A highly hydrophilic sweat-absorbing hydrogel foam material and a method for preparing the same

Abstract

The present application relates to the technical field of hydrogel foam materials, and specifically provides a high-hydrophilic sweat-absorbing hydrogel foam material and a preparation method thereof, which comprises the following steps: dispersing and dissolving excess chitosan in a low-concentration acetic acid solution to obtain a pre-preparation A; dissolving cellulose nanofiber in deionized water to obtain a pre-preparation B; injecting the pre-preparation A and the pre-preparation B into the same glass container according to a specific volume ratio for mixing, and under the acidic conditions provided by acetic acid, the cellulose nanofiber reacts to generate flocculent precipitate; then, a specific crosslinking agent is added to the foam for chemical crosslinking reaction to obtain a gel precursor solution. The preparation method of the present application does not involve complex equipment, the process is simple and easy to implement, the required raw materials are non-toxic and have strong biocompatibility, the prepared foam material has high water absorption and strong hydrophilicity, and has good form retention capability, and can be widely used in the fields of medical sponges, household cleaning supplies and the like for the purpose of sweat absorption detection.

Description

Technical Field

[0001] This invention relates to the field of foam materials, and more specifically, to a highly hydrophilic sweat-absorbing hydrogel foam material and its preparation method. Background Technology

[0002] Superabsorbent materials (SABs) possess a hydrophilic surface interface and a loose, porous internal structure, enabling them to easily absorb and retain several times, or even tens of times, their own weight in water within a short period. Due to their high absorbency and water retention capacity, SABs are widely used in daily life and the medical industry. Porous SABs not only have extremely strong water absorption properties but also offer advantages such as strong structural integrity, high biocompatibility, and rapid water absorption, making them highly promising for applications such as skin-mounted sweat wiping and sweat collection.

[0003] Foamed plastics are widely popular due to their high mechanical strength, wear resistance, and water absorption, insulation, and water retention properties. However, "white pollution" is becoming increasingly serious, especially the pollution caused by plastics in daily consumer and industrial products. The non-degradability of plastics has already caused great harm to the environment. Given the inherent shortcomings and deficiencies of plastics, how to prepare products that are biodegradable, environmentally friendly, and have strong water absorption capacity has become a current research hotspot.

[0004] Cellulose nanofibers are a class of cellulose-based materials with diameters less than 100 nanometers. Their molecular chains form rigid rod-like or fibrous structures through hydrogen-bonded networks, exhibiting high crystallinity, large specific surface area, and the ability to self-crosslink via hydrogen bonds. Because their chemical structure consists of glucose units, each with three hydrophilic hydroxyl groups, the resulting large specific surface area after nanostructuring exposes a large number of hydroxyl groups. Their three-dimensional nanonetwork structure also efficiently locks in water through capillary action and physical trapping. Therefore, cellulose nanofibers possess extremely strong hydrophilicity. Gel foams prepared from cellulose nanofibers are a class of porous polymeric materials with high hydrophilicity. While retaining the original physicochemical properties of cellulose nanofibers, gel foams possess extremely high porosity, resulting in advantages such as low density, excellent absorption performance, and a large relative surface area. Simultaneously, the matrix material itself possesses biodegradability, biocompatibility, and antibacterial properties, showing broad and safe application prospects.

[0005] Despite its many excellent properties, there are very few water-absorbing, moisture-wicking products made primarily of cellulose nanofibers (CNF). This is because cellulose nanofibers have a significant drawback: their ability to self-crosslink and form aerogels relies on extremely dense hydrogen bonds between hydroxyl groups. When a purely self-crosslinked aerogel comes into contact with water, water molecules immediately flood into its pores and form new hydrogen bonds with the hydroxyl groups on the cellulose. The connections between the CNF backbones are significantly weakened, causing the entire network structure to soften, collapse, or even dissolve, becoming a viscous gel, which is highly unfavorable for practical applications. To address this problem and maintain the integrity of the CNF aerogel's morphology after contact with water, numerous studies have proposed methods such as using chemical crosslinking agents to increase the degree of crosslinking and hydrophobic treatment of the gel surface. However, simply using chemical crosslinking agents is still insufficient to prevent collapse and dissolution. Hydrophobic treatment, on the other hand, contradicts the goal of preparing a highly hydrophilic water-absorbing material. Therefore, it is necessary to develop a low-cost and simple preparation method for CNF gel foam materials that effectively maintains its morphology upon contact with water. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a low-cost, simple, and highly hydrophilic porous CNF gel foam material. This method not only has low preparation cost but also simple process, and has significant practical significance and application value.

[0007] To address the aforementioned technical problems, this invention provides a method for preparing a highly hydrophilic, sweat-absorbing hydrogel foam material, comprising the following steps: (1) Chitosan powder was dissolved in an acetic acid solution containing a small amount of acetic acid under stirring at room temperature to obtain an excess of incompletely dissolved chitosan suspension as prepreg A; (2) Stir the cellulose nanofibers at room temperature until homogeneous to obtain a cellulose nanofiber solution as prepreg B; (3) Mix the pre-prepared liquids A and B obtained in steps (1) and (2) in a sealed glass container using a dropper; (4) Add chemical crosslinking agent dropwise to the mixed solution obtained in step (3), and mix evenly in an ice bath to obtain a mixed solution; (5) Pour the mixture into a mold, place the mold in an oven and continue to heat and dry to promote cross-linking, and obtain cellulose nanofiber chitosan gel; (6) The cellulose nanofiber chitosan gel was rapidly frozen in liquid nitrogen and then freeze-dried in a vacuum dryer until it became a highly hydrophilic sweat-absorbing hydrogel foam. (7) After taking it out, soak the highly hydrophilic sweat-absorbing hydrogel foam in deionized water until it is neutral and remove the residual chemical crosslinking agent. Then, use liquid nitrogen to quickly freeze it and vacuum dry it to obtain the highly hydrophilic sweat-absorbing hydrogel foam.

[0008] Furthermore, in step (1), the degree of deacetylation of the chitosan powder is ≥95%, the viscosity is 100~200 mPa·s, the volume ratio of acetic acid to deionized water is 1~5:1000, and the mass ratio of chitosan powder to deionized water is 0.1~10:20.

[0009] Furthermore, in step (2), the cellulose nanofibers are TEMPO cellulose nanofibers with a purity of ≥99% and a mass fraction of 1.2%.

[0010] Furthermore, in step (3), the pre-prepared liquid A and pre-prepared liquid B are mixed at a mass ratio of chitosan suspension to cellulose nanofiber solution of 1~10:20, and the mixing is carried out under the conditions of ice bath and high-speed stirring for 30 minutes.

[0011] Furthermore, the chemical crosslinking agent is epichlorohydrin, and the mass ratio of epichlorohydrin to cellulose nanofibers is 1~20:1000.

[0012] Furthermore, the stirring process in steps (1) to (4) has a stirring speed of 500 r / min.

[0013] Furthermore, the mixed solution obtained in step (4) is centrifuged at a speed of 4000 r / min, a temperature of 50~55℃, and a centrifugation time of 40 minutes to remove internal water and reduce volume.

[0014] Furthermore, in step (5), the oven temperature is 70°C, there is no ventilation, and the time is two hours.

[0015] Furthermore, in step (6), the temperature of the cold trap in the vacuum dryer is -85°C.

[0016] The present invention also provides a highly hydrophilic sweat-absorbing hydrogel foam material, which is prepared by a method for preparing highly hydrophilic sweat-absorbing hydrogel foam materials.

[0017] In the above-described scheme of the present invention, cellulose nanofibers are small in size, have a large specific surface area, and are rich in a large number of free hydroxyl groups, exhibiting high hydrophilicity. They are capable of hydrogen bond crosslinking and self-assembly. Under acidic conditions provided by acetic acid, CNFs produce flocculent precipitates, releasing a large amount of water that fills the gel, making it denser. The chemical crosslinking agent epichlorohydrin promotes crosslinking between CNFs. Rapid centrifugation at a high temperature can promote gelation while rapidly separating the water released from the gel, making the gel denser, maintaining structural integrity, and effectively preventing collapse. The greatest innovation of the present invention lies in the use of incompletely dissolved chitosan suspension. The long molecular chains of chitosan intertwine with CNFs and are tightly bound together by forming a large number of intermolecular hydrogen bond networks, significantly enhancing the mechanical properties and stability of the material and strengthening the gel skeleton. The excess incompletely dissolved chitosan particles, as hydrophobic polymer particles, are combined with CNFs to jointly construct the foam material skeleton, playing a supporting role. Relying on the excellent supporting effect of chitosan and the higher density gel foam obtained by shaking out water, the morphological structure is completely maintained after immersion in water, while also maintaining its strong hydrophilicity and porous structure, exhibiting strong water absorption performance.

[0018] Compared with the prior art, the beneficial effects of the present invention are: (1) The preparation method of the present invention overcomes the inherent defects of cellulose nanofibers and realizes that CNF gel foam material maintains its morphology after being immersed in water, without collapsing, shrinking, dissolving or liquefying.

[0019] (2) The gel foam material prepared by the present invention has strong hydrophilicity, large water absorption capacity and stable moisture absorption performance.

[0020] (3) The gel foam material prepared by the present invention has strong biocompatibility and, combined with its extremely high hydrophilicity, can effectively absorb and wipe away sweat through contact with the skin, thereby achieving the collection of sweat and facilitating subsequent sweat testing. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Figure 1 The images show a comparison of the physical morphology of the gel foam material prepared in this invention before and after water ingress, before and after modification.

[0023] Figure 2 Comparison of scanning electron microscope images of gel foam materials, where a and a are comparison of scanning electron microscope images of Examples 1-4, respectively.

[0024] Figure 3 Examples of the gel foam material prepared in this invention and comparison images of water absorption by other hydrophilic and water-absorbing materials obtained by high-speed photography.

[0025] Figure 4 The water absorption rate is the value of the gel foam material prepared in this invention.

[0026] Figure 5 This is a graph showing the change in water retention rate of the gel foam material prepared in this invention over time.

[0027] Figure 6 The mechanical test curves are for the gel foam material prepared in this invention.

[0028] Figure 7 The image shows the gel foam material prepared according to the present invention being applied to the surface of human skin to absorb sweat under the action of electrical stimulation to induce sweating. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0030] All reagents used in the examples were of analytical or chemical purity, and were commercially available or prepared by methods well known to those skilled in the art. The following examples all achieve the objectives of the present invention: Example 1: (1) 0.5 g of chitosan powder with a degree of deacetylation ≥95% and a viscosity of 100~200 mpa.s was dissolved in 10 mL of acetic acid solution containing 28 μL of acetic acid under stirring at room temperature. The mixture was stirred overnight to obtain an excess of incompletely dissolved chitosan suspension as prepreg A. (2) Weigh 20 g of TEMPO cellulose nanofibers with a purity ≥99% and a mass fraction of 1.2%, and stir them at room temperature until homogeneous to obtain a cellulose nanofiber solution as prepreg B; (3) Take 4 mL of the pre-prepared liquid A obtained in steps (1) and (2) and mix it with B in a sealed glass container through a dropper. Stir at 500 r / min for 20 minutes in an ice bath to make the pre-prepared liquid A and B completely mixed. (4) Add 100 μL of epichlorohydrin to the mixed solution obtained in step (2), and stir at high speed for 30 minutes in an ice bath until the mixture is homogeneous to obtain the mixed solution; (5) Centrifuge the mixed solution obtained in step (4) at 50 °C and 4000 r / min for 40 minutes to remove internal water and reduce volume; (6) Pour the mixture into a mold, place the mold in an oven and continue to bake at 70 °C for 2 h to promote cross-linking, and obtain cellulose nanofiber chitosan gel; (7) The cellulose nanofiber chitosan gel was rapidly frozen in liquid nitrogen; then it was freeze-dried in a vacuum dryer overnight to become a highly hydrophilic sweat-absorbing hydrogel foam. (8) After taking it out, soak the highly hydrophilic sweat-absorbing hydrogel foam in deionized water until it is neutral and remove the residual chemical crosslinking agent. Then, use liquid nitrogen to quickly freeze it and vacuum dry it to obtain the highly hydrophilic sweat-absorbing hydrogel foam.

[0031] Example 2: (1) Weigh 20 g of TEMPO cellulose nanofibers with a purity ≥99% and a mass fraction of 1.2%, and stir them until uniform under ice bath conditions to obtain a cellulose nanofiber solution as prepreg A; (2) Pour the pre-prepared liquid A obtained in step (1) into a mold and freeze it rapidly in liquid nitrogen; then place it in a vacuum dryer to freeze dry overnight to become a highly hydrophilic sweat-absorbing hydrogel foam; (3) After taking it out, soak the highly hydrophilic sweat-absorbing hydrogel foam in deionized water until it is neutral and remove the residual chemical crosslinking agent. Then, use liquid nitrogen to quickly freeze it and vacuum dry it to obtain the highly hydrophilic sweat-absorbing hydrogel foam.

[0032] Example 3: (1) 0.8 g of chitosan powder with a degree of deacetylation ≥95% and a viscosity of 100~200 mpa.s was dissolved in 10 mL of acetic acid solution containing 60 μL of acetic acid under stirring at room temperature. The mixture was stirred overnight to obtain an excess of incompletely dissolved chitosan suspension as prepreg A. (2) Weigh 20 g of TEMPO cellulose nanofibers with a purity ≥99% and a mass fraction of 1.2%, and stir them at room temperature until homogeneous to obtain a cellulose nanofiber solution as prepreg B; (3) Take 4 mL of the pre-prepared solution A obtained in steps (1) and (2) and mix it with B in a sealed glass container through a dropper. Stir at 500 r / min for 20 minutes in an ice bath to ensure that the pre-prepared solution A and B are completely mixed. (4) Add 100 μL of epichlorohydrin to the mixed solution obtained in step (2), and stir at high speed for 30 minutes in an ice bath until the mixture is homogeneous to obtain the mixed solution; (5) Centrifuge the mixed solution obtained in step (4) at 50 °C and 4000 r / min for 40 minutes to remove internal water and reduce volume; (6) Pour the mixture into a mold, place the mold in an oven and continue to bake at 70 °C for 2 h to promote cross-linking, and obtain cellulose nanofiber chitosan gel; (7) The cellulose nanofiber chitosan gel was rapidly frozen in liquid nitrogen; then it was freeze-dried in a vacuum dryer overnight to become a highly hydrophilic sweat-absorbing hydrogel foam. (8) After taking it out, soak the highly hydrophilic sweat-absorbing hydrogel foam in deionized water until it is neutral and remove the residual chemical crosslinking agent. Then, use liquid nitrogen to quickly freeze it and vacuum dry it to obtain the highly hydrophilic sweat-absorbing hydrogel foam.

[0033] Example 4: (1) 0.2 g of chitosan powder with a degree of deacetylation ≥95% and a viscosity of 100~200 mpa.s was dissolved in 10 mL of acetic acid solution containing 28 μL of acetic acid under stirring at room temperature and stirred overnight to obtain an excess of incompletely dissolved chitosan suspension as prepreg A; (2) Weigh 20 g of TEMPO cellulose nanofibers with a purity ≥99% and a mass fraction of 1.2%, and stir them at room temperature until homogeneous to obtain a cellulose nanofiber solution as prepreg B; (3) Take 4 mL of the pre-prepared liquid A obtained in steps (1) and (2) and mix it with B in a sealed glass container through a dropper. Stir at 500 r / min for 20 minutes in an ice bath to make the pre-prepared liquid A and B completely mixed. (4) Add 75 μL of epichlorohydrin to the mixed solution obtained in step (2), and stir at high speed for 30 minutes in an ice bath until the mixture is homogeneous to obtain the mixed solution; (5) Centrifuge the mixed solution obtained in step (4) at 50 °C and 4000 r / min for 40 minutes to remove internal water and reduce volume; (6) Pour the mixture into a mold, place the mold in an oven and continue to bake at 70 °C for 2 h to promote cross-linking, and obtain cellulose nanofiber chitosan gel; (7) The cellulose nanofiber chitosan gel was rapidly frozen in liquid nitrogen; then it was freeze-dried in a vacuum dryer overnight to become a highly hydrophilic sweat-absorbing hydrogel foam. (8) After taking it out, soak the highly hydrophilic sweat-absorbing hydrogel foam in deionized water until it is neutral and remove the residual chemical crosslinking agent. Then, use liquid nitrogen to quickly freeze it and vacuum dry it to obtain the highly hydrophilic sweat-absorbing hydrogel foam.

[0034] Tester serial number Foam patch weight before sweat absorption / mg Foam patch weight after sweat absorption / mg Absorbed sweat weight / mg Absorbed sweat volume / μL 1 451.8 584.0 132.2 131.6 2 454.2 583.7 129.5 128.9 3 473.1 523.1 50.0 49.77 Table 1.

[0035] Effect verification: As shown in the attached figures, the materials prepared in Examples 1, 3, and 4 ( Figure 2 a, c, and d) all exhibit a three-dimensional loose porous structure. Figure 1 It is clearly shown that the material of this invention retains its intact shape after being immersed in water, while the comparative example of pure CNF material completely collapsed and shrank, turning into a gel-like substance. Figure 3High-speed photography revealed that the material of this invention has an extremely fast water absorption rate, significantly superior to several other highly hydrophilic and absorbent materials used in comparison. This also demonstrates that the chitosan to cellulose nanofiber ratio used in Example 1 is optimal in terms of water absorption rate. Figure 4 This indicates that it has a high water absorption rate, capable of absorbing at least ten times its own weight in water. The reason why the water absorption performance of Examples 1, 3, and 4 is significantly worse than that of Example 2 may be due to the filling effect of chitosan microparticles and the precipitation of CNF under the action of acetic acid, resulting in a more compact material structure and reducing the space for water molecules. Figure 5 This demonstrates that the foam material possesses a certain degree of water retention. Examples 1, 3, and 4, which contain chitosan, exhibit significantly better water retention than Example 2, proving the water-retention effect of chitosan microparticles. Figure 6 Compared to Example 2, the modified Examples 1 and 4 showed enhanced mechanical properties and significantly increased maximum stress. However, Example 3 may have experienced a significant decrease in maximum stress due to excessive chitosan addition, which disrupted the overall material structure. Foam sheets prepared using the formulation from Example 1 were used for sweat collection. Figure 7 Table 1 confirms that it can effectively and thoroughly absorb sweat from the surface of human skin, leaving the surface clean and without residue, which facilitates cleaning and subsequent testing.

[0036] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a highly hydrophilic, sweat-absorbing hydrogel foam material, characterized in that, Includes the following steps: (1) Chitosan powder was dissolved in an acetic acid solution containing a small amount of acetic acid under stirring at room temperature to obtain an excess of incompletely dissolved chitosan suspension as prepreg A; (2) Stir the cellulose nanofibers at room temperature until homogeneous to obtain a cellulose nanofiber solution as prepreg B; (3) Mix the pre-prepared liquids A and B obtained in steps (1) and (2) in a sealed glass container using a dropper; (4) Add chemical crosslinking agent dropwise to the mixed solution obtained in step (3), and mix evenly in an ice bath to obtain a mixed solution; (5) Pour the mixture into a mold, place the mold in an oven and continue to heat and dry to promote cross-linking, and obtain cellulose nanofiber chitosan gel; (6) The cellulose nanofiber chitosan gel was rapidly frozen in liquid nitrogen and then freeze-dried in a vacuum dryer until it became a highly hydrophilic sweat-absorbing hydrogel foam. (7) After taking it out, soak the highly hydrophilic sweat-absorbing hydrogel foam in deionized water until it is neutral and remove the residual chemical crosslinking agent. Then, use liquid nitrogen to quickly freeze it and vacuum dry it to obtain the highly hydrophilic sweat-absorbing hydrogel foam.

2. The method for preparing a highly hydrophilic, sweat-absorbing hydrogel foam material as described in claim 1, characterized in that, In step (1), the degree of deacetylation of the chitosan powder is ≥95%, the viscosity is 100~200 mPa·s, the volume ratio of acetic acid to deionized water is 1~5:1000, and the mass ratio of chitosan powder to deionized water is 0.1~10:

20.

3. The method for preparing a highly hydrophilic, sweat-absorbing hydrogel foam material as described in claim 2, characterized in that, In step (2), the cellulose nanofibers are TEMPO cellulose nanofibers with a purity of ≥99% and a mass fraction of 1.2%.

4. The method for preparing a highly hydrophilic, sweat-absorbing hydrogel foam material as described in claim 3, characterized in that, In step (3), the pre-prepared liquid A and pre-prepared liquid B are mixed at a mass ratio of chitosan suspension to cellulose nanofiber solution of 1~10:20, and the mixing is carried out under the conditions of ice bath and high-speed stirring for 30 minutes.

5. The method for preparing a highly hydrophilic, sweat-absorbing hydrogel foam material as described in claim 4, characterized in that, The chemical crosslinking agent is epichlorohydrin, and the mass ratio of epichlorohydrin to cellulose nanofibers is 1~20:1000.

6. The method for preparing a highly hydrophilic, sweat-absorbing hydrogel foam material as described in claim 5, characterized in that, The stirring process in steps (1) to (4) has a stirring speed of 500 r / min.

7. The method for preparing a highly hydrophilic, sweat-absorbing hydrogel foam material as described in claim 6, characterized in that, The mixed solution obtained in step (4) is centrifuged at a speed of 4000 r / min, a temperature of 50~55℃, and a centrifugation time of 40 minutes to remove internal water and reduce volume.

8. The method for preparing a highly hydrophilic, sweat-absorbing hydrogel foam material as described in claim 6, characterized in that, In step (5), the oven temperature is 70°C, there is no ventilation, and the time is two hours.

9. The method for preparing a highly hydrophilic, sweat-absorbing hydrogel foam material as described in claim 6, characterized in that, In step (6), the temperature of the cold trap of the vacuum dryer is -85℃.

10. A highly hydrophilic, sweat-absorbing hydrogel foam material, characterized in that: The foam material is prepared by the preparation method described in any one of claims 1-9.

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