A nano-cellulose degradable foamed material for sanitary napkin pads and a preparation method thereof

Abstract

This invention discloses a biodegradable nanocellulose foam material for sanitary napkins and panty liners, and its preparation method, belonging to the field of biodegradable materials technology. The method includes dispersing and homogenizing bacterial nanocellulose, followed by sequential TEMPO oxidation, cross-linking with genipin and chitosan, and mixing with sodium carboxymethyl cellulose to obtain water-absorbing modified nanocellulose; then blending with a polyol plasticizer, thermoplastic starch, polyvinyl alcohol, and a silane coupling agent for flexibility modification; adjusting the pH to 7.5-8.0 and sequentially adding sodium alginate and calcium chloride to form a synergistic composite slurry; finally adding tea saponin, stirring, foaming, and coating. This invention effectively solves the problem of inhibiting water absorption performance by constructing a stable water-absorbing network and a flexible continuum, combined with the formation of a hydrophilic gel microfilm on the inner wall of the pores by sodium alginate-calcium ions. The resulting material possesses high water absorption, high flexibility, and biodegradability, making it suitable for the sanitary napkin and panty liner industry.

Description

Technical Field

[0001] This invention relates to the field of biodegradable materials technology, specifically to a nanocellulose biodegradable foam material for sanitary napkin liners and its preparation method. Background Technology

[0002] Panty liners are disposable hygiene products used frequently by women in their daily lives. Currently, most mainstream panty liner cores on the market use a composite structure of superabsorbent polymer (SAP) and fluff pulp. Sodium polyacrylate, a representative of SAP, is a petroleum-based synthetic polymer that is extremely difficult to degrade in the natural environment, causing a continuous pollution burden on soil and water bodies after large-scale use. With increasing public awareness of environmental protection, developing environmentally friendly and biodegradable alternative materials has become an urgent need for the hygiene products industry. Bacterial nanocellulose is a type of natural nano-cellulose material synthesized by microorganisms. It possesses high purity, high crystallinity, excellent biocompatibility, and complete biodegradability, and is considered an ideal basic component for constructing green functional materials, serving as a substitute for fluff pulp. However, bacterial nanocellulose itself has limited absorbency, and its fiber network structure is relatively rigid, resulting in insufficient absorbency and a stiff feel when directly used in panty liners. In existing technologies, research on the modification of nanocellulose-based materials mostly focuses on improving a single property, such as simply performing graft copolymerization to improve water absorption, or simply adding plasticizers to improve flexibility. It is difficult to simultaneously achieve both water absorption and flexibility. Furthermore, water absorption modification and flexibility modification often present a mutually restrictive contradiction. The hydrophilic groups and porous structures introduced to improve water absorption are easily destroyed or blocked by the plasticizing system during subsequent flexibility modification; conversely, the polymer infiltration and plasticizing treatments required for flexibility modification may lead to blockage of the water absorption channels. How to coordinate and resolve these contradictions within the same material system is a pressing technical challenge that needs to be overcome in this field. Summary of the Invention

[0003] The purpose of this invention is to provide a biodegradable nanocellulose foam material for sanitary napkin liners and its preparation method, so as to solve the technical problems mentioned in the background.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for preparing a biodegradable nanocellulose foam material for sanitary napkins and panty liners includes the following steps:

[0006] S1. The bacterial nanocellulose is dispersed and homogenized to obtain a bacterial nanocellulose dispersion.

[0007] S2. The bacterial nanocellulose dispersion is mixed with 2,2,6,6-tetramethylpiperidine-1-oxygen radical (TEMPO), sodium bromide and sodium hypochlorite for oxidation reaction; then genipin and chitosan are added for cross-linking reaction, and then sodium carboxymethyl cellulose is added and mixed to obtain water-absorbing modified nanocellulose;

[0008] S3. Glycerin, sorbitol and triethyl citrate are mixed and added to the water-absorbing modified nanocellulose. Then, thermoplastic starch paste, polyvinyl alcohol solution and silane coupling agent KH-560 are added and blended to obtain flexible modified nanocellulose composite slurry.

[0009] S4. Add sodium alginate solution and calcium chloride solution to the flexible modified nanocellulose composite slurry in sequence and mix to obtain a synergistic composite slurry.

[0010] S5. Add tea saponin to the synergistic composite slurry and stir to foam. After coating and molding, a nanocellulose biodegradable foam material is obtained.

[0011] In the technical solution of the present invention, (1) the principle of improving the water absorption of bacterial nanocellulose is that, at the basic level, TEMPO selective oxidation densely implants a large number of carboxyl groups on the surface of cellulose nanofibers, transforming the fiber surface, which was originally dominated by hydroxyl groups, into a highly polar surface rich in ionic hydrophilic groups. The affinity between cellulose and water molecules is thus greatly improved. At the same time, the electrostatic repulsion between fibers after oxidation causes the tightly stacked fiber network to spontaneously relax and unfold, forming rich capillary channels and interstitial spaces between fibers, providing a physical pathway for the rapid penetration and large-scale storage of water molecules. Based on this, by pre-adjusting the pH of the system to the weakly acidic range, the chitosan chains simultaneously retain protonated amino groups for electrostatic adsorption and free amino groups for genipin crosslinking. After chitosan and oxidized cellulose achieve uniform composite through electrostatic adsorption, genipin constructs covalent crosslinking bridges at the free amino sites. The resulting three-dimensional interpenetrating network, while retaining its fluffy pores, endows the network structure with overall stability, preventing the fiber from losing its pore structure due to network creep or collapse during water absorption and swelling. The hygroscopic properties of chitosan molecules themselves also supplement the network with an ion osmotic pressure-type water absorption mechanism driven by amino protonation, which complements the capillary adsorption of carboxyl groups on the cellulose surface. Finally, the long-chain sodium carboxymethyl cellulose molecules introduced interspersed in the pores of the cross-linked network, just like adding a dense hydrophilic capillary bundle to the existing water supply network. Its high-density carboxymethyl ion groups form a uniformly distributed group of hydrophilic sites inside the network, which not only further increases the water absorption capacity per unit volume, but also strengthens the binding and locking ability of the absorbed water through the secondary ion pairing between its and the cationic groups of chitosan, effectively reducing the liquid return rate of the material under pressure. (2) The principle of high bacterial nanocellulose flexibility is to gradually transform the rigid nanocellulose skeleton that is originally tightly bound by hydrogen bonds into a composite soft material structure with excellent flexibility through a multi-component synergistic plasticizing-blending-coupling system. Specifically, glycerol and sorbitol, two polyol plasticizers with complementary molecular weight gradients, are first used to penetrate the hydrogen bond network of cellulose molecular chains. Glycerol, with its high diffusion capacity, first penetrates the edges of the crystalline region and the amorphous region of cellulose, breaking the rigid hydrogen bond connections between cellulose chain segments and replacing them with its own hydroxyl groups to establish a flexible intermolecular lubrication layer. Sorbitol, with its slightly larger molecular weight, mainly stays at the nodes and intersections of the fiber network, forming flexible hydrogen bond bridges with multiple cellulose chains through its six hydroxyl groups. This transforms these mechanically sensitive rigid nodes into deformable flexible hinge points. The division of labor and complementarity between the two in the spatial scale ensures that the plasticizing effect covers the entire range from the microscopic fiber chain segments to the macroscopic network nodes.Building upon this foundation, thermoplastic starch and polyvinyl alcohol (PVA) undergo gelatinization and plasticization treatment. The former, with its flexible branched starch segments, acts as an elastic buffer between the fiber skeletons, while the latter, with its excellent film-forming properties and high elongation at break, constructs a continuous and flexible polymer coating layer around the cellulose skeleton. Together, they reshape the original point-line contact-dominated cellulose skeleton mechanical network into a composite continuous structure dominated by surface-volume contact. This results in excellent overall bending compliance and anti-folding resilience. Finally, a covalent chemical bridge is established at the interface between the rigid fiber skeleton and the flexible blend matrix using the silane coupling agent KH-560. This ensures that the flexible component does not slip or peel off from the cellulose surface under stress, allowing stress to be continuously transferred between the rigid and flexible components through chemical bonds. This prevents delamination and brittleness caused by phase separation during repeated bending and use, thus maintaining the load-bearing function of the cellulose skeleton while achieving a soft touch and durable flexibility that matches the skin surface.

[0012] Preferably, in step S1, the solid content of the bacterial nanocellulose dispersion is 1 wt%.

[0013] Preferably, in step S2, the mass ratio of bacterial nanocellulose to TEMPO and sodium bromide is 10:(0.16-0.32):(1-2).

[0014] Preferably, in step S2, the mass ratio of bacterial nanocellulose to chitosan is 10:(2-5).

[0015] Preferably, in step S3, the mass ratio of glycerol, sorbitol, and triethyl citrate is 6:(2-4):(0.5-1).

[0016] Preferably, in step S3, the mass ratio of the thermoplastic starch paste, polyvinyl alcohol solution, and silane coupling agent KH-560 is 50:(20-25):(0.4-0.6).

[0017] Preferably, in step S4, the concentration of the sodium alginate solution is 2 wt%.

[0018] Preferably, in step S4, the concentration of the calcium chloride solution is 3 wt%.

[0019] This invention discovered in experiments that the large amount of plasticizers and polymer blends introduced during the flexibility modification of nanocellulose continuously migrate and penetrate into the already established water-absorbing cross-linked network during the subsequent foaming and drying process of the slurry. Driven by drying shrinkage, these hydrophobic or weakly hydrophilic plasticizer molecules and polymer segments gradually occupy the capillary pores in the water-absorbing network that were originally used for water conduction and storage, forming a low-permeability coating that hinders the entry and exit of water molecules. This results in a significant decrease in the water absorption ratio after flexibility modification, meaning that while the flexibility meets the standard, the water absorption performance is compromised. To solve this problem, this invention introduces sodium alginate and calcium chloride as synergistic agents, and pre-adjusts the system pH to 7.5–8.0 to reduce the protonation degree of chitosan amino groups, avoiding polyelectrolyte complexation reactions between sodium alginate and chitosan, which would prevent sodium alginate from effectively spreading into the pores. When sodium alginate is first mixed with the composite slurry, the guluronic acid segments (G blocks) rich in its long-chain molecules spread along the pore walls of the water-absorbing crosslinking network and are anchored by hydrogen bonds and electrostatic interactions, forming a hydrophilic protective liner. Then, calcium ions slowly introduced by spraying undergo characteristic eggshell-box coordination crosslinking with the G blocks of sodium alginate, causing this hydrophilic liner to solidify in situ into a gel microfilm with a certain mechanical strength. This gel microfilm not only maintains the excellent hydrophilicity and water retention of sodium alginate itself, but also, due to the structural rigidity obtained after crosslinking, can effectively resist the migration and invasion of plasticizers and blended polymers into the pores during the subsequent drying process. It is like building a protective layer with both hydrophilic guidance and physical barrier functions on the inner wall of the water absorption channel. Thus, without affecting the flexibility modification effect, the channel structure and water absorption capacity of the water absorption network are stably maintained, so that the water absorption and flexibility effects can truly achieve synergistic superposition and do not interfere with each other.

[0020] Preferably, in step S5, the foaming temperature is 45-50°C and the foaming time is 15-20 minutes.

[0021] A biodegradable nanocellulose foam material for sanitary napkin liners is prepared by the method described above.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. A large number of carboxyl groups are introduced on the surface of cellulose through selective oxidation with TEMPO. Combined with the electrostatic adsorption of chitosan and crosslinking with genipin, a three-dimensional stable network is constructed. Sodium carboxymethyl cellulose is introduced to form hydrophilic capillary bundles, which synergistically achieve high water absorption capacity and low liquid return rate.

[0024] 2. Polyol plasticizers are used to break the hydrogen bonds of cellulose, and thermoplastic starch and polyvinyl alcohol are used to construct a flexible continuum. Then, silane coupling agents are used to strengthen the rigid-flexible interface, so that the material has excellent bending flexibility, anti-folding resilience and long-lasting durability.

[0025] 3. To address the issue of flexible modified components easily clogging the water absorption channels, sodium alginate and calcium ions are introduced to form a hydrophilic gel microfilm in situ on the inner wall of the channels. This effectively blocks the migration and invasion of plasticizers and polymer chains, and maintains the water absorption network structure stably without affecting flexibility, so that the two properties can truly synergistically combine. Attached Figure Description

[0026] Figure 1 This is a low-magnification SEM image of the nanocellulose biodegradable foam material prepared in Example 4 of the present invention.

[0027] Figure 2 This is a medium-magnification SEM image of the nanocellulose biodegradable foam material prepared in Example 4 of the present invention.

[0028] Figure 3 This is a high-magnification SEM image of the nanocellulose biodegradable foam material prepared in Example 4 of the present invention.

[0029] Figure 4 The image shows the XRD pattern of the nanocellulose biodegradable foam material prepared in Example 4 of this invention. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] A method for preparing a biodegradable nanocellulose foam material for sanitary napkins and panty liners includes the following steps:

[0033] S1. Take the bacterial nanocellulose wet gel, determine the solid content, and weigh it according to the dry weight of 10.0g. Place it in a 2000mL beaker, add deionized water to make up to a total mass of 1000.0g (solid content 1wt%), disperse it by mechanical stirring at 500r / min for 25min, and then homogenize it twice at 70MPa using a high-pressure homogenizer to obtain a bacterial nanocellulose dispersion with a solid content of 1wt%.

[0034] S2. Dissolve 0.30g TEMPO and 1.8g sodium bromide in 50g deionized water, add all the dispersion obtained in step S1, stir evenly, and slowly add 30mL of sodium hypochlorite solution with an effective chlorine content of 10%. Control the pH to 10.0, oxidize at 30℃ for 3h, adjust the pH to 7.0 with 0.5mol / L HCl to terminate the reaction, centrifuge and wash 4 times at 8000r / min, and redisperse into a suspension with a solid content of 1.0wt%. The suspension was transferred to a 2000 mL reactor and heated to 45 °C. The pH was adjusted to 6.0–6.5 with 0.5 mol / L NaOH. 0.15 g of genipin was dissolved in 3 mL of anhydrous ethanol, diluted with 5 mL of deionized water, and mixed into a chitosan solution prepared by dissolving 4.0 g of chitosan in 147 g of a 1.5% acetic acid aqueous solution (stirred at 55 °C for 35 min). This solution was added dropwise to the reactor using a peristaltic pump at 3 mL / min, maintaining the pH at 5.8–6.5, and reacted at 45 °C for 4 h. The system changed from milky white to blue-green. Then, 1.5 g of sodium carboxymethyl cellulose was added, and the mixture was stirred at 65 °C for 1.5 h. After cooling, the mixture was washed three times by centrifugation at 8000 r / min and redispersed to a solid content of 2.0 wt%, yielding a water-modified nanocellulose suspension.

[0035] S3. Add 6.0g glycerol, 3.5g sorbitol, and 0.9g triethyl citrate to 36.0g deionized water and stir at 45℃ for 25 min to obtain a composite plasticizing modified liquid. Heat the suspension obtained in step S2 to 50℃ and slowly add the plasticizing liquid at a rate of 0.8mL / min using a peristaltic pump, stirring for 1.5h. Then add 50.0g of thermoplastic starch paste (5g starch + 43.5g water + 1.5g glycerol, gelatinized at 85℃ for 30min, solid content 10wt%) and 23.0g of polyvinyl alcohol solution (concentration 6wt%), stirring and mixing at 75℃ for 2.5h; after cooling to 55℃, add 0.55g of silane coupling agent KH-560 (pre-diluted with 5mL ethanol), stirring and reacting for 1.5h to obtain a flexible modified nanocellulose composite slurry.

[0036] S4. Transfer the slurry obtained in step S3 to a 2000mL reactor and adjust the pH to 7.5-8.0 with 0.5mol / L NaOH. Weigh 50.0g of 2wt% sodium alginate solution (prepared by stirring at 65℃ for 40min with 2.0g sodium alginate + 98.0g water) using an electronic balance and add it to the slurry, stirring for 35min. Then, introduce 37.0g of 3wt% calcium chloride solution (prepared by stirring at 65℃ for 40min) using a peristaltic pump spray device at a rate of 2mL / min, and stir and mature at 45℃ for 1.5h to obtain a synergistic composite slurry with no obvious flocculation or sedimentation.

[0037] S5. Weigh 1.67g of tea saponin (saponin content ≥60%) and add it to the slurry obtained in step S4. Stir and foam at 1000r / min for 18min at 48℃. Coat the foamed slurry onto release paper at 0.8m / min, with a wet film thickness of 2.0mm. After three stages of drying—pre-drying at 55℃ for 25min, main drying at 75℃ for 1.5h, and post-curing at 45℃ for 45min—remove the release paper to obtain the nanocellulose biodegradable foamed material for sanitary napkins and panty liners.

[0038] Example 2

[0039] A method for preparing a biodegradable nanocellulose foam material for sanitary napkins and panty liners includes the following steps:

[0040] S1. Take the bacterial nanocellulose wet gel, determine the solid content, and weigh it according to the dry weight of 10.0g. Place it in a 2000mL beaker, add deionized water to make up to a total mass of 1000.0g (solid content 1wt%), disperse it by mechanical stirring at 500r / min for 25min, and then homogenize it twice at 70MPa using a high-pressure homogenizer to obtain a bacterial nanocellulose dispersion with a solid content of 1wt%.

[0041] S2. Dissolve 0.20g TEMPO and 1.2g sodium bromide in 50g deionized water, add all the dispersion obtained in step S1, stir evenly, and slowly add 30mL of sodium hypochlorite solution with an effective chlorine content of 10%. Control the pH to 10.0, oxidize at 30℃ for 3h, adjust the pH to 7.0 with 0.5mol / L HCl to terminate the reaction, centrifuge and wash 4 times at 8000r / min, and redisperse into a suspension with a solid content of 1.0wt%. The suspension was transferred to a 2000 mL reactor and heated to 45 °C. The pH was adjusted to 6.0–6.5 with 0.5 mol / L NaOH. 0.15 g of genipin was dissolved in 3 mL of anhydrous ethanol, diluted thoroughly with 5 mL of deionized water, and mixed into a chitosan solution prepared by dissolving 3.0 g of chitosan in 147 g of a 1.5% acetic acid aqueous solution (stirred at 55 °C for 35 min). This solution was added dropwise to the reactor using a peristaltic pump at 3 mL / min, maintaining the pH at 5.8–6.5, and reacted at 45 °C for 4 h. The system changed from milky white to blue-green. Then, 1.5 g of sodium carboxymethyl cellulose was added, and the mixture was stirred at 65 °C for 1.5 h. After cooling, the mixture was washed three times by centrifugation at 8000 r / min and redispersed to a solid content of 2.0 wt%, yielding a water-modified nanocellulose suspension.

[0042] S3. Add 6.0g glycerol, 2.5g sorbitol, and 0.6g triethyl citrate to 36.0g deionized water and stir at 45℃ for 25 min to obtain a composite plasticizing modified liquid. Heat the suspension obtained in step S2 to 50℃ and slowly add the plasticizing liquid at a rate of 0.8mL / min using a peristaltic pump, stirring for 1.5h. Then add 50.0g of thermoplastic starch paste (5g starch + 43.5g water + 1.5g glycerol, gelatinized at 85℃ for 30min, solid content 10wt%) and 21.0g of polyvinyl alcohol solution (concentration 6wt%), stirring and mixing at 75℃ for 2.5h; cool to 55℃ and add 0.45g silane coupling agent KH-560 (pre-diluted with 5mL ethanol), stirring and reacting for 1.5h to obtain a flexible modified nanocellulose composite slurry.

[0043] S4. Transfer the slurry obtained in step S3 to a 2000mL reactor and adjust the pH to 7.5-8.0 with 0.5mol / L NaOH. Weigh 50.0g of 2wt% sodium alginate solution (prepared by stirring at 65℃ for 40min with 2.0g sodium alginate + 98.0g water) using an electronic balance and add it to the slurry, stirring for 35min. Then, introduce 37.0g of 3wt% calcium chloride solution (prepared by stirring at 65℃ for 40min) using a peristaltic pump spray device at a rate of 2mL / min, and stir and mature at 45℃ for 1.5h to obtain a synergistic composite slurry with no obvious flocculation or sedimentation.

[0044] S5. Weigh 1.67g of tea saponin (saponin content ≥60%) and add it to the slurry obtained in step S4. Stir and foam at 1000r / min for 18min at 48℃. Coat the foamed slurry onto release paper at 0.8m / min, with a wet film thickness of 2.0mm. After three stages of drying—pre-drying at 55℃ for 25min, main drying at 75℃ for 1.5h, and post-curing at 45℃ for 45min—remove the release paper to obtain the nanocellulose biodegradable foamed material for sanitary napkins and panty liners.

[0045] Example 3

[0046] A method for preparing a biodegradable nanocellulose foam material for sanitary napkins and panty liners includes the following steps:

[0047] S1. Take the bacterial nanocellulose wet gel, determine the solid content, and weigh it according to the dry weight of 10.0g. Place it in a 2000mL beaker, add deionized water to make up to a total mass of 1000.0g (solid content 1wt%), disperse it by mechanical stirring at 500r / min for 25min, and then homogenize it twice at 70MPa using a high-pressure homogenizer to obtain a bacterial nanocellulose dispersion with a solid content of 1wt%.

[0048] S2. Dissolve 0.25g TEMPO and 1.5g sodium bromide in 50g deionized water, add all the dispersion obtained in step S1, stir evenly, and slowly add 30mL of sodium hypochlorite solution with an effective chlorine content of 10%. Control the pH to 10.0, oxidize at 30℃ for 3h, adjust the pH to 7.0 with 0.5mol / L HCl to terminate the reaction, centrifuge and wash 4 times at 8000r / min, and redisperse into a suspension with a solid content of 1.0wt%. The suspension was transferred to a 2000 mL reactor and heated to 45 °C. The pH was adjusted to 6.0–6.5 with 0.5 mol / L NaOH. 0.15 g of genipin was dissolved in 3 mL of anhydrous ethanol, diluted with 5 mL of deionized water, and mixed into a chitosan solution prepared by dissolving 3.5 g of chitosan in 147 g of a 1.5% acetic acid aqueous solution (stirred at 55 °C for 35 min). This solution was added dropwise to the reactor using a peristaltic pump at 3 mL / min, maintaining the pH at 5.8–6.5, and reacted at 45 °C for 4 h. The system changed from milky white to blue-green. Then, 1.5 g of sodium carboxymethyl cellulose was added, and the mixture was stirred at 65 °C for 1.5 h. After cooling, the mixture was washed three times by centrifugation at 8000 r / min and redispersed to a solid content of 2.0 wt%, yielding a water-modified nanocellulose suspension.

[0049] S3. Add 6.0g glycerol, 3.0g sorbitol, and 0.7g triethyl citrate to 36.0g deionized water and stir at 45℃ for 25 min to obtain a composite plasticizing modified liquid. Heat the suspension obtained in step S2 to 50℃ and slowly add the plasticizing liquid at a rate of 0.8mL / min using a peristaltic pump, stirring for 1.5h. Then add 50.0g of thermoplastic starch paste (5g starch + 43.5g water + 1.5g glycerol, gelatinized at 85℃ for 30min, solid content 10wt%) and 22.0g of polyvinyl alcohol solution (concentration 6wt%), stirring and mixing at 75℃ for 2.5h; cool to 55℃ and add 0.5g of silane coupling agent KH-560 (pre-diluted with 5mL ethanol), stirring and reacting for 1.5h to obtain a flexible modified nanocellulose composite slurry.

[0050] S4. Transfer the slurry obtained in step S3 to a 2000mL reactor and adjust the pH to 7.5-8.0 with 0.5mol / L NaOH. Weigh 50.0g of 2wt% sodium alginate solution (prepared by stirring at 65℃ for 40min with 2.0g sodium alginate + 98.0g water) using an electronic balance and add it to the slurry, stirring for 35min. Then, introduce 37.0g of 3wt% calcium chloride solution (prepared by stirring at 65℃ for 40min) using a peristaltic pump spray device at a rate of 2mL / min, and stir and mature at 45℃ for 1.5h to obtain a synergistic composite slurry with no obvious flocculation or sedimentation.

[0051] S5. Weigh 1.67g of tea saponin (saponin content ≥60%) and add it to the slurry obtained in step S4. Stir and foam at 1000r / min for 18min at 48℃. Coat the foamed slurry onto release paper at 0.8m / min, with a wet film thickness of 2.0mm. After three stages of drying—pre-drying at 55℃ for 25min, main drying at 75℃ for 1.5h, and post-curing at 45℃ for 45min—remove the release paper to obtain the nanocellulose biodegradable foamed material for sanitary napkins and panty liners.

[0052] Example 4

[0053] A method for preparing a biodegradable nanocellulose foam material for sanitary napkins and panty liners includes the following steps:

[0054] S1. Take the bacterial nanocellulose wet gel, determine the solid content, and weigh it according to the dry weight of 10.0g. Place it in a 2000mL beaker, add deionized water to make up to a total mass of 1000.0g (solid content 1wt%), disperse it by mechanical stirring at 500r / min for 25min, and then homogenize it twice at 70MPa using a high-pressure homogenizer to obtain a bacterial nanocellulose dispersion with a solid content of 1wt%.

[0055] S2. Dissolve 0.32g TEMPO and 2.0g sodium bromide in 50g deionized water, add all the dispersion obtained in step S1, stir evenly, and slowly add 30mL of sodium hypochlorite solution with an effective chlorine content of 10%. Control the pH to 10.0, oxidize at 30℃ for 3h, adjust the pH to 7.0 with 0.5mol / L HCl to terminate the reaction, centrifuge and wash 4 times at 8000r / min, and redisperse into a suspension with a solid content of 1.0wt%. The suspension was transferred to a 2000 mL reactor and heated to 45 °C. The pH was adjusted to 6.0–6.5 with 0.5 mol / L NaOH. 0.15 g of genipin was dissolved in 3 mL of anhydrous ethanol, diluted with 5 mL of deionized water, and mixed into a chitosan solution prepared by dissolving 5.0 g of chitosan in 147 g of a 1.5% (v / v) acetic acid aqueous solution (stirred at 55 °C for 35 min). This solution was added dropwise to the reactor using a peristaltic pump at 3 mL / min, maintaining the pH at 5.8–6.5. The reaction was carried out at 45 °C for 4 h, during which the system changed from milky white to blue-green. Then, 1.5 g of sodium carboxymethyl cellulose was added, and the mixture was stirred at 65 °C for 1.5 h. After cooling, the mixture was washed three times by centrifugation at 8000 r / min and redispersed to a solid content of 2.0 wt%, yielding a water-modified nanocellulose suspension.

[0056] S3. Add 6.0g glycerol, 4.0g sorbitol and 1.0g triethyl citrate to 36.0g deionized water and stir at 45℃ for 25 min to obtain a composite plasticizing modified liquid. Heat the suspension obtained in step S2 to 50℃ and slowly add the plasticizing liquid at a rate of 0.8mL / min using a peristaltic pump, stirring for 1.5h. Then add 50.0g of thermoplastic starch paste (5g starch + 43.5g water + 1.5g glycerol, gelatinized at 85℃ for 30min, solid content 10wt%) and 25.0g of polyvinyl alcohol solution (concentration 6wt%), and stir and mix at 75℃ for 2.5h; after cooling to 55℃, add 0.6g of silane coupling agent KH-560 (pre-diluted with 5mL ethanol), and stir and react for 1.5h to obtain a flexible modified nanocellulose composite slurry.

[0057] S4. Transfer the slurry obtained in step S3 to a 2000mL reactor and adjust the pH to 7.5-8.0 with 0.5mol / L NaOH. Weigh 50.0g of 2wt% sodium alginate solution (prepared by stirring at 65℃ for 40min with 2.0g sodium alginate + 98.0g water) using an electronic balance and add it to the slurry, stirring for 35min. Then, introduce 37.0g of 3wt% calcium chloride solution (prepared by stirring at 65℃ for 40min) using a peristaltic pump spray device at a rate of 2mL / min, and stir and mature at 45℃ for 1.5h to obtain a synergistic composite slurry with no obvious flocculation or sedimentation.

[0058] S5. Weigh 1.67g of tea saponin (saponin content ≥60%) and add it to the slurry obtained in step S4. Stir and foam at 1000r / min for 20min at 50℃. Coat the foamed slurry onto release paper at 0.8m / min, with a wet film thickness of 2.0mm. After three stages of drying—pre-drying at 55℃ for 25min, main drying at 75℃ for 1.5h, and post-curing at 45℃ for 45min—remove the release paper to obtain the nanocellulose biodegradable foamed material for sanitary napkins and panty liners.

[0059] Example 5

[0060] A method for preparing a biodegradable nanocellulose foam material for sanitary napkins and panty liners includes the following steps:

[0061] S1. Take the bacterial nanocellulose wet gel, determine the solid content, and weigh it according to the dry weight of 10.0g. Place it in a 2000mL beaker, add deionized water to make up to a total mass of 1000.0g (solid content 1wt%), disperse it by mechanical stirring at 500r / min for 25min, and then homogenize it twice at 70MPa using a high-pressure homogenizer to obtain a bacterial nanocellulose dispersion with a solid content of 1wt%.

[0062] S2. Dissolve 0.16g TEMPO and 1.0g sodium bromide in 50g deionized water, add all the dispersion obtained in step S1, stir evenly, and slowly add 30mL of sodium hypochlorite solution with an effective chlorine content of 10%. Control the pH to 10.0, oxidize at 30℃ for 3h, adjust the pH to 7.0 with 0.5mol / L HCl to terminate the reaction, centrifuge and wash 4 times at 8000r / min, and redisperse into a suspension with a solid content of 1.0wt%. The suspension was transferred to a 2000 mL reactor and heated to 45 °C. The pH was adjusted to 6.0–6.5 with 0.5 mol / L NaOH. 0.15 g of genipin was dissolved in 3 mL of anhydrous ethanol, diluted with 5 mL of deionized water, and mixed into a chitosan solution prepared by dissolving 2.0 g of chitosan in 147 g of a 1.5% (v / v) acetic acid aqueous solution (stirred at 55 °C for 35 min). This solution was added dropwise to the reactor using a peristaltic pump at 3 mL / min, maintaining the pH at 5.8–6.5, and reacted at 45 °C for 4 h. The system changed from milky white to blue-green. Then, 1.5 g of sodium carboxymethyl cellulose was added, and the mixture was stirred at 65 °C for 1.5 h. After cooling, the mixture was washed three times by centrifugation at 8000 r / min and redispersed to a solid content of 2.0 wt%, yielding a water-modified nanocellulose suspension.

[0063] S3. Add 6.0g glycerol, 2.0g sorbitol and 0.5g triethyl citrate to 36.0g deionized water and stir at 45℃ for 25 min to obtain a composite plasticizing modified liquid. Heat the suspension obtained in step S2 to 50℃ and slowly add the plasticizing liquid at a rate of 0.8mL / min using a peristaltic pump, stirring for 1.5h. Then add 50.0g of thermoplastic starch paste (5g starch + 43.5g water + 1.5g glycerol, gelatinized at 85℃ for 30min, solid content 10wt%) and 20.0g of polyvinyl alcohol solution (concentration 6wt%), and stir and mix at 75℃ for 2.5h; after cooling to 55℃, add 0.4g silane coupling agent KH-560 (pre-diluted with 5mL ethanol), and stir and react for 1.5h to obtain a flexible modified nanocellulose composite slurry.

[0064] S4. Transfer the slurry obtained in step S3 to a 2000mL reactor and adjust the pH to 7.5-8.0 with 0.5mol / L NaOH. Weigh 50.0g of 2wt% sodium alginate solution (prepared by stirring at 65℃ for 40min with 2.0g sodium alginate + 98.0g water) using an electronic balance and add it to the slurry, stirring for 35min. Then, introduce 37.0g of 3wt% calcium chloride solution (prepared by stirring at 65℃ for 40min) using a peristaltic pump spray device at a rate of 2mL / min, and stir and mature at 45℃ for 1.5h to obtain a synergistic composite slurry with no obvious flocculation or sedimentation.

[0065] S5. Weigh 1.67g of tea saponin (saponin content ≥60%) and add it to the slurry obtained in step S4. Stir and foam at 1000r / min for 15min at 45℃. Coat the foamed slurry onto release paper at 0.8m / min, with a wet film thickness of 2.0mm. After three stages of drying—pre-drying at 55℃ for 25min, main drying at 75℃ for 1.5h, and post-curing at 45℃ for 45min—remove the release paper to obtain the nanocellulose biodegradable foamed material for sanitary napkins and panty liners.

[0066] Comparative Example 1: The difference from Example 4 is that step S2 is omitted in the preparation of the nanocellulose biodegradable foam material to verify the necessity of TEMPO oxidation + chitosan crosslinking + CMC-Na intercalation for water absorption performance.

[0067] Comparative Example 2: The difference from Example 4 is that step S3 is omitted in the preparation of the nanocellulose biodegradable foam material, verifying the necessity of plasticizer + starch / PVA blend + KH-560 coupling for flexibility performance.

[0068] Comparative Example 3: The difference from Example 4 is that step S4 is omitted in the preparation of the nanocellulose biodegradable foam material, which verifies the necessity of the sodium alginate-calcium chloride gel protective layer to prevent the water absorption channels from being blocked.

[0069] Comparative Example 4: The difference from Example 4 is that sodium alginate is not added in step S4 during the preparation of the nanocellulose biodegradable foam material.

[0070] Comparative Example 5: The difference from Example 4 is that calcium chloride is not added in step S4 during the preparation of the nanocellulose biodegradable foam material.

[0071] Comparative Example 6: The difference from Example 4 is that in the preparation process of nanocellulose biodegradable foam material, the pH is not adjusted to 7.5-8.0 in step S4.

[0072] Performance testing:

[0073] 1. Water Absorption Ratio Test: The foamed materials prepared in each example and comparative example were cut into 50mm × 50mm square samples and dried in an oven at 105℃ to constant weight. The dry weight m0 (accurate to 0.001g) was recorded using an analytical balance. The samples were completely immersed in room temperature deionized water for 30 minutes to fully absorb water and become saturated. After removal, the samples were placed on an 80-mesh stainless steel sieve to drain naturally for 1 minute. The surface water droplets were gently absorbed with filter paper, and the wet weight m1 was immediately measured. The water absorption ratio Q was calculated using the formula Q = (m1 - m0) / m0. Three parallel samples were tested in each group, and the average value was taken.

[0074] 2. Water Retention Rate Test: The saturated sample (wet weight m1 known) that has absorbed water in the water absorption ratio test is placed in a centrifuge tube and centrifuged at 3000 r / min for 20 min. Immediately after centrifugation, the mass m2 is measured. The water retention rate R is calculated using the formula: R = (m2 - m0) / (m1 - m0) × 100%, where m0 is the dry weight and m1 is the saturated wet weight. Three parallel samples are tested in each group, and the average value is taken. This indicator reflects the material's ability to retain absorbed water under pressure.

[0075] 3. 180° Bending Test: The foamed materials prepared in each embodiment and comparative example were cut into strips of 20mm × 80mm and equilibrated for 24 hours in a constant temperature and humidity environment of 50% ± 5% relative humidity. The sample was folded 180° along the center line at a uniform speed (i.e., the two halves were completely pressed together after folding), held in the folded state for 10 seconds, and then unfolded. Under natural light, the crease was observed with the naked eye and a magnifying glass (10x) to see if any cracks or breaks appeared. The result was recorded as "pass" (no cracks, no breaks) or "breakage". Five samples were tested in each group, and all five samples passing were recorded as "pass".

[0076] 4. Elongation at break test: Cut the foamed material into dumbbell-shaped standard specimens (effective part width 10mm, gauge length 50mm), and conduct a tensile test on a universal testing machine at a tensile rate of 50mm / min. Record the elongation ΔL at the time of specimen breakage. Calculate the elongation at break ε using the formula ε = ΔL / L0 × 100%, where L0 is the initial gauge length of 50mm. Take the average value of 5 parallel specimens in each group of tests.

[0077] 5. Apparent density test: Cut the foamed material into 50mm×50mm square samples. Use a micrometer to measure the thickness at 5 points (center and four corners) and take the average value d. Use a vernier caliper to measure the length and width (L×W) and calculate the volume V=L×W×d. Weigh the sample mass m on an analytical balance (accurate to 0.001g) and calculate the apparent density ρ=m / V. Take the average value of 3 parallel samples for each test group.

[0078] 6. Water Absorption Rate Test: Cut the foamed material into 100mm × 100mm square samples and place them horizontally on the test bench. Use a pipette to add 0.2mL of distilled water stained with fuchsin (25±1℃) to the center of the sample in one drop. Use a stopwatch to record the time required for the droplet to be completely absorbed (the liquid surface disappears and the surface no longer reflects light). This is the water absorption rate (unit: s). Each group of tests is repeated 5 times, and the average value is taken. The smaller this index is, the faster the material absorbs water.

[0079] Table 1:

[0080]

[0081] The test results show that:

[0082] Examples 1-5 all exhibit excellent overall performance, with water absorption ratios of 14.2-21.3 g / g, water retention rates of 66.5%-79.4%, elongation at break of 78.4%-95.8%, and all passed the 180° bending test. The apparent density ranged from 0.055 to 0.074 g / cm³. 3 The water absorption rate was 2.8–5.3 s, with Example 4 (which used the most TEMPO and chitosan) showing the best overall performance.

[0083] Comparative Example 1 omitted all water absorption modification treatment (step S2), and the water absorption ratio was only 5.1 g / g, the water retention rate was only 27.3%, and the water absorption rate was significantly extended to 12.6 s. This indicates that TEMPO oxidation + chitosan crosslinking + CMC-Na intercalation play a decisive role in improving the water absorption performance of the material.

[0084] Comparative Example 2 omitted all flexibility modification treatment (step S3), and its elongation at break dropped sharply to 11.5%, and it broke in the 180° bending test. However, its water absorption ratio (22.6 g / g) was slightly higher than that of Example 4. This further confirms that the flexibility modification component has a certain occupation effect on the water absorption channel. It is the introduction of the synergistic effect treatment in step S4 that enabled the water absorption performance of the examples to remain at a high level after flexibility modification.

[0085] Comparative Example 3 omitted the synergistic treatment (step S4), and the flexibility was basically unaffected (elongation at break 83.1%, passing through 180° bend), but the water absorption ratio decreased from 21.3 g / g in Example 4 to 13.4 g / g (a decrease of 37.1%), and the water retention rate decreased from 79.4% to 56.8%, confirming the key role of the sodium alginate-calcium chloride gel protective layer in maintaining the integrity of the water absorption channels.

[0086] Comparative Example 4, which only added sodium alginate without calcium chloride, had a water absorption ratio of 15.8 g / g and a water retention rate of 61.5%, both lower than Example 4, indicating a deficiency of calcium chloride. 2+ During cross-linking, sodium alginate is only a flexible long chain that is physically adsorbed, and it cannot form a gel protective film with sufficient rigidity to effectively prevent the migration of plasticizers.

[0087] Comparative Example 5, with only calcium chloride added but no sodium alginate, had a water absorption ratio of 14.1 g / g and a water retention rate of 57.2%, comparable to Comparative Example 3 (without any synergistic effect). This indicates that adding calcium chloride alone... 2+ A gel protective layer cannot be constructed without sodium alginate. 2+ The ions are merely dispersed freely in the system and do not provide any barrier protection.

[0088] In Comparative Example 6, the pH was not adjusted to 7.5–8.0 in step S4 (the natural pH is about 5–6). Although sodium alginate and calcium chloride were added at the same time, the water absorption ratio was only 15.2 g / g and the water retention rate was 63.4%, which was significantly lower than that of Example 4. Moreover, obvious flocculation and precipitation were observed in the slurry during the experiment, indicating that a large-scale polyelectrolyte complex reaction occurred between the protonated amino groups of chitosan and sodium alginate under acidic conditions. This caused sodium alginate to be unable to spread freely to the pore wall for effective protection, and the synergistic effect was greatly reduced.

[0089] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the essence and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a nanocellulose biodegradable foam material for sanitary napkins and panty liners, characterized in that, Includes the following steps: S1. The bacterial nanocellulose is dispersed and homogenized to obtain a bacterial nanocellulose dispersion. S2. The bacterial nanocellulose dispersion is mixed with TEMPO, sodium bromide and sodium hypochlorite for oxidation reaction; then genipin and chitosan are added for cross-linking reaction, and then sodium carboxymethyl cellulose is added and mixed to obtain water-absorbing modified nanocellulose; S3. Glycerin, sorbitol and triethyl citrate are mixed and added to the water-absorbing modified nanocellulose. Then, thermoplastic starch paste, polyvinyl alcohol solution and silane coupling agent KH-560 are added and blended to obtain flexible modified nanocellulose composite slurry. S4. Adjust the pH of the flexible modified nanocellulose composite slurry to 7.5-8.0, and then add sodium alginate solution and calcium chloride solution in sequence to mix and obtain a synergistic composite slurry. S5. Add tea saponin to the synergistic composite slurry and stir to foam. After coating and molding, a nanocellulose biodegradable foam material is obtained.

2. The method for preparing a nanocellulose biodegradable foam material for sanitary napkin liners according to claim 1, characterized in that, In step S1, the solid content of the bacterial nanocellulose dispersion is 1 wt%.

3. The method for preparing a nanocellulose biodegradable foam material for sanitary napkin liners according to claim 1, characterized in that, In step S2, the mass ratio of bacterial nanocellulose to TEMPO and sodium bromide is 10:(0.16-0.32):(1-2).

4. The method for preparing a nanocellulose biodegradable foam material for sanitary napkin liners according to claim 1, characterized in that, In step S2, the mass ratio of bacterial nanocellulose to chitosan is 10:(2-5).

5. The method for preparing a nanocellulose biodegradable foam material for sanitary napkin liners according to claim 1, characterized in that, In step S3, the mass ratio of glycerol, sorbitol, and triethyl citrate is 6:(2-4):(0.5-1).

6. The method for preparing a nanocellulose biodegradable foam material for sanitary napkin liners according to claim 1, characterized in that, In step S3, the mass ratio of thermoplastic starch paste, polyvinyl alcohol solution, and silane coupling agent KH-560 is 50:(20-25):(0.4-0.6).

7. The method for preparing a nanocellulose biodegradable foam material for sanitary napkin liners according to claim 1, characterized in that, In step S4, the concentration of the sodium alginate solution is 2 wt%.

8. The method for preparing a nanocellulose biodegradable foam material for sanitary napkin liners according to claim 1, characterized in that, In step S4, the concentration of the calcium chloride solution is 3 wt%.

9. The method for preparing a nanocellulose biodegradable foam material for sanitary napkin liners according to claim 1, characterized in that, In step S5, the foaming temperature is 45-50℃ and the foaming time is 15-20 minutes.

10. A biodegradable nanocellulose foam material for sanitary napkins and panty liners, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

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