Paper pulp-based hydroxyethyl cellulose conductive hydrogel as well as preparation method and application thereof

Abstract

The invention relates to paper pulp-based hydroxyethyl cellulose conductive hydrogel as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) preparing paper pulp-based hydroxyethyl cellulose; (2) preparing a paper pulp based hydroxyethyl cellulose solution; (3) adding zinc chloride, ammonium persulfate and dimethyl sulfoxide into water, and uniformly stirring to obtain a mixed solution; and (4) adding the mixed solution into the paper pulp-based hydroxyethyl cellulose solution, stirring, and carrying out polymerization reaction to obtain the paper pulp-based hydroxyethyl cellulose conductive hydrogel. The paper pulp-based hydroxyethyl cellulose conductive hydrogel provided by the invention has excellent moisture retention, and the weight loss rate within 7 days is 5.86%; the prepared flexible strain sensor has excellent strong adhesion, anti-freezing performance, high ductility and tensile strength, can sensitively respond to human body movement, and can be applied to preparation of devices such as flexible strain sensors and the like.

Description

Technical Field

[0001] The invention relates to a pulp-based hydroxyethyl cellulose conductive hydrogel and a preparation method and application thereof, belonging to the technical field of cellulose hydrogels. Background Art

[0002] Traditionally, hydroxyethyl cellulose is produced using a slurry process using cotton cellulose as the raw material. However, cotton, a key textile raw material, is relatively expensive. In recent years, the price of refined cotton has continued to rise, and the supply of raw materials has been unstable. This has led to high production costs for hydroxyethyl cellulose, prompting increasing attention to the development and utilization of other celluloses.

[0003] Hydrogels are gel materials formed through physical or chemical crosslinking. Different crosslinking methods and matrix materials can impart tunable physical and chemical properties to hydrogels. The large amount of water packed into their three-dimensional network structure helps maintain good affinity between the hydrogel and the organism. Conductive hydrogels, by imparting electrical conductivity to the material, show promising applications in wearable / implantable medical sensors, neural network simulation, soft robotics, and electrically stimulated drug release. However, these applications typically require hydrogels to possess both excellent mechanical properties and electrical conductivity.

[0004] Chinese patent document CN117986701A discloses an ultra-strong, ultra-tough, all-weather, fatigue-resistant conductive hydrogel, its preparation method, and application. The hydrogel is prepared using an ice-templating method using a conductive filler, a polymer, and water as raw materials. The polymer comprises 1 to 40 wt% of the total raw materials, and the conductive filler is used in an amount of 0.01 to 10 mg / mL. However, this patent suffers from a complex preparation process, requiring freeze-drying using liquid nitrogen (-196°C) for more than 36 hours. Annealing and solvent exchange steps further increase production cycle time and energy consumption. Furthermore, the high cost of conductive fillers, such as graphene and silver nanowires, limits their application. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention provides a pulp-based hydroxyethyl cellulose conductive hydrogel and a preparation method and application thereof.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for preparing a pulp-based hydroxyethyl cellulose conductive hydrogel comprises the following steps:

[0008] (1) crushing, alkalizing, etherifying, neutralizing, cross-linking, washing and drying the pulp raw material to obtain pulp-based hydroxyethyl cellulose;

[0009] (2) adding pulp-based hydroxyethyl cellulose and hydroxyethyl acrylate to water and stirring uniformly to obtain a pulp-based hydroxyethyl cellulose solution;

[0010] (3) adding zinc chloride, ammonium persulfate and dimethyl sulfoxide to water and stirring uniformly to obtain a mixed solution;

[0011] (4) adding the mixed solution into the pulp-based hydroxyethyl cellulose solution, stirring for 25 to 35 minutes, sealing, polymerizing at 65 to 75° C. for 3.5 to 4.5 hours, and drying to obtain the pulp-based hydroxyethyl cellulose conductive hydrogel.

[0012] According to the present invention, preferably, in step (1), the pulp is dissolving pulp, broadleaf pulp, coniferous pulp or reed pulp.

[0013] According to a preferred embodiment of the present invention, in step (1), the preparation method of the pulp-based hydroxyethyl cellulose is as follows:

[0014] a. Soaking the pulp sheet in deionized water at a solid-liquid ratio of 1:15 for 24 hours, then deflocculently disintegrating the fibers and balancing the fibers to a moisture content of 8-10%, and crushing the pulp to obtain pulp;

[0015] b. In a reaction kettle, the dispersion medium, alkali solution and the pulp obtained in step a are uniformly mixed, and alkalized at 18-22° C. for 60-80 min. During the alkalization process, an inerting treatment is simultaneously performed, vacuuming to -0.05 MPa, and then filling with nitrogen to 0.2 MPa, and repeating this process 4 times to obtain alkalized pulp;

[0016] c. Continue to add ethylene oxide to the alkalized pulp obtained in step b and pressurize it to 0.32 MPa, stir for 5-15 minutes, react at 55-65° C. for 60-70 minutes, heat to 75-85° C. and continue to react for 70-90 minutes, cool to 40-45° C., add nitric acid, neutralize for 10-15 minutes, then add glyoxal, and cross-link for 5-15 minutes; finally, wash twice with acetone and dry at 55-65° C. for 5-8 hours to obtain pulp-based hydroxyethyl cellulose.

[0017] Further preferably, in step b, the dispersion medium is prepared by mixing tert-butanol, isopropanol and water in a mass ratio of 50:38:12.

[0018] Further preferably, in step b, the alkali solution is prepared by mixing the dispersion medium and sodium hydroxide in a mass ratio of 80:6.

[0019] Further preferably, in step b, the mass ratio of the dispersion medium, alkali solution and pulp is 120:86:10.

[0020] Further preferably, in step c, the mass ratio of the ethylene oxide to the alkalized pulp is (1-1.1):1; the mass ratio of the glyoxal to ethylene oxide is (3-5):(100-110); the mass concentration of the nitric acid is 35-45%, and the mass ratio of nitric acid to ethylene oxide is (220-240):(100-110).

[0021] Preferably, according to the present invention, in step (2), the mass volume ratio of the water, pulp-based hydroxyethyl cellulose and hydroxyethyl acrylate is 12 mL: (0.72-1.68) g: (4-20) mL.

[0022] Further preferably, the mass volume ratio of the water, pulp-based hydroxyethyl cellulose and hydroxyethyl acrylate is 12 mL:1.396 g:12.120 mL.

[0023] Preferably, according to the present invention, in step (3), the mass volume ratio of the water, zinc chloride, ammonium persulfate and dimethyl sulfoxide is 4 mL: (0.68-5.44) g: 0.01 g: (1.20-6.00) mL.

[0024] Further preferably, the mass volume ratio of the water, zinc chloride, ammonium persulfate and dimethyl sulfoxide is 4 mL:2.868 g:0.01 g:2.252 mL.

[0025] Preferably, according to the present invention, in step (4), the volume ratio of the mixed solution to the pulp-based hydroxyethyl cellulose solution is 24:(4-10).

[0026] Further preferably, in step (4), the volume ratio of the mixed solution added to the pulp-based hydroxyethyl cellulose solution is 24:6.4.

[0027] A pulp-based hydroxyethyl cellulose conductive hydrogel is prepared according to the method.

[0028] Application of the above pulp-based hydroxyethyl cellulose conductive hydrogel in the preparation of flexible strain sensors.

[0029] The technical features of the present invention are as follows:

[0030] The present invention first prepared pulp-based HEC based on pulp raw materials, and then adopted a one-pot in situ cross-linking strategy to successfully construct a pulp-based HEC conductive hydrogel with a HEC / HEA dual network substrate system and a ZnCl2 / DMSO binary solvent system. The optimal dosage of each component (pulp-based HEC: 1.396g, HEA: 12.120mL, ZnCl2: 2.868g, DMSO: 2.252mL) was obtained through central combination experiment optimization.

[0031] The formation mechanism of pulp-based hydroxyethyl cellulose conductive hydrogel is that HEA forms a covalently cross-linked double network with HEC through free radical polymerization (initiated by ammonium persulfate), and the Zn in ZnCl2 2+ Forming a coordination structure with the hydroxyl oxygen atoms of HEC / HEA, free Zn 2+ With Cl - DMSO provides ion migration channels to improve ion mobility. DMSO forms strong hydrogen bonds with water molecules through the S=O group to inhibit ice crystal nucleation. At the same time, the synergistic effect with HEC (AD interaction coefficient +47.33) significantly improves ductility.

[0032] Beneficial effects of the present invention:

[0033] 1. The present invention uses pulp as raw material to prepare pulp-based hydroxyethyl cellulose. First, the cellulose content in the pulp is more than 70%, with few impurities, high efficiency of the etherification reaction (with ethylene oxide), and easier control of the degree of substitution of the product. Secondly, the global annual output of pulp exceeds 100 million tons, the raw material supply is sufficient, and the large-scale production system is mature, which can ensure the continuity of hydroxyethyl cellulose production. Moreover, the price of pulp is significantly lower than that of cotton fiber, and is not affected by fluctuations in demand in the textile industry. It is low-cost and sustainable. By selecting different types of pulp, products with different viscosities, dissolution rates, and rheological properties can be customized to meet diverse needs; good biocompatibility; excellent solubility and thickening properties.

[0034] 2. The pulp-based hydroxyethyl cellulose conductive hydrogel provided by the present invention has excellent moisture retention, with a weight loss rate of 5.86% in 7 days; it has excellent strong adhesion, with an adhesion strength of >0.3MPa to substrates such as wood and steel plates; it has excellent antifreeze performance, with a ductility retention rate of >80% at -80°C; it has high ductility and tensile strength, with an elongation at break of up to 1251.27%, a tensile strength of 0.44MPa, and a compressive strength of 0.51MPa, and can sensitively respond to human body movements. When the finger is bent 45°, ΔR / R0 = 5.24%, and can be used to prepare flexible strain sensors and other devices.

[0035] 3. The preparation method provided by the present invention first constructs a pulp-based HEC synthesis system through a two-step alkalization-etherification method, and then dissolves HEC, polymerizes the monomer (HEA), and forms an ion conductive network (Zn 2+ ) and other steps are integrated into a single reaction system. The process integration is efficient and the operation is convenient. It reduces the transfer, washing and other operations in the multi-step method, does not require the separation or purification of intermediates, reduces the risk of human error, greatly shortens the preparation cycle and improves product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The morphology of the pulp raw material used in Example 1 and the prepared pulp-based hydroxyethyl cellulose.

[0037] Figure 2 Component analysis of broadleaf pulp 1, broadleaf pulp 2, coniferous pulp 1, coniferous pulp 2, coniferous pulp 3 and reed pulp used in Example 2.

[0038] Figure 3 The moisture content of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0039] Figure 4 The ash content of the pulp-based hydroxyethyl cellulose prepared in Example 2 is:

[0040] Figure 5 The pH value of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0041] Figure 6 The viscosity of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0042] Figure 7 The light transmittance of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0043] Figure 8 This is the bioenzyme stability of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0044] Figure 9 FTIR spectra of the pulp raw material used in Example 2 and the pulp-based hydroxyethyl cellulose prepared.

[0045] In the figure, (a) is pulp raw material; (b) is pulp-based hydroxyethyl cellulose.

[0046] Figure 10 This is the TGA spectrum of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0047] Figure 11 This is the DSC spectrum of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0048] Figure 12 This is the XRD pattern of the pulp-based hydroxyethyl cellulose prepared in Example 2.

[0049] Figure 13 The tensile properties of the pulp-based hydroxyethyl cellulose conductive hydrogel prepared in Example 3;

[0050] In the figure, (a) is the elongation at break; (b) is the stress-strain curve.

[0051] Figure 14 The effect of HEC4 dosage on the tensile properties of the conductive hydrogel in Example 3;

[0052] In the figure, (a) is the elongation at break; (b) is the stress-strain curve.

[0053] Figure 15 The effect of HEA dosage on the tensile properties of the conductive hydrogel in Example 3;

[0054] In the figure, (a) is the elongation at break; (b) is the stress-strain curve.

[0055] Figure 16 The effect of ZnCl2 dosage on the tensile properties of the conductive hydrogel in Example 3;

[0056] In the figure, (a) is the elongation at break; (b) is the stress-strain curve.

[0057] Figure 17 The effect of DMSO dosage on the tensile properties of the conductive hydrogel in Example 3;

[0058] In the figure, (a) is the elongation at break; (b) is the stress-strain curve.

[0059] Figure 18 This is a response surface diagram of the interaction of different factors on the elongation at break of the conductive hydrogel in Example 3.

[0060] Figure 19 This is the FTIR spectrum of the pulp-based HEC4 / HEA conductive hydrogel in Example 4.

[0061] Figure 20 This is the XRD pattern of the pulp-based HEC4 / HEA conductive hydrogel in Example 4.

[0062] Figure 21 The moisturizing results and stress-strain curves of the pulp-based HEC4 / HEA conductive hydrogel at different temperatures in Example 4 are shown;

[0063] In the figure, (a) is the moisturizing result; (b) is the stress-strain curve.

[0064] Figure 22 These are the tensile and compression curves of the pulp-based HEC4 / HEA conductive hydrogel in Example 4.

[0065] Figure 23 The adhesion results of the pulp-based HEC4 / HEA conductive hydrogel on different substrates in Example 4 are shown.

[0066] Figure 24 This is the sensing performance of the pulp-based HEC4 / HEA conductive hydrogel on the fingers and wrist of Example 4. DETAILED DESCRIPTION

[0067] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0068] The reagents and equipment involved in the present invention are all conventional products and can be obtained commercially.

[0069] Example 1. Preparation of pulp-based hydroxyethyl cellulose

[0070] A method for preparing dissolving pulp-based hydroxyethyl cellulose is as follows:

[0071] a. Tear the dissolving pulp sheet into sheets, soak them in deionized water at a solid-liquid ratio of 1:15 for 24 hours (25°C) to swell the fibers; then use a PFI refiner to gradually deflagrate the fibers, equilibrate them to a moisture content of 8-10% in a humidity-controlled air drying oven at 30% RH ± 3%, and finally use a wall breaker to crush them to obtain pulp;

[0072] b. In a reactor, uniformly mix the dispersion medium, alkali solution, and the pulp obtained in step a, open the cooling water of the reactor, start stirring, and alkalize at 20° C. for 70 minutes. During the alkalization process, perform an inerting treatment simultaneously, evacuate to -0.05 MPa, and then fill with nitrogen to 0.2 MPa, repeating this process 4 times to obtain alkalized pulp;

[0073] The dispersion medium is prepared by mixing tert-butyl alcohol, isopropyl alcohol and water in a mass ratio of 50:38:12.

[0074] The preparation method of alkali solution is as follows: in a reactor, a dispersion medium and caustic soda (NaOH) are mixed in a mass ratio of 80:6, stirring is started, and the jacket steam is turned on to increase the temperature. When the temperature reaches 45°C, heating is stopped and timing is started. The mixture is stirred for 30 minutes, and cooling water is turned on to cool the mixture to 20°C. The preparation is completed.

[0075] c. Ethylene oxide (EO) was further added to the alkalized pulp obtained in step b and the pressure was increased to 0.32 MPa. The mixture was stirred for 10 min, reacted at 60° C. for 60 min, heated to 80° C. and reacted for 90 min. The mixture was cooled to 42° C. and 40% nitric acid (HNO 3 ) was added. The mixture was neutralized for 15 min, and then 5 g of glyoxal was added and cross-linked for 10 min. The mixture was washed twice with acetone and dried at 60° C. for 6 h to obtain pulp-based hydroxyethyl cellulose, which was designated as HEC1.

[0076] According to the same method, hydroxyethyl cellulose was prepared using broadleaf pulp 1, broadleaf pulp 2, coniferous pulp 1, coniferous pulp 2, coniferous pulp 3 and reed pulp as raw materials to obtain another 6 different pulp-based hydroxyethyl celluloses, which were respectively recorded as HEC2, HEC3, HEC4, HEC5, HEC6 and HEC7.

[0077] Among them, broadleaf pulp 1 is made from eucalyptus and acacia; broadleaf pulp 2 is made from hybrid eucalyptus; coniferous pulp 1 is made from Siberian fir, Siberian spruce and Siberian pine; coniferous pulp 2 is made from Douglas pine; coniferous pulp 3 is made from radiata pine, southern pine, spruce and fir.

[0078] When preparing hydroxyethyl cellulose using coniferous pulp 1 and 3, steps a and b are exactly the same, and the difference in step c is: react at 60°C for 70 minutes, heat to 85°C and continue to react for 70 minutes, cool to 42°C, add nitric acid (HNO3) with a mass concentration of 42% for neutralization, and cross-link with 3g of glyoxal.

[0079] In the above method, the specific amount of each reagent is shown in Table 1 below.

[0080] Table 1. Specific dosage of drugs in the preparation process of pulp-based hydroxyethyl cellulose

[0081]

[0082] The morphology of the pulp raw material and the pulp-based hydroxyethyl cellulose prepared in this embodiment is as follows: Figure 1 shown.

[0083] Depend on Figure 1 Dissolving pulp is highly purified, with a high cellulose content, few impurities, and a smooth fiber surface. Broadleaf pulps 1-2 have shorter, thinner fibers with a smoother surface. Coniferous pulps 1-3 have longer, thicker fibers with a rougher surface and thicker fiber walls. Reed pulp has shorter, thinner fibers with looser arrangement and a lower overall density. All seven pulp-based hydroxyethyl celluloses are yellow, granular solids with irregular shapes and slightly rough surfaces.

[0084] Example 2: Analysis of Pulp-Based Hydroxyethyl Cellulose

[0085] 1. Since the core of the synthesis of pulp-based hydroxyethyl cellulose lies in the etherification reaction between cellulose in the pulp and ethylene oxide, the cellulose content in each pulp has a decisive influence on the product preparation. Therefore, the dissolving pulp and broadleaf pulp used in Example 1

[0086] The components of broadleaf pulp 1, broadleaf pulp 2, coniferous pulp 1, coniferous pulp 2, coniferous pulp 3 and reed pulp were compared and analyzed. The results are as follows: Figure 2 shown.

[0087] Depend on Figure 2As can be seen, the proportions of cellulose, hemicellulose, and lignin in different pulps vary significantly. Notably, dissolving pulp leads the pack with 83.27% cellulose, highlighting its significant advantage as a high-quality raw material. Reed pulp, on the other hand, exhibits a higher content of impurities, with hemicellulose at 14.2% and lignin at 3.92%. The cellulose content of all seven selected pulps exceeds 68%, with softwood pulp 2 and hardwood pulp 2 closely following dissolving pulp at 77.93% and 73.26%, respectively.

[0088] 2. The moisture content of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 was calculated according to the formula. The relative standard deviation (RSD) of three parallel experiments was controlled at ≤0.5% (n=3). The results are as follows: Figure 3 shown.

[0089] The formula is:

[0090] Where W1 represents the sample weight (g); W2 represents the weight of the weighing bottle after drying (g); W3 represents the weight of the weighing bottle and sample after drying (g).

[0091] Depend on Figure 3 It can be seen that the moisture contents of HEC1, HEC2, HEC3, HEC4, HEC5, HEC6 and HEC7 are 5.1%, 4.5%, 6.3%, 5.8%, 5.9%, 4.2% and 4.3% respectively.

[0092] 3. The ash contents of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 were quantitatively calculated by high-temperature ashing method. The results are as follows: Figure 4 shown.

[0093] Depend on Figure 4 It can be seen that the ash values of HEC1, HEC2, HEC3, HEC4, HEC5, HEC6 and HEC7 are 17.88%, 17.43%, 17.89%, 20.92%, 17.90%, 21.38% and 23.42% respectively.

[0094] 4. 1.00 g of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 were accurately weighed and prepared into a 1% by mass aqueous dispersion (dissolution temperature 25°C, magnetic stirring 30 min). The acid-base properties of the solution were characterized using a three-point calibrated precision pH meter (accuracy ±0.01). The parallelism control standard was set to relative standard deviation RSD ≤ 0.8% (n = 3). The results were as follows: Figure 5 As shown,

[0095] Depend on Figure 5It can be seen that the pH values of HEC1-HEC7 are 3.39, 3.40, 3.13, 3.17, 3.48, 3.71, and 4.54, respectively.

[0096] 5. Accurately weigh 1.00 g of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 and prepare aqueous dispersions with mass fractions of 1% and 2% (dissolution temperature 25°C, magnetic stirring 30 min). The viscosity characteristics of the solutions were characterized by a rotational viscometer system. The experiment adopted a stepwise concentration design (mass concentration of 1% and 2%). The results are as follows: Figure 6 shown.

[0097] Depend on Figure 6 It can be seen that HEC5 made from coniferous pulp 2 exhibits significant non-Newtonian fluid properties: the viscosity of its 2% solution reaches 368 mPa·s, which is 1372% higher than that of the 1% solution (25 mPa·s), and 951% higher than that of the lowest-performing HEC1 (2% solution = 35 mPa·s).

[0098] 6. Accurately weigh 1.00 g of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 and prepare a 2% by mass aqueous dispersion (dissolution temperature 25°C, magnetic stirring 30 min). The optical transparency of the dispersion is determined by spectrophotometry at 590 nm. The results are as follows: Figure 7 shown.

[0099] Depend on Figure 7 It can be seen that the transmittance of HEC1-7 shows significant differences: HEC4 made from coniferous pulp 1 shows the best optical properties, with a transmittance of 92.7%. In contrast, the transmittance of HEC7 drops sharply to 27.8%.

[0100] 7. The enzymatic hydrolysis resistance of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 was determined by the enzymatic hydrolysis-viscosity degradation method. The specific method is as follows: the initial viscosity of a 1% HEC aqueous solution is measured at 25±0.2°C, and then a freshly prepared cellulase solution is added. The reaction is kept at 25±0.5°C for 24 hours and then the viscosity after degradation is measured. The results are shown in FIG. Figure 8 shown.

[0101] Depend on Figure 8 The 24h bioenzyme stability of HEC1-7 showed significant heterogeneity (16.45%-37.23%). Among them, HEC1 and HEC7 showed the best resistance to enzymatic degradation, with stability reaching 37.23% and 37.20% respectively, which was 125% higher than the least stable HEC5 (16.45%).

[0102] 8. The pulp raw materials used in Example 1 and the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 were subjected to infrared spectroscopy (FTIR) analysis to determine their functional groups. The results are as follows: Figure 9 shown.

[0103] Depend on Figure 9 It can be seen that the pulp raw materials used in Example 1 and the 7 pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 have a relative humidity of 3660-3040 cm -1 The hydroxyl group absorption peak of the derivative changes from 3340 cm to 4360 cm. -1 Move to 3385cm -1 This red shift phenomenon originates from the reconstruction of the intermolecular hydrogen bond network caused by hydroxyethyl substitution, which quantitatively confirms the regulatory effect of etherification reaction on the supramolecular structure of cellulose.

[0104] 9. Thermogravimetric analysis (TGA) of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 was performed. The results are as follows: Figure 10 shown.

[0105] The thermogravimetric analysis (TGA) includes three stages: (1) initial desorption stage (30-100°C); (2) main chain depolymerization stage (200-330°C); and (3) carbonization stage (>330°C).

[0106] Depend on Figure 10 During the initial desorption phase, the sample experienced a slight loss of approximately 0.4% in mass. This is because hydroxyethyl cellulose is a hydrophilic cellulose ether that readily absorbs moisture from the environment. As the temperature rises, the adsorbed moisture in the hydroxyethyl cellulose begins to evaporate. As the temperature rises further, the moisture evaporates completely, and the sample mass stabilizes.

[0107] 10. The thermal transition behaviors of the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1 were analyzed by DSC. The results are as follows: Figure 11 shown.

[0108] Depend on Figure 11 It can be seen that HEC1-7 presents characteristic endothermic peaks in the range of 131.12-135.65℃. The appearance of these endothermic peaks indicates that the hydroxyethyl molecules in hydroxyethyl cellulose are semi-melted during the heating process.

[0109] 11. XRD analysis was performed on the seven pulp-based hydroxyethyl celluloses (HEC1-7) prepared in Example 1. The results are as follows: Figure 12 shown.

[0110] Depend on Figure 12It can be seen that the original pulp raw material presents a typical cellulose type I structure, and its characteristic diffraction peak is located at 2θ = 14.8° The hydroxyethylation reaction significantly reconstructed the supramolecular structure of cellulose: the modified product showed broadened diffuse diffraction peaks at 2θ=10.4° and 20.8°, which were significantly shifted and merged with the characteristic peaks of cellulose type II. The crystallinity was changed to 25.77%, 12.24%, 3.82%, 7.06%, 1.20%, 2.95% and 16.36%, respectively. This indicates that the crystallinity of cellulose decreased significantly after the etherification reaction with ethylene oxide.

[0111] Based on the above data, it can be found that the 2% aqueous solution of HEC5 (derived from coniferous pulp 2) has the best shear thinning properties, with a zero-shear viscosity of 368mPa·s (25°C), a 951% increase from the lowest value (HEC1 = 35mPa·s). The light transmittance of HEC4 (derived from coniferous pulp 1) reaches 92.7% ± 0.5%. This shows that HEC derived from pulps of different sources has potential applications in medical dressings (high light transmittance), oilfield thickening (high viscosity), and low-cost building material additives.

[0112] Example 3. Preparation and screening of pulp-based hydroxyethyl cellulose conductive hydrogel

[0113] 1. A method for preparing a pulp-based hydroxyethyl cellulose conductive hydrogel, comprising the following steps:

[0114] (1) According to the method described in Example 1, the pulp raw material was crushed, alkalized, etherified, neutralized, cross-linked, washed and dried to obtain 7 types of pulp-based hydroxyethyl cellulose (HEC1-7);

[0115] (2) adding pulp-based hydroxyethyl cellulose and hydroxyethyl acrylate (HEA) to water, and stirring with a magnetic stirrer at 25° C. and 800 rpm for 4 h to achieve complete dissolution to form a homogeneous colloid, thereby obtaining a pulp-based hydroxyethyl cellulose solution;

[0116] (3) adding zinc chloride (ZnCl2), ammonium persulfate (APS) and dimethyl sulfoxide (DMSO) to water and stirring uniformly to obtain a mixed solution;

[0117] (4) The mixed solution was added to the pulp-based hydroxyethyl cellulose solution, stirred for 30 min, sealed, and polymerized at 70 °C for 4 h. After drying, seven pulp-based hydroxyethyl cellulose conductive hydrogels were obtained, which were respectively recorded as pulp-based HEC1 / HEA-HEC7 / HEA conductive hydrogels.

[0118] The tensile properties of seven pulp-based HEC1 / HEA-HEC7 / HEA conductive hydrogels were tested, and the results are as follows: Figure 13shown.

[0119] The tensile test used a rectangular specimen (50 mm × 20 mm × 2 mm) at a tensile rate of 30 mm / min.

[0120] The compression test used a cylindrical hydrogel sample with a thickness of 15 mm and a diameter of 20 mm, and the loading rate was 30 mm / min.

[0121] Depend on Figure 13 It can be seen that among the seven pulp-based HEC1 / HEA-HEC7 / HEA hydrogels, the elongation at break of HEC4 / HEA hydrogel reached 149.01%, and the elongation at break of the other six (HEC1 / HEA, HEC2 / HEA, HEC3 / HEA, HEC5 / HEA, HEC6 / HEA, and HEC7 / HEA) were all less than 90%, that is, the elongation at break of HEC4 / HEA hydrogel was significantly higher than that of the other six, showing excellent deformation tolerance properties. In subsequent experiments, pulp-based HEC4 / HEA hydrogel was used as the test sample.

[0122] 2. Based on the method in point 1 of this embodiment, a single factor experimental analysis was performed according to the following experimental conditions. The results are as follows: Figures 14-17 The specific single-factor experimental conditions are shown in Table 2.

[0123] Experimental conditions:

[0124] The contents of HEC4 are 6%, 8%, 10%, 12% and 14% respectively.

[0125] The volumes of HEA were 4 mL, 8 mL, 12 mL, 16 mL, and 20 mL, respectively.

[0126] The contents of ZnCl2 are 0g, 0.68g, 1.36g, 2.72g, 4.08g and 5.44g respectively.

[0127] The volumes of DMSO were 0 mL, 1.2 mL, 2.4 mL, 3.6 mL, 4.8 mL, and 6.0 mL, respectively.

[0128] Table 2. Single-factor experimental conditions

[0129]

[0130] Depend on Figure 14 The relationship between HEC4 concentration and the ductility and fracture toughness of the hydrogels exhibits a nonlinear trend, first increasing and then decreasing. By systematically quantifying the structure-activity relationship between polymer concentration and macroscopic properties, combined with process feasibility assessment, the optimal HEC4 loading was determined to be 12 wt%.

[0131] Depend on Figure 15 It can be seen that HEA contains rich hydroxyl groups and can form high-performance hydrogels through hydrogen bond interactions. Under the synergistic effect of hydrogen bonds and the three-dimensional network structure formed by the interweaving of molecular chains, pure HEA hydrogel exhibits good moisturizing properties, moderate antifreeze and satisfactory mechanical properties. However, the synergistic effect of high-density hydrogen bonds enables HEA hydrogel to have both excellent rigidity and high modulus, but it also limits its ductility to a certain extent, resulting in a significant decrease in elongation at break. Quantitative analysis shows that the dosage of HEA and the elongation at break of the hydrogel show a volcano-shaped curve relationship, reaching a peak at 12 mL (152.26% ± 3.9%), which is about 3.7 times higher than the minimum value. Based on the above analysis, this concentration was finally selected as the optimal HEA addition amount.

[0132] Depend on Figure 16 It can be seen that Zn 2+ The addition of ZnCl2 gives the hydrogel high strength and ultra-tensile properties, which may be due to the -OH groups in the hydrated ZnCl2 reconstructing the hydrogel's three-dimensional network crosslinking density through dynamic hydrogen bonding, thereby significantly optimizing its mechanical response. As the ZnCl2 addition amount increases from 0g to 2.72g, the material's elongation at break shows an upward trend, reaching an excellent ductility of 766.43% at an addition amount of 2.72g; however, when the addition amount increases to 4.08g, the fracture strain shows a reverse decay of 2.50%, confirming the positive regulatory effect of appropriate amounts of metal ions on the polymer network. Experimental data clearly show that 2.72g of ZnCl2 is the optimal addition amount for this experiment.

[0133] Depend on Figure 17 It can be seen that when the amount of DMSO added is below 2.4 mL, the elongation at break of the hydrogel shows an increasing trend with increasing dosage. When the amount of DMSO added exceeds 2.4 mL, the elongation at break significantly reverses and decays. Experimental data show that the optimal amount of DMSO added is 2.4 mL.

[0134] 3. Based on the results of single-factor experimental analysis, the four core factors affecting the elongation at break of hydroxyethyl cellulose conductive hydrogel were determined: hydroxyethyl cellulose (HEC), hydroxyethyl acrylate (HEA), zinc chloride (ZnCl2), and dimethyl sulfoxide (DMSO). Based on the central composite design (CCD) method of Design-Expert software, this study constructed a four-factor five-level response surface model to explore the optimization rules of the tensile properties of hydrogels. The experimental zero-level parameters were set as: HEC4 dosage 1.44g, HEA dosage 12mL, ZnCl2 dosage 2.72g, and DMSO dosage 2.4mL. The gradient design of each factor level is detailed in Table 3.

[0135] Table 3. Four-factor five-level design table

[0136]

[0137] Then, according to the combination of the various influencing factors in Table 3, HEC4 was used to prepare pulp-based HEC4 / HEA conductive hydrogels under different conditions, and then tensile tests were performed. The specific combination methods and experimental results are shown in Table 4.

[0138] Table 4. Combination methods and experimental results

[0139]

[0140]

[0141]

[0142] Table 4 shows that the dosages of HEC4, HEA, ZnCl2, and DMSO each have an optimal range: 1.44 g of HEC4 yields optimal performance; excessive or insufficient amounts reduce elongation; 12 mL of HEA yields the best results; excessive or insufficient amounts impair crosslinking; 2.72 g of ZnCl2 forms the most stable crosslinked network; omission or excessive amounts significantly weaken performance; and 2.4 mL of DMSO is most conducive to molecular chain motion; excessive amounts dilute the crosslink density, while insufficient amounts impair solvation. The optimal ratio (1.44 g of HEC4, 12 mL of HEA, 2.72 g of ZnCl2, and 2.4 mL of DMSO) results in a stable elongation at break exceeding 1100%. This is attributed to the synergistic effects of the components: moderate amounts of HEC4 and ZnCl2 establish a stable crosslinked network, while appropriate amounts of HEA and DMSO optimize the gel's flexibility and molecular chain mobility. The experiment also found that the absence of ZnCl2 would cause the elongation to drop sharply to 600%, highlighting the importance of Zn 2+ Key role in cross-linking.

[0143] 5. Through model fitting, variance analysis and 3D response surface plot analysis, the results are as follows Figure 18 shown.

[0144] pass Figure 18It was determined that the interaction between HEC4-DMSO and HEC4-HEA significantly contributed to the elongation at break compared to the effects of each individual component. Using the Nelder-Mead optimization algorithm, a global optimization of the response surface curve was performed using Design-Expert. The optimal synthesis parameters for the pulp-based HEC4 hydrogel were obtained: HEC = 1.396 g, HEA = 12.120 mL, ZnCl2 = 2.868 g, and DMSO = 2.252 mL. The model predicted an elongation at break of 1134.123%, while the actual experimental verification yielded 1251.267%, with a relative error of approximately 10%.

[0145] Example 4: Pulp-based HEC4 / HEA conductive hydrogel

[0146] A method for preparing a pulp-based HEC4 / HEA conductive hydrogel comprises the following steps:

[0147] (1) According to the method described in Example 1, coniferous pulp 1 is used as raw material, and HEC4 is obtained after crushing, alkalization, etherification and neutralization, cross-linking, washing and drying;

[0148] (2) Weigh 1.396 g of HEC4 and place it in a 50 mL beaker. Add 12 mL of distilled water and 12.120 mL of HEA. Stir on a magnetic stirrer until the HEC4 is completely dissolved to obtain a HEC4 solution.

[0149] (3) Weigh 2.868 g of ZnCl2 and 0.01 g of APS, dissolve them in 4 mL of distilled water, then add 2.252 mL of DMSO and mix well to obtain a mixed solution;

[0150] (4) The mixed solution was added to the HEC4 solution and stirred on a magnetic stirrer for 30 min to ensure uniform mixing. The mixture was poured into a 9 cm glass plate, sealed with tin foil, and polymerized at 70°C for 4 h. After the polymerization was completed, the product was taken out and placed in a vacuum drying oven at 40°C for 30 h to obtain the pulp-based HEC4 / HEA conductive hydrogel.

[0151] 2. The pulp-based HEC4 / HEA conductive hydrogel prepared in this example was subjected to infrared spectroscopy (FTIR) analysis. The results are as follows: Figure 19 shown.

[0152] Depend on Figure 19 It can be seen that the multi-level chemical bonding network construction mechanism of pulp-based HEC4 / HEA conductive hydrogel. -1 The OH stretching vibration peak at 2918 cm is attributed to the hydroxyl groups in HEC and HEA, indicating the presence of abundant hydrophilic structures in the hydrogel. -1The CH stretching vibration peak at 1724 cm is derived from the methyl (-CH3) groups in HEC and DMSO, confirming the successful embedding of the solvent DMSO molecules. -1 The sharp C=O stretching vibration peak at 1070 cm comes from the ester group (-COO-) in HEA, indicating that HEA is successfully embedded in the cross-linked network of the hydrogel. -1 The COC stretching vibration peak at 1017 cm is related to the ether bond in HEC, while the peak at 1017 cm -1 The S=O stretching vibration peak at 507 cm further confirms the presence of DMSO. -1 The Zn-Cl stretching vibration peak at 100 nm indicates that ZnCl2 has been successfully introduced into the hydrogel system, providing ionic conductivity. These characteristic peaks jointly verify the coexistence of HEC4, HEA, ZnCl2, and DMSO, indicating that the pulp-based HEC4 / HEA conductive hydrogel has been successfully constructed through a multi-level chemical bonding network.

[0153] 3. The pulp-based HEC4 / HEA conductive hydrogel prepared in this example was subjected to X-ray diffraction analysis (XRD). The results are as follows: Figure 20 shown.

[0154] Depend on Figure 20 It can be seen that the diffraction peak at 2θ=21.9° is mainly derived from the amorphous structure of HEC4 and HEA. In-depth analysis found that the characteristic crystal peaks of ZnCl2 (2θ=15.5°, 25.3°, 30.1°) completely disappeared. This is because the Zn in ZnCl2 2+ This is caused by hydrogen bonding or coordination with the hydroxyl groups in HEC4 or HEA. 2+ The coordination effect with hydroxyl groups successfully inhibited the crystallization behavior of ZnCl2, and further confirmed the successful preparation of pulp-based HEC4 / HEA conductive hydrogel.

[0155] 4. The hydrogel was left to stand at room temperature (22°C, RH 20%) for 7 days, and the moisturizing properties of the pulp-based HEC4 / HEA conductive hydrogel prepared in this example were measured using the moisturizing rate calculation method. The results are as follows: Figure 21 shown.

[0156] Depend on Figure 21As shown in (a), the pulp-based HEC4 / HEA conductive hydrogel has a weight loss rate of only 5.86% after being stored at room temperature for 7 days, showing excellent water retention capacity. The excellent performance of the pulp-based HEC4 / HEA conductive hydrogel in moisturizing properties is not only attributed to the hydrophilic groups in its molecular structure, but also closely related to the ionic hydration of the added ZnCl2. The hydrophilic groups such as hydroxyl groups in the HEC and HEA molecules can form hydrogen bonds with water molecules. This hydrogen bonding is a strong and effective intermolecular force that can tightly bind water molecules to the network structure of the hydrogel, thereby effectively locking in moisture and preventing rapid loss of moisture. At the same time, the Zn in ZnCl2 2+ and Cl - Ions strongly bind to water molecules through ion-dipole interactions, forming stable hydrated clusters. This ion hydration not only hinders the evaporation of water molecules, but also inhibits their kinetic behaviors such as vibration, rotation, diffusion, and proton transfer, thereby further enhancing the hydrogel's moisturizing properties.

[0157] 5. The pulp-based HEC4 / HEA conductive hydrogel prepared in this example was placed at -20°C for 7 days and -80°C for 7 hours, and its tensile properties were tested and compared with those of the hydrogel at room temperature. The results are as follows: Figure 21 (b) shown.

[0158] Depend on Figure 21 (b) As can be seen, even at an extremely low temperature of -80°C, the pulp-based HEC4 / HEA conductive hydrogel still exhibits excellent flexibility, with an elongation at break as high as 947.77%. This result shows that the pulp-based HEC4 / HEA conductive hydrogel can not only maintain its physical integrity at low temperatures but also withstand large tensile deformations, meeting the material flexibility requirements for practical applications.

[0159] 6. A series of tensile and compression tests were designed and implemented to study the mechanical properties of the pulp-based HEC4 / HEA conductive hydrogel prepared in this example. The tensile test used a rectangular specimen (50mm×20mm×2mm) at a tensile rate of 30mm / min. The compression test used a cylindrical hydrogel specimen with a thickness of 15mm and a diameter of 20mm at a loading rate of 30mm / min. The tensile and compressive stress-strain test results are shown in Figure 6. Figure 22 shown.

[0160] Depend on Figure 22The pulp-based HEC4 / HEA conductive hydrogel exhibits remarkable ductility, with an elongation at break reaching 1251.27%. This exceptional performance means that the hydrogel can withstand significant deformation without breaking when subjected to external tension, demonstrating excellent flexibility and adaptability. Furthermore, its tensile strength of 0.44 MPa indicates that the pulp-based HEC4 / HEA conductive hydrogel effectively resists external forces and maintains its integrity during stretching, demonstrating excellent tensile properties. This combination of high ductility and tensile strength gives the pulp-based HEC4 / HEA conductive hydrogel a significant advantage in applications requiring repeated stretching or large deformation, such as wearable devices and flexible electronics. The hydrogel also performed well in compression testing, achieving a compressive strength of 0.51 MPa. This result demonstrates that when subjected to compressive loads, the pulp-based HEC4 / HEA conductive hydrogel effectively resists deformation, maintains its structural stability, and exhibits high compressive resistance.

[0161] 7. The test was conducted using a universal testing machine Instron 5963 (Instron, USA) at a peel speed of 30 mm / min. The hydrogel was placed between two relatively hard substrates (steel, acrylic plate and wood) to perform a lap shear test to verify the adhesion ability of the pulp-based HEC4 / HEA conductive hydrogel prepared in this example on various substrates. The results are shown in FIG. Figure 23 shown.

[0162] Depend on Figure 23 It can be seen that the pulp-based HEC4 / HEA conductive hydrogel can firmly adhere to hydrophilic and hydrophobic surfaces, including skin, latex gloves, wood chips, acrylic plates, rubber stoppers, and glass bottles, and there is no irritation or residue when it is removed from the skin. This wide range of adhesion ability makes the pulp-based HEC4 / HEA hydrogel have great application potential in biomedicine, tissue engineering, drug delivery, and flexible electronic devices. This is because the pulp-based HEC4 / HEA conductive hydrogel, due to its abundant hydrophilic groups (such as hydroxyl groups), can form a variety of non-covalent interactions with functional groups on the surfaces of different substrates, such as hydrogen bonds, van der Waals forces, and electrostatic interactions, thereby exhibiting excellent adhesion properties.

[0163] 8. The pulp-based HEC4 / HEA conductive hydrogel prepared in this example was used as a strain sensor and fixed on the finger joint to detect human body movement. The conductivity response of the pulp-based HEC4 / HEA conductive hydrogel prepared in this example under different strain conditions was determined by measuring the relative change in resistance (ΔR / R0). The results are shown in FIG. Figure 24 shown.

[0164] Depend on Figure 24As can be seen, the relative change in resistance gradually increases with the stretching of the pulp-based HEC4 / HEA conductive hydrogel, and the pulp-based HEC4 / HEA conductive hydrogel is able to return to its original state after rebound, demonstrating excellent reversibility and stability. This reversibility is attributed to the reversible changes in the internal structure of the pulp-based HEC4 / HEA conductive hydrogel during stretching and rebound, ensuring its stable performance under multiple cyclic loading. When the finger was bent to 45°, a relative change of ΔR / R0 of 5.24% was detected, indicating that the pulp-based HEC4 / HEA conductive hydrogel can sensitively respond to finger movement. When the wrist joint was bent 45°, the relative change in ΔR / R0 was 4.06%. These results demonstrate that the pulp-based HEC4 / HEA conductive hydrogel can effectively detect human joint movement with high sensitivity and repeatability.

[0165] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing pulp-based hydroxyethyl cellulose conductive hydrogel, characterized in that: The steps are as follows: (1) crushing, alkalizing, etherifying, neutralizing, cross-linking, washing and drying the pulp raw material to obtain pulp-based hydroxyethyl cellulose; (2) adding pulp-based hydroxyethyl cellulose and hydroxyethyl acrylate to water and stirring uniformly to obtain a pulp-based hydroxyethyl cellulose solution; (3) adding zinc chloride, ammonium persulfate and dimethyl sulfoxide to water and stirring uniformly to obtain a mixed solution; (4) adding the mixed solution into the pulp-based hydroxyethyl cellulose solution, stirring for 25 to 35 minutes, sealing, polymerizing at 65 to 75° C. for 3.5 to 4.5 hours, and drying to obtain the pulp-based hydroxyethyl cellulose conductive hydrogel.

2. The preparation method according to claim 1, wherein The pulp is dissolving pulp, broadleaf pulp, coniferous pulp or reed pulp.

3. The preparation method according to claim 1, wherein In step (1), the preparation method of the pulp-based hydroxyethyl cellulose is as follows: a. Soaking the pulp sheet in deionized water at a solid-liquid ratio of 1:15 for 24 hours, then deflocculently disintegrating the fibers and balancing the fibers to a moisture content of 8-10%, and crushing the pulp to obtain pulp; b. In a reaction kettle, the dispersion medium, alkali solution and the pulp obtained in step a are uniformly mixed, and alkalized at 18-22° C. for 60-80 min. During the alkalization process, an inerting treatment is simultaneously performed, vacuuming to -0.05 MPa, and then filling with nitrogen to 0.2 MPa, and repeating this process 4 times to obtain alkalized pulp; c. Continue to add ethylene oxide to the alkalized pulp obtained in step b and pressurize it to 0.32 MPa, stir for 5-15 minutes, react at 55-65° C. for 60-70 minutes, heat to 75-85° C. and continue to react for 70-90 minutes, cool to 40-45° C., add nitric acid, neutralize for 10-15 minutes, then add glyoxal, and cross-link for 5-15 minutes; finally, wash twice with acetone and dry at 55-65° C. for 5-8 hours to obtain pulp-based hydroxyethyl cellulose.

4. The preparation method according to claim 3, wherein In step b, the dispersion medium is prepared by mixing tert-butyl alcohol, isopropyl alcohol and water in a mass ratio of 50:38:12; the alkali solution is prepared by mixing the dispersion medium and sodium hydroxide in a mass ratio of 80:6; and the mass ratio of the dispersion medium, alkali solution and pulp is 120:86:

10.

5. The preparation method according to claim 3, wherein In step c, the mass ratio of the ethylene oxide to the alkalized pulp is (1-1.1):1; the mass ratio of the glyoxal to the ethylene oxide is (3-5):(100-110); the mass concentration of the nitric acid is 35-45%, and the mass ratio of nitric acid to ethylene oxide is (220-240):(100-110).

6. The preparation method according to claim 1, wherein In step (2), the mass volume ratio of water, pulp-based hydroxyethyl cellulose and hydroxyethyl acrylate is 12 mL: (0.72-1.68) g: (4-20) mL; Further preferably, the mass volume ratio of the water, pulp-based hydroxyethyl cellulose and hydroxyethyl acrylate is 12 mL:1.396 g:12.120 mL.

7. The preparation method according to claim 1, wherein In step (3), the mass volume ratio of the water, zinc chloride, ammonium persulfate and dimethyl sulfoxide is 4 mL: (0.68-5.44) g: 0.01 g: (1.20-6.00) mL; Further preferably, the mass volume ratio of the water, zinc chloride, ammonium persulfate and dimethyl sulfoxide is 4 mL:2.868 g:0.01 g:2.252 mL.

8. The preparation method according to claim 1, wherein In step (4), the volume ratio of the mixed solution to the pulp-based hydroxyethyl cellulose solution is (24): (4-10); Further preferably, in step (4), the volume ratio of the mixed solution added to the pulp-based hydroxyethyl cellulose solution is 24:6.

4.

9. A pulp-based hydroxyethyl cellulose conductive hydrogel, characterized in that: The invention is prepared according to the method according to any one of claims 1 to 8.

10. Use of the pulp-based hydroxyethyl cellulose conductive hydrogel according to claim 9 in the preparation of a flexible strain sensor.

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