Development of Multifunctional Polyurethane Composites With Synergistic Flame Retardancy, Thermal Insulation, and Controlled Antimicrobial Activity

Overview

This study presents the development of multifunctional polyurethane (PU) composites combining flame retardancy, thermal insulation, and antimicrobial activity through the incorporation of expandable graphite (EG), FeMg–BDC-based material, and silver nanoparticles (AgNPs). Structural characterization confirmed the successful integration of all components into the PU matrix. Thermal analysis showed that pure PU exhibited a low thermal conductivity of 0.021 W/m·K. The addition of EG increased this value to 0.053 W/m·K, while further incorporation of FeMg–BDC and AgNPs reduced it to 0.039–0.041 W/m·K, indicating improved heat insulation due to disruption of heat transfer pathways. Flame retardancy testing demonstrated that the optimized composite (PU-04) achieved a UL-94 V-0 rating, a limiting oxygen index (LOI) of approximately 31%, and a char residue above 22%, confirming significantly enhanced fire resistance. Antimicrobial results showed that only AgNP-containing samples exhibited activity. After 48 hours, PU-03 produced inhibition zones of 0.8–1.1 cm against Escherichia coli and Staphylococcus aureus, and 1.2–1.8 cm against Aspergillus fumigatus and Penicillium digitatum. In contrast, composites designed for controlled Ag+ release exhibited more sustained antimicrobial effects, with inhibition zones reaching 1.5–2.6 cm over extended time. Release studies confirmed gradual Ag+ release up to 85–90% at pH 5 after 120 hours, compared to faster release in non-controlled systems. These findings demonstrate a synergistic strategy for designing advanced polymer composites with simultaneous fire resistance and long-term antimicrobial activity, offering strong potential for applications in construction, healthcare, and protective environments.