Composite bandage with gradient liquid absorption function and hot press molding process thereof

Abstract

The invention relates to the technical field of medical dressing preparation, and discloses a composite bandage with a gradient liquid absorption function and a hot press molding process thereof, and the composite bandage is composed of a chitosan fiber and polyvinyl alcohol fiber blended matrix and an in-situ combined functional coating. The preparation process comprises the following steps: preparing a latent impregnation liquid containing a volatile alkaline regulator, impregnating a substrate, and then carrying out asymmetric hot pressing. Esterification crosslinking and hydrophobic modification are initiated by volatilization of a high-temperature side regulator, and an inhibition environment is maintained by retention of a low-temperature side regulator, so that a continuous chemical crosslinking density gradient and a hydrophilic and hydrophobic gradient are constructed in the thickness direction of a single matrix. According to the invention, a'heat-gas-chemical 'linkage mechanism is utilized, so that one-way liquid guide and low reverse osmosis performance of the bandage are realized, and the problems that the traditional laminated dressing is easy to layer and the storage stability of high-activity slurry is poor are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical dressing preparation, in particular to a composite bandage with gradient liquid absorption function and a hot press forming process thereof. BACKGROUND

[0002] In the field of chronic wound care, efficient management of exudate is a key factor in promoting healing. An ideal medical dressing should have a one-way liquid guiding function, i.e. it can quickly absorb and transport the exudate on the wound surface to the inside or back side of the dressing, while preventing the liquid from flowing back to the wound surface in a compressed state to avoid the skin around the wound from being soaked and reduce the risk of infection.

[0003] Currently, most one-way liquid guiding dressings on the market use a multi-layer composite structure, usually composed of a hydrophobic wound contact layer, a hydrophilic intermediate liquid absorption layer, and a breathable and water-impermeable backing layer bonded by physical adhesion or hot melt point bonding. However, this physical layering structure has significant interface compatibility problems in actual use. Due to the difference in polymer materials of each functional layer, the water absorption and swelling coefficients differ greatly. When the dressing absorbs a large amount of body fluid, the stress mismatch between layers easily leads to delamination or peeling, not only destroying the continuity of the liquid guiding channel, but also possibly causing material fragments to remain on the wound surface. In addition, the presence of interlayer adhesive often increases the liquid transmission resistance, weakening the driving force of capillary action.

[0004] To solve the problem of interlayer peeling, researchers have tried to build a pore size gradient or wettability gradient within a single matrix. Physical methods to build gradients are usually expensive, have low production efficiency, and have poor mechanical properties, making it difficult to meet the needs of industrialized continuous production. While chemical methods to build gradients have higher efficiency, they face the dual challenges of reaction control and slurry stability. In order to achieve rapid hydrophobic modification and crosslinking solidification, high-activity crosslinking systems are usually used, which makes the impregnating liquid prone to spontaneous pre-crosslinking or precipitation during storage and coating, resulting in a very short pot life of the slurry. At the same time, existing single-sided coating or single-sided light irradiation grafting processes cannot form a smooth and continuous chemical potential gradient in the thickness direction, often causing interface mutations or excessive penetration of modifying agents, which damages the overall liquid absorption capacity and softness of the material. Therefore, developing an integrated dressing preparation technology that combines structural stability, long-term slurry stability, and excellent one-way liquid guiding performance is a technical challenge that needs to be addressed in this field. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a composite bandage with gradient liquid absorption function and a hot-press forming process thereof, which solves the problem of the existing unidirectional liquid guiding dressing mainly adopting a physical laminated structure, facing the problems of easy delamination and large interlayer resistance due to liquid absorption swelling, and the single matrix gradient technology is limited by the technical bottlenecks of high preparation cost, poor mechanical properties and difficulty in balancing reaction efficiency and storage stability of high active chemical system.

[0006] To achieve the above object, the present application is implemented by the following technical scheme: a composite bandage with gradient liquid absorption function, comprising: The composite bandage is composed of a fiber matrix and a functional coating combined in situ on the fiber matrix; The fiber matrix is a non-woven fiber mat made of high deacetylation degree chitosan fibers and polyvinyl alcohol fibers mixed in a mass ratio of 60:40 to 80:20, and the area density is 120-180 g / m²; The functional coating is formed by non-symmetric hot-press reaction of a latent impregnation liquid, and the latent impregnation liquid contains a solvent, a crosslinking agent, a hydrophobic modifier and a volatile alkaline regulator; In the latent impregnation liquid, the mass percentage concentration of the crosslinking agent is 4.0%-8.0%, and the mass percentage concentration of the hydrophobic modifier is 0.5%-2.5%; The composite bandage has a chemical crosslinking density gradient and a hydrophilic-hydrophobic gradient induced by phase transition migration of the volatile alkaline regulator in the thickness direction.

[0007] Preferably, the crosslinking agent is selected from citric acid or 1,2,3,4 butane tetracarboxylic acid; the hydrophobic modifier is octadecenyl succinic anhydride; the deacetylation degree of the high deacetylation degree chitosan fiber is 90%-95%; and the alcoholysis degree of the polyvinyl alcohol fiber is 88%-99%.

[0008] A hot-press forming process for a composite bandage with gradient liquid absorption function, the process comprising the following steps: S1, dissolving and dispersing polyvinyl alcohol fibers, adding high deacetylation degree chitosan fibers, a crosslinking agent and a hydrophobic modifier, and dropping a volatile alkaline regulator, adjusting the solution to alkaline pH to form a latent impregnation liquid, and inhibiting the activity of the crosslinking agent by using an alkaline environment; S2, impregnating the fiber matrix in the latent impregnation liquid, performing low-temperature vacuum drying after padding, so that the matrix retains a certain moisture content, and the drying temperature is lower than the violent volatilization temperature of the volatile alkaline regulator; S3, placing the low-temperature dried matrix in a flat plate hot press with independent temperature control function for one-way hot pressing, wherein the upper mold is set to low temperature and the lower mold is set to high temperature, and the non-symmetric heat field is used to induce reaction; S4, after the hot pressing, the substrate is cleaned and dried to obtain a finished product.

[0009] Preferably, in step S1, the volatile alkaline regulator is ammonia water; the crosslinking agent is citric acid; and the hydrophobic modifier is octadecenyl succinic anhydride. The adjustment to the alkaline pH value is specifically adjusting the pH value to 7.8-8.5, so as to convert the carboxyl in the crosslinking agent into an ammonium salt form to lock the reaction activity.

[0010] Preferably, in step S1, the preparation process of the latent impregnating solution comprises: after the crosslinking agent and the hydrophobic modifier are added, dispersion is performed by a high-speed shearing emulsifier, the shearing rotation speed is 3000-5000 rpm, and the dispersion time is 10-15 minutes.

[0011] Preferably, in step S2, the belt liquid rate after the padding is controlled to be 150%-200%; The temperature of the low-temperature vacuum drying is controlled to be 40-50℃; The water content of the substrate is controlled to be 20%-30%.

[0012] Preferably, in step S3, the low temperature of the upper mold is set to be 45-55℃, and the high temperature of the lower mold is set to be 150-170℃.

[0013] Preferably, in step S3, the pressure applied by the one-way hot pressing is 3.0-6.0 MPa, and the pressure maintaining time is 60-120 seconds.

[0014] Preferably, in the one-way hot pressing process of step S3, the high temperature of the lower mold is used to decompose and escape the volatile alkaline regulator on the contact surface, so that the local pH value is reduced to be acidic, and the esterification reaction is triggered; meanwhile, the low temperature of the upper mold and the gas-phase diffusion generated at the lower part are used to maintain the alkaline inhibition environment in the upper layer region, so as to prevent the esterification reaction from occurring.

[0015] Preferably, in step S4, the cleaning step comprises ultrasonic cleaning of the hot-pressed substrate in deionized water, which is repeated for 3 times; and the drying temperature is 60-80℃.

[0016] The present application provides a composite bandage with gradient liquid absorption function and a hot pressing forming process thereof. 1、The present application utilizes the synergistic effect of asymmetric thermal field and volatile pH inhibitor to realize the continuous and gradual change of chemical properties from the contact surface to the backing surface inside the single fiber matrix; the high temperature side forms a dense hydrophobic layer due to the triggering of esterification reaction by ammonia gas escape, and the low temperature side retains the porous hydrophilic structure due to the inhibition of reaction by ammonia gas retention; the Laplace pressure difference generated by this endogenous gradient endows the bandage with excellent one-way liquid guiding function, which can actively pump the wound exudate outward and lock it, significantly reducing the reverse permeation of liquid.

[0017] 2、The present application discards the traditional physical layering process such as gluing and hot melt compounding, and adopts integrated hot pressing forming; since the hydrophobic layer and the liquid absorbing layer are generated by in-situ chemical modification based on the same matrix, there is no physical interface between them, but a natural transition through chemical bonding of polymer chains; therefore, even when the bandage absorbs a large amount of body fluid and swells violently, there will be no delamination or structural disintegration phenomenon, ensuring the safety of use.

[0018] 3、The present application successfully constructs a pH-sensitive chemical locking system by introducing a volatile alkaline regulator into the impregnating solution; during normal temperature storage and impregnation pretreatment, the system maintains in a weak alkaline environment, effectively inhibiting the acid catalytic activity of the polycarboxylic acid crosslinking agent, preventing the precursor solution from pre-crosslinking or precipitating, which greatly prolongs the shelf life of the slurry, making it more suitable for large-scale industrial production needs. DETAILED DESCRIPTION

[0019] All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor are within the scope of protection of the present application.

[0020] Embodiment: Embodiment 1: This embodiment prepares a composite bandage with gradient liquid absorbing function, and the specific preparation steps are as follows: Preparation of fiber matrix: Select high deacetylation degree chitosan fiber with deacetylation degree of 92% and polyvinyl alcohol fiber with alcoholysis degree of 95%, and mix them according to the mass ratio of 70:30. Non-woven fiber felt is prepared by carding and water jet reinforcement process, and the surface density is controlled to be 150g / m².

[0021] Preparation of latent impregnating solution: The latent impregnating solution was prepared by adding 6.0% citric acid in deionized water at room temperature and stirring until completely dissolved. Then, 1.5% octadecenyl succinic anhydride was added. The solution was sheared and dispersed for 12 minutes at 4000 rpm using a high-speed shearing emulsifier. Subsequently, 25% ammonia solution was added dropwise under stirring, and the pH value of the solution was adjusted to 8.2 in real time to obtain the latent impregnating solution.

[0022] Immersion and low-temperature pre-drying: The fiber substrate was completely immersed in the above-mentioned latent impregnating solution for 4 minutes. After being taken out, it was extruded by a two-roller mill to control the liquid rate to be 175%. Then, the wet substrate was placed in a vacuum drying oven for pre-drying at 45°C until the water content of the substrate was reduced to 25%.

[0023] Asymmetric hot-pressing: The pre-dried substrate was placed on the lower mold of a flat-plate hot press. The temperature of the upper mold was set to 50°C, and the temperature of the lower mold was set to 160°C. The mold was closed, and a pressure of 4.5 MPa was applied for 90 seconds. In this process, the asymmetric thermal field induced the volatilization of ammonia gas and esterification reaction at the bottom while maintaining an inhibitory alkaline environment at the top.

[0024] Post-processing: After the hot pressing was completed, the sample was cooled to room temperature. The sample was cleaned with deionized water for 3 times, each for 10 minutes. Finally, it was placed in a blast drying oven and dried at 70°C until the weight was constant to obtain the finished product.

[0025] Example 2: In this example, a composite bandage with gradient liquid absorption function was prepared, and the specific preparation steps were as follows: Preparation of the fiber substrate: High-deacetylation chitosan fibers with a deacetylation degree of 90% and polyvinyl alcohol fibers with an alcoholysis degree of 88% were selected and mixed according to a mass ratio of 60:40. A non-woven fiber mat was prepared, and the area density was controlled to be 120 g / m 2 .

[0026] Preparation of the latent impregnating solution: The latent impregnating solution was prepared by adding 4.0% citric acid in deionized water at room temperature and stirring until completely dissolved. Then, 0.5% octadecenyl succinic anhydride was added. The solution was sheared and dispersed for 10 minutes at 3000 rpm using a high-speed shearing emulsifier. Subsequently, 25% ammonia solution was added dropwise, and the pH value of the solution was adjusted to 7.8 to obtain the latent impregnating solution.

[0027] Immersion and low-temperature pre-drying: The fiber substrate was completely immersed in the impregnating solution for 3 minutes. After being squeezed by a roller, the liquid retention rate was controlled at 150%. Then, the substrate was placed in a vacuum drying oven for pre-drying at 40℃, and the moisture content of the substrate was controlled at 20%.

[0028] Asymmetric hot-pressing: The pre-dried substrate was placed in a flat-plate hot press. The temperature of the upper die was set at 45℃, and the temperature of the lower die was set at 150℃. The die was closed, and a pressure of 3.0 MPa was applied for 60 seconds.

[0029] Post-processing: The cooling and washing steps were the same as in Example 1. Finally, the product was obtained by drying to constant weight at 60℃.

[0030] Example 3: In this example, a composite bandage with gradient liquid absorption function was prepared, and the specific preparation steps were as follows: Preparation of the fiber substrate: Highly deacetylated chitosan fibers with a deacetylation degree of 95% and polyvinyl alcohol fibers with an alcoholysis degree of 99% were selected and mixed in a mass ratio of 80:20. A non-woven fiber mat was prepared, and the area density was controlled at 180 g / m 2 .

[0031] Preparation of the latent impregnating solution: At room temperature, deionized water was used as the solvent, and 8.0% citric acid by mass percentage was added and stirred to dissolve. 2.5% octadecenyl succinic anhydride by mass percentage was added. A high-speed shearing emulsifier was used to shear and disperse at a speed of 5000 rpm for 15 minutes. Then, 28% ammonia solution was added dropwise to adjust the pH value of the solution to 8.5, and the latent impregnating solution was prepared.

[0032] Impregnation and low-temperature pre-drying: The fiber substrate was completely immersed in the impregnating solution for 5 minutes. After being squeezed by a roller, the liquid retention rate was controlled at 200%. Then, the substrate was placed in a vacuum drying oven for pre-drying at 50℃, and the moisture content of the substrate was controlled at 30%.

[0033] Asymmetric hot-pressing: The pre-dried substrate was placed in a flat-plate hot press. The temperature of the upper die was set at 55℃, and the temperature of the lower die was set at 170℃. The die was closed, and a pressure of 6.0 MPa was applied for 120 seconds.

[0034] Post-processing: The cooling and washing steps were the same as in Example 1. Finally, the product was obtained by drying to constant weight at 80℃.

[0035] Comparative Example 1: The difference compared with Example 1 is that the volatile basicity regulator is replaced, specifically: using non-volatile sodium hydroxide solution instead of ammonia water to adjust the pH value of the impregnating solution to 8.2, and the remaining raw material components, proportions and process parameters are the same as those of Example 1.

[0036] Comparative Example 2: The difference compared with Example 1 is that the pH synergistic inhibitor is cancelled, specifically: when preparing the impregnating solution, no ammonia water is added, and the impregnating solution remains in a natural acidic state after citric acid is dissolved, and the remaining raw material components, proportions and process parameters are the same as those of Example 1.

[0037] Comparative Example 3: The difference compared with Example 1 is that the hot field condition of hot pressing is changed, specifically: using symmetrical high-temperature hot pressing, the temperature of the upper mold is set to 160°C, and the temperature of the lower mold is set to 160°C, and the remaining raw material components, proportions and process parameters are the same as those of Example 1.

[0038] Comparative Example 4: The difference compared with Example 1 is that the hydrophobic modifier is removed, specifically: when preparing the impregnating solution, no octadecenyl succinic anhydride is added, and the remaining raw material components, proportions and process parameters are the same as those of Example 1.

[0039] Test Example 1: Liquid penetration and reverse osmosis performance test Test equipment and materials: Electronic balance, stopwatch, standard weight, quantitative filter paper, pipette, 0.9wt% sodium chloride solution.

[0040] Test steps: The samples prepared in Examples 1-3 and Comparative Examples 1-4 were cut into 10cm x 10cm specifications.

[0041] The sample was laid flat on the test table, and the side that contacted the high-temperature mold during preparation was facing up as the test surface.

[0042] 5.0mL of 0.9wt% sodium chloride solution was taken with a pipette and vertically dropped onto the center of the sample test surface, with the drop height kept at 10mm.

[0043] The stopwatch was started at the same time as the drop, and stopped when the drop completely disappeared from the sample surface, and the time was recorded as the liquid penetration time. If it still did not penetrate after 300 seconds, it was recorded as ">300".

[0044] After the liquid penetration was completed, the sample was allowed to stand for 5 minutes.

[0045] A stack of pre-weighed (recorded as W0) quantitative filter papers was taken. A piece of dry filter paper (Whatman®) was placed at the wetted center of the sample surface, and a standard weight was applied over the filter paper, resulting in a pressure of 4 kPa for 60 seconds.

[0046] The weight was removed, and the filter paper stack was removed immediately and weighed (recorded as W2).

[0047] Test result data: The test data of each group of samples is recorded in the following table: Table 1: Fluid handling performance data table of different experimental groups Result analysis and summary: The test data of Examples 1 to 3 shows that the liquid penetration time is maintained between 2.13 seconds and 2.87 seconds, and the liquid backflow amount is less than 0.12 grams. This result shows that there is a difference in wettability in the thickness direction of the sample. During the asymmetric hot pressing process, the grafting reaction of octadecenyl succinic anhydride and the esterification crosslinking of polycarboxylic acid occur on the side in contact with the high-temperature mold, reducing the surface free energy of that side and limiting the relaxation of the polymer chain. This difference in surface energy creates a directed capillary driving force in the thickness direction, promoting the one-way transmission of liquid to the backing layer where no hydrophobic reaction has occurred. In contrast, Comparative Example 4, which lacks a hydrophobic modifier, cannot build a surface energy gradient, resulting in a backflow amount of 3.852 grams, confirming the necessity of introducing long-chain alkyl groups to block the return of liquid.

[0048] The test results of Comparative Examples 1 and 3 verify the switching effect of the phase change characteristics of volatile alkaline regulators. Comparative Example 1 uses a non-volatile base, which cannot reduce the pH value on the high-temperature side to the acidic catalytic interval, and no crosslinking reaction occurs, resulting in the disintegration of the sample structure when it comes into contact with water. Comparative Example 3 uses double-sided high-temperature hot pressing, resulting in esterification reactions and hydrophobic modification on both sides of the sample, with surface pores being blocked and the overall sample being hydrophobic, which blocks the entry channel of the liquid. This shows that the use of a single-sided thermal field to induce the escape of volatile components is a key process condition for achieving local reaction activation and overall structural differentiation.

[0049] The liquid penetration time of Comparative Example 2 is extended to 12.54 seconds, which is significantly higher than that of the Examples. In the Examples, the ammonia gas generated by the bottom heating diffuses upwards, maintaining a high concentration of gaseous alkali in the low-temperature backing layer region, effectively suppressing the reactivity of the crosslinking agent and the hydrophobic agent in the upper layer region, and preserving the number of hydrophilic groups. Comparative Example 2 lacks this in-situ suppression mechanism produced by gas-phase migration, resulting in a non-discriminatory distribution of acidic catalytic environments within the matrix, causing some hydrophobic agents to undergo unintended grafting or deposition on the backing layer or internal pore surfaces, reducing the overall hydrophilicity and liquid absorption rate.

[0050] ​​Test Example 2: Saturated liquid absorption capacity and wet state structure strength test Test equipment and materials: Electronic balance, universal material testing machine, stainless steel mesh basket, beaker, deionized water, paper cutter, steel ruler.

[0051] Test steps: Saturated liquid absorption rate test: Cut 5 cm x 5 cm test samples from the samples prepared in Examples 1-3 and Comparative Examples 1-4, dry them in an oven at 105°C to a constant weight, and weigh the dry weight, denoted as .

[0052] Put the dry test sample into a stainless steel mesh basket, and completely immerse the basket in a beaker containing deionized water.

[0053] Keep the sample immersed for 30 minutes to ensure that it is fully swollen.

[0054] Lift the basket so that it is suspended above the liquid surface, and let it drain for 3 minutes until no continuous droplets fall.

[0055] Quickly remove the test sample and weigh it, denoted as wet weight .

[0056] Calculate the saturated liquid absorption rate according to the formula .

[0057] Wet state breaking stress test: Cut each group of samples into long strip-shaped samples with a length of 100 mm and a width of 25 mm along the longitudinal direction.

[0058] Immerse the test sample in deionized water for 10 minutes, and then remove it and absorb the surface floating water with filter paper.

[0059] Clamp the wet test sample between the upper and lower clamps of the universal material testing machine, and set the clamp distance to 50 mm.

[0060] Set the tensile speed to 100 mm / min, and start the tensile program until the test sample breaks.

[0061] Record the maximum load value during the breaking process of the test sample, which is the wet state breaking stress.

[0062] Test result data: The physical property test data of each group of samples are recorded in the following table: Table 2: Liquid absorption performance and mechanical strength data table of different experimental groups Result analysis and summary: The data of examples 1 to 3 show that the composite bandage prepared by the technical solution has a high liquid absorption rate of 16.57 g / g to 21.85 g / g while having a wet state breaking stress of 14.91 N to 23.08 N. This performance balance is due to the asymmetric cross-linking structure built inside the material: on the side in contact with the high-temperature mold, the pH value decreases due to the volatilization of ammonia, and the esterification reaction between the polycarboxylic acid and the chitosan and polyvinyl alcohol occurs, forming a dense cross-linking network, which provides the necessary mechanical support in the wet state as a skeleton; while on the side in contact with the low-temperature mold and the middle layer, due to the upward migration and retention of ammonia, the environment remains alkaline, the carboxyl group remains in the form of stable ammonium salt, and no cross-linking reaction occurs, leaving a large number of hydrophilic hydroxyl and amino groups, thereby giving the material a high free swelling capacity and liquid containing space.

[0063] The extreme data of Comparative Example 1 and Comparative Example 3 reverse prove the importance of the reaction control mechanism. Comparative Example 1 uses a non-volatile base, which causes the entire system to be in a high-pH inhibition state during hot pressing, and no cross-linking network is formed, so the sample swells and disintegrates in water due to the disentanglement of the polymer chains, losing its value. On the contrary, Comparative Example 3 uses double-sided high-temperature hot pressing, which causes the entire matrix to be in a high-temperature acidic catalytic environment, resulting in high-density cross-linking of the fiber network in the thickness direction. This overall hardened structure greatly improves the mechanical strength, but due to the limited movement of the polymer chain segments and the large consumption of hydrophilic groups, its liquid absorption capacity is reduced to 3.41 g / g, losing the functional basis as a exudate management material.

[0064] The liquid absorption rate of Comparative Example 2 is significantly lower than that of the example group, only 9.24 g / g. In the absence of volatile alkaline regulators, the initial pH value inside the matrix is acidic, and even if the upper mold temperature is low, the heat conduction effect is still sufficient to cause a certain degree of pre-crosslinking reaction in the upper layer region, or to cause the crystallinity of the polyvinyl alcohol molecular chain to change in the acidic hot atmosphere. This unintended structural densification reduces the free volume and reduces the liquid absorption potential of the material. This result shows that the use of phase transition migration of gas components to establish an active chemical inhibition atmosphere on the low-temperature side is crucial for precisely preserving the liquid absorption function zone in a single matrix.

[0065] Test Example 3: Pre-impregnation precursor solution storage stability test Test equipment and materials: Rotary viscometer, constant temperature and humidity chamber, glass bottle with plug, stopwatch, glass rod.

[0066] Test steps: According to the formula and process steps of Example 1, Example 2, Example 3 and Comparative Example 2, respectively, 500 mL of fresh impregnation precursor solution was prepared from scratch.

[0067] Immediately pour the prepared solution into a wide-mouthed glass bottle, use a rotational viscometer to measure the initial viscosity value (denoted as , unit: mPa·s), and observe and record the initial appearance of the solution.

[0068] After measurement, immediately tighten the bottle cap to seal, and place the sample bottle in a constant temperature and humidity box for storage.

[0069] At the time nodes of 24 hours and 48 hours, respectively take out the sample bottle, gently shake to check the fluidity, and again use a rotational viscometer to measure the viscosity of the solution (denoted as and , respectively).

[0070] Observe whether the solution has stratification, flocculation precipitation or gelation phenomenon.

[0071] According to the formula , calculate the viscosity growth rate at 48 hours.

[0072] Test result data: The rheological property data of the precursor solution of each group over time are recorded in the following table: Table 3: Viscosity change and appearance state record table of precursor solution system over time Result analysis and summary: The test data of Example 1 to Example 3 show that after the introduction of volatile basicity regulator, the impregnation solution system shows excellent time stability, the viscosity growth rate within 48 hours is controlled between 3.63% and 7.22%, and the appearance always maintains a uniform fluid state. This stability is attributed to the acid-base balance mechanism in the system: in the sealed storage at room temperature, the ammonia and other basic components maintain the solution pH value in the weak alkaline interval of 7.8 to 8.5. In this pH environment, the carboxyl groups in citric acid and butane tetracarboxylic acid molecules are neutralized and converted into carboxylic acid ammonium salt. Since the esterification crosslinking reaction usually follows an acid catalysis mechanism, the salification of carboxyl groups effectively shields their electrophilic reactivity, thereby blocking the condensation path between polycarboxylic acid and the hydroxyl amino groups on the molecular chain of chitosan or polyvinyl alcohol at room temperature, realizing the chemical latency of reaction activity.

[0073] In contrast, the solution of Comparative Example 2 was initially in an acidic environment without the addition of a basic inhibitor. In this environment, the polycarboxylic acid remained in the free acid form, with a higher chemical potential energy. The data and appearance records showed that the viscosity of the solution of Comparative Example 2 increased sharply to 128.5 mPa·s after 24 hours of placement, and gelled at 48 hours. This indicates that under acidic conditions, even in room temperature environment, the intermolecular hydrogen bonding in the system is significantly enhanced, and due to the lower activation energy threshold, some carboxyl groups and hydroxyl groups undergo slow pre-crosslinking reactions, or the hydrophobic modifier undergoes hydrolysis and self-polymerization. This spontaneous thickening and gelation phenomenon makes the precursor solution lose flowability and permeability in a short time, which cannot adapt to the continuous industrial impregnation production process.

[0074] The technical solution of the present application solves the contradiction between the storage stability and rapid curing reaction of the high-activity crosslinking system through the phase change switch mechanism of normal temperature alkaline inhibition of high-temperature volatile acid recovery. The data of the example group confirms that during the storage and impregnation stage before the hot pressing process, the system can maintain long-term chemical inertia, ensuring uniform penetration of the liquid into the fiber matrix; and in combination with the results of the aforementioned Test Example 1, it can be known that once the asymmetric hot pressing process is entered, the ammonia gas escape caused by heating will quickly break this inert balance and start the crosslinking reaction in situ.

Claims

1. A composite bandage having a gradient absorption function, characterized by, include: The composite bandage consists of a fiber matrix and a functional coating in situ bonded to the fiber matrix; The fiber matrix is ​​a nonwoven fiber felt made by mixing high-deacetylation chitosan fiber and polyvinyl alcohol fiber in a mass ratio of 60:40 to 80:20, with a surface density of 120 to 180 g / m². The functional coating is formed by an asymmetric hot-pressing reaction of a latent impregnation liquid, wherein the latent impregnation liquid contains a solvent, a crosslinking agent, a hydrophobic modifier, and a volatile alkaline regulator. In the latent impregnation solution, the mass percentage concentration of the crosslinking agent is 4.0% to 8.0%, and the mass percentage concentration of the hydrophobic modifier is 0.5% to 2.5%. The composite bandage has a chemical crosslinking density gradient and a hydrophilic / hydrophobic gradient in the thickness direction induced by the phase transition migration of the volatile alkaline modifier.

2. The composite bandage having a gradient liquid absorption function according to claim 1, characterized in that, The crosslinking agent is selected from citric acid or 1,2,3,4-butanetetracarboxylic acid; the hydrophobic modifier is octadecenyl succinic anhydride; the degree of deacetylation of the high-degree-of-deacetylation chitosan fiber is 90%–95%; and the degree of alcoholysis of the polyvinyl alcohol fiber is 88%–99%.

3. A hot-pressing process of a composite bandage with gradient liquid absorption function, according to any one of claims 1-2, wherein, The process includes the following steps: S1. Dissolve and disperse polyvinyl alcohol fibers, add high-deacetylation chitosan fibers, crosslinking agents and hydrophobic modifiers, and add volatile alkaline regulators to adjust the solution to an alkaline pH value to form a latent impregnation solution, using the alkaline environment to inhibit the activity of the crosslinking agent; S2. The fiber matrix is ​​impregnated in the latent impregnation solution, and after being squeezed, it is dried under low temperature vacuum to ensure that the matrix retains a certain moisture content, and the drying temperature is lower than the violent volatilization temperature of the volatile alkaline regulator. S3. The substrate after low-temperature drying is placed in a flat plate hot press with independent temperature control for unidirectional hot pressing, wherein the upper mold is set to low temperature and the lower mold is set to high temperature, and the reaction is induced by the asymmetric thermal field. S4. After hot pressing, the substrate is cleaned and dried to obtain the finished product.

4. The thermoforming process of a composite bandage with gradient absorbent function according to claim 3, characterized in that, In step S1, the volatile alkaline regulator is ammonia; the crosslinking agent is citric acid; and the hydrophobic modifier is octadecenyl succinic anhydride. The adjustment to an alkaline pH value specifically involves adjusting the pH value to 7.8–8.5, thereby converting the carboxyl groups in the crosslinking agent into ammonium salts to lock in the reactivity.

5. The thermoforming process of a composite bandage with gradient absorbent function according to claim 3, characterized in that, In step S1, the preparation process of the latent impregnation solution includes: after adding a crosslinking agent and a hydrophobic modifier, dispersing the solution using a high-speed shear emulsifier with a shearing speed of 3000-5000 rpm and a dispersion time of 10-15 minutes.

6. The thermoforming process of a composite bandage with gradient absorbent function according to claim 3, characterized in that, In step S2, the liquid carryover rate after rolling is controlled at 150% to 200%; The temperature of the low-temperature vacuum drying is controlled at 40℃~50℃; The moisture content of the substrate is controlled at 20% to 30%.

7. The thermoforming process of a composite bandage with gradient absorbent function according to claim 3, characterized in that, In step S3, the upper mold is set to a low temperature of 45°C to 55°C, and the lower mold is set to a high temperature of 150°C to 170°C.

8. The thermoforming process of a composite bandage with gradient absorbent function according to claim 3, characterized in that, In step S3, the pressure applied by the unidirectional hot pressing is 3.0 to 6.0 MPa, and the holding time is 60 to 120 seconds.

9. The thermoforming process of a composite bandage with gradient absorbent function according to claim 3, characterized in that, In the one-way hot pressing process of step S3, the volatile alkaline regulator on the contact surface is decomposed and escaped by the high temperature of the lower mold, the local pH value is reduced to acidic, and the esterification reaction is initiated; at the same time, the upper layer region is maintained in an alkaline inhibition environment by the low temperature of the upper mold and the gas phase diffusion generated in the lower part, so as to prevent the esterification reaction from occurring.

10. The thermoforming process of a composite bandage with gradient absorbent function according to claim 3, characterized in that, In step S4, the cleaning step includes ultrasonic cleaning of the hot-pressed substrate in deionized water, repeated 3 times; the drying temperature is 60-80°C.

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