Effects of Intumescent Flame Retardants APP/CFA on Flame Retardancy and Mechanical Properties of PP/SEBS Foams

In this study, an intumescent flame retardant exhibiting a synergistic effect was synthesized through the combination of ammonium polyphosphate (APP) and a triazine-based char-forming agent (CFA). Polypropylene (PP), hydrogenated styrene-butadiene block copolymer (SEBS), ammonium polyphosphate (APP), triazine carbonating agent (CFA), azodicarbonamide (ADC) and SiO 2 nanoparticles were used as raw materials for the hot pressing of flame-retardant-modified PP/SEBS foams. The synergistic interaction between APP and CFA not only significantly improves the flame retardant properties of PP/SEBS foamed materials but also ensures the formation of an excellent cellular structure. Experimental findings indicate that when the mass ratio of APP:CFA is 3:1 and the total loading of APP/CFA is 25 wt%, the material achieves a V-0 rating in the UL-94 vertical burning test, with a limiting oxygen index (LOI) value of 30.6%. In the CTT, the PHRR and THR of APP/CFA (3:1) modified foam were 87.0% and 62.5% lower than those of pure PP/SEBS foam. The tensile strength of the material was 15.2 MPa, and the flexural strength was 23.9 MPa. The bubble diameter of the flame-retardant modified PP/SEBS foams was 72.36 μm, and the density of the bubble was 2.24 × 10 6 /cm 3 , providing a good case for the study of flame-retardant modified PP foams.