Abstract
This study systematically examines the effect of the morphology of cerium oxide (CeO(2)) on the flame retardancy, thermal stability, and mechanical properties of polypropylene composites with intumescent flame retardant (PP/IFR). Layer-CeO(2) (L-CeO(2)) outperforms Particulate-CeO(2) (P-CeO(2)) in enhancing the flame retardancy of PP/IFR composites, showing higher limiting oxygen index (LOI) and greater reductions in the total heat release rate (THR) and total smoke production (TSR). The substitution of 1% IFR with 1% L-CeO(2) significantly increased the LOI from 29.4% to 32.6%, while reducing the THR and TSR by 38.9% and 74.3%, respectively. L-CeO(2) incorporation improves thermal stability, increasing the residual char yield to 8.53% at 800 °C under air (vs. 3.87% for PP/IFR). Additionally, L-CeO(2) improved the mechanical properties of the composites, increasing tensile strength and rigidity. The synergistic flame-retardant mechanism is hypothesized to involve CeO(2) catalyzing the formation of a P-O-C crosslinked network in the carbon layer, leading to a denser carbon structure and improved flame-retardant performance in the PP/IFR composites. These findings demonstrate the efficacy of L-CeO(2) as a flame-retardant synergist, providing a foundation for developing fire-safe polymeric materials.