Preparation method and application of ramie fiber-based conductive anti-freezing hydrogel

Abstract

The invention discloses a preparation method of ramie fiber-based conductive anti-freezing hydrogel, which comprises the following steps: S1, treating ramie bones by using p-toluenesulfonic acid to obtain ramie fibers; s2, mixing ramie fibers, polyvinyl alcohol and ethylene glycol according to a set proportion, stirring at a preset temperature until the polyvinyl alcohol is completely dissolved, then adding sodium chloride and tannic acid into a system, and stirring at a set temperature until a first homogeneous solution is formed; s3, adding sodium polyacrylate and N, N-dimethyl bisacrylamide into the first homogeneous solution, stirring at a preset temperature until the sodium polyacrylate and the N, N-dimethyl bisacrylamide are completely dissolved, then adding ammonium persulfate into a system, fully reacting to form a hydrogel precursor solution, removing bubbles, and drying to obtain the ramie fiber-based conductive anti-freezing hydrogel. The PVA first network conductive hydrogel is prepared by adopting a binary solvent method, on the basis, an initiator and a cross-linking agent are added into a system to promote PAA-Na and PVA to form a cross-linked network, and strong hydrogen bond interaction is formed between rich hydroxyl groups and between hydroxyl groups and water molecules in the system, so that the hydrogel is endowed with excellent mechanical properties, good conductivity and environmental tolerance.

Description

Technical Field

[0001] The present invention belongs to the technical field of conductive hydrogels, and relates to a preparation method and application of a ramie fiber-based conductive and antifreeze hydrogel. Background Art

[0002] In recent years, hydrogels have achieved rapid development in flexible electronic fields such as ionic skin and motion monitoring due to their excellent mechanical properties, good biocompatibility and other characteristics. Traditional hydrogels generally use a single water as a solvent and have a single substrate, so they have deficiencies in various properties. Usually, the water content in the hydrogel is at least above 80%. Therefore, when the hydrogel is placed under high-temperature conditions, the water molecules in the gel system will inevitably evaporate, causing water loss and reducing the overall performance of the gel; when the temperature is too low, the water molecules in the internal network of the gel form an ordered arrangement, and ice crystals appear, resulting in a sharp decline in the toughness, elasticity, etc. of the gel, thus restricting the practical application of the hydrogel in complex environments.

[0003] In the prior art, the basic strategies for endowing hydrogels with antifreeze properties include the solvent replacement method and the ion gel method. Among them, the solvent replacement method is the fastest and most convenient method, such as simple operation, different time or replacement agents can be selected, and the replacement conditions are required to be low, etc., but it is difficult to achieve fine performance regulation, and the solvent replacement method may cause uneven material structure in some cases, affecting the final performance. The ion gel method is a method of forming a gel by ion crosslinking and other effects. Most ion gels have insufficient mechanical strength and are prone to deformation and fracture when subjected to large external forces. Moreover, the toughness of ion gels is often poor, the impact resistance is weak, and the preparation process is relatively complex and time-consuming.

[0004] Ramie is one of the important crops in China and is widely distributed in most parts of the country. The hemp bark and hemp leaves are both important economic crops, while the utilization value of the hemp stalk is relatively low. The traditional treatment method mainly focuses on incineration, but from the national development trend and policies in recent years, this way of incineration is about to become a thing of the past. Therefore, the treatment method of ramie and other crop straws is particularly important for the development trend of its industry. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a preparation method and application of a ramie fiber-based conductive and antifreeze hydrogel, which optimizes the conductive and antifreeze properties of the hydrogel by the binary solvent method, and prepares a double-network composite hydrogel with good conductivity, excellent mechanical properties and environmental tolerance.

[0006] The present invention provides a preparation method of a ramie fiber-based conductive and antifreeze hydrogel, comprising the following steps:

[0007] S1. Treat ramie bone with p-toluenesulfonic acid to obtain ramie fibers (CNFs).

[0008] S2. Mix the ramie fibers obtained in step S1, polyvinyl alcohol (PVA), and ethylene glycol (EG) in a set ratio, stir at a predetermined temperature until the polyvinyl alcohol is completely dissolved, then add sodium chloride and tannic acid (TA) to the system, and stir at the set temperature until a first homogeneous solution is formed.

[0009] S3. Add sodium polyacrylate (PAA-Na) and N,N-dimethylbisacrylamide (MBA) to the first homogeneous solution obtained in step S2, stir at a predetermined temperature until completely dissolved, then add ammonium persulfate (APS) to the system. After sufficient reaction, a hydrogel precursor solution is formed. Remove the bubbles and dry to obtain a ramie fiber-based conductive antifreeze hydrogel.

[0010] In a preferred embodiment, in step S1, the continuous treatment of ramie bone with p-toluenesulfonic acid includes two stages: lignin removal and nanofibrillated cellulose extraction. Specifically:

[0011] S11. Add ramie bone to concentrated sulfuric acid and / or sodium hydroxide solution for degumming treatment. Subsequently, wash the treated ramie bone with running water, dry, and pulverize and sieve it to obtain pretreated ramie bone.

[0012] S12. Add the pretreated ramie bone obtained in step S11 to a p-toluenesulfonic acid solution with a mass concentration of 65% - 75% of p-toluenesulfonic acid. Stir at a temperature of 80 - 90 °C for a reaction time of 50 - 70 min. After the reaction, perform solid-liquid separation to obtain fibers and acid solution.

[0013] S13. Add the fibers obtained in step S12 to the p-toluenesulfonic acid solution again with a mass concentration of 65% - 75% of p-toluenesulfonic acid. Stir at a temperature of 80 - 90 °C for a reaction time of 1 - 4 h. After the reaction, perform solid-liquid separation, and wash the obtained fibers until neutral to prepare a ramie fiber suspension for standby.

[0014] In a more preferred embodiment, in step S13, the mass fraction of the ramie fiber suspension is 0.1% - 1%, and deionized water or pure water is used as the solvent.

[0015] In a preferred embodiment, in step S2, dissolve polyvinyl alcohol in a mixed solution composed of ramie fiber suspension and ethylene glycol. The mass ratio of polyvinyl alcohol, ethylene glycol, and ramie fiber suspension is 1:(3 - 5):(6 - 10).

[0016] Preferably, in step S2, polyvinyl alcohol is added to a mixed solution composed of ramie fiber suspension and ethylene glycol, magnetically stirred at 80-90°C for 1-4 h, then sodium chloride and tannic acid are added, and stirring is continued at 60-80°C for 0.5-3 h, followed by ultrasonic treatment for 1-10 min to remove bubbles, obtaining a first homogeneous solution.

[0017] More preferably, the mass ratio of sodium chloride to polyvinyl alcohol is (0.1-0.5):1.

[0018] More preferably, the mass ratio of tannic acid to polyvinyl alcohol is (0.1-0.8):1.

[0019] Preferably, in step S3, the mass ratio of sodium polyacrylate, N-N dimethyl bisacrylamide, and ammonium persulfate is 1:(0.005-0.02):(0.02-0.04).

[0020] Preferably, in step S3, the mass ratio of sodium polyacrylate to polyvinyl alcohol is 1:(1-3).

[0021] Preferably, in step S3, sodium polyacrylate and N-N dimethyl bisacrylamide are added to the first homogeneous solution and stirred at 70-80°C until completely dissolved.

[0022] Preferably, in step S3, the drying temperature is 50-60°C and the drying time is 2-6 h.

[0023] The present invention also provides the application of the ramie fiber-based conductive antifreeze hydrogel, which is used to prepare a hydrogel-coated fabric.

[0024] Compared with the solvent replacement method, the binary solvent method can more precisely control the mixing ratio of solvents, thereby achieving better performance regulation of materials; secondly, the binary solvent method can better control the phase separation and crystallization process of materials, thereby obtaining a stable structure, which is of great significance for the preparation of gels; in addition, the binary solvent method is not only applicable to specific material systems, but also can be widely applied to different chemical and materials science fields, with high versatility and flexibility.

[0025] The present invention prepares a double-network cross-linked composite conductive hydrogel with excellent electrical conductivity, excellent mechanical properties, and good environmental tolerance using a step-by-step synthesis strategy. The PVA / CNFs / TA / NaCl / EG ionic conductive hydrogel is prepared by adding PVA as a substrate into a binary solvent composed of water and ethylene glycol (mass ratio 1:2), and then introducing cellulose nanofibers (CNFs), tannic acid (TA), and metal salt ions (NaCl), and continuously stirring at high temperature to obtain the first PVA network; then adding an initiator N,N-dimethylbisacrylamide (MBA) to the system, so that sodium polyacrylate (PAA-Na) added to the system forms a double network with PVA. The addition of ammonium persulfate (APS) enhances various intermolecular interactions, providing a basis for the composite hydrogel to maintain flexibility, stretchability, and conductivity under complex conditions. In addition, the hydrogen bond interaction formed between ethylene glycol and water and the cross-linking interaction between PVA and PAA-Na effectively enhance the overall mechanical properties of the hydrogel and effectively inhibit ice crystals at low temperatures and evaporation at high temperatures.

[0026] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0027] Using p-toluenesulfonic acid as an acidic water aid, a large amount of lignin and part of hemicellulose are dissolved during the reaction. The reaction is relatively mild and mainly penetrates into the amorphous region of the fiber without destroying its basic structure; at the same time, the surface pores of the treated fiber increase, which is beneficial to further research on subsequent resource utilization; the p-toluenesulfonic acid after the reaction is recyclable, with low cost and environmental friendliness.

[0028] The hydrogen bond interaction between water and ethylene glycol enhances the environmental tolerance of the hydrogel, inhibits the formation of ice crystals in a low-temperature environment of -40°C and the evaporation of water at a high temperature of 60°C. The solvent loss rate is low after storing at room temperature for one month. The introduction of ramie fibers and tannic acid effectively compensates for the decrease in the mechanical properties of the hydrogel caused by NaCl ions, enabling it to still have good sensitivity after being in a harsh environment and long-term storage, and is suitable for flexible wearable devices; the introduction of NaCl ions endows the organic hydrogel with high ionic conductivity and still maintains good conductivity after being placed in a harsh environment for 3 days.

[0029] The binary solvent method is used to prepare the PVA first-network conductive hydrogel. On this basis, an initiator (MBA) and a cross-linking agent (APS) are added to the system to promote the formation of a cross-linked network between PAA-Na and PVA. The abundant hydroxyl groups in the system form strong hydrogen bond interactions between hydroxyl groups and between hydroxyl groups and water molecules, giving the hydrogel excellent mechanical properties, good electrical conductivity, and environmental tolerance. Description of the Drawings

[0030] Figure 1 SEM image of ramie fibers in Example 1;

[0031] Among them: (a) and (b) are the original ramie bone samples and ramie fiber samples under 500 times magnification; (c) and (d) are the original ramie samples and ramie fiber samples under 1000 times magnification;

[0032] Figure 2 are the infrared spectra of ramie bone before and after treatment;

[0033] Among them: PP represents the untreated sample; PP-A represents the intermediate-treated sample; PP-CNFs represents the sample after complete treatment;

[0034] Figure 3 are the SEM images of ramie fiber-based conductive antifreeze hydrogels;

[0035] Among them, (a) is the PVA first cross-linked network sample (PCNTG); (b) is the ramie fiber-based conductive antifreeze hydrogel sample (PCNTG-PAA);

[0036] Figure 4 are the FT-IR spectra of PCNTG and PCNTG-PAA hydrogels;

[0037] Figure 5 is the change of water retention rate of PCNTG-PAA hydrogel with time at 60°C;

[0038] Figure 6 are the Nyquist curves of PCNTG-PAA hydrogels with different ramie fiber contents;

[0039] Figure 7 are the conductivities of PCNTG-PAA hydrogels with different ramie fiber contents;

[0040] Figure 8 are (a) the breaking strength-time curves of the fabric before and after treatment; (b) and (c) the breaking strength and elongation at break of the fabric before and after treatment; (d) the comparison of fabric softness before and after treatment;

[0041] Figure 9 is the change of conductivity of the modified fabric with time at room temperature;

[0042] Figure 10 are (a) the change of conductivity of the modified fabric with time at -20°C; (b) the change of conductivity of the modified fabric with time at 60°C. Specific embodiments

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] The present invention will be described below in conjunction with specific embodiments and the accompanying drawings.

[0045] Example 1

[0046] A preparation method of ramie fiber-based conductive antifreeze hydrogel, comprising the following steps:

[0047] (1) Continuously treat ramie hemp bone with p-toluenesulfonic acid, including two stages of removing lignin and extracting nanocellulose. Specifically:

[0048] S11. Add ramie hemp bone to concentrated sulfuric acid for degumming treatment. Subsequently, wash the treated ramie hemp bone with running water, dry it, and crush and sieve it to 60 mesh to obtain pretreated ramie hemp bone.

[0049] S12. Take 3.0 g of pretreated ramie hemp bone and add it to 100 ml of p-toluenesulfonic acid solution with a mass concentration of 70% of toluenesulfonic acid. Stir at a temperature of 90 °C for 60 min. After the reaction, perform solid-liquid separation to obtain fibers and acid solution.

[0050] S13. Add the fibers obtained in step S12 to the p-toluenesulfonic acid solution again with a mass concentration of 70% of toluenesulfonic acid. Stir at a temperature of 90 °C for 2 h. After the reaction, perform solid-liquid separation, and wash the obtained fibers until neutral to prepare a ramie fiber suspension with a mass fraction of 0.5%, which is reserved for use.

[0051] (2) Mix the EG solution (10 g) and the ramie fiber suspension (0.5 wt%) according to a mass ratio of 1:2, add 2.5 g of PVA solid, and stir magnetically at 85 °C for 2 h until the PVA is completely dissolved. Then add NaCl (0.6 g) and TA (0.8 g) to the system and continue to stir at 70 °C for 1 h until a homogeneous solution is formed to form a first PVA crosslinked network.

[0052] (3) Take 2 g of PAA-Na crystals and 0.02 g of MBA and add them to the homogeneous solution. Heat and stir at 75 °C until completely dissolved, and let it stand for 20 min. Add 0.06 g of APS to the mixed solution and stir to ensure uniform reaction in the system to form a hydrogel precursor solution. Ultrasonically vibrate for 30 min to remove air bubbles in the system, pour it into a mold, place it in an oven, and react at 50-60 °C for 4 h, and let it stand at room temperature to obtain a second PVA / PAA crosslinked network, that is, the ramie fiber-based conductive antifreeze hydrogel.

[0053] Figure 1Perform a morphological analysis on the surface of the ramie bone fiber prepared in Example 1. As can be seen from (a) and (c), the surface of the original ramie bone is smooth, with clear texture and good compactness; while for the samples treated with p-toluenesulfonic acid, namely (b) and (d), it can be known that the pores on the fiber surface increase and the cracks are obvious, indicating that a large amount of lignin, hemicellulose, etc. in the ramie bone are removed after the treatment with p-toluenesulfonic acid, and the overall compactness decreases, which is beneficial to the further extraction of nanocellulose.

[0054] Figure 2 The infrared spectra of the ramie bone before and after treatment in Example 1. The wavenumber in the figure is 3460 cm -1 is the vibration peak of -OH. The intensity of the peak of the treated sample is significantly weakened compared with that of the original sample, indicating that lignin and hemicellulose containing -OH in the ramie bone are significantly removed. The wavenumber is 1775 cm -1 to 1665 cm -1 The range is the characteristic peak of the carbonyl group and the downward trend is obvious, indicating that a large amount of hemicellulose is dissolved. The wavenumber is at 1514 cm -1 and 1227 cm -1 There are obvious changes here, which are the characteristic peaks of the benzene ring skeleton and ether bond respectively, indicating that lignin is removed. 896 cm -1 is the characteristic peak of the intermolecular glycosidic bond of cellulose molecules. There is no obvious change in the intensity of the vibration peak at this place before and after treatment. The analysis results show that the process of treating cellulose with p-toluenesulfonic acid is relatively mild, and the acid mainly penetrates into the amorphous region of the cellulose structure without changing the basic structure of ramie bone cellulose.

[0055] Example 2

[0056] A preparation method of a ramie fiber-based conductive antifreeze hydrogel, comprising the following steps:

[0057] (1) Continuously treat the ramie bone with p-toluenesulfonic acid, and the specific process is the same as that in Example 1;

[0058] (2) Dissolve 2 g of PVA in a mixed solution composed of 20 g of ramie fiber suspension (mass fraction is 0.5%) and 10 g of ethylene glycol (EG), and magnetically stir at 85 °C for 2 h until the PVA is completely dissolved. Then add NaCl (0.6 g) and TA (0.8 g) to the system, and continue to stir at 70 °C for 1.5 h until a homogeneous solution is formed to form the first cross-linked network of PVA (PCNTG);

[0059] (3) Take 2 g of PAA-Na crystals and 0.02 g of MBA and add them to the homogeneous solution. Heat and stir at 70 °C until completely dissolved, and then let it stand for 30 min. Add 0.06 g of APS to the mixed solution and stir to ensure uniform reaction in the system to form a hydrogel precursor solution. Ultrasonically vibrate for 20 min to remove the bubbles in the system, pour it into a mold, place it in an oven, and react at 50-60 °C for 3 h. Let it stand at room temperature to obtain the second cross-linked network of PVA / PAA, that is, the ramie fiber-based conductive antifreeze hydrogel (PCNTG-PAA).

[0060] Figure 3 SEM image of the ramie fiber-based conductive antifreeze hydrogel in Example 2. It can be observed that the introduction of PAA-Na makes the hydrogel system show a denser cross-linked network with a larger specific surface area, and its surface layer shows an obvious interlaced porous structure, which is beneficial to ensuring the good mechanical properties of the hydrogel.

[0061] Figure 4 FTIR spectra of PCNTG and PCNTG-PAA. The spectra of PCNTG and PCNTG-PAA are similar. As can be seen in the figure, the absorption peak at 1641 cm -1 is the stretching vibration peak of the carboxylate (COO-) group, and the peak at 1039 cm-1 is the stretching vibration peak of the N-H bond of MBA, indicating that PAA has been successfully grafted onto the PCNTG-PAA hydrogel; the peak at 1338 cm -1 is caused by the bending of -CH 2 -, and the peak at 1207 cm -1 is the vibration peak of phenolic -OH, which is due to the addition of TA and the hydrogen bond interaction with PVA, PAA, MBA and CNFs in the system, forming strong hydrogen bond interaction and further improving the mechanical properties of the hydrogel; the absorption intensity of the peak at 1039 cm -1 weakens, which is due to the addition of inorganic salt ions, resulting in a small decrease in the mechanical properties of the system. However, the introduction of PAA-Na significantly enhances the cross-linking degree, compensates for this shortcoming, and at the same time gives the hydrogel good conductivity.

[0062] Example 3

[0063] A preparation method of a ramie fiber-based conductive antifreeze hydrogel, comprising the following steps:

[0064] (1) Continuously treat ramie hemp bones with p-toluenesulfonic acid, and the specific process is the same as that in Example 1;

[0065] (2) Dissolve 2 g of PVA in a mixed solution composed of 20 g of ramie fiber suspension and 10 g of ethylene glycol (EG) (control the ramie fiber content in the hydrogel to be 0% - 2%). Stir magnetically at 90 °C for 1 h until the PVA is completely dissolved. Then add NaCl (0.4 g) and TA (0.6 g) to the system and continue stirring at 60 °C for 3 h until a homogeneous solution is formed to form the first PVA cross-linked network (PCNTG).

[0066] (3) Take 2 g of PAA-Na crystals and 0.01 g of MBA and add them to the homogeneous solution. Heat and stir at 70 °C until completely dissolved, and let it stand for 30 min. Add 0.04 g of APS to the mixed solution and stir to ensure uniform reaction in the system to form a hydrogel precursor solution. Ultrasonically vibrate for 30 min to remove the bubbles in the system, pour it into a mold, put it in an oven, react at 50 - 60 °C for 3 h, and let it stand at room temperature to obtain the second PVA / PAA cross-linked network, that is, the ramie fiber-based conductive antifreeze hydrogel (PCNTG-PAA).

[0067] Figure 5 For the change of water retention rate of the PCNTG-PAA hydrogel in Example 3 with time at 60 °C, the solvent loss rate is relatively fast in the range of 0 - 60 min. When the time is greater than 60 min, the solvent loss rate in the system significantly decreases and finally stays at about 71.5%, and the loss amount only accounts for about 28.5%. This is because EG partially replaces the water in the hydrogel system and hinders the evaporation of water at high temperatures.

[0068] Figure 6 Nyquist curves of PCNTG-PAA hydrogels with different ramie fiber contents; Figure 7is the conductivity of PCNTG-PAA hydrogels with different ramie fiber contents; the results show that the conductivity of the hydrogels will increase significantly after adding an appropriate amount of reinforcing materials. When the mass ratio of CNFs to the solvent increases from 0% to 0.5%, 1%, and 2%, the conductivity of the hydrogels increases from 1.01 S / m to 1.24 S / m, 1.49 S / m, and 1.35 S / m. It can be found that within the range of 0% - 2% of CNFs content, the conductivity of the hydrogels shows an upward trend because as the CNFs content in the system increases, the cross-linking density of the internal conductive network of the hydrogels increases, thereby increasing the conductivity of the hydrogels. However, when the CNFs content is greater than 2%, its conductivity decreases. This is because the hydrogels with a high degree of cross-linking have a denser network structure, resulting in a longer transmission path of ions in the PCNTG-PAA hydrogels, increasing the resistance of ion transmission and reducing its conductive performance; at the same time, too high a degree of cross-linking will lead to a decrease in the porosity of the hydrogels, thus restricting the diffusion and transmission of ions in the system and affecting its conductive performance. Therefore, introducing the reinforcing material CNFs appropriately within a certain range can achieve the purpose of enhancing conductivity.

[0069] Application Example 1

[0070] Immerse the pretreated cotton fabric into the hydrogel precursor solution in Example 1 for graft copolymerization to finally prepare a coated fabric with good sensing performance. The specific process is as follows:

[0071] Step 1: Preparation of the hydrogel precursor solution;

[0072] Step 2: Pretreatment of the cotton fabric and preparation of DES;

[0073] Cut the cotton fabric into small squares of 5 cm × 5 cm. Take a certain amount of sodium dodecylbenzenesulfonate (2.5 g / L), put the fabric into the solution and stir for 1.5 h; take an ethanol solution with a purity of 80%, immerse the fabric, stir for 2 h, remove the fabric and stir it with deionized water for 15 min, three times in total; finally, put it into an oven and dry it at 100 °C for 2 h to obtain the pretreated cotton fabric;

[0074] Take 139.62 g of choline chloride and 126.07 g of oxalic acid, then mix and stir the two at high temperature in a beaker, and heat at 110 °C for two hours to obtain a transparent solution, denoted as the deep eutectic solvent (DES).

[0075] Step 3: Graft treatment on the fabric surface;

[0076] Immerse the cotton fabric treated with the DES solvent into the hydrogel precursor solution and stir for 15 min, then dry it at 80 °C for 2 h to obtain an intermediate product. At this time, a layer of hydrogel film adheres to the surface between the fibers, but the fastness is relatively weak and further treatment is required;

[0077] Step 4: Fabric fastness treatment;

[0078] Take 6 g of polydimethylsiloxane (PDMS) (aq) and dissolve it in 100 ml of chloroform solution. Immerse the fabric and stir for 15 min, then dry it at 80 °C for 2 h to obtain the final sample fabric.

[0079] Figure 8 a - c are the comparisons of the breaking strength and elongation at break of the cotton fabric before and after grafting. It can be seen that after tensile measurement, the breaking strength of the untreated original cotton fabric can reach 308.57 N, and the elongation at break is 11.25%. While the breaking strength of the cotton fabric treated with PCNTG and PCNTG - PAA hydrogel precursor solution decreases to 265.35 N and 268.02 N respectively, and the elongation at break decreases to 9.12% and 9.37% respectively. Figure 8 As can be seen from d, the softness of the untreated original cotton fabric is about 9.1 mm. After immersion in the hydrogel precursor solution, the softness of the cotton fabric slightly decreases, but the range is not large, reaching 9.8 mm. Finally, after coating a layer of polydimethylsiloxane on the surface, the thickness reaches about 10.5 mm, and still shows good softness.

[0080] Figure 9 This is the change trend of the conductivity of the modified fabric with time at a temperature of 25 °C and a humidity of 40%. It can be seen that as time increases, its conductivity gradually decreases, but the trend slows down. This is because the degree of cross - linking inside it tends to be stable with time change, and finally it basically no longer changes when it reaches about 0.07 S / m.

[0081] Figure 10 This is the change trend of the conductivity of the modified fabric at - 20 °C and 60 °C. Under low - temperature conditions, with time change, the conductivity of the modified fabric gradually decreases from 0.075 S / m to 0.071 S / m, 0.069 S / m, 0.0667 S / m, 0.0604 S / m, and tends to be stable. Under high - temperature conditions, the conductivity of the modified fabric shows a trend of first increasing and finally tending to be stable. This is because in a high - temperature environment, the degree of ion solvation decreases, the thermal motion of molecules intensifies, resulting in a weakened intermolecular connection, thus increasing the ion migration rate and conductivity. When the time is too long, its conductivity basically remains unchanged.

[0082] The above - mentioned is only the preferred implementation mode of the present invention, and the protection scope of the present invention is not limited to the above - mentioned embodiments. For those skilled in the art of this technology, the improvements and transformations obtained without departing from the technical concept of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing ramie fiber-based conductive antifreeze hydrogel, characterized in that: The following steps are involved: S1, treating ramie fiber with p-toluenesulfonic acid to obtain ramie fiber; S2, mixing the ramie fiber, polyvinyl alcohol and ethylene glycol obtained in step S1 according to a set ratio, stirring at a predetermined temperature until the polyvinyl alcohol is completely dissolved, and then adding sodium chloride and tannic acid to the system, stirring at a set temperature until a first homogeneous solution is formed; S3, adding sodium polyacrylate and NN dimethyl bisacrylamide to the first homogeneous solution obtained in step S2, stirring at a predetermined temperature until completely dissolved, then adding ammonium persulfate to the system, forming a hydrogel precursor solution after sufficient reaction, removing bubbles and drying to obtain a ramie fiber-based conductive antifreeze hydrogel.

2. The method for preparing a ramie fiber-based conductive antifreeze hydrogel according to claim 1, characterized in that: In step S1, the ramie bone is continuously treated with p-toluenesulfonic acid, including two stages of removing lignin and extracting nanocellulose, specifically: S11, adding the ramie bone to concentrated sulfuric acid and / or sodium hydroxide solution for degumming treatment, and then washing the treated ramie bone with running water, drying, crushing and screening in sequence to obtain pretreated ramie bone; S12, adding the pretreated ramie bone obtained in step S11 into a p-toluenesulfonic acid solution, wherein the mass concentration of the toluenesulfonic acid is 65% to 75%, stirring at a temperature of 80 to 90° C., and the reaction time is 50 to 70 minutes. After the reaction is completed, the solid and liquid are separated to obtain fibers and acid solution; S13, adding the fiber obtained in step S12 into p-toluenesulfonic acid solution again, the mass concentration of toluenesulfonic acid is 65% to 75%, stirring at a temperature of 80 to 90°C, the reaction time is 1 to 4 hours, after the reaction is completed, the solid-liquid separation is performed, the obtained fiber is washed to neutrality, and a ramie fiber suspension is prepared for use.

3. The method for preparing a ramie fiber-based conductive antifreeze hydrogel according to claim 2, characterized in that: In step S13, the mass fraction of the ramie fiber suspension is 0.1% to 1%, and deionized water or purified water is used as the solvent.

4. The method for preparing a ramie fiber-based conductive antifreeze hydrogel according to claim 1, characterized in that: In step S2, polyvinyl alcohol is dissolved in a mixed solution of ramie fiber suspension and ethylene glycol, wherein the mass ratio of polyvinyl alcohol, ethylene glycol and ramie fiber suspension is 1:(3-5):(6-10).

5. The method for preparing a ramie fiber-based conductive antifreeze hydrogel according to claim 4, characterized in that: In step S2, polyvinyl alcohol is added to the mixed solution of ramie fiber suspension and ethylene glycol, and magnetically stirred at 80-90° C. for 1-4 hours, and then sodium chloride and tannic acid are added, and stirring is continued at 60-80° C. for 0.5-3 hours, and ultrasonic treatment is performed for 1-10 minutes to remove bubbles to obtain a first homogeneous solution.

6. The method for preparing a ramie fiber-based conductive antifreeze hydrogel according to claim 5, characterized in that: The mass ratio of the sodium chloride to the polyvinyl alcohol is (0.1-0.5):1; the mass ratio of the tannic acid to the polyvinyl alcohol is (0.1-0.8):

1.

7. The method for preparing a ramie fiber-based conductive antifreeze hydrogel according to claim 1, characterized in that: In step S3, the mass ratio of the sodium polyacrylate, NN dimethyl bisacrylamide and ammonium persulfate is 1: (0.005-0.02): (0.02-0.04).

8. The method for preparing a ramie fiber-based conductive antifreeze hydrogel according to claim 1, characterized in that: In step S3, the mass ratio of sodium polyacrylate to polyvinyl alcohol is: 1: (1-3).

9. The method for preparing a ramie fiber-based conductive antifreeze hydrogel according to claim 1, characterized in that: In step S3, sodium polyacrylate and NN dimethyl bisacrylamide are added to the first homogeneous solution and stirred at 70-80° C. until they are completely dissolved; in step S3, the drying temperature is 50-60° C. and the drying time is 2-6 hours.

10. Use of the ramie fiber-based conductive antifreeze hydrogel according to any one of claims 1 to 9 for preparing hydrogel-coated fabrics.

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