Preparation method of fast-swelling high-porosity liquid-type superabsorbent resin

Abstract

The application discloses a preparation method of a fast-swelling high-liquid-permeable superabsorbent resin and belongs to the technical field of superabsorbent resin preparation. Nanocellulose, silica sol and sodium chloride are compounded to prepare a ternary morphology control precursor suspension; acrylic acid is neutralized by alkali to a neutralization degree, and then is mixed with the precursor suspension, an internal crosslinking agent, inorganic fillers and an initiator to obtain a polymerization mixed solution; the polymerization mixed solution is transported to a belt reactor to form a liquid layer, and is polymerized under three temperature zones to obtain a water-containing superabsorbent resin gel; the gel is cut into a sheet shape to perform first stage drying, so that the water content is reduced, sodium chloride is extracted by water washing, and after second stage drying and smashing and screening, porous superabsorbent resin particles are obtained; the particles are contacted with a surface crosslinking agent solution containing triethanolamine and citric acid, and then are subjected to segmented heat treatment to obtain a final product. The obtained superabsorbent resin has the advantages of fast swelling and stable high-liquid-permeable performance under the condition of multiple liquid injection while maintaining a high absorption ratio.

Description

Technical Field

[0001] This invention relates to the technical field of resin preparation, and specifically to a method for preparing a fast-expanding, high-fluidity superabsorbent resin. Background Technology

[0002] Superabsorbent polymers (SAPs) are a class of functional polymers containing strongly hydrophilic groups and possessing a certain degree of cross-linking. They can absorb hundreds or even thousands of times their own weight in water and have wide applications in personal care products, agricultural water retention, and medical and health fields. Traditionally, superabsorbent polymers are mainly prepared by solution polymerization or reverse suspension polymerization of acrylic monomers. Industrially, belt continuous polymerization processes are commonly used to achieve large-scale production.

[0003] In the prior art, various preparation schemes related to belt reactors have been developed to achieve continuous production. For example, CN101050244A (A method for producing superabsorbent resin and a polymerization reactor) discloses a method for continuously polymerizing superabsorbent resin using a thin-layer belt reactor. This method involves spreading a monomer solution to a certain thickness and then performing polymerization, drying, and surface treatment within the belt device. While this method achieves continuous industrial production, it requires precise and coordinated control of the liquid layer thickness and temperature. Improper control can easily lead to gel adhesion or instability in the polymerization process, thus affecting the uniformity of the gel and the subsequent drying effect.

[0004] CN103408780A (A Method for Preparing a High-Performance, Highly Absorbent Resin) discloses a method for preparing a resin by polymerization in a continuous belt reactor to generate a gel, followed by crushing, drying, pulverizing, and surface treatment. This method improves the overall performance of the resin by optimizing polymerization conditions. While this technology has made some progress in continuous production, in practical large-scale applications, there is still room for optimization in matching the liquid layer thickness, conveying rate, and temperature zones during belt polymerization. This can easily lead to uneven gel moisture content distribution or significant randomness in pore formation.

[0005] Furthermore, to further improve the water absorption rate and structural stability of superabsorbent polymers, existing technologies have also introduced nanomaterial modification schemes. For example, CN120059089B (a method for preparing an anticoagulant superabsorbent polymer) discloses a technique that combines hydrolyzed tannic acid and nanocellulose through an oxidative coupling reaction, loads citric acid, and then mixes it with nano-silica, acrylic acid, etc., polymerizes it in a microchannel reactor, and uses ultraviolet light for surface crosslinking. This method explores nanomaterial composites; however, the dispersion process of nanocellulose and silica in the polymerization system still faces certain challenges, as secondary agglomeration can easily affect the uniformity of the final material.

[0006] CN109467738B (A Method for Preparing a Superabsorbent Resin) discloses a technical solution for preparing a superabsorbent resin by adding an internal crosslinking agent and an initiator to an unsaturated monomer aqueous solution for free radical polymerization, followed by extrusion granulation, drying, surface crosslinking, and anti-caking treatment (adding nanoscale adhesives such as fumed silica). This technology improves particle spacing and liquid permeability through post-treatment; however, the nanomaterials are mainly introduced at the surface or post-treatment stages, and their integration with morphology control in the polymerization precursor stage is insufficient, leaving room for further improvement in dispersion performance.

[0007] Regarding surface crosslinking, CN103450388B (A method for preparing a fast-absorbing superabsorbent resin) discloses a technical solution involving the formation of a gel via belt polymerization, followed by crushing, drying, pulverizing, continuous surface crosslinking agent coating, and heat treatment, aiming to improve the absorption rate. While this method achieves progress in rapid absorption performance, the matching between the surface crosslinking process and the internal structure (especially pore connectivity) still has certain limitations, making it difficult to simultaneously achieve ideal expansion rates and liquid permeation rates under high load conditions.

[0008] In summary, while existing technologies have made beneficial explorations in continuous production, nano-modification, and surface treatment, they generally suffer from problems such as insufficient uniformity of nanomaterial dispersion, imperfect control logic of tape polymerization, difficulty in controlling pore formation and connectivity, and the need to optimize the matching between surface crosslinking and overall expansion performance. These issues make it difficult for superabsorbent resins to simultaneously achieve both rapid expansion rate and high liquid permeability, thus failing to fully meet the higher requirements of high-end hygiene products and other fields. Summary of the Invention

[0009] Therefore, the purpose of this invention is to provide a method for preparing a fast-expanding, high-fluidity superabsorbent resin that maintains a high absorption ratio while also exhibiting fast expansion and stable high-fluidity performance under multiple injection conditions.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A method for preparing a fast-expanding, high-fluidity liquid-type superabsorbent resin includes the following steps:

[0012] S1. Preparation of morphology-modifying precursor: Nanocellulose is dispersed in water to obtain nanocellulose slurry. Silica sol and sodium chloride are added to the nanocellulose slurry to obtain a cellulose / silica / sodium chloride morphology-modifying precursor suspension.

[0013] S2. Preparation of the polymerization mixture: After neutralizing the acrylic acid with alkali, it is mixed with the morphology-regulating precursor suspension, internal crosslinking agent, inorganic filler and initiator to obtain a polymerization mixture with a solid content of 35-45 wt%.

[0014] S3. Polymerization: The polymerized mixture is conveyed to a belt reactor to form a liquid layer with a thickness of 2–4 mm. The conveyor belt speed of the belt reactor is controlled at 0.8–1.6 m / min. The inlet zone, middle zone and end zone are heated sequentially for 25–40 min, wherein the bottom plate temperature of the inlet zone is 20–25℃, the bottom plate temperature of the middle zone is 40–55℃ and the bottom plate temperature of the end zone is 65–75℃, to obtain a water-containing superabsorbent resin gel with a water content of 55–70 wt%.

[0015] S4. Segmented drying, semi-dry salt extraction and pulverization and sieving: The water-containing superabsorbent resin gel is cut into sheets for the first stage of drying, so that the water content of the gel is reduced to 35-45 wt%. Sodium chloride is extracted by washing with water at this water content. Then, the second stage of drying, pulverization and sieving are carried out to obtain porous superabsorbent resin particles with an average pore size of 80-250 μm and interconnected pores.

[0016] S5. Surface crosslinking: The porous superabsorbent resin particles are contacted with a surface crosslinking agent solution containing polyols and polycarboxylic acids, and subjected to segmented heat treatment at 120–200°C to obtain surface-crosslinked superabsorbent resin particles.

[0017] The present invention is further configured such that step S1 includes:

[0018] S11. Disperse nanocellulose in water to obtain nanocellulose slurry, wherein the mass fraction of nanocellulose is 1.5–2.5 wt%, the nanocellulose diameter is 20–50 nm, and the length is 0.5–2 μm;

[0019] S12. Add silica sol with a particle size of 10–30 nm and a solid content of 20–40 wt% to the nanocellulose slurry, so that the mass ratio of nanocellulose to silica solid is 1:(0.5–1.0), adjust the pH to 4.5–5.5, stir at 25–35°C for 30–60 min, and simultaneously apply ultrasonic-assisted dispersion with an ultrasonic power of 200–400 W and a frequency of 20–40 kHz.

[0020] S13. Slowly add sodium chloride solid to the system, so that the mass of sodium chloride is 10–25 wt% of the total mass of nanocellulose and silica solid, and stir at 300–500 rpm for 20–40 min to obtain a ternary morphology-modifying precursor suspension of cellulose / silica / sodium chloride.

[0021] The present invention is further configured such that step S2 includes:

[0022] S21. Use a 30–40 wt% sodium hydroxide aqueous solution to neutralize acrylic acid to a degree of neutralization of 65–75 mol%. The system temperature during the neutralization process does not exceed 35°C, resulting in a neutralized monomer solution with a monomer mass fraction of 25–45 wt%.

[0023] S22. The neutralized monomer solution is mixed with the ternary morphology-modifying precursor suspension to achieve a mass ratio of acrylic acid solid to total solids of nanocellulose + silica + sodium chloride of 100:(16–35), and the total solid content is adjusted to 35–45 wt%.

[0024] S23. Add N,N'-methylenebisacrylamide as an internal crosslinking agent, with an amount of 0.15–0.35 wt% of acrylic acid mass. Add nano-silica with a particle size of 50–200 nm as an inorganic filler, with an amount of 0.5–5 wt% of acrylic acid mass. Add an initiator, wherein sodium persulfate is used at an amount of 0.1–0.3 wt% of acrylic acid mass and sodium bisulfite is used at an amount of 0.05–0.2 wt% of acrylic acid mass. Stir for 10–20 min to obtain a homogeneous polymerization mixture.

[0025] The present invention is further configured such that in step S3:

[0026] The polymerization mixture is fed into a belt reactor at a rate of 0.8–1.5 kg / min, with the liquid layer thickness controlled at 2–4 mm.

[0027] The temperature of the substrate is controlled at 20–25℃ in the inlet zone, 40–55℃ in the middle zone, and 65–75℃ in the end zone, with a total residence time of 25–40 min, to obtain a water-containing superabsorbent resin gel with a water content of 55–70 wt%.

[0028] The present invention is further configured such that step S4 includes:

[0029] S41. Cut the water-containing superabsorbent resin gel with a water content of 55–70 wt% into sheets with a thickness of 3–6 mm, place them on a perforated tray, and dry them in hot air at 45–55℃ for 30–60 min to reduce the water content of the gel to 35–45 wt%.

[0030] S42. Transfer the gel sheet dried in the first stage to a water washing tank at 25–35°C and spray or soak it with deionized water for 10–20 min. The liquid-to-solid volume ratio is 5–10:1 to extract sodium chloride from the gel.

[0031] S43. After washing the gel sheet, dry it again under hot air at 50–80℃ for 40–80 min to reduce the water content to 10–18 wt%.

[0032] The present invention is further configured such that step S4 also includes:

[0033] S44. The gel sheets that have undergone the second stage of drying are fed into a roller mill for crushing, with a roller gap of 0.3–0.7 mm and a linear speed of 1.5–3.0 m / s.

[0034] S45. The pulverized product is subjected to multi-stage sieving to collect superabsorbent resin particles with a particle size of 150–850 μm, of which the content of micro powder with a particle size of less than 150 μm is 3–10 wt%.

[0035] The present invention is further configured such that: the surface crosslinking agent in step S5 includes triethanolamine and citric acid, wherein the amount of triethanolamine is 0.3–0.8 wt% of the mass of the superabsorbent resin particles, and the amount of citric acid is 0.2–0.6 wt% of the mass of the superabsorbent resin particles; the surface crosslinking agent is dissolved in a mixed solvent of water and isopropanol in a mass ratio of 1:1 to obtain a surface crosslinking agent solution with a solid content of 5–15 wt%.

[0036] The present invention is further configured such that step S5 includes:

[0037] S51. Place the porous superabsorbent resin particles in a rotary drum and roll them at a speed of 5–15 rpm under conditions of 30–40°C, and spray the surface crosslinking agent solution for 5–15 min.

[0038] S52. The sprayed superabsorbent resin particles are heat-treated sequentially at 120–140℃ for 10–20 min, at 160–180℃ for 10–20 min, and at 180–200℃ for 5–10 min.

[0039] The present invention is further configured such that: in step S1, the mass ratio of nanocellulose to silica solid is 1:(0.6–0.9), the mass of sodium chloride is 15–20 wt% of the total mass of nanocellulose and silica solid; the power of ultrasonic-assisted dispersion is 250–350 W and the frequency is 25–35 kHz.

[0040] The present invention is further configured such that the average pore size of the porous superabsorbent resin particles is 100–200 μm and the porosity is 65–85%.

[0041] Compared with the shortcomings of the prior art, the beneficial effects of the present invention are as follows:

[0042] By constructing a ternary precursor of nanocellulose / silica / sodium chloride, the invention achieves the controllable construction of porous structures inside particles. This invention synergistically combines nanocellulose, silica sol and sodium chloride within a specific pH window (4.5–5.5), enabling nanocellulose and silica to construct a dual support framework with both elasticity and rigidity, and confining sodium chloride within the network of this framework.

[0043] This effectively avoids problems such as salt crystals settling at the bottom of the liquid layer or being "locked" by localized highly cross-linked groups, thus obtaining a hydrogel with uniform sodium chloride distribution after the strip exits, providing a uniform pore precursor structure for the subsequent salt extraction and pore formation process.

[0044] By precisely controlling the salt moisture content window, the resulting particles can form continuous and interconnected three-dimensional channels, significantly improving the transfer efficiency of liquid under multiple injection and load conditions. Attached Figure Description

[0045] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0046] Reference Figure 1 The embodiments of the present invention will be further described below.

[0047] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Any reasonable changes to the process parameters made by those skilled in the art without departing from the concept of the present invention should fall within the scope of protection of the present invention.

[0048] Example 1:

[0049] 1. Preparation of morphology-modifying precursor: In this embodiment, a ternary morphology-modifying precursor suspension of cellulose / silica / sodium chloride was first prepared. 20g of nanocellulose, with a diameter of approximately 30nm and a length of approximately 1μm, was weighed and added to 780g of deionized water. The mixture was stirred at 500rpm for 30min to uniformly disperse the nanocellulose in the aqueous phase, resulting in a nanocellulose slurry with a mass fraction of approximately 2.5wt%.

[0050] 40g of silica sol was added to the above-mentioned nanocellulose slurry. The silica sol had a SiO2 solid content of 30wt% and a primary particle size of approximately 20nm, resulting in a mass ratio of nanocellulose to silica solids of approximately 1:0.6. The pH of the system was adjusted to 5.0 using dilute NaOH solution and dilute acetic acid alternately. The mixture was stirred at 300rpm for 45min at 30℃ to allow silica to preferentially form and distribute on the surface of the nanocellulose and near the network nodes. During the stirring process, ultrasonic-assisted dispersion was applied at a power of 300W and a frequency of 25kHz, with intermittent operation (10s on, 5s off) for a total of 15min, to break up any possible nanocellulose / silica agglomerates and obtain a stable cellulose / silica dispersion system.

[0051] 8g of crystalline sodium chloride was slowly added to the above system, making the mass of sodium chloride approximately 18wt% of the total mass of nanocellulose and silica solids. During the addition process, the stirring speed was controlled at 400rpm, and the mixture was continuously stirred at 30℃ for 30min to ensure uniform dispersion of sodium chloride in the cellulose-silica network, resulting in a ternary morphology-controlled precursor suspension of cellulose / silica / sodium chloride. Through the above-mentioned pH control and ultrasonic-assisted dispersion, silica was preferentially distributed at the nanocellulose network nodes, while sodium chloride was confined within the network, which is beneficial for the formation of interconnected channels during subsequent polymerization and salt extraction processes.

[0052] 2. Preparation of the polymerization mixture: 200g of acrylic acid was weighed into another stirred tank with a cooling jacket. A 30wt% sodium hydroxide aqueous solution was slowly added dropwise for neutralization control, resulting in a degree of acrylic acid neutralization of 70mol%. During neutralization, the system temperature was controlled to not exceed 35℃ using cooling water. After neutralization, a sodium acrylate-neutralized monomer solution was obtained, with a mass fraction of approximately 35wt% for acrylic acid and its salts.

[0053] After cooling the above-mentioned neutralized monomer solution to 25°C, it was mixed with the obtained ternary morphology-controlled precursor suspension under stirring, so that the mass ratio of acrylic acid solids to total solids of nanocellulose + silica + sodium chloride was approximately 100:25. The total solid content of the system was adjusted to 40 wt% by adding deionized water. Within this solid content range, the viscosity and heat release of the system during polymerization are under control, which is beneficial to maintaining the suspension distribution of sodium chloride in the liquid layer.

[0054] To the above mixture, 0.5 g of N,N'-methylenebisacrylamide was added as an internal crosslinking agent, with an amount equal to 0.25 wt% of the acrylic acid mass; 4 g of nano-silica with a particle size of approximately 80 nm was added as an inorganic filler, with an amount equal to 2 wt% of the acrylic acid mass; and 0.3 g of sodium persulfate and 0.15 g of sodium bisulfite were added to form a red oxygen initiation system, wherein the amount of sodium persulfate was 0.15 wt% of the acrylic acid mass and the amount of sodium bisulfite was 0.075 wt% of the acrylic acid mass. The mixture was stirred at 300 rpm for 15 min to ensure uniform dispersion of all components, resulting in a polymerization mixture.

[0055] 3. Controlled Thickness Polymerization in a Belt Reactor: The above-mentioned polymerization mixture is fed to the inlet of the belt reactor at a flow rate of approximately 1.0 kg / min, and the liquid layer thickness is controlled to 3 mm using a scraper. The bottom plate of the belt reactor is configured with three temperature zones along the conveying direction: an inlet zone, an intermediate zone, and an end zone. The temperature of the bottom plate in the inlet zone is controlled at 25°C, and the material resides in this zone for approximately 8 minutes for gentle heating and uniform prepolymerization. The temperature of the bottom plate in the intermediate zone is controlled at 47°C, with a residence time of approximately 15 minutes. Under these temperature and residence conditions, the acrylic acid crosslinking network gradually forms, the system viscosity is moderate, sodium chloride remains in good suspension, and the cellulose / silica skeleton begins to provide partial structural support. The temperature of the bottom plate in the end zone is controlled at 70°C, with a residence time of approximately 7 minutes, for completing the polymerization and internal crosslinking reactions.

[0056] When the temperature of the intermediate zone bottom plate is much lower than 40°C, the polymerization rate decreases significantly, the viscosity of the system increases slowly, and sodium chloride easily migrates to the bottom due to density differences. This results in salt enrichment in the lower layer and insufficient salt in the upper layer of the gel sheet, thus forming a non-uniform pore structure during subsequent salt extraction. When the temperature of the intermediate zone bottom plate is higher than 55°C, the polymerization and cross-linking rates accelerate significantly. In some areas, highly cross-linked gel clusters form before sodium chloride has fully migrated and distributed, locking sodium chloride within these local gel regions and causing the pores to be disconnected. In this embodiment, by controlling the temperature of the intermediate zone bottom plate at 47°C, the polymerization rate is matched with the migration rate of sodium chloride in the liquid layer, which is beneficial for forming a uniformly distributed salt crystal network that can be extracted subsequently.

[0057] Under the polymerization conditions described above in the belt reactor, the water-containing superabsorbent resin gel obtained at the end of the belt has a water content of approximately 60 wt%, and is in the form of a sheet-like soft gel. The internal structure has initially formed a three-dimensional network structure with cellulose / silica as the support and sodium chloride as the extractable phase.

[0058] 4. Segmented drying, semi-dry salt extraction, and pulverization and sieving: The above-mentioned water-containing superabsorbent resin gel is cut into sheets approximately 4 mm thick and laid flat on a perforated stainless steel tray. First, a first-stage drying process is carried out in a hot air drying oven at 50°C for 45 minutes, controlling the airflow rate at 0.5–1.0 m / s, reducing the moisture content of the gel sheets from approximately 60 wt% to approximately 38 wt%. Within this moisture content range, the gel network has a certain rigidity, maintaining its overall shape, while retaining sufficient internal moisture to allow sodium chloride to dissolve and migrate during the subsequent washing step.

[0059] The gel sheets dried in the first stage were immediately transferred to a 30°C water washing tank and sprayed with deionized water for 15 minutes. The spray intensity was controlled to maintain a liquid-to-solid volume ratio of approximately 8:1. The conductivity of the eluent was monitored online during the washing process, and washing was stopped when the conductivity stabilized. By weighing the soluble salt content in the gel before and after washing, the sodium chloride extraction rate was found to be approximately 90%. In this embodiment, salt extraction was performed in a semi-dry state with a water content of 35–45 wt%. This approach utilizes the partially cross-linked network and cellulose / silica framework to provide sufficient mechanical support, preventing the network from collapsing due to wet salt extraction. Furthermore, retaining a certain amount of moisture allows sodium chloride to maintain good diffusion and dissolution within the network, resulting in more continuous channels in three-dimensional space compared to complete drying before salt extraction.

[0060] After washing, the surface moisture of the gel sheet was drained and it was placed back into the perforated tray. The second stage of drying was carried out under hot air at 60°C for 60 minutes to reduce the moisture content of the gel sheet to about 12 wt%. During the drying process, the heating rate was controlled not to exceed 2°C / min to reduce the risk of internal moisture migration being hindered by the formation of a hard shell due to rapid surface drying.

[0061] The gel sheets, after the second stage of drying, were fed into a roller mill for pulverization. The roller gap was set to 0.5 mm, and the roller surface linear velocity was approximately 2.0 m / s, causing the gel sheets to be sheared and crushed into particles. The pulverized product was subjected to multi-stage sieving at 150 μm and 850 μm, collecting superabsorbent resin particles with a particle size of 150–850 μm. The content of micronized powder (particle size <150 μm) was determined to be approximately 5 wt%, and the median particle size D50 was approximately 350 μm. The average pore size of the obtained particles, measured by a pore size analyzer, was approximately 140 μm, with the pore size mainly concentrated in the range of 80–220 μm. The porosity was approximately 75%, and the pores were interconnected.

[0062] 5. Surface Crosslinking and Heat Treatment: To further improve the absorption capacity of the superabsorbent resin under load and maintain good liquid flow performance, this embodiment uses polyols and polycarboxylic acids as surface crosslinking agents to perform surface crosslinking treatment on the above-mentioned porous superabsorbent resin particles. Specifically, 0.5g of triethanolamine and 0.4g of citric acid were weighed and added to 9.1g of deionized water and 10g of isopropanol, and stirred and dissolved at room temperature to obtain a surface crosslinking agent solution with a solid content of approximately 8.3wt%.

[0063] Take 100g of porous superabsorbent resin particles obtained by crushing and sieving, place them in a liner-lined rotary drum, roll them at 10rpm at 35℃, and uniformly spray the above-mentioned surface crosslinking agent solution through a nozzle within 10min, so that the surface crosslinking agent is evenly distributed on the surface and near the surface of the particles.

[0064] After spraying, the moistened particles are immediately fed into a hot air circulating oven and subjected to segmented heat treatment according to the following temperature program: First, the particles are treated at 130°C for 15 minutes to promote further diffusion of the surface crosslinking agent on the particle surface; then, the temperature is raised to 170°C and held for 15 minutes to complete the esterification crosslinking reaction between the polyol and the polycarboxylic acid; finally, the temperature is raised to 190°C and held for 7 minutes to cure the surface crosslinking layer. After heat treatment, the particles are allowed to cool naturally to room temperature. If necessary, a small amount of agglomerated particles are removed by sieving, thus obtaining the fast-expanding high-fluid-passing superabsorbent resin of this embodiment, denoted as SAP-1.

[0065] Example 2: 15g of nanocellulose, approximately 25nm in diameter and 0.8μm in length, was weighed and added to 885g of deionized water. The mixture was stirred at 500rpm for 30min to obtain a nanocellulose slurry with a mass fraction of approximately 1.65wt%. 25g of silica sol, with a SiO2 solid content of 20wt% and a primary particle size of approximately 15nm, was added to the slurry, resulting in a nanocellulose to silica solid mass ratio of approximately 1:0.5. The pH was adjusted to 4.5 using dilute NaOH solution and dilute acetic acid. The mixture was stirred at 300rpm for 60min at 25℃, while ultrasonic dispersion was applied simultaneously. The ultrasonic power was 250W, the frequency was 25kHz, and the ultrasonic time was 20min, resulting in a cellulose / silica dispersion system. 4g of crystalline sodium chloride was slowly added to the system, making the mass of sodium chloride approximately 12wt% of the total mass of the nanocellulose and silica solids. During the addition process, the rotation speed was controlled at 300 rpm, and the mixture was stirred for 40 min at 25°C to obtain a ternary morphology-modifying precursor suspension of cellulose / silica / sodium chloride with low sodium chloride content.

[0066] In another reaction vessel, 200g of acrylic acid was weighed and neutralized by adding 30wt% sodium hydroxide aqueous solution to achieve a degree of neutralization of 65mol%. During the neutralization process, the system temperature was controlled to not exceed 30℃ by cooling, resulting in a neutralized monomer solution with a mass fraction of approximately 30wt% for acrylic acid and its salts. After cooling the neutralized monomer solution to 25℃, it was mixed with the obtained precursor suspension to achieve a mass ratio of acrylic acid solids to total solids of nanocellulose + silica + sodium chloride of approximately 100:16. Water was then added to adjust the total solid content of the system to 35wt%.

[0067] 0.3 g of N,N'-methylenebisacrylamide was added to the mixture as an internal crosslinking agent, at a dosage of 0.15 wt% of acrylic acid; 1 g of nano-silica with a particle size of approximately 50 nm was added as an inorganic filler, at a dosage of 0.5 wt% of acrylic acid; then 0.2 g of sodium persulfate and 0.1 g of sodium bisulfite were added, accounting for 0.1 wt% and 0.05 wt% of acrylic acid, respectively. The mixture was stirred at 250 rpm for 10 min to obtain a polymerization mixture with both solid and salt contents close to the lower limit.

[0068] The polymerization mixture is fed into the inlet of the belt reactor at a flow rate of 0.8 kg / min, and the liquid layer thickness is controlled to be 2 mm using a scraper. The bottom plate of the belt reactor is divided into three sections: the inlet zone, the intermediate zone, and the end zone. The temperature of the bottom plate in the inlet zone is controlled at 20°C, and the material residence time is approximately 10 min; the temperature of the bottom plate in the intermediate zone is controlled at 40°C, and the material residence time is approximately 15 min; the temperature of the bottom plate in the end zone is controlled at 65°C, and the material residence time is approximately 5 min, for a total residence time of approximately 30 min.

[0069] Under the above conditions, a highly absorbent resin gel with a water content of approximately 60 wt% was obtained upon exiting the belt. Because the temperature in the intermediate zone was at the lower limit of the range recommended by this invention and the sodium chloride content was low, the suspension stability of sodium chloride in the liquid layer was poor, and some salt crystals tended to settle downwards. The hydrogel was cut into sheets approximately 3 mm thick, laid on a perforated tray, and dried under hot air at 45°C for 60 minutes, reducing the gel water content from approximately 60 wt% to approximately 35 wt%.

[0070] The gel sheets, after the first stage of drying, were transferred to a water washing tank at 25°C and slowly rinsed with deionized water for 20 minutes at a liquid-to-solid volume ratio of approximately 10:1 to extract sodium chloride from the gel. Based on conductivity measurements and mass difference calculations, the sodium chloride extraction rate was approximately 85%.

[0071] The washed gel sheets were dried again under hot air at 50°C for 80 minutes to reduce the moisture content to about 10 wt%. They were then pulverized using a roller mill with a roller gap of 0.3 mm and a linear speed of 1.5 m / s, and sieved through a 150–850 μm sieve to collect highly absorbent resin particles within this size range. The micropowder content was measured to be approximately 8 wt%, designated SAP-2. The surface crosslinking steps were the same as in Example 1, except that the amount of triethanolamine was adjusted to 0.3 wt% and the amount of citric acid to 0.2 wt%. A heat treatment program of 120°C / 160°C / 180°C for 20 / 20 / 10 minutes was used to obtain the SAP-2 product.

[0072] Example 3: 25g of nanocellulose, approximately 40nm in diameter and 1.5μm in length, was weighed and added to 975g of deionized water. The mixture was stirred at 500rpm for 30min to obtain a nanocellulose slurry with a mass fraction of approximately 2.5wt%. 50g of silica sol, with a SiO2 solid content of 40wt% and a primary particle size of approximately 30nm, was added to the slurry, resulting in a nanocellulose to silica solid mass ratio of approximately 1:0.8. The pH was adjusted to 5.5 using dilute NaOH and dilute acetic acid. The mixture was stirred at 35℃ at 400rpm for 30min, while ultrasonic-assisted dispersion was applied at a power of 350W, a frequency of 35kHz, and a duration of 15min, resulting in a cellulose / silica dispersion system. 10g of crystalline sodium chloride was slowly added to the system, ensuring the sodium chloride mass was approximately 20wt% of the total mass of the nanocellulose and silica solids. During the addition process, the rotation speed was controlled at 500 rpm, and the mixture was stirred for 20 minutes at 35°C to obtain a ternary morphology-modifying precursor suspension with a high sodium chloride content.

[0073] Weigh 200g of acrylic acid and neutralize it to 75mol% in the presence of 30–40wt% sodium hydroxide aqueous solution. Control the temperature during neutralization to not exceed 35℃ to obtain a neutralized monomer solution with an acrylic acid and its salt mass fraction of approximately 45wt%. Cool the neutralized monomer solution to 25℃ and mix it with the precursor suspension, ensuring the mass ratio of acrylic acid solids to the total solids of nanocellulose + silica + sodium chloride is approximately 100:35. Adjust the total solids content of the system to 45wt% by reducing the amount of water added.

[0074] Add 0.7 g of N,N'-methylenebisacrylamide (0.35 wt% of acrylic acid) to the mixture, add 10 g of montmorillonite (5 wt% of acrylic acid) with a particle size of approximately 150 nm, then add 0.6 g of sodium persulfate (0.3 wt% of acrylic acid) and 0.4 g of sodium bisulfite (0.2 wt% of acrylic acid), and stir at 350 rpm for 20 min to obtain the polymerization mixture.

[0075] The polymerization mixture was fed into the inlet of the belt reactor at a flow rate of 1.5 kg / min, with the liquid layer thickness controlled at 4 mm. The bottom plate temperature of the belt reactor was set as follows: 25°C in the inlet zone, residence time approximately 7 min; 55°C in the middle zone, residence time approximately 18 min; and 75°C in the end zone, residence time approximately 5 min, for a total residence time of approximately 30 min. Due to the high total solids content and the high bottom plate temperature in the middle zone, the polymerization and crosslinking reaction rates were significantly increased. In some areas, highly crosslinked gel clusters formed before the sodium chloride was completely and uniformly distributed. Local salt crystals were "locked" in the highly crosslinked areas, resulting in a wider pore size distribution after subsequent salt extraction, with a considerable proportion of non-connected pores.

[0076] Gel with a moisture content of approximately 60 wt% was cut into sheets approximately 6 mm thick and laid on a perforated tray. It was dried at 55°C for 30 min to reduce the moisture content to approximately 45 wt%. The gel sheets were then transferred to a 35°C washing tank and sprayed with deionized water for 10 min at a liquid-to-solid volume ratio of 5:1 to extract sodium chloride from the gel, achieving a salt extraction rate of approximately 85%. The salt-extracted gel sheets were then dried again at 80°C for 40 min to reduce the moisture content to approximately 15 wt%. Subsequently, the gel was pulverized using a roller mill with a roller gap of 0.7 mm and a linear velocity of 3.0 m / s, and sieved through a 150–850 μm sieve to obtain highly absorbent resin particles with a particle size of 150–850 μm and a micron powder content of approximately 3 wt%, designated SAP-3.

[0077] The surface crosslinking agent solution was prepared as follows: 0.8 g (0.8 wt%) of triethanolamine, 0.6 g (0.6 wt%) of citric acid, 8.6 g of water and 10 g of isopropanol, with a solid content of approximately 12 wt%. 100 g of SAP-3 particles were rolled at 40°C and 15 rpm and sprayed with the above crosslinking agent solution for 10 min. Then, they were heat-treated sequentially at 140°C for 20 min, 180°C for 20 min, and 200°C for 10 min. After cooling, the SAP-3 finished product was obtained.

[0078] Comparative Example 1: Without using ternary morphology-modifying precursors, only salt pore formation was used.

[0079] Except for the following differences, the steps and process conditions in this comparative example are the same as in Example 1, and will not be repeated here:

[0080] Step S1 of Example 1 is not performed, and no nanocellulose or silica sol is added to the entire system.

[0081] Based on step S2 of Example 1, only the acrylic acid neutralizer, internal crosslinking agent and initiator are retained, and the addition of nanocellulose, silica and nanoSiO2 is removed.

[0082] Add 30g of crystalline sodium chloride directly to the neutralized monomer solution, so that the mass of sodium chloride is 15wt% of the mass of solid acrylic acid. Stir at 25℃ and 300rpm for 20min to disperse the sodium chloride as evenly as possible.

[0083] The total solids content of the system was adjusted to 40 wt% by adding water. Belt polymerization (S3), segmented drying and water washing for salt extraction (S4), crushing and sieving, and surface crosslinking (S5) were all the same as in Example 1.

[0084] Comparative Example 2: The preparation of the ternary morphology-controlled precursor, the preparation of the polymerization mixture, and the controlled thickness polymerization (S1, S2, S3) in this comparative example are all the same as in Example 1, except for the order of salt extraction and drying, which are different from Example 1.

[0085] The first-stage drying step in Example 1 is omitted, and the moisture content is not reduced to 35–45 wt%.

[0086] Aqueous superabsorbent resin gel sheets with a water content of approximately 60 wt% were directly transferred to a 30°C water washing tank and immersed in deionized water for 20 minutes. The liquid-to-solid volume ratio was approximately 8:1. Wet salt extraction was performed, with a salt extraction rate of approximately 90%.

[0087] After salt extraction, the product is directly dried under 60℃ hot air for 90 minutes to reduce the moisture content to approximately 12wt%, without distinguishing between the first and second stages of drying.

[0088] The crushing, sieving, and surface crosslinking steps are the same as in Example 1.

[0089] Comparative Example 3: The preparation of the ternary precursor, the preparation of the polymerization mixture, and the ribbon polymerization steps (S1, S2, S3) in this comparative example are all the same as in Example 1, except that the gel is completely dried before salt extraction, which is the reverse of the "semi-dry salt extraction" sequence in Example 1.

[0090] Gel sheets with a moisture content of about 60 wt% were continuously dried under hot air at 60°C for 120 min to reduce the moisture content to about 8 wt%, forming a relatively hard dry gel sheet.

[0091] The dried gel sheets were transferred to a 30°C water washing tank and immersed in deionized water for 30 min, with a liquid-to-solid volume ratio of approximately 10:1. Sodium chloride was extracted, with a salt extraction rate of approximately 80%. After salt extraction, the sheets were dried again at 60°C for 60 min to restore the moisture content to 10–12 wt%. The pulverization, sieving, and surface crosslinking conditions were the same as in Example 1.

[0092] The structural parameters and absorption properties of the superabsorbent resins obtained according to Examples 1-3 and Comparative Examples 1-3 were tested and evaluated according to the following methods:

[0093] Average pore size and pore size distribution: The porosity was determined using a mercury indentation porosimeter. Before testing, the resin particles were dried to constant weight at 60°C, and particle samples with a particle size of 150–850 μm were selected for testing.

[0094] The pore size-cumulative volume distribution curve obtained from the test is used to calculate the average pore size using a volume-weighted method, and the main pore size distribution range (the pore size interval corresponding to 80% volume fraction) is recorded.

[0095] Porosity: Calculated using the volume-mass method combined with mercury indentation results: The internal porosity (volume fraction) of the particles is obtained by measuring the ratio of the actual volume to the apparent volume of the dry resin particles.

[0096] Particle size distribution and micro powder content: The standard sieving method was used, and the pulverized resin was vibrated and sieved for 10 min using 150 μm and 850 μm standard sieves; the portion passing through the 150 μm sieve was weighed and the micro powder content was calculated; D10, D50 and D90 were calculated using cumulative distribution.

[0097] Free swelling and water absorption properties: Refer to the commonly used test methods for superabsorbent resins, and conduct free swelling tests in a 0.9wt% sodium chloride solution;

[0098] A certain mass m o Approximately 0.200 g of dry resin granules were placed in a water-permeable but granule-impermeable mesh bag and immersed in a sufficient amount of 0.9 wt% sodium chloride solution. The bag was removed after 60 s, 10 min, and 60 min, respectively. The surface free liquid was filtered off, and the wet mass m was measured. t ;

[0099] Water absorption ratio Q t =(m t -m o ) / m o ;

[0100] The average water absorption rate v in the first 60 seconds 60 Press Q 60 Calculate s / 1min (unit: g / g·min).

[0101] Water absorption performance under load (AUL): Following the AUL test protocol, the water absorption performance of 0.9wt% sodium chloride solution was tested under a vertical load of 0.3psi (approximately 2.07kPa).

[0102] A known mass of dry resin granules was evenly spread at the bottom of a standard test cylinder. Filter paper and a loading piston were placed on top, allowing the resin to contact the salt solution under a 0.3 psi load. The water absorption ratio (AUL) was recorded at 10 min and 60 min. 10 and AUL 60 .

[0103] Multiple injection and flow performance (gel bed breakthrough time): A certain mass of resin particles is packed into a transparent cylindrical container to form a particle bed with a height of about 3 cm. The particles are then wetted with a standard salt solution (0.9 wt% NaCl) and a stable gel bed is formed under an upper pressure of 0.3 psi.

[0104] A salt solution is injected from the top of the column at a constant volume Q (e.g., 50 mL) and a fixed injection rate. The time it takes for the liquid to penetrate the gel bed and flow out from the bottom is recorded as the first injection penetration time T1.

[0105] Repeat the injection process on the same gel bed for the second and third times, and record the corresponding breakthrough times T2 and T3 to evaluate the stability of the fluid flow under multiple injection conditions.

[0106] As shown in Table 1:

[0107]

[0108] Table 1 shows that the superabsorbent resin SAP-1 obtained in Example 1 of this invention exhibits a relatively balanced and excellent overall performance in terms of internal pore structure, initial water absorption rate, and liquid flow performance under multiple injection conditions. The average pore size of SAP-1 is approximately 140 μm, with the pore size mainly concentrated in the range of 80–220 μm, and the porosity is approximately 75%. Moreover, the pores are interconnected, which is attributed to the synergistic effect of processes such as the morphology-controlled precursor of nano-cellulose / silica / sodium chloride, the controlled thickness polymerization in the belt reactor, and the salt extraction under a semi-dry state with a water content of 35–45 wt%. Thanks to the aforementioned structural and process design, SAP-1 achieved an average water absorption rate of 18 g / g·min in the first 60 seconds in a 0.9 wt% sodium chloride solution, a water absorption ratio of 45 g / g after 10 minutes of free swelling, and an absorption ratio of 26 g / g after 10 minutes under a 0.3 psi load. In multiple injection and flow tests, the breakthrough time for the first injection was approximately 20 seconds, and the breakthrough time for the third injection was approximately 24 seconds, with minimal degradation in flow performance. This indicates that the present invention significantly improves flow stability under multiple injection and load conditions while balancing rapid expansion and high absorption capacity.

[0109] In contrast, Examples 2 and 3 correspond to the lower and upper limits of the process window parameters of the present invention, respectively, reflecting the sensitivity of key process parameters to pore structure and liquid flow performance. In Example 2, the total solids content was reduced to 35 wt%, the sodium chloride content in the ternary precursor was 12 wt%, and the bottom plate temperature in the middle zone of the belt reactor was 40°C, all close to the lower limit of the recommended range of the present invention. This resulted in insufficient suspension stability of sodium chloride in the liquid layer during polymerization, causing some salt crystals to settle. The pore structure formed after salt extraction was mainly composed of relatively small and poorly connected pores, with an average pore diameter of about 90 μm and a porosity of about 60%. Although the free swelling water absorption rate of SAP-2 can still reach 40 g / g, the water absorption rate drops to 14 g / g·min in the initial 60s. Under a load of 0.3 psi, the absorption rate is 24 g / g in 10min. In multiple injection and flow tests, the breakthrough time of the first injection is about 25s and the breakthrough time of the third injection is about 45s, indicating a significant decrease in flow performance. This suggests that if the sodium chloride content and the temperature of the intermediate zone are too low, it is difficult to form a highly interconnected porous structure that meets the requirements of this invention.

[0110] Example 3 uses a higher total solids content (45 wt%), a higher sodium chloride content (20 wt%), and a lower temperature in the intermediate zone (55°C), corresponding to the upper limit of the process window of this invention. At this point, the polymerization and crosslinking reaction rates are significantly accelerated. In some areas, highly crosslinked gel clusters form before the sodium chloride has fully migrated and evenly distributed. Some salt crystals are "locked" by locally highly crosslinked regions, resulting in a wider pore size distribution after salt extraction, with a certain proportion of non-connected pores. The average pore size of SAP-3 is approximately 170 μm, and the porosity is approximately 70%. Although the water absorption ratio after 10 minutes of free swelling can still reach 43 g / g, and the absorption ratio after 10 minutes under a 0.3 psi load is 25 g / g, the breakthrough time T3 after multiple injections has increased to 35–40 s, and the fluid flow performance is significantly lower than in Example 1. This indicates that if the solids content and the temperature in the intermediate zone are too high, although a larger pore size and higher overall porosity can be obtained, the fluid flow stability will still be affected under multiple injection conditions due to insufficient internal pore connectivity.

[0111] Comparative Example 1 did not prepare a ternary precursor of nanocellulose / silica / sodium chloride. Instead, 15 wt% sodium chloride was directly added to the acrylic acid neutralized monomer solution to create pores. Other polymerization, drying, salt removal, and surface crosslinking conditions were basically the same as in Example 1. The results showed that, due to the lack of a supporting framework constructed by nanocellulose and silica, the distribution of sodium chloride during polymerization was mainly affected by gravity and viscosity changes, making it difficult to form a stable three-dimensional network. The average pore size of the resin C1 obtained after salt removal was only about 80 μm, the porosity was about 55%, and the channels were mainly isolated pores with poor connectivity. Under the same test conditions, the average water absorption rate of C1 in the first 60 seconds was about 15 g / g·min, the water absorption ratio of free swelling in 10 minutes was about 42 g / g, and the absorption ratio of 10 minutes under a 0.3 psi load was about 23 g / g. However, the breakthrough time T3 of the third injection increased to about 60 seconds, and the liquid flow performance was significantly reduced. This indicates that it is difficult to achieve the goal of "controllable pore structure and interconnected pores" pursued by this invention by creating pores with sodium chloride alone without constructing a ternary precursor.

[0112] Comparative Example 2, under the same ternary precursor and ribbon polymerization conditions as Example 1, changed the timing of salt extraction. Specifically, salt extraction was performed directly while the gel was still wet with a moisture content of approximately 60 wt%, instead of extraction in a semi-dry state with a moisture content of 35–45 wt%. The results showed that during wet salt extraction, the rapid dissolution of salt caused localized shrinkage due to the insufficient mechanical support of the crosslinked network, leading to localized collapse of the gel structure. The average pore size of the resulting C2 resin after salt extraction was approximately 130 μm, with a porosity of approximately 65%, but the pore size distribution was uneven, with numerous irregular macropores and collapsed areas inside. Its initial water absorption performance (v... 60 and Q 10 Similar to Example 1, but in multiple injection and flow tests, T3 rose to 40–45 s, indicating that although wet salt extraction can obtain a certain amount of porosity, it cannot form a stable interconnected channel structure, and the flow stability is poor under multiple injections.

[0113] Comparative Example 3, using the same ternary precursor and polymerization conditions as Example 1, employed a "complete drying followed by salt extraction" process sequence. Specifically, the gel was first dried at 60°C to a water content of approximately 8 wt%, followed by water washing, salt extraction, and a second drying. In this process, a dense, hard shell easily formed on the gel surface. During salt extraction, water primarily penetrated along surface cracks and defects, restricting the dissolution channels of sodium chloride internally. The salt extraction process was accompanied by surface cracking and localized peeling. The resulting resin C3 after salt extraction had an average pore size of approximately 160 μm and a wide pore size distribution range (50–300 μm), with a porosity of approximately 68%. Although the overall porosity was not low, the salt extraction process, constrained by the hard surface shell and localized penetration paths, resulted in numerous non-connected cavities and poor pore connectivity. In multiple injection tests, the T3 of C3 was approximately 42–50 s, also exhibiting a significant decrease in fluid permeability.

[0114] In summary, the comparison results between Example 1 and Examples 2 and 3, as well as Comparative Examples 1 to 3, show that:

[0115] 1) The construction of the ternary morphology-regulating precursor of nanocellulose / silica / sodium chloride is the basis for the formation of interconnected pore networks. If sodium chloride is used as a pore-forming agent without the introduction of cellulose and silica framework, it is impossible to obtain a porous structure with both suitable average pore size and pore connectivity.

[0116] 2) The total solid content, liquid layer thickness and intermediate zone bottom plate temperature in the belt reactor need to be controlled within the window defined by this invention. When the solid content and intermediate zone temperature are too low or too high, the balance between the distribution of sodium chloride in the gel and the polymerization and crosslinking rate is disrupted, resulting in a smaller or uneven pore structure and a significant decrease in liquid flow performance.

[0117] 3) Salt extraction in a semi-dry state with a water content of 35–45 wt% is one of the key process steps of this invention. Wet salt extraction will damage the channels due to network collapse, while dry salt extraction will restrict the dissolution of salt due to the hard shell on the surface. Both are difficult to form a continuous and maintainable three-dimensional channel structure.

[0118] Therefore, this invention achieves the controllable construction of the porous structure inside superabsorbent resin particles through the synergistic design of steps such as ternary morphology-controlled precursor, controlled thickness polymerization, semi-dry salt extraction pore formation, and segmented surface crosslinking. This allows the resulting resin to maintain a high water absorption ratio while possessing a high initial expansion rate and significantly improved stability after multiple injections and flow cycles, overcoming the technical problem in the prior art that it is difficult to simultaneously achieve rapid expansion, high flow rate, and long-term stability of flow performance.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any ordinary changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a fast-expanding, high-fluidity liquid-type superabsorbent resin, characterized in that, Includes the following steps: S1. Preparation of morphology-modifying precursor: Nanocellulose is dispersed in water to obtain nanocellulose slurry. Silica sol and sodium chloride are added to the nanocellulose slurry to obtain a cellulose / silica / sodium chloride morphology-modifying precursor suspension. S2. Preparation of the polymerization mixture: After neutralizing the acrylic acid with alkali, it is mixed with the morphology-regulating precursor suspension, internal crosslinking agent, inorganic filler and initiator to obtain a polymerization mixture with a solid content of 35-45 wt%. S3. Polymerization: The polymerized mixture is conveyed to a belt reactor to form a liquid layer with a thickness of 2–4 mm. The conveyor belt speed of the belt reactor is controlled at 0.8–1.6 m / min. The inlet zone, middle zone and end zone are heated sequentially for 25–40 min, wherein the bottom plate temperature of the inlet zone is 20–25℃, the bottom plate temperature of the middle zone is 40–55℃ and the bottom plate temperature of the end zone is 65–75℃, to obtain a water-containing superabsorbent resin gel with a water content of 55–70 wt%. S4. Segmented drying, semi-dry salt extraction and pulverization and sieving: The water-containing superabsorbent resin gel is cut into sheets for the first stage of drying, so that the water content of the gel is reduced to 35-45 wt%. Sodium chloride is extracted by washing with water at this water content. Then, the second stage of drying, pulverization and sieving are carried out to obtain porous superabsorbent resin particles with an average pore size of 80-250 μm and interconnected pores. S5. Surface crosslinking: The porous superabsorbent resin particles are contacted with a surface crosslinking agent solution containing polyols and polycarboxylic acids, and subjected to segmented heat treatment at 120–200°C to obtain surface-crosslinked superabsorbent resin particles.

2. The method for preparing a fast-expanding, high-fluidity superabsorbent polymer according to claim 1, characterized in that, Step S1 includes: S11. Disperse nanocellulose in water to obtain nanocellulose slurry, wherein the mass fraction of nanocellulose is 1.5–2.5 wt%, the nanocellulose diameter is 20–50 nm, and the length is 0.5–2 μm; S12. Add silica sol with a particle size of 10–30 nm and a solid content of 20–40 wt% to the nanocellulose slurry, so that the mass ratio of nanocellulose to silica solid is 1:(0.5–1.0), adjust the pH to 4.5–5.5, stir at 25–35°C for 30–60 min, and simultaneously apply ultrasonic-assisted dispersion with an ultrasonic power of 200–400 W and a frequency of 20–40 kHz. S13. Slowly add sodium chloride solid to the system, so that the mass of sodium chloride is 10–25 wt% of the total mass of nanocellulose and silica solid, and stir at 300–500 rpm for 20–40 min to obtain a ternary morphology-modifying precursor suspension of cellulose / silica / sodium chloride.

3. The method for preparing a fast-expanding, high-fluidity superabsorbent polymer according to claim 2, characterized in that, Step S2 includes: S21. Use a 30–40 wt% sodium hydroxide aqueous solution to neutralize acrylic acid to a degree of neutralization of 65–75 mol%. The system temperature during the neutralization process does not exceed 35°C, resulting in a neutralized monomer solution with a monomer mass fraction of 25–45 wt%. S22. The neutralized monomer solution is mixed with the ternary morphology-modifying precursor suspension to achieve a mass ratio of acrylic acid solid to total solids of nanocellulose + silica + sodium chloride of 100:(16–35), and the total solid content is adjusted to 35–45 wt%. S23. Add N,N'-methylenebisacrylamide as an internal crosslinking agent, with an amount of 0.15–0.35 wt% of acrylic acid mass. Add nano-silica with a particle size of 50–200 nm as an inorganic filler, with an amount of 0.5–5 wt% of acrylic acid mass. Add an initiator, wherein sodium persulfate is used at an amount of 0.1–0.3 wt% of acrylic acid mass and sodium bisulfite is used at an amount of 0.05–0.2 wt% of acrylic acid mass. Stir for 10–20 min to obtain a homogeneous polymerization mixture.

4. The method for preparing a fast-expanding, high-fluidity superabsorbent polymer according to claim 3, characterized in that, In step S3: The polymerization mixture is fed into a belt reactor at a rate of 0.8–1.5 kg / min, with the liquid layer thickness controlled at 2–4 mm. The temperature of the substrate is controlled at 20–25℃ in the inlet zone, 40–55℃ in the middle zone, and 65–75℃ in the end zone, with a total residence time of 25–40 min, to obtain a water-containing superabsorbent resin gel with a water content of 55–70 wt%.

5. The method for preparing a fast-expanding, high-fluidity superabsorbent polymer according to claim 4, characterized in that, Step S4 includes: S41. Cut the water-containing superabsorbent resin gel with a water content of 55–70 wt% into sheets with a thickness of 3–6 mm, place them on a perforated tray, and dry them in hot air at 45–55℃ for 30–60 min to reduce the water content of the gel to 35–45 wt%. S42. Transfer the gel sheet dried in the first stage to a water washing tank at 25–35°C and spray or soak it with deionized water for 10–20 min. The liquid-to-solid volume ratio is 5–10:1 to extract sodium chloride from the gel. S43. After washing the gel sheet, dry it again under hot air at 50–80℃ for 40–80 min to reduce the water content to 10–18 wt%.

6. The method for preparing a fast-expanding, high-fluidity superabsorbent polymer according to claim 5, characterized in that, Step S4 also includes: S44. The gel sheets that have undergone the second stage of drying are fed into a roller mill for crushing, with a roller gap of 0.3–0.7 mm and a linear speed of 1.5–3.0 m / s. S45. The pulverized product is subjected to multi-stage sieving to collect superabsorbent resin particles with a particle size of 150–850 μm, of which the content of micro powder with a particle size of less than 150 μm is 3–10 wt%.

7. The method for preparing a fast-expanding, high-fluidity superabsorbent polymer according to claim 6, characterized in that, The surface crosslinking agent in step S5 includes triethanolamine and citric acid, wherein the amount of triethanolamine is 0.3–0.8 wt% of the mass of the superabsorbent resin particles, and the amount of citric acid is 0.2–0.6 wt% of the mass of the superabsorbent resin particles; the surface crosslinking agent is dissolved in a mixed solvent of water and isopropanol in a mass ratio of 1:1 to obtain a surface crosslinking agent solution with a solid content of 5–15 wt%.

8. The method for preparing a fast-expanding, high-fluidity superabsorbent polymer according to claim 7, characterized in that, Step S5 includes: S51. Place the porous superabsorbent resin particles in a rotary drum and roll them at a speed of 5–15 rpm under conditions of 30–40°C, and spray the surface crosslinking agent solution for 5–15 min. S52. The sprayed superabsorbent resin particles are heat-treated sequentially at 120–140℃ for 10–20 min, at 160–180℃ for 10–20 min, and at 180–200℃ for 5–10 min.

9. The method for preparing a fast-expanding, high-fluidity superabsorbent polymer according to claim 8, characterized in that, In step S1, the mass ratio of nanocellulose to silica solid is 1:(0.6–0.9), and the mass of sodium chloride is 15–20 wt% of the total mass of nanocellulose and silica solid; the power of ultrasonic-assisted dispersion is 250–350 W and the frequency is 25–35 kHz.

10. The method for preparing a fast-expanding, high-fluidity superabsorbent polymer according to claim 9, characterized in that, The porous superabsorbent resin particles have an average pore size of 100–200 μm and a porosity of 65–85%.

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