. The rest is the same as specific embodiments 1 to 3.

[0050] Specific embodiment 5: This embodiment is different from Specific embodiments 1 to 4 in that the mass ratio of cellulose to acrylic acid in the cellulose solution described in step 2 is 1:(0.95-1). Other aspects are the same as Specific embodiments 1 to 4.

[0051] Specific embodiment 6: This embodiment is different from Specific embodiments 1 to 5 in that the mass of the cellulose in step 2 is 6% to 8% of the mass of the polymerizable deep eutectic solvent. The rest is the same as Specific embodiments 1 to 5.

[0052] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that in step 3, the cellulose solution is subjected to acrylic acid polymerization for 20 min to 40 min under ultraviolet light irradiation with a wavelength of 320 nm to 400 nm and a power of 15 W to 25 W. Other steps are the same as specific embodiments 1 to 6.

[0053] Specific embodiment 8: This embodiment differs from Specific embodiments 1 to 7 in that: in step 4, the intermediate gel is placed in an ethanol solution at room temperature for regeneration for 15 to 30 minutes. The rest is the same as Specific embodiments 1 to 7.

[0054] Specific embodiment 9: This embodiment is different from specific embodiments 1 to 8 in that the mass percentage of the ethanol solution in step 4 is 70% to 99.9%. The rest is the same as specific embodiments 1 to 8.

[0055] Specific embodiment 10: This embodiment differs from Specific embodiments 1 to 9 in that the volume ratio of the mass of the intermediate gel described in step 4 to the ethanol solution is 1 g: (10-25) mL. The rest is the same as Specific embodiments 1 to 9.

[0056] The following examples are used to verify the beneficial effects of the present invention:

[0057] Embodiment 1:

[0058] A method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy is carried out in the following steps:

[0059] 1. Preparation of polymerizable low eutectic solvent:

[0060] At room temperature, 20 g ZnCl 2, 7.9 g of water and 2 g of acrylic acid were stirred and mixed to obtain a polymerizable low eutectic solvent;

[0061] 2. Preparation of cellulose solution:

[0062] At a temperature of 70°C and a rotation speed of 450 r / min, 2.1 g of cellulose was crushed and added to 29.9 g of a polymerizable low eutectic solvent, heated and stirred to dissolve for 30 min, and then centrifuged at a rotation speed of 9500 r / min for 20 min to obtain a cellulose solution;

[0063] The cellulose is pulp cellulose (wood pulp cellulose); the mass of the cellulose is 7% of the mass of the polymerizable low eutectic solvent;

[0064] 3. Ultraviolet irradiation:

[0065] Under the irradiation of ultraviolet light with a wavelength of 365nm and a power of 20W, the cellulose solution was polymerized with acrylic acid for 30min to obtain an intermediate gel;

[0066] 4. Regeneration:

[0067] The intermediate gel was placed in an ethanol solution at room temperature for 20 min to regenerate the gel and obtain a cellulose / PAA double network conductive gel.

[0068] The mass percentage of the ethanol solution is 99.9%; the volume ratio of the mass of the intermediate gel to the ethanol solution is 1g:20mL.

[0069] Comparative Example 1: This embodiment is different from Embodiment 1 in that step 3 is eliminated. The rest is the same as Embodiment 1.

[0070] Comparative Example 2: This example is different from Example 1 in that: in step 2, 0.3 g of cellulose is crushed and dissolved in 29.9 g of a polymerizable low eutectic solvent under the conditions of a temperature of 70° C. and a rotation speed of 450 r / min, and the mixture is heated, stirred and dissolved for 30 min; the mass of the cellulose in step 2 is 1% of the mass of the polymerizable low eutectic solvent. The rest is the same as in Example 1.

[0071] Comparative Example 3: This example is different from Example 1 in that: in step 2, 0.9 g of cellulose is crushed and dissolved in 29.9 g of a polymerizable low eutectic solvent under the conditions of a temperature of 70° C. and a rotation speed of 450 r / min, and the mixture is heated, stirred and dissolved for 30 min; the mass of the cellulose in step 2 is 3% of the mass of the polymerizable low eutectic solvent. The rest is the same as in Example 1.

[0072] Comparative Example 4: This example is different from Example 1 in that: in step 2, 1.5 g of cellulose is crushed and dissolved in 29.9 g of a polymerizable low eutectic solvent under the conditions of a temperature of 70° C. and a rotation speed of 450 r / min, and the mixture is heated, stirred and dissolved for 30 min; the mass of the cellulose in step 2 is 5% of the mass of the polymerizable low eutectic solvent. The rest is the same as in Example 1.

[0073] Performance characterization:

[0074] (1) Polarized light microscope imaging:

[0075] Figure 1 The polarized light microscope images of the pulp cellulose and the prepared cellulose solution described in step 2 of Example 1, a is the pulp cellulose, and b is the cellulose solution. The disappearance of the crystalline region during the dissolution of cellulose can be observed through the polarized light microscope, proving the complete dissolution of cellulose.

[0076] (2) FT-IR spectrum:

[0077] FT-IR analysis was used to characterize the changes in the chemical structure of cellulose. Figure 2 The FT-IR spectra of the pulp cellulose and the prepared cellulose solution after drying described in step 2 of Example 1 are shown in Table 1. The C=OO (1720 cm -1 ) characteristic peaks appear, -CH 2 (2930cm -1 ) stretching vibration is enhanced, proving that acrylic acid and cellulose undergo esterification reaction.

[0078] (3) 13 C NMR spectrum:

[0079] Figure 3 The pulp cellulose and the prepared cellulose solution after drying described in step 2 of Example 1 13 C NMR spectra. To further confirm the occurrence of esterification, pulp cellulose and cellulose dissolved in a polymerizable low eutectic solvent were subjected to 13 C NMR test, the test results show that the resonance peaks of C4 and C6 are significantly narrowed, and the main peak with higher chemical shift disappears, which proves the disappearance of cellulose crystallization area. At the same time, the new peak at 60ppm can also indicate that cellulose is esterified. This result proves that acrylic acid and cellulose undergo esterification reaction.

[0080] (4) Stress-strain curves of Example 1 and Comparative Examples 1 to 4

[0081] In order to study the mechanical properties of cellulose / polyacrylic acid conductive gel, the tensile curve of the sample was tested using a universal mechanical testing machine. The sample was prepared into a strip with a width of 0.5 cm, and its tensile mechanics was tested at room temperature. The tensile speed was set to 5 mm / min. Figure 4 It is a stress-strain curve diagram of the cellulose / PAA double network conductive gel prepared in Example 1 and Comparative Examples 1-4. Figure 5 The toughness diagram of the cellulose / PAA double network conductive gel prepared in Example 1 and Comparative Example 1. By comparison, it can be found that as the amount of cellulose dissolved gradually increases, the mechanical strength of the gel shows an increasing trend. When the mass of the cellulose is 7% of the mass of the polymerizable low eutectic solvent, the tensile strength of the gel reaches 12.6MPa and the toughness reaches 4.2MJ / m 3 , which is 13.5 times that of comparative example 1.

[0082] (5) EIS curve of Example 1

[0083] Figure 6 This is an EIS curve of the cellulose / PAA double network conductive gel prepared in Example 1. The conductivity of the gel can be calculated to be 0.47 S / m through the EIS curve.

[0084] (6) Example 1 is a sensor performance test

[0085] Figure 7 This is a diagram of the sensing performance of the cellulose / PAA double network conductive gel prepared in Example 1. The sensing performance of the gel was tested using a CHI60 electrochemical workstation. The results showed that the gel had sensitive electrical signal changes in response to finger bending.

Claims

1. A method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy, characterized in that It is carried out in the following steps:

1. Preparation of polymerizable low eutectic solvent: At room temperature, ZnCl2, water and acrylic acid are stirred and mixed uniformly to obtain a polymerizable low eutectic solvent; The mass ratio of ZnCl2 to water is 20:(5-9); the mass ratio of ZnCl2 to acrylic acid is 20:(2-4); 2. Preparation of cellulose solution: The cellulose is crushed and added into a polymerizable low eutectic solvent, heated and stirred to dissolve, and then centrifuged to remove bubbles to obtain a cellulose solution; 3. Ultraviolet irradiation: Under ultraviolet light, the cellulose solution is polymerized with acrylic acid to obtain an intermediate gel; 4. Regeneration: The intermediate gel is placed in an ethanol solution for regeneration, thereby completing the preparation method of strong, conductive cellulose / polyacrylic acid gel based on the in situ dissolution esterification strategy.

2. A method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy according to claim 1, characterized in that The cellulose described in step 2 is pulp cellulose; the pulp cellulose described is wood pulp cellulose.

3. A method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy according to claim 1, characterized in that The heating, stirring and dissolving in step 2 is specifically carried out at a temperature of 70° C. to 80° C. and a rotation speed of 400 r / min to 450 r / min for 20 min to 40 min.

4. A method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy according to claim 1, characterized in that The centrifugal degassing in step 2 is specifically performed at a rotation speed of 8500 r / min to 9500 r / min for 15 min to 20 min.

5. The method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy according to claim 1, characterized in that The mass ratio of cellulose to acrylic acid in the cellulose solution described in step 2 is 1:(0.95-1).

6. A method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy according to claim 1, characterized in that The mass of the cellulose in step 2 is 6% to 8% of the mass of the polymerizable deep eutectic solvent.

7. A method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy according to claim 1, characterized in that In step 3, the cellulose solution is subjected to acrylic acid polymerization reaction for 20 minutes to 40 minutes under the irradiation of ultraviolet light with a wavelength of 320nm to 400nm and a power of 15W to 25W.

8. The method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy according to claim 1, characterized in that In step 4, the intermediate gel is placed in an ethanol solution at room temperature for regeneration for 15 to 30 minutes.

9. A method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy according to claim 1, characterized in that The mass percentage of the ethanol solution described in step 4 is 70% to 99.9%.

10. A method for preparing a strong and conductive cellulose / polyacrylic acid gel based on an in-situ dissolution esterification strategy according to claim 1, characterized in that The volume ratio of the mass of the intermediate gel described in step 4 to the ethanol solution is 1 g: (10-25) mL.

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