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With the increasing requirements for indoor air quality in modern life, high-performance air filtration materials have become the focus of research. Although current mainstream filtration membranes can effectively intercept particulate matter, it is difficult for them to simultaneously possess long - term antibacterial and aromatic functions. Odor residues and microbial growth in enclosed spaces still pose health risks. Lavender essential oil has attracted much attention due to its natural antibacterial and soothing properties. However, its volatile and oxidizable characteristics pose challenges to the durability of traditional loading technologies. What's more, when traditional electrospinning processes incorporate essential oils, they tend to cause solution instability, resulting in fiber structure defects or rapid loss of active ingredients.
Recently, a team led by Professor Han Wang from the State Key Laboratory of Precision Electronic Manufacturing Technology and Equipment at Guangdong University of Technology published the latest research results on lavender essential oil - loaded composite fiber membranes in the Journal of Applied Polymer Science. The team successfully prepared an air filtration membrane with high - performance, antibacterial, and long - lasting aromatic properties through electrospinning machine coaxial electrospinning technology. This achievement provides an innovative material solution for air filtration systems. It can significantly improve air filtration efficiency and antibacterial performance while releasing a long - lasting lavender fragrance, opening up a new way to improve indoor and in - vehicle air quality.
The team prepared polycaprolactone nanofiber membranes loaded with lavender essential oil (LO/PCL) using coaxial electrospinning technology. This technology uses coaxial inner and outer nozzles to simultaneously spin the inner solution containing lavender essential oil and the outer polymer solution, forming core - shell structured nanofibers, as shown in Figure 1. In the electrospinning device, the core - shell structured nanofibers are gradually formed during the electrospinning process.
Figure 1: The preparation process of coaxial nanofiber membranes
Lavender essential oil (LO) in its pure form is usually non - conductive and does not have the ability to conduct free electrons or ions. Therefore, when used alone as the inner - layer solution in electrospinning, it is difficult to form uniform nanofibers. However, the incorporation of the polar solvent N, N - dimethylformamide (DMF) significantly enhances the conductivity of the inner solution. This increase in conductivity facilitates the formation of uniform nanofibers during the electrospinning process. To improve the conductivity of the three types of LO, the proportion of dimethylformamide (DMF) in the inner - layer solution was adjusted in the study to optimize fiber morphology and performance. When the DMF content in the inner - layer solution increased from 1 wt% to 5 wt%, the diameter of the LFO/PCL fiber decreased from 1175 nm to 912 nm. Conversely, when the DMF concentration was further increased to 10 wt%, the diameter of the LFO/PCL fiber increased to 1121 nm, as shown in Figure 2a - c. The electrospinning machine plays a crucial role in this process, ensuring the stability of the electrospinning parameters and the quality of the nanofibers.
Figure 2: SEM images of different membranes
As shown in Figure 3, the release efficiency of pure LO in air is significantly higher than that of the nanofiber membrane samples, indicating that the essential oil encapsulated using coaxial electrospinning technology exhibits excellent delayed - release performance. After analyzing the release percentages of the three coaxial nanofiber samples, the results show that they gradually increase over time. It was observed that the LO release percentage increased most rapidly during the first 1 - 3 days, and then the rate of increase slowed down, especially after the 4th day. This phenomenon is mainly attributed to the change in the LO concentration gradient. That is, the coaxial electrospinning technology can effectively slow down the release rate of LO, thus extending the duration of fragrance retention. The results also show that the encapsulation efficiency of LO in coaxial nanofibers reached 82.9%.
Figure 3: Percentage of essential oil release from LO/PCL nanofiber membranes of three LO types in air
The tests confirmed the effectiveness of coaxial electrospun fibers in air filtration, especially the LHO/PCL nanofiber membrane with an inner - layer DMF concentration of 5% performed outstandingly. The study details the filtration efficiencies of each fiber membrane for PM2.5, PM5, and PM10 under different conditions. It shows that the LHO/PCL nanofiber membrane can achieve a filtration efficiency of 99.75% for PM2.5 and over 99% for both PM5 and PM10 at this concentration, as shown in Figure 4. The electrospinning device used in the preparation of these nanofiber membranes affects their structure and performance, which in turn affects the air filtration effect.
Figure 4: a. Filtration efficiency b. Pressure drop c. Quality factor
The antibacterial properties of the LO/PCL nanofiber membranes against Escherichia coli (Gram - negative bacteria) and Staphylococcus aureus (Gram - positive bacteria) were investigated through in - vitro antibacterial experiments. The experimental results show that all fiber membranes containing LO can significantly reduce the survival rates of these two types of bacteria, especially the LHO/PCL and LSO/PCL formulations with the most prominent antibacterial effects. Specifically, the antibacterial rates of the fiber membranes containing LSO against the two types of bacteria exceeded 99.00%. The experimental data show that the antibacterial rates of these nanofiber membranes all exceeded 99.00%, proving their effective inhibitory effect on the two types of bacteria, as shown in Figure 5. The antibacterial activity of LO is attributed to its various bioactive compounds, such as carvacrol and eucalyptol. These components can damage the bacterial cell membrane and interfere with microbial metabolism, thus inhibiting or eliminating bacterial growth.
Figure 5: Antibacterial activity of LO/PCL nanofiber membranes a. Photographs of bacteria colonies b. Bacteriostatic rates of different samples
In conclusion, in this study, LO/PCL nanofiber membranes were successfully fabricated using coaxial electrospinning technology. Given the large specific surface area of coaxially electrospun nanofibers, this method was selected to optimize the loading and release of LO. The release of LO essential oil was monitored, revealing that coaxial electrospinning effectively ensures the encapsulation efficiency of LO while achieving prolonged fragrance release and sustained antibacterial effects. Additionally, the performance tests for particulate matter (PM) filtration confirmed the efficacy of coaxial electrospun fibers, notably the LHO/PCL nanofiber membrane performed well when the inner - layer DMF concentration was 5%. Moreover, in - vitro antibacterial experiments demonstrated that the LO/PCL nanofiber membranes possess significant antibacterial properties against both Escherichia coli (Gram - negative) and Staphylococcus aureus (Gram - positive), particularly in the LHO/PCL and LSO/PCL formulations. In summary, among the LO/PCL coaxially electrospun nanofibers, the LHO/PCL nanofiber membrane with 5% DMF demonstrated high filtration efficiency (quality factor is 0.13 Pa−1), sustained aroma retention for over 7 days, and exhibited antimicrobial properties, effectively inhibiting bacterial growth by 99% in testing. These nanofiber membranes offer significant advantages over existing air filtration materials, including sustained essential oil release, long - lasting fragrance, and broad - spectrum antibacterial efficacy, which collectively reduce the risk of infection. Therefore, these nanofiber membranes hold great promise as essential oil carriers for air filtration systems.
Article source: https://doi.org/10.1002/app.57000
