High-performance transparent polysulfone nanocomposites enhanced with masterbatch-based aramid nanofibers for improved toughness and flame retardancy

In the field of plastic additives, the development of multi-functional nanofillers that reinforce strength and toughness while simultaneously providing flame-retardant properties remains rare. In this study, we demonstrate that aramid nanofibers (ANFs) can serve as promising candidates for industrially accessible melt-compounding processing. An ANF-filled polysulfone (PSU) masterbatch (1 wt%) was prepared via in situ polycondensation and subsequently melt-diluted with commercial PSU (up to 20-fold: 0.05 wt%) to produce transparent nanocomposites with improved mechanical and flame-retardant properties. The nanocomposites exhibited 2.4- and 1.3-fold increases in tensile toughness and impact strength, respectively, compared to that of neat PSU. Cone calorimeter experiments conducted under a radiative heat flux of 50 kW m−2, simulating actual fire conditions, demonstrated that the nanocomposite containing 0.1 wt% ANF did not ignite and exhibited near-zero total smoke production, indicating exceptional flame inhibition and minimal smoke hazards. In contrast, neat PSU showed substantial smoke emission and complete combustion, reflecting its vulnerability to fire risks. Even under a flame temperature of 1300 °C, the self-extinguishing time of nanocomposites drastically decreased from 3–2 min to 3–0 s, depending on the ANF content. The highly dispersed ANFs contributed to flame retardancy via a dual mechanism—releasing non-combustible gases that inhibit flame propagation in the gas phase and promoting the formation of a protective char layer that insulates against heat transfer. These transparent, super engineering plastic nanocomposites represent a promising solution for advanced fire-fighting applications. Aramid nanofiber-reinforced polysulfone nanocomposites synthesized via scalable melt-compounding demonstrate superior strength, toughness, and rapid self-extinguishing properties, making them ideal materials for fire-resistant and safety–critical applications.