Super-absorbent sheet and preparation method thereof
By combining the wet-laid web forming principle with nanocapsules, a uniformly dispersed super absorbent sheet is prepared, which solves the problems of SAP particle position movement and sheet hardness in the existing technology, achieves high water absorbency and good mechanical properties, and is suitable for applications such as disposable sanitary products.
Patent Information
- Application Number
- CN202510857486.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-25
- Publication Date
- 2025-09-23
AI Technical Summary
Existing super absorbent sheets are easily displaced by external forces, resulting in localized lumps and fractures after absorbing urine, which makes them uncomfortable. In addition, the sheets prepared by traditional methods have a hard touch, which limits their application.
Using the wet-laid web-forming principle, millimeter-scale fibers, micron-scale SAP and nanoscale capsules are integrated. SAP is dispersed in anhydrous ethanol and pre-crosslinked with epichlorohydrin to prepare superabsorbent sheets, which are then combined with nanoscale capsules to improve wet mechanical properties.
It achieves uniform dispersion and excellent shape retention of super absorbent sheets, avoids local clumping, improves wet mechanical properties and water absorption properties, and is suitable for disposable sanitary products and other fields.
Smart Images
Figure CN120682589A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a functional material, in particular to a super absorbent sheet and a preparation method thereof. Background Art
[0002] Super absorbent polymer (SAP) is a cross-linked polymer material that can absorb large amounts of water, forming a gel-like structure. It exhibits excellent water retention, rapid water absorption, and high water absorption capacity. Polyacrylates, starch acrylate polymers, starch-acrylonitrile graft copolymers, and acrylamide-acrylonitrile-acrylic acid terpolymers can all serve as SAPs. These materials can quickly absorb hundreds or even thousands of times their own water content. SAP is widely used in the medical, health, and agricultural sectors. Based on their morphology, SAP is primarily classified into granular, fibrous, and flaky forms.
[0003] Because fibrous SAP has limited water absorption capacity and sheets made directly from SAP are relatively stiff, disposable hygiene products such as diapers, sanitary napkins, and spacers often use a sheet material made from a mixture of granular SAP and fluff pulp fibers, cotton fibers, and other materials as the absorbent core layer. This core layer relies primarily on fluff pulp fibers to encapsulate the SAP particles. However, this core layer not only uses a large amount of fluff pulp, making the diaper thick and heavy, but also the SAP particles in this core material are easily displaced by external forces, resulting in localized clumps and breaks in the diaper after absorbing urine, making it less comfortable.
[0004] CN116926953 A discloses a method for producing superabsorbent spunbonded polyester nonwoven fabric. The method involves impregnating the polyester nonwoven fabric with an acrylic prepolymer, removing excess finishing liquid from the nonwoven fabric using a pair of rollers, and finally baking the fabric at high temperature to produce a superabsorbent sheet formed from the SAP and nonwoven fabric. However, because the SAP prepolymer adheres to the nonwoven fabric in sheets, the dried sheet has a relatively hard feel, limiting its application. Summary of the Invention
[0005] Purpose of the invention: The purpose of the present invention is to provide a super absorbent sheet with strong water absorption, good shape retention and excellent mechanical properties.
[0006] Another object of the present invention is to provide a method for preparing the super absorbent sheet.
[0007] Technical solution: The super absorbent sheet of the present invention comprises millimeter-grade fibers, micron-grade SAP and nano-grade capsules, wherein the mass ratio of the micron-grade SAP to the millimeter-grade fibers is no more than 2:1, and the mass ratio of the nano-grade capsules to the millimeter-grade fibers is 1:10-50.
[0008] The method for preparing the super absorbent sheet of the present invention comprises the following steps:
[0009] (1) Adding SAP particles to a surface modification liquid, stirring evenly, filtering, and drying to obtain surface-modified SAP; the surface modification liquid is a mixture of epichlorohydrin and anhydrous ethanol;
[0010] (2) Blending the fiber and water in a grinder to obtain a fiber solution; filtering and adding the nanocapsule suspension to obtain a mixed slurry A;
[0011] (3) The modified SAP obtained in step (1) is added to anhydrous ethanol, and is added to the mixed slurry A during stirring, and is whipped, filtered, pressed to solid form, and dried to obtain a super absorbent sheet.
[0012] Preferably, the fiber described in step (2) is one of cotton fiber, viscose fiber and pulp fiber.
[0013] Preferably, the mass ratio of the fiber to water in step (2) is not greater than 1:40; the purpose of adding water is to beat the fiber into a slurry so that the fiber is evenly dispersed. In subsequent operations, the fiber solution needs to be filtered, so there is no need to limit the maximum amount of water added here.
[0014] Preferably, the volume ratio of the anhydrous ethanol described in step (3) to the water in the mixed slurry in step (2) is greater than 3:1, and more preferably 4:1; the purpose of adding anhydrous ethanol is to disperse the SAP and temporarily inhibit the water absorption of the SAP. In subsequent operations, all the anhydrous ethanol needs to be filtered out, so there is no need to limit the maximum amount of anhydrous ethanol added here.
[0015] Preferably, the concentration of the fiber and nanocapsule suspension in step (2) is 3-5 mg / mL, more preferably 4 mg / mL.
[0016] Preferably, the volume fraction of epichlorohydrin in the surface modification liquid of step (1) is 10-20%.
[0017] Preferably, the filtration in step (3) is performed under vacuum.
[0018] Preferably, the drying in step (3) is completed in a vacuum drying oven at 60° C. for 30 minutes.
[0019] Principle of the Invention: Based on the principle of wet-laid web formation, the present invention combines fibers with a granular absorbent resin to produce a sheet-like absorbent material. Taking advantage of SAP's non-ethanol absorption, anhydrous ethanol is used as the solvent for dispersing SAP, replacing the water used in traditional processes. This solves the problem of SAP swelling upon contact with water, ensuring uniform SAP dispersion while also maintaining excellent shape retention. Furthermore, the surface of the SAP is pre-crosslinked with epichlorohydrin to form a crosslinked network, enhancing its shape retention and preventing the SAP from colloidalizing during the molding process due to factors such as stirring and pressure, thereby enabling wet-laid integrated molding of the two.
[0020] To address the low wet strength of sheet-like absorbent materials, the present invention incorporates lavender nanocapsules encapsulated in ethyl cellulose, prepared using an instantaneous nanoprecipitation method, into superabsorbent sheets. This multi-scale integration of nanocapsules, micron-sized SAP, and millimeter-sized fibers enhances the sheet's wet mechanical properties. Furthermore, the aromatic aroma of lavender helps mitigate the odor produced by the superabsorbent sheet after use. High dry strength facilitates processing on mechanical assembly lines, while high wet strength helps maintain its integrity after absorbing liquid, preventing it from crumbling upon contact with water.
[0021] Based on the wet-laid web forming principle, the present invention integrates SAP particles and fibers to prepare super absorbent sheets, which not only solves the current problem of physical mixing of particles and fluff pulp fibers, but also the sheets prepared by the wet-laid web forming principle have a void structure, which can realize the dual liquid absorption mechanism of SAP chemical adsorption and physical void adsorption, and the water absorption is enhanced. It can be applied to disposable sanitary products, makeup removers, liquid-absorbing hemostatic materials, daily necessities and other fields.
[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) This method uses anhydrous ethanol as a solvent to disperse SAP, which makes the SAP evenly dispersed while also inhibiting the large amount of water absorption that occurs during the wet web forming process, so that the final sheet is well-formed and has excellent water absorption performance. This integrated sheet forming method avoids the occurrence of local clumping during use; (2) This method adds nanocapsules to the super absorbent sheet, effectively improving the wet mechanical properties of the sheet-like absorbent material; (3) The surface of SAP is pre-strengthened and cross-linked by epichlorohydrin, which is beneficial to improving the shape retention of SAP particles and further ensuring the porous structure of the final sheet. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 The following are scanning electron micrographs of the superabsorbent sheet prepared in Example 1, wherein 1a is a plan view of the sheet, 1b is a cross-sectional view of the sheet, and 1c and 1d are plan views at different magnifications.
[0024] Figure 2This is the surface morphology of the super absorbent sheet prepared in Example 1;
[0025] Figure 3 This is a picture showing the clamping of the wet super absorbent sheet prepared in Example 1;
[0026] Figure 4 This is the morphology of the mixed slurry B in Comparative Example 1;
[0027] Figure 5 This is the surface morphology of the super absorbent sheet prepared in Comparative Example 1;
[0028] Figure 6 This is a picture of the super absorbent sheet prepared in Comparative Example 1 when clamped in a wet state;
[0029] Figure 7 This is the morphology of mixed slurry B in comparative example 2;
[0030] Figure 8 This is the apparent morphology of the super absorbent sheet prepared in Comparative Example 2. DETAILED DESCRIPTION
[0031] The technical solution of the present invention will be further described below in conjunction with embodiments.
[0032] Example 1
[0033] The method for preparing the super absorbent sheet of the present invention comprises the following steps:
[0034] (1) Preparation of modified SAP: Weigh 7.5 ml of epichlorohydrin and add it to 42.5 ml of anhydrous ethanol. Stir magnetically to obtain a surface modification liquid with an epichlorohydrin volume fraction of 15%. Add 5 g of SAP particles to the surface modification liquid and stir magnetically at room temperature for 30 min. Filter to remove excess surface modification liquid. Place the particles on the filter paper in an oven, dry at 180°C for 30 min, then remove and cool to room temperature. Soak the cooled particles in anhydrous ethanol to wash away any unreacted surface modification liquid. Change the anhydrous ethanol every 4 hours for a total of three times to ensure that any unreacted surface modification liquid is completely washed away. Dry to obtain granular surface-modified SAP.
[0035] (2) 1 g of paper fragments was placed in a high-speed grinder filled with 100 ml of deionized water and beaten at 24,000 r / min for 2 min to obtain pulp fibers; the pulp fibers were poured into a sieve and some water was filtered out until the remaining wet pulp fiber mass was 31 g; then 10 mL of a 4 mg / mL lavender nanocapsule suspension was added to obtain a mixed slurry A.
[0036] (3) Weigh 0.5 g of 60-mesh modified SAP particles and place them in 120 ml of anhydrous ethanol. Pour them into the mixed slurry A during stirring, then transfer them to a high-speed grinder and beat them at 24,000 r / min for 10 s to obtain a mixed slurry B. Take 20 ml of the particles for vacuum filtration, keeping the negative pressure at 20 kPa until no liquid flows out and gradually returning to atmospheric pressure. Move the fiber mesh obtained by filtration from the filter membrane into a pressing device, clamp it up and down with absorbent paper, and then clamp it up and down with hard plastic plates to form a double-layer sandwich structure. Place a 500 g weight on the top plastic plate to apply downward pressure to the fiber mesh, squeeze the fiber mesh to solidify, and place it in a vacuum drying oven at 60°C for 30 min to obtain a super absorbent sheet.
[0037] In this embodiment, the volume ratio of anhydrous ethanol to water in the mixed slurry is 4:1.
[0038] The SAP particles described in step (1) are prepared according to the following method:
[0039] (11) Prepare a 5% wheat gluten (WG) solution.
[0040] (12) Acrylic acid (AA) was neutralized with 30% KOH solution in an ice-water bath. After the system temperature stabilized, 50% acrylamide (AM) aqueous solution was added to make the mass ratio of AA to AM 7:3. The mixture was magnetically stirred for 15 min to form a homogeneous mixture.
[0041] (13) To the homogeneous mixture of step (12), 0.8% (relative to the mass of monomers AA + AM) of initiator solution (potassium persulfate: sodium bisulfite mass ratio is 2:1) and 0.1% of cross-linking agent N,N-methylenebisacrylamide (NMBA) were added in sequence. After magnetic stirring for 10 minutes, the mixture was placed in a 90°C water bath and continued to react for 2 hours to obtain a block gel.
[0042] (14) Take out the gel and cut it into small pieces. Soak it in anhydrous ethanol, changing the anhydrous ethanol every 4 hours for a total of three times. Place the soaked gel in a 60°C oven and dry it to constant weight.
[0043] (15) The dried water-absorbing resin is crushed using a multifunctional crusher, and the crushed water-absorbing particles are sieved to obtain SAP particles of different particle sizes.
[0044] The nanocapsule suspension described in step (2) is prepared according to the following method:
[0045] (21) 0.32 g of ethyl cellulose powder was weighed and slowly added to 60 ml of anhydrous ethanol. The mixture was magnetically stirred for 2 h until the ethyl cellulose was completely dissolved. Then, 0.16 mg of lavender essential oil was added and magnetic stirring was continued for 10 min to obtain a mixed solution with a concentration of 8 mg / mL.
[0046] (22) Using two 50 mL syringes, 40 mL of deionized water and the mixed solution prepared in step (21) were measured, respectively. The two syringes were installed on a dual-channel syringe pump, and the injection flow rate was set to 40 mL / min. Subsequently, the syringe pumps were started simultaneously, and the two solutions collided and mixed at high speed in the mixer cavity. After flowing out of the lower outlet of the mixer, a nanocapsule suspension was formed. After the collision, the suspension was stirred with a glass rod for 2 minutes to prevent capsule aggregation.
[0047] The super absorbent sheet prepared in Example 1 was characterized by SEM. Figure 1 As shown in Figures (a) and (b), the morphology and distribution of SAP and fibers are shown; the red circles in Figures (c) and (d) show the morphology and distribution of nanocapsules. As can be seen from the figures, the nanocapsules, micron-sized SAP, and millimeter-sized fibers are evenly distributed in the superabsorbent sheet.
[0048] The surface morphology and wet state pictures of the super absorbent sheet prepared in Example 1 are as follows: Figure 2 、 Figure 3 As shown. Figure 2 and Figure 3 It can be seen that the surface morphology of the super absorbent sheet is relatively fine and will not break when clamped in a wet state.
[0049] The sheet prepared in Example 1 was subjected to water absorption and mechanical strength tests, and the water absorption rate was found to be about 280 g / g, and the dry breaking strength was about 410 kPa.
[0050] Related performance test methods:
[0051] (1) Mechanical properties test: A YG028 universal material testing machine was used to perform tensile mechanical tests according to GB / T 3923.1-2013 Textile fabrics — Tensile properties of fabrics — Part 1: Determination of breaking strength and elongation at break (strip method).
[0052] (2) Water absorption rate test: refer to Appendix H of GB / T-22875-2018 Superabsorbent resins for diapers and sanitary napkins for water absorption rate test.
[0053] Comparative Example 1
[0054] The similarities between this comparative example and Example 1 are not repeated here, except that:
[0055] The amount of lavender nanocapsule suspension added in step (2) is 0.
[0056] The morphology of the mixed slurry B in Comparative Example 1 and the surface morphology of the obtained super absorbent sheet are as follows: Figure 4 、 5 As shown, the wet clamping morphology is as follows Figure 6 The macroscopic morphology and water absorption rate of Comparative Example 1 are similar to those of Example 1, except that the mechanical properties have decreased. Its dry breaking strength is about 306 kPa, which is about 25% lower than that of the sheet with nanocapsules added in Example 1. The mechanical properties in the wet state are also significantly lower, the shape retention is poor, and it is easy to break after clamping. Figure 6 shown.
[0057] Comparative Example 2
[0058] The similarities between this comparative example and Example 1 are not repeated here, except that:
[0059] The amount of anhydrous ethanol added in step (3) is 45 mL. In this comparative example, the volume ratio of anhydrous ethanol to water in the mixed slurry is 1.5:1.
[0060] The morphology of the mixed slurry B and the surface morphology of the obtained super absorbent sheet in Comparative Example 2 are as follows: Figure 7 、 8 As shown in the figure, the water content in the mixed slurry B is higher than that in Example 1 and Comparative Example 1, the SAP particles are more dissolved, and the surface of the obtained sheet is rough after molding, and the morphology uniformity is poor, which does not meet the use requirements.
[0061] In summary, using anhydrous ethanol instead of water in the traditional process to disperse SAP particles, while ensuring that the ethanol content in the overall mixed solution is not less than a certain proportion, helps reduce the solubility of the SAP particles and improves the particle's shape retention. The superabsorbent sheet produced by this method has excellent mechanical properties. Compared with a superabsorbent sheet without nanocapsules (Comparative Example 1), the wet strength is significantly improved, and it does not deform or break when clamped with tweezers, indicating that the addition of nanocapsules can improve the wet mechanical properties of the superabsorbent sheet.
Claims
1. A super absorbent sheet, characterized in that: The invention comprises millimeter-grade fibers, micron-grade SAP and nanometer-grade capsules. The mass ratio of the micron-grade SAP to the millimeter-grade fibers is not greater than 2:1, and the mass ratio of the nanometer-grade capsules to the millimeter-grade fibers is 1:10-50.
2. A method for preparing the super absorbent sheet according to claim 1, characterized in that: The following steps are involved: (1) Adding SAP particles to a surface modification liquid, stirring evenly, filtering, and drying to obtain surface-modified SAP; the surface modification liquid is a mixture of epichlorohydrin and anhydrous ethanol; (2) Blending the fiber and water in a grinder to obtain a fiber solution; filtering and adding the nanocapsule suspension to obtain a mixed slurry A; (3) The modified SAP obtained in step (1) is added to anhydrous ethanol, and is added to the mixed slurry A during stirring, and is whipped, filtered, pressed to solid form, and dried to obtain a super absorbent sheet.
3. The preparation method according to claim 2, characterized in that The fiber described in step (2) is one of cotton fiber, viscose fiber and pulp fiber.
4. The preparation method according to claim 2, characterized in that The mass ratio of the fiber to water in step (2) is not greater than 1:
40.
5. The preparation method according to claim 2, characterized in that The volume ratio of the anhydrous ethanol described in step (3) to the water in the mixed slurry in step (2) is greater than 3:
1.
6. The preparation method according to claim 2, characterized in that The volume ratio of the anhydrous ethanol described in step (3) to the water in the mixed slurry in step (2) is 4:
1.
7. The preparation method according to claim 2, characterized in that The concentration of the fiber and nanocapsule suspension in step (2) is 3-5 mg / mL.
8. The preparation method according to claim 2, characterized in that The concentration of the fiber and nanocapsule suspension described in step (2) is 4 mg / mL.
9. The preparation method according to claim 2, characterized in that In the surface modification liquid described in step (1), the volume fraction of epichlorohydrin is 10-20%.
10. The preparation method according to claim 2, characterized in that The filtration in step (3) is completed under vacuum.