Bio-based super absorbent for dispersible sanitary napkins and preparation process of bio-based super absorbent

Abstract

The invention discloses a bio-based super absorbent for a dispersible sanitary towel and a preparation process of the bio-based super absorbent. The water absorbent is prepared by compounding functional polysaccharides such as sodium alginate, carboxymethylated pea protein, octenyl succinic starch ester and gellan gum with structured auxiliaries such as porous cyclodextrin polymer, nano kaolin, calcium hydrogen citrate and tartaric acid. The preparation process creatively adopts a pre-assembly dry method compounding and fluidized bed trigger type synchronous crosslinking-pore forming integrated technology, and the core is that calcium hydrogen citrate is utilized to synchronously generate CO and Ca in situ under the triggering of acid, and an ideal structure with gradient crosslinking core-shell and through open micropores is constructed by a one-step method. And the obtained product has the advantages of high water absorption rate, high multiplying power and strong pressure maintaining capability, and can be completely biodegraded.

Description

Technical Field

[0001] This invention relates to the field of hygiene products and biodegradable polymer materials, specifically to a bio-based superabsorbent for flushable sanitary napkins and its preparation process. Background Technology

[0002] With increasingly stringent global environmental regulations and a significant rise in consumer awareness of health and environmental protection, personal care products that combine functionality and environmental friendliness have become the mainstream of the industry. Among these, "fluffable and fully biodegradable" sanitary napkins, due to their ability to effectively address environmental problems caused by traditional products, such as solid waste landfill, pipe blockage, and microplastic pollution, have become a leading technological high ground in the transformation of feminine hygiene products. The core technological barrier to achieving this goal lies in its core component—the absorbent chip material. It must simultaneously meet four core performance indicators: "rapid absorption, high water retention, complete biodegradability, and biosafety," posing a severe challenge to existing material systems. Currently, the development of absorbent chip materials faces the following key bottlenecks, and their internal contradictions limit technological breakthroughs.

[0003] The environmental and safety hazards of mainstream petroleum-based superabsorbent polymers (SAPs) are prominent. The vast majority of sanitary napkins on the market rely on petroleum-based SAPs, represented by sodium polyacrylate, as their absorbent core. This material has inherent defects: (a) Non-biodegradability: Its stable polymer chains are difficult to decompose in the natural environment, which is the main reason why sanitary napkins become persistent solid waste, contradicting the environmentally friendly intention of being "flushable." (b) Potential health risks: Acrylic monomers that may remain during its synthesis process have been classified as Group 2B carcinogens (possibly carcinogenic to humans) by the International Agency for Research on Cancer, posing a safety hazard with long-term contact with sensitive skin areas. (c) High carbon footprint: Its raw material extraction and polymerization production processes are energy-intensive and generate large carbon emissions, which does not conform to the global trend of green and low-carbon development.

[0004] Traditional alternative bio-based absorbent materials suffer from severe performance deficiencies. To address environmental pressures, the industry has attempted to develop bio-based absorbents based on natural polysaccharides such as starch and cellulose. However, these first-generation products exhibit significant performance shortcomings: due to their reliance on simple physical blending or homogeneous chemical cross-linking processes, the materials cannot form a fine structure that effectively regulates water absorption, retention, and mechanical strength. Specifically: (a) Slow absorption rate: lacking rapid liquid-conducting channels, they struggle to cope with sudden bursts of liquid. (b) Low gel strength: the gel network formed after water absorption is fragile and easily damaged under pressure, leading to "re-seepage" or a sharp drop in "water retention," i.e., poor pressure retention. (c) Overall performance is substandard: Its key indicators such as absorbency (<20g / g) and pressure absorption capacity (<10 g / g) generally fail to meet the requirements of the national recommended standard GB / T 22875-2018 Super absorbent resin for diapers and sanitary napkins, and it is even more unable to compete with petroleum-based SAP (absorbency can reach 30-50 g / g, pressure absorption capacity >20 g / g), thus making it difficult to achieve commercial application.

[0005] Current bio-based material synthesis processes generate secondary pollution, violating the principles of green manufacturing. Current research on improving the performance of bio-based absorbent materials largely follows the solution polymerization or wet crosslinking processes of petroleum-based SAPs. To increase the degree of crosslinking, toxic organic crosslinking agents such as N,N'-methylenebisacrylamide (MBA) are often introduced. This process inevitably generates wastewater containing unreacted monomers, organic crosslinking agents, and high salinity, resulting in high treatment costs and significant environmental pollution. Furthermore, the traditional solution polymerization-precipitation-washing-drying process is cumbersome and energy-intensive, failing to meet the principles of clean production and a circular economy. This "solving one type of pollution may generate another" approach significantly diminishes the environmental value of bio-based materials.

[0006] In summary, existing technologies struggle to achieve synergy across the four dimensions of "environmental friendliness, safety, high performance, and green processes," resulting in a "one-sided approach" dilemma. The market and industry urgently need a solution: not only to achieve fully bio-based and completely biodegradable raw materials, but also to achieve precise control at the molecular and microstructural levels through material design and manufacturing processes. This would allow for the production of high-performance bio-based superabsorbent polymers that outperform petroleum-based products while maintaining a truly green and environmentally friendly production process. This is not only crucial for developing flushable sanitary napkins but also a core technological challenge driving the entire absorbent hygiene products industry towards sustainable development. Summary of the Invention

[0007] This invention provides a bio-based superabsorbent for flushable sanitary napkins and its preparation process to solve the problems mentioned in the background art.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, a bio-based superabsorbent for flushable sanitary napkins, comprising, by weight, the following raw materials: 60-75 parts of functionalized natural polysaccharides and 25-40 parts of structuring agents; wherein the functionalized natural polysaccharides include 35-50 parts of sodium alginate, 5-12 parts of carboxymethylated pea protein, 8-15 parts of octenyl succinate starch ester, and 2-5 parts of low-acyl gellan gum; wherein the structuring agents include 10-18 parts of porous cyclodextrin polymer, 8-12 parts of nano-calcined kaolin, 1.5-3 parts of dicalcium citrate, and 0.5-1.5 parts of L-tartaric acid.

[0009] The sodium alginate has a viscosity of 400-600 mPa·s (1% aqueous solution, 25℃), the carboxymethylated pea protein has a degree of carboxymethyl substitution of 0.05-0.12, and the nano-sized calcined kaolin has a particle size of 800-1250 mesh.

[0010] This invention provides a high-performance bio-based superabsorbent based on multi-component synergistic action and biomimetic structural design. By weight, it consists of precisely proportioned functionalized natural polysaccharides (60-75 parts) and structural additives (25-40 parts). Through the complementarity and synergistic effect of each component, a unique "core-shell-pore" composite structure is constructed for the absorbent. The functionalized natural polysaccharide system constructs a multi-layered, highly resilient three-dimensional hydrophilic network. This system aims to mimic the liquid absorption and water-locking mechanisms of natural tissues, achieving full-process control from rapid swelling to stable water locking through precise compatibility of different polysaccharides and proteins.

[0011] Sodium alginate (35-50 parts): serves as the anionic backbone and main crosslinking point of the system. Its molecular chain is rich in guluronic acid (G) units, which can undergo specific and high-strength "egg-box" coordination crosslinking with calcium ions (Ca²⁺). This is the basis for forming the initial gel framework and providing the final gel rigidity. This invention preferably uses a medium viscosity product with a viscosity of 400-600 mPa·s (1% aqueous solution, 25°C). This viscosity range ensures good processing flowability while providing a suitable molecular chain length, ultimately endowing the gel with excellent toughness and shape retention, avoiding excessive brittleness.

[0012] Carboxymethylated pea protein (5-12 parts): Innovatively introduced as a network enhancer and elasticity regulator. Through controlled partial hydrolysis and carboxymethylation modification of pea protein, carboxyl functional groups capable of crosslinking with Ca²⁺ are introduced while retaining the physical entanglement ability of the protein macromolecular chains. This component plays a dual role: on the one hand, its flexible long chains, like "molecular springs," interweave within the rigid network of sodium alginate, significantly absorbing stress through entanglement and hydrogen bonding, greatly enhancing the overall elasticity, tear resistance, and structural integrity of the gel after repeated liquid absorption; on the other hand, the introduced additional carboxyl groups increase the crosslinking density and, due to the amphiphilic nature of proteins, help improve the swelling stability of the gel in saline.

[0013] Octenyl succinate starch ester (8-15 parts): This acts as a hydrophobic association point and internal hydrophobic modifier. This chemically modified starch incorporates both hydrophobic octenyl groups and hydrophilic carboxyl groups into its molecular chain. Within the gel network, its hydrophobic segments undergo reversible hydrophobic association, forming dynamic physical cross-linking points. This not only effectively reduces the stickiness of the gel surface after water absorption and improves dryness, but also dissipates energy through association and dissociation under pressure, enhancing its compressive strength. Furthermore, this moderate internal hydrophobicity effectively inhibits excessive swelling of the gel in electrolyte solutions, improving its practical water retention capacity in simulated body fluid environments.

[0014] Low-acyl gellan gum (2-5 parts): Serves as a gel synergist and heat stabilizer. In the presence of calcium ions, low-acyl gellan gum exhibits a strong positive synergistic gelling effect with sodium alginate. It forms a denser secondary network around the sodium alginate-Ca²⁺ "egg carton" structure, resulting in a more uniform and dense gel structure and significantly improved mechanical strength. Crucially, the resulting gel possesses excellent thermal reversibility, maintaining a more stable network structure and water retention capacity at higher temperatures (such as 37°C or higher, close to body temperature), which is essential for the performance of sanitary napkins in practical use.

[0015] Structured additive system: Constructing intelligent carriers and triggering in-situ structural molding. The core of this system is to pre-construct a reactive "microstructural unit" and precisely trigger it in the final step to achieve synchronous and controllable construction of pore size and cross-linking network.

[0016] Porous cyclodextrin polymer (10-18 parts): As a molecular encapsulation and sustained-release carrier. The porous cyclodextrin polymer, prepared through cross-linking, possesses nanocavities with tunable internal and external hydrophilic / hydrophobic properties. Its main function is to act as a "micro-reaction warehouse," selectively encapsulating or adsorbing fine particles of calcium citrate into its cavities and pores during the pretreatment stage. This not only achieves high dispersion of reactants but, more importantly, enables control over the rate and initiation position of subsequent acid-triggered reactions through spatial confinement effects, preventing explosive polymerization and ensuring uniformity of pore formation and cross-linking.

[0017] Nanoscale calcined kaolin (8-12 parts, particle size 800-1250 mesh): used as a nano-reinforcing and rheology modifier filler. After high-temperature calcination, the kaolin loses its water of crystallization, increasing its activity and exhibiting a regular, sheet-like nanostructure. Its functions include: (a) Nano-reinforcing: The sheet-like particles dispersed in the polysaccharide matrix can effectively inhibit the propagation of microcracks, improving the mechanical strength and dimensional stability of the composite material; (b) Surface activity: Its exposed aluminum hydroxyl groups can weakly interact with the oxygen-containing functional groups on the polysaccharide chains, providing additional physical crosslinking points; (c) Processing aid: Its good flowability helps improve the processing performance of powders or pastes during mixing and granulation.

[0018] Calcium hydrogen citrate (1.5-3 parts): This serves as the core "integrated reaction source" of this invention. This substance innovatively integrates the crosslinking agent precursor (Ca²⁺) and the pore-forming agent precursor (CO₃²⁻ / HCO⁻) into the same molecule. In the final process step, when triggered by an externally introduced acid (H⁺), it decomposes, releasing Ca²⁺ and CO₂ gas in situ, synchronously, and equimolarly. This design achieves: ① Synergistic reaction: Perfect temporal and spatial matching between gas expansion pore-forming and ionic crosslinking pore-forming; ② Structural gradient: The reaction occurs progressively from the particle surface to the interior, naturally forming a "gradient shell" structure with decreasing crosslinking density from the outside to the inside; ③ Process controllability: The reaction rate can be precisely controlled by the acid concentration and contact method, avoiding excessive surface crosslinking and hardening.

[0019] L-Tartaric Acid (0.5-1.5 parts): Serves as a mild reaction trigger and pH adjuster. L-Tartaric acid, a natural organic acid, was chosen because of its moderate acidity and the mild, controllable rate of decomposition of calcium citrate. Preparing it as a dilute solution for atomization ensures uniform contact with the particle surface in the form of fine droplets, gradually penetrating and triggering the internal reaction. This allows for precise control over the reaction depth and uniformity, while simultaneously stabilizing the pH of the reaction system within a suitable range for polysaccharide cross-linking.

[0020] Through the synergistic design of the above raw material system, this invention lays the material foundation for the subsequent "pre-assembly-triggered reaction" preparation process. The ultimate goal is to obtain a high-performance product that integrates high-speed water absorption, high water retention, high pressure retention and complete biodegradability.

[0021] Secondly, a preparation process for a bio-based superabsorbent includes the following steps: 1) Preparation of structured carrier core: Dicalcium citrate, porous cyclodextrin polymer and nano-calcined kaolin are mixed and sprayed into an ethanol aqueous solution containing dispersant. The mixture is activated at 45-50℃ and then dried at 85-90℃ until the water content is <3% to obtain carrier core powder. 2) Gradient precision mixing: The carrier core powder, sodium alginate, carboxymethyl pea protein, octenyl succinate starch ester, and low-acyl gellan gum are sequentially added to a dual-motion mixer and mixed at a gradient speed to obtain composite functional dry powder. 3) Continuous low-temperature kneading: The composite functional dry powder is passed through a twin-screw extruder kneader, and ice-cold deionized water at 4-8℃ is injected within the range of 45-58℃. The mixture is kneaded for 2-3 minutes at a speed of 150-250 r / min to form a reaction precursor paste. 4) Combined drying and granulation: The reaction precursor paste is rapidly dried by microwave, and then dried by segmented hot air until the moisture content is ≤5% to form porous brittle flakes, which are then crushed to obtain primary granules; 5) Screening and shaping: Screen the primary particles and collect 40-100 mesh particles as raw material D; 6) Fluidized bed triggered reaction: Raw material D is preheated and fluidized in a fluidized bed with gas at 105-115℃; L-tartaric acid is prepared into a 3-5% aqueous solution, which is then sprayed into the fluidized bed after ultrasonic atomization, and the bed temperature is controlled at 118-128℃; Tartaric acid triggers the decomposition of calcium citrate in the particles, and CO2 is generated simultaneously to create pores and Ca²⁺ crosslinking reaction; After the reaction, drying and cooling are continued to obtain the finished product.

[0022] The mass of the ice-deionized water injected in step 3) is 1.8-2.2 times the mass of the composite functional dry powder.

[0023] In step 4), the power density of microwave drying is 1.0-2.0 W / g, and the time is 2-4 minutes; the temperatures of the three zones of segmented hot air drying are 90±5℃, 80±5℃, and 70±5℃, respectively.

[0024] In step 6), the fluidized bed uses ultrasonic atomization with a frequency of 1.5-2.5 MHz, and the resulting droplet size D50 is less than 30 μm.

[0025] Thirdly, the application of a bio-based superabsorbent in the preparation of washable sanitary napkins, high-end wound dressings, medical care pads, environmentally friendly diapers, fresh food preservation materials, or pet hygiene products.

[0026] The advantages of this invention over the prior art are as follows: 1. Breakthrough in Material Performance. This invention successfully constructs a biomimetic composite structure with a "gradient cross-linked core-shell" and "through-hole open micropores." This synergistic structure endows the product with superior liquid absorption performance: Ultra-high-speed absorption: Abundant internal through-hole micropores form a capillary network, enabling instantaneous liquid conduction and rapid absorption, quickly responding to surges. Ultra-high absorption rate and water retention: The high charge density polysaccharide network and intelligent microporous structure work together to achieve a high water absorption rate and significantly increase centrifugal water retention. Excellent pressure resistance and liquid retention: The "protein-enhanced network" and "dynamic hydrophobic association" mechanism enable the hydrogel to exhibit excellent elasticity and structural resilience under pressure, effectively solving the problem of backflow during use. Excellent environmental stability: Thanks to the synergistic effect of gellan gum and the hydrophobically modified starch, the product maintains high water retention and gel integrity in simulated body temperature environments (approximately 37°C) and electrolyte-containing liquids, broadening its application boundaries.

[0027] 2. The production process fully implements green chemistry, achieving a win-win situation for both economic and environmental benefits. The process design of this invention eliminates pollution at the source and significantly improves energy efficiency: Intrinsically safe and non-toxic: The entire production chain completely eliminates toxic organic crosslinking agents such as N,N'-methylenebisacrylamide and any organic solvents required by traditional processes, eliminating the risk of residual and contact with toxic and harmful substances at the source. Near-zero wastewater discharge: The innovative use of "dry compounding" and "low-temperature precision kneading" technologies ensures that most of the water added in the process is effectively combined into the product structure, resulting in no high-salt, high-COD process wastewater and completely solving the wastewater treatment problem in the production of bio-based materials. Significantly reduced overall energy consumption: The use of microwave-hot air combined drying technology utilizes the volumetric heating characteristics of microwaves to quickly remove internal moisture, saving approximately 40% more energy than traditional conductive drying; the unique fluidized bed synchronous crosslinking-pore-forming integrated technology combines the three separate steps of crosslinking, pore-forming, and drying in traditional processes into one continuous step, resulting in extremely high thermal energy utilization efficiency and significantly reduced production costs. The process is precise and controllable, resulting in excellent product consistency: From the preparation of the "prestructured carrier core" to gradient mixing, continuous twin-screw kneading, and finally ultrasonic atomization-triggered reaction, the entire process achieves digital parameter digitization and precise control. This ensures that different batches of products have excellent uniformity and stability in particle size distribution, reaction degree, and performance indicators (inter-batch RSD < 3%), fully meeting the requirements of large-scale, high-end production.

[0028] 3. Innovation in core raw materials and reaction mechanisms builds a solid technological barrier. High-end and functionalized raw materials: For the first time, carboxymethylated pea protein was introduced into the water-absorbing material system. Utilizing its unique dual characteristics of "flexible long-chain entanglement" and "ionic cross-linking sites," it revolutionarily improves gel toughness. Porous cyclodextrin polymers were selected as intelligent carriers, achieving nanoscale dispersion and controlled release of reactants. Original breakthrough in reaction mechanism: Calcium citrate was creatively used as an "integrated intelligent reaction source," which can release Ca²⁺ (cross-linking agent) and CO2 (pore-forming agent) in situ, synchronously, and equimolarly through external mild acid triggering. This mechanism achieves spatiotemporal self-coordination of pore-forming and pore-solidifying reactions, which is the core key and fundamental guarantee for obtaining the ideal "pore-shell" structure, forming an insurmountable technological barrier.

[0029] 4. Significantly enhanced product safety and added value. All major raw materials (sodium alginate, pea protein, cyclodextrin, gellan gum, dicalcium citrate, tartaric acid) meet food-grade or pharmaceutical excipient-grade standards. The product exhibits excellent biocompatibility and has passed relevant toxicological tests, meeting the highest safety requirements for prolonged contact with skin and wounds. This gives the product a competitive advantage in the high-end medical and personal care sectors, as well as brand premium capabilities.

[0030] 5. Significantly expanded application scenarios and broad market prospects. Based on its superior performance and absolute safety and environmental protection characteristics, this product breaks through the application limitations of traditional absorbent materials: Core applications: Perfectly suited for next-generation environmentally friendly sanitary napkins, panty liners, and diapers with mandatory requirements for flushability and biodegradability. High-end medical applications: Can be directly used in high-end wound dressings, surgical drapes, and incontinence pads that require rapid absorption and locking of large amounts of exudate and demand extremely high biocompatibility. Specialty fields: Can be expanded to areas such as highly absorbent padding materials for food preservation, humectants for cold chain transportation, and environmentally friendly industrial dehydration and oil-water separation materials.

[0031] This invention not only provides a high-performance product, but also offers a complete technical solution for the entire absorbent hygiene products and biomaterials industry to upgrade towards high performance, full degradation, and green manufacturing, possessing enormous market potential and social value. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The following description of at least one exemplary embodiment is illustrative in nature and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0034] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of components and steps set forth in these embodiments do not limit the scope of the invention. Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as exemplary and not as limiting. Therefore, other examples of exemplary embodiments may have different values. Example 1

[0035] A bio-based superabsorbent for flushable sanitary napkins, with a total raw material ratio of 100 kg, includes functionalized natural polysaccharides and structural additives. The functionalized natural polysaccharides (total 60 kg) are: sodium alginate: 35.0 kg (viscosity 400 mPa·s, 1% aqueous solution, 25℃), carboxymethylated pea protein (degree of substitution 0.05): 5.0 kg, octenyl succinate starch ester: 8.0 kg, and low-acyl gellan gum: 2.0 kg. The structural additives (total 25 kg) are: porous β-cyclodextrin polymer (specific surface area ≥200 m² / g): 10.0 kg, nano-calcined kaolin (800 mesh): 8.0 kg, calcium dicalcium citrate (food grade): 1.5 kg, and L-tartaric acid: 0.5 kg. Processing auxiliary materials: Ethanol aqueous solution (ethanol:water = 1:3, containing 0.1% lecithin): about 2.5 kg (for step 1); Ice-cold deionized water (4°C): about 90 kg (for step 3, based on 1.8 times the dry powder mass).

[0036] A process for preparing a bio-based superabsorbent includes the following steps: Step 1 (Structured Carrier Core): Calcium dicalcium citrate, cyclodextrin polymer, and kaolin are fed into a high-speed mixer equipped with a jacketed heating and spraying device, and mixed at 80 r / min. 2.5 kg of ethanol-water solution is atomized and sprayed into the mixture through the spraying device. The jacket steam is activated to mix and activate the materials at 45°C for 15 minutes. This process partially embeds the fine particles of calcium dicalcium citrate within the cyclodextrin cavities and kaolin layers, achieving uniform pre-wetting and bonding of the components. The pre-structured material is transferred to a disc dryer and dried under hot air at 85°C for 15 minutes to obtain a dry, loose carrier core powder with reactive potential and a moisture content of 2.5%.

[0037] Step 2 (gradient mixing): Mix all the carrier core powders obtained in Step 1 with sodium alginate at low speed (20 r / min revolution, 60 r / min rotation) for 5 minutes in a dual-motion mixer. Then add pea protein, modified starch, and gellan gum in sequence, and mix at higher speed (30 r / min revolution, 100 r / min rotation) for 12 minutes to obtain the composite dry powder.

[0038] Step 3 (Continuous Kneading): The compound dry powder is passed through a twin-screw kneader. The temperatures of each zone of the twin-screw are set as follows: Zone 1 45℃, Zone 2 55℃, Zone 3 58℃, and Zone 4 55℃. The screw speed is 150 r / min. 90 kg of 4℃ ice water is injected through a precision liquid pump. The low-temperature water addition aims to slow down the excessive swelling of polysaccharides and ensure more uniform mixing. The material is held for about 2 minutes. During this process, the material undergoes high shear, mixing, and compression to form a highly homogeneous, semi-dry reaction precursor paste at 58℃ with a moisture content of approximately 45%.

[0039] Step 4 (Combined Drying and Granulation): The precursor paste is evenly spread on a Teflon-coated mesh conveyor belt to a thickness of 5 mm. It is then microwave-dried (power density 1.0 W / g). Microwaves penetrate the material, causing water molecules to vibrate rapidly and generate heat, resulting in rapid and uniform heating and the creation of internal vapor pressure, initially forming internal channels. This stage takes 2 minutes. Afterwards, the material enters a segmented hot air drying section: the first zone has a hot air temperature of 90℃, the second zone 80℃, and the third zone 70℃. The conveyor belt speed is adjustable, keeping the total drying time within 15 minutes. The final output material is porous, brittle flakes with a moisture content of 4.8%. These flakes, with suitable brittleness, are then lightly crushed by a roller crusher to obtain primary granules.

[0040] Step 5 (Sieving and Shaping): Primary particles are conveyed by pneumatic conveying to a multi-stage planar rotary screen. The screen configuration is: upper layer 12 mesh, middle layer 40 mesh, and lower layer 100 mesh. Particles that pass through the 40 mesh screen but are retained on the 100 mesh screen (raw material D) are collected. These particles have a uniform size (150-380 μm) and good flowability, making them ideal for fluidized bed feed. Overly coarse particles are returned to crushing, while overly fine particles can be incorporated into the kneading process as return material. The target particle size yield is 95.1%.

[0041] Step 6 (Fluidized Bed Triggered Reaction): Introduce dehumidified and preheated nitrogen gas to 105°C, controlling the gas flow rate to achieve a stable "rapid fluidization" state in the bed; the empty tower gas velocity is 1.2 m / s. Preheat for 3 minutes, with the particles preheated and fluidized in the fluidized bed at 105°C nitrogen gas (empty tower gas velocity 1.2 m / s) for 3 minutes. Allow the particle temperature to rise uniformly to 100-110°C, activating surface reactivity. Dissolve L-tartaric acid in deionized water to prepare a 3% (w / w) dilute acid solution at 25°C. Atomize using a high-pressure peristaltic pump and ultrasonic atomizing nozzle at a frequency of 1.5 MHz, producing extremely fine (D50 < 20 μm) and uniform acid mist droplets. Initiate ultrasonic atomization to uniformly introduce the acid mist into the fluidized bed system from multiple points in the center. The key reaction occurs: the acid mist droplets contact and penetrate the surface and shallow layer of the preheated particles. The acid (H⁺) reacts with the calcium dicalcium citrate pre-embedded inside the particles: Calcium dicalcium citrate + H⁺ → Ca²⁺ + citric acid + CO₂↑ + H₂O. This reaction produces two key substances in situ and simultaneously: 1) CO₂ gas: generated inside the particles. Because the material is above the semi-molten glass transition temperature, the gas "expands" the polysaccharide network, forming interconnected open micropores. 2) Ca²⁺: released on the particle surface and near the pore walls, immediately undergoing ionic cross-linking with the carboxyl groups of sodium alginate and gellan gum, forming a gradient-distributed, dense cross-linked network (shell). The bed temperature in the reaction zone is precisely controlled at 118℃. At this temperature, the polysaccharide segments have sufficient mobility to form a good network, while moisture evaporates rapidly, fixing the newly formed structure. The atomization process lasts for 6 minutes. After completion, maintaining the fluidization state and temperature, drying continues for 4 minutes to thoroughly remove residual moisture and reaction byproducts, completing structural fixation. The product is cooled to below 40°C by the built-in fluidized bed cooling section and collected by a high-efficiency cyclone separator to obtain the final high-performance bio-based superabsorbent product. Example 2

[0042] A bio-based superabsorbent for flushable sanitary napkins, with a total raw material ratio of 100 kg, includes functionalized natural polysaccharides and structural additives. The functionalized natural polysaccharides (total 65 kg) are: sodium alginate: 42.0 kg (viscosity 500 mPa·s, 1% aqueous solution, 25℃), carboxymethylated pea protein (degree of substitution 0.08): 8.0 kg, octenyl succinate starch ester: 12.0 kg, and low-acyl gellan gum: 3.0 kg. The structural additives (total 26.5 kg) are: porous β-cyclodextrin polymer (specific surface area >300 m² / g): 13.0 kg, nano-calcined kaolin (1250 mesh): 10.0 kg, calcium dicalcium citrate (food grade): 2.5 kg, and L-tartaric acid: 1.0 kg. Processing additives: Ethanol aqueous solution (ethanol:water = 1:4, containing 0.1% polysorbate-80): about 2.7 kg (for step 1), ice-cold deionized water (6°C): about 130 kg (for step 3, based on 1.95 times the dry powder mass).

[0043] A process for preparing a bio-based superabsorbent includes the following steps: Step 1 (Structured Carrier Core): Calcium dicalcium citrate, cyclodextrin polymer, and kaolin were added to a high-speed mixer equipped with a jacketed heating system and a spraying device. The mixture was stirred at 100 r / min, and 2.7 kg of an ethanol-water solution was atomized and sprayed into the mixture through the spraying device. The jacket steam was activated to mix and activate the materials at 48°C for 18 minutes. This process partially embedded the fine particles of calcium dicalcium citrate within the cyclodextrin cavities and kaolin layers, achieving uniform pre-wetting and bonding of the components. The pre-structured material was transferred to a disc dryer and dried under hot air at 88°C for 17 minutes to obtain a dry, loose carrier core powder with reactive potential and a moisture content of 2.8%.

[0044] Step 2 (gradient mixing): Mix all the carrier core powders obtained in Step 1 with sodium alginate at low speed (20 r / min revolution, 60 r / min rotation) for 5 minutes in a dual-motion mixer. Then add pea protein, modified starch, and gellan gum in sequence, and mix at higher speed (30 r / min revolution, 100 r / min rotation) for 20 minutes to obtain composite dry powder.

[0045] Step 3 (Continuous Kneading): The compound dry powder is passed through a twin-screw kneader. The temperatures of each zone of the twin-screw are set as follows: Zone 1 45℃, Zone 2 55℃, Zone 3 58℃, and Zone 4 55℃. The screw speed is 200 r / min, and 130 kg of 6℃ ice water is injected through a precision liquid pump. The low-temperature water addition aims to slow down the excessive swelling of polysaccharides and ensure more uniform mixing. The material is held for about 2.5 minutes. During this process, the material undergoes high shear, mixing, and compression to form a highly homogeneous, semi-dry reaction precursor paste at 59℃ with a moisture content of approximately 48%.

[0046] Step 4 (Combined Drying and Granulation): The precursor paste is evenly spread on a Teflon-coated mesh conveyor belt to a thickness of 6 mm. It is then microwave-dried (power density 1.5 W / g). Microwaves penetrate the material, causing water molecules to vibrate rapidly and generate heat, resulting in rapid and uniform heating and the creation of internal vapor pressure, initially forming internal channels. This stage takes 3 minutes. The material then enters a segmented hot air drying section: zone 1 hot air temperature 90℃, zone 2 80℃, and zone 3 70℃. The conveyor belt speed is adjustable, keeping the total drying time within 22 minutes. The final output material is porous, brittle flakes with a moisture content of 4.5%. These flakes, with suitable brittleness, are then lightly crushed by a roller crusher to obtain primary granules.

[0047] Step 5 (Screening and Shaping): Primary particles are conveyed by pneumatic conveying to a multi-stage planar rotary screen. The screen configuration is: upper layer 12 mesh, middle layer 40 mesh, and lower layer 100 mesh. Particles that pass through the 40 mesh screen but are retained on the 100 mesh screen (raw material D) are collected. These particles have a uniform size (150-380 μm) and good flowability, making them ideal for fluidized bed feed. Overly coarse particles are returned to crushing, while overly fine particles can be incorporated into the kneading process as return material. The target particle size yield is 97.2%.

[0048] Step 6 (Fluidized Bed Triggered Reaction): Nitrogen gas, dehumidified and preheated to 110°C, is introduced. The gas flow rate is controlled to achieve a stable "rapid fluidization" state in the bed, with an empty tower gas velocity of 1.4 m / s. Preheating for 3.5 minutes ensures the particle temperature rises uniformly to 100-110°C, activating surface reactivity. L-tartaric acid is dissolved in deionized water to prepare a dilute acid solution with a mass concentration of 4% and a temperature of 25°C. Atomization is performed using a high-pressure peristaltic pump and an ultrasonic atomizing nozzle at a frequency of 1.8 MHz, producing extremely fine (D50 < 20 μm) and uniform acid mist droplets. Ultrasonic atomization is initiated, uniformly introducing the acid mist into the fluidized bed system from multiple points in the center. The key reaction occurs: the acid mist droplets contact and penetrate the preheated particle surface and shallow layer. The acid (H⁺) reacts with the calcium dicalcium citrate pre-embedded inside the particles: Calcium dicalcium citrate + H⁺ → Ca²⁺ + citric acid + CO₂↑ + H₂O. This reaction produces two key substances in situ and simultaneously: 1) CO₂ gas: generated inside the particles. Because the material is above the glass transition temperature (semi-molten), the gas "expands" the polysaccharide network, forming interconnected open micropores. 2) Ca²⁺: released on the particle surface and near the pore walls, immediately undergoing ionic cross-linking with the carboxyl groups of sodium alginate and gellan gum, forming a densely cross-linked network (shell) with a gradient distribution. The bed temperature in the reaction zone is precisely controlled at 125℃. At this temperature, the polysaccharide segments have sufficient mobility to form a good network, while moisture evaporates rapidly, fixing the newly formed structure. The atomization process lasts for 8 minutes. After completion, the fluidized state and temperature are maintained, and drying continues for 5 minutes to thoroughly remove residual moisture and reaction byproducts, completing the structural fixation. The product is cooled to below 40°C by the built-in fluidized bed cooling section and collected by a high-efficiency cyclone separator to obtain the final high-performance bio-based superabsorbent product. Example 3

[0049] A bio-based superabsorbent for flushable sanitary napkins, with a total raw material ratio of 100 kg, includes functionalized natural polysaccharides and structured additives. The functionalized natural polysaccharides (total 75 kg) are: sodium alginate: 50.0 kg (viscosity 600 mPa·s, 1% aqueous solution, 25℃), carboxymethylated pea protein (degree of substitution 0.12): 12.0 kg, octenyl succinate starch ester: 15.0 kg, and low-acyl gellan gum: 5.0 kg; the structured additives (total 40 kg) are: porous β-cyclodextrin polymer (specific surface area ≥350 m² / g): 18.0 kg. Nano-calcined kaolin (1250 mesh): 12.0 kg, calcium dicalcium citrate (food grade): 3.0 kg, L-tartaric acid: 1.5 kg. Processing auxiliary materials: ethanol aqueous solution (ethanol:water = 1:5, containing 0.1% lecithin): approximately 3.8 kg (for step 1), ice-cold deionized water (8°C): approximately 165 kg (for step 3, calculated as 2.2 times the dry powder mass).

[0050] A process for preparing a bio-based superabsorbent includes the following steps: Step 1 (Structured Carrier Core): Calcium dicalcium citrate, cyclodextrin polymer, and kaolin are added to a high-speed mixer equipped with a jacketed heating and spraying device, and mixed at 120 r / min. 3.8 kg of ethanol-water solution is atomized and sprayed into the mixture through the spraying device. The jacketed steam is activated to mix and activate the materials at 50°C for 20 minutes. This process partially embeds the fine particles of calcium dicalcium citrate within the cyclodextrin cavities and kaolin layers, achieving uniform pre-wetting and adhesion of the components. The pre-structured material is transferred to a disc dryer and dried under hot air at 90°C for 20 minutes to obtain carrier core powder with a moisture content of 2.2%.

[0051] Step 2 (gradient mixing): Mix all the carrier core powders obtained in Step 1 with sodium alginate at low speed (20 r / min revolution, 60 r / min rotation) for 5 minutes in a dual-motion mixer. Then add pea protein, modified starch, and gellan gum in sequence, and mix at higher speed (30 r / min revolution, 100 r / min rotation) for 18 minutes to obtain composite dry powder.

[0052] Step 3 (Continuous Kneading): The compound dry powder is passed through a twin-screw kneader. The temperatures of each zone of the twin-screw are set as follows: Zone 1 45℃, Zone 2 55℃, Zone 3 58℃, and Zone 4 55℃. The screw speed is 250 r / min. 165 kg of 8℃ ice water is injected through a precision liquid pump. The low-temperature water addition aims to slow down the excessive swelling of polysaccharides and ensure more uniform mixing. The material is held for about 3 minutes. During this process, the material undergoes high shear, mixing, and compression to form a highly homogeneous, semi-dry reaction precursor paste at 60℃ with a moisture content of approximately 50%.

[0053] Step 4 (Combined Drying and Granulation): The precursor paste is evenly spread on a Teflon-coated mesh conveyor belt to a thickness of 8 mm. It is then microwave-dried (power density 2.0 W / g). Microwaves penetrate the material, causing water molecules to vibrate rapidly and generate heat, resulting in rapid and uniform heating and the creation of internal vapor pressure, initially forming internal channels. This stage takes 4 minutes. The material then enters a segmented hot air drying section: zone 1 hot air temperature 90℃, zone 2 80℃, and zone 3 70℃. The conveyor belt speed is adjustable, keeping the total drying time within 25 minutes. The final output material is porous, brittle flakes with a moisture content of 4.2%. These flakes, with suitable brittleness, are then lightly crushed by a roller crusher to obtain primary granules.

[0054] Step 5 (Screening and Shaping): Primary particles are conveyed by pneumatic conveying to a multi-stage planar rotary screen. The screen configuration is: upper layer 12 mesh, middle layer 40 mesh, and lower layer 100 mesh. Particles that pass through the 40 mesh screen but are retained on the 100 mesh screen (raw material D) are collected. These particles have a uniform size (150-380 μm) and good flowability, making them ideal for fluidized bed feed. Overly coarse particles are returned to crushing, while overly fine particles can be incorporated into the kneading process as return material. The target particle size yield is 96.5%.

[0055] Step 6 (Fluidized Bed Triggered Reaction): Introduce dehumidified and preheated nitrogen gas to 115°C, controlling the gas flow rate to achieve a stable "rapid fluidization" state in the bed. The empty tower gas velocity is 1.6 m / s. Preheat for 4 minutes to uniformly raise the particle temperature to 100-110°C, activating surface reactivity. Dissolve L-tartaric acid in deionized water to prepare a 5% (w / w) dilute acid solution at 25°C. Atomize using a high-pressure peristaltic pump and ultrasonic atomizing nozzle at a frequency of 2.0 MHz to produce extremely fine (D50 < 20 μm) and uniform acid mist droplets. Initiate ultrasonic atomization to uniformly introduce the acid mist into the fluidized bed system from multiple points in the center. Key reaction occurs: the acid mist droplets contact and penetrate the preheated particle surface and shallow layer. The acid (H⁺) reacts with the calcium dicalcium citrate pre-embedded inside the particles: Calcium dicalcium citrate + H⁺ → Ca²⁺ + citric acid + CO₂↑ + H₂O. This reaction produces two key substances in situ and simultaneously: 1) CO₂ gas: generated inside the particles. Because the material is above the semi-molten glass transition temperature, the gas "expands" the polysaccharide network, forming interconnected open micropores. 2) Ca²⁺: released on the particle surface and near the pore walls, immediately undergoing ionic cross-linking with the carboxyl groups of sodium alginate and gellan gum, forming a gradient-distributed, dense cross-linked network (shell). The bed temperature in the reaction zone is precisely controlled at 128℃. At this temperature, the polysaccharide segments have sufficient mobility to form a good network, while moisture evaporates rapidly, fixing the newly formed structure. The atomization process lasts for 10 minutes. After completion, the fluidized state and temperature are maintained, and drying continues for 6 minutes to thoroughly remove residual moisture and reaction byproducts, completing the structural fixation. The product is cooled to below 40°C by the built-in fluidized bed cooling section and collected by a high-efficiency cyclone separator to obtain the final high-performance bio-based superabsorbent product.

[0056] The performance test data of the aluminum alloy powder materials prepared in Examples 1-3 are shown in Table 1 below: Table 1 Performance test data of bio-based superabsorbent polymers in Examples 1-3 Testing items Example 1 Example 2 Example 3 National Standard GB / T 22875-2018 requires Absorption rate (s) 17 16 15 <150 Water absorption ratio (blood simulant sample, g / g) 30 31 32 ≥20 Centrifugal water retention (g / g) 27 28 29 ≥20 Pressure absorption capacity (0.7 psi, g / g) 15 16 17 ≥10 Biodegradation rate (28 days, compost) ＞94% ＞96% ＞95% - The three embodiments described above represent the lower limit (Example 1), intermediate / preferred value (Example 2), and upper limit (Example 3) of the raw material ratio and process parameters range of the present invention, respectively, constituting a complete implementation boundary verification system. Experimental data consistently show that even with the lowest raw material load and mildest process conditions in Example 1, the product performance (absorption rate of 17 seconds, water absorption ratio of 30 g / g for blood simulation samples, and pressurized absorption of 15 g / g) fully exceeds the requirements of the national standard GB / T 22875-2018. Example 3, using the upper limit parameters, maintains process feasibility while increasing the water absorption ratio to 32 g / g and the pressurized absorption to 17 g / g, demonstrating further performance optimization potential. More importantly, the three embodiments exhibit regular and predictable trends in key performance indicators (e.g., with the increase of sodium alginate and calcium citrate dosage, the water absorption ratio and pressurized absorption increase synchronously), and the target particle size yield of all embodiments remains stable above 95%, with batch-to-batch relative standard deviations (RSD) of key performance indicators less than 5%. This fully demonstrates that the technical solution of the present invention not only possesses outstanding performance breakthrough capabilities, but also exhibits excellent process robustness, a wide operating window, and good reproducibility, providing a reliable technical foundation for industrial scale-up. Among them, Example 2 achieves the best balance between high performance (e.g., 16 g / g pressurized absorption), high yield (97.2%), and moderate raw material costs, and can be considered as a preferred technical solution for large-scale production.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A bio-based superabsorbent for flushable sanitary napkins, characterized by, By weight parts, consisting of: functionalized natural polysaccharide 60-75 parts, structured auxiliary 25-40 parts; the functionalized natural polysaccharide includes sodium alginate 35-50 parts, carboxymethylated pea protein 5-12 parts, octenyl succinate starch 8-15 parts, low acyl gellan gum 2-5 parts; the structured auxiliary includes porous cyclodextrin polymer 10-18 parts, nano-sized calcined kaolin 8-12 parts, calcium hydrogen citrate 1.5-3 parts, L-tartaric acid 0.5-1.5 parts.

2. The bio-based superabsorbent of claim 1, wherein, The viscosity of the sodium alginate is 400-600 mPa·s (1% aqueous solution, 25℃), the carboxymethyl substitution degree of the carboxymethylated pea protein is 0.05-0.12, and the particle size of the nano-sized calcined kaolin is 800-1250 mesh.

3. A process for the preparation of a bio-based superabsorbent according to any one of claims 1-2, characterized in that, It comprises the following steps: 1) Preparation of structured carrier core: mix calcium hydrogen citrate, porous cyclodextrin polymer, nano calcined kaolin, spray into an aqueous solution containing dispersant, mix and activate at 45-50℃, then dry at 85-90℃ to a water content of <3%, to obtain carrier core powder; 2) Gradient precision mixing: add carrier core powder, sodium alginate, carboxymethylated pea protein, octenyl succinate starch, and low acyl gellan gum into a double-motion mixer in sequence, and mix at gradient speed to obtain a composite functional dry powder; 3) Continuous low-temperature kneading: pass the composite functional dry powder through a double-screw extrusion kneader, inject 4-8℃ ice deionized water in the interval of 45-58℃, and knead at a speed of 150-250 r / min for 2-3 minutes to form a reaction precursor paste; 4) Combined drying and granulation: microwave the reaction precursor paste for rapid drying, then dry by staged hot air drying to a water content of ≤5% to form porous brittle flakes, and crush to obtain primary particles; 5) Screening and shaping: screen the primary particles, and collect 40-100 mesh particles as raw material D; 6) Fluidized bed trigger reaction: preheat the raw material D in a fluidized bed with 105-115℃ gas; prepare a 3-5% L-tartaric acid aqueous solution, ultrasonic atomize it, and spray it into the fluidized bed, with the bed temperature controlled at 118-128℃; the L-tartaric acid triggers the decomposition of calcium hydrogen citrate in the particles, simultaneously generating CO2 for pore formation and Ca²⁺ crosslinking reaction; continue to dry and cool after the reaction to obtain the finished product.

4. The manufacturing process of claim 3, wherein, The mass of the ice deionized water injected in step 3) is 1.8-2.2 times the mass of the composite functional dry powder.

5. The production method according to claim 3, characterized by, In step 4), the power density of microwave drying is 1.0-2.0 W / g, and the time is 2-4 minutes; the three-zone temperatures of staged hot air drying are 90±5℃, 80±5℃, and 70±5℃, respectively.

6. The method of claim 3, wherein, In step 6), the atomization used in the fluidized bed is ultrasonic atomization, with a frequency of 1.5-2.5 MHz, and the generated mist droplet particle size D50 is less than 30μm.

7. Use of the bio-based superabsorbent of any one of claims 1-2 in the preparation of flushable sanitary napkins, high-end wound dressings, medical nursing pads, environmentally friendly paper diapers, fresh-keeping materials for fresh foods, or pet hygiene products.