A porous hydrophilic polylactic acid fiber membrane material and a preparation method thereof

Abstract

The application belongs to the field of high polymer materials, and relates to a porous hydrophilic polylactic acid fiber film material and a preparation method thereof. The application provides a preparation method of a porous hydrophilic polylactic acid fiber film material, specifically: taking left-handed polylactic acid PLLA, right-handed polylactic acid PDLA and a multifunctional composite treatment agent as raw materials, a fiber film is prepared by using an electrostatic spinning method, the water-soluble homopolymer in the fiber film is etched away by using deionized water, and after annealing, the porous hydrophilic polylactic acid fiber film material with excellent piezoelectric performance is obtained. The fiber film material obtained by the application has excellent piezoelectricity and high porosity, the crystallinity of the obtained fiber film material is 28.7% to 40.2%, the crystal composition is 100% SC crystal; the surface and the inside have a porous structure, the fiber surface pore diameter is 164 to 524 nm, and the porosity is 82% to 94%; the fiber has good hydrophilic performance, and the water contact angle is 36 to 59 degrees. Moreover, the preparation process of the application is simple and efficient, and can be used in the fields of sewage treatment, catalytic degradation, tissue engineering and the like.

Description

Technical Field

[0001] This invention relates to a porous hydrophilic polylactic acid fiber membrane material with excellent piezoelectric properties and its preparation method, belonging to the field of polymer materials. Background Technology

[0002] The large-scale production and consumption of petroleum-based non-degradable polymer materials has not only exacerbated the shortage of petrochemical resources and increased carbon emissions, but also led to a rapid increase in plastic waste (especially white pollution and microplastics), posing a huge threat and challenge to the sustainable development of Earth's resources and ecological environment. Therefore, the development of biodegradable polymer materials made from biomass resources has received increasing attention.

[0003] Polylactic acid (PLA) is a bio-based, biodegradable, and biocompatible polymer with significant application value. Its synthesis raw materials can be entirely derived from renewable plant resources such as cassava starch and corn stalks. Its waste can be completely biodegraded into carbon dioxide and water in natural environments such as soil and water bodies. It possesses advantages such as being green and low-carbon, having good biocompatibility, good mechanical properties, and being easy to mold and process, making it a potential replacement for traditional polymer materials in fields such as biomedicine and industrial packaging. Recent research indicates that PLA is also an electroactive polymer with certain piezoelectric activity, showing broad application prospects in wastewater treatment, tissue-induced regeneration, and catalytic adsorption. However, PLA's applications are greatly limited by its weak intrinsic piezoelectric properties (many carbonyl dipole moments cancel each other out), poor stress sensitivity (large modulus, not easily deformed under external force), and poor hydrophilicity (high hydrophobicity leads to poor wettability). For example, in wastewater purification, weak piezoelectricity and low water flux (due to poor hydrophilicity and low porosity) will result in low piezoelectric catalytic efficiency, making it impossible to achieve efficient catalytic degradation of organic pollutants.

[0004] To address the aforementioned issues, Bai et al. prepared a porous polylactic acid (SC-PLA) powder with a lamellar lapis lazuli network structure through low-temperature melt blending. The porous structure of this SC-PLA powder resulted in high stress sensitivity and specific surface area, thereby significantly enhancing the piezoelectricity of the PLA particles (Biomacromolecules 2023, 24, 2, 797–806). However, the porous powder prepared by this method is not suitable for applications such as wastewater treatment, as it easily causes secondary pollution from the powder particles and also exhibits poor hydrophilicity.

[0005] Porous membrane materials can effectively solve the problem of secondary pollution from powder. Currently, common methods for preparing porous membranes include solution casting, melt spinning, electrospinning, and biaxial stretching. Among these, electrospinning, as a simple and efficient technique for preparing porous nanofiber membrane materials, not only forms pore structures between nanofibers but also stretches molecular chains under voltage to prepare porous fiber membrane materials with high orientation (reducing the mutual cancellation of carbonyl dipole moments), thus attracting widespread attention. Lü Jun et al. prepared SC-PLA nanofiber membranes with 100% SC crystal content via electrospinning. Through subsequent annealing and a drum collection device, they achieved high crystallinity and high orientation of the SC-PLA nanofibers, preparing composite fiber membranes with improved piezoelectric properties (Journal of Materials Chemistry A 2019, 7, 4, 1810-1823). The open-circuit voltage under a 10N stress load can reach as high as 4V. This method effectively improves the piezoelectric properties of PLA, but it still suffers from weak piezoelectricity and poor hydrophilicity in practical applications such as wastewater treatment. Therefore, the preparation of porous fiber membranes that combine high voltage electroactivity and hydrophilicity remains a challenge. Summary of the Invention

[0006] To address the problems of existing materials, this invention starts with the preparation of highly crystalline SC-PLA fibers with a special porous structure. A porous hydrophilic polylactic acid fiber membrane material with excellent piezoelectric properties is prepared by electrospinning with the addition of a multifunctional composite treatment agent (a mixture of a water-soluble homopolymer and an amphiphilic copolymer that can simultaneously act as a pore-forming agent and a hydrophilic modifier). This multifunctional composite treatment agent can promote SC crystallization between L- and D-polylactic acid (PLLA / PDLA) molecular chains, reduce the mutual cancellation of carbonyl dipole moments, and improve the intrinsic piezoelectricity of the material. Simultaneously, SC crystallization can induce the formation of water-soluble homopolymers. Phase separation occurs between the polymer and PLA. The water-soluble homopolymer, acting as a pore-forming agent, is etched by water to form a porous structure, ultimately constructing a large number of microporous structures on and inside the fiber surface. This enhances the material's stress sensitivity (easily deformed under external force) and specific surface area. Furthermore, the amphiphilic copolymer in the multifunctional composite treatment agent can construct an amphiphilic molecule layer at the PLA-water-soluble homopolymer phase interface. When the water-soluble homopolymer phase is etched away, this amphiphilic molecule layer remains intact because its lipophilic segments are embedded in the PLA phase, while its hydrophilic segments are distributed at the phase interface (pore interface), forming a hydrophilic layer and effectively improving the hydrophilicity of the fiber membrane. The porous hydrophilic polylactic acid fiber membrane prepared in this way exhibits excellent piezoelectric properties and has broad applications in wastewater purification, catalytic adsorption, and tissue engineering.

[0007] The technical solution of the present invention:

[0008] The first technical problem to be solved by the present invention is to provide a porous hydrophilic polylactic acid fiber membrane material with excellent piezoelectric properties. The raw materials include L-polylactic acid (PLLA), D-polylactic acid (PDLA), and a multifunctional composite treatment agent. The content of the multifunctional composite treatment agent is 30wt% to 60wt% based on 100% of the total raw materials. The multifunctional composite treatment agent includes a water-soluble homopolymer and an amphiphilic copolymer. The content of the amphiphilic copolymer is 4wt% to 6wt% based on 100% of the total multifunctional composite treatment agent.

[0009] The multifunctional composite treatment agent contains both water-soluble homopolymer and amphiphilic copolymer. The water-soluble homopolymer acts as a pore-forming agent, constructing numerous microporous structures on and within the fiber surface. The amphiphilic copolymer, on the other hand, builds a hydrophilic layer at the PLA-water-soluble homopolymer interface, effectively improving the hydrophilicity of the fiber membrane. Repeated experimental verification shows that the content of the amphiphilic copolymer in the multifunctional composite treatment agent cannot be too high or too low. A content above 6% significantly reduces or even eliminates the porous structure, while a content below 4% degrades the hydrophilicity of the membrane material, even making it hydrophobic. The dosage of the multifunctional composite treatment agent also needs to be within a specified range. A dosage below 30% results in poor hydrophilicity, while a dosage above 60% produces a microspherical structure, failing to yield a stable porous fibrous material.

[0010] Furthermore, the weight-average molecular weight of the L-polylactic acid is 1×10⁻⁶. 4 ~6×10 5 g / mol, optical purity ≥93%; the weight-average molecular weight of the dextrorotatory polylactic acid is 1×10⁻⁶ g / mol. 4 ~6×10 5 g / mol, optical purity ≥93%.

[0011] Furthermore, the water-soluble homopolymer is selected from one or more of the following: grafted starch, carboxymethylated starch, phosphorylated starch, starch xanthate, grafted cellulose, carboxymethylated cellulose, hydroxypropylated cellulose, xanthate cellulose, polyacrylates, polyvinyl alcohols, and polyoxyalkylene compounds, preferably one or more of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, and carboxymethyl cellulose.

[0012] Furthermore, the amphiphilic copolymer is a copolymer of hydrophilic and hydrophobic segments, wherein the hydrophilic segments are selected from one or more of polyethylene glycol, polyoxyethylene, polyvinyl alcohol, polyethyleneimine, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, and polystyrene sulfonate, and the hydrophobic segments are selected from one or more of polyoxypropylene, polystyrene, polysiloxane, polybutadiene, polymethyl methacrylate, polymethyl acrylate, and polybutyl acrylate.

[0013] Furthermore, the amphiphilic copolymer is a polyvinylpyrrolidone-polyoxypropylene-polyvinylpyrrolidone triblock copolymer (PVP-PPO-PVP) and / or a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer (PEO-PPO-PEO).

[0014] Furthermore, the porous hydrophilic polylactic acid fiber membrane material with excellent piezoelectric properties has a crystallinity of 28.7% to 40.2% and a crystal composition of 100% SC crystals.

[0015] Furthermore, the porous hydrophilic polylactic acid fiber membrane material with excellent piezoelectric properties has a porous structure on its surface and inside, with a fiber diameter of 1.6 to 2.3 μm, a fiber surface pore diameter of 164 to 524 nm, and a porosity of 82% to 94%.

[0016] Furthermore, the porous hydrophilic polylactic acid fiber membrane material with excellent piezoelectric properties has an open-circuit voltage Voc of 20–27V and a water contact angle of 36°–59° under a 10N stress load.

[0017] The second technical problem to be solved by the present invention is to provide a method for preparing a porous hydrophilic polylactic acid fiber membrane material with excellent piezoelectric properties. The preparation method is as follows: using L-polylactic acid (PLLA), D-polylactic acid (PDLA) and a multifunctional composite treatment agent as raw materials, a fiber membrane is prepared by electrospinning. After etching away the water-soluble homopolymer in the fiber membrane with deionized water and annealing, a porous hydrophilic polylactic acid fiber membrane material with excellent piezoelectric properties is obtained.

[0018] Furthermore, the preparation method of the above-mentioned porous hydrophilic polylactic acid fiber material with excellent piezoelectric properties includes the following steps:

[0019] 1) Dry the L-type polylactic acid (PLLA) and D-type polylactic acid (PDLA) raw materials;

[0020] 2) Dissolve L-polylactic acid (PLLA), D-polylactic acid (PDLA), and a multifunctional composite treatment agent in chloroform in a certain proportion, and stir at room temperature to prepare an electrospinning mixed solution;

[0021] 3) The spinning solution is subjected to electrospinning treatment, and the resulting fiber membrane is soaked in deionized water and then dried;

[0022] 4) The dried fiber membrane is annealed in a vacuum oven to obtain a porous hydrophilic polylactic acid fiber material with excellent piezoelectric properties.

[0023] Furthermore, in step 1), the drying process is carried out until the moisture content is less than 200 ppm.

[0024] Furthermore, in step 2), the concentration of the spinning solution is 120 g / L.

[0025] Furthermore, in step 3), the electrospinning propulsion speed is 2 ml / h, the working voltage is 15-25 kV, the distance from the syringe needle tip to the plate collector covered with aluminum foil is 13-18 cm, and the soaking time is 24 h.

[0026] Furthermore, in step 4), the annealing temperature is 90°C and the time is 1 hour.

[0027] The third technical problem to be solved by the present invention is to provide a method for preparing a porous hydrophilic polylactic acid fiber membrane material with excellent piezoelectric properties and its application in improving the piezoelectricity and / or hydrophilicity of polylactic acid fiber membrane materials, that is, to provide a method for improving the piezoelectricity and / or hydrophilicity of polylactic acid fiber membrane materials.

[0028] Technical effects of the present invention:

[0029] (1) The porous hydrophilic polylactic acid fiber material with excellent piezoelectric properties provided by the present invention has a 100% SC crystal structure, a crystallinity of 28.7% to 40.2%, a fiber diameter of 1.6 to 2.3 μm, a fiber surface pore diameter of 164 to 524 nm, a porosity of 82% to 94%, a water contact angle of 36° to 59°, an open circuit voltage of 20 to 27 V, and a degradation efficiency of up to 97% for indigo carmine under ultrasonic treatment for 3 hours. All of these are higher than the prior art and can be widely used in wastewater treatment, catalytic degradation, tissue engineering and other fields.

[0030] (2) The method for preparing porous hydrophilic polylactic acid fiber membrane material with excellent piezoelectric properties provided by the present invention is to prepare PLLA / PDLA / multifunctional composite treatment agent fiber membrane using a simple electrospinning device. The multifunctional composite treatment agent can simultaneously play the following three roles: 1) promote the crystallization of SC between PLLA / PDLA molecular chains, reduce the mutual cancellation of carbonyl dipole moments, and improve the intrinsic piezoelectricity of the material; 2) separate phase with PLA, construct a large number of microporous structures on the fiber surface and inside, and improve the stress sensitivity (easily deformed under external force) and specific surface area of ​​the material; 3) construct a hydrophilic layer on the surface of PLA fiber, thereby effectively improving the hydrophilicity of the fiber membrane.

[0031] (3) When preparing porous hydrophilic polylactic acid fiber materials with excellent piezoelectric properties, the method provided by the present invention can effectively regulate the porous structure and hydrophilic properties of polylactic acid fiber materials by changing the content and ratio of multifunctional composite treatment agents. On the basis of increasing the specific surface area of ​​the material, the method can increase the attachment sites of pollutants by improving the hydrophilicity of the material, thereby effectively improving the catalytic degradation efficiency of pollutants.

[0032] (4) Because the method provided by the present invention can easily etch away the water-soluble homopolymer in the selected multifunctional composite treatment agent when preparing porous hydrophilic polylactic acid fiber material with excellent piezoelectric properties, the biodegradability, biocompatibility and green low carbon properties of the polylactic acid fiber membrane are completely preserved.

[0033] (5) The preparation method provided by the present invention is simple, efficient and easy to operate, and can be mass-produced and continuously produced, making it easy to achieve large-scale industrial production. Attached Figure Description

[0034] Figure 1 The WAXD spectra of Examples 1-4 and Comparative Examples 1, 4, and 5 of this invention are shown.

[0035] Figure 2 These are SEM images of Examples 1-4 and Comparative Examples 1-6 of the present invention. Detailed Implementation

[0036] The following embodiments are given to specifically describe the present invention. However, it should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0037] It is worth noting that: 1) All parts of materials used in the following examples and comparative examples are by weight. 2) The WAXD spectra of the products obtained in the following examples and comparative examples were obtained by testing with a Philips X'Pertpro MPD multi-functional X-ray diffractometer from the Netherlands. The instrument is equipped with a Cu Kα radiation source, with an operating voltage of 4kV, a current of 40mA, a radiation wavelength of 0.154nm, a diffraction angle (2θ) range of 5° to 40°, and a scanning speed of 5° / min. 3) The SEM images of the materials obtained in the following examples and comparative examples were obtained by testing with an Aprio S HiVoc field emission scanning electron microscope from the USA. All samples were sputter-coated with gold before testing. 4) The water contact angle of the materials obtained in the following examples and comparative examples was obtained by characterizing the sample film using an optical contact angle meter (KRUSS, DSA25, Germany). The experimental mode was the droplet method, with a drop volume of 2μL each time. 5) In the pigment degradation experiment, indigo carmine was used as the target pigment. The specific experimental method is as follows: 10 mg of PLA fiber was soaked in 20 mL of 10 mg / L indigo carmine aqueous solution and sonicated (840 W, 40 kHz) for 3 h, and the concentration change of the pigment was characterized using a UV-Vis spectrophotometer (UV, Lambda 650, PerkinElmer).

[0038] Example 1

[0039] First, PLLA and PDLA raw materials are dried until the moisture content is below 200 ppm. Then, 35 parts of PLLA, 35 parts of PDLA, 28.5 parts of PEG, and 1.5 parts of PEO-PPO-PEO are dissolved in chloroform and stirred at room temperature for 5 hours to obtain an electrospinning solution. The electrospinning solution is then added to an electrospinning machine to obtain an initial fiber membrane. The Xiaohushi fiber membrane is soaked in deionized water for 24 hours and then annealed in a vacuum oven at 90℃ for 1 hour to obtain a fiber membrane.

[0040] Example 2

[0041] First, PLLA and PDLA raw materials are dried until the moisture content is less than 200 ppm. Then, 30 parts of PLLA, 30 parts of PDLA, 38 parts of PEG, and 2 parts of PEO-PPO-PEO are dissolved in chloroform and stirred at room temperature for 5 hours to obtain an electrospinning solution. The electrospinning solution is then added to an electrospinning machine to obtain an initial fiber membrane. The initial fiber membrane is soaked in deionized water for 24 hours and then annealed in a vacuum oven at 90°C for 1 hour to obtain a fiber membrane.

[0042] Example 3

[0043] First, PLLA and PDLA raw materials are dried until the moisture content is below 200 ppm. Then, 25 parts of PLLA, 25 parts of PDLA, 47.5 parts of PEG, and 2.5 parts of PEO-PPO-PEO are dissolved in chloroform and stirred at room temperature for 5 hours to obtain an electrospinning solution. The electrospinning solution is then added to an electrospinning machine to obtain an initial fiber membrane. The initial fiber membrane is soaked in deionized water for 24 hours and then annealed in a vacuum oven at 90°C for 1 hour to obtain a fiber membrane.

[0044] Example 4

[0045] First, PLLA and PDLA raw materials are dried until the moisture content is less than 200 ppm. Then, 20 parts of PLLA, 20 parts of PDLA, 57 parts of PEG, and 3 parts of PEO-PPO-PEO are dissolved in chloroform and stirred at room temperature for 5 hours to obtain an electrospinning solution. The electrospinning solution is then added to an electrospinning machine to obtain an initial fiber membrane. The initial fiber membrane is soaked in deionized water for 24 hours and then annealed in a vacuum oven at 90°C for 1 hour to obtain a fiber membrane.

[0046] Comparative Example 1

[0047] First, PLLA and PDLA raw materials are dried until the moisture content is below 200 ppm. Then, 50 parts of PLLA and 50 parts of PDLA are dissolved in chloroform and stirred at room temperature for 5 hours to obtain an electrospinning solution. The spinning solution is then added to an electrospinning machine to obtain an initial fiber membrane. The initial fiber membrane is soaked in deionized water for 24 hours and then annealed in a vacuum oven at 90°C for 1 hour to obtain a fiber membrane.

[0048] Comparative Example 2

[0049] First, PLLA and PDLA raw materials are dried until the moisture content is below 200 ppm. Then, 30 parts of PLLA, 30 parts of PDLA, 38.8 parts of PEG, and 1.2 parts of PEO-PPO-PEO are dissolved in chloroform and stirred at room temperature for 5 hours to obtain an electrospinning solution. The electrospinning solution is then added to an electrospinning machine to obtain an initial fiber membrane. The initial fiber membrane is soaked in deionized water for 24 hours and then annealed in a vacuum oven at 90°C for 1 hour to obtain a fiber membrane.

[0050] Comparative Example 3

[0051] First, PLLA and PDLA raw materials were dried until the moisture content was less than 200 ppm. Then, 30 parts of PLLA, 30 parts of PDLA, 37.2 parts of PEG, and 2.8 parts of PEO-PPO-PEO were dissolved in chloroform and stirred at room temperature for 5 h to obtain an electrospinning solution. The electrospinning solution was then added to an electrospinning machine to obtain an initial fiber membrane. The initial fiber membrane was soaked in deionized water for 24 h and then annealed in a vacuum oven at 90 °C for 1 h to obtain a fiber membrane.

[0052] Comparative Example 4

[0053] First, PLLA and PDLA raw materials are dried until the moisture content is below 200 ppm. Then, 45 parts of PLLA, 45 parts of PDLA, 9.5 parts of PEG, and 0.5 parts of PEO-PPO-PEO are dissolved in chloroform and stirred at room temperature for 5 hours to obtain an electrospinning solution. The electrospinning solution is then added to an electrospinning machine to obtain an initial fiber membrane. The initial fiber membrane is soaked in deionized water for 24 hours and then annealed in a vacuum oven at 90°C for 1 hour to obtain a fiber membrane.

[0054] Comparative Example 5

[0055] First, PLLA and PDLA raw materials are dried until the moisture content is less than 200 ppm. Then, 40 parts of PLLA, 40 parts of PDLA, 19 parts of PEG, and 1 part of PEO-PPO-PEO are dissolved in chloroform and stirred at room temperature for 5 h to obtain an electrospinning solution. The electrospinning solution is then added to an electrospinning machine to obtain an initial fiber membrane. The initial fiber membrane is soaked in deionized water for 24 h and then annealed in a vacuum oven at 90℃ for 1 h to obtain a fiber membrane.

[0056] Comparative Example 6

[0057] First, PLLA and PDLA raw materials are dried until the moisture content is below 200 ppm. Then, 15 parts of PLLA, 15 parts of PDLA, 66.5 parts of PEG, and 3.5 parts of PEO-PPO-PEO are dissolved in chloroform and stirred at room temperature for 5 hours to obtain an electrospinning solution. The electrospinning solution is then added to an electrospinning machine to obtain an initial fiber membrane. The initial fiber membrane is soaked in deionized water for 24 hours and then annealed in a vacuum oven at 90°C for 1 hour to obtain a fiber membrane.

[0058] To investigate the crystal structure and morphological characteristics of the linear high molecular weight SC-PLA prepared by the method of this invention, the samples obtained in Examples 1-4 and Comparative Examples 1, 4, and 5 were first tested using a wide-angle X-ray diffractometer (WAXD). The results are shown in the figure. Figure 1 Next, the surface morphology and porous structure of the samples obtained in Examples 1-4 and Comparative Examples 1-6 were observed using field emission scanning electron microscopy (SEM). The results are as follows: Figure 2 .

[0059] from Figure 1 As can be seen, without the addition of a multifunctional composite treatment agent, the polylactic acid fiber membrane prepared by mixing 50 parts of PLLA and PDLA has a relatively low degree of molecular chain mixing and poor molecular chain mobility. After annealing, a large amount of HC and SC crystals are generated simultaneously, meaning that fully stereostructured polylactic acid fibers cannot be obtained (see...). Figure 1 Comparative Example 1); however, using the method described in this invention, adding different amounts of PEG can improve the mobility of polylactic acid molecular chains and promote high orderliness between molecular chains, thereby forming 100% SC crystals after annealing, and obtaining a fully stereostructured composite polylactic acid fiber membrane (see Comparative Example 1); Figure 1 Examples 1-4). In Example 1, the crystallinity of SC crystals was the highest at 40.2%. However, in Examples 2-4, as the PEG content increased, the viscosity of the electrospinning solution increased, which reduced the mobility of PLLA and PDLA molecular chains and decreased the degree of pairing and mixing, thus resulting in a decrease in crystallinity.

[0060] from Figure 2 As can be seen, without the addition of a multifunctional composite treatment agent, the polylactic acid fiber membrane prepared by mixing 50 parts each of PLLA and PDLA resulted in uneven fiber diameters (distributed between 205-920 nm) and a large number of beads due to the low viscosity of the spinning solution. The surface of individual fibers was smooth and without microporous structures (see...). Figure 2Comparative Example 1) resulted in a low specific surface area and porosity of the fiber membrane, failing to form a high-performance porous polylactic acid fiber membrane. However, using the method described in this invention, adding different proportions of the multifunctional composite treatment agent increased the spinnability of the spinning solution, produced a uniform fiber diameter distribution (1.6–2.3 μm), and ensured that each fiber surface and interior contained a large number of microporous structures, significantly improving the specific surface area and porosity of the fiber membrane. This successfully prepared a porous polylactic acid fiber membrane with high stress sensitivity and a high specific surface area (see Comparative Example 1). Figure 2 Examples 1-4). The content of amphiphilic block copolymer in the multifunctional composite treatment agent also affects the formation of porous structures in polylactic acid fibers. When its content is lower than that of the present invention (3 wt%), porous structures can be formed on the fiber surface (see Examples 1-4). Figure 2 Comparative Example 2), if the content is higher than that of the present invention (7 wt%), it will cause the disappearance of the fiber surface and internal pore structure (see Comparative Example 2). Figure 2 Comparative Example 3). Furthermore, the content of the multifunctional composite treatment agent also affects the formation of the porous structure of polylactic acid fibers; when the content is higher than that of the present invention (70 wt%), an unstable microspherical structure is formed (see Comparative Example 3). Figure 2 Comparative Example 6).

[0061] Table 1. Piezoelectric output voltage, water contact angle, and degradation rate of indigo carmine under ultrasonication for 3 hours for each embodiment and comparative example.

[0062] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Output voltage 11V 25V 14V 14V 23V 6V Water contact angle 136° 103° 0° 132° 109° 0° Degradation rate 9％ 62％ 73％ 21％ 39％ 29％ Example 1 Example 2 Example 3 Example 4 Output voltage 26V 27V 22V 20V Water contact angle 59° 41° 39° 36° Degradation rate 93％ 97％ 91％ 89％

[0063] As shown in Table 1, without the addition of the multifunctional composite treatment agent (Comparative Example 1), the polylactic acid fiber membranes prepared by mixing 50 parts of PLLA and PDLA exhibited a piezoelectric output voltage of only 11V and a water contact angle of 136°, making them typical hydrophobic materials. After 3 hours of ultrasonication, the degradation rate of indigo carmine was only 9%. However, using the method described in this invention, with the increase of the amount of multifunctional composite treatment agent added, the piezoelectric output voltage of the fiber membranes increased, and their water contact angle decreased accordingly, indicating improved hydrophilicity. In Examples 1-4, the output voltage reached a maximum of 27V, and the water contact angle ranged from 36° to 59°, all of which were hydrophilic membranes. After 3 hours of ultrasonication, the degradation rate of indigo carmine reached a maximum of 97%. When the content of the amphiphilic block copolymer in the multifunctional composite agent is lower than that in the present invention (3 wt%), the multifunctional composite agent has little effect on improving the hydrophilicity of polylactic acid fiber, and the water contact angle is 103°, still a hydrophobic material (see Comparative Example 2 in Table 1); when its content is higher than that in the present invention (7 wt%), the water contact angle of polylactic acid fiber decreases significantly and gradually becomes 0° (see Comparative Example 3 in Table 1).

[0064] As shown in Example 2 and Comparative Examples 2-3, when the content of the amphiphilic block copolymer is the content of the present invention (5 wt%), the surface of the polylactic acid fiber has a porous structure (see Example 2). Figure 2Example 2) shows that the hydrophilicity of the fiber is significantly improved, with a water contact angle of 41°. The porous structure and good hydrophilicity result in high catalytic efficiency, with a degradation rate as high as 97% (see Table 2, Example 2). Furthermore, when the content of the amphiphilic block copolymer in the multifunctional composite agent is lower than the content of the present invention (3 wt%), the polylactic acid fiber surface still retains a porous structure (see Table 2, Example 2). Figure 2 Comparative Example 2), but compared with Example 4, the fiber has poor hydrophilicity, with a water contact angle of 103°, and is still a hydrophobic material. The poor hydrophilicity results in low catalytic activity, with a degradation rate of only 62% (see Table 1, Comparative Example 2). When the content of amphiphilic block copolymer is higher than that of the present invention (7 wt%), the water contact angle of polylactic acid fiber becomes 0°, becoming a completely hydrophilic material, but at this time the porous structure on the fiber surface disappears (see Table 1, Comparative Example 2). Figure 2 Comparative Example 3) shows that the piezoelectric response performance and specific surface area are reduced, resulting in lower catalytic efficiency and a degradation rate of only 73% (see Table 1, Comparative Example 3).

[0065] As can be seen from the above examples and comparative examples, in Comparative Example 1, the polylactic acid fiber membrane prepared without the addition of the multifunctional composite treatment agent has a crystal structure composed of HC and SC crystals. The fiber distribution is uneven and contains a large number of beads. The fiber surface is smooth, resulting in poor intrinsic piezoelectricity, small specific surface area, and low catalytic efficiency, making it difficult to achieve widespread application. However, using the method described in this invention, in Examples 1-4, adding different amounts of the multifunctional composite treatment agent can prepare fiber membranes with 100% SC crystals. These membranes have a large number of microporous structures on the fiber surface and inside, exhibiting high porosity and good hydrophilicity. The degradation rate of indigo carmine can reach up to 97% after 3 hours of ultrasonic treatment. Therefore, the porous hydrophilic polylactic acid fiber membrane material with excellent piezoelectric properties prepared by the method of this invention has high piezoelectric catalytic efficiency and can be widely used in wastewater purification, catalytic adsorption, drug sustained release, and tissue engineering.

Claims

1. A method for preparing a porous hydrophilic polylactic acid fiber membrane material, characterized in that: The raw materials include L-polylactic acid (PLLA), D-polylactic acid (PDLA), and a multifunctional composite treatment agent. Based on 100% of the total raw materials, the multifunctional composite treatment agent content is 30 wt% to 60 wt%. The multifunctional composite treatment agent comprises a water-soluble homopolymer and an amphiphilic copolymer. Based on 100% of the total multifunctional composite treatment agent content, the amphiphilic copolymer content is 4 wt% to 6 wt%. The crystallinity of the fiber membrane material is 28.7% to 40.2%, and the crystal composition is 100% SC crystals. The surface and interior of the fiber membrane material have a porous structure, with a fiber diameter of 1.6 to 2.3 μm, a fiber surface pore diameter of 164 to 524 nm, and a porosity of 82% to 94%. The open-circuit voltage (Voc) of the fiber membrane material under a 10 N stress load is 20 to 27 V, and the water contact angle is 36° to 59°. The preparation method includes the following steps: 1) Dry the L-type polylactic acid (PLLA) and D-type polylactic acid (PDLA) raw materials; 2) Dissolve L-polylactic acid (PLLA), D-polylactic acid (PDLA), and a multifunctional composite treatment agent in chloroform in a certain proportion, and stir at room temperature to prepare an electrospinning mixed solution; 3) Electrospin the spinning solution and then soak the resulting fiber membrane in deionized water and dry it. 4) The dried fiber membrane is annealed in a vacuum oven to obtain a porous hydrophilic polylactic acid fiber material with excellent piezoelectric properties.

2. The method for preparing a porous hydrophilic polylactic acid fiber membrane material as described in claim 1, characterized in that, The weight-average molecular weight of the L-polylactic acid is 1×10⁻⁶. 4 ~ 6×10 5 g / mol, optical purity ≥93%; the weight-average molecular weight of the dextrorotatory polylactic acid is 1×10⁻⁶ g / mol. 4 ~ 6×10 5 g / mol, optical purity ≥93%.

3. The method for preparing a porous hydrophilic polylactic acid fiber membrane material as described in claim 1 or 2, characterized in that, The water-soluble homopolymer is selected from one or more of the following: grafted starch, carboxymethylated starch, phosphorylated starch, starch xanthate, grafted cellulose, carboxymethylated cellulose, hydroxypropylated cellulose, xanthate cellulose, polyacrylates, polyvinyl alcohol, and polyoxyalkylene compounds.

4. The method for preparing a porous hydrophilic polylactic acid fiber membrane material according to claim 1 or 2, characterized in that, The water-soluble homopolymer is selected from one or more of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, and carboxymethyl cellulose.

5. The method for preparing a porous hydrophilic polylactic acid fiber membrane material as described in claim 1 or 2, characterized in that, The amphiphilic copolymer is a copolymer of hydrophilic and hydrophobic segments, wherein the hydrophilic segments are selected from one or more of polyethylene glycol, polyoxyethylene, polyvinyl alcohol, polyethyleneimine, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, and polystyrene sulfonate, and the hydrophobic segments are selected from one or more of polyoxypropylene, polystyrene, polysiloxane, polybutadiene, polymethyl methacrylate, polymethyl acrylate, and polybutyl acrylate.

6. The method for preparing a porous hydrophilic polylactic acid fiber membrane material as described in claim 1 or 2, characterized in that, The amphiphilic copolymer is a polyvinylpyrrolidone-polyoxypropylene-polyvinylpyrrolidone triblock copolymer and / or a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer.

7. A method for preparing a porous hydrophilic polylactic acid fiber membrane material as described in claim 1 or 2, characterized in that: In step 1), the drying process is carried out until the moisture content is below 200 ppm. In step 2), the concentration of the spinning solution is 120 g / L. In step 3), the electrospinning advance speed is 2 ml / h, the working voltage is 15 ~ 25 kV, the distance between the syringe needle tip and the plate collector covered with aluminum foil is 13 ~ 18 cm, and the soaking time is 24 h. In step 4), the annealing temperature is 90 ℃ and the time is 1 h.

8. The application of the method for preparing a porous hydrophilic polylactic acid fiber membrane material as described in any one of claims 1-7 in improving the piezoelectricity and / or hydrophilicity of polylactic acid fiber membrane materials.

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