INVESTIGATION ON THE APPLICATION OF POLYLACTIC ACID FIBROUS MEMBRANES IN PROTECTIVE MASKS

Commercial polypropylene masks are recognized as one of the most effective tools for individual protection, but its filtering efficiency decreases sharply with the decay of charges, and the environmental pollution caused by the low recycling rate and abandoned masks. Therefore, the development of degradable and reusable masks has become one of the most sustainable scenarios.

Polylactic acid (PLA), a biobased polymer, has received significant attention in air filtration media owing to its appealing features, such as good machinability, excellent biodegradability, and high mechanical properties. The air filtration efficiency of electrospun neat PLA masks, like that of other biopolymer fibers, is normally insufficient to meet application requirements, and their biodegradability is also limited by the initial hydrolysis.

In this thesis, diatom frustules (DFs) and PLA were used to produce PLA masks with excellent performances via electrospinning. The effects of DFs on the mechanical properties, thermodynamic properties and air filtration efficiency of the PLA fibers were studied. It was confirmed that the optimal concentration of DFs in the PLA/DFs fibers was 5%. According to the national mask standard, compared to disposable medical masks of N95 circulating on the market, the PLA/DFs nanofibrous membranes have a higher air filtration efficiency (> 99%), lower hydrostatic pressure resistance value (3.85 KPa), better performance of hydrophobic (134°) and ethylene oxide resistance. Moreover, durability test proved that the membranes can be reused repeatedly and eventually recycled.

We also evaluated the hydrolytic degradation of PLA in various solutions to investigate the effect of nanoparticles on the hydrolysis of the PLA fibers. Three different nanoparticles including SiO2, DFs and diamide were used in this thesis. It was proved that the incorporation of 5% DFs into the PLA fibers exhibits the fastest hydrolysis rate— 89% in alkaline solution in 14 days. The hydrolysis behavior and mechanism of PLA/DFs composites were systematically studied. The relationship between the hydrolysis rate and the content of the diatom shell in acid, alkali and neutral solutions was systematically investigated. The morphology changes of PLA/DFs composites under natural conditions proved the accelerated degradation effect of the PLA matrix.

In summary, the PLA/DFs nanofibrous membranes fabricated in this study have excellent filtration efficiency, durability and rapid degradation performance, which are superior in generate the green and reusable masks that are urgently needed at this stage and provide a new idea for the solving environmental pollution caused by the extensive use of masks.

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