Nonwoven fabric for polylactic acid-polycaprolactone degradable braided bag and preparation method thereof

Abstract

The application discloses polylactic acid-polycaprolactone degradable woven bag non-woven fabric and a preparation method thereof. The non-woven fabric is prepared from the following components: polylactic acid, polycaprolactone, sodium lauryl sulfate, dopamine-modified nano-titanium dioxide composite, a compound system of citric acid and epoxy soybean oil, a combination of sodium carboxymethyl cellulose and calcium dodecyl phosphate, and a combination of montmorillonite and D-isoascorbic acid palmitate. The above system forms a multi-level degradation regulation network structure with surface interface regulation, intermediate layer microstructure regulation and nano functional particle synergistic catalysis, and realizes controllable regulation of the degradation rate of polylactic acid-polycaprolactone blended materials. A preparation method is used to prepare the non-woven fabric. The application has the following beneficial effects: the problems of the prior art, such as difficult accurate regulation of the degradation rate of polylactic acid-polycaprolactone blended materials, poor environmental adaptability and limited application scenarios, are solved.

Description

Technical Field

[0001] This invention relates to the field of biodegradable textile materials, specifically to a polylactic acid-polycaprolactone biodegradable nonwoven fabric for woven bags and its preparation method. Background Technology

[0002] Biodegradable nonwoven fabrics have broad application prospects in medical and health fields, agricultural coverings, packaging materials, and environmental filtration. With increasing environmental awareness and the growing prominence of white pollution (plastic pollution), nonwoven fabrics made from biodegradable polymers are receiving increasing attention and research. Polylactic acid (PLA) and polycaprolactone (PVC), as two important biodegradable materials, have wide applications in medical and environmental materials.

[0003] Polylactic acid (PLA) is an aliphatic polyester produced from renewable resources, exhibiting good biocompatibility and biodegradability. Industrially, PLA is primarily prepared through the ring-opening polymerization of lactic acid. Its degradation product, lactic acid, is completely metabolized by the human body and is non-toxic and harmless. PLA possesses high tensile strength (40-60 MPa), high elastic modulus (3-4 GPa), and good thermal stability (heat distortion temperature approximately 55-60℃). However, its inherent brittleness and hydrophobicity limit its application in flexible materials. Furthermore, PLA has a relatively long degradation cycle, generally requiring 1-3 years for complete degradation, which makes it difficult to meet the diverse degradation rate requirements of different application scenarios.

[0004] Polycaprolactone (PVC) is a semi-crystalline aliphatic polyester prepared by ring-opening polymerization of caprolactone. It exhibits good flexibility (elongation at break >700%) and a low melting point (approximately 60°C). PVC possesses excellent processability and good compatibility with various polymers, with a complete degradation cycle of approximately 2-3 years. Compared to polylactic acid (PLA), PVC has better toughness and ductility, but its lower mechanical strength (tensile strength approximately 16 MPa) and relatively higher cost limit its large-scale application.

[0005] Theoretically, polylactic acid (PLA) and polycaprolactone (PCL) blends can combine the advantages of both materials, allowing for adjustments to mechanical properties and degradation rates. However, current PLA-PCL blends face several major challenges: poor compatibility leading to unstable mechanical properties; difficulty in controlling degradation rates due to differences in degradation mechanisms and rates between PLA and PCL; complex processing techniques hindering the formation of structures with high specific surface area and high porosity; a narrow performance adjustment range, making it difficult to meet the needs of various applications; and poor environmental adaptability, with significant differences in degradation behavior under different pH and temperature conditions.

[0006] Electrospinning technology, due to its ability to produce nano- to micron-sized fibers, is widely used in the preparation of functional nonwoven materials. This technology utilizes a high-voltage electrostatic field to form a charged jet from a polymer solution, and during the jet stretching and solvent evaporation processes, ultrafine fibers are formed, ultimately deposited on a receiving device to form a nonwoven material. Theoretically, electrospinning polylactic acid-polycaprolactone blends can solve the problem of existing processing methods failing to form structures with high specific surface area and high porosity. However, current methods still face challenges such as phase separation during spinning, uneven fiber diameter, and limited solvent selection.

[0007] Existing methods mainly regulate the degradation rate of polylactic acid-polycaprolactone blends through the following technical means: First, adjusting the ratio of polylactic acid to polycaprolactone, but the adjustment range is limited; second, adding single-function additives, such as chitosan, gelatin and other natural polymers as compatibilizers, but the improvement effect is limited; third, using coaxial electrospinning or emulsion electrospinning technology to prepare core-shell structured fibers to achieve layered control of degradation behavior, but the preparation process is complex; fourth, using post-treatment technologies such as plasma treatment and ultraviolet crosslinking to adjust the surface properties and degradation characteristics of the material, but the treatment effect has poor durability.

[0008] Therefore, it is of great significance to develop a simple and efficient preparation method to prepare polylactic acid-polycaprolactone biodegradable nonwoven fabric for woven bags with a controllable degradation rate, and to flexibly adjust its degradation process according to the needs of different application scenarios. Summary of the Invention

[0009] The purpose of this invention is to provide a nonwoven fabric for polylactic acid-polycaprolactone (PLA-PP) biodegradable woven bags and its preparation method, thereby solving the problems of difficulty in precisely adjusting the degradation rate of PLA-PP blends, poor environmental adaptability, and limited application scenarios in the prior art.

[0010] The polylactic acid-polycaprolactone biodegradable nonwoven fabric for woven bags provided by this invention is prepared from the following components:

[0011] Polylactic acid, with a number average molecular weight of 80,000-120,000 g / mol and a content of 15-25% by weight;

[0012] Polycaprolactone, with a number average molecular weight of 70,000-90,000 g / mol and a content of 5-15% by weight;

[0013] Sodium lauryl sulfate, with a content of 0.3-0.8% by weight;

[0014] Dopamine-modified nano-titanium dioxide composites with a particle size of 20-50 nanometers and a content of 0.5-2.0% by weight;

[0015] A compound system of citric acid and epoxidized soybean oil, wherein the mass ratio of citric acid to epoxidized soybean oil is 2:1 to 1:1, and the total content is 1.0-3.0% by weight;

[0016] A combination of sodium carboxymethyl cellulose and calcium dodecyl phosphate, wherein the mass ratio of sodium carboxymethyl cellulose to calcium dodecyl phosphate is 3:1 to 2:1, and the total content is 1.0-2.5% by weight.

[0017] The combination of montmorillonite and D-isoascorbyl palmitate, wherein the mass ratio of montmorillonite to D-isoascorbyl palmitate is 3:1 to 2:1, and the total content is 0.8-2.0% by weight.

[0018] The system forms a multi-level degradation regulation network structure with surface interface regulation, intermediate layer micro-region structure regulation and nano-functional particle synergistic catalysis, realizing controllable regulation of the degradation rate of polylactic acid-polycaprolactone blend materials.

[0019] This invention also provides a method for preparing nonwoven fabric, comprising the following steps:

[0020] (1) Weigh polylactic acid and polycaprolactone at a mass ratio of 3:1, with a total polymer concentration of 12% by weight, and add them to a mixed solvent of chloroform and N,N-dimethylformamide (volume ratio 7:3). Stir magnetically at room temperature for 12-24 hours until completely dissolved.

[0021] (2) Disperse sodium lauryl sulfate and sodium carboxymethyl cellulose in water to prepare an aqueous solution, and mix it with an alcoholic solution of calcium dodecyl phosphate, and sonicate for 30-60 minutes;

[0022] (3) Pre-react citric acid with epoxidized soybean oil at 60-70℃ for 2-4 hours, then cool to room temperature;

[0023] (4) Add the dopamine-modified nano-titanium dioxide complex, montmorillonite and D-isoascorbate palmitate to the solution in step (1) in sequence, and disperse by ultrasonication for 30-60 minutes.

[0024] (5) Add the products from steps (2) and (3) to the mixed solution from step (4) and continue stirring for 4-6 hours to form a uniform spinning solution;

[0025] (6) Electrospin the obtained spinning solution under the following conditions: voltage 15-20kV, liquid supply rate 0.5-2.0mL / h, collection distance 15-20cm, ambient temperature 25±2℃, relative humidity 40±5%;

[0026] (7) The fiber membrane obtained by electrospinning is vacuum dried at 40-50℃ for 24 hours to remove residual solvent and obtain nonwoven fabric.

[0027] The core of this invention lies in the establishment of a multi-level degradation regulation network. Through the synergistic effect of the following three complementary regulatory systems, precise regulation of the degradation behavior of polylactic acid-polycaprolactone blended nonwoven fabrics is achieved:

[0028] 1) Surface interface regulation system: Composed of sodium lauryl sulfate, sodium carboxymethyl cellulose, and calcium dodecyl phosphate, it forms an amphiphilic dynamic response layer on the fiber surface. The molecular self-assembly structure formed by sodium lauryl sulfate and sodium carboxymethyl cellulose exhibits reversible conformational changes under different pH conditions, regulating the water molecule permeation rate; calcium ions in calcium dodecyl phosphate form chelates with degradation products, controlling the release rate of degradation products.

[0029] 2) Intermediate layer microstructure regulation system: Composed of citric acid, epoxidized soybean oil, and montmorillonite, this system controls the phase separation structure within the fiber and the diffusion of degradation products. Citric acid and epoxidized soybean oil form a cross-linked network through a carboxyl-epoxy group reaction, controlling the release of degradation products; the layered structure of montmorillonite provides temporary storage space for degradation products, avoiding the autocatalytic effect of degradation products.

[0030] 3) Nanoparticle synergistic catalytic system: Composed of dopamine-modified nano-titanium dioxide composite and D-isoascorbate palmitate, it achieves photoresponsive and controllable degradation. Dopamine-modified nano-titanium dioxide generates a more selective redox environment under light irradiation, preferentially degrading polycaprolactone components; D-isoascorbate palmitate participates in the photocatalytic cycle when the temperature increases, achieving a dual response to temperature and light irradiation.

[0031] These three systems interact at the molecular level to form a four-dimensional regulatory system for material degradation behavior. Through synergistic effects in the spatial dimension (multi-level structure), the temporal dimension (stage degradation), the chemical environment dimension (pH response), and the external stimulus dimension (light and temperature response), they achieve precise regulation of the degradation rate of polylactic acid-polycaprolactone blend materials.

[0032] This invention achieves the following beneficial effects by setting a multi-level degradation regulation network structure:

[0033] 1. Precise adjustment of degradation rate: The nonwoven material of the present invention can precisely adjust the degradation cycle within the range of 1-18 months through various external stimulation (pH, light, temperature) response mechanisms to meet the needs of different application scenarios.

[0034] 2. Enhanced environmental adaptability: The nonwoven fabric material of the present invention exhibits controllable degradation behavior under different pH environments. The degradation rate slows down in acidic environments (pH<5) and increases controllably in neutral or alkaline environments, thus adapting to the needs of different application environments.

[0035] 3. Optimized mechanical properties: The nonwoven fabric material of the present invention overcomes the problem of poor compatibility of existing polylactic acid-polycaprolactone blends, and significantly improves the mechanical properties of the material, with tensile strength increased by 30-50% and elongation at break increased by 40-60%.

[0036] 4. Visualization of the degradation process: The nonwoven material of the present invention achieves visual monitoring of the degradation process through the controllable photocatalytic effect of the dopamine-modified nano-titanium dioxide composite. When the material begins to degrade, the color gradually changes from the initial light brown to grayish-white, which can be used to judge the degree of degradation.

[0037] 5. Improved processing performance: The system adopted in this invention significantly improves the electrospinning processing performance of polylactic acid-polycaprolactone blend system, with a more uniform fiber diameter distribution (200-800nm) and a fiber formation rate increased by 20-30%, greatly improving production efficiency.

[0038] In addition, this invention provides a detailed analysis of the mechanism of nonwoven fabric for polylactic acid-polycaprolactone biodegradable woven bags.

[0039] The core of this invention lies in setting up a multi-level degradation regulation network structure. Through the synergistic effect of five substances, three functionally complementary regulation systems are formed in the polylactic acid-polycaprolactone biodegradable woven bag nonwoven fabric:

[0040] 1) Surface interface conditioning system: composed of sodium lauryl sulfate, sodium carboxymethyl cellulose and calcium dodecyl phosphate, forming an amphiphilic dynamic response layer on the fiber surface;

[0041] 2) Intermediate layer micro-region structure regulation system: composed of citric acid, epoxidized soybean oil and montmorillonite, which controls the internal phase separation structure of the fiber and the diffusion of degradation products;

[0042] 3) Nanoparticle synergistic catalytic system: composed of dopamine-modified nano-titanium dioxide complex and D-isoascorbate palmitate, achieving photoresponsive controllable degradation.

[0043] These three systems interact at the molecular level to form a four-dimensional regulatory system for material degradation behavior. They work together in the spatial, temporal, chemical environment, and external stimulus dimensions to achieve precise regulation of the degradation rate of polylactic acid-polycaprolactone blends.

[0044] At the molecular level, the hydrolysis of ester bonds in polylactic acid (PLA) and polycaprolactone (PCL) is the core of their degradation. PLA uses L-lactic acid as the repeating unit and methyl groups as side groups, resulting in a highly rigid molecular chain; PCL uses caprolactone as the repeating unit, leading to a more flexible chain structure. This structural difference results in poor compatibility and significant phase separation in existing blend systems, leading to large differences in degradation rates.

[0045] This invention achieves three aspects of regulation at the molecular level:

[0046] 1) Regulation of molecular chain interactions: The ionic groups of sodium lauryl sulfate and calcium dodecyl phosphate form weak interactions with the ester groups of polylactic acid-polycaprolactone molecular chains, which changes the stacking state of the molecular chains.

[0047] 2) Interface coupling and compatibility regulation: Citric acid-epoxidized soybean oil forms a cross-linked network with multiple functional groups, which can form multi-point interactions with polylactic acid and polycaprolactone molecular chains, thus improving their compatibility.

[0048] 3) Micro-catalytic environment setup: The dopamine-modified nano-titanium dioxide nanocomposite forms uniformly dispersed catalytic sites in the system, providing a microenvironment for selective degradation.

[0049] The innovation of this invention lies in the fact that the three functional systems formed by the five substances establish a synergistic degradation regulation network:

[0050] The sodium lauryl sulfate-sodium carboxymethyl cellulose-calcium dodecyl phosphate surface system and the citric acid-epoxidized soybean oil-montmorillonite intermediate layer system form a synergistic mechanism of permeation-buffering-storage:

[0051] The surface layer formed by sodium lauryl sulfate and sodium carboxymethyl cellulose exhibits reversible conformational changes under different pH conditions. In acidic environments (pH < 5), the carboxyl groups of sodium carboxymethyl cellulose exist primarily in a nonionic form, forming a dense structure with the sulfate groups of sodium lauryl sulfate through hydrogen bonding, reducing water molecule permeation. However, in neutral or alkaline environments, the ionized carboxyl groups expand the molecular conformation with sodium lauryl sulfate through electrostatic repulsion, increasing water molecule permeation. This pH-responsive permeation behavior synergizes with the citric acid-epoxidized soybean oil system in the intermediate layer: citric acid releases H₂ during hydrolysis. + This lowers the local pH, creating a negative feedback regulation loop.

[0052] The long-chain alkyl group of calcium dodecyl phosphate forms a hydrophobic interaction with the polylactic acid-polycaprolactone molecular chain, while its calcium phosphate salt portion forms a coordination complex with sodium carboxymethyl cellulose, together setting up ion channels. When degradation products (mainly carboxylic acids) accumulate to a certain concentration, they competitively complex with calcium ions in calcium dodecyl phosphate, leading to a conformational change in the channel and promoting the expulsion of degradation products. This works in conjunction with the interlayer adsorption mechanism of the intermediate montmorillonite: montmorillonite can temporarily store some degradation products, preventing accelerated autocatalytic degradation caused by excessively high instantaneous concentrations.

[0053] The citric acid-epoxidized soybean oil-montmorillonite intermediate system and the dopamine-modified nano-titanium dioxide-D-isoascorbate palmitate nanocatalytic system form a confined catalysis-selective degradation synergistic mechanism:

[0054] Spatial synergy between micro-region structure and catalytic active sites: The cross-linked network formed by the reaction of citric acid and epoxidized soybean oil provides a specific spatial distribution for dopamine-modified titanium dioxide nanoparticles, restricting their aggregation. Simultaneously, the layered structure of montmorillonite further enhances this confinement effect. This spatially confined structure ensures that the catalytic reaction occurs only in specific micro-regions, avoiding the rapid overall degradation of the material caused by existing TiO2 catalysts.

[0055] Synergistic effect of stimulus response and degradation product treatment: When external UV light stimulation is applied, dopamine-modified nano-titanium dioxide generates reactive oxygen species (ROS) that preferentially attack the ester bonds of polycaprolactone (the ε-caprolactone structure of POS is more easily oxidized than the α-hydroxy ester structure of polylactic acid). D-isoascorbic acid palmitate acts as a free radical chelator to control the concentration of ROS, ensuring a controllable degradation process. Simultaneously, the montmorillonite interlayer can adsorb and temporarily store degradation products, avoiding the autocatalytic effect of the degradation products, while the epoxy groups of epoxidized soybean oil can react with the carboxyl groups generated during degradation, reducing the acidity of the system.

[0056] The dopamine-modified nano-titanium dioxide-D-isoascorbate palmitate nanocatalytic system and the sodium lauryl sulfate-sodium carboxymethyl cellulose-calcium dodecyl phosphate surface system formed a surface activation-internal cascade synergistic mechanism:

[0057] Dopamine-modified TiO2 surfaces form charge-transfer complexes. When photoexcited, electrons transfer from dopamine to the TiO2 conduction band, creating a confined redox environment. This electron transfer process interacts with the sodium lauryl sulfate-sodium carboxymethyl cellulose interface layer on the surface, altering the surface potential distribution and further influencing the distribution behavior of water and ions on the material surface.

[0058] D-isoascorbyl palmitate can donate electrons through its enol structure under light conditions to participate in the photocatalytic cycle of dopamine-modified nano-titanium dioxide. At the same time, its long-chain fatty acid ester portion forms a hydrophobic interaction with the alkyl chain of sodium lauryl sulfate, forming an activity gradient from the material surface to the interior, which facilitates the degradation process.

[0059] In addition, the addition of the above-mentioned substances has certain adverse effects on the existing technology:

[0060] 1. Sodium lauryl sulfate, as a surfactant, is shown in existing technologies to increase the hydrophilicity of materials, promote water molecule penetration, and accelerate the hydrolytic degradation of polyesters; sodium carboxymethyl cellulose has high hydrophilicity and water absorption and swelling properties, which generally indicates that it will destroy the structural stability of polyester materials; calcium dodecyl phosphate contains calcium ions, which will catalyze the degradation of polylactic acid and affect the long-term stability of materials.

[0061] In this invention, sodium lauryl sulfate, sodium carboxymethyl cellulose, and calcium dodecyl phosphate are compounded in a specific ratio (sodium lauryl sulfate:sodium carboxymethyl cellulose:calcium dodecyl phosphate = 1:2:1) and self-assemble during electrospinning to form a pH-responsive amphiphilic surface layer. The molecular arrangement of this surface layer allows the hydrophilic groups of sodium lauryl sulfate and the carboxyl groups of sodium carboxymethyl cellulose to form a network structure through ionic interactions, while the hydrophobic alkyl chains extend outwards to form a brush-like arrangement. This structure gives the material surface a controllable hydrophilic-hydrophobic transition characteristic: increased hydrophilicity in acidic environments and decreased hydrophilicity in alkaline environments, the opposite of the effect of existing surfactants. Calcium dodecyl phosphate is no longer a catalyst in the system, but rather acts as an ion-gated component, regulating the mass exchange rate through the interaction of its calcium ions with degradation products.

[0062] 2. Citric acid is a typical polycarboxylic acid, and existing technologies show that it catalyzes polyester hydrolysis and accelerates material degradation; epoxidized soybean oil, as a plasticizer, reduces the mechanical strength and thermal stability of the material; although montmorillonite can enhance material performance, it generally affects the electrospinning process, leading to fiber breakage or unstable spraying.

[0063] In this invention, citric acid and epoxidized soybean oil form a volume-confined cross-linked network structure through a carboxyl-epoxy group reaction. This cross-linked network allows for the controlled release of the carboxyl group of citric acid, avoiding initial explosive catalytic action. Montmorillonite in this system is intercalated and modified by the citric acid-epoxidized soybean oil network, forming a brick-wall-like nanostructure that does not affect the electrospinning process but instead improves spinning stability. The interlayer spaces of montmorillonite serve as temporary storage areas for degradation products, adsorbing and slowly releasing them during degradation, preventing autocatalytic acceleration caused by excessively high local concentrations of degradation products.

[0064] 3. TiO2 generates highly oxidizing reactive oxygen species under UV light, which, according to existing technologies, indiscriminately attacks polymer chains, leading to rapid material degradation; dopamine has strong adhesion and self-polymerization properties, which can affect the processing performance of materials; D-isoascorbate palmitate, as an antioxidant, is shown in existing technologies to prevent oxidative degradation and prolong the degradation cycle of materials.

[0065] In this system, dopamine forms a uniform coating of approximately 3-5 nm thickness on the TiO2 surface through self-polymerization, fundamentally altering the photocatalytic properties of TiO2. These core-shell nanoparticles no longer generate the existing strong oxidizing free radicals, but instead form an electron transfer regulation system, creating a more selective redox environment. D-isoascorbic acid palmitate in this system is not an antioxidant, but rather acts as an electron shuttle, capturing electrons under certain conditions and transferring them to the degradation site, achieving precise regulation of the degradation process. This selective catalysis preferentially degrades the polycaprolactone component, producing a microporous structure without causing overall structural destruction, thus enabling the subsequent controllable degradation of polylactic acid.

[0066] The five substances mentioned above form multiple synergistic mechanisms:

[0067] 1. Synergy between interface coupling and charge transfer

[0068] An interfacial charge-transfer structure is formed between the sodium lauryl sulfate-sodium carboxymethyl cellulose surface layer and the dopamine-modified titanium dioxide nanoparticles. The sulfate groups of sodium lauryl sulfate can form a charge-transfer complex with the amino groups on the dopamine layer through ion-dipole interactions. This complex alters the band structure of the dopamine-modified titanium dioxide nanoparticles, extending its photoresponse range to the visible light region (400-450 nm). Simultaneously, the carboxyl groups of sodium carboxymethyl cellulose can form hydrogen bonds with the dopamine layer, further stabilizing the interfacial structure. This synergistic effect enables the material to undergo controlled degradation even under weak light conditions, expanding its application scenarios.

[0069] 2. Synergistic effect of ion exchange and pH buffering

[0070] In calcium dodecyl phosphate, calcium ions form a dynamically balanced ion exchange system with citric acid. When the system pH decreases, citric acid partially protonates, reducing its binding affinity to calcium ions and releasing them. These calcium ions can then form chelates with the carboxyl termini produced during material degradation, neutralizing the acidity and preventing autocatalytic degradation caused by a continuous decrease in pH. This dynamic ion exchange process creates a self-regulating pH buffer system, enabling the material to maintain a relatively stable degradation rate under various environmental conditions.

[0071] 3. Synergistic effect of spatial confinement and selective catalysis

[0072] A synergistic mechanism of spatial confinement and catalytic activity is formed between the layered structure of montmorillonite and dopamine-modified titanium dioxide nanoparticles. Dopamine-modified titanium dioxide nanoparticles can be partially inserted into the interlayer of montmorillonite, restricting their aggregation and maintaining high dispersibility. Simultaneously, the positive charge between the montmorillonite layers attracts carboxyl termini generated during degradation, causing the degradation reaction to preferentially occur around the montmorillonite. This spatial confinement effect and the selective catalytic activity of dopamine-modified titanium dioxide nanoparticles mutually promote each other, achieving precise spatial regulation of the degradation process.

[0073] 4. Synergistic effect of temperature response and photocatalysis

[0074] A temperature-dependent interaction exists between D-isoascorbyl palmitate and epoxidized soybean oil. At low temperatures (<37°C), the long-chain alkyl group of D-isoascorbyl palmitate forms a hydrophobic association with the hydrophobic segment of epoxidized soybean oil, limiting its activity. When the temperature increases (>40°C), this hydrophobic interaction weakens, and D-isoascorbyl palmitate is released to participate in the photocatalytic cycle of dopamine-modified nano-titanium dioxide, accelerating the degradation process. This temperature-sensitive-photocatalytic synergistic mechanism enables the material to respond simultaneously to both temperature and light stimuli, achieving multi-factor-regulated degradation behavior.

[0075] Based on the above analysis, this invention establishes a four-dimensional degradation regulation network, which solves the problem of weak degradation control capabilities in existing biodegradable materials and achieves the technical objective of shifting from passively adapting to the environment to actively responding to needs. This molecular-level network transforms the degradation behavior of polylactic acid-polycaprolactone biodegradable woven bag nonwoven material from the existing single degradation pathway to multi-channel synergistic degradation. Detailed Implementation

[0076] The present invention designed the following experiments to verify the effectiveness of nonwoven fabrics for polylactic acid-polycaprolactone biodegradable woven bags:

[0077] 1. Experimental Objective

[0078] This experimental design comprehensively verifies the performance and mechanism of action of polylactic acid-polycaprolactone (PLA-polycaprolactone) biodegradable nonwoven fabric for woven bags with controllable degradation rates. The experiment will focus on verifying the effectiveness of the multi-level degradation regulation network structure proposed in the patent, including the formation and synergistic effect of the surface interface regulation system, the intermediate layer micro-region structure regulation system, and the nano-functional particle synergistic catalytic system. Through systematically designed control experiments and multi-dimensional testing methods, the system's regulatory effect on the degradation behavior of PLA-polycaprolactone blends under different application scenarios will be verified.

[0079] The experimental scheme consists of four parts: sample preparation, multi-condition degradation test, multi-dimensional performance characterization, and microstructure analysis. By comprehensively analyzing the performance differences between different experimental groups, the innovation and effectiveness of the present invention are verified.

[0080] 2. Experimental grouping and formulation design

[0081] The experimental group design is shown in Tables 1 and 2 below:

[0082] Table 1: Experimental Groups

[0083]

[0084] Table 2: Formulation Design Table (Unit: Weight Percentage)

[0085]

[0086] Control group design: Control group 1 represents the basic polylactic acid-polycaprolactone blend system without the addition of any substances; Control group 2 represents the conventional practice using the existing compatibilizer PEG.

[0087] Complete formulation design: Experimental group 1 contains all substances, forming a complete multi-level degradation regulation network structure.

[0088] Single-system design: Experimental groups 2, 3, and 4 each contain only one component of a functional system, used to verify the individual effects of each system.

[0089] Two-system group design: Experimental groups 5, 6, and 7 each contain a combination of components from two systems to verify the synergistic effect between different systems.

[0090] Material ratios: The ratios of each substance are based on the best embodiment, with the mass ratio of sodium lauryl sulfate: sodium carboxymethyl cellulose: calcium dodecyl phosphate being 1:1.8:0.8; the mass ratio of citric acid: epoxidized soybean oil being 1.5:1; and the mass ratio of montmorillonite: D-isoascorbate palmitate being 3:1.

[0091] 3. Experimental Design

[0092] (1) Preparation of dopamine-modified nano-titanium dioxide composite

[0093] Titanium dioxide nanoparticles (30 nm) were dispersed at a concentration of 2 mg / mL in a tris(hydroxymethyl)aminomethane buffer (10 mM, pH 8.5) containing dopamine hydrochloride (2 mg / mL).

[0094] The dopamine was magnetically stirred at room temperature for 18 hours to allow it to self-polymerize on the TiO2 surface and form a coating.

[0095] Collect the product by centrifugation at 12000 rpm for 10 minutes, and wash it three times with deionized water and ethanol in sequence.

[0096] Vacuum drying at 60℃ for 12 hours, followed by grinding and sieving, yielded dopamine-modified nano-titanium dioxide composite powder.

[0097] (2) Nonwoven fabric sample preparation process

[0098] Preparation of basic solution:

[0099] Polylactic acid and polycaprolactone were added to a mixture of chloroform and DMF (7:3, v / v) according to the designed ratio.

[0100] Stir magnetically at room temperature for 18 hours until completely dissolved to obtain a clear solution.

[0101] (3) Treatment of each functional system component:

[0102] Surface interface conditioning system: Sodium lauryl sulfate and sodium carboxymethyl cellulose were dissolved in a small amount of water, mixed with an ethanol solution of calcium dodecyl phosphate, and ultrasonically treated for 45 minutes.

[0103] Intermediate layer microstructure regulation system: Citric acid and epoxidized soybean oil were mixed, pre-reacted at 65°C for 3 hours, cooled to room temperature, and then montmorillonite was added to a small amount of DMF for dispersion.

[0104] Synergistic catalytic system of nanofunctional particles: Dopamine-modified nano-titanium dioxide complex and D-isoascorbate palmitate were dispersed in a small amount of chloroform and sonicated for 30 minutes.

[0105] Preparation of spinning solution: According to the formulation design of each group, the corresponding functional components are added to the base solution one by one and stirred for 5 hours to form a uniform spinning solution. Let it stand for 2 hours to remove air bubbles.

[0106] Electrospinning process: Voltage: 18kV; Liquid supply rate: 1.0mL / h; Collection distance: 18cm; Ambient temperature: 25±2℃; Relative humidity: 40±5%; Collection device: Rotating drum covered with aluminum foil, speed 400rpm; Spinning time: Keep consistent for each group to ensure similar thickness.

[0107] Post-processing: All samples were vacuum dried at 45°C for 24 hours to remove residual solvent; the dried samples were then cut to the required size for subsequent testing.

[0108] (3) Degradation conditions

[0109] To verify the performance of the multi-level degradation regulation network under different environmental conditions, the following treatment conditions were designed:

[0110] pH responsiveness test: Acidic environment: pH 5.0 acetate buffer, 37℃; Neutral environment: pH 7.4 phosphate buffer, 37℃; Alkaline environment: pH 9.0 carbonate buffer, 37℃.

[0111] Photoresponse test: Illumination group: 365nm ultraviolet light irradiation, 5mW / cm 2 The control group was exposed to light for 2 hours daily; the control group was stored away from light and all other conditions were the same.

[0112] Temperature response test: Low temperature group: 25℃, pH 7.4 phosphate buffer; Medium temperature group: 37℃, pH 7.4 phosphate buffer; High temperature group: 45℃, pH 7.4 phosphate buffer.

[0113] Simulated application environment testing: Medical environment simulation: pH 7.4 phosphate buffer + lipase (10U / mL), 37℃; Agricultural environment simulation: simulated soil solution (pH 6.5) + periodic wet-dry cycle (12 hours / 12 hours); Packaging environment simulation: simulated composting conditions, 58℃, relative humidity 90%, pH 8.0; Each sample group was degraded under each condition for 1, 3, 6, and 9 months, and samples were taken periodically for testing and analysis.

[0114] 4. Experimental Results

[0115] (1) Basic physical performance test

[0116] As shown in Table 3:

[0117] Table 3: Basic Physical Performance Test Conditions

[0118]

[0119] Based on the above tests, the physical performance test results are shown in Table 4.

[0120] Table 4: Basic Physical Properties

[0121]

[0122] (2) Mechanical property testing

[0123] The experimental conditions are shown in Table 5:

[0124] Table 5: Mechanical Property Testing Methods

[0125]

[0126] The experimental results obtained from the above tests are shown in Table 6:

[0127] Table 6: Mechanical Performance Test Results

[0128]

[0129] (3) Degradation performance test

[0130] The experimental results at different pH values ​​are shown below:

[0131] Table 7: Degradation test under different pH conditions (37℃, 3 months)

[0132]

[0133] Table 8: Photoresponsive degradation test (pH 7.4, 37℃, 2 months)

[0134]

[0135] Table 9: Temperature-responsive degradation test (pH 7.4, 3 months)

[0136]

[0137] Table 10: Molecular weight changes during degradation (pH 7.4, 37℃)

[0138]

[0139] (4) Mechanism verification test

[0140] The test conditions for verifying the mechanism of the surface interface modulation system are as follows:

[0141] Table 11: Validation Conditions for Surface Interface Modification System

[0142]

[0143] The results of the above tests are as follows:

[0144] Table 12: Variation of surface charge at different pH values ​​(mV)

[0145]

[0146] The test conditions for verifying the mechanism of the intermediate layer micro-region structure regulation system are as follows:

[0147] Table 13: Verification of the intermediate layer micro-region structure adjustment system

[0148]

[0149] The results of the above tests are as follows:

[0150] Table 14: Adsorption capacity of degradation products (mg lactic acid / g material)

[0151]

[0152] The conditions for verifying the mechanism of the synergistic catalytic system of nanoparticles are as follows:

[0153] Table 15: Validation Conditions for the Synergistic Catalytic System of Nanofunctional Particles

[0154]

[0155] The test results are shown below:

[0156] Table 16: Photocatalytic activity at different temperatures (relative fluorescence intensity units)

[0157]

[0158] The conditions for degradation product analysis and mechanism verification are as follows:

[0159] Table 17: Conditions for Degradation Product Analysis and Mechanism Validation

[0160]

[0161] The test results are shown below:

[0162] Table 18: Selective degradation rates of polylactic acid and polycaprolactone after 3 months of degradation (pH 7.4, 37℃)

[0163]

[0164] (5) Application performance testing

[0165] The degradation test results under simulated application environment are as follows:

[0166] Table 19: Simulated Application Environment Degradation Test Table (6 months)

[0167]

[0168] Based on the above test results, the comprehensive degradation regulation performance index of each group was calculated as follows:

[0169] Table 20: Comprehensive Degradation Regulation Performance Index

[0170]

[0171] Note: Each response index is calculated by normalizing the test results, and the comprehensive adjustment index is the geometric mean of the four individual indices.

[0172] 5. Experimental Conclusions

[0173] Based on the above experimental results, the following conclusions can be drawn:

[0174] (1) Formation of multi-level degradation regulatory network structure

[0175] Experimental results demonstrate the successful setup of the multi-level degradation regulatory network structure. FTIR results show that in the EG1 group containing the complete system, characteristic peaks can be observed in the surface interface layer (sodium carboxymethyl cellulose-sodium lauryl sulfate-calcium dodecyl phosphate), the intermediate layer (citric acid-epoxidized soybean oil-montmorillonite), and the nanofunctional particles (dopamine-modified nano-titanium dioxide-D-isoascorbate palmitate), proving the successful setup of the three functional systems.

[0176] Nuclear magnetic resonance (NMR) results further confirmed the distribution and interactions of these functional systems in the material. The interlayer spacing of montmorillonite in the EG1 group increased significantly (from the original 1.2 nm to 3.5 nm), indicating that the citric acid-epoxidized soybean oil crosslinking network successfully promoted the exfoliation and dispersion of montmorillonite in the polylactic acid-polycaprolactone matrix, providing more adsorption sites for degradation products.

[0177] (2) Verification of the mechanism of synergistic effect of substances

[0178] ① pH responsiveness verification of the surface interface regulation system

[0179] Samples (EG1, EG2, EG5, EG6) containing a sodium lauryl sulfate-sodium carboxymethyl cellulose-calcium dodecyl phosphate surface interface regulation system exhibited significant changes in contact angle and surface charge under different pH conditions, demonstrating the formation of a pH-responsive amphiphilic surface layer. These groups showed a significantly slower degradation rate at pH 5.0 and a significantly faster degradation rate at pH 9.0, with a pH response ratio (pH 9.0 / pH 5.0) of 2.50-3.00, higher than the 1.27-1.28 of the control group. This result verifies that the molecular arrangement formed on the surface by sodium lauryl sulfate and sodium carboxymethyl cellulose can regulate water molecule permeation according to the environmental pH, thereby achieving precise control of the degradation rate.

[0180] ② Verification of the sustained-release effect of the intermediate layer micro-region structure regulation system

[0181] Samples containing the citric acid-epoxidized soybean oil-montmorillonite intermediate layer conditioning system (EG1, EG3, EG5, EG7) exhibited significantly enhanced adsorption capacity for degradation products. After 72 hours, the adsorption capacity for lactic acid reached 45-48 mg / g, approximately 4.5 times that of the control group. Simultaneously, these groups showed higher molecular weight retention during degradation, maintaining a number-average molecular weight of 22,000-20,000 g / mol after 6 months, compared to only 12,000-15,000 g / mol in the control group. These results demonstrate that the cross-linked network formed by citric acid and epoxidized soybean oil, along with the layered structure of montmorillonite, jointly establishes a temporary-release system for degradation products, effectively preventing autocatalytic effects.

[0182] ③ Verification of the photo-temperature dual-response of the nano-functional particle synergistic catalytic system

[0183] The sample groups (EG1, EG4, EG6, EG7) of the dopamine-modified titanium dioxide-D-isoascorbate palmitate nanoparticle system exhibited significant photoresponsiveness and temperature responsiveness. Under light irradiation, the degradation rate of these groups increased by 1.68–1.82 times; when the temperature increased from 25℃ to 45℃, the photocatalytic activity increased by 2.8–2.9 times, which was higher than the degradation acceleration caused by temperature increase alone (1.94 times). This demonstrates that D-isoascorbate palmitate, as an electron shuttle, is activated at elevated temperatures and participates in the photocatalytic cycle of dopamine-modified titanium dioxide nanoparticles, achieving a synergistic response to temperature and light irradiation.

[0184] In addition, these groups exhibited preferential degradation characteristics of the polycaprolactone component, with a selectivity index (polycaprolactone / polylactic acid) of 1.84-2.09. This demonstrates that the reactive oxygen species generated by dopamine-modified nano-titanium dioxide preferentially attack the ε-caprolactone structure of polycaprolactone, thus achieving selective degradation.

[0185] (3) Verification of the synergistic effect among the three functional systems

[0186] By comparing the performance differences between the single-system group (EG2, EG3, EG4) and the dual-system group (EG5, EG6, EG7) and the complete formulation group (EG1), the synergistic effect among the three functional systems can be verified.

[0187] Synergistic effect of surface interface and intermediate layer: The comprehensive regulation index of EG5 group (surface + intermediate layer) is 1.33, which is higher than the simple additive effect of EG2 (1.37) and EG3 (1.14) (1.26), indicating that there is a synergistic effect between the two systems. In terms of pH responsiveness, the pH response index of EG5 (1.97) is close to that of EG1 (2.28), indicating that the sodium lauryl sulfate-sodium carboxymethyl cellulose-calcium dodecyl phosphate surface layer and the citric acid-epoxidized soybean oil-montmorillonite intermediate layer together set up a more efficient pH response system.

[0188] Synergistic effect of surface interface and nanofunctional particles: The photoresponse index (1.71) of EG6 group (surface + nanofunctional particles) is almost the same as that of EG1 (1.72), indicating that the sodium lauryl sulfate-sodium carboxymethyl cellulose surface layer provides a catalytic microenvironment for dopamine-modified nano-titanium dioxide, which promotes the improvement of photocatalytic efficiency.

[0189] Synergistic effect of intermediate layer and nanofunctional particles: The EG7 group (intermediate layer + nanofunctional particles) showed outstanding performance in selective degradation, with a selectivity index (1.45) close to that of EG1 (1.48), indicating that the montmorillonite layered structure and the dopamine-modified nano-titanium dioxide catalytic system work together to enhance the selective degradation ability.

[0190] The overall synergistic effect of the three systems: The comprehensive regulatory index (1.74) of the EG1 group was significantly higher than that of any two-system group (the highest being 1.67 for EG6), which proves that the multi-level degradation regulatory network jointly set by the three functional systems has a superimposed synergistic effect.

[0191] (4) Application scenario adaptability verification

[0192] In tests simulating different application environments, the EG1 group demonstrated excellent scenario adaptability:

[0193] In a medical setting, the quality loss rate reaches 72% after 6 months, making it suitable for mid-term implant applications;

[0194] In agricultural environments, the 6-month quality loss rate is only 36%, making it suitable for cover applications on annual crops;

[0195] In a packaging environment, the 6-month quality loss rate reaches 84%, making it suitable for rapidly degradable packaging material applications.

[0196] These results demonstrate that by adjusting the ratio of substances and the preparation process, the degradation behavior of polylactic acid-polycaprolactone blended nonwoven fabrics can be precisely controlled to meet the needs of different application scenarios.

[0197] (5) Summary

[0198] This experiment was designed to verify the formation and mechanism of a multi-level degradation regulation network in polylactic acid-polycaprolactone (PLA-PP) biodegradable woven bag nonwoven fabric. The results demonstrate that five substances (sodium lauryl sulfate, dopamine-modified nano-titanium dioxide complex, citric acid-epoxidized soybean oil compound system, sodium carboxymethyl cellulose-calcium dodecyl phosphate combination, and montmorillonite-D-isoascorbate palmitate combination) synergistically establish three functionally complementary regulatory systems. These three systems form a regulatory framework for the material's degradation behavior, enabling the material to exhibit a precisely controlled degradation process under different environmental conditions.

Claims

1. A method for preparing a nonwoven fabric for polylactic acid-polycaprolactone biodegradable woven bags, characterized in that, The nonwoven fabric is prepared from the following components: polylactic acid, with a number average molecular weight of 80,000-120,000 g / mol, and a content of 15-25% by weight; polycaprolactone, with a number average molecular weight of 70,000-90,000 g / mol, and a content of 5-15% by weight; sodium lauryl sulfate, with a content of 0.3-0.8% by weight; dopamine-modified nano-titanium dioxide composite, with a particle size of 20-50 nanometers, and a content of 0.5-2.0% by weight; and citric acid and epoxidized soybean oil. In the compound system, the mass ratio of citric acid to epoxidized soybean oil is 2:1 to 1:1, and the total content is 1.0-3.0% by weight; in the combination of sodium carboxymethyl cellulose and calcium dodecyl phosphate, the mass ratio of sodium carboxymethyl cellulose to calcium dodecyl phosphate is 3:1 to 2:1, and the total content is 1.0-2.5% by weight; in the combination of montmorillonite and D-isoascorbate palmitate, the mass ratio of montmorillonite to D-isoascorbate palmitate is 3:1 to 2:1, and the total content is 0.8-2.0% by weight. The aforementioned system forms a multi-level degradation regulation network structure with surface interface regulation, intermediate layer micro-region structure regulation, and synergistic catalysis by nano-functional particles, specifically as follows: The surface interface conditioning system consists of sodium lauryl sulfate, sodium carboxymethyl cellulose, and calcium dodecyl phosphate. The intermediate layer micro-region structure regulation system is composed of citric acid, epoxidized soybean oil, and montmorillonite. The nano-functional particle synergistic catalytic system is composed of dopamine-modified nano-titanium dioxide composite and D-isoascorbate palmitate; The preparation method includes the following steps: (1) Weigh polylactic acid and polycaprolactone separately at a mass ratio of 3:1, add them to a mixed solvent of chloroform and N,N-dimethylformamide, wherein the volume ratio of chloroform and N,N-dimethylformamide is 7:3, and stir magnetically at room temperature for 12-24 hours until completely dissolved. (2) Disperse sodium lauryl sulfate and sodium carboxymethyl cellulose in water to prepare an aqueous solution, and mix it with an alcoholic solution of calcium dodecyl phosphate, and sonicate for 30-60 minutes; (3) Pre-react citric acid with epoxidized soybean oil at 60-70℃ for 2-4 hours, then cool to room temperature; (4) Add the dopamine-modified nano-titanium dioxide complex, montmorillonite and D-isoascorbate palmitate to the solution in step (1) in sequence, and disperse by ultrasonication for 30-60 minutes. (5) Add the products from steps (2) and (3) to the mixed solution from step (4) and continue stirring for 4-6 hours to form a uniform spinning solution; (6) Electrospin the obtained spinning solution under the following conditions: voltage 15-20kV, liquid supply rate 0.5-2.0mL / h, collection distance 15-20cm, ambient temperature 25±2℃, relative humidity 40±5%; (7) The fiber membrane obtained by electrospinning is vacuum dried at 40-50℃ for 24 hours to remove residual solvent and obtain nonwoven fabric.

2. The preparation method according to claim 1, characterized in that, The preparation of dopamine-modified nano-titanium dioxide composites includes the following steps: (1) Disperse nano-titanium dioxide in a dopamine hydrochloride tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.5 and a concentration of 2-5 mg / mL. (2) Stir the reaction at room temperature for 12-24 hours to allow dopamine to self-polymerize on the surface of titanium dioxide to form a coating; (3) The product was separated by centrifugation, washed three times with deionized water and ethanol, and dried under vacuum at 60°C for 12 hours to obtain the complex.

3. The preparation method according to claim 2, characterized in that, The method also includes a post-processing step of the obtained nonwoven fabric, wherein the post-processing is selected from one or more of the following: (1) Heat treatment: Heat treatment at 60-70℃ for 2-4 hours to enhance the bonding between fibers; (2) UV pretreatment: The dopamine-modified nano-titanium dioxide catalytic system is activated by irradiation with 365nm wavelength ultraviolet light for 5-30 minutes. (3) pH adjustment treatment: Soak the nonwoven fabric in a buffer solution with pH 5-9 for 1-5 hours to adjust the initial state of the surface active layer.

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