Abstract:

Objective At present, the pollution of particulate matter is still serious, and hence preparation of fiber filter materials with multiple functions such as ultraviolet(UV) protection, antibacterial, high comfort and biodegradability is imperative and important in various application prospects. Magnesium oxide (MgO) nanoparticle is one type of nanostructured metal oxides, it had been chosen as antibacterial materials because of its broad-spectrum antibacterial property, biocompatibility, non-toxicity, high thermal stability, high chemical stability, and high surface reactivity. Polycaprolactone (PCL) possess good biodegradation, biocompatibility and non-toxicity. As an environmentally friendly polymer, PCL is often used in biomedical materials such as tissue engineering. This paper reports on a research that nanofibrous filter membrane with higher filtration efficiency, lower pressure drop, improved antibacterial property and excellent ultraviolet protection performance.

Method In this work, MgO nano-particles were added into polycaprolactone solution before preparing PCL/MgO nanofibrous filter membrane through electrospinning. The fibre characteristics including fibers morphologies, chemical group, crystalline texture and hydrophilic performance were tested and analyzed through scanning electron microscope, Fourier infrared spectrometer and X-ray diffraction. In addition, the filtration performance, antibacterial properties, UV protection performance and the mass fraction of MgO nanoparticles on the properties of nanofiber membrane were also studied and evaluated.

Results The morphologies of PCL and PCL/MgO nanofibers demonstrated smooth and interconnected fiber characters, and that when the MgO mass fraction was 1.5% and 2.0%, MgO nanoparticles gathered on the surface of PCL/MgO composite nanofibers. The average fiber diameter of PCL nanofiber were 147 nm, while the diameter of PCL/MgO composite nanofiber ranged from 216 to 285 nm. The addition of MgO increased the diameter of nanofiber, decreased the standard deviation of diameter, and PCL/MgO composite nanofibers showed more uniform fiber distribution. Pure PCL nanofiber membrane had lower air permeability and higher water vapor permeability, with the air permeability of 77.61 mm/s and the water vapor permeability of 3 095 g/(m²·d). The presence of MgO nanoparticles in PCL/MgO nanofibers increased the air permeability of nanofiber membranes, while decreased the water vapor permeability of nanofiber membranes. PCL and PCL/MgO nanofibers had the characteristic carbonyl peaks at 1 724 cm^-1, CH₂ stretching peaks at 2 945 cm^-1 (asymmetric) and 2 865 cm^-1 (symmetric), C—O stretching peaks at 1 050 cm^-1, C—O—C stretching peaks at 1 240 cm^-1 (asymmetric) and 1 163 cm^-1 (symmetric). PCL nanofiber membrane showed the characteristic diffraction peaks at 21.4° and 23.8°, relating to the semi-crystalline structure of PCL macromolecular. On the pattern of PCL/MgO nanofiber membrane, three characteristic diffraction peaks at 43.2°, 62.5° and 78.7° corresponded to the (200), (220) and (222) crystal planes of the face central cubic structure of MgO, indicating that the MgO NPs still maintained their crystalline structures. The UV protection factor (UPF) of pure PCL filtration membrane was 21.37, the transmittance to UVA was 5.36%, while the UPF of PCL/MgO composite filtration membranes were 53.86-76.21, the transmittance to UVA were 2.01%-1.45%. The insertion of MgO nanoparticles in PCL nanofibrous membranes enhancend the UV protection performance of PCL/MgO composite membranes significantly. The filtration efficiency of pure PCL nanofiber membrane was 92.11% and the pressure drop was 77.42 Pa, while the filtration efficiency of PCL/MgO nanofibrous filter membranes were 97.57%-98.87% with the pressure drop being 91.18-99.96 Pa. Compared to pure PCL nanofibrous filter membrane, the filtration performance of PCL/MgO nanofibrous filter membranes demonstrated effictive increases because of the higher surface reaction and higher absorption of MgO nanoparticles to particulate matters. When the mass fraction of MgO nanoparticles was 1.0%, the filtration performance of composite PCL nanofiber membrane was best with 98.87%, filtration efficiency, while its resistance pressure drop was 99.96 Pa. The maximum quality factor was 0.044 85. All PCL/MgO composite nanofibrous membranes possessed significant antibacterial efficiency in comparison with pure PCL nanofibers. When the MgO mass fraction was 0.5%, 1.0%, 1.5% and 2.0%, the antibacterial activities of PCL/MgO nanofibers membrane against Escherichia coli were 73.78%, 83.75%, 95.13% and 98.55% respectively, while the antibacterial activities against staphylococcus aureus were 53.61%, 62.63%, 93.02% and 97.56%. Antibacterial activity against Escherichia coli was stronger than that against staphylococcus aureus, which is mainly due to the intrinsic cell wall structure of these two bacterial. In addition, there were many lattice defects on the surface of MgO nanoparticles with positive charge, which were more likely to form strong interaction with negatively charged Escherichia coli, so as to inhibit the growth of bacteria.

Conclusion PCL/MgO composite nanofibrous filter membranes were prepared through electrospinning technology, the addition of MgO nanoparticles significantly increased the filtration performance, antibacterial performance and UV absorption protection performance of PCL/MgO composite nanofiber filter membrane, which can be developed as a multifunctional nanofiber filter material. This work showed the promise of PCL nanofibers and metal oxide antibacterial membrane in various biomedical applications, including in protective filter membranes. It laid a foundation for the further industrial development of biodegradable multifunctional mask filter materials.

Key words: MgO nanoparticle, polycaprolactone nanofiber, electrospinning, antibacterial property, filtration performance