Electro-blow spinning of fully biodegradable nanofibers membranes for air filtration applications

The global use of disposable plastic facemasks during and after the COVID-10 pandemic had a remarkable effect on ecosystems, marine life, and wildlife. Latest statistics reported that just in 2020, over 1.5 billion facemasks came into the oceans, which caused long-term harmful impacts to marine species that could last for tens or even hundreds of years. This PhD study offers a sustainable alternative to diminish the rising risks associated with the continued use of disposable plastic facemasks. The study focuses on the manufacturing of polylactic acid (PLA) biodegradable nanofibers facemasks via the hybridised electro-blow spinning (EBS) process. The produced nanofibers were subjected to physical and chemical modifications to enhance their surface, structural, and mechanical properties that could significantly affect their air filtration performance. The study has three experimental phases; phase 1 focuses on investigating the challenges and limitations of the solubility of PLA in green and eco-friendly solvents instead of the common toxic organic alternatives. Moreover, a parametric study about the most recommended processing parameters regarding polymer concentration, the applied EBS pressure and voltage was conducted to achieve a uniform nanofibers diameter and homogeneous structure. Phase 2 focuses on enhancing the properties of PLA nanofibers through annealing at a wide range of temperatures (80 - 140 °C) and correlating the impact of annealing with the air filtration performance of nanofibers. Most PLA polymers require more than a year for full degradation under standard environmental conditions, which limits its suitability for disposable and everyday-use applications. Thus, Phase 3 focuses on accelerating the degradation rate of nanofibers air filters by blending PLA with polybutylene succinate (PBS) and polybutylene succinate-co-adipate (PBSA) biodegradable polymers. Comprehensive characterisations of nanofibers were conducted across the three phases including, surface properties (morphology, pore size, contact angle, and surface roughness), structural properties (crystallinity, thermal properties, and chemical composition), and mechanical properties (tensile strength, elongation at break, and Young’s modulus) to provide an in-depth understanding on how the modifications influenced the properties of nanofibers. The filtration performance of the modified PLA nanofibers was evaluated via two different systems: (1) a customised air filtration setup to detect nanofibers filtration efficiency against burned wood smoke over a range of particulate matters (PM) sizes (10 μm - 2.5 μm), and (2) testing the most penetrating particle size (MPPS) of 0.3 μm or below using an automatic filter testing device (TSI 8130A) according to the European respirator standards (EN149). The biodegradability of nanofibers was assessed under various conditions, including composting, hydrolytic degradation, and UV exposure, to mimic their real degradation behaviours. These tests provided insights into the nanofibers lifespan and the suitability of nanofibers for indoor and outdoor filtration applications. This PhD study offers a comprehensive pathway for developing eco-friendly air filters that balance effective filtration with environmental sustainability.