Multifunctional bio-based polylactic acid fabric and preparation method thereof

Abstract

The invention relates to a multifunctional bio-based polylactic acid fabric and a preparation method thereof, and belongs to the technical field of polylactic acid fabrics. The preparation method comprises the following steps: S1, adding polylactic acid, a pore-foaming agent and nano negative ion powder into an organic solvent, stirring at the temperature of 90-110 DEG C and at the speed of 1200-1800 rpm for 0.5-1.5 h, and then cooling to 65-75 DEG C to obtain a precursor solution; s2, the surface of a polylactic acid fabric is coated with the precursor solution, then the polylactic acid fabric coated with the precursor solution is sequentially soaked in a hot water bath and a cold water bath in an inverted buckling mode for phase separation, and composite polylactic acid fabric is obtained through drying; s3, the composite polylactic acid fabric is sequentially soaked in an acid solution and an alkali solution for soaking treatment, and the multifunctional bio-based polylactic acid fabric is obtained after drying. Through the collaborative design of introduction of the nanometer negative ion powder, an acid-base regulation porous structure and the like, the synergistic interaction of cooling and negative ion release is realized.

Description

Technical Field

[0001] This invention belongs to the field of polylactic acid fabric technology, and particularly relates to a multifunctional bio-based polylactic acid fabric and its preparation method. Background Technology

[0002] Against the backdrop of a growing global energy crisis and environmental problems, passive radiative cooling technology has become a research hotspot in fields such as building energy conservation and outdoor living environment regulation due to its core advantages of requiring no additional energy input and being green and energy-saving. This technology achieves efficient reflection of sunlight and directional radiative heat dissipation in the mid-infrared band by regulating the optical properties of the materials themselves, thereby achieving autonomous cooling. In-depth and diverse explorations have been conducted in various carrier fields, including textiles.

[0003] Currently, the core technological path to achieving efficient daytime radiative cooling mainly focuses on synergistically improving the solar reflectivity and mid-infrared thermal emissivity of materials through precise material selection and refined structural design. For example, patent CN114481636A discloses a textile coating with radiative cooling function and its preparation method. It uses water-based acrylic resin combined with specific reflective pigments and fillers to construct a porous coating on the surface of a textile substrate through a one-step coating process, enabling the coating to achieve a high reflectivity of ≥85% and a high emissivity of ≥85%. Patent CN112126287A discloses a gel-type radiative cooling coating, its preparation method, and its application. It constructs a gel-type coating system with a water-based polymer as the matrix. Its unique hydrogel structure has a self-cleaning and regeneration capability after contamination, and can maintain a high solar reflectivity for a long time, ensuring the stability of cooling performance.

[0004] Meanwhile, with the popularization of the concept of healthy living, the demand for functions such as air purification has gradually become an important direction for materials research and development. For example, patent CN112044295A discloses a nano-tourmaline dispersion and its preparation method. The nano-tourmaline dispersion with excellent storage stability is prepared through homogenization and other processes, laying the technological foundation for introducing carriers such as coatings and textiles into the negative oxygen ion release functional unit to realize the air purification function of the material.

[0005] Despite progress in radiative cooling and single-function modification technologies, significant technical shortcomings and performance bottlenecks remain in practical applications, manifested in the following ways: First, functional singularity is prominent, with a lack of synergistic performance. Most radiative cooling materials focus solely on temperature regulation, failing to effectively integrate with needs such as air purification, thus struggling to meet diverse usage requirements in complex scenarios. Existing materials with negative ion release capabilities generally exhibit low ion release efficiency in static environments and fail to fully utilize the significant temperature gradient and thermal stress generated during radiative cooling to enhance negative ion release through actively stimulating the thermoelectric and piezoelectric effects of functional particles, lacking innovative designs to achieve synergistic gains in cooling and air purification functions. Second, unreasonable structural design limits performance improvement. Functional coatings prepared using conventional non-solvent-induced phase separation processes often fail to meet optimal design standards in terms of internal pore connectivity and specific surface area. This not only weakens the material's mechanical strength and other physical properties but also hinders sufficient contact between internal functional particles and air, severely limiting the efficient performance of composite functions. Third, poor green and environmentally friendly performance. Existing radiation cooling coatings mostly use traditional preparation processes and raw material systems. Some components have problems such as poor environmental compatibility and release of volatile harmful substances, which are contrary to the current green and low-carbon development concept and make it difficult to meet the application requirements of eco-friendly materials.

[0006] Polylactic acid (PLA) fabric, as a flexible substrate with advantages such as lightweight, breathability, and easy molding, is widely used in architectural interiors, outdoor products, and hygiene protection. Combining PLA with functions such as radiative cooling and air purification to prepare multifunctional bio-based PLA fabrics has broad market prospects. However, current technologies have not yet achieved efficient preparation and performance optimization of such multifunctional bio-based PLA fabrics.

[0007] Therefore, developing a multifunctional bio-based polylactic acid fabric that can achieve synergistic gains in radiative cooling and air purification functions, has a reasonable structural design, and is environmentally friendly, as well as its preparation method, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is to overcome the problems of single function, insufficient release of negative oxygen ions, and complex preparation process of coated fabrics in the prior art.

[0009] To address the aforementioned technical problems, this invention provides a multifunctional bio-based polylactic acid (PLA) fabric and its preparation method. By introducing multi-element natural mineral nano-negative ion powder with both high negative ion generation and far-infrared emissivity, the reflectivity of the bio-based PLA fabric is enhanced to improve its radiative cooling effect, while also endowing it with negative oxygen ion release capabilities. Simultaneously, acid-base treatment optimizes pore connectivity, and the temperature difference generated by radiative cooling strengthens the piezoelectric effect of the nano-negative ion powder, enabling the functional coating to actively release negative ions. This effectively overcomes the shortcomings of existing radiative cooling coatings, such as limited functionality and insufficient negative oxygen ion release.

[0010] The first objective of this invention is to provide a method for preparing a multifunctional bio-based polylactic acid fabric, comprising the following steps: S1. Add polylactic acid, pore-forming agent and nano-negative ion powder to an organic solvent, stir at 1200rpm-1800rpm for 0.5h-1.5h at 90℃-110℃, and then cool to 65℃-75℃ to obtain a precursor solution. S2. The precursor solution described in S1 is coated onto the surface of the polylactic acid fabric. Then, the polylactic acid fabric coated with the precursor solution is immersed in a hot water bath at 70℃-90℃ for 30s-50s and a cold water bath at 15℃-30℃ for 0.5h-1.5h in an upside-down manner to separate the phases. After drying, the composite polylactic acid fabric is obtained. S3. The composite polylactic acid fabric described in S2 is immersed in acid solution and alkaline solution for 25-35 minutes in sequence, and then dried to obtain the multifunctional bio-based polylactic acid fabric.

[0011] In one embodiment of the present invention, in S1, the molecular weight of the polylactic acid is 100,000 to 300,000; if the molecular weight of the polylactic acid is too large, it will cause the coating to have a poor feel, and if the molecular weight is too small, it will cause the coating to have insufficient strength. And / or, the pore-forming agent is selected from polyethylene glycol (PEG) and / or polyvinylpyrrolidone (PVP).

[0012] Furthermore, in S1, the pore-forming agent is polyethylene glycol (PEG), which has the dual functions of pore formation and plasticization. It can effectively control the pore size, pore distribution and pore structure of the coating, increase the pore density, improve the flexibility of the coating and enhance its chemical stability.

[0013] In one embodiment of the present invention, in S1, the nano-negative ion powder includes lanthanum oxide, cerium oxide, zinc oxide, and titanium dioxide. As a polar crystal with a special structure, this type of nano-negative ion powder can generate ions for a long time and continuously release negative ions into the air. Among them, lanthanum oxide and cerium oxide ions have high coordination numbers and can induce the ionization of H2O in the surrounding air through their special electron orbitals. Zinc oxide has significant thermoelectric and piezoelectric effects and can generate a micro-electric field under small deformations or temperature fluctuations on the coating surface during use, thereby ionizing H2O in the air. Titanium dioxide has good photocatalytic properties and can continuously ionize oxygen in the air into negative ions under light conditions.

[0014] And / or, the particle size of the nano-negative ion powder is 0.1μm-5μm.

[0015] In one embodiment of the present invention, in S1, the organic solvent is selected from one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0016] In one embodiment of the present invention, in S1, the mass ratio of polylactic acid, pore-forming agent and nano-negative ion powder is 10:(11-13.5):(2.8-3.2). And / or, the concentration of polylactic acid in the precursor solution is 480 mg / mL to 520 mg / mL.

[0017] In one embodiment of the present invention, in S2, the coating amount of the precursor solution is 10 g / m 2 -50g / m 2 The coating amount refers to the mass of precursor loaded on a unit area of ​​the substrate fabric. When this parameter is too low, the coating cannot completely cover the fabric substrate, making it difficult to achieve the expected cooling and heat preservation performance. When the parameter is too high, it can easily lead to a deterioration in the fabric's hand feel.

[0018] In one embodiment of the present invention, in S2, the drying method is air drying or oven drying.

[0019] In one embodiment of the present invention, the drying is performed at 50°C-70°C for 2-6 hours.

[0020] In one embodiment of the present invention, in S2, the acid solution is a 0.4 mol / L to 0.6 mol / L hydrochloric acid solution; the acid solution can slightly hydrolyze the polylactic acid bonds, thereby achieving the pore-enlarging effect. And / or, the alkaline solution is a 0.4 mol / L-0.6 mol / L sodium hydroxide solution; the alkaline solution can neutralize and clean residual acidic substances and pore-forming agents, thereby unblocking pores and improving the specific surface area and pore connectivity of the coating.

[0021] A second objective of this invention is to provide a multifunctional bio-based polylactic acid fabric prepared by the method described above.

[0022] The technical solution of the present invention has the following advantages compared with the prior art: (1) The preparation method of the present invention uses polylactic acid fabric as the substrate, polylactic acid as the coating skeleton and adds a pore-forming agent. Combined with non-solvent-induced phase separation technology, an anisotropic porous self-adhesive radiation cooling coating is constructed on the surface of polylactic acid fabric. At the same time, nano negative ion powder is introduced and the porous structure is optimized by acid and alkali regulation. Finally, a porous multifunctional bio-based polylactic acid fabric with a pore size of about 0.5 μm is prepared. Among them, the -CH3, C=O and COC groups in the polylactic acid molecular chain have strong infrared absorption in the atmospheric window and achieve high emissivity according to Kirchhoff's law. The nano negative ion powder, as a negative oxygen ion generator with permanent polarity, generates negative oxygen ions by ionizing air through piezoelectric effect under the stimulation of temperature difference between the coating and the environment. It has the function of autonomously releasing negative ions without additional intervention.

[0023] (2) The preparation method of the present invention uses polylactic acid fabric as the substrate and polylactic acid as the coating skeleton to construct a homogeneous structure of "polylactic acid coating + polylactic acid substrate". This structure uses a strong polar solvent in the precursor solution to perform micro-swelling treatment on the surface of polylactic acid fabric fibers. In the subsequent hot water phase separation process at 70℃-90℃, the polylactic acid molecular chains of the coating and the molecular chains of the fabric surface undergo local interpenetration to form a homogeneous heterogeneous bonding interface, which enhances the bonding force and has almost no loss of cooling performance.

[0024] (3) The preparation method described in this invention uses an inverted method for phase separation. By taking advantage of the difference in solvent displacement kinetics during the phase separation process, the coating near the substrate side and near the air side in the hot water bath form different solidification rates, thereby constructing an asymmetric structure similar to Janus. The dense layer near the substrate side can ensure the strong adhesion between the coating and the substrate, while the porous layer near the air side can fully ensure the performance of the function. This asymmetric distribution effectively avoids the functional particles being deeply buried in the polymer encapsulation layer, and finally achieves the unexpected effect of obtaining ultra-high functional performance with low functional particle addition.

[0025] (4) The preparation method of the present invention employs a stepwise soaking process of acid solution followed by alkali solution after phase separation and film formation. Chemical etching is used to perform secondary modification of the microscopic pores of the film. First, the polylactic acid bonds are micro-hydrolyzed to expand the pores. Then, the residual acid solution is neutralized and the pore-forming agent residue is cleaned, effectively opening up closed pores and removing impurities that clog the pores. This successfully constructs a highly interconnected pore network with a pore size of approximately 0.5 μm. This structure is the core foundation for the high negative ion release performance and high reflectivity of the bio-based polylactic acid fabric. After acid and alkali treatment, the overall reflectivity and emissivity of the coating are significantly improved, enabling the bio-based polylactic acid fabric to achieve strong light reflection under the solar spectrum and complete infrared radiation heat dissipation through atmospheric windows, achieving optimal radiative cooling effect. Compared with traditional coatings, its cooling range can reach approximately 11°C, while the negative oxygen ion release is as high as 5200 ions / (cm²). 3 •s).

[0026] (5) The multifunctional bio-based polylactic acid fabric of the present invention achieves synergistic effect of cooling and releasing negative ions through the introduction of nano negative ion powder and the synergistic design of acid-base regulation of porous structure. It has good application prospects and extremely high industrialization value in the fields of flexible cooling materials, air purification (which can prolong the survival time of negative oxygen ions by combining cooling effect), smart clothing, and building energy conservation. Attached Figure Description

[0027] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein: Figure 1 This is a pore size distribution diagram of the multifunctional coating of the present invention; Figure 2 This is a schematic diagram of the daytime passive radiation cooling performance testing device of the present invention; wherein, (a) is a schematic diagram of the radiation cooling performance testing device, and (b) is a schematic diagram of the testing environment; Figure 3 The images show actual pictures of the polylactic acid fabric of the present invention and the multifunctional bio-based polylactic acid fabric prepared in Example 1; wherein, the left image is the polylactic acid fabric and the right image is the multifunctional bio-based polylactic acid fabric. Figure 4 The image shows the spectral reflectance of the polylactic acid fabric of the present invention and the multifunctional bio-based polylactic acid fabric prepared in Example 1. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0029] In this invention, unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] In this invention, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] In this invention, unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0032] In this invention, unless otherwise stated, the polylactic acid used in the embodiments of this invention was purchased from Nature Works, USA, model number 2003D, with a molecular weight of approximately 180,000 to 200,000.

[0033] In this invention, unless otherwise stated, the polyethylene glycol used in the embodiments of this invention is polyethylene glycol 400 (PEG-400).

[0034] In this invention, unless otherwise stated, the polyvinylpyrrolidone used in the embodiments of this invention was purchased from Sinopharm Reagent Co., Ltd.

[0035] In this invention, unless otherwise stated, the nano-negative ion powder used in the embodiments of this invention was purchased from Xuancheng Jingrui New Materials Co., Ltd., model JR-NF50, with a particle size of 0.1μm-5μm. Example 1

[0036] The multifunctional bio-based polylactic acid fabric and its preparation method in this embodiment specifically include the following steps: S1, 10g polylactic acid (PLA), 10mL polyethylene glycol (PEG, 100% of PLA), 1g polyvinylpyrrolidone, 3g nano-anionic powder and 20mL N,N-dimethylacetamide were added to a round-bottom flask. The mixture was then magnetically stirred at 1500rpm for 1h under reflux condensation at 95℃ to ensure that all components were fully dissolved. The mixture was then cooled to 70℃ to obtain the precursor solution.

[0037] S2. The precursor solution was applied using a scraper at a concentration of 30 g / m³. 2 The coating solution was evenly applied to the surface of the polylactic acid fabric. After standing for 40 seconds, the polylactic acid fabric coated with the precursor solution was then immersed in an 80°C hot water bath for 40 seconds and a 25°C cold water bath for 1 hour in an upside-down manner to separate the phases. After drying at room temperature, the composite polylactic acid fabric was obtained.

[0038] S3. The bio-based polylactic acid fabric is immersed in 0.5 mol / L hydrochloric acid solution and 0.5 mol / L sodium hydroxide solution for 30 min in sequence, and then washed and dried to obtain a multifunctional bio-based polylactic acid fabric. Comparative Example 1

[0039] The basic formula is the same as in Example 1, except that no nano-negative ion powder is added. Comparative Example 2

[0040] The method is basically the same as in Example 1, except that the amount of nano negative ion powder used is 2g. Comparative Example 3

[0041] The method is basically the same as in Example 1, except that the amount of nano negative ion powder used is 4g. Comparative Example 4

[0042] The method is basically the same as in Example 1, except that the amount of nano negative ion powder used is 5g. Comparative Example 5

[0043] The process is basically the same as in Example 1, except that the hydrochloric acid solution and sodium hydroxide solution soaking treatment is not performed. Comparative Example 6

[0044] The process is basically the same as in Example 1, except that the concentrations of both the hydrochloric acid solution and the sodium hydroxide solution are 0.1 mol / L. Comparative Example 7

[0045] The process is basically the same as in Example 1, except that the concentrations of both the hydrochloric acid solution and the sodium hydroxide solution are 0.3 mol / L. Comparative Example 8

[0046] The process is basically the same as in Example 1, except that the concentrations of both the hydrochloric acid solution and the sodium hydroxide solution are 0.9 mol / L. Comparative Example 9

[0047] It is basically the same as Example 1, except that PEG is not added. Comparative Example 10

[0048] The method is basically the same as in Example 1, except that the amount of PEG used is 2 mL (20% of PLA). Comparative Example 11

[0049] The method is basically the same as in Example 1, except that the amount of PEG used is 4 mL (40% of PLA). Comparative Example 12

[0050] The method is basically the same as in Example 1, except that the amount of PEG used is 6 mL (60% of PLA). Comparative Example 13

[0051] The method is basically the same as in Example 1, except that the amount of PEG used is 8 mL (80% of PLA). Comparative Example 14

[0052] The method is basically the same as in Example 1, except that the amount of PEG used is 12 mL (120% of PLA). Comparative Example 15

[0053] The basic structure is the same as in Example 1, except that polylactic acid is replaced with PVDF. Comparative Example 16

[0054] The process is basically the same as in Example 1, except that the acid-base treatment is not performed by inverting the container. Test Example 1

[0055] Based on Example 1, pore size analysis was performed on the multifunctional coating in the multifunctional bio-based polylactic acid fabric, and the results are as follows: Figure 1 As shown. From Figure 1 It can be seen that the pore size of the multifunctional coating is concentrated at around 0.5μm. This pore size can ensure sufficient contact between the nano-negative ion powder and the air, avoid functional particles being buried by the polymer, and optimize the sunlight reflection path and mid-infrared radiation channel. This becomes the core structural basis for the bio-based polylactic acid fabric to achieve high reflectivity, high negative oxygen ion release and significant cooling. At the same time, in conjunction with the permanent polarity of the nano-negative ion powder, the piezoelectric effect is enhanced under the stimulation of the temperature difference formed by radiation cooling, further improving the functional synergistic gain effect. Test Example 2

[0056] Performance tests were conducted on the multifunctional bio-based polylactic acid fabrics (modified polylactic acid fabrics) and non-polylactic acid fabrics prepared in the examples and comparative examples: (1) Reflectance test: The spectral reflectance in the 200nm-2500nm band was tested and characterized using a Shimadzu UV3600 tester with BaSO4 as the standard backplate under AM1.5 solar spectrum conditions. (2) Temperature change test: such as Figure 2 As shown, a LIANYI SH-X (SH-16XL) multi-temperature tester manufactured by Dongguan Lianyi Instrument Co., Ltd. was used to measure and record temperature data. A radiative cooling performance testing device was constructed using a LIANYI K-type thermocouple. This thermocouple has a relative error of less than 0.5℃ and can be used to monitor the ambient temperature and the surface temperature of the upper and lower layers of the sample. The testing device includes a polystyrene foam box wrapped in aluminum foil to minimize heat transfer and reflect sunlight. Furthermore, a T620 infrared thermal imager manufactured by FLIR Systems, Sweden, was used to observe the thermal process in real time. (2) Negative oxygen ion concentration: The negative oxygen ion release of polylactic acid fabric was measured using a COM-3200PRO II air negative ion detector; Figures 3-4 Table 1 shows the final measured properties of the modified and unmodified polylactic acid (PLA) fabrics: Table 1

[0057] from Figures 3-4 As shown in Table 1, the unmodified polylactic acid (PLA) fabric exhibits the natural color of the substrate, with a smooth surface and no obvious texture. In contrast, the multifunctional bio-based PLA fabric obtained in Example 1 has a continuous and uniform white coating with a rough texture, confirming the good adhesion between the coating and the substrate and laying a physical foundation for improving the material's diffuse reflection effect. The spectral reflectance spectrum further shows that within the solar spectrum range of 200nm-2500nm, the reflectance curve of the multifunctional bio-based PLA fabric in Example 1 is consistently higher than that of the unmodified PLA fabric, indicating a significantly higher overall reflectance level, with an average reflectance of up to 95.2%. This fully demonstrates its efficient ability to reflect sunlight. Furthermore, this material can achieve a temperature reduction of up to 10.9℃ compared to the ambient temperature in summer, and its negative oxygen ion release is as high as 5200 ions / (cm³). 3 •s) successfully achieved the synergistic effect of radiation cooling and air purification functions.

[0058] Comparing Example 1 and Comparative Examples 1-4 (variable dosage of nano-negative ion powder), it can be seen that Comparative Example 1, without the addition of nano-negative ion powder, exhibits significantly lower performance than Example 1. This demonstrates that nano-negative ion powder is the core component that imparts negative oxygen ion release function to the bio-based polylactic acid fabric, and plays a crucial role in improving reflectivity and cooling effect. Comparative Examples 2-4 show a regular pattern in the variation with the dosage of nano-negative ion powder: the amount of negative oxygen ion release first increases and then decreases with increasing dosage; while solar reflectivity and cooling effect show inverse changes. This indicates that a dosage of approximately 3g of nano-negative ion powder can avoid the loss of product function due to insufficient dosage, prevent particle agglomeration and damage to coating uniformity caused by excessive addition, and reduce the risk of microporous channel blockage caused by excessive addition. It also avoids the problem of negative ions generated inside the powder not being able to escape effectively, as well as the problem of infrared radiation sites being squeezed out and the product's cooling ability being weakened, ultimately achieving the optimal balance between product function and application performance.

[0059] Comparing Example 1 and Comparative Examples 5-8 (acid and alkali solution concentration variables), it can be seen that Comparative Example 5, which did not undergo acid and alkali immersion treatment, had significantly lower solar reflectivity, cooling rate, and negative oxygen ion release than Example 1. This proves that stepwise acid and alkali immersion treatment is a necessary process for optimizing the coating pore structure and improving overall performance. Comparative Examples 6-7, due to low acid and alkali concentrations, had insufficient dissolving and etching ability of the acid, resulting in high residual pore agent rate and pore blockage. The nano-negative ion powder was encapsulated by polylactic acid, leading to high diffusion resistance of negative oxygen ions, low negative oxygen ion release, and the reflectivity and cooling rate did not reach ideal levels. Although Comparative Example 8 performed better than the low-concentration group, it was still lower than Example 1. This is because when the concentration is too high, strong acids and alkalis will slightly over-etch the polylactic acid matrix, affecting the integrity of the pore structure. This indicates that a concentration of around 0.5 mol / L can both construct a highly interconnected pore network through synergistic effects, stabilizing the negative oxygen ion release at the optimal level, and avoid damage to the substrate and coating, while also having a wide process window suitable for large-scale production.

[0060] Comparing Example 1 and Comparative Examples 9-14 (variable PEG dosage), Comparative Example 9, without PEG, exhibited poor performance in solar reflectivity, cooling effect, and negative ion release, indicating that PEG, as a pore-forming agent, is crucial for optimizing the coating's pore structure. In Comparative Examples 10-13, reflectivity, cooling effect, and negative ion release gradually increased with increasing PEG dosage, but none exceeded those of Example 1. Comparative Example 14 showed a slight increase in reflectivity and cooling effect, with a negative ion release reaching 3900 ions / (cm²). 3 However, excessive PEG leads to a brittle coating framework, decreased mechanical properties, and impaired practicality. This indicates that PEG regulates the pore structure through heterogeneous nucleation. Increasing the dosage can refine the pores, increase the pore density, enhance the Mie scattering effect, and improve reflectivity and mid-infrared emissivity. However, the volume fraction needs to be controlled at around 50%. At this level, a uniform porous structure and unique flower-like fracture morphology (increasing specific surface area) can be formed, while ensuring the coating's soft feel and mechanical stability.

[0061] Comparing Example 1 and Comparative Example 15 (with variations in coating skeleton material), it can be seen that Comparative Example 15, which replaces polylactic acid with PVDF, exhibits significantly lower performance than Example 1. This is because polylactic acid constructs a homogeneous structure of "polylactic acid coating + polylactic acid substrate." The precursor solution can cause micro-swelling of the substrate surface, with molecular chains intertwining to form a stable bonding interface. Furthermore, polylactic acid has a high intrinsic refractive index that matches the porous structure, and the ester and carbonyl groups in the molecular chains possess strong infrared emission capabilities within the 8μm-13μm atmospheric window. In contrast, PVDF has low surface energy, poor compatibility with the polylactic acid substrate, and cannot form an effective bond. Moreover, its optical and thermal properties are not suitable for radiative cooling requirements, and functional particles easily detach from the coating, resulting in a significant decrease in synergistic performance.

[0062] Comparing Example 1 and Comparative Example 16 (phase separation water entry method variable), it can be seen that Comparative Example 16, which did not use the inverted method, has significantly lower performance than Example 1. This is because in conventional front-mounted water entry processes, the nano-negative ion powder, due to its higher density than the precursor solution, will settle towards the bottom of the coating during phase separation, forming a "particle barrier." This barrier hinders the wetting and penetration of polylactic acid molecular chains into the substrate, reducing the coating's bonding strength. Simultaneously, the functional particles are deeply embedded, easily forming a dense "skin" on the surface, increasing the resistance to negative oxygen ion migration and weakening infrared radiation efficiency. In contrast, the inverted process in Example 1 uses gravity compensation to counteract the particle settling trend, resulting in a reasonable gradient distribution of nanoparticles in the coating thickness direction. This ensures both interfacial adhesion and effective exposure of functional particles and pore connectivity, ultimately achieving optimal performance.

[0063] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a multifunctional bio-based polylactic acid fabric, characterized in that, Includes the following steps: S1. Add polylactic acid, pore-forming agent and nano-negative ion powder to an organic solvent, stir at 1200rpm-1800rpm for 0.5h-1.5h at 90℃-110℃, and then cool to 65℃-75℃ to obtain a precursor solution. S2. The precursor solution described in S1 is coated onto the surface of the polylactic acid fabric. Then, the polylactic acid fabric coated with the precursor solution is immersed in a hot water bath at 70℃-90℃ for 30s-50s and a cold water bath at 15℃-30℃ for 0.5h-1.5h in an upside-down manner to separate the phases. After drying, the composite polylactic acid fabric is obtained. S3. The composite polylactic acid fabric described in S2 is immersed in acid solution and alkaline solution for 25-35 minutes in sequence, and then dried to obtain the multifunctional bio-based polylactic acid fabric.

2. The method for preparing the multifunctional bio-based polylactic acid fabric according to claim 1, characterized in that, In S1, the molecular weight of the polylactic acid is 100,000 to 300,000; And / or, the pore-forming agent is selected from polyethylene glycol and / or polyvinylpyrrolidone.

3. The method for preparing the multifunctional bio-based polylactic acid fabric according to claim 1, characterized in that, In S1, the nano-negative ion powder includes lanthanum oxide, cerium oxide, zinc oxide, and titanium dioxide; And / or, the particle size of the nano-negative ion powder is 0.1μm-5μm.

4. The method for preparing the multifunctional bio-based polylactic acid fabric according to claim 1, characterized in that, In S1, the organic solvent is selected from one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

5. The method for preparing the multifunctional bio-based polylactic acid fabric according to claim 1, characterized in that, In S1, the mass ratio of polylactic acid, pore-forming agent, and nano-negative ion powder is 10:(11-13.5):(2.8-3.2). And / or, the concentration of polylactic acid in the precursor solution is 480 mg / mL to 520 mg / mL.

6. The method for preparing the multifunctional bio-based polylactic acid fabric according to claim 1, characterized in that, In S2, the coating amount of the precursor solution is 10 g / m. 2 -50g / m 2 .

7. The method for preparing the multifunctional bio-based polylactic acid fabric according to claim 1, characterized in that, In S2, the drying method is air drying or oven drying.

8. The method for preparing the multifunctional bio-based polylactic acid fabric according to claim 1, characterized in that, The drying process involves drying at 50℃-70℃ for 2-6 hours.

9. The method for preparing the multifunctional bio-based polylactic acid fabric according to claim 1, characterized in that, In S2, the acid solution is a hydrochloric acid solution of 0.4 mol / L to 0.6 mol / L; And / or, the alkaline solution is a 0.4 mol / L to 0.6 mol / L sodium hydroxide solution.

10. A multifunctional bio-based polylactic acid fabric prepared by the method according to any one of claims 1-9.

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