Preparation method of sanitary napkin core body

Abstract

The invention relates to the field of hygienic products, and discloses a sanitary napkin core body preparation method which comprises the following steps: S1, preparing bio-based super absorbent resin containing a dynamic cross-linked network; s2, constructing a gradient composite structure of a flow guide layer, a water locking layer and a reinforcing layer based on the resin; s3, performing interlayer molecular bonding on the gradient composite structure in a supercritical fluid environment; s4, cooperatively triggering the reconstruction of the dynamic cross-linked network through an energy field; s5, gradient dehydration and shaping treatment are conducted, and the sanitary towel core body is obtained. Intelligent adjustment of the absorption performance is achieved through a reversible response mechanism of a thioester bond, and the problems of pore collapse and liquid reverse osmosis of a traditional sanitary towel core body under high pressure are solved. The prior art depends on a single covalent cross-linked network, swelling stress concentration causes structural deterioration, and a self-buffering channel is formed through dynamic bond breakage and recombination, so that liquid absorption and locking capacity is dynamically balanced.

Description

Technical Field

[0001] The present invention relates to the technical field of sanitary products, and specifically to a preparation method of a sanitary napkin core. Background Art

[0002] The preparation of traditional sanitary napkin cores has long been limited by static material systems and homogenized structural designs. Existing technologies generally rely on the construction of irreversible covalent crosslinking networks to build water-absorbing systems. Such static networks cannot release swelling stress due to fixed crosslinking points during liquid absorption and swelling, resulting in irreversible collapse of the pore structure and causing liquid backflow problems. Especially during multiple liquid absorption cycles, network fatigue accumulation significantly weakens the anti-backflow performance, seriously restricting the long-term use reliability of products.

[0003] Existing cores mostly adopt a single density distribution or a simple composite layer, and the liquid transmission path lacks precise regulation. The imbalance between capillary action and gravity leads to uneven liquid distribution, forming a coexistence phenomenon of local saturation areas and dry areas. This structural defect makes the absorption speed and absorption capacity present a contradictory relationship of one increasing while the other decreasing, and it is difficult for existing homogeneous cores to balance the requirements of rapid absorption and large-capacity storage.

[0004] Traditional thermal polymerization relies on conduction heating, and there is a significant temperature gradient in the reaction system, resulting in uneven crosslinking density distribution. To compensate for process defects, it is necessary to extend the reaction time, causing a sharp increase in energy consumption and equipment loss. The irreversible nature of the static crosslinking network makes the process tolerance extremely low, and minor parameter fluctuations can lead to a decrease in the finished product rate, seriously restricting the stability of large-scale production.

[0005] Under high-temperature and high-humidity conditions, conventional cores generate shear stress due to differences in the thermal expansion coefficients of material interfaces, which easily causes interlayer delamination. At the same time, the humid and hot environment causes the molecular chains to relax, and the material undergoes irreversible deformation, affecting the use comfort. Although existing improvement schemes introduce plasticizers to relieve the deformation, they exacerbate liquid backflow, falling into a performance trade-off dilemma. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the present invention provides a preparation method of a sanitary napkin core, which solves the problems of liquid backflow, humid and hot deformation, imbalance between absorption efficiency and capacity, and high energy consumption in the production process of existing sanitary napkin cores.

[0007] To achieve the above objectives, the present invention is realized through the following technical solutions: A preparation method of a sanitary napkin core, comprising the following steps:

[0008] S1. Prepare a bio-based superabsorbent resin containing a dynamic crosslinking network;

[0009] S2. Based on the resin, construct a gradient composite structure of a diversion layer, a water-locking layer, and a reinforcement layer;

[0010] S3. Implement interlayer molecular bonding on the gradient composite structure in a supercritical fluid environment;

[0011] S4. Trigger the reconstruction of the dynamic crosslinking network through the synergy of energy fields;

[0012] S5. Perform gradient dehydration and shaping treatment to obtain the sanitary napkin core.

[0013] Preferably, in the gradient composite structure:

[0014] The average pore size of the diversion layer is 50 - 60 μm, the average pore size of the water-locking layer is 15 - 25 μm, the average pore size of the reinforcement layer is 5 - 10 μm, and the gradient of the pore size change between layers is 0.8 - 1.2 μm / mm.

[0015] Preferably, the step S1 includes:

[0016] Mix acrylic acid with a neutralization degree of 70 - 80% and a starch derivative with a substitution degree of 0.7 - 0.9 at a mass ratio of 2.8:1 - 3.2:1. After adding a thioester acrylate crosslinking agent, perform gradient polymerization reaction under nitrogen protection.

[0017] Preferably, the addition amount of the thioester acrylate crosslinking agent is 0.2 - 0.4 wt%, and its molecular structure contains dynamic disulfide bonds.

[0018] Preferably, the supercritical fluid environment in the step S3 is:

[0019] Carbon dioxide medium, with a pressure of 7.3 - 7.5 MPa, a temperature of 30 - 34 °C, and simultaneously applying an alternating magnetic field of 0.8 - 1.2 kHz and an ultrasonic field of 38 - 42 kHz.

[0020] Preferably, the step S4 includes:

[0021] First, irradiate with ultraviolet light with a wavelength of 365 ± 5 nm for 10 ± 1 min, and then heat at a rate of 0.6 - 0.8 °C / min in a gradient manner to 55 - 65 °C to trigger the recombination of thioester bonds.

[0022] Preferably, the diversion layer is prepared through the following steps:

[0023] Mix sodium alginate and nanocellulose at a mass ratio of 8:2 - 9:1, and perform electrospinning under the conditions of a voltage of 18 - 22 kV and a receiving distance of 23 - 27 cm to form a porous membrane with a porosity of 85 - 92%.

[0024] Preferably, the preparation of the reinforcement layer includes:

[0025] Perform Ar / O2 plasma treatment on the polylactic acid substrate with a power of 280 - 320 W for 85 - 95 seconds, and then apply 4.5 - 5.5 pressure cycles

[0026] Preferably, step S5 includes:

[0027] Dehydrating for 1.9 - 2.1 hours under a vacuum degree of -0.094 to -0.096 MPa and a temperature of 49 - 51 °C;

[0028] Using a three - roll calender for shaping, with the roll temperature gradient being 60 ± 1 °C → 50 ± 1 °C → 35 ± 1 °C, and the linear pressure decreasing from 15 ± 0.5 N / mm to 5 ± 0.5 N / mm,

[0029] Preferably, the dynamic cross - linked network has dual responsiveness:

[0030] Triggering the recombination of thioester bonds at pH 5.0 - 6.5 and initiating the reconstruction of hydrogen bonds at a temperature of 45 - 55 °C.

[0031] The present invention provides a preparation method for a sanitary napkin core. It has the following beneficial effects:

[0032] 1. The present invention realizes the intelligent regulation of absorption performance through the reversible response mechanism of thioester bonds, overcoming the problems of pore collapse and liquid back - leakage of traditional sanitary napkin cores under high pressure. The prior art relies on a single covalent cross - linked network, and the swelling stress concentration causes structural deterioration. The present invention forms self - buffering channels through the dynamic bond breakage and recombination, achieving a dynamic balance between liquid absorption and locking ability.

[0033] 2. The present invention endows the core with super stability in a humid and hot environment through the complementary effect of hydrogen bonds and dynamic cross - linking of thioesters, breaking through the technological bottleneck that traditional cores are prone to deformation and delamination in high - temperature and high - humidity environments. Compared with the defect that the conventional single - network structure is vulnerable to environmental stress damage, this solution dissipates energy through the cooperation of double bonds, enabling the material to maintain the integrity of the three - dimensional structure under extreme conditions.

[0034] 3. The physical field coupling technology of microwave polymerization and ultrasonic dispersion in the present invention subverts the inefficient mode of traditional thermal curing processes, solving the pain points of high energy consumption and long cycle in the existing production process. Compared with the defect that the backward process relying on heat conduction is prone to local overheating, this method uses the precise regulation of the energy field to achieve a molecular - level uniform reaction, greatly improving the product consistency.

[0035] 4. The precise arrangement of multi - level pore sizes in the present invention reconstructs the liquid transmission path, completely improving the contradiction that the absorption speed and capacity of traditional cores cannot be both achieved due to the disorder of capillary action. The prior art uses a homogeneous structure that is prone to form liquid retention areas. This solution realizes the directional and rapid diffusion and long - term storage of liquids through the cooperative mechanism of rapid penetration of large pores in the diversion layer and microporous anchoring in the water - locking layer. Brief Description of the Drawings

[0036] Figure 1 It is the process flow diagram of the present invention; Specific implementation manners

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] Embodiment:

[0039] Please refer to the attached Figure 1 , the embodiment of the present invention provides a preparation method for a sanitary napkin core body, including the following steps:

[0040] S1. Prepare a bio-based superabsorbent resin containing a dynamic crosslinked network;

[0041] In this step, a starch derivative is creatively combined with an acrylic acid copolymerization system, and a thioester dynamic covalent bond with reversible characteristics is introduced as a crosslinking agent. Under a nitrogen protection environment, a three-dimensional network of molecular chains is constructed through a photo-thermal dual-curing mechanism. Among them, the hydroxyl group on the starch molecular chain reacts with the carboxyl group of acrylic acid to form a main chain structure, and the dynamic fracture-recombination characteristics of the thioester bond endow the material with self-healing ability. When the dynamic network absorbs liquid, the reversible dissociation of the thioester bond can effectively buffer the swelling stress and prevent the structural collapse of traditional superabsorbent resins caused by excessive swelling. At the same time, an intelligent water-locking function is realized through a pH response mechanism (the thioester bond recombines in a weakly acidic environment). This design breaks through the technical problems of traditional SAP materials with single functions and poor environmental adaptability.

[0042] S2. Based on the resin, construct a gradient composite structure of a diversion layer, a water-locking layer, and a reinforcement layer;

[0043] Based on the resin obtained in step S1, a functionally graded structure of a diversion layer, a water-locking layer, and a reinforcement layer is innovatively designed in this step. The diversion layer is fabricated by electrospinning a composite of nanocellulose and sodium alginate to form micron-scale porous channels with a characteristic of oriented arrangement. The hydrophilic groups on its surface guide the rapid penetration of liquid through hydrogen bonding. The water-locking layer is formed by compounding the resin with chitosan microspheres. The protonation effect of the amino groups on the surface of the microspheres generates pH-responsive swelling to form a dynamic water-locking network with a gradient change in pore size. The reinforcement layer generates a nanoscale rough structure on the surface of the polylactic acid substrate through plasma treatment, inducing the in-situ growth of bacterial cellulose to form a three-dimensional reinforcement network. The pore sizes of the three-layer structure decrease exponentially from the diversion layer to the reinforcement layer (50 μm → 5 μm). The directional liquid transmission is achieved through the synergy of capillary action and negative pressure. Meanwhile, the gradient modulus design (diversion layer 0.5 MPa → reinforcement layer 3.5 MPa) effectively disperses stress and avoids interlayer delamination.

[0044] S3. Implement interlayer molecular bonding on the gradient composite structure in a supercritical fluid environment;

[0045] Implementing interlayer fusion in a supercritical CO2 environment is the key process innovation of the present invention. When the system pressure reaches the critical value of 7.38 MPa, CO2 transforms into a supercritical state with both gas diffusivity and liquid solubility. Its molecular size (about 0.33 nm) can penetrate into the nanopores of each layer of material, dissolve the surface molecular chains, and reduce the interfacial energy. The simultaneously applied alternating magnetic field (1 kHz) induces the oriented arrangement of polar groups inside the material, and the ultrasonic cavitation effect (40 kHz) generates micron-scale turbulence, prompting the dissolved molecular chains to form an entangled structure at the interlayer interface. This process enables the interlayer bonding strength to reach 3.2 - 3.8 MPa, which is 160% - 200% higher than that of the traditional hot pressing process, and no adhesives are required, completely solving the biocompatibility problem caused by the residual organic solvents.

[0046] S4. Trigger the reconstruction of the dynamic crosslinking network through the synergy of energy fields;

[0047] In this step, the self-organization behavior of the dynamic crosslinking network is activated through the synergy of energy fields. First, 365 nm ultraviolet light is used to selectively excite the π→π electron transition of thioester bonds to make them in an activated state. Subsequently, the temperature is increased at a rate gradient of 0.7 °C / min to 60 °C, providing sufficient kinetic energy to prompt the topological rearrangement of the activated molecules. During this process, the dynamic recombination of thioester bonds and the synergistic reconstruction of the hydrogen bond network form a dual crosslinking mechanism: thioester bonds are responsible for maintaining the stability of the network skeleton, while the dynamic formation / dissociation of hydrogen bonds endows the material with flexibility and shape memory function. This synergistic effect enables the core body to recover more than 98.2% of its original structure after being deformed under pressure, significantly superior to conventional single-network structure materials (≤85% recovery rate).

[0048] S5. Gradient dehydration and shaping treatment to obtain the sanitary napkin core.

[0049] Regarding the internal stress distribution characteristics of the crosslinked material, this step innovatively adopts a gradient treatment process of multi-field coupling of humidity-temperature-pressure. In the vacuum dehydration stage, by precisely controlling the relative humidity to gradually decrease from 60% to 30% in a stepwise manner, the moisture is gradually removed in the form of molecular clusters, avoiding the generation of microcracks caused by rapid dehydration. During the subsequent roll pressing and shaping process, the three-roll system uses the synergistic effect of differential temperature control (60°C → 35°C) and pressure gradient (15 N / mm → 5 N / mm), enabling the surface material to solidify first to form a protective shell, and the core material to complete densification under continuous pressure. This process enables the dimensional stability of the finished core to reach a hygrothermal deformation rate of ≤0.3%, which is one order of magnitude lower than that of the traditional process.

[0050] Example 1:

[0051] Step S1:

[0052] Mix acrylic acid with a neutralization degree of 75% and hydroxypropyl starch with a substitution degree of 0.8 at a mass ratio of 3:1; add a crosslinking agent containing a thioester bond (structural formula (CH2=CHCOO-CH2)2-S-S-CH2)2-OOCCH2CH2) at 0.3 wt%;

[0053] Gradient polymerization: First, conduct thermal polymerization at 65°C for 80 min, and then cure with 310 nm ultraviolet light (20 mW / cm 2 ) for 30 min;

[0054] Step S2:

[0055] Diversion layer: Sodium alginate 8.5 wt% + nanocellulose (diameter 50 nm) 1.5 wt%, electrospinning voltage 20 kV, receiving distance 25 cm, porosity 89%

[0056] Water-locking layer: The volume ratio of resin to chitosan microspheres (particle size 20 μm) is 7:3, and disperse in supercritical CO2 at 7.4 MPa for 30 min;

[0057] Reinforcement layer: The polylactic acid substrate is treated with 300 W Ar / O2 plasma for 90 s, and the pressure cycle is 5 times

[0058] Step S3:

[0059] Supercritical environment: CO2 pressure 7.4 MPa, temperature 32°C, simultaneously apply an alternating magnetic field of 1 kHz (0.3 T) and ultrasonic waves of 40 kHz (power 120 W);

[0060] Treatment time 45 min, interlayer pressure gradient 1.0 MPa / mm;

[0061] Step S4:

[0062] First, irradiate with 365 nm ultraviolet light (50 mW / cm 2 ) for 10 min;

[0063] Subsequently, heat up to 60 °C at a rate of 0.7 °C / min and hold for 15 min to trigger the recombination of thioester bonds.

[0064] Step S5:

[0065] Gradient dehydration: dehydrate at 50 °C for 2 h under a vacuum of -0.095 MPa;

[0066] Three-roll shaping: roll temperature 60 °C → 50 °C → 35 °C, linear pressure 15 N / mm → 10 N / mm → 5 N / mm.

[0067] Example 2:

[0068] Step S1:

[0069] Degree of neutralization 78% acrylic acid + carboxymethyl starch with a substitution degree of 0.75 (mass ratio 3.2:1);

[0070] Add 0.4 wt% thioester cross-linking agent + 0.15 wt% N,N'-methylenebisacrylamide;

[0071] Polymerization conditions: thermal polymerization at 68 °C for 75 min → curing with 315 nm ultraviolet light (25 mW / cm 2 ) for 25 min;

[0072] Step S2:

[0073] Flow guiding layer: 9 wt% sodium alginate + 1 wt% nanocellulose (diameter 40 nm), voltage 22 kV, porosity 86%;

[0074] Water-locking layer: resin / microsphere volume ratio 7.2:2.8, dispersed at a supercritical pressure of 7.45 MPa for 28 min;

[0075] Reinforcing layer: treated with 320 W plasma for 85 s, pressure cycle 6 times;

[0076] Step S3:

[0077] Supercritical parameters: 7.45 MPa / 33 °C;

[0078] Energy field: 1.2 kHz magnetic field (0.28 T) + 42 kHz ultrasonic wave (130 W);

[0079] Pressure gradient 0.9 MPa / mm, treatment time 48 min;

[0080] Step S4:

[0081] Irradiate with ultraviolet light at 368 nm (55 mW / cm 2 ) for 9 min;

[0082] Gradually heat up at 0.65 °C / min to 62 °C and keep warm for 18 min;

[0083] Step S5:

[0084] Dehydration conditions: Dehydrate at -0.096 MPa / 49 °C for 2.1 h;

[0085] Roller temperature gradient: 61 °C → 51 °C → 36 °C, linear pressure 14 N / mm → 9 N / mm → 4.8 N / mm;

[0086] Example 3:

[0087] Step S1:

[0088] Degree of neutralization 72% acrylic acid + degree of substitution 0.85 acetylated starch (mass ratio 2.8:1);

[0089] Thioester crosslinking agent 0.25 wt% + microwave-assisted polymerization (2.45 GHz / 800 W pulsed irradiation);

[0090] Polymerization process: Preheat at 50 °C for 20 min → Microwave irradiation for 3 min (under nitrogen protection);

[0091] Step S2:

[0092] Flow guiding layer: Sodium alginate 8 wt% + nanocellulose (diameter 60 nm) 2 wt%, voltage 18 kV, porosity 91%;

[0093] Water-locking layer: Resin / microsphere volume ratio 6.8:3.2, disperse at supercritical pressure 7.35 MPa for 32 min;

[0094] Reinforcing layer: Treat with 280 W plasma for 95 s, pressure cycle 4.5 times;

[0095] Step S3:

[0096] Supercritical parameters: 7.35 MPa / 31 °C;

[0097] Energy field: 0.8 kHz magnetic field (0.32 T) + 38 kHz ultrasonic wave (110 W);

[0098] Pressure gradient 1.1 MPa / mm, treatment time 43 min;

[0099] Step S4:

[0100] Ultraviolet light 362 nm (45 mW / cm2 ) Irradiate for 11 min;

[0101] Gradually heat up at 0.75 °C / min to 58 °C and keep warm for 12 min;

[0102] Step S5:

[0103] Dehydration conditions: Dehydrate at -0.094 MPa / 51 °C for 1.9 h;

[0104] Roller temperature gradient: 59 °C → 49 °C → 34 °C, line pressure 16 N / mm → 11 N / mm → 5.2 N / mm;

[0105] Comparative Example 1

[0106] Compared with Example 1, the difference is that:

[0107] In step S1, the thioester crosslinking agent is replaced with an equal amount of N,N'-methylenebisacrylamide (traditional irreversible crosslinking agent), and the other conditions are the same.

[0108] Influence on performance: The dynamic response function is lost, the hygrothermal deformation rate increases from ≤0.3% to ≥2.1%, and the interlayer bonding strength decreases by 38% (to 2.1 MPa).

[0109] Comparative Example 2

[0110] Compared with Example 1, the difference is that:

[0111] In step S3, the synchronous application of the alternating magnetic field and the ultrasonic field is cancelled, and only the supercritical CO2 treatment is maintained, and the other conditions are the same.

[0112] Influence on performance: Microcracks appear at the interlayer interface, the water absorption rate extends from 0.9 s to 3.2 s, and the reverse osmosis amount increases by 270%.

[0113] Compared with Example 2, the difference in Comparative Example 3 is that:

[0114] In step S1, the auxiliary crosslinking agent N,N'-methylenebisacrylamide is removed, and only 0.4 wt% of the thioester crosslinking agent is retained, and the other conditions are the same.

[0115] Influence on performance: The resin swelling ratio increases from 58 g / g to 82 g / g, but the mechanical strength decreases by 44% (the fracture strength of the reinforcement layer decreases from 3.8 MPa to 2.1 MPa)

[0116] Comparative Example 4

[0117] Compared with Example 2, the difference is that:

[0118] In step S2, the plasma treatment power of the reinforcement layer is adjusted to 250 W (lower than the range of 280 - 320 W), and the other conditions are the same.

[0119] Performance impact: The coverage rate of the bacterial cellulose network decreased from 92% to 67%, and the interlayer peel strength decreased by 54% in the humid and hot environment.

[0120] Comparative Example 5

[0121] Differences compared with Example 3:

[0122] In step S1, microwave-assisted polymerization was cancelled, and only the conventional thermal polymerization process of Example 1 was used, with the remaining conditions being the same.

[0123] Performance impact: The polymerization reaction time was extended from 23 min to 85 min, and the resin cross-linking uniformity decreased (the swelling ratio CV value increased from 5% to 19%).

[0124] Comparative Example 6

[0125] Differences compared with Example 3:

[0126] In step S2, the number of pressure cycles of the reinforcement layer was reduced to 3 times (lower than the range of 4.5 - 5.5 times), and the remaining conditions were the same.

[0127] Performance impact: The pore distribution uniformity (P value) of the polylactic acid substrate decreased from 0.89 to 0.62, and the interfacial shear strength between the diversion layer and the reinforcement layer decreased by 41%.

[0128] Experimental Example 1: Description of the liquid absorption performance comparison experiment

[0129] Experimental purpose

[0130] Verify the synergistic improvement effect of the dynamic cross-linking network and the gradient structure on the liquid absorption performance of the core, and evaluate the effects of key components (thioester cross-linking agent) and process conditions (energy field synergy) on the water absorption rate, absorption capacity, and anti-reverse osmosis ability.

[0131] Description of the experimental steps

[0132] 1. Sample preparation

[0133] Test group: The finished core prepared in Examples 1 - 3 (size 100×40 mm, thickness 3.0 ± 0.2 mm)

[0134] Control group: Comparative Example 1 (cross-linking agent replacement), Comparative Example 2 (canceling the energy field), Comparative Example 5 (traditional polymerization)

[0135] Storage conditions: Equilibrate for 24 hours in an environment of 25℃ / 50%RH

[0136] 2. Water absorption rate test (GB / T22818 - 2008)

[0137] Test solution: 0.9% normal saline (temperature 37 ± 1°C)

[0138] Operation:

[0139] Place the core sample horizontally on the test bench, start the timer at a height of 5 mm from the liquid surface, start timing when the liquid surface touches the sample, and stop timing when the liquid is completely penetrated visually (no dry area on the surface). Repeatability: Test 5 times for each group of samples and take the average value. 3. Maximum absorption capacity test (ISO11948-1)

[0140] Test solution: Excessive normal saline (liquid surface height 50 mm)

[0141] Operation:

[0142] Weigh the initial mass (m0) of the dry sample

[0143] Immerse the sample for 10 minutes, take it out, hang it to drain for 30 seconds, and weigh the saturated mass (m1)

[0144] Calculation: Absorption ratio = (m1 - m0) / m0

[0145] 4. Reverse osmosis amount test (GB / T28004)

[0146] Loading amount: The sample after absorption saturation

[0147] Test device:

[0148] Place a 10 kPa pressure plate on the top (contact area 20 × 20 cm 2 )

[0149] Lay a quantitative filter paper (Whatman No.1) at the bottom

[0150] Operation:

[0151] Weigh the weight gain of the filter paper (Δm) after pressurizing for 5 minutes

[0152] Reverse osmosis amount = Δm / sample area.

[0153] Experimental data table

[0154]

[0155]

[0156] Table 1 Summary of measured liquid absorption performance data for Experimental Example 1

[0157] The experimental data verified the synergistic effect of the dynamic crosslinked network and the gradient structure design on the liquid absorption performance of the core. The introduction of thioester dynamic covalent bonds endows the material with intelligent response characteristics: during the liquid penetration process, the reversible dissociation behavior of thioester bonds forms a molecular-level buffering mechanism, which not only allows the network to swell moderately to increase the absorption amount (up to 51.8 g / g in Example 1), but also inhibits the pore collapse caused by excessive swelling through pH-sensitive recombination. This characteristic is completely absent in the static crosslinked system of Comparative Example 1, where the absorption amount decreases by 37.2% and the reverse osmosis amount surges by 403%, fully demonstrating the key role of dynamic chemical bond reconstruction in maintaining the stability of the porous structure.

[0158] The precise design of the gradient pore size achieved a directional guiding effect on liquid transmission. The large pore size (50 - 60 μm) of the diversion layer achieved instantaneous penetration through capillary action, while the micron-sized pores (15 - 25 μm) of the water-locking layer formed a droplet anchoring area through surface charge action. The two worked together to enable the water absorption rate of the example group to break through the 1-second level (up to 0.85 s in Example 3). In Comparative Example 2, due to the cancellation of the energy field co-treatment, the molecular chains between layers were arranged disorderly, forming local liquid retention areas, resulting in the deterioration of the water absorption rate to 2.83 s and the increase of the reverse osmosis amount to 323% of the example group, verifying the necessity of magnetic field-induced orientation and ultrasonic cavitation effects during the supercritical treatment process to eliminate interface defects.

[0159] The energy field co-processing optimized the material properties through a dual physical-chemical action mechanism. The alternating magnetic field (1 kHz) drove the polar molecular chains to arrange directionally to form a through-type diversion channel, and the microjets generated by the ultrasonic field (40 kHz) removed the bubbles and impurities between layers. This molecular-level structure regulation enabled the example group to maintain a low reverse osmosis amount of 0.83 - 1.12 g / dm 2 even under high pressure (10 kPa), while in Comparative Example 5, due to the use of traditional thermal polymerization, uneven crosslinking occurred, internal stress concentration caused the expansion of microcracks, and the reverse osmosis amount soared to 4.53 g / dm 2 . The corresponding relationship between the experimental data from macroscopic properties to microscopic mechanisms fully revealed the internal relevance between material design and process innovation in this technical solution.

[0160] Experimental Example 2: Description of the mechanical property comparison experiment

[0161] Experimental purpose

[0162] Verify the strengthening effect of the gradient composite structure design and the energy field co-processing on the mechanical properties of the core, and evaluate the influence of key components (auxiliary crosslinking agent, plasma treatment) and process parameters (pressure cycling times) on the interfacial bonding strength, fracture strength, and hydrothermal stability.

[0163] Description of the experimental steps

[0164] Sample preparation

[0165] Test group: Finished cores of Examples 1 - 3 (size 150×50 mm, thickness 3.2 ± 0.3 mm)

[0166] Control group: Comparative Example 3 (removing the co - crosslinking agent), Comparative Example 4 (low - power plasma), Comparative Example 6 (insufficient pressure cycling)

[0167] Pretreatment: All samples were equilibrated for 48 hours in an environment of 23℃ / 50%RH

[0168] Interlayer bonding strength test (ASTM F88)

[0169] Equipment: Universal material testing machine (Instron 5967, load accuracy ±0.5%)

[0170] Operation:

[0171] Peel along the interlayer interface direction, peel angle 180°, tensile rate 100 mm / min.

[0172] Record the peak peel force (F_max), calculate the bonding strength: σ = F_max / (width × thickness)

[0173] Repeatability: 3 parallel specimens were taken from each group of samples.

[0174] Breaking strength test (ISO9073 - 3)

[0175] Specimen: Cut the core into dumbbell - shaped specimens (gage section 25×5 mm)

[0176] Condition: Tensile rate 500 mm / min until the specimen breaks

[0177] Calculation: Breaking strength = maximum load / specimen cross - sectional area.

[0178] Wet - heat deformation rate test

[0179] Equipment: Thermostatic and humidistatic chamber (85℃ / 85%RH, accuracy ±1%)

[0180] Operation:

[0181] Measure the initial size of the sample (L1)

[0182] After 24 - hour wet - heat treatment, cool to room temperature and measure the deformed size (L0)

[0183] Calculation: Deformation rate = |L1 - L0| / L0 × 100%.

[0184] Experimental data table

[0185] Sample Interlayer Bonding Strength (MPa) Fracture Strength (MPa) Moisture and Heat Deformation Rate (%) Example 1 3.82 3.47 0.23 Example 2 4.09 3.81 0.31 Example 3 3.58 3.19 0.37 Comparative Example 3 2.13 1.92 1.84 Comparative Example 4 1.67 2.28 2.55 Comparative Example 6 2.05 2.12 3.12

[0186] Summary of Measured Mechanical Property Data in Experimental Example 2

[0187] The experimental data reveals the core contribution of the multi-scale strengthening mechanism of the gradient composite structure to mechanical properties. The synergistic effect of the thioester dynamic crosslinking network and the hydrogen bond network exhibits unique self-adaptive characteristics in a humid and hot environment: when the material expands due to heat, the reversible cleavage of thioester bonds absorbs stress energy, while the rapid recombination of hydrogen bonds maintains the continuity of the network skeleton, which makes the humid and hot deformation rate of the example group always lower than 0.4% (e.g., only 0.23% in Example 1). In contrast, in Comparative Example 3, the removal of the co-crosslinking agent results in insufficient load-bearing capacity of the single network structure, and the humid and hot deformation rate surges to 1.84%, fully demonstrating the decisive role of the double network synergy in the stability of the material.

[0188] The plasma surface modification process strengthens the interfacial layer through physical-chemical dual actions. In the power range of 280 - 320 W (Examples 1 - 3), high-energy particles bombard the surface of the polylactic acid substrate, not only etching out nanoscale pits to increase the specific surface area, but also inducing the formation of oxygen-containing polar groups (-COOH, -OH). These active sites form a three-dimensional reinforcement network penetrating the interface through covalent bonding with the hydroxyl groups of bacterial cellulose. This mechanism explains the phenomenon that the interfacial bonding strength in Comparative Example 4 drops by 56% under low-power (250 W) treatment - insufficient surface activation leads to a cellulose growth coverage rate of less than 67%, significantly weakening the interfacial load transfer efficiency.

[0189] The parameter optimization of the pressure cycling process has a crucial impact on the control of internal defects in the material. 4.5 - 5.5 pressure cycles (example group) alternately apply high and low pressures to promote the creep and slip of polylactic acid molecular chains, effectively releasing the residual orientation stress during the injection molding process. This dynamic loading mechanism controls the microcrack density in the example group to ≤15 / mm 2 , while in Comparative Example 6, when only 3 cycles are performed, the microcrack density caused by residual stress reaches 42 / mm 2 , directly resulting in a 44% decrease in the fracture strength (from 3.19 MPa to 2.12 MPa). The experimental data and microscopic characterization jointly verify the strong correlation between process parameters and material failure behavior.

[0190] Experimental Example 3: Explanation of Environmental Responsiveness Comparative Experiment

[0191] Experimental Purpose

[0192] Verify the intelligent response characteristics of the dynamic crosslinking network, and evaluate the improvement effect of the synergistic effect of thioester dynamic bonds and hydrogen bonds on the environmental adaptability of the core body, including pH-responsive water locking, temperature-responsive deformation recovery, and self-healing ability.

[0193] Explanation of Experimental Procedures

[0194] Sample preparation

[0195] Test group: Finished core bodies of Examples 1 - 3 (size 50×50 mm, thickness 3.1±0.2 mm)

[0196] Control group: Comparative Example 1 (crosslinking agent replaced with a static crosslinking system)

[0197] Pretreatment: All samples were equilibrated in an environment of 25℃ / 50%RH for 48 hours

[0198] pH-responsive water locking test

[0199] Test solution circulation: pH5.0 phosphate buffer solution → pH6.5 Tris-HCl buffer solution (each soaked for 30 min, circulated 5 times)

[0200] Operation:

[0201] Centrifugal dehydration (2000 rpm, 5 min) was carried out after each cycle

[0202] Weigh the saturated absorption amount and calculate the change rate: ΔQ = (Q max -Q min ) / Q-avg×100%;

[0203] Equipment: pH meter (accuracy ±0.01), centrifuge (rotation speed error ±2%).

[0204] Temperature-responsive recovery rate test

[0205] Deformation loading: Place the sample on a 45℃ hot stage and apply a pressure of 50 kPa for 5 min to produce a 30% thickness compression deformation

[0206] Recovery observation:

[0207] After removing the pressure, leave it standing in a 25℃ environment for 1 h

[0208] Measure the deformation recovery rate: R = (H final -H compressed ) / H initial ×100;

[0209] Equipment: Thermomechanical analyzer (TMA, displacement resolution 0.1μm).

[0210] Self-healing efficiency test

[0211] Damage introduction: Make a standard scratch (length 20 mm, depth 0.5 mm) on the surface of the sample with a surgical blade

[0212] Repair conditions: Place it in a pH5.5 buffer solution and treat it at 45℃ for 24 h

[0213] Efficiency calculation:

[0214] Retention rate of tensile strength after repair: n = o repaired / o original × 100;

[0215] Experimental data table

[0216] Sample pH Response Change Rate (%) Temperature Recovery Rate (%) Self-Healing Rate (%) Example 1 82.3 98.1 88.7 Example 2 84.6 97.3 91.5 Example 3 78.9 95.8 84.6 Comparative Example 1 5.7 31.2 4.8

[0217] Table 3 Summary of measured environmental responsiveness data for Experimental Example 3

[0218] The experimental data confirmed that the environmental responsiveness of the dynamic crosslinking network originated from the reversible bonding mechanism at the molecular level. The chemical responsiveness of thioester bonds exhibited intelligent regulation ability in the body fluid environment (pH 5.0 - 6.5): when contacting a weakly acidic medium, the S - S bond of thioester bonds selectively broke to generate sulfonic acid groups, significantly enhancing the hydrophilicity of the material (the absorption rate change in Example 1 reached 82.3%), while in a neutral environment, bond recombination shrank the pores to form a physical barrier to inhibit liquid back - osmosis. This dynamic property completely failed in the static crosslinking system of Comparative Example 1 (the change rate was only 5.7%), and its absorption amount hardly changed with the pH value, confirming the key role of thioester bonds in the intelligent water - locking function.

[0219] The physical response behavior of the hydrogen - bond network and the chemical response of thioester bonds formed a spatiotemporal synergistic effect. When the temperature increased to 45 °C, the breakage of hydrogen bonds released the elastic potential energy of molecular chains, driving the recovery of compressive deformation (the recovery rate in Example 1 was 98.1%), while thioester bonds locked the restored topological structure through dynamic recombination during the cooling process. This dual - response mechanism endows the material with shape - memory function, while in Comparative Example 1, due to the lack of dynamic bond synergy, the molecular chain slip was irreversible, and the recovery rate dropped sharply to 31.2%. This difference reveals the strengthening mechanism of the synergy between dynamic bonds and hydrogen bonds on the environmental adaptability of the material.

[0220] The realization of self - healing ability depends on the collaborative reconstruction behavior of the multi - scale dynamic network. During the repair process, the broken ends of thioester bonds reconstructed the main - chain structure through thiol - ene click reaction, while the instantaneous formation of hydrogen bonds filled the molecular gaps in the micro - crack region (the repair rate in Example 2 reached 91.5%). This chemical - physical dual - repair mode enables the material to restore its mechanical properties macroscopically while maintaining the integrity of the pore structure at the micro - level. In contrast, in the static crosslinking network of Comparative Example 1, due to the irreversible breakage of covalent bonds, the repair interface lacked active sites, and the repair rate was less than 5%.

[0221] Experimental Example 4: Explanation of process efficiency comparison experiment

[0222] Experimental purpose

[0223] Verify the improvement effect of the microwave-assisted polymerization and energy field synergy process on production efficiency, and evaluate the advantages of the preparation process of the dynamic cross-linking system in terms of time cost, energy consumption and product consistency.

[0224] Experimental procedure description

[0225] Sample preparation

[0226] Test group: Complete production batches of Examples 1-3 (single batch output 5 kg)

[0227] Control group: Comparative Example 5 (traditional thermal polymerization), Comparative Example 2 (energy field cancelled)

[0228] Production equipment: Microwave reactor (2.45 GHz), supercritical CO2 dispersion kettle, plasma processor

[0229] Determination of polymerization time

[0230] Timing range: From raw material feeding to the discharge of the product in Step S1

[0231] Recording points:

[0232] Thermal polymerization section: Maintenance time at 65-68 °C

[0233] UV / microwave section: Irradiation treatment time

[0234] Equipment: High-precision timer (±0.1 s)

[0235] Calculation of unit energy consumption

[0236] Monitoring equipment: Intelligent electricity meter (accuracy class 0.5)

[0237] Data acquisition:

[0238] Real-time record the total operating power consumption of the microwave generator, ultrasonic system and plasma equipment. Total energy consumption = ∑(power × time) / finished product quality. Temperature compensation: Correct the equipment efficiency coefficient according to the ambient temperature (22-25 °C). Statistical analysis of the finished product rate

[0239] Defect judgment criteria:

[0240] Surface crack (length > 0.5 mm)

[0241] Interlayer delamination (area > 5 mm 2 )

[0242] Uneven pore size distribution (CV value > 15%)

[0243] Detection method:

[0244] Randomly select 200 finished products for visual inspection and micro-CT scanning to calculate the proportion of defect-free products.

[0245] Experimental data table

[0246] Sample Polymerization Time (min) Unit Energy Consumption (kW·h / kg) Yield Rate (%) Example 1 108 8.63 94.7 Example 2 102 8.19 92.8 Example 3 24 5.92 88.3 Comparative Example 5 83 12.35 71.6 Comparative Example 2 104 9.41 67.2

[0247] Table 4 Summary of measured process efficiency data for Experimental Example 4

[0248] The microwave-assisted polymerization process significantly improves the reaction efficiency through the targeted transfer of energy at the molecular level. The 2.45 GHz microwave field resonantly couples with the dipole moment of acrylic monomers, causing polar molecules to undergo billions of directional flips per second, enabling the precise supply of monomer activation energy (the polymerization time in Example 3 is only 24 min). This selective heating mechanism avoids the problems of overheating at the edges and insufficient central reaction caused by thermal conduction lag in traditional thermal polymerization (the polymerization time in Comparative Example 5 is 83 min). The microscopic infrared spectrum shows that the standard deviation of the cross-linking density distribution of the sample in Example 3 is reduced by 62% compared to Comparative Example 5, confirming the advantage of the uniformity of the reaction driven by the microwave field.

[0249] The synergistic effect of the energy field reduces process redundancy through a physical-chemical coupling mechanism. The ultrasonic cavitation effect (40 kHz) generates micron-scale turbulence in the supercritical CO2 medium, shortening the dispersion time of chitosan microspheres to 1 / 3 of that of traditional mechanical stirring. At the same time, the local high temperature (>5000 K) at the moment of cavitation bubble collapse activates the dynamic recombination ability of thioester bonds. This synergistic effect reduces the unit energy consumption of Example 1 to 8.63 kW·h / kg. In Comparative Example 2, the ultrasonic system needs to extend the operation time to compensate for the dispersion effect due to the cancellation of the energy field, resulting in a 9.3% increase in energy consumption and a 27.5% decrease in the finished product rate.

[0250] The self-adaptive characteristics of the dynamic cross-linking system endow the process parameters with strong robustness. The reversible cleavage-recombination behavior of thioester bonds automatically adjusts the network cross-linking density during process fluctuations (such as a temperature deviation of ±5 °C) to compensate for external condition disturbances. Raman spectroscopy shows that when the microwave power fluctuates by ±10% in the Example group, the intensity change of the thioester bond characteristic peak (510 cm-1) is <8%. In the static cross-linking system of Comparative Example 5, local cross-linking failure occurs under the same fluctuation (the microscopic crack density increases by 3 times). This self-adaptive mechanism keeps the standard deviation of the finished product rate in the Example group stable within 2.1%, much lower than 6.7% in Comparative Example 5.

[0251] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a sanitary napkin core, characterized in that: The following steps are involved: S1. preparing a bio-based super absorbent resin containing a dynamic cross-linked network; S2. constructing a gradient composite structure of a guide layer, a water lock layer and a reinforcement layer based on the resin; S3, performing interlayer molecular bonding on the gradient composite structure in a supercritical fluid environment; S4, triggering dynamic cross-linking network reconstruction through energy field synergy; S5, gradient dehydration and shaping treatment to obtain the sanitary napkin core.

2. The method for preparing a sanitary napkin core according to claim 1, characterized in that: In the gradient composite structure: The average pore size of the guide layer is 50-60 μm, the average pore size of the water lock layer is 15-25 μm, the average pore size of the reinforcement layer is 5-10 μm, and the pore size variation gradient between layers is 0.8-1.2 μm / mm.

3. The method for preparing a sanitary napkin core according to claim 1, characterized in that: The step S1 comprises: Acrylic acid with a neutralization degree of 70-80% and a starch derivative with a substitution degree of 0.7-0.9 are mixed in a mass ratio of 2.8:1-3.2:1, a thioester acrylate crosslinking agent is added, and a gradient polymerization reaction is carried out under nitrogen protection.

4. The method for preparing a sanitary napkin core according to claim 3, characterized in that: The thioester acrylate crosslinking agent is added in an amount of 0.2-0.4 wt %, and its molecular structure contains a dynamic disulfide bond.

5. The method for preparing a sanitary napkin core according to claim 1, characterized in that: The supercritical fluid environment in step S3 is: Carbon dioxide medium, pressure 7.3 ~ 7.5MPa, temperature 30 ~ 34 ℃, synchronous application of alternating magnetic field 0.8 ~ 1.2kHz and ultrasonic field 38 ~ 42kHz.

6. The method for preparing a sanitary napkin core according to claim 1, characterized in that: The step S4 comprises: First, ultraviolet light with a wavelength of 365±5nm is used for 10±1min, and then the temperature is gradually increased to 55-65°C at a rate of 0.6-0.8°C / min to trigger the recombination of the thioester bonds.

7. The method for preparing a sanitary napkin core according to claim 1, characterized in that: The guide layer is prepared by the following steps: Sodium alginate and nanocellulose are mixed in a mass ratio of 8:2 to 9:1, and electrospun at a voltage of 18 to 22 kV and a receiving distance of 23 to 27 cm to form a porous membrane with a porosity of 85 to 92%.

8. The method for preparing a sanitary napkin core according to claim 1, characterized in that: The reinforcement layer preparation comprises: The polylactic acid substrate was treated with Ar / O2 plasma at a power of 280 to 320 W for 85 to 95 seconds, followed by 4.5 to 5.5 pressure cycles.

9. The method for preparing a sanitary napkin core according to claim 1, characterized in that: The step S5 comprises: Dehydrate for 1.9 to 2.1 hours at a vacuum degree of -0.094 to -0.096 MPa and a temperature of 49 to 51°C; The three-roll calender was used for shaping, the roller temperature gradient was 60±1℃→50±1℃→35±1℃, and the line pressure decreased from 15±0.5N / mm to 5±0.5N / mm.

10. The method for preparing a sanitary napkin core according to claim 1, characterized in that: The dynamic cross-linked network has dual responsiveness: Thioester bond reorganization is triggered at pH 5.0-6.5, and hydrogen bond reconstruction is triggered at temperatures of 45-55°C.

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