Designing high-performance polypropylene via synergistic free radical scavenging-intumescent flame retardancy: excellent mechanical performance and flame retardancy

Abstract

Polypropylene (PP) faces application limitations due to its inherent flammability. Although halogen-free intumescent flame retardants (IFRs) are environmentally friendly, they often suffer from low flame-retardant efficiency, poor compatibility, and mechanical performance deterioration. Herein, based on a two-phase synergistic flame-retardant mechanism, a highly reactive flame-retardant synergist-1,3-bis(2-acrylamidoethylamino) propane (BAAEP) was designed, and combined with the IFR system including ammonium polyphosphate (APP) and triazine-based char-forming agent (CFA) to achieve synergistic flame retardancy in PP. The multiple active groups in BAAEP (amide groups, CC double bonds, and amino groups) catalyzed crosslinking and char formation in the PP matrix while simultaneously scavenging gaseous free radicals. Furthermore, combined with the intumescent charring effect of IFR, a physical and chemical synergistic flame-retardancy mechanism was established, achieving the integration of high-efficiency flame retardancy and smoke suppression. At the same time, compared to pure PP, there was no significant decrease in thermal or mechanical performance. The optimal flame-retardancy effect was achieved when the addition amount of BAAEP was 4‰. The peak heat release rate (PHRR) of the composite material decreased by 74.3%, total smoke release (TSR) decreased by 83.9%, the vertical burning test (UL-94) rating reached V-0, and the limiting oxygen index (LOI) increased to 32.8%. This work presents a novel strategy for developing high-performance PP with integrated flame retardancy, smoke suppression, and mechanical performance.