A PLA / calendula filter membrane with UV protection, antibacterial properties, and high-efficiency filtration.

Abstract

The application provides an ultraviolet-proof, bacteriostatic and high-efficiency filtering PLA / calendula filtering membrane and relates to the technical field of air filtering materials. The filtering membrane comprises a PLA layer and a PLA layer loaded with calendula. The double-layer filtering membrane is made by selecting green mixed solvents dimethyl carbonate (DMC) and N, N-dimethylacetamide (DMAC) and by one-step electrospinning. Specifically, the PLA layer is spun first, and then the PLA layer loaded with calendula is continuously spun on the surface of the PLA layer, and the two layers of membranes are adhered by electrostatic force. The PLA layer is a fiber with bead-shaped structure, which can reduce air flow resistance. The fiber of the PLA layer loaded with calendula presents a smooth and curved shape, has high filtering efficiency, high breaking elongation, good bacteriostatic effect and ultraviolet absorption performance. The combination of the two layers of fibers realizes the effective combination of high filtering efficiency, low air flow resistance, antibiosis and ultraviolet protection.

Description

Technical Field

[0001] This invention relates to the field of air filtration materials technology, and in particular to a PLA / calendula filter membrane that is UV resistant, antibacterial, and highly efficient in filtration. Background Technology

[0002] PM2.5 particles with a diameter of less than 2.5 micrometers can persist in the atmosphere for a long time. These fine particles have a large specific surface area and easily adsorb aerosols carrying viruses and bacteria, spreading them in the air and inducing diseases such as cancer. Studies have shown that PM pollution can affect the physical and mental health of pregnant women and delivery outcomes (Exposure and Perception of PM2.5 Pollution on the Mental Stress of Pregnant Women. Environ. Int. 2021, 156, 106686). Fine particles adsorbing toxic substances can cross the placental barrier, leading to birth defects in newborns (Fine Particle-Induced Birth Defects: Impacts of Size, Payload, and Beyond. Birthdefects Res. Part C, Embryo Today 2016, 108(3), 196–206). Therefore, separating harmful fine particles, bacteria, and viruses from polluted air and avoiding their inhalation can effectively alleviate air pollution. The most common technology is PM filtration, which removes particles and traps droplets through a filter medium to achieve air separation and purification. Due to its porous structure and controllable pore size, fibrous filter materials offer better particle removal and airflow promotion than other filter materials.

[0003] Polymer fiber membranes have been widely studied and used in air filtration to effectively intercept particles and block the spread of harmful substances such as viruses. Examples include polypropylene (PP), polyethylene (PE), polyester (PET), and polyacrylonitrile (PAN) polymer fiber membranes. However, the accumulation of these non-degradable polymer fibers in oceans and soil after their use will bring new environmental problems. Polylactic acid (PLA), as one of the most promising biodegradable materials of the 21st century, has great potential to replace the aforementioned polymers. Regarding the selection of filter fiber preparation methods, in recent decades, electrospinning technology has been considered a simple and effective method for preparing nanofibers due to its controllable fiber diameter and morphology, interconnected network structure, high specific area, and high porosity. Currently, electrospun filter membranes all use solution methods to prepare fibers, and commonly used solvents include acetone, dichloromethane, and chloroform. During the spinning process, a large amount of solvent volatilization brings new environmental problems. Therefore, there is an urgent need to find a green solvent or solvent combination to replace the above-mentioned toxic solvents. Furthermore, in the field of electrospun filter membranes, many fiber structures, such as bead-like structures, have been explored to reduce airflow resistance and improve particle interception efficiency. The principle can be summarized as follows: the presence of beads reduces the membrane pore size and increases the collision area with PM, thereby enhancing the multiple effects of interception, diffusion (due to the Brownian motion of PM), and inertia (due to inertial collisions). On the other hand, since the PLA beads prepared during electrospinning are randomly stacked, the air path in the fiber membrane is tortuous and winding. Therefore, PM takes a long time to pass through the membrane, resulting in high PM filtration efficiency. In addition, the bead structure reduces the packing density of the fiber membrane to some extent, thereby reducing air resistance (Green-Solvent-Processable Biodegradable Poly(Lactic Acid) Nanofibrous Membranes with Bead-on-String Structure for Effective Air Filtration: “Kill Two Birds with OneStone.” Nano Energy 2022, 97(March), 107237). However, the decrease in the mechanical strength of these fibers, which are considered defective structures, has received little attention. The mechanical strength of the fiber membrane is essential for achieving efficient, stable, and long-term filtration performance.

[0004] In addition to high-efficiency filtration, the current trend is to endow fiber membranes with functionalities to adapt to different applications, such as antibacterial filter membranes. Regarding the selection of antibacterial agents, natural antibacterial agents have attracted widespread attention due to their good biocompatibility and non-toxic, non-irritating properties.

[0005] Calendula is a herbaceous plant belonging to the Asteraceae family. Besides its ornamental value, it also has medicinal, edible, and skincare benefits. Calendula contains various antibacterial active ingredients, among which flavonoids (such as paeoniflorin, isoflavones, and quercetin) are particularly important. These components can enhance the body's antibacterial ability and inhibit many bacteria. The antibacterial concentration is mainly related to the concentration of the extracted drug and experimental conditions. In addition, the flavonoids in calendula also have the function of absorbing ultraviolet light. This is beneficial for improving the resistance of biodegradable materials to ultraviolet degradation and for personal protection. However, the addition of calendula has a significant impact on the fiber diameter, leading to high airflow resistance. Reducing the fiber membrane thickness can reduce airflow resistance, but this also results in low filtration efficiency. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for preparing a PLA / calendula filter membrane with UV protection, antibacterial properties, and high-efficiency filtration. The raw materials used are inexpensive and readily available, and the solvents used are environmentally friendly and highly sustainable. The preparation process is simple, economical, and environmentally friendly.

[0007] The technical solution adopted in this invention is as follows: A PLA / calendula filter membrane with UV protection, antibacterial properties, and high-efficiency filtration, characterized in that: the membrane consists of a two-layer structure, one layer being a PLA fiber membrane with beads, and the other layer being a PLA fiber membrane loaded with calendula flowers. Both fiber membranes are prepared using solution electrospinning technology. The solvents used are dimethyl carbonate (DMC) and N,N-dimethylacetamide (DMAC). An evaluation of this mixed solvent according to the GSK Solvent Sustainability Guidelines showed that this mixed solvent has a higher degree of greenness than existing solvents such as acetone and chloroform. The volume ratio of DMC to DMAC is 7:3 or 5:5.

[0008] The preparation process includes the following:

[0009] (1) Preparation of PLA spinning solution

[0010] Prepare a mixed solvent in which the volume ratio of DMC to DMAC is 7:3. Add PLA powder (Mw = 160,000) to the mixed solvent and stir at 40°C for 12 hours until the PLA is completely dissolved, with a mass fraction of PLA of 10-12%.

[0011] (2) Preparation of PLA spinning solution containing calendula

[0012] A mixed solvent was prepared, with a volume ratio of DMC to DMAC of 5:5. PLA powder (Mw = 160,000) was added to the mixed solvent and stirred at 40°C for 12 hours, resulting in a PLA mass fraction of 12-14%. After the PLA was completely dissolved, 5-11% (by mass) of calendula extract was added to the solution, and stirring was continued until the calendula extract was uniformly mixed. Stirring was then stopped, and the solution was ultrasonically dispersed for 5-10 minutes to ensure good drug dispersion. The calendula extract is a plant extract, and the main extraction process is as follows: calendula raw material was pulverized, water extraction was circulated three times, the extract was concentrated, spray-dried, pulverized, sieved, tested, and packaged. The water to calendula raw material extraction ratio (w:w) was 20:1 and 30:1, respectively.

[0013] (3) Electrospinning to prepare double-layer filter membrane

[0014] Two 10ml syringes were used, one containing PLA spinning solution and the other containing calendula, to draw a certain amount of each. The syringes were gently tapped to expel air. The needle's inner diameter was 0.84mm, and a positive pressure of 15.5-16KV was connected to the needle tip. The receiving roller was connected to a negative pressure of 4.5-5KV. A skin-friendly non-woven fabric was wrapped around the roller as the receiving substrate, and the roller rotated at 120rpm. The collection distance from the needle tip to the roller was 18cm, and the spinning solution propulsion speed was 1.5ml / h. The syringe containing the PLA spinning solution was named syringe M, and the syringe containing the calendula PLA spinning solution was named syringe T. The syringes were further designated as Tx according to the amount of calendula added, where x represents the specific amount of calendula extract added. The bilayer membrane was prepared by spinning sequentially according to the above spinning process, first spinning syringe M, then spinning syringe T. The spinning time for each membrane was 45 minutes, with the spinning time ratios for M-type and T-type needles set to 1:2, 1:1, and 2:1, respectively. For example, after spinning for 15 minutes using an M-type needle, the voltage was turned off, and the needle was replaced with a Tx-type needle for another 30 minutes to obtain the first bilayer membrane, and so on. All fiber membranes were left at room temperature for one day to remove residual solvent.

[0015] Preferably, the PLA spinning solution contains 12% PLA by mass; the PLA spinning solution containing calendula contains 14% PLA by mass; the extraction ratio of calendula extract is 30:1, and the addition amount is 11 wt%.

[0016] Preferably, the positive voltage of the spinning process is 15.5KV and the negative voltage is 5KV.

[0017] Compared with the prior art, the advantages of the present invention are as follows:

[0018] 1. Green mixed solvents DMC and DMAC were selected to replace existing solvents such as acetone for spinning.

[0019] 2. A double-layer filter membrane was prepared using electrospinning technology, consisting of a pure PLA layer and a PLA layer loaded with calendula. The calendula-loaded PLA layer is composed of smooth nanofibers, which not only have excellent particle interception capabilities but also possess antibacterial and UV absorption properties due to the addition of calendula. This reduces the photodegradation damage of the PLA fiber membrane caused by ultraviolet radiation to a certain extent and enhances its protective capabilities. The pure PLA layer consists of fibers with a bead-like structure and a diameter of less than 100 nm, which can effectively intercept fine particles while reducing airflow resistance. The double-layer membrane design allows this filter membrane to have both antibacterial and UV protection effects, as well as low airflow resistance.

[0020] 3. The addition of calendula and the use of skin-friendly non-woven fabric as the receiving matrix result in a curled fiber membrane, which significantly improves the elongation at break of the fiber membrane. Attached Figure Description

[0021] Figure 1 These are scanning electron microscope (SEM) images of the pure PLA fiber membrane and the PLA fiber membrane loaded with calendula in Example 1 of this invention.

[0022] Figure 2 The graph shows the filtration efficiency and pressure drop data of the four groups of fiber membranes under different airflow velocities in Example 1 of this invention.

[0023] Figure 3 This is a graph showing the UV transmittance test data of the four groups of fiber membranes in Example 1 of the present invention.

[0024] Figure 4 This is a graph showing the UV absorption rate test data of the four groups of fiber membranes in Example 1 of the present invention.

[0025] Figure 5 The results of the anti-Staphylococcus aureus test of C-PLA-3 in Example 1 of this invention.

[0026] Figure 6 The stress-strain curves of the four groups of fiber membranes in Example 1 of this invention are shown. Detailed Implementation

[0027] Example 1

[0028] Preparation of PLA spinning solution: Prepare a mixed solvent in which the volume ratio of DMC to DMAC is 7:3. Add PLA powder (Mw = 160000) to the mixed solvent and stir at 40°C for 12 hours until PLA is completely dissolved. The mass fraction of PLA is 12%.

[0029] Preparation of PLA spinning solution containing calendula: Four identical mixed solvents were prepared, with a DMC to DMAC volume ratio of 5:5 in each case. PLA powder (Mw = 160,000) was added to the mixed solvents and stirred at 40°C for 12 hours, resulting in a PLA mass fraction of 14%. After the PLA was completely dissolved, 0%, 5%, 8%, and 11% calendula extract were added to the four solutions, respectively. Stirring continued until the calendula extract was uniformly mixed. Stirring was then stopped, and the solutions were ultrasonically dispersed for 8 minutes to ensure good drug dispersion. The extraction ratio of the calendula extract was 20:1.

[0030] Five 10ml syringes were used, each containing a certain amount of PLA spinning solution and PLA spinning solution containing calendula, respectively. The syringes were gently tapped to expel air. The needle inner diameter was 0.84mm, and the needle tip was connected to a 15.5KV positive pressure. The receiving roller was connected to a 5KV negative pressure. A skin-friendly non-woven fabric was wrapped around the roller as the receiving substrate, and the roller rotated at 120rpm. The collection distance from the needle tip to the roller was 18cm, and the spinning solution propulsion speed was 1.5ml / h. The syringe containing the PLA spinning solution was named syringe M, and the syringe containing the PLA spinning solution containing calendula was named syringe T. Based on the amount of calendula added, they were named T-0, T-5, T-8, and T-11, respectively. The spinning process was followed sequentially to prepare a bilayer membrane, spinning syringe M first, then syringe T. The spinning time for each membrane was 45min, and the ratio of spinning time for syringe M to syringe T was set to 2:1. For example: After spinning with a size M needle for 30 minutes, the voltage was turned off, and a size T-5 needle was used. The voltage was then turned on and spinning continued for 15 minutes to obtain a double-layer membrane. Four membranes were named C-PLA-0, C-PLA-1, C-PLA-2, and C-PLA-3 according to the different amounts of calendula added (0 wt%, 5 wt%, 8 wt%, and 11 wt%). All fiber membranes were left at room temperature for one day to remove residual solvent.

[0031] The presence of crimped fibers significantly increases the elongation at break of the fiber membrane, thereby improving stability during the filtration process. The fiber membrane with added calendula maintained a filtration efficiency above 99% at tested airflow velocities (32-85 L / min). In contrast, the filtration efficiency of the fiber membrane without added calendula, C-PLA-0, decreased from 99% to 98%. C-PLA-3, compared to C-PLA-0, showed a significant inhibitory effect on Staphylococcus aureus (antibacterial efficiency of 76%).

[0032] Matters not covered in this invention are common knowledge.

[0033] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A PLA / calendula filter film with ultraviolet-proof, antibacterial, and high-efficiency filtering, characterized in that: The film is composed of two layers of structure, one is a pure PLA fiber film with beaded structure, and the other is a PLA fiber film loaded with marigold; both layers of fiber film are prepared by using a solution electrospinning technology, and the solvent used is dimethyl carbonate (DMC) and N,N-dimethylacetamide (DMAC); in the spinning solution of the PLA fiber film loaded with marigold, the mass fraction of PLA is 14%, the mass fraction of marigold is between 5-11%, and the volume ratio of DMC to DMAC is 5:5; in the spinning solution of the pure PLA fiber film, the mass fraction of PLA is 12%, and the volume ratio of DMC to DMAC is 7:3; the double-layer film is prepared by using a one-step electrospinning method to spin successively, and the two layers of film are adhered together by the action of electrostatic force; the following spinning process is used: the inner diameter of the spinning needle is 0.84mm, the positive pressure is 15.5KV, the negative pressure is 5KV, the receiving distance is 18cm, the drum rotating speed is 120rpm, and the advancing speed is 1.5ml / h; the skin-friendly non-woven fabric wound on the drum makes the PLA fiber loaded with marigold present a curved shape, thereby improving the elongation at break of the fiber film. ​

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