Author ORCID Identifier

https://orcid.org/0000-0002-8525-9964

Date Available

7-23-2025

Year of Publication

2024

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department/School/Program

Chemical and Materials Engineering

First Advisor

Dr. Isabel C. Escobar

Abstract

Air filtration technology has proven effective in purifying air by trapping particulates which can cause adverse health effects. High Efficiency Particulate Air (HEPA) filters, capable of capturing over 99.99% of PM0.3, are recommended for critical applications. However, conventional non-woven HEPA filters rely on electrostatic interactions to trap smaller particles, which can deplete over time or after cleaning, reducing filtration efficiency and posing health risks. Additionally, these filters contribute to plastic waste.

This dissertation investigated the feasibility of using flat sheet polymeric membranes fabricated via nonsolvent-induced phase separation (NIPS) as reusable and biodegradable alternatives to commercially available non-biodegradable air filters, including face masks. Initial experiments involved fabricating pristine polysulfone (PSf) membranes via NIPS for air filtration. These membranes exhibited insufficient air flow due to small pore sizes and low porosity. To address this, polyethylene glycol (PEG) was introduced as a pore-forming additive. Increased concentrations and molecular weight of PEG resulted in enhanced porosity and higher air flow rates due to reduced thermodynamic stability. Surface analysis using X-ray photoelectron spectroscopy (XPS) and contact angle measurements indicated that some PEG remained on the membrane surface, contributing to higher hydrophilicity and reduced mechanical strength. To enhance mechanical strength, the membranes were adhered to 3D-printed mesh supports, significantly improving their robustness without compromising air flow or pressure drop. These enhanced membranes demonstrated filtration efficiency values comparable to double-layered N95 filters and superior to single-layer N95 filters, surgical masks, and MERV 11 HVAC filters, indicating their potential for use as face masks or air filters.

A subsequent study investigated the effect of common air filter decontamination processes on PSf membranes to assess their reusability. Treatments with isopropanol (IPA), detergent, ultraviolet C (UVc), and sodium hypochlorite (NaClO, bleach) revealed that detergent and IPA treatments drastically reduced filtration efficiency in surgical and N95 masks but not in PSf membranes. This discrepancy was attributed to differences in filtration mechanisms. Further analysis showed that surface electrostatic charge dissipation due to decontamination treatments caused reduced filtration efficiency in polypropylene based face masks but not in PSf membranes since aerosol filtration in the membranes was by mechanical filtration mechanism. Mechanical strength, contact angle, porosity, and air flow tests indicated no significant changes post-treatment in PSf membranes, suggesting their potential for reusable face mask filters in critical applications.

To impart antimicrobial properties on the membranes, AgNPs were covalently immobilized on PSf membranes through a thiol bonding process facilitated by cysteamine and poly (glycidyl methacrylate) (pGMA). XPS confirmed the presence of pGMA and successful thiolation and AgNP functionalization. The functionalized membranes demonstrated significant antimicrobial activity, effectively inhibiting the growth and adhesion of Escherichia coli (E. coli) as shown by Kirby-Bauer diffusion tests and scanning electron microscopy (SEM). Importantly, the functionalization process did not compromise air flow or filtration efficiency, validating this approach for antimicrobial air filtration membranes.

Finally, this work explored the fabrication of fully biodegradable membranes using polylactic acid (PLA) via NIPS. Solvents were selected based on their relative energy difference (RED) values, indicating high solvent-polymer affinity. Both petroleum-derived and biodegradable solvents were evaluated. PLA membranes fabricated with biodegradable solvents (ETAc and GBL) showed superior thermal stability compared to those made with petroleum-derived solvents (DMAc and NMP), attributed to reduced plasticization effects. Surface analysis confirmed no chemical interaction between PLA and the solvents. The membranes exhibited high aerosol capture performance, with filtration efficiencies exceeding 95% for 0.3 µm aerosols. Overall, this dissertation demonstrated the potential for flat sheet polymeric membranes fabricated via NIPS next generation reusable, biodegradable, and antimicrobial air filters.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2024.303

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Available for download on Wednesday, July 23, 2025

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