Layer-Selective Polyelectrolyte Functionalization of Surgical Mask and HEPA Filters for Enhanced Filtration Efficiency and Broad-Spectrum Antimicrobial Protection

Polypropylene (PP) fabrics are widely used in personal protective equipment, including surgical masks, respirators, and High-Efficiency Particulate Air (HEPA) filters, due to their favorable mechanical properties and filtration performance. However, their intrinsic chemical inertness and lack of antimicrobial activity limit their ability to mitigate contact-based pathogen transmission and long-term surface contamination. In this study, a layer-selective antimicrobial functionalization strategy was developed for PP-based filtration media using permanent charge engineering while preserving filtration efficiency and breathability. Cationic imidazolium-based antimicrobial polymers were applied as conformal coatings on spunbond (SB) fabrics via rapid UV-initiated photopolymerization, whereas anionic poly(4-styrenesulfonate) (PSS) was selectively grafted onto the air-facing outermost surface of melt-blown (MB) filters through an interfacial grafting reaction. This surface-localized approach enabled antimicrobial functionality to be introduced without disrupting the pore structure or electret characteristics of the MB layer. Comprehensive morphological, chemical, and wettability analyses confirmed uniform and selective functionalization. Filtration testing using NaCl and DOP aerosols demonstrated up to approximately 12% enhancement in overall filtration efficiency, with particularly improved performance in the submicron and most penetrating particle size regimes, while the pressure drop increases were modest, tunable, and remained within relevant breathability standards. Antimicrobial evaluations showed that IMHC and PSS coatings achieved 2.2–4.0 log and 1.2–4.6 log reductions in pathogen viability within 10 min, respectively, with IMHC providing rapid contact-mediated bactericidal activity and PSS reducing microbial adhesion while enhancing viral capture and inactivation. Collectively, these results establish a charge- and wettability-gradient multilayer architecture that integrates antimicrobial functionality into mask and HEPA filter systems without compromising structural integrity or functional usability, offering a practical pathway for advanced respiratory protection technologies.