Temperature-responsive cellulose-based hydrogel and preparation method thereof

Abstract

The invention discloses a temperature-responsive cellulose-based hydrogel and a preparation method thereof, and relates to a cellulose-based hydrogel and a preparation method thereof. The invention aims to solve the problems that the LCST can be obviously improved after a hydrophilic substance is added into the existing PNIPAM gel, and the success rate of preparing the gel with high transparency at low temperature is low. The temperature response cellulose-based hydrogel is prepared from deionized water, N-isopropylacrylamide, 2-hydroxy-3-tert-butoxy propyl hydroxyethyl cellulose, ammonium persulfate, N-N methylene bisacrylamide and sodium hydrogen sulfite, and the temperature response cellulose-based hydrogel is prepared from the deionized water, the N-isopropylacrylamide, the 2-hydroxy-3-tert-butoxy propyl hydroxyethyl cellulose, the ammonium persulfate, the N-N methylene bisacrylamide and the sodium hydrogen sulfite. The method comprises the following steps: 1, preparing a 2-hydroxy-3-tert-butoxy propyl hydroxyethyl cellulose crude product; 2, dialyzing, freezing and drying; (3) weighing; 4, mixing; and 5, carrying out low-temperature reaction. The invention is used for the temperature-responsive cellulose-based hydrogel and the preparation thereof.

Description

Technical Field

[0001] The present invention relates to a cellulose-based hydrogel and a preparation method thereof. Background Art

[0002] With the wide popularization and use of petrochemical products, ecological problems have become increasingly serious, and the extraction and preparation of fine chemicals and materials from the natural environment have attracted extensive attention from researchers. Biomass energy is extremely abundant in nature and is an important source of renewable energy. As a kind of biomass energy, cellulose is the most widely distributed and most abundant polysaccharide in nature, accounting for more than 50% of the carbon content in the plant kingdom. It has resource advantages and characteristics such as biodegradability and biocompatibility. For thousands of years, cellulose materials have been used as production materials in the form of plant fibers such as wood, cotton, and linen, and have been widely used in fields such as construction, medicine, and food, becoming an indispensable type of natural biological material in the development of human history.

[0003] Hydroxyethyl cellulose (HEC) is a derivative of cellulose. The temperature-responsive cellulose-based hydrogel material prepared after its simple etherification has high transparency and high sensitivity, while also having good mechanical flexibility and processability. Most importantly, its color-changing temperature is closer to the ambient temperature, giving it obvious advantages in practical applications such as temperature-responsive smart windows. The smart window prepared from the temperature-responsive cellulose-based hydrogel can automatically adjust the light transmittance according to the external environmental temperature, without additional energy consumption, and has a simple structure and low cost, which better meets the requirements of energy conservation and emission reduction. Its working principle is as follows: when the temperature is lower than the lower critical solution temperature (LCST), a large number of hydrogen bonds are formed between the hydrophilic molecular chains in the cellulose and water molecules, and the molecular chains are fully extended in the aqueous solution, macroscopically showing a transparent state. At this time, the smart window has high light transmittance and can appropriately increase the indoor temperature under the action of light; when the indoor temperature gradually rises until it exceeds the LCST, the hydrogen bonds between the hydrophilic chains of the cellulose and water molecules break, and the hydrophobic groups play a dominant role, causing the polymer to precipitate from the solution, macroscopically showing opacity. At this time, the smart window does not allow or only allows a small amount of light to pass through. When the indoor light radiation decreases, the temperature will gradually drop, resulting in a gradual decrease in the indoor temperature. The change in the external temperature causes the phase transition behavior of the temperature-responsive cellulose-based hydrogel, making the material change from transparent to opaque, realizing the modulation of the light transmittance, thereby preventing the indoor temperature from continuing to rise and achieving the intelligent control of the room temperature. Currently, PNIPAM-based hydrogels are the most widely used in temperature-responsive smart windows because of their obvious phase separation behavior. However, PNIPAM has poor high-temperature thermal stability, poor mechanical properties, and limited transparency, which still pose some limitations in practical applications. Adding hydrophilic substances such as cellulose derivatives can increase the hydrogen bond interaction between the hydrophilic molecular chains and water molecules, significantly improving the transparency while also enhancing the mechanical properties. Moreover, the advantages of cellulose, such as being inexpensive, readily available, natural, harmless, and biodegradable, can also be applied. However, the increase in hydrophilic substances will increase the LCST of PNIPAM, gradually losing its application in the field of temperature-responsive smart windows. At the same time, the traditional method of increasing the transparency of the gel requires polymerization at low temperatures. However, at low temperatures, the molecular motion slows down, and the reaction is not easy to occur, resulting in a low preparation success rate. Summary of the Invention

[0004] The present invention aims to solve the problems that adding hydrophilic substances to PNIPAM gels will significantly increase the LCST and the success rate of preparing gels with high transparency at low temperatures is relatively low, and further provides a temperature-responsive cellulose-based hydrogel and its preparation method.

[0005] A temperature-responsive cellulose-based hydrogel is prepared from 70 to 90 parts by mass of deionized water, 18 to 20 parts of N-isopropylacrylamide, 0.5 to 3 parts of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, 0.1 to 1 part of ammonium persulfate, 0.3 to 1 part of N,N-methylenebisacrylamide, and 0.1 to 1 part of sodium bisulfite;

[0006] The 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose is prepared by alkalizing hydroxyethyl cellulose with sodium hydroxide and then etherifying it with tert-butyl glycidyl ether.

[0007] A preparation method of a temperature-responsive cellulose-based hydrogel is carried out according to the following steps:

[0008] I. Alkalize hydroxyethyl cellulose in a sodium hydroxide solution, and then drop tert-butyl glycidyl ether to carry out an etherification reaction to obtain a crude product of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose;

[0009] II. Adjust the pH of the crude product of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose to neutral, then carry out dialysis, and freeze and dry the dialyzed product to obtain 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose;

[0010] III. Weigh 70 to 90 parts by mass of deionized water, 18 to 20 parts of N-isopropylacrylamide, 0.5 to 3 parts of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, 0.1 to 1 part of ammonium persulfate, 0.3 to 1 part of N,N-methylenebisacrylamide, and 0.1 to 1 part of sodium bisulfite;

[0011] IV. Under the condition of a temperature of 25°C to 30°C, stir the weighed 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, deionized water, and N-isopropylacrylamide evenly, and then under the condition of a temperature of 25°C to 30°C, add the weighed ammonium persulfate, N,N-methylenebisacrylamide, and sodium bisulfite and stir evenly to obtain a homogeneous solution;

[0012] V. Pour the homogeneous solution into a mold and react at a low temperature to obtain a temperature-responsive cellulose-based hydrogel.

[0013] The beneficial effects of the present invention are:

[0014] 1. The present invention combines the cellulose derivative 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose with the commonly used temperature-responsive polymer poly(N-isopropylacrylamide). Without significantly affecting the LCST of poly(N-isopropylacrylamide), the hydrophilic molecular chains in 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose can enhance the hydrogen bond interaction between the gel and water molecules, thereby significantly improving the gel transparency. Meanwhile, the addition of cellulose can enhance the mechanical properties of the gel and endow the gel with the advantage of biodegradability.

[0015] 2. The present invention overcomes the problem of low success rate in preparing high-transparency gels at low temperatures. The high-transparency gel prepared by the method of the present invention only needs to be stirred below the LCST and then reacted at low temperature, and the gel preparation success rate is over 90%.

[0016] 3. The temperature-responsive cellulose-based hydrogel prepared by the present invention has obvious phase separation behavior, has ultra-high transparency, and its LCST is around 31°C, which is close to the LCST (32°C) of poly(N-isopropylacrylamide), and is close to the ambient temperature of life, having obvious advantages in practical applications. Brief Description of the Drawings

[0017] Figure 1 It is a contrast diagram of the light transmittance of the temperature-responsive cellulose-based hydrogel prepared in Example 1 after 30 cycles at 25°C and 30°C;

[0018] Figure 2 It is the LCST curve of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 and the comparative experiments;

[0019] Figure 3 It is the single compression cycle of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 and the comparative experiments when the compression deformation is 50%;

[0020] Figure 4 It is the 50 compression cycles of the temperature-responsive cellulose-based hydrogel prepared in Example 1 when the compression deformation is 50%;

[0021] Figure 5 It is the deswelling rate of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 and the comparative experiments in deionized water at 60°C;

[0022] Figure 6 It is a contrast diagram of the success rate of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 and the comparative experiments;

[0023] Figure 7 It is a contrast diagram of the light transmittance of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 and the comparative experiments at 25°C;

[0024] Figure 8 Comparison graph of the temperature-responsive cellulose-based hydrogel smart window prepared in Example 5 at 25 °C and 32 °C. Detailed implementation manners

[0025] Detailed implementation manner 1: This detailed implementation manner is a temperature-responsive cellulose-based hydrogel, which is prepared from 70 to 90 parts by mass of deionized water, 18 to 20 parts by mass of N-isopropylacrylamide, 0.5 to 3 parts by mass of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, 0.1 to 1 part by mass of ammonium persulfate, 0.3 to 1 part by mass of N,N-methylenebisacrylamide, and 0.1 to 1 part by mass of sodium bisulfite;

[0026] The 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose is prepared by alkalizing hydroxyethyl cellulose with sodium hydroxide and then etherifying it with tert-butyl glycidyl ether.

[0027] The beneficial effects of this detailed implementation manner are as follows:

[0028] 1. In this detailed implementation manner, the cellulose derivative 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose is combined with the commonly used temperature-responsive polymer poly(N-isopropylacrylamide). Without significantly affecting the LCST of poly(N-isopropylacrylamide), the hydrophilic molecular chains in 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose can enhance the hydrogen bond interaction between the gel and water molecules, thereby significantly improving the gel transparency. At the same time, the addition of cellulose can enhance the mechanical properties of the gel and endow the gel with the advantage of biodegradability.

[0029] 2. This detailed implementation manner overcomes the problem of low success rate in preparing high-transparency gels at low temperatures. The high-transparency gel prepared by the method of this detailed implementation manner only needs to be stirred below the LCST and then reacted at low temperature, and the gel preparation success rate is above 90%.

[0030] 3. The temperature-responsive cellulose-based hydrogel prepared in this detailed implementation manner has obvious phase separation behavior, has ultra-high transparency, and its LCST is about 31 °C, which is close to the LCST (32 °C) of poly(N-isopropylacrylamide), and is close to the living environment temperature, showing obvious advantages in practical applications.

[0031] Detailed implementation manner 2: A preparation method of a temperature-responsive cellulose-based hydrogel in this detailed implementation manner is carried out according to the following steps:

[0032] 1. Alkalize hydroxyethyl cellulose in a sodium hydroxide solution, and then drop tert-butyl glycidyl ether for etherification reaction to obtain a crude product of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose;

[0033] II. Adjust the pH of the crude product of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose to neutral, then perform dialysis, and subject the dialyzed product to freezing and drying to obtain 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose;

[0034] III. Weigh 70 to 90 parts by mass of deionized water, 18 to 20 parts of N-isopropylacrylamide, 0.5 to 3 parts of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, 0.1 to 1 part of ammonium persulfate, 0.3 to 1 part of N,N-methylenebisacrylamide, and 0.1 to 1 part of sodium bisulfite;

[0035] IV. Under the condition of a temperature of 25°C to 30°C, stir the weighed 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, deionized water, and N-isopropylacrylamide evenly, and then under the condition of a temperature of 25°C to 30°C, add the weighed ammonium persulfate, N,N-methylenebisacrylamide, and sodium bisulfite and stir evenly to obtain a homogeneous solution;

[0036] V. Pour the homogeneous solution into a mold for low-temperature reaction to obtain a temperature-responsive cellulose-based hydrogel.

[0037] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 2 is that: the concentration of the sodium hydroxide solution described in Step I is 0.002 mol / L to 0.05 mol / L; the molar ratio of the hydroxyethyl cellulose to sodium hydroxide in the sodium hydroxide solution described in Step I is 1:(2 to 10); the molar ratio of the hydroxyethyl cellulose to tert-butyl glycidyl ether described in Step I is 1:(1 to 6). Others are the same as Specific Embodiment 2.

[0038] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 2 or 3 is that: the alkalization described in Step I is specifically carried out under the condition of a temperature of 50°C to 70°C for 0.5 h to 2 h. Others are the same as Specific Embodiment 2 or 3.

[0039] Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 2 to 4 is that: the etherification reaction described in Step I is specifically carried out under the condition of a temperature of 70°C to 110°C for 2 h to 13 h. Others are the same as Specific Embodiments 2 to 4.

[0040] Specific Embodiment 6: The difference between this embodiment and one of Specific Embodiments 2 to 5 is that: in Step II, glacial acetic acid with a concentration of 0.2 mol / L to 4 mol / L is used to adjust the pH of the crude product of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose to neutral. Others are the same as Specific Embodiments 2 to 5.

[0041] Embodiment 7: The difference between this embodiment and any one of Embodiments 2 to 6 is that: in Step 2, the dialysis is specifically carried out using a dialysis bag with a molecular weight cut-off of 8,000 to 14,000 Daltons. Others are the same as those in Embodiments 2 to 6.

[0042] Embodiment 8: The difference between this embodiment and any one of Embodiments 2 to 7 is that: in Step 2, the freezing is specifically carried out under the condition that the freezing temperature is -30°C to 0°C for 2 h to 18 h. Others are the same as those in Embodiments 2 to 7.

[0043] Embodiment 9: The difference between this embodiment and any one of Embodiments 2 to 8 is that: in Step 2, the drying is specifically carried out under the condition that the temperature is -60°C to 0°C for freeze-drying for 24 h to 72 h. Others are the same as those in Embodiments 2 to 8.

[0044] Embodiment 10: The difference between this embodiment and any one of Embodiments 2 to 9 is that: in Step 5, the low-temperature reaction is specifically carried out under the condition that the temperature is 0°C to 10°C for 2 h to 12 h. Others are the same as those in Embodiments 2 to 9.

[0045] The following examples are used to verify the beneficial effects of the present invention:

[0046] Example 1:

[0047] A preparation method of a temperature-responsive cellulose-based hydrogel is prepared according to the following steps:

[0048] I. Alkalize hydroxyethyl cellulose (HEC) in a sodium hydroxide solution, and then drop tert-butyl glycidyl ether for etherification reaction to obtain a crude product of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose;

[0049] The concentration of the sodium hydroxide solution is 0.018 mol / L; the molar ratio of hydroxyethyl cellulose to sodium hydroxide in the sodium hydroxide solution is 1:4.5; the molar ratio of hydroxyethyl cellulose to tert-butyl glycidyl ether is 1:3.9;

[0050] The alkalization is specifically carried out at a temperature of 70°C for 1 h;

[0051] The etherification reaction is specifically carried out at a temperature of 90°C for 9 h;

[0052] II. Using glacial acetic acid with a concentration of 1 mol / L, adjust the pH of the crude product of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose to neutral, and then use a dialysis bag with a molecular weight cut-off of 8,000 to 14,000 Daltons to dialyze for 3 days. Freeze and dry the dialyzed product to obtain 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose (HTBPEC);

[0053] The freezing is specifically carried out at a freezing temperature of -20°C for 12 hours;

[0054] The drying is specifically carried out at a temperature of -20°C for 48 hours;

[0055] III. Weigh 80.46 parts of deionized water, 18.39 parts of N-isopropylacrylamide (NIPAM), 0.57 part of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, 0.11 part of ammonium persulfate (APS), 0.35 part of N,N-methylenebisacrylamide (MBA), and 0.11 part of sodium bisulfite (NaHSO 3 ) by mass;

[0056] IV. Under the conditions of a temperature of 30°C and a rotation speed of 500 rpm, stir the weighed 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, deionized water, and N-isopropylacrylamide for 3 hours, and then under the conditions of a temperature of 30°C and a rotation speed of 500 rpm, add the weighed ammonium persulfate, N,N-methylenebisacrylamide, and sodium bisulfite and stir for 5 minutes to obtain a homogeneous solution;

[0057] V. Pour the homogeneous solution into a cylindrical mold with a diameter of 30 mm and a height of 10 mm, and carry out a low-temperature reaction at a temperature of 5°C for 12 hours to obtain a temperature-responsive cellulose-based hydrogel, named PH 1 .

[0058] Example 2: The difference between this example and Example 1 is that in step III, 80 parts of deionized water, 18.30 parts of N-isopropylacrylamide (NIPAM), 1.14 parts of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, 0.11 part of ammonium persulfate (APS), 0.34 part of N,N-methylenebisacrylamide (MBA), and 0.11 part of sodium bisulfite (NaHSO 3 ) are weighed by mass; the temperature-responsive cellulose-based hydrogel prepared in step V is named PH 2 . Others are the same as in Example 1.

[0059] Example 3: The difference between this example and Example 1 is that in step 3, 79.55 parts by mass of deionized water, 18.18 parts of N-isopropylacrylamide (NIPAM), 1.70 parts of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, 0.11 part of ammonium persulfate (APS), 0.34 part of N,N-methylenebisacrylamide (MBA), and 0.11 part of sodium bisulfite (NaHSO 3 ) are weighed by mass; the temperature-responsive cellulose-based hydrogel prepared in step 5 is named PH 3 . Others are the same as in Example 1.

[0060] Example 4: The difference between this example and Example 1 is that in step 3, 79.10 parts by mass of deionized water, 18.08 parts of N-isopropylacrylamide (NIPAM), 2.26 parts of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, 0.11 part of ammonium persulfate (APS), 0.34 part of N,N-methylenebisacrylamide (MBA), and 0.11 part of sodium bisulfite (NaHSO 3 ) are weighed by mass; the temperature-responsive cellulose-based hydrogel prepared in step 5 is named PH 4 . Others are the same as in Example 1.

[0061] Example 5: The difference between this example and Example 1 is that in step 4, the homogeneous solution is injected into a double-layer glass plate, and under the condition of a temperature of 5 °C, a low-temperature reaction is carried out for 12 h to form an intermediate layer, obtaining a temperature-responsive cellulose-based hydrogel intelligent window;

[0062] The single-piece glass thickness of the double-layer glass plate is 1 mm, the glass plate size is 10 cm × 10 cm, and the thickness of the intermediate layer is 2 mm.

[0063] Comparative experiment: The difference between this example and Example 1 is that in step 3, 81.92 parts by mass of deionized water, 18.50 parts of N-isopropylacrylamide (NIPAM), 0 part of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, 0.12 part of ammonium persulfate (APS), 0.35 part of N,N-methylenebisacrylamide (MBA), and 0.12 part of sodium bisulfite (NaHSO 3 ) are weighed by mass; the temperature-responsive cellulose-based hydrogel prepared in step 5 is named PH 0 . Others are the same as in Example 1.

[0064] The light transmittance test is carried out according to the GB / T 2410-2008 standard: Figure 1The figure shows the comparison of the light transmittance of the temperature-responsive cellulose-based hydrogel prepared in Example 1 after 30 cycles at 25 °C and 30 °C. As can be seen from the figure, the light transmittance of the temperature-responsive cellulose-based hydrogel is about 93% at 25 °C and 0% at 30 °C, and it can still maintain a stable conversion between transparency and opacity after 30 cycles, indicating that the temperature-responsive cellulose-based hydrogel has excellent transparency and opacity conversion properties and can stably maintain its light regulation performance.

[0065] The method for measuring the lower critical solution temperature (LCST) of the temperature-responsive cellulose-based hydrogel is as follows: Gradually increase the temperature starting from room temperature, hold for 3 minutes at each 1 °C increase, and simultaneously measure the light transmittance according to the GB / T 2410-2008 standard. Plot the points of the light transmittance corresponding to each temperature until the light transmittance reaches 0. Connecting these points gives the curve of the light transmittance changing with temperature. In this curve, when the temperature exceeds a certain temperature, the light transmittance rapidly drops by more than 50%, and this temperature is the LCST of the gel. Figure 2 The figure shows the LCST curves of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 and the comparative experiment. As can be seen from the figure, the LCSTs of the temperature-responsive cellulose-based hydrogels prepared in the comparative experiment and Examples 1 to 4 are 28 °C, 30 °C, 31 °C, 32 °C, and 33 °C respectively. This shows that compared with the LCST of the gel without adding cellulose derivatives, the LCST of the composite gel only slightly increases after adding cellulose derivatives, indicating that adding cellulose derivatives to the PNIPAM gel will not significantly increase the LCST of the PNIPAM gel. At the same time, it will also improve the transparency of the gel, making the application of the PNIPAM gel added with hydrophilic substances still have great advantages in the field of temperature-responsive smart windows.

[0066] Compression tests were carried out according to the GB / T 23561.3-2009 standard: Figure 3 The figure shows the single compression cycle of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 and the comparative experiment when the compression deformation is 50%. As can be seen from the figure, the compression strength of the temperature-responsive cellulose-based hydrogel prepared in the comparative experiment is 0.067 MPa, and the compression strengths of the temperature-responsive cellulose-based hydrogels corresponding to PH 1 ~PH 4 in Examples 1 to 4 are 0.103 MPa, 0.103 MPa, 0.102 MPa, and 0.084 MPa respectively, indicating that the compression strength of the gel block added with cellulose derivatives is significantly improved compared with the gel block without adding cellulose derivatives, and the maximum increase is 53.7%. This shows that the long-chain molecular structure of cellulose derivatives can intertwine with the gel molecular chains, and the high strength and toughness of cellulose can effectively disperse stress, enabling the gel to withstand greater external forces. This result indicates that the addition of cellulose derivatives can significantly improve the mechanical properties of the temperature-responsive cellulose-based hydrogel.Figure 4 50 compression cycles of the temperature-responsive cellulose-based hydrogel prepared in Example 1 at a compression deformation of 50%; as can be seen from the figure, the compression strength of the temperature-responsive cellulose-based hydrogel prepared in Example 1 increases with the increase of compression strain, reaches the peak at 50% strain, and the corresponding maximum stress is 0.103 MPa. The high coincidence of the curves can prove that the gel block has good elastic recovery and reversible deformation characteristics. After 50 compression cycles, the hydrogel can recover intact, and the stress is basically retained, which also proves the excellent and stable compression resistance of the hydrogel.

[0067] The deswelling rate of the gel block was tested according to the YY / T 1435-2016 standard: after the temperature-responsive cellulose-based hydrogel was soaked in deionized water at 25 °C until swelling equilibrium (the weight no longer changed), it was soaked in deionized water at 60 °C for 30 min, and then taken out to test the deswelling rate; Figure 5 The deswelling rates of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 and the comparative experiment in deionized water at 60 °C. As can be seen from the figure, the PH of the comparative experiment 0 The deswelling rate of the gel block is about 74.55% after heating at 60 °C for 30 min, and the mass decreases rapidly, indicating that the hydrogel has undergone severe volume shrinkage and dehydration. In contrast, the deswelling rates of the PH 1 、PH 2 、PH 3 、PH 4 gel blocks prepared in Examples 1 to 4 are 31.30%, 35.60%, 33.46%, and 30.92% respectively, indicating that the gels with cellulose derivatives added show significantly lower weight changes, showing relatively less dehydration and volume shrinkage. The test results show that the large number of hydrogen bonds in the cellulose derivatives endow them with good thermal stability, and the interaction formed between the gels with cellulose derivatives added and cellulose restricts the movement of the gel molecular chains when heated, resulting in the effective improvement of the thermal stability of the poly(N-isopropylacrylamide) hydrogel by the cellulose derivatives.

[0068] Figure 6Comparison chart of the success rates of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 and the comparative experiment; the test criterion for the success rate is as follows: the uniform solutions prepared in Steps 4 of Examples 1 to 4 and the comparative experiment are placed at 5 °C for reaction for 12 h, and ten samples are prepared respectively. Test whether a gel is finally formed after 12 h. If a gel can be solidified and formed, it is considered successful. If it remains in a solution state, it proves that the cross-linking fails. As can be seen from the figure, the success rate of the temperature-responsive smart window prepared in the comparative experiment is about 60%, and the success rates of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 are 100%, 100%, 90%, and 90% respectively. This shows that the success rate of gel preparation increases after adding cellulose derivatives, and adding cellulose derivatives is beneficial to promoting the reaction between molecular chains and cross-linking agents to form a cross-linked network structure.

[0069] Figure 7 Comparison chart of the light transmittance of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 and the comparative experiment at 25 °C; as can be seen from the figure, the light transmittance of the temperature-responsive hydrogel without cellulose prepared in the comparative experiment is 50%, and the light transmittances of the temperature-responsive cellulose-based hydrogels prepared in Examples 1 to 4 can reach 93%, 90%, 90%, and 83% respectively. The light transmittance of the temperature-responsive smart window after adding cellulose is higher than that of the temperature-responsive smart window without adding cellulose, and the highest increase in light transmittance is 43%. This shows that the hydrophilic molecular chains in cellulose derivatives can improve the hydrogen bond interaction between the gel and water molecules, thereby significantly improving the gel transparency.

[0070] Figure 8 Comparison chart of the temperature-responsive cellulose-based hydrogel smart window prepared in Example 5 at 25 °C and 32 °C. As can be seen from the figure, the smart window has high transparency at 25 °C, and the plants on its back are clearly visible. At 32 °C, the smart window becomes completely opaque, and the plants on the back of the part filled with the gel are not visible. This shows that at 25 °C, the ambient temperature is lower than its LCST, and the hydrophilic molecular chains play a role, forming hydrogen bonds with the surrounding water molecules, and the molecular chains stretch, macroscopically showing transparency; at 32 °C, the ambient temperature is higher than its LCST, and the hydrophobic molecular chains play a role, the hydrogen bonds break, the molecular chains separate from the water molecules, and precipitate from the solution, macroscopically showing opacity.

Claims

1. A temperature-responsive cellulose-based hydrogel, characterized in that It is prepared from 70 to 90 parts by mass of deionized water, 18 to 20 parts by mass of N-isopropyl acrylamide, 0.5 to 3 parts by mass of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, 0.1 to 1 part by mass of ammonium persulfate, 0.3 to 1 part by mass of NN methylenebisacrylamide and 0.1 to 1 part by mass of sodium bisulfite; The 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose is prepared by alkalizing hydroxyethyl cellulose with sodium hydroxide and then etherifying it with tert-butyl glycidyl ether.

2. A method for preparing a temperature-responsive cellulose-based hydrogel according to claim 1, characterized in that It is prepared according to the following steps:

1. Alkalize hydroxyethyl cellulose in sodium hydroxide solution, then drop tert-butyl glycidyl ether into it for etherification reaction to obtain crude 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose; 2. adjusting the pH of the crude product of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose to neutral, then dialyzing, and freezing and drying the dialyzed product to obtain 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose; 3. Weigh 70 to 90 parts of deionized water, 18 to 20 parts of N-isopropyl acrylamide, 0.5 to 3 parts of 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, 0.1 to 1 part of ammonium persulfate, 0.3 to 1 part of NN methylene bisacrylamide and 0.1 to 1 part of sodium bisulfite by mass; 4. Stir the weighed 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose, deionized water and N-isopropyl acrylamide at a temperature of 25°C to 30°C, then add the weighed ammonium persulfate, NN methylenebisacrylamide and sodium bisulfite at a temperature of 25°C to 30°C and stir to obtain a uniform solution; 5. Pour the uniform solution into a mold for low-temperature reaction to obtain a temperature-responsive cellulose-based hydrogel.

3. The method for preparing a temperature-responsive cellulose-based hydrogel according to claim 2, characterized in that The concentration of the sodium hydroxide solution described in step one is 0.002 mol / L to 0.05 mol / L; the molar ratio of the hydroxyethyl cellulose described in step one to the sodium hydroxide in the sodium hydroxide solution is 1:(2 to 10); the molar ratio of the hydroxyethyl cellulose described in step one to tert-butyl glycidyl ether is 1:(1 to 6).

4. The method for preparing a temperature-responsive cellulose-based hydrogel according to claim 2, characterized in that The alkalization in step 1 is specifically carried out at a temperature of 50° C. to 70° C. for 0.5 h to 2 h.

5. The method for preparing a temperature-responsive cellulose-based hydrogel according to claim 2, characterized in that The etherification reaction in step 1 is specifically carried out at a temperature of 70° C. to 110° C. for 2 h to 13 h.

6. The method for preparing a temperature-responsive cellulose-based hydrogel according to claim 2, characterized in that In step 2, glacial acetic acid with a concentration of 0.2 mol / L to 4 mol / L is used to adjust the pH of the crude 2-hydroxy-3-tert-butoxypropyl hydroxyethyl cellulose to neutral.

7. The method for preparing a temperature-responsive cellulose-based hydrogel according to claim 2, characterized in that The dialysis described in step 2 is specifically performed using a dialysis bag with a molecular weight cut-off of 8000 Dalton to 14000 Dalton.

8. The method for preparing a temperature-responsive cellulose-based hydrogel according to claim 2, characterized in that The freezing described in step 2 is specifically freezing at a freezing temperature of -30°C to 0°C for 2h to 18h.

9. The method for preparing a temperature-responsive cellulose-based hydrogel according to claim 2, characterized in that The drying described in step 2 is specifically freeze-drying at a temperature of -60°C to 0°C for 24h to 72h.

10. The method for preparing a temperature-responsive cellulose-based hydrogel according to claim 2, characterized in that The low temperature reaction described in step 5 is specifically carried out at a temperature of 0°C to 10°C for 2h to 12h.

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