Flexible and Self-Supporting Pre-oxidized PAN Fiber/PPS Composite with Excellent Electrical Insulation and Flame-Retardant Performance

Abstract The global energy transition is driving next-generation energy systems and high-end electronic equipment toward higher levels of integration, increasing the risk of coupled electrical breakdown and thermal runaway. High-performance composites that combine electrical insulation with flame retardancy are therefore of substantial engineering value. Here, a laminated design and a facile hot-rolling process were adopted to prepare multifunctional composites from pre-oxidized PAN fiber (POPF) felt and polyphenylene sulfide (PPS) nonwoven fabric. The effects of hot-rolling parameters and the number of PPS nonwoven layers on the microstructure and dielectric properties of the composites were systematically investigated. Their mechanical properties, thermal stability, hydrophobicity, flame retardancy, and thermal insulation performance were also evaluated. Compared with pure POPF felt, the composite showed markedly improved tensile properties, together with excellent electrical insulation, flame retardancy, and thermal insulation. Under the optimized rolling conditions, the composite containing 6 layers of PPS nonwoven fabric exhibited a tensile strength of 17.1 MPa, 639% higher than that of pure POPF felt, and a characteristic breakdown strength of up to 55.7 kV mm–1. Its thermal conductivity was as low as 0.079 W m–1 K–1, enabling effective heat blocking and thermal insulation. The limiting oxygen index reached 32%, and the flame-retardant rating met the UL-94 V-0 standard, satisfying service requirements in scenarios with strict flame-retardancy demands. The key design contribution is the integration of POPF felts and PPS nonwoven layers into a flexibility self-supporting sandwich architecture, in which the POPF outer framework and PPS core act cooperatively to provide mechanical integrity, electrical insulation, flame retardancy, and thermal insulation. This structure-property design provides a relatively simple hot-rolling route to multifunctional insulating and flame-retardant composites. The resulting POPF/PPS composites show potential for electrical insulation applications requiring a combination of dielectric strength, thermal insulation, flame retardancy, and flexibility.