Non-woven fabric for polylactic acid-polycaprolactone degradable woven bag and preparation method of non-woven fabric

Abstract

The invention discloses a non-woven fabric for a polylactic acid-polycaprolactone degradable woven bag and a preparation method of the non-woven fabric. The non-woven fabric is prepared from the following components: polylactic acid, polycaprolactone and sodium lauryl sulfate. A nano titanium dioxide compound modified by dopamine; a compound system of citric acid and epoxidized soybean oil; a combination of sodium carboxymethyl cellulose and calcium dodecyl phosphate; a combination of montmorillonite and D-isoascorbyl palmitate; wherein the system forms a multi-level degradation regulation network structure with surface interface regulation, middle layer micro-area structure regulation and nano functional particle concerted catalysis, and controllable regulation of the degradation rate of the polylactic acid-polycaprolactone blending material is realized. The preparation method is used for preparing the non-woven fabric. The polylactic acid-polycaprolactone blended material has the following beneficial effects that the problems that the degradation rate of the polylactic acid-polycaprolactone blended material is difficult to accurately adjust, the environmental adaptability is poor, the application scene is limited and the like in the prior art are solved.

Description

Technical Field

[0001] The invention relates to the field of degradable textile materials, and in particular to a polylactic acid-polycaprolactone degradable non-woven fabric for woven bags and a preparation method thereof. Background Art

[0002] Biodegradable nonwoven materials have broad application prospects in the fields of medical and health care, agricultural covering, packaging materials and environmental protection filtration. With the increasing awareness of environmental protection and the increasingly prominent problem of white pollution, nonwoven materials made of biodegradable polymers have received more and more attention and research. Polylactic acid and polycaprolactone, as two important biodegradable materials, are widely used in the fields of medical materials and environmental protection materials.

[0003] Polylactic acid is an aliphatic polyester prepared from renewable resources with good biocompatibility and degradability. Polylactic acid is mainly prepared in industry by ring-opening polymerization of lactic acid, and its degradation product, lactic acid, can be completely metabolized by the human body and is non-toxic and harmless. Polylactic acid has high tensile strength (40-60MPa), high elastic modulus (3-4GPa) and good thermal stability (heat deformation temperature of about 55-60°C), but its inherent brittleness and hydrophobicity limit its application in flexible materials. In addition, the degradation cycle of polylactic acid is relatively long. Generally speaking, it takes 1-3 years to completely degrade, which makes it difficult to meet the diverse requirements of degradation rates in different application scenarios.

[0004] Polycaprolactone is a semi-crystalline aliphatic polyester prepared by ring-opening polymerization of caprolactone. It has good flexibility (elongation at break > 700%) and a low melting point (about 60°C). Polycaprolactone has excellent processing properties and good compatibility with a variety of polymers. Its complete degradation cycle is about 2-3 years. Compared with polylactic acid, polycaprolactone has better toughness and ductility, but its mechanical strength is lower (tensile strength is about 16MPa) and its cost is relatively high, which limits its large-scale application.

[0005] The polylactic acid and polycaprolactone blend system can theoretically combine the advantages of the two materials to adjust the mechanical properties and degradation rate of the materials. However, the current polylactic acid-polycaprolactone blend system faces the following major problems: poor compatibility leads to unstable mechanical properties; the degradation rate is difficult to control, and there are problems with the different degradation mechanisms and rates of polylactic acid and polycaprolactone; the processing technology is complex, and it is difficult to form a structure with high specific surface area and high porosity; the performance adjustment range is narrow, and it is difficult to meet the needs of different application scenarios; the environmental adaptability is poor, and the degradation behavior under different pH and temperature conditions varies greatly.

[0006] Electrospinning technology is widely used in the preparation of functional non-woven materials because of its ability to produce nano- to micron-sized fibers. This technology uses a high-voltage electrostatic field to form a charged jet from a polymer solution, and forms ultrafine fibers during jet stretching and solvent volatilization, which are finally deposited on a receiving device to form a non-woven material. Electrospinning polylactic acid-polycaprolactone blends can theoretically solve the problem that existing processing methods are difficult to form high specific surface area and high porosity structures, but there are still problems such as phase separation during the spinning process, uneven fiber diameter, and limited solvent selection.

[0007] Existing methods mainly adjust 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-functional additives, such as chitosan, gelatin and other natural polymers as compatibilizers, but the improvement effect is limited; third, using coaxial electrospinning or emulsification electrospinning technology to prepare core-shell structured fibers to achieve hierarchical control of degradation behavior, but the preparation process is complicated; fourth, using post-treatment technologies such as plasma treatment and UV crosslinking to adjust the surface properties and degradation characteristics of the material, but the treatment effect is not durable.

[0008] Therefore, it is of great significance to develop a simple and efficient preparation method to prepare polylactic acid-polycaprolactone degradable non-woven fabric material for woven bags with 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 the present invention is to provide a polylactic acid-polycaprolactone degradable non-woven fabric for woven bags and a preparation method thereof, so as to solve the problems in the prior art that the degradation rate of polylactic acid-polycaprolactone blended materials is difficult to accurately adjust, has poor environmental adaptability, and has limited application scenarios.

[0010] The polylactic acid-polycaprolactone degradable non-woven fabric for woven bags with controllable degradation rate provided by the present invention is prepared from the following components: Polylactic acid, number average molecular weight of 80000-120000 g / mol, content of 15-25 weight percent; Polycaprolactone, number average molecular weight of 70000-90000 g / mol, content of 5-15 weight percent; Sodium lauryl sulfate, content of 0.3-0.8 weight percent; Dopamine modified nano titanium dioxide composite, particle size of 20-50 nanometers, content of 0.5-2.0 weight percent; 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 weight percent; A combination of sodium carboxymethyl cellulose and calcium lauryl phosphate, wherein the mass ratio of sodium carboxymethyl cellulose to calcium lauryl phosphate is 3:1 to 2:1, and the total content is 1.0-2.5 weight percent; The combination of montmorillonite and D-isoascorbyl palmitate has a mass ratio of montmorillonite to D-isoascorbyl palmitate of 3:1 to 2:1 and a total content of 0.8-2.0 weight percent.

[0011] 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, achieving controllable regulation of the degradation rate of polylactic acid-polycaprolactone blends.

[0012] The present invention also provides a method for preparing a nonwoven fabric, comprising the following steps: (1) Polylactic acid and polycaprolactone were weighed in a mass ratio of 3:1, and the total polymer concentration was 12 weight percent, and added into a mixed solvent of chloroform and N,N-dimethylformamide (volume ratio 7:3), and magnetically stirred at room temperature for 12-24 hours until completely dissolved; (2) dispersing sodium lauryl sulfate and sodium carboxymethyl cellulose in water to prepare an aqueous solution, mixing it with an alcohol solution of calcium dodecyl phosphate, and ultrasonically treating it for 30-60 minutes; (3) pre-reacting citric acid and epoxidized soybean oil at 60-70° C. for 2-4 hours and cooling to room temperature; (4) adding the dopamine-modified nano-titanium dioxide composite, montmorillonite and D-isoascorbyl palmitate to the solution of step (1) in sequence, and ultrasonically dispersing for 30-60 minutes; (5) adding the products of steps (2) and (3) to the mixed solution of step (4), and continuing stirring for 4-6 hours to form a uniform spinning solution; (6) electrospinning the obtained spinning solution under the following conditions: voltage 15-20 kV, liquid supply rate 0.5-2.0 mL / h, collection distance 15-20 cm, ambient temperature 25±2° C., relative humidity 40±5%; (7) The fiber membrane obtained by electrospinning is vacuum dried at 40-50° C. for 24 hours to remove the residual solvent and obtain a non-woven fabric.

[0013] The core point of the present invention is to set up a multi-level degradation regulation network, and achieve precise regulation of the degradation behavior of the polylactic acid-polycaprolactone blended non-woven fabric through the synergistic effect of the following three functionally complementary regulation systems: 1) Surface interface regulation system: It is composed of sodium lauryl sulfate, sodium carboxymethyl cellulose and calcium dodecyl phosphate to form 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 permeation rate of water molecules; the calcium ions in calcium dodecyl phosphate form chelates with degradation products to control the release rate of degradation products.

[0014] 2) Intermediate layer micro-region structure regulation system: composed of citric acid, epoxidized soybean oil and montmorillonite, it controls the internal phase separation structure of the fiber and the diffusion of degradation products. Citric acid and epoxidized soybean oil form a cross-linked network through carboxyl-epoxy reaction to control the release of degradation products; the layered structure of montmorillonite provides temporary storage space for degradation products to avoid the self-catalytic effect of degradation products.

[0015] 3) Nano-functional particle synergistic catalytic system: composed of dopamine-modified nano-titanium dioxide complex and D-isoascorbyl palmitate, it realizes light-responsive controllable degradation. Dopamine-modified nano-titanium dioxide produces a more selective redox environment under light, preferentially degrading the polycaprolactone component; D-isoascorbyl palmitate participates in the photocatalytic cycle when the temperature rises, realizing dual response to temperature and light.

[0016] These three systems interact with each other at the molecular level to form a four-dimensional regulation system for the material degradation behavior. They work synergistically in the spatial dimension - multi-level structure, the temporal dimension - staged degradation, the chemical environment dimension - pH response, and the external stimulus dimension - light and temperature response to achieve precise regulation of the degradation rate of polylactic acid-polycaprolactone blends.

[0017] The present invention achieves the following beneficial effects by setting a multi-level degradation regulation network structure: 1. Precise regulation of degradation rate: The non-woven fabric material of the present invention can precisely regulate the degradation period within the range of 1-18 months through a variety of external stimulus (pH, light, temperature) response mechanisms to meet the needs of different application scenarios.

[0018] 2. Enhanced environmental adaptability: The non-woven fabric material of the present invention exhibits controllable degradation behavior under different pH environments. The degradation rate slows down in an acidic environment (pH <5), and the degradation rate can be controllably increased in a neutral or alkaline environment, thereby adapting to the needs of different application environments.

[0019] 3. Optimization of mechanical properties: The non-woven fabric material of the present invention overcomes the problem of poor compatibility of existing polylactic acid-polycaprolactone blend materials, significantly improves the mechanical properties of the material, increases the tensile strength by 30-50%, and increases the elongation at break by 40-60%.

[0020] 4. Visualization of the degradation process: The nonwoven material of the present invention realizes the 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.

[0021] 5. Improved processing performance: The system adopted by the present invention significantly improves the electrospinning processing performance of the polylactic acid-polycaprolactone blend system, the fiber diameter distribution is more uniform (200-800nm), the fiber formation rate is increased by 20-30%, and the production efficiency is greatly improved.

[0022] In addition, the present invention conducts a detailed analysis on the mechanism of the non-woven fabric for the polylactic acid-polycaprolactone degradable woven bag.

[0023] The core of the present invention is to set 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 degradable non-woven fabric for woven bags: 1) Surface interface regulation system: composed of sodium lauryl sulfate, sodium carboxymethyl cellulose and calcium dodecyl phosphate, forming an amphiphilic dynamic response layer on the fiber surface; 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; 3) Nano-functional particle synergistic catalytic system: It is composed of dopamine-modified nano-titanium dioxide complex and D-isoascorbyl palmitate to achieve light-responsive controllable degradation.

[0024] These three systems interact with each other at the molecular level to form a four-dimensional regulation system for material degradation behavior, namely, they work together in the spatial dimension, time dimension, chemical environment dimension and external stimulus dimension to achieve precise regulation of the degradation rate of polylactic acid-polycaprolactone blend materials.

[0025] At the molecular level, the hydrolysis of the ester bond of polylactic acid and polycaprolactone is the core of degradation. Polylactic acid has L-lactic acid as a repeating unit and a methyl side group, and its molecular chain is rigid; polycaprolactone has caprolactone as a repeating unit and a more flexible chain structure. This structural difference leads to poor compatibility, obvious phase separation, and large differences in degradation rates between the two in the existing blending system.

[0026] The present invention achieves three aspects of regulation at the molecular level: 1) Regulation of molecular chain interaction: The ionic groups of sodium lauryl sulfate and calcium dodecyl phosphate form weak interactions with the ester groups of the polylactic acid-polycaprolactone molecular chains, changing the stacking state of the molecular chains; 2) Interface coupling and compatibility adjustment: Citric acid-epoxidized soybean oil forms a cross-linked network with multiple functional groups, which can form multi-point interactions with both polylactic acid and polycaprolactone molecular chains, thus improving the compatibility of the two. 3) Micro-area catalytic environment setting: Dopamine-modified nano-titanium dioxide nanocomposites form evenly dispersed catalytic sites in the system, providing a microenvironment for selective degradation.

[0027] The innovation of the present invention lies in the three functional systems formed by five substances establishing a synergistic degradation regulation network: The sodium lauryl sulfate-sodium carboxymethyl cellulose-calcium dodecyl phosphate surface system and the citric acid-epoxidized soybean oil-montmorillonite intermediate layer system formed a penetration-buffering-storage synergistic mechanism: The surface layer formed by sodium lauryl sulfate and sodium carboxymethyl cellulose exhibits reversible conformational changes under different pH conditions. In an acidic environment (pH < 5), the carboxyl group of sodium carboxymethyl cellulose mainly exists in a non-ionic form, and forms a dense structure with the sulfate group of sodium lauryl sulfate through hydrogen bonding, reducing the penetration of water molecules; while in a neutral or alkaline environment, the carboxyl group is ionized and expands the molecular conformation with sodium lauryl sulfate through electrostatic repulsion, increasing the penetration of water molecules. This pH-responsive permeation behavior forms a synergistic relationship with the citric acid-epoxidized soybean oil system in the middle layer: citric acid releases H during hydrolysis. + , lowering the local pH and forming a negative feedback regulation loop.

[0028] 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 forms a coordination complex with sodium carboxymethyl cellulose, together setting up an ion channel. When the degradation products (mainly carboxylic acid substances) accumulate to a certain concentration, they will competitively complex with the calcium ions in calcium dodecyl phosphate, causing the channel conformation to change and promoting the discharge of degradation products. Cooperating with the interlayer adsorption mechanism of the middle layer montmorillonite: montmorillonite can temporarily store some degradation products to prevent the acceleration of autocatalytic degradation caused by excessive instantaneous concentration.

[0029] The citric acid-epoxidized soybean oil-montmorillonite intermediate layer system and the dopamine-modified nano-titanium dioxide-D-isoascorbyl palmitate nanocatalytic system formed a confined catalysis-selective degradation synergistic mechanism: The 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 nano-titanium dioxide nanoparticles, limiting their aggregation, while the montmorillonite layered structure further strengthens this confinement effect. This spatial confinement structure ensures that the catalytic reaction only occurs in a specific micro-region, avoiding the overall rapid degradation of the material caused by the existing TiO2 catalyst.

[0030] Timing coordination of stimulus response and degradation product treatment: When UV light stimulation is applied externally, dopamine-modified nano-titanium dioxide produces reactive oxygen free radicals, which preferentially attack the ester bond of polycaprolactone (the ε-caprolactone structure of polycaprolactone is more easily oxidized than the α-hydroxy ester structure of polylactic acid). D-isoascorbyl palmitate acts as a free radical chelator to control the concentration of reactive oxygen and ensure that the degradation process is controllable. At the same time, the montmorillonite interlayer can adsorb and temporarily store degradation products to avoid the self-catalytic effect of degradation products, and the epoxy group of epoxidized soybean oil can react with the carboxyl group generated during the degradation process to reduce the acidity of the system.

[0031] The dopamine-modified nano-titanium dioxide-D-isoascorbyl palmitate nanocatalytic system and the sodium lauryl sulfate-sodium carboxymethyl cellulose-calcium dodecyl phosphate surface system formed a surface activation-internal cascade synergistic mechanism: The dopamine-modified TiO2 surface forms a charge transfer complex. When excited by light, electrons are transferred from dopamine to the TiO2 conduction band, creating a restricted redox environment. This electron transfer process interacts with the sodium lauryl sulfate-sodium carboxymethyl cellulose interface layer on the surface, changing the surface potential distribution and further affecting the distribution behavior of water and ions on the material surface.

[0032] Under light conditions, D-isoascorbyl palmitate can provide electrons through its enol structure to participate in the photocatalytic cycle of dopamine-modified nano-titanium dioxide. At the same time, its long-chain fatty acid ester part forms hydrophobic interactions with the alkyl chain of sodium lauryl sulfate, forming an active gradient from the surface to the inside of the material, allowing the degradation process to proceed smoothly.

[0033] In addition, the addition of the above substances has certain adverse effects in the prior art: 1. Sodium lauryl sulfate is used as a surfactant. The prior art shows that it will increase the hydrophilicity of the material, promote the penetration of water molecules, and accelerate the hydrolysis and degradation of polyester. Sodium carboxymethyl cellulose is highly hydrophilic and has 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 the material.

[0034] In the system of the present 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-assembled during the electrospinning process to form an amphiphilic surface layer with pH responsiveness. 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 outward to form a brush-like arrangement. This structure allows the surface of the material to exhibit controllable hydrophilic-hydrophobic transition characteristics: the hydrophilicity is enhanced in an acidic environment and reduced in an alkaline environment, which is opposite to the effect of existing surfactants. Calcium dodecyl phosphate is no longer a catalyst in the system, but acts as an ion-gated component, regulating the material exchange rate through the interaction between its calcium ions and degradation products.

[0035] 2. Citric acid is a typical polycarboxyl organic acid. The prior art shows that it will catalyze the hydrolysis of polyester and accelerate the degradation of the material. Epoxidized soybean oil, as a plasticizer, will reduce the mechanical strength and thermal stability of the material. Although montmorillonite can enhance the performance of the material, it generally affects the electrospinning process, resulting in fiber breakage or unstable jetting.

[0036] In the present invention, citric acid and epoxidized soybean oil form a volume-limited cross-linked network structure through a carboxyl-epoxy reaction. This cross-linked network allows the carboxyl portion of citric acid to be released in a controlled manner, thereby avoiding an initial explosive catalytic effect. Montmorillonite is modified by a citric acid-epoxidized soybean oil network intercalation in this system to form a brick-wall-like nanostructure, which does not affect the electrostatic spinning process but improves the spinning stability. The interlayer space of montmorillonite serves as a temporary storage area for degradation products, which can adsorb and slowly release degradation products during the degradation process, thereby preventing the degradation products from being accelerated by autocatalysis due to excessive local concentrations.

[0037] 3. TiO2 will produce highly oxidizing active oxygen under UV light, and the prior art shows that it will indiscriminately attack polymer chains, causing rapid degradation of the material; dopamine has strong adhesion and self-polymerization, which will affect the processing performance of the material; D-isoascorbyl palmitate is an antioxidant, and the prior art shows that it will prevent oxidative degradation and prolong the degradation cycle of the material.

[0038] In this system, dopamine forms a uniform coating with a thickness of about 3-5nm on the surface of TiO2 through self-polymerization, which completely changes the photocatalytic properties of TiO2. This core-shell structured nanoparticle no longer produces the existing strong oxidizing free radicals, but instead forms an electron transfer regulation system to produce a more selective redox environment. D-isoascorbyl palmitate is not an antioxidant in this system, but acts as an electron shuttle that can capture electrons under certain conditions and transfer them to the site, achieving precise regulation of the degradation process. This selective catalytic effect allows the polycaprolactone component to be preferentially degraded, producing a microporous structure, but does not cause damage to the overall structure, achieving subsequent controllable degradation of polylactic acid.

[0039] The five substances mentioned above form multiple synergistic mechanisms: 1. Interfacial coupling and charge transfer synergy An interfacial charge transfer structure is formed between the surface layer of sodium lauryl sulfate-sodium carboxymethyl cellulose and dopamine-modified nano-titanium dioxide nanoparticles. The sulfate group of sodium lauryl sulfate can form a charge transfer complex with the amino group on the dopamine layer through ion-dipole interaction. This complex changes the band structure of dopamine-modified nano-titanium dioxide, extending its light response range to the visible light region (400-450nm). At the same time, the carboxyl group of sodium carboxymethyl cellulose can form hydrogen bonds with the dopamine layer, further stabilizing the interfacial structure. This synergistic effect enables the material to achieve controllable degradation even under weak light conditions, expanding the application scenarios.

[0040] 2. Synergy of ion exchange and pH buffering The calcium ions in calcium dodecyl phosphate form a dynamic equilibrium ion exchange system with citric acid. When the pH of the system decreases, the citric acid is partially protonated, reducing its ability to bind to calcium ions and releasing calcium ions; these calcium ions can form chelates with the carboxyl ends produced by material degradation, neutralizing their acidity and preventing autocatalytic degradation caused by a continuous decrease in pH. This dynamic ion exchange process realizes a self-regulating pH buffer system, allowing the material to maintain a relatively stable degradation rate under various environmental conditions.

[0041] 3. Spatial confinement and selective catalysis synergy The layered structure of montmorillonite and dopamine-modified nano-titanium dioxide nanoparticles form a synergistic mechanism of spatial confinement and catalytic activity. Dopamine-modified nano-titanium dioxide nanoparticles can be partially inserted into the interlayers of montmorillonite to limit their aggregation and maintain high dispersibility; at the same time, the interlayer positive charge of montmorillonite can attract the carboxyl end produced during the degradation process, so that the degradation reaction occurs preferentially around the montmorillonite. This spatial confinement effect and the selective catalytic effect of dopamine-modified nano-titanium dioxide promote each other, achieving precise spatial regulation of the degradation process.

[0042] 4. Temperature response and photocatalysis synergy There is a temperature-related interaction between D-isoascorbyl palmitate and epoxidized soybean oil. Under low temperature conditions (<37°C), the long-chain alkyl of D-isoascorbyl palmitate forms a hydrophobic association with the hydrophobic segments of epoxidized soybean oil, limiting its activity; when the temperature rises (>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 thermosensitive-photocatalytic synergistic mechanism enables the material to respond to both temperature and light, two external stimuli, simultaneously, achieving multi-factor regulated degradation behavior.

[0043] Based on the above analysis, the present invention sets up a four-dimensional degradation regulation network, which solves the problem of weak degradation control ability of existing biodegradable materials and realizes the technical purpose of changing from passive adaptation to the environment to active response to demand. This molecular-level network transforms the degradation behavior of the polylactic acid-polycaprolactone degradable non-woven fabric material for woven bags from the existing single degradation pathway to multi-channel synergistic degradation. DETAILED DESCRIPTION

[0044] The present invention designs the following experiment to verify the effect of the polylactic acid-polycaprolactone degradable non-woven fabric for woven bags: 1. Purpose of the experiment This experimental scheme comprehensively verifies the performance and mechanism of PLA-polycaprolactone degradable non-woven fabric for woven bags with controllable degradation rate. The experiment will focus on verifying the effectiveness of the multi-level degradation regulation network structure proposed in the patent, including the formation and synergy 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 regulation effect of the system on the degradation behavior of PLA-polycaprolactone blends in different application scenarios is verified.

[0045] The experimental plan includes four parts: sample preparation, multi-condition degradation test, multi-dimensional performance characterization and microstructure analysis. The innovation and effectiveness of the present invention are verified by comprehensively analyzing the performance differences between different experimental groups.

[0046] 2. Experimental grouping and formulation design The experimental group design is shown in Table 1 and Table 2: Table 1: Experimental groups Table 2: Formula design table (unit: weight percentage) Control group design: Control group 1 represents the basic polylactic acid-polycaprolactone blend system without adding any substances; Control group 2 represents the conventional practice of using the existing compatibilizer PEG.

[0047] Complete formula group design: Experimental group 1 contains all substances to form a complete multi-level degradation regulation network structure.

[0048] Single system group design: Experimental groups 2, 3, and 4 each contain components of only one functional system, which is used to verify the individual effects of each system.

[0049] Dual-system group design: Experimental groups 5, 6, and 7 contain component combinations of two systems, respectively, to verify the synergistic effects between different systems.

[0050] Material ratio: The ratio of each material is based on the best embodiment, the mass ratio of sodium lauryl sulfate: sodium carboxymethyl cellulose: calcium dodecyl phosphate is 1:1.8:0.8; the mass ratio of citric acid: epoxidized soybean oil is 1.5:1; the mass ratio of montmorillonite: D-isoascorbyl palmitate is 3:1.

[0051] 3. Experimental Design (1) Preparation of dopamine-modified nano-titanium dioxide composites Titanium dioxide nanoparticles (30 nm) were dispersed in dopamine hydrochloride (2 mg / mL) in Tris buffer (10 mM, pH 8.5) at a concentration of 2 mg / mL.

[0052] The mixture was stirred magnetically at room temperature for 18 hours to allow dopamine to self-polymerize on the TiO2 surface to form a coating.

[0053] The product was collected by centrifugation at 12000 rpm for 10 min and washed three times with deionized water and ethanol.

[0054] The mixture was vacuum dried at 60° C. for 12 hours, and ground and sieved to obtain dopamine-modified nano-titanium dioxide composite powder.

[0055] (2) Non-woven fabric sample preparation process Preparation of base solution: Polylactic acid and polycaprolactone were added into a mixed solvent of chloroform and DMF (7:3, v / v) according to the designed ratio. Stir magnetically at room temperature for 18 hours until completely dissolved to obtain a transparent solution (3) Processing of components of each functional system: Surface interface regulation 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 subjected to ultrasonic treatment for 45 minutes.

[0056] Intermediate layer micro-region structure regulation system: citric acid and epoxidized soybean oil were mixed, pre-reacted at 65°C for 3 hours and then cooled to room temperature, and then montmorillonite was added into a small amount of DMF for dispersion.

[0057] Nano-functional particle synergistic catalytic system: The dopamine-modified nano-titanium dioxide complex and D-isoascorbyl palmitate were dispersed in a small amount of chloroform and ultrasonicated for 30 minutes.

[0058] Preparation of spinning solution: According to the formula design of each group, the corresponding functional components were added into the basic solution one by one and stirred for 5 hours to form a uniform spinning solution, and then allowed to stand for 2 hours to eliminate bubbles.

[0059] Electrospinning process: voltage: 18 kV; liquid supply rate: 1.0 mL / h; collection distance: 18 cm; ambient temperature: 25 ± 2 °C; relative humidity: 40 ± 5%; collection device: rotating drum covered with aluminum foil, speed 400 rpm; spinning time: keep the same for each group to ensure similar thickness.

[0060] Post-treatment: All samples were vacuum dried at 45 °C for 24 h to remove residual solvents; the dried samples were cut into required sizes for subsequent testing.

[0061] (3) Degradation condition treatment In order to verify the performance of the multi-level degradation regulation network under different environmental conditions, the following treatment conditions were designed: pH responsiveness test: Acidic environment: pH 5.0 acetate buffer, 37°C; Neutral environment: pH 7.4 phosphate buffer, 37°C; Alkaline environment: pH 9.0 carbonate buffer, 37°C.

[0062] Photoresponsiveness test: Illumination group: 365nm UV irradiation, 5mW / cm 2 , irradiated for 2 hours every day; control group: stored in the dark, other conditions were the same.

[0063] Temperature responsiveness test: low temperature group: 25°C, pH 7.4 phosphate buffer; medium temperature group: 37°C, pH 7.4 phosphate buffer; high temperature group: 45°C, pH 7.4 phosphate buffer.

[0064] Simulated application environment test: Medical environment simulation: pH 7.4 phosphate buffer + lipase (10U / mL), 37°C; Agricultural environment simulation: simulated soil solution (pH 6.5) + periodic wet-dry cycle (12 hours / 12 hours); Packaging environment simulation: simulated composting conditions, 58°C, 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 regularly for testing and analysis.

[0065] 4. Experimental Results (1) Basic physical properties test As shown in Table 3: Table 3: Basic physical properties test conditions Through the above tests, the physical properties test table shown in Table 4 was obtained: Table 4: Basic physical properties (2) Mechanical properties test The experimental conditions are shown in Table 5: Table 5: Mechanical properties test methods Through the above tests, the experimental results are shown in Table 6: Table 6: Mechanical properties test results (3) Degradation performance test The experimental results under different pH are as follows: Table 7: Degradation test under different pH conditions (37°C, 3 months) Table 8: Light response degradation test (pH 7.4, 37°C, 2 months) Table 9: Temperature responsive degradation test (pH 7.4, 3 months) Table 10: Molecular weight changes during degradation (pH 7.4, 37°C) (4) Mechanism verification test The test conditions for verification of the surface interface regulation system mechanism are as follows: Table 11: Surface interface adjustment system verification conditions Through the above test, the results are as follows: Table 12: Changes in surface charge at different pH values ​​(mV) The test conditions for verification of the mechanism of the intermediate layer micro-region structure regulation system are as follows: Table 13: Verification of the micro-region structure regulation system of the intermediate layer After the above tests, the results are as follows: Table 14: Adsorption capacity of degradation products (mg lactic acid / g material) The verification conditions of the mechanism of nano-functional particle synergistic catalytic system are as follows: Table 15: Nano-functional particle synergistic catalytic system verification conditions The test results are as follows: Table 16: Photocatalytic activity at different temperatures (relative fluorescence intensity units) The conditions for degradation product analysis and mechanism verification are as follows: Table 17: Degradation product analysis and mechanism verification conditions The test results are as follows: Table 18: Selective degradation rate of polylactic acid and polycaprolactone after 3 months of degradation (pH 7.4, 37°C) (5) Application performance testing The results of the simulated application environment degradation test are as follows: Table 19: Simulated application environment degradation test table (6 months) Based on the above test results, the comprehensive degradation regulation performance index of each group is calculated as follows: Table 20: Comprehensive degradation regulation performance index table Note: Each response index is calculated by normalizing the test results. The comprehensive adjustment index is the geometric mean of the four individual indices.

[0066] 5. Experimental conclusion Based on the above experimental results, the following conclusions are drawn: (1) Formation of a multi-level degradation regulatory network structure The experimental results proved the successful setting of the multi-level degradation regulation network structure. FTIR results showed that in the EG1 group containing the complete system, the characteristic peaks of the surface interface layer (sodium carboxymethyl cellulose-sodium lauryl sulfate-calcium dodecyl phosphate), the characteristic peaks of the intermediate layer (citric acid-epoxidized soybean oil-montmorillonite) and the characteristic peaks of the nano-functional particles (dopamine-modified nano-titanium dioxide-D-isoascorbyl palmitate) could be observed, proving the successful setting of the three functional systems.

[0067] The NMR results further demonstrated the distribution and interaction 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 cross-linking network successfully promoted the exfoliation and dispersion of montmorillonite in the polylactic acid-polycaprolactone matrix, providing more adsorption sites for degradation products.

[0068] (2) Verification of the synergistic mechanism of substances ① pH responsiveness verification of surface interface regulation system The sample groups (EG1, EG2, EG5, EG6) containing the sodium lauryl sulfate-sodium carboxymethyl cellulose-calcium dodecyl phosphate surface interface regulation system showed significant changes in contact angle and surface charge under different pH conditions, proving the formation of a pH-responsive amphiphilic surface layer. The degradation rate of these groups was significantly slowed down under pH 5.0 conditions, and the degradation rate was significantly accelerated under pH 9.0 conditions. The pH response ratio (pH 9.0 / pH 5.0) reached 2.50-3.00, which was higher than 1.27-1.28 of the control group. This result verifies that the molecular arrangement formed by sodium lauryl sulfate and sodium carboxymethyl cellulose on the surface can regulate the penetration of water molecules according to the environmental pH, thereby achieving precise control of the degradation rate.

[0069] ②Verification of the sustained release effect of the micro-region structure regulation system in the intermediate layer The sample groups (EG1, EG3, EG5, EG7) containing the citric acid-epoxidized soybean oil-montmorillonite intermediate layer adjustment system showed significantly enhanced degradation product adsorption capacity, and the adsorption of lactic acid reached 45-48 mg / g after 72 hours, which was about 4.5 times that of the control group. At the same time, these groups showed a higher molecular weight retention rate during the degradation process, and the number average molecular weight remained at 22,000-20000 g / mol after 6 months, while the control group was only 12,000-15,000 g / mol. These results prove that the cross-linked network formed by citric acid and epoxidized soybean oil and the layered structure of montmorillonite jointly set up a temporary storage-slow release system for degradation products, effectively preventing the self-catalytic effect of degradation products.

[0070] ③Verification of the light-temperature dual responsiveness of the nano-functional particle synergistic catalytic system The sample groups (EG1, EG4, EG6, EG7) containing dopamine-modified nano-titanium dioxide-D-isoascorbyl palmitate nanofunctional particle systems showed significant light responsiveness and temperature responsiveness. Under light conditions, the degradation rate of these groups increased by 1.68-1.82 times; when the temperature increased from 25°C to 45°C, the photocatalytic activity increased by 2.8-2.9 times, which was higher than the degradation acceleration caused by the simple temperature increase (1.94 times). This proves that D-isoascorbyl palmitate is activated as an electron shuttle when the temperature rises, participating in the photocatalytic cycle of dopamine-modified nano-titanium dioxide, and achieving a synergistic response of temperature and light.

[0071] In addition, these groups showed preferential degradation properties for the polycaprolactone component, with the selectivity index (polycaprolactone / polylactic acid) reaching 1.84-2.09, which proved that the reactive oxygen generated by dopamine-modified nano-titanium dioxide preferentially attacked the ε-caprolactone structure of polycaprolactone, achieving selective degradation.

[0072] (3) Verification of the synergy between the three functional systems By comparing the performance differences between the single system group (EG2, EG3, EG4) and the dual system group (EG5, EG6, EG7) and the complete formula group (EG1), the synergistic effect between the three functional systems can be verified: Synergistic effect of surface interface and middle layer: The comprehensive regulation index of EG5 group (surface + middle layer) is 1.33, which is higher than the simple superposition effect of EG2 (1.37) and EG3 (1.14) (1.26), indicating that there is 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 middle layer jointly set up a more efficient pH response system.

[0073] Synergistic effect of surface interface and nanofunctional particles: The light response index of EG6 group (surface + nanofunctional particles) (1.71) 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, promoting the improvement of photocatalytic efficiency.

[0074] Synergistic effect of the intermediate layer and nano-functional particles: Group EG7 (intermediate layer + nano-functional particles) performed outstandingly in terms of 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 worked synergistically to enhance the selective degradation ability.

[0075] The overall synergistic effect of the three systems: The comprehensive regulation index (1.74) of the EG1 group was significantly higher than that of any dual-system group (the highest was 1.67 of EG6), proving that the multi-level degradation regulation network jointly set up by the three functional systems has a superimposed synergistic effect.

[0076] (4) Verification of adaptability to application scenarios In tests simulating different application environments, the EG1 group showed excellent adaptability to different scenarios: In medical environments, the 6-month mass loss rate reaches 72%, which is suitable for mid-term implant applications; In agricultural environments, the 6-month mass loss rate is only 36%, which is suitable for mulching applications on annual crops; In the packaging environment, the mass loss rate reaches 84% ​​in 6 months, which is suitable for the application of rapidly degradable packaging materials.

[0077] These results indicate that by adjusting the material ratio and preparation process, the degradation behavior of polylactic acid-polycaprolactone blended non-woven fabrics can be precisely adjusted to meet the needs of different application scenarios.

[0078] (5) Summary This experimental design verifies the formation and mechanism of multi-level degradation regulation network in polylactic acid-polycaprolactone degradable non-woven fabric for woven bags. The experimental results show that five substances (sodium lauryl sulfate, dopamine-modified nano-titanium dioxide composite, citric acid-epoxidized soybean oil complex system, sodium carboxymethyl cellulose-calcium dodecyl phosphate combination, montmorillonite-D-isoascorbyl palmitate combination) set up three functional complementary regulation systems through synergistic action. These three systems form a regulation system for the degradation behavior of the material, so that the material exhibits a precisely controlled degradation process under different environmental conditions.

Claims

1. A polylactic acid-polycaprolactone degradable non-woven fabric for woven bags, characterized in that: Nonwoven fabrics are made from the following components: Polylactic acid, number average molecular weight of 80000-120000 g / mol, content of 15-25 weight percent; Polycaprolactone, number average molecular weight of 70000-90000 g / mol, content of 5-15 weight percent; Sodium lauryl sulfate, content of 0.3-0.8 weight percent; Dopamine modified nano titanium dioxide composite, particle size of 20-50 nanometers, content of 0.5-2.0 weight percent; 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 weight percent; A combination of sodium carboxymethyl cellulose and calcium lauryl phosphate, wherein the mass ratio of sodium carboxymethyl cellulose to calcium lauryl phosphate is 3:1 to 2:1, and the total content is 1.0-2.5 weight percent; A 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 weight percent; The above 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, thereby achieving controllable regulation of the degradation rate of polylactic acid-polycaprolactone blended materials.

2. The nonwoven fabric according to claim 1, characterized in that The mass ratio of sodium lauryl sulfate: sodium carboxymethyl cellulose: calcium dodecyl phosphate is 1:2:

1.

3. The nonwoven fabric according to claim 1, characterized in that In the dopamine-modified nano-titanium dioxide composite, dopamine forms a uniform coating with a thickness of 3-5 nanometers on the surface of TiO2, which changes the photocatalytic properties of TiO2, causing it to produce a more selective redox environment under light conditions, thereby achieving preferential degradation of the polycaprolactone component.

4. A method for preparing a polylactic acid-polycaprolactone degradable non-woven fabric for woven bags according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: (1) Polylactic acid and polycaprolactone were weighed in a mass ratio of 3:1, added into a mixed solvent of chloroform and N,N-dimethylformamide (volume ratio 7:3), and magnetically stirred at room temperature for 12-24 hours until completely dissolved; (2) dispersing sodium lauryl sulfate and sodium carboxymethyl cellulose in water to prepare an aqueous solution, mixing it with an alcohol solution of calcium dodecyl phosphate, and ultrasonically treating it for 30-60 minutes; (3) pre-reacting citric acid and epoxidized soybean oil at 60-70° C. for 2-4 hours and cooling to room temperature; (4) adding the dopamine-modified nano-titanium dioxide composite, montmorillonite and D-isoascorbyl palmitate to the solution of step (1) in sequence, and dispersing by ultrasonication for 30-60 minutes; (5) adding the products of steps (2) and (3) to the mixed solution of step (4), and continuing stirring for 4-6 hours to form a uniform spinning solution; (6) electrospinning the obtained spinning solution under the following conditions: voltage 15-20 kV, liquid supply rate 0.5-2.0 mL / h, collection distance 15-20 cm, ambient temperature 25±2° C., relative humidity 40±5%; (7) The fiber membrane obtained by electrospinning is vacuum dried at 40-50° C. for 24 hours to remove the residual solvent and obtain a non-woven fabric.

5. The preparation method according to claim 4, characterized in that The preparation of dopamine-modified nano-titanium dioxide composite includes the following steps: (1) dispersing nano-titanium dioxide in dopamine hydrochloride tris (hydroxymethylaminomethane) buffer (pH 8.5) at a concentration of 2-5 mg / mL; (2) stirring 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 a composite.

6. The preparation method according to claim 5, characterized in that The method further comprises the step of post-treating the obtained nonwoven fabric, wherein the post-treatment is selected from one or more of the following: (1) Heat treatment: Heat treatment at 60-70°C for 2-4 hours to enhance the bonding between fibers; (2) UV pretreatment: irradiation with 365 nm UV light for 5-30 minutes to activate the dopamine-modified nano-titanium dioxide catalyst system; (3) pH adjustment treatment: The nonwoven fabric is immersed in a buffer solution of pH 5-9 for 1-5 hours to adjust the initial state of the surface active layer.

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